JP2004020629A - Manufacturing method of polarizing film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of polarizing films with little color shade and causing little curling when formed into a polarizing plate. <P>SOLUTION: This manufacturing method of the polarizing film is characterized in that polyvinyl alcohol film having a thickness of 10-50 μm and a width of 2-3.5 m is drawn by a dry process using a drawing roll at 80-140°C. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a polarizing film useful as a material for a polarizing plate used as a component of a liquid crystal display device.
[0002]
[Prior art]
A polarizing plate having a function of transmitting and blocking light is a fundamental component of a liquid crystal display device (LCD) together with a liquid crystal having a function of switching light. This LCD can be applied to small devices such as calculators and watches in the early stages of development, but recently to laptop computers, word processors, liquid crystal color projectors, in-vehicle navigation systems, liquid crystal televisions, personal phones, and indoor and outdoor measuring instruments. Thus, a polarizing plate having a large area and a uniform optical performance over the entire area has been required more than conventional products.
[0003]
A polarizing plate is generally used for uniaxially stretching and dyeing a polyvinyl alcohol film (hereinafter, polyvinyl alcohol film may be abbreviated as “PVA” and polyvinyl alcohol film may be abbreviated as “PVA film”), or after dyeing and uniaxially stretching. A protective film such as a cellulose triacetate (TAC) film or a cellulose acetate / butyrate (CAB) film is applied to a polarizing film obtained by performing a fixing treatment with a boron compound (the dyeing and the fixing treatment may be performed simultaneously). It is configured to be stuck.
[0004]
[Problems to be solved by the invention]
By the way, a polarizing plate sometimes has color spots having variations in optical performance over the entire area. There are various causes for the occurrence of the color spots, and it is difficult to confirm the color spots unless it is a final product (polarizing plate) in which a protective film or the like is laminated on a polarizing film. If color spots appear at the stage of the final product, secondary materials such as a protective film having no problem in quality are also discarded together with the polarizing plate as defective, resulting in a large loss. Conventionally, as a method for reducing color spots, studies have been made on reducing the thickness spots and birefringence spots of a PVA film as proposed in Japanese Patent Application Laid-Open No. 6-138319. By the method of reducing the thickness unevenness and birefringence unevenness of the PVA film, the color unevenness of the polarizing plate can be reduced to some extent, and it became possible to satisfy the required level at the time, but the performance in recent years has been improved. It has proven difficult to reduce the level of color spots that is problematic in the final product (polarizers and liquid crystal display devices).
[0005]
Also, with the increase in the size of the liquid crystal display device, a polarizing film having a large area has been required. Conventional liquid crystal display devices have a relatively small display area and use a polarizing plate alone, so color spots rarely become a problem.However, when the display area is large, the uniformity of the entire display area is low. Is required, and the film is often used in combination with another film such as a film for correcting a viewing angle. In particular, in the case of a polarizing film produced by uniaxially stretching a PVA film in the film flow direction, streak-like color spots are likely to occur in the film flow direction. It is considered that this is because the film is not stretched uniformly in the width direction, and the stretching variation appears as optical color spots. In the case where a PVA film having a film width of less than 2 m was stretched as in the related art, it was relatively easy to uniformly stretch the film in the width direction. As it spreads, uniform stretching has become more difficult. In particular, when the PVA film is uniaxially stretched by the dry method, as compared with the case where the PVA film is uniaxially stretched by the wet method, streak-like color spots which are considered to be caused by stretch spots are more remarkable.
Since color spots cause phenomena such as brightness spots when incorporated in a liquid crystal display device or the like, there is a problem that causes quality deterioration. In particular, as the screen becomes larger, if a streak-like color spot exists in the flow direction, it becomes difficult to collect the product while avoiding the spot, which is a big industrial problem.
[0006]
In addition, polarizing plates are often used by coating them with an adhesive and bonding them to the front glass of liquid crystal display devices.However, as the size of liquid crystal display devices increases, curling due to stress inherent in the polarizing film occurs. This is likely to occur, making it difficult to evenly bond a large-area polarizing plate. Curling often occurs due to the difference in the magnitude of the stresses on the front and back of the film, and the problem that the difference in the stretching stress in the production of the polarizing film is large in the thickness direction tends to cause a problem. Further, color unevenness as described above may occur due to the inability to perform uniform stretching in the thickness direction.
