JP2013205720A - Polarizing plate and laminated optical member using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizing plate in which a photocurable adhesive is used to bond a polarizer composed of a polyvinyl alcohol-based resin film to a protective film and the polarizer and the protective film are strongly bonded to each other.SOLUTION: There is provided a polarizing plate which is obtained by bonding a transparent protective film via an adhesive layer to a polyvinyl alcohol based polarizer in which a dichroic dye is adsorbed and aligned, wherein the adhesive layer is a cationic polymerization curing layer of a photocurable adhesive containing (B) 1 to 10 pts.wt. of a photo-cation polymerization initiator and (C) 0.1 to 20 pts.wt. of a partially saponified polyvinyl alcohol-based resin in which the degree of saponification is 20 to 50 mol% and the viscosity of a 5 wt.% solution in a mixed solution with an equal weight ratio of water/methanol is 5 mPa.sec or less, based on 100 pts.wt. of a photo-cation curable component containing (A) (A1) 50 to 90 wt.% of a diepoxy compound having an alicyclic ring and two epoxy groups in the molecule and (A2) 10 to 50 wt% of a reactive aliphatic compound selected from an aliphatic epoxy compound and an oxetane compound.

Description

  The present invention relates to a polarizing plate in which 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 on which a dichroic dye is adsorbed and oriented via an adhesive layer. It is about. The present invention also relates to a laminated optical member in which another optical layer such as a retardation film is laminated 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 to provide a protective film only on one side of the polarizer, but in many cases, the other side is not just a protective film, but a layer having another optical function also serves as the protective film. Pasted together.

  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. The polarizer thus obtained has problems such as weak physical strength and easy tearing in the processing direction. Therefore, as described above, a protective film is bonded to at least one side, usually both sides, via an adhesive layer. Is done. As an adhesive for this purpose, a water-based adhesive made of an aqueous solution of a polyvinyl alcohol resin has been traditionally used. Traditionally, a triacetyl cellulose film having a thickness of 30 to 100 μm has been used as a protective film.

  Triacetyl cellulose is excellent in transparency, easy to form 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. Since it has an excellent advantage as a protective film that it can be smoothly performed, it is still widely used today. On the other hand, due to the large moisture permeability, a polarizing plate bonded with a triacetyl cellulose film as a protective film tends to cause deterioration under wet heat, for example, at a temperature of 70 ° C. and a relative humidity of 90%. There was a problem. Therefore, it is also known that the protective film is an amorphous polyolefin resin having a moisture permeability smaller than that of triacetyl cellulose, for example, a norbornene resin as a representative example, for applications in which such a problem is likely to manifest.

  When a protective film made of a resin with low moisture permeability is bonded 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 a low moisture permeability is generally hydrophobic, and water as a solvent cannot be sufficiently dried due to a 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 the polarizer, and a cellulose resin such as triacetyl cellulose is bonded to the other surface of the polarizer. There is also a proposal to bond 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 resin having a high moisture permeability 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, JP-A-2004-245925 (Patent Document 1) discloses an adhesive mainly composed of an epoxy compound not containing 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. JP-A-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.

  On the other hand, it is also known to use a polyvinyl alcohol resin having a low saponification degree as an aqueous adhesive. For example, JP 2010-134448 A (Patent Document 3) discloses that a polyvinyl alcohol polarizing film is bonded via an adhesive layer mainly composed of a polyvinyl alcohol resin having a saponification degree of 30 to 70 mol%. It is disclosed that a hydrophobic protective film having a water contact angle of 20 to 90 degrees on the surface is laminated. According to this technology, it is described that even a highly hydrophobic protective film such as a cellulose acetate-based resin or a cyclic olefin-based resin has excellent adhesion between the polarizer and the protective film.

JP 2004-245925 A JP 2008-257199 A JP 2010-134448 A

  As disclosed in Patent Document 3, a water-based adhesive mainly composed of polyvinyl alcohol resin is mainly composed of polyvinyl alcohol resin, which is the same material as the polarizer. Thus, the polarizer and the protective film can be firmly bonded. On the other hand, since the photocurable adhesive disclosed in Patent Documents 1 and 2 can be cured by irradiation with active energy rays as described above, it is not necessary to dry the water unlike an aqueous adhesive. For this reason, adhesion time can be shortened and the manufacturing process of a polarizing plate can be shortened. However, in the conventional photo-curing adhesive, the adhesive force between the polarizer and the protective film is not always sufficient. Therefore, when the end face of the polarizing plate is polished, the polarizer and the protective film are easily peeled off. There was a problem.

  Therefore, the object of the present invention is to use a photo-curable adhesive for bonding between a polarizer made of a polyvinyl alcohol resin and a protective film, and to cure in a short time, and the two are firmly bonded. It is to provide a polarizing plate. 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.

  As a result of intensive studies to solve such problems, the present inventors have completed the present invention. Specifically, a polarizing plate in which a protective film made of a transparent resin is bonded to at least one surface of a polarizer made of a polyvinyl alcohol resin film on which a dichroic dye is adsorbed and oriented via an adhesive layer In which a photocationic polymerization initiator and a specific polyvinyl alcohol-based resin having a low degree of saponification are provided in combination with a specific two kinds of compounds as a photocationic curable component forming the adhesive layer. It has been found that it is effective to use a quantitatively blended composition (photocurable adhesive). That is, it has been found that such a photocurable adhesive having a specific composition strongly bonds the polarizer and the protective film.

  According to 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 on which a dichroic dye is adsorbed and oriented via an adhesive layer. The adhesive layer consists of (A) (A1) 50 to 90% by weight of a diepoxy compound having an alicyclic ring in the molecule and two epoxy groups, and (A2) a fat having no aromatic ring in the molecule. 1 to 10 parts by weight of (B) photocationic polymerization initiator for 100 parts by weight of the photocationic curable component containing 10 to 50% by weight of a reactive aliphatic compound selected from the group consisting of aromatic epoxy compounds and oxetane compounds And (C) Viscosity measured by a B-type viscometer of a solution having a saponification degree of 20 mol% or more and 50 mol% or less and dissolved at a concentration of 5 wt% in a 50/50 water / methanol mixed solvent. A polarizing plate is provided a light curable adhesive agent containing 0.1 to 20 parts by weight of partially saponified polyvinyl alcohol resin is less than 5 mPa · sec is a layer cured by cationic polymerization.

  In this polarizing plate, the protective film bonded to one surface of the polarizer can be composed of an acetylcellulose-based resin film in which an ultraviolet absorber is blended. In this case, the protective film is formed as described above. What is necessary is just to bond to a polarizer through the photocurable adhesive of this. For example, a protective film made of an acetylcellulose-based resin film containing an ultraviolet absorber is bonded to one surface of a polarizer, and an acetylcellulose-based material not containing an ultraviolet absorber is bonded to the other surface of the polarizer. A form in which a resin film is bonded is also effective. In this case, the acetylcellulose-based resin film not containing an ultraviolet absorber can be a retardation film.

