JP2008233768A - Method for manufacturing polarizing plate, polarizing plate, and image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method in which deterioration of optical characteristics of a polarizing plate due to drying after bonding between a polarizer and a polarizer protection film is suppressed when the polarizing plate using the polarizer protection film with low moisture permeability having excellent optical characteristics is manufactured, the polarizing plate obtained by such the manufacturing method and furthermore, high quality image display device including such the polarizing plate. <P>SOLUTION: In the method for manufacturing the polarizing plate, the polarizing plate is manufactured by bonding a first transparent protection film to one surface of the polarizer and bonding a second transparent protection film to the other surface, wherein moisture percentage of the polarizer is made 14-31 weight% and moisture permeability of at least one of the first transparent protection film and the second transparent protection film is made 150g/m<SP>2</SP>-24h or less. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a polarizing plate manufacturing method, a polarizing plate, and an image display device such as a liquid crystal display device, an organic EL display device, or a PDP, which includes at least one polarizing plate.

  In the liquid crystal display device, it is indispensable to dispose polarizing plates on both sides of the glass substrate on which the liquid crystal panel surface is formed because of the image forming method. In general, a polarizing plate is made of a transparent protective film (polarizer protective film) using triacetyl cellulose (TAC) on both sides of a polarizer made of a polyvinyl alcohol film and a dichroic material such as iodine. Those bonded with an alcohol-based adhesive are used.

  A polarizing plate using TAC as a polarizer protective film has a high gas transmission rate and moisture permeability of TAC, so that it is easily affected by oxygen and water vapor on the polarizer, and in a high temperature and high humidity environment. There is a problem that durability is not sufficient.

  As a film having low moisture permeability, there is a thermoplastic resin film (see Patent Documents 1-4). When such a thermoplastic resin film is used as a polarizer protective film, the above problem is solved to some extent.

However, if the moisture permeability of the polarizer protective film is low, when the polarizer and the polarizer protective film are bonded together with an adhesive and dried in the manufacturing process of the polarizing plate, the moisture contained in the adhesive is protected by the polarizer. Since it is difficult to pass through the film and discharge, the polarizer is in a steamed state, resulting in a problem that the initial optical characteristics of the obtained polarizing plate are deteriorated.
JP 2006-220731 A JP 2006-220732 A JP 2006-259623 A JP 2006-317560 A

  The present invention has been made in order to solve the above-mentioned problems, and the purpose of the present invention is to manufacture a polarizing plate using a polarizer protective film having a low moisture permeability with good optical properties. It is providing the manufacturing method which suppressed the fall of the optical characteristic of the polarizing plate by the drying after bonding of a child protective film. Moreover, it is providing the polarizing plate obtained by such a manufacturing method. Furthermore, it is providing the high quality image display apparatus containing such a polarizing plate.

The manufacturing method of the polarizing plate of the present invention is as follows:
A method for producing a polarizing plate by laminating a first transparent protective film on one surface of a polarizer and a second transparent protective film on the other surface,
The moisture content of the polarizer is 14 to 31% by weight,
The water vapor transmission rate of at least one of the first transparent protective film and the second transparent protective film is 150 g / m ² · 24 h or less.

  In a preferred embodiment, the first transparent protective film is bonded to one surface of the polarizer and the second transparent protective film is bonded to the other surface, and then dried at a temperature of 90 ° C. or lower.

  In a preferred embodiment, at least one of the first transparent protective film and the second transparent protective film is at least one selected from a (meth) acrylic resin film, a polyimide resin film, and a norbornene resin film. is there.

  According to another aspect of the present invention, a polarizing plate is provided. This polarizing plate is obtained by the production method of the present invention.

  According to another aspect of the present invention, an image display device is provided. This image display device includes at least one polarizing plate of the present invention.

  According to the present invention, in producing a polarizing plate using a low-moisture-permeable polarizer protective film with good optical properties, the optical properties of the polarizing plate are reduced by drying after the polarizer and the polarizer protective film are bonded together. The manufacturing method which suppressed can be provided. Moreover, the polarizing plate obtained by such a manufacturing method can be provided. Furthermore, a high-quality image display device including such a polarizing plate can be provided.

  Hereinafter, although preferable embodiment of this invention is described, this invention is not limited to these embodiment.

[Polarizer]
The polarizer is formed from a polyvinyl alcohol-based resin. As the polarizer, one obtained by uniaxially stretching a polyvinyl alcohol-based resin film dyed with a dichroic substance (typically iodine or a dichroic dye) is used. The polymerization degree of the polyvinyl alcohol resin constituting the polyvinyl alcohol resin film is preferably 100 to 5000, and more preferably 1400 to 4000.

  The polyvinyl alcohol-based resin film constituting the polarizer can be formed by any suitable method (for example, a casting method in which a solution obtained by dissolving a resin in water or an organic solvent is cast, a casting method, an extrusion method). . The thickness of the polarizer can be appropriately set according to the purpose and application of the LCD in which the polarizing plate is used, but is typically 5 to 80 μm.

  As a method for producing a polarizer, any appropriate method can be adopted depending on the purpose, materials used, conditions, and the like. Typically, a method is employed in which the polyvinyl alcohol-based resin film is subjected to a series of production steps including swelling, dyeing, crosslinking, stretching, washing with water, and drying steps. In each processing step except the drying step, the treatment is performed by immersing the polyvinyl alcohol-based resin film in a bath containing a solution used in each step. The order, frequency, and presence / absence of each treatment of swelling, dyeing, crosslinking, stretching, washing with water, and drying can be appropriately set according to the purpose, materials used, conditions, and the like. For example, several processes may be performed simultaneously in one process, and a specific process may be omitted. More specifically, for example, the stretching process may be performed after the dyeing process, may be performed before the dyeing process, or may be performed simultaneously with the swelling process, the dyeing process, and the crosslinking process. Further, for example, it can be suitably employed to perform the crosslinking treatment before and after the stretching treatment. Further, for example, the water washing process may be performed after all the processes, or may be performed only after a specific process.

