TWI893119B - Method for manufacturing polarizing film - Google Patents

Abstract

This invention provides a method for manufacturing a polarizing film suppressing the formation of spot defects.

The method for manufacturing polarizing film from a polyvinyl alcohol-based resin film contains the following steps in this order:

a coating-surface forming step of forming a first surface coated with the treatment liquid on the polyvinyl alcohol-based resin film by adhering the treatment liquid to the polyvinyl alcohol-based resin film, and

an adjustment step for adjusting the amount of the treatment liquid on the first surface,

wherein, the adjusting step is any one of the steps of: a step of maintaining the state to be covered by supplying the treatment liquid the first surface, or a step of adjust the first surface in a state of substantially absent of droplets of the treatment liquid by removing droplets of the treatment liquid from the polyvinyl alcohol-based resin film.

Description

Polarizing film manufacturing method

The present invention relates to a method for manufacturing a polarizing film made from a polyvinyl alcohol-based resin film.

Polarizing films have long been known, produced by adsorbing and orienting a dichroic dye, such as iodine, onto a uniaxially stretched polyvinyl alcohol resin film. For example, Japanese Patent Application Laid-Open No. 2001-141926 (Patent Document 1) discloses a method of producing a polarizing film by sequentially dyeing the polyvinyl alcohol resin film with a dichroic dye, crosslinking the film with a crosslinking agent, and drying the film, and then stretching the polyvinyl alcohol resin film between these steps.

[Prior Art Literature]

[Patent Literature]

[Patent Document 1] Japanese Patent Application Laid-Open No. 2001-141926

Polarizing film is industrially produced using a method in which a long strip of polyvinyl alcohol-based resin film is continuously conveyed along a film conveyor path within a polarizing film manufacturing apparatus while being sequentially immersed in various tanks within the conveyor path, where dyeing and crosslinking treatments are performed. While producing high-transmittance polarizing film using this method, the inventors discovered that scattered speckle defects were visible on the film during post-production visual inspection. Because these speckle defects can be detected as hue variations, the inventors sought to develop a technology that prevents these defects.

In view of the above facts, the object of the present invention is to provide a method for manufacturing a polarizing film that suppresses the formation of spot defects on the polarizing film.

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

[1] A method for manufacturing a polarizing film, wherein the polarizing film is made from a polyvinyl alcohol resin film and sequentially comprises:

The step of forming a coated surface is performed by allowing the treatment liquid to adhere to the aforementioned polyvinyl alcohol-based resin film, thereby forming a first surface coated with the aforementioned treatment liquid on the aforementioned polyvinyl alcohol-based resin film; and

The adjustment step involves adjusting the amount of the treatment solution mentioned above on page 1;

The conditioning step is either a step of replenishing the treatment liquid on the first surface to maintain the coated state, or a step of removing the treatment liquid from the polyvinyl alcohol-based resin film to condition the first surface to a state substantially free of droplets of the treatment liquid.

[2] The method for manufacturing a polarizing film as described in [1], wherein the adjustment step is started within 3.1 seconds after the completion of the coating surface forming step.

[3] The method for manufacturing a polarizing film as described in [1] or [2], wherein, at the start of the adjustment step, the first surface is maintained in a state of being covered with the treatment liquid.

[4] The method for producing a polarizing film as described in any one of [1] to [3], wherein the polyvinyl alcohol-based resin film is continuously conveyed from at least the start of the coating surface forming step to the end of the adjustment step.

According to the present invention, a method for manufacturing a polarizing film that suppresses the formation of spot defects on the polarizing film can be provided.

10: Film made of polyvinyl alcohol resin

11: Embryonic membrane roll

13: Swelling bath

14: Dye bath

15: Cross-linking bath

16: Color touch up bath

17: Cleansing Bath

21: Drying furnace

23:Polarizing film

30~32,34~36,38~40,42~46: Guide Roller

50~52,53a,53b,54~55: Clamping Roll

A: Adjustment measures

Figure 1 is a cross-sectional view schematically showing an example of a polarizing film manufacturing apparatus used in the manufacturing method according to this embodiment.

The following describes a method for manufacturing a polarizing film according to one embodiment of the present invention (hereinafter also referred to as the "manufacturing method according to this embodiment") with reference to the drawings. However, the present invention is not limited to this embodiment.

[Polarizing film manufacturing method]

The manufacturing method according to this embodiment is a method for producing a polarizing film from a polyvinyl alcohol-based resin film. Specifically, the method sequentially comprises: a coating surface forming step, in which a treatment liquid is adhered to the polyvinyl alcohol-based resin film to form a first surface coated with the treatment liquid; and an adjustment step, in which the amount of the treatment liquid applied to the first surface is adjusted. In particular, the adjustment step is either a step of replenishing the treatment liquid to maintain the first surface in a coated state; or a step of removing the treatment liquid from the polyvinyl alcohol-based resin film to adjust the first surface to a state substantially free of treatment liquid droplets. With these features, the manufacturing method of this embodiment can suppress the formation of spot defects on the polarizing film.

While the details of the factors that cause speckle defects in polarizing films are unclear, the inventors speculate the following factors. Specifically, in conventional polarizing film manufacturing methods, during each treatment step, starting with the dyeing step, a treatment liquid is applied to a polyvinyl alcohol-based resin film (hereinafter simply referred to as the "film"), forming a coating surface coated with the treatment liquid. During this process, if the treatment liquid begins to repel water from the film and a portion of the coating surface is damaged, the film will form wetted and dried areas, sometimes resulting in treatment liquid drying marks. It is speculated that these treatment liquid drying marks manifest as speckle defects in the resulting polarizing film.

Based on the factors speculated above, the inventors of the present invention developed the following solution and finally completed the present invention. That is, they realized that in the treatment step, after the polyvinyl alcohol-based resin film forms a coating surface covered with the treatment liquid, because a portion of the coating surface may be damaged, before the film forms a wetted portion and a dried portion, by either replenishing the treatment liquid to the film or fully removing the treatment liquid from the film, the film does not form drying marks of the treatment liquid. In this specification, the state in which the film is "covered with the treatment liquid" means the state in which at least one side of the film is entirely covered with the treatment liquid, and the so-called "state in which the film is entirely covered with the treatment liquid" means that the area covered with the treatment liquid occupies more than about 90% of the film surface in a certain area. Here, the term "predetermined area" refers to the area from the point of removal from any treatment bath (i.e., any of the swelling baths, dyeing baths, crosslinking baths, touch-up baths, and cleaning baths described below) to the point where the treatment liquid is replenished or removed. Furthermore, the phrase "a portion of the coating surface is damaged" means that a gap of a predetermined size has formed in the coating surface, thereby removing the "coating state" of the treatment liquid. The following describes the manufacturing method of this embodiment in detail.

