JPWO2016093259A1 - POLYVINYL ALCOHOL POLYMER FILM AND PROCESS FOR PRODUCING THE SAME - Google Patents

Abstract

The present invention is a PVA film having a thickness of 50 μm or less, and when the sample of the PVA film is immersed in water at 30 ° C. for 30 seconds, the elongation amount WMD30 in the length direction in the length direction 250 mm portion before immersion is A PVA film having a width direction elongation WTD300 of 53 mm or more and 65 mm or less at a portion of the width direction 250 mm before immersion when the sample of the PVA film is immersed in water at 30 ° C. for 300 seconds for 35 mm or more and 60 mm or less. is there.

Description

  The present invention relates to a polyvinyl alcohol polymer film having a thickness of 50 μm or less (hereinafter, “polyvinyl alcohol polymer” may be abbreviated as “PVA”), a production method thereof, and a polarization produced from the PVA film. The present invention relates to an optical film such as a film.

  A polarizing plate having a light transmission and shielding function is an important component of a liquid crystal display (LCD) together with a liquid crystal having a light switching function. This LCD can be applied to small devices such as calculators and watches in the early days of development, notebook computers, liquid crystal monitors, liquid crystal color projectors, liquid crystal televisions, in-vehicle navigation systems, mobile phones, measuring devices used indoors and outdoors, etc. Has expanded to various fields. In particular, in applications such as wall-mounted televisions and mobile phones, there is a strong demand for thinner LCDs from the viewpoint of weight reduction and cost reduction. For that purpose, thinner polarizing plates are effective.

  In general, a polarizing plate is a method in which a long PVA film wound in a roll is unwound and uniaxially stretched and then dyed using iodine or a dichroic dye, and the unrolled PVA film is dyed and uniaxially stretched. After that, a polarizing film is produced by a method of performing a fixing treatment with a boron compound, a method of performing a fixing treatment simultaneously with dyeing in any of the above methods, and a cellulose triacetate film on one or both sides of the polarizing film obtained thereby. It is manufactured industrially by laminating a protective film such as an acetic acid / butyric acid cellulose film.

  To make the polarizing plate thinner, it is effective to make the protective film thin, which occupies most of the thickness of the polarizing plate. However, since the polarizing film manufactured using the PVA film having the conventional thickness has a large shrinkage stress, the protective film If only the thin film is made thin, there is a problem that the entire polarizing plate is easily deformed. For this problem, it is conceivable to make the polarizing film itself thinner by using a thinner PVA film as a raw film.

By the way, the width when the film is immersed in water at 30 ° C. for 5 minutes to swell as a PVA film that is excellent in stretchability and can obtain a polarizing film with less unevenness of staining (spots in the width direction of orthogonal transmittance). (TD) direction of the degree of swelling _{(X TD)} and machine direction (MD) of the swelling ratio _{(X MD) (X TD /} X MD) is known PVA film in the range of 1.000 to 1.020 (See Patent Document 1).

JP 2012-32789 A

  Usually, when a PVA film is immersed in water, it swells and extends in the length direction and width direction. However, a thin PVA film has a relatively thick PVA due to a high drying speed in the film forming process. The amount of elongation in the length direction during swelling is relatively smaller than the amount of elongation in the width direction during swelling compared to the film. Here, by changing the crystallinity of the PVA film, for example, by changing the heat treatment conditions, it is possible to increase or decrease both the amount of elongation in the length direction and the width direction during swelling. However, in a thin PVA film, if the amount of elongation in the length direction is set to a specific value or more in order to improve the stretchability, the amount of elongation in the width direction becomes too large. For example, a polarizing film conventionally used When the polarizing film is manufactured by the manufacturing apparatus, the end of the swollen PVA film is likely to be in contact with the wall of the apparatus, and an abnormal end is likely to occur. On the other hand, if an attempt is made to reduce the elongation in the width direction to a specific value or less in order to eliminate the edge abnormality, the elongation in the length direction becomes too small and the stretchability is lowered. In some cases, the resulting polarizing film is dyed. Spots are likely to occur. Therefore, it is difficult to obtain a thin PVA film that has excellent stretchability and is less likely to cause an abnormal end during use, and a thin PVA film that can easily produce a thin polarizing film with reduced staining spots. This is not achieved even by the technique of Patent Document 1 described above.

  Therefore, the present invention provides a thin PVA film that can easily produce a thin PVA film that has excellent stretchability and is less likely to cause abnormal end portions during use, and preferably a thin polarizing film with reduced dyeing spots. For the purpose. Moreover, an object of this invention is to provide optical films, such as a polarizing film manufactured from the said PVA film.

  As a result of intensive studies to achieve the above object, the inventors of the present invention have a specific range of elongation in the length direction (MD) when immersed in water at 30 ° C. for 30 seconds in a thin PVA film. And adjusting the elongation in the width direction (TD) when immersed in water at 30 ° C. for 300 seconds to a specific range, it is excellent in stretchability even when it is a thin PVA film. It has been found that the PVA film can be easily produced as a thin polarizing film in which abnormal end portions are hardly generated and the dyeing spots are reduced. Furthermore, the inventors of the present invention, when manufacturing a thin PVA film using a film forming apparatus including a plurality of drying rolls and a plurality of heat treatment rolls whose rotation axes are parallel to each other, By making the ratio of the peripheral speed between the heat treatment roll located on the most downstream side within a specific range and the surface temperature of the heat treatment roll within a specific range, the above PVA film can be produced smoothly and continuously with high productivity. Found that you can. The present inventors have further studied based on these findings and completed the present invention.

That is, the present invention
[1] A PVA film having a thickness of 50 μm or less, and when the sample of the PVA film is immersed in water at 30 ° C. for 30 seconds, an elongation amount W _MD30 in a length direction in a portion having a length direction of 250 mm before immersion is A PVA film that is 35 mm or more and 60 mm or less, and has a width direction extension amount W _TD300 of 53 mm or more and 65 mm or less in a 250 mm width portion before immersion when the PVA film sample is immersed in water at 30 ° C. for 300 seconds. ;
[2] The PVA film of the above [1], having a width of 2 m or more;
[3] The PVA film of the above [1] or [2], which is a raw film for producing an optical film;
[4] The PVA film of the above [3], wherein the optical film is a polarizing film;
[5] A method for producing a PVA film having a thickness of 50 μm or less, wherein a film forming apparatus including a drying roll and a heat treatment roll having rotation axes parallel to each other is used, and PVA is applied to the first drying roll of the film forming apparatus. The film-forming stock solution is discharged in a film form and dried, followed by further drying with a drying roll, and then heat treatment with a plurality of heat treatment rolls to produce a PVA film, where the heat treatment roll located on the most upstream side Is the heat treatment roll A, and the heat treatment roll located on the most downstream side is the heat treatment roll B, the volatile fraction of the PVA film immediately before contacting the heat treatment roll A is 3% by mass or more and 7% by mass or less. peripheral speed peripheral speed of the heat treatment roll B to _{(S a)} of the roll a ratio _{(S B) (S B /} S a) is 0.999 or less, from the heat treatment roll a to the heat treatment roll B of the heat treatment roll A production method wherein the surface temperature is 87 ° C. or higher and 121 ° C. or lower;
[6] When the drying roll when the volatile content ratio of the PVA film is 12% by mass is the drying roll X and the drying roll located immediately before the heat treatment roll A is the drying roll Y, the first drying roll The surface temperature of each drying roll up to the drying roll X is 70 ° C. or more, and the surface temperature of each drying roll from the drying roll located immediately after the drying roll X to the drying roll Y is 40 ° C. or more and 70 ° C. The production method of the above-mentioned [5], which is less than
[7] The above [5], wherein the ratio (S _B / S ₁ ) of the peripheral speed (S _B ) of the heat treatment roll B to the peripheral speed (S ₁ ) of the first drying roll is 0.900 or more and 1.050 or less. Or the production method of [6];
[8] When the drying roll located immediately before the heat treatment roll A is the drying roll Y, the front and back surfaces of the PVA film are alternately opposed to each drying roll between the first drying roll and the drying roll Y. Any one of the production methods of [5] to [7] above;
[9] The method for producing any one of the above [5] to [8], which is a method for producing an original film for producing an optical film;
[10] The method according to [9] above, wherein the optical film is a polarizing film;
[11] An optical film produced from the PVA film of [3] above;
[12] A polarizing film produced from the PVA film of [4] above;
About.

