TWI452050B - Polyvinyl alcohol film - Google Patents

Description

Polyvinyl alcohol film [connection application]

The priority of Japanese Patent Application No. 2007-213444, filed on Jan. 20,,,,,,,,,,,,,,

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

A polarizing plate having a light penetrating and shielding function is a basic constituent element of a liquid crystal having a light conversion function and a liquid crystal display (LCD).

The field of application of this LCD has been extended from small devices such as computers and watches at the beginning of development to personal computers, LCD screens, liquid crystal color projectors, LCD TVs, car navigation systems, mobile phones, and indoor and outdoor use. Measuring a wide range of machines and the like. In particular, in the fields of screens, televisions, and the like, the large-screening of liquid crystal displays is rapidly progressing, and polarizing plates excellent in uniformity in optical performance are required even in a large area over the past.

The polarizing plate is generally obtained by dyeing with iodine or a dichroic dye after uniaxially stretching a polyvinyl alcohol-based film, or uniaxially stretching after dyeing, to obtain a dyed uniaxially stretched film, and a boron compound. The method of performing the fixing treatment, or the method of fixing the boron compound at the same time as the uniaxial stretching and dyeing treatment, and the method of fixing the boron compound, and bonding the triacetate fiber on the surface of the polarizing film Prime (TAC) thin A protective film of a film, an alicyclic polyolefin (COP) film or the like to produce a polarizing plate. In the case of obtaining a polarizing plate having uniform polarizing performance, the polyvinyl alcohol-based film used in the production has a uniform thickness and uniformly dyed polyvinyl alcohol-based film, and the surface of the polarizing film does not adhere to the surface. A protective film of a spot or the like is important, but it is particularly important that the polyvinyl alcohol-based film has a uniform quality.

In order to cope with a large screen of a liquid crystal display in the field of screens, televisions, etc., it is necessary to manufacture a polarizing film using a wide-type polyvinyl alcohol-type film. However, only the polyvinyl alcohol-based film is made to have a wide width, and as long as the result of forming a so-called attracting optical spot on the obtained polarizing film is compared with the case of using a narrow-sized polyvinyl alcohol-based film, There is a problem that the area of the polarizing film which can be used is remarkably reduced, and the yield of the polarizing film product is extremely lowered.

In addition, the optical plaque referred to herein is a general term for optically uneven spots that can be observed on a polarizing film, and particularly refers to fine speckle-like spots existing in a size of about 1 cm, and such optical plaques. There is a situation in which the display quality of the screen and the television is lowered. Most of these are caused by the uneven dyeing and elongation of the polyvinyl alcohol-based film. That is, when the polyvinyl alcohol-based film is dyed using an iodine solution or a dichroic dye solution, dyeing spots are generated due to uneven dyeing state, which causes the polarizing film to have uneven wear. Transparency and become unusable for display use. Further, when the polyvinyl alcohol-based film is stretched, when the film is stretched When there is a portion having a different thickness or modulus in the TD direction, since the stretching cannot be performed uniformly, the transmittance and the degree of polarization of the polarizing film are changed, and the yield of the polarizing film which can be used for display purposes is obtained. The reason for the extreme decrease.

In order to eliminate the disadvantage of the polyvinyl alcohol-based film used for producing a polarizing film, it is known that the thickness of the film in the TD direction is 12% or less (Patent Document 1), and the thickness variation in the film TD direction is 0.5 μm/mm or less ( Patent Document 2), the retardation value difference between two points separated by 1 cm in the TD direction of the film is 5 nm or less (Patent Document 3), and the hot water cut temperature spot in the film TD direction is 1.5 ° C or less (Patent Document 4) The ratio (SM/ST) of the stretched length (SM) in the MD direction of the film to the stretched length (ST) in the TD direction is 0.7 to 1.3 (Patent Document 5), and the structure of the polyvinyl alcohol-based film is different. The method of reducing directionality.

However, even with such a method, there is still an optical spot which cannot be eliminated in the polarizing film, and the present situation cannot sufficiently respond to the demand for providing a polarizing film which can correspond to a large screen of a liquid crystal display.

In addition, the optical polyvinyl alcohol film (Patent Document 6) in which the difference between the maximum value and the minimum value of the concentration of the plasticizer in the film direction of the film is 1% or less is used, although the fluctuation of the large spot can be suppressed. However, it was not possible to suppress the occurrence of fine speckle-like spots of about 1 cm.

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

[Patent Document 1] Japanese Laid-Open Patent Publication No. 2001-323077 (Patent Application Scope) Patent Document 2: JP-A-2002-31720 (Patent Application) Patent Document 3: JP-A-2002-28938 (Application No.) Patent Document 4: JP-A-2002-30163 (Patent Application) Patent Document 5: JP-A-2002-30164 (Patent Application) Patent Document 6: JP-A-2004-20630 (Application No.)

SUMMARY OF THE INVENTION An object of the present invention is to provide a polyvinyl alcohol-based film which has a small number of fine optical spots in a large area and which has a uniform quality.

As a result of intensive review, the inventors of the present invention found that a polyvinyl alcohol-based film formed by a film-forming stock solution containing a polyvinyl alcohol-based polymer and a plasticizer was found in the polyvinyl alcohol-based film. In the TD direction (for the orthogonal direction of the film flow direction (MD)), the maximum content difference (Ry) of the average value of the plasticizer contained in the film is 2% or less, and in the TD direction of the plasticizer content. The polyvinyl alcohol-based film having an average interval (Sm) of a variable amount of irregularities of 5 cm or more was completed, and the present invention was finally completed.

The polyvinyl alcohol-based film of the present invention (hereinafter, simply referred to as "PVA-based film") is preferably a ratio of the maximum content difference (Rye) in the film end portion to the maximum content difference (Ryc) in the central portion of the film. (Rye/Ryc) is 0.8 or more and 1.3 or less.

Further, in the PVA-based film of the present invention, the ratio (Sme/Smc) of the average interval (Sme) of the unevenness of the unevenness in the film end portion to the average interval (Smc) of the unevenness in the center portion of the film is 0.7 or more. Below 1.4 is preferred.

Here, the term "the center portion of the film" means that the center point of the total width in the TD direction of the film is extended to the range of 25% to the total of 50% on the left and right sides, and the so-called film end portion means the film. The range of its total width.

