KR101544625B1

KR101544625B1 - Polyvinyl alcohol film

Info

Publication number: KR101544625B1
Application number: KR1020107003671A
Authority: KR
Inventors: 데츠시 하야시
Original assignee: 가부시키가이샤 구라레
Priority date: 2007-08-20
Filing date: 2008-08-01
Publication date: 2015-08-17
Also published as: TW200914468A; JPWO2009025068A1; CN102816339A; KR20100042283A; TWI452050B; WO2009025068A1; CN101778888B; CN101778888A; CN102816339B; JP5351760B2

Abstract

A wide polyvinyl alcohol-based film effective for producing a high-performance polarizing film with little optical unevenness caused by uneven dyeing or stretching unevenness is provided. The polyvinyl alcohol-based film is a polyvinyl alcohol-based film produced from a film-forming stock solution containing a polyvinyl alcohol-based polymer and a plasticizer, wherein the maximum content of the plasticizer in the TD direction relative to the average value of the content of the plasticizer contained in the film And the average distance Sm of the variation irregularities in the TD direction of the plasticizer content is 5 cm or more.

Description

Polyvinyl alcohol film {POLYVINYL ALCOHOL FILM}

Related application

This application claims the benefit of Japanese Patent Application No. 2007-213444, filed on August 20, 2007, which is hereby incorporated by reference in its entirety.

The present invention relates to a polyvinyl alcohol-based film having a uniform quality over a large area.

A polarizing plate having light transmission and shielding functions is a fundamental component of a liquid crystal display (LCD) together with a liquid crystal having a light switching function. The application field of this LCD is also used in small electronic devices such as an electronic calculator and a wrist watch at the early stage of development, and recently, a notebook PC, a liquid crystal monitor, a liquid crystal color projector, a liquid crystal television, a car navigation system, a personal phone, And so on. Particularly in the field of monitors and televisions, the liquid crystal display is rapidly becoming larger in size, and a polarizing plate having better uniformity of optical performance over a larger area than the conventional one is required.

The polarizing plate is generally obtained by uniaxially stretching a polyvinyl alcohol film, then dyeing it with iodine or a dichroic dye, or uniaxially stretching it after dyeing to make a dyed monoaxially stretched film, fixing it with a boron compound (TAC) film, alicyclic polyolefin (COP), and the like are coated on the surface of the polarizing film by a method in which the polarizing film is stained with a boron compound at the same time as the monoaxial stretching / ) Film or the like. In order to obtain a polarizing plate having a uniform polarization performance, it is preferable that the thickness of the polyvinyl alcohol-based film used for the production thereof is uniform, that the polyvinyl alcohol-based film is uniformly dyed, that the surface of the polarizing film is not stained It is particularly important that the polyvinyl alcohol film has a uniform quality.

In order to cope with the large screen of a liquid crystal display in a field of a monitor, a television, etc., it is necessary to produce a polarizing film by using a wide polyvinyl alcohol film. However, in the case where the polyvinyl alcohol film is merely subjected to a wide width, as compared with the case where a narrow polyvinyl alcohol film is used, only a result that the optical unevenness becomes conspicuous in the polarizing film is generated, There is a problem that the area of the polarizing film is remarkably reduced and the yield as a polarizing film product is extremely lowered.

The term "optical unevenness" as used herein refers to a general term of optically non-uniform unevenness observed on a polarizing film. In particular, the term "optical unevenness" refers to a minute unevenness of a spot having a size of about 1 cm. There is a case that the quality is lowered. This is often caused by non-uniform dyeing and stretching of the polyvinyl alcohol-based film. That is, when the polyvinyl alcohol film is dyed by using an iodine solution or a dichroic dye solution, uneven dyeing results, resulting in uneven dyeing. This causes the polarizing film to have uneven transmittance, Can not be used. Further, when the polyvinyl alcohol film is stretched, if there is a portion having a different thickness or elastic modulus in the TD direction of the film, the stretching can not be performed uniformly. Therefore, the transparency and the degree of polarization of the polarizing film are varied, It is a cause of extremely lowering the yield of the polarizing film usable for use.

In order to solve the drawbacks of the polyvinyl alcohol film used in the production of the polarizing film, the thickness variation in the TD direction of the film is set to 12% or less (Patent Document 1) (Patent Document 2), the retardation difference between two points of 1 cm apart in the TD direction of the film is set to 5 nm or less (Patent Document 3), and the deviation of hot water cutting temperature in the TD direction of the film is set to 1.5 DEG C or lower (Patent Document 4), and the ratio (S _M / S _T ) of the tensile elongation (S _M ) in the MD direction and the tensile elongation (S _T ) in the TD direction of the film is set to 0.7 to 1.3 There is known a method for reducing a structural deviation and anisotropy of a vinyl alcohol-based film.

However, even with these methods, there still exists optical unevenness that can not be solved in the polarizing film, and it is currently impossible to meet the demand for providing a polarizing film corresponding to a large screen of a liquid crystal display.

It is also possible to suppress fluctuation of large unevenness by using a polyvinyl alcohol film for optical use (Patent Document 6) characterized in that the difference between the maximum value and the minimum value of the plasticizer concentration in the film width direction is 1% or less , It is not possible to suppress the occurrence of fine spot-like unevenness of about 1 cm described above.

The prior art document information related to the invention of this application is as follows.

(Patent Document 1) Japanese Laid-Open Patent Publication No. 2001-323077 (scope of Patent Office)

(Patent Document 2) Japanese Laid-Open Patent Publication No. 2002-31720 (scope of Patent Office)

(Patent Document 3) Japanese Laid-Open Patent Publication No. 2002-28938 (scope of Patent Office)

(Patent Document 4) Japanese Laid-Open Patent Publication No. 2002-30163 (scope of Patent Office)

(Patent Document 5) Japanese Laid-Open Patent Publication No. 2002-30164 (scope of Patent Office)

(Patent Document 6) Japanese Laid-Open Patent Publication No. 2004-20630 (scope of Patent Office)

It is an object of the present invention to provide a polyvinyl alcohol-based film having a small area of fine optical unevenness and a uniform quality even in a large area.

