JP6630677B2 - Polyvinyl alcohol polymer film and method for producing the same - Google Patents

Description

  The present invention relates to a polyvinyl alcohol-based polymer film having a thickness of 50 μm or less (hereinafter, “polyvinyl alcohol-based polymer” may be abbreviated as “PVA”), a method for producing the same, and polarized light produced from the PVA film. The present invention relates to an optical film such as a film.

  A polarizing plate having a light transmitting 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 wristwatches in the early stages of development, from notebook computers, LCD monitors, LCD color projectors, LCD TVs, in-car navigation systems, mobile phones, and measurement equipment used indoors and outdoors. Is expanding to various fields. In particular, in applications such as wall-mounted televisions and mobile phones, thinning of LCDs is strongly demanded from the viewpoint of weight reduction and cost reduction, and for this purpose, thinning of polarizing plates is effective.

  A polarizing plate is generally a method of unwinding a long PVA film wound in a roll shape and uniaxially stretching and then dyeing using iodine or a dichroic dye, and dyeing the unwound PVA film and uniaxially stretching. After the method of performing a fixing treatment with a boron compound, a polarizing film is produced by a method of performing a fixing treatment simultaneously with dyeing in any of the above-described methods, and a cellulose triacetate film on one or both surfaces of the resulting polarizing film or It is manufactured industrially by laminating a protective film such as an acetic acid / butyrate cellulose film.

  To reduce the thickness of the polarizing plate, it is effective to reduce the thickness of the protective film, which occupies a large part of the thickness of the polarizing plate. However, the polarizing film manufactured using a conventional thickness of PVA film has a large shrinkage stress. When only the thickness is reduced, there is a problem that the entire polarizing plate is easily deformed. To solve this problem, it is conceivable to reduce the thickness of the polarizing film itself by using a thinner PVA film as a raw film.

By the way, as a PVA film excellent in stretchability and capable of obtaining a polarizing film with less staining unevenness (uniformity in the cross direction in the width direction), the width when the film is immersed in water at 30 ° C. for 5 minutes and swollen. (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 elongates in its length and width directions. However, a thin PVA film has a relatively thick PVA film due to a high drying speed in the film forming process. The amount of elongation in the length direction during swelling relative to the amount of elongation in the width direction during swelling tends to be relatively smaller than that of a film. Here, by changing the crystallinity of the PVA film by changing the heat treatment conditions or the like, it is possible to increase or decrease both the elongation in the length direction and the width direction during swelling. However, in a thin PVA film, if the elongation in the length direction is increased to a specific value or more in order to improve the stretchability, the elongation in the width direction becomes too large. When the polarizing film is manufactured by the manufacturing apparatus of (1), the end of the swollen PVA film is in contact with the wall of the apparatus, so that an abnormal end is easily generated. On the other hand, when the amount of elongation in the width direction is reduced to a specific value or less to eliminate the end abnormalities, the amount of elongation in the length direction becomes too small and the stretchability is reduced, and in some cases, the obtained polarizing film is dyed. Spots are likely to occur. Therefore, it is difficult to obtain a thin PVA film that is excellent in stretchability and that does not easily cause edge abnormalities during use, and a thin PVA film that can easily produce a thin polarizing film with reduced staining spots. This is not achieved by the technique of Patent Document 1 described above.

  Therefore, the present invention provides a thin PVA film that is excellent in stretchability and is less likely to cause edge abnormalities during use, and preferably a thin PVA film that can easily produce a thin polarizing film with reduced stain spots. The purpose is to. Another object of the present invention is to provide an optical film such as a polarizing film manufactured from the PVA film.

  The present inventors have conducted intensive studies to achieve the above object, and as a result, in a thin PVA film, the amount of elongation in the longitudinal direction (MD) when immersed in water at 30 ° C. for 30 seconds is specified. When the elongation in the width direction (TD) when immersed in water at 30 ° C. for 300 seconds is adjusted to a specific range, it is excellent in stretchability, despite being a thin PVA film. It has been found that a PVA film that can easily produce a thin polarizing film in which edge abnormalities are unlikely to occur and in which stain spots are reduced is found. Furthermore, the present inventors, when manufacturing a thin PVA film using a film forming apparatus having a plurality of drying rolls and a plurality of heat treatment rolls whose rotation axes are parallel to each other, a heat treatment roll positioned at the most upstream side By making the ratio of the peripheral speed to the heat treatment roll located on the most downstream side in a specific range and the surface temperature of the heat treatment roll in a specific range, the above PVA film can be produced smoothly and continuously with good productivity. I found that I can do it. 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,
A sample of 40 mm in width direction (TD) x 270 mm in length direction (MD) is cut out from the center of the PVA film in the width direction , and a marking line is inserted inwardly by 10 mm from both ends of the 270 mm length of the sample. After clipping the outside part with clips (chuck width 40 mm, mass 7.8 g (weight in water 7.3 g)), fix one clip with a rod-shaped jig, and confirm that the distance between the marked lines is 250 mm The sample with the clip was immediately immersed vertically (vertically) in pure water adjusted to 30 ° C. stored in a water tank so that the entire sample could enter the water. The sample jig was hooked on the upper part and fixed so that the long side of the sample was vertical (vertical). The distance between the reference lines measured 30 seconds after immersion of the sample and the original distance between the reference lines (250 mm) Elongation amount _{W MD30} minus is at 60mm or less than 35mm,
A sample of 270 mm in width direction (TD) × 40 mm in length direction (MD) is cut out from the center in the width direction of the PVA film , and a marking line is inserted inwardly by 10 mm from both ends of the 270 mm length of the sample. After clipping the outside part with clips (chuck width 40 mm, mass 7.8 g (weight in water 7.3 g)), fix one clip with a rod-shaped jig, and confirm that the distance between the marked lines is 250 mm The sample with the clip was immediately immersed vertically (vertically) in pure water adjusted to 30 ° C. stored in a water tank so that the entire sample could enter the water. The rod-shaped jig was hooked on the upper part, and the long side of the sample was fixed vertically (vertically), and the original distance between the reference lines (250 elongation amount _{W TD300} minus m) is less than 53 mm 65 mm, PVA film;
[2] The PVA film of the above-mentioned [1], wherein the width is 2 m or more;
[3] The PVA film according to the above [1] or [2], which is a raw film for producing an optical film;
[4] The PVA film of the above-mentioned [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, using a film forming apparatus including a drying roll and a heat treatment roll whose rotation axes are parallel to each other, and depositing PVA on a first drying roll of the film forming apparatus. The film-forming stock solution is discharged in the form of a film and dried, followed by further drying with a drying roll, and then heat-treating with a plurality of heat-treating rolls to produce a PVA film, wherein the heat-treating roll located at the most upstream side Is the heat treatment roll A, and the heat treatment roll located at the most downstream side is the heat treatment roll B, and the volatile content of the PVA film immediately before coming into contact with the heat treatment roll A is 3% by mass or more and 7% by mass or less. The ratio (SB / SA) of the peripheral speed (SB) of heat treatment roll B to the peripheral speed (SA) of roll A is 0.999 or less, and the surface of each heat treatment roll from heat treatment roll A to heat treatment roll B A production method wherein the temperature is from 87 ° C to 121 ° C;
[6] When the drying roll when the volatile content 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. Less than the production method of the above [5];
[7] The above-mentioned [5] or [6], wherein the ratio (SB / S1) of the peripheral speed (SB) of the heat treatment roll B to the peripheral speed (S1) of the first drying roll is 0.900 or more and 1.050 or less. Production method;
[8] 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 PVA film are alternately opposed to each drying roll. The production method according to any one of the above [5] to [7];
[9] The method according to any one of the above [5] to [8], which is a method for producing a raw film for producing an optical film;
[10] The method of the above-mentioned [9], wherein the optical film is a polarizing film;
[11] An optical film produced from the PVA film of the above [3];
[12] A polarizing film produced from the PVA film of the above [4];
About.

