JP5514700B2 - Manufacturing method of polarizing plate - Google Patents

Description

  The present invention relates to a method for producing a polarizing plate.

  A polarizing plate is widely used as a polarization supplying element in a display device such as a liquid crystal display device. As such a polarizing plate, a polarizing film (polarizer layer) made of a polyvinyl alcohol resin and a protective film made of triacetyl cellulose are conventionally used. However, in recent years, notebook personal computers for liquid crystal display devices have been used. With the development of mobile devices such as mobile phones and mobile phones, there is a need to reduce the thickness and weight.

  Conventionally, after a film made of a polyvinyl alcohol resin is stretched alone or while being stretched, a polarizing film is produced by performing a dyeing treatment or a crosslinking treatment, and laminating this on a protective film or the like to form a polarizing plate. Although it was manufactured, it was possible to reduce the thickness only to the limit thickness of the polarizing film alone. For this reason, after providing the polyvinyl alcohol-type resin layer of a polarizer layer on the surface of a base film, the polyvinyl alcohol-type resin layer is extended | stretched with the base film, and after passing through a dyeing | staining and bridge | crosslinking process and a subsequent drying process, a polyvinyl alcohol type By making the resin layer a polarizer layer, the total thickness of the base film and the polarizer layer can be reduced to the limit, and the thickness as the polarizer layer (polarizing film) can be made thinner than before. Methods are known (see, for example, Patent Documents 1 and 2).

  However, in the method described in Patent Document 1, the laminated film is dried at room temperature after the crosslinking treatment, and further dried at 50 ° C. for 5 minutes, and then the protective film is bonded. Moreover, in the method of patent document 2, after carrying out the drying for 4 minutes at 60 degreeC after the bridge | crosslinking process, the protective film is bonded. In such a drying step immediately after the cross-linking step, there is a problem that the cross-linking reaction proceeds remarkably and the polyvinyl alcohol-based resin layer shrinks in the width direction of the film. In this case, when the film is to be produced continuously, only the polyvinyl alcohol-based resin layer of the laminated film composed of the base film and the polyvinyl alcohol-based resin layer contracts in the width direction, so that the polyvinyl alcohol-based resin layer together with the base film There was a problem that the end of the fold would be folded.

JP 2000-338329 A JP 2009-98653 A

  In view of the above problems, an object of the present invention is to produce a polarizing plate that is thin and has high polarization performance.

The present invention is a method for producing a polarizing plate comprising a polarizer layer and a protective film formed on one surface of the polarizer layer,
A resin layer forming step of forming a polyvinyl alcohol resin layer on one surface of the base film to obtain a laminated film;
A stretching step of dry stretching the laminated film;
A dyeing step of forming a polarizer layer by dyeing the polyvinyl alcohol-based resin layer of the laminated film with a dichroic dye and performing a crosslinking treatment;

A cleaning step for cleaning the laminated film;
A protective film laminating step of laminating a protective film via a pressure-sensitive adhesive layer or an adhesive layer on the surface opposite to the base film side surface of the laminated film;
A bonding drying step of drying the pressure-sensitive adhesive layer or the adhesive layer;
A base film peeling step for peeling the base film from the laminated film;
In this order, and maintaining the atmospheric temperature between after the washing step and before the pasting step at less than 40 ° C.

  In the bonding drying step, it is preferable to perform drying at a temperature of at least 70 ° C. or higher.

  The thickness of the polarizer layer of the polarizing plate is preferably 10 μm or less.

  In the present invention, the atmospheric temperature from after washing to pasting is maintained below 40 ° C., and after laminating a laminated film composed of a base film and a polyvinyl alcohol-based resin layer, it is subjected to a pasting step. This fold can be avoided.

  Moreover, in order to perform the temperature control as described above, the substantial drying of the polyvinyl alcohol resin layer is performed in the bonding drying step after the bonding step, but sufficient drying is performed in this bonding drying step. If it is carried out, a practical polarizing plate with excellent heat and heat resistance can be obtained.

  At this time, with the polarizer layer having sufficient moisture, it is subjected to a bonding and drying step at a high temperature (70 ° C. or higher), so that the polarizer layer is in a steamed state. It can also be improved.

It is a flowchart which shows one Embodiment of the manufacturing method of the polarizing plate of this invention.

  In this specification, the laminated body provided with the polyvinyl alcohol-type resin layer (layer which consists of polyvinyl alcohol-type resin) on one surface of a base film is called "laminated film." In addition, a polyvinyl alcohol-based resin layer having a function as a polarizer is referred to as a “polarizer layer”, and a laminate including a protective film on one surface of the polarizer layer is referred to as a “polarizing plate”. Hereinafter, each component will be described in detail.

[Base film]
As the resin used for the base film, for example, thermoplastic resins excellent in transparency, mechanical strength, thermal stability, stretchability, etc. are used, and an appropriate resin can be selected according to their Tg or Tm. Specific examples of thermoplastic resins include polyolefin resins, polyester resins, cyclic polyolefin resins (norbornene resins), (meth) acrylic resins, cellulose ester resins, polycarbonate resins, polyvinyl alcohol resins, vinyl acetate. Resin, polyarylate resin, polystyrene resin, polyethersulfone resin, polysulfone resin, polyamide resin, polyimide resin, and mixtures and copolymers thereof.

  The base film may be a film made of only one kind of the above-mentioned resin, or may be a film made by blending two or more kinds of resins. The base film may be a single layer film or a multilayer film.

  Examples of the polyolefin resin include polyethylene and polypropylene, which are preferable because they can be stably stretched at a high magnification. Further, an ethylene-polypropylene copolymer obtained by copolymerizing propylene with ethylene can also be used. Copolymerization can be performed with other types of monomers, and examples of other types of monomers copolymerizable with propylene include ethylene and α-olefins. As the α-olefin, an α-olefin having 4 or more carbon atoms is preferably used, and more preferably an α-olefin having 4 to 10 carbon atoms. Specific examples of the α-olefin having 4 to 10 carbon atoms include linear monoolefins such as 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene and 1-decene; Branched monoolefins such as 3-methyl-1-butene, 3-methyl-1-pentene, 4-methyl-1-pentene; vinylcyclohexane and the like. The copolymer of propylene and other monomers copolymerizable therewith may be a random copolymer or a block copolymer. The content of the structural unit derived from the other monomer in the copolymer is determined by infrared (IR) spectrum according to the method described on page 616 of “Polymer Analysis Handbook” (1995, published by Kinokuniya). It can be obtained by measuring.

  Among the above, propylene-based resins constituting the propylene-based resin film include propylene homopolymer, propylene-ethylene random copolymer, propylene-1-butene random copolymer, and propylene-ethylene-1-butene. Random copolymers are preferably used.

  The stereoregularity of the propylene resin constituting the propylene resin film is preferably substantially isotactic or syndiotactic. A propylene-based resin film made of a propylene-based resin having substantially isotactic or syndiotactic stereoregularity has relatively good handleability and excellent mechanical strength in a high-temperature environment.

