JP2004020636A - Method of manufacturing polarizing film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for a polarizing film which has little color shade and is useful as a polarizing plate material for liquid crystal display of high quality. <P>SOLUTION: When the polarizing film is manufactured by drawing a polyvinyl alcohol film by a dry method using a heating roll, an angle θ which is formed with a line linking a heating roll and a roll located at a downstream side of the heating roll and with an extended line of the polyvinyl alcohol film on a roll located at an upstream side of the heating roll in a state being in contact with the heating roll, is between 5° and 30°. <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. Therefore, a polarizing plate having a large area and a uniform optical performance over the entire area is required more than conventional products.
[0003]
The polarizing plate is generally uniaxially stretched and dyed with a polyvinyl alcohol film (hereinafter, the polyvinyl alcohol film may be abbreviated as “PVA”, and the polyvinyl alcohol film may be abbreviated as “PVA film”), or dyed and uniaxially stretched. 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]
In some cases, the polarizing plate has color spots caused by variations in optical performance over the entire area. Since there are various causes for the occurrence of this color spot, it is difficult to confirm it unless it is a final product (polarizing plate) on which a protective film or the like is laminated. If color spots appear at the stage of the final product, secondary materials such as a protective film having no problem in terms of quality are also discarded together with the polarizing plate as defectives, 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 end products (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, it has become difficult to stretch uniformly. In particular, when the PVA film is uniaxially stretched by the dry method, as compared to 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]
Accordingly, an object of the present invention is to provide a method for producing a polarizing film which is useful as a material for a polarizing plate for a high quality liquid crystal display with less color spots.
[0007]
[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 characterized in that, when a polyvinyl alcohol film is stretched by a dry method using a heating roll to produce a polarizing film, a roll located upstream of the heating roll The angle θ formed by a line extending from the upper polyvinyl alcohol film in contact with the heating roll and a line connecting the heating roll and the roll located downstream thereof is 5 to 30 degrees. Things.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
In the production of the polarizing film according to the method of the present invention, the PVA film is stretched by a dry method using a heating roll, and at this time, as shown in FIG. 1, polyvinyl alcohol on a roll located on the upstream side of the heating roll is used. It is necessary that the angle θ between the line extended while the film is in contact with the heating roll and the line connecting the heating roll and the roll located downstream thereof is 5 to 30 degrees, and 8 to 30 degrees. Is preferably, more preferably 10 to 30 degrees, and particularly preferably 10 to 25 degrees. If the angle θ is less than 5 degrees, the adhesion between the film and the heating roll tends to be insufficient due to the stretching device or the vibration of the film, and stretch unevenness is likely to occur. On the other hand, if the angle is larger than 30 degrees, the air tends to be caught between the PVA film and the heating roll, and if the air is caught, the thermal conductivity of the portion becomes different from that of the surroundings. And may cause color spots.
[0009]
In the present invention, the contact time between an arbitrary portion of the PVA film and the heating roll is preferably 10 seconds or less, more preferably 8 seconds or less, and particularly preferably 7 seconds or less. If the contact time exceeds 10 seconds, heat is applied to the PVA film by the heat of the heating roll, and problems such as poor dyeing in the subsequent steps are likely to occur. In addition, it becomes easier for air to be trapped between the PVA film and the heating roll, and when the air is trapped, the thermal conductivity of that part becomes different from the surroundings, causing unevenness in the heat treatment state and causing color spots. It may be. Further, if the contact time between the heating roll and the PVA film is too short, the time required for heating the film cannot be sufficiently obtained, and this may cause stretch unevenness. Therefore, the lower limit of the contact time is 0.2 seconds. It is.
[0010]
The PVA used in the present invention is produced, for example, by saponifying a polyvinyl ester obtained by polymerizing a vinyl ester. Modified PVA in which unsaturated carboxylic acid or its derivative, unsaturated sulfonic acid or its derivative, α-olefin having 2 to 30 carbon atoms, or the like is graft-copolymerized in the main chain of PVA at a ratio of less than 5 mol%; Manufactured by saponifying a modified polyvinyl ester obtained by copolymerizing an 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 in a proportion 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.
