TWI741984B - Polyvinyl alcohol polymer film and its manufacturing method, optical film and its manufacturing method - Google Patents

Abstract

The present invention relates to a PVA film, which is a PVA film with a thickness of 55μm or less, in which irregularities are arranged in a period of 0.01~10mm in a straight line of 10cm or more in the flow direction of the film. The dotted lines are formed by the width of the film. The direction is less than 5 per 1m; and a method of manufacturing PVA film, which is a method of manufacturing PVA film with a thickness of 55μm or less, in which a film forming device equipped with a plurality of drying rolls whose rotating shafts are parallel to each other is used to form the film The film-forming stock solution containing PVA is discharged on the first drying roller of the device to form a film and dried, and then further dried on the drying rollers after the second drying roller to form a PVA film, the discharge rate of the film-forming stock solution (S ₀ ) is set to 2.5~5.0m/min.

Description

Polyvinyl alcohol polymer film and its manufacturing method, optical film and its manufacturing method

The present invention relates to a thin polyvinyl alcohol-based polymer film (hereinafter sometimes abbreviated as "PVA") that can produce polarizing films and other optical films with fewer optical defects, and its manufacturing method. Optical films such as polarizing films made of PVA films, and methods for manufacturing the optical films.

The polarizing plate with the function of light penetration and shielding is equivalent to the liquid crystal with the light switching function as one of the important components of the liquid crystal display (LCD). LCD series are used in a wide range of small devices such as computers and watches, notebook computers, LCD monitors, LCD color projectors, LCD TVs, car navigation systems, mobile phones, tablet terminals, indoor and outdoor measuring instruments, etc. . Among the application areas of these LCDs, LCD TVs, LCD monitors, etc., in addition to the development of large screens, are also developing toward thinness. Moreover, in recent years, the fairly popular tablet terminals have also developed towards thinness. The methods used to achieve the thinning of the LCD include: thinning the glass used in the LCD, but from the viewpoint of solving the subsequent problem of glass warpage caused by the shrinkage stress of the polarizing plate, polarized light The board also needs to be thinner.

A polarizing plate is generally produced by dyeing and uniaxially stretching a PVA film to produce a polarizing film, and then bonding a protective film such as a triacetate cellulose (TAC) film on the surface of the polarizing film. Therefore, in order to achieve the thinning of the polarizing plate, it is necessary to use a thinner PVA film to produce a thin polarizing film. The thickness of the specific PVA film needs to be 55 μm or less, or even 30 μm or less.

So far, various methods for manufacturing PVA films are known. For example, it is known that when the film-making raw materials containing PVA are discharged onto the rotating barrel of a barrel-type film making machine or on the conveyor belt of a conveyor-belt film making machine to produce PVA film, the speed of the barrel or the conveyor belt is adjusted to The rate ratio of the discharge rate of the film raw material is 1 to 5, thereby making it possible to produce a PVA film having a uniform thickness and excellent smoothness even in a large area (see Patent Document 1). Specifically, Patent Document 1 has described that a PVA film having a thickness of about 75 μm and a thickness variation of about 1.6 to 3.0 μm is produced by this method.

[Prior Technical Literature] [Patent Literature]

[Patent Document 1] JP 2002-79530 A

As mentioned above, there is a need for a thinner PVA film. However, when a thin PVA film is simply manufactured using the conventional film forming method, the following new problem arises: Many nanometers are generated along the flow direction of the film. Dotted lines (dotted lines) formed by arranging the unevenness of the grade. The inventors of the present invention have realized that if this kind of dotted line is used In the conventional thin PVA film, optical defects often occur in the obtained optical film.

Therefore, the object of the present invention is to provide a thin PVA film capable of producing optical films such as polarizing films with fewer optical defects, and the object of the present invention is to provide an optical film produced from the PVA film with fewer optical defects.

The inventors of the present invention conducted intensive studies to achieve the above-mentioned objects and found that when thin PVA films are used to produce optical films such as polarizing films, the number of dotted line stripes of the PVA film can be easily controlled below a specific value. Thus, an optical film with fewer optical defects can be obtained. At the same time, it was also discovered that a film forming apparatus equipped with a plurality of drying rolls with rotating shafts parallel to each other was used, and the PVA-containing film forming stock solution was discharged into a film on the first drying roll located on the uppermost side of the film forming apparatus, and then dried. When a thin PVA film is produced by further drying on the drying rollers following the second drying roller downstream of the first drying roller to produce a thin PVA film, by setting the discharge rate (S ₀ ) of the film-forming stock solution within a specific range, It is possible to smoothly and continuously manufacture a thin PVA film with a small number of dotted lines, which is not available in the past. The inventors of the present invention conducted further intensive studies based on these knowledge and findings, and completed the present invention.

That is, the present invention relates to: [1] A PVA film, which is a PVA film with a thickness of 55 μm or less, in which irregularities are arranged in a line of more than 10 cm in the flow direction of the film at a period of 0.01 to 10 mm. The dotted line stripes are 5 or less per 1m in the width direction of the film; [2] The PVA film as in [1] above, with a width of 2m or more; [3] A method for manufacturing a PVA film with a thickness of 55μm or less The manufacturing method of PVA film uses a film forming apparatus equipped with a plurality of drying rolls whose rotating shafts are parallel to each other. On the first drying roll of the film forming apparatus, the PVA-containing film forming stock solution is discharged into a film shape and then dried. When the second drying roll and subsequent drying rolls are further dried to form a PVA film, the discharge speed (S ₀ ) of the film-forming stock solution is set to 2.5~5.0m/min; [4] The manufacturing method described in [3] above , Which sets the ratio (S ₁ /S ₀ ) of the peripheral speed (S ₁ ) of the first drying roller to the discharge speed (S ₀ ) of the film-forming stock solution to be 7 or less; [5] as in [3] or [4] The manufacturing method, which is a method of manufacturing a PVA film with a width of 2m or more; [6] An optical film, which is an optical film made from the PVA film of [1] or [2] above; [7] The optical film of [6] above, which is a polarizing film; [8] A method of manufacturing an optical film, which has the step of uniaxial stretching using the PVA film of [1] or [2] above; [9] Like the manufacturing method of [8] above, it is a manufacturing method of a polarizing film.

According to the present invention, it is possible to provide a thin PVA film capable of producing optical films such as polarizing films with few optical defects and a method for producing the same, an optical film produced from the PVA film with few optical defects, and a method for producing the optical film.

