WO2022004536A1 - ポリビニルアルコールフィルム、及びそれを用いた光学フィルムの製造方法 - Google Patents

ポリビニルアルコールフィルム、及びそれを用いた光学フィルムの製造方法 Download PDF

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WO2022004536A1
WO2022004536A1 PCT/JP2021/023876 JP2021023876W WO2022004536A1 WO 2022004536 A1 WO2022004536 A1 WO 2022004536A1 JP 2021023876 W JP2021023876 W JP 2021023876W WO 2022004536 A1 WO2022004536 A1 WO 2022004536A1
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Prior art keywords
film
pva
pva film
mass
stretching
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PCT/JP2021/023876
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English (en)
French (fr)
Japanese (ja)
Inventor
喬士 練苧
稔 岡本
さやか 清水
修 風藤
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Kuraray Co Ltd
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Kuraray Co Ltd
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Priority to JP2022533924A priority Critical patent/JP7601876B2/ja
Priority to CN202180047228.4A priority patent/CN115996974B/zh
Priority to KR1020227041800A priority patent/KR20230029609A/ko
Publication of WO2022004536A1 publication Critical patent/WO2022004536A1/ja
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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
    • C08J5/18—Manufacture of films or sheets
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/30—Polarising elements

Definitions

  • the present invention relates to a polyvinyl alcohol film and a method for producing an optical film using the polyvinyl alcohol film.
  • a polarizing plate having a light transmitting and shielding function is a basic component of a liquid crystal display (LCD) together with a liquid crystal that changes the polarization state of light.
  • the polarizing plate is generally formed on a polyvinyl alcohol film (hereinafter, "polyvinyl alcohol” may be abbreviated as "PVA") in a dyeing step, a stretching step (uniaxial stretching step), and if necessary, further fixing treatment with a boron compound or the like.
  • PVA polyvinyl alcohol film
  • TAC cellulose triacetate
  • LCDs have come to be used in a wide range of small devices such as calculators and watches, notebook computers, liquid crystal monitors, liquid crystal color projectors, liquid crystal televisions, in-vehicle navigation systems, mobile phones, and measuring devices used indoors and outdoors. ..
  • the performance of polarizing plates which are the components of LCDs, is also required to be improved.
  • the polarizing film used for the polarizing plate is also required to have better optical performance (polarization performance) and a small shrinkage stress at high temperature.
  • Patent Document 1 describes that a polarizing film having excellent polarization performance and low shrinkage stress can be obtained by using a PVA film containing PVA having an average degree of polymerization of 2500 to 3500 and adopting a predetermined cross-linking and stretching step. ing.
  • a polarizing film is manufactured by the method described in Patent Document 1, it may be difficult to achieve both the polarizing performance and the shrinkage stress of the obtained polarizing film depending on the film forming conditions of the PVA film, and the crystals of the PVA film may be difficult. There was room for improvement from a structural point of view.
  • Patent Document 2 the in-plane polarization performance (polarization degree, single transmittance) is obtained by using a PVA film having a long period obtained by a small-angle X-ray scattering method and a thickness of an amorphous portion within a specific range. It is described that a polarizing film having excellent uniformity and corresponding to a large area and high definition can be obtained. Further, Patent Document 3 describes that a polarizing film having a high absorbance in a long wavelength region and a high degree of polarization can be produced by using a PVA film having a crystal length period in water in a specific range. However, in Patent Documents 2 and 3, the shrinkage stress of the polarizing film is not considered, and naturally, the compatibility between the polarizing performance of the polarizing film and the shrinkage stress is not considered.
  • an object of the present invention is to provide a PVA film capable of producing an optical film having excellent optical performance and a small shrinkage stress at high temperature, and a method for producing an optical film using such a PVA film. ..
  • the present invention relates to the following [1] to [7].
  • [1] From the crystal length period Ds obtained from the small-angle X-ray scattering measurement performed in a water / methanol mixed solvent (volume ratio: 2/8) and the small-angle X-ray scattering measurement performed before immersion in the mixed solvent.
  • the PVA film according to [1] wherein the crystal length period Da is 10.0 to 12.5 nm.
  • [3] The PVA film according to [1] or [2], wherein the PVA contained in the PVA film contains ethylene units and the content thereof is 1 to 8 mol%.
  • the present invention provides a PVA film capable of producing an optical film having excellent optical performance and a small shrinkage stress at high temperatures, a method for producing an optical film using such a PVA film, and an optical film.
  • the PVA film of the present invention has a crystal length period Ds obtained from a small-angle X-ray scattering measurement performed in a water / methanol mixed solvent (volume ratio: 2/8) and a small angle performed before immersion in the mixed solvent.
  • the crystal length period Da obtained from the X-ray scattering measurement satisfies the equation of 0.3 ⁇ (Ds-Da) / Da ⁇ 0.5.
  • small-angle X-ray scattering measurement when a sample is irradiated with X-rays, the diffraction caused by the X-rays being scattered or interfering with the electrons around the atom is analyzed.
  • the structure of the sample to be measured can be evaluated, and the structure usually has a size of several nm to several tens of nm. It is said that it can be evaluated.
  • the crystal length period (the average value of the intercrystal distances randomly present in the polymer) of the sample to be measured can be evaluated.
  • the PVA film has a crystalline portion (lamella crystal) in which the molecular chain of PVA is folded and an amorphous portion in which the molecular chain of PVA is not folded and unfolded.
  • the average value of the inter-crystal distances between the crystal portions (lamella crystals) is defined as the crystal length period.
  • This crystal length period can be obtained from the diffraction peak of the scattering curve obtained by performing small-angle X-ray scattering measurement on the PVA film.
  • the diffraction peak derived from this crystal length period may have a scattering vector q (nm -1 ) appearing in the vicinity of 0.5 nm -1.
  • a scattering vector q (nm -1 ) appearing in the vicinity of 0.5 nm -1.
  • a PVA film to be measured for small-angle X-ray scattering was prepared as follows and used as a measurement sample. First, a plurality of PVA films to be measured were cut into a size of 2 cm ⁇ 1 cm regardless of the width direction (TD direction) and the machine flow direction (MD direction). The cut PVA film was stored for 24 hours under the conditions of a temperature of 20 ° C. and a humidity of 65%, and then 10 sheets were laminated in a measurement cell to prepare a measurement sample.
  • the crystal length period Da obtained from the scattering curve obtained when this measurement sample is subjected to small-angle X-ray scattering measurement in air is the crystal length period Da described later.
