Polyvinyl alcohol film and method for producing the same

Abstract

To provide a PVA film having a polarization performance for ultraviolet light, particularly ultraviolet light in a region in the vicinity of a wavelength of 345 nm and to provide a method for producing the PVA film.SOLUTION: A polyvinyl alcohol film contains (A) a polyvinyl alcohol and (B) a particle including metal in which the particle (B) has an aspect ratio of 1.1 to 10; and the metal includes at least one kind selected from a group consisting of zinc, cadmium, manganese, iron and cobalt.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a polyvinyl alcohol film and a method for producing the same.

Background Art

[0002] Ultraviolet polarizing plates are used in spectroscopic analyzers such as fluorescence spectrometers, exposure apparatuses that irradiate ultraviolet rays, ultraviolet polarizing sunglasses, and the like. As constituent members of ultraviolet polarizing plates, prism polarizers, polarizing films, and the like are known. However, in the case of prism polarizers, it is difficult to increase the size, and it is difficult to obtain polarized light of a large area. Further, as a polarizing film, an iodine-based polarizing film in which iodine, which is a dichroic dye, is contained in a base material such as a stretched and oriented polyvinyl alcohol (hereinafter, "polyvinyl alcohol" may be abbreviated as "PVA") film is known. The iodine-based polarizing film has the advantage of being easily enlarged, but its durability due to heat generation from an ultraviolet light source is not sufficient.

[0003] Therefore, an ultraviolet-absorbing grid polarizing element in which a grid formed of a metal or the like is arranged in stripes on a transparent substrate has been proposed (see Patent Document 1). Further, a polarizing film for a near-ultraviolet polarizing plate in which a monoazo compound or a salt thereof is contained in a uniaxially stretched PVA film has been proposed (see Patent Document 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] The grid polarizing element described in Patent Document 1 is considered to have high durability, but like the prism polarizing element, it is difficult to increase its size. Also, the polarizing film described in Patent Document 2 is considered to have improved durability compared to the iodine-based polarizing film. However, the polarizing film described in Patent Document 2 has polarizing performance in the near-ultraviolet region with a wavelength of 370 to 400 nm, and its polarizing performance for ultraviolet rays in a region with a lower wavelength is not sufficient. For example, there is also a demand for a polarizing film corresponding to ultraviolet rays in the region near a wavelength of 345 nm, such as the third harmonic (THG: 355 nm) of a solid laser such as a YAG laser and the i-line (365 nm) frequently used in exposure in photolithography.

[0006] The present invention has been made based on the above circumstances, and an object thereof is to provide a PVA film having polarizing performance for ultraviolet rays, particularly in the region near a wavelength of 345 nm, and a method for manufacturing such a PVA film.

Means for Solving the Problems

[0007] As a result of intensive studies to achieve the above object, the inventors of the present invention stretched a raw film (material film) containing PVA and specific metal ions and then performed a precipitation treatment, whereby particles containing a metal and oriented in the stretching direction were precipitated with good dispersibility, and it was found that the obtained PVA film had polarizing performance for ultraviolet rays in the region near a wavelength of 345 nm. Based on these findings, further studies were conducted to complete the present invention.

[0008] That is, the present invention is [1] A PVA film containing PVA (A) and particles (B) containing a metal, wherein the aspect ratio of the particles (B) is 1.1 or more and 10 or less, and the metal contains at least one selected from the group consisting of zinc, cadmium, manganese, iron, and cobalt; [2] The PVA film of [1] above, wherein the metal is zinc; [3] The PVA film of [1] or [2] above, having a polarization degree of 5% or more at an ultraviolet wavelength of 345 nm; [4] A PVA film according to any one of [1] to [3] above, having a transmittance of 40% or more in visible light with a wavelength of 540 nm; [5] A PVA film according to any one of [1] to [4] above, wherein the content of the above metal with respect to 100 parts by mass of PVA (A) is 0.1 part by mass or more and 10 parts by mass or less; [6] A PVA film according to any one of [1] to [5] above, which is a uniaxially stretched film and in which the long axis of the particles (B) is oriented in the stretching direction; [7] A method for producing a PVA film, comprising a step of obtaining a stretched film containing PVA and metal ions, and a step of subjecting the stretched film to a precipitation treatment of the particles containing the metal, wherein the step of obtaining the stretched film is a step of stretching a raw film containing PVA and the metal ions in water or in air, or a step of stretching a raw film containing PVA in an aqueous solution containing the metal ions, and the metal contains at least one selected from the group consisting of zinc, cadmium, manganese, iron, and cobalt; (relates to).

Effect of the Invention

[0009] According to the present invention, it is possible to provide a PVA film having polarization performance with respect to ultraviolet rays, particularly in the region near a wavelength of 345 nm, and a method for producing such a PVA film.

Brief Description of the Drawings

[0010]

Figure 1

Embodiments for Carrying Out the Invention

[0011] Hereinafter, the PVA film of the present invention and its manufacturing method will be described in detail. <PVA Film> The PVA film of the present invention contains PVA (A) and particles (B) containing a metal.

[0012] (PVA (A)) PVA (polyvinyl alcohol) (A) is usually the main component of the PVA film of the present invention. The main component refers to the component with the highest content based on mass. As the content of PVA (A) in the PVA film of the present invention, for example, 50% by mass or more and 99% by mass are preferable, 70% by mass or more and 98% by mass or less may be more preferable, and 80% by mass or more and 95% by mass or less may be even more preferable.

[0013] PVA (A) is a polymer having vinyl alcohol units (-CH2-CH(OH)-) as the main structural units. PVA (A) may have vinyl ester units and other units in addition to vinyl alcohol units.

