JP2005173217A - 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 a polarizing film which has an excellent surface state and hardly causes the irregularity of dyeing, and to provide a manufacturing method of polarizing plate and a manufacturing method of optical laminate using the polarizing film. <P>SOLUTION: In the manufacturing method of polarizing film, uniaxial stretching is performed before and/or during a process of treating a polyvinyl alcohol base film in order of swelling, dyeing and borating. Prior to the borating process, dyeing baths of two steps or more are disposed and the dyeing is performed successively and boric acid is included in the final dyeing bath. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a polarizing film having a good surface state and little unevenness of dyeing, a method for producing a polarizing plate using this polarizing film, and a method for producing an optical laminate.

  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 used as 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, Patent Document 1 discloses that after a polyvinyl alcohol film is immersed in an aqueous solution of iodine and potassium iodide, it is treated with boric acid while being stretched, washed with water, and then again with iodine and potassium iodide. A method of dipping in an aqueous solution and drying is described.

  In Patent Document 2, the stretched film is immersed in a dichroic dye-containing aqueous solution, and further immersed in another dichroic dye-containing aqueous solution, and then stretched in a boric acid aqueous solution and dried in the thickness direction. A method for producing a polarizing film provided with two adsorption orientation layers is described.

  In Patent Document 3, a stretched polyvinyl alcohol film is immersed in an aqueous solution of a specific dichroic dye (staining solution A), then immersed in an aqueous solution of iodine and potassium iodide (staining solution B), and then boric acid. A method for producing a polarizing film by treating and washing with water is described.

  Patent Document 4 describes that a polyvinyl alcohol film is immersed and dyed in an aqueous solution containing iodine, potassium iodide and boric acid, then uniaxially stretched, and then treated with boric acid to produce a polarizing film. Yes.

  However, the methods of Patent Documents 1 to 3 in which the dyeing process is performed twice have a problem that the surface state is poor and specular reflection cannot be obtained, and the appearance is poor. On the other hand, in the method of Patent Document 4 in which dyeing is performed with a dyeing bath containing boric acid, there is a problem that there are many dyeing irregularities.

JP-A-9-133809 JP-A-60-66205 JP 62-70802 A Example of Japanese Patent Publication No. 3-23881

  The main subject of this invention is providing the manufacturing method of the polarizing film using this polarizing film, and the manufacturing method of an optical laminated body which has a favorable surface state, and there are few dyeing | staining unevenness, and this polarizing film.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors performed iodine staining in order in two or more stages of dyeing baths before the boric acid treatment step, and contains boric acid in the last dyeing bath. Discovered a new fact that a polarizing film having a good surface condition and little uneven dyeing was obtained, and completed the present invention.

  That is, the manufacturing method of the polarizing film concerning this invention is the manufacturing method of the polarizing film which performs uniaxial stretching before the process of processing a polyvinyl alcohol-type film in order of a swelling process, a dyeing process, and a boric acid process, and / or a process process. Then, two or more stages of dyeing baths are provided before the boric acid treatment step and dyeing is performed in order, and boric acid is contained in the last dyeing bath.

The boric acid concentration in the last dye bath is determined as follows. That is, the boric acid content in the last dye bath is set to a part by weight per 100 parts by weight of water, and the total draw ratio from the original polyvinyl alcohol film (unstretched film) to the last dye bath is determined. When b is set, it is preferable that a and b satisfy the following formula.

  The boric acid content in the last dyeing bath is usually preferably about 0.05 to 2.0 parts by weight per 100 parts by weight of water. Further, the temperature of the dye bath having two or more stages is preferably about 10 to 40 ° C.

  The manufacturing method of the polarizing plate concerning this invention bonds a protective film on the at least single side | surface of the polarizing film obtained by the said method, It is characterized by the above-mentioned. The protective film preferably has any of the functions of a retardation film, a brightness enhancement film, a viewing angle improvement film, and a transflective film.

  The manufacturing method of the optical laminated body concerning this invention pastes at least 1 sort (s) chosen from a phase difference film, a brightness improvement film, a viewing angle improvement film, and a transflective film to the polarizing plate obtained by the said method. It is characterized by.