  • a plurality of PVA films cut into a size of 2 cm ⁇ 1 cm were immersed in a water / methanol mixed solvent (volume ratio: 2/8) for 24 hours, and then 10 sheets were laminated in a measurement cell filled with the mixed solvent. Then, it was used as a measurement sample.
  • the crystal length period obtained from the scattering curve obtained when the small-angle X-ray scattering measurement is performed on this measurement sample is the crystal length period Ds described later.
  • the measurement cell used a 7.5 ⁇ m-thick Kapton film as the window material on the incident light side and the reflected light side, and the distance between the window materials was set to about 1.5 mm. With such a structure, the measurement sample can be sealed in the measurement cell. Further, by using this measurement cell, the PVA film to be measured can be arranged in the mixed solvent in the usual measurement arrangement in the following measuring device.
  • the small-angle X-ray scattering measurement was performed by the nanoscale X-ray structure evaluation device "NanoViewer” (manufactured by Rigaku Co., Ltd.).
  • the measurement conditions are as follows.
  • the scattering peak derived from the crystal length period of the PVA film appears in the scattering curve near the scattering vector q (nm -1 ) of 0.5 nm -1. do.
  • the crystal length period Ds and the crystal length period Da were calculated from the values of the scattering vector q (nm -1 ) at the peak top of the diffraction peak.
  • this peak top is an inflection point in which the scattering curve becomes convex upward in the range where the scattering vector q (nm -1 ) is 0.2 or more and 1.0 or less (see FIG. 1).
  • Crystal length period (nm) 2 ⁇ / q
  • the crystal length period Ds obtained from the small-angle X-ray scattering measurement performed in a water / methanol mixed solvent (volume ratio: 2/8) and the small-angle X-ray scattering measurement performed before immersion in the mixed solvent It is important that the crystal length period obtained from Da is satisfied with the equation of 0.3 ⁇ (Ds-Da) / Da ⁇ 0.5.
  • (Ds-Da) / Da means the rate of increase in the crystal length cycle before and after immersion in the water / methanol mixed solvent (volume ratio: 2/8).
  • (Ds-Da) / Da (hereinafter, may be referred to as "increased rate of crystal length period") is preferably less than 0.5, and more preferably less than 0.4.
  • (Ds-Da) / Da is preferably 0.3 or more, and more preferably 0.32 or more.
  • the distance between the lamella crystals in the PVA film tends to increase due to the swelling of the PVA film with a solvent such as water in the swelling step in manufacturing the optical film. That is, it is considered that the interaction of the molecular chains of PVA tends to be small in the amorphous portion existing between the lamellar crystals in the PVA film.
  • the stretching stress applied to the PVA film may not sufficiently contribute to the orientation of the molecular chains of PVA, and the optical performance of the obtained optical film may be lowered.
  • the rate of increase in the crystal length cycle is too small, it is considered that the amorphous portion in the PVA film is difficult to swell with a solvent such as water in the swelling step when manufacturing the optical film. That is, in the stretching step when manufacturing an optical film, the lamella crystals in the PVA film are difficult to dissolve and the stretching stress tends to concentrate on the crystal portion. As a result, the molecular chains of PVA may not be sufficiently oriented in the amorphous portion of the PVA film, and the optical performance and shrinkage stress of the obtained optical film may not be compatible.
  • the crystal length period Da of the PVA film which is obtained from the small-angle X-ray scattering measurement performed before immersion in the water / methanol mixed solvent (volume ratio: 2/8), is preferably 10.0 nm or more. .. Further, the crystal length period Da is preferably 12.5 nm or less.
  • the crystal length period Da is obtained by performing small-angle X-ray scattering measurement before immersion in a water / methanol mixed solvent (volume ratio: 2/8), that is, in air (temperature 20 ° C., humidity 65%). ..
  • the lower limit of the crystal length period Da is more preferably 11.0 nm.
  • the upper limit of the crystal length period Da is more preferably 12.3 nm.
  • the crystal length period Da is less than 10.0 nm, it is presumed that the thickness of the lamella crystal in the PVA film is small and the crystal structure is small.
  • the thickness of the lamella crystal is small, the fine crystals of the lamella crystal in the PVA film are easily dissolved when the PVA film is immersed in a solvent such as water in the swelling step in manufacturing the optical film. As a result, the PVA film becomes soft, and there is a risk that wrinkles are likely to occur in the PVA film in the swelling step.
  • the crystal length period Da is larger than 12.5 nm, it is presumed that the thickness of the lamellar crystals in the PVA film is large, or the distance between the lamellar crystals is long and the crystal structure has many amorphous portions.
  • the lamella crystals in the PVA film are not sufficiently dissolved in the swelling step when manufacturing the optical film, and the stretching tension of the PVA film tends to be high in the stretching step when manufacturing the optical film. As a result, the shrinkage stress of the obtained optical film may increase.
  • the swelling step in manufacturing the optical film when the PVA film is immersed in a solvent such as water, the amorphous portion in the PVA film easily takes in water. As a result, the PVA film becomes soft, the stretching tension of the PVA film becomes low in the stretching step when manufacturing the optical film, and the optical performance of the obtained optical film may be insufficient.
  • the crystal length period Ds obtained from the small-angle X-ray scattering measurement performed in a water / methanol mixed solvent (volume ratio: 2/8) is preferably 12.0 nm or more. Further, the crystal length period Ds is preferably 18.0 nm or less. The lower limit of the crystal length period Ds is more preferably 13.0 nm. The upper limit of the crystal length period Ds is more preferably 17.0 nm. When the crystal length period Ds exceeds 18.0 nm, the molecular chain of PVA tends to spread when the PVA film is immersed in a solvent such as water in the swelling step when manufacturing the optical film, and the obtained optical film can be obtained. Moisture resistance may deteriorate.
  • the crystal length period Ds is less than 12.0 nm
  • water is generated in the amorphous portion of the PVA film when the PVA film is immersed in a solvent such as water in the swelling step when manufacturing the optical film. It is difficult to get in.
  • the stretching tension of the PVA film increases in the stretching step when manufacturing the optical film, and the shrinkage stress of the obtained optical film may increase.
  • the method of adjusting the crystal length period Ds and the crystal length period Da and controlling the increase rate of the crystal length period within the above range is as follows: (1) Discharge, drying, and heating conditions for forming a film. The degree of interaction between the molecular chains of PVA is adjusted by the method of adjusting the crystal state of PVA by control, and (2) the type of PVA (degree of saponification, amount of modification, etc.), and the spread of amorphous parts in the PVA film. , (3) A method of adjusting the size of lamella crystals by adding a plasticizing agent, (4) A method of adjusting the cross-linking structure between molecular chains of PVA by adding a cross-linking agent, etc. Examples thereof include a method of adjusting the spread of the amorphous portion and a method of adjusting by a combination thereof.
