CN113752598A

CN113752598A - Method for producing polarizing film

Info

Publication number: CN113752598A
Application number: CN202110609372.4A
Authority: CN
Inventors: 松久英树; 白川庆一; 北河佑介
Original assignee: Sumitomo Chemical Co Ltd
Current assignee: Sumitomo Chemical Co Ltd
Priority date: 2020-06-04
Filing date: 2021-06-01
Publication date: 2021-12-07
Also published as: TW202200356A; JP2021189387A; KR20210150986A

Abstract

The invention provides a method for manufacturing a polarizing film, which can inhibit the phenomenon of spot defect. The present invention is a method for producing a polarizing film from a polyvinyl alcohol resin film, comprising the steps of: a covering surface forming step of forming a 1 st surface covered with the treatment liquid on the polyvinyl alcohol resin film by attaching the treatment liquid to the polyvinyl alcohol resin film; and an adjustment step of adjusting the amount of the treatment liquid on the 1 st surface, wherein the adjustment step is any of a step of replenishing the treatment liquid on the 1 st surface to maintain a coated state, and a step of removing the treatment liquid from the polyvinyl alcohol-based resin film to adjust the 1 st surface to a state substantially free of droplets of the treatment liquid.

Description

Method for producing polarizing film

Technical Field

The present invention relates to a method for producing a polarizing film by using a polyvinyl alcohol resin film as a polarizing film.

Background

Conventionally, a polarizing film is known which is obtained by adsorbing a dichroic dye such as iodine to a uniaxially stretched polyvinyl alcohol resin film and orienting the resin film. For example, japanese patent application laid-open No. 2001-141926 (patent document 1) discloses that a polarizing film is produced by sequentially performing a dyeing treatment for dyeing a polyvinyl alcohol resin film with a dichroic dye, a crosslinking treatment for treating the polyvinyl alcohol resin film with a crosslinking agent, and a film drying treatment, and further performing a stretching treatment on the polyvinyl alcohol resin film during the production process.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2001-141926

Disclosure of Invention

Problems to be solved by the invention

A polarizing film is industrially produced by applying a production method in which a long polyvinyl alcohol resin film is sequentially immersed in each tank on a transport path of a film included in a polarizing film production apparatus while continuously transporting the film along the transport path, and the above-described dyeing treatment, crosslinking treatment, and the like are performed. The present inventors found that, in the case of manufacturing a polarizing film of high transmittance according to the above-described method, spot defects are visible anywhere in the polarizing film in appearance inspection after the manufacture. Since the spot defect appears as uneven color tone, there is a demand for development of a technique for preventing the spot defect from being formed.

In view of the above circumstances, an object of the present invention is to provide a method for manufacturing a polarizing film in which a phenomenon of forming a spot defect in the polarizing film is suppressed.

Means for solving the problems

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

[ 1 ] A method for producing a polarizing film, which comprises the steps of:

a covering surface forming step of forming a 1 st surface covered with the treatment liquid on the polyvinyl alcohol resin film by attaching the treatment liquid to the polyvinyl alcohol resin film; and

an adjustment step of adjusting the amount of the treatment liquid on the 1 st surface,

the adjusting procedure comprises the following steps:

and a step of replenishing the treatment solution to the 1 st surface to maintain a coated state, or a step of removing the treatment solution from the polyvinyl alcohol-based resin film to adjust the 1 st surface to a state substantially free of droplets of the treatment solution.

[ 2 ] the method for producing a polarizing film according to [ 1 ], wherein the adjusting step is started within 3.1 seconds after the completion of the cover surface forming step.

[ 3 ] the method for producing a polarizing film according to [ 1 ] or [ 2 ], wherein the 1 st surface is maintained in a state of being covered with the treatment liquid at a start time of the adjustment step.

The method for producing a polarizing film according to any one of [ 1 ] to [ 3 ], wherein the polyvinyl alcohol resin film is continuously conveyed at least from a start of the cover surface forming step to an end of the adjusting step.

Effects of the invention

According to the present invention, a polarizing film manufacturing method in which a phenomenon of forming a spot defect in a polarizing film is suppressed can be provided.

Drawings

Fig. 1 is a cross-sectional view schematically showing an example of a polarizing film manufacturing apparatus used in the manufacturing method of the present embodiment.

Description of the reference numerals

10 comprises a raw material film of a polyvinyl alcohol resin, 11 raw material reels, 13 swelling baths, 14 dyeing baths, 15 crosslinking baths, 16 color compensating baths, 17 cleaning baths, 21 drying furnaces, 23 polarizing films, 30-32, 34-36, 38-40, 42-46 guide rollers, 50-52, 53a, 53b, 54-55 clamping rollers and an A adjusting mechanism.

Detailed Description

Hereinafter, a method for producing a polarizing film (hereinafter, also referred to as "the production method of the present embodiment") according to one embodiment of the present invention will be described with reference to the drawings. However, the present invention is not limited to this embodiment.

[ method for producing polarizing film ]

The production method of the present embodiment is a method for producing a polarizing film in which a polarizing film is produced from a polyvinyl alcohol resin film. Specifically, the present invention comprises, in order: a covering surface forming step of forming a 1 st surface covered with the treatment liquid on the polyvinyl alcohol resin film by attaching the treatment liquid to the polyvinyl alcohol resin film; and an adjustment step of adjusting the amount of the treatment liquid on the 1 st surface. In particular, the adjusting step is any of a step of maintaining a coated state by replenishing the treatment liquid to the 1 st surface, and a step of adjusting the 1 st surface to a state substantially free of droplets of the treatment liquid by removing the treatment liquid from the polyvinyl alcohol-based resin film. With such a feature, the production method of the present embodiment can suppress the formation of a spot defect in the polarizing film.

Although the cause of the formation of the spot defect in the polarizing film is not known in detail, the present inventors presume the following cause. That is, in the conventional polarizing film manufacturing method, a treatment liquid is attached to a polyvinyl alcohol resin film (hereinafter also simply referred to as "film") in each treatment step represented by a dyeing step, thereby forming a cover surface covered with the treatment liquid on the film. In this case, when the film is partially broken due to the start of shrinkage of the treatment liquid (refer to き in japanese text: は), that is, the film forms a wet portion and a dry portion, which may result in uneven drying of the treatment liquid. It is estimated that the drying unevenness of the treatment liquid appears as a spot defect in the polarizing film after production.

