JP7364751B2 - Polarizing film manufacturing method and polarizing film manufacturing device - Google Patents

Description

The present invention relates to a method and apparatus for manufacturing a polarizing film that can be used, for example, as a component of a polarizing plate.

BACKGROUND ART As a polarizing film, a film in which a dichroic dye such as iodine is adsorbed and oriented on a uniaxially stretched polyvinyl alcohol resin film is conventionally used. In general, polarizing films are produced by sequentially applying a dyeing process in which the polyvinyl alcohol resin film is dyed with a dichroic dye, a crosslinking process in which the film is treated with a crosslinking agent, and a film drying process. [For example, Japanese Patent Laid-Open No. 2001-141926 (Patent Document 1)].

Japanese Patent Application Publication No. 2001-141926

Normally, polarizing films are produced industrially by continuously transporting a long polyvinyl alcohol resin film along a film transport path of a polarizing film manufacturing apparatus. The product is manufactured by including a wet treatment step of sequentially immersing the product in a dyeing treatment tank for performing a dyeing treatment and a crosslinking treatment tank for performing a crosslinking treatment.

When a polarizing film is continuously manufactured according to the above method, the polyvinyl alcohol resin gradually dissolves into the treatment liquid in which the polyvinyl alcohol resin film is immersed. This dissolved polyvinyl alcohol resin may precipitate from the processing solution for some reason, and when precipitation occurs, the precipitate adheres to the polyvinyl alcohol resin film during wet processing, and ultimately to the surface of the polarizing film. May adversely affect the appearance and quality of polarizing films.
In addition, as the concentration of the polyvinyl alcohol resin dissolved into the processing solution gradually increases, the surface of the polyvinyl alcohol resin film that has been immersed in the processing solution and then pulled out of the processing solution contains polyvinyl alcohol resin. Solids may precipitate. Such precipitates can also adversely affect the appearance and quality of the polarizing film.

An object of the present invention is to provide a method and apparatus capable of stably and continuously producing a polarizing film while suppressing the adhesion of the precipitates to the film.

The present invention provides a polarizing film manufacturing method and manufacturing apparatus shown below.
[1] A method for producing a polarizing film from a polyvinyl alcohol resin film, comprising:
The polyvinyl alcohol resin film is conveyed along a conveyance path passing through a first treatment tank configured with a plurality of rolls and containing an organic solvent-containing treatment liquid, and the polyvinyl alcohol resin film is transferred to the organic solvent-containing treatment liquid. a step of soaking the
dropping the liquid into the first treatment tank;
including methods.
[2] According to [1], the dropping step includes a step of dropping the organic solvent-containing treatment liquid that has moved from inside the first treatment tank to outside the first treatment tank and returning it to the first treatment tank. Method described.
[3] A method for producing a polarizing film from a polyvinyl alcohol resin film, comprising:
The polyvinyl alcohol resin film is conveyed along a conveyance path passing through a first treatment tank configured with a plurality of rolls and containing an organic solvent-containing treatment liquid, and the polyvinyl alcohol resin film is transferred to the organic solvent-containing treatment liquid. a step of soaking the
dropping the organic solvent-containing treatment liquid that has moved from the inside of the first treatment tank to the outside of the first treatment tank to a location different from the first treatment tank, and then returning it to the first treatment tank;
including methods.
[4] The transport route further passes through one or more processing tanks that are arranged upstream of the first processing tank and that contain processing liquid,
[1] to [3], wherein the temperature of the organic solvent-containing treatment liquid is lower than the temperature of the treatment liquid accommodated in a treatment tank located closest to the first treatment tank among the one or more treatment tanks; ] The method described in any of the above.
[5] The method according to any one of [1] to [4], wherein the organic solvent-containing processing liquid contains at least one of a dichroic dye and a crosslinking agent.
[6] The one or more processing tanks include, in order from the upstream side of the transport route, a second processing tank and a third processing tank,
The method according to [4], wherein the second processing tank contains a dichroic dye, and the third processing tank and the first processing tank contain a crosslinking agent.
[7] An apparatus for producing a polarizing film from a polyvinyl alcohol resin film,
A transport path for polyvinyl alcohol resin film composed of multiple rolls,
a first processing tank disposed on the transport path and containing an organic solvent-containing processing liquid in which the polyvinyl alcohol resin film is immersed;
a liquid supply unit that drops the liquid into the first processing tank;
equipment, including.
[8] The liquid supply section includes a processing liquid recovery section that drops the organic solvent-containing processing liquid that has moved from the inside of the first processing tank to the outside of the first processing tank and returns it into the first processing tank. 7].
[9] An apparatus for producing a polarizing film from a polyvinyl alcohol resin film, comprising:
A transport path for polyvinyl alcohol resin film composed of multiple rolls,
a first processing tank disposed on the transport path and containing an organic solvent-containing processing liquid in which the polyvinyl alcohol resin film is immersed;
a liquid supply unit that returns the organic solvent-containing treatment liquid that has moved from the inside of the first treatment tank to the outside of the first treatment tank to a location different from the first treatment tank and then returns to the first treatment tank;
equipment, including.
[10] A processing tank disposed upstream of the first processing tank on the transport path, further including one or more processing tanks that contain a processing liquid,
The temperature of the organic solvent-containing treatment liquid is lower than the temperature of the treatment liquid accommodated in a treatment tank located closest to the first treatment tank among the one or more treatment tanks [7] to [9]. ].
[11] The apparatus according to any one of [7] to [10], wherein the organic solvent-containing processing liquid contains at least one of a dichroic dye and a crosslinking agent.
[12] The one or more processing tanks include, in order from the upstream side of the transport route, a second processing tank and a third processing tank,
The apparatus according to [10], wherein the second processing tank contains a dichroic dye, and the third processing tank and the first processing tank contain a crosslinking agent.

It is possible to provide a method that can stably and continuously produce a polarizing film while suppressing the attachment of precipitates containing polyvinyl alcohol resin to the film.

It is a schematic diagram which shows an example of the manufacturing method of a polarizing film, and the polarizing film manufacturing apparatus used for it.

Hereinafter, a method and apparatus for manufacturing a polarizing film will be described while showing embodiments.

The present invention relates to a manufacturing method and a manufacturing apparatus for manufacturing a polarizing film from a polyvinyl alcohol resin film (hereinafter also referred to as "PVA resin film"). A polarizing film is manufactured by subjecting a PVA-based resin film to a series of treatments including immersion treatment in a treatment tank (wet treatment), drying treatment, and the like.
The polarizing film according to the present invention has a dichroic dye adsorbed and oriented on a stretched PVA-based resin film.

An example of a polarizing film manufacturing apparatus is shown in FIG. The polarizing film manufacturing apparatus shown in FIG. 1 is an apparatus for continuously manufacturing a long polarizing film 25 from a long PVA resin film 10 that is a raw material film. The arrow in FIG. 1 indicates the direction of film transport.
In manufacturing the polarizing film 25 using the manufacturing apparatus shown in FIG. and a cleaning treatment tank 19, and finally passed through a drying oven 21 for drying treatment to obtain a polarizing film 25. The polarizing film 25 manufactured as a long product may be wound up one after another on a take-up roll 27, or without being wound up, a thermoplastic resin film such as a protective film may be adhered to one or both sides of the polarizing film 25. The polarizing plate may be subjected to a polarizing plate manufacturing process.

The polarizing film manufacturing apparatus includes a wet processing section including a swelling processing tank 13, a dyeing processing tank 15, a crosslinking processing tank 17, a cleaning processing tank 19, etc. (wet processing is performed using a processing tank containing a processing solution in which the film is immersed) It usually has a drying processing section such as a drying oven 21 (a zone in which drying processing is performed on the film after wet processing).
The polarizing film manufacturing apparatus shown in FIG. 1 has a transport path for a PVA resin film 10 that includes a wet processing section and a dry processing section. By conveying the PVA-based resin film 10 along this conveyance path, a series of treatments including wet treatment and drying treatment are performed, and a polarizing film 25 is obtained.
The conveyance speed of the PVA resin film 10 conveyed along the conveyance path is usually 1 to 50 m/min, and preferably 5 m/min or more from the viewpoint of production efficiency.