  • the ejection conditions for film formation are, for example, a volatile fraction of the film-forming stock solution of 10% by mass or more and 40% by mass. % Or less is preferable.
  • the shear rate at the exit of the film-like dispensing device is 75s -1 or more, preferably 1000 s -1.
  • the drying conditions for forming the film are, for example, preferably 60 ° C. or higher, and preferably 100 ° C. or lower, for the surface temperature of the support on which the film-forming stock solution is spilled.
  • the temperature of the hot air blown to the non-contact surface side of the PVA film on the support is preferably 50 ° C.
  • the temperature of the drying oven or the average temperature of the drying roll (the average value of the surface temperature of the drying roll) is preferably 40 ° C. or higher, and preferably 110 ° C. or lower.
  • the surface temperature of the heat treatment roll is preferably 135 ° C. or lower.
  • the saponification degree of PVA is preferably, for example, 85 mol% or more and 95 mol% or less.
  • the amount of PVA modified is preferably, for example, 0.3 mol% or more and 8 mol% or less.
  • the content of the plasticizer may be 2 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of PVA. preferable. Further, as the plasticizer, it is preferable to use ethylene glycol, glycerin, diethylene glycol, or diglycerin.
  • PVA polymer produced by saponifying a vinyl ester polymer obtained by polymerizing a vinyl ester monomer
  • the vinyl ester monomer include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerianate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, vinyl versatic acid and the like.
  • vinyl acetate is preferable as the vinyl ester monomer.
  • the vinyl ester polymer is not particularly limited, but a polymer obtained by using only one kind or two or more kinds of vinyl ester monomers as a monomer is preferable, and only one kind of vinyl ester monomer is used as a monomer. The obtained polymer is more preferable.
  • the vinyl ester polymer may be a copolymer of one or more kinds of vinyl ester monomers and another monomer copolymerizable with one or more kinds of vinyl ester monomers.
  • Ethylene is preferable as the other monomer. That is, the PVA contained in the PVA film of the present invention preferably contains ethylene units.
  • the content of ethylene units is preferably 1 mol% or more based on the number of moles of all structural units constituting the vinyl ester polymer.
  • the ethylene unit content is preferably 8 mol% or less, and more preferably 5 mol% or less. When the content of the ethylene unit is in the above range, both the optical performance and the shrinkage stress of the obtained optical film can be achieved at the same time.
  • the dye in the dyeing step is easily adsorbed on the hydrophobic ethylene unit in the PVA film, and is adsorbed by the stretching stress applied to the PVA film. It is presumed that this is because the orientation of the dye is enhanced.
  • Other monomers include olefins having 3 to 30 carbon atoms such as propylene, 1-butyl, and isobutene; acrylic acid or a salt thereof; methyl acrylate, ethyl acrylate, n-propyl acrylate, and the like.
  • Acrylic acid esters such as i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate; methacrylic acid or a salt thereof.
  • -Vinyl ethers such as butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether; vinyl cyanide such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride and vinylidene fluoride; allyl acetate.
  • Allyl compounds such as allyl chloride; maleic acid or salts thereof, esters or acid anhydrides; itaconic acid or salts thereof, esters or acid anhydrides; vinylsilyl compounds such as vinyltrimethoxysilane; isopropenyl acetate and the like.
  • the vinyl ester polymer can have a structural unit derived from one or more of the above-mentioned other monomers.
  • the proportion of structural units derived from the monomers other than ethylene is not necessarily limited as long as it does not interfere with the effects of the present invention, but is 15 mol% or less based on the number of moles of all structural units constituting the vinyl ester polymer. It is preferably 5 mol% or less, more preferably 1 mol% or less, and even more preferably 0.1 mol% or less.
  • the degree of polymerization of PVA is not particularly limited, but is preferably 1,000 or more.
  • the degree of polymerization of PVA is preferably 8,000 or less.
  • the degree of polymerization of PVA is more preferably 1,500 or more, and even more preferably 2,000 or more, from the viewpoint of enhancing the optical performance and moist heat resistance of the obtained optical film.
  • the upper limit of the degree of polymerization is more preferably 5,000 or less, and further preferably 4,000 or less, from the viewpoint of increasing the productivity of PVA.
  • the lower limit of the saponification degree of PVA is preferably 98.7 mol%, more preferably 99.0 mol%, still more preferably 99.5 mol%, and 99.8. It is particularly preferably mol%, preferably 99.9 mol%.
  • the saponification degree is at least the above lower limit, an optical film having excellent optical performance and moisture heat resistance can be obtained.
  • the upper limit of the saponification degree is not particularly limited, but is preferably 99.99 mol% or less from the viewpoint of PVA productivity.
  • the degree of saponification of PVA is determined by the number of moles of vinyl alcohol units with respect to the total number of moles of structural units (typically vinyl ester monomer units) that can be converted into vinyl alcohol units by saponification. It refers to the proportion (mol%).
  • the degree of saponification of PVA can be measured according to the description of JIS K 6726-1994.
  • the PVA film of the present invention may contain one type of PVA alone, or may contain two or more types of PVA having different degrees of polymerization, saponification, modification, and the like.
  • the upper limit of the ratio of the PVA content in the PVA film is not particularly limited.
  • the lower limit of the content ratio of PVA is preferably 50% by mass, more preferably 80% by mass, and even more preferably 85% by mass.
  • the PVA film of the present invention preferably contains a plasticizer. Since the PVA film contains a plasticizer, the stretchability of the PVA film can be enhanced in the stretching step when producing the optical film.
  • a polyhydric alcohol is preferable as the plasticizer. Examples of the polyhydric alcohol include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylolpropane and the like. Among these, glycerin is preferable from the viewpoint of improving the stretchability.
  • the plasticizer may be used alone or in combination of two or more.
  • the amount of lamella crystals or the size of the lamella crystals can be adjusted.
  • the PVA film containing a small amount of plasticizer is more likely to undergo crystal growth by heat treatment than the PVA film containing no plasticizer. It is presumed that this is because a small amount of plasticizer makes it easier for the PVA molecules in the PVA film to move, which makes it easier to obtain a more energetically stable crystal structure. Then, as the crystal growth of the PVA film progresses, the size of the lamella crystals in the PVA film tends to increase, and the crystal length period Da tends to increase.