Means for Solving the Problems The present inventors have intensively studied in order to attain the above object. As a result, the present inventors have found that a polyvinyl alcohol-based film formed from a raw film-forming solution containing a polyvinyl alcohol-based polymer and a plasticizer, wherein the polyvinyl alcohol- (Direction perpendicular to the flow direction MD of the film), the maximum content difference Ry with respect to the average value of the plasticizer content in the film is 2% or less, and the variation amount of the plasticizer content in the TD direction A polyvinyl alcohol film having an average gap (Sm) of 5 cm or more was found, and the present invention was accomplished.

The polyvinyl alcohol film (hereinafter abbreviated as " PVA film ") of the present invention has a maximum content difference Rye at the end portion of the film and a maximum content difference Ryc at the center portion of the film The ratio (Rye / Ryc) is preferably 0.8 or more and 1.3 or less.

In the PVA film of the present invention, the ratio (Sme / Smc) of the average interval (Sme) of the variation irregularities at the end portion of the film to the average interval (Smc) Or less.

Here, the center portion of the film refers to a range up to 50% of the total amount spreading by 25% in the same direction from the center point with respect to the entire width in the TD direction of the film, and the end portion of the film means the It points to the rest of the range.

The width of the PVA-based film of the present invention is preferably 2 m or more.

The present invention also includes a method for producing a polyvinyl alcohol-based film. The production method is characterized by comprising a raw liquid preparing step of preparing a stock solution of a film forming agent with a polyvinyl alcohol polymer, a plasticizer and a solvent, and a step of mixing the raw film forming solution with a mixing means to mix the polyvinyl alcohol polymer and the plasticizer uniformly A discharging step of discharging the uniformly mixed stock film stock solution from the die to the roll, and a drying step of drying the discharged stock solution. In this production method, the polyvinyl alcohol-based polymer, the plasticizer and the solvent may be fed to an extruder and kneaded to prepare a stock solution for film-forming in the stock solution preparation step. The mixing means may be at least one selected from the group consisting of a mixer, a continuous vibration stirrer, and a local homogenizer.

The PVA film of the present invention has an excellent feature that the plasticizer is uniformly present in the TD direction, and by producing such a polarizing film using the PVA film, even if a large area is caused by uneven dyeing or stretching unevenness A high-performance polarizing film with less optical unevenness can be obtained.

The polarizing film obtained in this way can be used in a wide variety of applications such as electronic calculators, wrist watches, notebook PCs, liquid crystal monitors, liquid crystal color projectors, liquid crystal televisions, vehicle navigation systems, mobile phones, It can be effectively used for manufacturing a polarizing plate which is a component of a liquid crystal display device for which display quality is required.

The present invention will be more clearly understood from the following description of the preferred embodiments with reference to the accompanying drawings. However, the embodiments and figures are merely for purposes of illustration and description, and should not be used to define the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing a variation curve of the content of the plasticizer in the TD direction of the PVA-based film. FIG. In this figure, Rp, Rv, Ry and Smi are respectively defined below. That is, Rp is a content corresponding to the difference between the average value of the plasticizer content and the plasticizer content in the fluctuation curve, and Rv is the content of the average value of the plasticizer content and the plasticizer content Ry is the sum of Rp and Rv, Smi is a peak portion that exceeds the average value of the plasticizer content, and an average value adjacent to this peak Is a gap occupied in the TD direction by the variation irregularity type formed by one each of the valleys below the center of the tapered portion.

Carrying out the invention Best form for

Hereinafter, the present invention will be described in detail.

The film forming stock solution used for forming the PVA film of the present invention contains a polyvinyl alcohol polymer and a plasticizer. The polyvinyl alcohol polymer (hereinafter abbreviated as " PVA polymer ") can be produced, for example, by saponifying a polyvinyl ester obtained by polymerizing a vinyl ester. Other examples of the PVA polymer include an unsaturated carboxylic acid or a derivative thereof, an unsaturated sulfonic acid or a derivative thereof, an unsaturated carboxylic acid having a carbon number of 2 to 30

-Vinyl esters and unsaturated carboxylic acids or derivatives thereof, unsaturated sulfonic acids or derivatives thereof, vinyl esters having 2 to 30 carbon atoms

- Modified PVA polymer produced by saponifying a modified polyvinyl ester copolymerized with an olefin or the like; so-called polyvinyl acetal resin in which a part of the hydroxyl groups of the unmodified or modified PVA polymer is crosslinked with aldehydes such as formaldehyde, benzaldehyde And the like.

Examples of the vinyl ester used in the production of the PVA polymer include vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate and vinyl benzoate Among these, vinyl acetate is preferable from the viewpoint of productivity.

The above-mentioned comonomer used for the production of the modified PVA polymer is copolymerized mainly for the purpose of modifying PVA, and is used within a range that does not hinder the purpose of the present invention. As such comonomers, for example, olefins such as ethylene, propylene, 1-butene, and isobutene (for example,

-C ₂ _- ₄ olefin); Acrylic acid and its salts; Acrylic esters such as methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate and octadecyl acrylate for example, acrylic -C ₁ _- ₆ alkyl ester); Methacrylic acid and its salts; Methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2- ethylhexyl methacrylate pH decyl methacrylate, octadecyl such as methacrylic acid esters (e.g., methacrylic acid, -C ₁ _- ₆ alkyl ester); Acrylamide, N-methylacrylamide, N-ethyl acrylamide, N, N-dimethylacrylamide, diacetone acrylamide, acrylamide propane sulfonic acid and salts thereof, acrylamide propyldimethylamine and salts thereof, Acrylamide derivatives such as amide and derivatives thereof; Methacrylamides such as methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamide propanesulfonic acid and salts thereof, methacrylamidopropyldimethylamine and salts thereof, N-methylolmethacrylamide and derivatives thereof Acrylamide derivatives; N-vinyl amides such as N-vinyl formamide, N-vinyl acetamide and N-vinyl pyrrolidone; Vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether and stearyl vinyl ether Ethers; 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; Unsaturated carboxylic acids such as maleic acid and itaconic acid, and derivatives thereof such as salts and esters thereof; Vinylsilyl compounds such as vinyltrimethoxysilane; Isopropenyl acetate, and isopropenyl acetate. Among these,

-Olefins are preferred, and ethylene is particularly preferred. The modified amount of the modified PVA polymer is preferably less than 15 mol%, more preferably not more than 5 mol%.

