JP2014032270A - Retardation film and composite polarizing plate using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a retardation film which comprises an olefin resin and hardly causes cracks or breakage in a thermal history even after the film is brought into contact with an organic chemical such as a solvent in a process of assembling an image display device, that is, excels in solvent crack resistance.SOLUTION: The retardation film has a protective film formed by cation polymerization curing on both surfaces of an olefin resin film having an in-plane retardation of 50 nm or more. The protective film can be formed of a curable resin composition containing an epoxy compound having no aromatic ring as a curable component. A composite polarizing plate is provided, which is a laminate of the above retardation film and a polarizing plate having a polarization film in which a dichroic dye is adsorbed and oriented to a polyvinyl alcohol resin. The retardation film having the protective film on both surfaces can be laminated with the polarizing plate via a pressure-sensitive adhesive.

Description

  The present invention relates to a retardation film suitably used for an image display device such as a liquid crystal display device, and a composite polarizing plate in which the retardation film is bonded to a polarizing plate. The retardation film of the present invention is excellent in resistance to chemicals that come into contact in the assembly process of an image display device, in particular, solvent crack resistance, and for the purpose of reducing the thickness and weight of modules in recent years and increasing the brightness, liquid crystal panels, etc. A cover glass or a cover glass with a touch sensor module (the latter is often simply called “touch panel”) is bonded to the surface of the image display panel using LOCA (Liquid Optically-Clear Adhesive). This is useful for various image display devices having the above-described configuration.

  Conventionally, liquid crystal display devices have been used in desktop calculators and electronic watches, but more recently, they have come to be used regardless of screen size, from mobile devices such as mobile phones to large-sized TVs. The use is expanding rapidly. In addition, as an image display device other than a liquid crystal display device, an organic electroluminescence (organic EL) display device tends to increase in demand mainly for mobile applications. In a liquid crystal display device, a pair of polarizing plates is usually disposed on the front and back of a liquid crystal cell to form a liquid crystal panel. In an organic EL display device, a polarizing plate, particularly an elliptical or circularly polarizing plate is disposed on the viewing side of the organic EL element, and an organic EL panel having an antireflection function is often obtained. An elliptical or circularly polarizing plate is obtained by laminating a quarter-wave retardation plate (that is, a λ / 4 plate) on a linear polarizing plate so that both axes intersect at a predetermined angle. As for the polarizing plates used in these image display devices, not only the demand is increasing with the development thereof, but also the performance suitable for each application is required.

  A polarizing plate (linear polarizing plate) widely used in the image display apparatus as described above is a liquid adhesive on both surfaces of a polarizer in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol resin film. And a transparent protective film, typically a triacetyl cellulose film. An image display element such as a liquid crystal cell or an organic EL element using a pressure-sensitive adhesive (also referred to as a pressure-sensitive adhesive) as it is or in a form in which an optical layer such as a retardation film having optical characteristics is bonded as it is. To form a display panel and further an image display device.

  As the retardation film, a film obtained by stretching and aligning a film made of an olefin resin having excellent performance in heat resistance, optical characteristics, transparency, electrical characteristics and the like is widely used. However, even in the case of olefin resins, which are generally considered to have excellent chemical resistance, when they come into contact with organic chemicals such as solvents in a stressed state, they are easily cracked and broken. In other words, depending on the type of organic chemical that comes into contact, the solvent crack resistance may be poor.

  Japanese Patent Application Laid-Open No. 8-259784 (Patent Document 1) discloses a resin composition having improved solvent resistance and chemical resistance by using a cyclic olefin resin having an epoxy group and crosslinking it. ing. Although this resin composition can improve the solvent crack resistance, it is difficult to control the cross-linking, and by-products may be generated or a polymerization initiator may remain. The resulting resin film becomes brittle and mechanical strength such as impact resistance may be lowered. In general, when a retardation film is handled in a long roll state, a tension is applied so that the film does not loosen. Therefore, a decrease in mechanical strength causes the film to break when the tension is applied. There was a possibility, and it was a big problem from the viewpoint of productivity.

  JP 2007-16102 A (Patent Document 2) discloses a resin composition in which an amorphous cyclic olefin polymer having no melting point is blended with a crystalline cyclic olefin polymer having a melting point. Thus, it is disclosed that a molded body having excellent transparency and solvent crack resistance can be obtained by a molding method such as injection molding, compression molding, or extrusion molding. However, when a crystalline resin is blended with an amorphous resin, the transparency of the resin tends to decrease. In an optical film used for an image display device, since a decrease in transparency leads to a decrease in image quality, it has been difficult to apply the resin composition disclosed in this document to an optical film.

  On the other hand, with the advancement of display quality and thinning of image display devices in recent years, the polarizing plate is also being thinned. The thin polarizing plate has poor stiffness as a film and is difficult to handle. For example, the pressure sensitive adhesive used to attach the polarizing plate to the display device adheres to the surface of the image display device or the polarizing plate surface. There was a problem that it would end up. The pressure-sensitive adhesive that adheres to the surface of the image display device or the surface of the polarizing plate is often wiped off with a soft cloth soaked with an organic solvent, but the organic solvent contacts the edge of the polarizing plate during the wiping operation. There was a concern of causing solvent cracks.

  Furthermore, in order to improve the display quality of a display device including a touch switch (touch panel), Japanese Patent Application Laid-Open No. 9-274536 (Patent Document 3) includes a display panel surface on which a polarizing plate is attached and a touch panel back surface. It has been proposed to bond using a liquid transparent adhesive (LOCA described above). As disclosed in Japanese Patent Application Laid-Open No. 2004-5540 (Patent Document 4), a technique for bonding a display panel surface and a touch panel back surface with a pressure-sensitive adhesive (adhesive) has also been proposed. When used, both the display panel and the touch panel are difficult to bend, so that it is difficult to bond them without mixing bubbles, and the liquid adhesive can be operated under atmospheric pressure and has higher productivity. The same applies when a transparent protective cover is attached to the display panel surface. If the display panel surface and the protective cover or touch panel are bonded together with a liquid transparent adhesive, reflection at the interface between them can be prevented, display quality is improved, and thinning is possible with integration, Since the adhesive is in a liquid state, dripping at the end of the polarizing plate occurs, and there is a concern that a solvent crack may occur due to the solvent constituting the adhesive.