[Polyvinyl alcohol resin film]

Polarizing films are obtained, for example, by adsorbing a uniaxially stretched polyvinyl alcohol resin film with a directional dichroic pigment (iodine, dichroic dye, etc.). The polyvinyl alcohol resin film refers to a film composed of a polyvinyl alcohol resin, for example, a saponified polyvinyl acetate resin. Examples of polyvinyl acetate resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable with vinyl acetate (for example, ethylene-vinyl acetate copolymers). Examples of other copolymerizable monomers include unsaturated carboxylic acids, alkenes, vinyl ethers, and unsaturated sulfonic acids. The degree of polymerization of polyvinyl alcohol resins is generally about 1,000 to 10,000, preferably about 1,500 to 5,000. The saponification degree is usually above 85 mol%, preferably above 90 mol%, and more preferably 99 to 100 mol%. These polyvinyl alcohol-based resins can be modified. For example, polyvinyl formaldehyde, polyvinyl acetal, and polyvinyl butyral modified with aldehydes can be used.

In the manufacturing method of this embodiment, the starting material for the polyvinyl alcohol-based resin film can be an unstretched polyvinyl alcohol-based resin film (embryo) having a thickness of 80 μm or less, preferably 60 μm or less, more preferably 45 μm or less, and even more preferably 30 μm or less. This allows for the production of polarizing films, which are increasingly in demand in the market. The width of the embryo is not particularly limited; for example, it can be between 400 mm and 8000 mm, preferably between 2000 mm and 5500 mm. The thickness of the unstretched polyvinyl alcohol-based resin film can be between 10 μm and 20 μm or more. The embryo is prepared, for example, as a roll of unstretched polyvinyl alcohol-based resin film (embryo roll). The unstretched polyvinyl alcohol-based resin film (embryo) is typically supplied in roll form.

The polyvinyl alcohol-based resin film can be laminated onto a substrate film supporting the polyvinyl alcohol-based resin film. Specifically, the polyvinyl alcohol-based resin film can be prepared as a laminated film comprising a substrate film and the polyvinyl alcohol-based resin film laminated thereon. The polyvinyl alcohol-based resin film can be produced, for example, by applying a coating liquid containing the polyvinyl alcohol-based resin to at least one surface of a substrate film and then drying the coating liquid.

The substrate film may be, for example, a film made of a thermoplastic resin. Specific examples include light-transmitting thermoplastic resins, preferably films made of optically transparent thermoplastic resins, such as polyolefin resins such as chain polyolefin resins (polypropylene resins, etc.) and cyclic polyolefin resins (norbornene resins, etc.); cellulose resins such as triacetyl cellulose and diacetyl cellulose; polyester resins such as polyethylene terephthalate and polybutylene terephthalate; polycarbonate resins; and Methyl methacrylate resins, (meth)acrylic resins; polystyrene resins; polyvinyl chloride resins; acrylonitrile/butadiene/styrene resins; acrylonitrile/styrene resins; polyvinyl acetate resins; polyvinylidene chloride resins; polyamide resins; polyacetal resins; modified polyphenylene ether resins; polysulfone resins; polyethersulfone resins; polyarylate resins; polyamide-imide resins; polyimide resins, etc.

[Processing steps]

The manufacturing method according to this embodiment is a method for producing a polarizing film from a polyvinyl alcohol-based resin film. Hereinafter, the term "processing step" will be used in this specification to describe the series of manufacturing steps leading up to the production of a polarizing film from a polyvinyl alcohol-based resin film. In other words, the manufacturing method according to this embodiment can produce a polarizing film from a polyvinyl alcohol-based resin film by performing one or more processing steps. The one or more treatment steps mentioned above include, for example, various treatments such as swelling, dyeing, crosslinking, recoloring, and cleaning of the polyvinyl alcohol-based resin film, including a swelling step, a dyeing step, a crosslinking step (boric acid step), a recoloring step, and a cleaning step.

Specifically, the swelling step involves contacting a swelling solution with the embryonic membrane to perform a swelling treatment. The dyeing step involves contacting a dyeing solution with the polyvinyl alcohol-based resin membrane (hereinafter, also referred to as the "swelling membrane") that has undergone the swelling treatment to perform a dyeing treatment. The crosslinking step (boric acid step) involves contacting a crosslinking solution with the polyvinyl alcohol-based resin membrane (hereinafter, also referred to as the "dyed membrane") that has undergone the dyeing treatment to perform a crosslinking treatment. The color-correcting step involves contacting a color-correcting solution with the polyvinyl alcohol-based resin membrane (hereinafter, also referred to as the "crosslinked membrane") that has undergone the crosslinking treatment to perform a color adjustment treatment. Furthermore, the cleaning step involves applying a cleaning solution to the color-corrected polyvinyl alcohol-based resin film (hereinafter also referred to as the "color correction film") to remove excess boric acid, iodine, and other chemicals that have adhered to the film during the crosslinking and color correction steps. The aforementioned one or more treatment steps are not limited to the aforementioned steps and may include other steps as long as they achieve the effects of the present invention. The aforementioned one or more treatment steps may also be appropriately combined with the aforementioned steps and other steps.

The above-mentioned treatment step preferably includes uniaxially stretching the polyvinyl alcohol-based resin membrane before or during any of the above-mentioned swelling steps. For example, an unstretched embryonic membrane is uniaxially stretched in air or an inert gas (dry stretching), followed by a swelling step, a dyeing step, a crosslinking step, a color retouching step, and a washing step. Alternatively, an unstretched embryonic membrane is subjected to a swelling step, a dyeing step, a crosslinking step, a color retouching step, and a washing step, followed by a wet stretching of the polyvinyl alcohol-based resin membrane before or during the crosslinking step.

The following will specifically describe the manufacturing method according to this embodiment, with reference to Figure 1. Figure 1 is a cross-sectional view schematically showing an example of a polarizing film manufacturing apparatus used in the manufacturing method according to this embodiment.

