JP4104916B2 - Optical polyvinyl alcohol film and method for producing the same - Google Patents

Description

[0001]
BACKGROUND 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 light transmission and shielding function is a basic component of a liquid crystal display device (LCD) together with a liquid crystal having a light switching function. This LCD can be applied to small devices such as calculators and wristwatches in the early days 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 devices. A polarizing plate having a large area with less color spots than conventional products has been demanded.
[0003]
The polarizing plate is generally obtained by uniaxially stretching and dyeing a polyvinyl alcohol film (hereinafter, polyvinyl alcohol may be abbreviated as “PVA” and polyvinyl alcohol film as “PVA film”), or after dyeing and uniaxially stretching. In addition, a protective film such as a cellulose triacetate (TAC) film or an acetic acid / cellulose butyrate (CAB) film is applied to a polarizing film obtained by performing a fixing process with a boron compound (the dyeing and fixing process may be simultaneous). It has a laminated structure.
[0004]
[Problems to be solved by the invention]
Even if it is a PVA film that looks uniform in appearance, the polarizing film obtained by uniaxially stretching the PVA film may have color spots or streak-like defects that are difficult to distinguish. This color spot is difficult to confirm unless it is a final product (polarizing plate) in which a protective film or the like is laminated. If color spots appear at the final product stage, secondary materials such as a protective film that have no problem in quality are discarded together with the polarizing plate as defective products, resulting in a large loss. As a conventional method for reducing color spots, studies have been made to reduce thickness spots and birefringence spots on PVA films as proposed in JP-A-6-138319. By 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 has become possible to satisfy the required level at that time, but the performance in recent years has improved. It has been found difficult to reduce the level of color spots that would be problematic in the final product (polarizer and liquid crystal display device).
[0005]
In addition, a large-area polarizing film has been demanded with an increase in size of a liquid crystal display device. Conventional liquid crystal display devices have a relatively small display area and a polarizing plate is used alone, so color spots are rarely a problem, but when the display area increases, the entire display area becomes uniform. The problem of color spots has become apparent due to the demand for the color and the increased use of the film in combination with other films such as a film for correcting the viewing angle. In particular, in the case of a polarizing film produced by stretching a PVA film uniaxially in the film flow direction, streak-like color spots are likely to occur in the film flow direction. This is thought to be emphasized because there is a thickness variation in the width direction of the film and it is uniaxially stretched in the flow direction. Since the variation in thickness of the polarizing film causes uneven transmittance, there is a problem that when the polarizing film is incorporated in a liquid crystal display device or the like, the quality deteriorates. In particular, as the display screen of the liquid crystal display device becomes larger, when there are continuous streaks in the flow direction, it becomes difficult to collect a product by avoiding that portion, which is a serious problem industrially.
[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 few color spots.
[0007]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventors have uniaxially stretched a normal polyvinyl alcohol film when the polyvinyl alcohol film having a moisture content in the width direction of the film is uniaxially stretched. As compared with the case where it was stretched, it was found that the color spots of the obtained polarizing film were remarkably reduced, and the present invention was completed.
That is, the present invention is an optical polyvinyl alcohol film characterized in that the difference between the maximum value and the minimum value of the moisture content in the width direction of the film is 1% or less.
Since the optical polyvinyl alcohol film of the present invention is heated and stretched by a dry method in particular, wrinkles can be prevented from occurring during stretching, and therefore streaks (color spots) generated in the flow direction of the polarizing film. This has the excellent effect of reducing
[0008]
DETAILED DESCRIPTION OF THE INVENTION
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 width direction of the film needs to be 1% or less. If the difference between the maximum value and the minimum value of the moisture content exceeds 1%, it is not preferable because stained spots are generated or optical spots are strongly generated when the polarizing film is produced. In the optical PVA film, the difference between the maximum value and the minimum value of the moisture 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 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.It is.
[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 heated by a dry method and uniaxially stretched. Moreover, when the average thickness of a film exceeds 50 micrometers, when a film is uniaxially stretched by heating by a dry method, it will become easy to generate | occur | produce stretching spots.
