WO2024127733A1

WO2024127733A1 - Curable composition, polarizing film, optical film, and image display device

Info

Publication number: WO2024127733A1
Application number: PCT/JP2023/031397
Authority: WO
Inventors: 慎太朗三木; 亮菅野
Original assignee: 日東電工株式会社
Priority date: 2022-12-12
Filing date: 2023-08-30
Publication date: 2024-06-20
Also published as: JP2024083671A; TW202428821A

Abstract

This curable composition contains: a polythiol compound having two or more secondary thiol groups; a curable component; and a radical generator. This polarizing film is obtained by layering an optical film on at least one surface of a polarizer via an adhesive layer. The adhesive layer is a layer of a cured product of the curable composition. If the total amount of the composition is taken to be 100 mass%, the content of the polythiol compound is preferably 0.5-10 mass%. If the total amount of the composition is taken to be 100 mass%, the content of the radical generator is preferably 0.5-5 mass%. If the content of the polythiol compound is taken to be a mass% and the content of the radical generator is taken to be b mass%, the value of a/b is preferably 0.5-10.

Description

CURABLE COMPOSITION, POLARIZING FILM, OPTICAL FILM AND IMAGE DISPLAY DEVICE

The present invention relates to a curable composition that is a raw material for the adhesive layer of a polarizing film in which an optical film is laminated via an adhesive layer on at least one surface of a polarizer, and to the polarizing film. The polarizing film can be used alone or as a laminated optical film to form image displays such as liquid crystal displays (LCDs), organic electroluminescence displays, CRTs, and PDPs.

In recent years, image display devices have become thinner and more flexible, and as a result, the polarizing films that are a component of these devices have also become thinner. However, the thinner the polarizing film, the more likely it is that the degree of polarization will decrease in high-temperature, high-humidity environments, and the optical properties will deteriorate.

The following Patent Document 1 describes a photocurable adhesive for polarizing plates that contains a polythiol compound having two or more thiol groups in one molecule, a polyene compound having two or more carbon-carbon double bonds in one molecule, and a photopolymerization initiator.

The following Patent Document 2 describes a photocurable adhesive composition for bonding a polyvinyl alcohol-based polarizing film and a protective film, the photocurable adhesive composition containing at least (a) 50 to 99% by weight of a hydroxyl group-containing alkyl (meth)acrylate, (b) 0.5 to 10% by weight of a photopolymerization initiator, and (c) 0.2 to 5% by weight of one selected from acryloxy group- or methacryloxy group-containing silane coupling agents.

JP 2005-139401 A JP 2010-18721 A

The technology described in Patent Document 1 aims to provide a photocurable adhesive for polarizing plates that has excellent adhesion between the polarizing plate and a light-transmitting member such as a liquid crystal display cell, and also has excellent transparency. Similarly, the technology described in Patent Document 2 aims to improve productivity, reduce equipment costs, reduce material costs, improve adhesion, and increase the freedom of combination configurations of protective films, etc., when manufacturing polarizing plates. In other words, neither document describes or suggests the humidification reliability of the polarization properties of polarizing films.

The present invention was developed in consideration of the above situation, and aims to provide a curable composition that is a raw material for a polarizing film with excellent humidification reliability of its polarization properties, and a polarizing film with excellent humidification reliability of its polarization properties.

Furthermore, the object is to provide an optical film using the polarizing film, and to provide an image display device using the polarizing film or optical film.

The above problem can be solved by the following configuration. That is, the present invention relates to a curable composition (1) that contains a polythiol compound having two or more secondary thiol groups, a curable component, and a radical generator.

In the above curable composition (1), a curable composition (2) in which the radical generator is a photopolymerization initiator is preferred.

In the above curable composition (1) or (2), when the total amount of the composition is taken as 100 mass%, a curable composition (3) is preferred in which the content of the polythiol compound is 0.5 to 10 mass%.

In any of the above curable compositions (1) to (3), when the total amount of the composition is taken as 100 mass%, the content of the radical generator is preferably 0.5 to 5 mass% (curable composition (4)).

In the above curable composition (4), when the content of the polythiol compound is a mass % and the content of the radical generator is b mass %, a/b is preferably 0.5 to 10 in the curable composition (5).

Among the above curable compositions (1) to (5), the curable composition is preferably a curable composition (6) that is an active energy ray-curable composition.

The present invention also relates to a polarizing film (7) in which an optical film is laminated to at least one surface of a polarizer via an adhesive layer, the adhesive layer being a cured product layer of any one of the curable compositions (1) to (6).

In the above polarizing film (7), a polarizing film (8) in which the thickness of the polarizer is 7 μm or less is preferred.

In the above polarizing film (7) or (8), polarizing film (9) is preferred in which the optical film is a transparent protective film.

Among the above polarizing films (7) to (9), polarizing film (10) is preferred in which the optical film is a triacetyl cellulose-based resin film.

Among the above polarizing films (7) to (10), polarizing film (11) is preferred in which the polarizer is a polyvinyl alcohol-based film in which a dichroic dye is adsorbed and oriented.

In any of the above polarizing films (7) to (11), polarizing film (12) is preferred in which the polarizer is a polyvinyl alcohol-based film in which iodine is adsorbed and oriented.

The present invention also relates to an optical film (13) that is characterized by having at least one layer of any of the above polarizing films (7) to (12) laminated thereon, and further relates to an image display device (14) that is characterized by using any of the above polarizing films (7) to (12) or the above optical film (13).

As described above, as polarizing films become thinner, the degree of polarization decreases in high-temperature, high-humidity environments, causing problems with deterioration of optical properties. The curable composition of the present invention contains a polythiol compound having two or more secondary thiol groups, a curable component, and a radical generator. When such a curable composition is used as a raw material for an adhesive layer for laminating a polarizer and an optical film, the humidification reliability of the polarization properties of the polarizing film is improved. The reason for this effect is unclear, but can be assumed as follows.

In order to achieve both excellent polarization properties and thinness, it is necessary to suppress the phenomenon of iodine escaping from within the polarizer under high temperature and high humidity conditions (hereinafter also referred to as "iodine escaping"). As a result of intensive research by the present inventors, it was found that when such a curable composition is used as a raw material for an adhesive layer for laminating a polarizer and an optical film, the conversion rate (reaction rate) of the double bonds in the curable component increases, improving the curability and promoting the high molecular weight of the polymer constituting the adhesive layer, thereby suppressing iodine escaping from within the polarizer. Here, the curable composition according to the present invention contains a polythiol compound having two or more secondary thiol groups in addition to the curable component and the radical generator, thereby significantly improving the humidification reliability of the polarization properties of the polarizing film. This is because the secondary thiol group in the polythiol compound has a good balance of moderate steric hindrance and acidity, and does not impair the polarization properties of the polarizer. If it were a primary thiol group, it would have little steric hindrance and high acidity, and would therefore impair the polarization properties of the polarizer under high temperature and humidity conditions.

As described above, when the polarizing film according to the present invention is a polarizing film in which an optical film is laminated on at least one surface of a polarizer via an adhesive layer, and the adhesive layer is a cured layer of the curable composition, the humidification reliability of the polarization properties of the polarizing film is improved. However, in the present invention, when the thickness of the polarizer is 7 μm or less, the humidification reliability of the polarization properties of the polarizing film is particularly improved. The reason for this effect is not clear, but can be assumed as follows.

Polarizers with a thickness of 7 μm or less (hereinafter also referred to as "thin polarizers") inevitably have a high iodine concentration in order to maintain their polarization properties, so iodine loss tends to occur easily under high temperature and high humidity conditions due to the influence of moisture that penetrates into the polarizer. However, if the curable composition that is the raw material for the adhesive layer contains a polythiol compound having two or more secondary thiol groups in addition to the curable component and radical generator, it is possible to suppress iodine loss from the polarizer and maintain a high iodine concentration in the thin polarizer. This particularly improves the humidification reliability of the polarization properties of the polarizing film.

The curable composition of the present invention contains a polythiol compound having two or more secondary thiol groups, a curable component, and a radical generator.

