CN108474896B

CN108474896B - Photocurable adhesive, polarizing plate and laminated optical member using the photocurable adhesive

Info

Publication number: CN108474896B
Application number: CN201680078232.6A
Authority: CN
Inventors: 久米悦夫; 古川达也; 松土和彦; 渡边智志; 渡边一平
Original assignee: Adeka Corp; Sumitomo Chemical Co Ltd
Current assignee: Adeka Corp; Sumitomo Chemical Co Ltd
Priority date: 2016-01-08
Filing date: 2016-12-22
Publication date: 2021-10-08
Anticipated expiration: 2036-12-22
Also published as: KR102649140B1; KR20180100163A; TW201736556A; TWI721078B; CN108474896A; WO2017119323A1

Abstract

本发明提供一种光固化性粘接剂，是用于将热塑性树脂膜粘接于聚乙烯醇系偏振片的光固化性粘接剂，相对于光阳离子固化性成分(A)100重量份，含有1～10重量份的光阳离子聚合引发剂(B)、以及0.1～15重量份的支链醇化合物(C)，光阳离子固化性成分(A)以其全部量为基准，含有：30～85重量％的以式(I)表示的脂环式二环氧化合物(A1)、以及1～70重量％的以式(II)表示的二缩水甘油基化合物(A2)，此外还提供使用了该光固化性粘接剂的偏振板。The present invention provides a photocurable adhesive for adhering a thermoplastic resin film to a polyvinyl alcohol-based polarizer, wherein 100 parts by weight of the photocationic curable component (A) are Contains 1 to 10 parts by weight of the photocationic polymerization initiator (B) and 0.1 to 15 parts by weight of the branched alcohol compound (C), and the photocationic curable component (A) is based on the total amount of: 30 to 85% by weight of the alicyclic diepoxy compound (A1) represented by the formula (I), and 1 to 70% by weight of the diglycidyl compound (A2) represented by the formula (II), in addition to using The polarizing plate of this photocurable adhesive.

Description

Photocurable adhesive, and polarizing plate and laminated optical member using same

Technical Field

The present invention relates to a photocurable adhesive for bonding a thermoplastic resin film to a polyvinyl alcohol-based polarizer, and a polarizing plate and a laminated optical member using the photocurable adhesive.

Background

Polarizing plates are useful as one of optical members constituting a liquid crystal display device. The polarizing plate is generally configured by laminating protective films on both sides of a polarizer, and is incorporated in a liquid crystal display device. Although it is known to provide a protective film only on one side of a polarizing plate, in many cases, a film having another optical function is bonded to the other side of the polarizing plate as a protective film, instead of a simple protective film. As a method for producing a polarizing plate, a method of subjecting a uniaxially stretched polyvinyl alcohol resin film dyed with a dichroic dye to a boric acid treatment, and then drying the resin after washing with water is widely used.

In general, a protective film is adhered to the polarizer immediately after the above-mentioned washing and drying. This is because the physical strength of the dried polarizing plate is weak, and when the polarizing plate is wound, the polarizing plate is likely to be cracked in the machine direction. Therefore, usually, an aqueous adhesive, which is an aqueous solution of a polyvinyl alcohol resin, is applied immediately to the polarizer after drying, and protective films are simultaneously adhered to both surfaces of the polarizer with the adhesive interposed therebetween. In general, a triacetyl cellulose film having a thickness of 30 to 100 μm is used as the protective film.

Triacetyl cellulose has excellent advantages as a protective film, such as excellent transparency, easy formation of various surface treatment layers and optical functional layers on the surface thereof, high moisture permeability, and smooth drying after bonding to a polarizing plate using the above-mentioned aqueous adhesive, but, on the other hand, a polarizing plate using triacetyl cellulose as a protective film has a problem that deterioration is easily caused under humid and hot conditions, for example, under conditions of a temperature of 70 ℃ and a relative humidity of 90%, due to high moisture permeability. Therefore, it is also known that an amorphous polyolefin resin having a lower moisture permeability than triacetyl cellulose, for example, a norbornene resin, is used as a protective film.

When a protective film made of a resin having low moisture permeability is bonded to a polyvinyl alcohol polarizer, if an aqueous solution of a polyvinyl alcohol resin, which has been conventionally used for bonding a polyvinyl alcohol polarizer and a triacetyl cellulose film, is used as an adhesive, there is a problem that the bonding strength is insufficient and the appearance of the resulting polarizing plate is poor. This is because the resin film having a low moisture permeability is generally hydrophobic, or because of its low moisture permeability, water as a solvent cannot be sufficiently dried. On the other hand, it is also known to bond different types of protective films to both surfaces of a polarizing plate. For example, there is also proposed a polarizing plate in which a protective film made of a resin having a low moisture permeability such as an amorphous polyolefin resin is bonded to one surface of the polarizing plate, and a protective film made of a resin having a high moisture permeability such as a cellulose resin including triacetyl cellulose is bonded to the other surface of the polarizing plate.

Therefore, attempts have been made to use a photocurable adhesive as an adhesive for imparting a high adhesive force between a protective film made of a resin having a low moisture permeability and a polyvinyl alcohol-based polarizing plate and also for imparting a high adhesive force between a resin having a high moisture permeability, such as a cellulose-based resin, and a polyvinyl alcohol-based polarizing plate. For example, japanese patent application laid-open No. 2004-24925 (patent document 1) discloses an adhesive containing an epoxy compound containing no aromatic ring as a main component, which is cured by cationic polymerization by irradiation with active energy rays, specifically, irradiation with ultraviolet rays, to bond a polarizing plate and a protective film. In addition, japanese patent application laid-open No. 2008-257199 (patent document 2) discloses a technique in which a photocurable adhesive, which combines an alicyclic epoxy compound with an epoxy compound having no alicyclic epoxy group and further contains a photocationic polymerization initiator, is used for adhesion between a polarizing plate and a protective film.

In addition, jp 2013-205719 a (patent document 3) proposes a photocurable adhesive containing (B) a photocationic polymerization initiator and (C) a diol compound having two hydroxyl groups in the molecule, as (a) a photocationic curable component.

Prior patent literature

Patent document

Patent document 1, Japanese patent laid-open No. 2004-245857

Patent document 2 Japanese laid-open patent publication No. 2008-257199

Patent document 3 Japanese patent laid-open publication No. 2013-205719

Disclosure of Invention

Problems to be solved by the invention

The adhesives of the compositions specifically disclosed in patent documents 1 to 3 do not necessarily have sufficiently low viscosity, and are not necessarily easy to coat on a polarizing plate or a thermoplastic resin film laminated thereon to form a thin and uniform adhesive layer. In addition, bubble defects may occur in the cured adhesive layer.

The purpose of the present invention is to provide a photocurable adhesive which is used for bonding a thermoplastic resin film to a polyvinyl alcohol-based polarizer, has a viscosity sufficiently low enough to enable application at room temperature, and can be used to produce a polarizing plate without causing bubble defects in the cured adhesive layer. Another object of the present invention is to provide a laminated optical member in which another optical layer is laminated on the polarizing plate, and which is suitably used for a liquid crystal display device.

Means for solving the problems

The invention provides a photocurable adhesive, a polarizing plate, and a laminated optical member shown below.

[1] A photocurable adhesive for bonding a thermoplastic resin film to a polyvinyl alcohol-based polarizing plate,

comprising 1 to 10 parts by weight of a photo cation polymerization initiator (B) and 0.1 to 15 parts by weight of a branched alcohol compound (C) per 100 parts by weight of a photo cation curable component (A),

the photo cation curable component (A) contains, based on the total amount thereof:

30 to 85 wt% of an alicyclic diepoxy compound (A1) represented by the following formula (I):

(in the formula, R¹And R²Each independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and when the number of carbon atoms is 3 or more, the alkyl group optionally has an alicyclic structure;

x represents an oxygen atom, an alkanediyl group having 1 to 6 carbon atoms, or a 2-valent group represented by any one of the following formulae (Ia) to (Id):

here, Y¹～Y⁴Each represents an alkanediyl group having 1 to 20 carbon atoms, and optionally has an alicyclic structure when the number of carbon atoms is 3 or more;

a and b each represent an integer of 0 to 20. ) (ii) a And

1 to 70% by weight of a diglycidyl compound (A2) represented by the following formula (II):

(wherein Z represents a branched alkylene group having 3 to 8 carbon atoms, or represented by the formula-C_mH_2m－Z¹－C_nH_2nA 2-valent radical of formula (I), where-Z¹-represents-O-, -CO-O-or-O-CO-, one of m and n represents an integer of 1 or more, the other represents an integer of 2 or more, the total of both is 8 or less, and C_mH_2mAnd C_nH_2nOne of them represents a branched saturated hydrocarbon group having a valence of 2. ).

[2] The photocurable adhesive according to [1], wherein the branched alcohol compound (C) has a molecular weight of 400 or less.

[3] The photocurable adhesive according to [1] or [2], wherein the branched alcohol compound (C) is a branched alkylene glycol compound.

[4] The photocurable adhesive according to any one of [1] to [3], further comprising 0.1 to 5 parts by weight of 1 or more compounds selected from anthracene compounds represented by the following formula (IVa) and naphthalene compounds represented by the following formula (IVb) per 100 parts by weight of the photocationic curable component (A):

(in the formula, R³And R⁴Each independently represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms or an alkoxyalkyl group having 2 to 12 carbon atoms, R⁵Represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. )

(in the formula, R⁶And R⁷Each independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. ).

