Polyvinyl alcohol film and its manufacturing method

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 technology]

[0002] UV polarizing plates are used in spectroscopic analysis devices such as fluorescence spectrophotometers, exposure devices that irradiate UV light, UV polarized sunglasses, etc. Prism polarizers, polarizing films, etc. are known as components of UV polarizing plates. However, it is difficult to increase the size of prism polarizers, making it difficult to obtain polarized light over a large area. Another known polarizing film is an iodine-based polarizing film, which contains iodine, a dichroic dye, in a substrate such as a stretched and oriented polyvinyl alcohol (hereinafter, "polyvinyl alcohol" may be abbreviated as "PVA") film. Iodine-based polarizing films have the advantage of being easily scalable, but they lack sufficient durability against heat generated by UV light sources.

[0003] Therefore, an ultraviolet absorption-type grid polarizer has been proposed in which a grid made of metal or the like is arranged in a striped pattern on a transparent substrate (see Patent Document 1). Also, a polarizing film for a near-ultraviolet polarizer has been proposed, in which a monoazo compound or a salt thereof is incorporated into a uniaxially stretched PVA film (see Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-071138 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-357719 Summary of the Invention [Problem to be solved by the invention]

[0005] The grid polarizer described in Patent Document 1 is considered to have high durability, but like a prism polarizer, it is difficult to increase the size. The polarizing film described in Patent Document 2 is also considered to have improved durability compared to iodine-based polarizing films. However, the polarizing film described in Patent Document 2 has polarization performance in the near-ultraviolet region with wavelengths of 370 to 400 nm, and its polarization performance for ultraviolet light in the lower wavelength region is insufficient. For example, there is also a demand for polarizing films that are compatible with ultraviolet light in the wavelength region around 345 nm, such as the third harmonic (THG: 355 nm) of solid-state lasers such as YAG lasers, and the i-line (365 nm) often used for exposure in photolithography.

[0006] The present invention has been made based on the above circumstances, and its object is to provide a PVA film having polarizing properties for ultraviolet rays, particularly ultraviolet rays in the wavelength region around 345 nm, and a method for producing such a PVA film. [Means for solving the problem]

[0007] As a result of extensive research to achieve the above-mentioned object, the inventors have found that by stretching a raw film (material film) containing PVA and specific metal ions and then subjecting it to a precipitation treatment, particles containing the metal and oriented in the stretching direction are precipitated with good dispersibility, and that the resulting PVA film has polarization properties for ultraviolet light in the wavelength range around 345 nm. Based on these findings, further research led to the completion of the present invention.

[0008] That is, the present invention is [1] A PVA film containing PVA (A) and metal-containing particles (B), 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 according to [1] above, wherein the metal is zinc; [3] The PVA film according to [1] or [2] above, which has a polarization degree of 5% or more when exposed to ultraviolet light with a wavelength of 345 nm; [4] The PVA film according to any one of [1] to [3] above, which has a transmittance of 40% or more for visible light with a wavelength of 540 nm; [5] The PVA film of any one of [1] to [4] above, wherein the content of the metal per 100 parts by mass of PVA (A) is 0.1 parts by mass or more and 10 parts by mass or less; [6] The PVA film according to any one of the above [1] to [5], which is a uniaxially stretched film in which the major axes of the particles (B) are oriented in the stretching direction; [7] A method for producing a PVA film, comprising the steps of obtaining a stretched film containing PVA and ions of a metal, and precipitating particles containing the metal on the stretched film, wherein the step of obtaining the stretched film is a step of stretching a raw film containing the PVA and ions of the metal in water or air, or a step of stretching a raw film containing the PVA in an aqueous solution containing ions of the metal, and the metal is at least one selected from the group consisting of zinc, cadmium, manganese, iron, and cobalt; Regarding. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a PVA film having polarizing properties for ultraviolet light, particularly for ultraviolet light in the wavelength region around 345 nm, and a method for producing such a PVA film. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a differential interference microscope image of the PVA film of Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0011] The PVA film of the present invention and the method for producing the same will be described in detail below. <PVAフィルム> The PVA film of the present invention contains PVA (A) and metal-containing particles (B).

