CN112505818B

CN112505818B - Polyvinyl alcohol polymer film

Info

Publication number: CN112505818B
Application number: CN202011492727.8A
Authority: CN
Inventors: 笹井弘治; 丰岛悠; 水口广行; 大福幸一; 胜野良治; 风藤修
Original assignee: Kuraray Co Ltd
Current assignee: Kuraray Co Ltd
Priority date: 2012-03-30
Filing date: 2013-03-19
Publication date: 2022-09-16
Anticipated expiration: 2033-03-19
Also published as: WO2013146459A1; CN104204045B; KR20140143206A; KR102392226B1; KR20200023490A; CN107656334B; JP6216848B2; TW201404806A; KR20200110456A; JP2016216741A; CN107656334A; JPWO2013146459A1; TWI639636B; KR102346772B1; TWI557164B; KR102260000B1; TW201638169A; TW201638170A; JP6088976B2; CN112505818A

Abstract

The present invention relates to a polyvinyl alcohol polymer film. Provided are a PVA polymer film which can produce a polarizing film and a polarizing plate having few defects with high yield, and a film roll which can produce a polarizing film and a polarizing plate having small differences in surface properties from the winding start portion to the winding end portion of the PVA polymer film and having stable quality. The present invention provides a PVA polymer film having a surface depression of 400 μm in area ² The number of defects having a depth of 0.3 μm or more is 0.25/m ² The following; and a film roll formed by continuously winding a long PVA polymer film, wherein the film roll is recessed from the surface of the film and has an area of 400 [ mu ] m ² The above and depth of 0.3 μm or moreThe number of the defects in the winding completion portion of the PVA-based polymer film is 1.4 times or less of the number of the defects in the winding start portion of the PVA-based polymer film.

Description

Polyvinyl alcohol polymer film

The present application is a divisional application of the application having application number 201710976700.8 (application date 3/19 of 2013) and entitled "polyvinyl alcohol polymer film". The application with the application number of 201710976700.8 is a divisional application of an invention patent application with the name of "polyvinyl alcohol polymer film" invented on 3.19.2013.2013, PCT patent application PCT/JP2013/057792 (application number of 201380018266.2 entering china).

Technical Field

The present invention relates to a polyvinyl alcohol polymer film (hereinafter, referred to as "polyvinyl alcohol" for short as "PVA" in some cases) useful as a starting film for producing a polarizing film, a method for producing a polarizing film using the same, a polarizing film, a film roll formed by continuously winding a PVA polymer film, and a method for producing a PVA polymer film.

Background

PVA polymer films are used in various applications utilizing unique properties related to transparency, seeding optical characteristics, seeding mechanical strength, water solubility and the like, and in particular, recently, the use of the PVA polymer films as a raw material (initial film) for producing a polarizing film as a polarizing plate, which is a basic component constituting a Liquid Crystal Display (LCD), has been expanded by utilizing their excellent optical characteristics. Although the screen size is rapidly increasing in the field of liquid crystal monitors and liquid crystal televisions, if a polarizing plate has a defect, the polarizing plate cannot be mounted on a product, and the yield (product yield) is reduced, so that a polarizing plate and a polarizing film having fewer defects than those of the conventional polarizing plate are required.

However, various techniques have been known for optical films including a polarizing film, a protective film, a retardation film, and the like. For example, in the case of producing a film for optical use or the like by heating a thermoplastic resin such as polyester, polyamide, polyolefin or the like to a melting point or higher to prepare a molten polymer, extruding the molten polymer through a nozzle and cooling the extruded polymer, oligomers (oligomers) present in the polymer precipitate on the surface in the film production and adhere to the surface of a casting drum or a roll, and this is a solution for solving the problem, and there is known a film production apparatus using a drum or a roll for film production having a surface roughness of the outer peripheral surface of 1S or less and a chromium plating film having a carbon atom content (by atomic number) of 0.5 to 5% with respect to a chromium atom on the surface (see patent document 1). Patent document 1 specifically describes: when polyethylene terephthalate is melted at 275 ℃, extruded from a T die, quenched by a casting drum cooled to 25 ℃ to produce an amorphous sheet, and then heated or cooled by a plurality of metal rollers disposed downstream of the casting drum, a roller having a specific chromium plating film is used as a part of the plurality of metal rollers.

In addition, in the case of producing a film by casting a polymer resin solution on a support to form a film from the solution, in order to obtain a polymer resin film which eliminates surface defects (the defect of floating in a projecting manner on the film surface) and is excellent in transparency and surface flatness which are useful for optical applications, the number of defects having a specific size existing on the surface of the support used per unit area is set to a specific numerical value or less (see patent document 2). Patent document 2 specifically describes: an aromatic polycarbonate film was produced by using a solution obtained by dissolving an aromatic polycarbonate resin in a mixed solvent of ethanol and methylene chloride and a support having specific surface characteristics (a mirror-polished plate made of SUS-316), adjusting the temperature of both of them to about 15 ℃, manually applying the solution on the support, and drying the applied solution.

Further, in the case of producing an optical film by a melt-casting film-forming method in which a film-like thermoplastic resin (alicyclic structure-containing polymer, cellulose ester, or the like) melt-extruded from an extruder is cooled by a cooling drum, it is known that as a method for solving the problem of occurrence of a defect in appearance called "pressure damage" caused by adhesion of dirt or foreign matter to the cooling drum, an organic solvent is adhered to the surface of the cooling drum, then the surface of the cooling drum is wiped by a wiping device to remove the dirt on the surface of the cooling drum together with the organic solvent, and then the film-like thermoplastic resin melt-extruded by the extruder is adhered to the wiped surface portion of the cooling drum and cooled to produce an optical film (see patent document 3). Patent document 3 describes that a mixture containing a hydrogenated product of a norbornene ring-opening polymer or cellulose acetate propionate is melt-extruded, and a film-shaped resin melt is adhered to a cooling drum (a surface of a hardened chromium plating film having a vickers hardness of 800 or a surface of an amorphous chromium plating film having a vickers hardness of 1200) provided with a specific cleaning device, and is cooled and solidified while being transported, thereby producing a resin sheet.

Documents of the prior art

Patent document

Patent document 1, Japanese patent laid-open publication No. 9-207210

Patent document 2 Japanese laid-open patent publication No. 2000-84960

Patent document 3 Japanese laid-open patent application No. 2006-82261

Patent document 4 Japanese examined patent publication No. Hei 1-19477

Patent document 5 Japanese laid-open patent publication No. 2005-238833

Patent document 6 Japanese patent application laid-open No. 9-1568

Patent document 7, Japanese patent laid-open No. 2001-315138.

Disclosure of Invention

Technical problem to be solved by the invention

However, simply adopting the above-described conventional techniques makes it difficult to produce a polarizing film or a polarizing plate having few defects at a level required in recent years. That is, in the method of patent document 1, it is necessary to heat a thermoplastic resin to a temperature not lower than its melting point to prepare a molten polymer, but a PVA polymer is not a thermoplastic resin except for a special modified PVA polymer, and it is difficult to apply such a film-forming method to the production of a PVA polymer film, and even if it can be used, a film having excellent surface properties cannot be obtained. Further, as a method for forming a PVA-based polymer film, there is known a method for forming a film by casting and drying a film-forming stock solution in which a PVA-based polymer is dissolved in a liquid medium or a film-forming stock solution in which a PVA-based polymer is melted and contains a PVA-based polymer and a liquid medium on a metal support, but this method is greatly different from a method for forming a film by cooling a molten polymer substantially not containing a liquid medium on a casting drum as described in patent document 1, and therefore, even if the film-forming stock solution is simply used and cast and dried on the film-forming drum as described in patent document 1, fine defects due to fine cracks existing on the surface of a chromium plating film included in the film-forming drum cannot be sufficiently controlled, and a polarizing plate or film manufactured using the obtained PVA-based polymer film cannot sufficiently achieve a quality level required by recent years .

On the other hand, patent document 2 relates to a film forming method in which a solution containing a polymer resin and a solvent as main components is cast on a support and then dried to remove the solvent, but even if the method of patent document 2 is simply adopted to eliminate the disadvantage of floating in a protruding state on the film surface, the disadvantage of dents from the film surface cannot be sufficiently controlled, and a polarizing plate or a polarizing film produced using the obtained PVA-based polymer film cannot achieve the quality level required in recent years.

In addition, the method of patent document 3 is a method of cooling a melt of a thermoplastic resin with a cooling drum, as in the method of patent document 1, and therefore it is difficult to apply the method of patent document 3 to the production of a PVA-based polymer film, and even if it can be used, a film having excellent surface properties cannot be obtained. Further, if the wiping method described in patent document 3 is simply adopted, even if a PVA polymer film is produced by casting and drying on a metal support using a film-forming stock solution in which a PVA polymer is dissolved in a liquid medium or a film-forming stock solution in which a PVA polymer is melted containing a PVA polymer and a liquid medium, there is a disadvantage that the concavity cannot be sufficiently controlled, and instead, a defect such as a scratch is generated on the surface of the metal support due to the contact of the surface of the metal support with a wiping device, and the surface characteristics of the resulting PVA polymer film may be deteriorated.

Under the circumstances described above, an object of the present invention is to provide a PVA-based polymer film capable of efficiently producing a polarizing film and a polarizing plate having few defects. Another object of the present invention is to provide a film roll in which a long PVA polymer film is continuously wound, which can manufacture a polarizing film and a polarizing plate having stable quality with little difference in surface characteristics from a winding start portion to a winding end portion of the PVA polymer film.

In addition, the PVA polymer film is often produced in the form of a film roll in which a long PVA polymer film is continuously wound up due to the ease of storage and transportation, the ability to be continuously used, and the like, and wrinkles are likely to be generated in the film roll due to poor sliding properties between films, and the wrinkles are likely to cause a reduction in the quality of the produced polarizing film. On the other hand, it is sometimes required to reduce uneven dyeing different from the above-described defects in the polarizing film. Accordingly, another object of the present invention is to provide a PVA-based polymer film which is a polarizing film in which wrinkles are not easily generated in a film roll and which has reduced uneven dyeing, and a film roll obtained by continuously winding the PVA-based polymer film.

In addition, in the case of producing a polarizing film using a PVA-based polymer film as an initial film, dyeing, uniaxial stretching, fixing treatment, and the like are generally performed on the PVA-based polymer film, but in the case of uniaxial stretching in a dry manner, in the dyeing step or fixing treatment step, and in the case of uniaxial stretching in a wet manner, in addition to these steps, in the swelling step before the uniaxial stretching or in the uniaxial stretching step, a part of the PVA-based polymer may be eluted in a treatment bath used, and the eluted PVA-based polymer may precipitate in the treatment bath to adhere to the film or precipitate on the film, and remain as foreign matter in the obtained polarizing film, thereby deteriorating the quality and yield thereof. Accordingly, an object of the present invention is to provide a method for producing a polarizing film having a small amount of such foreign matter, and a polarizing film having a small amount of foreign matter produced by the method.

It is another object of the present invention to provide a method for producing a PVA polymer film, which can easily produce the PVA polymer film or the film roll.

Means for solving the technical problem

The present inventors have made intensive studies in order to achieve the above object, and as a result, have found that, when a PVA polymer film is produced by casting and drying a PVA polymer in a solution state or a molten state on the surface of a metal support such as a drum or a belt, foreign matter regarded as resin deposits adheres to a small portion of numerous cracks existing on the surface of the metal support, and a PVA polymer film having a large number of defects recessed from the surface of the film is formed by transferring a convex shape caused by the foreign matter to the film or the like; and such PVA polymer films have problems such as a large number of defects in polarizing films and polarizing plates produced therefrom, failure to sufficiently achieve the quality level required in recent years, and a decrease in yield of polarizing films and polarizing plates.

Further, it has been found that when a metal support having a chromium plating layer on the surface thereof and having a surface hardness within a specific range is used, the number of cracks existing on the surface of the metal support can be easily reduced by a usual treatment such as buffing or grinding applied to the surface of the metal support before starting film production, the number of defects recessed from the film surface of the obtained PVA polymer film can be further reduced than before, and when such a PVA polymer film is used as a starting film for producing a polarizing film, a polarizing film or a polarizing plate having few defects and satisfying the quality level required in recent years can be produced with good yield.

In addition, in addition to the above findings, it was also found that: when a metal support having a chromium plating layer on the surface and having a surface hardness within a specific range is used, even if a PVA polymer film is continuously produced for a long period of time, the variation in the number of defects recessed from the film surface can be kept at a level lower than that in the conventional case.

