JP6592509B2 - Polyvinyl alcohol film - Google Patents

Description

  The present invention relates to a polyvinyl alcohol film that is less likely to be stretched during stretching and is useful as a raw film for producing an optical film such as a polarizing film, and a method for producing an optical film using the same.

  A polarizing plate having a light transmission and shielding function is a basic component of a liquid crystal display (LCD) together with a liquid crystal that changes a polarization state of light. LCDs are used in a wide range of small devices such as calculators and watches, notebook computers, liquid crystal monitors, liquid crystal color projectors, liquid crystal televisions, in-vehicle navigation systems, mobile phones, and measuring devices used indoors and outdoors. . Among these LCD application fields, liquid crystal televisions, liquid crystal monitors, and the like are becoming larger and thinner, and as the glass used is thinner, the polarizing plate is also required to be thinner from the viewpoint of shrinkage stress.

  In general, a polarizing plate is obtained by dyeing, uniaxially stretching a polyvinyl alcohol film (hereinafter, “polyvinyl alcohol” may be abbreviated as “PVA”), and optionally further fixing with a boron compound or the like. After the production, it is produced by bonding a protective film such as a cellulose triacetate (TAC) film on the surface of the polarizing film. Therefore, it is required to produce a thin polarizing film using a thinner PVA film in order to achieve a thinner polarizing plate. The specific thickness of the PVA film is 50 μm or less, further 40 μm or less. Is required to be 30 μm or less.

JP 2006-342236 A

  By the way, when manufacturing an optical film using a thin PVA film, it is easy to generate | occur | produce extending | stretching at the time of uniaxial stretching compared with the case where a thick PVA film is used. This stretching breakage is considered to be caused by the occurrence of folds at the end of a thin PVA film after a water bath immersion treatment such as a swelling treatment or a dyeing treatment performed before uniaxially stretching the PVA film. A method for reducing the degree of swelling of the PVA film can be considered as a method for reducing the occurrence of the fold, but when the degree of swelling is simply lowered by a conventionally known method such as heat treatment, the softening point temperature is increased, There is a problem in that the stretching stress rises and the stretching stress increases, and this time the stretching stress frequently occurs due to the increasing stretching stress.

  A method for producing a PVA film by extruding an aqueous solution containing PVA from a T-type slit die and casting it on the outer peripheral surface of a rotating drum-type roll is known for the purpose of uniformity of thickness and suppression of contamination. However, the above problem cannot be solved even by this method.

  Therefore, although the present invention is a thin PVA film, it is difficult to bend at the end after the water bath immersion treatment, and the stress at the time of stretching is low. It aims at providing the PVA film which can manufacture an optical film with sufficient yield. Moreover, an object of this invention is to provide the manufacturing method of optical films, such as a polarizing film using the said PVA film.

  As a result of intensive studies to achieve the above object, the inventors of the present invention have developed a new PVA film having a low softening point temperature when the swelling degree of the PVA film is lowered to 110% or more and less than 190% while being in contact with water vapor. According to the PVA film, although it is a thin PVA film, it is difficult to bend at the end after the water bath immersion treatment, and the stress at the time of stretching is low. It was found that an optical film such as a polarizing film can be produced with good yield, and further studies were made based on the findings 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 production method of the above [2], wherein the optical film is a polarizing film;
About.

  According to the present invention, although it is a thin PVA film, it is difficult to bend at the end after the water bath immersion treatment, and the stress at the time of stretching is low. A PVA film capable of producing the above optical film with high yield and a method for producing an optical film using the same are provided.

The present invention is described in detail below.
The PVA film of the present invention has a thickness of 50 μm or less, a degree of swelling in the range of 110% to less than 190%, and a softening point temperature in the range of 60 ° C. to 68 ° C. Usually, when the degree of swelling 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 degree of swelling of the PVA film of the present invention is 110% or more. Despite being in a low range of less than 190%, the softening point temperature is different from the conventional PVA film in that the softening point temperature is also in a low range of 60 ° C. or higher and 68 ° C. or lower.

