TW201708858A - Method for producing polarizing film - Google Patents

Abstract

Provided is a method for producing a polarizing film, the method comprising: a widthwise restraining step for restraining in the widthwise direction a polyvinyl alcohol-based resin film, which had been brought into contact with a treatment solution, by bringing the film into contact with at least one free roll having a diameter of 150 mm or greater; and a drying step for drying the polyvinyl alcohol-based resin film after the widthwise restraining step.

Description

Method for manufacturing polarizing film

The present invention relates to a method of producing a polarizing film which can be used as a constituent member of a polarizing plate.

Regarding the polarizing film, it has been previously used in a uniaxially stretched polyvinyl alcohol-based resin film to adsorb a dichroic dye such as iodine or a dichroic dye. The polarizing film is usually formed by laminating a protective film on one surface or both sides thereof with an adhesive to form a polarizing plate, and is used for an image display device typified by a liquid crystal display device such as a liquid crystal television, a display for personal computers, and a mobile phone. In recent years, with the reduction in thickness of liquid crystal display devices, a thinned polarizing film has been demanded.

In general, a polarizing film is produced by performing various treatments such as swelling, dyeing, crosslinking, and stretching on a long-sized polyvinyl alcohol-based resin film that has been continuously conveyed in a bath, followed by drying treatment and drying (for example, Reference is made to Japanese Patent Laid-Open Publication No. 2009-48179.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2009-48179

In order to carry out the stretching treatment, the polyvinyl alcohol-based resin film to be subjected to the drying step shrinks in the width direction when the moisture is removed by the drying step, and the thickness tends to increase due to shrinkage in the width direction, and the thickness cannot be satisfied. Claim.

Patent Document 1 describes that in the drying step, a polyvinyl alcohol resin is used. The film is dried by contact with a plurality of heat rolls to suppress shrinkage in the width direction in the drying step, and a thin polarizing film is provided. However, when the polyvinyl alcohol-based resin film having a high water content is brought into contact with the heat roller and restrained in the width direction, the polyvinyl alcohol-based resin film is liable to be broken.

On the other hand, since the water content of the polyvinyl alcohol-based resin film is somewhat low, a method of suppressing shrinkage in the width direction by performing a drying step is also considered. However, by such a method, polyvinyl alcohol is used. Since the frictional force between the resin film and the roll is lowered, if only the polyvinyl alcohol-based resin film is brought into contact with the roll, the width direction cannot be sufficiently restrained, and the width direction must be mechanically fixed by a tenter cloth or the like. The polyvinyl alcohol-based resin film is easily broken.

An object of the present invention is to provide a method for producing a polarizing film which can suppress shrinkage in the width direction while suppressing breakage of the polyvinyl alcohol-based resin film, thereby producing a thin polarizing film having a small shrinkage force.

The present invention provides a method for producing a polarizing film shown below.

[1] A method of producing a polarizing film, comprising: a width confinement step of contacting a polyvinyl alcohol-based resin film after contacting the treatment liquid with at least one free roller having a diameter of 150 mm or more and restraining in a width direction; The drying step is performed by drying the polyvinyl alcohol resin film after the width confinement step.

[2] The method for producing a polarizing film according to [1], wherein in the width confinement step, the polyvinyl alcohol-based resin film is in contact with a plurality of rolls including the free roll, and is in contact with the first roll. At least 40% of the time between the last roll release is in contact with either roll.

[3] The method for producing a polarizing film according to [1], wherein the polyvinyl alcohol resin film is in contact with the width within about 20 seconds after the contact with the treatment liquid is completed. The first roll in the bundle step.

[4] The method for producing a polarizing film according to any one of [1], wherein the polyvinyl alcohol-based resin film has a water content of 30% at the time of contacting the first roll in the width confinement step. %the above.

According to the method of the present invention, it is possible to suppress the shrinkage in the width direction while suppressing the breakage of the polyvinyl alcohol-based resin film, and to manufacture a polarizing film which is thin and has a small shrinkage force.

10‧‧‧Material film containing polyvinyl alcohol resin

11‧‧‧ Raw material reel

13‧‧‧Swelling bath

15‧‧‧dye bath

17‧‧‧Cross-link bath

19‧‧‧Clean bath

21‧‧‧ drying oven

23‧‧‧ polarizing film

30‧‧‧guide roller

31‧‧‧guide roller

32‧‧‧guide roller

33‧‧‧guide roller

34‧‧‧guide roller

35‧‧‧guide roller

36‧‧‧guide roller

37‧‧‧guide roller

38‧‧‧guide roller

39‧‧‧guide roller

40‧‧‧guide roller

41‧‧‧guide roller

50‧‧‧ nip rollers

51‧‧‧ nip rollers

52‧‧‧ nip rollers

53‧‧‧ nip rollers

54‧‧‧ nip rollers

60‧‧‧guide roller

61‧‧‧guide roller

70‧‧‧Width Constraint

71‧‧‧Free roll

72‧‧‧Free roll

73‧‧‧Free roll

74‧‧‧Hot air dryer

74a‧‧‧Mechanical components of hot air dryer

74b‧‧‧Mechanical components of hot air dryer

75‧‧‧hot air dryer

75a‧‧‧Mechanical components of hot air dryer

75b‧‧‧Mechanical components of hot air dryer

76‧‧‧hot air dryer

76a‧‧‧Mechanical components of hot air dryer

76b‧‧‧Mechanical components of hot air dryer

81‧‧‧guide roller

82‧‧‧ nip rollers

83‧‧‧ nip rollers

90‧‧‧ drying oven

711‧‧‧Free roll

712‧‧‧Free roll

713‧‧‧Free roll

721‧‧‧Free roll

722‧‧‧Free roll

723‧‧‧Free roll

731‧‧‧Free roll

732‧‧‧Free roll

733‧‧‧Free roll

741‧‧‧Free roll

P1‧‧‧ position

P2‧‧‧ position

P3‧‧‧ position

P4‧‧‧ position

Fig. 1 is a cross-sectional view schematically showing an example of a method for producing a polarizing film of the present invention and a polarizing film producing apparatus therefor.

Fig. 2 is a cross-sectional view schematically showing an example of a roller structure in a width restricting portion.

Fig. 3 is a cross-sectional view schematically showing an example of a roller structure in a width restricting portion.

Fig. 4 is a cross-sectional view schematically showing an example of a roller structure in a width restricting portion.