[0007]
[Problems to be solved by the invention]
Therefore, an object of the present invention is to provide a method for manufacturing a polarizing film which has a small amount of color spots and a small degree of curl when formed into a polarizing plate in order to meet the high required performance of a liquid crystal display which is becoming larger. is there.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, a method for producing a polarizing film according to the present invention is a method in which a polyvinyl alcohol film having a thickness of 10 to 50 μm and a film width of 2 to 3.5 m is drawn by using a stretching roll at 80 to 140 ° C. It is characterized by stretching.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
The PVA film used in the method for producing a polarizing film of the present invention has a thickness of 10 to 50 μm. If the thickness of the PVA film is less than 10 μm, it is not preferable because the film is frequently cut during stretching and it becomes difficult to increase the stretching ratio. When the thickness of the PVA film is larger than 50 μm, a temperature difference or the like occurs between the surface of the PVA film that contacts the stretching roll and the surface that does not contact the stretching roll, and the stretching state is different. A difference in physical properties is generated in the thickness direction, which causes problems such as curling, which is not preferable.
The thickness of the PVA film is preferably from 15 to 45 μm, particularly preferably from 20 to 40 μm.
[0010]
The PVA film used in the present invention has a film width of 2 to 3.5 m. Even if the film width is smaller than 2 m, a polarizing film with less color unevenness can be obtained. However, when a PVA film with a narrow film width is stretched, color unevenness is originally hardly generated, so that the effect of reducing color unevenness is difficult to understand. . When the film width is larger than 3.5 m, it is difficult to uniformly stretch the PVA film in the width direction, so that the effect of reducing color spots is small.
The film width of the PVA film is preferably 2.3 to 3.5 m, more preferably 2.5 to 3.5 m, and particularly preferably 2.8 to 3.5 m.
[0011]
The method for producing a polarizing film of the present invention is characterized in that a polyvinyl alcohol film having a specific thickness and width is stretched by a dry method using a stretching roll at 80 to 140 ° C. If the setting temperature of the stretching roll is lower than 80 ° C., the stretching stress of the polyvinyl alcohol film becomes too high, and it becomes difficult to perform uniform stretching in the width direction, which is likely to cause color unevenness. When the set temperature of the stretching roll is higher than 140 ° C., the film is softened and easily stretched. However, even if stretching is performed under such conditions, the obtained polarizing film does not exhibit good polarizing performance, which is not preferable. The set temperature of the stretching roll is preferably from 90 to 130 ° C, particularly preferably from 100 to 120 ° C. It is important that the polyvinyl alcohol film is stretched on a stretching roll.
[0012]
In the present invention, stretching a PVA film by a dry method means an operation of stretching a PVA film in air, and stretching performed in water or an aqueous solution such as boric acid aqueous solution, or in a solvent such as a plasticizer. It is distinguished from the law. There are various methods for stretching a film by a dry method, for example, a method in which the whole film is heated and stretched by being pulled between tenters or rolls, such as a film made of polyester or nylon, or a vinyl chloride film. And a method of stretching by applying a force in the thickness direction of the film while rolling the film, such as that described in (1). In the present invention, the PVA film is brought into contact with a stretching roll set at a specific temperature sufficiently higher than the temperature of the PVA film, and the temperature of the PVA film is raised and softened only at the point of contact with the stretching roll, It is important that the PVA film is stretched only on stretch rolls. Therefore, the difference between the temperature of the PVA film before contact with the stretching roll and the temperature of the stretching roll is preferably at least 10 ° C, more preferably 15 ° C or more, still more preferably 20 ° C or more, and 25 ° C. The above is particularly preferred. If the temperature difference is smaller than 10 ° C., unnecessary stretching may occur at a portion other than on the stretching roll due to the tension applied to the film by the stretching roll.
[0013]
In the present invention, it is preferable that the PVA film is heated using a preheating roll at 50 to 70 ° C. before being stretched using the stretching roll. If the film is preheated before stretching by the stretching roll, the temperature difference in the thickness direction of the film becomes small when the film is heated by the stretching roll, so that uniform stretching in the thickness direction is facilitated, and color unevenness is reduced. This is preferable because the problem such as curling of the polarizing plate is reduced. When the temperature of the preheating roll is lower than 50 ° C., the effect of the preheating is small, and there is no difference from the case where the preheating roll is not used. If the temperature of the preheating roll is higher than 70 ° C., the film is likely to be softened, and unnecessary stretching is likely to occur at locations other than on the stretching roll.
The temperature of the preheating roll is preferably 55 to 70 ° C, particularly preferably 60 to 70 ° C.
[0014]
In the present invention, the preheating roll is preferably provided on the surface opposite to the surface of the PVA film in contact with the stretching roll. If the preheating roll is placed on the opposite side of the film surface that is in contact with the stretching roll, the temperature difference in the thickness direction of the film during heating of the film by the stretching roll is small, so that uniform stretching in the thickness direction is easy. As a result, color spots are easily reduced and problems such as curling of the polarizing plate are reduced, which is preferable.
