TWI765093B - Polyvinyl alcohol film and method for producing same - Google Patents

Abstract

To provide a polyvinyl alcohol film having a width of 3 m or more, a length of 1,000 m or more, a thickness of 15 to 65 μm, and a hysteresis value measured with a pitch in the longitudinal direction of 15 m and a pitch in the width direction of 10 mm satisfying the following Formulas (1)~(4). This film has excellent stretchability even if it is thin and wide, and the width fluctuation after stretching is small. Therefore, by using this film, a thin and wide optical film and the like excellent in optical performance can be produced with good productivity.

A(nm)=Re _{maximum value} -Re _{minimum value} ≦10 (1)

2≦ _ReTotal ≦20 (3)

0.3<A/Re _total (4)

Description

Polyvinyl alcohol film and method for producing the same

The present invention relates to a polyvinyl alcohol film (hereinafter, "polyvinyl alcohol" may be simply referred to as "PVA") and a method for producing the same.

A polarizing plate having functions of transmitting and shielding light is an important constituent element of a liquid crystal display device (LCD). Liquid crystal display devices are used in a wide range of fields, such as notebook computers, liquid crystal screens, liquid crystal color projectors, liquid crystal televisions, in-vehicle navigation systems, mobile phones, and measuring equipment used both indoors and outdoors.

The polarizing plate is usually dyed and uniaxially stretched from the PVA film unrolled from the roll. After the polarizing film is produced by a method of fixing treatment with a boron compound, etc., the polarizing film is laminated on one or both sides of the obtained polarizing film. Triacetate cellulose film or acetic acid. It is industrially produced as a protective film such as a cellulose butyrate film.

In recent years, large-screen LCD screens, LCD TVs, and the like, and lightweight systems such as notebook computers and mobile phones are progressing. In addition, it is also required to reduce the cost of the polarizing plate. Due to this, a thin and wide polarizing film is required. In the production of such a polarizing film, although a thin and wide PVA film is used as an original roll, the stretchability of such a PVA film is insufficient and there are problems.

Patent Document 1 describes a method, which is a method for producing a PVA film, in which (a) a film forming apparatus having a plurality of drying rolls whose rotation axes are parallel to each other is used, and a film containing PVA is discharged on the first drying roll of the film forming apparatus. After the film-forming stock solution was partially dried, it was further dried with the subsequent drying rollers and formed into a film; at this time, (b) the peripheral speed (SL) of the final drying roller was compared to the peripheral speed (S _L ) of the first drying roller ( The ratio (S _L /S ₁ ) of S ₁ ) is set to 0.955 to 0.980; (c) the width (H ₂₀ ) of the PVA film when the volatile content ratio is 20 mass % and the PVA when the volatile content ratio is 9 mass % The shrinkage ratio [(1-H ₉ /H ₂₀ )×100] (%) calculated from the width (H ₉ ) of the film is set to 1% or more; for the drying roll when the volatile content rate of the PVA film is 20% by mass , the surface temperature of each drying roll of the drying roll when the volatile content ratio of the PVA film becomes 9 mass %, the average value of these shall be 85°C or more. However, the PVA film obtained by this method has insufficient stretchability.

Patent Document 2 describes a method for producing a PVA film, wherein (a) a film forming apparatus having three or more drying rolls whose rotation axes are parallel to each other is used, and the most upstream of the drying rolls is located. After the film-forming stock solution containing PVA was discharged from the first drying roll and partially dried, it was further dried with the subsequent drying rolls to form a film; at this time, (b) the PVA film when peeled from the first drying roll was The volatile matter ratio was set to 20 to 40 mass %; (c) the ratio (S 2 /S 1 ) of the peripheral speed (S ₂ ) of the second drying roll to the peripheral speed (S ₁ ) of the first drying roll (S ₂ /S ₁ ) was set to 1.015 ~1.050; (d) The volatile matter ratio between the drying roll (xth drying roll) and the PVA film when the volatile matter ratio of the PVA film in the second drying roll or the drying roll downstream thereof is 20% by mass and the PVA film is set to 10 Between the drying rolls (y-th drying rolls) at mass %, the peripheral speed (S _n+1 ) of the downstream drying roll among the two adjacent drying rolls versus the peripheral speed (S _n ) of the upstream drying roll The ratios (S _n+1 /S _n ) were all set to 0.992 to 0.999. However, this method is not suitable for making thin PVA films.

prior art literature Patent Literature

Patent Document 1 WO2016/084836

Patent Document 2 WO2014/050696

The present invention has been accomplished in order to solve the above-mentioned problems, and an object thereof is to provide a thin and wide PVA film having excellent stretchability and little variation in width after stretching, and a simple method for producing the same.

The above problem is solved by providing a PVA film having a width of 3 m or more, a length of 1,000 m or more, and a thickness of 15 to 65 μm, characterized in that the pitch in the longitudinal direction is 15 m and the pitch in the width direction is 15 m. The hysteresis value measured at a distance of 10 mm satisfies the following equations (1) to (4).

A(nm)=Re _{maximum value} -Re _{minimum value} ≦10 (1)

2≦ _ReTotal ≦20 (3)

0.3<A/Re _total (4)

In the formula, Re _{maximum value} (nm): the maximum value of the hysteresis at the position 10mm away from the end

Re _{minimum value} (nm): the minimum value of the hysteresis at the position 10mm away from the end

Re _{average value} (nm): average value of hysteresis at a position 10mm from the end

Re _i (nm): the hysteresis value of the measurement point i (i=1~n, n is an integer) at a position 10mm away from the end

Re _total (nm): the average value of the hysteresis of all measurement points.

The above-mentioned problems are also solved by providing a method for producing a PVA film, which is the method for producing the PVA film, which uses a film forming apparatus having a plurality of drying rolls whose rotation axes are parallel to each other, wherein the plurality of drying rolls include a The 1st drying roll to the mth drying roll (m represents an integer of 3 or more), and after the film is obtained by discharging the film-forming stock solution containing PVA from the die onto the first drying roll and drying it, the second drying roll is used. In the step of further drying the film from the roll to the mth drying roll, the volatile content of the film when peeled from the first drying roll is 12 to 20%, and the peripheral speed (S ₂ ) of the second drying roll is relative to the first drying roll. The ratio (S ₂ /S ₁ ) of the peripheral speed (S ₁ ) is 1.015 to 1.050, and the peripheral speed (S _x ) of the drying roll (xth drying roll) that first comes into contact after the volatile content of the film becomes 11 mass % or less The ratio (S _x /S ₂ ) to the peripheral speed (S ₂ ) of the second drying roll is 0.970 to 0.995, and the average of the roll temperatures from the second drying roll to the xth drying roll is 63 to 81°C.

