Classifications

• • 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
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B27/00—Layered products comprising a layer of synthetic resin
  • B32B27/06—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material
  • B32B27/08—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B27/00—Layered products comprising a layer of synthetic resin
  • B32B27/30—Layered products comprising a layer of synthetic resin comprising vinyl (co)polymers; comprising acrylic (co)polymers
  • B32B27/306—Layered products comprising a layer of synthetic resin comprising vinyl (co)polymers; comprising acrylic (co)polymers comprising vinyl acetate or vinyl alcohol (co)polymers
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L29/00—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an alcohol, ether, aldehydo, ketonic, acetal or ketal radical; Compositions of hydrolysed polymers of esters of unsaturated alcohols with saturated carboxylic acids; Compositions of derivatives of such polymers
  • C08L29/02—Homopolymers or copolymers of unsaturated alcohols
  • C08L29/04—Polyvinyl alcohol; Partially hydrolysed homopolymers or copolymers of esters of unsaturated alcohols with saturated carboxylic acids
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B2255/00—Coating on the layer surface
  • B32B2255/10—Coating on the layer surface on synthetic resin layer or on natural or synthetic rubber layer
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B2255/00—Coating on the layer surface
  • B32B2255/26—Polymeric coating
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B2307/00—Properties of the layers or laminate
  • B32B2307/30—Properties of the layers or laminate having particular thermal properties
  • B32B2307/306—Resistant to heat
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B2307/00—Properties of the layers or laminate
  • B32B2307/70—Other properties
  • B32B2307/724—Permeability to gases, adsorption
  • B32B2307/7242—Non-permeable
  • B32B2307/7246—Water vapor barrier
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B2307/00—Properties of the layers or laminate
  • B32B2307/70—Other properties
  • B32B2307/726—Permeability to liquids, absorption
  • B32B2307/7265—Non-permeable
• • 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
  • C08J2329/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an alcohol, ether, aldehydo, ketonic, acetal, or ketal radical; Hydrolysed polymers of esters of unsaturated alcohols with saturated carboxylic acids; Derivatives of such polymer
  • C08J2329/02—Homopolymers or copolymers of unsaturated alcohols
  • C08J2329/04—Polyvinyl alcohol; Partially hydrolysed homopolymers or copolymers of esters of unsaturated alcohols with saturated carboxylic acids
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/0008—Organic ingredients according to more than one of the "one dot" groups of C08K5/01 - C08K5/59
  • C08K5/0041—Optical brightening agents, organic pigments
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B5/00—Optical elements other than lenses
  • G02B5/30—Polarising elements
  • G02B5/3025—Polarisers, i.e. arrangements capable of producing a definite output polarisation state from an unpolarised input state
  • G02B5/3033—Polarisers, i.e. arrangements capable of producing a definite output polarisation state from an unpolarised input state in the form of a thin sheet or foil, e.g. Polaroid

Definitions

• the present invention relates to a polyvinyl alcohol film, a method for producing the same, and a stretched film.
• Polyvinyl alcohol films are used in a wide range of applications, including packaging films, water-soluble films, agricultural films, release films, and optical films.
• nitrogen-containing compounds may be blended as dyes or pigments, or the films may be stretched in an aqueous treatment bath that contains an organic metal such as cobalt ions in addition to dyes or pigments, and then used as stretched films (e.g., Patent Document 1).
• General methods for producing PVA-based films include removing the solvent from a solution in which a PVA-based resin and an N-containing compound are dissolved, and immersing a PVA-based film in an aqueous solution containing an N-containing compound and then drying it.
• a conventional PVA-based film is stretched in an aqueous treatment bath, the N-containing compound is likely to come off from the surface of the film, making it difficult to adjust the concentration of the N-containing compound throughout the film and sometimes causing contamination of the aqueous treatment bath. For this reason, such PVA-based films are required to have water resistance that can suppress the come-off of the N-containing compound.
• stretched films obtained by stretching PVA-based films can be widely used not only indoors but also outdoors, they are required to have durability against external environments such as temperature and humidity, i.e., moist heat resistance.
• the stretched film contains an N-containing compound
• the N-containing compound can be decomposed by the influence of the external environment, so better moist heat resistance is required.
• conventional stretched films containing N-containing compounds sometimes did not have sufficient moist heat resistance.
• an object of the present invention is to provide a PVA-based film having excellent water resistance and a method for producing the same.
• Another object of the present invention is to provide a stretched film having excellent resistance to moist heat, a PVA-based film capable of forming the stretched film, and a method for producing the same.
• the present invention includes the following preferred embodiments.
• P MAX the point at which the intensity value of the CN signal derived from the nitrogen-containing compound ( ⁇ ) is maximum
• P MAX the point at which it is minimum
• A represents the intensity value of the CN signal derived from the nitrogen-containing compound ( ⁇ ) at the P min
• B indicates the intensity value of the C 2 H 3 O 2 -signal derived from the polyvinyl alcohol-based resin ( ⁇ ) at the P min
• C represents the intensity value of the CN signal originating from the nitrogen-containing compound ( ⁇ ) in the P MAX
• D indicates the intensity value of the C 2 H 3 O
• a polyvinyl alcohol-based film that satisfies the above requirements.
• the nitrogen-containing compound ( ⁇ ) is a dye or a pigment.
• the polyvinyl alcohol-based resin ( ⁇ 3) is the same as at least one selected from the group consisting of the polyvinyl alcohol-based resin ( ⁇ 1) and the polyvinyl alcohol-based resin ( ⁇ 2).
• a stretched film comprising a polyvinyl alcohol-based resin ( ⁇ ) and a nitrogen-containing compound ( ⁇ ),
• E represents the intensity value of the CN signal derived from the nitrogen-containing compound ( ⁇ ) at the P min
• F represents the intensity value of the C 2 H 3 O 2 -signal derived from the polyvinyl alcohol-based resin ( ⁇ ) at the P min value
• G represents the intensity value of the CN signal originating from the nitrogen-containing compound ( ⁇ ) at the P MAX
• H indicates the intensity value of
• the stretched film according to any one of [9] to [15] which is any one of a polarizing film, a photon upconversion film, and a light control film.
• the PVA-based film of the present invention is excellent in water resistance and can be formed into a stretched film having excellent resistance to moist heat.
• the stretched film of the present invention has excellent resistance to moist heat.
• FIG. 1 shows a schematic cross-sectional view of a PVA-based film according to one embodiment of the present invention.
• 1 shows measurement data of a PVA-based film according to one embodiment of the present invention, measured by TOF-SIMS.
• the polyvinyl alcohol-based film of the present invention contains a polyvinyl alcohol-based resin ( ⁇ ) and a nitrogen-containing compound ( ⁇ ) (hereinafter sometimes abbreviated as compound ( ⁇ )), and has the following formula (I): (C/D)/(A/B) ⁇ 5 (I) [In the formula, at least 20 points equally spaced in the thickness direction within a central 60% range of the film in the thickness direction are measured using a time-of-flight secondary ion mass spectrometer (sometimes referred to as TOF-SIMS), and in the measurement data, the point at which the intensity value of the CN signal derived from compound ( ⁇ ) is maximum is P MAX and the point at which it is minimum is P min .] A represents the intensity value of the CN signal derived from the compound ( ⁇ ) at the P min ; B indicates the intensity value of the C 2 H 3 O 2 -signal derived from the polyvinyl alcohol-based resin ( ⁇ ) at the P min ,
• Figure 1 shows a schematic cross-sectional view of a PVA-based film (100) according to one embodiment of the present invention
• Figure 2 shows measurement data obtained by measuring the PVA-based film (100) according to one embodiment of the present invention by TOF-SIMS.
• a TOF-SIMS the surface layer of a PVA-based film is irradiated with sputtering ions, and sputtering and measurement are alternately repeated to perform composition analysis throughout the entire thickness direction of the film.
• the 20 points are spaced 0.03X apart in the thickness direction.
• the measurement data of TOF-SIMS is represented by cycles on the horizontal axis and intensity on the vertical axis as shown in Fig. 2. Since TOF-SIMS is measured in the entire thickness direction, cycles on the horizontal axis correspond to the thickness of the PVA-based film (100). Therefore, the central 60% range (2) (120 to 480 cycles in Fig. 2) of the horizontal axis (600 cycles in Fig. 2) corresponds to the central 0.6X range of the PVA-based film (100) in Fig. 1.
• the signal intensity ratio (C/D)/(A/B) in formula (I) at least 20 signal intensity values are measured within a range of 60% of the center in the thickness direction, and at least 20 of these equally spaced points are used. For example, in the embodiment of FIG. 2, 360 points (360 cycles) are measured within the range, and 20 of these equally spaced points [(10) and (11) in FIG. 2] are used to calculate the signal intensity ratio (C/D)/(A/B).
• the intensity value (9) of the CN signal originating from compound ( ⁇ ) the point where the intensity value is maximum among the at least 20 points is designated as P MAX ((4) in FIG. 2), and the point where the intensity value is minimum is designated as P min ((7) in FIG.
• the intensity value of the CN signal originating from compound ( ⁇ ) at P min is designated as A ((7) in FIG. 2), and the intensity value of the C 2 H 3 O 2 signal originating from the PVA-based resin ( ⁇ ) at P min is designated as B ((6) in FIG. 2).
• the intensity value of the CN signal originating from compound ( ⁇ ) at P MAX is designated as C ((4) in FIG. 2), and the intensity value of the C 2 H 3 O 2 signal originating from the PVA-based resin ( ⁇ ) at P MAX is designated as D ((5) in FIG. 2).
• the signal intensity ratio (C/D)/(A/B) is calculated from these intensity values A, B, C and D.
• the TOF-SIMS measurement can be carried out, for example, by the method described in the Examples.
