JP2009092775A - Optical film, polarizing plate, and image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical film having superior optical characteristics such as reduced haze, superior transparency, low double refraction, or the like, satisfactory mechanical strength and thermal insulation properties, and superior moisture permeability, to provide a polarizing plate using this optical film, and to provide an image display device that uses the polarizing plate. <P>SOLUTION: This optical film for a protection film for polarizer is formed by polypropylene resin synthesized by metallocene catalyst and has melt flow rate (MFR: a value measured under the conditions of 230°C and 2.16 kg load, in compliance with JIS K7210) of 20g/10 min or larger. The polarizing plate is constituted, by forming the optical film on at least one face of the polarizer, and the image display device is constituted by using the polarizing plate. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention provides an optical film for a protective film of a polarizer having excellent optical properties such as low haze, excellent transparency, low birefringence, good mechanical strength and heat resistance, and excellent moisture permeability, and The present invention relates to a polarizing plate using a film as a protective film on one or both sides of a polarizer, and an image display apparatus using the polarizing plate.

  The polarizing plate is a material having a function of transmitting only light having a specific vibration direction and shielding other light, and is widely used as one of components constituting a liquid crystal display device, for example. As such a polarizing plate, what has the structure on which the polarizer and the protective film were laminated | stacked is generally used. The polarizer has a function of transmitting only light having a specific vibration direction. For example, a film of polyvinyl alcohol (hereinafter sometimes referred to as “PVA”) is stretched, and iodine or a dichroic dye is used. The film dye | stained by etc. is generally used. Recently, a coating-type polarizer is also used.

The protective film has a function of holding a polarizer and imparting practical strength to the entire polarizing plate. For example, a triacetyl cellulose (hereinafter referred to as “TAC”) film of a cellulose-based film or the like. Is commonly used. Cellulose film has excellent properties as a polarizer protective film because it has excellent optical uniformity such as good transparency and low birefringence, practical heat resistance and excellent mechanical strength. ing.
In addition, since it has high moisture permeability, when it is bonded to a polarizer such as PVA, it is generally used as a polarizer protective film because it has good workability such as excellent moisture permeability of PVA and adhesive (for example, Patent Document 1).
However, since the cellulose-based film (for example, TAC film) has high water absorption, there have been problems such as deterioration in performance of the polarizer and dimensional stability due to water absorption.

In order to solve this problem, attempts have been made to improve dimensional stability by using a film material having a lower water absorption rate than the conventional TAC film as a polarizer protective film. Films and polyethylene terephthalate films have a large photoelastic constant, and a change in phase difference is caused by the action of external stress, resulting in a deterioration in performance as a polarizing plate.
Therefore, a uniaxially stretched high-density polyethylene or polypropylene film having a low moisture permeability has been proposed as a polarizer protective film. (For example, see Patent Document 2.)
However, the uniaxially stretched polyethylene or polypropylene has a problem in that a phase difference occurs and the function as a polarizing plate is lowered.

JP-A-7-120617 Japanese Patent Publication No. 6-12362

  In view of the above problems, the present invention provides a protective film for a polarizer having excellent optical properties such as low haze, excellent transparency, low birefringence, excellent mechanical strength and heat resistance, and excellent moisture permeability. It is an object to provide an optical film, a polarizing plate using the film as a protective film on one or both sides of a polarizer, and an image display device using the polarizing plate.

As a result of intensive studies to achieve the above object, the present inventors have found that an optical film using a polypropylene resin having a predetermined melt flow rate synthesized by a metallocene catalyst is used for a protective film of a polarizer. It was found that the above-mentioned problems can be solved.
That is, the present invention
[1] It is composed of a polypropylene resin synthesized with a metallocene catalyst, and the melt flow rate (MFR; measured value under conditions of 230 ° C. and 2.16 kg load according to JIS K7210) of the polypropylene resin is 20 g / 10 An optical film for a protective film of a polarizer,
[2] The optical film according to [1], wherein the optical film is an unstretched film,
[3] The optical film as described in [1] or [2] above, further containing 0.03 to 0.5 parts by mass of a dibenzylidene sorbitol-based additive with respect to 100 parts by mass of the polypropylene resin. ,
[4] The optical film according to any one of [1] to [3], wherein the thickness direction retardation Rth of the optical film is 20 to 60 nm.
[5] A polarizing plate formed by forming the optical film according to any one of [1] to [4] on at least one surface of a polarizer, and [6] the polarizing plate according to [5]. Image display device,
Is to provide.

The optical film of the present invention has excellent optical properties such as low haze, excellent transparency, low birefringence, and excellent moisture permeability. In addition, it has excellent durability such as heat resistance and moist heat resistance, can improve the polarization degree of the polarizing plate without affecting the optical function of the polarizing plate, and is flexible and rich in elasticity. . Furthermore, since the optical film of the present invention has resistance to external impact and deformation, a polarizing plate with significantly improved strength and reliability as a liquid crystal display element can be obtained by bonding to a polarizer. It is done.
In addition, the optical film of the present invention has a protective function equivalent to or higher than that of a conventionally used TAC film. In particular, the TAC film is hydrophilic and hardly moisture proof, whereas the optical film of the present invention is hydrophobic, so that the durability of the polarizing plate can be greatly improved.

The optical film of the present invention is composed of a polypropylene resin synthesized with a metallocene catalyst, and its melt flow rate (MFR; measured value under conditions of 230 ° C. and 2.16 kg load according to JIS K7210) is 20 g. / 10 minutes or more.
The polypropylene resin used in the present invention is synthesized by a metallocene catalyst described later, and is preferably a copolymer of propylene and α-olefin. As the α-olefin, ethylene, 1-olefin having 4 to 18 carbon atoms is used. Specifically, ethylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-heptene, 4- And methyl-pentene-1, 4-methyl-hexene-1, 4,4-dimethylpentene-1. The proportion of propylene units in the copolymer is preferably 80 mol% or more, and the comonomer is 20 mol% or less. As the comonomer, the above α-olefin is not limited to one type, and two or more types can be used, and the copolymer can be a multi-component copolymer such as a terpolymer.