[0015]
It is preferable that the PVA film used in the present invention is heated with air at 50 to 120 ° C. before being stretched using a stretching roll. If the PVA film is heated with air at 50 to 120 ° C. before stretching, the temperature difference in the thickness direction becomes small when the film is heated by the stretching roll, so that uniform stretching in the thickness direction is facilitated. This is preferable because spots are easily reduced and problems such as curling of the polarizing plate are reduced.
If the PVA film is heated using a preheating roll, the PVA film is heated with air before heating by the preheating roll.
[0016]
In the present invention, the stretching of the PVA film is performed in two stages, ie, the first stage is stretched 2 to 4 times, and the second stage is stretched 1.5 to 3 times, and finally the stretching ratio of the film is 4 to 5 times. Preferably it is doubled. By performing stretching in two stages, uniform stretching in the thickness direction is facilitated, and color spots are likely to be reduced, which is preferable. In addition, the effect of improving the polarization performance can be expected by performing the stretching in two stages. When the stretching ratio is out of the above-mentioned range, the effect of reducing color spots is reduced. The stretching ratio is a stretching ratio with respect to the PVA film before stretching.
[0017]
When the stretching of the PVA film is performed in two stages, it is preferable that the surface of the PVA film contacting the stretching roll is different between the first stage and the second stage. In the first-stage stretching, since there is a difference in temperature, stress, and the like between the film surface on the side contacting the stretching roll and the film surface on the air side, the stretching state tends to be different in the thickness direction, and curling tends to occur. However, in the second-stage stretching, if the stretching operation is performed so as to come into contact with the stretching roll from the side different from the first-stage stretching, a difference in the thickness direction is less likely to appear, so that an effect that curling is reduced is brought about. It is.
[0018]
Before the PVA film used in the present invention is stretched using a stretching roll, the humidity of the air contacting the film within 1 m upstream from the stretching roll is preferably 50 to 95% RH. When the film is heated by the stretching roll, the difference in moisture in the thickness direction is reduced, so that uniform stretching in the thickness direction is facilitated. As a result, color spots are easily reduced and problems such as curling of the polarizing plate are also reduced. If the humidity of the air is lower than 50% RH, the moisture release from the film is large, and the fluctuation of water in the film becomes large. Even if the humidity of the air is higher than 95% RH, the film absorbs a large amount of moisture, and the moisture fluctuation in the film increases, which is likely to cause color spots after stretching. The humidity of the air contacting the film within 1 m upstream from the stretching roll is more preferably 60 to 90% RH.
[0019]
The PVA used in the present invention is produced, for example, by saponifying a polyvinyl ester obtained by polymerizing a vinyl ester. A modified PVA in which an unsaturated carboxylic acid or a derivative thereof, an unsaturated sulfonic acid or a derivative thereof, an α-olefin having 2 to 30 carbon atoms, and the like are graft-copolymerized in a main chain of PVA at a ratio of less than 5 mol%; Manufactured by saponifying a modified polyvinyl ester obtained by copolymerizing a vinyl ester with an unsaturated carboxylic acid or a derivative thereof, an unsaturated sulfonic acid or a derivative thereof, an α-olefin having 2 to 30 carbon atoms at a ratio of less than 15 mol%. And so-called polyvinyl acetal resin obtained by cross-linking a part of hydroxyl groups of unmodified or modified PVA with aldehydes such as formalin, butyraldehyde and benzaldehyde.
[0020]
Examples of the vinyl ester include vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate, and vinyl benzoate.
[0021]
The comonomer used for the modified PVA is copolymerized mainly for the purpose of modifying the PVA, and is used within a range that does not impair the purpose of the present invention. Examples of such comonomers include α-olefins such as ethylene, propylene, 1-butene, and isobutene; acrylic acid and its salts; methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, Acrylates such as n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate; methacrylic acid and its salts; methyl methacrylate; Ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, etc. Methacrylic acid Ters; acrylamide, N-methylacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide, diacetoneacrylamide, acrylamidepropanesulfonic acid and its salts, acrylamidopropyldimethylamine and its salts, N-methylolacrylamide and its derivatives, etc. Methacrylamide derivatives such as methacrylamide, N-methyl methacrylamide, N-ethyl methacrylamide, methacrylamide propanesulfonic acid and salts thereof, methacrylamidopropyl dimethylamine and salts thereof, N-methylol methacrylamide and derivatives thereof N-vinyl amides such as N-vinyl formamide, N-vinyl acetamide, N-vinyl pyrrolidone; methyl vinyl ether , Vinyl ethers such as 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 and stearyl vinyl ether; nitriles such as acrylonitrile and methacrylonitrile; Vinyl halides such as vinyl, vinylidene chloride, vinyl fluoride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid and its salts or esters; itaconic acid and its salts or esters; vinyl trimethoxy Vinylsilyl compounds such as silane; and isopropenyl acetate. Of these, α-olefins are preferred, and ethylene is particularly preferred. The amount of modification of the modified PVA is preferably less than 15 mol%.