  The polyester resin is a polymer having an ester bond and is mainly a polycondensate of a polyvalent carboxylic acid and a polyhydric alcohol. As the polyvalent carboxylic acid used, divalent dicarboxylic acid is mainly used, and examples thereof include isophthalic acid, terephthalic acid, dimethyl terephthalate, and dimethyl naphthalenedicarboxylate. In addition, divalent diol is mainly used as the polyhydric alcohol used, and examples thereof include propanediol, butanediol, neopentyl glycol, and cyclohexanedimethanol. Specific examples of the resin include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polytrimethylene terephthalate, polytrimethylene naphthalate, polycyclohexane dimethyl terephthalate, polycyclohexane dimethyl naphthalate, and the like. . These blend resins and copolymers can also be suitably used.

  As the cyclic polyolefin resin, a norbornene resin is preferably used. Cyclic polyolefin resin is a general term for resins that are polymerized using cyclic olefin as a polymerization unit, and is described in, for example, JP-A-1-240517, JP-A-3-14882, JP-A-3-122137, and the like. Resin. Specific examples include ring-opening (co) polymers of cyclic olefins, addition polymers of cyclic olefins, cyclic olefins and α-olefins such as ethylene and propylene (typically random copolymers), And graft polymers obtained by modifying them with an unsaturated carboxylic acid or a derivative thereof, and hydrides thereof. Specific examples of the cyclic olefin include norbornene monomers.

  Various products are commercially available as cyclic polyolefin resins. As specific examples, Topas (registered trademark) (manufactured by Ticona), Arton (registered trademark) (manufactured by JSR Corporation), ZEONOR (registered trademark) (manufactured by Nippon Zeon Corporation), ZEONEX (ZEONEX) (Registered trademark) (manufactured by ZEON CORPORATION) and Apel (registered trademark) (manufactured by Mitsui Chemicals, Inc.).

  Any appropriate (meth) acrylic resin can be adopted as the (meth) acrylic resin. 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, C1-6 alkyl poly (meth) acrylates, such as poly (meth) acrylate methyl, are mentioned. More preferably, as the (meth) acrylic resin, a methyl methacrylate-based resin containing methyl methacrylate as a main component (50 to 100% by weight, preferably 70 to 100% by weight) is used.

  The cellulose ester resin is an ester of cellulose and a fatty acid. Specific examples of the cellulose ester resin include cellulose triacetate, cellulose diacetate, cellulose tripropionate, and cellulose dipropionate. Moreover, these copolymers and those obtained by modifying a part of the hydroxyl group with other types of substituents are also included. Among these, cellulose triacetate is particularly preferable. Many products of cellulose triacetate are commercially available, which is advantageous in terms of availability and cost. Examples of commercially available products of cellulose triacetate include Fujitac (registered trademark) TD80 (manufactured by Fuji Film Co., Ltd.), Fujitac (registered trademark) TD80UF (manufactured by Fuji Film Co., Ltd.), Fujitac (registered trademark) TD80UZ (Fuji Film ( Co., Ltd.), Fujitac (registered trademark) TD40UZ (Fuji Film Co., Ltd.), KC8UX2M (Konica Minolta Opto Co., Ltd.), KC4UY (Konica Minolta Opto Co., Ltd.), and the like.

  The polycarbonate resin is an engineering plastic made of a polymer in which monomer units are bonded via a carbonate group, and is a resin having high impact resistance, heat resistance, and flame retardancy. Moreover, since it has high transparency, it is suitably used in optical applications. In optical applications, resins called modified polycarbonates in which the polymer skeleton is modified in order to lower the photoelastic coefficient, copolymerized polycarbonates with improved wavelength dependency, and the like are commercially available and can be suitably used. Such polycarbonate resins are widely commercially available. For example, Panlite (registered trademark) (Teijin Chemicals Ltd.), Iupilon (registered trademark) (Mitsubishi Engineering Plastics), SD Polyca (registered trademark) (Sumitomo) Dow Co., Ltd.), Caliber (registered trademark) (Dow Chemical Co., Ltd.) and the like.

  Arbitrary appropriate additives other than said thermoplastic resin may be added to the base film. Examples of such additives include 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 exemplified above in the base 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. This is because, if the content of the thermoplastic resin in the base film is less than 50% by weight, the high transparency inherent in the thermoplastic resin may not be sufficiently exhibited.

  Although the thickness of the base film before stretching can be determined as appropriate, in general, from the viewpoint of workability such as strength and handleability, it is preferably 1 to 500 μm, more preferably 1 to 300 μm, and still more preferably 5 to 5 μm. 200 μm, most preferably 5 to 150 μm.

  The base film may be subjected to corona treatment, plasma treatment, flame treatment or the like on at least the surface on which the polyvinyl alcohol resin layer is formed in order to improve the adhesion with the polyvinyl alcohol resin layer. Moreover, in order to improve adhesiveness, you may form thin layers, such as a primer layer and an adhesive bond layer, in the surface of the side by which the polyvinyl alcohol-type resin layer of a base film is formed.

(Primer layer)
When the primer layer is formed on the surface of the base film on which the polarizer layer is formed, the primer layer is a material that exhibits a certain degree of strong adhesion to both the base film and the polyvinyl alcohol resin layer. If there is no particular limitation. For example, a thermoplastic resin excellent in transparency, thermal stability, stretchability, etc. is used. Specific examples include acrylic resins and polyvinyl alcohol resins, but are not limited thereto. Among these, a polyvinyl alcohol resin having good adhesion is preferably used.

  As a polyvinyl alcohol-type resin used as a primer layer, polyvinyl alcohol resin and its derivative (s) are mentioned, for example. Derivatives of polyvinyl alcohol resin include polyvinyl formal, polyvinyl acetal, etc., olefins such as ethylene and propylene, unsaturated carboxylic acids such as acrylic acid, methacrylic acid and crotonic acid, and alkyl esters of unsaturated carboxylic acids. And those modified with acrylamide or the like. Among the above-mentioned polyvinyl alcohol-based resin materials, it is preferable to use a polyvinyl alcohol resin.

  In order to increase the strength of the primer layer, a crosslinking agent may be added to the thermoplastic resin. As the cross-linking agent to be added to the thermoplastic resin, known ones such as organic and inorganic can be used. What is necessary is just to select a more suitable thing suitably with respect to the thermoplastic resin to be used. For example, in addition to low molecular crosslinkers such as epoxy crosslinkers, isocyanate crosslinkers, dialdehyde crosslinkers, metal chelate crosslinkers, high molecular weight polymers such as methylolated melamine resins and polyamide epoxy resins. A crosslinking agent or the like can also be used. When a polyvinyl alcohol resin is used as the thermoplastic resin, it is particularly preferable to use a polyamide epoxy resin, a methylolated melamine, a dialdehyde, a metal chelate crosslinking agent, or the like as the crosslinking agent.