  The PVA film of the present invention needs to have a degree of swelling in 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 on the PVA film, and usually the heat treatment conditions are strengthened. Thus, the degree of swelling can be lowered. When the degree of swelling of the PVA film is less than 110%, the stress at the time of stretching increases, resulting in frequent stretching breaks. On the other hand, if the degree of swelling is 190% or more, the end portion is likely to be broken after the water bath immersion treatment, which is not preferable from the viewpoint of stretching. From such a viewpoint, the degree of swelling of the PVA film is preferably 130% or more, more preferably 150% or more, further preferably 160% or more, and particularly preferably 170% or more. Moreover, it is preferable that it is 185% or less, and 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 further 180% or less, the effect of the present invention is more remarkably exhibited.

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

  The PVA film of the present invention needs to have a softening point temperature in the range of 60 ° C. or higher and 68 ° C. or lower. When 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 becomes high, and stretching breakage 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, further preferably 64 ° C. or higher, and 67 ° C. or lower. Is preferable, and it is more preferable that it is 66 degrees C or less.

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

  Examples of the PVA constituting the PVA film of the present invention include vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate, vinyl benzoate, Examples thereof include those obtained by saponifying a polyvinyl ester obtained by polymerizing one or more vinyl esters such as propenyl. Among the above vinyl esters, vinyl acetate is preferable from the viewpoints of ease of production of PVA, availability, cost, and the like.

  The polyvinyl ester is preferably obtained using only one or two or more vinyl esters as monomers, and more preferably obtained using only one vinyl ester as a monomer. However, as long as it does not impair the effects of the present invention, it may be a copolymer of one or more vinyl esters and other monomers copolymerizable therewith.

  Examples of other monomers copolymerizable with the vinyl ester include, for example, α-olefins having 2 to 30 carbon atoms such as ethylene, propylene, 1-butene and isobutene; (meth) acrylic acid or a salt thereof; (Meth) methyl acrylate, (meth) ethyl acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, ( (Meth) acrylic acid esters such as t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate and octadecyl (meth) acrylate; (meth) acrylamide; N-methyl ( (Meth) acrylamide, N-ethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, diacetone (meth) acryl (Meth) acrylamide derivatives such as amide, (meth) acrylamide propanesulfonic acid or salts thereof, (meth) acrylamidepropyldimethylamine or salts thereof, N-methylol (meth) acrylamide or derivatives thereof; N-vinylformamide, N-vinyl N-vinylamides such as acetamide and N-vinylpyrrolidone; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, etc. Vinyl ether; vinyl cyanide such as (meth) acrylonitrile; halogenated vinyl such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride; vinegar Allyl compounds such as allyl acid and allyl chloride; maleic acid or salts thereof, esters or acid anhydrides; itaconic acid or salts thereof, esters or acid anhydrides; vinylsilyl compounds such as vinyltrimethoxysilane; unsaturated sulfonic acids or salts thereof And so on. Said polyvinyl ester can have a structural unit derived from 1 type, or 2 or more types of an above described other monomer. When the polyvinyl ester is a copolymer of one or more vinyl esters and the other monomer, the polyvinyl ester is only a vinyl ester and a C2-C30 α-olefin as a monomer. It is preferable that the polymer is obtained using only vinyl ester and ethylene as monomers.

The proportion of structural units derived from the other monomers described above in the polyvinyl ester is preferably 15 mol% or less based on the number of moles of all structural units constituting the polyvinyl ester, and is preferably 10 mol%. More preferably, it is more preferably 5 mol% or less.
In particular, when the other monomer described above is a monomer that may promote water solubility of the obtained PVA, such as (meth) acrylic acid or unsaturated sulfonic acid, the obtained PVA In order to prevent PVA from dissolving when the film is used as a raw film for producing an optical film, the proportion of structural units derived from these monomers in the polyvinyl ester Based on the number of moles of the structural unit, it is preferably 5 mol% or less, and more preferably 3 mol% or less.

