TW201922865A - Manufacturing method of polarizing film and manufacturing apparatus of polarizing film - Google Patents

Abstract

An objective of the present invention is to provide a manufacturing method of polarizing film capable of stably and continuously manufacturing a polarizing film while suppressing adhesion of precipitates deposited from a treatment liquid used for wet treatment of a polyvinyl alcohol-based resin film to the above-mentioned film. The manufacturing method of polarizing film of the present invention comprises: a step of immersing a polyvinyl alcohol-based resin film in a dyeing treatment tank containing a dyeing treatment liquid; a step of immersing the polyvinyl alcohol-based resin film after the step of immersing in the dyeing treatment tank in a crosslinking treatment tank containing a crosslinking treatment liquid; a step of obtaining a particle-containing liquid containing particles comprising a polyvinyl alcohol-based resin by applying a shearing force to at least a part of the crosslinking treatment liquid withdrawn from the crosslinking treatment liquid in the crosslinking treatment tank; and a step of removing the particles from the particle-containing liquid.

Description

   Method for manufacturing polarizing film and device for manufacturing polarizing film   

The present invention relates to, for example, a method for producing a polarizing film that can be used as a polarizing plate constituent member, and a device for producing a polarizing film.

The polarizing film has been conventionally used for a dichroic dye such as iodine that is adsorbed and oriented by a uniaxially stretched polyvinyl alcohol-based resin film. Generally speaking, a polarizing film is a polyvinyl alcohol-based resin film that is sequentially subjected to a dyeing treatment with a dichroic dye, a crosslinking treatment with a cross-linking agent, and a film drying treatment. The polyvinyl alcohol-based resin film is produced by stretching treatment [for example, Japanese Patent Application Laid-Open No. 2001-141926 (Patent Document 1)].

    [Prior technical literature]         [Patent Literature]    

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

Generally, in the industry, a polarizing film is manufactured by a wet processing step in which a long polyvinyl alcohol resin film is continuously conveyed along a film conveying path included in a polarizing film manufacturing apparatus. At the same time, the above-mentioned dyeing treatment tank for performing dyeing treatment and the cross-linking treatment tank for performing cross-linking treatment are sequentially immersed in the transport path.

If the polarizing film is continuously produced by the method described above, the polyvinyl alcohol-based resin will gradually dissolve into the treatment liquid impregnated with the polyvinyl alcohol-based resin film. The dissolved polyvinyl alcohol-based resin will be precipitated from the treatment solution due to some factors. If precipitation occurs, the precipitates will adhere to the surface of the polyvinyl alcohol-based resin film in the wet process or even the surface of the polarizing film, and will be polarized. The appearance and quality of the film adversely affect.

In addition, if the concentration of the polyvinyl alcohol-based resin eluted into the treatment solution gradually increases, solids containing the polyvinyl alcohol-based resin may precipitate, and the polyvinyl alcohol may be drawn out of the treatment solution after being immersed in the treatment solution. This is the case of the surface of a resin film. Such precipitates also adversely affect the appearance and quality of the polarizing film.

An object of the present invention is to provide a method and an apparatus capable of stably and continuously manufacturing a polarizing film while suppressing the above-mentioned precipitates from adhering to a film.

The present invention provides a manufacturing method and a manufacturing apparatus of a polarizing film shown below.

[1] A method for manufacturing a polarizing film, comprising the steps of: immersing a polyvinyl alcohol-based resin film in a dyeing treatment tank containing a dyeing treatment liquid; and polyvinyl alcohol-based resin after the step of immersing in a dyeing treatment tank A step of immersing the membrane in a cross-linking treatment tank containing the cross-linking treatment liquid; applying a shear force to at least a part of the cross-linking treatment liquid extracted from the cross-linking treatment liquid in the cross-linking treatment tank, thereby obtaining a particle-containing liquid, The particle-containing liquid is a step of containing particles containing a polyvinyl alcohol-based resin; and a step of removing the particles from the particle-containing liquid.

[2] The manufacturing method according to [1], wherein the step of obtaining the particle-containing liquid includes a step of adjusting a content of the particles in the particle-containing liquid or a particle size distribution of the particles.

[3] The manufacturing method according to [2], wherein the control step includes a step of cooling the at least a part of the crosslinking treatment liquid.

[4] The manufacturing method according to [3], which applies a shear force to at least a part of the cross-linking treatment liquid after cooling or while cooling.

[5] The manufacturing method according to any one of [1] to [4], further including a step of returning at least a part of the liquid from which the particles have been removed to the crosslinking treatment tank.

[6] A polarizing film manufacturing device, comprising: a dyeing treatment tank, a tank for impregnating a polyvinyl alcohol-based resin film, and a dyeing treatment liquid; a cross-linking treatment tank, for immersing the dyeing treatment The tank of the polyvinyl alcohol-based resin film after the tank is immersed, and is used to receive the cross-linking treatment liquid; the shear force imparting portion is used to cross-link at least a part of the cross-linking treatment liquid extracted from the cross-linking treatment tank The treatment liquid is given a shearing force to obtain a particle-containing liquid, and the particle-containing liquid system contains particles containing a polyvinyl alcohol-based resin; and a particle removing unit is used to remove the particles from the particle-containing liquid.

[7] The manufacturing apparatus according to [6], further including a cooling section for cooling the at least a part of the crosslinking treatment liquid.

[8] The manufacturing device according to [6] or [7], further including a circulation channel, wherein the circulation channel is used to return at least a part of the liquid from which the particles have been removed to the crosslinking treatment tank.

The invention provides a method and an apparatus for stably and continuously producing a polarizing film while suppressing the adhesion of precipitates containing a polyvinyl alcohol resin to a film.