Fig. 5 is a cross-sectional view schematically showing an example of a roller structure in a width restricting portion.

<Method of Manufacturing Polarized Film>

In the present invention, the polarizing film is one in which a uniaxially stretched polyvinyl alcohol-based resin film is adsorbed to a dichroic dye (iodine or a dichroic dye). The polyvinyl alcohol-based resin constituting the polyvinyl alcohol-based resin film is usually obtained by saponifying a polyvinyl acetate-based resin. The degree of saponification is usually about 85 mol% or more, preferably about 90 mol% or more, more preferably about 99 mol% or more. The polyvinyl acetate-based resin may be, for example, a polyvinyl acetate which is a homopolymer of vinyl acetate, or a copolymer of vinyl acetate and another monomer copolymerizable therewith. Examples of the other monomer which can be copolymerized include unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids. The degree of polymerization of the polyvinyl alcohol-based resin is usually from about 1,000 to 10,000, preferably from about 1,500 to 5,000.

These polyvinyl alcohol-based resins may also be modified, for example, may also be used: modified with aldehydes Polyvinyl formal, polyvinyl acetal, polyvinyl butyral, and the like.

In the present invention, as the starting material for producing a polarizing film, an unstretched polyethylene having a thickness of 65 μm or less (for example, 60 μm or less), preferably 50 μm or less, more preferably 35 μm or less, and still more preferably 30 μm or less is used. An alcohol resin film (raw material film). Thereby, a polarizing film of a film which is increasingly required in the market can be obtained. The thinner the raw material film, the more easily the film breaks during the stretching treatment. However, according to the present invention, even when the raw material film is thin, the film breakage can be effectively suppressed. The raw material film may be a polyvinyl alcohol-based resin film which has been subjected to elongation treatment in advance in the vapor phase.

The width of the raw material film is not particularly limited, and may be, for example, about 400 to 6000 mm. However, the larger the film width, the more likely the film breaks during the stretching treatment.

In the present invention, the raw material film is prepared as a roll (raw material roll) of a long stretched polyvinyl alcohol-based resin film.

The polarizing film can be subjected to a processing step of continuously transporting the long-length raw material film from the raw material sheet roll while being conveyed along the film transport path of the polarizing film manufacturing apparatus to be in contact with the processing liquid, and then performing a width constraint. The step is followed by a drying step to continuously produce a long polarizing film.

The processing step may include, for example, a swelling treatment step of immersing the raw material film in a swelling bath and pulling it out; and performing a dyeing treatment step of immersing the film after the swelling treatment in the dyeing bath and then pulling it out; In the joint treatment step, the dyed film is immersed in a crosslinking bath and then pulled out. Further, the uniaxial stretching process is performed by wet or dry between the series of processing steps (i.e., before any one or more of the processing steps and/or in any one or more of the processing steps). Additional processing steps can be added as needed. Each of the above treatment steps may be a treatment of immersing the membrane in a bath, or a treatment of sequentially immersing in two or more baths.

The width restricting step is such that the polyvinyl alcohol-based resin film after the contact with the treatment liquid in the above-mentioned treatment step is in contact with at least one free roller having a diameter of 150 mm or more (hereinafter, also A step called "large diameter free roller") and restrained in the width direction. The roll contacting the polyethylene-based alcohol resin film in the width confinement step may also include one or a plurality of large-diameter free rolls, and a free roll having a diameter of less than 150 mm, and a drive roll. In the present specification, the contact of the polyvinyl alcohol-based resin film with the roller is not in point contact but is in contact with the surface (the polyvinyl alcohol-based resin film has a width in the longitudinal direction and is in contact with the free roller). The polyvinyl alcohol-based resin film is restrained in the width direction by surface contact.

Here, the free roller means a roller that does not have a drive mechanism such as a motor. By using a free roller as a mechanism for restricting the width direction of the polyvinyl alcohol-based resin film that is in contact with the treatment liquid as described above, the breakage of the polyvinyl alcohol-based resin film can be suppressed. In the present invention, the polyvinyl alcohol-based resin film can be slowly dried in a state of being restrained in the width direction by providing such a width-constraining step, and a large load is not applied to the polyvinyl alcohol-based resin film to suppress it. The shrinkage in the width direction produces a polarizing film which is thin and has a small shrinkage force.

In the drying step, the polyvinyl alcohol-based resin film subjected to the width-limiting step is dried to obtain a polarizing film, and is reduced to, for example, a moisture content of less than 15% by weight.

Hereinafter, a method of manufacturing a polarizing film of the present invention will be described in more detail with reference to FIG. 1. Fig. 1 is a cross-sectional view schematically showing an example of a method for producing a polarizing film of the present invention and a polarizing film producing apparatus therefor. The polarizing film manufacturing apparatus shown in FIG. 1 is configured such that a blank (unstretched) film 10 including a polyvinyl alcohol-based resin is continuously unwound along the film by the raw material sheet roll 11 while being conveyed along the film. The path is conveyed, and the swelling bath 13 provided in the film transport path, the dye bath 15, the cross-linking bath 17, and the cleaning bath 19 are sequentially passed through, and then passed through the width restricting portion 70 and finally passed through the drying furnace 90. The obtained polarizing film can be directly transferred to the next polarizing plate producing step (step of bonding the protective film to one side or both sides of the polarizing film 23), for example. The arrows in Fig. 1 indicate the direction in which the film is conveyed.

In addition, although FIG. 1 shows an example in which the swelling bath 13, the dye bath 15, the crosslinking bath 17, and the cleaning bath 19 are provided in each of the tanks, any one or more of them may be used as needed. The bath (to be treated as a "treatment bath" for the treatment of the polyvinyl alcohol-based resin film provided on the film transport path such as the swelling bath 13, the dye bath 15, the cross-linking bath 17, and the cleaning bath 19) Above the slot.

The film transport path of the polarizing film manufacturing apparatus can be constructed by the processing bath, the width restricting unit 70, and the drying furnace 90, and the guide rolls 30 to 41, 60, 61, 81 and the nip rollers 50 to 54 can be used. 82, 83 are arranged at appropriate positions, wherein the guide rollers 30-41, 60, 61, 81 can support the film to be transported, or can further change the film transport direction; the nip rollers 50-54, 82, 83 The film to be conveyed can be pressed and held, and the driving force by the rotation can be applied to the film, or the film conveying direction can be changed. The guide roller or the nip roller can be disposed in the treatment bath, before or after the drying oven, or in the treatment bath, whereby the film can be introduced into the treatment bath, immersed, and pulled out from the treatment bath [see FIG. 1]. For example, a film may be conveyed along the guide rolls by arranging one or more guide rolls in each treatment bath, and the film may be immersed in each treatment bath.