  The PVA may be modified with one or two or more types of graft copolymerizable monomers as long as the effects of the present invention are not significantly impaired. Examples of the graft copolymerizable monomer include unsaturated carboxylic acids or derivatives thereof; unsaturated sulfonic acids or derivatives thereof; α-olefins having 2 to 30 carbon atoms, and the like. The proportion of structural units derived from the graft copolymerizable monomer in PVA is preferably 5 mol% or less based on the number of moles of all structural units constituting PVA.

  In the PVA, a part of the hydroxyl groups may be cross-linked or may not be cross-linked. The PVA may have a hydroxyl group partially reacted with an aldehyde compound such as acetaldehyde or butyraldehyde to form an acetal structure, or may not react with these compounds to form an acetal structure. Also good.

  The degree of polymerization of the PVA is not particularly limited, but is preferably in the range of 1,500 or more and 6,000 or less, the degree of polymerization is more preferably 1,800 or more, and 2,000 or more. Is more preferably 5,000 or less, and further preferably 4,000 or less. When the degree of polymerization is not less than the above lower limit, the durability of the obtained optical film is improved. On the other hand, when the degree of polymerization is not more than the above lower limit, the production cost can be reduced, and the process passability during film formation can be improved. In addition, the polymerization degree of PVA as used in this specification means the average degree of polymerization measured according to description of JIS K6726-1994.

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

  The PVA film of the present invention preferably contains a plasticizer. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylolpropane, and the PVA film of the present invention One or more of these plasticizers can be included. Among these, glycerin is preferable in terms of the effect of improving stretchability.

  The content of the plasticizer in the PVA film of the present invention is preferably in the range of 1 to 20 parts by mass, preferably in the range of 3 to 17 parts by mass with respect to 100 parts by mass of PVA contained therein. It is more preferable that it is within the range of 5 parts by mass or more and 15 parts by mass or less. When the content is 1 part by mass or more, the stretchability of the PVA film can be further improved. On the other hand, when the content is 20 parts by mass or less, it can be suppressed that the PVA film becomes too flexible and the handleability is lowered.

  In addition, when the PVA film is produced using a film-forming stock solution for producing a PVA film, which will be described later, the film-forming property is improved and the occurrence of thickness unevenness of the PVA film is suppressed, and the film is rolled. When a belt or belt is used, the PVA film can be easily peeled off from these rolls or belts. Therefore, it is preferable to include a surfactant in the film-forming stock solution. When a PVA film is produced from a film-forming stock solution containing a surfactant, the PVA film may contain a surfactant. Although the kind of said surfactant is not specifically limited, From a peelable viewpoint from a roll, a belt, etc., an anionic surfactant or a nonionic surfactant is preferable, and a nonionic surfactant is especially preferable. Surfactant may be used individually by 1 type, or may use 2 or more types together.

  Suitable examples of the anionic surfactant include carboxylic acid types such as potassium laurate; sulfate ester types such as polyoxyethylene lauryl ether sulfate and octyl sulfate; and sulfonic acid types such as dodecylbenzene sulfonate.

  Nonionic surfactants include, for example, alkyl ether types such as polyoxyethylene oleyl ether; alkylphenyl ether types such as polyoxyethylene octylphenyl ether; alkyl ester types such as polyoxyethylene laurate; polyoxyethylene laurylamino Alkylamine type such as ether; alkylamide type such as polyoxyethylene lauric acid amide; polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether; alkanolamide type such as lauric acid diethanolamide and oleic acid diethanolamide; polyoxy An allyl phenyl ether type such as alkylene allyl phenyl ether is preferred.

  When the surfactant is contained in the film-forming stock solution, the content of the surfactant in the film-forming stock solution, and thus the content of the surfactant in the PVA film, is 100 parts by mass of PVA contained in the film-forming stock solution or PVA film. On the other hand, it is preferably within a range of 0.01 parts by mass or more and 0.5 parts by mass or less, more preferably within a range of 0.02 parts by mass or more and 0.3 parts by mass or less, and 0.05 parts by mass. It is particularly preferable that the amount be in the range of 0.1 part 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, the film forming property and the 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, the surfactant bleeds out on the surface of the PVA film, resulting in blocking, and handling properties are reduced. Can be suppressed.