1a, 1b, 1c, 1d, 1e, 1f, 1g, 1h, 1i, 1j, 1k, 1l‧‧‧ guide rollers

2a, 2b, 2c, 2d, 2e, 2f

10‧‧‧Polyvinyl alcohol resin film (PVA resin film)

11‧‧‧ unwinding roller

13‧‧‧Swelling tank

15‧‧‧dyeing treatment tank

17‧‧‧ Cross-linking treatment tank

19‧‧‧washing treatment tank

21‧‧‧ drying furnace

25‧‧‧ polarizing film

27‧‧‧ Winding roller

28, 29‧‧‧ Connected channels

30‧‧‧Cooling Department

40‧‧‧Shear force imparting department

41‧‧‧connection channel

50‧‧‧ particle removal section

51‧‧‧Circulation channel

FIG. 1 is a schematic diagram showing an example of a polarizing film manufacturing apparatus and a manufacturing method of a polarizing film using the same.

FIG. 2 is a graph showing the results of Experimental Example 1. FIG.

Fig. 3 is a graph showing the results of Experimental Example 2.

The following shows the embodiment, and describes a method for manufacturing a polarizing film and a device for manufacturing a polarizing film.

The present invention relates to a manufacturing method and a manufacturing apparatus for manufacturing a polarizing film from a polyvinyl alcohol-based resin film (hereinafter also referred to as "PVA-based resin film"). The polarizing film is manufactured by subjecting a PVA-based resin film to a series of processes including a process of immersing in a processing tank (wet process) and a drying process.

The polarizing film of the present invention is one in which a stretched PVA-based resin film adsorbs directional dichroic pigments.

FIG. 1 shows an example of a polarizing film manufacturing apparatus of the present invention. The polarizing film manufacturing apparatus shown in FIG. 1 is a device for continuously manufacturing a long polarizing film 25 from a long PVA-based resin film 10 of a raw film. In FIG. 1, arrows indicate the transport direction of the film or the flow direction of the liquid.

When the polarizing film 25 is manufactured using the manufacturing apparatus shown in FIG. 1, the PVA-based resin film 10 is continuously rolled out by the unwinding roller 11, and is sequentially immersed in the swelling treatment tank 13, the dyeing treatment tank 15, and the crosslinking treatment. The tank 17 and the cleaning processing tank 19 are finally dried by passing through a drying furnace 21 to obtain a polarizing film 25. The polarizing film 25 manufactured as an elongated object may be sequentially wound on a winding roller 27, or may be provided without being wound for a polarizing plate manufacturing step. The polarizing plate manufacturing step is followed by protection on one or both sides of the polarizing film 25 A thermoplastic resin film such as a film.

A polarizing film manufacturing apparatus generally includes a wet processing section (a region in which wet processing is performed using a processing tank) including a swelling processing tank 13, a dyeing processing tank 15, a cross-linking processing tank 17, and a cleaning processing tank 19. Those who hold the treatment solution for impregnating the film); and the drying processing section (the area where the film after the wet processing is dried) such as the drying furnace 21.

The polarizing film manufacturing apparatus shown in FIG. 1 includes a PVA-based resin film 10 conveying path including a wet processing section and a drying processing section. The polarizing film 25 is obtained by carrying the PVA-based resin film 10 along this conveying path and performing a series of processes including wet processing and drying processing.

The conveyance speed of the PVA-based resin film 10 conveyed along the conveyance path is usually 1 to 50 m / min, and from the viewpoint of production efficiency, it is preferably 5 m / min or more.

As shown in FIG. 1, the above-mentioned conveying path is constructed by a plurality of rollers, and the plurality of rollers support and guide the moving film (PVA-based resin film 10 and Polarizing film 25). The plurality of rollers are guide rollers of a single-sided free roll including a supporting film, and / or a pair of rollers (usually including a driving roller). The pair of rollers is, for example, sandwiching the film on both sides or sandwiching and Press the pinch roller. In the example shown in FIG. 1, the polarizing film manufacturing apparatus includes guide rollers 1a to 11 and nip rollers 2a to 2f. The plurality of rollers defining the conveying path may include a suction roll belonging to a driving roller. Generally, these rollers will contact one surface or two surfaces (main surface) of the film in the conveying path and support the film. These rollers can be arranged at appropriate positions such as before and after each processing tank and drying mechanism (drying furnace), inside the processing tank and drying mechanism (drying furnace).

The driving roller is a roller which can provide a driving force for conveying the film to the film in contact with the driving roller, and may be a roller or the like directly or indirectly connected to a roller driving source such as a motor. A live roll is a roll that supports the moving film and can rotate freely according to the conveyance of the film.

The method for manufacturing a polarizing film of the present invention includes the steps of: immersing a PVA-based resin film in a dyeing treatment tank containing a dyeing treatment solution, and the dyeing treatment solution contains a dichroic pigment (dyeing treatment step S101); A step of immersing the PVA-based resin film in step S101 in a cross-linking treatment tank containing a cross-linking treatment liquid, and the cross-linking treatment liquid contains a cross-linking agent (cross-linking treatment step S102); At least a part of the cross-linking treatment liquid withdrawn from the cross-linking treatment liquid imparts a shearing force, thereby obtaining a particle-containing liquid, the step of the particle-containing liquid system containing particles containing a polyvinyl alcohol-based resin (particle generation step S201); and A step of removing the particles by the particle liquid (particle removing step S202).

The obtained polarizing film 25 is obtained by a stretching process (usually a uniaxial stretching process). Therefore, the manufacturing apparatus of the polarizing film may include a stretching mechanism (wet stretching mechanism) of the PVA-based resin film 10, and the manufacturing method of the polarizing film may include a stretching processing step (wet stretching processing step) of the PVA-based resin film 10.