• the present inventors have found that, in a PVA-based film containing a PVA-based resin ( ⁇ ) and a compound ( ⁇ ), the water resistance of the PVA-based film and a stretched film obtained by stretching the PVA-based film can be improved and the release of the compound ( ⁇ ) in an aqueous bath can be suppressed when the signal intensity ratio (C/D)/(A/B) is 5 or more. Furthermore, they have found that, when the signal intensity ratio (C/D)/(A/B) is 5 or more, the moist heat resistance of the stretched film obtained by stretching the PVA-based film can be improved and problems such as decomposition of the compound ( ⁇ ) can be suppressed even when the film is left for a long time under high temperature and high humidity.
• the above-mentioned effect is presumed to be due to the fact that the PVA-based film satisfying formula (I) and the stretched film formed from the PVA-based film have a high concentration of compound ( ⁇ ) in the center of the thickness direction, so that compound ( ⁇ ) in the film is less susceptible to the influence of the external environment.
• water resistance refers to the property of being able to suppress the release of compound ( ⁇ ) from the film in water
• moist heat resistance refers to the property of being able to suppress defects such as the decomposition of compound ( ⁇ ) when the film is exposed to high temperature and high humidity.
• the stretched film obtained by stretching the PVA-based film is a polarizing film
• moist heat resistance may be evaluated by measuring the change in the dichroic ratio after exposure to high temperature and high humidity.
• the upper limit and lower limit of the numerical range can be arbitrarily combined.
• the PVA-based film and/or the stretched film may be simply referred to as a film.
• the signal intensity ratio (C/D)/(A/B) of the PVA-based film is less than 5, the water resistance of the PVA-based film and the moist heat resistance and water resistance of the stretched film obtained by stretching the PVA-based film tend to decrease.
• the signal intensity ratio (C/D)/(A/B) can be appropriately selected depending on the concentration of compound ( ⁇ ) and is preferably 10 or more, more preferably 20 or more, even more preferably 30 or more, even more preferably 40 or more, particularly preferably 50 or more, and particularly preferably 60 or more, and may be, for example, 70 or more, 90 or more, 100 or more, 120 or more, 140 or more, 160 or more, or 170 or more.
• the signal intensity ratio (C/D)/(A/B) is equal to or greater than the above lower limit, the water resistance of the PVA-based film and the moist heat resistance and water resistance of the stretched film obtained by stretching the PVA-based film can be improved.
• the signal intensity ratio (C/D)/(A/B) of the PVA-based film is preferably 1000 or less, more preferably 500 or less, and even more preferably 250 or less.
• the film can be easily produced with good productivity while suppressing the production cost of the film.
• the position of C in formula (I) is preferably within the central 50% range in the thickness direction of the film, more preferably within the 40% range, even more preferably within the 30% range, and even more preferably within the 20% range.
• the concentration of compound ( ⁇ ) tends to be higher in the central portion, so that the water resistance of the PVA-based film and the moist heat resistance and water resistance of the stretched film obtained by stretching this film tend to be high.
• the position of A in formula (I) is preferably within the central 20-60% range in the thickness direction of the film, more preferably within the 30-60% range, and even more preferably within the 40-60% range. When the position of A is within the above range, the water resistance of the PVA-based film and the moist heat resistance and water resistance of the stretched film obtained by stretching this film tend to be high.
• the PVA resin ( ⁇ ) is a resin containing a vinyl alcohol polymer.
• the vinyl alcohol polymer is a polymer containing a vinyl alcohol unit as a monomer unit.
• the vinyl alcohol polymer is obtained by saponifying a vinyl ester polymer obtained by polymerizing a vinyl ester monomer, which is a raw material monomer, and the vinyl alcohol polymer after saponification may contain a vinyl ester unit in addition to the vinyl alcohol unit.
• the vinyl alcohol polymer may be a modified vinyl alcohol copolymer containing monomer units other than vinyl alcohol units and vinyl ester units, which is obtained by saponifying a copolymer obtained by copolymerizing a vinyl ester monomer, which is a raw material monomer, with another monomer.
• the PVA resin ( ⁇ ) may also contain multiple types of vinyl alcohol polymers with different physical properties.
• vinyl ester monomers used as raw material monomers for vinyl alcohol polymers include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and vinyl versatate, and among these, vinyl acetate is preferred from the standpoints of ease of production and availability, cost, etc.
• the vinyl alcohol polymer may be a modified vinyl alcohol copolymer containing, in addition to vinyl alcohol units and vinyl ester units, other monomer units other than the vinyl ester units.
• other monomers include ⁇ -olefins such as ethylene, propylene, n-butene, and isobutylene; acrylic acid and its salts; acrylic acid esters; methacrylic acid and its salts; methacrylic acid esters; acrylamide; acrylamide derivatives such as N-methylacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetoneacrylamide, acrylamidopropanesulfonic acid and its salts, acrylamidopropyldimethylamine and its salts or its quaternary salts, and N-methylolacrylamide and its derivatives; methacrylamide; methacrylamide derivatives such as N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidopropanesulfonic
• the other monomer is an ⁇ -olefin such as ethylene.
• the content (modification amount) of these other monomer units varies depending on the purpose and application of use. In one embodiment, the content (modification amount) of the other monomer units is preferably 10 mol% or less, more preferably 5 mol% or less, and is preferably 0 mass% or more, more preferably 0.1 mass% or more, and even more preferably 0.5 mass% or more.
• some of the hydroxyl groups may or may not be crosslinked.
• some of the hydroxyl groups may react with aldehyde compounds such as acetaldehyde and butylaldehyde to form an acetal structure, or they may not react with these compounds to form an acetal structure.
• the PVA-based resin ( ⁇ ) preferably contains at least one vinyl alcohol-based polymer selected from the group consisting of unmodified vinyl alcohol polymers and ⁇ -olefin-vinyl alcohol copolymers, and more preferably contains an ⁇ -olefin-vinyl alcohol copolymer.
• the degree of saponification of the vinyl alcohol polymer contained in the PVA-based resin ( ⁇ ) is preferably 88 mol% or more, more preferably 90 mol% or more, even more preferably 93 mol% or more, even more preferably 96 mol% or more, particularly preferably 97 mol% or more, particularly more preferably 98 mol% or more, particularly more preferably 99 mol% or more, and preferably 99.9 mol% or less, more preferably 99.7 mol% or less, and even more preferably 99.5 mol% or less.
• the degree of saponification of the vinyl alcohol polymer contained in the PVA-based resin ( ⁇ ) is within the above range, the water resistance of the PVA-based film and the moist heat resistance and water resistance of the stretched film are easily improved. In addition, the thermal stability of the PVA-based film is improved, and molding and film formation are easily performed stably.
• the degree of saponification of the vinyl alcohol-based polymer means the ratio (mol%) of the number of moles of the vinyl alcohol unit to the total number of moles of the structural unit (typically a vinyl ester unit) that can be converted into a vinyl alcohol unit by saponification and the vinyl alcohol unit contained in the vinyl alcohol-based polymer.
• the degree of saponification of vinyl alcohol polymers can be measured in accordance with JIS K6726 (1994).
• the viscosity average degree of polymerization (sometimes referred to as degree of polymerization) of the PVA-based resin ( ⁇ ) is preferably 200 or more, more preferably 300 or more, even more preferably 500 or more, even more preferably 800 or more, and particularly preferably 1200 or more, and is preferably 4000 or less, more preferably 3500 or less, and even more preferably 3000 or less.
• degree of polymerization is equal to or more than the above lower limit, the mechanical strength of the film is easily increased, and when the degree of polymerization is equal to or less than the above upper limit, the process passability, stretchability, and film formability during production are easily increased.
• the degree of polymerization of the PVA-based resin ( ⁇ ) can be measured in accordance with JIS-K6726 (1994).
• the polymerization degree of the PVA-based resin ( ⁇ ) means an average polymerization degree calculated from the polymerization degree and blending ratio of each vinyl alcohol-based polymer.
• the polymerization degree of the vinyl alcohol-based polymer is the polymerization degree of the PVA-based resin ( ⁇ ).
• the polymerization degree of the PVA-based resin ( ⁇ ) may be adjusted to the above-mentioned range by mixing vinyl alcohol-based polymers having different polymerization degrees at an appropriate blending ratio.
• the content of the PVA-based resin ( ⁇ ) is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 85% by mass or more, and particularly preferably 87% by mass or more, relative to the mass of the PVA-based film, and is preferably 99.99% by mass or less, more preferably 99.9% by mass or less, even more preferably 99% by mass or less, even more preferably 98% by mass or less, particularly preferably 95% by mass or less, and particularly preferably 93% by mass or less.
• the content of the PVA-based resin ( ⁇ ) is equal to or more than the above lower limit, the film formability of the film is easily improved, and when the content of the PVA-based resin ( ⁇ ) is equal to or less than the above upper limit, the stretchability of the film is easily improved.
• the PVA resin ( ⁇ ) contains a vinyl alcohol polymer.
• the vinyl alcohol polymer can be obtained, for example, by polymerizing a vinyl ester monomer or a vinyl ester monomer with another monomer to obtain a vinyl ester polymer or copolymer (the polymer and the copolymer may be collectively referred to as a vinyl ester polymer), and then saponifying the polymer.
• Methods for polymerizing vinyl ester monomers and the like include known methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization.
• bulk polymerization and solution polymerization which are performed without a solvent or in a solvent such as alcohol, are preferably used.
• alcohols used as a solvent during solution polymerization include lower alcohols such as methanol, ethanol, and propanol.
• initiators used in copolymerization include known initiators such as azo initiators or peroxide initiators, such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethyl-valeronitrile), benzoyl peroxide, and n-propyl peroxydicarbonate.
• the polymerization temperature is not particularly limited, but is preferably in the range of 0° C. to 150° C.
• the vinyl alcohol polymer is an ethylene-vinyl alcohol copolymer or the like, it is preferable to copolymerize a vinyl ester monomer and a monomer such as ethylene by the above-mentioned method.
• the vinyl ester polymer obtained in the polymerization step can be saponified in an organic solvent by alcoholysis or hydrolysis in the presence of a catalyst.
