JP6534305B2 - Evaluation method of optical spots of polyvinyl alcohol film - Google Patents

Description

  The present invention relates to a method for evaluating optical spots of a polyvinyl alcohol film and a method for producing an optical film such as a polarizing film using the method.

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 the 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, and a polyvinyl alcohol film (hereinafter referred to as “polyvinyl alcohol film” is used as a polarizing film constituting a polarizing plate. Dichroic dyes such as iodine dyes (I ₃ ^- and I ₅ ^- etc.) and dichroic organic dyes are adsorbed on a stretched film oriented by uniaxially stretching an alcohol (sometimes abbreviated as "PVA"). What you are doing is mainstream. Such a polarizing film uniaxially stretches a PVA film containing a dichroic dye in advance, adsorbs a dichroic dye simultaneously with uniaxial stretching of the PVA film, or uniaxially stretches a PVA film Manufactured by, for example, adsorbing a dye.

  LCDs are used in a wide range of applications such as small devices such as calculators and watches, notebook computers, LCD monitors, LCD color projectors, LCD TVs, in-vehicle navigation systems, mobile phones, and measuring devices used indoors and outdoors . In recent years, reduction in power consumption has been particularly strongly demanded, and it has become important in LCDs to be able to maintain high screen brightness even when the intensity of the backlight is low. As means for achieving that, it is conceivable to improve the light transmittance of the polarizing film and thus the polarizing plate by making the thickness of the polarizing film thinner or weakening the degree of dyeing, but the light transmittance A polarizing plate having a high light transmittance has a problem that color spots are more noticeable as compared with a polarizing plate having a low light transmittance, and the degree of the color spots itself is also required to be further reduced than before.

  By the way, as a method of inspecting color spots of a polarizing plate or polarizing film, the inspection polarizing plate or inspection polarizing film to be inspected is disposed between two reference polarizing plates, and at this time, the inspection polarizing plate or inspection polarizing film An inspection polarizing plate or inspection arranged between an absorption axis and an absorption axis of two reference polarizing plates or a reference polarizing plate disposed between two reference polarizing plates disposed so that the absorption axes are parallel to each other There is known a method of rotating a polarizing film (see, for example, Patent Documents 1 to 3 and the like).

JP, 2011-149741, A Japanese Patent Publication No. 2010-534351 Unexamined-Japanese-Patent No. 2012-233886

  The above-mentioned methods are all for evaluating the color spots of the polarizing plate or the polarizing film, but in the method of evaluating the color spots after producing such a polarizing plate or the polarizing film, these are produced, for example. Even if the optical spots causing the color spots are inherent in the PVA film used as a raw film for producing, it is not possible to confirm the occurrence of the color spots until the polarizing plate or the polarizing film is formed. It is not efficient because the cost and time in the production of the plate or polarizing film are wasted. On the other hand, it is relatively difficult to evaluate the optical spots inherent in the PVA film, and in particular, it is even more difficult to assess the optical spots causing the color spots, the reduction of which is required in recent years.

  Then, an object of this invention is to provide the evaluation method of the optical spot of the PVA film which can fully evaluate the optical spot which is inherent in the PVA film. Moreover, this invention aims at providing the manufacturing method of optical films, such as a polarizing film which utilized such an evaluation method.

  As a result of intensive studies by the present inventors in order to achieve the above-mentioned purpose, after swelling and immersing the PVA film in water and then evaluating optical spots such as phase difference spots and orientation axis angle spots, it is found that swelling occurs. The optical spots present in the PVA film can be sufficiently evaluated as compared with the case of the non-PVA film, and the optical spots present in advance are evaluated using the evaluation method, and the optical spots are evaluated. By selecting a small PVA film with no or no degree, and using the PVA film as a raw film to manufacture a polarizing film and thus a polarizing plate, it is possible to use a small polarizing film or a polarizing plate with no or few color spots. The inventors have found that they can be obtained efficiently, and have further studied based on these findings to complete the present invention.

