JP2004020630A - Polyvinyl alcohol film for optical use and manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyvinyl alcohol film that has less color spots and that is useful as the raw material for manufacturing a polarizing film for high quality liquid crystal display. <P>SOLUTION: The polyvinyl alcohol film is characterized in that a difference between the maximum and the minimum moisture percentage is 1% or below in the width direction of the film. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical polyvinyl alcohol film and a method for producing the same.
[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. The application fields of this LCD include small devices such as calculators and wristwatches in the early stages of development, and in recent years, 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 with less color spots than conventional products has been required.
[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]
Even if a PVA film looks uniform in appearance, a polarizing film obtained by uniaxially stretching the film sometimes has inherent color spots and streak-like defects that are difficult to distinguish. This color spot is difficult to confirm 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 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 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 are rarely a problem.However, when the display area is large, the entire display area is uniform. For example, the problem of color unevenness has become apparent due to the demand for high performance and the increased use of the film in combination with other films 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. This is thought to be due to a thickness variation in the width direction of the film, which is emphasized because it is uniaxially stretched in the flow direction. Variations in the thickness of the polarizing film cause irregularities in transmittance and the like, so that when the polarizing film is incorporated in a liquid crystal display device or the like, there is a problem that the quality is reduced. In particular, as the display screen of the liquid crystal display device becomes larger, if there are continuous streaks in the flow direction, it becomes difficult to collect the product while avoiding such locations, which is a major industrial problem.
[0006]
Therefore, an object of the present invention is to provide a PVA film that is useful as a raw material for producing a polarizing film for a high-quality liquid crystal display with less color spots.
[0007]
[Means for Solving the Problems]
The present inventors have conducted intensive studies in order to solve the above problems, and as a result, when a polyvinyl alcohol film having a moisture content in the width direction of the film in a specific range is uniaxially stretched, a normal polyvinyl alcohol film is uniaxially stretched. The present inventors have found that color unevenness of the obtained polarizing film is significantly reduced as compared with the case where the film is stretched, and completed the present invention.
That is, the present invention is an optical polyvinyl alcohol film, wherein a difference between a maximum value and a minimum value of a moisture content in a width direction of the film is 1% or less.
The optical polyvinyl alcohol film of the present invention can be prevented from wrinkling at the time of stretching, particularly by heating and stretching by a dry method. Therefore, stripes (color spots) generated in the flow direction of the polarizing film can be prevented. Has an excellent effect of reducing the
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
In the optical PVA film of the present invention, the difference between the maximum value and the minimum value of the water content in the width direction of the film needs to be 1% or less. When the difference between the maximum value and the minimum value of the water content exceeds 1%, it is not preferable because a stain is generated when the polarizing film is manufactured, and an optical spot is strongly generated. In the optical PVA film, the difference between the maximum value and the minimum value of the water content in the width direction of the film is more preferably 0.8% or less, and particularly preferably 0.5% or less.
[0009]
The optical PVA film of the present invention preferably has an average thickness of 10 to 50 μm, a moisture content of 2 to 5% by weight, a film width of 2 to 3.5 m, and a retardation in the TD direction of 10 to 50 nm.
[0010]
When the average thickness of the film is less than 10 μm, the film strength is small, and thus the film is easily broken when the film is heated by a dry method and stretched uniaxially. When the average thickness of the film exceeds 50 μm, stretch unevenness is likely to occur when the film is uniaxially stretched by heating in a dry method.
If the moisture content in the film is less than 2% by weight, the film becomes too hard, and the stretchability tends to decrease when the film is heated by a dry method and stretched uniaxially. When the water content exceeds 5% by weight, the film becomes too soft, and wrinkles and the like are likely to be formed when the film is heated by a dry method and stretched uniaxially.
In general, the larger the width of the film, the more difficult it is to achieve uniform stretching in the width direction. The optical PVA film of the present invention can be stretched uniformly in the width direction even if the width is large, and the effect of being excellent in stretchability tends to appear as the width increases. However, if the width of the film is too large, stretching becomes difficult, so the preferred width of the film is 2 to 3.5 m. Since it is relatively easy to stretch a film having a small film width uniformly in the width direction, if the width of the film is smaller than 2 m, the effect of using the optical PVA film of the present invention hardly appears.
