Polyvinyl alcohol film and stretched film

Abstract

The present invention pertains to a polyvinyl alcohol-based film containing a polyvinyl alcohol-based resin (alpha) and a nitrogen-containing compound (beta), the polyvinyl alcohol-based film having a signal intensity ratio in TOF-SIMS measurement data satisfying the following formula (I): (C / D) / (A / B) gt; 5 (I). [In the formula, A represents the intensity value of the CN-signal derived from the nitrogen-containing compound (beta) at Pmin, B represents the intensity value of the C2H3O2-signal derived from the polyvinyl alcohol resin (alpha) at Pmin, C represents the intensity value of the CN-signal derived from the nitrogen-containing compound (beta) at PMAX, and D represents the intensity value of the C2H3O2-signal derived from the polyvinyl alcohol resin (alpha) at PMAX].

Description

Technical Field

[0001] This patent application claims priority under the Paris Convention based on Patent Application No. 2022-166806 (filing date: October 18, 2022), and the entire content thereof is incorporated herein by reference.

[0002] The present invention relates to a polyvinyl alcohol-based membrane, a method for producing the same, and a stretched film. Background Art

[0003] Polyvinyl alcohol-based membranes (hereinafter, "polyvinyl alcohol" may sometimes be abbreviated as "PVA") are used in a wide range of applications such as packaging films, water-soluble films, agricultural films, release films, and optical films.

[0004] Regarding such PVA-based membranes, in order to impart optical properties and the like, for example, a nitrogen-containing compound (sometimes simply referred to as an N-containing compound) may be compounded as a dye / pigment or the like, and a stretching treatment may be performed in an aqueous treatment bath containing an organic metal such as cobalt ions on the basis of the dye / pigment or the like, and it is used in the form of a stretched film (for example, Patent Document 1).

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Patent Laid-Open No. 56-48601 Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] As a method for producing a PVA-based membrane, generally, a method of removing a solvent from a solution in which a PVA-based resin and an N-containing compound or the like are dissolved, a method of immersing the PVA-based membrane in an aqueous solution containing an N-containing compound or the like and drying it, etc. can be cited. However, when stretching a conventional PVA-based membrane in an aqueous treatment bath, the N-containing compound sometimes easily detaches from the surface layer of the membrane, it is difficult to adjust the N-containing compound concentration of the entire membrane, and the aqueous treatment bath is contaminated. Therefore, for such a PVA-based membrane, water resistance capable of suppressing the detachment of the N-containing compound is required.

[0010] Furthermore, the stretched film obtained by stretching the PVA-based membrane is not limited to indoor use, and may also be widely used outdoors. Therefore, durability against external environments such as temperature and humidity, that is, heat and humidity resistance is required. In particular, when the stretched film contains an N-containing compound, the N-containing compound may be decomposed due to the influence of the external environment. Therefore, more excellent heat and humidity resistance is required. However, conventional stretched films containing an N-containing compound sometimes have insufficient heat and humidity resistance.

[0011] Accordingly, an object of the present invention is to provide a PVA-based membrane excellent in water resistance and a method for producing the same.

[0012] Another object of the present invention is to provide a stretched film excellent in damp heat resistance, and a PVA-based membrane capable of forming the stretched film and a method for producing the same.

[0013] Means for Solving the Problem

[0014] The present inventors repeatedly conducted in-depth studies to achieve the above problems, and as a result, found that: if a PVA-based membrane and a stretched film containing a polyvinyl alcohol-based resin (α) and a nitrogen-containing compound (β) and having a specific signal intensity ratio measured by a time-of-flight secondary ion mass spectrometer (TOF-SIMS) within a specific range are used, the above problems can be solved, and thus the present invention was completed.

[0015] That is, the present invention includes the following preferred embodiments.

[0016] [1] A polyvinyl alcohol-based membrane containing a polyvinyl alcohol-based resin (α) and a nitrogen-containing compound (β), the polyvinyl alcohol-based membrane satisfying the following formula (I):

[0017] (C / D) / (A / B)≥5 (I)

[0018] [In the formula, within a range of 60% of the central portion in the thickness direction of the above-mentioned membrane, at least 20 points equally spaced in the thickness direction are measured by TOF-SIMS, and in the measurement data, the point where the intensity value of the CN - signal of the nitrogen-containing compound (β) reaches the maximum is set as P MAX , and the point where it reaches the minimum is set as P min When

[0019] A represents the intensity value of the CN min signal of the nitrogen-containing compound (β) when it is the above-mentioned P - ,

[0020] B represents the intensity value of C min of the polyvinyl alcohol-based resin (α) when it is the above-mentioned P 2 H 3 O 2 - signal,

[0021] C represents the intensity value of the CN MAX signal of the nitrogen-containing compound (β) when it is the above-mentioned P - ,

[0022] D represents the intensity value of C MAX of the polyvinyl alcohol-based resin (α) when it is the above-mentioned P 2 H3 O 2 - Signal intensity value

[0023] [2] The polyvinyl alcohol-based membrane according to [1], wherein the nitrogen-containing compound (β) has an aromatic ring.

[0024] [3] The polyvinyl alcohol-based membrane according to [1] or [2], wherein the nitrogen-containing compound (β) is a dye or pigment.

[0025] [4] The polyvinyl alcohol-based membrane according to any one of [1] to [3], wherein the content of the nitrogen-containing compound (β) is 0.01 to 20 parts by mass with respect to 100 parts by mass of the polyvinyl alcohol-based resin (α).

[0026] [5] The polyvinyl alcohol-based membrane according to any one of [1] to [4], wherein the content of the polyvinyl alcohol-based resin (α) is 60 to 99.99% by mass with respect to the mass of the polyvinyl alcohol-based membrane.

[0027] [6] The polyvinyl alcohol-based membrane according to any one of [1] to [5], having a thickness of 1 to 250 μm.

[0028] [7] A method for producing the polyvinyl alcohol-based membrane according to any one of [1] to [6], comprising: laminating a polyvinyl alcohol-based membrane 1 containing a polyvinyl alcohol-based resin (α1) and a polyvinyl alcohol-based membrane 2 containing a polyvinyl alcohol-based resin (α2) by means of a polyvinyl alcohol-based resin aqueous solution containing a polyvinyl alcohol-based resin (α3) and a nitrogen-containing compound (β).

[0029] [8] The production method according to [7], wherein the polyvinyl alcohol-based resin (α3) is the same as at least one selected from the polyvinyl alcohol-based resin (α1) and the polyvinyl alcohol-based resin (α2).

[0030] [9] A stretched film comprising a polyvinyl alcohol-based resin (α) and a nitrogen-containing compound (β), the stretched film satisfying the following formula (II):

[0031] (G / H) / (E / F)>3 (II)

[0032] [In the formula, within the range of 60% of the central portion in the thickness direction of the stretched film, at least 20 points equally spaced along the thickness direction are measured by TOF-SIMS, and in this measurement data, the CN - point where the signal intensity value of the nitrogen-containing compound (β) reaches the maximum is set as P MAX and the point where it reaches the minimum is set as P min When

[0033] E represents the CN min signal intensity value from the nitrogen-containing compound (β) when P is as described above - as described above,

[0034] F represents the C min from the polyvinyl alcohol-based resin (α) when P is as described above 2 H 3 O 2 - signal intensity value,

[0035] G represents the CN MAX signal intensity value from the nitrogen-containing compound (β) when P is as described above - as described above,

[0036] H represents the C MAX from the polyvinyl alcohol-based resin (α) when P is as described above 2 H 3 O 2 - signal intensity value

[0037]

[10] The stretched film according to [9], wherein the nitrogen-containing compound (β) has an aromatic ring.

[0038]

[11] The stretched film according to [9] or

[10] , wherein the nitrogen-containing compound (β) is a dye or a pigment.

[0039]

[12] The stretched film according to any one of [9] to

[11] , wherein the content of the nitrogen-containing compound (β) is 0.01 to 20 parts by mass with respect to 100 parts by mass of the polyvinyl alcohol-based resin (α).

[0040]

[13] The stretched film according to any one of [9] to

[12] , wherein the content of the polyvinyl alcohol-based resin (α) is 65 to 99.99% by mass with respect to the mass of the stretched film.

[0041]

[14] The stretched film according to any one of [9] to

[13] , having a thickness of 0.1 to 200 μm.

[0042]

[15] The stretched film according to any one of [9] to

[14] , which is obtained by stretching the polyvinyl alcohol-based film according to any one of [1] to [6].

[0043]

[16] The stretched film according to any one of [9] to

[15] , wherein the stretched film is any one of a polarizing film, a photon upconversion film, or a light control film.

[0044] Advantages of the Invention

[0045] The PVA-based membrane of the present invention can form a stretched film with excellent water resistance and excellent heat and humidity resistance.

[0046] The stretched film of the present invention has excellent heat and humidity resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 Schematic cross-sectional view showing the PVA-based membrane according to one embodiment of the present invention.

[0048] Figure 2 Measurement data obtained by measuring the PVA-based membrane according to one embodiment of the present invention using TOF-SIMS. DETAILED DESCRIPTION OF THE INVENTION

[0049] Hereinafter, embodiments of the present invention will be described in detail. It should be noted that the scope of the present invention is not limited to the embodiments described herein, and various modifications can be made without departing from the gist of the present invention.

[0050] [Polyvinyl Alcohol-Based Membrane]

[0051] The polyvinyl alcohol-based membrane of the present invention contains a polyvinyl alcohol-based resin (α) and a nitrogen-containing compound (β) (hereinafter sometimes abbreviated as compound (β)), and satisfies the following formula (I):

[0052] (C / D) / (A / B)≥5 (I)

[0053] [In the formula, within the range of 60% of the central portion in the thickness direction of the aforementioned membrane, at least 20 points equally spaced in the thickness direction are measured using a time-of-flight secondary ion mass spectrometer (sometimes denoted as TOF-SIMS). In this measurement data, the point where the intensity value of the CN - signal derived from compound (β) reaches the maximum is designated as P MAX , and the point where it reaches the minimum is designated as P min ,

[0054] A represents the intensity value of the CN min signal derived from compound (β) in the aforementioned P - ,

[0055] B represents the intensity value of C min H 2 H 3 O 2 - signal derived from the polyvinyl alcohol-based resin (α) at the aforementioned P

[0056] C represents the intensity value of the CN MAX signal derived from compound (β) in the aforementioned P - signal.

[0057] D represents the aforementioned P MAX when the C derived from the polyvinyl alcohol-based resin (α) 2 H 3 O 2 - intensity value of the signal

[0058] It should be noted that the PVA-based membrane of the present invention refers to an unstretched PVA-based membrane without stretching treatment.

[0059] Hereinafter, use Figure 1 and Figure 2 to illustrate the method for obtaining A, B, C, and D in formula (I). Figure 1 represents a schematic cross-sectional view of the PVA-based membrane (100) according to an embodiment of the present invention, Figure 2 represents the measurement data obtained by measuring the PVA-based membrane (100) according to an embodiment of the present invention using TOF-SIMS.

[0060] (i) Using TOF-SIMS, irradiate the surface layer of the PVA-based membrane with sputtering ions, alternately repeat sputtering and measurement, and perform compositional analysis over the entire range in the thickness direction of the membrane.

[0061] (ii) For the intensity value (9) of the CN signal derived from the compound (β) and the C - derived from the polyvinyl alcohol-based resin (α) in the measurement data obtained by (i) 2 H 3 O 2 - intensity value (8) of the signal, in the range of 60% of the central portion in the thickness direction (2), extract at least 20 points existing at equal intervals along the thickness direction. "In the range of 60% of the central portion in the thickness direction" means: for example Figure 1 as shown, when the thickness of the PVA-based membrane (100) is set to X, the range from the center (102) of the membrane in the thickness direction to 0.3X toward each surface (outer side), that is, a total range of 0.6X. In addition, when extracting 20 points in this range, for example, the 20 points exist at an interval of 0.03X along the thickness direction.

[0062] Here, regarding the aforementioned measurement data of TOF-SIMS, as Figure 2 shown, the horizontal axis is denoted as Cycles and the vertical axis is denoted as Intensity. TOF-SIMS measures the entire range in the thickness direction, so the horizontal axis of Cycles corresponds to the thickness of the PVA-based membrane (100). Therefore, the horizontal axis (at Figure 2within the range of 60% of the central part (for 600 cycles), (2) (in Figure 2 for 120 to 480 cycles) corresponding to Figure 1 the range of 0.6X of the central part of the PVA-based membrane (100) in

[0063] It should be noted that for the calculation of the signal intensity ratio (C / D) / (A / B) in formula (I), within the range of 60% of the central part in the thickness direction, the signal intensity values of at least 20 points are measured, and at least 20 points existing at equal intervals among them can be used. For example, in Figure 2 in the embodiment of Figure 2 , 360 points (360 cycles) are measured within this range, and 20 points Figure 2 existing at equal intervals among them Figure 2 of (10) and (11)] are used to calculate the signal intensity ratio (C / D) / (A / B).