The present inventors have reached the following solution based on the factors estimated as described above, and have completed the present invention. That is, it is conceivable that, after a covering surface covered with a treatment liquid is formed on a polyvinyl alcohol resin film in a treatment step, the treatment liquid is replenished to the film before the film is formed into a wet part and a dry part due to partial loss of the covering surface; or the treatment liquid is sufficiently removed from the film, and by any of these operations, uneven drying of the treatment liquid in the film can be prevented. In the present specification, the "state where the film is covered with the treatment liquid" means a state where at least one surface of the film is entirely covered with the treatment liquid, and the "state where the entire surface is covered with the treatment liquid" means that a portion covered with the treatment liquid occupies about 90% or more of the area of the film surface in a certain region. The "fixed region" refers to a region from a portion taken out of any one of the treatment baths (i.e., any one of a swelling bath, a dyeing bath, a crosslinking bath, a color compensation bath, and a cleaning bath, which will be described later) to a portion where the treatment liquid is supplemented or removed. The term "partially broken" of the covering surface means that the covering surface is released from being "covered with the treatment liquid" by forming a gap of a predetermined size. The production method of the present embodiment will be specifically described below.

[ polyvinyl alcohol resin film ]

The polarizing film can be obtained by, for example, adsorbing a dichroic dye (iodine, dichroic dye, or the like) to a uniaxially stretched polyvinyl alcohol resin film and orienting the film. The polyvinyl alcohol resin film is a film containing a polyvinyl alcohol resin, and examples thereof include saponified polyvinyl acetate resins. Examples of the polyvinyl acetate resin include polyvinyl acetate which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith (e.g., ethylene-vinyl acetate copolymers). Examples of the other copolymerizable monomer include unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids. The polymerization degree of the polyvinyl alcohol resin is usually about 1000 to 10000, preferably about 1500 to 5000. The saponification degree is usually 85 mol% or more, preferably 90 mol% or more, and more preferably 99 to 100 mol%. These polyvinyl alcohol resins may be modified, and for example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral, or the like modified with aldehydes may be used.

As the polyvinyl alcohol resin film to be used as a starting material in the production method of the present embodiment, an unstretched polyvinyl alcohol resin film (raw material film) having a thickness of 80 μm or less, preferably 60 μm or less, more preferably 45 μm or less, and still more preferably 30 μm or less can be used. Thereby, a thin polarizing film with an increasingly high market demand can be obtained. The width of the raw material film is not particularly limited, and is, for example, 400mm or more and 8000mm or less, and preferably 2000mm or more and 5500mm or less. The thickness of the unstretched polyvinyl alcohol resin film may be 10 μm or more, or 20 μm or more. The raw material film is prepared, for example, in the form of a roll (raw material roll) of a long unstretched polyvinyl alcohol resin film. The unstretched polyvinyl alcohol resin film (raw material film) is usually supplied in the form of a roll film.

The polyvinyl alcohol resin film may be laminated on a base film supporting the polyvinyl alcohol resin film. That is, the polyvinyl alcohol resin film may be prepared as a laminated film of a base film and a polyvinyl alcohol resin film laminated thereon. In this case, the polyvinyl alcohol resin film can be produced, for example, by applying a coating liquid containing a polyvinyl alcohol resin to at least one surface of the base film and then drying the coating liquid.

As the substrate film, for example, a film containing a thermoplastic resin can be used. Specifically, the film is formed of a light-transmitting thermoplastic resin, preferably an optically transparent thermoplastic resin, and examples thereof include polyolefin resins such as chain polyolefin resins (polypropylene resins and the like) and cyclic polyolefin resins (norbornene resins and the like); cellulose resins such as triacetyl cellulose and diacetyl cellulose; polyester resins such as polyethylene terephthalate and polybutylene terephthalate; a polycarbonate-based resin; (meth) acrylic resins such as methyl methacrylate resins; a polystyrene-based resin; a polyvinyl chloride resin; acrylonitrile-butadiene-styrene resins; acrylonitrile-styrene resins; polyvinyl acetate resin; a polyvinylidene chloride resin; a polyamide resin; a polyacetal resin; modified polyphenylene ether resin; a polysulfone-based resin; a polyether sulfone-based resin; a polyarylate-based resin; a polyamide imide resin; polyimide resins, and the like.

[ treatment procedure ]

The production method of the present embodiment is a method for producing a polarizing film in which a polarizing film is produced from a polyvinyl alcohol resin film. Hereinafter, in the present specification, a series of manufacturing steps from a polyvinyl alcohol resin film to a polarizing film production will be described using the term "treatment step". That is, the production method of the present embodiment can produce a polarizing film from a polyvinyl alcohol resin film by performing 1 or more treatment steps. Examples of the 1 or more treatment steps include a swelling step, a dyeing step, a crosslinking step (boric acid step), a color compensating step, and a cleaning step for subjecting the polyvinyl alcohol resin film to various treatments such as swelling, dyeing, crosslinking, color compensating, and cleaning.

Specifically, the swelling step is a step of bringing a swelling solution into contact with the raw material film to perform a swelling treatment. The dyeing step is a step of bringing a dyeing solution into contact with the polyvinyl alcohol resin film after the swelling treatment (hereinafter, also referred to as "swollen film") to perform the dyeing treatment. The crosslinking step (boric acid step) is a step of bringing the crosslinking liquid into contact with the dyed polyvinyl alcohol resin film (hereinafter also referred to as "dyed film") to perform crosslinking treatment. The complementary color step is a step of bringing a complementary color liquid into contact with a crosslinked polyvinyl alcohol resin film (hereinafter also referred to as a "crosslinked film") to perform a color adjustment treatment. The cleaning step is a step of performing a cleaning treatment for removing excess chemical agents such as boric acid and iodine adhered in the crosslinking step, the color correction step, and the like by adhering a cleaning liquid to the polyvinyl alcohol resin film (hereinafter also referred to as a "color correction film") after the color adjustment treatment. The above-mentioned 1 or more treatment steps are not limited to the above-mentioned steps, and may include other steps as long as the effects of the present invention are exhibited. The above-described 1 or more treatment steps may be combined with other steps as appropriate.

The treatment step preferably includes an operation of uniaxially stretching the polyvinyl alcohol resin film before or during any of the steps such as the swelling step. For example, the method may include uniaxially stretching (dry stretching) an unstretched base material film in air or an inert gas, and then sequentially performing a swelling step, a dyeing step, a crosslinking step, a color compensating step, and a washing step. In addition, the swelling step, the dyeing step, the crosslinking step, the color correction step, and the washing step may be performed in this order using an unstretched base material film, and the polyvinyl alcohol resin film may be uniaxially stretched in a wet manner before or during the crosslinking step.

Hereinafter, the manufacturing method according to the present embodiment will be described in detail by way of example with reference to fig. 1. Fig. 1 is a cross-sectional view schematically showing an example of a polarizing film manufacturing apparatus used in the manufacturing method of the present embodiment.