The polarizing film manufacturing apparatus shown in FIG1 is constructed in the following manner: an embryonic (unstretched) membrane 10 made of a polyvinyl alcohol-based resin is continuously rolled out from an embryonic membrane roll 11 and simultaneously transported along a membrane transport path, passing through a swelling bath (swelling liquid contained in a swelling tank) 13, a dyeing bath (dyeing liquid contained in a dyeing tank) 14, a crosslinking bath (crosslinking liquid contained in a crosslinking tank) 15, a color-correcting bath (color-correcting liquid contained in a color-correcting tank) 16, and a cleaning bath (cleaning liquid contained in a cleaning tank) 17 arranged on the membrane transport path, thereby sequentially performing a swelling step, a dyeing step, a crosslinking step, a color-correcting step, and a cleaning step. The unstretched film 10, which has passed through the aforementioned treatment baths, finally passes through a drying furnace 21, thereby obtaining a polarizing film 23. The polarizing film manufacturing apparatus can then directly transport the polarizing film 23 to, for example, the following polarizing plate manufacturing step (the step of laminating a protective film to one or both sides of the polarizing film 23). The arrows in Figure 1 indicate the film transport direction. The structure of the cleaning bath 17 is described below.

In the description of Figure 1, "processing tank" is a collective term encompassing the swelling tank, dyeing tank, crosslinking tank, color-correcting tank, and cleaning tank; "processing liquid" is a collective term encompassing the swelling liquid, dyeing liquid, crosslinking liquid, color-correcting liquid, and cleaning liquid; and "processing bath" is a collective term encompassing the swelling bath, dyeing bath, crosslinking bath, color-correcting bath, and cleaning bath. The swelling bath, dyeing bath, crosslinking bath, color-correcting bath, and cleaning bath respectively constitute the swelling section, dyeing section, crosslinking section, color-correcting section, and cleaning section of the polarizing film manufacturing apparatus described above.

In addition to the aforementioned treatment bath, the film transport path of the polarizing film manufacturing apparatus is comprised of guide rollers 30 to 32, 34 to 36, 38 to 40, 42 to 46, and clamping rollers 50 to 52, 53a, 53b, and 54 to 55 positioned appropriately. Guide rollers 30 to 32, 34 to 36, 38 to 40, and 42 to 46 support the film being transported and change its direction of transport. Clamping rollers 50 to 52, 53a, 53b, and 54 to 55 squeeze and clamp the film being transported along the film transport path, apply a rotational driving force to the film, and change its direction of transport. Guide rollers and clamping rollers can be positioned before, after, and within each treatment bath to facilitate the introduction of the membrane into the treatment bath, as well as its immersion and removal from the treatment bath. For example, one or more guide rollers can be positioned in each treatment bath, and the membrane can be transported along these guide rollers to immerse the membrane in each treatment bath.

The polarizing film manufacturing apparatus employs rollers 50 to 52, 53a, 53b, and 54 positioned before and after each treatment bath. This allows for longitudinal uniaxial stretching in any one or more treatment baths by applying a circumferential speed differential between the rollers positioned before and after the treatment bath. The following describes the steps involved.

<Swelling Step>

The swelling step is performed to remove foreign matter from the surface of the embryonic membrane 10, remove plasticizers from the embryonic membrane 10, impart dyeability, and plasticize the embryonic membrane 10. Treatment conditions are determined to achieve these objectives without causing undesirable conditions such as extreme dissolution and devitrification of the embryonic membrane 10.

The swelling step described above allows the embryonic membrane 10 to be continuously rolled out from the embryonic membrane roll 11 while being transported along the membrane transport path. The embryonic membrane 10 is immersed in the swelling bath 13 for a predetermined period of time and then pulled out as a swollen membrane, thereby performing the swelling treatment. The swelling fluid used in the swelling bath can be pure water or an aqueous solution containing approximately 0.01 to 10% by mass of boric acid (Japanese Patent Application Publication No. 10-153709), chloride (Japanese Patent Application Publication No. 06-281816), inorganic acids, inorganic salts, water-soluble organic solvents, alcohols, or the like.

The temperature of the swelling bath 13 is, for example, approximately 10 to 70°C, preferably approximately 15 to 50°C, and more preferably approximately 15 to 35°C. The immersion time of the embryonic membrane 10 is preferably approximately 10 to 600 seconds, more preferably approximately 15 to 300 seconds.

The aforementioned swelling process, which causes the embryonic membrane 10 to swell in its widthwise direction, can easily lead to wrinkles in the expanded membrane. One method for removing these wrinkles while simultaneously conveying the expanded membrane is to use a conventional width-expanding roller or a conventional width-expanding device. Another method for suppressing wrinkles is to apply a stretching process. For example, a uniaxial stretching process can be applied in the swelling bath 13 by utilizing the circumferential speed difference between the nip rollers 50 and 51.

Since the swelling treatment involves swelling and expansion of the membrane in the direction of transport, and therefore does not actively stretch the embryonic membrane, it is preferable to eliminate any slack in the membrane in the transport direction by, for example, controlling the speed of the rollers 50 and 51 positioned before and after the swelling bath 13. Furthermore, to stabilize the transport of the membrane in the swelling bath 13, a water jet can be used to control the water flow in the swelling bath 13, or an EPC device (Edge Position Control: a device that detects the membrane's edges and prevents it from meandering) can be used in conjunction.

In the example shown in Figure 1, the expanded film drawn from the expanding bath 13 is sequentially passed through the guide roller 32 and the clamping roller 51 and introduced into the dyeing bath 14.

<Dyeing Steps>

The dyeing step is performed to allow the swollen polyvinyl alcohol-based resin film to absorb and orient a dichroic dye, such as iodine, and then align it. Treatment conditions are determined to achieve this objective without causing undesirable conditions such as extreme dissolution and devitrification of the film. The dyeing step can be performed by conveying the swollen film through a film conveying path constructed by nip roller 51, guide rollers 34 and 35, and nip roller 52. The film is immersed in a dye bath 14 for a predetermined period of time and then drawn out as a dyed film. To improve the dyeability of dichroic dyes, the expandable film supplied to the dyeing step is preferably one that has been subjected to at least some degree of uniaxial stretching. It is preferred that the uniaxial stretching be performed during the dyeing process, replacing the uniaxial stretching prior to dyeing, or in addition to the uniaxial stretching prior to dyeing.