  • the PVA film contains an excessive amount of plasticizer, crystal growth is likely to be inhibited. It is presumed that this is because the amount of the plasticizer that interacts with the hydroxyl group of the PVA molecule increases and the interaction between the PVA molecules weakens. Further, when the PVA film contains a plasticizer, the amorphous portion in the PV film easily takes in water, and the rate of increase in the crystal length cycle tends to increase.
  • the content of the plasticizer is 2 parts by mass with respect to 100 parts by mass of PVA.
  • the above is preferable.
  • the content of the plasticizer is preferably 20 parts by mass or less with respect to 100 parts by mass of PVA.
  • the size of the lamella crystals in the PVA film tends to be too small.
  • the crystal length period Da may become smaller, and the rate of increase in the crystal length period of the PVA film may be out of the predetermined range.
  • the content of the plasticizer is more preferably 5 parts by mass or more, and further preferably 8 parts by mass or more with respect to 100 parts by mass of PVA.
  • the content of the plasticizer is more preferably 17 parts by mass or less, and further preferably 15 parts by mass or less with respect to 100 parts by mass of PVA.
  • the PVA film of the present invention preferably contains a surfactant.
  • a surfactant By producing a PVA film using a film-forming stock solution containing a surfactant, the film-forming property of the PVA film is improved. As a result, the occurrence of thickness unevenness of the PVA film is suppressed, and the PVA film can be easily peeled off from the metal roll or belt used for film formation.
  • the obtained PVA film contains the surfactant.
  • the type of the surfactant is not particularly limited, but an anionic surfactant and a nonionic surfactant are preferable from the viewpoint of the peelability of the PVA film from the metal roll or the belt.
  • anionic surfactant examples include a carboxylic acid type such as potassium laurate; a sulfate ester type such as polyoxyethylene lauryl ether sulfate and octyl sulfate; and a sulfonic acid type such as dodecylbenzene sulfonate.
  • carboxylic acid type such as potassium laurate
  • a sulfate ester type such as polyoxyethylene lauryl ether sulfate and octyl sulfate
  • a sulfonic acid type such as dodecylbenzene sulfonate.
  • nonionic surfactant examples include an alkyl ether type such as polyoxyethylene oleyl ether; an alkylphenyl ether type such as polyoxyethylene octylphenyl ether; an alkyl ester type such as polyoxyethylene laurate; and polyoxyethylene laurylamino ether.
  • Alkylamine type such as; Alkylamide type such as polyoxyethylene lauric acid amide; Polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether; Alkanolamide type such as lauric acid diethanolamide and oleic acid diethanolamide; Polyoxyalkylene Examples thereof include allylphenyl ether type such as allylphenyl ether.
  • the surfactant can be used alone or in combination of two or more.
  • the lower limit of the content of the surfactant in the PVA film is preferably 0.01 part by mass and 0.02 part by mass with respect to 100 parts by mass of PVA. Is more preferable, and 0.05 part by mass is further preferable.
  • the upper limit of the content of the surfactant in the PVA film is preferably 0.5 parts by mass, more preferably 0.3 parts by mass, and 0.2 parts by mass with respect to 100 parts by mass of PVA. It is more preferable to be a part.
  • the PVA film of the present invention includes a filler, a processing stabilizer such as a copper compound, a weathering stabilizer, a colorant, an ultraviolet absorber, a light stabilizer, an antioxidant, an antistatic agent, a flame retardant, and other substances.
  • a processing stabilizer such as a copper compound, a weathering stabilizer, a colorant, an ultraviolet absorber, a light stabilizer, an antioxidant, an antistatic agent, a flame retardant, and other substances.
  • Additives such as thermoplastic resins, lubricants, fragrances, defoamers, deodorants, bulking agents, release agents, mold release agents, reinforcing agents, cross-linking agents, antistatic agents, preservatives, and crystallization rate retarders It may be contained as appropriate as needed.
  • the total proportion of PVA, plasticizer and surfactant in the PVA film of the present invention is preferably 80% by mass or more, more preferably 90% by mass or more, and 95% by mass or more. Is even more preferable, and in some cases, 99% by mass or more is even more preferable. Since the PVA film of the present invention is substantially composed of PVA, a plasticizer and a surfactant, a polarizing film having excellent polarizing performance can be obtained when a polarizing film is produced using the PVA film of the present invention. Obtainable.
  • the PVA film of the present invention is a so-called raw film for producing an optical film, which is used as a material for an optical film.
  • the PVA film of the present invention is not limited to a roll-shaped film.
  • the average thickness of the PVA film of the present invention is not particularly limited.
  • the lower limit of the average thickness of the PVA film is preferably 1 ⁇ m, more preferably 5 ⁇ m, further preferably 10 ⁇ m, and particularly preferably 15 ⁇ m.
  • the upper limit of the average thickness is preferably 60 ⁇ m, more preferably 50 ⁇ m, further preferably 45 ⁇ m, and even more preferably 35 ⁇ m.
  • the "average thickness” refers to the average value of the thickness measured at any five points (hereinafter, the same applies to the average thickness).
  • the PVA film of the present invention may be a single-layer film composed of one PVA layer or a multilayer film including one PVA layer.
  • the PVA film of the present invention is used as a raw film for producing a polarizing film, it is preferably a single-layer film.
  • the lower limit of the average thickness of the PVA layer is preferably 1 ⁇ m, more preferably 5 ⁇ m, still more preferably 10 ⁇ m, and 15 ⁇ m. Is particularly preferable.
  • the average thickness is at least the above lower limit, it is possible to suppress the breakage of the PVA film in the stretching step when manufacturing the optical film.
  • the upper limit of the average thickness of the PVA layer is preferably 60 ⁇ m, more preferably 50 ⁇ m, further preferably 45 ⁇ m, and even more preferably 35 ⁇ m. When the average thickness is not more than the above upper limit, the effect of the present invention can be fully exerted.
  • a multilayer film is a film having two or more layers.
  • the number of layers of the multilayer film may be 5 or less, and may be 3 or less.
  • Examples of the multilayer film include a laminated film having a laminated structure of a base resin layer and a PVA layer.
  • the average thickness of the base resin layer is preferably 20 ⁇ m or more, for example.
  • the average thickness of the base resin layer is preferably 500 ⁇ m or less, for example.
  • the base resin layer in the multilayer film is preferably one that can be uniaxially stretched together with the PVA layer.