The polarizing film manufacturing apparatus shown in fig. 1 is configured such that a raw material (unstretched) film 10 made of a polyvinyl alcohol resin is continuously unwound from a raw material roll 11, conveyed along a film conveying path, and sequentially passed through a swelling bath (swelling solution contained in a swelling tank) 13, a dyeing bath (dyeing solution contained in a dyeing tank) 14, a crosslinking bath (crosslinking solution contained in a crosslinking tank) 15, a color correction bath (color correction solution contained in a color correction tank) 16, and a cleaning bath (cleaning solution contained in a cleaning tank) 17 provided in the film conveying path, whereby the swelling step, the dyeing step, the crosslinking step, the color correction step, and the cleaning step can be sequentially performed. Then, the raw material (unstretched) film 10 passed through the treatment bath in this order is finally passed through a drying furnace 21, thereby obtaining a polarizing film 23. Then, the polarizing film manufacturing apparatus can convey the polarizing film 23 to the following polarizing plate manufacturing process (process of bonding a protective film to one or both surfaces of the polarizing film 23) as it is, for example. The arrows in fig. 1 indicate the direction of transport of the film. The structure of the cleaning bath 17 will be described later.

In the description of fig. 1, "treatment bath" is a generic term including a swelling bath, a dyeing bath, a crosslinking bath, a color replenishment bath, and a cleaning bath, "treatment solution" is a generic term including a swelling solution, a dyeing solution, a crosslinking solution, a color replenishment solution, and a cleaning solution, "treatment bath" is a generic term including a swelling bath, a dyeing bath, a crosslinking bath, a color replenishment bath, and a cleaning bath. The swelling bath, dyeing bath, crosslinking bath, color complementing bath, and cleaning bath constitute the swelling section, dyeing section, crosslinking section, color complementing section, and cleaning section of the polarizing film manufacturing apparatus, respectively.

Guide rollers 30 to 32, 34 to 36, 38 to 40, 42 to 46 and nip rollers 50 to 52, 53a, 53b, 54 to 55 are disposed at appropriate positions in addition to the above treatment bath, thereby constituting a film transport path of the polarizing film manufacturing apparatus. The guide rollers 30 to 32, 34 to 36, 38 to 40, and 42 to 46 can support the film to be conveyed and can change the film conveying direction. The nip rollers 50 to 52, 53a, 53b, 54 to 55 can press and nip the film conveyed along the film conveying path, and can apply a driving force due to rotation to the film, and can change the film conveying direction. The guide roll and the nip roll may be disposed before and after each treatment bath and in the treatment bath, whereby introduction, immersion, and withdrawal of the film into and from the treatment bath can be performed. For example, by providing 1 or more guide rolls in each treatment bath and carrying the film along these guide rolls, the film can be immersed in each treatment bath.

The polarizing film manufacturing apparatus has nip rollers 50 to 52, 53a, 53b, and 54 disposed before and after each treatment bath. Thus, in any 1 or more treatment baths, it is possible to perform the inter-roll stretching in which the peripheral speed difference is provided between the nip rolls disposed before and after the nip rolls and the longitudinal uniaxial stretching is performed. Hereinafter, each step will be explained.

< swelling step >

The swelling step is performed for the purpose of removing foreign matter on the surface of the raw material film 10, removing a plasticizer in the raw material film 10, imparting dyeability, plasticizing the raw material film 10, and the like. The processing conditions are determined within a range that can achieve the above object and does not cause problems such as extreme dissolution and devitrification of the raw material film 10.

In the swelling step, the raw material film 10 is continuously unwound from the raw material roll 11 and conveyed along the film conveying path, and the raw material film 10 is immersed in the swelling bath 13 for a predetermined time and then drawn out as a swollen film, thereby performing swelling treatment. As the swelling liquid used in the swelling bath, pure water may be used, and an aqueous solution in which boric acid (JP-A-10-153709), a chloride (JP-A-06-281816), an inorganic acid, an inorganic salt, a water-soluble organic solvent, an alcohol, etc. are added in an amount of about 0.01 to 10% by mass may be used.

The temperature of the swelling bath 13 is, for example, about 10 to 70 ℃, preferably about 15 to 50 ℃, and more preferably about 15 to 35 ℃. The dipping time of the raw material film 10 is preferably about 10 to 600 seconds, and more preferably about 15 to 300 seconds.

In the swelling treatment, since the raw material film 10 swells in the width direction, a problem of wrinkles being formed in the swollen film is likely to occur. As 1 method for conveying the swollen film while removing the wrinkles, a known roll having a tenter function or a known tenter can be used. Another method for suppressing the generation of wrinkles is to perform a stretching treatment. For example, the uniaxial stretching treatment may be performed in the swelling bath 13 by utilizing the difference in peripheral speed between the nip roller 50 and the nip roller 51.

In the swelling treatment, since the film swells and expands in the film transport direction, it is preferable to adopt a method of controlling the speed of the nip

rollers

50 and 51 disposed before and after the swelling bath 13, for example, in order to eliminate the slack of the film in the transport direction without actively stretching the raw material film. For the purpose of stabilizing the transport of the film in the swelling bath 13, it is also useful to Control the water flow in the swelling bath 13 with a shower or to use an EPC device (Edge Position Control device: a device for detecting the end of the film and preventing the meandering of the film) in combination.

In the example shown in fig. 1, the swollen film drawn out from the swelling bath 13 passes through the guide roll 32 and the nip roll 51 in this order and is then introduced into the dyeing bath 14.

< dyeing Process >

The dyeing step is performed for the purpose of adsorbing a dichroic dye such as iodine to the swollen polyvinyl alcohol resin film and aligning the resin film. The treatment conditions are determined within a range that can achieve the above object and does not cause extreme problems such as dissolution and devitrification of the film. In the dyeing step, the swollen film after the swelling treatment is carried along a film carrying path constituted by the nip roller 51, the guide rollers 34 to 35, and the nip roller 52, immersed in the dyeing bath 14 for a predetermined time, and then drawn out as a dyed film, whereby the dyeing treatment can be performed. In order to improve the dyeing property of the dichroic dye, the swollen film to be subjected to the dyeing step is preferably a film subjected to at least some uniaxial stretching treatment, and it is preferable to perform the uniaxial stretching treatment at the time of the dyeing treatment instead of the uniaxial stretching treatment before the dyeing treatment, or to perform the uniaxial stretching treatment at the time of the dyeing treatment in addition to the uniaxial stretching treatment before the dyeing treatment.

Iodine is preferably used as the dichroic dye, and as the dyeing liquid used in the dyeing bath 14, for example, an aqueous solution having a concentration of iodine/potassium iodide/water of about 0.003 to 1/about 0.1 to 20/100 in terms of mass ratio can be used. Instead of potassium iodide, other iodides such as zinc iodide may be used, or potassium iodide and other iodides may be used in combination. In addition, compounds other than iodide, for example, boric acid, zinc chloride, cobalt chloride, and the like may be coexistent. The addition of boric acid differs from the crosslinking liquid described later in that it contains a dichroic dye. In the present specification, when the aqueous solution contains the dichroic dye in an amount of about 0.003 parts by mass or more per 100 parts by mass of water, the aqueous solution may be regarded as a dyeing solution. The temperature of the dyeing bath 14 for dipping the swollen membrane is usually about 10 to 45 ℃, preferably 10 to 40 ℃, more preferably 20 to 35 ℃, and the dipping time of the swollen membrane is usually about 20 to 600 seconds, preferably 30 to 300 seconds.

