JP2019066681A - Method for manufacturing polarizing film - Google Patents

Abstract

To provide a method capable of continuously and stably manufacturing a polarizing film while suppressing adhesion of the deposit deposited from a process liquid used for wet processing of a polyvinyl alcohol resin film to the polyvinyl alcohol resin film.SOLUTION: There is provided a method for manufacturing a polarizing film from a polyvinyl alcohol resin film comprising the steps of: immersing the polyvinyl alcohol resin film in a process liquid by transporting the polyvinyl alcohol resin film along a transportation path passing a processing tank storing the process liquid; and forming a droplet of the process liquid and depositing a solid containing the polyvinyl alcohol resin film from the droplet.SELECTED DRAWING: Figure 1

Description

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

  As a polarizing film, a uniaxially stretched polyvinyl alcohol-based resin film in which a dichroic dye such as iodine is adsorbed and oriented is conventionally used. In general, a polarizing film is sequentially subjected to a dyeing process of dyeing a polyvinyl alcohol-based resin film with a dichroic dye, a crosslinking process of treating with a crosslinking agent, and a film drying process, and to the polyvinyl alcohol-based film during the manufacturing process. Manufactured by subjecting to a stretching treatment [e.g., JP-A-2001-141926 (Patent Document 1)].

JP 2001-141926 A

  In general, the polarizing film industrially transports a long polyvinyl alcohol-based resin film continuously along the transport path of the film possessed by the apparatus for producing a polarizing film while the above-mentioned polarizing membrane is on the transport path. It is manufactured including a wet treatment process of sequentially immersing 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 manufactured continuously according to the above method, the polyvinyl alcohol-based resin gradually dissolves in the treatment liquid in which the polyvinyl alcohol-based resin film is immersed. The dissolved polyvinyl alcohol-based resin may be precipitated from the processing solution for some reason, and when precipitation occurs, the precipitate adheres to the surface of the polyvinyl alcohol-based resin film during wet processing, and hence to the polarizing film, It may adversely affect the appearance and quality of the polarizing film.
In addition, when the concentration of the polyvinyl alcohol-based resin dissolved in the treatment liquid is gradually increased, the polyvinyl alcohol-based resin is contained on the surface of the polyvinyl alcohol-based resin film drawn from the treatment liquid after being immersed in the treatment liquid. Solids may also precipitate out. 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 capable of stably and continuously producing a polarizing film while suppressing the deposition of the precipitate on the film.

The present invention provides a method for producing a polarizing film described below.
[1] A method for producing a polarizing film from a polyvinyl alcohol resin film,
Conveying the polyvinyl alcohol-based resin film along a transport path passing through a treatment tank containing the treatment liquid, and immersing the polyvinyl alcohol-based resin film in the treatment liquid;
Forming a droplet of the treatment liquid and depositing a solid containing a polyvinyl alcohol resin from the droplet;
Method, including.
[2] The method according to [1], wherein the depositing step includes decreasing the temperature of the treatment liquid or the droplets.
[3] The method according to [1] or [2], further comprising the step of removing at least a part of the solid after the depositing step.
[4] The method according to [3], further including the step of returning at least a portion of the liquid recovered by the removing step to the treatment tank.
[5] The method according to any one of [1] to [4], wherein the treatment liquid contains at least one of a dichroic dye and a crosslinking agent.

  It is possible to provide a method capable of stably and continuously producing a polarizing film while suppressing adhesion of a precipitate containing a polyvinyl alcohol-based resin to a film.

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

  Hereinafter, the manufacturing method of a polarizing film is demonstrated, showing embodiment.

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

An example of a polarizing film manufacturing apparatus is shown in FIG. The polarizing film manufacturing apparatus shown by FIG. 1 is an apparatus for manufacturing the elongate polarizing film 25 continuously from the elongate PVA-type resin film 10 which is a raw material film. Arrows in FIG. 1 indicate the transport direction of the film or the flow direction of the liquid or the like.
In the production of the polarizing film 25 using the production apparatus shown in FIG. 1, the swelling treatment tank 13, the dyeing treatment tank 15, and the crosslinking treatment tank 17 while continuously unwinding the PVA-based resin film 10 from the unwinding roll 11. Then, the polarizing film 25 is obtained by sequentially immersing in the cleaning treatment tank 19 and finally passing it through a drying furnace 21 to perform a drying treatment. The polarizing film 25 manufactured as a long product may be wound up sequentially on the winding roll 27, or a thermoplastic resin film such as a protective film is adhered to one side or both sides of the polarizing film 25 without being wound up. It may be provided to a polarizing plate manufacturing process.