  The thickness of a primer layer becomes like this. Preferably it is 0.05-1 micrometer, More preferably, it is 0.1-0.4 micrometer. If the thickness is less than 0.05 μm, the adhesion between the base film and the polyvinyl alcohol layer is reduced, and if it is greater than 1 μm, the polarizing plate becomes thick.

[Polarizer layer]
Specifically, the polarizer layer is obtained by adsorbing and orienting a dichroic dye on a uniaxially stretched polyvinyl alcohol-based resin layer.

  As the polyvinyl alcohol resin constituting the polyvinyl alcohol resin layer, a saponified polyvinyl acetate resin can be used. Examples of the polyvinyl acetate resin include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers with other monomers copolymerizable with vinyl acetate. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and acrylamides having an ammonium group.

  The polyvinyl alcohol resin constituting the polarizer layer (polyvinyl alcohol resin layer) is preferably a completely saponified product. The range of the saponification degree is preferably 80.0 mol% to 100.0 mol%, more preferably 90.0 mol% to 99.5 mol%, and further 94.0 mol%. Most preferred is a range of ˜99.0 mol%. When the degree of saponification is less than 80.0 mol%, there is a problem that the water resistance and heat-and-moisture resistance after the polarizing plate are remarkably inferior. In addition, when a polyvinyl alcohol-based resin having a saponification degree exceeding 99.5 mol% is used, the dyeing speed is remarkably slow, and a polarizing laminated film having sufficient polarization performance may not be obtained. In some cases, the production takes several times longer than usual.

The saponification degree as used herein is a unit ratio (mol%) representing the ratio of the acetate group contained in the polyvinyl acetate resin, which is a raw material for the polyvinyl alcohol resin, to a hydroxyl group by the saponification step. Is a numerical value defined by the following formula. It can be determined by the method defined in JIS K 6726 (1994).

Saponification degree (mol%) = (number of hydroxyl groups) ÷ (number of hydroxyl groups + number of acetate groups) × 100

The higher the degree of saponification, the higher the proportion of hydroxyl groups, that is, the lower the proportion of acetate groups that inhibit crystallization.

  Further, the polyvinyl alcohol resin used in the present invention may be a modified polyvinyl alcohol partially modified. For example, polyvinyl alcohol resins modified with olefins such as ethylene and propylene, unsaturated carboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid, alkyl esters of unsaturated carboxylic acids, acrylamide, and the like can be used. The proportion of modification is preferably less than 30 mol%, and more preferably less than 10%. When modification exceeding 30 mol% is performed, it becomes difficult to adsorb the dichroic dye, resulting in a problem that the polarization performance is lowered.

  The average degree of polymerization of the polyvinyl alcohol-based resin is not particularly limited, but is preferably 100 to 10,000, more preferably 1500 to 8000, and most preferably 2000 to 5000. The average degree of polymerization here is also a numerical value determined by a method defined by JIS K 6726 (1994).

  Examples of the polyvinyl alcohol resin having such characteristics include PVA124 (degree of saponification: 98.0 to 99.0 mol%) and PVA117 (degree of saponification: 98.0 to 99.0) manufactured by Kuraray Co., Ltd. Mol%), PVA624 (degree of saponification: 95.0-96.0 mol%) and PVA617 (degree of saponification: 94.5-95.5 mol%); for example, AH- manufactured by Nippon Synthetic Chemical Industry Co., Ltd. 26 (degree of saponification: 97.0-98.8 mol%), AH-22 (degree of saponification: 97.5-98.5 mol%), NH-18 (degree of saponification: 98.0-99. 0 mol%), and N-300 (degree of saponification: 98.0 to 99.0 mol%); for example, JC-33 (degree of saponification: 99.0 mol% or more) of Nippon Vinegar Pival Co., Ltd. , JM-33 (degree of saponification: 93.5 to 95.5 mol%), JM-26 Saponification degree: 95.5-97.5 mol%), JP-45 (saponification degree: 86.5-89.5 mol%), JF-17 (degree of saponification: 98.0-99.0 mol) %), JF-17L (degree of saponification: 98.0 to 99.0 mol%), JF-20 (degree of saponification: 98.0 to 99.0 mol%) and the like. It can be used suitably.

  By forming such a polyvinyl alcohol resin, a polyvinyl alcohol resin layer is formed. The method for forming the polyvinyl alcohol-based resin is not particularly limited, and can be formed by a known method, but from the viewpoint of easily obtaining a polarizer layer having a desired thickness, the polyvinyl alcohol-based resin is formed. It is preferable to form a film by applying the above solution on a substrate film.

  Such a polyvinyl alcohol-based resin layer is stretched and oriented together with the base film, and further, a dichroic dye is adsorbed and oriented to form a polarizer layer. The draw ratio is preferably more than 5 times, more preferably more than 5 times and not more than 17 times.

  The thickness of the polarizer layer (the thickness of the stretched polyvinyl alcohol-based resin layer) is 10 μm or less, preferably 7 μm or less. By setting the thickness of the polarizer layer to 10 μm or less, a thin polarizing plate can be configured. On the other hand, if it is too thin, it will be inferior in heat-and-moisture resistance, so it is preferably 1 μm or more, more preferably 3 μm or more, and most preferably 4 μm or more.

  Examples of the dichroic dye used in the polarizer layer include iodine and organic dyes. Examples of organic dyes include Red BR, Red LR, Red R, Pink LB, Rubin BL, Bordeaux GS, Sky Blue LG, Lemon Yellow, Blue BR, Blue 2R, Navy RY, Green LG, Violet LB, Violet B, Black H, Black B, Black GSP, Yellow 3G, Yellow R, Orange LR, Orange 3R, Scarlet GL, Scarlet KGL, Congo Red, Brilliant Violet BK, Spura Blue G, Spura Blue GL, Spura Orange GL, Direct Sky Blue, Direct First Orange S, First Black, etc. can be used. One kind of these dichroic substances may be used, or two or more kinds may be used in combination.

[Protective film]
The protective film may be a simple protective film having no optical function, or may be a protective film having both optical functions such as a retardation film and a brightness enhancement film.

  The material of the protective film is not particularly limited, but for example, a cyclic polyolefin resin film, a cellulose acetate resin film made of a resin such as triacetyl cellulose or diacetyl cellulose, polyethylene terephthalate, polyethylene naphthalate, poly Examples of the film that have been widely used in the art include polyester-based resin films made of a resin such as butylene terephthalate, polycarbonate-based resin films, acrylic-based resin films, and polypropylene-based resin films.

  Examples of the cyclic polyolefin-based resin include appropriate commercial products such as Topas (registered trademark) (manufactured by Ticona), Arton (registered trademark) (manufactured by JSR Corporation), ZEONOR (registered trademark) (Nippon ZEON ( ZEONEX (registered trademark) (manufactured by Nippon Zeon Co., Ltd.), Apel (registered trademark) (manufactured by Mitsui Chemicals, Inc.) can be suitably used. When such a cyclic polyolefin resin is formed into a film, a known method such as a solvent casting method or a melt extrusion method is appropriately used. In addition, pre-filmed cyclic polyolefins such as Essina (registered trademark) (manufactured by Sekisui Chemical Co., Ltd.), SCA40 (manufactured by Sekisui Chemical Co., Ltd.), Zeonoa (registered trademark) film (manufactured by Optes Co., Ltd.) A commercial product of a film made of a resin may be used.