  Moreover, the protective film bonded to one surface of the polarizer may be composed of a resin film having a low moisture permeability, such as an amorphous polyolefin resin, a polyester resin, and a chain polyolefin resin. it can. In this case as well, such a protective film made of a resin film having a low moisture permeability may be bonded to the polarizer via the above-mentioned photocurable adhesive. These resin films with low moisture permeability can be bonded to both sides of the polarizer as desired. When the protective film on the liquid crystal cell side when applied to a liquid crystal display device is composed of such a resin film with low moisture permeability, the resin film with low moisture permeability on the liquid crystal cell side is a retardation film. You can also. A protective film made of an acetylcellulose-based resin film in which the above ultraviolet absorber is blended is bonded to one surface of the polarizer, and the other surface of the polarizer has a low moisture permeability. A form of laminating a film is also effective.

  By using the above-mentioned photo-curable adhesive, the polarizing plate of the present invention is such that the adhesive strength according to the 180 degree peel test between the polarizer and the protective film is 0.5 N / 25 mm or more. it can.

  Moreover, according to this invention, the laminated optical member which consists of a laminated body of one of the said polarizing plates and another optical layer is also provided. The other optical layer constituting the laminated optical member advantageously includes a retardation film.

  The adhesive layer constituting the polarizing plate of the present invention comprises a diepoxy compound (A1) having an alicyclic ring in the molecule and two epoxy groups, an aliphatic epoxy compound and an oxetane having no aromatic ring in the molecule. Polyvinyl alcohol partially saponified with a photocationic polymerization initiator (B) in a photocationic curable component (A) in which a reactive aliphatic compound (A2) selected from the group consisting of compounds is blended at a predetermined ratio. It is formed from a photo-curing adhesive in which a predetermined amount of each of the system resins (C) is blended. A polarizing plate obtained by laminating a polarizer and a protective film via this photo-curable adhesive and curing the adhesive is excellent in adhesive force between the polarizer and the protective film. . If another optical layer is laminated on this polarizing plate, a laminated optical member having a polarizing plate excellent in adhesion between the polarizer and the protective film is obtained.

  Hereinafter, embodiments of the present invention will be described in detail. 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 on which a dichroic dye is adsorbed and oriented with an adhesive layer, To do. This adhesive layer is formed from a photocurable adhesive containing a photocationic curable component (A), a photocationic polymerization initiator (B), and a partially saponified polyvinyl alcohol resin (C). Specifically, this photo-curable adhesive is cured by ultraviolet irradiation to form an adhesive layer. The obtained polarizing plate can be laminated with another optical layer to form a laminated optical member. For the photocurable adhesive, the polarizer, and the protective film used for the production of the polarizing plate, and the laminated optical member produced by laminating another optical layer on the polarizing plate, the explanation will be advanced step by step. I will do it.

[Photocurable adhesive]
The photocurable adhesive is 1 to 10 parts by weight of the cationic photopolymerization initiator (B) with respect to 100 parts by weight of the cationic photocurable component (A), and the saponification degree is 20 mol% or more and 50 mol% or less. A partially saponified polyvinyl alcohol resin having a viscosity of 5 mPa · sec or less measured by a B-type viscometer of a solution dissolved at a concentration of 5% by weight in a mixed solvent of water / methanol at a weight ratio of 50/50 0.1 to 20 parts by weight of (C) is contained. Hereinafter, the component (C) may be simply referred to as “partially saponified polyvinyl alcohol resin (C)”. In addition, the photocationic curable component (A) includes 50 to 90% by weight of a diepoxy compound (A1) having an alicyclic ring and two epoxy groups in the molecule, and an aliphatic group having no aromatic ring in the molecule. 10 to 50% by weight of a reactive aliphatic compound (A2) selected from the group consisting of an epoxy compound and an oxetane compound. Of course, the sum of these (A1) and (A2) does not exceed 100% by weight.

  The adhesive force between a polarizer and a protective film can be improved by making content of diepoxy compound (A1) into 50 weight or more among the whole photocationic curable components (A). On the other hand, when the amount exceeds 90% by weight, the amount of the reactive aliphatic compound (A2) described below becomes relatively small, and the polarizer and protective film of the photocurable adhesive contemplated in the present invention It becomes difficult to improve the adhesion between the two. The diepoxy compound (A1) is more preferably contained in an amount of 60% by weight or more, particularly 70% by weight or more based on the total amount of the photocationic curable component (A).

  Moreover, the adhesive force between a polarizer and a protective film can be heightened by making a reactive aliphatic compound (A2) into 10 weight% or more among the whole photocationic curable components (A). On the other hand, when the amount exceeds 50% by weight, the adhesive force between the polarizer and the protective film becomes insufficient. In order to obtain a more preferable value than the adhesive force between the polarizer and the protective film, the amount of the reactive aliphatic compound (A2) in the photocationic curable component (A) is more preferably 25% by weight or less. .

  By blending 1 part by weight or more of the cationic photopolymerization initiator (B) per 100 parts by weight of the cationic photocurable component (A), the cationic photocurable component (A) can be sufficiently cured and obtained. Gives high mechanical strength and adhesive strength to the polarizing plate. On the other hand, when the amount increases, the ionic compound increases in the adhesive layer, which is a cured product, so that the hygroscopicity of the adhesive layer increases and the durability of the polarizing plate may be lowered. Therefore, the amount of the cationic photopolymerization initiator (B) is 10 parts by weight or less per 100 parts by weight of the cationic photocurable 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).

  Moreover, the adhesive force of a polarizer and a protective film can be improved by mix | blending 0.1 weight part or more of partially saponified polyvinyl alcohol-type resin (C) per 100 weight part of photocationic curable components (A). . On the other hand, when the amount of the partially saponified polyvinyl alcohol resin (C) increases, the amount of the photocationic curable component (A) and the photocationic polymerization initiator (B) decreases relatively. The adhesive strength of the film will be weakened. Therefore, the blending amount of the partially saponified polyvinyl alcohol resin (C) is 20 parts by weight or less per 100 parts by weight of the photocationic curable component (A). The blending amount of the partially saponified polyvinyl alcohol resin (C) is preferably 0.5 parts by weight or more and preferably 10 parts by weight or less per 100 parts by weight of the photocation curable component (A). .

(Photocationic curable component)
The photocationic curable component (A), which is the main component of the photocurable adhesive and gives adhesive strength by polymerization and curing, is (A1) a diepoxy compound having an alicyclic ring in the molecule and two epoxy groups. (A2) A reactive aliphatic compound selected from the group consisting of an aliphatic epoxy compound having no aromatic ring in its molecule and an oxetane compound is contained.