  The PVA film of the present invention may be composed only of PVA, or may be composed only of PVA and the above-described plasticizer and / or surfactant, but if necessary, an antioxidant, an antifreezing agent, pH You may contain other components other than above-mentioned PVA, a plasticizer, and surfactant, such as a regulator, a masking agent, a coloring inhibitor, and an oil agent.

  The PVA content in the PVA film is preferably in the range of 50% by mass to 100% by mass, more preferably in the range of 80% by mass to 100% by mass, and more preferably 85% by mass to 100%. More preferably, it is in the range of mass% or less.

  The thickness of the PVA film of the present invention is such that a thin polarizing film can be obtained, the shrinking force of the polarizing film using the polarizing film and thus the polarizing film is reduced, and the thin glass laminated is prevented from warping. In view of the above, it is necessary to be 50 μm or less, preferably 40 μm or less, more preferably 35 μm or less, further preferably 30 μm or less, 25 μm or less, 15 μm or less, and further 10 μm. It may be the following. In particular, when the thickness of the PVA film is 40 μm or less, the effects of the present invention are more remarkably exhibited. Although there is no restriction | limiting in particular in the minimum of the thickness of a PVA film, Since the polarizing film can be manufactured more smoothly, it is preferable that the said thickness is 1 micrometer or more, and it is more preferable that it is 3 micrometers or more.

  The shape of the PVA film of the present invention is not particularly limited, but a more uniform PVA film can be easily produced continuously, and it can be continuously produced even when an optical film such as a polarizing film is produced using the PVA film. It is preferable that the film is a long film. The length of the long film (length in the length direction) is not particularly limited, and can be appropriately set according to the application, 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 set as appropriate according to the use of the PVA film or an optical film produced from the PVA film. Further, the enlargement of the screen of the liquid crystal monitor is progressing, and it is suitable for these uses when the width of the PVA film is 2 m or more, more preferably 3 m or more, and further preferably 4 m or more. On the other hand, if the width of the PVA film is too wide, it tends to be difficult to perform uniaxial stretching uniformly when an optical film is produced with a device that has been put to practical use. Therefore, the width of the PVA film is 7 m or less. Preferably there is.

  There is no particular limitation on the form of the PVA film, either in the form of a single layer or in the form of a laminate such as a PVA film formed on a thermoplastic resin film by a coating method or the like. However, a single-layered form is preferred from the viewpoints of the effects of the present invention being more prominent, the complexity of laminating (coating and the like) work, and the cost of the thermoplastic resin film.

  Although there is no restriction | limiting in particular in the manufacturing method for manufacturing the PVA film of this invention, Since the PVA film of this invention can be manufactured smoothly, the film forming stock solution containing PVA is dried and the PVA film which has the said thickness After manufacturing, a gas having a temperature of 70 ° C. or higher and 100 ° C. or lower (preferably 75 ° C. or higher and 100 ° C. or lower) and a relative humidity of 60% or higher and 100% or lower (preferably 80% or higher and 100% or lower) is contacted. It is preferable to employ a method of reducing the degree of swelling to 110% or more and less than 190%.

  Examples of the film-forming stock solution containing PVA (film-forming stock solution for producing a PVA film) include, for example, the above-described PVA constituting the PVA film, and, if necessary, a plasticizer, a surfactant and other components. A film-forming stock solution in which one or more of them are dissolved in a liquid medium, PVA, and optionally one or two of a plasticizer, a surfactant, other components, and a liquid medium Examples include a film-forming stock solution in which PVA is melted. When the film-forming stock solution contains at least one of a plasticizer, a surfactant and other components, it is preferable that these components are uniformly mixed.

  Examples of the liquid medium used for the preparation of the membrane forming stock solution include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol. , Trimethylolpropane, ethylenediamine, diethylenetriamine and the like, and one or more of them can be used. Among these, water is preferable from the viewpoint of environmental load and recoverability.