  The cyclic polyolefin resin film may be uniaxially stretched or biaxially stretched. An arbitrary retardation value can be imparted to the cyclic polyolefin-based resin film by stretching. Stretching is usually performed continuously while unwinding the film roll, and is stretched in the heating furnace in the roll traveling direction, the direction perpendicular to the traveling direction, or both. The temperature of the heating furnace is usually in the range from the vicinity of the glass transition temperature of the cyclic polyolefin resin to the glass transition temperature + 100 ° C. The draw ratio is usually 1.1 to 6 times, preferably 1.1 to 3.5 times in one direction.

  Since the cyclic polyolefin resin film generally has poor surface activity, surface treatment such as plasma treatment, corona treatment, ultraviolet irradiation treatment, flame (flame) treatment, saponification treatment is performed on the surface to be bonded to the polarizing film. preferable. Among these, plasma treatment and corona treatment that can be performed relatively easily are preferable.

  Examples of the cellulose acetate-based resin film include commercially available products such as Fujitac (registered trademark) TD80 (manufactured by Fuji Film Co., Ltd.), Fujitac (registered trademark) TD80UF (manufactured by Fuji Film Co., Ltd.), and Fujitac (registered trademark). TD80UZ (Fuji Film Co., Ltd.), Fujitac (registered trademark) TD40UZ (Fuji Film Co., Ltd.), KC8UX2M (Konica Minolta Opto Co., Ltd.), KC4UY (Konica Minolta Opto Co., Ltd.) are preferably used. be able to.

  A liquid crystal layer or the like may be formed on the surface of the cellulose acetate-based resin film in order to improve viewing angle characteristics. Moreover, in order to provide a phase difference, what stretched the cellulose acetate type-resin film may be used. The cellulose acetate-based resin film is usually subjected to a saponification treatment in order to improve the adhesiveness with the polarizing film. As the saponification treatment, a method of immersing in an alkaline aqueous solution such as sodium hydroxide or potassium hydroxide can be employed.

  Optical layers such as a hard coat layer, an antiglare layer, and an antireflection layer can be formed on the surface of the protective film as described above. The method for forming these optical layers on the surface of the protective film is not particularly limited, and a known method can be used.

  The thickness of the protective film is preferably as thin as possible from the demand for thinning, is preferably 90 μm or less, and more preferably 50 μm or less. On the other hand, if it is too thin, the strength is lowered and the processability is poor, and therefore it is preferably 5 μm or more.

[Other optical layers]
In practical use, the polarizing plate can be used as a polarizing plate in which other optical layers are laminated. Moreover, the said protective film may have a function of these optical layers.

  Examples of other optical layers include a reflective polarizing film that transmits certain types of polarized light and reflects polarized light that exhibits the opposite properties, a film with an antiglare function having an uneven shape on the surface, and a surface antireflection function. Examples thereof include an attached film, a reflective film having a reflective function on the surface, a transflective film having both a reflective function and a transmissive function, and a viewing angle compensation film.

  Commercially available products corresponding to reflective polarizing films that transmit certain types of polarized light and reflect polarized light that exhibits the opposite properties include DBEF (available from 3M, Sumitomo 3M Co., Ltd.), APF (Available from 3M, available from Sumitomo 3M Limited). Examples of the viewing angle compensation film include an optical compensation film coated with a liquid crystal compound on the surface of the substrate and oriented, a retardation film made of a polycarbonate resin, and a retardation film made of a cyclic polyolefin resin. Commercially available products corresponding to an optical compensation film coated with a liquid crystal compound on the substrate surface and oriented are WV film (Fuji Film Co., Ltd.), NH film (Shin Nippon Oil Co., Ltd.), NR Examples include films (manufactured by Nippon Oil Corporation). Commercial products corresponding to retardation films made of cyclic polyolefin resins include Arton (registered trademark) film (manufactured by JSR Corporation), Essina (registered trademark) (manufactured by Sekisui Chemical Co., Ltd.), Zeonor ( Registered trademark) film (manufactured by Optes Co., Ltd.).

<Production method of polarizing plate>
FIG. 1 is a flowchart showing an embodiment of a method for producing a polarizing plate. As shown in FIG. 1, the manufacturing method of the polarizing plate is as follows:
A resin layer forming step (S10) for forming a polyvinyl alcohol resin layer on one surface of the base film to obtain a laminated film;
Stretching step (S20) for dry stretching the laminated film,
Dyeing process (S30) which forms a polarizer layer by dyeing the polyvinyl alcohol system resin layer of a lamination film with a dichroic dye, and giving a crosslinking treatment,
A cleaning step (S40) for cleaning the laminated film;
Protective film laminating step (S50) for laminating a protective film via a pressure-sensitive adhesive layer or an adhesive layer on the surface opposite to the base film side surface of the laminated film,
Bonding drying step (S60) for drying the pressure-sensitive adhesive layer or the adhesive layer, and
Substrate film peeling step for peeling the substrate film from the laminated film (S70)
Are performed in this order.

  The manufacturing method of the polarizing plate of this invention maintains the atmospheric temperature between after the said washing | cleaning process and before the said bonding process below 40 degreeC. By this manufacturing method, a polarizing plate provided with a polarizer layer having a thickness of 10 μm or less and having sufficient polarization performance on the protective film can be obtained. This polarizing plate can be used by, for example, bonding to another optical film or a liquid crystal cell via a pressure-sensitive adhesive.

<Each manufacturing process>
Hereafter, each process of S10-S70 in FIG. 1 is demonstrated in detail.

[Resin Layer Forming Step (S10)]
Here, the laminated film which consists of a base film and a polyvinyl alcohol-type resin layer is obtained by forming a polyvinyl alcohol-type resin layer in one surface of a base film.

  Suitable materials for the base film are as described in the description of the configuration of the polarizing plate. In addition, it is preferable to use a base film that can be stretched in a temperature range suitable for stretching a polyvinyl alcohol-based resin.

  The thickness (before stretching) of the polyvinyl alcohol resin layer to be formed is preferably more than 3 μm and not more than 30 μm, and more preferably 5 to 20 μm. If it is 3 μm or less, it becomes too thin after stretching and the dyeability is remarkably deteriorated. If it exceeds 30 μm, the thickness of the finally obtained polarizer layer may exceed 10 μm.

