TW201731931A - Apparatus and method for manufacturing polarizing film, and polarizing film - Google Patents

Abstract

An object of the present invention is to provide an apparatus and a method for manufacturing a polarizing film which is difficult to cause a bright spot (light leakage) when applied to a liquid crystal display device. The present invention provides an apparatus for manufacturing a polarizing film from a polyvinyl alcohol-based resin film, a manufacturing method using the same, and a polarizing film having a density of specific irregular defects of 20 pieces/m2 or less. The apparatus comprises: a plurality of rolls which constitute a conveying path for a polyvinyl alcohol-based resin film and is arranged so as to be in contact with the surface of a polyvinyl alcohol based resin film; a wet processing section including one or more processing tanks for storing a processing liquid which is arranged on the conveying path and to which a polyvinyl alcohol-based resin film is immersed; a drying processing section disposed on the conveying path for drying the wet-processed polyvinyl alcohol based resin film, wherein the plurality of rolls include a low rotation resistance roll having a rotational resistance of 0.025 N or less.

Description

Polarizing film manufacturing apparatus and manufacturing method, and polarizing film

The present invention relates to a manufacturing apparatus and a manufacturing method of a polarizing film which can be used as a constituent member of a polarizing plate, for example. And the present invention relates to a polarizing film.

In the case of the polarizing film, a dichroic dye such as iodine or a dichroic dye is adsorbed and adsorbed on a polyvinyl alcohol-based resin film after uniaxial stretching. In general, the polarizing film is sequentially applied: a dyeing treatment in which a polyvinyl alcohol-based resin film is dyed with a dichroic dye, a crosslinking treatment in which a crosslinking agent is treated, and a film drying treatment, and is carried out between manufacturing steps. It is manufactured by a uniaxial stretching process (for example, JP-A-2001-141926 (Patent Document 1)).

The apparatus for producing a polarizing film usually has a treatment tank such as a dyeing treatment tank or a crosslinking treatment tank, and a transport path of a polyvinyl alcohol-based resin film that passes through a drying device or the like. The polyvinyl alcohol-based resin film conveyed along this path is supported by a roller such as a guide roll or a roll that holds the film.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2001-141926

One of the main uses of the polarizing film is a polarizing plate used as an essential component of a liquid crystal display device. The polarizing plate refers to an optical member in which a protective layer (a protective film or the like) is typically laminated on one surface or both surfaces of a polarizing film by using an adhesive. In recent years, the visibility (brightness) of liquid crystal display devices has been demanded to increase, and with this demand, backlights having higher brightness have been gradually used for liquid crystal display devices.

Based on such a situation, the present inventors are faced with a new problem: if the brightness of the backlight is raised to a certain level or more, when the brightness is lower than the above case, the screen of the liquid crystal display device is not recognized without causing a problem. Point-like highlights (light leakage) are recognized. For example, in a liquid crystal panel, when a polarizing plate is bonded to an adhesive layer of a liquid crystal cell and a bubble is mixed between the liquid crystal cell, the bubble becomes dominant and a bright spot (light leakage) is known, although several kinds have been proposed. The technique for suppressing the incorporation of the air bubbles, but the above-mentioned bright spots that the inventors have renewed, it is clear that they are not caused by air bubbles mixed between the adhesive layer and the liquid crystal cell. Further, as a result of investigation by the present inventors, it has been found that the main cause of the above-mentioned bright spots lies in the polarizing film constituting the polarizing plate.

SUMMARY OF THE INVENTION An object of the present invention is to provide an apparatus and method for producing a polarizing film which is less likely to cause a bright spot (light leakage) which the present inventors have faced again when applied to a liquid crystal display device. Moreover, other objects of the invention The system provides a polarizing film that is less prone to the above-mentioned bright spots (light leakage).

The present inventors have found that the main cause of the above-mentioned bright spots (light leakage) is a specific unevenness defect (hereinafter also referred to as "specific unevenness defect") which is generated on the surface of the polyvinyl alcohol-based resin film in the production process of the polarizing film, and by the following The apparatus and method for producing a polarizing film of the present invention shown in the present invention can effectively suppress specific uneven defects of the polarizing film and even bright spots (light leakage).

That is, the present invention provides a manufacturing apparatus, a manufacturing method, and a polarizing film of the polarizing film described below.

[1] A manufacturing apparatus for manufacturing a polarizing film from a polyvinyl alcohol-based resin film, comprising: a plurality of rolls constituting a transport path of the polyvinyl alcohol-based resin film, and arranged in the same manner as described above The surface of the polyvinyl alcohol-based resin film is in contact with each other; the wet processing unit is disposed on the transport path, and includes one or more treatment tanks for containing the treatment liquid in which the polyvinyl alcohol-based resin film is immersed; and a drying treatment unit And being disposed on the transport path for drying the polyvinyl alcohol-based resin film after the wet treatment; wherein the plurality of rolls include a low rotational resistance roller having a rotational resistance of 0.025 N or less.

[2] The manufacturing apparatus according to [1], wherein the low rotational resistance roller is disposed in a conveying path from the wet processing unit to the drying processing unit Any of the locations.

[3] The manufacturing apparatus according to [2], wherein the wet processing unit comprises, in order, a dyeing treatment tank containing a dyeing treatment liquid containing a dichroic dye; and a crosslinking treatment containing a crosslinking agent. The cross-linking treatment tank of the liquid; the low-rotation resistance roller is disposed after the cross-linking treatment tank.

[4] The manufacturing apparatus according to any one of [1] to [3] wherein the low rotational resistance roller has a surface having a contact angle with water of 60 degrees or more.

[5] The production apparatus according to [4], wherein the surface is made of a fluorine-based resin, a halogen-containing resin, carbon or diamond-like carbon.

[6] The manufacturing apparatus according to any one of [1] to [5] wherein the weight of the low rotational resistance roller per unit volume is 1,500 kg/m ³ or less.

[7] The manufacturing apparatus according to any one of [1] to [6] wherein the low rotational resistance roller is a guide roller.

[8] The production apparatus according to any one of [1] to [7], wherein the polyvinyl alcohol-based resin film that is in contact with the low rotational resistance roller has a thickness of 15 μm or less.

[9] A production method for producing a polarizing film from a polyvinyl alcohol-based resin film And a method comprising: the wet processing step of transporting the polyvinyl alcohol resin film along a transport path formed by a plurality of rolls arranged to be in contact with the surface of the polyvinyl alcohol resin film And immersing in the one or more processing liquids, and the drying treatment step of drying the polyvinyl alcohol-based resin film after the wet treatment while transporting the polyvinyl alcohol-based resin film along the transport path The plurality of rolls include a low rotational resistance roller having a rotational resistance of 0.025 N or less.

[10] The production method according to [9], wherein the low rotational resistance roller is disposed at any one of a transport path from the wet processing step to the drying processing step.

[11] The production method according to [10], wherein the wet processing step sequentially comprises: a step of immersing in a dyeing treatment liquid containing a dichroic dye; and immersing in a crosslinking treatment containing a crosslinking agent. The step of the liquid; the low rotational resistance roller is disposed in the transport path after the step of immersing in the crosslinking treatment liquid.

[12] The production method according to any one of [9] to [11] wherein the low rotational resistance roller has a surface having a contact angle with water of 60 degrees or more.

[13] The production method according to [12], wherein the surface is composed of a fluorine-based resin, a halogen-containing resin, carbon or diamond-like carbon.

[14] The production method according to any one of [9] to [13] wherein the low rotational resistance roller has a weight per unit volume of 1,500 kg/m ³ or less.

[15] The production method according to any one of [9] to [14] wherein the low rotational resistance roller is a guide roller.

The production method according to any one of the above aspects, wherein the polyvinyl alcohol-based resin film that is in contact with the low rotational resistance roller has a thickness of 15 μm or less.

[17] A polarizing film in which a dichroic dye is adsorbed to a polyvinyl alcohol-based resin film, wherein a density of at least one surface unevenness defect is 20 pieces/m ² or less, and the unevenness defect is one convex type. And a combination of a concave portion and a long diameter of 0.5 to 5 mm, wherein the one convex portion protrudes more than the reference based on the polarizing film surface other than the unevenness defect, and the one concave portion is formed. It is more trapped than the aforementioned reference and is adjacent to the aforementioned convex portion.

According to the present invention, it is possible to provide a polarizing film which is less likely to cause bright spots (light leakage) due to specific uneven defects on the surface of the film even when applied to a liquid crystal display device using a backlight having high luminance.

1a, 1b, 1c, 1d, 1e, 1f, 1g, 1h, 1i, 1j, 1k, 1l, 1m, 1n, 1o, 1p, 1q, 1r, 1s‧‧‧ guide rolls

2a, 2b, 2c, 2d, 2e, 2f‧‧‧ rolls

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

11‧‧‧Rolling roll

13‧‧‧Swelling treatment tank

15‧‧‧Dyeing tank

17‧‧‧crosslinking processing tank

19‧‧‧Washing treatment tank

20‧‧‧ Wet treatment department

21‧‧‧ drying oven

22‧‧‧Drying and Processing Department

25‧‧‧ polarizing film

27‧‧‧Winding roller

Fig. 1 is a schematic cross-sectional view showing an example of a polarizing film production apparatus of the present invention.

Fig. 2 is an enlarged schematic cross-sectional view showing a drying treatment portion of the polarizing film manufacturing apparatus shown in Fig. 1.

