KR20230028563A - Polyvinyl alcohol film - Google Patents

Abstract

The present invention is 110% or more and less than 190%, a softening point temperature of 60 ° C. or more and 68 ° C. or less, a polyvinyl alcohol film having a thickness of 50 μm or less, and production of an optical film having a step of uniaxially stretching using the polyvinyl alcohol film way.

Description

Polyvinyl alcohol film {POLYVINYL ALCOHOL FILM}

The present invention relates to a polyvinyl alcohol film useful as a raw film or the like for producing an optical film such as a polarizing film without easily causing breakage in stretching during stretching, and a method for manufacturing an optical film using the same.

BACKGROUND OF THE INVENTION A polarizing plate having functions of transmitting and shielding light is a basic component of a liquid crystal display (LCD) together with a liquid crystal that changes the polarization state of light. LCDs are intended to be used in a wide range of small devices such as electronic desk calculators and wristwatches, laptop computers, liquid crystal monitors, liquid crystal color projectors, liquid crystal televisions, in-vehicle navigation systems, mobile phones, and measuring instruments used indoors and outdoors. Among the application fields of these LCDs, in liquid crystal televisions, liquid crystal monitors, etc., enlargement and thinning are progressing, and with thinning of the glass used, thinning is also requested|required of the polarizing plate from a viewpoint of shrinkage stress.

A polarizing plate generally polarizes a polyvinyl alcohol film (hereinafter, "polyvinyl alcohol" may be abbreviated as "PVA") by dyeing, uniaxial stretching, and, if necessary, further fixing with a boron compound or the like. After manufacturing a film, it manufactures by bonding protective films, such as a cellulose triacetate (TAC) film, to the surface of the polarizing film. Therefore, in order to achieve thinning of the polarizing plate, it is required to manufacture a thin polarizing film using a thinner PVA film, and with respect to the specific thickness of the PVA film, 50 μm or less, furthermore 40 μm or less, in some cases 30 It is required to be less than μm.

Japanese Unexamined Patent Publication No. 2006-342236

However, in the case of manufacturing an optical film using a thin PVA film, breakage during uniaxial stretching is likely to occur compared to the case of using a thick PVA film. It is thought that this stretching breakage originates from the occurrence of folds at the ends of the thin PVA film after water bath immersion treatment such as swelling treatment and dyeing treatment performed before the PVA film is uniaxially stretched. As a method for reducing the occurrence of the fold. A method of lowering the degree of swelling of the PVA film is conceivable, but when the degree of swelling is simply lowered by a conventionally known method such as heat treatment, the softening point temperature rises, the film becomes hard and the stretching stress rises, which is due to the increase in the stretching stress this time There arises a problem that the break in drawing occurs frequently.

For the purpose of uniformity in thickness and suppression of contamination of foreign substances, etc., a method is known for producing a PVA film by extruding an aqueous solution containing PVA from a T-shaped slit die and casting it on the outer circumferential surface of a rotating drum roll ( See Patent Literature 1), the above problem cannot be solved even by the method.

Therefore, despite the fact that the present invention is a thin PVA film, folds do not easily occur at the ends after immersion in a water bath, and the stress during stretching is low. It is an object to provide a PVA film capable of producing the film in good yield. Moreover, this invention aims at providing the manufacturing method of optical films, such as a polarizing film using the said PVA film.

As a result of repeated intensive studies in order to achieve the above object, the inventors of the present invention have found that when the swelling degree of the PVA film is reduced to 110% or more and less than 190% while being brought into contact with water vapor, a novel PVA film having a low softening point temperature is obtained, and the PVA According to the film, although it is a thin PVA film, folds do not easily occur at the ends after water bath immersion treatment, and the stress during stretching is low, so that breakage in stretching does not occur easily during stretching, and optical films such as polarizing films was found to be able to be produced in good yield, and further studies were repeated based on the knowledge to complete the present invention.

That is, the present invention,

[1] A polyvinyl alcohol film having a swelling degree of 110% or more and less than 190%, a softening point temperature of 60 ° C. or more and 68 ° C. or less, and a thickness of 50 μm or less;

[2] A method for producing an optical film having a step of uniaxially stretching using the PVA film of [1] above;

[3] The manufacturing method of the above [2], wherein the optical film is a polarizing film;

It is about.

According to the present invention, even though it is a thin PVA film, folds do not easily occur at the ends after immersion in water bath, and the stress during stretching is low, so that breakage in stretching does not occur easily during stretching, and optical properties such as polarizing films A PVA film capable of producing a film in good yield and a method for producing an optical film using the same are provided.

The present invention will be described in detail below.