[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 by mass. The content of PVA (A) in the PVA film of the present invention is, for example, preferably 50% by mass or more and 99% by mass, more preferably 70% by mass or more and 98% by mass or less, and even more preferably 80% by mass or more and 95% by mass or less.

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

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

[0015] The polyvinyl ester is preferably one obtained by using only one or more vinyl esters as a monomer, more preferably one obtained by using only one vinyl ester as a monomer, but may also be a copolymer resin of one or more vinyl esters with other monomers copolymerizable therewith, as long as the effects of the present invention are not significantly impaired.

[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 even more preferably 1 mol%, based on the 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 a salt thereof; (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; N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, diacetone(meth)acrylamide, (meth)acrylamidopropanesulfonic acid or a salt thereof, (meth)acrylamidopropyldimethylamine or a salt thereof, and N-methyl (meth)acrylamide. Examples of the vinyl ether include (meth)acrylamide derivatives such as tyrol (meth)acrylamide and derivatives thereof; 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 a salt, ester, or acid anhydride thereof; itaconic acid, or a salt, ester, or acid anhydride thereof; vinylsilyl compounds such as vinyltrimethoxysilane; and unsaturated sulfonic acids or a salt thereof.

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

[0019] PVA (A) that has not been graft-copolymerized can be preferably used. However, PVA (A) may be modified with one or more graft-copolymerizable monomers, as long as the effects of the present invention are not significantly impaired. 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 derivatives thereof; unsaturated sulfonic acids or derivatives thereof; and α-olefins having 2 to 30 carbon atoms. 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] The hydroxy groups of the PVA (A) may or may not be crosslinked, and some of the hydroxy groups of the PVA (A) may react with an aldehyde compound such as acetaldehyde or butylaldehyde to form an acetal structure.

[0021] The lower limit of the degree of polymerization of PVA (A) is preferably 1,000, more preferably 1,500, and even more preferably 1,700. When the degree of polymerization of PVA (A) is equal to or greater than the lower limit, the flexibility of the PVA film can be improved. On the other hand, the upper limit of this degree of polymerization is preferably 10,000, more preferably 8,000, and even more preferably 5,000. When the degree of polymerization of PVA (A) is equal to or less than the 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 in accordance with 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, even more preferably 99 mol% or more, and particularly preferably 99.3 mol% or more, because this improves the moist heat resistance of the PVA film. 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 in accordance with the description of JIS K6726-1994.

[0023] (Particle (B)) The particles (B) have an aspect ratio of 1.1 or more and 10 or less. The particles (B) are usually rod-shaped particles. The aspect ratio is preferably 2.0 or more and 9.6 or less, more preferably 3.0 or more and 9.2 or less, even 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 the particles (B) is 1.1 or more, sufficient polarization performance against ultraviolet light can be exhibited. On the other hand, when the aspect ratio of the 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 longest. The minor axis direction refers to the direction perpendicular to the major axis direction. The major axis and minor axis directions 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] The particles (B) contain a metal. The metal contained in the particles (B) contains at least one metal selected from the group consisting of zinc, cadmium, manganese, iron, and cobalt. The use of particles (B) containing such a metal can exhibit good polarization performance against ultraviolet light. These metals are also preferred because they can be effectively precipitated into particles by the precipitation treatment described below. The metal preferably contains at least one of zinc and manganese, and more preferably contains zinc. The 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. The use of zinc as the metal can improve polarization performance against ultraviolet light and also improve visible light transmittance.

[0026] The metal contained in the particles (B) may exist as a simple metal or as a compound. Examples of the compound include oxides, sulfides, nitrides, etc. Among these, it is preferable that the metal exists as a sulfide. That is, the particles (B) are preferably particles of sulfides of the above metals. The existence of the metal in such a form can further improve the polarization performance against ultraviolet light. Furthermore, when the metal is a sulfide, it can be effectively produced by a method using a precipitation treatment described below.