Iodine is preferably used as the dichroic pigment. The dyeing solution used in dye bath 14 can be, for example, an aqueous solution having a mass ratio of iodine/potassium iodide/water = approximately 0.003 to 1/approximately 0.1 to 20/100. Other iodides such as zinc iodide can be used in place of potassium iodide, or potassium iodide and other iodides can be used together. Furthermore, compounds other than iodides, such as boric acid, zinc chloride, and cobalt chloride, can be coexisted. The addition of boric acid indicates that the dichroic pigment is present, distinguishing it from the crosslinking solution described below. In this specification, an aqueous solution is considered a dyeing solution if it contains approximately 0.003 parts by mass or more of a dichroic pigment per 100 parts by mass of water. The temperature of the dye bath 14 during immersion of the expandable film is typically between 10 and 45°C, preferably between 10 and 40°C, and more preferably between 20 and 35°C. The immersion time of the expandable film is typically between 20 and 600 seconds, preferably between 30 and 300 seconds.

As described above, during the dyeing step, the expandable film can be uniaxially stretched in the dye bath 14. This uniaxial stretching of the expandable film can be achieved by applying a circumferential speed difference between the nip rollers 51 and 52 disposed before and after the dye bath 14.

In the dyeing process, in order to remove wrinkles and simultaneously transport the polyvinyl alcohol-based resin film, similar to the swelling process, the guide rollers 34, 35, and 36 may be conventionally equipped with a width-expanding device or equipped with conventional width-expanding devices. Another method for suppressing wrinkles is to perform a stretching process, similar to the swelling process.

In the example shown in Figure 1, the dyed film drawn from the dye bath 14 is sequentially passed through the guide roller 36 and the clamping roller 52 and introduced into the crosslinking bath 15.

<Cross-linking step>

The crosslinking step is performed to impart water resistance to the dyed film. This crosslinking step can be performed once or multiple times. The dyed film, which is transported along the film transport path formed by the nip roller 52, guide rollers 38 to 40, and nip roller 53a, is immersed in the crosslinking bath 15 for a predetermined period of time and then pulled out as a crosslinked film for crosslinking.

The crosslinking liquid is a solution of a crosslinking agent dissolved in a solvent. Examples of crosslinking agents include boric acid, boron compounds such as borax, glyoxal, and glutaraldehyde. These agents may be used alone or in combination. The solvent may be water, but may also include a water-miscible organic solvent. The concentration of the crosslinking agent in the crosslinking liquid is not limited thereto, but is preferably in the range of 0.1 to 15 mass %, and more preferably 1 to 12 mass %.

During the crosslinking treatment, other crosslinking agents may be used in place of boric acid, or in combination with other crosslinking agents, as needed. The crosslinking bath temperature for immersion-dyed films is typically between 20 and 85°C, preferably between 30 and 70°C, and the immersion time is typically between 10 and 600 seconds, preferably between 20 and 300 seconds. Furthermore, when dyeing and crosslinking are sequentially performed on pre-stretched polyvinyl alcohol-based resin films before the swelling treatment, the crosslinking bath temperature is typically above 50°C, preferably between 50 and 85°C.

The crosslinking treatment can be performed once or multiple times. The composition and temperature of the crosslinking baths used can be the same or different, as long as they are within the above ranges. Furthermore, uniaxial stretching can be performed in the crosslinking bath by utilizing the difference in peripheral speed between the nip rolls.

During the crosslinking process, similar to the swelling process, to remove wrinkles while conveying the polyvinyl alcohol-based resin film, guide rollers 38, 39, and 40 can be equipped with conventional rolls with a width expansion function, or with conventional width expansion devices. Another method for suppressing wrinkles is to perform a stretching process, similar to the swelling process.

In the example shown in Figure 1, the crosslinked film drawn from the crosslinking bath 15 passes sequentially through the guide roller 40 and the clamping roller 53a and is introduced into the color-correcting bath 16.

<Coloring Steps>

The color correction step is performed to adjust the hue of the crosslinked film. This step involves immersing the crosslinked film, which is conveyed along a film conveying path formed by nip roller 53a, guide rollers 42 to 44, and nip roller 53b, in a color correction bath 16 for a predetermined time. The film is then pulled out as a color correction film for color correction. The temperature of the color correction bath during immersion is typically between 20 and 65°C, and the immersion time is typically between 1 and 300 seconds, preferably between 2 and 100 seconds.

Alternatively, a uniaxial stretching treatment can be applied to the color correction bath 16 by utilizing the circumferential speed difference between the nip rollers 53a and 53b positioned before and after the color correction bath 16. In the example shown in Figure 1, the color correction film drawn from the color correction bath 16 is introduced along a film transport path into the cleaning bath 17 used in the cleaning step described below.

<Extended steps>

As described above, the polyvinyl alcohol-based resin film is preferably subjected to a uniaxial stretching treatment, either wet or dry, between a series of treatment steps (i.e., within one or more treatment steps, before or after any step, and/or within one or more treatment steps). Specific methods of uniaxial stretching include, for example, inter-roll stretching, which applies a circumferential speed difference between two nip rolls forming a film transport path (e.g., two nip rolls positioned before and after the treatment bath) to perform longitudinal uniaxial stretching, hot roll stretching as described in Japanese Patent No. 2731813, and tenter stretching. Inter-roll stretching is preferred. The uniaxial stretching step can be performed multiple times from the embryonic membrane of the polyvinyl alcohol-based resin film used as the starting material to the polarizing film obtained. Stretching is also effective in suppressing the occurrence of wrinkles in the film.

The final cumulative stretch ratio of the polarizing film based on the above-mentioned embryonic membrane is typically around 3.5 to 7 times, preferably 4 to 6.5 times. The stretching step can be performed at any processing step. If stretching is performed in two or more processing steps, stretching can also be performed at any step.

<Cleaning Steps>

In the manufacturing method according to this embodiment, the cleaning step may sequentially include: a coating surface forming step of allowing the treatment liquid to adhere to the polyvinyl alcohol-based resin film to form a first surface coated with the treatment liquid on the polyvinyl alcohol-based resin film; and an adjustment step of adjusting the amount of the treatment liquid on the first surface. In particular, the adjustment step may be either a step of replenishing the treatment liquid to maintain the first surface in a coated state, or a step of removing the treatment liquid from the polyvinyl alcohol-based resin film to adjust the first surface to a state substantially free of treatment liquid droplets.

