JP6571955B2 - 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 an optical film such as a polarizing film obtained using the polyvinyl alcohol film. About.

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. Many polarizing plates have a structure in which a protective film such as a cellulose triacetate (TAC) film is bonded to the surface of a polarizing film. As a polarizing film constituting the polarizing plate, a polyvinyl alcohol film (hereinafter referred to as “polyvinyl”). alcohol "and" PVA "and is sometimes abbreviated) iodine dye stretched film was oriented uniaxially stretched (I ₃ ^- and I ₅ ^-, etc.), such as a dichroic organic dye dichroic dye is adsorbed What you are doing is the mainstream. Such a polarizing film can be obtained by uniaxially stretching a PVA film preliminarily containing a dichroic dye, adsorbing a dichroic dye simultaneously with uniaxial stretching of the PVA film, or dichroic after uniaxially stretching the PVA film. Manufactured by adsorbing dyes.

  LCDs are used in a wide range of devices such as small devices such as calculators and wrist 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. However, in recent years, it is often used for mobile applications such as small notebook personal computers and mobile phones, and there is an increasing demand for thinner polarizing plates.

  One way to reduce the thickness of the polarizing plate is to reduce the thickness of the polarizing film. To this end, it is conceivable to reduce the thickness of the PVA film that is the raw material of the polarizing film. However, a thin PVA film is likely to be stretched at the time of stretching, and the productivity and yield of the polarizing film are lowered, which leads to high costs.

  As a technique for producing a thin polarizing film without causing breakage during stretching, a method is known in which a thin PVA layer is formed on a thermoplastic resin film by a coating method and the laminate is stretched (for example, patents). See references 1 and 2).

Japanese Patent No. 4804588 Japanese Patent No. 4815544 JP 2003-268128 A

  However, the methods described in Patent Documents 1 and 2 are used because the coating operation and the subsequent drying operation are complicated, and it is necessary to perform heat treatment for insolubilizing the PVA layer in the state of the laminate. There is a problem that the thermoplastic resin film is limited to a film that can be stretched even after heat treatment, resulting in an increase in cost.

  Even when a thin PVA film is used, the present invention can be obtained by using a PVA film that can hardly be stretched during stretching and can produce an optical film such as a polarizing film with high yield, and the PVA film. An object is to provide an optical film.

  As a result of intensive studies to achieve the above object, the inventors of the present invention, when manufacturing an optical film such as a polarizing film using a thin PVA film, both ends of the PVA film in the width direction during the stretching process. It is easy to cause curling, and it is easy to cause breakage of stretching, and by making the degree of swelling in a limited range at both ends in the width direction of the PVA film specific, It was found that curling at both ends in the width direction of the PVA film was suppressed during processing, and the occurrence of stretch breakage could be reduced, and further studies were made based on these findings to complete the present invention.

That is, the present invention
[1] On an arbitrary straight line in the width direction of the PVA film having a thickness of 40 μm or less , one end is a1, the other end is b1, and a point advanced by 2 mm from a1 to b1 is a2, b1 to a1 The entire range C from c1 to c2, where b2 is a point advanced by 2 mm toward c, c1 is a point advanced 100 mm from a1 to b1, and c2 is a point advanced 100 mm from b1 to a1 The swelling degree C of the polyvinyl alcohol film at 190 to 230%, and the swelling degree A of the PVA film in the whole range A from a1 to a2 and the swelling degree B of the PVA film in the whole range B from b1 to b2 are both PVA film that is 145-175%;
[2] An optical film obtained using the PVA film of [1 ] above ;
[3] The optical film of the above [ 2 ], which is a polarizing film;
About.

  According to the present invention, even when a thin PVA film is used, stretch breakage hardly occurs at the time of stretching, and a PVA film capable of producing an optical film such as a polarizing film with high yield and the PVA film are used. The resulting optical film is provided.

It is the schematic which shows the range AC in this invention. FIG. 2 is an enlarged view of a part of FIG. 1.