[0027] The PVA film of the present invention is usually a uniaxially stretched film, and it is preferable that the long axes of the particles (B) are oriented in the stretching direction of the PVA film. When the long axis direction of the particles (B) is oriented in the stretching direction, the polarization performance against ultraviolet light is improved. It is possible to confirm whether the long axes of the particles (B) are oriented in the stretching direction by observing the PVA film with a differential interference microscope. For example, of any 10 particles (B) observed with a differential interference microscope, the number of particles (B) whose acute angle between the stretching direction of the PVA film (the orientation direction of the PVA (A)) and the direction of the long axes of the particles (B) is 10° or less (even 5° or less) is preferably 8 or more, more preferably 9 or more, and even more preferably 10.

[0028] The major axis (length in the major axis direction) of particles (B) is, for example, preferably 10 nm to 200 μm, more preferably 100 nm to 100 μm, and even more preferably 1 μm to 50 μm. When the major axis of particles (B) is 10 nm or more, more sufficient polarization performance against ultraviolet light can be exhibited. On the other hand, when the major axis of particles (B) is 200 μm or less, visible light transmittance can be improved. The major axis is the average value of the measured values of any 10 particles (B) observed when the PVA film is viewed in the normal direction using a differential interference microscope.

[0029] The content of the metal relative to 100 parts by mass of PVA (A) in the PVA film of the present invention may be, for example, 0.01 to 20 parts by mass, preferably 0.1 to 10 parts by mass, more preferably 1 to 9 parts by mass, even more preferably 2 to 8 parts by mass, even more preferably 3 to 7 parts by mass, and even more preferably 6 parts by mass or less, 5 parts by mass or less, or 4 parts by mass or less. By setting the content of the metal to 0.1 parts by mass or more, the polarization performance against ultraviolet light can be improved. On the other hand, by setting the content of the metal to 10 parts by mass or less, the transmittance of visible light, ultraviolet light, etc. can be increased.

[0030] The content of the metal (metal contained in particles (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, even 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 even more preferably 6% by mass or less, 5% by mass or less, or 4% by mass or less. By setting the content of the metal to 0.1% by mass or more, the polarization performance for ultraviolet light can be improved. On the other hand, by setting the content of the metal to 10% by mass or less, the transmittance of visible light, ultraviolet light, etc. can be increased.

[0031] (Other ingredients) The PVA film of the present invention may contain a plasticizer. By including a plasticizer in the PVA film, the handling and stretchability of the PVA film are improved, resulting in better polarization performance. Polyhydric alcohols are preferred as plasticizers, and specific examples include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, and trimethylolpropane. Among these, glycerin is preferred because it improves the stretchability of the PVA film. One 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 even more preferably 4 parts by mass or more and 14 parts by mass or less, relative to 100 parts by mass of PVA (A). When the content of the plasticizer is 1 part by mass or more relative 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, when the content of the plasticizer is 20 parts by mass or less relative to 100 parts by mass of PVA (A), it is possible to prevent the plasticizer from bleeding out onto the surface of the PVA film, which would otherwise reduce the handleability of the PVA film.

[0033] Furthermore, when the raw film (material film) of the PVA film of the present invention is produced using the film-forming solution described below, it is preferable to incorporate a surfactant into the film-forming solution, as this improves film-forming properties and suppresses the occurrence of unevenness in film thickness, and also facilitates peeling of the raw film from metal rolls or belts when these are used for film formation. When the raw film is produced from the film-forming solution containing a surfactant, the surfactant may be contained in the final PVA film. The type of surfactant incorporated into the film-forming solution for producing the raw film, and therefore the surfactant contained in the PVA film, is not particularly limited. However, from the viewpoint of peelability from metal rolls or belts, anionic surfactants and nonionic surfactants are preferred, and nonionic surfactants are particularly preferred.

[0034] Preferred anionic surfactants include carboxylic acid surfactants such as potassium laurate; sulfate ester surfactants such as octyl sulfate; and sulfonic acid surfactants such as dodecylbenzenesulfonate.

