TWI475261B - Polarizing plate and production method thereof - Google Patents

Description

Polarizing plate and manufacturing method thereof

The present invention relates to a polarizing plate used in a liquid crystal display device or the like and a method of manufacturing the same.

The polarizing plate is used as a supply element for polarized light in a liquid crystal display device, and a detecting element for polarized light. Conventionally, a polarizing plate is used for at least one side of a polarizer composed of a polyvinyl alcohol (PVA) film which is doped with iodine or the like, and is bonded to a protective film composed of cellulose triacetate (TAC). Wait. At this time, if the protective film itself has birefringence, the function as a polarizing plate is greatly reduced. Therefore, in order to prevent this, a TAC film having no optical anisotropy produced by a solvent casting method has been used.

In the above-mentioned conventional polarizing plate, in order to extend the PVA film at a high magnification, a large stress is generated in the relaxation direction. The protective film needs to have rigidity to withstand this stress. When TAC is used as a protective film, in a large-screen use such as a liquid crystal television, the contraction stress of the polarizer at the peripheral portion of the film sometimes exceeds the rigidity of the TAC and causes deformation. The birefringence of the TAC protective film resulting from this causes fading to occur.

In JP-A-2005-92112, a cured product of an active energy ray-curable resin composition has been proposed as a substitute for a TAC protective film. According to this technique, a polarizing plate having a small birefringence and excellent moist heat resistance can be obtained. However, only the birefringence is small, and the birefringence at which the contraction stress of the polarizer described above is large is still changed, so that the function as a polarizing plate is impaired.

Prior technical literature

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2005-92112

SUMMARY OF THE INVENTION An object of the present invention is to provide a polarizing plate which is transparent and which does not easily change its birefringence even if stress is applied, and a method for producing the same.

As a result of intensive studies to achieve the above object, the present inventors have found that a polarizing plate protected by at least one surface of a polarizing mirror by a protective film composed of a cured product of an active energy ray-curable resin composition of a specific resin, a protective film thereof In order to be transparent, the birefringence is not easily changed even if stress is applied, and the present invention has been completed.

That is, the present invention provides a polarizing plate having a structure in which at least one surface of a polarizing mirror is protected by a protective film made of a resin, characterized in that the resin is an active energy ray-curable resin containing a cellulose derivative. a cured product of the composition; the cellulose derivative, which is a part of the hydroxyl group of the glucose skeleton, is substituted with a group containing an unsaturated carboxylic acid thiol group. The above-mentioned group containing an unsaturated carboxylic acid thiol group contains a group represented by the following formula (1):

(wherein R ¹ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; A ¹ and A ² are the same or different and represent a divalent organic group; and X ¹ and X ² are the same or different, and An oxygen atom, a sulfur atom, or an -NR ² - group; R ² represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms; n is 0 or 1).

The cellulose derivative is preferably at least one selected from the group consisting of a methyl cellulose derivative, an ethyl cellulose derivative, and a cellulose acetate derivative.

The present invention also provides a method of producing a polarizing plate, characterized in that an active energy ray-curable resin composition containing a cellulose derivative is coated on at least one side of a polarizing mirror, and then the active energy ray-curable resin composition is applied The film is cured to form a protective film; the cellulose derivative, which is a part of the hydroxyl group of the glucose skeleton, is substituted with a group containing an unsaturated carboxylic acid thiol group.

According to the polarizing plate of the present invention, since the cured product of the active energy ray-curable resin composition containing the specific resin is used as the protective film of the polarizer, the protective film is transparent, and the birefringence is not easily changed even if stress is applied. In addition, the birefringence is also small. According to the production method of the present invention, a polarizing plate having the above-described excellent characteristics can be easily produced.

Form of implementing the invention

The polarizing plate of the present invention has a structure in which at least one surface of the polarizer is protected by a protective film made of a resin. The polarizer is not particularly limited, and may be extended by using a substrate doped with iodine or a dichroic dye in polyvinyl alcohol (PVA), an acetal, an ethylene-vinyl acetate copolymer, or a saponified product thereof. The obtained film, or the film obtained by the crosslinking treatment, or the like. Among these, the iodine-containing polyvinyl alcohol film obtained by stretching polyvinyl alcohol doped with iodine or the above-mentioned cross-linking with boric acid or the like is particularly preferable.