  JP-A 2011-59663 (Patent Document 5) uses a liquid crystalline composition containing a (meth) acrylic compound having an oxetane ring in order to fix homeotropic alignment directly on a cyclic olefin-based resin film. Technology is disclosed.

JP-A-8-259784 JP 2007-16102 A Japanese Patent Laid-Open No. 9-274536 JP 2004-5540 A JP 2011-59663 A

  One problem of the present invention is that it is made of an olefin resin, and even when it comes into contact with organic chemicals such as a solvent during the assembly process of an image display device, it is less likely to be cracked or broken in the subsequent heat history, that is, solvent resistant. An object of the present invention is to provide a retardation film having excellent cracking properties. Another object of the present invention is to provide a composite polarizing plate having an optical compensation function and excellent solvent crack resistance by combining this retardation film with a polarizing plate.

  That is, according to the present invention, there is provided a retardation film having a protective film formed by cationic polymerization curing on both surfaces of an olefin resin film having an in-plane retardation of 50 nm or more. In the retardation film, the protective film is preferably formed from a curable resin composition containing an epoxy compound having no aromatic ring as a curable component.

  According to the present invention, there is also provided a composite polarizing plate in which the retardation film defined above and a polarizing plate having a polarizing film having a dichroic dye adsorbed and oriented on a polyvinyl alcohol resin are laminated. . In this composite polarizing plate, the retardation film having a protective film on both sides and the polarizing plate can be laminated via a pressure-sensitive adhesive.

  The retardation film of the present invention has excellent solvent crack resistance by having protective films formed by cationic polymerization curing on both surfaces. The composite polarizing plate in which the retardation film is laminated on the polarizing plate is also excellent in durability because the retardation film is not easily cracked or broken due to environmental changes. These retardation films and composite polarizing plates can be used effectively for display panels including liquid crystal panels and organic EL panels, particularly display panels that may come into contact with organic chemicals.

  In the present invention, a protective film is formed by cationic polymerization curing on both surfaces of an olefin resin film having an in-plane retardation of 50 nm or more to obtain a retardation film with improved solvent crack resistance.

[Olefin resin film]
The olefin resin has a structural unit derived from a cyclic olefin such as a chain aliphatic olefin such as ethylene or propylene, or norbornene or a substituted product thereof (hereinafter collectively referred to as a norbornene monomer). Resin. The olefin resin may be a copolymer using two or more kinds of monomers. Among these, a cyclic olefin resin mainly composed of a structural unit derived from a cyclic olefin is preferably used.

  A typical monomer constituting the cyclic olefin resin is norbornene. Here, norbornene is a compound in which one carbon-carbon bond of norbornane is a double bond, and it is named bicyclo [2,2,1] hept-2-ene according to the IUPAC nomenclature. Is. Examples of substituted norbornene include 3-substituted, 4-substituted, 4,5-disubstituted, etc., with the norbornene double bond located in the 1,2-position, and dicyclopentadiene. And dimethanooctahydronaphthalene can also be used as monomers constituting the cyclic olefin-based resin.

  The cyclic olefin-based resin having a norbornene-based monomer as a structural unit may have a norbornane ring in the main chain or may not have a norbornane ring. Examples of the norbornene-based monomer that forms a cyclic olefin-based resin having no norbornane ring in the main chain include, for example, those that become a five-membered ring by ring opening, typically norbornene, dicyclopentadiene, 1- or 4-methyl Examples include norbornene and 4-phenylnorbornene. When the cyclic olefin-based resin is a copolymer, the arrangement state of the molecules is not particularly limited, and may be a random copolymer, a block copolymer, or a graft copolymer. There may be.

  More specific examples of cyclic olefin resins include ring-opening polymers of norbornene monomers, ring-opening copolymers of norbornene monomers and other monomers, and addition of maleic acid and cyclopentadiene. Modified polymers, polymers or copolymers obtained by hydrogenation of these, addition polymers of norbornene monomers, addition copolymers of norbornene monomers and other monomers, and the like. Other monomers in the case of a copolymer include α-olefins, cycloalkenes, non-conjugated dienes and the like. Among these, the cyclic olefin-based resin is preferably a resin obtained by hydrogenating a ring-opening polymer using a norbornene-based monomer.

  The cyclic olefin-based resin can be subjected to a stretching process on the raw film formed therefrom to obtain a retardation film, and in addition to stretching, a shrinkable film having a predetermined shrinkage rate is bonded to the film. By applying, a retardation film having high uniformity and a large retardation value can be obtained.

  Examples of commercially available cyclic olefin resins using norbornene-based monomers are “Zeonex” and “Zeonor” sold by Nippon Zeon Co., Ltd., and JSR Corp. There is “Arton”. Commercially available products of these cyclic olefin-based resin films and stretched films thereof are also available, for example, “Zeonor Film” and JSR Co., Ltd., both of which are sold by Nippon Zeon Co., Ltd. "Arton Film" sold by Sekisui Chemical Co., Ltd. and "Essina Retardation Film" sold by Sekisui Chemical Co., Ltd.

  Moreover, the film which consists of a mixed resin which contains 2 or more types of olefin resin, and the film which consists of mixed resin of an olefin resin and another thermoplastic resin can also be used for retardation film. For example, examples of the mixed resin containing two or more types of olefin resins include a mixture of the above-described cyclic olefin resin and chain aliphatic olefin resin. When a mixed resin of an olefin resin and another thermoplastic resin is used, the other thermoplastic resin may be selected appropriately according to the purpose. Specific examples include polyvinyl chloride resin, cellulose resin, polystyrene resin, acrylonitrile / butadiene / styrene copolymer resin, acrylonitrile / styrene copolymer resin, (meth) acrylic resin, polyvinyl acetate resin, poly Vinylidene chloride resin, polyamide resin, polyacetal resin, polycarbonate resin, modified polyphenylene ether resin, polybutylene terephthalate resin, polyethylene terephthalate resin, polyphenylene sulfide resin, polysulfone resin, polyethersulfone resin, poly Examples include ether ether ketone resins, polyarylate resins, liquid crystalline resins, polyamideimide resins, polyimide resins, and polytetrafluoroethylene resins. A thermoplastic resin can be used individually by 1 type or in combination of 2 or more types. The thermoplastic resin can also be used after any appropriate polymer modification. Examples of polymer modification include copolymerization, crosslinking, molecular terminal modification, and stereoregularity.