As described above, in the dyeing step, the swelling film may be uniaxially stretched in the dyeing bath 14. The uniaxial stretching of the swollen film can be performed by providing a circumferential speed difference between the nip roll 51 and the nip roll 52 disposed before and after the dyeing bath 14.

In the dyeing process, as in the swelling process, in order to remove wrinkles and convey the polyvinyl alcohol resin film, known rolls having a tenter function may be used as the guide rolls 34, 35, and 36, or a known tenter may be provided. Another method for suppressing the generation of wrinkles is to perform stretching treatment, as in the swelling treatment.

In the example shown in fig. 1, the dyed film drawn out from the dyeing bath 14 passes through the guide roll 36 and the nip roll 52 in this order and is then introduced into the crosslinking bath 15.

< crosslinking step >

The crosslinking step is performed for the purpose of imparting water resistance to the dyed film. The above-mentioned crosslinking step may be carried out 1 or more times. In the crosslinking step, the dyed film conveyed along the film conveying path constituted by the nip roll 52, the guide rolls 38 to 40, and the nip roll 53a is immersed in the crosslinking bath 15 for a predetermined time and then drawn out as a crosslinked film, thereby performing crosslinking treatment.

As the crosslinking liquid, a solution in which a crosslinking agent is dissolved in a solvent can be used. Examples of the crosslinking agent include boric acid, boron compounds such as borax, glyoxal, and glutaraldehyde. These may be used alone or in combination of two or more. As the solvent, for example, water may be used, and an organic solvent having compatibility with water may be further contained. The concentration of the crosslinking agent in the crosslinking liquid is preferably in the range of 0.1 to 15% by mass, more preferably 1 to 12% by mass, but is not limited thereto.

In the crosslinking treatment, if necessary, boric acid may be used in place of boric acid, or boric acid and another crosslinking agent may be used in combination. The temperature of the cross-linking bath for dipping the dyed film is usually about 20 to 85 ℃, preferably 30 to 70 ℃, and the dipping time of the dyed film is usually about 10 to 600 seconds, preferably 20 to 300 seconds. When the polyvinyl alcohol resin film stretched in advance before the swelling treatment is subjected to the dyeing treatment and the crosslinking treatment in this order, the temperature of the crosslinking bath is usually 50 ℃ or higher, preferably 50 to 85 ℃.

The crosslinking treatment may be performed 1 or more times. In this case, the composition and temperature of the crosslinking bath to be used may be the same or different as long as they are within the above-mentioned ranges. Further, the uniaxial stretching treatment may be performed in the crosslinking bath by utilizing the difference in peripheral speed between the nip rollers.

In the crosslinking treatment, as in the swelling treatment, in order to remove wrinkles and convey the polyvinyl alcohol resin film, known rolls having a tentering function may be used as the guide rolls 38, 39, and 40, or a known tenter may be provided. Another method for suppressing the generation of wrinkles is to perform stretching treatment, as in the swelling treatment.

In the example shown in fig. 1, the crosslinked film drawn out from the crosslinking bath 15 passes through the guide roll 40 and the nip roll 53a in this order and is then introduced into the complementary color bath 16.

< color complementing Process >

The complementary color step is performed for the purpose of adjusting the color tone of the crosslinked film. In the color correction step, the cross-linked film conveyed along the film conveying path constituted by the nip roll 53a, the guide rolls 42 to 44, and the nip roll 53b is immersed in the color correction bath 16 for a predetermined time and then drawn out as a color correction film, thereby performing color correction processing. The temperature of the complementary color bath for dipping the crosslinked film is usually about 20 to 65 ℃, and the dipping time of the crosslinked film is usually about 1 to 300 seconds, preferably 2 to 100 seconds.

The uniaxial stretching treatment may be performed in the complementary color bath 16 by the circumferential speed difference between the nip

rollers

53a and 53b arranged before and after the complementary color bath 16. In the example shown in fig. 1, the color correction film drawn out from the complementary color bath 16 is introduced into a cleaning bath 17 used in a cleaning step described below along a film transport path.

< stretching Process >

Here, as described above, the polyvinyl alcohol resin film is preferably subjected to the uniaxial stretching treatment in a wet or dry manner during a series of treatment steps (i.e., before or after any one of 1 or more treatment steps and/or in any 1 or more treatment steps). Specific methods of the uniaxial stretching treatment include, for example, inter-roll stretching in which 2 nip rolls constituting a film transport path (for example, 2 nip rolls disposed before and after a treatment bath) are subjected to longitudinal uniaxial stretching with a circumferential speed difference therebetween, hot roll stretching as described in japanese patent No. 2731813, tenter stretching, and the like, and preferably, inter-roll stretching. The uniaxial stretching step may be performed a plurality of times from a starting material film of the polyvinyl alcohol resin film as a starting material to the obtaining of the polarizing film. The stretching treatment is also effective for suppressing the generation of wrinkles in the film.

The final cumulative stretching ratio of the polarizing film based on the raw material film is usually about 3.5 to 7 times, preferably 4 to 6.5 times. The stretching step may be performed in any treatment step, and when the stretching treatment is performed in 2 or more treatment steps, the stretching treatment may be performed in any treatment step.

< cleaning Process >

In the manufacturing method of the present embodiment, the cleaning step may sequentially include: a covering surface forming step of forming a 1 st surface covered with the treatment liquid on the polyvinyl alcohol resin film by attaching the treatment liquid to the polyvinyl alcohol resin film; and an adjustment step of adjusting the amount of the treatment liquid on the 1 st surface. In particular, the adjusting step may be any of a step of replenishing the treatment liquid to the 1 st surface to maintain a coated state and a step of removing the treatment liquid from the polyvinyl alcohol-based resin film to adjust the 1 st surface to a state substantially free of droplets of the treatment liquid.

The cleaning step is intended to remove excess chemical agents such as boric acid and iodine that have adhered to the film in the crosslinking step, the color-compensating step, and the like. For example, in the cleaning bath 17 of the polarizing film manufacturing apparatus shown in fig. 1, the color correction film after the color compensation step may be subjected to a cleaning process while being conveyed along a film conveying path constituted by guide rollers 45 and 46 (hereinafter, also referred to as "1 st guide roller 45" and "2 nd guide roller 46" respectively) provided in the cleaning bath 17 and 2 nip rollers 53b and 54 (hereinafter, also referred to as "1 st nip roller 53 b" and "2 nd nip roller 54" respectively) arranged before and after the cleaning bath 17. The 1 st nip roller 53b and the 2 nd nip roller 54 each function as a water removal roller, and thereby the excess chemical agent such as boric acid or iodine adhering to the color correction film can be cleaned and removed. As will be described later, the cleaning bath 17 is provided with an adjustment mechanism a for adjusting the amount of the treatment liquid on the 1 st surface of the film, thereby suppressing the formation of a spot defect in the polarizing film.

