Polyvinyl alcohol film and polarizing film using the same

Abstract

Provided are a PVA film which is excellent in release property from a support and in which optical unevenness is less likely to occur and a polarizing film obtained using the PVA film. The polyvinyl alcohol film of the present invention is a non-water-soluble polyvinyl alcohol film, and when one of two surfaces of the aforementioned polyvinyl alcohol film orthogonal to the thickness direction is defined as a first surface, the proportion of sodium element in all elements (Na1S) obtained by analyzing the aforementioned first surface by X-ray photoelectron spectroscopy is 0.3 to 1.5 mol%, and the proportion of sodium element in all elements (Na1B) obtained by analyzing the surface at a depth of 0.01 μm from the aforementioned first surface by X-ray photoelectron spectroscopy is 0.3 mol% or less.

Description

TECHNICAL FIELD

[0001] The present application relates to a polyvinyl alcohol film which is excellent in release property from a support at the time of film production and in which a polarizing film having less optical unevenness can be produced, and a polarizing film using the same. BACKGROUND

[0002] A polarizing plate having a light-transmitting and light-blocking function and a liquid crystal having a light switching function are both essential components of a liquid crystal display (LCD). In recent years, the application field of the LCD has been expanded from small-sized devices such as calculators and wristwatches at the time of development to various fields such as notebook computers, liquid crystal monitors, liquid crystal color projectors, liquid crystal televisions, car-mounted navigation systems, cellular phones, and measuring devices used indoors and outdoors.

[0003] A polarizing plate is produced by attaching a protective film such as a triacetyl cellulose (TAC) film or a cellulose acetate butyrate (CAB) film to the surface of a polarizing film. Further, the polarizing film is generally produced by subjecting a polyvinyl alcohol film (hereinafter, "polyvinyl alcohol" is sometimes referred to as "PVA") to a dyeing treatment and then to uniaxial stretching, or by subjecting the PVA film to uniaxial stretching while performing the dyeing treatment, or by subjecting the PVA film to uniaxial stretching and then to the dyeing treatment, producing a dyed uniaxially stretched film, and subjecting the film to a fixation treatment with a boron compound, thereby producing the polarizing film. Note that the fixation treatment with the boron compound is sometimes performed simultaneously with the uniaxial stretching or the dyeing treatment.

[0004] In the PVA film for the use, various additives such as a plasticizer are compounded in order to improve various physical properties, and a surfactant is added in order to improve the release property from a support such as a metal roll, a metal belt, or the like used at the time of film production.

[0005] Further, in recent years, as the demand for the PVA film increases, improvement in productivity is desired. The productivity can be improved by increasing the film production speed of the PVA film, but in this case, the release property from the support at the time of production of the PVA film is sometimes insufficient. As a result, there are problems that the PVA film is likely to have surface roughness, film defects, and the polarizing film obtained from the PVA film is likely to have optical unevenness. Thus, in order to improve the release property from the support at the time of production of the PVA film, it is conceivable to add more surfactant to the film production dope of the PVA film. However, if a large amount of surfactant is added, there are problems that optical unevenness derived from the surfactant is likely to occur when the obtained PVA film is used to produce a polarizing film.

[0006] In order to solve such problems of the release property from the support at the time of production of the PVA film, Patent Literature 1 describes that a surfactant containing fluorine is added to the film production dope of the PVA film. Further, Patent Literature 2 describes that a cast substrate is subjected to a coating treatment with a fluorine-containing resin to form a firm fluorine-based resin film.

[0007] Prior Art Documents

[0008] Patent Documents

[0009] Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 2006-307059

[0010] Patent Document 2: Japanese Patent Application Laid-Open (JP-A) No. 2006-305924 SUMMARY

[0011] PROBLEMS TO BE SOLVED BY THE INVENTION

[0012] However, in the method described in Patent Document 1, it is sometimes difficult to cope with environmental pollution due to the use of a fluorine-containing surfactant as a halogen substance. In addition, in the method described in Patent Document 2, since a fluorine resin film is formed on a support such as a roll or a belt as a casting base material, there are problems that the cost for forming or maintaining the fluorine resin film becomes high, and the manufacturing cost of the PVA film easily becomes high.

[0013] Thus, an object of the present application is to provide a PVA film peeled from a support with good peelability, and a polarizing film obtained using such a PVA film. In addition, an object of the present application is to provide a PVA film capable of manufacturing a polarizing film with less optical unevenness, and a polarizing film obtained using such a PVA film.

[0014] MEANS FOR SOLVING THE PROBLEMS

[0015] The present inventors and others have conducted intensive research repeatedly, and as a result, have found that for a non-water-soluble PVA film, when one of two surfaces orthogonal to the thickness direction of the PVA film is set as a first surface, the proportion of sodium element in all elements obtained by analyzing the first surface by X-ray photoelectron spectroscopy is set to a specific range, and the proportion of sodium element in all elements obtained by analyzing the surface at a depth of 0.01 μm from the first surface by X-ray photoelectron spectroscopy is set to a specific range, thereby the above problems can be solved, and further research has been conducted based on this insight, thereby completing the present application.

[0016] In addition, the present inventors and others have conducted intensive research repeatedly, and as a result, have found that for a non-water-soluble PVA film, when one of two surfaces orthogonal to the thickness direction of the PVA film is set as a first surface, the surface at a depth of 0.01 μm from the first surface is analyzed by X-ray photoelectron spectroscopy, and the proportion of sodium element in all elements is set to a specific range, thereby the above problems can be solved, and further research has been conducted based on this insight, thereby completing the present application.

[0017] That is, the present application relates to the following [1] to [8]. [1] A PVA film, wherein when one of two surfaces orthogonal to the thickness direction of the PVA film is set as a first surface, the proportion of sodium element in all elements obtained by analyzing the first surface by X-ray photoelectron spectroscopy is 0.01% or less, and the proportion of sodium element in all elements obtained by analyzing the surface at a depth of 0.01 μm from the first surface by X-ray photoelectron spectroscopy is 0.01% or less. [2] The PVA film according to [1], wherein the proportion of sodium element in all elements obtained by analyzing the first surface by X-ray photoelectron spectroscopy is 0.005% or less. [3] The PVA film according to [1] or [2], wherein the proportion of sodium element in all elements obtained by analyzing the surface at a depth of 0.01 μm from the first surface by X-ray photoelectron spectroscopy is 0.005% or less. [4] The PVA film according to any one of [1] to [3], wherein the proportion of sodium element in all elements obtained by analyzing the first surface by X-ray photoelectron spectroscopy is 0.001% or less. [5] The PVA film according to any one of [1] to [4], wherein the proportion of sodium element in all elements obtained by analyzing the surface at a depth of 0.01 μm from the first surface by X-ray photoelectron spectroscopy is 0.001% or less. [6] The PVA film according to any one of [1] to [5], wherein the proportion of sodium element in all elements obtained by analyzing the first surface by X-ray photoelectron spectroscopy is 0.0005% or less. [7] The PVA film according to any one of [1] to [6], wherein the proportion of sodium element in all elements obtained by analyzing the surface at a depth of 0.01 μm from the first surface by X-ray photoelectron spectroscopy is 0.0005% or less. [8] The PVA film according to any one of [1] to [7], wherein the proportion of sodium element in all elements obtained by analyzing the first surface by X-ray photoelectron spectroscopy is 0.0001% or less.

[0018] [1] A polyvinyl alcohol film which is a non-water-soluble polyvinyl alcohol film, when one of two surfaces of the polyvinyl alcohol film orthogonal to a thickness direction is set as a first surface, a proportion of sodium element in all elements (Na1S) obtained by analyzing the first surface by X-ray photoelectron spectroscopy is 0.3 to 1.5 mol%, and a proportion of sodium element in all elements (Na1B) obtained by analyzing a surface at a depth of 0.01 μm from the first surface by X-ray photoelectron spectroscopy is 0.3 mol% or less;

[0019] [2] The polyvinyl alcohol film according to the preceding [1], wherein, when a surface of the polyvinyl alcohol film opposite to the first surface among the two surfaces orthogonal to the thickness direction is set as a second surface, a proportion of sodium element in all elements (Na2S) obtained by analyzing the second surface by X-ray photoelectron spectroscopy is 0.3 to 1.5 mol%, and a proportion of sodium element in all elements (Na2B) obtained by analyzing a surface at a depth of 0.01 μm from the second surface by X-ray photoelectron spectroscopy is 0.3 mol% or less;

[0020] [3] The polyvinyl alcohol film according to the preceding [1] or [2], which contains a sodium sulfate type surfactant or a sodium sulfonate type surfactant, the sodium element originating from the sodium sulfate type surfactant or the sodium sulfonate type surfactant;