That is, the present invention
[1] A method for evaluating the optical spots of a film, wherein the PVA film is swollen without being stretched while immersed in water, and the optical spots of the PVA film are attached to the surface of the PVA film How to evaluate without wiping water ;
[2] The method of the above-mentioned [1], wherein the optical plaque is evaluated by evaluating retardation spots and / or orientation axial angular spots of the PVA film after swelling with water;
[3] The method of the above-mentioned [ 1 ], wherein the temperature of water at the time of immersing the PVA film in water is 20 to 50 ° C .;
[4] The method of the above-mentioned [ 1 ], wherein the immersion time for immersing the PVA film in water is 10 to 300 seconds;
[5] The method according to any one of the above [1] to [ 4 ], wherein the PVA film is a raw film for producing an optical film;
[6] The method of the above-mentioned [ 5 ], wherein the optical film is a polarizing film;
[7] An optical film comprising: a step of evaluating optical spots of a PVA film by the method of the above [ 5 ] or [ 6 ], and a step of producing an optical film using the PVA film of which the optical spots are evaluated. Production method;
About.

  ADVANTAGE OF THE INVENTION According to this invention, the evaluation method of the optical spots of the PVA film which can fully evaluate the optical spots inherent in a PVA film is provided. Further, according to the present invention, there is provided a method of producing an optical film using the above-mentioned evaluation method capable of efficiently obtaining an optical film such as a polarizing film.

The present invention will be described in detail below.
In the method of the present invention for evaluating the optical spots of PVA film, the optical spots of PVA film after swelling with water are evaluated. The water is not limited to pure water, and may be an aqueous solution in which various components are dissolved, but distilled water, pure water, and the like can be evaluated more effectively because the optical spots present in the PVA film can be evaluated more effectively. It is preferable that it is water with high purity, such as demineralized water.

In the present invention, the PVA film after swelling with water for evaluating the optical spots can be obtained by spraying water on the PVA film, etc., but the optical spots inherent in the PVA film are more effective. It is preferable that it is what was taken out from water, after immersing a PVA film in water, since it can evaluate. In this case, the sample of the PVA film collected by cutting out from the evaluation target may be immersed in water.
While immersing the PVA film in water, it may be stretched by applying a load in the lengthwise direction of the PVA film, etc., but the optical spots present in the PVA film can be evaluated more effectively. Since the operation is also simple, it is preferable not to stretch during immersion in water.

  The temperature of water when immersing the PVA film in water is preferably 20 ° C. or more, more preferably 25 ° C. or more, and more preferably 30 ° C. or more, because the PVA film can be sufficiently swollen. Is more preferred. Further, from the viewpoint of preventing the PVA film from melting or welding, the temperature is preferably 50 ° C. or less, more preferably 45 ° C. or less, and 40 ° C. or less. Is more preferred.

  The immersion time for immersing the PVA film in water is preferably 10 seconds or more, more preferably 20 seconds or more, and preferably 30 seconds or more, because the PVA film can be sufficiently swollen. Is more preferred. In addition, the immersion time is preferably 300 seconds or less, and preferably 180 seconds or less, because it is possible to evaluate optical spots corresponding to color spots in the target optical film such as a polarizing film, etc. It is more preferable that it is 120 seconds or less.

  After immersing the PVA film in water as described above, the swollen PVA film is taken out of the water, and if the optical spots are evaluated without wiping off the water adhering to the surface, the optical inherent in the PVA film Plaques can be evaluated more effectively, which is preferable.

  There is no particular limitation on the type of optical spots of the PVA film to be evaluated in the present invention, and various optical spots may be evaluated, but the reason is such as to cope more with color spots in the target optical film such as a polarizing film. Therefore, it is preferable that they are phase difference spots and / or orientation axis angle spots.