Further, it has been found that when a metal support having a chromium plating layer on the surface thereof and having a surface hardness in a specific range is used, a PVA polymer film having surface characteristics in specific ranges on both surfaces of the film can be easily obtained, wrinkles are less likely to occur in a film roll formed by continuously winding the PVA polymer film, deterioration in the quality of a polarizing film can be suppressed, and a polarizing film having reduced uneven dyeing can be easily obtained from the PVA polymer film; and a polarizing film with less foreign matter can be easily obtained when the polarizing film is produced by a specific method using the PVA polymer film.

The present inventors have further studied based on the above findings, and have completed the present invention.

Namely, the present invention relates to:

[1] a PVA polymer film (hereinafter, this PVA polymer film may be referred to as "PVA polymer film (1)") having a surface area of 400 μm recessed from the film surface ² The number of defects having a depth of 0.3 μm or more is 0.25/m ² The following;

[2] the PVA based polymer film according to the above [ 1 ], wherein the number of the above-mentioned defects is 0.15/m ² The following;

[3] the PVA based polymer film according to [ 1 ] or [ 2 ], wherein a degree of polymerization of the PVA based polymer contained in the PVA based polymer film is 3000 or more and 10000 or less;

[4] the PVA based polymer film according to any one of the above [ 1 ] to [ 3 ], which is a long PVA based polymer film;

[5] the PVA based polymer film according to the above [ 4 ], which has a length of 6000m or more;

[6] the PVA based polymer film according to the above [ 4 ] or [ 5 ], wherein the above-mentioned disadvantages include the disadvantage that the film is substantially present at substantially the same position in the width direction of the film at substantially constant intervals in the longitudinal direction of the film;

[7] a film roll (hereinafter, this film roll may be referred to as "film roll (1)") in which a long PVA polymer film is continuously wound, wherein the PVA polymer film is recessed from the film surface and has an area of 400 μm ² A defect of 0.3 μm or more in depth, wherein the number of defects at the winding completion portion of the PVA-based polymer film is 1.4 times or less relative to the number of defects at the winding start portion of the PVA-based polymer film;

[8] the roll of film according to the above [ 7 ], wherein the number of the above-mentioned defects is 0.25/m ² The following;

[9] the film roll according to the above [ 7 ], wherein the number of the above-mentioned defects is 0.15/m ² The following;

[10] the film roll according to any one of the above [ 7 ] to [ 9 ], wherein a polymerization degree of the PVA polymer contained in the PVA based polymer film is 3000 or more and 10000 or less;

[11] the film roll according to any one of the above [ 7 ] to [ 10 ], wherein the PVA based polymer film has a length of 6000m or more;

[12] the film roll according to any one of the above [ 7 ] to [ 11 ], wherein the defects include defects that are present at substantially the same position in the film width direction at substantially constant intervals in the film length direction;

[13] a PVA-based polymer film (hereinafter, this PVA-based polymer film may be referred to as "PVA-based polymer film (2)"), wherein, when root mean square roughness is measured on both surfaces of the film, the difference between 2 root mean square roughness values obtained is 0.3nm or more and 10nm or less, and the smaller root mean square roughness value is 10nm or less;

[14] the PVA based polymer film according to [ 13 ], wherein the large root mean square roughness is 1nm or more and 20nm or less;

[15] the PVA based polymer film according to the above [ 13 ] or [ 14 ], which is a long PVA based polymer film;

[16] a roll of the PVA based polymer film according to [ 15 ] (hereinafter, this roll of the PVA based polymer film may be referred to as "roll (2)");

[17] a method for producing a polarizing film using the PVA-based polymer film according to any one of the above [ 13 ] to [ 15 ] as an initial film, the method comprising a dyeing step, a uniaxial stretching step, a fixing treatment step, and a drying step, wherein when leaving a final treatment bath before entering the drying step, an angle formed between a liquid surface of the treatment bath and a film surface is 30 ° or more and 85 ° or less, and a surface on an upper side of the film is a surface having a small root-mean-square roughness in the polyvinyl alcohol-based polymer film;

[18] a polarizing film produced by the production method of [ 17 ];

[19] a method for producing a PVA polymer film, which comprises a step of casting and drying a PVA polymer in a solution state or a molten state on a surface of a metal support having a chromium plating layer on the surface, a Vickers hardness of 550HV or more and less than 900HV, and a surface temperature of 50 ℃ or more and 115 ℃ or less, wherein the Vickers hardness is, to form a film; before casting of the PVA based polymer in a solution state or a molten state, the area of the surface of the metal support (product of the maximum width and the maximum end pitch) was 200 μm ² The number of cracks was 0.7/mm or more ² The following;

[20] the production method of the above [ 19 ], wherein the PVA based polymer in a solution state or a molten state is in a form of a film-forming dope containing the PVA based polymer and water;

[21] the production method of the above [ 19 ] or [ 20 ], wherein the PVA based polymer has a degree of polymerization of 3000 to 10000;

[22] the production method according to any one of the above [ 19 ] to [ 21 ], wherein the surface hardness of the metal support is 600HV or more and less than 800HV in terms of Vickers hardness;

[23] the production method according to any one of the above [ 19 ] to [ 22 ], which comprises a step of providing a metal support having a chromium plating layer on the surface thereof at a temperature change rate of 0.5 ℃/hr or more and having a surface hardness of 550HV or more and less than 900HV in terms of Vickers hardness, wherein the surface temperature of the metal support is 50 ℃ or more and 115 ℃ or less;

[24] [ 19 ] to [ 23 ] which is a method for producing the PVA based polymer film according to any one of [ 1 ] to [ 6 ] and [ 13 ] to [ 15 ].

Effects of the invention

According to the present invention, a PVA-based polymer film capable of producing a polarizing film and a polarizing plate having few defects in high yield can be provided. Further, according to the present invention, it is possible to provide a film roll in which a long PVA polymer film is continuously wound, and which can manufacture a polarizing film and a polarizing plate having a small difference in surface characteristics from a winding start portion to a winding end portion of the PVA polymer film and stable quality.

Further, according to the present invention, it is possible to provide a PVA-based polymer film which is less likely to cause wrinkles in a film roll and which can easily produce a polarizing film having reduced uneven dyeing, a film roll obtained by continuously winding the PVA-based polymer film, a method for producing a polarizing film having less foreign matters, and a polarizing film having less foreign matters produced by the method.

Further, the present invention can provide a method for producing a PVA polymer film, which can easily produce the PVA polymer film and the film roll.

Detailed Description

The present invention will be described in more detail below.

[ PVA-based Polymer film (1) ]

In the PVA-based polymer film of the present invention (PVA-based polymer film (1)), the area of the film surface is 400 μm with a depression formed therein ² The number of defects (hereinafter, this defect may be referred to as "defect A") having a depth of 0.3 μm or more is 0.25/m ² The following. As disadvantages present in plastic films, there may be mentioned: voids (bubbles) in the film; so-called fish eyes resulting from the incorporation of foreign matter and the seeding attachment; scratches (mostly groove-like depressions) generated during handling of the film; the inventors of the present invention have found that the number of the defects A is particularly controlled, thereby obtaining a film having a high degree of uniformity in the thickness directionThe excellent effect of producing a polarizing film, a polarizing plate, or the like with few defects in a high yield can be achieved. In view of the above-described drawback a, the transfer of the convex shape on the film forming apparatus is considered to be caused by 1, and particularly, when a PVA-based polymer film is produced using a metal support such as a drum or a belt as described below, it is considered that one of the causes is that the convex shape due to a foreign substance which is considered to be a resin deposit adhering to the metal support is transferred to the film. For this reason, when the defect a is generated in the long PVA polymer film, at least a part of the defect a tends to be as follows: a plurality of (for example, 3 or more) films are arranged at substantially the same position at substantially constant intervals in the longitudinal direction of the film and in the width direction of the film. Here, the above-mentioned length corresponds to a length of a metal support such as a roller or a belt of 1-cycle size (a total-cycle length) at substantially constant intervals, but may correspond to an integral multiple of the length of the 1-cycle size in some cases. Further, the convex shape due to the foreign matter can be formed in plural on the metal support, and thus the set of the defects a arranged as described above may be present in plural.

As described above, the number of defects A required in the PVA-based polymer film (1) of the present invention is 0.25/m ² The following. If the number of the defects A exceeds 0.25/m ² The polarizing film and the polarizing plate produced therefrom have many defects, and thus the quality level required in recent years cannot be sufficiently achieved, or the yield of these products is lowered by discarding the polarizing film and the polarizing plate having many defects. From this viewpoint, the number of the disadvantages A is preferably 0.20/m ² Less than, more preferably 0.15 pieces/m ² The number of molecules is preferably 0.10/m or less ² The number of them is preferably 0.075/m ² The following.

On the other hand, the lower limit of the number of defects a is not necessarily limited, and when the number of defects a is extremely reduced, there is a possibility that the cost for installing the film deposition equipment becomes extremely high, and the like, and therefore the number of defects a is preferably 0.001 piece/m ² More than or equal to 0.003 pieces/m, and more preferably ² More preferably 0.005 pieces/m or more ² The above.

Disadvantage A is dishing and dishing from the film surfaceProduct of 400 μm ² The above depth is 0.3 μm or more. Here, the defect a may be recessed from either of both surfaces of the film toward the inside of the film, and usually, most of the defect a is recessed from the surface in contact with a metal support described later used in film formation toward the inside of the film. In addition, the area of the defect a means the opening area of the defect a. Further, the depth of the defect a means a depth at the deepest position in the direction perpendicular to the film surface from the opening of the defect a.

Number of disadvantages A (in units of units/m) ² ) The area (m) of the PVA polymer film examined until 10 defects a are found can be determined by searching for the defects a from one end of the PVA polymer film as the target ² ) The number of the particles is 10 (or more), and specifically, the number can be determined by the method described later in examples. Here, the determination as to whether each of the defects is the defect a may be performed using a non-contact surface shape measuring machine.

The shape of the PVA polymer film (1) is not particularly limited, and in the case where the PVA polymer film (1) is used as a starting film for producing a polarizing film, or the like, a long PVA polymer film is preferable because a polarizing film or the like can be continuously produced with good productivity.

The length of the long PVA polymer film is not particularly limited, and may be set as appropriate depending on the use of the PVA polymer film (1), and specifically, the length is preferably 1000m or more, more preferably 4000m or more, further preferably 6000m or more, particularly preferably 7000m or more, and most preferably 8000m or more. In particular, according to the method for producing a PVA polymer film described later, the number of defects a of the PVA polymer film can be reduced, and since the fluctuation in the number of defects a can be kept low even when the PVA polymer film is continuously produced for a long time, the PVA polymer film having a reduced number of defects a can be easily obtained even when the length is long (for example, 6000m or more). Further, when a polarizing film is continuously produced from such a long PVA-based polymer film, a product having few defects and satisfying the quality level required in recent years can be produced stably in a yield over a long period of time, and the trouble and time loss associated with replacement of a film roll can be reduced. The upper limit of the length of the long PVA polymer film is not particularly limited, and if it is too long, the weight and roll diameter become too large when the film is wound up, the handling property is deteriorated, and the storage and transportation become difficult with time, and the like, and therefore the length is preferably 30000m or less, more preferably 25000m or less, and further preferably 20000m or less.

The width of the long PVA polymer film is not particularly limited, and may be, for example, 0.5m or more, and since a wide polarizing film is required in recent years, it is preferably 1m or more, more preferably 2m or more, and still more preferably 4m or more. The upper limit of the width of the long PVA polymer film is not particularly limited, and if the width is too wide, it tends to be difficult to uniformly stretch the PVA polymer film in the case of producing a polarizing film using a practically used apparatus, and therefore the width of the PVA polymer film is preferably 7m or less.

The thickness of the PVA-based polymer film (1) is not particularly limited, and may be set as appropriate depending on the use of the PVA-based polymer film and the like, and specifically, the thickness is preferably 300 μm or less, more preferably 150 μm or less, and further preferably 100 μm or less. In addition, a thinner polarizing film is also required in recent years, and from such a viewpoint and the like, the thickness of the PVA polymer film (1) is preferably 45 μm or less, more preferably 35 μm or less, and still more preferably 25 μm or less. The lower limit of the thickness of the PVA-based polymer film (1) is not particularly limited, and the thickness is preferably 3 μm or more, more preferably 5 μm or more, from the viewpoint of enabling the polarizing film to be produced more smoothly.