[0011]
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.
[0012]
The comonomer used for the modified PVA is copolymerized mainly for the purpose of modifying the PVA, and is used in 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%.
[0013]
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.
[0014]
The degree of saponification of the PVA indicates the ratio of units actually saponified to vinyl alcohol units among units that can be converted to vinyl alcohol units by saponification. In addition, the saponification degree of PVA was measured by the method described in JIS.
[0015]
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 degree of polymerization of PVA is preferably 8000 or less, more preferably 6000 or less.
[0016]
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.
[0017]
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.
[0018]
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.
[0019]
The proportion of PVA in the PVA solution or the water-containing PVA used in 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. Yes, 30 to 55% by weight is more preferred, and 35 to 50% by weight is most preferred. 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.
[0020]
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.
[0021]
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 property 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.
[0022]
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. Examples of the nonionic surfactant include an alkyl ether type such as polyoxyethylene oleyl ether, an alkyl phenyl ether type such as polyoxyethylene octyl phenyl ether, an alkyl ester type 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.
[0023]
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 difficult to appear, and when the amount is more than 1 part by weight, the surfactant elutes on the surface of the PVA film. This may cause blocking and reduce the handleability.
[0024]
The PVA film used in the present invention preferably has a width of 2 m or more, more preferably 2.5 m or more, further preferably 2.8 m or more, and particularly preferably 3 m or more.
[0025]
The present invention relates to a method for producing a polarizing film by uniaxially stretching a PVA film by a dry method under specific conditions using a heating roll. 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 boric acid aqueous solution. It refers to an operation of stretching in a solvent such as a plasticizer, and the two are distinguished.
[0026]
In the method for producing a polarizing film according to the present invention, a heating roll is used when stretching a PVA film, but this heating roll may also serve as a stretching roll. The temperature of the heating roll during use is preferably 30 ° C. or higher, preferably 50 ° C. or higher, and more preferably 80 ° C. or higher. As shown in FIG. 1, the heating roll is disposed in contact with the PVA film, and is used to increase the temperature of the PVA film by heat conduction. The stretching roll is a driving roll having a higher peripheral speed than the roll located on the upstream side (the unwinding side of the film), and the film is stretched by a speed difference between these rolls.
[0027]
In the method for producing a polarizing film of the present invention, the heating roll can also serve as a stretching roll, and in that case, the surface roughness of the heating roll is preferably 0.1S to 1S, and is preferably 0.2S to 0.9S. More preferably, it is particularly preferably 0.3S to 0.8S. If the surface roughness of the heating roll is smaller than 0.1 S, air entrapment may increase. On the other hand, if it is larger than 1S, the adhesion between the heating roll and the PVA film becomes low, and the film may start to slip at the time of stretching, making it difficult to stretch the film uniformly in the width direction. If the film is not stretched uniformly in the width direction, it causes color spots.
It is preferable that a nip roll is attached to the heating roll. The nip roll is attached to a portion where the PVA film is in close contact with the heating roll, and improves uniform stretching in the width direction by reducing slippage of the film during stretching. Further, in order to reduce air entrapment, uniform stretching in the width direction is improved.
[0028]
As another embodiment, it is also preferable to separately provide a stretching roll in addition to the heating roll, and to arrange the stretching roll on the downstream side of the heating roll. In this case, the temperature of the heating roll is preferably 30 ° C. or higher, preferably 50 ° C. or higher, more preferably 80 ° C. or higher, and particularly preferably 100 ° C. or higher. The heating roll is disposed in contact with the PVA film, and is used to increase the temperature of the PVA film by heat conduction. The stretching roll is a driving roll having a higher peripheral speed than the roll located on the upstream side (the unwinding side of the film), and the film is stretched by a speed difference between these rolls.