  According to the present invention, a thin PVA film that is excellent in stretchability, hardly causes abnormal end portions during use, and can easily produce a thin polarizing film with reduced staining spots, and the PVA film. An optical film such as a produced polarizing film is provided. Moreover, according to this invention, the manufacturing method of the PVA film which can manufacture the said PVA film continuously smoothly with sufficient productivity is provided.

The present invention is described in detail below.
[PVA film]
The PVA film of the present invention has a thickness of 50 μm or less. And as for the PVA film of this invention, when the sample is immersed in 30 _degreeC water for 30 second, elongation amount _WMD30 of the length direction in the part of the length direction 250mm before immersion is 35 mm or more and 60 mm or less. Furthermore, in the PVA film of the present invention, when the sample is immersed in water at 30 ° C. for 300 seconds, the amount of elongation _WTD300 in the width direction in the portion in the width direction 250 mm before immersion is more than 53 mm and not more than 65 mm.

  The thickness of the PVA film of the present invention is required to be 50 μm or less because a thin optical film can be obtained, and the thickness is preferably 45 μm or less, more preferably 40 μm or less. It is preferably 35 μm or less, particularly preferably 30 μm or less, and may be 20 μm or less. Thus, the effect of the present invention becomes more remarkable in a thin PVA film. On the other hand, the lower limit of the thickness of the PVA film is not particularly limited, but considering the handleability of the PVA film, the process passability during the production of the optical film, the optical performance of the resulting optical film (the polarizing performance of the polarizing film, etc.) The thickness is preferably 3 μm or more, more preferably 5 μm or more, further preferably 7 μm or more, and particularly preferably 10 μm or more. The thickness of the PVA film can be obtained as an average value obtained by measuring the thicknesses at arbitrary five locations.

The PVA film of the present invention has a length (MD) elongation in a specific range when immersed in water at 30 ° C. for 30 seconds. Specifically, when the sample cut out from the PVA film of the present invention is immersed in water at 30 ° C. for 30 seconds, the elongation amount W _MD30 in the length direction 250 mm before immersion is 35 mm or more and 60 mm or less. Is in range. When _WMD30 is less than 35 mm, the PVA film is insufficiently swelled at the time of use, so that the plasticization of the film becomes insufficient and the stretchability is lowered. From this viewpoint, _WMD30 is preferably 37 mm or more, more preferably 39 mm or more, and further preferably 42 mm or more. In addition, when _WMD30 exceeds 60 mm, the degree of swelling of the PVA film tends to be excessive, and the PVA film is wrinkled or broken due to the slackness of the PVA film generated thereby, and the breakage is based on this. It can happen. From this viewpoint, _WMD30 is preferably 55 mm or less, more preferably 50 mm or less, further preferably 47 mm or less, and particularly preferably 46 mm or less. In _WMD30 , the amount of elongation when a sample is immersed in water at 30 ° C. for 30 seconds is specified. This is a thin film when a thin PVA film is used to manufacture an optical film such as a polarizing film. From the viewpoint of preventing the PVA film from dissolving, a shorter time is often adopted as a process time in the process performed before the stretching process such as a swelling process, and the time of 30 seconds corresponds well to the process time. This is because the relevance to stretchability is particularly great.

The PVA film of the present invention has a specific range of elongation in the width direction (TD) when immersed in water at 30 ° C. for 300 seconds. Specifically, when the sample cut out of the PVA film of the present invention is immersed in water at 30 ° C. for 300 seconds, the width extension amount W _TD300 in the width direction 250 mm portion before immersion is in the range of 53 mm to 65 mm. It is in. When _WTD300 is less than 53 mm, stained spots are likely to occur in the obtained polarizing film. In this respect, W _TD300 is preferably 54 mm or more, more preferably 55 mm or more, and further preferably 57 mm or more. On the other hand, when _WTD300 exceeds 65 mm, the PVA film is excessively spread in the width direction at the time of use, and end abnormalities such as film breakage _tend to occur. In this respect, W _TD300 is preferably 62 mm or less, and more preferably 60 mm or less. _WTD300 defines the amount of elongation when a sample is immersed in water at 30 ° C. for 300 seconds, and this correlates with the WMD300 and abnormal end portions at the time of use and _{staining spots of the} obtained polarizing film. Because there is.

_{Said WMD30} can be _{calculated | required} with the following method. That is, first, a rectangular sample having a width direction (TD) of 40 mm × a length direction (MD) of 270 mm is cut out from a PVA film to be measured. Here, for example, the sample may be cut out from the center in the width direction of the target PVA film. Next, a marked line is put with an oily magic (line thickness is 0.3 mm) inward by 10 mm from both ends of the 270 mm length of the sample. The outer part from the marked lines at both ends is sandwiched between commercially available clips (chuck width 40 mm, mass 7.8 g (weight in water 7.3 g)), and one clip is fixed with a rod-shaped jig such as a number wire. After confirming that the distance between the marked lines is 250 mm, put the sample with the clip into the pure water adjusted to 30 ° C stored in a cylindrical transparent water tank (such as a graduated cylinder) so that the entire sample enters the water. Immediately immerse the long side of the sample vertically. Immediately after the immersion, a rod-shaped jig is hooked on the upper part of the water tank so that the long side of the sample is fixed vertically. Thereafter, a metal ruler is immersed in water, and the distance between marked lines is measured 30 seconds after the immersion of the sample. The elongation (W _MD30 ) (unit: mm) is calculated by subtracting the original distance between marked lines (250 mm) from the measured value read in 0.5 mm increments.

On the other hand, the _{WTD 300} can be obtained by the following method. That is, first, a rectangular sample of width direction (TD) 270 mm × length direction (MD) 40 mm is cut out from the PVA film to be measured. Here, for example, the sample may be cut out from the center in the width direction of the target PVA film. Next, a marked line is put with an oily magic (line thickness is 0.3 mm) inward by 10 mm from both ends of the 270 mm length of the sample. The outer part from the marked lines at both ends is sandwiched between commercially available clips (chuck width 40 mm, mass 7.8 g (weight in water 7.3 g)), and one clip is fixed with a rod-shaped jig such as a number wire. After confirming that the distance between the marked lines is 250 mm, put the sample with the clip into the pure water adjusted to 30 ° C stored in a cylindrical transparent water tank (such as a graduated cylinder) so that the entire sample enters the water. Immediately immerse the long side of the sample vertically. Immediately after the immersion, a rod-shaped jig is hooked on the upper part of the water tank so that the long side of the sample is fixed vertically. Then, a metal ruler is immersed in water, and the distance between marked lines is measured 300 seconds after the sample is immersed. The elongation (W _TD300 ) (unit: mm) is calculated by subtracting the original distance between marked lines (250 mm) from the measured value read in 0.5 mm increments.