  The metallocene catalyst used in the present invention may be a single-site catalyst having a uniform active site or a multi-site catalyst having a non-uniform active site, and is preferably a multi-site catalyst. Generally, a group 4-6 transition metal compound such as Zr, Ti, Hf, etc., in particular, a group 4 transition metal compound and an organic transition metal compound having a cyclopentadienyl group or a cyclopentadienyl derivative group is used. be able to.

  As the group of the cyclopentadienyl derivative, an alkyl substituent such as pentamethylcyclopentadienyl or a group in which two or more substituents are combined to form a saturated or unsaturated cyclic substituent may be used. Typically, an indenyl group, a fluorenyl group, an azulenyl group, or a partial hydrogenated product thereof can be given. Moreover, what combined several cyclopentadienyl group with the alkylene group, the silylene group, the germylene group etc. can be mentioned suitably.

  The co-catalyst is selected from the group consisting of an ionic compound capable of reacting with an aluminum oxy compound, a metallocene compound to convert a metallocene compound component into a cation, or a Lewis acid, a solid acid, or an ion-exchange layered silicate. At least one compound selected can be used. Moreover, an organoaluminum compound can be added with these compounds as needed.

  The above-mentioned layered silicate refers to a silicate compound having a crystal structure in which structured surfaces are stacked in parallel with each other with a weak binding force by ionic bonding or the like. In the present invention, the layered silicate is preferably ion-exchangeable. Here, the ion exchange property means that the interlayer cation of the layered silicate can be exchanged. Most layered silicates are naturally produced mainly as the main components of clay minerals, but these layered silicates are not limited to natural ones, and may be artificially synthesized products.

Specific examples of the layered silicate are not particularly limited as long as they are known layered silicates, for example, kaolins such as dickite, nacrite, kaolinite, anorxite, metahalloysite, halloysite; chrysotile, lizardite, Serpentine group such as antigolite; Smectite group such as montmorillonite, sauconite, beidellite, nontronite, saponite, teniolite, hectorite, stevensite; vermiculite group such as vermiculite; mica, illite, sericite, sea green stone, etc. Attapulgite; sepiolite; palygorskite; bentonite; pyrophyllite; talc; chlorite group. These may form a mixed layer.
Among these, montmorillonite, sauconite, beidellite, nontronite, saponite, hectorite, stevensite, bentonite, teniolite and the like are preferable smectite group, vermiculite group and mica group.

  These layered silicates can be chemically treated. Here, as the chemical treatment, any of a surface treatment for removing impurities adhering to the surface and a treatment that affects the crystal structure and chemical composition of the layered silicate can be used. Specific examples include (i) acid treatment, (b) alkali treatment, (c) salt treatment, and (d) organic matter treatment. These treatments remove impurities on the surface, exchange cations between layers, elute cations such as Al, Fe, and Mg in the crystal structure, resulting in ion complexes, molecular complexes, organic derivatives, etc. The surface area, interlayer distance, solid acidity, etc. can be changed. These processes may be performed independently or two or more processes may be combined.

  As a method (polymerization method) for synthesizing a polypropylene resin using the metallocene catalyst, a slurry method using an inert solvent, a gas phase method without using a solvent, a solution method, or a polymerization in the presence of these catalysts. Examples include bulk polymerization using a monomer as a solvent.

Next, the polypropylene resin in the present invention requires a melt flow rate (hereinafter sometimes referred to as MFR) to be 20 g / 10 min or more, and preferably 20 to 40 g / 10 min. Here, MFR is a value measured according to JIS K7210, and the measurement conditions are 230 ° C. and 2.16 kg load. If the MFR of the polypropylene resin is within the above range, sufficient strength as an optical film can be obtained, and post-processing can be easily performed. If the MFR is within the above range, the resin will not be distorted, so that it will be difficult for the phase difference to occur, and it will be easy to stabilize the MFR within the production lot, so that stable molding can be achieved, and the MFR regulator, etc. Since the amount of the additive added can be suppressed, the physical properties are not adversely affected. The MFR of the polypropylene resin can be adjusted with a general MFR adjuster.
The polypropylene resin preferably has a melting point (Tm) of 130 ° C. or higher. If the melting point (Tm) is 130 ° C. or higher, the unstretched film is preferable because the flexural modulus is increased, the strength of the optical film is increased, and post-processing is not affected.
Furthermore, the polypropylene resin preferably has a tensile strength of 20 MPa or more. When the pressure is 20 MPa or more, the orientation of the optical film is not applied when the optical film is bonded to the polarizer via the adhesive layer by the roll-to-roll method, and no retardation is generated in the optical film. Performance can be maintained.
The polypropylene resin in the present invention preferably has a flexural modulus of 700 MPa or more, and more preferably 900 MPa or more. When the flexural modulus is within the above range, sufficient strength as an optical film can be obtained, and post-processing can be easily performed.

In the present invention, additives may be added in order to improve the tensile strength and improve transparency. As the additive, a dibenzylidene sorbitol-based additive having a small influence on the phase difference is preferable.
Dibenzylidene sorbitol-based additives used in the present invention are di-substituted dibenzylidene sorbitols such as 1,3-2,4-dibenzylidene sorbitol, 1,3-2,4-diparamethyldibenzylidene sorbitol, and di- -The thing etc. which mix | blended substituted benzylidene sorbitol and diglycerol mono-fatty acid ester can be used conveniently.
Dibenzylidene sorbitol-based additives are known to contribute to improving the transparency and strength of polypropylene resins as a clearing nucleating agent, and when used in an optical film for a protective film of a polarizer, Excellent performance with little effect on phase difference.

  Of the above-mentioned dibenzylidene sorbitol-based additives, dibenzylidene sorbitol-based nucleating agents added with diglycerin monofatty acid ester which is stable with little bleeding are desirable. As the diglycerin monofatty acid ester, diglycerin monolaurate, diglycerin monomyristic acid ester, diglycerin monostearic acid ester and the like are preferable, and these are used alone or in combination.

It is preferable that content of the said additive is the range of 0.03-0.5 mass part with respect to 100 mass parts of polypropylene resins. When it is 0.03 parts by mass or more, it is possible to improve transparency and sufficiently improve strength. On the other hand, adding more than 0.5 parts by mass does not lead to further improvement in transparency and strength, which is disadvantageous in cost.
In particular, when di-substituted benzylidene sorbitol added with diglycerin monofatty acid ester is used, 0.01 to 0.3 parts by mass of di-substituted benzylidene sorbitol is mixed with 100 parts by mass of polypropylene resin. The diglycerin monofatty acid ester is preferably 0.01 to 0.2 parts by mass.