Here, the film transport path constructed in the cleaning bath 17 shown in fig. 1 has a form in which the film passing through the 2 nd guide roll 46 is pulled out vertically upward from the cleaning bath 17. However, the film transport path is not limited to the above-described form, and may be a form in which the film passed through the 2 nd guide roll 46 is pulled out obliquely upward from the cleaning bath 17. The film drawn out of the cleaning bath 17 by the second guide roll 2 may have a treatment liquid (cleaning liquid) adhered to both surfaces thereof, or may have a treatment liquid (cleaning liquid) adhered to only one surface thereof. In the present specification, when both surfaces of the film are covered with the treatment liquid (cleaning liquid), the both surfaces correspond to "1 st surface", and when one surface of the film is covered with the treatment liquid (cleaning liquid), the one surface corresponds to "1 st surface".

In the above-described washing step, as in the swelling step and the like, for the purpose of conveying the polyvinyl alcohol resin film while removing wrinkles, known rolls having a tenter function may be used as the guide rolls 45 and 46, or a known tenter may be provided. In the cleaning step, stretching treatment may be performed to suppress the occurrence of wrinkles.

As the cleaning liquid used in the cleaning step, water and conventionally known cleaning liquids used for cleaning such a polyvinyl alcohol resin film can be used. The temperature range of the cleaning liquid used in the cleaning step may be the same as that of the conventional one (for example, 2 to 60 ℃). In the case where the cleaning liquid is removed from the film after the cleaning step is completed, for example, a mechanism which has a nip roller 54 and removes the cleaning liquid by blowing air to the film in addition to the nip roller; a blade, a suction roll, a dewatering roll, etc. for removing the liquid in contact with the film.

As one embodiment of the cleaning process, the method sequentially comprises: a covered surface forming step of forming a 1 st surface covered with the cleaning liquid on the polyvinyl alcohol resin film by attaching a treatment liquid (hereinafter, also referred to as "cleaning liquid" in the description of the cleaning step) to the polyvinyl alcohol resin film; and an adjusting step of adjusting the amount of the cleaning liquid on the 1 st surface. The adjusting step may be a step of maintaining a coated state by replenishing the cleaning liquid to the 1 st surface (hereinafter, also referred to as "cleaning step of the 1 st aspect"). As another embodiment of the cleaning step, there may be provided: a covering surface forming step of forming a 1 st surface covered with the cleaning liquid on the polyvinyl alcohol resin film by attaching the cleaning liquid to the polyvinyl alcohol resin film; and an adjusting step of adjusting the amount of the cleaning liquid on the 1 st surface. The adjusting step may be a step of adjusting the 1 st surface to a state substantially free from droplets of the cleaning liquid by removing the cleaning liquid from the polyvinyl alcohol resin film (hereinafter, also referred to as "cleaning step of the 2 nd aspect").

Here, in the manufacturing method of the present embodiment, the cleaning step is not limited to the method (the cleaning step of the 1 st aspect and the cleaning step of the 2 nd aspect) exemplified below as long as the effects of the present invention can be obtained, and all changes can be made within the meaning equivalent to the scope of the claims and within the scope thereof. In the manufacturing method of the present embodiment, the covering surface forming step and the adjusting step included in the cleaning step of the above-described 1 st aspect and the cleaning step of the above-described 2 nd aspect are not limited to the application to the cleaning step, and may be applied to the swelling step, the dyeing step, the crosslinking step, the color compensating step, and the like described above. In these cases, uneven drying of the various treatment liquids due to the swelling liquid, the dyeing liquid, the crosslinking liquid, and the color-compensating liquid can be suppressed, and therefore, the formation of a spot defect can be suppressed, and a polarizing film free from poor observation due to color unevenness can be provided.

When the covering surface forming step and the adjusting step are applied to the swelling step, the dyeing step, the crosslinking step, and the color compensating step, the respective components provided in the cleaning bath in the cleaning step described later may be replaced with the respective components provided in the swelling bath, the dyeing bath, the crosslinking bath, or the color compensating bath corresponding to the respective processes, and the respective processes may be performed after the cleaning liquid is replaced with the swelling liquid, the dyeing liquid, the crosslinking liquid, or the color compensating liquid corresponding to the respective processes.

When the production method of the present embodiment includes a plurality of treatment steps, the method may further include a step of bringing a pretreatment liquid into contact with the polyvinyl alcohol resin film to perform pretreatment (hereinafter also referred to as a "pretreatment step") and a step of removing the pretreatment liquid adhering to the polyvinyl alcohol resin film in the pretreatment step (hereinafter also referred to as a "pretreatment liquid removal step") before the cleaning step is started. In the present specification, the "pretreatment step" may refer to any one of the swelling step, the dyeing step, the crosslinking step, and the color-compensating step before the washing step is started. The "pretreatment liquid removing step" may be a step of removing any of the above-mentioned swelling liquid, dyeing liquid, crosslinking liquid, and color correction liquid by a nip roll, a blade, a mechanism for removing liquid by blowing air, a suction roll, a water removal roll, or the like. The "pretreatment liquid removing step" may refer to, for example, each step of removing any one of the swelling liquid, the dyeing liquid, the crosslinking liquid, and the complementary color liquid by using the nip rolls 51, 52, 53a, and 53b in the polarizing film manufacturing apparatus shown in fig. 1. Hereinafter, the cleaning step of embodiment 1 and the cleaning step of embodiment 2 in the manufacturing method of the present embodiment will be specifically described.

(cleaning step of embodiment 1)

The cleaning step of embodiment 1 includes, as described above, the following steps in order: a covering surface forming step of forming a 1 st surface covered with the cleaning liquid on the polyvinyl alcohol resin film by attaching the cleaning liquid to the polyvinyl alcohol resin film; and an adjusting step of adjusting the amount of the cleaning liquid on the 1 st surface. In particular, the adjusting step is a step of maintaining a coated state by replenishing the cleaning liquid to the 1 st surface. In the cleaning step of embodiment 1, the cleaning bath 17 may perform a cleaning process while conveying the film along the film conveying path constituted by the 1 st guide roller 45, the 2 nd guide roller 46, the 1 st nip roller 53b, and the 2 nd nip roller 54. The cleaning bath 17 may include a shower (not shown) for discharging a cleaning liquid as an adjusting mechanism a for adjusting the amount of the cleaning liquid on the 1 st surface of the film. The shower may be provided at any position as long as the cleaning liquid can be attached to the 1 st surface, or may be provided at a position where the cleaning liquid can be attached to the polyvinyl alcohol resin film present on the roll. In the case where the cleaning liquid is attached to the polyvinyl alcohol resin film existing on the roll, the shower may be connected to the roll. The flow rate of the cleaning liquid discharged from the shower may be appropriately adjusted according to the size of the film.

