WO2012133161A1

WO2012133161A1 - Photocurable adhesive, polarizing plate, and laminate optical member

Info

Publication number: WO2012133161A1
Application number: PCT/JP2012/057475
Authority: WO
Inventors: 悦夫久米; 岩田　智
Original assignee: 住友化学株式会社; 株式会社Adeka
Priority date: 2011-03-29
Filing date: 2012-03-23
Publication date: 2012-10-04
Also published as: CN103443236A; JP2012208250A; KR20140020978A; TWI582200B; JP5677883B2; CN103443236B; TW201245382A; KR101979467B1

Abstract

Provided is a photocurable adhesive for pasting a protective film comprising a transparent resin onto a polarizer comprising a polyvinyl alcohol resin film, wherein the photocurable adhesive contains 100 parts by weight of a photo cation curable component (A) and 1-10 parts by weight of a photo cation polymerization initiator (B), the photo cation curable component (A) containing the following (A1)-(A3) at the following amounts relative to the total amount thereof: 60-75 wt% of an alicyclic diepoxy compound (A1) represented by formula (I); 5-35 wt% of a diglycidyl compound (A2) represented by formula (II); and 2-15 wt% of a monofunctional epoxy compound (A3) represented by formula (III).

Description

Photo-curable adhesive, polarizing plate and laminated optical member

The present invention uses a photocurable adhesive for bonding a polarizer made of a polyvinyl alcohol-based resin film on which a dichroic dye is adsorbed and oriented and a protective film made of a transparent resin, and the photocurable adhesive. The present invention also relates to a polarizing plate formed by laminating a protective film on a polarizer, and a laminated optical member obtained by laminating another optical layer such as a retardation film on the polarizing plate.

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 a polarizer, but in many cases, a layer having another optical function is attached to the other side as a protective film instead of a simple protective film. Combined. Further, 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 is excellent in transparency, easily forms various surface treatment layers and optical functional layers, has high moisture permeability, and can be dried after being bonded to a polarizer using an aqueous adhesive as described above. While having an excellent advantage as a protective film such that it can be performed smoothly, the polarizing plate bonded as a protective film due to its high moisture permeability is, for example, at a temperature of 70 ° C. and a relative humidity of 90 under wet heat. %, There was a problem such as easy to cause deterioration. 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 bonding a protective film made of a resin with low moisture permeability to a polyvinyl alcohol polarizer, an aqueous solution of a polyvinyl alcohol resin generally used for bonding a polyvinyl alcohol polarizer and a triacetyl cellulose film is conventionally used. When the adhesive is used, there are problems 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, a protective film made of a resin with low moisture permeability such as an amorphous polyolefin resin is bonded to one surface of a polarizer, and a cellulose resin such as triacetyl cellulose is bonded to the other surface of the polarizer. There is also a proposal of bonding a protective film made of a resin with high moisture permeability such as.

Therefore, a high adhesion force is provided between the protective film made of a resin having a low moisture permeability and the polyvinyl alcohol polarizer, and a high adhesion between a highly moisture permeable resin such as a cellulose resin and the polyvinyl alcohol polarizer. There is an attempt to use a photo-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 irradiation with active energy rays, specifically irradiation with ultraviolet rays. It has been proposed that this adhesive is cured by cationic polymerization by, thereby bonding the polarizer and the protective film. Japanese Patent Application Laid-Open No. 2008-257199 (Patent Document 2) discloses a photocurable adhesive comprising a combination of an alicyclic epoxy compound and an epoxy compound having no alicyclic epoxy group, and further containing a photocationic polymerization initiator. A technique using an agent for bonding a polarizer and a protective film is disclosed.

JP 2004-245925 A JP 2008-257199 A

However, the adhesive of the composition specifically disclosed in Patent Document 1 and Patent Document 2 does not necessarily have a sufficiently low viscosity, and is applied to a polarizer or a protective film bonded thereto, and is uniform in a thin film. It was not always easy to form an adhesive layer. In addition, these adhesives do not necessarily exhibit a sufficient storage elastic modulus after curing, and as a result, when the resulting polarizing plate is subjected to a severe temperature history, for example, at a low temperature and at a high temperature. When subjected to a thermal shock test in which the above-mentioned holding was repeated, the polarizer sometimes cracked.

Furthermore, although these known photocurable adhesives adhere the polarizer and the protective film with an appropriate adhesive force, the adhesive force is not necessarily sufficient. For example, the photocurable adhesive can be polarized using the photocurable adhesive. A polarizing plate obtained by bonding a polarizer and a protective film is applied to a liquid crystal display device. When the edge is polished in a state of being cut into a predetermined size, the protective film is peeled off from the polarizer at the edge. There was something to do.

The object of the present invention is to have a sufficiently low viscosity that can be applied at room temperature when bonding a protective film to a polarizer, and exhibit a sufficient storage elastic modulus after curing, resulting in an intense temperature history. It is an object of the present invention to provide a photo-curing adhesive that gives a polarizing plate that is less likely to crack the polarizer even when it is received and that also has improved adhesion between the polarizer and the protective film. Another object of the present invention is to bond a polarizer and a protective film using this photo-curable adhesive, and have excellent adhesion between them, and even when subjected to intense temperature history, the polarizer is cracked. It is to provide a polarizing plate which is not easily generated. Yet another object of the present invention is to provide a laminated optical member suitably used for a liquid crystal display device by laminating another optical layer such as a retardation film on the polarizing plate.

The present inventors have intensively studied to solve such a problem, and as a result, the present invention has been completed. Specifically, in a photocurable adhesive obtained by blending a predetermined amount of a photocationic polymerization initiator with a photocationic curable component, the photocationic curable component mainly comprises a specific alicyclic diepoxy compound. In addition, a diglycidyl compound having two epoxy groups that are not bonded to an alicyclic ring in the molecule and a diglycidyl compound that does not have an aromatic ring, and a single epoxy group that is not bonded to an alicyclic ring in the molecule. It has been found that it is effective to use a composition containing a small amount of a functional epoxy compound. That is, the photocurable adhesive having such a specific composition exhibits a low viscosity at room temperature and gives good coating suitability, and also exhibits a high storage elastic modulus after curing, thereby firmly bonding the polarizer and the protective film. I found out. The present invention includes the following.