[0022]
The degree of saponification of PVA is preferably at least 95 mol%, more preferably at least 98 mol%, further preferably at least 99 mol%, and most preferably at least 99.5 mol%, from the viewpoint of polarization performance and durability.
[0023]
The saponification degree of the PVA indicates the ratio of units actually saponified to vinyl alcohol units among units that can be converted to vinyl alcohol units when the polyvinyl ester is saponified. In addition, the saponification degree of PVA was measured by the method described in JIS.
[0024]
The polymerization degree of PVA is preferably 500 or more, more preferably 1000 or more, still more preferably 1500 or more, and most preferably 2500 or more, from the viewpoint of polarization performance and durability. The upper limit of the PVA polymerization degree is preferably 8000 or less, more preferably 6000 or less.
[0025]
The polymerization degree of the PVA is measured according to JIS K 6726. That is, it is determined from the intrinsic viscosity measured in water at 30 ° C. after the PVA is re-saponified and purified.
[0026]
As a method for producing a PVA film using the above PVA, for example, a PVA solution (a stock solution of a polyvinyl alcohol film) in which PVA is dissolved in a solvent is used in addition to a film forming method by a melt extrusion method using hydrated PVA. Casting method, wet film forming method (discharge into poor solvent), gel film forming method (after once cooling and gelling the PVA aqueous solution, the solvent is extracted and removed, and the PVA film is removed. And a method based on a combination thereof. Among these, the casting film forming method and the melt extrusion film forming method are preferable because a good polarizing film can be obtained.
[0027]
As a solvent for dissolving PVA used in producing a PVA film, for example, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, Examples thereof include trimethylolpropane, ethylenediamine, diethylenetriamine, glycerin, and water, and one or more of these can be used. Among them, dimethyl sulfoxide, water, or a mixed solvent of glycerin and water is preferably used.
[0028]
The proportion of PVA in the PVA solution or the hydrated PVA used when producing the PVA film varies depending on the degree of polymerization of PVA, but is preferably 20 to 70% by weight, more preferably 25 to 60% by weight. And more preferably from 30 to 55% by weight, and most preferably from 35 to 50% by weight. When the proportion of PVA is large, the viscosity becomes too high, so that filtration and defoaming become difficult, and it becomes difficult to obtain a film free of foreign matter and defects. If the proportion of PVA is small, drying takes a lot of time and energy, which is not preferable from an industrial viewpoint. Further, the PVA solution or the water-containing PVA may contain a plasticizer, a surfactant, a dichroic dye, and the like, if necessary.
[0029]
When producing a PVA film, it is preferable to add a polyhydric alcohol as a plasticizer. Examples of the polyhydric alcohol include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylolpropane, and the like. One or more of these may be used. can do. Among these, diglycerin, ethylene glycol, and glycerin are preferably used because they have an excellent effect of improving stretchability.
[0030]
The amount of the plasticizer added is preferably 1 to 30 parts by weight, more preferably 3 to 25 parts by weight, and most preferably 5 to 20 parts by weight based on 100 parts by weight of PVA. If the amount is less than 1 part by weight, the dyeing properties and the stretchability may be reduced. If the amount is more than 30 parts by weight, the PVA film may be too flexible and the handleability may be reduced.
[0031]
When producing a PVA film, it is preferable to add a surfactant. The type of the surfactant is not particularly limited, but an anionic or nonionic surfactant is preferable. Suitable examples of the anionic surfactant include a carboxylic acid type such as potassium laurate, a sulfate type such as octyl sulfate, and a sulfonic acid type such as dodecylbenzenesulfonate. Nonionic surfactants include, for example, alkyl ether types such as polyoxyethylene oleyl ether, alkyl phenyl ether types such as polyoxyethylene octyl phenyl ether, alkyl ester types such as polyoxyethylene laurate, and polyoxyethylene lauryl amino. Alkylamine type such as ether, alkylamide type such as polyoxyethylene lauric amide, polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether, alkanolamide type such as diethanolamide oleate, polyoxyalkylene allyl phenyl ether Nonionic surfactants such as the allyl phenyl ether type are preferred. These surfactants can be used alone or in combination of two or more.
