JPWO2019244968A1 - Polyvinyl alcohol film and its manufacturing method - Google Patents

Abstract

The width direction of the PVA film is the TD direction, the machine flow direction is the MD direction, and there are 5 or less streaky defects with a height difference of 0.15 μm or more that extend continuously and linearly in the MD direction by 1.5 m or more. There are no streak-like defects with a height difference of 0.50 μm or more extending linearly in the MD direction for 1.5 m or more in the entire width of the film, and the thickness of the central portion in the TD direction is 0.5 mm in the MD direction. When the maximum value is tMAX, the minimum value is tMIN, and the average value is tAVE, the tAVE is 35 μm or less, and the thickness spot rate defined by the following formula (1) is 5. A polyvinyl alcohol film having a content of 5.5% or less. Even if the film is thin, there are few streaky defects and thickness unevenness in the MD direction is reduced, so that wrinkles are suppressed during stretching. Thickness spot rate = (tMAX-tMIN) / tAVE x 100 (%) (1)

Description

The present invention relates to a polyvinyl alcohol film having few film surface defects and a uniform thickness, and a method for producing the same.

A polarizing plate having a function of transmitting and shielding light is a basic component of a liquid crystal display (LCD) together with a liquid crystal that changes the polarization state of light. LCDs are widely used in small devices such as calculators and wristwatches, laptop computers, LCD monitors, LCD color projectors, LCD TVs, in-vehicle navigation systems, mobile phones, and measuring devices used indoors and outdoors. .. Among the fields of application of these LCDs, LCD TVs and LCD monitors are becoming thinner, and the demand for thin film is increasing.

An ordinary polarizing plate has a structure in which a protective film such as a cellulose triacetate (TAC) film is attached to a polarizing film produced by uniaxially stretching a polyvinyl alcohol film and dyeing it.

As a method for producing a polyvinyl alcohol film having a uniform thickness, for example, in Patent Document 1, a stock solution is prepared by dissolving polyvinyl alcohol in a solvent such as water, and then the stock solution is poured onto a drum (roll). In the manufacturing method of forming a film and heating and drying the film on the drum, a manufacturing method in which the speed ratio between the speed of the drum and the discharge speed of the undiluted solution is 1 to 5 is described. Patent Document 1 describes that a polyvinyl alcohol film having a uniform thickness and excellent smoothness can be produced even in a large area by using such a speed ratio.

Patent Document 2 discloses a polyvinyl alcohol film having a thickness of 5 to 60 μm, a width of 2 m or more, and a length of 2 km or more, in which the coefficient of variation of the thickness on the entire surface of the film is 1% or less. In Patent Document 2, in order to reduce the coefficient of variation to 1% or less, the touch line where the aqueous solution of polyvinyl alcohol touches the cast drum (roll) is stabilized by an air knife in the MD direction (film flow direction). A method for reducing the thickness unevenness of the above is described.

Further, in Patent Document 3, the polyvinyl alcohol film obtained by containing a nonionic surfactant in polyvinyl alcohol does not generate die lines or foreign substances, and is particularly excellent in long-term film forming property, and has a thickness of 120 μm. It is stated that no die lines or gels were generated even when the polyvinyl alcohol film was produced and then biaxially stretched for 60 consecutive days.

Japanese Unexamined Patent Publication No. 2002-79530 Japanese Unexamined Patent Publication No. 2016-172851 Japanese Unexamined Patent Publication No. 2001-259393

The difference between the maximum thickness and the minimum thickness of the film obtained by the method of adjusting the speed ratio between the drum speed and the undiluted solution discharge speed described in Patent Document 1 was 1.6 μm or more. In the thickness (for example, 45 μm to 70 μm) of the polyvinyl alcohol film (hereinafter, polyvinyl alcohol may be referred to as PVA) used for the conventional polarizing plate, the mechanical flow direction of the PVA film (hereinafter, the mechanical flow direction is referred to as MD direction). The thickness spots that occur in) were not a major problem. However, due to the recent thinning of the PVA film, a problem that the thickness spot ratio (ratio of thickness spots to the average thickness) deteriorates has become apparent, especially when the thickness is 35 μm or less.

In the method described in Patent Document 2, since the polyvinyl alcohol aqueous solution (film-forming stock solution) discharged from the T-die is physically pressed against the drum roll with an air knife, the lip tip of the T-die comes into contact with the discharged film-forming stock solution. As a result, streaky defects may occur continuously in the MD direction.