At this time, it is preferable that the volatile matter ratio of the film-forming stock solution containing PVA is 60 to 75 mass %, and the peripheral speed (S ₁ ) of the first drying roll is 8 to 25 m/min.

The PVA film of the present invention has excellent stretchability even if it is thin and wide, and the width variation after stretching is small. Such a PVA thin film can be easily produced by the production method of the present invention. By using such a PVA film, a thin and wide optical film and the like excellent in optical performance can be produced with high productivity.

1‧‧‧PVA film

2, 3‧‧‧End

4‧‧‧Length direction

5‧‧‧Pitch

6‧‧‧Width direction

FIG. 1 is a schematic diagram showing measurement points of hysteresis in a PVA film.

The form in which the invention is carried out

The PVA film of the present invention has a width of 3 m or more, a length of 1,000 m or more, and a thickness of 15 to 65 μm, and the hysteresis value measured with the pitch in the longitudinal direction of 15 m and the pitch in the width direction of 10 mm satisfies the following formula (1 )~(4).

A(nm)=Re _{maximum value} -Re _{minimum value} ≦10 (1)

2≦ _ReTotal ≦20 (3)

0.3<A/Re _total (4)

In the formula, Re _{maximum value} (nm): the maximum value of the hysteresis at the position 10mm away from the end

Re _{minimum value} (nm): the minimum value of the hysteresis at the position 10mm away from the end

Re _{average value} (nm): average value of hysteresis at a position 10mm from the end

Re _i (nm): the hysteresis value of the measurement point i (i=1~n, n is an integer) at a position 10mm away from the end

Re _total (nm): the average value of the hysteresis of all measurement points.

In the PVA film of the present invention, the hysteresis values measured by setting the pitch in the longitudinal direction to 15 m and the pitch in the width direction to 10 mm satisfy the above equations (1) to (4). Here, the retardation Re (nm) of the thin film is represented by the following formula. Specifically, the hysteresis Re (nm) of the PVA thin film can be measured by the method described in the examples.

Re=d×△n

[In the formula, d is the thickness of the film (nm), and Δn is the birefringence of the film. ]

The Re _{maximum value} , Re _{minimum value} , Re _{average value} , and Re _i in the above formulae (1) and (2) were obtained by measuring the hysteresis value at a position 10 mm from the end of the PVA film. FIG. 1 is a schematic diagram showing a measurement point i (i=1 to n, where n is an integer) in the PVA film 1 at this time. The hysteresis was measured at positions 10 mm from both ends 2 and 3 of the PVA film 1 with a pitch 5 of 15 m in the longitudinal direction 4 of the PVA film 1 . At this time, the hysteresis value of each measurement point i (i=1 to n, n is an integer) at positions 10 mm from both ends 2 and 3 of the PVA film 1 is Re _i . The maximum value of hysteresis in all measurement points i at positions 10 mm from both ends 2 and 3 of the PVA film 1 is the Re _{maximum value} , the minimum value is the Re _{minimum value} , and the number average value is the Re _{average value} . As will be described later, when the both ends (ears) of the dried PVA film are cut, the hysteresis is measured at positions 10 mm away from both ends 2 and 3 of the cut PVA film 1 to obtain Re _i , Re _{maximum value} , Re _{minimum value} , and Re _{average value} .

As will be described later, in order to obtain the _total Re in the above formula (3), the hysteresis of the entire PVA film 1 is measured. Usually, at this time, the measurement is performed so as to include positions 10 mm from both ends 2 and 3 of the PVA film 1 . Using the measured values at this time, Re _i , the Re _{maximum value} , the Re _{minimum value} , and the Re _{average value} are obtained together with the Re _total .

A in the above-mentioned formula (1) and B in the above-mentioned formula (2) are both indicators of the unevenness of hysteresis in the longitudinal direction of the PVA film of the present invention. The PVA film of the present invention, which satisfies the above formulae (1) and (2) and has a small variation in hysteresis in the longitudinal direction, is excellent in stretchability and also has a small variation in width after stretching. The optical film produced by stretching the PVA film has excellent optical properties. When A in the above formula (1) exceeds 10 nm, the optical properties of the obtained optical film become insufficient. In addition, the stretchability and the uniformity of the film width after stretching also decreased. A is preferably 9.5 nm or less. When B in the above formula (2) exceeds 1.5 nm, the optical properties of the resulting optical film become insufficient. In addition, the stretchability and the uniformity of the film width after stretching also decreased. B is preferably 1.2 nm or less. On the other hand, B is usually 0.1 nm or more.

The _total Re (nm) in the above formula (3) is the average value of the number of hysteresis at all measurement points when the pitch in the longitudinal direction is 15 m and the pitch in the width direction is 10 mm, and the hysteresis is measured for the entire PVA film . By making the _total Re into the range shown by the said Formula (3), the stretchability of the PVA film improves. The _total of Re is preferably 18 nm or less. As described above, when measuring the hysteresis with respect to the entire PVA film, the measurement is usually performed so as to include positions 10 mm from both ends 2 and 3 of the PVA film 1 . Using the measured values at this time, Re _i , the Re _{maximum value} , the Re _{minimum value} , and the Re _{average value} are obtained together with the Re _total .

The above formula (4) defines the ratio of A to the _total of Re (A/ _Total of Re). A is the difference between the _maximum value Re of the retardation and the _minimum value Re of the retardation at a position 10 mm from the end of the PVA film, and it is considered that the smaller the difference, the better the optical properties of the optical film obtained. However, the inventors of the present invention have surprisingly found that by making the ratio of A to the _total Re (A/Re _total ) When it becomes 0.3 or more, the optical performance hardly deteriorates, and the stretchability is remarkably improved. The aforementioned ratio ( _total A/Re) is more preferably 0.4 or more. On the other hand, the aforementioned ratio ( _total A/Re) is preferably 2 or less, more preferably 1 or less.

