WO2013146556A1

WO2013146556A1 - Polarizing plate

Info

Publication number: WO2013146556A1
Application number: PCT/JP2013/058191
Authority: WO
Inventors: 智恵阪上; 悠司淺津; 岩田　智
Original assignee: 住友化学株式会社
Priority date: 2012-03-30
Filing date: 2013-03-14
Publication date: 2013-10-03
Also published as: TW201346356A; JP2013210445A

Abstract

A polarizing plate in which a protective membrane comprising a transparent resin film is bonded, via an adhesive, to a polarizer comprising a polyvinyl alcohol-based resin on which a dichroic dye is adsorbed and oriented, wherein the adhesive comprises a photocurable composition that contains a photocurable component containing an epoxy compound having an alicyclic epoxy group, a silane coupling agent and a photo cationic polymerization initiator.

Description

Polarizer

The present invention relates to a polarizing plate in which a protective film made of a transparent resin is bonded to a polarizer made of a polyvinyl alcohol resin.

The polarizing plate is useful as one of the optical components constituting the liquid crystal display device. A polarizing plate usually has a structure in which protective films are laminated on both sides of a polarizer, and is incorporated in a liquid crystal display device. It is also known that a protective film is provided only on one side of the polarizer, but in many cases, a layer having an optical function as another function is not provided on the other side. It is also pasted. As a method for producing a polarizer, a method in which a uniaxially stretched polyvinyl alcohol-based resin film dyed with a dichroic dye is treated with boric acid, washed with water and dried is widely adopted.
Usually, a protective film is bonded to the polarizer immediately after washing and drying as described above. This is because the dried polarizer has a weak physical strength, and once it is wound, there is a problem that it is easily broken in the processing direction. Therefore, usually, a water-based adhesive that is an aqueous solution of a polyvinyl alcohol resin is immediately applied to the polarizer after drying, and protective films are simultaneously bonded to both sides of the polarizer via this adhesive. Usually, a triacetyl cellulose film having a thickness of 30 to 100 μm is used as the protective film.
Triacetyl cellulose has a high moisture permeability, and the polarizing plate bonded as a protective film has a problem of causing deterioration under wet heat, for example, at a temperature of 70 ° C. and a relative humidity of 90%. Therefore, it is also known to use an amorphous polyolefin resin having a lower moisture permeability than that of triacetyl cellulose, for example, an amorphous polyolefin resin represented by a norbornene resin as a protective film.
When a protective film made of a resin with low moisture permeability is bonded to a polyvinyl alcohol polarizer, a polyvinyl alcohol resin that has been conventionally used as an adhesive for bonding a polyvinyl alcohol polarizer and triacetyl cellulose. The aqueous solution has a problem that the adhesive strength is not sufficient or the appearance of the obtained polarizing plate becomes poor. This is because a resin film having low moisture permeability is generally hydrophobic, and water that is a solvent cannot be sufficiently dried due to low moisture permeability. On the other hand, it is also known to bond different types of protective films on both sides of the polarizer. For example, one side of the polarizer is made of a resin with low moisture permeability such as an amorphous polyolefin resin. There is also a proposal for bonding a protective film and bonding a protective film made of a highly moisture-permeable resin such as cellulose resin including triacetyl cellulose to the other surface of the polarizer.
Therefore, high adhesion between a protective film made of a resin with low moisture permeability and a polyvinyl alcohol polarizer and high adhesion between a resin with high moisture permeability such as a cellulose resin and a polyvinyl alcohol polarizer. There is an attempt to use an active energy ray-curable adhesive as an adhesive that gives force. For example, Japanese Patent Application Laid-Open No. 2004-245925 (Patent Document 1) discloses an adhesive mainly composed of an epoxy compound that does not contain an aromatic ring, and this adhesive is obtained by cationic polymerization by irradiation with active energy rays. It has been proposed to cure and bond the polarizer and the protective film. JP-A-2008-257199 (Patent Document 2) discloses a photocurable adhesive in which an alicyclic epoxy compound and an epoxy compound having no alicyclic epoxy group are combined and blended with a cationic photopolymerization initiator. A technique using an agent for bonding a polarizer and a protective film is disclosed.
However, although the adhesive of the composition specifically disclosed in Patent Document 1 and Patent Document 2 adheres the polarizer and the protective film with an appropriate adhesive force, the adhesive force is not necessarily sufficient, for example, When the polarizing plate obtained by adhering the polarizer and the protective film using the photocurable adhesive is cut into a predetermined size or when the cut polarizing plate is handled, an impact is exerted on the end of the polarizing plate. When given, the protective film sometimes peeled off from the polarizer at the end.
In addition, a polarizing plate obtained by adhering a polarizer and a protective film using these photocurable adhesives is discolored by sunlight or the heat of a backlight when applied to a liquid crystal display device. Are known. As a method for solving this, for example, JP 2010-32766 (Patent Document 3) combines a glycidyl ether group-containing resin, a hydrolyzable silyl group, and an epoxy group-containing compound, and is combined with a photocationic polymerization initiator. The technique which uses the photocurable adhesive agent used for bonding with a polarizer and a protective film is disclosed.
However, the photocurable adhesive having the composition specifically disclosed in Patent Document 3 expresses an appropriate adhesive force, and the discoloration of the polarizing plate due to heat can be moderately suppressed, but the adhesive layer after curing is not necessarily provided. As a result, when the polarizing plate is subjected to a severe temperature history such as a thermal shock test in which the high temperature holding and the low temperature holding are repeated rapidly, the cured film of the adhesive does not shrink the polarizer. There is a problem that the polarizer cannot be sufficiently suppressed and the polarizer is broken.

Accordingly, an object of the present invention is to provide a polarizing plate that has excellent adhesion between the polarizer and the protective film, suppresses discoloration of the polarizer due to heat, and does not easily crack the polarizer even when subjected to a severe temperature history. It is.
As a result of intensive studies to solve such problems, the present inventors have determined that a predetermined amount of a silane coupling agent and a photocationic polymerization initiator is added to a photocurable component containing an epoxy compound having an alicyclic epoxy group. Blended, and used for bonding the polarizer and protective film, the polarizer and protective film are firmly bonded, heat resistance is excellent, and the polarizer is prevented from cracking due to intense temperature history It discovered that a board was obtained and came to complete this invention.
That is, in the present invention, a protective film made of a transparent resin film is bonded via an adhesive to a polarizer made of a polyvinyl alcohol-based resin in which a dichroic dye is adsorbed and oriented. Provided is a polarizing plate which is formed from a photocurable composition containing a photocurable component containing an epoxy compound having a formula epoxy group, a silane coupling agent, and a photocationic polymerization initiator. .
The silane coupling agent preferably has a glycidyloxy group or a cyclic epoxy group in the molecule.
Moreover, it is desirable that the photocurable component forming the adhesive further contains an aliphatic epoxy compound in the molecule.
The photocurable composition preferably contains 4 to 40 parts by weight of the silane coupling agent with respect to 100 parts by weight of the photocurable component.
In these polarizing plates, a cycloolefin-based resin form is bonded to one surface of the polarizer via the adhesive, and an acetylcellulose-based resin film is bonded to the other surface of the polarizer via the adhesive. It is desirable that a pressure-sensitive adhesive layer having an antistatic function is formed on the surface opposite to the surface on which the polarizing film of the acetylcellulose-based resin film is bonded.