  When using a mixed resin of an olefin resin and another thermoplastic resin, the content of the other thermoplastic resin is usually 50% by weight or less, and further 40% by weight or less based on the entire resin. preferable. By setting the content of other thermoplastic resin within this range, the absolute value of the photoelastic coefficient is small, the wavelength dispersion characteristic is good, and the retardation film has excellent durability, mechanical strength and transparency. Can be obtained.

  The olefin resin can be formed into a film by a casting method from a solution, a melt extrusion method, or the like. When forming a film from two or more kinds of mixed resins, for example, a method of producing a film by a casting method using a uniform solution obtained by stirring and mixing a resin component with a solvent at a predetermined ratio, The method of melt-mixing and producing a film by melt extrusion can be employed.

  The olefin resin film may contain components such as a residual solvent, a stabilizer, a plasticizer, an anti-aging agent, an antistatic agent, and an ultraviolet absorber as necessary. Further, a leveling agent can be contained in order to reduce the surface roughness.

The olefin resin film used in the present invention has an in-plane retardation, and the in-plane retardation is 50 nm or more. Here, the in-plane retardation Re, the refractive index in the in-plane slow axis direction n _x of the film, in-plane fast axis direction of the refractive index n _y, the refractive index in the thickness direction n _z, and the film It is defined by the following formula (1), where d is the thickness.
_{Re = (n x -n y)} × d (1)

  When the in-plane retardation Re is 50 nm or more, the stretched orientation as a retardation film is sufficiently achieved, and the effect of the solvent crack resistance according to the present invention is effectively exhibited. The greater the in-plane retardation Re, the greater the orientation by stretching, so the effect of developing the solvent crack resistance according to the present invention also increases. The in-plane retardation Re is appropriately set to a value required for a liquid crystal display device or an organic EL display device to which the retardation film of the present invention is applied, but is generally 300 nm or less.

In addition to this, there is a thickness direction retardation Rth, which is defined by the following equation (2). Further, the Nz coefficient that is a measure of the biaxiality of the retardation film is defined by the following equation (3).
Rth = _{[(n x + n y) /} 2-n z ] × d (2)
Nz factor _{= (n x -n z) /} (n x -n y) (3)

  When the Nz coefficient is 1, the stretched orientation of the retardation film is completely uniaxial, and the effect of the solvent crack resistance according to the present invention is the greatest. As the Nz coefficient increases, the orientation becomes biaxial, and the effect of the solvent crack resistance according to the present invention is hardly exhibited. Therefore, the Nz coefficient of the olefin resin film used in the present invention is preferably in the range of 1 to 3, more preferably in the range of 1 to 2. These phase difference values and Nz coefficients can be values at wavelengths near the center of visible light, but in this specification, values at a wavelength of 590 nm are used unless otherwise specified.

  The olefin resin film having the refractive index anisotropy as described above is an appropriate method such as free end longitudinal uniaxial stretching, tenter transverse uniaxial stretching, simultaneous biaxial stretching, and sequential biaxial stretching. In addition to appropriately adjusting the draw ratio and the draw speed, various temperatures such as preheating temperature, drawing temperature, heat set temperature, and cooling temperature at the time of drawing, and respective change patterns as appropriate By selecting, a film giving a desired refractive index anisotropy can be obtained.

Phase difference film, if the same value is in-plane retardation Re, should the thickness d is thin, the in-plane slow axis direction refractive indices n _x and plane fast axis direction refractive index n _y and the It means that the difference is large and therefore the orientation by stretching is large. The olefin resin film used in the present invention preferably has a thickness in the range of 10 to 50 μm, and more preferably in the range of 15 to 30 μm.

[Protective film]
Protective films are formed on both surfaces of the olefin resin film having the in-plane retardation described above. This protective film is formed by cationic polymerization curing. Therefore, a curable resin composition containing a cationic polymerizable component is used for forming the protective film. In addition to a cationic polymerizable component, a resin composition in which a radical polymerizable component such as an acrylic compound or a methacrylic compound is blended can also be used.

  Examples of the cationic polymerizable component include epoxy compounds and oxetane compounds. Of these, epoxy compounds are preferably used. The cationically polymerizable epoxy compound used for forming the protective film is a compound or oligomer having an average of two or more epoxy groups in the molecule and cured by reaction. Among the epoxy compounds, it is preferable to use an epoxy compound having no aromatic ring in the molecule as a main component from the viewpoint of weather resistance, refractive index, cationic polymerization, and the like. Examples of such epoxy compounds that do not contain an aromatic ring in the molecule include hydrogenated epoxy compounds, alicyclic epoxy compounds, and aliphatic epoxy compounds.

  A hydrogenated epoxy compound is a compound in which an aromatic ring of an aromatic epoxy compound is hydrogenated. The hydride of an aromatic epoxy compound is a nuclear water obtained by selectively subjecting an aromatic polyhydroxy compound, which is a raw material of an aromatic epoxy compound, to an aromatic ring in the presence of a catalyst and under pressure. The additive polyhydroxy compound can be obtained by a method of glycidyl etherification. Examples of the aromatic epoxy compound include bisphenol type epoxy compounds such as diglycidyl ether of bisphenol A, diglycidyl ether of bisphenol F, and diglycidyl ether of bisphenol S; phenol novolac epoxy resin, cresol novolac epoxy resin, and Examples include novolak-type epoxy resins such as hydroxybenzaldehyde phenol novolak epoxy resins; glycidyl ethers of tetrahydroxydiphenylmethane, glycidyl ethers of tetrahydroxybenzophenone, and polyfunctional epoxy resins such as epoxidized polyvinylphenol. If these raw materials are nucleated with an aromatic polyhydroxy compound typified by bisphenol as described above and epichlorohydrin is reacted with the hydroxyl group, a hydride of the aromatic epoxy compound is obtained. can get. Of these, hydrogenated diglycidyl ether of bisphenol A is preferable as the hydride of the aromatic epoxy compound.

  Next, the alicyclic epoxy compound will be described. This is a compound having at least one epoxy group bonded to the alicyclic ring in the molecule as shown in the following formula, and m in the formula is 2 to 5: Represents an integer.