  • polyester, polyolefin or the like can be used as the resin constituting the base resin layer.
  • amorphous polyester is preferable, and polyethylene terephthalate and amorphous polyester obtained by copolymerizing polyethylene terephthalate with a copolymerization component such as isophthalic acid and 1,4-cyclohexanedimethanol are preferably used.
  • An adhesive layer may be provided between the base resin layer and the PVA layer.
  • the width of the PVA film of the present invention is not particularly limited and can be determined according to its use and the like.
  • the lower limit of the width of the PVA film is preferably 3 m. Since the lower limit of the width is 3 m, it is suitable for applications of liquid crystal televisions and liquid crystal monitors whose screens are becoming larger in recent years.
  • the upper limit of the width of the PVA film is preferably 7 m. By setting the upper limit of the width to 7 m, it is possible to efficiently perform the stretching process (uniaxial stretching process) when manufacturing an optical film such as a polarizing film with a practical device.
  • the degree of swelling of the PVA film of the present invention is preferably 140% or more from the viewpoint of productivity and optical performance of the obtained optical film. Further, the swelling degree of the PVA film of the present invention is preferably 400% or less. The lower limit of the degree of swelling is more preferably 170%, further preferably 180%, and particularly preferably 190%. Further, the upper limit of the degree of swelling is more preferably 220%, further preferably 210%. The degree of swelling of the PVA film can be adjusted to a smaller value, for example, by increasing the temperature of the heat treatment of the PVA film.
  • N represents the mass (g) of the sample after immersing the sample taken from the PVA film in distilled water at 30 ° C. for 30 minutes and then removing the water on the surface.
  • M represents the mass (g) of the sample after drying the sample in a dryer at 105 ° C. for 16 hours.
  • the PVA film of the present invention is usually a film that is not substantially stretched (non-stretched film, unstretched film).
  • the in-plane retardation of the PVA film is preferably 100 nm or less, more preferably 50 nm or less.
  • an optical film can be obtained by stretching a PVA film of the present invention (uniaxial stretching treatment or biaxial stretching treatment) or the like.
  • the PVA film of the present invention it is possible to manufacture an optical film having excellent optical performance and a small shrinkage stress at high temperatures.
  • the optical film that can be produced by the PVA film of the present invention include a polarizing film, a retardation film, a viewing angle improving film, a brightness improving film, and the like, and a polarizing film is preferable.
  • the film-forming method of the PVA film is a casting film-forming method or a wet film-forming method (in a poor solvent) using a film-forming stock solution homogenized by adding a solvent, an additive, etc. to PVA. Discharge), dry-wet film-forming method, gel film-forming method (a method in which a membrane-forming stock solution is once cooled and gelled, and then the solvent is extracted and removed to obtain a PVA-based polymer film), or a method of forming a film by a combination thereof.
  • the film can be formed by any method such as a melt extrusion film forming method or an inflation forming method, in which the above-mentioned undiluted film-forming solution is obtained by using an extruder or the like and extruded from a T-die or the like to form a film. ..
  • the casting film forming method and the melt extrusion film forming method are preferable because a homogeneous film can be obtained with high productivity.
  • a casting film forming method or a melt extrusion film forming method for a PVA film will be described.
  • the above-mentioned film forming stock solution is poured into a film on a support such as a metal roll or a metal belt and heated to generate a solvent. By being removed, it solidifies into a film.
  • the solidified film is peeled off from the support, dried by a drying roll, a drying oven, etc. as necessary, further heat-treated as necessary, and wound up to form a long roll-shaped PVA film. Obtainable.
  • the film-forming stock solution (hereinafter, may be referred to as "PVA film”) that has been drowned on the support undergoes crystallization on the support and during the subsequent drying step.
  • PVA film The film-forming stock solution
  • the membrane-forming stock solution is heated in a state of high volatile fraction (moisture content)
  • the mobility of the molecular chain of PVA in the membrane-forming stock solution (PVA film) becomes high, and crystallization proceeds.
  • the amount of lamella crystals in the PVA film tends to increase, and the crystal length period Da tends to decrease.
  • the drying speed is too fast, the crystallization of the PVA film does not proceed sufficiently, the amount of lamella crystals tends to decrease, and the crystal length period Da tends to increase.
  • the drying rate is too slow, the crystal growth of the PVA film progresses, the size of the lamella crystal becomes large, and the crystal length period Da tends to be large.
  • the amount of heat given is too large, the size of the lamella crystals in the PVA film tends to be large, the crystal length period Da tends to be too large, and the rate of increase in the crystal length period tends to be too small.
  • the volatile content of the film-forming stock solution (ratio of volatile components such as solvents removed by volatilization or evaporation during film-forming) is preferably 50% by mass or more, more preferably 55% by mass or more. preferable.
  • the volatile fraction of the film-forming stock solution is preferably 90% by mass or less, and more preferably 80% by mass or less. If the volatile fraction is less than 50% by mass, the viscosity of the film-forming stock solution becomes high, and it may be difficult to form a PVA film. On the other hand, when the volatile content concentration exceeds 90% by mass, the viscosity becomes low and the uniformity of the thickness of the PVA film tends to be impaired.
  • the "volatile fraction of the film-forming stock solution” in the present invention means the volatile fraction obtained by the following formula.
  • Volatile fraction of membrane-forming stock solution (mass%) ⁇ (Wa-Wb) / Wa ⁇ x 100
  • Wa represents the mass (g) of the film-forming stock solution
  • Wb represents the mass (g) when the film-forming stock solution of Wa (g) is dried in an electric heating dryer at 105 ° C. for 16 hours.
  • the method for preparing the undiluted film-forming solution for example, a method of dissolving PVA and additives such as a plasticizer and a surfactant in a dissolution tank or the like, or PVA in a water-containing state using a uniaxial or twin-screw extruder.
  • a method of melt-kneading together with a plasticizer, a surfactant, and the like when melt-kneading for example, a method of dissolving PVA and additives such as a plasticizer and a surfactant in a dissolution tank or the like, or PVA in a water-containing state using a uniaxial or twin-screw extruder.
  • a method of melt-kneading together with a plasticizer, a surfactant, and the like when melt-kneading for example, a method of melt-kneading together with a plasticizer, a surfactant, and the like when melt-knea
  • the above-mentioned film forming stock solution is spilled from the film-like discharge device onto a support such as a metal roll or a metal belt in the form of a film. By heating and removing the solvent, it solidifies and forms a film.
