JP2007256569A - Polarizing plate and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress generation of curls in a polarizing plate formed by layering a cycloolefin based resin film on one surface of a polarizing film made of a polyvinyl alcohol based resin via an adhesive and a cellulose acetate based film on the other surface via an adhesive. <P>SOLUTION: When the polarizing plate is manufactured by layering the cycloolefin based resin film on one surface of the polarizing film made of the polyvinyl alcohol based resin via the adhesive and the cellulose acetate based film on the other surface via the adhesive, the cellulose acetate based film is made to adhere to the polarizing film on the concave side of the curl generated after the cellulose acetate based film is left at 80°C for 24 hr. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is a polarizing film in which a cycloolefin resin film is laminated on one surface of a polarizing film made of polyvinyl alcohol resin via an adhesive, and a cellulose acetate film is laminated on the other surface via an adhesive. It is related with a board and its manufacturing method. More specifically, the present invention relates to a polarizing plate that suppresses the occurrence of curling and prevents air bubbles from being mixed when bonded to a liquid crystal cell, and a manufacturing method thereof.

  A polarizing plate is usually a transparent resin film, for example, a cellulose acetate-based protective film typified by triacetylcellulose, on both sides of a polarizing film made of a polyvinyl alcohol-based resin adsorbed and oriented with a dichroic dye. It is the structure which laminated | stacked. In addition, when an optical film with a cycloolefin-based resin film or the like stretched is attached to a polarizing plate via an adhesive, it is visible from various angles when applied to a liquid crystal cell as a liquid crystal display device. Is improved and a good viewing angle is obtained.

  It is also known that a cycloolefin-based resin film is bonded to a polyvinyl alcohol-based polarizing film. For example, in JP-A-5-212828 (Patent Document 1), at least one surface of a polyvinyl alcohol-based sheet has an acrylic film. It describes that a thermoplastic saturated norbornene-based resin sheet is laminated through an adhesive and is heat-pressed to form a polarizing plate. However, the pressure sensitive adhesive such as acrylic (also called pressure sensitive adhesive) itself has a thickness of about 10 to 50 μm, so the liquid crystal display device must be thick, and the polarizing film and cycloolefin It was complicated to stick the resin films one by one.

  On the other hand, it is also known that a cycloolefin-based resin film is bonded to a polarizing film made of a polyvinyl alcohol-based resin through an adhesive. For example, JP 2005-70140 A (Patent Document 2), JP 2005-2005 A JP-A-181817 (Patent Document 3) and JP-A-2005-208456 (Patent Document 4) describe a water-based adhesive containing a urethane resin, particularly a polyester ionomer type urethane resin, on a polarizing film made of polyvinyl alcohol resin. It describes that a cycloolefin resin film is laminated through an agent. According to the techniques described in these publications, a cycloolefin-based protective film can be directly laminated on a polyvinyl alcohol-based polarizing film by a roll-to-roll method.

  Moreover, in the polarizing plate which laminated the protective film on both surfaces of the polarizing film, what is called curl that the polarizing plate warps to one surface side may become a problem. For example, Japanese Patent Application Laid-Open No. 2004-184809 (Patent Document 5) describes two types of protective sheets having a curl and both sides of the polarizing film so that the directions of the curls are opposite to each other. A method of pasting to a sheet is disclosed.

  Furthermore, it is also known to paste a cycloolefin resin film on one surface of a polarizing film made of a polyvinyl alcohol resin and a cellulose acetate film on the other surface. Japanese Patent Laid-Open No. 2005-352011 (Patent Document 6) discloses such a configuration. A polarizing plate in which a cycloolefin-based resin film is bonded to one surface of a polyvinyl alcohol-based polarizing film and a cellulose acetate-based film is bonded to the other surface has an asymmetric configuration, and the cycloolefin-based resin film itself Since the curl of the film is extremely small, the amount of curling tends to be large compared to a polarizing plate having a symmetrical structure in which a cellulose acetate film is laminated on both sides of a polyvinyl alcohol polarizing film, and bubbles are formed when pasting to a liquid crystal cell. There was a problem of easy mixing.