The polarizing film manufacturing apparatus is a wet processing unit including a swelling processing tank 13, a staining processing tank 15, a crosslinking processing tank 17, a cleaning processing tank 19 and the like (a wet processing is performed using a processing tank containing a processing liquid in which a film is immersed). A zone to be carried out) and a drying section (zone for carrying out the drying process on the film after the wet process) such as the drying furnace 21 are usually included.
The polarizing film manufacturing apparatus shown by FIG. 1 has a conveyance path | route of the PVA-type resin film 10 containing a wet process part and a drying process part. By conveying the PVA-based resin film 10 along this conveyance path, a series of treatments including wet treatment and drying treatment are performed to obtain the polarizing film 25.
The conveyance speed of the PVA-based 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 transport path is constructed by a plurality of rolls supporting and guiding the film (PVA-based resin film 10 and polarizing film 25) in motion so as to pass through the wet processing unit and the drying processing unit. Be done. The plurality of rolls consists of a guide roll, which is a free roll supporting one side of the film, and / or a pair of rolls (usually including a drive roll), which, for example, have two sides of the film. It is a nip roll which sandwiches or presses from there. 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 defining the transport path may include a suction roll (a suction roll) which is one of drive rolls. Usually, these rolls support the film in contact with one or both surfaces (main surfaces) of the film in the transport path. These rolls can be disposed at appropriate positions, such as before and after each treatment tank and drying means (drying oven), or in the treatment tank and drying means (drying oven).

  The drive roll refers to a roll that can provide a driving force for film transport to the film in contact therewith, and can be a roll or the like to which a roll drive source such as a motor is directly or indirectly connected. . The free roll plays a role of supporting a traveling film and refers to a roll that can freely rotate in accordance with the transport of the film.

The method for producing a polarizing film according to the present invention comprises the following steps:
A step of conveying the PVA-based resin film along a transport path passing through the treatment tank containing the treatment liquid, and immersing the PVA-based resin film in the treatment liquid (wet treatment step S101); Forming and depositing a solid containing the PVA-based resin from the droplets (solid deposition step S201)
including.

  The polarizing film 25 obtained is one that has been subjected to a stretching process (usually a uniaxial stretching process). For this reason, the manufacturing apparatus of a polarizing film can include a stretching means (wet stretching means) of the PVA-based resin film 10, and a method of producing a polarizing film comprises a stretching process step (wet stretching process) of the PVA-based resin film 10. Process) can be included.

(1) PVA-Based Resin Film The PVA-based resin film 10 to be subjected to the wet treatment step S101 (introduced to the wet treatment section) is composed of a polyvinyl alcohol-based resin (hereinafter also referred to as "PVA-based resin"). Film. The PVA-based resin refers to a resin containing 50% by weight or more of a structural unit derived from vinyl alcohol. As PVA system resin, what saponified polyvinyl acetate system resin can be used. Examples of polyvinyl acetate 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, (meth) acrylamides having an ammonium group, and the like.
In addition, "(meth) acryl" represents at least 1 sort (s) chosen from the group which consists of an acryl and methacryl. The same applies to other terms with "(meth)".

  The saponification degree of the PVA-based 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 94.0 to 0. It is in the range of 100.0 mol%, more preferably in the range of 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 including the same may be reduced.