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

Moreover, the present invention also includes a method for producing a polyvinyl alcohol-based film. The production method includes a raw material preparation step of preparing a film forming stock solution from a polyvinyl alcohol polymer, a plasticizer, and a solvent; mixing the film forming stock solution by mixing means, and uniformly mixing the polyvinyl alcohol polymer and the plasticizer a mixing step; a step of discharging the film-forming stock solution uniformly discharged from the die to the roll; and a drying step of drying the discharged stock solution. In the production method, in the raw material preparation step, a polyvinyl alcohol-based polymer, a plasticizer, and a solvent may be supplied to an extruder, and kneaded to prepare a film-forming stock solution. Further, the mixing means may be selected from at least one of the group consisting of a mixer, a continuous vibration mixer, and a partial homogenizer.

The PVA-based film of the present invention has an excellent characteristic that the plasticizer is uniformly present in the TD direction, and by using such a PVA-based film to produce a polarizing film, even a large area can be caused by staining or stretching. A high performance polarizing film with few optical spots.

The polarizing film obtained in this way exhibits the above-described excellent characteristics and can be effectively used in the manufacture of computers, watches, personal computers, liquid crystal screens, liquid crystal color projectors, liquid crystal televisions, car navigation systems, mobile phones, and indoor and outdoor housing. A component of a liquid crystal display device that requires high display quality, such as a measuring device, is used for the production of a polarizing plate.

The present invention will be more clearly understood from the following description of the preferred embodiments. However, the embodiment and drawings are only for illustration And the description should not be taken as limiting the scope of the invention.

Fig. 1 is a graph showing the variation of the plasticizer content in the TD direction of the PVA-based film. In addition, in this figure, each of Rp, Rv, Ry, and Smi is defined as follows. That is, the Rp is in the variation curve, the average value of the plasticizer content and the difference between the peak of the plasticizer is very large, and the Rv is in the variation curve, and the average value of the plasticizer content is equivalent to The content of the plasticizer is a very small difference between the bottom lines, Ry is the sum of Rp and Rv, and the Smi is made up of the mountain portion which exceeds the average value of the plasticizer content, and the valley which is adjacent to the mountain and below the average value. The fluctuation amount of each of the sections is a difference in the shape of the concavities and convexities in the TD direction.

Best form for implementing the invention

Hereinafter, the present invention will be described in detail.

The film forming stock solution for forming a PVA-based film of the present invention comprises a polyvinyl alcohol-based polymer and a plasticizer. A polyvinyl alcohol-based polymer (hereinafter, simply referred to as "PVA-based polymer") can be produced by, for example, polymerizing a vinyl ester and saponifying the obtained polyvinyl ester. Other PVA-based polymers include, for example, graft copolymerization of an unsaturated carboxylic acid or a derivative thereof, an unsaturated sulfonic acid or a derivative thereof, and an α-olefin having 2 to 30 carbon atoms in a main chain of PVA. The modified PVA-based polymer is obtained by copolymerizing a vinyl ester with an unsaturated carboxylic acid or a derivative thereof, an unsaturated sulfonic acid or a derivative thereof, and an α-olefin having a carbon number of 2 to 30 by saponification. The modified PVA-based polymer produced by the polyvinyl ester, a part of the hydroxyl group of the unmodified or modified PVA-based polymer is cross-linked by the aldehydes of formalin, butyraldehyde, benzaldehyde, etc. Polyvinyl acetal resin and the like.

The vinyl ester used for the production of the PVA-based polymer may, for example, be vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate or vinyl alkane carboxylic acid (Versatic acid). Ester, vinyl laurate, vinyl stearate, vinyl benzoate, etc. Among these, vinyl acetate is preferred from the viewpoint of productivity.

Since the above-mentioned comonomer used for the production of the modified PVA-based polymer is mainly copolymerized by the modified PVA, it can be used without departing from the gist of the present invention. Examples of such a copolymerization system include olefins such as ethylene, propylene, 1-butene, and isobutylene (for example, α-C _2-4 olefins); acrylic acid and salts thereof; methyl acrylate and ethyl acrylate; Acrylates such as n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate (for example, acrylic acid-C _1-6 alkyl ester); methacrylic acid and its salts; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, methacrylic acid Methacrylates such as n-butyl ester, isobutyl methacrylate, tert-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate Class (for example, C _1-6 alkyl methacrylate); acrylamide, N-methyl acrylamide, N-ethyl acrylamide, N, N-dimethyl decylamine, diacetone Acrylamide, acrylamide propylene sulfonic acid and its salt, acrylamide dimethylamine and its Acrylamide derivatives such as salts, N-methylol acrylamide and its derivatives; methacrylamide, N-methyl methacrylamide, N-ethyl methacrylamide, methyl a methacrylamide derivative such as acrylamide propylene sulfonic acid and its salt, methacrylamide propyl dimethylamine and its salt, N-methylol methacrylamide and its derivatives; - N-vinylguanamines such as vinylformamide, N-vinylacetamide, N-vinylpyrrolidone, etc.; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl Vinyl ethers of ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tert-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, etc. Nitriles such as acrylonitrile and methacrylonitrile; halogenated vinyls such as vinyl chloride, vinylidene chloride, vinyl fluoride and vinylidene fluoride; allyl acetates such as allyl acetate and allyl chloride; a base compound; an unsaturated carboxylic acid such as maleic acid or itaconic acid, or a salt thereof or a derivative thereof; a vinyl decane such as vinyl trimethoxy decane Compound; isopropenyl acetate and the like. Among these, α-olefin is preferred, and ethylene is particularly preferred. The modified mass of the modified PVA-based polymer is preferably less than 15 mol%, more preferably 5 mol% or less.

The degree of saponification of the PVA-based polymer is 95, from the viewpoint of the polarizing performance and durability of the uniaxially stretched PVA-based film to form a polarizing film, and the polarizing performance and durability of the polarizing plate produced by the polarizing film. More preferably, the molar percentage is more than 98%, more preferably 98% by mole or more, more preferably 99% by mole or more, and most preferably 99.3% by mole or more.

The degree of saponification referred to in the present specification means the degree of saponification measured according to the method described in JIS K 6726, and is converted into a unit of vinyl alcohol by saponification, and actually represents saponified in a vinyl alcohol unit. The proportion of units.

The degree of polymerization of the PVA-based polymer is a polarizing property and durability when a PVA-based film is uniaxially stretched to form a polarizing film, and the polarizing film The polarizing performance and durability of the produced polarizing plate are preferably 1,000 or more, more preferably 1,500 or more, and most preferably 2,000 or more. The degree of polymerization of the PVA-based polymer is preferably 8000 or less, particularly preferably 6,000 or less, from the viewpoints of easiness and elongation of a homogeneous PVA-based film.

