JP7599296B2 - Manufacturing method and manufacturing device for polarizing film - Google Patents

Description

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

Polarizing plates are widely used as polarizing elements in image display devices such as liquid crystal display devices. Polarizing plates are generally made by laminating a transparent resin film (such as a protective film) to one or both sides of a polarizing film using an adhesive or the like.

Polarizing films are mainly produced by immersing a raw film made of polyvinyl alcohol resin in a dye bath containing a dichroic dye such as iodine, then immersing it in a crosslinking bath containing a crosslinking agent such as boric acid, and uniaxially stretching the film at one of these stages. There are two types of uniaxial stretching: dry stretching, in which stretching is performed in the air, and wet stretching, in which stretching is performed in a liquid such as the dye bath or crosslinking bath.

Conventionally, in the manufacturing method of polarizing film, efforts have been made to suppress the variation in optical properties in the width direction. JP 2018-32026 A (Patent Document 1) describes a method of suppressing the variation in optical properties in the width direction by irradiating a polyvinyl alcohol-based resin film with electromagnetic waves including infrared rays with an irradiation heat amount that has a distribution in the width direction.

JP 2018-32026 A

The present invention aims to provide a novel method and apparatus for manufacturing polarizing films that can reduce variation in optical properties in the width direction.

The present invention provides a method and an apparatus for producing a polarizing film as described below.
[1] A method for producing a polarizing film from a polyvinyl alcohol-based resin film, comprising the steps of:
The polyvinyl alcohol-based resin film is subjected to a treatment in a treatment liquid.
At least one of the plurality of treatment steps is a multi-stage treatment step including a uniform contact step of contacting the polyvinyl alcohol-based resin film with a uniform amount of treatment liquid over the entire width, and a controlled contact step of contacting the polyvinyl alcohol-based resin film with an amount of the treatment liquid controlled according to a position in the width direction of the entire width,
The method for producing a polarizing film, wherein the treatment liquid used in the multi-stage treatment process contains at least one of a dichroic dye and a boron compound.
[2] The method for producing a polarizing film according to [1], wherein in the multi-stage treatment process, the treatment liquid is a dye liquid, a crosslinking liquid, or a complementary liquid.
[3] The method for producing a polarized film according to [1] or [2], wherein in the adjusting contact step, the polyvinyl alcohol-based resin film is divided into a center portion and both end portions across its entire width, and the amount of the treatment liquid brought into contact with the center portion is adjusted to be greater than the amount of the treatment liquid brought into contact with the both end portions.
[4] The method for producing a polarized film according to [3], wherein in the adjusting and contacting step, the central portion of the polyvinyl alcohol-based resin film occupies 5 to 80% of the entire width.
[5] The method for producing a polarized film according to [3] or [4], wherein in the adjusting contacting step, the treatment liquid is brought into contact with the central portion of the polyvinyl alcohol-based resin film, and the treatment liquid is not brought into contact with both end portions of the polyvinyl alcohol-based resin film.
[6] The method for producing a polarized film according to any one of [1] to [5], wherein the uniform contact step is a step of immersing the polyvinyl alcohol-based resin film in the treatment liquid contained in a treatment tank.
[7] The method for producing a polarized film according to any one of [1] to [6], wherein the conditioning contact step is a step of showering the treatment liquid onto the polyvinyl alcohol-based resin film.
[8] The method for producing a polarized film according to any one of [1] to [9], wherein the polyvinyl alcohol-based resin film has a total width of 400 mm or more and 8,000 mm or less.
[9] A polarizing film manufacturing apparatus for producing a polarizing film from a polyvinyl alcohol-based resin film, comprising:
a plurality of processing sections for contacting the polyvinyl alcohol-based resin film with a processing solution;
At least one of the plurality of treatment sections is a multi-stage treatment section having a uniform contact section for contacting the polyvinyl alcohol-based resin film with a uniform amount of treatment liquid over the entire width, and an adjusted contact section for contacting the polyvinyl alcohol-based resin film with an amount of the treatment liquid adjusted depending on a position in the width direction of the entire width,
The apparatus for producing a polarizing film, wherein the processing liquid used in the multi-stage processing section contains at least one of a dichroic dye and a boron compound.

The present invention provides a method and apparatus for manufacturing a polarizing film that reduces the variation in the optical properties of the polarizing film in the width direction.

1 is a cross-sectional view that illustrates an example of a polarizing film manufacturing method and a polarizing film manufacturing apparatus used in the method according to the present invention. FIG. 2 is a top view of the dyeing section of the production apparatus shown in FIG. 1 . 11 is a cross-sectional view for explaining a method for adjusting the amount of dye liquid sprayed from the shower device. FIG. 1 is a graph plotting the luminosity-corrected polarization degree Py of Examples 1 and 2 and Comparative Example 1. 1 is a graph plotting the luminosity-corrected polarization degree Py of Examples 3 and 4 and Comparative Example 2.

<Method of manufacturing polarizing film>
The present invention relates to a method for producing a polarizing film from a polyvinyl alcohol-based resin film, the method comprising a plurality of treatment steps of contacting the polyvinyl alcohol-based resin film with a treatment liquid, at least one of which is a multi-stage treatment step having a uniform contact step of contacting the polyvinyl alcohol-based resin film with a uniform amount of the treatment liquid over the entire width and an adjusted contact step of contacting the polyvinyl alcohol-based resin film with an amount of the treatment liquid adjusted according to the position in the width direction of the entire width. The treatment liquid used in the multi-stage treatment step contains at least one of a dichroic dye and a boron compound, and is, for example, a dyeing liquid, a crosslinking liquid, a complementary color liquid, or the like.

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

These polyvinyl alcohol resins may be modified, for example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral, etc., modified with aldehydes may also be used.