  According to the present invention, a thin PVA film that is excellent in stretchability, hardly causes edge abnormalities during use, and can easily produce a thin polarizing film with reduced stain spots, and from the PVA film An optical film such as a manufactured polarizing film is provided. Further, according to the present invention, there is provided a method for producing a PVA film capable of producing the PVA film smoothly and continuously with good productivity.

Hereinafter, the present invention will be described in detail.
[PVA film]
The PVA film of the present invention has a thickness of 50 μm or less. The PVA film of the present invention has a lengthwise elongation _WMD30 of 35 mm or more and 60 mm or less in a 250 mm long portion before immersion when the sample is immersed in water at 30 ° C. for 30 seconds. Furthermore, when the sample is immersed in water at 30 ° C. for 300 seconds, the PVA film of the present invention has an elongation amount W _TD300 in the width direction of 250 mm before immersion of more than 53 mm and not more than 65 mm.

  The PVA film of the present invention needs to have a thickness of 50 μm or less, for example, 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 more preferably 35 μm or less, particularly preferably 30 μm or less, and may be 20 μm or less. As described above, 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 in consideration of the handleability of the PVA film, the processability during the production of the optical film, the optical performance of the obtained optical film (such as the polarizing performance of the polarizing film), and the like. The thickness is preferably at least 3 μm, more preferably at least 5 μm, further preferably at least 7 μm, particularly preferably at least 10 μm. The thickness of the PVA film can be determined as an average value by measuring the thickness at any five points.

The PVA film of the present invention has a specific range of elongation in the machine direction (MD) 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 at a portion of 250 mm in the length direction before immersion is 35 mm or more and 60 mm or less. In range. If W _MD30 is less than 35 mm, the plasticization of the film is insufficient due to insufficient swelling of the PVA film during use, and the stretchability is reduced. In this respect, the W _MD30 is preferably _equal to or greater than 37 mm, more preferably _equal to or greater than 39 mm, and still more preferably _equal to or greater than 42 mm. Further, when the W _MD30 exceeds 60 mm, the degree of swelling of the PVA film tends to be excessive, and the PVA film becomes wrinkled or broken due to sagging of the PVA film, thereby causing breakage as a base point. Can occur. In this respect, the W _MD30 is preferably equal to or less than 55 mm, more preferably equal to or less than 50 mm, further preferably equal to or less than 47 mm, and particularly preferably equal to or less than 46 mm. In addition, in _WMD30 , the amount of elongation when a sample is immersed in water at 30 ° C. for 30 seconds is specified. This is because when a thin PVA film is used to manufacture an optical film such as a polarizing film, a thin film is used. From the viewpoint of preventing the PVA film from dissolving, a shorter time is often used as a process time in a process performed before the stretching process such as a swelling process, and a time of 30 seconds corresponds well to the process time. This is because the relationship with stretchability is particularly large.

Further, 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 a sample cut out from the PVA film of the present invention is immersed in water at 30 ° C. for 300 seconds, the elongation amount W _TD300 in the width direction at a portion of 250 mm in the width direction before immersion is in a range of 53 mm or more and 65 mm or less. It is in. If W _TD300 is less than 53 mm, stains are likely to occur on the obtained polarizing film. In this respect, the W _TD300 is preferably _equal to or greater than 54 mm, more preferably _equal to or greater than 55 mm, and still more preferably _equal to or greater than 57 mm. Further, when the _{WTD 300} exceeds 65 mm, the PVA film spreads too much in the width direction during use, so that an edge abnormality such as film breakage tends to occur. In this respect, the W _TD300 is preferably equal to or less than 62 mm, and more preferably equal to or less than 60 mm. Although defines the amount of elongation when immersed for 300 seconds the sample in W _TD300 to 30 ° C. water, which is correlated to the Senshokumadara of the W _MD300 and a polarization film ends in use abnormalities or obtained Because there is.