The degree of polymerization of the PVA-based polymer in the present specification is preferably determined according to the degree of polymerization measured in accordance with JIS K 6726, and is obtained by re-saponifying the PVA-based polymer and purifying it, and then determining the ultimate viscosity measured in water at 30 ° C. .

A method of producing a PVA-based film using the above PVA-based polymer is, for example, a melt-squeezing film forming method in which a PVA-based polymer in a molten state is melted and extruded, and a PVA-based polymer in which a PVA-based polymer is dissolved in a solvent. Solution, cast film forming method, wet film forming method (dissolved in a poor solvent), gel film forming method (a method in which a PVA-based polymer aqueous solution is temporarily cooled and gelled, and a solvent is removed to obtain a PVA-based film) ), and the combination of these methods. Among these, a cast film forming method and a melt extrusion film forming method are particularly preferable from the viewpoint of obtaining a good polarizing film.

The solvent for dissolving the PVA-based polymer used for producing the PVA-based film may, for example, be water or a water-soluble organic solvent (for example, an anthracene such as dimethyl hydrazine; dimethylformamide or dimethyl ketone; An amidoxime group such as a guanamine; an ether such as N-methylpyrrolidone; an amine such as ethylenediamine or diethylenetriamine; and the like may be used alone or in combination of two or more. Among these, a mixed solvent of dimethyl hydrazine, water, or dimethyl hydrazine and water is particularly preferable.

The concentration of the PVA-based polymer in the PVA-based polymer solution used in the production of the PVA-based film or the PVA-based polymer in the aqueous state may be changed depending on the degree of polymerization of the PVA-based polymer, and is preferably 20 to 70% by mass. At 25 ~60% by mass is preferred, and 30 to 50% by mass is most preferred. When the concentration of the PVA-based polymer is higher than 70% by mass, the viscosity of the PVA-based polymer solution or the PVA-based polymer in a hydrated state is too high, and filtration or defoaming is performed when a PVA-based film is formed into a film-forming stock solution. It is difficult, and it is difficult to obtain a PVA-based film having no foreign matter or no defects. When the concentration of the PVA-based polymer is less than 20% by mass, the viscosity of the PVA-based polymer solution or the PVA-based polymer in a hydrated state is too low, and it is difficult to produce a PVA-based film having a desired thickness. tendency.

A PVA-based polymer solution 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 hydrated state as a film-forming stock solution. It is preferred that the plasticizer used for this purpose be a polyol. Examples of the polyhydric alcohols include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, and trimethylolpropane. These may be used alone or in combination of two or more. . Among these, in particular, diglycerin, ethylene glycol, and glycerin are suitably used from the viewpoint of improving the elongation effect, and glycerin is most preferable.

The plasticizer is preferably used in an amount of from 1 to 30 parts by mass, more preferably from 3 to 25 parts by mass, even more preferably from 5 to 20 parts by mass, based on 100 parts by mass of the PVA-based polymer. It is particularly good to use in an amount of 10 to 20 parts by mass. When the amount of the plasticizer is less than 1 part by mass, the dyeability or elongation of the PVA-based film is lowered. When the amount is more than 30 parts by mass, the PVA-based film is too soft and the handleability is lowered. .

In the film forming stock solution for producing a PVA-based film, it is preferred to add a surfactant in advance, and by adding a surfactant, the film forming property is improved and the PVA is suppressed. At the same time as the occurrence of the thickness of the film, it is easy to peel off the PVA-based film from the metal roll or the conveyor belt used for film formation. The type of the surfactant is not particularly limited, and from the viewpoint of the releasability of a metal roll or a conveyor belt, an anionic or nonionic surfactant is preferred, and a nonionic surfactant is particularly preferred. The anionic surfactant may, for example, be a carboxylic acid type such as potassium laurate or a sulfate type such as octyl sulfate or a sulfonic acid type anionic surfactant such as dodecylbenzenesulfonate. Examples of the nonionic surfactant include alkyl ether type such as polyethylene oxide oleyl ether, alkyl phenyl ether type such as polyethylene oxide octyl phenyl ether, and polyethylene oxide. Alkyl ester type such as lauric acid ester, alkylamine type such as polyethylene oxide lauryl amine ether, alkyl guanamine type such as polyethylene oxide laurate amide group, polyepoxy a polypropylene glycol ether type such as an alkane propylene oxide ether, an alkanolamine type such as an oleic acid diethanol amide group, or an allyl phenyl ether type such as a polyoxyalkylene allyl ether. Nonionic surfactants are suitable. These surfactants may be used alone or in combination of two or more.

In the case where a surfactant is added to the film forming solution, the amount thereof is 0.01 to 0.5 parts by mass, preferably 0.02 to 0.3 parts by mass, particularly preferably 0.05 to 0.1 parts by mass, per 100 parts by mass of the PVA-based polymer. When the amount of the surfactant added is less than 0.01 parts by mass, the effect of improving the film forming property and the peeling property may be difficult to express due to the addition of the surfactant. On the other hand, when the amount is more than 0.5 part by mass, There is a case where the surfactant leaks on the surface of the PVA-based film to cause adhesion, and the handleability is lowered.

The film forming solution may contain various additives such as a stabilizer (for example, an antioxidant, insofar as it does not impair the characteristics of the PVA film of the present invention. A UV absorber, a thermal stabilizer, etc.), a compatibilizing agent, an anti-blocking agent, a flame retardant, an antistatic agent, a slip agent, a dispersing agent, a fluidizing agent, an antibacterial agent, and the like. These additives may be used alone or in combination of two or more.

The PVA-based film of the present invention has a value of a maximum content difference (Ry) of the average value of the plasticizer content contained in the film in the TD direction of the film of 2% or less, and in the TD direction of the film. In the variation curve of the plasticizer content, the average interval (Sm) averaged by the interval (Smi) in the TD direction formed by each of the mountain portion of the variation curve and the valley portion adjacent to the mountain is 5 cm or more. The PVA-based film satisfying this condition is very uniform in the TD direction because the content of the plasticizer is used, and when such a PVA-based film is used to produce a polarizing film, optical spots due to dye spots or extended spots are small and high. The polarizing film of the performance can suppress the occurrence of fine speckle spots of about 1 cm which cannot be suppressed in the conventional large-area PVA film.

In the TD direction, when the maximum content difference (Ry) of the average value of the plasticizer content is more than 2%, when the PVA-based film is swollen during the production of the polarizing film, the difference between the swelling of the PVA-based film becomes large. Therefore, staining spots or extended spots occur in the polarizing film. The maximum content difference (Ry) of the average value of the plasticizer content is preferably 1.85% or less, more preferably 1.5% or less, and still more preferably 1% or less.