[0064] (iii) Next, for the intensity value (9) of the CN - signal derived from compound (β), the point with the maximum intensity value among the aforementioned at least 20 points is set as P MAX (in Figure 2 for (4) in min ), and the point with the minimum intensity value is set as P min (in Figure 2 for (7) in Figure 2 ). At this time, the intensity value of the CN min signal derived from compound (β) in P min is set as A (in - for (7) in Figure 2 ), and the intensity value of the C min signal derived from the PVA-based resin (α) in P min is set as B (in 2 H 3 O 2 - in - for (6) in Figure 2 ). In addition, the intensity value of the CN MAX signal derived from compound (β) in P MAX is set as C (in - for (4) in Figure 2 ), and the intensity value of the C MAX signal derived from the PVA-based resin (α) in P MAX is set as D (in 2 H 3 O 2 - in - for (5) in Figure 2 ).

[0065] (iv) Finally, the signal intensity ratio (C / D) / (A / B) is calculated based on these intensity values A, B, C, and D.

[0066] The above TOF-SIMS measurement can be carried out by the method described in the examples, for example.

[0067] The present inventors have found that: for a PVA-based membrane containing a PVA-based resin (α) and a compound (β), if the signal intensity ratio (C / D) / (A / B) is 5 or more, the water resistance of the PVA-based membrane and the stretched membrane obtained by stretching the PVA-based membrane can be improved, and the detachment of the compound (β) in the aqueous bath can be suppressed. Furthermore, it has been found that: if the aforementioned signal intensity ratio (C / D) / (A / B) is 5 or more, the damp heat resistance of the stretched membrane obtained by stretching the PVA-based membrane can also be improved, and even when left for a long time under high temperature and high humidity, adverse conditions such as decomposition of the compound (β) can be suppressed.

[0068] It is presumed that the above effects are due to the fact that: in the PVA-based membrane satisfying formula (I) and the stretched membrane formed from the PVA-based membrane, the concentration of the compound (β) in the central portion in the thickness direction is high, and thus the compound (β) in the membrane is not easily affected by the external environment. It should be noted that, in this specification, water resistance refers to the property of being able to suppress the detachment of the compound (β) from the membrane in water, and damp heat resistance refers to the property of being able to suppress adverse conditions such as decomposition of the compound (β) when the membrane is exposed under high temperature and high humidity. For example, when the stretched membrane obtained by stretching the PVA-based membrane is a polarizing film, the damp heat resistance can be evaluated by measuring the change in the dichroic ratio after exposure under high temperature and high humidity. In this specification, the upper and lower limits of the numerical range can be arbitrarily combined. In this specification, the PVA-based membrane and / or the stretched membrane are sometimes simply referred to as the membrane.

[0069] If the signal intensity ratio (C / D) / (A / B) of the PVA-based membrane is less than 5, there is a tendency for the water resistance of the PVA-based membrane and the damp heat resistance and water resistance of the stretched membrane obtained by stretching it to decrease. In the PVA-based membrane of the present invention, the signal intensity ratio (C / D) / (A / B) can be appropriately selected according to the concentration of the compound (β) etc., and is preferably 10 or more, more preferably 20 or more, further preferably 30 or more, still further preferably 40 or more, particularly preferably 50 or more, more particularly preferably 60 or more, and can 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. If the signal intensity ratio (C / D) / (A / B) is above the above lower limit, the water resistance of the PVA-based membrane and the damp heat resistance and water resistance of the stretched membrane obtained by stretching it can be improved. In addition, the signal intensity ratio (C / D) / (A / B) of the PVA-based membrane is preferably 1000 or less, more preferably 500 or less, further preferably 250 or less. If the signal intensity ratio (C / D) / (A / B) is below the above upper limit, it is easy to suppress the manufacturing cost of the membrane and manufacture the membrane with good productivity.

[0070] In one embodiment of the present invention, the position of C in formula (I) is preferably within the range of 50% of the central portion in the thickness direction of the film, more preferably within the range of 40%, further preferably within the range of 30%, and further preferably within the range of 20%. If the position of C is within the above range, the concentration of compound (β) tends to be higher in the central portion. Therefore, the water resistance of the PVA-based film and the moisture and heat resistance and water resistance of the stretched film obtained by stretching it are likely to be improved. In addition, in one embodiment of the present invention, the position of A in formula (I) is preferably within the range of 20 to 60% of the central portion in the thickness direction of the film, more preferably within the range of 30 to 60%, and further preferably within the range of 40 to 60%. If the position of A is within the above range, the water resistance of the PVA-based film and the moisture and heat resistance and water resistance of the stretched film obtained by stretching it are likely to be improved.

[0071] <Polyvinyl alcohol-based resin (α)>

[0072] PVA-based resin (α) is a resin containing a vinyl alcohol-based polymer. The vinyl alcohol-based polymer is a polymer containing vinyl alcohol units as monomer units. The vinyl alcohol-based polymer is obtained by saponifying a vinyl ester-based polymer obtained by polymerizing a vinyl ester monomer as its raw material monomer. After saponification, the vinyl alcohol-based polymer may contain vinyl ester units in addition to vinyl alcohol units.

[0073] The vinyl alcohol-based polymer may be a modified vinyl alcohol-based copolymer obtained by saponifying a copolymer obtained by copolymerizing a vinyl ester monomer as its raw material monomer with other monomers and containing other monomer units in addition to vinyl alcohol units and vinyl ester units. In addition, PVA-based resin (α) may contain a plurality of vinyl alcohol-based polymers having different physical properties.

[0074] Examples of the vinyl ester monomer used as the raw material monomer of the vinyl alcohol-based polymer include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and vinyl versatate. Among them, vinyl acetate is preferred from the viewpoints of ease of production and acquisition, cost, etc.

[0075] As described above, 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. Examples of other monomers include α-olefins such as ethylene, propylene, n-butene, and isobutene; acrylic acid and its salts; acrylate esters; methacrylic acid and its salts; methacrylate esters; acrylamide; acrylamide derivatives such as N-methylacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetoneacrylamide, acrylamidopropylsulfonic acid and its salts, acrylamidopropyldimethylamine and its salts or quaternary salts, and N-hydroxymethylacrylamide and its derivatives; methacrylamide; methacrylamide derivatives such as N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidopropylsulfonic acid and its salts, methacrylamidopropyldimethylamine and its salts or quaternary salts, and N-hydroxymethylmethacrylamide and its derivatives; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tert-butyl vinyl ether, dodecyl vinyl ether, and stearyl vinyl ether; nitriles such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride and vinyl fluoride; vinylidene halides such as vinylidene chloride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; unsaturated dicarboxylic acids such as maleic acid, itaconic acid, and fumaric acid and their salts or esters; vinylsilyl compounds such as vinyltrimethoxysilane; isopropyl acetate; vinyl compounds such as dimethylallyl vinyl ketone, N-vinylpyrrolidone, ethylene carbonate vinyl ester, 2,2-dialkyl-4-vinyl-1,3-dioxolane, glycerol monoallyl ether, and 3,4-diacetoxy-1-butene. Among these, from the viewpoint of ease of industrial production, other monomers are preferably α-olefins such as ethylene. The content (modification amount) of these other monomer units varies depending on the purpose of use, application, etc. In one embodiment, the content (modification amount) of other monomer units may preferably be 10 mol% or less, more preferably 5 mol% or less, and preferably 0 mass% or more, more preferably 0.1 mass% or more, and further preferably 0.5 mass% or more.

[0076] Some of the hydroxyl groups in the vinyl alcohol polymer may be crosslinked or uncrosslinked. In addition, some of the hydroxyl groups in the vinyl alcohol polymer may react with aldehyde compounds such as acetaldehyde and butyraldehyde to form an acetal structure, or may not react with these compounds to form no acetal structure.

[0077] Regarding the PVA-based resin (α), from the viewpoints of easily improving the water resistance of the PVA-based film and the damp heat resistance and water resistance of the stretched film, as the vinyl alcohol polymer, it is preferably to contain at least one selected from unmodified vinyl alcohol polymers and α-olefin-vinyl alcohol copolymers, and more preferably to contain an α-olefin-vinyl alcohol copolymer.

[0078] In one embodiment of the present invention, the saponification degree of the vinyl alcohol polymer contained in the PVA-based resin (α) is preferably 88 mol% or more, more preferably 90 mol% or more, further preferably 93 mol% or more, still further preferably 96 mol% or more, particularly preferably 97 mol% or more, more particularly preferably 98 mol% or more, and especially further preferably 99 mol% or more, and preferably 99.9 mol% or less, more preferably 99.7 mol% or less, and further preferably 99.5 mol% or less. If the saponification degree of the vinyl alcohol polymer contained in the PVA-based resin (α) is within the above range, it is easy to improve the water resistance of the PVA-based film, as well as the heat and humidity resistance and water resistance of the stretched film. In addition, the thermal stability of the PVA-based film becomes good, and it is easy to perform molding and film formation stably. In this specification, the saponification degree of the vinyl alcohol polymer means the proportion (mol%) of the number of moles of the vinyl alcohol unit relative to the total number of moles of the structural units (typically vinyl ester units) that can be converted into vinyl alcohol units by saponification in the vinyl alcohol polymer. The saponification degree of the vinyl alcohol polymer can be measured in accordance with JIS K6726 (1994).

[0079] In one embodiment of the present invention, the viscosity-average degree of polymerization (sometimes referred to as the degree of polymerization) of the PVA-based resin (α) is preferably 200 or more, more preferably 300 or more, further preferably 500 or more, still further preferably 800 or more, particularly preferably 1200 or more, and preferably 4000 or less, more preferably 3500 or less, and further preferably 3000 or less. If the degree of polymerization is above the above lower limit, it is easy to improve the mechanical strength of the film. In addition, if the degree of polymerization is below the above upper limit, it is easy to improve the process passability, stretchability, and film formability during manufacturing. The degree of polymerization of the PVA-based resin (α) can be measured in accordance with JIS-K6726 (1994).

[0080] It should be noted that when the PVA-based resin (α) contains two or more vinyl alcohol polymers, the degree of polymerization of the PVA-based resin (α) means the average degree of polymerization calculated based on the degree of polymerization and blending ratio of each vinyl alcohol polymer. When the PVA-based resin (α) contains only one vinyl alcohol polymer, the degree of polymerization of the vinyl alcohol polymer is the degree of polymerization of the PVA-based resin (α). When the PVA-based resin (α) contains two or more vinyl alcohol polymers, it is only necessary to mix the vinyl alcohol polymers with different degrees of polymerization at an appropriate blending ratio and adjust the degree of polymerization of the PVA-based resin (α) to the above range.

[0081] In one embodiment of the present invention, the content of the PVA-based resin (α) is preferably 60% by mass or more, more preferably 70% by mass or more, further preferably 80% by mass or more, still more preferably 85% by mass or more, particularly preferably 87% by mass or more, and preferably 99.99% by mass or less, more preferably 99.9% by mass or less, further preferably 99% by mass or less, still more preferably 98% by mass or less, particularly preferably 95% by mass or less, and even more particularly preferably 93% by mass or less, based on the mass of the PVA-based membrane. If the content of the PVA-based resin (α) is above the above lower limit, it is easy to improve the film-forming property of the membrane. If the content of the PVA-based resin (α) is below the above upper limit, it is easy to improve the stretchability of the membrane.

[0082] <Method for producing polyvinyl alcohol-based resin (α)>

[0083] As described above, the PVA-based resin (α) contains a vinyl alcohol-based polymer. The vinyl alcohol-based polymer can be obtained, for example, by polymerizing a vinyl ester monomer or copolymerizing a vinyl ester monomer with other monomers to obtain a vinyl ester polymer or copolymer (sometimes collectively referred to as a vinyl ester-based polymer), and then subjecting it to saponification. As a method for polymerizing a vinyl ester monomer or the like, known methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization can be cited. Among them, bulk polymerization and solution polymerization, which are carried out under solvent-free conditions or in a solvent such as alcohol, are preferably used. As the alcohol used as a solvent in solution polymerization, lower alcohols such as methanol, ethanol, and propanol can be cited. As an initiator used in copolymerization, known initiators such as azo-based initiators or peroxide-based initiators such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), benzoyl peroxide, and n-propyl peroxydicarbonate can be cited. There is no particular limitation on the polymerization temperature, and a range of 0°C to 150°C is preferred. In addition, for example, when the vinyl alcohol-based polymer is an ethylene-vinyl alcohol copolymer or the like, it is preferred to copolymerize a vinyl ester monomer with a monomer such as ethylene by the above method.