The degree of saponification of the PVA polymer is preferably not less than 95 mol% in view of the polarizing performance and durability when the PVA film is uniaxially stretched to form a polarizing film and the polarizing performance and durability of the polarizing plate produced from the polarizing film , More preferably 98 mol% or more, still more preferably 99 mol% or more, and most preferably 99.3 mol% or more.

The term "degree of saponification" as used herein means the degree of saponification as measured by the method described in JIS K 6726, and indicates the ratio of units actually saponified with vinyl alcohol units among units capable of being converted into vinyl alcohol units by saponification will be.

The degree of polymerization of the PVA polymer is preferably 1000 or more in view of the polarizing performance and durability when the PVA film is uniaxially stretched into a polarizing film and the polarizing performance and durability of the polarizing plate produced from the polarizing film, And more preferably 2,000 or more. From the standpoints of easiness of production of a homogeneous PVA-based film, stretching property and the like, the degree of polymerization of the PVA-based polymer is preferably 8000 or less, particularly 6000 or less.

The degree of polymerization of the PVA polymer in the present specification refers to the degree of polymerization measured according to JIS K 6726. The degree of polymerization of the PVA polymer is obtained from the intrinsic viscosity measured at 30 캜 after saponification and purification of the PVA polymer.

Examples of the method for producing a PVA film using the PVA polymer include a melt extrusion film forming method in which a PVA polymer in a water content state is melted and extruded, a PVA film in which a PVA polymer is dissolved in a solvent (PVA) polymer aqueous solution is once cooled and gelled, and then the solvent is extracted and removed to obtain a PVA film, And a method of combining them), or the like. Of these, the flexible film forming method and the melt extrusion film forming method are preferable from the viewpoint of obtaining a favorable polarizing film.

Examples of the solvent for dissolving the PVA polymer used in the production of the PVA film include water, a water-soluble organic solvent (for example, sulfoxides such as dimethyl sulfoxide; amides such as dimethylformamide and dimethylacetamide; Ethers such as N-methylpyrrolidone; and amines such as ethylenediamine and diethylenetriamine). These solvents may be used alone or in combination of two or more. Among them, dimethylsulfoxide, water or a mixed solvent of dimethyl sulfoxide and water is preferably used.

The concentration of the PVA polymer in the PVA polymer solution used in the production of the PVA film or in the aqueous PVA polymer varies depending on the degree of polymerization of the PVA polymer but is preferably 20 to 70 mass% More preferably from 25 to 60% by mass, and most preferably from 30 to 50% by mass. If the concentration of the PVA polymer is higher than 70% by mass, the viscosity of the PVA polymer solution or the PVA polymer in the aqueous state becomes excessively high, which makes filtration and deaeration, which are performed when forming the film forming solution of the PVA film, difficult, There is a tendency that it becomes difficult to obtain a defect-free PVA-based film. When the concentration of the PVA polymer is lower than 20 mass%, the viscosity of the PVA polymer solution or the PVA polymer in the aqueous state becomes excessively low, and it tends to be difficult to produce a PVA film having a desired thickness.

The PVA-based film of the present invention can be produced by using a PVA-based polymer solution to which a plasticizer is added or a PVA-based polymer in a water-based state as a raw film-forming solution. As the plasticizer that can be used for this purpose, a polyhydric alcohol is preferably used. Examples of the polyhydric alcohol include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol and trimethylolpropane, and they may be used alone or in combination of two or more Can be used. Of these, diglycerin, ethylene glycol and glycerin are preferably used from the viewpoint of improving the stretchability, and glycerin is most preferably used.

The plasticizer is preferably used in an amount of 1 to 30 parts by mass based on 100 parts by mass of the PVA polymer, more preferably 3 to 25 parts by mass, still more preferably 5 to 20 parts by mass , And it is particularly preferable to use it in an amount of 10 to 20 parts by mass. If the amount of the plasticizer is less than 1 part by mass, the dyeability and stretchability of the PVA-based film may be deteriorated. If the amount is more than 30 parts by mass, the PVA-based film may become excessively flexible and handleability may be deteriorated.

It is preferable to add a surfactant to the raw film forming solution for producing the PVA film. The addition of the surfactant improves the film forming property to suppress the occurrence of the thickness variation of the PVA film, Peeling of the PVA film from the roll or the belt is facilitated. The kind of the surfactant is not particularly limited, but anionic or nonionic surfactant is preferable from the viewpoint of releasability from a metal roll or a belt, and a nonionic surfactant is particularly preferable. As the anionic surfactant, for example, a carboxylic acid type such as potassium laurate, a sulfuric acid ester type such as octylsulfate and a sulfonic acid type anionic surfactant such as dodecylbenzenesulfonate are preferable. Examples of the nonionic surfactant include alkyl ether types such as polyoxyethylene oleyl ether and the like, alkylphenyl ether types such as polyoxyethylene octylphenyl ether and the like, alkyl ester types such as polyoxyethylene oleate, polyoxyethylene Alkyl amines such as lauryl amino ether, alkyl amides such as polyoxyethylene lauric acid amide, polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether, alkanolamides such as oleic acid diethanolamide, poly And an allyl phenyl ether type surfactant such as oxyalkylene allyl phenyl ether. These surfactants may be used alone or in combination of two or more.

When a surfactant is added to the stock solution, 0.01 to 0.5 parts by mass, more preferably 0.02 to 0.3 parts by mass, particularly 0.05 to 0.1 part by mass, of the addition amount is preferably added to 100 parts by mass of the PVA polymer. When the addition amount of the surfactant is less than 0.01 part by mass, the effect of improving the film formability and the peelability by the addition of the surfactant may be less likely to be exhibited. On the other hand, if the amount exceeds 0.5 parts by mass, Resulting in blocking, which may lower the handling property.

The film-forming raw liquid may contain various additives, for example, a stabilizer (for example, an antioxidant, an ultraviolet absorber, a heat stabilizer, etc.), a compatibilizing agent, an antiblocking agent, A flame retardant, an antistatic agent, a lubricant, a dispersant, a fluidizing agent, an antimicrobial agent, and the like. These additives may be used alone or in combination of two or more.

