JP5855947B2 - Photocurable adhesive, polarizing plate and laminated optical member using the same - Google Patents

Description

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

  The polarizing plate is useful as one of the optical components constituting the liquid crystal display device. A polarizing plate usually has a structure in which protective films are laminated on both sides of a polarizer, and is incorporated in a liquid crystal display device. It is also known that a protective film is provided only on one side of the polarizer, but in many cases, a layer having another optical function also serves as a protective film on the other side, not just as a protective film. Pasted together. Further, as a method for producing a polarizer, a method in which a uniaxially stretched polyvinyl alcohol-based resin film dyed with a dichroic dye is treated with boric acid, washed with water, and dried is widely adopted.

  Usually, a protective film is bonded to the polarizer immediately after washing with water and drying. This is because the dried polarizer has a weak physical strength, and once it is wound, there is a problem that it is easily broken in the processing direction. Therefore, usually, a water-based adhesive that is an aqueous solution of a polyvinyl alcohol resin is immediately applied to the polarizer after drying, and protective films are simultaneously bonded to both sides of the polarizer via this adhesive. Usually, a triacetyl cellulose film having a thickness of 30 to 100 μm is used as the protective film.

  Triacetyl cellulose is excellent in transparency, easily forms various surface treatment layers and optical functional layers, has high moisture permeability, and can be dried after being bonded to a polarizer using an aqueous adhesive as described above. While having an excellent advantage as a protective film such that it can be performed smoothly, the polarizing plate bonded as a protective film due to its high moisture permeability is, for example, at a temperature of 70 ° C. and a relative humidity of 90 under wet heat. %, There was a problem such as easy to cause deterioration. Therefore, it is also known to use an amorphous polyolefin resin having a lower moisture permeability than that of triacetyl cellulose, for example, an amorphous polyolefin resin represented by a norbornene resin as a protective film.

  When bonding a protective film made of a resin with low moisture permeability to a polyvinyl alcohol polarizer, an aqueous solution of a polyvinyl alcohol resin generally used for bonding a polyvinyl alcohol polarizer and a triacetyl cellulose film is conventionally used. When the adhesive is used, there are problems that the adhesive strength is not sufficient or the appearance of the obtained polarizing plate becomes poor. This is because a resin film having low moisture permeability is generally hydrophobic, and water that is a solvent cannot be sufficiently dried due to low moisture permeability. On the other hand, it is also known to bond different types of protective films on both sides of the polarizer. For example, a protective film made of a resin with low moisture permeability such as an amorphous polyolefin resin is bonded to one surface of a polarizer, and a cellulose resin such as triacetyl cellulose is bonded to the other surface of the polarizer. There is also a proposal of bonding a protective film made of a resin with high moisture permeability such as.

  Therefore, a high adhesion force is provided between the protective film made of a resin with low moisture permeability and the polyvinyl alcohol polarizer, and the protective film made of a resin with 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 a high adhesive strength even between them. For example, JP-A-2004-245925 (Patent Document 1) discloses an adhesive mainly composed of an epoxy compound that does not contain an aromatic ring. It has been proposed to cure the adhesive by polymerization and bond 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. Patent Document 2 describes that, when a photosensitizer made of an anthracene compound is used in combination, even when the protective film contains an ultraviolet absorber, a good adhesive force is given.

  That is, a photocationic polymerization initiator is blended in order to cure a cationically polymerizable compound such as an epoxy compound, and such a photocationic polymerization initiator is generally a compound that exhibits a maximum absorption in the vicinity of 300 nm or shorter. Therefore, by adding a photosensitizer exhibiting maximum absorption to light having a longer wavelength range, specifically longer than 380 nm, it is sensitive to light having a wavelength in the vicinity of the photocation polymerization initiator. Generation of cationic species or acids can be promoted.

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

  Furthermore, when a protective film is bonded to both surfaces of the polarizer, an ultraviolet absorber is often blended in one protective film. And when using the photocurable adhesive agent disclosed by the said patent document 1 or the patent document 2, if one protective film contains a ultraviolet absorber and the other protective film does not contain a ultraviolet absorber, Usually, the respective protective films are bonded to both sides of the polarizer via the photo-curable adhesive, and the adhesive is cured by irradiating ultraviolet rays from the protective film side not containing the ultraviolet absorber. Some resin films that do not contain an ultraviolet absorber hardly transmit light on the short wavelength side of the ultraviolet region, and in the transmittance spectrum, the transmittance suddenly rises from near the wavelength of more than 300 nm. Therefore, even if a photosensitizer is blended in the photocurable adhesive, in the case of a protective film that does not have a very high transmittance in the vicinity of a wavelength of 340 nm, there is sufficient adhesion between the polarizer and the protective film. Sometimes it was not possible.

JP 2004-245925 A JP 2008-257199 A

  An object of the present invention is to provide a photocurable adhesive that exhibits a sufficiently low viscosity that can be applied at room temperature and has little influence on polarizing plate properties when a protective film is bonded to a polarizer. is there. Another object of the present invention is to provide a photo-curing adhesive that provides a good adhesive force with a polarizer even when a protective film having a transmittance of around 340 nm is not so large. Another object of the present invention is to provide a polarizing plate having excellent adhesive strength by bonding a polarizer and a protective film using this adhesive. Yet another object of the present invention is to provide a laminated optical member suitably used for a liquid crystal display device by laminating another optical layer such as a retardation plate on the polarizing plate.

  As a result of intensive studies to solve the above problems, the present inventors have completed the present invention. Specifically, in a photocurable adhesive obtained by blending a predetermined amount of a photocationic polymerization initiator and a photosensitizer having a specific structure with a photocationic curable component, a specific fat is used as the photocationic curable component. A diepoxy compound mainly composed of a cyclic diepoxy compound and having an alicyclic epoxy structure and an epoxy group not bonded to the alicyclic ring in the molecule, and two epoxy groups not bonded to the alicyclic ring in the molecule The present inventors have found that it is effective to use a composition in which a diglycidyl compound having no aromatic ring is blended so that there are at least three photocationic curable components. That is, the photocurable adhesive having such a specific composition exhibits a low viscosity at room temperature and gives good coating suitability, and also exhibits a high storage elastic modulus after curing, thereby firmly bonding the polarizer and the protective film. I found out. Further, this photo-curable adhesive was also found to firmly bond the polarizer and the protective film even when the protective film on the light irradiation side does not exhibit a very high transmittance in the vicinity of a wavelength of 340 nm. .

That is, the present invention is an adhesive for bonding a protective film made of a transparent resin to a polarizer made of a polyvinyl alcohol-based resin film in which a dichroic dye is adsorbed and oriented,
(A) For 100 parts by weight of the photocation curable component,
(B) 1 to 10 parts by weight of a cationic photopolymerization initiator, and (C) the following formula (I):

[Wherein, R and R ′ each independently represents an alkyl group having 1 to 6 carbon atoms or an alkoxyalkyl group having 2 to 12 carbon atoms; R ″ represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. ]
0.1 to 2 parts by weight of an anthracene photosensitizer represented by the above, and the above-mentioned photocationic curable component (A) is based on the total amount of the following (A1), (A2) and ( A photocurable adhesive containing each component of A3) is provided.

  (A1) 50 to 70% by weight of an alicyclic diepoxy compound represented by the following formula (II).

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

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

  (A2) 15 to 35% by weight of an oxirane ring-containing epoxycyclohexane compound represented by the following formula (III).