  As PVA which comprises the PVA film of this invention, what is manufactured by saponifying the polyvinyl ester-type polymer obtained by superposing | polymerizing vinyl ester can be used. Examples of the vinyl ester include vinyl formate, vinyl acetate, vinyl propionate, vinyl valelate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, vinyl versatate, and the like. Among the above vinyl esters, vinyl acetate is preferable from the viewpoints of availability, cost, ease of production of PVA, and the like.

  The above-mentioned polyvinyl ester polymer is preferably obtained using only one or two or more kinds of vinyl esters as a monomer, and obtained using only one kind of vinyl ester as a monomer. Is more preferable, but it may be a copolymer of one or more vinyl esters and other monomers copolymerizable therewith.

  Examples of such other monomers copolymerizable with vinyl ester include ethylene; olefins having 3 to 30 carbon atoms such as propylene, 1-butene and isobutene (α-olefins); acrylic acid or a salt thereof. Methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate Acrylic acid esters such as octadecyl acrylate; methacrylic acid or salts thereof; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, methacrylic acid t-butyl, 2-ethylhexyl methacrylate, methacrylic acid Methacrylic acid esters such as decyl and octadecyl methacrylate; acrylamide; N-methyl acrylamide, N-ethyl acrylamide, N, N-dimethyl acrylamide, diacetone acrylamide, acrylamide propane sulfonic acid or salt thereof, acrylamidopropyldimethylamine or salt thereof, Acrylamide derivatives such as N-methylolacrylamide or derivatives thereof; methacrylamide; N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidepropanesulfonic acid or salt thereof, methacrylamidepropyldimethylamine or salt thereof, N-methylolmethacrylamide Or a methacrylamide derivative such as a derivative thereof; N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone N-vinylamides such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, and other vinyl ethers; acrylonitrile, methacrylo Vinyl cyanides such as nitriles; 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 its salts, esters or acid anhydrides; itaconic acid Or a salt, ester or acid anhydride thereof; a vinylsilyl compound such as vinyltrimethoxysilane; and isopropenyl acetate. Said polyvinyl ester-type polymer can have a structural unit derived from 1 type, or 2 or more types of these other monomers.

  The proportion of structural units derived from the other monomers in the polyvinyl ester polymer is 15 mol% or less based on the number of moles of all structural units constituting the polyvinyl ester polymer. Preferably, it is 10 mol% or less, more preferably 5 mol% or less.

  The PVA may be modified with one or two or more types of graft copolymerizable monomers. Examples of the graft copolymerizable monomer include unsaturated carboxylic acids or derivatives thereof; unsaturated sulfonic acids or derivatives thereof; α-olefins having 2 to 30 carbon atoms, and the like. The proportion of structural units derived from the graft copolymerizable monomer in PVA is preferably 5 mol% or less based on the number of moles of all structural units constituting PVA.

  In the PVA, a part of the hydroxyl groups may be cross-linked or may not be cross-linked. Moreover, said PVA may react with aldehyde compounds, such as acetaldehyde and a butyraldehyde, etc. to form an acetal structure, and the said PVA does not react with these compounds and does not form an acetal structure. May be.

  The degree of polymerization of PVA is not particularly limited, but from the viewpoint of the strength of the PVA film and the durability of the optical film produced from the PVA film, it is preferably 500 or more, more preferably 1,000 or more, It is more preferably 1,500 or more, and particularly preferably 2,000 or more. On the other hand, if the degree of polymerization is too high, it tends to lead to an increase in production cost and poor processability during film formation. Therefore, the degree of polymerization of PVA is preferably 10,000 or less, and is 9,000 or less. More preferably, it is more preferably 8,000 or less, and particularly preferably 7,000 or less. In addition, the polymerization degree of PVA in this specification means the average polymerization degree measured according to description of JIS K6726-1994.

  The saponification degree of PVA is not particularly limited, but is preferably 90 mol% or more, more preferably 95 mol% or more, from the viewpoint of optical performance or durability of an optical film produced from a PVA film, It is further preferably 98 mol% or more, particularly preferably 99 mol% or more, and may be 99.2 mol% or more. On the other hand, considering the dyeability of the PVA film, the saponification degree of PVA is preferably 99.99 mol% or less. In this specification, the degree of saponification of PVA refers to the total number of moles of structural units (typically vinyl ester units) that can be converted into vinyl alcohol units by saponification and the vinyl alcohol units of PVA. The proportion (mol%) occupied by the number of moles of vinyl alcohol units. The degree of saponification of PVA can be measured according to the description of JIS K6726-1994.

  As the PVA, one type of PVA may be used alone, or two or more types of PVA having different types of modification, modification rate, polymerization degree, saponification degree, and the like may be used in combination. However, in the case where excellent secondary processability is required for the PVA film of the present invention, such as when used as a raw film when manufacturing an optical film, the PVA film is acidic such as carboxyl group and sulfonic acid group. PVA having a functional group; PVA having an acid anhydride group; PVA having a basic functional group such as an amino group; and PVA having a functional group that promotes a crosslinking reaction such as a neutralized product thereof. The secondary processability of the PVA film may decrease due to the crosslinking reaction. Therefore, in the above case, the PVA film preferably contains neither PVA having an acidic functional group, PVA having an acid anhydride group, PVA having a basic functional group, or a neutralized product thereof. As a PVA produced by saponifying a polyvinyl ester polymer obtained by using only vinyl ester as a monomer, and / or only vinyl ester and ethylene and / or olefin having 3 to 30 carbon atoms. It is more preferable to include only PVA produced by saponifying a polyvinyl ester polymer obtained using a monomer, and as a PVA, a polyvinyl ester system obtained using only a vinyl ester as a monomer PVA produced by saponifying the polymer and / or vinyl ester and ethyl That is more preferably containing only PVA produced by saponifying a polyvinyl ester polymer obtained by using a monomer N'nomi.

  The PVA content in the PVA film is preferably in the range of 50 to 100% by mass, more preferably in the range of 80 to 100% by mass, and in the range of 85 to 100% by mass. Further preferred.

  The PVA film of the present invention preferably contains a plasticizer because it can improve mechanical properties such as impact strength and process passability during secondary processing. As the plasticizer, polyhydric alcohol is preferably used, and examples thereof include ethylene glycol, glycerin, diglycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and trimethylolpropane. The PVA film of the present invention can contain one or more of these plasticizers. Among these plasticizers, one or more of glycerin, diglycerin and ethylene glycol are preferred from the viewpoint of excellent stretchability when the PVA film of the present invention is stretched and used.

  The content of the plasticizer in the PVA film is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and more preferably 5 parts by mass or more with respect to 100 parts by mass of PVA contained in the PVA film. More preferably, it is preferably 30 parts by mass or less, more preferably 25 parts by mass or less, and further preferably 20 parts by mass or less. When the content is 1 part by mass or more, the stretchability of the PVA film can be further improved. On the other hand, when the content is 30 parts by mass or less, the handleability of the PVA film is improved.

  The PVA film of the present invention preferably contains a surfactant from the viewpoint of its handleability and the improvement of peelability from the film forming apparatus when the PVA film is produced. There is no limitation in particular in the kind of surfactant, For example, anionic surfactant, nonionic surfactant, etc. are mentioned.

