TW202346441A - Polyvinyl alcohol film, and method for producing polyvinyl alcohol film - Google Patents

Abstract

A poly(vinyl alcohol) film comprising poly(vinyl alcohol) having a degree of saponification of 98 mol% or higher and a degree of polymerization of 1,500-8,000, characterized in that the poly(vinyl alcohol), when having an absolute molecular weight of 1*106, has an intrinsic viscosity of 7.5-11 dl/g, which is determined with a gel permeation chromatograph equipped with a light scattering detector and a viscometer at a temperature of 40 DEG C using hexafluoroisopropanol containing 20mM sodium trifluoroacetate as a mobile phase solvent. Such poly(vinyl alcohol) film has a stable film width, fluctuates little in edge thickness, and has excellent stretchability. With this PVA film, it is hence possible to efficiently produce a polarizing film having a wide width and excellent optical performance.

Description

Polyvinyl alcohol film and manufacturing method of polyvinyl alcohol film

The present invention relates to a polyvinyl alcohol film (hereinafter, "polyvinyl alcohol" may be abbreviated as "PVA") that can be suitably used for the production of polarizing films and the like, and a method for producing the PVA film.

Liquid crystal display devices (LCDs) can be used in small machines such as computers and watches, notebook computers, LCD monitors, LCD color projectors, LCD TVs, car navigation systems, mobile phones, and measurement equipment used both indoors and outdoors. used in a wide range of fields. Polarizing films with light transmission and shielding functions are the basic components of liquid crystals and LCDs with light switching functions.

As a polarizing film, the mainstream is a two-color film in which iodine-based dyes (I ₃ ^- , I ₅ ^-, etc.) are adsorbed on a substrate made by uniaxially stretching a PVA film (a stretched film aligned by uniaxial stretching). Sex pigments. This type of polarizing film will first uniaxially stretch the PVA film containing dichroic pigments, or adsorb the dichroic pigments simultaneously with the uniaxial stretching of the PVA film, or uniaxially stretch the PVA film after uniaxially stretching the dichroic pigments. Pigment adsorption, etc. to produce.

[Problem to be solved by the invention]

In recent years, along with the expansion of LCD applications, there has been a demand for more efficient production of PVA films. PVA films are generally produced by attaching them to a support such as a metal roller or a metal belt, and ejecting the film-making stock solution containing PVA from a mold into a film shape, drying and solidifying it. In order to effectively produce PVA film, it is effective to increase the discharge volume of the raw solution and the production line speed. However, when trying to increase the discharge volume of high-viscosity film-making raw liquid, there is a limit on the device in order to increase the pressure at the mold inlet. If the mold temperature is raised, the viscosity of the original solution may decrease, but at this time, the width of the film-like PVA original solution immediately after being discharged from the mold (commonly known as the "neck-in phenomenon") will change, and the resulting PVA film will have The width will also change. Therefore, it is necessary to increase the width of the film end portion by cutting it, which easily causes problems such as reduced productivity and insufficient film width. Furthermore, when the mold temperature is increased, the stretchability of the PVA film tends to decrease, so there is a problem that the production line speed cannot be increased as desired.

The present invention was completed in order to solve the above-mentioned problems, and its object is to provide a PVA film that can be used for polarizing film production, etc., in which the mold pressure is difficult to increase even if it is produced at a relatively fast production line speed, and the PVA thin mold It is a PVA film with good optical properties, stable film width and good extensibility. Furthermore, the object is to provide a polarizing film using such a PVA film as a raw material. [Means used to solve problems]

As a method for grasping the molecular weight and degree of polymerization of a polymer, there is gel permeation chromatography (hereinafter, sometimes referred to as GPC). GPC is known as a general analysis method. Generally speaking, molecular weight is measured using the relative molecular weight of a detection line obtained from a known standard material. A light scattering detector, a viscosity detector, etc. may also be used in combination. , to calculate the absolute molecular weight according to Rayleigh's theoretical formula.

On the other hand, it is known that the branched structure of the polymer chain will affect the polymer properties such as solution viscosity, rheological properties, solubility, and crystallinity. Quantitative information on branching is indispensable for the development of polymer materials with excellent properties and the understanding of the polymerization process. The branch state can also be grasped by NMR, IR, rheometry, etc. However, when the number of branch points is small or the structure of the branch site is similar to that of the main chain, analysis becomes difficult. In GPC measurement, the branched structure can be analyzed by using a light scattering detector and a viscosity detector together.

Regarding the branching degree of the polymer chain, Zimm and Kilb et al. advocated a calculation method based on the branching degree of the ultimate viscosity. A graph plotting the calculated absolute molecular weight and ultimate viscosity is called a Mark-Houwink diagram. When polymers of the same molecular weight are compared with each other, it can be seen that in a branched polymer chain , compared with linear polymer chains, the expansion of molecular chains in the solvent becomes smaller, so the interaction between molecular chains is inhibited and the viscosity becomes lower.

The inventors of the present invention investigated the relationship between the molecular weight and ultimate viscosity of PVA contained in various PVA films through GPC measurement. After careful and repeated studies, they found that when a film composed of this resin is subjected to GPC analysis, if the film has a specific molecular weight, A PVA film whose ultimate viscosity satisfies a certain value can solve the above problems. Based on this knowledge and further examination, the present invention was completed.

That is, the present invention is based on [1] a PVA film, which is a PVA film containing PVA with a saponification degree of 98 mol% or more and a polymerization degree of 1500 to 8000. It is characterized by using a light scattering detector and a viscosity detector. Gel permeation chromatography, using hexafluoroisopropanol containing 20mM Na trifluoroacetate as the mobile phase solvent at a measuring temperature of 40°C, the ultimate viscosity of the PVA was measured to be 7.5 when the absolute molecular weight of the PVA was 1×10 ⁶ ~11dl/g; [2] The PVA film as described in the aforementioned [1], which is a modified PVA with an ethylene modification amount of the aforementioned PVA of 0.5 to 12 mol%; [3] A film as described in the aforementioned [1] or [ 2] The described method for manufacturing a PVA film uses PVA with a saponification degree of 98 mol% or more, a polymerization degree of 1500 to 8000, and a concentration of long-chain aldehydes of C6 or higher of 0.35 to 2.5 μmol%. The raw solution is used to form a film; [4] The method for manufacturing a PVA film as described in the above [3], wherein the long-chain aldehyde with C6 or above includes selected from the group consisting of 2,4-Hexadienal (2,4-Hexadienal), 2 , at least one of the group consisting of 4,6-octatrienal (2,4,6-octatrienal) and 2,4,6,8-decatetraenal (2,4,6,8-Decatetraenal) 1 type; [5] The method for manufacturing a PVA film as described in the aforementioned [3] or [4], wherein the concentration of crotonaldehyde in the aforementioned PVA is 0.70 μmol% or less; [6] One type as described in the aforementioned [3] or [4] ] The method for manufacturing a polyvinyl alcohol film as described in [1] or [2] above, which includes the step of heat-treating the PVA film produced at a temperature of 80° C. or higher; [7] The PVA film as described in [1] or [2] above, which It is an optical film; and it can be achieved. [Effects of the invention]

The PVA film of the present invention has a stable film width, little thickness variation at the ends, and excellent extensibility. Therefore, if the PVA film of the present invention is used, a wide-width polarizing film with excellent optical properties can be effectively produced. In addition, the PVA film can be efficiently produced by the production method of the present invention.

[Form used to implement the invention]

[PVA film] The PVA film of the present invention contains PVA with a saponification degree of 98 mol% or more and a polymerization degree of 1500 to 8000. Using a gel permeation chromatograph equipped with a light scattering detector and a viscosity detector, the measurement temperature is 40°C. The ultimate viscosity of PVA with an absolute molecular weight of 1×10 ⁶ measured using hexafluoroisopropanol containing 20mM Na trifluoroacetate as the mobile phase solvent (hereinafter, the ultimate viscosity with an absolute molecular weight of 1×10 ⁶ will be referred to as The ultimate viscosity [eta] ₆ ) is 7.5~11dl/g.

In the PVA film of the present invention, the reason why the effects of the present invention can be obtained by having the ultimate viscosity [eta] ₆ of 7.5 to 11 dl/g is not necessarily clear, but it can be speculated as follows. The ultimate viscosity of a polymer corresponds to the expansion of the molecular chain in a solution or melt. The expansion of the molecular chain of a high molecular weight component of 1×10 ⁶ in the resin will strongly affect interactions such as interactions between molecules. When the ultimate viscosity of high molecular weight components is too large, that is, when the molecular chain expands too widely, the viscosity of the solution or melt will increase, and the pressure loss in the mold will increase. Therefore, when trying to increase the discharge volume during high-speed film production, there is a risk that the pressure in the mold may exceed the device limit. On the other hand, when the ultimate viscosity of the high molecular weight component is too small, that is, when the expansion of the molecular chain is too narrow, the stringability of the solution or melt becomes low. Therefore, the solution or melt ejected from the mold gap will easily accumulate due to the effect of necking, especially at the end of the mold. Then, when the melt accumulates to a certain extent at the end of the mold, it adopts a periodic behavior called flow, so that the film width of the coating film discharged from the mold becomes prone to variation. Accordingly, in order to obtain the effect of the present invention, it is necessary to control the ultimate viscosity of the high molecular weight component in PVA within a specific range.