[0035] Preferred 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 and oleic acid diethanolamide; and allyl phenyl ether types such as polyoxyalkylene allyl phenyl ether.

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

[0037] When a surfactant is blended into the film-forming solution for producing a raw film, the content of the surfactant in the film-forming solution, and therefore the content of the surfactant in the PVA film, is preferably 0.01 to 0.5 parts by mass, and more preferably 0.02 to 0.3 parts by mass, per 100 parts by mass of PVA (A) contained in the film-forming solution or PVA film. Having a surfactant content of 0.01 parts by mass or more per 100 parts by mass of PVA (A) can improve film-forming properties and peelability. On the other hand, having a surfactant content of 0.5 parts by mass or less per 100 parts by mass of PVA (A) can prevent the surfactant from bleeding out onto the surface of the raw film or PVA film, causing blocking and reducing handleability.

[0038] The PVA film of the present invention may contain, as necessary, other components in addition to the above-described PVA (A), particles (B), plasticizer, and surfactant, such as antioxidants, antifreeze agents, pH adjusters, opacifying agents, color inhibitors, oils, etc. However, the content of these other components may preferably be 10 parts by mass or less, and may preferably be 1 part by mass or less, or 0.1 part by mass or less, per 100 parts by mass of PVA (A).

[0039] (physical properties, size, use, etc.) The PVA film of the present invention has polarization properties for ultraviolet light with a wavelength of 345 nm. The polarization degree of the PVA film of the present invention for ultraviolet light with 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 polarization degree for ultraviolet light with a wavelength of 345 nm is not particularly limited, and may be, for example, 80%, 60%, or 40%.

[0040] The lower limit of the transmittance of the PVA film of the present invention for ultraviolet light with a wavelength of 345 nm is preferably 20%, more preferably 40%, even more preferably 50%, and in some cases even more preferably 60% or 70%. When the transmittance for ultraviolet light with a wavelength of 345 nm is equal to or greater than the above lower limit, the amount of light from the ultraviolet light source can be reduced, for example, when the PVA film of the present invention is used in an ultraviolet polarizing plate for a spectroscopic analyzer, exposure device, or the like. On the other hand, the upper limit of the transmittance for ultraviolet light with a wavelength of 345 nm may be, for example, 90%, and in some cases 80%, 70%, or 60% is preferred. For example, when the PVA film of the present invention is used in polarized sunglasses, a relatively low ultraviolet transmittance may be preferred.

[0041] The transmittance of the PVA film of the present invention for visible light with a wavelength of 540 nm is preferably 40% or more, more preferably 50% or more, and in some cases even more preferably 60% or more, 70% or more, 75% or more, 80% or more, or 85% or more. For example, when the PVA film of the present invention is used in polarized sunglasses, a high visible light transmittance is preferred. When the PVA film of the present invention has such a high visible light transmittance, the range of uses can be expanded. On the other hand, the upper limit of the transmittance for 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 may be, for example, 50 μm, preferably 40 μm, more preferably 30 μm, and even more preferably 20 μm or 10 μm. On the other hand, the lower limit of this average thickness is preferably 1 μm, more preferably 3 μm, and even more preferably 5 μm. By keeping the average thickness of the PVA film within the above range, handleability and the like can be improved. The average thickness is the average value of measurements taken 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, etc. For example, it can be within 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, but in recent years, a wide polarizing film has been demanded, so it is preferably 1 m or more, more preferably 2 m or more, and even more preferably 4 m or more. There is no particular limitation on the upper limit of the width of the long film, but 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 multi-layer film (laminate). However, from the viewpoints of the complexity and cost of the lamination (coating, etc.) work, etc., a single-layer film is preferred.

[0045] The PVA film of the present invention is usually a stretched film (stretched film). In addition, the PVA film of the present invention is preferably 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, polarized sunglasses, etc.