  Examples of the anionic surfactant include carboxylic acid types such as potassium laurate; sulfate ester types such as octyl sulfate; and sulfonic acid types such as dodecylbenzene sulfonate.

  Nonionic surfactants include, for example, alkyl ether types such as polyoxyethylene oleyl ether; alkylphenyl ether types such as polyoxyethylene octylphenyl ether; alkyl ester types such as polyoxyethylene laurate; polyoxyethylene laurylamino Alkylamine type such as ether; alkylamide type such as polyoxyethylene lauric acid amide; polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether; alkanolamide type such as lauric acid diethanolamide and oleic acid diethanolamide; polyoxy Examples include allyl phenyl ether type such as alkylene allyl phenyl ether.

  The PVA film of the present invention can contain one or more of these surfactants. Among these surfactants, nonionic surfactants are preferred because of their excellent effect of reducing film surface abnormalities during film formation, and alkanolamide type surfactants are particularly preferred, and aliphatic carboxylic acids (for example, Further, dialkanolamides (for example, diethanolamide etc.) of C8-30 saturated or unsaturated aliphatic carboxylic acid etc. are more preferred.

  The content of the surfactant in the PVA film is such that the handleability of the PVA film and the peelability from the film forming apparatus when producing the PVA film can be further improved, and the occurrence of blocking can be reduced. It is preferably 0.01 parts by mass or more, more preferably 0.02 parts by mass or more, further preferably 0.05 parts by mass or more, relative to 100 parts by mass of PVA contained in the PVA film. Moreover, it is preferable that it is 1 mass part or less, It is more preferable that it is 0.5 mass part or less, It is further more preferable that it is 0.3 mass part or less.

  The PVA film of the present invention is optionally provided with stabilizers (antioxidants, ultraviolet absorbers, heat stabilizers, etc.), compatibilizers, antiblocking agents, flame retardants, antistatic agents, lubricants, dispersants, Various additives such as a fluidizing agent and an antibacterial agent may be included. The PVA film of the present invention can contain one or more of these additives.

  The volatile content of the PVA film is preferably in the range of 1% by mass or more and 5% by mass or less from the viewpoint of handleability, and the volatile content is more preferably 2% by mass or more. More preferably, it is 4 mass% or less. The volatile content of the PVA film can be determined in the same manner as the volatile content of the PVA film described later.

  The shape of the PVA film of the present invention is not particularly limited, but a more uniform PVA film can be continuously and smoothly manufactured, and is also continuous when an optical film such as a polarizing film is manufactured using the PVA film. It is preferable that the film is a long film. The long film is preferably in the form of a film roll by winding it around a cylindrical core. In the case of a long film, the length of the PVA film (length in the length direction (MD)) is not particularly limited and can be set as appropriate according to the use, etc., but is continuously wound from the film roll. Since the loss at the time of switching a film roll can be reduced, so that the length of a PVA film is longer in the case of taking out and using, the length is preferably 5 m or more, and more preferably 100 m or more. , 500 m or more, more preferably 1,000 m or more, 5,000 m or more, and even 8,000 m or more. Although there is no restriction | limiting in particular in the upper limit of the said length, The said length can be 50,000 m or less, for example, Furthermore, it can be 20,000 m or less.

  The width of the PVA film of the present invention is not particularly limited, and can be set as appropriate according to the use of the PVA film or an optical film such as a polarizing film produced from the PVA film. In view of the progress of screen formation, it is suitable for these uses when the width of the PVA film is 2 m or more, more preferably 3 m or more, and further preferably 4 m or more. On the other hand, if the width of the PVA film is too wide, it is difficult to uniformly carry out uniaxial stretching itself when producing an optical film with a device that has been put to practical use, so the width of the PVA film should be 8 m or less. Is preferably 7 m or less, and may be 6 m or less.

[Production method of PVA film]
Although the manufacturing method of the PVA film of this invention is not specifically limited, According to the manufacturing method of the following this invention, the PVA film of this invention can be manufactured smoothly with sufficient productivity.

That is, the manufacturing method of the present invention for manufacturing a PVA film having a thickness of 50 μm or less uses a film forming apparatus including a drying roll and a heat treatment roll whose rotation axes are parallel to each other, and the first drying roll of the film forming apparatus. A film-forming stock solution containing PVA is discharged into a film and dried, followed by further drying with a drying roll, and then heat treatment with a plurality of heat treatment rolls to produce a PVA film. When the heat treatment roll located is heat treatment roll A and the heat treatment roll located on the most downstream side is heat treatment roll B, the volatile fraction of the PVA film immediately before contacting the heat treatment roll A is 3 mass% or more and 7 mass% or less. The ratio (S _B / S _A ) of the peripheral speed (S _B ) of the heat treatment roll B to the peripheral speed (S _A ) of the heat treatment roll _A is 0.999 or less, and the heat treatment roll A to the heat treatment roll B Each of the heat treatment rolls has a surface temperature of 87 ° C or higher and 121 ° C or lower.

  In a film forming apparatus including a drying roll and a heat treatment roll whose rotation axes are parallel to each other used for manufacturing a PVA film, a more uniform PVA film can be obtained, and the number of drying rolls may be 4 or more. Preferably, it is 5 or more, more preferably 6 or more, particularly preferably 8 or more, preferably 30 or less, more preferably 20 or less. preferable. In addition, in this specification, the drying roll (drying roll which discharges a film forming undiluted solution) located in the most upstream side among the said drying rolls is called a 1st drying roll, and it is downstream from a 1st drying roll about the remaining drying rolls. In order toward the side, they are referred to as a second drying roll, a third drying roll, a fourth drying roll,. In addition, the drying roll when the volatile content of the PVA film during film formation becomes 12% by mass (or the drying roll on the downstream side when it becomes 12% by mass between two drying rolls) is “dried” The drying roll positioned immediately before the heat treatment roll is referred to as “drying roll Y”.

  In the film forming apparatus, the number of heat treatment rolls is not particularly limited as long as it is 2 or more. However, from the viewpoint of uniformly heat-treating both the front and back surfaces of the PVA film, the number of heat treatment rolls is 3 or more. Preferably, it is 4 or more, more preferably 10 or less, and even more preferably 8 or less. In the present specification, as described above, the heat treatment roll located on the most upstream side of the heat treatment rolls is referred to as “heat treatment roll A”, and the heat treatment roll located on the most downstream side is referred to as “heat treatment roll B”.

  The drying roll and / or heat treatment roll is preferably made of a metal such as nickel, chromium, copper, iron, stainless steel, and the like, and in particular, the surface of the roll is hard to corrode and has a specular gloss. More preferably, it is formed from. In order to increase the durability of the drying roll and / or heat treatment roll, a roll plated with a single layer or a combination of two or more nickel layers, chromium layers, nickel / chromium alloy layers, etc. is used as the drying roll and / or heat treatment roll. It is preferable to use it.

  In drying the PVA film using a plurality of drying rolls, the PVA film can be dried more uniformly, and in particular during the secondary processing of the PVA film obtained by reducing the physical property difference between the front and back surfaces of the PVA film. Since the film can be prevented from curling, it is preferable that the front and back surfaces of the PVA film are alternately opposed to each drying roll between the first drying roll and the drying roll Y. That is, as the orientation of the PVA film in the process from the first drying roll to the drying roll Y, the film surface (first drying roll contact surface) that contacts the first drying roll and the first drying in any part of the PVA film It is preferable to dry so that the film surface that does not contact the roll (first drying roll non-contact surface) alternately faces each drying roll from the first drying roll to the drying roll Y.

