JP2005173216A - Manufacturing method of polarizing film, manufacturing method of polarizing plate and manufacturing method of optical laminate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of polarizing film by which more neutral black display is possible, a manufacturing method of a polarizing plate and a manufacturing method of an optical laminate. <P>SOLUTION: The manufacturing method of the polarizing film comprises: performing boric acid treatment after performing adsorption orientation of iodine to polyvinyl alcohol based film, wherein immersion treatment of the polyvinyl alcohol based film is performed after the boric acid treatment in an aqueous solution of about 28 to 50 pts.wt. of iodide such as potassium iodide to 100 pts.wt. of water. The polarizing plate is obtained by pasting a protection film on at least one surface of the obtained polarizing film. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a polarizing film capable of more neutral black display, a method for producing a polarizing plate in which a protective film is laminated on at least one surface of the polarizing film, a retardation film, a brightness enhancement film, a viewing angle improvement film, and The present invention relates to a method for producing an optical laminate in which any one of the semi-transmissive reflective films is bonded alone or in combination.

  As a polarizing film, conventionally, a film obtained by adsorbing and orienting a dichroic dye on a polyvinyl alcohol film and treating with boric acid has been used. That is, an iodine polarizing film using iodine as a dichroic dye, a dye polarizing film using a dichroic dye as a dichroic dye, and the like are known. These polarizing films are usually used as polarizing plates by attaching a protective film such as triacetyl cellulose to one or both sides of the polarizing film via an adhesive made of an aqueous solution of a polyvinyl alcohol resin.

  In some cases, after boric acid treatment, immersion treatment is performed in an aqueous solution of iodide. For example, in Patent Document 1, after a polyvinyl alcohol film is dyed with a dichroic dye and treated with boric acid, it is immersed in an aqueous solution of iodide having a concentration of 0.2 to 15% by weight for a predetermined contact time and dried. The polarizing film is manufactured. According to Patent Document 1, it is said that by dipping in an iodide aqueous solution, precipitation of boric acid from the film can be prevented and defects such as unevenness and foreign matter can be eliminated.

  In Patent Document 2, a polarizing film is produced by immersing in a bath containing 4 to 20% by weight of iodide after the boric acid treatment step while stretching the film at a predetermined stretching ratio. According to the description of Patent Document 2, it is said that both high transmittance and high polarization can be achieved.

  However, the conventional method for producing a polarizing film does not provide a polarizing film with sufficiently satisfactory optical properties, for example, there is a problem that black is bluish, and therefore, polarized light capable of a more neutral black display. A film was sought.

JP 2001-290027 A JP 2001-296428 A

  This invention makes it a subject to provide the manufacturing method of the polarizing film in which more neutral black display is possible, the manufacturing method of a polarizing plate, and the manufacturing method of an optical laminated body.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors are able to display a more neutral black color when immersing a boric acid-treated polyvinyl alcohol film in a higher concentration aqueous solution of iodide. As a result, the present inventors have completed the present invention.

  That is, the method for producing a polarizing film of the present invention is a production method in which iodine is adsorbed and oriented on a polyvinyl alcohol film and then boric acid treated, and the boric acid-treated polyvinyl alcohol film is treated with 100 wt. It is characterized by being immersed in an aqueous solution in which 28 to 50 parts by weight of iodide is dissolved. Examples of the iodide include potassium iodide.

  Moreover, the manufacturing method of the polarizing plate concerning this invention bonds a protective film to the at least single side | surface of the said polarizing film, It is characterized by the above-mentioned. This protective film may have any of the functions of a retardation film, a brightness enhancement film, a viewing angle improvement film, and a transflective film. Or at least 1 sort (s) chosen from a phase difference plate, a brightness improvement film, a viewing angle improvement film, and a transflective plate is pasted on the polarizing plate which stuck a protective film on at least one side, and manufactures an optical layered product. can do.