[The form of implementing the invention]

The present invention will be described in detail below.

[PVA film]

The thickness of the PVA film of the present invention is 55μm or less, and the irregularities are arranged slightly linearly in the flow direction of the film at a period of 0.01 to 10mm. The dotted line stripes are 5 or less per 1m in the film width direction. .

As described above, in the present invention, the number of broken-line stripes is defined by arranging irregularities at a period of 0.01 to 10 mm in a substantially straight line of 10 cm or more in the flow direction of the film. Generally, the dotted line stripes are generated along the flow direction of the film, and the length of one dotted line is far more than 10cm. However, in order to distinguish from the shortcomings of the dotted line that is less than 10cm in length, it is difficult to say that it is a dotted line. Those having a length of 10 cm or more (the ones formed by arranging irregularities of 10 cm or more in a substantially linear manner in the flow direction of the film at the aforementioned period) are treated as broken-line stripes.

There are no particular restrictions on the types of the above-mentioned concavities and convexities. Examples include: arranging convex parts protruding from the film surface to form concavities and convexities; arranging concave parts concave from the film surface to form concavities and convexities ; By arranging the convex portions protruding from the film surface and the concave portions recessed from the film surface alternately, the result is uneven; etc.

The above-mentioned broken-line stripes are formed by arranging the irregularities at a period of 0.01 to 10 mm in a substantially straight line of 10 cm or more in the flow direction of the film. Here, the period refers to the length of the flow direction of the film with respect to a set of concavities and convexities (a group of adjacent concavities and convexities). In the above-mentioned dotted line stripes, all the target concavities and convexities have a period in 0.01~10mm range Inside. The period, for example, may be in the range of 0.1 to 5 mm, and further may be in the range of 0.2 to 1 mm.

In the set of irregularities that constitute the dotted line stripes, the difference in thickness between the highest height and the lowest height is in most cases within the range of 1 to 500 nm, for example, it can be in the range of 10 to 300 nm. In the range of 20~100nm, especially in the range of 30~90nm.

Regarding the target PVA film, the number of the above-mentioned broken-line stripes that cross the line on a straight line in the width direction passing through any position in the flow direction is measured for the entire width direction, and the number is divided by The width (unit: m) of the PVA film allows the number of dotted line stripes described above to be calculated in terms of the number of strips per 1 m width. Here, the dotted line stripe system can be confirmed by using a scanning white interference microscope or the like, for example. Specifically, the number of broken-line stripes is obtained by the method described later in the embodiment.

In the PVA film of the present invention, the number of dotted lines per 1 m in the width direction of the film must be 5 or less, preferably 3 or less, more preferably 2 or less, may be 1.5 or less, and even more may be 1 the following. When the number of dotted lines is within the above range, an optical film with fewer optical defects can be easily obtained. On the other hand, in a thin PVA film of 55 μm or less, when the operating conditions are adjusted so that the number of dotted stripes is less than 0.05 per 1 m in the width direction, the optical film has fewer striped optical defects. However, the reason is not clear. However, the film tends to cause problems such as uneven thickness. Therefore, the number of dotted stripes per 1 m in the width direction is preferably 0.05 or more, more preferably 0.10 or more, and still more preferably 0.15 or more, The best is 0.20 or more.

As for the PVA forming the PVA film, for example: PVA (unmodified PVA) obtained by saponifying the polyvinyl ester obtained by polymerizing vinyl ester; The obtained modified PVA; the modified PVA made by saponifying the modified polyvinyl ester obtained by copolymerizing vinyl ester and comonomer; the unmodified PVA or part of the hydroxyl group of the modified PVA is formaldehyde , Butyraldehyde, benzaldehyde and other aldehydes are cross-linked to obtain so-called polyvinyl acetal resins.

In the case where the PVA forming the PVA film is a modified PVA, the modified mass of the PVA is preferably 15 mol% or less, more preferably 5 mol% or less.

The aforementioned vinyl esters used in the manufacture of PVA include, for example, vinyl acetate, vinyl formate, vinyl laurate, vinyl propionate, vinyl butyrate, trimethyl vinyl acetate, and trimethyl propylene. Vinyl acid, vinyl stearate, vinyl benzoate, etc. These vinyl esters can be used alone or in combination. Among these vinyl esters, from the viewpoint of productivity, vinyl acetate is preferred.

In addition, the aforementioned comonomers include, for example, olefins (α-olefins, etc.) with 2 to 30 carbon atoms such as ethylene, propylene, 1-butene, and isobutylene; acrylic acid or its salts; methyl acrylate, acrylic acid Acrylates such as ethyl, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tertiary butyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, stearyl acrylate, etc. (For example: acrylic acid with carbon number 1~18 alkyl ester, etc.); methacrylic acid or its salt; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, methyl methacrylate N-butyl acrylate, isobutyl methacrylate, methacrylate Methacrylates such as butyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, stearyl methacrylate, etc. (e.g., alkyl methacrylate with 1 to 18 carbon atoms, etc.) ; Acrylamide, N-methyl acrylamide, N-ethyl acrylamide, N,N-dimethyl acrylamide, diacetone acrylamide, acrylamide Propanesulfonic acid or its salt, acrylamide propyl dimethylamine or its salt, N-methylol acrylamide or its derivatives and other acrylamide derivatives; methacrylamide (methacrylamide), N- N-methyl methacrylamide (N-methyl methacrylamide), N-ethyl methacrylamide, methacrylamide propane sulfonic acid or its salt, methacrylamide propyl dimethyl amine or its salt , N-methylolmethacrylamide or its derivatives and other methacrylamide derivatives; N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone, etc. Amines; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tertiary butyl ethylene Vinyl ether, dodecyl vinyl ether, stearyl vinyl ether and other vinyl ethers; acrylonitrile, methacrylonitrile and other nitriles; vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride and other halogenated Ethylenes; allyl compounds such as allyl acetate and chloropropylene; unsaturated dicarboxylic acids such as maleic acid and itaconic acid, their salts or their derivatives such as esters; vinyl silyl groups such as vinyl trimethoxysilane Compound; Isopropenyl acetate; Unsaturated sulfonic acid or its derivatives, etc. Among these, α-olefins are preferred, and ethylene is particularly preferred.