As shown in FIG. 1, the conveyance path is constructed by a plurality of rolls that support and guide the running film (PVA resin film 10 and polarizing film 25) so as to pass through a wet processing section and a dry processing section. be done. The plurality of rolls includes a guide roll, which is a free roll that supports one side of the film, and/or a pair of rolls (usually including a drive roll), and the pair of rolls can, for example, hold the film on both sides. It is a nip roll that pinches or presses by pinching. In the example shown in FIG. 1, the polarizing film manufacturing apparatus includes guide rolls 1a to 1l and nip rolls 2a to 2f. The plurality of rolls that define the conveyance path may include a suction roll that is one type of drive roll. Normally, each of these rolls supports the film in contact with one or both surfaces (principal surfaces) of the film within the transport path. These rolls can be placed at appropriate positions, such as before and after each processing tank and drying means (drying oven), or inside the processing tank and drying means (drying oven).

The drive roll refers to a roll that can provide driving force for transporting the film to the film that comes into contact with it, and can be a roll that is directly or indirectly connected to a roll drive source such as a motor. . A free roll is a roll that supports a running film and is freely rotatable as the film is transported.

A method for manufacturing a polarizing film according to one embodiment of the present invention includes the following steps:
The PVA resin film is immersed in the organic solvent-containing treatment liquid by conveying the PVA-based resin film along a conveyance path passing through a first treatment tank configured with a plurality of rolls and containing an organic solvent-containing treatment liquid. a step (wet treatment step S101), and a step of dropping the liquid into the first treatment tank (liquid supply step S201)
including.
A method for manufacturing a polarizing film according to another embodiment of the present invention includes the following steps:
The PVA resin film is immersed in the organic solvent-containing treatment liquid by conveying the PVA-based resin film along a conveyance path passing through a first treatment tank configured with a plurality of rolls and containing an organic solvent-containing treatment liquid. step (wet treatment step S101), and a step of dropping the organic solvent-containing treatment liquid that has moved from the inside of the first treatment tank to the outside of the first treatment tank to a place different from the first treatment tank, and then returning it to the first treatment tank ( Liquid supply step S201)
including.

The polarizing film 25 obtained has been subjected to a stretching process (usually a uniaxial stretching process). For this purpose, the polarizing film manufacturing apparatus can include a stretching means (wet stretching means) for the PVA resin film 10, and the polarizing film manufacturing method includes a stretching treatment step (wet stretching treatment) for the PVA resin film 10. step).

(1) PVA-based resin film The PVA-based resin film 10 subjected to the wet processing step S101 (introduced into the wet processing section) is made of polyvinyl alcohol-based resin (hereinafter also referred to as "PVA-based resin"). It is a film that PVA-based resin refers to a resin containing 50% by weight or more of constitutional units derived from vinyl alcohol. As the PVA resin, a saponified polyvinyl acetate resin can be used. Examples of polyvinyl acetate-based resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith.
Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and (meth)acrylamides having an ammonium group.
In addition, "(meth)acrylic" represents at least one type selected from the group consisting of acrylic and methacryl. The same applies to other terms with "(meta)" added.

The degree of saponification of the PVA resin can be in the range of 80.0 to 100.0 mol%, preferably in the range of 90.0 to 100.0 mol%, and more preferably in the range of 94.0 to 100.0 mol%. The range is 100.0 mol%, more preferably 98.0 to 100.0 mol%. If the degree of saponification is less than 80.0 mol%, the water resistance and moist heat resistance of the resulting polarizing film 25 and the polarizing plate containing the same may decrease.

Saponification degree is the rate at which the acetate groups (acetoxy groups: -OCOCH ₃ ) contained in polyvinyl acetate resin, which is the raw material for PVA resin, is converted into hydroxyl groups during the saponification process, expressed as a unit ratio (mol%). The following formula:
Degree of saponification (mol%) = 100 x (number of hydroxyl groups) / (number of hydroxyl groups + number of acetic acid groups)
Defined by The degree of saponification can be determined in accordance with JIS K 6726 (1994).

The average degree of polymerization of the PVA resin is preferably 100 to 10,000, more preferably 1,500 to 8,000, and even more preferably 2,000 to 5,000. The average degree of polymerization of polyvinyl alcohol resin can also be determined in accordance with JIS K 6726 (1994). When the average degree of polymerization is less than 100, it is difficult to obtain a polarizing film 25 with preferable polarizing performance, and when it exceeds 10,000, solubility in a solvent deteriorates, making it difficult to form (film forming) the PVA-based resin film 10. It can be.

An example of the PVA-based resin film 10 is an unstretched film formed from the above-mentioned PVA-based resin. The film forming method is not particularly limited, and known methods such as melt extrusion and solvent casting can be employed.
Another example of the PVA-based resin film 10 is a stretched film obtained by stretching the above-mentioned unstretched film. This stretching is usually uniaxial stretching, preferably longitudinal uniaxial stretching. Longitudinal stretching refers to stretching in the machine direction (MD) of the film, that is, in the longitudinal direction of the film.
When the PVA-based resin film 10 to be subjected to the wet processing step S101 (introduced into the wet processing section) is a stretched film, this stretching is preferably dry stretching. Dry stretching refers to stretching performed in the air, and is usually longitudinal uniaxial stretching.

For dry stretching, a film is passed between a heated roll whose surface is heated and a guide roll (or a heated roll may be used) that has a different circumferential speed from the heated roll, and the film is heated using the heated roll. Hot roll stretching that performs vertical stretching at the bottom; A process between two nip rolls installed at a distance that performs longitudinal stretching by the difference in circumferential speed between the two nip rolls while passing through a heating means (such as an oven) between the rolls. Stretching; tenter stretching; compression stretching, etc. can be mentioned.
The stretching temperature (surface temperature of a hot roll, oven temperature, etc.) is, for example, 80 to 150°C, preferably 100 to 135°C.

The stretching ratio of the above-mentioned stretching depends on whether or not wet stretching is performed in the wet processing step S101 described later and the stretching ratio in the wet stretching, but is usually 1.1 to 8 times, preferably 2. .5 to 5 times.

The PVA resin film 10 can contain additives such as plasticizers. Preferred examples of plasticizers are polyhydric alcohols, specific examples of which include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, triglycerin, tetraethylene glycol, trimethylolpropane, and polyethylene glycol. Can be mentioned. The PVA-based resin film 10 can contain one or more types of plasticizer.
The content of the plasticizer is usually 5 to 20 parts by weight, preferably 7 to 15 parts by weight, based on 100 parts by weight of the PVA resin constituting the PVA resin film 10.

The thickness of the PVA resin film 10 subjected to the wet processing step S101 (introduced into the wet processing section) is usually 10 to 150 μm, depending on whether the PVA resin film 10 is a stretched film or not. From the viewpoint of reducing the thickness of the resulting polarizing film 25, the thickness is preferably 100 μm or less, more preferably 65 μm or less, even more preferably 50 μm or less, particularly preferably 35 μm or less (for example, 30 μm or less, and even 20 μm or less).

(2) Wet processing section and wet processing step S101
The wet processing section in which the wet processing step S101 is performed is a zone disposed on the conveyance path of the PVA resin film 10, and includes a processing tank containing a processing liquid in which the PVA resin film 10 is immersed. In this wet processing section, a wet processing step S101 is performed in which the PVA resin film 10 is immersed in a processing liquid while being conveyed.

The wet treatment section usually includes a dyeing treatment tank 15 and a crosslinking treatment tank 17 as the treatment tanks, and preferably further includes a swelling treatment tank 13 and a cleaning treatment tank 19. These processing tanks are normally arranged in the order of swelling processing tank 13, dyeing processing tank 15, crosslinking processing tank 17, and cleaning processing tank 19 from the upstream side of the transport route (see FIG. 1).
Although FIG. 1 shows an example in which one swelling treatment tank 13, one dyeing treatment tank 15, one crosslinking treatment tank 17, and one cleaning treatment tank 19 are provided, two or more dyeing treatment tanks 15 may be provided as necessary. may be provided, and two or more crosslinking treatment tanks 17 may be provided. The same applies to the swelling treatment tank 13 and the cleaning treatment tank 19, and two or more tanks may be provided in each.

(2-1) Swelling treatment tank and swelling treatment process Swelling treatment is carried out as necessary for the purpose of removing foreign substances from the PVA resin film 10, removing plasticizer, imparting dyeability, plasticizing the film, etc. It is processing.
Referring to FIG. 1, in the swelling treatment step, the PVA resin film 10 is conveyed along the film conveyance path while being continuously unwound from the unwinding roll 11. This can be carried out by immersing it in the containing swelling treatment tank 13 for a predetermined time and then pulling it out.