  The retardation spots of the PVA film after swelling with water are obtained by, for example, measuring the retardation value in the film surface of a sample collected from the PVA film to be evaluated, and distributing the distribution in the surface by analysis software etc. It can be evaluated by visualizing it as The retardation value in the film plane is, for example, light (for example, light with a wavelength of 543 nm) traveling in a direction (film thickness direction) perpendicular to the film plane using a birefringence measurement device or a cell gap measurement device etc. It can be measured based on The said phase difference spots can be specifically evaluated by the method mentioned later in an Example.

  Further, for example, with regard to the orientation axis angle unevenness of the PVA film after swelling with water, the angle of the slow axis in the film plane is measured as the orientation axis angle for a sample collected from the PVA film to be evaluated. It can be evaluated by visualizing as a distribution in the plane by analysis software or the like. Here, the angle of the slow axis is usually determined by the orientation state of the PVA molecule at the measurement position and the like. Similarly to the retardation value in the film plane, the orientation axis angle also travels in a direction (film thickness direction) perpendicular to the film plane using, for example, a birefringence measurement device or a cell gap measurement device For example, it can be measured based on light having a wavelength of 543 nm. The orientation axis angular unevenness can be specifically evaluated by the method described later in the examples.

Examples of PVA constituting the PVA film include vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl benzoate, and isopropenyl acetate. What is obtained by saponifying a polyvinyl ester obtained by polymerizing one or more of the esters can be used. Among the above-mentioned vinyl esters, compounds having a vinyloxycarbonyl group (H ₂ C−CH—O—CO—) in the molecule are preferable in terms of easiness of production of PVA, easiness of availability, cost and the like, Vinyl acetate is more preferred.

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

  Examples of other monomers copolymerizable with the above-mentioned vinyl esters include α-olefins of 2 to 30 carbon atoms 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 ( (Meth) acrylic acid esters such as t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate, octadecyl (meth) acrylate; (meth) acrylic acid; N-methyl (meth) acrylamide Meta) acrylamide, N-ethyl (meth) acrylamide, N, N- dimethyl (meth) acrylamide, diacetone (meth) acrylic (Meth) acrylamide derivatives such as (meth) acrylamidopropane sulfonic acid or salts thereof, (meth) acrylamidopropyldimethylamine or salts thereof, N-methylol (meth) acrylamide or derivatives thereof; N-vinyl formamide, N-vinyl N-vinyl amides such as acetamide and N-vinyl pyrrolidone; 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 ethers; vinyl cyanides such as (meth) acrylonitrile; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride; vinegar Acids allyl, allyl compounds such as allyl chloride; maleic acid or its salt, ester or acid anhydride; itaconic acid or its salt, ester or acid anhydride; vinylsilyl compounds such as vinyltrimethoxysilane; unsaturated sulfonic acid or its salt And the like. The polyvinyl ester described above can have a structural unit derived from one or more of the other monomers described above.

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

  As the above-mentioned PVA, those which have not been graft copolymerized can be preferably used, but within the range not greatly impairing the effects of the present invention, PVA can be graft copolymerized alone or as a mixture of two or more. It may be one modified by a monomer. The graft copolymerization can be performed on at least one of a 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; 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 polyvinyl ester or PVA is 5 mol% or less based on the mole number of all the structural units which comprise polyvinyl ester or PVA.

  In the above PVA, part of its hydroxyl groups may be crosslinked or may not be crosslinked. Further, in the above PVA, a part of the hydroxyl groups may react with an aldehyde compound such as acetaldehyde or butyraldehyde to form an acetal structure, or do not react with these compounds to form an acetal structure. It is also good.

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

  The saponification degree of PVA is preferably 95 mol% or more, more preferably 98 mol% or more, and still more preferably 99 mol% or more, since the moisture and heat resistance of the obtained polarizing film is improved. And 99.3 mol% or more is particularly preferable. The degree of saponification of PVA in the present specification refers to the total number of moles of structural units (typically, vinyl ester units) and vinyl alcohol units that can be converted to vinyl alcohol units by saponification of PVA. The ratio (mol%) of the number of moles of 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-mentioned PVA. When the PVA film contains a plasticizer, the handling of the PVA film, the improvement of the stretchability, and the like can be achieved. As the plasticizer, polyhydric alcohol is preferably used, and specific examples thereof include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylolpropane and the like, and a PVA film May 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, more preferably 3 to 17 parts by mass, and still more preferably 4 to 14 parts by mass with respect to 100 parts by mass of PVA. . 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 is prevented from bleeding out on the surface of the PVA film and the handleability of the PVA film is reduced. be able to.