As the PVA polymer constituting the PVA polymer film (1), those produced by saponifying a vinyl ester polymer obtained by polymerizing a vinyl ester monomer can be used. Examples of the vinyl ester monomer include: vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, vinyl versatate, and the like, and among them, vinyl acetate is preferable.

The vinyl ester polymer is preferably obtained by using only 1 or 2 or more vinyl ester monomers as monomers, more preferably 1 vinyl ester monomer as monomers, but may be a copolymer of 1 or 2 or more vinyl ester monomers and another monomer copolymerizable therewith.

Examples of such other monomers copolymerizable with the vinyl ester monomer include: ethylene; olefins having 3 to 30 carbon atoms such as propylene, 1-butene, and isobutylene; acrylic acid or a salt thereof; acrylic esters such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, and octadecyl acrylate; methacrylic acid or a salt thereof; methacrylates such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, and octadecyl methacrylate; acrylamide derivatives such as acrylamide, N-methylacrylamide, N-ethylacrylamide, N-dimethylacrylamide, diacetoneacrylamide, acrylamidopropanesulfonic acid or a salt thereof, acrylamidopropyldimethylamine or a salt thereof, and N-methylolacrylamide or a derivative thereof; methacrylamide derivatives such as methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidopropanesulfonic acid or a salt thereof, methacrylamidopropyldimethylamine or a salt thereof, and N-methylolmethacrylamide or a derivative thereof; n-vinylamides such as N-vinylformamide, N-vinylacetamide, and N-vinylpyrrolidone; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tert-butyl vinyl ether, dodecyl vinyl ether and stearyl vinyl ether; vinyl cyanide groups such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid or a salt, ester or anhydride thereof; itaconic acid or a salt, ester or anhydride thereof; vinyl silyl compounds such as vinyltrimethoxysilane; isopropenyl acetate, and the like. The vinyl ester polymer may have 1 or 2 or more kinds of structural units derived from the other monomers.

The proportion of the structural unit derived from the other monomer in the vinyl ester polymer is not particularly limited, but is preferably 15 mol% or less, more preferably 5 mol% or less, based on the number of moles of the entire structural units constituting the vinyl ester polymer.

The polymerization degree of the PVA polymer is not limited, and the film strength tends to decrease with a decrease in the polymerization degree, and therefore, the polymerization degree is preferably 200 or more, more preferably 300 or more, further preferably 400 or more, and particularly preferably 500 or more. Further, if the polymerization degree is too high, the viscosity of the aqueous solution or the molten PVA polymer becomes high, and film formation tends to be difficult, and therefore, 10000 or less, more preferably 9000 or less, still more preferably 8000 or less, and particularly preferably 7000 or less are preferable. The polymerization degree of the PVA based polymer is an average polymerization degree measured according to JIS K6726-1994, and can be determined from the following equation based on the intrinsic viscosity [ eta ] (unit: deciliter/g) measured in water at 30 ℃ after the PVA based polymer is re-saponified and purified.

Degree of polymerization ([. eta. ]. times.10) ³ /8.29） ^（1/0.62）

Further, when a PVA polymer film is produced by a method described later using a PVA polymer having a polymerization degree in the range of 3000 to 10000, a PVA polymer film having an extremely small number of defects a can be obtained, and variation in the number of defects a can be kept at a low level even if the PVA polymer film is continuously produced for a long time, which is preferable. From such a viewpoint, the polymerization degree of the PVA polymer is more preferably 4000 or more, and still more preferably 5000 or more. The reason why the above-described effects are achieved by using a PVA polymer having a polymerization degree in the range of 3000 to 10000 is not necessarily clear, but it is assumed that the more easily the PVA polymer in a solution state or a molten state enters cracks existing on the surface of the metal support, the more the number of defects a in the PVA polymer film increases, and the more the PVA polymer having the polymerization degree is used, the more the above-described entrance is suppressed.

The saponification degree of the PVA-based polymer is not particularly limited, and for example, 60 mol% or more of the PVA-based polymer may be used, but particularly in the case where the PVA-based polymer film is used as a starting film for producing an optical film such as a polarizing film, the saponification degree of the PVA-based polymer is preferably 95 mol% or more, more preferably 98 mol% or more, and still more preferably 99 mol% or more. Here, the saponification degree of the PVA polymer means a proportion (mol%) of the number of moles of the vinyl alcohol unit to the total number of moles of the structural unit (typically, vinyl ester monomer unit) and the vinyl alcohol unit that the PVA polymer has and that can be converted into the vinyl alcohol unit by saponification. The degree of saponification of the PVA based polymer can be measured according to JIS K6726-1994.

In the production of the PVA polymer film (1), 1 type of PVA polymer may be used alone, or 2 or more types of PVA polymers different from each other in 1 or 2 or more of the polymerization degree, saponification degree, modification degree, and the like may be used in combination. The content of the PVA-based polymer in the PVA-based polymer film (1) is preferably 50 mass% or more, more preferably 70 mass% or more, and still more preferably 85 mass% or more.

The PVA polymer film (1) preferably contains a plasticizer. The PVA polymer film (1) contains a plasticizer, and thus can prevent the occurrence of wrinkles when being formed into a film roll or improve the process throughput during secondary processing. As the plasticizer, polyhydric alcohols are preferable, and specific examples thereof include: ethylene glycol, glycerol, diglycerol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, etc. These plasticizers may be used alone in 1 kind or in combination of 2 or more kinds. Among these plasticizers, ethylene glycol and glycerin are preferable from the viewpoint of compatibility with the PVA-based polymer, availability, and the like.

The content of the plasticizer in the PVA polymer film (1) is preferably in the range of 1 to 30 parts by mass, more preferably 3 to 25 parts by mass, and still more preferably 5 to 20 parts by mass, based on 100 parts by mass of the PVA polymer.

The PVA polymer film (1) preferably contains a surfactant from the viewpoints of improving the peeling performance from the metal support used for the production thereof, improving the workability of the PVA polymer film, and the like. The type of the surfactant is not particularly limited, and an anionic surfactant or a nonionic surfactant can be preferably used.

Examples of the anionic surfactant include: carboxylic acid type such as potassium laurate, sulfate type such as octyl sulfate, and sulfonic acid type such as dodecylbenzenesulfonate.

Examples of the nonionic surfactant include: alkyl ether type such as polyoxyethylene oleyl ether, alkylphenyl ether type such as polyoxyethylene octylphenyl ether, alkyl ester type such as polyoxyethylene laurate, alkylamine type such as polyoxyethylene lauryl amino ether, alkylamide type such as polyoxyethylene lauramide, polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether, alkanolamide type such as lauric acid diethanolamide and oleic acid diethanolamide, and allylphenyl ether type such as polyoxyalkylene allylphenyl ether.

These surfactants can be used alone in 1 or more than 2.

The content of the surfactant in the PVA polymer film (1) is preferably in the range of 0.01 to 1 part by mass, more preferably in the range of 0.02 to 0.5 part by mass, and still more preferably in the range of 0.05 to 0.3 part by mass, based on 100 parts by mass of the PVA polymer, from the viewpoints of the peeling performance from the metal support, the handling property of the PVA polymer film, and the like.

The PVA polymer film (1) may further contain other components than the PVA polymer, the plasticizer, and the surfactant, as necessary. Examples of such other components include: water, an antioxidant, an ultraviolet absorber, a lubricant, a colorant, a filler (inorganic particles, starch, etc.), a preservative, a fungicide, and a polymer compound other than the above components.

[ roll of film (1) ]

The film roll (1)) of the present invention is a film roll formed by continuously winding a long PVA-based polymer film, wherein the number of the defects a in a winding start portion (a film portion when the PVA-based polymer film starts to be wound into the film roll) of the PVA-based polymer film is 1.4 times or less the number of the defects a in a winding end portion (a film portion when the PVA-based polymer film is wound into the film roll) of the PVA-based polymer film. In such a film roll, since the difference in surface properties from the winding start portion to the winding end portion of the PVA polymer film is small, a polarizing film and a polarizing plate having stable quality can be manufactured from the film roll. From such a viewpoint, the number of the above-described defects a at the winding end portion of the PVA-based polymer film is preferably 1.3 times or less, more preferably 1.2 times or less, and still more preferably 1.1 times or less, relative to the number of the above-described defects a at the winding start portion of the PVA-based polymer film. In addition, in the film formation of a long PVA polymer film, the number of defects a generally tends to increase with time, and therefore the number of defects a in the winding end portion of the PVA polymer film is usually 0.6 times or more as large as the number of defects a in the winding start portion of the PVA polymer film, and from the viewpoint of manufacturing a polarizing film and a polarizing plate having stable quality, the number of defects a in the winding end portion of the PVA polymer film is preferably 0.7 times or more, more preferably 0.75 times or more, further preferably 0.8 times or more, and particularly preferably 0.9 times or more as large as the number of defects a in the winding start portion of the PVA polymer film.

The number of defects a per unit area in the PVA-based polymer film in the film roll (1) of the present invention is not particularly limited, and as the number of defects a in the PVA-based polymer film (1) of the present invention, if the above number is satisfied, that is, if the number of defects a is 0.25 pieces/m ² The following (preferably 0.20/m in terms of upper limit) ² Less than, more preferably 0.15 pieces/m ² The number of molecules is preferably 0.10/m or less ² The number of them is preferably 0.075/m ² Hereinafter, and the lower limit is preferably 0.001 pieces/m ² More preferably 0.003 pieces/m or more ² More than, preferably 0.005/m ² As above), a polarizing film is continuously producedIn the case of the method, a product having few defects and satisfying the quality level required in recent years can be produced stably with good yield over a long period of time, and therefore, such a method is preferable. The number of the defects a per unit area is considered to be satisfied in the entire PVA-based polymer film as long as the number is satisfied in both the winding start portion and the winding end portion of the PVA-based polymer film.

The length (winding length) of the PVA polymer film used in the film roll (1) of the present invention is not particularly limited, and may be appropriately set according to the use of the PVA polymer film, and the like, and specifically, the length may be set to 1000m or more. However, in recent years, in order to reduce the trouble and time loss associated with the replacement of the film roll, a PVA polymer film having a length longer than about 4000m in the past is sometimes required, and even if a polarizing film is continuously produced for a long time using such a longer PVA polymer film, the quality of the product can be stabilized, and therefore the length of the PVA polymer film is preferably 6000m or more, more preferably 7000m or more, and further preferably 8000m or more. The upper limit of the length of the long PVA polymer film is not particularly limited, and if it is too long, the weight or the roll diameter becomes too large when the film is wound up, the handling property is lowered, the storage and transportation become difficult with time, and the film roll satisfying the requirements of the present invention tends to be difficult to manufacture, and therefore, the length is preferably 30000m or less, more preferably 25000m or less, and still more preferably 20000m or less. If the length is 14000m or less, and further 10000m or less, it is easier to manufacture a film roll satisfying the requirements of the present invention.

The other structure of the PVA polymer film used in the film roll (1) of the present invention may be the same as that described above as the description of the PVA polymer film (1) of the present invention, and therefore, the repeated description thereof is omitted here.

The film roll (1) of the present invention is formed by continuously winding a long PVA polymer film, for example, by continuously winding a long PVA polymer film around a cylindrical core. When a cylindrical core is used, it is preferable that protruding portions protruding from the end faces of the film roll are formed at both end portions of the core.

The type of the cylindrical core is not particularly limited, and examples thereof include a metal core, a plastic core, a paper core, and a wooden core. Furthermore, it is also possible to use: a core in a composite form such as a core using both metal and plastic, a core using both metal and paper, and a core using both plastic and paper. Among them, in view of strength, durability, low dust emission property, and the like, a metal and/or plastic core is preferable, and a metal core is more preferable in view of being less susceptible to abrasion and the like even when used repeatedly. Examples of the metal include iron, stainless steel, and aluminum, and 1 kind of them may be used alone, or 2 or more kinds may be used in combination. Examples of the plastic include polyvinyl chloride, polyvinylidene chloride, polyester, polycarbonate, polyamide, epoxy resin, polyurethane, polyurea, silicone resin, and the like, and 1 kind of these may be used alone or 2 or more kinds may be used in combination. From the viewpoint of strength and the like, the plastic may be a Fiber Reinforced Plastic (FRP) such as a carbon fiber reinforced plastic.