[0032]
The addition amount of the surfactant is preferably 0.01 to 1 part by weight, more preferably 0.02 to 0.5 part by weight, and most preferably 0.05 to 0.3 part by weight based on 100 parts by weight of PVA. When the amount is less than 0.01 part by weight, the effect of improving the film forming property and the releasability to be brought about by the addition of the surfactant is hardly exhibited, and when the amount is more than 1 part by weight, the surfactant is eluted on the surface of the PVA film. This may cause blocking and reduce handling.
[0033]
The present invention relates to a method for producing a polarizing film by uniaxially stretching a PVA film by a dry method. In order to produce a polarizing film from a PVA film using this method, for example, uniaxial stretching of a PVA film by a dry method, dyeing, if necessary, uniaxial stretching of a second step by a dry method or a wet method, fixing treatment, A drying treatment and, if necessary, a heat treatment may be performed, and there is no particular limitation on the order of the dyeing, the second-stage uniaxial stretching by the dry method or the wet method, and the fixing treatment. The second-stage uniaxial stretching by a dry method or a wet method may be performed twice or more times.
In the present invention, the stretching by the dry method refers to an operation of stretching the PVA film in the air, while the stretching by the wet method refers to stretching the PVA film in water or an aqueous solution such as an aqueous boric acid solution or a plasticizer. And the like, which is an operation for stretching in a solvent, and the two are distinguished.
[0034]
The dyeing of the PVA film may be performed at any stage before, during or after the uniaxial stretching. Dyes used for dyeing include iodine-potassium iodide; direct black 17, 19, 154; direct brown 44, 106, 195, 210, 223; direct red 2, 23, 28, 31, 37, 39, 79, 81. Direct Blue 1, 15, 22, 78, 90, 98, 151, 168, 202, 236, 249, 270; Direct Violet 9, 12, 51, 98; Direct Green 1, 85; Dichroic dyes such as Yellow 8, 12, 44, 86, 87 and Direct Orange 26, 39, 106, 107 can be used alone or in a mixture of two or more. The dyeing of the PVA film is generally performed by immersing the PVA film in a solution containing the dye, but the processing method and processing conditions such as mixing the dye with the PVA film to form a film are as follows. There is no particular limitation.
[0035]
For the second-stage uniaxial stretching, the PVA film is stretched in a warm aqueous solution such as a boric acid aqueous solution (which may be in a solution containing the dye or in a fixing bath described below). A dry stretching method of stretching in air can be used. The stretching temperature is not particularly limited, but is preferably 30 to 90 ° C. when the PVA film is stretched in a warm aqueous solution or the like, and 50 to 180 ° C. when the PVA film is stretched in air. The thickness of the stretched film is preferably from 3 to 45 μm, more preferably from 5 to 30 μm.
[0036]
In order to strengthen the adsorption of the dye to the PVA film, a fixing treatment is often performed. Usually, boric acid and / or a boron compound is added to the treatment bath used for the fixing treatment. Further, an iodine compound may be added to the treatment bath as needed.
[0037]
The drying treatment (heat treatment) of the obtained polarizing film is preferably performed at 30 to 150 ° C, more preferably at 50 to 150 ° C.
[0038]
The polarizing film obtained as described above is usually used as a polarizing plate by bonding an optically transparent protective film having mechanical strength to both surfaces or one surface thereof. As the protective film, a cellulose triacetate (TAC) film, a cellulose acetate / butyrate (CAB) film, an acrylic film, a polyester film, or the like is used. Examples of the adhesive used for bonding include a PVA-based adhesive and a urethane-based adhesive. Among them, a PVA-based adhesive is preferable. In the polarizing plate thus obtained, the thickness of the adhesive layer is preferably in the range of 0.5 to 10 μm.
[0039]
In the present invention, the curling degree of the polarizing plate obtained by laminating the protective film on the polarizing film after standing for 24 hours at 60 ° C. and 90% RH is preferably 90 ° or less. If the degree of curl of the polarizing plate exceeds 90 degrees, when the polarizing plate is bonded to the front glass plate or the like of the liquid crystal display device, the end portions may be bent and the bonding becomes difficult, which is not preferable. The curl degree of the polarizing plate is more preferably 80 degrees or less, and particularly preferably 60 degrees or less.