[1] A photocurable adhesive for bonding a protective film made of a transparent resin to at least one surface of a polarizer made of a polyvinyl alcohol resin film in which a dichroic dye is adsorbed and oriented,
100 parts by weight of the photocationically curable component (A),
Containing 1 to 10 parts by weight of the cationic photopolymerization initiator (B),
The photocationic curable component (A) is a photocurable adhesive containing the following (A1), (A2) and (A3) in the following amounts based on the total amount.

60 to 75% by weight of an alicyclic diepoxy compound (A1) represented by the following formula (I);

In the formula, each of R ¹ and R ² independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and when the alkyl group has 3 or more carbon atoms, it may have an alicyclic structure; An oxygen atom, an alkanediyl group having 1 to 6 carbon atoms, or the following formulas (Ia) to (Id):

In which Y ¹ to Y ⁴ each represent an alkanediyl group having 1 to 20 carbon atoms, and when it has 3 or more carbon atoms, it has an alicyclic structure. A and b each represents an integer of 0 to 20.

5 to 35% by weight of a diglycidyl compound (A2) represented by the following formula (II);

In the formula, Z is an alkylene group having 1 to 9 carbon atoms, an alkylidene group having 3 or 4 carbon atoms, a divalent alicyclic hydrocarbon group, or a formula —C _m H _2m —Z ¹ —C _n H _2n —. And —Z ¹ — represents —O—, —CO—O—, —O—CO—, —SO ₂ —, —SO—, or —CO—, m And n each independently represents an integer of 1 or more, but the total of both is 9 or less.

2 to 15% by weight of a monofunctional epoxy compound (A3) represented by the following formula (III);

In the formula, R ³ represents an alkyl group having 1 to 15 carbon atoms.
[2] The photocurable adhesive according to [1], wherein in the formula (III) representing the monofunctional epoxy compound (A3), R ³ is an alkyl group having 6 to 10 carbon atoms.

[3] The photocurable adhesive according to [1] or [2], which has a viscosity at 25 ° C. of 100 mPa · sec or less.

[4] The photocurable adhesive according to any one of [1] to [3], wherein the cured product exhibits a storage elastic modulus of 1,000 MPa or more at 80 ° C.

[5] A polarizer composed of a polyvinyl alcohol-based resin film in which a dichroic dye is adsorbed and oriented, and a protective film composed of a transparent resin bonded to at least one surface of the polarizer via an adhesive. The polarizing plate is a cured product of the photocurable adhesive according to any one of [1] to [4].

[6] The polarizing plate according to [5], wherein the protective film bonded to at least one surface of the polarizer is made of an acetylcellulose-based resin mixed with an ultraviolet absorber.

[7] The protective film bonded to at least one surface of the polarizer is made of a transparent resin selected from the group consisting of an amorphous polyolefin resin, a polyester resin, and a chain polyolefin resin. Polarizing plate.

[8] The polarizing plate according to any one of [5] to [7], wherein an adhesive strength by a 180 degree peeling test between the polarizer and the protective film is 0.6 N / 25 mm or more.

[9] A laminated optical member comprising a laminate of the polarizing plate according to any one of [5] to [8] and another optical layer.

[10] The laminated optical member according to [9], wherein the optical layer includes a retardation film.

The photo-curable adhesive of the present invention includes a predetermined amount of each of an alicyclic diepoxy compound (A1), a diglycidyl compound (A2), and a monofunctional epoxy compound (A3) as a photocationic curable component (A). In addition to improving the storage elastic modulus of the adhesive layer after curing, the adhesive strength between the polarizer and the protective film can be increased. Therefore, a polarizing plate in which a protective film made of a transparent resin is bonded to at least one surface of the polarizer via this adhesive will crack the polarizer even when subjected to a severe temperature history such as a thermal shock test. It is hard to occur and has excellent thermal shock resistance. A laminated optical member obtained by laminating another optical layer on this polarizing plate also has excellent thermal shock resistance while fully expressing the function of the polarizing plate.

Hereinafter, embodiments of the present invention will be described in detail. The present invention provides a photocurable adhesive for adhering a protective film made of a transparent resin to a polarizer made of a polyvinyl alcohol-based resin film. The present invention also provides a polarizing plate in which a protective film made of a transparent resin is bonded to the polarizer using the photocurable adhesive, and a laminated optical member in which another optical layer is laminated on the polarizing plate. Is also provided. These photocurable adhesives, polarizing plates, and laminated optical members will be described in order.

[Photocurable adhesive]
In this invention, the photocurable adhesive for adhere | attaching the protective film which consists of transparent resins on the polarizer which consists of a polyvinyl alcohol-type resin film contains the following two components (A) and (B).
(A) a photocationic curable component, and (B) a photocationic polymerization initiator.

(Photocationic curable component)
The photocationic curable component (A), which is a main component of the photocurable adhesive and provides adhesive strength by polymerization curing, contains the following three types of compounds.
(A1) An alicyclic diepoxy compound represented by the formula (I),
(A2) a diglycidyl compound represented by the formula (II), and (A3) a monofunctional epoxy compound represented by the formula (III).

The amount of the alicyclic diepoxy compound (A1) in the photocationic curable component (A) is 60 to 75% by weight based on the total amount of the photocationic curable component (A). By containing 60% by weight or more of the alicyclic diepoxy compound (A1) in the photocationic curable component (A), the storage elastic modulus after curing the photocurable adhesive containing it is increased, for example, The storage elastic modulus at 80 ° C. can be set to 1,000 MPa or more, and even when a polarizing plate having a polarizer and a protective film bonded through the adhesive is exposed to a severe temperature history, the polarizer is prevented from cracking. be able to. On the other hand, when the amount exceeds 75% by weight, the amount of the diglycidyl compound (A2) and the monofunctional epoxy compound (A3) described below becomes relatively small, and the photocurable adhesive contemplated in the present invention It is difficult to achieve both low viscosity and improved adhesion between the polarizer / protective film. More preferably, the alicyclic diepoxy compound (A1) is contained in an amount of 70% by weight or more based on the total amount of the photocationic curable component (A).