  According to the present invention, since the dyeing is performed in order in two or more stages of dyeing baths, uneven coloring of the polarizing film can be reduced, and by adding boric acid to the last dyeing bath, in the boric acid treatment step. It can suppress that the surface state of a film deteriorates, and there exists an effect that an optical characteristic improves.

Hereinafter, the present invention will be described in detail.
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-based resin is about 1000 to 10,000, preferably about 1500 to 5,000.

  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 treated in the order of swelling treatment, dyeing treatment, boric acid treatment, and water washing treatment, and finally dried to obtain a polyvinyl alcohol polarizing film having a thickness of, for example, about 5 to 50 μm.

  The polarizing film of the present invention is a polyvinyl alcohol-based uniaxially stretched film in which a dichroic dye is adsorbed and oriented, and the production methods 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 and water washing treatment, followed by drying. Secondly, an unstretched polyvinyl alcohol film is treated with an aqueous solution in the order of swelling treatment, dyeing treatment, boric acid treatment and water washing treatment, and uniaxial stretching is performed in a wet manner in the boric acid treatment step and / or the previous step. This is a method of performing drying 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. 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. 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. As an example of this process, after boric acid treatment, immersion treatment (iodide treatment) with an aqueous iodide solution not containing boric acid or immersion treatment (zinc treatment) step with an aqueous solution containing zinc chloride not containing boric acid, etc. Can be mentioned.

  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 0.01 to 10% by weight can also be used.

The dyeing process is performed for the purpose of adsorbing and orienting the dichroic dye 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. In the present invention, dyeing is performed in sequence by providing two or more dyeing baths. The dyeing bath is suitably 2 to 4 stages. At this time, boric acid is contained in the last dyeing bath. It is preferable that each dye bath except the last dye bath does not contain boric acid. In each dyeing bath, it is preferable to perform the dyeing process while performing uniaxial stretching, but the dyeing process may be performed while maintaining a tension state.
When boric acid is added, it is distinguished from the following boric acid treatment in that it contains a dichroic dye. If 100 parts by weight of water contains about 0.003 parts by weight or more of dichroic dye and the temperature is about 40 ° C. or less, it can be regarded as a dyeing tank.

  When iodine is used as the dichroic dye, the concentration of each dyeing bath except the last dyeing bath is iodine / potassium iodide / water by weight ratio = about 0.003 to 0.2 / about 0.1 to 10 / 100, preferably about 0.01 to 0.1 / about 0.1 to 3.0 / 100. The concentration of the final dyeing bath is iodine / potassium iodide / boric acid / water by weight ratio = about 0.003 to 0.2 / about 0.1 to 10 / about 0.05 to 2.0 / 100, preferably Is about 0.01-0.1 / about 0.1-3.0 / about 0.1-1.5 / 100. The iodine content may be the same for each dyeing bath, or the content may be reduced or increased within the above range in the order of the dyeing treatment.

  It is preferable to adjust the potassium iodide concentration in each dyeing bath so as to increase in the order of the dyeing treatment. When the concentration of potassium iodide is the same in each dyeing bath or decreases in the order of treatment, the balance of the liquid concentration is lost when operating for a long time, and the quality of the polarizing film cannot be maintained stably.

  Further, instead of potassium iodide, other iodides such as zinc iodide may be used. Other iodides may be used in combination with potassium iodide. In these cases, it is preferable to adjust the iodide concentration so as to increase in the order of the dyeing treatment. Moreover, compounds other than iodide, such as zinc chloride and cobalt chloride, may coexist.

ここで、ａは水１００重量部当りのホウ酸含有量（重量部）、ｂはポリビニルアルコール系フィルムの原反から前記最後の染色浴を出るまでの総延伸倍率をそれぞれ示す。 The boric acid concentration in the final dyeing bath is as described above, but it is preferable to satisfy the following formula with the draw ratio. If this relationship is not satisfied, the surface state of the polarizing film may be deteriorated. is there.