The polythiol compound may be any compound having two or more secondary thiol groups. Examples of compounds having two secondary thiol groups include 1,4-bis(3-mercaptobutyryloxy)butane, 2,3-butanedithiol, and meso-2,3-dimercaptosuccinic acid. Examples of compounds having three secondary thiol groups include trimethylolpropane tris(3-mercaptobutyrate) and 1,3,5-tris(2-(3-sulfanylbutanoyloxy)ethyl)-1,3,5-triazinane-2,4,6-trione. Examples of compounds having four secondary thiol groups include pentaerythritol tetrakis(3-mercaptobutyrate).

From the viewpoint of improving the humidification reliability of the polarization properties of the polarizing film, when the total amount in the composition is taken as 100 mass%, the content of the polythiol compound is preferably 0.1 to 20 mass%, and more preferably 0.5 to 10 mass%.

In addition, when a polythiol compound having two or more secondary thiol groups is used in combination with a radical generator, particularly a photopolymerization initiator, it is possible to increase the molecular weight of the polymer constituting the adhesive layer while improving the curability of the curable component without impairing the polarization properties of the polarizer. In the curable composition, particularly the active energy ray curable composition, where the content of the polythiol compound is a mass % and the content of the radical generator, particularly the photopolymerization initiator, is b mass %, it is preferable that a/b is 0.5 to 10 because the above-mentioned effect is particularly excellent.

The curable composition according to the present invention contains a radical generator. The curable composition according to the present invention is preferably an active energy ray curable composition that is cured by irradiation with active energy rays, and the active energy ray curable composition preferably contains a photopolymerization initiator as a radical generator. The amount of the radical generator, particularly the photopolymerization initiator, is preferably 0.1 to 10 mass %, and more preferably 0.5 to 5 mass %, when the total amount of the active energy ray curable composition is taken as 100 parts by mass.

The photopolymerization initiator is appropriately selected depending on the active energy ray. When curing is performed with ultraviolet or visible light, a photopolymerization initiator that is cleaved by ultraviolet or visible light is used. Examples of the photopolymerization initiator include benzophenone-based compounds such as benzil, benzophenone, benzoylbenzoic acid, and 3,3'-dimethyl-4-methoxybenzophenone; aromatic ketone compounds such as 4-(2-hydroxyethoxy)phenyl(2-hydroxy-2-propyl)ketone, α-hydroxy-α,α'-dimethylacetophenone, 2-methyl-2-hydroxypropiophenone, and α-hydroxycyclohexylphenylketone; acetophenone-based compounds such as methoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxyacetophenone, and 2-methyl-1-[4-(methylthio)-phenyl]-2-morpholinopropane-1; benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, and benzoin methyl ether. These include benzoin ether compounds such as benzoin butyl ether and anisoin methyl ether; aromatic ketal compounds such as benzyl dimethyl ketal; aromatic sulfonyl chloride compounds such as 2-naphthalenesulfonyl chloride; photoactive oxime compounds such as 1-phenone-1,1-propanedione-2-(o-ethoxycarbonyl)oxime; thioxanthone compounds such as thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-dichlorothioxanthone, 2,4-diethylthioxanthone, 2,4-diisopropylthioxanthone, and dodecylthioxanthone; camphorquinone; halogenated ketones; acylphosphinoxides; and acylphosphonates.

When using an active energy ray-curable composition as a visible light-curable type, it is preferable to use a photopolymerization initiator that is highly sensitive to light of 380 nm or more. Photopolymerization initiators that are highly sensitive to light of 380 nm or more will be described later.

The photopolymerization initiator may be a compound represented by the following general formula (3):

(wherein R ⁷ and R ⁸ are -H, -CH ₂ CH ₃ , -iPr or Cl, and R ⁷ and R ⁸ may be the same or different) is used alone, or it is preferable to use a compound represented by general formula (3) in combination with a photopolymerization initiator highly sensitive to light of 380 nm or more, which will be described later. When a compound represented by general formula (3) is used, the adhesiveness is superior to that when a photopolymerization initiator highly sensitive to light of 380 nm or more is used alone. Among the compounds represented by general formula (3), diethylthioxanthone, in which R ⁷ and R ⁸ are -CH ₂ CH ₃ , is particularly preferable. The amount of the compound represented by general formula (3) in the active energy ray curable composition is preferably 0.1 to 4 mass%, and more preferably 0.5 to 3 mass%, when the total amount of the curable composition is taken as 100 mass%.

It is also preferable to add a polymerization initiator aid as necessary. Examples of polymerization initiator aids include triethylamine, diethylamine, N-methyldiethanolamine, ethanolamine, 4-dimethylaminobenzoic acid, methyl 4-dimethylaminobenzoate, ethyl 4-dimethylaminobenzoate, and isoamyl 4-dimethylaminobenzoate, with ethyl 4-dimethylaminobenzoate being particularly preferable. When a polymerization initiator aid is used, the amount added is preferably 0.1 to 3 parts by mass, and more preferably 0.3 to 1 part by mass, when the total amount of the active energy ray-curable composition is taken as 100 parts by mass.

If necessary, a known photopolymerization initiator can be used in combination. Since the optical functional layer and the base film having UV absorbing ability do not transmit light of 380 nm or less, it is preferable to use a photopolymerization initiator that is highly sensitive to light of 380 nm or more. Specific examples include 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1, 2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone, 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, bis(η5-2,4-cyclopentadiene-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)-phenyl)titanium, and the like.

The curable composition according to the present invention contains a curable component. The curable composition according to the present invention is preferably an active energy ray curable composition. Active energy ray curable compositions can be divided into radical polymerization curable compositions and cationic polymerization curable compositions. In the present invention, active energy rays with a wavelength range of 10 nm to less than 380 nm are referred to as ultraviolet rays, and active energy rays with a wavelength range of 380 nm to 800 nm are referred to as visible light.

The curable component constituting the radical polymerization curable composition may be, for example, a compound represented by the following general formula (2):

(wherein ^R4 is a hydrogen atom or a methyl group, ^R5 and ^R6 are each independently a hydrogen atom, an alkyl group, a hydroxyalkyl group, an alkoxyalkyl group, or a cyclic ether group, and ^R5 and ^R6 may form a cyclic heterocycle). The number of carbon atoms in the alkyl moiety of the alkyl group, hydroxyalkyl group, and/or alkoxyalkyl group is not particularly limited, and examples thereof include those having 1 to 4 carbon atoms. In addition, an example of the cyclic heterocycle which may be formed by ^R5 and ^R6 is N-acryloylmorpholine.

Specific examples of compounds represented by general formula (2) include N-alkyl group-containing (meth)acrylamide derivatives such as N-methyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-butyl(meth)acrylamide, and N-hexyl(meth)acrylamide; N-hydroxyalkyl group-containing (meth)acrylamide derivatives such as N-methylol(meth)acrylamide, N-hydroxyethyl(meth)acrylamide, and N-methylol-N-propane(meth)acrylamide; and N-alkoxy group-containing (meth)acrylamide derivatives such as N-methoxymethylacrylamide and N-ethoxymethylacrylamide. Examples of (meth)acrylamide derivatives containing a cyclic ether group include heterocyclic (meth)acrylamide derivatives in which the nitrogen atom of the (meth)acrylamide group forms a heterocyclic ring, such as N-acryloylmorpholine, N-acryloylpiperidine, N-methacryloylpiperidine, and N-acryloylpyrrolidine. Among these, N-hydroxyethylacrylamide and N-acryloylmorpholine are preferred because of their excellent reactivity, ability to produce a cured product with a high modulus of elasticity, and excellent adhesion to polarizers.

From the standpoint of improving the adhesion and water resistance between the polarizer and the adhesive layer, particularly when the polarizer and the transparent protective film are bonded via an adhesive layer, the content of the compound represented by general formula (2) in the curable composition is preferably 10 to 80 mass %, and more preferably 20 to 60 mass %.