  • the rate of increase in the crystal length cycle before and after immersion in a water / methanol mixed solvent is within a specific range. It is estimated that this rate of increase is affected by the degree of entanglement of the molecular chains of PVA in the amorphous part existing between the lamellar crystals in the PVA film. Therefore, the rate of increase in the crystal length cycle of the PVA film can be controlled by adjusting the shear rate at the outlet of the film-like discharge device, where the film-forming stock solution receives a strong shearing force.
  • the shear rate at the outlet of the film-like discharge device is preferably 75 s -1 or more, more preferably 100 s -1 or more, and further preferably 125 s -1 or more.
  • the shear rate at the outlet of the film-shaped discharge device is preferably 1000s -1 or less, more preferably 900s -1 or less, and even more preferably 800s -1 or less.
  • the shear rate is not more than the above upper limit, it is possible to prevent the rate of increase in the crystal length period from becoming too small.
  • the shear rate is at least the above lower limit, it is possible to prevent the rate of increase in the crystal length period from becoming too large.
  • the shear rate at the outlet of the film-shaped discharge device refers to the shear rate on the wall surface of the membrane-forming stock solution flow path in the die lip in the case of a general T-die or I-die, and can be calculated by the following formula.
  • ⁇ 6Q / Wh 2
  • ⁇ 6Q / Wh 2
  • W is the width of the die lip (cm)
  • h is the opening degree of the die lip (cm)
  • Q is the discharge rate of the membrane-forming stock solution from the die lip (cm 3 /).
  • the surface temperature of the support on which the membrane-forming stock solution is spilled is preferably 50 ° C. or higher. Further, the surface temperature of the support for flowing the membrane-forming stock solution is preferably 110 ° C. or lower. When the surface temperature is less than 50 ° C., the time required for drying the film-forming stock solution becomes long and the productivity tends to decrease. On the other hand, when the surface temperature exceeds 110 ° C., the film surface of the PVA film tends to be abnormal due to foaming or the like. Further, as the film-forming stock solution is rapidly dried, the crystallization of the PVA film does not proceed sufficiently, the amount of lamella crystals tends to decrease, and the crystal length period Da tends to increase.
  • the surface temperature of the support is preferably 60 ° C. or higher, more preferably 65 ° C. or higher.
  • the surface temperature of the support is preferably 100 ° C. or lower, more preferably 95 ° C. or lower.
  • hot air having a wind speed of 1 to 10 m / sec may be uniformly blown over the entire region on the non-contact surface side of the PVA film to adjust the drying rate.
  • the temperature of the hot air blown to the non-contact surface side is preferably 50 ° C. or higher, and more preferably 70 ° C. or higher from the viewpoint of drying efficiency and uniformity of drying.
  • the temperature of the hot air blown to the non-contact surface is preferably 150 ° C. or lower, more preferably 120 ° C. or lower, from the viewpoint of drying efficiency and uniformity of drying.
  • the PVA film is preferably dried on the support to a volatile fraction of 5 to 50% by mass, then peeled off and further dried if necessary.
  • the drying method is not particularly limited, and examples thereof include a method of contacting with a drying furnace or a drying roll. When drying with a plurality of drying rolls, it is preferable to alternately bring one side and the other side of the film into contact with the drying rolls in order to make both sides uniform.
  • the number of dry rolls is preferably 3 or more, more preferably 4 or more, and even more preferably 5 or more. Further, the number of dry rolls is more preferably 30 or less.
  • the upper limit of the temperature of the drying oven or the average temperature of the drying roll is preferably 110 ° C., more preferably 100 ° C., and even more preferably 90 ° C. It is more preferably 85 ° C. If the temperature of the drying oven or the average temperature of the drying roll is too high, the crystal growth of the PVA film proceeds, and the size of the lamella crystals in the PVA film tends to increase. As a result, the crystal length period Da may become large, and the rate of increase in the crystal length period may become too small.
  • the lower limit of the temperature of the drying oven or the average temperature of the drying roll is preferably 40 ° C, more preferably 45 ° C, and even more preferably 50 ° C. If the temperature of the drying oven or the average temperature of the drying roll is too low, the crystal growth of the PVA film becomes insufficient, and the size of the lamella crystals in the PVA film tends to be small. As a result, the crystal length period Da may become too small, or the rate of increase in the crystal length period may become too large.
  • the dried PVA film can be further heat-treated if necessary. By performing the heat treatment, the strength, swelling degree, birefringence, etc. of the PVA film can be adjusted.
  • the surface temperature of the heat treatment roll for performing the heat treatment is preferably 60 ° C. or higher.
  • the surface temperature of the heat treatment roll is preferably 135 ° C. or lower, more preferably 130 ° C. or lower. If the surface temperature of the heat-treated roll is too high, the amount of heat given is too large and the size of the lamella crystals in the PVA film becomes large, the crystal length period Da becomes too large, or the rate of increase in the crystal length period becomes too small. Tend.
  • the PVA film produced in this way is further subjected to humidity control treatment, cutting of both ends (ears) of the film, and the like, and is wound into a roll on a cylindrical core, if necessary. It is packaged in a moisture-proof package and becomes a product.
  • the volatile fraction of the PVA film finally obtained by the above-mentioned series of treatments is not necessarily limited, but the volatile fraction of the PVA film is preferably 1% by mass or more, more preferably 2% by mass or more. preferable.
  • the volatile fraction of the PVA film is preferably 5% by mass or less, and more preferably 4% by mass or less.
  • a multilayer film can be produced, for example, by applying a film-forming stock solution on a substrate resin film (base resin layer).
  • a film-forming stock solution on a substrate resin film (base resin layer).
  • the surface of the base resin film may be modified or an adhesive may be applied to the surface of the base resin film. good.
  • the method for producing an optical film of the present invention includes a step of uniaxially stretching the above-mentioned PVA film.
  • a method for producing a polarizing film will be specifically described as an example of a method for producing an optical film.
  • a dyeing step for dyeing a PVA film As a method for producing a polarizing film, a dyeing step for dyeing a PVA film, a stretching step for uniaxially stretching, a swelling step for further swelling, a cross-linking step for cross-linking, a fixing treatment step for fixing treatment, and a washing step are performed. Examples thereof include a method including a cleaning step, a drying step of drying, a heat treatment step of heat treatment, and the like.
  • the order of each step is not particularly limited, but for example, the swelling step, the dyeing step, the crosslinking step, the stretching step, the fixing treatment step, and the like can be performed in this order. Further, one or more steps can be performed simultaneously, and each step can be performed twice or more.