[0047] <Manufacturing method of PVA film> Although the method for producing the PVA film of the present invention is not particularly limited, a preferred method is to impregnate a raw film (material film) with metal ions, followed by uniaxial stretching and precipitation treatment to convert the metal ions into particles, in order to enhance the dispersibility of the particles (B). The raw film refers to an unstretched PVA film before the PVA film of the present invention is obtained. A stretched film is obtained by stretching the raw film, and the PVA film of the present invention is obtained by processing the stretched film. The method for impregnating the raw film with metal ions is not particularly limited, but preferred are a method in which metal ions are impregnated during the production of the raw film, and a method in which metal ions are impregnated during the production of the PVA film of the present invention from the raw film by uniaxial stretching in an aqueous solution containing metal ions.

[0048] That is, the method for producing a PVA film of the present invention is as follows: A step (step B) of obtaining a stretched film containing PVA and metal ions; and A step (step C) of subjecting the stretched film to a precipitation treatment of particles containing the metal. Equipped with The step of obtaining the stretched film (step B) A step (step B1) of stretching a raw film containing the PVA and ions of the metal in water or air; or A step (step B2) of stretching the raw film containing the PVA in an aqueous solution containing ions of the metal. and The metal includes at least one selected from the group consisting of zinc, cadmium, manganese, iron, and cobalt.

[0049] The manufacturing method includes: Process for producing raw film (Process A) It may further comprise:

[0050] The production 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, the precipitation treatment may be carried out while the film is being stretched. Each step will be described in detail below.

[0051] (Process A) In this process, a raw film containing PVA is produced. The raw film may further contain metal ions. The method for producing the raw film is not particularly limited, and a production method that results in more uniform thickness and width can be preferably used. For example, the raw film can be produced using a film-forming solution in which the PVA constituting the raw film, and optionally one or more of a plasticizer, surfactant, and other components, are dissolved in a liquid medium, or a film-forming solution in which the PVA is melted and contains PVA, and optionally one or more of a plasticizer, surfactant, other components, and a liquid medium. When the film-forming solution contains at least one of a plasticizer, surfactant, and other components, it is preferable that these components are uniformly mixed.

[0052] Examples of the liquid medium used to prepare the membrane-forming solution include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, diethylenetriamine, etc. One or more of these may be used. Among these, water is preferred from the viewpoints of its low environmental impact and ease of recovery.

[0053] When performing step B1, the film-forming solution further contains metal ions or metal salts (salts containing metal ions). Examples of metal salts include metal nitrates, metal sulfates, and metal acetates. One or more of these salts can be used. Among these, metal nitrates (zinc nitrate, cadmium nitrate, manganese nitrate, iron nitrate, and cobalt nitrate) are preferred because they improve the polarization performance of the resulting PVA film. The content of the metal salt in the film-forming solution relative to 100 parts by mass of PVA is preferably 0.5 parts by mass to 70 parts by mass, more preferably 1 part by mass to 60 parts by mass, and even more preferably 2 parts by mass to 50 parts by mass.

[0054] The specific form and preferred form of each component contained in the film-forming solution are the same as those of each component other than the particles (B) contained in the PVA film of the present invention. In addition, the specific content and preferred content of each component other than the PVA (A), particles (B) and liquid medium contained in the film-forming solution relative to the PVA (A) are also the same as those of each component contained in the PVA film of the present invention.

[0055] The volatile content of the membrane-forming solution (the content in the membrane-forming solution of volatile components such as the liquid medium that are removed by volatilization or evaporation during membrane formation) varies depending on the membrane-forming method, membrane-forming conditions, etc., but is preferably 50 to 95% by mass, more preferably 55 to 90% by mass, and even more preferably 60 to 85% by mass. Having a volatile content of 50% by mass or more of the membrane-forming solution prevents the membrane-forming solution from becoming too viscous, facilitating filtration and degassing during preparation of the membrane-forming solution, and facilitating the production of a raw film and a final PVA film with fewer foreign matter and defects. On the other hand, having a volatile content of 95% by mass or less prevents the concentration of the membrane-forming solution from becoming too low, facilitating the industrial production of a raw film and a final PVA film.