In the present invention, as the resin constituting the protective film, a cured product of an active energy ray-curable resin composition containing a cellulose derivative in which a part of a hydroxyl group of a glucose skeleton is unsaturated is used is used. Substituted by a carboxylic acid thiol group. The cellulose derivative in which the hydroxyl group of the glucose skeleton is substituted with a group containing an unsaturated carboxylic acid thiol group may be used singly or in combination of two or more. In the present specification, the active energy ray-curable resin composition means a composition capable of forming a cured resin by irradiation with an active energy ray.

a cellulose derivative in which a hydroxyl group of a glucose skeleton is substituted with a group containing an unsaturated carboxylic acid thiol group, and a part of a hydroxyl group at the 2, 3, and 6 positions of the glucose skeleton in the molecule is contained in an unsaturated carboxylic acid. The radical-curable cellulose derivative substituted with the thiol group is not particularly limited. Examples of the unsaturated carboxylic acid thiol group include an acrylonitrile group, a methacryl fluorenyl group, an α-ethyl propylene fluorenyl group, an α-propyl acryl fluorenyl group, an α-butyl acryl fluorenyl group, a decyl decenoate group, and the like. The unsaturated carboxylic acid sulfhydryl group having a carbon number of about 3 to 10 or the like.

A representative example of the group containing an unsaturated carboxylic acid thiol group is a group represented by the above formula (1). In the formula (1), R ¹ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; A ¹ and A ² are the same or different and represent a divalent organic group; and X ¹ and X ² are the same or different. And represents an oxygen atom, a sulfur atom, or an -NR ² - group; R ² represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms; and n is 0 or 1.

Examples of the alkyl group having 1 to 4 carbon atoms in R ¹ include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, and a tert-butyl group. As R ¹ , a hydrogen atom or a methyl group is particularly preferable.

Examples of the divalent organic group in A ¹ and A ² include a divalent hydrocarbon group, a divalent heterocyclic group, or two or more of these groups, or one or two or more linking groups. Combine the base of the 2 price.

Examples of the divalent hydrocarbon group include a methylene group, an exoethyl group, a propyl group, a trimethylene group, a butyl group, a pentyl group, a hexyl group, a decyl group, a fluorene group, and a twelfth group. a chain or branched acetylene group having 1 to 20 carbon atoms; a cyclopentyl group, a cyclohexylene group, a cyclooctyl group, a pentylene group, a hexylene group, an adamantanediyl group, etc. 3 to a 15-membered divalent alicyclic hydrocarbon group (cycloalkylene group, a divalent crosslinked alicyclic group, etc.); an arylene group such as a phenyl group or a naphthyl group; and a combination of two or more valences Base and so on.

Examples of the divalent heterocyclic group include an oxacyclohexane ring, an oxetane ring, an oxolane ring, a pyrrolidine ring, a piperidine ring, a furan ring, a thiophene ring, a pyridine ring, and a quinoline. A group in which at least one hydrogen atom, a sulfur atom, and a nitrogen atom are contained in a ring or the like, and a hydrogen atom is removed from an aromatic or non-aromatic ring.

The divalent hydrocarbon group and the divalent heterocyclic group may have a substituent. Examples of the substituent include a halogen atom such as a fluorine atom or a chlorine atom; an alkyl group having a carbon number of 1 to 6 such as a methyl group, an ethyl group, a propyl group, an isopropyl group or a butyl group; and a trifluoromethyl group; And the like, wherein the carbon number is 1 to 6 haloalkyl groups; the methoxy group, the ethoxy group, the propoxy group, the isopropoxy group, the butoxy group and the like have an alkoxy group having 1 to 6 carbon atoms; The carbon number of the fluorenyl group, the benzamidine group or the like is 1 to 10, and the carbon number of the ethoxy group, the propenyloxy group, the benzamidineoxy group, the (meth)acryloxy group, and the like is 1 to An alkoxycarbonyl group having a carbon number of 2 to 6 such as a methoxycarbonyl group or an ethoxycarbonyl group; a nitro group; a cyano group;

Examples of the linking group include -O-, -S-, -NR ³ -, -CO-, and the like. R ³ above represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.

Examples of the alkyl group having 1 to 6 carbon atoms in R ² and R ³ include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a t-butyl group, a pentyl group, a hexyl group, and the like. .

The cellulose derivative in which a part of the hydroxyl group of the glucose skeleton is substituted with a group containing an unsaturated carboxylic acid thiol group may, for example, be a part or the whole of the etherified cellulose ether derivative of the glucose skeleton, and the remainder of the glucose skeleton. a cellulose organic acid ester derivative in which a part or all of a hydroxyl group is partially or wholly organically esterified, a cellulose mineral acid ester derivative partially or wholly partially oxidized by a mineral acid, a part of a residual hydroxyl group of a glucose skeleton, or All of the urethanated cellulose urethane derivative, a part or all of the remaining hydroxy group of the glucose skeleton, an acetalized cellulose acetal derivative or the like.