[0011]
The optical PVA film of the present invention preferably has an arbitrary point retardation in the TD direction of 10 to 50 nm. When the retardation is smaller than 10 nm, an error due to the measurement is large, and the measurement cannot be substantially performed. If the retardation is larger than 50 nm, the stretchability of the film may decrease.
[0012]
In the present invention, the retardation of the PVA film is represented by the following formula (1). In the formula, Re is the retardation (nm), d is the thickness (nm) of the film, and Δn is the birefringence.
Re = d × Δn (1)
[0013]
The optical PVA film of the present invention preferably has a thickness unevenness in the width direction of the film of 5 μm or less. When the thickness unevenness in the width direction of the film exceeds 5 μm, the optical unevenness of the polarizing film obtained by stretching the film becomes large. The thickness unevenness in the width direction of the film is more preferably 3 μm or less, and most preferably 1 μm or less.
In the present invention, the thickness unevenness in the width direction of the film means a difference between the thickness of the thickest portion and the thickness of the thinnest portion in the width direction.
[0014]
The PVA used for the optical PVA film of 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.
[0015]
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.
[0016]
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%.
[0017]
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.
[0018]
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.
[0019]
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.
[0020]
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.
[0021]
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.
[0022]
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.
[0023]
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, the amount of water evaporation in the drying step increases, so that drying takes too much time, which is problematic in terms of productivity. Further, the PVA solution or the water-containing PVA may contain a plasticizer, a surfactant, a dichroic dye, and the like, if necessary.
[0024]
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, and glycerin is most preferably used, because the effect of improving stretchability is excellent.
[0025]
The amount of the plasticizer added is preferably 8 to 15 parts by weight, and most preferably 9 to 14 parts by weight, per 100 parts by weight of PVA. If the amount of the plasticizer is less than 8 parts by weight, the dyeability and stretchability of the PVA film may be reduced. If the amount is more than 14 parts by weight, the PVA film becomes too flexible and the handleability is reduced. There is.
[0026]
In the present invention, the difference between the maximum value and the minimum value of the concentration (%) of the plasticizer in the width direction of the PVA film is preferably 1% or less. When the difference between the maximum value and the minimum value of the plasticizer concentration (%) exceeds 1%, the uniformity of the film is impaired, and color unevenness when the film is uniaxially stretched tends to be intensified.
The difference between the maximum value and the minimum value of the concentration (%) of the plasticizer in the width direction of the PVA film is more preferably 0.8% or less, and most preferably 0.5% or less. In addition, in this invention, the density | concentration of the plasticizer in a PVA film shows the weight of the plasticizer extracted from the film using the arbitrary solvent which does not melt | dissolve PVA but only a plasticizer by weight% with respect to a film. Value.
[0027]
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.
[0028]
The amount of the surfactant added 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.
[0029]
In the optical PVA film of the present invention, the difference between the maximum value and the minimum value of the moisture content in the flow direction of the film is 1.5% or less, the difference between the maximum value and the minimum value of the concentration of the plasticizer is 2% or less, and the thickness unevenness. Is preferably not more than 10 μm. The difference between the maximum value and the minimum value of the moisture content in the film flow direction exceeds 1.5%, the difference between the maximum value and the minimum value of the concentration of the plasticizer exceeds 2%, or the maximum value and the minimum value of uneven thickness. When the difference is more than 10 μm, the uniformity of the film is impaired, and color unevenness when the film is uniaxially stretched tends to be severe.
[0030]
In the present invention, the optical PVA film having a difference between the maximum value and the minimum value of the moisture content in the width direction of the film of 1% or less is obtained by heating a PVA film formed from PVA with warm air at 30 to 80 ° C. for 5 seconds. It can be manufactured by adjusting the moisture content in the PVA film by contacting for the above time. The time for performing the humidity control is preferably 5 seconds or more in the above process. If the contact time between the PVA film and the hot air is shorter than 5 seconds, the fluctuation of the water content in the width direction of the film becomes large, and the intended optical PVA film cannot be obtained. The longer the contact time between the PVA film and the warm air, the better, but the preferred upper limit of the contact time from an industrial point of view is 10 minutes.