In the present invention, an unstretched polyvinyl alcohol resin film (raw film) having a thickness of 65 μm or less (for example, 60 μm or less), preferably 50 μm or less, more preferably 35 μm or less, and even more preferably 30 μm or less, is used as the starting material for the manufacture of the polarizing film. This makes it possible to obtain a thin polarizing film, for which market demand is increasing. The width of the raw film is not particularly limited, and is, for example, 400 mm or more and 8000 mm or less, preferably 2000 mm or more and 5500 mm or less. In particular, when the width of the raw film is 2000 mm or more, the properties of the polarizing film in the width direction tend to vary, but the manufacturing method of the present invention can reduce this variation. The raw film is prepared, for example, as a roll (raw roll) of a long unstretched polyvinyl alcohol resin film.

The polyvinyl alcohol-based resin film used in the present invention may be laminated to a substrate film that supports it, that is, the polyvinyl alcohol-based resin film may be prepared as a laminate film of a substrate film and a polyvinyl alcohol-based resin film laminated thereon. In this case, the polyvinyl alcohol-based resin film can be produced, for example, by applying a coating liquid containing a polyvinyl alcohol-based resin to at least one surface of the substrate film and then drying it.

As the substrate film, for example, a film made of a thermoplastic resin can be used. Specific examples include a film made of a thermoplastic resin having translucency, preferably an optically transparent thermoplastic resin, and examples of the film include polyolefin resins such as linear 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; (meth)acrylic resins such as methyl methacrylate 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; polyamideimide resins; polyimide resins, etc.

The polarizing film can be continuously manufactured as a long polarizing film by continuously conveying the long raw film from the raw roll along the film conveying path of the polarizing film manufacturing device, immersing it in a treatment liquid (hereinafter also referred to as a "treatment bath") contained in a treatment tank, withdrawing it, and then drying it. The treatment process is not limited to the method of immersing the film in the treatment bath as long as it is a method of contacting the film with the treatment liquid and treating it, and may be a method of showering the treatment liquid on the film surface. A suitable method of showering the treatment liquid on the film surface is a method of showering the treatment liquid on the film surface. Here, the shower of the treatment liquid means a flow of the treatment liquid sprayed from multiple spray ports, and the treatment liquid may be included intermittently in the flow (for example, in the form of particles or mist) or may be included continuously. A shower device is a device that has multiple spray ports and sprays liquid from them to create a flow of liquid. A shower device is usually used to shower the treatment liquid on the film surface. When the processing step is performed by immersing the film in a processing bath, the number of processing baths used for one processing step is not limited to one, and one processing step may be completed by sequentially immersing the film in two or more processing baths.

Examples of the above-mentioned processing liquid include a swelling liquid, a dyeing liquid, a crosslinking liquid, a color-complementing liquid, and a cleaning liquid. Examples of the above-mentioned processing steps include a swelling step in which a swelling liquid is brought into contact with the raw film to perform a swelling process, a dyeing step in which a dyeing liquid is brought into contact with the film after the swelling process to perform a dyeing process, a crosslinking step in which a crosslinking liquid is brought into contact with the film after the dyeing process to perform a crosslinking process, a color-complementing liquid is brought into contact with the film after the crosslinking process to perform a color adjustment process, and a cleaning step in which a cleaning liquid is brought into contact with the film after the color-complementing process to perform a cleaning process. In addition, between these processing steps (i.e., before or after any one or more processing steps and/or during any one or more processing steps), a uniaxial stretching process is performed in a wet or dry manner. Other processing steps may be added as necessary.

The inventors have come to the present invention based on the discovery that, from the viewpoint of suppressing variation in optical properties in the width direction in a processing step using a processing solution containing at least one of a dichroic dye and a boron compound, a multi-stage processing step having a uniform contact step in which the film is contacted with a uniform processing solution over the entire width, and an adjusted contact step in which the film is contacted with an amount of processing solution adjusted according to the position in the width direction of the entire width is preferable. Examples of processing steps using a processing solution containing at least one of a dichroic dye and a boron compound include a dyeing step, a crosslinking step, and a complementary color step.

Hereinafter, an example of the manufacturing method of the polarizing film according to the present invention will be described with reference to FIG. 1. FIG. 1 is a cross-sectional view showing an example of the manufacturing method of the polarizing film according to the present invention and a polarizing film manufacturing apparatus used therein. The polarizing film manufacturing apparatus shown in FIG. 1 is configured to convey an original (unstretched) film 10 made of a polyvinyl alcohol resin along a film conveying path while continuously unwinding it from an original roll 11, so that the film passes through a swelling bath (swelling liquid contained in a swelling tank) 13, a dyeing bath (dyeing liquid contained in a dyeing tank) 15, a crosslinking bath (crosslinking liquid contained in a crosslinking tank) 17a, a complementary color bath (complementary color liquid contained in a crosslinking tank) 17b, and a cleaning bath (cleaning liquid contained in a cleaning tank) 19 provided on the film conveying path in sequence, and finally pass through a drying oven 21. The obtained polarizing film 23 can be conveyed, for example, directly to the next polarizing plate manufacturing process (a process of laminating a protective film on one or both sides of the polarizing film 23). The arrow in FIG. 1 indicates the conveying direction of the film. A shower device 16 is installed in the dye bath 15, and the film 10 that has passed through the dye bath 15 is then configured to pass through the shower device 16.

In the explanation of FIG. 1, the "treatment tank" is a general term including the swelling tank, dyeing tank, crosslinking tank, complementary color tank, and washing tank, the "treatment liquid" is a general term including the swelling liquid, dyeing liquid, crosslinking liquid, complementary color tank liquid, and washing liquid, and the "treatment bath" is a general term including the swelling bath, dyeing bath, crosslinking bath, complementary color bath, and washing bath. The swelling bath, dyeing bath and shower device, crosslinking bath, complementary color bath, and washing bath respectively constitute the swelling section, dyeing section, crosslinking section, complementary color section, and washing section in the manufacturing apparatus of the present invention.

