JP7260266B2 - Polarizing film manufacturing equipment - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a polarizing film and an apparatus for producing a polarizing film, which can be used, for example, as a constituent member of a polarizing plate.

As a polarizing film, a uniaxially stretched polyvinyl alcohol resin film to which a dichroic dye such as iodine is adsorbed and oriented is conventionally used. In general, a polarizing film is subjected to a dyeing treatment in which the polyvinyl alcohol resin film is dyed with a dichroic dye, a cross-linking treatment in which the film is treated with a cross-linking agent, and a film drying treatment in that order. It is produced by subjecting it to stretching treatment [for example, Japanese Patent Application Laid-Open No. 2001-141926 (Patent Document 1)].

Japanese Patent Application Laid-Open No. 2001-141926

Usually, the polarizing film is industrially produced by continuously transporting a long polyvinyl alcohol-based resin film along the transport path of the film possessed by the manufacturing apparatus of the polarizing film. The production includes a wet treatment step of sequentially immersing in a dyeing treatment tank for dyeing treatment and a cross-linking treatment tank for cross-linking treatment.

When the polarizing film is continuously produced according to the above method, the polyvinyl alcohol-based resin gradually dissolves into the treatment liquid in which the polyvinyl alcohol-based resin film is immersed. This eluted polyvinyl alcohol-based resin may precipitate from the treatment solution for some reason, and when precipitation occurs, the precipitate adheres to the polyvinyl alcohol-based resin film being wet-treated and, in turn, to the surface of the polarizing film, It can adversely affect the appearance and quality of the polarizing film.
Further, when the concentration of the polyvinyl alcohol resin dissolved in the treatment liquid gradually increases, the polyvinyl alcohol resin is contained on the surface of the polyvinyl alcohol resin film pulled out from the treatment liquid after being immersed in the treatment liquid. Solids may 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 and apparatus capable of stably and continuously producing a polarizing film while suppressing adhesion of the precipitate to the film.

The present invention provides the following manufacturing method and manufacturing apparatus for a polarizing film.
[1] A step of immersing a polyvinyl alcohol-based resin film in a dyeing tank containing a dyeing liquid;
A step of immersing the polyvinyl alcohol-based resin film after the step of immersing it in a dyeing treatment tank in a cross-linking treatment tank containing a cross-linking treatment solution;
obtaining a particle-containing liquid containing particles containing a polyvinyl alcohol-based resin by applying a shearing force to at least a portion of the cross-linking liquid extracted from the cross-linking liquid in the cross-linking tank;
removing the particles from the particle-containing liquid;
A method for producing a polarizing film, comprising:
[2] The production method according to [1], wherein the step of obtaining the particle-containing liquid includes controlling the content of the particles or the particle size distribution of the particles in the particle-containing liquid.
[3] The manufacturing method according to [2], wherein the step of controlling includes a step of cooling at least a portion of the cross-linking treatment liquid.
[4] The production method according to [3], wherein a shearing force is applied to at least a portion of the cross-linking treatment liquid after or while cooling.
[5] The production method according to any one of [1] to [4], further comprising a step of returning at least part of the liquid from which the particles have been removed to the cross-linking treatment tank.
[6] A tank for immersing a polyvinyl alcohol-based resin film, the dyeing treatment tank for containing a dyeing treatment liquid;
A bath for immersing the polyvinyl alcohol-based resin film immersed in the dyeing treatment bath, the cross-linking treatment bath for containing the cross-linking treatment liquid;
A shearing force for obtaining a particle-containing liquid containing particles containing a polyvinyl alcohol-based resin by applying a shearing force to at least a portion of the cross-linking liquid extracted from the cross-linking liquid in the cross-linking tank. a granting unit;
a particle removal unit for removing the particles from the particle-containing liquid;
A manufacturing apparatus for a polarizing film, comprising:
[7] The manufacturing apparatus according to [6], further including a cooling unit for cooling the at least part of the cross-linking treatment liquid.
[8] The production apparatus according to [6] or [7], further including a circulation path for returning at least part of the liquid from which the particles have been removed to the cross-linking treatment tank.

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

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which shows an example of a polarizing film manufacturing apparatus and the manufacturing method of a polarizing film using the same. FIG. 5 is a diagram showing the results of Experimental Example 1; FIG. 10 is a diagram showing the results of Experimental Example 2;

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

TECHNICAL FIELD 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 produced 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 is a stretched PVA-based resin film in which a dichroic dye is adsorbed and oriented.