[PVA] As the PVA contained in the PVA film of the present invention, those produced by saponifying a vinyl ester polymer obtained by polymerizing a vinyl ester monomer can be used. Examples of the vinyl ester monomer include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl laurate, vinyl stearate, vinyl benzoate, and trimethylvinyl acetate. , vinyl versatate, etc., among them, vinyl acetate is preferred from the viewpoint of availability, cost, productivity of PVA, etc.

The above-mentioned vinyl ester polymer is preferably obtained by using only one or more than two types of vinyl ester monomers as the monomer, and more preferably is obtained by using only one type of vinyl ester monomer as the monomer. It may also be a copolymer of one or more vinyl ester monomers and other monomers copolymerizable with them.

Examples of other monomers copolymerizable with such vinyl ester monomers include ethylene; olefins having 3 to 30 carbon atoms such as propylene, 1-butene, and isobutylene; acrylic acid or its salts; methyl acrylate, Acrylic acid such as ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tertiary butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, stearyl acrylate, etc. Esters; methacrylic acid or its salts; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, Methacrylate esters such as tertiary butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, stearyl methacrylate; acrylamide, N-methacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetone acrylamide, acrylamide propyl sulfonic acid or its salts, acrylamide propyldimethylamine or its salts, Acrylamide derivatives such as N-hydroxymethylacrylamide or its derivatives; methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamide Aminopropyl sulfonic acid or its salts, methacrylamide propyldimethylamine or its salts, N-hydroxymethylmethacrylamide or its derivatives, etc. methacrylamide derivatives; N -N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone, etc.; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, Isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tertiary butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether and other vinyl ethers; acrylonitrile Acrylonitrile (vinyl cyanide) such as (acrylonitrile), methacrylonitrile, etc.; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, etc.; olefins such as allyl acetate, allyl chloride, etc. Propyl compounds; maleic acid or its salts, esters or anhydrides; itaconic acid or its salts, esters or anhydrides; vinylsilyl compounds such as vinyltrimethoxysilane; isopropylene acetate, etc. The above-mentioned vinyl ester polymer may have one or more structural units derived from these other monomers.

The proportion of the structural units derived from the above-mentioned other monomers in the vinyl ester polymer is not particularly limited as long as it does not impair the purpose of the present invention. Based on the ratio of all the structural units constituting the vinyl ester polymer, The number of ears is preferably 15 mol% or less, more preferably 5 mol% or less.

Among other monomers that can be copolymerized with the above-mentioned vinyl ester monomer, ethylene-modified PVA that can be copolymerized with ethylene is preferred because it can improve the extensibility of the PVA film. The modification amount of ethylene is preferably in the range of 0.5 to 12 mol%. When the amount of modification is less than 0.5 mol%, the elongation improvement effect cannot be fully confirmed, and when the amount of modification exceeds 12 mol%, the optical properties of the resulting polarizing film may be reduced. The modification amount of ethylene is preferably in the range of 0.7 to 8 mol%, and more preferably in the range of 0.9 to 5 mol%.

In the PVA film of the present invention, the degree of polymerization of PVA is 1500 or more. When the degree of polymerization of PVA is less than 1500, there is a risk that the polarizing performance of the polarizing film obtained using the PVA as a raw material will be impaired. The degree of polymerization of PVA is preferably 1,700 or more, more preferably 2,000 or more, and particularly preferably 2,500 or more from the viewpoint of obtaining a polarizing film with extremely high polarizing performance. Furthermore, in the present invention, the degree of polymerization of PVA is 8,000 or less. When the degree of polymerization of PVA exceeds 8,000, the viscosity of the aqueous solution or molten PVA becomes high, making it difficult to form a film. The degree of polymerization of PVA is preferably 6,000 or less, preferably 5,000 or less, more preferably 4,000 or less. Here, the so-called degree of polymerization means the average degree of polymerization (Po) measured in accordance with the description of JIS K6726-1994, based on the ultimate viscosity measured in 30°C water after re-saponification and purification of PVA (A). [η] (unit: dl (combined)/g) is obtained from the following formula. Po=([η]×10 ³ /8.29) ^{( 1/0.62)}

In the PVA film of the present invention, the saponification degree of PVA is 98 mol% or more. When the saponification degree of PVA is less than 98 mol%, there is a risk that sufficient polarizing performance cannot be obtained. The saponification degree of PVA is preferably 99 mol% or more, preferably 99.5 mol% or more, more preferably 99.7 mol% or more, particularly preferably 99.9 mol% or more. In addition, the degree of saponification of PVA here refers to the ratio of the total of structural units (typically, vinyl ester monomer units) and vinyl alcohol units that PVA has that can be converted into vinyl alcohol units by saponification. Number of ears, the proportion of the number of moles of the vinyl alcohol unit (mol%). The saponification degree of PVA can be measured according to the records of JIS K6726-1994. In addition, when a plurality of PVAs with different saponification degrees are mixed, the saponification degree of the mixture of PVAs can be specified by obtaining a weighted average of the saponification degrees of the plurality of PVAs.

For the PVA film of the present invention, the PVA content is preferably 75 mass% or more of the total mass of the PVA film, more preferably 80 mass% or more, and still more preferably 85 mass% or more.

[Intrinsic viscosity of PVA [η] ₆ ] Regarding the PVA film of the present invention, the method for measuring the intrinsic viscosity [η] ₆ of PVA is as shown in the Examples described below. As will be described later, in the present invention, hexafluoroisopropanol (HFIP) containing Na trifluoroacetate at a concentration of 20 mM (mmol/L) is used as the mobile phase solvent.

The ultimate viscosity [eta] ₆ of the PVA contained in the PVA film of the present invention is 7.5 to 11 dl/g. When the ultimate viscosity [eta] ₆ exceeds 11 dl/g, there is a risk that the optical properties of the polarizing film made from the PVA film will be reduced. The ultimate viscosity [eta] ₆ is preferably 10.5 dl/g or less, more preferably 10.0 dl/g or less, more preferably 9.5 dl/g or less, particularly preferably 9.0 dl/g or less. On the other hand, when the ultimate viscosity [eta] ₆ is less than 7.5 dl/g, the film width stability during high-speed film production is likely to deteriorate. The ultimate viscosity [eta] ₆ is preferably 7.6 dl/g or more, more preferably 7.7 dl/g or more, more preferably 7.8 dl/g or more.

In the present invention, the reason why the ultimate viscosity [eta] ₆ of PVA, that is, the ultimate viscosity of PVA in the high molecular weight field affects the film-forming properties of the PVA film is not necessarily clear. As mentioned above, it can be speculated that it is because the melting temperature is high. The rheological properties of molecules and polymer solutions such as viscosity and stringability are strongly affected by high molecular weight components. In addition, even if the average molecular weight of the PVA contained in the PVA film is reduced, it is possible to obtain the same effect. However, in this case, there is a risk that the optical properties of the polarizing film produced from the PVA film will be reduced.

[Surfactant] The PVA film system of the present invention may contain surfactants. By containing a surfactant, the following well-known effects can be obtained: preventing adhesion to a metal support such as a drum during the film forming step, improving the slipperiness of the PVA film, and suppressing the tendency of the PVA film to be rolled into a long strip. Wrinkles occur in the film roll.

In the PVA film of the present invention, the content of the surfactant is preferably 0.001 parts by mass or more, preferably 0.005 parts by mass or more, and more preferably 0.01 parts by mass or more based on 100 parts by mass of PVA. The content of the surfactant is preferably 1 part by mass or less, preferably 0.8 part by mass or less, and more preferably 0.5 part by mass or less based on 100 parts by mass of PVA. When the content of the surfactant is less than 0.001 parts by mass, the above effects may not be fully obtained. In addition, when the content of the surfactant fat exceeds 1 part by mass, the film tends to be colored and the transparency is reduced. In addition, rib-like defects may occur on the surface of the film.

The type of surfactant is not particularly limited, and examples thereof include anionic surfactants, nonionic surfactants, and the like.

Examples of the anionic surfactant include Carboxylic acid type such as potassium laurate; Sulfate ester type such as octyl sulfate; Sulfonic acid type of dodecyl benzene sulfonate, etc.

Examples of the nonionic surfactant include: Alkyl ether type such as polyoxyethylene oil ether; Alkylphenyl ether type such as polyoxyethylene octylphenyl ether; Alkyl ester type of polyoxyethylene laurate; Alkyl amine type such as polyoxyethylene lauryl amine ether; Alkyl amide types such as polyoxyethylene lauric acid amide; Polyoxyethylene polyoxypropylene ether and other polypropylene glycol ether types; Alkanolamide types such as lauric acid diethanolamide and oleic acid diethanolamide; Allyl phenyl ether type of polyoxyalkylene allyl phenyl ether, etc.