The PVA film of the present invention has a thickness of 50 μm or less, a degree of swelling within the range of 110% or more and less than 190%, and a softening point temperature within the range of 60°C or more and 68°C or less. Usually, when the swelling degree of the PVA film is lowered to the above range by a conventionally known method such as heat treatment, the softening point temperature increases accordingly, but the PVA film of the present invention has a swelling degree as low as 110% or more and less than 190% Although in the range, the softening point temperature is also within the low range of 60°C or more and 68°C or less, and is different from conventional PVA films.

The PVA film of the present invention needs to have a degree of swelling within the range of 110% or more and less than 190%. The degree of swelling is an index indicating the water retention ability when the PVA film is immersed in water, and can be easily adjusted by adjusting the degree of heat treatment for the PVA film, and usually the degree of swelling can be lowered by strengthening the conditions for heat treatment. . If the degree of swelling of the PVA film is less than 110%, the stress at the time of stretching becomes high and the stretching breakage occurs frequently. On the other hand, if the degree of swelling is 190% or more, it is not preferable from the viewpoint of breakage in stretching, because folds tend to occur at the ends after the water bath immersion treatment. From such a viewpoint, the degree of swelling of the PVA film is preferably 130% or more, more preferably 150% or more, still more preferably 160% or more, particularly preferably 170% or more, and preferably 185% or less, It is more preferable that it is 180 % or less. In particular, when the degree of swelling of the PVA film is 185% or less, and furthermore 180% or less, the effect of the present invention appears more remarkably.

The degree of swelling of the PVA film can be obtained as a percentage by dividing the mass after immersing a sample of the PVA film in distilled water at 30 ° C. for 30 minutes by the mass after immersion and drying at 105 ° C. for 16 hours. Specifically, in the examples can be measured by the method described below. In addition, what is necessary is just to collect|collect from the center part of the width direction of the PVA film as a representative position as a sample of the said PVA film.

Moreover, the softening point temperature of the PVA film of this invention needs to be in the range of 60 degreeC or more and 68 degreeC or less. If the softening point temperature of the PVA film is less than 60°C, wrinkles are generated during stretching, which is not preferable from the viewpoint of process passability. On the other hand, when the softening point temperature exceeds 68°C, the stress at the time of stretching increases and the break in stretching occurs frequently. From such a viewpoint, the softening point temperature of the PVA film is preferably 62°C or higher, more preferably 63°C or higher, still more preferably 64°C or higher, and preferably 67°C or lower, more preferably 66°C or lower. .

The softening point temperature of the PVA film can be obtained as the hydrothermal deformation temperature when a sample of the PVA film is placed in distilled water at 25 ° C. and heated at a heating rate of 5 ° C./min. Specifically, the method described later in Examples can be measured by In addition, what is necessary is just to collect|collect from the center part of the width direction of the PVA film as a representative position as a sample of the said PVA film.

PVA constituting the PVA film of the present invention, for example, vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate, vinyl benzoate, isopropyl acetate What is obtained by saponifying the polyvinyl ester obtained by superposing|polymerizing 1 type(s) or 2 or more types of vinyl esters, such as phenyl, is mentioned. Among the above vinyl esters, vinyl acetate is preferable from the viewpoints of the ease of manufacture of PVA, ease of availability, cost, and the like.

The polyvinyl esters described above are preferably those obtained by using only one or two or more vinyl esters as monomers, and more preferably those obtained by using only one type of vinyl esters as monomers. If it is an inner surface, the copolymer of 1 type, or 2 or more types of vinyl ester, and the other monomer copolymerizable with this may be sufficient.

Examples of other monomers copolymerizable with the above vinyl ester include C2-C30 α-olefins such as ethylene, propylene, 1-butene, and isobutene; (meth)acrylic acid or a salt thereof; 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, (meth) (meth)acrylic acid esters such as 2-ethylhexyl acrylate, dodecyl (meth)acrylate, octadecyl (meth)acrylate; (meth)acrylamide; N-methyl (meth)acrylamide, N-ethyl (meth)acrylamide , N,N-dimethyl(meth)acrylamide, diacetone(meth)acrylamide, (meth)acrylamidepropanesulfonic acid or its salt, (meth)acrylamidepropyldimethylamine or its salt, N-methylol (meth) (meth)acrylamide derivatives such as acrylamide or derivatives thereof; N-vinylamides such as N-vinylformamide, N-vinylacetamide, and N-vinylpyrrolidone; methyl vinyl ether, ethyl vinyl ether, and n-propyl Vinyl ethers such as 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; Cyanation such as (meth)acrylonitrile Vinyl; Vinyl halide, such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride; Allyl compounds, such as allyl acetate and allyl chloride; Maleic acid or its salt, ester, or acid anhydride; Itaconic acid or its salt, ester, or acid Anhydride; Vinyl silyl compounds, such as vinyl trimethoxysilane; Unsaturated sulfonic acid or its salt etc. are mentioned. Said polyvinyl ester may have a structural unit derived from 1 type, or 2 or more types of said other monomers. When the polyvinyl ester is a copolymer of one or more vinyl esters and the other monomers, the polyvinyl ester is preferably obtained by using only the vinyl ester and an α-olefin having 2 to 30 carbon atoms as monomers, and the monomers It is more preferable that it is obtained using only vinyl ester and ethylene.