In the formula, R ³ and R ⁴ 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 have an alicyclic structure; c Represents an integer of 0-20.

  (A3) 5 to 25% by weight of a diglycidyl compound represented by the following formula (IV).

In the formula, Z is an alkylene group having 1 to 9 carbon atoms, an alkylidene group having 3 or 4 carbon atoms, a divalent alicyclic hydrocarbon group, or a formula —C _m H _2m —Z ¹ —C _n H _2n —. Represents a divalent group shown, wherein -Z ^1- represents -O-, -CO-O-, -O-CO-, -SO _2- , -SO-, or -CO-; And n each independently represents an integer of 1 or more, but the total of both is 9 or less.

  In this photocurable adhesive, the photocationic curable component (A) can further contain an oxetane compound in a proportion of 20% by weight or less as a component (A4) based on the total amount.

  The photocurable adhesive preferably has a viscosity at 25 ° C. of 100 mPa · sec or less. Moreover, it is preferable that the hardened | cured material shows the storage elastic modulus of 1000 Mpa or more in 80 degreeC, and the hardened | cured material which gives such a high storage elastic modulus by setting the photocurable adhesive as said specific composition. Can be formed.

  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, and the adhesion is made. There is also provided a polarizing plate in which the agent layer is a cured product of any of the above photocurable adhesives.

  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. Moreover, the protective film bonded on at least one surface of the polarizer can be composed of a film having a transmittance of 60% or less at a wavelength of 340 nm. In this case, as an example of a protective film having a transmittance of 60% or less at a wavelength of 340 nm, a protective film having a layer of an acetyl cellulose resin not containing an ultraviolet absorber, more specifically, an acetyl cellulose resin film An optical compensation film in which liquid crystal is aligned and fixed can be mentioned. Furthermore, the protective film bonded to at least one surface of the polarizer has a low moisture permeability such as an amorphous polyolefin resin, a polyester resin, an acrylic resin, a polycarbonate resin, and a chain polyolefin resin. It can also be composed of a resin film.

  The present invention further provides a laminated optical member comprising a laminate of any one of the above polarizing plates and another optical layer. The other optical layer constituting the laminated optical member advantageously includes a retardation plate.

  The photocurable adhesive of the present invention was formulated with a predetermined amount of each of an alicyclic diepoxy compound (A1), an oxirane ring-containing epoxycyclohexane compound (A2), and a diglycidyl compound (A3) as the photocationic curable component (A). Thus, the storage elastic modulus of the adhesive layer after curing can be improved while maintaining the adhesive strength between the polarizer and the protective film. Therefore, a polarizing plate in which a protective film made of a transparent resin is bonded to at least one surface of the polarizer via this adhesive will crack the polarizer even when subjected to a severe temperature history such as a thermal shock test. It is hard to occur and has excellent thermal shock resistance. Further, this polarizing plate hardly changes its polarization degree even when it is placed in a wet heat environment, and exhibits good wet heat resistance. A laminated optical member obtained by laminating another optical layer on this polarizing plate also has excellent thermal shock resistance and moist heat resistance while fully expressing the function of the polarizing plate.

Transmission spectrum of optical compensation film “WV-EA” (manufactured by FUJIFILM Corporation) used in Examples and Comparative Examples, absorbance spectra of photopolymerization initiator and photosensitizer, respectively, and UV absorption for reference It is a graph which shows the transmittance | permeability spectrum of the triacetyl cellulose film which does not contain an agent.

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

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

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

  The amount of the alicyclic diepoxy compound (A1) in the photocationic curable component (A) is 50 to 70% by weight based on the total amount of the photocationic curable component (A). Inclusion of 50% by weight or more of the alicyclic diepoxy compound (A1) in the photocationic curable component (A) increases the storage elastic modulus after curing the photocurable adhesive containing it, for example, The storage elastic modulus at 80 ° C. can be set to 1,000 MPa or more, and when the polarizing plate bonded with the polarizer and the protective film through the adhesive is exposed to a severe temperature history, the polarizer is cracked. Can be prevented. On the other hand, when the amount exceeds 70% by weight, the amount of the oxirane ring-containing epoxycyclohexane compound (A2) and diglycidyl compound (A3) described below becomes relatively small, and the photocurable adhesive contemplated in the present invention. It becomes difficult to reduce the viscosity of the agent and increase the elastic modulus of the cured product.

  Moreover, the quantity of the oxirane ring containing epoxycyclohexane compound (A2) in a photocationic curable component (A) shall be 15-35 weight%. By blending 15% by weight or more of the oxirane ring-containing epoxycyclohexane compound (A2) in the photocationic curable component (A), the viscosity of the photocurable adhesive containing the oxirane ring is reduced, and good coatability is exhibited. It becomes like this. On the other hand, when the amount exceeds 35% by weight, the storage elastic modulus after curing the photocurable adhesive tends not to be sufficiently high, and the polarizer and the protective film are bonded via the adhesive. When the obtained polarizing plate is exposed to a severe temperature history, the polarizer is easily broken.

  Furthermore, the amount of the diglycidyl compound (A3) in the photocationically curable component (A) is 5 to 25% by weight. By blending 5% by weight or more of the diglycidyl compound (A3) in the photocationic curable component (A), while maintaining a high storage elastic modulus after curing the photocurable adhesive containing the diglycidyl compound (A3), polarized light The adhesion between the child and the protective film can be improved. On the other hand, when the amount exceeds 25% by weight, the storage elastic modulus after curing the photocurable adhesive tends not to be sufficiently high, and a polarizer and a protective film are pasted through the adhesive. When the combined polarizing plate is exposed to a severe temperature history, the polarizer is liable to break.

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

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

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

The alicyclic diepoxy compound (A1) represented by the formula (II) will be described more specifically. A compound in which X in the formula (II) is represented by the formula (IIa) and a in the formula is 0 Are 3,4-epoxycyclohexylmethanol (an alkyl group having 1 to 6 carbon atoms may be bonded to the cyclohexane ring) and 3,4-epoxycyclohexanecarboxylic acid (having 1 to 6 carbon atoms on the cyclohexane ring). The alkyl group may be bonded to each other). Specific examples thereof include 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate [formula (II) (wherein X is a divalent group represented by formula (IIa) where a = 0). , R ¹ = R ² = H compound], 3,4-epoxy-6-methylcyclohexylmethyl 3,4-epoxy-6-methylcyclohexanecarboxylate [in formula (II) having the same X as above, R ¹ = 6-methyl, R ² = 6-methyl compound], 3,4-epoxy-1-methylcyclohexylmethyl 3,4-epoxy-1-methylcyclohexanecarboxylate [in formula (II) having the same X as above , R ¹ = 1-methyl, R ² = 1-methyl compound], 3,4-epoxy-3-methylcyclohexylmethyl 3,4-epoxy-3- Methylcyclohexanecarboxylate [compound of formula (II) having the same X as in the above, R ¹ = 3-methyl, R ² = 3-methyl].