  The polyvinyl alcohol-based resin layer is preferably dried by applying a polyvinyl alcohol-based resin solution obtained by dissolving a polyvinyl alcohol-based resin powder in a good solvent onto one surface of the base film and evaporating the solvent. It is formed by doing. By forming the polyvinyl alcohol-based resin layer in this manner, the polyvinyl alcohol-based resin can be thinned. As a method of coating a polyvinyl alcohol resin solution on a base film, a wire bar coating method, a reverse coating, a roll coating method such as gravure coating, a die coating method, a comma coating method, a lip coating method, a spin coating method, a screen A known method such as a coating method, a fountain coating method, a dipping method, or a spray method can be appropriately selected and employed. A drying temperature is 50-200 degreeC, for example, Preferably it is 60-150 degreeC. The drying time is, for example, 2 to 20 minutes.

  Moreover, in order to improve the adhesiveness of a base film and a polyvinyl alcohol-type resin layer, you may provide a primer layer between a base film and a polyvinyl alcohol-type resin layer. The primer layer is preferably formed from a composition containing a polyvinyl alcohol-based resin and a crosslinking agent from the viewpoint of adhesion. Materials suitable for the primer layer are as described in the description of the configuration of the polarizing plate.

[Stretching step (S20)]
Here, the laminated film consisting of the base film and the polyvinyl alcohol-based resin layer is dry-stretched. Preferably, uniaxial stretching is performed so that the stretching ratio is more than 5 times and not more than 17 times. More preferably, it is uniaxially stretched so that the stretch ratio is more than 5 times and not more than 8 times. When the draw ratio is 5 times or less, the polyvinyl alcohol-based resin layer is not sufficiently oriented, and as a result, the degree of polarization of the polarizer layer may not be sufficiently high. On the other hand, when the draw ratio exceeds 17 times, the laminated film is liable to break during stretching, and at the same time, the thickness of the laminated film after stretching becomes unnecessarily thin, and the workability and handling properties in the subsequent process are lowered. There is a fear. The stretching process in the stretching step (S20) is not limited to one-stage stretching, and can be performed in multiple stages. In the case of performing in multiple stages, the stretching process is performed so that the stretching ratio is more than 5 times by combining all stages of the stretching process.

  In the stretching step (S20) in the present embodiment, a longitudinal stretching process performed in the longitudinal direction of the laminated film, a lateral stretching process stretching in the width direction, and the like can be performed. Examples of the longitudinal stretching method include an inter-roll stretching method and a compression stretching method, and examples of the transverse stretching method include a tenter method.

  Moreover, it is preferable that the extending | stretching process in this invention is performed using the dry-type extending | stretching method. By stretching the polyvinyl alcohol resin layer together with the base film before the dyeing step, the polyvinyl alcohol resin film (polarizer layer) that is thinner than before can be stretched at a high magnification without breaking. This is because the polarizing plate to be manufactured can be thinned.

[Dyeing step (S30)]
Here, the polyvinyl alcohol resin layer of the laminated film is dyed with a dichroic dye. Examples of the dichroic dye include iodine and organic dyes. Examples of organic dyes include Red BR, Red LR, Red R, Pink LB, Rubin BL, Bordeaux GS, Sky Blue LG, Lemon Yellow, Blue BR, Blue 2R, Navy RY, Green LG, Violet LB, Violet B, Black H, Black B, Black GSP, Yellow 3G, Yellow R, Orange LR, Orange 3R, Scarlet GL, Scarlet KGL, Congo Red, Brilliant Violet BK, Spura Blue G, Spura Blue GL, Spura Orange GL, Direct Sky Blue, Direct First Orange S, First Black, etc. can be used. One kind of these dichroic substances may be used, or two or more kinds may be used in combination.

  A dyeing process is performed by immersing the whole stretched film in the solution (dyeing solution) containing the said dichroic dye, for example. As the staining solution, a solution in which the above dichroic dye is dissolved in a solvent can be used. As a solvent for the dyeing solution, water is generally used, but an organic solvent compatible with water may be further added. The concentration of the dichroic dye is preferably 0.01 to 10% by weight, more preferably 0.02 to 7% by weight, and particularly preferably 0.025 to 5% by weight.

  When iodine is used as the dichroic dye, it is preferable to further add an iodide because the dyeing efficiency can be further improved. Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and iodide. Examples include titanium. The addition ratio of these iodides is preferably 0.01 to 20% by weight in the dyeing solution. Of the iodides, it is preferable to add potassium iodide. When potassium iodide is added, the ratio of iodine to potassium iodide is preferably in the range of 1: 5 to 1: 100, more preferably in the range of 1: 6 to 1:80 by weight. , Particularly preferably in the range of 1: 7 to 1:70.

  The immersion time of the stretched film in the dyeing solution is not particularly limited, but is usually preferably in the range of 15 seconds to 15 minutes, and more preferably 1 minute to 3 minutes. Moreover, it is preferable that it is in the range of 10-60 degreeC, and, as for the temperature of a dyeing | staining solution, it is more preferable that it exists in the range of 20-40 degreeC.

  In the dyeing step, a crosslinking treatment can be performed after the dyeing. The crosslinking treatment is performed, for example, by immersing the laminated film in a solution containing a crosslinking agent (crosslinking solution). Conventionally known substances can be used as the crosslinking agent. Examples thereof include boron compounds such as boric acid and borax, glyoxal, and glutaraldehyde. One kind of these may be used, or two or more kinds may be used in combination.

  As the crosslinking solution, a solution in which a crosslinking agent is dissolved in a solvent can be used. As the solvent, for example, water can be used, but an organic solvent compatible with water may be further included. Although the density | concentration of the crosslinking agent in a crosslinking solution is not limited to this, It is preferable to exist in the range of 1-20 weight%, and it is more preferable that it is 6-15 weight%.

  Iodide may be added to the crosslinking solution. By adding iodide, the in-plane polarization characteristics of the resin layer can be made more uniform. Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. Is mentioned. The iodide content is 0.05 to 15% by weight, more preferably 0.5 to 8% by weight.

  The immersion time of the stretched film in the crosslinking solution is usually preferably from 15 seconds to 20 minutes, and more preferably from 30 seconds to 15 minutes. Moreover, it is preferable that the temperature of a crosslinking solution exists in the range of 10-80 degreeC.

  Through the above dyeing step (S30), the polyvinyl alcohol-based resin layer has a function as a polarizer layer.

[Washing step (S40)]
Next, it is preferable to perform a washing process. As the washing step, a water washing treatment can be performed. The water washing treatment can usually be performed by immersing the stretched film in pure water such as ion exchange water or distilled water. The water washing temperature is usually in the range of 3 to 50 ° C, preferably 4 to 20 ° C. The immersion time is usually 2 to 300 seconds, preferably 3 to 240 seconds.

  In the washing step, washing treatment with an iodide solution and water washing treatment may be combined, and a solution in which liquid alcohol such as methanol, ethanol, isopropyl alcohol, butanol, propanol or the like is appropriately blended may be used. Moreover, you may provide the process of draining using a nip roll, an air knife, etc. after a washing | cleaning process.