[5] The photocurable adhesive according to any one of [1] to [4], wherein the moisture content is more than 0 part by weight and not more than 4 parts by weight relative to 100 parts by weight of the photocationic curable component (A).

[6] The photocurable adhesive according to any one of [1] to [5], wherein the viscosity at 25 ℃ is 100 mPas or less.

[7] A polarizing plate, comprising: a polyvinyl alcohol polarizing plate, and a thermoplastic resin film laminated on at least one surface of the polyvinyl alcohol polarizing plate with a cured product of the photocurable adhesive according to any one of [1] to [6] interposed therebetween.

[8] A laminated optical member comprising the polarizing plate according to [7] and a laminate of 1 or more other optical layers.

[9] The laminated optical member according to [8], wherein the other optical layer includes a retardation plate.

Effects of the invention

The present invention can provide a photocurable adhesive which has low viscosity and excellent coating suitability, and in which bubbles are less likely to form in the adhesive layer after curing. According to the photocurable adhesive of the present invention, the polyvinyl alcohol-based polarizing plate and the thermoplastic resin film can be bonded with high bonding strength. The polarizing plate and the laminated optical member using the same according to the present invention can have excellent durability and can suppress bubble defects in the adhesive layer.

Detailed Description

< Photocurable adhesive >

The photocurable adhesive of the present invention is an adhesive for adhering a thermoplastic resin film to a polyvinyl alcohol-based polarizing plate, and contains a photocationic-curable component (a), a photocationic polymerization initiator (B), and a branched alcohol compound (C).

(1) Photo cation curable component (A)

The photo cation curable component (a) which is a main component of the photo curable adhesive and gives an adhesive force by polymerization curing is a curable component which can be cationically polymerized by irradiation with an active energy ray in the coexistence of a photo cation polymerization initiator (B) described later. Among them, the photocationic curable component (a) contains the following two compounds from the viewpoints of reducing the viscosity of the photocurable adhesive, suppressing bubble defects in the cured adhesive layer, and improving the adhesive strength between the polyvinyl alcohol-based polarizing plate and the thermoplastic resin film.

(A1) An alicyclic diepoxy compound represented by the formula (I) above, and

(A2) a diglycidyl compound represented by the above formula (II).

In the above formula (I) representing the alicyclic diepoxy compound (A1), R¹And R²Each independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and the alkyl group optionally has an alicyclic structure when the number of carbon atoms is 3 or more. When the position of the cyclohexane ring bonded to X in the formula (I) is set to the 1-position (thus, the positions of the epoxy groups in both cyclohexane rings are 3, 4-positions), the alkyl group may be bonded to any one of the 1-position to 6-position. The alkyl group may be a straight chain, or may be a branched chain when the number of carbon atoms is 3 or more. In addition to the above-mentioned features, as described above,optionally, the alicyclic structure is present when the number of carbon atoms is 3 or more. 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 a 2-valent group represented by any one of the formulae (Ia) to (Id). Here, alkanediyl is a concept including alkylene groups and alkylidene groups, and the alkylene groups may be linear or branched when the number of carbon atoms is 3 or more. A in the formula (Ia) and b in the formula (Id) each represent an integer of 0 to 20.

When X is a 2-valent group represented by any one of the formulae (Ia) to (Id), the linking group Y in each formula¹、Y²、Y³And Y⁴Each of which is an alkanediyl group having 1 to 20 carbon atoms, and optionally having an alicyclic structure when the number of carbon atoms is 3 or more. These alkanediyl groups may be straight-chain ones, and may be branched when the number of carbon atoms is 3 or more. When the number of carbon atoms is 3 or more, the alicyclic structure is optionally contained, as described above. Typical examples of the alkanediyl group having an alicyclic structure include a cyclopentylene group and a cyclohexylene group.

Specifically, the alicyclic diepoxy compound (a1) represented by the formula (I) is an esterified compound of 3, 4-epoxycyclohexylmethanol (an alkyl group having 1 to 6 carbon atoms may be bonded to the cyclohexane ring) and 3, 4-epoxycyclohexanecarboxylic acid (an alkyl group having 1 to 6 carbon atoms may be bonded to the cyclohexane ring) in which X in the formula (I) is a group having a valence of 2 represented by the formula (Ia). Specific examples thereof include:

in 3, 4-epoxycyclohexylmethyl 3, 4-epoxycyclohexanecarboxylate [ formula (I) (wherein X is a 2-valent group represented by formula (Ia) wherein a is 0 ], R is¹＝R²H, a compound of,

3, 4-epoxy-6-methylcyclohexylmethyl 3, 4-epoxy-6-methylcyclohexanecarboxylate [ R in formula (I) having the same X as above¹6-methyl, R²6-methyl compound ],

3, 4-epoxy-1-methylcyclohexylmethyl 3, 4-epoxy-1-methylcyclohexanecarboxylate [ R in formula (I) having the same X as above¹1-methyl, R²1-methyl compound (I),

3, 4-epoxy-3-methylcyclohexylmethyl 3, 4-epoxy-3-methylcyclohexanecarboxylate [ R in formula (I) having the same X as above¹3-methyl, R²3-methyl group, and the like.

The compound of formula (I) wherein X is a 2-valent group represented by formula (Ib) is an ester of an alkylene glycol with 3, 4-epoxycyclohexanecarboxylic acid (to which an alkyl group having 1 to 6 carbon atoms may be bonded to the cyclohexane ring). The compound of formula (I) wherein X is a group having a valence of 2 represented by formula (Ic) is an ester of an aliphatic dicarboxylic acid and 3, 4-epoxycyclohexylmethanol (an alkyl group having 1 to 6 carbon atoms may be bonded to the cyclohexane ring). The compound of formula (I) in which X is a group having a valence of 2 represented by formula (Id) is an ether of 3, 4-epoxycyclohexylmethanol (an alkyl group having 1 to 6 carbon atoms may be bonded to the cyclohexane ring thereof) (in the case where b is 0), or an etherate of an alkylene glycol or polyalkylene glycol with 3, 4-epoxycyclohexylmethanol (an alkyl group having 1 to 6 carbon atoms may be bonded to the cyclohexane ring thereof) (in the case where b > 0).

In the above formula (II) representing the diglycidyl compound (A2), Z is a branched alkylene group having 3 to 8 carbon atoms or represented by the formula-C_mH_2m－Z¹－C_nH_2n-a 2-valent radical of formula (I). Here, -Z¹-is-O-, -C (═ O) -O-, or-O-C (═ O) -, one of m and n is an integer of 1 or more, and the other is an integer of 2 or more, and the sum of both is 8 or less, and C is_mH_2mAnd C_nH_2nOne of (1) is a branched saturated hydrocarbon group having a valence of 2. In view of reducing the ability of a photocurable adhesive described later to dissolve a thermoplastic resin film adhered to a polyvinyl alcohol-based polarizing plate (hereinafter, this ability will also be referred to simply as "dissolving power"), Z is the branched alkylene described aboveRadicals, or the 2-valent radicals mentioned above, are advantageous.

The compound of formula (II) wherein Z is a branched alkylene group is a diglycidyl ether of a branched alkylene glycol. Specific examples thereof include propylene glycol diglycidyl ether, 1, 3-butanediol diglycidyl ether, 1, 2-butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, 3-methyl-1, 5-pentanediol diglycidyl ether, 2-methyl-1, 8-octanediol diglycidyl ether, and 1, 4-cyclohexanedimethanol.

In the formula (II), Z is represented by the formula-C_mH_2m－Z¹－C_nH_2nThe compound having a 2-valent group represented by-corresponds to the case where Z is a branched alkylene group and the C-C bond of the alkylene group is interrupted by-O-, -CO-O-or-O-CO-.

The content of the alicyclic diepoxy compound (A1) in the photocationic curable component (A) is 30 to 85% by weight based on the total amount of the photocationic curable component (A). The content thereof is preferably 40 to 80% by weight, more preferably 60 to 75% by weight. If the content of the alicyclic diepoxy compound (a1) in the photocationic curable component (a) is too small, the elastic modulus of the cured product decreases, and the frequency of cracking of the polarizing plate in the cold-heat cycle test increases. On the other hand, if the content is too large, the amount of the diglycidyl compound (a2) described below becomes relatively small, and it becomes difficult to reduce the viscosity of the photocurable adhesive.

The content of the diglycidyl compound (A2) having a branched structure at the linking group in the photocationic curable component (A) is 1 to 70% by weight. The content thereof is preferably 5 to 50% by weight, more preferably 5 to 30% by weight. If the content of the diglycidyl compound (a2) in the photocationic curable component (a) is more than 70% by weight, curing becomes insufficient, and the adhesion between the polarizing plate and the thermoplastic resin film is reduced. If the content of the diglycidyl compound (a2) is less than 1 wt%, the viscosity of the photocurable adhesive is less likely to be lowered.

The photocationic curable component (a) constituting the photocurable adhesive contains the alicyclic diepoxy compound (a1) described above and the diglycidyl compound (a2) having a branched structure in the linking group in the proportions described above. In order to more effectively reduce the viscosity of the photocurable adhesive before curing and to improve the adhesion between the polarizing plate and the thermoplastic resin film by the cured product thereof, or in order to further reduce the ability of the photocurable adhesive to dissolve the thermoplastic resin film, the content of the diglycidyl compound (a2) is preferably 25 wt% or more based on the total amount of the photocationic curable component (a).