Hereinafter, the present invention will be described in detail. The polarizing plate of the present invention is obtained by bonding a protective film to at least one surface of a polarizer via an adhesive layer.
[Polarizer]
The polarizer is composed of a polyvinyl alcohol-based resin film in which a dichroic dye is adsorbed and oriented. The polyvinyl alcohol resin constituting the polarizer can be obtained by saponifying a polyvinyl acetate resin. Examples of the polyvinyl acetate resin include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith. Examples of other monomers copolymerized with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids. The saponification degree of the polyvinyl alcohol-based resin is usually in the range of 85 to 100 mol%, preferably 98 to 100 mol%. The polyvinyl alcohol-based resin may be further modified, and for example, polyvinyl formal or polyvinyl acetal modified with aldehydes may be used. The degree of polymerization of the polyvinyl alcohol-based resin is usually 1,000 to 10,000, preferably 1,500 to 5,000.
The polarizer is a process of uniaxially stretching such a polyvinyl alcohol-based resin film, a step of dyeing the polyvinyl alcohol-based resin film with a dichroic dye and adsorbing the dichroic dye, and a dichroic dye being adsorbed It is manufactured through a step of treating the polyvinyl alcohol resin film with a boric acid aqueous solution.
The uniaxial stretching may be performed before dyeing with a dichroic dye, may be performed simultaneously with dyeing with a dichroic dye, or may be performed after dyeing with a dichroic dye. When uniaxial stretching is performed after dyeing with a dichroic dye, this uniaxial stretching may be performed before boric acid treatment or during boric acid treatment. Of course, it is also possible to perform uniaxial stretching in these plural stages. For uniaxial stretching, stretching may be performed between rolls having different peripheral speeds, or stretching may be performed by sandwiching between rolls. Moreover, the dry-type extending | stretching which extends | stretches in air | atmosphere may be sufficient, and the wet extending | stretching which extends | stretches in the state swollen with the solvent may be sufficient. The draw ratio is usually about 4 to 8 times.
In order to dye the polyvinyl alcohol resin film with the dichroic dye, for example, the polyvinyl alcohol resin film may be immersed in an aqueous solution containing the dichroic dye. Specifically, iodine or a dichroic organic dye is used as the dichroic dye.
When iodine is used as the dichroic dye, a method of dyeing a polyvinyl alcohol-based resin film in an aqueous solution containing iodine and potassium iodide is usually employed. The content of iodine in this aqueous solution is usually about 0.01 to 0.5 parts by weight per 100 parts by weight of water, and the content of potassium iodide is usually about 0.5 to 10 parts by weight per 100 parts by weight of water. It is. The temperature of this aqueous solution is usually about 20 to 40 ° C., and the immersion time (dyeing time) in this aqueous solution is usually about 30 to 300 seconds.
On the other hand, when a dichroic organic dye is used as the dichroic dye, a method of dyeing a polyvinyl alcohol-based resin film in an aqueous solution containing a water-soluble dichroic organic dye is usually employed. The content of the dichroic organic dye in this aqueous solution is usually 1 × 10 5 per 100 parts by weight of water.^-3~ 1 × 10^-2About parts by weight. This aqueous solution may contain an inorganic salt such as sodium sulfate. The temperature of this aqueous solution is usually about 20 to 80 ° C., and the immersion time (dyeing time) in this aqueous solution is usually about 30 to 300 seconds.
The boric acid treatment after dyeing with a dichroic dye is performed by immersing the dyed polyvinyl alcohol resin film in an aqueous boric acid solution. The boric acid content in the boric acid aqueous solution is usually about 2 to 15 parts by weight, preferably about 5 to 12 parts by weight per 100 parts by weight of water. When iodine is used as the dichroic dye, the aqueous boric acid solution preferably contains potassium iodide. The content of potassium iodide in the boric acid aqueous solution is usually about 2 to 20 parts by weight, preferably 5 to 15 parts by weight per 100 parts by weight of water. The immersion time in the boric acid aqueous solution is usually about 100 to 1,200 seconds, preferably about 150 to 600 seconds, and more preferably about 200 to 400 seconds. The temperature of the boric acid aqueous solution is usually 50 ° C. or higher, preferably 50 to 85 ° C.
The polyvinyl alcohol resin film after the boric acid treatment is usually washed with water. The water washing treatment is performed, for example, by immersing a boric acid-treated polyvinyl alcohol resin film in water. A drying process is performed after water washing, and a polarizer is obtained. The water temperature in the water washing treatment is usually about 5 to 40 ° C., and the immersion time is usually about 2 to 120 seconds. The drying process performed after that is normally performed using a hot air dryer or a far-infrared heater. The drying temperature is usually 40 to 100 ° C. Further, the drying treatment time is usually about 120 to 600 seconds.
Thus, the thickness of the polarizer which consists of a polyvinyl alcohol-type resin film obtained can be about 10-50 micrometers.
[Adhesive layer]
The polarizer thus obtained has a protective film made of a transparent resin bonded to at least one surface thereof through an adhesive layer to form a polarizing plate. In the present invention, the adhesive for bonding the protective film to the polarizer is a photocurable component composed of an epoxy compound having an alicyclic epoxy group, a silane coupling agent, and a photocationic polymerization initiator. It is formed from the composition.
(Cationically polymerizable compound)
The above alicyclic epoxy compound will be described as shown in the following formula (I) (CH₂)_mIt is a compound in which a group in the form of removing one or more hydrogen atoms is bonded to another chemical structure. Form an alicyclic ring (CH₂)_mOne or a plurality of hydrogen atoms therein may be appropriately substituted with a linear alkyl group such as a methyl group or an ethyl group.