In the manufacturing apparatus shown in FIG. 1, the dyeing section is configured so that a uniform contact step is performed in the dye bath 15, followed by a conditioning contact step by passing through the shower device 16, thereby performing a multi-stage processing step. In other words, the dyeing section is configured as a multi-stage processing section that includes the dye bath 15, which is a uniform contact section, and the shower device 16, which is a conditioning contact section.

The film transport path of the polarizing film manufacturing device can be constructed by arranging in appropriate positions, in addition to the above-mentioned treatment baths and shower devices, guide rolls 30-35, 37-48, 60, 61 that support the film being transported or can further change the film transport direction, and nip rolls 50-56 that press and clamp the film being transported and can apply a driving force to the film by rotating it or can further change the film transport direction. The guide rolls and nip rolls can be arranged before, after, or within each treatment bath, which allows the film to be introduced into and immersed in the treatment bath and withdrawn from the treatment bath (see Figure 1). For example, one or more guide rolls can be provided in each treatment bath, and the film can be immersed in each treatment bath by transporting the film along these guide rolls.

The polarizing film manufacturing apparatus shown in Figure 1 has nip rolls arranged before and after each treatment bath (nip rolls 50 to 54, 56), which makes it possible to carry out inter-roll stretching in one or more treatment baths, in which longitudinal uniaxial stretching is performed by applying a peripheral speed difference between the nip rolls arranged before and after the treatment bath. Each process will be described below.

(Swelling process)
The swelling process is carried out for the purposes of removing foreign matter on the surface of the raw film 10, removing plasticizers in the raw film 10, imparting ease of dyeing, plasticizing the raw film 10, etc. The treatment conditions are determined within a range in which the purposes can be achieved and in which defects such as extreme dissolution or devitrification of the raw film 10 do not occur.

Referring to FIG. 1, the swelling process can be carried out by continuously unwinding the original film 10 from the original roll 11, transporting the original film 10 along the film transport path, immersing the original film 10 in the swelling bath 13 for a predetermined time, and then pulling it out. In the example of FIG. 1, from the time the original film 10 is unwound until it is immersed in the swelling bath 13, the original film 10 is transported along the film transport path formed by the guide rolls 60, 61 and the nip roll 50. In the swelling process, the original film 10 is transported along the film transport path formed by the guide rolls 30-32 and the nip roll 51.

As the swelling liquid for the swelling bath 13, in addition to pure water, it is also possible to use an aqueous solution containing boric acid (JP Patent Publication No. 10-153709), chlorides (JP Patent Publication No. 06-281816), inorganic acids, inorganic salts, water-soluble organic solvents, alcohols, etc., in an amount of about 0.01 to 10% by mass.

The temperature of the swelling bath 13 is, for example, about 10 to 50°C, preferably about 10 to 40°C, and more preferably about 15 to 30°C. The immersion time of the original film 10 is preferably about 10 to 300 seconds, and more preferably about 20 to 200 seconds. In addition, when the original film 10 is a polyvinyl alcohol resin film that has been stretched in gas in advance, the temperature of the swelling bath 13 is, for example, about 20 to 70°C, and preferably about 30 to 60°C. The immersion time of the original film 10 is preferably about 30 to 300 seconds, and more preferably about 60 to 240 seconds.

In the swelling process, the original film 10 tends to swell in the width direction, which can cause problems such as wrinkles in the film. One method for transporting the film while removing these wrinkles is to use rolls with a width-expanding function, such as expander rolls, spiral rolls, and crown rolls, as the guide rolls 30, 31, and/or 32, or to use other width-expanding devices such as cross guiders, bend bars, and tenter clips. Another method for suppressing the occurrence of wrinkles is to perform a stretching process. For example, a uniaxial stretching process can be performed in the swelling bath 13 by utilizing the difference in peripheral speed between the nip rolls 50 and 51.

During the swelling process, the film also swells and expands in the film transport direction, so if the film is not actively stretched, it is preferable to take measures such as controlling the speed of the nip rolls 50, 51 placed before and after the swelling bath 13 to eliminate slack in the film in the transport direction. In addition, in order to stabilize the film transport in the swelling bath 13, it is also useful to control the water flow in the swelling bath 13 with an underwater shower device or to use an EPC device (Edge Position Control device: a device that detects the edge of the film and prevents the film from meandering) in combination.

In the example shown in FIG. 1, the film pulled out from the swelling bath 13 passes through the guide roll 32, the nip roll 51, and the guide roll 33 in that order before being introduced into the dye bath 15.

(Dyeing process)
The dyeing process is carried out for the purpose of adsorbing and orienting a dichroic dye such as iodine on the polyvinyl alcohol-based resin film after the swelling process. The treatment conditions are determined within a range in which the purpose can be achieved and in which defects such as extreme dissolution or devitrification of the film do not occur. With reference to FIG. 1, the dyeing process can be carried out by conveying the film along a film conveying path constructed by a nip roll 51, guide rolls 33 to 35, and nip rolls 56 and 52, immersing the film after the swelling process in a dye bath 15 (a treatment liquid contained in a dyeing tank) for a predetermined time, and then passing the film through a shower device 16 after being pulled out. In order to enhance the dyeability of the dichroic dye, it is preferable that the film to be subjected to the dyeing process is a film that has been subjected to at least some degree of uniaxial stretching, or it is preferable to perform a uniaxial stretching process during the dyeing process instead of or in addition to the uniaxial stretching process before the dyeing process.

It is preferable to use iodine as the dichroic dye, and the dyeing solution of the dye bath 15 may be, for example, an aqueous solution having a mass ratio of iodine/potassium iodide/water = 0.003-0.3/0.1-10/100. Other iodides such as zinc iodide may be used instead of potassium iodide, or potassium iodide may be used in combination with other iodides. In addition, compounds other than iodides, such as boric acid, zinc chloride, cobalt chloride, etc., may be allowed to coexist. When boric acid is added, it is distinguished from the crosslinking solution described below in that it contains a dichroic dye, and if the aqueous solution contains 0.003 parts by mass or more of dichroic dye per 100 parts by mass of water, it can be considered as a dyeing solution. The temperature of the dye bath 15 when the film is immersed is usually about 10 to 45°C, preferably 10 to 40°C, and more preferably 20 to 35°C, and the immersion time of the film is usually about 30 to 600 seconds, preferably 60 to 300 seconds.