Patent Document 3 does not describe that the thickness spot ratio deteriorates particularly when the thickness of the polyvinyl alcohol film is 35 μm or less, and there is no description or suggestion of a solution thereof.

An object of the present invention is to provide a PVA film having a thickness of 35 μm or less, which reduces thickness unevenness in the MD direction and has few streaky defects continuously generated in the MD direction, and a method for producing the film.

The above object is achieved by the present invention described below.

That is, the present invention
[1] The width direction of the PVA film is the TD direction, the machine flow direction is the MD direction, and streak-like defects having a height difference of 0.15 μm or more extending linearly continuously for 1.5 m or more in the MD direction are 5 in the entire film width. There are no streaky defects with a height difference of 0.50 μm or more extending linearly for 1.5 m or more in the MD direction, and the thickness of the central portion in the TD direction is 0 in the MD direction. _{When the maximum value is t MAX} , the minimum value is t _MIN, and the average value is t _AVE when measured over 1.0 m at 5 mm intervals, t _AVE is 35 μm or less and is specified by the following formula (1). Polyvinyl alcohol film having a thickness spot ratio of 5.5% or less;
Thickness spot rate = (t _MAX −t _MIN ) / t _AVE × 100 (%) (1)
[2] The PVA film of the above [1] having a width of 2.0 m or more and 7.0 m or less;
[3] Production of the polyvinyl alcohol film according to the above [1] or [2], wherein a film-forming stock solution containing polyvinyl alcohol at 94 to 98 ° C. is poured onto a roll at 88 to 92 ° C. to form a film. Method;
Is.

According to the present invention, even if the thickness of the film is as thin as 35 μm or less, a PVA film having few streaky defects continuously generated in the MD direction and reduced thickness unevenness in the MD direction and a method for producing the PVA film can be obtained. Provided. Further, by using the PVA film of the present invention, it is possible to obtain a polarizing film in which the generation of wrinkles is suppressed. Further, since the wrinkles of the polarizing film are suppressed, when the protective film is attached to the polarizing film and processed into a polarizing plate, air bubbles do not get caught between the polarizing film and the protective film, and the result can be obtained. The quality of the polarizing plate is improved.

The PVA film of the present invention is characterized in that the average thickness t _AVE is 35 μm or less and the thickness spot ratio in the MD direction is 5.5% or less. The thickness unevenness in the present invention means that the width direction of the film is the TD direction, the mechanical flow direction of the film is the MD direction, and the thickness of the central portion of the film in the TD direction is 1.0 m at 0.5 mm intervals in the MD direction. When the maximum value of the film thickness is t _MAX , the minimum value of _{the film thickness is t MIN} , and the average value of the film thickness is t _AVE , it is defined by the following formula (1).
Thickness spot rate = (t _MAX −t _MIN ) / t _AVE × 100 (%) (1)

With a PVA film thicker than 35 μm, the problem of streak-like defects that continuously occur in the MD direction is extremely unlikely to become apparent regardless of the value of the thickness spot ratio. The lower limit of the average thickness t _AVE is not particularly limited, but if it is too thin, stretch breakage is likely to occur during uniaxial stretching for producing a polarizing film. Therefore, the average value t _AVE is preferably 5 μm or more, more preferably 10 μm or more, and particularly preferably 15 μm or more.

As the PVA constituting the PVA film of the present invention, a vinyl ester polymer obtained by polymerizing a vinyl ester monomer is saponified and the vinyl ester unit is a vinyl alcohol unit. Examples of the vinyl ester monomer include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, vinyl versatic acid and the like, and among them, acetic acid. It is preferable to use vinyl.