The amount of the diglycidyl compound (A2) in the photocationic curable component (A) is 5 to 35% by weight. By blending 5% by weight or more of the diglycidyl compound (A2) in the photocationic curable component (A), while maintaining the storage elastic modulus after curing the photocurable adhesive containing the diglycidyl compound (A2), The adhesion between the child and the protective film can be increased. On the other hand, if the amount exceeds 35% by weight, the adhesion between the polarizer and the protective film is not sufficient, and the storage elastic modulus after curing the photocurable adhesive tends to be low. . In order to make the adhesion between the polarizer and the protective film and the storage elastic modulus after curing of the photocurable adhesive more preferable, the amount of the diglycidyl compound (A2) in the photocationically curable component (A) Is more preferably 25% by weight or less.

Furthermore, the amount of the monofunctional epoxy compound (A3) in the photocationic curable component (A) is 2 to 15% by weight. By blending 2% by weight or more of the monofunctional epoxy compound (A3) in the photocationic curable component (A), the viscosity of the photocurable adhesive is reduced, and good coatability is exhibited. The effect of increasing the adhesion between the polarizer and the protective film is exhibited. On the other hand, when the amount exceeds 15% by weight, the storage elastic modulus after curing the photocurable adhesive is not sufficiently high, and the polarization is obtained by bonding the polarizer and the protective film through the adhesive. When the plate is exposed to a severe temperature history, the polarizer is prone to cracking.

In the formula (I) representing the alicyclic diepoxy compound (A1), R ¹ and R ² are each independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, but the alkyl group has 3 or more carbon atoms. In some cases, it may have an alicyclic structure. This alkyl group is represented by the 1-position where the position of the cyclohexane ring bonded to X in formula (I) is the 1-position (therefore, the positions of the epoxy groups in the two cyclohexane rings are both 3,4-position). It can be bonded to any of the 6-positions. Of course, this alkyl group may be a straight chain or may be branched when it has 3 or more carbon atoms. Moreover, as above-mentioned, in C3 or more, you may have an alicyclic structure. Typical examples of the alkyl group having an alicyclic structure include cyclopentyl and cyclohexyl.

Similarly, in the formula (I), X connecting two 3,4-epoxycyclohexane rings is an oxygen atom, an alkanediyl group having 1 to 6 carbon atoms, or 2 represented by any one of the formulas (Ia) to (Id). Is a valent group. Here, the alkanediyl group is a concept including alkylene and alkylidene, and the alkylene may be a straight chain or may be branched when it has 3 or more carbon atoms.

Further, when X is a divalent group represented by any one of the formulas (Ia) to (Id), the linking groups Y ¹ , Y ² , Y ³ and Y ⁴ in each formula each have 1 to When the alkanediyl group has 3 or more carbon atoms, it may have an alicyclic structure. Of course, these alkanediyl groups may be linear, or may be branched when having 3 or more carbon atoms. Moreover, as above-mentioned, in C3 or more, you may have an alicyclic structure. Typical examples of alkanediyl groups having an alicyclic structure include cyclopentylene and cyclohexylene.

The alicyclic diepoxy compound (A1) represented by the formula (I) will be specifically described. X in the formula (I) is a divalent group represented by the formula (Ia), and a in the formula is The compound which is 0 includes 3,4-epoxycyclohexylmethanol (an alkyl group having 1 to 6 carbon atoms may be bonded to the cyclohexane ring) and 3,4-epoxycyclohexanecarboxylic acid (carbon is added to the cyclohexane ring). The esterified product may have an alkyl group of 1 to 6 attached thereto. Specific examples thereof include 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate [formula (I) (wherein X is a divalent group represented by formula (Ia) where a = 0)]. , R ¹ = R ² = H compound], 3,4-epoxy-6-methylcyclohexylmethyl 3,4-epoxy-6-methylcyclohexanecarboxylate [in formula (I) having the same X as above, R ¹ = 6-methyl, R ² = 6-methyl compound], 3,4-epoxy-1-methylcyclohexylmethyl 3,4-epoxy-1-methylcyclohexanecarboxylate [in formula (I) having the same X as above , Compound of R ¹ = 1-methyl, R ² = 1-methyl], 3,4-epoxy-3-methylcyclohexylmethyl 3,4-epoxy-3- Methylcyclohexanecarboxylates [compounds of formula (I) having the same X as above, R ¹ = 3-methyl, R ² = 3-methyl].

A compound in which X in the formula (I) is a divalent group represented by the formula (Ib) is an alkylene glycol and 3,4-epoxycyclohexanecarboxylic acid (an alkyl group having 1 to 6 carbon atoms is bonded to the cyclohexane ring) It may be an esterified product. A compound in which X in the formula (I) is a divalent group represented by the formula (Ic) includes an aliphatic dicarboxylic acid and 3,4-epoxycyclohexylmethanol (an alkyl group having 1 to 6 carbon atoms bonded to the cyclohexane ring) It may be an esterified product. Further, a compound in which X in the formula (I) is a divalent group represented by the formula (Id) is 3,4-epoxycyclohexylmethanol (an alkyl group having 1 to 6 carbon atoms bonded to the cyclohexane ring). May be an ether form (when b = 0), or an alkylene glycol or polyalkylene glycol and 3,4-epoxycyclohexylmethanol (an alkyl group having 1 to 6 carbon atoms is bonded to the cyclohexane ring). Or etherified product (when b> 0).

In the formula (II) representing the diglycidyl compound (A2), Z represents an alkylene group having 1 to 9 carbon atoms, an alkylidene group having 3 or 4 carbon atoms, a divalent alicyclic hydrocarbon group, or a formula —C _m A divalent group represented by H _2m —Z ¹ —C _n H _2n —, wherein —Z ¹ — is —O—, —CO—O—, —O—CO—, —SO ₂ —, —SO— or —CO—, and m and n are each independently an integer of 1 or more, but the sum of the two is 9 or less. Typical examples of the divalent alicyclic hydrocarbon group include cyclopentylene and cyclohexylene.