• catalysts used in the saponification step include basic catalysts such as sodium hydroxide, potassium hydroxide, and sodium methoxide; or acidic catalysts such as sulfuric acid, hydrochloric acid, and p-toluenesulfonic acid.
• the organic solvent used in the saponification step is not particularly limited, and examples include alcohols such as methanol and ethanol; esters such as methyl acetate and ethyl acetate; ketones such as acetone and methyl ethyl ketone; and aromatic hydrocarbons such as benzene and toluene.
• the amount of the saponification catalyst used is preferably 0.001 to 0.5 in terms of a molar ratio to the vinyl ester monomer units in the vinyl ester polymer.
• the molar ratio is more preferably 0.002 or more, even more preferably 0.4 or less, and even more preferably 0.3 or less.
• a preferred embodiment of the saponification step is as follows. First, a saponification catalyst such as sodium hydroxide is added to the vinyl ester polymer solution obtained in the polymerization step and mixed.
• the solvent used here is preferably methanol.
• the mixture is first mixed, it is a homogeneous liquid, but as the saponification reaction progresses and the vinyl ester units in the polymer are saponified and converted to vinyl alcohol units, the solubility in the solvent decreases and the polymer precipitates in the solution. At this time, the solution contains methyl acetate produced by alcoholysis with methanol. As the saponification reaction progresses, the amount of polymer precipitated gradually increases and becomes a slurry, after which it loses fluidity. Therefore, in order to allow the saponification reaction to proceed uniformly, it is preferable to mix thoroughly before losing fluidity.
• the method for mixing the vinyl ester polymer solution with the saponification catalyst is not particularly limited, and various methods can be used, such as a static mixer, kneader, or stirring blade, but it is preferable to use a static mixer, as this allows for continuous, uniform mixing.
• a static mixer it is preferable to add the saponification catalyst to the vinyl ester polymer solution after the polymerization step in a pipe connected to the polymerization tank, and then pass the mixture through a static mixer to mix and obtain a paste.
• the temperature of the reaction liquid in the static mixer is usually 20 to 80°C.
• the method of proceeding with the saponification reaction of the vinyl ester polymer in the paste that has passed through the static mixer is not particularly limited, but a method in which the paste is placed on a moving belt and the saponification reaction is proceeded while the belt is moved in a tank maintained at a constant temperature is preferred.
• the paste on the belt loses its fluidity and becomes solid, and the saponification reaction proceeds in the solid state.
• This method allows the saponification reaction to proceed continuously in the solid state, and a solid block containing the vinyl alcohol polymer and the solvent is obtained.
• the saponification temperature is preferably 20 to 60°C, preferably 25°C or higher, more preferably 30°C or higher, and preferably 55°C or lower, more preferably 50°C or lower.
• the saponification time is preferably 5 minutes to 2 hours.
• the saponification time is more preferably 8 minutes or more, even more preferably 10 minutes or more, more preferably 1.5 hours or less, and even more preferably 1 hour or less.
• a washing step may be added to wash the vinyl alcohol polymer in order to remove impurities such as sodium acetate.
• the washing liquid include methanol, acetone, methyl acetate, ethyl acetate, hexane, and water, and among these, methanol, methyl acetate, and water alone or in a mixture are more preferable.
• the amount of washing liquid is usually preferably 30 to 10,000 parts by mass, and more preferably 50 to 3,000 parts by mass, per 100 parts by mass of the vinyl alcohol polymer.
• the washing temperature is preferably 5 to 80°C, and more preferably 20 to 70°C.
• the washing time is preferably 20 minutes to 10 hours, and more preferably 1 hour to 6 hours.
• Known methods such as a batch method and a countercurrent washing method can be used as the washing method. Note that a commercially available vinyl alcohol polymer can also be used.
• the PVA-based film of the present invention contains one or more nitrogen-containing compounds ( ⁇ ).
• the compound ( ⁇ ) is a compound containing a nitrogen element (N element) and can impart optical properties (such as polarizing properties or luminescence properties) to the film.
• the nitrogen-containing compound ( ⁇ ) is not limited as long as it contains an N element, but it is preferable that the compound ( ⁇ ) has an aromatic ring from the viewpoint of easily improving the water resistance and optical properties of the PVA-based film, and the moist heat resistance, water resistance and optical properties of the stretched film. Examples of the aromatic ring include an aromatic hydrocarbon ring or an aromatic heterocycle.
• the compound ( ⁇ ) may have one or more aromatic rings.
• aromatic hydrocarbon rings examples include monocyclic aromatic hydrocarbon rings, condensed polycyclic aromatic hydrocarbon rings, and ring-assembly aromatic hydrocarbon rings.
• Examples of monocyclic aromatic hydrocarbon rings include a benzene ring, and examples of condensed polycyclic aromatic hydrocarbon rings include a naphthalene ring, an anthracene ring, a phenanthrene ring, a tetracene ring, a pyrene ring, a perylene ring, a tetracene ring, a benzpyrene ring, a chrysene ring, a triphenylene ring, an acenaphthene ring, a fluoranthene ring, and a fluorene ring.
• a ring-assembled aromatic hydrocarbon ring means two or more monocyclic aromatic hydrocarbon rings, two or more condensed polycyclic aromatic hydrocarbon rings, or one or more monocyclic aromatic hydrocarbon rings and one or more condensed polycyclic aromatic hydrocarbon rings bonded to each other via a single bond, and examples of such rings include a biphenyl ring, a phenylnaphthyl ring, a terphenyl ring, a perylene ring, a phenylanthracene ring, and a diphenylanthracene ring.
• aromatic heterocycles include monocyclic aromatic heterocycles, condensed polycyclic aromatic heterocycles, and ring-assembly aromatic heterocycles.
• Monocyclic aromatic heterocycles contain at least one heteroatom selected from sulfur, nitrogen, and oxygen atoms, and examples thereof include pyrrole rings, pyrazole rings, imidazole rings, pyridine rings, pyrazine rings, pyridazine rings, pyrimidine rings, triazine rings, isocyanuric rings, diazabenzene rings, furan rings, thiophene rings, azole rings, diazole rings, triazole rings, oxazole rings, oxadiazole rings, and thiadiazole rings.
• the fused polycyclic aromatic heterocycle contains at least one heteroatom selected from a sulfur atom, a nitrogen atom, and an oxygen atom.
• heteroatom selected from a sulfur atom, a nitrogen atom, and an oxygen atom.
• Examples thereof include a Bodipy ring, a fullerene ring, a porphyrin ring, an azanaphthalene (quinoline) ring, a diazanaphthalene ring, a carbazole ring, a dibenzofuran ring, a dibenzothiophene ring, a dibenzosilole ring, a phenoxazine ring, a phenothiazine ring, an acridine ring, an indole ring, a pyrroloimidazole ring, a pyrrolopyrazole ring, a pyrrolopyrrole ring, a thienopyrrole ring, a thien
• the ring assembly aromatic heterocycle includes not only two or more monocyclic aromatic heterocycles, two or more condensed polycyclic aromatic heterocycles, or one or more monocyclic aromatic heterocycles and one or more condensed polycyclic aromatic heterocycles bonded to each other via a single bond, but also one or more monocyclic aromatic hydrocarbon rings and one or more condensed polycyclic aromatic heterocycles, or one or more monocyclic aromatic heterocycles and one or more condensed polycyclic aromatic hydrocarbon rings bonded to each other via a single bond.
• ring assembly aromatic heterocycles include bipyridine rings, terpyridine rings, tetraphenylporphyrin rings, and phthalocyanine rings.
• the aromatic ring preferably includes at least one selected from a monocyclic aromatic hydrocarbon ring, a condensed polycyclic aromatic hydrocarbon ring, a ring assembly aromatic hydrocarbon ring, a condensed polycyclic aromatic heterocycle, and a ring assembly aromatic heterocycle, from the viewpoint of easily improving the water resistance, moist heat resistance, and optical properties of the PVA-based film, and the water resistance, moist heat resistance, and optical properties of the stretched film.
• the aromatic ring preferably includes at least one selected from the group consisting of a benzene ring, a naphthalene ring, an anthracene ring, a pyrene ring, a perylene ring, a tetracene ring, a bodipy ring, a porphyrin ring, a phthalocyanine ring, a biphenyl ring, a phenylnaphthyl ring, a phenylanthracene ring, a diphenylanthracene ring, and a tetraphenylporphyrin ring, from the viewpoint of easily improving the water resistance, moist heat resistance, and optical properties of the film, and more preferably includes at least one selected from the group consisting of a benzene ring, a naphthalene ring, a biphenyl ring, a diphenylanthracene ring, from the viewpoint of easily
• aromatic ring contains a porphyrin ring, a phthalocyanine ring, or a fullerene ring
• these rings may contain metal atoms such as Pt, Pd, Zn, Ru, Re, Ir, Os, Cu, Ni, Co, Cd, Au, Ag, Sn, Sb, Pb, P, and As.
• the aromatic ring may have a substituent (referred to as "substituent A").
• the aromatic ring may have one or more substituents A.
• halogen atoms include fluorine, chlorine, bromine, and iodine atoms.
• alkyl groups include alkyl groups having 1 to 12 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, 2-methylbutyl, 3-methylbutyl, 2-ethylpropyl, and n-hexyl, and preferably alkyl groups having 1 to 8 carbon atoms.
• alkylene groups include alkylene groups having 1 to 10 carbon atoms, such as ethylene, propylene, trimethylene, butylene, isobutylene, pentylene, hexylene, heptylene, octylene, nonylene, and decylene, and preferably alkylene groups having 1 to 5 carbon atoms.
• alkoxy group examples include alkoxy groups having 1 to 12 carbon atoms, such as methoxy, ethoxy, propyloxy, isopropyloxy, n-butoxy, isobutoxy, sec-butoxy, tert-butoxy, pentyloxy, hexyloxy, and cyclohexyloxy, preferably alkoxy groups having 1 to 8 carbon atoms, and more preferably alkoxy groups having 1 to 4 carbon atoms.