In addition, the curable composition used in the present invention may contain, in addition to the compound represented by formula (2), other monofunctional radical polymerizable compounds as curable components. Examples of monofunctional radical polymerizable compounds include various (meth)acrylic acid derivatives having a (meth)acryloyloxy group. Specific examples include (meth)acrylic acid (C1-20) alkyl esters such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, 2-methyl-2-nitropropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, n-pentyl (meth)acrylate, t-pentyl (meth)acrylate, 3-pentyl (meth)acrylate, 2,2-dimethylbutyl (meth)acrylate, n-hexyl (meth)acrylate, cetyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 4-methyl-2-propylpentyl (meth)acrylate, and n-octadecyl (meth)acrylate.

The (meth)acrylic acid derivatives include, for example, cycloalkyl (meth)acrylates such as cyclohexyl (meth)acrylate and cyclopentyl (meth)acrylate; aralkyl (meth)acrylates such as benzyl (meth)acrylate; 2-isobornyl (meth)acrylate, 2-norbornylmethyl (meth)acrylate, 5-norbornen-2-yl-methyl (meth)acrylate, 3-methyl-2-norbornylmethyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxy (meth)acrylate, and the like. Examples of suitable methacrylates include polycyclic (meth)acrylates such as diethyl (meth)acrylate and dicyclopentanyl (meth)acrylate; alkoxy or phenoxy group-containing (meth)acrylates such as 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-methoxymethoxyethyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, ethyl carbitol (meth)acrylate, phenoxyethyl (meth)acrylate, and alkylphenoxy polyethylene glycol (meth)acrylate; and the like. Among these, dicyclopentenyloxyethyl acrylate and phenoxyethyl acrylate are preferred because of their excellent adhesion to various protective films.

Furthermore, the (meth)acrylic acid derivatives include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, and 12-hydroxylauryl (meth)acrylate. (meth)acrylate, hydroxyl group-containing (meth)acrylates such as [4-(hydroxymethyl)cyclohexyl]methyl acrylate, cyclohexanedimethanol mono(meth)acrylate, and 2-hydroxy-3-phenoxypropyl (meth)acrylate; epoxy group-containing (meth)acrylates such as glycidyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate glycidyl ether; 2,2,2-trifluoroethyl (meth)acrylate, 2,2,2-trifluoroethylethyl (meth)acrylate, and 2,2,2-trifluoroethylethyl (meth)acrylate; Halogen-containing (meth)acrylates such as acrylates, tetrafluoropropyl (meth)acrylate, hexafluoropropyl (meth)acrylate, octafluoropentyl (meth)acrylate, heptadecafluorodecyl (meth)acrylate, and 3-chloro-2-hydroxypropyl (meth)acrylate; alkylaminoalkyl (meth)acrylates such as dimethylaminoethyl (meth)acrylate; 3-oxetanylmethyl (meth)acrylate, 3-methyl-oxetanylmethyl (meth)acrylate; Examples of suitable (meth)acrylates include oxetane group-containing (meth)acrylates such as 3-ethyl-oxetanylmethyl (meth)acrylate, 3-butyl-oxetanylmethyl (meth)acrylate, and 3-hexyl-oxetanylmethyl (meth)acrylate; (meth)acrylates having a heterocycle such as tetrahydrofurfuryl (meth)acrylate and butyrolactone (meth)acrylate; hydroxypivalic acid neopentyl glycol (meth)acrylic acid adduct; and p-phenylphenol (meth)acrylate. Among these, 2-hydroxy-3-phenoxypropyl acrylate is preferred due to its excellent adhesion to various protective films.

In addition, examples of monofunctional radically polymerizable compounds include carboxyl group-containing monomers such as (meth)acrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid.

Examples of monofunctional radically polymerizable compounds include lactam-based vinyl monomers such as N-vinylpyrrolidone, N-vinyl-ε-caprolactam, and methylvinylpyrrolidone; and vinyl monomers having nitrogen-containing heterocycles such as vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, and vinylmorpholine.

Furthermore, as the monofunctional radical polymerizable compound, a radical polymerizable compound having an active methylene group can be used. The radical polymerizable compound having an active methylene group is a compound having an active double bond group such as a (meth)acrylic group at the end or in the molecule, and also having an active methylene group. Examples of the active methylene group include an acetoacetyl group, an alkoxymalonyl group, and a cyanoacetyl group. It is preferable that the active methylene group is an acetoacetyl group. Specific examples of radical polymerizable compounds having an active methylene group include acetoacetoxyalkyl (meth)acrylates such as 2-acetoacetoxyethyl (meth)acrylate, 2-acetoacetoxypropyl (meth)acrylate, and 2-acetoacetoxy-1-methylethyl (meth)acrylate; 2-ethoxymalonyloxyethyl (meth)acrylate, 2-cyanoacetoxyethyl (meth)acrylate, N-(2-cyanoacetoxyethyl)acrylamide, N-(2-propionylacetoxybutyl)acrylamide, N-(4-acetoacetoxymethylbenzyl)acrylamide, and N-(2-acetoacetylaminoethyl)acrylamide. The radical polymerizable compound having an active methylene group is preferably an acetoacetoxyalkyl (meth)acrylate.

A bifunctional or higher polyfunctional radically polymerizable compound can be blended as a curable component constituting the radically polymerizable composition. Examples of polyfunctional radically polymerizable compounds include polyfunctional (meth)acrylamide derivatives such as N,N'-methylenebis(meth)acrylamide, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol diacrylate, 2-ethyl-2-butylpropanediol di(meth)acrylate, bisphenol A di(meth)acrylate, bisphenol A ethylene oxide adduct di(meth)acrylate, bisphenol A propylene oxide adduct di(meth)acrylate, bisphenol A diglycidyl ether di(meth)acrylate, and bisphenol A diglycidyl ether di(meth)acrylate. esters of (meth)acrylic acid and polyhydric alcohols such as ethyl acrylate, neopentyl glycol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, cyclic trimethylolpropane formal (meth)acrylate, dioxane glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and EO-modified diglycerin tetra(meth)acrylate; and 9,9-bis[4-(2-(meth)acryloyloxyethoxy)phenyl]fluorene. Specific examples include Aronix M-220 (manufactured by Toagosei Co., Ltd.), Light Acrylate 1,9ND-A (manufactured by Kyoeisha Chemical Co., Ltd.), Light Acrylate DGE-4A (manufactured by Kyoeisha Chemical Co., Ltd.), Light Acrylate DCP-A (manufactured by Kyoeisha Chemical Co., Ltd.), SR-531 (manufactured by Sartomer Co., Ltd.), and CD-536 (manufactured by Sartomer Co., Ltd.). If necessary, various epoxy (meth)acrylates, urethane (meth)acrylates, polyester (meth)acrylates, and various (meth)acrylate monomers may be used. In addition, polyfunctional (meth)acrylamide derivatives have a high polymerization rate and excellent productivity, and also have excellent crosslinking properties when the resin composition is cured, so they are preferably contained in the curable composition.

From the viewpoint of achieving both adhesion to polarizers and various transparent protective films and optical durability in harsh environments, it is preferable to use a combination of a monofunctional radically polymerizable compound and a polyfunctional radically polymerizable compound. The amount of the monofunctional radically polymerizable compound in the curable composition is preferably 20 to 90 mass%, and more preferably 30 to 60 mass%. The amount of the polyfunctional radically polymerizable compound in the curable composition is preferably 10 to 80 mass%, and more preferably 40 to 70 mass%.

The curable composition according to the present invention has the following general formula (1):

(wherein X is a reactive group, Y is an alkylene group having 1 to 12 carbon atoms which may have a branched chain, or a phenylene group which may have a substituent, and R ¹ and R ² each independently represent a hydrogen atom, an aliphatic hydrocarbon group which may have a substituent, an aryl group, or a heterocyclic group). Examples of the aliphatic hydrocarbon group include a linear or branched alkyl group having 1 to 20 carbon atoms which may have a substituent, a cyclic alkyl group having 3 to 20 carbon atoms which may have a substituent, and an alkenyl group having 2 to 20 carbon atoms. Examples of the aryl group include a phenyl group having 6 to 20 carbon atoms which may have a substituent, and a naphthyl group having 10 to 20 carbon atoms which may have a substituent, and examples of the heterocyclic group include a 5- or 6-membered ring group which contains at least one hetero atom and may have a substituent. These may be linked together to form a ring. In the general formula (1), R ¹ and R ² are preferably a hydrogen atom or a linear or branched alkyl group having 1 to 3 carbon atoms, and most preferably a hydrogen atom.