When the average interval (Sm) of the unevenness of the amount of the plasticizer in the TD direction is less than 5 cm, the occurrence of optical spots is remarkable because the stretching spots appear steeply in the polarizing film. The average interval (Sm) of the content of the plasticizer in the TD direction is 6 cm or more. Preferably, 7 cm or more is preferred, and 9 cm or more is more preferred.

Here, the maximum content difference (Ry) of the content of the plasticizer in the TD direction and the average interval (Sm) of the unevenness of the content of the plasticizer in the TD direction can be obtained by the following method. In other words, a sample having a rectangular shape (1 cm in the TD direction × 2 mm in the MD direction (length direction of the film)) was taken from the end portion or the central portion of the PVA-based film continuously in the TD direction at an arbitrary width Lcm (20 cm or more).

Further, the value obtained at either the end portion or the central portion can be used as the representative values (Ry) and (Sm) of the film, and the value obtained at the center portion is preferably used as a representative value of the film. That is to say, in other words, the maximum content difference (Ry) of the content of the plasticizer in the TD direction and the average interval (Sm) of the amount of the plasticizer in the TD direction, the amount of the unevenness in the TD direction is sufficient in either the central portion or the end portion. The value specified in the invention is good, and the special value is sufficient in the central portion to have the value specified by the present invention. Further, the width L described above can be selected to have an arbitrary width depending on the width of the PVA-based film, and can be handled by a value of 1/10 of the film width.

Each sample obtained above was put into DMSO-d ₆ to have a concentration of about 5% by mass, and the temperature was raised to 90 ° C or higher, and then dissolved for 2 hours, and 500 MHz, ¹ H-NMR and PD (pulse delay time) were used. The measurement was carried out under the conditions of seconds, measurement temperature of 30 ° C, and cumulative number of times of 256 times, and the content of the plasticizer in each sample was measured from the obtained NMR spectrum. For example, when glycerin is used in the case of a plasticizer, the peak of the two hydrogen portions of the methylene group of glycerol is about 3.3 ppm (the integrated intensity of the peak is Sg), PVA according to the NMR spectrum obtained by the above measurement. The peak of the two hydrogen moieties of the methylene group is detected in the vicinity of 1.5 ppm (the integrated intensity of the peak is Sp), and the amount of glycerin in the PVA-based film R (% by mass) can be calculated by using the integrated strength and the following formula (1). .

R=(92/44)×(Sg/Sp)×100 (1)

Using the obtained measured value, a variation curve of the plasticizer content per 1 cm in an arbitrary width (Lcm) in the TD direction (Fig. 1) was obtained, and the content of the plasticizer was determined from the following formula (2). The maximum content difference (Ry) in the TD direction.

Ry=Rp+Rv (2)

In the formula (2), Rp represents a content corresponding to the difference between the average value of the plasticizer content and the peak of the plasticizer, and Rv means that the average value of the plasticizer content and the content of the plasticizer are Very little content of the difference between the bottom lines.

The average interval (Sm) of the amount of plasticizer in the TD direction is the mountain portion which exceeds the average value of the plasticizer content in the variation curve (Fig. 1), and the valley portion which is adjacent to the mountain and below the average value. The fluctuation amount of each of the fluctuations is determined, and the interval (Smi) occupied by the TD direction is obtained, and is obtained by an arithmetic mean represented by the following formula (3). Further, in the case where the concavo-convex shape is intermittent at both ends of the extracted portion, the discontinuous concavo-convex shape is not included in the interval (Smi).

The PVA-based film of the present invention has a ratio (Rye/Ryc) of a maximum content difference (Rye) of a plasticizer content to a maximum content (Ryc) of a plasticizer content in a central portion of the film (Rye/Ryc) of 0.8 or more. It is preferably 1.3 or less from the viewpoint of obtaining a polarizing film having few optical spots.

When the ratio of Rye to Ryc (Rye/Ryc) is less than 0.8 or more than 1.3, the content of the plasticizer at the end portion and the central portion of the PVA-based film is detrimental to uniformity, and at the time of manufacturing the polarizing film There is a tendency for optical spots to become more stressed. The ratio of Rye to Ryc (Rye/Ryc) is preferably 0.9 or more and 1.2 or less, and more preferably 0.95 or more and 1.1 or less.

Further, in the PVA-based film of the present invention, from the viewpoint of obtaining a polarizing film having few optical spots, the average interval (Sme) of the unevenness in the end portion of the film and the variation in the central portion of the film are uneven The ratio of the average interval (Smc) of the shapes (Sme/Smc) is preferably 0.7 or more and 1.4.

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

By depositing (casting) a film forming stock solution containing a PVA-based polymer solution or a PVA-based polymer in a water state from a T-slot mold onto a drum roll, and drying the formed PVA-based polymer film, PVA film. The material of the drum roll is not particularly limited. Generally, stainless steel is suitably used, and a plated metal for preventing scratching is preferably applied to the surface of the roll. The type of plating metal to be used is, for example, chrome plating, nickel plating, galvanization, or the like, and a single layer or two or more plating layers may be formed on the surface of the roll. From the viewpoint of smoothing the surface of the PVA-based film or obtaining a PVA-based film excellent in durability, it is preferable to apply chromium plating to the outermost surface of the drum roll. The surface of the drum roller is preferably protected. The smoothness and the surface roughness (the unevenness of the roll surface) are expressed by the average interval S of the partial peaks of the roughness curve of JIS B 0604, preferably 3 S or less, more preferably 1.5 S or less, and particularly preferably 0.5 S or less. .

The surface temperature of the drum roll which discharges a PVA type polymer solution or a PVA type polymer in a hydrated state is preferably 50 to 120 °C. The PVA-based polymer film formed on the drum roll is peeled off from the drum roll at a time when the water content thereof reaches 5 to 30% by mass, and then it is preferred to use a plurality of rolls to alternately dry the inside of the film. . The PVA-based polymer film subjected to the drying treatment may be subjected to heat treatment, humidity conditioning treatment, or the like as needed, and finally, the obtained PVA-based film is wound into a roll shape at a predetermined length in a core tube.

The PVA-based film may be coated with anti-adhesion agents such as cerium oxide, titanium oxide, clay, bentonite, stearic acid or a salt thereof for the purpose of preventing adhesion.