The thickness of the PVA film of the present invention is 15-65 μm, and the width is 3 m or more. The PVA film of the present invention satisfying the above-mentioned formulae (1) to (4) has excellent stretchability even if it is thin and wide, and the variation of the width after stretching is small. By using such a PVA film, a thin and wide optical film excellent in optical performance can be produced with high productivity.

From the viewpoint of further improving the stretchability of the PVA film, the thickness of the PVA film is preferably 20 μm or more. Moreover, it is preferable that the width|variety of the said PVA film is 3.5 m or more. On the other hand, when an optical film such as a polarizing film is produced by an actual production machine, if the width of the film is too wide, uniform uniaxial stretching becomes difficult. Therefore, the width of the PVA film is preferably 8 m or less.

The length of the PVA film of the present invention is 1,000 m or more. The PVA film of the present invention is excellent in stretchability. Therefore, by using the PVA film as the original roll of the optical film, the optical film can be stably produced over a long period of time. The length of the PVA film is preferably 50,000 m or less, more preferably 20,000 m or less.

As the PVA used for the film of the present invention, one produced by saponifying polyvinyl ester obtained by polymerizing vinyl ester can be used. Examples of vinyl esters include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl laurate, vinyl stearate, vinyl benzoate, Vinyl versatate and the like. Among the above-mentioned vinyl esters, vinyl acetate is preferred from the viewpoints of availability, cost, ease of production of PVA, and the like.

The above-mentioned polyvinyl ester is preferably obtained by using only one or two or more kinds of vinyl esters as monomers, more preferably obtained by using only one kind of vinyl esters as monomers, and may be one kind or two or more kinds. Copolymers of vinyl esters, and other monomers copolymerizable therewith.

Examples of other monomers that can be copolymerized with such vinyl esters include: ethylene; olefins (α-olefins, etc.) having 3 to 30 carbon atoms such as propylene, 1-butene, and isobutylene; acrylic acid or its salts; acrylic acid Methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tertiary butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate Acrylates such as alkyl esters; methacrylic acid or its salts; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, methacrylic acid Methacrylates of isobutyl, tertiary butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, etc.; acrylamide, N- Methacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetone acrylamide, acrylamide propane sulfonic acid or its salt, acrylamide propyl dimethylamine acrylamide derivatives such as its salts, N-methylol acrylamide or its derivatives; methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, Methacrylamide derivatives such as methacrylamidopropanesulfonic acid or its salts, methacrylamidopropyl dimethylamine or its salts, N-methylolmethacrylamide or its derivatives, etc. ; N-vinyl amide such as N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone, etc.; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether , isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tertiary butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether and other vinyl ethers ; vinyl cyanide such as acrylonitrile and methacrylonitrile; vinyl halide such as vinyl chloride, vinylidene chloride, vinyl fluoride, and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic Acid or its salt, ester or acid anhydride; Iconic acid or its salt, ester or acid anhydride; Vinylsilyl compounds such as vinyltrimethoxysilane; Isopropylene acetate, etc. The above-mentioned polyvinyl ester may have one kind or two or more kinds of structural units derived from these other monomers.

The ratio of the structural units from the above-mentioned other monomers occupied in the above-mentioned polyvinyl ester is preferably less than 15 mol %, more preferably less than 5 mol % according to the number of moles of all structural units constituting the polyvinyl ester .

The above-mentioned PVA may be modified by one kind or two or more kinds of graft-copolymerizable monomers. Examples of the graft copolymerizable monomer include unsaturated carboxylic acid or derivatives thereof; unsaturated sulfonic acid or derivatives thereof; α-olefins having 2 to 30 carbon atoms. The ratio of the structural unit derived from the graft-copolymerizable monomer in the PVA is preferably 5 mol % or less based on the molar number of all the structural units constituting the PVA.

A part of the hydroxyl group of the above-mentioned PVA system may or may not be cross-linked. In addition, a part of the hydroxyl group of the above-mentioned PVA system may react with aldehyde compounds such as acetaldehyde and butyraldehyde to form an acetal structure, or may not react with these compounds to form an acetal structure.

The degree of polymerization of PVA is not particularly limited, but is preferably 500 or more, more preferably 1,000 or more, still more preferably 1,500 or more, and particularly preferably 2,000 or more, from the viewpoints of film strength and durability of the resulting optical film. On the other hand, if the polymerization is too high, there is a tendency for an increase in manufacturing cost or poor step-throughability during film formation. Therefore, the degree of polymerization of PVA is preferably 10,000 or less, more preferably 9,000 or less, and still more Preferably it is 8,000 or less, and particularly preferably 7,000 or less. In addition, the polymerization degree of PVA in this specification means the average degree of polymerization measured according to the description of JIS K6726-1994.

The degree of saponification of PVA is not particularly limited, but the degree of saponification of PVA is preferably 95 mol % or more, more preferably 98 mol % or more, from the viewpoint of the optical properties and durability of the optical film produced from the obtained PVA film. , more preferably 99 mol % or more, particularly preferably 99.2 mol % or more. In addition, the saponification degree of PVA in this specification refers to the total number of moles of a structural unit (typically a vinyl ester unit) and a vinyl alcohol unit that PVA has and is converted into a vinyl alcohol unit by saponification energy, The molar ratio (mol%) of the vinyl alcohol unit. The saponification degree of PVA can be measured according to the description of JIS K6726-1994.

As the raw material of the PVA film of the present invention, one type of PVA may be used alone, or two or more types of PVA having different types of modification, modification rate, degree of polymerization, degree of saponification, etc. may be used in combination. However, when the PVA film of the present invention is required to have excellent secondary processability, such as when it is used as a raw roll when manufacturing an optical film, if the PVA film contains PVA having an acidic functional group such as a carboxyl group and a sulfonic acid group, etc. ; PVA with acid anhydride groups; PVA with basic functional groups such as amine groups; PVA with functional groups that promote cross-linking reactions such as neutralizers, sometimes due to the cross-linking reaction between PVA molecules. Reduce the secondary processability of PVA film. For this reason, in the case as described above, 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 neutralizers thereof. As PVA, it is more preferable to include only PVA produced by saponifying polyvinyl ester obtained by using only vinyl ester as a monomer, and/or by combining only vinyl ester with ethylene and/or carbon number of 3 to 30 PVA produced by saponification of polyvinyl ester obtained from olefin as a monomer, as PVA, it is further preferable to include only PVA produced by saponification of polyvinyl ester obtained by using only vinyl ester as a monomer, and/ Or PVA produced by saponifying polyvinyl ester obtained using only vinyl ester and ethylene as monomers.