X in the compound represented by general formula (1) is a reactive group, which is a functional group that can react with the curable component that constitutes the cured material layer, particularly the adhesive layer, and examples of such groups include a hydroxyl group, an amino group, an aldehyde group, a carboxyl group, a vinyl group, a (meth)acrylic group, a styryl group, a (meth)acrylamide group, a vinyl ether group, an epoxy group, an oxetane group, an α,β-unsaturated carbonyl group, a mercapto group, and a halogen group. When the curable composition constituting the cured product layer, particularly the adhesive layer, is active energy ray curable, the reactive group X is preferably at least one reactive group selected from the group consisting of vinyl group, (meth)acrylic group, styryl group, (meth)acrylamide group, vinyl ether group, epoxy group, oxetane group and mercapto group, and when the cured product layer, particularly the adhesive layer, is radically polymerizable, the reactive group X is preferably at least one reactive group selected from the group consisting of (meth)acrylic group, styryl group and (meth)acrylamide group, and when the compound represented by general formula (1) has a (meth)acrylamide group, it is more preferable because it has high reactivity and increases the copolymerization rate with the curable component in the cured product layer, particularly the adhesive layer. In addition, it is also preferable from the viewpoint that the polarity of the (meth)acrylamide group is high and the adhesiveness is excellent, so that the effect of the present invention can be efficiently obtained. When the curable composition constituting the cured product layer, particularly the adhesive layer, is cationic polymerizable, the reactive group X preferably has at least one functional group selected from a hydroxyl group, an amino group, an aldehyde, a carboxyl group, a vinyl ether group, an epoxy group, an oxetane group, and a mercapto group. In particular, when the reactive group X has an epoxy group, this is preferred because the resulting cured product layer, particularly the adhesive layer, has excellent adhesion to the adherend, and when the reactive group X has a vinyl ether group, this is preferred because the curability of the curable composition is excellent.

Preferred specific examples of the compound represented by formula (1) include the following compounds (1a) to (1d), in which ^R3 in formulas (1a) and (1b) is a hydrogen atom or a methyl group.

Other examples of compounds represented by general formula (1) include esters of (meth)acrylates and boric acid, such as esters of hydroxyethylacrylamide and boric acid, esters of methylol acrylamide and boric acid, esters of hydroxyethyl acrylate and boric acid, and esters of hydroxybutyl acrylate and boric acid.

In the present invention, the curable composition may contain an acrylic oligomer obtained by polymerizing a (meth)acrylic monomer. By containing an acrylic oligomer in the curable composition, it is possible to reduce the cure shrinkage when the composition is irradiated with active energy rays and cured, and to reduce the interfacial stress between the adhesive layer and the adherend, such as the optical functional layer and the base film. As a result, it is possible to suppress a decrease in adhesion between the adhesive layer and the adherend.

In consideration of workability and uniformity during application, it is preferable that the active energy ray curable composition has a low viscosity, and therefore it is preferable that the acrylic oligomer obtained by polymerizing a (meth)acrylic monomer also has a low viscosity. As an acrylic oligomer that has a low viscosity and can prevent the curing shrinkage of the adhesive layer, one having a weight average molecular weight (Mw) of preferably 15,000 or less, more preferably 10,000 or less, and particularly preferably 5,000 or less is preferred. On the other hand, in order to sufficiently suppress the curing shrinkage of the cured layer (adhesive layer), the weight average molecular weight (Mw) of the acrylic oligomer is preferably 500 or more, more preferably 1,000 or more, and particularly preferably 1,500 or more. Specific examples of (meth)acrylic monomers constituting acrylic oligomers include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, 2-methyl-2-nitropropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, S-butyl (meth)acrylate, t-butyl (meth)acrylate, n-pentyl (meth)acrylate, t-pentyl (meth)acrylate, 3-pentyl (meth)acrylate, 2,2-dimethylbutyl (meth)acrylate, n-hexyl (meth)acrylate, cetyl (meth)acrylate, (meth)acrylic acid (C1-20) alkyl esters such as (meth)acrylic acid (C1-20) alkyl esters, such as n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 4-methyl-2-propylpentyl (meth)acrylate, and N-octadecyl (meth)acrylate; further, for example, cycloalkyl (meth)acrylates (for example, cyclohexyl (meth)acrylate, cyclopentyl (meth)acrylate, etc.), aralkyl (meth)acrylates (for example, benzyl (meth)acrylate, etc.), polycyclic (meth)acrylates (for example, 2-isobornyl (meth)acrylate, 2-norbornylmethyl (meth)acrylate, 5-norbornene-2-methyl-3-phenylenediamine (meth)acrylate, etc.), -yl-methyl (meth)acrylate, 3-methyl-2-norbornylmethyl (meth)acrylate, etc.), hydroxyl group-containing (meth)acrylic acid esters (for example, hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2,3-dihydroxypropylmethyl-butyl (meth)methacrylate, etc.), alkoxy group or phenoxy group-containing (meth)acrylic acid esters (2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-methoxymethoxyethyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, ethyl carbitol (meth)acrylate, phenoxy group oxyethyl (meth)acrylate, etc.), epoxy group-containing (meth)acrylic acid esters (e.g., glycidyl (meth)acrylate, etc.), halogen-containing (meth)acrylic acid esters (e.g., 2,2,2-trifluoroethyl (meth)acrylate, 2,2,2-trifluoroethylethyl (meth)acrylate, tetrafluoropropyl (meth)acrylate, hexafluoropropyl (meth)acrylate, octafluoropentyl (meth)acrylate, heptadecafluorodecyl (meth)acrylate, etc.), alkylaminoalkyl (meth)acrylates (e.g., dimethylaminoethyl (meth)acrylate, etc.). These (meth)acrylates can be used alone or in combination of two or more kinds. Specific examples of the acrylic oligomer (E) include "ARUFON" manufactured by Toagosei Co., Ltd., "Actflow" manufactured by Soken Chemical & Engineering Co., Ltd., and "JONCRYL" manufactured by BASF Japan Ltd.

The curable composition used in the present invention may contain a silane coupling agent. Specific examples of silane coupling agents include active energy ray curable compounds such as vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, p-styryltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, and 3-acryloxypropyltrimethoxysilane.

Preferred are 2-(3,4 epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 3-glycidoxypropyltriethoxysilane.

Specific examples of silane coupling agents other than those mentioned above that are not curable by active energy rays include 3-ureidopropyltriethoxysilane, 3-chloropropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, bis(triethoxysilylpropyl)tetrasulfide, 3-isocyanatopropyltriethoxysilane, and imidazole silane.