  The volatile fraction of the film-forming stock solution (the content ratio of volatile components such as a liquid medium removed by volatilization or evaporation during film formation in the film-forming stock solution) varies depending on the film-forming method, film-forming conditions, etc., but 50 mass % In the range of 95% to 95% by weight, more preferably in the range of 55% to 90% by weight, and still more preferably in the range of 60% to 85% by weight. . When the volatile fraction of the film-forming stock solution is 50% by mass or more, the viscosity of the film-forming stock solution does not become too high, and filtration and defoaming are smoothly performed during preparation of the film-forming stock solution, and there are few foreign matters and defects. Film production is facilitated. On the other hand, when the volatile fraction of the film-forming stock solution is 95% by mass or less, the concentration of the film-forming stock solution does not become too low, and an industrial PVA film can be easily formed.

  Examples of the film forming method for forming a PVA film using the above-described film forming stock solution include a cast film forming method, an extrusion film forming method, a wet film forming method, a gel film forming method, and the like. A membrane method and an extrusion film forming method are preferred. These film forming methods may be used alone 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 because a PVA film having uniform thickness and width and good physical properties can be obtained.

  Although it does not specifically limit as a concrete film forming method, On the surrounding surface of the heated roll (or belt) which rotates a film forming undiluted solution using T type slit die, a hopper plate, I-die, a lip coater die, etc. The volatile component is evaporated from one side of the film discharged onto the roll (or belt) and dried to form a PVA film, or after drying in this way, one piece Alternatively, there is a method of forming a PVA film by further drying on the peripheral surfaces of a plurality of rotating rolls, or by passing through a hot air drying apparatus and further drying.

  As surface temperature of the roll used for film forming, it can be in the range of 50 to 100 degreeC, for example. Moreover, as a drying temperature in the case of discharging a film forming undiluted solution on a belt, it can be in the range of 50 degreeC or more and 100 degrees C or less, for example.

  The PVA film formed as described above has a temperature of 70 ° C. to 100 ° C. (preferably 75 ° C. to 100 ° C.) and a relative humidity of 60% to 100% (preferably 80% to 100%). The following method is used to reduce the degree of swelling to 110% or more and less than 190% (hereinafter sometimes referred to as “gas contact treatment”), thereby smoothening the PVA film of the present invention. Can be manufactured. Here, the type of gas having the above relative humidity is not particularly limited, and examples include water vapor itself, air containing water vapor, nitrogen containing water vapor, and argon containing water vapor.

  In the gas contact treatment, the contact time with the gas is preferably 2 minutes or more, and more preferably 3 minutes or more in order to make the degree of swelling within a range of 110% or more and less than 190%. More preferably, it is 4 minutes or more. The upper limit of the contact time is not particularly limited, but in consideration of productivity, the contact time is preferably 1 hour or less, more preferably 15 minutes or less, and further preferably 12 minutes or less. . From the viewpoint of sufficiently exerting the effect of the gas contact treatment, the degree of swelling of the PVA film before the gas contact treatment is preferably 200% or more, more preferably 205% or more, and 210% or more. More preferably. The upper limit of the degree of swelling of the PVA film before the gas contact treatment is not particularly limited, but considering productivity, it is preferably less than 250%, more preferably 230% or less, and 225% or less. More preferably.

  After making it contact with said gas, it can dry further and the target PVA film can be obtained. Here, the drying is preferably performed at a lower temperature in order to prevent the degree of swelling finally obtained from becoming too low and the softening point temperature from rising. The drying temperature may be 60 ° C. or less, preferably 50 ° C. or less, for example, although it depends on the degree of swelling of the PVA film after the gas contact treatment.

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

  The use of the PVA film of the present invention is not particularly limited. For example, a film for drug packaging, a base film for hydraulic transfer, a base film for embroidery, a release film for molding artificial marble, a film for seed packaging, and a bag for waste container Although it can be used for various water-soluble film applications such as a film, the PVA film of the present invention is thin, but is less likely to bend at the end after immersion in a water bath and has low stress during stretching. The film is preferably used as a raw film for producing an optical film such as a polarizing film or a retardation film because it is difficult to cause stretching during stretching, and a polarizing film having high polarization performance can be easily produced. Since it can do, it is preferable to use as a raw film especially for manufacturing a polarizing film.