The above-mentioned _{WMD 30} can be obtained by the following method. That is, first, a rectangular sample of 40 mm in the width direction (TD) × 270 mm in the length direction (MD) is cut out from the PVA film to be measured. Here, the sample may be cut, for example, from the center in the width direction of the target PVA film. Next, a marked line is drawn by oil-based magic (thickness of the line is 0.3 mm) inside the sample by 10 mm from both ends of the 270 mm length. The portion outside 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 by a bar-shaped jig such as a number line. After confirming that the distance between the marked lines is 250 mm, place the clipped sample in pure water controlled at 30 ° C stored in a cylindrical transparent water tank (such as a graduated cylinder) so that the entire sample enters the water. Then, immediately immerse the long side of the sample vertically. Immediately after immersion, a rod-shaped jig is hooked on the upper part of the water tank, and the sample is fixed so that the long side of the sample is vertical (vertical). Thereafter, the metal ruler is immersed in water, and the distance between the marked lines is measured 30 seconds after the immersion of the sample. The original distance between the reference lines (250 mm) is subtracted from the measured values read at 0.5 mm intervals to calculate the amount of elongation (W _MD30 ) (unit: mm).

On the other hand, the above-mentioned W _TD300 can be obtained by the following method. That is, first, a rectangular sample of 270 mm in the width direction (TD) × 40 mm in the length direction (MD) is cut out from the PVA film to be measured. Here, the sample may be cut, for example, from the center in the width direction of the target PVA film. Next, a marked line is drawn by oil-based magic (thickness of the line is 0.3 mm) inside the sample by 10 mm from both ends of the 270 mm length. The portion outside 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 by a bar-shaped jig such as a number line. After confirming that the distance between the marked lines is 250 mm, place the clipped sample in pure water controlled at 30 ° C stored in a cylindrical transparent water tank (such as a graduated cylinder) so that the entire sample enters the water. Then, immediately immerse the long side of the sample vertically. Immediately after immersion, a rod-shaped jig is hooked on the upper part of the water tank, and the sample is fixed so that the long side of the sample is vertical (vertical). Thereafter, the metal ruler is immersed in water, and the distance between the marked lines is measured 300 seconds after the immersion of the sample. The original inter-marker distance (250 mm) is subtracted from the measured value read at 0.5 mm intervals to calculate the amount of elongation (W _TD300 ) (unit: mm).

  As the PVA constituting the PVA film of the present invention, a PVA film produced by saponifying a polyvinyl ester-based polymer obtained by polymerizing a vinyl ester can be used. Examples of the vinyl ester include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and vinyl versatate. Among the above-mentioned vinyl esters, vinyl acetate is preferable from the viewpoints of availability, cost, and ease of PVA production.

  The above-mentioned polyvinyl ester-based polymer is preferably obtained by using only one or two or more vinyl esters as a monomer, and is obtained by using only one vinyl ester as a monomer. Is more preferable, but a copolymer of one or more vinyl esters and another monomer copolymerizable therewith may be used.

  Other monomers copolymerizable with such vinyl esters include, for example, ethylene; olefins having 3 to 30 carbon atoms such as propylene, 1-butene and isobutene (α-olefins and the like); acrylic acid or salts 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 And acrylates such as octadecyl acrylate; methacrylic acid or a salt 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-methylacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide, diacetoneacrylamide, acrylamidepropanesulfonic acid or a salt thereof, acrylamidopropyldimethylamine or a salt thereof, Acrylamide derivatives such as N-methylol acrylamide or derivatives thereof; methacrylamide; N-methyl methacrylamide, N-ethyl methacrylamide, methacrylamide propanesulfonic acid or a salt thereof, methacrylamidopropyl dimethylamine or a salt thereof, N-methylol methacrylamide 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 and stearyl vinyl ether; acrylonitrile, methacryloyl Vinyl cyanide such as nitrile; vinyl halide such as vinyl chloride, vinylidene chloride, vinyl fluoride and vinylidene fluoride; allyl compound such as allyl acetate and allyl chloride; maleic acid or a salt, ester or acid anhydride thereof; itaconic acid Or a salt, ester or acid anhydride thereof; a vinylsilyl compound such as vinyltrimethoxysilane; and isopropenyl acetate. The polyvinyl ester-based polymer can have structural units derived from one or more of these other monomers.

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

  The above PVA may be modified with one or more kinds of graft copolymerizable monomers. Examples of the graft copolymerizable monomer include an unsaturated carboxylic acid or a derivative thereof; an unsaturated sulfonic acid or a derivative thereof; and an α-olefin having 2 to 30 carbon atoms. 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 above-mentioned PVA, a part of the hydroxyl groups may or may not be crosslinked. Further, in the above PVA, a part of its hydroxyl group may react with an aldehyde compound such as acetaldehyde or butyl aldehyde to form an acetal structure, or may not react with these compounds to form an acetal structure. May be.

  The degree of polymerization of PVA is not particularly limited, but is preferably 500 or more, more preferably 1,000 or more, from the viewpoint of the strength of the PVA film and the durability of the optical film manufactured from the PVA film. It is more preferably at least 1,500, particularly preferably at least 2,000. On the other hand, if the degree of polymerization is too high, the production cost tends to increase, and poor processability at the time of film formation tends to be caused. Therefore, the degree of polymerization of PVA is preferably 10,000 or less, more preferably 9,000 or less. More preferably, it is more preferably 8,000 or less, particularly preferably 7,000 or less. In addition, the polymerization degree of PVA in this specification means the average polymerization degree measured according to the description of JISK6726-1994.

  Although the saponification degree of PVA is not particularly limited, it is preferably 90 mol% or more, more preferably 95 mol% or more, from the viewpoint of the optical performance and durability of the optical film produced from the PVA film, The content is more 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 degree of saponification 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 a structural unit (typically, a vinyl ester unit) and a vinyl alcohol unit of PVA which can be converted into a vinyl alcohol unit by saponification. It means the ratio (mol%) occupied by the number of moles of the vinyl alcohol unit. The degree of saponification of PVA can be measured according to the description of JIS K6726-1994.