(1) PVA resin film

The PVA-based resin film 10 introduced into the wet processing section (for the wet processing step) is a film composed of a polyvinyl alcohol-based resin (hereinafter also referred to as "PVA-based resin"). The PVA-based resin is a resin containing 50% by weight or more of a structural unit derived from vinyl alcohol. The PVA-based resin can be obtained by saponification using a polyvinyl acetate-based resin. Except for polyvinyl acetate, which is a homopolymer of vinyl acetate, polyvinyl acetate-based resins may include copolymers of vinyl acetate and other monomers capable of copolymerizing with vinyl acetate.

As for other monomers that can be copolymerized with vinyl acetate, for example, unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and (meth) acrylamide with ammonium groups, etc. .

Moreover, "(meth) acrylic acid" means at least 1 sort (s) chosen from the group which consists of acrylic acid and methacrylic acid. The same applies to other terms with "(methyl)".

The degree of saponification of the PVA resin can be in the range of 80.0 to 100.0 mol%, preferably in the range of 90.0 to 100.0 mol%, more preferably in the range of 94.0 to 100.0 mol%, and even more preferably 98.0 to 100.0 mol%. % Range. If the degree of saponification is less than 80.0 mol%, the water resistance and humidity and heat resistance of the obtained polarizing film 25 and a polarizing plate containing the polarizing film will decrease.

The degree of saponification refers to the ratio of the acetic acid group (acetoxy: -OCOCH ₃ ) contained in the polyvinyl acetate resin which is a PVA-based resin raw material to the unit ratio (mol%) to the hydroxyl group by the saponification step. It is defined by the following formula: degree of saponification (mol%) = 100 × (number of hydroxyl groups) / (number of hydroxyl groups + number of acetate groups).

The degree of saponification can be determined in accordance with JIS K 6726 (1994).

The average polymerization degree of the PVA-based resin is preferably 100 to 10,000, more preferably 1500 to 8000, and still more preferably 2,000 to 5,000. The average degree of polymerization of the polyvinyl alcohol-based resin can also be obtained in accordance with JIS K 6726 (1994). When the average degree of polymerization is less than 100, it is difficult to obtain a polarizing film 25 having better polarizing performance. If it exceeds 10,000, the solubility in a solvent is deteriorated, and it becomes difficult to form (film-form) the PVA-based resin film 10.

An example of the PVA-based resin film 10 is an unstretched film made of the PVA-based resin film. The film forming method is not particularly limited, and known methods such as a melt extrusion method and a solvent casting method can be adopted.

Another example of the PVA-based resin film 10 is an stretched film formed by stretching the unstretched film. The extension is usually a uniaxial extension, preferably a longitudinal uniaxial extension. Longitudinal extension refers to the mechanical flow direction (MD) of the membrane, that is, to the longitudinal direction of the membrane.

When the PVA-based resin film 10 introduced into the wet processing section (for the wet processing step) is an stretched film, the stretching is preferably dry stretching. Dry extension refers to extension in air, usually longitudinal uniaxial extension.

Dry stretching can be exemplified by hot roll stretching, which allows the film to pass between the heated roll on the surface and a guide roll (or a heated roll) with a different speed from the heated roll. Extension; Roll-to-roll extension is through a heating mechanism (oven, etc.) set between two nip rollers separated by a distance, and at the same time, longitudinal extension is performed by the speed difference between the two nip rollers; tenter extension; compression Extension, etc.

The elongation temperature (surface temperature of the hot roll or temperature in the oven, etc.) is, for example, 80 to 150 ° C, and preferably 100 to 135 ° C.

The stretching magnification of the above-mentioned stretching varies depending on whether wet stretching is performed in the wet processing step described below and the stretching magnification of the wet stretching, but is usually 1.1 to 8 times, preferably 2.5 to 5 times.

The PVA-based resin film 10 may contain additives such as a plasticizer. Preferable examples of the plasticizer are polyhydric alcohols, and specific examples thereof include ethylene glycol, glycerol, propylene glycol, diethylene glycol, diglycerol, triethylene glycol, triglyceride, tetraethylene glycol, and triethylene glycol. Methylolpropane, polyethylene glycol, etc. The PVA-based resin film 10 may contain one or more plasticizers.

The content of the plasticizer is usually 5 to 20 parts by weight, and preferably 7 to 15 parts by weight, based on 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 introduced into the wet processing section (for the wet-processing step) varies depending on whether the PVA-based resin film 10 is an stretched film, but is usually 10 to 150 μm to obtain the polarizing film. From the viewpoint of the thickness of 25, it 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, and further 20 μm or less).

(2) Wet processing section and wet processing steps

The wet processing unit is a region disposed on the conveyance path of the PVA-based resin film 10 and includes a processing tank that stores a processing liquid in which the PVA-based resin film 10 is impregnated. In this wet processing section, a wet processing step is performed. This step is carried out while immersing the PVA-based resin film 10 in the processing liquid.

In the wet processing section, the processing tank usually includes a dyeing processing tank 15 and a cross-linking processing tank 17, and preferably further includes a swelling processing tank 13 and a cleaning processing tank 19. These processing tanks are usually arranged in the order of the swelling processing tank 13, the dyeing processing tank 15, the crosslinking processing tank 17, and the washing processing tank 19 from the upstream side of the conveyance path (see FIG. 1).

Fig. 1 shows an example in which one swelling treatment tank 13, dyeing treatment tank 15, cross-linking treatment tank 17, and washing treatment tank 19 are respectively provided, and two or more dyeing treatment tanks 15 may be provided as required. Two or more crosslinking treatment tanks 17 are provided. Similarly, two or more swelling processing tanks 13 and washing processing tanks 19 may be provided.