  In the diepoxy compound (A1) having an alicyclic ring in the molecule and two epoxy groups, the epoxy group may be directly bonded to the alicyclic ring, or a site different from the alicyclic ring. May be present.

  A compound having two epoxy groups directly bonded to an alicyclic ring in the molecule is also called an alicyclic diepoxy compound. Here, as shown in the following formula (I), an epoxy group directly bonded to an alicyclic ring is a bridge formed by bridging two carbon atoms (usually adjacent carbon atoms) constituting the alicyclic ring. It means an oxygen atom -O- to be connected, and p in the following formula (I) represents an integer of 2 to 5.

An epoxy group in which one or more hydrogen atoms in (CH ₂ ) _p in the above formula (I) are removed and bonded to another chemical structure, and directly bonded to such an alicyclic ring Can be an alicyclic diepoxy compound. One or more hydrogen atoms in (CH ₂ ) _p forming the alicyclic ring may be appropriately substituted with a linear alkyl group such as a methyl group or an ethyl group. Among them, an alicyclic diepoxy compound having an epoxycyclopentane ring [p = 3 in the above formula (I)] or an epoxycyclohexane ring [p = 4 in the above formula (I)] has excellent adhesion. It is preferably used because it imparts sex. Specific examples of the alicyclic diepoxy compound are listed below. Here, the compound name is given first, and then the chemical formula corresponding to each is shown, and the same symbol is attached to the chemical name and the corresponding chemical formula.

A: 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate,
B: 3,4-epoxy-6-methylcyclohexylmethyl 3,4-epoxy-6-methylcyclohexanecarboxylate,
C: ethylene bis (3,4-epoxycyclohexanecarboxylate),
D: Bis (3,4-epoxycyclohexylmethyl) adipate,
E: bis (3,4-epoxy-6-methylcyclohexylmethyl) adipate,
F: Diethylene glycol bis (3,4-epoxycyclohexyl methyl ether),
G: ethylene glycol bis (3,4-epoxycyclohexyl methyl ether),
H: 2,3,14,15-diepoxy-7,11,18,21-tetraoxatrispiro [5.2.2.5.2.2] henicosane,
I: 3- (3,4-epoxycyclohexyl) -8,9-epoxy-1,5-dioxaspiro [5.5] undecane,
J: bis (2,3-epoxycyclopentyl) ether,
K: Dicyclopentadiene dioxide and the like.

  A compound having an alicyclic ring in the molecule and having two epoxy groups at a site different from the alicyclic ring is typically a diglycidyl ether of an alicyclic diol. For example, it can be a diglycidyl ether of cycloalkanediol, typically cyclohexanediol, but can also be a compound in which an aromatic ring of an aromatic diepoxy compound is hydrogenated. The latter uses a dihydric alcohol obtained by selectively subjecting an aromatic dihydroxy compound, which is a raw material of an aromatic diepoxy compound, to a hydrogenation reaction in the presence of a catalyst and under pressure. In the presence of an acidic catalyst such as boron or tin tetrachloride, epichlorohydrin is reacted to produce chlorohydrin ether, and the resulting chlorohydrin ether is produced by a two-stage method in which intramolecular ring closure is performed with alkali. be able to. Examples of the aromatic diepoxy compound include bisphenol type epoxy compounds such as diglycidyl ether of bisphenol A, diglycidyl ether of bisphenol F, and diglycidyl ether of bisphenol S. The nuclear hydrogenated product of these aromatic diepoxy compounds is a diepoxy compound (A1) having an alicyclic ring in the molecule and two epoxy groups. Among them, hydrogenated bisphenol A glycidyl ether Is preferred.

  Next, the reactive aliphatic compound (A2) will be described. The reactive aliphatic compound (A2) is an aliphatic epoxy compound or oxetane compound having no aromatic ring in the molecule. Among these, an aliphatic epoxy compound having no aromatic ring in the molecule is a compound having at least one oxirane ring (3-membered cyclic ether) bonded to an aliphatic carbon atom in the molecule. For example, monofunctional epoxy compounds such as butyl glycidyl ether and 2-ethylhexyl diether, and tri- or higher functional epoxy compounds such as trimethylolpropane triglycidyl ether and pentaerythritol tetraglycidyl ether also fall under this category. Is preferably an aliphatic diepoxy compound having two oxirane rings bonded to an aliphatic carbon atom in the molecule. Such a suitable aliphatic diepoxy compound can be represented by the following formula (II), for example.

  Y in the formula is an alkylene group having 2 to 9 carbon atoms, an alkylene group having 4 to 9 carbon atoms having an ether bond therebetween, or a divalent hydrocarbon group having 6 to 18 carbon atoms having an alicyclic structure. is there.

  Specifically, the aliphatic epoxy compound having no aromatic ring in the molecule represented by the formula (II) specifically includes diglycidyl ether of alkanediol, diglycidyl ether of oligoalkylene glycol having up to about 4 repetitions, or fat Diglycidyl ether of cyclic diol.

  Specific examples of the diol (glycol) that can be an aliphatic diepoxy compound represented by the formula (II) are listed below. Examples of alkanediol include ethylene glycol, propylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, and 1,4-butanediol. Neopentyl glycol, 3-methyl-2,4-pentanediol, 2,4-pentanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 2-methyl-2,4-pentane Diol, 2,4-diethyl-1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 3,5-heptanediol, 1,8-octanediol, 2-methyl-1,8 -Octanediol, 1,9-nonanediol and the like. Examples of the oligoalkylene glycol include diethylene glycol, triethylene glycol, tetraethylene glycol, and dipropylene glycol.

Among these aliphatic diepoxy compounds, diglycidyl ethers of alkanediols are preferable. Among them, 1,4-butanediol diglycidyl ether is particularly preferable because it is easily available. This compound is a compound of the formula (II) in which —Y— is — (CH ₂ ) ₄ —, that is, 1,4-butanediyl.

Among the reactive aliphatic compounds (A2), the oxetane compound is a compound having an oxetane ring that is a 4-membered ring ether in the molecule, and a compound having an oxetane ring and a hydroxyl group is particularly preferable. Preferable oxetane compounds include oxetane alcohol compounds represented by the following formula (III), where R ¹ represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms.

  Specific examples of the oxetane alcohol compound represented by the above formula (III) include 3-hydroxymethyl oxetane, 3-hydroxymethyl-3-methyl oxetane, 3-hydroxymethyl-3-ethyl oxetane, 3-hydroxymethyl- Examples include 3-propyloxetane, 3-hydroxymethyl-3-butyloxetane, 3-hydroxymethyl-3-pentyloxetane, and 3-hydroxymethyl-3-hexyloxetane.