An example of a polarizing film manufacturing apparatus according to the present invention 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-based resin film 10 as a raw material film. The arrows in FIG. 1 indicate the transport direction of the film or the flow direction of the liquid.
In manufacturing the polarizing film 25 using the manufacturing apparatus shown in FIG. 1, the PVA-based resin film 10 is continuously unwound from the unwinding roll 11, and the swelling treatment tank 13, dyeing treatment tank 15, and cross-linking treatment tank 17 are carried out. Then, the polarizing film 25 is obtained by immersing it in the washing treatment bath 19 in order and finally passing it through the drying oven 21 for drying treatment. The polarizing film 25 manufactured as a long product may be sequentially wound on a winding roll 27, or may be unwound and a thermoplastic resin film such as a protective film is adhered to one side or both sides of the polarizing film 25. It may be subjected to a polarizing plate manufacturing process.

The polarizing film manufacturing apparatus includes a wet treatment section (a treatment tank containing a treatment liquid in which the film is immersed) including a swelling treatment tank 13, a dyeing treatment tank 15, a cross-linking treatment tank 17, a washing treatment tank 19, and the like. and a drying processing section such as a drying oven 21 (a zone for drying the wet-processed film).
The polarizing film manufacturing apparatus shown in FIG. 1 has a transport path for the PVA-based resin film 10 including a wet processing section and a dry processing section. By conveying the PVA-based resin film 10 along this conveying route, a series of treatments including wet treatment and drying treatment are performed to obtain the polarizing film 25 .
The transport speed of the PVA-based resin film 10 transported along the transport route 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 that support and guide the running film (the PVA-based resin film 10 and the polarizing film 25) so as to pass through the wet processing section and the drying processing section. be done. The plurality of rolls consists of 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). It is a nip roll that pinches from or pinches and presses. In the example shown in FIG. 1, the polarizing film manufacturing apparatus includes guide rolls 1a-1l and nip rolls 2a-2f. The plurality of rolls that define the transport path may include suction rolls, which are a type of drive roll. Each of these rolls generally contacts and supports one or both surfaces (major surfaces) of the film in the transport path. These rolls can be arranged at appropriate positions such as before and after each processing bath and drying means (drying oven), inside the processing bath and drying means (drying oven), and the like.

A driving roll is a roll that can apply a driving force for transporting a film to a film in contact therewith, and can be a roll that is directly or indirectly connected to a roll driving 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.

The method for producing a polarizing film according to the present invention comprises the following steps:
A step of immersing the PVA-based resin film in a dyeing treatment tank containing a dyeing treatment liquid containing a dichroic dye (dyeing treatment step S101);
A step of immersing the PVA-based resin film after the dyeing treatment step S101 in a cross-linking treatment tank containing a cross-linking treatment liquid containing a cross-linking agent (cross-linking treatment step S102);
A step of obtaining a particle-containing liquid containing particles containing a polyvinyl alcohol-based resin by applying a shearing force to at least a portion of the cross-linking liquid extracted from the cross-linking liquid in the cross-linking tank (particle-generating step). S201), and a step of removing the particles from the particle-containing liquid (particle removal step S202)
including.

The obtained polarizing film 25 is stretched (usually uniaxially stretched). For this reason, the polarizing film manufacturing apparatus can include stretching means (wet stretching means) for the PVA-based resin film 10, and the polarizing film manufacturing method includes a stretching treatment step for the PVA-based resin film 10 (wet stretching treatment). step).

(1) PVA-based resin film The PVA-based resin film 10 introduced into the wet processing section (to be subjected to the wet processing step) is composed of a polyvinyl alcohol-based resin (hereinafter also referred to as "PVA-based resin"). It's a film. A PVA-based resin refers to a resin containing 50% by weight or more of structural units derived from vinyl alcohol. As the PVA-based resin, a saponified polyvinyl acetate-based 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 with other monomers copolymerizable therewith.
Other monomers copolymerizable with vinyl acetate include, for example, unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and (meth)acrylamides having an ammonium group.
In addition, "(meth)acryl" represents at least one selected from the group consisting of acryl and methacryl. The same applies to other terms with "(meta)" attached.

The degree of saponification of the PVA-based resin can range from 80.0 to 100.0 mol%, preferably from 90.0 to 100.0 mol%, more preferably from 94.0 to 100.0 mol%. 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 resulting polarizing film 25 and the polarizing plate including the same may have reduced water resistance and moist heat resistance.