Moreover, according to the desired physical property of the film obtained, various olefin resins and additives can be mix | blended with the optical film in this invention in the range which does not impair required transparency.
As the olefin resin, a small amount of homopolypropylene, random polypropylene or the like synthesized with a Ziegler catalyst may be blended within a range not exceeding 10% by mass.
Examples of the additive include a weather resistance improver, an abrasion resistance improver, a polymerization inhibitor, a crosslinking agent, an infrared absorber, an antistatic agent, an adhesion improver, a leveling agent, a thixotropic agent, and a coupling agent. , Surfactants, polymer electrolytes, conductive complexes, antiblocking agents, lubricants, plasticizers, antifoaming agents, fillers, solvents, and the like.

Here, as the weather resistance improving agent, an ultraviolet absorber or a light stabilizer can be used.
The ultraviolet absorber may be either inorganic or organic, and as the inorganic ultraviolet absorber, titanium dioxide, cerium oxide, zinc oxide or the like having an average particle diameter of about 5 to 120 nm can be preferably used. Moreover, as an organic type ultraviolet absorber, benzotriazole type, for example, 2- (2-hydroxy-5-methylphenyl) benzotriazole, 2- (2-hydroxy-3,5-di-tert-) is specifically mentioned. Amylphenyl) benzotriazole, 3- [3- (benzotriazol-2-yl) -5-tert-butyl-4-hydroxyphenyl] propionic acid ester of polyethylene glycol, and the like.
On the other hand, examples of the light stabilizer include hindered amines, specifically 2- (3,5-di-tert-butyl-4-hydroxybenzyl) -2′-n-butylmalonate bis (1,2,2). , 6,6-pentamethyl-4-piperidyl), bis (1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, tetrakis (2,2,6,6-tetramethyl-4-piperidyl)- 1,2,3,4-butanetetracarboxylate and the like.
Further, as the ultraviolet absorber or light stabilizer, a reactive ultraviolet absorber or light stabilizer having a polymerizable group such as a (meth) acryloyl group in the molecule can be used.

  Examples of the wear resistance improver include, for inorganic substances, spherical particles such as α-alumina, silica, kaolinite, iron oxide, diamond, and silicon carbide. Examples of the particle shape include a sphere, an ellipsoid, a polyhedron, a scale shape, and the like. Although there is no particular limitation, a spherical shape is preferable. Organic materials include synthetic resin beads such as cross-linked acrylic resin and polycarbonate resin. The particle size is usually about 30 to 200% of the film thickness of the optical film. Among these, spherical α-alumina is particularly preferable because it has high hardness and a large effect on improving wear resistance, and it is relatively easy to obtain spherical particles.

  Examples of the polymerization inhibitor include hydroquinone, p-benzoquinone, hydroquinone monomethyl ether, pyrogallol, and t-butylcatechol. Examples of the crosslinking agent include a polyisocyanate compound, an epoxy compound, a metal chelate compound, an aziridine compound, and an oxazoline compound. Used.

As the filler, for example, barium sulfate, talc, clay, calcium carbonate, aluminum hydroxide and the like are used.
As the infrared absorber, for example, a dithiol metal complex, a phthalocyanine compound, a diimmonium compound, or the like is used.

  Various additives are added to the optical film for various functions, for example, high hardness and scratch resistance, so-called hard coating function, anti-fogging coating function, anti-fouling coating function, anti-glare coating function, anti-reflection A coating function, an ultraviolet shielding coating function, an infrared shielding coating function, and the like can also be imparted.

[Method for producing optical film]
Hereinafter, the manufacturing method of the optical film of this invention is demonstrated.
The optical film can be produced directly on the polarizer by various molding methods such as extrusion coating molding method, casting method, T-die extrusion molding method, inflation method, injection molding method, etc. ( (See FIG. 1). Moreover, the optical film 1 may be produced by the above-described various molding methods, and then bonded to a polarizer via an adhesive layer.
In the present invention, since it is desired that the optical film produced on the polarizer is not oriented, unstretched T-die extrusion that does not stretch is desirable.

  The thickness of the optical film is preferably in the range of 10 to 200 μm, more preferably 30 to 150 μm. When the thickness is 10 μm or more, the strength as a protective film of the polarizer is sufficiently ensured, and when it is 200 μm or less, sufficient flexibility is obtained, and since it is lightweight, handling is easy. It is also advantageous in terms of cost.

A method for producing an optical film directly on a polarizer is shown in FIG. In FIG. 1, an adhesive layer 5 is applied on the polarizer 3 in advance, and a polypropylene molten resin 1 is formed by an extrusion method (FIG. 1, left diagram). The formed polypropylene resin is solidified to form the protective film 4.
Alternatively, the protective film 4 may be formed in advance by the T-die method, and the adhesive layer 2 may be applied in advance and bonded to the polarizer 3.

  In the present invention, the retardation Rth in the thickness direction of the optical film is almost equal to Rth 45 nm of a TAC film (thickness 80 μm) that has been conventionally used in consideration of the case where it is used together with TAC as a protective film for a polarizer. It is hoped that there will be. The retardation Rth in the thickness direction of the optical film is preferably in the range of 20 to 60 nm, more preferably in the range of 20 to 50 nm, for use as a protective film for a polarizer. The retardation Rth in the thickness direction of the optical film can be set within a desired numerical range by adjusting the film thickness according to the Rth of TAC used in combination.

[Polarizer]
The polarizing plate according to the present invention is obtained by bonding the optical film of the present invention to one side or both sides of a polarizer. Here, the optical film is bonded to a polarizer and functions as a protective film.