In the PVA film of the present invention, the percentage of the maximum content difference Ry to the average value of the plasticizer content in the film in the TD direction is 2% or less, and in the TD direction of the film The average interval Sm obtained by averaging the intervals Smi in the TD direction of the crests of the fluctuation curves and the curvatures adjacent to the crests of the fluctuation curves is 5 cm or more. In the PVA film satisfying this condition, the plasticizer content becomes very uniform in the TD direction, or when the polarizing film is produced using such a PVA film, the optical unevenness caused by uneven dyeing or stretching unevenness is small A high-performance polarizing film can be obtained. In particular, it is possible to suppress the occurrence of minute spot-like unevenness of about 1 cm, which can not be suppressed in the conventional large-area PVA film.

If the maximum content difference Ry with respect to the average value of the plasticizer content in the TD direction exceeds 2%, the difference in degree of swelling of the PVA-based film at the time of swelling the PVA-based film during production of the polarizing film becomes large, Uneven dyeing or stretching unevenness occurs in the polarizing film. The maximum content difference Ry with respect to the average value of the plasticizer content is preferably 1.85% or less, more preferably 1.5% or less, and further preferably 1% or less.

Variation in Content of Plasticizer Content in the TD Direction When the average spacing Sm of the concavo-convex patterns is less than 5 cm, uneven stretching appears in the polarizing film as a steep fluctuation, so that optical unevenness becomes remarkable. Variation in the TD direction of the plasticizer content The average spacing Sm of the concavo-convex forms is preferably 6 cm or more, more preferably 7 cm or more, and further preferably 9 cm or more.

Here, the maximum content difference Ry in the TD direction of the plasticizer content and the average spacing Sm of the variation irregularities in the TD direction of the plasticizer content can be obtained by the following method. That is, a sample of a rectangle (1 cm in the TD direction and 2 cm in the MD direction (longitudinal direction of the film)) continuous in the TD direction from the end portion or the central portion of the PVA film is collected in an arbitrary width L cm (20 cm or more).

Further, the values obtained at either the end or the center can be used as the representative values Ry and Sm of the film, and it is preferable to use the value obtained at the center as the representative value of the film. In other words, in other words, the maximum content difference Ry in the TD direction of the plasticizer content and the average spacing Sm of the fluctuation amount irregularities in the TD direction of the plasticizer content, It is preferable that the value specified by the present invention is satisfied at the central portion. In addition, the width L can be arbitrarily selected in accordance with the width of the PVA-based film, and 1/10 of the film width can be handled as a representative value.

In each sample, obtained above in DMSO-d ₆ so that a concentration of about 5% by weight and was dissolved over 2 hours, then heated over 90 ℃, 500 MHz, PD (pulse delay by using a ¹ H-NMR Time) of 20 seconds, a measurement temperature of 30 占 폚, and a cumulative number of times of 256, and the plasticizer content of each sample is measured from the obtained NMR spectrum. For example, when glycerin is used as the plasticizer, the NMR spectrum obtained by the above measurement shows that the peak of two methylene hydrogens of glycerin is near 3.3 ppm (the integral intensity of the peak is Sg), two methylene hydrogens of PVA (The integral intensity of the peak is Sp) is detected at around 1.5 ppm, and the amount of glycerol R (mass%) in the PVA-based film can be calculated by the following formula have.

R = (92/44) x (Sg / Sp) x 100 (1)

From the obtained measurement values, a variation curve (Fig. 1) of the plasticizer content per 1 cm at an arbitrary width (L cm) in the TD direction was prepared and from the following equation (2) The maximum content difference Ry in the surface area is found.

Ry = Rp + Rv (2)

In the formula (2), Rp represents a content corresponding to the difference between the average values of the plasticizer content and the plasticizer content, and Rv represents the average value of the plasticizer content and the plasticizer content, Indicating a substantial content.

The average interval (Sm) of variation of the plasticizer content in the TD direction is determined by the difference between the peak of the peak of the plasticizer content in the fluctuation curve (Fig. 1) and the peak of the valley (Smi) occupied by the fluctuation amount unevenness type in the TD direction can be obtained by arithmetic averaging as shown in the following equation (3). If the concavo-convex shape is broken at both ends of the take-out portion, the concavo-convex concavo-convex shape is not counted in the interval Smi.

In the PVA film of the present invention, the ratio (Rye / Ryc) of the maximum content difference (Rye) between the maximum content difference (Rye) of the plasticizer content at the end portion of the film and the maximum content difference (Ryc) Or less, from the viewpoint of obtaining a polarizing film having less optical unevenness.

When the ratio of Rye to Ryc (Rye / Ryc) is less than 0.8 or more than 1.3, the uniformity of the end portions of the PVA film and the plasticizer content at the central portion is impaired, It tends to be emphasized more. The ratio of Rye to Ryc (Rye / Ryc) is preferably 0.9 or more and 1.2 or less, more preferably 0.95 or more and 1.1 or less.

The PVA film of the present invention is further characterized in that the ratio (Sme / Smc) of the average interval (Sme) of the fluctuation amount irregularities at the end portion of the film to the average interval (Smc) And is preferably 1.4 or less from the viewpoint of obtaining a polarizing film having less optical unevenness.

When the ratio of Sme to Smc (Sme / Smc) is less than 0.7 or more than 1.4, when the PVA-based film is dyed, the difference in size between the end portion and the central portion of the film becomes too extreme Therefore, optical unevenness tends to be conspicuous when a polarizing film is produced. The ratio of Sme to Smc (Sme / Smc) is preferably 0.85 or more and 1.3 or less, more preferably 0.9 or more and 1.2 or less.

A PVA film is obtained by discharging (spinning) a film forming stock solution containing a PVA polymer solution or a PVA polymer in a water state from a T-shaped slit die to a drum type roll (softening) and drying the formed PVA polymer film. The material of the drum-type roll is not particularly limited, but stainless steel is preferably used, and the surface of the roll is preferably plated with metal to prevent scratching. As the kind of the metal plating to be used, for example, chromium plating, nickel plating, and zinc plating are preferable, and a single layer or two or more layers of plating layers can be formed on the roll surface by using them. From the viewpoint of smoothing the surface of the PVA-based film or obtaining a PVA-based film having excellent durability, it is preferable that the outermost surface of the drum-shaped roll is chromium-plated. It is preferable that the surface of the drum-shaped roll is kept smooth and the surface roughness (the difference in unevenness of the roll surface) is preferably not more than 3 S as expressed by the average interval S of roughness curves of JIS B 0604, Preferably 1.5 S or less, particularly preferably 0.5 S or less.