The degree of saponification is expressed as a unit ratio (mol%) of the ratio of the acetic acid group (acetoxy group: —OCOCH ₃ ) contained in the polyvinyl acetate resin, which is the raw material of the PVA resin, to the hydroxyl group through the saponification process. and is given by the following formula:
Degree of saponification (mol%) = 100 x (number of hydroxyl groups) / (number of hydroxyl groups + number of acetic groups)
defined by The degree of saponification can be determined according to JIS K 6726 (1994).

The average degree of polymerization of the PVA-based resin is preferably 100-10000, more preferably 1500-8000, still more preferably 2000-5000. The average degree of polymerization of the polyvinyl alcohol resin can also be determined according to JIS K 6726 (1994). If the average degree of polymerization is less than 100, it is difficult to obtain a polarizing film 25 having preferable polarizing performance. 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 known methods such as a melt extrusion method and a solvent casting method can be employed.
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 direction (MD) of the film, that is, in the longitudinal direction of the film.
When the PVA-based resin film 10 introduced into the wet processing section (to be subjected to the wet processing step) is a stretched film, the stretching is preferably dry stretching. Dry stretching refers to stretching in the air, and is usually longitudinal uniaxial stretching.

For dry stretching, the film is passed between a hot roll whose surface is heated and a guide roll (or a hot roll may be used) having a different peripheral speed from the hot roll, and the film is heated using the hot roll. Heated roll stretching in which longitudinal stretching is performed below: between rolls in which longitudinal stretching is performed by the difference in peripheral speed between the two nip rolls while passing through a heating means (such as an oven) between two nip rolls placed at a distance Stretching; tenter stretching; compression stretching and the like can be mentioned.
The stretching temperature (surface temperature of hot rolls, oven temperature, etc.) is, for example, 80 to 150°C, preferably 100 to 135°C.

The draw ratio for the above-mentioned drawing is usually 1.1 to 8 times, preferably 2.0 times, although it depends on whether or not wet drawing is carried out in the wet treatment step described below and the draw ratio in the wet drawing. 5 to 5 times.

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

The thickness of the PVA-based resin film 10 introduced into the wet-processing section (to be subjected to the wet-processing step) is usually 10 to 150 μm, depending on whether the PVA-based resin film 10 is a stretched film. From the viewpoint of thinning the obtained polarizing film 25, the thickness is preferably 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).

(2) Wet processing section and wet processing step The wet processing section is a zone arranged on the conveying path of the PVA-based resin film 10, and includes a processing tank containing a processing liquid in which the PVA-based resin film 10 is immersed. . In this wet processing section, a wet processing step is performed in which the PVA-based resin film 10 is immersed in the processing liquid while being transported.

The wet treatment section normally includes a dyeing treatment tank 15 and a cross-linking treatment tank 17 as the treatment tanks, and preferably further includes a swelling treatment tank 13 and a washing treatment tank 19 . These treatment tanks are usually arranged in order from the upstream side of the transport path in the order of swelling treatment tank 13, dyeing treatment tank 15, cross-linking treatment tank 17, and washing treatment tank 19 (see FIG. 1).
FIG. 1 shows an example in which one swelling treatment tank 13, one dyeing treatment tank 15, one cross-linking treatment tank 17, and one cleaning treatment tank 19 are provided. may be provided, and two or more cross-linking treatment tanks 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 for each.

(2-1) Swelling Treatment Tank and Swelling Treatment Step Swelling treatment is performed as necessary for the purpose of removing foreign matter from the PVA-based resin film 10, removing the plasticizer, imparting easy dyeability, and plasticizing the film. processing.
Referring to FIG. 1, in the swelling treatment step, the PVA-based resin film 10 is continuously unwound from an unwinding roll 11 and conveyed along the film conveying path, and the PVA-based resin film 10 is fed with the swelling treatment liquid. It can be carried out by immersing it in the swelling treatment bath 13 to be accommodated for a predetermined period of time and then pulling it out.

The treatment liquid (swelling treatment liquid) contained in the swelling treatment tank 13 may 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 liquid may also contain boric acid, chlorides, inorganic acids, inorganic salts 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-based resin film 10 is usually 10 to 600 seconds, preferably 15 to 300 seconds.