[0021] [4] The polyvinyl alcohol film according to the preceding [3], wherein the sodium sulfate type surfactant or the sodium sulfonate type surfactant is at least one selected from the group consisting of sodium alkyl sulfate, sodium polyoxyethylene alkyl ether sulfate, sodium polyoxypropylene alkyl ether sulfate, sodium polyoxyethylene alkyl phenyl ether sulfate, sodium alkyl sulfonate, sodium alkyl benzene sulfonate, disodium dodecyl diphenyl ether disulfonate, sodium alkyl naphthalene sulfonate, disodium alkyl sulfosuccinate, and disodium polyoxyethylene alkyl sulfosuccinate;

[0022] [5] The polyvinyl alcohol film according to the preceding [3] or [4], wherein a molecular weight of the sodium sulfate type surfactant or the sodium sulfonate type surfactant is 200 to 10,000, and a content of the sodium sulfate type surfactant or the sodium sulfonate type surfactant is 0.02 to 0.4 parts by mass with respect to 100 parts by mass of polyvinyl alcohol contained in the polyvinyl alcohol film;

[0023] [6] The polyvinyl alcohol film according to any one of the preceding [1] to [5], which is a film for manufacturing an optical film;

[0024] [7] The polyvinyl alcohol film according to the preceding [6], wherein the optical film is a polarizing film;

[0025] [8]According to the method for manufacturing a polarizing film, a polarizing film is manufactured using the polyvinyl alcohol film described in any one of the foregoing [1] to [7].

[0026] Advantages of the Invention

[0027] According to the present invention, a PVA film having good peelability from a support and a polarizing film obtained using such a PVA film can be provided. Further, according to the present invention, a PVA film capable of manufacturing a polarizing film with little optical non-uniformity and a polarizing film obtained using such a PVA film can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a perspective view of the PVA film of the present invention.

[0029] Figure 2 is a view of the PVA film of the present invention observed in the thickness direction. DETAILED DESCRIPTION

[0030] Hereinafter, the present invention will be described in detail.

[0031] <PVA Film>

[0032] (Ratio of sodium element in all elements)

[0033] Figure 1 is a perspective view of the PVA film. Figure 2 is a view of the PVA film of the present invention observed in the thickness direction. In the present invention, as shown in Figure 1 and Figure 2 , one of the two surfaces of the PVA film orthogonal to the thickness direction 2 is defined as the first surface 3. In the present invention, the ratio (Na1S) of sodium element in all elements determined by analyzing the first surface 3 of the PVA film 1 by X-ray photoelectron spectroscopy (hereinafter sometimes referred to as XPS) is preferably 0.3 to 1.5 mol%. When Na1S is less than 0.3 mol%, the peelability from the support during the manufacture of the PVA film 1 becomes insufficient. Na1S is preferably 0.3 mol% or more, more preferably 0.5 mol% or more, and still more preferably 0.6 mol% or more. On the other hand, when Na1S exceeds 1.5 mol%, surface defects are likely to occur during the manufacture of the PVA film 1, and as a result, optical films such as the resulting polarizing film are likely to have optical non-uniformity. Na1S is preferably not more than 1.5 mol%, more preferably not more than 1.3 mol%. By appropriately adjusting the content of the plasticizer, the content of the surfactant, the evaporation fraction of the film-forming stock solution, the thickness of the PVA film, the surface temperature of the support, the drying temperature, and the heat treatment temperature during the manufacture of the PVA film, Na1S can be set to 0.3 to 1.5 mol%.

[0034] ​​​​In this invention, the proportion of sodium (Na1B) in all elements, determined by analyzing a surface 0.01 μm deep from the first surface 3 of the PVA film 1 using XPS, is preferably 0.3 mol% or less. Here, the surface 0.01 μm deep from the first surface is also orthogonal to the thickness direction 2 of the PVA film. When Na1B exceeds 0.3 mol%, defects easily occur on the surface of the PVA film 1 during the manufacture of optical films such as polarizing films, resulting in optical inhomogeneity in the obtained polarizing films. Na1B can be 0 mol%, that is, below the detection limit of the XPS measuring device. The detection limit of a typical XPS measuring device is usually around 0.1 mol%. Na1B is preferably 0.3 mol% or less, and more preferably 0.25 mol% or less. By appropriately adjusting the content of plasticizer, surfactant, volatile fraction of film-forming solution, thickness of PVA film, surface temperature of support during PVA film manufacturing, drying temperature, and heat treatment temperature, Na1B can be set to below 0.3 mol%.

[0035] In this invention, such as Figure 1 and Figure 2 As shown, among the two surfaces of the PVA film orthogonal to the thickness direction 2, the surface opposite to the aforementioned first surface 3 is defined as the second surface 4. In this invention, the proportion of sodium (Na2S) in the total elements, determined by analyzing the second surface 4 of the PVA film 1 using XPS, is preferably 0.3 to 1.5 mol%. That is, the proportion of sodium (Na1S, Na2S) in the total elements, determined by analyzing the two surfaces of the PVA film 1 orthogonal to the thickness direction using XPS, is preferably 0.3 to 1.5 mol%. When Na2S is less than 0.3 mol%, the peelability from the support during the manufacture of the PVA film 1 becomes insufficient. Na2S is preferably 0.3 mol% or more, more preferably 0.5 mol% or more, and even more preferably 0.6 mol% or more. On the other hand, when Na2S exceeds 1.5 mol%, surface defects are easily generated during the manufacture of the PVA film 1, resulting in optical inhomogeneity in the obtained optical films such as polarizing films. Na2S is preferably not more than 1.5 mol%, more preferably not more than 1.3 mol%. By appropriately adjusting the content of plasticizer, surfactant, volatile fraction of film-forming solution, thickness of PVA film, surface temperature of support during PVA film manufacturing, drying temperature, and heat treatment temperature, the content of Na2S can be set to 0.3–1.5 mol%.

[0036] In the present application, the proportion of sodium element in the total elements (Na2B) calculated by analyzing the surface at a depth of 0.01 μm from the aforementioned second surface of the PVA film 1 using XPS is preferably 0.3 mol% or less. That is, for both surfaces of the PVA film orthogonal to the thickness direction 2, the proportion of sodium element in the total elements (Na1B, Na2B) calculated by analyzing the surface at a depth of 0.01 μm from the surfaces using XPS is preferably 0.3 mol% or less. Here, the surface at a depth of 0.01 μm from the second surface is also a surface of the PVA film orthogonal to the thickness direction 2. In the case where Na2B exceeds 0.3 mol%, defects are easily generated on the surface of the PVA film 1 when an optical film such as a polarizing film is manufactured, as a result of which optical unevenness is easily generated in the obtained optical film such as a polarizing film. Na2B can be 0 mol%, that is, can be below the detection limit of the measurement device of XPS. Na2B is preferably 0.3 mol% or less, and further preferably 0.2 mol% or less. By appropriately adjusting the content of the plasticizer, the content of the surfactant, the volatile fraction of the film- forming solution, the thickness of the PVA film, the surface temperature of the support at the time of manufacturing the PVA film, the drying temperature, and the heat treatment temperature at the time of manufacturing the PVA film, Na2B can be set to 0.3 mol% or less.

[0037] (XPS)

[0038] In the present application, the amount of sodium element and other elements in the first surface or the second surface of the PVA film, or the surface at a depth of 0.01 μm from the first surface or the second surface is measured using XPS. XPS refers to the identification and quantification of elements present on the surface of a sample, and the analysis of the chemical bonding state by exciting the inner shell electrons of atoms by irradiating X-rays onto the surface of the sample, and detecting the kinetic energy of photoelectrons released thereby. In the present application, the elements measured using XPS are carbon (1s orbital electron), nitrogen (1s orbital electron), oxygen (1s orbital electron), sodium (1s orbital electron), silicon (2p orbital electron), phosphorus (2p orbital electron), and sulfur (2p orbital electron). These elements are quantified, and the proportion of sodium element with respect to the total amount thereof is set as Na1S, Na1B, Na2S, or Na2B.

[0039] In XPS, the surface of the film can also be subjected to etching treatment by C60 (buckminsterfullerene), argon cluster, or the like, and analyzed along the depth direction. In the present application, by using C60, etching treatment is performed for 30 seconds under the conditions of an acceleration voltage of 10 kV, a sample current of 20 nA, and a scanning range of 0.5 x 2.0 mm, thereby exposing the surface at a depth of about 0.01 μm from the surface of the film, and Na1B or Na2B is quantified.