A water-soluble dichroic dye may be used together with iodine as the dichroic pigment, and the dyeing solution of the dye bath 15 may be, for example, an aqueous solution having a mass ratio of dichroic dye/water of about 0.001 to 0.1/100. This dyeing solution may contain dyeing auxiliaries, for example, inorganic salts such as sodium sulfate and surfactants. Only one type of dichroic dye may be used alone, or two or more types of dichroic dyes may be used in combination.

As described above, in the dyeing process, the film can be uniaxially stretched in the dye bath 15. The film can be uniaxially stretched by, for example, creating a difference in peripheral speed between the nip roll 51 and the nip roll 56 arranged before and after the dye bath 15.

In the dyeing process, in order to transport the polyvinyl alcohol-based resin film while removing wrinkles from the film, as in the swelling process, the guide rolls 33, 34, and/or 35 may be rolls with a width-expanding function, such as expander rolls, spiral rolls, or crown rolls, or other width-expanding devices, such as cross guiders, bend bars, or tenter clips. Another means for suppressing the occurrence of wrinkles is to carry out a stretching process, as in the swelling process.

In the example shown in FIG. 1, the film pulled out from the dye bath 15 passes through the shower device 16, and then passes through the nip roll 56, the nip roll 52, and the guide roll 37 in that order before being introduced into the crosslinking bath 17a. Thus, in the example shown in FIG. 1, the dyeing process is a multi-stage process. The details of the multi-stage process will be described later.

(Crosslinking process)
The crosslinking step is a treatment carried out for the purpose of making the film water-resistant by crosslinking. The crosslinking step may be carried out multiple times. With reference to Fig. 1, the crosslinking step can be carried out by conveying the film after the dyeing step along a film conveying path formed by nip rolls 52, guide rolls 37 to 40, and nip roll 53a, immersing the film in a crosslinking bath 17a (a crosslinking liquid contained in a crosslinking tank) for a predetermined time, and then pulling out the film.

The crosslinking liquid may be a solution in which a crosslinking agent is dissolved in a solvent. Examples of crosslinking agents include boron compounds such as boric acid and borax, glyoxal, and glutaraldehyde. These may be used alone or in combination of two or more. The solvent may be, for example, water, but may also contain an organic solvent that is compatible with water. The concentration of the crosslinking agent in the crosslinking solution is not limited to this, but is preferably in the range of 1 to 20% by mass, and more preferably 4 to 15% by mass.

The crosslinking liquid may be an aqueous solution containing, for example, about 1 to 10 parts by mass of boric acid per 100 parts by mass of water. When the dichroic dye used in the dyeing process is iodine, the crosslinking liquid preferably contains an iodide in addition to boric acid, and the amount may be, for example, 1 to 30 parts by mass per 100 parts by mass of water. Examples of iodides include potassium iodide and zinc iodide. Compounds other than iodides, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, and sodium sulfate, may also be present.

In the crosslinking treatment, the concentrations of boric acid and iodide, and the temperature of the crosslinking bath 17 can be appropriately changed depending on the purpose. For example, the solution can be an aqueous solution with a mass ratio of boric acid/iodide/water = 3-10/1-20/100. If necessary, other crosslinking agents may be used instead of boric acid, or boric acid may be used in combination with other crosslinking agents. The temperature of the crosslinking bath 17a when the film is immersed is usually about 50-70°C, preferably 53-65°C, and the immersion time of the film is usually about 10-600 seconds, preferably 20-300 seconds, more preferably 20-200 seconds.

The crosslinking process may be carried out multiple times, usually 2 to 5 times. In this case, the composition and temperature of each crosslinking bath used may be the same or different as long as they are within the above range. In addition, uniaxial stretching can be carried out in the crosslinking bath 17a by utilizing the difference in peripheral speed between the nip roll 52 and the nip roll 53a.

In the crosslinking process, in order to transport the polyvinyl alcohol-based resin film while removing wrinkles from the film, as in the swelling process, the guide rolls 38, 39, 40, 41, 42, 43 and/or 44 may be rolls having a width-widening function, such as expander rolls, spiral rolls, or crown rolls, or other width-widening devices, such as cross guiders, bend bars, or tenter clips. Another means for suppressing the occurrence of wrinkles is to carry out a stretching process, as in the swelling process.

(Complementary color process)
As a complementary color liquid for adjusting the hue, for example, when iodine is used as a dichroic dye in a dyeing solution, a concentration of boric acid/iodide/water = 1 to 5/3 to 30/100 in mass ratio can be used. The temperature of the complementary color bath 17b when the film is immersed is usually about 20 to 65°C, and the immersion time of the film is usually about 1 to 300 seconds, preferably 2 to 100 seconds.

The difference in peripheral speed between nip roll 52 and nip roll 53a can be used to perform uniaxial stretching in crosslinking bath 17a. Also, the difference in peripheral speed between nip roll 53a and nip roll 53b can be used to perform uniaxial stretching in complementary bath 17b.

In the example shown in FIG. 1, the film pulled out from the complementary color bath 17b passes through the guide roll 44 and the nip roll 53b in that order before being introduced into the cleaning bath 19.

(Washing process)
In the example shown in Fig. 1, a cleaning step is included after the crosslinking step. The cleaning treatment is performed for the purpose of removing excess chemicals such as boric acid and iodine attached to the polyvinyl alcohol-based resin film. The cleaning step is performed, for example, by immersing the crosslinked polyvinyl alcohol-based resin film in a cleaning bath 19. Note that the cleaning step can also be performed by showering the film with a cleaning liquid instead of immersing the film in the cleaning bath 19, or by combining immersion in the cleaning bath 19 and showering the film with a cleaning liquid.