The photocationic curable component (a) may further contain another cationically polymerizable compound in the above-described amount range of the alicyclic diepoxy compound (a1) and the diglycidyl compound (a2) having a branched structure in the linking group.

(2) Photo cation polymerization initiator (B)

The photocurable adhesive contains a photocationic polymerization initiator (B). In this way, the photo cation curable component (a) can be cured by cationic polymerization by irradiation with active energy rays to form the adhesive layer. The photo cation polymerization initiator (B) generates a cation species or lewis acid by irradiation of active energy rays such as visible rays, ultraviolet rays, X-rays, and electron beams, and initiates a polymerization reaction of the photo cation curable component (a). Since the photo cation polymerization initiator (B) exerts a catalytic action by light, it is excellent in storage stability and handling property even when it is mixed in the photo cation curable component (a). Examples of the compound which can be used as the photo cation polymerization initiator (B) and generates a cationic species or a lewis acid by irradiation with an active energy ray include aromatic diazonium salts; onium salts such as aromatic iodonium salts and aromatic sulfonium salts; iron-arene complexes, and the like.

Examples of the aromatic diazonium salt include:

benzene diazonium hexafluoroantimonate,

Benzene diazonium hexafluorophosphate,

Hexafluoro-boratobenzene diazonium salt.

Examples of the aromatic iodonium salt include:

diphenyliodonium tetrakis (pentafluorophenyl) borate,

Diphenyliodonium hexafluorophosphate,

Diphenyliodonium hexafluoroantimonate,

Bis (4-nonylphenyl) iodonium hexafluorophosphate.

Examples of the aromatic sulfonium salt include:

triphenylsulfonium hexafluorophosphate,

Triphenylsulfonium hexafluoroantimonate,

Triphenylsulfonium tetrakis (pentafluorophenyl) borate,

4, 4' -bis (diphenylsulfonium) diphenylsulfide bis (hexafluorophosphate),

4, 4' -bis (di (beta-hydroxyethoxy) phenylsulfone) diphenylsulfide bis (hexafluoroantimonate),

4, 4' -bis (di (beta-hydroxyethoxy) phenylsulfonium) diphenylsulfide bis (hexafluorophosphate),

7- [ di (p-tolyl) sulfonium ] -2-isopropylthioxanthone hexafluoroantimonate,

7- [ di (p-tolyl) sulfonium ] -2-isopropylthioxanthone tetrakis (pentafluorophenyl) borate,

4-phenylcarbonyl-4' -diphenylsulfonium-diphenylsulfide hexafluorophosphate,

4- (p-tert-butylphenylcarbonyl) -4' -diphenylsulfonium-diphenylsulfide hexafluoroantimonate,

4- (p-tert-butylphenylcarbonyl) -4' -di (p-tolyl) sulfonium-diphenylsulfide tetrakis (pentafluorophenyl) borate.

Examples of the iron-arene complex include:

xylene-cyclopentadienyl iron (II) hexafluoroantimonate,

Cumene-cyclopentadienyl iron (II) hexafluorophosphate,

Xylene-cyclopentadienyl iron (II) tris (trifluoromethylsulfonyl) methanide.

The cationic photopolymerization initiator (B) may be used alone in 1 kind, or two or more kinds may be used in combination. Among the above, aromatic sulfonium salts are particularly preferably used because they have ultraviolet absorption characteristics even in the wavelength region of about 300nm and thus provide an adhesive layer having excellent curability and good mechanical strength and adhesive strength.

The content of the photo cation polymerization initiator (B) is 1 to 10 parts by weight, preferably 2 to 6 parts by weight, based on 100 parts by weight of the entire photo cation curable component (A). By containing the photo cation polymerization initiator (B) in an amount of 1 part by weight or more, the photo cation curable component (a) can be sufficiently cured, and high mechanical strength and adhesive strength can be imparted to the obtained polarizing plate. On the other hand, if the content is increased, the ionic substance in the cured product increases, and thus the hygroscopicity of the cured product increases, and there is a possibility that the durability of the polarizing plate is lowered, and therefore the content of the photo cation polymerization initiator (B) is 10 parts by weight or less with respect to 100 parts by weight of the photo cation curable component (a).

(3) Branched alcohol compound (C)

The photocurable adhesive contains a branched alcohol compound (C) in addition to the photocationic curable component (a) and the photocationic polymerization initiator (B). The photocurable adhesive of the present invention containing these components exhibits low viscosity at room temperature and good coating suitability, and can firmly bond the polyvinyl alcohol-based polarizing plate and the thermoplastic resin film while suppressing bubble defects that may occur in the adhesive layer after curing. As is clear from the studies by the present inventors, the bubble defect generated in the adhesive layer is related to the ability (dissolving power) of the photocurable adhesive to dissolve the thermoplastic resin film.

It is also advantageous to include the branched alcohol compound (C) in the photocurable adhesive in order not to increase the ability (dissolving power) of dissolving the thermoplastic resin film adhered to the polyvinyl alcohol-based polarizing plate. As is clear from the studies by the present inventors, it has been found that, in a photocurable adhesive containing a linear alcohol, if the solubility of the photocurable adhesive is high, bubble defects are likely to occur in the adhesive layer after curing. This is presumably because the film dissolves in the photocurable adhesive, thereby increasing the viscosity. According to the photocurable adhesive of the present invention containing the branched alcohol compound (C), since the contribution to the dissolving power of the photocurable adhesive is extremely small, there is no change in the frequency of generation of bubbles before and after the addition. On the other hand, when a straight-chain alcohol compound is used instead of the branched alcohol compound (C), a large amount of bubble defects are generated.

Among them, it is advantageous to include a branched alcohol compound (C) having a molecular weight of 400 or less in the photocurable adhesive in order to reduce the ability to dissolve (dissolving power) a thermoplastic resin film bonded to a polyvinyl alcohol-based polarizing plate. According to the photocurable adhesive of the present invention containing the branched alcohol compound (C) having a molecular weight of 400 or less, bubble defects in the adhesive layer due to dissolution of the thermoplastic resin film can be reduced. In order to reduce bubble defects in the adhesive layer caused by dissolution of the thermoplastic resin film, it is useful to include the above-mentioned diglycidyl compound (a2) in the above-mentioned content as the photocationic curable component (a) and to contain a branched alcohol compound (C) having a molecular weight of 400 or less. On the other hand, when a straight-chain alcohol compound is used instead of the branched alcohol compound (C), it is difficult to reduce bubble defects.

The branched alcohol compound (C) is a compound represented by the following formula (III):

R⁸represents an n-valent hydrocarbon group having a branched structure. n is an integer of 1 or more, represents the number of hydroxyl groups per 1 molecule of the branched alcohol compound (C), and is the same as the valence of the hydrocarbon group. The term "the hydrocarbon group has a branched structure" means that when the main chain of the branched alcohol compound (C) is set so as to include at least 1 of the hydroxyl groups represented by the above formula (III) and so as to have the largest number of carbon atoms, R is the number of the hydroxyl groups⁸In the hydrocarbon group represented, there are one or two or moreA side chain comprising a carbon atom branched from the above main chain.

With R⁸The hydrocarbon group having a branched structure may be, for example, a saturated hydrocarbon group or an unsaturated hydrocarbon group having 3 or more carbon atoms, and is preferably a saturated hydrocarbon group, more preferably an aliphatic saturated hydrocarbon group, and further preferably an alkylene group. The hydrocarbon group may contain a C atom such as an O atom, S atom, P atom, halogen atom, etc., and an atom (hetero atom) other than H atom. For example, the hydrocarbon group may contain one or more methylene groups (-CH) as in the case where the hydrocarbon group is an alkylene group₂-) in the case of the above-mentioned methylene group, 1 or more of the methylene groups may be substituted with a linking group having a valence of 2, for example, -O-, -C (═ O) -O-, or-O-C (═ O) -. The 2-valent linking group which replaces methylene is preferably-O-.

Specific examples of the branched alcohol compound (C) include monofunctional alcohols such as isopropyl alcohol, isobutyl alcohol, 2-butanol, 2-methyl-1-pentanol, 2-ethylhexanol, 2-nonyltridecanol, 2-undecylpentadecanol, 2-heptylundecyl alcohol, 2-ethylhexanol, 2-pentanol, isopentyl alcohol, isoheptyl alcohol, isooctanol, isononyl alcohol, isodecyl alcohol, isoundecyl alcohol, isododecyl alcohol, isotridecyl alcohol, isotetradecyl alcohol, isotentadecyl alcohol, isopalmyl alcohol, isostearyl alcohol, and isoeicosyl alcohol; 1, 2-propanediol, 1, 2-butanediol, 1, 3-butanediol, 1, 5-hexanediol, dipropylene glycol, tripropylene glycol, 2-methyl-1, 3-propanediol, 2-dimethyl-1, 3-propanediol (neopentyl glycol), 1' - [ 1-methyl-1, 2-ethanediylbis (oxy) ] bis (2-propanol) (tripropylene glycol), 2-diethyl-1, 3-propanediol, 3-methyl-1, 5-pentanediol, polyfunctional alcohols (compounds having two or more hydroxyl groups in the molecule) such as 2-ethyl-1, 3-hexanediol, 2, 4-trimethyl-1, 3-pentanediol, 2-methyl-1, 8-octanediol, glycerol, trimethylolpropane, trimethylolethane, pentaerythritol, ditrimethylolpropane, tris (trimethylol) propane, dipentaerythritol and tripentaerythritol. Commercially available branched alcohol compounds (C) can also be used. The branched alcohol compound (C) shown in the above examples is also a specific example of the branched alcohol compound (C) having a molecular weight of 400 or less.