The aforementioned PVA film was produced using the PVA thus obtained. The production method of the PVA film of the present invention is not particularly limited, and it is preferably produced by the following method: using a film production apparatus having a plurality of drying rolls whose rotation axes are parallel to each other, and the plurality of drying rolls include the first drying roll to the second drying roll. m drying rolls (m represents an integer of 3 or more), which is used to obtain a film by discharging the film-forming stock solution containing polyvinyl alcohol from the die onto the first drying roll and drying it, and then using the second drying roll to the mth drying roll. In the step of further drying the film by the drying roller, the volatile content of the film when peeled from the first drying roller is 12 to 20%, and the peripheral speed (S 2 ) of the second drying roller is relative to the peripheral speed (S ₂ ) of the first drying roller. ₁ ) The ratio (S ₂ /S ₁ ) is 1.015 to 1.050, and the peripheral speed (S _x ) of the drying roll (x-th drying roll) contacted first after the volatile content ratio of the film becomes 11 mass % or less is effective for the second drying The ratio (S _x /S ₂ ) of the peripheral speed (S ₂ ) of the rolls was 0.970 to 0.995, and the average of the roll temperatures from the second drying roll to the xth drying roll was 63 to 81°C.

As a film-forming stock solution, a solution in which PVA and a liquid medium are mixed, or a melt in which a PVA chip containing a liquid medium or the like is melted is used. These can be prepared using a stirring mixer, a melt extruder, or the like. Examples of the liquid medium used at this time include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylenediamine, and ethylenetriamine. Wait. These liquid media may be used individually by 1 type, and may use 2 or more types together. Among these, it is preferable to use water, dimethyl sulfoxide, or a mixture thereof, and it is more preferable to use water.

From the point of further improving the stretchability of the obtained PVA film, the film-forming stock solution preferably contains a plasticizer. A PVA film containing a plasticizer is obtained by using a film-forming stock solution containing a plasticizer. As the plasticizer, polyhydric alcohols are preferably used, and examples thereof include ethylene glycol, glycerol, diglycerol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and trimethylol. Propane etc. A plasticizer may be used individually by 1 type, and may use 2 or more types together. Among them, it is preferable to use one or more of glycerol, diglycerol, and ethylene glycol.

The content of the plasticizer is preferably 0.1 to 30 parts by mass, more preferably 3 to 25 parts by mass, and particularly preferably 5 to 20 parts by mass, relative to 100 parts by mass of PVA. By making content of a plasticizer 30 mass parts or less with respect to 100 mass parts of PVA, the handleability of the PVA film obtained improves.

From the viewpoints of improving the peelability from the drying roll when producing the PVA film, the handleability of the resulting PVA film, and the like, it is preferable that the film-forming stock solution contains a surfactant. The PVA film containing the surfactant is obtained by using the film-forming stock solution containing the surfactant. The type of the surfactant is not particularly limited, but an anionic surfactant or a nonionic surfactant is preferably used. These surfactants may be used alone or in combination of two or more.

As the anionic surfactant, for example, a carboxylic acid type anionic surfactant such as potassium laurate, a sulfate type such as octyl sulfate, and a sulfonic acid type anionic surfactant such as dodecylbenzenesulfonate are suitable.

In addition, examples of nonionic surfactants include alkyl ether types such as polyoxyethylene oleyl ether, alkyl phenyl ether types such as polyoxyethylene octyl phenyl ether, and alkyl groups such as polyoxyethylene laurate. Ester type, alkylamine type such as polyoxyethylene lauryl amino ether, alkyl amide type such as polyoxyethylene lauric acid amide, polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether, dilauric acid Nonionic surfactants of alkanolamide type such as glycolamide and diethanolamide oleate, and allylphenyl ether type such as polyoxyalkylene allylphenyl ether are suitable.

The content of the surfactant is preferably 0.01 to 1 part by mass, more preferably 0.02 to 0.5 part by mass, and even more preferably 0.05 to 0.3 part by mass, relative to 100 parts by mass of PVA. By making the content of the surfactant to be 0.01 part by mass or more with respect to 100 parts by mass of PVA, the stretchability and dyeability are further improved. Moreover, the handleability of a PVA film improves by making content of a surfactant to 1 mass part or less with respect to 100 mass parts of PVA.

The film-forming stock solution may contain stabilizers (antioxidants, ultraviolet absorbers, heat stabilizers, etc.), compatibilizers, anti-blocking agents, flame retardants, antistatic agents, lubricants, dispersants, fluidizers, and antibacterial agents various additives. These additives may be used alone or in combination of two or more.

The volatile matter ratio of the membrane-forming stock solution for producing the PVA thin film is preferably 60 to 75% by mass. The membrane-forming stock solution with a volatile content of 60% by mass or more has a moderate viscosity, and thus the membrane-forming properties are improved. A preferable volatile matter ratio is 65 mass % or more. On the other hand, the uniformity of the thickness of the obtained PVA film is improved by making the volatile content rate 75 mass % or less. In addition, in this invention, the volatile matter rate of a membrane-forming stock solution is calculated|required by following formula (i).

Volatile fraction (mass %)={(Wa-Wb)/Wa}×100 (i)

[In the formula, Wa represents the mass (g) of the film-forming stock solution, and Wb represents the mass (g) of the components remaining after drying the film-forming stock solution of Wa (g) in an electric heat dryer at 105° C. for 16 hours. ]

In the film forming apparatus used for producing the aforementioned PVA film, it is preferable that the surface of the drying roll is not easily corroded and has a specular gloss. From such a viewpoint, the drying roll is preferably formed of a metal such as nickel, chromium, copper, iron, and stainless steel. Furthermore, from the viewpoint of improving the durability of the drying roll, it is also preferable to form a plating layer such as nickel, chromium, nickel/chromium alloy, or the like on the surface of the drying roll as a single layer or multiple layers.

The film forming apparatus used in the present invention may include a hot-air oven-type hot-air drying apparatus, a heat treatment apparatus, a humidity control apparatus, and the like after the drying roll, as necessary.