• aryl group examples include phenyl, tolyl, naphthyl, and biphenyl groups.
• alkylamino group examples include amino groups having an alkyl chain with 1 to 12 carbon atoms, preferably amino groups having an alkyl chain with 1 to 8 carbon atoms.
• alkylene oxide group examples include ethylene oxide and propylene oxide groups.
• the nitrogen-containing compound ( ⁇ ) preferably contains at least one selected from the group consisting of a compound represented by the following formula (1), a compound represented by the following formula (2), and a compound represented by the following formula (6), and more preferably contains a compound represented by the following formula (1).
• Ar a , Ar b , and Ar c each independently represent an aryl group which may have a substituent.
• R 1 to R 4 each independently represent a hydrogen atom, a cyano group, a halogen atom, an amino group having an alkyl chain having 1 to 8 carbon atoms, an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an ethylene oxide chain represented by formula (3) or formula (4) below, or an ammonium ion represented by formula (5) below, l and m each independently represent an integer of 1 to 4, and n and o each independently represent an integer of 1 to 5.
• R5 represents an alkyl group having 1 to 3 carbon atoms
• p represents an integer of 1 to 4
• * represents a bond.
• R 6 and R 7 each independently represent an alkyl group having 1 to 3 carbon atoms
• q and r each independently represent an integer of 1 to 4, and * represents a bond.
• R 12 to R 19 each independently represent a hydrogen atom, a cyano group, a halogen atom, an amino group having an alkyl chain of 1 to 8 carbon atoms, an alkyl group of 1 to 12 carbon atoms, an alkoxy group of 1 to 12 carbon atoms, or an ethylene oxide chain represented by the following formula (7);
• M represents a hydrogen atom, palladium, platinum, copper, or zinc;
• Ar 1 to Ar 4 each independently represent a hydrogen atom, a substituent represented by the following formula (8), formula (9), or formula (10), or an ammonium ion represented by the following formula (11)]
• R 20 represents an alkyl group having 1 to 3 carbon atoms, t represents an integer of 1 to 4, and * represents a bond.
• R 21 represents an alkyl group having 1 to 3 carbon atoms, u represents an integer of
• the aryl groups of Ar a , Ar b , and Ar c in formula (1) include, for example, groups in which one hydrogen atom has been removed from the above aromatic ring, preferably groups in which one hydrogen atom has been removed from a benzene ring, a naphthalene ring, or a biphenyl ring.
• substituents that the aryl group may have include those exemplified as the above substituent A.
• Ar a , Ar b , and Ar c in formula (1) are represented by formula (a), formula (b), and formula (c), respectively.
• R a to R v each independently represent a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, an aryl group, an amino group, a hydroxyl group, a sulfo group, or a salt thereof, and * represents a bond.
• alkyl group alkoxy group and aryl group in R a to R v
• those exemplified above as the alkyl group, alkoxy group and aryl group for the substituent A can be mentioned, respectively.
• Rb , Rd , Re , Rm, Rk , Rj , Rp , Rq , Rr , Rs , Rv , and Ru each represent a hydrogen atom
• Ra , Rc , Rf , Rq , Rh , Ri , Rl , Rn , Ro , and Rt each independently represent a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, an aryl group, an amino group, a hydroxyl group, a sulfo group, or a salt thereof
• Rb , Rd , Re , Rm, Rk , Rj , Rp , Rq , Rr , Rs , Rv , and Ru each represent a hydrogen atom
• Examples of compounds represented by formula (1) include Direct Black 17, 19, 154; Direct Brown 44, 106, 195, 210, 223; Direct Red 2, 23, 28, 31, 37, 39, 79, 81, 240, 242, 247; Direct Blue 1, 15, 22, 78, 90, 98, 151, 168, 202, 236, 249, 270; Direct Violet 9, 12, 51, 98; Direct Green 1, 85; Direct Yellow 8, 12, 44, 86, 87; Direct Orange 26, 39, 106, 107, etc.
• Direct Blue 15 is preferred from the viewpoint of improving the water resistance of the PVA-based film, and the optical properties (particularly the polarization performance), water resistance, and moist heat resistance of the stretched film.
• Nitrogen-containing compounds ( ⁇ ) having hydrophilic groups such as alkoxy groups; alkylene oxide chains such as ethylene oxide chains and propylene oxide chains; hydroxyl groups; carboxyl groups; amino groups; and ammonium ions are water-soluble and therefore suitable for use in wet stretching of films.
• the degree of water solubility can also be controlled by appropriately selecting the number of these functional groups and the chain length of the alkylene oxide chain.
• the compounds represented by formula (1), formula (2), and formula (3) may be produced by conventional methods or commercially available products may be used.
• the compound ( ⁇ ) is not particularly limited, but is preferably a dye or a pigment.
• the compound ( ⁇ ) when the compound ( ⁇ ) is a dye or a pigment, the compound ( ⁇ ) can act as a dichroic pigment, so that the stretched film obtained by stretching the PVA-based film can be a polarizing film.
• the PVA-based film when the compound ( ⁇ ) is a dye or a pigment, the PVA-based film can be a photon up-conversion film by containing two or more compounds ( ⁇ ) that function as donors or acceptors.
• the compound ( ⁇ ) when the compound ( ⁇ ) contains a compound represented by the formula (1), it is likely to function as a dichroic pigment, and when the compound ( ⁇ ) contains a compound represented by the formula (2) and a compound represented by the formula (3), it is likely to function as a donor and an acceptor of a photon up-conversion film, respectively.
• photon up-conversion refers to the phenomenon of converting low-energy light into high-energy light.
• optical properties refer to optical properties, and in the case where the stretched film obtained by stretching a PVA-based film is a polarizing film, it refers to polarization performance, etc., and in the case where it is a photon up-conversion film, it refers to luminous efficiency, etc.
• the content of the nitrogen-containing compound ( ⁇ ) is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, even more preferably 0.07 parts by mass or more, even more preferably 0.1 parts by mass or more, and is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, even more preferably 10 parts by mass or less, even more preferably 5 parts by mass or less, and particularly preferably 1 part by mass or less, relative to 100 parts by mass of the PVA-based resin ( ⁇ ).
• the content of the compound ( ⁇ ) is equal to or more than the above lower limit, the optical properties of the film are easily improved, and when the content of the compound ( ⁇ ) is equal to or less than the above upper limit, the film can be easily produced with good productivity while suppressing the production cost of the film.
• the content of the compound ( ⁇ ) based on the mass of the PVA-based film may also be selected from the above range.
• the PVA-based film of the present invention contains a PVA-based resin ( ⁇ ) and a nitrogen-containing compound ( ⁇ ) and satisfies the formula (I), and therefore has excellent water resistance. Therefore, when the PVA-based film is stretched in an aqueous bath, the compound ( ⁇ ) can be prevented from being released from the surface layer of the film, making it easy to adjust the concentration of the compound ( ⁇ ) in the entire film and preventing the aqueous bath from being contaminated.
• the PVA-based film of the present invention can also form a stretched film with excellent moist heat resistance. Therefore, even if the stretched film is exposed to high temperature and high humidity for a long period of time, the compound ( ⁇ ) can be prevented from causing problems such as decomposition.
• the PVA-based film of the present invention can also form a stretched film with excellent water resistance, and can prevent the compound ( ⁇ ) from being released from the surface layer of the stretched film in water or an aqueous solution. Therefore, the aqueous bath can be prevented from being contaminated when the stretched film is treated in the aqueous bath. Therefore, the PVA-based film of the present invention can be suitably used as a polarizing film, a photon up-conversion film, etc.
• the PVA-based film of the present invention has excellent water resistance and can suppress the release of compound ( ⁇ ) in an aqueous solution. Therefore, the absorbance X of the pure water after the PVA-based film is immersed in pure water at 30°C for 5 minutes and the film is removed is small.
• the absorbance X is the maximum absorbance in the visible light wavelength region (380 to 750 nm) of the pure water after the PVA-based film is immersed.
• the wavelength (maximum absorption wavelength) at the absorbance X coincides with the maximum absorption wavelength of the compound ( ⁇ ) released in the pure water.
• the absorbance X (Abs) of the pure water after the PVA-based film is immersed is preferably 0.01 or less, more preferably 0.005 or less, and even more preferably 0.003 or less.
• the absorbance X can be measured, for example, by the method described in the Examples.
• the PVA-based film of the present invention can form a stretched film with excellent moist heat resistance. Therefore, when compound ( ⁇ ) is a dye or pigment, the change in the dichroic ratio before and after a moist heat resistance test (sometimes referred to as ⁇ dichroic ratio) can be suppressed.
• the ⁇ dichroic ratio before and after leaving the PVA-based film of the present invention in an atmosphere at a temperature of 60° C. and a humidity of 90% for 500 hours is preferably less than 10, more preferably 8 or less, and even more preferably 6 or less, and may be, for example, 5 or less or 4 or less.
• the ⁇ dichroic ratio can be measured, for example, by the method described in the Examples.
• the PVA-based film of the present invention can form a stretched film with excellent water resistance. Therefore, the absorbance Y of the pure water after the stretched film is immersed in pure water at 50°C for 15 minutes and the film is removed is small.
• the absorbance Y is the maximum absorbance in the visible light wavelength region (380 to 750 nm) of the pure water after the stretched film is immersed.
• the wavelength (maximum absorption wavelength) at the absorbance Y coincides with the maximum absorption wavelength of the compound ( ⁇ ) released in the pure water.
• the absorbance Y (Abs) of the pure water after the stretched film is immersed is preferably 0.003 or less, more preferably 0.002 or less.
• the absorbance Y can be measured, for example, by the method described in the Examples.
• the PVA-based film of the present invention may further contain a plasticizer.
• plasticizers include polyhydric alcohols such as ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, and trimethylolpropane, and the PVA-based film of the present invention may contain one or more of these plasticizers.
• glycerin is preferred from the viewpoint of being easy to improve stretchability.