Among the alicyclic epoxy compounds represented by the above formula (I), an alicyclic ring having an epoxycyclopentane ring (m = 3 in the above formula) or an epoxycyclohexane ring (m = 4 in the above formula). The formula diepoxy compound is preferably used because it provides excellent adhesion. Specific examples of the alicyclic epoxy compound are listed below. Here, the compound name is given first, and then the chemical formula corresponding to each is shown, and the same symbol is attached to the chemical name and the corresponding chemical formula.
A: 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate,
B: 3,4-epoxy-6-methylcyclohexylmethyl 3,4-epoxy-6-methylcyclohexanecarboxylate,
C: ethylene bis (3,4-epoxycyclohexanecarboxylate),
D: Bis (3,4-epoxycyclohexylmethyl) adipate,
E: Bis (3,4-epoxy-6-methylcyclohexylmethyl) adipate,
F: Diethylene glycol bis (3,4-epoxycyclohexyl methyl ether),
G: Ethylene glycol bis (3,4-epoxycyclohexyl methyl ether),
H: 2,3,14,15-diepoxy-7,11,18,21-tetraoxatrispiro [5.2.2.5.2.2] henicosane,
I: 3- (3,4-epoxycyclohexyl) -8,9-epoxy-1,5-dioxaspiro [5.5] undecane,
J: bis (2,3-epoxycyclopentyl) ether,
K: Dicyclopentadiene dioxide and the like.

An aliphatic epoxy compound is a compound having in its molecule at least one oxirane ring (3-membered cyclic ether) bonded to an aliphatic carbon atom. For example, a monofunctional compound such as butyl glycidyl ether or 2-ethylhexyl glycidyl ether. And trifunctional or higher functional epoxy compounds such as trimethylolpropane triglycidyl ether and pentaerythritol tetraglycidyl ether. An epoxy compound having one epoxy group directly bonded to an alicyclic ring and an oxirane ring bonded to an aliphatic carbon atom, such as 4-vinylcyclohexene dioxide and limonene dioxide, also falls under this category. Specifically, an aliphatic diepoxy compound having two oxirane rings bonded to an aliphatic carbon atom in the molecule is preferable. Such a suitable aliphatic diepoxy compound can be represented by the following formula (II), for example.