The purpose of the cleaning step is to remove excess boric acid, iodine, and other chemicals that adhere to the film during the crosslinking and color correction steps. For example, in the cleaning bath 17 of the polarizing film manufacturing apparatus shown in FIG1 , the color correction film after the color correction step is transported along a film transport path formed by guide rollers 45 and 46 (hereinafter referred to as "first guide roller 45" and "second guide roller 46," respectively) disposed within the cleaning bath 17 and two clamping rollers 53b and 54 (hereinafter referred to as "first clamping roller 53b" and "second clamping roller 54," respectively) disposed before and after the cleaning bath 17, while being cleaned. The first and second rollers 53b and 54 serve as dewatering rollers, respectively, to clean and remove excess boric acid, iodine, and other chemicals adhering to the color correction film. Furthermore, the cleaning bath 17, as described below, includes adjustment means A for adjusting the amount of treatment solution applied to the first surface of the film, thereby suppressing the formation of spot defects on the polarizing film.

Here, the membrane transport path constructed in the cleaning bath 17 shown in FIG1 is configured such that the membrane is pulled vertically upward from the cleaning bath 17 via the second guide roller 46. However, the membrane transport path is not limited to this configuration; the membrane may be pulled diagonally upward from the cleaning bath 17 via the second guide roller 46. Furthermore, the membrane pulled from the cleaning bath 17 via the second guide roller 46 may have the treatment liquid (cleaning liquid) attached to both surfaces or only to one surface. In this specification, when both sides of the film are coated with a treatment liquid (cleaning liquid), both sides are referred to as the "first side." When only one side of the film is coated with a treatment liquid (cleaning liquid), only one side is referred to as the "first side."

In the aforementioned cleaning step, similar to the swelling step, to remove wrinkles while conveying the polyvinyl alcohol-based resin film, guide rollers 45 and 46 may be equipped with conventional rolls that have a width expansion function, or with conventional width expansion devices. Furthermore, a stretching treatment may be applied during the cleaning step to suppress the formation of wrinkles.

The cleaning liquid used in the cleaning step can be water or any of the conventional cleaning liquids used for cleaning polyvinyl alcohol-based resin films. The temperature range of the cleaning liquid used in the cleaning step can also be set to the same temperature range as conventionally used (e.g., 2 to 60°C). Furthermore, when removing the cleaning liquid from the film after the cleaning step, the cleaning liquid removal means may include, for example, a nip roller 54. In addition to the nip roller, a means for removing the liquid by blowing air toward the film, a scraper contacting the film, a suction roller, a water removal roller, etc. may also be used.

One aspect of the cleaning step sequentially comprises: a coating surface forming step of allowing a treatment liquid (hereinafter referred to as "cleaning liquid" in the description of the cleaning step) to adhere to the polyvinyl alcohol-based resin film to form a first surface coated with the cleaning liquid on the polyvinyl alcohol-based resin film; and an adjustment step of adjusting the amount of the cleaning liquid on the first surface. The adjustment step may be a step of replenishing the cleaning liquid on the first surface to maintain the coated state (hereinafter referred to as "cleaning step of the first aspect"). Furthermore, another aspect of the cleaning step sequentially comprises: a coating surface forming step of causing the polyvinyl alcohol-based resin film to adhere with a cleaning liquid, thereby forming a first surface coated with the cleaning liquid on the polyvinyl alcohol-based resin film; and an adjustment step of adjusting the amount of the cleaning liquid on the first surface. The adjustment step may be a step of removing the cleaning liquid from the polyvinyl alcohol-based resin film to adjust the first surface to a state substantially free of cleaning liquid droplets (hereinafter also referred to as the "cleaning step of the second aspect").

Here, in the manufacturing method related to this embodiment, the cleaning step is not limited to the methods exemplified below (the cleaning step of the first embodiment and the cleaning step of the second embodiment), as long as the effects of the present invention can be achieved. All modifications can be made within the meaning and scope of the patent application. Furthermore, in the manufacturing method related to this embodiment, the coating surface forming step and the adjustment step included in the cleaning step of the first embodiment and the cleaning step of the second embodiment are not limited to application in the cleaning step, but can be applied to the swelling step, dyeing step, crosslinking step, and color-replenishing step described above. This can suppress drying streaks caused by various treatment solutions such as swelling solutions, dye solutions, crosslinking solutions, and toner solutions, thereby preventing the formation of spot defects. This allows for the provision of polarizing films free of poor visibility caused by hue streaks.

When applying the coating formation and conditioning steps to the aforementioned swelling, dyeing, crosslinking, and touch-up steps, the cleaning bath components in the cleaning step described below can be replaced with the components of the swelling, dyeing, crosslinking, or touch-up bath corresponding to the respective treatment. Furthermore, the cleaning solution can be replaced with the swelling, dyeing, crosslinking, or touch-up solution corresponding to the respective treatment, and the respective treatment can be performed.

When the production method of this embodiment includes multiple treatment steps, prior to the start of the cleaning step, it may further include a step of contacting a pretreatment liquid with the polyvinyl alcohol-based resin film to perform pretreatment (hereinafter also referred to as the "pretreatment step"), and a step of removing the pretreatment liquid adhered to the polyvinyl alcohol-based resin film during the pretreatment step (hereinafter also referred to as the "pretreatment liquid removal step"). In this specification, the term "pretreatment step" may sometimes refer to any of the swelling step, dyeing step, crosslinking step, and color-correcting step before the start of the cleaning step. Furthermore, the term "pre-treatment liquid removal step" sometimes refers to the step of removing any of the aforementioned swelling liquid, dyeing liquid, crosslinking liquid, and toner solution by means of a nip roller, a scraper, air blowing, a suction roller, a water removal roller, or the like. For example, in the polarizing film manufacturing apparatus shown in Figure 1, the "pre-treatment liquid removal step" may refer to the steps of removing any of the swelling liquid, dyeing liquid, crosslinking liquid, and toner solution by using nip rollers 51, 52, 53a, and 53b. The following describes in detail the cleaning steps of the first and second aspects of the manufacturing method according to this embodiment.

(Cleaning step for the first example)

The cleaning process of the first embodiment, as described above, sequentially comprises: a coating surface forming step, in which a treatment liquid is allowed to adhere to the polyvinyl alcohol-based resin film, thereby forming a first surface coated with the cleaning liquid; and an adjustment step, in which the amount of the cleaning liquid on the first surface is adjusted. In particular, the adjustment step involves replenishing the cleaning liquid on the first surface to maintain the coated state. In the cleaning process of the first embodiment, the cleaning bath 17 can transport the film along the film transport path formed by the first guide roller 45, the second guide roller 46, the first clamping roller 53b, and the second clamping roller 54, while simultaneously performing the cleaning process. Furthermore, the cleaning bath 17 may include a water jet (not shown) for dispensing cleaning liquid as adjustment means A for adjusting the amount of cleaning liquid applied to the first surface of the membrane. The water jet can be located at any position, as long as it allows the cleaning liquid to adhere to the first surface, or it can be located at a position where it allows the cleaning liquid to adhere to the polyvinyl alcohol-based resin film on the roller. To allow the cleaning liquid to adhere to the polyvinyl alcohol-based resin film on the roller, the water jet can be connected to the roller. Furthermore, the flow rate of the cleaning liquid dispensed from the water jet can be appropriately adjusted to suit the size of the membrane.