From the viewpoints of the polarization performance and durability of the obtained polarizing film, the average degree of polymerization of PVA is preferably 1,000 or more, more preferably 1,500 or more, and still more preferably 2,000 or more. On the other hand, regarding the level of PVA The upper limit of the average degree of polymerization is preferably 8,000 or less, particularly preferably 6,000 or less from the viewpoints of easy manufacturability and stretchability of a homogeneous PVA film.

Here, the "average degree of polymerization" of PVA in this specification refers to the average degree of polymerization measured in accordance with JIS K6726-1994, which can be obtained from the ultimate viscosity measured in water at 30°C after re-saponification and purification of PVA.

From the viewpoints of the polarization performance and durability of the obtained polarizing film, the degree of saponification of PVA is preferably 95.0 mol% or more, more preferably 98.0 mol% or more, and still more preferably 99.0 mol% or more.

Here, the "degree of saponification" of PVA in this specification refers to the total number of moles of structural units (usually vinyl ester units) and vinyl alcohol units that can be converted into vinyl alcohol units by saponification. The ratio of moles of vinyl alcohol units (mol%). The degree of saponification of PVA can be measured in accordance with the description of JIS K6726-1994.

The PVA constituting the PVA film may be one type of PVA, or may be two or more types of PVA in which one or more of the average polymerization degree, saponification degree, and modification degree are different from each other. The content of PVA in the PVA film is preferably in the range of 50-100% by mass, more preferably in the range of 80-100% by mass, and still more preferably in the range of 85-100% by mass.

It can improve mechanical properties such as impact strength, process passability or stretchability during secondary processing, etc. PVA films preferably contain plasticizers. As far as the preferred plasticizer is concerned, polyhydric alcohols can be cited, specifically, for example: ethylene glycol, glycerol, diglycerol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, triethylene glycol, and triethylene glycol. The PVA film system such as methylol propane can contain one or two or more of these plasticizers. Plastic in this Among the chemical agents, from the viewpoint of the effect of improving stretchability when the PVA film is stretched and used, it is preferable to use one or more of glycerin, diglycerin, and ethylene glycol, and more preferably Use glycerin.

The content of the plasticizer in the PVA film, relative to the PVA contained in 100 parts by mass of the PVA film, is preferably 1 part by mass or more, more preferably 3 parts by mass or more, still more preferably 5 parts by mass or more, and , Preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and still more preferably 15 parts by mass or less. When the content is 1 part by mass or more, the stretchability of the PVA film can be improved. On the other hand, when the content is 30 parts by mass or less, it is possible to prevent the PVA film from becoming too soft and lowering the handleability.

From the viewpoints of the handling of the PVA film and the improvement of the peelability of the film forming apparatus when the PVA film is produced, the PVA film preferably contains a surfactant. The type of surfactant is not particularly limited, and examples include anionic surfactants and nonionic surfactants.

Examples of anionic surfactants include carboxylic acid types such as potassium laurate; sulfate ester types such as octyl sulfate; sulfonic acid types such as dodecylbenzenesulfonate.

Examples of nonionic surfactants include alkyl ether types such as polyoxyethylene lauryl ether and polyoxyethylene lauryl ether; polyoxyethylene octyl Alkyl phenyl ether type such as phenyl ether; Alkyl ester type such as polyoxyethylene laurate; Alkylamine type such as polyoxyethylene lauryl amino ether; Polyoxyethylene laurate amide Alkyl amide type; Polyoxyethylene polyoxypropylene ether and other polypropylene glycol ether type; Lauric acid diethanolamide (lauric acid diethanolamide) , Alkanolamide type such as diethanolamide oleic acid; Allyl phenyl ether type such as polyoxyalkylene allyl phenyl ether, etc.

The PVA film system can contain one or more of these surfactants. Among these surfactants, in view of the excellent effect of reducing film surface abnormalities during film formation, etc., nonionic surfactants are preferred, and in particular, alkanolamide type surfactants are more preferred. More preferred is a dialkanolamide (for example, diethanolamide, etc.) of an aliphatic carboxylic acid (for example, saturated or unsaturated aliphatic carboxylic acid having 8 to 30 carbon atoms, etc.).

From the perspective of the operability of the PVA film and the further improvement of the peelability of the film forming device when the PVA film is produced, and the ability to reduce the occurrence of agglomeration, the content of the surfactant in the PVA film is relative to 100 parts by mass of PVA In particular, it is preferably 0.01 parts by mass or more, more preferably 0.02 parts by mass or more, still more preferably 0.05 parts by mass or more, more preferably 1 part by mass or less, more preferably 0.5 parts by mass or less, and still more preferably 0.3 parts by mass The following.

The PVA film may optionally further contain antioxidants, ultraviolet absorbers, lubricants, coloring agents, preservatives, antifungal agents, other high-molecular compounds other than the above-mentioned components, moisture and other components. PVA film systems can contain these. One or more of other ingredients.

From the viewpoint of being able to manufacture thin optical films (polarizing films, etc.), the thickness of the PVA film must be 55 μm or less, preferably 40 μm or less, and may be 30 μm or less, and more preferably 20 μm or less. In a thinner PVA film, the dotted line stripes are more likely to become a problem. In a PVA film having such a thickness, the effect of the present invention can be significantly achieved in particular. The other party On the other hand, the lower limit of the thickness of the PVA film is not particularly limited, but if you consider the handling of the PVA film, the process passability during the manufacture of the optical film, and the optical properties of the resulting optical film (polarization properties of the polarizing film, etc.), etc., The thickness is preferably 3 μm or more, more preferably 5 μm or more, and still more preferably 10 μm or more. The thickness of the PVA film can be obtained by measuring the thickness at any five places and making the average value.

The shape of the PVA film is not particularly limited, but from the point of view that it can be used continuously and smoothly to produce a more uniform PVA film and it can be used continuously even when it is used to produce optical films such as polarizing films. It is preferably a long film. The long film is preferably wound on a cylindrical core or the like to form a film roll. When used as a long film, the length of the PVA film (the length in the flow direction) is not particularly limited, and can be appropriately set according to the application. However, from the case of continuous use from a film roll, PVA The longer the film length, the more it can reduce the loss when switching the film roll. The length is preferably 500 m or more, more preferably 1,000 m or more, still more preferably 5,000 m or more, and particularly preferably 8,000 m or more. There is no special restriction on the upper limit of the length, but the length can be set below 30,000m.