A cellulose ether derivative comprising a methylcellulose derivative, an ethylcellulose derivative, a carboxymethylcellulose derivative, a cyanoethylcellulose derivative, a hydroxyethylcellulose derivative, hydroxypropylcellulose Derivatives, ethyl hydroxyethyl cellulose derivatives, and the like. The cellulose organic acid ester derivative comprises a cellulose acetate derivative, cellulose acetate propionate, cellulose acetate butyrate, benzoate cellulose derivative, and the like. The inorganic acid ester cellulose derivative includes a nitrocellulose derivative, a cellulose sulfate derivative, and the like. The urethane cellulose derivative may, for example, be a phenyl carbamate cellulose derivative.

Among these, cellulose ether derivatives and organic acid ester cellulose derivatives are preferred; methyl cellulose derivatives, ethyl cellulose derivatives, and cellulose acetate derivatives are particularly preferred.

In the cellulose derivative in which the hydroxyl group of the glucose skeleton is substituted with a group containing an unsaturated carboxylic acid thiol group, the degree of substitution of the group containing an unsaturated carboxylic acid thiol group may be, for example, 0.1 to 1.0, preferably 0.2. ~0.6. Further, in the cellulose derivative in which the hydroxyl group of the glucose skeleton is substituted with a group containing an unsaturated carboxylic acid thiol group, the degree of substitution of a substituent other than the group containing an unsaturated carboxylic acid thiol group may be, for example, 2.0 to ～. 2.9, preferably 2.4 to 2.8. The degree of substitution is appropriately selected in consideration of solvent solubility, usability, optical properties, and the like.

A cellulose derivative in which a part of the hydroxyl group of the glucose skeleton is substituted with a group containing an unsaturated carboxylic acid thiol group can be produced by a conventional reaction using a conventional cellulose derivative as a raw material.

For example, a cellulose derivative in which a part of the hydroxyl group of the glucose skeleton is substituted with a group containing an unsaturated carboxylic acid thiol group (wherein n = 1) represented by the above formula (1), for example, may have a free hydroxyl group The cellulose derivative, a polyisocyanate compound represented by the following formula (2), and an unsaturated carboxylic acid derivative represented by the following formula (3) are reacted and produced.

OCN-A ¹ -NCO (2)

(where A ¹ is the same as above)

(wherein R ¹ , A ² , X ¹ , and X ² are the same as described above)

The cellulose derivative having a free hydroxyl group is a cellulose derivative having a degree of substitution of less than 3, and examples thereof include methyl cellulose, ethyl cellulose, carboxymethyl cellulose, cyanoethyl cellulose, and hydroxyethyl ether. Cellulose ethers such as cellulose, hydroxypropyl cellulose, ethyl hydroxyethyl cellulose; cellulose organic acids such as cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate benzoate, etc. An ester; a cellulose inorganic acid ester such as nitrocellulose or cellulose sulfate; a urethane cellulose such as cellulose phenylamine, or an acetal cellulose. Among these, cellulose ether and cellulose organic acid ester are preferred; methyl cellulose, ethyl cellulose, and cellulose acetate are particularly preferred.

The polyisocyanate compound represented by the formula (2) is not particularly limited as long as it is a compound having at least two isocyanate groups in the molecule. The polyisocyanate compound contains, for example, an aliphatic polyisocyanate, an alicyclic polyisocyanate, an aromatic polyisocyanate, an aromatic aliphatic polyisocyanate or the like. The polyisocyanate compounds may be used alone or in combination of two or more.

Examples of the aliphatic polyisocyanate include 1,5-pentamethylene diisocyanate, 1,6-hexamethylene diisocyanate, 2-methyl-1,5-pentamethylene diisocyanate, and 3-methyl-1. , 5-pentamethylene diisocyanate, 2,4,4-trimethyl-1,6-hexamethylene diisocyanate, 2,2,4-trimethyl-1,6-hexamethylene diisocyanate, 2 An aliphatic diisocyanate such as 6-diisocyanate methyl acrylate or a diisocyanate diisocyanate.

Examples of the alicyclic polyisocyanate include 1,3-cyclopentane diisocyanate, 1,4-cyclohexane diisocyanate, 3-isocyanate methyl-3,5,5-trimethylcyclohexyl isocyanate, and 4 , 4'-methylenebis(cyclohexyl isocyanate), methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 1,3-bis(isocyanate methyl) An alicyclic diisocyanate such as cyclohexane, 1,4-bis(isocyanatemethyl)cyclohexane, isophorone diisocyanate or norbornane diisocyanate.