In the formula (II), the compound in which Z is an alkylene group is diglycidyl ether of alkylene glycol. Specific examples thereof include ethylene glycol diglycidyl ether, 1,3-propanediol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether and the like.

In the formula (II), when Z is a divalent group represented by the formula —C _m H _2m —Z ¹ —C _n H _2n —, Z is an alkylene group having 2 or more carbon atoms, and the alkylene This corresponds to the C—C bond of the group being interrupted by —O—, —CO—O—, —O—CO—, —SO ₂ —, —SO—, or —CO—.

In the formula (III) representing the monofunctional epoxy compound, R ³ is an alkyl group having 1 to 15 carbon atoms. Of course, this alkyl group may be linear, or may be branched when it has 3 or more carbon atoms. This alkyl group has a relatively large number of carbon atoms, for example, preferably 6 or more, and more preferably in the range of 6 to 10 carbon atoms. Of these, a branched alkyl group is preferred. A typical example of the monofunctional epoxy compound represented by the formula (III) is 2-ethylhexyl glycidyl ether.

The photocationic curable component (A) constituting the photocurable adhesive has the alicyclic diepoxy compound (A1), diglycidyl compound (A2) and monofunctional epoxy compound (A3) described above, respectively. Contains in proportions. In order to more effectively reduce the viscosity of the photocurable adhesive before curing, improve the storage elastic modulus of the cured product, and improve the adhesion between the polarizer and the protective film, the photocurable adhesive The total amount of the diglycidyl compound (A2) and the monofunctional epoxy compound (A3) is preferably 25% by weight or more based on the total amount.

The photocationic curable component (A) contains other cation polymerizable compounds within the range in which the alicyclic diepoxy compound (A1), diglycidyl compound (A2) and monofunctional epoxy compound (A3) are in the amounts described above. May be included.

(Photocationic polymerization initiator)
In the present invention, the photocationic curable component as described above is cured by cationic polymerization by irradiation of active energy rays to form an adhesive layer. Therefore, the photocurable adhesive composition includes a photocationic polymerization initiator. (B) is blended. 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 the polymerization reaction of the photocationic curable component (A). Is. Since the cationic photopolymerization initiator acts catalytically by light, it is excellent in storage stability and workability even when mixed with the cationic photocurable component (A). Examples of the compound that generates a cationic species or a Lewis acid upon irradiation with active energy rays include aromatic diazonium salts; onium salts such as aromatic iodonium salts and aromatic sulfonium salts; iron-allene complexes.

Examples of the aromatic diazonium salt include the following compounds.
Benzenediazonium hexafluoroantimonate,
Benzenediazonium hexafluorophosphate,
Benzenediazonium hexafluoroborate, etc.

Examples of the aromatic iodonium salt include the following compounds.
Diphenyliodonium tetrakis (pentafluorophenyl) borate,
Diphenyliodonium hexafluorophosphate,
Diphenyliodonium hexafluoroantimonate,
Di (4-nonylphenyl) iodonium hexafluorophosphate, etc.

Examples of the aromatic sulfonium salt include the following compounds.
Triphenylsulfonium hexafluorophosphate,
Triphenylsulfonium hexafluoroantimonate,
Triphenylsulfonium tetrakis (pentafluorophenyl) borate,
4,4′-bis [diphenylsulfonio] diphenyl sulfide bishexafluorophosphate,
4,4′-bis [di (β-hydroxyethoxy) phenylsulfonio] diphenyl sulfide bishexafluoroantimonate,
4,4′-bis [di (β-hydroxyethoxy) phenylsulfonio] diphenyl sulfide bishexafluorophosphate,
7- [di (p-toluyl) sulfonio] -2-isopropylthioxanthone hexafluoroantimonate,
7- [di (p-toluyl) sulfonio] -2-isopropylthioxanthone tetrakis (pentafluorophenyl) borate,
4-phenylcarbonyl-4′-diphenylsulfonio-diphenyl sulfide hexafluorophosphate,
4- (p-tert-butylphenylcarbonyl) -4′-diphenylsulfonio-diphenyl sulfide hexafluoroantimonate,
4- (p-tert-butylphenylcarbonyl) -4′-di (p-toluyl) sulfonio-diphenyl sulfide tetrakis (pentafluorophenyl) borate and the like.

Examples of the iron-allene complex include the following compounds.
Xylene-cyclopentadienyl iron (II) hexafluoroantimonate,
Cumene-cyclopentadienyl iron (II) hexafluorophosphate,
Xylene-cyclopentadienyl iron (II) tris (trifluoromethylsulfonyl) methanide and the like.

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

The blending amount of the photocationic polymerization initiator (B) is 1 to 10 parts by weight with respect to 100 parts by weight of the entire photocationic curable component (A). By blending 1 part by weight or more of the cationic photopolymerization initiator per 100 parts by weight of the cationic photocurable component (A), the cationic photocurable component (A) can be sufficiently cured, and the resulting polarizing plate is high. Gives mechanical strength and adhesive strength. On the other hand, when the amount increases, the ionic substance in the cured product increases, so that the hygroscopic property of the cured product increases and the durability performance of the polarizing plate may be lowered. ) Is 10 parts by weight or less per 100 parts by weight of the photocationic curable component (A). The compounding amount of the photocationic polymerization initiator (B) is preferably 2 parts by weight or more and preferably 6 parts by weight or less per 100 parts by weight of the photocationic curable component (A).

(Other components that can be blended in the photo-curable adhesive)
The photocurable adhesive of the present invention is blended in a general photocurable resin or adhesive in addition to the photocationic curable component (A) and the photocationic polymerization initiator (B) containing the epoxy compound as described above. Other ingredients known to do can also be included. Preferable examples of other components include a photosensitizer and a photosensitization aid. The photosensitizer is a compound that exhibits maximum absorption at a wavelength longer than the maximum absorption wavelength indicated by the photocationic polymerization initiator (B) and promotes the polymerization initiation reaction by the photocationic polymerization initiator (B). The photosensitizing assistant is a compound that further promotes the action of the photosensitizer. Depending on the type of the protective film, it may be preferable to add such a photosensitizer and further a photosensitizer.