Japanese Patent Laid-Open No. 5-212828 JP-A-2005-70140 JP 2005-181817 A JP-A-2005-208456 Japanese Patent Laid-Open No. 2004-184809 JP 2005-352011 A

  Therefore, an object of the present invention is to laminate a cycloolefin resin film on one surface of a polarizing film made of polyvinyl alcohol resin via an adhesive, and a cellulose acetate film on the other surface via an adhesive. In the polarizing plate thus formed, curling is to be suppressed.

  As a result of intensive studies under such a purpose, the present inventors have found that a cycloolefin resin film is laminated on one surface of a polarizing film made of a polyvinyl alcohol resin via an adhesive, and the other surface. In the polarizing plate in which a cellulose acetate film is laminated on an adhesive, the present invention has been achieved by paying attention to the adhesive surface of the cellulose acetate film to the polarizing film.

  That is, according to the present invention, a cycloolefin resin film is laminated on one surface of a polarizing film made of a polyvinyl alcohol resin via an adhesive, and a cellulose acetate film is laminated on the other surface via an adhesive. Thus, the cellulose acetate film is provided with a polarizing plate in which the convex side of the curl generated after standing at 80 ° C. for 24 hours is an adhesive surface to the polarizing film.

  Further, according to the present invention, a cycloolefin resin film is laminated on one surface of a polarizing film made of polyvinyl alcohol resin via an adhesive, and a cellulose acetate film is adhered on the other surface via an adhesive. When producing a polarizing plate by laminating, a method for producing a polarizing plate is also provided in which the cellulose acetate-based film adheres to the polarizing film on the convex surface side of a curl generated after standing at 80 ° C. for 24 hours.

  According to the present invention, a cycloolefin resin film is laminated on one surface of a polarizing film made of polyvinyl alcohol resin via an adhesive, and a cellulose acetate film is laminated on the other surface via an adhesive. In the polarizing plate, the occurrence of curling can be reduced.

  Hereinafter, the present invention will be described in detail. In the polarizing plate of the present invention, a cycloolefin-based resin film is laminated on one surface of a polarizing film made of a polyvinyl alcohol-based resin via an adhesive, and a cellulose acetate-based film is bonded on the other surface via an adhesive. Laminated.

  Specifically, the polarizing film made of a polyvinyl alcohol-based resin is obtained by adsorbing and orienting a dichroic dye on a uniaxially stretched polyvinyl alcohol-based resin film.

  The polyvinyl alcohol resin constituting the polarizing film 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, copolymers of vinyl acetate and other monomers copolymerizable therewith. Examples of other monomers copolymerized with vinyl acetate include unsaturated carboxylic acids, unsaturated sulfonic acids, olefins, vinyl ethers, and acrylamides having an ammonium group. The saponification degree of the polyvinyl alcohol resin is usually about 85 to 100 mol%, preferably 98 mol% or more. The polyvinyl alcohol-based resin may be further modified, and for example, polyvinyl formal or polyvinyl acetal modified with aldehydes may be used. The degree of polymerization of the polyvinyl alcohol resin is usually about 1,000 to 10,000, preferably about 1,500 to 5,000.

  A film obtained by forming such a polyvinyl alcohol resin is used as a raw film of a polarizing film. The method for forming a polyvinyl alcohol-based resin is not particularly limited, and can be formed by a known method. Although the film thickness of a polyvinyl alcohol-type raw film is not specifically limited, For example, it is about 10-150 micrometers.

  A polarizing film usually has a step of uniaxially stretching such a polyvinyl alcohol resin film, a step of dyeing a polyvinyl alcohol resin film with a dichroic dye and adsorbing the dichroic dye, and a dichroic dye adsorbed. It is manufactured through a step of treating the polyvinyl alcohol-based resin film with a boric acid aqueous solution and a step of washing with water after the treatment with the boric acid aqueous solution.

  Uniaxial stretching may be performed before dyeing, simultaneously with dyeing, or after dyeing. When uniaxial stretching is performed after dyeing, this uniaxial stretching may be performed before boric acid treatment or during boric acid treatment. Of course, it is also possible to perform uniaxial stretching in these plural stages. In uniaxial stretching, it may be uniaxially stretched between rolls having different peripheral speeds, or may be uniaxially stretched using a hot roll. Further, it may be dry stretching such as stretching in the air, or may be wet stretching in which stretching is performed in a state swollen with a solvent. The draw ratio is usually about 2 to 8 times.