The degree of saponification refers to the ratio of acetic acid group (acetoxy group: -OCOCH ₃ ) contained in polyvinyl acetate resin, which is a raw material of PVA resin, changed to hydroxyl group in the saponification process in unit ratio (mol%) And the following formula:
Degree of saponification (mol%) = 100 × (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-based resin is preferably 100 to 10,000, more preferably 1,500 to 8,000, and still more preferably 2,000 to 5,000. The average degree of polymerization of the PVA-based 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 the polarizing film 25 having preferable polarization performance, and when it exceeds 10000, the solubility in a solvent is deteriorated and the formation (film formation) of the PVA resin film 10 is difficult. It can be

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

In dry stretching, a film is passed between a heat roll whose surface is heated and a guide roll (or a heat roll) having a circumferential speed different from that of the heat roll, and heating is performed using the heat roll. Hot roll drawing which performs longitudinal drawing under; between rolls performing longitudinal drawing by the circumferential speed difference between these two nip rolls while passing a heating means (such as an oven) between two nip rolls placed at a distance. Stretching; tenter stretching; compression stretching etc. can be mentioned.
The stretching temperature (the surface temperature of the heat roll, the temperature in the oven, etc.) is, for example, 80 to 150 ° C., preferably 100 to 135 ° C.

  Although the draw ratio of the said extending | stretching is based also on whether it implements wet extending | stretching in wet processing process S101 mentioned later, and the draw ratio in the said wet extending | stretching, it is 1.1 to 8 times normally, Preferably 2 5 to 5 times.

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

  The thickness of the PVA-based resin film 10 to be subjected to the wet treatment step S101 (introduced to the wet treatment section) is usually 10 to 150 μm, depending on whether or not the PVA-based resin film 10 is a stretched film. Preferably, the thickness is 100 μm or less, more preferably 65 μm or less, still more preferably 50 μm or less, and particularly preferably 35 μm or less (for example, 30 μm or less, further 20 μm or less) from the viewpoint of thinning the obtained polarizing film 25.

(2) Wet treatment process S101
The wet processing unit in which the wet processing step S101 is performed is a zone disposed on the transport path of the PVA-based resin film 10, and includes a processing tank that accommodates the processing liquid in which the PVA-based resin film 10 is immersed. In the wet processing unit, a wet processing step S101 is performed in which the PVA-based resin film 10 is immersed in the processing liquid while transporting the PVA-based resin film 10.

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

(2-1) Swelling Step The swelling treatment is a treatment which is carried out as necessary for the purpose of removing foreign matter, removing the plasticizer, imparting easy dyeability, plasticizing the film, etc. of the PVA-based resin film 10.
Referring to FIG. 1, in the swelling treatment step, the PVA-based resin film 10 is conveyed along the film conveyance path while being unwound continuously from the unwinding roll 11, and the PVA-based resin film 10 is subjected to the swelling treatment solution. It can be implemented by immersing in the swelling treatment tank 13 to be stored for a predetermined time and then withdrawing.

The treatment liquid (swelling treatment liquid) contained in the swelling treatment tank 13 can be, for example, water (pure water or the like), or may be an aqueous solution to which a water-soluble organic solvent such as alcohol is added. The swelling treatment solution can also contain boric acid, chlorides, inorganic acids, inorganic salts and the like.
The temperature of the swelling treatment solution is usually 10 to 70 ° C, preferably 15 to 50 ° C, and more preferably 15 to 35 ° C. The immersion time (retention time in the swelling treatment liquid) of the PVA-based resin film 10 is usually 10 to 600 seconds, preferably 15 to 300 seconds.

During the swelling process, the PVA-based 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, uniaxial stretching can be performed in swelling treatment tank 13 using, for example, the difference in peripheral speed between nip roll 2a and nip roll 2b.
In the example shown in FIG. 1, the film drawn from the swelling treatment tank 13 is introduced into the dyeing treatment tank 15 sequentially through the guide roll 1 c and the nip roll 2 b.

(2-2) Dyeing process process A dyeing process is a process implemented for the purpose of making a PVA-type resin film 10 adsorb | suck and orientate a dichroic dye.
Referring to FIG. 1, the dyeing process can be carried out by conveying along the film conveying path, immersing the PVA-based resin film 10 in the dyeing tank 15 for a predetermined time, and then pulling it out. The dyeing processing tank 15 is a tank for immersing the PVA-based resin film 10 in the dyeing processing solution contained therein. The PVA-based resin film 10 to be immersed in the dyeing treatment solution is preferably a film after the swelling treatment step (immersed in the swelling treatment tank 13).
The staining solution contained in the staining 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. The dichroic dyes may be used alone or in combination of two or more.