The photosensitizer is preferably a compound that exhibits maximum absorption in light having a wavelength longer than 380 nm. The cationic photopolymerization initiator (B) exhibits maximum absorption at a wavelength near or shorter than 300 nm, generates a cationic species or a Lewis acid in response to light having a wavelength near the wavelength, and is a photocationic curable component. The cationic polymerization of (A) is started. However, if a photosensitizer as described above is blended, it becomes sensitive to light having a longer wavelength, particularly longer than 380 nm. As such a photosensitizer, an anthracene compound is advantageously used. Specific examples of the anthracene photosensitizer include the following compounds.

9,10-dimethoxyanthracene,
9,10-diethoxyanthracene,
9,10-dipropoxyanthracene,
9,10-diisopropoxyanthracene,
9,10-dibutoxyanthracene,
9,10-dipentyloxyanthracene,
9,10-dihexyloxyanthracene,
9,10-bis (2-methoxyethoxy) anthracene,
9,10-bis (2-ethoxyethoxy) anthracene,
9,10-bis (2-butoxyethoxy) anthracene,
9,10-bis (3-butoxypropoxy) anthracene,
2-methyl- or 2-ethyl-9,10-dimethoxyanthracene,
2-methyl- or 2-ethyl-9,10-diethoxyanthracene,
2-methyl- or 2-ethyl-9,10-dipropoxyanthracene,
2-methyl- or 2-ethyl-9,10-diisopropoxyanthracene,
2-methyl- or 2-ethyl-9,10-dibutoxyanthracene,
2-methyl- or 2-ethyl-9,10-dipentyloxyanthracene,
2-methyl- or 2-ethyl-9,10-dihexyloxyanthracene and the like.

By blending the above photosensitizer with the photocurable adhesive, the curability of the adhesive is improved as compared with the case where it is not blended. Such an effect is expressed by blending 0.1 part by weight or more of the photosensitizer with respect to 100 parts by weight of the photocationic curable component (A). On the other hand, if the blending amount of the photosensitizer increases, problems such as precipitation during low-temperature storage occur, so the amount is 2 parts by weight or less with respect to 100 parts by weight of the photocationic curable component (A). Is preferred. From the viewpoint of maintaining the neutral gray of the polarizing plate, it is advantageous to reduce the amount of the photosensitizer in the range in which the adhesive force between the polarizer and the protective film is maintained appropriately. More preferably, the amount of the photosensitizer is in the range of 0.1 to 0.5 parts by weight, more preferably 0.1 to 0.3 parts by weight with respect to 100 parts by weight of the active ingredient (A).

Next, the photosensitizing aid will be described. There are various types of photosensitizers, but naphthalene compounds are advantageously used. Specific examples of naphthalene-based photosensitization aids include the following compounds.

4-methoxy-1-naphthol,
4-ethoxy-1-naphthol,
4-propoxy-1-naphthol,
4-butoxy-1-naphthol,
4-hexyloxy-1-naphthol,
1,4-dimethoxynaphthalene,
1-ethoxy-4-methoxynaphthalene,
1,4-diethoxynaphthalene,
1,4-dipropoxynaphthalene,
1,4-dibutoxynaphthalene and the like.

By blending a naphthalene photosensitizer with a photocurable adhesive, the curability of the adhesive is improved as compared with the case where it is not blended. By blending 0.1 part by weight or more of the naphthalene photosensitizer with 100 parts by weight of the photocationic curable component (A), such an effect is exhibited. On the other hand, when the blending amount of the naphthalene photosensitizer is increased, problems such as precipitation during low-temperature storage occur. Therefore, the amount is 5 parts by weight with respect to 100 parts by weight of the photocation curable component (A). The content is preferably as follows, and more preferably 3 parts by weight or less.

(Physical properties of photo-curing adhesive)
The photocurable adhesive of this invention is used in order to paste a protective film on the polarizer which consists of a polyvinyl alcohol-type resin film as above-mentioned. After apply | coating this adhesive agent to at least one bonding surface among these polarizers and protective films, both are piled up through the adhesive bond layer, and an adhesive agent is hardened. And in order to improve the applicability | paintability to a polarizer and / or a protective film, the one where the viscosity of the adhesive agent is low is preferable. In the present invention, as the photocationic curable component (A), by blending the above-mentioned specific three kinds of compounds at a predetermined ratio, the viscosity of the photocurable adhesive is lowered and the coating suitability is improved. Is done. Specifically, the photocurable adhesive can have a viscosity at 25 ° C. of 100 mPa · sec or less.

Also, in order to improve the adhesion between the polarizer and the protective film, the higher the storage elastic modulus of the adhesive layer obtained by curing this adhesive is preferable. In the present invention, the three specific compounds described above are blended at a predetermined ratio as the photocation curable component (A), so that the viscosity before curing is kept at a low value as described above. The storage elastic modulus of the cured product can be increased while maintaining suitability. Specifically, the hardened | cured material of the photocurable adhesive agent can be made to show the storage elastic modulus of 1000 Mpa or more in 80 degreeC.

[Polarizer]
In the present invention, a protective film made of a transparent resin is bonded to at least one surface of a polarizer made of a polyvinyl alcohol-based resin film via the photocurable adhesive described above, and the photocurable adhesive is used. Is cured into a polarizing plate. In this invention, as above-mentioned, the storage elastic modulus of the adhesive bond layer which is a hardened | cured material of a photocurable adhesive agent can be raised, and the adhesiveness between a polarizer and a protective film can be improved. Therefore, the adhesive strength according to the 180 degree peeling test between the polarizer and the protective film can be 0.6 N / 25 mm or more. Here, the 180 degree peeling test is performed according to JIS K 6854-2: 1999 “Adhesive—Peeling peel strength test method—Part 2: 180 degree peeling”.