Examples of the aromatic polyisocyanate include inter-phenylene diisocyanate, p-phenylene diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, naphthalene-1,4-diisocyanate, and naphthalene- 1,5-diisocyanate, 4,4'-diphenyldiisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenyl ether An aromatic diisocyanate such as an isocyanate.

Examples of the aromatic aliphatic polyisocyanate include 1,3-benzenedimethyl diisocyanate, 1,4-benzenedimethyl diisocyanate, and ω,ω'-diisocyanate-1,4-diethylbenzene. , 3-bis(1-isocyanate-1-methylethyl)benzene, 1,4-bis(1-isocyanate-1-methylethyl)benzene, 1,3-bis(α,α-dimethyl An aromatic aliphatic diisocyanate such as isocyanate methyl)benzene or the like.

When an aliphatic polyisocyanate, an alicyclic polyisocyanate, or an aromatic aliphatic polyisocyanate is used as the polyisocyanate compound, a resin having less discoloration can be obtained. Further, in the present invention, as the polyisocyanate compound, the above-exemplified aliphatic polyisocyanate, alicyclic polyisocyanate, aromatic polyisocyanate, dimer or trimer of aromatic aliphatic polyisocyanate, reaction product or a polymer (for example, a dimer or a trimer of diphenylmethane diisocyanate, a reaction product of trimethylolpropane and toluene diisocyanate, trimethylolpropane and hexamethylene diisocyanate) Reaction product, polymethylene polyphenyl isocyanate, polyether polyisocyanate, polyester polyisocyanate, etc.). As the polyisocyanate compound, an alicyclic diisocyanate such as isophorone diisocyanate is particularly preferable.

Further, as the polyisocyanate compound represented by the formula (2), a two-terminal isocyanate urethane prepolymer obtained by reacting a polyol with a polyisocyanate can be used. The polyhydric alcohols include general polyols, polyether polyols, polyester polyols, polycarbonate polyols, and the like.

Examples of the unsaturated carboxylic acid derivative represented by the formula (3) include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, and 3-hydroxypropyl (methyl). a (meth) acrylate having a hydroxyl group at the terminal, such as acrylate, 4-hydroxybutyl (meth) acrylate, polyethylene glycol (meth) acrylate, polypropylene glycol (meth) acrylate; -Aminoethyl (meth) acrylate or the like having a amine group at the terminal (meth) acrylate or (meth) acrylamide; 2-thiol ethyl (meth) acrylate or the like A thiol group (meth) acrylate or the like. Among these, a (meth) acrylate having a hydroxyl group at the terminal is preferably a 2-hydroxyethyl (meth) acrylate or the like.

As a reaction sequence of the cellulose derivative having a free hydroxyl group, the polyisocyanate compound represented by the formula (2), and the unsaturated carboxylic acid derivative represented by the formula (3), any of the following methods may be employed: (i) having a free form The cellulose derivative of the hydroxyl group is reacted with the polyisocyanate compound represented by the formula (2) to form a cellulose derivative having an isocyanate group at the terminal, and then the reaction product and the unsaturated carboxyl group represented by the formula (3) The acid derivative is reacted; (ii) the polyisocyanate compound represented by the formula (2) is reacted with the unsaturated carboxylic acid derivative represented by the formula (3) to form an unsaturated carboxylic acid derivative having an isocyanate group at the terminal. The reaction product is then reacted with a cellulose derivative having a free hydroxyl group. In the method (i), since the gelation is caused by the initial reaction, the method of (ii) is preferred.

Further, in order to prevent deactivation of the polyisocyanate compound and white turbidity of the system, the cellulose derivative having a free hydroxyl group is preferably subjected to dehydration treatment before being used for the reaction.

For each of the above reactions, a method generally used in the reaction of a polyisocyanate compound with a compound having an active hydrogen can be used. The reaction is carried out in a suitable organic solvent such as butyl acetate. A catalyst such as a tin compound can also be used in the reaction. The reaction temperature can be, for example, from 0 to 180 ° C, preferably from about 20 to 150 ° C.

Further, a part of the hydroxyl group of the glucose skeleton is a cellulose derivative substituted with a group containing an unsaturated carboxylic acid thiol group (wherein n = 0) represented by the above formula (1), for example, by having a free hydroxyl group The cellulose derivative is produced by reacting with a compound having an unsaturated carboxylic acid sulfhydryl group and an isocyanate group represented by the following formula (4).

(wherein, R ¹ , A ² , and X ² are the same as described above)

As the cellulose derivative having a free hydroxyl group, the above can be used.

Representative examples of the compound represented by the formula (4) include 2-(meth)acryloyloxyethyl isocyanate and 2-[2-(methyl)acryloxyethoxyethoxy]ethyl isocyanate.