The treatment liquid (swelling treatment liquid) accommodated in the swelling treatment tank 13 can be, for example, water (pure water, etc.) or water containing an organic solvent. Further, the swelling treatment liquid can also contain boric acid, chloride, inorganic acid, inorganic salt, and the like.
The temperature of the swelling treatment liquid is usually 10 to 70°C, preferably 15 to 50°C, more preferably 15 to 35°C. The immersion time (residence time in the swelling treatment liquid) of the PVA resin film 10 is usually 10 to 600 seconds, preferably 15 to 300 seconds.

During the swelling process, the PVA resin film 10 may be subjected to a wet stretching process (usually a uniaxial stretching process). In that case, the stretching ratio is usually 1.2 to 3 times, preferably 1.3 to 2.5 times. Referring to FIG. 1, for example, uniaxial stretching treatment can be performed in swelling treatment tank 13 using the difference in peripheral speed between nip roll 2a and nip roll 2b.
In the example shown in FIG. 1, the film pulled out from the swelling treatment tank 13 passes through the guide roll 1c and the nip roll 2b in order and is introduced into the dyeing treatment tank 15.

(2-2) Dyeing Treatment Tank and Dyeing Treatment Step The dyeing treatment is a treatment carried out for the purpose of adsorbing and orienting the dichroic dye to the PVA resin film 10.
Referring to FIG. 1, the dyeing process can be carried out by transporting the PVA resin film 10 along the film transport path, immersing it in a dyeing tank 15 for a predetermined time, and then pulling it out. The dyeing treatment tank 15 is a tank for immersing the PVA-based resin film 10 in the dyeing treatment liquid contained therein. The PVA resin film 10 immersed in the dyeing treatment liquid is preferably a film that has undergone a swelling treatment step (immersed in the swelling treatment tank 13).
The dyeing solution contained in the dyeing tank 15 is a solution (usually an aqueous solution) containing a dichroic dye. The dichroic dye can be iodine or a dichroic organic dye, preferably iodine. One type of dichroic dye may be used alone or two or more types may be used in combination.
The dyeing treatment liquid may contain an organic solvent.

When using iodine as the dichroic dye, an aqueous solution containing iodine and potassium iodide can be used as the dyeing solution. Instead of potassium iodide, other iodides such as zinc iodide may be used, or potassium iodide and other iodides may be used together. Further, compounds other than iodide, such as boric acid, zinc chloride, cobalt chloride, etc., may be coexisting. When boric acid is added, it is distinguished from the crosslinking solution described later in that it contains iodine. For example, if the aqueous solution contains about 0.003 parts by weight or more of iodine per 100 parts by weight of water, it can be considered a dyeing solution. The content of iodine in the dyeing solution is usually 0.003 to 1 part by weight per 100 parts by weight of water. The content of iodide such as potassium iodide in the dyeing solution is usually 0.1 to 20 parts by weight per 100 parts by weight of water.

The temperature of the dyeing solution is usually 10 to 45°C, preferably 10 to 40°C, more preferably 20 to 35°C. The immersion time (residence time in the dyeing solution) of the PVA resin film 10 is usually 20 to 600 seconds, preferably 30 to 300 seconds.

As described above, the polarizing film manufacturing apparatus can include two or more dyeing treatment tanks 15. In this case, the composition and temperature of each dyeing solution may be the same or different.

In order to improve the dyeability of the dichroic dye, the PVA resin film 10 to be subjected to the dyeing process is preferably subjected to at least some stretching treatment (usually uniaxial stretching treatment). Instead of the stretching treatment before the dyeing treatment, or in addition to the stretching treatment before the dyeing treatment, the stretching treatment may be performed while the dyeing treatment is being performed. The cumulative stretching ratio up to the dyeing process (or the stretching ratio in the dyeing process if there is no stretching process before the dyeing process) is usually 1.6 to 4.5 times, preferably 1.8 to 4 times. . Referring to FIG. 1, for example, the uniaxial stretching process can be performed in the dyeing process tank 15 by utilizing the difference in peripheral speed between the nip rolls 2b and the nip rolls 2c.
In the example shown in FIG. 1, the film pulled out from the dyeing treatment tank 15 passes through the guide roll 1f and the nip roll 2c in order and is introduced into the crosslinking treatment tank 17.

(2-3) Crosslinking treatment tank and crosslinking treatment process Crosslinking treatment is a treatment carried out for the purpose of water resistance, hue adjustment (complementary color), etc. by crosslinking.
Referring to FIG. 1, the crosslinking process is carried out by transporting the PVA resin film 10 along the film transport path and immersing the PVA resin film 10 after the dyeing process S101 (immersed in the dyeing tank 15) in the crosslinking tank 17 for a predetermined time. This can be done by pulling and then withdrawing. The crosslinking treatment tank 17 is a tank for immersing the PVA resin film 10 in the crosslinking treatment liquid contained therein.
The crosslinking treatment liquid contained in the crosslinking treatment tank 17 is a liquid (usually an aqueous solution) containing a crosslinking agent. A crosslinking process is performed by immersing the PVA resin film 10 after the dyeing process in this crosslinking process liquid.
The crosslinking treatment liquid may contain an organic solvent.

Examples of the crosslinking agent contained in the crosslinking treatment solution include boric acid, glyoxal, and glutaraldehyde, with boric acid being preferred. Two or more types of crosslinking agents can also be used in combination.
The content of the crosslinking agent in the crosslinking solution is generally 0.1 to 15 parts by weight, preferably 1 to 12 parts by weight per 100 parts by weight of water.

When the dichroic dye is iodine, the crosslinking treatment liquid preferably contains iodide in addition to the crosslinking agent.
Examples of iodides include potassium iodide and zinc iodide.
The content of iodide in the crosslinking solution is generally 0.1 to 20 parts by weight, preferably 5 to 15 parts by weight, per 100 parts by weight of water.

The crosslinking treatment liquid may contain compounds other than iodide. Examples of the compound include zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, and sodium sulfate.

The temperature of the crosslinking solution is generally 20 to 85°C, preferably 30 to 70°C. The immersion time (residence time in the crosslinking treatment liquid) of the PVA resin film 10 is generally 10 to 600 seconds, preferably 20 to 300 seconds.

As described above, the polarizing film manufacturing apparatus can include two or more crosslinking treatment tanks 17. In this case, the composition and temperature of each crosslinking treatment liquid may be the same or different. The crosslinking treatment liquid may have a concentration of a crosslinking agent, an iodide, etc., and a temperature depending on the purpose of immersing the PVA-based resin film 10. The crosslinking treatment for water resistance by crosslinking and the crosslinking treatment for hue adjustment (complementary color) may be performed in a plurality of steps, respectively.
Generally, when performing both cross-linking treatment for water resistance and hue adjustment (complementary color), the tank (complementary color tank) that performs the cross-linking treatment for hue adjustment (complementary color) is placed in the latter stage. Placed. The temperature of the processing liquid stored in the complementary color tank is, for example, 10 to 55°C, preferably 20 to 50°C. The content of the crosslinking agent in the processing liquid stored in the complementary color tank is, for example, 1 to 5 parts by weight per 100 parts by weight of water. The iodide content in the processing liquid stored in the complementary color tank is, for example, 3 to 30 parts by weight per 100 parts by weight of water.

Stretching treatment (usually uniaxial stretching treatment) may be performed while performing crosslinking treatment. Referring to FIG. 1, for example, the uniaxial stretching process can be performed in the crosslinking treatment tank 17 using the difference in circumferential speed between the nip roll 2c and the nip roll 2d.
In the example shown in FIG. 1, the film pulled out from the crosslinking treatment tank 17 passes through the guide roll 1i and the nip roll 2d in this order and is introduced into the cleaning treatment tank 19.

(2-4) Cleaning tank and cleaning process The polarizing film manufacturing method can further include a cleaning process after the crosslinking process, and for this purpose, the polarizing film manufacturing apparatus is installed on the downstream side of the crosslinking tank 17. The cleaning tank 19 may further include a cleaning treatment tank 19 disposed in the cleaning tank 19 . The cleaning process is a process performed for the purpose of removing excess chemicals adhering to the PVA resin film 10 after the crosslinking process.
Referring to FIG. 1, the cleaning process involves transporting the PVA resin film 10 along the film transport path and immersing the PVA resin film 10 after the crosslinking process (immersed in the crosslinking tank 17) in the cleaning tank 19 for a predetermined time. , and then by retrieving. Alternatively, the cleaning treatment may be a treatment in which the PVA resin film 10 after the crosslinking treatment step is sprayed with a cleaning liquid, for example, as a shower, or immersion in the cleaning treatment tank 19 and spraying of the cleaning liquid may be combined. . FIG. 1 shows an example in which a PVA-based resin film 10 is immersed in a cleaning treatment tank 19 to perform cleaning treatment.