  In order to dye the polyvinyl alcohol resin film with the dichroic dye, for example, the polyvinyl alcohol resin film may be immersed in an aqueous solution containing the dichroic dye. Specifically, iodine or a dichroic dye is used as the dichroic dye. In addition, it is preferable that the polyvinyl alcohol-type resin film performs the immersion process to water before a dyeing process.

  When iodine is used as the dichroic dye, a method of dyeing a polyvinyl alcohol resin film by dipping in an aqueous solution containing iodine and potassium iodide is usually employed. The iodine content in this aqueous solution is usually about 0.01 to 1 part by weight per 100 parts by weight of water, and the potassium iodide content is usually about 0.5 to 20 parts by weight per 100 parts by weight of water. . The temperature of the aqueous solution used for dyeing is usually about 20 to 40 ° C., and the immersion time (dyeing time) in this aqueous solution is usually about 20 to 1,800 seconds.

On the other hand, when a dichroic dye is used as the dichroic dye, a method of immersing and dyeing a polyvinyl alcohol-based resin film in an aqueous solution containing a water-soluble dichroic dye is usually employed. The content of the dichroic dye in this aqueous solution is usually about 1 × 10 ⁻⁴ to 10 parts by weight, preferably about 1 × 10 ⁻³ to 1 part by weight per 100 parts by weight of water. This aqueous solution may contain an inorganic salt such as sodium sulfate as a dyeing assistant. The temperature of the aqueous dye solution used for dyeing is usually about 20 to 80 ° C., and the immersion time (dyeing time) in this aqueous solution is usually about 10 to 1,800 seconds.

  The boric acid treatment after dyeing with the dichroic dye is performed by immersing the dyed polyvinyl alcohol-based resin film in a boric acid-containing aqueous solution. The amount of boric acid in the boric acid-containing aqueous solution is usually about 2 to 15 parts by weight, preferably about 5 to 12 parts by weight per 100 parts by weight of water. When iodine is used as the dichroic dye, this boric acid-containing aqueous solution preferably contains potassium iodide. The amount of potassium iodide in the boric acid-containing aqueous solution is usually about 0.1 to 15 parts by weight, preferably about 5 to 12 parts by weight per 100 parts by weight of water. The immersion time in the boric acid-containing aqueous solution is usually about 60 to 1,200 seconds, preferably about 150 to 600 seconds, and more preferably about 200 to 400 seconds. The temperature of the boric acid-containing aqueous solution is usually 50 ° C. or higher, preferably 50 to 85 ° C., more preferably 60 to 80 ° C.

  The polyvinyl alcohol resin film after the boric acid treatment is usually washed with water. The water washing treatment is performed, for example, by immersing a boric acid-treated polyvinyl alcohol resin film in water. The water temperature in the water washing treatment is usually about 5 to 40 ° C., and the immersion time is usually about 1 to 120 seconds. After washing with water, a drying process is performed to obtain a polarizing film. The drying process is usually performed using a hot air dryer or a far infrared heater. The temperature of the drying treatment is usually about 30 to 100 ° C, preferably 50 to 80 ° C. The time for the drying treatment is usually about 60 to 600 seconds, preferably about 120 to 600 seconds.

  In this way, the polyvinyl alcohol resin film is subjected to uniaxial stretching, dyeing with a dichroic dye, and boric acid treatment to obtain a polarizing film. The thickness of this polarizing film is about 5 to 40 μm. In the present invention, a cycloolefin resin film is laminated on one surface of the polarizing film via an adhesive, and a cellulose acetate film is laminated on the other surface via an adhesive.

  The cycloolefin resin is a thermoplastic resin having a monomer unit made of a cyclic olefin (cycloolefin) such as norbornene or a polycyclic norbornene monomer. This cycloolefin-based resin can be a hydrogenated product of the above-mentioned cycloolefin ring-opening polymer or a ring-opening copolymer using two or more kinds of cycloolefins, as well as cycloolefins and chain olefins or vinyl groups. It may be an addition copolymer with an aromatic compound having Those having a polar group introduced are also effective.