In the active energy ray-curable resin composition of the present invention, only a part of the hydroxyl group of the glucose skeleton may be substituted with a cellulose derivative substituted with a group of an unsaturated carboxylic acid thiol group as an active energy ray-curable compound. Other active energy ray-curable compounds may be further included. Examples of the other active energy ray-curable compound include a radical curable compound and a cationic curable compound.

Examples of the radical curable compound include at least one ethylenic double bond in the molecule and an active energy ray (for example, ultraviolet light, visible light, electron beam, X-ray, etc.) in the presence of a polymerization initiator. A compound that is polymerized by irradiation. Examples of the above compound include (meth)acrylic acid; methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, and (meth)acrylic acid. Third-butyl ester, 2-ethylhexyl (meth)acrylate, decyl (meth)acrylate, benzyl (meth)acrylate, cyclohexyl (meth)acrylate, (meth)acrylic acid Cyclopentenyl ester, glycidyl (meth)acrylate, methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, tetrahydrofuran methyl (meth)acrylate, (methyl) 2-hydroxyethyl acrylate, 2-hydroxypropyl (meth)acrylate, phenoxyethyl (meth)acrylate, norbornyl (meth)acrylate, isodecyl (meth)acrylate, (methyl) a monofunctional (meth) acrylate monomer such as acryloyl morpholine or γ-(meth) propylene methoxy propyl trimethoxy decane; styrene, α-methyl styrene, vinyl toluene, vinyl acetate a vinyl monomer such as ester, allyl acetate, vinyl propionate, vinyl benzoate, N-vinylpyrrolidone, N-vinylimidazole, N-ethylene caprolactam or the like; 1,4-butanediol II ( methyl Acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol di(methyl) Acrylate, polypropylene glycol di(meth)acrylate, bisphenol A-diepoxypropyl ether di(meth)acrylate, ethylene oxide modified bisphenol A-di(meth)acrylate, etc. Bifunctional (meth) acrylate; trimethylolpropane tri(meth) acrylate, pentaerythritol tetra (meth) acrylate, pentaerythritol penta (meth) acrylate, pentaerythritol hexa (meth) acrylate Ethylene oxide addition trimethylolpropane tri(meth) acrylate, dipentaerythritol penta (meth) acrylate, triallyl cyanurate, triallyl cyanurate, A trifunctional or higher polyfunctional monomer such as 1,3,5-tripropylene decyl hexahydroindenyl hydrazine. Among these, a polyfunctional monomer having two or more functional groups is preferred. These radical curable compounds may be used alone or in combination of two or more.

Further, as the radical curable compound, (meth)acrylate, (meth)acrylic acid urethane, (meth)acrylic acid epoxy ester, (meth)acrylic acid acrylate or the like (methyl group) can be used. ) acrylate oligomers.

Examples of the cation-curable compound include a vinyl ether compound, an epoxy compound, and an oxetane compound.

Examples of the vinyl ether compound include ethylene oxide-modified bisphenol A-divinyl ether and ethylene oxide-modified hydroquinone divinyl ether.

Examples of the epoxy compound include 1,2-epoxycyclohexane, limonene diepoxide, and 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate. , 1,4-butanediol diepoxypropyl ether, trimethylolpropane diepoxypropyl ether, bis(3,4-epoxy-6-methylcyclohexylmethyl) adipate , biphenyl A-diglycidyl ether, biphenyl F-diglycidyl ether, biphenyl S-diepoxypropyl ether, hydrogenated biphenyl A-diepoxypropyl ether and the like.

Examples of the oxetane-based compound include 3-ethyl-3-hydroxymethyloxetane, 3-ethyl-3-(phenoxymethyl)oxetane, and two [( 3-ethyl-3-oxetanyl)methyl]ether or the like.

The active energy ray-curable resin composition of the present invention may contain a thermosetting compound in addition to the active energy ray-curable compound.

The ratio of a part of the hydroxyl groups of the above-mentioned glucose skeleton which is contained in the total curable compound in the active energy ray-curable resin composition to the cellulose derivative substituted with a group containing an unsaturated carboxylic acid thio group, for example, may be 30% by weight The above is preferably 50% by weight or more, more preferably 70% by weight or more, and particularly preferably 90% by weight or more.

Further, in the active energy ray-curable resin composition, in addition to the above-mentioned curable compound, a photopolymerization initiator may be blended, and if necessary, a photo-sensitizer, a photocationic polymerization initiator, or a thermal cation may be blended. A polymerization initiator, a thermal radical polymerization initiator, a light accelerator, a photostabilizer, a UV absorber, a leveling agent, an antifoaming agent, and the like.