When the moisture content contained 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 uniaxially stretched. When the moisture content exceeds 5% by weight, the film becomes too soft and wrinkles and the like are likely to occur when the film is heated by a dry method and uniaxially stretched.
Generally, the larger the width of the film, the more difficult it is to uniformly stretch in the width direction. The optical PVA film of the present invention can be uniformly stretched in the width direction even if the width is large, and the effect that the stretchability is excellent as the width increases is more likely to appear. However, if the width of the film is too large, stretching becomes difficult, so a suitable 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, the effect of using the optical PVA film of the present invention is hardly exhibited when the film width is smaller than 2 m.
[0011]
In the optical PVA film of the present invention, the retardation at an arbitrary point in the TD direction is preferably 10 to 50 nm. When the retardation is smaller than 10 nm, the error due to the measurement is large and the measurement cannot be made substantially. When the retardation is larger than 50 nm, the stretchability of the film may be lowered.
[0012]
In the present invention, the retardation of the PVA film is represented by the following formula (1). In the formula, Re is retardation (nm), d is film thickness (nm), and Δn is birefringence.
Re = d × Δn (1)
[0013]
The optical PVA film of the present invention has a thickness variation of 5 μm or less in the width direction of the film.It is.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 increases. The thickness variation 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 part and the thickness of the thinnest part 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. Further, a modified PVA obtained by graft-copolymerizing unsaturated carboxylic acid or a derivative thereof, unsaturated sulfonic acid or a derivative thereof, an α-olefin having 2 to 30 carbon atoms, or the like in a proportion of less than 5 mol% on the main chain of PVA, Manufactured by saponifying a modified polyvinyl ester obtained by copolymerizing a vinyl ester with an unsaturated carboxylic acid or derivative thereof, an unsaturated sulfonic acid or derivative thereof, an α-olefin having 2 to 30 carbon atoms, or the like at a ratio of less than 15 mol%. And a so-called polyvinyl acetal resin obtained by crosslinking a part of hydroxyl groups 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, vinyl benzoate and the like.
[0016]
The comonomer used for the modified PVA is copolymerized mainly for the purpose of modifying the PVA, and is used within a range not impairing the gist of the present invention. Examples of such comonomers include α-olefins such as ethylene, propylene, 1-butene, and isobutene; acrylic acid and salts thereof; methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, Acrylic esters such as n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate; methacrylic acid and salts thereof; 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. Of methacrylate Tellurides; acrylamide, N-methylacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide, diacetoneacrylamide, acrylamidepropanesulfonic acid and its salt, acrylamidopropyldimethylamine and its salt, N-methylolacrylamide and its derivatives, etc. Methacrylamide derivatives such as methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidepropanesulfonic acid and salts thereof, methacrylamidepropyldimethylamine and salts thereof, N-methylolmethacrylamide and derivatives thereof N-vinylamides such as N-vinylformamide, N-vinylacetamide and N-vinylpyrrolidone; 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, stearyl vinyl ether; nitriles such as acrylonitrile and methacrylonitrile; Vinyl halides such as vinyl, vinylidene chloride, vinyl fluoride, vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid and its salts or esters thereof; itaconic acid and its salts or esters thereof; vinyltrimethoxy And vinyl silyl compounds such as silane; isopropenyl acetate and the like. Among these, α-olefins are preferable, and ethylene is particularly preferable. The modified amount of the modified PVA is preferably less than 15 mol%.
[0017]
The saponification degree of PVA is preferably 95 mol% or more, more preferably 98 mol% or more, further preferably 99 mol% or more, and most preferably 99.5 mol% or more from the viewpoint of polarization performance and durability.
[0018]
The saponification degree of the PVA indicates a ratio of units actually converted to vinyl alcohol units among units that can be converted into vinyl alcohol units when polyvinyl ester is saponified. The saponification degree of PVA was measured by the method described in JIS.