The present invention is described in detail below.
As shown schematically in FIGS. 1 and 2, the PVA film of the present invention has one end a1 on one arbitrary line L in the width direction of the PVA film F, the other end b1, and the a1 to b1. The point advanced 2 mm toward a2 is a2, the point advanced 2 mm from b1 to a1, b2, the point advanced 100 mm from a1 to b1, c1, and the point advanced 100 mm from b1 to a1 c2. In this case, the swelling degree C of the PVA film in the range C from c1 to c2 is in the range of 180 to 230%, and the swelling degree A of the PVA film in the range A from a1 to a2 and from b1 to b2. The swelling degree B of the PVA film in the range B is in the range of 145 to 175%.

  The degree of swelling C needs to be in the range of 180 to 230%. When the degree of swelling C is lower than 180%, the tension applied to the film being stretched becomes too high, resulting in frequent stretching. On the other hand, when the degree of swelling C is higher than 230%, the film is melted during the stretching process, resulting in frequent stretching. From the above viewpoint, the degree of swelling C is preferably 185% or more, more preferably 190% or more, more preferably 220% or less, and more preferably 210% or less. preferable.

  Further, both the swelling degree A and the swelling degree B need to be in the range of 145 to 175%. When at least one of the swelling degrees A and B is lower than 145%, the tension applied to the end portion in the width direction of the film being stretched becomes too high, resulting in frequent stretching breaks. On the other hand, when at least one of the swelling degrees A and B is higher than 175%, the end in the width direction of the film is curled during the stretching process, and the stretching is frequently broken. In view of the above, the degree of swelling A and B is preferably 150% or more, more preferably 155% or more, and preferably 170% or less, and 165% or less. More preferably.

  By the way, although the PVA film which reduced gradually the distribution of the swelling degree in the width direction of the PVA film used as an original fabric for the purpose of reduction of the color spot etc. of the polarizing film obtained is known (patent) The PVA film of the present invention is different in that the swelling degree C of the PVA film in that portion is in a specific numerical range higher than the swelling degrees A and B over the entire range C. As compared with the case where the PVA film described in the above is used, an optical film excellent in the uniformity in the width direction is easily obtained.

  The degree of swelling of the PVA film can be easily adjusted, for example, by adjusting the degree of heat treatment, and the degree of swelling of the part can usually be lowered by strengthening the conditions of heat treatment in the predetermined range part. .

  In addition, the degree of swelling of the PVA film in each range is obtained by immersing the mass of the PVA film sample taken from the portion after immersion in distilled water at 30 ° C. for 15 minutes and then performing centrifugal dehydration at 3,000 rpm for 5 minutes. It can be determined as a percentage of the value obtained by dividing by the mass after drying at 105 ° C. for 16 hours. Although the degree of swelling of the PVA film is usually constant in the length direction, although depending on the production method, the degree of swelling of the PVA film in each range includes the range, and the sample is continuous for a certain length in the length direction. Can be measured. Moreover, in order to confirm that the requirement concerning the degree of swelling C is satisfied, all the degree of swelling of the PVA film in each range in the width direction in the range C (for example, a range of 2 mm in the width direction) is measured. Although it can also be performed by confirming that the value is within the numerical range related to the degree of swelling C, as will be described later, once a PVA film having a uniform degree of swelling in the width direction has been produced, In the case where the PVA film of the present invention is manufactured by performing a treatment for reducing the degree of swelling such as heat treatment, both the width direction ends (c1 and c2) and the width direction center portion (c3) in the range C are respectively The degree of swelling of the PVA film in each range in the width direction (for example, a range of 2 mm in the width direction) (a total of three points for each one point) is measured. By verifying that is within range, it can be estimated to meet the requirements of the degree of swelling C. Specifically, the degree of swelling of the PVA film in each range can be determined by the method described later in Examples.

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, isopropenyl acetate, etc. Those obtained by saponifying a polyvinyl ester obtained by polymerizing one or more of these vinyl esters can be used. Among the above-mentioned vinyl esters, a compound having a vinyloxycarbonyl group (H ₂ C═CH—O—CO—) in the molecule is preferable from the viewpoint of ease of production of PVA, availability, cost, etc. More preferred is vinyl acetate.