The cleaning liquid stored in the cleaning tank 19 or the cleaning liquid sprayed may be, for example, water (pure water, etc.), or may be an aqueous solution containing a water-soluble organic solvent such as alcohol. The temperature of the cleaning bath is, for example, 2 to 40°C.
The cleaning liquid stored in the cleaning tank 19 and the cleaning liquid sprayed may contain an organic solvent.

Stretching treatment (usually uniaxial stretching treatment) may be performed while performing washing treatment. Referring to FIG. 1, for example, the uniaxial stretching process can be performed in the cleaning treatment tank 19 using the difference in circumferential speed between the nip roll 2d and the nip roll 2e.

(2-5) Stretching means and stretching treatment step In the wet treatment step, the PVA resin film 10 may be subjected to wet stretching. Wet stretching is usually uniaxial stretching, and can be performed while performing any one of swelling treatment, dyeing treatment, crosslinking treatment, and washing treatment, or during two or more treatments selected from these.
Wet stretching is preferably performed during the crosslinking process or at one or more stages prior to the crosslinking process. As described above, in order to improve the dyeability of the dichroic dye and obtain the polarizing film 25 having good polarizing properties, the PVA resin film 10 to be subjected to the dyeing process is subjected to at least some stretching treatment. It is more preferable that the
From the viewpoint of the polarizing properties of the resulting polarizing film 25, the stretching ratio of the wet stretching is preferably the final cumulative stretching ratio of the polarizing film 25 (when the PVA resin film 10 to be subjected to wet processing is a stretched film). The cumulative stretching ratio (including this stretching) is adjusted to 3 to 8 times.

When carrying out the wet stretching process, the polarizing film manufacturing apparatus includes wet stretching means for the PVA resin film 10. The wet stretching means is preferably a stretching means that performs stretching between rolls. Taking as an example the case where wet inter-roll stretching is performed during the crosslinking process, the stretching means that performs the inter-roll stretching are two nip rolls 2c and 2d arranged before and after the crosslinking tank 17. Similarly, when stretching is performed during other wet treatments, two nip rolls placed apart from each other can be used as the wet stretching means.

(3) Drying processing step The drying processing section in which the drying processing step is performed is located on the conveyance path of the PVA resin film 10 and downstream of the wet processing section, and the PVA resin after the wet processing step S101 This is a zone for drying the film 10. A drying process can be performed by introducing the PVA-based resin film 10 after the wet processing step S101 into a drying processing section while continuing to transport the film, thereby obtaining a polarizing film 25 (see FIG. 1).

The drying section includes a film drying means (heating means). A suitable example of the drying means is a drying oven. The drying oven is preferably one in which the temperature inside the oven can be controlled. The drying oven is, for example, a hot air oven that can increase the temperature inside the oven by supplying hot air or the like. Further, the drying process by the drying means may be a process in which the PVA resin film 10 after the wet process step is brought into close contact with one or more heating bodies having a convex curved surface, or a process in which the film is heated using a heater. good.

Examples of the heating body include a roll (for example, a guide roll that also serves as a heat roll) that is equipped with a heat source (for example, a heat medium such as hot water or an infrared heater) and can increase the surface temperature. Examples of the heater include an infrared heater, a halogen heater, and a panel heater. FIG. 1 shows an example in which the PVA resin film 10 after the wet treatment step S101 is introduced into the drying oven 21 and subjected to drying treatment.

The temperature of the drying process (for example, the temperature inside the drying oven 21, the surface temperature of the heat roll, etc.) is usually 30 to 100°C, preferably 50 to 90°C.

The polarizing film 25 is a stretched (usually uniaxially stretched) PVA resin film on which a dichroic dye is adsorbed and oriented. The thickness of the polarizing film 25 is usually 2 to 40 μm. From the viewpoint of reducing the thickness of the polarizing plate including the polarizing film 25, the thickness of the polarizing film 25 is preferably 20 μm or less, more preferably 15 μm or less, and still more preferably 10 μm or less.

The visibility correction single transmittance Ty of the obtained polarizing film 25 is preferably 40 to 47%, more preferably 41 to 45%, taking into consideration the balance with the visibility correction polarization degree Py. The visibility correction polarization degree Py is preferably 99.9% or more, more preferably 99.95% or more.
Ty and Py can be measured by using an absorption photometer with an integrating sphere and performing visibility correction on the obtained transmittance and degree of polarization using a 2-degree field of view (C light source) according to JIS Z 8701.

The obtained polarizing film 25 may be sequentially wound onto a take-up roll 27 to form a roll, or it may be used as it is in the polarizing plate production process without being wound (a thermoplastic resin film (protective film, etc.) is applied to one or both sides of the polarizing film 25 ) can also be applied to a step of laminating layers.

(4) Liquid supply section and liquid supply process S201
(4-1) First Embodiment In the first embodiment, the method for manufacturing a polarizing film includes, as a liquid supply step S201, a step of dropping a liquid into a first processing tank. In this case, the polarizing film manufacturing apparatus includes a liquid supply section for dropping the liquid into the first processing tank.
The first processing tank here is at least one of the processing tanks (of the wet processing section) that is arranged on the transport path of the PVA resin film 10 and used in the wet processing step S101.

Among the processing tanks, the first processing tank refers to a processing tank that accommodates a processing liquid containing an organic solvent (hereinafter also referred to as "organic solvent-containing processing liquid"), and includes the swelling processing tank 13 and the dyeing processing tank 15. , a crosslinking treatment tank 17, a cleaning treatment tank 19, etc. Details of the first treatment tank will be described later.
"Dropping" the liquid means dropping the liquid from a point higher than the level of the processing liquid stored in the first processing tank toward the level of the processing liquid without transmitting it through walls, piping, etc. It means that.

The fact that the polarizing film manufacturing method includes the liquid supply step S201 (the polarizing film manufacturing apparatus includes a liquid supply section that drops the liquid into the first processing tank) is to improve the polarizing film 25 obtained, as will be described later. This is preferable from the viewpoints of appearance, quality, etc., and productivity of the polarizing film 25.
However, when the above-mentioned liquid is dropped onto the surface of the processing solution in the processing tank, the PVA resin that has dissolved into the processing solution in the processing tank may precipitate due to the impact etc. Problems (adverse effects on the appearance and quality of the polarizing film 25) caused by the precipitates containing the PVA resin as described above may occur.
According to the present invention, in which the processing liquid contained in the first processing tank, which is the object of dropping the liquid, is an organic solvent-containing processing liquid, even if an impact or the like occurs due to the dropping of the liquid, PVA-based It is possible to suppress the precipitation of precipitates containing resin, thereby suppressing the problem of the precipitates adhering to the PVA resin film 10, and to stably and continuously produce a polarizing film 25 having good appearance and quality. can do.

(4-1-1) Organic solvent contained in organic solvent-containing treatment liquid Examples of organic solvents contained in organic solvent-containing treatment liquid include monohydric alcohols such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, and butanol. (preferably liquid alcohol); polyhydric alcohol such as ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, triglycerin, tetraethylene glycol, trimethylolpropane, polyethylene glycol; acetone, tetrahydrofuran, 1,4 -dioxane, N,N-dimethylformamide, dimethyl sulfoxide and the like.

From the viewpoint of suppressing precipitation of precipitates containing PVA resin, the content of the organic solvent is preferably 1 to 50% by weight, more preferably 5 to 50% by weight when the total amount of the organic solvent-containing treatment liquid is 100% by weight. It is 30% by weight. If the content of the organic solvent is too large, the functionality of the treatment liquid may deteriorate.
The organic solvent-containing treatment liquid is preferably an aqueous solution containing an organic solvent.
The organic solvent is preferably an organic solvent that is compatible with water.

