JP5568353B2 - Manufacturing method of polarizing film - Google Patents

Description

  The present invention relates to a method for producing a polarizing film having an excellent appearance.

  Conventionally, a polarizing film in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol film 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 formed into polarizing plates by attaching a protective film such as triacetyl cellulose to at least one surface, preferably both surfaces, with an adhesive made of an aqueous solution of a polyvinyl alcohol resin.

  As a method for producing a polarizing film, a nip roll and a guide roll are used, and the polyvinyl alcohol film is dyed with the dichroic dye, stretched, and then the polyvinyl alcohol film is used to fix iodine to the film. A method of drying after acid treatment, washing treatment such as water washing and the like is known.

  However, in the manufacturing method, in the cleaning treatment, wrinkles are generated on the film, or a boric acid compound resulting from the boric acid treatment is deposited on the film surface to generate foreign matter defects. There are problems that foreign matter defects, dents, etc. occur and the appearance deteriorates.

  For example, Patent Document 1 describes that a boron atom content in a film is set to a predetermined value as a method for producing a polarizing film excellent in optical performance and dimensional stability. According to this document, it is described that the boron atom content in the polarizing film can be adjusted by washing with water.

  However, in Patent Document 1, there is no specific description of the boron compound content in the film before and after the cleaning treatment, and even if the method described in Patent Document 1 is used, it is not always sufficient for wrinkles and foreign matter defects. The current situation is that the generation has not been suppressed.

  On the other hand, Patent Documents 2 and 3 describe setting a film width before and after boric acid treatment to a predetermined value as a method for producing a polarizer having a high degree of polarization. Patent Document 3 describes, as a method for producing a polarizing film having excellent durability, uniaxial stretching during the treatment with a boron compound and setting the film width before and after the stretching to a predetermined value.

  However, in Patent Documents 2 and 3, there is no specific description of the film width before and after the cleaning treatment, and even if the methods described in these Patent Documents 2 and 3 are used, wrinkles and foreign matter defects are not always sufficient. In the present situation, the generation of the polarizing film has not been suppressed, and development of a method for producing a polarizing film having a more excellent appearance is desired.

Japanese Patent No. 397688 JP 2003-240947 A JP-A-8-327823

  The subject of this invention is providing the manufacturing method of the polarizing film which has the outstanding external appearance.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have found a solution means having the following constitution and have completed the present invention.
(1) A method for producing a polarizing film in which a polyvinyl alcohol-based film is processed in the order of swelling treatment, dyeing treatment, boric acid treatment and washing treatment, and uniaxial stretching is performed before and / or during these treatments. When the boron compound content in the film before is Y and the boron compound content in the film after the cleaning treatment is X, the residual ratio of the boron compound content in the film before and after one cleaning treatment (X / Y) A method comprising setting 0.7 to 0.98.
(2) The method according to (1), wherein the cleaning treatment is performed at least twice.

(3) When the boron compound content in the film before the first cleaning process is Yp and the boron compound content in the film after the last cleaning process is Xp, the boron compound content in the film before and after the entire cleaning process The method according to (2), wherein the residual ratio (Xp / Yp) is 0.7 to 0.98.
(4) A method for producing a polarizing film in which a polyvinyl alcohol-based film is processed in the order of swelling treatment, dyeing treatment, boric acid treatment and washing treatment, and uniaxial stretching is performed before and / or during these treatments. A method comprising setting A / B before and after one cleaning process to 0.97 to 1.03, where A is the film width before and B is the film width after the cleaning process.
(5) The method according to (4), wherein the washing treatment is performed at least twice.
(6) The method according to (5), wherein Ap / Bp before and after the entire cleaning treatment is 0.97 to 1.03, where Ap is the film width before the first washing treatment and Bp is the film width after the treatment. .
(7) When the boron compound content in the film before the cleaning process is Y and the boron compound content in the film after the cleaning process is X, the boron compound content in the film before and after one cleaning process The method according to (4) or (5), wherein the residual ratio (X / Y) is 0.7 to 0.98.
(8) When the cleaning process is performed at least twice, and the boron compound content in the film before the first cleaning process is Yp and the boron compound content in the film after the last cleaning process is Xp, the entire cleaning process (7) The residual ratio (Xp / Yp) of the boron compound content in the film before and after is set to 0.7 to 0.98.