[0014] As PVA (A), those obtained by saponifying polyvinyl esters obtained by polymerizing one or more vinyl esters can be used. Examples of vinyl esters include vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate, vinyl benzoate, isopropenyl acetate, and the like. Among vinyl esters, compounds having a vinyloxycarbonyl group (H2C=CH-O-CO-) in the molecule are preferable from the viewpoints of ease of production, availability, cost, etc., and vinyl acetate is more preferable.

[0015] The polyvinyl ester is preferably obtained using only one or more vinyl esters as monomers, and more preferably a polyvinyl ester obtained using only one vinyl ester as a monomer. Within a range that does not significantly impair the effects of the present invention, it may be a copolymer resin of one or more vinyl esters and other monomers copolymerizable therewith.

[0016] The upper limit of the proportion of structural units derived from other copolymerizable monomers is preferably 15 mol%, more preferably 10 mol%, even more preferably 5 mol%, and still more preferably 1 mol% based on the total number of moles of all structural units constituting the copolymer resin.

[0017] Examples of other monomers copolymerizable with vinyl esters include α-olefins having 2 to 30 carbon atoms such as ethylene, propylene, 1-butene, and isobutene; (meth)acrylic acid or its salts; (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, i-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, dodecyl (meth)acrylate, and octadecyl (meth)acrylate; (meth)acrylamide; (meth)acrylamide derivatives such as N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, diacetone(meth)acrylamide, (meth)acrylamidepropanesulfonic acid or its salts, (meth)acrylamidepropyldimethylamine or its salts, and N-methylol(meth)acrylamide or its derivatives; N-vinylamides such as N-vinylformamide, N-vinylacetamide, and N-vinylpyrrolidone; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, and stearyl vinyl ether; vinyl cyanides such as (meth)acrylonitrile; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid or its salts, esters, or acid anhydrides; itaconic acid or its salts, esters, or acid anhydrides; vinylsilyl compounds such as vinyltrimethoxysilane; unsaturated sulfonic acids or their salts, etc.

[0018] The polyvinyl ester can have structural units derived from one or more of the above monomers.

[0019] As PVA(A), those without graft copolymerization can be preferably used. However, within a range that does not significantly impair the effects of the present invention, PVA(A) may be modified with one or more graft copolymerizable monomers. The graft copolymerization can be carried out on at least one of polyvinyl ester and PVA obtained by saponifying it. Examples of graft copolymerizable monomers include unsaturated carboxylic acids or their derivatives; unsaturated sulfonic acids or their derivatives; α-olefins having 2 to 30 carbon atoms, etc. The proportion of structural units derived from graft copolymerizable monomers in polyvinyl ester or PVA is preferably 5 mol% or less based on the number of moles of all structural units constituting polyvinyl ester or PVA.

[0020] Part of the hydroxy groups of PVA(A) may be crosslinked or may not be crosslinked. Also, part of the hydroxy groups of PVA(A) may react with aldehyde compounds such as acetaldehyde and butyraldehyde to form an acetal structure.

[0021] As the lower limit of the degree of polymerization of PVA(A), 1,000 is preferable, 1,500 is more preferable, and 1,700 is even more preferable. By the degree of polymerization of PVA(A) being not less than the above lower limit, the flexibility of the PVA film can be improved. On the other hand, as the upper limit of this degree of polymerization, 10,000 is preferable, 8,000 is more preferable, and 5,000 is even more preferable. By the degree of polymerization of PVA(A) being not more than the above upper limit, an increase in the production cost of PVA(A) and the occurrence of defects during film formation can be suppressed. The degree of polymerization of PVA means the average degree of polymerization measured according to the description of JIS K6726-1994.

[0022] The saponification degree of PVA(A) is preferably 90 mol% or more, more preferably 95 mol% or more, still more preferably 99 mol% or more, and particularly preferably 99.3 mol% or more, since the PVA film has good wet heat resistance. The upper limit of the saponification degree of PVA(A) may be 100 mol%. The saponification degree of PVA(A) refers to the ratio (mol%) of the number of moles of vinyl alcohol units to the total number of moles of structural units (typically vinyl ester units) that can be converted to vinyl alcohol units by saponification and vinyl alcohol units. The saponification degree can be measured according to the description in JIS K6726-1994.

[0023] (Particles (B)) Particles (B) are particles having an aspect ratio of 1.1 or more and 10 or less. Particles (B) are usually rod-shaped particles. The above aspect ratio is preferably 2.0 or more and 9.6 or less, more preferably 3.0 or more and 9.2 or less, still more preferably 4.0 or more and 8.8 or less, even more preferably 5.0 or more and 8.4 or less, and particularly preferably 6.0 or more and 8.0 or less. When the aspect ratio of particles (B) is 1.1 or more, sufficient polarization performance against ultraviolet rays can be exhibited. On the other hand, when the aspect ratio of particles (B) is 10 or less, productivity can be increased and sufficient visible light transmittance can be exhibited.

[0024] The aspect ratio of particles (B) refers to the ratio (major axis / minor axis) of the length in the major axis direction (major axis) to the length in the minor axis direction (minor axis). The major axis direction refers to the direction in which the particle size is the longest. The minor axis direction refers to the direction perpendicular to the major axis direction. The above major axis direction and minor axis direction are based on the shape of particles (B) when the PVA film is observed in the normal direction. The aspect ratio is the average value of the measured values of any 10 particles (B) observed when the PVA film is observed in the normal direction using a differential interference electron microscope or the like.

[0025] Particle (B) contains a metal. The metal contained in particle (B) contains at least one selected from the group consisting of zinc, cadmium, manganese, iron, and cobalt. By using particle (B) containing such a metal, good polarization performance against ultraviolet rays can be exhibited. Also, since these metals can be effectively precipitated in a particulate form by the precipitation treatment described later, they are preferable. It is preferable that the above metal contains at least one of zinc and manganese, and more preferably contains zinc. Also, the above metal is preferably at least one selected from the group consisting of zinc, cadmium, manganese, iron, and cobalt, more preferably at least one of zinc and manganese, and even more preferably zinc. By using zinc as the above metal, the polarization performance against ultraviolet rays can be enhanced, and the visible light transmittance can also be enhanced.