  When a copolymer of a cycloolefin and a chain olefin or an aromatic compound having a vinyl group is used, examples of the chain olefin include ethylene and propylene, and examples of the aromatic compound having a vinyl group Examples thereof include styrene, α-methylstyrene, and nuclear alkyl-substituted styrene. In such a copolymer, the monomer unit composed of cycloolefin may be 50 mol% or less, for example, about 15 to 50 mol%. In particular, when a ternary copolymer of a cycloolefin, a chain olefin, and an aromatic compound having a vinyl group is used, the amount of monomer units composed of cycloolefin can be relatively small. In such a terpolymer, the unit of monomer composed of a chain olefin is usually about 5 to 80 mol%, and the unit of monomer composed of an aromatic compound having a vinyl group is usually about 5 to 80 mol%.

  Commercially available thermoplastic cycloolefin resins such as “Topas” sold by Ticona in Germany, “Arton” sold by JSR Corporation, and “ZEONOR” sold by Nippon Zeon Corporation. ) ”And“ ZEONEX ”and“ Apel ”sold by Mitsui Chemicals, Inc. (both are trade names). Such a cycloolefin-based resin is formed into a film, and a known method such as a solvent casting method or a melt extrusion method is appropriately used for forming the film. Formed cycloolefin resin films are also available on the market, such as “Essina” and “SCA40” sold by Sekisui Chemical Co., Ltd., “Zeonor Film” sold by Optes Co., Ltd. (Both are trade names).

  The cycloolefin-based resin film may be stretched uniaxially or biaxially to exhibit predetermined birefringence characteristics. The draw ratio in this case is usually about 1.1 to 5 times, preferably 1.1 to 3 times.

  The cellulose acetate film used as the other protective film in the present invention is a cellulose part or a complete acetate ester, and examples thereof include a triacetyl cellulose film and a diacetyl cellulose film. Commercially available triacetyl cellulose films include “Fujitack TD80”, “Fujitack TD80UF” and “Fujitack TD80UZ” sold by Fuji Photo Film Co., Ltd., “KC8UX2MW” sold by Konica Minolta Opto and There is “KC8UY”.

  The cellulose acetate film is preferably subjected to saponification treatment on the surface in order to increase the adhesive force with the adhesive. The saponification treatment can be performed by a method of immersing in an alkaline aqueous solution such as sodium hydroxide or potassium hydroxide.

  Further, prior to bonding to the polarizing film, it is preferable to perform a pretreatment that is immersed in water and then dried, in order to reduce curling. In the first treatment step of pretreatment, the cellulose acetate film is immersed in water at a temperature of 10 to 50 ° C. for 5 to 10 seconds to swell. At this time, when the temperature is high, streak-like defects may be formed on the film. Therefore, the temperature is preferably 20 to 45 ° C. In the second treatment step, the cellulose acetate film surface is dried. The drying process is usually performed using a hot air dryer or a far infrared heater. The temperature of the drying treatment is usually about 30 to 100 ° C, preferably 40 to 60 ° C. The drying time is usually about 20 to 600 seconds, preferably about 20 to 60 seconds. Under the present circumstances, the surface which bonds a cellulose acetate type | system | group film and a polarizing film can be adjusted by changing the roll | feeding-out direction of a roll suitably.

  The cellulose acetate film may be subjected to surface treatment such as antiglare treatment, hard coat treatment, antistatic treatment, and antireflection treatment on the surface opposite to the surface to be bonded to the polarizing film. In addition, a coat layer made of a liquid crystalline compound or a high molecular weight compound thereof may be formed.

  In the present invention, the cellulose acetate film is adhered to the polyvinyl alcohol polarizing film on the convex side of the curl generated after being left at 80 ° C. for 24 hours. A cellulose acetate film used as a protective film for a polarizing plate is generally produced by a solvent casting method in which a resin is dissolved in a solvent and cast on a support made of a metal belt or the like to volatilize the solvent. In that case, the surface which becomes an air side is called A surface, and the surface which becomes the reverse support body side is called B surface. As for the film used in the Example mentioned later, the A surface side became convex. As described above, by setting the convex surface side to be an adhesive surface to the polarizing film, the curl amount of the obtained polarizing plate is reduced as compared with the case where it is reversed.

  The thickness of each of the cycloolefin-based resin film and the cellulose acetate-based film disposed on both sides of the polarizing film is preferably thin, but if it is too thin, the strength decreases, and the processability is inferior. Problems such as a decrease in transparency and an increase in the weight of the polarizing plate occur. Therefore, a suitable thickness of the cycloolefin-based resin film is, for example, about 5 to 200 μm, preferably 10 to 150 μm, and more preferably 20 to 100 μm. Moreover, the suitable thickness of a cellulose acetate type | system | group film is about 20-200 micrometers, Preferably it is 20-100 micrometers.