The number of drying rolls in the film forming apparatus is three or more, preferably 5 to 30. In this invention, from the drying roll arrange|positioned upstream, it is called a 1st drying roll, a 2nd drying roll, a 3rd drying roll, a 4th drying roll, ... m-th drying roll in this order. The above-mentioned film forming apparatus includes known discharge apparatuses (casting apparatuses) such as a T-slot die, a hopper plate, an I-die, and a lip coater die. From the die of this apparatus, the above-mentioned film-forming stock solution was discharged (cast) into a thin film on the first drying roll.

The film was peeled off from the first drying roll after the film was obtained by drying the above-mentioned film-forming stock solution discharged onto the first drying roll on the first drying roll. Here, the volatile matter ratio of the film at the time of peeling from the 1st drying roll needs to be 12-20 mass %.

When the volatile matter ratio of the film at the time of peeling from the 1st drying roll is less than 12 mass %, stretchability falls remarkably. On the other hand, when the volatile matter ratio of the film at the time of peeling from the first drying roll exceeds 20 mass %, the peelability of the film from the first drying roll deteriorates, and the thickness unevenness in the flow direction becomes large. The aforementioned volatile matter ratio is preferably 19% by mass or less, more preferably 18% by mass or less, and still more preferably 16% by mass or less. In this invention, the volatile matter ratio of a film is calculated|required by following formula (ii) after collecting the film after peeling from a 1st drying roll.

Volatile fraction (mass %)={(Wc-Wd)/Wc}×100 (ii)

[wherein, Wc represents the mass (g) of the collected thin film, and Wd represents the mass (g) of the thin film Wc (g) after drying the above-mentioned thin film Wc (g) in a dryer at a temperature of 105° C. for 16 hours. ]

Using polyols (plasticizers) such as PVA and glycerol, surfactants, and water to prepare a film-forming stock solution, and drying the PVA film obtained using the film-forming stock solution under the above-mentioned conditions, the components other than water are substantially ineffective. Since it volatilizes and remains in the film, the volatile matter ratio of the film is substantially the same as the moisture content (moisture content) contained in the film.

The surface temperature of the first drying roll is preferably 80 to 120° C. from the viewpoints of drying uniformity, drying speed, and the like. When the surface temperature is lower than 80° C., drying on the first drying roll tends to be insufficient, and this tends to cause poor peeling. The surface temperature is more preferably 85°C or higher. On the other hand, when the said surface temperature exceeds 120 degreeC, there exists a tendency for a film to become easy to foam. The aforementioned surface temperature is preferably 105°C or lower, more preferably 99°C or lower.

From the viewpoints of drying uniformity, drying speed, productivity, and the like, the peripheral speed (S ₁ ) of the first drying roll is preferably 8 to 25 m/min. When the peripheral speed (S ₁ ) is less than 8 m/min, there is a possibility that the productivity will decrease. The peripheral speed (S ₁ ) is more preferably 10 m/min or more, further preferably 12 m/min or more. On the other hand, when the peripheral speed (S ₁ ) exceeds 25 m/min, the drying of the first drying roll tends to be insufficient. Moreover, it is more preferable that it is 23 m/min or less, and it is still more preferable that it is 22 m/min or less.

The drying of the film-forming stock solution discharged in the form of a film on the first drying roll may be carried out using only the first drying roll, or may be carried out by heating from both sides of the film by blowing hot air to the film surface that is not in contact with the first drying roll dry. Thereby, the uniformity of drying and the drying speed are further improved. The wind speed of the hot air is preferably 1 to 10 m/sec, more preferably 2 to 8 m/sec, and further preferably 3 to 8 m/sec.

When the said wind speed is too slow, condensation will generate|occur|produce on the 1st drying roll, this water droplet may fall to a film, and there exists a possibility that a defect will generate|occur|produce in the PVA film obtained. On the other hand, if the wind speed is too fast, unevenness in thickness occurs in the obtained PVA film, and there is a possibility that a problem such as uneven dyeing occurs.

The temperature of the hot air is preferably 50 to 150°C, more preferably 70 to 120°C, further preferably 80 to 95°C, from the viewpoints of drying efficiency, drying uniformity, and the like. In addition, the dew point temperature of the hot air is preferably 10 to 15°C. When the temperature of the hot air is too low, drying efficiency, drying uniformity, and the like tend to decrease. On the other hand, when the temperature of the hot air is too high, foaming tends to occur.

The method of blowing hot air to the film on the first drying roll is not particularly limited, but a nozzle method, a straightening plate method, or a combination of these are preferably used. Moreover, it is preferable to discharge|release the volatile matter and the blown hot air which generate|occur|produce at the time of drying of the film on the 1st drying roll.

The film dried to a volatile content rate of 12 to 20 mass % by the first drying roll is peeled off from the roll, and the film is further dried on the second drying roll. When drying the said film on the 2nd drying roll, it is preferable to make the side opposite to the surface which contacted with the 1st drying roll of this film contact with a 2nd drying roll, and it is made to dry.

The ratio (S ₂ /S ₁ ) of the peripheral speed (S ₂ ) of the second drying roll to the peripheral speed (S ₁ ) of the first drying roll is preferably 1.015 to 1.050. When this ratio (S ₂ /S ₁ ) is less than 1.015, it is difficult to peel off the film from the first drying roll, and the uniformity of the obtained PVA film in the width direction may decrease. On the other hand, when the aforementioned ratio (S ₂ /S ₁ ) exceeds 1.050, the unevenness of the tension of the film applied between the first drying roll and the second drying roll becomes large, and there is a uniformity of the obtained PVA film. Danger of damage.

The ratio (S _x /S ₂ ) of the peripheral speed (S _x ) of the drying roll (x-th drying roll) contacted first after the volatile content rate of the film becomes 11 mass % or less to the peripheral speed (S ₂ ) of the second drying roll ) is preferably 0.970 to 0.995. The measurement of the volatile content was carried out just before the aforementioned films were brought into contact with each drying roll. The drying roll contacted with the film after the volatile content ratio becomes 11 mass % or less at first is "the drying roll (xth drying roll) which is contacted first after the volatile content ratio of the film becomes 11 mass % or less". In the case where the ratio (S _x /S ₂ ) of the peripheral speed (S _x ) of the x-th drying roll to the peripheral speed (S ₂ ) of the second drying roll is less than 0.970, since A and B exceed the upper limit, respectively, there is an optical The optical properties of the film become insufficient. In addition, the stretchability of the PVA film or the uniformity of the film width after stretching may decrease. On the other hand, when the ratio (S _x /S ₂ ) of the peripheral speed (S _x ) of the x-th drying roll to the peripheral speed (S ₂ ) of the second drying roll exceeds 0.995, the amount of Re in the obtained PVA film will be higher than 0.995. If the _total exceeds 20 nm, the stretchability may be lowered.