Y in the formula is an alkylene group having 2 to 9 carbon atoms, an alkylene group having 4 to 9 carbon atoms having an ether bond between them, or a divalent hydrocarbon group having 6 to 18 carbon atoms having an alicyclic structure. is there.
Specifically, the aliphatic diepoxy compound represented by the above formula (II) is diglycidyl ether of alkanediol, diglycidyl ether of oligoalkylene glycol having a repetition number of up to about 4, or diglycidyl ether of alicyclic diol. is there.
Specific examples of diol (glycol) that can be an aliphatic diepoxy compound represented by the formula (II) are listed below. Examples of alkanediol include ethylene glycol, propylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, and 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-pentane Diol, 2,4-diethyl-1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 3,5-heptanediol, 1,8-octanediol, 2-methyl-1,8 -Octanediol, 1,9-nonanediol and the like. Examples of the oligoalkylene glycol include diethylene glycol, triethylene glycol, tetraethylene glycol, and dipropylene glycol. Examples of the alicyclic diol include cyclohexanediol, cyclohexanedimethanol, hydrogenated bisphenol A, and hydrogenated bisphenol F.
Among these aliphatic diepoxy compounds, diglycidyl ethers of alkanediols are preferred, and particularly preferred ones because of their availability are 1,4-butanediol diglycidyl ether, neopentyl glycol diglycidyl ether and the like. is there.
When the alicyclic epoxy compound and the aliphatic epoxy compound are used in combination, the blending ratio of both is 50 to 95% by weight of the alicyclic epoxy compound and the aliphatic epoxy compound based on the total amount of the cationic polymerizable compound. It is preferably 5% by weight or more. By blending 50% by weight or more of the alicyclic epoxy compound, especially the alicyclic diepoxy compound in the whole cationically polymerizable compound, the storage elastic modulus at 80 ° C. of the cured product becomes 1,000 MPa or more. Thus, the polarizer in the polarizing plate in a state where the polarizer and the protective film are bonded is not easily broken. In addition, by blending an aliphatic epoxy compound, for example, a diglycidyl ether compound of the formula (II) in an amount of 5% by weight or more based on the whole cationic polymerizable compound, the adhesion between the polarizer and the protective film is further improved. When the amount is too large, the storage elastic modulus of the cured product is lowered and the polarizer is easily cracked. Therefore, the amount is preferably 45% by weight or less based on the total amount of the cationically polymerizable compound. In addition, the sum total of the mixture ratio of an alicyclic epoxy compound and an aliphatic epoxy compound does not exceed 100 weight%.
When the alicyclic epoxy compound of the formula (I) and the diglycidyl ether compound of the formula (II) as described above are used in combination as the cationic polymerizable compound constituting the photocurable composition, each is explained above. In addition to these, other cationically polymerizable compounds may be included within the range of the above amount. Examples of other cationically polymerizable compounds include epoxy compounds and oxetane compounds that do not fall under the formula (I) and formula (II). Epoxy compounds not corresponding to formula (I) include compounds having only one epoxy group directly bonded to the alicyclic ring in the molecule, and epoxy compounds not corresponding to formula (II) include those other than formula (II) An aliphatic epoxy compound having an oxirane ring bonded to an aliphatic carbon atom, an aromatic epoxy compound, and the like are included. An oxetane compound is a compound having an oxetane ring (4-membered ring ether).
Examples of aliphatic epoxy compounds having an oxirane ring bonded to an aliphatic carbon atom other than formula (II) include triglycidyl ether of glycerin, triglycidyl ether of trimethylolpropane, and diglycidyl ether of polyethylene glycol. .
The aromatic epoxy compound may be a glycidyl ether of an aromatic polyhydroxy compound having at least two phenolic hydroxyl groups in the molecule. Specific examples thereof include diglycidyl ether of bisphenol A and diglycidyl ether of bisphenol F. Bisphenol S diglycidyl ether, phenol novolac resin glycidyl ether, and the like.
An oxetane compound is a compound having a 4-membered ring ether (oxetanyl group) in the molecule, and specific examples thereof include the following compounds.
3-ethyl-3-hydroxymethyloxetane, 1,4-bis [(3-ethyl-3-oxetanyl) methoxymethyl] benzene, 3-ethyl-3- (phenoxymethyl) oxetane, di [(3-ethyl-3 -Oxetanyl) methyl] ether, 3-ethyl-3- (2-ethylhexyloxymethyl) oxetane, 3-ethyl-3- (cyclohexyloxymethyl) oxetane, phenol novolac oxetane, 1,3-bis [(3-ethyloxetane -3-yl) methoxy] benzene, oxetanylsilsesquioxane, oxetanyl silicate and the like.
The oxetane compound described above is improved in curability as compared with the case where only the epoxy compound is used as the cationic polymerizable compound by blending at a ratio of 30% by weight or less based on the total amount of the cationic polymerizable compound. An effect may be expected.
(Silane coupling agent)
The silane coupling agent can be a compound in which at least one hydrolyzable alkoxy group and another organic group are bonded to a silicon atom. By adding a silane coupling agent, for example, hydrogen fluoride produced as a by-product due to decomposition of the photocationic polymerization initiator is captured and discoloration of the polarizer is suppressed, and as a result, discoloration of the polarizing plate can be suppressed.
Examples of silane coupling agents include methyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris (2-methoxyethoxy) silane, 3-glycidoxypropyltrimethoxysilane, and 3-glycidoxypropylmethyldimethoxysilane. 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, 3-chloropropylmethyldimethoxysilane, 3-chloropropyltrimethoxysilane, 3-methacryloyloxypropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3 -Glycidoxypropyltriethoxysilane, 3-glycidoxypropyldimethoxymethylsilane, 3-glycidoxypropylethoxydimethylsilane, 2- (3,4-epoxycyclohexyl) Such as triethoxysilane and the like. Among these silane coupling agents, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, 2- (3,4- Epoxycyclohexyl) ethyltriethoxysilane has a glycidyloxy group or an alicyclic epoxy group in the molecule, so that when the photocurable composition is irradiated with active energy rays, it is cation with a photocurable component. Cures by polymerization reaction. Therefore, these additions do not particularly reduce the elastic modulus of the resin and the adhesive force between the polarizer and the protective film, and thus are particularly preferably used.
The silane coupling agent may be used alone or in combination of two or more.
The compounding amount of the silane coupling agent is about 4 to 50 parts by weight, preferably 7 to 50 parts by weight, and more preferably about 7 to 20 parts by weight with respect to 100 parts by weight of the photocurable component. When the amount of the silane coupling agent with respect to 100 parts by weight of the photocurable component is 4 parts by weight or less, the effect of suppressing the change in hue at the time of heating is not sufficient, and further, the adhesion with the polarizer and the protective film is improved. Almost no effect is obtained. Further, when the amount of the silane coupling agent with respect to 100 parts by weight of the photocurable component is 50 parts by weight or more, the viscosity change with time in the photocurable composition increases, or the storage elastic modulus in the adhesive after curing. Tend to decrease significantly.
(Photocationic polymerization initiator)
In the present invention, the photocurable component described above is cured by cationic polymerization by irradiation with active energy rays to form an adhesive layer, and therefore a photocationic polymerization initiator is blended in the photocurable composition. The cationic photopolymerization initiator generates a cationic species or a Lewis acid upon irradiation with an active energy ray such as visible light, ultraviolet ray, X-ray, or electron beam, and initiates a polymerization reaction of the photocationic curable component. . Since the cationic photopolymerization initiator acts catalytically by light, it is excellent in storage stability and workability even when mixed with the cationic photocuring component. Examples of the compound that generates a cationic species or a Lewis acid upon irradiation with active energy rays include onium salts such as aromatic iodonium salts and aromatic sulfonium salts, aromatic diazonium salts, and iron-arene complexes.
The aromatic iodonium salt is a compound having a diaryl iodonium cation, and typical examples of the diaryl iodonium cation include a diphenyl iodonium cation. An aromatic sulfonium salt is a compound having a triarylsulfonium cation, and typical examples of the triarylsulfonium cation include triphenylsulfonium cation and 4,4′-bis (diphenylsulfonio) diphenylsulfide cation. Can do. The aromatic diazonium salt is a compound having a diazonium cation, and typical examples of the diazonium cation include a benzenediazonium cation. The iron-arene complex is typically a cyclopentadienyl iron (II) arene cation complex salt.
The cations shown above constitute a photocationic polymerization initiator in pairs with anions (anions). Examples of anions constituting the photocationic polymerization initiator include hexafluorophosphate anion PF₆ ⁻, Hexafluoroantimonate anion SbF₆ ⁻, Pentafluorohydroxyantimonate anion SbF₅(OH)⁻, Hexafluoroarsenate anion AsF₆ ⁻, Tetrafluoroborate anion BF₄ ⁻, Tetrakis (pentafluorophenyl) borate anion B (C₆F₅)₄ ⁻and so on.
Among these cationic photopolymerization initiators, especially aromatic sulfonium salts have ultraviolet absorption characteristics even in the wavelength region near 300 nm, and therefore provide a cured product having excellent curability and good mechanical strength and adhesive strength. Therefore, it is preferably used.
Various photocationic polymerization initiators are commercially available. Examples of commercially available products include the “CPI” series sold by Sun Apro Co., Ltd., the “CYRACURE UVI” series sold by Dow Chemical Co., Ltd., and the “Adekaoptomer” sold by ADEKA Corporation. "SP" series, "IRGACURE" series sold by BASF Germany (however, classified as a cationic photopolymerization initiator), "Sun-Aid SI" series sold by Sanshin Chemical Industry Co., Ltd., There are “UVACURE 1590” sold by Daicel-Cytec.
The compounding amount of the photocationic polymerization initiator is 1 to 10 parts by weight based on 100 parts by weight of the whole cationic polymerizable compound. By blending 1 part by weight or more of the cationic photopolymerization initiator per 100 parts by weight of the cationically polymerizable compound, the cationically polymerizable compound can be sufficiently cured, and high mechanical strength and adhesive strength are given to the obtained polarizing plate. On the other hand, when the amount increases, the ionic substance in the cured product increases, which may increase the hygroscopicity of the cured product and reduce the durability of the polarizing plate. And 10 parts by weight or less per 100 parts by weight of the cationically polymerizable compound. The amount of the cationic photopolymerization initiator is preferably 2 parts by weight or more per 100 parts by weight of the cationic polymerizable compound, and preferably 6 parts by weight or less.
(Other components that can be added to the photo-curable adhesive)
The photocurable composition may contain other components in addition to the photocationic curable component and the photocationic polymerization initiator described above. Specific examples of other components that can be blended include photosensitizers, photosensitizers, thermal cationic polymerization initiators, chain transfer agents, thermoplastic resins, flow regulators, antifoaming agents, leveling agents, organic There are solvents. Depending on the type of protective film to be bonded to the polarizer, it may be preferable to blend a photosensitizer and further a photosensitization aid.
The photosensitizer is a compound that exhibits maximum absorption at a wavelength longer than the maximum absorption wavelength exhibited by the photocationic polymerization initiator and promotes the polymerization initiation reaction by the photocationic polymerization initiator. As such a photosensitizer, an anthracene compound is preferably used. As anthracene compounds that can be used as photosensitizers, 9,10-dimethoxyanthracene, 9,10-diethoxyanthracene, 9,10-dipropoxyanthracene, 9,10-diisopropoxyanthracene, 9,10-dibutoxyanthracene 9,10-dipentyloxyanthracene, 9,10-dihexyloxyanthracene and the like.
The photosensitizing assistant is a compound that further promotes the action of the photosensitizer. As such a photosensitizing assistant, naphthalene compounds are preferably used. 1,4-dimethoxynaphthalene, 1-ethoxy-4-methoxynaphthalene, 1,4-diethoxynaphthalene, 1,4-dipropoxynaphthalene, 1,4-dibutoxy as naphthalene compounds that can serve as photosensitizers And naphthalene.
In the case of blending these other components, the amount thereof is, for example, in the range of 10 parts by weight or less to the blending purpose with respect to 100 parts by weight of the photocationic curable component that is the main component of the photocurable composition. May be selected as appropriate.
[Protective film]
In the present invention, a polarizer comprising the above-described polyvinyl alcohol-based resin film is laminated with a protective film via the photocurable composition described above, and the photocurable composition is cured to form a polarizing plate. To do. The protective film can be composed of an acetylcellulose-based resin film such as triacetylcellulose, which has been most widely used as a protective film for polarizing plates, or a resin film having a lower moisture permeability than triacetylcellulose. The moisture permeability of triacetyl cellulose is approximately 400 g / m.²/ 24 hr.
In one preferred embodiment, the protective film bonded to at least one surface of the polarizer is composed of an acetylcellulose-based resin. In another preferred embodiment, the protective film bonded to at least one surface of the polarizer is a resin film having a moisture permeability lower than that of triacetyl cellulose, such as a moisture permeability of 300 g / m.²/ 24hr or less of resin film. Examples of the resin constituting such a resin film with low moisture permeability include amorphous polyolefin resin, polyester resin, acrylic resin, polycarbonate resin, and chain polyolefin resin. In still another preferred embodiment, a protective film made of an acetylcellulose-based resin is bonded to one surface of the polarizer via the adhesive layer, and the other surface of the polarizer is also interposed via the adhesive layer. Then, a protective film made of a transparent resin having a low moisture permeability as described above is bonded.
An acetyl cellulose resin is a resin in which at least a part of hydroxyl groups in cellulose is acetate esterified, even if it is a mixed ester in which part is acetated and partly esterified with another acid. Good. Specific examples of the acetyl cellulose resin include triacetyl cellulose, diacetyl cellulose, cellulose acetate propionate, and cellulose acetate butyrate.
An amorphous polyolefin-based resin is a polymer having a polymerized unit of cyclic olefin, such as norbornene, tetracyclododecene (also known as dimethanooctahydronaphthalene), or a compound having a substituent bonded thereto. It may be a copolymer obtained by copolymerizing a chain olefin and / or an aromatic vinyl compound. In the case of a homopolymer of a cyclic olefin or a copolymer of two or more kinds of cyclic olefins, a double bond remains by ring-opening polymerization, and hydrogenated ones are generally used as amorphous polyolefin-based resins. Used. Of these, thermoplastic norbornene resins are typical.
The polyester resin is a polymer obtained by condensation polymerization of a dibasic acid and a dihydric alcohol, and polyethylene terephthalate is representative. Acrylic resin is a polymer with methyl methacrylate as the main monomer. In addition to methyl methacrylate homopolymer, methyl methacrylate and acrylic esters and aromatic vinyl compounds such as methyl acrylate It may be a copolymer. The polycarbonate-based resin is a polymer having a carbonate bond (—O—CO—O—) in the main chain, and is typically obtained by condensation polymerization of bisphenol A and phosgene. The chain polyolefin-based resin is a polymer mainly containing a chain olefin such as ethylene or propylene, and can be a homopolymer or a copolymer. Among them, a propylene homopolymer and a copolymer in which a small amount of ethylene is copolymerized with propylene are representative.
Such a protective film has various surface treatment layers such as a hard coat layer, an antireflection layer, an antiglare layer, and an antistatic layer on the surface opposite to the surface to be bonded to the polarizer. Also good. The protective film can have a thickness of about 5 to 150 μm including the case where such a surface treatment layer is formed. The thickness is preferably 10 μm or more, preferably 120 μm or less, more preferably 100 μm or less.
[Adhesion between polarizer and protective film]