• the content of the plasticizer is preferably 1 part by mass or more, more preferably 3 parts by mass or more, even more preferably 5 parts by mass or more, even more preferably 7 parts by mass or more, and preferably 30 parts by mass or less, more preferably 25 parts by mass or less, even more preferably 20 parts by mass or less, even more preferably 15 parts by mass or less, and particularly preferably 12 parts by mass or less, per 100 parts by mass of the PVA-based resin ( ⁇ ).
• the content of the plasticizer is equal to or more than the above lower limit, the stretchability of the PVA-based film is easily improved, and when the content of the plasticizer is equal to or less than the above upper limit, it is advantageous from the viewpoint of handleability.
• the content of the plasticizer based on the mass of the PVA-based film may also be selected from the above range.
• the PVA-based film of the present invention may further contain a surfactant.
• a surfactant By containing a surfactant, the film-forming properties during film production are improved, making it easier to suppress the occurrence of uneven thickness in the PVA-based film, and it also makes it easier to peel the PVA-based film from the rolls and belts used in film production.
• surfactants anionic surfactants or nonionic surfactants are preferred from the viewpoint of improving the peelability from rolls, belts, etc. during film production.
• anionic surfactants include carboxylic acid types such as potassium laurate; sulfate ester types such as polyoxyethylene lauryl ether sulfate and octyl sulfate; and sulfonic acid types such as dodecylbenzenesulfonate.
• nonionic surfactants include alkyl ether types such as polyoxyethylene oleyl ether; alkyl phenyl ether types such as polyoxyethylene octylphenyl ether; alkyl ester types such as polyoxyethylene laurate; alkyl amine types such as polyoxyethylene lauryl amino ether; alkyl amide types such as polyoxyethylene lauric acid amide; polypropylene glycol ether types such as polyoxyethylene polyoxypropylene ether; alkanolamide types such as oleic acid diethanolamide; and allyl phenyl ether types such as polyoxyalkylene allyl phenyl ether.
• the surfactants can be used alone or in combination of two or more.
• the content of the surfactant is preferably 0.01 parts by mass or more, more preferably 0.02 parts by mass or more, even more preferably 0.05 parts by mass or more, and preferably 5 parts by mass or less, more preferably 1 part by mass or less, even more preferably 0.5 parts by mass or less, and even more preferably 0.3 parts by mass or less, relative to the PVA-based resin ( ⁇ ).
• the content of the surfactant is equal to or more than the above lower limit, the film-forming property and peelability during film production are easily improved.
• the content of the surfactant is equal to or less than the above upper limit, the surfactant can be prevented from bleeding out onto the film surface and causing blocking, and the handleability is easily improved.
• the content of the surfactant based on the mass of the PVA-based film may also be selected from the above range.
• the PVA-based film of the present invention may further contain additives such as antioxidants, antifreeze agents, pH adjusters, masking agents, color inhibitors, oils, and resins other than PVA-based resins, as necessary.
• additives such as antioxidants, antifreeze agents, pH adjusters, masking agents, color inhibitors, oils, and resins other than PVA-based resins, as necessary.
• the content of the additives is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less, relative to the mass of the PVA-based film, and is preferably 0.01% by mass or more.
• the PVA-based film of the present invention may be a monolayer film or a multilayer film as long as it satisfies formula (I).
• the composition and thickness of the films constituting the multilayer film may be the same or different for each film.
• the interface between the films in the multilayer film may be completely or partially invisible. That is, the interface between the films may be invisible during production, and the film may appear to be a monolayer film.
• the PVA-based resin ( ⁇ ) and the compound ( ⁇ ) are each contained in at least one film constituting the multilayer film so that the multilayer film itself satisfies formula (I), and preferably the PVA-based resin ( ⁇ ) is contained in all films.
• the mass of the PVA-based film as a reference in the respective contents of the PVA-based resin ( ⁇ ) and the additive means the mass of the entire multilayer film, and in the respective contents of the compound ( ⁇ ), the plasticizer, and the surfactant, the mass of the PVA-based resin ( ⁇ ) as a reference means the mass of the PVA-based resin ( ⁇ ) contained in the entire multilayer film (i.e., the total amount of the PVA-based resin ( ⁇ ) contained in the multilayer film).
• these contents may be calculated taking into consideration the amounts charged when forming the multilayer film and the thickness of the layers or films that make up the multilayer film.
• Examples of the method for adjusting the concentration within the range of formula (I) include, in the case of a multilayer PVA-based film, a method for adjusting the order, composition and thickness of layers or film so that a portion having a high concentration of compound ( ⁇ ) based on the concentration of PVA-based resin ( ⁇ ) is located within a central 60% of the film in the thickness direction; and, in the case of a monolayer film, a method for partially removing compound ( ⁇ ) from a PVA-based film containing compound ( ⁇ ) so that a portion having a high concentration of compound ( ⁇ ) based on the concentration of PVA-based resin ( ⁇ ) is located within a central 60% of the film in the thickness direction.
• the PVA-based film is preferably a multilayer film.
• the multilayer film may be a multilayer film whose interface is not visible, that is, a film that appears to be a single layer film.
• the monolayer film may be, for example, a monolayer PVA-based film containing a PVA-based resin ( ⁇ ) and a compound ( ⁇ ).
• a PVA-based film A having, in this order, a PVA-based film 1 containing a PVA-based resin ( ⁇ 1)/a PVA-based resin layer containing a PVA-based resin ( ⁇ 3) and a compound ( ⁇ )/a PVA-based film 2 containing a PVA-based resin ( ⁇ 2);
• a PVA-based film B having, in this order, a PVA-based film 1 containing a PVA-based resin ( ⁇ 1)/a PVA-based resin layer containing a PVA-based resin ( ⁇ 3) and a compound ( ⁇ 1)/a PVA-based film 2 containing a PVA-based resin ( ⁇ 2)/a PVA-based resin layer containing a PVA-based resin ( ⁇ 4) and a compound ( ⁇ 2)/a PVA-based film 3 containing a PVA-based resin ( ⁇ 5);
• the PVA-based resin ( ⁇ 3) is preferably the same as at least one selected from the group consisting of the PVA-based resin ( ⁇ 1) and the PVA-based resin ( ⁇ 2), and more preferably the same as both the PVA-based resin ( ⁇ 1) and the PVA-based resin ( ⁇ 2).
• the PVA-based film 1 and the PVA-based film 2 do not contain the compound ( ⁇ ) as an essential component, but the PVA-based film 1 and/or the PVA-based film 2 may contain the compound ( ⁇ ) to the extent that formula (I) is satisfied.
• the PVA-based resin ( ⁇ 3) and the PVA-based resin ( ⁇ 4) are preferably the same as at least one selected from the group consisting of the PVA-based resin ( ⁇ 1), the PVA-based resin ( ⁇ 2) and the PVA-based resin ( ⁇ 5), from the viewpoint of easily increasing the water resistance of the PVA-based film and the moist heat resistance and water resistance of the stretched film, more preferably the same as at least two, and even more preferably the same as all. Furthermore, the PVA-based resin ( ⁇ 3) and the PVA-based resin ( ⁇ 4) may be the same or different.
• the compounds ( ⁇ 1) and ( ⁇ 2) may be the same or different, but are preferably the same from the viewpoint of easily increasing the water resistance of the PVA-based film and the moist heat resistance and water resistance of the stretched film.
• PVA-based film B does not contain compound ( ⁇ ) as an essential component in PVA-based films 1, 2, and 3, but at least one of PVA-based films 1, 2, and 3 may contain compound ( ⁇ ) as long as formula (I) is satisfied.
• the number of films and layers constituting the multilayer film is not particularly limited, but is preferably 2 or more, more preferably 3 or more, and preferably 9 or less, more preferably 7 or less, and even more preferably 5 or less.
• the PVA-based film of the present invention may contain other films or layers on one or both sides.
• the thickness of the PVA-based film of the present invention can be appropriately selected depending on the application, and is preferably 1 ⁇ m or more, more preferably 5 ⁇ m or more, even more preferably 10 ⁇ m or more, even more preferably 20 ⁇ m or more, particularly preferably 30 ⁇ m or more, especially more preferably 40 ⁇ m or more, and preferably 250 ⁇ m or less, more preferably 150 ⁇ m or less, even more preferably 100 ⁇ m or less, and even more preferably 80 ⁇ m or less. If the thickness of the PVA-based film is equal to or greater than the above lower limit, breakage is unlikely to occur during stretching, and the water resistance of the PVA-based film, as well as the moist heat resistance and water resistance of the stretched film, are easily improved.
• the thickness of the PVA-based film is equal to or less than the above upper limit, the stretched film can be easily produced with good productivity, which is advantageous from the viewpoint of optical properties and thinning.
• the thickness of the PVA-based film means the thickness of the multilayer film itself (i.e., the total thickness of the films constituting the multilayer film).
• the thickness of the PVA-based film can be measured using a film thickness meter, for example, by the method described in the Examples.
• the method for producing the PVA-based film of the present invention is not particularly limited, but may include a method for laminating layers or films so as to satisfy formula (I).
• the production method of the present invention will be described below using a preferred embodiment of the present invention, but the present invention is not limited to this embodiment.
• the PVA-based film of the present invention can be produced by a method including a step of laminating a PVA-based film 1 containing a PVA-based resin ( ⁇ 1) and a PVA-based film 2 containing a PVA-based resin ( ⁇ 2) via a PVA-based resin aqueous solution (sometimes referred to as a PVA-based aqueous solution) containing a PVA-based resin ( ⁇ 3) and a compound ( ⁇ ).
• the resulting PVA-based film is the above-mentioned PVA-based film A [PVA-based film 1/PVA-based resin layer/PVA-based film 2].
• the interface between each film or layer may not be observed.
• the PVA-based film 1 used in the above process can be obtained by forming a film from a film-forming stock solution containing the PVA-based resin ( ⁇ 1).
• the PVA-based film 2 can be obtained by forming a film from a film-forming stock solution containing the PVA-based resin ( ⁇ 2).