[0084] The vinyl ester polymer obtained in the polymerization step can be saponified by an alcoholysis or hydrolysis reaction in an organic solvent in the presence of a catalyst. Examples of the catalyst 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 thereof 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. They can be used alone or in combination of two or more. Among them, it is preferable to use methanol or a mixed solution of methanol and methyl acetate as the solvent and carry out the saponification reaction in the presence of sodium hydroxide as a basic catalyst because it is simple. The amount of the saponification catalyst is preferably 0.001 to 0.5 in terms of the molar ratio relative to the vinyl ester monomer unit in the vinyl ester polymer. This molar ratio is more preferably 0.002 or more, further preferably 0.4 or less, and still further preferably 0.3 or less.

[0085] A suitable 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 at this time is preferably methanol. Initially, the mixture is a homogeneous liquid, but as the saponification reaction proceeds and the vinyl ester units in the polymer are saponified and converted into vinyl alcohol units, the solubility in the solvent decreases, and the polymer precipitates in the solution. At this time, methyl acetate generated by the alcoholysis based on methanol is contained in the solution. As the saponification reaction proceeds, the amount of the precipitated polymer gradually increases and becomes a slurry state, and then it loses its fluidity. Therefore, in order to carry out the saponification reaction uniformly, it is preferable to mix well until it loses its fluidity.

[0086] The method of mixing the vinyl ester polymer solution and the saponification catalyst is not particularly limited, and various methods such as a static mixer, a kneader, and a stirring blade can be used. From the aspect of enabling continuous and uniform mixing, it is preferable to use a static mixer. In this case, 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 it through the static mixer and mix to obtain a paste. The temperature of the reaction liquid in the static mixer is usually 20 to 80°C.

[0087] The method for conducting the saponification reaction of the vinyl ester polymer in the paste after passing through the static mixer is not particularly limited, and the following method is suitable: placing the paste on a moving belt and conducting the saponification reaction while moving the belt in a tank maintained at a specified temperature. The paste on the belt loses fluidity and assumes a solid state, and further, the saponification reaction is conducted in a solid state. By this method, the saponification reaction can be continuously conducted in a solid state, and a solid mass containing a vinyl alcohol polymer and a solvent can be obtained. The saponification temperature is preferably 20 to 60°C, more preferably 25°C or higher, still more preferably 30°C or higher, and preferably 55°C or lower, more preferably 50°C or lower. If the saponification temperature is at or above the above lower limit, it is easy to suppress the decrease in the reaction rate. If the saponification temperature is at or below the above upper limit, it is easy to suppress the decrease in the solvent content rate in the obtained solid mass and is easy to suppress the deterioration of the solubility of the obtained vinyl alcohol polymer. The saponification time is preferably 5 minutes to 2 hours. The saponification time is more preferably 8 minutes or longer, still more preferably 10 minutes or longer, and more preferably 1.5 hours or shorter, still more preferably 1 hour or shorter.

[0088] If necessary, for the purpose of removing impurities such as sodium acetate, a washing step can be applied to wash the vinyl alcohol polymer. Examples of the washing liquid include methanol, acetone, methyl acetate, ethyl acetate, hexane, water, etc. Among these, a single or mixed liquid of methanol, methyl acetate, and water is more preferred. As the amount of the washing liquid, generally, per 100 parts by mass of the vinyl alcohol polymer, it is preferably 30 to 10,000 parts by mass, more preferably 50 to 3,000 parts by mass. As the washing temperature, it is preferably 5 to 80°C, more preferably 20 to 70°C. As the washing time, it is preferably 20 minutes to 10 hours, more preferably 1 hour to 6 hours. As the washing method, known methods such as the batch method and the convection washing method can be applied. It should be noted that commercially available products can also be used as the vinyl alcohol polymer.

[0089] <Compound (β) containing a nitrogen element>

[0090] The PVA-based film of the present invention contains one or two or more compounds (β) containing a nitrogen element. Compound (β) is a compound containing a nitrogen element (N element) and can impart optical properties (such as polarization performance or luminescence performance, etc.) to the film. The compound (β) containing a nitrogen element is not limited as long as it contains the N element. From the viewpoints of easily improving the water resistance and optical properties of the PVA-based film, as well as the hygrothermal resistance, water resistance, and optical properties of the stretched film, it preferably has an aromatic ring. Examples of the aromatic ring include an aromatic hydrocarbon ring or an aromatic heterocyclic ring. Compound (β) may have one or two or more aromatic rings.

[0091] Examples of the aromatic hydrocarbon ring include, for example, a monocyclic aromatic hydrocarbon ring, a fused polycyclic aromatic hydrocarbon ring, or a ring-assembled aromatic hydrocarbon ring.

[0092] Examples of the monocyclic aromatic hydrocarbon ring include, for example, a benzene ring. Examples of the fused polycyclic aromatic hydrocarbon ring include, for example, a naphthalene ring, an anthracene ring, a phenanthrene ring, a tetracene ring, a pyrene ring, a perylene ring, a tetracene ring, a benzopyrene ring, a chrysene ring, a benzo[a]phenanthrene ring, an acenaphthene ring, a fluoranthene ring, a fluorene ring, etc. The ring-aggregated aromatic hydrocarbon ring refers to a ring obtained by bonding two or more monocyclic aromatic hydrocarbon rings, two or more fused polycyclic aromatic hydrocarbon rings, or one or more monocyclic aromatic hydrocarbon rings and one or more fused polycyclic aromatic hydrocarbon rings to each other via a single bond. Examples thereof include a biphenyl ring, a phenylnaphthalene ring, a terphenyl ring, a perylene ring, a phenylanthracene ring, a diphenylanthracene ring, etc.

[0093] Examples of the aromatic heterocycle include, for example, a monocyclic aromatic heterocycle, a fused polycyclic aromatic heterocycle, or a ring-aggregated aromatic heterocycle. The monocyclic aromatic heterocycle contains at least one heteroatom selected from a sulfur atom, a nitrogen atom, and an oxygen atom. Examples thereof include a pyrrole ring, a pyrazole ring, an imidazole ring, a pyridine ring, a pyrazine ring, a pyridazine ring, a pyrimidine ring, a triazine ring, an isocyanuric ring, a diazine ring, a furan ring, a thiophene ring, an oxazole ring, a dioxazole ring, a triazole ring, an oxadiazole ring, a thiadiazole ring, etc. The fused polycyclic aromatic heterocycle contains at least one heteroatom selected from a sulfur atom, a nitrogen atom, and an oxygen atom. Examples thereof include a Bodipy (boron difluoride dipyrrole) ring, a fullerene ring, a porphyrin ring, a quinoline ring, a phthalazine 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 thiophenopyrrole ring, a thiophenothiophene ring, a furanopyrrole ring, a furanofuran ring, a thiophenofuran ring, a thiazole ring, a benzisoxazole ring, a benzisothiazole ring, a benzimidazole ring, an isoquinoline ring, a cinnoline ring, a quinoxaline ring, a phenanthridine ring, a phthalazine ring, a quinazoline ring, a quinazolinone ring, an azulene ring, etc. The ring-aggregated aromatic heterocycle includes a ring obtained by bonding two or more monocyclic aromatic heterocycles, two or more fused polycyclic aromatic heterocycles, or one or more monocyclic aromatic heterocycles and one or more fused polycyclic aromatic heterocycles to each other via a single bond. On this basis, it also includes a ring obtained by bonding one or more monocyclic aromatic hydrocarbon rings and one or more fused polycyclic aromatic heterocycles, or one or more monocyclic aromatic heterocycles and one or more fused polycyclic aromatic hydrocarbon rings to each other via a single bond. Examples of the ring-aggregated aromatic heterocycle include a bipyridine ring, a terpyridine ring, a tetraphenylporphyrin ring, a phthalocyanine ring, etc.

[0094] In one embodiment of the present invention, from the viewpoint of easily improving the water resistance and optical properties of the PVA-based membrane, as well as the moisture and heat resistance, water resistance and optical properties of the stretched film, the aromatic ring preferably contains at least one selected from monocyclic aromatic hydrocarbon rings, fused polycyclic aromatic hydrocarbon rings, ring assembly aromatic hydrocarbon rings, fused polycyclic aromatic heterocycles and ring assembly aromatic heterocycles. In one embodiment of the present invention, from the viewpoint of easily improving the water resistance, moisture and heat resistance, and optical properties of the film, the aromatic ring preferably contains at least one selected from benzene rings, naphthalene rings, anthracene rings, pyrene rings, perylene rings, tetracene rings, Bodipy rings, porphyrin rings, phthalocyanine rings, biphenyl rings, phenylnaphthalene rings, phenylanthracene rings, diphenylanthracene rings and tetraphenylporphyrin rings, and more preferably contains at least one selected from benzene rings, naphthalene rings, biphenyl rings, diphenylanthracene rings, porphyrin rings and tetraphenylporphyrin rings. It should be noted that when the aromatic ring contains a porphyrin ring, a phthalocyanine ring or a fullerene ring, these rings may have metal atoms such as Pt, Pd, Zn, Ru, Re, Ir, Os, Cu, Ni, Co, Cd, Au, Ag, Sn, Sb, Pb, P, As, etc.

[0095] The aforementioned aromatic ring may have a substituent (referred to as substituent A). There is no particular limitation on substituent A, and examples thereof include a hydrogen atom, a halogen atom, an alkyl group, an alkylene group, an alkoxy group, an aryl group, an amino group, an alkylamino group, a hydroxyphenyl group, a carboxyphenyl group, a hydroxyl group, a cyano group, an epoxyalkylene group, an ether group, an ester group, an azo group (-N=N-), a carboxyl group or its salt, a sulfo group or its salt, etc. The aromatic ring may have one or more than two substituents A.

[0096] Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc. Examples of the alkyl group include alkyl groups having 1 to 12 carbon atoms such as a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a n-pentyl group, a 2-methylbutyl group, a 3-methylbutyl group, a 2-ethylpropyl group, a n-hexyl group, etc., and preferably alkyl groups having 1 to 8 carbon atoms, etc. Examples of the alkylene group include alkylene groups having 1 to 10 carbon atoms such as an ethylene group, a propylene group, a trimethylene group, a butylene group, an isobutylene group, a pentylene group, a hexylene group, a heptylene group, an octylene group, a nonylene group, a decylene group, etc., and preferably alkylene groups having 1 to 5 carbon atoms, etc. Examples of the alkoxy group include alkoxy groups having 1 to 12 carbon atoms such as a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a n-butoxy group, an isobutoxy group, a sec-butoxy group, a tert-butoxy group, a pentyloxy group, a hexyloxy group, a cyclohexyloxy group, etc., preferably alkoxy groups having 1 to 8 carbon atoms, and more preferably alkoxy groups having 1 to 4 carbon atoms, etc. Examples of the aryl group include a phenyl group, a tolyl group, a naphthyl group, a biphenyl group, etc. Examples of the alkylamino group include an amino group having an alkyl chain with 1 to 12 carbon atoms, and preferably an amino group having an alkyl chain with 1 to 8 carbon atoms, etc. Examples of the epoxyalkylene group include an epoxyethyl group, an epoxypropyl group, etc.

[0097] In a preferred embodiment of the present invention, from the viewpoint of easily improving the water resistance and optical properties of the PVA-based film, as well as the heat and humidity resistance, water resistance and optical properties of the stretched film, the nitrogen-containing compound (β) preferably contains at least one selected from the compounds represented by the following formula (1), the compounds represented by the following formula (2), and the compounds represented by the following formula (6), and more preferably contains the compounds represented by the following formula (1).

[0098] [Chemical formula 1]

[0099] Ar 3 -N=N-Ar b -N=N-Ar c (1)

[0100] [In formula (1), Ar a , Ar b and Ar c each independently represent an aryl group optionally having a substituent.]

[0101] [Chemical formula 2]

[0102]

[0103] [In formula (2), R 1 to R 4 each independently represent a hydrogen atom, a cyano group, a halogen atom, an amino group having an alkyl chain with 1 to 8 carbon atoms, an alkyl group with 1 to 12 carbon atoms, an alkoxy group with 1 to 12 carbon atoms, an ethylene oxide chain represented by the following formula (3) or the following formula (4), or an ammonium ion represented by the following formula (5), l and m each independently represent an integer from 1 to 4, and n and o each independently represent an integer from 1 to 5.]

[0104] [Chemical formula 3]

[0105]

[0106] [In formula (3), R 5 represents an alkyl group with 1 to 3 carbon atoms, p represents an integer from 1 to 4, and * represents a connecting bond.]