(9) The method according to any one of (1) to (8), wherein a cleaning temperature in the cleaning treatment is 30 ° C. or lower.
(10) A method for producing a polarizing plate, wherein a protective film is bonded to at least one surface of a polarizing film obtained by the method according to any one of (1) to (9).

  According to the present invention, since it is possible to suppress the occurrence of wrinkles and foreign matter defects in the film in the cleaning treatment, it is possible to obtain a polarizing film having an excellent appearance free from color unevenness, foreign matter defects, dents, and the like. There is an effect that can be done.

<Production method of polarizing film>
Hereinafter, an embodiment of a method for producing a polarizing film according to the present invention will be described. The polyvinyl alcohol-based resin forming the polyvinyl alcohol-based film in this embodiment is typically exemplified by a saponified polyvinyl acetate-based resin. The degree of saponification is about 85 mol% or more, preferably about 90 mol% or more, more preferably about 99 to 100 mol%. Examples of the polyvinyl acetate resin 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. Etc. 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 can be used. Usually, an unstretched film of a polyvinyl alcohol-based resin film having a thickness of about 20 to 100 μm, preferably about 30 to 80 μm is used as a starting material for manufacturing a polarizing film. Industrially, the width of the film is practically about 1500 to 4000 mm.

  The unstretched film is treated in the order of swelling treatment, dyeing treatment, boric acid treatment, and washing treatment, and finally dried, and before and / or treatment of the swelling treatment, dyeing treatment, boric acid treatment, and washing treatment. The thickness of the polyvinyl alcohol polarizing film obtained by uniaxial stretching is, for example, about 5 to 50 μm.

  The polarizing film of the present embodiment is a polyvinyl alcohol uniaxially stretched film in which a dichroic dye is adsorbed and oriented, and there are roughly two production methods as its production method. 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 and washing treatment, and finally drying. The other is a solution treatment of an unstretched polyvinyl alcohol film with an aqueous solution in the order of swelling treatment, dyeing treatment, boric acid treatment and washing treatment, and then uniaxially stretching by boric acid treatment and / or previous treatment in a wet manner. And finally drying.

  In any of the methods, uniaxial stretching may be performed by one treatment or two or more treatments, but is preferably performed by a plurality of treatments. 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, tenter stretching method and the like. The order of treatment is basically as described above, but there are no restrictions on the number of treatment baths, treatment conditions, and the like.

  It goes without saying that processing not described in the above processing can be freely inserted for another purpose. Examples of this treatment include immersion treatment with an aqueous iodide solution not containing boric acid (iodide treatment) or immersion treatment with an aqueous solution containing zinc chloride not containing boric acid (zinc treatment) after boric acid treatment. It is done.

  The swelling treatment is performed for the purpose of removing foreign matter on the film surface, removing the plasticizer in the film, imparting easy dyeability in the subsequent treatment, and plasticizing the film. The treatment conditions can be 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 substrate film do not occur. When the film previously stretched in the gas is swollen, for example, the film is immersed in an aqueous solution of about 20 to 70 ° C., preferably about 30 to 60 ° C. The immersion time of the film is about 30 seconds to 300 seconds, 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 about 10 to 50 ° C., preferably about 20 to 40 ° C., for example. The immersion time of the film is about 30 seconds to 300 seconds, preferably about 60 seconds to 240 seconds.

  The swelling treatment tends to cause problems such as film swelling in the width direction and wrinkling of the film, so known widening rolls such as widening rolls (expander rolls), spiral rolls, crown rolls, cross guiders, bend bars, tenter clips, etc. It is preferable to transport the film while removing wrinkles of the film with an apparatus. Also, for the purpose of stabilizing the film transport in the bath, the water flow in the swelling bath is controlled with an underwater shower, or the EPC device (Edge Position Control device: detects the edge of the film to prevent the film from meandering) It is also useful to use a device together. In this treatment, 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 carrying roll before and after the treatment tank in order to eliminate the slack of the film in the carrying direction. Further, as the swelling treatment bath to be used, boric acid (described in JP-A-10-153709), chloride (described in JP-A-06-281816), inorganic acid, inorganic salt, as well as (pure) water An aqueous solution to which a water-soluble organic solvent, alcohols and the like are added in an amount of about 0.01 to 10% by weight can also be used. In the swelling treatment, the film may be stretched in the same manner as the dyeing treatment described later.