The curable composition used in the present invention may be a cationic polymerization curable composition. The cationic polymerizable compound used in the cationic polymerization curable composition is classified into a monofunctional cationic polymerizable compound having one cationic polymerizable functional group in the molecule and a polyfunctional cationic polymerizable compound having two or more cationic polymerizable functional groups in the molecule. Since the liquid viscosity of the monofunctional cationic polymerizable compound is relatively low, the liquid viscosity can be reduced by including it in the cationic polymerization curable composition. In addition, the monofunctional cationic polymerizable compound often has a functional group that exhibits various functions, and by including it in the cationic polymerization curable composition, various functions can be exhibited in the cationic polymerization curable composition and/or the cured product of the cationic polymerization curable composition. Since the polyfunctional cationic polymerizable compound can three-dimensionally crosslink the cured product of the cationic polymerization curable composition, it is preferable to include it in the cationic polymerization curable composition. The ratio of the monofunctional cationic polymerizable compound to the polyfunctional cationic polymerizable compound is preferably in the range of 10 to 1000 parts by mass of the polyfunctional cationic polymerizable compound to 100 parts by mass of the monofunctional cationic polymerizable compound. Examples of the cationic polymerizable functional group include an epoxy group, an oxetanyl group, and a vinyl ether group. Examples of the compound having an epoxy group include an aliphatic epoxy compound, an alicyclic epoxy compound, and an aromatic epoxy compound. Since the cationic polymerizable resin composition of the present invention has excellent curability and adhesiveness, it is particularly preferable that the composition contains an alicyclic epoxy compound. Examples of the alicyclic epoxy compound include 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, caprolactone-modified products, trimethylcaprolactone-modified products, and valerolactone-modified products of 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, and specifically, CELLOXIDE 2021, CELLOXIDE 2021A, CELLOXIDE 2021P, CELLOXIDE 2081, CELLOXIDE 2083, CELLOXIDE 2085 (all manufactured by Daicel Chemical Industries, Ltd.), Cyracure UVR-61 No. 05, Cyracure UVR-6107, Cyracure 30, R-6110 (all manufactured by Dow Chemical Japan, Ltd.). A compound having an oxetanyl group is preferably contained since it has the effect of improving the curability of the cationic polymerizable resin composition and reducing the liquid viscosity of the composition. Examples of compounds having an oxetanyl group include 3-ethyl-3-hydroxymethyloxetane, 1,4-bis[(3-ethyl-3-oxetanyl)methoxymethyl]benzene, 3-ethyl-3-(phenoxymethyl)oxetane, di[(3-ethyl-3-ox Examples of such a compound include 3-ethyl-3-(2-ethylhexyloxymethyl)oxetane, phenol novolak oxetane, and the like. ARON OXETANE OXT-101, ARON OXETANE OXT-121, ARON OXETANE OXT-211, ARON OXETANE OXT-221, ARON OXETANE OXT-212 (all manufactured by Toagosei Co., Ltd.) and the like are commercially available. Compounds having a vinyl ether group are preferably contained since they have the effect of improving the curability of the cationically polymerizable resin composition and reducing the liquid viscosity of the composition. Examples of compounds having a tere group include 2-hydroxyethyl vinyl ether, diethylene glycol monovinyl ether, 4-hydroxybutyl vinyl ether, diethylene glycol monovinyl ether, triethylene glycol divinyl ether, cyclohexane dimethanol divinyl ether, cyclohexane dimethanol monovinyl ether, tricyclodecane vinyl ether, cyclohexyl vinyl ether, methoxyethyl vinyl ether, ethoxyethyl vinyl ether, and pentaerythritol tetravinyl ether.

The cationic polymerization curable composition contains at least one compound selected from the compounds having an epoxy group, the compounds having an oxetanyl group, and the compounds having a vinyl ether group described above as a curable component, and since all of these are cured by cationic polymerization, a photocationic polymerization initiator is blended. This photocationic polymerization initiator generates cationic species or Lewis acid by irradiation with active energy rays such as visible light, ultraviolet light, X-rays, and electron beams, and initiates the polymerization reaction of the epoxy group or the oxetanyl group. As the photocationic polymerization initiator, a photoacid generator described below is preferably used. In addition, when using a cationic polymerizable resin composition as a visible light curable composition, it is preferable to use a photocationic polymerization initiator that is highly sensitive to light of 380 nm or more, but since photocationic polymerization initiators are generally compounds that show maximum absorption in the vicinity of 300 nm or shorter wavelengths, by blending a photosensitizer that shows maximum absorption in the longer wavelength region, specifically, light of wavelengths longer than 380 nm, it is possible to promote the generation of cationic species or acid from the photocationic polymerization initiator by responding to light of wavelengths in this vicinity. Examples of photosensitizers include anthracene compounds, pyrene compounds, carbonyl compounds, organic sulfur compounds, persulfides, redox compounds, azo and diazo compounds, halogen compounds, photoreducible dyes, etc., and these may be used in combination of two or more types. Anthracene compounds are particularly preferred because of their excellent photosensitizing effect, and specific examples include Anthracure UVS-1331 and Anthracure UVS-1221 (manufactured by Kawasaki Chemical Industries, Ltd.). The content of the photosensitizer is preferably 0.1% to 5% by mass, and more preferably 0.5% to 3% by mass.

In the present invention, the active energy ray curable composition may contain a photoacid generator. When the active energy ray curable composition contains a photoacid generator, the water resistance and durability of the adhesive layer can be dramatically improved compared to when the composition does not contain a photoacid generator. The photoacid generator can be represented by the following general formula (4).

General formula (4)

(wherein L ⁺ represents any onium cation, and X ⁻ represents a counter anion selected from the group consisting of PF6 ₆ ⁻ , SbF ₆ ⁻ , AsF ₆ ⁻ , SbCl ₆ ⁻ , BiCl ₅ ⁻ , SnCl ₆ ⁻ , ClO ₄ ⁻ , a dithiocarbamate anion, and SCN−.)

Next, the counter anion X ⁻ in the general formula (4) will be described.

The counter anion X ⁻ in the general formula (4) is not particularly limited in principle, but is preferably a non-nucleophilic anion. When the counter anion X ⁻ is a non-nucleophilic anion, nucleophilic reactions are unlikely to occur in the cations coexisting in the molecule or in various materials used in combination, and as a result, it is possible to improve the stability over time of the photoacid generator represented by the general formula (4) itself and the composition using it. The non-nucleophilic anion here refers to an anion that has a low ability to cause a nucleophilic reaction. Examples of such anions include PF ₆ ⁻ , SbF ₆ ⁻ , AsF ₆ ⁻ , SbCl ₆ ⁻ , BiCl ₅ ⁻ , SnCl ₆ ⁻ , ClO ₄ ⁻ , B(C ₆ H ₅ ) ₄ ⁻ , dithiocarbamate anion, SCN ⁻ and the like.

Specific examples include "Cyracure UVI-6992", "Cyracure UVI-6974" (all manufactured by Dow Chemical Japan Co., Ltd.), "ADEKA OPTOMER SP150", "ADEKA OPTOMER SP152", "ADEKA OPTOMER SP170", "ADEKA OPTOMER SP172" (all manufactured by ADEKA Corporation), "Omnicat250" (manufactured by IGM Resins B.V.), "CI-5102", "CI-2855" (all manufactured by Nippon Soda Co., Ltd.), "SAN-AID SI-60L", "SAN-AID SI-80L", "SAN-AID SI-100L", "SAN-AID SI-110L", "SAN-AID SI-1 80L (all manufactured by Sanshin Chemical Industry Co., Ltd.), "IK-1", "CPI-100P", "CPI-101A", "CPI-110P", "CPI-200K", "CPI-210S", "CPI-310B", "CPI-410B", "CPI-410S" (all manufactured by San-Apro Co., Ltd.), "WPI-069", "WPI-113", "WPI-116", "WPI-041", "WPI-044", "WPI-054", "WPI-055", "WPAG-281", "WPAG-567", and "WPAG-596" (all manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) are preferred specific examples of the photoacid generator of the present invention.

The polarizing film according to the present invention is a polarizing film in which an optical film is laminated to at least one surface of a polarizer via an adhesive layer, and the adhesive layer is a cured layer of the curable composition.

The thickness of the cured layer (adhesive layer) is preferably 0.5 μm or more and 5.0 μm or less from the viewpoint of improving the humidification reliability of the polarization properties of the polarizing film.

In the present invention, the polarizer is not particularly limited, and various polarizers can be used. Examples of polarizers include those in which a dichroic dye, especially iodine, is adsorbed and oriented on a hydrophilic polymer film such as a polyvinyl alcohol film, a partially formalized polyvinyl alcohol film, or an ethylene-vinyl acetate copolymer partially saponified film. Among these, a polyvinyl alcohol film in which a dichroic dye is adsorbed and oriented is preferred as a polarizer, and a polyvinyl alcohol film in which iodine is adsorbed and oriented is more preferred. The thickness of the polarizer can be, for example, 3 to 20 μm.

However, in the present invention, from the viewpoint of improving humidification reliability in harsh environments such as high temperature and high humidity, it is preferable to use a thin polarizer having a thickness of 3 μm or more and 15 μm or less as the polarizer. In particular, it is preferable that the thickness is 12 μm or less, and even more preferable that the thickness is 10 μm or less, and especially preferable that the thickness is 7 μm or less. Such a thin polarizer has little thickness unevenness, excellent visibility, and also has excellent durability against thermal shock due to little dimensional change.