The polarizing film manufacturing apparatus shown in FIG. 1 is disposed before the respective processing baths, and then the nip rolls (nip rolls 50 to 54) are disposed, whereby the stretching between the rolls can be performed, and the stretching between the rolls is performed in any one or more of the processing baths. A longitudinal uniaxial extension is performed by applying a circumferential speed difference between the nip rolls disposed before and after. Hereinafter, each step will be described.

(swelling treatment step)

The swelling treatment step is performed for the removal of foreign matter on the surface of the raw material film 10, the removal of the plasticizer in the raw material film 10, the imparting of the dyeability, the plasticization of the raw material film 10, and the like. The treatment conditions are determined within a range in which the object can be achieved, and in a range in which no abnormality such as dissolution or devitrification of the raw material film 10 occurs.

Referring to Fig. 1, the swelling treatment step can be carried out by continuously unwinding the raw material film 10 by the raw material sheet roll 11 while conveying along the film transport path, and allowing the raw material film 10 to be in the swelling bath 13. Dip for a specific time and then pull out. In the example of FIG. 1, since the raw material film 10 is unwound to be immersed in the swelling bath 13, the raw material film 10 can be guided along The film transport path constructed by the rollers 60 and 61 and the nip roller 50 is transported. In the swelling treatment, the film is conveyed along the film transport path constructed by the guide rolls 30 to 32.

As the swelling liquid of the swelling bath 13, in addition to the pure water, a boric acid (Japanese Patent Laid-Open No. Hei 10-153709), a chloride (Japanese Patent Laid-Open No. Hei 06-281816), an inorganic acid, an inorganic salt may be used. An aqueous solution obtained by adding a water-soluble organic solvent or an alcohol in an amount of about 0.01 to 10% by weight.

The temperature of the swelling bath 13 is, for example, about 10 to 50 ° C, preferably about 10 to 40 ° C, more preferably about 15 to 30 ° C. The immersion time of the raw material film 10 is preferably about 10 to 300 seconds, more preferably about 20 to 200 seconds. In the case where the raw material film 10 is a polyvinyl alcohol-based resin film which is formed by extending in advance in a gas, the temperature of the swelling bath 13 is, for example, about 20 to 70 ° C, preferably about 30 to 60 ° C. The immersion time of the raw material film 10 is preferably about 30 to 300 seconds, more preferably about 60 to 240 seconds.

In the swelling treatment, the problem that the raw material film 10 is swollen in the width direction and wrinkles are formed on the film is likely to occur. As a method for conveying the film while removing the wrinkles, a guide roll 30, 31, and/or 32 may be used, such as a spreader roll, a spiral roll, a medium-high roll having a widening function, or a guide such as a guide. Other expansion devices for cloth rolls, bending rolls, and tented fabrics. Another method for suppressing the generation of wrinkles is to perform an extension process. For example, the uniaxial stretching treatment can be performed in the swelling bath 13 by using the circumferential speed difference between the nip roller 50 and the nip roller 51.

In the swelling treatment, since the film is swollen and expanded in the direction in which the film is conveyed, when the film is not actively stretched, in order to relax the film in the conveying direction, for example, it is preferable to seek a swelling bath. The method of controlling the speed of the nip rollers 50 and 51 arranged before and after 13 is performed. Further, in order to stabilize the film transport in the swelling bath 13, the water flow in the swelling bath 13 is controlled by an underwater sprinkler, or an EPC device (Edge Position Control) device is used to detect the end of the film to prevent It is also useful for devices such as membranes.

In the example shown in FIG. 1, the film pulled out from the swelling bath 13 is sequentially passed through the guide rolls 32 and the clips. The roller 51 is introduced into the dyeing bath 15.

(dye processing step)

The dyeing treatment step is carried out by adsorbing a dichroic dye to the polyvinyl alcohol-based resin film after the swelling treatment, and aligning the dye. The treatment conditions are within the range in which the object can be achieved, and are determined not to cause a range of adverse conditions such as extreme melting or devitrification of the film. Referring to Fig. 1, the dyeing treatment step can be carried out by transporting along the film transport path constructed by the guide rolls 33 to 35 and the nip rolls 51, and swelling the film in the dye bath 15 (contained in dyeing) The tank treatment liquid is immersed for a specific time and then pulled out. In order to improve the dyeability of the dichroic dye, the film to be subjected to the dyeing treatment step is preferably a film which has been subjected to at least a certain degree of uniaxial stretching treatment, or preferably to replace the uniaxial stretching treatment before the dyeing treatment, or In addition to the uniaxial stretching treatment before the dyeing treatment, uniaxial stretching treatment is performed at the time of dyeing treatment.

In the case where iodine is used as the dichroic dye, the dyeing liquid of the dyeing bath 15 may be, for example, an aqueous solution having a concentration by weight of iodine/potassium iodide/water = about 0.003 to 0.3/about 0.1 to 10/100. Instead of potassium iodide, other iodides such as zinc iodide may be used, and potassium iodide and other iodides may be used in combination. Further, a compound other than the iodide such as boric acid, zinc chloride, cobalt chloride or the like may be allowed to coexist. In the case where boric acid is added, the iodine is distinguished from the crosslinking treatment described below, and the dyeing bath 15 can be regarded as long as the aqueous solution contains about 0.003 parts by weight or more of iodine per 100 parts by weight of water. The temperature of the dye bath 15 when the film is impregnated is usually about 10 to 45 ° C, preferably 10 to 40 ° C, more preferably 20 to 35 ° C, and the immersion time of the film is usually about 30 to 600 seconds, preferably 60 to 60. 300 seconds.

When a water-soluble dichroic dye is used as the dichroic dye, the dyeing liquid of the dyeing bath 15 may be, for example, an aqueous solution having a concentration of dichroic dye/water = about 0.001 to 0.1/100 by weight. In the dyeing bath 15, a dyeing aid or the like may be allowed to coexist, and an inorganic salt such as sodium sulfate or a surfactant may be contained. The dichroic dye may be used alone or in combination of two or more dichroic dyes. The temperature of the dye bath 15 when the film is impregnated For example, it is about 20 to 80 ° C, preferably 30 to 70 ° C, and the immersion time of the film is usually about 30 to 600 seconds, preferably about 60 to 300 seconds.