The photopolymerization initiator is appropriately selected depending on the type of active energy ray of the curing means. Examples of the photopolymerization initiator include acetophenone, 3-methylacetophenone, diphenylketone, 4-chlorodiphenyl ketone, 4,4-diaminodiphenyl ketone, and 1- Hydroxy-cyclohexyl-phenyl-ketone, 2,2-dimethoxy-2-acetophenone, Xanthone fluorenone, benzaldehyde, hydrazine, benzoin ethyl ether, benzoin propyl ether, benzyl dimethyl ketal, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropane 1-ketone, 4-ylideflavone, camphorquinone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinylpropan-1-one, and the like.

The content of the cellulose derivative in which the partial hydroxyl group of the glucose skeleton is substituted by the group containing the unsaturated carboxylic acid thiol group in the active energy ray-curable resin composition is relative to the solid content of the active energy ray-curable resin composition. (containing a component which hardens by hardening), for example, may be 30 to 99.9% by weight, preferably 50 to 99.5% by weight, more preferably 70 to 99% by weight, particularly preferably 90 to 99% by weight.

The content of the photopolymerization initiator in the active energy ray-curable resin composition is, for example, 0.1 to 10% by weight based on the total solid content (including a component which is cured by hardening) in the active energy ray-curable resin composition. Preferably, it is about 1 to 8 weight%.

The polarizing plate of the present invention is produced by coating the active energy ray-curable resin composition on at least one surface of a polarizing mirror, and then curing the active energy ray-curable resin composition to form a protective film.

The coating method of the active energy ray-curable resin composition is not particularly limited, and various coating methods such as blade coating, wire bar coating, slit coating, and gravure coating can be used. A solvent may also be used at the time of coating to adjust the viscosity of the hardened resin composition.

The coating film composed of the active energy ray-curable resin composition is cured by irradiation with an active energy ray to form a protective film. Examples of the active energy ray include ultraviolet rays, visible light, electron beams, and X-rays. Among these, it is preferred to use ultraviolet rays. Examples of the source of the ultraviolet rays include a low pressure mercury lamp, a medium pressure mercury lamp, a high pressure mercury lamp, an ultra high pressure mercury lamp, a chemical lamp, a xenon lamp, a black lamp, and a metal halide lamp.

The thickness of the protective film may be, for example, 10 to 200 μm, or preferably 30 to 100 μm, from the viewpoints of thinness, lightness, protection, handleability, and the like.

The polarizing plate of the present invention is protected by using a cured product of an active energy ray-curable resin composition containing a compound having an unsaturated carboxylic acid sulfhydryl group and an alicyclic skeleton and a cellulose derivative as a protective film for a polarizer. The film is transparent, and its birefringence is not easily changed even if stress is applied.

Example

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to the examples. Further, the photoelastic coefficient and the phase difference of the cured film and the measurement of the glass transition temperature were measured by the following methods.

[Measurement of Photoelastic Coefficient and Phase Difference]

A cured film having a thickness of 100 μm was produced and measured using a three-dimensional double refractometer ("KOBRA-WR") manufactured by Oji Scientific Instruments Co., Ltd.

[Measurement of glass transition temperature]

An active energy ray-curable resin composition (thickness: 40 μm) was applied to a cold-rolled steel sheet (thickness: 0.3 mm, width: 20 mm, length: 50 mm), and a small UV irradiation machine ("ECS-401GX" manufactured by EYE GRAPHICS Co., Ltd.) was used. The rated voltage of 200 V and a high-pressure mercury lamp were irradiated with ultraviolet rays having a cumulative light amount of 350 mJ/cm ² from a distance of 11 cm to obtain a cured film of the active energy ray-curable resin composition. The film was heated to 25 ° C from 25 ° C using a rigid-body viscoelasticity measuring apparatus ("RPT-3000W" manufactured by A&D Co., Ltd.), and the glass transition temperature (Tg) was measured.

Synthesis Example 1

80.4 parts by weight of ethyl cellulose having a hydroxyl value of 32.9 mgKOH/g was dissolved in 723.6 parts by weight of butyl acetate, and dehydration of ethyl cellulose was carried out while distilling off butyl acetate at 128 °C. After distilling 124.8 parts by weight of a mixed solution of butyl acetate and water, the moisture in the ethyl acetate butyl acetate solution was measured by Karl Fischer Moisture Titrator, and the moisture was 0.025 by weight. %. Further, after dehydration, a portion of the distilled butyl acetate was added to the ethyl acetate butyl acetate solution to adjust the concentration of the ethyl cellulose to 10% by weight.