Therefore, the alicyclic epoxy compound is a compound having at least one structure represented by the above formula and having a total of two or more epoxy groups in the molecule including the structure. A compound in which one or more hydrogen atoms in (CH ₂ ) _m in the above formula are removed and bonded to another chemical structure can be an alicyclic epoxy compound. Further, the hydrogen forming the alicyclic ring may be appropriately substituted with a linear alkyl group such as a methyl group or an ethyl group. Among them, it is preferable to use an epoxy compound having an epoxycyclopentane ring (m = 3 in the above formula) or an epoxycyclohexane ring (m = 4 in the above formula). Specific examples of the alicyclic epoxy compound are shown below.

  (1) Epoxycyclohexylmethyl epoxycyclohexanecarboxylates corresponding to the following formula (I):

In formula, R < ¹ > and R < ² > represents a hydrogen atom or a C1-C5 linear alkyl group mutually independently.

  (2) Epoxycyclohexanecarboxylates of alkanediol corresponding to the following formula (II):

In the formula, R ³ and R ⁴ each independently represent a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms, and n represents an integer of 2 to 20.

  (3) Epoxycyclohexylmethyl esters of dicarboxylic acid corresponding to the following formula (III):

In the formula, R ⁵ and R ⁶ each independently represent a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms, and p represents an integer of 2 to 20.

  (4) Polyethylene glycol epoxy cyclohexyl methyl ethers corresponding to the following formula (IV):

Wherein, R ⁷ and R ⁸ each independently represent a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms, q is an integer of 2 to 10.

  (5) Epoxycyclohexyl methyl ethers of alkanediol corresponding to the following formula (V):

In the formula, R ⁹ and R ¹⁰ independently represent a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms, and r represents an integer of 2 to 20.

  (6) Diepoxy trispiro compound corresponding to the following formula (VI):

In the formula, R ¹¹ and R ¹² each independently represent a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms.

  (7) Diepoxy monospiro compound corresponding to the following formula (VII):

In the formula, R ¹³ and R ¹⁴ each independently represent a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms.

  (8) Vinylcyclohexene diepoxides corresponding to the following formula (VIII):

In the formula, R ¹⁵ represents a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms.

  (9) Epoxycyclopentyl ethers corresponding to the following formula (IX):

In the formula, R ¹⁶ and R ¹⁷ each independently represent a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms.

  (10) Diepoxytricyclodecanes corresponding to the following formula (X):

In the formula, R ¹⁸ represents a hydrogen atom or a linear alkyl group having 1 to 5 carbon atoms.

Among these, typical alicyclic epoxy compounds are listed below.
3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate [compound of formula (I) wherein R ¹ = R ² = H],
3,4-epoxy-6-methylcyclohexylmethyl 3,4-epoxy-6-methylcyclohexanecarboxylate [compound of formula (I), R ¹ = 6-CH ₃ , R ² = 6-CH ₃ ],
Ethylene bis (3,4-epoxycyclohexanecarboxylate) [compound of formula (II) wherein R ³ = R ⁴ = H, n = 2],
Bis (3,4-epoxycyclohexylmethyl) adipate [compound of formula (III) wherein R ⁵ = R ⁶ = H, p = 4],
Bis (3,4-epoxy-6-methylcyclohexylmethyl) adipate [compound of formula (III), R ⁵ = 6-CH ₃ , R ⁶ = 6-CH ₃ , p = 4],
Ethylene glycol bis (3,4-epoxycyclohexylmethyl ether) [compound of formula (V), R ⁹ = R ¹⁰ = H, r = 2].

  Next, the aliphatic epoxy compound will be described. The aliphatic epoxy compound includes an aliphatic polyhydric alcohol or a polyglycidyl ether of an alkylene oxide adduct thereof. Examples of these are 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, glycerin triglycidyl ether, trimethylolpropane triglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol Polyglycidyl of a polyether polyol obtained by adding one or more alkylene oxides (ethylene oxide or propylene oxide) to an aliphatic polyhydric alcohol such as diglycidyl ether, ethylene glycol, propylene glycol or glycerin Examples include ether.

  The epoxy compounds may be used alone or in combination with a plurality of epoxy compounds. In addition, a small amount of a monofunctional epoxy compound, that is, a compound having one epoxy group in the molecule can be blended for the purpose of improving coating properties.

  The epoxy compound used in the present invention has an epoxy equivalent of usually 30 to 3,000 g / equivalent, preferably 50 to 1,500 g / equivalent. If the epoxy equivalent is less than 30 g / equivalent, the flexibility of the protective film after curing may be reduced, or the adhesive strength to the olefin resin film may be reduced. On the other hand, if the epoxy equivalent exceeds 3,000 g / equivalent, the compatibility with other components may decrease.

  In the present invention, the protective films on both sides of the olefin resin film are formed by cationic polymerization curing. Therefore, it is preferable to add a cationic polymerization initiator to the curable resin composition containing a cationic polymerizable component for forming a protective film. The cationic polymerization initiator generates a cationic species or a Lewis acid by irradiation or heating of active energy rays such as visible light, ultraviolet rays, X-rays, and electron beams, and a polymerization reaction of a cationic polymerizable component, typically an epoxy compound. To start.

  When a photocationic polymerization initiator is used, a protective film can be formed at room temperature, and the need to consider the heat resistance of the olefin resin film or distortion due to expansion can be reduced, so that the protective film can be formed satisfactorily. In addition, since the photocationic polymerization initiator acts catalytically by light, it is excellent in storage stability and workability even when mixed with a cationically polymerizable component. Examples of compounds that generate cation species and Lewis acids 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.

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'-diphenylsulfoniodiphenyl sulfide hexafluorophosphate,
4- (p-tert-butylphenylcarbonyl) -4'-diphenylsulfoniodiphenyl sulfide hexafluoroantimonate,
4- (p-tert-butylphenylcarbonyl) -4'-di (p-toluyl) sulfonio-diphenyl sulfide tetrakis (pentafluorophenyl) borate and the like.

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

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

  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 have ultraviolet absorption characteristics even in a wavelength region of 300 nm or more, and can provide a cured product having excellent curability and good mechanical strength and adhesive strength. It is done.