Fig. 3 is a flow chart showing an example of a method for producing a polarizing film of the present invention.

<Manufacturing device and manufacturing method of polarizing film>

The present invention relates to a manufacturing apparatus and a manufacturing method for producing a polarizing film from a polyvinyl alcohol-based resin film (hereinafter also referred to as "PVA-based resin film"). The polarizing film is produced by performing a series of processes such as immersion treatment (wet treatment) and drying treatment on the PVA-based resin film. The polarizing film is a method in which an extended PVA-based resin film is adsorbed to a dichroic dye.

An example of the polarizing film production apparatus of the present invention is shown in Fig. 1. Fig. 2 is a schematic cross-sectional view showing the drying treatment unit of the polarizing film manufacturing apparatus shown in Fig. 1 enlarged. The polarizing film manufacturing apparatus shown in FIG. 1 and FIG. 2 is a device for continuously producing a long polarizing film 25 from a long PVA-based resin film 10 as a raw material film. The arrows in Figs. 1 and 2 indicate the conveying direction of the film. In the production of the polarizing film 25 using the manufacturing apparatus shown in FIGS. 1 and 2, the PVA-based resin film 10 is continuously wound up from the take-up roll 11 and sequentially immersed in the swelling portion. The treatment tank 13, the dyeing treatment tank 15, the crosslinking treatment tank 17, and the washing treatment tank 19 are finally dried by the drying furnace 21 to obtain a polarizing film 25. The polarizing film 25 for producing a long strip can be sequentially wound up on the take-up roll 27.

In the polarizing film manufacturing apparatus, the wet processing tank is used to accommodate one or more processing tanks in which the processing liquid of the thin film is immersed, such as the swelling treatment tank 13, the dyeing treatment tank 15, the crosslinking treatment tank 17, and the cleaning treatment tank 19. In the present specification, it is referred to as a "wet processing unit" (the wet processing unit 20 shown in Fig. 1). Further, in the drying furnace 21, the region where the wet-processed film is subjected to the drying treatment is referred to as a "drying treatment portion" (the drying treatment portion 22 shown in Figs. 1 and 2). The polarizing film production apparatus of the present invention has a transport path including the PVA-based resin film 10 of the wet processing unit and the drying processing unit. By transporting the PVA-based resin film 10 along the transport path, a series of processes can be performed to obtain the polarizing film 25. The transport speed of the PVA-based resin film 10 transported along the transport path is usually 10 to 50 m/min, and is preferably 15 m/min or more from the viewpoint of production efficiency.

As shown in Fig. 1, the transport path is a plurality of rollers that support/guide the moving film (PVA-based resin film 10 and polarizing film 25) by the wet processing unit 20 and the drying processing unit 22. And built into. The plurality of rollers are composed of a guide roller belonging to a free roller on one side of the support film, and/or a pair of rollers (usually a drive roller), and may include a roller pressed from the double bread clip film or after being sandwiched . In the examples shown in Figs. 1 and 2, the manufacturing apparatus includes guide rolls 1a to 1s and rolls 2a to 2f. The plurality of rolls defining the conveying path may also include one type of suction rolls (suction rolls) belonging to the driving rolls. Typically, the rolls are each one of the films in the transport path The surface or the double surface (main surface) is joined to support the film. These rolls can be disposed at appropriate positions in the front and rear of each treatment tank and drying means (drying furnace) or in the treatment tank and drying means (drying furnace).

Further, the driving roller refers to a roller which can impart a driving force for conveying a film to a film which is in contact therewith, and may be a roller which is directly or indirectly connected to a roller driving source such as a motor. The free roller refers to a roller which serves only as a supporting film for moving, and does not impart a driving force for conveying the film.

A flowchart of an example of a method for producing a polarizing film of the present invention is shown in Fig. 3. Referring to Fig. 3, the method for producing a polarizing film of the present invention comprises the following steps: a wet processing step S101, which is a transport path formed by a plurality of rolls arranged to be in contact with the surface of the polyvinyl alcohol-based resin film. The PVA-based resin film is immersed in one or more treatment liquids, and the drying treatment step S102 is performed by transporting the PVA-based resin film along the transport path while performing the wet-processed PVA system. The resin film was dried.

The wet processing step S101 is the processing performed by the wet processing unit 20 described above, and the drying processing step S102 is the processing performed by the drying processing unit 22 described above.

The obtained polarizing film 25 is subjected to an elongation treatment (usually a uniaxial stretching treatment). Therefore, the apparatus for producing a polarizing film of the present invention may include an extending means of the PVA-based resin film 10 (wet stretching means), and the method of manufacturing the polarizing film of the present invention may include an extending treatment step of the PVA-based resin film 10 (wet type) Extend the processing steps).

(1) PVA resin film

The PVA-based resin film 10 introduced into the wet processing unit 20 (supplied to the wet processing step S101) is a film made of a polyvinyl alcohol-based resin. The polyvinyl alcohol-based resin can be saponified using a polyvinyl acetate-based resin. As the polyvinyl acetate-based resin, in addition to the polyvinyl acetate which is a homopolymer of vinyl acetate, a copolymer of vinyl acetate and another monomer copolymerizable with the vinyl acetate can be exemplified. Examples of the other monomer copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and (meth) acrylamides having an ammonium group. Further, "(meth)acrylic acid" means at least one selected from the group consisting of acrylic acid and methacrylic acid. Other terms with "(methyl)" are also the same.

The degree of saponification of the polyvinyl alcohol-based resin may 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%, still more preferably from 98.0 °. 100.0% of the range of moles. When the degree of saponification is less than 80.0 mol%, the water resistance and the moist heat resistance of the polarizing plate containing the obtained polarizing film 25 are lowered.

The degree of saponification refers to the ratio of the acetoxy group (acetoxy group: -OCOCH ₃ ) contained in the polyvinyl acetate-based resin which is a raw material of the polyvinyl alcohol-based resin to a hydroxyl group by a saponification step, and is expressed in units. The ratio (% by mole) is defined by the following formula: degree of saponification (% by mole) = 100 × (hydroxyl number) / (hydroxyl number + number of acetate groups)

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

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

One example of the PVA-based resin film 10 is not stretched and thinned by a film made of the above polyvinyl alcohol-based resin. The film forming method is not particularly limited, and a known method such as a melt extrusion method or a solvent casting method can be employed. Another example of the PVA-based resin film 10 is such that the extension is thin and the extension is thin. The extension is typically a uniaxial extension, preferably a longitudinal uniaxial extension. Longitudinal extension refers to the mechanical flow direction (MD) of the film, that is, the extension to the length of the film. The extension is preferably a dry extension. Dry extension refers to an extension in air, usually a longitudinal uniaxial extension. In the case of dry stretching, there may be mentioned a heat roller extension which is obtained by passing a film through a surface heated heated roller and a guide roller having a circumferential rotation speed different from that of the heat roller (or may be a heat roller), using a heat roller Longitudinal extension under heating; extending between rolls, the film is passed through a heating means (oven, etc.) between two sets of rolls disposed at a holding distance, and longitudinally extended by the circumferential rotation speed difference between the two sets of rolls; Amplitude extension; compression extension, etc. The stretching temperature (surface temperature of the hot roll, temperature in the oven, etc.) is, for example, 80 to 150 ° C, preferably 100 to 135 ° C.

The extension ratio of the above extension is usually 1.1 to 8 times, preferably 2.5 to 5 times, depending on whether or not the wet stretching step S101 described later is performed, and the stretching ratio at the time of the wet stretching. .

The PVA-based resin film 10 may contain an additive such as a plasticizer. A preferred example of the plasticizer is a polyhydric alcohol, and specific examples thereof include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, triglycerin, tetraethylene glycol, trimethylolpropane, Polyethylene glycol and the like. The PVA-based resin film 10 may contain one type or two or more types of plasticizers. The content of the plasticizer is usually 5 to 20 parts by weight, preferably 7 to 15 parts by weight, per 100 parts by weight of the polyvinyl alcohol-based resin constituting the PVA-based resin film 10.

The thickness of the PVA-based resin film 10 introduced into the wet processing section 20 (supplied to the wet processing step S101) is usually 10 to 150 μm depending on whether or not the PVA-based resin film 10 is subjected to elongation treatment. The thickness of the polarizing film 25 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, or even 20 μm or less). The smaller the thickness of the PVA-based resin film 10, the smaller the thickness of the polarizing film 25, and thus the smaller the thickness of the polarizing film, the less likely the specific unevenness is likely to occur. Therefore, in the present invention, when the PVA-based resin film 10 having a small thickness (for example, a thickness of 65 μm or less, or even 50 μm or less, or more, 35 μm or less) is used, or a polarizing film 25 having a small thickness (for example, a thickness of 20 μm or less, or even 15 μm or less) is used. It is particularly advantageous when it is more than 10 μm.

(2) Wet processing section and wet processing step S101

The wet processing unit 20 is a region disposed on the transport path of the PVA-based resin film 10 and includes one or more processing tanks for accommodating the processing liquid impregnated with the PVA-based resin film 10 . In the wet processing unit 20, it is carried out while conveying The PVA-based resin film 10 is immersed in the wet processing step S101 of the one or more treatment liquids. As described above, the transport path is constructed by a plurality of rollers that support/guide the moving film, and some of the plurality of rollers are usually disposed in the wet processing unit 20.