  The swelling step is typically performed by immersing the polyvinyl alcohol resin film in a treatment bath (swelling bath) filled with water. By this treatment, dirt on the surface of the polyvinyl alcohol-based resin film and an anti-blocking agent can be washed, and unevenness such as uneven dyeing can be prevented by swelling the polyvinyl alcohol-based resin film. Glycerin, potassium iodide, or the like can be appropriately added to the swelling bath. The temperature of the swelling bath is typically about 20 to 60 ° C., and the immersion time in the swelling bath is typically about 0.1 to 10 minutes.

  The dyeing step is typically performed by immersing the polyvinyl alcohol resin film in a treatment bath (dye bath) containing a dichroic substance such as iodine. As the solvent used for the dye bath solution, water is generally used, but an appropriate amount of an organic solvent compatible with water may be added. The dichroic substance is typically used at a ratio of 0.1 to 1.0 part by weight with respect to 100 parts by weight of the solvent. When iodine is used as the dichroic substance, the dye bath solution preferably further contains an auxiliary agent such as iodide. This is because the dyeing efficiency is improved. The auxiliary is preferably used in a proportion of 0.02 to 20 parts by weight, more preferably 2 to 10 parts by weight, with respect to 100 parts by weight of the solvent. Specific examples of iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and iodide. Titanium is mentioned. The temperature of the dyeing bath is typically about 20 to 70 ° C., and the immersion time in the dyeing bath is typically about 1 to 20 minutes.

  The crosslinking step is typically performed by immersing the dyed polyvinyl alcohol resin film in a treatment bath (crosslinking bath) containing a crosslinking agent. Arbitrary appropriate crosslinking agents can be employ | adopted as a crosslinking agent. Specific examples of the crosslinking agent include boron compounds such as boric acid and borax, glyoxal, and glutaraldehyde. These can be used alone or in combination. As the solvent used for the solution of the crosslinking bath, water is generally used, but an appropriate amount of an organic solvent having compatibility with water may be added. The crosslinking agent is typically used at a ratio of 1 to 10 parts by weight with respect to 100 parts by weight of the solvent. When the concentration of the crosslinking agent is less than 1 part by weight, sufficient optical properties cannot often be obtained. When the concentration of the crosslinking agent exceeds 10 parts by weight, the stretching force generated in the film during stretching increases, and the resulting polarizing plate may shrink. The solution of the crosslinking bath preferably further contains an auxiliary agent such as iodide. This is because it is easy to obtain uniform characteristics in the plane. The concentration of the auxiliary agent is preferably 0.05 to 15% by weight, more preferably 0.5 to 8% by weight. Specific examples of iodide are the same as those in the dyeing process. The temperature of the crosslinking bath is typically about 20 to 70 ° C, preferably 40 to 60 ° C. The immersion time in the crosslinking bath is typically about 1 second to 15 minutes, preferably 5 seconds to 10 minutes.

  The stretching process may be performed at any stage as described above. Specifically, it may be performed after the dyeing process, may be performed before the dyeing process, may be performed simultaneously with the swelling process, the dyeing process, and the crosslinking process, or may be performed after the crosslinking process. The cumulative draw ratio of the polyvinyl alcohol-based resin film needs to be 5 times or more, preferably 5 to 7 times, and more preferably 5 to 6.5 times. When the cumulative draw ratio is less than 5 times, it may be difficult to obtain a polarizing plate with a high degree of polarization. When the cumulative draw ratio exceeds 7 times, the polyvinyl alcohol-based resin film (polarizer) may be easily broken. Arbitrary appropriate methods may be employ | adopted as a specific method of extending | stretching. For example, when the wet stretching method is adopted, the polyvinyl alcohol-based resin film is stretched at a predetermined magnification in a treatment bath (stretching bath). As the stretching bath solution, a solution in which various metal salts, iodine, boron or zinc compounds are added to a solvent such as water or an organic solvent (for example, ethanol) is preferably used.

  The water washing step is typically performed by immersing the polyvinyl alcohol-based resin film subjected to the above-described various treatments in a treatment bath (water washing bath). An unnecessary residue of the polyvinyl alcohol-based resin film can be washed away by the water washing step. The washing bath may be pure water or an aqueous solution of iodide (for example, potassium iodide or sodium iodide). The concentration of the iodide aqueous solution is preferably 0.1 to 10% by mass. An auxiliary agent such as zinc sulfate or zinc chloride may be added to the aqueous iodide solution. The temperature of the washing bath is preferably 10 to 60 ° C, more preferably 30 to 40 ° C. The immersion time is typically 1 second to 1 minute. The water washing step may be performed only once, or may be performed a plurality of times as necessary. When implemented several times, the kind and density | concentration of the additive contained in the washing bath used for each process can be adjusted suitably. For example, the water washing step includes a step of immersing the polymer film in an aqueous potassium iodide solution (0.1 to 10% by mass, 10 to 60 ° C.) for 1 second to 1 minute, and a step of rinsing with pure water.

  Any appropriate drying method (for example, natural drying, air drying, heat drying) may be employed as the drying step. For example, in the case of heat drying, the drying temperature is typically 20 to 80 ° C., and the drying time is typically 1 to 10 minutes.

  In the manufacturing method of this invention, the moisture content of a polarizer shall be 14 to 31 weight%. The moisture content of the polarizer is preferably 15 to 30% by weight. When the moisture content of the polarizer is out of the above range, it is possible to suppress the deterioration of the optical properties of the polarizing plate due to drying when producing a polarizing plate by drying after bonding a transparent protective film on both sides of the polarizer. It can be difficult.

  In the production method of the present invention, any appropriate means can be adopted as means for adjusting the moisture content of the polarizer to 14 to 31% by weight. For example, it is preferable to set the conditions in the drying step to any appropriate conditions. More specifically, for example, the drying temperature (for example, drying oven temperature) is preferably 20 to 60 ° C., more preferably 25 to 50 ° C., and the wind speed is preferably 1 to 10 m / sec, more preferably 2 -7 m / sec and the drying time is preferably 10 seconds to 5 minutes, more preferably 30 seconds to 2 minutes.