  When iodine is used as the dichroic dye, an aqueous solution containing iodine and potassium iodide can be used as the staining solution. Instead of potassium iodide, other iodides such as zinc iodide may be used, and potassium iodide and other iodides may be used in combination. In addition, compounds other than iodide, for example, boric acid, zinc chloride, cobalt chloride and the like may coexist. When boric acid is added, it is distinguished from the crosslinking treatment 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 with respect to 100 parts by weight of water, it can be regarded as a staining 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 staining solution is usually 10 to 45 ° C, preferably 10 to 40 ° C, and more preferably 20 to 35 ° C. The immersion time (residence time in the staining solution) of the PVA-based 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 vessels 15. In this case, the composition and temperature of each staining solution may be the same or different.

In order to enhance the dyeability of the dichroic dye, the PVA-based resin film 10 to be subjected to the dyeing process is preferably at least partially subjected to a stretching process (usually a uniaxial stretching process). Instead of the stretching process before the dyeing process, or in addition to the stretching process before the dyeing process, the stretching process may be performed while performing the dyeing process. The stretching ratio of integration up to the dyeing process (the stretching ratio in the dyeing process when there is no drawing process up to the dyeing process) is usually 1.6 to 4.5 times, preferably 1.8 to 4 times . Referring to FIG. 1, for example, uniaxial stretching can be performed in the dyeing processing tank 15 by utilizing the peripheral speed difference between the nip roll 2b and the nip roll 2c.
In the example shown in FIG. 1, the film drawn from the dyeing treatment tank 15 is introduced into the crosslinking treatment tank 17 by sequentially passing through the guide roll 1 f and the nip roll 2 c.

(2-3) Crosslinking treatment step Crosslinking treatment is treatment to be carried out for the purpose of water resistance by crosslinking, hue adjustment (complementary color) and the like.
Referring to FIG. 1, the crosslinking treatment is carried along the film conveyance path, and the PVA-based resin film 10 after the dyeing treatment step S101 (immersed in the dyeing treatment tank 15) is dipped in the crosslinking treatment tank 17 for a predetermined time And then withdraw it. The crosslinking treatment tank 17 is a tank for immersing the PVA-based resin film 10 in the crosslinking treatment liquid contained therein.
The crosslinking treatment liquid accommodated in the crosslinking treatment tank 17 is a liquid (usually, an aqueous solution) containing a crosslinking agent. The crosslinking treatment is performed by immersing the PVA-based resin film 10 after the dyeing treatment step in the crosslinking treatment solution.

Examples of the crosslinking agent contained in the crosslinking solution include boric acid, glyoxal, glutaraldehyde and the like, with preference given to boric acid. Two or more crosslinkers can also be used in combination.
The content of the crosslinking agent in the crosslinking treatment 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 solution preferably contains an iodide in addition to the crosslinking agent.
Examples of the iodide 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 solution may contain compounds other than iodide. Examples of the compound include zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate and the like.

  The temperature of the crosslinking solution is generally in the range of usually 20 to 85 ° C, preferably 30 to 70 ° C. The immersion time (residence time in the crosslinking treatment solution) of the PVA-based 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 vessels 17. In this case, the composition and temperature of each crosslinking treatment solution may be the same or different. The crosslinking treatment liquid may have a concentration of a crosslinking agent, an iodide, or the like according to the purpose of immersing the PVA-based resin film 10, or a temperature. The crosslinking treatment for waterproofing by crosslinking and the crosslinking treatment for hue adjustment (complementary color) may be performed in a plurality of steps.
Generally, when carrying out both the crosslinking treatment for water resistance-ization by crosslinking and the crosslinking treatment for hue adjustment (complementary color), the tank (complementary vessel) for carrying out the crosslinking treatment for hue adjustment (complementary color) is Be placed. The temperature of the processing solution 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 treatment liquid contained in the complementary color tank is, for example, 1 to 5 parts by weight per 100 parts by weight of water. The content of iodide in the processing solution contained in the complementary color tank is, for example, 3 to 30 parts by weight per 100 parts by weight of water.