  In this invention, after the said washing | cleaning process (S40), before the next protective film bonding process (S50) (until just before bonding a protective film), the laminated | multilayer film after dyeing | staining is below 40 degreeC atmosphere. It is essential to maintain the When the laminated film after dyeing is heated to 40 ° C or higher before being bonded to the protective film, the laminated film curls in the width direction and ends (both ends in the width direction) are folded. The problem of becoming. In order to prevent curling of the laminated film more reliably, after the cleaning step (S40), until the next protective film bonding step (S50) is completed (until the protective film is bonded to the laminated film), the ambient temperature Is preferably maintained below 40 ° C.

  Regarding drying, in the conventional method, drying is performed at a temperature of 40 ° C. or higher in the state of “base film / PVA” before bonding the protective film, and after bonding the protective film, “base film / Further drying is performed in the state of “PVA / protective film”. However, in the present invention, it is necessary to maintain an atmospheric temperature of less than 40 degrees in the state of “base film / PVA” before bonding the protective film. Thereby, folding of the end can be prevented. What is necessary is just to fully dry after bonding a protective film, when obtaining water resistance. In this state, since both sides are sandwiched between the protective film and the base material film, curling is unlikely to occur and problems such as folding of the end portions do not occur.

[Protective film pasting step (S50)]
Here, a protective film is bonded to the surface opposite to the surface on the base film side of the polarizer layer of the laminated film that has undergone the above-described steps. As a method of bonding a polarizer layer and a protective film, the method of bonding a polarizer layer and a protective film through an adhesive layer or an adhesive layer is mentioned. Materials suitable as the protective film are as described in the description of the structure of the polarizing plate.

(Adhesive layer)
The pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer is usually a composition in which an acrylic resin, a styrene resin, a silicone resin, or the like is used as a base polymer and a crosslinking agent such as an isocyanate compound, an epoxy compound, or an aziridine compound is added thereto. Become. Furthermore, a pressure-sensitive adhesive layer exhibiting light scattering properties can be formed by mixing fine particles in the pressure-sensitive adhesive.

  The thickness of the pressure-sensitive adhesive layer is preferably 1 to 40 μm, but it is preferably applied thinly, and more preferably 3 to 25 μm, as long as the workability and durability characteristics are not impaired. When it is 3 to 25 μm, it has good processability and is also suitable for suppressing the dimensional change of the polarizing film. When the pressure-sensitive adhesive layer is less than 1 μm, the tackiness is lowered, and when it exceeds 40 μm, problems such as the pressure-sensitive adhesive protruding easily occur.

  The method of forming the pressure-sensitive adhesive layer on the protective film or the polarizer is not particularly limited, and a solution containing each component including the above-mentioned base polymer is applied to the protective film surface or the polarizer layer surface, After forming the pressure-sensitive adhesive layer by drying, it may be bonded to a separator or other types of film, or after forming the pressure-sensitive adhesive layer on the separator, it is laminated on the protective film surface or the polarizer layer surface. Also good. Further, when forming the pressure-sensitive adhesive layer on the surface of the protective film or the polarizer layer, if necessary, the protective film or the polarizer layer surface, or one or both of the pressure-sensitive adhesive layers may be subjected to an adhesion treatment such as corona treatment. Good.

(Adhesive layer)
Examples of the adhesive constituting the adhesive layer include a water-based adhesive using a polyvinyl alcohol-based resin aqueous solution, a water-based two-component urethane-based emulsion adhesive, and the like. Among these, a polyvinyl alcohol resin aqueous solution is preferably used. Polyvinyl alcohol resins used as adhesives include vinyl alcohol homopolymers obtained by saponifying polyvinyl acetate, which is a homopolymer of vinyl acetate, as well as other single quantities copolymerizable with vinyl acetate. And vinyl alcohol copolymers obtained by saponifying the copolymer with the polymer, and modified polyvinyl alcohol polymers obtained by partially modifying the hydroxyl groups. A polyhydric aldehyde, a water-soluble epoxy compound, a melamine compound, a zirconia compound, a zinc compound, or the like may be added as an additive to the water-based adhesive. When such a water-based adhesive is used, the adhesive layer obtained therefrom is usually much thinner than 1 μm, and even when the cross section is observed with a normal optical microscope, the adhesive layer is practically not observed.

  The method of laminating the film using the water-based adhesive is not particularly limited, and the adhesive is evenly applied or poured on the surface of the film, and the other film is laminated on the coated surface and laminated with a roll or the like. And a drying method. Usually, an adhesive agent is apply | coated at the temperature of 15-40 degreeC after the preparation, and the bonding temperature is the range of 15-30 degreeC normally.

  When using a water-system adhesive, after bonding a film, in order to remove the water contained in a water-system adhesive, it is made to dry. The temperature of the drying furnace is preferably 30 ° C to 90 ° C. If it is less than 30 ° C., the adhesive surface tends to be peeled off. If it is 90 ° C. or higher, the optical performance of the polarizer or the like may be deteriorated by heat. The drying time can be 10 to 1000 seconds.

  After drying, it may be further cured at room temperature or slightly higher temperature, for example, at a temperature of about 20 to 45 ° C. for about 12 to 600 hours. The temperature at the time of curing is generally set lower than the temperature adopted at the time of drying.

  Moreover, a photocurable adhesive can also be used as a non-aqueous adhesive. Examples of the photocurable adhesive include a mixture of a photocurable epoxy resin and a photocationic polymerization initiator.

  As a method of laminating a film with a photocurable adhesive, a conventionally known method can be used. For example, casting method, Mayer bar coating method, gravure coating method, comma coater method, doctor plate method, die coating method Examples of the method include applying an adhesive to the adhesive surface of the film by a dip coating method, a spraying method, and the like, and superimposing two films. The casting method is a method in which two films as an object to be coated are moved in a substantially vertical direction, generally in a horizontal direction, or in an oblique direction between the two, and an adhesive is allowed to flow down and spread on the surface. is there.

  After the adhesive is applied to the surface of the film, it is bonded by sandwiching the film with a nip roll or the like. Moreover, the method of pressing this laminated body with a roll etc. and spreading it uniformly can also be used suitably. In this case, a metal, rubber, or the like can be used as the material of the roll. Furthermore, a method in which this laminate is passed between rolls and pressed to spread is preferably employed. In this case, these rolls may be made of the same material or different materials. The thickness of the adhesive layer after being bonded using the nip roll or the like before drying or curing is preferably 5 μm or less and 0.01 μm or more.

  In order to improve adhesiveness, surface treatment such as plasma treatment, corona treatment, ultraviolet irradiation treatment, flame (flame) treatment, and saponification treatment may be appropriately performed on the adhesion surface of the film. Examples of the saponification treatment include a method of immersing in an aqueous alkali solution such as sodium hydroxide or potassium hydroxide.

  When a photocurable resin is used as an adhesive, the photocurable adhesive is cured by irradiating active energy rays after laminating the films. The light source of the active energy ray is not particularly limited, but an active energy ray having a light emission distribution at a wavelength of 400 nm or less is preferable, and specifically, a low pressure mercury lamp, a medium pressure mercury lamp, a high pressure mercury lamp, an ultrahigh pressure mercury lamp, a chemical lamp, a black light lamp A microwave excitation mercury lamp, a metal halide lamp and the like are preferably used.