(2-1) Swelling treatment tank and swelling treatment steps

The swelling treatment is a treatment that can be performed as necessary in accordance with the purpose of removing foreign matter, removing plasticizers, imparting easy dyeability, and plasticizing the film of the PVA-based resin film 10.

Referring to FIG. 1, the swelling treatment step can be performed by continuously unwinding the PVA-based resin film 10 by the unwinding roller 11 and carrying it along the film conveying path, and storing the PVA-based resin film 10 in a container. The swelling treatment tank 13 of the swelling treatment liquid is immersed for a predetermined time, and then pulled out.

The processing liquid (swelling processing liquid) contained in the swelling processing tank 13 may be, for example, water (pure water), or an aqueous solution to which a water-soluble organic solvent such as an alcohol is added. The swelling treatment liquid may contain boric acid, chloride, inorganic acid, inorganic salt, and the like.

The temperature of the swelling treatment liquid is usually 10 to 70 ° C, preferably 15 to 50 ° C, and 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.

In the swelling treatment, the PVA-based resin film 10 may be subjected to a wet stretching treatment (usually a uniaxial stretching treatment). The stretching ratio at this time is usually 1.2 to 3 times, preferably 1.3 to 2.5 times. Referring to FIG. 1, for example, a uniaxial stretching process may be performed in the swelling treatment tank 13 by using a difference in rotational speed between the nip rolls 2 a and 2 b.

In the example shown in FIG. 1, the film system drawn out from the swelling processing tank 13 is sequentially introduced into the dyeing processing tank 15 through the guide roller 1 c and the nip roller 2 b.

(2-2) Dyeing treatment tank and dyeing process step S101

The dyeing treatment is performed for the purpose of adsorbing a dichroic dye and orienting the PVA-based resin film 10 and the like.

Referring to FIG. 1, the dyeing process step S101 can be carried out by conveying along the film conveying path, immersing the PVA-based resin film 10 in the dyeing treatment tank 15 for a predetermined time, and then pulling it out. The dyeing processing tank 15 is a tank for dipping the PVA-based resin film 10 in the dyeing processing solution contained therein. The PVA-based resin film 10 immersed in the dyeing treatment liquid is preferably a film after the swelling treatment step (soaked in the swelling treatment tank 13).

The dyeing treatment liquid contained in the dyeing treatment tank 15 is a liquid (usually an aqueous solution) containing a dichroic pigment. The dichroic pigment may be iodine or a dichroic organic dye, and iodine is preferred. The dichroic pigment may be used alone or in combination of two or more.

When the dichroic dye uses iodine, it can be used for an aqueous solution containing iodine and potassium iodide in the dyeing liquid. Instead of potassium iodide, other iodides such as zinc iodide may be used, or potassium iodide may be used in combination with other iodides. In addition, compounds other than iodide may be coexisted, such as boric acid, zinc chloride, and cobalt chloride. When boric acid is added, it is different from a 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 per 100 parts by weight of water, it can be regarded as a dyeing treatment liquid. The content of iodine in the dyeing treatment liquid 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 treatment liquid is usually 0.1 to 20 parts by weight per 100 parts by weight of water.

The temperature of the dyeing treatment liquid is usually 10 to 45 ° C, preferably 10 to 40 ° C, and more preferably 20 to 35 ° C. The impregnation time (residence time in the dyeing treatment liquid) 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 may include two or more dyeing treatment tanks 15. In this case, the composition and temperature of the respective dyeing treatment liquids may be the same or different.

In order to improve the dyeability of the dichroic pigment, the PVA-based resin film 10 to be subjected to the dyeing treatment is preferably subjected to at least a certain degree of stretching treatment (usually a uniaxial stretching treatment). It is also possible to perform an extension treatment at the same time as the dyeing treatment to replace the extension treatment before the dyeing treatment, or to perform the extension treatment at the same time as the dyeing treatment in addition to the extension treatment before the dyeing treatment. The cumulative extension ratio up to the dyeing treatment (the extension ratio in the dyeing treatment when there is no extension step until the dyeing treatment) is usually 1.6 to 4.5 times, preferably 1.8 to 4 times. Referring to FIG. 1, for example, a uniaxial stretching process can be performed in the dyeing treatment tank 15 by using a difference in rotational speed between the nip roll 2 b and the nip roll 2 c.

In the example shown in FIG. 1, the film system drawn out from the dyeing treatment tank 15 passes through the guide roller 1 f and the nip roller 2 c in this order and is introduced into the crosslinking treatment tank 17.

(2-3) Cross-linking treatment tank and cross-linking treatment step S102

The cross-linking treatment is performed for the purpose of water resistance or color adjustment due to cross-linking.

Referring to FIG. 1, the cross-linking treatment can be carried out by transporting along the film transport path, and placing the PVA-based resin film 10 after the dyeing treatment step S101 (immersed in the dyeing treatment tank 15) in the cross-linking treatment tank 17 Dip for a given time and then pull out. 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 contained in the crosslinking treatment tank 17 is a liquid (usually an aqueous solution) containing a crosslinking agent. The cross-linking treatment is performed by immersing the PVA-based resin film 10 after the dyeing treatment step S101 in the cross-linking treatment liquid.

Examples of the cross-linking agent contained in the cross-linking treatment liquid include boric acid, glyoxal, and glutaraldehyde. Boric acid is preferred. Two or more types of crosslinking agents may 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 treatment liquid preferably contains iodide in addition to the crosslinking agent.

Examples of the iodide include potassium iodide and zinc iodide.