The wet processing unit 20 generally includes the dyeing treatment tank 15 and the crosslinking treatment tank 17 in the treatment tank, and preferably further includes a swelling treatment tank 13 and a washing treatment tank 19. These treatment tanks are usually arranged in the order of the swelling treatment tank 13, the dyeing treatment tank 15, the crosslinking treatment tank 17, and the washing treatment tank 19 from the upstream side of the transport path (see Fig. 1). In the first embodiment, the swell treatment tank 13, the dyeing treatment tank 15, the crosslinking treatment tank 17, and the washing treatment tank 19 are each provided with one tank. However, it is also possible to provide two or more tanks as needed. The dyeing treatment tank 15 or the cross-linking treatment tank 17 of two or more tanks is provided. The same applies to the swelling treatment tank 13 and the washing treatment tank 19.

The treatment liquid contained in the swelling treatment tank 13 may be, for example, water (pure water or the like) or an aqueous solution to which a water-soluble organic solvent such as an alcohol is added. Further, the treatment liquid (swelling bath) may contain boric acid, chloride, inorganic acid, inorganic salt or the like. The swelling treatment can be carried out by immersing the PVA-based resin film 10 in a swelling bath. The swelling treatment is based on the removal of the foreign matter of the PVA-based resin film 10, the removal of the plasticizer, the imparting of the dyeability, the plasticization of the film, and the like, and the treatment to be carried out as needed. The PVA-based resin film 10 can be subjected to a wet stretching treatment (usually a uniaxial stretching treatment) in the swelling treatment. The stretching ratio at this time is usually 1.2 to 3 times, preferably 1.3 to 2.5 times. The temperature of the swelling bath is usually from 10 to 70 ° C, preferably from 15 to 50 ° C. The immersion time (residence time in the swelling bath) of the PVA-based resin film 10 is usually 10 to 600 seconds, preferably 20 to 300 seconds.

The treatment liquid contained in the dyeing treatment tank 15 is a dyeing treatment liquid containing a dichroic dye. The dyeing treatment can be performed by immersing the PVA-based resin film 10 in the dyeing treatment liquid. Thereby, the PVA-based resin film 10 can adsorb the dichroic dye. The dichroic dye may be iodine or a dichroic organic dye, which is preferably iodine. The dichroic dye may be used alone or in combination of two or more.

When iodine is used as the dichroic dye, an aqueous solution containing iodine and potassium iodide can be used in the dyeing treatment liquid. Other iodides such as zinc iodide may be used instead of potassium iodide, and potassium iodide and other iodides may be used in combination. Further, a compound other than the iodide such as boric acid, zinc chloride, cobalt chloride or the like may be allowed to coexist. When boric acid is added, it differs from the crosslinking treatment liquid mentioned later in the point which contains iodine. 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 the 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 from 10 to 45 ° C, preferably from 10 to 40 ° C, more preferably from 20 to 35 ° C. The immersion 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.

When a dichroic organic dye is used as the dichroic dye, an aqueous solution containing a dichroic organic dye can be used in the dyeing treatment liquid. The content of the dichroic organic dye in the dyeing treatment liquid is usually from 1 × 10 ^-4 to 10 parts by weight, preferably from 1 × 10 ^-3 to 1 part by weight, per 100 parts by weight of water. A dyeing aid or the like may be coexisted in the dyeing treatment liquid, and for example, an inorganic salt such as sodium sulfate or a surfactant may be contained. The dichroic organic dye may be used alone or in combination of two or more. The temperature of the dyeing treatment liquid containing the dichroic organic dye is, for example, 20 to 80 ° C, preferably 30 to 70 ° C. The immersion time of the PVA-based resin film 10 is usually from 30 to 600 seconds, preferably from 60 to 300 seconds.

In order to improve the dyeability of the dichroic dye, the PVA-based resin film 10 supplied to the dyeing treatment is preferably subjected to at least a certain degree of stretching treatment (usually a uniaxial stretching treatment). Instead of the stretching treatment before the dyeing treatment, or in addition to the stretching treatment before the dyeing treatment, the stretching treatment may be performed while performing the dyeing treatment. The cumulative stretching ratio until the dyeing treatment (the stretching ratio in the dyeing treatment until the dyeing treatment has not been performed) is usually 1.6 to 4.5 times, preferably 1.8 to 4 times.

The treatment liquid contained in the crosslinking treatment tank 17 contains a crosslinking treatment liquid of a crosslinking agent. The crosslinking treatment can be carried out by immersing the PVA-based resin film 10 after the dyeing treatment in the crosslinking treatment liquid. Thereby, it is possible to perform water resistance, hue adjustment, and the like of the PVA-based resin film 10 which is crosslinked. The stretching treatment (usually a uniaxial stretching treatment) may be performed while performing the crosslinking treatment.

The crosslinking agent may, for example, be boric acid, glyoxal or glutaraldehyde, and boric acid may preferably be used. Two or more kinds of crosslinking agents may be used in combination. The content of the crosslinking agent in the crosslinking treatment liquid is usually from 0.1 to 15 parts by weight, preferably from 1 to 12 parts by weight, per 100 parts by weight of water. When the dichroic pigment is iodine, The crosslinking treatment liquid preferably contains an iodide in addition to the crosslinking agent. The content of the iodide in the crosslinking treatment liquid is usually from 0.1 to 20 parts by weight, preferably from 5 to 15 parts by weight, per 100 parts by weight of water. Examples of the iodide include potassium iodide, zinc iodide, and the like. Further, the crosslinking treatment liquid may contain a compound other than iodide, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate or the like. The temperature of the crosslinking treatment liquid is usually from 50 to 85 ° C, preferably from 50 to 70 ° C. The PVA-based resin film 10 is preferably immersed for 10 to 600 seconds, preferably 20 to 300 seconds.

The treatment liquid contained in the cleaning treatment tank 19 may be, for example, water (pure water or the like), or an aqueous solution to which a water-soluble organic solvent such as an alcohol is added. The cleaning treatment can be performed by immersing the PVA-based resin film 10 after the crosslinking treatment in the treatment liquid (washing bath). The cleaning treatment is based on the purpose of removing the unnecessary crosslinking agent or the dichroic dye attached to the PVA-based resin film 10, and performing the treatment as needed. The temperature of the washing bath is, for example, 2 to 40 °C. The stretching treatment (usually a uniaxial stretching treatment) may be performed while performing the cleaning treatment.

The washing treatment may be a treatment of spraying the cleaning liquid onto the PVA-based resin film 10 after the crosslinking treatment, or may be combined with the immersion of the cleaning bath and the spraying of the cleaning liquid. In the first embodiment, the PVA-based resin film 10 is immersed in the water in the cleaning treatment tank 19 to perform a washing treatment.

As described above, the PVA-based resin film 10 can be wet-stretched in the wet processing step S101. Wet extension is usually uniaxially extended The stretching treatment is carried out by any one of swelling treatment, dyeing treatment, crosslinking treatment, and washing treatment, or in two or more treatments selected from the above. The wet stretching is preferably carried out in the cross-linking treatment step or at one or more stages before the stretching treatment. As described above, in order to improve the dyeability of the dichroic dye, a polarizing film 25 having excellent polarizing characteristics is obtained and supplied to the PVA-based resin film 10 subjected to the dyeing treatment, and it is more preferable to perform at least a certain degree of elongation treatment. From the viewpoint of the polarization characteristics of the obtained polarizing film 25, the stretching ratio of the wet stretching is preferably such that the final cumulative stretching ratio of the polarizing film 25 is supplied (when the PVA-based resin film 10 supplied to the wet processing is subjected to elongation processing) , which also includes the cumulative stretch ratio of the extension, which is adjusted to be 3 to 8 times.

When the wet stretching treatment step is carried out, the polarizing film production apparatus is a wet stretching means including the PVA-based resin film 10. The wet stretching means is preferably an extending means for extending between rolls. In the case where the stretching between the rolls is carried out in a wet manner in the crosslinking treatment, the stretching means for extending between the rolls is the two rolls 2c and 2d disposed before and after the crosslinking treatment tank 17. Similarly, in the case of stretching in other wet treatments, the two sets of rolls which are disposed separately can be used as a wet stretching means.

(3) Drying processing section and drying processing step S102

The drying processing unit 22 is disposed on the transport path of the PVA-based resin film 10 and disposed on the downstream side of the wet processing unit 20 to dry the PVA-based resin film 10 after the wet processing step S101. By continuing to transport the PVA-based resin film 10 after the wet processing step S101, The film is introduced into the drying treatment unit 22, and a drying treatment can be performed, whereby the polarizing film 25 can be obtained.

The drying treatment unit 22 includes a drying means (heating means) of the film. A suitable example of the drying means is a drying oven. The drying furnace is preferably one that can control the temperature inside the furnace. The drying furnace system can be, for example, a hot air oven which raises the temperature in the furnace by supplying hot air or the like. In addition, the drying treatment by the drying means may be performed by laminating one or two or more heating bodies having a convex curved surface with the PVA-based resin film 10 after the wet processing step S101, or by heating with a heater. The treatment of the film.

The heating body may be a roller having a heat source (for example, a heat medium such as warm water or an infrared heater) and having a surface temperature (for example, a guide roller having a heat roller). Examples of the heater include an infrared heater, a halogen heater, a plate heater, and the like. In the first and second drawings, the PVA-based resin film 10 after the wet processing step S101 is introduced into the drying furnace 21, and the film is conveyed along the guide rolls 1m to 1s in the furnace. An example of drying treatment. In the polarizing film manufacturing apparatus, a part (one or two or more) of a plurality of rolls that are formed in the transport path of the PVA-based resin film 10 can be disposed in the drying processing unit 22 (drying means).