The light irradiation intensity to the photocurable adhesive is appropriately determined depending on the composition of the photocurable adhesive and is not particularly limited, but the irradiation intensity in the wavelength region effective for activating the polymerization initiator is 0.1 to 6000 mW / it is preferable that the cm ^2. When the irradiation intensity is 0.1 mW / cm ² or more, the reaction time does not become too long, and when it is 6000 mW / cm ² or less, the epoxy is generated by the heat radiated from the light source and the heat generated when the photo-curable adhesive is cured. There is little risk of yellowing of the resin or deterioration of the polarizing film. The light irradiation time to the photocurable adhesive is not particularly limited and is applied according to the photocurable adhesive to be cured, but the integrated light amount expressed as the product of the irradiation intensity and the irradiation time. Is preferably set to be 10 to 10,000 mJ / cm ² . When the cumulative amount of light to the photocurable adhesive is 10 mJ / cm ² or more, a sufficient amount of active species derived from the polymerization initiator can be generated to allow the curing reaction to proceed more reliably, and at 10,000 mJ / cm ² or less. In some cases, irradiation time does not become too long and good productivity can be maintained. The thickness of the adhesive layer after irradiation with active energy rays is usually about 0.001 to 5 μm, preferably 0.01 μm or more and 2 μm or less, more preferably 0.01 μm or more and 1 μm or less. .

  When curing a photocurable adhesive of a film containing a polarizer layer or a protective film by irradiation with active energy rays, various polarizing plate properties such as the degree of polarization, transmittance and hue of the polarizer layer, and the transparency of the protective film, etc. It is preferable to perform the curing under conditions where the function does not decrease.

[Bonding and drying step (S60)]
Next, drying of the polyvinyl alcohol-type resin layer of the laminated film which bonded the protective form is implemented. In this bonding drying step, the polyvinyl alcohol-based resin layer may also be dried and the pressure-sensitive adhesive layer and the adhesive layer used for bonding the protective film may be combined. It is preferable that a bonding drying process (S60) includes the drying process at the temperature of 70 degreeC or more. Furthermore, it is more preferable to include a drying step at a temperature of 80 ° C. or higher. Of course, a multi-step drying process with different temperatures may be included. In that case, it is preferable to provide a drying process at a temperature of 70 ° C. or more in the first half of the multi-stage drying process as much as possible. This is because the polarizing performance of the finally obtained polarizing plate is likely to be improved.

  In the bonding drying step (S60), after the protective film is bonded to the laminated film maintained at an atmospheric temperature of less than 40 ° C. after washing and before the bonding, the polyvinyl alcohol resin layer of the laminated film is dried. In order to carry out, after pasting a protective film on the laminated film which was dried as the atmosphere temperature between after washing and before pasting as 40 ° C or more like usual, more than the case where it is further subjected to a drying process, It is necessary to increase the drying power. Examples of a method for increasing the drying power include a method of increasing the drying time and / or increasing the drying temperature. Increasing the drying time is extremely effective in terms of enhancing the drying power, but it is preferable that the drying time is not so long from the viewpoint of productivity. For this reason, it is very effective to shorten the drying time by providing a drying step at a temperature of at least 70 ° C., and it is more preferable to provide a drying step at a temperature of 80 ° C. or higher.

  In order to enhance the drying power in addition to the temperature, the hot air circulation method such as the air volume and the wind direction may be optimized, or an IR heater that can apply heat locally may be provided. These aids further improve the efficiency of drying and contribute to productivity improvement.

  The upper limit of the drying temperature is preferably lower than the boiling point of water, and preferably less than 100 ° C. Furthermore, it is preferably 95 ° C. or lower, and most preferably 90 ° C. or lower.

[Base film peeling step (S70)]
Substrate film peeling process (S70) which peels a base film from a lamination film is performed after a pasting drying process (S60). The peeling method of a base film is not specifically limited, The method similar to the peeling film peeling process performed with a normal polarizing plate with an adhesive can be employ | adopted. After the bonding drying step (S60), it may be peeled off as it is, or after it is wound up into a roll, it may be peeled off by providing another peeling step.

[Example 1]
A polarizing plate was produced according to the production method shown in FIG.

(Base film)
A homopolymer which is a propylene homopolymer on both sides of a resin layer consisting of a random copolymer of propylene / ethylene containing about 5% by weight of ethylene units (“Sumitomo Nobrene W151” manufactured by Sumitomo Chemical Co., Ltd., melting point Tm = 138 ° C.) A base film having a three-layer structure in which a resin layer made of polypropylene (“Sumitomo Noblen FLX80E4” manufactured by Sumitomo Chemical Co., Ltd., melting point Tm = 163 ° C.) was arranged was produced by coextrusion molding using a multilayer extrusion molding machine. The total thickness of the obtained base film was 90 μm, and the thickness ratio (FLX80E4 / W151 / FLX80E4) of each layer was 3/4/3.

(Primer layer formation process)
Polyvinyl alcohol powder (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., average polymerization degree 1100, saponification degree 99.5 mol%, trade name: Z-200) is dissolved in 95 ° C. hot water to give an aqueous solution having a concentration of 3% by weight. Prepared. The resulting aqueous solution was mixed with 5 parts by weight of a crosslinking agent (manufactured by Sumitomo Chemical Co., Ltd., trade name: Sumirez (registered trademark) Resin 650) with respect to 6 parts by weight of polyvinyl alcohol powder. The obtained mixed aqueous solution was applied on a corona-treated base film using a micro gravure coater and dried at 80 ° C. for 10 minutes to form a primer layer having a thickness of 0.2 μm.

(Resin layer forming process)
Polyvinyl alcohol powder having a concentration of 8% by weight by dissolving polyvinyl alcohol powder (manufactured by Kuraray Co., Ltd., average polymerization degree 2400, saponification degree 98.0-99.0 mol%, trade name: PVA124) in hot water at 95 ° C. An aqueous solution was prepared. The obtained aqueous solution was coated on the primer layer using a lip coater and dried at 80 ° C. for 20 minutes to prepare a laminated film composed of a base film, a primer layer, and a resin layer.

(Stretching process)
The laminated film was subjected to 5.8-fold free end uniaxial stretching at 160 ° C. using a tenter apparatus. The thickness of the polyvinyl alcohol-based resin layer of the laminated film after stretching was 5.1 μm.

(Dyeing process and washing process)
Thereafter, the laminated film is immersed in a 60 ° C. bath for 60 seconds, and then dyed by immersion for about 150 seconds in a dyeing solution, which is a mixed aqueous solution of iodine and potassium iodide at 30 ° C., and then with pure water at 10 ° C. Excess iodine solution was washed away. Subsequently, it was immersed for 600 second in the bridge | crosslinking solution which is a 76 degreeC mixed aqueous solution of boric acid and potassium iodide. Thereafter, it was washed with pure water at 10 ° C. for 4 seconds, and finally, excess water on the surface was removed with a nip roll.