As described above, in the dyeing treatment step, the uniaxial stretching of the film can be carried out in the dyeing bath 15. The uniaxial stretching of the film can be carried out by a method of applying a peripheral speed difference between the nip roller 51 and the nip roller 52 disposed before and after the dyeing bath 15.

In the dyeing treatment, the polyvinyl alcohol-based resin film is conveyed while removing the wrinkles of the film in the same manner as the swelling treatment, and the guide rolls 33, 34, and/or 35 may be used, for example, a spreader roll, a spiral roll, or a medium-high roll. For the roller of the expansion function, other expansion devices such as a guide roller, a bending roller, and a tenter cloth can be used. One method for suppressing the generation of wrinkles is to perform the stretching treatment in the same manner as the swelling treatment.

In the example shown in FIG. 1, the film drawn from the dyeing bath 15 is introduced into the crosslinking bath 17 through the guide rolls 35 and the nip rolls 52 in this order.

(cross-linking processing steps)

The crosslinking treatment step is a treatment for hydration resistance or hue adjustment (prevention of film-like cyan, etc.) by crosslinking or the like. Referring to Fig. 1, the cross-linking treatment can be carried out by transporting along a film transport path constructed by guide rolls 36-38 and nip rolls 52, in cross-linking bath 17 (cross-linking liquid accommodated in the cross-linking tank) The film after the dyeing treatment is immersed for a specific time and then pulled out.

The cross-linking liquid of the cross-linking bath 17 may be an aqueous solution containing, for example, about 1 to 10 parts by weight of boric acid per 100 parts by weight of water. In the case where the dichroic dye used in the dyeing treatment is iodine, the cross-linking liquid preferably contains iodide in addition to boric acid, and the amount thereof can be, for example, 1 to 100 parts by weight of water. 30 parts by weight. Examples of the iodide include potassium iodide and zinc iodide. Further, a compound other than the iodide such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate or the like may be allowed to coexist.

In the crosslinking treatment, the concentration of boric acid and iodide and the temperature of the crosslinking bath 17 can be appropriately changed depending on the purpose. For example, the purpose of cross-linking treatment is by cross-linking In the case where the polyvinyl alcohol-based resin film is sequentially subjected to swelling treatment, dyeing treatment, and crosslinking treatment, the crosslinking agent-containing liquid of the crosslinking bath may be a concentration by weight of boric acid/iodide/ Water = 3~10/1~20/100 aqueous solution. If necessary, other crosslinking agents such as glyoxal or glutaraldehyde may be used instead of boric acid, and boric acid and other crosslinking agents may be used in combination. The temperature of the crosslinking bath when immersing the film is usually about 50 to 70 ° C, preferably 53 to 65 ° C, and the immersion time of the film is usually about 10 to 600 seconds, preferably 20 to 300 seconds, more preferably 20 to 20 200 seconds. Further, in the case where the polyvinyl alcohol-based resin film which is previously stretched before the swelling treatment is subjected to the dyeing treatment and the crosslinking treatment in this order, the temperature of the crosslinking bath 17 is usually about 50 to 85 ° C, preferably 55 to 80. °C.

In the cross-linking treatment for the purpose of hue adjustment, for example, when iodine is used as the dichroic dye, the concentration can be used in terms of weight ratio of boric acid/iodide/water = 1 to 5/3 to 30/100. A liquid containing a crosslinking agent. The temperature of the crosslinking bath when immersing the film is usually about 10 to 45 ° C, and the immersion time of the film is usually about 1 to 300 seconds, preferably 2 to 100 seconds.

The cross-linking treatment can also be carried out plural times, usually 2 to 5 times. In this case, the composition and temperature of each of the crosslinking baths used may be the same or different as long as they are within the above range. The cross-linking treatment for water resistance by cross-linking and the cross-linking treatment for hue adjustment can also be carried out using a plurality of steps, respectively.

The uniaxial stretching treatment can be performed in the crosslinking bath 17 by the circumferential speed difference between the nip roller 52 and the nip roller 53.

In the cross-linking treatment, the polyvinyl alcohol-based resin film is conveyed while removing the wrinkles of the film in the same manner as the swelling treatment, and the guide rolls 36, 37, and/or 38 can be used, for example, a spreader roll, a spiral roll, or a medium-high roll. Rollers with a widening function, or other expansion devices such as a guide roll, a bending roll, and a tenter cloth. Another method for suppressing the generation of wrinkles is to carry out the stretching treatment in the same manner as the swelling treatment.

In the example shown in Fig. 1, the film drawn from the crosslinking bath 17 is introduced into the film cleaning bath 19 through the guide rolls 38 and the nip rolls 53 in this order.

(cleaning process step)

The manufacturing method of the present invention may include a washing treatment step after the crosslinking treatment step. The cleaning treatment is performed in order to remove excess boric acid or iodine adhering to the polyvinyl alcohol-based resin film. The cleaning treatment can be carried out, for example, by immersing the crosslinked polyvinyl alcohol resin film in the film cleaning bath 19, or by spraying the film cleaning liquid as a shower, or by using these.

FIG. 1 shows an example in which a polyvinyl alcohol-based resin film is immersed in a cleaning bath 19 and subjected to a cleaning treatment. The temperature of the film cleaning bath 19 in the film cleaning treatment is usually about 2 to 40 ° C, and the immersion time of the film is usually about 2 to 120 seconds.

Further, in the cleaning process, the polyvinyl alcohol-based resin film is conveyed while removing the wrinkles, and the guide rolls 39, 40, and/or 41 can be expanded by using, for example, a spreader roll, a spiral roll, or a medium-high roll. Rollers, or other expansion devices such as cloth rolls, bending rolls, and tenter fabrics can be used. Further, in the film cleaning treatment, in order to suppress the occurrence of wrinkles, an extension treatment may be performed.

(Extension processing step)

As described above, the raw material film 10 is uniaxially wetted or dried by a series of processing steps (i.e., before any one or more of the processing steps and/or in any one or more of the processing steps). Extended processing. The specific method of the uniaxial stretching treatment may be, for example, applying a peripheral speed difference between two nip rolls constituting the film conveying path (for example, two nip rolls disposed before the processing bath) to perform longitudinal uniaxial stretching between the rolls The extension, such as the extension of the heat roller described in Japanese Patent No. 2731813, the extension of the tenter, etc., is preferably extended between the rolls. The uniaxial stretching treatment step can be carried out several times between the raw material film 10 and the obtained polarizing film 23. As described above, the elongation treatment is also advantageous for suppressing the generation of wrinkles of the film.