For the die used for the PVA-based film formation, a die such as a chocker bar method and a flexible lip method can be used, and in particular, the integrally formed retention portion is a non-flexible mold. In the lip type die, it is preferable to obtain a PVA-based film having a small thickness variation in the TD direction.

In order to adjust the PVA-based film to an appropriate state, it is preferable to provide a heat treatment device or a humidity control device, and a speed adjustment mechanism such as a motor for each roller drive or a speed changer.

The drying treatment in the production step of the PVA-based film is generally carried out at a drying temperature of 50 to 150 ° C, particularly 60 ° C to 120 ° C, and is excellent in elongation and dyeability from the production of a polarizing film. Place It is preferable that the obtained polarizing film has good polarizing performance or durability.

Conventionally, the properties of plasticizers in film-forming stock solutions have not been noticed, and it is considered that they can be homogenized with PVA-based polymers in a series of processing steps. For this reason, conventionally, the PVA-based polymer was stirred, or only kneaded at the time of melt extrusion, and the PVA and the plasticizer were mixed to produce a PVA-based film in a sufficient understanding. However, it is known that this new knowledge causes the plasticizer to be uniformly mixed with the PVA-based polymer in a general treatment step to produce a concentration spot. Further, the PVA-based film composed of the film-forming stock solution for producing the concentration of the plasticizer has a distribution of the plasticizer content which is not uniform in the TD direction of the film.

In order to prevent the concentration of the plasticizer from being formed in the film forming solution, it is desirable to sufficiently knead the film forming solution, or to knead using a mixer or a kneader, or to increase the kneading time. Thereby, the fluctuation of the content of the plasticizer contained in the PVA-based film in the TD direction can be adjusted.

In particular, in order to uniformly mix the PVA-based polymer and the plasticizer, a mixing means for mixing the plasticizer with the PVA-based polymer in a molten state, for example, static mixing, is used in a flow path that reaches the die discharge port. A tandem mixer represented by a tandem mixer, a tandem continuous vibration stirrer represented by a cold-mixed industrial company, and a tandem partial homogenizer represented by an instant mixing device manufactured by Sakura Equipment Co., Ltd. The use is better. These mixing means can be used in a general kneading step, preferably in combination with a plurality of mixing means. Based on this point of view, a tandem mixer is used in series with a continuous vibrating mixer or in series. The combination of the device and the series local homogenizer is preferred.

From the viewpoint of the viscosity of the film forming stock solution, the static mixer is preferably a spiral type, and the number of components is preferably 12 or more, more preferably 24 or more. When the number of components is less than 12, the mixing of PVA and the plasticizer in the film forming stock solution may be incomplete, and it is difficult to obtain the desired effect. Further, there is no upper limit on the number of components, and from the viewpoint of cost and effect, it is preferably 48 or less, and preferably 42 or less. Even if an element exceeding 48 is provided, it is difficult to obtain the effect of improving the miscibility of the above-mentioned film forming stock solution. In addition, the number of components here is the number calculated by the number of components per unit static mixer × the number of used cells.

In the present invention, it is important to obtain a PVA-based film having a PVA-based film having a width of 2 m or more and a large area, in accordance with the increase in the size of the liquid crystal display. Further, from the viewpoint of large screen size, the film width is preferably 2.3 m or more, and more preferably 2.6 m or more.

On the other hand, when the width of the PVA-based film exceeds 6 m, it is difficult to uniformly perform uniaxial stretching when a polarizing film is used in a practical device, so the width of the PVA-based film is It is preferably 6 m or less, and preferably 5 m or less.

In particular, it is pointed out that the width of the PVA-based film is narrow. In the polarizing film produced by using such a PVA-based film, the optical plaque originally caused by the dyed spot or the extended spot is not noticeable. However, when the width of the PVA-based film is 2 m or more, even if the conventionally produced production method is employed, uniform stretchability cannot be ensured when the polarizing film is produced (the width direction of the PVA-based film, that is, in the TD direction). can The concentration of the plasticizer is presumed to be a cause. In such a polarizing film, an optical spot caused by a dyed spot or an extended spot is highly noticeable, and the transmittance and the degree of polarization of the polarizing film are changed. Therefore, in order to suppress the occurrence of the concentration spot of such a plasticizer, it is particularly important to adopt a manufacturing method in which the uniformity of the plasticizer distribution in the TD direction of the PVA-based film is taken into consideration.

The average thickness of the PVA-based film is not particularly limited, and is generally preferably 20 to 120 μm, preferably 40 to 120 μm, and more preferably 50 to 100 μm. When the average thickness of the PVA-based film is less than 20 μm, there is a fear that elongation cracking may occur in the uniaxial stretching for producing a polarizing film. Further, when the average thickness of the PVA-based film exceeds 120 μm, there is a fear that an extended spot may occur when the uniaxial stretching of the polarizing film is performed.

The method for producing a polarizing film when a polarizing film is produced from a PVA-based film is not particularly limited. When a PVA-based film is used as an unprocessed film to produce a polarizing film, any conventional method may be employed.

In order to produce a polarizing film from a PVA-based film, for example, water conditioning, dyeing, uniaxial stretching, fixing treatment, drying treatment, and heat treatment as needed are preferably performed for the PVA-based film, and the operation sequence of dyeing, uniaxial stretching, and fixing treatment is preferably performed. The system is not particularly limited. Further, the uniaxial stretching system may be carried out in two or more stages, or may be carried out simultaneously with dyeing or fixing treatment.

The dyeing system is preferably performed using iodine, and the dyeing period may be any one of uniaxial stretching, uniaxial stretching, and uniaxial stretching. Usually, the dyeing is generally carried out by immersing the PVA film in a solution containing iodine-potassium iodide (especially an aqueous solution), and a dyeing method using an aqueous solution containing iodine and potassium iodide can also be suitably employed in the present invention. The concentration of iodine in the aqueous solution for dyeing is The concentration of 0.01 to 0.5% by mass and potassium iodide is preferably 0.01 to 10% by mass. Further, the temperature of the dye bath is preferably 20 to 50 ° C, particularly preferably 25 to 40 ° C.

The uniaxial stretching system can be carried out by either a wet stretching method performed in a solvent such as water or a dry heat stretching method performed in air or the like. By the wet stretching method, uniaxial stretching in water, uniaxial stretching in a dye solution containing no boric acid, uniaxial stretching in a dye solution containing boric acid, uniaxial stretching in an aqueous boric acid solution And proceeding across multiple extensions of the above steps.

The stretching temperature is not particularly limited, and the wet stretching PVA film is preferably 30 to 90 ° C, and the dry heat is preferably 50 to 180 ° C.