Among these oxetane alcohol compounds, 3-hydroxymethyl-3-ethyloxetane [a compound in which R ¹ = —C ₂ H ₅ in formula (III)] is preferable because it is easily available.

  The reactive aliphatic compound (A2) may be either one or both of an aliphatic epoxy compound and an oxetane compound that do not have an aromatic ring in the molecule. When these two components are used in combination, the adhesive strength tends to be higher than when only one of them is used, which is preferable. The blending ratio of the aliphatic epoxy compound having no aromatic ring in the molecule and the oxetane compound is not particularly limited, but is usually an aliphatic epoxy compound having no aromatic ring in the molecule by weight ratio: oxetane compound = 10: 1 to 1 Within the range of 1: 5.

  In addition to the above-mentioned diepoxy compound (A1) and reactive aliphatic compound (A2), other photocationic curings are possible as long as their quantitative ratio is in the range described above and does not inhibit the functions of these two components. Sexual components may be blended. Examples of other photocationic curable components include monofunctional epoxy compounds that do not correspond to the above diepoxy compound (A1) and reactive aliphatic compound (A2), and monofunctional vinyl ether compounds. Epoxy compounds not corresponding to (A1) and (A2) include compounds having only one epoxy group directly bonded to the alicyclic ring in the molecule, aromatic epoxy compounds, and the like.

  Specific examples of the monofunctional epoxy compound include methyl glycidyl ether, ethyl glycidyl ether, n-butyl glycidyl ether, allyl glycidyl ether, 2-ethylhexyl glycidyl ether, 1,2-epoxyhexane, 1,2-epoxyoctane, 1 , 2-epoxydecane, 1,2-epoxydodecane, 1,2-epoxytetradecane, 1,2-epoxyhexadecane, 1,2-epoxyoctadecane, styrene oxide, phenylglycidyl ether, cresylglycidyl ether, p-sec- Examples include butylphenyl glycidyl ether, nonylphenyl glycidyl ether, glycidyl acrylate, glycidyl methacrylate, 1-vinyl-3,4-epoxycyclohexane, and α-pinene oxide. You may use these in combination of 2 or more type as needed.

  Specific examples of monofunctional vinyl ethers include ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, 2-ethylhexyl vinyl ether, octadecyl vinyl ether, dodecyl vinyl ether, cyclohexyl vinyl ether, cyclohexane methanol monovinyl ether, dicyclohexane. Examples include pentadiene vinyl ether, allyl vinyl ether, norbornenyl vinyl ether, hydroxyethyl vinyl ether, hydroxybutyl vinyl ether, diethylene glycol monovinyl ether, tricyclodecane vinyl ether, benzyl vinyl ether, and ethyloxetane methyl vinyl ether. These may be used in combination of two or more as required.

(Photocationic polymerization initiator)
In the present invention, the photocationic curable component (A) described above is cured by cationic polymerization by irradiation of active energy rays to form an adhesive layer. (B) is blended. The cationic photopolymerization initiator generates a cationic species or a Lewis acid by irradiation with an active energy ray such as visible light, ultraviolet ray, X-ray, or electron beam, and initiates a polymerization reaction of the photocationic curable component (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 onium salts such as aromatic iodonium salts and aromatic sulfonium salts, aromatic diazonium salts, and iron-arene complexes.

  An aromatic iodonium salt is a compound having a diaryl iodonium cation, and typical examples of the diaryl iodonium cation include a diphenyl iodonium cation. An aromatic sulfonium salt is a compound having a triarylsulfonium cation, and typical examples of the triarylsulfonium cation include triphenylsulfonium cation and 4,4′-bis (diphenylsulfonio) diphenylsulfide cation. Can do. The aromatic diazonium salt is a compound having a diazonium cation, and typical examples of the diazonium cation include a benzenediazonium cation. The iron-arene complex is typically a cyclopentadienyl iron (II) arene cation complex salt.

The cation shown above forms a photocationic polymerization initiator in combination with an anion (anion). Examples of anions constituting the photocationic polymerization initiator include hexafluorophosphate anion PF ₆ ⁻ , hexafluoroantimonate anion SbF ₆ ⁻ , pentafluorohydroxyantimonate anion SbF ₅ (OH) ⁻ , hexafluoroarsenate anion. AsF ₆ ⁻ , tetrafluoroborate anion BF ₄ ⁻ , tetrakis (pentafluorophenyl) borate anion B (C ₆ F ₅ ) ₄ ^{— and the} like are available.

  Among these photocationic polymerization initiators, especially aromatic sulfonium salts have ultraviolet absorption characteristics even in the wavelength region near 300 nm, and therefore provide a cured product having excellent curability and good mechanical strength and adhesive strength. Therefore, it is preferably used.

  Various photocationic polymerization initiators are commercially available. Examples of commercially available products include the “CPI” series sold by Sun Apro Co., Ltd., the “CYRACURE UVI” series sold by Union Carbide, Inc., and the “Adekaoptomer” sold by ADEKA Corporation. "SP" series, "IRGACURE" series sold by BASF Germany (but classified as a cationic photopolymerization initiator), "Sun Aid SI" series sold by Sanshin Chemical Industry Co., Ltd., There is “UVACURE 1590” sold by Daicel-Cytec.

(Polyvinyl alcohol resin)
A polyvinyl alcohol-type resin (C) is mix | blended in order to improve adhesiveness with the member which consists of polyvinyl alcohol-type resins, such as a polarizer. In the present invention, a polyvinyl alcohol resin obtained by partially saponifying a polyvinyl ester resin obtained by polymerizing a vinyl ester monomer represented by vinyl acetate is used. Such a partially saponified polyvinyl alcohol resin has a vinyl alcohol structural unit and a vinyl ester structural unit.

  As the polyvinyl alcohol resin, a so-called low saponification resin having a saponification degree in the range of 20 mol% or more and 50 mol% or less is adopted. When the degree of saponification is less than 20 mol%, the adhesiveness with a polarizer made of a polyvinyl alcohol resin tends to deteriorate. On the other hand, when the degree of saponification exceeds 50 mol%, the compatibility with the photocationic curable component (A) is lowered and it becomes difficult to dissolve. The saponification degree of the polyvinyl alcohol resin is preferably in the range of 32 to 42 mol%. The degree of saponification of the polyvinyl alcohol resin can be measured according to JIS K 6726: 1994 “Testing method for polyvinyl alcohol”.

  The average degree of polymerization of the polyvinyl alcohol-based resin (C) is preferably 300 to 4,000, more preferably 400 to 3,000, and particularly preferably 500 to 2,000. When the average degree of polymerization is less than 300, the cohesive force of the cured adhesive becomes small, and the adhesive force tends to decrease. When the average degree of polymerization exceeds 4,000, the viscosity becomes too high and the coating property on the adhesive surface tends to deteriorate. The average degree of polymerization can also be measured according to the above JIS K 6726: 1994.