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

(2-2) Dyeing treatment tank and dyeing treatment step S101
The dyeing process is a process performed for the purpose of adsorbing and orienting a dichroic dye on the PVA-based resin film 10 .
Referring to FIG. 1, the dyeing treatment step S101 can be carried out by transporting the PVA-based resin film 10 along the film transport path, immersing the PVA-based resin film 10 in the dyeing treatment bath 15 for a predetermined period of time, and then withdrawing the film. 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-based resin film 10 to be immersed in the dyeing treatment liquid is preferably a film after the swelling treatment step (immersed in the swelling treatment bath 13).
The dyeing treatment liquid contained in the dyeing treatment tank 15 is a liquid (usually an aqueous solution) containing a dichroic dye. The dichroic dye can be iodine or a dichroic organic dye, preferably iodine. Dichroic dyes may be used singly 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 dyeing treatment liquid. Instead of potassium iodide, other iodides such as zinc iodide may be used, or potassium iodide and other iodides may be used in combination. Compounds other than iodide, such as boric acid, zinc chloride, and cobalt chloride, may coexist. When boric acid is added, it is distinguished from the cross-linking treatment liquid 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 dyeing treatment liquid. 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-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 tanks 15 . In this case, the composition and temperature of each dyeing 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 dyed is preferably stretched to at least some degree (usually uniaxially stretched). 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 draw ratio up to the dyeing treatment (the draw ratio in the dyeing treatment when there is no drawing step before the dyeing treatment) is usually 1.6 to 4.5 times, preferably 1.8 to 4 times. . Referring to FIG. 1, for example, the uniaxial stretching treatment can be performed in the dyeing treatment 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 pulled out from the dyeing treatment tank 15 is introduced into the cross-linking treatment tank 17 through the guide roll 1f and the nip roll 2c in order.

(2-3) Cross-linking treatment tank and cross-linking treatment step S102
The cross-linking treatment is a treatment that is performed for the purpose of water resistance by cross-linking, color adjustment, and the like.
Referring to FIG. 1, in the cross-linking treatment, the PVA-based resin film 10 after the dyeing treatment step S101 (immersed in the dyeing treatment bath 15) is immersed in the cross-linking treatment bath 17 for a predetermined time by being transported along the film transport path. and then withdraw. The cross-linking treatment tank 17 is a tank for immersing the PVA-based resin film 10 in the cross-linking treatment liquid contained therein.
The cross-linking treatment liquid contained in the cross-linking treatment tank 17 is a liquid (usually an aqueous solution) containing a cross-linking agent. The cross-linking treatment is performed by immersing the PVA-based resin film 10 after the dyeing treatment step S101 in this cross-linking treatment liquid.

The cross-linking agent contained in the cross-linking solution includes, for example, boric acid, glyoxal, glutaraldehyde and the like, preferably boric acid. Two or more cross-linking agents can be used in combination.
The content of the cross-linking agent in the cross-linking 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 cross-linking treatment liquid preferably contains iodide in addition to the cross-linking agent.
Examples of iodides include potassium iodide and zinc iodide.
The content of iodide in the cross-linking 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 cross-linking treatment liquid may contain compounds other than iodide. Examples of such compounds include zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate and the like.

The temperature of the cross-linking treatment solution is generally 20 to 85°C, preferably 30 to 70°C. The immersion time (residence time in the cross-linking 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 cross-linking treatment tanks 17 . In this case, the composition and temperature of each cross-linking treatment liquid may be the same or different. The cross-linking treatment liquid may have the concentration and temperature of the cross-linking agent and iodide according to the purpose of immersing the PVA-based resin film 10 . The cross-linking treatment for water resistance by cross-linking and the cross-linking treatment for hue adjustment may be carried out in a plurality of steps.

Stretching treatment (usually uniaxial stretching treatment) may be performed while cross-linking treatment is performed. Referring to FIG. 1, for example, the uniaxial stretching treatment can be performed in a cross-linking treatment bath 17 by utilizing the peripheral speed difference between the nip roll 2c and the nip roll 2d.
In the example shown in FIG. 1, the film pulled out from the cross-linking treatment tank 17 is introduced into the washing treatment tank 19 through the guide roll 1i and the nip roll 2d in order.

(2-4) Washing Treatment Tank and Washing Treatment Step The method for manufacturing a polarizing film can further include a washing treatment step after the cross-linking treatment step S102. A cleaning treatment tank 19 disposed on the side may be further included. The washing treatment is a treatment performed for the purpose of removing excess chemicals adhering to the PVA-based resin film 10 after the cross-linking treatment step S102.
Referring to FIG. 1, in the cleaning treatment, the PVA-based resin film 10 after the cross-linking treatment step S102 (immersed in the cross-linking treatment tank 17) is immersed in the cleaning treatment tank 19 for a predetermined period of time. and then withdraw. Alternatively, the cleaning treatment may be a treatment in which a cleaning solution is sprayed, for example, as a shower onto the PVA-based resin film 10 after the cross-linking treatment step S102, or a combination of immersion in the cleaning treatment tank 19 and spraying of the cleaning solution. good. FIG. 1 shows an example in which the PVA-based resin film 10 is immersed in a cleaning tank 19 to be cleaned.