Further, the stretching ratio of the uniaxial stretching (the stretching ratio in the case where the uniaxial stretching is performed in a plurality of stages) is preferably 4 times or more, particularly 5 times or more, from the viewpoint of the polarizing performance of the obtained polarizing film. The upper limit of the stretching ratio is not particularly limited, and is preferably 8 times or less from the point of uniform extension.

When the polarizing film is produced, in order to make the adsorption system of iodine to the PVA-based film firm, the fixing treatment can be performed a plurality of times, and the present invention is preferably carried out even when the polarizing film is produced. In the treatment bath used for the fixation treatment, one or two or more aqueous solutions containing a boron compound such as boric acid or borax are generally used. Further, an iodine compound or a metal compound may be added to the treatment bath for fixing treatment as needed. The concentration of the boron compound in the treatment bath for the fixation treatment is generally 2 to 15% by mass, particularly preferably about 3 to 10% by mass. The temperature of the treatment bath at the time of the fixing treatment is preferably 15 to 60 ° C, particularly 25 to 40 ° C.

The above-described uniaxial stretching, dyeing treatment, fixing treatment, and the like are carried out, and then the obtained polarizing film is dried. The drying treatment of the obtained polarizing film is preferably carried out at 30 to 150 ° C, particularly 50 to 150 ° C. When the moisture content of the polarizing film is about 10% or less, when the tension is applied to the polarizing film and the heat treatment is performed at about 80 to 120 ° C for about 1 to 5 minutes, dimensional stability and durability can be obtained. Excellent polarizing film.

The polarizing film obtained as described above is generally applied to both surfaces or one side thereof, and is bonded to an optically transparent protective film having mechanical strength to be used as a polarizing plate. As the protective film, a cellulose triacetate (TAC) film, an alicyclic polyolefin (COP) film, an acrylic film, a polyester film, or the like can be used. Moreover, the adhesive for bonding is, for example, a PVA-based adhesive or an urethane-based adhesive, and among them, a PVA-based adhesive is particularly preferable.

The polarizing plate obtained as described above is applied to a glass substrate by applying an adhesive such as an acrylic or the like, and is used as a component of a liquid crystal display device. At the same time, it can also be bonded to a retardation film, a viewing angle enhancement film, a brightness enhancement film, and the like.

Example

Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited by the examples. The scope of the invention is determined by the scope of the appended claims.

In addition, in the following examples and comparative examples, the measurement of the content of the plasticizer contained in the PVA-based film, the difference in the maximum content (Ry), and the determination of the average interval (Sm) of the unevenness of the unevenness type, and the optical properties of the polarizing film were Measurement and optics The evaluation of the spots was carried out in accordance with the method shown below.

The content of plasticizer contained in the PVA film:

From the TD direction of the PVA-based film obtained in the examples or the comparative examples, the center point of the total width was sampled on average about 1/10 of the total width of the film (35 cm in Examples 1 and 2, and Examples 3 to 5). Comparative Examples 1 and 2 were 30 cm), and the content of the plasticizer per 1 cm in the PVA-based film was measured in accordance with the method described above.

The maximum difference (Ry) and the average interval (Sm) of the variation of the unevenness type:

Based on the above-described measured values, the variation curve of the plasticizer content of the PVA-based film in the TD direction was determined, and the maximum content difference (Ry) and the average interval (Sm) of the fluctuation amount of the unevenness type were determined according to the method described above. In addition, Ry and Sm obtained here are used as Ryc and Smc in the center part. Further, in relation to the MD direction of the film, the maximum content difference (Rye) at the end portion existing at the same position as the center portion and the average interval (Sme) of the fluctuation amount uneven type are obtained by lowering the obtained PVA-based film roll From the end portion on the left-hand side, the portion inserted in the direction of the center point of 20 cm in the TD direction is sampled at 1/10 of the total width of the film, and the content of the plasticizer per 1 cm is measured in the same manner as the central portion, and the variation curve is determined. .

Optical properties of polarizing film:

(i) penetration rate

From the center portion in the width direction of the polarizing film obtained in the examples or the comparative examples, two square samples of 4 cm × 4 cm parallel to the alignment direction of the polarizing film were used, and two sheets were respectively used by Hitachi High-Tech Co., Ltd. Spectrophotometer U-4100 (Auxiliary Integrating Sphere), in accordance with JIS Z 8722 The measurement method of the body color), the C-light source, and the visibility correction in the visible light field of the 2 degree field of view, and the light transmittance and the inclination -45 degrees when the polarizing film sample is tilted by 45 degrees in the direction of the extension axis is measured for one piece of the polarizing film sample. The light transmittance of the case, and the average value (Y1) of them is obtained.

Further, another polarizing film sample was measured for the light transmittance of the case where the light transmittance was inclined at 45 degrees in the direction of the extension axis and the inclination was -45 degrees, in order to obtain the average value thereof. Y2).

The Y1 and Y2 obtained as described above were averaged as the transmittance (Y) (%) of the polarizing film.

(ii) Polarization:

The two polarizing films taken in the above (i) are measured in the same manner as the above-described method for measuring the transmittance, and the light transmittance (Y ∥) and the extension in the case where the stretching directions are overlapped in parallel are measured. The direction is the light transmittance (Y ⊥) in the case of overlapping in an orthogonal manner, and the degree of polarization is obtained by the following equation.

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

Optical spot of polarizing film:

Between two polarizing plates in a parallel Nicols state (single transmittance of 42.3%, and a degree of polarization of 99.99%), the polarizing film produced was formed to have a direction of extension of 90 degrees with respect to the two polarizing plates described above. After the insertion, a light box having a brightness of 10000 cd/m ² was used in the dark room, and the optical spot was observed in a penetrating mode (a spot size of about 1 cm in the TD direction and about several cm to several tens of cm in the MD direction, respectively). ) and evaluate according to the following criteria.

○: It is impossible to confirm that there is no speckle-like optical spot.

△: A spotted optical spot was slightly observed.

×: Spotted optical spots were clearly observed.

Example 1

100 parts by mass of a PVA-based polymer having a degree of saponification of 99.95 mol%, a viscosity average degree of polymerization of 2,400, 12 parts by mass of glycerin, and 191 parts by mass of water were supplied to a uniaxial extruder, and melted as a film forming solution [volume fraction] (water content) 63% by mass]. Three spiral type static component mixers (the total number of components 18) were placed in the piping of the film forming solution, and the film forming solution was discharged from the T-die to the drum roll (roller surface temperature 93). After the above, the PVA film was peeled off at a moisture content of 24% by mass, and then dried on a metal roll to obtain a PVA-based film having a width of 3.5 m and a thickness of 75 μm.