The temperature of the drying treatment (e.g., the temperature in the furnace of the drying furnace 21, the surface temperature of the hot roll, etc.) is usually 30 to 100 ° C, preferably 50 to 90 ° C. The drying time is not particularly limited, but is, for example, 30 to 600 seconds.

The moisture content of the film can be reduced by drying. The moisture content of the polarizing film 25 obtained by the drying treatment is usually 5 to 20 by weight. %, preferably 8 to 15% by weight. When the water content is less than 5% by weight, the flexibility of the polarizing film 25 may be excessively lowered, and the polarizing film 25 may be damaged or broken during subsequent conveyance or handling. On the other hand, when the water content of the polarizing film 25 is more than 20% by weight, the thermal stability of the polarizing film 25 is liable to lower. The water content referred to herein is determined by the dry weight method.

The polarizing film 25 is a method in which a PVA-based resin film which is stretched (usually uniaxially stretched) is adsorbed to a dichroic dye. The thickness of the polarizing film 25 is usually 2 to 40 μm. 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 from the viewpoint of film formation of the polarizing plate including the polarizing film 25. As described above, the present invention is particularly advantageous in producing a polarizing film 25 having a small thickness (for example, a thickness of 20 μm or less, or even 15 μm or less, and more preferably 10 μm or less).

Considering the balance with the luminosity correction polarization Py, the luminescence correction monomer transmittance Ty of the obtained polarizing film 25 is preferably from 40 to 47%, more preferably from 41 to 45%. The luminescence correction corrected polarization Py is preferably 99.9% or more, more preferably 99.95% or more. When the illuminance factor correction unit transmittance Ty of the polarizing film 25 is larger, the above-mentioned bright point (light leakage) is more easily recognized when applied to a liquid crystal display device. Therefore, the present invention is particularly advantageous in the production of the polarizing film 25 having the light-emitting factor correction monomer transmittance Ty of 41% or more, or even 42% or more, and more preferably 43% or more. Ty and Py are measured according to the description of the examples described later.

The obtained polarizing film 25 can be sequentially wound up on the take-up roll 27 to form a roll form, or can be directly supplied to the polarizing plate manufacturing step without being wound up (one-side or double-area protective layer on the polarizing film 25 (protection) Membrane, etc.) step).

(4) Low rotation resistance roller

The plurality of rollers that are disposed to define a transport path of the polarizing film manufacturing apparatus and are disposed to be in contact with the surface of the PVA-based resin film 10 to be transported include at least one low rotational resistance roller having a rotational resistance of 0.025 N or less. Thereby, specific uneven defects generated on the surface of the polarizing film 25 can be suppressed. From the viewpoint of more effectively suppressing specific unevenness defects, the rotational resistance of the low rotational resistance roller is preferably 0.01 N or less. The rotational resistance of the roller is usually 0.001 N or more.

The rotational resistance of the roller referred to herein means the value of the rotational resistance measured in the following manner. That is, after the thin film is wound around the roller, the outer end portion of the wound film is fixed to the spring balance, and the load applied to the spring balance when the spring balance is pulled at a constant speed to make the number of rotations of the roller 100 rpm.

By using a low-rotation resistance roller, it is possible to suppress a specific unevenness defect, and it is presumed that the tension of the PVA-based resin film 10 during transportation is lowered when it comes into contact with the low-rotation resistance roller, so that the low-rotation resistance roller and the PVA-based resin film 10 in contact therewith are obtained. As a result, the adhesion between the PVA-based resin film 10 and the PVA-based resin film 10 from the low rotational resistance roller is continuously adhered to the above-mentioned adhesion force of the low rotational resistance roller, and the resistance is accompanied by the resistance. The deformation of the PVA-based resin film 10 can be suppressed.

The type of the low-rotation resistance roller is not particularly limited, and may be a free roll such as a guide roll, or a drive roll such as a roll or a suction roll. When a low rotational resistance roller is applied to a roll, it constitutes one of the rolls, and Only one of them is a low rotational resistance roller, and both of them are low rotational resistance rollers. When the low rotational resistance roller is a free roller that does not have a driving force for transporting the film, the effect of suppressing the specific unevenness defect can be improved, and therefore, it is preferably a guide roller.

For example, the rotation resistance of the roller can be reduced by reducing the weight per unit volume of the roller or by using a bearing having a small friction torque. Among these, the method of reducing the weight per unit volume of the roll is effective in reducing the rotational resistance of the roll. In order to set the rotational resistance of the roller to the above range, the weight per unit volume of the low rotational resistance roller is preferably 1,500 kg/m ³ or less, more preferably 1,000 kg/m ³ or less, still more preferably 700 kg/m ³ or less. The weight per unit volume of the roll can be reduced by using a lightweight material such as carbon or aluminum in the core material of the roll (or the material of the roll as a whole) or by using a hollow roll. The weight per unit volume of the roll is usually 200 kg/m ³ or more.

As a result of the investigation by the present inventors, it has been understood that the low wettability of the surface of the low rotational resistance roller (the surface in contact with the PVA-based resin film 10 being conveyed) is advantageous in suppressing the specific unevenness. This is presumed to contribute to the reduction of the above-described adhesion between the low rotational resistance roller and the PVA-based resin film 10 that is in contact therewith. Therefore, the low rotational resistance roller is preferably a surface having low wettability (a surface in contact with the PVA-based resin film 10 being conveyed), and specifically, the low rotational resistance roller has a contact angle with respect to water. The (water contact angle) is preferably a surface of 60 degrees or more, more preferably 80 degrees or more, still more preferably 100 degrees or more. The maximum contact angle for water is usually about 120 degrees. The contact angle of the surface of the low rotational resistance roller with respect to water is measured according to the description of the examples described later.

a surface having a large contact angle with water as described above The roller may be a surface layer (coating layer) provided with a material having a large contact angle with water on the surface of the roller. Specific examples of the material having a large contact angle with water include a fluorine-based resin such as polytetrafluoroethylene, a halogen-containing resin such as a siloxane-based resin, and a carbon material such as carbon or diamond-like carbon (DLC).

The number of arrangement of the low rotational resistance rollers is not particularly limited, and the low rotational resistance roller can be disposed at any position of the transport path of the polarizing film manufacturing apparatus. Therefore, two or more low rotational resistance rollers can be disposed in the transport path, and all the rollers that are in contact with the surface of the PVA-based resin film 10 being transported can be low-rotation resistance rollers, but in order to obtain a specific concave-convex defect suppression effect Preferably, the low rotational resistance roller is disposed at least from any of the wet processing unit 20 (wet processing step S101) to the transport path of the drying processing unit 22 (drying step S102). In the wet processing unit 20 (wet processing step S101), for example, when the first wet processing is swelling treatment, the upstream end of the swelling treatment tank 13 is referred to (the PVA resin film 10 is immersed in the swelling bath). Time). The "drying processing unit 22 (drying processing step S102)" refers to the downstream end of the drying processing unit 22 (drying means) (the point at which the drying process ends).

Among them, it is more preferable to select the position of the low rotational resistance roller after considering the following points.

[a] It has been confirmed by the inventors that the PVA-based resin film 10 which has been subjected to the crosslinking treatment tends to be more likely to cause specific unevenness defects when it is in contact with the roll before the crosslinking treatment. Therefore, at least one low path is disposed in the transport path after the cross-linking treatment tank 17 (the cross-linking treatment tank 17 or the downstream side thereof) It is preferable that the rotary resistance roller has a plurality of rolls in the transport path after the cross-linking treatment tank 17, and it is preferable to use all of the rolls as low-rotation resistance rolls.

[b] It has been confirmed by the inventors that the PVA-based resin film 10 after the wet treatment is more likely to cause specific unevenness defects when it is brought into contact with the rolls in the wet treatment. Therefore, it is preferable to arrange at least one low rotational resistance roller on the transport path downstream of the cross-linking treatment tank 17, and to have a plurality of rollers on the downstream side of the cross-linking treatment tank 17 so that a plurality of rollers are present These rolls are all preferably low rotational resistance rolls. When the wet treatment such as the washing treatment is performed after the cross-linking treatment, it is preferable to dispose at least one low-rotation resistance roller on the transport path downstream of the wet processing unit 20, and the wet processing unit 20 is preferable. Further, when a plurality of rolls are present in the conveying path on the downstream side, it is preferable that all of the rolls are low-rotation resistance rolls.

[c] It has been confirmed by the inventors that the PVA-based resin film 10 having a water content lower than that after the wet treatment (just after leaving the last wet treatment tank) is in contact with the roll, It tends to produce a specific uneven defect. Therefore, it is preferable to arrange at least one low rotational resistance roller on the transport path downstream of the wet processing unit 20, and to have a plurality of rollers on the downstream side of the wet processing unit 20 so that a plurality of rollers are present. It is preferred that the rolls are all low rotational resistance rolls. In particular, immediately after the completion of the wet treatment, when the PVA-based resin film 10 before the polarizing film 25 having a desired moisture content is brought into contact with the roll by the completion of the drying treatment, specific unevenness defects are likely to occur. Therefore, the transport path connecting the wet processing unit 20 and the drying processing unit 22, It is preferable that at least one low rotational resistance roller is disposed in the transport path of the first half of the drying processing unit 22, and the transport path connecting the wet processing unit 20 and the drying processing unit 22 and the transport of the first half of the drying processing unit 22 are preferable. When there are a plurality of rolls in the path, it is preferable that all of the rolls are low-rotation resistance rolls. The water content of the PVA-based resin film 10" having a water content lower than that of the moisture treatment after the wet treatment (just after leaving the last wet treatment tank) is, for example, 8 to 30% by weight. Even 10 to 25% by weight. The meaning of the water content (measurement method) is the same as described above.