Hereinafter, a polarizer and a protective film constituting the polarizing plate of the present invention will be described, and a manufacturing method of the polarizing plate will be briefly described.

(Polarizer)
The polarizer is composed of a polyvinyl alcohol-based resin film on which a dichroic dye is adsorbed and oriented. The polyvinyl alcohol resin constituting the polarizer can be obtained by saponifying a polyvinyl acetate resin. The polyvinyl acetate resin may be a copolymer of vinyl acetate, which is a homopolymer of vinyl acetate, or a copolymer 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 degree of saponification of the polyvinyl alcohol resin is usually in the range of 85 to 100 mol%, preferably 98 to 100 mol%. The polyvinyl alcohol resin may be further modified, for example, polyvinyl formal or polyvinyl acetal modified with aldehydes may be used. The degree of polymerization of the polyvinyl alcohol resin is usually in the range of 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, rolls having different peripheral speeds may be uniaxially stretched or uniaxially stretched using a hot roll. 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 resin film by immersing it 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 immersing and 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 about 1 × 10 ⁻³ to 1 × 10 ⁻² parts by weight per 100 parts by weight of water. This aqueous solution may contain an inorganic salt such as sodium sulfate. The temperature of this aqueous solution is usually about 20 to 80 ° C., and the immersion time (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. After washing with water, a drying process is performed to obtain a polarizer. The temperature of water 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 thereafter is usually performed using a hot air dryer or a far infrared heater. The drying temperature is usually 40 to 100 ° C. Further, the drying process time is usually about 120 to 600 seconds.

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

(Protective film)
A protective film is bonded to the polarizer composed of the polyvinyl alcohol-based resin film described above via the photocurable adhesive described above, and the photocurable adhesive is cured to obtain a polarizing plate. 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. Moisture permeability of triacetyl cellulose is approximately 400g ^/ m 2 ^/ 24hr approximately.

In one preferable form, the protective film bonded to at least one surface of the polarizer is composed of an acetylcellulose-based resin. In particular, the protective film bonded to one surface of the polarizer can be composed of an acetyl cellulose resin in which an ultraviolet absorber is blended. In another preferred embodiment, the protective film stuck on at least one surface of the polarizer, lower resin films than the triacetyl cellulose moisture permeability, for example, moisture permeability in the following resin film 300g ^/ m 2 / 24hr Composed. 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. Among these, amorphous polyolefin resins, polyester resins, and chain polyolefin resins are preferably used. 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 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, or an antistatic layer on the surface opposite to the surface to be bonded to the polarizer. It may be. 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.

(Production method of polarizing plate)
In the production of the polarizing plate, the photocurable adhesive coating layer described above is formed on one or both of the bonding surfaces of the polarizer and the protective film, and the polarizer and the protective film are formed via the coating layer. The coating layer of the uncured photocurable adhesive thus bonded is cured by irradiation with active energy rays, and the protective film is fixed on the polarizer. The application layer of a photocurable adhesive may be formed on the bonding surface of the polarizer, or may be formed on the bonding surface of the 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, it is also possible to employ a method in which an adhesive is cast while a polarizer and a protective film are continuously supplied so that the bonding surfaces of both are 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 adhesive satisfactorily without reducing the optical performance of the polarizer is used, but there is no particular limitation on the type thereof. 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 is usually 20 μm or less, preferably 10 μm or less, more preferably 5 μm or less. When the adhesive layer is thick, the reaction rate of the adhesive is lowered, and the wet heat resistance of the polarizing plate tends to deteriorate.

When bonding the polarizer and the protective film, the corona discharge treatment, plasma treatment, flame treatment, primer treatment, or anchor coating treatment is performed before forming the coating layer of the adhesive on one or both of the bonding surfaces of both. Such an easy adhesion treatment may be performed.

The light source used for irradiating active energy rays to the coating layer of the photocurable adhesive may be any one that generates ultraviolet rays, electron beams, X-rays, and the like. In particular, for example, 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 active energy ray irradiation intensity to the photocurable adhesive is determined for each target composition and is not particularly limited. However, the irradiation intensity in the wavelength region effective for activating the photocationic polymerization initiator is not limited. It is preferable to be 0.1 to 100 mW / cm ² . If the light irradiation intensity on the photocurable adhesive is too small, the reaction time becomes too long. On the other hand, if the light irradiation intensity is too large, the heat radiated from the lamp and the heat generation during polymerization of the photocurable adhesive will occur. This may cause yellowing of the photocurable adhesive and deterioration of the polarizer. The light irradiation time to the photocurable adhesive is controlled for each composition to be cured and is not particularly limited, but the integrated light amount represented by the product of the irradiation intensity and the irradiation time is 10 to 5 It is preferably set to be 000 mJ / cm ² . If the cumulative amount of light to the photocurable adhesive is too small, the generation of active species derived from the photocationic polymerization initiator may not be sufficient, and the resulting adhesive layer may be insufficiently cured, while that If an attempt is made to increase the integrated light quantity, the irradiation time becomes very long, which is disadvantageous for improving productivity.

When a protective film is bonded to both sides of the polarizer, the active energy ray may be irradiated from either side of the protective film. 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.

[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 may be bonded via a photocurable adhesive, and an optical layer may 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 adhesive 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 arranged on the front side of the liquid crystal cell and the polarizing plate arranged on the back side of the liquid crystal cell, a retardation film laminated on the side of the polarizing plate facing the liquid crystal cell, etc. There is.

The reflective layer, transflective layer, or light diffusing layer is a reflective polarizing plate (optical member), a transflective polarizing plate (optical member), or a diffusing polarizing plate (optical member), respectively. 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. The optical member as a reflective polarizing plate can form a reflective layer, for example, by attaching a foil or a vapor deposition film made of a metal such as aluminum to a protective film on a polarizer. The 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, optical members as diffusion type polarizing plates can be applied to 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 that acts as a polarizing plate for both reflection and diffusion can be formed. 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 used. Can be adopted. 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 brightness 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 vacuum deposition, ion plating, or vapor deposition such as 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 diameter of 0.1 to 30 μm. It may be inorganic fine particles, organic fine particles such as a crosslinked or non-crosslinked polymer, 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 oriented film of a cholesteric liquid crystal polymer, and a circularly polarized light separation sheet in which the oriented liquid crystal layer is supported on a film substrate.