  The dyeing treatment with the dichroic dye is performed for the purpose of adsorbing and orienting the dichroic dye on the film. The treatment conditions can be 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 substrate film do not occur. When iodine is used as the dichroic dye, for example, at a temperature of about 10 to 45 ° C., preferably about 20 to 35 ° C., and in a weight ratio, iodine / potassium iodide / 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. Further, 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. Any dye containing about 0.003 parts by weight or more of iodine with respect to 100 parts by weight of water can be regarded as a dyeing tank.

  When a water-soluble dichroic dye is used as the dichroic dye, for example, at a temperature of about 20 to 80 ° C., preferably about 30 to 70 ° C., and a weight ratio of dichroic dye / water = about 0.001. The immersion treatment is carried out at about 0.1 / 100 for about 30 seconds to 600 seconds, preferably about 60 seconds to 300 seconds. The aqueous solution of the dichroic dye to be used may contain a dyeing assistant or the like, for example, an inorganic salt such as sodium sulfate, a surfactant or the like. The dichroic dye may be used alone, or two or more dichroic dyes may be used at the same time.

  As described above, the film may be stretched in a dyeing tank. Stretching can be performed by a method of giving a peripheral speed difference to the nip rolls before and after the dyeing tank. Similarly to the swelling treatment, a widening roll (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.

  The boric acid treatment is performed by immersing a polyvinyl alcohol film dyed with a dichroic dye in an aqueous solution containing boric acid at a ratio of about 1 to 10 parts by weight with respect to 100 parts by weight of water.

  When the dichroic dye is iodine, it is preferable to contain iodide in a proportion of about 1 to 30 parts by weight. Examples of the iodide include potassium iodide and zinc iodide. Further, as a compound other than iodide, for example, zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate and the like may coexist.

  This boric acid treatment is carried out for water resistance by crosslinking, hue adjustment such as prevention of bluish tint, and the like. 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.

  In addition, the boric acid treatment for water resistance may be referred to by names such as water resistance treatment, crosslinking treatment, and immobilization treatment. In addition, boric acid treatment for hue adjustment may be referred to by a name such as complementary color treatment or re-dyeing treatment.

  This boric acid treatment is performed by appropriately changing the concentrations of boric acid and iodide and the temperature of the treatment bath according to the purpose. Although boric acid treatment for water resistance and boric acid treatment for hue adjustment are not particularly distinguished, they can be carried out under the following conditions.

  When the raw film is swelled, dyed and treated with boric acid, and the boric acid treatment is aimed at water resistance by crosslinking, boric acid is about 3 to 10 parts by weight with respect to 100 parts by weight of water, A boric acid treatment bath containing about 1 to 20 parts by weight of iodide is used, and is usually performed at a temperature of about 50 to 70 ° C, preferably about 55 to 65 ° C. The immersion time is usually about 30 to 600 seconds, preferably about 60 to 420 seconds, and more preferably about 90 to 300 seconds. In addition, when dye | staining and boric-acid treatment the film extended | stretched previously, the temperature of a boric-acid treatment bath is about 50-85 degreeC normally, Preferably it is about 55-80 degreeC.

  You may perform the boric-acid process for hue adjustment after the boric-acid process for water resistance. For example, when the dichroic dye is iodine, a boric acid treatment bath containing about 1 to 5 parts by weight of boric acid and about 3 to 30 parts by weight of iodide for 100 parts by weight of water is used for this purpose. And is usually carried out at a temperature of about 10 to 45 ° C. The immersion time is usually about 3 to 300 seconds, preferably about 10 to 240 seconds. The boric acid treatment for hue adjustment is usually performed at a lower boric acid concentration, a higher iodide concentration, and a lower temperature than the boric acid treatment for water resistance.

  These boric acid treatments may be performed a plurality of times and are usually performed 2 to 5 times in many cases. In this case, the aqueous solution composition and temperature of each boric acid treatment tank to be used may be the same or different within the above range. The boric acid treatment for water resistance and the boric acid treatment for hue adjustment may each be performed a plurality of times. In the boric acid treatment, the film may be stretched in the same manner as the dyeing treatment. The final cumulative draw ratio is about 4.5 to 7 times, preferably about 5 to 6.5 times.