  • the PVA film of the present invention can suppress the generation of swelling wrinkles in the swelling step, and is therefore useful as a film used in a method for producing a polarizing film having a swelling step.
  • the swelling step can be performed by immersing the PVA film in a swelling treatment bath containing water or the like.
  • the temperature of the swelling treatment bath is preferably 20 ° C. or higher, more preferably 22 ° C. or higher, and even more preferably 25 ° C. or higher.
  • the temperature of the swelling treatment bath is preferably 55 ° C. or lower, more preferably 50 ° C. or lower, and even more preferably 45 ° C. or lower.
  • the time for immersing in the swelling treatment bath is preferably, for example, 0.1 minutes or longer, and more preferably 0.5 minutes or longer.
  • the time for immersing in the swelling treatment bath is, for example, preferably 5 minutes or less, and more preferably 3 minutes or less.
  • the water used in the swelling treatment bath is not limited to pure water, and may be an aqueous solution in which various components are dissolved, or may be a mixture of water and an aqueous medium.
  • the dyeing step can be performed by bringing the PVA film into contact with a solution containing a dichroic dye (dyeing treatment bath).
  • Iodine-based dyes are generally used as the dichroic dyes.
  • the timing of dyeing may be any stage before uniaxial stretching, during uniaxial stretching, and after uniaxial stretching.
  • a solution containing iodine-potassium iodide is preferable, and this solution is preferably an aqueous solution.
  • the concentration of iodine in the dyeing treatment bath is preferably 0.01% by mass or more.
  • the iodine concentration is preferably 0.5% by mass or less.
  • the concentration of potassium iodide is preferably 0.01% by mass or more.
  • the concentration of potassium iodide is preferably 10% by mass or less.
  • the temperature of the dyeing treatment bath is preferably 20 ° C. or higher, more preferably 25 ° C. or higher.
  • the temperature of the dyeing treatment bath is preferably 50 ° C. or lower, more preferably 40 ° C. or lower.
  • the dyeing time is preferably 0.2 minutes or more.
  • the staining time is preferably 5 minutes or less.
  • the crosslinking step is performed after the dyeing step and before the stretching step.
  • the cross-linking step can be performed by immersing the PVA film in an aqueous solution (cross-linking treatment bath) containing a cross-linking agent.
  • a cross-linking agent one kind or two or more kinds of boron compounds such as borate such as boric acid and borax can be used.
  • the concentration of the cross-linking agent in the cross-linking treatment bath is preferably 1% by mass or more, more preferably 1.5% by mass or more, and further preferably 2% by mass or more.
  • the concentration of the cross-linking agent is preferably 15% by mass or less, more preferably 7% by mass or less, and further preferably 6% by mass or less.
  • the cross-linking treatment bath may contain potassium iodide or the like.
  • the temperature of the cross-linking treatment bath is preferably 20 ° C. or higher, more preferably 25 ° C. or higher.
  • the temperature of the cross-linking treatment bath is preferably 60 ° C. or lower, more preferably 55 ° C. or lower. By keeping the temperature within the above range, the PVA film can be efficiently crosslinked.
  • the stretching step of uniaxially stretching the PVA film may be performed by either a wet stretching method or a dry stretching method.
  • the wet stretching method it can be carried out in an aqueous solution containing boric acid (stretching treatment bath), in the above-mentioned dyeing treatment bath or in the fixation treatment bath described later.
  • stretching may be carried out at room temperature (25 ° C.), stretching may be carried out while heating, or may be carried out in the air using a PVA film after water absorption.
  • the wet stretching method is preferable because it can be stretched with high uniformity in the width direction, and uniaxial stretching is more preferable in the stretching treatment bath.
  • the concentration of boric acid in the stretching treatment bath is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and further preferably 1.5% by mass or more.
  • the boric acid concentration in the stretching bath is preferably 6.0% by mass or less, more preferably 5.0% by mass or less, and further preferably 4.0% by mass or less.
  • the stretching treatment bath may contain potassium iodide, and the concentration of potassium iodide is preferably 0.01% by mass or more.
  • the concentration of potassium iodide is preferably 10% by mass or less.
  • the stretching temperature in uniaxial stretching is preferably 30 ° C. or higher, more preferably 40 ° C. or higher, and even more preferably 50 ° C. or higher.
  • the stretching temperature in uniaxial stretching is preferably 90 ° C. or lower, more preferably 80 ° C. or lower, and even more preferably 75 ° C. or lower.
  • the draw ratio in uniaxial stretching is preferably 5 times or more, and more preferably 5.5 times or more from the viewpoint of the polarization performance of the obtained polarizing film.
  • the upper limit of the draw ratio is not particularly limited, but the draw ratio is preferably 8 times or less.
  • the maximum draw stress of the PVA film in a uniaxial stretching is preferably at 50 N / mm 2 or less, more preferably more preferably 25 N / mm 2 or less, 15N / mm 2 or less, 10 N / mm 2
  • the maximum stretching stress is a value obtained by dividing the stretching tension of the PVA film applied between adjacent rolls in the stretching treatment bath by the cross-sectional area of the PVA film.
  • the stretching tension of the PVA film can be measured by a tension roll installed between adjacent rolls in the stretching treatment bath, and when three or more rolls are used in the stretching treatment bath, the maximum value among them.
  • the cross-sectional area of the PVA film is determined from the unstretched PVA film before being used for producing the polarizing film.
  • the maximum stretching stress is usually 1 N / mm 2 or more.
  • uniaxial stretching in the long direction can be adopted. Since a polarizing film having excellent polarizing performance can be obtained, uniaxial stretching in the long direction is preferable.
  • Uniaxial stretching in the long direction can be performed by using a stretching device including a plurality of rolls parallel to each other and changing the peripheral speed between the rolls.
  • the horizontal uniaxial stretching can be performed using a tenter type stretching machine.
  • a fixing treatment step can be performed after the stretching step.
  • an aqueous solution containing one or more kinds of boron compounds such as boric acid and borax can be used.
  • an iodine compound or a metal compound may be added to the fixing treatment bath.
  • the concentration of the boron compound in the fixing treatment bath is preferably 2% by mass or more, more preferably 3% by mass or more.
  • the concentration of the boron compound in the fixing treatment bath is preferably 15% by mass or less, and more preferably 10% by mass or less.
  • the temperature of the fixing treatment bath is preferably 15 ° C. or higher, more preferably 25 ° C. or higher.