[ PVA-based Polymer film (2) ]

When the root mean square roughness of each of the two surfaces of the PVA polymer film (2)) of the present invention is measured, the difference between the 2 root mean square roughness values obtained is 0.3nm or more and 10nm or less, and the smaller root mean square roughness value is 10nm or less. In a conventional film roll in which a PVA type polymer film is continuously wound, wrinkles are likely to occur in the film due to poor sliding properties between films, and the occurrence of wrinkles can be reduced by the PVA type polymer film (2) of the present invention. The wrinkles of the film roll include: wrinkles generated when the PVA-based polymer film is wound, and wrinkles generated due to poor sliding properties between films when the PVA-based polymer film is stretched by stress remaining in the PVA-based polymer film when it is once wound into a roll and stored in a warehouse or the like; the PVA-based polymer film (2) of the present invention can effectively reduce the occurrence of wrinkles in the former and also reduce the occurrence of wrinkles in the latter. In addition, according to the PVA-based polymer film (2) of the present invention, a polarizing film having reduced uneven dyeing different from the above-described defects can be easily produced.

The root mean square roughness in the present invention means JIS B0601: 2001, the root mean square roughness (Rq) can be obtained by averaging the squares of deviations from the average line to the roughness curve obtained from the surface of the film. The root mean square roughness of each of both surfaces of the PVA polymer film can be measured by the method described later in examples.

In the PVA-based polymer film (2) of the present invention, when the root mean square roughness is measured on both surfaces of the film, the difference between the 2 root mean square roughness values obtained needs to be 0.3nm to 10 nm. The difference between the two is 0.3nm or more, whereby the occurrence of wrinkles in the film roll can be effectively reduced. On the other hand, when the difference between the two is 10nm or less, the uneven dyeing in the polarizing film can be effectively reduced. From such a viewpoint, the difference between the two is preferably 0.5nm or more, more preferably 0.8nm or more, further preferably 1.2nm or more, particularly preferably 1.5nm or more, most preferably 2nm or more, and further preferably 7nm or less, more preferably 5nm or less.

In addition, the PVA based polymer film (2) of the present invention is required to have a small root mean square roughness of 10nm or less. When the root mean square roughness is small and 10nm or less, the uneven dyeing in the polarizing film can be effectively reduced. From such a viewpoint, the small root-mean-square roughness is preferably 8nm or less, more preferably 6nm or less, and further preferably 4nm or less. Since special processing is required to extremely reduce the root mean square roughness and the manufacturing cost of the PVA polymer film is easily increased, the small root mean square roughness is preferably 0.3nm or more, more preferably 0.6nm or more, further preferably 0.9nm or more, and particularly preferably 1.2nm or more.

In the PVA-based polymer film (2), the large root-mean-square roughness is preferably 1nm or more and 20nm or less. The occurrence of wrinkles in the film roll can be more effectively reduced by having a large root mean square roughness of 1nm or more. On the other hand, when the large root mean square roughness is 20nm or less, the uneven dyeing in the polarizing film can be more effectively reduced. From such a viewpoint, the large root mean square roughness is more preferably 2nm or more, further preferably 4nm or more, and further preferably 15nm or less, further preferably 11nm or less, particularly preferably 8nm or less, and most preferably 6nm or less.

The shape of the PVA polymer film (2) is not particularly limited, and in the case where the PVA polymer film (2) is used as a starting film for producing a polarizing film, a long PVA polymer film is preferable because a polarizing film can be continuously produced with good productivity.

The length of the long PVA polymer film is not particularly limited, and may be set as appropriate depending on the use of the PVA polymer film (2), and specifically, the length is preferably 1000m or more, more preferably 4000m or more, further preferably 6000m or more, particularly preferably 7000m or more, and most preferably 8000m or more. Such a longer PVA polymer film can reduce the trouble and time loss associated with the replacement of the roll. The upper limit of the length of the long PVA polymer film is not particularly limited, and if it is too long, the weight and roll diameter become too large when the film is wound up, the handling property is deteriorated, and the storage and transportation become difficult with time, and the like, and therefore the length is preferably 30000m or less, more preferably 25000m or less, and further preferably 20000m or less. One of the causes of the wrinkles occurring when the film roll is stored is tension due to stress remaining in the PVA polymer film, and the tension is easily strongly exhibited by a relatively long and wide PVA polymer film, so that the effects of the present invention are more remarkably exhibited by a relatively long PVA polymer film.

The width of the long PVA polymer film is not particularly limited, and may be, for example, 0.5m or more, and since a wide polarizing film is required in recent years, it is preferably 1m or more, more preferably 2m or more, and still more preferably 4m or more. The upper limit of the width of the long PVA polymer film is not particularly limited, and if the width is too wide, it tends to be difficult to uniformly stretch the PVA polymer film in the case of producing a polarizing film using a practically used apparatus, and therefore the width of the PVA polymer film is preferably 7m or less. Similarly to the description of the length of the PVA polymer film, the effect of the present invention is more remarkably achieved in a PVA polymer film having a wider width because the tension is easily strongly exhibited in a PVA polymer film having a longer length.

The thickness of the PVA-based polymer film (2) is not particularly limited, and may be set as appropriate depending on the use of the PVA-based polymer film and the like, and specifically, the thickness is preferably 300 μm or less, more preferably 150 μm or less, and further preferably 100 μm or less. In addition, a thinner polarizing film is also required in recent years, and from such a viewpoint and the like, the thickness of the PVA polymer film (2) is preferably 45 μm or less, more preferably 35 μm or less, and still more preferably 25 μm or less. The lower limit of the thickness of the PVA-based polymer film (2) is not particularly limited, and the thickness is preferably 3 μm or more, more preferably 5 μm or more, from the viewpoint of enabling the polarizing film to be produced more smoothly. Since wrinkles are more likely to occur in the film roll as the thickness of the PVA-based polymer film is thinner, the effect of the present invention is more remarkably achieved in a thinner PVA-based polymer film.

The other structure of the PVA polymer film (2) of the present invention may be the same as that described above as the description of the PVA polymer film (1) of the present invention, and therefore, the overlapping description thereof will be omitted here.

The method for producing the PVA polymer film (2) is not particularly limited, but the method for producing the PVA polymer film of the present invention to be described later is preferable because the target PVA polymer film (2) can be easily produced. In this case, the surface in contact with the surface of the metal support is likely to have a large root-mean-square roughness. In addition to this manufacturing method, it is also possible to consider: a method of passing a PVA-based polymer film between metal rolls having different surface roughnesses; a method of adjusting the root mean square roughness of both surfaces by adding ultrafine inorganic particles to a film-forming solution while removing foreign matter (deteriorated resin, contamination from the outside, or the like) in the film-forming solution used for producing a PVA-based polymer film with a filter or the like, and forming a film on a smooth surface.

[ roll of film (2) ]

The film roll (2)) of the present invention is formed by continuously winding a long PVA polymer film as the PVA polymer film (2), and is formed by continuously winding a long PVA polymer film as the PVA polymer film (2) around a cylindrical core, for example. When a cylindrical core is used, it is preferable that protruding portions protruding from the end faces of the film roll are formed at both end portions of the core. As the core, those described above as the description of the film roll (1) can be used, and a repetitive description is omitted here.

Other configurations related to the film roll (2) of the present invention may be the same as those described above as the description of the film roll (1) of the present invention, and therefore, a repetitive description thereof will be omitted here.

The film roll (2) of the present invention can reduce the occurrence of wrinkles which are likely to occur when the film roll is stored in the past. The temperature at which the film roll is stored is preferably 40 ℃ or lower, more preferably 35 ℃ or lower, and still more preferably 30 ℃ or lower, because when the temperature is too high, the PVA polymer film is easily deformed and wrinkled. On the other hand, the lower limit of the temperature at the time of storing the film roll is not particularly limited, but the temperature is preferably-10 ℃ or higher, more preferably-5 ℃ or higher, and still more preferably 0 ℃ or higher.

[ method for producing PVA-based Polymer film ]

The production method of the present invention for producing a PVA-based polymer film includes the steps of: a PVA polymer in a solution state or a molten state is cast and dried on the surface of a metal support having a chromium plating layer on the surface, a surface hardness of 550HV or more and less than 900HV in terms of Vickers hardness, and a surface temperature of 50 ℃ or more and 115 ℃ or less to form a film. Then, before casting of the PVA based polymer in a solution state or a molten state, the area of the surface of the metal support (product of the maximum width and the maximum end portion pitch) was 200. mu.m ² The number of cracks was 0.7/mm or more ² The following. According to this production method, the PVA polymer films of the present invention (PVA polymer films (1) and (2)) or a long PVA polymer film continuously wound around the film roll of the present invention (film rolls (1) and (2)) can be easily produced.

Examples of the metal support used in the present invention include a roller, a belt, and the like, and the surface thereof has a chromium plating layer. Here, the surface of the metal support means a surface (film forming surface) on which the PVA-based polymer in a solution state or a molten state is cast, and in the case of a drum, the metal support may have a chromium plating layer on the outer circumferential surface of the drum, and in the case of a belt, the metal support may have a chromium plating layer on the outer side surface of the continuous surface of the belt.

The thickness of the chromium plating layer is not particularly limited, and is preferably in the range of 10 μm or more and 500 μm from the viewpoint of more effectively preventing corrosion of the surface of the metal support and easily reducing the number of cracks described later. For example, when the chromium plating layer is formed in a plurality of times, the irregularities on the surface of the chromium plating layer may be removed by polishing or the like after the chromium plating layer is formed temporarily, and the chromium plating layer may be further formed thereon. By doing so, pinholes in the chromium plating layer can be reduced. Further, as described in patent document 4 and the like, when a nickel plating layer is provided under a chromium plating layer, cracks in the chromium plating layer can be further reduced.

In the above metal support having a chromium plating layer on the surface, the surface hardness thereof needs to be 550HV or more and less than 900HV in terms of vickers hardness. Although the reason is not clear when a metal support having a specific surface hardness such as that of the present invention is used, the number of cracks existing on the surface of the metal support can be easily reduced by a normal treatment performed on the surface of the metal support before film formation such as buffing and polishing, the number of the above-mentioned defects a in the obtained PVA polymer film can be further reduced than before, and the variation in the number of the above-mentioned defects a can be kept at a level lower than before even if the PVA polymer film is continuously produced over a long period of time. Further, the root mean square roughness of both surfaces of the film can be adjusted to a desired range. When the surface hardness is 900HV or more in terms of vickers hardness, it is difficult to reduce the number of cracks existing on the surface of the metal support, and when a PVA polymer film is continuously produced over a long period of time, the fluctuation in the number of the defects a increases. Further, the root mean square roughness of both sides of the film deviates from the desired range. From the above-described viewpoint, the surface hardness is preferably less than 800HV, more preferably less than 780HV on the vickers scale. On the other hand, if the surface hardness is less than 550HV on the vickers scale, problems such as damage tend to occur during continuous film formation or during cleaning of the surface of the metal support, and the number of the defects a fluctuates greatly when the PVA polymer film is continuously produced over a long period of time. Further, the root mean square roughness of both sides of the film deviates from the desired range. From such a viewpoint, the surface hardness is preferably 600HV or more, more preferably 650HV or more, and further preferably 700HV or more in terms of vickers hardness.

The surface hardness of the metal support can be determined by measuring the vickers hardness of the surface of the chromium plating layer at a plurality of places using a hardness meter or the like and averaging the vickers hardness. The measurement of the surface hardness (vickers hardness) can be performed on the surface (film formation surface) on which the PVA polymer in a solution state or a molten state is cast, but the quality of the PVA polymer film obtained may be deteriorated due to damage generated during the measurement, and therefore, even in the vicinity of the surface (film formation surface) on which the PVA polymer in a solution state or a molten state is cast, such as a portion where a chromium plating layer is formed in an end portion of a drum or a belt, or the surface (film formation surface) on which the PVA polymer in a solution state or a molten state is cast, the surface hardness can be measured on the surface corresponding to the film portion removed by ear cutting or the like after film formation, and the value is the surface hardness specified in the present invention. The surface hardness of the metal support can be specifically determined by the method described later in examples.

The adjustment of the surface hardness of the metal support having a chromium plating layer on the surface thereof can be easily performed by a known method per se, and specifically, can be performed by the following method: a method of adjusting the temperature of a chromium plating bath used in chromium plating treatment to a specific range; a method of adjusting the current density at the time of chromium plating treatment to a specific range; a method of adjusting the composition of the chromium plating bath; a method of adjusting the concentration of hydrogen occluded in the chromium plating layer by heat treatment (annealing) or exposure to hydrogen gas or the like after the chromium plating treatment, and the like. Wherein,from the viewpoint of ease of operation, etc., a method of adjusting the temperature of the chromium plating bath to a specific range is preferable; a method of adjusting the current density at the time of chromium plating treatment to a specific range; the method of adjusting the concentration of hydrogen occluded in the chromium plating layer after the chromium plating treatment is more preferably a method of adjusting the temperature of the chromium plating bath to a specific range. The method uses a chromic acid-sulfuric acid aqueous solution as a general chromium plating bath, and has a temperature of 40 ℃ to 70 ℃ inclusive and a current density of 60A/dm ² When the chromium plating treatment is performed in the following range, the surface hardness tends to be generally lower as the temperature of the chromium plating bath is higher and the current density is lower. Further, the hydrogen concentration occluded in the chromium plating layer tends to be lowered as the temperature of the heat treatment is increased or the treatment time is prolonged, and the surface hardness tends to be lowered in general.