  Moreover, when heat-treating a PVA film using a plurality of heat treatment rolls, the PVA film can be applied to each heat treatment roll between the heat treatment roll A and the heat treatment roll B because the heat treatment can be performed more uniformly. It is preferable that both the front and back sides of the front and back are alternately opposed.

  In said manufacturing method, the film-forming stock solution containing PVA is discharged in the form of a film on the 1st drying roll of a film-forming apparatus, and it dries. In discharging the film forming stock solution, for example, a known film forming device (film casting device) such as a T-shaped slit die, a hopper plate, an I-die, a lip coater die is used, and the film forming stock solution is used. May be discharged (cast) into a film on the first drying roll. At this time, the thickness of the obtained PVA film can be adjusted by adjusting the discharge amount by adjusting the film-like discharge device.

  The film-forming stock solution containing PVA can be prepared by mixing PVA with a liquid medium to make a solution, or melting a PVA chip containing the liquid medium or the like to make a melt. The film-forming stock solution can be prepared using a stirring mixer, a melt extruder, or the like. Examples of the liquid medium include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylenediamine, and diethylenetriamine. These liquid media may be used alone. Or you may use 2 or more types together. Among these, water, dimethyl sulfoxide, or a mixture of both is preferably used, and water is particularly preferably used.

  If desired, the film-forming stock solution is preferably blended with one or more of the plasticizers, surfactants, various additives and the like as described above in the description of the PVA film in the above-described amounts.

The volatile fraction of the film-forming stock solution is preferably in the range of 50% by mass or more and 90% by mass or less, and the volatile fraction is more preferably 55% by mass or more and 80% by mass or less. It is more preferable. If the volatile content is too low, the viscosity of the film-forming stock solution may become too high, making film formation difficult. On the other hand, if the volatile content is too high, the uniformity of the thickness of the obtained PVA film may be impaired. In addition, “the volatile matter rate of the film-forming stock solution” in this specification refers to the volatile matter rate obtained by the following formula (1).
Volatile content (% by mass) of the film-forming stock solution = 100 × (W _a −W _b ) / W _a (1)
(Where, _{W a} represents a film-forming stock solution mass (g), _{W b} is _W a (g) mass when a film-forming solution was dried 16 hours in a 105 ° C. of the heating dryer of (g) Represents.)

  The surface temperature of the first drying roll is preferably in the range of 80 ° C. or higher and 120 ° C. or lower from the viewpoint of uniformity of drying of the PVA film, productivity, and the like, and the surface temperature is 85 ° C. or higher. Is more preferably 90 ° C. or higher, particularly preferably 93 ° C. or higher, more preferably 105 ° C. or lower, and further preferably 99 ° C. or lower. When the surface temperature is 80 ° C. or higher, the drying efficiency on the first drying roll is improved. On the other hand, when the surface temperature is 120 ° C. or lower, foaming of the PVA film can be more effectively suppressed.

  The film-forming stock solution discharged in the form of a film may be dried on the first drying roll only by the heat from the first drying roll, but at the same time as the first drying roll is heated, the first drying roll is not contacted. It is possible to apply heat from both sides of the PVA film by spraying hot air on the surface or by heating with an infrared heater from the first drying roll non-contact surface side. It is preferable from the point. The PVA film can also be heated by a dielectric heating device.

The peripheral speed (S ₁ ) of the first drying roll is preferably 8 m / min or more and 30 m / min or less from the viewpoint of the uniformity of drying of the PVA film, the drying speed, the productivity of the PVA film, and the like. It is more preferably from 27 to 27 m / min, even more preferably from 12 to 25 m / min.

The film-forming stock solution discharged in the form of a film on the first drying roll is dried on the first drying roll and peeled off from the first drying roll. If the volatile content of the PVA film at the time of peeling from the first drying roll is too low, the productivity of the PVA film tends to decrease, while the volatile content of the PVA film at the time of peeling from the first drying roll. If the rate is too high, peeling from the first drying roll is likely to be difficult, and in some cases, breakage or spots are likely to occur. From the above viewpoint, the volatile fraction of the PVA film at the time of peeling from the first drying roll is preferably 13% by mass or more, more preferably 14% by mass or more, and 15% by mass or more. More preferably, it is preferably 30% by mass or less, more preferably 27% by mass or less, and further preferably 25% by mass or less.
Here, “the volatile content of the PVA film” in this specification refers to the volatile content determined by the following formula (2).
Volatile content (% by mass) of PVA membrane = 100 × (W _c −W _d ) / W _c } (2)
(Here, _{W c} represents the mass (g) of the sample taken from PVA film, _{W d} is placed in the sample _W c (g) of temperature 50 ° C., a pressure 0.1kPa following vacuum dryer 4 (The mass (g) when dried for hours is shown.)

  The PVA film dried on the first drying roll is peeled off from the first drying roll, and this time, it is further dried by the drying rolls subsequent to the second drying roll. In drying with the second drying roll, it is preferable that the first drying roll non-contact surface of the PVA film is opposed to the second drying roll.

  When drying the PVA film using a plurality of drying rolls, the surface temperature of each drying roll is not particularly limited, but the surface temperature of each drying roll from the first drying roll to the drying roll X is the same as that of the present invention described above. In view of being able to obtain a PVA film more efficiently, all are preferably 70 ° C. or higher, more preferably 72 ° C. or higher, further preferably 73 ° C. or higher, and 120 ° C. More preferably, it is 105 degrees C or less, More preferably, it is 99 degrees C or less. Since the surface temperature of each drying roll from the second drying roll to the drying roll X can obtain the above-described PVA film of the present invention more efficiently, it is 90 ° C. or lower, 85 ° C. or lower, and further 80 ° C. or lower. It may be.

  Moreover, the surface temperature of each drying roll from the drying roll located immediately after the drying roll X to the drying roll Y can improve the uniformity of drying while maintaining an appropriate drying temperature. It is preferable that both are 40 degreeC or more and less than 70 degreeC from the ability to obtain the PVA film of more efficiently, and the said surface temperature is more preferable that all are 45 degreeC or more, and 50 degreeC or more More preferably, it may be 55 ° C. or higher, more preferably 65 ° C. or lower, and further preferably 63 ° C. or lower.

  The PVA film dried by the drying roll is then heat-treated by a plurality of heat treatment rolls. By performing heat treatment with a plurality of heat treatment rolls, the physical property difference between the front and back surfaces of the PVA film can be reduced, and the secondary workability can be improved. The PVA film immediately before being subjected to the heat treatment, that is, the volatile content ratio of the PVA film immediately before contacting the heat treatment roll located on the most upstream side (heat treatment roll A) can effectively perform the heat treatment, etc. It is necessary that it is 3 mass% or more and 7 mass% or less, and it is preferable that the said volatile fraction is 4 mass% or more, and it is preferable that it is 6 mass% or less. Note that the volatile content of the PVA film may change during the heat treatment.