The content of iodide in the crosslinking treatment liquid is generally 0.1 to 20 parts by weight, and preferably 5 to 15 parts by weight per 100 parts by weight of water.

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

The temperature of the crosslinking treatment liquid is generally 20 to 85 ° C, and 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, and preferably 20 to 300 seconds.

As described above, the polarizing film manufacturing apparatus may include two or more crosslinking treatment tanks 17. In this case, the composition and temperature of the respective crosslinking treatment liquids may be the same or different. The cross-linking treatment liquid may have a concentration or temperature of a cross-linking agent, iodide, and the like according to the purpose of impregnating the PVA-based resin film 10. The cross-linking treatment for making the cross-linking water-resistant and the cross-linking treatment for adjusting the hue may be performed in a plurality of steps, respectively.

The stretching treatment (usually a uniaxial stretching treatment) may be performed simultaneously with the crosslinking treatment. Referring to FIG. 1, for example, a uniaxial stretching treatment can be performed in the cross-linking treatment tank 17 by using a difference in rotational speed between the nip roller 2 c and the nip roller 2 d.

In the example shown in FIG. 1, the film system drawn out from the crosslinking treatment tank 17 is sequentially introduced into the cleaning treatment tank 19 through the guide roller 1 i and the nip roller 2 d.

(2-4) Washing treatment tank and washing treatment steps

The method for manufacturing a polarizing film may further include a washing process step after the cross-linking process step S102. Therefore, the polarizing film manufacturing apparatus may further include a washing process tank 19 disposed downstream of the cross-linking process tank 17. The washing treatment is carried out for the purpose of removing, for example, the excess medicine adhered to the PVA-based resin film 10 after the crosslinking treatment step S102.

Referring to FIG. 1, the cleaning treatment can be carried out by transporting along the film conveyance path, and placing the PVA-based resin film 10 after the crosslinking treatment step S102 (immersed in the crosslinking treatment tank 17) in the cleaning treatment tank. It was immersed in 19 for a predetermined time and then pulled out. Alternatively, the washing treatment may be a treatment in which the washing solution is sprayed on the PVA-based resin film 10 after the cross-linking treatment step S102, for example, or may be an immersion and washing solution in the washing treatment tank 19. The spray is combined. Fig. 1 shows an example of a case where the PVA-based resin film 10 is immersed in a cleaning treatment tank 19 and a cleaning treatment is performed.

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

When the cleaning process is performed, an extension process (usually a uniaxial extension process) can be performed at the same time. Referring to FIG. 1, for example, a uniaxial stretching process can be performed in the cleaning processing tank 19 by using a difference in rotational speed between the nip rollers 2 d and the nip rollers 2 e.

(2-5) Extension mechanism and extension processing steps

The PVA-based resin film 10 may be subjected to wet stretching in the wet processing step. Wet extension is usually uniaxial, and it can be performed at the same time as any one of swelling treatment, dyeing treatment, cross-linking treatment, and washing treatment, or it can be two or more treatments selected from these treatments. Medium.

The wet stretching is preferably performed at the crosslinking treatment step S102 or at one or two or more stages before the crosslinking treatment step S102. As described above, in order to improve the dyeability of the dichroic pigment and obtain the polarizing film 25 having good polarizing characteristics, it is more preferable that the PVA-based resin film 10 used in the dyeing process step S101 is subjected to at least a certain degree of stretching treatment.

From the viewpoint of the polarizing characteristics of the obtained polarizing film 25, the stretch magnification of the wet stretching is preferably the final cumulative stretching magnification of the polarizing film 25 (when the PVA-based resin film 10 for wet processing is an stretching film, it also includes The cumulative extension magnification of this extension is adjusted so that it becomes 3 to 8 times.

When the wet stretching process step is performed, the polarizing film manufacturing apparatus includes a wet stretching mechanism of the PVA-based resin film 10. The wet extension mechanism is preferably an extension mechanism for extending between rollers. Taking the case where the roll-to-roll stretching is performed in the cross-linking processing step S102 as an example, the stretching mechanism for the roll-to-roll stretching is arranged at the two nip rolls 2c and 2d before and after the cross-linking treatment tank 17. In the case where the stretching is performed in other wet processes, two separate nip rollers may be used as the wet stretching mechanism.

(3) Drying section and drying process steps

The drying processing section is disposed on the PVA-based resin film 10 conveying path and downstream of the wet processing section, and is a region for drying the PVA-based resin film 10 after the wet processing step. The PVA-based resin film 10 after the wet processing step is continuously conveyed, and the film is introduced into a drying processing section, whereby a drying treatment can be performed, and a polarizing film 25 can be obtained (see FIG. 1).

The drying processing unit is a drying mechanism (heating mechanism) including a film. A preferred example of the drying mechanism is a drying furnace. The drying furnace is preferably one capable of controlling the temperature in the furnace. The drying furnace is, for example, a hot air oven that can increase the temperature in the furnace by supplying hot air or the like. In addition, the drying treatment by the drying mechanism may be a treatment in which the PVA-based resin film 10 after the wet processing step is adhered to one or more heating bodies having a convex curved surface, and a heater may be used. The film is heated.

Examples of the heating body include a roller (for example, a guide roller that also has a heat roller) that has a heat source (for example, a heat medium such as warm water or an infrared heater) inside and can increase the surface temperature. Examples of the heater include an infrared heater, a halogen heater, and a flat heater. The first figure shows an example in which the PVA-based resin film 10 after the wet processing step is introduced into a 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 roller, etc.) is usually 30 to 100 ° C, preferably 50 to 90 ° C.

The polarizing film 25 is for a stretched (usually uniaxially stretched) PVA-based resin film that adsorbs and orients a dichroic pigment. The thickness of the polarizing film 25 is usually 2 to 40 μm. From the viewpoint of thinning the polarizing plate containing 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.