The molecular weight of the branched alcohol compound (C) is preferably 400 or less, more preferably 300 or less, and even more preferably 200 or less, from the viewpoint of not increasing the dissolving power of the photocurable adhesive, and from the viewpoint of lowering the viscosity, accelerating the curing, and improving the adhesive strength. Accordingly, the number of carbon atoms of the hydrocarbon group is preferably 20 or less. The molecular weight of the branched alcohol compound (C) is usually 60 or more, preferably 80 or more, and more preferably 100 or more.

The branched alcohol compound (C) may be a monofunctional alcohol, but is preferably a polyfunctional alcohol (a compound having two or more hydroxyl groups in the molecule) from the viewpoint of acceleration of curing and adhesive strength, that is, n in the formula (III) is preferably 2 or more. n is usually 12 or less, preferably 10 or less, and more preferably 8 or less. n is more preferably an integer of 2 to 6.

The branched alcohol compound (C) is preferably a polyfunctional alcohol having a molecular weight of 60 to 400, more preferably a polyfunctional alcohol having a molecular weight of 80 to 300, and still more preferably a polyfunctional alcohol having a molecular weight of 100 to 200. Suitable examples of the branched alcohol compound (C) include branched alkylene glycol compounds such as dipropylene glycol, tripropylene glycol, and neopentyl glycol from the viewpoints of easiness in obtaining and safety, prevention of increase in the dissolving power of the photocurable adhesive, reduction in viscosity, acceleration of curing, and adhesive strength. The branched alkylene glycol compound may be a monoalkylene glycol, a dialkylene glycol, a trialkylene glycol, a polyalkylene glycol, or the like. The diol refers to a diol (2-functional alcohol) in which two hydroxyl groups are bonded to different carbon atoms. The dipropylene glycol and the tripropylene glycol are compounds represented by the following formulae (a) and (b), respectively.

The content of the branched alcohol compound (C) is 0.1 to 15 parts by weight, preferably 0.5 to 12 parts by weight, and more preferably 0.8 to 8 parts by weight, based on 100 parts by weight of the entire photocationic-curable component (A). By containing 0.1 part by weight or more of the branched alcohol compound (C), the effects of lowering viscosity, accelerating curing and improving adhesive strength can be remarkably obtained. On the other hand, if the content is more than 15 parts by weight, curing of the photocationic curable component (a) tends to become insufficient.

(4) Other components capable of being incorporated into a photocurable adhesive

The photocurable adhesive may contain other components known to be blended into a general photocurable resin or adhesive. Examples of suitable other components include a photosensitizer and a photosensitizing assistant. The photosensitizer has a maximum absorption at a wavelength longer than the maximum absorption wavelength exhibited by the photo cation polymerization initiator (B), and is a compound that promotes the polymerization initiation reaction by the photo cation polymerization initiator (B). In addition, the photosensitizing assistant is a compound that further promotes the action of the photosensitizer. Depending on the type of the thermoplastic resin film, it may be preferable to add such a photosensitizer or further a photosensitizing assistant.

Examples of the photosensitizer and the photosensitizing assistant include anthracene compounds and naphthalene compounds. Examples of the anthracene compound include compounds represented by the following formula (IVa).

In the formula, R³And R⁴Each independently represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms or an alkoxyalkyl group having 2 to 12 carbon atoms, R⁵Represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. Specific examples of the anthracene compound represented by the formula (IVa) include the following compounds.

9, 10-dimethoxy anthracene,

9, 10-diethoxyanthracene,

9, 10-dipropoxyanthracene,

9, 10-diisopropoxylanthracene,

9, 10-dibutoxyanthracene,

9, 10-dipentyloxy anthracene,

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-diisopropoxylanthracene,

2-methyl-or 2-ethyl-9, 10-dibutoxyanthracene,

2-methyl-or 2-ethyl-9, 10-dipentyloxy anthracene,

2-methyl-or 2-ethyl-9, 10-dihexyloxyanthracene, and the like.

Examples of the naphthalene-based compound include compounds represented by the following formula (IVb).

In the formula, R⁶And R⁷Each independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. Specific examples of the naphthalene-based compound represented by the formula (IVb) 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-dipropoxy naphthalene,

1, 4-dibutoxynaphthalene, and the like.

By adding the above-mentioned photosensitizer and auxiliary photosensitizer to the photocurable adhesive, the curability of the adhesive can be improved as compared with the case where the photosensitizer and auxiliary photosensitizer are not added. Such an effect can be exhibited by blending the photosensitizer and the photosensitizing auxiliary agent in an amount of 0.1 part by weight or more based on 100 parts by weight of the photocationic curable component (a).

The content of the anthracene compound is preferably 0.1 to 0.3 parts by weight with respect to 100 parts by weight of the photocationic curable component (a) from the viewpoint of maintaining the neutral gray color of the polarizing plate and from the viewpoint of suppressing problems such as precipitation during storage at low temperatures. The content of the naphthalene compound is preferably 5 parts by weight or less, more preferably 3 parts by weight or less, based on 100 parts by weight of the photocationic curable component (a), from the viewpoint of suppressing problems such as precipitation during storage at low temperatures.

The photocurable adhesive may contain other additive components than the photosensitizer and the auxiliary photosensitizer as long as the effects of the present invention are not impaired. Examples of the other additive components include a thermal cationic polymerization initiator, an alcohol compound other than the branched alcohol compound (C) (e.g., a polyhydric alcohol other than the branched alcohol compound), an ion scavenger, an antioxidant, a light stabilizer, a chain transfer agent, a thickener, a thermoplastic resin, a filler, a flow control agent, a plasticizer, a defoaming agent, a leveling agent, a pigment, and an organic solvent.

When the additive component is contained, the content thereof is preferably 1000 parts by weight or less based on 100 parts by weight of the photocationic-curable component (a). When the content is 1000 parts by weight or less, the effects of suppressing bubble defects caused by dissolution of the thermoplastic resin film in the cured adhesive layer, reducing the viscosity of the photocurable adhesive and improving the coatability thereof, and the excellent adhesive strength between the polyvinyl alcohol-based polarizing plate and the thermoplastic resin film, which are brought about by the combination of the photocationic curable component (a), the photocationic polymerization initiator (B), and the branched alcohol compound (C) as essential components, can be exhibited well.

(5) Moisture content of the photo-curable adhesive

The photocurable adhesive may contain moisture. The content of water is usually 4 parts by weight or less, preferably 3 parts by weight or less, and more preferably less than 3 parts by weight, based on 100 parts by weight of the photocationic-curable component (a). When the amount of water is more than 0 part by weight, the adhesive strength between the polyvinyl alcohol-based polarizing plate and the thermoplastic resin film is improved. The content of water is usually 0.01 part by weight or more, preferably 0.03 part by weight or more, and more preferably 0.04 part by weight or more, based on 100 parts by weight of the photocationic-curable component (a). However, if the moisture content is too high, separation between the photocurable adhesive and water may occur, and the photocurable adhesive may not be uniformly applied to the surface of the polarizing plate or the thermoplastic resin film, or the curability of the photocurable adhesive may deteriorate. Moisture may be intentionally added to the photocurable adhesive, and in this case, purified water such as distilled water or pure water may be used without particular limitation. The moisture may be moisture derived from raw materials, moisture mixed in the production process, or the like. The moisture content of the photocurable adhesive was measured by the karl fischer capacity method.

(6) Physical Properties of Photocurable adhesive

The photocurable adhesive of the present invention can have low viscosity by containing a predetermined amount of the above-mentioned predetermined photocationic curable component (a) and the branched alcohol compound (C), and thus can exhibit excellent coating suitability when a thermoplastic resin film is bonded to a polyvinyl alcohol-based polarizing plate by the photocurable adhesive. Specifically, the photocurable adhesive of the present invention can exhibit a viscosity in the range of 2 to 300 mPas at 25 ℃. The viscosity referred to herein is a viscosity in a state substantially not containing a solvent. If the viscosity is less than 2mPa · s, the polarizing plate may be peeled off from the thermoplastic resin film during transportation after bonding, and if the viscosity is more than 300mPa · s, bubbles may be easily mixed into the space between the polarizing plate and the thermoplastic resin film, that is, the adhesive layer, when the polarizing plate and the thermoplastic resin film are bonded with the adhesive interposed therebetween, particularly when the adhesive layer is thin. The viscosity is preferably 5 to 200 mPas, more preferably 10 to 150 mPas, still more preferably 100 mPas or less, and particularly preferably 80 mPas or less. The viscosity of the photocurable adhesive was measured using an E-type viscometer.