[0040]
The polarizing plate obtained as described above is used as a component of a liquid crystal display device by being coated with a pressure-sensitive adhesive such as an acrylic resin and then bonded to a glass substrate. When bonding a polarizing plate to a glass substrate, a retardation film, a viewing angle improving film, a brightness improving film, and the like may be simultaneously bonded. There are various types of display methods of liquid crystal display devices, and there are various types of methods of using a polarizing plate.However, usually, a stretching direction of a polarizing film is opposed to a right angle direction with a liquid crystal substrate interposed therebetween. Two polarizing plates are used. The polarizing plate obtained from the polarizing film obtained by the method of the present invention is preferably used on the front side (the front side of the liquid crystal display device) where quality requirements are stricter, since the problem of color spots and the like is small.
[0041]
【Example】
Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto. In the following Examples and Comparative Examples, the optical performance of the polarizing film and the color spots and curling degree of the polarizing plate were evaluated by the following methods.
[0042]
Optical performance of polarizing film:
A sample of a polarizing film of about 4 cm × 4 cm was measured using a spectrophotometer UV-2200 (supplied with an integrating sphere) manufactured by Shimadzu Corporation in accordance with the standards of the Japan Electronics Machinery Manufacturers Association (EIAJ) LD-201-1983, using a C light source. The Y value was corrected for the visibility in the visible light region of the 2 degree visual field, and the transmittance was determined from the average value in the 45 ° and −45 ° directions with respect to the stretching axis direction of the polarizing film. In the same manner as above, the Y values of the parallel Nicols and the cross Nicols were measured to determine the degree of polarization.
[0043]
Color spots on polarizing plate:
A polarizing plate having a full width was placed in a direction orthogonal to a polarizing plate for observation (two laminated in parallel, a degree of polarization of 99.99% or more), and the degree of color spot was determined by visual observation.
[0044]
Curling degree of polarizing plate:
After leaving the 1 m square polarizing plate at 60 ° C. and 90% RH for 24 hours, the polarizing plate is placed on a horizontal table with the surface curled inward facing upward, and 1 cm from the end of the polarizing plate. The angle between the extension of the plane of the area and the horizontal platform was determined.
[0045]
Example 1
100 parts by weight of PVA having a degree of saponification of 99.95 mol% and a degree of polymerization of 2400, impregnated with 10 parts by weight of glycerin and 170 parts by weight of water are melt-kneaded. Filmed. Thereafter, the PVA film obtained by drying and heat treatment had a thickness of 30 μm and a width of 3 m.
The obtained PVA film was continuously processed in the order of uniaxial stretching by a dry method, preliminary swelling, dyeing, uniaxial stretching by a wet method, fixing treatment, drying and heat treatment to prepare a polarizing film.
The PVA film was heated with warm air at 80 ° C., preheated using a preheating roll, and then subjected to uniaxial stretching by a dry method. The temperature of the preheating roll was 60 ° C, and the temperature of the stretching roll used for uniaxial stretching by the dry method was 100 ° C. The preheating roll was positioned to contact the PVA film upstream of the stretch roll, and the contacting surface was opposite the stretch roll. The air passing before the PVA film came into contact with the stretching roll had been adjusted to a temperature of 90 ° C. and a humidity of 80% RH. The PVA film was stretched by the difference between the peripheral speed of the stretching roll and the peripheral speed of the driving roll disposed upstream thereof, and the stretching was performed in two stages. The film was stretched 3 times in the first step and further 1.5 times in the second step. The first-stage stretching roll and the second-stage stretching roll were arranged so as to be in contact with the PVA film on opposite sides of the film. Most of the stretching of the PVA film was performed in the vicinity where the PVA film was in contact with the heating roll, and stretching unevenness in the width direction was not visually observed.
The PVA film after uniaxial stretching by the dry method was immersed in water at 30 ° C. for 30 seconds to pre-swell, and immersed in an aqueous solution of 35 ° C. having an iodine concentration of 0.6 g / l and a potassium iodide concentration of 40 g / l for 3 minutes. . Subsequently, the film was uniaxially stretched 1.5 times in a 50% aqueous solution having a boric acid concentration of 4% to obtain a potassium iodide concentration of 60 g / l, a boric acid concentration of 40 g / l, and a zinc chloride concentration of 10 g / l at 30 ° C. It was immersed in an aqueous solution for 5 minutes to perform a fixing process. Thereafter, the obtained PVA film was taken out, dried with hot air at 40 ° C., and further heat-treated at 100 ° C. for 5 minutes. The polarizing performance of the polarizing film thus obtained was such that the transmittance was 43.5%, the degree of polarization was 99.9%, and the dichroic ratio was 56.7.