The final cumulative stretching ratio of the polarizing film 23 based on the raw material film 10 is usually about 4.5 to 7 times, preferably 5 to 6.5 times.

The extension processing step may also use any of the above as long as it is before the width constraint step The processing steps are performed. When the extension processing is performed by using two or more processing steps, the extension processing may be performed by using any one of the processing steps.

(width constraint step)

After the cleaning treatment step, a step of restraining the width direction of the width direction by contacting the polyvinyl alcohol-based resin film with at least one large-diameter free roller having a diameter of 150 mm or more is performed.

In the width confinement step, the polyvinyl alcohol-based resin film does not need to be in constant contact with the roll, but from the viewpoint of effective width restriction, it is preferably 0.5 second or more, and more preferably 2 seconds or more. Continuous contact time. The present invention comprises at least one large diameter free roll having a diameter of 150 mm or more as a roll used in the width restricting step. With the large diameter free roller, it becomes easy to ensure a continuous contact time as described above. The diameter of the large diameter free roller is preferably 200 mm or more, and more preferably 300 mm or more. The diameter of the large diameter free roller is preferably less than 450 mm. When the diameter is 450 mm or more, a load is applied to the polyvinyl alcohol-based resin film due to the rotational resistance of the free roller, and the polyvinyl alcohol-based resin film is likely to be broken. In the width confinement step, it is preferred to include two or more large diameter free rolls.

The roller used in the width-constraining step can adjust the conveying direction of the polyvinyl alcohol-based resin film, and in the case of forced crimping, it is preferable to include a plurality of the large-diameter free rolls, and more preferably 3 or more and 5 Below. In the case where a plurality of rolls are used, the polyvinyl alcohol-based resin film preferably contacts any one of the rolls in the width restricting step in contact with at least 40% of the time from the initial roll to the last roll release. A sufficient width restraining effect can be obtained by making the time of contact with the roller 40% or more. The time of contact with the roll is further preferably 70% or more. The time of contact with the rolls can be adjusted by the number of rolls, the arrangement position of the rolls, and the angle of the hugs of the rolls. Further, from the viewpoint of effective width restriction, the time during which the polyvinyl alcohol-based resin film is not in contact with the roll is preferably 2 seconds or shorter.

Furthermore, in this specification, the initial roll will be contacted in the width constraint step. The point is used as the lead point of the width constraint step, and the point from the last roll is taken as the derivation point from the width constraint step. In the case where the roller used in the width confinement step is one, the first roller and the last roller become the same roller. The time from the beginning to the end of the width constraint step is preferably 5 seconds or more. Also, the time from the beginning to the end of the width constraint step is preferably less than 60 seconds. In the case of 60 seconds or more, the drying of the polyvinyl alcohol-based resin film in the width-constraining step is carried out more than necessary, and the polyvinyl alcohol-based resin film is broken in the drying step in the subsequent stage.

In the width-constraining step, the polyvinyl alcohol-based resin film can be slowly dried in a state of being restrained in the width direction, and a large load is not applied to the polyvinyl alcohol-based resin film, shrinkage in the width direction is suppressed, and thinning and shrinkage are produced. A polarizing film with a small force. In order to control the dry state in the width confinement step, for example, a method of drying with a hot air dryer, an infrared heater, or the like is preferably employed. In the width confinement step, the maximum temperature at which the polyvinyl alcohol-based resin film reaches is, for example, 30 to 100 ° C, preferably 50 to 80 ° C.

In FIG. 1, a width constraint step is performed in the width constraint portion 70. In the width restricting portion 70 shown in Fig. 1, three free rolls 71, 72, and 73 are provided, and hot air dryers 74, 75, and 76 are disposed so as to face the rolls 71, 72, and 73, respectively. . Each of the hot air dryers 74, 75, and 76 includes a member 74a, 75a, and 76a that is disposed on the line in the width direction from the upstream side in the downstream direction in which the hot air is sent out; and the members 74b and 75b. And 76b, which is disposed on the line in the width direction from the downstream side in which the hot air is sent out from the downstream side. The hot air blown by the hot air dryers 74, 75, and 76 blows the polyvinyl alcohol-based resin film that is in contact with the opposing free rolls 71, 72, and 73 to suppress the drying of the polyvinyl alcohol-based resin film in the width-limiting step. status. The three free rolls 71, 72, 73 are all large diameter free rolls. In the width restricting portion 70 shown in Fig. 1, the point at which the polyvinyl alcohol-based resin film contacts the free roller 71 is the introduction point of the width restricting step, and the point where the free roller 73 is released is the derivation point from the width restricting step.

The configuration of the rolls in the width restricting portion 70 is not limited to the form shown in Fig. 1 . Figure 2~ In Fig. 5, other forms in the width restricting portion 70 are schematically shown. In FIG. 2 to FIG. 5, the transport path of the polyvinyl alcohol-based resin film 10 in the width confinement step is indicated by a solid line, and the transport path of the polyvinyl alcohol-based resin film 10 before and after the width confinement step is indicated by a broken line. The transport direction is indicated by an arrow. Further, similarly to Fig. 1, the guide roller immediately before the introduction of the width restricting step is used as the guide roller 54, and the guide roller immediately after the width restricting step is taken as the guide roller 81. The transport direction of the polyvinyl alcohol-based resin film in the front and rear of the width-constraining step and the width-constraining step is not necessarily the same as the example shown in FIG. 1, but the transport direction can be appropriately adjusted by using a guide roller or the like.

In the example shown in Fig. 2, three free rolls 711, 712, and 713 having a diameter of 300 mm are disposed. The polyvinyl alcohol-based resin film is released from the free roller 711 at P12 after P11 is brought into contact with the free roller 711 and introduced into the width restricting step. Thereafter, the next free roller 712 is contacted at P13, and released by the free roller 712 at P14. Also, the P15 is contacted with the last free roller 713, the P16 is released by the free roller 713, and is derived from the width constraint step. In the example shown in Fig. 2, when the transport speed of the film is set to 10 m/min, the time required for transport between the respective places is P11 to P12 of 2.83 seconds, P12 to P13 is 1.8 seconds, and P13 to P14. The rolls 711, 712, and 713 and the front and rear guide rolls were disposed in a manner of 2.83 seconds, P14 to P15 of 1.8 seconds, and P15 to P16 of 2.83 seconds. In this case, the time required for the width confinement step was 12.09 seconds, wherein the time during which the polyvinyl alcohol-based resin film was in contact with the roll was 8.49 seconds. Therefore, 70% of the time of the width constraint step is in contact with any of the rolls.