Among these, from the viewpoint of excellent reduction effect on film surface abnormalities during film formation, a nonionic surfactant is preferred, an alkanolamide type surfactant is more preferred, and a surfactant having a carbon number of 8 to 30 is more preferred. Saturated or unsaturated aliphatic carboxylic acids, aliphatic carboxylic acids, diethanolamides, and dialkanolamides. In addition, one type of surfactant system may be used alone, or two or more types may be used in combination.

[Plasticizer] The PVA film of the present invention may contain plasticizer. Compared with other plastic films, PVA films are relatively rigid, so the impact strength and passability during secondary processing may be insufficient. However, the PVA film can improve these by containing the above-mentioned plasticizer. Undesirable condition.

Examples of plasticizers include polyols and the like. Examples of the polyhydric alcohol include ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, and the like. Among these, ethylene glycol and glycerin are preferred from the viewpoint of improving the stretchability of the optical PVA film. In addition, these plasticizers may be used individually by 1 type, and may be used in combination of 2 or more types.

In the PVA film of the present invention, the content of the plasticizer is preferably 1 part by mass or more, preferably 2 parts by mass or more, and more preferably 3 parts by mass or more relative to 100 parts by mass of PVA. The content of the plasticizer is preferably 30 parts by mass or less, preferably 25 parts by mass or less, and more preferably 20 parts by mass or less relative to 100 parts by mass of PVA. When the plasticizer content is less than 1 part by mass, the above effects may not be obtained. When it exceeds 30 parts by mass, the PVA film becomes too soft and handleability may be reduced.

[Other optional ingredients] The PVA film of the present invention can further contain any other ingredients other than PVA, surfactants and plasticizers within the scope that does not impair the efficacy of the present invention. Examples of such other optional components include water, antioxidants, ultraviolet absorbers, lubricants, colorants, preservatives, antifungal agents, and other polymer compounds other than the above components.

In the PVA film of the present invention, the content of the other optional components mentioned above is preferably 40% by mass or less, preferably 20% by mass or less, more preferably 10% by mass or less, and particularly preferably 5% by mass, based on the total mass of the PVA film. %the following.

The thickness of the PVA film of the present invention is not particularly limited. When used as a raw material for polarizing films, the average thickness is preferably in the range of 5 to 150 μm. In addition, the average thickness of the PVA film can be obtained by measuring the thickness at any 10 locations (for example, any 10 locations on a straight line drawn in the width direction of the PVA film) and taking the average value thereof. In addition, the film width of the PVA film can be adjusted to a size suitable for the intended use. The film width of the PVA film is usually 0.1m or more, preferably 0.5m or more, and more preferably 1.0m or more. The film width of the PVA film is usually 7.5m or less, preferably 7.0m or less, and more preferably 6.5m or less. The volatile component concentration of the PVA film of the present invention is preferably 0.5% by mass or more, more preferably 1% by mass or more. On the other hand, the volatile component concentration is preferably 5 mass% or less.

[Manufacturing method of PVA film] The manufacturing method of the PVA film of the present invention is not particularly limited, but it is preferable that the PVA film of the present invention can be obtained efficiently by the following manufacturing method. That is, as a method for manufacturing the PVA film of the present invention, a method for manufacturing a polyvinyl alcohol film is preferably used, which uses PVA containing a saponification degree of 98 mol% or more and a polymerization degree of 1500 to 8000, and in the above-mentioned PVA The film-making stock solution of PVA has a concentration of long-chain aldehydes above C6 of 0.35 to 2.5 μmol%.

In the manufacturing method of the PVA film of the present invention, as the PVA used in the film-making stock solution, the concentration of long-chain aldehydes with C (carbon number) 6 or more in the PVA is preferably 0.35 to 2.5 μmol%. Here, the concentration of long-chain aldehydes above C6 (μmol%) in PVA refers to (1) the structural units in PVA that can be converted into vinyl alcohol units by saponification (typically vinyl ester monomers). (unit), (2) vinyl alcohol units in PVA and (3) the total molar number of long-chain aldehydes with C6 or higher in PVA, the proportion of the molar number of long-chain aldehydes with C6 or higher (mol% ). Generally speaking, aldehydes can easily initiate an acetalization reaction with PVA under high temperature conditions and in the presence of catalysts such as acetic acid contained in PVA. When long-chain aldehydes with C6 or above initiate an acetalization reaction with PVA, acetal units containing side chains (aldehyde chains) with C6 or above will be generated on the main chain of PVA. It is speculated that the expansion of the molecular chain of PVA will be inhibited by the side chain (aldehyde chain) above C6. At least part of the long-chain aldehydes with C6 or higher contained in the PVA may also form the acetal unit. In addition, even in the manufacturing steps of the PVA film such as the heat treatment step of the PVA film described later, the acetalization reaction of long-chain aldehydes with C6 or higher and PVA will be initiated to generate the aforementioned acetal units. In addition, in the "μmol%" unit of the concentration of long-chain aldehydes mentioned above, "μ" is the prefix of the International System of Units (SI), and "μmol%" means 10 ^-6 times (0.000001 times) of "mol%" . For example, 0.35μmol%=0.35×10 ^-6 mol%.

In the manufacturing method of the PVA film of the present invention, the concentration of long-chain aldehydes above C6 in the PVA used in the film-making stock solution is 2.5 μmol% or less, so that the polarizing film produced from the PVA film can be The optical performance becomes easy to improve. The concentration of the aforementioned long-chain aldehyde is preferably 2.2 μmol% or less, preferably 1.9 μmol% or less. On the other hand, when the concentration of the long-chain aldehyde that passes through is 0.35 μmol% or more, the film width of the PVA film can be easily stabilized when the PVA film is produced at high speed. The concentration of the aforementioned long-chain aldehyde is preferably 0.37 μmol% or more, and more preferably 0.40 μmol% or more.

In the manufacturing method of the PVA film of the present invention, the long-chain aldehyde in the PVA used in the film-making stock solution is preferably C12 or less, more preferably C10 or less. When the carbon number of the long-chain aldehyde is equal to or less than the above range, the crystallinity of PVA is easily increased, and the optical properties of the polarizing film produced from the obtained PVA film are easily improved.

In the manufacturing method of the PVA film of the present invention, the long-chain aldehyde containing C6 or higher in the PVA used in the film-making stock solution is not necessarily limited. From the viewpoint of suitably good affinity and reactivity with PVA, it is preferable to include At least one selected from the group consisting of 2,4-hexadienal, 2,4,6-octatrienal and 2,4,6,8-decatetraenal.

In the manufacturing method of the PVA film of the present invention, it is also preferred that the concentration of crotonaldehyde in the PVA used in the film-forming stock solution is 0.70 μmol% or less. Here, the concentration of crotonaldehyde (μmol%) in PVA refers to (1) the structural units in PVA that can be converted into vinyl alcohol units through saponification (typically vinyl ester monomer units), ( 2) The total molar number of vinyl alcohol units in PVA and (3) crotonaldehyde in PVA, and the proportion of the molar number of crotonaldehyde (mol%). It is also possible that at least part of the crotonaldehyde contained in the aforementioned PVA forms an acetal unit of the PVA main chain by initiating an acetalization reaction with PVA. In addition, in the "μmol%" unit of the concentration of crotonaldehyde mentioned above, "μ" is the prefix of the International System of Units (SI), and "μmol%" means 10 ^-6 times (0.000001 times) of "mol%".

In the manufacturing method of the PVA film of the present invention, the concentration of crotonaldehyde in the PVA used in the film-forming stock solution is 0.70 μmol% or less, thereby making it easier to reduce the yellow tint of the PVA film obtained. The content of the aforementioned crotonaldehyde is preferably 0.50 μmol% or less, and more preferably 0.40 μmol% or less. The lower limit of the crotonaldehyde content is not particularly limited, but it is preferably 0.0010 μmol% or more, more preferably 0.010 μmol% or more, and more preferably 0.050 μmol% or more. When the content of the crotonaldehyde is equal to or higher than the lower limit, the step of strengthening PVA cleaning can be omitted, thereby improving the productivity of the PVA film.

In the manufacturing method of the PVA film of the present invention, the method for adjusting the concentration of the long-chain aldehyde of C6 or higher or crotonaldehyde in the PVA contained in the film-making stock solution is not particularly limited. An example of this is the use of an organic solvent to convert the PVA into the film. This is a method of adding long-chain aldehydes above C6 or crotonaldehyde after extracting and removing the aldehydes and other impurities contained in the product. In addition, when PVA is produced by saponifying vinyl acetate, a stabilizer such as hydroquinone is usually added to the vinyl acetate. Alternatively, the amount of the stabilizer may be intentionally reduced to cause decomposition of the vinyl acetate. The method of producing aldehyde. Among these methods, the former method is preferred because the concentration of long-chain aldehydes with C6 or higher or crotonaldehyde in the PVA contained in the film-making stock solution can be easily controlled.