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

(2-4) Cleaning treatment process The manufacturing method of a polarizing film can further include the washing treatment process after a crosslinking treatment process, and, for this reason, a polarizing film manufacturing device is arranged in the lower stream side of a crosslinking treatment tank 17. The washing processing tank 19 can further be included. The washing treatment is a treatment to be carried out for the purpose of removing an excess drug attached to the PVA-based resin film 10 after the crosslinking treatment step.
Referring to FIG. 1, the cleaning process is carried along the film transport path, and the PVA-based resin film 10 after the crosslinking process (immersed in the crosslinking process tank 17) is immersed in the cleaning process tank 19 for a predetermined time. , And then by pulling out. Alternatively, the cleaning process may be a process of spraying the cleaning solution as a shower, for example, on the PVA-based resin film 10 after the crosslinking process step, or the immersion in the cleaning processing tank 19 and the spraying of the cleaning solution may be combined. . In FIG. 1, the example in the case of immersing the PVA-type resin film 10 in the washing process tank 19 and performing a washing process is shown.

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

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

(2-5) Stretching Step In the wet step, wet stretching may be performed on the PVA-based resin film 10. The wet stretching is usually uniaxial stretching and can be performed while performing any of a swelling treatment, a dyeing treatment, a crosslinking treatment, and a washing treatment, or during two or more treatments selected therefrom.
Wet stretching is preferably done in one or more steps prior to the crosslinking step or steps. As described above, in order to enhance the dyeability of the dichroic dye and obtain the polarizing film 25 having good polarization characteristics, the PVA-based resin film 10 subjected to the dyeing treatment step is subjected to at least a certain degree of stretching treatment. It is more preferable that
The stretching magnification of the wet stretching is preferably the final cumulative stretching magnification of the polarizing film 25 (in the case where the PVA-based resin film 10 to be subjected to the wet processing is a stretched film), from the viewpoint of the polarization properties of the polarizing film 25 obtained. In this case, the cumulative stretching ratio (including this stretching) is adjusted to be 3 to 8 times.

  When the wet stretching treatment step is carried out, the polarizing film production apparatus includes a wet stretching means of the PVA-based resin film 10. The wet stretching means is preferably a stretching means that performs inter-roll stretching. Taking the case of performing stretching between rolls by wet processing in the crosslinking treatment step as an example, stretching means for performing stretching between rolls are two nip rolls 2c and 2d disposed before and after the crosslinking treatment tank 17. Similarly, in the case of performing stretching during other wet processing, two nip rolls arranged at a distance can be used as a wet stretching means.

(3) Drying Process Step The drying process section in which the drying process process is performed is a PVA-based resin after the wet process process S101, which is disposed on the transport path of the PVA-based resin film 10 and downstream of the wet process system. It is a zone for drying the film 10. While the PVA-based resin film 10 after the wet treatment step S101 is continuously transported, a drying process can be performed by introducing the film into the drying process section, whereby a polarizing film 25 is obtained (see FIG. 1).

  The drying processing unit includes a drying unit (heating unit) of the film. A preferred example of the drying means is a drying oven. The drying furnace is preferably capable of controlling the temperature in the furnace. The drying furnace is, for example, a hot air oven capable of increasing the temperature in the furnace by supply of hot air or the like. Further, the drying process by the drying means is a process of bringing the PVA-based resin film 10 after the wet treatment process into close contact with one or more heating members having a convex curved surface, or a process of heating the film using a heater. Good.

  As said heating body, a heat source (for example, heat mediums, such as warm water, infrared heater) can be included inside, and the roll (for example, guide roll which served as the heat roll) which can raise surface temperature can be mentioned. As said heater, an infrared heater, a halogen heater, a panel heater etc. can be mentioned. FIG. 1 shows an example in which the PVA-based resin film 10 after the wet treatment step S101 is introduced into the drying furnace 21 and dried.

  The temperature of the drying treatment (for example, the temperature in the furnace of the drying furnace 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 one in which a dichroic dye is adsorbed and oriented on a stretched (usually uniaxially stretched) PVA-based resin film. The thickness of the polarizing film 25 is usually 2 to 40 μm. From the viewpoint of thinning 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%, in consideration of the balance with the visibility correction polarization degree Py. The visibility correction polarization degree Py is preferably 99.9% or more, and more preferably 99.95% or more.
Ty and Py can be measured by using an absorptiometer equipped with an integrating sphere and performing visibility correction on the obtained transmittance and polarization degree with a two-degree field of view (C light source) of JIS Z 8701.