  On one side of the polarizing film is a cycloolefin-based resin film as described above via an adhesive, and on the other side is an cellulose acetate as described above via an adhesive. System films are laminated to form a polarizing plate.

  The adhesive used for joining the polarizing film and the cycloolefin-based resin film, and the adhesive used for joining the polarizing film and the cellulose acetate-based film are water-based, that is, an adhesive from the viewpoint of thinning the adhesive layer. A component dissolved in water or a component dispersed in water is preferred. For example, a composition using a polyvinyl alcohol-based resin or a urethane resin as a main component can be mentioned as a preferred adhesive. Moreover, as long as suitable adhesiveness is obtained, it is preferable that the adhesive applied to both surfaces of the polarizing film has the same composition because the manufacturing process can be simplified.

  When a polyvinyl alcohol-based resin is used as the main component of the adhesive, the polyvinyl alcohol-based resin includes partially saponified polyvinyl alcohol and fully saponified polyvinyl alcohol, as well as carboxyl group-modified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, and methylol group. It may be a modified polyvinyl alcohol resin such as modified polyvinyl alcohol or amino group-modified polyvinyl alcohol. When using a polyvinyl alcohol resin, the aqueous solution serves as an adhesive. The density | concentration of the polyvinyl alcohol-type resin in an adhesive agent is about 1-10 weight part normally with respect to 100 weight part of water, Preferably it is 1-5 weight part.

  It is preferable to add a curable component such as glyoxal or a water-soluble epoxy resin or a crosslinking agent to the adhesive composed of an aqueous solution of a polyvinyl alcohol-based resin in order to increase the adhesiveness. The water-soluble epoxy resin is, for example, a polyamide epoxy resin obtained by reacting an epichlorohydrin with a polyamide polyamine obtained by reacting a polyalkylene polyamine such as diethylenetriamine or triethylenetetramine with a dicarboxylic acid such as adipic acid. Can be. Examples of commercially available polyamide epoxy resins include “Smiles Resin 650” and “Smiles Resin 675” sold by Sumika Chemtex Co., Ltd., and “WS” sold by Japan PMC Co., Ltd. -525 ”etc. The addition amount of these curable components or crosslinking agents is usually 1 to 100 parts by weight, preferably 1 to 50 parts by weight, as solid content, with respect to 100 parts by weight of the polyvinyl alcohol resin. If the amount added is small, the effect of improving the adhesiveness is reduced, while if the amount added is large, the adhesive layer tends to be brittle.

  When a urethane resin is used as the main component of the adhesive, examples of suitable adhesive compositions include a mixture of a polyester ionomer type urethane resin and a compound having a glycidyloxy group. The polyester-based ionomer type urethane resin here is a urethane resin having a polyester skeleton, into which a small amount of an ionic component (hydrophilic component) is introduced. Such an ionomer-type urethane resin is suitable as a water-based adhesive because it is emulsified directly in water without using an emulsifier to form an emulsion. Polyester-based ionomer-type urethane resins are known per se, and are described, for example, in JP-A-7-97504 as examples of polymer dispersants for dispersing phenolic resins in an aqueous medium. Patent Documents 2 to 4 show a mode in which a cycloolefin resin film is bonded to a polarizing film made of a polyvinyl alcohol resin using a mixture of a polyester ionomer type urethane resin and a compound having a glycidyloxy group as an adhesive. ing.

  The polyester ionomer type urethane resin can be produced, for example, by a method of emulsifying a hydrophilic group-containing urethane resin obtained by reacting a hydrophilic group-containing compound, a polyester polyol and a polyisocyanate in water. In this case, in addition to the polyester polyol, other high molecular weight polyol components and low molecular weight active hydrogen-containing compounds may be used in combination. Examples of the high molecular weight polyol include polyether polyol, polycarbonate polyol, polyacetal polyol, polyacrylate polyol, polyesteramide polyol, and polythioether polyol. Examples of the low molecular weight active hydrogen-containing compound include polyhydroxy compounds such as ethylene glycol, neopentyl glycol, 1,6-hexanediol, glycerin and trimethylolpropane, and diamine compounds such as ethylenediamine and piperazine. Especially, it is a preferable form to use a low molecular weight active hydrogen containing compound together.