When polymerizing the vinyl ester monomer, if necessary, a monomer copolymerizable with the vinyl ester monomer is provided in a range that does not impair the gist of the present invention (preferably 15 mol with respect to all the monomer units in PVA). % Or less, more preferably 5 mol% or less) may be copolymerized. Examples of such monomers include olefins having 3 to 30 carbon atoms such as ethylene, propylene, 1-butyl, and isobutene; acrylic acid and salts thereof; methyl acrylate, ethyl acrylate, n-propyl acrylate, and acrylic. Acrylic acid esters such as i-propyl acid, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate; methacrylic acid and salts thereof. Methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate , Methacrylate esters such as octadecyl methacrylate; acrylamide, N-methylacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide, diacetoneacrylamide, acrylamidepropanesulfonic acid and its salts, acrylamidepropyldimethylamine and its salts, Acrylamide derivatives such as N-methylol acrylamide and derivatives thereof; methacrylamide, N-methylmethacrylate, N-ethylmethacrylate, methacrylamide propanesulfonic acid and its salts, methacrylicamidepropyldimethylamine and its salts, N-methylolmethacrylicamide. And methacrylicamide derivatives such as derivatives thereof; N-vinylamides such as N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone; methylvinyl ether, ethylvinyl ether, n-propylvinyl ether, i-propylvinyl ether, n-butylvinyl ether. Vinyl ethers such as i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether; nitriles such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride and vinylidene fluoride. Allyl compounds such as allyl acetate and allyl chloride; maleic acid and its salts or esters thereof; itaconic acid and its salts or esters thereof; vinylsilyl compounds such as vinyltrimethoxysilane; isopropenyl acetate, N-vinylformamide, N-vinyl Examples thereof include N-vinylamides such as acetoamide and N-vinylpyrrolidone.

The average degree of polymerization of PVA constituting the PVA film of the present invention is preferably 500 or more from the viewpoint of the strength of the PVA film, more preferably 1000 or more from the viewpoint of polarization performance, further preferably 2000 or more, and particularly preferably 3500 or more. preferable. On the other hand, the upper limit of the degree of polymerization of PVA is preferably 10,000 or less from the viewpoint of film forming property of the PVA film of the present invention.

The saponification degree of the PVA constituting the PVA film of the present invention is preferably 95 mol% or more, more preferably 96 mol% or more, from the viewpoint of water resistance of the polarizing film obtained by uniaxially stretching the film. It is preferably 98 mol% or more, and more preferably 98 mol% or more. The degree of saponification of PVA in the present specification refers to structural units (typically vinyl ester units) and vinyl _{possessed by PVA that can be converted into vinyl alcohol units (-CH 2-CH (OH)-) by saponification.} The ratio (mol%) of the number of moles of the vinyl alcohol unit to the total number of moles of the vinyl alcohol unit.

When producing the PVA film of the present invention, it is preferable to add a polyhydric alcohol as a plasticizer to PVA. Examples of the polyhydric alcohol include ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane and the like, and one of these may be used alone or in combination of two or more. it can. Among them, ethylene glycol or glycerin is preferably used because of the effect of improving stretchability.

The amount of the polyhydric alcohol added is preferably 1 to 30 parts by mass, more preferably 3 to 25 parts by mass, still more preferably 5 to 20 parts by mass with respect to 100 parts by mass of PVA. If the amount added is less than 1 part by mass, the dyeability and stretchability may be lowered, and if it is more than 30 parts by mass, the PVA film may become too flexible and the handleability may be lowered.

Further, when producing the PVA film of the present invention, it is preferable to add a surfactant. The surfactant is not particularly limited, but an anionic or nonionic surfactant is preferable. 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 anionic surfactant such as dodecylbenzene sulfonate. Examples of the nonionic surfactant include an alkyl ether type such as polyoxyethylene oleyl ether, an alkylphenyl ether type such as polyoxyethylene octylphenyl ether, an alkyl ester type such as polyoxyethylene laurate, and polyoxyethylene laurylamino. Alkylamine type such as ether, alkylamide type such as polyoxyethylene lauric acid amide, polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether, alkanolamide type such as laurate diethanolamide and oleic acid diethanolamide, polyoxy Nonionic surfactants such as allylphenyl ether type such as alkyleneallylphenyl ether can be mentioned. As the nonionic surfactant, an alkanolamide type nonionic surfactant is preferable, and lauric acid diethanolamide is more preferable. These surfactants can be used alone or in combination of two or more.

When a surfactant is added, the amount of the surfactant added is preferably 0.01 to 1 part by mass, more preferably 0.02 to 0.5 parts by mass, and 0.05 to 0.3 parts by mass with respect to 100 parts by mass of PVA. Part is particularly preferable. If the amount added is less than 0.01 parts by mass, the effects of improving stretchability and dyeability are less likely to appear, and if it is more than 1 part by mass, the surfactant elutes on the surface of the PVA film to block the PVA films. It may cause a decrease in handleability.