[0031]
In contacting the PVA film with warm air, a step (1) of contacting the PVA film with warm air having a temperature of 30 to 80 ° C. and a humidity of 60 to 100% RH, and a step of contacting the PVA film at a temperature of 30 to 80 ° C. and a humidity of 40 to 60 Preferably, the method includes a step (2) of bringing the film into contact with hot air of% RH, and by employing this method, the moisture content in the width direction of the film can be easily adjusted to a specific range. If the humidity of the hot air in the step (2) is lower than 40% RH, the rate at which moisture is released from the film becomes too fast, and it becomes difficult to adjust the moisture content in the film. When it is higher than 60% RH, the distinction from the step (1) is substantially eliminated, and the provision of the step (2) becomes meaningless.
The order of the step (1) and the step (2) may be arbitrary, and the step (1) and the step (2) may each be provided in two or more steps. Step (1) and step (2) are performed, for example, in step (1) → step (2), step (2) → step (1), step (1) → step (2) → step (1), step (1). 2) → Step (1) → Step (2), Step (1) → Step (2) → Step (1) → Step (2), Step (2) → Step (1) → Step (2) → Step ( 1) and the like.
[0032]
In the present invention, it is preferable that the PVA film is brought into contact with warm air while applying tension to the PVA film, thereby suppressing problems such as generation of slack in the film, bending of the end portion, and winding around the roll. it can. However, if the tension applied to the film is too large, a part of the film is stretched, and in the stretching step of the PVA film when obtaining a polarizing film, it tends to be a cause of inhibiting uniform stretching in the width direction. is necessary. It is desirable to apply tension to the PVA film using a driving roll.
[0033]
In order to produce a polarizing film from the optical PVA film of the present invention, for example, the PVA film is monoaxially stretched by a dry method, dyed, and if necessary, the second-stage uniaxially stretched by a dry method or a wet method, fixed, and dried. The treatment and, if necessary, the heat treatment may be performed. 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. 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. 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 obtained in this way, the thickness of the adhesive layer is preferably 0.5 to 10 μm, more preferably 0.8 to 8 μm, and particularly preferably 1 to 5 μm. It is preferable that the thickness of the adhesive layer is larger than the fine irregularities of the film so that the thickness of the polarizing plate after bonding is constant. If the thickness is less than 0.5 μm, uniform adhesion tends to be difficult, and bubbles may be formed, which may cause a problem since optical defects are easily formed. When the thickness is larger than 10 μm, it takes a long time to dry, and if an inadvertent force is applied while drying is inadequate, it tends to cause an optical defect. Further, it is not preferable because it has a disadvantage that air bubbles easily enter.
[0039]
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.
[0040]
【Example】
Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto. In Examples and Comparative Examples, the change in the water content in the width direction of the PVA film, the average thickness and uneven thickness of the film, the change in the concentration of the plasticizer, the retardation, the change in the water content in the flow direction of the film. The amount of change in the concentration of the plasticizer, the thickness unevenness of the film, the optical performance of the polarizing film, and the color unevenness of the polarizing plate were evaluated by the following methods.
[0041]
Change in moisture content in the width direction of the PVA film:
The PVA film was sampled at an arbitrary position in the flow direction at an interval of 5 cm from the end of the film at 5 cm intervals in a size of 5 cm × 5 cm, and dried at 50 ° C. × 24 hours under reduced pressure. The moisture content was calculated from the change in weight before and after the film was dried.
Water content (%) = (film weight before drying−film weight after drying) / (film weight before drying) × 100
Of all the measured values of the moisture content, the change in the moisture content was determined from the maximum value and the minimum value.
Change in moisture percentage (%) = (maximum moisture percentage (%))-(minimum moisture percentage (%))
[0042]
Average thickness and thickness unevenness in the width direction of the PVA film:
The thickness in the width direction of the PVA film was continuously measured using a contact thickness gauge (K-402B, head size 5 mm, manufactured by Anritsu Corporation), and the average value was determined. Further, the same measurement was performed at two locations 25 cm and 50 cm apart from the first measurement location in the MD direction. The thickness unevenness was obtained by calculating the difference between the maximum value and the minimum value among all the measured values.
[0043]
Change in plasticizer concentration in the width direction of the PVA film:
Using a sample in which the amount of change in the moisture content in the width direction of the film was measured in the above, after performing Soxhlet extraction with methanol, the weight after drying under reduced pressure was measured, and the plasticity was determined from the change in weight before and after the extraction. The amount of the agent was calculated.
Plasticizer concentration (%) = (film weight before extraction−film weight after extraction) / (film weight before extraction) × 100 (absolute dry basis).
The change amount of the plasticizer was determined from the maximum value and the minimum value among all the measured values.