The method for forming the chromium plating layer is not particularly limited as long as it is a method capable of forming a metal support having a surface hardness satisfying the above range, and known methods can be used, and typical methods include: a method in which the surface of a metal support is first polished by a method such as buffing or grinding with a grinder to remove surface irregularities as much as possible, then subjected to a base treatment such as immersion degreasing, electrolytic degreasing, or hydrochloric acid aqueous solution immersion, and then subjected to a chromium plating treatment using a chromium plating bath, and further subjected to a heat treatment. Representative of the chromium plating bath is a Sagitter bath (サージエント bath), which can be preferably used. Examples of the composition of the sagitt bath and the conditions of the chromium plating treatment are shown below.

Composition of Sagitter bath

Chromic anhydride: 100 to 300g/L (concentration based on the drug)

Sulfuric acid: 1/50-1/150 mass percent of chromic anhydride is used.

< condition of chromium plating treatment >

The current density is 10 to 60A/dm ²

The temperature of the chromium plating bath greatly affects the surface hardness of the metal support obtained as described above. The specific temperature of the chromium plating bath depends on other conditions used in the chromium plating treatment, heat treatment conditions after the chromium plating treatment, and the like, but is preferably 50 ℃ or higher, more preferably 53 ℃ or higher, and still more preferably 54 ℃ or higher. If the temperature of the chromium plating bath is too low, the surface hardness of the resulting metal support tends to be too high. On the other hand, the temperature of the chromium plating bath is preferably 66 ℃ or lower, more preferably 63 ℃ or lower, still more preferably 61 ℃ or lower, and particularly preferably 58 ℃ or lower. If the temperature of the chromium plating bath is too high, the surface hardness of the resulting metal support tends to be too low.

It is preferable to perform heat treatment (annealing) after the chromium plating treatment. When the heat treatment is performed at a high temperature, the time required for the heat treatment can be shortened, but if the temperature is too high, cracks are likely to be generated in the chromium plating layer, and therefore the temperature of the heat treatment is preferably 130 ℃ or less, more preferably 120 ℃ or less. On the contrary, when the heat treatment is performed at a low temperature, the risk of occurrence of cracks is reduced, but the time required for the heat treatment is increased, and therefore the temperature of the heat treatment is preferably 70 ℃ or more, more preferably 90 ℃ or more. The time of the heat treatment depends on the conditions of the chromium plating treatment, the temperature of the heat treatment, and the like, and can be set within a range of 24 to 120 hours.

Examples of the PVA polymer in a solution state or a molten state include: a film-forming stock solution containing a PVA-based polymer and a liquid medium, such as a film-forming stock solution in which the PVA-based polymer is dissolved in a liquid medium, or a film-forming stock solution in which the PVA-based polymer is melted while containing the PVA-based polymer and a liquid medium. The film-forming stock solution may further contain the above-mentioned plasticizer, surfactant, and other components as necessary.

Examples of the liquid medium in the film-forming stock solution include: water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, diethylenetriamine, etc., and 1 or 2 or more of these can be used. Among them, water is preferable from the viewpoint of a small load on the environment and recyclability. That is, as a preferable example of the PVA polymer in a solution state or a molten state, there can be mentioned a film-forming dope containing the PVA polymer and water.

The volatile component ratio of the film-forming stock solution (the content ratio of volatile components such as a liquid medium removed by volatilization or evaporation in film formation in the film-forming stock solution) varies depending on the film-forming method, the film-forming conditions, and the like, and is preferably within a range of 50 to 90 mass%, and more preferably within a range of 55 to 80 mass%. By setting the volatile component ratio of the film-forming dope to 50 mass% or more, the viscosity of the film-forming dope does not become excessively high, filtration and deaeration at the time of preparation of the film-forming dope are smoothly performed, and production of a PVA polymer film having few foreign matters and defects is facilitated. On the other hand, when the volatile content ratio of the film-forming dope is 90 mass% or less, the concentration of the film-forming dope does not become too low, and the production of an industrial PVA polymer film becomes easy.

The method for producing the film-forming dope is not particularly limited, and examples thereof include: a method in which a PVA-based polymer is dissolved in a liquid medium such as water, and at least 1 of a plasticizer, a surfactant, and other components is added as needed; or a method in which a PVA polymer in a state containing a liquid medium such as water is melt-kneaded by an extruder, and at least 1 of a plasticizer, a surfactant, and other components is melt-kneaded together as necessary.

The production method of the present invention for producing a PVA-based polymer film includes the steps of: the PVA polymer in the solution state or the molten state is cast on the surface of the metal support having a surface temperature of 50 ℃ to 115 ℃ and dried to form a film. When the surface temperature of the metal support exceeds 115 ℃, the number of defects a in the PVA-based polymer film obtained increases. Further, the root mean square roughness of both surfaces of the film easily deviates from a desired range. From this viewpoint, the surface temperature of the metal support is preferably 105 ℃ or lower, more preferably 102 ℃ or lower, still more preferably 99 ℃ or lower, particularly preferably 96 ℃ or lower, and most preferably 95 ℃ or lower. On the other hand, if the surface temperature of the metal support is less than 50 ℃, problems such as difficulty in peeling the film from the metal support, or deterioration in transparency of the film tend to occur. From such a viewpoint, the surface temperature of the metal support is preferably 60 ℃ or more, more preferably 70 ℃ or more, and still more preferably 80 ℃ or more. The surface temperature of the metal support may be an average value (average temperature) of the surface temperatures at any number of locations (for example, 10 or more) on the surface of the metal support.

The method of bringing the surface temperature of the metal support to the above-mentioned range before starting the film formation is not particularly limited, and for example, when a roll is used as the metal support, there can be adopted: a method of introducing a heat medium such as water, oil, or steam into the inside of the drum, heating the inside of the drum by an induction heating heater provided inside the drum, or heating the inside of the drum by an infrared heater or a hot air heating device provided so as to face the surface of the drum.

The temperature swing rate when the surface temperature of the metal support is brought to the above range before the start of film formation can be set to 3 ℃/hr or less, for example, as described in patent document 5, but in the production method of the present invention using a metal support having a chromium plating layer on the surface and having the above surface hardness, although the reason is not clear, it has been found that the increase in the number of cracks existing on the surface of the metal support can be suppressed even if the temperature swing rate is relatively increased, and the number of the above-mentioned defects a of the PVA polymer film obtained can be controlled to a low level even if the temperature adjustment time is reduced to improve the productivity. From such a viewpoint, the temperature change rate when the surface temperature of the metal support is brought within the above range before the film formation is started is preferably 0.5 ℃/hr or more, more preferably 1 ℃/hr or more, and may be 3.5 ℃/hr or more, 4 ℃/hr or more, 4.5 ℃/hr or more, further 5 ℃/hr or more. In addition, the temperature change rate is preferably 10 ℃/hr or less, more preferably 7 ℃/hr or less, from the viewpoint of reducing the number of cracks.

When the surface temperature of the metal support is within the above range before the film formation is started, it is preferable to reduce the temperature difference in the width direction of the metal support, specifically, to continuously measure the surface temperature of the metal support in the width direction, and when the obtained temperature distribution data is plotted with the position in the width direction as the horizontal axis and the temperature as the vertical axis, the maximum value of the absolute value of the slope is preferably 10 ℃/m or less, more preferably 5 ℃/m or less, still more preferably 4 ℃/m or less, and particularly preferably 3 ℃/m or less.

In the production method of the present invention for producing a PVA based polymer film, the area of the surface of the metal support is 200 μm before casting of the PVA based polymer in a solution state or a molten state is started ² The number of cracks was 0.7/mm or more ² The following. Here, the area of the crack means the product of the maximum width of the crack and the maximum tip interval. Generally, cracks such as cracks of the chromium plating layer are present on the surface of the metal support before the start of film formation. Then, it is considered that a foreign substance, which is considered to be a resin deposit during film formation, gradually adheres to such a crack to form a convex shape, and the convex shape is transferred to the film to cause a defect a in the film. In particular, since the PVA polymer has high hydrophilicity and good affinity with a metal as compared with other polymers, it is considered that the PVA polymer easily enters cracks existing on the surface of the metal support and adheres as a resin deposit, and a convex shape is likely to be formed and grown when a dried film is peeled off from the metal support. From such a reason, in order to reduce the number of defects a, it is preferable to reduce the number of cracks existing on the surface of the metal support as much as possible, but as described above, when the metal support having a chromium plated layer on the surface and having the above surface hardness is used, although the reason is not clear, the number of cracks existing on the surface of the metal support can be easily reduced by a usual treatment performed on the surface of the metal support before starting film formation such as buffing, the number of defects a of the obtained PVA-based polymer film can be reduced more than ever, and even if the PVA-based polymer film is continuously produced over a long period of time, the variation in the number of defects a can be kept to a level lower than ever. The number of the cracks on the surface of the metal support is more than 0.7/mm ² The number of defects a in the PVA-based polymer film obtained increases. From the reduction of the PVA-based polymer obtainedFrom the viewpoint of the number of defects A in the polymer film, the number of cracks on the surface of the metal support is preferably 0.3/mm before casting of the PVA-based polymer in a solution state or a molten state ² Less than, more preferably 0.15/mm ² The following. On the other hand, since it is troublesome to extremely reduce the number of the above-mentioned cracks on the surface of the metal support and the effect tends to be limited, the number is preferably 0.005 pieces/mm ² More than, preferably 0.01 pieces/mm ² The above.

The surface of the metal support had an area of 200 μm ² The number of cracks can be determined by the following method: the surface of the metal support was determined to have an arbitrary 25 spots, each of which was specified to be 2 mm. times.2 mm (4 mm) by a microscope ² ) In the range of (1) < area > 200 μm ² The 4mm crack "was determined ² In the range of (2) × 25 "the area is 200 μm ² The number of cracks "was counted, and the number of cracks was calculated from the number of cracks at intervals of 1mm ² The number of (2). Here, the area of the crack means the product of the maximum width of each crack and the maximum end pitch, which means the end pitch (straight line distance) of the cracks when the ends thereof are only 2, and means the maximum distance among the plurality of end pitches when the ends thereof are a plurality of ends. Specifically, the surface of the metal support has an area of 200 μm ² The number of cracks can be determined by the method described later in examples.

The width of the metal support can be appropriately set according to the width of the target PVA-based polymer film. The specific width of the metal support is, for example, 0.5m or more depending on the width of the target PVA-based polymer film, and is preferably 4.5m or more, more preferably 5.0m or more, and further preferably 5.5m or more from the viewpoint of efficiently producing a wide PVA-based polymer film capable of producing a wide polarizing film. In addition, in view of the cost of the metal support, ease of maintenance, and the like, the width of the metal support is preferably 7.5m or less, preferably 7.0m or less, and more preferably 6.5m or less.

The method for casting the PVA polymer in a solution state or a molten state on the surface of the metal support is not particularly limited, and can be carried out by a known method using a T-slot die, a hopper plate, an I-die, a lip coater die, or the like. The temperature of the PVA polymer in a molten state or a solution state is preferably in a range of 50 ℃ to 105 ℃.

The drying after casting may be performed by a known method, and may be performed by heat applied from a metal support or by blowing hot air. Further, the desired PVA polymer film may be produced by drying only on the surface of the metal support, or may be produced by partially drying on the surface of the metal support by a known method or the like, and then further drying by 1 or 2 or more drying rolls or a hot air dryer arranged on the downstream side of the metal support and having the metal support and the rotation axis parallel to each other.

The PVA polymer film thus obtained may be subjected to heat treatment or may be cut at both ends (ear portions) in the width direction as necessary. Further, the roll may be continuously wound as a film roll as described above.

[ use ]

The PVA-based polymer film of the present invention (PVA-based polymer films (1) and (2)) or the PVA-based polymer film wound from the roll of the present invention (rolls (1) and (2)) can exhibit a small number of defects a; the quality is stable; the film is used for various applications because the advantages such as wrinkles are less likely to occur, and is preferably used as a starting film for producing an optical film such as a polarizing film or a retardation film, and more preferably used as a starting film for producing a polarizing film, from the viewpoint of more remarkably achieving the effects of the present invention.