[0107] [Chemical formula 4]

[0108]

[0109] [In formula (4), R 6 and R 7 each independently represent an alkyl group with 1 to 3 carbon atoms, q and r each independently represent an integer from 1 to 4, and * represents a connecting bond.]

[0110] [Chemical formula 5]

[0111]

[0112] [In formula (5), s represents an integer from 1 to 8, R 8 ~R 11 each independently represents an alkyl group having 1 to 6 carbon atoms, and * represents a linking bond.]

[0113] [Chemical formula 6]

[0114]

[0115] [In formula (6), R 12 ~R 19 each independently represents a hydrogen atom, a cyano group, a halogen atom, an amino group having an alkyl chain with 1 to 8 carbon atoms, an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 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, and Ar 1 ~Ar 4 each independently represents a hydrogen atom, a substituent represented by the following formula (8), the following formula (9), or the following formula (10), or an ammonium ion represented by the following formula (11).]

[0116] [Chemical formula 7]

[0117]

[0118] [In formula (7), R 20 represents an alkyl group having 1 to 3 carbon atoms, t represents an integer from 1 to 4, and * represents a linking bond.]

[0119] [Chemical formula 8]

[0120]

[0121] [In formula (8), * represents a linking bond.]

[0122] [Chemical formula 9]

[0123]

[0124] [In formula (9), * represents a linking bond.]

[0125] [Chemical formula 10]

[0126]

[0127] [In formula (10), R 21 represents an alkyl group having 1 to 3 carbon atoms, u represents an integer from 1 to 4, and * represents a linking bond.]

[0128] [Chemical formula 11]

[0129]

[0130] [In formula (11), v represents an integer from 1 to 8, and R 22 ~R 25 each independently represents an alkyl group having 1 to 6 carbon atoms, and * represents a linking bond.]

[0131] As the aryl groups of Ar a , Ar b and Ar c in formula (1), groups obtained by removing one hydrogen atom from the above aromatic rings can be exemplified, and groups obtained by removing one hydrogen atom from a benzene ring, a naphthalene ring or a biphenyl ring are preferably exemplified. As the substituents that the aryl group may optionally have, the groups exemplified as the above substituent A can be exemplified.

[0132] In a preferred embodiment, Ar a , Ar b and Ar c in formula (1) are respectively represented by formula (a), formula (b) and formula (c).

[0133] [Chemical formula 12]

[0134]

[0135] [In the formula, R a ~R v each independently represents 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 linking bond.]

[0136] As the alkyl groups, alkoxy groups and aryl groups in R a ~R v , the groups exemplified above as the alkyl groups, alkoxy groups and aryl groups of substituent A can be respectively exemplified.

[0137] In one embodiment of the present invention, from the viewpoints of easily improving the water resistance of the PVA-based membrane and the optical properties (especially polarization performance), water resistance and heat and humidity resistance of the stretched film, R b , R d , R e , R m , R k , R j , R p , R q , R r , R s , R v and R u respectively represent hydrogen atoms, and R a , R c , R f, R q , R h , R i , R l , R n , R o and R t each independently preferably represents 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, R b , R d , R e , R m , R k , R j , R p , R q , R r , R s , R v and R u each represent a hydrogen atom, R o and R t each represent an alkoxy group, R a , R c , R f , R g , R h , R i , R l and R n each independently more preferably represents an amino group, a hydroxyl group, a sulfo group or a salt thereof, R b , R d , R e , R m , R k , R j , R p , R q , R r , R s , R v and R u each represent a hydrogen atom, R o and R t each represent an alkoxy group, R c and R l each represent a sulfo group or a salt thereof, R a and R n each represent an amino group, R g and R h each further preferably represents a hydroxyl group.

[0138] Examples of the compound represented by the 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. Among these, from the viewpoints of easily improving the water resistance of the PVA-based film, and the optical properties (especially polarization performance), water resistance, and moisture and heat resistance of the stretched film, Direct Blue 15 is preferred.

[0139] The nitrogen-containing compound (β) having a hydrophilic group such as an alkoxy group; an alkylene oxide chain such as an ethylene oxide chain or a propylene oxide chain; a hydroxyl group; a carboxyl group; an amino group; an ammonium ion is water-soluble, and thus can be suitably used in the case of wet stretching of the film. By appropriately selecting the number of these functional groups, the chain length of the alkylene oxide chain, etc., the degree of water solubility can also be controlled. The compounds represented by the formula (1), the compounds represented by the formula (2), and the compounds represented by the formula (3) can be produced by conventional methods, or commercially available products can also be used.

[0140] The compound (β) is not particularly limited, and a dye or a pigment is preferred. In one embodiment of the present invention, when the compound (β) is a dye or a pigment, the compound (β) can function as a dichroic pigment, and thus a stretched film obtained by stretching the PVA-based film can form a polarizing film. Further, in one embodiment of the present invention, when the compound (β) is a dye or a pigment, by containing two or more kinds of compounds (β) that function as a donor or an acceptor, the PVA-based film can form a photon upconversion film. For example, when the compound (β) contains the compound represented by the aforementioned formula (1), it easily functions as a dichroic pigment, and when the compound (β) contains the compound represented by the aforementioned formula (2) and the compound represented by the aforementioned formula (3), they easily function as a donor and an acceptor of the photon upconversion film, respectively. It should be noted that photon upconversion refers to the phenomenon of converting low-energy light into high-energy light. In addition, in this specification, the optical property refers to an optical property. When the stretched film obtained by stretching the PVA-based film is a polarizing film, it refers to polarization performance, etc., and when it is a photon upconversion film, it refers to luminous efficiency, etc.

[0141] The content of the nitrogen-containing compound (β) is preferably 0.01 part by mass or more, more preferably 0.05 part by mass or more, further preferably 0.07 part by mass or more, still more preferably 0.1 part by mass or more, and preferably 20 parts by mass or less, more preferably 15 parts by mass or less, further preferably 10 parts by mass or less, still 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 (α). If the content of the compound (β) is above the above lower limit, it is easy to improve the optical properties of the film. In addition, if the content of the compound (β) is below the above upper limit, it is easy to suppress the manufacturing cost of the film and manufacture the film with good productivity. It should be noted that the content of the compound (β) based on the mass of the PVA-based film can also be selected from the above range.

[0142] <PVA-based film>

[0143] The PVA-based film of the present invention contains a PVA-based resin (α) and a nitrogen-containing compound (β) and satisfies the aforementioned formula (I), and thus has excellent water resistance. Therefore, when the PVA-based film is stretched in an aqueous bath, etc., it is possible to suppress the detachment of the compound (β) from the surface layer of the film. Therefore, it is easy to adjust the concentration of the compound (β) in the whole film, and in addition, it is also possible to prevent the aqueous bath from being contaminated. In addition, the PVA-based film of the present invention can also form a stretched film with excellent heat and humidity resistance. Therefore, even when the stretched film is exposed at high temperature and high humidity for a long time, it is possible to suppress adverse conditions such as the decomposition of the compound (β). Furthermore, the PVA-based film of the present invention can also form a stretched film with excellent water resistance, and can suppress the detachment of the compound (β) from the surface layer of the stretched film in water or an aqueous solution. Therefore, when the stretched film is treated in an aqueous bath, it is possible to prevent the aqueous bath from being contaminated. Therefore, the PVA-based film of the present invention can be suitably used as a polarizing film, a photon up-conversion film, etc.

[0144] As described above, the PVA-based film of the present invention has excellent water resistance and can suppress the detachment of the compound (β) in an aqueous solution. Therefore, when the PVA-based film is immersed in pure water at 30 °C for 5 minutes and the pure water after taking out the film has a small absorbance X. In this specification, the absorbance X refers to the maximum value of the absorbance of the pure water after immersing the PVA-based film in the visible light wavelength region (380 - 750 nm). Usually, the wavelength (maximum absorption wavelength) at the time of the absorbance X is the same as the maximum absorption wavelength of the compound (β) that detaches in pure water. In one embodiment of the present invention, the absorbance X (Abs) of the pure water after immersing the PVA-based film is preferably 0.01 or less, more preferably 0.005 or less, and further preferably 0.003 or less. The absorbance X can be measured by, for example, the method described in the examples.

[0145] As described above, the PVA-based membrane of the present invention can form a stretched film with excellent heat and humidity resistance. Therefore, when the compound (β) is a dye or a pigment, it is possible to suppress the change in the dichroic ratio (sometimes denoted as Δ dichroic ratio) before and after the heat and humidity resistance test. In one embodiment of the present invention, the Δ dichroic ratio before and after leaving the PVA-based membrane of the present invention standing for 500 hours in an atmosphere of 60 °C and 90% humidity is preferably less than 10, more preferably 8 or less, and still more preferably 6 or less. For example, it can be 5 or less or 4 or less. The Δ dichroic ratio can be measured by, for example, the method described in the examples.

[0146] As described above, the PVA-based membrane of the present invention can form a stretched film with excellent water resistance. Therefore, when the stretched film is immersed in pure water at 50 °C for 15 minutes and the absorbance Y of the pure water after taking out the film is small. In this specification, the absorbance Y refers to the maximum value of the absorbance of the pure water after immersing the stretched film in the visible light wavelength region (380 to 750 nm). Usually, the wavelength (maximum absorption wavelength) at the time of the absorbance Y coincides with the maximum absorption wavelength of the compound (β) that dissociates in pure water. In one embodiment of the present invention, the absorbance Y (Abs) of the pure water after immersing the stretched film is preferably 0.003 or less, more preferably 0.002 or less. The absorbance Y can be measured by, for example, the method described in the examples.

[0147] The PVA-based membrane of the present invention may further contain a plasticizer. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, and trimethylolpropane. The PVA-based membrane of the present invention may contain one or more of these plasticizers. Among these, from the viewpoint of easily improving stretchability, glycerin is preferred.

[0148] When the PVA-based membrane of the present invention contains a plasticizer, the content of the plasticizer is preferably 1 part by mass or more, more preferably 3 parts by mass or more, still more preferably 5 parts by mass or more, 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, still 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, relative to 100 parts by mass of the PVA-based resin (α). If the content of the plasticizer is above the above lower limit, it is easy to improve the stretchability of the PVA-based membrane. In addition, if the content of the plasticizer is below the above upper limit, it is advantageous from the viewpoint of processability. It should be noted that the content of the plasticizer based on the mass of the PVA-based membrane can also be selected from the above range.

[0149] The PVA-based membrane of the present invention may further contain a surfactant. By including a surfactant, the film-forming property is improved during film production, the occurrence of uneven thickness of the PVA-based membrane is easily suppressed, and in addition, the PVA-based membrane is easily peeled off from the rollers and belts used in film production. Among surfactants, from the viewpoint of easily improving the peelability from rollers, belts, etc. during film production, an anionic surfactant or a nonionic surfactant is preferred.

[0150] Examples of the anionic surfactant include carboxylic acid types such as potassium laurate; sulfate ester types such as polyoxyethylene lauryl ether sulfate and octyl sulfate; sulfonic acid types such as dodecylbenzenesulfonate, etc.

[0151] Examples of the nonionic surfactant are preferably 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 laurylamide; polypropylene glycol ether types such as polyoxyethylene polyoxypropylene ether; alkanolamide types such as diethanolamine oleate; allyl phenyl ether types such as polyoxyalkylene allyl phenyl ether, etc. The surfactants can be used alone or in combination of two or more.

[0152] When the PVA-based membrane of the present invention contains a surfactant, the content of the surfactant is preferably 0.01 part by mass or more, more preferably 0.02 part by mass or more, further preferably 0.05 part by mass or more, and preferably 5 parts by mass or less, more preferably 1 part by mass or less, further preferably 0.5 part by mass or less, and even more preferably 0.3 part by mass or less, relative to the PVA-based resin (α). If the content of the surfactant is above the above lower limit, the film-forming property and peelability during film production are easily improved. If the content of the surfactant is below the above upper limit, the adhesion caused by the surfactant oozing out to the film surface can be suppressed, and the processability is easily improved. It should be noted that the content of the surfactant based on the mass of the PVA-based membrane can also be selected from the above range.

[0153] The PVA-based membrane of the present invention may further contain additives such as antioxidants, antifreezing agents, pH adjusters, masking agents, anti-coloring agents, oil agents, and other resins other than the PVA-based resin, as needed. When the PVA-based membrane contains this additive, the content of the additive is preferably 10% by mass or less, more preferably 5% by mass or less, further preferably 1% by mass or less, and preferably 0.01% by mass or more, relative to the mass of the PVA-based membrane.