The surface temperature of the drum-type roll for discharging the PVA polymer solution or the PVA polymer in the water state is preferably 50 to 120 ° C. The PVA polymer film formed on the drum-shaped roll is peeled off from the drum-shaped roll when the moisture content reaches 5 to 30 mass%, and then the front and back surfaces of the film are alternately dried using a multi-stage roll. The dried PVA polymer film is subjected to heat treatment, humidity conditioning treatment and the like as necessary, and the obtained PVA film is finally rolled into a core tube with a predetermined length.

The PVA film may be coated with an antiblocking agent such as silicon oxide, titanium dioxide, clay, bentonite, stearic acid or a salt thereof on the surface of the film for the purpose of preventing blocking.

For example, a die such as a chuck bar type or a flexible lip type can be used as a die used for forming a PVA film. Especially when a die of a flexible lap type which is integrally molded and has no retention portion is used, A PVA film having a small variation in local thickness is obtained.

In order to adjust the PVA film to a proper state, it is preferable to install a heat treatment device, a humidity control device, and a speed adjusting mechanism such as a motor for driving rolls or a transmission.

The drying treatment in the production process of the PVA film is generally carried out at a drying temperature of 50 to 150 캜, particularly 60 to 120 캜, in order to obtain a PVA film having excellent stretchability and dyeability at the time of producing a polarizing film, In addition, it is preferable in that the polarizing performance and durability of the resulting polarizing film are improved.

Conventionally, the behavior of the plasticizer in the stock solution for film formation is not noticed, and it has been considered that the plasticizer is homogenized with the PVA polymer in a series of processing steps. For this reason, conventionally, PVA-based films have been produced under the recognition that mixing of PVA and plasticizer is sufficient by stirring at the time of dissolving the PVA polymer or by screw kneading at the time of melt extrusion. However, as a new knowledge at this time, it has been found that the plasticizer is not uniformly mixed with the PVA-based polymer in the usual treatment step, resulting in concentration unevenness. Further, in the PVA-based film made of the film-forming stock solution in which the concentration nonuniformity of the plasticizer has occurred, the distribution of the plasticizer content in the TD direction of the film becomes uneven.

In order to prevent the concentration unevenness of the plasticizer from occurring in the stock solution, the kneading may be performed by using a mixer or a kneader or by increasing the kneading time so that the stock solution for the film formation is sufficiently kneaded. Thereby, the fluctuation in the TD direction of the content of the plasticizer contained in the PVA film can be adjusted.

Particularly, in order to uniformly mix the PVA polymer and the plasticizer, a mixing means for mixing the plasticizer with the PVA polymer in a molten state in the flow path from the die outlet to the injection port, for example, an inline type Line type continuous vibration stirrer typified by a mixer or a vibrator mixer manufactured by Cooling Industrial Co., Ltd., and an inline type local homogenizer typified by an instantaneous mixing device manufactured by Sakura Plant Co., These mixing means may be used in addition to the ordinary kneading step, and it is more preferable to perform a combination of a plurality of mixing means. From this viewpoint, it is preferable to use a combination of an in-line type mixer and an in-line type continuous vibration agitator, or a combination of an in-line type mixer and an in-line type local homogenizer.

From the viewpoint of the viscosity of the stock film raw solution to be treated, it is preferable to select the spiral type, and the number of the elements is preferably 12 or more, and more preferably 24 or more. If the number of elements is less than 12, mixing of the PVA and the plasticizer in the stock solution may be incomplete, and it is difficult to obtain an expected effect. There is no upper limit to the number of elements, but from the viewpoint of cost effectiveness, 48 or less is preferable, and 42 or less is more preferable. Even when an element exceeding 48 is provided, it is difficult to obtain the effect of further improving the mixing property of the stock film-forming liquid. In addition, the number of elements referred to here is a number calculated by the number of elements per unit of the stitic mixer x the number of used units.

In the present invention, it is important to obtain a PVA-based film in which the width of the PVA-based film is 2 m or more in correspondence with the increase in the size of the liquid crystal display. From the viewpoint of a large screen, the film width is preferably 2.3 m or more, more preferably 2.6 m or more.

On the other hand, when the width of the PVA-based film is more than 6 m, it may be difficult to uniformly conduct the uniaxial stretching when the polarizing film is produced by using a practical apparatus. Therefore, the width of the PVA- More preferably 5 m or less.

It should be noted that when the width of the PVA-based film is narrow, the polarizing film produced by using such a PVA-based film does not exist as much as the optical unevenness originally caused by uneven dyeing or stretching unevenness. However, if the width of the PVA-based film is 2 m or more, even if the conventional production method is used as it is, uniform stretchability can not be ensured when the polarizing film is produced (the width direction of the PVA- Direction). In such a polarizing film, optical unevenness caused by uneven dyeing or stretched unevenness is remarkably exhibited, which causes variations in the transmittance and polarization degree of the polarizing film. Therefore, in order to suppress the occurrence of such unevenness in the concentration of the plasticizer, it is particularly important to adopt a production method that takes into consideration the uniformity of the plasticizer distribution in the TD direction of the PVA film.

The average thickness of the PVA-based film is not particularly limited, but is generally from 20 to 120 탆, preferably from 40 to 120 탆, more preferably from 50 to 100 탆. If the average thickness of the PVA-based film is less than 20 占 퐉, stretching failure may occur during uniaxial stretching for producing a polarizing film. If the PVA film has an average thickness exceeding 120 탆, uneven drawing may occur during uniaxial stretching for producing a polarizing film.

The method for producing a polarizing film when the polarizing film is produced by using a PVA film is not particularly limited, and any method conventionally employed when a polarizing film is produced using a PVA film as the original film may be employed.

In order to produce a polarizing film with a PVA film, for example, the PVA film may be subjected to moisture control, dyeing, uniaxial stretching, fixing treatment, drying treatment and, if necessary, heat treatment. And the like are not particularly limited. The uniaxial stretching may be performed in two or more stages, or may be carried out simultaneously with dyeing or fixing treatment.