Figure 1 shows an example of a cleaning process in which a polyvinyl alcohol resin film is immersed in a cleaning bath 19. The temperature of the cleaning bath 19 during the cleaning process is usually about 2 to 50°C, and the immersion time of the film is usually about 2 to 120 seconds.

In addition, in the cleaning process, in order to transport the polyvinyl alcohol-based resin film while removing wrinkles, the guide rolls 45, 46, 47 and/or 48 may be rolls having a width expanding function, such as expander rolls, spiral rolls, and crown rolls, or other width expanding devices, such as cross guiders, bend bars, and tenter clips. In addition, in the film cleaning process, a stretching process may be performed to suppress the occurrence of wrinkles.

(Stretching process)
As described above, the raw film 10 is uniaxially stretched in a wet or dry manner during the series of processing steps (i.e., before and after any one or more processing steps and/or during any one or more processing steps). Specific methods of uniaxial stretching include, for example, inter-roll stretching in which longitudinal uniaxial stretching is performed with a difference in peripheral speed between two nip rolls (e.g., two nip rolls arranged before and after a processing bath) constituting a film transport path, hot roll stretching as described in Japanese Patent No. 2731813, tenter stretching, etc., and preferably inter-roll stretching. The uniaxial stretching process can be performed multiple times from the raw film 10 to the polarizing film 23. As described above, the stretching process is also advantageous in suppressing the occurrence of wrinkles in the film.

The final cumulative stretch ratio of the polarizing film 23 based on the original film 10 is usually about 4.5 to 7 times, and preferably 5 to 6.5 times. The stretching process may be performed in any of the processing steps, and even if the stretching process is performed in two or more processing steps, the stretching process may be performed in any of the processing steps.

(Drying process)
After the washing step, it is preferable to perform a process of drying the polyvinyl alcohol-based resin film. The drying of the film is not particularly limited, but can be performed using a drying oven 21 as in the example shown in FIG. 1. The drying oven 21 can be equipped with, for example, a hot air dryer. The drying temperature is, for example, about 30 to 100° C., and the drying time is, for example, about 30 to 600 seconds. The process of drying the polyvinyl alcohol-based resin film can also be performed using a far-infrared heater. The thickness of the polarizing film 23 obtained in the above manner is, for example, about 5 to 30 μm.

(Multi-stage processing)
In the polarizing film production apparatus shown in Fig. 1, the dyeing step is a multi-stage treatment step, which includes a uniform contact treatment step in a dye bath 15 and a conditioned contact step in a shower device 16. The dyeing liquid in the dye bath 15 and the dyeing liquid sprayed from the shower device 16 preferably have the same or similar composition. In addition, the temperature of the dyeing liquid sprayed from the shower device 16 is preferably adjusted within the temperature range of the dye bath described above. The dyeing liquid sprayed from the shower device 16 is preferably a dyeing liquid derived from within the dye bath 15, and is preferably collected in the dye bath 15 after being sprayed onto the film.

The shower device 16 is configured to spray an amount of dyeing liquid onto the film being treated that is adjusted according to the widthwise position of the entire width. In this way, the dyeing process is a multi-stage process that has a uniform contact process and an adjusted contact process, so that uneven dyeing in the width direction of the film can be suppressed, and the variation in the optical properties of the resulting polarized film can be reduced.

Figure 2 is a top view of the dyeing section in the polarizing film manufacturing apparatus shown in Figure 1, where the dyeing process is performed. As shown in Figure 2, the film 10 is transported in the direction of the arrow in the figure by the transport guide roll 33. As a result, the film 10 is immersed in the dye bath 15 and then passes through the shower device 16. The shower device 16 consists of two shower bars 16a and 16b arranged to face each other on both sides of the film 10, and each shower bar 16a and 16b has a plurality of shower nozzles 161 arranged in the width direction of the film, and the dyeing liquid is sprayed from each shower nozzle 161. By adjusting the amount of dyeing liquid sprayed from each shower nozzle 161, it is possible to contact the film 10 with an amount of dyeing liquid adjusted according to the position in the width direction of the entire width of the film 10. After passing through the shower device 16, the film 10 is sent to the nip roll 56. The nip roll 56 also functions as a liquid removal means for removing the dyeing liquid attached to the surface of the film 10.

Figure 3 is a cross-sectional view for explaining a method for adjusting the amount of dyeing liquid sprayed from the shower device 16. One method for adjusting the amount of dyeing liquid sprayed from the shower device 16 is to divide the shower nozzles 161 arranged in the width direction of the film 10 into shower nozzles 161a corresponding to the center of the film 10 and shower nozzles 161b corresponding to both ends of the film, and adjust the spray amount of the shower nozzles 161a corresponding to the center of the film 10 and the spray amount of the shower nozzles 161b corresponding to both ends of the film 10.

For example, as shown in FIG. 3, in the shower device 16, the dyeing liquid is sprayed only from the shower nozzle 161a in the portion of the shower nozzle 161 that corresponds to the center of the film 10, and the dyeing liquid is not sprayed from the shower nozzle 161b in the portions that correspond to both ends of the film 10.

The central portion of the film is preferably 5 to 80% of the total width of the film, more preferably 20 to 70%, and even more preferably 40 to 60%. The ratio of the central portion to the total width of the film can be selected depending on the degree of variation in the optical properties to be improved. The two ends of the film are located at both ends of the central portion of the film, and it is preferable that the width of one end is the same as the width of the other end.

One of the reasons for the variation in the optical properties of the polarizing film is believed to be that in each of the above-mentioned processing steps, the processing liquid penetrates more easily from the edge than from the surface of the polyvinyl alcohol-based resin film, resulting in a difference in the amount of processing liquid penetrating between the edge and center, resulting in a difference in the degree of processing. Another reason is believed to be that the thickness varies in the width direction due to stretching, resulting in a difference in the degree of processing in each processing step depending on the thickness. Based on these factors, the polyvinyl alcohol-based resin film is not limited to the method of dividing the film into "edge/center/edge" in the width direction as described above, but may be divided so that there is one or more regions between the edge and center, and an adjustment contact process may be performed in which the amount of dyeing liquid contacted in each region is adjusted.