  The obtained polarizing film 25 may be sequentially wound on a winding roll 27 to form a roll form, or a polarizing plate production process (a thermoplastic resin film (protective film etc. on one side or both sides of the polarizing film 25 as it is) without being wound. ) Can also be used in the step of laminating).

(4) Solid precipitation step S201
This step is a step of forming droplets of the treatment liquid used in the wet treatment step S101 and depositing a solid containing a PVA-based resin from the droplets.
According to the method of once forming a droplet of the treatment liquid and depositing a solid from the droplet, it is possible to deposit the solid efficiently. By removing the solid and returning the remaining liquid to the treatment tank, the concentration of the PVA-based resin in the treatment liquid in the treatment tank can be suppressed from the above-mentioned failure that the precipitate containing the PVA-based resin adheres to the film. It can be reduced or maintained to some extent.

The treatment liquid to be subjected to the solid precipitation step S201 is one or more treatment liquids selected from the group consisting of a swelling treatment liquid, a staining treatment liquid, a crosslinking treatment liquid, and a washing treatment liquid. For example, when there are two or more crosslinking treatment vessels 17, the solid deposition step S201 may be performed for each of the crosslinking treatment solutions contained in two or more vessels selected from these. The same applies to the swelling treatment tank 13, the staining treatment tank 15, and the washing treatment tank 19.
Among the above-mentioned treatment liquids, a treatment liquid containing at least one of a dichroic dye and a crosslinking agent is preferable because the PVA-based resin is easily precipitated or the concentration of the PVA-based resin is easily increased, that is, Preferably, it is at least one of a staining treatment solution and a crosslinking treatment solution. For the same reason, it is more preferable to carry out the solid precipitation step S201 at least for the crosslinking treatment liquid, and it is further preferable to carry out the solid precipitation step S201 for at least the crosslinking treatment liquid used in the complementary bath.
The concentration of the PVA-based resin in the treatment liquid to be subjected to the solid precipitation step S201 may be, for example, about 5 ppm to about 5000 ppm by weight.
The precipitated solid may further include other components (for example, in the case of a crosslinking treatment solution, a crosslinking agent, an iodide, and the like) other than the PVA-based resin.

  The solid precipitation step S201 can be implemented by extracting at least a part of the treatment liquid in the treatment tank from the treatment tank and introducing the same into the droplet generation unit to generate droplets. Solids are deposited in the process of vaporization of the droplets. FIG. 1 shows an example in which the droplet generation unit 30 is connected to the crosslinking treatment tank 17 via the connection path (connection line) 29.

Although solid precipitation process S201 is not specifically limited, For example, it can implement with the following method.
[A] A method of forming droplets by using a gas spray device as the droplet generation unit 30, and spraying a treatment liquid to which pressure is applied by gas from the tip of a nozzle.
Examples of the gas include, in addition to air, inert gases such as nitrogen, helium and argon.
[B] A method of using a spray nozzle as the droplet generation unit 30, pressurizing the processing liquid using a piston, a pump or the like, and spraying it from the tip of the nozzle to form a mist (mist) -like droplet.
[C] A method of forming a mist (mist) -like droplet by spraying a treatment liquid using an air brush as the droplet generation unit 30.
The air brush is a sprayer utilizing the Venturi effect accompanying the supply of gas. Examples of the gas include, in addition to air, inert gases such as nitrogen, helium and argon.
[D] A method of forming a mist (fog) -like droplet by applying an ultrasonic wave to the treatment liquid using an ultrasonic atomizer as the droplet generation unit 30.
[E] A method of forming a mist-like droplet by spraying the treatment liquid by the action of electrostatic force using an electrospray apparatus as the droplet generation unit 30.
[F] A method of using a spin spray apparatus as the droplet generation unit 30, and forming smaller droplets from the processing liquid or the droplets thereof.
A spin spray device is a device that has a rotatable plate that can rotate at high speed, and distributes the liquid by centrifugal force by disposing the liquid there.
[G] A method of using a boiling device as the droplet generation unit 30 to boil or bump the treatment liquid to form droplets.
As a boiling device, for example, a pressure reducing device that causes boiling or bumping by reducing the pressure of the environment in which the treatment liquid is placed (a heated plate or the like) that causes boiling or bumping by contacting the treatment liquid Etc.