The dyeing may be carried out using iodine, and the dyeing may be performed at any stage of the uniaxial stretching, the uniaxial stretching, and the uniaxial stretching. In general, dyeing is generally carried out by immersing the PVA film in a solution (particularly an aqueous solution) containing iodine-potassium iodide, and in the present invention, a dyeing method using an aqueous solution containing iodine and potassium iodide is preferably employed do. It is preferable that the concentration of iodine in the dyeing aqueous solution is 0.01 to 0.5 mass% and the concentration of potassium iodide is 0.01 to 10 mass%. The temperature of the dyeing bath is preferably 20 to 50 캜, particularly 25 to 40 캜.

The uniaxial stretching may be carried out by wet stretching in a solvent such as water or dry stretching in air or the like. In the case of the wet stretching method, uniaxial stretching in water, uniaxial stretching in a dyeing solution containing no boric acid, uniaxial stretching in a dyeing solution containing boric acid, uniaxial stretching in an aqueous solution of boric acid, For example, by multi-stage drawing.

Although the stretching temperature is not particularly limited, it is preferably 30 to 90 占 폚 in the case of wet-drawing a PVA-based film, and 50 to 180 占 폚 in case of dry stretching.

The stretching magnification (uniaxial stretching ratio in the case of uniaxial stretching in multiple stages) of the uniaxial stretching is preferably 4 times or more, particularly 5 times or more, in terms of the polarizing performance of the resulting polarizing film. The upper limit of the draw ratio is not particularly limited, but is preferably 8 times or less in terms of uniform drawing.

In the production of the polarizing film, a fixed treatment is often carried out in order to enhance the adsorption of iodine to the PVA-based film, and in the present invention, it is preferable to perform the fixing treatment at the time of producing the polarizing film. As a treatment bath to be used for the fixing treatment, an aqueous solution to which one kind or two or more kinds of boron compounds such as boric acid, borax and the like are added is used. If necessary, an iodine compound or a metal compound may be added to the treatment bath for fixed treatment. The concentration of the boron compound in the treatment bath for fixed treatment is generally preferably about 2 to 15 mass%, particularly about 3 to 10 mass%. The temperature of the treatment bath at the time of fixed treatment is preferably 15 to 60 ° C, particularly 25 to 40 ° C.

The above uniaxial stretching, dyeing treatment, fixation treatment and the like are carried out, and then the obtained polarizing film is dried. The drying of the obtained polarizing film is preferably carried out at 30 to 150 ° C, particularly at 50 to 150 ° C. When the moisture content of the polarizing film becomes about 10% or less after the drying treatment, the polarizing film is subjected to heat treatment at about 80 to 120 ° C for about 1 to 5 minutes by applying a tension to the polarizing film, whereby a polarizing film having better dimensional stability and durability can be obtained.

The polarizing film thus obtained is usually used as a polarizing plate by attaching a protective film having optically transparent and mechanical strength on both sides or one side thereof. As the protective film, a cellulose triacetate (TAC) film, an alicyclic polyolefin (COP) film, an acrylic film, a polyester film, or the like is used. As the adhesive for adhering, a PVA adhesive, a urethane adhesive, or the like can be mentioned. Among them, a PVA adhesive is preferable.

The polarizing plate obtained as described above is used as a component of a liquid crystal display device after being coated with a pressure-sensitive adhesive such as acrylic or the like and then attached to a glass substrate. At the same time, it may be attached to a retardation film, a viewing angle improving film, a luminance improving film or the like.

Example

Hereinafter, the present invention will be described in detail by way of examples, but the present invention is not limited at all by these examples. The scope of the invention is defined by the appended claims.

In the following Examples and Comparative Examples, measurement of the plasticizer content contained in the PVA film, determination of the maximum content difference (Ry) and the average interval (Sm) of the fluctuation amount irregularities, measurement of the optical performance of the polarizing film, The optical unevenness was evaluated according to the following method.

Content of plasticizer in PVA film:

From the center point of the entire width of the PVA film obtained in the example or the comparative example, it is the same from left to right and 1/10 of the entire film width (35 cm in Examples 1 and 2, Examples 3 to 5, 30 cm in Examples 1 and 2) was sampled and the content of the plasticizer per 1 cm in the PVA film was measured according to the above-described method.

Maximum content difference (Ry) and mean spacing (Sm) of variation irregularities:

From the measured values, a variation curve of the plasticizer content of the PVA film in the TD direction was prepared, and the maximum content difference Ry and the average interval (Sm) of the variation irregularities were determined according to the above-described method. It is assumed that Ry and Sm obtained here are treated as Ryc and Smc in the center portion. With respect to the MD direction of the film, the maximum content difference (Rye) and the mean spacing (Sme) of the fluctuation amount irregularities at the end portion existing at the same position as the center portion were obtained by bringing the obtained PVA- 1/10 of the entire film width was sampled from a portion of the film in the direction of the center point by 20 cm in the TD direction from the end of the film, and the content of the plasticizer was measured every 1 cm as in the central portion.

Optical performance of polarizing film:

(i) transmittance

Two square samples each having a size of 4 cm x 4 cm in parallel in the alignment direction of the polarizing film were collected from the central portion in the width direction of the polarizing film obtained in the Example or the Comparative Example and a spectrophotometer manufactured by Hitachi High Technologies Co., The visual acuity of the C light source and the visible light region in the 2-degree field of view was corrected in accordance with JIS Z 8722 (measurement method of object color) using a U-4100 (with an integrating sphere) , The transmittance of light when tilted 45 degrees with respect to the stretching axis direction and the transmittance of light when tilted at -45 degrees were measured to obtain an average value Y1 thereof.

As for the other polarizing film sample, the transmittance of light when tilted 45 degrees and the transmittance of light when tilted -45 degrees were measured in the same manner as described above, and the average value (Y2) thereof was determined.

Y1 and Y2 obtained above were averaged to obtain the transmittance Y (%) of the polarizing film.

(Ii) Polarization degree:

The transmittance (Y∥) of light when the two polarizing films collected in (i) above are superimposed so that the stretching directions thereof are parallel to each other and the transmittance (Y⊥) of light when the stretching directions are orthogonally crossed, , And the degree of polarization was obtained from the following formula.