The method for producing a polarizing film using the PVA-based polymer film as a starting film is not particularly limited, and a known method can be used, and for example, dyeing, uniaxial stretching, fixing treatment, drying, and washing and heat treatment as needed can be performed using the PVA-based polymer film. Here, the order of the respective treatments such as dyeing, uniaxial stretching, and fixing treatment is not particularly limited, and 1 or 2 or more treatments may be simultaneously performed. Further, 1 or 2 or more treatments may be performed 2 times or more, and for example, uniaxial stretching may be performed 2 times or more. Before each step such as dyeing, uniaxial stretching, fixing treatment, etc., swelling treatment may be performed as necessary.

The dyeing may be carried out at any stage of before, during, or after the uniaxial stretching. As the dye used for dyeing, 1 or 2 or more of the following may be used: iodine-potassium iodide; direct black 17, 19, 154; direct brown 44, 106, 195, 210, 223; direct red 2, 23, 28, 31, 37, 39, 79, 81, 240, 242, 247; direct blue 1, 15, 22, 78, 90, 98, 151, 168, 202, 236, 249, 270; direct violet 9, 12, 51, 98; direct green 1, 85; direct yellow 8, 12, 44, 86, 87; dichroic dyes such as direct orange 26, 39, 106, 107, and the like. The dyeing can be performed by immersing the PVA-based polymer film in a solution (dyeing bath) containing the above dye. The dye may be contained in advance when the PVA polymer film is produced.

The uniaxial stretching may be performed by either a wet stretching method or a dry heat stretching method, may be performed in warm water (including the above-mentioned dyeing bath or a fixing treatment bath described later), or may be performed in air using a PVA-based polymer film after water absorption.

The temperature at the time of uniaxial stretching is not particularly limited, but when the PVA-based polymer film is uniaxially stretched in warm water (wet stretching), it is preferably in the range of 30 ℃ to 90 ℃, and when the PVA-based polymer film is dry-heat stretched, it is preferably in the range of 50 ℃ to 180 ℃.

The stretching ratio of the uniaxial stretching (total stretching ratio in the case of uniaxial stretching in multiple stages) is preferably 4 times or more, and more preferably 5 times or more, from the viewpoint of polarization performance. The upper limit of the stretching magnification is not particularly limited, but it is preferable that the stretching magnification is 8 times or less because the uniaxial stretching is easily and stably performed. The thickness of the film after uniaxial stretching depends on the thickness of the PVA-based polymer film used, and is preferably in the range of 3 μm to 75 μm, more preferably in the range of 5 μm to 50 μm.

In order to make the adsorption of the dye to the PVA polymer film strong, fixing treatment is often performed. As the fixing treatment bath used for the fixing treatment, an aqueous solution containing 1 or 2 or more kinds of boron compounds such as boric acid and borax may be used. An iodine compound may be added to the fixing treatment bath as required.

After each treatment such as dyeing, uniaxial stretching, fixing treatment, and the like, it is preferable to wash the film before drying to remove treatment baths, foreign matters, and the like adhering to the surface of the film. Pure water may be used as the washing liquid used for washing, and water to which these chemicals are added in a small amount may be used in order to suppress the outflow of the dye or boron compound due to washing. The cleaning solution may be sprayed onto the surface of each treated film by spraying or the like, or the treated film may be immersed in a cleaning bath.

The drying and heat treatment are preferably performed in the range of 30 ℃ to 150 ℃, more preferably 50 ℃ to 150 ℃.

In the case where the PVA polymer film (2) or the PVA polymer film wound from the film roll (2) is used as the starting film for producing the polarizing film and the polarizing film is produced through the respective steps of the dyeing step, the uniaxial stretching step, the fixing step, the drying step, and the like, when the polarizing film is separated from the last treatment bath (for example, the fixing treatment bath, the washing bath, and the like) before entering the drying step, if the angle formed between the liquid surface of the treatment bath and the film surface (the angle on the acute angle side) is 30 ° or more and 85 ° or less and the surface on the upper side of the film is a surface having a small root mean square roughness among the PVA polymer films used as the starting film, the polarizing film having few foreign matters can be easily obtained, which is preferable.

The reason why the above-described effects are achieved is not clear, but it is considered that the adhesion of the PVA-based polymer precipitated in each treatment bath and the treatment liquid used in each treatment is reduced by producing the polarizing film as described above. When leaving the last treatment bath before entering the drying step, the angle formed between the liquid surface of the treatment bath and the film surface is too large or too small, and the precipitated PVA-based polymer or treatment liquid is likely to be attached and seeded, and therefore, the angle is preferably 35 ° or more, more preferably 40 ° or more, further preferably 50 ° or more, and further preferably 80 ° or less, more preferably 75 ° or less, and further preferably 70 ° or less.

The polarizing film obtained as described above is generally used as a polarizing plate by laminating optically transparent protective films having mechanical strength on both or one side thereof. As the protective film, a Triacetylcellulose (TAC) film, an acetic acid seed or butyrate Cellulose (CAB) film, an acrylic film, a polyester film, or the like can be used. Further, as the adhesive used for bonding, a PVA-based adhesive, a urethane-based adhesive, or the like can be given, and among them, a PVA-based adhesive is preferable.

Examples

The present invention will be described more specifically with reference to the following examples, but the present invention is not limited to these examples. The following measurement or evaluation methods used in the preparation examples, reference examples, and comparative examples are shown below.

[ measurement of surface hardness of film-Forming Cylinder ]

On the surface (circumferential surface) of the film-forming drum, 4 points were determined at each end so as to divide the entire circumferential length of the film-forming drum into 4 equal parts on a line extending from both ends to the inside of 5mm, for a total of 8 points. Next, the Vickers hardness of the chromium plating layer surface was measured for each point by a UCI type hardness tester MIC10 (GE センシング & インスペクション, manufactured by Ger テクノロジーズ Co., Ltd.; probe using MIC-2101-A), and the average value of these was used as the surface hardness of the film-forming drum.

[ area of surface of film-forming roll: 200 μm ² Measurement of the number of cracks above ]

On the surface (peripheral surface) of the film-forming roll, 25 arbitrary spots were defined, and for each spot, the position was adjusted to 2mm × 2mm (4 mm) at a magnification of 1000 times using a digital video microscope VHX-900 (manufactured by キーエンス) ² ) A photograph of cracks (cracks on the chromium plating layer) in the range of (1) was taken. Then, the maximum width and the maximum end pitch of each crack observed on the photograph were obtained in μm units (the end pitch is referred to when the number of ends is only 2, and is referred to when the number of ends is plural)Maximum distance in the tip pitch) and calculating the product thereof, the product being 200 μm ² The cracks were regarded as "area 200 μm ² The above cracks ". This was carried out at 4mm above ² Obtained in the region of (2) × 25 "area 200 μm ² The number of cracks mentioned above, and the number of cracks is calculated from the number per 1mm ² The number of (c) is as follows.

[ measurement of surface temperature of film-Forming Cylinder ]

A 1-line in the width direction passing through an arbitrary 1-point on the surface (circumferential surface) of the film-forming roll and the other 3-lines parallel to the 1-line and equally dividing the circumferential surface 4 together with the 1-line (i.e., lines on which the film-forming roll is positioned on the same line every 1/4 cycles) were identified, and the temperature distribution on the 4-lines was measured using Thermo trap TH9100MR (NEC Avio infrared テクノロジー co. Then, from the obtained temperature distribution data, for each straight line, the temperature of each of 3 points (12 points in total) at the center in the width direction and at a position 20cm from both ends toward the center was obtained, and the 12-point temperatures were averaged to obtain the obtained value as the surface temperature of the film-forming drum at that time. The temperature distribution data of each of the obtained straight lines was prepared as 4 curves each having a position in the width direction as the horizontal axis and a temperature as the vertical axis, and the maximum value of the absolute value of the slope was obtained and used as the maximum temperature gradient of the deposition drum at that time.

[ measurement of the number of defects of PVA film ]

When the PVA film was wound up from the film roll and the fluorescent lamp placed behind the PVA film was observed through the film, the film was found to have defects by distortion of the image of the fluorescent lamp, and the periphery thereof was circled with an oil-based universal pen. Next, the observed defect was observed with a noncontact surface shape measuring instrument "NewView" 6300 (manufactured by ザイゴ Co.), and it was judged whether or not the film was dented from the surface and had an area (opening area) of 400 μm ² The above and a depth of 0.3 μm or more (disadvantage A). The number of defects a was found to be 10 by starting the above operation from the winding end portion of the produced film roll (to reduce the error, the portion from the end portion of the film in the longitudinal direction to 10m is excluded)The area of the PVA film up to that time (length from start of operation to the 10 th defect A. times. the width of the film; unit m ² ) The number of defects A at the winding end portion (unit is one/m) was calculated by dividing the area by 10 (pieces) ² ). Of the 10 defects a, 2 or more defects (hereinafter, sometimes referred to as "rotation period defects") which are located at substantially the same positions in the film width direction and in which the interval in the film length direction substantially matches the integral multiple of the entire circumferential length of the film-forming roll used were determined (this defect includes a portion to be measured, and it is considered that 3 or more defects are arranged at substantially constant intervals (integral multiple of the entire circumferential length of the film-forming roll) in the film length direction, and the number of defects was divided by the area (unit m is m) described above ² ) The number of rotation period defects at the winding end portion (unit is number/m) is calculated from the above ² ）。

Next, after a polarizing film (polarizing film produced from a PVA film on the winding end portion side) is produced as described below using the remaining film roll, the PVA film is wound out from the remaining film roll in which most of the PVA films are not used, and is rewound into a new film roll, whereby the winding start portion of the first film roll is positioned outside the new film roll. The same operation as described above was performed using the new film roll to determine the number of defects a and the number of defects in the rotational cycle (in units of one/m) at the winding start portion of the first film roll ² ) A polarizing film (a polarizing film made of a PVA film on the winding start portion side) is manufactured as described later using the remaining film roll.

[ evaluation of wrinkles on film roll ]

The film roll was visually observed, and wrinkles were evaluated by the following criteria.

A level: no wrinkles were observed

B stage: slightly wrinkled, but practically unproblematic level

C level: there are horizontal wrinkles that are a practical problem.

[ measurement of root mean square roughness of PVA film ]

The root mean square roughness of one surface of the PVA film was measured at any 10 places using a white interference microscope NV6300 (manufactured by ザイゴ), and the average value thereof was taken as the root mean square roughness of the surface. Next, the same operation was performed on the other surface of the PVA film, and the root mean square roughness was obtained.

[ evaluation of polarizing film (20 tests) ]

The PVA film rolled out from the above film roll is subjected to treatment continuously in the order of preliminary swelling, seed dyeing, seed uniaxial stretching, seed fixation, seed drying, seed heat treatment, and the like to produce a polarizing film.

That is, the PVA film was immersed in water at 30 ℃ for 30 seconds to preliminarily swell the film, and then immersed in an aqueous solution (dye bath) at 35 ℃ containing 0.4g/L of iodine and 40g/L of potassium iodide for 3 minutes to dye the film. Next, the resulting film was uniaxially stretched at a stretch ratio of 5 times in the longitudinal direction in a 50 ℃ aqueous solution (stretching bath) having a boric acid concentration of 4%, and further immersed in a 30 ℃ aqueous solution (fixing bath) having a potassium iodide concentration of 40g/L, a boric acid concentration of 40g/L, and a zinc chloride concentration of 10g/L for 5 minutes to perform fixing treatment. Then, the film was hot-air dried at 40 ℃ and further heat-treated at 100 ℃ for 5 minutes.

From an arbitrary position of the obtained polarizing film, 20 test pieces of 50cm in the longitudinal direction and 25cm in the width direction were collected. On the other hand, a 50cm × 50cm polarizing plate with few defects was prepared, and the above test pieces were superimposed on the polarizing plate so that the orientation axes were perpendicular to each other, and placed on an illumination box (シャウカッセン) for X-ray photograph observation to confirm defects in the test pieces. When there is no defect in the test piece, the overlapped polarizing plate/test piece is completely black, and when there is a defect in the test piece, the light leakage at that portion is recognized as a dot-like bright defect. The test piece in which 2 or more bright defects were observed was regarded as a defect, and the yield of 20 test pieces was calculated.