[0026] The metal contained in particle (B) may exist as a simple metal or as a compound. Examples of the compound include oxides, sulfides, nitrides, and the like. Among these, it is preferable that it exists as a sulfide. That is, particle (B) is preferably particles of a sulfide of the above metal. By the metal existing in such a form, the polarization performance against ultraviolet rays can be further enhanced, etc. Also, in the case of a metal sulfide, it can be effectively produced by the method using the precipitation treatment described later.

[0027] The PVA film of the present invention is usually a uniaxially stretched film, and it is preferable that the major axis of the particle (B) is oriented in the stretching direction of this PVA film. Thus, when the major axis direction of the particle (B) is oriented in the stretching direction, the polarization performance with respect to ultraviolet rays becomes better. In addition, by performing differential interference microscopy observation of the PVA film, it is possible to confirm whether the major axis of the particle (B) is oriented in the stretching direction. For example, among any 10 particles (B) observed with a differential interference microscope, it is preferable that there are 8 or more particles (B) in which the acute angle formed by the stretching direction of the PVA film (the orientation direction of PVA (A)) and the major axis direction of the particle (B) is 10° or less (more preferably 5° or less), more preferably 9 or more, and even more preferably 10.

[0028] As the major diameter (length in the major axis direction) of the particle (B), for example, 10 nm or more and 200 μm or less is preferable, 100 nm or more and 100 μm or less is more preferable, and 1 μm or more and 50 μm or less is even more preferable. When the major diameter of the particle (B) is 10 nm or more, more sufficient polarization performance with respect to ultraviolet rays can be exhibited. On the other hand, when the major diameter of the particle (B) is 200 μm or less, the visible light transmittance can be increased, etc. Further, the major diameter is the average value of the respective measured values of any 10 particles (B) observed when the PVA film is observed in the normal direction with a differential interference microscope.

[0029] The content of the above metal with respect to 100 parts by mass of PVA (A) in the PVA film of the present invention may be, for example, 0.01 part by mass or more and 20 parts by mass or less, but 0.1 part by mass or more and 10 parts by mass or less is preferable, 1 part by mass or more and 9 parts by mass or less is more preferable, 2 parts by mass or more and 8 parts by mass or less is even more preferable, 3 parts by mass or more and 7 parts by mass or less is even more preferable, and in some cases, 6 parts by mass or less, 5 parts by mass or less, or 4 parts by mass or less is even more preferable. By setting the content of the above metal to 0.1 part by mass or more, the polarization performance with respect to ultraviolet rays can be enhanced. On the other hand, by setting the content of the above metal to 10 parts by mass or less, the transmittance of visible light, ultraviolet rays, etc. can be increased.

[0030] The content of the above metal (the metal contained in particle (B)) in the PVA film of the present invention may be, for example, 0.01% by mass or more and 20% by mass or less, preferably 0.1% by mass or more and 10% by mass or less, more preferably 1% by mass or more and 9% by mass or less, still more preferably 2% by mass or more and 8% by mass or less, even more preferably 3% by mass or more and 7% by mass or less, and may even more preferably be 6% by mass or less, 5% by mass or less, or 4% by mass or less. By setting the content of the above metal to 0.1% by mass or more, the polarization performance with respect to ultraviolet rays can be enhanced. On the other hand, by setting the content of the above metal to 10% by mass or less, the transmittance of visible light, ultraviolet rays, etc. can be increased.

[0031] (Other components) The PVA film of the present invention may contain a plasticizer. By the PVA film containing a plasticizer, the handleability, stretchability, etc. of the PVA film are enhanced, and as a result, the polarization performance becomes better. A polyhydric alcohol is preferable as the plasticizer, and specifically, ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylolpropane, etc. may be mentioned. Among these, glycerin is preferable because the stretchability of the PVA film becomes better. Also, one type or two or more types of plasticizers can be used.

[0032] The content of the plasticizer in the PVA film of the present invention is preferably 1 part by mass or more and 20 parts by mass or less, more preferably 3 parts by mass or more and 17 parts by mass or less, and still more preferably 4 parts by mass or more and 14 parts by mass or less with respect to 100 parts by mass of PVA (A). By the content of the plasticizer being 1 part by mass or more with respect to 100 parts by mass of PVA (A), the stretchability is improved and the polarization performance of the PVA film is enhanced. On the other hand, by the content of the plasticizer being 20 parts by mass or less with respect to 100 parts by mass of PVA (A), it is possible to suppress the plasticizer from bleeding out on the surface of the PVA film and the handleability of the PVA film from deteriorating.

[0033] Further, when manufacturing the base film (material film) of the PVA film of the present invention using the film-forming stock solution described below, the film-forming property is improved and the occurrence of film thickness unevenness is suppressed. In addition, when using a metal roll or belt for film formation, since the release of the base film from these metal rolls or belts becomes easier, it is preferable to blend a surfactant in the film-forming stock solution. When manufacturing a base film from the film-forming stock solution containing a surfactant, the surfactant may be contained in the finally obtained PVA film. The type of surfactant blended in the film-forming stock solution for manufacturing the base film, and thus the type of surfactant contained in the PVA film, is not particularly limited. However, from the viewpoint of releasability from metal rolls and belts, anionic surfactants and nonionic surfactants are preferable, and nonionic surfactants are particularly preferable.

[0034] Examples of anionic surfactants include carboxylic acid types such as potassium laurate; sulfate ester types such as octyl sulfate; sulfonic acid types such as dodecylbenzenesulfonate, etc. are preferable.