Considering the balance with the photometric correction polarization degree Py, the photometric correction monomer transmittance Ty of the obtained polarizing film 25 is preferably 40 to 47%, more preferably 41 to 45%. The photometric correction polarization degree Py is preferably 99.9% or more, and more preferably 99.95% or more.

Ty and Py can be measured using an absorbance photometer with an integrating sphere, and the obtained transmittance and polarization degree can be photometrically corrected with a 2-degree field of view (C light source) according to JIS Z 8701.

The obtained polarizing film 25 can be sequentially wound on the winding roller 27 to form a roll form, or it can be directly supplied to the polarizing plate production step without being wound. [The single-sided or two-area thermoplastic resin film (protection Film, etc.)].

(4) Generation and removal of particles containing polyvinyl alcohol resin

The method for manufacturing a polarizing film of the present invention includes the following steps: A shear force is applied to at least a part of the cross-linking treatment liquid extracted from the cross-linking treatment liquid in the cross-linking treatment tank 17, thereby obtaining a particle-containing liquid. It is a step (particle generation step S201) containing particles containing a polyvinyl alcohol-based resin; and a step (particle removal step S202) for removing the particles from the particle-containing liquid.

Therefore, the polarizing film manufacturing apparatus of the present invention includes a shearing force imparting unit configured to impart shearing force to at least a part of the crosslinking treatment liquid extracted from the crosslinking treatment liquid in the crosslinking treatment tank 17, thereby obtaining particles containing The particle-containing liquid system contains particles containing a polyvinyl alcohol-based resin; and a particle removing unit for removing the particles from the particle-containing liquid.

FIG. 1 is a schematic diagram showing an example of a polarizing film manufacturing apparatus having a shear force imparting portion and a particle removing portion attached to the crosslinking treatment tank 17 and a method of manufacturing a polarizing film manufactured using the manufacturing device.

The polarizing film manufacturing apparatus shown in FIG. 1 includes a cooling section 30 connected to the cross-linking treatment tank 17 and configured to extract at least a part of the cross-linking treatment liquid from the cross-linking treatment liquid in the cross-linking treatment tank 17. Cooling; shearing force applying unit 40 is connected to cooling unit 30 to apply shearing force to at least a part of the cross-linked treatment liquid after cooling to obtain the particle-containing liquid; and particle removing unit 50 is connected The shear force applying unit 40 is used to remove the particles from the particle-containing liquid.

The cross-linking treatment tank 17 and the cooling section 30 are connected through a connection channel (connection line) 28. The cooling section 30 and the shear force applying section 40 are connected through a connection channel (connection line) 29. The shear force applying section 40 and The particle removal section 50 is connected via a connection channel (connection line) 41.

The concentration of the polyvinyl alcohol-based resin in the crosslinking treatment liquid drawn out from the crosslinking treatment tank 17 may be, for example, about 5 ppm to 5000 ppm on a weight basis.

In the manufacturing method of the polarizing film using the polarizing film manufacturing apparatus shown in FIG. 1, firstly, at least a part of the crosslinking treatment liquid is drawn out from the crosslinking treatment tank 17 through the connection channel (connection line) 28, and the extracted The crosslinking treatment liquid is cooled in the cooling section 30 (cooling step). A part of the particles are precipitated from the crosslinking treatment liquid by cooling. The temperature of the crosslinking treatment liquid after cooling is, for example, 0 to 60 ° C, and preferably 10 to 40 ° C.

The cooling unit 30 may use a known mechanism, for example, a sleeve capable of introducing a refrigerant, a room (or tank) having a cooling mechanism such as a heat exchanger, a connection passage (cooling line, cooling pipe), and the like. Since the introduced cross-linking treatment liquid can be continuously cooled, and the cross-linking treatment liquid after continuous cooling can be led out, the cooling section 30 is preferably a connection channel (cooling line, cooling pipe) with a cooling mechanism. .

The cooling section 30 is located at an arbitrary position, and it is not necessary to provide the cooling section 30 depending on the temperature of the crosslinking treatment liquid in the crosslinking treatment tank 17.

In the manufacturing method of the polarizing film using the polarizing film manufacturing apparatus shown in FIG. 1, the cross-linking treatment liquid system after cooling is introduced into the shear force imparting portion 40 and the shear force is imparted, thereby generating a polyvinyl alcohol resin-containing resin. The particles (particle generation step S201). The precipitated particles may contain, in addition to the polyvinyl alcohol-based resin, a crosslinking agent, an iodide, and the like contained in the crosslinking treatment liquid.

The shear force imparting portion 40 may be, for example, a room (or a groove) having a shear force imparting mechanism, a connection passage (a line, a pipe), or the like. Since the cross-linking treatment liquid introduced into the shearing force imparting portion 40 can continuously impart shearing force and continuously lead out the particle-containing liquid, the shearing force imparting portion 40 is a connection channel (line, piping) having a shearing force imparting mechanism. Is better.

The shearing force imparting mechanism may be, for example, a stirring wing; a convection generating mechanism for convecting liquid by bringing in a liquid by a rotating member or the like of a general homogenizer; a protrusion or a disturbance protruding from a space through which the liquid passes. Shock-giving mechanisms such as flow plates (baffles); high-frequency generators; ultrasonic generators; and combinations of two or more of these.

The shearing force imparted to the crosslinking treatment liquid is preferably 40 to 350 Pa, and more preferably 50 to 260 Pa. When the shearing force given to the crosslinking treatment liquid is within this range, particles (particles containing polyvinyl alcohol resin) are efficiently precipitated, and they are easily separated during solid-liquid separation in the particle removal step S202 described later, and Easy to adjust particle size. When a shear force is imparted to a liquid by rotation of a member such as a stirring blade, the shear force which can be imparted to a crosslinking treatment liquid can be calculated by the following formula.