  Moreover, when manufacturing using the film forming undiluted | stock solution for manufacturing the PVA film which mentions a PVA film later, while being able to improve film forming property and suppressing generation | occurrence | production of the thickness spot of a film, a metal roll is used for film forming. When using a belt or a belt, it is preferable to blend a surfactant in the film-forming solution since peeling of the PVA film from the metal roll or the belt becomes easy. In the case where a PVA film is produced from a film-forming stock solution containing a surfactant, the surfactant may be contained in the PVA film. There are no particular limitations on the type of surfactant contained in the stock solution for producing a PVA film, and hence the type of surfactant contained in the PVA film, but from the viewpoint of releasability from metal rolls and belts, anions 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 sulfuric acid ester type such as octyl sulfate; and a sulfonic acid type such as dodecylbenzene sulfonate are preferable.

Examples of nonionic surfactants include alkyl ether type such as polyoxyethylene oleyl ether; alkyl phenyl ether type such as polyoxyethylene octyl phenyl ether; alkyl ester type such as polyoxyethylene laurate; polyoxyethylene lauryl amino Alkyl amine type such as ether; alkyl amide 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; Allyl phenyl ether type such as alkylene allyl phenyl ether is preferable.
These surfactants can be used alone or in combination of two or more.

  When a surfactant is blended in a film forming solution for producing a PVA film, the content of the surfactant in the film forming solution, and hence the content of the surfactant in the PVA film is a film forming solution or a PVA film It is preferable to exist 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 to exist 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 releasability 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 to cause blocking and the handling property is lowered. It can be suppressed.

  The PVA film may consist only of PVA, or may consist only of PVA and the above-mentioned plasticizer and / or surfactant, but if necessary, an antioxidant, an antifreeze agent, a pH adjuster, You may contain other components other than the above-mentioned PVA, a plasticizer, a surfactant, etc., such as a masking agent, a coloring inhibitor, and an oil agent.

  The content of PVA 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 preferred.

  The thickness of the PVA film is not particularly limited, but if it is too thick, it will be difficult to rapidly dry when producing an optical film such as a polarizing film, while if it is too thin, it will be at the time of uniaxial stretching when producing an optical film. The thickness is preferably 1 μm or more, more preferably 2 μm or more, still more preferably 3 μm or more, and preferably 150 μm or less, or 120 μm or less, because the film easily breaks. Is more preferable, and 80 μm or less is more preferable.

  The shape of the PVA film is not particularly limited, but is preferably a long film because an optical film such as a polarizing film can be continuously produced with high productivity. The length of the long film is not particularly limited, but a more uniform PVA film can be continuously and smoothly produced, and continuously used also when producing an optical film using it It is preferable to exist in the range of 5-50,000 m, and it is more preferable to exist in the range of 100-20,000 m from that it can be carried out. The width of the long film is not particularly limited, and may be, for example, 50 cm or more. However, in recent years, since the liquid crystal television and monitor have a large screen, in order to be able to effectively use them, 1 m It is preferable that it is more than, It is more preferable that it is 2 m or more, It is still more preferable that it is 4 m or more. Moreover, when manufacturing optical films, such as a polarizing film, with a realistic production machine, since uniform uniaxial stretching may become difficult when the width of a film is too wide, the width of a PVA film is 8 m or less Is preferred. In addition, in evaluating the optical spots of a PVA film, it is not necessary to evaluate the whole PVA film of the above-mentioned size, it cuts out the sample for evaluating an optical spot from the said PVA film, etc. Is swollen with water to evaluate the optical plaque, and the result may be regarded as the optical plaque of the whole PVA film.