In the manufacturing method of the PVA film of the present invention, the preferred and specific aspects of the PVA contained in the film-making stock solution are the same as those mentioned above. The above-mentioned interface activity may also be included within the scope that does not impair the efficacy of the present invention. agents, plasticizers, and other optional ingredients.

In the present invention, as a method of forming a PVA film, a conventional method can be used. Examples of commonly known methods include cast film forming methods, wet film forming methods, dry and wet film forming methods, gel film forming methods, melt extrusion film forming methods, and methods that combine these methods. . Among these, the melt extrusion film forming method is preferred from the viewpoint that a PVA film with high transparency and little coloring can be efficiently obtained.

By the above-mentioned melt extrusion film forming method, the PVA film of the present invention can be produced as follows, for example. First, using the above method, the PVA chips (PVA chips) whose content of long-chain aldehydes above C6 have been adjusted are immersed in distilled water at 10°C to 50°C for 10 to 48 hours, and then centrifuged and dehydrated. PVA water-containing chips with a volatile component concentration of 30% by mass to 90% by mass are obtained. At this time, the amount of long-chain aldehydes above C6 in PVA is slightly reduced, so it is necessary to pay attention not to excessively increase the temperature and prevent the time from becoming too long.

In the above-mentioned PVA water-containing chips, appropriate amounts of plasticizers such as glycerin, surfactants, solvents such as water, etc. can be added and mixed. This mixture is put into a twin-screw extruder, and melt-extrusion film formation is performed continuously by a conventional method. Specifically, the above mixture is heated and melted using a twin-screw extruder with a maximum temperature of 100°C to 200°C, and then cooled to 80°C to 120°C in a heat exchanger to prepare a film-forming stock solution. The film-forming stock solution is discharged from a T-shaped mold at 80°C to 120°C, cast on a metal drum at 75°C to 115°C, and dried to produce a water-containing film with a moisture content of 15% by mass to 40% by mass. film. After the film is peeled off from the above-mentioned metal drum, it is passed through a hot air drying oven at 50°C to 100°C or contacted with a drying drum at 50°C to 100°C, and dried until the moisture content is less than 15% by mass, and then heat treated. The PVA film of the present invention can be produced. In the present invention, the heat treatment temperature is preferably 80°C or higher. By performing heat treatment above 80°C, the reaction between PVA and long-chain aldehydes can be accelerated. The heat treatment temperature is preferably 90°C or higher, more preferably 100°C or higher, and particularly preferably 110°C or higher. In addition, when the heat treatment temperature is too high, there is a risk of undesirable phenomena such as film coloration, so it is preferably 170°C or lower, preferably 160°C or lower, and more preferably 150°C or higher. In addition, the heat treatment time is preferably 1 second or more. By setting the heat treatment time to more than 1 second, the reaction between PVA and long-chain aldehydes can be accelerated. The heat treatment time is preferably at least 5 seconds, and more preferably at least 10 seconds. In addition, when the heat treatment time is too long, there is a risk of adverse phenomena such as film coloration, so it is preferably 60 seconds or less, preferably 45 seconds or less, and more preferably 30 seconds or less.

The PVA film produced is usually rolled into a drum shape using known methods to produce a film roll. As a specific manufacturing method of the above-mentioned film roll, for example, the two ends of the optical PVA-based polymer film in the width direction are cut into 0.5cm to 20cm respectively, and a conventional winding machine is used to 1.0Kgf/cm to 10Kgf/cm. The film tension is used to roll the film on a cylindrical core, thereby producing a PVA film roll.

The outer diameter of the core (in the case of a rectangular cylinder, the diameter of its circumscribed circle) is preferably 10 cm or more. When the above-mentioned outer diameter is less than 10cm, the film roll will be distorted due to its own weight and may have wrinkles. In addition, the length of the core may be the same as the width of the PVA film, or may be longer than the width of the film, and is preferably 10 cm or more longer than the width of the film. When the length of the core is shorter than the width of the film, breakage is likely to occur from the ends in the width direction of the film during stretching, making it difficult to extend uniformly. In addition, the core is preferably in a cylindrical shape with an outer surface made of metal or plastic so as to prevent wrinkles during winding.

The length of the PVA film rolled into a roll is preferably 1300m or more. When the length of the PVA film rolled into a roll is less than 1,300 m, it is undesirable because the loss caused by switching of film rolls during the polarizing film manufacturing process is large. The upper limit of the length of the PVA film rolled into a roll is not particularly limited. If it is too long, the weight of the film roll will become too heavy, and the handleability will deteriorate, or the film roll will become twisted and the film will easily become loose. There is a risk of wrinkles and other problems, so the length of the PVA film should be less than 20,000m.

PVA film rolled into a roll should be packed in moisture-proof packaging and stored/transported in a suspended state that supports the weight of the entire core of the film roll or both ends of the core. Preferable methods for storing/transporting in the suspended state include a method of placing the core protruding from both end surfaces of the drum on a support body, and a method of hoisting the core protruding from both end faces of the drum using the support body. , a method of inserting a part of the support body into the core, a method of placing a rod-shaped jig inserted into the core on the support body, and a method of using the support body to lift the rod-shaped jig inserted into the core. Among others, the preferred method is to place the cores protruding from both end surfaces of the drum on the support. In addition, PVA is highly hygroscopic. When stored/transported in environments other than low-humidity conditions, it is likely to easily absorb moisture/swell and cause wrinkles on the film. Therefore, it is expected that in such an environment In the case of storage/transportation, adequate moisture-proof packaging is necessary.

[Manufacturing method of optical film] The use of the PVA film of the present invention is not particularly limited. For example, it can be used as a raw material film for manufacturing optical films. Examples of the optical film include polarizing films, viewing angle improving films, retardation films, brightness improving films, etc., with polarizing films being preferred. Hereinafter, as an example of the manufacturing method of an optical film, a manufacturing method of a polarizing film will be mentioned and demonstrated in detail.

Polarizing films usually use PVA film as the raw material film, and can be manufactured through processing steps such as swelling steps, dyeing steps, cross-linking steps, stretching steps, and fixing steps. Specific examples of the treatment liquid used in each step include a swelling treatment liquid used in swelling treatment, a dyeing treatment liquid (dyeing liquid) used in dyeing treatment, a cross-linking treatment liquid used in cross-linking treatment, and stretching treatment. The extending treatment liquid used for treatment, the fixing treatment liquid used for fixing treatment, the cleaning treatment liquid (cleaning liquid) used for cleaning treatment, etc.

Each processing step that can be adopted in the manufacturing method for manufacturing a polarizing film is described in detail below. In addition, in the manufacturing method of the polarizing film, one or more of the following processes may be omitted, the same process may be performed a plurality of times, or other processes may be performed simultaneously.

[Cleaning treatment before swelling treatment] Preferably, the PVA film should be washed before the PVA film is swollen. Through such cleaning treatment before the swelling treatment, the anti-caking agent etc. attached to the PVA film can be removed, and the various processing liquids in the manufacturing steps of the polarizing film can be prevented from being contaminated by the anti-caking agent etc. The cleaning treatment is preferably performed by immersing the PVA film in the cleaning treatment liquid. Alternatively, the cleaning treatment liquid may be sprayed onto the PVA film. As the cleaning liquid, for example, water can be used. The temperature of the cleaning solution is preferably above 20°C, preferably above 22°C, more preferably above 24°C, particularly preferably above 26°C. When the temperature of the cleaning treatment liquid is 20° C. or higher, the anti-caking agent and the like attached to the PVA film can be easily removed. In addition, the temperature of the cleaning treatment liquid is preferably 40°C or lower, preferably 38°C or lower, more preferably 36°C or lower, particularly preferably 34°C or lower. By keeping the temperature of the cleaning treatment liquid below 40°C, it is possible to prevent part of the surface of the PVA film from dissolving and causing the films to adhere to each other and reduce the handleability.

(swelling treatment) The swelling treatment can be performed by immersing the PVA film in a swelling treatment liquid such as water. The temperature of the swelling treatment liquid is preferably above 20°C, preferably above 22°C, and more preferably above 24°C. The temperature of the swelling treatment liquid is preferably below 40°C, preferably below 38°C, more preferably below 36°C. Moreover, the time for immersing in the swelling treatment liquid is, for example, preferably 0.1 minutes or more, more preferably 0.5 minutes or more. Moreover, the time for immersing in the swelling treatment liquid is preferably 5 minutes or less, for example, more preferably 3 minutes or less. In addition, the water system used as the swelling treatment liquid is not limited to pure water, and may be an aqueous solution in which various components such as a boron-containing compound are dissolved, or may be a mixture of water and an aqueous medium. The type of boron-containing compound is not particularly limited, but from the viewpoint of handleability, boric acid or borax is preferred. When the swelling treatment liquid contains a boron-containing compound, from the viewpoint of improving the stretchability of the PVA film, the concentration is preferably 6 mass % or less.