There are no special restrictions on the form of the PVA film, whether it is a single-layer form (single-layer film) or, for example, the form of a laminate of a PVA film formed on a thermoplastic resin film by a coating method, etc., both can be used. However, from the viewpoints of achieving the effects of the present invention more significantly, the complexity of the lamination (coating, etc.) work, and the cost of the thermoplastic resin film, a single-layer form is preferred.

There is no special limit to the width of the PVA film. It is appropriately set according to the use of PVA film or optical film such as polarizing film made from it. However, from the point of view that LCD TVs or LCD monitors have developed toward large screens in recent years, the width of PVA film is set to 2m or more. It is more preferably 3m or more, and even more preferably 4m or more, it is suitable for these purposes. On the other hand, if the width of the PVA film is too large, it is likely to be quite difficult to uniformly uniaxially stretch when manufacturing an optical film in a practical device. Therefore, the width of the PVA film is preferably 7 m or less.

[Manufacturing method of PVA film]

The manufacturing method of the PVA film of the present invention is not particularly limited, but according to the following manufacturing method of the present invention, the PVA film of the present invention can be manufactured smoothly and continuously.

That is, the manufacturing method of the present invention for manufacturing a PVA film with a thickness of 55 μm or less is: a manufacturing method that uses a plurality of drying rollers that are parallel to the rotating shaft (called sequentially from the uppermost side to the lower side) It is the first drying roll, the second drying roll...) of the film forming device. On the first drying roll of the film forming device, the PVA-containing film forming stock solution is discharged into a film and then dried. When the second drying roll and subsequent drying rolls are further dried to form a PVA film, the discharge speed (S ₀ ) of the film forming stock solution is set to 2.5 to 5.0 m/min.

In the production method of the present invention, a film forming apparatus equipped with a plurality of drying rolls whose rotating shafts are parallel to each other is used, and the PVA-containing film forming stock solution is discharged into a film on the first drying roll of the film forming apparatus, and then dried. It is further dried on the drying rolls subsequent to the second drying roll to the downstream side of the first drying roll to form a PVA film. In the film forming apparatus, the number of drying rollers is preferably 3 or more, more preferably 4 or more, and still more preferably 5-30 indivual.

The plurality of drying rollers are preferably formed of metals such as nickel, chromium, copper, iron, stainless steel, etc., and it is more preferable that the surface of the drying rollers is not easily corroded and is formed of a metal material with a specular luster. In addition, in order to improve the durability of the drying roll, it is more preferable to use a drying roll plated with a single layer of nickel, chromium, nickel/chromium alloy layer, or a combination of two or more nickel layers, chromium layers, nickel/ Dry roller made of chromium alloy layer, etc.

Regarding the heating direction when the film is dried from the first drying roll to the final drying roll, from the viewpoint that the film can be dried more uniformly, it is preferable that any part of the film is in contact with the first drying roll. (Hereinafter sometimes referred to as the "first drying roll contact surface") and the film surface not in contact with the first drying roll (hereinafter sometimes referred to as the "first drying roll non-contact surface") to move from the first drying roll to the final Drying rollers of the drying rollers face each other alternately to dry.

When spitting out the PVA-containing film-forming stock solution into a film on the first drying roll of the film-forming device, only a T-shaped slit die, a hopper plate, an I-shaped die, and a lip coater die can be used. A known film discharge device (film casting device) such as a lip coater die may discharge (cast) the film-forming stock solution containing PVA on the first drying roll into a film.

_{The discharge speed (S 0} ) of the film-forming stock solution must be 2.5~5.0m/min. Theoretically, even if the ratio of the peripheral speed (S ₁ ) of the first drying roller to the ejection speed (S ₀ ) of the _{film forming solution (S 1} /S _{) is increased while reducing the discharge speed (S 0) of the film forming solution 0} ), or conversely, even by increasing the discharge speed (S ₀ ) of the film-forming stock solution while reducing the peripheral speed (S ₁ ) of the first drying roller relative to the discharge speed (S ₀ ) of the film-forming stock solution Compared with (S ₁ /S ₀ ), it is possible to produce PVA films with the same thickness at a specific production speed. However, the inventors found that the film-forming stock solution can be discharged when producing thin PVA films with a thickness of 55 μm or less. When the speed (S ₀ ) is set in the above range, it is possible to smoothly and continuously manufacture a thin PVA film with fewer dotted lines, which cause problems especially in thin PVA films, which is not available in the past. For reasons such as being able to further reduce the number of dotted lines, the discharge speed (S ₀ ) of the film-forming dope is preferably 2.6 m/min or more, more preferably 2.7 m/min or more, and still more preferably 2.8 m/min. Points or more. _{On the other hand, if the discharge speed (S 0} ) of the film-forming stock solution is too high, it tends to be difficult to produce a PVA film stably. Therefore, the discharge speed (S ₀ ) of the film-forming stock solution is preferably 4.8 m/min or less , More preferably 4.5m/min or less, still more preferably 4.2m/min or less, particularly preferably 4.0m/min or less. In addition, the discharge rate (S ₀ ) of the film-forming stock solution refers to the linear velocity in the flow direction of the film-forming stock solution, and it can be obtained by dividing the volume of the film-forming stock solution discharged from the film-like discharge device per unit time by the film-like discharge The opening area of the slit portion of the device (the product of the slit width of the film-like ejection device and the average value of the slit opening) was obtained.

The film-forming stock solution containing the PVA film can be prepared by mixing PVA with a liquid medium to form a solution, or melting PVA pellets containing a liquid medium and the like to form a molten liquid.

Regarding the liquid medium used at this time, for example, water, dimethyl sulfide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylenediamine, diethylenetris Amines, etc., and these liquid medium systems may be used alone or in combination of two or more. Among these, water, dimethyl sulfoxide, or a mixture of the two are preferably used, and water is more preferably used.

It is preferable to use PVA film in the film-forming stock solution according to the expectation. In the description, one or more of the above-mentioned plasticizers, surfactants, and other ingredients are blended in the above-mentioned amounts.

The volatile component ratio of the film-forming stock solution used to manufacture the PVA film is preferably in the range of 50 to 90% by mass, more preferably in the range of 55 to 80% by mass, and still more preferably in the range of 60 to 75% by mass. If the volatile component ratio of the film-forming stock solution is too low, the viscosity of the film-forming stock solution may become too high, making it difficult to filter or defoam, or the film forming itself may be difficult to achieve. On the other hand, if the volatile component ratio of the film-forming stock solution is too high, the viscosity may become too low and the thickness uniformity of the PVA film may be impaired.