The photocurable adhesive of the present invention can be used for manufacturing a polarizing plate by bonding a thermoplastic resin film to a polyvinyl alcohol polarizer. At this time, if the adhesive dissolves the thermoplastic resin film, bubble defects are generated in the adhesive layer of the polarizing plate due to the dissolution as described above. The photocurable adhesive of the present invention can be an adhesive having high safety and a small ability to dissolve a thermoplastic resin film (dissolving power) by blending the photocationic curable component (a) and the branched alcohol compound (C) containing the above-described two specific compounds at a given ratio. As the diglycidyl compound (a2) which is one of the photocationic-curable components (a), it is advantageous to use a diglycidyl compound (a2) in which the linking group Z has a branched structure, typically a compound in which the linking group Z is a branched alkylene group, from the viewpoint of improving safety and suppressing an increase in dissolving power. In order to further improve safety and suppress an increase in dissolving power, it is preferable to use a diglycidyl compound (a2) having a branched structure in the linking group Z, typically a diglycidyl compound (a2) in which the linking group Z is a branched alkylene group, and a branched polyfunctional alcohol (particularly a branched alkylene glycol compound) as the branched alcohol compound (C), and more preferably a branched alcohol compound (C) having a molecular weight of 400 or less. The photocurable adhesive of the present invention may be used in an amount such that when the thermoplastic resin film adhered to the polyvinyl alcohol-based polarizing plate is immersed at 23 ℃ for 2 days, the weight reduction of the thermoplastic resin film is 0 to 30 wt%, and more preferably 25 wt% or less. The photocurable adhesive of the present invention can have a small dissolving power for a stretched acetyl cellulose resin film, for example. Examples of the stretched acetyl cellulose resin film include an acetyl cellulose resin film having an in-plane retardation value of 10nm or more, and more specifically 50nm or more at a wavelength of 590 nm.

The weight reduction when the thermoplastic resin film was immersed in the photocurable adhesive was determined as follows. That is, first, the thermoplastic resin film is cut into an appropriate size, and the weight thereof is determined. Then, the cut thermoplastic resin film was immersed in a photocurable adhesive prepared in a liquid state and kept at 23 ℃ for 2 days, and then taken out, and the adhesive attached to the surface was wiped off, and the weight thereof was determined. Thereafter, the weight loss after immersion was determined according to the following formula:

weight reduction (%) { (weight of film before immersion-weight of film after immersion)/weight of film before immersion } × 100.

< polarizing plate >

The polarizing plate of the present invention comprises a polyvinyl alcohol-based polarizer and a thermoplastic resin film bonded to at least one surface thereof with an adhesive layer interposed therebetween, the adhesive layer being a cured product of the photocurable adhesive. Since the photocurable adhesive of the present invention is used for the polarizing plate, the mixing of bubbles (bubble defect) due to the dissolution of the thermoplastic resin film in the cured adhesive layer is suppressed.

In addition, the cured adhesive layer in the polarizing plate of the present invention may have a high tensile elastic modulus. Accordingly, the polarizing plate of the present invention can have good adhesion strength between the polarizer and the thermoplastic resin film. The polarizing plate of the present invention may have a tensile modulus of elasticity of the adhesive layer of, for example, 1000MPa or more, and more preferably 1500MPa or more at 80 ℃. The peeling strength between the polarizing plate and the thermoplastic resin film in the polarizing plate of the present invention may be 0.5N/25mm or more, more preferably 0.7N/25mm or more, and still more preferably 1.0N/25mm or more. The tensile elastic modulus at 80 ℃ of the adhesive layer and the peel strength between the polarizing plate and the thermoplastic resin film were measured in accordance with the description of one of the examples described later.

(1) Polyvinyl alcohol polarizing plate

The polyvinyl alcohol-based polarizing plate is composed of a polyvinyl alcohol-based resin film having a dichroic dye adsorbed thereon and oriented. The polyvinyl alcohol resin constituting the polarizing plate is 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 with vinyl acetate. Examples of the other monomer copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids. The saponification degree 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, and for example, polyvinyl formal, polyvinyl acetal, or the like modified with aldehydes may be used. The polymerization degree of the polyvinyl alcohol resin is usually 1000 to 10000, preferably 1500 to 5000.

The polarizing plate is produced by subjecting the polyvinyl alcohol resin film to uniaxial stretching, dyeing the polyvinyl alcohol resin film with a dichroic dye to adsorb the dichroic dye, and treating the polyvinyl alcohol resin film adsorbed with the dichroic dye with an aqueous boric acid solution.

The uniaxial stretching may be performed before dyeing with the dichroic dye, may be performed simultaneously with dyeing with the dichroic dye, or may be performed after dyeing with the dichroic dye. In the case where uniaxial stretching is performed after dyeing with a dichroic dye, the uniaxial stretching may be performed before boric acid treatment or may be performed during boric acid treatment. Uniaxial stretching may also be performed in a plurality of stages of these. The method of uniaxial stretching is not particularly limited, and stretching may be performed uniaxially between rolls having different peripheral speeds, or may be performed uniaxially using a heat roll. The stretching may be performed in a dry manner by stretching in the air, or may be performed in a wet manner by stretching in a state of being swollen with a solvent. The draw ratio is usually about 4 to 8 times.

The polyvinyl alcohol resin film can be caused to adsorb the dichroic dye by immersing the film in an aqueous solution containing the dichroic dye. Iodine or a dichroic organic dye is used as the dichroic dye.

When iodine is used as the dichroic dye, a method of immersing the polyvinyl alcohol resin film in an aqueous solution containing iodine and potassium iodide to dye the film is generally used. The aqueous solution generally contains about 0.01 to about 0.5 part by weight of iodine per 100 parts by weight of water, and the aqueous solution generally contains about 0.5 to about 10 parts by weight of potassium iodide per 100 parts by weight of water. The temperature of the aqueous solution is usually about 20 to 40 ℃, and the immersion time (dyeing time) in the 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 the polyvinyl alcohol resin film in an aqueous solution containing a water-soluble dichroic organic dye to dye the film is generally used. The content of the dichroic organic dye in the aqueous solution is usually 1X 10 per 100 parts by weight of water^-3～1×10^-2About the weight portion. The aqueous solution may contain an inorganic salt such as sodium sulfate. The temperature of the aqueous solution is usually about 20 to 80 ℃, and the immersion time (dyeing time) in the aqueous solution is usually about 30 to 300 seconds.

The boric acid treatment after dyeing is performed by immersing the dyed polyvinyl alcohol resin film in an aqueous boric acid solution. The boric acid content of the aqueous boric acid 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 aqueous boric acid 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 aqueous boric acid solution is usually about 100 to 1200 seconds, preferably about 150 to 600 seconds, and more preferably about 200 to 400 seconds. The temperature of the aqueous boric acid solution is usually 50 ℃ or higher, preferably 50 to 85 ℃.

The polyvinyl alcohol resin film after the boric acid treatment is usually subjected to a water washing treatment. The water washing treatment can be performed by, for example, immersing the boric acid-treated polyvinyl alcohol resin film in water. After washing with water, the resultant was dried to obtain a polarizing plate. The temperature of water in the water washing treatment is usually about 5 to 40 ℃, and the immersion time is usually about 2 to 120 seconds. The subsequent drying treatment can be performed by using a hot air dryer or a far infrared heater. The drying temperature is usually 40 to 100 ℃. The drying time is usually about 120 to 600 seconds. The thickness of the polyvinyl alcohol-based polarizing plate may be about 5 to 50 μm.

(2) Thermoplastic resin film

The thermoplastic resin film may be an acetyl cellulose resin film such as triacetyl cellulose, or a transparent resin film having a lower moisture permeability than triacetyl cellulose, which has been most widely used as a protective film for a polarizing plate. The moisture permeability of triacetyl cellulose is approximately 400g/m²And/24 hr or so. The moisture permeability of the thermoplastic resin film is measured at a temperature of 40 ℃ and a relative humidity of 90% by a cup method (cup method) specified in JIS Z0208.

The thermoplastic resin film may be any of a film which is not stretched or a film which is uniaxially or biaxially stretched. The thermoplastic resin film may be, for example, a protective film for a polarizing plate, or an optical compensation film such as a retardation film.

In a preferred embodiment, the thermoplastic resin film bonded to at least one surface of the polarizing plate is made of an acetyl cellulose resin. The acetyl cellulose resin film may contain an ultraviolet absorber. In another preferred embodiment, the thermoplastic resin film to be bonded to at least one surface of the polarizing plate is a thermoplastic resin film having a moisture permeability lower than that of triacetylcellulose, for example, a thermoplastic resin film having a moisture permeability of 300g/m²A thermoplastic resin film of 24hr or less. Examples of the resin constituting such a thermoplastic resin film having low moisture permeability include amorphous polyolefin resins, polyester resins, (meth) acrylic resins, polycarbonate resins, and chain polyolefin resins. Among them, amorphous polyolefin resins, polyester resins, and chain polyolefin resins are preferably used. In another preferred embodiment, a first thermoplastic resin film made of an acetyl cellulose resin is bonded to one surface of a polarizing plate with an adhesive layer as a cured product of the photocurable adhesive of the present invention interposed therebetween, and the polarizing plate is bonded to the other surface of the polarizing plate with the adhesive layer interposed therebetweenThe other surface of the second thermoplastic resin film is similarly bonded to the other surface of the second thermoplastic resin film through the adhesive layer which is a cured product of the photocurable adhesive of the present invention, the second thermoplastic resin film being formed of the transparent resin having a lower moisture permeability as described above.