[0056] Examples of film-forming methods for producing raw film using the film-forming solution described above include cast film-forming, extrusion film-forming, wet film-forming, and gel film-forming, with cast film-forming and extrusion film-forming being preferred. These film-forming methods may be used alone or in combination of two or more. Among these film-forming methods, extrusion film-forming is more preferred because it can produce raw film with uniform thickness and width and good physical properties. The raw film can be dried or heat-treated as needed.

[0057] There are no particular restrictions on the heat treatment temperature, and it may be adjusted appropriately depending on the swelling degree of the raw film, etc. If the heat treatment temperature is too high, discoloration and deterioration of the raw film may occur, so the heat treatment temperature is preferably 210°C or less, more preferably 200°C or less, and even more preferably 190°C or less. The lower limit of the heat treatment temperature is, for example, 100°C, or may be 120°C.

[0058] There is no particular restriction on the heat treatment time, which may be adjusted appropriately depending on the swelling degree of the raw film. However, from the viewpoint of efficiently producing the PVA film of the present invention, a time of 1 second or more and 30 minutes or less is preferred, and a time of 3 seconds or more and 15 minutes or less is even more preferred.

[0059] The upper limit of the average thickness of the obtained raw film is not particularly limited, but is, for example, 100 μm, preferably 80 μm, more preferably 60 μm, and even more preferably 40 μm. On the other hand, the lower limit of this average thickness is preferably 5 μm, more preferably 10 μm, and even more preferably 15 μm. By keeping the average thickness of the raw film within the above range, handling properties can be improved.

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

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

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

[0063] The swelling treatment can be carried out by immersing the raw film in water. The temperature of the water during immersion is preferably 20°C to 40°C, more preferably 22°C to 38°C, and even more preferably 25°C to 35°C. The immersion time is preferably, for example, 0.1 to 5 minutes, more preferably 0.5 to 3 minutes. The water used for immersion is not limited to pure water, and may be an aqueous solution in which various components are dissolved, or 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. The crosslinking step introduces a crosslinked structure into the raw film, allowing uniaxial stretching at a relatively high temperature. The crosslinking agent used can be one or more boron compounds, such as boric acid, borax, and other borates. The concentration of the crosslinking agent in the aqueous solution is preferably 1% by mass or more and 15% by mass or less, 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 more and 50°C or less, more preferably 25°C or more and 40°C or less.

[0065] When the raw film does not contain metal ions, uniaxial stretching is performed in an aqueous solution containing metal ions. Examples of aqueous solutions containing metal ions include aqueous solutions of metal salts such as metal nitrate solutions, metal sulfate solutions, and metal acetate solutions. Among these, uniaxial stretching is preferably performed in an aqueous zinc nitrate solution, as this improves the polarization performance of the resulting PVA film. The concentration of the metal salt, such as zinc nitrate, in the aqueous solution is preferably 0.5% by mass to 10% by mass, more preferably 1% by mass to 8% by mass, and even more preferably 2% by mass to 6% by mass. The aqueous solution may also contain boric acid or potassium iodide, with the concentration preferably being 0.01% by mass to 6% by mass.

[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 even more preferably 50°C or higher and 70°C or lower.

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

[0068] The stretching ratio in 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 resulting polarizing film, it is preferably 3 times or more, more preferably 4 times or more, even more preferably 5 times or more, and particularly preferably 6 times or more. There is no particular upper limit to the stretching ratio, but the stretching ratio is preferably 10 times or less, more preferably 8 times or less.

[0069] (Process C) In this step, a stretched film (stretched raw film) containing PVA and metal ions is subjected to a precipitation treatment of the metal-containing particles. By carrying out the precipitation treatment, the metal ions present in the stretched film can be precipitated as metal-containing particles.

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

[0071] The precipitation treatment is preferably carried out while applying ultrasonic waves to the raw film. This allows the precipitation reaction to proceed uniformly. After the precipitation treatment, the surface of the film may be washed with water or an organic solvent.

[0072] Alternatively, the deposition process may involve a reduction reaction using a reducing agent to deposit metal particles.