[d] The smaller the thickness of the PVA-based resin film 10 that is in contact with the roll, the more likely the specific unevenness is likely to occur. Therefore, the PVA-based resin film 10 having a small thickness change due to the wet stretching treatment is made lower than the thickness of the PVA-based resin film 10 supplied to the wet processing step S101. It is preferred to use a rotating resistance roller. When a plurality of the rollers are present, it is preferred that all of the rollers are low rotational resistance rollers. Specifically, after the dyeing treatment tank 15 that is frequently wet-stretched (the dyeing treatment tank 15 or the downstream side thereof) or the crosslinking treatment tank 17 (the crosslinking treatment tank 17 or the downstream side thereof) It is preferable that at least one low rotational resistance roller is disposed in the path, and when there are a plurality of rollers in the transport path, it is preferable that all of the rollers are low rotational resistance rollers. The thickness of the PVA-based resin film 10 which is smaller in thickness due to the wet stretching treatment than the thickness of the PVA-based resin film 10 which is supplied to the wet processing step S101 is, for example, 15 μm or less. It is even 12 μm or less, and more preferably 10 μm or less.

[e] When the direction of transport of the PVA-based resin film 10 is not changed before and after the contact with the roller, there is a tendency that a specific unevenness defect tends to occur when it is changed. Therefore, it is preferable to use a roller having a low rotation resistance roller in which the conveying direction of the PVA-based resin film 10 that is in contact therewith is changed. The transport direction vector of the PVA-based resin film 10 before the contact with the roll is set to A, and the transport direction vector of the PVA-based resin film 10 immediately after the roll is set to B, and the PVA-based resin before the contact with the roll When the conveying direction of the film 10 and the conveying direction of the PVA-based resin film 10 immediately after leaving the roller are in the same direction, the angle formed by the vectors A and B (the conveying direction changing angle) α is regarded as 0°. When the transport direction of the PVA-based resin film 10 before the contact with the roller is reversed from the transport direction of the PVA-based resin film 10 immediately after leaving the roller, the angle α formed by the vectors A and B is regarded as 180°. The present invention is advantageous when the angle α satisfies 30 to 180°, and further satisfies 45 to 180°.

(5) Specific concave and convex defects

The specific unevenness defect referred to in the present specification which is generated on the surface of the polarizing film causes a bright spot (light leakage) when the polarizing film is applied to a liquid crystal display device. This bright spot is a defect that can be recognized when the brightness of the backlight is raised to a certain level or more, which is a new subject first discovered by the inventors. The above-mentioned "when the brightness of the backlight is increased to a certain level or more" means that the brightness of the backlight measured by the luminance meter is about 10,000 cd/m ² or more. The brightness of the backlight is approximately the brightness of the light emitted from the liquid crystal display device including the backlight and the liquid crystal panel disposed on the liquid crystal panel (the liquid crystal cell and the polarizing plate disposed on both sides of the liquid crystal panel). It is equivalent to 500 cd/m ² or more.

The specific unevenness defect is generally composed of a combination of one convex portion that protrudes from the reference and one concave portion that is in the reference and that is adjacent to the convex portion, with reference to the polarizing film surface other than the unevenness defect. Usually, there is a convex portion on the upstream side in the film transport direction and a concave portion on the downstream side. In the conventional polarizing film, a plurality of concavo-convex portions composed of the convex portion and the concave portion are distributed over the entire surface of the polarizing film and randomly formed into dots. When the polarizing film is viewed from above (when viewed from a direction perpendicular to the film surface), the shape of the uneven portion is, for example, a circular shape or an elliptical shape, but may be irregular. When the polarizing film is viewed from above (when viewed from a direction perpendicular to the film surface), the long diameter (maximum diameter) of the specific unevenness defect is about 0.5 to 5 mm (for example, 1 to 3 mm). Regarding the specific unevenness defect, the height of the convex portion and the depth of the concave portion are typically about 0.05 to 0.5 μm with respect to the above reference. The height difference (the distance from the top of the convex portion to the bottom of the concave portion in the film thickness direction) of the specific unevenness is about 0.1 to 1 μm. When the long diameter or the height difference of the specific unevenness defect is out of the above range, the unevenness does not cause a bright spot, and there is a tendency that the problem is less likely to occur. The presence of a specific uneven defect can be confirmed, for example, by using a magnifying glass or the like. The long diameter and the height difference of the specific unevenness defects were measured according to the method described in the examples of the examples to be described later.

According to the present invention, it is possible to suppress or prevent the occurrence of specific unevenness defects as described above on the surface of the polarizing film. Thereby, even when the polarizing film is applied to a liquid crystal display device using a backlight having a high luminance, bright spots (light leakage) can be effectively suppressed or prevented.

The polarizing film of the present invention preferably has a density of at least one surface of the specific unevenness defect of 20 pieces/m ² or less, more preferably 15 pieces/m ² or less, still more preferably 10 pieces/m ² or less. The density of the specific unevenness defect on at least one surface of the polarizing film is desirably 0 / m ² , but if it is 20 / m ² or less, the brightness of the screen when viewing the screen of the liquid crystal display device is almost independent of the size of the screen, and hardly Affect the recognition of the picture. On the other hand, when the density of the specific unevenness defect exceeds 20/m ² , the visibility is hindered by the size of the screen. The density of the specific unevenness defects is measured by the method described in the examples of the examples to be described later. Further, when a specific unevenness defect is found on one surface of the polarizing film, a specific unevenness defect in which the convex portion and the concave portion are reversed is usually formed at the same position on the other surface.

<Polarizing plate>

A polarizing plate can be obtained by forming a protective layer on one or both sides of the polarizing film 25. The protective layer may be a cured layer of an active energy ray-curable resin composition in addition to a protective film made of a thermoplastic resin. When a protective film is used, a polarizing plate can be obtained by bonding a protective film to the one surface or both surfaces of the polarizing film 25 via the adhesive layer. When a protective film is bonded to both surfaces of the polarizing film 25, the thermoplastic resin constituting the protective film may be of the same kind or different kind.

The thermoplastic resin constituting the protective film is a translucent thermoplastic resin, preferably an optically transparent thermoplastic resin. The thermoplastic resin may be, for example, a polyolefin resin such as a chain polyolefin resin (such as a polypropylene resin) or a cyclic polyolefin resin (such as a decene-based resin); for example, cellulose triacetate or diacetic acid. Cellulose-like cellulose resin; such as poly pair A polyester resin such as ethylene phthalate or polybutylene terephthalate; a polycarbonate resin; a (meth)acrylic resin such as a methyl methacrylate resin; and a polystyrene resin Resin; polyvinyl chloride resin; acrylonitrile/butadiene/styrene resin; acrylonitrile/styrene resin; polyvinyl acetate resin; polyvinylidene chloride resin; polyamine resin; Acetal-based resin; modified polyphenylene ether resin; polyfluorene-based resin; polyether fluorene-based resin; polyacrylate-based resin; polyamidoximine-based resin; polyimide-based resin.

In addition to a homopolymer of a chain olefin such as a polyethylene resin or a polypropylene resin, a chain polyolefin resin may be a copolymer composed of two or more kinds of chain olefins. More specific examples include a polypropylene resin (a polypropylene resin belonging to a homopolymer of propylene or a copolymer mainly composed of propylene), a polyethylene resin (a polyethylene resin belonging to a homopolymer of ethylene, Or a copolymer based on ethylene).

The cyclic polyolefin resin is a general term for a resin obtained by polymerizing a cyclic olefin as a polymerization unit. Specific examples of the cyclic polyolefin-based resin include a ring-opening (co)polymer of a cyclic olefin, an addition polymer of a cyclic olefin, and a copolymerization of a cyclic olefin with a chain olefin such as ethylene or propylene. The material (representative is a random copolymer), and the graft polymer modified by the unsaturated carboxylic acid or its derivative, and the like, and the like. Among them, a norbornene-based resin having a norbornene-based monomer such as a norbornene or a polycyclic norbornene-based monomer as a cyclic olefin can be preferably used.

The term "cellulosic resin" refers to the hydroxyl group of cellulose obtained from the raw material cellulose such as cotton linters or wood pulp (broadwood pulp, conifer pulp). A cellulose organic acid ester or a cellulose organic acid mixed ester in which a part or all of a hydrogen atom is substituted with an ethyl fluorenyl group, a propyl fluorenyl group, and/or a butyl group. For example, it is composed of cellulose acetate, propionate, butyrate, and a mixed ester of these. Among them, cellulose triacetate, cellulose diacetate, cellulose acetate propionate, and cellulose acetate butyrate are preferred.

The polyester resin has an ester bond and is a resin other than the above cellulose resin, and is generally composed of a polycondensate of a polyvalent carboxylic acid or a derivative thereof and a polyhydric alcohol. As the polyvalent carboxylic acid or a derivative thereof, a divalent dicarboxylic acid or a derivative thereof can be used, and examples thereof include terephthalic acid, isophthalic acid, dimethyl terephthalate, and dimethyl naphthalene dicarboxylate. As the polyol, a divalent diol can be used, and examples thereof include ethylene glycol, propylene glycol, butanediol, neopentyl glycol, and cyclohexane dimethanol. Examples of suitable polyester resins include polyethylene terephthalate.