In the present invention, the adhesive layer that comes into contact with a thin polarizer, which is particularly thicker than 7 μm, has a high iodine density, and is prone to iodine loss, is formed from a cured layer of a curable composition that contains a polythiol compound having two or more secondary thiol groups in addition to a curable component and a photopolymerization initiator. This makes it possible to suppress iodine loss from within the polarizer and maintain a high iodine concentration within the thin polarizer. This particularly improves the humidification reliability of the polarization properties of the polarizing film.

A polarizer obtained by dyeing a polyvinyl alcohol film with iodine and stretching it uniaxially can be produced, for example, by immersing the polyvinyl alcohol in an aqueous solution of iodine to dye it and stretching it to 3 to 7 times its original length. If necessary, the solution may contain boric acid, zinc sulfate, zinc chloride, etc., or it may be immersed in an aqueous solution of potassium iodide, etc. Furthermore, if necessary, the polyvinyl alcohol film may be immersed in water and washed before dyeing. Washing the polyvinyl alcohol film with water not only washes away dirt and blocking inhibitors on the surface of the polyvinyl alcohol film, but also swells the polyvinyl alcohol film to prevent unevenness such as uneven dyeing. Stretching may be performed after dyeing with iodine, or the film may be stretched while being dyed, or it may be dyed with iodine after stretching. Stretching may be performed in an aqueous solution of boric acid, potassium iodide, etc., or in a water bath.

The polarizer preferably contains boric acid from the viewpoints of stretching stability and humidification reliability. Furthermore, the boric acid content in the polarizer is preferably 22% by mass or less, and more preferably 20% by mass or less, based on the total amount of the polarizer, from the viewpoints of suppressing the occurrence of through cracks. From the viewpoints of stretching stability and humidification reliability, the boric acid content in the polarizer is preferably 10% by mass or more, and more preferably 12% by mass or more, based on the total amount of the polarizer.

Representative examples of thin polarizers include:
Patent No. 4751486,
Patent No. 4751481,
Patent No. 4815544,
Patent No. 5048120,
International Publication No. 2014/077599,
International Publication No. 2014/077636,
or a thin polarizer obtained by the manufacturing method described therein.

The thin polarizer is preferably obtained by a manufacturing method including a step of stretching in a boric acid aqueous solution as described in Patent Nos. 4751486, 4751481, and 4815544, among which a step of stretching in a laminate and a step of dyeing, because it can be stretched at a high ratio and the polarization performance can be improved. In particular, it is preferable to obtain a thin polarizer by a manufacturing method including a step of supplementary air stretching before stretching in a boric acid aqueous solution as described in Patent Nos. 4751481 and 4815544. These thin polarizers can be obtained by a manufacturing method including a step of stretching a polyvinyl alcohol resin (hereinafter also referred to as PVA-based resin) layer and a resin substrate for stretching in a laminate and a step of dyeing. With this manufacturing method, even if the PVA-based resin layer is thin, it can be stretched without problems such as breakage due to stretching because it is supported by the resin substrate for stretching.

An example of an optical film constituting a polarizing film is a transparent protective film. A thermoplastic resin having excellent transparency, mechanical strength, thermal stability, moisture blocking properties, isotropy, etc. is used as a material constituting a transparent protective film. Specific examples of such thermoplastic resins include cellulose resins such as triacetyl cellulose-based resin films, polyester resins, polyethersulfone resins, polysulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, (meth)acrylic resins, cyclic polyolefin resins (norbornene-based resins), polyarylate resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof. Among these, it is preferable to use a triacetyl cellulose-based resin film for the polarizing film according to the present invention. In the case of a polarizing film in which a triacetyl cellulose-based resin film is laminated on at least one surface of a polarizer via an adhesive layer, the triacetyl cellulose-based resin film has high moisture permeability and poor wet heat durability, so that the humidification reliability of the polarization properties of the polarizing film tends to deteriorate. However, in the polarizing film according to the present invention, since the adhesive layer is formed by a cured layer of a curable composition containing a polythiol compound having two or more secondary thiol groups, a curable component, and a radical generator, even if the polarizing film has a triacetyl cellulose-based resin film, the humidification reliability of the polarization properties of the polarizing film is improved, which is preferable. The transparent protective film may contain one or more suitable additives. Examples of additives include ultraviolet absorbers, antioxidants, lubricants, plasticizers, release agents, coloring inhibitors, flame retardants, nucleating agents, antistatic agents, pigments, and colorants. The content of the thermoplastic resin in the transparent protective film is preferably 50 to 100% by weight, more preferably 50 to 99% by weight, even more preferably 60 to 98% by weight, and particularly preferably 70 to 97% by weight. If the content of the thermoplastic resin in the transparent protective film is 50% by weight or less, the inherent high transparency of the thermoplastic resin may not be fully expressed.

Furthermore, as a material for forming the transparent protective film, one having excellent transparency, mechanical strength, thermal stability, moisture blocking properties, isotropy, etc. is preferred, and one having a moisture permeability of 150 g/ ^m2 /24 h or less is more preferred, one having a moisture permeability of 140 g/ ^m2 /24 h or less is particularly preferred, and one having a moisture permeability of 120 g/ ^m2 /24 h or less is even more preferred.

　Functional layers such as a hard coat layer, an anti-reflection layer, an anti-sticking layer, a diffusion layer, or an anti-glare layer can be provided on the surface of the transparent protective film to which the polarizer is not attached. The above-mentioned functional layers such as the hard coat layer, the anti-reflection layer, the anti-sticking layer, the diffusion layer, and the anti-glare layer can be provided on the transparent protective film itself, or can be provided separately from the transparent protective film.

The thickness of the transparent protective film can be determined as appropriate, but is generally about 1 to 500 μm in terms of strength, ease of handling, thinness, etc., with 1 to 300 μm being preferred, and 5 to 200 μm being more preferred. Furthermore, 10 to 200 μm is more preferred, and 20 to 80 μm is more preferred.

As the transparent protective film, a retardation film having a front retardation of 40 nm or more and/or a thickness direction retardation of 80 nm or more can be used. The front retardation is usually controlled to be in the range of 40 to 200 nm, and the thickness direction retardation is usually controlled to be in the range of 80 to 300 nm. When a retardation film is used as the transparent protective film, the retardation film also functions as the transparent protective film, making it possible to achieve a thinner film.

Examples of retardation films include birefringent films made by uniaxially or biaxially stretching polymer materials, oriented films of liquid crystal polymers, and films in which an oriented layer of liquid crystal polymer is supported by a film. There are no particular restrictions on the thickness of the retardation film, but it is generally around 20 to 150 μm.

The retardation film may be any of the following formulas (1) to (3):
0.70<Re[450]/Re[550]<0.97... (1)
1.5 × 10 ⁻³ < Δn < 6 × 10 ⁻³ ... (2)
1.13<NZ<1.50...(3)
(wherein Re[450] and Re[550] are in-plane retardation values of the retardation film measured with light having wavelengths of 450 nm and 550 nm at 23° C., respectively; Δn is in-plane birefringence, which is nx-ny, where nx and ny are the refractive indices in the slow axis direction and fast axis direction of the retardation film, respectively; and NZ is the ratio of nx-nz, which is the thickness direction birefringence, to nx-ny, which is the in-plane birefringence, where nz is the refractive index in the thickness direction of the retardation film.) A reverse wavelength dispersion type retardation film that satisfies the above may be used.

The polarizing film according to the present invention may be provided with a retardation layer. The retardation layer may be a single layer or multiple layers, and the retardation layer may also serve as a protective layer for the polarizer.

A liquid crystal compound is preferably used to form the retardation layer, and a solvent containing the liquid crystal compound can be applied using, for example, a wire bar, a gap coater, a comma coater, a gravure coater, a slot die, or the like. In this case, the applied liquid crystal solution may be dried naturally or by heating. It is preferable that the liquid crystal solution is applied at a concentration lower than the isotropic phase-liquid crystal phase transition concentration, i.e., in an isotropic phase state. In this case, stable alignment can be achieved by a method such as rubbing treatment or photoalignment.