As the polarizer used in the polarizing plate of the present invention, any polarizer may be used as long as it has a function of transmitting only light having a specific vibration direction. For example, a polyvinyl alcohol film is stretched, and iodine or two-color Polyvinyl alcohol polarizers dyed with reactive dyes; polyene polarizers such as dehydrated polyvinyl alcohol and dehydrochlorinated polyvinyl chloride; reflective polarizers using cholesteric liquid crystals; thin film crystal film polarizers Among them, polyvinyl alcohol polarizers are preferably used.
Examples of the polyvinyl alcohol polarizer include hydrophilic polymer films such as polyvinyl alcohol films, partially formalized polyvinyl alcohol films, ethylene / vinyl acetate copolymer partially saponified films, iodine and dichroic dyes, etc. A dichroic substance is adsorbed and uniaxially stretched. Among these, a polarizer composed of a polyvinyl alcohol film and a dichroic substance such as iodine is preferably used. The thickness of these polarizers is not particularly limited, and is generally about 1 to 100 μm.

A PVA resin suitably used as a resin constituting the polarizer can be obtained by saponifying a polyvinyl acetate resin. Examples of the polyvinyl acetate resin include, in addition to polyvinyl acetate, which is a homopolymer of vinyl acetate, copolymerization of vinyl acetate and other monomers copolymerizable therewith. Examples of other monomers copolymerized with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids.
The degree of saponification of the PVA-based resin is usually 85 to 100 mol%, preferably 98 to 100 mol%. This PVA-based resin may be further modified. For example, polyvinyl formal or polyvinyl acetal modified with aldehydes may be used. The degree of polymerization of the PVA resin is usually in the range of 1,000 to 10,000, preferably 1,500 to 10,000.

  The polarizing plate is, for example, a step of uniaxially stretching a PVA resin film as described above, a step of dyeing a PVA resin film with a dichroic dye, and adsorbing the dichroic dye, and a dichroic dye adsorbing A process of treating the prepared PVA resin film with an aqueous boric acid solution, a process of washing with water after the treatment with an aqueous boric acid solution, and a uniaxially stretched PVA resin film on which dichroic dyes are adsorbed and oriented by applying these steps Manufactured through a process of laminating films.

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

In order to dye the PVA resin film with the dichroic dye, for example, the PVA resin film may be immersed in an aqueous solution containing the dichroic dye. Specifically, iodine or a dichroic dye is used as the dichroic dye.
When iodine is used as the dichroic dye, a method of immersing and dyeing a PVA resin film in an aqueous solution containing iodine and potassium iodide is usually employed. The content of iodine in this aqueous solution is usually about 0.01 to 0.5 parts by mass per 100 parts by mass of water, and the content of potassium iodide is usually about 0.5 to 10 parts by mass per 100 parts by mass of water. It is. The temperature of this aqueous solution is usually about 20 to 40 ° C., and the immersion time in this aqueous solution is usually about 30 to 300 seconds.

On the other hand, when a dichroic dye is used as the dichroic dye, a method of immersing and dyeing a PVA resin film in an aqueous solution containing a water-soluble dichroic dye is usually employed. The content of the dichroic dye in this aqueous solution is usually about 1 × 10 ⁻³ to 1 × 10 ⁻² parts by mass per 100 parts by mass of water. This aqueous solution may contain an inorganic salt such as sodium sulfate. The temperature of this aqueous solution is usually about 20 to 80 ° C., and the immersion time in this aqueous solution is usually about 30 to 300 seconds.
The boric acid treatment after dyeing with a dichroic dye is performed by immersing the dyed PVA resin film in an aqueous boric acid solution. The boric acid content in the boric acid aqueous solution is usually about 2 to 15 parts by mass, preferably about 5 to 12 parts by mass per 100 parts by mass of water.
When iodine is used as the dichroic dye, the aqueous boric acid solution preferably contains potassium iodide. The content of potassium iodide in the boric acid aqueous solution is usually about 2 to 20 parts by mass, preferably 5 to 15 parts by mass per 100 parts by mass of water. The immersion time in the boric acid aqueous solution is usually about 100 to 1,200 seconds, preferably about 150 to 600 seconds, and more preferably about 200 to 400 seconds. The temperature of the boric acid aqueous solution is usually 50 ° C. or higher, preferably 50 to 85 ° C.

The PVA resin film after boric acid treatment is usually washed with water. The water washing treatment is performed, for example, by immersing a boric acid-treated PVA resin film in water. After washing with water, a drying process is performed to obtain a polarizer. The temperature of water in the water washing treatment is usually about 5 to 40 ° C., and the immersion time is usually about 2 to 120 seconds. The drying process performed thereafter is usually performed using a hot air dryer or a far infrared heater. The drying temperature is usually 40 to 100 ° C. The processing time in the drying process is usually about 120 to 600 seconds.
In this way, a polarizer comprising a PVA resin film in which iodine or dichroic dye is adsorbed and oriented is obtained.

[Adhesive layer]
In the present invention, the bonding between the optical film and the polarizer is performed via the adhesive layer as described above.
As an adhesive for forming the adhesive layer, a PVA adhesive, an epoxy adhesive, an acrylic adhesive, a polyolefin grafted with an unsaturated carboxylic acid or an anhydride thereof, or a polyolefin system blended with the grafted polyolefin Examples include adhesives. In addition, an adhesive having transparency, for example, an adhesive such as polyvinyl ether or rubber can be used. Among these, a PVA adhesive is preferable.

The PVA-based adhesive contains a PVA-based resin and a cross-linking agent. Examples of the PVA-based resin include PVA obtained by saponifying polyvinyl acetate and its derivatives, and a single copolymer having a copolymerizable property with vinyl acetate. Examples thereof include a saponified product of a copolymer with a monomer, a modified PVA obtained by acetalizing, urethanizing, etherifying, grafting or phosphoric esterifying PVA. These PVA resins can be used singly or in combination of two or more. Monomers copolymerizable with vinyl acetate include (anhydrous) maleic acid, fumaric acid, crotonic acid, itaconic acid, (meth) acrylic acid and other unsaturated carboxylic acids and esters thereof, ethylene and propylene, etc. α-olefin, (meth) allylsulfonic acid (soda), sulfonic acid soda (monoalkylmalate), disulfonic acid soda alkylmalate, N-methylolacrylamide, acrylamide alkylsulfonic acid alkali salt, N-vinylpyrrolidone, N- Examples include vinyl pyrrolidone derivatives.
The degree of polymerization of the PVA-based resin is not particularly limited, but since the adhesiveness and the like are improved, the average degree of polymerization is about 100 to 3000, preferably 500 to 3000, and the average saponification degree is about 85 to 100 mol%, preferably It is preferable to use about 90-100 mol%.