Change in plasticizer concentration (%) = (maximum plasticizer concentration (%))-(minimum plasticizer concentration (%))
[0044]
Retardation in the width direction of the PVA film:
Using an automatic birefringence meter KOBRA21SDH manufactured by Oji Scientific Instruments, the retardation at an arbitrary point in the width direction of the film was measured.
[0045]
The amount of change in the water content in the flow direction of the PVA film, the amount of change in the plasticizer concentration, and the thickness unevenness:
Sampling was performed at a total of 10 points from an arbitrary position of the PVA film to a position of 1000 m every 100 m, and various physical properties in the width direction of each point were measured by the method described above. The difference between the maximum value and the minimum value among all the measured values was calculated to be each variation.
[0046]
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 standard of the Electronic Machine Manufacturers Association of Japan (EIAJ) LD-201-1983, and a C light source. The Y value was corrected for the visibility in the visible light region of the visual field of 2 degrees, and the transmittance was determined from the average value in the directions of 45 degrees and -45 degrees 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.
[0047]
Color spots on polarizing plate:
A polarizing plate having a full width was placed in a direction perpendicular to a polarizing plate for observation (two stacked on parallel Nicols, the degree of polarization of 99.99% or more), and the degree of color spot was determined by visual observation.
[0048]
Example 1
100 parts by weight of PVA having a degree of saponification of 99.95 mol% and a degree of polymerization of 2,400, impregnated with 10 parts by weight of glycerin and 170 parts by weight of water are melt-kneaded. After defoaming, the mixture is melt-extruded from a T-die onto a metal roll. A film was formed. Thereafter, a step of contacting the film obtained by drying and heat treatment with hot air at a temperature of 65 ° C. and a humidity of 90% RH, and subsequently, a step of contacting the film with a hot air at a temperature of 50 ° C. and a humidity of 45% RH are performed in both steps. It was passed for 6 seconds for a total of required time to pass and conditioned to obtain a PVA film. The average thickness of the obtained PVA film was 41 μm, the moisture content was 4.3%, the width of the film was 3 m, and the retardation was 23 nm. The change in the water content in the width direction of the film was 0.8%, the change in the concentration of the plasticizer was 0.5%, and the thickness unevenness in the width direction was 2 μm. The amount was 1.1%, the change in the concentration of the plasticizer was 0.9%, and the thickness unevenness was 4 μm.
The above-mentioned PVA film was continuously processed in the order of preliminary swelling, dyeing, uniaxial stretching, fixing treatment, drying and heat treatment to prepare a polarizing film. The PVA film was pre-swelled by immersing it in water at 30 ° C. for 30 seconds, and immersed in an aqueous solution at 35 ° C. having an iodine concentration of 0.4 g / l and a potassium iodide concentration of 40 g / l for 3 minutes. Subsequently, the film was uniaxially stretched 5 times in an aqueous solution of boric acid having a concentration of 4% at 50 ° C., and was subjected to a 30 ° C. aqueous solution having a potassium iodide concentration of 40 g / l, a boric acid concentration of 40 g / l, and a zinc chloride concentration of 10 g / l. 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 obtained polarizing film was a transmittance of 43.90%, a degree of polarization of 99.42%, and a dichroic ratio of 44.91.
The obtained polarizing film was bonded to a triacetate film using an adhesive of a 10% PVA aqueous solution (PVA117H manufactured by Kuraray) 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.
[0049]
Example 2
100 parts by weight of PVA having a degree of saponification of 99.95 mol% and a degree of polymerization of 2,400, impregnated with 10 parts by weight of glycerin and 170 parts by weight of water are melt-kneaded. After defoaming, the mixture is melt-extruded from a T-die onto a metal roll. A film was formed. Thereafter, a step of bringing the film obtained by drying and heat treatment into contact with hot air at a temperature of 60 ° C. and a humidity of 80% RH, and subsequently, a step of contacting the film with a hot air at a temperature of 55 ° C. and a humidity of 40% RH are performed in both steps. Passage was performed for 9 seconds for a total of required time, and humidity was controlled to obtain a PVA film. The average thickness of the obtained PVA film was 40 μm, the moisture content was 4.2%, the width of the film was 3 m, and the retardation was 21 nm. The change in the water content in the width direction of the film was 0.5%, the change in the concentration of the plasticizer was 0.4%, and the thickness unevenness in the width direction was 3 μm. The amount was 0.9%, the change in the concentration of the plasticizer was 0.7%, and the thickness unevenness was 5 μm.