The order of the uniform contact step and the conditioning contact step in the multi-stage processing step is not limited. Therefore, the position of the shower device is not limited to the outlet side of the dye bath 15 as shown in FIG. 1, but may be the inlet side, or may be provided on both the inlet side and the outlet side. Furthermore, in a configuration in which the shower device is provided on the outlet side, the shower device may be provided upstream or downstream of the nip roll 56, which is also a liquid removal means. From the viewpoint of showering a specific area, it may be provided downstream of the nip roll 56, which is a liquid removal means. Also, from the viewpoint of preventing the formation of a clear boundary in the optical properties between two areas with different amounts of dyeing liquid contact, it may be provided upstream of the nip roll 56, which is a liquid removal means, and the conditioning contact step may be performed in a state in which the dyeing liquid remains on the film surface immediately after immersion.

The shower may be applied to both surfaces of the film, or only one surface. When showering a film transported in a direction having a predetermined angle with respect to the vertical direction, that is, when showering a film transported in a state in which both sides of the film can be distinguished into an upper side and a lower side with respect to the vertical direction, it is preferable to shower at least the upper side of the film from the viewpoint of liquid cutting and uniformity. In the showering region, the total amount of the shower applied per unit area of the film is, for example, 0.05 to 20 L/ ^m2 , and preferably 0.1 to 10 L/ ^m2 . The total amount of the shower applied to the film can be adjusted by adjusting the amount of treatment liquid sprayed from the shower device, adjusting the film transport speed, etc.

As a means for removing the dyeing liquid from the surface of the film, in addition to the nip roll 56 shown in FIG. 1, a means for blowing air onto the film to remove the liquid, a scraper that comes into contact with the film to remove the liquid, etc. may also be used.

It is preferable that at least one of the dyeing step, crosslinking step, and color-complementing step is a multi-stage processing step, and all of the dyeing step, crosslinking step, and color-complementing step may be multi-stage processing steps. When the crosslinking step and/or color-complementing step are multi-stage processing steps, the crosslinking section and color-complementing section may have the same configuration as the dyeing section described above. When the processing step to which the multi-stage processing step is applied is configured to sequentially immerse the film in two or more processing baths, it is sufficient that a shower device is installed in one of the processing baths.

The multi-stage processing step is not limited to the dyeing step, crosslinking step, and color complementing step, and the cleaning step may be a multi-stage processing step. When the cleaning step is a multi-stage processing step, it is preferable that the adjustment contact step is adjusted so that the amount of cleaning liquid brought into contact with both ends of the film is greater than the amount of cleaning liquid brought into contact with the center of the film.

When the multiple processing steps are multi-stage processing steps, a different adjustment method can be used for each adjustment contact step of each multi-stage processing step, and for example, the width of the central portion can be different for each adjustment contact step.

(Other treatment steps for polyvinyl alcohol-based resin film)
Treatments other than those described above may also be added. Examples of treatments that can be added include immersion treatment in an aqueous solution containing zinc chloride or the like but not a boron compound (zinc treatment) performed after the crosslinking step.

<Polarizing film>
The above-mentioned method can provide a polarizing film with reduced variation in optical properties in the width direction. The luminosity-corrected single transmittance Ty of the obtained polarizing film is preferably 40 to 47%, more preferably 41 to 45%, taking into consideration the balance with the luminosity-corrected polarization degree Py. The luminosity-corrected polarization degree Py is preferably 99.9% or more, more preferably 99.95% or more at any position in the width direction. The difference between the maximum and minimum values of the luminosity-corrected polarization degree Py in the width direction is preferably 0.0015% or less, and the smaller the difference, the more preferable.

The MD transmittance and TD transmittance of the polarizing film were measured in the wavelength range of 380 to 780 nm using a spectrophotometer equipped with an integrating sphere ("V7100" manufactured by JASCO Corporation), and the transmittance was calculated using the following formula:
Single piece transmittance (%) = (MD + TD) / 2
Degree of polarization (%) = {(MD-TD)/(MD+TD)}×100
The single transmittance and the degree of polarization at each wavelength are calculated based on the above.

The "MD transmittance" is the transmittance when the direction of the polarized light exiting the Glan-Thompson prism is parallel to the transmission axis of the polarized film sample, and is represented as "MD" in the above formula. The "TD transmittance" is the transmittance when the direction of the polarized light exiting the Glan-Thompson prism is perpendicular to the transmission axis of the polarized film sample, and is represented as "TD" in the above formula. The obtained single transmittance and degree of polarization are subjected to luminosity correction using a 2-degree visual field (C light source) according to _JIS Z ₈₇₀₁ :1999 "Method of displaying color-XYZ color system and _X10Y10Z10 color system" to determine the luminosity-corrected single transmittance (Ty) and luminosity-corrected degree of polarization (Py).

The width of the polarizing film of the present invention is, for example, 50 mm or more and 5000 mm or less, and preferably 500 mm or more and 4000 mm or less. The obtained polarizing film may be wound up on a winding roll to form a roll, or it may be directly subjected to the polarizing plate production process (a process of laminating a protective film or the like on one or both sides of the polarizing film) without being wound up.

<Polarizing Plate>
A polarizing plate can be obtained by bonding a protective film to at least one side of the polarizing film produced as described above via an adhesive. Examples of the protective film include films made of acetylcellulose-based resins such as triacetylcellulose and diacetylcellulose; films made of polyester-based resins such as polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate; polycarbonate-based resin films, cycloolefin-based resin films; acrylic-based resin films; and films made of linear olefin-based resins such as polypropylene-based resins.