  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 the effect of the present invention is not significantly impaired, a copolymer of one or more vinyl esters and other monomers copolymerizable therewith may be used.

  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.

  The proportion of structural units derived from the other monomers 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% or less. More preferably, it is more preferably 5 mol% or less.

  As the above-mentioned PVA, those not graft-copolymerized can be preferably used, but PVA can be used for one or more kinds of graft copolymer as long as the effects of the present invention are not significantly impaired. It may be modified with a monomer. The said graft copolymerization can be performed with respect to at least one of polyvinyl ester and PVA obtained by saponifying it. 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 the polyvinyl ester or PVA is preferably 5 mol% or less based on the number of moles of all structural units constituting the polyvinyl ester or PVA.

  In the PVA, a part of the hydroxyl group may be cross-linked or may not be cross-linked. In addition, 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 above PVA is not particularly limited, but is preferably 1,000 or more. When the degree of polymerization of PVA is 1,000 or more, the polarizing performance of the obtained polarizing film can be further improved. If the degree of polymerization of PVA is too high, it tends to lead to an increase in the production cost of PVA and poor processability during film formation, so the degree of polymerization of PVA is in the range of 1,000 to 10,000. Is more preferable, it is still more preferable to be in the range of 1,500 to 8,000, and it is particularly preferable to be in the range of 2,000 to 5,000. In addition, the polymerization degree of PVA as used in this specification means the average degree of polymerization measured according to description of JISK6726-1994.

  The degree of saponification of PVA is preferably 95 mol% or more, more preferably 98 mol% or more, and even more preferably 99 mol% or more because the heat and heat resistance of the resulting polarizing film is improved. 99.3 mol% or more is particularly preferable. 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 may contain a plasticizer together with the above PVA. When the PVA film contains a plasticizer, it is possible to improve the handleability and stretchability of the PVA film. As the plasticizer, polyhydric alcohol is preferably used, and specific examples include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylolpropane, and the like. PVA film Can contain one or more of these plasticizers. Among these, glycerin is preferable because the stretchability of the PVA film becomes better.

  The content of the plasticizer in the PVA film is preferably 2 to 20 parts by mass with respect to 100 parts by mass of PVA, more preferably 3 to 17 parts by mass, and still more preferably 4 to 14 parts by mass. . When the content of the plasticizer in the PVA film is 2 parts by mass or more with respect to 100 parts by mass of PVA, the stretchability of the PVA film is improved. On the other hand, when the content of the plasticizer in the PVA film is 20 parts by mass or less with respect to 100 parts by mass of PVA, the plasticizer bleeds out on the surface of the PVA film and the handling property of the PVA film is reduced. be able to.

  In addition, when a 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 film thickness unevenness is suppressed, and a metal roll is used for film-forming. Since a PVA film can be easily peeled off from these metal rolls and belts when a belt or a belt is used, it is preferable to add a surfactant to 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. There are no particular limitations on the type of surfactant that is blended in the film-forming stock solution for producing the PVA film, and thus the surfactant contained in the PVA film, but from the viewpoint of releasability from a metal roll or belt, an anion is used. Surfactants or nonionic surfactants are preferred, and nonionic surfactants are particularly preferred.

  As the anionic surfactant, for example, a carboxylic acid type such as potassium laurate; a sulfate ester type such as octyl sulfate; a sulfonic acid type such as dodecylbenzene sulfonate and the like are suitable.

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

  When a surfactant is blended in a film-forming stock solution for producing a PVA film, the content of the surfactant in the film-forming stock solution, and thus the content of the surfactant in the PVA film is determined as the film-forming stock solution or the PVA film. It is preferable that it exists in the range of 0.01-0.5 mass part with respect to 100 mass parts of PVA contained in, and it is more preferable that it exists in the range of 0.02-0.3 mass part. 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 may be composed only of PVA, or may be composed only of PVA and the above-described plasticizer and / or surfactant. If necessary, an antioxidant, an antifreeze agent, a pH adjuster, You may contain other components other than above-mentioned PVA, a plasticizer, and surfactant, such as a masking agent, a coloring inhibitor, and an oil agent.