The cleaning liquid contained in the cleaning tank 19 and the cleaning liquid to be sprayed may 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 temperature of the cleaning treatment liquid and cleaning liquid is, for example, 2 to 40.degree.

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

(2-5) Stretching Means and Stretching Process In the wet process, the PVA-based resin film 10 may be wet stretched. Wet stretching is usually uniaxial stretching, and can be carried out while performing any one of swelling treatment, dyeing treatment, cross-linking treatment, and washing treatment, or during two or more treatments selected from these.
Wet stretching is preferably performed in one or more steps prior to or in the cross-linking treatment step S102. 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-based resin film 10 subjected to the dyeing treatment step S101 is stretched to at least a certain extent. More preferably.
From the viewpoint of the polarization properties of the polarizing film 25 to be obtained, the draw ratio of the wet stretching is preferably the final cumulative draw ratio of the polarizing film 25 (when the PVA-based resin film 10 subjected to the wet treatment is a stretched film , the cumulative draw ratio including this draw 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-based resin film 10 . The wet stretching means is preferably a stretching means that performs roll-to-roll stretching. Taking the case of performing the wet stretching between rolls during the cross-linking treatment step S102 as an example, two nip rolls 2c and 2d arranged before and after the cross-linking treatment tank 17 are used as stretching means for performing the stretching between rolls. Similarly, when stretching is performed during other wet processing, two nip rolls spaced apart can be used as the wet stretching means.

(3) Drying Processing Section and Drying Processing Process The drying processing section dries the PVA-based resin film 10 after the wet processing process, which is arranged on the transport path of the PVA-based resin film 10 and downstream of the wet processing section. It is a zone for After the wet treatment step, the PVA-based resin film 10 is continuously transported and introduced into the drying treatment section for drying treatment, whereby the polarizing film 25 is obtained (see FIG. 1).

The drying processing section includes film drying means (heating means). A preferred example of drying means is a drying oven. The drying oven is preferably one capable of controlling the temperature inside the oven. The drying oven is, for example, a hot air oven capable of increasing the temperature inside the oven by supplying hot air or the like. Moreover, the drying treatment by the drying means may be a treatment of adhering the PVA-based resin film 10 after the wet treatment step to one or more heating bodies having a convex curved surface, or a treatment of heating the film using a heater. good.

Examples of the heating member include a roll (for example, a guide roll that also serves as a heat roll) that has a heat source (for example, a heat medium such as hot water or an infrared heater) inside and can increase the surface temperature. Examples of the heater include infrared heaters, halogen heaters, panel heaters, and the like. FIG. 1 shows an example in which the PVA-based resin film 10 after the wet treatment process is introduced into the drying oven 21 and dried.

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

The polarizing film 25 is a stretched (usually uniaxially stretched) PVA-based resin film in which a dichroic dye is adsorbed and oriented. The thickness of the polarizing film 25 is usually 2-40 μm. From the viewpoint of thinning 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 even more preferably 10 μm or less.

The visibility-corrected 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-corrected 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 absorptiometer with an integrating sphere and subjecting the obtained transmittance and degree of polarization to visual sensitivity correction using a 2-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, or may be directly applied to the polarizing plate manufacturing process (a thermoplastic resin film (protective film, etc.) on one side or both sides of the polarizing film 25 without being wound. ) can also be subjected to the step of laminating).

(4) Generation and Removal of Particles Containing Polyvinyl Alcohol-Based Resin
A step of obtaining a particle-containing liquid containing particles containing a polyvinyl alcohol-based resin by applying a shearing force to at least a portion of the cross-linking liquid extracted from the cross-linking liquid in the cross-linking tank 17 (particle formation step S201), and a step of removing the particles from the particle-containing liquid (particle removal step S202)
including.
For this reason, the polarizing film manufacturing apparatus according to the present invention is
A shearing force for obtaining a particle-containing liquid containing particles containing a polyvinyl alcohol-based resin by applying a shearing force to at least a portion of the cross-linking liquid extracted from the cross-linking liquid in the cross-linking tank 17. an application section; and a particle removal section for removing the particles from the particle-containing liquid.