[0154] The PVA-based membrane of the present invention can be a single-layer membrane or a multi-layer membrane as long as it satisfies formula (I). The composition and thickness of the membranes constituting the multi-layer membrane can be the same or different in each membrane. The interface between the membranes in the multi-layer membrane may not be visible completely or partially. That is, the interface between the membranes is not visible during manufacturing, and a single-layer membrane can be formed in appearance. In the case of a multi-layer membrane, in such a way that the multi-layer membrane itself satisfies formula (I), the PVA-based resin (α) and the compound (β) are respectively contained in at least one of the membranes constituting the multi-layer membrane, and preferably the PVA-based resin (α) is contained in all the membranes. In addition, in the case of a multi-layer membrane, for the respective contents of the above-mentioned PVA-based resin (α) and the additives, the mass of the PVA-based membrane used as a reference refers to the mass of the entire multi-layer membrane, and for the respective contents of the above-mentioned compound (β), plasticizer, and surfactant, the mass of the PVA-based resin (α) used as a reference refers to the mass of the PVA-based resin (α) contained in the entire multi-layer membrane (that is, the total amount of the PVA-based resin (α) contained in the multi-layer membrane). In addition, these contents can be calculated considering the feeding amount during the formation of the multi-layer membrane, the thickness of the layers or membranes constituting the multi-layer membrane, etc.

[0155] As a method for adjusting to the range of formula (I), in the case where the PVA-based membrane is a multi-layer membrane, a method for adjusting the order, composition, and thickness of the layers or membranes in such a way that the portion with a higher concentration of the compound (β) based on the concentration of the PVA-based resin (α) is within the range of 60% of the central portion in the thickness direction of the membrane; in the case of a single-layer membrane, a method for partially removing the compound (β) from the PVA-based membrane containing the compound (β) in such a way that the portion with a higher concentration of the compound (β) based on the concentration of the PVA-based resin (α) is within the range of 60% of the central portion in the thickness direction of the membrane, etc.

[0156] From the viewpoint of facilitating the adjustment of the concentration of the compound (β) in the thickness direction of the membrane and easily adjusting to the range of formula (I), the PVA-based membrane is preferably a multi-layer membrane. It should be noted that, as described above, this multi-layer membrane can be a multi-layer membrane in which the interface is not visible, that is, a membrane that can be regarded as a single-layer membrane in appearance.

[0157] Specifically, as a single-layer membrane, for example, a single-layer PVA-based membrane containing the PVA-based resin (α) and the compound (β) can be cited. As a multi-layer membrane, for example:

[0158] The PVA-based membrane A having, in sequence, a PVA-based membrane 1 containing the PVA-based resin (α1) / a PVA-based resin layer containing the PVA-based resin (α3) and the compound (β) / a PVA-based membrane 2 containing the PVA-based resin (α2);

[0159] A PVA film B having, in order, a PVA film layer 1 containing a PVA-based resin (α1) / a PVA-based resin layer containing a PVA-based resin (α3) and a compound (β1) / a PVA film layer 2 containing a PVA-based resin (α2) / a PVA-based resin layer containing a PVA-based resin (α4) and a compound (β2) / a PVA film layer 3 containing a PVA-based resin (α5).

[0160] Among these, from the viewpoint of easily improving the water resistance of the PVA film layer, and the damp heat resistance and water resistance of the stretched film, PVA film layer A is more preferred. It should be noted that the PVA-based resins (α1) to (α5) are respectively PVA-based resins selected from the aforementioned PVA-based resin (α). In addition, the compounds (β1) and (β2) are respectively nitrogen element-containing compounds selected from the aforementioned compound (β).

[0161] In PVA film layer A, from the viewpoint of easily improving the water resistance of the PVA film layer, and the damp heat resistance and water resistance of the stretched film, the PVA-based resin (α3) is preferably the same as at least one selected from the PVA-based resin (α1) and the PVA-based resin (α2), and more preferably the same as both the PVA-based resin (α1) and the PVA-based resin (α2). It should be noted that with respect to PVA film layer A, the compound (β) is not contained as an essential component in the PVA film layer 1 and the PVA film layer 2, but the PVA film layer 1 and / or the PVA film layer 2 may contain the compound (β) within the range satisfying the formula (I).

[0162] In PVA film layer B, from the viewpoint of easily improving the water resistance of the PVA film layer, and the damp heat resistance and water resistance of the stretched film, the PVA-based resin (α3) and the PVA-based resin (α4) are preferably the same as at least one selected from the PVA-based resin (α1), the PVA-based resin (α2), and the PVA-based resin (α5), more preferably the same as at least two kinds, and further preferably the same as all kinds. In addition, the PVA-based resin (α3) and the PVA-based resin (α4) may be the same or different. In addition, the compounds (β1) and (β2) may be the same or different, and are preferably the same from the viewpoint of easily improving the water resistance of the PVA film layer, and the damp heat resistance and water resistance of the stretched film. It should be noted that with respect to PVA film layer B, the compound (β) is not contained as an essential component in the PVA film layers 1, 2, and 3, but at least one of the PVA film layers 1, 2, and 3 may contain the compound (β) within the range satisfying the formula (I).

[0163] In the case where the PVA-based membrane of the present invention is a multilayer membrane, the number of membranes and layers constituting the multilayer membrane is not particularly limited, preferably 2 or more, more preferably 3 or more, and preferably 9 or less, more preferably 7 or less, and further preferably 5 or less. In addition, from the viewpoints of easily improving the stretchability and water resistance of the PVA-based membrane, and the hydrothermal resistance and water resistance of the stretched membrane, all the membranes and layers constituting the multilayer membrane preferably contain a PVA-based resin.

[0164] The PVA-based membrane of the present invention may contain other membranes or layers on one side or both sides.

[0165] The thickness of the PVA-based membrane of the present invention can be appropriately selected according to the use, preferably 1 μm or more, more preferably 5 μm or more, further preferably 10 μm or more, still further preferably 20 μm or more, particularly preferably 30 μm or more, and more particularly preferably 40 μm or more, and preferably 250 μm or less, more preferably 150 μm or less, further preferably 100 μm or less, and still further preferably 80 μm or less. If the thickness of the PVA-based membrane is above the above lower limit, it is not likely to break during stretching, and it is easy to improve the water resistance of the PVA-based membrane, and the hydrothermal resistance and water resistance of the stretched membrane. In addition, if the thickness of the PVA-based membrane is below the above upper limit, it is easy to manufacture a stretched membrane with good productivity, which is advantageous from the viewpoints of optical properties and thinning. It should be noted that in the case where the PVA-based membrane is a multilayer membrane, the thickness of the above PVA-based membrane refers to the thickness of the multilayer membrane itself (that is, the total thickness of the membranes constituting the multilayer membrane). In addition, the thickness of the PVA-based membrane can be measured using a film thickness meter, and can be measured by, for example, the method described in the examples.

[0166] 〔Method for manufacturing a polyvinyl alcohol-based membrane〕

[0167] As the method for manufacturing the PVA-based membrane of the present invention, there is no particular limitation, and examples thereof include a method of laminating layers or membranes in a manner that satisfies formula (I). Hereinafter, the manufacturing method of the present invention will be described using a preferred embodiment of the present invention, but the present invention is not limited to this embodiment.

[0168] In a preferred embodiment of the present invention, the PVA-based membrane of the present invention can be manufactured by the following method, which includes a step of laminating a PVA-based membrane 1 containing a PVA-based resin (α1) and a PVA-based membrane 2 containing a PVA-based resin (α2) by means of a PVA-based resin aqueous solution (sometimes referred to as a PVA-based aqueous solution) containing a PVA-based resin (α3) and a compound (β). The obtained PVA-based membrane is the above PVA-based membrane A [PVA-based membrane 1 / PVA-based resin layer / PVA-based membrane 2]. In the case of such a layer structure, since the PVA-based resin is contained in all the membranes and layers, the interfaces of the respective membranes or layers may sometimes not be observed.

[0169] The PVA-based membrane 1 used in the foregoing process can be obtained by forming a film from a film-forming stock solution containing the foregoing PVA-based resin (α1). Regarding the PVA-based membrane 2, it can be similarly obtained by forming a film from a film-forming stock solution containing the foregoing PVA-based resin (α2).

[0170] The film-forming stock solution can be prepared by mixing the foregoing PVA-based resin (α1) or the foregoing PVA-based resin (α2), and optionally the foregoing plasticizer, the foregoing surfactant, the foregoing additive, and a liquid solvent. Examples of the liquid solvent include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, diethylenetriamine, etc. These liquid solvents can be used alone or in combination of two or more. Among these, water can be suitably used from the viewpoints of environmental burden and recyclability.

[0171] The volatile fraction (water content) of the film-forming stock solution varies depending on the film-forming method, film-forming conditions, etc., and is usually preferably 50 to 95% by mass, more preferably 55 to 85% by mass, and further preferably 60 to 80% by mass. If the volatile fraction of the film-forming stock solution is above the above lower limit, it is easy to prevent the viscosity of the film-forming stock solution from becoming too high and difficult to perform filtration and defoaming during the preparation of the film-forming stock solution, which is advantageous from the viewpoint of manufacturing a film with few foreign matters and defects. In addition, if the volatile fraction of the film-forming stock solution is below the above upper limit, it is easy to prevent the concentration of the film-forming stock solution from becoming too low and difficult to perform industrial film formation.

[0172] As the film-forming method when forming a film using the film-forming stock solution, for example, a wet film-forming method, a gel film-forming method, a casting film-forming method, an extrusion film-forming method, etc. can be adopted. In addition, a method based on a combination thereof can also be adopted. Among the above film-forming methods, the casting film-forming method or the extrusion film-forming method is preferred because a PVA-based membrane with uniform thickness and width and good physical properties can be obtained.

[0173] As a specific film-forming method, there is no particular limitation, and examples include: using a T-slot die, a hopper plate, an I-die, a lip coater die, etc., uniformly spraying the film-forming stock solution onto the circumferential surface of a rotating and heated roller or belt, evaporating the volatile components from one surface of the film sprayed onto the roller or belt, and drying to form a film; or, after drying in this way, further drying on the circumferential surface of one or more rotating rollers or passing it through a hot air drying device to further dry and thus form a film. In addition, after peeling from the foregoing roller, heat treatment can be performed using other rollers or hot air.

[0174] As the surface temperature of the roller or belt used in film formation, it is preferably 50°C or higher, more preferably 60°C or higher, further preferably 65°C or higher, still further preferably 70°C or higher, and preferably 120°C or lower, more preferably 100°C or lower, further preferably 95°C or lower, still further preferably 90°C or lower. If the surface temperature is above the above lower limit, it is easy to remove moisture with good productivity. In addition, if the surface temperature is below the above upper limit, it is easy to suppress the occurrence of surface unevenness caused by rapid moisture evaporation.

[0175] By operating in this way, the PVA-based membrane 1 and the PVA-based membrane 2 used in the foregoing process can be manufactured.

[0176] The PVA-based aqueous solution used in the foregoing process can be prepared by mixing the foregoing PVA-based resin (α3), the foregoing compound (β), and optionally the foregoing plasticizer, the foregoing surfactant, the foregoing additive, and the foregoing liquid solvent. The content of the PVA-based resin in the PVA-based aqueous solution is not particularly limited, and can be, for example, 1 to 50% by mass, preferably 3 to 20% by mass, relative to the mass of the PVA-based aqueous solution. If the content of the PVA-based resin (α3) is within the above range, it is easy to improve the adhesiveness between the PVA-based membrane 1 and the PVA-based membrane 2, and it is easy to obtain a PVA-based membrane with excellent adhesion.

[0177] In the foregoing process of the present invention, the PVA-based membrane 1 and the PVA-based membrane 2 are laminated with the aid of the foregoing PVA-based aqueous solution. The lamination method is not particularly limited, and examples thereof include: a method of dropping the PVA-based aqueous solution between the PVA-based membrane 1 and the PVA-based membrane 2 and laminating using a laminator, a roll, etc.; a method of dropping or coating the PVA-based aqueous solution on one or both of the PVA-based membrane 1 and the PVA-based membrane 2 and then laminating the two membranes. Among these, from the viewpoint of being easily adjusted to the range of formula (I), a method of dropping the PVA-based aqueous solution between the PVA-based membrane 1 and the PVA-based membrane 2 and laminating using a laminator or the like is preferred. The temperature at the time of lamination, for example, the lamination temperature, can be appropriately selected according to the composition, combination, etc. of the membranes to be laminated, and is preferably 15 to 40°C, more preferably 15 to 30°C. After laminating the membranes, it can be dried using a dryer or the like. The drying temperature is not particularly limited, and can be, for example, 30 to 100°C, preferably 40 to 80°C.