In order to improve the adhesion between the polarizing film and the protective film, the bonding surface of the polarizing film and/or the protective film may be subjected to a surface treatment such as corona treatment, flame treatment, plasma treatment, ultraviolet irradiation, primer coating treatment, or saponification treatment. Examples of adhesives used to bond the polarizing film and the protective film include active energy ray curable adhesives such as ultraviolet curable adhesives, aqueous solutions of polyvinyl alcohol resins or aqueous solutions containing crosslinking agents, and water-based adhesives such as urethane emulsion adhesives. The ultraviolet curable adhesive may be a mixture of an acrylic compound and a photoradical polymerization initiator, or a mixture of an epoxy compound and a photocationic polymerization initiator. It is also possible to use a combination of a cationic polymerizable epoxy compound and a radical polymerizable acrylic compound, and a combination of a photocationic polymerization initiator and a photoradical polymerization initiator as the initiator.

The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[Production of Polarizing Film]
Example 1
The polarized film of Example 1 was produced using a production apparatus having, in order from the upstream side, a swelling bath, two dyeing baths (a first dyeing bath and a second dyeing bath), two crosslinking baths (a first crosslinking bath and a second crosslinking bath), a complementary color bath, and a washing bath, with shower devices disposed at the inlet and outlet sides of the first dyeing bath, the inlet side of the second dyeing bath, and the inlet and outlet sides of the complementary color bath, the other configuration of which was the same as that of the production apparatus shown in FIG. 1.

Specifically, a long polyvinyl alcohol (PVA) raw film (manufactured by Mitsubishi Chemical under the trade name "M6000" and with a saponification degree of 99.9 mol% or more) with a width of 4260 mm and a thickness of 60 μm was continuously transported while being unwound from a roll, and was immersed in a swelling bath (26°C) consisting of pure water for a residence time of 15 seconds (swelling process). The film was then pulled out of the swelling bath and continuously immersed in a first dyeing bath (100 parts by weight of water, 0.028 parts by weight of iodine, 1.3 parts by weight of potassium iodide) at 30°C containing iodine and a second dyeing bath (100 parts by weight of water, 0.023 parts by weight of iodine, 1.7 parts by weight of potassium iodide, 0.4 parts by weight of boric acid) at 30°C for a total residence time of 58 seconds in the first and second dyeing baths (dyeing process). Next, the film removed from the second dyeing bath was immersed in a first crosslinking bath at 56°C with a 12/5/100 (mass ratio) potassium iodide/boric acid/water for a residence time of 20 seconds, and in a second crosslinking bath at 58°C with the same liquid composition for a residence time of 38 seconds. It was then immersed in a complementary color bath at 40°C with a 13/5/100 (mass ratio) potassium iodide/boric acid/water for a residence time of 17 seconds (complementary color step). The film was then immersed in a washing bath of pure water at 5°C (washing step).

In the first dyeing bath, the shower device installed on the inlet side and the outlet side of the first dyeing bath showered the dyeing solution of the same composition as the first dyeing bath only on the central 2420 mm (50% of the central part to the total width) of the film width of 4803 mm. In the second dyeing bath, the shower device installed on the inlet side showered the dyeing solution of the same composition as the second dyeing bath only on the central 2310 mm (50% of the central part to the total width) of the film width of 4646 mm. In the complementary color bath, the shower device installed on the inlet side and the outlet side showered the complementary color solution of the same composition as the complementary color bath only on the central 1210 mm (50% of the central part to the total width) of the film width of 2406 mm. In addition, in the dyeing process, crosslinking process, and complementary color process, longitudinal uniaxial stretching was performed by inter-roll stretching in the bath, and the total stretching ratio based on the original film was 6 times. After the washing process, the film was first dried at a temperature of 48°C, and then dried at a temperature of 91°C to obtain a polarized film with a thickness of 24 μm and a width of 1,920 mm.

Example 2
In Example 1, the step of spraying a treatment liquid using a shower device was performed by showering a dyeing liquid having the same composition as that of the first dyeing bath only onto a central 2,420 mm portion of the film width of 4,803 mm (the proportion of the central portion to the total width: 50%) using only the shower devices installed on the inlet and outlet sides of the first dyeing bath, and a polarized film was produced in the same manner as in Example 1, except that the shower devices installed in the second dyeing bath and complementary color bath were not operated.

<Comparative Example 1>
Polarizing films were produced in the same manner as in Example 1, except that in none of the treatment baths was the shower device operated and no step of showering the film with the treatment solution was performed.

<Measurement of the degree of polarization>
In the obtained polarizing films of Examples 1 and 2 and Comparative Example 1 having a width of 1920 mm, the luminosity-corrected polarization degree (Py) was measured based on the above-mentioned method at seven positions, 20 mm (position 1), 100 mm (position 2), 500 mm (position 3), 960 mm (position 4), 1420 mm (position 5), 1820 mm (position 6), and 1900 mm (position 7) from the left end of three straight lines extending in the width direction. Table 1 shows the average luminosity-corrected polarization degree (Py) of the three straight lines at the seven positions (the average value is taken as the luminosity-corrected polarization degree (Py) at each position). Table 1 also shows the calculated values of the difference between the maximum and minimum luminosity-corrected polarization degrees at the seven positions. FIG. 4 is a graph plotting the polarization degrees shown in Table 1.

The results shown in Table 1 and Figure 4 show that the polarizing films of Examples 1 and 2 have a smaller difference between the maximum and minimum values of the visibility-corrected polarization degree in the width direction than Comparative Example 1, and that the variation in the visibility-corrected polarization degree in the width direction is suppressed.

Example 3
In Example 1, a polyvinyl alcohol raw film having a width of 3390 mm was used as the polarizing film.