  After the boric acid treatment, the washing treatment is performed. This cleaning treatment is performed, for example, by immersing a polyvinyl alcohol film that has been treated with boric acid for water resistance and / or color tone adjustment in the cleaning solution, spraying the cleaning solution as a shower, or using both immersion and spraying. In the washing process, the film may be stretched in the same manner as the dyeing process.

  Here, in this embodiment, the residual ratio of the boron compound content in the film before and after one cleaning treatment is 0.7 to 0.98. Thus, by controlling the content of the boron compound before and after the cleaning process to a specific value, it is possible to suppress the occurrence of wrinkles and foreign matter defects in the film during the cleaning process. On the other hand, if the residual ratio is less than 0.7, wrinkles are likely to occur in the film during the cleaning process. The reason for this is that when the residual ratio is less than 0.7, it is highly possible that the boric acid treatment is non-uniform, and therefore it is presumed that wrinkles are generated in a part of the film by the washing treatment. Moreover, since the boron compound content in a film will become excess when the said residual rate exceeds 0.98, a foreign material defect will generate | occur | produce easily in a washing process.

  The remaining rate can be calculated as follows. That is, first, the boron compound content in the film before and after the cleaning treatment is calculated. Specifically, after a predetermined amount of each film before and after the washing treatment is immersed in hot water at 95 ° C. for 60 minutes to completely dissolve each film, each solution is neutralized and titrated to determine the weight and titration of the film. From this, the boron compound content in each film is calculated. Next, each of the obtained values is applied to the following formula (I) to calculate the remaining rate.

  The boron compound content in the film before the washing treatment is 2.5 to 5% by weight, preferably about 3 to 4.7% by weight. The boron compound content in the film after the washing treatment is 2 It is about -4.5% by weight, preferably about 2.5-4.3% by weight. The weight% is a value relative to the film weight before the swelling treatment (that is, untreated).

The residual ratio can be controlled to 0.7 to 0.98 by adjusting the cleaning temperature, the composition of the cleaning liquid, the cleaning time, and the like in one cleaning process.
Moreover, the frequency | count of washing | cleaning is not limited to 1 time, It can select arbitrarily from the range of about 2 to 4 times.
When the number of times of cleaning is multiple times, when the boron compound content in the film before the first cleaning process is Yp and the boron compound content in the film after the last cleaning process is Xp, before and after the entire cleaning process The residual ratio of the boron compound content in the film is preferably 0.7 to 0.98.

  The washing temperature is 30 ° C. or lower, preferably 3 to 30 ° C. As the cleaning liquid, for example, an aqueous solution containing boric acid in addition to water can be used. Boric acid is preferably contained at a ratio of about 0.01 to 0.5 parts by weight with respect to 100 parts by weight of water. When a boric acid-containing aqueous solution is employed as the cleaning liquid, it is preferable that a small amount of iodide coexists in the liquid. These exemplified cleaning liquids may be used alone or in combination of two or more.

  The cleaning time is preferably about 1 to 20 seconds when water is used as the cleaning liquid, and preferably about 5 to 50 seconds when a boric acid-containing aqueous solution is used.

  Generally, within the above range, the remaining rate is lowered by setting the cleaning temperature to a higher side, not containing boric acid in the cleaning liquid, or lowering the content rate, and increasing the cleaning time. Tend to. In order to control the residual rate within the range of 0.7 to 0.98, the cleaning temperature, the composition of the cleaning liquid, the cleaning time, etc. are determined experimentally (for example, the cleaning temperature is 15 ° C., the cleaning liquid-water, the cleaning is performed). (Time 10 seconds, etc.) Perform cleaning treatment and check remaining rate. As a result, if the obtained residual ratio is out of this range, the cleaning process is performed again by appropriately adjusting each condition in consideration of the tendency of the conditions such as the cleaning temperature, the composition of the cleaning liquid, and the cleaning time on the residual ratio. The residual rate is confirmed and this is repeated until the residual ratio is in the range of 0.7 to 0.98, whereby each condition can be adjusted and determined.

  The drying treatment after the washing treatment can be performed in a drying furnace at a temperature of about 40 to 100 ° C. for about 60 to 600 seconds, whereby the polarizing film of this embodiment is obtained. In the present embodiment, it is preferable to control the tension so that the tension of the film becomes substantially constant in each process after the stretching process. When the drawing is completed by the dyeing process, it is preferable to control the tension in the subsequent boric acid treatment and washing treatment.