[0029]
In the method for producing a polarizing film of the present invention, when the stretching roll is disposed downstream of the heating roll, the surface roughness of the stretching roll is preferably 0.1S to 1S, and 0.2S to 0.9S. Is more preferable, and particularly preferably 0.3S to 0.8S. If the surface roughness of the stretching roll is smaller than 0.1 S, air entrapment may increase. On the other hand, if it is larger than 1S, the adhesion between the stretching roll and the PVA film may be low, and the film may begin to slip during stretching, making it difficult to stretch uniformly in the width direction. If the film is not stretched uniformly in the width direction, it causes color spots.
The temperature of the stretching roll is preferably from 10 to 50 ° C, more preferably from 10 to 40 ° C, and particularly preferably from 10 to 30 ° C. If the temperature of the stretching roll is lower than 10 ° C., moisture in the air or the like may condense on the roll and contaminate the film. If the temperature is higher than 50 ° C., the PVA film is stretched on the stretching roll, and it may be difficult to stretch the film uniformly in the width direction. Since it is important to stretch the PVA film on a heating roll in order to achieve uniform stretching in the width direction, it is preferable to set the temperature of the heating roll higher than the temperature of the stretching roll.
Further, the surface roughness of the heating roll is preferably 50S or more, more preferably 60S or more, and particularly preferably 70S or more. If the surface roughness of the heating roll is less than 50S, the movement of the PVA film in the width direction is hindered, so that wrinkles may occur, and it may be difficult to uniformly stretch the film in the width direction. If the surface roughness of the heating roll is too large, the adhesion to the PVA film is reduced and the heat conduction is reduced. Therefore, the upper limit of the surface roughness of the heating roll is preferably 200S.
The method of separately providing the heating roll and the stretching roll, and disposing the stretching roll on the downstream side of the heating roll, compared to the method in which the stretching roll also serves as the heating roll, is that the width of the PVA film shrinks on the heating roll. It is more preferable because the effect of improving the polarization performance can be obtained.
[0030]
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. Usually, the dyeing is generally performed by immersing the PVA film in a solution containing the dye, but the processing method and processing conditions, such as mixing with the PVA film to form a film, are particularly limited. is not.
[0031]
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.
Further, the stretching ratio of uniaxial stretching (in the case of performing uniaxial stretching in multiple stages, the total stretching ratio) is preferably at least 4 times, particularly preferably at least 5 times, from the viewpoint of polarization performance. The upper limit of the stretching ratio is not particularly limited, but is preferably 8 times or less since uniform stretching is easily obtained. In particular, in order to perform uniform stretching in the width direction, the first-stage stretching preferably exceeds 4 times, more preferably 4.2 times or more, and particularly preferably 4.5 times or more. The thickness of the stretched film is preferably from 3 to 45 μm, more preferably from 5 to 30 μm.
[0032]
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.
[0033]
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.
[0034]
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 0.5 to 10 μm.
[0035]
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 the liquid crystal display device, and there are various types of usages of the polarizing plate. However, usually, a polarizing film is sandwiched between liquid crystal substrates so that the stretching axes of the polarizing films are orthogonal to each other. Two polarizing plates are used. Since the polarizing plate obtained from the polarizing film obtained by the method of the present invention has a small problem such as color spots, it is easy to be visually observed, and is used on the front side (the surface side of the liquid crystal display device) where the quality requirements are stricter. Is preferred.
[0036]
【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 unevenness of the polarizing plate were evaluated by the following methods.
[0037]
Optical performance of polarizing film:
A sample of a polarizing film of about 4 cm × 4 cm was measured using a spectrophotometer UV-2200 manufactured by Shimadzu Corporation (with an integrating sphere) in accordance with the standards of the Japan Electronics Machinery Manufacturers Association (EIAJ) LD-201-1983, and 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.
[0038]
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.
[0039]
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, by performing drying and heat treatment, a PVA film having a film width of 3 m and an average thickness of 50 μm was obtained.