[Transparent protective film]
As a transparent protective film that can be used in the present invention, the moisture permeability of at least one of the first transparent protective film to be bonded to one surface of the polarizer and the second transparent protective film to be bonded to the other surface is 150 g / m ^2. -Any appropriate transparent protective film having a length of 24 hours or less can be adopted. The moisture permeability is preferably 10 to 150 g / m ² · 24 h, more preferably 30 to 120 g / m ² · 24 h, and still more preferably 50 to 100 g / m ² · 24 h. When the moisture permeability exceeds 150 g / m ² · 24 h, there is a possibility that a polarizing plate having insufficient durability at high temperature and high humidity may be obtained.

  The first transparent protective film and the second transparent protective film (in the present specification, these may be collectively referred to simply as a transparent protective film) may be the same film or different films. It may be. Further, each of these transparent protective films may be composed of only one layer, or may be a laminate of two or more layers. Further, it may have a phase difference (in-plane phase difference or thickness direction phase difference).

In the production method of the present invention, as a means for producing a transparent protective film having a moisture permeability of 150 g / m ² · 24 h or less (in this specification, sometimes referred to as a low moisture-permeable transparent protective film), any means can be used. Any appropriate means can be employed. For example, a film can be selected by selecting any appropriate material.

  The thickness of the transparent protective film can be appropriately set according to the purpose. The thickness of the transparent protective film is preferably 500 μm or less, more preferably 5 to 300 μm, and still more preferably 10 to 150 μm.

  Examples of the material constituting the transparent protective film include thermoplastic resins that are excellent in transparency, mechanical strength, thermal stability, moisture barrier properties, isotropy, and the like. Specific examples of such thermoplastic resins include cellulose resins such as triacetyl cellulose (TAC), polyester resins, polyethersulfone resins, polysulfone resins, polycarbonate resins, polyamide resins, polyimide resins, Examples include polyolefin resins, (meth) acrylic resins, norbornene resins, polyarylate resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof. In addition, thermosetting resins such as (meth) acrylic, urethane-based, acrylurethane-based, epoxy-based, and silicone-based or ultraviolet curable resins may be used. The thermoplastic resin may be used alone or in combination of two or more. Particularly preferred are cellulose resins, (meth) acrylic resins, polyimide resins, and norbornene resins.

  The low moisture permeability transparent protective film is preferably at least one selected from a (meth) acrylic resin film, a polyimide resin film, and a norbornene resin film. More preferably, it is a (meth) acrylic resin film.

  One specific example of the transparent protective film is a cellulose resin. Preferred is an ester of cellulose and a fatty acid. Specific examples of such a cellulose resin include cellulose triacetate (triacetyl cellulose: TAC), cellulose diacetate, cellulose tripropionate, and cellulose dipropionate. Cellulose triacetate (triacetyl cellulose: TAC) is particularly preferred. This is because it has low birefringence and high transmittance. Many products are commercially available, and TAC is advantageous in terms of availability and cost. However, as described above, in the present invention, it is preferable that at least one of the transparent protective films is not a triacetyl cellulose film.

  Specific examples of TAC commercial products are trade names “UV-50”, “UV-80”, “SH-50”, “SH-80”, “TD-80U”, “TD” manufactured by Fuji Photo Film Co., Ltd. -TAC "," UZ-TAC ", trade name" KC series "manufactured by Konica, and trade name" cellulose triacetate 80 [mu] m series "manufactured by Lonza Japan.

  Another specific example of the transparent protective film is a (meth) acrylic resin film. The (meth) acrylic resin constituting the film has a Tg (glass transition temperature) of preferably 115 ° C. or higher, more preferably 120 ° C. or higher, still more preferably 125 ° C. or higher, and particularly preferably 130 ° C. or higher. . When Tg (glass transition temperature) is 115 ° C. or higher, it can be excellent in durability. Although the upper limit of Tg of the said (meth) acrylic-type resin is not specifically limited, From viewpoints of a moldability etc., Preferably it is 170 degrees C or less.

As the (meth) acrylic resin, any appropriate (meth) acrylic resin can be adopted as long as the effects of the present invention are not impaired. For example, poly (meth) acrylic acid ester such as polymethyl methacrylate, methyl methacrylate- (meth) acrylic acid copolymer, methyl methacrylate- (meth) acrylic acid ester copolymer, methyl methacrylate-acrylic acid ester -(Meth) acrylic acid copolymer, (meth) acrylic acid methyl-styrene copolymer (MS resin, etc.), polymer having an alicyclic hydrocarbon group (for example, methyl methacrylate-cyclohexyl methacrylate copolymer) And methyl methacrylate- (meth) acrylate norbornyl copolymer). Preferably, poly (meth) acrylic acid C _1-6 alkyl such as poly (meth) acrylate methyl is used. More preferably, a methyl methacrylate resin containing methyl methacrylate as a main component (50 to 100% by weight, preferably 70 to 100% by weight) is used.

  Specific examples of the (meth) acrylic resin include (meth) acrylic resin having a ring structure in the molecule described in, for example, Acrypet VH and Acrypet VRL20A manufactured by Mitsubishi Rayon Co., Ltd., and JP-A-2004-70296. And high Tg (meth) acrylic resins obtained by intramolecular crosslinking or intramolecular cyclization reaction.

  As the (meth) acrylic resin, a (meth) acrylic resin having a lactone ring structure can also be used. This is because it has high heat resistance, high transparency, and high mechanical strength.

  Examples of the (meth) acrylic resin having a lactone ring structure include JP 2000-230016, JP 2001-151814, JP 2002-120326, JP 2002-254544, and JP 2005. Examples thereof include (meth) acrylic resins having a lactone ring structure described in Japanese Patent No. 146084.