(4-1-2) Liquid to be dropped into the first processing tank The liquid to be dropped into the first processing tank can be, for example, one or more types selected from the following liquids.
[a] A liquid (roll cleaning liquid) used as a cleaning liquid for cleaning at least one of the plurality of rolls that construct the transport path of the PVA-based resin film 10. This liquid also includes liquid that has adhered to the surface of the roll due to the roll cleaning.
[b] A liquid (film cleaning liquid) used as a cleaning liquid for cleaning the surface of the PVA resin film 10 being transported along the transport route. This liquid also includes the liquid that has adhered to the surface of the PVA resin film 10 that is being transported along the transport route due to the film cleaning.
[c] Gas is applied to the surface of at least one of the plurality of rolls that construct the transport route of the PVA resin film 10 and/or the surface of the PVA resin film 10 being transported along the transport route. A liquid that is drained by supplying, etc.
[d] A liquid that is replenished to adjust the amount and composition of the processing liquid contained in the first processing tank.

The roll cleaning liquid in [a] above is such that as a result of the treatment liquid adhering to the roll surface, solids such as salts derived from the treatment liquid are precipitated on the roll surface, and furthermore, this precipitate is deposited on the PVA resin film 10 during conveyance. This is a liquid used to clean the roll surface to prevent it from being transferred and attached to the surface.
Roll cleaning can be performed by directing a roll cleaning liquid toward the roll surface, for example, in the form of a shower.
By performing roll cleaning, it is possible to suppress the above-mentioned precipitates from adhering to the surface of the PVA-based resin film 10 being transported and, ultimately, the polarizing film 25 obtained. This is advantageous in improving the appearance and quality of the polarizing film 25.
If the roll cleaning liquid after cleaning the roll surface is dropped into the first treatment tank, it can be reused as part of the treatment liquid, which is advantageous from the viewpoint of productivity of the polarizing film 25.

The roll cleaning liquid is at least a part of the organic solvent-containing treatment liquid extracted from the organic solvent-containing treatment liquid in the first treatment tank (which may contain the PVA resin eluted from the PVA resin film 10). It may be the above-mentioned organic solvent, or it may be a liquid having the same composition as the organic solvent-containing processing liquid stored in the first processing tank except that it does not contain an organic solvent. A combination of two or more selected from these may be used.
The roll cleaning liquid preferably contains at least a portion of the organic solvent-containing treatment liquid extracted from the organic solvent-containing treatment liquid in the first treatment tank.

The film cleaning liquid [b] above is applied to the PVA resin film 10 during transportation in order to prevent solids such as salts from precipitating from the treatment liquid adhering to the surface of the PVA resin film 10 after being immersed in the treatment liquid. A liquid used to clean or keep a surface moist.
Film cleaning can be performed by directing the film cleaning liquid toward the surface of the PVA-based resin film 10, for example, in the form of a shower.
By carrying out film cleaning, it is possible to suppress the precipitation of the solids on the surface of the PVA-based resin film 10 being transported and, ultimately, the polarizing film 25 obtained. This is advantageous in improving the appearance and quality of the polarizing film 25.
If the film cleaning liquid after cleaning the film is dropped into the first processing tank, it can be reused as part of the processing liquid, which is advantageous from the viewpoint of productivity of the polarizing film 25.

The film cleaning liquid is at least a part of the organic solvent-containing treatment liquid (which may contain the PVA resin eluted from the PVA resin film 10) extracted from the organic solvent-containing treatment liquid in the first treatment tank. It may be the above-mentioned organic solvent, or it may be a liquid having the same composition as the organic solvent-containing processing liquid stored in the first processing tank except that it does not contain an organic solvent. A combination of two or more selected from these may be used.
The film cleaning liquid preferably contains at least a portion of the organic solvent-containing treatment liquid extracted from the organic solvent-containing treatment liquid in the first treatment tank.

The liquid [c] above is removed by removing excess processing liquid that adheres to the roll surface or the surface of the PVA resin film 10 after being immersed in the processing liquid, using a means to supply gas to the surface. It is a liquid produced by
By draining the liquid, excess processing liquid adhering to the roll surface or the surface of the PVA-based resin film 10 dries and it is possible to suppress precipitation of solids such as salts. This is advantageous in improving the appearance and quality of the polarizing film 25.
Examples of the gas include air and inert gases such as nitrogen, helium, and argon. Examples of means for supplying gas include an air shower and an air knife.
The liquid in [c] above may be a liquid generated by draining the liquid attached to the roll surface during the roll washing in [a] above, or may be a liquid generated by removing the liquid attached to the roll surface by washing the roll in [b] above, or it may be a liquid produced by removing the liquid from the PVA resin film 10 by washing the film in [b] above. The liquid may be generated by draining the liquid adhering to the surface of the surface.
If the drained liquid is dropped into the first processing tank, it can be reused as part of the processing liquid, which is advantageous from the viewpoint of productivity of the polarizing film 25.

The liquid in [d] above may be a fresh organic solvent-containing processing solution, an organic solvent, or a liquid having the same composition as the organic solvent-containing processing solution stored in the first processing tank except that it does not contain an organic solvent. Can be mentioned.

(4-1-3) Liquid supply unit The liquid supply unit for dropping the liquid into the first processing tank is capable of dropping the liquid from a point higher than the liquid level of the processing liquid contained in the first processing tank. There are no particular restrictions as much as possible.
As the liquid supply section, for example,
[A] A lead-out pipe (delivery line) for leading out the liquid, the lead-out pipe having a liquid outlet at a position higher than the liquid level of the processing liquid contained in the first processing tank;
[B] Liquid that flows down from the roll surface after roll cleaning (including roll cleaning liquid that is drawn toward the roll surface and bounces off the surface), liquid that flows down from the surface of the PVA resin film 10 after film cleaning (includes roll cleaning liquid that is directed toward the roll surface and bounces off the surface). ), and/or the liquid that is blown off or flowing down from the roll surface or the surface of the PVA resin film 10 by draining is collected and stored in the first treatment tank. Means for guiding the processing liquid to a position higher than the liquid level (collection/guiding means)
etc.
The liquid guided by the collecting/guiding means to a position higher than the level of the processing liquid contained in the first processing tank can be caused to fall into the first processing tank by free fall.
The collecting/guiding means may be, for example, an inclined tray or the like. The saucer may be a tank, a sheet, or the like.

The liquid supply section [A] above can be used, for example, when the liquid to be dropped into the first processing tank is the liquid [d] above.
The liquid supply unit (collection/guiding means) in [B] above may be used, for example, when the liquid to be dropped into the first processing tank is the liquid in [a], [b], and/or [c] above. I can do it.

(4-1-4) Step of returning the organic solvent-containing treatment liquid into the first treatment tank The liquid supply step S201 (step of dropping the liquid into the first treatment tank) is carried out from inside the first treatment tank to outside the first treatment tank. It is preferable to include a step of dropping the organic solvent-containing treatment liquid that has been moved to the first treatment tank and returning it to the first treatment tank. In this case, the liquid dropped into the first processing tank includes the organic solvent-containing processing liquid that was contained in the first processing tank.
Returning the organic solvent-containing processing liquid into the first processing tank is advantageous from the viewpoint of productivity of the polarizing film 25 because it can be reused as a part of the processing liquid.

When the liquid supply step S201 includes a step of dropping the organic solvent-containing treatment liquid that has moved from the inside of the first treatment tank to the outside of the first treatment tank and returning it to the first treatment tank, the organic solvent contained in the first treatment tank From the viewpoint of minimizing compositional fluctuations in the solvent-containing processing liquid, it is preferable that the liquid that is dropped into the first processing tank is only the organic solvent-containing processing liquid that has moved from inside the first processing tank to outside the first processing tank. However, for the purpose of adjusting the composition of the organic solvent-containing treatment liquid stored in the first treatment tank, the above-mentioned liquid may not contain an organic solvent or an organic solvent. A liquid having the same composition as the contained organic solvent-containing processing liquid may be further dropped into the first processing tank.
Examples of the "organic solvent-containing processing liquid that has moved from the inside of the first processing tank to the outside of the first processing tank" include liquids included in [a] to [c] above.

To explain more specifically with reference to FIG. 1, for example, the first treatment tank is the swelling treatment tank 13, and the guide roll 1c and nip roll 2b arranged after the swelling treatment tank 13 are replaced by the rolls [a] above. In the case of cleaning using a cleaning liquid, the "organic solvent-containing treatment liquid that has moved from the inside of the first treatment tank to the outside of the first treatment tank" is the swelling treatment liquid extracted from the swelling treatment tank 13, and is not used for cleaning. The organic solvent-containing processing liquid is led out toward the guide roll 1c and the nip roll 2b, for example, in the form of a shower, and then flows down from these rolls or bounces off the roll surface. The organic solvent-containing processing liquid that flows down from the roll or bounces off the roll surface is guided to a position higher than the liquid level of the processing liquid stored in the first processing tank using, for example, the above-mentioned collecting/guiding means, and is dropped from there. This allows the organic solvent-containing processing liquid to be returned into the first processing tank.
The swelling treatment liquid can be extracted from the swelling treatment tank 13 using, for example, a pump.