  The compound in which X in the formula (II) is a divalent group represented by the formula (IIb) is an alkylene glycol and 3,4-epoxycyclohexanecarboxylic acid (an alkyl group may be bonded to the cyclohexane ring) ) And an esterified product. The compound in which X in the formula (II) is a divalent group represented by the formula (IIc) is an aliphatic dicarboxylic acid and 3,4-epoxycyclohexylmethanol (an alkyl group may be bonded to the cyclohexane ring). ) And an esterified product. The compound in which X in the formula (II) is a divalent group represented by the formula (IId) is an ether of 3,4-epoxycyclohexylmethanol (an alkyl group may be bonded to the cyclohexane ring). (When b = 0), or etherified product of alkylene glycols or polyalkylene glycols and 3,4-epoxycyclohexylmethanol (an alkyl group may be bonded to the cyclohexane ring) (b> 0) In the case of

In Formula (III) representing the oxirane ring-containing epoxycyclohexane compound (A2), R ³ and R ⁴ are each independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and the alkyl group has 3 or more carbon atoms. In some cases, it may have an alicyclic structure. When R ³ bonded to the epoxycyclohexane ring is an alkyl group, the alkyl group is defined as the 1-position of the cyclohexane ring in which the bond in formula (III) comes out (therefore, the position of the epoxy group in the cyclohexane ring is It can be bonded to any position from the 1-position to the 6-position. Of course, this alkyl group may be linear, or may be branched when it has 3 or more carbon atoms. Moreover, as above-mentioned, in the case of C3 or more, you may have an alicyclic structure. Typical examples of the alkyl group having an alicyclic structure include cyclopentyl and cyclohexyl. Similarly, in formula (III), c, which means the number of ethylene oxide repeats, is an integer of 0-20.

Many of the oxirane ring-containing epoxycyclohexane compounds represented by the formula (III) are liquid at room temperature and have a low viscosity, and are therefore sometimes used as reactive diluents in the field of epoxy resins. In particular, a compound in which c in the formula is 0 is representative. Specific examples thereof include 4-vinylcyclohexene diepoxide [compound of formula (III) with c = 0, R ³ = R ⁴ = H], limonene diepoxide [compound of formula (III) with c = 0, R ³ = 4-methyl (where the position number is as described above), R ⁴ = methyl compound] and the like.

In the formula (IV) representing the diglycidyl compound (A3), Z represents an alkylene group having 1 to 9 carbon atoms, an alkylidene group having 3 or 4 carbon atoms, a divalent alicyclic hydrocarbon group, or a formula —C _m H _2m —Z ¹ —C _n H _2n —, wherein —Z ¹ — is —O—, —CO—O—, —O—CO—, —SO ₂ —, —SO— or —CO—, and m and n are each independently an integer of 1 or more, but the total of both is 9 or less. Of course, this alkylene group may be linear, or may be branched when it has 3 or more carbon atoms. When Z is an alkylidene group, a bond may come out from a terminal carbon atom such as propylidene or butylidene, or a bond may come out from a non-terminal carbon atom such as isopropylidene. Typical examples of the divalent alicyclic hydrocarbon group include cyclopentylene and cyclohexylene.

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

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

  The photocationic curable component (A) constituting the photocurable adhesive is the alicyclic diepoxy compound (A1), oxirane ring-containing epoxycyclohexane compound (A2) and diglycidyl compound (A3) described above. Other cationically polymerizable compounds may be included within the ranges described. Examples of other cationically polymerizable compounds include epoxy compounds other than formula (II), formula (III) and formula (IV), oxetane compounds and the like.

  Epoxy compounds other than those of formula (II), formula (III) and formula (IV) have an epoxy group bonded to at least one alicyclic ring in the molecule other than formula (II) and formula (III). Alicyclic epoxy compound, aliphatic epoxy compound having an oxirane ring bonded to an aliphatic carbon atom other than formula (IV), aromatic epoxy compound having an aromatic ring and an epoxy group in the molecule, aromaticity in the aromatic epoxy compound Examples include hydrogenated epoxy compounds in which a group ring is hydrogenated.

  Examples of aliphatic epoxy compounds having an oxirane ring bonded to an aliphatic carbon atom other than formula (IV) include triglycidyl ether of glycerin, triglycidyl ether of trimethylolpropane, and diglycidyl ether of polyethylene glycol. .

  The aromatic epoxy compound having an aromatic ring and an epoxy group in the molecule can be a glycidyl ether of an aromatic polyhydroxy compound having at least two phenolic hydroxyl groups in the molecule. Specific examples include diglycidyl ether of bisphenol A, diglycidyl ether of bisphenol F, diglycidyl ether of bisphenol S, and glycidyl ether of phenol novolac resin.

  The hydrogenated epoxy compound in which the aromatic ring in the aromatic epoxy compound is hydrogenated is compared with the aromatic polyhydroxy compound having at least two phenolic hydroxyl groups in the molecule as the raw material of the aromatic epoxy compound. A hydrogenated polyhydroxy compound obtained by selectively hydrogenating an aromatic ring under pressure in the presence of a catalyst can be obtained by glycidyl etherification. Specific examples thereof include diglycidyl ether of hydrogenated bisphenol A, diglycidyl ether of hydrogenated bisphenol F, and diglycidyl ether of hydrogenated bisphenol S.

  Further, the oxetane compound that can optionally be a part of the photocation curable component (A) is a compound having a 4-membered ring ether (oxetanyl group) in the molecule. Specific examples include 3-ethyl-3-hydroxymethyloxetane, 1,4-bis [(3-ethyl-3-oxetanyl) methoxymethyl] benzene, 3-ethyl-3- (phenoxymethyl) oxetane, di [(3-ethyl-3-oxetanyl) methyl] ether, 3-ethyl-3- (2-ethylhexyloxymethyl) oxetane, 3-ethyl-3- (cyclohexyloxymethyl) oxetane, phenol novolak oxetane, 1,3- Bis [(3-ethyloxetane-3-yl) methoxy] benzene, oxetanylsilsesquioxane, oxetanyl silicate, and the like.

  By blending the oxetane compound in a proportion of 20% by weight or less based on the total amount of the photocationic curable component (A), the curability is higher than when only the epoxy compound is used as the cation curable component (A). In some cases, an improvement can be expected.

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

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

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

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

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

  These cationic photopolymerization initiators may be used alone or in combination of two or more. Among these, aromatic sulfonium salts are particularly preferably used because they exhibit ultraviolet absorption characteristics even in the wavelength region near 300 nm, and can give a cured product having excellent curability and good mechanical strength and adhesive strength. It is done.

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

(Photosensitizer)
The photocurable adhesive of the present invention exhibits maximum absorption in light having a wavelength longer than 380 nm, in addition to the photocationic curable component (A) and the photocationic polymerization initiator (B) containing the epoxy compound as described above. Contains a photosensitizer (C). The above-mentioned photocationic polymerization initiator (B) exhibits a maximum absorption at a wavelength around 300 nm or shorter, generates a cationic species or a Lewis acid in response to light having a wavelength in the vicinity thereof, and is a photocationic curable component. Although the cationic polymerization of (A) is started, a photosensitizer (C) that exhibits maximum absorption in light having a wavelength longer than 380 nm is blended so as to be sensitive to light having a longer wavelength. In the present invention, the anthracene compound represented by the formula (I) is used as the photosensitizer (C). Specific examples of the anthracene photosensitizer (C) represented by the formula (I) include the following compounds.