The polarizing film according to the present invention can be manufactured, for example, by the following manufacturing method.

A method for producing a polarizing film in which an optical film is laminated on at least one surface of a polarizer via an adhesive layer, the adhesive layer being a cured layer of a curable composition, the curable composition being a curable composition containing a polythiol compound having two or more secondary thiol groups, a curable component, and a photopolymerization initiator, the method comprising a coating step of coating the curable composition on either or both of the lamination surface of the polarizer and the lamination surface of the transparent protective film, a lamination step of laminating the polarizer and the optical film, and an adhesion step of bonding the polarizer and the optical film via the adhesive layer obtained by irradiating the polarizer surface or the optical film surface with active energy rays to cure the curable composition. Each step will be described below.

The method for applying the curable composition is appropriately selected depending on the viscosity of the composition and the desired thickness, and examples include a reverse coater, gravure coater (direct, reverse or offset), bar reverse coater, roll coater, die coater, bar coater, and rod coater. The viscosity of the curable composition is preferably 3 to 100 mPa·s, more preferably 5 to 50 mPa·s, and most preferably 10 to 30 mPa·s. If the viscosity of the composition is high, it is not preferable because the surface smoothness after application is poor and a poor appearance occurs. For this reason, each composition can be heated or cooled to adjust the viscosity to a preferred range before application.

The polarizer and/or optical film may be subjected to a surface modification treatment before the coating process. In particular, it is preferable to perform a surface modification treatment on the polarizer. Examples of surface modification treatments include corona treatment, plasma treatment, and itro treatment, with corona treatment being particularly preferable. Corona treatment generates reactive functional groups such as carbonyl groups and amino groups on the polarizer surface, improving adhesion to the adhesive layer. In addition, the ashing effect removes foreign matter from the surface and reduces surface irregularities, making it possible to create a polarizing film with excellent appearance characteristics.

The polarizer and the optical film are bonded together using a roll laminator or the like via the curable composition applied as described above (bonding process).

After the polarizer and the optical film are bonded together, they are irradiated with active energy rays (electron beams, ultraviolet rays, visible light, etc.) to cure the curable composition and form an adhesive layer. The irradiation direction of the active energy rays (electron beams, ultraviolet rays, visible light, etc.) can be any appropriate direction.

When irradiating with electron beams, any suitable irradiation conditions can be adopted as long as the above-mentioned curable composition can be cured. For example, the acceleration voltage of the electron beam irradiation is preferably 5 kV to 300 kV, more preferably 10 kV to 250 kV. If the acceleration voltage is less than 5 kV, the electron beam may not reach the adhesive, resulting in insufficient curing, and if the acceleration voltage is more than 300 kV, the penetration force through the sample may be too strong, resulting in damage to the polarizer and transparent protective film. The irradiation dose is 5 to 100 kGy, more preferably 10 to 75 kGy. If the irradiation dose is less than 5 kGy, the adhesive may not be cured sufficiently, and if it exceeds 100 kGy, the optical functional layer and the base film may be damaged, resulting in a decrease in mechanical strength and yellowing, and the desired optical characteristics may not be obtained.

Electron beam irradiation is usually performed in an inert gas, but if necessary it can be performed in air or with a small amount of oxygen introduced. Depending on the materials of the polarizer and transparent protective film, by appropriately introducing oxygen, oxygen inhibition can be intentionally created on the optical functional layer and base film surface that are first hit by the electron beam, preventing damage to the polarizer and transparent protective film and allowing the electron beam to be efficiently irradiated only on the adhesive.

When manufacturing the polarizing film of the present invention, it is preferable to use as the active energy rays those containing visible light in the wavelength range of 380 nm to 450 nm, and in particular those with the greatest exposure to visible light in the wavelength range of 380 nm to 450 nm. When using ultraviolet rays and visible light and a transparent protective film with ultraviolet absorption ability (ultraviolet-opaque transparent protective film) is used, light with wavelengths shorter than approximately 380 nm is absorbed, so that light with wavelengths shorter than 380 nm does not reach the curable composition and does not contribute to the polymerization reaction. Furthermore, light with wavelengths shorter than 380 nm absorbed by the polarizer or transparent protective film is converted into heat, and the polarizer or transparent protective film itself generates heat, causing defects such as curling and wrinkling of the polarizing film. Therefore, when ultraviolet rays and visible light are employed in the present invention, it is preferable to use an active energy ray generator that does not emit light with a wavelength shorter than 380 nm, and more specifically, the ratio of the integrated illuminance in the wavelength range of 380 to 440 nm to the integrated illuminance in the wavelength range of 250 to 370 nm is preferably 100:0 to 100:50, more preferably 100:0 to 100:40. When producing the polarizing film according to the present invention, the active energy ray is preferably a gallium-encapsulated metal halide lamp or an LED light source that emits light in the wavelength range of 380 to 440 nm. Alternatively, a light source containing ultraviolet rays and visible light such as a low pressure mercury lamp, a medium pressure mercury lamp, a high pressure mercury lamp, an ultra-high pressure mercury lamp, an incandescent lamp, a xenon lamp, a halogen lamp, a carbon arc lamp, a metal halide lamp, a fluorescent lamp, a tungsten lamp, a gallium lamp, an excimer laser, or sunlight can be used, and a bandpass filter can be used to block ultraviolet rays with a wavelength shorter than 380 nm. In order to prevent curling of the polarizing film while improving the adhesive performance of the adhesive layer between the polarizer and the transparent protective film, it is preferable to use a gallium-filled metal halide lamp and active energy rays obtained through a bandpass filter capable of blocking light with wavelengths shorter than 380 nm, or active energy rays with a wavelength of 405 nm obtained using an LED light source.

When the polarizing film according to the present invention is produced on a continuous line, the line speed depends on the curing time of the curable composition, but is preferably 1 to 500 m/min, more preferably 5 to 300 m/min, and even more preferably 10 to 100 m/min. If the line speed is too slow, productivity will be poor, or the damage to the optical polarizer or transparent protective film will be too great, making it impossible to produce a polarizing film that can withstand durability tests and the like. If the line speed is too high, the curable composition will not cure sufficiently, and the desired adhesion may not be obtained.

The above-mentioned polarizing film and the laminated optical film having at least one layer of polarizing film can also be provided with an adhesive layer for bonding to other components such as liquid crystal cells. There are no particular limitations on the adhesive that forms the adhesive layer, but it is possible to appropriately select and use an adhesive whose base polymer is, for example, an acrylic polymer, a silicone polymer, polyester, polyurethane, polyamide, polyether, a fluorine-based polymer, or a rubber-based polymer. In particular, it is preferable to use an adhesive that has excellent optical transparency, such as an acrylic adhesive, and adhesive properties such as moderate wettability, cohesion, and adhesion, and has excellent weather resistance and heat resistance.

The adhesive layer can be provided on one or both sides of the polarizing film or optical film as a superimposed layer of different compositions or types. When provided on both sides, the adhesive layers on the front and back of the polarizing film or optical film can be of different compositions, types, thicknesses, etc. The thickness of the adhesive layer can be determined appropriately depending on the intended use, adhesive strength, etc., and is generally 1 to 500 μm, preferably 1 to 200 μm, and particularly preferably 1 to 100 μm.

A separator is temporarily attached to cover the exposed surface of the adhesive layer to prevent contamination until it is put into practical use. This prevents contact with the adhesive layer during normal handling. As a separator, apart from the thickness conditions mentioned above, any suitable thin material such as plastic film, rubber sheet, paper, cloth, nonwoven fabric, net, foam sheet, metal foil, or laminates thereof, coated as necessary with a suitable release agent such as silicone, long-chain alkyl, fluorine, or molybdenum sulfide, may be used in accordance with conventional methods.