Here, "the volatile component ratio of the film-forming stock solution" in this specification means the volatile component ratio calculated using the following formula [I].

The volatile component ratio of the film-forming stock solution (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) when the film-forming stock solution of Wa(g) is dried in an electrothermal dryer at 105°C for 16 hours.)

The surface temperature of the first drying roll is not particularly limited, but from the viewpoint of film drying uniformity, productivity, etc., it is preferably in the range of 70 to 120°C, more preferably in the range of 80 to 105°C , Preferably within the range of 85~95℃.

The drying system on the first drying roll from which the film-forming dope solution has been discharged can be performed only by heating from the first drying roll, but from the viewpoints of uniform dryness, drying speed, etc., it is preferably While the first drying roll is heated, hot air is blown to the non-contact surface of the first drying roll, and heat is applied from both sides of the film for drying.

When blowing hot air to the non-contact surface of the first drying roll of the film located on the first drying roll, it is preferable to blow hot air with a velocity of 1 to 10 m/sec to the entire area of the non-contact surface of the first drying roll, more preferably blowing Hot air with a wind speed of 2~8m/sec, and preferably a hot air with a wind speed of 3~8m/sec. If the wind speed of the hot air blown to the non-contact surface of the first drying roller is too low, condensation of water vapor and the like may occur during drying on the first drying roller, and the water droplets will drip onto the film and the resulting PVA film Produce defects. On the other hand, if the wind speed of the hot air blown to the non-contact surface of the first drying roll is too high, uneven thickness will occur in the finally obtained PVA film, and there will be problems such as uneven dyeing. Case.

From the viewpoints of drying efficiency and drying uniformity, the temperature of the hot air blown to the non-contact surface of the first drying roll of the film is preferably 50 to 150°C, more preferably 70 to 120°C, and even more preferably 80 to 95°C. In addition, the dew point temperature of the hot air blown to the non-contact surface of the first drying roll of the film is preferably 5 to 20°C, more preferably 10 to 15°C.

The method of blowing hot air to the non-contact surface of the first drying roll of the film is not particularly limited. Any type of hot air can be used to blow uniform wind speed and temperature to the non-contact surface of the first drying roll of the film, preferably uniform throughout The method of ground blowing is preferably a nozzle method, a rectifying plate method, or a combination of these. The blowing direction of the hot air to the non-contact surface of the first drying roll of the film may be a direction facing the non-contact surface of the first drying roll, or may be a direction substantially along the circumferential shape of the non-contact surface of the first drying roll of the film ( The direction substantially along the circumference of the roll surface of the first drying roll), or other directions may be used.

In addition, it is preferable that when the film is dried on the first drying roller, The volatile components generated from the film after drying and the blown hot air are discharged. The method of exhausting is not particularly limited, but it is better to use an exhausting method that does not cause uneven wind speed and temperature unevenness of the hot air blown to the non-contact surface of the first drying roll of the film.

In view of the fact that the number of dotted lines can be reduced and the stability during production is also excellent, the peripheral speed (S ₁ ) of the first drying roll is preferably in the range of 12 to 35 m/min. The first drying The peripheral speed (S ₁ ) of the roll is more preferably 15 m/min or more, more preferably 30 m/min or less, still more preferably 28 m/min or less, and particularly preferably 26 m/min or less.

From the viewpoint of being able to further reduce the number of dotted lines and excellent stability during production, the ratio of the peripheral speed (S _{1 ) of the first drying roll to the discharge speed (S 0} ) of the film-forming dope (S 0) ₁ /S ₀ ) is preferably 7 or less, more preferably 6.8 or less, still more preferably 6.5 or less, particularly preferably 6.3 or less, more preferably more than 3, more preferably more than 5, still more preferably 5.2, particularly preferably It is more than 5.5, preferably more than 6.

The film-forming stock solution is discharged on the first drying roll and dried on the first drying roll. The volatile component ratio of the film (the volatile component ratio of the film when peeled from the first drying roll) is preferably 5-30 mass %, more preferably 7-20% by mass, still more preferably 8-15% by mass, peeling from the first drying roll. When the volatile component ratio of the film when peeled from the first drying roll is 5% by mass or more, the difference in the drying speed between the contact surface of the first drying roll and the non-contact surface of the first drying roll becomes larger, which can prevent the film from becoming easy The condition of warpage. In addition, since the volatile component ratio of the film at the time of peeling from the first drying roll is 30% by mass or less, it is possible to suppress the increase in thickness unevenness.

Here, "the volatile component ratio of the film" in this manual refers to The ratio of volatile components determined using the following formula [II].

The volatile component ratio of the film (mass%)={(Wc-Wd)/Wc}×100[II]

(In the formula, Wc is the mass (g) of the sample sampled from the film, and Wd is the mass when the aforementioned sample of Wc (g) is dried in a vacuum dryer at a temperature of 50°C and a pressure of 0.1 kPa or less for 4 hours (g).)

On the first drying roller, it is preferable to peel off the film dried to a volatile content ratio of 5 to 30% by mass from the first drying roller. In this case, it is preferable to make the non-contact surface of the first drying roller face the second drying roller. Then, the film is dried on the second drying roller.

As long as the film dried on the second drying roll can be peeled off from the second drying roll, the third, fourth, and fifth drying rolls are used in accordance with the number of drying rolls installed in the film forming device, etc.... .. Wait for multiple drying rollers to dry sequentially.

From the viewpoint of uniform dryness, drying speed, etc., the surface temperature of each drying roll from the second drying roll to the final drying roll is preferably 40°C or higher, more preferably 45°C or higher, and still more preferably 50°C or higher, Furthermore, it is preferably less than 100°C, more preferably less than 90°C, still more preferably less than 85°C, and particularly preferably less than 80°C.

It is preferable to apply a heat treatment to the dried film that has passed on the final drying roll as described above. The heat treatment system can be performed using heat treatment rolls or other well-known heat treatment devices. When heat treatment is applied using heat treatment rolls, there may be one heat treatment roll or multiple heat treatment rolls.

In view of moderate crystallization to obtain a PVA film with excellent hot water resistance, the surface temperature of the heat treatment roll is preferably 90°C or higher. It is more preferably 100°C or higher, and still more preferably 110°C or higher. In addition, from the viewpoint of improving the stretchability of the obtained PVA film, the surface temperature of the heat treatment roll is preferably 150°C or lower, more preferably 140°C or lower, and still more preferably 130°C or lower.