The obtained polarizing film was bonded to a triacetate film using a 10% PVA aqueous solution adhesive to obtain a polarizing plate. Observation of the color spots on the polarizing plate revealed no color spots over the entire surface of the polarizing plate and was favorable. The curling degree of the polarizing plate was 30 degrees. When this polarizing plate was incorporated in a liquid crystal display device, it was good without color spots.
[0046]
Example 2
A PVA film having a width of 3 m and a thickness of 40 μm obtained in the same manner as in Example 1 is continuously treated in the order of uniaxial stretching by dry method, preliminary swelling, dyeing, uniaxial stretching by wet method, fixing treatment, drying and heat treatment. Thus, a polarizing film was produced.
Uniaxial stretching by a dry method was performed in the same manner as in Example 1 except that the temperature of the stretching roll was 110 ° C. Visual observation of the PVA film obtained by uniaxial stretching showed no stretching unevenness in the width direction.
Next, the PVA film after the uniaxial stretching was immersed in water at 30 ° C. for 30 seconds for pre-swelling, and immersed in an aqueous solution of 35 ° C. having an iodine concentration of 0.6 g / l and a potassium iodide concentration of 40 g / l for 3 minutes. Subsequently, the film was uniaxially stretched 1.5 times in a 50% aqueous solution having a boric acid concentration of 4% to obtain a potassium iodide concentration of 60 g / l, a boric acid concentration of 40 g / l, and a zinc chloride concentration of 10 g / l at 30 ° C. It was immersed in an aqueous solution for 5 minutes to perform a fixing process. Thereafter, the obtained PVA film was taken out, dried with hot air at 40 ° C., and further heat-treated at 100 ° C. for 5 minutes.
The obtained polarizing film was bonded to a triacetate film using a 10% PVA aqueous solution adhesive to obtain a polarizing plate. Observation of the color spots on the polarizing plate revealed no color spots over the entire surface of the polarizing plate and was favorable. The curling degree of the polarizing plate was 45 degrees. When this polarizing plate was incorporated in a liquid crystal display device, it was good without color spots.
[0047]
Example 3
The PVA film having a width of 3 m and a thickness of 30 μm obtained in the same manner as in Example 1 is continuously treated in the order of uniaxial stretching by dry method, preliminary swelling, dyeing, uniaxial stretching by wet method, fixing treatment, drying and heat treatment. Thus, a polarizing film was produced.
Uniaxial stretching by a dry method was performed in the same manner as in Example 1 except that the first-stage stretching ratio was 4.2 times. Visual observation of the PVA film obtained by uniaxial stretching showed no stretching unevenness in the width direction.
Next, the PVA film after the uniaxial stretching was immersed in water at 30 ° C. for 30 seconds for pre-swelling, and immersed in an aqueous solution of 35 ° C. having an iodine concentration of 0.6 g / l and a potassium iodide concentration of 40 g / l for 3 minutes. Subsequently, the film was uniaxially stretched 1.5 times in a 50% aqueous solution having a boric acid concentration of 4% to obtain a potassium iodide concentration of 60 g / l, a boric acid concentration of 40 g / l, and a zinc chloride concentration of 10 g / l at 30 ° C. It was immersed in an aqueous solution for 5 minutes to perform a fixing process. Thereafter, the obtained PVA film was taken out, dried with hot air at 40 ° C., and further heat-treated at 100 ° C. for 5 minutes.
The obtained polarizing film was bonded to a triacetate film using a 10% PVA aqueous solution adhesive to obtain a polarizing plate. When the color spots of the polarizing plate were observed, slight color spots were observed over the entire surface of the polarizing plate, but at a practically acceptable level. The curling degree of the polarizing plate was 60 degrees. When this polarizing plate was incorporated in a liquid crystal display device, color spots were slightly recognizable and relatively good.
[0048]
Comparative Example 1
The PVA film having a width of 3 m and a thickness of 30 μm obtained in the same manner as in Example 1 is continuously treated in the order of uniaxial stretching by dry method, preliminary swelling, dyeing, uniaxial stretching by wet method, fixing treatment, drying and heat treatment. Thus, a polarizing film was produced.
Uniaxial stretching by a dry method was performed in the same manner as in Example 1 except that the temperature of the stretching roll was 70 ° C. During the uniaxial stretching, the film slipped on the stretching roll, and wrinkles occurred in the film. However, when the film was visually observed, stretching unevenness in the width direction was not recognized.