The proportion of structural units derived from the above-mentioned other monomers in the polyvinyl ester is preferably 15 mol% or less, more preferably 10 mol% or less, based on the number of moles of all structural units constituting the polyvinyl ester. and more preferably 5 mol% or less.

In particular, when the other monomers described above are monomers that may promote the water solubility of the obtained PVA, such as (meth)acrylic acid and unsaturated sulfonic acid, the PVA is dissolved when the obtained PVA film is used as a raw film for optical film production, etc. In order to prevent this from happening, the ratio of structural units derived from these monomers in polyvinyl ester is preferably 5 mol% or less, based on the number of moles of all structural units constituting polyvinyl ester, and 3 mol% It is more preferable that it is below.

Said PVA may be modified with the monomer which can graft-copolymerize 1 type, or 2 or more types, as long as it exists in the range which does not significantly impair the effect of this invention. Examples of the monomer capable of graft copolymerization include unsaturated carboxylic acids or derivatives thereof; unsaturated sulfonic acids or derivatives thereof; and α-olefins having 2 to 30 carbon atoms. It is preferable that the ratio of the structural unit derived from the monomer which can be graft-copolymerized in PVA is 5 mol% or less based on the number of moles of all the structural units which comprise PVA.

As for said PVA, some of the hydroxyl groups may or may not be crosslinked. Further, in the PVA described above, some of its hydroxyl groups may react with aldehyde compounds such as acetaldehyde and butyraldehyde to form an acetal structure, or may not form an acetal structure without reacting with these compounds.

The degree of polymerization of the PVA is not particularly limited, but is preferably within the range of 1,500 or more and 6,000 or less, and the degree of polymerization is more preferably 1,800 or more, still more preferably 2,000 or more, more preferably 5,000 or less, and 4,000 or less. it is more preferable Durability of the optical film obtained improves because the said degree of polymerization is more than the said lower limit. On the other hand, when the degree of polymerization is equal to or less than the above lower limit, manufacturing cost can be reduced and process passability at the time of film forming can be improved. In addition, the degree of polymerization of PVA as used herein means the average degree of polymerization measured according to description of JISK6726-1994.

The degree of saponification of the above PVA is preferably 98.0 mol% or more, more preferably 98.5 mol% or more, still more preferably 99.0 mol% or more, from the viewpoint of the water resistance of the resulting optical film. In addition, the saponification degree of PVA in this specification is the number of moles of the total number of moles of a structural unit (typically, a vinyl ester unit) and a vinyl alcohol unit that can be converted into a vinyl alcohol unit by saponification of the PVA. It refers to the ratio (mol%) occupied by the number of moles. The degree of saponification can be measured according to the description of JIS K6726-1994.

It is preferable that the PVA film of this invention contains a plasticizer. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, and trimethylolpropane. The PVA film of the present invention may contain one or two or more of these plasticizers. Among these, glycerin is preferable from the viewpoint of the effect of improving the stretchability.

The content of the plasticizer in the PVA film of the present invention is preferably in the range of 1 part by mass or more and 20 parts by mass or less, and is in the range of 3 parts by mass or more and 17 parts by mass or less with respect to 100 parts by mass of PVA contained therein. More preferably, it is more preferably within the range of 5 parts by mass or more and 15 parts by mass or less. When the said content is 1 mass part or more, the ductility of a PVA film can be improved more. On the other hand, when the said content is 20 mass parts or less, it can suppress that a PVA film becomes soft too much and handleability falls.

In addition, when a PVA film is produced using a film forming undiluted solution for producing a PVA film described later, the film forming property is improved and the occurrence of unevenness in the thickness of the PVA film is suppressed, and when a roll or belt is used for film forming, From the viewpoint of facilitating the peeling of the PVA film from these rolls or belts, it is preferable to contain a surfactant in the film forming stock solution. When a PVA film is produced from a film forming stock solution containing a surfactant, the surfactant may be contained in the PVA film. Although the kind of said surfactant is not specifically limited, From a viewpoint of peelability from a roll, a belt, etc., anionic surfactant or nonionic surfactant is preferable, and a nonionic surfactant is especially preferable. Surfactant may be used individually by 1 type, and may use 2 or more types together.

Examples of the anionic surfactant include carboxylic acid types such as potassium laurate; sulfuric acid ester types such as polyoxyethylene lauryl ether sulfate and octyl sulfate; and sulfonic acid types such as dodecylbenzenesulfonate. do.