  The method for producing a polarizing film using the PVA film of the present invention as a raw film is not particularly limited, and any method conventionally employed may be employed. Examples of such a method include a method of uniaxial stretching using the PVA film of the present invention, and specifically, swelling, dyeing, uniaxial stretching, and as required for the PVA film of the present invention. Furthermore, a method of performing fixing treatment, drying, heat treatment, etc. can be mentioned. In this case, the order of each treatment such as swelling, dyeing, uniaxial stretching, and fixing treatment is not particularly limited, and one or two or more treatments can be performed simultaneously. Also, one or more of each process can be performed twice or more.

  The swelling can be performed by immersing the PVA film in water. The temperature of the water when immersed in water is preferably within a range of 20 ° C. or higher and 40 ° C. or lower, more preferably within a range of 22 ° C. or higher and 38 ° C. or lower, and 25 ° C. or higher and 35 ° C. or lower. More preferably, it is within the range. 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 immersing in water is not limited to a pure water, The aqueous solution in which various components melt | dissolved may be sufficient, and the mixture of water and an aqueous medium may be sufficient.

  Dyeing is preferably performed using an iodine-based dye, and the dyeing time may be any stage before uniaxial stretching, during uniaxial stretching, or after uniaxial stretching. Dyeing is generally performed by immersing the PVA film in a solution (particularly an aqueous solution) containing iodine-potassium iodide as a dyeing bath, and such a dyeing method is also preferably used in the present invention. . The concentration of iodine in the dyeing bath is preferably in the range of 0.01% by mass to 0.5% by mass, and the concentration of potassium iodide is in the range of 0.01% by mass to 10% by mass. Is preferred. The temperature of the dyeing bath is preferably 20 ° C. or more and 50 ° C. or less, and particularly preferably 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 drawing method, it can be carried out in an aqueous solution containing boric acid, or can be carried out in the dyeing bath described above or in a fixing treatment bath described later. Moreover, in the case of the dry-type extending | stretching method, it can carry out in air using the PVA film after water absorption. Among these, the wet stretching method is preferable, and uniaxial stretching is more preferable in an aqueous solution containing boric acid. The concentration of boric acid in the boric acid aqueous solution is preferably in the range of 0.5% by mass to 6.0% by mass, and preferably in the range of 1.0% by mass to 5.0% by mass. More preferably, it is particularly preferably in the range of 1.5% by mass or more and 4.0% by mass or less. Further, the boric acid aqueous solution may contain potassium iodide, and the concentration is preferably in the range of 0.01% by mass to 10% by mass.

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

  In addition, the draw ratio in uniaxial stretching is preferably 5 times or more, more preferably 5.5 times or more, and particularly preferably 6 times or more from the viewpoint of the polarizing performance of the polarizing film to be obtained. The upper limit of the draw ratio is not particularly limited, but the draw ratio is preferably 8 times or less.

  In producing the polarizing film, it is preferable to perform a fixing treatment in order to strengthen the adsorption of the dye (iodine or the like) to the PVA film. As the fixing treatment bath used for the fixing treatment, an aqueous solution containing one or more of boron compounds such as boric acid and borax can be used. Moreover, you may add an iodine compound and a metal compound in a fixed treatment bath as needed. The concentration of the boron compound in the fixing treatment bath is generally 2% by mass or more and 15% by mass or less, and particularly preferably about 3% by mass or more and 10% by mass or less. The temperature of the fixing treatment bath is preferably 15 ° C. or more and 60 ° C. or less, particularly preferably 25 ° C. or more and 40 ° C. or less.

  Drying is preferably performed at 30 ° C. or higher and 150 ° C. or lower, and more preferably 50 ° C. or higher and 130 ° C. or lower. When the polarizing film has a moisture content of 10% or less due to drying, tension is applied to the polarizing film and heat treatment is performed at 80 ° C. or higher and 120 ° C. or lower for about 1 minute to 5 minutes, dimensional stability, durability, etc. Can be obtained.