(Dyeing treatment) The dyeing treatment can be performed using an iodine-based dye as a dichroic dye, and the dyeing period can be any stage before the stretching treatment, during the stretching treatment, or after the stretching treatment. The dyeing treatment is preferably performed by using a solution containing iodine-potassium iodide (preferably an aqueous solution) as the dyeing treatment liquid, and immersing the PVA film in the dyeing treatment liquid. The concentration of iodine in the dyeing solution is preferably in the range of 0.005 to 0.2% by mass. Potassium iodide/iodine (mass) is preferably in the range of 20 to 100. The temperature of the dyeing solution is preferably above 20°C, more preferably above 25°C. The temperature of the dyeing solution is preferably below 50°C, and more preferably below 40°C. The dyeing solution may contain boron-containing compounds such as boric acid as a cross-linking agent. In addition, if the PVA film used as the raw material film contains a dichroic dye in advance, the dyeing process can be omitted. Furthermore, a boron-containing compound such as boric acid or borax may be preliminarily contained in the PVA film used as the raw material film.

(cross-linking treatment) In the production of polarizing films, cross-linking treatment can be performed after dyeing for the purpose of making the dichroic pigment firmly adsorbed to the PVA film. The cross-linking treatment can be performed by using a solution (preferably an aqueous solution) containing a cross-linking agent as the cross-linking treatment liquid and immersing the PVA film in the cross-linking treatment liquid. As the cross-linking agent, one or more types of boron-containing compounds such as boric acid and borax can be used. If the concentration of the cross-linking agent in the cross-linking treatment liquid is too high, the cross-linking reaction will proceed excessively, making it difficult to perform sufficient stretching in the subsequent stretching treatment. On the other hand, if the concentration is too low, the cross-linking reaction will proceed excessively. The effect of cross-linking treatment tends to be reduced. The concentration of the cross-linking agent in the cross-linking treatment liquid is preferably 1 mass % or more, preferably 1.5 mass % or more, and more preferably 2 mass % or more. The concentration of the cross-linking agent in the cross-linking treatment liquid is preferably 6 mass % or less, preferably 5.5 mass % or less, more preferably 5 mass % or less.

In order to suppress the dissolution of the dichroic dye from the PAV film after the dyeing process, the cross-linking treatment liquid may contain an iodine-containing compound such as potassium iodide. If the concentration of the iodine-containing compound in the cross-linking treatment liquid is too high, the heat resistance of the resulting polarizing film tends to decrease although the reason is unclear. In addition, if the concentration of the iodine-containing compound in the cross-linking treatment liquid is too low, the effect of inhibiting the elution of the dichroic dye will tend to be reduced. Based on the aforementioned reasons, the concentration of the iodine-containing compound in the cross-linking treatment liquid is preferably 1 mass% or more, preferably 1.5 mass% or more, and more preferably 2 mass% or more. The concentration of the iodine-containing compound in the cross-linking treatment liquid is preferably 6 mass% or less, preferably 5.5 mass% or less, more preferably 5 mass% or less.

If the temperature of the cross-linking treatment liquid is too high, the dichroic pigment will be eluted, and stains may easily occur on the resulting polarizing film. If the temperature is too low, the effect of the cross-linking treatment may be reduced. The temperature of the cross-linking treatment liquid is preferably in the range of 20°C to 40°C. The temperature of the cross-linking treatment liquid is preferably above 22°C, and more preferably above 25°C. The temperature of the cross-linking treatment liquid is preferably 45°C or lower, preferably 40°C or lower, more preferably 35°C or lower.

In addition to the stretching treatment described below, the PVA film can also be stretched during each of the above-mentioned treatments. By performing such stretching (front stretching), it is possible to prevent wrinkles on the surface of the PVA film. The total stretch ratio of the pre-stretching (the ratio of the sum of the stretching ratios of each process) is based on the polarizing properties of the obtained polarizing film. Based on the original length of the raw material PVA film before stretching, it is preferably 4 times or less. . The total extension ratio of the front extension should be less than 3.5 times. The total stretching ratio before stretching is based on the polarizing properties of the obtained polarizing film, etc., and is preferably 1.5 times or more based on the original length of the PVA film as the raw material before stretching. The stretching ratio in the swelling treatment is based on the original length of the PVA film, and is preferably more than 1.1 times, preferably more than 1.2 times, and more preferably more than 1.4 times. The stretching ratio in the swelling treatment is based on the original length of the PVA film, and is preferably 3 times or less, preferably 2.5 times or less, and more preferably 2.3 times or less. The stretch ratio in the dyeing process is based on the original length of the PVA film, and should be 2 times or less, preferably 1.8 times or less, and more preferably 1.5 times or less. The stretch ratio during dyeing is based on the original length of the PVA film, preferably 1.1 times or more. The stretching ratio in the cross-linking treatment is based on the original length of the PVA film, and is preferably 2 times or less, preferably 1.5 times or less, and more preferably 1.3 times or less. The stretch ratio during cross-linking treatment is based on the original length of the PVA film, preferably 1.05 times or more.

(Extended processing) The stretching treatment can be carried out according to the wet stretching method or the dry stretching method. In the case of a wet stretching method, a solution (preferably an aqueous solution) containing a boron-containing compound such as boric acid can be used as the stretching treatment liquid, and can be carried out in the stretching treatment liquid. It can also be carried out in a dyeing treatment liquid, which will be described later. It is carried out in the fixation solution. In addition, in the case of dry stretching method, the PVA film after absorbing water can be used in the air. Among them, the wet stretching method is preferred, and uniaxial stretching in an aqueous solution containing boric acid is more preferred. When the stretching treatment liquid contains a boron-containing compound, the concentration of the boron-containing compound in the stretching treatment liquid is preferably 1.5 mass % or more, preferably 2.0 mass % or more, and more preferably 2.0 mass % or more, in order to improve the extensibility of the PVA film. 2.5% by mass or more. The concentration of the boron-containing compound in the stretching treatment liquid is preferably 7 mass% or less, preferably 6.5 mass% or less, and more preferably 6 mass% or less, in order to improve the extensibility of the PVA film.

It is preferable that the elongation treatment liquid contains an iodine-containing compound such as potassium iodide. If the concentration of the iodine-containing compound in the stretching treatment liquid is too high, the hue of the obtained polarizing film tends to change to a strong blue hue. If it is too low, the heat resistance of the polarizing film obtained tends to decrease although the reason is not clear. The concentration of the iodine-containing compound in the extension treatment liquid is preferably 2 mass% or more, preferably 2.5 mass% or more, and more preferably 3 mass% or more. The concentration of the iodine-containing compound in the extension treatment liquid is preferably 8 mass% or less, preferably 7.5 mass% or less, and more preferably 7 mass% or less.

If the temperature of the stretching treatment liquid is too high, the PVA film will tend to melt, become soft, and become easily broken. If the temperature is too low, the elongation will tend to decrease. The temperature of the stretching treatment liquid is preferably above 50°C, preferably above 52.5°C, and more preferably above 55°C. The temperature of the stretching treatment liquid is preferably 70°C or lower, preferably 67.5°C or lower, and more preferably 65°C or lower. In addition, the preferred range of the stretching temperature when performing stretching treatment by dry stretching method is also as mentioned above.

The stretching ratio in the stretching process is preferably 1.2 times or more, preferably 1.5 times or more, and more preferably 2 times or more, because the higher one can obtain a polarizing film with better polarizing properties. In addition, the total stretching magnification (the sum of the stretching magnifications of each step), which also includes the stretching magnification of the above-mentioned pre-stretching, is based on the original length of the raw material PVA film before stretching, and is based on the polarizing performance of the obtained polarizing film. , preferably 5.5 times or more, preferably 5.7 times or more, more preferably 5.9 times or more. The upper limit of the stretching ratio is not particularly limited. When the stretching ratio is too high, stretching fracture is likely to occur, so the stretching ratio is preferably 8 times or less.

The method of stretching by uniaxial stretching is not particularly limited, and uniaxial stretching in the longitudinal direction and transverse uniaxial stretching in the width direction can be used. In the case of manufacturing a polarizing film, from the viewpoint of obtaining one with excellent polarization performance, uniaxial stretching in the longitudinal direction is preferred. Uniaxial stretching in the longitudinal direction can be performed by using an stretching device with a plurality of rollers parallel to each other and changing the peripheral speed between the rollers.

In the present invention, the maximum stretching speed (%/min) when performing stretching treatment by uniaxial stretching is not particularly limited, but is preferably 200%/min or more, preferably 300%/min or more, and more preferably 400%/min. min or above. Here, the so-called maximum stretching speed refers to the fastest stretching speed among the stages when using three or more rollers with different circumferential speeds and dividing the PVA film into two or more stages. In addition, when the stretching process of the PVA film is performed in a single stage without being divided into two or more stages, the stretching speed in this stage becomes the maximum stretching speed. In addition, the so-called stretching speed is the increase in the length of the PVA film per unit time relative to the length of the PVA film before stretching. For example, the so-called stretching speed of 100%/min refers to the length of the PVA film within one minute. The speed at which the length is deformed from the length before extension to twice the length. It is preferable that the maximum stretching speed is larger because the stretching process (uniaxial stretching) of the PVA film can be performed at a high speed. As a result, the productivity of the polarizing film is improved. On the other hand, when the maximum stretching speed becomes too high, excessive tension may be locally applied to the PVA film during the stretching process (uniaxial stretching) of the PVA film, and stretch fracture may easily occur. Based on this point of view, the maximum extension speed is preferably not more than 900%/min.