  The PVA content in the PVA film is preferably in the range of 50 to 100% by mass, more preferably in the range of 80 to 100% by mass, and in the range of 85 to 100% by mass. Is more preferable.

  Although there is no restriction | limiting in particular in the thickness of a PVA film, Since said curl is easy to generate | occur | produce with a thin PVA film and the effect of this invention is show | played more notably in a thin PVA film, the said thickness may be 40 micrometers or less. Preferably, it is 30 μm or less, more preferably 20 μm or less, 15 μm or less, and even 10 μm or less. 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.

  Although there is no restriction | limiting in particular in the shape of a PVA film, Since a polarizing film can be manufactured continuously with sufficient productivity, it is preferable that it is a long film. The length of the long film is not particularly limited, and can be set as appropriate according to the application of the polarizing film to be produced. For example, the length can be in the range of 5 to 20,000 m. There is no restriction | limiting in particular in the width | variety of the said elongate film, For example, although it can be 50 cm or more, since the wide polarizing film is calculated | required in recent years, it is preferable that it is 1 m or more, and it is 2 m or more more. Preferably, it is 4 m or more. There is no particular limitation on the upper limit of the width of the long film, but if the width is too wide, it tends to be difficult to stretch uniformly when a polarizing film is produced with an apparatus in practical use. Therefore, the width of the PVA film is preferably 7 m or less.

  There is no particular limitation on the shape 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 by a coating method on a thermoplastic resin film, for example. 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.

  The production method of the PVA film is not particularly limited, and a production method in which the thickness and width of the film after film formation are more uniform can be preferably adopted. For example, the above-described PVA constituting the PVA film, and as necessary In addition, a film-forming stock solution in which one or more of plasticizers, surfactants and other components are dissolved in a liquid medium, PVA, and optionally plasticizers, surfactants, other It can be produced using a film-forming stock solution containing one or more of components and liquid medium and 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 a small 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. It is preferably in the range of 95% by mass, more preferably in the range of 55-90% by mass, and still more preferably in the range of 60-85% by mass. 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 the production of an industrial PVA film becomes easy.

  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 extrusion film forming method is more preferable because a PVA film having a uniform thickness and width and good physical properties can be obtained. The PVA film can be dried or heat-treated as necessary.

  For the PVA film having a uniform degree of swelling in the width direction formed as described above, the PVA film of the present invention can be easily obtained by applying a treatment for further reducing the degree of swelling to the areas A and B. Can be manufactured.

  Although there is no restriction | limiting in particular in the method of the process for reducing a swelling degree, The method to heat-process is preferable from the simple and efficient manufacture of the PVA film of this invention. As a specific method for performing heat treatment on the areas A and B, for example, a method in which only the areas A and B of the PVA film are brought into contact with the heating roll; hot air is directly applied only to the areas A and B A method in which only both end faces of the film roll wound with the PVA film are directly brought into contact with the heating plate, a method in which only the portions in the ranges A and B are brought into contact with the heating roll, and the ranges A and B A method in which hot air is directly applied to only the part is preferred.

  There is no restriction | limiting in particular in heat processing temperature, What is necessary is just to adjust suitably according to the swelling degree of the PVA film in each range. The heat treatment temperature is preferably 210 ° C. or lower, more preferably 200 ° C. or lower, and even more preferably 190 ° C. or lower because discoloration or deterioration of the PVA film is observed when it is too high.

  There is no restriction | limiting in particular in heat processing time, What is necessary is just to adjust suitably according to the swelling degree of the PVA film in each range, but from a viewpoint which manufactures the PVA film of this invention efficiently, it may exist in the range of 1-60 seconds. Preferably, it is in the range of 2 to 40 seconds, more preferably in the range of 3 to 30 seconds.