  According to the present invention, a more neutral black color is obtained by immersing a polyvinyl alcohol film obtained by adsorption-orienting iodine and treating with boric acid in an aqueous solution of 28 to 50 parts by weight of iodide with respect to 100 parts by weight of water. There is an effect that display becomes possible. By using the polarizing plate and the optical laminate obtained by the present invention for a liquid crystal display device, a thin and high-quality liquid crystal display can be obtained.

  Examples of the polyvinyl alcohol-based resin that forms the polyvinyl alcohol-based film in the present invention include those obtained by saponifying a polyvinyl acetate-based resin. The degree of saponification is about 85 mol% or more, preferably about 90 mol% or more, more preferably about 99 mol% to 100 mol%. Polyvinyl acetate resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith, such as ethylene-vinyl acetate copolymer. Examples include coalescence. Examples of other copolymerizable monomers include unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids. The degree of polymerization of the polyvinyl alcohol resin is about 1000 to 10000, preferably about 1500 to 5000.

These polyvinyl alcohol resins may be modified. For example, polyvinyl formal modified with aldehydes, polyvinyl acetal, polyvinyl butyral, and the like may be used. Usually, an unstretched film of a polyvinyl alcohol-based resin film having a thickness of about 20 μm to 100 μm, preferably about 30 μm to 80 μm is used as a starting material for manufacturing a polarizing film. Industrially, the width of the film is practically about 1500 mm to 4000 mm.
The unstretched film is subjected to swelling treatment, dyeing treatment, boric acid treatment (crosslinking treatment), immersion treatment, water washing treatment, and finally dried to obtain a polyvinyl alcohol polarizing film having a thickness of about 5 to 50 μm, for example. is there. Here, the immersion treatment refers to an immersion treatment in a high-concentration iodide aqueous solution, that is, an aqueous solution of about 28 to 50 parts by weight of iodide with respect to 100 parts by weight of water.

  The polarizing film of the present invention is a polyvinyl alcohol-based uniaxially stretched film in which iodine is adsorbed and oriented, and the production methods thereof are roughly divided into two production methods. One is a method in which a polyvinyl alcohol film is uniaxially stretched in air or an inert gas, followed by solution treatment in the order of swelling treatment, dyeing treatment, boric acid treatment, dipping treatment, and water washing treatment, followed by drying. Second, an unstretched polyvinyl alcohol film is treated with an aqueous solution in the order of swelling treatment, dyeing treatment, boric acid treatment, dipping treatment, and water washing treatment, and wet treatment is performed in the boric acid treatment step and / or the previous step. This is a method of performing uniaxial stretching and finally drying.

  In any method, the uniaxial stretching may be performed in one step or in two or more steps, but is preferably performed in a plurality of steps. The order of the steps is basically as described above, but there are no restrictions on the number of treatment baths or treatment conditions. Needless to say, a process not described in the above process can be freely inserted for another purpose.

  The swelling step is performed for the purpose of removing foreign matter from the film surface, removing the plasticizer in the film, imparting easy dyeability in the next step, and plasticizing the film. The treatment conditions are determined within a range in which these objects can be achieved and within a range in which problems such as extreme dissolution and devitrification of the base film do not occur. When the film previously stretched in gas is swollen, for example, the film is immersed in an aqueous solution of about 20 ° C. to 70 ° C., preferably about 30 ° C. to 60 ° C. The immersion time of the film is about 30 seconds to 300 seconds, more preferably about 60 seconds to 240 seconds. When the unstretched raw film is swollen from the beginning, the film is immersed in an aqueous solution of, for example, about 10 ° C to 50 ° C, preferably about 20 ° C to 40 ° C. The immersion time of the film is about 30 seconds to 300 seconds, more preferably about 60 seconds to 240 seconds.

  In the swelling treatment process, the film is likely to swell in the width direction and wrinkles into the film, so that the film may be spread with a known widening device such as an expander roll, a spiral roll, a crown roll, a cross guider, a bend bar, or a tenter clip. It is preferable to transport the film while removing wrinkles. In order to stabilize the film transport in the bath, the water flow in the swelling bath is controlled with an underwater shower, or an EPC device (Edge Position Control device: a device that detects the edge of the film and prevents meandering of the film) It is also useful to use these together. In this step, since the film swells and expands in the running direction of the film, it is preferable to take measures such as controlling the speed of the transport roll before and after the treatment tank in order to eliminate the slack of the film in the transport direction. In addition to pure water, the swelling treatment bath used is boric acid (described in JP-A-10-153709), chloride (described in JP-A-06-281816), inorganic acid, inorganic salt, water-soluble An aqueous solution to which an organic solvent, alcohol or the like is added in an amount of about 0.01 to 10% by weight can also be used.