[0073] (Other processes) After step C, the film (PVA film) may be subjected to, for example, a drying treatment or a heat treatment. The drying treatment is preferably carried out at a temperature of 30° C. or higher and 150° C. or lower, and more preferably at a temperature of 50° C. or higher and 130° C. or lower. Drying at a temperature within the above range makes it easier to obtain a PVA film (polarizing film) with excellent dimensional stability.

[0074] <Polarizing plate> The PVA film of the present invention may be used as a laminate (polarizing plate) having an optically transparent and mechanically strong protective film disposed on at least one side thereof. 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 protective films include triacetyl cellulose (TAC) films, cycloolefin polymer (COP) films, cellulose acetate butyrate (CAB) films, acrylic films, and polyester films.

[0076] The PVA film and the protective film may be bonded together via an adhesive, such as a PVA adhesive or an ultraviolet-curable adhesive. [Example]

[0077] The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. The evaluation methods used in the following examples and comparative examples are shown below.

[0078] [Metal (metal ion) content] The metal content in the PVA film obtained in each of the following Examples and Comparative Examples was measured based on the PVA film before the precipitation treatment. That is, the PVA film before the precipitation treatment was sampled and dissolved in water, and the amount of metal ions was measured using an ICP emission spectrometer to determine the metal content (content per 100 parts by mass of PVA). The PVA film obtained in Example 1 below was subjected to a dry decomposition treatment and the amount of metal ions was measured in the same manner. The value was the same as the amount of metal ions measured using the PVA film before the above-mentioned precipitation treatment.

[0079] [Particle aspect ratio] The PVA films obtained in the following examples and comparative examples were observed with a differential interference microscope to determine the aspect ratio of the particles present in the PVA film.

[0080] [Transmittance of ultraviolet light with a wavelength of 345 nm and visible light with a wavelength of 540 nm] Two square samples measuring 3 cm in length and 3 cm in width were taken from the PVA films obtained in the following Examples or Comparative Examples. The two samples were subjected to luminosity correction in the visible light region under a C light source and a 2° field of view in accordance with JIS Z8722:2009 (measurement method for object color) using a spectrophotometer equipped with an integrating sphere (V7100 manufactured by JASCO Corporation). For one sample, the transmittance was measured when tilted at 45° and -45° relative to the length direction, and the average transmittance value T1 (%) was calculated. For the other sample, the transmittance was measured when tilted at 45° and -45° relative to the length direction, and the average transmittance value T2 (%) was calculated. The transmittance T (%) was calculated by averaging the values T1 and T2 calculated above. Next, the two samples were stacked so that their length directions were parallel, and the transmittance was measured when tilted at 45° and -45° to the length direction, and the average parallel transmittance T∥ (%) was calculated. Furthermore, the films were stacked so that the longitudinal direction was perpendicular, and the transmittance was measured when tilted at 45° and -45° relative to the longitudinal direction, and the average value T⊥ (%) of the orthogonal transmittance was calculated. The transmittance T, parallel transmittance T∥, and crossed transmittance T⊥ were measured for ultraviolet light with a wavelength of 345 nm and visible light with a wavelength of 540 nm.