The polycarbonate resin is an engineering plastic composed of a polymer that bonds a monomer unit through a carbonate group, and has a resin having high impact resistance, heat resistance, flame retardancy, and transparency. The polycarbonate resin may be a resin called a modified polycarbonate or a copolymerized polycarbonate having improved wavelength dependence, in which a polymer skeleton is modified to lower the photoelastic coefficient.

The (meth)acrylic resin is a polymer containing a constituent unit derived from a (meth)acrylic monomer. The polymer is typically a polymer containing methacrylate. It is preferred to contain a polymer having a ratio of structural units derived from methacrylate of 50% by weight or more based on the total structural unit. The (meth)acrylic resin may be a homopolymer of methacrylate, It may be a copolymer containing a constituent unit derived from another polymerizable monomer. In this case, the ratio of the constituent units derived from the other polymerizable monomer is preferably 50% by weight or less based on the total structural unit.

A methacrylate of a (meth)acrylic resin may be formed, and an alkyl methacrylate is preferable. The alkyl methacrylate may, for example, be methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, or A methacrylic acid alkyl ester having a carbon number of 1 to 8 such as a third butyl acrylate, a 2-ethylhexyl methacrylate, a cyclohexyl methacrylate or a 2-hydroxyethyl methacrylate-based alkyl group. The alkyl group contained in the alkyl methacrylate preferably has 1 to 4 carbon atoms. In the (meth)acrylic resin, the methacrylate may be used alone or in combination of two or more.

Examples of the other polymerizable monomer which can constitute the (meth)acrylic resin include acrylates and other compounds having a polymerizable carbon-carbon double bond in the molecule. The other polymerizable monomers may be used alone or in combination of two or more. The acrylate is preferably an alkyl acrylate. The alkyl acrylate may, for example, be methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate, acrylic acid. An alkyl acrylate having a carbon number of 1 to 8 such as an alkyl group of cyclohexyl ester or 2-hydroxyethyl acrylate. The alkyl group contained in the alkyl acrylate preferably has 1 to 4 carbon atoms. In the (meth)acrylic resin, the acrylate may be used alone or in combination of two or more.

Other compounds having a polymerizable carbon-carbon double bond in the molecule include vinyl compounds such as ethylene, propylene, and styrene or such as C. A vinyl cyanide compound of a nitrile. Other compounds having a polymerizable polymerizable carbon-carbon double bond in the molecule may be used alone or in combination of two or more.

The protective film may also be a film having an optical function such as a retardation film or a brightness enhancement film. For example, a retardation film which has been given an arbitrary retardation value can be formed by stretching a film made of the above thermoplastic resin (uniaxial stretching or biaxial stretching or the like) or forming a liquid crystal layer or the like on the film. The protective film may have a surface treatment layer (coating layer) laminated on the surface thereof such as a hard coat layer, an antiglare layer, an antireflection layer, an antistatic layer, and an antifouling layer.

The thickness of the protective film is usually from 1 to 100 μm, and is preferably from 5 to 60 μm, more preferably from 5 to 50 μm, from the viewpoints of strength, handleability, film formation of a polarizing plate and the like.

An adhesive used for bonding the polarizing film 25 and the protective film may be an aqueous adhesive, an active energy ray-curable adhesive or a thermosetting adhesive, which is preferably an aqueous adhesive or active energy ray curability. Follow-up agent. When the protective film is bonded to both surfaces of the polarizing film 25, the adhesive for bonding the protective films may be the same type of adhesive, or may be a different type of adhesive.

The aqueous adhesive is one in which the adhesive component is dissolved in water or dispersed in water. An aqueous adhesive which can be preferably used is, for example, an adhesive composition using a polyvinyl alcohol-based resin or a urethane resin as a main component.

When a polyvinyl alcohol-based resin is used as a main component of the adhesive, the polyvinyl alcohol-based resin may be a polyvinyl alcohol resin such as partially saponified polyvinyl alcohol or fully saponified polyvinyl alcohol, or may be, for example, a carboxyl group. change A modified polyvinyl alcohol-based resin of a polyvinyl alcohol, an ethylene glycol-modified polyvinyl alcohol, a methylol-modified polyvinyl alcohol, or an amine-modified polyvinyl alcohol. Polyvinyl alcohol-based resin In addition to the vinyl alcohol homopolymer obtained by saponification of polyvinyl acetate which is a homopolymer of vinyl acetate, there are copolymers of vinyl acetate and other monomers copolymerizable therewith. The polyvinyl alcohol-based copolymer obtained by saponification treatment.

An aqueous binder containing a polyvinyl alcohol-based resin as an adhesive component is usually an aqueous solution of a polyvinyl alcohol-based resin. The concentration of the polyvinyl alcohol-based resin in the subsequent agent is usually 1 to 10 parts by weight, preferably 1 to 5 parts by weight, per 100 parts by weight of water.

In order to improve adhesion, an adhesive composed of an aqueous solution of a polyvinyl alcohol-based resin preferably contains, for example, a polyvalent aldehyde, a melamine-based compound, a zirconia compound, a zinc compound, a glyoxal, a glyoxal derivative, and a water-soluble ring. A hardening component or a crosslinking agent of an oxygen resin. As the water-soluble epoxy resin, for example, a polyamidamine obtained by reacting a polyalkyleneamine such as diethylenetriamine or triethylenetetramine with a dicarboxylic acid such as adipic acid can be suitably used. Polyamine polyamine epoxy resin obtained by reacting with epichlorohydrin. Commercial products of the polyamine polyamine epoxy resin include "Sumirez Resin 650" (manufactured by Tajika Chemical Industry Co., Ltd.), "Sumirez Resin 675" (made by Tiangang Chemical Industry Co., Ltd.), and "WS-525". (Japan PMC (share) system) and so on. The amount of the curable component or the crosslinking agent to be added (total amount when the curable component and the crosslinking agent are simultaneously added) is usually 1 to 100 parts by weight based on 100 parts by weight of the polyvinyl alcohol resin. It is 1 to 50 parts by weight. The amount of the curable component or the crosslinking agent added is less than 1 weight based on 100 parts by weight of the polyvinyl alcohol resin. In the case of a part, the effect of the adhesion improvement tends to be small, and when the amount added exceeds 100 parts by weight based on 100 parts by weight of the polyvinyl alcohol-based resin, the adhesive layer tends to be brittle.

Moreover, a suitable example of the case where a urethane resin is used as a main component of the adhesive agent is a mixture of a polyester-based ionic polymer-type urethane resin and a compound having a glycidoxy group. The polyester-based ionic polymer type urethane resin refers to a urethane resin having a polyester skeleton, and a small amount of an ionic component (hydrophilic component) is introduced therein. Since the ionic polymer type urethane resin is directly emulsified in water to form an emulsion without using an emulsifier, it is suitable as an aqueous adhesive.

The active energy ray-curable adhesive is an adhesive which is hardened by irradiation of active energy rays such as ultraviolet rays, visible rays, electron beams, and X-rays. When an active energy ray-curable adhesive is used, the adhesive layer of the polarizing plate is a cured layer of the adhesive.

The active energy ray-curable adhesive may be an adhesive containing an epoxy compound which is cured by cationic polymerization as a curable component, and is preferably an ultraviolet curable adhesive containing the epoxy compound as a curable component. The epoxy compound referred to herein means a compound having an average of one or more, preferably two or more epoxy groups in the molecule. The epoxy compound may be used alone or in combination of two or more.

Specific examples of the epoxy-based compound which can be suitably used include a hydrogenated epoxy compound obtained by reacting an alicyclic polyol obtained by hydrogenating an aromatic ring of an aromatic polyol with epichlorohydrin ( a glycidyl ether of a polyol having an alicyclic ring; such as an aliphatic polyol or An aliphatic epoxy compound of a polyglycidyl ether of an alkylene oxide adduct; an alicyclic epoxy having one or more epoxy compounds bonded to an epoxy group of an alicyclic ring in a molecule a compound.

The active energy ray-curable adhesive may contain a radically polymerizable (meth)acrylic compound as a curable component instead of the epoxy compound or both an epoxy compound and a (meth)acrylic compound. . Examples of the (meth)acrylic compound include a (meth) acrylate monomer having at least one (meth) acryloxy group in the molecule; and reacting two or more compounds containing a functional group. Further, a compound containing a (meth)acryloxy group such as a (meth) acrylate oligomer having at least two (meth) acryloxy groups in the molecule.

When the active energy ray-curable adhesive contains an epoxy compound which is cured by cationic polymerization as a curable component, it is preferred to contain a photocationic polymerization initiator. The photocationic polymerization initiator may, for example, be an aromatic diazonium salt; an onium salt such as an aromatic onium salt or an aromatic onium salt; an iron-aromatic hydrocarbon complex or the like. Further, when the active energy ray-curable adhesive contains a radically polymerizable curable component such as a (meth)acrylic compound, it is preferred to contain a photoradical polymerization initiator. The photoradical polymerization initiator may, for example, be an acetophenone-based initiator, a diphenylketone-based initiator, a benzoin ether-based initiator, a thioxanthone-based initiator, xanthone or an anthrone. , camphor, benzaldehyde, hydrazine and so on.