[0019]
The degree of polymerization of PVA is preferably 500 or more, more preferably 1000 or more, further 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 PVA polymerization is preferably 8000 or less, and more preferably 6000 or less.
[0020]
The degree of polymerization of the PVA is measured according to JIS K 6726. That is, it is obtained from the intrinsic viscosity measured in 30 ° C. water after re-saponifying and purifying PVA.
[0021]
As a method for producing a PVA film using the above PVA, for example, a PVA solution (polyvinyl alcohol film undiluted solution) in which PVA is dissolved in a solvent is used in addition to a film forming method by a melt extrusion method using hydrous PVA. Casting film casting method, casting film casting method, wet film forming method (discharging into poor solvent), gel film forming method (after once cooling and gelling PVA aqueous solution, solvent is extracted and removed, and PVA film is removed) And a method using a combination thereof can be employed. 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]
Examples of the solvent for dissolving PVA used in producing the PVA film include dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, Examples thereof include trimethylolpropane, ethylenediamine, diethylenetriamine, glycerin, water, and the like, and one or more of these can be used. Among these, dimethyl sulfoxide, water, or a mixed solvent of glycerin and water is preferably used.
[0023]
The proportion of PVA in the PVA solution or hydrous 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. 30 to 55% by weight is more preferred, and 35 to 50% by weight is most preferred. When the ratio of PVA is large, the viscosity becomes too high, and filtration and defoaming become difficult, and it becomes difficult to obtain a film free from foreign matters and defects. If the proportion of PVA is small, the amount of water evaporation in the process increases in drying, so that it takes too much time to dry and there is a problem in terms of productivity. In addition, the PVA solution or the hydrous PVA may contain a plasticizer, a surfactant, a dichroic dye, or the like as 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, etc., and one or more of these are used. can do. Among these, diglycerin, ethylene glycol, and glycerin are preferably used because the effect of improving stretchability is excellent, and the use of glycerin is most preferable.
[0025]
The addition amount of the plasticizer is preferably 8 to 15 parts by weight, and most preferably 9 to 14 parts by weight with respect to 100 parts by weight of PVA. When the added amount of the plasticizer is less than 8 parts by weight, the dyeability and stretchability of the PVA film may be deteriorated. When it is more than 14 parts by weight, the PVA film becomes too flexible and the handleability is deteriorated. There is.
[0026]
In the present invention, the difference between the maximum value and the minimum value of the plasticizer concentration (%) 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 concentration (%) of the plasticizer exceeds 1%, the uniformity of the film is impaired, and color spots tend to become intense when the film is uniaxially stretched.
The difference between the maximum value and the minimum value of the plasticizer concentration (%) in the width direction of the PVA film is more preferably 0.8% or less, and most preferably 0.5% or less. In the present invention, the concentration of the plasticizer in the PVA film means the weight of the plasticizer extracted from the film using an arbitrary solvent that does not dissolve PVA but dissolves only the plasticizer. 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. As the anionic surfactant, for example, a carboxylic acid type such as potassium laurate, a sulfate type such as octyl sulfate, and a sulfonic acid type anionic surfactant such as dodecylbenzenesulfonate are suitable. Nonionic surfactants include, for example, alkyl ether types such as polyoxyethylene oleyl ether, alkylphenyl ether types such as polyoxyethylene octylphenyl ether, alkyl ester types such as polyoxyethylene laurate, and polyoxyethylene laurylamino. Alkylamine type such as ether, alkylamide type such as polyoxyethylene lauric acid amide, polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether, alkanolamide type such as oleic acid diethanolamide, polyoxyalkylene allyl phenyl ether, etc. Nonionic surfactants such as allyl phenyl ether type are preferred. These surfactants can be used alone or in combination of two or more.
[0028]
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 with respect to 100 parts by weight of PVA. . If the amount is less than 0.01 part by weight, the effect of improving the film forming property and the peelability to be brought about by the addition of the surfactant is difficult to appear. If the amount is more than 1 part by weight, the surfactant is eluted on the surface of the PVA film. It may cause blocking and handleability may be reduced.