  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 films such as films, the PVA film of the present invention hardly stretches during stretching and can be stably stretched to a high magnification, so that a polarizing film or a retardation film can be used. It is preferable to use it as a raw film for manufacturing an optical film such as a polarizing film having a high polarizing performance, so that it can be easily manufactured. preferable.

  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, for example, the PVA film of the present invention. On the other hand, a polarizing film can be produced by performing a swelling treatment, a dyeing treatment, uniaxial stretching, and, if necessary, a crosslinking treatment, a fixing treatment, a drying treatment, and a heat treatment. In this case, the order of each treatment such as swelling treatment, dyeing treatment, 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 treatment can be performed by immersing the PVA film in water. The temperature of water when immersed in water is preferably in the range of 20 to 40 ° C, more preferably in the range of 22 to 38 ° C, and preferably in the range of 25 to 35 ° C. Further preferred. Moreover, as time to immerse in water, for example, it is preferably within a range of 0.1 to 5 minutes, and more preferably within a range of 0.5 to 3 minutes. 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.

  The dyeing treatment is preferably performed using an iodine dye, and the dyeing time may be any stage before uniaxial stretching, at the time of 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 iodine concentration in the dyeing bath is preferably in the range of 0.01 to 0.5% by mass, and the potassium iodide concentration is preferably in the range of 0.01 to 10% by mass. Moreover, it is preferable that the temperature of a dyeing bath shall be 20-50 degreeC, especially 25-40 degreeC.

  The crosslinking treatment can be performed by immersing the PVA film in an aqueous solution containing a crosslinking agent. When the cross-linking step is performed, cross-linking is introduced into the PVA film, and PVA can be effectively prevented from being eluted into water when uniaxial stretching is performed at a relatively high temperature and wet. From such a viewpoint, the crosslinking treatment is preferably performed after the dyeing treatment. As a crosslinking agent used, 1 type (s) or 2 or more types of boron compounds, such as boric acid salts, such as boric acid and borax, can be used. The concentration of the crosslinking agent in the aqueous solution containing the crosslinking agent is preferably in the range of 1 to 15% by mass, and more preferably in the range of 2 to 7% by mass. The aqueous solution containing a crosslinking agent may contain an auxiliary agent such as potassium iodide. The temperature of the aqueous solution containing the crosslinking agent is preferably in the range of 20 to 50 ° C, and more preferably in the range of 25 to 40 ° C.

  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 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 a 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 to 6.0% by mass, more preferably in the range of 1.0 to 5.0% by mass, It is especially preferable to be within the range of ˜4.0% by mass. Moreover, the boric acid aqueous solution may contain potassium iodide, and the concentration is preferably in the range of 0.01 to 10% by mass.

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

  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 about 2 to 15% by mass, particularly about 3 to 10% by mass. The temperature of the fixing treatment bath is preferably 15 to 60 ° C, particularly preferably 25 to 40 ° C.

  The drying treatment is preferably performed at 30 to 150 ° C, more preferably 50 to 130 ° C. A polarizing film excellent in dimensional stability is easily obtained by drying at a temperature within the above range.

  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 evaluation method employ | adopted in the following examples and comparative examples is shown below.

A sample (about 0.5 g) of a tape-like PVA film that was 2 mm in the width direction and continuous in the length direction was taken from the portion to be measured. This was cut into about 2 mm square, wrapped in a mesh, immersed in distilled water at 30 ° C. for 15 minutes, centrifuged at 3,000 rpm for 5 minutes, and the mass (W1) was determined. Subsequently, the cut PVA film was dried with a dryer at 105 ° C. for 16 hours, and then the mass (W2) was determined. And the swelling degree of the PVA film in the range was computed by the following formula.
Swelling degree (%) = (W1) / (W2) × 100