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

  By mix | blending anthracene type photosensitizer (C) with a photocurable adhesive agent, the sclerosis | hardenability of an adhesive agent improves compared with the case where it is not mix | blended. Such an effect can be obtained by setting the blending amount of the anthracene photosensitizer (C) to 0.1 parts by weight or more with respect to 100 parts by weight of the photocationic curable component (A) constituting the photocurable adhesive. To express. On the other hand, when the blending amount of the anthracene photosensitizer (C) is increased, problems such as precipitation during low-temperature storage occur. Therefore, the amount is 2 with respect to 100 parts by weight of the photocation curable component (A). Less than parts by weight. From the viewpoint of maintaining the neutral gray of the polarizing plate, it is advantageous to reduce the blending amount of the anthracene photosensitizer (C) within a range in which the adhesive force between the polarizer and the protective film is maintained appropriately. For example, with respect to 100 parts by weight of the photocationic curable component (A), the amount of the anthracene photosensitizer (C) is in the range of 0.1 to 1.5 parts by weight, further 0.1 to 1 part by weight. It is preferable to do this.

(Physical properties of photo-curing adhesive)
A predetermined amount of each of the photocationic curable component (A), the photocationic polymerization initiator (B), and the anthracene photosensitizer (C) represented by the formula (I) described above is blended, and photocurable. An adhesive is constructed. Although this photocurable adhesive is obtained in a liquid state, it is preferable that the viscosity at 25 ° C. is 100 mPa · sec or less from the viewpoint of coating properties as an adhesive. In particular, a predetermined amount of the oxirane ring-containing epoxycyclohexane compound (A2) represented by the formula (III) and the diglycidyl compound (A3) represented by the formula (IV) are respectively present in the photocationic curable component (A). In this way, such a low viscosity can be achieved. Although there is no special restriction | limiting in the minimum of the viscosity in 25 degreeC, if the compounding ratio demonstrated so far is maintained, it will be 30 mPa * sec or more in general. From the viewpoint of providing high adhesion between the polarizer and the protective film while maintaining good coating properties, it is preferable to exhibit at least this level of viscosity.

  Moreover, in order to fully express the protective property by the protective film bonded to the polarizer through the cured product of the photocurable adhesive, the cured product of the photocurable adhesive is 1 at 80 ° C. It is preferable that the storage elastic modulus is 000 MPa or more. The photocurable adhesive has the above-mentioned specific composition, and in particular, the photocationic curable component (A) contains the oxirane ring-containing epoxycyclohexane compound (A2) and the diglycidyl compound (A3) in a predetermined amount, respectively. The presence of 50% by weight or more of the alicyclic diepoxy compound (A1) makes it possible to form a cured product that gives such a high storage elastic modulus. Although there is no special restriction | limiting in the upper limit of this storage elastic modulus, if the compounding ratio demonstrated so far is maintained, it will be about 3,000 MPa or less.

[Polarizer]
The photocurable adhesive described above is used for bonding a polarizer made of a polyvinyl alcohol resin film on which a dichroic dye is adsorbed and oriented, and a protective film made of a transparent resin. The polarizing plate of the present invention is a protective material made of a transparent resin on at least one surface of a polarizer made of a polyvinyl alcohol-based resin film on which a dichroic dye is adsorbed and oriented via the photocurable adhesive described above. A film is bonded and the adhesive layer is cured.

(Polarizer)
The polarizer is composed of a polyvinyl alcohol-based resin film on which a dichroic dye is adsorbed and oriented. The polyvinyl alcohol resin constituting the polarizer can be obtained by saponifying a polyvinyl acetate resin. The polyvinyl acetate resin may be a copolymer of vinyl acetate, which is a homopolymer of vinyl acetate, or a copolymer of vinyl acetate and other monomers copolymerizable therewith. Examples of other monomers copolymerized with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids. The saponification degree of the polyvinyl alcohol-based resin is usually 85 to 100 mol%, preferably 98 to 100 mol%. The polyvinyl alcohol resin may be modified. For example, polyvinyl formal or polyvinyl acetal modified with aldehydes may be used. The degree of polymerization of the polyvinyl alcohol-based resin is usually 1,000 to 10,000, preferably 1,500 to 5,000.

  A polarizer is a process of uniaxially stretching such a polyvinyl alcohol-based resin film, a step of dyeing a polyvinyl alcohol-based resin film with a dichroic dye, and adsorbing the dichroic dye, and an adsorbing of the dichroic dye It is manufactured through a process of treating the polyvinyl alcohol resin film thus prepared with an aqueous boric acid solution.

  Uniaxial stretching may be performed before dyeing with a dichroic dye, may be performed simultaneously with dyeing with a dichroic dye, or may be performed after dyeing with a dichroic dye. When uniaxial stretching is performed after dyeing with a dichroic dye, the uniaxial stretching may be performed during boric acid treatment or may be performed before boric acid treatment. Of course, it is also possible to perform uniaxial stretching in these plural stages. Uniaxial stretching may be performed between rolls having different peripheral speeds, or may be performed using a hot roll. Moreover, the dry-type extending | stretching which extends | stretches in air | atmosphere may be sufficient, and the wet extending | stretching which extends | stretches in the state swollen with the solvent may be sufficient. The draw ratio is usually about 4 to 8 times.

  In order to dye the polyvinyl alcohol resin film with the dichroic dye, for example, the polyvinyl alcohol resin film may be immersed in an aqueous solution containing the dichroic dye. Specifically, iodine or a dichroic organic dye is used as the dichroic dye.

  When iodine is used as the dichroic dye, a method of dyeing a polyvinyl alcohol resin film by dipping it in an aqueous solution containing iodine and potassium iodide is usually employed. The content of iodine in this aqueous solution is usually about 0.01 to 0.5 parts by weight per 100 parts by weight of water, and the content of potassium iodide is usually about 0.5 to 10 parts by weight per 100 parts by weight of water. It is. The temperature of this aqueous solution is usually about 20 to 40 ° C., and the immersion time (dyeing time) in this aqueous solution is usually about 30 to 300 seconds.

On the other hand, when a dichroic organic dye is used as the dichroic dye, a method of immersing and dyeing a polyvinyl alcohol-based resin film in an aqueous solution containing a water-soluble dichroic organic dye is usually employed. The content of the dichroic organic dye in this aqueous solution is usually about 1 × 10 ⁻³ to 1 × 10 ⁻² parts by weight per 100 parts by weight of water. This aqueous solution may contain an inorganic salt such as sodium sulfate. The temperature of this aqueous solution is usually about 20 to 80 ° C., and the immersion time (dyeing time) in this aqueous solution is usually about 30 to 300 seconds.

  The boric acid treatment after dyeing with the 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, this aqueous boric acid solution preferably contains potassium iodide. The content of potassium iodide in the boric acid aqueous solution is usually about 2 to 20 parts by weight, preferably 5 to 15 parts by weight per 100 parts by weight of water. The immersion time in the boric acid aqueous solution is usually about 100 to 1,200 seconds, preferably about 150 to 600 seconds, and more preferably about 200 to 400 seconds. The temperature of the boric acid aqueous solution is usually 50 ° C. or higher, preferably 50 to 85 ° C.

  The polyvinyl alcohol resin film after the boric acid treatment is usually washed with water. The water washing treatment is performed, for example, by immersing a boric acid-treated polyvinyl alcohol resin film in water. After washing with water, a drying process is performed to obtain a polarizer. The temperature of water in the water washing treatment is usually about 5 to 40 ° C., and the immersion time is usually about 2 to 120 seconds. The drying process performed thereafter is usually performed using a hot air dryer or a far infrared heater. The drying temperature is usually 40 to 100 ° C. 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 10-50 micrometers.