As a nonionic surfactant, For example, Alkyl ether types, such as polyoxyethylene oleyl ether; Alkyl phenyl ether types, such as polyoxyethylene octylphenyl ether; Alkyl ester types, such as polyoxyethylene laurate; Polyoxy Alkyl amine type such as ethylene laurylamino ether; Alkyl amide type such as polyoxyethylene lauric acid amide; Polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether; Diethanol lauric acid amide, oleic acid diethanol amide, etc. alkanolamide type of; allylphenyl ether type, such as polyoxyalkylene allylphenyl ether, etc. are preferable.

When the surfactant is contained in the film-forming stock solution, the content of the surfactant in the film-forming stock solution, and furthermore, the content of the surfactant in the PVA film is 0.01 parts by mass or more with respect to 100 parts by mass of PVA contained in the film-forming stock solution or PVA film. It is preferably in the range of 0.5 parts by mass or less, more preferably in the range of 0.02 parts by mass or more and 0.3 parts by mass or less, and particularly preferably in the range of 0.05 parts by mass or more and 0.1 parts by mass or less. When the content of the surfactant is 0.01 parts by mass or more with respect to 100 parts by mass of PVA, film forming properties and peelability can be improved. On the other hand, when the content of the surfactant is 0.5 parts by mass or less with respect to 100 parts by mass of PVA, it is possible to prevent the surfactant from bleeding out on the surface of the PVA film to cause blocking and deterioration in handling properties.

The PVA film of the present invention may consist of only PVA, or may consist of only PVA and the plasticizer and / or surfactant described above, but, if necessary, an antioxidant, an antifreeze agent, a pH adjuster, a masking agent, an anticolorant, an oil agent, etc. It may contain other components other than PVA, plasticizer, and surfactant.

The PVA content in the PVA film is preferably in the range of 50 mass% or more and 100 mass% or less, more preferably in the range of 80 mass% or more and 100 mass% or less, and is 85 mass% or more and 100 mass% or less. It is more preferable that it is within the range of

The thickness of the PVA film of the present invention is 50 μm or less from the viewpoint of obtaining a thin polarizing film, reducing the shrinkage force of the polarizing film and further using the polarizing plate using it, and preventing the thin glass to be laminated from bending. It is necessary, and it is preferably 40 μm or less, more preferably 35 μm or less, still more preferably 30 μm or less, and may be 25 μm or less, 15 μm or less, or even 10 μm or less. In particular, when the thickness of the PVA film is 40 μm or less, the effect of the present invention appears more remarkably. Although there is no particular restriction on the lower limit of the thickness of the PVA film, the thickness is preferably 1 μm or more, and more preferably 3 μm or more, from the viewpoint of being able to more smoothly manufacture the polarizing film.

The shape of the PVA film of the present invention is not particularly limited, but a more uniform PVA film can be produced continuously and easily, and it can be used continuously even when optical films such as polarizing films are produced using it. From this point of view, it is preferable that it is a long film. The length (length in the longitudinal direction) of the elongated film is not particularly limited, and can be appropriately set depending on the application and the like, and can be, for example, within a range of 5 m or more and 30,000 m or less.

The width of the PVA film of the present invention is not particularly limited, and can be appropriately set according to the use of the PVA film or the optical film produced therefrom, for example, 50 cm or more, but recently, LCD televisions and LCD monitors is progressing, and the width of the PVA film is 2 m or more, more preferably 3 m or more, still more preferably 4 m or more, it is preferable for these applications. On the other hand, if the width of the PVA film is too wide, it tends to be difficult to uniformly uniaxially stretch when manufacturing an optical film with a device that has been put into practical use, so the width of the PVA film is preferably 7 m or less. .

The form of the PVA film is not particularly limited, and it may be in the form of a single layer or a laminated body, such as a PVA film formed by a coating method on a thermoplastic resin film, for example. From the viewpoints of more prominent appearance, complexity of lamination (coating, etc.) work, cost of the thermoplastic resin film, and the like, a single layer form is preferred.

The production method for producing the PVA film of the present invention is not particularly limited, but since the PVA film of the present invention can be produced smoothly, a PVA film having the above thickness is prepared by drying a film-forming stock solution containing PVA. After that, the temperature is 70 ° C. or more and 100 ° C. or less (preferably 75 ° C. or more and 100 ° C. or less), and the relative humidity is 60% or more and 100% or less (preferably 80% or more and 100% or less). It is preferable to employ|adopt the method of reducing to 110 % or more and less than 190 %.

As the film forming stock solution containing the above PVA (film forming stock solution for producing a PVA film), for example, the above PVA constituting the PVA film and, if necessary, further plasticizers, surfactants and other components 1 A film forming stock solution in which one or more species are dissolved in a liquid medium, PVA, and, if necessary, one or more of plasticizers, surfactants, other components, and liquid media, and PVA is molten. A film forming undiluted solution etc. are mentioned. When the film forming dope contains at least one of a plasticizer, a surfactant and other components, it is preferable that these components are mixed uniformly.