  The dyeing step with iodine is performed for the purpose of adsorbing and orienting iodine on the film. The treatment conditions are determined within a range in which these objects can be achieved and within a range in which problems such as extreme dissolution and devitrification of the base film do not occur. For example, at a temperature of about 10 ° C. to 45 ° C., preferably about 20 ° C. to 35 ° C. and a weight ratio of iodine / KI / water = about 0.003 to 0.2 / about 0.1 to 10/100 For about 30 seconds to 600 seconds, preferably about 60 seconds to 300 seconds. Instead of potassium iodide, other iodides such as zinc iodide may be used. Other iodides may be used in combination with potassium iodide. Furthermore, compounds other than iodide, such as boric acid, zinc chloride, cobalt chloride, etc. may coexist. When boric acid is added, it is distinguished from the following boric acid treatment in that it contains iodine. If it contains about 0.003 parts by weight or more of iodine with respect to 100 parts by weight of water and the temperature is about 40 ° C. or less, it can be regarded as a dyeing tank.

  As described above, the film may be stretched in a dyeing tank. Stretching is performed by a method of giving a peripheral speed difference between the nip rolls before and after the dyeing tank. Similarly to the swelling step, an expander roll, a spiral roll, a crown roll, a cross guider, a bend bar, and the like can be installed in the dyeing bath and / or at the bath entrance / exit. Further, after the swelling treatment, the polyvinyl alcohol film may be subjected to a wet stretching treatment before the dyeing treatment.

  The boric acid treatment after dyeing is performed by immersing the dyed polyvinyl alcohol film in an aqueous solution containing about 1 to 10 parts by weight of boric acid with respect to 100 parts by weight of water. Usually, it is performed by immersing in an aqueous solution at about 10 to 70 ° C. for about 3 to 600 seconds. The boric acid-containing aqueous solution preferably contains about 1 to 30 parts by weight of iodide.

  Examples of iodide include potassium iodide and zinc iodide. Further, compounds other than iodide, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate, etc. may coexist.

  This boric acid treatment is carried out for water resistance and hue adjustment (for example, to prevent bluish tint) by crosslinking. In the case of water resistance by cross-linking, a cross-linking agent such as glyoxal or glutaraldehyde can be used in addition to or together with boric acid, if necessary.

  This boric acid treatment is carried out by appropriately changing the concentration of boric acid and iodide and the temperature of the treatment bath according to the purpose, but boric acid treatment for water resistance and boric acid treatment for hue adjustment. Are not particularly distinguished. In the boric acid treatment step, the film may be stretched as in the dyeing step.

  After the boric acid treatment, the film is immersed in an aqueous iodide solution having a predetermined concentration. Examples of the iodide include potassium iodide, sodium iodide, lithium iodide, zinc iodide and the like. The aqueous solution is prepared by dissolving iodide in an amount of about 28 to 50 parts by weight, preferably about 28 to 45 parts by weight, more preferably about 28 to 40 parts by weight with respect to 100 parts by weight of water. If the amount of iodide added is less than the above range, it may be difficult to display a more neutral black color, and there may be a problem that black is bluish. If it exceeds 1, it may be difficult to dissolve iodide in water.

In addition to iodide, other components such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, and sodium sulfate may be added to the aqueous iodide solution. It is preferable not to contain. This is because the waste liquid treatment is easy because boric acid is not contained in the waste liquid in the next washing step. Moreover, since boric acid does not precipitate on the surface of the nip roll in the dipping process, there is also an advantage that there is no possibility of foreign matter defects occurring on the film.
The temperature of the iodide aqueous solution for the immersion treatment is about 10 to 60 ° C, preferably about 20 to 45 ° C. Then, the film is immersed in this iodide aqueous solution for about 2 to 120 seconds, preferably about 3 to 90 seconds, more preferably about 5 to 60 seconds.