(Protective film)
In the present invention, a polarizer comprising the polyvinyl alcohol-based resin film described above is laminated with a protective film via the photocurable adhesive described above, and the photocurable adhesive is cured to form a polarizing plate. . It protective film is typically a temperature 40 ° C., at a relative humidity of 90% for, 0.1g / m ^2/24 hours or more, it shows the following moisture permeability 1,000g / m ^2/24 hours Can do. For example, it can be composed of an acetylcellulose-based resin film such as triacetylcellulose that has been most widely used as a protective film for polarizing plates, or a resin film having a lower moisture permeability than triacetylcellulose. Moisture permeability of triacetyl cellulose, in the above-mentioned circumstances, it is generally 400 g / m ² / about 24h.

  In one preferable form, the protective film bonded to one surface of the polarizer is composed of an acetylcellulose-based resin film. This acetylcellulose-based resin film may contain a UV absorber.

  In another preferred embodiment, the protective film bonded to at least one surface of the polarizer is composed of a resin film having a transmittance of 60% or less at a wavelength of 340 nm. As an example of a protective film having a slightly low transmittance in the near-ultraviolet region close to the visible region, one having an acetylcellulose-based resin layer not containing an ultraviolet absorber, more specifically, an acetylcellulose-based resin An optical compensation film in which liquid crystal is aligned and fixed on the film can be mentioned. For example, on one side of a triacetyl cellulose film, the discotic liquid crystal has a liquid crystal disk surface approximately parallel to the film surface on the film surface side, and the liquid crystal disk surface at a certain angle with respect to the film surface on the side far from the film surface. There is an optical compensation film that is hybrid-oriented. Such an optical compensation film is available from FUJIFILM Corporation under the trade name “Wide View” (WV) series. In this case, a protective film having a slightly low transmittance in the near-ultraviolet region is bonded to the polarizer via a photocurable adhesive, and active energy rays, particularly ultraviolet rays are irradiated from the protective film side. In many cases, the photocurable adhesive is cured, but in order to sufficiently cure the adhesive, it is preferable to exhibit a certain degree of transmittance at the wavelength (340 nm), for example, a transmittance of 30% or more. It is preferable.

In another preferred form, the protective film bonded to at least one surface of the polarizer is 300 g in a transparent resin film having a moisture permeability lower than that of triacetyl cellulose, for example, in an environment having a temperature of 40 ° C. and a relative humidity of 90%. / M ² / Consists of a resin film having a moisture permeability of 24 hours or less. Examples of the resin constituting such a resin film with low moisture permeability include amorphous polyolefin resin, polyester resin, acrylic resin, polycarbonate resin, and chain polyolefin resin.

  In the case where a protective film is bonded to both sides of a polarizer, in one preferred embodiment, an acetyl cellulose resin, more preferably an ultraviolet absorber, is blended on one side of the polarizer via the adhesive layer. A protective film made of a cellulose-based resin is bonded, and through the same adhesive layer on the other surface of the polarizer, a protective film having a slightly low transmittance in the near ultraviolet region close to the visible region as described above, for example, An optical compensation film in which liquid crystal is oriented and fixed is bonded to an acetylcellulose-based resin film. In another preferred embodiment in which protective films are bonded to both sides of the polarizer, an acetylcellulose-based resin, more preferably an ultraviolet absorber, is blended on one side of the polarizer via the adhesive layer. A protective film made of acetylcellulose-based resin is bonded, and the protective film made of a transparent resin with low moisture permeability as described above is bonded to the other surface of the polarizer through the adhesive layer.

  An acetylcellulose-based resin is a resin in which at least a part of hydroxyl groups in cellulose is esterified. It may be a mixed ester that is partly esterified and partly 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-based resin is a polymer having polymerized units 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 cyclic olefin with a chain olefin and / or an aromatic vinyl compound. In the case of a homopolymer of a cyclic olefin or a copolymer of two or more kinds of cyclic olefins, a double bond remains by ring-opening polymerization, and hydrogenated ones are generally used as amorphous polyolefin-based resins. Used. Of these, thermoplastic norbornene resins are typical.

  The polyester resin is a polymer obtained by condensation polymerization of a dibasic acid and a dihydric alcohol, and is typically polyethylene terephthalate. The acrylic resin is a polymer having methyl methacrylate as a main monomer. In addition to a homopolymer of methyl methacrylate, it may be a copolymer of methyl methacrylate and an acrylic ester such as methyl acrylate or an aromatic vinyl compound. The polycarbonate resin is a polymer having a carbonate bond (—O—CO—O—) in the main chain and is typically produced by condensation polymerization of bisphenol A and phosgene. The chain polyolefin-based resin is a polymer mainly containing a chain olefin such as ethylene or propylene, and can be a homopolymer or a copolymer. Among them, a propylene homopolymer and a copolymer in which a small amount of ethylene is copolymerized with propylene are representative.

  Such a protective film has various surface treatment layers such as a hard coat layer, an antireflection layer, an antiglare layer, and an antistatic layer on the surface opposite to the surface to be bonded to the polarizer. Also good. The protective film can have a thickness of about 5 to 150 μm including the case where such a surface treatment layer is formed. The thickness is preferably 10 μm or more, preferably 120 μm or less, more preferably 100 μm or less.

(Adhesion of polarizer and protective film)
In bonding the polarizer and the protective film, the photocurable adhesive coating layer described above is formed on one or both of the bonding surfaces of the polarizer and the protective film, and the polarizer and the protective film are interposed through the coating layer. The protective film is bonded, and the uncured photocurable adhesive coating layer thus formed is cured by irradiation with active energy rays, thereby fixing the protective film on the polarizer. The application layer of a photocurable adhesive may be formed on the bonding surface of the polarizer, or may be formed on the bonding surface of the protective film. The coating layer can be formed by using various coating methods such as a doctor blade, a wire bar, a die coater, a comma coater, and a gravure coater. Moreover, the system which casts a photocurable adhesive agent in the meantime can also be employ | adopted, supplying a polarizer and a protective film continuously so that both bonding surfaces may become inside. Since each coating method has an optimum viscosity range, it is also useful to adjust the viscosity using a solvent. As the solvent for this purpose, a solvent that dissolves the photocurable adhesive satisfactorily without reducing the optical performance of the polarizer is used, but there is no particular limitation on the type thereof. For example, organic solvents such as hydrocarbons typified by toluene and esters typified by ethyl acetate can be used. The thickness of the adhesive layer is usually 20 μm or less, preferably 10 μm or less, more preferably 5 μm or less. When the adhesive layer becomes thick, the reaction rate of the photocurable adhesive decreases, and the heat and humidity resistance of the polarizing plate tends to deteriorate.

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

The light source used for irradiating active energy rays to the coating layer of the photocurable adhesive may be any one that generates ultraviolet rays, electron beams, X-rays, and the like. In particular, for example, a low pressure mercury lamp, a medium pressure mercury lamp, a high pressure mercury lamp, an ultrahigh pressure mercury lamp, a chemical lamp, a black light lamp, a microwave excitation mercury lamp, a metal halide lamp or the like having a light emission distribution at a wavelength of 400 nm or less is preferably used. The active energy ray irradiation intensity to the photocurable adhesive is determined for each composition of the target adhesive and is not particularly limited, but the irradiation intensity in the wavelength region effective for activation of the initiator is 0. It is preferable to be 1 to 500 mW / cm ² . If the light irradiation intensity to the photocurable adhesive composition is small, the reaction time becomes too long. On the other hand, if the intensity is too large, it is caused by heat radiated from the lamp and heat generated during polymerization of the photocurable adhesive. There is a possibility of causing yellowing of the photocurable adhesive and deterioration of the polarizer. The light irradiation time to the photocurable adhesive is controlled for each composition of the adhesive to be cured and is not particularly limited, but the integrated light amount represented by the product of the irradiation intensity and the irradiation time is 10 to 10. It is preferably set to be 5,000 mJ / cm ² . If the amount of light integrated into the photocurable adhesive is small, active species derived from the initiator may not be sufficiently generated, and the adhesive coating layer may be insufficiently cured, while the amount of integrated light is large. If too much, the irradiation time becomes very long, which is disadvantageous for productivity.