  Examples of the epoxy adhesive include a hydrogenated epoxy resin, an alicyclic epoxy resin, and an aliphatic epoxy resin. The epoxy resin may further contain a compound that promotes cationic polymerization, such as okitacenes and polyols.

  Acrylic adhesives include acrylic esters such as butyl acrylate, ethyl acrylate, methyl acrylate and 2-ethylhexyl acrylate, and α-mono such as acrylic acid, maleic acid, itaconic acid, methacrylic acid and crotonic acid. Those mainly composed of copolymers with olefin carboxylic acids (including those added with vinyl monomers such as acrylonitrile, vinyl acetate and styrene) are particularly preferred because they do not interfere with the polarization characteristics of the polarizer. .

  Further, a polyolefin grafted with an unsaturated carboxylic acid or an anhydride thereof or a polyolefin blended with the grafted polyolefin can also be used as an adhesive. Examples of polyolefins used for grafting include low density polyethylene, high density polyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-pentene, ethylene-propylene copolymer, and ethylene-1-butene copolymer. , Propylene-1-butene copolymer, and mixtures thereof. Examples of the unsaturated carboxylic acid or anhydride thereof used for polyolefin grafting include acrylic acid, methacrylic acid, maleic acid, maleic anhydride, citraconic acid, citraconic anhydride, itaconic acid, and itaconic anhydride. The modified polyolefin thus obtained may be used as it is, but can also be used by blending with polyolefin.

  The adhesive layer is formed by applying an adhesive on either or both sides of the optical film and the polarizer. The thickness of the adhesive layer is preferably 0.01 to 10 μm, more preferably 0.03 to 5 μm.

  Moreover, when bonding the said optical film with a polarizer, an easily bonding process can be performed for the adhesive improvement to the surface which contact | connects the polarizer of an optical film. Examples of the easy adhesion treatment include surface treatment such as corona treatment, plasma treatment, low-pressure UV treatment, and saponification treatment, and a method of forming an anchor layer, and these can be used in combination. Among these, a corona treatment, a method of forming an anchor layer, and a method of using these in combination are preferable.

  Next, an adhesive layer is formed on the surface subjected to the easy adhesion treatment as described above, and the optical film of the present invention and the polarizer are bonded through the adhesive layer. This bonding can be performed by a roll laminator or the like. The heating drying temperature and drying time are appropriately determined according to the type of adhesive.

  The polarizing plate of the present invention, which is bonded to at least one surface of the polarizer as the protective film of the polarizer of the present invention, is laminated with the optical film of the present invention on the other surface of the polarizer, if necessary. It is also possible to laminate films made of other resins. Examples of other resin films include fumaric acid diester resins, triacetyl cellulose films, polyether sulfone films, polyarylate films, polyethylene terephthalate films, polynaphthalene terephthalate films, polycarbonate films, cyclic polyolefin films, and maleimide resins. Examples thereof include a film and a fluorine resin film. The film made of the other resin may be a retardation film having a specific retardation.

The polarizing plate of the present invention is preferably a laminate having at least one hard coat layer in order to improve surface properties and scratch resistance. Examples of the hard coat layer include a hard coat layer made of, for example, a silicone resin, an acrylic resin, an acrylic silicone resin, an ultraviolet curable resin, a urethane hard coat agent, etc. Among them, transparency, scratch resistance, From the viewpoint of chemical resistance, a hard coat layer made of an ultraviolet curable resin is preferable. One or more of these hard coat layers can be used.
Examples of the ultraviolet curable resin include one or more ultraviolet curable resins selected from ultraviolet curable acrylic urethane, ultraviolet curable epoxy acrylate, ultraviolet curable (poly) ester acrylate, ultraviolet curable oxetane, and the like.
As for the thickness of a hard-coat layer, 0.1-100 micrometers is preferable, Especially preferably, it is 1-50 micrometers, More preferably, it is 2-20 micrometers. Further, a primer treatment can be performed between the hard coat layers.

  Moreover, the polarizing plate of this invention can perform well-known anti-glare processes, such as antireflection and a low reflection process, as needed.

[Image display device]
The polarizing plate formed by forming the optical film of the present invention on at least one side is used by being bonded to a liquid crystal cell, for example. In FIG. 2, the structural example of the liquid crystal cell which has the optical film and polarizing plate of this invention is shown. In FIG. 2, 6 indicates a liquid crystal cell. Examples of the liquid crystal cell 6 include an active matrix drive type typified by a thin film transistor type and a simple matrix drive type typified by a twist nematic type and a super twist nematic type. In the configuration example of the liquid crystal cell in FIG. 2, a retardation plate 8 is laminated on the liquid crystal cell 6 via an adhesive layer (not shown; the same applies hereinafter), and an adhesive layer ( The polarizing plate 7 of the present invention is laminated through a not-shown). Here, the optical element 2 is formed by laminating the retardation plate 8 and the polarizing plate 7, and the polarizing plate 7 has the polarizer 3 at the center, and the adhesive layer 5 is provided on the surfaces on both sides thereof. The protective film 4 made of the optical film of the present invention is laminated. When laminating the polarizing plate 7 and the retardation plate 8 and the retardation plate 8 and the liquid crystal cell 6 of the present invention, an adhesive layer may be provided on the polarizing plate 7, the retardation plate 8 and the liquid crystal cell 6 in advance.

  The pressure-sensitive adhesive for laminating the polarizing plate and the liquid crystal cell of the present invention is not particularly limited. For example, an acrylic polymer, silicone polymer, polyester, polyurethane, polyamide, polyether, fluorine-based or rubber-based polymer is a base polymer. Can be appropriately selected and used. The pressure-sensitive adhesive is required to be excellent in optical transparency, suitable wettability, cohesive properties such as cohesiveness, adhesiveness, weather resistance, heat resistance and the like. Furthermore, the moisture absorption rate is low in terms of preventing foaming and peeling due to moisture absorption, reducing optical characteristics due to thermal expansion differences, preventing warping of liquid crystal cells, and, in turn, forming a high-quality and durable image display device. Therefore, a pressure-sensitive adhesive layer having excellent heat resistance is required. From such a viewpoint, an acrylic adhesive is preferable.