  Next, other embodiment of the manufacturing method of the polarizing film concerning this invention is described. In this embodiment, when the film width before the cleaning process is A (hereinafter also referred to as film width A) and the film width after the cleaning process is B (hereinafter also referred to as film width B), one cleaning is performed. A / B before and after the treatment is set to 0.97 to 1.03. Thus, wrinkles can be prevented from occurring in the cleaning process by controlling the film width before and after the single cleaning process to a specific value. On the other hand, if the (A / B) is less than 0.97 or greater than 1.03, the change in the film width before and after the cleaning process increases, so that wrinkles are likely to occur in the film during the cleaning process. Become.

  As the film widths A and B before and after the cleaning treatment, desired values can be adopted according to the width of the raw film, the degree of uniaxial stretching, the width of the obtained polarizing film, and the like. That is, A / B can adopt a desired value in the range of 0.97 to 1.03.

(A / B) can be controlled to 0.97 to 1.03 depending on the cleaning temperature, the composition of the cleaning liquid, and the cleaning time in the cleaning process, as in the above-described embodiment.
Generally, the (A / B) tends to decrease when the cleaning temperature is high, the boric acid is not contained in the cleaning liquid or the content is low, the cleaning time is long, and the like. In order to control (A / B) within the range of 0.7 to 0.98, the cleaning temperature, the composition of the cleaning liquid, the cleaning time, etc. are determined experimentally (for example, the cleaning temperature is 15 ° C., the cleaning liquid − Perform cleaning treatment (water, cleaning time 10 seconds, etc.) and check the value of (A / B). As a result, if the obtained value is out of this range, each condition is appropriately adjusted in consideration of the tendency of the conditions such as the washing temperature, the composition of the washing solution, and the washing time on the value of (A / B). Then, the cleaning process is performed again, the value of (A / B) is confirmed, and this is repeated until the value falls within the range of 0.7 to 0.98, whereby each condition can be adjusted and determined.

Moreover, the frequency | count of washing | cleaning is not limited to 1 time, It can select arbitrarily from the range of about 2 to 4 times.
When the number of times of cleaning is multiple, Ap / Bp before and after the entire cleaning process is 0.97 to 1.03, where Ap is the film width before the first cleaning process and Bp is the film width after the processing. It is preferable to do.

  Similarly to the above-described embodiment, when the boron compound content in the film before the cleaning process is Y and the boron compound content in the film after the cleaning process is X, before and after one cleaning process. It is preferable that the residual ratio (X / Y) of the boron compound content in the film is 0.7 to 0.98. When the number of times of cleaning is multiple times, when the boron compound content in the film before the first cleaning process is Yp and the boron compound content in the film after the last cleaning process is Xp, before and after the entire cleaning process The residual ratio of the boron compound content in the film is preferably 0.7 to 0.98. Other configurations are the same as those of the above-described embodiment, and thus description thereof is omitted.

<Production method of polarizing plate>
A polarizing plate is obtained by bonding a protective film to at least one surface of the polarizing film produced as described above with an adhesive. 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, a film made of a polycarbonate resin, Examples include films made of cycloolefin resins. 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., “APEL” (trademark registered) sold by Mitsui Chemicals, Inc., and the like. What formed such a cycloolefin type resin into a film is employable as a protective film. For film formation, known methods such as a solvent casting method and a melt extrusion method can be employed. The formed cycloolefin-based resin film is commercially available, and for example, “Essina” sold by Sekisui Chemical Co., Ltd. is suitable.

  The thickness of the protective film is preferably thin, but if it is too thin, the strength is lowered and the processability is poor. On the other hand, if it is too thick, problems such as a decrease in transparency and a longer curing time after lamination are caused. Therefore, 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, 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, and a solventless adhesive. Examples of water-based adhesives include polyvinyl alcohol-based resin aqueous solutions and aqueous two-component urethane emulsion adhesives. Examples of organic solvent-based adhesives include two-component urethane adhesives and solventless adhesives. Examples of the agent include one-pack type urethane adhesives. In the case of using an acetylcellulose-based film whose surface to be bonded to the polarizing film has been hydrophilized by saponification or the like as a protective film, a polyvinyl alcohol-based resin aqueous solution is suitably used as an adhesive. The polyvinyl alcohol resin used as an adhesive includes a vinyl alcohol homopolymer obtained by saponifying polyvinyl acetate, which is a homopolymer of vinyl acetate, and other single quantities copolymerizable with vinyl acetate. And vinyl alcohol copolymers obtained by saponifying the copolymer with the polymer, and further modified polyvinyl alcohol polymers obtained by partially modifying the hydroxyl groups thereof. 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 of 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 overlapped on the coated surface by a roll or the like. The method of bonding and drying is mentioned.