In the PVA film of the present invention, it is important that the thickness spot ratio defined by the above formula (1) is 5.5% or less. If the thickness spot ratio of the PVA film is larger than this, wrinkles will occur in the obtained polarizing film. The thickness spot ratio is more preferably 4% or less. It is necessary to further raise the drying roll temperature in order to reduce the thickness spot ratio to less than 3%, but when the drying roll temperature is set to, for example, 96 ° C. or higher, cracks are likely to occur in the plating layer on the roll surface. Further, even if the thickness spot ratio is less than 3%, the streak-like defects are not significantly improved, so that the thickness spot ratio is preferably 3% or more.

In the present invention, there are 5 or less streaky defects having a height difference of 0.15 μm or more and extending linearly in the MD direction by 1.5 m or more in the entire width of the PVA film, and 1.5 m or more continuously in the MD direction. It is necessary that there are no streak-like defects extending linearly with a height difference of 0.50 μm or more in the entire width of the PVA film. A streak-like defect is a defect that appears as a continuous single line of 1.5 m or more extending in the MD direction, and is caused by a height difference in thickness from the periphery. When the height difference is 0.15 μm or more, the color spots after dyeing become dark, and when the number of such streak-like defects of the height difference is more than 5 in the entire width of the film, a practical problem arises. Further, when the height difference is 0.5 μm or more, the color spots after dyeing become darker, and if even one such streak-like defect of the height difference exists, a problem arises in practical use. The streaky defects are evaluated by the method described in Examples.

The width of the PVA film of the present invention is not particularly limited and may be, for example, 0.5 m or more. In recent years, since a wide polarizing film has been demanded, the width is preferably 2.0 m or more, more preferably 2.5 m or more, and further preferably 3.5 m or more. On the other hand, if the PVA film is too wide, the manufacturing cost of the film forming apparatus may increase, or it may be difficult to uniformly stretch the PVA film when manufacturing the optical film with the manufacturing apparatus which has been put into practical use. Therefore, the width of the PVA film is preferably 7.0 m or less, and more preferably 6.5 m or less.

In the present invention, in order to produce a PVA film, a roll film forming machine equipped with one or more rotating rolls and a drying device, a humidity control device, a winding device and the like is used. Motors, transmissions, etc. are used to drive each device, and the transfer speed is adjusted. The drying temperature of the PVA film is generally 50 to 150 ° C. As the film-forming method, for example, a cast film-forming method using a film-forming stock solution in a solution state in which PVA is dissolved in a solvent, or a roll film-forming method in which a film-forming stock solution made of hydrous polyvinyl alcohol is extruded and poured onto a roll is adopted. The latter is preferable. The film-forming stock solution made of the hydrous polyvinyl alcohol may contain an organic solvent.

When producing the PVA film of the present invention, the PVA-containing film-forming stock solution supplied on the roll is preferably 94 to 98 ° C. at the die inlet, and more preferably 94.5 to 96.5 ° C. preferable. If the temperature of the film-forming stock solution is less than 94 ° C., the leveling property of the film-forming stock solution supplied on the roll is lowered and the thickness unevenness tends to be large. On the other hand, when the temperature exceeds 98 ° C., the viscosity of the film-forming stock solution decreases and the lip tip interferes with the discharged film-forming stock solution, so that streak-like defects in the MD direction are likely to occur.

The volatile fraction of the PVA-containing film-forming stock solution used in producing the PVA film is preferably 50 to 90% by mass, more preferably 55 to 80% by mass. If the volatile fraction is less than 50% by mass, the viscosity becomes high and film formation may be difficult. If the volatile fraction is larger than 90% by mass, the viscosity may become too low and the thickness uniformity of the PVA film may be impaired.

When producing a PVA film, it is preferable to use a die made of a flexible lip and supply the film-forming stock solution from the die onto a roll of a roll film-forming machine. Examples of the die include a T-die, an I-die, and a lip coater die. Next, the water content in the film-forming stock solution and the volatile components such as the organic solvent are evaporated on the roll.