  The polyvinyl alcohol-based resin (C) is particularly preferably a partially saponified product of polyvinyl acetate consisting of a structural unit represented by the following formula (IV), where m and n are both Represents an integer of 1 or more.

  Since various types of polyvinyl alcohol resins are commercially available, those satisfying the conditions defined as partially saponified polyvinyl alcohol resins (C) in the present invention may be selected and used. For example, “LM-10HD”, “LM-15”, “LM-20” and “LM-25” sold by Kuraray Co., Ltd., Nippon Synthetic Chemical Industry Co., Ltd. "Gosefemamer L-5407" and "Gosefiemer L-7514" (all are trade names) sold by

(Other components that can be blended in the photo-curable adhesive)
The photocurable adhesive may contain other components in addition to the photocationic curable component (A), the photocationic polymerization initiator (B), and the polyvinyl alcohol resin (C) described above. Examples of other components that can be incorporated include photosensitizers, photosensitizers, thermal cationic polymerization initiators, chain transfer agents, thermoplastic resins, flow regulators, antifoaming agents, leveling agents, organic solvents. and so on. Depending on the type of protective film to be bonded to the polarizer, it may be preferable to blend a photosensitizer and further a photosensitization aid.

  The photosensitizer is a compound that exhibits maximum absorption at a wavelength longer than the maximum absorption wavelength indicated by the photocationic polymerization initiator (B) and promotes the polymerization initiation reaction by the photocationic polymerization initiator (B). As such a photosensitizer, an anthracene compound is preferably used. As anthracene compounds that can be used as photosensitizers, 9,10-dimethoxyanthracene, 9,10-diethoxyanthracene, 9,10-dipropoxyanthracene, 9,10-diisopropoxyanthracene, 9,10-dibutoxyanthracene 9,10-dipentyloxyanthracene, 9,10-dihexyloxyanthracene and the like.

  The photosensitizing assistant is a compound that further promotes the action of the photosensitizer. As such a photosensitizing assistant, naphthalene compounds are preferably used. 1,4-dimethoxynaphthalene, 1-ethoxy-4-methoxynaphthalene, 1,4-diethoxynaphthalene, 1,4-dipropoxynaphthalene, 1,4-dibutoxy as naphthalene compounds that can serve as photosensitizers And naphthalene.

  When these other components are blended, the amount is blended from, for example, a range of 10 parts by weight or less with respect to 100 parts by weight of the photocationic curable component (A) which is the main component of the photocurable adhesive. What is necessary is just to select suitably according to the objective.

(Preparation of photocurable adhesive)
A photocurable adhesive agent can be prepared by mixing the photocationic curable component (A) and photocationic polymerization initiator (B) which were demonstrated until now, and another component as needed. At the time of mixing, it heats at about 30-50 degreeC as needed, and stirs until it becomes uniform with a stirrer. The stirring time is not particularly limited, but is usually about 5 to 20 minutes.

[Polarizer]
The polarizer is a film having a function of converting natural light into linearly polarized light, and is composed of a polyvinyl alcohol resin film adsorbed and oriented with a dichroic dye. The polyvinyl alcohol resin 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-based resin is usually 85 to 100 mol%, preferably 98 to 100 mol%. The polyvinyl alcohol-based resin may be modified, and for example, polyvinyl formal or polyvinyl acetal modified with aldehydes may be used. The degree of polymerization of the polyvinyl alcohol resin is usually 1,000 to 10,000, preferably 1,500 to 5,000.

  What formed such a polyvinyl alcohol-type resin into a film is used as a raw film of a polarizer. The film formation of the polyvinyl alcohol resin can be performed by a known method. The original film of polyvinyl alcohol resin has a thickness of, for example, about 20 to 100 μm.

  The polarizer described above is a step of uniaxially stretching a polyvinyl alcohol-based resin film, a step of dyeing a polyvinyl alcohol-based resin film with a dichroic dye, and a step of adsorbing the dichroic dye, a polyvinyl on which the dichroic dye is adsorbed It is manufactured through a process of treating an alcohol-based resin film with an aqueous boric acid solution.

  Uniaxial stretching of the polyvinyl alcohol-based resin film 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. Also good. When uniaxial stretching is performed after dyeing with a dichroic dye, the uniaxial stretching may be performed before boric acid treatment or during boric acid treatment. Moreover, uniaxial stretching can also be performed in these several steps. For uniaxial stretching, rolls having different peripheral speeds may be uniaxially stretched or may be stretched uniaxially using a hot roll. Furthermore, it may be dry stretching in which stretching is performed in the air, or may be wet stretching in which stretching is performed in a state where a polyvinyl alcohol-based resin is swollen using a solvent such as water. The draw ratio is usually about 3 to 8 times.

  The polyvinyl alcohol resin film can be dyed with a dichroic dye by, for example, a method of immersing the polyvinyl alcohol resin film 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 dipping 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 part by weight per 100 parts by weight of water. This aqueous solution may contain an inorganic salt such as sodium sulfate as a dyeing assistant. The temperature of this aqueous solution is usually about 20 to 80 ° C. Moreover, 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 about 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 60 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 after washing with water is performed using a hot air dryer or a far infrared heater. A drying temperature is about 40-100 degreeC normally, Preferably it is about 50-80 degreeC. The time for the drying treatment is usually about 120 to 600 seconds.

  Thus, the thickness of the polarizer which consists of a polyvinyl alcohol-type resin film can be about 10-40 micrometers.

[Protective film]
The protective film is provided on the surface of the polarizer for the purpose of compensating for the polarizer composed of the polyvinyl alcohol-based resin film described above, since the physical strength is poor as described above. A protective film is bonded to the polarizer 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. The moisture permeability of triacetyl cellulose is approximately 400g / m ² / 24hr approximately.

  In one preferable form of the present invention, the protective film bonded to at least one surface of the polarizer is composed of an acetylcellulose-based resin film. An acetyl cellulose resin is a resin in which at least a part of hydroxyl groups in cellulose is esterified, and a mixed ester in which part is acetated and partly esterified with another acid. Good. Examples of the acetyl cellulose resin include triacetyl cellulose, diacetyl cellulose, cellulose acetate propionate, and cellulose acetate butyrate.

The acetyl cellulose resin may contain an ultraviolet absorber. One surface of the polarizer, specifically, the surface that is far from the liquid crystal cell of the polarizing plate that is bonded to the liquid crystal cell, that is, the surface that becomes the viewing side or the backlight side, is blended with an ultraviolet absorber. Often, the resin film is bonded as a protective film. As ultraviolet absorbers, salicylic acid ester compounds, benzophenone compounds, benzotriazole compounds, cyanoacrylate compounds, nickel complex compounds, and the like are known.