The heat treatment time is not particularly limited, but from the viewpoint that the target PVA film can be manufactured more smoothly, it is preferably in the range of 3 to 60 seconds, and more preferably in the range of 5 to 30 seconds.

The above-mentioned film forming apparatus may optionally include a hot air drying device, a humidity control device, and the like.

The film obtained as described above may be further subjected to humidity control treatment, cutting of both ends (edges) of the film, etc., if necessary, and finally can be rolled into a roll with a set length to form the PVA film of the present invention.

Through the above-mentioned series of treatments, the volatile component ratio of the finally obtained PVA film is preferably in the range of 1 to 5% by mass, and more preferably in the range of 2 to 4% by mass.

[Use of PVA film]

The application of the PVA film of the present invention is not particularly limited, but if the PVA film of the present invention is used, an optical film with fewer optical defects can be produced. Therefore, the PVA film of the present invention is preferably used for the production of polarizing films or retardation films. It is used as the raw material film of optical film. Such an optical film can be manufactured by, for example, using the PVA film of the present invention and applying treatments such as uniaxial stretching.

There are no special restrictions on the method of manufacturing a polarizing film using the PVA film of the present invention as a raw material film, and any method used in the past can be used. In terms of such methods, for example: A method of applying dyeing and uniaxial stretching to PVA films, or applying uniaxial stretching to PVA films containing dyes. A more specific method for manufacturing a polarizing film may include a method of applying dyeing, uniaxial stretching, fixing treatment, drying treatment, and further heat treatment as necessary to the PVA film of the present invention. The order of dyeing and uniaxial stretching is not particularly limited. The dyeing may be performed before the uniaxial stretching, the dyeing may be performed simultaneously with the uniaxial stretching, or the dyeing may be performed after the uniaxial stretching. In addition, the steps such as uniaxial stretching and dyeing can be repeated several times. In particular, once the uniaxial stretching is divided into two or more stages, it becomes easy to perform uniform stretching, which is preferable. Also, in the case of a laminate in the form of a PVA film formed on a thermoplastic resin film, uniaxial stretching is applied in the state where the thermoplastic resin film is laminated, so that cracks during uniaxial stretching can be further reduced. .

As far as the dyes used for dyeing PVA films are concerned, iodine or dichroic organic dyes can be used (for example: DirectBlack 17, 19, 154; DirectBrown 44, 106, 195, 210, 223; DirectRed 2, 23, 28, 31, 37, 39, 79, 81, 240, 242, 247; DirectBlue 1, 15, 22, 78, 90, 98, 151, 168, 202, 236, 249, 270; DirectViolet 9, 12, 51, 98; DirectGreen 1 , 85; DirectYellow 8, 12, 44, 86, 87; DirectOrange 26, 39, 106, 107 and other dichroic dyes) etc. These dyes can be used alone or in combination of two or more. Dyeing can usually be performed by immersing the PVA film in a solution containing the above-mentioned dye, but the treatment conditions or treatment methods are not particularly limited.

The uniaxial stretching of PVA film can be wet stretching or dry Any of the heat stretching methods are performed, but from the viewpoint of the performance and quality stability of the polarizing film to be obtained, the wet stretching method is preferred. For the wet stretching method, a method of stretching a PVA film in pure water, an aqueous solution containing various components such as additives or an aqueous medium, or an aqueous dispersion in which the various components are dispersed can be cited, and the wet stretching method is used. Specific examples of the uniaxial stretching method of the method include: a method of uniaxial stretching in warm water containing boric acid, a method of uniaxial stretching in a solution containing the aforementioned dye or in a fixed treatment bath described later Wait. In addition, the PVA film after water absorption may be used to uniaxially stretch in the air, or another method may be used to uniaxially stretch. Uniaxial stretching is preferably carried out in the flow direction of the PVA film.

The stretching temperature during uniaxial stretching is not particularly limited, but in the case of wet stretching, it is preferably 20 to 90°C, more preferably 25 to 70°C, and even more preferably 30 to 65°C. In the case of dry heat stretching, the temperature within the range is preferably a temperature within the range of 50 to 180°C.

From the point of view of polarization performance, the stretching magnification of uniaxial stretching (the total stretching magnification in the case of multi-stage uniaxial stretching) should be stretched as far as possible before the film is cut. Specifically, it is better than It is preferably 4 times or more, more preferably 5 times or more, and still more preferably 5.5 times or more. As long as the film does not break, the upper limit of the stretching ratio is not particularly limited, but for uniform stretching, it is preferably 8.0 times or less.

The thickness of the uniaxially stretched film (polarizing film) is preferably 1 to 30 μm, particularly preferably 3 to 25 μm. In addition, the thickness can be obtained by measuring the thickness at any five places and making the average value.

In order to make the adsorption of the dye to the uniaxially stretched film firm when manufacturing a polarizing film, a fixation process is often performed. The fixation treatment generally adopts a method of immersing the film in a fixation treatment bath added with boric acid and/or a boron compound. In this case, an iodine compound may be added to the treatment bath as needed.

It is preferable to perform drying treatment (heat treatment) successively on the film that has been uniaxially stretched, or uniaxially stretched and fixed. The temperature of the drying treatment (heat treatment) is preferably 30 to 150°C, particularly preferably 50 to 140°C. If the temperature of the drying treatment (heat treatment) is too low, the dimensional stability of the obtained polarizing film is likely to deteriorate; on the other hand, if it is too high, degradation of the polarization performance accompanying dye decomposition and the like is likely to occur.

A protective film that is optically transparent and has mechanical strength can be bonded to both sides or one side of the polarizing film obtained as described above to produce a polarizing plate. As the protective film at this time, cellulose triacetate (TAC) film, cellulose acetate butyrate (CAB) film, acrylic film, polyester film, etc. can be used. In addition, as for the adhesive for bonding the protective film, a PVA-based adhesive or a urethane-based adhesive is generally used, and among them, a PVA-based adhesive is preferably used.

The polarizing plate obtained as described above can be used as an element of a liquid crystal display device after being coated with an adhesive such as acrylic and then bonded to a glass substrate. It can also be used as an element of a liquid crystal display device when the polarizing plate is bonded to the glass substrate. Differential film, viewing angle enhancement film, brightness enhancement film, etc.