In adhering the polarizer and the protective film, the photocurable composition described above is applied to one or both of the bonded surfaces of the polarizer and the protective film, and the polarizer and the protective film are interposed through the coating layer. The application layer of the uncured photocurable composition is bonded and cured by irradiating active energy rays, and the protective film is fixed on the polarizer. The coating layer of a photocurable composition may be formed in the bonding surface of a polarizer, and may be formed in the bonding surface of a protective film. For forming the coating layer, various coating methods such as a doctor blade, a wire bar, a die coater, a comma coater, and a gravure coater can be used. Moreover, the system which casts a photocurable composition in the meantime can also be employ | adopted, supplying a polarizer and a protective film continuously so that both bonding surfaces may become inside. Since each coating method has an optimum viscosity range, it is also a useful technique to adjust the viscosity using a solvent. As the solvent for this purpose, a solvent that dissolves the photocurable composition satisfactorily without degrading the optical performance of the polarizer is used, but the type is not particularly limited. For example, organic solvents such as hydrocarbons typified by toluene and esters typified by ethyl acetate can be used. The thickness of the adhesive layer after curing is usually 20 μm or less, preferably 10 μm or less, more preferably 5 μm or less. When the adhesive layer becomes thick, the reaction rate of the adhesive composition decreases, and the wet heat resistance of the polarizing plate tends to deteriorate.
In adhering the polarizer and the protective film, the corona discharge treatment, plasma treatment, flame treatment, primer treatment, anchor coating treatment is performed on one or both of the bonding surfaces of the polarizer before applying the photocurable composition. Such an easy adhesion treatment may be performed.
The light source used for irradiating the application layer of the photocurable composition with active energy rays may be any light source that generates ultraviolet rays, electron beams, X-rays, and the like. In particular, a low-pressure mercury lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp, an ultrahigh-pressure mercury lamp, a chemical lamp, a black light lamp, a microwave excitation mercury lamp, a metal halide lamp and the like having a light emission distribution at a wavelength of 400 nm or less are preferably used. The irradiation intensity of the active energy ray to the photocurable composition is determined for each composition of the photocurable composition, and is not particularly limited, but the irradiation intensity in the wavelength region effective for activation of the initiator. 0.1 ~ 100mW / cm²It is preferable that Irradiation intensity to the photocurable composition is 0.1 mW / cm²If it is less than 100 mW / cm, the reaction time becomes too long.²If it exceeds 1, the heat radiated from the lamp and the heat generated during polymerization of the photocurable composition may cause yellowing of the photocurable composition or deterioration of the polarizer. The light irradiation time to the photocurable composition is controlled for each composition to be cured and is not particularly limited, but the integrated light amount expressed as the product of the irradiation intensity and the irradiation time is 10 to 5,000 mJ. / Cm²It is preferable to set so that. Integrated light quantity to the photocurable composition is 10 mJ / cm²When the amount is less than 1, the generation of active species derived from the initiator is not sufficient, and the resulting adhesive layer may be insufficiently cured, while the integrated light amount is 5,000 mJ / cm.²If it exceeds 1, irradiation time becomes very long, which is disadvantageous for productivity improvement.
When a protective film is bonded to both sides of the polarizer, active energy rays may be irradiated from either protective film side. For example, one protective film contains an ultraviolet absorber and the other protective film When the ultraviolet absorber is not contained, it is preferable to irradiate the active energy ray from the protective film side not containing the ultraviolet absorber in order to effectively utilize the irradiated active energy ray and increase the curing rate.
[Optical characteristics of polarizing plate]
The polarizing plate of the present invention is excellent in heat resistance because it hardly deteriorates even when exposed to high temperature conditions by blending a predetermined amount of a silane coupling agent into the photocurable composition. For example, an ab value expressed by the square root value of the sum of the square value of the a value and the square value of the b value of the transmitted hue is 0. Since it can be kept in the range of 5 to 4, discoloration of the polarizing plate due to high temperature hardly occurs.
The above transmission hue means the hue of light transmitted from the other surface when light is applied from one surface of the polarizing plate. The hue here can be expressed by a value and b value in the Lab color system, and is measured using standard light. In the present invention, the transmission hue of the polarizing plate was actually measured on the polarizing film with a protective film (a cycloolefin-based film and an acetylcellulose-based film in the examples described later) stuck on the acetylcellulose-based film. An adhesive layer is provided and the adhesive layer is bonded to the glass plate. The Lab color system is represented by Hunter's lightness index L and hues a and b, as described in “5.5 Accelerated weather resistance test” of JIS K 5981: 2006 “Synthetic resin powder coating”. Is. As a concept similar to the Lab color system, JIS Z 8729: 2004 “Color Display Method-L^*a^*b^*Color system and L^*u^*v^*L defined in "color system"^*a^*b^*Although there is a color system, the Lab color system is adopted in the present invention. The values of the lightness index L and hues a and b are calculated from the tristimulus values X, Y and Z defined in JIS Z 8722: 2009 “Color Measurement Method-Reflection and Transmission Object Color” by the following formula: .
L = 10Y^1/2
A = 17.5 (10.2X-Y) / Y^1/2
B = 7.0 (Y-0.847Z) / Y^1/2.
In the Lab color system, the hue a value and b value can indicate positions corresponding to saturation, and when the hue a value increases, the hue changes to red, and when the hue b value increases, the hue changes to yellow. Each changes. The ab value representing the change in hue is calculated by the following formula (III).
Ab = (a²+ B²)^1/2(III)
[Laminated optical member]
The polarizing plate of the present invention can be made into a laminated optical member by laminating optical layers having optical functions other than the polarizing plate. Typically, a laminated optical member is obtained by laminating and attaching an optical layer to a protective film of a polarizing plate via an adhesive or a pressure-sensitive adhesive. According to the invention, a protective film can be bonded via a photocurable composition, and an optical layer can be laminated and bonded to the other surface of the polarizer via an adhesive or a pressure-sensitive adhesive. In the latter case, if the photocurable composition defined in the present invention is used as an adhesive for adhering the polarizer and the optical layer, the optical layer can simultaneously be a protective film defined in the present invention.
As an example of the optical layer laminated on the polarizing plate, for the polarizing plate arranged on the back side of the liquid crystal cell, the reflective layer is laminated on the opposite side of the polarizing plate from the side facing the liquid crystal cell. A layer, a transflective layer, a light diffusion layer, a light collector, a brightness enhancement film, and the like. In addition, for both the polarizing plate disposed on the front side of the liquid crystal cell and the polarizing plate disposed on the back side of the liquid crystal cell, a retardation plate laminated on the side of the polarizing plate facing the liquid crystal cell, etc. There is.
The reflective layer, transflective layer, or light diffusion layer is a reflective polarizing plate (optical member), a transflective polarizing plate (optical member), or a diffusing polarizing plate (optical member), respectively. Is provided. The reflective polarizing plate is used in a liquid crystal display device of a type that reflects and displays incident light from the viewing side. Since a light source such as a backlight can be omitted, the liquid crystal display device can be easily thinned. The transflective polarizing plate is used as a reflection type in a bright place and used in a liquid crystal display device that displays light from a backlight in a dark place. An optical member as a reflective polarizing plate can form a reflective layer by attaching a foil or a vapor deposition film made of a metal such as aluminum to a protective film on a polarizer, for example. An optical member as a transflective polarizing plate can be formed by using the reflective layer as a half mirror, or by adhering a reflective plate containing a pearl pigment or the like and exhibiting light transmittance to the polarizing plate. On the other hand, an optical member as a diffusion type polarizing plate can be obtained by various methods such as a method of performing a mat treatment on a protective film on a polarizing plate, a method of applying a resin containing fine particles, and a method of adhering a film containing fine particles. Use to form a fine relief structure on the surface.
Furthermore, an optical member can be formed as a polarizing plate for both reflection and diffusion. In that case, for example, a method of providing a reflective layer reflecting the concavo-convex structure on the fine concavo-convex structure surface of the diffusing polarizing plate is adopted. it can. The reflective layer having a fine concavo-convex structure has advantages such that incident light is diffused by irregular reflection, directivity and glare can be prevented, and uneven brightness can be suppressed. In addition, the resin layer or film containing fine particles also has an advantage that incident light and its reflected light are diffused when passing through the fine particle-containing layer, and light and dark unevenness can be suppressed. The reflective layer reflecting the surface fine concavo-convex structure can be formed by directly attaching a metal to the surface of the fine concavo-convex structure by a method such as vapor deposition such as vacuum deposition, ion plating, sputtering, or plating. The fine particles to be blended to form the fine surface uneven structure include, for example, silica, aluminum oxide, titanium oxide, zirconia, tin oxide, indium oxide, cadmium oxide, and antimony oxide having an average particle size of 0.1 to 30 μm. It can be inorganic fine particles, organic fine particles such as crosslinked or non-crosslinked polymers, and the like.
The condensing plate is used for the purpose of optical path control and can be formed as a prism array sheet, a lens array sheet, or a dot-attached sheet.
The brightness enhancement film is used for the purpose of improving the brightness in a liquid crystal display device. For example, a plurality of thin film films having different refractive index anisotropies are laminated to produce anisotropy in reflectance. Examples thereof include a reflective polarization separation sheet designed as described above, an alignment film of a cholesteric liquid crystal polymer, and a circular polarization separation sheet in which the alignment liquid crystal layer is supported on a film substrate.
On the other hand, the above-mentioned retardation plate as an optical layer is used for the purpose of compensation of retardation by a liquid crystal cell. Examples thereof include a birefringent film made of a stretched film of various plastics, a film in which a discotic liquid crystal or a nematic liquid crystal is oriented and fixed, and a film substrate on which the above liquid crystal layer is formed. When the liquid crystal layer is formed on the film substrate, a cellulose resin film such as triacetyl cellulose is preferably used as the film substrate.
Examples of the plastic forming the birefringent film include amorphous polyolefin resins, polycarbonate resins, acrylic resins, chain polyolefin resins such as polypropylene, polyvinyl alcohol, polystyrene, polyarylate, polyamide, and the like. It is done. The stretched film can be processed by an appropriate method such as uniaxial or biaxial. Two or more retardation plates may be used in combination for the purpose of controlling optical characteristics such as broadening the band.
Among the laminated optical members, those including a retardation plate as an optical layer other than the polarizing plate are preferably used because optical compensation can be effectively performed when applied to a liquid crystal display device. The optimum retardation value (in-plane and thickness direction) of the retardation plate may be selected according to the liquid crystal cell to be applied.
The laminated optical member can be a laminate of two layers or three or more layers by combining a polarizing plate and one or more layers selected according to the purpose of use from the various optical layers described above. In that case, the various optical layers forming the laminated optical member are integrated with the polarizing plate using an adhesive or pressure-sensitive adhesive, but the adhesive or pressure-sensitive adhesive layer used for this purpose is good. As long as it is formed, there is no particular limitation. It is preferable to use a pressure-sensitive adhesive (also referred to as a pressure-sensitive adhesive) from the viewpoint of easy bonding work and prevention of optical distortion. As the pressure-sensitive adhesive, those having a base polymer such as an acrylic polymer, a silicone polymer, polyester, polyurethane, or polyether can be used. Among them, like acrylic adhesives, it has excellent optical transparency, retains appropriate wettability and cohesion, has excellent adhesion to substrates, and has weather resistance and heat resistance. However, it is preferable to select and use a material that does not cause peeling problems such as floating and peeling under the conditions of heating and humidification. In acrylic adhesives, alkyl esters of (meth) acrylic acid having an alkyl group having 20 or less carbon atoms such as methyl, ethyl and butyl groups, and (meth) acrylic acid and hydroxyethyl (meth) acrylate Based on an acrylic copolymer having a weight average molecular weight of 100,000 or more, which is blended with a functional group-containing acrylic monomer comprising a glass transition temperature of preferably 25 ° C. or less, more preferably 0 ° C. or less. Useful as a polymer.
The pressure-sensitive adhesive layer is formed on the polarizing plate by, for example, dissolving or dispersing the pressure-sensitive adhesive composition in an organic solvent such as toluene or ethyl acetate to prepare a 10 to 40% by weight solution, which is directly applied on the polarizing plate. It can be performed by a coating method or a method in which a pressure-sensitive adhesive layer is previously formed on a protective film and then transferred onto a polarizing plate. The thickness of the pressure-sensitive adhesive layer is determined according to the adhesive force and the like, but a range of about 1 to 50 μm is appropriate.
In addition, the pressure-sensitive adhesive layer is filled with glass fiber, glass beads, resin beads, metal powder, other inorganic powders, pigments, colorants, antioxidants, antistatic agents, UV absorbers, etc., as necessary. Can be contained. Antistatic agents include ionic compounds and nonionic compounds. Examples of ultraviolet absorbers include salicylic acid ester compounds, benzophenone compounds, benzotriazole compounds, cyanoacrylate compounds, and nickel complex compounds.
The laminated optical member can be arranged on one side or both sides of the liquid crystal cell. The liquid crystal cell to be used is arbitrary. For example, a liquid crystal display device using various liquid crystal cells such as an active matrix drive type typified by a thin film transistor type and a simple matrix drive type typified by a super twisted nematic type. Can be formed. A pressure-sensitive adhesive is usually used for bonding the laminated optical member and the liquid crystal cell.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples. In the examples, “parts” and “%” representing amounts used or contents are based on weight unless otherwise specified. Moreover, the cationically polymerizable compound, the silane coupling agent, and the photocationic polymerization initiator used in the following examples are as follows, and are denoted by respective symbols below.
<Cationically polymerizable compound>
(A1) 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate: obtained from Daicel Chemical Industries, Ltd., trade name Celoxide 2021P. In Table 1 below, it is abbreviated as “(a1)”.
(A2) 1,4-butanediol diglycidyl ether: obtained from Nagase ChemteX Corporation, trade name EX-214L. In Table 1 below, it is abbreviated as “(a2)”.
<Silane coupling agent>
KBM-403: 3-glycidoxypropyltrimethoxysilane, liquid, obtained from Shin-Etsu Chemical Co., Ltd. In Table 1 below, it is abbreviated as “KBM-403”.
KBM-303: 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, liquid, obtained from Shin-Etsu Chemical Co., Ltd. In Table 1 below, it is abbreviated as “KBM-303”.
<Photocationic polymerization initiator>
CPI-100P: 4,4′-bis (diphenylsulfonio) phenyl sulfide bis (hexafluorophosphate) photocationic polymerization initiator, obtained from San Apro Co., Ltd. In Table 1 below, it is abbreviated as “CPI-100P”.
[Examples 1 to 8 and Comparative Example 1]
(1) Preparation of photocurable composition After mixing each component by the mixture ratio (unit is a part) shown in Table 1, it degas | defoamed and prepared the photocurable composition. In addition, a photocationic polymerization initiator was mix | blended as a 50% propylene carbonate solution, and displayed in Table 1 with the solid content.