[0040]
This 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 angle between the line connecting the heating roll and the upstream roll and the line connecting the heating roll and the downstream roll so that the angle between the heating roll and the upstream roll and the downstream roll is 20 degrees. The PVA film was passed through a stretching device arranged, and the PVA film was stretched 4.1 times in a uniaxial direction by a dry method. The heating roll used had a surface roughness of 0.7S and a roll temperature of 90 ° C. The center of the film was marked, and the time during which the film was in contact with the heating roll was measured to be 5 seconds.
The uniaxially stretched PVA film was immersed in water at 30 ° C. for 30 seconds for preliminary swelling, and immersed in an aqueous solution at a temperature 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 PVA film was taken out, dried with hot air at 40 ° C., and heat-treated at 100 ° C. for 5 minutes. The polarizing performance of the obtained polarizing film was 44.00% in transmittance, 99.72% in degree of polarization and 51.84 in dichroic ratio.
[0041]
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. When this polarizing plate was incorporated in a liquid crystal display device, it was good without color spots.
[0042]
Example 2
The PVA film obtained in the same manner as in Example 1 was continuously processed in the order of uniaxial stretching by a dry method, preliminary swelling, dyeing, wet uniaxial stretching, fixing treatment, drying and heat treatment to prepare a polarizing film. In the stretching apparatus used for the uniaxial stretching by the dry method, the angle formed between the line connecting the heating roll and the upstream roll and the line connecting the heating roll and the downstream roll was 25 degrees. The stretching ratio in the uniaxial direction of the PVA film was 4.1 times. The heating roll used had a surface roughness of 0.6S and a roll temperature of 100 ° C. Marking was performed at the center of the film, and the time during which the film was in contact with the heating roll was measured to be 7 seconds.
The uniaxially stretched PVA film was immersed in water at 30 ° C. for 30 seconds for preliminary swelling, and immersed in an aqueous solution at a temperature 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 PVA film was taken out, dried with hot air at 40 ° C., and 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. When this polarizing plate was incorporated in a liquid crystal display device, it was good without color spots.
[0043]
Example 3
The PVA film obtained in the same manner as in Example 1 was continuously processed in the order of uniaxial stretching by a dry method, preliminary swelling, dyeing, wet uniaxial stretching, fixing treatment, drying, and heat treatment to prepare a polarizing film. In the stretching apparatus used for the uniaxial stretching by the dry method, the angle between the line connecting the heating roll and the roll on the upstream side and the line connecting the heating roll and the subsequent roll is set to 15 degrees, and the downstream of the heating roll A draw roll was placed on the side. The stretching ratio in the uniaxial direction of the PVA film was 4.1 times. The heating roll used had a surface roughness of 80S, the surface roughness of the stretching roll was 0.7S, and the roll temperature was 100 ° C for the heating roll and 20 ° C for the stretching roll. The center of the film was marked, and the time during which the film was in contact with the heating roll was measured to be 2 seconds.
The uniaxially stretched PVA film was immersed in water at 30 ° C. for 30 seconds for preliminary swelling, and immersed in an aqueous solution at a temperature 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 PVA film was taken out, dried with hot air at 40 ° C., and 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. When this polarizing plate was incorporated in a liquid crystal display device, it was good without color spots.
[0044]
Comparative Example 1
A PVA film obtained in the same manner as in Example 1 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 produce a polarizing film. did. In the stretching apparatus used for the uniaxial stretching by the dry method, the angle between the line connecting the heating roll and the upstream roll and the line connecting the heating roll and the subsequent roll was set to 3 degrees. The stretching ratio in the uniaxial direction of the PVA film was about 2.5 times. The heating roll used had a surface roughness of 0.7 S and a roll temperature of 90 ° C. Marking was performed at the center of the film, and the time during which the film was in contact with the heating roll was measured to be 0.1 second. When the PVA film was uniaxially stretched by a dry method, contact between the heating roll and the PVA film was unstable, and when the stretching ratio was increased to 2.5 times or more, the film was broken. Further, when the stretching behavior of the PVA film was visually observed, uniform stretching was not performed in the width direction on the heating roll, and stretching between the rolls seemed to occur.