[0178] In one embodiment of the present invention, the PVA-based resin (α3) contained in the PVA-based membrane A is preferably the same as at least one selected from the PVA-based resin (α1) and the PVA-based resin (α2), and more preferably the same as both the PVA-based resin (α1) and the PVA-based resin (α2). If it is in this form, problems in processing such as warping are less likely to occur.

[0179] In the above-described embodiments, the aforementioned PVA-based membranes 1 and 2 may not contain the compound (β), but may contain the compound (β) if the formula (I) is satisfied. Further, the thicknesses of the PVA-based membranes 1 and 2 may be the same or different from each other, and are preferably the same from the viewpoint of facilitating adjustment to the range of the formula (I).

[0180] The thicknesses of the PVA-based membranes 1 and 2 are each preferably 0.5 μm or more, more preferably 3 μm or more, still more preferably 5 μm or more, even more preferably 10 μm or more, particularly preferably 15 μm or more, and most preferably 20 μm or more, and are preferably 130 μm or less, more preferably 80 μm or less, still more preferably 50 μm or less, and even more preferably 40 μm or less.

[0181] Further, from the viewpoint of facilitating improvement of the adhesiveness of the film, the thickness of the PVA-based resin layer formed from the PVA-based aqueous solution is preferably 0.30 μm or more, more preferably 0.40 μm or more, still more preferably 0.50 μm or more, and is preferably 20 μm or less, more preferably 10 μm or less, still more preferably 5 μm or less, and even more preferably 3 μm or less.

[0182] 〔Stretched film〕

[0183] The present invention includes a stretched film containing a PVA-based resin (α) and a nitrogen-containing compound (β) and satisfying the following formula (II):

[0184] (G / H) / (E / F)>3 (II)

[0185] [In the formula, within the range of 60% of the central portion in the thickness direction of the aforementioned stretched film, at least 20 points equally spaced in the thickness direction are measured by TOF-SIMS. In the measurement data, when the point where the intensity value of the CN - signal derived from the nitrogen-containing compound (β) reaches the maximum is defined as P MAX and the point where it reaches the minimum is defined as P min ,

[0186] E represents the intensity value of the CN min signal derived from the nitrogen-containing compound (β) at the time of P - ,

[0187] F represents the intensity value of the C min signal derived from the polyvinyl alcohol-based resin (α) at the time of P 2 H 3 O 2 - ,

[0188] G represents the intensity value of the signal at the time of P MAXCN from the compound (β) containing a nitrogen element at - The intensity value of the signal,

[0189] H represents the aforementioned P MAX C from the polyvinyl alcohol-based resin (α) at 2 H 3 O 2 - The intensity value of the signal

[0190] The present inventors found that: in a stretched film containing a PVA-based resin (α) and a compound (β), if the signal intensity ratio (G / H) / (E / F) exceeds 3, the moisture and heat resistance can be improved, and even when left for a long time under high temperature and high humidity, adverse conditions such as decomposition of the compound (β) can be suppressed. Furthermore, the present inventors found that: if the aforementioned signal intensity ratio (G / H) / (E / F) exceeds 3, the water resistance can also be improved, and the detachment of the compound (β) in water or an aqueous solution can be suppressed. Therefore, for example, when treating the stretched film in an aqueous bath, contamination of the aqueous bath can be prevented. It is speculated that this is because: the concentration of the compound (β) in the central portion in the thickness direction of the stretched film satisfying formula (II) is high, and thus the compound (β) in the film is not easily affected by the external environment.

[0191] If the signal intensity ratio (G / H) / (E / F) is 3 or less, there is a tendency for the moisture and heat resistance and water resistance of the stretched film to decrease. In the stretched film of the present invention, the signal intensity ratio (G / H) / (E / F) can be appropriately selected according to the concentration of the compound (β) etc., preferably 4 or more, more preferably 5 or more, further preferably 7 or more, for example, it can be 10 or more, 13 or more, 15 or more, or 17 or more. If the signal intensity ratio (G / H) / (E / F) is above the above lower limit, the moisture and heat resistance and water resistance of the stretched film can be improved. In addition, the signal intensity ratio (G / H) / (E / F) is preferably 300 or less, more preferably 100 or less, further preferably 50 or less, still more preferably 40 or less, and particularly preferably 25 or less. If the signal intensity ratio (G / H) / (E / F) is below the above upper limit, the manufacturing cost of the film can be suppressed and the film can be manufactured with good productivity.

[0192] In one embodiment of the present invention, the position of G in formula (I) is preferably within the range of 50% of the central portion in the thickness direction of the film, more preferably within the range of 40%, further preferably within the range of 30%, and further preferably within the range of 20%. If the position of G is within the above range, the concentration of compound (β) tends to be higher in the central portion. Therefore, the heat and humidity resistance and water resistance of the stretched film are likely to be improved. In addition, in one embodiment of the present invention, the position of E in formula (I) is preferably within the range of 20 to 60% of the central portion in the thickness direction of the film, more preferably within the range of 30 to 60%, and further preferably within the range of 40 to 60%. If the position of E is within the above range, the heat and humidity resistance and water resistance of the stretched film tend to be improved.

[0193] The left side of the aforementioned formula (II) is obtained by replacing (C / D) / (A / B) in the aforementioned formula (I) with (G / H) / (E / F). By performing TOF-SIMS measurement using the same method as for the aforementioned formula (I), the left side of formula (II) can be determined.

[0194] The PVA-based resin (α) contained in the stretched film satisfying formula (II) is the same as the above-mentioned PVA-based resin (α) contained in the PVA-based film satisfying formula (I).

[0195] In addition, the nitrogen-containing compound (β) contained in the stretched film satisfying formula (II) is the same as the above-mentioned nitrogen-containing compound (β) contained in the PVA-based film satisfying formula (I). That is, the nitrogen-containing compound (β) contained in the stretched film preferably has the aforementioned aromatic ring, and / or is preferably a dye or pigment.

[0196] In one embodiment of the present invention, the content of the PVA-based resin (α) contained in the stretched film is preferably 65% by mass or more, more preferably 70% by mass or more, further preferably 80% by mass or more, still further preferably 85% by mass or more, particularly preferably 90% by mass or more, more particularly preferably 95% by mass or more, and especially further preferably 97% by mass or more, and is preferably 99.99% by mass or less, more preferably 99.9% by mass or less, relative to the mass of the stretched film. If the content of the PVA-based resin (α) is above the above lower limit, the mechanical strength, heat and humidity resistance, and water resistance of the stretched film are likely to be improved. If the content of the PVA-based resin (α) is below the above upper limit, the optical properties of the stretched film are likely to be improved.

[0197] In one embodiment of the present invention, the content of the nitrogen-containing compound (β) contained in the stretch film is preferably 0.01 part by mass or more, more preferably 0.05 part by mass or more, further preferably 0.07 part by mass or more, particularly preferably 0.1 part by mass or more, and preferably 20 parts by mass or less, more preferably 15 parts by mass or less, further preferably 10 parts by mass or less, still 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 (α). If the content of the compound (β) is above the above lower limit, it is easy to improve the optical properties of the stretch film. In addition, if the content of the compound (β) is below the above upper limit, it is easy to suppress the manufacturing cost of the film and manufacture the film with good productivity. It should be noted that the content of the compound (β) based on the mass of the stretch film can also be selected from the above range.

[0198] The stretch film of the present invention may further contain at least one selected from the aforementioned plasticizer, the aforementioned surfactant, and the aforementioned additive. The content of each of the aforementioned plasticizer, the aforementioned surfactant, and the aforementioned additive can be selected from the range of each content described in the item "<PVA-based film>".

[0199] The stretch film of the present invention can be a single-layer film or a multilayer film as long as it satisfies the formula (II). The composition and thickness of the films constituting the multilayer film can be the same or different in each film. The interface between the films in the multilayer film may not be visible completely or partially. That is, the interface between the films is not visible during manufacturing, and a single-layer film can be formed in appearance. In the case of a multilayer film, the PVA-based resin (α) and the compound (β) are respectively contained in at least one of the films constituting the multilayer film in such a manner that the multilayer film itself satisfies the formula (II), and preferably the PVA-based resin (α) is contained in all the films.

[0200] As a method for adjusting to the range of the formula (II), the same methods as those for adjusting to the range of the above formula (I) can be cited. As the layer structure when the stretch film is a multilayer film, the same layer structure as that of the PVA-based film when it is a multilayer film can be cited. In addition, when the stretch film of the present invention has the same layer structure as the above PVA-based film A, similarly to the PVA-based film A, from the viewpoint of easily improving the heat and humidity resistance and water resistance, the PVA-based resin (α3) is preferably the same as at least one selected from the PVA-based resin (α1) and the PVA-based resin (α2), and more preferably the same as both the PVA-based resin (α1) and the PVA-based resin (α2).

[0201] When the stretch film of the present invention has the same layer constitution as the above-mentioned PVA-based film B, from the viewpoint of easily improving the moisture and heat resistance and water resistance, regarding the relationship between the PVA-based resin (α3) and PVA-based resin (α4) and the PVA-based resins (α1), (α2), and (α5), it is preferably the same as the above-mentioned PVA-based film B.

[0202] The thickness of the stretch film can be appropriately selected according to the use, and is preferably 0.1 μm or more, more preferably 1 μm or more, further preferably 5 μm or more, still further preferably 10 μm or more, particularly preferably 20 μm or more, and even more particularly preferably 25 μm or more, and is preferably 200 μm or less, more preferably 100 μm or less, and further preferably 50 μm or less. If the thickness of the stretch film is above the above lower limit, it is easy to improve the moisture and heat resistance and water resistance. In addition, if the thickness of the stretch film is below the above upper limit, it is advantageous from the viewpoints of optical properties and thinning. It should be noted that in the case where the stretch film is a multilayer film, the thickness of the above-mentioned stretch film refers to the thickness of the multilayer film itself (that is, the total thickness of the films constituting the multilayer film). In addition, the thickness of the stretch film can be measured using a film thickness meter and can be measured by, for example, the method described in the examples.

[0203] As described above, the stretch film of the present invention has excellent water resistance and can suppress the detachment of the compound (β) in water or an aqueous solution. Therefore, when the stretch film is immersed in pure water at 50 °C for 15 minutes and then the film is taken out, the absorbance Y of the pure water is small. The absorbance Y of the stretch film can be selected from the numerical range of the absorbance Y described in the item "<PVA-based film>".

[0204] As described above, the stretch film of the present invention has excellent moisture and heat resistance. Therefore, when the compound (β) functions as a dye or pigment, it is possible to suppress the change in the dichroic ratio before and after the moisture and heat resistance test. In other words, even when the stretch film of the present invention is left for a long time under high temperature and high humidity, it is possible to suppress the reduction of the polarization performance. The Δ dichroic ratio of the stretch film can be selected from the numerical range of the Δ dichroic ratio described in the item "<PVA-based film>".

[0205] In a preferred embodiment of the present invention, the stretch film that satisfies the formula (II) of the present invention is sometimes obtained by stretching the PVA-based film that satisfies the formula (I) of the present invention.

[0206] 〔Manufacturing method of stretch film〕

[0207] The manufacturing method of the stretched film of the present invention is not particularly limited, and examples thereof include: a method of stretching a PVA-based film containing a PVA-based resin (α) and a compound (β) in a manner that satisfies formula (II). As long as the stretched film satisfies formula (II) after stretching, the type of the PVA-based film as the raw material is not particularly limited, and a PVA-based film that satisfies formula (I) can be used, or a PVA-based film that does not satisfy formula (I) can also be used. From the viewpoint of easily adjusting to the range of formula (II), it is preferable to use a PVA-based film that satisfies formula (I) of the present invention.

[0208] The stretching can be uniaxial stretching, biaxial stretching or other multi-axial stretching, and uniaxial stretching is preferred, and it can be carried out by any one of a wet stretching method or a dry stretching method. In the case of the wet stretching method, it can be carried out in an aqueous solution containing boric acid. In addition, in the case of the dry stretching method, a water-absorbed PVA-based film can be used and carried out in the air. Among these, from the viewpoint of easily adjusting to the range of formula (II), the wet stretching method is preferred, and it is more preferably to carry out uniaxial stretching in an aqueous solution containing boric acid. The concentration of boric acid in the boric acid aqueous solution is preferably 0.5 to 6% by mass, more preferably 1 to 5% by mass, and further preferably 1.5 to 4% by mass. It should be noted that the boric acid aqueous solution can contain potassium iodide.

[0209] The stretching temperature is preferably 30 to 90 °C, more preferably 40 to 80 °C, and further preferably 50 to 70 °C. The stretching ratio is preferably 3 times or more, more preferably 4 times or more, and further preferably 5 times or more. If the stretching ratio is above the above lower limit, it is easy to improve the optical properties (such as polarization performance, luminous efficiency, etc.). The upper limit of the stretching ratio is not particularly limited, and it is preferably 10 times or less, more preferably 8 times or less.