Before the protective film is bonded to the polarizing film, the bonding surface of the polarizing film and/or the protective film may be subjected to surface activation treatment such as plasma treatment, corona treatment, ultraviolet irradiation treatment, flame treatment, or saponification treatment. By the surface activation treatment, the adhesion between the polarizing film and the protective film can be improved.

(Example)

Hereinafter, the present invention will be more specifically described by showing examples and comparative examples, but the present invention is not limited to the examples. The measurement or evaluation is based on the following method.

(1) Determination of film thickness

The measurement was performed using a digital micrometer "MH-15M" manufactured by Nikon Co., Ltd.

(2) Determination of moisture content of film

Using a plurality of polyvinyl alcohol film samples having different water contents, the correlation between the water content obtained by the dry weight method and the measured value of the infrared absorption type moisture meter ("IRMA1100" manufactured by CHINO) was used. Checking line (converted). The measured value is obtained by using the above-described water content meter, and the measured value is substituted into the above-mentioned calibration curve (converted formula), and converted into a water content (% by weight) obtained by a dry weight method to obtain the water content of the film. The water content obtained by the dry weight method is W1 when the weight of the polyvinyl alcohol film sample heat-treated at 105 ° C for 120 minutes is W1, and when the weight of the polyvinyl alcohol film sample before heat treatment is W0, according to the following formula Determining: moisture content obtained by dry weight method [% by weight] = {(W0-W1) ÷ W0} × 100

The above-mentioned calibration curve is formed depending on the thickness of the film to be measured.

(3) Confirmation and evaluation of specific concave and convex defects

When one surface of the polarizing film obtained by the magnifying glass is observed (when a specific uneven defect is found on one surface, a specific uneven defect is usually formed at the same position on the other surface), and the presence or absence of a specific uneven defect is confirmed. As described above, the convex film surface other than the unevenness defect is composed of a combination of one convex portion that protrudes from the reference and one concave portion that is recessed from the reference and that is adjacent to the convex portion. When a specific unevenness defect is present, the long diameter (average long diameter) of the average specific unevenness defect and the average height difference of the specific unevenness defect (average height difference) are measured using a white light dry meter "VertScan" manufactured by Ryoka Systems Co., Ltd. The average distance from the top of the convex portion to the bottom of the concave portion in the film thickness direction (see (4) below). Further, in the obtained polarizing film, three samples having a penetration axis direction of 200 mm × an absorption axis direction of 300 mm were cut out from random regions, and each of them was observed with a magnifying glass, and the number of specific uneven defects was measured. The density of the specific unevenness defect (the number of specific uneven defects per unit area of the polarizing film, unit: m/m ² ) was determined. Specifically, the density of the specific unevenness defect is calculated according to the following formula: Density of specific concave-convex defects (number/m ² ) = (total number of specific uneven defects in three-piece samples) / (3 pieces of sample Total area)

The results are shown in Table 1. In addition, the above-mentioned specific unevenness defects were confirmed only on one surface of the obtained polarizing film. However, in the following examples and comparative examples, the specific unevenness defects were confirmed on the same surface of the polarizing film.

(4) Determination of the average long diameter and the average height difference of specific concave and convex defects

A white light dry meter "VertScan" manufactured by Ryoka Systems Co., Ltd. was used for the measurement. The long diameter (maximum diameter) refers to a specific bump viewed from above. The longest distance from the outer end of the convex portion to the outer end of the concave portion at the time of the defect (when viewed from the direction perpendicular to the film surface). Ten specific concave and convex defects are arbitrarily selected, and the average value of the long diameters is set to "average long diameter". Further, the height difference is measured for the ten specific uneven defects, and the average value is set to "average height difference". The results are shown in Table 1. Further, in the examples and the comparative examples, the long diameter of each of the specific uneven defects measured was in the range of 0.5 to 5 mm, and the height difference was in the range of 0.1 to 1 μm.

(5) Confirmation and evaluation of highlights (light leakage)

Three samples having a penetration axis direction of 200 mm × an absorption axis direction of 300 mm were cut out from the random region of the obtained polarizing film, and the evaluation of the bright spots (light leakage) was performed separately. Specifically, in the dark room, a polarizing plate for inspection is placed on a backlight having a luminance of 20,000 cd/m ² (measured by a brightness meter "BM-5A" manufactured by Topcon Technohouse Co., Ltd.), and is disposed above the polarizing plate. The above polarizing film sample. In this case, the polarizing plate for inspection and the polarizing film sample are placed such that the transmission axis of the polarizing film contained in the polarizing plate for inspection is perpendicular to the transmission axis of the polarizing film sample. Next, the backlight was turned on, and it was visually confirmed from the side of the polarizing film sample whether or not there was a dot-like bright spot (light leakage) on the surface of the sample. When a bright spot is found, the number thereof is measured, and the density (the number of bright spots per unit area, unit: m/m ² ) is obtained. Specifically, the density of the bright spots is calculated according to the following formula: density of bright spots (number / m ² ) = (total number of bright spots in three samples) / (total area of three samples)

The results are shown in Table 1.

In addition, the density of the bright spots was obtained in the same manner as described above except that any of the following conditions (A) or (B) was applied when the brightness was confirmed under the above conditions. The results are shown in Table 1.

(A) A neutral density filter having an average transmittance of 50% was further disposed between the backlight and the polarizing plate for inspection (in this case, the substantial luminance of the backlight was 10,000 cd/m ² ).

(B) A full-wavelength dimming mirror having an average transmittance of 3% was further disposed between the backlight and the polarizing plate for inspection (in this case, the substantial luminance of the backlight was 600 cd/m ² ).

(6) Determination of luminescence factor correction monomer transmittance Ty and luminescence factor correction polarization Py

Using a spectrophotometer ("V7100" manufactured by JASCO Corporation) equipped with an integrating sphere, the obtained transmittance and polarization degree were corrected by luminescence factor using a 2 degree angle of view (C light source) of JIS Z 8701, and the luminescence was measured. The factor correction monomer transmittance Ty and the luminescence factor correction polarization degree Py.

(7) Determination of the rotational resistance of the guide roller

After winding a thin film (polyethylene terephthalate film having a thickness of 25 μm) on the roller, the outer end portion of the wound film is fixed to the spring balance, and the spring balance is pulled at a certain speed to rotate the roller. When the pressure reached 100 rpm, the load applied to the spring balance was measured and used as the rotational resistance of the guide roller.

(8) Determination of the contact angle of water on the surface of the guide roller (water contact angle)

Using a contact angle meter (automatic contact angle meter "DM-701" manufactured by Kyowa Interface Science Co., Ltd.), the measurement was carried out under the conditions of a temperature of 23 ° C and a relative humidity of 50% by a droplet method.

<Example 1>

The drying treatment unit includes a total of 15 guide rolls (free rolls) (all connected to the surface of the film), and is continuous from the long PVA-based resin film 10 by using a polarizing film manufacturing apparatus similar to that of Figs. 1 and 2 . A long polarizing film 25 is produced. Next, a polarizing plate was produced using the obtained polarizing film 25. The details are as follows.

(1) Preparation of PVA-based Resin Film 10

The PVA-based resin film a as follows was prepared as the PVA-based resin film 10. In the PVA-based resin film a, the polyvinyl alcohol film having a thickness of 30 μm was uniaxially stretched to 4.1 times in a dry manner, and the degree of saponification of the polyvinyl alcohol constituting the film was 99.9 mol% or more, and the average degree of polymerization was 2,400. The plasticizer was used in an amount of 10 parts by weight based on 100 parts by weight of the polyvinyl alcohol constituting the film.

(2) Wet processing step S101

The PVA-based resin film a was taken up from the take-up roll 11, while tension was applied to maintain continuous conveyance in a stretched state, and immersed in a swelling treatment tank 13 containing pure water at 40 ° C for a residence time of 60 seconds. On the other hand, the PVA-based resin film a is sufficiently swollen (swelling treatment step). The film which is pulled out from the swelling treatment tank 13 is immersed in the iodine/potassium iodide/water for a residence time of 60 seconds. The dyeing treatment tank 15 of the dyeing treatment liquid having a ratio of 0.1/6/100 of 30 ° C was simultaneously subjected to uniaxial stretching (stretching between rolls in the bath) during this period (dyeing treatment step). The film which was taken out from the dyeing treatment tank 15 was immersed in the crosslinking treatment tank 17 of the crosslinking treatment liquid containing potassium iodide/boric acid/water at a weight ratio of 15/5.5/100 at 68 ° C for a residence time of 130 seconds. Uniaxial stretching (stretching between rolls in the bath) was performed during this period (crosslinking treatment step). The film pulled out from the crosslinking treatment tank 17 was immersed in a washing treatment tank 19 containing pure water at 20 ° C for 3 seconds, and washed (washing treatment step). The cumulative stretching ratio based on the PVA-based resin film a was 4.5 times.

(3) Drying process step S102

Then, the film which was taken out from the cleaning treatment tank 19 was continuously conveyed and introduced into a drying oven 21 as a hot air oven, and dried for a residence time of 90 seconds and a temperature of 60 ° C to obtain a polarizing film 25. The obtained polarizing film 25 had a thickness of 12 μm, a luminous factor correction monomer transmittance Ty of 42.5%, a luminous factor correction polarization degree Py of 99.993%, and a water content of 10% by weight. The obtained polarizing film 25 was confirmed for specific unevenness defects. The results are shown in Table 1. Further, the thickness of the film when it is connected to the first low rotational resistance roller is substantially the same as the thickness of the polarizing film 25.