  • the temperature of the fixing treatment bath is preferably 60 ° C. or lower, more preferably 40 ° C. or lower.
  • the cleaning process is generally performed by immersing the film in distilled water, pure water, an aqueous solution, or the like.
  • an aqueous solution cleaning treatment bath
  • the concentration of iodide is preferably 0.5% by mass or more.
  • the concentration of iodide is preferably 10% by mass or less.
  • the temperature of the washing treatment bath is preferably 5 ° C. or higher, more preferably 10 ° C. or higher, and even more preferably 15 ° C. or higher.
  • the temperature of the washing treatment bath is preferably 50 ° C. or lower, more preferably 45 ° C. or lower, and even more preferably 40 ° C.
  • the conditions of the drying step are not particularly limited, but the drying temperature of the PVA film is preferably 30 ° C. or higher, more preferably 50 ° C. or higher.
  • the drying temperature of the PVA film is preferably 150 ° C. or lower, more preferably 130 ° C. or lower.
  • An optical film other than the polarizing film, such as a retardation film, can also be manufactured by a method including a step of uniaxially stretching the PVA film of the present invention.
  • a specific production method a conventionally known method can be adopted except that the PVA film of the present invention is used.
  • the dichroism ratio (R) of the polarizing film is preferably 100 or more.
  • the dichroism ratio (R) is more preferably 150 or more, and even more preferably 160 or more.
  • the dichroism ratio (R) is, for example, preferably 350 or less, and preferably 300 or less.
  • the degree of polarization (V) at a predetermined simple substance transmittance (T) can be calculated.
  • the transmittance (T') when the predetermined simple substance transmittance (T) is obtained from the above formula (a).
  • the predetermined simple substance transmittance (T) can be obtained.
  • the degree of polarization (V) can be obtained.
  • the polarizing film obtained as described above is usually used as a polarizing plate by laminating a protective film that is optically transparent and has mechanical strength on both sides or one side thereof.
  • a protective film a cellulose triacetate (TAC) film, a cycloolefin polymer (COP) film, a cellulose acetate / butyrate cellulose (CAB) film, an acrylic film, a polyester film and the like are used.
  • the adhesive for bonding include a PVA-based adhesive, a urethane-based adhesive, and an acrylate-based ultraviolet curable adhesive. That is, the polarizing plate has a polarizing film and a protective film laminated directly on one side or both sides of the polarizing film or via an adhesive layer.
  • the polarizing plate can be used as a component of an LCD by, for example, being coated with an adhesive such as an acrylic and then bonded to a glass substrate. Further, a retardation film, a viewing angle improving film, a brightness improving film and the like may be bonded to the polarizing plate.
  • polarizing film was prepared using the PVA films obtained in the following Examples and Comparative Examples. First, a PVA film is stretched 2.0 times in the MD direction in pure water (swelling treatment bath) at 25 ° C., and then an aqueous solution at 32 ° C. containing 0.03% by mass of iodine and 0.7% by mass of potassium iodide. It was stretched in (dyeing treatment bath) so that the total stretch ratio was 2.4 times. Subsequently, it was stretched in an aqueous solution (crosslinking treatment bath) at 32 ° C.
  • Optical performance of polarizing film A rectangle 4 cm in the mechanical flow direction (MD direction) of the polarizing film and 1.5 cm in the width direction (TD direction) from the center of the obtained polarizing film in the width direction (TD direction). Measurement sample was taken. For this measurement sample, a spectrophotometer with an integrating sphere (“V7100” manufactured by Nippon Spectroscopy Co., Ltd.) was used, and in accordance with JIS Z8722 (measurement method of object color), a C light source and a visible light region with a 2 ° field of view were used. After correcting the visual sensitivity of, the single transmittance and the degree of polarization were measured. By the method described above, the degree of polarization with a single transmittance of 44.0% was calculated.
  • Example 1 100 parts by mass of PVA (saponification degree 99.9 mol%, degree of polymerization 2400) obtained by saponification of polyvinyl acetate, 14 parts by mass of glycerin as a plasticizer, 0.1 parts by mass of lauric acid diethanolamide as a surfactant. , And a film-forming stock solution consisting of water and having a volatile content of 73% by mass was prepared.
  • the filtered film-forming stock solution is discharged from the T-die onto the support (surface temperature 90 ° C.) at a shear rate of 207s-1 in the form of a film, and the entire non-contact surface with the support is discharged on the support.
  • the final drying roll (19th drying roll) immediately before the heat treatment roll from the first drying roll so that one surface and the other surface of the PVA film alternately contact each drying roll by peeling from the support. After further drying up to), the film was peeled off from the final drying roll. At this time, the average value of the surface temperature of each dry roll from the first dry roll to the final dry roll was set to 70 ° C. Finally, after heat treatment was performed with a heat treatment roll having a surface temperature of 104 ° C., the film was wound into a roll to obtain a PVA film (thickness 45 ⁇ m, width 3.3 m).
  • the crystal length period Da was 12.6 nm
  • the crystal length period Ds was 16.8 nm
  • the rate of increase in the crystal length period was 0.33. Met.
  • the swelling degree of the PVA film it was 197%.
  • a polarizing film was produced using the obtained PVA film.
  • the maximum draw stress was 9.0 N / mm 2 .
  • the optical performance of the obtained polarizing film it was calculated that the single transmittance was 43.8% and the degree of polarization was 99.935%, and the degree of polarization when the single transmittance was 44.0% was 99.873%. rice field.
  • the shrinkage stress of the polarizing film it was 43.7 N / mm 2 .
  • Example 2 Example 3 and Comparative Examples 1 to 4> A PVA film was obtained in the same manner as in Example 1 except that the type of PVA, the amount of plasticizer, and the production conditions were changed as shown in Table 1.
  • Table 1 ethylene modification having an ethylene unit content of 3 mol% is abbreviated as “ ⁇ Et3”.
  • Table 1 shows the evaluation results of the obtained PVA film and polarizing film.
  • FIG. 2 shows a graph in which the degree of polarization of the polarizing films obtained in Examples 1 to 3 and Comparative Examples 1 to 3 when the single transmittance is 44.0% is plotted against the shrinkage stress. Since the PVA film of Comparative Example 4 was dissolved in distilled water at 30 ° C., the degree of swelling could not be measured. Further, since the PVA film of Comparative Example 4 was dissolved in pure water (swelling treatment bath) at 25 ° C., a polarizing film could not be produced.
  • the polarizing film produced from the PVA film of the present invention has excellent optical performance and low shrinkage stress at high temperatures.

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