（一般式（１）中、Ｒ^１、Ｒ^２およびＲ^３は、それぞれ独立に、水素原子または炭素数１〜２０の有機残基を表す。なお、有機残基は酸素原子を含んでいても良い。） The (meth) acrylic resin having a lactone ring structure preferably has a lactone ring structure represented by the following general formula (1).

(In the general formula (1), R ¹ , R ² and R ³ each independently represent a hydrogen atom or an organic residue having 1 to 20 carbon atoms. The organic residue may contain an oxygen atom. good.)

  The content ratio of the lactone ring structure represented by the general formula (1) in the structure of the (meth) acrylic resin having a lactone ring structure is preferably 5 to 90% by weight, more preferably 10 to 70% by weight, The amount is preferably 10 to 60% by weight, particularly preferably 10 to 50% by weight. When the content of the lactone ring structure represented by the general formula (1) in the structure of the (meth) acrylic resin having a lactone ring structure is less than 5% by weight, heat resistance, solvent resistance, and surface hardness are poor. May be sufficient. If the content of the lactone ring structure represented by the general formula (1) in the structure of the (meth) acrylic resin having a lactone ring structure is more than 90% by weight, the moldability may be poor.

  The (meth) acrylic resin having a lactone ring structure has a mass average molecular weight (sometimes referred to as a weight average molecular weight) of preferably 1,000 to 2,000,000, more preferably 5,000 to 1,000,000, still more preferably 10,000 to 500,000. Is 50,000 to 500,000. If the mass average molecular weight is out of the above range, the effects of the present invention may not be sufficiently exhibited.

  The (meth) acrylic resin having a lactone ring structure has a Tg (glass transition temperature) of preferably 115 ° C. or higher, more preferably 125 ° C. or higher, still more preferably 130 ° C. or higher, particularly preferably 135 ° C., most preferably 140 ° C. or higher. When Tg is 115 ° C. or higher, for example, when incorporated in a polarizing plate as a polarizer protective film, it can be excellent in durability. Although the upper limit of Tg of the (meth) acrylic resin having the lactone ring structure is not particularly limited, it is preferably 170 ° C. or less from the viewpoint of moldability and the like.

  The (meth) acrylic resin having a lactone ring structure is preferably as the total light transmittance of a molded product obtained by injection molding measured by a method according to ASTM-D-1003 is higher, preferably 85. % Or more, more preferably 88% or more, and still more preferably 90% or more. The total light transmittance is a measure of transparency. If the total light transmittance is less than 85%, the transparency may be lowered.

  Another specific example of the transparent protective film is a cyclic olefin-based resin film, and a norbornene-based resin film is particularly preferable. The cyclic olefin-based resin constituting the cyclic olefin-based resin film is a general term for resins that are polymerized using a cyclic olefin as a polymerization unit. For example, JP-A-1-240517, JP-A-3-14882, and JP-A-3 -122137 etc. resin etc. are mentioned. Specific examples include ring-opening (co) polymers of cyclic olefins, addition polymers of cyclic olefins, copolymers of cyclic olefins and α-olefins such as ethylene and propylene (typically random copolymers). And graft modified products in which these are modified with an unsaturated carboxylic acid or a derivative thereof, and hydrides thereof. Specific examples of the cyclic olefin include norbornene monomers.

  Examples of the norbornene-based monomer include norbornene, and alkyl and / or alkylidene substituted products thereof such as 5-methyl-2-norbornene, 5-dimethyl-2-norbornene, 5-ethyl-2-norbornene, and 5-butyl. 2-Norbornene, 5-ethylidene-2-norbornene, etc., polar substituents such as halogens; dicyclopentadiene, 2,3-dihydrodicyclopentadiene, etc .; dimethanooctahydronaphthalene, its alkyl and / or alkylidene Substituents and polar group substituents such as halogen such as 6-methyl-1,4: 5,8-dimethano-1,4,4a, 5,6,7,8,8a-octahydronaphthalene, 6- Ethyl-1,4: 5,8-dimethano-1,4,4a, 5,6,7,8,8a-oct Hydronaphthalene, 6-ethylidene-1,4: 5,8-dimethano-1,4,4a, 5,6,7,8,8a-octahydronaphthalene, 6-chloro-1,4: 5,8-dimethano -1,4,4a, 5,6,7,8,8a-octahydronaphthalene, 6-cyano-1,4: 5,8-dimethano-1,4,4a, 5,6,7,8,8a -Octahydronaphthalene, 6-pyridyl-1,4: 5,8-dimethano-1,4,4a, 5,6,7,8,8a-octahydronaphthalene, 6-methoxycarbonyl-1,4: 5 8-dimethano-1,4,4a, 5,6,7,8,8a-octahydronaphthalene and the like; 3-pentamer of cyclopentadiene, for example, 4,9: 5,8-dimethano-3a, 4 4a, 5,8,8a, 9,9a-octahydro-1H-benzoin 4,11: 5,10: 6,9-trimethano-3a, 4,4a, 5,5a, 6,9,9a, 10,10a, 11,11a-dodecahydro-1H-cyclopentanthracene and the like. It is done.

  The norbornene-based monomer may be used in combination with other cycloolefin capable of ring-opening polymerization within the range not impairing the object of the present invention. Specific examples of such cycloolefins include compounds having one reactive double bond such as cyclopentene, cyclooctene, and 5,6-dihydrodicyclopentadiene.

  The cyclic olefin-based resin preferably has a number average molecular weight (Mn) measured by a gel permeation chromatography (GPC) method using a toluene solvent, preferably 25,000 to 200,000, and more preferably 30,000 to 100,000. Most preferably, it is 40,000-80,000. When the number average molecular weight is in the above range, a material having excellent mechanical strength, good solubility, moldability, and casting operability can be obtained.

  When the cyclic olefin resin is obtained by hydrogenating a ring-opening polymer of a norbornene monomer, the hydrogenation rate is preferably 90% or more, more preferably 95% or more, Preferably it is 99% or more. Within such a range, the heat deterioration resistance and light deterioration resistance are excellent.