The polarizing film or optical film of the present invention can be preferably used in the formation of various devices such as liquid crystal display devices. The formation of liquid crystal display devices can be carried out in a conventional manner. That is, liquid crystal display devices are generally formed by appropriately assembling components such as a liquid crystal cell, a polarizing film or optical film, and, if necessary, a lighting system, and incorporating a driving circuit, but in the present invention, there are no particular limitations other than the use of the polarizing film or optical film of the present invention, and the method can be carried out in a conventional manner. As for the liquid crystal cell, any type can be used, such as TN type, STN type, or π type.

It is possible to form suitable liquid crystal display devices, such as those in which an optical laminate is disposed on one or both sides of a liquid crystal cell, or those in which a backlight or reflector is used in the lighting system. In such cases, the optical laminate according to the present invention can be disposed on one or both sides of a liquid crystal cell. When optical laminates are disposed on both sides, they may be the same or different. Furthermore, when forming a liquid crystal display device, suitable components such as a diffuser plate, anti-glare layer, anti-reflection film, protective plate, prism array, lens array sheet, light diffuser plate, backlight, etc. can be disposed in one or more layers in suitable positions.

The following are examples of the present invention, but the present invention is not limited to these.

<Polarizer>
A laminate having a 9 μm-thick PVA layer formed on an amorphous PET substrate was subjected to auxiliary air stretching at a stretching temperature of 130° C. to produce a stretched laminate, the stretched laminate was then dyed to produce a colored laminate, and the colored laminate was further stretched in boric acid water at a stretching temperature of 65° C. to produce an optical film laminate including a 5 μm-thick PVA layer, in which the PVA molecules of the PVA layer formed on the amorphous PET substrate were highly oriented by such two-stage stretching, and an optical film laminate including a 5.5 μm-thick PVA layer was obtained, which constitutes a thin polarizer in which iodine adsorbed by dyeing was highly oriented in one direction as a polyiodine ion complex.

<Optical film (transparent protective film)>
Optical film 1: Triacetyl cellulose-based resin film (product name "KC2UA", manufactured by Konica Minolta)

<Active energy rays>
Visible light (gallium-filled metal halide lamp) was used as the active energy ray. Irradiation device: Light HAMMER10 manufactured by Fusion UV Systems, Inc. Bulb: V bulb Peak illuminance: 1600 mW/cm ² , cumulative irradiation amount 1000/mJ/cm ² (wavelength 380 to 440 nm) was used. The illuminance of visible light was measured using a Sola-Check system manufactured by Solatell.

(Preparation of Curable Composition)
Curable compositions of Examples 1 to 7 and Comparative Examples 1 and 2 were prepared according to the formulations in Table 1. The values in the table indicate the weight percentages when the total amount of each composition is taken as 100 mass %.

The materials constituting the curable composition are shown below.
(Polythiol Compound)
Pentaerythritol tetrakis(3-mercaptobutyrate): Trade name "Karenz MT-PE1", manufactured by Showa Denko K.K. 1,4-bis(3-mercaptobutyryloxy)butane: Trade name "Karenz MT-BD1", manufactured by Showa Denko K.K. (curable component)
N-Acryloylmorpholine (compound represented by general formula (2)): Trade name "ACMO", manufactured by Kohjin Co., Ltd. Tripropylene glycol diacrylate: Trade name "TPGDA", manufactured by Toagosei Co., Ltd. (initiator)
Bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide: Trade name "Omnirad 819", manufactured by IGM Resins B.V.

(Production of polarizing film)
Examples 1 to 7 and Comparative Examples 1 to 2
Using an MCD coater (manufactured by Fuji Machinery Co., Ltd.) (cell shape: honeycomb, gravure roll line count: 1000 rolls/inch, rotation speed 140%/to line speed), the effective resin composition shown in Table 1 was applied to the bonding surface of the transparent protective film 1 (coating step). Next, the transparent optical film 1 and the optical film laminate including the thin polarizer were bonded together from the coated side by a roller (bonding step). Thereafter, the above-mentioned visible light was irradiated from the bonded transparent protective film side by an active energy ray irradiation device to cure the curable composition, thereby bonding the thin polarizer and the transparent protective film together via an adhesive layer obtained. Next, the amorphous PET substrate of the optical film laminate was peeled off.

<Evaluation of Humidification Reliability of Polarizing Properties of Polarizing Film>
The polarizing films produced in Examples 1 to 7 and Comparative Examples 1 and 2 were attached to one side of a 0.7 mm thick alkali-free glass sheet via an adhesive layer (thickness 20 μm) to prepare polarizing films (samples for evaluating humid durability test). Using the samples, a humid reliability test of the polarization characteristics was carried out in an environment of 85° C. and 85% humidity. Details of the humid reliability test are shown below.

The obtained polarizing film was exposed to an environment of 85°C and 85% humidity for 120 hours, and the degree of polarization before and after insertion was measured using a spectrophotometer with an integrating sphere (V7100 manufactured by JASCO Corporation), and the change in the degree of polarization ΔPz (%) = | (degree of polarization before insertion (%)) - (degree of polarization after insertion (%)) | was calculated. It was determined that the smaller the change in the degree of polarization ΔPz (%), the better the humidification reliability of the polarization characteristics in a harsh humid environment.

<Evaluation of Curing Property of Adhesive Layer>
A double-sided tape (No. 500, manufactured by Nitto Denko Corporation) was attached to the PVA surface of the polarizing film obtained by the above manufacturing method. The polarizing film was then cut into a size of 200 mm parallel to the stretching direction and 15 mm perpendicular to the stretching direction, and a cut was made between the polarizing film and the transparent protective film with a cutter knife. The release film of the double-sided tape was then peeled off, and the adhesive surface was attached to a glass plate. The polarizing film and the transparent protective film were peeled off, and the transparent protective film side after peeling was measured by FT-IR (ATR method). When only the peak of the TAC film was detected, it was marked as ◯, and when the peak of the adhesive component was detected, it was marked as ×, indicating that the adhesive had cohesive failure.

The results in Table 1 show that the polarizing films of Examples 1 to 7 have excellent humidification reliability of polarization properties. In addition, the adhesive layer also has excellent curing properties, which indicates that the polarizing films have excellent durability and reliability. On the other hand, the polarizing film of Comparative Example 1 cannot suppress iodine loss under high temperature and humidity conditions, which indicates that the humidification reliability is deteriorated. The polarizing film of Comparative Example 2 has insufficient curing properties, which indicates that the peel strength of the adhesive layer is deteriorated, which indicates that the polarizing film has poor durability and reliability.

Claims

A curable composition comprising a polythiol compound having two or more secondary thiol groups, a curable component, and a radical generator.
The curable composition according to claim 1, wherein the radical generator is a photopolymerization initiator.
The curable composition according to claim 1 or 2, wherein the content of the polythiol compound is 0.5 to 10 mass % when the total amount of the composition is 100 mass %.
The curable composition according to any one of claims 1 to 3, wherein the content of the radical generator is 0.5 to 5 mass % when the total amount of the composition is 100 mass %.
The curable composition according to claim 4, wherein the content of the polythiol compound is a mass % and the content of the radical generator is b mass %, and a/b is 0.5 to 10.
The curable composition according to any one of claims 1 to 5, wherein the curable composition is an active energy ray curable composition.
A polarizing film in which an optical film is laminated on at least one surface of a polarizer via an adhesive layer, the adhesive layer being a layer of a cured product of the curable composition according to any one of claims 1 to 6.
The polarizing film according to claim 7, wherein the thickness of the polarizer is 7 μm or less.
The polarizing film according to claim 7 or 8, wherein the optical film is a transparent protective film.
The polarizing film according to any one of claims 7 to 9, wherein the optical film is a triacetyl cellulose-based resin film.
The polarizing film according to any one of claims 7 to 10, wherein the polarizer is a polyvinyl alcohol-based film on which a dichroic dye is adsorbed and oriented.
The polarizing film according to any one of claims 7 to 11, wherein the polarizer is a polyvinyl alcohol-based film in which iodine is adsorbed and oriented.
An optical film comprising at least one laminate of the polarizing film according to any one of claims 7 to 12.
An image display device comprising the polarizing film according to any one of claims 7 to 12 or the optical film according to claim 13.