  When a protective film is bonded to both sides of the polarizer, the active energy ray may be irradiated from either side of the protective film. For example, one protective film contains an ultraviolet absorber and the other protective film When the ultraviolet absorber is not contained, it is preferable to irradiate the active energy ray from the protective film side not containing the ultraviolet absorber in order to effectively utilize the irradiated active energy ray and increase the curing rate.

[Laminated optical member]
The polarizing plate of the present invention can be made into a laminated optical member by laminating optical layers having optical functions other than the polarizing plate. Typically, a laminated optical member is obtained by laminating and attaching an optical layer to a protective film of a polarizing plate via an adhesive or a pressure-sensitive adhesive. According to the invention, a protective film may be bonded via a photocurable adhesive, and an optical layer may be laminated and bonded to the other surface of the polarizer via an adhesive or a pressure-sensitive adhesive. In the latter case, if the photocurable adhesive defined in the present invention is used as an adhesive for adhering the polarizer and the optical layer, the optical layer can simultaneously be a protective film defined in the present invention.

  As an example of the optical layer laminated on the polarizing plate, for the polarizing plate arranged on the back side of the liquid crystal cell, the reflective layer is laminated on the opposite side of the polarizing plate from the side facing the liquid crystal cell. A layer, a transflective layer, a light diffusion layer, a light collector, a brightness enhancement film, and the like. In addition, for both the polarizing plate arranged on the front side of the liquid crystal cell and the polarizing plate arranged on the back side of the liquid crystal cell, a retardation plate laminated on the side of the polarizing plate facing the liquid crystal cell, etc. There is.

  The reflective layer, transflective layer, or light diffusing layer is a reflective polarizing plate (optical member), a transflective polarizing plate (optical member), or a diffusing polarizing plate (optical member), respectively. Provided. The reflective polarizing plate is used in a liquid crystal display device of a type that reflects and displays incident light from the viewing side. Since a light source such as a backlight can be omitted, the liquid crystal display device can be easily thinned. The transflective polarizing plate is used as a reflection type in a bright place and used in a liquid crystal display device that displays light from a backlight in a dark place. The optical member as the reflective polarizing plate can be formed, for example, by attaching a reflective layer made of a metal foil such as an aluminum foil or a vapor deposition film to the protective film on the polarizer. The optical member as a transflective polarizing plate can be formed by using the reflective layer as a half mirror, or by adhering a reflective plate containing a pearl pigment or the like and exhibiting light transmittance to the polarizing plate. On the other hand, optical members as diffusion type polarizing plates can be applied to various methods such as a method of performing a mat treatment on a protective film on a polarizing plate, a method of applying a resin containing fine particles, and a method of adhering a film containing fine particles. And can be formed by providing a fine concavo-convex structure on the surface.

  Furthermore, an optical member can be formed as a polarizing plate for both reflection and diffusion. In this case, for example, a method of providing a reflective layer reflecting the concavo-convex structure on the fine concavo-convex structure surface of the diffusing polarizing plate is adopted. it can. The reflective layer having a fine concavo-convex structure has advantages such that incident light is diffused by irregular reflection, directivity and glare can be prevented, and uneven brightness can be suppressed. In addition, the resin layer or film containing fine particles has an advantage that incident light and its reflected light are diffused when passing through the fine particle-containing layer, and unevenness in brightness can be suppressed. The reflective layer reflecting the surface fine concavo-convex structure can be formed, for example, by attaching a metal directly to the surface of the fine concavo-convex structure by a method such as vapor deposition such as vacuum deposition, ion plating, sputtering, or plating. The fine particles to be blended to form the 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 may be inorganic fine particles, organic fine particles such as a crosslinked or non-crosslinked polymer, and the like.

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

  The brightness enhancement film is used for the purpose of improving the brightness in a liquid crystal display device. For example, a plurality of thin film films having different refractive index anisotropies are laminated to produce anisotropy in reflectance. A reflective linearly polarized light separating sheet designed as described above, an oriented film of a cholesteric liquid crystal polymer, and a reflective circularly polarized light separating sheet in which the oriented liquid crystal layer is supported on a film substrate.

  On the other hand, the above-described retardation plate as an optical layer is used for the purpose of compensation of retardation by a liquid crystal cell. Examples thereof include a birefringent film made of a stretched film of various plastics, a film in which a discotic liquid crystal or a nematic liquid crystal is oriented and fixed, and a film substrate on which the above liquid crystal layer is formed. When the liquid crystal layer is formed on the film substrate, a cellulose resin film such as triacetyl cellulose is preferably used as the film substrate.

  Examples of the plastic forming the birefringent film include amorphous polyolefin resins, polycarbonate resins, acrylic resins, chain polyolefin resins such as polypropylene, polyvinyl alcohol, polystyrene, polyarylate, polyamide, and the like. It is done. The stretched film can be processed by an appropriate method such as uniaxial or biaxial. Note that two or more retardation plates may be used in combination for the purpose of controlling optical characteristics such as broadening the bandwidth.

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

  The laminated optical member can be a laminate of two layers or three or more layers by combining a polarizing plate and one or more layers selected according to the purpose of use from the various optical layers described above. . In that case, the various optical layers forming the laminated optical member are integrated with the polarizing plate using an adhesive or pressure-sensitive adhesive, but the adhesive or pressure-sensitive adhesive layer used for this purpose is good. As long as it is formed, there is no particular limitation. It is preferable to use a pressure-sensitive adhesive (also referred to as a pressure-sensitive adhesive) from the viewpoint of easy bonding work and prevention of optical distortion. As the pressure-sensitive adhesive, those having an acrylic polymer, a silicone polymer, polyester, polyurethane, polyether, or the like as a base polymer can be used. Among them, like acrylic adhesives, it has excellent optical transparency, retains appropriate wettability and cohesion, has excellent adhesion to substrates, and has weather resistance and heat resistance. However, it is preferable to select and use a material that does not cause peeling problems such as floating and peeling under the conditions of heating and humidification. In acrylic adhesives, alkyl esters of (meth) acrylic acid having an alkyl group having 20 or less carbon atoms such as methyl, ethyl and butyl groups, and (meth) acrylic acid and hydroxyethyl (meth) acrylate An acrylic copolymer having a weight average molecular weight of 100,000 or more, which is obtained by blending and polymerizing a functional group-containing acrylic monomer having a glass transition temperature of preferably 0 ° C. or lower, is a base polymer. Useful as.

  The pressure-sensitive adhesive layer is formed on the polarizing plate by, for example, dissolving or dispersing the pressure-sensitive adhesive composition in an organic solvent such as toluene or ethyl acetate to prepare a 10 to 40% by weight solution, which is directly applied on the polarizing plate. It can be performed by a coating method, a method in which a pressure-sensitive adhesive layer is previously formed on a protective film, and transferred onto a polarizing plate. Although the thickness of an adhesive layer is determined according to the adhesive force etc., the range of about 1-50 micrometers is suitable.