[0035] Examples of nonionic surfactants include alkyl ether types such as polyoxyethylene oleyl ether; alkyl phenyl ether types such as polyoxyethylene octylphenyl ether; alkyl ester types such as polyoxyethylene laurate; alkyl amine types such as polyoxyethylene lauryl amino ether; alkyl amide types such as polyoxyethylene lauric acid amide; polypropylene glycol ether types such as polyoxyethylene polyoxypropylene ether; alkanolamide types such as lauric acid diethanolamide, oleic acid diethanolamide, etc.; allyl phenyl ether types such as polyoxyalkylene allyl phenyl ether, etc. are preferable.

[0036] These surfactants can be used alone or in combination of two or more.

[0037] When a surfactant is blended in the film-forming stock solution for producing the base film, the content of the surfactant in the film-forming stock solution, and thus the content of the surfactant in the PVA film, are preferably 0.01 part by mass or more and 0.5 part by mass or less, more preferably 0.02 part by mass or more and 0.3 part by mass or less, based on 100 parts by mass of PVA(A) contained in the film-forming stock solution or the PVA film. By the surfactant content being 0.01 part by mass or more based on 100 parts by mass of PVA(A), the film-forming property and peelability can be improved. On the other hand, by the surfactant content being 0.5 part by mass or less based on 100 parts by mass of PVA(A), it is possible to suppress the surfactant from bleeding out on the surface of the base film or the PVA film and causing blocking, which would reduce the handleability.

[0038] The PVA film of the present invention may, if necessary, contain other components other than the above-described PVA(A), particles (B), plasticizer, and surfactant, such as an antioxidant, an antifreezing agent, a pH adjuster, a masking agent, an anti-coloring agent, an oil agent, etc. However, the content of these other components is preferably 10 parts by mass or less, more preferably 1 part by mass or less, or even more preferably 0.1 part by mass or less, based on 100 parts by mass of PVA(A).

[0039] (Physical properties, size, uses, etc.) The PVA film of the present invention has polarization performance with respect to ultraviolet rays having a wavelength of 345 nm. The degree of polarization of the PVA film of the present invention at ultraviolet rays having a wavelength of 345 nm is preferably 5% or more, more preferably 10% or more, and even more preferably 15% or more. On the other hand, the upper limit of the degree of polarization at ultraviolet rays having a wavelength of 345 nm is not particularly limited, and may be, for example, 80%, or may be 60% or 40%.

[0040] The lower limit of the transmittance of the PVA film of the present invention at ultraviolet light with a wavelength of 345 nm is preferably 20%, more preferably 40%, still more preferably 50%, and may be even more preferably 60% or 70%. By the transmittance at ultraviolet light with a wavelength of 345 nm being not less than the above lower limit, for example, when the PVA film of the present invention is used for an ultraviolet polarizing plate such as a spectroscopic analyzer or an exposure apparatus, the amount of light of the ultraviolet light source can be reduced. On the other hand, the upper limit of the transmittance at ultraviolet light with a wavelength of 345 nm may be, for example, 90%, and may preferably be 80%, 70% or 60%. For example, when the PVA film of the present invention is used for polarized sunglasses, it may be preferable that the ultraviolet transmittance is relatively low.

[0041] As for the transmittance of the PVA film of the present invention at visible light with a wavelength of 540 nm, it is preferably 40% or more, more preferably 50% or more, and may be still more preferably 60% or more, 70% or more, 75% or more, 80% or more or 85% or more. For example, in the case where the PVA film of the present invention is used for polarized sunglasses, it is preferable that the visible light transmittance is high. In the PVA film of the present invention, when the visible light transmittance is high in this way, the range of uses can be expanded, etc. On the other hand, the upper limit of the transmittance at visible light with a wavelength of 540 nm may be, for example, 99.9%, or may be 99% or 95%.

[0042] The upper limit of the average thickness of the PVA film of the present invention is not particularly limited, but is, for example, 50 μm, preferably 40 μm, more preferably 30 μm, and may be still more preferably 20 μm or 10 μm. On the other hand, as the lower limit of this average thickness, 1 μm is preferable, 3 μm is more preferable, and 5 μm is still more preferable. By the average thickness of the PVA film being within the above range, handleability etc. can be improved. The average thickness is the average value of the measured values at any five points.

[0043] The shape of the PVA film of the present invention is not particularly limited, but it is preferably a long film. The length of the long film is not particularly limited and can be appropriately set according to applications such as polarizing films. For example, it can be in the range of 5 m or more and 20,000 m or less. There is no particular limitation on the width of the long film. For example, it can be 50 cm or more. However, in recent years, wide polarizing films have been demanded, so it is preferably 1 m or more, more preferably 2 m or more, and still more preferably 4 m or more. There is no particular limitation on the upper limit of the width of the long film. However, if the width is too wide, it tends to be difficult to stretch uniformly when manufacturing a PVA film (polarizing film) with a commercially available device. Therefore, the width of the PVA film is preferably 7 m or less.

[0044] The shape of the PVA film of the present invention is not particularly limited, and it may be a single-layer film or a multilayer film (laminate). However, from the viewpoints of the complexity and cost of the lamination (coating, etc.) operation, a single-layer film is preferred.

[0045] The PVA film of the present invention is usually a stretched film (stretched film). Further, the PVA film of the present invention is suitably used as an ultraviolet polarizing film. Note that a PVA film in a non-stretched form is also within the scope of the present invention.

[0046] The PVA film of the present invention can be used as an ultraviolet polarizing film in spectroscopic analysis devices such as fluorescence spectrometers, exposure devices that irradiate ultraviolet light, and polarized sunglasses.