[0040] (Physical properties)

[0041] The PVA film of the present application is preferably non-water-soluble. By making the PVA film non-water-soluble, even if the maximum stretching speed is high, the PVA film can be stretched without breaking during uniaxial stretching when manufacturing an optical film such as a polarizing film in an aqueous solution. Here, in the present application, non-water-soluble means that the PVA film does not completely dissolve but at least a portion remains dissolved when the PVA film is immersed in water (deionized water) at 30°C according to the following <1> to <4>.

[0042] <1> The PVA film is placed in a constant temperature and humidity chamber adjusted to 20°C and -65% RH for 16 hours or more to adjust the humidity.

[0043] <2> After cutting a rectangular sample of 40 mm in length x 35 mm in width from the PVA film whose humidity has been adjusted, the sample is sandwiched between two plastic plates of 50 mm x 50 mm having a rectangular window (hole) of 35 mm in length x 23 mm in width in such a manner that the length direction of the sample is parallel to the length direction of the window and the sample is positioned at the approximate center of the width direction of the window, and is fixed.

[0044] <3> 300 mL of deionized water is put into a 500 mL beaker, and a magnetic stirrer having a 3 cm long rod is used to stir the water at a rotation speed of 280 rpm while adjusting the water temperature to 30°C.

[0045] <4> While paying attention not to contact the rod of the magnetic stirrer that is rotating with the sample fixed to the plastic plate in <2> above, the sample is immersed in the deionized water in the beaker for 1000 seconds.

[0046] (PVA)

[0047] In the PVA film of the present application, as the PVA, a polymer produced by saponifying a vinyl ester-based polymer obtained by polymerizing a vinyl ester-based monomer can be used. As the vinyl ester-based monomer, for example, vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, vinyl versatate, and the like can be exemplified. Among these, as the vinyl ester-based monomer, vinyl acetate is preferable.

[0048] The vinyl ester-based polymer is preferably a polymer obtained by using only one or two or more kinds of vinyl ester-based monomers as the monomer, and more preferably a polymer obtained by using only one kind of vinyl ester-based monomer as the monomer. Note that the vinyl ester-based polymer can be a copolymer of one or two or more kinds of vinyl ester-based monomers and other monomers copolymerizable therewith.

[0049] As other monomers, there can be mentioned, for example, ethylene; olefins having 3 to 30 carbon atoms such as propylene, 1-butene, isobutene; acrylic acid or a salt thereof; acrylic esters such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, stearyl acrylate; methacrylic acid or a salt thereof; methacrylic esters such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, stearyl methacrylate; acrylamide derivatives such as acrylamide, N-methyl acrylamide, N-ethyl acrylamide, N,N-dimethyl acrylamide, diacetone acrylamide, acrylamidopropanesulfonic acid or a salt thereof, acrylamidopropyl dimethylamine or a salt thereof, N-hydroxymethyl acrylamide or a derivative thereof; methacrylamide derivatives such as methacrylamide, N-methyl methacrylamide, N-ethyl methacrylamide, methacrylamidopropanesulfonic acid or a salt thereof, methacrylamidopropyl dimethylamine or a salt thereof, N-hydroxymethyl methacrylamide or a derivative thereof; N-vinyl amides such as N-vinyl formamide, N-vinyl acetamide, N-vinyl pyrrolidone; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether; cyanoethylenes such as acrylonitrile, methacrylonitrile; halogenated ethylenes such as chloroethylene, vinylidene chloride, fluoroethylene, vinylidene fluoride; allyl compounds such as allyl acetate, allyl chloride; maleic acid or a salt, ester or anhydride thereof; itaconic acid or a salt, ester or anhydride thereof; vinyl silyl compounds such as vinyltrimethoxysilane; isopropenyl acetate, and the like. It is to be noted that the vinyl ester-based polymer can have a structural unit derived from one or more than two of these other monomers.

[0050] The proportion of the structural unit derived from the other monomer in the vinyl ester-based polymer is preferably 15 mol% or less, more preferably 8 mol% or less, based on the total number of moles of the structural units constituting the vinyl ester-based polymer.

[0051] The polymerization degree of the PVA is preferably 200 or more, more preferably 300 or more, and further preferably 500 or more. By setting the polymerization degree of the PVA to be the above lower limit or more, it is possible to prevent excessive crystallization of the PVA and to ensure the mechanical strength of the obtained PVA film. On the other hand, the polymerization degree of the PVA is preferably 8,000 or less, more preferably 6,000 or less, and further preferably 4,000 or less.

[0052] The polymerization degree of the PVA refers to the average polymerization degree measured according to the description of JIS K 6726-1994. That is, the polymerization degree (Po) is calculated by the following formula (1).

[0053] Polymerization degree Po = ([η] x 10 4 / 8.29) (1 / 0.62) (1)

[0054] In the above formula (1), η is the intrinsic viscosity (dl / g) measured in water at 30°C after the PVA is resaponified and refined.

[0055] The saponification degree of the PVA is preferably 90 mol% or more, more preferably 95 mol% or more, further preferably 99 mol% or more, and particularly preferably 99.8 mol% or more. By making the saponification degree of the PVA 99 mol% or more, the resulting PVA film 1 easily becomes water-insoluble. The definition of water-insolubility is as described above.

[0056] The saponification degree of the PVA refers to the proportion (mol%) of the number of moles of vinyl alcohol units with respect to the total number of moles of structural units that can be converted to vinyl alcohol units by saponification (typically, vinyl ester-based monomer units) and vinyl alcohol units. The saponification degree of the PVA can be measured according to the description of JIS K 6726-1994.

[0057] The PVA can contain only one kind of PVA, or two or more kinds of PVA that differ in polymerization degree, saponification degree, and modification degree, etc.

[0058] The content of the PVA in the PVA film of the present application is not necessarily limited, and is preferably 50 mass% or more, more preferably 80 mass% or more, and further preferably 85 mass% or more.

[0059] (Plasticizer)

[0060] The PVA film of the present application preferably contains a plasticizer. By containing a plasticizer, the PVA film can be imparted with the same softness as other plastic films, and the PVA film can be inhibited from breaking during the film formation and stretching processes of the PVA film.

[0061] As the plasticizer, polyhydric alcohols such as ethylene glycol, glycerol, diglycerol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, sorbitol, etc. can be exemplified. These plasticizers can be used alone or in combination with two or more kinds. Among these, from the reasons that it is difficult for the plasticizer to exude to the surface of the PVA film, etc., ethylene glycol or glycerol is preferable as the plasticizer, and glycerol is more preferable.

[0062] The content of the plasticizer in the PVA film of the present application is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and further preferably 5 parts by mass or more, relative to 100 parts by mass of PVA. On the other hand, the content of the plasticizer is preferably 40 parts by mass or less, more preferably 30 parts by mass or less, and further preferably 20 parts by mass or less, relative to 100 parts by mass of PVA. If the content of the plasticizer is within the above range, it is easy to adjust the proportion of sodium element in the PVA film (Na1S, Na2S, Na1B, Na2B) to the above range. The effect of improving the mechanical properties such as impact strength can be sufficiently obtained. In addition, it is possible to prevent the PVA film from becoming too soft and handling properties from being reduced, or the plasticizer from bleeding to the surface of the PVA film.

[0063] (Surfactant)

[0064] In the present application, the proportion of sodium element in the first surface or the second surface of the PVA film (Na1S, Na2S), or the proportion of sodium element in the surface at a depth of 0.01 μm from the first surface or the second surface (Na1B, Na2B) is preferably within a certain range. That is, the PVA film of the present application is characterized in that sodium element exists on the surface and inside of the film. In the present application, this sodium element is preferably contained in a sodium sulfate type surfactant or a sodium sulfonate type surfactant. That is, the PVA film of the present application preferably contains a sodium sulfate type surfactant or a sodium sulfonate type surfactant.

[0065] As the aforementioned sodium sulfate type surfactant, for example, sodium alkyl sulfate, sodium polyoxyethylene alkyl ether sulfate, sodium polyoxypropylene alkyl ether sulfate, sodium polyoxyethylene alkyl phenyl ether sulfate, and the like can be exemplified. As the aforementioned alkyl group, an alkyl group having 8 to 20 carbon atoms is preferred, and among them, a lauryl group is more preferred.

[0066] As the aforementioned sodium sulfonate type surfactant, for example, sodium alkyl sulfonate, sodium alkylbenzene sulfonate, disodium dodecyl diphenyl ether disulfonate, sodium alkyl naphthalene sulfonate, disodium alkyl sulfosuccinate, and polyoxyethylene alkyl sulfosuccinate, and the like can be exemplified. As the aforementioned alkyl group, an alkyl group having 8 to 20 carbon atoms is preferred, and among them, a dodecyl group is more preferred.