  As the above-mentioned PVA, one kind of PVA may be used alone, or two or more kinds of PVA having different types of modification, modification rate, degree of polymerization, degree of saponification and the like may be used in combination. However, in the case where the PVA film of the present invention is required to have excellent secondary workability, such as when used as a raw film in the production of an optical film, the PVA film may have an acidic property such as a carboxyl group or a sulfonic acid group. A PVA having a functional group; a PVA having an acid anhydride group; a PVA having a basic functional group such as an amino group; The secondary processing property of the PVA film may decrease due to the crosslinking reaction of the PVA film. Therefore, in the above case, the PVA film preferably does not contain any of PVA having an acidic functional group, PVA having an acid anhydride group, PVA having a basic functional group, and a neutralized product thereof. As PVA produced by saponifying a polyvinyl ester-based polymer obtained using only vinyl ester as a monomer, and / or vinyl ester and ethylene and / or olefin having 3 to 30 carbon atoms only. 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 polymer obtained using only a vinyl ester as a monomer PVA produced by saponifying a polymer and / or vinyl ester That it is more preferably containing only PVA produced by saponifying a polyvinyl ester polymer obtained by using a monomer N'nomi.

  The content of PVA 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 more preferably in the range of 85 to 100% by mass. More preferred.

  The PVA film of the present invention preferably contains a plasticizer because it can improve the mechanical properties such as impact strength and the processability during secondary processing. As the plasticizer, a 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 include 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 based on 100 parts by mass of PVA contained in the PVA film. More preferably, it is preferably at most 30 parts by mass, more preferably at most 25 parts by mass, even more preferably at most 20 parts by mass. 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 the releasability from a film forming apparatus when producing the PVA film. The type of the surfactant is not particularly limited, and examples thereof include an anionic surfactant and a nonionic surfactant.

  Examples of the anionic surfactant include a carboxylic acid type such as potassium laurate; a sulfate ester type such as octyl sulfate; and a sulfonic acid type such as dodecylbenzenesulfonate.

  Nonionic surfactants include, for example, alkyl ether type such as polyoxyethylene oleyl ether; alkyl phenyl ether type such as polyoxyethylene octyl phenyl ether; alkyl ester type such as polyoxyethylene laurate; polyoxyethylene lauryl amino Alkylamine type such as ether; alkylamide type such as polyoxyethylene lauric amide; polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether; alkanolamide type such as lauric acid diethanolamide and oleic acid diethanolamide; polyoxy Allyl phenyl ether type such as alkylene allyl phenyl ether and the like can be mentioned.

  The PVA film of the present invention can include one or more of these surfactants. Among these surfactants, nonionic surfactants are preferable, and alkanolamide-type surfactants are more preferable, because they are excellent in the effect of reducing film surface abnormality during film formation, and aliphatic carboxylic acids (for example, And a dialkanolamide (e.g., diethanolamide) having a saturated or unsaturated aliphatic carboxylic acid having 8 to 30 carbon atoms.

  Since the content of the surfactant in the PVA film, the handleability of the PVA film, and the releasability from the film forming apparatus when producing the PVA film is further improved, and the occurrence of blocking can be reduced, Based on 100 parts by mass of PVA contained in the PVA film, it is preferably at least 0.01 part by mass, more preferably at least 0.02 part by mass, even more preferably at least 0.05 part by mass, Further, it is preferably at most 1 part by mass, more preferably at most 0.5 part by mass, even more preferably at most 0.3 part by mass.

  The PVA film of the present invention may contain a stabilizer (antioxidant, ultraviolet absorber, heat stabilizer, etc.), a compatibilizer, an antiblocking agent, a flame retardant, an antistatic agent, a lubricant, a dispersant, if necessary. Various additives such as a fluidizing agent and an antibacterial agent may be included. The PVA film of the present invention can include 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. And more preferably 4% by 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.

  Although the shape of the PVA film of the present invention is not particularly limited, a more uniform PVA film can be continuously and smoothly produced, and even when an optical film such as a polarizing film is produced using the same, the PVA film can be produced continuously. It is preferable that the film is a long film because it can be used. The long film is preferably formed into a film roll by winding it around a cylindrical core. In the case of a long film, the length of the PVA film (the length in the length direction (MD)) is not particularly limited and can be appropriately set depending on the application and the like. In the case where the PVA film is taken out and used, for example, the longer the length of the PVA film, the more the loss when switching the film roll can be reduced. Therefore, 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, particularly preferably 5,000 m or more, and even more preferably 8,000 m or more. Although there is no particular upper limit on the length, the length can be, for example, 50,000 m or less, and further 20,000 m or less.

  The width of the PVA film of the present invention is not particularly limited, and can be appropriately set according to the use of the PVA film or an optical film such as a polarizing film produced therefrom. In view of the progress of screen formation, if the width of the PVA film is 2 m or more, more preferably 3 m or more, and still more preferably 4 m or more, it is suitable for these uses. On the other hand, if the width of the PVA film is too wide, it becomes difficult to uniformly perform the uniaxial stretching itself when manufacturing an optical film using a practically used apparatus. Therefore, the width of the PVA film should be 8 m or less. Is preferably 7 m or less, and more preferably 6 m or less.

[Production method of PVA film]
The method for producing the PVA film of the present invention is not particularly limited, but according to the following production method of the present invention, the PVA film of the present invention can be produced smoothly and continuously with good 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. The film-forming stock solution containing PVA is discharged in a film form and dried, then further dried with a drying roll, and then heat-treated with a plurality of heat-treatment rolls to produce a PVA film. When the positioned heat treatment roll is heat treatment roll A and the most downstream heat treatment roll is heat treatment roll B, the volatile content of the PVA film immediately before contact with heat treatment roll A is 3% by mass or more and 7% by 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. , The surface temperature of each heat treatment roll is 87 ° C. or more and 121 ° C. or less.

  In a film forming apparatus having a drying roll and a heat treatment roll whose rotation axes are parallel to each other used for the production of the PVA film, the number of the drying rolls may be 4 or more because a more uniform PVA film is obtained. The number is more preferably 5 or more, still more preferably 6 or more, particularly preferably 8 or more, more preferably 30 or less, and more preferably 20 or less. preferable. In the present specification, of the above-mentioned drying rolls, the drying roll located at the most upstream side (drying roll for discharging the stock solution) is referred to as a first drying roll, and the remaining drying rolls are downstream from the first drying roll. In the order toward the side, they are referred to as a second drying roll, a third drying roll, a fourth drying roll, and so on. Further, the drying roll when the volatile content of the PVA membrane during film formation becomes 12% by mass (when the mass ratio between the two drying rolls becomes 12% by mass, the drying roll on the downstream side thereof) is “dried”. The drying roll located immediately before the heat treatment roll is referred to as “dry roll Y”.