[0210] After stretching, drying is preferably carried out. 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.

[0211] 〔Use〕

[0212] The PVA-based film and the stretched film of the present invention can be used as a polarizing film, a photon up-conversion film, a light-adjusting film, etc. Among these, they can be suitably used as a polarizing film and a photon up-conversion film.

[0213] Examples

[0214] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples at all.

[0215] It should be noted that the following shows the respective evaluation methods used in the following examples and comparative examples.

[0216] <Saponification degree and viscosity-average polymerization degree of PVA-based resin (α)>

[0217] The saponification degree and viscosity-average polymerization degree of PVA-based resin (α) were measured in accordance with JIS K6726 (1994).

[0218] <Measurement of thickness of PVA-based membranes 1 and 2, PVA-based membrane, and stretched membrane>

[0219] For the PVA-based membranes 1, PVA-based membrane 2, PVA-based membrane, and stretched membrane obtained in each example or comparative example, the thickness of the central part in the width direction of each membrane was measured using a film thickness gauge (manufactured by Ono Sokki Co., Ltd., "DG-5100").

[0220] <TOF-SIMS measurement of PVA-based membrane 1 and PVA-based membrane>

[0221] For the PVA-based membrane 1 obtained in each comparative example and the PVA-based membrane obtained in each example, a time-of-flight secondary ion mass spectrometer (TOF-SIMS) was used to measure the intensity values of the TOF-SIMS signals of C 2 H 3 O 2 - from PVA-based resin (α) and the intensity values of the TOF-SIMS signals of CN - from the nitrogen-containing compound (β) throughout the entire thickness direction of each membrane. Specifically, first, sputtering ions were irradiated onto the surface layer of each membrane, and sputtering and measurement were alternately repeated to perform compositional analysis throughout the entire thickness direction of each membrane. And the following intensity values were extracted: the TOF-SIMS signals of C 2 H 3 O 2 - or CN -Among the intensity values of the signals, when the thickness of each film is set to X (μm), the intensity values of the TOF-SIMS signals at 20 points equally spaced along the thickness direction within the range from the center of the film thickness direction to each surface (outer side) up to 0.3X (μm), that is, within a total range of 0.6X. For example, as in Example 1 described later, when the thickness of the PVA-based film is 61 (μm), the intensity values of the TOF-SIMS of C 2 H 3 O 2 - or CN - from the PVA-based resin (α) or the nitrogen-containing compound (β) are extracted at 20 points existing at intervals of 1.83 (μm) along the thickness direction within the range from the center of the film thickness direction to the outside up to 18.3 (μm) respectively, with a total range of 36.6 (μm) (actually, based on the measurement accuracy, 20 points existing at intervals of 1.8 μm along the thickness direction). And among the 20 points where the intensity values of the TOF-SIMS signals are extracted, the point where the intensity value of the CN - signal from the nitrogen-containing compound (β) reaches the maximum is set as P MAX , and the point where it reaches the minimum is set as P min . Further, when it is P min , the intensity value of the CN - signal of the TOF-SIMS from the nitrogen-containing compound (β) is set as A, when it is P min , the intensity value of the C 2 H 3 O 2 - signal of the TOF-SIMS from the PVA-based resin (α) is set as B, when it is P MAX , the intensity value of the CN - signal of the TOF-SIMS from the nitrogen-containing compound (β) is set as C, when it is P MAX , the intensity value of the C 2 H 3 O 2 - signal of the TOF-SIMS from the PVA-based resin (α) is set as D, and the intensity values A, B, C, D and their ratio ((C / D) / (A / B)) are calculated. In addition, the measurement conditions of TOF-SIMS are as follows.

[0222] (Measurement conditions of TOF-SIMS)

[0223] High-resolution mode

[0224] Device name: Manufactured by ION-TOF, "TOF-SIMS5"

[0225] Primary ion source: Bi 3 ++ Bu mode, 0.2 pA at 25 keV (10 kHz)

[0226] Sputtering ion source: Ar 1600 + , 7 nA at 20 keV (100 μsec)

[0227] Charge correction: Electron Flooding On

[0228] Measurement range: 500×500 μm Sputtering, 200×200 μm Analysis

[0229] One cycle: 2 flames analysis / 7 flames sputtering

[0230] <TOF-SIMS Measurement of Stretched Films>

[0231] For the stretched films obtained in each example or each comparative example, a time-of-flight secondary ion mass spectrometer (TOF-SIMS) was used to measure the intensity values of the TOF-SIMS signals of C 2 H 3 O 2 - from the PVA-based resin (α) and the intensity values of the TOF-SIMS signals of CN - from the nitrogen-containing compound (β) throughout the entire thickness direction of each film. Specifically, first, sputtering ions were irradiated onto the surface layer of each film, and sputtering and measurement were alternately repeated to perform compositional analysis throughout the entire thickness direction of each film. And the following intensity values were extracted: the TOF-SIMS signals of C 2 H 3 O 2 - or CN -Among the intensity values of the signals, when the thickness of each film is set to Y (μm), the intensity values of the TOF-SIMS signals at 20 points that are equally spaced along the thickness direction within the range from the center of the film thickness direction to each surface (outer side) up to 0.3Y (μm), that is, within a total range of 0.6Y. For example, as in Example 1 described later, when the thickness of the stretched film is 34 μm, the intensity values of the TOF-SIMS signals at 20 points (actually 20 points spaced at 1.0 μm intervals along the thickness direction based on the measurement accuracy) within the range from the center of the film thickness direction to the outer side up to 10.2 (μm) respectively, that is, within a total range of 20.4 (μm), and originating from the PVA-based resin (α) or the nitrogen-containing compound (β) are C 2 H 3 O 2 - or CN - intensity values of the signals. And among the 20 points where the intensity values of the TOF-SIMS signals are extracted, the point where the intensity value of the CN - signal of the TOF-SIMS originating from the nitrogen-containing compound (β) reaches the maximum is designated as P MAX , and the point where it reaches the minimum is designated as P min . Further, the intensity value of the CN min signal of the TOF-SIMS originating from the nitrogen-containing compound (β) when at P - is set as E, the intensity value of the C min signal of the TOF-SIMS originating from the PVA-based resin (α) when at P 2 H 3 O 2 - is set as F, the intensity value of the CN MAX signal of the TOF-SIMS originating from the nitrogen-containing compound (β) when at P - is set as G, and the intensity value of the C MAX signal of the TOF-SIMS originating from the PVA-based resin (α) when at P 2 H 3 O 2 - is set as H, and the ratio ((G / H) / (E / F)) of these intensity values E, F, G, H is calculated. In addition, the measurement conditions of TOF-SIMS are as follows.

[0232] (Measurement conditions of TOF-SIMS)

[0233] High-resolution mode

[0234] Device name: Manufactured by ION-TOF, "TOF-SIMS5"

[0235] Primary ion source: Bi 3 ++ Bu mode, 0.2 pA at 25 keV (10 kHz)

[0236] Sputtering ion source: Ar 1600 + , 7 nA at 20 KeV (100 μsec)

[0237] Charge correction: Electron Flooding On

[0238] Measurement range: 500×500 μm Sputtering, 200×200 μm Analysis

[0239] One cycle: 2 flames analysis / 7 flames sputtering

[0240] <Absorbance X of pure water after impregnating the PVA mesoporous membrane>

[0241] Samples with a width of 3 cm × a length of 5 cm were cut from the central part of the PVA mesoporous membranes obtained in each comparative example and the PVA mesoporous membranes obtained in each example. The samples were immersed in 40 mL of pure water at 30°C for 5 minutes, and then the membranes were taken out. Subsequently, using a spectrophotometer with an integrating sphere (manufactured by Hitachi, Ltd., "U4100"), the absorbance of the pure water after membrane impregnation was measured, and the maximum value of the absorbance in the visible light wavelength region (380 - 750 nm) was determined as the absorbance X. It should be noted that the wavelength (maximum absorption wavelength) of the absorbance X in Example 1 was 650 nm. Therefore, in Example 2 and Comparative Examples 1 and 2, the absorbance at 650 nm was also set as the absorbance X.

[0242] <Absorbance Y of pure water after impregnating the stretched film>

[0243] Samples with a width of 2 cm × a length of 2 cm were cut from the central part of the stretched films obtained in each example or comparative example. The samples were immersed in 20 mL of pure water at 50°C for 15 minutes, and then the membranes were taken out. Subsequently, using a spectrophotometer with an integrating sphere (manufactured by Hitachi, Ltd., "U4100"), the absorbance of the pure water after membrane impregnation was measured, and the maximum value of the absorbance in the visible light wavelength region (380 - 750 nm) was determined as the absorbance Y. It should be noted that the wavelength (maximum absorption wavelength) of the absorbance Y in Example 1 was 650 nm. Therefore, in Example 2 and Comparative Examples 1 and 2, the absorbance at 650 nm was also set as the absorbance Y.

[0244] <Δ dichroic ratio of the stretched film>

[0245] A sample with a width of 1.5 cm and a length of 3 cm was cut out from the central part of the stretched film obtained in each embodiment or comparative example. Next, a spectrophotometer with an integrating sphere (manufactured by JASCO Corporation, "V7100") was used, and the measurement wavelength was set to the maximum absorption wavelength (650 nm) in the measurement of the above absorbance Y, and the monomer transmittance Ts (%) and polarization degree P (%) of the sample before the moisture and heat resistance test were calculated. In addition, the dichroic ratio Rd at the above maximum absorption wavelength (650 nm) before the moisture and heat resistance test was calculated using the following formula, and this value was set to Rd1. Next, the sample was fixed to a metal frame and left to stand for 500 hours in an atmosphere of 60°C / 90%RH, thereby conducting a moisture and heat resistance test. In addition, a spectrophotometer with an integrating sphere (manufactured by JASCO Corporation, "V7100") was used in the same manner, and the measurement wavelength was set to the above-mentioned maximum absorption wavelength (650 nm), and the single transmittance Ts (%) and polarization degree P (%) of the sample after the moisture and heat resistance test were obtained. Furthermore, the dichroic ratio Rd at the above-mentioned maximum absorption wavelength (650 nm) after the moisture and heat resistance test was obtained using the following formula, and this value was set as Rd2. The value obtained by subtracting Rd1 from Rd2 was calculated as the Δ dichroic ratio.

[0246] Rd=log(Ts / 100-Ts / 100×P / 100) / log(Ts / 100+Ts / 100×P / 100)

[0247] [Example 1]

[0248] (PVA film 1)

[0249] As the PVA-based resin (α1) constituting the PVA-based membrane 1, an ethylene-vinyl alcohol copolymer (saponified product of a copolymer of ethylene-vinyl acetate, degree of polymerization: 2,400, saponification degree: 99.3 mol%, ethylene modification amount: 2.5 mol%) is used. First, a film-forming stock solution is prepared, which contains 100 parts by mass of the PVA-based resin (α1), 10 parts by mass of glycerol as a plasticizer, 0.1 part by mass of sodium lauryl polyoxyethylene ether sulfate as a surfactant, and water as a liquid medium, with a volatile fraction of 66% by mass. The film-forming stock solution is extruded in a film shape from a T-slit die onto a first drying roll (surface temperature: 88°C, circumferential speed: 20.0 m / min). On the first drying roll, hot air (temperature: 90°C, dew point temperature: 10°C) is uniformly blown onto the entire surface that does not contact the first drying roll at a wind speed of 5 m / s, while drying until the volatile fraction of the resin film reaches 25% by mass. Then, it is peeled off from the first drying roll, and using a film-forming apparatus equipped with 18 drying rolls with parallel rotating shafts, it is dried with the second drying roll and subsequent drying rolls (surface temperature: 84°C, circumferential speed: 20.5 m / min) in such a way that the surface of the resin film that contacted the first drying roll and the surface that did not contact the first drying roll face the respective drying rolls alternately. Furthermore, after cutting / removing both ends (corners) in the width direction of the obtained film, it is wound into a roll shape to continuously manufacture a long PVA-based membrane 1 with a thickness of 30 μm.

[0250] (PVA-based membrane 2)

[0251] In the same manner as the production of the PVA-based membrane 1, a long PVA-based membrane 2 with a thickness of 30 μm is continuously manufactured. It should be noted that, as shown in Table 1, the PVA-based resin constituting the PVA-based membrane 2 is designated as the PVA-based resin (α2).