  The form of the PVA film is not particularly limited, and may be a single layer form or a laminate form such as a PVA film formed by a coating method on a thermoplastic resin film, for example. Although it may be used, a single-layered form is preferable from the viewpoint that the effect of the present invention is more remarkably exhibited, complexity of laminating (coating etc.) operation, cost of thermoplastic resin film, etc.

  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 become more uniform can be preferably adopted, for example, the above-mentioned PVA constituting the PVA film and Film forming solution in which one or more of a plasticizer, a surfactant and other components are dissolved in a liquid medium, PVA, and further, if necessary, a plasticizer, a surfactant, and the like It can manufacture using the film-forming undiluted | stock solution which contains 1 type, or 2 or more types in a component and a liquid medium, and PVA is fuse | melting. When the said film forming undiluted | stock solution contains at least 1 sort (s) of a plasticizer, surfactant, and another component, it is preferable that those components are mixed uniformly.

  Examples of the liquid medium used for the preparation of the membrane-forming solution include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol And trimethylolpropane, ethylenediamine, diethylenetriamine and the like, and one or more of them can be used. Among them, water is preferable from the viewpoint of small impact on the environment and recovery.

  Although the volatilization fraction of the membrane-forming stock solution (the content ratio of the volatile component such as liquid medium to be removed by volatilization or evaporation in film-forming in the membrane-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 to 90% by mass, and still more preferably in the range of 60 to 85% by mass. When the volatilization fraction of the membrane-forming solution is 50% by mass or more, the viscosity of the membrane-forming solution does not become too high, and filtration and degassing are smoothly performed during the preparation of the membrane-forming solution. The manufacture of the film is facilitated. On the other hand, when the volatilization fraction of the membrane-forming solution is 95% by mass or less, the concentration of the membrane-forming solution does not become too low, and the industrial production of PVA film becomes easy.

  As a film forming method when forming a PVA film into a film using the film forming solution described above, for example, a cast film forming method, an extrusion film forming method, a wet film forming method, a gel film forming method, etc. may be mentioned. The membrane method and the extrusion film forming method are preferable. These film forming methods may be used alone or in combination of two or more. Among these film forming methods, a cast film forming method and an extrusion film forming method are more preferable because a PVA film having uniform thickness and width and excellent physical properties can be obtained. The PVA film may be subjected to drying or heat treatment as required.

  As an example of the specific manufacturing method of a PVA film, for example, T-type slit die, a hopper plate, an I-die, a lip coater die etc. are used, The heating which rotates said film forming undiluted | stock solution on the most upstream side The film is uniformly discharged or cast on the circumferential surface of the first roll (or belt), and volatile components are discharged from one surface of the film discharged or cast on the circumferential surface of the first roll (or belt). After being evaporated to dryness and then further dried on the periphery of one or more rotating heated rolls located downstream thereof, or after passing through a hot air dryer for further drying, A method of winding by a winding device can be preferably adopted industrially. Drying with a heated roll and drying with a hot air drying apparatus may be carried out in combination as appropriate.

  There are no particular limitations on the application of the PVA film for which the optical spots are evaluated by the method of the present invention, and for example, films for drug packaging, base films for hydraulic transfer, base films for embroidery, mold release films for artificial marble molding, seeds Although it can also be used for the use of various water-soluble films, such as a film for packaging, a film for waste accommodation bags, using the said PVA film as an original film for manufacturing optical films, such as a polarizing film and retardation film. In particular, it is preferable to use as a raw film for producing a polarizing film.