[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 film flow direction is 1.5% or less, the difference between the maximum value and the minimum value of the plasticizer concentration is 2% or less, The difference between the maximum value and the minimum value is preferably 10 μm or less. The difference between the maximum and minimum values of moisture content in the film flow direction exceeds 1.5%, the difference between the maximum and minimum values of plasticizer concentration exceeds 2%, or the maximum and minimum values of thickness spots If the difference exceeds 10 μm, the uniformity of the film is impaired, and color spots tend to become intense when the film is uniaxially stretched.
[0030]
In the present invention, the PVA film for optics 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 changing the PVA film formed from PVA into hot air at 30 to 80 ° C. for 5 seconds. It can manufacture by making it contact for the above time and adjusting the moisture content contained in a PVA film. It is preferable to perform the conditioning for 5 seconds or more in the above process. When the contact time between the PVA film and the warm air is shorter than 5 seconds, the fluctuation of the moisture content in the width direction of the film becomes large, and the intended optical PVA film cannot be obtained. The longer the time for contacting the PVA film and the hot air, the better. However, the upper limit of the preferable contact time is 10 minutes from the industrial viewpoint.
[0031]
In contacting the PVA film with warm air, the step (1) of bringing the PVA film into contact with hot air of 30 to 80 ° C. and humidity of 60 to 100% RH, and the PVA film at 30 to 80 ° C. and humidity of 40 to 60 It is preferable to include the step (2) of contacting with warm 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 warm air in step (2) is lower than 40% RH, the rate at which moisture is released from the film becomes too fast, making it difficult to adjust the moisture content in the film, If it is higher than 60% RH, the distinction between the step (1) and the step (1) is substantially lost, and the meaning of providing the step (2) is lost.
The order of the step (1) and the step (2) may be arbitrary, and the step (1) and the step (2) can be provided in two or more steps. Step (1) and Step (2) are, for example, 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).
[0032]
In the present invention, the PVA film is preferably brought into contact with warm air while applying tension to the PVA film, thereby suppressing problems such as sagging of the film and bending of the end portion or winding of 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 process of the PVA film when obtaining a polarizing film, it becomes easy to cause uniform stretching in the width direction, so be careful. is required. It is desirable to apply tension to the PVA film using a drive roll.
[0033]
In order to produce a polarizing film from the optical PVA film of the present invention, for example, the PVA film is uniaxially stretched and dyed by a dry method, and if necessary, the second uniaxially stretched by a dry method or a wet method, fixed, and dried. There is no particular limitation on the order of the treatment and further the heat treatment as necessary, and the order of the dyeing, the second-stage uniaxial stretching by the dry method or the wet method, and the fixing treatment. Further, the second-stage uniaxial stretching by a dry method or a wet method may be performed twice or more times.
In the present invention, stretching by the dry method refers to an operation of stretching the PVA film in the air, while stretching by the wet method means that the PVA film is stretched in an aqueous solution such as water or boric acid aqueous solution or a plasticizer. It refers to the operation of stretching in a solvent such as, and both are distinguished.
[0034]
The dyeing of the PVA film may be performed at any stage before uniaxial stretching, during uniaxial stretching, or after uniaxial stretching. As dyes used for dyeing, 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 , 240, 242, 247; Direct Blue 1, 15, 22, 78, 90, 98, 151, 168, 202, 236, 249, 270; Direct Violet 9, 12, 51, 98; Direct Green 1, 85; Direct Dichroic dyes such as yellow 8, 12, 44, 86, 87; direct orange 26, 39, 106, 107 can be used in one kind or a mixture of two or more kinds. Dyeing of PVA film is generally carried out by immersing the PVA film in a solution containing the above dye, but the processing method and processing conditions such as forming a film by mixing the dye with the PVA film are as follows. There is no particular limitation.