  Examples of the pressure-sensitive adhesive include natural and synthetic resins, in particular, tackifier resins, fillers and pigments made of glass fibers, glass beads, metal powders, other inorganic powders, colorants, antioxidants, and the like. Etc. may be contained. Moreover, the adhesive layer which contains microparticles | fine-particles and shows light diffusibility may be sufficient.

The application of the pressure-sensitive adhesive to the polarizing plate of the present invention is not particularly limited, and can be performed by an appropriate method. For example, a pressure-sensitive adhesive solution of about 10 to 40% by mass in which a base polymer or a composition thereof is dissolved or dispersed in a solvent composed of an appropriate solvent alone or a mixture such as toluene or ethyl acetate is prepared, and the resulting solution is allowed to flow. A method of coating directly on the polarizing plate of the present invention by an appropriate development method such as a rolling method or a coating method, or forming an adhesive layer on a releasable base film according to this method and applying it to the present invention. The method of transferring to a polarizing plate is mentioned.
As the coating method, various methods such as gravure coating, bar coating, roll coating, reverse roll coating, comma coating and the like are possible, but gravure coating is the most common.

The pressure-sensitive adhesive layer can also be provided on one or both sides of the polarizing plate of the present invention as a superimposed layer of different compositions or types. Moreover, when providing in both surfaces, the adhesive does not need to be the same composition in the front and back of the polarizing plate of this invention, and it is not necessary to be the same thickness. It can also be set as the adhesive layer of a different composition and different thickness.
The thickness of the pressure-sensitive adhesive layer can be appropriately determined according to the purpose of use and adhesive force, and is generally 1 μm to 500 μm, preferably 5 μm to 200 μm, particularly preferably 10 μm to 100 μm.

  The exposed surface of the pressure-sensitive adhesive layer is preferably temporarily covered with a release film for the purpose of preventing the contamination until it is put to practical use. Thereby, it can prevent contacting an adhesive layer in the usual handling state. As the releasable film, for example, an appropriate thin leaf body such as a plastic film, rubber sheet, paper, cloth, non-woven fabric, net, foamed sheet or metal foil, or a laminate thereof, silicone type or long chain alkyl type as necessary Conventionally known materials such as those coated with an appropriate release agent such as fluorine-based or molybdenum sulfide can be used.

  In the present invention, the polarizer, the protective film layer, the pressure-sensitive adhesive layer, and the like include, for example, salicylic acid ester compounds, benzophenol compounds, benzotriazole compounds, cyanoacrylate compounds, nickel complex compounds, and the like. Ultraviolet absorbing ability may be imparted by a method of treating with an ultraviolet absorber.

  The polarizing plate of the present invention can be preferably used for forming various devices such as an image display device. Examples of the image display device include a liquid crystal display including a liquid crystal cell, an organic EL display device, a touch panel, and the like, and there is no limitation on the type of the image display device as long as a polarizing plate is used. In the case of a liquid crystal display, an image display device is generally formed by appropriately assembling components such as a liquid crystal cell, an optical film, and an illumination system as necessary, and incorporating a drive circuit. In the invention, the configuration of the image display device is not particularly limited except that the polarizing plate is used. For example, an appropriate image display device such as an image display device in which a polarizing plate is disposed on one side or both sides of a liquid crystal cell, or a backlight or a reflection plate as an illumination system is exemplified. As the liquid crystal cell, any type such as a TN type, an STN type, or a π type can be used. In configuring the image display device, for example, a single layer of appropriate parts such as a diffusion plate, an antiglare layer, an antireflection film, a protective plate, a prism array, a lens array sheet, a light diffusion plate, and a backlight are provided at appropriate positions. Alternatively, two or more layers can be arranged.

[Application to organic EL display devices]
The polarizing plate of the present invention can be suitably used for an organic EL display device.
Generally, in an organic EL display device, a transparent electrode, an organic light emitting layer, and a metal electrode are sequentially laminated on a transparent substrate to form a light emitter (organic electroluminescent light emitter). Here, the organic light emitting layer is a laminate of various organic thin films, for example, a laminate of a hole injection layer made of a triphenylamine derivative and the like and a light emitting layer made of a fluorescent organic solid such as anthracene, Or, a structure having various combinations such as a stacked body of an electron injection layer composed of such a light emitting layer and a perylene derivative, a stacked body of these hole injection layer, light emitting layer, and electron injection layer is known. Yes.

In organic EL display devices, holes and electrons are injected into the organic light-emitting layer by applying a voltage to the transparent electrode and the metal electrode, and the energy generated by recombination of these holes and electrons excites the phosphor material. Then, light is emitted on the principle that the excited fluorescent material emits light when returning to the ground state. The mechanism of recombination in the middle is the same as that of a general diode, and as can be predicted from this, the current and the emission intensity show strong nonlinearity with rectification with respect to the applied voltage.
In an organic EL display device, in order to extract light emitted from the organic light emitting layer, at least one of the electrodes must be transparent, and a transparent electrode usually formed of a transparent conductor such as indium tin oxide (ITO) is used as an anode. It is used as. On the other hand, in order to facilitate electron injection and increase luminous efficiency, it is important to use a material having a small work function for the cathode, and usually metal electrodes such as Mg—Ag and Al—Li are used.

  In the organic EL display device having such a configuration, the organic light emitting layer is formed of a very thin film having a thickness of about 10 nm. For this reason, the organic light emitting layer transmits light almost completely like the transparent electrode. As a result, light that is incident from the surface of the transparent substrate at the time of non-light emission, passes through the transparent electrode and the organic light emitting layer, and is reflected by the metal electrode is again emitted to the surface side of the transparent substrate. The display surface of the organic EL display device looks like a mirror surface.

  In an organic EL display device comprising an organic electroluminescent light emitting device comprising a transparent electrode on the surface side of an organic light emitting layer that emits light upon application of a voltage and a metal electrode on the back side of the organic light emitting layer, the surface of the transparent electrode The polarizing plate of the present invention can be provided on the side, and a birefringent layer (retardation plate) can be provided between the transparent electrode and the polarizing plate.