[ evaluation of polarizing film (100-sheet test) ]

The yield of 100 test pieces was calculated in the same manner as the above-described 20 test pieces except that the number of test pieces was changed from 20 to 100, and that a test piece in which 1 or more bright defects were observed was regarded as a defect.

[ evaluation of uneven dyeing and foreign matter in polarizing film ]

A test piece of 50cm in the longitudinal direction and 25cm in the width direction was sampled from an arbitrary position of the obtained polarizing film. On the other hand, a 50cm × 50cm polarizing plate with a small amount of dyeing unevenness and foreign substances was prepared, the test piece was superimposed on the polarizing plate so that the orientation axis was perpendicular to the polarizing plate, and placed on an illumination box for X-ray observation, and the dyeing unevenness and the foreign substances in the test piece were evaluated according to the following criteria.

Seed and seed dyeing

A level: no uneven dyeing was observed

B stage: slightly uneven dyeing but at a level that is practically unproblematic

C level: there is a level of uneven dyeing which is a practical problem

Seed or seed of foreign matter

A level: no foreign matter was observed

B stage: a level at which foreign matter is slightly present but there is no practical problem

C level: there are foreign substances at a level that is practically problematic.

[ preparation example 1 ]

Preparation of the roller 1

The surface (circumferential surface) of a cylinder for film formation made of carbon steel having a width of 1.0m was polished and subjected to a base treatment such as degreasing treatment, and then the surface of the cylinder was subjected to a chromium plating treatment using a chromium plating bath under the following conditions. The chromium plating bath was prepared by dissolving the chemical in distilled water so that the concentration of the chemical was 200g/L chromic anhydride and 2g/L sulfuric acid, respectively.

Temperature of seed plating chromium plating bath: 55 deg.C

Seed current density: 20A/dm ²

Seeding chromium plating layer thickness (after grinding): 50 μm

After the completion of the chromium plating treatment, the film-forming drum was subjected to heat treatment at 102 ℃ for 50 hours, and then cooled.

The surface hardness of the film-forming drum having a chromium plating layer formed on the surface (circumferential surface) thereof by the chromium plating treatment and the heat treatment was measured by the above-described method, and was 760 HV. Hereinafter, this film-forming roll is referred to as "roll 1".

[ preparation example 2 ]

Preparation of Drum 2

A film-forming drum having a chromium plating layer formed on the surface (peripheral surface) thereof was prepared in the same manner as in preparation example 1, except that the chromium plating bath temperature was changed to 52 ℃. The surface hardness of the film-forming roll was measured in accordance with the above method, and the result was 840 HV. Hereinafter, this film-forming roll is referred to as "roll 2".

[ preparation example 3 ]

Preparation of Drum 3

A film-forming drum having a chromium plating layer formed on the surface (peripheral surface) thereof was prepared in the same manner as in preparation example 1, except that the chromium plating bath temperature was changed to 48 ℃. The film-forming roll had a surface hardness of 950HV as measured by the above method. Hereinafter, this film-forming roll will be referred to as "roll 3".

[ preparation example 4 ]

Preparation of Drum 4

A film-forming drum having a chromium plating layer formed on the surface (peripheral surface) thereof was prepared in the same manner as in preparation example 1, except that the chromium plating bath temperature was changed to 67 ℃. The surface hardness of the film-forming roll was measured by the above-described method, and found to be 525 HV. Hereinafter, this film-forming roll is referred to as "roll 4".

[ example 1 ]

The drum 1 is installed in a casting film-making apparatus and connected to a warm water circulating device. Next, the peripheral surface of the drum 1 is polished. The area of the surface (peripheral surface) of the barrel 1 after polishing was measured by the above-mentioned method to be 200 μm ² The number of cracks was 0.10/mm ² . Then, the surface temperature of the drum 1 was raised at a variable temperature rate of 1 deg.c/hour by a warm water circulating means and maintained at 90 deg.c. Maximum temperature at this timeThe gradient was 3.8 ℃ C/m at the maximum.

On the other hand, 100 parts by mass of a PVA (saponified homopolymer of vinyl acetate) having a saponification degree of 99.9 mol% and a polymerization degree of 2400 was immersed in 2500 parts by mass of distilled water at 35 ℃ for 24 hours, and then subjected to centrifugal dehydration to obtain a PVA-containing chip. The volatile content ratio in the PVA hydrous pellets was 70% by mass. To 333 parts by mass of the PVA hydrous pellets (100 parts by mass in terms of PVA in a dry state), 12 parts by mass of glycerin and 0.3 part by mass of a surfactant (containing 95% by mass of lauric diethanolamide) were added, and then the mixture was sufficiently mixed to prepare a mixture, and the mixture was heated and melted by a biaxial extruder with vent holes having a maximum temperature of 130 ℃. The obtained molten PVA was cooled to 100 ℃ by a heat exchanger, and then extruded from a 900mm wide coat hanger die onto the drum 1 having a surface temperature adjusted to 90 ℃ to form a film, which was then introduced into a hot air drying furnace to be dried, and both ends (ear portions) in the width direction were cut, thereby continuously producing a long PVA film having a width of 0.7 m. The film forming speed was set to 8 m/min. The PVA film (thickness 60 μm, length 8000 m) after film formation stabilization was continuously wound around a cylindrical core made of aluminum having a diameter of 6 inches to prepare a film roll.

Using the obtained film roll, the number of defects of the PVA film and the evaluation of the polarizing film (20-sheet test) were carried out by the above-mentioned methods, and as a result, the number of defects A at the winding start portion was 0.102 pieces/m ² (wherein the spin period defect is 0.031 pieces/m ² ) The polarizing film produced from the PVA film on the winding start portion side had a yield of 100% in 20-sheet test, and the number of defects a in the winding end portion was 0.098/m ² (wherein the spin period defect is 0.029 pieces/m ² ) The yield in 20 tests of the polarizing film produced from the PVA film on the winding start portion side was 100%. The number of the defects a of the winding end portion was calculated to be 0.96 times as large as the number of the defects a of the winding start portion.

[ example 2 ]

A PVA film was continuously produced and made into a film roll in the same manner as in example 1, except that the length of the PVA film was changed from 8000m to 3000 m. Note thatThe area of the surface (peripheral surface) of the barrel 1 after polishing was measured by the above-mentioned method to be 200 μm ² The number of cracks was 0.11/mm ² 。

Using the obtained film roll, the number of defects of the PVA film and the evaluation of the polarizing film (20-sheet test) were carried out by the above-mentioned methods, and as a result, the number of defects A at the winding start portion was 0.110 pieces/m ² (wherein the spin cycle defect is 0.044/m ² ) The polarizing film produced from the PVA film on the winding start portion side had a yield of 100% in 20-sheet tests, and the number of defects A in the winding end portion was 0.121 pieces/m ² (wherein the spin period defect is 0.036/m ² ) The yield in 20 tests of the polarizing film produced from the PVA film on the winding start portion side was 100%. The number of the defects a of the winding end portion was calculated to be 1.10 times as large as the number of the defects a of the winding start portion.

[ reference example 1 ]

A PVA film was continuously produced and made into a film roll in the same manner as in example 1, except that the length of the PVA film was changed from 8000m to 15000 m. The area of the surface (circumferential surface) of the barrel 1 after polishing was measured to be 200 μm by the above-mentioned method ² The number of cracks was 0.10/mm ² 。

Using the obtained film roll, the number of defects of the PVA film was measured by the above-mentioned method, and as a result, the number of defects A at the start of winding was 0.108/m ² (wherein the spin period defect is 0.032 pieces/m ² ) The number of defects A at the end of winding was 0.160 pieces/m ² (wherein the spin cycle defect is 0.096 pieces/m ² ). The number of the defects a of the winding end portion was calculated to be 1.48 times as large as the number of the defects a of the winding start portion.

[ example 3 ]

A PVA film was continuously produced and made into a film roll in the same manner as in example 1, except that the polymerization degree of PVA was changed from 2400 to 3300 and the length of the PVA film was changed from 8000m to 15000m at the same time. Incidentally, the roll after polishing and grinding was measured by the above-mentioned methodThe area on the surface (circumferential surface) of the cylinder 1 was 200 μm ² The number of cracks was 0.10/mm ² 。

Using the obtained film roll, the number of defects of the PVA film and the evaluation of the polarizing film (100-sheet test) were carried out by the above-mentioned methods, and as a result, the number of defects A at the winding start portion was 0.088/m ² (wherein the spin cycle defect is 0.018 counts/m ² ) The polarizing film produced from the PVA film on the winding start portion side had a yield of 98% in 100 tests, and the number of defects A in the winding end portion was 0.118 pieces/m ² (wherein the spin cycle defect is 0.024/m ² ) The yield in 100 tests of the polarizing film produced from the PVA film on the winding start portion side was 95%. The number of the defects a of the winding end portion was calculated to be 1.34 times as large as the number of the defects a of the winding start portion.

[ example 4 ]

A PVA film was continuously produced and made into a film roll in the same manner as in example 1, except that the polymerization degree of PVA was changed from 2400 to 6000 and the length of the PVA film was changed from 8000m to 15000m at the same time. The area of the surface (circumferential surface) of the barrel 1 after polishing was measured to be 200 μm by the above-mentioned method ² The number of cracks was 0.13/mm ² 。

Using the obtained film roll, the number of defects of the PVA film and the evaluation of the polarizing film (100-sheet test) were carried out by the above-mentioned methods, and as a result, the number of defects A at the winding start portion was 0.067 pieces/m ² (wherein the spin cycle defect is 0.007 pieces/m ² ) The polarizing film produced from the PVA film on the winding start portion side had a yield of 99% in 100 tests, and the number of defects a in the winding end portion was 0.074 pieces/m ² (wherein the spin cycle defect is 0.007 pieces/m ² ) The yield in 100 tests of the polarizing film produced from the PVA film on the winding start portion side was 99%. The number of the defects a of the winding end portion was calculated to be 1.10 times as large as the number of the defects a of the winding start portion.

[ example 5 ]

Instead of a roller1 and a PVA film was continuously produced and manufactured into a film roll in the same manner as in example 1, except that the length of the PVA film was changed from 8000m to 3000m while using the roll 2. The area of the surface (circumferential surface) of the barrel 2 after polishing was measured to be 200 μm by the above-mentioned method ² The number of cracks was 0.39/mm ² 。

Using the obtained film roll, the number of defects of the PVA film and the evaluation of the polarizing film (20-sheet test) were carried out by the above-mentioned methods, and as a result, the number of defects A at the winding start portion was 0.172 pieces/m ² (wherein the spin cycle defect is 0.052/m ² ) The polarizing film produced from the PVA film on the winding start portion side had a yield of 90% in 20-sheet tests, and the number of defects A in the winding end portion was 0.224 pieces/m ² (wherein the spin period disadvantage is 0.134 pieces/m ² ) The yield in 20 tests of the polarizing film produced from the PVA film on the winding start portion side was 85%. The number of the defects a of the winding end portion was calculated to be 1.30 times as large as the number of the defects a of the winding start portion.

[ example 6 ]

A PVA film was continuously produced and manufactured into a film roll in the same manner as in example 1, except that the surface temperature of the drum 1 was changed from 90 ℃ to 110 ℃ while the length of the PVA film was changed from 8000m to 3000 m. The area of the surface (peripheral surface) of the barrel 1 after polishing was measured by the above-mentioned method and found to be 200 μm ² The number of cracks was 0.13/mm ² 。

Using the obtained film roll, the measurement of the number of defects of the PVA film and the evaluation of the polarizing film (20-sheet test) were carried out by the above-mentioned methods, and as a result, the number of defects A at the winding start portion was 0.132 pieces/m ² (wherein the spin cycle defect is 0.053 pieces/m ² ) The polarizing film produced from the PVA film on the winding start portion side had a yield of 95% in 20-sheet test, and the number of defects A in the winding end portion was 0.180 pieces/m ² (wherein the spin cycle disadvantage is 0.090/m ² ) And pass in 20-sheet test of polarizing film produced from PVA film on winding start portion sideThe rate was 90%. The number of the defects a of the winding end portion was calculated to be 1.36 times as large as the number of the defects a of the winding start portion.

[ example 7 ]

A PVA film was continuously produced and made into a film roll in the same manner as in example 1, except that the temperature change rate was changed from 1 ℃/hr to 5 ℃/hr. The area of the surface (circumferential surface) of the barrel 1 after polishing was measured to be 200 μm by the above-mentioned method ² The number of cracks was 0.10/mm ² 。

Using the obtained film roll, the number of defects of the PVA film was measured by the above-mentioned method, and as a result, the number of defects A at the start of winding was 0.110/m ² (wherein the spin cycle defect is 0.044/m ² ) The number of defects A at the end of winding was 0.122/m ² (wherein the spin cycle defect is 0.049 pieces/m ² ). The number of the defects a of the winding end portion was calculated to be 1.11 times as large as the number of the defects a of the winding start portion.