Shear force [Pa] = viscosity of the cross-linking treatment solution [mPa‧s] × number of rotation of the stirring blade [rpm] × 0.001 × 60.

In the above formula, the viscosity of the crosslinking treatment liquid is usually from 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 shear force imparting portion 40 is disposed behind the cooling portion 30, but the shear force imparting portion 40 may include the cooling portion 30. Thereby, in the particle generation step S201, the cross-linking treatment liquid can be cooled while being given a shear force.

The particle generation step S201 preferably includes a step (control step) of controlling the content of the particles in the obtained particle-containing liquid or the particle size distribution of the particles. By adjusting 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 described later can be improved.

An example of the control step is the above-mentioned cooling step (the temperature control step of the crosslinking treatment liquid). By applying a shear force to the crosslinking treatment liquid after cooling or while cooling, the amount of particle precipitation can be increased.

Another example of the control step includes a step of adjusting the time of applying the shear force, a step of adjusting the magnitude of the shear force, and a step of adjusting the flow rate of the crosslinking treatment liquid by the shear force imparting portion 40. The particle content in the particle-containing liquid can be adjusted by appropriately adjusting the temperature of the cross-linking treatment liquid to which the shear force is applied, the time of applying the shear force, the magnitude of the shear force, and the flow rate of the cross-linking treatment liquid passing through the shear force imparting portion 40. (Amount of particle precipitation) and particle size distribution (particle size).

After the particle-containing liquid is obtained in the particle generation step S201, the particles precipitated from the particle-containing liquid are removed (particle removal step S202). By this step, a liquid (particle-removed cross-linking treatment liquid) from which the precipitated particles are removed can be obtained.

The polarizing film manufacturing apparatus includes a particle removing unit 50 for removing the particles from a particle-containing liquid.

A step of cooling the particle-containing liquid may be provided before the particle removal step S202 and after the particle generation step S201. At this time, the polarizing film manufacturing device is further provided between the shear force imparting section 40 and the particle removing section 50. To cool the cooling part containing the particle liquid.

The particle removal unit 50 may be a known solid-liquid separation device such as a filter.

The method for producing a polarizing film further includes a step of returning at least a part of the cross-linked treatment liquid from which the particles have been removed to the cross-linking treatment tank 17, so that the polyvinyl alcohol-based system in the cross-linking treatment liquid in the cross-linking treatment tank 17 can be performed. The concentration of the resin is reduced or maintained to a low concentration that does not precipitate in the cross-linking treatment tank 17, so that the precipitates deposited in the cross-linking treatment tank 17 can be prevented from adhering to the PVA-based resin film even in the wet process. Defective surface of polarizing film.

The method for manufacturing a polarizing film further includes a step of returning at least a part of the particle-removed cross-linking treatment liquid to the cross-linking treatment tank 17. The polarizing film manufacturing apparatus further includes a circulation channel 51, which is used to make the At least a part of the crosslinking treatment liquid from which the particles are removed is returned to the crosslinking treatment tank 17. The circulation channel 51 is a connection channel connecting the particle removal section 50 and the crosslinking treatment tank 17.

The operation of "extracting at least a part of the cross-linking treatment liquid from the cross-linking treatment tank 17 and performing treatment on the extracted cross-linking treatment liquid and returning at least a part of the liquid obtained by the treatment to the cross-linking treatment tank 17" For example, it can be performed using a pump or the like.

In order to adjust the amount of the cross-linking treatment liquid in the cross-linking treatment tank 17, it may be at the same time as at least a part of the cross-linking treatment liquid from which the particles have been removed is returned to the cross-linking treatment tank 17, or during the cross-linking treatment with the removed particles. At least a part of the liquid is returned to the crosslinking treatment tank 17 at different timings, and the crosslinking treatment tank 17 is replenished with fresh crosslinking treatment liquid.

When the polarizing film manufacturing apparatus includes the cross-linking treatment tank 17 having two or more grooves, the shear force applying section 40 and the particle removing section 50 (and a cooling section provided as necessary) may be provided in one cross-linking treatment tank 17 or may be provided. It is provided in two or more or all of the crosslinking treatment tanks 17. It is preferable that the shear force imparting portion 40 and the particle removing portion 50 (and the cooling portion provided if necessary) are provided at least in the crosslinking treatment tank 17 which is liable to cause precipitation of a polyvinyl alcohol resin in the crosslinking treatment tank. Such a cross-linking treatment tank 17 may be, for example, a cross-linking treatment tank having a relatively higher temperature than the other cross-linking treatment tanks.

(5) Experimental example 1: particle generation using a homogeneous disperser

The polarizing film 25 was continuously manufactured from a long polyvinyl alcohol film using the polarizing film manufacturing apparatus shown in FIG. 1. The polyvinyl alcohol film used is a uniaxially stretched polyvinyl alcohol film having a thickness of 30 μm to 4.1 times in a dry manner. The degree of saponification of the polyvinyl alcohol constituting the film is 99.9 mol% or more, and the average polymerization degree is 2400.