Here, a represents the boric acid content (parts by weight) per 100 parts by weight of water, and b represents the total draw ratio from the original fabric of the polyvinyl alcohol film to the last dye bath.

  In the dyeing treatment in each dyeing bath, for example, an immersion treatment is performed at a temperature of about 10 ° C. to 40 ° C., preferably about 20 ° C. to 35 ° C. for about 30 seconds to 600 seconds, preferably about 60 seconds to 300 seconds. Here, when the temperature of each dyeing bath is less than about 10 ° C., boric acid is difficult to dissolve, and conversely when it exceeds about 40 ° C., dissolution of polyvinyl alcohol may increase.

  In performing uniaxial stretching in each dyeing bath, it is preferable to adjust the stretching ratio independently in each dyeing bath. For this purpose, for example, it is preferable to provide nip rolls on the inlet side and the outlet side of each dyeing bath so that the rotational speed ratio of both nip rolls can be changed. Further, uniaxial stretching can be performed by installing an expander roll, a spiral roll, a crown roll, a cross guider, a bend bar or the like 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, and may be uniaxially stretched in at least one of the dyeing baths if necessary, or may be a washing bath. May be provided in at least one between each dyebath.

  When performing uniaxial stretching in each of two or more stages of dyeing baths, the stretching ratio is not particularly limited, but it is preferable to employ one of the following two aspects.

  (1) The stretching ratio in the first dyeing bath is made higher than the total stretching ratio in the second and subsequent dyeing baths. Thereby, since the drying neck-in at the time of drying after washing with water becomes small, the occurrence frequency of wrinkles in the drying furnace decreases. Specifically, the draw ratio in the first dye bath is in the range of about 1.1 to 3.0 times, and the total draw ratio in the second and subsequent dye baths is about 1.05 to 2. It is preferably about 0 times.

  (2) Make the draw ratio in the final dye bath higher than the total draw ratio in the previous dye bath. Thereby, it becomes difficult to relieve | moderate a film in the process after a boric-acid treatment process, and a polarizing film with a high degree of polarization is obtained. Specifically, the draw ratio in the final dye bath is in the range of about 1.05 to 2.0 times, and about 1.1 to 3.0 times the total draw ratio in the previous dye bath. It is preferable that it is about.

  The boric acid treatment is carried out by immersing the iodine-stained 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. The aqueous boric acid 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 not only for water resistance by cross-linking but also for hue adjustment (for example, to prevent bluish tint). 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 a name such as a crosslinking treatment or an immobilization treatment. Further, when boric acid treatment is performed for hue adjustment, such boric acid treatment may be referred to as a complementary color treatment, a re-dyeing treatment, or the like. In the present invention, boric acid treatment for water resistance and boric acid treatment for hue adjustment are both simply referred to as boric acid treatment.

  The boric acid treatment for water resistance and the boric acid treatment for hue adjustment are not particularly distinguished, but are carried out under the following conditions.

When the raw film is swollen, dyed or treated with boric acid, and the boric acid treatment is aimed at water resistance by crosslinking, about 3 to 10 parts by weight of boric acid and 100% by weight of iodide, iodide Is carried out at a temperature of about 50 ° C. to 70 ° C., preferably about 55 ° C. to 65 ° C. The immersion time is usually about 30 to 600 seconds, preferably about 60 to 420 seconds, 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 to 85 degreeC normally, Preferably it is about 55 to 80 degreeC.

  After boric acid treatment for water resistance, boric acid treatment for hue adjustment may be performed. For this purpose, 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. Performed at a temperature of ° C. The immersion time is usually about 3 to 300 seconds, preferably about 10 to 240 seconds. The boric acid treatment for adjusting the hue 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 in a plurality of steps and are usually performed in 2 to 5 steps. 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 be performed in a plurality of steps, respectively. In the boric acid treatment process, the film may be stretched in the same manner as in the dyeing process. The final cumulative draw ratio is about 4.5 to 7.0 times, preferably about 5.0 to 6.5 times.