Comparative example 1

A PVA film was continuously produced and made into a film roll in the same manner as in example 1, except that the roll 3 was used instead of the roll 1. The area of the surface (circumferential surface) of the barrel 3 after polishing was measured by the above-described method to be 200 μm ² The number of cracks was 0.73/mm ² 。

Using the obtained film roll, the number of defects of the PVA film and the evaluation of the polarizing film (20-sheet test) were carried out by the above-mentioned methods, and as a result, the number of defects A at the winding start portion was 0.291 pieces/m ² (wherein the spin period defect is 0.175 pieces/m ² ) The polarizing film produced from the PVA film on the winding start portion side had a yield of 80% in 20-sheet test, and the number of defects a in the winding end portion was 0.938 pieces/m ² (wherein the spin period defect is 0.750 pieces/m ² ) The yield in 20 tests of the polarizing film produced from the PVA film on the winding start portion side was 50%. The number of the defects A of the winding end part relative to the number of the defects A of the winding start partMesh was calculated to be 3.22 times.

Comparative example 2

A PVA film was continuously produced and manufactured into a film roll in the same manner as in example 1, except that the surface temperature of the drum 1 was changed from 90 ℃ to 120 ℃ while the length of the PVA film was changed from 8000m to 3000 m. The area of the surface (circumferential surface) of the barrel 1 after polishing was measured to be 200 μm by the above-mentioned method ² The number of cracks was 0.11/mm ² 。

Using the obtained film roll, the number of defects of the PVA film and the evaluation of the polarizing film (20-sheet test) were carried out by the above-mentioned methods, and as a result, the number of defects A at the winding start portion was 0.252 pieces/m ² (wherein the spin cycle defect is 0.101/m ² ) The polarizing film produced from the PVA film on the winding start portion side had a yield of 80% in 20-sheet test, and the number of defects A in the winding end portion was 0.358 pieces/m ² (wherein the spin cycle disadvantage is 0.251/m ² ) The yield of the polarizing film produced from the PVA film on the winding start portion side in 20 tests was 65%. The number of the defects a of the winding end portion was calculated to be 1.42 times with respect to the number of the defects a of the winding start portion.

Comparative example 3

In example 1, the production of the PVA film was attempted by changing the surface temperature of the drum 1 from 90 ℃ to 40 ℃, but the drying on the drum was insufficient and the film was difficult to peel off from the drum, and thus each evaluation was not performed.

Comparative example 4

A PVA film was continuously produced and made into a film roll in the same manner as in comparative example 1, except that the temperature change rate was changed from 1 ℃/hr to 5 ℃/hr. The area of the surface (circumferential surface) of the barrel 3 after polishing was measured by the above-described method to be 200 μm ² The number of cracks was 0.73/mm ² 。

Using the obtained film roll, the number of defects A of the PVA film was measured by the above-mentioned method, and as a result, the number of defects A at the start of winding was 0.332 pieces/m ² (wherein, the period of rotationThe disadvantage is 0.166 pieces/m ² ) The number of defects A at the end of winding was 1.349/m ² (wherein the spin cycle disadvantage is 1.214/m ² ). The number of the defects a of the winding end portion was calculated to be 4.06 times as large as the number of the defects a of the winding start portion.

[ example 8 ]

The drum 1 is installed in a casting film-making apparatus and connected to a warm water circulating device. Next, the peripheral surface of the drum 1 is polished. The area of the surface (peripheral surface) of the barrel 1 after polishing was measured by the above-mentioned method to be 200 μm ² The number of cracks was 0.10/mm ² . Then, the surface temperature of the drum 1 is raised by the warm water circulating means and maintained at 90 ℃.

On the other hand, 100 parts by mass of a PVA (saponified homopolymer of vinyl acetate) having a saponification degree of 99.9 mol% and a polymerization degree of 2400 was immersed in 2500 parts by mass of distilled water at 35 ℃ for 24 hours, and then subjected to centrifugal dehydration to obtain a PVA-containing chip. The volatile content ratio in the PVA hydrous pellets was 70% by mass. To 333 parts by mass of the PVA hydrous pellets (100 parts by mass in terms of PVA in a dry state), 12 parts by mass of glycerin and 0.3 part by mass of a surfactant (containing 95% by mass of lauric diethanolamide) were added, and then the mixture was sufficiently mixed to prepare a mixture, and the mixture was heated and melted by a biaxial extruder with vent holes having a maximum temperature of 130 ℃. The obtained molten PVA was cooled to 100 ℃ by a heat exchanger, and then extruded from a 900mm wide coat hanger die onto the drum 1 having a surface temperature adjusted to 90 ℃ to form a film, which was then introduced into a hot air drying furnace to be dried, and both ends (ear portions) in the width direction were cut, thereby continuously producing a long PVA film having a width of 0.7 m. The film forming speed was set to 8 m/min. The PVA film (thickness 60 μm, length 12000 m) after the film formation stabilization was continuously wound around a cylindrical core made of aluminum having a diameter of 6 inches to prepare a film roll.

The obtained film roll was evaluated for wrinkles (wrinkles generated when the PVA film was wound) by the above-described method, and the result was grade a. Further, the root mean square roughness of the PVA film was measured by the above-described method using the PVA film wound up from the obtained film, and as a result, the root mean square roughness of the surface of the PVA film in contact with the surface of the drum 1 was 4.1nm, and the root mean square roughness of the other surface was 1.9 nm. The difference between the two was calculated to be 2.2 nm.

The PVA film rolled out from the film roll is subjected to continuous treatment in the order of pre-swelling, seed dyeing, seed fixation, seed uniaxial stretching, seed washing, seed drying, and the like to produce a polarizing film. That is, the PVA film was immersed in water at 30 ℃ for 60 seconds to preliminarily swell the film, and then immersed in an aqueous solution (dye bath) at 35 ℃ containing 0.4g/L of iodine and 40g/L of potassium iodide for 110 seconds to dye the film. Subsequently, the sheet was immersed in a 30 ℃ aqueous solution (fixing bath) containing 30g/L of boric acid for 90 seconds to perform fixing treatment, and further uniaxially stretched at a stretching ratio of 5 times in the longitudinal direction in a 50 ℃ aqueous solution (stretching bath) containing 4% of boric acid. Then, the film was immersed in an aqueous solution (washing bath) of 30 ℃ containing 15g/L boric acid for 10 seconds, washed, and dried with hot air at 55 ℃ to obtain a polarizing film. The angle formed by the liquid surface of the washing bath and the film surface when leaving the washing bath, which is the last treatment bath before the drying step, was set to 60 ° by changing the position of the guide roller, and the upper surface of the film at this time was set to a surface having a small root mean square roughness of the PVA film used.

The polarizing film obtained was evaluated for uneven dyeing by the above method, and found to be a-grade. Further, the polarizing film obtained was evaluated for foreign matter by the above method, and as a result, was a grade a.

[ example 9 ]

A PVA film was continuously produced and wound into a film roll in the same manner as in example 8, except that the roll 2 was used instead of the roll 1. The area of the surface (circumferential surface) of the barrel 2 after polishing was measured to be 200 μm by the above-mentioned method ² The number of cracks was 0.37/mm ² 。

The obtained film roll was evaluated for wrinkles (wrinkles generated when the PVA film was wound) by the above-described method, and the result was grade B. Further, the root mean square roughness of the PVA film was measured by the above-described method using the PVA film wound up from the obtained film, and as a result, the root mean square roughness of the surface of the PVA film in contact with the surface of the drum 2 was 6.7nm, and the root mean square roughness of the other surface was 2.0 nm. The difference between the two was calculated to be 4.7 nm.

A polarizing film was produced in the same manner as in example 8 for the PVA film wound up from the above-described roll. The polarizing film obtained was evaluated for uneven dyeing by the above method, and found to be grade B. Further, the polarizing film obtained was evaluated for foreign matter by the above method, and as a result, was B-grade.

Comparative example 5

A PVA film was continuously produced and wound into a film roll in the same manner as in example 8, except that the roll 3 was used instead of the roll 1. The area of the surface (circumferential surface) of the barrel 3 after polishing was measured by the above-described method to be 200 μm ² The number of cracks was 0.73/mm as a result ² 。

The obtained film roll was evaluated for wrinkles (wrinkles generated when the PVA film was wound) by the above-described method, and the result was grade a. Further, the root mean square roughness of the PVA film was measured by the above-described method using the PVA film wound up from the obtained film, and as a result, the root mean square roughness of the surface of the PVA film in contact with the surface of the drum 3 was 28.3nm, and the root mean square roughness of the other surface was 2.6 nm. The difference between the two was calculated to be 25.7 nm.

A polarizing film was produced in the same manner as in example 8 for the PVA film wound up from the above-described roll. The polarizing film obtained was evaluated for uneven dyeing by the above method, and found to be grade C. Further, the polarizing film obtained was evaluated for foreign matter by the above method, and as a result, was grade C.

Comparative example 6

A PVA film was continuously produced and wound into a film roll in the same manner as in example 8, except that the roll 4 was used instead of the roll 1. The area of the surface (circumferential surface) of the barrel 4 after polishing was measured by the above-described method to be 200 μm ² The number of cracks was 0.15/mm ² 。

The obtained film roll was evaluated for wrinkles (wrinkles generated when the PVA film was wound) by the above-described method, and the result was grade C. Further, the root mean square roughness of the PVA film was measured by the above-described method using the PVA film wound up from the obtained film, and as a result, the root mean square roughness of the surface of the PVA film in contact with the surface of the drum 4 was 2.8nm, and the root mean square roughness of the other surface was 2.6 nm. The difference between the two was calculated to be 0.2 nm.

A polarizing film was produced in the same manner as in example 8 for the PVA film wound up from the above-described film roll. The polarizing film obtained was evaluated for uneven dyeing by the above method, and found to be a-grade. Further, the polarizing film obtained was evaluated for foreign matter by the above method, and as a result, was a grade a.

[ example 10 ]

A polarizing film was produced in the same manner as in example 8, except that the roll obtained in example 8 was used, and the angle formed between the liquid surface of the washing bath and the film surface when leaving the washing bath was changed from 60 ° to 45 °. The polarizing film obtained was evaluated for uneven dyeing by the above method, and found to be a-grade. Further, the polarizing film obtained was evaluated for foreign matter by the above method, and as a result, was B-grade.

Comparative example 7

A polarizing film was produced in the same manner as in example 8, except that the roll obtained in example 8 was used, and the upper surface of the film when leaving the washing bath was changed to a surface having a large root-mean-square roughness of the PVA film used. The polarizing film obtained was evaluated for uneven dyeing by the above method, and found to be a-grade. Further, the polarizing film obtained was evaluated for foreign matter by the above method, and as a result, was grade C.

Comparative example 8

A polarizing film was produced in the same manner as in example 8, except that the roll obtained in example 8 was used, and the angle formed between the liquid surface of the washing bath and the film surface when leaving the washing bath was changed from 60 ° to 25 °. The polarizing film obtained was evaluated for uneven dyeing by the above method, and found to be a-grade. Further, the polarizing film obtained was evaluated for foreign matter by the above method, and as a result, was grade C.

Comparative example 9

A polarizing film was produced in the same manner as in example 8, except that the roll obtained in example 8 was used, and the angle formed between the liquid surface of the washing bath and the film surface when leaving the washing bath was changed from 60 ° to 88 °. The polarizing film obtained was evaluated for uneven dyeing by the above method, and found to be a-grade. Further, the polarizing film obtained was evaluated for foreign matter by the above method, and as a result, was grade C.

Claims

1. A polyvinyl alcohol polymer film, wherein when the root mean square roughness is measured on both surfaces of the film, the difference between the 2 root mean square roughness values obtained is 0.3nm to 10nm, the larger root mean square roughness value is 1nm to 20nm, the smaller root mean square roughness value is 10nm,

root mean square roughness means JIS B0601: 2001, the root mean square roughness is obtained by averaging the square of the deviation from the average line to the roughness curve in the roughness curve obtained from the surface of the film.

2. The polyvinyl alcohol-based polymer film according to claim 1, which is a long-length polyvinyl alcohol-based polymer film.

3. A film roll obtained by continuously winding the polyvinyl alcohol polymer film according to claim 2.