  Further, in the above film forming apparatus, the number of heat treatment rolls is not particularly limited as long as it is two or more, but from the viewpoint of uniformly heat treating the front and back surfaces of the PVA film, the number of heat treatment rolls is three or more. The number is preferably 4 or more, more preferably 10 or less, and even more preferably 8 or less. As described above, in the present specification, the heat treatment roll located at the most upstream side among the heat treatment rolls is referred to as “heat treatment roll A”, and the heat treatment roll located at the most downstream side is referred to as “heat treatment roll B”.

  The drying roll and / or the heat treatment roll are preferably formed of, for example, a metal such as nickel, chromium, copper, iron, and stainless steel. In particular, a metal material in which the surface of the roll is less likely to corrode and has a mirror gloss Is more preferably formed. Further, in order to enhance the durability of the drying roll and / or the heat treatment roll, a roll formed by plating a single layer or a combination of two or more layers of a nickel layer, a chromium layer, a nickel / chromium alloy layer, etc. is used as the drying roll and / or the heat treatment roll. Preferably, it is used.

  In drying the PVA film using a plurality of drying rolls, the PVA film can be dried more uniformly, and in particular, PVA film can be dried at the time of secondary processing of the PVA film obtained by reducing the difference in physical properties between the front and back surfaces of the PVA film. From the viewpoint of preventing the film from curling, it is preferable that the front and back surfaces of the PVA film are alternately opposed to the respective drying rolls from the first drying roll to 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, in any part of the PVA film, the film surface in contact with the first drying roll (the first drying roll contact surface) and the first drying roll It is preferable that the film is dried so that the film surface that is not in contact with the roll (the first dry roll non-contact surface) alternately faces each of the drying rolls from the first drying roll to the drying roll Y.

  In addition, even when the PVA film is heat-treated using a plurality of heat treatment rolls, the heat treatment can be performed more uniformly. It is preferred that the front and back surfaces of the above are alternately opposed.

  In the above-mentioned production method, a film-forming stock solution containing PVA is discharged in a film form on a first drying roll of a film-forming apparatus and dried. In discharging the film-forming stock solution, for example, using a known film-shaped discharging device (film-like casting device) such as a T-shaped slit die, a hopper plate, an I-die, and a lip coater die, the film forming stock solution is used. May be discharged (cast) on the first drying roll in the form of a film. At this time, the thickness of the obtained PVA film can be adjusted by adjusting the ejection amount by adjusting the film-shaped ejection device or the like.

  The stock solution containing PVA can be prepared by mixing PVA with a liquid medium to form a solution, or by melting a PVA chip containing a liquid medium or the like to form a molten liquid. Preparation of the film forming stock solution can be performed using a stirring type mixing device, a melt extruder, or the like. Examples of the above liquid medium include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylenediamine, diethylenetriamine, and the like.These liquid media can be used alone. Alternatively, two or more kinds may be used in combination. Among these, water, dimethyl sulfoxide, or a mixture of both is preferably used, and water is more preferably used.

  It is preferable that one or more of the plasticizers, surfactants, various additives, and the like described above in the description of the PVA film be mixed in the above-described amount in the film-forming stock solution, if desired.

The volatile content of the film forming solution is preferably in the range of 50% by mass to 90% by mass, and the volatile content is more preferably 55% by mass or more, and is 80% by mass or less. Is more preferable. If the volatile content is too low, the viscosity of the stock solution may be too high to make the 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. The term “volatile content of the film-forming stock solution” as used herein refers to the volatile content determined by the following equation (1).
Volatile content (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 more and 120 ° C. or less from the viewpoint of uniformity of drying of the PVA film, productivity, and the like, and the surface temperature is 85 ° C. or more. Is more preferably 90 ° C. or higher, particularly preferably 93 ° C. or higher, further 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 less, foaming of the PVA film can be more effectively suppressed.

  Drying of the film-forming stock solution discharged in the form of a film on the first drying roll may be performed only by heat from the first drying roll. It is possible to apply heat from both sides of the PVA film to perform drying by spraying hot air on the surface or heating from the side of the first drying roll non-contact surface with an infrared heater. Preferred from the point. Further, the PVA film can 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, and more preferably 10 m / min, from the viewpoint of the uniformity of drying of the PVA film, the drying speed, and the productivity of the PVA film. It is more preferably at least 12 m / min and at most 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 tends to decrease. If the ratio is too high, peeling from the first drying roll tends to be difficult, and in some cases, the film may be broken or spots may be easily generated. From the above viewpoint, the volatile content 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 more preferably 15% by mass or more. More preferably, the content is 30% by mass or less, more preferably 27% by mass or less, even more 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 equation (2).
Volatile content of the PVA film _{(wt%) = 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) after drying for an hour is shown.)

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

  In drying the PVA membrane using a plurality of drying rolls, there is no particular limitation on the surface temperature of each drying roll, 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. From the viewpoint that a PVA film can be more efficiently obtained, the temperature is preferably 70 ° C. or higher, more preferably 72 ° C. or higher, further preferably 73 ° C. or higher, and 120 ° C. It is more preferably at most 105 ° C, more preferably at most 105 ° C, particularly preferably at most 99 ° C. The surface temperature of each of the drying rolls from the second drying roll to the drying roll X is 90 ° C. or lower, 85 ° C. or lower, and further 80 ° C. or lower, because the above-mentioned PVA film of the present invention can be obtained more efficiently. It may be.