The acetyl cellulose resin is a resin in which at least a part of hydroxyl groups in cellulose is esterified with acetic acid, and may be a mixed ester in which a part is esterified with acetic acid and a part is esterified with another acid. Specific examples of the acetyl cellulose resin include triacetyl cellulose, diacetyl cellulose, cellulose acetate propionate, and cellulose acetate butyrate.

The amorphous polyolefin resin is a polymer having a polymerization unit of a cyclic olefin such as norbornene, tetracyclododecene (also referred to as "dimethanonaphthalene"), or a compound having a substituent bonded thereto, and may be a copolymer obtained by copolymerizing a linear olefin and/or an aromatic vinyl compound with a cyclic olefin. In the case of a homopolymer of a cyclic olefin or a copolymer of two or more cyclic olefins, a double bond remains due to ring-opening polymerization, and therefore a product obtained by hydrogenating the double bond is widely used as an amorphous polyolefin resin. Among them, the thermoplastic norbornene resin is a representative resin.

The polyester resin is a polymer obtained by condensation polymerization of a dibasic acid and a glycol, and polyethylene terephthalate is a representative polymer. The (meth) acrylic resin is a polymer containing methyl methacrylate as a main monomer, and may be a homopolymer of methyl methacrylate or a copolymer of methyl methacrylate and a monomer other than methyl methacrylate (e.g., a (meth) acrylic monomer such as an acrylic acid ester of methyl acrylate, an aromatic vinyl compound, etc.). In the present specification, "(meth) acrylic" means at least one selected from acrylic acid and methacrylic acid.

The polycarbonate-based resin is a polymer having a carbonate bond (-O-CO-O-) in the main chain, and a polymer obtained by condensation polymerization of bisphenol A and phosgene is a typical polymer. The chain polyolefin resin is a polymer containing a chain olefin such as ethylene or propylene as a main monomer, and may be a homopolymer or a copolymer. Among them, a homopolymer of propylene or a copolymer obtained by copolymerizing propylene with a small amount of ethylene is a representative polymer.

The thermoplastic resin film may contain known additives as needed. Examples of the known additives include lubricants, antiblocking agents, heat stabilizers, ultraviolet absorbers, antioxidants, antistatic agents, light stabilizers, impact modifiers, and surfactants. Examples of the ultraviolet absorber include salicylate-based compounds, benzophenone-based compounds, benzotriazole-based compounds, cyanoacrylate-based compounds, and nickel complex-based compounds. However, since transparency is required as a thermoplastic resin film to be laminated on a polarizing plate, it is preferable to limit the amount of these additives to a minimum.

As the thermoplastic resin film, a film to which an optical compensation function is imparted may be used. An acetyl cellulose resin film may also be used. Examples of the optical compensation film include a retardation film in which a compound having a retardation adjusting function is contained in an acetyl cellulose resin, a retardation film in which a compound having a retardation adjusting function is applied to a surface of an acetyl cellulose resin, and a retardation film obtained by uniaxially or biaxially stretching an acetyl cellulose resin. As the optical compensation film, a film made of another thermoplastic resin may be used.

The thickness of the thermoplastic resin film is usually about 5 to 200 μm, preferably 10 to 120 μm, and more preferably 10 to 100 μm. The thermoplastic resin film may have various surface treatment layers (coating layers) such as a hard coat layer, an antireflection layer, an antiglare layer, an antistatic layer, and a light diffusion layer on the surface opposite to the surface to be bonded to the polarizing plate.

(3) Manufacture of polarizing plates

The polarizing plate can be obtained by bonding a thermoplastic resin film to at least one surface of the polarizer using the photocurable adhesive. Specifically, after the coating layer of the above-mentioned photocurable adhesive is formed on the bonding surface of the polarizing plate and/or the thermoplastic resin film, and the polarizing plate and the thermoplastic resin film are bonded to each other with the coating layer interposed therebetween, the coating layer of the uncured photocurable adhesive is cured by irradiation with an active energy ray, and the thermoplastic resin film is fixed to the polarizing plate. For forming the coating layer of the photocurable adhesive, various coating methods such as a blade, a wire bar, a die coater, a comma coater, and a slot roll coater can be used. Further, a method may be adopted in which the adhesive is cast between the polarizing plate and the thermoplastic resin film while continuously supplying them so that the adhesive surface therebetween is on the inside.

The viscosity of the photocurable adhesive may be adjusted by using a solvent according to the application method of the photocurable adhesive. The solvent is not particularly limited in its kind, and a solvent that can dissolve the photocurable adhesive well without degrading the optical performance of the polarizing plate is used. For example, organic solvents such as hydrocarbons typified by toluene and esters typified by ethyl acetate can be used. However, when the solvent is contained, it is preferable to use no solvent as much as possible because a drying step for removing the solvent is required before the irradiation with the active energy ray.

The thickness of the cured adhesive layer can be arbitrarily set according to the characteristic design of the polarizing plate, but is preferably small from the viewpoint of reducing the cost of the adhesive material. Generally, it is 0.01 to 20 μm, preferably 0.1 to 10 μm, and more preferably 0.5 to 5 μm. If the thickness of the adhesive layer is reduced, mixing of air bubbles into the adhesive layer and reduction in adhesion and durability are likely to occur, but according to the photocurable adhesive of the present invention, these problems can be effectively suppressed. If the adhesive layer is too thick, the reactivity of the adhesive decreases, and the moist heat resistance of the polarizing plate tends to deteriorate.

When the thermoplastic resin film is bonded to only one surface of the polarizing plate, for example, a pressure-sensitive adhesive layer for bonding to another optical member such as a liquid crystal cell may be directly provided on the other surface of the polarizing plate. On the other hand, when thermoplastic resin films are bonded to both surfaces of the polarizing plate, the thermoplastic resin films may be formed of the same kind of resin or different kinds of resins. The thermoplastic resin film bonded to one surface of the polarizing plate is bonded using the above-described photocurable adhesive of the present invention, and the thermoplastic resin film bonded to the other surface of the polarizing plate may be bonded using the photocurable adhesive of the present invention or may be bonded using another adhesive.

Before the adhesion of the thermoplastic resin film to the polarizing plate, the adhesion surface of the thermoplastic resin film and/or the polarizing plate may be subjected to an easy adhesion treatment such as saponification treatment, corona treatment, plasma treatment, undercoating treatment, anchor coat treatment, flame treatment, or the like.

The light source for irradiating the coating layer of the photocurable adhesive with active energy rays may be any light source that can generate ultraviolet rays, electron beams, X-rays, or the like. In particular, a low-pressure mercury lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp, an ultra-high pressure mercury lamp, a chemical lamp, a black light lamp, a microwave-excited mercury lamp, a metal halide lamp, or the like having a light emission distribution at a wavelength of 400nm or less can be suitably used.

The irradiation intensity of the active energy ray to the photocurable adhesive is not particularly limited, but is preferably 0.1 to 3000mW/cm in a wavelength region effective for activation of the photocationic polymerization initiator (B)². If it is less than 0.1mW/cm²The reaction time becomes excessively long, and if it is more than 3000mW/cm²The heat radiated from the lamp and the heat generated during polymerization of the photocurable adhesive may cause yellowing of the photocurable adhesive and deterioration of the polarizing plate.

The light irradiation time of the photocurable adhesive is not particularly limited, but the cumulative light amount expressed as the product of the irradiation intensity and the irradiation time is preferably 10 to 5000mJ/cm²The mode of (2) is set. If it is less than 10mJ/cm²If the amount of accumulated light exceeds 5000mJ/cm, the generation of active species from the photo cation polymerization initiator (B) may be insufficient, and the curing of the resulting adhesive layer may be insufficient²The irradiation time becomes very long, which is disadvantageous in productivity improvement.

In the case where the thermoplastic resin films are bonded to both surfaces of the polarizing plate, the irradiation with the active energy ray may be performed from either side of the thermoplastic resin film, but for example, in the case where one thermoplastic resin film contains an ultraviolet absorber and the other thermoplastic resin film does not contain an ultraviolet absorber, it is preferable to irradiate the active energy ray from the side of the thermoplastic resin film not containing an ultraviolet absorber, from the viewpoint of effectively utilizing the irradiated active energy ray and improving the curing speed.

The polarizing plate obtained by curing the photocurable adhesive preferably has a peel strength between the polarizer and the thermoplastic resin film of 0.5N/25mm or more, more preferably 0.7N/25mm or more, measured as described in the example. If the peel strength is less than 0.5N/25mm, peeling may occur between the polarizer and the adhesive layer when the polarizing plate is cut.

< stacked optical Member and liquid Crystal display device >

The polarizing plate of the present invention may be a laminated optical member obtained by laminating optical layers having optical functions other than polarizing plates. Typically, the laminated optical member is produced by laminating and bonding an optical layer on a thermoplastic resin film of a polarizing plate with an adhesive or a pressure-sensitive adhesive interposed therebetween, and in addition thereto, for example, a thermoplastic resin film may be laminated and bonded with a photocurable adhesive of the present invention interposed therebetween on one surface of a polarizing plate, and an optical layer may be laminated and bonded with an adhesive or a pressure-sensitive adhesive interposed therebetween on the other surface of the polarizing plate. In the latter case, if the photocurable adhesive of the present invention is used as an adhesive for bonding the polarizing plate and the optical layer, the optical layer can also be a thermoplastic resin film. Two or more optical layers may be stacked on the polarizing plate.