  Dropping the treatment liquid tends to cause precipitation of a solid. However, if the size of the droplets is too large, solid deposition hardly occurs. Therefore, the size of the droplet of the treatment liquid is preferably in the range of, for example, about 1 nm to 1 mm.

  In order to be able to easily recover the solid-liquid product (the processing liquid in which the solid is precipitated) obtained in the solid precipitation step S201, dropletization (and solid precipitation) of the processing liquid is usually carried out in a closed space. Be done.

The solid deposition step S201 may include the step of reducing the temperature of the treatment liquid or the droplets formed therefrom. If solids are precipitated after lowering the temperature of the treatment liquid, or while lowering the temperature of the treatment liquid, or when the temperature of the droplets is lowered, the solubility of the PVA-based resin in water decreases, so the amount of solids precipitation Tend to increase By increasing the precipitation amount of the solid, the removal efficiency of the PVA-based resin eluted in the treatment liquid can be enhanced.
The cooling temperature of the treatment liquid or droplet is, for example, 0 to 25 ° C, preferably 0 to 15 ° C.
The lowering of the temperature of the treatment liquid or the droplet includes the temperature lowering caused by the heat being taken away as the heat of vaporization when a part of the droplet is vaporized.

  The solid deposition step S201 may be performed in a connection path for extracting the treatment liquid from the treatment tank. That is, the connection path itself may double as the droplet generation unit 30.

(5) Solid removal step S202
The manufacturing method of a polarizing film can further include the process of removing at least one copy of solid (solid containing PVA system resin) produced at solid precipitation process S201.
It does not restrict | limit especially as a method to remove a solid, The method to remove a solid using physical adsorption, such as activated carbon treatment, and a solid-liquid separation (filtration) using solid-liquid separation apparatuses, such as a filtration filter And the like.
FIG. 1 shows an example of removing the solid by introducing the solid-liquid product (the treatment liquid in which the solid is separated) obtained in the solid precipitation step S201 into the filter 40 through the connection path (connection line) 31. There is. The connection path (connection line) 31 connects the droplet generation unit 30 and the filtration filter 40.

(6) Reuse process S203
The method for producing a polarizing film may further include the step of returning at least a part of the liquid (the treatment liquid after removal of the solid) recovered by the solid removal step S202 to the treatment tank.
The liquid is returned to the treatment tank after temperature adjustment and the like, as necessary.
Referring to FIG. 1, the liquid can be returned to the treatment tank through connection passage 41 connecting filtration filter 40 and the treatment tank (crosslinking treatment tank 17).

  The liquid returned to the treatment tank is one in which the concentration of the PVA-based resin is reduced through the solid removal step S202. Therefore, the concentration of the PVA-based resin in the treatment liquid in the treatment tank can be precipitated by including the PVA-based resin by continuously performing the series of steps of the solid precipitation step S201, the solid removal step S202, and the reuse step S203. It can be reduced or maintained to such an extent that the above-mentioned failure that an object adheres to a film can be suppressed.

  In order to adjust the amount of treatment liquid in the treatment tank, at least a part of the liquid collected in the solid removal step S202 is returned to the treatment tank, or at least a part of the liquid collected in the solid removal step S202 is treated The processing bath may be replenished with fresh processing liquid at a timing different from the process of returning to the bath.

(7) Experimental Example A polarizing film production apparatus similar to the apparatus shown in FIG. 1 is used except that two crosslinking treatment tanks are provided (referred to as first crosslinking treatment tank 17a and second crosslinking treatment tank 17b, respectively). The polarizing film 25 was continuously manufactured from a long polyvinyl alcohol film (PVA-based resin film 10). The polyvinyl alcohol film used was a polyvinyl alcohol film having a thickness of 60 μm, and the degree of saponification of polyvinyl alcohol constituting the film was 99.9 mol% or more, and the average degree of polymerization was 2400.