Polarization degree (V /%) = {(Y∥ -Y⊥) / (Y∥ + Y⊥)} ^1/2 × 100

Optical Unevenness of Polarizing Film:

The prepared polarizing film was sandwiched between two polarizing plates in a parallel Nicol state (a single light transmittance of 42.3% and a polarization degree of 99.99%) so that the stretching direction was 90 degrees with respect to the two polarizing plates described above. Using a light box, optical unevenness (spot-shaped unevenness scattered by about 1 cm in the TD direction and scattered in a size of several centimeters to several tens centimeters in the MD direction) in the transmission mode was observed and evaluated according to the following criteria .

○: The optical unevenness of the spot shape can not be confirmed at all

?: A slight unevenness of optical spot on the spot shape was confirmed

&Lt; / RTI > < RTI ID = 0.0 > x: < / RTI >

Example 1

100 parts by mass of a PVA polymer having a degree of saponification of 99.95 mol% and a viscosity-average degree of polymerization of 2400, 12 parts by mass of glycerin and 191 parts by mass of water were supplied to a monoaxial extruder and melted to obtain a stock solution (volatile content (moisture content) 63% . Three stator mixers of 6 spiral type and number of elements were arranged in series (total number of elements was 18) in the tube of the film-forming stock solution, and the stock solution was discharged from the T-shaped die onto a drum type roll Thereafter, the PVA film was peeled off when the moisture content of the PVA film reached 24 mass%, and further dried on a metal roll to obtain a PVA film having a width of 3.5 m and a thickness of 75 탆.

The maximum content difference Ry with respect to the average value of the plasticizer content in the TD direction of the obtained PVA-based film was 1.8%, and the average spacing Sm of the fluctuation amount irregularities of the plasticizer content in the TD direction was 6 cm. The ratio (Rye / Ryc) between the maximum content difference (Rye) at the edge of the PVA film and the maximum content difference (Ryc) at the center of the film was 1.2, and the average The ratio (Sme / Smc) of the interval (Sme) to the average spacing (Smc) of the variation irregularities at the center of the film was 1.3.

Using this PVA film, preliminary swelling, dyeing, uniaxial stretching, fixing treatment, drying and heat treatment were successively carried out in this order to produce a polarizing film. That is, the PVA-based film was immersed in water at 30 DEG C for 30 seconds to preliminarily swell and immersed in an aqueous solution at 35 DEG C in which the concentration ratio of iodine / potassium iodide was 1/100, for 3 minutes. Subsequently, the coated substrate was uniaxially stretched 6 times in an aqueous solution having a boric acid concentration of 40 g / l at 50 캜 and immersed in an aqueous solution having a potassium iodide concentration of 70 g / l and a boric acid concentration of 40 g / l for 5 minutes Respectively. Thereafter, the PVA film was taken out, dried at 40 캜 by hot air, and further heat-treated at 100 캜 to obtain a polarizing film.

The obtained polarizing film had a transmittance of 43.5% and a polarization degree of 99.92%. In this polarizing film, no uneven dyeing was observed, and the degree of optical unevenness was evaluated. As a result, the evaluation was good.

Example 2

In Example 1, PVA having a width of 3.5 m and a thickness of 75 占 퐉 was prepared in the same manner as in Example 1, except that two spiral-type stator mixers of 6 elements were provided in the stock solution of the film-forming solution (the total number of elements was 12) Based film.

The maximum content difference Ry with respect to the average value of the plasticizer content in the TD direction of the obtained PVA-based film was 2.0%, and the average spacing Sm of the variation amount irregularities in the TD direction of the plasticizer content was 5 cm. The ratio (Rye / Ryc) of the maximum content difference (Rye) at the end of the PVA film to the maximum content difference (Ryc) at the center of the film was 0.7, and the average The ratio (Sme / Smc) of the interval (Sme) to the average spacing (Smc) of the variation irregularities at the center of the film was 1.5.

Using this PVA-based film, a polarizing film was produced in the same manner as in Example 1.

The polarizing film thus obtained had a transmittance of 43.4% and a polarization degree of 99.91%. No uneven dyeing was observed in this polarizing film, and the degree of optical unevenness was evaluated. As a result, the judgment was " DELTA ", which was a level that could be used for a small-sized liquid crystal display.

Example 3

In addition to the stitic mixer (total number of elements: 12) in the raw liquid pipe in Example 2, in order to further uniformly mix the molten film forming stock solution, an instant mixer S-1 mixer (manufactured by Sakura Plant Co., Ltd.) , A PVA film having a width of 3 m and a thickness of 75 탆 was obtained in the same manner as in Example 1.

The maximum content difference Ry with respect to the average value of the plasticizer content in the TD direction of the obtained PVA-based film was 1.7%, and the average spacing Sm of the fluctuation amount unevenness types in the TD direction of the plasticizer content was 7 cm. The ratio (Rye / Ryc) between the maximum content difference (Rye) at the edge of the PVA film and the maximum content difference (Ryc) at the center of the film was 0.9, and the average The ratio (Sme / Smc) of the interval (Sme) to the average spacing (Smc) of the variation irregularities at the center of the film was 1.3.

The obtained polarizing film had a transmittance of 43.5% and a polarization degree of 99.93%. In this polarizing film, no uneven dyeing was observed, and the degree of optical unevenness was evaluated. As a result, the evaluation was good.

Example 4

Example 1 was repeated except that a continuous vibration stirrer vibro mixer (manufactured by Hyoka Kogyo Co., Ltd.) was used to more uniformly mix the stock solution of the melted coating film in place of the stitic mixer in the raw liquid pipe in Example 1, , A PVA film having a width of 3 m and a thickness of 75 탆 was obtained.

The maximum content difference Ry with respect to the average value of the plasticizer content in the TD direction of the obtained PVA-based film was 0.9%, and the average spacing Sm of the fluctuation amount irregularities in the TD direction of the plasticizer content was 8 cm. The ratio (Rye / Ryc) between the maximum content difference (Rye) at the edge of the PVA film and the maximum content difference (Ryc) at the center of the film was 0.9, and the average The ratio (Sme / Smc) of the interval Sme to the mean spacing Smc of the variation irregularities at the center of the film was 1.1.

The polarizing film thus obtained had a transmittance of 43.3% and a polarization degree of 99.96%. In this polarizing film, no uneven dyeing was observed, and the degree of optical unevenness was evaluated. As a result, the evaluation was good.