  After the preparation, the adhesive is applied at a temperature of about 15 to 40 ° C., and the bonding temperature is usually in the range of about 15 to 30 ° C. After the pasting, a drying process is performed to remove a solvent such as water contained in the adhesive. The drying temperature at this time is usually about 30 to 85 ° C, preferably about 40 to 80 ° C. is there. 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, the polarizing plate by which the protective film was bonded by the single side | surface or both surfaces of the polarizing film through the adhesive bond 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, and 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 a function of a brightness enhancement film.

  For example, the above-mentioned 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. Further, two or more layers having different central wavelengths of selective reflection are formed by forming micropores in the protective film by a method as described in JP-A No. 2002-169025 and JP-A No. 2003-29030. 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, by using an appropriate adhesive, a brightness enhancement film such as trade name: DBEF (manufactured by 3M Co., Ltd.), a product name: viewing angle improving film such as WV film (manufactured by Fuji Photo Film Co., Ltd.), trade name, etc. : A commercially available optical functional film such as a retardation film such as Sumikalite (registered trademark) (Sumitomo Chemical Co., Ltd.) may be directly bonded to the polarizing film.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited by these Examples. In addition, the measuring method and evaluation method of each physical property are as follows.

(Remaining rate of boron compound content)
First, the boron compound content in the film before and after one cleaning treatment was calculated. That is, 0.2 g of each film before and after the cleaning treatment was immersed in 100 ml of hot water at 95 ° C. for 60 minutes for complete dissolution, and then each solution was neutralized and titrated. The boron compound content in the film was calculated. Subsequently, each value obtained was applied to the above formula (I), and the residual ratio of the boron compound content in the film before and after washing was calculated.

(Wrinkle / foreign matter defect occurrence)
The film was visually observed.

  A polyvinyl alcohol film (Kurarevinylon VF-PS # 7500, polymerization degree 2,400, saponification degree 99.9 mol% or more) having a width of 450 mm and a thickness of 75 μm is tensioned with pure water at 30 ° C. so that the film does not loosen. The film was sufficiently swollen by immersion for about 100 seconds while maintaining the state.

  Next, uniaxial stretching was performed while being immersed in an aqueous solution of iodine / potassium iodide / water at a weight ratio of 0.02 / 1.5 / 100. Thereafter, the potassium iodide / boric acid / water is immersed in a 55 ° C. aqueous solution having a weight ratio of 12 / 4.4 / 100 and treated with boric acid (waterproofing treatment), and the cumulative draw ratio from the original fabric is 5 After uniaxial stretching until it became 5 times, potassium iodide / boric acid / water was immersed in a 40 ° C. aqueous solution having a weight ratio of 9 / 2.9 / 100.

  Subsequently, it was immersed and washed with pure water at 5 ° C. for 8 seconds. After this washing treatment, the film was dried at 70 ° C. for 3 minutes to obtain a polarizing film having a thickness of 28 μm. The boron compound content in the film before the cleaning treatment at this time was 4.25% by weight, and the boron compound content in the film after the cleaning treatment was 4.17% by weight. And the residual rate of the boron compound content in the film before and after this washing was 0.98, and no wrinkles were observed on the film in the washing treatment. Further, no foreign matter defects were observed, and the obtained polarizing film had an excellent appearance free from color unevenness, foreign matter defects, dents and the like. In addition, the said weight% is a value with respect to the film weight before a swelling process (namely, unprocessed).

  Two washing tanks are provided. In the first stage, potassium iodide / boric acid / water is 15% aqueous solution with a weight ratio of 0.3 / 0.15 / 100 by weight of 0.3 / 0.15 / 100 for 8 seconds. A polarizing film having a thickness of 28 μm was obtained in the same manner as in Example 1 except that it was immersed and washed with water for 3 seconds.