(2) Preparation of polarizing plate Corona discharge treatment was applied to the surface of a cycloolefin film [trade name “ZEONOR”, obtained from Nippon Zeon Co., Ltd.] having a thickness of 50 μm, and a bar coater was used on the corona discharge treatment surface. Each of the photocurable compositions prepared above was applied so that the film thickness after curing was about 3.5 μm. A 28 μm-thick polyvinyl alcohol-iodine polarizer was bonded to the coated surface. In addition, a 40 μm thick acetylcellulose film (trade name “N-TAC KC4FR-1”, obtained from Konica Minolta Opto Co., Ltd.) was subjected to corona discharge treatment, and the corona discharge treatment surface was The same photocurable composition was applied with a bar coater so that the film thickness after curing was about 3.5 μm. On the coated surface, the polarizer having the cycloolefin-based film prepared above bonded on one side was bonded on the polarizer side to prepare a laminate. From the acetylcellulose film side of this laminate, ultraviolet rays were irradiated using an ultraviolet irradiation device with a belt conveyor (the lamp uses a “D bulb” manufactured by Fusion UV Systems) so that the integrated light amount was 500 mJ / cm ^2. The photocurable composition was cured. Thus, a polarizing plate in which protective films were bonded to both sides of the polarizer was produced.
Next, the polarizing plate with an adhesive was produced using the polarizing plate produced above. The following were used as the isocyanate-based crosslinking agent, silane coupling agent and antistatic agent.
<Isocyanate-based crosslinking agent>
Coronate L: Trimethylolpropane adduct of tolylene diisocyanate in ethyl acetate solution (solid content: 75%), obtained from Nippon Polyurethane Co., Ltd.
<Silane coupling agent>
KBM-403: 3-glycidoxypropyltrimethoxysilane, liquid, obtained from Shin-Etsu Chemical Co., Ltd.
<Antistatic agent>
1-hexylpyridinium hexafluorophosphate, a compound represented by the following formula (IV) and having a melting point of 45 ° C.