In heat-treating the PVA film using a plurality of heat treatment rolls, the ratio (S _B / S _A ) of the peripheral speed (S _B ) of the heat treatment roll B to the peripheral speed (S _A ) of the heat treatment roll _A is 0.999 or less. It is necessary to be. When the ratio (S _B / S _A ) exceeds 0.999, W _{MD30 of the} obtained PVA film is lowered. Since the PVA film of the present invention can be obtained more efficiently, the ratio (S _B / S _A ) is preferably 0.995 or less, and more preferably 0.993 or less. In addition, from the viewpoint of effectively preventing wrinkles from being generated in the obtained PVA film, the ratio (S _B / S _A ) is preferably 0.985 or more, and 0.988 or more. More preferably.

Moreover, when heat-treating a PVA film using a plurality of heat treatment rolls, the surface temperature of each heat treatment roll from the heat treatment roll A to the heat treatment roll B must be 87 ° C. or more and 121 ° C. or less. When the surface temperature is less than 87 ° C, the _WTD300 value of the obtained PVA film becomes too high, and when the surface temperature exceeds 121 ° C, the _WTD300 value of the obtained PVA film becomes too low. The surface temperature is preferably 92 ° C. or higher, more preferably 93 ° C. or higher, and 119 ° C. or lower because the PVA film of the present invention can be obtained more efficiently. The temperature is preferably 117 ° C. or lower, more preferably 114 ° C. or lower.

  The surface temperatures of the heat treatment rolls from the heat treatment roll A to the heat treatment roll B may be the same as each other or may be partially or entirely different. Similarly, the surface temperatures of the heat treatment roll A and the heat treatment roll B may be the same or different from each other, but the surface temperature of the heat treatment roll B should be 5 ° C. higher than the surface temperature of the heat treatment roll A. It is preferably 10 ° C. or higher, more preferably 12 ° C. or higher, even more preferably 15 ° C. or higher, particularly preferably 25 ° C. or lower, more preferably 20 ° C. or lower, more preferably 18 ° C. or higher. More preferably, the temperature is higher than or equal to ° C.

The ratio (S _B / S ₁ ) of the peripheral speed (S _B ) of the heat treatment roll B to the peripheral speed (S ₁ ) of the first drying roll can obtain the above-described PVA film of the present invention more efficiently. From 0.900 to 1.050, and the ratio (S _B / S ₁ ) is more preferably 0.920 or more, and further preferably 0.940 or more. Preferably, it is 0.950 or more, more preferably 1.020 or less, still more preferably 1.010 or less, and particularly preferably 1.000 or less.

  The PVA film heat-treated as described above can be subjected to humidity conditioning treatment as necessary, and wound into a roll with a predetermined length to obtain the PVA film of the present invention. In addition, before winding in the roll shape, at one or more of the stage in the roll shape and after unwinding from the roll, both ends (ears) in the width direction of the PVA film are cut and removed. May be.

  The volatile content of the PVA film finally obtained by the above-described series of treatments is preferably in the range of 1% by mass to 5% by mass, and the volatile content is more preferably 2% by mass or more. Moreover, it is more preferable that it is 4 mass% or less.

[Use of PVA film]
Although there is no restriction | limiting in particular in the use of the PVA film of this invention, since it is excellent in extending | stretching and an end part abnormality does not arise easily at the time of use, the PVA film of this invention should be used as an original film at the time of manufacturing an optical film. Is preferred. Examples of the optical film include a polarizing film and a retardation film. In particular, according to the PVA film of the present invention, since a thin polarizing film with reduced dyeing spots can be easily produced, the PVA film of the present invention is more preferably used as a raw film for producing a polarizing film. preferable.

  The optical film can be produced by a production method having a step of uniaxially stretching using the PVA film of the present invention. Specifically, the PVA film of the present invention itself or a swelling treatment described later is applied. PVA films derived from the PVA film of the present invention (hereinafter referred to as “PVA film of the present invention” and “PVA film derived from the PVA film of the present invention” collectively referred to as “PVA film based on the present invention”) Can be produced by a method having a step of uniaxial stretching.

  The method for producing a polarizing film using the PVA film of the present invention as a raw film is not particularly limited, and any method conventionally employed may be employed. As such a method, for example, there is a method of dyeing and uniaxially stretching a PVA film based on the present invention, or uniaxially stretching a PVA film based on the present invention containing a dichroic dye. Can be mentioned. As a more specific method for producing the polarizing film, the PVA film based on the present invention is subjected to swelling, dyeing, uniaxial stretching, and further, if necessary, fixing treatment, drying treatment, heat treatment, etc. Is mentioned. In this case, the order of each treatment such as swelling, dyeing, uniaxial stretching, and fixing treatment is not particularly limited, and one or two or more treatments can be performed simultaneously. Also, one or more of each process can be performed twice or more.

  The swelling can be performed by immersing the PVA film according to the present invention in water. The temperature of the water when immersed in water is preferably within a range of 20 ° C. or higher and 40 ° C. or lower, more preferably 22 ° C. or higher, and further preferably 25 ° C. or higher. Moreover, it is more preferable that it is 38 degrees C or less, and it is still more preferable that it is 35 degrees C or less. Moreover, as time to immerse in water, it is preferable that it is 0.1 minute or more, for example, it is more preferable that it is 0.3 minute or more, and it is preferable that it is 5 minutes or less, It is 3 minutes or less. More preferably. In addition, the water at the time of immersing in water is not limited to pure water, The aqueous solution in which various components melt | dissolved may be sufficient, and the mixture of water and an aqueous medium may be sufficient.

  Dyeing can be performed by bringing a dichroic dye into contact with the PVA film according to the present invention. The dyeing time may be any stage before uniaxial stretching, during uniaxial stretching, or after uniaxial stretching. Dyeing is generally performed by immersing the PVA film in a solution (especially an aqueous solution) containing iodine-potassium iodide which is a dyeing bath. In the present invention, such a dyeing method is suitably employed. The The concentration of iodine in the dyeing bath is preferably in the range of 0.01% by mass to 0.5% by mass, and the concentration of potassium iodide is in the range of 0.01% by mass to 10% by mass. Is preferred. The temperature of the dyeing bath is preferably 20 ° C. or more and 50 ° C. or less, and particularly preferably 25 ° C. or more and 40 ° C. or less.

Examples of the dichroic dye include iodine-based dyes and dichroic organic dyes (for example, DirectBlack 17, 19, 154; DirectBrown 44, 106, 195, 210, 223; DirectRed 2, 23, 28, 31, 37, 39, 79, 81, 240, 242, 247; DirectBlue 1, 15, 22, 78, 90, 98, 151, 168, 202, 236, 249, 270; DirectViolet 9, 12, 51, 98; DirectGreen 1, 85 Direct Yellow 8, 12, 44, 86, 87; Direct Orange 26, 39, 106, 107, etc.), and iodine dyes are preferred. The iodine dye can be generated, for example, by bringing iodine (I ₂ ) into contact with potassium iodide (KI). These dichroic dyes may be used alone or in combination of two or more.

  Uniaxial stretching of the PVA film according to the present invention may be performed by either a wet stretching method or a dry heat stretching method. In the case of the wet stretching method, it can be carried out in an aqueous solution containing boric acid, or can be carried out in the dyeing bath described above or in a fixing treatment bath described later. In the case of the dry heat stretching method, the PVA film after water absorption can be used in the air. Among these, the wet stretching method is preferable, and uniaxial stretching is more preferable in an aqueous solution containing boric acid. The concentration of boric acid in the boric acid aqueous solution is preferably in the range of 0.5% by mass or more and 6.0% by mass or less, and the concentration is more preferably 1.0% by mass or more. The content is more preferably at least mass%, more preferably at most 5.0 mass%, further preferably at most 4.0 mass%. The boric acid aqueous solution may contain potassium iodide, and the concentration of potassium iodide is preferably in the range of 0.01 mass% to 10 mass%.