  Various products are commercially available as cyclic olefin resins. As specific examples, trade names “ZEONEX” and “ZEONOR” manufactured by ZEON CORPORATION, trade names “ARTON” manufactured by JSR, “TOPASS” manufactured by TICONA, and trade names manufactured by Mitsui Chemicals, Inc. “APEL” may be mentioned.

  Another specific example of the transparent protective film is a polyimide resin film. For example, a polymer film formed from a resin composition as described in JP-A-2001-343529 (WO01 / 37007) can be used as a transparent protective film. More specifically, it is a mixture of a thermoplastic resin having a substituted imide group or an unsubstituted imide group in the side chain and a thermoplastic resin having a substituted phenyl group or an unsubstituted phenyl group and a cyano group in the side chain. Specific examples include a resin composition having an alternating copolymer composed of isobutene and N-methylenemaleimide and an acrylonitrile / styrene copolymer. For example, an extruded product of such a resin composition can be used.

  The transparent protective film may contain one or more arbitrary appropriate additives. Examples of the additive include other resins, ultraviolet absorbers, antioxidants, lubricants, plasticizers, mold release agents, anti-coloring agents, flame retardants, nucleating agents, antistatic agents, pigments, and coloring agents. . The content of the thermoplastic resin in the transparent protective film is preferably 50 to 100% by weight, more preferably 50 to 99% by weight, still more preferably 60 to 98% by weight, and particularly preferably 70 to 97% by weight. . If the content of the thermoplastic resin in the transparent protective film is less than 50% by weight, the high transparency inherent in the thermoplastic resin may not be sufficiently exhibited.

  In the manufacturing method of this invention, after bonding a transparent protective film on both surfaces of the said polarizer, it is preferable to make it dry at arbitrary appropriate drying temperature. More specifically, it is preferable to dry at a temperature of 90 ° C. or lower. The said drying temperature becomes like this. More preferably, it is 50-90 degreeC, More preferably, it is 60-90 degreeC, Most preferably, it is 70-90 degreeC. By drying at a temperature of 90 ° C. or lower, the effects of the present invention may be further exhibited. Drying can also be carried out by raising the temperature stepwise within the above temperature range.

〔Polarizer〕
One preferred embodiment of the polarizing plate according to the present invention is shown in FIG. As shown in FIG. 1, the polarizing plate 30 according to the present invention includes a first transparent protective film 32, a polarizer 31, and a second transparent protective film 33 in this order. In FIG. 1, optional layers other than the first transparent protective film 32, the polarizer 31, and the second transparent protective film 33 are omitted.

  Any appropriate adhesive layer may be present between the polarizer and the transparent protective film (first transparent protective film, second transparent protective film). Preferably, it is an adhesive layer formed from a polyvinyl alcohol-based adhesive.

  In the present invention, the polyvinyl alcohol-based adhesive contains a polyvinyl alcohol-based resin and a crosslinking agent.

  The polyvinyl alcohol-based resin is not particularly limited. For example, polyvinyl alcohol obtained by saponifying polyvinyl acetate; a derivative thereof; and a saponified product of a copolymer with a monomer having copolymerizability with vinyl acetate. Modified polyvinyl alcohol obtained by acetalization, urethanization, etherification, grafting, phosphoric esterification, etc. of polyvinyl alcohol. Examples of the monomer include unsaturated carboxylic acids such as (anhydrous) maleic acid, fumaric acid, crotonic acid, itaconic acid, (meth) acrylic acid, and esters thereof; α-olefins such as ethylene and propylene, (meth) Examples include allyl sulfonic acid (soda), sulfonic acid soda (monoalkyl malate), disulfonic acid soda alkyl maleate, N-methylol acrylamide, acrylamide alkyl sulfonic acid alkali salt, N-vinyl pyrrolidone, N-vinyl pyrrolidone derivatives, and the like. . These polyvinyl alcohol resins may be used alone or in combination of two or more.

  From the viewpoint of adhesiveness, the polyvinyl alcohol-based resin preferably has an average degree of polymerization of 100 to 3000, more preferably 500 to 3000, and an average degree of saponification of preferably 85 to 100 mol%, more preferably 90. ˜100 mol%.

  As the polyvinyl alcohol resin, a polyvinyl alcohol resin having an acetoacetyl group can be used. A polyvinyl alcohol-based resin having an acetoacetyl group is a polyvinyl alcohol-based adhesive having a highly reactive functional group, and is preferable in terms of improving the durability of the polarizing plate.

  A polyvinyl alcohol-based resin containing an acetoacetyl group is obtained by reacting a polyvinyl alcohol-based resin with diketene by a known method. For example, a method in which a polyvinyl alcohol resin is dispersed in a solvent such as acetic acid and diketene is added thereto, and a polyvinyl alcohol resin is previously dissolved in a solvent such as dimethylformamide or dioxane, and diketene is added thereto. And the like. Moreover, the method of making diketene gas or liquid diketene contact directly to polyvinyl alcohol is mentioned.

  The degree of acetoacetyl group modification of the polyvinyl alcohol resin having an acetoacetyl group is not particularly limited as long as it is 0.1 mol% or more. If it is less than 0.1 mol%, the water resistance of the adhesive layer is insufficient, which is inappropriate. The degree of acetoacetyl modification is preferably 0.1 to 40 mol%, more preferably 1 to 20 mol%. When the degree of acetoacetyl modification exceeds 40 mol%, the number of reaction points with the cross-linking agent decreases, and the effect of improving water resistance is small. The degree of acetoacetyl modification is a value measured by NMR.