(3) Production of polarizing plate with pressure-sensitive adhesive Acrylic pressure-sensitive adhesive prepared by adding an isocyanate-based crosslinking agent, a silane coupling agent, and an antistatic agent to a copolymer of butyl acrylate, methyl acrylate, acrylic acid, and hydroxyethyl acrylate. An organic solvent solution of the agent is applied to the release treatment surface of a 38 μm-thick polyethylene terephthalate film (trade name “SP-PLR382020”, obtained from Lintec Co., Ltd., called release film) that has been subjected to a release treatment. The film was dried with a filter so that the thickness after drying was 20 μm, and a sheet-like adhesive with a release film was produced. Next, the surface (adhesive surface) opposite to the release film of the sheet-like pressure-sensitive adhesive obtained above was bonded to the acetylcellulose-based film surface of the polarizing plate prepared in (2) above with a laminator, and the temperature was 23. Curing was carried out for 7 days under the conditions of ° C. and relative humidity of 65% to obtain a polarizing film with an adhesive.
(4) Evaluation of optical properties of polarizing plate The polarizing plate with the adhesive prepared in (3) above was cut into a size of 30 mm × 30 mm, and the surface of the adhesive that was exposed by peeling off the release film was alkali-free glass [product Name “EAGLE XG”, obtained from Corning Inc.], and the a value and b value of each transmitted hue were measured. For measurement, an ultraviolet / visible spectrophotometer “UV-2450” manufactured by Shimadzu Corporation is used with an optional accessory “film holder with polarizer” set, and a polarizing plate in the wavelength range of 380 nm to 780 nm The transmission spectrum was obtained, and the a value and b value of the transmission hue were calculated by software “UV-Probe” attached to the spectrophotometer. Based on this measured value, the ab value of the transmitted hue was calculated according to the following equation.
ab = (a ² + b ² ) ^1/2 (III)
(5) Durability evaluation of polarizing plate under heating A heating test is performed in which the polarizing plate bonded to the alkali-free glass prepared in (4) above is stored in a heating environment at a temperature of 90 ° C. for 24 hours. The a value and b value of the transmission hue of the polarizing plate were measured. The measurement and the calculation of the ab value were performed by the same method as in (4) above. Table 2 shows the change Δab value of the transmitted hue before and after the heating test.
Δab = ab value after heating test−ab value before heating test (6) 180 degree peeling test The polarizing plate produced in the above (2) was cut into a size of 200 mm length × 25 mm width. Then, an acrylic pressure-sensitive adhesive layer is provided on the acetylcellulose-based film side to form a test piece for measuring the peel strength between the acetylcellulose-based film and the polarizer, and this pressure-sensitive adhesive layer is attached to a glass plate. Put a cutter blade between the polarizer and the protective film (acetylcellulose film) on the adhesive side, peel off 30 mm from the end in the length direction, and test the peeled cycloolefin film and polarizer I grabbed at the grip part. The test piece in this state was subjected to JIS K 6854-2: 1999 “Adhesive—Peeling adhesive strength test method—Part 2: 180 degree peeling” in an atmosphere at a temperature of 23 ° C. and a relative humidity of 55%. A 180 degree peeling test was performed at a gripping moving speed of 300 mm / min, and an average peeling force over a length of 170 mm excluding 30 mm of the gripping part was obtained. When the peel strength is less than 0.5 N / 25 mm, when the polarizing plate is cut, or when an impact is applied to the end of the polarizing plate when handling the cut polarizing plate, the polarizer at the end Since the protective film may be peeled off, the value is preferably 0.5 N / 25 mm or more. The results are shown in Table 2.
(7) Measurement of storage modulus of cured product Polyethylene terephthalate film [trade name “Toyobo Ester Film E7002” manufactured by Toyobo Co., Ltd.] on one side, coating machine [Bar coater, manufactured by Daiichi Rika Co., Ltd.] Each of the photocurable compositions prepared in (1) above was applied so that the film thickness after curing was about 30 μm. Next, the photocurable composition was cured by irradiating ultraviolet rays with a “D bulb” manufactured by Fusion UV Systems Co., Ltd. so that the integrated light amount was 3,000 mJ / cm ² . This was cut into a size of 5 mm wide × 30 mm long, and the polyethylene terephthalate film was peeled off to obtain a sheet-like cured product of the photocurable composition. This sheet-like cured product is gripped at a distance of 2 cm between grips using a dynamic viscoelasticity measuring device “DVA-220” manufactured by IT Measurement Control Co., Ltd. so that its long side is in the pulling direction. The storage elastic modulus at temperatures of 30 ° C. and 80 ° C. was measured by setting the frequency of tension and shrinkage to 10 Hz and the temperature rising rate to 3 ° C./min. The results are shown in Table 2.