Examples of the optical layer laminated on the polarizing plate include a reflective layer, a semi-transmissive reflective layer, a light diffusion layer, a light collecting plate, and a brightness enhancement film laminated on the polarizing plate on the side opposite to the liquid crystal cell. Examples of the polarizing plate disposed on the front side of the liquid crystal cell and/or the polarizing plate disposed on the back side of the liquid crystal cell include a retardation plate (retardation film) laminated on the liquid crystal cell side of the polarizing plate.

The reflective layer, the semi-transmissive reflective layer, and the light diffusion layer are provided for forming a laminated optical member as a reflective polarizing plate, a semi-transmissive reflective polarizing plate, and a diffusion polarizing plate, respectively. In a liquid crystal display device of a type in which a reflective polarizing plate is used to reflect incident light from a visible side for display, a light source such as a backlight can be omitted, and thus the liquid crystal display device can be easily thinned. Further, the transflective polarizing plate is used in a liquid crystal display device of a type which displays light from a backlight in a bright place while reflecting light in a dark place. The reflective polarizing plate can be produced by forming a reflective layer by attaching a foil made of a metal such as aluminum or a vapor-deposited film to a thermoplastic resin film on a polarizing plate, for example. The semi-transmissive polarizing plate can be produced by forming the above reflective layer into a semi-transparent mirror, or by bonding a reflective plate containing a pearl pigment or the like to the polarizing plate to exhibit light transmittance. On the other hand, the diffusion type polarizing plate can be produced by forming a fine uneven structure on the surface by various methods such as a method of applying a matte treatment to a thermoplastic resin film on the polarizing plate, a method of applying a resin containing fine particles, and a method of bonding a film containing fine particles.

The laminated optical member may be a polarizing plate for both reflection and diffusion. The polarizing plate for both reflection and diffusion can be produced by, for example, providing a reflection layer reflecting the uneven structure on the fine uneven structure surface of the diffusion-type polarizing plate. The reflective layer having a fine uneven structure diffuses incident light by diffuse reflection, and has advantages of preventing directivity or glare, suppressing unevenness of light and shade, and the like. Further, the resin layer or film containing fine particles has an advantage that unevenness in brightness can be suppressed because incident light and reflected light thereof are diffused. The reflective layer reflecting the surface fine uneven structure can be formed by directly applying a metal to the surface of the fine uneven structure by a method such as vapor deposition or plating such as vacuum vapor deposition, ion plating or sputtering. The fine particles to be blended for forming the fine uneven surface structure may be, for example, inorganic fine particles such as silica, alumina, titania, zirconia, oxide, indium oxide, cadmium oxide, and antimony oxide having an average particle diameter of 0.1 to 30 μm, or organic fine particles such as crosslinked or non-crosslinked polymers.

The condensing plate is a member used for the purpose of optical path control or the like, and may be formed as a prism array plate, a lens array plate, a plate with dots, or the like.

The brightness enhancement film is a member used for the purpose of enhancing the brightness of a liquid crystal display device, and specific examples thereof include a reflection-type polarization separation sheet designed to generate anisotropy in reflectance by laminating a plurality of film layers having different refractive index anisotropy from each other, and a circularly polarized light separation sheet in which an alignment film of a cholesteric liquid crystal polymer or an alignment liquid crystal layer thereof is supported on a film base material.

A retardation plate (retardation film) is used for the purpose of compensating for a retardation caused by a liquid crystal cell. Specific examples thereof include birefringent films formed from stretched films of various plastics and the like, films in which discotic liquid crystals or nematic liquid crystals are fixed in an aligned state, and films in which the above-described liquid crystal layer is formed on a film substrate. When a liquid crystal layer is formed on a film substrate, an acetyl 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, (meth) acrylic resins, chain polyolefin resins such as polypropylene, polyvinyl alcohol, polystyrene, polyarylate, and polyamide. The stretched film may be a film treated in an appropriate manner such as monoaxially or biaxially. For the purpose of controlling optical characteristics such as a wide bandwidth, two or more phase difference plates may be used in combination.

Since optical compensation can be effectively performed when the optical member is applied to a liquid crystal display device, a laminated optical member including a retardation plate (retardation film) as an optical layer other than a polarizing plate is preferably used as the laminated optical member. The retardation value (in-plane and thickness direction) of the retardation plate can be adjusted according to the liquid crystal cell to be applied.

The laminated optical member may be a laminate of two or more layers, which is obtained by combining a polarizing plate with one or more layers selected from the above-mentioned various optical layers depending on the purpose of use. In this case, the various optical layers forming the laminated optical member are integrated with the polarizing plate using an adhesive or a pressure-sensitive adhesive (also referred to as a pressure-sensitive adhesive), and the adhesive or the pressure-sensitive adhesive used for this purpose is not particularly limited as long as the adhesive layer or the pressure-sensitive adhesive layer can be satisfactorily formed. From the viewpoints of simplicity of the bonding operation, prevention of occurrence of optical distortion, and the like, an adhesive is preferably used. As the binder, a binder using a (meth) acrylic polymer, a silicone polymer, polyester, polyurethane, polyether, or the like as a base polymer can be used. Among them, it is preferable to select and use an adhesive which is excellent in optical transparency, retains appropriate wettability and cohesive force, is excellent in adhesion to a substrate, has weather resistance, heat resistance and the like, and does not cause problems such as lifting and peeling under heating and humidifying conditions, such as a (meth) acrylic adhesive. Among (meth) acrylic adhesives, useful as a base polymer is a (meth) acrylic copolymer obtained by blending an alkyl ester of (meth) acrylic acid having an alkyl group having 20 or less carbon atoms such as a methyl group, an ethyl group, or a butyl group with a functional group-containing (meth) acrylic monomer such as (meth) acrylic acid or hydroxyethyl (meth) acrylate so that the glass transition temperature is preferably 25 ℃ or less, more preferably 0 ℃ or less, and the weight average molecular weight is 10 ten thousand or more.

The adhesive layer can be formed on the polarizing plate by, for example, dissolving or dispersing the adhesive composition in an organic solvent such as toluene or ethyl acetate to prepare a 10 to 40 wt% solution, and directly applying the solution to the polarizing plate; an adhesive layer is formed on a spacer film (release film) in advance, and the adhesive layer is transfer-bonded to a polarizing plate. The thickness of the adhesive layer is determined by the adhesive strength, etc., but is preferably in the range of about 1 to 50 μm.

The pressure-sensitive adhesive layer may contain, as necessary, fillers made of glass fibers, glass beads, resin beads, metal powder, or other inorganic powder, pigments, colorants, antioxidants, ultraviolet absorbers, and the like. Examples of the ultraviolet absorber include salicylate-based compounds, benzophenone-based compounds, benzotriazole-based compounds, cyanoacrylate-based compounds, and nickel complex-based compounds.

The liquid crystal display device includes a liquid crystal cell and the polarizing plate or the laminated optical member disposed on at least one surface thereof. The polarizing plate or the laminated optical member may be laminated on one side or both sides of the liquid crystal cell with an adhesive layer interposed therebetween. The polarizing plate and the laminated optical member may be a polarizing plate with an adhesive layer and a laminated optical member with an adhesive layer laminated on the outer surfaces of the polarizing plate and the laminated optical member, respectively, for bonding to the liquid crystal cell. The liquid crystal cell used is arbitrary, and various liquid crystal cells such as an active matrix drive type liquid crystal cell typified by a thin film transistor type and a simple matrix drive type liquid crystal cell typified by a super twisted nematic type can be used to form a liquid crystal display device.

Examples

The present invention will be further specifically explained below with reference to examples and comparative examples, but the present invention is not limited to these examples. Hereinafter, the parts and% indicating the amount of use or content are based on weight unless otherwise specified. The photocationic-curable component (a), the photocationic polymerization initiator (B), the branched alcohol compound (C) or the linear alcohol compound (C'), and the photosensitizer/photosensitizing auxiliary agent (D) used in the following examples are shown below and denoted by the respective symbols. In the table, these components are abbreviated as (a), (B), (C'), and (D), respectively.

[ Photocationically curable component (A) ]

(a1)3, 4-epoxycyclohexylmethyl 3, 4-epoxycyclohexanecarboxylate [ R in the above formula (I) ]¹＝R²＝H、X＝－C(＝O)－O－CH₂-the compound of (a),

(a21) Neopentyl glycol diglycidyl ether [ in the above formula (II): Z ═ CH₂C(CH₃)₂CH₂-the compound of (a),

(a22)1, 4-butanediol diglycidyl ether [ in the above formula (II), Z ═ CH₂)₄-a compound of (a).

[ Photocationic polymerization initiator (B) ]

(b1) A 50% solution of propylene carbonate in a mixture of a compound represented by the following formula (V) and a compound represented by the following formula (VI).

[ branched alcohol Compound (C) ]

(c1) Dipropylene glycol (a compound represented by the above formula (a)),

(c2) Tripropylene glycol (a compound represented by the formula (b)),

(c3) Neopentyl glycol,

(c4) 3-methyl-1, 5-pentanediol.

[ straight-chain alcohol Compound (C') ]

(c5) Triethylene glycol.

[ photosensitizer/photosensitizer aid (D) ]

(d1)1, 4-diethoxynaphthalene,

(d2)9, 10-dibutoxynaphthalene.