  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. The liquid crystal cell to be used is arbitrary. For example, a liquid crystal display device using various liquid crystal cells such as an active matrix drive type represented by a thin film transistor type and a simple matrix drive type represented by a super twisted nematic type. Can be formed. A pressure-sensitive adhesive is usually used for bonding the laminated optical member and the liquid crystal cell.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative 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 photosensitizer used in the following examples are as follows, and are represented by the following symbols.

(A) Photocationic curable component (A1) to (A3) Epoxy compound:
(A1) Alicyclic diepoxy compound:
(A1) 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate.

(A2) An oxirane ring-containing epoxycyclohexane compound:
(A2) Limonene diepoxide.

(A3) Diglycidyl compound:
(A31) 1,4-butanediol diglycidyl ether,
(A32) neopentyl glycol diglycidyl ether,
(A33) 1,6-hexanediol diglycidyl ether,
(A36) cyclohexanedimethanol diglycidyl ether,
(A37) Hydrogenated bisphenol A diglycidyl ether.

(A4) Oxetane compound (abbreviated as “oxetane” in the table):
(A4) 3-ethyl-3- (2-ethylhexyloxymethyl) oxetane.

  The photocationic curable components (epoxy compounds and oxetane compounds) shown here have the following chemical structures, respectively.

(B) Photocationic polymerization initiator (abbreviated as “initiator” in the table)
(B1) Aromatic sulfonium salt photocationic polymerization initiator, trade name “SP-500” sold by ADEKA Corporation.

(C) Photosensitizer (c1) 9,10-dibutoxyanthracene [a compound in which R = R ′ = butyl and R ″ = H in the formula (I)].

[Examples 1 to 4 and Comparative Examples 1 to 4]
Each component was mixed at a blending ratio shown in Table 1 (unit is part), and then defoamed to prepare a photocurable adhesive liquid. In addition, a photocationic polymerization initiator (b1) was mix | blended as a 50% propylene carbonate solution, and displayed in Table 1 with the solid content.

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

(2) Measurement of storage elastic modulus at 80 ° C. of cured product Each adhesive solution prepared above was applied to one side of a polyethylene terephthalate film [trade name “Toyobo Ester Film E7002”, manufactured by Toyobo Co., Ltd.] Using a machine tool (Bar Coater, manufactured by Daiichi Rika Co., Ltd.), coating was performed so that the film thickness after curing was about 10 μm. Next, the adhesive was cured by irradiating ultraviolet rays so that the integrated light amount became 1,000 mJ / cm ² by a “D bulb” manufactured by Fusion UV Systems. This was cut into a size of 5 mm × 30 mm, and the polyethylene terephthalate film was peeled off to obtain a cured film of an adhesive. The cured film obtained in this manner was gripped with a gripper spacing of 2 cm using a dynamic viscoelasticity measuring device “DVA-220” manufactured by IT Measurement Control Co., Ltd. so that its long side is in the pulling direction. The storage elastic modulus at a temperature of 80 ° C. was determined by setting the frequency of tension and contraction to 1 Hz and the temperature increase rate to 3 ° C./min. The results are shown in Table 2.

(3) Transmittance measurement of protective film Optical compensation film in which discotic liquid crystal is oriented and fixed on one side of a triacetyl cellulose film not containing an ultraviolet absorber [trade name “WV-EA”, manufactured by Fuji Film Co., Ltd.] Was cut into a size of 30 mm × 30 mm, and the transmittance was measured at a wavelength of 200 to 510 nm. For the measurement, a UV-visible spectrophotometer “UV-2450” manufactured by Shimadzu Corporation and an optional accessory “film holder with polarizer” set therein were used. The result is shown by a thin solid line 1 in FIG. The transmittance of this optical compensation film at a wavelength of 340 nm was 52%.

(4) Application of adhesive liquid and evaluation of coating surface uniformity (coating property) Surface of 80 μm thick triacetylcellulose film (trade name “Fujitac”, manufactured by Fuji Film Co., Ltd.) containing UV absorber The corona discharge treatment was applied to the surface, and each of the adhesive liquids prepared above was coated on the corona discharge treatment surface using a bar coater so that the film thickness after curing was about 1.0 μm. A polyvinyl alcohol-iodine polarizer was bonded to the adhesive layer. Further, the triacetyl cellulose film surface of the optical compensation film “WV-EA” shown in (3) above is subjected to corona discharge treatment, and the same adhesive solution as above is cured on the corona discharge treatment surface. Coating was performed using a bar coater so as to have a thickness of about 1.0 μm. The polarizer side of the laminated film which bonded the triacetyl cellulose film on the single side | surface of the polarizer above was bonded to the adhesive bond layer. The uniformity of the surface state when the adhesive solution was applied to each triacetyl cellulose film was visually observed and evaluated, and the results are shown in Table 2. The same adhesion is applied when applied on a triacetylcellulose film containing an ultraviolet absorber and when applied on a triacetylcellulose film (optical compensation film) in which a discotic liquid crystal is oriented and fixed on one side. If it was an agent, the surface state was almost the same.

(5) Production of Polarizing Plate Triacetyl, in which a triacetyl cellulose film containing an ultraviolet absorber is bonded to one side of a polarizer and a discotic liquid crystal is aligned and fixed to the other side by the method shown in (4) above. A laminate in which a cellulose film (optical compensation film “WV-EA”) was bonded was prepared. From the optical compensation film “WV-EA” side of this laminate, the integrated light quantity becomes 750 mJ / cm ² using an ultraviolet irradiation device with a belt conveyor (the lamp uses “D bulb” manufactured by Fusion UV Systems). In this way, the adhesive was cured by irradiating with ultraviolet rays. Thus, a polarizing plate in which protective films were bonded to both sides of the polarizer was produced.

(6) Durability Evaluation of Polarizing Plate under Humid Heat The polarizing plate produced in (5) above is cut into a size of 30 mm × 30 mm and moist heat is left for 240 hours in a humid heat environment at a temperature of 85 ° C. and a relative humidity of 85%. The test was performed and the polarization degree of the polarizing plate before and after the test was measured. For the measurement of the degree of polarization, a UV-visible spectrophotometer “UV-2450” manufactured by Shimadzu Corporation, which is set with an optional accessory “film holder with polarizer”, is used in a wavelength range of 380 nm to 780 nm. The transmission spectrum in the transmission axis direction and the absorption axis direction of the polarizing plate was obtained, and the degree of polarization was calculated by software “UV-Probe” attached to the spectrophotometer. The results are shown in Table 2.

(7) Durability evaluation of polarizing plate in thermal shock test The polarizing plate produced in (5) above was cut into a size of 170 mm × 110 mm, and an adhesive layer was provided on the optical compensation film “WV-EA” side, The pressure-sensitive adhesive layer was attached to a glass plate, and a thermal shock test (heat shock test) was performed. In the thermal shock test, an operation of holding the polarizing plate sample bonded to the above glass plate at -35 ° C for 1 hour, then raising the temperature to 70 ° C and holding it for 1 hour is defined as one cycle. This was done by repeating 30 cycles. This test was performed for each of the six polarizing plate samples, and evaluation was made based on the ratio to the total number of samples (6) although cracks were observed in the polarizer after the test. The results are shown in Table 2.