When the first treatment tank is the dyeing treatment tank 15 and the guide roll 1f and nip roll 2c placed after the dyeing treatment tank 15 are cleaned using the roll cleaning liquid of [a] above, "From inside the first treatment tank The "organic solvent-containing treatment liquid that has moved out of the first treatment tank" is the dyeing treatment liquid extracted from the dyeing treatment tank 15, and is directed toward the guide roll 1f and the nip roll 2c for cleaning, for example, in the form of a shower. After being discharged, the organic solvent-containing processing liquid flows down from these rolls or bounces off the roll surface.

When the first treatment tank is the crosslinking treatment tank 17 and the guide roll 1i and nip roll 2d placed after the crosslinking treatment tank 17 are cleaned using the roll cleaning liquid of [a] above, "from inside the first treatment tank The "organic solvent-containing treatment liquid that has moved out of the first treatment tank" is the crosslinking treatment liquid extracted from the crosslinking treatment tank 17, and is directed toward the guide roll 1i and the nip roll 2d for cleaning, for example, in the form of a shower. After being discharged, the organic solvent-containing processing liquid flows down from these rolls or bounces off the roll surface.

When the first processing tank is the cleaning tank 19 and the guide roll 1l and nip roll 2e placed after the cleaning tank 19 are cleaned using the roll cleaning liquid of [a] above, The organic solvent-containing treatment liquid that has moved out of the first treatment tank is a cleaning treatment liquid extracted from the cleaning treatment tank 19, and is directed toward the guide roll 1l and the nip roll 2e for cleaning, for example, in a shower-like manner. After being discharged, the organic solvent-containing processing liquid flows down from these rolls or bounces off the roll surface.

The first treatment tank is the swelling treatment tank 13, and the PVA resin film 10 after being immersed in the swelling treatment tank 13 and pulled out from there (for example, the PVA resin film 10 between the guide roll 1c and the nip roll 2b) When cleaning using the film cleaning solution in [b] above, "the organic solvent-containing processing solution that has moved from the inside of the first processing tank to the outside of the first processing tank" is the swelling processing solution extracted from the swelling processing tank 13. This is an organic solvent-containing processing liquid that is directed toward the PVA-based resin film 10 for film cleaning, for example, in the form of a shower, and then flows down from the film or bounces off the film surface. The organic solvent-containing processing liquid that flows down from the film or bounces off the film surface is guided to a position higher than the liquid level of the processing liquid contained in the first processing tank using, for example, the above-mentioned collecting/guiding means, and is dropped from there. This allows the organic solvent-containing processing liquid to be returned into the first processing tank.

The first treatment tank is a dyeing treatment tank 15, and the PVA resin film 10 after being immersed in the dyeing treatment tank 15 and pulled out from there (for example, the PVA resin film 10 between the guide roll 1f and the nip roll 2c) When cleaning using the film cleaning solution in [b] above, "the organic solvent-containing processing solution that has moved from the inside of the first processing tank to the outside of the first processing tank" is the dyeing processing solution extracted from the dyeing processing tank 15. This is an organic solvent-containing processing liquid that is directed toward the PVA-based resin film 10 for film cleaning, for example, in the form of a shower, and then flows down from the film or bounces off the film surface.

The first treatment tank is a crosslinking treatment tank 17, and the PVA resin film 10 after being immersed in the crosslinking treatment tank 17 and pulled out from there (for example, the PVA resin film 10 between the guide roll 1i and the nip roll 2d) When cleaning the film using the film cleaning liquid in [b] above, the "organic solvent-containing treatment liquid that has moved from inside the first treatment tank to outside the first treatment tank" is the crosslinking treatment liquid extracted from the crosslinking treatment tank 17. This is an organic solvent-containing processing liquid that is directed toward the PVA-based resin film 10 for film cleaning, for example, in the form of a shower, and then flows down from the film or bounces off the film surface.

The first treatment tank is a cleaning treatment tank 19, and the PVA resin film 10 after being immersed in the cleaning treatment tank 19 and pulled out from there (for example, the PVA resin film 10 between the guide roll 1l and the nip roll 2e) When cleaning the film using the film cleaning liquid in [b] above, the "organic solvent-containing treatment liquid that has moved from the inside of the first treatment tank to the outside of the first treatment tank" is the cleaning treatment liquid extracted from the cleaning treatment tank 19. This is an organic solvent-containing processing liquid that is directed toward the PVA-based resin film 10 for film cleaning, for example, in the form of a shower, and then flows down from the film or bounces off the film surface.

To give an example where the "organic solvent-containing treatment liquid that has moved from inside the first treatment tank to outside the first treatment tank" is the liquid [c] above, the first treatment tank is the crosslinking treatment tank 17, and the crosslinking This is the liquid that is generated when the PVA resin film 10 (for example, the PVA resin film 10 located between the guide roll 1i and the nip roll 2d) is drained after being immersed in the processing tank 17 and pulled out from there. The organic solvent-containing treatment liquid (crosslinking treatment liquid) drained from the film is collected from the surface of the crosslinking treatment liquid stored in the first treatment tank (crosslinking treatment tank 17) using, for example, the above-mentioned collection/guiding means. By guiding it to a high position and dropping it from there, the drained organic solvent-containing processing liquid can be returned to the first processing tank. The same applies to the case where the first treatment tank is the swelling treatment tank 13, the dyeing treatment tank 15, or the cleaning treatment tank 19.

When the liquid supply step S201 includes a step of dropping the organic solvent-containing treatment liquid that has moved from the inside of the first treatment tank to the outside of the first treatment tank and returns it to the first treatment tank, the polarizing film manufacturing apparatus includes a liquid supply section As such, it is preferable to include a processing liquid recovery section for dropping the organic solvent-containing processing liquid that has moved from the inside of the first processing tank to the outside of the first processing tank and returning it to the inside of the first processing tank.
As the processing liquid recovery section, for example,
[B1] A means (such as a pump) for extracting at least part of the organic solvent-containing processing solution from the organic solvent-containing processing solution in the first processing tank, using the extracted organic solvent-containing processing solution as a roll cleaning solution, and using this as a roll cleaning solution. A means for directing the liquid toward the surface (such as a shower sprayer), and collecting the liquid flowing down from the roll surface after the roll cleaning (including the roll cleaning liquid that is directed toward the roll surface and bouncing off the surface), and performing a first treatment. A combination of collecting and guiding means that guides the processing liquid contained in the tank to a position higher than the liquid level;
[B2] A means (such as a pump) for extracting at least part of the organic solvent-containing processing solution from the organic solvent-containing processing solution in the first processing tank, and using the extracted organic solvent-containing processing solution as a film cleaning solution. A means for directing the liquid toward the surface (such as a shower sprayer), and collecting the liquid that flows down from the surface of the PVA resin film 10 after film cleaning (including the film cleaning liquid that is directed toward the film surface and bounces off the surface). and a combination of collecting and guiding means for guiding the processing liquid contained in the first processing tank to a position higher than the liquid level;
[B3] Remove the excess organic solvent-containing treatment liquid that has adhered to the roll surface or the surface of the PVA-based resin film 10 after being immersed in the organic solvent-containing treatment liquid from the roll surface or the surface of the PVA-based resin film 10. A liquid cutting means (air shower, air knife, etc.) is used to collect the liquid that is blown off or flowing down from the roll surface or the surface of the PVA resin film 10 by the liquid cutting, and the processing liquid is stored in the first processing tank. Examples include a combination of collection and guiding means that guides the liquid to a position higher than the liquid level.

(4-1-5) First Treatment Tank The first treatment tank containing the organic solvent-containing treatment liquid is selected from the swelling treatment tank 13, the dyeing treatment tank 15, the crosslinking treatment tank 17, the cleaning treatment tank 19, and the like. The polarizing film manufacturing apparatus may have two or more first processing tanks.
Among these, the first processing tank is preferably a processing tank in which precipitation of PVA-based resin is likely to occur due to impact, etc. when the liquid is dropped onto the surface of the processing liquid in the processing tank.
Note that the concentration of the PVA resin in the organic solvent-containing treatment liquid stored in the first treatment tank may be, for example, about 5 ppm to 5000 ppm on a weight basis.