Since the polarizing plate of the present invention has a function of polarizing light incident from the outside and reflected by the metal electrode, there is an effect that the mirror surface of the metal electrode is not visually recognized from the outside by the polarization action. In particular, if the birefringent layer is composed of a λ / 4 plate and the angle between the polarizing direction of the polarizing plate and the birefringent layer is adjusted to π / 4, the mirror surface of the metal electrode can be completely shielded. .
That is, only the linearly polarized light component of the external light incident on the organic EL display device is transmitted by the polarizing plate. This linearly polarized light generally becomes elliptically polarized light by the birefringent layer, but becomes circularly polarized light when the birefringent layer is a λ / 4 plate and the angle formed by the polarization direction with the polarizing plate is π / 4. This circularly polarized light is transmitted through the transparent substrate, the transparent electrode, and the organic thin film, is reflected by the metal electrode, is again transmitted through the organic thin film, the transparent electrode, and the transparent substrate, and becomes linearly polarized light again at the birefringent layer. And since this linearly polarized light is orthogonal to the polarization direction of a polarizing plate, it cannot permeate | transmit a polarizing plate. As a result, the mirror surface of the metal electrode can be completely shielded.

[Applied to touch panel]
The optical film of this invention can be used conveniently also for the polarizing plate of a touchscreen. In general, a touch panel is a device in which an operator operates a device or a system by touching a transparent surface provided at the top of a display screen with a pen or a finger. In recent years, touching directly on the screen has become more and more popular in recent years because it is more direct and intuitive than pressing the cursor with a direction key to determine the position. . In recent years, the growth of mobile terminals such as mobile phones and PDAs (Personal Digital Assistants) has been remarkable, and there is a strong demand for visibility under the sunlight and thin and light weight. Became. There are various types of touch panels, and they are properly used depending on their advantages and disadvantages. The touch panel includes a resistive film method, an optical method, a capacitive coupling method (also called an analog capacitive coupling method), an infrared method, an ultrasonic method, and an electromagnetic induction method. Here, an example of a resistive film type touch panel will be described.

  Resistive touch panels include a glass / glass type and a glass / film type. In the glass / glass type, a glass substrate with a transparent conductive layer and a glass substrate with a transparent conductive layer are held via a space, and this is mounted on the display surface. The glass / film type is a touch panel of the type in which an upper glass substrate with a transparent conductive layer is replaced with an optical film because a lighter and thinner one is desired in a vehicle-mounted or portable touch panel.

A glass / glass type touch panel is shown in FIG. 3, and a glass / film type touch panel is shown in FIG. A glass / glass type touch panel and a glass / film type touch panel will be described below with reference to FIGS.
If a linearly polarizing plate or a circularly polarizing plate made by combining a polarizing plate with a λ / 4 plate is used on the outermost surface of the touch panel, sufficient strength can be obtained as a touch panel, and visibility can be improved due to the antireflection effect. Will improve. The polarizing plates of the touch panel are 9 in FIG. 3 and 17 in FIG. The optical film of this invention can be used conveniently for the polarizing plate of these touch panels.
A polarizing plate and a λ / 4 plate comprising the optical film of the present invention and a polarizer are laminated so that the angle between the slow axis in the plane of the λ / 4 plate and the polarizing axis of the polarizing plate is substantially 45 °. A circularly polarizing plate is then obtained. Substantially 45 ° means 40 ° to 50 °. The angle between the slow axis in the plane of the λ / 4 plate and the polarization axis of the polarizing film is preferably 41 to 49 °, more preferably 42 to 48 °, and 43 to 47 °. Is more preferable, and it is most preferable that it is 44-46 degrees.

The optical film of the present invention can be used for any of the upper, lower and lower outer layers (lightweight reduction film provided with ITO) of the polarizing plate. There are two types of anti-reflection for touch panels: linearly polarized light type and circularly polarized light type (linearly polarized light has a higher reflectance than circularly polarized light). Can also be used.
The circularly polarizing plate or linearly polarizing plate using the optical film of the present invention can be used for both transmissive and reflective touch panels.

EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by this example.
(Evaluation methods)
1. Measurement of MFR Using a melt indexer (“F-W01 (model number)”; manufactured by Toyo Seiki Seisakusho), MFR under conditions of 230 ° C. and 2.16 kg load was measured in accordance with JIS K7210.
2. Tensile strength It was performed in accordance with ASTM D638.
3. Evaluation of in-plane retardation The in-plane retardation was measured using a phase difference measuring machine (“KOBRA-WR (model number)” manufactured by Oji Scientific Instruments) at a wavelength of 589.3 nm and an incident angle of 0 degree.
4). Transparency (haze)
The measurement was performed according to JIS K7105.
5). Heat resistance and moisture resistance A polarizer comprising a polyvinyl alcohol-based resin film in which iodine is adsorbed and oriented using PVA obtained by saponifying polyvinyl acetate as an optical film obtained in each of Examples and Comparative Examples. Was adhered to both surfaces to obtain a polarizing plate.
A 150 mm square test piece was cut out from the polarizing plate, and as an evaluation of heat resistance, the appearance of the polarizing plate after maintaining at 90 ° C. for 1,000 hours was observed. A case where no deformation, coloring or the like occurred was indicated by “◯”, and a case where deformation, coloring or the like occurred and the optical characteristics were deteriorated was indicated by “X”.
In addition, as an evaluation of moisture resistance, the appearance of the polarizing plate was observed after being held at 70 ° C. and a relative humidity of 95% for 1,000 hours. A case where no deformation, coloring or the like occurred was indicated by “◯”, and a case where deformation, coloring or the like occurred and the optical characteristics were deteriorated was indicated by “X”.
6). Flexural modulus Measured according to JIS K7171.
7). Measurement of Rth The optical films obtained in Examples 1 to 3 and Comparative Example 3 were measured at a wavelength of 589.3 nm using a phase difference measuring device (“KOBRA-WR (model number)” manufactured by Oji Scientific Instruments). The angle-dependent phase difference at an incident angle of −50 to 50 ° was measured every 10 °, and the retardation Rth in the thickness direction of the optical film was calculated using this result.