[0067] The surfactant can be used alone or in combination with two or more. That is, the aforementioned sodium sulfate type surfactant or sodium sulfonate type surfactant is preferably at least one selected from the group consisting of sodium alkyl sulfate, sodium polyoxyethylene alkyl ether sulfate, sodium polyoxypropylene alkyl ether sulfate, sodium polyoxyethylene alkyl phenyl ether sulfate, sodium alkyl sulfonate, sodium alkyl benzene sulfonate, disodium dodecyl diphenyl ether disulfonate, sodium alkyl naphthalene sulfonate, disodium alkyl sulfosuccinate, and disodium polyoxyethylene alkyl sulfosuccinate. The sodium polyoxyethylene alkyl ether sulfate is preferable in terms of the viewpoint that it is easily present on the surface of the PVA film 1, and the peelability from the support at the time of manufacturing the PVA film 1 becomes good.

[0068] In addition, a surfactant other than the aforementioned sodium sulfate type surfactant or sodium sulfonate type surfactant can be contained. As the surfactant other than the sodium sulfate type surfactant or sodium sulfonate type surfactant, a nonionic surfactant is preferable, an alkanolamide type surfactant is more preferable, and a dialkanolamide of a fatty acid (for example, a saturated or unsaturated fatty acid having 8 to 30 carbon atoms, etc.) is further preferable, in terms of the viewpoint that the effect of reducing surface abnormalities at the time of manufacturing the PVA film is excellent, etc.

[0069] The molecular weight of the aforementioned sodium sulfate type surfactant or sodium sulfonate type surfactant is preferably 200 or more, and more preferably 250 or more. The molecular weight of the aforementioned sodium sulfate type surfactant or sodium sulfonate type surfactant is preferably 10,000 or less, and preferably 5,000 or less. By making the molecular weight within the aforementioned range, a film having a small number of aggregates of the surfactant on the surface of the PVA film and good peelability and film surface quality can be obtained.

[0070] The content of the aforementioned sodium sulfate type surfactant or sodium sulfonate type surfactant in the PVA film of the present application is preferably 0.02 parts by mass or more, more preferably 0.03 parts by mass or more, and further preferably 0.05 parts by mass or more, relative to 100 parts by mass of PVA. The content of the aforementioned sodium sulfate type surfactant or sodium sulfonate type surfactant is preferably 0.4 parts by mass or less, more preferably 0.3 parts by mass or less, further preferably 0.2 parts by mass or less, and particularly preferably 0.1 parts by mass or less, relative to 100 parts by mass of PVA. If the content of the surfactant is within the above range, it is easy to adjust the proportion of sodium elements (Na1S, Na2S, Na1B, Na2B) in the total elements in the PVA film to the above range. In addition, if the content of the surfactant is within the above range, it is possible to prevent adhesion (hereinafter also referred to as "blocking") between PVA films. In addition, it is possible to prevent the surfactant from bleeding to the surface of the PVA film or the appearance of the PVA film from deteriorating due to aggregation of the surfactant. In addition, the PVA film of the present application can contain a surfactant other than the aforementioned sodium sulfate type surfactant or sodium sulfonate type surfactant. In this case, the total content of the surfactants in the PVA film is preferably 0.04 parts by mass or more, more preferably 0.1 parts by mass or more, and further preferably 0.15 parts by mass or more, relative to 100 parts by mass of PVA. The total content of the surfactants in the PVA film is preferably 10 parts by mass or less, more preferably 1 part by mass or less, and further preferably 0.5 parts by mass or less.

[0071] (Other components)

[0072] In the PVA film of the present application, in addition to PVA, a water-soluble polymer, moisture, an antioxidant, an ultraviolet absorber, a lubricant, a crosslinking agent, a coloring agent, a filler, a preservative, a mold inhibitor, another polymer compound, or the like can be contained within a range that does not interfere with the effects of the present application. The proportion of the total of the mass of the components other than PVA, the surfactant, the plasticizer, and PVA in the total mass of the PVA film is preferably 60 to 100 mass%, more preferably 80 to 100 mass%, and further preferably 90 to 100 mass%.

[0073]

[0074] ​The method for producing the PVA film of the present application is not particularly limited, and any method such as the following can be employed. As the method, there can be mentioned a method in which a film- forming raw solution obtained by adding a solvent, an additive, or the like to PVA and homogenizing it is subjected to film formation by a casting film formation method, a wet film formation method (a method in which a poor solvent is sprayed), a dry-wet film formation method, a gel film formation method (a method in which a film- forming raw solution is temporarily cooled and gelled, and then a solvent is extracted and removed), or a combination thereof; a melt extrusion film formation method, a blow molding method, or the like in which a film- forming raw solution obtained using an extruder or the like is extruded from a T die or the like, whereby film formation is performed. Among these, as the method for producing the PVA film, a casting film formation method and a melt extrusion film formation method are preferred. If these methods are used, a homogeneous PVA film can be obtained with good productivity. Hereinafter, a case in which a PVA film is produced using a casting film formation method or a melt extrusion film formation method will be described.

[0075] In the production of the PVA film of the present application using a casting film formation method or a melt extrusion film formation method, first, a film- forming raw solution containing PVA, a solvent, and an additive such as a plasticizer as needed is prepared. Next, the film- forming raw solution is cast (supplied) on a support such as a metal roll, a metal belt, or the like that is rotating, in a film shape. Thereby, a liquid film of the film- forming raw solution is formed on the support. The liquid film is solidified by heating on the support and removing the solvent, and film formation is performed. The method of heating the liquid film can be exemplified by a method in which the support itself is subjected to high-temperature treatment with a heating medium or the like, a method in which hot air is blown against the opposite face of the face of the liquid film that is in contact with the support, or the like. The solidified long film (PVA film) is peeled from the support, dried as needed using a drying roll, a drying furnace, or the like, and further subjected to heat treatment as needed, and wound into a roll shape.

[0076] In the drying process (solvent removal process) of the liquid film cast on the support, and the drying process of the PVA film thereafter, the PVA is crystallized during the period in which it is heated. The crystallization speed at this time is affected not only by the aforementioned proportion of the structural unit derived from another monomer in the PVA, the polymerization degree of the PVA, the saponification degree of the PVA, and the content of the plasticizer, but also by the moisture rate, the temperature, and the draft (stretching elongation rate in the flow direction) in the PVA.

[0077] Generally, drying of the PVA film is performed by gradual volatilization of the volatile components from the film surface not in contact with the support, drying roll, or the like. Therefore, in the process during drying, a concentration distribution of the volatile components such as water is generated in the thickness direction of the PVA film, and thus, depending on the temperature and the drawing conditions at that time, a distribution of the sodium element is generated in the thickness direction of the PVA film. The distribution of the sodium element, i.e., the proportion of the sodium element in the entire elements in the first surface of the PVA film (Na1S, Na1B) and the proportion of the sodium element in the entire elements in the second surface of the PVA film (Na2S, Na2B) can be adjusted by the surface temperature of the support, the time of contact with the support, the hot air temperature and the hot air amount, and the temperature of the drying roll or the drying furnace, or the like. Thus, the distribution of the sodium element can be adjusted by appropriately adjusting each of the above elements.

[0078] The volatile fraction of the film-forming dope (the concentration of the volatile components such as the solvent removed by volatilization and evaporation at the time of film formation) is preferably 50% by mass or more, and more preferably 55% by mass or more. The volatile fraction of the film-forming dope is preferably 90% by mass or less, and more preferably 80% by mass or less. If the volatile fraction is within the above range, the viscosity of the film-forming dope can be adjusted to a suitable range, and thus, the film formability of the liquid coating film cast on the support is improved, and a PVA film having a uniform thickness can be easily obtained. In addition, if the volatile fraction is within the above range, the proportion of the sodium element in the entire elements in the first surface of the obtained PVA film (Na1S, Na1B) and the proportion of the sodium element in the entire elements in the second surface of the PVA film (Na2S, Na2B) can be easily adjusted to the above range. The film-forming dope can contain a dichroic dye as necessary. In addition, the volatile fraction of the film-forming dope refers to a value obtained by the following formula (2).

[0079] Volatilization fraction of film-forming dope (% by mass) = {(Wa - Wb) / Wa} x 100 (2)

[0080] In the above formula (2), Wa represents the mass (g) of the film-forming dope, and Wb represents the mass (g) of the film-forming dope of Wa (g) dried in an electric heating dryer at 105°C for 16 hours.

[0081] As the adjustment method of the film-forming dope, there is no particular limitation, and examples include a method in which PVA and additives such as a plasticizer and a surfactant are dissolved in a solvent in a dissolving tank or the like; a method in which a PVA in a water-containing state is melt-kneaded together with additives such as a plasticizer and a surfactant using a single-screw extruder or a twin-screw extruder; or the like.