The maximum content difference (Ry) of the average value of the plasticizer content in the TD direction of the obtained PVA-based film was 1.8%, and the average interval (Sm) of the unevenness of the plasticizer content in the TD direction was 6 cm. Further, the ratio (Rye/Ryc) of the maximum content difference (Rye) at the end portion of the PVA-based film to the maximum content (Ryc) at the central portion of the film was 1.2, and the amount of variation at the end portion of the PVA-based film was uneven. The ratio (Sme/Smc) of the average interval (Sme) to the average interval (Smc) of the unevenness of the fluctuation amount in the central portion of the film was 1.3.

The PVA-based film was continuously applied in the order of pre-swelling, dyeing, uniaxial stretching, fixing treatment, drying, and heat treatment to prepare a polarizing film. That is, the PVA-based film was pre-swelled by immersing in water at 30 ° C for 30 seconds, and immersed in a 35 ° C aqueous solution having a concentration ratio of iodine/potassium iodide of 1/100 for 3 minutes. Secondly, it is uniaxially stretched 6 times in a 50 ° C aqueous solution having a boric acid concentration of 40 g / liter, followed by a potassium iodide concentration of 70 g / liter, boron. The mixture was immersed in an aqueous solution of 30 ° C having an acid concentration of 40 g / liter for 5 minutes to carry out a fixing treatment.

Then, the PVA-based film was taken out and dried by hot air at 40 ° C, and then heat-treated at 100 ° C to obtain a polarizing film.

The obtained polarizing film had a transmittance of 43.5% and a degree of polarization of 99.92%. In the polarizing film, when the dye spots were not observed and the left and right of the optical spots were evaluated, it was judged to be ○ and was good.

Example 2

In the same manner as in Example 1, except that two spiral type and six element static mixers (total number of elements 12) were provided in the piping for forming the film forming solution of Example 1, a width of 3.5 m and a thickness of 75 μm were obtained. PVA film.

The maximum content difference (Ry) of the average value of the plasticizer content in the TD direction of the obtained PVA-based film was 2.0%, and the average interval (Sm) of the unevenness of the plasticizer content in the TD direction was 5 cm. Further, the ratio (Rye/Ryc) of the maximum content difference (Rye) at the end portion of the PVA-based film to the maximum content (Ryc) at the central portion of the film was 0.7, and the amount of variation at the end portion of the PVA-based film was uneven. The ratio (Sme/Smc) of the average interval (Sme) to the average interval (Smc) of the unevenness of the fluctuation amount in the central portion of the film was 1.5.

A polarizing film was produced in the same manner as in Example 1 using this PVA-based film.

The obtained polarizing film had a transmittance of 43.4% and a degree of polarization of 99.91%. In the polarizing film, when the dyed spots were not observed and the left and right of the optical spots were evaluated, it was judged as Δ, which was used as a level for a small liquid crystal display.

Example 3

In addition to the static mixer (the total number of components 12) in the raw material piping of Example 2, and the use of the instant mixing device S-1 mixer for further uniform mixing of the melted film forming solution (Sakura Equipment Co., Ltd.) In the same manner as in Example 1, a PVA-based film having a width of 3 m and a thickness of 75 μm was obtained in the same manner as in Example 1.

The maximum content difference (Ry) of the average value of the plasticizer content in the TD direction of the obtained PVA-based film was 1.7%, and the average interval (Sm) of the unevenness of the plasticizer content in the TD direction was 7 cm. Further, the ratio (Rye/Ryc) of the maximum content difference (Rye) at the end portion of the PVA-based film to the maximum content (Ryc) at the central portion of the film was 0.9, and the variation amount at the end portion of the PVA-based film was uneven. The ratio (Sme/Smc) of the average interval (Sme) to the average interval (Smc) of the unevenness of the fluctuation amount in the central portion of the film was 1.3.

A polarizing film was produced in the same manner as in Example 1 using this PVA-based film.

The obtained polarizing film had a transmittance of 43.5% and a degree of polarization of 99.93%. In the polarizing film, when the dye spots were not observed and the left and right of the optical spots were evaluated, it was judged to be ○ and was good.

Example 4

In addition to the use of a continuous vibration stirrer vibrating stirrer (manufactured by Cold Chemical Co., Ltd.) for further uniformly mixing the melted film forming stock solution, in place of the use of the static mixer in the raw material piping in the first embodiment, 1 A PVA film having a width of 3 m and a thickness of 75 μm was obtained in the same manner.

Average of the amount of plasticizer in the TD direction of the obtained PVA film The maximum content difference (Ry) of the value was 0.9%, and the average interval (Sm) of the unevenness of the plasticizer content in the TD direction was 8 cm. Further, the ratio (Rye/Ryc) of the maximum content difference (Rye) at the end portion of the PVA-based film to the maximum content (Ryc) at the central portion of the film was 0.9, and the variation amount at the end portion of the PVA-based film was uneven. The ratio (Sme/Smc) of the average interval (Sme) to the average interval (Smc) of the unevenness of the fluctuation amount in the central portion of the film was 1.1.

A polarizing film was produced in the same manner as in Example 1 using this PVA-based film.

The obtained polarizing film had a transmittance of 43.3% and a degree of polarization of 99.96%. In the polarizing film, when the dye spots were not observed and the left and right of the optical spots were evaluated, it was judged to be ○ and was good.

Example 5

In addition to the use of the static mixer in the raw material piping of Example 1 (total number of components 18), a continuous vibration stirrer vibration stirrer for further mixing the melted film forming raw materials was used (Cold Chemical Industry Co., Ltd.) In the same manner as in Example 1, a PVA-based film having a width of 3 m and a thickness of 75 μm was obtained.

The maximum content difference (Ry) of the average value of the plasticizer content in the TD direction of the obtained PVA-based film was 0.8%, and the average interval (Sm) of the unevenness of the plasticizer content in the TD direction was 10 cm. Further, the ratio (Rye/Ryc) of the maximum content difference (Rye) at the end portion of the PVA-based film to the maximum content (Ryc) at the central portion of the film was 1.0, and the amount of variation at the end portion of the PVA-based film was uneven. The ratio (Sme/Smc) of the average interval (Sme) to the average interval (Smc) of the unevenness of the fluctuation amount in the central portion of the film was 0.9.

A polarizing film was produced in the same manner as in Example 1 using this PVA-based film.