[0047] <Manufacturing method of PVA film> The manufacturing method of the PVA film of the present invention is not particularly limited. However, in order to enhance the dispersibility of the particles (B), a method in which after incorporating metal ions into the base film (material film), uniaxial stretching is performed and precipitation treatment is carried out to granulate the metal ions is preferable. The base film refers to the unstretched PVA film before obtaining the PVA film of the present invention. By stretching the base film, a stretched film is obtained, and by processing the stretched film, the PVA film of the present invention is obtained. There is no particular limitation on the method of incorporating metal ions into the base film. However, a method of incorporating metal ions when manufacturing the base film and a method of incorporating metal ions into the base film by performing uniaxial stretching in an aqueous solution containing metal ions when manufacturing the PVA film of the present invention from the base film are preferable.

[0048] That is, the manufacturing method of the PVA film of the present invention comprises a step of obtaining a stretched film containing PVA and metal ions (step B), and a step of performing precipitation treatment of the particles containing the above metal on the above stretched film (step C) and the step of obtaining the above stretched film (step B) is a step of stretching the base film containing the above PVA and the metal ions in water or in air (step B1), or a step of stretching the base film containing the above PVA in an aqueous solution containing the metal ions (step B2) and the above metal contains at least one selected from the group consisting of zinc, cadmium, manganese, iron, and cobalt.

[0049] The manufacturing method may further include a step of manufacturing the base film (step A). It may further include.

[0050] In addition, the manufacturing method is usually carried out in the order of step A, step B, and step C, but a plurality of steps may be carried out simultaneously. For example, precipitation treatment may be carried out while stretching. Hereinafter, each step will be described in detail in order.

[0051] (Project A) In this project, a raw film containing PVA is manufactured. The raw film may further contain metal ions. The manufacturing method of the raw film is not particularly limited, and a manufacturing method that makes the thickness and width more uniform can preferably be adopted. For example, a film-forming stock solution in which PVA constituting the raw film and, if necessary, one or more of a plasticizer, a surfactant, and other components are dissolved in a liquid medium, or a film-forming stock solution containing PVA and, if necessary, one or more of a plasticizer, a surfactant, other components, and a liquid medium, and in which PVA is melted can be used for manufacturing. When the film-forming stock solution contains at least one of a plasticizer, a surfactant, and other components, it is preferable that these components are uniformly mixed.

[0052] Examples of the liquid medium used for preparing the film-forming stock solution include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, diethylenetriamine, etc., and one or more of these can be used. Among these, water is preferable from the viewpoints of low environmental load and recyclability.

[0053] When performing the above step B1, the film-forming stock solution further contains metal ions or metal salts (salts containing metal ions). Examples of the metal salts include metal nitrates, metal sulfates, metal acetates, etc. One or more of these salts can be used. Among these, metal nitrates (zinc nitrate, cadmium nitrate, manganese nitrate, iron nitrate, cobalt nitrate) are preferable because the polarization performance of the obtained PVA film becomes better. The content of the metal salt with respect to 100 parts by mass of PVA in the film-forming stock solution is preferably 0.5 part by mass or more and 70 parts by mass or less, more preferably 1 part by mass or more and 60 parts by mass or less, and still more preferably 2 parts by mass or more and 50 parts by mass or less.

[0054] The specific forms and preferred forms of each component contained in the film-forming stock solution are the same as those of each component other than the particles (B) contained in the PVA film of the present invention. Also, the specific content and preferred content of each component other than PVA (A), particles (B), and the liquid medium contained in the film-forming stock solution with respect to PVA (A) are the same as those of each component contained in the PVA film of the present invention.

[0055] The volatile fraction of the film-forming stock solution (the content ratio of volatile components such as the liquid medium removed by volatilization or evaporation during film formation in the film-forming stock solution) varies depending on the film-forming method, film-forming conditions, etc., but is preferably 50 parts by mass or more and 95% by mass or less, more preferably 55% by mass or more and 90% by mass or less, and even more preferably 60% by mass or more and 85% by mass or less. When the volatile fraction of the film-forming stock solution is 50% by mass or more, the viscosity of the film-forming stock solution does not become too high, filtration and defoaming during the preparation of the film-forming stock solution are smoothly performed, and the production of a base film with few foreign substances and defects and the finally obtained PVA film becomes easy. On the other hand, when the volatile fraction of the film-forming stock solution is 95% by mass or less, the concentration of the film-forming stock solution does not become too low, and the production of an industrial base film and the finally obtained PVA film becomes easy.

[0056] Examples of the film-forming method for forming a base film using the above-described film-forming stock solution include a casting film-forming method, an extrusion film-forming method, a wet film-forming method, a gel film-forming method, etc., and the casting film-forming method and the extrusion film-forming method are preferred. These film-forming methods may be employed alone or in combination of two or more. Among these film-forming methods, the extrusion film-forming method is more preferred because a base film with uniform thickness and width and good physical properties can be obtained. The base film can be dried and heat-treated as necessary.

[0057] There is no particular limitation on the heat treatment temperature, and it may be appropriately adjusted according to the degree of swelling of the raw film, etc. If the heat treatment temperature is too high, discoloration and deterioration of the raw film may be observed. Therefore, it is preferably 210 °C or lower, more preferably 200 °C or lower, and still more preferably 190 °C or lower. As the lower limit of the heat treatment temperature, for example, it may be 100 °C or 120 °C.

[0058] There is no particular limitation on the heat treatment time, and it may be appropriately adjusted according to the degree of swelling of the raw film. However, from the viewpoint of efficiently producing the PVA film of the present invention, it is preferably 1 second or more and 30 minutes or less, and more preferably 3 seconds or more and 15 minutes or less.