From the second drying roll to the xth drying roll, the ratio of the peripheral speed (S _a+1 ) of the downstream drying roll among the two adjacent drying rolls to the peripheral speed (S _a ) of the upstream drying roll ( S _a+1 /S _a ), preferably 0.975~1. The ratio (S _a+1 /S _a ) in all the adjacent two drying rolls from the second drying roll to the xth drying roll is more preferably 0.975 to 1.

The average of the roll temperatures from the second drying roll to the x-th drying roll is preferably 63 to 81°C. When the average of the roll temperature is less than 63° C. or exceeds 81° C., since A and B exceed the upper limit, respectively, the optical properties of the obtained optical film may become insufficient. In addition, the stretchability of the PVA film and the uniformity of the film width after stretching may also decrease.

The roll temperatures from the second drying roll to the xth drying roll are preferably all 50 to 95°C. When this roll temperature is less than 50 degreeC or when it exceeds 95 degreeC, since A and B exceed the upper limit, respectively, the optical performance of the optical film obtained may become inadequate. In addition, the stretchability and the uniformity of the film width may also decrease.

When a drying roll is further arranged downstream of the xth drying roll, from the xth drying roll to the mth drying roll, the peripheral speed (S _b+1 ) of the downstream drying roll is the difference between the two adjacent drying rolls. The ratio (S _b+1 /S _b ) of the peripheral speed (S _b ) of the upstream drying roll is preferably 0.975~1. The roll temperatures from the x+1-th drying roll to the m-th drying roll are preferably all 50 to 130°C.

When the drying rolls are further arranged downstream of the xth drying roll, it is preferable to raise the surface temperature of at least a part of the drying rolls. Thereby, drying and heat treatment of the PVA film can be performed simultaneously. The roll temperature at this time is preferably 90 to 140°C, more preferably 95 to 130°C.

When contacting each drying roll and the film, it is preferable to alternately contact each drying roll with one side and the other side of the film from the point of being able to dry more uniformly.

The ratio (S _m /S ₁ ) of the peripheral speed (S _m ) of the m-th drying roll to the peripheral speed (S ₁ ) of the first drying roll is not particularly limited, but is preferably in the range of 0.900 to 1.100, more preferably 0.950 Within the range of ~1.050, more preferably within the range of 0.980 to 1.020, and particularly preferably within the range of 0.990 to 1.010.

Preferably, both ends (ears) in the width direction of the dried PVA film are cut. In this case, the ratio (W _T /W ₁ ) of the film width (W _T ) after cutting both ends (ears) to the film width (W ₁ ) when discharged from the die is preferably 0.6 or more, more preferably is 0.7 or more. The PVA film produced by the conventional method has a high hysteresis value at the edge portion, and such a PVA film has insufficient stretchability. Although the stretchability can be improved by widely cutting the end portion of the PVA film, it is a problem that the width of the obtained PVA film becomes narrow, and the discarded portion increases, which increases the cost. On the other hand, according to the manufacturing method of this invention, since the retardation value of the edge part of the PVA film after film formation can be reduced, it is not necessary to cut the edge part widely, and a wide PVA film excellent in stretchability can be obtained.

The dried PVA film can be subjected to humidity control treatment, etc. as required, and can also be wound into a roll shape. The volatile content of the finally obtained PVA film is preferably 1 to 5 mass %, more preferably 2 to 4 mass %. In addition, the content of PVA in the PVA film is preferably 50% by mass or more, more preferably 80% by mass or more.

The PVA film of the present invention has excellent stretchability even if it is thin and wide, and the variation in the width after stretching is small. By using such a PVA film, a thin and wide optical film, especially a polarizing film, which is excellent in optical performance can be produced with high productivity. In recent years, the large-screen system of LCD TVs and screens is progressing. In addition, the weight reduction of notebook computers, mobile phones, and the like is also progressing. The PVA film of the present invention is suitable for use as a raw roll or the like of an optical film used in these. The optical film can be produced by a production method having a step of uniaxially stretching the PVA film of the present invention.

As a method of producing a polarizing film using the PVA film of the present invention as an original roll, dyeing, uniaxial stretching, fixing treatment, drying treatment, and heat treatment as necessary using the PVA film of the present invention can be exemplified. The order of dyeing and uniaxial stretching is not particularly limited, and dyeing may be performed before uniaxial stretching, simultaneously with uniaxial stretching, or after uniaxial stretching. In addition, the steps of uniaxial stretching, dyeing, etc. may be repeated a plurality of times.

As dyes for dyeing PVA films, iodine or dichroic organic dyes (for example, Direct Black 17, 19, 154; Direct Brown 44, 106, 195, 210, 223; Direct Red 2, 23, 28, 31) can be used , 37, 39, 79, 81, 240, 242, 247; Direct Blue 1, 15, 22, 78, 90, 98, 151, 168, 202, 236, 249, 270; Direct Violet 9, 12, 51, 98 ; Direct Green 1, 85; Direct Yellow 8, 12, 44, 86, 87; Direct Orange 26, 39, 106, 107 and other dichroic dyes) and the like. These dyes may be used alone or in combination of two or more. Dyeing can usually be performed by immersing a PVA film in a solution containing the above-mentioned dye, and the treatment conditions and treatment methods are not particularly limited.

The uniaxial stretching of the PVA film can be performed by either a wet stretching method or a dry heat stretching method. In the case of uniaxial stretching by the wet stretching method, uniaxial stretching can be carried out in warm water containing boric acid, uniaxial stretching can be carried out in the aforementioned solution containing dye or in the fixing treatment bath described later, and water absorption can be used. The resulting PVA film is uniaxially stretched in the air, and can also be uniaxially stretched by other methods. The stretching temperature during the uniaxial stretching treatment is not particularly limited, but when the PVA film is stretched in warm water (wet stretching), it is preferably 30 to 90°C, more preferably 40 to 70°C, and further. Preferably, a temperature of 45 to 65°C is used, and in the case of dry heat stretching, a temperature of 50 to 180°C is preferably used. In addition, the stretching ratio of uniaxial stretching (the total stretching ratio in the case of performing uniaxial stretching in multiple stages) is preferably stretched as much as possible before the film is cut from the viewpoint of polarizing performance. Specifically, In other words, it is preferably 4 times or more, more preferably 5 times or more, and still more preferably 5.5 times or more. The upper limit of the stretching ratio is not particularly limited as long as the film is not broken, but it is preferably 8.0 times or less for uniform stretching. In addition, the stretching ratio in this specification is based on the length of the film before stretching, and the state without stretching corresponds to 1 times the stretching ratio. The thickness of the stretched film (polarizing film) is preferably 5 to 35 μm, particularly preferably 20 to 30 μm.