  The polyester-based ionomer-type urethane resin preferably has a weight average molecular weight of 5,000 or more, more preferably 10,000 to 300,000. If the weight average molecular weight is less than 5,000, sufficient strength of the adhesive layer cannot be obtained. If the weight average molecular weight is more than 300,000, the viscosity when it is used as an aqueous dispersion becomes high and handling becomes difficult.

  The polyester ionomer type urethane resin is used as a water-based adhesive in a state of being dispersed in water. The viscosity of this aqueous adhesive is preferably 2,000 mPa · sec or less, more preferably 1,000 mPa · sec or less, and particularly preferably 500 mPa · sec or less. The lower the viscosity, the easier the application of the adhesive and the better the appearance of the resulting polarizing plate. The solid content concentration of the polyester ionomer type urethane resin in this water-based adhesive is preferably in the range of 10 to 70% by weight, particularly 20% by weight or more and 50% by weight or less from the viewpoint of viscosity and adhesive strength. Even more preferred.

  Polyethylene glycol, polyoxyethylene, or a surfactant may be further added to the aqueous dispersion of the polyester ionomer type urethane resin. Furthermore, water-soluble resins such as polyhydroxyethyl methacrylate, polyhydroxyethyl acrylate, polyacrylic acid, and polyvinyl alcohol resins may be added.

  Examples of commercially available polyester ionomer type urethane resins include “Hydran AP-20” and “Hydran APX-101H” sold by Dainippon Ink and Chemicals, Inc.

  The adhesive comprising an aqueous dispersion of a polyester ionomer type urethane resin preferably further contains a compound having a glycidyloxy group. By using together the compound which has a glycidyloxy group, the adhesiveness of a polarizing film and the cycloolefin type resin film or cellulose acetate type film laminated | stacked on it improves. The glycidyloxy group here is to be called a 2,3-epoxypropoxy group purely. Examples of compounds having a glycidyloxy group include polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, polytetramethylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, diglycerin diglycidyl ether, ethylene glycol diglycidyl ether, propylene Glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, resorcin diglycidyl ether, glycerin triglycidyl ether, trimethylolpropane Triglycidyl ether, pentaerythritol polyglycidyl ether, Ruby tall polyglycidyl ether, sorbitan polyglycidyl ether, such as polyglycerol polyglycidyl ether can be mentioned.

  The mixing ratio of the polyester ionomer type urethane resin and the compound having a glycidyloxy group is such that the compound having a glycidyloxy group is in the range of about 5 to 100 parts by weight with respect to 100 parts by weight of the solid content of the polyester ionomer type urethane resin. It is preferable to select appropriately so that the compound having a glycidyloxy group is 5 to 60 parts by weight, particularly 5 to 30 parts by weight. If the ratio of the compound having a glycidyloxy group is too low, sufficient adhesive strength cannot be obtained, and if the ratio is too high, the viscosity of the adhesive becomes high and handling becomes difficult.

  A water-based adhesive containing a polyester ionomer-type urethane resin and a compound having a glycidyloxy group does not require the use of an organic solvent, so there is no risk of causing environmental or worker health problems. At the same time, the use of a compound having a glycidyloxy group gives high adhesive strength.

  When using polyester ionomer type urethane resin as an adhesive, use a compound having an isocyanato group, especially a polyisocyanate compound having at least two isocyanato groups in the molecule, in order to improve the adhesion to a cellulose acetate film. Is preferred. Examples of such isocyanato group-containing compounds include monomers or oligomers such as 2,4-tolylene diisocyanate, phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 1,6-hexamethylene diisocyanate, isophorone diisocyanate, and the like. The reaction material of a compound and a polyol is mentioned. Examples of the polyol used for this purpose include 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, and the like. The molecular weight of these isocyanato group-containing compounds is preferably 5,000 or less in terms of weight average molecular weight even in the case of reaction products with the above oligomers and polyols. Examples of suitable commercially available isocyanato group-containing compounds include “Hydran Assist C1” sold by Dainippon Ink and Chemicals, Inc.