• the film-forming stock solution can be prepared by mixing the PVA-based resin ( ⁇ 1) or the PVA-based resin ( ⁇ 2), and optionally the plasticizer, the surfactant, the additive, and the liquid solvent.
• liquid solvents include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, and diethylenetriamine. These liquid solvents can be used alone or in combination of two or more. Among these, water is preferably used from the viewpoint of environmental load and recoverability.
• the volatile fraction (water content) of the film-forming solution varies depending on the film-forming method and film-forming conditions, but is generally preferably 50 to 95% by mass, more preferably 55 to 85% by mass, and even more preferably 60 to 80% by mass. If the volatile fraction of the film-forming solution is equal to or greater than the lower limit, it is easy to prevent the viscosity of the film-forming solution from becoming too high, which would make filtration and degassing difficult when preparing the film-forming solution, and is advantageous from the viewpoint of producing a film with fewer foreign matter and defects. If the volatile fraction of the film-forming solution is equal to or less than the upper limit, it is easy to prevent the concentration of the film-forming solution from becoming too low, which would make industrial film production difficult.
• a wet film-forming method, a gel film-forming method, a casting film-forming method, an extrusion film-forming method, or the like can be used.
• a combination of these methods can also be used.
• the casting film-forming method or the extrusion film-forming method is preferred because it is easy to obtain a PVA-based film that is uniform in thickness and width and has good physical properties.
• Specific film-forming methods include, but are not limited to, using a T-type slit die, hopper plate, I-die, lip coater die, etc. to uniformly extrude the film-forming solution onto the peripheral surface of a rotating heated roll or belt, and then evaporating volatile components from one side of the film extruded onto the roll or belt to dry it into a film, or, after drying in this manner, further drying on the peripheral surface of one or more rotating rolls, or further drying by passing through a hot air dryer to produce a film.
• heat treatment may be performed with another roll or hot air.
• the surface temperature of the roll or belt used for film production is preferably 50°C or higher, more preferably 60°C or higher, even more preferably 65°C or higher, even more preferably 70°C or higher, and is preferably 120°C or lower, more preferably 100°C or lower, even more preferably 95°C or lower, and even more preferably 90°C or lower. If the surface temperature is above the lower limit above, moisture can be easily removed with good productivity. Also, if the surface temperature is below the upper limit above, it is easy to prevent surface unevenness caused by rapid evaporation of moisture.
• PVA-based film 1 and PVA-based film 2 used in the above process can be produced.
• the PVA-based aqueous solution used in the above process can be prepared by mixing the PVA-based resin ( ⁇ 3), the compound ( ⁇ ), and, optionally, the plasticizer, the surfactant, the additive, and the liquid solvent.
• the content of the PVA-based resin in the PVA-based aqueous solution is not particularly limited, but may be, for example, 1 to 50 mass%, preferably 3 to 20 mass%, relative to the mass of the PVA-based aqueous solution.
• the content of the PVA-based resin ( ⁇ 3) is within the above range, it is easy to increase the adhesion between the PVA-based film 1 and the PVA-based film 2, and it is easy to obtain a PVA-based film with excellent adhesion.
• the PVA-based film 1 and the PVA-based film 2 are laminated via the PVA-based aqueous solution.
• the lamination method is not particularly limited, but examples include a method of laminating the PVA-based film 1 and the PVA-based film 2 using a laminator, nip rolls, etc. while dropping a PVA-based aqueous solution between them; a method of dropping or applying a PVA-based aqueous solution to one or both of the PVA-based film 1 and the PVA-based film 2, and then laminating both films; and the like.
• a method of laminating the PVA-based film 1 and the PVA-based film 2 using a laminator or the like while dropping a PVA-based aqueous solution between them is preferred.
• the temperature during lamination for example, the lamination temperature, can be appropriately selected depending on the composition and combination of the films to be laminated, and is preferably 15 to 40°C, more preferably 15 to 30°C.
• After laminating the films they may be dried with a dryer or the like.
• the drying temperature is not particularly limited and may be, for example, 30 to 100°C, preferably 40 to 80°C.
• the PVA-based resin ( ⁇ 3) contained in the PVA-based film A is preferably the same as at least one selected from the group consisting of the PVA-based resin ( ⁇ 1) and the PVA-based resin ( ⁇ 2), and more preferably the same as both the PVA-based resin ( ⁇ 1) and the PVA-based resin ( ⁇ 2). In this form, handling problems such as curling are less likely to occur.
• the PVA-based films 1 and 2 do not contain the compound ( ⁇ ), but may contain the compound ( ⁇ ) as long as formula (I) is satisfied.
• the thicknesses of the PVA-based films 1 and 2 may be the same or different, but are preferably the same from the viewpoint of ease of adjustment to the range of formula (I).
• each of the PVA-based films 1 and 2 is preferably 0.5 ⁇ m or more, more preferably 3 ⁇ m or more, even more preferably 5 ⁇ m or more, even more preferably 10 ⁇ m or more, particularly preferably 15 ⁇ m or more, especially more preferably 20 ⁇ m or more, and is preferably 130 ⁇ m or less, more preferably 80 ⁇ m or less, even more preferably 50 ⁇ m or less, and even more preferably 40 ⁇ m or less.
• the thickness of the PVA-based resin layer formed from the PVA-based aqueous solution is preferably 0.30 ⁇ m or more, more preferably 0.40 ⁇ m or more, even more preferably 0.50 ⁇ m or more, and is preferably 20 ⁇ m or less, more preferably 10 ⁇ m or less, even more preferably 5 ⁇ m or less, and even more preferably 3 ⁇ m or less.
• the present invention includes a PVA-based resin ( ⁇ ) and a nitrogen-containing compound ( ⁇ ), and the PVA-based resin ( ⁇ ) is represented by the following formula (II): (G/H)/(E/F)>3 (II) [In the formula, at least 20 points equally spaced in the thickness direction within a central 60% range of the stretched film in the thickness direction are measured by TOF-SIMS, and in the measurement data, the point at which the intensity value of the CN signal derived from the nitrogen-containing compound ( ⁇ ) is maximum is P MAX and the point at which the intensity value is minimum is P min .]
• E represents the intensity value of the CN signal derived from the nitrogen-containing compound ( ⁇ ) at the P min ;
• F represents the intensity value of the C 2 H 3 O 2 -signal derived from the polyvinyl alcohol-based resin ( ⁇ ) at the P min value ;
• G represents the intensity value of the CN signal originating from the nitrogen-containing compound ( ⁇ ) at the P MAX ; H
• the inventors have found that in a stretched film containing a PVA-based resin ( ⁇ ) and a compound ( ⁇ ), when the signal intensity ratio (G/H)/(E/F) exceeds 3, the moist heat resistance can be improved and problems such as decomposition of the compound ( ⁇ ) can be suppressed even when the film is left in a high-temperature and high-humidity environment for a long period of time.
• the inventors have found that when the signal intensity ratio (G/H)/(E/F) exceeds 3, the water resistance can also be improved and the release of the compound ( ⁇ ) in water or an aqueous solution can be suppressed, so that, for example, contamination of the aqueous bath can be prevented when the stretched film is treated in the aqueous bath.
• a stretched film satisfying formula (II) has a high concentration of the compound ( ⁇ ) in the center in the thickness direction, and therefore the compound ( ⁇ ) in the film is less susceptible to the effects of the external environment.
• the signal intensity ratio (G/H)/(E/F) is 3 or less, the moist heat resistance and water resistance of the stretched film tend to decrease.
• the signal intensity ratio (G/H)/(E/F) can be appropriately selected depending on the concentration of the compound ( ⁇ ), etc., and is preferably 4 or more, more preferably 5 or more, and even more preferably 7 or more, for example, 10 or more, 13 or more, 15 or more, or 17 or more. If the signal intensity ratio (G/H)/(E/F) is equal to or greater than the above lower limit, the moist heat resistance and water resistance of the stretched film can be improved.
• the signal intensity ratio (G/H)/(E/F) is preferably equal to or less than 300, more preferably equal to or less than 100, even more preferably equal to or less than 50, even more preferably equal to or less than 40, and particularly preferably equal to or less than 25. If the signal intensity ratio (G/H)/(E/F) is equal to or less than the above upper limit, the film can be produced with good productivity while suppressing the production cost of the film.
• the position of G in formula (I) is preferably within the central 50% range in the thickness direction of the film, more preferably within the 40% range, even more preferably within the 30% range, and even more preferably within the 20% range.
• the concentration of compound ( ⁇ ) tends to be higher in the central portion, and the stretched film is likely to have high moist heat resistance and water resistance.
• the position of E in formula (I) is preferably within the central 20-60% range in the thickness direction of the film, more preferably within the 30-60% range, and even more preferably within the 40-60% range. When the position of E is within the above range, the stretched film is likely to have high moist heat resistance and water resistance.
• the left side of formula (II) is obtained by replacing (C/D)/(A/B) in formula (I) with (G/H)/(E/F), and the left side of formula (II) can be obtained by performing TOF-SIMS measurement in the same manner as formula (I).
• the PVA-based resin ( ⁇ ) contained in the stretched film satisfying the formula (II) is the same as the PVA-based resin ( ⁇ ) contained in the PVA-based film satisfying the formula (I).
• the nitrogen-containing compound ( ⁇ ) contained in the stretched film satisfying formula (II) is the same as the nitrogen-containing compound ( ⁇ ) contained in the PVA-based film satisfying formula (I). That is, the nitrogen-containing compound ( ⁇ ) contained in the stretched film preferably has the aromatic ring and/or is a dye or a pigment.
• the content of the PVA-based resin ( ⁇ ) in the stretched film is preferably 65% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 85% by mass or more, particularly preferably 90% by mass or more, particularly more preferably 95% by mass or more, especially more preferably 97% by mass or more, and is preferably 99.99% by mass or less, more preferably 99.9% by mass or less.