In the case of uniaxially stretching a long PVA film, the direction of uniaxial stretching is not particularly limited, and uniaxial stretching in the longitudinal direction or uniaxial stretching in the transverse direction can be used, since it is possible to obtain a film with better polarizing properties. The polarizing film is preferably uniaxially stretched in the longitudinal direction. Uniaxial stretching in the longitudinal direction can be performed by using a stretching device provided with a plurality of rolls parallel to each other and changing the peripheral speed between the rolls. On the other hand, transverse uniaxial stretching can be performed using a tenter type stretching machine.

In the manufacture of polarizing films, in order to enhance the adsorption of dyes on the uniaxially stretched film, it is preferable to perform fixing treatment. As the fixation treatment, a method of immersing a thin film in a fixation treatment bath to which a boron compound such as boric acid and borax is added is exemplified. At this time, an iodine compound may be added to the stationary treatment bath as needed.

Preferably, the film subjected to uniaxial stretching, or uniaxial stretching and fixing treatment is then subjected to drying treatment (heat treatment). The temperature of the drying treatment (heat treatment) is preferably in the range of 30 to 150°C, and particularly preferably in the range of 50 to 140°C. If the temperature of the drying treatment (heat treatment) is too low, the dimensional stability of the polarizing film obtained tends to decrease, and on the other hand, if it is too high, the polarization performance tends to decrease due to decomposition of the dye and the like.

A polarizing plate can be formed by laminating an optically transparent and mechanically strong protective film on both sides or one side of the polarizing film obtained as described above. As a protective film in this case, triacetate cellulose (TAC) film, acetic acid can be used. Cellulose butyrate (CAB) film, acrylic film, polyester film, etc. Moreover, as an adhesive agent for bonding a protective film, a PVA-type adhesive agent, a urethane-type adhesive agent, etc. are mentioned, Among them, a PVA-type adhesive agent is preferable.

The polarizing plate obtained as described above can be used as a component of a liquid crystal display device by being bonded to a glass substrate after being coated with an acrylic adhesive or the like. When bonding a polarizing plate to a glass substrate, a retardation film, a viewing angle enhancement film, a brightness enhancement film, etc. can be bonded.

[Example]

Hereinafter, the present invention will be specifically described by way of examples.

Hysteresis value measurement

The hysteresis value of the PVA film before being wound through the drying step was measured. The hysteresis value in the thickness direction of the thin film at 25° C. was measured based on light having a wavelength of 590 nm using a plurality of hysteresis measuring devices arranged in the vertical direction with respect to the flow direction of the thin film. The pitch in the longitudinal direction (flow direction) of the film was 15 m and the pitch in the width direction was 10 mm. After measuring the hysteresis value of the entire film surface, the number average Re of _hysteresis at all measurement points was obtained. Furthermore, from the hysteresis (Re _i ) of the measurement point i (i=1~n, n is an integer) at a position 10 mm from the end of the PVA film, the maximum value (Re _{maximum value} ) is obtained by the above-mentioned method. ), the minimum value (Re _{minimum value} ), and the number average value (Re _{average value} ), A and B are calculated by introducing the above-mentioned formulae (1) and (2).

Example 1 (1) Manufacture of PVA film

100 parts by mass of PVA (saponified product of vinyl acetate homopolymer, degree of polymerization 2,400, degree of saponification 99.9 mol %), 12 parts by mass of glycerol, and 0.1 part by mass of diethanolamide laurate were used And a membrane-forming stock solution with a volatile content rate of 66% by mass of water. As a film forming apparatus, what was equipped with a T-slot die (width 4.9m) and 18 drying rolls whose rotation axes were parallel to each other was used. The above-mentioned film-forming stock solution was discharged into a film form from a T-slot die on a first drying roll (surface temperature 93.5°C, peripheral speed (S ₁ ) 14.5 m/min). At this time, hot air (temperature 90°C, dew point temperature 10°C) was uniformly blown over the entire film at a wind speed of 5 m/sec to the film on the first drying roll. Next, the film was peeled off from the first drying roll (the volatile content of the film after peeling from the first drying roll was 18.2 mass %), and the film surface that was not in contact with the first drying roll was brought into contact with the second drying roll for drying. The film was dried by sequentially contacting the film from the 3rd drying roll to the 18th drying roll so that the one side and the other side of the film alternately contacted each drying roll. Then, after cutting both ends (ears) of the film, it was wound into a roll shape to obtain a PVA film (thickness 60 μm, width 4 m, length 5,000 m, volatile content rate 3 mass %). After cutting both ends of the film, the hysteresis value of the PVA film was measured by the method described above before winding. The volatile matter ratio of the thin film was obtained as follows. After peeling the film from the first drying roll, a sample was collected from the center of the film. Moreover, samples were taken from the center part of the film just before contacting the 2nd - 18th drying roll, respectively. After drying each sample in a dryer at 105° C. for 16 hours, the volatile content ratio was determined from the mass of the film before and after drying. The surface temperature of each drying roll is shown in Table 2, and the peripheral speed ratio of the adjacent drying roll is shown in Table 3.

The volatile content rate of the film just before contacting the seventh drying roll was 10.8 mass %. That is, the drying roll contacted first after the volatile matter ratio of the film became 11 mass % or less was the seventh drying roll (x=7). The ratio (S 7 /S 2 ) of the peripheral speed (S ₇ ) of the seventh drying roll to the peripheral speed (S ₂ ) of the second drying roll (S ₇ /S ₂ ) was 0.971, and the peripheral speed (S 2 ) of the second drying roll to the peripheral speed (S ₂ ) of the first drying The ratio (S ₂ /S ₁ ) of the peripheral speeds (S ₁ ) of the rolls was 1.050. The average of the roll surface temperature from the 2nd drying roll to the xth drying roll was 80 degreeC. These results are shown in Table 1. In addition, Table 1 shows the _sum of A, B, and Re and the _sum of A/Re calculated using the hysteresis value of the PVA film.