  At this time, the boron compound content in the film before the first-stage cleaning treatment was 4.25 wt%, and the boron compound content in the film after the washing treatment was 4.03 wt%. Further, the boron compound content in the film before the second stage washing treatment was 4.03 wt%, and the boron compound content in the film after the washing treatment was 3.95 wt%. The residual ratio at the first stage was 0.95, and the residual ratio at the second stage was 0.98, and no wrinkles were observed on the film in each cleaning treatment. Further, no foreign matter defects were observed, and the obtained polarizing film had an excellent appearance free from color unevenness, foreign matter defects, dents and the like.

  A polarizing film having a thickness of 28 μm was obtained in the same manner as in Example 1 except that it was immersed and washed in a 25 ° C. aqueous solution of potassium iodide / boric acid / water at a weight ratio of 0.6 / 0.3 / 100 for 48 seconds. It was. The boron compound content in the film before the cleaning treatment at this time was 4.25% by weight, and the boron compound content in the film after the cleaning treatment was 3.40% by weight. The residual rate was 0.80, and no wrinkles were observed on the film during the cleaning process. Further, no foreign matter defects were observed, and the obtained polarizing film had an excellent appearance free from color unevenness, foreign matter defects, dents and the like.

[Comparative Example 1]
A polarizing film having a thickness of 29 μm was obtained in the same manner as in Example 1 except that it was immersed and washed with pure water at 35 ° C. for 48 seconds. The boron compound content in the film before the cleaning treatment at this time was 4.25% by weight, and the boron compound content in the film after the cleaning treatment was 2.76% by weight. And the said residual rate was 0.65, and the wrinkle generate | occur | produced in the film in the washing process.

[Comparative Example 2]
A polarizing film having a thickness of 28 μm was obtained in the same manner as in Example 1 except that the film was immersed and washed with pure water at 2 ° C. for 1 second. The boron compound content in the film before the cleaning treatment at this time was 4.25% by weight, and the boron compound content in the film after the cleaning treatment was 4.22% by weight. The residual ratio was 0.99, and no wrinkle was observed on the film in the cleaning treatment, but boric acid began to precipitate on the roll in a short time, and foreign matter defects were generated on the film.

The evaluation results of Examples 1 to 3 and Comparative Examples 1 and 2 are shown in Table 1.

  A polyvinyl alcohol film (Kurarevinylon VF-PS # 7500, polymerization degree 2,400, saponification degree 99.9 mol% or more) having a width of 450 mm and a thickness of 75 μm is tensioned with pure water at 30 ° C. so that the film does not loosen. While maintaining the state, the film was immersed for about 100 seconds to sufficiently swell the film.

  Next, uniaxial stretching was performed while being immersed in an aqueous solution of iodine / potassium iodide / water at a weight ratio of 0.02 / 1.5 / 100. Thereafter, the potassium iodide / boric acid / water is immersed in a 55 ° C. aqueous solution having a weight ratio of 12 / 4.4 / 100 and treated with boric acid (waterproofing treatment), and the cumulative draw ratio from the original fabric is 5 After uniaxial stretching until it became 5 times, potassium iodide / boric acid / water was immersed in a 40 ° C. aqueous solution having a weight ratio of 9 / 2.9 / 100.

  Subsequently, it was immersed and washed with pure water at 5 ° C. for 8 seconds. After this washing treatment, the film was dried at 70 ° C. for 3 minutes to obtain a polarizing film having a thickness of 28 μm. At this time, the boron compound content in the film before the cleaning treatment is 4.25% by weight, the boron compound content in the film after the cleaning treatment is 4.17% by weight, and the boron in the film before and after the cleaning treatment. The residual ratio of the compound content was 0.98. The film width A before washing is 270 mm, and the film width B after washing is 271 mm (A / B = 1.00). No wrinkles are observed on the film in the washing treatment, and the obtained polarizing film is It had an excellent appearance without color unevenness, foreign matter defects, dents and the like.

  Two washing tanks are provided. In the first stage, potassium iodide / boric acid / water is 15% aqueous solution with a weight ratio of 0.3 / 0.15 / 100 by weight of 0.3 / 0.15 / 100 for 8 seconds. A polarizing film having a thickness of 28 μm was obtained in the same manner as in Example 4 except that it was immersed and washed with water for 8 seconds.

  At this time, the boron compound content in the film before the first-stage cleaning treatment was 4.25 wt%, and the boron compound content in the film after the washing treatment was 4.03 wt%. Further, the boron compound content in the film before the second stage washing treatment was 4.03 wt%, and the boron compound content in the film after the washing treatment was 3.95 wt%. The residual ratio at the first stage was 0.95, and the residual ratio at the second stage was 0.98.