  After the immersion treatment, the film is washed with water. The water washing treatment is performed, for example, by immersing a boric acid-treated polyvinyl alcohol film in water, spraying water as a shower, or combining immersion and spraying. The temperature of water in the water washing treatment is usually about 2 to 40 ° C., and the immersion time is preferably about 2 to 120 seconds. The drying step after washing with water is performed in a drying furnace at a temperature of about 40 to 100 ° C. for about 60 to 600 seconds.

  In the present invention, uniaxial stretching is performed in at least one step before or during the swelling treatment, dyeing treatment, boric acid treatment step, and immersion treatment. Or you may add the wet extending process for performing uniaxial stretching between said processes. Although uniaxial stretching may be performed in one step, it is preferably performed in a plurality of steps. As a stretching method, a known method can be adopted. For example, stretching between rolls in which stretching is performed with a difference in peripheral speed between two nip rolls for transporting a film, hot roll stretching as described in Japanese Patent No. 2731813 Method and tenter stretching method. In addition, the polyvinyl alcohol film may be uniaxially stretched in advance in a gas such as air or an inert gas before the swelling step. The final cumulative draw ratio is about 4.5 to 7.0 times, preferably about 5.0 to 6.5 times.

A polarizing plate is obtained by bonding a protective film with an adhesive on at least one side of the polarizing film thus produced.
As the protective film, for example, a film made of an acetyl cellulose resin such as triacetyl cellulose or diacetyl cellulose, a film made of a polyester resin such as polyethylene terephthalate, polyethylene naphthalate or polybutylene terephthalate, or a film made of a polycarbonate resin And a film made of a cycloolefin resin. Examples of commercially available thermoplastic cycloolefin resins include “Topas” (registered trademark) sold by Ticona of Germany and “Arton” (trademark) sold by JSR Co., Ltd. Registered), “ZEONOR” and “ZEONEX” (both registered trademarks) sold by Nippon Zeon Co., Ltd., and “APEL” (trademark registered) sold by Mitsui Chemicals, Inc. A film formed from such a cycloolefin-based resin is used as a protective film. For the film formation, a known method such as a solvent casting method or a melt extrusion method is appropriately used. The formed cycloolefin resin film is also commercially available, for example, “Essina” and “SCA40” sold by Sekisui Chemical Co., Ltd.

  The thickness of the protective film is preferably thin. However, if it is too thin, the strength is lowered and the processability is inferior. On the other hand, if it is too thick, the transparency is lowered and the curing time required after lamination is increased. Problems occur. Accordingly, a suitable thickness of the protective film is, for example, about 5 to 200 μm, preferably about 10 to 150 μm, and more preferably about 20 to 100 μm.

  In order to improve the adhesiveness between the adhesive and the polarizing film and / or protective film, the polarizing film and / or protective film may be subjected to corona treatment, flame treatment, plasma treatment, ultraviolet irradiation, primer coating treatment, saponification treatment, etc. A surface treatment may be applied.

The protective film may be subjected to surface treatment such as anti-glare treatment, anti-reflection treatment, hard coat treatment, antistatic treatment, and antifouling treatment alone or in combination. The protective film and / or the protective film surface protective layer may have a UV absorber such as a benzophenone compound or a benzotriazole compound, or a plasticizer such as a phenyl phosphate compound or a phthalate compound.
Such a protective film may be bonded to one side of the polarizing film or may be bonded to both sides.

  The polarizing film and the protective film are laminated using an adhesive such as a water solvent adhesive, an organic solvent adhesive, a hot melt adhesive, or a solventless adhesive. Examples of aqueous solvent adhesives include aqueous polyvinyl alcohol resins and aqueous two-component urethane emulsion adhesives, and examples of organic solvent adhesives include two-component urethane adhesives as solvent-free adhesives. For example, a one-pack type urethane adhesive may be used. When an acetylcellulose-based film whose surface to be bonded to the polarizing film is hydrophilized by saponification or the like is used as a protective film, a polyvinyl alcohol-based resin aqueous solution is suitably used as an adhesive. 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. For this adhesive, a polyvalent aldehyde, a water-soluble epoxy compound, a melamine compound or the like may be used as an additive.