FIG. 1 is a schematic diagram showing an example of a polarizing film manufacturing apparatus in which a shear force imparting section and a particle removing section are attached to a cross-linking treatment tank 17, and a method of manufacturing a polarizing film using the apparatus.
The polarizing film manufacturing apparatus shown in FIG. 1 is connected to the cross-linking treatment tank 17, and is for cooling at least a part of the cross-linking treatment liquid extracted from the cross-linking treatment liquid in the cross-linking treatment tank 17; 30 for obtaining the particle-containing liquid by applying a shear force to at least part of the cross-linking treatment liquid after cooling; A particle removal section 50 is included for removing the particles from the contained liquid.
The cross-linking treatment tank 17 and the cooling unit 30 are connected by a connection path (connection line) 28, and the cooling unit 30 and the shearing force applying unit 40 are connected by a connection path (connection line) 29. The force applying section 40 and the particle removing section 50 are connected by a connection path (connection line) 41 .
The concentration of the polyvinyl alcohol-based resin in the cross-linking treatment liquid extracted from the cross-linking treatment bath 17 may be, for example, about 5 ppm to 5000 ppm on a weight basis.

In the method of manufacturing a polarizing film using the polarizing film manufacturing apparatus shown in FIG. The treatment liquid is cooled by the cooling unit 30 (cooling step). Some of the particles may be precipitated from the cross-linking treatment liquid by cooling. The temperature of the cross-linking treatment liquid after cooling is, for example, 0 to 60°C, preferably 10 to 40°C.

As the cooling unit 30, known means can be used, for example, a jacket capable of introducing a refrigerant, a chamber (or tank) having a cooling means such as a heat exchanger, a connection path (cooling line, cooling pipe), etc. It's okay. Since the cooling unit 30 can continuously cool the introduced cross-linking treatment liquid and continuously lead out the cross-linking treatment liquid after cooling, the cooling part 30 preferably has a connection path (cooling line, cooling pipe) having a cooling means. is.
The cooling unit 30 is an arbitrary part, and depending on the temperature of the cross-linking treatment liquid in the cross-linking treatment bath 17, the cooling part 30 is not necessarily required.

In the method for manufacturing a polarizing film using the polarizing film manufacturing apparatus shown in FIG. 1, the cross-linking treatment liquid after cooling is introduced into the shearing force imparting unit 40 to be imparted with a shearing force, thereby containing a polyvinyl alcohol-based resin. The particles are generated (particle generation step S201). The precipitated particles may further contain a cross-linking agent, iodide, etc. contained in the cross-linking treatment liquid, in addition to the polyvinyl alcohol-based resin.

The shearing force applying unit 40 may be, for example, a chamber (or tank) having a shearing force applying means, a connection path (line, pipe), or the like. The shearing force applying unit 40 can continuously apply a shearing force to the cross-linking treatment liquid introduced into the shearing force applying unit 40, and continuously draw out the particle-containing liquid. It is a connection path (line, pipe) having force applying means.
Examples of means for imparting a shearing force include stirring blades; convection generating means for generating convection in liquid by a method such as drawing in liquid by rotating members, such as in a general homomixer; impact imparting means such as projections and baffles; high frequency generating means; ultrasonic wave generating means; and combinations of two or more of these.

The shearing force applied to the cross-linking treatment liquid is preferably 40-350 Pa, more preferably 50-260 Pa. By setting the shear force applied to the cross-linking treatment liquid within this range, the particles (particles containing the polyvinyl alcohol-based resin) are efficiently precipitated, and the particles are separated during the solid-liquid separation in the particle removal step S202 described later. Easy to control the particle size. When a shearing force is imparted to the liquid by rotating a member such as a stirring blade, the shearing force imparted to the cross-linking treatment liquid can be calculated by the following formula.
Shearing force [Pa] = Viscosity of cross-linking treatment liquid [mPa s] x Stirring blade rotation speed [rpm] x 0.001 x 60
In the above formula, the viscosity of the cross-linking treatment liquid is usually 0.65 to 1.20 mPa·s at a liquid temperature of 10 to 40°C.

In the polarizing film manufacturing apparatus shown in FIG. 1 , the shearing force applying section 40 is arranged after the cooling section 30 , but the shearing force applying section 40 may include the cooling section 30 . As a result, in the particle generation step S201, a shearing force can be applied to the cross-linking treatment liquid while it is being cooled.

The particle generation step S201 preferably includes a step (control step) of controlling the content of the particles or the particle size distribution of the particles in the obtained particle-containing liquid. By controlling the content of the particles or the particle size distribution of the particles, the removal efficiency of the particles and the operability of the particle removal step S202, which will be described later, can be improved.
An example of the control process is the above-described cooling process (the process of controlling the temperature of the cross-linking treatment liquid). By applying a shearing force to the cross-linking treatment liquid after cooling or while cooling, the amount of particles precipitated can be increased.