• the content of the PVA-based resin ( ⁇ ) is equal to or more than the above lower limit, the mechanical strength, moist heat resistance, and water resistance of the stretched film are easily improved, and when the content of the PVA-based resin ( ⁇ ) is equal to or less than the above upper limit, the optical properties of the stretched film are easily improved.
• the content of the nitrogen-containing compound ( ⁇ ) contained in the stretched film is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, even more preferably 0.07 parts by mass or more, particularly preferably 0.1 parts by mass or more, and is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, even more preferably 10 parts by mass or less, even more preferably 5 parts by mass or less, particularly preferably 1 part by mass or less, relative to 100 parts by mass of the PVA-based resin ( ⁇ ).
• the content of the compound ( ⁇ ) is equal to or more than the above lower limit, the optical properties of the stretched film are easily improved, and when the content of the compound ( ⁇ ) is equal to or less than the above upper limit, the film can be easily produced with good productivity while suppressing the production cost of the film.
• the content of the compound ( ⁇ ) based on the mass of the stretched film may also be selected from the above range.
• the stretched film of the present invention may further contain at least one selected from the group consisting of the plasticizer, the surfactant, and the additive.
• the content of each of the plasticizer, the surfactant, and the additive can be selected from the content ranges described in the ⁇ PVA-based film> section.
• the stretched film of the present invention may be a monolayer film or a multilayer film so long as it satisfies formula (II).
• the compositions and thicknesses of the films constituting the multilayer film may be the same or different for each film.
• the interfaces between the films of the multilayer film may be entirely or partially invisible. That is, the interfaces between the films may become invisible during production, and the film may appear to be a monolayer film.
• the PVA-based resin ( ⁇ ) and the compound ( ⁇ ) are each contained in at least one film constituting the multilayer film, and preferably the PVA-based resin ( ⁇ ) is contained in all of the films, so that the multilayer film itself satisfies formula (II).
• the method of adjusting the range of formula (II) can be the same as the method of adjusting the range of formula (I) above.
• the layer structure can be the same as the layer structure when the PVA-based film is a multilayer film.
• the PVA-based resin ( ⁇ 3) is preferably the same as at least one selected from the group consisting of the PVA-based resin ( ⁇ 1) and the PVA-based resin ( ⁇ 2), and more preferably the same as both the PVA-based resin ( ⁇ 1) and the PVA-based resin ( ⁇ 2).
• the stretched film of the present invention has the same layer structure as the above-mentioned PVA-based film B, from the viewpoint of easily improving the moist heat resistance and water resistance, it is preferable that the relationship between the PVA-based resin ( ⁇ 3) and the PVA-based resin ( ⁇ 4) and the PVA-based resin ( ⁇ 1), the PVA-based resin ( ⁇ 2) and the PVA-based resin ( ⁇ 5) is the same as that of the above-mentioned PVA-based film B.
• the thickness of the stretched film can be appropriately selected depending on the application, and is preferably 0.1 ⁇ m or more, more preferably 1 ⁇ m or more, even more preferably 5 ⁇ m or more, even more preferably 10 ⁇ m or more, particularly preferably 20 ⁇ m or more, especially more preferably 25 ⁇ m or more, and is preferably 200 ⁇ m or less, more preferably 100 ⁇ m or less, and even more preferably 50 ⁇ m or less. If the thickness of the stretched film is equal to or greater than the lower limit, it is easy to improve the resistance to moist heat and water resistance, and if the thickness of the stretched film is equal to or less than the upper limit, it is advantageous in terms of optical properties and thinning.
• the thickness of the stretched film means the thickness of the multilayer film itself (i.e., the total thickness of the films constituting the multilayer film).
• the thickness of the stretched film can be measured using a film thickness meter, for example, by the method described in the examples.
• the stretched film of the present invention has excellent water resistance and can suppress the release of compound ( ⁇ ) in water or an aqueous solution. Therefore, when the stretched film is immersed in pure water at 50°C for 15 minutes and then removed, the absorbance Y of the pure water is small.
• the absorbance Y of the stretched film can be selected from the range of absorbance Y values described in the ⁇ PVA-based film> section.
• the stretched film of the present invention has excellent moist heat resistance. Therefore, when compound ( ⁇ ) functions as a dye or pigment, the change in dichroic ratio before and after the moist heat resistance test can be suppressed. In other words, the stretched film of the present invention can suppress the deterioration of the polarization performance even if it is left under high temperature and high humidity for a long period of time.
• the ⁇ dichroic ratio of the stretched film can be selected from the numerical range of ⁇ dichroic ratio described in the ⁇ PVA-based film> section.
• the stretched film satisfying formula (II) of the present invention is preferably obtained by stretching a PVA-based film satisfying formula (I) of the present invention.
• the method for producing the stretched film of the present invention is not particularly limited, but includes a method of stretching a PVA-based film containing a PVA-based resin ( ⁇ ) and a compound ( ⁇ ) so as to satisfy formula (II).
• the type of PVA-based film used as the raw material is not particularly limited, and a PVA-based film satisfying formula (I) or a PVA-based film not satisfying formula (I) may be used. From the viewpoint of easy adjustment to the range of formula (II), it is preferable to use a PVA-based film satisfying formula (I) of the present invention.
• the stretching may be multiaxial stretching such as uniaxial stretching or biaxial stretching, but is preferably uniaxial stretching, and may be performed by either wet stretching or dry stretching.
• wet stretching it may be performed in an aqueous solution containing boric acid.
• dry stretching it may be performed in air using a PVA-based film that has absorbed water.
• the wet stretching method is preferred, and uniaxial stretching in an aqueous solution containing boric acid is more preferred.
• the concentration of boric acid in the aqueous boric acid solution is preferably 0.5 to 6 mass%, more preferably 1 to 5 mass%, and even more preferably 1.5 to 4 mass%.
• the aqueous boric acid solution may contain potassium iodide.
• the stretching temperature is preferably 30 to 90°C, more preferably 40 to 80°C, and even more preferably 50 to 70°C.
• the stretching ratio is preferably 3 times or more, more preferably 4 times or more, and even more preferably 5 times or more. If the stretching ratio is equal to or greater than the lower limit mentioned above, the optical properties (e.g., polarization performance, luminous efficiency, etc.) are likely to be improved. There is no particular upper limit to the stretching ratio, but it is preferably 10 times or less, and more preferably 8 times or less.
• the drying temperature is preferably 30 to 150°C, more preferably 50 to 130°C.
• the drying time is preferably 30 seconds to 24 hours, more preferably 1 minute to 1 hour.
• the PVA-based film and stretched film of the present invention can be used as a polarizing film, a photon up-conversion film, a light control film, etc., and among these, it is preferably used as a polarizing film and a photon up-conversion film.
• the surface layer of each film was irradiated with sputter ions, and sputtering and measurement were alternately repeated to perform composition analysis over the entire thickness direction of each film. Then, among the intensity values of TOF-SIMS C 2 H 3 O 2 - or CN - signals derived from the PVA-based resin ( ⁇ ) or the nitrogen-containing compound ( ⁇ ) throughout the thickness direction of each film, when the thickness of each film is X ( ⁇ m), the intensity values of the TOF-SIMS signals were extracted from 20 points equally spaced in the thickness direction in a range of 0.3X ( ⁇ m) from the center of the film in the thickness direction toward each surface (outside), that is, in a total range of 0.6X.
• the intensity values of the TOF-SIMS C 2 H 3 O 2 - or CN - signals derived from the PVA-based resin ( ⁇ ) or the nitrogen-containing compound ( ⁇ ) were extracted at 20 points (actually, for the sake of measurement accuracy, 20 points were extracted at 1.8 ⁇ m intervals in the thickness direction) in the range from the center of the film to the outside in the thickness direction to 18.3 ( ⁇ m) , totaling 36.6 ( ⁇ m).
• the point at which the intensity value of the CN - signal derived from the nitrogen-containing compound ( ⁇ ) was maximum was designated as P MAX
• P min the point at which it was minimum
• the intensity value of the CN signal by TOF-SIMS derived from the nitrogen-containing compound ( ⁇ ) at P min was designated as A
• the intensity value of the C 2 H 3 O 2 -signal by TOF-SIMS derived from the PVA-based resin ( ⁇ ) at P min was designated as B
• the intensity value of the CN signal by TOF-SIMS derived from the nitrogen-containing compound ( ⁇ ) at P MAX was designated as C
• the intensity value of the C 2 H 3 O 2 -signal by TOF-SIMS derived from the PVA-based resin ( ⁇ ) at P MAX was designated as D.
• These intensity values A, B, C, D and their ratio ((C/D)/(A/B)) were calculated.
• the measurement conditions for TOF-SIMS were as follows:
• TOF-SIMS time-of-flight secondary ion mass spectrometer
• the intensity values of TOF-SIMS C 2 H 3 O 2 - or CN - signals derived from the PVA-based resin ( ⁇ ) or the nitrogen-containing compound ( ⁇ ) throughout the thickness direction of each film were extracted from 20 points equally spaced in the thickness direction in a range of 0.3Y ( ⁇ m) from the center of the thickness direction of the film toward each surface (outside), that is, in a total range of 0.6Y, where Y ( ⁇ m) is the thickness of each film.
• the intensity values of the TOF-SIMS C 2 H 3 O 2 - or CN - signal derived from the PVA-based resin ( ⁇ ) or the nitrogen-containing compound ( ⁇ ) were extracted at 20 points (actually, for the sake of measurement accuracy, 20 points were extracted at 1.0 ⁇ m intervals in the thickness direction) in the range from the center of the film in the thickness direction to the outside of 10.2 ( ⁇ m) , i.e. , in a total range of 20.4 ( ⁇ m).