Examples of the liquid medium used for preparation of the film forming stock solution include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, Triethylene glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, diethylenetriamine, etc. are mentioned, One type or two or more types of these can be used. Among them, water is preferable from the viewpoint of load on the environment and recoverability.

The volatile content of the film-forming dope (the content of volatile components such as liquid media removed by volatilization or evaporation in the film-forming dope in the film-forming dope) varies depending on the film-forming method, film-forming conditions, etc., but is 50% by mass or more and 95% by mass It is preferably within the following ranges, more preferably within the range of 55 mass% or more and 90 mass% or less, and even more preferably within the range of 60 mass% or more and 85 mass% or less. When the volatile content of the membrane-forming stock solution is 50% by mass or more, the viscosity of the membrane-forming stock solution does not increase too much, filtration and defoaming are smoothly performed during preparation of the membrane-forming stock solution, and production of a PVA film with fewer foreign substances and defects is facilitated. On the other hand, when the volatile content of the film-forming dope is 95% by mass or less, the concentration of the film-forming dope does not become too low, and industrial PVA film formation becomes easy.

Examples of the film forming method for forming a PVA film using the above film forming undiluted solution include a cast film forming method, an extrusion film forming method, a wet film forming method, and a gel film forming method. law is preferred These film forming methods may be employed singly or in combination of two or more. Among these film forming methods, the cast film forming method or the extrusion film forming method is preferable in terms of obtaining a PVA film having uniform thickness and width and good physical properties.

The specific film forming method is not particularly limited, but by using a T-shaped slit die, a hopper plate, an I-die, a lip coater die or the like, the film forming undiluted solution is uniformly coated on the circumferential surface of a rotating heated roll (or belt) After discharging, volatile components are evaporated from one side of the film discharged on this roll (or belt) and dried to form a PVA film, or after drying in this way, addition is added on the circumferential surface of one or a plurality of rotating rolls A method of forming a PVA film into a film by drying with or passing through a hot air drying device and further drying is exemplified.

The surface temperature of the roll used for film forming can be, for example, within a range of 50°C or higher and 100°C or lower. Further, the drying temperature in the case of discharging the film-forming undiluted solution onto the belt can be, for example, within a range of 50°C or higher and 100°C or lower.

The PVA film formed as described above has a temperature of 70°C or more and 100°C or less (preferably 75°C or more and 100°C or less), and a relative humidity of 60% or more and 100% or less (preferably 80% or more and 100% or less). ) The PVA film of the present invention can be produced smoothly by adopting a method of reducing the swelling degree to 110% or more and less than 190% by contacting with a phosphorus gas (hereinafter sometimes referred to as “gas contact treatment”). Here, the type of gas having the relative humidity is not particularly limited, and examples thereof include water vapor itself, air containing water vapor, nitrogen containing water vapor, and argon containing water vapor.

In the above gas contact treatment, the contact time with the gas is preferably 2 minutes or more, more preferably 3 minutes or more, and further 4 minutes or more in order to keep the swelling degree within the range of 110% or more and less than 190%. desirable. The upper limit of the contact time is not particularly limited, but considering productivity and the like, the contact time is preferably 1 hour or less, more preferably 15 minutes or less, and still more preferably 12 minutes or less. Further, from the viewpoint of sufficiently exhibiting the effect of the above gas contact treatment, the degree of swelling of the PVA film before gas contact treatment is preferably 200% or more, more preferably 205% or more, and still more preferably 210% or more. The upper limit of the degree of swelling of the PVA film before gas contact treatment is not particularly limited, but considering productivity and the like, it is preferably less than 250%, more preferably 230% or less, and even more preferably 225% or less.

After contacting with the above gas, further drying can be performed to obtain the target PVA film. Here, in order to prevent that the degree of swelling finally obtained becomes too low or a softening point temperature rises, it is preferable to carry out the said drying at a lower temperature. The temperature of the drying may be, for example, 60°C or lower, preferably 50°C or lower, although depending on the degree of swelling of the PVA film after gas contact treatment and the like.

The volatile content of the PVA film finally obtained as described above is preferably within the range of 1% by mass or more and 5% by mass or less, and the volatile content is more preferably 2% by mass or more, and is 4% by mass or less. it is more preferable

The use of the PVA film of the present invention is not particularly limited, and examples thereof include a film for drug packaging, a base film for hydraulic pressure transfer, a base film for embroidery, a release film for molding artificial marble, a film for seed packaging, and a bag for containing dirt. Although it can be used for various water-soluble films such as films, the PVA film of the present invention, despite its thinness, does not easily generate folds at the ends after immersion in a water bath, and has a low stress during stretching. It is preferable to use it as a raw film for producing an optical film such as a polarizing film or a retardation film, because it does not easily cause breakage in stretching, and in that a polarizing film having high polarization performance can be easily produced, particularly It is preferable to use as a raw film for manufacturing a polarizing film.