  As shown in Table 1 and Table 2, Comparative Example 1 in which the amount of the alicyclic diepoxy compound (A1) was increased without adding the oxirane ring-containing epoxycyclohexane compound (A2) was The viscosity was high and the uniformity of the coated surface was insufficient. Also, Comparative Examples 2 and 3 in which a diglycidyl compound having an alicyclic ring in the molecule was blended, an oxirane ring-containing epoxycyclohexane compound (A2) was not blended, and the amount of the alicyclic diepoxy compound (A1) was increased. The viscosity of the adhesive liquid at room temperature was high, and the uniformity of the coated surface was still insufficient. On the other hand, in Comparative Example 4 in which the proportion of the diglycidyl compound (A3) was increased without blending the oxirane ring-containing epoxycyclohexane compound (A2), the viscosity of the adhesive solution was lowered, and the coating property itself was good, The storage modulus of the cured product was low, and the polarizer was easily broken by a thermal shock test.

  On the other hand, Examples 1-4 which mix | blended predetermined amount of the oxirane ring containing epoxycyclohexane compound (A2) (here limonene diepoxide) while keeping the ratio of the diglycidyl compound (A3) small are room temperature of adhesive liquid. It was confirmed that the viscosity of the cured product was low and good coatability was ensured, the storage modulus of the cured product was also high, and the properties of protecting the polarizer were sufficient.

  FIG. 1 shows an optical compensation film “WV-EA” in which a discotic liquid crystal is oriented and fixed on one side of a triacetyl cellulose film that does not contain an ultraviolet absorber and is used as one protective film in the above examples and comparative examples. FIG. 2 is a graph showing the transmittance spectrum of the photocatalyst and the absorbance spectra of the photocationic polymerization initiator “SP-500” and 9,10-dibutoxyanthracene used as a photosensitizer. In the figure, the thin solid line 1 marked “WV-EA” in the legend is the transmittance spectrum of the optical compensation film “WV-EA”, and the thick solid line 3 marked “initiator” in the legend is the photopolymerization initiator. The absorbance spectrum and the thick broken line 4 labeled “photosensitizer” in the legend are the absorbance spectrum of the photosensitizer. The thin broken line 2 marked “TAC” in the legend is a transmittance spectrum of a triacetyl cellulose film not containing an ultraviolet absorber, and is shown for reference. If only the triacetylcellulose film containing no ultraviolet absorber is used, the transmittance spectrum rises from a lower wavelength than the transmittance spectrum 1 of the optical compensation film “WV-EA”.

  As shown in this figure, the photopolymerization initiator exhibits maximum absorption near a wavelength of 300 nm, and the photosensitizer exhibits maximum absorption near a wavelength of 380 nm. Then, the low absorption in the wavelength region exceeding 350 nm of the photopolymerization initiator is supplemented by the high absorption in the wavelength region near 380 nm of the photosensitizer, and a cationic species is generated from the photopolymerization initiator by ultraviolet irradiation, and the epoxy compound mainly The photocationic curable component is cured. At this time, the transmittance spectrum of the optical compensation film “WV-EA” on the ultraviolet irradiation side rises from the vicinity of a wavelength of 320 nm, and gradually shows a high transmittance in a wavelength region where absorption of the photopolymerization initiator gradually disappears. It is effective to add a photosensitizer that exhibits absorption in this wavelength range.

  In such a combination of an adhesive and a protective film, the adhesive layer can be applied uniformly with a thin film thickness of about 1 μm, and the storage elastic modulus of the cured product is increased to 1,000 MPa or more. The present invention is particularly useful when manufacturing a polarizing plate that does not crack in the element.

  DESCRIPTION OF SYMBOLS 1 Transmittance spectrum of optical compensation film "WV-EA", 2 Transmittance spectrum of triacetyl cellulose film not containing ultraviolet absorber, 3 Absorbance spectrum of photopolymerization initiator, 4 Absorbance spectrum of photosensitizer

Claims (12)

An adhesive for bonding a protective film made of a transparent resin to a polarizer made of a polyvinyl alcohol-based resin film on which a dichroic dye is adsorbed and oriented,
(A) For 100 parts by weight of the photocation curable component,
(B) 1 to 10 parts by weight of a cationic photopolymerization initiator, and (C) the following formula (I):

[Wherein, R and R ′ each independently represents an alkyl group having 1 to 6 carbon atoms or an alkoxyalkyl group having 2 to 12 carbon atoms;
R ″ represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.]
0.1 to 2 parts by weight of an anthracene photosensitizer represented by
The photocationic curable component (A) is based on the total amount thereof.
(A1) The following formula (II):

[Wherein, 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 have an alicyclic structure;
X is an oxygen atom, an alkanediyl group having 1 to 6 carbon atoms, or the following formulas (IIa) to (IId):

In which Y ¹ to Y ⁴ each represent an alkanediyl group having 1 to 20 carbon atoms, and in the case of 3 or more carbon atoms, it has an alicyclic structure. Well;
a and b each represents an integer of 0 to 20. ]
50 to 70% by weight of an alicyclic diepoxy compound represented by
(A2) The following formula (III):

[Wherein, R ³ and R ⁴ each independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and when the alkyl group has 3 or more carbon atoms, it may have an alicyclic structure;
c represents an integer of 0 to 20. ]
15 to 35% by weight of an oxirane ring-containing epoxycyclohexane compound represented by the formula (IV):

[In the formula, Z is an alkylene group having 1 to 9 carbon atoms, an alkylidene group having 3 or 4 carbon atoms, a divalent alicyclic hydrocarbon group, or a formula —C _m H _2m —Z ¹ —C _n H _2n — -Z ^1- represents -O-, -CO-O-, -O-CO-, -SO _2- , -SO-, or -CO-, m and n each independently represents an integer of 1 or more, but the total of both is 9 or less. ]
The photocurable adhesive agent containing 5-25 weight% of diglycidyl compounds shown by. 2. The photocurable adhesive according to claim 1, wherein the photocationic curable component (A) further contains (A4) an oxetane compound in a proportion of 20 wt% or less based on the total amount thereof.   The photocurable adhesive according to claim 1 or 2, wherein the viscosity at 25 ° C is 100 mPa · sec or less.   The photocurable adhesive according to any one of claims 1 to 3, wherein the cured product exhibits a storage elastic modulus of 1,000 MPa or more at 80 ° C.   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, and the adhesive layer is Item 5. A polarizing plate, which is a cured product of the photocurable adhesive according to any one of Items 1 to 4.   The polarizing plate according to claim 5, wherein the protective film bonded to one surface of the polarizer is composed of an acetylcellulose-based resin film in which an ultraviolet absorber is blended.   The polarizing plate according to claim 5, wherein the protective film bonded to at least one surface of the polarizer exhibits a transmittance of 60% or less at a wavelength of 340 nm.   The polarizing plate according to claim 7, wherein the protective film having a transmittance of 60% or less at a wavelength of 340 nm has a layer containing an acetylcellulose-based resin in which no ultraviolet absorber is blended.   The polarizing plate according to claim 8, wherein the protective film having a transmittance of 60% or less at a wavelength of 340 nm is obtained by aligning and fixing a liquid crystal on an acetylcellulose-based resin film.   The protective film bonded to at least one surface of the polarizer is a resin film selected from the group consisting of an amorphous polyolefin resin, a polyester resin, an acrylic resin, a polycarbonate resin, and a chain polyolefin resin. The polarizing plate according to claim 5.   The laminated optical member which consists of a laminated body of the polarizing plate in any one of Claims 5-10, and another optical layer.   The laminated optical member according to claim 11, wherein the other optical layer includes a retardation plate.

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