  In addition, the surface temperature of each of the drying rolls from the drying roll located immediately after the drying roll X to the drying roll Y can improve drying uniformity while maintaining an appropriate drying temperature. From the viewpoint that the PVA film of the above can be obtained more efficiently, it is preferable that all are 40 ° C. or more and less than 70 ° C., and the surface temperatures are more preferably 45 ° C. or more, and 50 ° C. or more. The temperature is more preferably 55 ° C. or higher, more preferably 65 ° C. or lower, and even more 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 difference in physical properties between the front and back surfaces of the PVA film can be reduced, and its secondary workability can be improved. The volatile content of the PVA film immediately before being subjected to the heat treatment, that is, the PVA film immediately before being brought into contact with the heat treatment roll (heat treatment roll A) located on the most upstream side, can be effectively heat-treated. It is necessary to be 3% by mass or more and 7% by mass or less, and the volatile content is preferably 4% by mass or more, and more preferably 6% by 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, the _{WMD 30 of the} obtained PVA film decreases. 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, more preferably 0.993 or less. From the viewpoint of effectively preventing wrinkles from occurring in the obtained PVA film, the ratio (S _B / S _A ) is preferably 0.985 or more, and more preferably 0.988 or more. More preferably, there is.

In heat-treating the PVA film using a plurality of heat treatment rolls, the surface temperature of each heat treatment roll from heat treatment roll A to heat treatment roll B needs to be 87 ° C. or more and 121 ° C. or less. If the surface temperature is less than 87 ° C., the value of W _TD300 of the obtained PVA film is too high, and if the surface temperature exceeds 121 ° C., the value of W _TD300 of the obtained PVA film is too low. Since the PVA film of the present invention can be obtained more efficiently, the surface temperature is preferably 92 ° C. or higher, more preferably 93 ° C. or higher, and 119 ° C. or lower. It 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 or partly 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, but the surface temperature of the heat treatment roll B is higher than the surface temperature of the heat treatment roll A by 5 ° C. or more. Is preferably higher than 10 ° C., more preferably higher than 12 ° C., particularly preferably higher than 15 ° C., more preferably higher than 25 ° C., more preferably higher than 20 ° C., and 18 It is more preferable that the temperature is higher than 0 ° 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 is such that the above-described PVA film of the present invention can be obtained more efficiently. Therefore, the ratio is preferably in the range of 0.900 or more and 1.050 or less, and the ratio (S _B / S ₁ ) is more preferably 0.920 or more, and further preferably 0.940 or more. Preferably, it is particularly preferably 0.950 or more, more preferably 1.020 or less, further preferably 1.010 or less, particularly preferably 1.000 or less.

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

  The volatile content of the PVA film finally obtained by the above series of processing is preferably in the range of 1% by mass or more and 5% by mass or less, and the volatile content is preferably 2% by mass or more. Preferably, it is more preferably at most 4% by mass.

[Use of PVA film]
The use of the PVA film of the present invention is not particularly limited, but since it has excellent stretchability and is unlikely to cause edge abnormalities during use, the PVA film of the present invention is used as a raw film when producing 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, a thin polarizing film with reduced staining spots can be easily produced. Therefore, the PVA film of the present invention is more preferably used as a raw film when 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 itself of the present invention, or a swelling treatment or the like described later is performed. The resulting PVA film derived from the PVA film of the present invention (hereinafter, the “PVA film derived from the PVA film of the present invention” and the “PVA film derived from the PVA film of the present invention” are 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 conventionally employed method may be employed. Examples of such a method include a method of dyeing and uniaxially stretching a PVA film according to the present invention, and a method of uniaxially stretching a PVA film according to the present invention containing a dichroic dye. No. As a more specific method for producing a polarizing film, a method of subjecting a PVA film according to the present invention to swelling, dyeing, uniaxial stretching, and, if necessary, further performing a fixing treatment, a drying treatment, a heat treatment, and the like. Is mentioned. In this case, the order of each process such as swelling, dyeing, uniaxial stretching, and fixing is not particularly limited, and one or two or more processes can be performed simultaneously. Further, one or two or more of the processes can be performed twice or more.

  Swelling can be performed by immersing the PVA film according to the present invention in water. The temperature of water when immersed in water is preferably in the range of 20 ° C. or more and 40 ° C. or less, and the temperature is more preferably 22 ° C. or more, and even more preferably 25 ° C. or more. The temperature is more preferably 38 ° C. or lower, and further preferably 35 ° C. or lower. The time for immersion in water is, for example, preferably 0.1 minutes or more, more preferably 0.3 minutes or more, and preferably 5 minutes or less, and more preferably 3 minutes or less. More preferably, there is. The water used for immersion in water is not limited to pure water, and may be an aqueous solution in which various components are dissolved, or may be a mixture of water and an aqueous medium.

  Dyeing can be performed by bringing a dichroic dye into contact with the PVA film according to the present invention. The dyeing may be performed at any stage before, during, or after the uniaxial stretching. Dyeing is generally performed by immersing the PVA film in a solution containing iodine-potassium iodide (especially an aqueous solution), which is a dyeing bath. In the present invention, such a dyeing method is suitably adopted. You. The concentration of iodine in the dye 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 from 20 ° C to 50 ° C, particularly preferably from 25 ° C to 40 ° C.

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 an iodine dye is preferable. 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.

  The uniaxial stretching of the PVA film according to the present invention may be performed by any of a wet stretching method and a dry heat stretching method. In the case of the wet stretching method, the stretching can be performed in an aqueous solution containing boric acid, or can be performed in the above-described dyeing bath or a fixing bath described later. In the case of the dry heat stretching method, the stretching can be performed in air using a PVA film after water absorption. Among these, a wet stretching method is preferred, and uniaxial stretching in an aqueous solution containing boric acid is more preferred. 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, more preferably 1.0% by mass or more, and 1.5% by mass or more. It is still more preferably at least 5.0% by mass, more preferably at most 5.0% by mass, even more preferably at most 4.0% by mass. The aqueous boric acid solution may contain potassium iodide, and the concentration of potassium iodide is preferably in the range of 0.01% by mass to 10% by mass.

  The stretching temperature in the uniaxial stretching is not particularly limited. In the case of the wet stretching method, the stretching temperature is preferably in a range of 30 ° C. or more and 90 ° C. or less, and the stretching temperature is more preferably 40 ° C. or more, and 45 ° C. The temperature is more preferably at least 70 ° C., and even more preferably at most 65 ° C. In the case of the dry heat drawing method, the temperature is preferably in the range of 50 ° C. or more and 180 ° C. or less.