  According to the method of the present invention for evaluating optical spots, it is possible to sufficiently evaluate the optical spots inherent in the PVA film. By selecting a PVA film of a small degree and using the PVA film as a raw film, it is possible to efficiently obtain an optical film having no color spots or a degree of that degree. That is, the present invention includes a method for producing an optical film, which comprises the steps of: evaluating optical spots of a PVA film by the method described above; and producing an optical film using the PVA film of which the optical spots are evaluated. Do. In the method for producing an optical film, it is not necessary to use the PVA film itself for which the optical spots are evaluated for the production of the optical film, and a sample for evaluating the optical spots is cut out from the PVA film and collected. The optical spots may be evaluated by swelling, and the results may be regarded as the optical spots of the remaining PVA film from which the sample was collected, and then the optical film may be produced using the remaining PVA film. In addition, as a method of manufacturing an optical film from a PVA film, the method of extending | stretching the said PVA film etc. are mentioned, for example.

  The specific method for producing a polarizing film using the above PVA film as a raw film is not particularly limited, and any conventionally adopted method may be adopted, for example, to the above PVA film On the other hand, a polarizing film can be produced by performing swelling treatment, dyeing treatment, stretching treatment, and, if necessary, crosslinking treatment, fixing treatment, drying treatment, heat treatment and the like. In this case, the order of the treatments such as the swelling treatment, the dyeing treatment, the stretching treatment, and the fixation treatment is not particularly limited, and one or more treatments may be performed simultaneously. Also, one or more of each treatment may 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 further preferably in the range of 25 to 35 ° C. preferable. Moreover, as immersion time in water, it is preferable to exist in the range of 0.1 to 5 minutes, for example, and it is more preferable to exist in the range for 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 which various components melt | dissolved may be sufficient, and the mixture of water and an aqueous medium may be sufficient.

  The dyeing process is preferably performed using an iodine based dye, and the time of dyeing may be any stage before, during, or after the stretching process. 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 suitably employed in the present invention as well. . The concentration of iodine in the dyeing bath is preferably in the range of 0.01 to 0.5% by mass, and the concentration of potassium iodide is preferably in the range of 0.01 to 10% by mass. Further, the temperature of the dyeing bath is preferably 20 to 50 ° C, particularly 25 to 40 ° C.

  The crosslinking treatment can be performed by immersing the PVA film in an aqueous solution containing a crosslinking agent. When the crosslinking treatment is carried out, the crosslinking is introduced into the PVA film, and the elution of the PVA into water can be effectively prevented when the stretching treatment is carried out at a relatively high temperature and in a wet manner. From such a point of view, the crosslinking treatment is preferably performed after the dyeing treatment. As the said crosslinking agent, 1 type (s) or 2 or more types of boron compounds, such as boric acid and boric acid salts, such as 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 the crosslinking agent may contain an auxiliary 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.

  The stretching treatment 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 above-mentioned dyeing bath or in a fixed treatment bath described later. Moreover, in the case of the dry 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 in an aqueous solution containing boric acid is more preferable. The concentration of boric acid in the aqueous boric acid 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, and 1.5 It is particularly preferable to be in the range of -4.0% by mass. The boric acid aqueous solution may contain potassium iodide, and the concentration thereof is preferably in the range of 0.01 to 10% by mass.

  The stretching temperature in the stretching treatment 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 the drawing treatment (the total draw ratio obtained by multiplying the individual draw ratios when drawing in multiple stages) is preferably 5 or more from the viewpoint of the polarization performance of the obtained polarizing film, It is more preferably 0.5 times or more, particularly preferably 6 times or more. The upper limit of the draw ratio is not particularly limited, but the draw ratio is preferably 8 times or less.

  In the production of the polarizing film, it is preferable to carry out a fixing treatment in order to strengthen the adsorption of the dye (iodine etc.) to the PVA film. As a fixing process bath used for a fixing process, the aqueous solution containing 1 type, or 2 or more types of boron compounds, such as boric acid and borax, can be used. In addition, if necessary, an iodine compound or a metal compound may be added to the fixing treatment bath. In general, the concentration of the boron compound in the fixing treatment bath is preferably about 0.5 to 15% by mass, particularly about 1 to 10% by mass. The temperature of the fixing treatment bath is preferably 15 to 60 ° C, particularly 20 to 40 ° C.