Next, the PVA film after the uniaxial stretching was immersed in water at 30 ° C. for 30 seconds for pre-swelling, and immersed in an aqueous solution of 35 ° C. having an iodine concentration of 0.6 g / l and a potassium iodide concentration of 40 g / l for 3 minutes. Subsequently, the film was uniaxially stretched 1.5 times in a 50% aqueous solution having a boric acid concentration of 4% to obtain a potassium iodide concentration of 60 g / l, a boric acid concentration of 40 g / l, and a zinc chloride concentration of 10 g / l at 30 ° C. It was immersed in an aqueous solution for 5 minutes to perform a fixing process. Thereafter, the obtained PVA film was taken out, dried with hot air at 40 ° C., and further heat-treated at 100 ° C. for 5 minutes.
The obtained polarizing film was bonded to a triacetate film using a 10% PVA aqueous solution adhesive to obtain a polarizing plate. When color spots on the polarizing plate were observed, streak-shaped color spots were observed in the flow direction of the polarizing plate. The curling degree of the polarizing plate was 120 degrees. When this polarizing plate was incorporated into a liquid crystal display device, color spots were observed at almost the same positions as those where color unevenness was observed on the polarizing plate, and the product was rejected.
[0049]
Comparative Example 2
The PVA film having a width of 3 m and a thickness of 30 μm obtained in the same manner as in Example 1 is continuously treated in the order of uniaxial stretching by dry method, preliminary swelling, dyeing, uniaxial stretching by wet method, fixing treatment, drying and heat treatment. Thus, a polarizing film was produced.
Uniaxial stretching was performed by a dry method in the same manner as in Example 1 except that the temperature of the stretching roll was set to 150 ° C. No abnormality of the film on the stretching roll was observed during the uniaxial stretching, and when the film was visually observed, stretching unevenness in the width direction was not observed.
Next, the PVA film after the uniaxial stretching was immersed in water at 30 ° C. for 30 seconds for pre-swelling, and immersed in an aqueous solution of 35 ° C. having an iodine concentration of 0.6 g / l and a potassium iodide concentration of 40 g / l for 3 minutes. Subsequently, the film was uniaxially stretched 1.5 times in a 50% aqueous solution having a boric acid concentration of 4% to obtain a potassium iodide concentration of 60 g / l, a boric acid concentration of 40 g / l, and a zinc chloride concentration of 10 g / l at 30 ° C. It was immersed in an aqueous solution for 5 minutes to perform a fixing process. Thereafter, the obtained PVA film was taken out, dried with hot air at 40 ° C., and further heat-treated at 100 ° C. for 5 minutes.
The obtained polarizing film was bonded to a triacetate film using a 10% PVA aqueous solution adhesive to obtain a polarizing plate. When color spots on the polarizing plate were observed, streak-shaped color spots were observed in the flow direction of the polarizing plate. The streak-like color spots had low polarization performance. The curling degree of the polarizing plate was 150 degrees. When this polarizing plate was incorporated into a liquid crystal display device, color spots were observed at almost the same positions as those where color unevenness was observed on the polarizing plate, and the product was rejected.
[0050]
【The invention's effect】
The polarizing film obtained by the production method of the present invention has a small number of color spots and a small degree of curl when formed into a polarizing plate, and thus is useful as a material for the polarizing plate. Utilizing the performance, it can be effectively used as a component of a liquid crystal display device having a large display screen.

Claims (7)

A method for producing a polarizing film, comprising: stretching a polyvinyl alcohol film having a thickness of 10 to 50 µm and a film width of 2 to 3.5 m by a dry method using a stretching roll at 80 to 140 ° C. The method for producing a polarizing film according to claim 1, wherein the polyvinyl alcohol film is heated using a preheating roll at 50 to 70 ° C before being stretched by a dry method using a stretching roll. The method for producing a polarizing film according to claim 2, wherein the preheating roll is provided on a surface opposite to a surface of the polyvinyl alcohol film that is in contact with the stretching roll. The method for producing a polarizing film according to claim 3, wherein the polyvinyl alcohol film is heated with air at 50 to 120C before being stretched by a dry method using a stretching roll. The stretching of the polyvinyl alcohol film is divided into two stages, the first stage is stretched 2 to 4 times, and the second stage is stretched 1.5 to 3 times, and finally the stretching ratio of the film is 4 to 5 times The method for producing a polarizing film according to any one of claims 1 to 4, wherein: The method for producing a polarizing film according to claim 5, wherein the surface of the polyvinyl alcohol film in contact with the stretching roll is different between the first stage and the second stage. The method for producing a polarizing film according to any one of claims 1 to 6, wherein the humidity of air in contact with the polyvinyl alcohol film within 1 m upstream of the stretching roll is 50 to 95% RH. .