  The mixing ratio of the polyester ionomer type urethane resin and the isocyanato group-containing compound is suitably set so that the isocyanate group-containing compound is in the range of about 5 to 100 parts by weight with respect to 100 parts by weight of the solid content of the polyester ionomer type urethane resin. It is preferable to select, and more preferably, the isocyanato group-containing compound is selected in the range of 5 to 60 parts by weight, particularly 5 to 30 parts by weight. If the ratio of the isocyanato group-containing compound is too low, sufficient adhesive strength cannot be obtained. If the ratio is too high, the viscosity of the adhesive becomes high and handling becomes difficult.

  The method of bonding a cycloolefin resin film or a cellulose acetate film to a polarizing film with an adhesive may be generally known, for example, casting method, Meyer bar coating method, gravure coating method, die coating method, dip coating Examples thereof include a method of applying an adhesive to the adhesive surface of the polarizing film and / or the film bonded thereto by a coating method, a spraying method, and the like, and superimposing both. The casting method is a method of spreading and spreading an adhesive on the surface of a film to be coated while moving the film in a substantially vertical direction, a substantially horizontal direction, or an oblique direction between the two. After applying the adhesive, the polarizing film and the film bonded thereto are sandwiched by nip rolls and bonded together.

  Moreover, in order to improve adhesiveness, surface treatments such as plasma treatment, corona treatment, ultraviolet irradiation treatment, flame (flame) treatment, and saponification treatment may be appropriately performed on the adhesion surface.

  After laminating a cycloolefin resin film on one surface of the polarizing film and laminating a cellulose acetate film on the other surface, a drying treatment is performed. The drying process is performed, for example, by blowing hot air, and the temperature at that time is appropriately selected from the range of about 40 to 100 ° C., preferably 60 to 100 ° C. The drying time is about 20 to 1,200 seconds. The thickness of the adhesive layer after drying is usually about 0.001 to 5 μm, preferably 0.01 μm or more, preferably 2 μm or less, more preferably 1 μm or less. If the thickness of the adhesive layer becomes too large, the appearance of the polarizing plate tends to be poor.

  After bonding, sufficient adhesive strength can be obtained by performing curing at a temperature of room temperature or higher for at least half a day, usually several days or longer. A preferable curing temperature is 30 to 50 ° C, more preferably 35 to 45 ° C. When the curing temperature is 50 ° C. or higher, so-called “roll tightening” is likely to occur in the roll winding state. In addition, the humidity at the time of curing may be moderate, and the relative humidity may be in the range of about 0% RH to 70% RH. The curing time is usually 1 day to 10 days, preferably 2 days to 7 days.

  In the polarizing plate of the present invention, an optical functional film may be attached to the surface of the cellulose acetate film disposed on the side opposite to the cycloolefin-based resin film via an adhesive. As an optical functional film, for example, a liquid crystal compound is applied to the surface of a base material, an optical compensation film that is oriented, a reflection that transmits a certain kind of polarized light, and reflects polarized light that shows the opposite property. Examples thereof include a polarizing polarization separation film, a film with an antiglare function having a concavo-convex shape on the surface, a film with a surface antireflection treatment, a reflective film having a reflective function, and a transflective film having both a reflective function and a transmissive function. Commercially available products corresponding to the optical compensation film coated with a liquid crystal compound on the substrate surface and aligned are "WV film" sold by Fuji Photo Film Co., Ltd., and Nippon Oil Corporation. There are “NH film” and “NR film” (both are trade names) on the market. A commercial product equivalent to a reflective polarized light separation film that transmits certain types of polarized light and reflects polarized light that exhibits the opposite properties is Minnesota Mining and Manufacturing (3M) (Sumitomo 3M Limited in Japan). "DBEF" (product name) etc. sold from)).

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited by these examples. In the examples, “%” and “part” representing the content or amount used are based on weight unless otherwise specified.

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

[Production Example 2] Preparation of adhesive In 100 parts of water, 3 parts of carboxyl group-modified polyvinyl alcohol ["Kuraraypoval KL318" obtained from Kuraray Co., Ltd.] and water-soluble polyamide epoxy resin [from Sumika Chemtex Co., Ltd.] Obtained “SUMIREZ RESIN 650” (Aqueous Solution with Solid Concentration of 30%)] 1.5 parts were added to obtain a polyvinyl alcohol-based adhesive.