Photocationic polymerization initiators are readily available from the market. Examples of commercially available products are “Kayarad PCI-220” and “Kayarad PCI-620” sold by Nippon Kayaku Co., Ltd., and “UVI-” sold by Dow Chemical. "6990", "Adekaoptomer SP-150" and "Adekaoptomer SP-170" sold by ADEKA Corporation, "CI-5102", "CIT-1370" sold by Nippon Soda Co., Ltd. "," CIT-1682 "," CIP-1866S "," CIP-2048S "and" CIP-2064S "," DPI-101 "," DPI-102 "," DPI "sold by Midori Chemical Co., Ltd. -103 ”,“ DPI-105 ”,“ MPI-103 ”,“ MPI-105 ”,“ BBI-101 ”,
“BBI-102”, “BBI-103”, “BBI-105”, “TPS-101”, “TPS-102”, “TPS-103”,
There are "TPS-105", "MDS-103", "MDS-105", "DTS-102" and "DTS-103", "PI-2074" sold by Rhodia.

  The compounding amount of the photocationic polymerization initiator is usually 0.5 to 20 parts by weight, preferably 1 part by weight or more, and preferably 15 parts per 100 parts by weight of the cationically polymerizable component typified by an epoxy compound. Less than parts by weight. When the amount is too small, the curing becomes insufficient, and the mechanical strength and adhesive strength of the protective film are lowered. On the other hand, if the amount is too large, the amount of ionic substances in the protective film is increased, so that the hygroscopic property of the protective film is increased and the durability performance is likely to be lowered.

  Furthermore, a photosensitizer can be used in combination as necessary. By using a photosensitizer, the reactivity is improved, and the mechanical strength and adhesive strength of the cured product can be improved. Examples of the photosensitizer include carbonyl compounds, organic sulfur compounds, persulfides, redox compounds, azo and diazo compounds, halogen compounds, and photoreductive dyes. Specific photosensitizers include, for example, benzoin derivatives such as benzoin methyl ether, benzoin isopropyl ether, α, α-dimethoxy-α-phenylacetophenone; benzophenone, 2,4-dichlorobenzophenone, o-benzoylbenzoic acid Benzophenone derivatives such as methyl, 4,4′-bis (dimethylamino) benzophenone, 4,4′-bis (diethylamino) benzophenone; thioxanthone derivatives such as 2-chlorothioxanthone and 2-isopropylthioxanthone; 2-chloroanthraquinone, Anthraquinone derivatives such as 2-methylanthraquinone; acridone derivatives such as N-methylacridone and N-butylacridone; other α, α-diethoxyacetophenone, benzyl, fluorenone, oxa Intons, uranyl compounds, halogen compounds, and the like. These photosensitizers may be used alone or in combination. The photosensitizer is preferably contained in the range of 0.1 to 20 parts by weight when the photocationically polymerizable resin composition for forming the protective film is 100 parts by weight.

  Next, the thermal cationic polymerization initiator will be described. Examples of the compound that generates a cationic species or a Lewis acid by heating include benzylsulfonium salt, thiophenium salt, thiolanium salt, benzylammonium, pyridinium salt, hydrazinium salt, carboxylic acid ester, sulfonic acid ester, and amine imide. Thermal cationic polymerization initiators are also readily available from the market. Examples of commercially available products are all trade names, “ADEKA OPTON CP77” and “ADEKA OPTON CP66” sold by ADEKA Corporation, “CI-2639” and “" sold by Nippon Soda Co., Ltd. CI-2624 ”,“ Sun-Aid SI-60L ”,“ Sun-Aid SI-80L ”and“ Sun-Aid SI-100L ”sold by Sanshin Chemical Industry Co., Ltd.

  It is also a useful technique to combine the photocationic polymerization and the thermal cationic polymerization described above.

  The curable resin composition for forming a protective film in the present invention may contain a compound that promotes cationic polymerization, such as an oxetane compound or a polyol compound, in addition to an epoxy compound. As described above, the oxetane compound is also a compound that is cured by cationic polymerization.

  An oxetane compound is a compound having a 4-membered ring ether in the molecule, such as 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, phenol novolac oxetane and the like. Oxetane compounds are also readily available from the market. Examples of commercial products are trade names sold by Toagosei Co., Ltd., “Aron Oxetane OXT-101”, “Aron Oxetane OXT-121”, “Aron Oxetane OXT-211”, “Aron” There are Oxetane OXT-221 ”and“ Aron Oxetane OXT-212 ”. The oxetane compound is usually used in a proportion of 5 to 95% by weight, preferably 30 to 70% by weight in the curable resin composition.

  The polyol compound preferably has no acidic group other than a phenolic hydroxyl group. For example, a polyol compound having no functional group other than a hydroxyl group, a polyester polyol compound, a polycaprolactone polyol compound, and a polyol compound having a phenolic hydroxyl group. And polycarbonate polyol compounds. The molecular weight of these polyols is usually 48 or more, preferably 62 or more, more preferably 100 or more, and preferably 1,000 or less. The compounding quantity of these polyol compounds is 50 weight% or less normally in a curable resin composition, Preferably it is 30 weight% or less.

  Furthermore, unless the effects of the present invention are impaired, the curable resin composition has other additives such as ion trapping agents, antioxidants, chain transfer agents, sensitizers, tackifiers, thermoplastic resins, fillings. An agent, a flow regulator, a plasticizer, an antifoaming agent, an infrared absorber, and the like can be blended. Examples of the ion trapping agent include inorganic compounds such as powdered bismuth, antimony, magnesium, aluminum, calcium, titanium, and mixtures thereof. Antioxidants include, for example, hindered phenolic antioxidants. Examples of the infrared absorber include cyanine-based, oxonol-based, thiopyrylium squarylium-based, thiopyrylium croconium-based, pyrylium squarylium-based, and pyrylium croconium-based compounds. If a protective film is formed from a curable resin composition to which an infrared absorber is added, the resulting retardation film or composite polarizing plate can be easily cut by irradiation with laser light.

  The protective film is formed by coating an uncured curable resin composition on the surface of the olefin-based resin film, and then irradiating the coating layer with active energy rays such as visible light, ultraviolet rays, X-rays, electron beams, or the like. / And cured by heating to form. The protective film on both sides of the olefin resin film may be formed by repeating the above coating and curing for each side of the film, or by applying a curable resin composition on both sides of the film and simultaneously curing both sides. You may form by doing.