[0035]
For the uniaxial stretching of the second stage, a wet stretching method in which a PVA film is stretched in a warm aqueous solution such as an aqueous boric acid solution (in a solution containing the dye or in a fixing treatment bath described later), A dry stretching method that stretches in the 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, and 50 to 180 ° C when it is stretched in the air. Further, the stretching ratio of uniaxial stretching (the total stretching ratio when uniaxial stretching is performed in multiple stages) is preferably 4 times or more, particularly preferably 5 times or more from the viewpoint of polarization performance. Although there is no restriction | limiting in particular about the upper limit of a draw ratio, Since uniform extending | stretching is easy to be obtained if it is 8 times or less, it is preferable. The thickness of the film after stretching is preferably from 3 to 45 μm, more preferably from 5 to 30 μm.
[0036]
Fixing treatment is often performed for the purpose of strengthening the adsorption of the dye to the PVA film. Usually, boric acid and / or boron compounds are added to the treatment bath used for the fixing treatment. Moreover, you may add an iodine compound in a processing 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 attaching a protective film optically transparent and having mechanical strength on both sides or one side. As the protective film, a cellulose triacetate (TAC) film, an acetic acid / cellulose butyrate (CAB) film, an acrylic film, a polyester film, or the like is used. Examples of the adhesive used for the 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, more preferably 0.8 to 8 μm, and particularly preferably 1 to 5 μm. It is preferable to make the thickness of the adhesive layer larger than the fine irregularities of the film so that the thickness of the polarizing plate after adhesion is constant. If the thickness is smaller than 0.5 μm, uniform adhesion tends to be difficult, and bubbles may be formed, and optical defects may be easily formed, which may be a problem. If it is larger than 10 μm, drying tends to take a long time, and if an inadvertent force is applied while the drying is insufficient, an optical defect tends to occur, which is difficult for industrial production. Moreover, since it has the fault that a bubble tends to enter, it is not preferable.
[0039]
The polarizing plate obtained as described above is used as a component of a liquid crystal display device after being coated with an acrylic adhesive or the like and then bonded to a glass substrate. When the polarizing plate is bonded to the glass substrate, a retardation film, a viewing angle improving film, a brightness improving film, or the like may be bonded simultaneously.
[0040]
【Example】
Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In Examples and Comparative Examples, the amount of change in the moisture content in the width direction of the PVA film, the average thickness and thickness unevenness of the film, the amount of change in the plasticizer concentration, the retardation, and the amount of change in the moisture content in the film flow direction. 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 amount of moisture content in width direction of PVA film:
The PVA film was sampled at 5 cm × 5 cm in the width direction from the edge of the film at an arbitrary position in the flow direction, and dried at 50 ° C. for 24 hours under reduced pressure. The moisture content was calculated from the change in weight before and after drying the film.
Moisture content (%) = (film weight before drying−film weight after drying) / (film weight before drying) × 100
Of all the measured values of moisture content, the amount of change in moisture content was determined from the maximum and minimum values.
Change in moisture content (%) = (maximum value of moisture content (%))-(minimum value of moisture content (%))
[0042]
Average thickness and thickness unevenness in the width direction of the PVA film:
Using a contact-type thickness meter (K-402B, head size 5 mm, manufactured by Anritsu Corporation), the thickness in the width direction of the PVA film was continuously measured, and an average value was obtained. 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 difference between the maximum value and the minimum value among all the measured values was calculated to obtain thickness spots.
[0043]
Change amount of plasticizer concentration in width direction of PVA film:
In the above, using the sample that measured the amount of change in the moisture content in the width direction of the film, after Soxhlet extraction with methanol, the weight after drying under reduced pressure was measured, and plasticity was determined from the change in weight before and after extraction. The amount of agent was calculated.
Concentration of plasticizer (%) = (film weight before extraction−film weight after extraction) / (film weight before extraction) × 100 (absolutely dry basis).
Of all the measured values, the amount of change in the plasticizer was determined from the maximum value and the minimum value.