On the other hand, the above-mentioned retardation film acting 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 films may be used in combination for the purpose of controlling optical characteristics such as broadening the bandwidth.

Among the laminated optical members, those including a retardation film as an optical layer other than the polarizing plate are preferably used because they can effectively ensure optical security when applied to a liquid crystal display device. The optimum retardation value (in-plane and thickness direction) of the retardation film may be selected according to the applied liquid crystal cell.

The laminated optical member can be a laminate of two layers or three or more layers by combining a polarizing plate and one layer or two 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 a pressure-sensitive adhesive, but the adhesive layer or the pressure-sensitive adhesive layer is good for the adhesive or pressure-sensitive adhesive used for that purpose. 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 one 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 with 20 or less carbon atoms such as methyl, ethyl and butyl groups, and (meth) acrylic acid and hydroxyethyl (meth) acrylate An acrylic copolymer having a weight average molecular weight of 100,000 or more, in which a glass transition temperature is preferably 25 ° C. or lower, more preferably 0 ° C. or lower, with a functional group-containing acrylic monomer consisting of Useful as a base 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 carried out by a coating method, a method in which an adhesive layer is previously formed on a protective film, and 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 blended with fillers made of glass fibers, glass beads, resin beads, metal powders and other inorganic powders, pigments, colorants, antioxidants, UV absorbers, etc. as necessary. It may be. 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 represented by a thin film transistor type and a simple matrix drive type represented by a super twisted nematic type. Can be formed. For adhesion between the laminated optical member and the liquid crystal cell, the same adhesive as described above is usually used.

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, “%” and “part” representing the content or amount used are based on weight unless otherwise specified. Moreover, the photocationic curable component and the photocationic polymerization initiator used in the following examples are as follows, and are indicated by respective symbols below.

(A) Photocationic curable component (a1) 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate [in the above formula (I), R ¹ = R ² = H, X = —COOCH ₂ — ],
(A2) 1,4-butanediol diglycidyl ether [compound of the formula (II), Z = — (CH ₂ ) ₄ —],
(A3) 2-ethylhexyl glycidyl ether [compound of the formula (III) wherein R ³ = CH ₃ (CH ₂ ) ₃ —CH (CH ₂ CH ₃ ) —CH ₂ —]].

(B) Photocationic polymerization initiator (abbreviated as “initiator” in the table)
(B1) Triarylsulfonium hexafluorophosphate.

[Examples 1 and 2 and Comparative Examples 1 to 9]
(1) Preparation of photocurable adhesive After mixing each component by the compounding ratio (a part is a part) shown in Table 1, it defoamed and prepared the photocurable adhesive liquid. In addition, a photocationic polymerization initiator (b1) was mix | blended as a 50% propylene carbonate solution, and displayed in Table 1 with the solid content.

(2) Viscosity measurement of adhesive liquid at 25 ° C. For each of the adhesive liquids prepared above, the viscosity at a temperature of 25 ° C. is measured using a rotary viscoelasticity measuring device “Physica MCR 301” manufactured by Anton Paar. did. The results are shown in Table 2.

(3) Measurement of storage elastic modulus at 80 ° C. of cured product Polyethylene terephthalate film [trade name “Toyobo Ester Film E7002”, manufactured by Toyobo Co., Ltd.] on one side, coating machine [Bar Coater, Daiichi Rika Co., Ltd. Each of the adhesive solutions prepared in (1) was applied so that the film thickness after curing was about 30 μm. Next, the adhesive 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 × 30 mm, and the polyethylene terephthalate film was peeled off to obtain a cured film of an adhesive. The cured film is gripped with a distance of 2 cm between grips using a dynamic viscoelasticity measuring device “DVA-220” manufactured by IT Measurement Control Co., Ltd. The storage elastic modulus at a temperature of 80 ° C. was determined by setting the frequency of 1 Hz and the temperature rising rate to 3 ° C./min. The results are shown in Table 2.

(4) Preparation of polarizing plate Corona discharge treatment was performed on the surface of a 80 μm thick triacetyl cellulose film (trade name “Konica Catac KC8UX2MW”, manufactured by Konica Minolta Opto Co., Ltd.) containing an ultraviolet absorber. On the surface, each adhesive solution prepared above was applied using a bar coater so that the film thickness after curing was about 2 μm. A 28 μm-thick polyvinyl alcohol-iodine polarizer was bonded to the adhesive layer. In addition, a corona discharge treatment was applied to the surface of a retardation film [trade name “N-TAC KC4FR-1”, manufactured by Konica Minolta Opto Co., Ltd.] having a thickness of 40 μm made of an acetylcellulose-based resin. The same adhesive solution as above was applied using a bar coater so that the film thickness after curing was about 2 μm. The adhesive layer was bonded to the polarizer side of the polarizer having the triacetylcellulose film prepared above bonded on one side, to prepare a laminate. From the acetylcellulose-based phase difference film side of this laminate, using an ultraviolet irradiation device with a belt conveyor (the lamp uses a “D bulb” manufactured by Fusion UV Systems), the ultraviolet light is adjusted so that the integrated light quantity becomes 250 mJ / cm ^2. To cure the adhesive. Thus, a polarizing plate in which protective films were bonded to both sides of the polarizer was produced.