  As said crosslinking agent, what is used for the polyvinyl alcohol-type adhesive agent can be especially used without a restriction | limiting. As the crosslinking agent, a compound having at least two functional groups having reactivity with the polyvinyl alcohol resin can be used. For example, alkylenediamines having two alkylene groups and two amino groups such as ethylenediamine, triethyleneamine and hexamethylenediamine (hexamethylenediamine is preferred); tolylene diisocyanate, hydrogenated tolylene diisocyanate, trimethylene propane tolylene Isocyanate adduct, triphenylmethane triisocyanate, methylene bis (4-phenylmethane triisocyanate, isophorone diisocyanate and isocyanates such as ketoxime block product or phenol block product; ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin di Or triglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylo Epoxys such as rupropane triglycidyl ether, diglycidyl aniline, diglycidyl amine; monoaldehydes such as formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde; glyoxal, malondialdehyde, succindialdehyde, glutardialdehyde, maleindialdehyde And dialdehydes such as phthaldialdehyde; amino-formaldehyde resins such as methylol urea, methylol melamine, alkylated methylol urea, alkylated methylolated melamine, acetoguanamine, condensates of benzoguanamine and formaldehyde; sodium, potassium, magnesium Divalent metals such as calcium, aluminum, iron and nickel, or salts of trivalent metals and oxides thereof. Is to, melamine-based crosslinking agent is preferably, suitable in particular melamine.

  The amount of the crosslinking agent is preferably 0.1 to 35 parts by weight, more preferably 10 to 25 parts by weight with respect to 100 parts by weight of the polyvinyl alcohol resin. On the other hand, in order to further improve the durability, the crosslinking agent can be blended in a range of more than 30 parts by weight and 46 parts by weight or less with respect to 100 parts by weight of the polyvinyl alcohol resin. In particular, when a polyvinyl alcohol-based resin containing an acetoacetyl group is used, it is preferable to use the crosslinking agent in an amount exceeding 30 parts by weight. Water resistance improves by mix | blending a crosslinking agent in the range of more than 30 weight part and 46 weight part or less.

  The polyvinyl alcohol-based adhesive further includes coupling agents such as silane coupling agents and titanium coupling agents, various tackifiers, ultraviolet absorbers, antioxidants, heat stabilizers, hydrolysis stabilizers, and the like. A stabilizer or the like can also be blended.

  The transparent protective film in the present invention may be subjected to easy adhesion treatment on the surface in contact with the polarizer in order to improve adhesion. Examples of the easy adhesion treatment include corona treatment, plasma treatment, low-pressure UV treatment, and saponification treatment. Further, after the easy adhesion treatment, a polyethyleneimine layer may be formed on the treated surface.

  The thickness of the adhesive layer is preferably 0.01 to 10 μm, more preferably 0.03 to 5 μm, since it is not preferable in terms of adhesiveness when the thickness after drying becomes too thick.

  The polarizing plate of the present invention may have an adhesive layer on the side opposite to the polarizer of the transparent protective film (such a polarizing plate may be referred to as an adhesive polarizing plate).

  The pressure-sensitive adhesive forming the pressure-sensitive adhesive layer is not particularly limited. For example, an acrylic polymer, silicone polymer, polyester, polyurethane, polyamide, polyether, fluorine-based or rubber-based polymer is used as a base polymer. It can select suitably and can be used. In particular, those having excellent optical transparency such as an acrylic pressure-sensitive adhesive, exhibiting appropriate wettability, cohesiveness, and adhesive pressure-sensitive adhesive properties, and being excellent in weather resistance and heat resistance can be preferably used. In particular, an acrylic pressure-sensitive adhesive made of an acrylic polymer having 4 to 12 carbon atoms is preferable.

  In addition to the above, in terms of prevention of foaming and peeling phenomena due to moisture absorption, deterioration of optical properties and liquid crystal cell warpage due to differences in thermal expansion, etc., as well as formability of liquid crystal display devices with high quality and excellent durability An adhesive layer having a low moisture absorption rate and excellent heat resistance is preferred.

  The pressure-sensitive adhesive layer is, for example, a natural or synthetic resin, in particular, a tackifier resin, a filler or pigment made of glass fiber, glass beads, metal powder, other inorganic powders, a colorant, an antioxidant. An additive to be added to the pressure-sensitive adhesive layer such as an agent may be contained.

  Moreover, the adhesive layer etc. which contain microparticles | fine-particles and show light diffusibility may be sufficient.

  The attachment of the pressure-sensitive adhesive layer can be performed by an appropriate method. For example, a pressure sensitive adhesive solution of about 10 to 40% by weight in which a base polymer or a composition thereof is dissolved or dispersed in a solvent composed of a suitable solvent alone or a mixture such as toluene and ethyl acetate is prepared. A method in which it is directly attached on the transparent protective layer (A) by an appropriate development method such as a casting method or a coating method, or an adhesive layer is formed on the separator according to the above and the transparent protective layer (A ) The method of transferring to the top.

  The pressure-sensitive adhesive layer can be provided as an overlapping layer of different compositions or types.

  The thickness of the pressure-sensitive adhesive layer can be appropriately determined according to the purpose of use and adhesive force, and is preferably 1 to 40 μm, more preferably 5 to 30 μm, and particularly preferably 10 to 25 μm. When the thickness is less than 1 μm, the durability is deteriorated. When the thickness is more than 40 μm, floating or peeling due to foaming or the like is liable to occur, resulting in poor appearance.

  In order to improve the adhesion between the transparent protective film and the pressure-sensitive adhesive layer, an anchor layer can be provided between the layers.

  As the anchor layer, an anchor layer selected from polyurethane, polyester and polymers containing an amino group in the molecule is preferably used, and polymers containing an amino group in the molecule are particularly preferably used. Polymers containing amino groups in the molecule are good because the amino groups in the molecule exhibit interactions such as reaction or ionic interaction with carboxyl groups in the adhesive and polar groups in the conductive polymer. Adhesion is ensured.

  Examples of the polymer containing an amino group in the molecule include, for example, polyethyleneimine, polyallylamine, polyvinylamine, polyvinylpyridine, polyvinylpyrrolidine, and amino-containing groups such as dimethylaminoethyl acrylate shown as a copolymer monomer of the acrylic pressure-sensitive adhesive. Examples thereof include polymers of contained monomers.