In the first dye bath, shower devices installed on the inlet and outlet sides of the first dye bath showered dyeing solution with the same composition as the first dye bath only on the central 1925 mm of the film width of 3859 mm (50% of the central part of the total width). In the second dye bath, shower devices installed on the inlet side showered dyeing solution with the same composition as the second dye bath only on the central 1760 mm of the film width of 3751 mm (47% of the central part of the total width). In the complementary color bath, shower devices installed on the inlet and outlet sides showered complementary color solution with the same composition as the complementary color bath only on the central 990 mm of the film width of 1962 mm (50% of the central part of the total width).

In addition, in the dyeing process, crosslinking process, and color-complementing process, longitudinal uniaxial stretching was performed by inter-roll stretching in a bath, and the total stretching ratio based on the original film was 6 times. After the washing process, the film was first dried at a temperature of 46°C, and then dried at a temperature of 92°C to obtain a polarized film with a thickness of 24 μm and a width of 1,460 mm. Apart from the above, the polarized film was produced using the same manufacturing method as in Example 1.

Example 4
In Example 3, a polarized film was produced in the same manner as in Example 3, except that in the step of showering a treatment liquid using a shower device, a shower of a dyeing liquid having the same composition as that of the first dyeing bath was only applied to a central 1,925 mm portion of the film width of 3,859 mm (the proportion of the central portion to the total width: 50%) using only the shower devices installed on the inlet and outlet sides of the first dyeing bath, and the shower devices installed in the second dyeing bath and complementary color bath were not operated.

<Comparative Example 2>
In Example 3, a polarizing film was produced in the same manner as in Example 1, except that the step of showering the treatment solution using a shower device was not carried out for any of the treatment baths.

<Measurement of the degree of polarization>
For the obtained polarizing films of Examples 3 and 4 and Comparative Example 2 having a width of 1460 mm, the luminosity-corrected polarization degree (Py) was calculated according to the above-mentioned method at five positions, 20 mm (position 1), 100 mm (position 2), 730 mm (position 3), 1360 mm (position 4), and 1440 mm (position 5) from the left end of the four straight lines extending in the width direction. Table 2 shows the average luminosity-corrected polarization degree (Py) of the four straight lines at the five positions (the average value is taken as the luminosity-corrected polarization degree (Py) at each position). Table 2 also shows the calculated difference between the maximum and minimum luminosity-corrected polarization degree (Py) at the five positions. FIG. 5 is a graph plotting the luminosity-corrected polarization degree (Py) shown in Table 2.

The results shown in Table 2 and Figure 5 show that the polarizing films of Examples 3 and 4 have a smaller difference between the maximum and minimum values of the visibility-corrected polarization degree in the width direction than those of Comparative Example 2, and that the variation in the visibility-corrected polarization degree in the width direction is suppressed.

10: Raw film made of polyvinyl alcohol resin, 11: Raw roll, 13: Swelling bath, 15: Dyeing bath, 16: Shower device, 17a: Crosslinking bath, 17b: Complementary color bath, 19: Cleaning bath, 21: Drying furnace, 23: Polarizing film, 30-35, 37-48, 60, 61: Guide roll, 50-52, 53a, 53b, 54, 55, 56: Nip roll.

Claims (6)

A method for producing a polarizing film from a polyvinyl alcohol-based resin film, comprising the steps of:
The polyvinyl alcohol-based resin film is subjected to a treatment in a treatment liquid.
At least one of the plurality of treatment steps is a multi-stage treatment step including a uniform contact step of contacting the polyvinyl alcohol-based resin film with a uniform amount of treatment liquid over the entire width, and a controlled contact step of contacting the polyvinyl alcohol-based resin film with an amount of treatment liquid controlled according to a position in the width direction of the entire width,
In the adjusted contact step, the polyvinyl alcohol-based resin film is divided into a central portion and both end portions across the entire width, and the amount of the treatment liquid brought into contact with the central portion is adjusted to be greater than the amount of the treatment liquid brought into contact with the both end portions, and the treatment liquid is brought into contact with the central portion and not brought into contact with the both end portions,
In the multi-stage treatment process, the treatment liquid used in the uniform contact step and the treatment liquid used in the conditioning contact step are both dyeing liquids, crosslinking liquids, or complementary liquids, and further, both have the same composition ;
The composition includes at least one of a dichroic dye and a boron compound.
A method for producing a polarizing film. The method for producing a polarizing film according to claim 1, wherein in the adjusting contact process, the central portion of the polyvinyl alcohol-based resin film is 5 to 80% of the total width. 3 . The method for producing a polarizing film according to claim 1 , wherein the uniform contact step is a step of immersing the polyvinyl alcohol-based resin film in the treatment liquid contained in a treatment tank. 4. The method for producing a polarizing film according to claim 1, wherein the conditioning contact step is a step of showering the treatment liquid onto the polyvinyl alcohol-based resin film. The method for producing a polarizing film according to any one of claims 1 to 4 , wherein the polyvinyl alcohol-based resin film has a total width of 400 mm or more and 8000 mm or less. A polarizing film manufacturing apparatus for producing a polarizing film from a polyvinyl alcohol-based resin film, comprising:
a plurality of processing sections for contacting the polyvinyl alcohol-based resin film with a processing solution;
At least one of the plurality of treatment sections is a multi-stage treatment section having a uniform contact section for contacting the polyvinyl alcohol-based resin film with a uniform amount of treatment liquid over the entire width, and an adjusted contact section for contacting the polyvinyl alcohol-based resin film with an amount of treatment liquid adjusted depending on a position in the width direction of the entire width,
In the adjusted contact portion, the polyvinyl alcohol-based resin film is divided into a central portion and both end portions across the entire width, and the amount of the treatment liquid brought into contact with the central portion is adjusted to be greater than the amount of the treatment liquid brought into contact with the both end portions, and the treatment liquid is brought into contact with the central portion and not brought into contact with the both end portions;
In the multi-stage treatment section, the treatment liquid used in the uniform contact section and the treatment liquid used in the adjusted contact section are both a dyeing liquid, a crosslinking liquid, or a complementary liquid, and further, both have the same composition ;
The composition includes at least one of a dichroic dye and a boron compound.

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