Change amount of plasticizer concentration (%) = (maximum value of plasticizer concentration (%)) − (minimum value of plasticizer concentration (%))
[0044]
Retardation in the width direction of the PVA film:
The retardation at an arbitrary point in the width direction of the film was measured using an automatic birefringence meter KOBRA21SDH manufactured by Oji Scientific Instruments.
[0045]
Change amount of moisture content in flow direction of PVA film, change amount of plasticizer concentration, thickness spot:
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 at 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 as each change amount.
[0046]
Optical performance of polarizing film:
Using a spectrophotometer UV-2200 (attached to an integrating sphere) manufactured by Shimadzu Corporation as a sample of a polarizing film film of about 4 cm × 4 cm, C light source The Y value corrected for visibility in the visible light region of the 2-degree visual field was measured, and the transmittance was determined from the average values in the 45 ° and −45 ° directions with respect to the stretching axis direction of the polarizing film. The Y value of parallel Nicols and crossed Nicols was measured by the same method as above to determine the degree of polarization.
[0047]
Color spots on the polarizing plate:
A polarizing plate having a full width was placed in an orthogonal direction between polarizing plates for observation (two stacked parallel Nicols, polarization degree of 99.99% or more), and the degree of color spots was determined by visual observation.
[0048]
Example 1
100 parts by weight of PVA having a saponification degree of 99.95 mol% and a polymerization degree of 2400 was melt-kneaded with 10 parts by weight of glycerin and 170 parts by weight of water, and after defoaming, melt extrusion 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 hot air having a temperature of 65 ° C. and a humidity of 90% RH, and subsequently bringing the film into contact with hot air having a temperature of 50 ° C. and a humidity of 45% RH are performed. The PVA film was obtained by adjusting the humidity by passing it over 6 seconds for the total required time. 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. In addition, the amount of change in the moisture content in the width direction of the film is 0.8%, the amount of change in the plasticizer concentration is 0.5%, and the thickness unevenness in the width direction is 2 μm. The amount was 1.1%, the amount of change in the concentration of the plasticizer was 0.9%, and the thickness spot was 4 μm.
The aforementioned PVA film was continuously processed in the order of preliminary swelling, dyeing, uniaxial stretching, fixing treatment, drying, and heat treatment to produce 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 / liter and a potassium iodide concentration of 40 g / liter for 3 minutes. Subsequently, uniaxial stretching was performed 5 times in a 50 ° C. aqueous solution with a boric acid concentration of 4%. For 5 minutes, and fixed. Thereafter, the obtained PVA film was taken out, dried with hot air at 40 ° C., and further subjected to heat treatment at 100 ° C. for 5 minutes. The polarization 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 a 10% PVA aqueous solution (Kuraray PVA117H) adhesive to obtain a polarizing plate. When the color spots of the polarizing plate were observed, there was no color spot over the entire surface of the polarizing plate, and it was good. 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 saponification degree of 99.95 mol% and a polymerization degree of 2400 was melt-kneaded with 10 parts by weight of glycerin and 170 parts by weight of water, and after defoaming, melt extrusion 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 hot air having a temperature of 60 ° C. and a humidity of 80% RH, and subsequently bringing the film into contact with hot air having a temperature of 55 ° C. and a humidity of 40% RH are performed. The PVA film was obtained by adjusting the humidity by passing for 9 seconds in the total required time. 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. In addition, the amount of change in the moisture content in the width direction of the film is 0.5%, the amount of change in the concentration of the plasticizer is 0.4%, and the thickness unevenness in the width direction is 3 μm. The amount was 0.9%, the amount of change in the plasticizer concentration was 0.7%, and the thickness variation was 5 μm.
The aforementioned film was processed in the same manner as in Example 1 to produce a polarizing film. The polarization 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 a 10% PVA aqueous solution (Kuraray PVA117H) adhesive to obtain a polarizing plate. When the color spots of the polarizing plate were observed, there was no color spot over the entire surface of the polarizing plate, and it was good. When this polarizing plate was incorporated in a liquid crystal display device, it was good without color spots.