(5) 180 degree peeling test The polarizing plate produced by said (4) was cut | judged to the magnitude | size of length 200mm x width 25mm. And, by providing an acrylic pressure-sensitive adhesive layer on the acetylcellulose-based retardation film side, a test piece for measuring the peel strength between the acetylcellulose-based retardation film and the polarizer, separately from this, An acrylic pressure-sensitive adhesive layer was provided on the 80 μm-thick triacetylcellulose film side to obtain a test piece for measuring the peel strength between the 80 μm-thick triacetylcellulose film and the polarizer. The adhesive layer of each test piece is attached to a glass plate, a cutter blade is inserted between the polarizer and the protective film on the adhesive side (acetylcellulose phase retardation film or 80 μm thick triacetylcellulose film). It peeled 30 mm from the end in the vertical direction, and the peeled part was grasped by the grasping part of the testing machine. 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. The results are shown in Table 2. In the section of 180 degree peel strength in Table 2, the column “N-TAC / PVA” represents the peel strength between the acetylcellulose-based retardation film and the polyvinyl alcohol-iodine polarizer. The column “/ PVA” represents the peel strength between the 80 μm thick triacetyl cellulose film and the polyvinyl alcohol-iodine polarizer.

(6) Durability evaluation of polarizing plate by thermal shock test The polarizing plate produced in the above (4) is cut into a size of 170 mm × 110 mm, and an acrylic pressure-sensitive adhesive layer is provided on the acetylcellulose-based retardation film side. The pressure-sensitive adhesive layer was attached to a glass plate, and a cold shock test (heat shock test) was performed. In the thermal shock test, the operation of holding the polarizing plate sample bonded to the above glass plate at −35 ° C. for 1 hour, then raising the temperature to 70 ° C. and holding it for 1 hour is defined as one cycle. This was carried out by repeating 300 cycles. This test was performed for each of the six polarizing plate samples, and evaluation was made based on the ratio to the total number of samples (6) although cracks were observed in the polarizer after the test. The results are shown in Table 2.

As can be seen from Tables 1 and 2, in Comparative Examples 1 and 2 in which the photocationic curable component (A) is a binary system of (a1) and (a2), the peel strength between the protective film and the polarizer However, neither N-TAC / PVA nor TAC / PVA can be greater than 0.6 N / 25 mm. Moreover, in the comparative example 3, the elasticity modulus of adhesive hardened | cured material is low, and a polarizer may be cracked in a thermal shock test. In Comparative Examples 4 and 5 in which the photocationic curable component (A) is a binary system of (a1) and (a3), the elastic modulus of the cured adhesive is low, and the polarizer breaks in the thermal shock test. Even when the photocationic curable component (A) is a ternary system of (a1), (a2) and (a3), 20 parts of (a3) [20% in the photocationic curable component (A)] In Comparative Examples 8 and 9, since the elastic modulus of the cured adhesive was also low, the polarizer was cracked in the thermal shock test, while the blending amount of (a1) was 80 parts or more [photocation curable component (A) In Comparative Examples 6 and 7, which are 80% or more of the above, the peel strength between the protective film and PVA does not become 0.6 N / 25 mm or more. On the other hand, since the adhesive which mix | blended (a1), (a2), and (a3) by the predetermined ratio like Example 1 and 2 is low viscosity, and the hardened | cured material gives a high elasticity modulus, The polarizer is hard to break and gives a polarizing plate with high adhesion.

Claims

A photocurable adhesive for pasting a protective film made of a transparent resin on at least one surface of a polarizer made of a polyvinyl alcohol-based resin film on which a dichroic dye is adsorbed and oriented,
100 parts by weight of the photocationically curable component (A),
Containing 1 to 10 parts by weight of the cationic photopolymerization initiator (B),
The photocationic curable component (A) is based on the total amount thereof.
Formula (I):

(Wherein R 1 and R 2 each independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and when the alkyl group has 3 or more carbon atoms, it may have an alicyclic structure;
X is an oxygen atom, an alkanediyl group having 1 to 6 carbon atoms, or the following formulas (Ia) to (Id):

In which Y 1 to Y 4 each represent an alkanediyl group having 1 to 20 carbon atoms, and when it has 3 or more carbon atoms, it has an alicyclic structure. Well;
a and b each represents an integer of 0 to 20. )
60 to 75% by weight of an alicyclic diepoxy compound (A1) represented by
Formula (II):

(In the formula, Z is an alkylene group having 1 to 9 carbon atoms, an alkylidene group having 3 or 4 carbon atoms, a divalent alicyclic hydrocarbon group, or a formula —C m H 2m —Z 1 —C n H 2n — Wherein —Z 1 — represents —O—, —CO—O—, —O—CO—, —SO 2 —, —SO—, or —CO—, m and n each independently represents an integer of 1 or more, but the sum of both is 9 or less.)
5 to 35% by weight of the diglycidyl compound (A2) represented by formula (III):

(In the formula, R 3 represents an alkyl group having 1 to 15 carbon atoms.)
A photocurable adhesive containing 2 to 15% by weight of a monofunctional epoxy compound (A3) represented by the formula:
The photocurable adhesive according to claim 1, wherein in the formula (III) representing the monofunctional epoxy compound (A3), R 3 is an alkyl group having 6 to 10 carbon atoms.
The photocurable adhesive according to claim 1, wherein the viscosity at 25 ° C is 100 mPa · sec or less.
The photocurable adhesive according to claim 1, wherein the cured product exhibits a storage elastic modulus of 1,000 MPa or more at 80 ° C.
It comprises a polarizer comprising a polyvinyl alcohol-based resin film in which a dichroic dye is adsorbed and oriented, and a protective film comprising a transparent resin bonded to at least one surface of the polarizer via an adhesive, The polarizing plate is a cured product of the photocurable adhesive according to claim 1.
The polarizing plate according to claim 5, wherein the protective film bonded to at least one surface of the polarizer is made of an acetylcellulose-based resin mixed with an ultraviolet absorber.
The polarizing plate according to claim 5, wherein the protective film bonded to at least one surface of the polarizer is made of a transparent resin selected from the group consisting of an amorphous polyolefin resin, a polyester resin, and a chain polyolefin resin. .
The polarizing plate according to claim 5, wherein an adhesive strength by a 180 degree peeling test between the polarizer and the protective film is 0.6 N / 25 mm or more.
A laminated optical member comprising a laminate of the polarizing plate according to claim 5 and another optical layer.
The laminated optical member according to claim 9, wherein the optical layer includes a retardation film.