In order to produce the PVA film, the temperature of the roll to which the film-forming stock solution is supplied is preferably 88 ° C. to 92 ° C., more preferably 89 ° C. to 90 ° C. If the temperature is lower than 88 ° C., the peelability from the roll may be deteriorated due to poor drying, and the thickness unevenness may become large. Further, when the temperature exceeds 92 ° C., crystallization of PVA proceeds on the surface of the film in contact with the roll, and a difference in crystallinity from the other surface may occur. If there is a difference in crystallinity between one surface and the other surface of the film, the water absorption characteristics will be different, so that the film is likely to curl in the processing process of immersing the film in water, and the process passability is deteriorated.

The peripheral speed of the roll is preferably in the range of 10.0 to 50.0 m / min. If the peripheral speed is less than the above lower limit, the productivity is poor. When the peripheral speed exceeds the above upper limit, the time in contact with the roll is shortened, so that the PVA film tends to be insufficiently dried.

The PVA film peeled from the roll is dried and humidity-controlled to prepare an appropriate PVA film, and then the PVA film is wound up.

In order to produce a polarizing film from the PVA film of the present invention, for example, the PVA film is dyed, uniaxially stretched, fixed, dried, and further heat-treated if necessary. The order of each step is not particularly limited, and two steps such as dyeing and uniaxial stretching may be carried out at the same time. Moreover, each step may be repeated a plurality of times. Although dyeing can be performed before uniaxial stretching, during uniaxial stretching, or after uniaxial stretching, PVA tends to increase its crystallinity due to uniaxial stretching and may reduce dyeability. It is preferably carried out in any step prior to stretching or during uniaxial stretching.

Dyes used for dyeing include iodine-potassium iodide; direct black 17, 19, 154; direct brown 44, 106, 195, 210, 223; direct red 2, 23, 28, 31, 37, 39, 79, 81. , 240, 242, 247; Direct Blue 1, 15, 22, 78, 90, 98, 151, 168, 202, 236, 249, 270; Direct Violet 9, 12, 51, 98; Direct Green 1, 85; Direct Yellow 8, 12, 44, 86, 87; bicolor dyes such as Direct Orange 26, 39, 106, 107 can be used alone or as a mixture of two or more. Dyeing is generally performed by immersing a PVA film in a solution containing the dye, but the treatment conditions and treatment methods include, for example, mixing the dye with a film-forming stock solution containing PVA to form a film. There are no particular restrictions.

As the uniaxial stretching method performed in the length direction of the PVA film, a wet stretching method in which the PVA film is stretched while immersed in a solution, or a dry heat stretching method in which the PVA film is absorbed in water and then stretched in the air can be adopted. The PVA film may be uniaxially stretched in a solution containing the dye or in a fixing treatment bath described later. Stretching is preferably carried out at a stretching ratio as high as possible within a range in which the PVA film is not cut, specifically, 4 times or more, more preferably 5 times or more, and particularly preferably 6 times or more. If the draw ratio is smaller than 4 times, it is difficult to obtain practically sufficient polarization performance and durability performance. The stretching temperature is not particularly limited, but is preferably 30 to 90 ° C. when the PVA film is stretched in water (wet stretching), and 50 to 180 ° C. when it is dry heat stretched. The thickness of the film after stretching is preferably 2 to 25 μm, more preferably 5 to 20 μm.

An immobilization treatment can be performed for the purpose of strengthening the adsorption of the dye on the PVA film. Boric acid and boron compounds are usually added to the treatment bath used for the fixation treatment. Further, if necessary, an iodine compound may be added to the treatment bath.

The drying treatment (heat treatment) of the PVA film is preferably performed at 30 to 150 ° C, more preferably 50 to 150 ° C.

The polarizing film obtained as described above is usually used as a polarizing plate by laminating a protective film that is optically transparent and has mechanical strength on both sides or one side thereof. As the protective film, a cellulose acetate film, an acrylic film, a polyester film or the like is usually used.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples. The analysis, measurement and evaluation in Examples and Comparative Examples were carried out by the methods shown below.