(fixed processing) During the production of the polarizing film, in order to firmly adsorb the dichroic dye to the PVA film, it is preferable to perform a fixing process. The fixing treatment can be performed by using one or more solutions (preferably aqueous solutions) containing boron-containing compounds such as boric acid, borax, etc. as the fixing treatment liquid to make the PVA film (preferably the PVA film after stretching treatment) Immerse in the fixing solution. Furthermore, the fixing liquid may contain a boron-containing compound or a metal compound as necessary. The concentration of the boron-containing compound in the fixation treatment liquid is preferably 2 mass% or more, more preferably 3 mass% or more. The concentration of the boron-containing compound in the fixation solution is preferably 15% by mass or less, more preferably 10% by mass or less. The temperature of the fixation solution is preferably above 15°C, and preferably above 25°C. The temperature of the fixation solution is preferably below 60°C, more preferably below 40°C.

(washing process after dyeing process) Preferably, the PVA film after dyeing treatment, preferably after stretching treatment, is washed. The cleaning treatment is preferably performed by immersing the PVA film in the cleaning treatment liquid, but may also be performed by spraying the cleaning treatment liquid on the PVA film. As the cleaning liquid, for example, water can be used. The water system is not limited to pure water, but may also contain iodine-containing compounds such as potassium iodide. In addition, the cleaning treatment liquid may contain a boron-containing compound. In this case, the concentration of the boron-containing compound is preferably 2.0 mass% or less.

The temperature of the cleaning solution is preferably above 5°C, preferably above 7°C, and more preferably above 10°C. In addition, the temperature of the cleaning liquid is preferably 40°C or lower, preferably 38°C or lower, more preferably 35°C or lower. By keeping the temperature of the cleaning treatment liquid at 5°C or above, the breakage of the PVA film caused by the freezing of moisture can be suppressed. In addition, by keeping the temperature of the cleaning treatment liquid below 40°C, the optical properties of the polarizing film obtained are improved.

Specific methods for producing a polarizing film include methods of dyeing, stretching, cross-linking and/or fixing a PVA film. As a preferred example, a method in which the PVA film is sequentially subjected to swelling treatment, dyeing treatment, cross-linking treatment, stretching treatment (especially uniaxial stretching treatment), and washing treatment can be cited. In addition, the stretching treatment may be performed in any of the previous processing steps, or may be performed in two or more stages.

By drying the PVA film that has been subjected to the above-mentioned treatments, a polarizing film can be obtained. The drying treatment method is not particularly limited, and examples thereof include a contact method in which the film is brought into contact with a heated roller, a method in which the film is dried in a hot air dryer, and a floating method in which the film is dried using hot air while hanging.

(Polarizing plate) The polarizing film obtained in the above manner is preferably used by laminating an optically transparent and mechanically strong protective film on both sides or one side thereof to form a polarizing plate. As the protective film, triacetylcellulose (TAC) film, cycloolefin polymer (COP) film, cellulose acetate/butyrate (CAB) film, acrylic film, polyester film, etc. can be used. In addition, examples of adhesives used for lamination include PVA-based adhesives, urethane-based adhesives, and the like, and PVA-based adhesives are preferred.

The polarizing plate obtained by proceeding as above can be laminated with an acrylic adhesive or the like and then bonded to a glass substrate to be used as an LCD component. At the same time, it can also be used to laminate retardation films, viewing angle improvement films, brightness improvement films, etc.

The PVA film of the present invention can be used as an optical film. Specifically, it can be suitably used as a raw material for optical films such as polarizing films, retardation films, and special condensing films with few optical defects. It can also be used as Other uses include packaging materials, water-soluble films for laundry bags, etc., and release films for manufacturing artificial marble, etc. [Example]

The present invention will be specifically described below through examples, but the present invention is not limited by these examples.

(1) Ultimate viscosity of PVA [η] ₆ (I) Cleaning of PVA film Cut the PVA film obtained in the following examples or comparative examples into A4 size (ISO 216, international standard size). In terms of PVA film quality Immerse in 20 times more deionized water at 23°C for more than 10 minutes, and take out the PVA film from the water. After shaking the PVA film to simply remove the water on the surface, it is again immersed in deionized water with a mass of 20 times or more of the PVA film at 23°C for more than 10 minutes, and the PVA film is taken out of the water. Repeat this one more time. That is, the operation of immersing the PVA film in water is repeated three times in total to remove the plasticizer etc. contained in the PVA film. Finally, use filter paper to absorb and remove the water attached to the surface of the PVA film, and then dry it in a vacuum dryer set at 60°C for 24 hours.

(II) GPC Measurement Weigh the PVA film obtained in the above "Washing of PVA film", and adjust the sample so that the PVA concentration becomes 0.1 mass/volume % (for example, add a mobile phase solvent to 5.15 mg of PVA film) 5.15ml). After dissolving the PVA film by heating the sample at 40°C for 2 hours, conduct GPC measurement according to the following measurement conditions to obtain the ultimate viscosity [eta] ₆ (dl/g) of the PVA contained in the PVA film.

＜GPC measurement conditions＞ Measuring device: "Omnisec (Reveal, Resolve)" manufactured by Marvern Corporation Analysis software: "Omnisec (analysis software included with the device)" made by Marvern Corporation Sample concentration: 0.1 mass/volume % Mobile phase solvent: Add 20mM HFIP with sodium trifluoroacetate Injection volume: 100μl Flow rate: 0.8ml/minute Measuring temperature: 40℃ Sample dissolution conditions: 40℃, 2 hours Sample filter filtration: 0.45μm PTFE filter Column: 1 HFIP-LG (protection column manufactured by Shodex) + 1 HFIP-806M (manufactured by Shodex) Detector: RI detector, LS detector, viscosity detector included with the device Standard product for device calibration: PMMA50K made by Marvern Company (Mw=50923, Mn=49909)

(2) The concentration of long-chain aldehydes above C6 or crotonaldehyde in PVA In the following examples or comparative examples, about 0.5g of the dried PVA fragments obtained by "adding aldehyde to PVA fragments" was frozen and pulverized, and was placed in a glass test tube of a thermal desorption gas chromatography mass analysis device. Weigh 50.0mg and make a sample test tube. Use the following thermal desorption gas chromatography mass analysis device to heat the sample test tube under the following conditions. After all the volatile gases released from the sample test tube are adsorbed on the adsorption tube at one time, column separation is performed by adsorption. The gas is released again from the tube and the peaks of each component are detected. Here, a calibration line is drawn from the peak areas of the standard samples of crotonaldehyde, 2,4-hexadienal, 2,4,6-octatrienal, and 2,4,6,8-decatetraenal. The concentration (μmol%) of long-chain aldehydes above C6 or crotonaldehyde in PVA fragments were determined by the absolute calibration line method. In addition, when measuring a standard sample, an adsorption tube that allows the standard sample to penetrate into the adsorption tube is used instead of the sample test tube. The temperature when the sample is released after adsorption is changed from the temperature of the sample test tube 180°C to the temperature of the adsorption tube 260°C. , except that the measurement is carried out in the same manner as when measuring the sample test tube.

(Thermal desorption department) Device: "TurboMatrix-ATD" manufactured by Perkin Elmer Japan Co., Ltd. Adsorption tube: "Tenax" made by Carboxen The temperature when the sample is adsorbed on the adsorption tube: 170℃ (sample test tube), -30℃(adsorption tube), 250℃(valve), 260℃(transportation pipeline) Adsorption time for adsorption tubes: 10 minutes Temperature when the sample is released after adsorption: 180℃ (sample test tube), 260℃(adsorption tube), 250℃(valve), 260℃(transportation pipeline) Adsorption tube release time: 35 minutes Flow rate of carrier gas in helium column: 1.0ml/min Pressure: 120kPa

(Gas Chromatography Quality Analysis Department) Device: 7890B GC System manufactured by Agilent Technology Co., Ltd., 7977B MSD Column: DB-WAX UI (length: 30m, inner diameter: 0.25mm, film thickness: 0.50μm) Column oven temperature: After maintaining at 40°C for 5 minutes, adjust the temperature to 240°C at a heating rate of 10°C/min, and then maintain it for 10 minutes (a total of 35 minutes of temperature measurement) Transport pipeline (connection part) temperature: 240℃ Ionization conditions: EI+ Detection ion mass range: m/z=29-600 Detection method: SCAN

(standard sample) Crotonaldehyde: Sigma-Aldrich (registered trademark), manufactured by Merck 2,4-Hexadienal: Sigma-Aldrich (registered trademark), manufactured by Merck 2,4,6-octatrienal: manufactured by NARD Research Institute Co., Ltd. 2,4,6,8-Dedecatetraenal: manufactured by NARD Research Institute Co., Ltd.