The method in particular at the time of manufacturing a polarizing film using the PVA film of this invention as a raw film is not restrict|limited, You may employ|adopt any method conventionally employ|adopted. As such a method, for example, a method of uniaxial stretching using the PVA film of the present invention is exemplified. Specifically, with respect to the PVA film of the present invention, swelling, dyeing, uniaxial stretching and, if necessary, According to the method, a method of additionally performing a fixation treatment, drying, heat treatment, and the like may be exemplified. In this case, the order of each treatment, such as swelling, dyeing, uniaxial stretching, and a fixing treatment, is not particularly limited, and one or two or more treatments may be performed simultaneously. Moreover, one or two or more of each process can also be performed twice or more.

Swelling can be performed by immersing the PVA film in water. The temperature of the water when immersed in water is preferably within the range of 20°C or more and 40°C or less, more preferably within the range of 22°C or more and 38°C or less, and even more preferably within the range of 25°C or more and 35°C or less. do. Moreover, as time to immerse in water, it is preferable to exist in the range of 0.1 minute or more and 5 minutes or less, for example, and it is more preferable to exist in the range of 0.5 minute or more and 3 minutes or less. In addition, the water at the time of immersion in water is not limited to pure water, An aqueous solution in which various components were dissolved may be sufficient, and a mixture of water and an aqueous medium may be sufficient as it.

It is preferable to perform dyeing using an iodine-type dye, and as a dyeing time, any stage before uniaxial stretching, at the time of uniaxial stretching, and after uniaxial stretching may be sufficient. Dyeing is generally carried out by immersing the PVA film in a solution (particularly aqueous solution) containing iodine-potassium iodide as a dyeing bath, and such a dyeing method is preferably employed in the present invention as well. The concentration of iodine in the dyeing bath is preferably in the range of 0.01% by mass or more and 0.5% by mass or less, and the concentration of potassium iodide is preferably in the range of 0.01% by mass or more and 10% by mass or less. In addition, the temperature of the dyeing bath is preferably 20°C or more and 50°C or less, particularly 25°C or more and 40°C or less.

Uniaxial stretching may be performed by either a wet stretching method or a dry stretching method. In the case of the wet stretching method, it may be carried out in an aqueous solution containing boric acid, or in the above dyeing bath or in a fixing treatment bath described later. In addition, in the case of the dry stretching method, it can be carried out in air using a PVA film after water absorption. Among these, a wet stretching method is preferable, and uniaxial stretching in an aqueous solution containing boric acid is more preferable. The concentration of boric acid in the aqueous solution of boric acid is preferably in the range of 0.5% by mass or more and 6.0% by mass or less, more preferably in the range of 1.0% by mass or more and 5.0% by mass or less, and in the range of 1.5% by mass or more and 4.0% by mass or less. It is particularly preferred that it is within. Moreover, boric acid aqueous solution may contain potassium iodide, and it is preferable to carry out the concentration in the range of 0.01 mass % or more and 10 mass % or less.

The stretching temperature in uniaxial stretching is preferably within the range of 30°C or more and 90°C or less, more preferably within the range of 40°C or more and 80°C or less, and particularly preferably within the range of 50°C or more and 70°C or less. .

Moreover, as for the draw ratio in uniaxial stretching, it is preferable that it is 5 times or more, it is more preferable that it is 5.5 times or more, and it is especially preferable that it is 6 times or more from the point of the polarization performance of the polarizing film obtained. The upper limit of the draw ratio is not particularly limited, but the draw ratio is preferably 8 times or less.

In manufacture of a polarizing film, it is preferable to perform a fixation process in order to make adsorption|suction of dye (iodine etc.) to a PVA film strong. As a fixation treatment bath used for a fixation treatment, the aqueous solution containing 1 type(s) or 2 or more types of boron compounds, such as boric acid and borax, can be used. Moreover, you may add an iodine compound or a metal compound to the fixation treatment bath as needed. The concentration of the boron compound in the fixation treatment bath is generally 2% by mass or more and 15% by mass or less, and preferably 3% by mass or more and 10% by mass or less. The temperature of the fixed treatment bath is preferably 15°C or more and 60°C or less, particularly 25°C or more and 40°C or less.

Drying is preferably carried out at 30°C or higher and 150°C or lower, and more preferably 50°C or higher and 130°C or lower. When the moisture content of the polarizing film is reduced to 10% or less by drying, tension is applied to the polarizing film and heat treatment is performed at a temperature of 80°C or more and 120°C or less for about 1 minute or more and 5 minutes or less to obtain a polarizing film with better dimensional stability and durability. can be obtained.