(Evaluation of streaky defects)
A streak-like defect is a defect that can be seen as a continuous single line of 1.5 m or more extending in the mechanical flow direction (MD direction) during film formation. Light is irradiated to the film using a light source, and the light transmitted through the film is emitted. When projected onto a white wall, it is confirmed as a continuous bright or dark pattern extending in the MD direction. A film having streaky defects has a height difference of 0.15 μm or more in the concave portion or the convex portion on the surface, and can be observed as the bright pattern or the dark pattern. Specifically, a sample piece cut out from the PVA film obtained in the following Example or Comparative Example at an overall width of 1.5 m in the MD direction was hung so as to be up and down in the MD direction, and separated from the film surface by 350 cm. A halogen lamp light source manufactured by Eswan Co., Ltd. having a luminous intensity of about 550 Lux was installed at the position, and the light was projected perpendicularly to the film surface. Next, the streak-like bright or dark pattern observed when the light transmitted through the film was projected onto a white wall 10 cm away from the film was determined to be a streak-like defect. Then, each part of the film corresponding to the streak-like defect is measured by the contact type thickness gauge "KG601A" manufactured by Anritsu Co., Ltd. for the total number of streak-like defects by measuring the height difference between the defect portion and the surrounding portion in the film thickness direction. did. In this way, in the entire width of the PVA film, the number of streaky defects in the range of 0.15 to 0.50 μm and the height difference extending linearly in the MD direction for 1.5 m or more and for 1.5 m or more in the MD direction are continuous. The presence or absence of streaky defects with a height difference of 0.5 μm or more extending in a straight line was determined and evaluated according to the following criteria. If the height difference exceeds 0.50 μm, even one streak-like defect poses a practical problem.
A: The total width of the PVA film has 5 or less streaks in the range of 0.15 to 0.50 μm, and there are no streaks with a height difference of 0.5 μm or more. B: The full width of the PVA film. There are more than five streaky defects with a height difference of 0.15 to 0.50 μm, or there are streak-like defects with a height difference of 0.5 μm or more.

(Measurement of PVA film thickness and calculation of thickness spot rate)
The thickness of the central portion of the PVA film in the TD direction (width direction) was measured over 1.0 m at a pitch of 0.5 mm in the MD direction. The measurement was performed using a contact type thickness gauge "KG601A" manufactured by Anritsu Co., Ltd. The maximum value of the measured values was t _MAX (μm), the minimum value was t _MIN (μm), and the average value was t _AVE (μm). Using the obtained value, the thickness spot ratio was determined by the following formula (1).
Thickness spot rate = (t _MAX −t _MIN ) / t _AVE × 100 (%) ・ ・ ・ (1)

(Evaluation of wrinkles on polarizing film)
After stretching the PVA film 2.6 times in the MD direction with a continuous stretching machine, the presence or absence of wrinkles lined up in the TD direction was visually observed and evaluated according to the following criteria.
A: No wrinkles or very slight wrinkles.
B: Significant wrinkles occurred.

[Example 1]
Using a roll film-forming machine, a volatile content of 70 parts consisting of 100 parts by mass of PVA having a saponification degree of 99.9 mol% and an average degree of polymerization of 2400, 12 parts by mass of glycerin, 0.1 parts by mass of diethanolamide laurate, and water. A mass% film-forming stock solution is discharged from the T-die at 96 ° C. to a first drying roll (surface temperature 91.7 ° C., peripheral speed 24.8 m / min), then peeled off with a second drying roll, and then peeled off with a second drying roll. After that, drying was performed at an average of 85 ° C. Finally, a PVA film (thickness t _AVE 21.1 μm, width 3000 mm) was obtained by winding with a winding device. The obtained film had a thickness spot ratio of 3.79%, and the number of streaky defects in the range of 0.15 to 0.50 μm in height difference was two in total width, and streaks having a height difference of 0.5 μm or more. There were no condition defects. In addition, after stretching 2.6 times in the MD direction, no wrinkles lined up in the TD direction occurred.

[Example 2]
Using a roll film-forming machine, a volatile content of 70 parts consisting of 100 parts by mass of PVA having a saponification degree of 99.9 mol% and an average degree of polymerization of 2400, 12 parts by mass of glycerin, 0.1 parts by mass of diethanolamide laurate, and water. A mass% film-forming stock solution is discharged from the T-die at 94 ° C. to a first drying roll (surface temperature 89.7 ° C., peripheral speed 24.8 m / min), then peeled off with a second drying roll, and then peeled off with a second drying roll. After that, drying was performed at an average of 85 ° C. Finally, a PVA film (thickness t _AVE 20.7 μm, film width 3000 mm) was obtained by winding with a winding device. The obtained film had a thickness spot ratio of 4.55%, and the number of streaky defects in the range of 0.15 to 0.50 μm in height difference was one in the entire width, and streaks having a height difference of 0.5 μm or more. There were no condition defects. Further, after stretching 2.6 times in the MD direction, extremely slight wrinkles lined up in the TD direction were generated.