Other examples of the control process include a process of controlling the application time of the shearing force, a process of controlling the magnitude of the shearing force, the flow rate of the cross-linking treatment liquid passing through the shearing force applying section 40, and the like. By appropriately adjusting the temperature of the cross-linking treatment liquid to which the shear force is applied, the application time of the shear force, the magnitude of the shear force, the flow rate of the cross-linking treatment liquid passing through the shear force applying unit 40, etc., the particle-containing liquid It is possible to adjust the content of particles (amount of precipitation of particles) and the particle size distribution of particles (particle size).

After the particle-containing liquid is obtained in the particle-generating step S201, particles precipitated from the particle-containing liquid are removed (particle-removing step S202). Through this step, a liquid from which precipitated particles have been removed (a cross-linking treatment liquid from which particles have been removed) is obtained.
The polarizing film manufacturing apparatus includes a particle removing section 50 for removing the particles from the particle-containing liquid.
Before performing the particle removing step S202 and after the particle generating step S201, a step of cooling the particle-containing liquid may be provided. A cooling unit for cooling the particle-containing liquid is further provided between.
As the particle removal unit 50, a known solid-liquid separation device such as a filtration filter can be used.

The method for producing a polarizing film further includes a step of returning at least part of the cross-linking treatment liquid from which particles have been removed to the cross-linking treatment tank 17, so that the concentration of the polyvinyl alcohol-based resin in the cross-linking treatment liquid in the cross-linking treatment tank 17 is reduced to , it can be reduced or maintained at a low concentration that does not precipitate in the cross-linking treatment tank 17, so that the precipitates precipitated in the cross-linking treatment tank 17 adhere to the surface of the PVA-based resin film during wet treatment and, in turn, the polarizing film. It is possible to suppress the trouble that occurs.

When the method for producing a polarizing film further includes a step of returning at least part of the cross-linking treatment liquid from which particles have been removed to the cross-linking treatment tank 17, the polarizing film production apparatus returns at least part of the cross-linking treatment liquid from which particles have been removed. to the cross-linking treatment bath 17. The circulation path 51 is a connection path that connects the particle removal section 50 and the cross-linking treatment tank 17 .
The operation of extracting at least part of the cross-linking treatment liquid from the cross-linking treatment tank 17, treating the withdrawn cross-linking treatment liquid, and returning at least part of the liquid obtained by the treatment to the cross-linking treatment tank 17 is performed by using a pump or the like. can be performed using

In order to adjust the amount of the cross-linking treatment liquid in the cross-linking treatment tank 17, at least part of the cross-linking treatment liquid from which the particles have been removed is returned to the cross-linking treatment tank 17, or at least the cross-linking treatment liquid from which the particles have been removed is The cross-linking treatment tank 17 may be replenished with a fresh cross-linking treatment liquid at a timing different from the step of returning part of the solution to the cross-linking treatment tank 17 .

When the polarizing film manufacturing apparatus includes two or more cross-linking treatment tanks 17, the shearing force applying unit 40 and the particle removal unit 50 (and the cooling unit provided as necessary) are provided in one cross-linking treatment tank 17. Alternatively, it may be provided in two or more or all of the cross-linking treatment tanks 17 . Preferably, the shearing force applying unit 40 and the particle removing unit 50 (and the cooling unit provided as necessary) are provided at least in the cross-linking treatment tank 17 in which precipitation of the polyvinyl alcohol-based resin tends to occur in the cross-linking treatment tank. . An example of such a cross-linking treatment tank 17 is a cross-linking treatment tank in which the temperature of the cross-linking treatment liquid is relatively higher than that of other cross-linking treatment tanks.

(5) Experimental Example 1: Generation of Particles Using Homodisper Using the polarizing film manufacturing apparatus shown in FIG. 1, polarizing films 25 were continuously manufactured from long polyvinyl alcohol films. The polyvinyl alcohol film used was obtained by uniaxially stretching a polyvinyl alcohol film with a thickness of 30 μm to 4.1 times in a dry process. was 2400.