In the example shown in Fig. 3, three free rolls 721, 722, and 723 having a diameter of 150 mm are disposed. The polyvinyl alcohol-based resin film is released from the free roller 721 at P22 after the P21 is brought into contact with the free roller 721 and introduced into the width restricting step. Thereafter, the next free roller 722 is contacted at P23, and released by the free roller 722 at P24. Also, the P25 is contacted with the last free roller 723, the P26 is released by the free roller 723, and is derived from the width constraint step. In the example shown in FIG. 3, when the transport speed of the film is set to 10 m/min, the time required for transport between the respective places is 0.9 seconds for P21 to P22, 1.59 seconds for P22 to P23, and P23 to P24. for Each of the rollers 731, 732, and 733 and the front and rear guide rollers were disposed in a manner of 0.38 seconds, P24 to P25 of 1.59 seconds, and P25 to P26 of 0.9 seconds. In this case, the time required for the width confinement step was 5.36 seconds, wherein the time during which the polyvinyl alcohol-based resin film was in contact with the roll was 2.18 seconds. Therefore, 41% of the time of the width constraint step is in contact with any of the rolls.

In the example shown in Fig. 4, two free rolls 731, 733 having a diameter of 120 mm and a free roll 732 having a diameter of 450 mm are disposed. The polyvinyl alcohol-based resin film is released from the free roller 731 at P32 after the P31 is brought into contact with the free roller 731 and introduced into the width restricting step. Thereafter, P33 is brought into contact with the next free roller 732, and P34 is released by the free roller 732. Also, the P35 is contacted with the last free roller 733, the P36 is released by the free roller 733, and is derived from the width constraint step. In the example shown in FIG. 4, when the transport speed of the film is set to 10 m/min, the time required for transport between the respective places is 0.85 seconds for P31 to P32, 0.88 seconds for P32 to P33, and P33 to P34. Each of the rolls 721, 722, and 723 and the front and rear guide rolls were disposed in a manner of 6.36 seconds, P34 to P35 of 0.88 seconds, and P35 to P36 of 0.85 seconds. In this case, the time required for the width confinement step was 9.82 seconds, wherein the time during which the polyvinyl alcohol-based resin film was in contact with the roll was 8.06 seconds. Therefore, 82% of the time of the width constraint step is in contact with any of the rolls.

In the example shown in Fig. 5, a free roller 741 having a diameter of 550 mm is disposed. The polyvinyl alcohol-based resin film is released from the free roller 741 at P42 after being contacted with the free roller 741 and introduced into the width restricting step, and is derived from the width restricting step. In the example shown in Fig. 5, when the transport speed of the film is set to 10 m/min, the free roller 741 and the front and rear guide rollers are disposed such that the time required for the transfer between the respective places is P11 to P42 of 5.18 seconds. . In this case, the roll of the polyvinyl alcohol-based resin film was contacted for a total time of 5.18 seconds as the time indicated by the width restricting step, that is, 100% of the width confinement step.

The width confinement step is preferably carried out immediately after the treatment step of bringing the polyvinyl alcohol-based resin film into contact with the treatment liquid and treating it. In the example of Fig. 1, the step before the width confinement step is followed by a washing step to treat the liquid cleaning treatment liquid. About the width constraint step The treatment liquid which is in contact with the polyvinyl alcohol-based resin film before the step may be the dyeing treatment liquid in the dyeing treatment step, the crosslinking treatment liquid in the crosslinking treatment step, or the treatment of other treatments (complementary color treatment or zinc treatment) described below. liquid. The method of contacting the treatment liquid for the polyvinyl alcohol-based resin film is a conventionally known method such as immersion in a treatment bath, blowing of a treatment liquid by a water sprayer or the like, and application of a treatment liquid.

The polyvinyl alcohol-based resin film is preferably introduced into the width confinement step within 20 seconds after the end of the contact of the treatment liquid in the step immediately before the width confinement step. When the polyvinyl alcohol-based resin film is slowly dried in a state where it is not subjected to the width constraint for a period of more than 20 seconds, the effect of the width-constraining effect cannot be sufficiently exhibited. In addition, the point at which the contact with the treatment liquid in the previous step is completed is the point at which the cleaning bath 19 is pulled out when it is in the example shown in Fig. 1 .

Moreover, the water content of the polyvinyl alcohol-based resin film at the time of introduction into the width-constraining step is preferably 30% by weight or more. When the water content of the polyvinyl alcohol-based resin film is less than 30% by weight, the effect of the width constraint cannot be sufficiently exhibited. Further, in the apparatus shown in Fig. 1, the water content at the time of introduction to the width restricting step can be regarded as the same as the moisture content at the position P1 immediately before introduction to the width restricting portion 70.

In the width confinement step, the maximum temperature at which the polyvinyl alcohol-based resin film reaches is, for example, 30 to 100 ° C, preferably 50 to 80 ° C.

(drying step)

After the width confinement step, a drying step of subjecting the polyvinyl alcohol-based resin film to a drying treatment is performed. The drying step is a step of further reducing the water content of the polyvinyl alcohol-based resin film, for example, a step of lowering the moisture content from 15% by weight or more and less than 30% by weight to a moisture content of less than 15% by weight. The method of the drying treatment may, for example, be a hot air dryer, an infrared heater, or a method in which the drying is carried out in combination.

In the drying step, the maximum temperature at which the polyvinyl alcohol-based resin film reaches is, for example, 30 to 100 ° C, preferably 50 to 90 ° C. The drying step is, for example, 60 to 600 seconds, preferably 120~600 seconds. By the width-constraining step and the drying step as described above, it is possible to efficiently produce a thin-type polarizing film having a desired moisture content while suppressing breakage of the polyvinyl alcohol-based resin film. The thickness of the polarizing film 23 obtained by the above method is, for example, about 5 to 30 μm, and the shrinkage force measured by the following method is, for example, less than 2.70 N.