  Various coating methods such as a doctor blade, a wire bar, a die coater, a comma coater, and a gravure coater can be used to apply the curable resin composition to the olefin resin film. In addition, since each coating method has an optimum viscosity range, it is also a useful technique to adjust the viscosity using a solvent. As the solvent for this purpose, a solvent that dissolves the curable resin composition satisfactorily without reducing the optical performance of the olefin resin film is used. For example, organic solvents such as hydrocarbons typified by toluene and esters typified by ethyl acetate can be used.

When curing by irradiation with active energy rays, the light source used has a light emission distribution at a wavelength of 400 nm or less, 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 And metal halide lamps. Although the light irradiation intensity to the curable resin composition is determined for each target composition, the irradiation intensity in the wavelength region effective for activating the initiator is, for example, about 0.1 to 100 mW / cm ^2. What should be done. If the light irradiation intensity to the curable resin composition is small, the reaction time becomes too long. On the other hand, if it is large, the heat radiation from the lamp and the heat generated during the polymerization of the composition cause the protective film after curing. There is a possibility of causing yellowing and deterioration of the olefin resin film. The light irradiation time to the curable resin composition is also controlled for each composition, but is set so that the integrated light amount represented by the product of irradiation intensity and irradiation time is 10 to 5,000 mJ / cm ^2. It is preferable. If the integrated light amount to the curable resin composition is small, active species derived from the initiator may not be sufficiently generated, and the resulting protective film may be insufficiently cured, while increasing the integrated light amount. If so, the irradiation time becomes longer, which is disadvantageous for improving productivity.

  In the case of curing by heating, heating may be performed under generally known conditions, and heating is usually performed at a temperature higher than the temperature at which the thermal cationic polymerization initiator compounded in the curable resin composition generates a cationic species or a Lewis acid. For example, at a temperature of about 50 to 200 ° C.

  In the case of curing under any condition of irradiation with active energy rays or heating, it is preferable to cure under conditions where various properties such as optical characteristics and transmittance of the olefin resin film do not change. The thickness of the protective film is preferably 0.1 μm or more and 10 μm or less, more preferably 0.1 μm or more and 5 μm or less, from the viewpoints of thin and light weight, protection function, and handleability. The protective film provided on both surfaces of the olefin resin film may have different compositions on the front and back sides.

  This protective film may have a phase difference and be provided with an optical compensation function, or may not have a phase difference. For example, the protective film provided on one surface of the olefin-based resin film may have no retardation, and the protective film provided on the other surface may have a retardation and be provided with an optical compensation function. In the case of imparting a retardation to the protective film, a liquid crystalline compound is contained in the curable resin composition for forming the protective film, and the liquid crystalline compound is aligned by coating on the film, and then cationic polymerization is performed. A method of curing by the method and fixing the alignment state is preferably employed. A technique for forming an oriented protective film by applying a curable resin composition containing a liquid crystalline compound to an olefin-based resin film is disclosed in Japanese Patent Application Laid-Open No. 2011-59663. In accordance with the disclosure of this document, a curable resin composition in which a liquid crystalline compound is blended with a (meth) acrylic compound having an oxetane ring is applied to an olefin-based resin film, and is cured by cationic polymerization. A protective film provided with a phase difference can be formed.

[Polarizing plate and composite polarizing plate]
According to the present invention, a retardation film having protective films formed on both sides of an olefin resin film can be combined with a polarizing plate to form a composite polarizing plate. The polarizing plate used here is a linear polarizing plate, that is, an optical element having a function of extracting linearly polarized light from incident natural light, and this function is a polarizing film in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol resin. Brought about by.

  The polarizing film is produced by subjecting a polyvinyl alcohol resin film to uniaxial stretching, dyeing with a dichroic dye, and crosslinking treatment using boric acid after dyeing. Uniaxial stretching can be performed before dyeing, can be performed simultaneously with dyeing, or can be performed simultaneously with, for example, crosslinking treatment after dyeing. Of course, you may perform uniaxial stretching in these several steps. By combining uniaxial stretching and dyeing with a dichroic dye, the dichroic dye is adsorbed and oriented on the polyvinyl alcohol-based resin film, absorbs linearly polarized light having a vibration surface in the orientation direction, and has a vibration surface orthogonal thereto. A function of transmitting linearly polarized light is exhibited. As the dichroic pigment, iodine or a dichroic organic dye is generally used.

  A polarizing film itself in which a dichroic dye is adsorbed and oriented to such a polyvinyl alcohol-based resin can be used as a polarizing plate and can be laminated on the retardation film described above. Or it becomes a polarizing plate in the state by which the protective film was bonded on both surfaces. The protective film to be bonded to the polarizing film may be a transparent resin film, and as the resin, for example, an acetylcellulose-based resin typified by triacetylcellulose, or the ring described above typified by norbornene-based resin. A chain olefin resin represented by an olefin resin and a polypropylene resin is used.

  An adhesive is generally used for bonding the protective film to the polarizing film. The adhesive for this purpose is a water-based adhesive whose representative example is an aqueous solution of a polyvinyl alcohol-based resin, an ultraviolet curable adhesive containing an epoxy compound or an acrylic compound as a curable component, and a polymerization initiator. be able to.

[Lamination of retardation film and polarizing plate]
For the lamination of the retardation film and the polarizing plate, a pressure sensitive adhesive can be used. The pressure-sensitive adhesive is composed of an acrylic pressure-sensitive adhesive in which an acrylic resin obtained by copolymerizing a small amount of a functional group-containing monomer with an acrylate ester is blended with a crosslinking agent composed of an isocyanate compound or the like. It is common.

[Chip cut of composite polarizing plate]
The composite polarizing plate obtained as described above is usually manufactured in a long roll shape or a large sheet shape, and in order to obtain a composite polarizing plate having a desired shape and an optical axis, Furthermore, it is cut (chip cut) by a cutting tool having a sharp blade or by irradiation with laser light. Furthermore, the outer peripheral end may be continuously cut by a rotary blade or a fly-cut method as necessary. In the composite polarizing plate of the present invention, in order to prevent fine cracks generated at the time of cutting from becoming a base point of chemical cracks, it is preferable to cut by laser light irradiation or to cut the end face after cutting. .