Covering surface forming process

The covered surface forming step is a step of forming the 1 st surface covered with the cleaning liquid on the film by attaching the cleaning liquid to the polyvinyl alcohol resin film. Specifically, in the cover surface forming step, first, the film (color correction film) drawn out from the complementary color bath 16 is conveyed to the position of the 1 st nip roller 53b along the film conveying path. At the position of the 1 st nip roller 53b, the color replenishment liquid is removed from the film by the action of the 1 st nip roller 53b, and then the film is introduced into the cleaning bath 17. In this case, since the film is substantially free from droplets formed by the color correction liquid, a portion wetted with the color correction liquid and a portion dried are not generated in some cases. Then, the film is immersed in the cleaning liquid in the cleaning bath 17 or adheres to the cleaning liquid in the cleaning bath 17 by passing through the 1 st guide roller 45 and the 2 nd guide roller 46 along the film transport path, and then is pulled out from the cleaning bath 17. Thereby, the 1 st surface covered with the cleaning liquid can be formed on the film.

Adjustment procedure

The adjusting step may include a step of replenishing the cleaning solution to the 1 st surface. Specifically, in the conditioning step, the film drawn out from the cleaning bath 17 is conveyed, and the cleaning liquid is discharged onto the 1 st surface by using a shower, whereby the cleaning liquid can be replenished onto the 1 st surface. In other words, the adjusting step is preferably a step of maintaining the 1 st surface covered with the cleaning liquid by the shower.

Here, the cleaning step of the 1 st aspect may be performed by discharging a cleaning liquid onto the 1 st surface of the film through the guide roller to replenish the 1 st surface with the cleaning liquid.

In the cleaning step of claim 1, it is preferable that the adjusting step is started within 3.1 seconds after the covering surface forming step is completed. Specifically, the adjustment step is preferably started within 3.1 seconds after the end of the covering surface forming step, more preferably within 2.5 seconds after the end of the covering surface forming step, and still more preferably within 2.1 seconds after the end of the covering surface forming step.

In the above-described conditioning step, after the 1 st surface covered with the cleaning liquid is formed, the cleaning liquid may be supplied to the 1 st surface before the wet portion and the dry portion are formed due to the shrinkage of the cleaning liquid. Therefore, drying unevenness may not occur in the film formation. That is, it is preferable that the 1 st surface is maintained in a state of being covered with the cleaning liquid at the start time of the adjustment step. In the present specification, the term "maintaining" the coated state of the 1 st surface means that the portion of the 1 st surface of the film coated with the cleaning solution is about 90% or more of the total area of the 1 st surface.

The film subjected to the adjustment process is conveyed vertically upward along the film conveying path toward the 2 nd nip roller 54. At this time, when the cleaning liquid is discharged from the shower (not shown) to the 2 nd nip roller 54, the film is exposed to the cleaning liquid flowing and falling through the 2 nd nip roller 54, and the 1 st surface is continuously covered with the cleaning liquid. This makes it possible to prevent the film from being unevenly dried.

Finally, after the film reaches the position of the 2 nd nip roller 54 along the film transport path, the cleaning liquid is removed by the 2 nd nip roller 54 functioning. Thus, since the film is substantially free from droplets formed by the cleaning liquid, there is no possibility that a portion wetted with the cleaning liquid and a portion dried with the cleaning liquid are generated, and thus there is no possibility that uneven drying is generated. As described above, the production method of the present embodiment can suppress the formation of spot defects in the polarizing film.

(cleaning step of embodiment 2)

The cleaning step of the 2 nd aspect includes, as described above, the following steps in order: a covered surface forming step of forming a 1 st surface covered with the cleaning liquid on the polyvinyl alcohol resin film by attaching the cleaning liquid to the polyvinyl alcohol resin film; and an adjusting step of adjusting the amount of the cleaning liquid on the 1 st surface. In particular, the adjusting step is a step of adjusting the 1 st surface to a state substantially free from droplets of the cleaning liquid by removing the cleaning liquid from the polyvinyl alcohol resin film. The cleaning step of embodiment 2 may be performed by carrying the film along the film carrying path formed by the 1 st guide roller 45, the 2 nd guide roller 46, the 1 st nip roller 53b, and the 2 nd nip roller 54 of the cleaning bath 17, and simultaneously performing the cleaning process, as in the cleaning step of embodiment 1. On the other hand, in the cleaning step of the 2 nd aspect, the cleaning bath 17 is different from the cleaning step of the 1 st aspect, and as the adjusting means a for adjusting the amount of the cleaning liquid on the 1 st surface of the film, a liquid removing means (not shown) for removing the cleaning liquid from the film during conveyance is provided. Hereinafter, the description of the cleaning step of the 2 nd aspect will not be repeated with respect to the configuration (nip roll, guide roll, etc.) that is repeated with the cleaning step of the 1 st aspect.

Covering surface forming process

The covering surface forming step in the cleaning step of the 2 nd aspect may be the same as the covering surface forming step in the cleaning step of the 1 st aspect. This makes it possible to form the 1 st surface covered with the cleaning liquid on the film.

Adjustment procedure

The adjusting step may include a step of removing the cleaning liquid from the polyvinyl alcohol resin film to adjust the 1 st surface to a state substantially free of droplets of the cleaning liquid. The term "droplets of the cleaning liquid" as used herein means droplets formed by the beginning of shrinkage of the cleaning liquid, and the droplets form wet portions and dry portions. Specifically, in the adjustment step, the film drawn out from the cleaning bath 17 is first conveyed to the position of the liquid removing mechanism. As the liquid removing means, any conventionally known means capable of removing the cleaning liquid from the film may be used, and examples thereof include a water removing roll, a suction roll, a means for removing the liquid by blowing air, a blade for removing the liquid by contacting the film, and the like. The liquid removing means functions at a position of the liquid removing means, whereby the cleaning liquid can be removed from the film so as to be substantially free from the droplets of the cleaning liquid.

Here, in the cleaning step of aspect 2, it is also preferable that the adjusting step is started within 3.1 seconds after the covering surface forming step is completed. Specifically, the adjustment step is preferably started within 3.1 seconds after the end of the covering surface forming step, more preferably within 2.5 seconds after the end of the covering surface forming step, and still more preferably within 2.1 seconds after the end of the covering surface forming step.

In the above-described adjustment step, after the film is formed on the 1 st surface covered with the cleaning liquid, the 1 st surface can be adjusted to a state substantially free from droplets of the cleaning liquid while maintaining the state covered with the cleaning liquid. Therefore, drying unevenness may not occur in the film formation. In the present specification, the "state substantially free of droplets of the cleaning liquid" means a "dry state" in which the cleaning liquid is removed from the film by the liquid removing mechanism so that the film is not unevenly dried.