  A protective film made of an acetyl cellulose resin containing an ultraviolet absorber is bonded to one surface of the polarizer, and an acetyl cellulose resin not containing an ultraviolet absorber is bonded to the other surface of the polarizer. It is also effective to form a retardation film having a phase difference.

In another preferred embodiment of the present invention, the protective film bonded to at least one surface of the polarizer is composed of a resin film having a moisture permeability lower than that of triacetyl cellulose. As such a resin film, for example, moisture permeability can be cited the following resin film 300g / m ² / 24hr. Specifically, amorphous polyolefin resin, polyester resin, acrylic resin, polycarbonate resin, chain polyolefin resin, and the like correspond to this.

  Amorphous polyolefin resin is a polymer having a polymer 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 polyolefin and / or an aromatic vinyl compound. In the case of a homopolymer of a cyclic olefin or a copolymer of two or more types of cyclic olefins, a double bond remains by ring-opening polymerization, and hydrogenated ones are generally used as amorphous polyolefin resins. Used for. Of these, thermoplastic norbornene resins are typical.

  The polyester resin is a polymer obtained by condensation polymerization of a dibasic acid and a dihydric alcohol, and polyethylene terephthalate is representative. Acrylic resin is a polymer with methyl methacrylate as the main monomer. In addition to methyl methacrylate homopolymer, methyl methacrylate and acrylic esters and aromatic vinyl compounds such as methyl acrylate It may be a copolymer. The polycarbonate-based resin is a polymer having a carbonate bond (—O—CO—O—) in the main chain, and is typically obtained by condensation polymerization of bisphenol A and phosgene. The chain polyolefin-based resin is a polymer having a chain polyolefin such as ethylene or propylene as a main monomer, 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.

  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.

  These protective films are subjected to various surface treatments such as hard coat treatment, antireflection treatment, antiglare treatment, antistatic treatment, or antifouling treatment on the surface opposite to the surface to be bonded to the polarizer. Can be applied.

[Production method of polarizing plate]
The polarizer and the protective film are bonded via an adhesive. In bonding the polarizer and the protective film, the photocurable adhesive coating layer described above is formed on one or both of the bonded surfaces of the polarizer and the protective film, and the polarizer and the protective film are interposed through the coating layer. A protective film is pasted. Easy adhesion treatment such as corona discharge treatment, plasma treatment, flame treatment, primer treatment, anchor coating treatment on one or both of the bonded surfaces of the polarizer and protective film before forming the adhesive coating layer May be applied. And an active energy ray is irradiated and hardened to the application layer of an uncured photocurable adhesive agent, and a protective film is fixed on a polarizer.

  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 of the photocurable adhesive 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.

  The active energy ray light source used for curing the coating layer of the photocurable adhesive may be any one that generates ultraviolet rays, electron beams, X-rays, and the like. In particular, a light source having a light emission distribution at a wavelength of 400 nm or less is preferable, and examples thereof include 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, and a metal halide lamp.

The active energy ray irradiation intensity to the photocurable adhesive is determined for each target composition and is not particularly limited, but the light irradiation intensity in the wavelength region effective for the activation of the photocationic polymerization initiator. Is preferably 0.1 to 100 mW / cm ² . If the light irradiation intensity is too small, the reaction time becomes too long. On the other hand, if the light irradiation intensity is too large, the photocurable adhesive is caused by heat radiated from the lamp and heat generated during polymerization of the photocurable adhesive. May cause yellowing and deterioration of the polarizer. The light irradiation time to the photocurable adhesive is also controlled for each composition to be cured and is not particularly limited, but the integrated light amount expressed as the product of the light irradiation intensity and the light irradiation time is 10 to 10. It is preferably set to be 5,000 mJ / cm ² . If the integrated light amount is too small, the generation of active species derived from the initiator may not be sufficient, and the resulting adhesive layer may be insufficiently cured. On the other hand, if the integrated light amount is too large, the light irradiation time Tends to be very long and disadvantageous for productivity improvement.

  When bonding a protective film on both surfaces of a polarizer, irradiation of an active energy ray may be performed from which protective film side. For example, when one protective film contains an ultraviolet absorber and the other protective film does not contain an ultraviolet absorber, it is preferable to irradiate active energy rays from the protective film side that does not contain the ultraviolet absorber. By irradiating in this way, it is possible to effectively use the irradiated active energy rays and increase the curing rate.

  In this invention, the adhesiveness between a polarizer and a protective film can be improved by using the photocurable adhesive mentioned above. Therefore, the adhesive strength by the 180 degree peeling test between the polarizer and the protective film can be set to 0.5 N / 25 mm or more. Here, the 180 degree peeling test is performed according to JIS K 6854-2: 1999 “Adhesive—Peeling adhesive strength test method—Part 2: 180 degree peeling” as shown in the examples described later.

[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 an 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 an optical layer laminated on a polarizing plate, a polarizing plate arranged on the back side of the liquid crystal cell is laminated on the side opposite to the side facing the liquid crystal cell of the polarizing plate. Examples include a light plate, a brightness enhancement film, a reflective layer, a transflective layer, and a light diffusion layer. In addition, for both the polarizing plate disposed on the front side of the liquid crystal cell and the polarizing plate disposed on the back side of the liquid crystal cell, a retardation film laminated on the side of the polarizing plate facing the liquid crystal cell, etc. There is.

  The light collector is used for the purpose of optical path control, and may be a prism array sheet, a lens array sheet, or a dot-attached sheet.

  The brightness enhancement film is used for the purpose of improving brightness in a liquid crystal display device. Specifically, a reflective polarized light separation sheet, an alignment film of a cholesteric liquid crystal polymer, and an alignment film that are designed so that anisotropy occurs in the reflectance by laminating a plurality of thin film films having different refractive index anisotropies Examples thereof include a circularly polarized light separating sheet having a liquid crystal layer supported on a film substrate.

  The reflective layer, the transflective layer, or the light diffusing layer is provided to make the polarizing plate into a reflective optical member, a transflective optical member, or a diffusing optical member, respectively. A reflective optical member including a polarizing plate is used in a liquid crystal display device of a type that reflects incident light from the viewing side and displays a light source such as a backlight. Therefore, the liquid crystal display device can be easily thinned. A transflective optical member including a polarizing plate is used as a reflective liquid crystal display device in a bright place and a liquid crystal display device that displays light from a backlight in a dark place. In addition, a diffusing optical member including a polarizing plate is used in a liquid crystal display device that imparts light diffusibility and suppresses display defects such as moire.