Evaluation of stretchability

As shown below, the film roll of the obtained PVA film was continuously subjected to swelling treatment, dyeing, uniaxial stretching, and drying treatment in this order to produce a polarizing film. As swelling treatment, the PVA film was immersed in distilled water for 1 minute. Next, it was immersed for 1 minute in an aqueous solution containing an iodine-based dye (iodine concentration: 0.3 mass %, potassium iodide concentration: 2.1 mass %, temperature 30° C.) to contain an iodine-based dye. Next, it stretched 6.2 times in the flow direction in a boric acid aqueous solution (boric acid concentration: 4 mass %, potassium iodide concentration: 6 mass %, temperature: 60° C.). Then, it was made to dry at 60 degreeC for 1 minute, and the polarizing film was obtained. In the case where the number of times of occurrence of breakage when a 1,000 m PVA film roll was stretched under the above conditions was 0 times, the evaluation of stretchability was set to A, and the evaluation of stretchability was set to B when it was 1 to 3 times. In the case of 4 times or more, the evaluation of stretchability was made C.

Evaluation of Width Variation

The width of the obtained polarizing film was measured at intervals of 100 m, and the difference α (cm) between the maximum value and the minimum value was calculated. The percentage (100×α/β) of the aforementioned difference α (cm) to the PVA film width β (cm) of the original roll was calculated. When the percentage is less than 0.5%, the evaluation of the width fluctuation is A, when the percentage is 0.5% or more and less than 1.0%, the evaluation of the width fluctuation is B, and when the percentage is 1.0% or more, the evaluation of the width fluctuation is C. .

Examples 2 and 3, Comparative Examples 1 to 4, Reference Examples 1 and 2

The production and evaluation of the PVA film were performed in the same manner as in Example 1, except that the production conditions of the PVA film were as shown in Tables 1 to 3. The results are shown in Table 1.

The PVA film of the present invention satisfying the above formulas (1) to (4) is excellent in stretchability, and also has a uniform width during stretching. The ratio (S x /S 2 ) of the peripheral speed (S _x ) of the xth drying roll to the peripheral speed (S ₂ ) of the second drying roll (S _x /S ₂ ) is less than 0.970, and the average of the roll temperature from the second drying roll to the xth drying roll When it exceeds 81 degreeC (Comparative Examples 1 and 2), A and B of the obtained PVA film exceed the upper limit prescribed|regulated by the said Formula (1) and (2), and the uniformity of the stretchability and the width|variety at the time of stretching falls. In addition, A and B are indicators of the hysteresis unevenness in the longitudinal direction of the PVA film, and the optical properties of the optical films obtained by the PVA films of Comparative Examples 1 and 2 having such large values are considered to be insufficient.

When the average roll temperature from the second drying roll to the xth drying roll was less than 63°C (Comparative Example 3), A and B of the obtained PVA film also exceeded the upper limits specified by the above formulas (1) and (2), The stretchability and the uniformity of the width during stretching are reduced. It is considered that the optical properties of the optical film obtained from the PVA film of Comparative Example 3 in which A and B are large are insufficient. The average of the roll temperature from the second drying roll to the xth drying roll is less than 63°C, and the ratio of the peripheral speed (S _x ) of the xth drying roll to the peripheral speed (S ₂ ) of the second drying roll (S _x /S ₂ ) exceeds 0.995 (Comparative Example 4), the _total Re of the obtained PVA film exceeds the upper limit defined by the above formula (3), and the stretchability and the uniformity of the width during stretching are reduced.

Reference Example 1 is an example in which both ends of the PVA film formed in the same manner as in Comparative Example 3 were cut, and the ends were cut wider than Comparative Example 3. Although the performance of the obtained PVA film is sufficient, it has a practical problem due to its narrow width. Reference Example 2 is an example of a conventional thick (75 μm) PVA thin film.

Claims (3)

A polyvinyl alcohol film having a width of 3 m or more and 8 m or less, a length of 1,000 m or more and 50,000 m or less, and a thickness of 15 to 65 μm, characterized in that the pitch in the longitudinal direction is 15 m and the pitch in the width direction is 15 m. The hysteresis value measured at 10mm satisfies the following equations (1) to (4), A(nm)=Re _{maximum value} -Re _{minimum value} ≦10 (1)

2≦ _ReTotal ≦20 (3) 0.3<A/ _ReTotal (4) In the formula, Re _{maximum value} (nm): the maximum value of the hysteresis at a position 10mm away from the end Re _{minimum value} (nm): at the distance end The minimum value of the hysteresis at the position of 10mm from the end Re _{average value} (nm): the average value of the hysteresis at the position of 10mm from the end Re _i (nm): the measurement point i at the position of 10mm from the end (i=1~ n, n is an integer) _total hysteresis value Re (nm): average value of hysteresis of all measurement points. A method for producing a polyvinyl alcohol film, which is the method for producing a polyvinyl alcohol film as claimed in claim 1, using a film forming apparatus having a plurality of drying rolls whose rotation axes are parallel to each other, wherein the plurality of drying rolls include a first drying Roll to the m-th drying roll (m represents an integer of 3 or more), and after the film is obtained by discharging the film-forming stock solution containing polyvinyl alcohol from the die onto the first drying roll and drying it, the second drying roll is used~ In the step of further drying the film with the mth drying roll, the volatile content of the film when peeled from the first drying roll is 12 to 19%, the peripheral speed (S ₂ ) of the second drying roll is relative to the peripheral speed of the first drying roll The ratio (S ₂ /S ₁ ) of (S ₁ ) is 1.015 to 1.050, and the peripheral speed (S _x ) of the drying roll (the x-th drying roll) that first comes into contact after the volatile content of the film becomes 11% by mass or less The ratio (S _x /S ₂ ) of the peripheral speeds (S ₂ ) of the two drying rolls was 0.970 to 0.995, and the average of the roll temperatures from the second drying roll to the xth drying roll was 63 to 81°C. The method for producing a polyvinyl alcohol film according to claim 2, wherein the volatile content of the film-forming stock solution containing polyvinyl alcohol is 60 to 75% by mass, and the peripheral speed (S ₁ ) of the first drying roll is 8 to 25 m/min .

Images