Specifically, the first processing tank is preferably a processing tank containing a processing liquid containing at least one of a dichroic dye and a crosslinking agent.
A dyeing treatment tank 15 is an example of a treatment tank that stores a treatment liquid containing a dichroic dye.
Examples of the treatment tank containing the treatment liquid containing the crosslinking agent include the swelling treatment tank 13, the dyeing treatment tank 15, and the crosslinking treatment tank 17. The first processing tank containing a processing liquid containing a crosslinking agent is preferably a processing tank containing a processing liquid containing a crosslinking agent and an iodide (such as potassium iodide). An example of such a treatment tank is the crosslinking treatment tank 17.
The dyeing treatment tank 15 and the crosslinking treatment tank 17, especially the crosslinking treatment tank 17 (including the crosslinking treatment tank for water resistance by crosslinking and the crosslinking treatment tank for hue adjustment (complementary color)), are used for the swelling treatment tank 13 and the cleaning treatment tank. Compared to the treatment tank 19, the temperature of the treatment liquid stored therein is generally set higher, and therefore, when the PVA-based resin film 10 is immersed, the PVA-based resin is likely to elute, resulting in , precipitation of solids containing PVA-based resin from the processing solution is likely to occur.
Therefore, the present invention is more effective when the first treatment tank is the dyeing treatment tank 15 and/or the crosslinking treatment tank 17, especially when it is the crosslinking treatment tank 17.

In addition, if the treatment tank is prone to precipitation of PVA-based resin due to the impact caused when the liquid is dropped onto the surface of the treatment liquid in the treatment tank, it should be stored in another treatment tank located upstream of the treatment tank. For example, a processing tank containing a processing liquid whose temperature is lower than that of the processing liquid used in the processing can be mentioned.
That is, when the transport path of the PVA-based resin film 10 further passes through one or more other processing tanks arranged upstream of a certain processing tank, the temperature of the processing liquid stored in the certain processing tank is as follows: When the temperature is lower than the temperature of the processing liquid accommodated in the other processing tank, it is preferable that the certain processing tank is used as a first processing tank containing the organic solvent-containing processing liquid.
As described above, the present invention is more effective when the first processing tank is a processing tank that accommodates a processing liquid with a lower temperature and is placed after a processing tank that contains a processing liquid with a higher temperature.

In one embodiment, the other one or more processing tanks further include a second processing tank and a third processing tank in order from the upstream side of the transport route for the PVA resin film 10 (from the upstream side of the transport route, (in order of second treatment tank, third treatment tank, and first treatment tank), the second treatment tank contains a dichroic dye, and the third processing tank and the first processing tank contain a crosslinking agent.
The dyeing treatment tank 15 is an example of the second treatment tank that stores the treatment liquid containing the dichroic dye.
The third treatment tank and the first treatment tank that contain the treatment liquid containing the crosslinking agent include the swelling treatment tank 13, the dyeing treatment tank 15, the crosslinking treatment tank 17, etc., but preferably, the treatment liquid containing the crosslinking agent and iodine is This is a crosslinking treatment tank 17 that stores a treatment liquid containing compounds (potassium iodide, etc.).
In this embodiment, when both the third treatment tank and the first treatment tank are the crosslinking treatment tank 17, the temperature of the organic solvent-containing treatment liquid stored in the first treatment tank is the same as that of the third treatment tank. Lower than the temperature of the processing liquid. An example of such a combination of the third treatment tank and the first treatment tank is that the third treatment tank is a crosslinking treatment tank for water resistance by crosslinking, and the first treatment tank is a crosslinking treatment tank for hue adjustment (complementary color). This combination is a processing tank (complementary color tank).

(4-2) Second Embodiment In the second embodiment, the method for manufacturing a polarizing film includes, as a liquid supply step S201, an organic solvent-containing treatment liquid that has been moved from the inside of the first treatment tank to the outside of the first treatment tank. It includes the step of dropping the first treatment tank to a different location and then returning it to the first treatment tank. In this case, the polarizing film manufacturing apparatus drops the organic solvent-containing treatment liquid that has moved from the inside of the first treatment tank to the outside of the first treatment tank to a location different from the first treatment tank, and then returns it to the first treatment tank. Includes a liquid supply section (processing liquid recovery section) for processing.

In the second embodiment, the meaning of the first treatment tank is the same as in the first embodiment.
"Dropping" the organic solvent-containing treatment liquid that has been moved from the inside of the first treatment tank to the outside of the first treatment tank to a place different from the first treatment tank means storing it at a point higher than the bottom of the different place or in the different place. This means dropping the organic solvent-containing processing liquid from a point higher than the liquid level of the organic solvent-containing processing liquid onto the bottom surface or the liquid surface without transmitting it through walls, piping, etc.

Returning the processing liquid that has moved from the inside of the first processing tank to the outside of the first processing tank as a result of being used as a cleaning liquid or the like is important from the viewpoint of the appearance and quality of the polarizing film 25 to be obtained, and from the viewpoint of the polarizing film 25. This is preferable from the viewpoint of productivity.
However, if the process of returning the treatment liquid to the first treatment tank includes a step of dropping the treatment liquid to a location different from the first treatment tank, the liquid may dissolve into the treatment liquid due to the impact of the drop, etc. PVA resin may precipitate. If the treatment solution containing the precipitate is returned to the first treatment tank, the above-mentioned problems caused by the precipitate containing the PVA resin (adverse effect on the appearance and quality of the polarizing film 25) may occur.
According to the present invention, in which the treatment liquid stored in the first treatment tank is an organic solvent-containing treatment liquid, even if the above-mentioned impact due to falling occurs, precipitation of precipitates containing PVA resin can be suppressed. As a result, even if the organic solvent-containing treatment liquid is returned to the first treatment tank, the problem of deposits adhering to the PVA resin film 10 can be suppressed, and the polarizing film 25 with good appearance and quality can be obtained. Can be stably and continuously manufactured.

(4-2-1) Organic solvent-containing treatment liquid to be dropped The organic solvent-containing treatment liquid to be dropped to a location different from the first treatment tank is an organic solvent-containing treatment that has been moved from inside the first treatment tank to outside the first treatment tank. It is a liquid.
The organic solvent contained in the organic solvent-containing treatment liquid is the same as in the first embodiment, and the description regarding the first embodiment is cited.
The "organic solvent-containing treatment liquid that has moved from the inside of the first treatment tank to the outside of the first treatment tank" includes the organic solvent-containing treatment liquids included in [a] to [c] in (4-1-2) above. Can be mentioned.
If the organic solvent-containing treatment liquid included in [a] to [c] is returned to the first treatment tank, it can be reused as part of the treatment liquid, which is advantageous from the viewpoint of productivity of the polarizing film 25. .

(4-2-2) Liquid supply section (processing liquid recovery section)
A liquid supply unit for dropping the organic solvent-containing treatment liquid that has moved from inside the first treatment tank to outside the first treatment tank to a place different from the first treatment tank and then returning it to the first treatment tank is located at a place different from the first treatment tank. The organic solvent-containing treatment liquid can be dropped from a point higher than the bottom surface or a point higher than the liquid level of the organic solvent-containing treatment liquid stored in the different location, and the organic solvent-containing treatment liquid that has finished falling is transferred to the first treatment tank. There are no particular restrictions as long as it can be returned.
As the liquid supply section (processing liquid recovery section), for example,
[B1'] A means (such as a pump) for extracting at least part of the organic solvent-containing treatment liquid from the organic solvent-containing treatment liquid in the first treatment tank, using the extracted organic solvent-containing treatment liquid as a roll cleaning liquid; A means for directing the liquid toward the roll surface (such as a shower sprayer), and collecting the liquid that falls from the roll surface after cleaning the roll (including roll cleaning liquid that is directed toward the roll surface and bounces off the surface). a combination of collecting and guiding means for returning the treated organic solvent-containing treatment liquid to the first treatment tank;
[B2'] A means (such as a pump) for extracting at least part of the organic solvent-containing processing solution from the organic solvent-containing processing solution in the first processing tank, using the extracted organic solvent-containing processing solution as a film cleaning solution; A means (such as a shower sprayer) that directs the liquid toward the film surface, and a liquid that falls from the surface of the PVA resin film 10 after film cleaning (including the film cleaning liquid that is directed toward the film surface and bounces off the surface). a combination of collection and guiding means for collecting and returning the collected organic solvent-containing treatment liquid to the first treatment tank;
[B3'] Remove the excess organic solvent-containing treatment liquid that has adhered to the roll surface or the surface of the PVA-based resin film 10 after being immersed in the organic solvent-containing treatment liquid from the roll surface or the surface of the PVA-based resin film 10. A liquid cutting means (air shower, air knife, etc.) for cutting the liquid, and a liquid that falls from the roll surface or the surface of the PVA resin film 10 by liquid cutting are collected, and the collected organic solvent-containing processing liquid is transferred to the first processing tank. For example, a combination of collection and guidance methods to return to the original state.