In the first embodiment, the guide roller that constructs the transport path of the first half of the drying furnace 21 (the upstream of the 15 guide rollers) is formed in the guide roller that constructs the transport path of the film of the polarizing film manufacturing apparatus. All 8) are set to low rotation resistance rollers. These low rotational resistance rollers use the following low rotational resistance roller I. Constructing a guiding path for the front half of the drying oven 21 The guide rolls (the seven on the downstream side) other than the rolls used the following guide rolls II. The guide rolls of the wet processing section also all use the following guide rolls II.

[Low Rotational Resistance Roller I]

‧Composition: a guide roll that uses carbon on the core material and is coated with a fluorine-based resin layer on the surface

‧Rotational resistance: 0.008N

‧ Weight per unit volume: 640kg/m ³

‧ surface water contact angle: 95 degrees

‧ The angle α of the film in each of the low rotational resistance rollers (the angle of change in the conveying direction): 90° or 180° (common to the respective examples and comparative examples).

[Guide Roller II]

‧Composition: Guide rolls with SUS304 on the core and chrome plating on the surface

‧Rotational resistance: 0.03N

‧ Weight per unit volume: 1600kg/m ³

‧ surface contact angle of water: 75 degrees

With respect to the obtained polarizing film 25, evaluation of specific unevenness defects and bright spots (light leakage) was performed by the above-described method. The results are shown in Table 1.

(4) Production of polarizing plate

The obtained polarizing film 25 was continuously conveyed, and the first protective film [Konica Minolta Opto Co., Ltd. TAC film "KC2UAW", thickness: 25 μm] and a second protective film (a cyclic polyolefin resin film made of JSR), which is sold under the trade name "FEKB015D3" and a thickness of 15 μm, continuously between the polarizing film 25 and the first protective film, and An aqueous adhesive is injected between the polarizing film 25 and the second protective film, and passes between the bonding rolls to form a first protective film/aqueous adhesive layer/polarizing film 25/aqueous adhesive layer/second protective film. A laminated film formed.

In the above-mentioned aqueous solution, an aqueous solution obtained by dissolving a polyvinyl alcohol powder (trade name "Gohsefimer" manufactured by Nippon Synthetic Chemical Industry Co., Ltd., average polymerization degree 1100) in hot water at 95 ° C is used. In the aqueous solution of polyvinyl alcohol having a concentration of 3% by weight, a crosslinking agent (sodium glyoxylate manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) was mixed at a ratio of 1 part by weight based on 10 parts by weight of the polyvinyl alcohol powder. Aqueous solution.

Next, the obtained laminated film was conveyed and passed through a hot air dryer to carry out heat treatment at 80 ° C for 300 seconds, whereby the aqueous adhesive layer was dried to obtain a polarizing plate.

<Example 2>

A polarizing film 25 (thickness: 12 μm) was produced in the same manner as in Example 1 except that the following low rotational resistance roller III was used, and then a polarizing plate was produced. The evaluation results of specific uneven defects and bright spots (light leakage) are shown in Table 1.

[Low Rotational Resistance Roller III]

‧Composition: guidance on the use of carbon in the core material and coating the surface with a diamond-like carbon layer Roll

‧Rotational resistance: 0.008N

‧ Weight per unit volume: 640kg/m ³

‧ surface contact angle of water: 105 degrees

<Example 3>

In addition to all the guide rollers that construct the transport path of the first half of the drying furnace 21, and all the guide rollers that are connected to the transport path of the cleaning processing tank 19 and the drying furnace 21, the low-rotation resistance roller I is used. A polarizing film 25 (thickness: 12 μm) was produced in the same manner as in Example 1, and a polarizing plate was produced next. The evaluation results of specific uneven defects and bright spots (light leakage) are shown in Table 1.

<Examples 4 to 6>

A PVA-based resin film b in which a polyvinyl alcohol film having a thickness of 20 μm was uniaxially stretched to 4.1 times in a dry manner was used, and a polarizing film was produced in the same manner as in Examples 1 to 3 except that the PVA-based resin film 10 was used. 25 (thickness: 7 μm), and secondly, a polarizing plate was produced. The evaluation results of specific uneven defects and bright spots (light leakage) are shown in Table 1.

<Comparative Example 1>

The polarizing film 25 was produced in the same manner as in the first embodiment except that the low-rotation resistance roller I was not used as the guide roller II of the transport path of the film having the polarizing film manufacturing apparatus. thickness 12 μm), followed by making a polarizing plate. The evaluation results of specific uneven defects and bright spots (light leakage) are shown in Table 1.

<Comparative Example 2>

A polarizing film 25 was produced in the same manner as in Comparative Example 1 except that the PVA-based resin film b was obtained by uniaxially stretching the polyvinyl alcohol film having a thickness of 20 μm to 4.1 times. The thickness was 7 μm), and a polarizing plate was produced next. The evaluation results of specific uneven defects and bright spots (light leakage) are shown in Table 1.

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

2a, 2b, 2c, 2d, 2e, 2f‧‧‧ rolls

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

11‧‧‧Rolling roll

13‧‧‧Swelling treatment tank

15‧‧‧Dyeing tank

17‧‧‧crosslinking processing tank

19‧‧‧Washing treatment tank

20‧‧‧ Wet treatment department

21‧‧‧ drying oven

22‧‧‧Drying and Processing Department

25‧‧‧ polarizing film

27‧‧‧Winding roller

Claims (17)

A manufacturing apparatus for producing a polarizing film from a polyvinyl alcohol-based resin film, comprising: a plurality of rolls constituting a transport path of the polyvinyl alcohol-based resin film, and being disposed in combination with the polyvinyl alcohol-based resin The surface of the film is in contact with each other; the wet processing unit is disposed on the transport path, and includes one or more treatment tanks for containing the treatment liquid impregnated with the polyvinyl alcohol resin film; and a drying treatment unit disposed on the surface The polyvinyl alcohol-based resin film after the wet treatment is dried on the transport path, and the plurality of rolls include a low rotational resistance roller having a rotational resistance of 0.025 N or less. The manufacturing apparatus according to claim 1, wherein the low rotational resistance roller is disposed at any one of a transport path from the wet processing unit to the drying processing unit. The manufacturing apparatus according to claim 2, wherein the wet processing unit comprises, in order, a dyeing treatment tank containing a dyeing treatment liquid containing a dichroic dye; and a crosslinking treatment containing a crosslinking agent. The cross-linking treatment tank of the liquid; the low-rotation resistance roller is disposed after the cross-linking treatment tank. The manufacturing apparatus according to any one of claims 1 to 3, wherein the low rotational resistance roller has a surface having a contact angle with water of 60 degrees or more. The manufacturing apparatus according to claim 4, wherein the surface is made of a fluorine-based resin, a halogen-containing resin, carbon or diamond-like carbon. The manufacturing apparatus according to any one of claims 1 to 5, wherein the low rotational resistance roller has a weight per unit volume of 1,500 kg/m ³ or less. The manufacturing apparatus according to any one of claims 1 to 6, wherein the low rotational resistance roller is a guide roller. The manufacturing apparatus according to any one of the first to seventh aspects, wherein the polyvinyl alcohol-based resin film that is in contact with the low rotational resistance roller has a thickness of 15 μm or less. A manufacturing method for producing a polarizing film from a polyvinyl alcohol-based resin film, comprising the steps of: a wet processing step along a plurality of portions arranged to be in contact with a surface of the polyvinyl alcohol-based resin film The transport path formed by the roller is immersed in one or more processing liquids while transporting the polyvinyl alcohol-based resin film, and the drying step is performed to transport the polyvinyl alcohol-based resin along the transport path. The film is dried by a wet-processed polyvinyl alcohol-based resin film, wherein the plurality of rolls contain a low rotational resistance roller having a rotational resistance of 0.025 N or less. The manufacturing method according to claim 9, wherein the low rotational resistance roller is disposed at any one of a transport path from the wet processing step to the drying processing step. The manufacturing method according to claim 10, wherein the wet processing step sequentially comprises: a step of immersing in a dyeing treatment liquid containing a dichroic dye; and immersing in a crosslinking treatment containing a crosslinking agent. The step of the liquid; the low-rotation resistance roller is disposed in the transport path after the step of immersing in the cross-linking treatment liquid. The manufacturing method according to any one of claims 9 to 11, wherein the low rotational resistance roller has a surface having a contact angle with water of 60 degrees or more. The production method according to claim 12, wherein the surface is made of a fluorine-based resin, a halogen-containing resin, carbon or diamond-like carbon. The manufacturing method according to any one of claims 9 to 13, wherein the low rotational resistance roller has a weight per unit volume of 1,500 kg/m ³ or less. The manufacturing method according to any one of claims 9 to 14, wherein the low rotational resistance roller is a guide roller. The production method according to any one of the above-mentioned claims, wherein the polyvinyl alcohol-based resin film that is in contact with the low rotational resistance roller has a thickness of 15 μm or less. A polarizing film in which a dichroic dye is adsorbed to a polyvinyl alcohol-based resin film, wherein a density of at least one surface unevenness defect is 20/m ² or less, and the unevenness defect is composed of one convex portion and one The combination of the concave portions and the long diameter of 0.5 to 5 mm, the one convex portion is more prominent than the reference based on the polarizing film surface other than the unevenness defect, and the one concave portion is higher than the reference More trapped and adjacent to the aforementioned convex portion.