[0082] The film-forming dope generally passes through the die lip of a die such as a T-die and is cast onto a support such as a metal roll or a metal belt in a film shape. On the support, the solvent gradually volatilizes from the face of the cast film-shaped dope that does not contact the support (hereinafter sometimes referred to as the free face), whereas it does not substantially volatilize from the face that contacts the support (hereinafter sometimes referred to as the contact face), and thus a distribution is produced in which the solvent concentration is low on the free face side and the solvent concentration is high on the contact face side with respect to the thickness direction of the film. Thus, the solidification of the PVA also proceeds first from the free face.

[0083] The surface temperature of the support on which the film-forming dope is to be cast is preferably 65°C or higher, more preferably 70°C or higher, and further preferably 75°C or higher. The surface temperature of the support on which the film-forming dope is to be cast is preferably 110°C or lower, more preferably 100°C or lower, and further preferably 95°C or lower. If the surface temperature is within the above range, the drying of the liquid coating film cast on the support and the segregation of sodium elements in the vicinity of the surface of the film proceed at a moderate rate, and thus it is easy to adjust the proportion of sodium elements in the total elements in the first surface of the PVA film (Na1S, Na1B) and the proportion of sodium elements in the total elements in the second surface of the PVA film (Na2S, Na2B) to the above ranges. As a result, the film surface of the PVA film can be normally produced and the peelability from the support becomes good.

[0084] The PVA film is preferably peeled from the support after being dried (solvent removed) to a volatile fraction of 5 to 50 mass% on the support, and further dried as necessary. The drying method is not particularly limited, and methods in which it is passed through a drying oven or brought into contact with a drying roll can be given. In the case where a plurality of drying rolls are used to dry the PVA film, it is preferable to alternately bring one surface and the other surface of the PVA film into contact with the drying rolls. By this, it is possible to adjust the proportion of sodium elements in the total elements at both faces (two surfaces orthogonal to the thickness direction) of the PVA film. In this case, the number of drying rolls is preferably 3 or more, more preferably 4 or more, and further preferably 5 or more. The number of drying rolls is preferably 30 or less, more preferably 25 or less, and further preferably 20 or less.

[0085] The temperature of the drying oven or the surface temperature of the drying roll is preferably 40°C or higher, more preferably 45°C or higher, and further preferably 50°C or higher. The temperature of the drying oven or the surface temperature of the drying roll is preferably 120°C or lower, more preferably 110°C or lower, and further preferably 100°C or lower. By setting the temperature of the drying oven or the surface temperature of the drying roll within the above range, it is easy to adjust the proportion of sodium elements in the total elements in the first surface of the PVA film (Na1S, Na1B) and the proportion of sodium elements in the total elements in the second surface of the PVA film (Na2S, Na2B) to the above ranges.

[0086] After peeling the PVA film from the drying roll, heat treatment can be performed. The heat treatment is performed by alternately contacting one face and the other face of the PVA film to a plurality of heat treatment rolls (for example, 2 heat treatment rolls). The surface temperature of the heat treatment roll is preferably 70°C or higher, more preferably 80°C or higher. The surface temperature of the heat treatment roll is preferably 150°C or lower, more preferably 140°C or lower. By setting the surface temperature of the heat treatment roll to the above range, the proportion of sodium element in the entirety of the first surface of the PVA film (Na1S, Na1B) and the proportion of sodium element in the entirety of the second surface of the PVA film (Na2S, Na2B) are easily adjusted to the aforementioned ranges.

[0087] The PVA film manufactured by such an operation is, after further performing humidity adjustment treatment, cutting of both end portions (edge portions) of the film, and the like as needed, wound in a roll shape on a cylindrical core, and subjected to moisture-proof packaging to form a product.

[0088] The volatile component of the PVA film finally obtained by the series of processes is not necessarily limited. The volatile component of the PVA film is preferably 1% by mass or more, more preferably 2% by mass or more. The volatile component of the PVA film is preferably 5% by mass or less, more preferably 4% by mass or less.

[0089] The thickness of the PVA film finally obtained by the series of processes is not necessarily limited. The thickness of the PVA film is preferably 10 μm or more, more preferably 20 μm or more. The thickness of the PVA film is preferably 90 μm or less, more preferably 80 μm or less. There is a tendency that the thicker the PVA film, the smaller the proportion of sodium element in the entirety of the first surface of the PVA film (Na1S, Na1B) and the proportion of sodium element in the entirety of the second surface of the PVA film (Na2S, Na2B); the thinner the PVA film, the larger the proportion of sodium element in the entirety of the first surface of the PVA film (Na1S, Na1B) and the proportion of sodium element in the entirety of the second surface of the PVA film (Na2S, Na2B). The thickness of the PVA film can be adjusted by the concentration of the film- forming stock solution, the roll temperature, and the like.

[0090] <Method for manufacturing optical film>

[0091] The PVA film of the present application is preferably a film for manufacturing an optical film. That is, the PVA film of the present application can be suitably used as a raw material film when manufacturing an optical film. As the optical film, a polarizing film, a field-of-view angle improving film, a phase difference film, a brightness enhancing film, and the like can be exemplified, and a polarizing film is preferable. Hereinafter, as an example of a method for manufacturing an optical film, a method for manufacturing a polarizing film will be concretely described.

[0092] The polarizing film can be generally produced by using a PVA film as a raw material film and subjecting it to a swelling process, a dyeing process, a cross-linking process, a stretching process, a fixation treatment process, and the like. As specific examples of the treatment liquid used in each process, there can be mentioned a swelling treatment liquid used in the swelling treatment, a dyeing treatment liquid (dyeing liquid) used in the dyeing treatment, a cross-linking treatment liquid used in the cross-linking treatment, a stretching treatment liquid used in the stretching treatment, a fixation treatment liquid used in the fixation treatment, and a cleaning treatment liquid (cleaning liquid) used in the cleaning treatment, and the like.

[0093] Each process that can be employed in the production method for producing a polarizing film will be described in detail below. Note that in the production method for producing a polarizing film, one or more than two of the following processes can be omitted, the same process can be performed multiple times, another process can be performed simultaneously.

[0094] (Cleaning treatment before the swelling treatment)

[0095] Before the PVA film is subjected to the swelling treatment, the PVA film is preferably subjected to a cleaning treatment. By this cleaning treatment before the swelling treatment, the anti-blocking agent and the like adhered to the PVA film can be removed, and the treatment liquids in the production process of the polarizing film can be prevented from being contaminated by the anti-blocking agent and the like. The cleaning treatment is preferably performed by immersing the PVA film in a cleaning treatment liquid, and can be performed by blowing the cleaning treatment liquid against the PVA film. As the cleaning treatment liquid, water, for example, can be used. The temperature of the cleaning treatment liquid is preferably in the range of 20 to 40°C. By making the temperature of the cleaning treatment liquid 20°C or higher, the removal of the anti-blocking agent and the like adhered to the PVA film is facilitated. In addition, by making the temperature of the cleaning treatment liquid 40°C or lower, the dissolution of a part of the surface of the PVA film, the sticking of the films to each other, and the reduction of the processability can be prevented. The temperature of the cleaning treatment liquid is more preferably 22°C or higher, further preferably 24°C or higher, and particularly preferably 26°C or higher. In addition, the temperature of the cleaning treatment liquid is more preferably 38°C or lower, further preferably 36°C or lower, and particularly preferably 34°C or lower.

[0096] (Swelling treatment)

[0097] The swelling treatment can be performed by immersing the PVA film in a swelling treatment liquid such as water. The temperature of the swelling treatment liquid is preferably 20°C or higher, more preferably 22°C or higher, and further preferably 24°C or higher. The temperature of the swelling treatment liquid is preferably 40°C or lower, more preferably 38°C or lower, and further preferably 36°C or lower. In addition, the time of immersion in the swelling treatment liquid is preferably, for example, 0.1 minutes or more, and more preferably 0.5 minutes or more. The time of immersion in the swelling treatment liquid is preferably, for example, 5 minutes or less, and more preferably 3 minutes or less. Note that the water used as the swelling treatment liquid is not limited to pure water, and can be an aqueous solution in which various components such as a boron-containing compound are dissolved, or a mixture of water and an aqueous medium. The type of the boron-containing compound is not particularly limited, and from the viewpoint of processability, boric acid or borax is preferred. In the case where the swelling treatment liquid contains a boron-containing compound, the concentration thereof is preferably 6% by mass or less from the viewpoint of improving the stretchability of the PVA film.