[Example 1]
(1) Manufacture of PVA film A long PVA film having a thickness of 30 μm and a width of 1 m (including PVA, glycerin and a surfactant, and the content of glycerin is 12 parts by mass with respect to 100 parts by mass of PVA. The PVA film is 0.03 parts by mass with respect to 100 parts by mass of PVA, which is a saponified product of vinyl acetate homopolymer, the degree of polymerization of PVA is 2,400, and the degree of saponification of PVA is 99 .9 mol%. The overall swelling degree of the PVA film is 200%.) While continuously unwinding from the film roll, heat treatment was performed by applying hot air of 135 ° C. for 5 seconds to the width of 2 mm from both ends. did. The heat-treated PVA film was wound into a roll.
About the PVA film heat-processed as mentioned above, the swelling degree in the range A, the range B, and the range C was calculated | required by the method mentioned above. As for the degree of swelling C, the degree of swelling C1 of the PVA film in the range from c1 to c2 in the width direction up to 2 mm, the degree of swelling C2 of the PVA film in the range from c2 to 2 mm in the width direction from c2 and The swelling degree C3 of the PVA film in the range of 2 mm in the width direction centering on the width direction center part (c3) was measured. These results are shown in Table 1.

(2) Production of Polarizing Film A polarizing film was continuously produced by subjecting the PVA film heat-treated in (1) to swelling treatment, dyeing treatment, crosslinking treatment, uniaxial stretching, fixing treatment, and drying treatment. In addition, as a swelling process, the PVA film heat-processed by (1) was immersed in distilled water (temperature: 30 degreeC) for 1 minute, and was extended | stretched by the draw ratio 2 time in the meantime. In addition, as a dyeing treatment, an aqueous solution containing iodine pigment (concentration of iodine used: 0.05 mass%, concentration of potassium iodide used: 1.2 mass%, temperature: 30 ° C.) for 2 minutes. It was immersed and stretched at a stretch ratio of 1.2 times during that time. Further, as a crosslinking treatment, the film was immersed in an aqueous boric acid solution (boric acid concentration: 2.6 mass%, temperature: 30 ° C.) for 2 minutes, and stretched at a stretching ratio of 1.1 times during that time. Subsequently, as uniaxial stretching, the film was stretched at a stretching ratio of 2.4 times in a boric acid aqueous solution (boric acid concentration: 2.8% by mass, potassium iodide concentration: 5% by mass, temperature: 57 ° C.) (water contact step). The total draw ratio including the draw ratio of pre-stretching at 6.3 times). Further, as a fixing treatment, it was immersed in an aqueous boric acid solution (boric acid concentration: 1.5%, potassium iodide concentration: 5%, temperature: 22 ° C.) for 10 seconds. Finally, as a drying treatment, the stretched PVA film was dried at 60 ° C. for 1 minute to obtain a polarizing film.
In the production of the above polarizing film, no curling was observed at both ends in the width direction of the PVA film, and the number of stretch breaks when the polarizing film was produced for 8 hours continuously was 0. The above results are summarized in Table 1.

[Example 2]
In Example 1 (1), a PVA film having a thickness of 20 μm and an overall swelling degree of 195% was used, and heat treatment was performed by applying hot air of 190 ° C. for 5 seconds to a range of 2 mm width from both ends. In the same manner as in Example 1 (1), a heat-treated PVA film (roll shape) was obtained.
About the PVA film heat-processed as mentioned above, the swelling degree in the range A, the range B, and the range C was calculated | required similarly to (2) of Example 1. FIG. These results are shown in Table 1. Moreover, the polarizing film was continuously manufactured similarly to (2) of Example 1 using the said heat-processed PVA film. In the production of the polarizing film, no curling was observed at both ends in the width direction of the PVA film, and the number of stretch breaks when the polarizing film was produced for 8 hours continuously was 0. The above results are summarized in Table 1.

[Comparative Example 1]
In Example 2 (1), a PVA film (roll shape) was obtained in the same manner as in Example 2 (1) except that heat treatment was not applied to the range of 2 mm in width from both ends.
About the said PVA film, it carried out similarly to (2) of Example 1, and calculated | required the swelling degree in the range A, the range B, and the range C. FIG. These results are shown in Table 1. Moreover, the polarizing film was continuously manufactured similarly to (2) of Example 1 using the said PVA film. In the production of the polarizing film, occurrence of curling was observed at both ends in the width direction of the PVA film, and the number of stretching breaks when the polarizing film was produced for 8 hours continuously was 12 times. The above results are summarized in Table 1.