[Example 3]
Using a roll film-forming machine, a volatile content of 70 parts consisting of 100 parts by mass of PVA having a saponification degree of 99.9 mol% and an average degree of polymerization of 2400, 12 parts by mass of glycerin, 0.1 parts by mass of diethanolamide laurate, and water. A mass% film-forming stock solution is discharged from the T-die at 97 ° C. to a first drying roll (surface temperature 89.7 ° C., peripheral speed 24.8 m / min), then peeled off with a second drying roll, and then peeled off with a second drying roll. After that, drying was performed at an average of 85 ° C. Finally, a PVA film (thickness t _AVE 20.4 μm, film width 3000 mm) was obtained by winding with a winding device. The obtained film had a thickness spot ratio of 5.11%, and no streak-like defects occurred in the entire width. Further, after stretching 2.6 times in the MD direction, extremely slight wrinkles lined up in the TD direction were generated.

[Example 4]
Using a roll film-forming machine, a volatile content of 70 parts consisting of 100 parts by mass of PVA having a saponification degree of 99.9 mol% and an average degree of polymerization of 2400, 12 parts by mass of glycerin, 0.1 parts by mass of diethanolamide laurate, and water. A mass% film-forming stock solution is discharged from the T-die at 96 ° C. to a first drying roll (surface temperature 88.0 ° C., peripheral speed 24.8 m / min), then peeled off with a second drying roll, and then peeled off with a second drying roll. After that, drying was performed at an average of 85 ° C. Finally, a PVA film (thickness t _AVE 20.1 μm, film width 3000 mm) was obtained by winding with a winding device. The obtained film had a thickness spot ratio of 5.22%, and no streak-like defects occurred in the entire width. Further, after stretching 2.6 times in the MD direction, extremely slight wrinkles lined up in the TD direction were generated.

[Comparative Example 1]
Using a roll film-forming machine, a volatile content of 70 parts consisting of 100 parts by mass of PVA having a saponification degree of 99.9 mol% and an average degree of polymerization of 2400, 12 parts by mass of glycerin, 0.1 parts by mass of diethanolamide laurate, and water. The mass% of the film-forming stock solution was discharged from the T-die at 96.0 ° C. to a first drying roll (surface temperature 92.3 ° C., peripheral speed 24.8 m / min), then peeled off by a second drying roll, and the second After the drying roll, drying was performed at an average of 85 ° C. Finally, a PVA film (thickness t _AVE 20.1 μm, film width 3000 mm) was obtained by winding with a winding device. The obtained film had a thickness spot ratio of 4.13%, and the number of streaky defects in the height difference range of 0.15 to 0.50 μm was 12 in total width. In addition, after stretching 2.6 times in the MD direction, remarkable wrinkles lined up in the TD direction occurred.

[Comparative Example 2]
Using a roll film-forming machine, a volatile content of 70 parts consisting of 100 parts by mass of PVA having a saponification degree of 99.9 mol% and an average degree of polymerization of 2400, 12 parts by mass of glycerin, 0.1 parts by mass of diethanolamide laurate, and water. The mass% of the film-forming stock solution was discharged from the T-die at 98.5 ° C. to a first drying roll (surface temperature 89.7 ° C., peripheral speed 24.8 m / min), then peeled off by a second drying roll, and the second After the drying roll, drying was performed at an average of 85 ° C. Finally, a PVA film (thickness t _AVE 20.4 μm, film width 3000 mm) was obtained by winding with a winding device. The obtained film had a thickness spot ratio of 7.13%, and the number of streaky defects in the height difference range of 0.15 to 0.50 μm was 50 or more in total width. In addition, after stretching 2.6 times in the MD direction, remarkable wrinkles lined up in the TD direction occurred.