[0098] (Dyeing treatment)

[0099] The dyeing treatment can be performed using an iodine-based colorant as a dichroic dye, and can be performed at any stage before, during, or after the stretching treatment. The dyeing treatment is preferably performed by immersing the PVA film in a dyeing treatment liquid containing a solution (preferably an aqueous solution) of iodine-potassium iodide, using the solution as the dyeing treatment liquid. The concentration of iodine in the dyeing treatment liquid is preferably in the range of 0.005 to 0.2% by mass, and the mass ratio of potassium iodide / iodine is preferably in the range of 20 to 100. The temperature of the dyeing treatment liquid is preferably 20°C or higher, and more preferably 25°C or higher. The temperature of the dyeing treatment liquid is preferably 50°C or lower, and more preferably 40°C or lower. The dyeing treatment liquid can contain a boron-containing compound such as boric acid as a crosslinking agent. Note that if the PVA film used as the base film contains a dichroic dye in advance, the dyeing treatment can be omitted. In addition, the PVA film used as the base film can contain a boron-containing compound such as boric acid or borax in advance.

[0100] (Crosslinking treatment)

[0101] In the production of a polarizing film, a cross-linking treatment is preferably performed after the dyeing treatment for the purpose of firmly adsorbing the dichroic dye to the PVA film or the like. The cross-linking treatment can be performed by using a solution (suitably an aqueous solution) containing a cross-linking agent as a cross-linking treatment liquid and immersing the PVA film in the cross-linking treatment liquid. As the cross-linking agent, one or two or more kinds of a boron-containing compound such as boric acid, borax or the like can be used. If the concentration of the cross-linking agent in the cross-linking treatment liquid is too high, there is a tendency that the cross-linking reaction excessively proceeds and it is difficult to perform sufficient stretching in the stretching treatment performed thereafter. In addition, if the concentration of the cross-linking agent in the cross-linking treatment liquid is too low, there is a tendency that the effect of the cross-linking treatment decreases. Therefore, the concentration of the cross-linking agent in the cross-linking treatment liquid is preferably 1% by mass or more, more preferably 1.5% by mass or more, and further preferably 2% by mass or more. The concentration of the cross-linking agent in the cross-linking treatment liquid is preferably 6% by mass or less, more preferably 5.5% by mass or less, and further preferably 5% by mass or less.

[0102] In order to suppress the elution of the dichroic dye from the PVA film after the dyeing treatment, the cross-linking treatment liquid can contain an iodine-containing compound such as potassium iodide or the like. If the concentration of the iodine-containing compound in the cross-linking treatment liquid is too high, although the reason is not clear, there is a tendency that the heat resistance of the obtained polarizing film decreases. In addition, if the concentration of the iodine-containing compound in the cross-linking treatment liquid is too low, there is a tendency that the effect of suppressing the elution of the dichroic dye decreases. The concentration of the iodine-containing compound in the cross-linking treatment liquid is preferably 1% by mass or more, more preferably 1.5% by mass or more, and further preferably 2% by mass or more. The concentration of the iodine-containing compound in the cross-linking treatment liquid is preferably 6% by mass or less, more preferably 5.5% by mass or less, and further preferably 5% by mass or less.

[0103] If the temperature of the cross-linking treatment liquid is too high, there is a tendency that the polarizing film obtained by the elution of the dichroic dye is likely to have uneven dyeing, and if it is too low, the effect of the cross-linking treatment sometimes decreases. The temperature of the cross-linking treatment liquid is preferably 20°C or higher, more preferably 22°C or higher, and further preferably 25°C or higher. The temperature of the cross-linking treatment liquid is preferably 45°C or lower, more preferably 40°C or lower, and further preferably 35°C or lower.

[0104] In each of the above treatments and between the treatments, the PVA film can be stretched differently from the stretching treatment described later. By performing such stretching (pre-stretching), it is possible to prevent wrinkles from being generated on the surface of the PVA film. From the viewpoint of the polarizing properties and the like of the obtained polarizing film, the total stretching ratio (a ratio obtained by multiplying the stretching ratios in each of the treatments) of the pre-stretching is preferably 4 times or less, and more preferably 3.5 times or less, based on the original length of the PVA film of the raw material before stretching. From the viewpoint of the polarizing properties and the like of the obtained polarizing film, the total stretching ratio of the pre-stretching is preferably 1.5 times or more, and preferably 2 times or more, based on the original length of the PVA film of the raw material before stretching.

[0105] The stretching ratio in the swelling treatment is preferably 1.1 times or more, more preferably 1.2 times or more, and further preferably 1.4 times or more. The stretching ratio in the swelling treatment is preferably 3 times or less, more preferably 2.5 times or less, and further preferably 2.3 times or less.

[0106] The stretching ratio in the dyeing treatment is preferably 2 times or less, more preferably 1.8 times or less, and further preferably 1.5 times or less. The stretching ratio in the dyeing treatment is preferably 1.1 times or more, more preferably 1.15 times or more, and further preferably 1.2 times or more.

[0107] The stretching ratio in the cross-linking treatment is preferably 2 times or less, more preferably 1.5 times or less, and further preferably 1.3 times or less. The stretching ratio in the cross-linking treatment is preferably 1.05 times or more, more preferably 1.1 times or more, and further preferably 1.15 times or more.

[0108] (Stretching treatment)

[0109] The stretching treatment can be performed using either of a wet stretching method or a dry stretching method. In the case of the wet stretching method, a solution containing a boron-containing compound such as boric acid (suitably an aqueous solution) can be used as a stretching treatment liquid, and the stretching treatment can be performed in the stretching treatment liquid, or can be performed in a dyeing treatment liquid or a fixing treatment liquid described later. In the case of the dry stretching method, the PVA film after water absorption can be used and the stretching treatment can be performed in air. Among these, the wet stretching method is preferable, and uniaxial stretching in an aqueous solution containing boric acid is more preferable. In the case where the stretching treatment liquid contains a boron-containing compound, the stretchability of the PVA film can be improved, and thus the concentration of the boron-containing compound in the stretching treatment liquid is preferably 1.5% by mass or more, more preferably 2.0% by mass or more, and further preferably 2.5% by mass or more. In addition, from the viewpoint of improving the stretchability of the PVA film, the concentration of the boron-containing compound in the stretching treatment liquid is preferably 7% by mass or less, more preferably 6.5% by mass or less, and further preferably 6% by mass or less.

[0110] The stretching treatment liquid preferably contains an iodine-containing compound such as potassium iodide. If the concentration of the iodine-containing compound in the stretching treatment liquid is too high, there is a tendency for the hue of the obtained polarizing film to be significantly blue. In addition, if the concentration of the iodine-containing compound in the stretching treatment liquid is too low, although the reason is unknown, there is a tendency for the heat resistance of the obtained polarizing film to decrease. The concentration of the iodine-containing compound in the stretching treatment liquid is preferably 2% by mass or more, more preferably 2.5% by mass or more, and further preferably 3% by mass or more. The concentration of the iodine-containing compound in the stretching treatment liquid is preferably 8% by mass or less, more preferably 7.5% by mass or less, and further preferably 7% by mass or less.

[0111] If the temperature of the stretching treatment liquid is too high, there is a tendency for the PVA film to dissolve and become soft and easily broken. In addition, if the temperature of the stretching treatment liquid is too low, there is a tendency for the stretchability of the PVA film to decrease. The temperature of the stretching treatment liquid is preferably 50°C or higher, more preferably 52.5°C or higher, and further preferably 55°C or higher. The temperature of the stretching treatment liquid is preferably 70°C or lower, more preferably 67.5°C or lower, and further preferably 65°C or lower. Note that the preferable range of the stretching temperature when the stretching treatment is performed using a dry stretching method is as described above.

[0112] From the viewpoint that a polarizing film or the like having more excellent polarizing properties can be obtained when the stretching ratio in the stretching treatment is high, the stretching ratio in the stretching treatment is preferably 1.2 or higher, more preferably 1.5 or higher, and further preferably 2 or higher. In addition, from the viewpoint of the polarizing properties of the obtained polarizing film, the total stretching ratio (a ratio obtained by multiplying the stretching ratios in each process) including the stretching ratio of the aforementioned preliminary stretching is preferably 5.5 or higher, more preferably 5.7 or higher, and further preferably 5.9 or higher, depending on the original length of the PVA film of the raw material before stretching. The upper limit of the stretching ratio is not particularly limited, and if the stretching ratio is too high, stretching breakage easily occurs, and thus the stretching ratio is preferably 8 or lower.

[0113] The method of performing the stretching treatment by uniaxial stretching is not particularly limited, and uniaxial stretching in the length direction, transverse uniaxial stretching in the width direction, or the like can be used. In the case of manufacturing a polarizing film, uniaxial stretching in the length direction is preferable from the viewpoint of obtaining a polarizing film having excellent polarizing properties. Uniaxial stretching in the length direction can be performed using a stretching device provided with a plurality of rollers parallel to each other, and by changing the circumferential speed between the rollers.