  A method for forming these reflective layer, transflective layer, and light diffusion layer will be described. The reflective layer constituting the reflective optical member can be formed, for example, by attaching a foil or vapor deposition film made of a metal such as aluminum on the protective film on the polarizer. The semi-transmissive reflective layer constituting the semi-transmissive optical member is 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. it can. The light diffusing layer constituting the diffusing optical member is formed by, for example, a method of performing a mat treatment on a protective film on a polarizing plate, a method of applying a resin containing fine particles, a method of bonding a film containing fine particles, It can be formed as a surface layer having a fine relief structure. The resin layer or film containing fine particles has an advantage that incident light and its reflected light are diffused when passing through the fine particle-containing layer, and light and dark unevenness can be suppressed. The fine particles to be blended for forming the surface fine concavo-convex structure are, for example, silica, aluminum oxide, titanium oxide, zirconia, tin oxide, indium oxide, cadmium oxide, antimony oxide having an average particle diameter of 0.1 to 30 μm. It can be inorganic fine particles, organic fine particles such as a crosslinked or non-crosslinked polymer, and the like.

  The laminated optical member may be a reflection / diffusion polarizing plate. The reflection / diffusion polarizing plate can be produced by, for example, a method of providing a reflective layer reflecting the uneven structure on the fine uneven structure surface of the diffusion optical member including the polarizing plate. 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 unevenness in brightness and darkness can be suppressed. The reflective layer reflecting the surface fine concavo-convex structure can be formed by directly attaching a metal to the surface of the fine concavo-convex structure by a method such as vapor deposition or plating such as vacuum deposition, ion plating, or sputtering.

  The retardation film acting as an optical layer is used for the purpose of compensation of retardation by a liquid crystal cell. Examples of retardation plates include birefringent films made of stretched films of various plastics, films in which discotic liquid crystals and nematic liquid crystals are oriented and fixed, and those in which the above liquid crystal layer is formed on a substrate film, etc. Can be mentioned. When the liquid crystal layer is formed on the base film, a cellulose acetate resin film such as triacetyl cellulose is preferably used as the base film.

  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.

  The laminated optical member is preferable because optical compensation can be effectively performed when a retardation film is applied to the liquid crystal display device as an optical layer other than the polarizing plate. The optimum retardation value (in-plane and thickness direction) of the retardation film may be selected according to the applied liquid crystal cell.

  A laminated optical member can be made into a laminated body 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 pressure-sensitive adhesive, but the adhesive or pressure-sensitive adhesive layer used for this purpose is good. As long as it is formed, there is no particular limitation. It is preferable to use a pressure-sensitive adhesive (also referred to as a pressure-sensitive adhesive) from the viewpoint of easy bonding work and prevention of optical distortion. Usually, an adhesive layer is also provided on the surface of the laminated optical member to be bonded to the liquid crystal cell.

  As the pressure-sensitive adhesive for integrating the various optical layers and the polarizing plate, those having a base polymer such as an acrylic polymer, a silicone polymer, polyester, polyurethane, or polyether can be used. Above all, like acrylic adhesives, it has excellent transparency, retains appropriate wettability and cohesion, has excellent adhesion to the substrate, and has weather resistance, heat resistance, etc. It is preferable to select and use a material that does not cause separation problems such as floating and peeling under humidification conditions. In acrylic adhesives, alkyl esters of (meth) acrylic acid having an alkyl group having 20 or less carbon atoms such as methyl, ethyl and butyl groups, and (meth) acrylic acid and hydroxyethyl (meth) acrylate 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 less, more preferably 0 ° C. or less, and a functional group-containing acrylic monomer comprising Useful as a base polymer.

  The pressure-sensitive adhesive layer is formed on the polarizing plate or the laminated optical member by, for example, preparing a 10 to 40% by weight solution by dissolving or dispersing the pressure-sensitive adhesive composition in an organic solvent such as toluene or ethyl acetate. Direct coating on the target surface of the film (polarizing plate or laminated optical member), or by previously forming an adhesive layer on the protective film and applying it to the target film (polarizing plate or laminated optical member) This can be done by transferring to the surface. 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 disposed on one side or both sides of the liquid crystal cell via the above-mentioned pressure-sensitive adhesive layer. The liquid crystal cell to be used is arbitrary. For example, a liquid crystal display device using various liquid crystal cells such as an active matrix drive type typified by a thin film transistor type and a simple matrix drive type typified by a super twisted nematic type. Can be formed.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples. In the examples, “%” and “part” representing the content or amount used are based on weight unless otherwise specified. Moreover, the photocationic curable component, the photocationic polymerization initiator, and the polyvinyl alcohol-based resin used in the following examples are as follows, respectively, and may be indicated by symbols at the beginning of each.

(A) Photocationic curable component (A1) Diepoxy compound having an alicyclic ring in the molecule
(a1) 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate: trade name “Celoxide 2021P” obtained from Daicel Chemical Industries, Ltd.

(A2) Reactive aliphatic compound
(a21) 1,4-butanediol diglycidyl ether: trade name “Denacol EX-121” obtained from Nagase Chemkex Co., Ltd.
(a22) 3-hydroxymethyl-3-ethyloxetane: trade name “Aron Oxetane OXT-101” obtained from Toagosei Co., Ltd.

  The three types of photocationic curable components shown here are compounds each having a structure of the following formula.

(B) Photocationic polymerization initiator (b1) 50% propylene carbonate solution of triarylsulfonium salt-based photocationic polymerization initiator: trade name “CPI-100P” obtained from San Apro Co., Ltd.

(C) Polyvinyl alcohol resin
(c1) Low saponification degree polyvinyl alcohol having a saponification degree of 33 to 38 mol%: trade name “LM-25” obtained from Kuraray Co., Ltd.
(c2) Low saponification degree polyvinyl alcohol having a saponification degree of 34 to 41 mol%: Obtained from Nippon Synthetic Chemical Industry Co., Ltd., trade name “Goseifamer L-5407”.
(c3) Polyvinyl acetate: Trade name “Goselan” obtained from Nippon Synthetic Chemical Industry Co., Ltd.
L-301 "(degree of saponification 0 mol%).
(c4) Low saponification degree polyvinyl alcohol having a saponification degree of 34 to 38 mol%: trade name “Gosefimer L-7514” obtained from Nippon Synthetic Chemical Industry Co., Ltd.
(c5) Highly saponified polyvinyl alcohol having a saponification degree of 98.5 mol%: “Gosefimer Z-100”, a trade name obtained from Nippon Synthetic Chemical Industry Co., Ltd.

[Examples 1 to 9 and Comparative Examples 1 to 5]
(1) Preparation of Photocurable Adhesive Solution The photocationic curable component was blended in the proportions shown in Table 1 (100 parts in total), and the photocationic polymerization initiator (b1) shown above was used as a solid content. 25 parts and polyvinyl alcohol resins (c1) to (c5) were blended in the proportions shown in Table 1, respectively, and then stirred at room temperature for 12 hours to prepare a photocurable adhesive solution.