  In order to impart antistatic properties to the anchor layer, an antistatic agent may be added. Antistatic agents for imparting antistatic properties include ionic surfactant systems, conductive polymer systems such as polyaniline, polythiophene, polypyrrole, and polyquinoxaline, and metal oxide systems such as tin oxide, antimony oxide, and indium oxide. In particular, a conductive polymer system is preferably used from the viewpoint of optical characteristics, appearance, antistatic effect, and stability of the antistatic effect when heated and humidified. Among these, water-soluble conductive polymers such as polyaniline and polythiophene or water-dispersible conductive polymers are particularly preferably used. This is because, when a water-soluble conductive polymer or a water-dispersible conductive polymer is used as a material for forming the antistatic layer, it is possible to suppress deterioration of the optical film substrate due to an organic solvent during the coating process.

  In the present invention, the polarizer, the transparent protective layer, and the like that form the polarizing plate described above, and the pressure-sensitive adhesive layer, for example, include salicylic acid ester compounds, benzophenol compounds, benzotriazole compounds, and cyanoacrylate compounds. Further, it may be one having an ultraviolet absorbing ability by a method such as a method of treating with an ultraviolet absorber such as a nickel complex compound.

  The polarizing plate of the present invention may be provided on either the viewing side or the backlight side of the liquid crystal cell, or on both sides. The polarizing plate provided on the viewing side of the liquid crystal cell is provided such that at least the low moisture permeability transparent protective film side of the polarizing plate is located on the opposite side of the liquid crystal cell as viewed from the polarizer.

(Image display device)
Next, the image display apparatus of the present invention will be described. The image display device of the present invention includes at least one polarizing plate of the present invention. Here, a liquid crystal display device will be described as an example, but it goes without saying that the present invention can be applied to any display device that requires a polarizing plate. Specific examples of the image display device to which the polarizing plate of the present invention can be applied include a self-luminous display device such as an electroluminescence (EL) display, a plasma display (PD), and a field emission display (FED: Field Emission Display). Can be mentioned. FIG. 2 is a schematic cross-sectional view of a liquid crystal display device according to a preferred embodiment of the present invention. In the illustrated example, a transmissive liquid crystal display device will be described, but it goes without saying that the present invention is also applied to a reflective liquid crystal display device and the like.

  The liquid crystal display device 100 includes a liquid crystal cell 10, retardation films 20 and 20 ′ disposed across the liquid crystal cell 10, and polarizing plates 30 and 30 ′ disposed outside the retardation films 20 and 20 ′. A light guide plate 40, a light source 50, and a reflector 60 are provided. The polarizing plates 30 and 30 'are arranged so that their polarization axes are orthogonal to each other. The liquid crystal cell 10 includes a pair of glass substrates 11 and 11 ′ and a liquid crystal layer 12 as a display medium disposed between the substrates. One substrate 11 is provided with a switching element (typically a TFT) for controlling the electro-optical characteristics of the liquid crystal, a scanning line for supplying a gate signal to the switching element, and a signal line for supplying a source signal ( Neither is shown). The other glass substrate 11 ′ is provided with a color layer constituting a color filter and a light shielding layer (black matrix layer) (both not shown). The distance (cell gap) between the substrates 11 and 11 ′ is controlled by the spacer 13. In the liquid crystal display device of the present invention, the polarizing plate of the present invention described above is employed as at least one of the polarizing plates 30 and 30 '.

  For example, in the case of the TN mode, in such a liquid crystal display device 100, when no voltage is applied, the liquid crystal molecules of the liquid crystal layer 12 are arranged in a state in which the polarization axis is shifted by 90 degrees. In such a state, incident light that is transmitted through only light in one direction by the polarizing plate is twisted 90 degrees by liquid crystal molecules. As described above, since the polarizing plates are arranged so that their polarization axes are orthogonal to each other, the light (polarized light) reaching the other polarizing plate is transmitted through the polarizing plate. Therefore, when no voltage is applied, the liquid crystal display device 100 performs white display (normally white method). On the other hand, when a voltage is applied to such a liquid crystal display device 100, the arrangement of liquid crystal molecules in the liquid crystal layer 12 changes. As a result, the light (polarized light) that has reached the other polarizing plate cannot be transmitted through the polarizing plate, resulting in black display. An image is formed by switching such display for each pixel using an active element.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to these Examples. Unless otherwise indicated, parts and percentages (%) in the examples are based on weight.

<Measurement of thickness>
When the thickness was less than 10 μm, measurement was performed using a thin film spectrophotometer [manufactured by Otsuka Electronics Co., Ltd., “instant multiphotometry system MCPD-2000”]. When the thickness was 10 μm or more, measurement was performed using an Anritsu digital micrometer “KC-351C type”.

<Measurement of moisture permeability>
It measured according to the moisture permeability measuring method of JIS-Z-0208.

<Measurement of moisture content of polarizer>
The polarizer obtained after the completion of (drying process step) obtained in Production Example 1 described later was held at 120 ° C. for 2 hours, and the weight loss before and after the measurement was measured.
Moisture content (%) = {(polarizer weight before holding at 120 ° C.) − (Polarizer weight after holding at 120 ° C.)} / (Polarizer weight before holding at 120 ° C.)

<Measure the number of nicks>
Samples were prepared by cutting out the polarizing plates of Examples and Comparative Examples to a size of 1000 mm × 1000 mm, respectively. Place the sample polarizing plate on top of another polarizing plate so that their absorption axes are orthogonal to each other, and apply light from a fluorescent lamp in the dark room from the side of the other polarizing plate, and then visually escape the light (knic defect) ) Was counted.

<Measurement of degree of polarization after annealing>
It measured by DOT-3 made by Oji Scientific Instruments.