  The drying treatment is preferably performed at 30 to 150 ° C., and more preferably 50 to 130 ° C. The polarizing film which is excellent in dimensional stability is easy to be obtained by drying at the temperature within the said range.

  A protective film having optical transparency and mechanical strength can be bonded to both surfaces or one surface of the polarizing film obtained as described above to make a polarizing plate. As a protective film in that case, a cellulose triacetate (TAC) film, a cycloolefin polymer (COP) film, a cellulose acetate and butyrate (CAB) film, an acrylic film, a polyester film and the like are used. Moreover, as an adhesive agent for bonding together a protective film, a PVA-type adhesive agent, a urethane type adhesive agent, etc. are mentioned, Among these, a PVA-type adhesive agent is preferable.

  The polarizing plate obtained as described above can be used as a component of an LCD by bonding it to a glass substrate after covering it with an acrylic or other adhesive. When the polarizing plate is bonded to the glass substrate, a retardation film, a viewing angle improving film, a brightness improving film, or the like may be bonded.

  EXAMPLES Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to the following examples.

Comparative Example 1
Evaluation of Optical Mottle of PVA Film In order to demonstrate the effect of the method of the present invention, the following test was performed using a PVA film whose degree of color mottle when used as a polarizing plate is known. That is, any position in the length direction (MD) of each of the PVA film (raw 1) with a large degree of color spots and the PVA film (raw 2) with a small degree of color spots when producing a polarizing plate From this, samples of 20 cm in the length direction (MD) and 15 cm in the width direction (TD) were taken three sheets along the width direction of the PVA film. Then, the phase difference and the orientation axis angle in the film plane of each sample are advanced in the direction perpendicular to the film plane using "WPA-100-L (two-dimensional retardation measurement device)" manufactured by Photonic Lattice. It measured based on the light of wavelength 543nm. Next, the distribution of retardation and orientation axis angle in the film plane of each sample was determined by displaying the in-plane distribution of retardation and orientation axis angle in color using analysis software “WPA-View”. In addition, the color display range of retardation is set to “0 to the maximum value (nm) of retardation in the film surface”, and the color display cycle of orientation axis angle is “30 °”. The optical spots of the PVA film were evaluated by sensory evaluation on the basis of the following criteria for each of the original fabrics 1 and 2. The results are shown in Table 1.
Good: Notable streak-like phase difference spots or orientation axis angle spots are not visible in all samples.
X: remarkable streak-like phase difference spots or orientation axis angle spots were observed in one or more samples.
The raw fabric 1 and the raw fabric 2 are both PVA films containing PVA having a degree of polymerization of 2,400 and a degree of hydrolysis of 99.9 mol% obtained by saponifying a homopolymer of polyvinyl acetate. A long, single-layer PVA film having a glycerin content of 12% by mass, a thickness of 60 μm, a width of 65 cm and a length of 1,000 m was used.

Example 1
-Evaluation of the optical spots of PVA film About all the samples extract | collected by the comparative example 1, it was made to swell for 30 seconds, without extending | stretching in distilled water of 30 degreeC, so that samples may not stick. After that, the sample is pulled out of the water, and it is spread on the sample stage of “WPA-100-L” made by Photonic Lattice, without wiping off the water adhering to the surface, and the phase difference and orientation axis in the film plane of each sample The distribution of the angle was determined in the same manner as in Comparative Example 1, and the optical spots of the PVA film were evaluated based on the same determination criteria as in Comparative Example 1 for each of the source films 1 and 2. The results are shown in Table 1.