The polarizing film obtained as described above is usually used as a polarizing plate by bonding a protective film that is optically transparent and has mechanical strength to both surfaces or one side thereof. As the protective film, a cellulose triacetate (TAC) film, a cycloolefin polymer (COP) film, a cellulose acetate-butyrate (CAB) film, an acrylic film, a polyester film, or the like is used. Moreover, as an adhesive for bonding, a PVA-type adhesive and a urethane-type adhesive are mentioned, but a PVA-type adhesive is especially preferable.

After coating adhesives, such as an acrylic type, the polarizing plate obtained by doing it above can be bonded together to a glass substrate, and can be used as a component of LCD. At the same time, you may bond together with retardation film, a viewing angle improvement film, a brightness improvement film, etc.

Example

The present invention will be specifically described by the following examples, but the present invention is not limited at all by these examples. In addition, each measurement or evaluation method adopted in the following Examples and Comparative Examples is shown below.

[Measurement of swelling degree of PVA film]

A rectangular sample of 10 cm in the width direction and 20 cm in the length direction was cut from the central part in the width direction of the PVA film to be measured, and this sample was further cut into strips with a width of 2 to 3 mm and a length of 20 cm ( It was cut with 短冊狀. Thereafter, all of these strip-shaped samples were immersed as they were in 1,000 g of distilled water at 30°C. After being immersed for 30 minutes, a strip sample was taken out, centrifuged at 3,000 rpm for 5 minutes using a centrifuge (KOKUSAN XEM-KL-5886), and the mass after dehydration "N" (the sum of all the strip samples) was measured. Then, after drying the strip-shaped sample in a dryer at 105°C for 16 hours, the mass "M" (sum of all strip-shaped samples) was measured, and the degree of swelling was calculated by the following formula.

Degree of swelling (%) = 100 x N/M

[Measurement of softening point temperature of PVA film]

A square sample of 3 cm in the width direction and 3 cm in the length direction was cut from the central part in the width direction of the PVA film to be measured, and the sample was measured using an automatic softening point measuring device "EX-820" manufactured by Dai-ichi Rika Co., Ltd. The softening point temperature was measured. Specifically, the above sample was prepared by combining a stainless steel plate 1 mm thick and 3 cm wide with a circular hole with a diameter of 1 cm in the center and a rectangular hole 1 cm × 2 cm in the center with a thickness of 1 mm and It is placed between stainless steel plates with a width of 3 cm, and the stainless plate with a circular hole is installed on a mount with the upper surface facing, and a steel ball specified in JIS B 1501: 2009 is placed on the film located in the center of the circular hole. ) (name: 3/8 (9.525 mm in diameter), grade: G60, mass: 3.5 g ± 0.05 g). Subsequently, 750 ml of 25°C distilled water was added, the temperature was raised at 5°C per minute, and the temperature when the sample descended from the mount to a position of 25 mm was taken as the softening point temperature of the film.

[Measurement of elongation stress]

A sample of 3 cm in the width direction and 10 cm in the length direction is cut from the center of the PVA film to be measured in the width direction, and in order to uniaxially stretch in the length direction, this is placed between stretching jigs so that the distance between chucks is 1.5 cm, It was immersed in 30 degreeC distilled water for 1 minute. Thereafter, the stress with respect to the draw ratio was continuously measured while uniaxially stretching in the longitudinal direction at a stretching speed of 36 mm/min (240%/min). And the stress in case the draw ratio was 4.0 times was made into drawing stress. In addition, for the measurement of stress, an autograph (AG-I) manufactured by Shimadzu Corporation was used, and the measured force was divided by the cross-sectional area before stretching (sample thickness × sample width (3 cm)) to obtain stress.

[Evaluation of end fold after water bath immersion treatment]

Cut a sample of 5 cm in the width direction and 10 cm in the length direction from the center of the PVA film to be measured in the width direction, and uniaxially stretch it in the length direction. It was immersed in 30 degreeC distilled water. Immediately after immersion, it was uniaxially stretched for 1 minute in the longitudinal direction at a stretching speed of 50 mm/min (100%/min). Immediately after the stretching, the PVA film was pulled up from the water bath at a speed of 50 mm/sec, and the presence or absence of folds at the edges at that time was visually evaluated. Those with end folds were evaluated as "x", and those without end folds were evaluated as "○".

[Example 1]

100 parts by mass of PVA (saponified product of a homopolymer of vinyl acetate, degree of polymerization 2,400, degree of saponification 99.95 mol%), 10 parts by mass of glycerin as a plasticizer, 0.1 part by mass of sodium polyoxyethylene lauryl ether sulfate as a surfactant, and volatile fraction 66 consisting of water The film-forming dope solution of mass % was cast|flow_spreaded on a 95 degreeC metal drum, and it dried until the volatile matter rate became 10 mass %, and obtained the PVA film whose swelling degree is 212 %. Then, the temperature was 80 degreeC and the relative humidity was made to contact with the air of 90% for 5 minutes. Then, it was dried at a temperature of 50°C so that the swelling degree did not change substantially, and finally a PVA film having a volatile content of 3% by mass and a thickness of 30 µm was obtained.