[Display panel]
A composite polarizing plate in which a retardation film and a polarizing plate are laminated is attached to a display element such as a liquid crystal cell or an organic EL element to form a display panel. At this time, generally, it arrange | positions so that the phase difference film side may face a display element. An acrylic pressure-sensitive adhesive is usually used for attaching the composite polarizing plate to the display element. Since display elements such as liquid crystal cells and organic EL elements often have a glass surface, the pressure-sensitive adhesive used for sticking to them is in addition to the acrylic resin and crosslinking agent described above. In general, a silane compound is blended in order to improve adhesion to glass.

  As for the retardation film of this invention, the protective film is formed on both surfaces of the olefin resin film to which the phase difference was provided. Although the olefin-based resin is exposed on the end face, the presence of the protective film makes it stick to the display cell as a composite polarizing plate, and touches organic chemicals such as solvents when assembling the display panel. Even if it receives a thermal history in that state, it is possible to effectively prevent so-called solvent cracks, which are likely to enter the direction in which the stress of the olefin resin film is applied (the direction in which the draw ratio is large, that is, the slow axis direction). it can.

  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.

[Example 1]
(A) Preparation of photocurable resin composition and measurement of physical properties The following components were mixed and defoamed to prepare a photocurable resin composition in a liquid state.

3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate 75 parts 1,4-butanediol diglycidyl ether 20 parts 2-ethylhexyl glycidyl ether 5 parts triarylsulfonium hexafluorophosphate-based photocationic polymerization initiator
2.25 parts

  The photocationic polymerization initiator used was obtained in the form of a 50% propylene carbonate solution. The blending amount (2.25 parts) shown above is the solid content.

(B) Production of Retardation Film with Protective Films Formed on Both Sides Retardation Film Consisting of Cyclic Olefin Resin [Product Name “Arton Film” Obtained from JSR Corporation, Width Direction of Long Roll Film (TD) Is subjected to corona discharge treatment on one side of Re = 115 nm, Nz coefficient = 1.4, thickness 20 μm), and the photocurable resin composition prepared above is cured on the corona discharge treatment side. Coating was performed using a bar coater so that the subsequent film thickness was about 2 μm. Using a UV irradiation device with a belt conveyor to which a UV lamp “D bulb” manufactured by Fusion UV Systems Co., Ltd. is attached, the photocurable resin composition is cured by irradiating with UV light so that the integrated light amount becomes 250 mJ / cm ^2. It was. Similarly, on the other side of “Arton Film”, corona discharge treatment, application of the photocurable resin composition, and curing of the photocurable resin composition by ultraviolet irradiation are performed, and a protective film is formed on both sides of “Arton Film”. A retardation film having the following characteristics was prepared.

(C) Preparation of aqueous adhesive 3 parts of carboxyl group-modified polyvinyl alcohol [“KL-318” obtained from Kuraray Co., Ltd.] is dissolved in 100 parts of water, and polyamide epoxy which is a water-soluble epoxy resin is dissolved in the aqueous solution. 1.5 parts of a system additive [trade name “Smile Resin 650 (30)” obtained from Taoka Chemical Co., Ltd., aqueous solution with a solid content of 30%] was added to obtain a water-based adhesive.

(D) Production of Polarizing Plate A polyvinyl alcohol film having an average degree of polymerization of about 2,400 and a saponification degree of 99.9 mol% or more and a thickness of 75 μm was uniaxially stretched about 5 times in a dry process, and further maintained a tension state. The sample was immersed in pure water at 60 ° C. for 1 minute, and then immersed in an aqueous solution having a weight ratio of iodine / potassium iodide / water of 0.05 / 5/100 at 28 ° C. for 60 seconds. Then, it was immersed in an aqueous solution having a weight ratio of potassium iodide / boric acid / water of 8.5 / 8.5 / 100 at 72 ° C. for 300 seconds. Subsequently, it was washed with pure water at 26 ° C. for 20 seconds and then dried at 65 ° C. to obtain a polarizing film in which iodine was adsorbed and oriented on polyvinyl alcohol.

  On one surface of this polarizing film, a 40 μm thick triacetyl cellulose film (trade name “Konica Katak KC4UYW” obtained from Konica Minolta Opto Co., Ltd.) having a saponified surface was bonded. On one side, a corona discharge treatment is applied to one side of a 23 μm-thick cyclic olefin resin film (trade name “Zeonor Film ZF14-023” obtained from Nippon Zeon Co., Ltd.), and the corona discharge treatment surface is applied. Thus, a polarizing plate was produced. For pasting, each of the water-based adhesives previously shown was used, and after the pasting, the triacetyl cellulose film and the cyclic olefin resin film were adhered to the polarizing film by drying at 80 ° C. for 5 minutes. The obtained polarizing plate was then cured at 40 ° C. for 168 hours.

(E) Pressure-sensitive adhesive sheet The following were obtained from pressure-sensitive adhesive manufacturers.

Pressure sensitive adhesive sheet A: Acrylic resin mainly composed of butyl acrylate and copolymerized with a small amount of acrylic acid is blended with isocyanate cross-linking agent and UV curable component, and the storage elastic modulus is increased by UV curing. The obtained 15 μm thick adhesive layer is formed on a 38 μm thick polyethylene terephthalate film (separator).
Pressure-sensitive adhesive sheet B: 25 μm thick in which an isocyanate-based crosslinking agent and a silane compound are blended in an acrylic resin mainly composed of butyl acrylate and copolymerized with a small amount of 2-hydroxyethyl acrylate and acrylic acid The pressure-sensitive adhesive layer is formed on a polyethylene terephthalate film (separator) having a thickness of 38 μm.

(F) Preparation of composite polarizing plate After pressure-sensitive adhesive sheet A was bonded to the cyclic olefin resin film side of the polarizing plate prepared in (D) above and the separator was peeled off, the pressure-sensitive adhesive surface Further, the retardation film having protective films on both surfaces produced in (B) above was bonded so that the slow axis of the retardation film and the absorption axis of the polarizing plate were almost orthogonal. In addition, a pressure sensitive adhesive sheet B was bonded to the surface of the retardation film opposite to the polarizing plate to produce a composite polarizing plate having the following layer structure (however, the display of the adhesive layer was omitted). .