<Coating Surface Formation Step>

The coating surface forming step involves attaching a cleaning liquid to the polyvinyl alcohol-based resin film, thereby forming a first surface coated with the cleaning liquid. Specifically, the coating surface forming step involves first conveying the film (color correction film) drawn from the color correction bath 16 along the film conveying path to the position of the first nip roller 53b. At the first nip roller 53b, the color correction liquid is removed from the film, and the film is then introduced into the cleaning bath 17. At this point, the film is substantially free of droplets of the color correction liquid, and thus has no wetted or dried areas. The film then passes along the film transport path, passing through first and second guide rollers 45 and 46, where it is immersed in the cleaning liquid in cleaning bath 17 or, after adhering to the cleaning liquid in cleaning bath 17, is pulled out of cleaning bath 17. This forms a first surface of the film coated with the cleaning liquid.

Adjustment Steps

The conditioning step can include replenishing the cleaning liquid onto the first surface. Specifically, the conditioning step involves conveying the membrane drawn from the cleaning bath 17 and dispensing the cleaning liquid toward the first surface using a water jet, thereby replenishing the cleaning liquid onto the first surface. In other words, the conditioning step preferably involves maintaining the first surface coated with the cleaning liquid using the water jet.

Here, the cleaning step of the first aspect can also be performed by releasing the cleaning liquid toward the first surface of the membrane on the guide roller, thereby replenishing the cleaning liquid on the first surface.

In the cleaning step of the first aspect, the conditioning step preferably begins within 3.1 seconds after the completion of the coating surface forming step. Specifically, the conditioning step preferably begins within 3.1 seconds after the completion of the coating surface forming step, more preferably within 2.5 seconds after the completion of the coating surface forming step, and even more preferably within 2.1 seconds after the completion of the coating surface forming step.

By performing this conditioning step, after the first surface of the membrane is coated with the cleaning liquid, the cleaning liquid can be replenished on the first surface until the cleaning liquid begins to repel water, forming wet and dry areas. This prevents the formation of dry spots on the membrane. In other words, at the start of the conditioning step, the first surface is preferably coated with the cleaning liquid. In this specification, "maintaining" the first surface coated means that approximately 90% or more of the total area of the first surface of the membrane is covered with the cleaning liquid.

After the conditioning step, the film is conveyed vertically upward along the film conveying path toward the second roller 54. As a water jet (not shown) releases cleaning liquid toward the second roller 54, the film is exposed to the dripping cleaning liquid as it passes through the second roller 54, coating the first surface with the cleaning liquid. This prevents the film from forming dry streaks.

Finally, after the film reaches the second nip roller 54 along the film transport path, the second nip roller 54 removes the cleaning liquid. This ensures that the film is substantially free of cleaning liquid droplets, eliminating the presence of wetted and dried portions. Thus, the formation of dryness lines is eliminated. The manufacturing method of this embodiment can suppress the formation of spot defects on the polarizing film.

(Cleaning step for the second embodiment)

The cleaning step of the second aspect, as described above, sequentially comprises: a coating surface forming step of attaching a cleaning liquid to the polyvinyl alcohol-based resin film to form a first surface coated with the cleaning liquid on the polyvinyl alcohol-based resin film; and an adjustment step of adjusting the amount of the cleaning liquid on the first surface. In particular, the adjustment step is a step of removing the cleaning liquid from the polyvinyl alcohol-based resin film to adjust the first surface to a state substantially free of cleaning liquid droplets. The cleaning step of the second embodiment is similar to the cleaning step of the first embodiment, in that the membrane is transported along the membrane transport path constructed by the first guide roller 45, the second guide roller 46, the first clamping roller 53b, and the second clamping roller 54 of the cleaning bath 17 while being cleaned. However, in the cleaning step of the second embodiment, unlike the cleaning step of the first embodiment, the cleaning bath 17 is equipped with a liquid removal means (not shown) for removing the cleaning liquid from the transported membrane, serving as an adjustment means A for adjusting the amount of cleaning liquid on the first surface of the membrane. The following description of the cleaning step of the second embodiment does not repeat the description of the components (clamping roller, guide roller, etc.) of the cleaning step of the first embodiment.

<Coating Surface Formation Step>

The coating surface forming step in the cleaning step of the second embodiment can be the same as the coating surface forming step in the cleaning step of the first embodiment. This allows the first surface of the membrane to be coated with the cleaning solution.

Adjustment Steps

The conditioning step involves removing the cleaning liquid from the polyvinyl alcohol-based resin film, thereby conditioning the first surface to a state substantially free of cleaning liquid droplets. Here, "cleaning liquid droplets" refer to droplets formed when the cleaning liquid begins to repel water. The formation of these droplets creates wetted and dried areas. Specifically, the conditioning step involves first conveying the film, which has been drawn from the cleaning bath 17, to the position of the liquid removal means. The liquid removal means can be any conventionally known means for removing cleaning liquid from the film, such as a water removal roller, a suction roller, a means for removing liquid by blowing air, or a scraper that contacts the film to remove liquid. In the position of the liquid removal means, the liquid removal means can remove the cleaning liquid from the membrane in a manner that is substantially free of droplets of the cleaning liquid.

In the cleaning step of the second embodiment, the conditioning step preferably begins within 3.1 seconds after the completion of the coating surface forming step. Specifically, the conditioning step preferably begins within 3.1 seconds after the completion of the coating surface forming step, more preferably within 2.5 seconds after the completion of the coating surface forming step, and even more preferably within 2.1 seconds after the completion of the coating surface forming step.

Through this conditioning step, after the membrane forms a first surface coated with the cleaning liquid, while maintaining the cleaning liquid coating, the first surface can be conditioned to be substantially free of cleaning liquid droplets. Consequently, the membrane can be free of drying streaks. In this specification, the phrase "substantially free of" cleaning liquid droplets means that the membrane has been "dried" to the extent that drying streaks do not form, after the cleaning liquid has been removed from the membrane by a liquid removal device.