[Production Example 1]: Production of Polarizers (A) to (F) Swelling using a polyvinyl alcohol (PVA) film (made by Kuraray Co., Ltd., polymerization degree 2400) having a thickness of 75 μm and an initial raw film width of 100 mm. A polarizing film having a thickness of 28 μm was obtained through dyeing, crosslinking, stretching, washing with water and drying treatment steps. In each processing step, as shown in FIG. 1 and FIG. 2 of JP-A-2004-341515, the film is transported using a roll, and stretched by utilizing the peripheral speed difference between the pinch rolls before and after the processing step. It was.
The conditions in each process are as follows.
(Swelling treatment process) Stretching 2.5 times in pure water at 30 ° C. (distance between stretching 60 mm).
(Dyeing process) Stretching to a total draw ratio of 2.8 times accumulated at the same time as dyeing in a 0.05 Wt% iodine aqueous solution (I / KI (weight ratio) = 1/10) at 30 ° C. (distance between draws) 60 mm).
(Crosslinking treatment step) Stretching to a total draw ratio of 3.0 times accumulated at the same time as immersion in an aqueous solution (40 ° C.) of 3 Wt% boric acid + 2 Wt% KI for 30 seconds (distance between stretches: 60 mm).
(Stretching treatment step) In a 4 Wt% boric acid + 3 Wt% KI aqueous solution (60 ° C.), stretching to a final total stretching ratio of 5.8 times (distance between stretching 60 mm).
(Washing process) Immerse in a 5 Wt% KI aqueous solution (25 ° C.) for 30 seconds.
(Drying process step) While maintaining tension, drying oven temperature: 27 to 47 ° C., air volume: 5 m / sec, drying time: 1 minute, and a polarizer (A) to (F) having a thickness of 26 μm. Got.
Table 1 shows the drying oven temperature and the moisture content of the polarizer for the obtained polarizers (A) to (F).

[Production Example 2]: Production of transparent protective films (X) and (Y) Lactone ring-containing acrylic resin film described in JP-A No. 2006-171464 (thickness 40 μm, moisture permeability = 95.5 g / m ² · 24 h) And water content = 2.5%). Let the obtained lactone ring containing acrylic resin film be transparent protective film (X).
As the transparent protective film (Y), a triacetyl cellulose film (manufactured by Konica, product name: KC4UWY, thickness 40 μm, moisture permeability = 400 g / m ² · 24 h, moisture content = 2.5%) was used.

[Production Example 3]: Production of aqueous adhesive solution 100 parts of polyvinyl alcohol resin containing acetoacetyl groups (average polymerization degree: 1200, saponification degree: 98.5 mol%, acetoacetylation degree: 5 mol%) On the other hand, 30 parts of methylolmelamine was dissolved in pure water under a temperature condition of 30 ° C. to obtain an aqueous adhesive solution adjusted to a solid content concentration of 3.7%.

[Examples 1-12, Comparative Examples 1-7]
In the combination as shown in Table 2, the transparent protective film (X) or (Y) obtained in Production Example 2 is applied to either side of the polarizer (A) to (F) obtained in Production Example 1. , Bonding using the adhesive aqueous solution obtained in Production Example 3, and putting in an oven (70 ° C. or 80 ° C. or 90 ° C.) for 5 minutes to dry the adhesive, polarizing plates (1) to (12), (C1) to (C7) were produced.
Table 2 shows the nick number of the obtained polarizing plate and the degree of polarization after the annealing treatment.
The number of nicks was evaluated with a polarizing plate before annealing. In the annealing treatment, the polarizing plate obtained by drying the adhesive for 5 minutes in the examples and comparative examples was further heat-treated at 70 ° C.

  From the results shown in Table 2, when the moisture content of the polarizer is 32% (polarizer (A)), the degree of polarization greatly decreases under the conditions where the adhesive drying temperature is 70 ° C, 80 ° C, and 90 ° C. You can see that It can also be seen that when the moisture content of the polarizer is 13% (polarizer (F)), many nicks are generated, making it difficult to use as a polarizing plate. Furthermore, it can be seen that at the adhesive drying temperatures of 70 ° C., 80 ° C., and 90 ° C., the lower the moisture content of the polarizer, the higher the polarization degree. Further, comparing data with the same moisture content of the polarizer, it can be seen that the degree of polarization is higher when the adhesive drying temperature is 70 ° C. and 80 ° C. than when the adhesive drying temperature is 90 ° C. It is considered that the lower the moisture content of the polarizer and the lower the drying temperature of the adhesive, the better the steaming state is avoided and the better results are shown.

  The polarizing plate of the present invention can be suitably used for various image display devices (liquid crystal display devices, organic EL display devices, PDPs, etc.).

It is sectional drawing which shows an example of the polarizing plate of this invention. 1 is a schematic cross-sectional view of a liquid crystal display device according to a preferred embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Liquid crystal cell 11, 11 'Glass substrate 12 Liquid crystal layer 13 Spacer 20, 20' Retardation film 30, 30 'Polarizing plate 31 Polarizer 32 First transparent protective film 33 Second transparent protective film 40 Light guide plate 50 Light source 60 Reflector 100 Liquid crystal display device

Claims (5)

A method for producing a polarizing plate by laminating a first transparent protective film on one surface of a polarizer and a second transparent protective film on the other surface,
The moisture content of the polarizer is 14 to 31% by weight,
The moisture permeability of at least one of the first transparent protective film and the second transparent protective film is 150 g / m ² · 24 h or less,
Manufacturing method of polarizing plate.   The manufacturing method according to claim 1, wherein the first transparent protective film is bonded to one surface of the polarizer and the second transparent protective film is bonded to the other surface, and then dried at a temperature of 90 ° C. or lower.   2. At least one of the first transparent protective film and the second transparent protective film is at least one selected from a (meth) acrylic resin film, a polyimide resin film, and a norbornene resin film. 2. The production method according to 2.   A polarizing plate obtained by the production method according to claim 1.   An image display device comprising at least one polarizing plate according to claim 4.

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