[Comparative Example 3]
Using a roll film-forming machine, a volatile content of 70 parts consisting of 100 parts by mass of PVA having a saponification degree of 99.9 mol% and an average degree of polymerization of 2400, 12 parts by mass of glycerin, 0.1 parts by mass of diethanolamide laurate, and water. A mass% film-forming stock solution was discharged from the T-die at 93.5 ° C. to a first drying roll (surface temperature 88.0 ° C., peripheral speed 24.8 m / min), then peeled off by a second drying roll, and a second. After the drying roll, drying was performed at an average of 85 ° C. Finally, a PVA film (thickness t _AVE 20.3 μm, film width 3000 mm) was obtained by winding with a winding device. The obtained film had a thickness spot ratio of 5.95%, and the number of streaky defects in the range of 0.15 to 0.50 μm in height difference was 2 in total width, and streaks having a height difference of 0.5 μm or more. There were no condition defects. In addition, after stretching 2.6 times in the MD direction, remarkable wrinkles lined up in the TD direction occurred.

[Comparative Example 4]
Using a roll film-forming machine, a volatile content of 70 parts consisting of 100 parts by mass of PVA having a saponification degree of 99.9 mol% and an average degree of polymerization of 2400, 12 parts by mass of glycerin, 0.1 parts by mass of diethanolamide laurate, and water. A mass% film-forming stock solution was discharged from the T-die at 96.0 ° C. to a first drying roll (surface temperature 86.7 ° C., peripheral speed 24.8 m / min), then peeled off by a second drying roll, and a second. After the drying roll, drying was performed at an average of 85 ° C. Finally, a PVA film (thickness t _AVE 20.6 μm, film width 3000 mm) was obtained by winding with a winding device. The obtained film has a thickness spot ratio of 7.22%, and the number of streaky defects in the range of 0.15 to 0.50 μm in height difference is one in the entire width, and the streaks having a height difference of 0.5 μm or more are present. There were no condition defects. In addition, after stretching 2.6 times in the MD direction, remarkable wrinkles lined up in the TD direction occurred.

[Reference example 1]
Using a roll film-forming machine, a volatile content of 67 parts consisting of 100 parts by mass of PVA having a saponification degree of 99.9 mol% and an average degree of polymerization of 2400, 12 parts by mass of glycerin, 0.1 parts by mass of diethanolamide laurate, and water. The mass% of the film-forming stock solution was discharged from the T-die at 99.6 ° C. to the first drying roll (surface temperature 90.0 ° C., peripheral speed 17.5 m / min), then peeled off by the second drying roll, and the second. After the drying roll, drying was performed at an average of 85 ° C. Finally, a PVA film (thickness t _AVE 44.7 μm, film width 3000 mm) was obtained by winding with a winding device. The obtained film had a thickness spot ratio of 6.71%, and the number of streaky defects in the range of 0.15 to 0.50 μm in height difference was one in the entire width, and streaks having a height difference of 0.5 μm or more. There were no condition defects. In addition, after stretching 2.6 times in the MD direction, no wrinkles lined up in the TD direction occurred.

Table 1 shows the production conditions of the PVA film and the evaluation results of the obtained PVA film in Examples, Comparative Examples, and Reference Examples.

According to the present invention, it is possible to produce a polyvinyl alcohol film in which streak-like defects are suppressed even if it is thin and wrinkles do not occur even during stretching.

Claims (3)

The width direction of the polyvinyl alcohol film is the TD direction, the machine flow direction is the MD direction, and there are 5 or less streaky defects with a height difference of 0.15 μm or more that extend continuously and linearly in the MD direction by 1.5 m or more. In addition, there are no streak-like defects with a height difference of 0.50 μm or more extending linearly in the MD direction for 1.5 m or more in the entire width of the film, and the thickness of the central portion in the TD direction is 0.5 mm in the MD direction. When the maximum value when measured over 1.0 m at intervals is t _MAX , the minimum value is t _MIN, and the average value is t _AVE , t _AVE is 35 μm or less and is defined by the following formula (1). A polyvinyl alcohol film having a thickness spot ratio of 5.5% or less.
Thickness spot rate = (t _MAX- t _MIN ) / t _AVE x 100 (%) (1) The polyvinyl alcohol film according to claim 1, wherein the width is 2.0 m or more and 7.0 m or less. The method for producing a polyvinyl alcohol film according to claim 1 or 2, wherein a film-forming stock solution containing polyvinyl alcohol at 94 to 98 ° C. is poured onto a roll at 88 to 92 ° C. to form a film.