• the point at which the intensity value of the TOF-SIMS CN - signal derived from the nitrogen-containing compound ( ⁇ ) was maximum was designated as P MAX
• P min the point at which it was minimum
• the intensity value of the CN signal by TOF-SIMS derived from the nitrogen-containing compound ( ⁇ ) at P min was designated as E
• the intensity value of the C 2 H 3 O 2 -signal by TOF-SIMS derived from the PVA-based resin ( ⁇ ) at P min was designated as F
• the intensity value of the CN signal by TOF-SIMS derived from the nitrogen-containing compound ( ⁇ ) at P MAX was designated as G
• the intensity value of the C 2 H 3 O 2 -signal by TOF-SIMS derived from the PVA-based resin ( ⁇ ) at P MAX was designated as H
• these intensity values E, F, G, H and their ratio ((G/H)/(E/F)) were calculated.
• the measurement conditions for TOF-SIMS were as follows:
• ⁇ Absorbance X of pure water after immersion in PVA-based film A sample having a width of 3 cm and a length of 5 cm was cut from the center of the PVA-based film 1 obtained in each comparative example and the PVA-based film obtained in each example. The sample was immersed in 40 mL of pure water at 30° C. for 5 minutes, and the film was taken out. Next, the absorbance of the pure water after the film was immersed was measured using a spectrophotometer with an integrating sphere (manufactured by Hitachi, Ltd., "U4100"), and the maximum value of the absorbance in the visible light wavelength region (380 to 750 nm) was determined as the absorbance X. Since the wavelength (maximum absorption wavelength) at the absorbance X in Example 1 was 650 nm, the absorbance at 650 nm was also determined as the absorbance X in Example 2 and Comparative Examples 1 and 2.
• ⁇ Absorbance Y of pure water after immersion in stretched film A sample of 2 cm width x 2 cm length was cut from the center of the stretched film obtained in each Example or Comparative Example. This sample was immersed in 20 mL of pure water at 50°C for 15 minutes, and the film was taken out. Next, the absorbance of the pure water after the film was immersed was measured using a spectrophotometer with an integrating sphere (manufactured by Hitachi, Ltd., "U4100"), and the maximum value of the absorbance in the visible light wavelength region (380 to 750 nm) was determined as absorbance Y. Note that since the wavelength (maximum absorption wavelength) at absorbance Y in Example 1 was 650 nm, the absorbance at 650 nm was also determined as absorbance Y in Example 2 and Comparative Examples 1 and 2.
• ⁇ dichroism ratio of stretched film> A sample having a width of 1.5 cm and a length of 3 cm was cut from the center of the stretched film obtained in each Example or Comparative Example. Then, using a spectrophotometer with an integrating sphere (manufactured by JASCO Corporation, "V7100"), the measurement wavelength was set to the maximum absorption wavelength (650 nm) in the measurement of the absorbance Y, and the single transmittance Ts (%) and the polarization degree P (%) of the sample before the moist heat resistance test were obtained. Then, the dichroic ratio Rd at the maximum absorption wavelength (650 nm) before the moist heat resistance test was obtained by the following formula, and the value was designated as Rd1.
• the sample was fixed to a metal frame and left to stand for 500 hours under an atmosphere of 60°C/90% RH to perform a moist heat resistance test.
• the measurement wavelength was set to the maximum absorption wavelength (650 nm), and the single transmittance Ts (%) and the polarization degree P (%) of the sample after the moist heat resistance test were obtained.
• the dichroic ratio Rd at the maximum absorption wavelength (650 nm) after the moist heat resistance test was calculated by the following formula, and this value was designated as Rd2.
• Rd log (Ts/100 - Ts/100 x P/100) / log (Ts/100 + Ts/100 x P/100)
• Example 1 (PVA-based film 1)
• an ethylene-vinyl alcohol copolymer (a saponified product of an ethylene-vinyl acetate copolymer, polymerization degree 2400, saponification degree 99.3 mol%, ethylene modification amount 2.5 mol%) was used.
• a film-forming stock solution with a volatile content of 66% by mass was prepared, which contained 100 parts by mass of the PVA-based resin ( ⁇ 1), 10 parts by mass of glycerin as a plasticizer, 0.1 parts by mass of sodium polyoxyethylene lauryl ether sulfate as a surfactant, and water as a liquid medium.
• This film-forming stock solution was discharged in the form of a film onto a first drying roll (surface temperature 88 ° C., peripheral speed 20.0 m / min) from a T-shaped slit die, and dried on the first drying roll until the volatile content of the resin film reached 25% by mass while blowing hot air (temperature 90 ° C., dew point temperature 10 ° C.) uniformly onto the entire non-contact surface of the first drying roll at a wind speed of 5 m / sec.
• a first drying roll surface temperature 88 ° C., peripheral speed 20.0 m / min
• the film was peeled off from the first drying roll, and dried with the second drying roll and subsequent drying rolls (surface temperature 84° C., peripheral speed 20.5 m/min) in a film-forming device equipped with 18 drying rolls whose rotation axes are parallel to each other so that the first drying roll contact surface and the first drying roll non-contact surface of the resin film alternately face each drying roll. Furthermore, both ends (edges) of the obtained film in the width direction were cut and removed, and then the film was wound up into a roll to continuously produce a long PVA-based film 1 with a thickness of 30 ⁇ m.
• PVA-based film 2 A long PVA-based film 2 having a thickness of 30 ⁇ m was continuously produced in the same manner as in the production of the PVA-based film 1. As shown in Table 1, the PVA-based resin constituting the PVA-based film 2 was designated as PVA-based resin ( ⁇ 2).
• PVA-based aqueous solution A PVA-based aqueous solution was produced containing 100 parts by mass of an ethylene-vinyl alcohol copolymer (saponification product of ethylene-vinyl acetate copolymer, degree of polymerization 2400, degree of saponification 99.3 mol%, amount of ethylene modification 2.5 mol%) as the PVA-based resin ( ⁇ 3) contained in the PVA-based aqueous solution and 60 parts by mass of Direct Blue 15 as the nitrogen-containing compound ( ⁇ ), and the content of the PVA-based resin ( ⁇ 3) was 8% by mass.
• Example 2 PVA-based films 1 and 2, PVA-based aqueous solutions, PVA-based films, and stretched films
• PVA-based film 1 and 2 PVA-based aqueous solutions, PVA-based films, and stretched films
• PVA-based film 1 and 2 PVA-based aqueous solutions, PVA-based films, and stretched film
• PVA-based film 2 PVA-based aqueous solution, PVA-based film, and stretched film were produced in the same manner as in Example 1, except that the content of Direct Blue 15 in the PVA-based aqueous solution was changed to 12 parts by mass.
• PVA-based film 1 was produced in the same manner as in Example 1, except that the thickness of PVA-based film 1 was changed to 60 ⁇ m.
• the sample was uniaxially stretched in the length direction by 1.9 times (total 5.0 times) while immersed in a 58°C boric acid aqueous solution (stretching bath) containing 3.9% by mass of boric acid (stretching treatment). Then, the sample was immersed in a 30°C boric acid aqueous solution (washing bath) containing 1.5% by mass of boric acid for 1 second without stretching and washed (washing treatment). Then, both ends of the sample were fixed so that dimensional change did not occur in the length direction, and the sample was dried in a dryer at 70°C for 3 minutes (drying treatment) to obtain a stretched film.
• PVA-based film 1 As the PVA-based resin ( ⁇ 1) constituting the PVA-based film 1, an ethylene-vinyl alcohol copolymer (saponified product of ethylene-vinyl acetate copolymer, polymerization degree 2400, saponification degree 99.3 mol%, ethylene modification amount 2.5 mol%) was used.
• an aqueous solution containing 100 parts by mass of the PVA-based resin ( ⁇ 1), 10 parts by mass of glycerin as a plasticizer, 0.1 parts by mass of sodium polyoxyethylene lauryl ether sulfate as a surfactant, and 0.75 parts by mass of Direct Blue 15 as a dye and having a PVA content of 10% by mass was prepared as a film-forming stock solution.
• This film-forming stock solution was dried on a metal roll at 60 ° C., and the obtained film was heat-treated in a hot air dryer at a temperature of 124 ° C. for 10 minutes to produce a long PVA-based film 1 having a thickness of 60 ⁇ m.
• Table 1 shows the polymerization degree of the PVA-based resin ( ⁇ ); the degree of saponification and its content; the type and content of the nitrogen-containing compound ( ⁇ ); and the thickness of each film measured by the above method for the PVA-based film 1, PVA-based film 2, PVA-based aqueous solution, PVA-based film, and stretched film obtained in each Example or Comparative Example.
• the thickness, TOF-SIMS, absorbances X and Y of pure water after immersion of the film, and ⁇ dichroic ratio were measured for the PVA-based films and stretched films obtained in Examples 1 and 2, and the PVA-based films 1 and stretched films obtained in Comparative Examples 1 and 2, according to the above-mentioned methods.
• the results are shown in Table 2.
• the positions of C and G in formulas (I) and (II) were within the central 20% range in the thickness direction of the film, respectively, and the positions of A and E in formulas (I) and (II) were within the central 40-60% range in the thickness direction of the film, respectively.
• the thickness of the PVA-based resin layer in the PVA-based films 1 and 2 in Example 1 was 0.75 ⁇ m
• the thickness of the PVA-based resin layer in the PVA-based films 1 and 2 in Example 2 was 0.75 ⁇ m.
• the PVA-based films of Examples 1 and 2 in which the signal intensity ratio (C/D)/(A/B) is 5 or more, had a lower absorbance X (650 nm) of pure water after immersion in the film, compared to the PVA-based film of Comparative Example 2, in which the signal intensity ratio (C/D)/(A/B) is less than 5. This confirmed that the PVA-based film of the present invention has excellent water resistance.
• the stretched films of Examples 1 and 2 in which the signal intensity ratio (G/H)/(E/F) exceeds 3, showed lower ⁇ dichroism ratios before and after the moist heat resistance test, and lower absorbance Y (650 nm) of pure water after immersion in the film, compared to the PVA-based films of Comparative Examples 1 and 2, in which the signal intensity ratio (G/H)/(E/F) is 3 or less.
• the stretched films of the present invention have excellent moist heat resistance and water resistance.

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