In an atmosphere mixed with nitrogen and oxygen (oxygen concentration 5%), 38.06 parts by weight of butyl acetate, 100 parts by weight of isophorone diisocyanate (IPDI), and 0.046 parts by weight of dibutyltin dilaurate [relative to IPDI and 2 The concentration of the reactant of hydroxyethyl acrylate (HEA) was 300 ppm by weight], mixed in a flask, and heated to 40 °C. At this time, 52.25 parts by weight of HEA was added dropwise over 1 hour. When the isocyanate concentration (NCO concentration in the solution) was 9.94% by weight, it was cooled to room temperature to obtain a (meth) acrylate (isophorone diisocyanate 1 mol and 2-hydroxyethyl acrylate 1 Mo) A solution having an isocyanate group at the end after the ear reaction.

475 parts by weight of butyl acetate solution (10% by weight solution) of ethyl cellulose having a hydroxyl value of 32.9 mgKOH/g after dehydration in an atmosphere of nitrogen and oxygen (5% concentration), and a laurel 0.0282 parts by weight of dibutyltin acid was placed in a flask and stirred, and the temperature was raised to 100 °C. 19.42 parts by weight of the prepared solution containing (meth) acrylate (having an isocyanate group at the terminal) was added dropwise over 1 hour. Thereafter, the ripening is carried out, and when the isocyanate concentration is 0.1% by weight or less, the mixture is cooled to room temperature to obtain a solution containing a cellulose derivative (the hydroxyl group of the ethyl cellulose is substituted by a group containing an acrylonitrile group) (solid content 16.4) weight%).

Synthesis Example 2

Cellulose acetate (manufactured by Daicel Chemical Industry Co., Ltd., L-20) was dried at 150 ° C for 24 hours to make the water content in the cellulose acetate 0.86 wt%. The hydroxyl value at this time was 97.13 mgKOH/g. 35 parts by weight of this dried cellulose acetate was mixed with 316 parts by weight of cyclohexanone and 65 parts by weight of toluene, and a mixture of cyclohexanone, toluene, and water was distilled off at 155 ° C, and then Karl Fischer moisture meter (Karl) was used. Fischer Moisture Titrator) measured the moisture in the cellulose acetate cyclohexanone solution, and the moisture content was 0.015 wt%. Further, after dehydration, the concentration of cellulose acetate was adjusted to 10.9% by weight with cyclohexanone.

211 parts by weight of a cyclohexanone solution (10.9% by weight solution) of cellulose acetate having a hydroxyl group content of 97.13 mgKOH/g after dehydration treatment was mixed with a nitrogen and oxygen atmosphere (5% oxygen concentration), and stirred. And warmed to 70 ° C. After reaching 70 ° C, 4.6 parts by weight of isocyanate acrylate (2-propenyloxyethyl isocyanate; manufactured by Showa Denko, AOI-VM) was added. After 2 hours from the addition of AOI-VM, 0.08 parts by weight of dibutyltin dilaurate was placed in a flask and stirred to continue the reaction. Thereafter, the aging is carried out, and when the isocyanate concentration is 0.1% by weight or less, it is cooled to room temperature to obtain a solution containing a cellulose derivative (the hydroxyl group of cellulose acetate is substituted by a group containing an acrylonitrile group) (solid content 12.8 by weight) %).

Example 1

To 100 parts by weight of a solution containing the cellulose derivative (the hydroxyl group of ethyl cellulose is substituted by a group containing an acrylonitrile group) prepared in Synthesis Example 1, a weight of 1-hydroxy-cyclohexyl-phenyl-ketone 0.82 was mixed. The active energy ray-curable resin composition 1 was obtained. The active energy ray-curable resin composition 1 was applied to a glass plate to a film thickness of 600 μm using an applicator, and then dried at 80° C. for 1 hour, and then a small UV irradiation machine (ECS-401GX, manufactured by EYE GRAPHICS Co., Ltd.) was used. In the ultraviolet light of a cumulative light amount of 500 mJ/cm ² from the distance of 11 cm, a single cured film (thickness: 98 μm) of the active energy ray-curable resin composition 1 was obtained. The appearance of the obtained cured film was visually observed, and the photoelastic coefficient and the phase difference were measured.

Example 2

To 100 parts by weight of a solution containing a cellulose derivative (the cellulose acetate-containing hydroxyl group substituted by a propylene group-containing group) prepared in Synthesis Example 2, 0.82 parts by weight of 1-hydroxy-cyclohexyl-phenyl-one was mixed. The active energy ray-curable resin composition 2 was obtained. The active energy ray-curable resin composition 2 was coated on a glass plate with a film thickness of 600 μm using an applicator, and dried at 80° C. for 1 hour, and then a small UV irradiation machine (ECS-401GX, manufactured by EYE GRAPHICS Co., Ltd.) was used. In the ultraviolet light of 500 mJ/cm ² of the cumulative light amount, the ultraviolet light of the active energy ray-curable resin composition 2 was obtained from the distance of 11 cm. The appearance of the obtained cured film was visually observed, and the photoelastic coefficient and the phase difference were measured.