(3) Film width stability during film production In the following examples or comparative examples, the film-forming stock solution containing PVA was ejected from a 1000mm wide T-shaped mold on the support (rotation speed 15m/min, surface temperature 85°C) to form a film, and the film was formed on the support. Liquid membrane. On the support, the entire non-contact surface of the support with the liquid film was blown with hot air at 90°C at a speed of 7.5 m/sec to dry, thereby obtaining a PVA film (moisture content: 25% by mass). The difference between the maximum width and the minimum width of the film width of the PVA film when this film formation was performed for 1 minute was measured and evaluated based on the following criteria. A: The difference between the maximum width and the minimum width of the film width is less than 5mm B: The difference between the maximum width and the minimum width of the film width is more than 5mm and less than 10mm C: The difference between the maximum width and the minimum width of the film width is more than 10mm

(4)Hue In the following examples or comparative examples, a PVA film of 5 cm in the width direction and 100 cm in the length direction was cut out from the center part in the width direction of the obtained PVA film. The film cut out of the metal rod with a diameter of 1cm is rolled up to make a PVA film roll with a width of 5cm. Place a PVA film roll with a width of 5cm with the metal rod removed on high-quality paper, and visually observe the color of the end surface of the roll from the side of the roll under a fluorescent lamp, and evaluate it based on the following standards. A: The roll end surface has no color and no coloring is confirmed. B: The end surface of the roll has a slight yellow tint C: The end surface of the roll is obviously yellowish.

(5)Extensibility In the following Examples or Comparative Examples, 2 m was cut out from the obtained PVA film roll, and after adjusting the humidity for 24 hours in an environment of 23°C and 50% RH, the film was cut from both ends to include both ends. Cut out 10 test pieces each with a length of 150mm and a width of 15mm. A total of 20 test pieces were obtained. Using Autograph (manufactured by Shimadzu Corporation, "AG-1"), these 20 test pieces were stretched in an environment of 23°C-50%RH at a stretching speed of 500mm/min and a distance between clamps of 50mm. The distance between the clamps is 310mm (extension ratio 6.2 times), and the evaluation is based on the number of broken test pieces among 20 test pieces.

(6) Degree of Polarization Two square samples with a side of 1.5 cm parallel to the alignment direction of the polarizing film were taken from the center portion in the width direction of the polarizing film obtained in the following Examples or Comparative Examples. For each sample, Hitachi The manufactured spectrophotometer V-7100 (with integrating sphere) is used to correct the visual sensitivity of the visible light area of C light source and 2-degree field of view in accordance with JIS Z8722 (Measurement method of object color), and for a polarizing film sample, The light transmittance when tilted at 45 degrees with respect to the extension axis direction and the light transmittance when tilted at -45 degrees were measured to obtain the average value (Y1). For another polarizing film sample, the light transmittance when tilted at 45 degrees and the light transmittance when tilted at -45 degrees were measured in the same manner as above to obtain the average value (Y2). The average of Y1 and Y2 obtained above is regarded as the transmittance (Y) (%) of the polarizing film. Using the same method as the above method for measuring the transmittance, measure the transmittance (Y ∥ ) when the two polarizing film samples taken above are overlapped with their alignment directions parallel, and the light transmittance (Y ∥ ) with the alignment directions positive. The light transmittance (Y⊥) when superimposed in an intersection manner, and the degree of polarization (V) (%) is obtained from the following formula. Polarization (V)(%)={(Y ∥ -Y⊥)/(Y ∥ +Y⊥)} ^1/2 ×100

[Example 1] (i) Cleaning of PVA fragments In the washing tank, add PVA chips with a saponification degree of 99.9 mol% and a polymerization degree of 2400 and methanol in an amount that is 10 times the mass of the PVA chips. After stirring and washing at 25°C for 4 hours, separate the PVA chips and Methanol. To the washed PVA fragments, an amount of methanol that is 10 times the mass of the PVA fragments before washing was added again. After stirring and washing at 25°C for 4 hours, the PVA fragments and methanol were separated. To the washed PVA fragments, an amount of methanol that is 10 times the mass of the PVA fragments before washing was added again, and after stirring and washing at 25° C. for 4 hours, the PVA fragments and methanol were separated.

(ii) Add aldehyde to PVA fragments To the PVA fragments obtained in the above "Cleaning of PVA fragments", add 25 mg of 2,4-hexadienal, 25 mg of 2,4,6-octatrienal, per 1kg of PVA fragments before washing. After careful stirring, 25 mg of 2,4,6,8-decyltetraenal and 40 mg of crotonaldehyde were dried at 60°C for 16 hours in an explosion-proof vacuum dryer. For the dried PVA chips, the amount of aldehyde in the PVA chips was measured using the above method. The results are shown in Table 1. In addition, only very trace amounts of aldehydes other than 2,4-hexadienal, 2,4,6-octatrienal, 2,4,6,8-decatetraenal and crotonaldehyde were detected.

(iii) Production of PVA film Using a melt extruder, 100 parts by mass of the dried PVA chips obtained in the above "adding aldehyde to PVA chips", and 0.2 parts by mass of lauric acid diethanolamide as a surfactant, and 217.6 parts by mass of deionized water were melted and mixed to prepare a film-making stock solution (volatile fraction 66 mass%). Next, the film-forming stock solution was ejected from a 1000mm wide T-shaped die onto a support (rotation speed 15 m/min, surface temperature 85°C) to form a film, and a liquid film was formed on the support. On the support, 90° C. hot air was blown at a speed of 7.5 m/sec to the entire non-contact surface of the support with the liquid film, and dried to obtain a PVA film (moisture content: 25% by mass). The maximum value of the film width when film production is continued for 1 minute is 978mm, and the minimum value is 975mm, with a difference of 3mm. Next, the PVA film is peeled off from the support, and each drying roller is moved from the first drying roller to the final drying roller (19th drying roller) located in front of the heat treatment roller so that one side and the other side of the PVA film are in contact with each other. After further drying, it is peeled off from the final drying drum. At this time, the surface temperature of each drying drum from the first drying drum to the final drying drum is 70°C. Furthermore, the PVA film is peeled off from the final drying roller, and heat treatment is performed so that one side and the other side of the PVA film are in contact with each other on each drying roller. At this time, the heat treatment is performed using two heat treatment rollers. The surface temperatures of the heat treatment rollers are both 120°C, and the heat treatment time is 15 seconds. Both ends of the obtained film were cut so that it became 930 mm wide, and it was wound around a cylindrical core into a roll shape. The thickness of the obtained PVA film was 60 μm. The ultimate viscosity [η] ₆ of the PVA contained in the PVA film was measured according to the above method, and the result was 8.0 dl/g.

(iv) Manufacturing and evaluation of polarizing films The obtained PVA film is cut into a width of 650 mm, and the film is sequentially subjected to swelling treatment, dyeing treatment, cross-linking treatment, stretching treatment, washing treatment, and drying treatment to continuously produce a polarizing film. The swelling treatment was performed by uniaxially extending the film 2.00 times in the longitudinal direction while immersing it in 25° C. pure water (swelling treatment liquid). The dyeing process is carried out while immersing in a potassium iodide/iodine dyeing solution (dyeing treatment solution) with a temperature of 32°C (potassium iodide/iodine (mass ratio) of 23, iodine concentration in the range of 0.03 to 0.05 mass%), while performing a single step in the length direction. The axis is extended to 1.26 times. For this dyeing treatment, the iodine concentration in the dyeing treatment solution is adjusted to 0.03 to 0.05 so that the monomer transmittance of the polarizing film obtained after uniaxial stretching in the stretching treatment falls into the range of 43.5% ± 0.2%. Within the range of mass %. The cross-linking treatment was performed by uniaxially extending the film 1.19 times in the longitudinal direction while immersing it in a boric acid aqueous solution (cross-linking treatment liquid) at 32° C. (boric acid concentration: 2.6% by mass). The stretching treatment was performed by uniaxially extending 2.00 times in the length direction while immersing in a 55° C. boric acid/potassium iodide aqueous solution (stretching liquid) (boric acid concentration: 2.8 mass%, potassium iodide concentration: 5 mass%). The maximum extension speed of uniaxial extension in this stretching process is 400%/min. The cleaning treatment is performed by immersing in a potassium iodide/boric acid aqueous solution (cleaning treatment liquid) at 22°C (potassium iodide concentration 3 to 6 mass%, boric acid concentration 1.5 mass%) for 12 seconds without stretching. The drying treatment was performed by hot air drying at 80° C. for 1.5 minutes without stretching to obtain a polarizing film.

The obtained PVA film and polarizing film were evaluated according to the above method. The evaluation results are shown in Table 1.