  Furthermore, the film width A before the first stage cleaning is 270 mm, the film width B after the cleaning is 273 mm (A / B = 0.99), the film width A before the second stage cleaning is 273 mm, and the film after the cleaning. The width B is 278 mm (A / B = 0.98), no wrinkles are observed in each cleaning process, and the obtained polarizing film has an excellent appearance free from color unevenness, foreign matter defects, dents and the like. Was.

  A polarizing film having a thickness of 28 μm was obtained in the same manner as in Example 4 except that it was immersed and washed with a 25 ° C. aqueous solution of potassium iodide / boric acid / water at a weight ratio of 0.6 / 0.3 / 100 for 48 seconds. It was. At this time, the boron compound content in the film before the cleaning treatment is 4.25% by weight, the boron compound content in the film after the cleaning treatment is 3.40% by weight, and the residual ratio is 0.80. Met. And the film width A before washing | cleaning is 270 mm, and the film width B after washing | cleaning is 278 mm (A / B = 0.97), generation | occurrence | production of a wrinkle is not seen in a film in washing | cleaning process, The obtained polarizing film is It had an excellent appearance without color unevenness, foreign matter defects, dents and the like.

[Comparative Example 3]
A polarizing film having a thickness of 29 μm was obtained in the same manner as in Example 4 except that it was immersed and washed with pure water at 35 ° C. for 48 seconds. At this time, the boron compound content in the film before the cleaning treatment is 4.25% by weight, the boron compound content in the film after the cleaning treatment is 2.76% by weight, and the residual ratio is 0.65%. Met. The film width A before washing was 270 mm, and the film width B after washing was 282 mm (A / B = 0.96), and wrinkles were generated on the film in the washing treatment.

[Comparative Example 4]
Example 4 except that after stretching, it was immersed in a 55 ° C. aqueous solution of potassium iodide / boric acid / water in a weight ratio of 12 / 4.4 / 100, and then immersed in pure water at 2 ° C. for 1 second. Similarly, a polarizing film having a thickness of 30 μm was obtained. At this time, the boron compound content in the film before the cleaning treatment is 4.42% by weight, the boron compound content in the film after the cleaning treatment is 4.37% by weight, and the residual ratio is 0.99. Met. The film width A before washing was 268 mm, and the film width B after washing was 258 mm (A / B = 1.04), and wrinkles and foreign object defects were generated in the film during the washing treatment.

The evaluation results of Examples 4 to 6 and Comparative Examples 3 and 4 are shown in Table 2.

Claims (6)

A method for producing a polarizing film in which a polyvinyl alcohol film is treated in the order of swelling treatment, dyeing treatment, boric acid treatment and washing treatment, and uniaxial stretching is performed before and / or during these treatments,
In the cleaning treatment, water or a boric acid-containing aqueous solution is used as a cleaning solution, and the boron compound content in the film after the cleaning treatment is 2.5 to 4.3% by weight at a temperature of 30 ° C. or less. What to do,
When the boron compound content in the film before the cleaning process is Y and the boron compound content in the film after the cleaning process is X, the residual ratio of the boron compound content in the film before and after one cleaning process (X / Y) between 0.7 and 0.98 , and
When the film width before the cleaning process is A and the film width after the cleaning process is B, the ratio (A / B) of the film width before and after one cleaning process is 0.97 to 1.03. Method.   The method according to claim 1, wherein the washing treatment is performed at least twice.   When the boron compound content in the film before the first cleaning process is Yp, and the boron compound content in the film after the last cleaning process is Xp, the residual ratio of the boron compound content in the film before and after the entire cleaning process The method according to claim 2, wherein (Xp / Yp) is 0.7 to 0.98.   The ratio of the film width before and after the entire cleaning process (Ap / Bp) is 0.97 to 1.03 when the film width before the first cleaning process is Ap and the film width after the process is Bp. 3. The method according to 3.   The method according to any one of claims 1 to 4, wherein the cleaning treatment is performed using an aqueous solution containing boric acid in a proportion of 0.01 to 0.5 parts by weight with respect to 100 parts by weight of water as a cleaning liquid. The manufacturing method of the polarizing plate which bonds a protective film on the at least single side | surface of the polarizing film obtained by the method in any one of Claims 1-5 .