While unwinding the polyvinyl alcohol film 10 from the unwinding roll 11, it is continuously conveyed while being tensioned and immersed in a swelling treatment tank 13 containing pure water at 40° C. for a residence time of 60 seconds. to swell the polyvinyl alcohol film 10 (swelling treatment step). The film pulled out from the swelling treatment tank 13 is immersed in a dyeing treatment tank 15 containing a dyeing treatment solution having a weight ratio of iodine/potassium iodide/water of 0.1/6/100 at 30° C. for a residence time of 60 seconds. In the meantime, uniaxial stretching (stretching between rolls in a bath) was performed (dyeing treatment step). The film pulled out from the dyeing treatment bath 15 was placed in a cross-linking treatment bath 17 containing a cross-linking treatment solution having a weight ratio of potassium iodide/boric acid/water of 15/5.5/100 at 68° C. for a residence time of 130 seconds. While being immersed, uniaxial stretching (stretching between rolls in a bath) was carried out (crosslinking treatment step). The film pulled out from the cross-linking treatment tank 17 was washed by being immersed in a washing treatment tank 19 containing pure water at 20° C. for a residence time of 3 seconds (washing treatment step). The cumulative stretch ratio based on the polyvinyl alcohol film before dry uniaxial stretching was 4.5 times.

A cross-linking treatment liquid was sampled from the cross-linking treatment tank 17 after continuous production of the polarizing film, and the following particle deposition experiment was performed. When the polyvinyl alcohol concentration in the sampled cross-linking treatment liquid was measured by GPC (gel permeation chromatography), it was about 1500 ppm on a weight basis.

The sampled cross-linking treatment solution is placed in a Primix Homo Disper (Homo Disper 2.5 type (blade type), capacity 800 mL), and a shearing force is applied to the cross-linking treatment solution under the following conditions to remove polyvinyl alcohol. A particle-containing liquid containing solid particles containing
Temperature: 3 conditions of 14°C, 29°C and 39°C Rotation speed of stirring blade: 2 conditions of 1000 rpm and 5000 rpm Treatment time by homodisper: 10 minutes

FIG. 2 shows the results of measuring the particle size distribution of the obtained solid particles. The horizontal axis indicates the particle size of the generated solid particles, and the vertical axis (detected number) corresponds to the number of solid particles. The particle size distribution of the solid particles shown in FIG. 2 is the result of measuring the obtained particle-containing liquid using a liquid particle counter ("light shielding particle detector (KS-42D)" manufactured by Rion). (the same applies to the particle size distribution of the solid particles shown in FIG. 3).

(6) Experimental Example 2: Generation of Particles Using a Homomixer In order to apply a shearing force to the cross-linking treatment solution, a homomixer manufactured by Primix (homomixer 2.5 type (cylindrical type), volume 800 mL) was used, and a particle-containing liquid containing solid particles containing polyvinyl alcohol was obtained in the same manner as in Experimental Example 1, except that a shearing force was applied to the cross-linking treatment liquid under the following conditions.
FIG. 3 shows the results of measuring the particle size distribution of the obtained solid particles.
Temperature: 3 conditions of 14°C, 29°C and 39°C Rotation speed of inner blade of homomixer: 1000 rpm and 5000 rpm Treatment time by homodisper: 3 conditions of 10 seconds, 1 minute and 10 minutes

1a, 1b, 1c, 1d, 1e, 1f, 1g, 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 roll, 13 swelling treatment tank, 15 dyeing treatment tank, 17 cross-linking treatment tank, 19 washing treatment tank, 21 drying furnace, 25 polarizing film, 27 winding roll, 28, 29 connection path, 30 cooling part, 40 shearing force application section, 41 connection path, 50 particle removal section, 51 circulation path.

Claims (3)

A dyeing treatment tank for immersing a polyvinyl alcohol-based resin film, the dyeing treatment tank containing a dyeing treatment liquid;
A bath for immersing the polyvinyl alcohol-based resin film immersed in the dyeing treatment bath, the cross-linking treatment bath for containing the cross-linking treatment liquid;
A shearing force for obtaining a particle-containing liquid containing particles containing a polyvinyl alcohol-based resin by applying a shearing force to at least a portion of the cross-linking liquid extracted from the cross-linking liquid in the cross-linking tank. a granting unit;
a particle removal unit for removing the particles from the particle-containing liquid;
including
The shearing force applying unit is a homomixer or a homodisper,
The apparatus for manufacturing a polarizing film, wherein the shearing force application unit includes a cooling unit for cooling the at least part of the cross-linking treatment liquid . 2. The manufacturing apparatus according to claim 1 , further comprising a circulation path for returning at least part of the liquid from which the particles have been removed to the cross-linking treatment tank. 3. The production apparatus according to claim 1 , wherein a shearing force of 40 to 350 Pa is applied to said at least part of the cross-linking treatment liquid.

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