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

[0082] [Example 1] <Preparation of film-forming solution (PVA aqueous solution)> PVA (A) (a saponified product of a vinyl acetate homopolymer, degree of polymerization 2,400, saponification degree 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 PVA film> A test piece with a length of 9 cm and a width of 5 cm was taken from the original film obtained above. Both ends in the length direction of the test piece 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 uniaxially stretched in the length direction to 4 times the original length at a stretching speed of 12 cm / min in air. Then, the test piece (stretched film) was fixed to a metal frame, and precipitation treatment was performed by applying ultrasonic waves while immersing it in an aqueous solution of 1.2% by mass of sodium sulfide for 3 minutes. 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, the 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 amount of zinc nitrate mixed in the film-forming solution was 50 parts by mass relative to 100 parts by mass of PVA. The amount of zinc (zinc ions) contained in the raw film was 9.0 parts by mass relative to 100 parts by mass of PVA. The particle aspect ratio, transmittance of ultraviolet light with a wavelength of 345 nm and visible light with a wavelength of 540 nm, and polarization degree of ultraviolet light with a wavelength of 345 nm were measured for the obtained PVA film by the methods 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 amount of zinc nitrate mixed in the film-forming solution was 10 parts by mass relative to 100 parts by mass of PVA. The amount of zinc (zinc ions) contained in the raw film was 2.0 parts by mass relative to 100 parts by mass of PVA. The particle aspect ratio, transmittance of ultraviolet light with a wavelength of 345 nm and visible light with a wavelength of 540 nm, and polarization degree of ultraviolet light with a wavelength of 345 nm were measured for the obtained PVA film by the methods 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 amount of zinc nitrate mixed in the film-forming solution was 50 parts by mass relative to 100 parts by mass of PVA and the stretching ratio in the uniaxial stretching was 1.7 times. The amount of zinc (zinc ions) contained in the raw film was 9.0 parts by mass relative to 100 parts by mass of PVA. The particle aspect ratio, transmittance of ultraviolet light with a wavelength of 345 nm and visible light with a wavelength of 540 nm, and polarization degree of ultraviolet light with a wavelength of 345 nm were measured for the obtained PVA film by the methods 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 manganese nitrate hexahydrate was used instead of zinc nitrate in preparing the film-forming solution. The amount of manganese (manganese ions) contained in the raw film was 3.4 parts by mass relative to 100 parts by mass of PVA. The particle aspect ratio, transmittance of ultraviolet light with a wavelength of 345 nm and visible light with a wavelength of 540 nm, and polarization degree of ultraviolet light with a wavelength of 345 nm were measured for the obtained PVA film by the methods 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 film-forming solution. The transmittance of the obtained PVA film to ultraviolet light with a wavelength of 345 nm and visible light with a wavelength of 540 nm, as well as the polarization degree to ultraviolet light with a wavelength of 345 nm, were measured by the methods described above. The results are shown in Table 1.

[0091] Comparative Example 2 Except for not performing uniaxial stretching, a PVA film was produced in the same manner as in Example 1. The amount of zinc (zinc ions) contained in the raw film was 3.8 parts by mass relative to 100 parts by mass of PVA. The particle aspect ratio, transmittance of ultraviolet light with a wavelength of 345 nm and visible light with a wavelength of 540 nm, and polarization degree of ultraviolet light with a wavelength of 345 nm were measured for the obtained PVA film by the methods described above. The results are shown in Table 1.

[0092] [Table 1]

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

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

Claims

1. The present invention relates to a method for producing a coating composition comprising: a coating composition including 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 metal includes at least one selected from the group consisting of zinc, cadmium, manganese, iron, and cobalt; The particles (B) are particles of sulfide of the metal, the content of the metal relative to 100 parts by mass of the polyvinyl alcohol (A) is 0.1 parts by mass or more and 10 parts by mass or less, It is a uniaxially stretched film, The major axes of the particles (B) are oriented in the stretching direction, A polyvinyl alcohol film, wherein the particles (B) have a major axis of 10 nm or more and 50 μm or less.

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

3. 3. The polyvinyl alcohol film according to claim 1, wherein the film has a polarization degree of 5% or more when exposed to ultraviolet light having 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. A method for producing the polyvinyl alcohol film according to any one of claims 1 to 4, Obtaining a uniaxially stretched film containing polyvinyl alcohol and metal ions; and A step of subjecting the uniaxially stretched film to a precipitation treatment of particles containing the metal. Equipped with The step of obtaining the uniaxially stretched film comprises: a step of uniaxially stretching a raw film containing the polyvinyl alcohol and the metal ions in water or air; or A step of uniaxially stretching the raw film containing the polyvinyl alcohol in an aqueous solution containing ions of the metal. and the metal includes at least one selected from the group consisting of zinc, cadmium, manganese, iron, and cobalt; The method for producing a polyvinyl alcohol film, wherein the precipitation treatment is carried out by immersing the uniaxially stretched film in an aqueous solution containing sulfide ions.

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