[0114] In the present application, the maximum stretching speed (%) in the stretching treatment by uniaxial stretching is not particularly limited, and is preferably 200% / min or more, more preferably 300% / min or more, and further preferably 400% / min or more. Here, the maximum stretching speed refers to the fastest stretching speed in the stage in which the stretching treatment of the PVA film is performed in two or more stages using three or more rollers having different circumferential speeds. Note that, in the case where the stretching treatment of the PVA film is performed in one stage without being divided into two or more stages, the stretching speed in the stage becomes the maximum stretching speed. In addition, the stretching speed refers to the amount of increase in the length of the PVA film by stretching with respect to the length of the PVA film before stretching per unit time. For example, a stretching speed of 100% / min refers to the speed at which the PVA film is made to be doubled in length in one minute. The greater the maximum stretching speed, the more the stretching treatment (uniaxial stretching) of the PVA film can be performed at a high speed, and as a result, the productivity of the polarizing film is improved, and thus is preferred. On the other hand, if the maximum stretching speed becomes too large, a large tension is sometimes applied to a part of the PVA film in the stretching treatment (uniaxial stretching) of the PVA film, and stretching breakage is likely to occur. From this viewpoint, the maximum stretching speed is preferably 900% / min or less.

[0115] (Fixing treatment)

[0116] In the production of the polarizing film, in order to firmly adsorb the dichroic dye to the PVA film, a fixing treatment is preferably performed. The fixing treatment can be performed by using a solution (suitably an aqueous solution) containing one or two or more kinds of boron-containing compounds such as boric acid, borax, and the like as a fixing treatment liquid, and immersing the PVA film (suitably the PVA film after the stretching treatment) in the fixing treatment liquid. In addition, the fixing treatment liquid can contain an iodine-containing compound, a metal compound, as needed. The concentration of the boron-containing compound in the fixing treatment liquid is preferably 2% by mass or more, and more preferably 3% by mass or more. The concentration of the boron-containing compound in the fixing treatment liquid is preferably 15% by mass or less, and more preferably 10% by mass or less. The temperature of the fixing treatment liquid is preferably 15°C or higher, and more preferably 25°C or higher. The temperature of the fixing treatment liquid is preferably 60°C or lower, and more preferably 40°C or lower.

[0117] (Cleaning treatment after the dyeing treatment)

[0118] After the dyeing treatment, the PVA film after the stretching treatment is preferably subjected to a cleaning treatment. The cleaning treatment is preferably performed by immersing the PVA film in a cleaning treatment liquid, or can be performed by blowing the cleaning treatment liquid against the PVA film. As the cleaning treatment liquid, water, for example, can be used. The water is not limited to pure water, and can contain an iodine-containing compound such as potassium iodide, for example. Note that the cleaning treatment liquid can contain a boron-containing compound, in which case the concentration of the boron-containing compound is preferably 2.0% by mass or less.

[0119] The temperature of the cleaning treatment liquid is preferably in the range of 5 to 40°C. By making the temperature 5°C or higher, the breakage of the PVA film due to the freezing of moisture can be suppressed. In addition, by making the temperature 40°C or lower, the optical properties of the resulting polarizing film are improved. The temperature of the cleaning treatment liquid is more preferably 7°C or higher, and further preferably 10°C or higher. In addition, the temperature of the cleaning treatment liquid is more preferably 38°C or lower, and further preferably 35°C or lower.

[0120] As a specific method in the production of a polarizing film, a method in which a PVA film is subjected to a dyeing treatment, a stretching treatment, and a crosslinking treatment and / or a fixing treatment can be given. As a preferred example, a method in which a PVA film is subjected to a swelling treatment, a dyeing treatment, a crosslinking treatment, a stretching treatment (particularly, a uniaxial stretching treatment), and a cleaning treatment in this order can be given. In addition, the stretching treatment can be performed in any treatment step earlier than the above-described steps, or can be performed in multiple stages of two or more stages.

[0121] By subjecting the PVA film after the above-described various treatments to a drying treatment, a polarizing film can be obtained. The method of the drying treatment is not particularly limited, and a contact method in which the film is brought into contact with a heating roller, a method in which the film is dried in a hot air dryer, a floating method in which the film is dried using hot air while floating, and the like can be given.

[0122] < Polarizing plate >

[0123] The polarizing film obtained by the above operation is preferably attached to both faces or a single face with a protective film that is optically transparent and has mechanical strength, and is used as a polarizing plate. As the protective film, a triacetyl cellulose (TAC) film, a cyclic olefin polymer (COP) film, a cellulose acetate butyrate (CAB) film, an acrylic film, a polyester film, and the like can be used. In addition, as an adhesive for the attachment, a PVA-based adhesive, a urethane-based adhesive, and the like can be given, and a PVA-based adhesive is preferred.

[0124] The polarizing plate obtained by the above operation can be used as a member of an LCD by being attached to a glass substrate after being laminated with an adhesive such as an acrylic adhesive. A phase difference film, a viewing angle improvement film, a brightness enhancement film, and the like can also be simultaneously attached.

[0125] Example

[0126] Hereinafter, the present application will be specifically described by way of examples, but the present application is by no means limited to the following examples.

[0127] (1) XPS measurement of PVA film

[0128] (1-1) Measurement of the proportion of sodium element in all elements (Na1S and Na2S)

[0129] The PVA film obtained in the following examples or comparative examples was cut into a size of 5 mm x 5 mm, and was disposed on a measurement base of an XPS measurement device with the aid of a conductive double-sided tape. Furthermore, XPS measurement was performed on the first surface and the second surface (two surfaces of the PVA film orthogonal to the thickness direction) of the PVA film, respectively, under the following measurement conditions, and XPS spectra were obtained.

[0130] (XPS measurement conditions)

[0131] Measurement device: Ohi Quantera SXM (ULVAX-PHI. INC.)

[0132] Analysis software: Multi Pack ver 9.0 (ULVAX-PHI. INC.)

[0133] X-ray source: Monochromatic Al Kα (1486.6 eV)

[0134] X-ray beam diameter:

[0135] Measurement range: 100 μm x 300 μm

[0136] Signal reading angle: 45°

[0137] Charging neutralization conditions: Neutralizing electron gun, Ar+ ion gun

[0138] Vacuum degree: 1 x 10 -6 Pa

[0139] Measurement elements (peaks of excited inner layer atoms used in quantification): B (1s), C (1s), N (1s), O (1s), Na (1s), Si (2p), P (2p), S (2p)

[0140] The XPS spectra obtained were analyzed with the above analysis software, and the proportion of sodium element in all elements (Na1S and Na2S) in the first surface and the second surface of the PVA film was calculated. Here, S is the first letter of surface.

[0141] (1-2) Measurement of the proportion of sodium element in all elements (Na1B and Na2B)

[0142] The PVA film obtained in each of the following Examples and Comparative Examples was cut into a size of 5 mm x 5 mm, and the first surface and the second surface (the two surfaces of the PVA film orthogonal to the thickness direction) of the PVA film were etched to a depth of 0.01 μm from the thickness direction of the PVA film using the following conditions in the above-described XPS measurement device. Also, XPS measurement and analysis were performed on the surface to a depth of 0.01 μm from the first surface or the second surface of the PVA film under the same conditions as described above, and the proportion of the sodium element in the surface to a depth of 0.01 μm from the first surface or the second surface (Na1B and Na2B) was calculated.

[0143] (Etching treatment conditions)

[0144] Treatment conditions: acceleration voltage 10 kV

[0145] Sample current: 20 mA

[0146] Scanning range: 0.5 mm x 2.0 mm

[0147] Etching rate: 20 nm / min

[0148] Etching material: C60 (Buckminsterfullerene)

[0149] (2) Evaluation of peelability of PVA film from support

[0150] In each of the following Examples and Comparative Examples, when the PVA film was produced, the state of peeling of the PVA film from the support was observed by visual observation, and the evaluation was performed in accordance with the following criteria.

[0151] Evaluation criteria for peelability:

[0152] A: The peeling position remained horizontal along the width direction of the PVA film, and no wrinkles or stretching of the surface of the PVA film occurred.

[0153] B: The peeling position remained horizontal along the width direction of the PVA film, but wrinkles or stretching of the surface of the PVA film occurred.

[0154] C: The peeling position was corrugated along the width direction of the PVA film, and wrinkles or stretching of the surface of the PVA film occurred.