The polyvinyl alcohol film 10 is unwound from the unwinding roller 11 while being tensioned, and is continuously conveyed while being kept in a tight state. The polyvinyl alcohol film 10 is dipped in a swelling treatment tank 13 containing 40 ° C pure water for a retention time of 60 seconds to make the polymer The vinyl alcohol film 10 swells (swelling process step). The film was pulled out from the swelling treatment tank 13, and the film was dipped in a dyeing treatment tank 15 containing a 30 ° C dyeing treatment solution of iodine / potassium iodide / water at a weight ratio of 0.1 / 6/100 with a retention time of 60 seconds while being soaked Uniaxial stretching (roll-to-roll stretching in the bath) is performed (dyeing treatment step). The film was pulled out from the dyeing treatment tank 15, and the film was immersed in a crosslinking treatment tank 17 containing a crosslinking treatment solution at a temperature of 68 ° C with a weight ratio of 15 / 5.5 / 100 of potassium iodide / boric acid / water. Simultaneously, uniaxial extension (extension between rolls in the bath) was performed therebetween (crosslinking treatment step). The film was pulled out from the crosslinking treatment tank 17, and the film was immersed in a cleaning treatment tank 19 containing pure water at 20 ° C. for a dwell time of 3 seconds and washed (washing treatment step). The cumulative stretching ratio based on the polyvinyl alcohol film before dry uniaxial stretching is 4.5 times.

The cross-linking treatment liquid was sampled from the cross-linking treatment tank 17 after the continuous production of the above-mentioned polarizing film, and the following particle precipitation experiment was performed. The polyvinyl alcohol concentration in the sampled cross-linking treatment liquid was about 1500 ppm on a weight basis when measured by a GPC (colloidal permeation chromatography) method.

The sampled cross-linking treatment liquid was placed in a homogeneous disperser [Homogeneous Disperser 2.5 (paddle type), capacity 800 mL] manufactured by PRIMIX, and a shear force was applied to the cross-linking treatment liquid under the following conditions to obtain a particle-containing liquid. This particle-containing liquid system contains solid particles containing polyvinyl alcohol.

Temperature: 3 conditions of 14 ° C, 29 ° C and 39 ° C.

The number of rotations of the stirring blade: 2 conditions of 1000 rpm and 5000 rpm.

Processing time of homogeneous disperser: 10 minutes.

Fig. 2 shows the measurement results of the particle size distribution of the obtained solid particles. The horizontal axis represents the particle diameter of the solid particles generated, and the vertical axis (number of detections) corresponds to the number of solid particles. The particle size distribution of the solid particles shown in Fig. 2 is a result of measuring the obtained particle-containing liquid using a liquid particle counter ("Light-shielding Particle Detector (KS-42D) manufactured by RION Corporation)" (No. 3 The particle size distribution of the solid particles shown in the figure is the same).

(6) Experimental example 2: particle generation using a homogenizer

In order to impart shearing force to the cross-linking treatment liquid, a homogenizer [Homogenizer 2.5 type (cylinder type), capacity 800 mL] manufactured by PRIMIX was used instead of the homogeneous disperser, and the cross-linking treatment liquid was given shear force under the following conditions. Other than that, a particle-containing liquid was obtained in the same manner as in Experimental Example 1, and the particle-containing liquid contained solid particles containing polyvinyl alcohol.

FIG. 3 shows the measurement results of the particle size distribution of the obtained solid particles.

Temperature: 3 conditions of 14 ° C, 29 ° C and 39 ° C.

The number of rotations of the inner blade of the homogenizer: two conditions of 1000 rpm and 5000 rpm.

Homogeneous disperser processing time: 10 seconds, 1 minute, 10 minutes of three conditions.

Claims (8)

    A method for manufacturing a polarizing film includes the steps of: immersing a polyvinyl alcohol-based resin film in a dyeing treatment tank containing a dyeing treatment solution; and immersing the polyvinyl alcohol-based resin film after the step of dipping in the dyeing treatment tank. A step of receiving a crosslinking treatment tank containing a crosslinking treatment solution; applying a shear force to at least a part of the crosslinking treatment solution extracted from the crosslinking treatment solution in the aforementioned crosslinking treatment tank, thereby obtaining a particle-containing liquid, the particle-containing liquid A step of removing particles containing a polyvinyl alcohol-based resin; and a step of removing the particles from a particle-containing liquid.         The manufacturing method according to item 1 of the scope of the patent application, wherein the step of obtaining the particle-containing liquid includes: a step of adjusting a content of the particles in the particle-containing liquid or a particle size distribution of the particles.         The manufacturing method according to item 2 of the scope of patent application, wherein the aforementioned control step includes the step of cooling the at least a part of the crosslinking treatment liquid.         The manufacturing method as described in item 3 of the scope of patent application, which applies a shear force to at least a part of the crosslinking treatment liquid before or after cooling.         The manufacturing method according to any one of claims 1 to 4, further comprising: a step of returning at least a part of the liquid from which the particles have been removed to the crosslinking treatment tank.         A polarizing film manufacturing device comprises: a dyeing treatment tank, which is a tank for impregnating a polyvinyl alcohol resin film, and is used for containing a dyeing treatment liquid; a cross-linking treatment tank, which is used for immersion after being dipped in the dyeing treatment tank The polyvinyl alcohol-based resin film is a slot for containing a crosslinking treatment liquid; and a shear force imparting section is used to impart at least a part of the crosslinking treatment liquid withdrawn from the crosslinking treatment liquid in the aforementioned crosslinking treatment tank. A shearing force is used to obtain a particle-containing liquid, and the particle-containing liquid contains particles containing a polyvinyl alcohol-based resin; and a particle removing portion is used to remove the particles from the particle-containing liquid.         The manufacturing device described in item 6 of the patent application scope further includes a cooling section, and the cooling section is used to cool the at least a part of the crosslinking treatment liquid.         The manufacturing device according to item 6 or 7 of the scope of the patent application, further comprising a circulation channel, wherein the circulation channel is used to return at least a part of the liquid from which the particles have been removed to the crosslinking treatment tank.