After the adjustment step, the film is then conveyed vertically upward along the film conveying path toward the second roller 54. The cleaning liquid is then removed by the second roller 54. Therefore, the manufacturing method of this embodiment can suppress the formation of spot defects on the polarizing film.

As described above, in the first and second cleaning steps, after the film forms the first surface coated with the cleaning liquid, before the film forms wetted and dried areas, either the cleaning liquid is replenished on the first surface or the cleaning liquid is fully removed from the film. This prevents the formation of drying lines on the film due to the cleaning liquid. This prevents the formation of spot defects on the polarizing film. Furthermore, the above cleaning step can be applied not only to films classified as high-transmittance polarizing films but also to polarizing films with various transmittances.

Here, in the manufacturing method of this embodiment, the step of contacting the first surface with the surface of a contact body moistened with the cleaning liquid, instead of immersing the membrane in the cleaning liquid in a cleaning bath or allowing the cleaning liquid in the cleaning bath to adhere to the membrane, as in the first and second cleaning steps described above, can be replaced with the step of contacting the first surface with the surface of a contact body moistened with the cleaning liquid. The contact body can be, for example, a guide roller. Specifically, the surface of the guide roller can be maintained moistened with the cleaning liquid, and the membrane can be brought into contact with the surface of the guide roller, thereby forming the first surface coated with the cleaning liquid on the membrane.

In the manufacturing method of this embodiment, the coating surface formation step can also be performed using a water jet that releases a cleaning liquid toward the polyvinyl alcohol-based resin film. In this case, the conditioning step can be applied to either the cleaning step described in the first embodiment or the cleaning step described in the second embodiment.

Furthermore, in the manufacturing method of this embodiment, the aforementioned conditioning step can also be performed by conveying the film, which has undergone the aforementioned coating forming step, to the second nip roller 54 within a specific time (e.g., within approximately 3 seconds), and using the second nip roller 54 to remove the cleaning liquid.

<Other steps: such as drying step>

The manufacturing method of this embodiment may include steps other than the aforementioned processing steps. For example, a drying step is included. The drying step involves drying the polyvinyl alcohol-based resin film after the washing step. The drying method employed in this drying step is not particularly limited, but for example, hot air drying can be performed using the drying oven 21 shown in Figure 1 . The drying temperature is, for example, approximately 30 to 100°C, and the drying time is, for example, approximately 30 to 600 seconds. Drying the polyvinyl alcohol-based resin film can also be performed using a far-infrared heater. Using the above method, a polarizing film can be produced. The thickness of the polarizing film is, for example, approximately 5 to 50 μm.

<Evaluation Method for Spot Defects>

Whether the polarizing film obtained by the manufacturing method of the present embodiment can suppress the formation of spot defects can be evaluated by applying the following method of the orthogonal transmission test (the so-called orthogonal polarization test). First, a polarizing film is obtained by the above-mentioned manufacturing method. By cutting out 10 slices of 150mm×200mm from the above-mentioned polarizing film, 10 samples for spot defect inspection are obtained. Secondly, a stacking polarizing film (sensitivity correction single body transmittance Ty: 43%, sensitivity correction polarization Py: 99.99%) is prepared for the orthogonal polarization test of the above-mentioned spot defect inspection sample. Then, by overlapping the above-mentioned spot defect inspection sample and the stacking polarizing film in the orthogonal polarization state, the same is backlit for visual observation. Next, use a commercially available oil-based marker to mark the visually identified spots on the sample. Finally, calculate the area ratio (%) of the spot defects on the sample by determining the area of the marked spots. If the average spot defect area ratio for the 10 spot defect inspection samples is 10% or less, it can be evaluated that spot formation on the polarizing film surface is suppressed. An average area ratio of 7% or less is optimal.

<Polarizing film>

The manufacturing method of this embodiment can produce a polarizing film with suppressed red spot formation on its surface. The sensitivity correction monomer transmittance Ty of the polarizing film is preferably 43 to 50%, more preferably 43 to 49%, and even more preferably 44 to 48%, considering the balance with the sensitivity correction polarization Py. The sensitivity correction polarization Py is preferably 90.0% or higher, and more preferably 98.0% or higher, at any position along the width direction.

The sensitivity-corrected single transmittance (Ty) and sensitivity-corrected polarization (Py) can be determined using the following measurement methods. First, the MD transmittance and TD transmittance of the polarizing film are measured using a spectrophotometer with an integrating sphere (V7100 manufactured by JASCO Corporation) within the wavelength range of 380 to 780 nm. The values are calculated using the following formula:

Single-body penetration rate (%) = (MD + TD) / 2

Polarization degree (%) = {(MD-TD)/(MD+TD)} × 100

Calculate the monomer transmittance and polarization degree at each wavelength.

Here, "MD transmittance" refers to the transmittance when the direction of polarized light emitted from the Glan-Thompson prism is parallel to the transmission axis of the polarizing film sample, and is represented by "MD" in the above formula. Furthermore, "TD transmittance" refers to the transmittance when the direction of polarized light emitted from the Glan-Thompson prism is perpendicular to the transmission axis of the polarizing film sample, and is represented by "TD" in the above formula. Next, the aforementioned single-element transmittance and polarization are corrected for sensitivity using a two-dimensional field (light source C) according to JIS Z 8701:1999, "Methods of displaying colors— _XYZ colorimetric system and _{X10Y10Z10 colorimetric} system." This yields the sensitivity-corrected single-element transmittance (Ty) and sensitivity-corrected polarization (Py).

The width of the polarizing film is, for example, 50 mm to 5000 mm, preferably 500 mm to 4000 mm. The polarizing film can be wound up on a take-up roller to form a roll, or it can be directly supplied to the polarizing plate manufacturing step (such as laminating a protective film on one or both sides of the polarizing film) without being wound up.

<Polarizing plate>

Polarizing plates can be obtained by laminating a protective film to at least one side of the polarizing film produced as described above, via an adhesive. Examples of protective films include films made of acetylcellulose resins such as triacetylcellulose and diacetylcellulose; films made of polyester resins such as polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate; polycarbonate resin films, cycloolefin resin films; acrylic resin films; and films made of chain olefin resins such as polypropylene resins.

To improve the adhesion between the polarizing film and the protective film, the laminating surface of the polarizing film and/or protective film can be subjected to surface treatments such as corona treatment, flame treatment, plasma treatment, UV irradiation, primer coating, and saponification. Examples of adhesives used for laminating the polarizing film and protective film include UV-curable adhesives, active energy ray-curable adhesives, aqueous solutions of polyvinyl alcohol-based resins or aqueous solutions containing a crosslinking agent, and water-based adhesives such as urethane emulsion adhesives.