The obtained polarizing film had a transmittance of 43.5% and a degree of polarization of 99.93%. In the polarizing film, when the dye spots were not observed and the left and right of the optical spots were evaluated, it was judged to be ○ and was good.

Comparative example 1

A PVA-based film having a width of 3 m and a thickness of 75 μm was obtained in the same manner as in Example 1 except that the static mixer provided in the piping was not used in the first embodiment.

The maximum content difference (Ry) of the average value of the plasticizer content in the TD direction of the obtained PVA-based film was 3.0%, and the average interval (Sm) of the unevenness of the plasticizer content in the TD direction was 2 cm. Further, the ratio (Rye/Ryc) of the maximum content difference (Rye) at the end portion of the PVA-based film to the maximum content (Ryc) at the central portion of the film was 1.8, and the variation amount at the end portion of the PVA-based film was uneven. The ratio (Sme/Smc) of the average interval (Sme) to the average interval (Smc) of the unevenness of the fluctuation amount in the central portion of the film was 1.6.

A polarizing film was produced in the same manner as in Example 1 using this PVA-based film.

The obtained polarizing film had a transmittance of 43.5% and a degree of polarization of 99.92%. In the polarizing film, when the dyed spots are observed and the left and right of the optical spots are evaluated, it is judged that X is extremely poor, and the liquid crystal display used for television use or the like is insufficient.

Comparative example 2

PVA100 mass with a saponification degree of 99.95 mol% and a polymerization degree of 2400 The fraction, glycerin 10 parts by mass, and 170 parts by mass of water were supplied to a uniaxial extruder, and melted to prepare a film forming solution [volatility (water content) 60.7 mass%]. Subsequently, film formation was carried out in the same manner as in Comparative Example 1, and then the steps of contacting with warm air having a temperature of 65 ° C and a humidity of 90% RH followed by contact with warm air having a temperature of 50 ° C and a humidity of 45% RH were combined. The time required for the step was passed for 6 seconds to obtain a PVA-based film having a width of 3 m and a thickness of 40 μm.

The maximum content difference (Ry) of the average value of the plasticizer content in the TD direction of the obtained PVA-based film was 2.4%, and the average interval (Sm) of the unevenness of the plasticizer content in the TD direction was 3.3 cm. Further, the ratio (Rye/Ryc) of the maximum content difference (Rye) at the end portion of the PVA-based film to the maximum content (Ryc) at the central portion of the film was 1.1, and the amount of variation at the end portion of the PVA-based film was uneven. The ratio (Sme/Smc) of the average interval (Sme) to the average interval (Smc) of the unevenness of the fluctuation amount in the central portion of the film was 0.8.

A polarizing film was produced in the same manner as in Example 1 using this PVA-based film.

The obtained polarizing film had a transmittance of 43.9% and a degree of polarization of 99.50%. In the polarizing film, although the dyed spot is not observed, it is judged that X is very poor when the left and right of the optical spot is evaluated, and the liquid crystal display for use in television or the like is insufficient.

Industrial utilization possibility

The PVA-based film of the present invention has an excellent characteristic that the plasticizer can be uniformly present in the TD direction, and the use of such a PVA-based film to produce a polarizing film can be smoothly obtained due to staining or stretching. A polarizing film with low optical spots and high performance.

The polarizing film obtained in this way can be effectively used for the production of a component of a liquid crystal display device requiring high display quality, that is, a polarizing plate.

In the above description, a suitable embodiment will be described with reference to the drawings, and various changes and modifications can be easily made by those skilled in the art with reference to the description herein. Therefore, such changes and modifications can be construed as being within the scope of the invention as defined by the scope of the claims.

Fig. 1 is a graph showing the variation of the plasticizer content in the TD direction of the PVA-based film.

Claims (12)

A polyvinyl alcohol-based film which is a polyvinyl alcohol-based film formed by a film-forming stock solution containing a polyvinyl alcohol-based polymer and a plasticizer, wherein (a) is in the TD direction of the film, and is a film. The maximum content difference (Ry) of the average value of the plasticizer content contained is 2% or less, and (b) in the variation curve of the plasticizer content in the TD direction of the film, respectively, exceeding the average value of the plasticizer content. The average interval (Sm) at which the interval (Smi) occupied by the fluctuation portion of the mountain portion and the valley portion adjacent to the mountain portion is averaging is 5 cm or more. A polyvinyl alcohol-based film according to the first aspect of the invention, wherein a ratio of a maximum content difference (Rye) at a film end portion to a maximum content difference (Ryc) at a central portion of the film (Rye/Ryc) is 0.8 or more, 1.3. the following. The polyvinyl alcohol-based film according to claim 1 or 2, wherein the average interval (Sme) of the unevenness at the end portion of the film and the average interval (Smc) of the unevenness at the central portion of the film are The ratio (Sme/Smc) is 0.7 or more and 1.4 or less. The polyvinyl alcohol-based film of the first or second aspect of the invention, wherein the ratio of the plasticizer is from 1 to 30 parts by mass based on 100 parts by mass of the polyvinyl alcohol-based polymer. A polyvinyl alcohol-based film according to claim 1 or 2, wherein the film has a width of 2 m or more. The polyvinyl alcohol-based film according to claim 1 or 2, wherein the average interval (Sm) is 7 cm or more. A polarizing film produced by using the polyvinyl alcohol-based film according to any one of claims 1 to 6. A method for producing a polyvinyl alcohol-based film according to any one of claims 1 to 6, which comprises a step of preparing a stock solution of a film forming stock solution from a polyvinyl alcohol-based polymer, a plasticizer, and a solvent; a mixing step of mixing the above-mentioned film forming stock solution by mixing means and uniformly mixing the polyvinyl alcohol-based polymer and the plasticizer; discharging the uniformly mixed film forming raw liquid onto the roll from the die; and discharging the discharged Drying step of drying the stock solution. A manufacturing method according to the eighth aspect of the invention, wherein the polyvinyl alcohol-based polymer, the plasticizer, and the solvent are supplied to an extruder in the raw material preparation step, and kneaded to prepare a film forming stock solution. The manufacturing method of claim 8 or 9, wherein the mixing means is at least one selected from the group consisting of a mixer, a continuous vibration mixer, and a partial homogenizer. The manufacturing method of claim 8 or 9, wherein the mixing means is a static mixer having a number of elements of 12 or more. The manufacturing method of claim 8 or 9, wherein the mixing means is a series continuous vibrating mixer, or a combination of a static mixer and a series continuous vibrating mixer, or a static mixer and a series local homogenizer. The combination.