  The stretching ratio in uniaxial stretching (the overall stretching ratio obtained by multiplying each stretching ratio in the case of performing uniaxial stretching in multiple stages) is preferably as much as possible from the point of polarization performance until just before the film is cut, and specifically, It is preferably at least 4 times, more preferably at least 5 times, even more preferably at least 5.5 times. The upper limit of the stretching 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 stretching. Note that the stretching ratio in the present specification is based on the length of the film before stretching, and a state where the film is not stretched corresponds to a stretching ratio of 1. 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, and particularly preferably 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, or even 5 μm or more.

  The direction of uniaxial stretching in the case of uniaxially stretching a long PVA film is not particularly limited, and uniaxial stretching in the length direction or uniaxial stretching in the lateral direction can be adopted. From the viewpoint of being obtained, uniaxial stretching in the length direction is preferred. Uniaxial stretching in the length direction can be performed by using a stretching device having a plurality of rolls parallel to each other and changing the peripheral speed between the rolls. 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 on the film. The fixing treatment can be performed by immersing the film in a fixing treatment bath. As the fixing 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. If necessary, an iodine compound or a metal compound may be added to the fixing bath. The concentration of the boron compound in the fixing bath is generally 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 fixed treatment bath is preferably in the range of 15 ° C to 60 ° C, particularly preferably in the range of 25 ° C to 40 ° C.

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

  The polarizing film obtained as described above is usually used as a polarizing plate by laminating an optically transparent protective film having mechanical strength on both surfaces or one surface thereof. As the protective film, a cellulose triacetate (TAC) film, a cycloolefin polymer (COP) film, a cellulose acetate / butyrate (CAB) film, an acrylic film, a polyester film, or the like is used. Examples of the adhesive for bonding the protective film include a PVA-based adhesive, a urethane-based adhesive, and an acrylate-based adhesive, and among them, the PVA-based adhesive is preferable.

  The polarizing plate obtained as described above can be used as an LCD component after being coated with an adhesive such as an acrylic resin 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 attached.

  Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to the following Examples. In addition, each measurement or evaluation method adopted in the following Examples, Comparative Examples and Reference Examples is shown below.

[Measurement of W _MD30 ]
A rectangular sample of 40 mm in the width direction (TD) × 270 mm in the length direction (MD) was cut out from the center in the width direction of the PVA film. Next, a marked line was drawn by oil-based magic (thickness of the line was 0.3 mm) inside the sample by 10 mm from both ends of the 270 mm length. The portion outside the marked lines at both ends was sandwiched between commercially available clips (chuck width: 40 mm, mass: 7.8 g (weight in water: 7.3 g)), and one clip was fixed with a rod-shaped jig. After confirming that the distance between the marked lines is 250 mm, quickly place the sample with the clip in pure water controlled at 30 ° C stored in a cylindrical transparent water tank so that the whole sample enters the water. The long side was immersed vertically (vertically). Immediately after immersion, a rod-shaped jig was hooked on the upper part of the water tank, and the sample was fixed such that the long side of the sample was vertical (vertical). Thereafter, the 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 the reference lines (250 mm) from the measured values read at 0.5 mm intervals.

[Measurement of W _TD300 ]
A rectangular sample of 270 mm in the width direction (TD) × 40 mm in the length direction (MD) was cut out from the center in the width direction of the PVA film. Next, a marked line was drawn by oil-based magic (thickness of the line was 0.3 mm) inside the sample by 10 mm from both ends of the 270 mm length. The portion outside the marked lines at both ends was sandwiched between commercially available clips (chuck width: 40 mm, mass: 7.8 g (weight in water: 7.3 g)), and one clip was fixed with a rod-shaped jig. After confirming that the distance between the marked lines is 250 mm, immediately place the sample with the clip in pure water controlled at 30 ° C stored in a cylindrical transparent water tank so that the whole sample enters the water. The long side was immersed vertically (vertically). Immediately after immersion, a rod-shaped jig was hooked on the upper part of the water tank, and the sample was fixed such that the long side of the sample was vertical (vertical). Thereafter, the metal ruler was immersed in water, and the distance between the marked lines was measured 300 seconds after the immersion of the sample. The original distance between the reference lines (250 mm) was subtracted from the measured values read at 0.5 mm intervals to calculate the elongation (W _TD300 ) (unit: mm).

[Evaluation of stretchability of PVA film]
As an index of the stretchability of the PVA film, the tension during stretching in a 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 △: More than 15 MPa and 18 MPa or less ×: Less than 10 MPa or more than 18 MPa

[Evaluation of edge abnormality]
The edge abnormality of the film in the roll immediately after passing through the swelling bath was evaluated according to the following criteria.
：: No abnormality at the edge can be confirmed at all △: Abnormality at the edge can be slightly confirmed ×: Abnormal at the edge can be clearly confirmed

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

[Example 1]
<< Manufacture of PVA film >>
PVA (ethylene-modified PVA obtained by saponifying ethylene-modified polyvinyl acetate obtained by copolymerizing ethylene and vinyl acetate, content of ethylene unit 2.0 mol%, polymerization degree 2,400, saponification 100 parts by mass), 10 parts by mass of glycerin, 0.1 parts by mass of lauric acid diethanolamide, and 66% by mass of a water-soluble film-forming stock solution having a volatile content of 66% by mass. The film is discharged on 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. While drying the entire surface of the first dry roll non-contact surface with hot air at 90 ° C. at a wind speed of 5 m / sec on the first dry roll, the first dry roll is dried until the volatile content becomes 15% by mass, and peeled from the first dry roll. .
Next, while the front and back surfaces of the PVA film are alternately opposed to each of the drying rolls such that the non-contact surface of the first drying roll of the PVA film faces the second drying roll, the drying rolls after the second drying roll are used. The PVA membrane was further dried until its volatile content was 5% by mass. The drying roll (drying roll X) when the volatile content of the PVA film became 12% by mass was the fifth drying roll, and the surface temperature of each of the drying rolls from the second drying roll to the fifth drying roll was determined. The temperature was 75 ° C., and the surface temperature of each of the drying rolls after the sixth drying roll was 60 ° C.
Thereafter, a heat treatment was performed on the PVA film with a plurality of heat treatment rolls while alternately opposing the front and back surfaces of the PVA film to each heat treatment roll. At this time, the ratio (S _B of the peripheral speed of the heat treatment roll located on the most downstream side with respect to the peripheral speed of the heat treatment roll located on the most upstream side (the heated rollers A) (S _A) (heat treatment roll B) (S _B) / S _A ) was set to 0.991, and the surface temperature of each heat treatment roll was set to 99 to 115 ° C. (the surface temperature of heat treatment roll A is 99 ° C., and 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 the heat treatment as described above, the film was wound up to obtain a roll-shaped PVA film (thickness: 45 μm, width: 3 m, length: 5,000 m, volatile content: 3% by mass).
With respect to the obtained PVA film, _WMD30 and _WTD300 were measured according to the method described above. The results are shown in Table 1.