< examples 1 to 18, comparative examples 1 to 4 >

(1) Preparation of Photocurable adhesive

The components shown in table 1 were mixed in the mixing ratios shown in table 1, and then deaerated to prepare a photocurable adhesive (liquid). The unit of the blending amount of each component in table 1 is "part". The photo cation polymerization initiator (B) was a 50% propylene carbonate solution, and the amount of the photo cation polymerization initiator (B) added based on the amount of solid components is shown in table 1.

[ Table 1]

(2) Measurement of viscosity at 25 ℃ of Photocurable adhesive

The viscosity (mPa · s) at 25 ℃ was measured for each photocurable adhesive (adhesive liquid) prepared in (1) above using an E-type viscometer "TVE-25L" manufactured by eastern industries, ltd. The results are shown in table 2.

(3) Measurement of moisture at 25 ℃ in Photocurable adhesive

For each of the photocurable adhesives (adhesive liquids) prepared in (1), the moisture content (parts by weight per 100 parts by weight of the photocationic curable component (a)) at a temperature of 25 ℃ was measured using a moisture meter "AQV-2100 ST" manufactured by heimian industries, ltd. The results are shown in table 2.

(4) Measurement of ability (dissolving power) of photo-curable adhesive dissolving thermoplastic resin film

A retardation film (trade name "N-TAC KC4 FR-1", manufactured by Konica Minolta Opto Co., Ltd.) having a thickness of 40 μm and made of triacetyl cellulose (TAC) was prepared. The retardation film is used for producing a polarizing plate by laminating a thermoplastic resin film having an optical compensation function on a polyvinyl alcohol polarizing plate. The retardation film was cut into a size of 10mm × 40mm, and then immersed in 20g of each of the above-prepared photocurable adhesives (adhesive solutions) at a temperature of 23 ℃ for 2 days. After 2 days, the retardation film was taken out, and the adhesive liquid adhering to the retardation film was wiped off with a wiping sheet (ベンコットン) to measure the weight. The weight loss of the film was determined from the weight of the film before immersion in the adhesive solution and the weight of the film after immersion by the following formula:

weight reduction (%) { (weight of film before immersion-weight of film after immersion)/weight of film before immersion } × 100

This was taken as the dissolving power. The results are shown in table 2. The greater the weight loss, the higher the solvency.

(5) Measurement of tensile modulus of elasticity at 80 ℃ of adhesive layer

Each of the photocurable adhesives (adhesive liquids) prepared in (1) above was applied to an untreated polyethylene terephthalate film (trade name "Softshine", manufactured by Toyobo Co., Ltd.) with a bar coater #20, and an ultraviolet irradiation apparatus (metal halide lamp) with a conveyor belt was used so that the cumulative light amount was made to be equal to3000mJ/cm²The ultraviolet ray is irradiated in the form of (UVA). After 24 hours, the cured adhesive (cured adhesive layer) was peeled from the polyethylene terephthalate film, and the tensile elastic modulus (MPa) at 80 ℃ was measured using a viscoelasticity measuring apparatus (DMA7100) manufactured by Hitech Science. The results are shown in table 2.

(6) Fabrication of polarizing plates

A surface of a 50 μm thick phase difference film (trade name "ZEONOR", manufactured by japan ZEON corporation) formed of a norbornene-based resin (cyclic polyolefin-based resin) (abbreviated as "COP" in table 2), an unstretched thermoplastic resin film (abbreviated as "TAC" in table 2) formed of 80 μm thick triacetyl cellulose (TAC) containing an ultraviolet absorber, or a 40 μm thick phase difference film (trade name "N-TAC KC4 FR-1", manufactured by Konica Minolta opta corporation) formed of triacetyl cellulose (TAC) (abbreviated as "to TAC" in table 2) was subjected to corona treatment, and the photocurable adhesive (adhesive liquid) prepared in the above (1) was applied to these corona-treated surfaces using an adhesive application apparatus. A polyvinyl alcohol-iodine polarizing plate having a thickness of 25 μm was laminated on the coating layer of the adhesive, and the laminate was bonded using a nip roll (pressing pressure: 1.5 MPa). Then, the total cumulative light quantity (cumulative quantity of light irradiation intensity in the wavelength region of 320 to 400 nm) by irradiation is about 350mJ/cm²The adhesive layer was cured with Ultraviolet (UVA) (measurement value obtained by UV Power PuckII, manufactured by Fusion UV Co., Ltd.) to obtain a polarizing plate having a thermoplastic resin film bonded to one surface of a polarizer. The thickness of the adhesive layer was set to 2.8 μm in terms of the thickness after curing.

(7) 180 degree peel test of polarizing plate

The polarizing plate produced in (6) above was cut into a size of 200mm in length × 25mm in width, and then an acrylic pressure-sensitive adhesive layer was provided on the thermoplastic resin film side to prepare a test piece for measuring the peel strength between the thermoplastic resin film and the polarizing plate. The test piece was bonded to a glass plate using the adhesive layer thereof, a blade of a dicing blade was inserted between the polarizing plate and the thermoplastic resin film, and the test piece was peeled off 30mm from the end portion in the longitudinal direction, and the peeled portion was held by a holding portion of a testing machine. The test piece in this state was subjected to a temperature of 23 ℃ and a relative humidity of 55% in an atmosphere in accordance with JIS K6854-2: 1999 adhesive-peel adhesion Strength test method-part 2: 180 degree peel test was performed at a holding moving speed of 300 mm/min, and an average peel force of 170mm length excluding 30mm of the holding portion was obtained as the peel strength between the thermoplastic resin film and the polarizing plate. The peel strength was measured for each of the three types of thermoplastic resin films. The measurement was performed 24 hours after the polarizing plate was produced. The results are shown in table 2.

[ Table 2]

The polarizing plate produced in (6) above was cut into a size of 2000mm in length by 1000mm in width, and the presence or absence of 50 μm or more of bubbles in the adhesive layer after curing was confirmed by observing the surface at a magnification of 100 times using a microscope (measuring instrument: digital microscope "VHX-500" manufactured by Keyence corporation). In each of examples and comparative examples, the series of experiments (1) to (7) was performed twice. Table 2 shows the results of two measurements for comparative example 4. In the examples and other comparative examples, the results of the two measurements were the same.

Claims

1. A photocurable adhesive, which is a photocurable adhesive for bonding a thermoplastic resin film to a polyvinyl alcohol-based polarizer,

With respect to 100 parts by weight of the photocationic curable component (A), 1 to 10 parts by weight of the photocationic polymerization initiator (B) and 0.1 to 15 parts by weight of the branched alcohol compound (C) are contained,

The photocationic curable component (A) contains the alicyclic diepoxide compound (A1) represented by the following formula (I) in an amount of 65% by weight to 85% by weight, and 1% by weight to 35% by weight of the diglycidyl compound (A2) represented by the following formula (II):

In the formula, R ¹ and R ² each independently represent 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 optionally have an alicyclic structure;

X represents an oxygen atom, an alkanediyl group having 1 to 6 carbon atoms, or a divalent group represented by any one of the following formulae (Ia) to (Id):

Here, Y ¹ to Y ⁴ each represent an alkanediyl group having 1 to 20 carbon atoms, and may have an alicyclic structure when the number of carbon atoms is 3 or more;

a and b each represent an integer from 0 to 20;

In the formula, Z represents a branched alkylene group having 3 to 8 carbon atoms, or a divalent group represented by the formula -C _m H _2m -Z ¹ -C _n H _2n -, where -Z ¹ - represents -O-, -CO-O- or -O-CO-, one of m and n represents an integer of 1 or more, the other represents an integer of 2 or more, the total of both is 8 or less, and C _m H _2m and C One of _n H _2n represents a branched divalent saturated hydrocarbon group.

2 . The photocurable adhesive according to claim 1 , wherein the branched alcohol compound (C) has a molecular weight of 400 or less. 3 .

3 . The photocurable adhesive according to claim 1 , wherein the branched alcohol compound (C) is a branched alkylene glycol compound. 4 .

4. The photocurable adhesive according to claim 1 or 2, which further contains 0.1 to 5 parts by weight of a compound selected from the following groups based on 100 parts by weight of the photocationic curable component (A). An anthracene-based compound represented by the formula (IVa), and one or more compounds among the naphthalene-based compounds represented by the following formula (IVb):

In the formula, R ³ and R ⁴ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or an alkoxyalkyl group having 2 to 12 carbon atoms, and R ⁵ represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. the alkyl group;

In the formula, R ⁶ and R ⁷ each independently represent a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.

5 . The photocurable adhesive according to claim 1 , wherein the water content is more than 0 parts by weight and 4 parts by weight or less with respect to 100 parts by weight of the photocationically curable component (A). 6 .

6 . The photocurable adhesive according to claim 1 , wherein the viscosity at 25° C. is 100 mPa·s or less. 7 .

7. A polarizing plate comprising:

Polyvinyl alcohol-based polarizers, and

The thermoplastic resin film laminated|stacked via the hardened|cured material of the photocurable adhesive agent in any one of Claims 1-6 on at least one surface of the said polyvinyl alcohol-type polarizing plate.

8 . A laminated optical member comprising a laminated body of the polarizing plate according to claim 7 and one or more other optical layers. 9 .

9. The laminated optical member according to claim 8, wherein the other optical layer includes a retardation plate.