(Other processing steps for the polyvinyl alcohol resin film)

Processing other than the above processing may be added. Examples of the additional treatment include: immersion treatment (complementing treatment) in an aqueous solution of boric acid-free iodide after the crosslinking treatment step, and immersion treatment in an aqueous solution containing no boric acid and containing zinc chloride or the like ( Zinc treatment).

<Polarizing plate>

The polarizing plate can be obtained by bonding a protective film via an adhesive to at least one surface of the polarizing film manufactured as described above. The protective film may, for example, be a film comprising an ethyl phthalocyanine resin such as triethylene fluorene cellulose or diethyl cerium cellulose; and includes, for example, polyethylene terephthalate or polyethylene naphthalate. A film of a polyester resin of polybutylene terephthalate; a polycarbonate resin film, a cycloolefin resin film; an acrylic resin film; and a film of a chain olefin resin containing a polypropylene resin.

In order to improve the adhesion between the polarizing film and the protective film, the surface of the polarizing film and/or the protective film may be subjected to corona treatment, flame treatment, plasma treatment, ultraviolet irradiation, primer coating treatment, saponification treatment, etc. deal with. Examples of the adhesive for bonding the polarizing film and the protective film include an active energy ray-curable adhesive such as an ultraviolet curable adhesive, or an aqueous solution of a polyvinyl alcohol-based resin, or a crosslinking agent formulated therein. An aqueous solution, such as an aqueous binder of a urethane-based latex adhesive. The ultraviolet curable adhesive may be a mixture of an acrylic compound and a photoradical polymerization initiator, or a mixture of an epoxy compound and a photocationic polymerization initiator. Further, a cationically polymerizable epoxy compound may be used in combination with a radically polymerizable acrylic compound, and a photocationic polymerization initiator and light may be used. A radical polymerization initiator is used as a starter.

[Examples]

Hereinafter, the present invention will be more specifically described by way of examples, but the invention is not limited by the examples. Further, in the following examples, the film thickness and the contraction force were measured by the following methods.

[Measurement of film thickness]

The film thickness of the polarizing film was measured by a contact type film thickness meter (trade name "DIGIMICRO MH-15M" manufactured by Nikon Co., Ltd.). Further, the film thickness of the polarizing film was measured at 15 points in the width direction, and the average value was calculated. The average value is shown in Table 1.

[Measurement of contraction force]

An evaluation sample having a width of 2 mm and a length of 50 mm was cut out by a super-cutting machine (manufactured by Takino Seiki Seisakusho Co., Ltd.) so that the absorption axis direction (extension direction) of the polarizing film became a long axis. The shrinkage force of the obtained short strip-shaped evaluation sample was measured using a thermomechanical analyzer (manufactured by SII NanoTechnology Co., Ltd., type TMA/6100). The measurement was carried out in the following manner: in a constant mode (the distance between the chucks was set to 10 mm), and the test piece was placed in a room at 20 ° C for a sufficient period of time, and the temperature of the sample was set from 20 ° C. The temperature was raised to 80 ° C in 1 minute, and after heating, the temperature in the sample was maintained at 80 ° C. After the temperature was raised for further 4 hours, the contraction force in the longitudinal direction of the test piece was measured in an environment of 80 °C. In this measurement, the static load was set to 0 mN, and the jig was made of a probe made of SUS (Steel Use Stainless).

<Example 1>

A polarizing film was produced using the same apparatus as the polarizing film manufacturing apparatus shown in FIG. As the free rollers 71, 72, and 73 disposed in the width restricting portion 70, a diameter of 300 mm is used. Further, in the drying furnace 90, three hot air dryers of No. 1 to No. 3 were used for drying.

(1) Swelling treatment steps

A polyvinyl alcohol film having a thickness of 30 μm [Kuraray polyvinyl alcohol film VF-PE #3000 manufactured by Kuraray Co., Ltd., a polymerization degree of 2400, a saponification degree of 99.9 mol% or more] was continuously conveyed, and a dry type was used. The uniaxial extension is about 4 times. The obtained stretched polyvinyl alcohol film was continuously unwound while being conveyed by the raw material sheet roll 11, and was placed in a swelling bath 13 containing pure water at 40 ° C to maintain the stretching without loosening the film. The state was immersed for 60 seconds.

(2) Dyeing process steps

Then, the film of the nip roller 51 was immersed in the dye bath 15 of 28 ° C of iodine/potassium iodide/water (weight ratio) of 0.1/5/100 for 60 seconds.

(3) Cross-linking processing steps

Then, in order to carry out the cross-linking treatment for water resistance, the film passing through the nip roller 52 is Immersion in the first crosslinking bath 17 at 68 ° C of potassium iodide/boric acid/water (weight ratio) of 10.5/7.5/100 300 seconds.

(4) Cleaning process steps

The film after the second crosslinking treatment was immersed in a cleaning bath 19 filled with pure water at 5 °C.

(5) Width constraint step

Then, the film after the cleaning process is passed through the width restricting portion 70. The temperature of the hot air blown from the three hot air dryers 74 to 76 in the width restricting portion 70 is as shown in Table 1. In addition, the moisture content of the film immediately before the width constraint portion 70 (position P1) was measured by a moisture content meter (product name: moisture meter IRMA1100, manufactured by CHINO). The results are shown in Table 1. The time taken to remove the film from the cleaning bath 19 to contact the free roller 71 was 12 seconds. Further, the time in which the film is in contact with the first free roller 71 in the width restricting portion 70 to the release of the last free roller 73 (the time of the width restricting step), between the free roller 71 and the free roller 72, and the free roller 72 are measured. The time between the free rolls 73 that is not in contact. The time for the width confinement step was 8.1 seconds, the time during which the film was not in contact with the free roll was 2 seconds or less, and the time required for the film to contact the free rolls 71, 72, 73 with respect to the width confinement step was 78%.

(6) Drying step

The film that has passed through the width restricting portion 70 is passed through a drying furnace 90 to produce a polarizing film. The temperature of the hot air sent out from the three hot air dryers No. 1 to No. 3 in the drying furnace 90 is as shown in Table 1. In addition, the water content of the film immediately before the introduction to the drying furnace 90 (position P3) and immediately after the drying from the drying furnace 90 (position P4) is measured by a water content meter (product name: moisture meter IRMA110, manufactured by CHINO) The measurement was carried out. The results are shown in Table 1.