The above-mentioned film was treated in the same manner as in Example 1 to produce a polarizing film. The polarizing performance of the obtained polarizing film was a transmittance of 43.77%, a degree of polarization of 99.55%, and a dichroic ratio of 46.04.
The obtained polarizing film was bonded to a triacetate film using an adhesive of a 10% PVA aqueous solution (PVA117H manufactured by Kuraray) 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.
[0050]
Example 3
A mixture of 100 parts by weight of PVA having a degree of saponification of 99.89 mol% and a degree of polymerization of 4000 impregnated with 10 parts by weight of glycerin and 240 parts by weight of water is melt-kneaded, and after defoaming, is melt-extruded from a T-die onto an endless belt. A film was formed. Thereafter, a step of bringing the film obtained by drying and heat treatment into contact with hot air at a temperature of 60 ° C. and a humidity of 80% RH, and subsequently, a step of contacting the film with a hot air at a temperature of 55 ° C. and a humidity of 40% RH are performed in both steps. The PVA film was conditioned by passing over 11 seconds for a total required time to obtain a PVA film. The average thickness of the obtained film was 35 μm, the moisture content was 3.8%, and the width of the film was 2.3 m. The retardation was 15 nm. Further, the variation of the moisture percentage in the width direction of the film is 0.6%, the variation of the concentration of the plasticizer is 0.6%, the thickness unevenness in the width direction is 3 μm, and the variation of the moisture in the flow direction of the film is The plasticizer concentration change amount was 0.7%, and the thickness unevenness was 3 μm.
The PVA film described above was treated in the same manner as in Example 1 to produce a polarizing film. The polarizing performance of the obtained polarizing film was such that the transmittance was 44.43%, the degree of polarization was 99.26%, and the dichroic ratio was 46.94.
The obtained polarizing film was bonded to a triacetate film using an adhesive of a 10% PVA aqueous solution (PVA117H manufactured by Kuraray) to obtain a polarizing plate. Observation of the color spots on the polarizing plate revealed that the color spots were small and good enough to be visually recognized over the entire surface of the polarizing plate. Although the degree of color spots of the liquid crystal display device incorporating the polarizing plate was larger than that observed when the color spots of the polarizing plate were visually observed, they were relatively small and good.
[0051]
Comparative Example 1
100 parts by weight of PVA having a degree of saponification of 99.95 mol% and a degree of polymerization of 2,400, impregnated with 10 parts by weight of glycerin and 170 parts by weight of water are melt-kneaded. After defoaming, the mixture is melt-extruded from a T-die onto a metal roll. A film was formed. Thereafter, both the steps of contacting the film obtained by drying and heat treatment with warm air at a temperature of 65 ° C. and a humidity of 90% RH, and subsequently contacting the film with warm air at a temperature of 50 ° C. and a humidity of 45% RH are performed. It was passed for 3 seconds for a total of required time to pass and conditioned to obtain a PVA film. The average thickness of the obtained film was 41 μm, the water content was 4.5%, the width of the film was 3 m, and the retardation was 35 nm. The change in the water content in the width direction of the film was 1.9%, the change in the concentration of the plasticizer was 0.8%, the thickness unevenness in the width direction was 2 μm, and the water content in the flow direction of the film was Was 3.9%, the change in the plasticizer concentration was 0.9%, and the thickness unevenness was 4 μm.
The above-mentioned PVA film was continuously processed in the order of preliminary swelling, dyeing, uniaxial stretching, fixing treatment, drying and heat treatment to prepare a polarizing film. The PVA film was pre-swelled by immersing it in water at 30 ° C. for 30 seconds, and immersed in an aqueous solution at 35 ° C. having an iodine concentration of 0.4 g / l and a potassium iodide concentration of 40 g / l for 3 minutes. Subsequently, the film is uniaxially stretched 5 times in an aqueous solution of boric acid at a concentration of 4% at 50 ° C. to obtain a solution of potassium iodide at a concentration of 40 g / l, boric acid at a concentration of 40 g / l, and zinc chloride at a concentration of 10 g / l at 30 ° C. 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 a transmittance of 43.75%, a degree of polarization of 99.24%, and a dichroic ratio of 41.55.