Thereafter, the film having undergone the adjustment step is conveyed vertically upward along the film conveying path toward the 2 nd nip roller 54, and then the cleaning liquid is further removed by the 2 nd nip roller 54. Therefore, the production method of the present embodiment can suppress the formation of a spot defect in the polarizing film.

As described above, in the cleaning step of the 1 st aspect and the cleaning step of the 2 nd aspect, after the 1 st surface covered with the cleaning liquid is formed, the cleaning liquid is supplied to the 1 st surface before the wetted portion and the dried portion of the film, or the cleaning liquid is sufficiently removed from the film, and the film may be dried unevenly by any of the above operations. This can suppress the formation of spot defects in the polarizing film. The above-described cleaning process can be applied not only as a cleaning process for producing a film classified into a polarizing film having a high transmittance, but also as a cleaning process for a polarizing film having various transmittances.

Here, in the manufacturing method of the present embodiment, the step of bringing the 1 st surface into contact with the surface of the contact body having the surface wetted with the cleaning liquid may be performed not by immersing the film in the cleaning liquid in the cleaning bath or by adhering the cleaning liquid in the cleaning bath to perform the step of forming the covered surface as in the cleaning step of the 1 st aspect and the cleaning step of the 2 nd aspect described above. The contact body may be a guide roller. Specifically, the first surface 1 covered with the cleaning liquid can be formed on the guide roller by keeping the surface of the guide roller wet with the cleaning liquid and bringing the film into contact with the surface of the guide roller.

In the production method of the present embodiment, the covering surface forming step may be performed by a shower that discharges a cleaning liquid to the polyvinyl alcohol resin film. In this case, any of the adjusting steps described in the cleaning step of the 1 st aspect and the cleaning step of the 2 nd aspect can be applied to the adjusting step.

In the manufacturing method of the present embodiment, the adjustment step may be performed by conveying the film subjected to the cover surface forming step to the 2 nd nip roller 54 within a predetermined time (for example, within about 3 seconds) and removing the cleaning liquid by the 2 nd nip roller 54.

< other steps: for example, drying Process >

The manufacturing method of the present embodiment may include steps other than the above-described respective treatment steps. Examples of the other step include a drying step. The drying step is a step of drying the polyvinyl alcohol resin film after the washing step. The drying method in the drying step is not particularly limited, and for example, hot air drying may be performed in the drying furnace 21 shown in fig. 1. In this case, the drying temperature is, for example, about 30 to 100 ℃, and the drying time is, for example, about 30 to 600 seconds. The polyvinyl alcohol resin film may be dried by using a far infrared heater. The polarizing film can be produced as described above. The thickness of the polarizing film is, for example, about 5 to 50 μm.

< evaluation method of Spot Defect >

With respect to the polarizing film obtained by the manufacturing method of the present embodiment, whether or not the phenomenon of forming the spot defect is suppressed can be evaluated by the following method to which a cross transmission test (so-called cross nicol test) is applied. First, a polarizing film was obtained by the above-described production method. 10 specimens for spot defect inspection were obtained by cutting 10 pieces of 150mm × 200 mm-sized cut pieces out of the polarizing film. Then, a polarizing film for superposition (visibility correction monomer transmittance Ty: 43%, visibility correction polarization degree Py: 99.99%) was prepared for the cross nicol prism test on the spot defect inspection sample. Then, the spot defect inspection sample and the polarizing film for superposition were superposed in a crossed nicols state, and the superposed polarizing film was irradiated with a backlight to be visually observed. Then, the spot defect portion on the sample was marked by visual observation using a commercially available oil pen. Finally, the area of the marked portion in the sample is determined, and the area ratio (%) of the spot defect in the sample is calculated. In this case, when the area ratio of the spot defects in the 10 spot defect inspection samples is 10% or less on average, it can be evaluated that the phenomenon of forming spots on the surface of the polarizing film is suppressed. The area ratio is preferably 7% or less on average.

< polarizing film >

With the production method of the present embodiment, a polarizing film in which the formation of red spots on the surface is suppressed can be obtained. The visibility-correcting monomer transmittance Ty of the polarizing film is preferably 43 to 50%, more preferably 43 to 49%, and further preferably 44 to 48% in consideration of the balance with the visibility-correcting polarization degree Py. The visibility correction polarization degree Py is preferably 90.0% or more, and more preferably 98.0% or more at any position in the width direction.

The visibility-correcting individual transmittance (Ty) and the visibility-correcting polarization degree (Py) can be obtained by the following measurement methods. First, the MD transmittance and TD transmittance in the wavelength range of 380 to 780nm were measured for the polarizing film using a spectrophotometer with an integrating sphere ("V7100" manufactured by japan spectro corporation), and the monomer transmittance and degree of polarization at each wavelength were calculated based on the following formulas:

monomer transmittance (%) - (MD + TD)/2

Degree of polarization (%) { (MD-TD)/(MD + TD) } × 100

The "MD transmittance" herein refers to a transmittance when the direction of polarized light emitted from the glan thomson prism is parallel to the transmission axis of the polarizing film sample, and is expressed as "MD" in the above formula. The "TD transmittance" is a transmittance obtained when the direction of polarized light emitted from the grazing thomson prism is perpendicular to the transmission axis of the polarizing film sample, and is expressed as "TD" in the above formula. Then, with respect to the above monomer transmittance and polarization degree, the following were measured in accordance with JIS Z8701: 1999 "color expression method-XYZ color system and X₁₀Y₁₀Z₁₀The visibility correction single transmittance (Ty) and the visibility correction polarization degree (Py) can be obtained by performing visibility correction on the 2-degree field of view (C light source) of the color system ".

The width of the polarizing film is, for example, 50mm or more and 5000mm or less, and preferably 500mm or more and 4000mm or less. The polarizing film may be wound around a winding roll in sequence to be wound into a roll shape, or may be directly supplied to a process for producing a polarizing plate (a process for laminating a protective film or the like on one surface or both surfaces of the polarizing film) without winding.

< polarizing plate >

The polarizing plate can be obtained by bonding a protective film to at least one surface of the polarizing film produced as described above via an adhesive. Examples of the protective film include films containing an acetyl cellulose resin such as triacetyl cellulose and diacetyl cellulose; films comprising polyester resins such as polyethylene terephthalate, polyethylene naphthalate and polybutylene terephthalate; polycarbonate resin films and cycloolefin resin films; an acrylic resin film; a film containing a chain olefin resin such as a polypropylene resin.

In order to improve the adhesiveness between the polarizing film and the protective film, the surface of the polarizing film and/or the protective film to be bonded may be subjected to surface treatment such as corona treatment, flame treatment, plasma treatment, ultraviolet irradiation, primer coating treatment, saponification treatment, or the like. Examples of the adhesive used for bonding the polarizing film and the protective film include an active energy ray-curable adhesive such as an ultraviolet-curable adhesive, an aqueous solution of a polyvinyl alcohol resin, an aqueous solution containing a crosslinking agent, and an aqueous adhesive such as a urethane emulsion adhesive.