Example 5

In order to more uniformly mix the molten film forming stock solution in addition to the use of the stichic mixer (total number of elements 18) in the undiluted solution piping in Example 1, using a continuous vibration stirrer Vibro Mixer (manufactured by Chugoku Kogyo Co., Ltd.) , A PVA film having a width of 3 m and a thickness of 75 탆 was obtained in the same manner as in Example 1.

The maximum content difference Ry with respect to the average value of the plasticizer content in the TD direction of the obtained PVA-based film was 0.8%, and the average spacing Sm of the variation amount irregularities in the TD direction of the plasticizer content was 10 cm. The ratio (Rye / Ryc) of the maximum content difference (Rye) at the edge of the PVA film to the maximum content difference (Ryc) at the center of the film was 1.0, and the average The ratio (Sme / Smc) of the interval (Sme) to the average interval (Smc) of the variation irregularities at the center of the film was 0.9.

Comparative Example 1

A PVA film having a width of 3 m and a thickness of 75 탆 was obtained in the same manner as in Example 1 except that a stitic mixer provided in a pipe was not used.

The maximum content difference (Ry) with respect to the average value of the plasticizer content in the TD direction of the obtained PVA-based film was 3.0%, and the average spacing (Sm) of the variation amount irregularities in the TD direction of the plasticizer content was 2 cm. The ratio (Rye / Ryc) between the maximum content difference Rye at the end of the PVA film and the maximum content difference Ryc at the center of the film was 1.8, and the average The ratio (Sme / Smc) of the interval (Sme) to the average spacing (Smc) of the variation irregularities at the center of the film was 1.6.

The obtained polarizing film had a transmittance of 43.5% and a polarization degree of 99.92%. The polarizing film was found to have uneven dyeing, and the degree of optical unevenness was evaluated. As a result, the judgment was poor and the result was insufficient for liquid crystal displays for television applications.

Comparative Example 2

100 parts by mass of PVA having a degree of saponification of 99.95 mol% and a degree of polymerization of 2400, 10 parts by mass of glycerin and 170 parts by mass of water were supplied to a monoaxial extruder and melted to obtain a stock solution (volatile content (moisture content) of 60.7% by mass). Subsequently, a film was formed in the same manner as in Comparative Example 1, further brought into contact with warm air at a temperature of 65 DEG C and a humidity of 90% RH, and subsequently brought into contact with warm air at a temperature of 50 DEG C and a humidity of 45% For 6 seconds to obtain a PVA film having a width of 3 m and a thickness of 40 탆.

The maximum content difference (Ry) with respect to the average value of the plasticizer content in the TD direction of the obtained PVA-based film was 2.4%, and the average spacing (Sm) of fluctuation amount of the plasticizer content in the TD direction was 3.3 cm. The ratio (Rye / Ryc) of the maximum content difference (Rye) at the edge of the PVA film to the maximum content difference (Ryc) at the center of the film was 1.1, and the average The ratio (Sme / Smc) of the spacing Sme to the average spacing Smc of the variation irregularities at the center of the film was 0.8.

The polarizing film thus obtained had a transmittance of 43.9% and a polarization degree of 99.50%. Although no uneven dyeing was observed in this polarizing film, the degree of optical unevenness was evaluated. As a result, the judgment was extremely poor and the result was insufficient for liquid crystal displays for television applications.

Industrial availability

INDUSTRIAL APPLICABILITY The PVA film of the present invention has an excellent feature that the plasticizer exists uniformly in the TD direction, and by producing such a polarizing film using the PVA film, the optical unevenness caused by uneven dyeing or stretching unevenness A low-performance polarizing film can be smoothly obtained.

The polarizing film thus obtained can be effectively used for producing a polarizing plate which is a component of a liquid crystal display device which requires a high display quality.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. Accordingly, such changes and modifications are to be construed as being within the scope of the invention as defined in the claims.

Claims

A polyvinyl alcohol-based film formed from an undiluted solution containing a polyvinyl alcohol-based polymer and a plasticizer,
(a) the maximum content difference (Ry) with respect to the average value of the plasticizer content in the film in the TD direction is 2% or less and (b) the fluctuation curve of the plasticizer content in the TD direction of the film , Wherein the average interval (Sm) obtained by averaging the intervals (Smi) occupied by the fluctuation amount irregularities in the TD direction of the peak portions exceeding the average value of the plasticizer content and the curved portions adjoining to the acid is 5 cm or more, Alcohol film.

The method according to claim 1,
Wherein the ratio (Rye / Ryc) of the maximum content difference (Rye) at the end portion of the film to the maximum content difference (Ryc) at the central portion of the film is 0.8 or more and 1.3 or less.

The method according to claim 1,
Wherein the ratio (Sme / Smc) of the average spacing (Sme) of the variation irregularities at the end portion of the film to the average spacing (Smc) of the variation irregularities at the center portion of the film is 0.7 or more and 1.4 or less.

The method according to claim 1,
Wherein the ratio of the plasticizer to 100 parts by mass of the polyvinyl alcohol-based polymer is 1 to 30 parts by mass.

The method according to claim 1,
Wherein the film has a width of at least 2 m.

The method according to claim 1,
Wherein the average interval (Sm) is 7 cm or more.

A polarizing film produced by using the polyvinyl alcohol film according to any one of claims 1 to 6.

A crude liquid preparation process for preparing a stock solution for film formation with a polyvinyl alcohol polymer, a plasticizer and a solvent,
A mixing step of mixing the film-forming raw liquid with a mixing means, mixing the polyvinyl alcohol-based polymer and the plasticizer uniformly,
A discharging step of discharging the film-forming stock solution uniformly mixed from the die to the roll,
The method for producing a polyvinyl alcohol-based film according to any one of claims 1 to 6, comprising a drying step of drying the discharged raw liquid.

9. The method of claim 8,
Wherein the polyvinyl alcohol polymer, the plasticizer, and the solvent are fed to an extruder in the step of preparing the stock solution, and these are kneaded to prepare a stock solution for film formation.

9. The method of claim 8,
Wherein the mixing means is at least one selected from the group consisting of a mixer, a continuous vibration stirrer, and a local homogenizer.

9. The method of claim 8,
Wherein the mixing means is a stator mixer having a number of elements of 12 or more.

9. The method of claim 8,
Wherein the mixing means is a combination of an in-line continuous vibratory stirrer or a combination of a stitic mixer and an in-line continuous vibratory stirrer, or a stitic mixer and an in-line local homogenizer.