[Example]

The following examples are given to specifically illustrate the present invention, but the present invention is not limited by these. Also, compare the following examples and The various measurement and evaluation methods used in the comparative and reference examples are shown below.

[Number of dotted stripes]

At any position of the PVA film to be measured, set an area of 60 cm in the flow direction × the entire width direction, and use a scanning white interference microscope ("New View" 7300, manufactured by ZYGO) to measure the vicinity of striped defects considered to be dotted lines To confirm whether this stripe-shaped defect is the dashed-line stripe specified in the present invention. In this way, the number of dotted lines crossing the "straight line in the width direction through any part of the flow direction" in the above-mentioned area is measured as a whole in the width direction of the line, and the number is divided by the PVA film The width of, to find the number of dotted lines per 1m width.

[Optical Defects of Polarizing Film]

After the polarizing film is appropriately divided in the width direction, place it in the orthogonal direction between the observation polarizers (two paralleled nicols superimposed, with a degree of polarization of 99.99% or more), and visually observe optical defects. And use the following benchmarks for evaluation.

○: Completely or almost impossible to find optical defects

×: Optical defects can be found easily

××: Optical defects can be found very easily

[Example 1]

[Manufacturing of PVA film]

100 parts by mass of PVA (average degree of polymerization 2,400, saponification degree of 99.9 mol%) obtained by saponifying polyvinyl acetate, 12 parts by mass of glycerin, 0.1 parts by mass of diethanolamide laurate, and volatile components of water The film-forming stock solution with a ratio of 70% by mass is discharged from the T-shaped slit die at a discharge speed (S ₀ ) of 2.8 m/min, on the first drying roll of the film forming device equipped with a plurality of drying rolls and heat treatment rolls whose rotating shafts are parallel to each other. (Circular speed (S ₁ ) 17m/min) is discharged into a film, and the first drying roll is dried while blowing hot air at 90°C on the non-contact surface of the first drying roll at a wind speed of 5m/sec, and then from the first drying roll. The drying roll peels off, and after further drying between the second drying roll and the final drying roll before the heat treatment roll so that the surface and back of any part of the film face each drying roll alternately, it is peeled from the final drying roll. Next, heat treatment is performed on a heat treatment roll with a surface temperature of 120°C, the ends (edges) are cut, and then wound on a cylindrical core to finally produce a thickness of 30.3μm, a length of 2,000m, and a width of 2.6m. , A long PVA film (single layer film) with a volatile component ratio (water content) of 2% by mass.

After measuring the number of dotted lines on the PVA film using the above method, it was found that the unevenness of 50-60nm height difference was arranged in a straight line with a period of 0.3-0.7mm in the flow direction of the film for 10cm or more. There are 6 stripes (2.3 stripes per 1 m in the width direction of the film). The above results are shown in Table 1.

[Manufacturing of Polarizing Film]

Each process was applied while winding the obtained PVA film, and the polarizing film with a thickness of 12 micrometers was manufactured continuously.

That is, while the PVA film was immersed in water at 30°C, it was uniaxially stretched in the direction of flow (MD) (first-stage stretch) to 2.2 times its original length, and then immersed in iodine containing 0.03% by mass. And 3% by mass of potassium iodide in a 30°C iodine/potassium iodide aqueous solution while uniaxially stretched in the flow direction (MD) (second-stage stretch) to 3.3 times the original length, and then immersed in 3% by mass of boric acid and 3% by mass of potassium iodide in a 30°C boric acid/potassium iodide aqueous solution were uniaxially stretched in the flow direction (MD) (third-stage stretching) to 3.6 times the original length, and then immersed in Containing 4% by mass of boric acid and 5% by mass of potassium iodide in a boric acid/potassium iodide aqueous solution at 63°C during uniaxial stretching in the flow direction (MD) (fourth stage stretching) to 6.7 times the original length, and then immersing After being in a 30°C potassium iodide aqueous solution containing 3% by mass of potassium iodide, it was dried in a 60°C dryer for 4 minutes to produce a polarizing film.

The above-mentioned method was used to evaluate optical defects for this polarizing film, and the results are shown in Table 1.

[Example 2]

100 parts by mass of PVA (average degree of polymerization 2,400, saponification degree of 99.9 mol%) obtained by saponifying polyvinyl acetate, 12 parts by mass of glycerin, 0.1 parts by mass of diethanolamide laurate, and volatile components of water The film-forming stock solution with a ratio of 66% by mass is discharged from the T-slot die at a discharge speed (S ₀ ) of 2.8 m/min, on the first drying roll of the film forming device equipped with a plurality of drying rolls and heat treatment rolls whose rotating shafts are parallel to each other. (Circular speed (S ₁ ) 17m/min) is discharged into a film, and the first drying roll is dried while blowing hot air at 90°C on the non-contact surface of the first drying roll at a wind speed of 5m/sec, and then from the first drying roll. The drying roll peels off, and after further drying between the second drying roll and the final drying roll before the heat treatment roll so that the surface and back of any part of the film face each drying roll alternately, it is peeled from the final drying roll. Next, heat treatment is performed on a heat treatment roll with a surface temperature of 115°C. After cutting both ends (edges), they are wound on a cylindrical core to finally produce a thickness of 40.6μm, a length of 2,000m, and a width of 2.6m. , A long PVA film (single layer film) with a volatile component ratio (water content) of 2% by mass.

After measuring the number of dotted lines on the PVA film using the above method, it was found that the unevenness of 50-60nm height difference was arranged in a straight line with a period of 0.3-0.7mm in the flow direction of the film for 10cm or more. There are 5 stripes (1.9 stripes per 1 m in the width direction of the film). In addition, the obtained PVA film was used in the same manner as in Example 1 to produce a 17 μm-thick polarizing film, and the optical defects were evaluated using the above-mentioned method. The above results are shown in Table 1.