[Example 1]
A 80 μm thick triacetyl cellulose film (“KC8UX2MW” obtained from Konica Minolta Opto Co., Ltd.) was saponified, then immersed in water at 30 ° C. for 10 seconds, followed by swelling treatment at 80 ° C. Second drying was performed. About this film, the curl after being allowed to stand at 80 ° C. for 24 hours was observed to confirm the convex side. This convex side was A side (air side at the time of solvent casting) when compared with information from the manufacturer.

  The above triacetyl cellulose film is bonded to the other surface of the polarizing film on one side of the polarizing film obtained in Production Example 1 via the adhesive obtained in Production Example 2 on the convex side of the curl. Was bonded with a 73 μm thick protective film made of norbornene resin through the same adhesive. Then, it was dried for 5 minutes at a temperature of 60 ° C. to 90 ° C., and further cured for 7 days in an environment of 40 ° C. to obtain a polarizing plate.

  The obtained polarizing plate was cut into a square of 15 cm × 15 cm so that each side forms an angle of 45 ° with respect to the absorption axis (stretching direction), and the temperature was 23 ° C. and the relative humidity was 50%. After adjusting the humidity for a time, the curl amount was measured. As a result, the square curl of the polarizing plate was 0 to 20 mm.

  The curl amount of the polarizing plate was measured as follows. That is, as shown in FIG. 1, a curled polarizing plate 1 is placed on a reference surface 5 (for example, a plane on a desk) with its concave surface up. In this figure, the surface when it is assumed that there is no curl in the polarizing plate is displayed as a virtual surface 3 represented by a square ABCD. Then, one corner A in the virtual plane 3 is at the position A1 in the curled polarizing plate 1, and another corner C is in the position C1 in the curled polarizing plate 1, and the other corners B and D are curled. In the polarizing plate 1, B1 and D1 are positioned, B1 and B are in the same position, and D1 and D are also in the same position (that is, there is no floating at corners B and D of the polarizing plate). Equivalent to In practice, however, three or four of the four corners of the polarizing plate may be lifted. Thus, for each of the four corners A1, B1, C1, and D1 of the polarizing plate, the height H from the reference surface was measured and used as the curl amount.

[Comparative Example 1]
A polarizing plate was obtained in the same manner as in Example 1 except that the adhesion surface of the triacetyl cellulose film to the polarizing film was the concave side of the curl. The obtained polarizing plate was cut in the same manner as in Example 1 and conditioned, and the curl amount was measured. As a result, the square curl of the polarizing plate was 0 to 60 mm, and the maximum value of the curl amount was three times that of Example 1.

[Example 2]
A polarizing plate was obtained in the same manner as in Example 1 except that the drying after the saponification treatment and swelling treatment of the triacetylcellulose film was performed at 60 ° C. for 53 seconds. The obtained polarizing plate was cut in the same manner as in Example 1 and conditioned, and the curl amount was measured. As a result, the square curl of the polarizing plate was 0 to 3 mm.

[Comparative Example 2]
A polarizing plate was obtained in the same manner as in Example 2 except that the adhesion surface of the triacetyl cellulose film to the polarizing film was the concave side of the curl. The obtained polarizing plate was cut in the same manner as in Example 1 and conditioned, and the curl amount was measured. As a result, the square curl of the polarizing plate was 0 to 10 mm, and the maximum curl amount was more than three times that of Example 2.

It is a perspective view which shows typically the curl amount measurement state of the polarizing plate in an Example.

Explanation of symbols

1 ... Curled polarizing plate,
3 ... Virtual plane on the reference plane when assuming that the polarizing plate is not curled,
5 ... Reference plane,
A, B, C, D ... corners on the virtual surface,
A1, B1, C1, D1 ... Curled polarizer corners,
H: Curling amount (height from the reference surface to the corner of the polarizing plate).

Claims (2)

  A cellulose acetate film is laminated on one surface of a polarizing film made of a polyvinyl alcohol resin via an adhesive, and a cellulose acetate film is laminated on the other surface via an adhesive. The polarizing plate is characterized in that the convex side of the curl generated after being left at 80 ° C. for 24 hours is an adhesive surface to the polarizing film. A polarizing plate is produced by laminating a cycloolefin resin film on one surface of a polarizing film made of polyvinyl alcohol resin via an adhesive and laminating a cellulose acetate film on the other surface via an adhesive. In this case, the cellulose acetate film is adhered to the polarizing film on the convex surface side of the curl generated after standing at 80 ° C. for 24 hours.

Images