The obtained polarizing film was bonded to a triacetate film using an adhesive of a 10% PVA aqueous solution (PVA117H manufactured by Kuraray) to obtain a polarizing plate. Observation of the color spots on the polarizing plate revealed that there were 10 color spots noticeable by visual observation in the flow direction over the entire surface of the polarizing plate, which was unsuitable as a commercial-grade polarizing plate. When this polarizing plate was assembled in a liquid crystal display device, color spots in the flow direction were visually recognizable, and were unsuitable as a liquid crystal display device.
[0052]
Comparative Example 2
100 parts by weight of PVA having a degree of saponification of 99.95 mol% and a degree of polymerization of 2,400, impregnated with 10 parts by weight of glycerin and 170 parts by weight of water are melt-kneaded. After defoaming, the mixture is melt-extruded from a T-die onto a metal roll. A film was formed. Thereafter, the film obtained by drying and heat treatment was passed through a step of contacting with hot air having a temperature of 20 ° C. and a humidity of 80% RH for 10 seconds to adjust the humidity to obtain a PVA film. The average thickness of the obtained film was 42 μm, the water content was 4.0%, the width of the film was 3 m, and the retardation was 29 nm. The change in the water content in the width direction of the film was 2.5%, the change in the concentration of the plasticizer was 0.8%, and the thickness unevenness in the width direction was 3 μm. The amount was 4.9%, the change in the concentration of the plasticizer was 1.0%, and the thickness unevenness was 5 μm.
The above-mentioned PVA film was treated in the same manner as in Example 1 to produce a polarizing film. The polarizing performance of the obtained polarizing film was a transmittance of 43.92%, a degree of polarization of 99.45%, and a dichroic ratio of 45.51.
The obtained polarizing film was bonded to a triacetate film using an adhesive of a 10% PVA aqueous solution (Kuraray's PVA117H) to obtain a polarizing plate. When the color spots of the polarizing plate were observed, over the entire surface of the polarizing plate, there were countless color spots that were conspicuous by visual observation in the flow direction, and color spots in which light and shade were seen in a spot shape, which were unsuitable as a product-level polarizing plate. there were. When this polarizing plate was incorporated into a liquid crystal display device, the flow direction and spot-like color spots were visually recognizable, and were unsuitable as a liquid crystal display device.
[0053]
【The invention's effect】
When the polyvinyl alcohol film for optical use of the present invention is uniaxially stretched, it suppresses the generation of wrinkles at the time of stretching and reduces the occurrence of streaks (color spots) in the film flow direction. The polarizing film obtained in this manner can be effectively used as a component of a high-quality liquid crystal display device by utilizing its characteristics.

Claims (8)

A polyvinyl alcohol film for optical use, wherein a difference between a maximum value and a minimum value of a moisture content in a width direction of the film is 1% or less. The optical polyvinyl alcohol film according to claim 1, having a thickness of 10 to 50 µm, a moisture content of 2 to 5% by weight, a film width of 2 to 3.5 m, and a retardation in the TD direction of 10 to 50 nm. The optical polyvinyl alcohol film according to claim 1, wherein a difference between a maximum value and a minimum value of a plasticizer concentration in a width direction of the film is 1% or less. The polyvinyl alcohol film for optical use according to any one of claims 1 to 3, wherein a thickness unevenness in a width direction of the film is 5 µm or less. The difference between the maximum value and the minimum value of the water content in the film flow direction is 1.5% or less, the difference between the maximum value and the minimum value of the concentration of the plasticizer is 2% or less, and the difference between the maximum value and the minimum value of the thickness unevenness is The optical polyvinyl alcohol film according to any one of claims 1 to 4, wherein the thickness is 10 µm or less. 2. The production of the optical polyvinyl alcohol film according to claim 1, wherein the moisture content of the polyvinyl alcohol film is adjusted by contacting the polyvinyl alcohol film with warm air of 30 to 80 ° C. for 5 seconds or more. Law. A step of contacting the polyvinyl alcohol film with warm air at 30 to 80 ° C. and a humidity of 60 to 100% RH, and a step of contacting the polyvinyl alcohol film with warm air at a temperature of 30 to 80 ° C. and a humidity of 40 to 60% RH. The method for producing an optical polyvinyl alcohol film according to claim 6. The method for producing an optical polyvinyl alcohol film according to claim 6, wherein the polyvinyl alcohol film is brought into contact with warm air while applying tension to the polyvinyl alcohol film.