Comparative example 1

500 parts by weight of an ethyl acetate solution of 10% by weight of a hydroxyl group of 32.9 mgKOH/g of ethyl cellulose, 50 parts by weight of pentaerythritol triacrylate, and 5 parts by weight of 1-hydroxy-cyclohexyl-phenyl-ketone were mixed. The active energy ray-curable resin composition 3 was obtained. The active energy ray-curable resin composition 3 was applied to a glass plate to a film thickness of 550 μm using an applicator, and dried at 80° C. for 1 hour, and then irradiated with ultraviolet rays in the same manner as in Example 1 to obtain an active energy ray-curable type. A single cured film (thickness: 100 μm) of the resin composition 3. The appearance of the obtained cured film was visually observed, and the photoelastic coefficient and the phase difference were measured.

Comparative example 2

500 parts by weight of an ethyl acetate solution of 10% by weight of a hydroxyl group of 32.9 mgKOH/g of ethyl cellulose, 50 parts by weight of dipentaerythritol hexaacrylate, and 5 parts by weight of 1-hydroxy-cyclohexyl-phenyl-ketone are mixed. The active energy ray-curable resin composition 4 was obtained. The active energy ray-curable resin composition 4 glass plate was coated with a film thickness of 550 μm using an applicator, and dried at 80° C. for 1 hour, and then irradiated with ultraviolet rays in the same manner as in Example 1 to obtain an active energy ray-curable resin. A separate cured film of composition 4 (thickness 100 μm). The appearance of the obtained cured film was visually observed, and the photoelastic coefficient and the phase difference were measured.

Comparative example 3

500 parts by weight of an ethyl acetate solution of 10% by weight of a hydroxyl group of 32.9 mgKOH/g of ethyl cellulose, 50 parts by weight of pentaerythritol ethoxytetraacrylate, and 5 parts by weight of 1-hydroxy-cyclohexyl-phenyl-one The mixture was mixed to obtain an active energy ray-curable resin composition 5. The active energy ray-curable resin composition 5 was coated on a glass plate with a film thickness of 550 μm using an applicator, and dried at 80 ° C for 1 hour, and then irradiated with ultraviolet rays in the same manner as in Example 1 to obtain active energy ray hardening. A single cured film of the resin composition 5 (thickness: 100 μm). The appearance of the obtained cured film was visually observed, and the photoelastic coefficient and the phase difference were measured.

The results of measurement of the appearance, glass transition temperature, photoelastic coefficient, and phase difference of the cured film obtained in the examples and the comparative examples are shown in Table 1. In the table, "-" indicates that measurement is not possible.

Claims (3)

A polarizing plate having a structure in which at least one surface of a polarizer is protected by a protective film made of a resin, wherein the resin is a cured product of an active energy ray-curable resin composition containing a cellulose derivative; In the cellulose derivative, a part of the hydroxyl group of the glucose skeleton is substituted with a group containing an unsaturated carboxylic acid thiol group; and the above-mentioned group containing an unsaturated carboxylic acid thiol group is a group represented by the following formula (1): In the formula, R ¹ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; A ¹ and A ² are the same or different and represent a divalent organic group; and X ¹ and X ² are the same or different, and represent oxygen. An atom, a sulfur atom, or a -NR ² - group; R ² represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms; n is 0 or 1. The polarizing plate of claim 1, wherein the cellulose derivative is at least one selected from the group consisting of a methyl cellulose derivative, an ethyl cellulose derivative, and a cellulose acetate derivative. A method for producing a polarizing plate, characterized in that an active energy ray-curable resin composition containing a cellulose derivative is applied to at least one surface of a polarizing mirror, and then the active energy ray-curable resin composition is cured to form a protective layer. a membrane; the cellulose derivative, wherein a hydroxyl group of the glucose skeleton is substituted with a group containing an unsaturated carboxylic acid thiol group; and the above-mentioned group containing an unsaturated carboxylic acid thiol group is represented by the following formula (1) Base: In the formula, R ¹ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; A ¹ and A ² are the same or different and represent a divalent organic group; and X ¹ and X ² are the same or different, and represent oxygen. An atom, a sulfur atom, or a -NR ² - group; R ² represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms; n is 0 or 1.