Example 1
A polypropylene resin synthesized by a metallocene catalyst (manufactured by Nippon Polypro Co., Ltd., trade name: Wintech, MFR; 24 g / 10 min, melting point 142 ° C., hereinafter referred to as “mPP-A”) is processed at a processing temperature of 200 ° C. An optical film was obtained by T-die single layer extrusion molding with a thickness of 100 μm under the condition of a take-up roll temperature of 50 ° C.
The optical film was evaluated by the above evaluation method. The results are shown in Tables 1 and 2.

Example 2
Instead of mPP-A used in Example 1, a polypropylene resin synthesized by a metallocene catalyst (manufactured by Nippon Polypro Co., Ltd., trade name: Wintech, MFR; 30 g / 10 min, melting point: 135 ° C., hereinafter “mPP-B An optical film was obtained in the same manner as in Example 1 except that the above was used. The results evaluated in the same manner as in Example 1 are shown in Tables 1 and 2.

Example 3
In addition to mPP-A used in Example 1, di-substituted dibenzylidene sorbitol nucleating agent master batch (manufactured by Riken Vitamin Co., Ltd., trade name Riquemaster, PN-10R, nucleating agent 10% by mass) mPP- 3 parts by mass (transparent nucleating agent content; 0.1 parts by mass) was added to 100 parts by mass of A, and an optical film was obtained in the same manner as in Example 1. The results evaluated in the same manner as in Example 1 are shown in Tables 1 and 2.

Comparative Example 1
Instead of mPP-A used in Example 1, polypropylene resin synthesized by metallocene catalyst (manufactured by Nippon Polypro Co., Ltd., trade name: Wintech, MFR; 15 g / 10 min, melting point 125 ° C., hereinafter “mPP-C An optical film was obtained in the same manner as in Example 1 except that the above was used. The results of evaluation in the same manner as in Example 1 are shown in Table 1.

Comparative Example 2
In place of mPP-A used in Example 1, polypropylene resin synthesized by Ziegler catalyst (manufactured by Prime Polymer Co., Ltd., trade name: Prime Polypro, MFR; 25 g / 10 min, melting point: 135 ° C., hereinafter “random” An optical film was obtained in the same manner as in Example 1 except that “PP” was used. The results of evaluation in the same manner as in Example 1 are shown in Table 1.

＊１，フィルム端部に応力がかかるために、面内位相差にばらつきを有する。

* 1: Since stress is applied to the film edge, the in-plane retardation varies.

  The optical films obtained in Examples 1 to 3 were shown to have excellent performance. On the other hand, it was shown that the comparative example 1 cannot be used for the polarizing plate because stress is easily applied to the film edge, the in-plane retardation varies from 5 to 27 nm, and the film has a high region. Further, the optical film obtained in Comparative Example 2 has an in-plane retardation of 25 nm, much higher than 10 nm and a large haze, which indicates that it is unsuitable for use in a polarizing plate.

Comparative Example 3
Rth of a commercially available TAC film (“Fujitac (trade name)”: manufactured by Fuji Film Co., Ltd., thickness: 80 μm) was measured by the above measuring method. The results are shown in Table 2.

  Rth of the polypropylene resin film used in Examples 1 to 3 was equivalent to Rth of a commercially available TAC film, and the retardation performance was shown to be the same as that of the TAC film.

According to the present invention, it is suitable as a protective film for a polarizer having excellent optical properties such as low haze, excellent transparency, low birefringence, excellent mechanical strength and heat resistance, and excellent moisture permeability. An optical film can be provided. Moreover, the optical film of the present invention is excellent in various durability such as heat resistance, moist heat resistance, and cold heat cycle, and improves the polarization degree of the polarizing plate without affecting the optical function of the polarizing plate. And it is flexible and elastic.
Further, since the optical film of the present invention has resistance to external impacts and deformations, the strength and reliability as a liquid crystal display element can be remarkably improved by using the optical film by being bonded to a polarizer. A polarizing plate can be provided.
Furthermore, the optical film of the present invention is more hydrophobic than the conventionally used TAC film, whereas the optical film of the present invention is hydrophobic, whereas the optical film of the present invention is hydrophobic. The durability of the polarizing plate can be greatly improved. Therefore, the optical film of the present invention can be suitably used as a protective film laminated on at least one surface of the polarizing plate and bonded to the liquid crystal cell surface substrate, and can also be used as a protective film on the other side of the polarizing plate. it can.

It is a schematic diagram which shows the manufacturing process of the polarizing plate of this invention. It is a schematic diagram which shows the structural example of the liquid crystal cell which has the polarizing plate of this invention. It is a schematic diagram which shows the structural example of the resistive film type touchscreen (glass / glass type) which has the polarizing plate of this invention. It is a schematic diagram which shows the structural example of the resistive film type touchscreen (glass / film type) which has the polarizing plate of this invention.

Explanation of symbols

1: Molten resin (PP)
2: Optical element 3: Polarizer 4: Protective film (optical film)
5: Adhesive layer 6: Liquid crystal cell 7: Polarizing plate 8: Phase difference plate (birefringent plate)
9: Polarizing plate of touch panel 10: Antireflection film 11: λ / 4 plate 12: Protective film for polarizer [top]
12 ': Polarizer protective film [bottom]
13: Polarizer (PVA)
14: Glass 15: ITO protective film 16: Protective film for polarizer [lower and outer]
17: Polarizing plate for touch panel

Claims (6)

  It is composed of a polypropylene resin synthesized with a metallocene catalyst, and the melt flow rate of the polypropylene resin (MFR; measured value under conditions of 230 ° C. and 2.16 kg load according to JIS K7210) is 20 g / 10 min or more. An optical film for a protective film of a certain polarizer.   The optical film according to claim 1, wherein the optical film is an unstretched film.   The optical film according to claim 1 or 2, further comprising 0.03 to 0.5 parts by mass of a dibenzylidene sorbitol-based additive with respect to 100 parts by mass of the polypropylene resin.   The optical film according to claim 1, wherein the optical film has a thickness direction retardation Rth of 20 to 60 nm.   The polarizing plate formed by forming the optical film in any one of Claims 1-4 on the at least single side | surface of a polarizer.   An image display device using the polarizing plate according to claim 5.

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