[Comparative Example 1]

It will contain 100 parts by mass of PVA obtained by saponifying polyvinyl acetate (average degree of polymerization 2,400, saponification degree of 99.9 mol%), 12 parts by mass of glycerin, 0.1 parts by mass of diethanolamide laurate, and volatile components of water The film-forming stock solution with a ratio of 66% by mass is discharged from the T-shaped slit die at a discharge speed (S ₀ ) of 2.4 m/min, on the first drying roll of the film forming device equipped with a plurality of drying rolls and heat treatment rolls whose rotating shafts are parallel to each other. (Peripheral speed (S ₁ ) 18m/min), spit out into a film, on the first drying roll while blowing hot air at 90°C on the non-contact surface of the first drying roll at a wind speed of 5m/sec, and then dry it from the first drying roll. The drying roll peels off, and after further drying between the second drying roll and the final drying roll before the heat treatment roll so that the surface and back of any part of the film face each drying roll alternately, it is peeled from the final drying roll. Next, heat treatment is performed on a heat treatment roll with a surface temperature of 115°C. After cutting both ends (edges), they are wound on a cylindrical core to finally produce a thickness of 29.6μm, a length of 2,000m, and a width of 2.6m. , A long PVA film (single layer film) with a volatile component ratio (water content) of 2% by mass.

After measuring the number of dotted lines on the PVA film using the method described above, it was found that the unevenness with a height difference of 60 to 70 nm was adjusted to 0.3 to 0.7 mm. There are 24 broken-line stripes arranged in a line of 10 cm or more in the flow direction of the film in a period of 10 cm or more (9.2 stripes per 1 m in the width direction of the film). In addition, using the obtained PVA film, a polarizing film having a thickness of 12 μm was produced in the same manner as in Example 1, and the optical defects were evaluated by the above-mentioned method. The above results are shown in Table 1.

[Comparative Example 2]

100 parts by mass of PVA (average degree of polymerization 2,400, saponification degree of 99.9 mol%) obtained by saponifying polyvinyl acetate, 12 parts by mass of glycerin, 0.1 parts by mass of diethanolamide laurate, and volatile components of water The film-forming stock solution with a ratio of 66% by mass is discharged from the T-slot die at a discharge speed (S ₀ ) of 2.0 m/min, on the first drying roll of the film forming device equipped with a plurality of drying rolls and heat treatment rolls whose rotating shafts are parallel to each other. (Peripheral speed (S ₁ ) 15m/min) spit out into a film, on the first drying roll while blowing hot air at 90°C on the non-contact surface of the first drying roll at a wind speed of 5m/sec, and then dry it from the first drying roll. The drying roll peels off, and after further drying between the second drying roll and the final drying roll before the heat treatment roll so that the surface and back of any part of the film face each drying roll alternately, it is peeled from the final drying roll. Next, heat treatment is performed on a heat treatment roll with a surface temperature of 115°C. After cutting both ends (edges), they are wound on a cylindrical core to finally produce a thickness of 30.3μm, a length of 2,000m, and a width of 2.6m. , A long PVA film (single layer film) with a volatile component ratio (water content) of 2% by mass.

After measuring the number of dotted lines on this PVA film using the above method, it was found that the unevenness of the height difference of 80~90nm was arranged in a line of 0.3~0.7mm in a period of 0.3~0.7mm in the flow direction of the film and the dotted line was formed by linearly arranging more than 10cm in the flow direction of the film. There are 37 stripes (14.2 stripes per 1m in the width direction of the film) ). In addition, the obtained PVA film was used to produce a polarizing film with a thickness of 12 μm in the same manner as in Example 1, and the optical defects were evaluated by the above-mentioned method. The above results are shown in Table 1.

[Reference example]

100 parts by mass of PVA (average degree of polymerization 2,400, saponification degree of 99.9 mol%) obtained by saponifying polyvinyl acetate, 12 parts by mass of glycerin, 0.1 parts by mass of diethanolamide laurate, and volatile components of water The film-forming stock solution with a ratio of 66% by mass is discharged from the T-shaped slit die at a discharge speed (S ₀ ) of 2.4 m/min, on the first drying roll of the film forming device equipped with a plurality of drying rolls and heat treatment rolls whose rotating shafts are parallel to each other. (Circular speed (S ₁ ) 11m/min) is discharged into a film, and the first drying roll is dried while blowing hot air at 90°C on the non-contact surface of the first drying roll at a wind speed of 5m/sec, and then from the first drying roll. The drying roll peels off, and after further drying between the second drying roll and the final drying roll before the heat treatment roll so that the surface and back of any part of the film face each drying roll alternately, it is peeled from the final drying roll. Next, heat treatment is performed on a heat treatment roll with a surface temperature of 105°C. After cutting both ends (edges), they are wound on a cylindrical core to finally produce a thickness of 74.5μm, a length of 2,000m, and a width of 2.6m. , A long PVA film (single layer film) with a volatile component ratio (water content) of 2% by mass.

I tried to measure the number of broken-line stripes for this PVA film using the method described above, but the broken-line stripes were not seen. The above results are shown in Table 1.

Claims (8)

A polyvinyl alcohol-based polymer film, which is a polyvinyl alcohol-based polymer film with a thickness of 55μm or less, in which the irregularities are arranged in a straight line with a period of 0.01 to 10mm in the direction of the film's flow. The dotted line is formed by 10cm or more The stripes are 5 or less per 1 m in the width direction of the film. For example, the polyvinyl alcohol-based polymer film of claim 1 has a width of 2 m or more. A method for manufacturing a polyvinyl alcohol-based polymer film, which is the method for manufacturing a polyvinyl alcohol-based polymer film as claimed in claim 1 or 2, in which a film-making device equipped with a plurality of drying rollers whose rotating shafts are parallel to each other is used. The film-forming stock solution containing polyvinyl alcohol-based polymer is discharged on the first drying roll of the film forming apparatus into a film and dried, and further dried on the drying rolls following the second drying roll to produce polyvinyl alcohol When using a polymer film, set the discharge speed (S ₀ ) of the film-forming stock solution to 2.5 to 5.0 m/min, and set the peripheral speed (S ₁ ) of the first drying roller relative to the discharge speed of the film-forming stock solution (S _{0 ).} The ratio (S ₁ /S ₀ ) of) is set to exceed 5.2 and be 7 or less. Such as the manufacturing method of claim 3, which is a method of manufacturing a polyvinyl alcohol-based polymer film with a width of 2 m or more. An optical film, which is an optical film made of the polyvinyl alcohol-based polymer film of claim 1 or 2. Such as the optical film of claim 5, which is a polarizing film. A method for manufacturing an optical film, which has a step of uniaxially stretching the polyvinyl alcohol-based polymer film as claimed in claim 1 or 2. Such as the manufacturing method of claim 7, which is a manufacturing method of a polarizing film.