  The method for laminating the polarizing film and the protective film is not particularly limited. For example, an adhesive is uniformly applied to the surface of the polarizing film or the protective film, and the other film is stacked on the coated surface by a roll or the like. The method of pasting and drying is mentioned.

Usually, an adhesive agent is apply | coated at the temperature of about 15-40 degreeC after preparation, and the bonding temperature is the range of about 15-30 degreeC normally. After pasting, a drying treatment is performed to remove a solvent such as water contained in the adhesive, and the drying temperature in this case is usually about 30 to 85 ° C, preferably about 40 to 80 ° C. . Thereafter, the adhesive may be cured by curing for about 1 to 90 days under a temperature environment of about 15 to 85 ° C, preferably about 20 to 50 ° C, more preferably about 35 to 45 ° C. When this curing period is long, productivity deteriorates, so the curing period is about 1 to 30 days, preferably about 1 to 7 days.
Thus, a polarizing plate in which the protective film is bonded to one side or both sides of the polarizing film through the adhesive layer is obtained.

  In the present invention, the protective film has a function as a retardation film, a function as a brightness enhancement film, a function as a reflection film, a function as a transflective film, a function as a diffusion film, a function as an optical compensation film, etc. It can also have an optical function. In this case, for example, by laminating an optical functional film such as a retardation film, a brightness enhancement film, a reflection film, a transflective film, a diffusion film, an optical compensation film on the surface of the protective film, it has such a function. In addition, the protective film itself can be given such a function. Further, the protective film itself may have a plurality of functions such as a diffusion film having the function of a brightness enhancement film.

  For example, the protective film is subjected to a stretching process described in Japanese Patent No. 2841377, Japanese Patent No. 3094113, etc., or a process described in Japanese Patent No. 3168850, etc. The function as can be provided. In addition, by forming micropores in the above protective film by a method as described in JP 2002-169025 A or JP 2003-29030 A, two or more layers having different central wavelengths of selective reflection are formed. By superimposing these cholesteric liquid crystal layers, a function as a brightness enhancement film can be imparted. By forming a metal thin film on the above protective film by vapor deposition or sputtering, a function as a reflective film or a transflective film can be imparted. By coating the protective film with a resin solution containing fine particles, a function as a diffusion film can be imparted. Moreover, the function as an optical compensation film can be provided by coating and aligning liquid crystalline compounds, such as a discotic liquid crystalline compound, on said protective film. In addition, using an appropriate adhesive, a brightness enhancement film such as a trade name: DBEF (manufactured by 3M Co., Ltd.), a trade name: a viewing angle improving film such as a WV film (manufactured by Fuji Photo Film Co., Ltd.), a trade name : Commercially available optical functional films such as retardation films such as Sumikalite (registered trademark) (Sumitomo Chemical Co., Ltd.) may be directly bonded to the polarizing film.

EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated further more concretely, this invention is not limited by these examples.
In the following Examples and Comparative Examples, various treatments were performed while a long film of polyvinyl alcohol was transported by a continuous transport device in which a nip roll and a free roll were combined. Uniaxial stretching was performed with a difference in peripheral speed between the driving nip rolls before and after the treatment tank.
The optical performance was measured by measuring the UV-visible spectrum of the polarizing plate in the transmission direction and absorption direction by setting the optional film holder with a polarizer on the UV2450 UV-Vis spectrophotometer manufactured by Shimadzu Corporation. The hue when the two polarizing plates are arranged in crossed Nicols, the orthogonal hue, the orthogonal L ^* , the orthogonal a ^* , and the orthogonal b ^*, were calculated and calculated according to JIS-Z8729.