[Comparative Example 2]
In Example 2 (1), heat-treated PVA was performed in the same manner as in Example 2 (1) except that heat treatment was performed by applying a hot air of 135 ° C. for 5 seconds to a width of 2 mm from both ends. A film (roll shape) was obtained.
About the PVA film heat-processed as mentioned above, the swelling degree in the range A, the range B, and the range C was calculated | required similarly to (2) of Example 1. FIG. These results are shown in Table 1. Moreover, the polarizing film was continuously manufactured similarly to (2) of Example 1 using the said heat-processed PVA film. In the production of the polarizing film, occurrence of curling was observed at both ends in the width direction of the PVA film, and the number of stretching breaks when the polarizing film was produced for 8 hours continuously was 10 times. The above results are summarized in Table 1.

[Comparative Example 3]
In Example 2 (1), heat-treated PVA was performed in the same manner as in Example 2 (1) except that heat treatment was performed by applying hot air of 210 ° C. for 5 seconds to the width of 2 mm from both ends. A film (roll shape) was obtained.
About the PVA film heat-processed as mentioned above, the swelling degree in the range A, the range B, and the range C was calculated | required similarly to (2) of Example 1. FIG. These results are shown in Table 1. Moreover, the polarizing film was continuously manufactured similarly to (2) of Example 1 using the said heat-processed PVA film. In the production of the polarizing film, no curling was observed at both ends in the width direction of the PVA film, but the number of stretch breaks when the polarizing film was produced continuously for 8 hours because the swelling degrees A and B were too low. Was 8 times. The above results are summarized in Table 1.

[Comparative Example 4]
In Example 2 (1), a heat-treated PVA film (roll shape) was obtained in the same manner as in Example 1 (1) except that a PVA film having a total swelling degree of 250% was used.
About the PVA film heat-processed as mentioned above, the swelling degree in the range A, the range B, and the range C was calculated | required similarly to (2) of Example 1. FIG. These results are shown in Table 1. Moreover, the polarizing film was continuously manufactured similarly to (2) of Example 1 using the said heat-processed PVA film. In the production of the polarizing film, no curling was observed at both ends in the width direction of the PVA film, but the number of stretch breaks when the polarizing film was produced for 8 hours continuously was probably 5 because the swelling degree C was too high. It was times. The above results are summarized in Table 1.

[Comparative Example 5]
In Example 2 (1), a heat-treated PVA film (roll shape) was obtained in the same manner as in Example 1 (1) except that a PVA film having a total swelling degree of 170% was used.
About the PVA film heat-processed as mentioned above, the swelling degree in the range A, the range B, and the range C was calculated | required similarly to (2) of Example 1. FIG. These results are shown in Table 1. Moreover, the polarizing film was continuously manufactured similarly to (2) of Example 1 using the said heat-processed PVA film. In the production of the polarizing film, no curling was observed at both ends in the width direction of the PVA film, but when the polarizing film was produced continuously for 8 hours because the degree of swelling C was too low and the stretching tension was high. The number of stretch cuts was 7 times. The above results are summarized in Table 1.

Claims (3)

On an arbitrary straight line in the width direction of the polyvinyl alcohol film having a thickness of 40 μm or less , one end is a1, the other end is b1, and a point advanced 2 mm from a1 to b1 is directed to a2 and b1 to a1. Polyvinyl alcohol in the entire range C from c1 to c2, where b2 is a point advanced by 2 mm and c1 is a point advanced 100 mm from a1 to b1 and c2 is a point advanced 100 mm from b1 to a1. The swelling degree C of the alcohol film is 190 to 230%, and the swelling degree A of the polyvinyl alcohol film in the whole range A from a1 to a2 and the swelling degree B of the polyvinyl alcohol film in the whole range B from b1 to b2 are both The polyvinyl alcohol film which is 145 to 175%. An optical film obtained using the polyvinyl alcohol film according to claim 1 . The optical film according to claim 2 , which is a polarizing film.