-Production of polarizing plate Each of the PVA films (raw fabrics 1 and 2) from which samples were collected above were subjected to swelling treatment, dyeing treatment, crosslinking treatment, stretching treatment, fixation treatment, and drying treatment to form a polarizing film. A polarizing plate was manufactured.
That is, as a swelling process, the PVA film was immersed in distilled water (temperature: 30 ° C.) for 1 minute, and in the meantime, uniaxial stretching was performed in the lengthwise direction at a draw ratio of 2 times. In addition, as a dyeing process, it is immersed in an aqueous solution containing an iodine dye (the concentration of iodine: 0.02% by mass, the concentration of potassium iodide: 0.4% by mass, the temperature: 30 ° C.) for 1 minute while stretching The film was uniaxially stretched in the length direction at a magnification of 1.2 times. Further, as a crosslinking treatment, it was immersed for 2 minutes in a boric acid aqueous solution (boric acid concentration: 2.6% by mass, temperature: 30 ° C.), and in the meantime, uniaxial stretching was performed in the lengthwise direction at a draw ratio of 1.1. Subsequently, as a stretching treatment, uniaxial stretching in the length direction at a stretching ratio of 2.4 in a boric acid aqueous solution (boric acid concentration: 2.8% by mass, potassium iodide concentration: 5% by mass, temperature: 57 ° C.) (Total stretch ratio 6.3 times). Furthermore, as a fixing process, it was immersed for 10 seconds in a boric acid aqueous solution (boric acid concentration: 1.5% by mass, potassium iodide concentration: 5% by mass, temperature: 22 ° C.). Then, as a drying treatment, the stretched PVA film was dried at 60 ° C. for 1 minute to obtain a polarizing film having a high single transmittance of 44.5%.
Next, a TAC film (80 μm in thickness) was bonded to both sides of the polarizing film obtained above using a PVA aqueous solution as an adhesive, and dried at 70 ° C. for 3 minutes to obtain a polarizing plate.

Evaluation of Color Spots of Polarizing Plate The color spots of the polarizing plates obtained from the PVA films (raw films 1 and 2) as described above were evaluated.
That is, a polarizing plate for observation (using a polarizing film having a transmittance of about 43%) is placed on a surface light source (backlight) in a dark room, and crossed nicols with respect to the polarizing plate for observation. The above polarizing plate was placed to be Next, the polarizing plate is irradiated with light from the back light through the observing polarizing plate (light intensity 15,000 cd), and the polarizing plate is visually observed from 1 m from directly above the polarizing plate, based on the following judgment criteria The color spots of the polarizing plate were evaluated by sensory evaluation. The results are shown in Table 1.
:: color spots that are problematic in recent years are not recognized.
X: Color spots that became a problem in recent years were visually recognized.

  As is clear from the above results, in the case of Example 1, the degree of optical spots (retardation spots and orientation axis angle spots) and the degree of color spots of the polarizing plate in the PVA film (raw films 1 and 2) It can be seen that the optical spots present in the PVA film can be sufficiently evaluated. On the other hand, in the case of Comparative Example 1, in the case of using the original sheet 1, although the degree of color spots is large when made into a polarizing plate, the degree of retardation spots and orientation axis angle spots is small, It can be seen that it has not been possible to sufficiently evaluate the optical spots that cause color spots that are particularly problematic in polarizing plates having a high light transmittance in recent years that are inherent in PVA films.

Claims (7)

A method for evaluating the optical spots of polyvinyl alcohol film, a polyvinyl alcohol film was swollen without stretching in while immersed in water, the optical spots of the polyvinyl alcohol film, the surface of the polyvinyl alcohol film A method to evaluate the attached water without removing it .   The method according to claim 1, wherein the optical plaque is evaluated by evaluating retardation spots and / or orientation axial angular spots of the polyvinyl alcohol film after swelling with water. The method according to claim 1 , wherein the temperature of water at the time of immersing the polyvinyl alcohol film in water is 20 to 50 ° C. The method according to claim 1 , wherein the immersion time for immersing the polyvinyl alcohol film in water is 10 to 300 seconds. The method according to any one of claims 1 to 4 , wherein the polyvinyl alcohol film is a raw film for producing an optical film. The method according to claim 5 , wherein the optical film is a polarizing film. And a step of evaluating the optical spots of polyvinyl alcohol film by the method of claim 5 or 6, and a process for manufacturing an optical film by using a polyvinyl alcohol film in which the optical spots is evaluated, method for producing an optical film .