  The polarizing film obtained as described above is usually used as a polarizing plate by bonding a protective film having optical transparency and mechanical strength on both sides or one side. As the protective film, a cellulose triacetate (TAC) film, a cycloolefin polymer (COP) film, an acetic acid / cellulose butyrate (CAB) film, an acrylic film, a polyester film, or the like is used. Examples of the adhesive for bonding include PVA adhesives and urethane adhesives, among which PVA adhesives are suitable.

  The polarizing plate obtained as described above can be used as a component of an LCD after being coated with an acrylic adhesive or the like and then bonded to a glass substrate. At the same time, it may be bonded to a retardation film, a viewing angle improving film, a brightness improving film, or the like.

  The present invention will be specifically described with reference to the following examples, but the present invention is not limited to these examples. In addition, each measurement thru | or evaluation method employ | adopted in the following example and the comparative example are 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 out from the central portion in the width direction of the PVA film to be measured, and this sample was further cut into a strip shape having a width of 2 to 3 mm and a length of 20 cm. . Thereafter, all the strip-shaped samples were immersed in 1,000 g of distilled water at 30 ° C. as they were. Remove the strip-shaped sample after immersion for 30 minutes, spin-dry using a centrifuge (KOKUSAN XEM-KL-5886) for 5 minutes at 3,000 rpm, and dehydrated mass “N” (all the strip-shaped samples Total). Then, after drying the strip-shaped sample for 16 hours with 105 degreeC dryer, mass "M" (total of all the strip-shaped samples) was measured, and swelling degree was computed by the following formula.
Swelling degree (%) = 100 × 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 is cut out from the central portion in the width direction of the PVA film to be measured, and an automatic softening point measuring device “EX-820” manufactured by Daiichi Rika Co., Ltd. is used. The softening point temperature of the sample was measured. Specifically, the above sample is made into a 1 mm thick 3 cm square stainless steel plate with a 1 cm diameter circular hole in the center and a 1 mm thick 3 cm square stainless steel plate with a 1 cm × 2 cm rectangular hole in the center. A stainless steel plate with a circular hole in between is installed on the base with the upper surface facing upward, and a steel ball (nominal: 3/8 (diameter 9) is defined on JIS B 1501: 2009 on the film located in the center of the circular hole. 525 mm), 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 was lowered to a position of 25 mm from the gantry was defined as the softening point temperature of the film.

[Measurement of stretching stress]
A sample of 3 cm in the width direction and 10 cm in the length direction is cut out from the center in the width direction of the PVA film to be measured, and stretched uniaxially in the length direction so that the gap between the chucks is 1.5 cm. It was sandwiched between jigs and immersed in distilled water at 30 ° C. for 1 minute. Then, the stress with respect to the draw ratio was continuously measured while uniaxially stretching in the length direction at a stretching speed of 36 mm / min (240% / min). And the stress when a draw ratio is 4.0 times was made into drawing stress. 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)). Stress was used.

[Evaluation of edge break after water bath immersion treatment]
A 5 cm long and 10 cm long sample is cut out from the central portion in the width direction of the PVA film to be measured, and in order to stretch uniaxially in the length direction, it is stretched so that the gap between the chucks is 5 cm. And immersed in distilled water at 30 ° C. Immediately after the immersion, the film was uniaxially stretched in the length direction for 1 minute at a stretching speed of 50 mm / min (100% / min). Immediately after stretching, the PVA film was pulled up from the water bath at a speed of 50 mm / second, and the presence or absence of bending at the end was visually evaluated. The case where the end portion was broken was evaluated as “×”, and the case where there was no end portion was evaluated as “◯”.