Triacetyl cellulose film /
Polarizing film /
Cyclic olefin resin film “Zeonor film ZF14-023” /
Pressure sensitive adhesive sheet A /
Cured protective film /
Cyclic olefin-based retardation film “Arton Film” /
Cured protective film /
Pressure sensitive adhesive sheet B /
Separator

  In addition, in laminating the pressure sensitive adhesive sheet to each film, the corona discharge treatment was applied to each laminating surface with an output intensity of 280 W while moving each film or sheet at a speed of 10 m / min. The adhesive sheet and the film were bonded together after improving adhesion.

[Example 2]
A retardation film having a protective film formed on both surfaces and a composite polarizing plate were prepared in the same manner as in Example 1 except that the composition of the photocurable resin composition was changed as follows.

3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate 70 parts 1,4-butanediol diglycidyl ether 20 parts 2-ethylhexyl glycidyl ether 10 parts triarylsulfonium hexafluorophosphate-based photocationic polymerization initiator
2.25 parts

[Comparative Example 1]
A composite polarizing plate was produced in the same manner as in Example 1 except that a protective film was not formed on the retardation film “Arton film” made of a cyclic olefin resin, and the protective film was used as it was.

[Evaluation test of optical characteristics]
Retardation measurement made by Oji Scientific Instruments Co., Ltd. with respect to the retardation film formed with protective films on both surfaces produced in Examples 1 and 2 and the retardation film with no protective film used in Comparative Example 1 The in-plane phase difference was measured using the device “KOBRA-WPR”, and the haze was measured using a haze meter “HM-150” manufactured by Murakami Color Research Laboratory. The results are shown in Table 1. . From the results of Table 1, it was confirmed that the retardation films of Examples 1 and 2 in which a protective film was formed compared to the retardation film of Comparative Example 1 without a protective film, virtually showed no change in optical properties. It was.

[Evaluation test of mechanical properties]
A test piece having a width of 10 mm and a length of 200 mm was cut out from the retardation film having protective films formed on both surfaces produced in Examples 1 and 2 and the retardation film having no protective film used in Comparative Example 1. The distance between the marked lines was set to 100 mm, and this was set on a universal testing machine “Autograph AG-I” manufactured by Shimadzu Corporation. A tensile test was performed at a tensile speed of 50 mm / min to obtain Young's modulus and breaking strength. . The test is performed for each of the test piece cut out with the machine direction (length direction, MD) of the long roll film as the long side and the test piece cut out with the width direction (MD) of the long roll film as the long side, The results are shown in Table 2. From the results in Table 2, it was confirmed that the retardation films of Examples 1 and 2 in which a protective film was formed compared to the retardation film of Comparative Example 1 without a protective film, showed virtually no change in mechanical strength. It was.

[Evaluation test for solvent crack resistance]
From the composite polarizing plates produced in Examples 1 and 2 and Comparative Example 1, the size is 60 mm × 100 mm, the long side (side of 100 mm) is the reference (0 °), and the cyclic olefin phase difference film and Super Cutter (Kanno Seiki Co., Ltd.) so that the counterclockwise direction when viewed with the pressure-sensitive adhesive is positive, the absorption axis of the polarizing plate is 83 °, and the slow axis of the retardation film is 173 ° And manufactured by Seisakusho. The separator is peeled off from each composite polarizing plate, and the exposed pressure-sensitive adhesive surface is bonded to alkali-free glass (trade name “Eagle-XG” obtained from Corning), and 20 at a temperature of 50 ° C. and a pressure of 0.5 MPa. The autoclave process was performed for a minute, and the composite polarizing plate was sufficiently adhered to the alkali-free glass.

  Next, oleic acid [the first grade reagent obtained from Wako Pure Chemical Industries, Ltd.] is applied to the short-side end face of the glass-bonded composite polarizing plate (that is, the end face substantially orthogonal to the slow axis of the retardation film). It was dripped. The cover glass was covered so that the oleic acid (solvent) would not evaporate and left for 3 hours, and then the cover glass was removed and the solvent was wiped off. Then, it was put in a thermal shock test tank set at a holding time of 30 minutes at a temperature of −40 ° C., a holding time of 30 minutes at a temperature of 85 ° C., and a temperature transition time of 0 minutes, and “30 at a temperature of −40 ° C. The thermal shock test was repeated for 50 cycles (50 hours) of “minute hold → change temperature to 80 ° C. → hold 30 minutes at that temperature → change temperature to −40 ° C.”. Moreover, about the glass bonding composite polarizing plate of the comparative example 1, the same thermal shock test as the above was done even in the state where oleic acid (solvent) is not dripped.

  For the glass-bonded composite polarizing plate after the test, the end surface on which the solvent was dropped was observed from the polarizing plate side, and the presence or absence of cracks in the retardation film was confirmed. The length was measured. The results are shown in Table 3.

  As can be seen from Table 3, in Comparative Example 1 in which a composite polarizing plate was prepared from a retardation film in which no protective film was formed, no crack was generated when a thermal shock test was performed without contact with a solvent. However, in the thermal shock test after the solvent touched the end face, a crack occurred on the end face touched by the solvent. On the other hand, in Example 1 and 2 which produced the composite polarizing plate from the retardation film in which the protective film was formed, the crack did not generate | occur | produce also in the thermal shock test after a solvent touched an end surface. From this, it was confirmed that forming a cured protective film on both surfaces of a retardation film made of an olefin resin is effective in improving the solvent crack resistance, although the end surface itself is in contact with the solvent.

Claims (4)

  A retardation film comprising protective films formed by cationic polymerization curing on both surfaces of an olefin resin film having an in-plane retardation of 50 nm or more.   The retardation film according to claim 1, wherein the protective film is formed from a curable resin composition containing an epoxy compound having no aromatic ring as a curable component.   3. A composite polarizing plate comprising the retardation film according to claim 1 and a polarizing plate having a polarizing film having a dichroic dye adsorbed and oriented on a polyvinyl alcohol resin.   The composite polarizing plate according to claim 3, wherein the retardation film and the polarizing plate are laminated via a pressure sensitive adhesive.