[0155] (3) Evaluation of optical unevenness of polarizing film

[0156] The optical unevenness of the polarizing film obtained in each of the following Examples and Comparative Examples was observed by visual observation, and the evaluation was performed in accordance with the following criteria.

[0157] A: The optical unevenness was hardly noticeable.

[0158] B: Optical unevenness was observed.

[0159] C: Optical unevenness was significantly observed.

[0160] <Example 1>

[0161] A film-forming solution (volatile matter content: 66 mass%) was prepared by melt-mixing using 100 parts by mass of PVA (saponification degree: 99.9 mol%, polymerization degree: 2400), 12 parts by mass of glycerin as a plasticizer, 0.08 parts by mass of polyoxyethylene lauryl ether sodium sulfate (average molecular weight: 430) as a surfactant, 0.16 parts by mass of lauric acid diethanolamide, and 217.6 parts by mass of water, using a melt extruder. Next, the film-forming solution was discharged from a T-die in a film shape onto a support (surface temperature: 80°C) to form a liquid film on the support. The film-forming solution was cast on the support, and after the PVA film was peeled off from the support, the PVA film was further dried between the first drying roll and the final drying roll (the nineteenth drying roll) located immediately in front of the heat treatment roll, with one side and the other side of the PVA film being alternately brought into contact with each drying roll. At this time, the surface temperature of each drying roll from the first drying roll to the final drying roll was set to 75°C. Furthermore, the PVA film was peeled off from the final drying roll, and heat treatment was performed by alternately bringing one side and the other side of the PVA film into contact with each heat treatment roll. At this time, the heat treatment was performed using two heat treatment rolls, and the surface temperature of each heat treatment roll was set to 90°C, thereby obtaining a PVA film (thickness: 60 μm, width: 1200 mm).

[0162] As a result of XPS measurement of the obtained PVA film, the Na1S of the first surface of the PVA film was 0.7 mol%, and the Na1B was 0.2 mol%. In addition, the Na2S of the second surface of the PVA film was 0.6 mol%, and the Na2B was 0.1 mol%. Note that the first surface of the PVA film is the surface of the film-forming solution in contact with the support. In addition, the second surface of the PVA film is the surface (free surface) of the film-forming solution not in contact with the support.

[0163] The obtained PVA film was cut to 650 mm in width, and the film was subjected to swelling treatment, dyeing treatment, cross-linking treatment, stretching treatment, cleaning treatment, and drying treatment in this order to continuously produce a polarizing film. The swelling treatment was performed by uniaxially stretching to 2.00 times along the length direction while dipping in pure water (swelling treatment liquid) at 25°C. The dyeing treatment was performed by uniaxially stretching to 1.26 times along the length direction while dipping in a potassium iodide / iodine dyeing liquid (dyeing treatment liquid) (mass ratio of potassium iodide / iodine: 23, iodine concentration: 0.03 to 0.05 mass%) at a temperature of 32°C. In the dyeing treatment, the monomer transmittance of the polarizing film after uniaxial stretching in the stretching treatment was adjusted to be in the range of 43.5% ± 0.2% by adjusting the iodine concentration in the dyeing treatment liquid in the range of 0.03 to 0.05 mass%. The cross-linking treatment was performed by uniaxially stretching to 1.19 times along the length direction while dipping in a boric acid aqueous solution (cross-linking treatment liquid) at 32°C (boric acid concentration: 2.6 mass%). The stretching treatment was performed by uniaxially stretching to 2.00 times along the length direction while dipping in a boric acid / potassium iodide aqueous solution (stretching treatment liquid) at 55°C (boric acid concentration: 2.8 mass%, potassium iodide concentration: 5 mass%). The maximum stretching speed of the uniaxial stretching in the stretching treatment was 400% / min. The cleaning treatment was performed by dipping for 12 seconds without stretching in a potassium iodide / boric acid aqueous solution (cleaning treatment liquid) at 22°C (potassium iodide concentration: 3 to 6 mass%, boric acid concentration: 1.5 mass%). The drying treatment was performed by hot air drying at 80°C for 1.5 minutes without stretching to obtain a polarizing film. At this time, the peelability evaluation of the PVA film from the support was "A", and the optical unevenness evaluation of the polarizing film was "A". The results are shown in Table 1.

[0164] <Example 2>

[0165] The kind of PVA was changed to PVA having a saponification degree of 99.0 mol% and a polymerization degree of 2400, the surface temperature of each of the drying rollers from the first drying roller to the final drying roller was set to 70°C, the surface temperature of the heat treatment roller was set to 85°C, and the thickness of the PVA film was changed to 30 μm, and the production and evaluation of the PVA film and the polarizing film were performed in the same manner as in Example 1 except for these. The results are shown in Table 1.

[0166] <Example 3>

[0167] The kind of PVA was changed to PVA having a saponification degree of 99.9 mol% and a polymerization degree of 4100, the surface temperature of each of the drying rollers from the first drying roller to the final drying roller was set to 85°C, the surface temperature of the heat treatment roller was set to 97°C, and the thickness of the PVA film was changed to 30 μm, and the production and evaluation of the PVA film and the polarizing film were performed in the same manner as in Example 1 except for these. The results are shown in Table 1.

[0168] <Comparative Example 1>

[0169] The manufacture and evaluation of the PVA film and the polarizing film were performed in the same manner as in Example 1 except that polyoxyethylene lauryl ether sodium sulfate as a surfactant was not used. The results are shown in Table 1.

[0170] <Comparative Example 2>

[0171] The manufacture and evaluation of the PVA film and the polarizing film were performed in the same manner as in Example 1 except that the amount of polyoxyethylene lauryl ether sodium sulfate as a surfactant was changed to 0.45 parts by mass. The results are shown in Table 1.

[0172]

[0173] According to the above results, the PVA film of the present application can manufacture a polarizing film which is peeled from a support with good peelability and has less optical unevenness using a small amount of a surfactant without using a fluorine-containing surfactant.

[0174] Explanation of Reference Signs

[0175] 1 PVA film

[0176] 2 Thickness direction of PVA film

[0177] 3 First surface

[0178] 4 Second surface

Claims

1. Polyvinyl alcohol film, which is a water-insoluble polyvinyl alcohol film. When one of the two surfaces of the polyvinyl alcohol film orthogonal to the thickness direction is designated as the first surface, The proportion of sodium in the total elemental composition (Na1S) determined by X-ray photoelectron spectroscopy analysis of the first surface is 0.5–1.5 mol%. The proportion of sodium (Na1B) in all elements was determined by analyzing the surface at a depth of 0.01 μm from the first surface using X-ray photoelectron spectroscopy, and was found to be less than 0.3 mol%.

2. The polyvinyl alcohol film according to claim 1, wherein, When the surface of the polyvinyl alcohol film that is orthogonal to the thickness direction and opposite to the first surface is designated as the second surface. The proportion of sodium in the total elemental composition (Na₂S) determined by X-ray photoelectron spectroscopy analysis of the second surface is 0.3–1.5 mol%. The proportion of sodium (Na₂B) in the total elements was determined to be less than 0.3 mol% by analyzing the surface at a depth of 0.01 μm from the second surface using X-ray photoelectron spectroscopy.

3. The polyvinyl alcohol film according to claim 1 or 2, wherein it contains a sodium sulfate-type surfactant or a sodium sulfonate-type surfactant. The sodium element is derived from the sodium sulfate-type surfactant or the sodium sulfonate-type surfactant.

4. The polyvinyl alcohol film according to claim 3, wherein, The sodium sulfate-type surfactant or the sodium sulfonate-type surfactant is selected from at least one of alkyl sulfate, polyoxyethylene alkyl ether sulfate, polyoxypropylene alkyl ether sulfate, polyoxyethylene alkylphenyl ether sulfate, alkyl sulfonate, alkylbenzene sulfonate, disodium dodecyl diphenyl ether disulfonate, alkylnaphthalene sulfonate, disodium alkyl sulfosuccinate, and disodium polyoxyethylene alkyl sulfosuccinate.

5. The polyvinyl alcohol film according to claim 3, wherein, The sodium sulfate-type surfactant or the sodium sulfonate-type surfactant has a molecular weight of 200 to 10,000, and the content of the sodium sulfate-type surfactant or the sodium sulfonate-type surfactant is 0.02 to 0.4 parts by mass relative to 100 parts by mass of polyvinyl alcohol contained in the polyvinyl alcohol film.

6. The polyvinyl alcohol film according to claim 1 or 2, wherein it is a film for manufacturing optical films.

7. The polyvinyl alcohol film according to claim 6, wherein, The optical film is a polarizing film.

8. A method for manufacturing a polarizing film, wherein, The polarizing film is manufactured using the polyvinyl alcohol film according to any one of claims 1 to 7.

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