As shown in Table 2, in Examples 1 to 8 using a photocurable composition containing a photocurable component containing an epoxy compound having an alicyclic epoxy group, a silane coupling agent, and a photocationic polymerization initiator It was confirmed that the obtained polarizing plate can suppress the discoloration of the polarizing plate after heating, the adhesiveness between the protective film and the polarizer is good, and the elastic modulus of the cured product of the resin is also good.

Claims

A protective film made of a transparent resin film is bonded via an adhesive to a polarizer made of a polyvinyl alcohol-based resin on which a dichroic dye is adsorbed and oriented,
The adhesive is formed from a photocurable composition containing a photocurable component containing an epoxy compound having an alicyclic epoxy group, a silane coupling agent, and a photocationic polymerization initiator. Board.
The polarizing plate according to claim 1, wherein the silane coupling agent has a glycidyloxy group or an alicyclic epoxy group in the molecule.
The polarizing plate according to claim 1 or 2, wherein the photocurable component forming the adhesive further contains an aliphatic epoxy compound.
4. The polarizing plate according to claim 1, wherein the photocurable composition contains 4 to 50 parts by weight of the silane coupling agent with respect to 100 parts by weight of the photocurable component.
A cycloolefin-based resin film is bonded to one side of the polarizer via the adhesive, and an acetylcellulose-based resin film is bonded to the other surface of the polarizer via the adhesive, and the acetylcellulose-based resin film. 5. The polarizing plate according to claim 1, wherein a pressure-sensitive adhesive layer having an antistatic function is formed on the side opposite to the surface in contact with the polarizer.