The collecting/guiding means may be, for example, an inclined tray or the like. The saucer may be a tank, a sheet, or the like. A pump or the like may also be used as a means for returning the collected organic solvent-containing treatment liquid to the first treatment tank.
Note that when the organic solvent-containing treatment liquid is returned to the first treatment tank by the collecting/guiding means, the organic solvent-containing treatment liquid may be dropped into the first treatment tank, but this embodiment is different from the first embodiment. belong to In this embodiment, the organic solvent-containing treatment liquid is not dropped, but is returned to the liquid surface of the first treatment tank, or is returned to the organic solvent-containing treatment liquid in the first treatment tank. .

(5) Experimental example A polarizing film manufacturing apparatus similar to the apparatus shown in FIG. 1 was used, except that it had two crosslinking tanks (referred to as a first crosslinking tank 17a and a second crosslinking tank 17b, respectively). A polarizing film 25 was continuously produced from a long polyvinyl alcohol film (PVA resin film 10). The polyvinyl alcohol film used was a polyvinyl alcohol film with a thickness of 60 μm, and the degree of saponification of the polyvinyl alcohol constituting the film was 99.9 mol% or more, and the average degree of polymerization was 2,400.

[a] Swelling treatment process The PVA resin film 10 is continuously unwound and conveyed from the unwinding roll 11, and while being immersed in the swelling treatment tank 13 containing pure water at 30°C, a nip roll is used to prevent the film from loosening. Swelling treatment was performed by applying 2.5 times inter-roll stretching (longitudinal uniaxial stretching) with a peripheral speed difference between 2a and 2b.

[b] Dyeing process Next, the PVA resin film 10 that has passed through the nip roll 2b is placed in a dyeing tank 15 at 30°C in which the ratio of iodine/potassium iodide/water (weight ratio) is 0.05/2/100. It was immersed for 120 seconds. In this dyeing treatment, a peripheral speed difference was established between the nip rolls 2b and 2c, and inter-roll stretching (longitudinal uniaxial stretching) was performed at a rate of 1.1 times.

[c] Crosslinking treatment step Next, in order to perform a first crosslinking treatment for the purpose of making it water resistant, the PVA resin film 10 that has passed through the nip roll 2c is treated with potassium iodide/boric acid/water (weight ratio) of 12 The sample was immersed in the first crosslinking treatment tank 17a at 56° C./4.4/100 for 30 seconds. In this first crosslinking treatment as well, a peripheral speed difference was established between the nip rolls, and 1.9 times the inter-roll stretching (longitudinal uniaxial stretching) was performed. Next, the PVA resin film 10 after the first crosslinking treatment is placed in a second crosslinking treatment tank 17b at 40° C. in which potassium iodide/boric acid/water (weight ratio) is 9/2.9/100 for 15 seconds. immersion (second crosslinking treatment). In this second crosslinking treatment as well, a peripheral speed difference was established between the nip rolls, and 1.05 times the inter-roll stretching (longitudinal uniaxial stretching) was performed.
Thereafter, the PVA resin film 10 after the second crosslinking treatment is immersed in a cleaning treatment tank 19 containing pure water at 15°C, and then dried at 70°C for 3 minutes by passing through a drying oven 21, and then polarized. Film 25 was produced.

The crosslinking treatment liquid was sampled from the second crosslinking treatment tank 17b after the continuous production of the polarizing film described above was carried out, and the following experiment was conducted. The polyvinyl alcohol concentration in the sampled crosslinking solution was measured by GPC (gel permeation chromatography) and was found to be about 1300 ppm on a weight basis.

400 mL of cross-linking treatment liquid was extracted from the second cross-linking treatment tank 17b after carrying out the continuous production of the polarizing film described above, and 40 mL of pure water was added thereto. When the resulting mixed solution was dropped over a period of 5 minutes from a height of 30 cm, generation of a solid containing PVA resin was observed.
On the other hand, when a similar experiment was conducted by adding 40 mL of ethanol instead of 40 mL of pure water, no generation of solids containing PVA-based resin was observed.

1a, 1b, 1c, 1d, 1e, 1f, 1g, 1h, 1i, 1j, 1k, 1l Guide roll, 2a, 2b, 2c, 2d, 2e, 2f Nip roll, 10 Polyvinyl alcohol resin film (PVA resin film ), 11 unwinding roll, 13 swelling treatment tank, 15 dyeing treatment tank, 17 crosslinking treatment tank, 19 cleaning treatment tank, 21 drying oven, 25 polarizing film, 27 winding roll.

Claims (8)

A method for producing a polarizing film from a polyvinyl alcohol resin film, the method comprising:
The polyvinyl alcohol resin film is conveyed along a conveyance path passing through a first treatment tank configured with a plurality of rolls and containing an organic solvent-containing treatment liquid, and the polyvinyl alcohol resin film is transferred to the organic solvent-containing treatment liquid. a step of soaking the
dropping the organic solvent-containing treatment liquid that has moved from the inside of the first treatment tank to the outside of the first treatment tank to a location different from the first treatment tank, and then returning it to the first treatment tank;
including;
The organic solvent-containing treatment liquid moved from the inside of the first treatment tank to the outside of the first treatment tank,
an organic solvent-containing treatment liquid used as a cleaning liquid for cleaning at least one roll among the plurality of rolls;
an organic solvent-containing treatment liquid used as a cleaning liquid for cleaning the surface of the polyvinyl alcohol resin film being conveyed along the conveyance route, and
An organic solvent-containing treatment liquid that is drained by supplying gas to the surface of at least one roll among the plurality of rolls.
The method is one or more selected from the group consisting of : The transport route further passes through one or more processing tanks that are arranged upstream of the first processing tank and that contain processing liquid,
The temperature of the organic solvent-containing treatment liquid is lower than the temperature of the treatment liquid accommodated in a treatment tank located closest to the first treatment tank among the one or more treatment tanks. Method. The method according to claim 1 or 2, wherein the organic solvent-containing processing liquid contains at least one of a dichroic dye and a crosslinking agent. The one or more processing tanks include, in order from the upstream side of the transport route, a second processing tank and a third processing tank,
The method according to claim 2, wherein the second processing tank contains a dichroic dye, and the third processing tank and the first processing tank contain a crosslinking agent. An apparatus for producing a polarizing film from a polyvinyl alcohol resin film,
A transport path for polyvinyl alcohol resin film composed of multiple rolls,
a first processing tank disposed on the transport path and containing an organic solvent-containing processing liquid in which the polyvinyl alcohol resin film is immersed;
a liquid supply unit that returns the organic solvent-containing treatment liquid that has moved from the inside of the first treatment tank to the outside of the first treatment tank to a location different from the first treatment tank and then returns to the first treatment tank;
including;
The organic solvent-containing treatment liquid moved from the inside of the first treatment tank to the outside of the first treatment tank,
an organic solvent-containing treatment liquid used as a cleaning liquid for cleaning at least one roll among the plurality of rolls;
an organic solvent-containing treatment liquid used as a cleaning liquid for cleaning the surface of the polyvinyl alcohol resin film being conveyed along the conveyance route, and
An organic solvent-containing treatment liquid that is drained by supplying gas to the surface of at least one roll among the plurality of rolls.
A device that is one or more types selected from the group consisting of . A processing tank disposed upstream of the first processing tank on the transport route, further including one or more processing tanks that contain a processing liquid,
The temperature of the organic solvent-containing treatment liquid is lower than the temperature of the treatment liquid accommodated in a treatment tank located closest to the first treatment tank among the one or more treatment tanks. Device. The apparatus according to claim 5 or 6, wherein the organic solvent-containing processing liquid contains at least one of a dichroic dye and a crosslinking agent. The one or more processing tanks include, in order from the upstream side of the transport route, a second processing tank and a third processing tank,
The apparatus according to claim 6, wherein the second processing tank contains a dichroic dye, and the third processing tank and the first processing tank contain a crosslinking agent.

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