[Example 2] In the above "(i) Cleaning of PVA chips", PVA chips modified with 2 mol% of ethylene with a degree of saponification of 99.3 mol% and a degree of polymerization of 2400 were used as PVA chips. In addition, the same procedure as in Example 1 was used. PVA chips, PVA films and polarizing films were obtained in the same manner. Table 1 shows the evaluation results of the obtained PVA chips, PVA film, and polarizing film.

[Example 3] In the above "(i) Cleaning of PVA chips", PVA chips and a PVA film were obtained in the same manner as in Example 1, except that PVA chips with a saponification degree of 99.9 mol% and a polymerization degree of 6000 were used as PVA chips. and polarizing films. Table 1 shows the evaluation results of the obtained PVA chips, PVA film, and polarizing film.

[Example 4] In the above "(ii) Adding aldehydes to PVA chips", 3 mg of 2,4-hexadienal, 3 mg of 2,4,6-octatrienal, and 150 mg of 2 were added per 1 kg of PVA chips before washing. , 4,6,8-decatetraenal and 3 mg of crotonaldehyde, except that PVA chips, PVA films and polarizing films were obtained in the same manner as in Example 1. Table 1 shows the evaluation results of the obtained PVA chips, PVA film, and polarizing film.

[Example 5] In the above "(ii) Adding aldehydes to PVA chips", 25 mg of 2,4-hexadienal, 25 mg of 2,4,6-octatrienal, and 25 mg of 2 are added per 1kg of PVA chips before washing. , 4,6,8-decatetraenal and 100 mg of crotonaldehyde, except that PVA chips, PVA films and polarizing films were obtained in the same manner as in Example 1. Table 1 shows the evaluation results of the obtained PVA chips, PVA film, and polarizing film.

[Example 6] In the above (iii) "Manufacture of PVA film", PVA chips, a PVA film and a polarizing film were obtained in the same manner as in Example 1, except that the surface temperatures of both heat treatment rollers were changed to 70°C. Table 1 shows the evaluation results of the obtained PVA chips, PVA film, and polarizing film.

[Example 7] In the above "(ii) Adding aldehydes to PVA chips", 250 mg of 2,4-hexadienal, 25 mg of 2,4,6-octatrienal, and 25 mg of 2 are added per 1kg of PVA chips before washing. , 4,6,8-decatetraenal and 40 mg of crotonaldehyde, except that PVA chips, PVA films and polarizing films were obtained in the same manner as in Example 1. Table 1 shows the evaluation results of the obtained PVA chips, PVA film, and polarizing film.

[Comparative example 1] In the above "(ii) Adding aldehydes to PVA chips", 3 mg of 2,4-hexadienal, 3 mg of 2,4,6-octatrienal, and 3 mg of 2 are added per 1 kg of PVA chips before washing. , 4,6,8-decatetraenal and 3 mg of crotonaldehyde, except that PVA chips, PVA films and polarizing films were obtained in the same manner as in Example 1. Table 1 shows the evaluation results of the obtained PVA chips, PVA film, and polarizing film.

[Comparative example 2] In the above "(ii) Adding aldehydes to PVA chips", 3 mg of 2,4-hexadienal, 3 mg of 2,4,6-octatrienal, and 700 mg of 2 are added per 1kg of PVA chips before washing. , 4,6,8-decatetraenal and 3 mg of crotonaldehyde, except that PVA chips, PVA films and polarizing films were obtained in the same manner as in Example 1. Table 1 shows the evaluation results of the obtained PVA chips, PVA film, and polarizing film.

[Table 1] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Comparative example 1 Comparative example 2 Raw materialPVA degree of polymerization 2400 2400 6000 2400 2400 2400 2400 2400 2400 Saponification degree (mol%) 99.9 99.3 99.9 99.9 99.9 99.9 99.9 99.9 99.9 modified Kind - Ethylene - - - - - - - Amount(mol%) - 2 - - - - - - - Long-chain aldehydes above C6 (µmol%) 2,4-HDE 0.174 0.222 0.148 0.0239 0.180 0.174 1.73 0.0146 0.0343 2,4,6-OTE 0.137 0.187 0.114 0.0156 0.138 0.137 0.137 0.00900 0.0287 2,4,6,8-DTE 0.109 0.115 0.0897 0.661 0.0931 0.109 0.109 0.00607 2.90 plan 0.42 0.52 0.35 0.70 0.41 0.42 1.98 0.030 3.0 CA (µmol%) 0.27 0.39 0.27 0.036 0.79 0.27 0.27 0.029 0.047 Film making Heat treatment temperature (℃) 120 120 120 120 120 70 120 120 120 Heat treatment time (seconds) 15 15 15 15 15 15 15 15 15 PVA film Thickness(µm) 60 60 60 30 60 60 60 60 60 Ultimate viscosity [η] ₆ (dl/g) when the absolute molecular weight is 1×10 ⁶ 8.0 10.5 8.0 7.8 8.0 8.0 7.6 11.5 7.2 Evaluation results Film stability during film production A A A A A A A C B PVA film hue A A A A B A B A B Elongation (number of fracture test pieces) 1 0 3 1 2 3 1 18 5 Polarization(%) 99.997 99.996 99.999 99.996 99.997 99.995 99.993 99.994 99.981 2,4-HDE＝2,4-hexadienal 2,4,6-OTE＝2,4,6-octatrienal 2,4,6,8-DTE＝2,4,6,8- Decatetraenal CA = Crotonaldehyde

As shown in Table 1, the film width stability of the PVA films of Examples 1 to 7 in which the intrinsic viscosity [eta] ₆ of the PVA contained in the PVA film was 7.5 to 11 dl/g was evaluated as "A" ( The difference between the maximum width and the minimum width of the film is less than 5mm), and the film width is stable during film production. Moreover, when the PVA films of Examples 1 to 7 were made into PVA film rolls, the hue evaluation of the roll end surface was "A" (the roll end surface had no color and no coloring was confirmed), and the thickness of the end portion of the PVA film varied little. In addition, in the evaluation of stretchability of the PVA films of Examples 1 to 7, the number of broken test pieces was 0 to 3, which was relatively small. However, during the production of polarizing films, the PVA films were less broken and could be produced efficiently. Polarizing film. In addition, when the PVA films of Examples 1 to 7 are made into polarizing films, the polarization degree is 99.993 to 99.999%, and the optical properties are excellent. That is, the PVA film of the present invention has a stable film width, little thickness variation at the ends, and excellent stretchability. Therefore, if the PVA film of the present invention is used, a wide-width polarizing film with excellent optical properties can be produced efficiently. In addition, the PVA film can be efficiently produced by the production method of the present invention.

On the other hand, as shown in Table 1, the PVA film of Comparative Example 1 in which the intrinsic viscosity [eta] ₆ of the PVA contained in the PVA film exceeded 11 dl/g was evaluated as "C" ( The difference between the maximum width and the minimum width of the film width is more than 10mm). In addition, in the evaluation of stretchability of the PVA film of Comparative Example 1, the number of broken test pieces was 18, which was too high. On the other hand, the PVA film of Comparative Example 2 in which the limiting viscosity [eta] ₆ of the PVA contained in the PVA film was less than 7.5 dl/g was evaluated in the elongation, and the number of broken test pieces was 5, which is relatively large. . In addition, when the PVA film of Comparative Example 2 was made into a polarizing film, the degree of polarization was 99.981%, but the optical properties were poor.

without

without

without.

Claims (7)

A polyvinyl alcohol film, which is a polyvinyl alcohol film containing polyvinyl alcohol with a saponification degree of 98 mol% or more and a polymerization degree of 1500 to 8000. It is characterized by using a gel permeable layer equipped with a light scattering detector and a viscosity detector. Analyzer, using hexafluoroisopropanol containing 20mM Na trifluoroacetate as the mobile phase solvent at a measuring temperature of 40°C, the ultimate viscosity of the polyvinyl alcohol when the absolute molecular weight of the polyvinyl alcohol is 1×10 ⁶ is 7.5 to 11 dl/ g. For example, the polyvinyl alcohol film of claim 1 is a modified polyvinyl alcohol with an ethylene modification amount of 0.5 to 12 mol%. A method for manufacturing a polyvinyl alcohol film according to claim 1 or 2, which uses a long-chain aldehyde with a saponification degree of 98 mol% or more, a polymerization degree of 1500 to 8000, and a C6 or higher concentration of 0.35 to 2.5 μmol%. The film was formed using the film-forming stock solution obtained from polyvinyl alcohol. For example, the method for manufacturing a polyvinyl alcohol film according to claim 3, wherein the long-chain aldehyde having C6 or higher includes a compound selected from the group consisting of 2,4-hexadienal, 2,4,6-octatrienal and 2,4,6, At least 1 species from the group consisting of 8-decardenal. The method for manufacturing a polyvinyl alcohol film according to claim 3 or 4, wherein the concentration of crotonaldehyde in the polyvinyl alcohol is 0.70 μmol% or less. A method for manufacturing a polyvinyl alcohol film according to claim 3 or 4, which includes the step of heat-treating the polyvinyl alcohol film produced at a temperature above 80°C. For example, the polyvinyl alcohol film of claim 1 or 2 is an optical film.