[0059] The upper limit of the average thickness of the obtained raw film is not particularly limited. For example, it may be 100 μm, preferably 80 μm, more preferably 60 μm, and still more preferably 40 μm. On the other hand, as the lower limit of this average thickness, 5 μm is preferable, 10 μm is more preferable, and 15 μm is still more preferable. When the average thickness of the raw film is within the above range, handleability and the like can be improved.

[0060] The specific forms and preferred forms regarding the types and contents of PVA(A), plasticizer, surfactant, and other components contained in the obtained raw film are the same as those of these components contained in the PVA film of the present invention. Further, when the raw film contains metal ions, the specific and preferred contents of these metal ions are the same as the specific and preferred contents of the metals contained in the PVA film of the present invention.

[0061] (Steps B1, B2) In this step, the raw film is stretched (usually uniaxially stretched) to obtain a stretched film containing PVA and metal ions. When the raw film contains metal ions, either a wet stretching method of stretching in water (aqueous solution) or a dry stretching method of stretching in air may be employed (Step B1). On the other hand, when the raw film does not contain metal ions, a wet stretching method is employed (Step B2).

[0062] (Wet stretching method) Uniaxial stretching in water of the raw film can be carried out by a known method. If necessary, the raw film may be subjected to swelling treatment, crosslinking treatment, drying treatment, heat treatment, etc. The order of each treatment such as swelling treatment, uniaxial stretching, crosslinking treatment, etc. is not particularly limited, and one or more treatments can also be carried out simultaneously. Also, one or more of each treatment can be carried out two or more times.

[0063] The swelling treatment can be carried out by immersing the raw film in water. As the temperature of the water when immersing in water, 20°C or higher and 40°C or lower is preferable, 22°C or higher and 38°C or lower is more preferable, and 25°C or higher and 35°C or lower is even more preferable. Also, as the time of immersion in water, for example, 0.1 minute or more and 5 minutes or less is preferable, and 0.5 minute or more and 3 minutes or less is more preferable. Note that the water when immersing in water is not limited to pure water, and may be an aqueous solution in which various components are dissolved, or may be a mixture of water and an aqueous medium.

[0064] The crosslinking treatment can be carried out by immersing the raw film in an aqueous solution containing a crosslinking agent. When the crosslinking step is carried out, a crosslinked structure is introduced into the raw film, and uniaxial stretching can be carried out at a relatively high temperature. As the crosslinking agent to be used, one or more boron compounds such as borate salts such as boric acid and borax can be used. The concentration of the crosslinking agent in the aqueous solution containing the crosslinking agent is preferably 1% by mass or more and 15% by mass or less, and more preferably 2% by mass or more and 7% by mass or less. The temperature of the aqueous solution containing the crosslinking agent is preferably 20°C or higher and 50°C or lower, and more preferably 25°C or higher and 40°C or lower.

[0065] When the raw film does not contain metal ions, the uniaxial stretching is carried out in an aqueous solution containing metal ions. Examples of the aqueous solution containing metal ions include aqueous solutions of metal salts such as metal nitrate aqueous solution, metal sulfate aqueous solution, and metal acetate aqueous solution. Among these, it is preferable to carry out uniaxial stretching in an aqueous solution of zinc nitrate because the polarization performance of the obtained PVA film becomes better. The concentration of the metal salt such as zinc nitrate in the aqueous solution is preferably 0.5% by mass or more and 10% by mass or less, more preferably 1% by mass or more and 8% by mass or less, and still more preferably 2% by mass or more and 6% by mass or less. The above aqueous solution may also contain boric acid or potassium iodide, and the concentration thereof is preferably 0.01% by mass or more and 6% by mass or less.

[0066] The stretching temperature in the uniaxial stretching is preferably 30°C or higher and 90°C or lower, more preferably 40°C or higher and 80°C or lower, and still more preferably 50°C or higher and 70°C or lower.

[0067] (Dry stretching method) The uniaxial stretching of the raw film in the air can be carried out by a known method. In the dry stretching method, the uniaxial stretching may be carried out at room temperature, may be carried out while heating, or may be carried out after the raw film is made to absorb water. The upper limit of the stretching temperature in the uniaxial stretching is preferably 90°C, more preferably 80°C, and still more preferably 70°C. On the other hand, the lower limit of the above temperature is preferably 30°C, more preferably 40°C, and still more preferably 50°C.

[0068] The stretching ratio in the uniaxial stretching may be, for example, 1.1 times or more regardless of the stretching method, but from the viewpoint of the polarization performance of the obtained polarizing film, 3 times or more is preferable, 4 times or more is more preferable, 5 times or more is still more preferable, and 6 times or more is particularly preferable. The upper limit of the stretching ratio is not particularly limited, but the stretching ratio is preferably 10 times or less, and more preferably 8 times or less.

[0069] (Step C) In this process, a stretching film (stretched raw film) containing PVA and metal ions is subjected to a precipitation treatment of the particles containing the above metal. When the precipitation treatment is carried out, the metal ions present in the stretching film can be precipitated as particles containing the metal.

[0070] The precipitation treatment can be carried out, for example, by immersing the above stretching film in an aqueous solution containing sulfide ions as a precipitation treatment bath. In this case, the metal ions are precipitated as metal sulfides to form particles (B). Examples of the aqueous solution containing sulfide ions include an aqueous sodium sulfide solution and an aqueous hydrogen sulfide solution, and an aqueous sodium sulfide solution is preferred. The concentration of sodium sulfide in the precipitation treatment bath is preferably 0.1% by mass or more and 5% by mass or less, more preferably 0.5% by mass or more and 4% by mass or less, and even more preferably 1% by mass or more and 3% by mass or less.

[0071] The precipitation treatment is preferably carried out while applying ultrasonic waves to the raw film. By doing so, the precipitation reaction can proceed uniformly. Further, after the precipitation treatment, the surface of the film may be washed with water or an organic solvent.