[A] Swelling Step A nip roll so that the film is not slackened while being conveyed while continuously unwinding the PVA-based resin film 10 from the unwinding roll 11 and being immersed in the swelling treatment tank 13 containing pure water at 30 ° C. It was subjected to swelling processing by performing 2.5 times roll-to-roll stretching (longitudinal uniaxial stretching) with a circumferential speed difference between 2a and 2b.

[B] Dyeing Step Next, the PVA-based resin film 10 which has passed through the nip roll 2b is placed in a dyeing treatment tank 15 at 30 ° C. in which iodine / potassium iodide / water (weight ratio) is 0.05 / 2/100. Soak for 120 seconds. In this dyeing process, a circumferential speed difference was provided between the nip rolls 2b and 2c to perform 1.1-fold inter-roll stretching (longitudinal uniaxial stretching).

[C] Crosslinking treatment step Next, in order to perform the first crosslinking treatment for the purpose of water resistance, the PVA-based resin film 10 which has passed through the nip roll 2c is made of potassium iodide / boric acid / water (weight ratio) 12 It was immersed for 30 second in the 1st bridge | crosslinking processing tank 17a of 56 degreeC which is /4.4/100. Also in the first crosslinking treatment, the inter-roll stretching (longitudinal uniaxial stretching) of 1.9 times was performed with a circumferential speed difference between the nip rolls. Next, the PVA resin film 10 after the first crosslinking treatment is added to the 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. Soaked (second crosslinking treatment). Also in the second crosslinking treatment, the difference in peripheral speed was made between the nip rolls, and the in-roll stretching (longitudinal uniaxial stretching) of 1.05 times was performed.
Thereafter, the PVA resin film 10 after the second crosslinking treatment is immersed in the washing treatment tank 19 containing pure water at 15 ° C., and then passed through the drying furnace 21 to be dried at 70 ° C. for 3 minutes to obtain polarized light. Film 25 was produced.

  The crosslinking treatment solution was sampled from the second crosslinking treatment tank 17b after the continuous production of the polarizing film, and the following solid precipitation experiment was performed. The polyvinyl alcohol concentration in the sampled crosslinking treatment liquid was measured by GPC (gel permeation chromatography) and found to be about 1300 ppm by weight.

(1) The crosslinking treatment solution (400 mL) at 40 ° C. was left at room temperature. After standing for 30 minutes, the temperature of the crosslinking solution became 37 ° C., but no precipitation of solid was observed.
(2) The crosslinking solution (400 mL) at 40 ° C. was cooled to 15 ° C. over 30 minutes, but no precipitation of solid was observed.
(3) In a plastic bag, the crosslinking treatment solution (400 mL) at 40 ° C. was sprayed using a spray nozzle for 20 minutes. A large amount of solid containing a PVA-based resin was precipitated in the crosslinking solution accumulated in the bag. The temperature of the crosslinking solution accumulated in the bag was 19 ° C.

  1a, 1b, 1c, 1d, 1e, 1f, 1h, 1i, 1j, 1k, 1l Guide rolls, 2a, 2b, 2c, 2d, 2e, 2f Nip rolls, 10 polyvinyl alcohol resin film (PVA resin film ), 11 unwinding rolls, 13 swelling processing tanks, 15 dyeing processing tanks, 17 crosslinking processing tanks, 19 washing processing tanks, 21 drying furnaces, 25 polarizing films, 27 winding rolls, 29 connection paths, 30 droplet generating parts, 31 connections, 40 filtration filters, 41 connections.

Claims (5)

A method for producing a polarizing film from a polyvinyl alcohol resin film,
Conveying the polyvinyl alcohol-based resin film along a transport path passing through a treatment tank containing the treatment liquid, and immersing the polyvinyl alcohol-based resin film in the treatment liquid;
Forming a droplet of the treatment liquid and depositing a solid containing a polyvinyl alcohol resin from the droplet;
Method, including.   The method according to claim 1, wherein the depositing step comprises reducing the temperature of the treatment liquid or the droplets.   The method according to claim 1 or 2, further comprising the step of removing at least a portion of the solid after the depositing step.   The method according to claim 3, further comprising the step of returning at least a portion of the liquid recovered by the removing step to the processing tank.   The method according to any one of claims 1 to 4, wherein the treatment liquid contains at least one of a dichroic dye and a crosslinking agent.

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