The mixing ratio of the dyeing solution and the crosslinking solution is
<Dyeing solution>
Water: 100 parts by weight Iodine: 0.6 parts by weight Potassium iodide: 10 parts by weight <Crosslinking solution>
Water: 100 parts both parts Boric acid: 9.5 parts by weight Potassium iodide: 5 parts by weight

  Thereafter, the film was transported while being kept in an atmosphere of less than 40 ° C. so that the washed film was not exposed to an ambient temperature of 40 ° C. or higher, and no problems such as curling occurred. Under the same ambient temperature, the protective film was bonded under the following conditions.

(Protective film bonding process)
Polyvinyl alcohol powder (manufactured by Kuraray Co., Ltd., average polymerization degree 1800, trade name: KL-318) was dissolved in 95 ° C. hot water to prepare an aqueous solution having a concentration of 3% by weight. The resulting aqueous solution was mixed with 1 part by weight of a crosslinking agent (manufactured by Sumitomo Chemical Co., Ltd., trade name: Sumirez (registered trademark) Resin 650) with respect to 2 parts by weight of polyvinyl alcohol powder to obtain an adhesive solution. After the above-mentioned polyvinyl alcohol-based adhesive is applied to the surface on the side opposite to the base film side of the polarizer layer of the laminated film, a protective film (TAC: KC4UY manufactured by Konica Minolta Opto Co., Ltd.) is bonded. And the laminated body (polarizing plate with a base film) which consists of five layers of a protective film, an adhesive bond layer, a polarizer layer, a primer layer, and a base film was obtained.

(Bonding drying process and substrate film peeling process)
After the above laminate was dried at 80 ° C. for 5 minutes, the substrate film was peeled from the laminate. The base film was easily peeled off to obtain a polarizing plate comprising four layers of a protective film, an adhesive layer, a polarizer layer, and a primer layer. The thickness of the polarizer layer was 5.1 μm.

[Comparative Example 1]
A polarizing plate was produced in the same manner as in Example 1 except that the drying temperature in the bonding drying step was 50 ° C. for 15 minutes. Since the film was transported while being kept in an atmosphere of less than 40 ° C. so that the washed film was not exposed to an ambient temperature of 40 ° C. or higher, problems such as curling did not occur.

[Comparative Example 2]
A polarizing plate was produced in the same manner as in Example 1 except that drying was performed at 80 ° C. for 5 minutes after the washing step. In this case, the laminated film composed of the base film and the polyvinyl alcohol-based resin layer is significantly shrunk in the width direction, causing a problem that the end of the laminated film is folded, and the laminated film is stably Continuous conveyance was not possible.

  In order to evaluate the polarization performance and the like, curling was partially suppressed while manually holding the edge of the laminated film, and a protective film was bonded in the same manner as in Example 1. Then, drying for 5 minutes was implemented at 80 degreeC, the base film was peeled, and the polarizing plate was obtained. However, since the protective film could not be pasted cleanly due to the curl of the laminated film, a small piece with relatively clean pasting was cut out and subjected to measurement of polarization performance described later.

[Comparative Example 3]
A polarizing plate was produced in the same manner as in Comparative Example 2 except that the drying after the dyeing step was set to 60 ° C. Again, curling of the end portion occurred, and the film could not be continuously conveyed.

[Comparative Example 4]
A polarizing plate was produced in the same manner as in Comparative Example 2 except that the drying after the washing step was 40 ° C. Again, curling of the end portion occurred, and the film could not be continuously conveyed.

[Measurement of polarization performance of polarizing plate]
The polarizing plate obtained in Example 1 and Comparative Examples 1 and 2 was bonded to the anti-air surface of soda lime glass via a pressure sensitive adhesive, and polarization performance (Ty: visibility corrected single transmittance and Py : Visibility corrected polarization degree) was measured with a spectrophotometer (V7100) manufactured by JASCO Corporation. During the measurement, the incident direction of light was from the glass side.

  The measurement results of Example 1 were Ty = 41.6% and Py = 99.997%, and the polarizing plate of Example 1 was excellent in polarization performance. In addition, after the glass-bonded polarizing plate used for the measurement was taken out for 250 hours in an atmosphere of 60 ° C. and 90% RH, the polarization performance was confirmed again. Was kept.

  The measurement results of Comparative Example 1 were Ty = 41.4% and Py = 99.992%, and the polarizing plate of Comparative Example 1 was inferior in polarization performance. Further, when the glass-bonded polarizing plate used for the measurement was put out and taken out in an atmosphere of 60 ° C. and 90% RH for 250 hours, and the polarization performance was confirmed again, significant deterioration occurred.

  The measurement results of Comparative Example 2 were Ty = 41.5% and Py = 99.991%, and the polarizing plate of Comparative Example 2 was inferior in polarization performance. In addition, when the glass-bonded polarizing plate used for the measurement was put in and removed for 250 hours in an atmosphere of 60 ° C. and 90% RH, and the polarization performance was confirmed again, the initial polarization performance was maintained without much deterioration. It was.

  The measurement results and the like are summarized in Table 1. In Table 1, the case where Py is 99.995% or more is indicated by ◯, the case where 99.990% or more and less than 99.995% are indicated by Δ, and the case where it is less than 99.990 is indicated by ×. Moreover, the case where end part folding has occurred is indicated by ×, and the case where it has not occurred is indicated by ○.

  As shown in Table 1, the polarizing plate of Example 1 manufactured without drying after the cleaning process did not cause end folding. On the other hand, edge folding occurred in the polarizing plates of Comparative Examples 2 to 4 which were dried after the dyeing process. In Comparative Example 1, since the polarizing plate was produced without drying after the dyeing step, no end folding occurred, but the drying temperature after bonding was less than 70 ° C. A high visibility correction polarization degree (Py) of 995% or more was not obtained.

Claims (3)

A method for producing a polarizing plate comprising a polarizer layer and a protective film formed on one surface of the polarizer layer,
A resin layer forming step of forming a polyvinyl alcohol resin layer on one surface of the base film to obtain a laminated film;
A stretching step of dry stretching the laminated film;
A dyeing step of forming a polarizer layer by dyeing the polyvinyl alcohol-based resin layer of the laminated film with a dichroic dye and performing a crosslinking treatment;

A cleaning step of cleaning the laminated film;
A protective film laminating step of laminating a protective film via a pressure-sensitive adhesive layer or an adhesive layer on the surface opposite to the base film side surface of the laminated film;
A bonding drying step of drying the pressure-sensitive adhesive layer or the adhesive layer;
A base film peeling step for peeling the base film from the laminated film;
In this order, and maintaining the ambient temperature between after the washing step and before the pasting step at less than 40 ° C.   The manufacturing method of the polarizing plate of Claim 1 which implements drying at the temperature of at least 70 degreeC or more in the said bonding drying process.   The manufacturing method of the polarizing plate of Claim 1 whose thickness of the said polarizer layer of the said polarizing plate is 10 micrometers or less.

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