[0072] In addition, as the precipitation treatment, precipitation as metal particles can also be carried out by a reduction reaction using a reducing agent.

[0073] (Other processes) After the above step C, for example, a drying treatment or a heat treatment may be applied to the film (PVA film). The drying treatment is preferably carried out at 30°C or more and 150°C or less, and more preferably at 50°C or more and 130°C or less. By drying at a temperature within the above range, a PVA film (polarizing film) excellent in dimensional stability is easily obtained.

[0074] <Polarizing plate> The PVA film of the present invention may be used as a laminate (polarizing plate) in which a protective film that is optically transparent and has mechanical strength is disposed on at least one surface. That is, the polarizing plate is a laminate having the PVA film of the present invention and a protective film laminated on the PVA film.

[0075] Examples of the protective film include a triacetyl cellulose (TAC) film, a cycloolefin polymer (COP) film, a cellulose acetate butyrate (CAB) film, an acrylic film, a polyester film, and the like.

[0076] The PVA film and the protective film may be bonded via an adhesive. Examples of the adhesive include a PVA-based adhesive and an ultraviolet curable adhesive.

Examples

[0077] The present invention will be specifically described by the following examples, but the present invention is not limited to these examples. Each evaluation method adopted in the following examples and comparative examples is shown below.

[0078] [Content of metal (metal ion)] The content of the metal contained in the PVA film obtained in each of the following examples or comparative examples was measured based on the PVA film before the precipitation treatment. That is, the PVA film before the precipitation treatment was sampled, dissolved in water, and then the amount of metal ions was measured using an ICP emission spectrometer to obtain the content of the metal (content relative to 100 parts by mass of PVA). In addition, after the PVA film obtained in Example 1 below was subjected to dry decomposition treatment, the amount of metal ions was measured in the same manner, but it was the same value as the amount of metal ions measured using the above-mentioned PVA film before the precipitation treatment.

[0079] [Aspect ratio of particles] Regarding the PVA films obtained in each of the following examples or comparative examples, differential interference microscopy observation was performed to obtain the aspect ratio of the particles present in the PVA film.

[0080] [Transmittance in ultraviolet light with a wavelength of 345 nm and visible light with a wavelength of 540 nm] Two square samples with a length of 3 cm and a width of 3 cm were taken from the PVA films obtained in the following examples or comparative examples. For the two samples, using a spectrophotometer with an integrating sphere (V7100 manufactured by JASCO Corporation), in accordance with JIS Z8722:2009 (Method for Measuring Object Color), visual sensitivity correction in the visible light region with a C light source and a 2° field of view was performed. For one sample, the transmittance when tilted at 45° with respect to the length direction and the transmittance when tilted at -45° were measured, and the average value T1 (%) of the transmittance was obtained. For the other sample, the transmittance when tilted at 45° with respect to the length direction and the transmittance when tilted at -45° were also measured, and the average value T2 (%) of the transmittance was obtained. T1 and T2 obtained above were averaged to obtain the transmittance T (%). Next, the two samples were overlapped so that their length directions were parallel, and the transmittance when tilted at 45° with respect to the length direction and the transmittance when tilted at -45° were measured, and the average value T∥ (%) of the parallel transmittance was obtained. Furthermore, they were overlapped so that the length directions were perpendicular, and the transmittance when tilted at 45° with respect to the length direction and the transmittance when tilted at -45° were measured, and the average value T⊥ (%) of the perpendicular transmittance was obtained. The transmittance T, parallel transmittance T∥, and perpendicular transmittance T⊥ were measured for ultraviolet light with a wavelength of 345 nm and visible light with a wavelength of 540 nm, respectively.

[0081] [Degree of polarization in ultraviolet light with a wavelength of 345 nm] From T∥ and T⊥ in the ultraviolet light with a wavelength of 345 nm obtained above, the degree of polarization V (%) in the ultraviolet light with a wavelength of 345 nm was obtained by the following formula (1). V = {(T∥ - T⊥) / (T∥ + T⊥)} 1 / 2 × 100 (1)

[0082] [Example 1] [Preparation of film-forming stock solution (PVA aqueous solution)] PVA (A) (a saponified product of a homopolymer of vinyl acetate, degree of polymerization 2,400, degree of saponification 99.95 mol %), zinc nitrate (20 parts by mass with respect to 100 parts by mass of PVA), glycerin (10 parts by mass with respect to 100 parts by mass of PVA), a surfactant (0.03 parts by mass with respect to 100 parts by mass of PVA), and water were mixed, and PVA (A) etc. was dissolved at 90 °C for 4 hours to obtain a film-forming stock solution (PVA aqueous solution).

[0083] <Production of the original film> The film-forming stock solution obtained above was cast on a glass plate and dried at room temperature for 4 days to obtain an original film. The average thickness of the obtained original film was 30 μm. Also, the amount of zinc (zinc ions) contained in the original film was 3.8 parts by mass with respect to 100 parts by mass of PVA.

[0084] <Production of the PVA film> From the original film obtained above, a test piece with a length of 9 cm in the length direction and a width of 5 cm in the width direction was taken. Both ends of the test piece in the length direction were fixed to a stretching jig so that the size of the stretched part was 5 cm in the length direction and 5 cm in the width direction, and it was uniaxially stretched in the length direction to 4 times the original length at a stretching speed of 12 cm / min in the air. Then, the test piece (stretched film) was fixed to a metal frame, and ultrasonic waves were applied while immersing it in an aqueous solution of 1.2% by mass of sodium sulfide for 3 minutes for precipitation treatment. Then, it was immersed in water at 30 °C and methanol at 30 °C in order for washing, and then dried in a dryer at 65 °C for 10 minutes to obtain a PVA film.