A 75 μm-thick polyvinyl alcohol film (Kurarevinylone VF-PS # 7500, polymerization degree 2,400, saponification degree 99.9 mol% or more) is kept in 30 ° C. pure water so that the film does not loosen. The film was immersed for about 130 seconds to fully swell the film. Next, uniaxial stretching was performed while dipping in an aqueous solution of iodine / potassium iodide / water in a weight ratio of 0.02 / 1.5 / 100.
After that, it is immersed in a boric acid-containing aqueous solution containing potassium iodide / boric acid / water at a weight ratio of 10/5/100 and a temperature of 60 ° C., and integrated stretching from the original fabric while performing crosslinking treatment (water resistance treatment). Uniaxial stretching was performed until the magnification reached 5.9 times. Further, while maintaining the tension state, it was immersed in an aqueous solution of potassium iodide / water at a weight ratio of 30/100 at 28 ° C. for about 30 seconds, and then washed with pure water at 15 ° C. for about 5 seconds. The film was dried at a temperature of 50 ° C. for 5 minutes to obtain a polarizing film.
The optical performance of this polarizing film was measured, and orthogonal a ^* and orthogonal b ^* were measured. As a result, the film was a polarizing film having orthogonal a ^* = 0.31 and orthogonal b ^* = − 0.05 and capable of black display with a more neutral hue.

[Comparative Example 1]
A polarizing film was obtained in the same manner as in Example 1 except that the film after the crosslinking treatment was immersed in an aqueous potassium iodide solution having a concentration of potassium iodide / water of 12/100 by weight.
The optical performance of this polarizing film was measured, and orthogonal a * and orthogonal b * were measured. As a result, the orthogonality a ^* = 1.8 and the orthogonality b ^* = − 4.9, and the color was bluish black.

A 75 μm-thick polyvinyl alcohol film (Kurarevinylone VF-PS # 7500, polymerization degree 2,400, saponification degree 99.9 mol% or more) is kept in 30 ° C. pure water so that the film does not loosen. The film was immersed for about 130 seconds to fully swell the film. Next, the film was immersed in an aqueous solution of iodine / potassium iodide / water in a weight ratio of 0.02 / 1.5 / 100 and uniaxially stretched while being dyed.
Thereafter, the total draw ratio from the original fabric is 5.9 times while being immersed in a first boric acid-containing aqueous solution having a weight ratio of potassium iodide / boric acid / water of 10/5/100 and a temperature of 60 ° C. Uniaxial stretching was performed until Furthermore, it was immersed in a second boric acid-containing aqueous solution having a potassium iodide / boric acid / water weight ratio of 20/3/100 and a temperature of 30 ° C. for approximately 30 seconds.
Further, while maintaining the tension state, it was immersed in a potassium iodide aqueous solution having a potassium iodide / water ratio of 30/100 by weight at 28 ° C. for about 30 seconds. Subsequently, it was washed with pure water at 10 ° C. for about 10 seconds. The film was dried at 60 ° C. for 2 minutes to obtain a polarizing film.
The optical performance of this polarizing film was orthogonal a ^* = 0.15 and orthogonal b ^* = − 0.03, and it was a polarizing film capable of black display with a more neutral hue.

Claims (5)

  A method for producing a polarizing film in which iodine is adsorbed and oriented on a polyvinyl alcohol film and then treated with boric acid, wherein the boric acid-treated polyvinyl alcohol film is 28 to 50 parts by weight with respect to 100 parts by weight of water. A method for producing a polarizing film, comprising immersing in an aqueous solution of iodide.   The method for producing a polarizing film according to claim 1, wherein the iodide is potassium iodide.   A method for producing a polarizing plate, comprising: bonding a protective film to at least one surface of a polarizing film obtained by the method according to claim 1.   The manufacturing method of the polarizing plate of Claim 3 with which the said protective film is equipped with the function in any one of a phase difference film, a brightness improvement film, a viewing angle improvement film, and a transflective film. An optical laminate comprising: a polarizing plate obtained by the method according to claim 3; and at least one selected from a retardation film, a brightness enhancement film, a viewing angle improvement film, and a transflective film. Production method.