  Although the stretching temperature in uniaxial stretching is not particularly limited, in the case of a wet stretching method, it is preferably within a range of 30 ° C. or higher and 90 ° C. or lower, and the stretching temperature is more preferably 40 ° C. or higher, and 45 ° C. More preferably, it is more preferably 70 ° C. or less, and further preferably 65 ° C. or less. In the case of the dry heat stretching method, it is preferably in the range of 50 ° C. or higher and 180 ° C. or lower.

  The stretching ratio in uniaxial stretching (the total stretching ratio obtained by multiplying the stretching ratios when performing uniaxial stretching in multiple stages) is preferably stretched as much as possible from the point of polarization performance until just before the film is cut. It is preferably 4 times or more, more preferably 5 times or more, and even more preferably 5.5 times or more. The upper limit of the draw ratio is not particularly limited as long as the film is not broken, but is preferably 8 times or less in order to perform uniform drawing. In addition, the draw ratio in this specification is based on the length of the film before extending | stretching, and the state which is not extending | stretched corresponds to 1 time of draw ratios. The thickness of the stretched film (polarizing film) is preferably 25 μm or less, more preferably 23 μm or less, further preferably 20 μm or less, particularly preferably 18 μm or less, 15 μm or less, Furthermore, it may be 10 μm or less. The lower limit of the thickness of the stretched film (polarizing film) is not particularly limited, and may be, for example, 1 μm or more, 2 μm or more, 3 μm or more, and further 5 μm or more.

  In the case of uniaxially stretching a long PVA film, there is no particular limitation on the direction of uniaxial stretching, and uniaxial stretching in the length direction and uniaxial stretching in the lateral direction can be adopted. Since it is obtained, uniaxial stretching in the length direction is preferable. Uniaxial stretching in the length direction can be performed by changing the peripheral speed between the rolls using a stretching apparatus including a plurality of rolls parallel to each other. On the other hand, uniaxial stretching in the transverse direction can be performed using a tenter type stretching machine.

  In the production of the polarizing film, it is preferable to perform a fixing treatment in order to strengthen the adsorption of the dichroic dye to the film. The fixing treatment can be performed by immersing the film in a fixing treatment bath. As the fixing treatment bath used for the fixing treatment, an aqueous solution containing one or more of boron compounds such as boric acid and borax can be used. Moreover, you may add an iodine compound and a metal compound in a fixed treatment bath as needed. The concentration of the boron compound in the fixed treatment bath is generally preferably in the range of 2% by mass to 15% by mass, particularly preferably in the range of 3% by mass to 10% by mass. The temperature of the fixing treatment bath is preferably in the range of 15 ° C. or higher and 60 ° C. or lower, particularly in the range of 25 ° C. or higher and 40 ° C. or lower.

  The drying treatment (heat treatment) is in the range of 30 ° C. or higher and 150 ° C. or lower, particularly in the range of 50 ° C. or higher and 140 ° C. or lower, in order to improve the dimensional stability of the obtained polarizing film and suppress the deterioration of the polarizing performance. It is preferable to carry out with.

  The polarizing film obtained as described above is usually used as a polarizing plate by laminating a protective film that is optically transparent and has mechanical strength on both sides or one side. As the protective film, a cellulose triacetate (TAC) film, a cycloolefin polymer (COP) film, an acetic acid / cellulose butyrate (CAB) film, an acrylic film, a polyester film, or the like is used. Examples of the adhesive for attaching the protective film include PVA adhesives, urethane adhesives, acrylate adhesives, etc. Among them, PVA adhesives are preferable.

  The polarizing plate obtained as described above can be used as a component of an LCD after being coated with an acrylic adhesive or the like and then bonded to a glass substrate. At this time, a retardation film, a viewing angle improving film, a brightness improving film, and the like may be further bonded.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following examples. In addition, each measurement or evaluation method employ | adopted in the following example, a comparative example, and a reference example is shown below.

[Measurement of W _MD30 ]
A rectangular sample having a width direction (TD) of 40 mm × a length direction (MD) of 270 mm was cut out from the center in the width direction of the PVA film. Next, a marked line was put with oily magic (the thickness of the line was 0.3 mm) on the inner side by 10 mm from both ends of the 270 mm length of the sample. The outer part from the marked lines at both ends was sandwiched between commercially available clips (chuck width 40 mm, mass 7.8 g (weight 7.3 g in water)), and one clip was fixed with a rod-shaped jig. After confirming that the distance between the marked lines is 250 mm, the sample with the clip is quickly put into the pure water adjusted to 30 ° C stored in a cylindrical transparent water tank so that the entire sample enters the water. The long side was immersed vertically. Immediately after the immersion, a rod-shaped jig was hooked on the upper part of the water tank, and the long side of the sample was fixed so as to be vertical (vertical). Thereafter, a metal ruler was immersed in water, and the distance between the marked lines was measured 30 seconds after the immersion of the sample. The elongation (W _MD30 ) (unit: mm) was calculated by subtracting the original distance between marked lines (250 mm) from the measured value read in 0.5 mm increments.

[Measurement of _WTD300 ]
A rectangular sample having a width direction (TD) of 270 mm and a length direction (MD) of 40 mm was cut out from the center in the width direction of the PVA film. Next, a marked line was put with oily magic (the thickness of the line was 0.3 mm) on the inner side by 10 mm from both ends of the 270 mm length of the sample. The outer part from the marked lines at both ends was sandwiched between commercially available clips (chuck width 40 mm, mass 7.8 g (weight 7.3 g in water)), and one clip was fixed with a rod-shaped jig. After confirming that the distance between the marked lines is 250 mm, the sample with the clip is quickly put into the pure water adjusted to 30 ° C stored in a cylindrical transparent water tank so that the entire sample enters the water. The long side was immersed vertically. Immediately after the immersion, a rod-shaped jig was hooked on the upper part of the water tank, and the long side of the sample was fixed so as to be vertical (vertical). Thereafter, a metal ruler was immersed in water, and the distance between marked lines was measured 300 seconds after the immersion of the sample. The amount of elongation (W _TD300 ) (unit: mm) was calculated by subtracting the original distance between marked lines (250 mm) from the measured value read in 0.5 mm increments.

[Evaluation of stretchability of PVA film]
As an index of the stretchability of the PVA film, the tension during stretching in the stretching bath was measured, and the stretchability was evaluated according to the following criteria.
◎: 10 MPa or more and 12 MPa or less ○: More than 12 MPa and 15 MPa or less Δ: More than 15 MPa and 18 MPa or less ×: Less than 10 MPa or more than 18 MPa

[Evaluation of edge abnormalities]
The abnormal end of the film in the roll immediately after passing through the swelling bath was evaluated according to the following criteria.
○: Edge abnormalities cannot be confirmed at all △: Edge abnormalities can be slightly confirmed ×: Edge abnormalities can be clearly confirmed

[Evaluation of stained spots on polarizing film]
A light having a luminance of 10,000 cd / m ^{2 in} a dark room after sandwiching the produced polarizing film between two polarizing plates in a crossed Nicol state (single transmittance 42.3%, polarization degree 99.99%) The stained spots when light was transmitted using a box were observed and evaluated according to the following criteria.
◎: Stained spots cannot be confirmed at all ○: Stained spots can be confirmed slightly △: Stained spots can be confirmed relatively clearly ×: Stained spots can be confirmed clearly