[Example 1]
100 parts by weight of PVA (saponified vinyl acetate homopolymer, degree of polymerization 2,400, degree of saponification 99.95 mol%), 10 parts by weight of glycerin as a plasticizer, sodium polyoxyethylene lauryl ether sulfate as a surfactant 0 A PVA having a volatile content of 66% by mass consisting of 1 part by mass and water is cast on a metal drum at 95 ° C. and dried until the volatile content reaches 10% by mass, and the degree of swelling is 212%. A film was obtained. Then, it was made to contact for 5 minutes with the air whose temperature is 80 degreeC and relative humidity is 90%. Subsequently, it was dried at a temperature of 50 ° C. so that the degree of swelling 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 ° C. Moreover, when measurement or evaluation of the end stress after the immersion stress and the water bath immersion treatment was performed according to the above-described method using this PVA film, the stretch stress was 14.3 MPa, and the evaluation result of the end bend was “ ○ ”.

[Example 2]
In Example 1, the temperature was 80 ° C. and the humidity was 90% relative to air for 5 minutes, but the temperature was 85 ° C. and the humidity was 90% relative humidity for 3 minutes. Obtained a PVA film having a volatile content of 3% by mass and a thickness of 30 μm in the same manner as in Example 1.
The swelling degree of this PVA film was 179%, and the softening point temperature was 65.2 ° C. Moreover, when measurement or evaluation of the end stress after the immersion stress and the water bath immersion treatment was performed according to the above-described method using this PVA film, the stretch stress was 13.8 MPa, and the evaluation result of the end bend was “ ○ ”.

[Comparative Example 1]
100 parts by weight of PVA (saponified vinyl acetate homopolymer, degree of polymerization 2,400, degree of saponification 99.95 mol%), 10 parts by weight of glycerin as a plasticizer, sodium polyoxyethylene lauryl ether sulfate as a surfactant 0 A PVA having a volatilization ratio of 66% by mass comprising 1 part by mass and water is cast on a metal drum at 95 ° C. and dried to a volatile content of 5% by mass, and the degree of swelling is 212%. A film was obtained. 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 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 ° C. Further, when the stretching stress was measured using this PVA film according to the method described above, it was very high as 20.0 MPa, and stretching breakage was likely to occur during stretching.

[Comparative Example 2]
In Comparative Example 1, instead of contacting with air having a temperature of 130 ° C. (relative humidity is 1% or less) for 10 minutes, contacting with air having a temperature of 115 ° C. (relative humidity is 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 heat treatment was performed.
The swelling degree of this PVA film was 198%, and the softening point temperature was 67.8 ° C. In addition, when this PVA film was used for the measurement and evaluation of the stretching stress and the end fold after the water bath immersion treatment according to the method described above, the stretching stress was as high as 17.8 MPa, and stretching breakage occurred during stretching. In addition, the evaluation result of edge breakage was also “x”.

[Comparative Example 3]
In Comparative Example 1, instead of contacting with air having a temperature of 130 ° C. (relative humidity of 1% or less) for 10 minutes, contacting with air having a temperature of 95 ° C. (relative humidity of 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 heat treatment was performed.
The swelling degree of this PVA film was 231%, and the softening point temperature was 63.2 ° C. Moreover, when the measurement or evaluation of the end stress after the immersion stress and the water bath immersion treatment was performed according to the above-described method using this PVA film, the extension stress was 12.1 MPa. Was “x”, and the film was easily stretched during stretching.

[Comparative Example 4]
In Example 1, instead of contacting with air having a temperature of 80 ° C. and a relative humidity of 90% for 5 minutes, except contacting with air having a temperature of 70 ° C. and a relative humidity of 90% for 1 minute. Obtained a PVA film having a volatile content of 3% by mass and a thickness of 30 μm in the same manner as in Example 1.
The swelling degree of this PVA film was 209%, and the softening point temperature was 65.4 ° C. Moreover, when the measurement and evaluation of the end stress after the immersion stress and the water bath immersion treatment were performed according to the above-described method using this PVA film, the extension stress was 13.6 MPa. Was “x”, and the film was easily stretched during stretching.

Claims (3)

  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.   The manufacturing method of the optical film which has the process of carrying out uniaxial stretching using the polyvinyl alcohol film of Claim 1.   The manufacturing method of Claim 2 whose optical film is a polarizing film.