[0252] (PVA-based aqueous solution)

[0253] As the PVA-based resin (α3) contained in the PVA-based aqueous solution, a PVA-based aqueous solution is prepared, which contains 100 parts by mass of an ethylene-vinyl alcohol copolymer (saponified product of a copolymer of ethylene-vinyl acetate, degree of polymerization: 2,400, saponification degree: 99.3 mol%, ethylene modification amount: 2.5 mol%), 60 parts by mass of Direct Blue 15 as a nitrogen-containing compound (β), and the content rate of the PVA-based resin (α3) is 8% by mass.

[0254] (Production of PVA-based membrane)

[0255] Samples measuring 10 cm in width and 15 cm in length were cut from the central portions in the width directions of the manufactured PVA meshes 1 and 2. While dropping the above-manufactured PVA-based aqueous solution between the two cut samples, the two cut samples were pasted using a laminator (manufactured by YOUBON Co., Ltd., "LAMIMAN IKO-650E"). The lamination temperature during lamination was 25°C. The two ends of the pasted film were fixed so that no dimensional change occurred in the length direction, and it was dried for 10 minutes using a dryer at 60°C to obtain a PVA mesh. The PVA mesh is a film having PVA mesh 1 / PVA-based resin layer / PVA mesh 2 in sequence.

[0256] (Stretched film)

[0257] Samples measuring 5 cm in width and 8 cm in length were cut from the central portions in the width and length directions of the above-manufactured PVA mesh in such a way that uniaxial stretching could be performed in a range of 5 cm in width and 5 cm in length. For this sample, during immersion in a 40°C boric acid aqueous solution containing 3.0% by mass of boric acid, it was uniaxially stretched to 5 times its original length in the length direction (stretching treatment). Then, the two ends of the sample were fixed so that no dimensional change occurred in the length direction, and it was dried for 5 minutes using a dryer at 60°C (drying treatment) to obtain a stretched film.

[0258] [Example 2]

[0259] (PVA meshes 1 and 2, PVA-based aqueous solution, PVA mesh, and stretched film)

[0260] The content of Direct Blue 15 contained in the PVA-based aqueous solution was changed to 12 parts by mass, and otherwise, the same operations as in Example 1 were performed to manufacture PVA mesh 1, PVA mesh 2, PVA-based aqueous solution, PVA mesh, and stretched film.

[0261] [Comparative Example 1]

[0262] (PVA mesh 1)

[0263] The thickness of PVA mesh 1 was changed to 60 μm, and otherwise, the same operations as in Example 1 were performed to manufacture PVA mesh 1.

[0264] (Stretched film)

[0265] The sample with a width of 5 cm × a length of 9 cm was cut out from the central part in the width direction of the above-produced PVA film 1 in such a way that uniaxial stretching could be carried out in the range of a width of 5 cm × a length of 5 cm. For this sample, during the period of immersion in water at 48°C for 2 minutes, it was uniaxially stretched (first-stage stretching) to 1.3 times its original length along the length direction to cause swelling (swelling treatment). Then, during the period of immersion in a direct blue 15 solution (dyeing bath) at 48°C containing 0.013% by mass of direct blue 15, 0.42% by mass of sodium sulfate, and 0.42% by mass of sodium tripolyphosphate for 5 minutes, while being uniaxially stretched (second-stage stretching) to 1.8 times (2.4 times in total) along the length direction, dyeing (dyeing treatment) was carried out. Then, during the period of immersion in a boric acid aqueous solution (crosslinking bath) at 40°C containing 2.0% by mass of boric acid for 1 minute, while being uniaxially stretched (third-stage stretching) to 1.1 times (2.7 times in total) along the length direction, crosslinking (crosslinking treatment) was carried out. Then, during the period of immersion in a boric acid aqueous solution (stretching bath) at 58°C containing 3.9% by mass of boric acid, it was uniaxially stretched (fourth-stage stretching) to 1.9 times (5.0 times in total) along the length direction (stretching treatment). Then, it was immersed in a boric acid aqueous solution (washing bath) at 30°C containing 1.5% by mass of boric acid for 1 second without stretching for washing (washing treatment). Then, both ends of the sample were fixed so that no dimensional change occurred in the length direction, and it was dried in a dryer at 70°C for 3 minutes (drying treatment) to obtain a stretched film.

[0266] [Comparative Example 2]

[0267] (PVA film 1)

[0268] As the PVA-based resin (α1) constituting the PVA film 1, an ethylene-vinyl alcohol copolymer (saponified product of a copolymer of ethylene-vinyl acetate, polymerization degree of 2400, saponification degree of 99.3 mol%, and ethylene modification amount of 2.5 mol%) was used. First, as a film-forming stock solution, an aqueous solution containing 100 parts by mass of the PVA-based resin (α1), 10 parts by mass of glycerol as a plasticizer, 0.1 part by mass of polyoxyethylene lauryl ether sulfate as a surfactant, 0.75 part by mass of direct blue 15 as a pigment, and a PVA content of 10% was prepared. This film-forming stock solution was dried on a metal roller 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 manufacture a long strip-shaped PVA film 1 with a thickness of 60 μm.

[0269] (Stretched film)

[0270] Using the above-produced PVA film 1, a stretched film was manufactured in the same manner as in Example 1.

[0271] For the PVA-based membranes 1 and 2, the PVA-based aqueous solution, the PVA-based membrane, and the stretched film obtained in each of the examples or comparative examples, the degree of polymerization, the saponification degree, and the content of the PVA-based resin (α), the type and content of the nitrogen-containing compound (β), and the thickness of each membrane measured by the above method are shown in Table 1.

[0272] For the PVA-based membranes and stretched films obtained in Examples 1 and 2, and the PVA-based membranes 1 and stretched films obtained in Comparative Examples 1 and 2, the thickness, TOF-SIMS, the absorbances X and Y of pure water after membrane immersion, and the Δ dichroism ratio were measured according to the above method. The results are shown in Table 2. It should be noted that in Examples 1 and 2 and Comparative Examples 1 and 2, the positions of C and G in formulas (I) and (II) are respectively within the range of the central 20% in the thickness direction of the membrane, and the positions of A and E in formulas (I) and (II) are respectively within the range of 40 - 60% in the central part of the thickness direction of the membrane. In addition, the thickness of the PVA-based resin layer in the PVA-based membranes 1 and 2 of Example 1 is 0.75 μm, and the thickness of the PVA-based resin layer in the PVA-based membranes 1 and 2 of Example 2 is 0.75 μm.

[0273] [Table 1]

[0274]

[0275] [Table 2]

[0276]

[0277] As shown in Table 2, compared with the PVA-based membrane of Comparative Example 2 where the signal intensity ratio (C / D) / (A / B) is less than 5, the PVA-based membranes of Examples 1 and 2 where the signal intensity ratio (C / D) / (A / B) is 5 or more gave a lower absorbance X (650 nm) of pure water after membrane immersion. From this, it can be confirmed that the PVA-based membrane of the present invention has excellent water resistance.

[0278] In addition, compared with the PVA-based membranes of Comparative Examples 1 and 2 where the signal intensity ratio (G / H) / (E / F) is 3 or less, the stretched films of Examples 1 and 2 where the signal intensity ratio (G / H) / (E / F) exceeds 3 gave lower Δ dichroism ratios before and after the damp heat resistance test and lower absorbance Y (650 nm) of pure water after membrane immersion. From this, it can be confirmed that the stretched film of the present invention has excellent damp heat resistance and water resistance.

[0279] Explanation of reference numerals

[0280] 1, 3... The range of 20% starting from the surface in the thickness direction of the PVA-based membrane

[0281] 2... The range of 60% in the central part in the thickness direction of the PVA-based membrane

[0282] 4… For the CN - signal intensity value, among the 20 points within the range of 60% of the central part in the thickness direction, the point (P MAX )

[0283] 5… P MAX when the C 2 H 3 O 2 - signal intensity value from the PVA-based resin (α)

[0284] 6… P min when the C 2 H 3 O 2 - signal intensity value from the PVA-based resin (α)

[0285] 7… For the CN - signal intensity value, among the 20 points within the range of 60% of the central part in the thickness direction, the point (P min )

[0286] 8… C 2 H 3 O 2 - signal intensity value from the PVA-based resin (α)

[0287] 9… CN - signal intensity value from the compound (β)

[0288] 10… For the CN - signal intensity value from the compound (β), 20 points within the range of 60% of the central part in the thickness direction

[0289] 11… For the C 2 H 3 O 2 - signal intensity value from the PVA-based resin (α), 20 points within the range of 60% of the central part in the thickness direction

[0290] 100… PVA membrane

[0291] 102… When the thickness of the PVA membrane is set to X, the center in the thickness direction of the membrane

Claims

1. A polyvinyl alcohol film comprising a polyvinyl alcohol resin (α) and a nitrogen-containing compound (β), wherein the polyvinyl alcohol film satisfies the following formula (I): (C / D) / (A / B)≥5(I) In formula (I), within 60% of the central portion in the thickness direction of the film, At least 20 points at equal intervals along the thickness direction are measured by TOF-SIMS, and the CN derived from the nitrogen-containing compound (β) is included in the measurement data. - The point where the signal strength reaches the maximum is set as P MAX , the point where the minimum is reached is set as P min hour, A represents the P min CN from nitrogen-containing compounds (β) - The signal strength value, B represents the P min When C derived from the polyvinyl alcohol-based resin (α) 2 H 3 O 2 - The signal strength value, C represents the P MAX CN from nitrogen-containing compounds (β) - The signal strength value, D represents the P MAX When C derived from the polyvinyl alcohol-based resin (α) 2 H 3 O 2 - The signal strength value.

2. The polyvinyl alcohol film according to claim 1, in, The nitrogen-containing compound (β) has an aromatic ring.

3. The polyvinyl alcohol film according to claim 1 or 2, in, The nitrogen-containing compound (β) is a dye or a pigment.

4. The polyvinyl alcohol film according to claim 1 or 2, in, The content of the nitrogen-containing compound (β) is 0.01 to 20 parts by mass based on 100 parts by mass of the polyvinyl alcohol-based resin (α).

5. The polyvinyl alcohol film according to claim 1 or 2, in, The content of the polyvinyl alcohol-based resin (α) is 60 to 99.99% by mass based on the mass of the polyvinyl alcohol-based film. The polyvinyl alcohol film according to claim 1 or 2, which has a thickness of 1 to 250 μm.

7. The method for producing a polyvinyl alcohol film according to claim 1 or 2, wherein include: A step of laminating a polyvinyl alcohol film 1 containing a polyvinyl alcohol resin (α1) and a polyvinyl alcohol film 2 containing a polyvinyl alcohol resin (α2) using a polyvinyl alcohol resin aqueous solution containing a polyvinyl alcohol resin (α3) and a nitrogen-containing compound (β).

8. The manufacturing method according to claim 7, in, The polyvinyl alcohol-based resin (α3) is the same as at least one selected from the polyvinyl alcohol-based resin (α1) and the polyvinyl alcohol-based resin (α2).

9. A stretched film comprising a polyvinyl alcohol-based resin (α) and a nitrogen-containing compound (β), wherein the stretched film satisfies the following formula (II): (G / H) / (E / F)>3(II) In formula (II), at least 20 points at equal intervals along the thickness direction are measured by TOF-SIMS within 60% of the central portion in the thickness direction of the stretched film, and in the measurement data, CN derived from the nitrogen-containing compound (β) is - The point where the signal strength reaches the maximum is set as P MAX , the point where the minimum is reached is set as P min hour, E represents the P min CN from nitrogen-containing compounds (β) - The signal strength value, F represents the P min When C derived from the polyvinyl alcohol-based resin (α) 2 H 3 O 2 - The signal strength value, G represents the P MAX CN from nitrogen-containing compounds (β) - The signal strength value, H represents the P MAX When C derived from the polyvinyl alcohol-based resin (α) 2 H 3 O 2 - The signal strength value.

10. The stretched film according to claim 9, in, The nitrogen-containing compound (β) has an aromatic ring.

11. The stretched film according to claim 9 or 10, in, The nitrogen-containing compound (β) is a dye or a pigment.

12. The stretched film according to claim 9 or 10, in, The content of the nitrogen-containing compound (β) is 0.01 to 20 parts by mass based on 100 parts by mass of the polyvinyl alcohol-based resin (α).

13. The stretched film according to claim 9 or 10, in, The content of the polyvinyl alcohol-based resin (α) is 65 to 99.99% by mass based on the mass of the stretched film.

14. The stretched film according to claim 9 or 10, which has a thickness of 0.1 to 200 μm. 15 . The stretched film according to claim 9 or 10 , which is obtained by stretching the polyvinyl alcohol-based film according to claim 1 .

16. The stretched film according to claim 9 or 10, in, The stretched film is any one of a polarizing film, a photon up-conversion film or a dimming film.

Images