<Example 2>

The temperature of the hot air sent from the three hot air dryers 74 to 76 in the width restricting portion 70 was as shown in Table 1, and a polarizing film was produced in the same manner as in Example 1. In the same manner as in the first embodiment, the moisture content of the film immediately before introduction to the width restricting portion 70 (position P1), immediately before introduction to the drying furnace 90 (position P3), and immediately after the drying from the drying furnace 90 (position P4) was measured. The results are shown in Table 1.

<Example 3>

The temperature of the hot air sent from the three hot air dryers No. 1 to No. 3 in the drying furnace 90 in the drying step was as shown in Table 1, except that the polarizing was produced in the same manner as in Example 1. membrane. In the same manner as in the first embodiment, the moisture content of the film immediately before the introduction of the width restriction step 70 (position P1), immediately before introduction to the drying furnace 90 (position P3), and immediately after the drying from the drying furnace 90 (position P4) was measured. The results are shown in Table 1.

<Example 4>

The temperature of the hot air sent from the three hot air dryers 74 to 76 in the width restricting unit 70 and the temperature of the hot air sent from the three hot air dryers No. 1 to No. 3 in the drying furnace 90 in the drying step A polarizing film was produced in the same manner as in Example 1 except that the results are shown in Table 1. In the same manner as in the first embodiment, the moisture content of the film immediately before introduction to the width restriction step 7 (position P1), immediately before introduction to the drying furnace (position P3), and immediately after the drying furnace 90 (position P4) was measured. The results are shown in Table 1.

<Example 5>

In the configuration of the width restricting portion 70, the free roller 72 and the hot air dryer 75 opposed thereto are not provided, and the temperature of the hot air sent from the remaining two hot air dryers 74, 76 is as shown in Table 1. A polarizing film was produced in the same manner as in Example 1 except the above. In the same manner as in the first embodiment, the moisture content of the film immediately before introduction to the width restricting portion 70 (position P1), immediately before introduction to the drying furnace 90 (position P3), and immediately after the drying from the drying furnace 90 (position P4) was measured. The results are shown in Table 1. Further, the time in which the inner film of the width restricting portion 70 is in contact with the first free roller 71 to the release of the last free roller 73 (the time of the width restricting step), and the contact between the free roller 71 and the free roller 73 are measured. time. The time for the width confinement step was 6.2 seconds, the time during which the film was not in contact with the free roll was 2 seconds or less, and the time required for the film to contact the free rolls 71, 73 with respect to the width confinement step was 44%.

<Example 6>

A polarizing film was produced in the same manner as in Example 1 except that the three hot air dryers 74 to 76 in the width restricting portion 70 were not used. In the same manner as in the first embodiment, the moisture content of the film immediately before introduction to the width restricting portion 70 (position P1), immediately before introduction to the drying furnace 90 (position P3), and immediately after the drying from the drying furnace 90 (position P4) was measured. The results are shown in Table 1.

<Example 7>

The temperature of the hot air sent from the three hot air dryers 74 to 76 in the width restricting unit 70 and the three hot air dryers No. 1 to No. 3 in the drying furnace 90 in the drying step is set as shown in the table. A polarizing film was produced in the same manner as in Example 1 except for the above. In the same manner as in the first embodiment, the moisture content of the film immediately before introduction to the width restricting portion 70 (position P1), immediately before introduction to the drying furnace 90 (position P3), and immediately after the drying from the drying furnace 90 (position P4) was measured. The results are shown in Table 1.

<Comparative Example 1>

A polarizing film was produced in the same manner as in Example 1 except that the width restricting step (not passing through the width restricting portion 70) was performed. In the same manner as in the first embodiment, the film immediately before being introduced into the main drying furnace 90 (position P3) and immediately after being discharged from the main drying furnace 90 (position P4) was measured. Moisture content. The results are shown in Table 1.

10‧‧‧Material film containing polyvinyl alcohol resin

11‧‧‧ Raw material reel

13‧‧‧Swelling bath

15‧‧‧dye bath

17‧‧‧Cross-link bath

19‧‧‧Clean bath

23‧‧‧ polarizing film

30‧‧‧guide roller

31‧‧‧guide roller

32‧‧‧guide roller

33‧‧‧guide roller

34‧‧‧guide roller

35‧‧‧guide roller

36‧‧‧guide roller

37‧‧‧guide roller

38‧‧‧guide roller

39‧‧‧guide roller

40‧‧‧guide roller

41‧‧‧guide roller

50‧‧‧ nip rollers

51‧‧‧ nip rollers

52‧‧‧ nip rollers

53‧‧‧ nip rollers

54‧‧‧ nip rollers

60‧‧‧guide roller

61‧‧‧guide roller

70‧‧‧Width Constraint

71‧‧‧Free roll

72‧‧‧Free roll

73‧‧‧Free roll

74‧‧‧Hot air dryer

74a‧‧‧Mechanical components of hot air dryer

74b‧‧‧Mechanical components of hot air dryer

75‧‧‧hot air dryer

75a‧‧‧Mechanical components of hot air dryer

75b‧‧‧Mechanical components of hot air dryer

76‧‧‧hot air dryer

76a‧‧‧Mechanical components of hot air dryer

76b‧‧‧Mechanical components of hot air dryer

81‧‧‧guide roller

82‧‧‧ nip rollers

83‧‧‧ nip rollers

90‧‧‧ drying oven

P1‧‧‧ position

P2‧‧‧ position

P3‧‧‧ position

P4‧‧‧ position

Claims (4)

A method for producing a polarizing film, comprising: a width confinement step of contacting a polyvinyl alcohol-based resin film after contacting the treatment liquid with at least one free roller having a diameter of 150 mm or more and restraining in a width direction; and a drying step, After the width confinement step, the polyvinyl alcohol resin film is dried. The method for producing a polarizing film according to claim 1, wherein in the width confinement step, the polyvinyl alcohol resin film is in contact with a plurality of rolls including the free roll, and is contacted from the first roll to the last roll. At least 40% of the time is in contact with any of the rolls. The method for producing a polarizing film according to claim 1 or 2, wherein the polyvinyl alcohol-based resin film is in contact with the first one of the width restricting steps within 20 seconds after the contact with the processing liquid is completed. The method for producing a polarizing film according to claim 1 or 2, wherein the polyvinyl alcohol-based resin film has a water content of 30% by weight or more at the time of contacting the first roll in the width restricting step.