  After boric acid treatment, it 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 the water in the washing treatment is usually about 2 to 40 ° C., and the immersion time is preferably about 2 to 120 seconds. Drying 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, it is preferable to perform tension control so that the tension of the film becomes substantially constant in each step after the stretching treatment. When stretching is completed in the dyeing process, tension control is performed in the subsequent boric acid treatment process and the water washing process.

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, an appropriate 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 is deteriorated, 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, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

A 75 μm-thick polyvinyl alcohol film (Kurarayvinilon VF-PS # 7500, polymerization degree 2,400, saponification degree 99.9 mol% or more) was kept in pure water at 30 ° C. while keeping the film from loosening. The film was sufficiently swollen by immersion for 130 seconds (swelled by about 1.2 times).
Next, the film was uniaxially stretched 1.75 times while being immersed in a 30 ° C. aqueous solution of iodine / potassium iodide / water at a weight ratio of 0.02 / 1.0 / 100. Further, while immersing iodine / potassium iodide / boric acid / water in a 30 ° C. aqueous solution having a weight ratio of 0.02 / 1.5 / 0.2 / 100, uniaxially stretching 1.4 times, The total draw ratio from was set to 3 times. Thereafter, the film is immersed in a 60 ° C. aqueous solution of potassium iodide / boric acid / water at a weight ratio of 10/5/100, and uniaxially stretched until the cumulative draw ratio from the raw material becomes 5.9 times while water-resistant. Went. After the water resistance treatment, it was washed with pure water at 10 ° C. for about 10 seconds. After washing with water and drying at 60 ° C. for 2 minutes, an iodine-based polarizing film having a thickness of 28 μm was obtained. When the surface state of this polarizing film was visually observed, the film surface showed favorable specular reflection.
Polyvinyl alcohol adhesive is applied to both sides of this polarizing film, and protective films are applied to both sides [Triacetylcellulose film with surface saponification treatment, “Fujitac (registered trademark) T80UNL”, manufactured by Fuji Photo Film Co., Ltd.] , 80 μm thick], and dried at 60 ° C. for 5 minutes to obtain a polarizing plate. When this polarizing plate was visually observed in a dark room in a crossed Nicol state, the uneven dyeing was slight. The uneven dyeing was confirmed by the degree of light leakage from the polarizing plate.

[Comparative Example 1]
A polarizing film was obtained in the same manner as in Example 1 except that boric acid was not added to the second dyeing bath. When the surface state of this polarizing film was visually observed, the reflected light of the fluorescent lamp did not show specular reflection and looked somewhat whitish, and the appearance was poor.

[Comparative Example 2]
A polarizing film was obtained in the same manner as in Example 1 except that 0.2 parts by weight of boric acid was added to the first dyeing bath. When this polarizing plate was visually observed in a dark room in a crossed Nicol state, staining unevenness was observed more than in Example 1.

Claims (7)

  A method for producing a polarizing film in which a polyvinyl alcohol film is uniaxially stretched before and / or during a treatment process in the order of swelling treatment, dyeing treatment, and boric acid treatment, and two or more steps before the boric acid treatment step The method for producing a polarizing film is characterized in that the dyeing bath is provided and dyeing is performed in order, and the last dyeing bath contains boric acid. The boric acid content in the last dye bath is a part by weight per 100 parts by weight of water, and when the total draw ratio from the original film of the polyvinyl alcohol film to the last dye bath is b, The method for producing a polarizing film according to claim 1, wherein a and b satisfy the following formula.

  The method for producing a polarizing film according to claim 1 or 2, wherein the boric acid content in the last dyeing bath is 0.05 to 2.0 parts by weight per 100 parts by weight of water.   The method for producing a polarizing film according to any one of claims 1 to 3, wherein the temperature of the two or more dyeing baths is 10 to 40 ° C.   The manufacturing method of the polarizing plate characterized by bonding a protective film to the at least single side | surface of the polarizing film obtained by the method in any one of Claims 1-4.   The manufacturing method of the polarizing plate of Claim 5 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 5; and at least one selected from a retardation film, a brightness enhancement film, a viewing angle improvement film, and a transflective film. Production method.