[Example 1]
<< Manufacture of PVA film >>
PVA (ethylene-modified PVA obtained by saponifying ethylene-modified polyvinyl acetate obtained by copolymerizing ethylene and vinyl acetate, ethylene unit content of 2.0 mol%, polymerization degree 2,400, saponification Degree of 99.9 mol%) 100 parts by mass, glycerin 10 parts by mass, lauric acid diethanolamide 0.1 parts by mass, and a volatile fraction of 66% by mass of a film-forming stock solution from the T-type slit die to each other with the rotation axis A first drying roll (surface temperature 93.5 ° C., peripheral speed (S ₁ ) 14.5 m / min) of a film forming apparatus including a plurality of parallel drying rolls and a plurality of heat treatment rolls is discharged into a film shape, While drying 90 ° C hot air at a wind speed of 5 m / second on the entire surface of the first drying roll non-contact on one drying roll, it is dried to a volatile content of 15% by mass and peeled off from the first drying roll. .
Next, with the first drying roll non-contact surface of the PVA film facing the second drying roll, while the front and back surfaces of the PVA film are alternately opposed to each drying roll, The PVA membrane was further dried until its volatile content was 5% by mass. In addition, the drying roll (drying roll X) when the volatile content rate of a PVA film | membrane becomes 12 mass% is a 5th drying roll, and surface temperature of each drying roll from a 2nd drying roll to a 5th drying roll is set. The surface temperature of each drying roll after the sixth drying roll was set to 60 ° C.
Thereafter, the PVA film was subjected to heat treatment with a plurality of heat treatment rolls while the front and back surfaces of the PVA film were alternately opposed to each heat treatment roll. At this time, the ratio of the peripheral speed (S _B ) of the heat treatment roll (heat treatment roll B) located on the most downstream side to the peripheral speed (S _A ) of the heat treatment roll (heat treatment roll A) located on the most upstream side (S _B / S _A ) is 0.991, and the surface temperature of each heat treatment roll is 99 to 115 ° C. (the surface temperature of heat treatment roll A is 99 ° C., the surface temperature of heat treatment roll B is 115 ° C.). The ratio (S _B / S ₁ ) of the peripheral speed (S _B ) of the heat treatment roll B to the peripheral speed (S ₁ ) of the first drying roll was 0.965.
After heat-treating as described above, it was wound up to obtain a roll-like PVA film (thickness 45 μm, width 3 m, length 5,000 m, volatile content 3 mass%).
About the obtained PVA film, _WMD30 and _WTD300 were measured according to the above-mentioned method. The results are shown in Table 1.

<Manufacture of polarizing film>
The PVA film obtained above was unwound from a roll and slit to continuously cut out a portion having a width of 650 mm from the central portion in the width direction, and then subjected to each treatment to continuously produce a polarizing film.
That is, the PVA film was immersed in a swelling bath (water temperature 30 ° C.), followed by a dyeing bath (water temperature 32 ° C., an aqueous solution containing 0.07 mass% iodine and 1.6 mass% potassium iodide), Fixed treatment bath (water temperature 32 ° C., aqueous solution containing 2.6% by mass of boric acid), stretching bath (water temperature 58 ° C., aqueous solution containing 2.8% by mass of boric acid and 5.0% by mass of potassium iodide) The film is immersed in a washing bath (water temperature 22 ° C., aqueous solution containing 1.5% by mass of boric acid and 5.0% by mass of potassium iodide) and dried in a drying furnace (temperature 40 ° C.) to obtain a polarizing film. Manufactured. In addition, as time to immerse in a swelling bath, in order to respond | correspond to a thin PVA film, the comparatively short 40 second was employ | adopted. The total draw ratio was 6.3 times.
In manufacture of the said polarizing film, while extending | stretching the PVA film used according to the above-mentioned method, evaluation of edge part abnormality was performed. Further, the obtained polarizing film was evaluated for stained spots according to the method described above. The results are shown in Table 1.

<< Examples 2 and 3 and Comparative Examples 1 to 3 >>
A PVA film was produced in the same manner as in Example 1 except that the production conditions of the PVA film were as shown in Table 1, and a polarizing film was produced in the same manner as in Example 1. Each evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

Claims (12)

A polyvinyl alcohol polymer film having a thickness of 50 μm or less, and a sample of the polyvinyl alcohol polymer film in the length direction at a portion of 250 mm in the length direction before immersion when immersed in water at 30 ° C. for 30 seconds. _Elongation amount W _MD30 is 35 mm or more and 60 mm or less, and when the sample of the polyvinyl alcohol polymer film is immersed in water at 30 ° C. for 300 seconds, the elongation amount W _TD300 in the width direction in the width direction 250 mm portion before immersion is A polyvinyl alcohol polymer film having a thickness of 53 mm or more and 65 mm or less.   The polyvinyl alcohol polymer film according to claim 1, wherein the width is 2 m or more.   The polyvinyl alcohol polymer film according to claim 1, which is a raw film for producing an optical film.   The polyvinyl alcohol polymer film according to claim 3, wherein the optical film is a polarizing film. A method for producing a polyvinyl alcohol polymer film having a thickness of 50 μm or less, wherein a film forming apparatus comprising a drying roll and a heat treatment roll having rotation axes parallel to each other is used, and polyvinyl on the first drying roll of the film forming apparatus A film-forming stock solution containing an alcohol polymer is discharged into a film and dried, followed by further drying with a drying roll, and then heat treatment with a plurality of heat treatment rolls to produce a polyvinyl alcohol polymer film, where When the heat treatment roll located on the most upstream side is the heat treatment roll A and the heat treatment roll located on the most downstream side is the heat treatment roll B, the volatile fraction of the polyvinyl alcohol polymer film immediately before contacting the heat treatment roll A There is at most 3 mass% or more and 7 wt%, the ratio _(S B / S of the peripheral speed of the heat treatment roll a peripheral speed of the heat treatment roll B to _{(S a) (S B)} ) Is 0.999 or less, the surface temperature of each heat treatment roll from the heated rollers A to the heat treatment roll B is 121 ° C. or less all of which are 87 ° C., the manufacturing method.   When the drying roll when the volatile fraction of the polyvinyl alcohol polymer film is 12% by mass is the drying roll X and the drying roll located immediately before the heat treatment roll A is the drying roll Y, the first drying roll The surface temperature of each drying roll from the drying roll X to the drying roll X is 70 ° C. or more, and the surface temperature of each drying roll from the drying roll located immediately after the drying roll X to the drying roll Y is 40 ° C. to 70 ° C. The manufacturing method of Claim 5 which is less than degreeC. The ratio (S _B / S ₁ ) of the peripheral speed (S _B ) of the heat treatment roll B to the peripheral speed (S ₁ ) of the first drying roll is 0.900 or more and 1.050 or less. Manufacturing method.   When the drying roll located immediately before the heat treatment roll A is the drying roll Y, between the first drying roll and the drying roll Y, the front and back surfaces of the polyvinyl alcohol polymer film are alternately placed on each drying roll. The manufacturing method of any one of Claims 5-7 made to oppose.   The manufacturing method of any one of Claims 5-8 which is a manufacturing method of the raw film for optical film manufacture.   The manufacturing method according to claim 9, wherein the optical film is a polarizing film.   An optical film produced from the polyvinyl alcohol polymer film according to claim 3. A polarizing film produced from the polyvinyl alcohol polymer film according to claim 4.