Examples

The present invention will be described in further detail with reference to examples, but the present invention is not limited to the examples below. In the following examples, a polarizing film sample having a visibility-correcting monomer transmittance Ty of 45 ± 0.5% was prepared by adjusting the chemical solution concentration in the dyeing bath.

[ example 1 ]

< sample 1 >

(production of polarizing film)

A polarizing film was produced by the following procedure using the polarizing film production apparatus shown in fig. 1. First, a polyvinyl alcohol film (Kuraray vinyl VF-PS #7500, polymerization degree 2400, saponification degree 99.9 mol% or more) having a thickness of 75 μm and a width of 3000mm was immersed in pure water while maintaining a stretched state without relaxing the film, and the film was sufficiently swelled (swelling step). Then, the resultant was immersed in an aqueous solution containing iodine and potassium iodide to be dyed, and simultaneously uniaxially stretched (dyeing step).

The dyed film is subjected to a crosslinking treatment by immersing in an aqueous boric acid solution containing potassium iodide, boric acid and water, and then uniaxially stretched (crosslinking step). Thereafter, the substrate is immersed in the aqueous boric acid solution (color compensation step).

The film subjected to the complementary color step is subjected to a cleaning step in the following procedure. In the cleaning step, the boric acid aqueous solution is first removed from the surface of the film by the 1 st nip roller 53 b. Then, the film is conveyed along the film conveying path, and the cleaning liquid in the cleaning bath 17 is attached to one surface of the film, thereby forming the 1 st surface covered with the cleaning liquid on the one surface (a covered surface forming step).

Then, the film drawn out of the cleaning bath 17 is sprayed with the cleaning liquid over the entire 1 st surface using a shower provided at the position a in fig. 1 (adjustment step). Thereby replenishing the cleaning liquid to the 1 st surface. The film drawn out from the cleaning bath 17 is kept in a state where the 1 st surface is covered with the cleaning liquid before receiving the shower of the cleaning liquid.

Here, the conditioning step was started 1.5 seconds after the completion of the covering surface forming step for sample 1. Thereafter, the cleaning liquid is removed from the film by the 2 nd nip roller 54.

Finally, the above film was dried at 70 ℃ for 3 minutes in a drying process, thereby manufacturing a polarizing film of sample 1.

< sample 2 >

(production of polarizing film)

The polarizing film of sample 2 was manufactured in the same manner as in sample 1, except that the conditioning step was started 2.1 seconds after the end of the cover surface forming step.

< sample 3 >

(production of polarizing film)

The polarizing film of sample 3 was manufactured in the same manner as in sample 1, except that the conditioning step was started 2.5 seconds after the end of the cover surface forming step.

< sample 4 >

(production of polarizing film)

The polarizing film of sample 4 was manufactured in the same manner as in sample 1, except that the conditioning step was started 3.1 seconds after the end of the cover surface forming step.

< sample 5 >

(production of polarizing film)

The polarizing film of sample 5 was produced in the same manner as in sample 1 except that the conditioning step was not performed until the cleaning liquid was removed by the 2 nd nip roller 54 of fig. 1 (4.1 seconds) after the cover surface forming step was completed. In the polarizing film of sample 5, a plurality of portions covered with the cleaning liquid and changed into droplets were present on the film at the time of removing the cleaning liquid by the 2 nd nip roller 54 in fig. 1.

[ evaluation ]

< evaluation of suppression of formation of Spot Defect >

With respect to the polarizing films of the above samples 1 to 5, whether or not the phenomenon of forming a spot defect in the polarizing film was suppressed was evaluated by the above-described method. The results are shown in table 1.

Here, the symbols (AA, a, B, and C) shown in table 1 represent the evaluation results shown below.

AA: no spot defect was observed at all (the area ratio of the spot defect was 0%).

A: although some spot defects were observed, the formation thereof was sufficiently suppressed (the area ratio of the spot defects was more than 0% and 7% or less).

B: although the spot defect was observed, it can be said that the formation thereof was suppressed, and the influence of visibility was estimated to be within an allowable range (the area ratio of the spot defect was more than 7% and 10% or less).

C: a spot defect was observed, and it cannot be said that the formation thereof was suppressed (the area ratio of the spot defect was more than 10%).

< measurement of the ratio of the area covered with the cleaning liquid at the start of the adjustment step >

An image is obtained by imaging the 1 st surface of the film at the start time of the adjustment step, and the ratio (%) of the area covered with the cleaning solution on the 1 st surface in the image is determined. The results are shown in table 1. The image was obtained by taking an image from a position about 1m from the film so as to illuminate the entire width of the film using CANON IXY650 (product name, manufactured by CANON co., ltd.). In the above-described image, the coverage was determined by analyzing the film imaged in an area of 50cm in width x transport length at equal magnification. Since the conditioning step was not performed on the polarizing film of the sample 5, an image was obtained by imaging the film at the position of the 2 nd nip roller 54, and the ratio (%) of the area covered with the cleaning solution on the 1 st surface in the image was obtained.

The polarizing films of samples 1 to 4 are examples, and the polarizing film of sample 5 is a comparative example.

[ TABLE 1 ]

About 1 time from the end of the cover surface forming process to the 2 nd nip roll

The ratio of the area covered with the cleaning liquid at the time of arrival at the 2 nd nip roller 2 is about

According to table 1, the formation of spot defects was suppressed by the polarizing films (sample 1 to sample 4) produced by including the cover surface forming step and the conditioning step in this order according to the present invention. Accordingly, it can be understood that the polarizing film in which the formation of the spot defect is suppressed can be obtained by the production method of the present embodiment. Polarizing plates using such polarizing films are effective for various display devices including liquid crystal display devices.

Claims

1. A method for producing a polarizing film, which comprises producing a polarizing film from a polyvinyl alcohol resin film,

the manufacturing method sequentially comprises the following steps:

the adjusting step is any of a step of maintaining a coated state by replenishing the treatment liquid to the 1 st surface, and a step of adjusting the 1 st surface to a state substantially free of droplets of the treatment liquid by removing the treatment liquid from the polyvinyl alcohol-based resin film.

2. The method for manufacturing a polarizing film according to claim 1,

the adjusting step is started within 3.1 seconds after the covering surface forming step is completed.

3. The method for manufacturing a polarizing film according to claim 1 or 2,

at the start of the adjustment step, the 1 st surface is maintained in a state of being covered with the processing liquid.

4. The polarizing film production method according to any one of claims 1 to 3,

the polyvinyl alcohol resin film is continuously conveyed at least from the start of the covering surface forming step to the end of the conditioning step.