The swelling degree of this PVA film was 166%, and the softening point temperature was 67.4 degreeC. In addition, as a result of measuring or evaluating the stretching stress and end folding after immersion in a water bath according to the method described above using this PVA film, the stretching stress was 14.3 MPa, and the evaluation result of end folding was "○".

[Example 2]

In Example 1, instead of contacting air with a temperature of 80°C and a relative humidity of 90% for 5 minutes, it was contacted with air with a temperature of 85°C and a relative humidity of 90% for 3 minutes. In the same manner as in 1, a PVA film having a volatile content of 3% by mass and a thickness of 30 μm was obtained.

The swelling degree of this PVA film was 179%, and the softening point temperature was 65.2 degreeC. In addition, as a result of measuring or evaluating the stretching stress and the edge folding after the water bath immersion treatment according to the above method using this PVA film, the stretching stress was 13.8 MPa, and the evaluation result of the edge folding was "○".

[Comparative Example 1]

100 parts by mass of PVA (saponified product of a homopolymer of vinyl acetate, degree of polymerization 2,400, degree of saponification 99.95 mol%), 10 parts by mass of glycerin as a plasticizer, 0.1 part by mass of sodium polyoxyethylene lauryl ether sulfate as a surfactant, and volatile fraction 66 consisting of water The film-forming dope solution of mass % was cast|flow_spreaded on a 95 degreeC metal drum, and it dried until the volatile matter rate became 5 mass %, and obtained the PVA film whose swelling degree is 212 %. Thereafter, heat treatment was performed by contacting with air having a temperature of 130°C (relative humidity of 1% or less) for 10 minutes, and finally a PVA film having a volatile content of 2% by mass and a thickness of 30 μm was obtained.

The swelling degree of this PVA film was 177%, and the softening point temperature was 69.2 degreeC. In addition, as a result of measuring the stretching stress according to the above method using this PVA film, it was very high as 20.0 MPa, and it was found that stretching breakage easily occurs during stretching.

[Comparative Example 2]

In Comparative Example 1, instead of contacting air having a temperature of 130° C. (relative humidity 1% or less) for 10 minutes, heat treatment was performed by contacting air with a temperature of 115° C. (relative humidity 1% or less) for 3 minutes. A PVA film having a volatile content of 3% by mass and a thickness of 30 µm was obtained in the same manner as in Comparative Example 1 except that it had been carried out.

The swelling degree of this PVA film was 198%, and the softening point temperature was 67.8 degreeC. In addition, as a result of measuring or evaluating the stretching stress and the end fold after immersion in a water bath according to the above method using this PVA film, the stretching stress is very high at 17.8 MPa, so that breakage in stretching tends to occur during stretching, and , The evaluation result of the end fold was also "x".

[Comparative Example 3]

In Comparative Example 1, instead of contacting air having a temperature of 130° C. (relative humidity 1% or less) for 10 minutes, heat treatment was performed by contacting air with a temperature of 95° C. (relative humidity 2% or less) for 1 minute. A PVA film having a volatile content of 3% by mass and a thickness of 30 µm was obtained in the same manner as in Comparative Example 1 except that it had been carried out.

The swelling degree of this PVA film was 231%, and the softening point temperature was 63.2 degreeC. In addition, as a result of measurement and evaluation of the stretching stress and edge folding after the water bath immersion treatment using this PVA film according to the above method, the stretching stress was 12.1 MPa, but the evaluation result of the edge folding was "x" at the time of stretching. It became a thing which the breakage of drawing tends to generate|occur|produce.

[Comparative Example 4]

In Example 1, instead of contacting air with a temperature of 80°C and a relative humidity of 90% for 5 minutes, instead of contacting air with a temperature of 70°C and a relative humidity of 90% for 1 minute. In the same manner as in 1, a PVA film having a volatile content of 3% by mass and a thickness of 30 μm was obtained.

The swelling degree of this PVA film was 209 %, and the softening point temperature was 65.4 degreeC. In addition, as a result of measurement and evaluation of the stretching stress and the edge folding after the water bath immersion treatment using this PVA film according to the above method, the stretching stress was 13.6 MPa, but the evaluation result of the edge folding was "x" at the time of stretching. It became a thing which the breakage of drawing tends to generate|occur|produce.

Claims (3)

A polyvinyl alcohol film having a swelling degree of 110% or more and less than 190% and a softening point temperature of 60°C or more and 68°C or less and a thickness of 50 μm or less. The manufacturing method of the optical film which has the process of uniaxially stretching using the polyvinyl alcohol film of Claim 1. According to claim 2,
A manufacturing method in which the optical film is a polarizing film.