《Manufacture of polarizing film》
The PVA film obtained above was unwound from a roll, slit and continuously cut out from the center in the width direction to a portion having a width of 650 mm, and then subjected to various treatments to continuously produce a polarizing film.
That is, the PVA film is immersed in a swelling bath (water temperature 30 ° C.), followed by a dyeing bath (water temperature 32 ° C., an aqueous solution containing 0.07% by mass of iodine and 1.6% by mass of potassium iodide), Fixing 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) Then, the polarizing film was sequentially immersed in a washing bath (water temperature 22 ° C., an aqueous solution containing 1.5% by mass of boric acid and 5.0% by mass of potassium iodide), and further dried in a drying oven (40 ° C.) to obtain a polarizing film. Manufactured. The time of immersion in the swelling bath was set to a relatively short 40 seconds in order to correspond to a thin PVA film. The total stretching ratio was 6.3 times.
In the production of the polarizing film, the stretchability of the PVA film used in accordance with the above-described method was evaluated, and the edge abnormality was evaluated. 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-based polymer film having a thickness of 50 μm or less,
A sample of 40 mm in width direction (TD) × 270 mm in length direction (MD) is cut out from the center in the width direction of the polyvinyl alcohol-based polymer film , and marked lines are drawn inward by 10 mm from both ends of the sample at 270 mm length. Is sandwiched between clips (chuck width: 40 mm, mass: 7.8 g (weight in water: 7.3 g)), one of the clips is fixed with a rod-shaped jig, and the distance between the marked lines is 250 mm. After confirming that, the sample with the clip is immediately immersed vertically (vertically) in pure water adjusted to 30 ° C. stored in a water tank so that the entire sample enters the water. Immediately afterwards, a rod-shaped jig is hooked on the upper part of the water tank, and the long side of the sample is fixed so as to be vertical (vertical). Elongation amount _{W MD30} minus between the distance (250 mm) is at 60mm or less than 35 mm,
A sample of 270 mm in width direction (TD) × 40 mm in length direction (MD) is cut out from the center in the width direction of the polyvinyl alcohol-based polymer film , and marked lines are drawn inward by 10 mm from both ends of the sample at 270 mm length. Is sandwiched between clips (chuck width: 40 mm, mass: 7.8 g (weight in water: 7.3 g)), one of the clips is fixed with a rod-shaped jig, and the distance between the marked lines is 250 mm. After confirming that, the sample with the clip is immediately immersed vertically (vertically) in pure water adjusted to 30 ° C. stored in a water tank so that the entire sample enters the water. Immediately after, the 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). From the distance between the marked lines measured 300 seconds after immersion of the sample, The gauge length elongation amount _{W TD300} minus (250 mm) is less than 53 mm 65 mm, polyvinyl alcohol polymer film.   The polyvinyl alcohol-based polymer film according to claim 1, wherein the width is 2 m or more.   The polyvinyl alcohol-based polymer film according to claim 1 or 2, which is a raw film for producing an optical film.   The polyvinyl alcohol-based polymer film according to claim 3, wherein the optical film is a polarizing film.   A method for producing a polyvinyl alcohol-based polymer film having a thickness of 50 μm or less, comprising using a film forming apparatus having a drying roll and a heat treatment roll whose rotation axes are parallel to each other, and forming a polyvinyl alcohol on a first drying roll of the film forming apparatus. A film-forming stock solution containing an alcohol-based polymer is discharged and dried in the form of a film, and further dried with a subsequent drying roll, and then heat-treated with a plurality of heat-treatment rolls to produce a polyvinyl alcohol-based polymer film. When the heat treatment roll located at the most upstream side is heat treatment roll A and the heat treatment roll located at the most downstream side is heat treatment roll B, the volatile content of the polyvinyl alcohol polymer film immediately before contact with heat treatment roll A Is 3% by mass or more and 7% by mass or less, and the ratio of the peripheral speed (SB) of the heat treatment roll B to the peripheral speed (SA) of the heat treatment roll A (SB / SA) Is 0.999 or less, and the surface temperature of each heat treatment roll from heat treatment roll A to heat treatment roll B is 87 ° C or more and 121 ° C or less.   When the drying roll when the volatile content of the polyvinyl alcohol-based polymer film becomes 12% by mass is referred to as a drying roll X and the drying roll located immediately before the heat treatment roll A is referred to as a drying roll Y, the first drying roll is used. The surface temperature of each of the drying rolls from to the drying roll X is 70 ° C. or more, and the surface temperature of each of the drying rolls from the drying roll located immediately after the drying roll X to the drying roll Y is 40 ° C. or more. The production method according to claim 5, wherein the temperature is lower than 0C.   The method according to claim 5, wherein a ratio (SB / S1) of a peripheral speed (SB) of the heat treatment roll B to a peripheral speed (S1) of the first drying roll is 0.900 or more and 1.050 or less.   When the drying roll located immediately before the heat treatment roll A is a drying roll Y, between the first drying roll and the drying roll Y, the front and back surfaces of the polyvinyl alcohol-based polymer film are alternately arranged on each drying roll. The manufacturing method according to any one of claims 5 to 7, which is opposed.   The method according to any one of claims 5 to 8, which is a method for producing a raw film for producing an optical film.   The method according to claim 9, wherein the optical film is a polarizing film.   An optical film produced from the polyvinyl alcohol-based polymer film according to claim 3.   A polarizing film produced from the polyvinyl alcohol-based polymer film according to claim 4.