(2) Viscosity of polyvinyl alcohol-based resin solution In a mixed solvent of 47.5 g of water and 47.5 g of ethanol, 5.0 g of each of the polyvinyl alcohol-based resins (c1) to (c5) shown above is blended to obtain polyvinyl alcohol. A 5% strength solution of the resin was prepared and stirred at room temperature for 12 hours. About each solution, the viscosity in 25 degreeC temperature was measured using the Brookfield B-type viscometer. The results are shown in Table 2.

(3) Solubility of polyvinyl alcohol resin in photocurable adhesive liquid The adhesive liquid prepared in (1) above was visually observed and evaluated according to the following criteria. The results are shown in Table 2. It was.
○: There is no undissolved residue of the polyvinyl alcohol resin.
X: The polyvinyl alcohol resin remains undissolved.

(4) Preparation of polarizing plate Corona discharge treatment was applied to the surface of a 80 μm thick triacetylcellulose film (trade name “Konicatak KC8UX2MW”) containing an ultraviolet absorber obtained from Konica Minolta Opto Co., Ltd. Each adhesive solution prepared in the above (1) was coated on the treated surface using a bar coater so that the film thickness after curing was about 4 μm. A 28 μm-thick polyvinyl alcohol-iodine polarizer was bonded to the adhesive layer. In addition, the surface of a 40 μm thick retardation film [trade name “N-TAC KC4FR-1”] made of acetylcellulose resin obtained from Konica Minolta Opto Co., Ltd. was subjected to corona discharge treatment, and its corona discharge treatment surface Further, the same adhesive solution as above was applied using a bar coater so that the film thickness after curing was about 4 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, UV light is applied so that the accumulated light quantity becomes 250 mJ / cm ² using an ultraviolet irradiation device with a belt conveyor (using a “D bulb” manufactured by Fusion UV Systems). Irradiated 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 in the above (4) was cut into a size of 200 mm × 25 mm, and a polyvinyl alcohol-iodine polarizer and an acetylcellulose retardation film “N-TAC KC4FR-1” The peel strength between them was calculated. First, an acrylic pressure-sensitive adhesive layer was provided on the exposed surface of the acetylcellulose-based retardation film, and the pressure-sensitive adhesive layer was attached to a glass plate. And put the blade of the cutter between the polarizer and the protective film on the adhesive side (acetylcellulose-based retardation film “N-TAC KC4FR-1”), peel off 30 mm from the end in the length direction, and the peeled part Was grabbed by the gripping part of the testing machine. Next, the test piece in this state is 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%. Then, 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. The peel strength at this time is a value between the acetylcellulose-based retardation film “N-TAC KC4FR-1” and the polyvinyl alcohol-iodine polarizer, so that “N-TAC / PVA” is shown in Table 2. displayed.

(6) Cutter test The polarizing plate produced in (4) above was allowed to stand at room temperature for 1 hour, and then a cutter blade was inserted between the polarizer and the acetylcellulose retardation film “N-TAC KC4FR-1”. The method of entering the blade when trying to push the blade forward was evaluated according to the following criteria, and the results are shown in Table 2.
A: The cutter blade enters less than 1 mm between the polarizer and the retardation film.
B: The cutter blade enters 1 to 3 mm between the polarizer and the retardation film.
C: The cutter blade enters more than 3 mm between the polarizer and the retardation film.

  From the composition shown in Table 1 and the results shown in Table 2, Comparative Examples 1 and 2 in which only the photocationic polymerization initiator (B) was blended with the photocationic curable component (A) to form an adhesive were: The adhesive force between the protective film and the protective film was not sufficient. Comparative Example 3 is a composition in which vinyl acetate is mixed with the photocationic curable component (A) together with the photocationic polymerization initiator (B) to form an adhesive, and vinyl acetate is a photocationic curable component (A). Although the solubility with respect to is good, the adhesive strength of the adhesive containing the adhesive to the polarizer and the protective film was not sufficient. In Comparative Example 4, a polyvinyl alcohol having a saponification degree of 34 to 38 mol% was blended with the photocationic curable component (A) together with the photocationic polymerization initiator (B) to form an adhesive. Alcohol had good solubility in the photocationic curable component (A), but the viscosity of a solution dissolved in a mixed solvent having a water / methanol weight ratio of 50/50 at a concentration of 5% was 6.0 mPa · It was big with sec. For this reason, the adhesive force of the adhesive containing this polyvinyl alcohol to the polarizer and the protective film was not sufficient. Since the viscosity of the 5% solution was large, it was presumed that it was probably not the optimum polymer chain for developing adhesiveness. In Comparative Example 5, an adhesive was formed by blending a photocationic curable component (A) with a photocationic polymerization initiator (B) and polyvinyl alcohol having a saponification degree of 98.5 mol%. The alcohol had low solubility in the photocation curable component (A). For this reason, no polarizing plate was prepared in this example.

  On the other hand, the photocationic curable component (A) has a saponification degree in the range of 33 to 41 mol% and a water / methanol weight ratio of 50/50 together with the photocationic polymerization initiator (B). Examples 1 to 9, in which a predetermined amount of polyvinyl alcohol (c1) or (c2) having a viscosity of 5 mPa · sec or less dissolved in a mixed solvent was mixed to form an adhesive, Adhesive strength (peeling strength) with the protective film was high. The polyvinyl alcohols (c1) and (c2) used here also had good solubility in the photocationic curable component (A).

Claims (4)

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 on which a dichroic dye is adsorbed and oriented through an adhesive layer,
The adhesive layer is
(A) (A1) 50 to 90% by weight of a diepoxy compound having an alicyclic ring and two epoxy groups in the molecule;
(A2) 10-50% by weight of a reactive aliphatic compound selected from the group consisting of an aliphatic epoxy compound having no aromatic ring in the molecule and an oxetane compound
To 100 parts by weight of the photocationic curable component containing
(B) 1 to 10 parts by weight of a cationic photopolymerization initiator, and (C) 5% by weight in a mixed solvent having a saponification degree of 20 to 50% by mole and a water / methanol weight ratio of 50/50. A photocurable adhesive containing 0.1 to 20 parts by weight of a partially saponified polyvinyl alcohol resin having a viscosity measured by a B-type viscometer of a solution dissolved at a concentration of 5 mPa · sec or less was cured by cationic polymerization. A polarizing plate characterized by being a layer.   2. The polarizing plate according to claim 1, wherein an adhesive strength by a 180-degree peeling test between the polarizer and the protective film is 0.5 N / 25 mm or more.   A laminated optical member comprising a laminate of the polarizing plate according to claim 1 and another optical layer.   The laminated optical member according to claim 3, wherein the other optical layer includes a retardation film.