[Example]

The present invention is described in more detail below using examples, but the present invention is not limited to the following examples. In the following examples, a sample of a polarizing film with a sensitivity-corrected single-element transmittance Ty of 45±0.5% was produced by adjusting the concentration of the dye bath.

[Example 1]

<Sample 1>

(Polarizing film manufacturing)

Polarizing film production was performed using the polarizing film production apparatus shown in Figure 1, following the following procedure. First, a 75μm-thick, 3000mm-wide polyvinyl alcohol film (KURARAY VINYLON VF-PS #7500, degree of polymerization 2400, saponification degree 99.9 mol% or greater) was directly immersed in pure water while maintaining a firm, stretched state to allow the film to swell fully (swelling step). Next, the film was dyed by immersion in an aqueous solution containing iodine and potassium iodide, while simultaneously undergoing uniaxial stretching (dyeing step).

The dyed membrane is crosslinked by immersing it in an aqueous boric acid solution containing potassium iodide, boric acid, and water, followed by uniaxial stretching (crosslinking step). It is then immersed in the aforementioned aqueous boric acid solution (recoloring step).

After the color-correction step, the membrane is cleaned in the following order. First, the boric acid solution is removed from the membrane surface by the first roller 53b. Then, the membrane is passed along the membrane transport path, allowing the cleaning solution in the cleaning bath 17 to adhere to one side of the membrane, forming a first surface coated with the cleaning solution (coated surface formation step).

Next, the membrane pulled from the cleaning bath 17 is sprayed with cleaning liquid across the entire first surface using the sprayer located at position A in Figure 1 (conditioning step). This replenishes the cleaning liquid onto the first surface. The membrane pulled from the cleaning bath 17 remains coated with the cleaning liquid until the sprayer is fully activated.

For Sample 1, the conditioning step was started 1.5 seconds after the coating formation step. The cleaning solution was then removed from the membrane using the second roller 54.

Finally, in the drying step, the film was dried at 70°C for 3 minutes to produce the polarizing film of Sample 1.

<Sample 2>

(Polarizing film manufacturing)

The polarizing film for Sample 2 was produced using the same method as Sample 1, except that the conditioning step began 2.1 seconds after the coating step.

<Sample 3>

(Polarizing film manufacturing)

The polarizing film for Sample 3 was produced using the same method as Sample 1, except that the conditioning step began 2.5 seconds after the coating step.

<Sample 4>

(Polarizing film manufacturing)

The polarizing film for Sample 4 was produced using the same method as Sample 1, except that the conditioning step began 3.1 seconds after the coating step.

<Sample 5>

(Polarizing film manufacturing)

The polarizing film of Sample 5 was produced using the same method as Sample 1, except that no adjustment step was performed from the time the cleaning solution was removed by the second nip roller 54 in Figure 1 after the coating step (4.1 seconds). In the polarizing film of Sample 5, at the time the cleaning solution was removed by the second nip roller 54 in Figure 1, multiple areas on the film where the cleaning solution coating had transformed into droplets existed.

〔evaluate〕

<Evaluation of Stain Defect Inhibition>

For the polarizing films of Samples 1 to 5, the ability to suppress the formation of spot defects on the polarizing films using the above-mentioned method was evaluated. The results are shown in Table 1.

Here, the symbols (AA, A, B, and C) shown in Table 1 represent the following evaluation results.

AA: No spot defects were observed (the area ratio of spot defects was 0%).

A: Some spot defects were observed, but their formation was sufficiently suppressed (the area ratio of spot defects was between 0% and 7%).

B: Although speckle defects were observed, their formation was suppressed, and the impact on visibility was estimated to be within the acceptable range (the area ratio of speckle defects was 7% or more and 10% or less).

C: Spot defects are observed, and their formation is difficult to suppress (the area ratio of spot defects is 10% or more).

<Measured as the ratio of the area covered by the cleaning liquid at the start of the adjustment step>

An image was taken of the first surface of the film at the start of the conditioning step. The percentage (%) of the area covered by the cleaning solution on the first surface was determined from this image. The results are shown in Table 1. These images were obtained using a CANOX IXY650 (manufactured by CANON Co., Ltd.) from a distance of approximately 1 meter, capturing the entire width of the film. In these images, the coverage was determined by analyzing an area equal to the film width x the transport length of 50 cm at equal magnification. For the polarizing film of Sample 5, since no adjustment step was performed, an image was obtained by photographing the film at the position of the second nip roller 54. The ratio (%) of the area covered with the cleaning solution on the first side in the image was determined.

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

[Table 1]

Table 1 shows that the polarizing films (Samples 1 to 4) manufactured according to the present invention by sequentially including a coating surface forming step and an adjustment step can suppress the formation of speckle defects. Therefore, it can be understood that the manufacturing method of this embodiment can produce a polarizing film in which speckle defect formation is suppressed. Polarizing plates using such polarizing films are effective for various display devices, including liquid crystal displays.

10: Film made of polyvinyl alcohol resin

11: Embryonic membrane roll

13: Swelling bath

14: Dye bath

15: Cross-linking bath

16: Color touch up bath

17: Cleansing Bath

21: Drying furnace

23:Polarizing film

30~32,34~36,38~40,42~46: Guide Roller

50~52,53a,53b,54~55: Clamping Roll

A: Adjustment measures

Claims (5)

A method for manufacturing a polarizing film from a polyvinyl alcohol-based resin film sequentially comprises: a coating surface forming step of allowing a treatment liquid to adhere to the polyvinyl alcohol-based resin film to form a first surface of the polyvinyl alcohol-based resin film coated with the treatment liquid; an adjustment step of adjusting the amount of the treatment liquid on the first surface; the adjustment step comprises replenishing the treatment liquid on the first surface to maintain the coated state. The method for manufacturing a polarizing film as described in claim 1, wherein the adjustment step is started within 3.1 seconds after the completion of the coating surface forming step. The method for manufacturing a polarizing film as described in claim 1 or 2, wherein, at the start of the adjustment step, the first surface is maintained in a state of being covered with the treatment liquid. In the method for producing a polarizing film as described in claim 1 or 2, the polyvinyl alcohol-based resin film is continuously conveyed at least from the start of the coating surface forming step to the end of the adjustment step. The method for producing a polarizing film as described in claim 3, wherein the polyvinyl alcohol-based resin film is continuously conveyed from at least the start of the coating surface forming step to the end of the adjustment step.