The uniaxially stretched PVA film was immersed in water at 30 ° C. for 30 seconds for preliminary swelling, and immersed in an aqueous solution at a temperature 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 3.0 times in an aqueous solution having a boric acid concentration of 4% at 50 ° C. 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 PVA film was taken out, dried with hot air at 40 ° C., and 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, large continuous color spots were observed to some extent. When this polarizing plate was assembled into a liquid crystal display device, and a portion where color spots were observed on the polarizing plate was observed, color spots were also observed on the liquid crystal display device, and it was determined that the liquid crystal display device was unsuitable.
[0045]
Comparative Example 2
A PVA film obtained in the same manner as in Example 1 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 produce a polarizing film. did. In the stretching apparatus used for the uniaxial stretching by the dry method, the angle between the line connecting the heating roll and the upstream roll and the line connecting the heating roll and the subsequent roll was set to 40 degrees. The stretching ratio in the uniaxial direction of the PVA film was about 4.1 times. The heating roll used had a surface roughness of 0.7S and a roll temperature of 90 ° C. Marking was performed at the center of the film, and the time during which the film was in contact with the heating roll was measured to be 12 seconds. Visual observation of the stretching behavior of the PVA film on the heating roll revealed that air was trapped between the heating roll and the PVA film and that uniform stretching in the width direction on the heating roll was impeded. Was.
The uniaxially stretched PVA film was immersed in water at 30 ° C. for 30 seconds for preliminary swelling, and immersed in an aqueous solution at a temperature 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 PVA film was taken out, dried with hot air at 40 ° C., and 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 relatively small elliptical color spots. When this polarizing plate was assembled into a liquid crystal display device, and a portion where color spots were observed on the polarizing plate was observed, color spots were also observed on the liquid crystal display device, and it was determined that the liquid crystal display device was unsuitable.
[0046]
【The invention's effect】
The polarizing film produced by the method of the present invention has few color spots, and such a polarizing film can be effectively used as a component of a liquid crystal display device having a large display screen by utilizing its excellent characteristics.
[Brief description of the drawings]
FIG. 1 is a schematic view showing one embodiment of a method for producing a polarizing film of the present invention.
FIG. 2 is a schematic view showing one embodiment of a method for producing a polarizing film of the present invention.
FIG. 3 is a schematic view showing one embodiment of a method for producing a polarizing film of the present invention.
[Explanation of symbols]
A Roll on the upstream side of the heating roll B Heating roll C Roll on the downstream side of the heating roll θ The angle formed by the line connecting the polyvinyl alcohol film between the heating roll and the upstream roll, and the line connecting the heating roll and the subsequent roll D Nip roll E Stretch roll

Claims (8)

When a polyvinyl alcohol film is stretched by a dry method using a heating roll to produce a polarizing film, a line extended in a state where the polyvinyl alcohol film on the roll located on the upstream side of the heating roll is in contact with the heating roll. Wherein the angle θ between the heating roll and a line connecting the roll located downstream of the heating roll is 5 to 30 degrees. The method for producing a polarizing film according to claim 1, wherein the contact time between the polyvinyl alcohol film and the heating roll is 10 seconds or less. The method for producing a polarizing film according to claim 1, wherein the heating roll is a stretching roll. The method for producing a polarizing film according to any one of claims 1 to 3, wherein the surface roughness of the heating roll is 0.1S to 1S. The method for producing a polarizing film according to any one of claims 1 to 4, wherein a nip roll is attached to the heating roll. The method for producing a polarizing film according to claim 1, wherein the stretching roll is disposed downstream of the heating roll. The method for producing a polarizing film according to claim 6, wherein the surface roughness of the stretching roll is 0.1S to 1S, and the temperature is 10 to 50C. The method for producing a polarizing film according to claim 6, wherein the surface roughness of the heating roll is 50S or more.

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