[0085] Regarding the obtained PVA film, the aspect ratio of the particles, the transmittance at ultraviolet light with a wavelength of 345 nm and visible light with a wavelength of 540 nm, and the degree of polarization at ultraviolet light with a wavelength of 345 nm were determined by the method described above. The results are shown in Table 1. Also, a differential interference microscope image of the obtained PVA film is shown in FIG. 1. In FIG. 1, the left-right direction is the stretching direction. The presence of particles with a high aspect ratio can be confirmed.

[0086] [Example 2] A PVA film was produced in the same manner as in Example 1, except that the mixing amount of zinc nitrate in the film-forming stock solution was 50 parts by mass with respect to 100 parts by mass of PVA. The amount of zinc (zinc ions) contained in the original film was 9.0 parts by mass with respect to 100 parts by mass of PVA. For the obtained PVA film, the aspect ratio of the particles, the transmittance at ultraviolet light with a wavelength of 345 nm and visible light with a wavelength of 540 nm, and the degree of polarization at ultraviolet light with a wavelength of 345 nm were determined by the method described above. The results are shown in Table 1.

[0087] [Example 3] A PVA film was produced in the same manner as in Example 1, except that the mixing amount of zinc nitrate in the film-forming stock solution was 10 parts by mass with respect to 100 parts by mass of PVA. The amount of zinc (zinc ions) contained in the original film was 2.0 parts by mass with respect to 100 parts by mass of PVA. For the obtained PVA film, the aspect ratio of the particles, the transmittance at ultraviolet light with a wavelength of 345 nm and visible light with a wavelength of 540 nm, and the degree of polarization at ultraviolet light with a wavelength of 345 nm were determined by the method described above. The results are shown in Table 1.

[0088] [Example 4] A PVA film was produced in the same manner as in Example 1, except that the mixing amount of zinc nitrate in the film-forming stock solution was 50 parts by mass with respect to 100 parts by mass of PVA, and the draw ratio in uniaxial drawing was 1.7 times. The amount of zinc (zinc ions) contained in the original film was 9.0 parts by mass with respect to 100 parts by mass of PVA. For the obtained PVA film, the aspect ratio of the particles, the transmittance at ultraviolet light with a wavelength of 345 nm and visible light with a wavelength of 540 nm, and the degree of polarization at ultraviolet light with a wavelength of 345 nm were determined by the method described above. The results are shown in Table 1.

[0089] [Example 5] A PVA film was produced in the same manner as in Example 1, except that zinc nitrate was replaced with manganese(II) nitrate hexahydrate in the preparation of the film-forming stock solution. The amount of manganese (manganese ions) contained in the original film was 3.4 parts by mass with respect to 100 parts by mass of PVA. Regarding the obtained PVA film, the aspect ratio of the particles, the transmittance at ultraviolet light with a wavelength of 345 nm and visible light with a wavelength of 540 nm, and the degree of polarization at ultraviolet light with a wavelength of 345 nm were determined by the method described above. The results are shown in Table 1.

[0090] [Comparative Example 1] A PVA film was produced in the same manner as in Example 1, except that zinc nitrate was not mixed in the preparation of the film-forming stock solution. Regarding the obtained PVA film, the transmittance at ultraviolet light with a wavelength of 345 nm and visible light with a wavelength of 540 nm, and the degree of polarization at ultraviolet light with a wavelength of 345 nm were determined by the method described above. The results are shown in Table 1.

[0091] [Comparative Example 2] A PVA film was produced in the same manner as in Example 1, except that uniaxial stretching was not performed. The amount of zinc (zinc ions) contained in the original film was 3.8 parts by mass with respect to 100 parts by mass of PVA. Regarding the obtained PVA film, the aspect ratio of the particles, the transmittance at ultraviolet light with a wavelength of 345 nm and visible light with a wavelength of 540 nm, and the degree of polarization at ultraviolet light with a wavelength of 345 nm were determined by the method described above. The results are shown in Table 1.

[0092] [Table 1]

[0093] As shown in Table 1, it was confirmed that the PVA films of Examples 1 to 5 had a degree of polarization at ultraviolet light with a wavelength of 345 nm of 5% or more and had sufficient ultraviolet polarization performance. [Industrial Applicability]

[0094] The PVA film of the present invention can be suitably used as an ultraviolet polarization film.

Claims

1. Contains polyvinyl alcohol (A) and metal-containing particles (B), The aspect ratio of the particles (B) is 1.1 or more and 10 or less, The polyvinyl alcohol film, wherein the metal includes at least one selected from the group consisting of zinc, cadmium, manganese, iron and cobalt.

2. 2. The polyvinyl alcohol film of claim 1, wherein the metal is zinc.

3. 3. The polyvinyl alcohol film according to claim 1, which has a polarization degree of 5% or more when exposed to ultraviolet light with a wavelength of 345 nm.

4. The polyvinyl alcohol film according to any one of claims 1 to 3, which has a transmittance of 40% or more for visible light with a wavelength of 540 nm.

5. The polyvinyl alcohol film according to any one of claims 1 to 4, wherein the content of the metal per 100 parts by mass of the polyvinyl alcohol (A) is 0.1 parts by mass or more and 10 parts by mass or less.

6. It is a uniaxially stretched film, The polyvinyl alcohol film according to any one of claims 1 to 5, wherein the major axes of the particles (B) are oriented in the stretching direction.

7. Obtaining a stretched film containing polyvinyl alcohol and metal ions; and A step of subjecting the stretched film to a precipitation treatment of particles containing the metal. Equipped with The step of obtaining the stretched film comprises: A step of stretching an original film containing the polyvinyl alcohol and the metal ions in water or air; or A step of stretching the raw film containing the polyvinyl alcohol in an aqueous solution containing ions of the metal. and The method for producing a polyvinyl alcohol film, wherein the metal includes at least one selected from the group consisting of zinc, cadmium, manganese, iron and cobalt.

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