[0050]
Example 3
100 parts by weight of PVA having a saponification degree of 99.89 mol% and a polymerization degree of 4000 was melt-kneaded with 10 parts by weight of glycerin and 240 parts by weight of water, defoamed, and then melt extruded from a T die onto an endless belt, A film was formed. Thereafter, both the steps of contacting the film obtained by drying and heat treatment with hot air having a temperature of 60 ° C. and a humidity of 80% RH, and subsequently bringing the film into contact with hot air having a temperature of 55 ° C. and a humidity of 40% RH are performed. The PVA film was obtained by passing it through for 11 seconds for the total required time to obtain a PVA film. The average thickness of the obtained film was 35 μm, the moisture content was 3.8%, the width of the film was 2.3 m, The retardation was 15 nm. In addition, the amount of change in the water content in the width direction of the film is 0.6%, the amount of change in the concentration of the plasticizer is 0.6%, and the thickness variation in the width direction is 3 μm. The amount of change in the plasticizer concentration was 0.7%, and the thickness variation was 3 μm.
The aforementioned PVA film was processed in the same manner as in Example 1 to produce a polarizing film. The polarization performance of the obtained polarizing film was a transmittance of 44.43%, a degree of polarization of 99.26%, and a dichroic ratio of 46.94.
The obtained polarizing film was bonded to a triacetate film using a 10% PVA aqueous solution (Kuraray PVA117H) adhesive to obtain a polarizing plate. When the color spots of the polarizing plate were observed, the color spots that were discernable by visual observation over the entire surface of the polarizing plate were small and good. The degree of color spots of the liquid crystal display device incorporating this polarizing plate was larger than that when visually observing the color spots of the polarizing plate, but was relatively small and good.
[0051]
Comparative Example 1
100 parts by weight of PVA having a saponification degree of 99.95 mol% and a polymerization degree of 2400 was melt-kneaded with 10 parts by weight of glycerin and 170 parts by weight of water, and after defoaming, melt extrusion 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 hot air having a temperature of 65 ° C. and a humidity of 90% RH, and subsequently bringing the film into contact with hot air having a temperature of 50 ° C. and a humidity of 45% RH are performed. The PVA film was obtained by adjusting the humidity by passing it for 3 seconds for the total required time. The obtained film had an average thickness of 41 μm, a moisture content of 4.5%, a film width of 3 m, and a retardation of 35 nm. Further, the change in the moisture content in the width direction of the film is 1.9%, the change in the concentration of the plasticizer is 0.8%, the thickness variation in the width direction is 2 μm, and the moisture content in the flow direction of the film. The amount of change was 3.9%, the amount of change in the plasticizer concentration was 0.9%, and the thickness variation was 4 μm.
The aforementioned PVA film was continuously processed in the order of preliminary swelling, dyeing, uniaxial stretching, fixing treatment, drying, and heat treatment to produce 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 / liter and a potassium iodide concentration of 40 g / liter for 3 minutes. Subsequently, uniaxial stretching was performed 5 times in a 50 ° C. aqueous solution with a boric acid concentration of 4%. For 5 minutes, and fixed. Thereafter, the PVA film was taken out, dried with hot air at 40 ° C., and further subjected to heat treatment at 100 ° C. for 5 minutes. The polarization 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 a 10% PVA aqueous solution (Kuraray PVA117H) adhesive to obtain a polarizing plate. When the color spots of the polarizing plate were observed, there were 10 color spots that were conspicuous by visual observation in the flow direction over the entire surface of the polarizing plate, which was not suitable as a polarizing plate at the product level. When this polarizing plate was incorporated in a liquid crystal display device, color spots in the flow direction could be visually recognized, which was unsuitable as a liquid crystal display device.
[0052]
Comparative Example 2
100 parts by weight of PVA having a saponification degree of 99.95 mol% and a polymerization degree of 2400 was melt-kneaded with 10 parts by weight of glycerin and 170 parts by weight of water, and after defoaming, melt extrusion from a T die onto a metal roll, A film was formed. Thereafter, the film obtained by drying and heat treatment was subjected to a step of bringing the film into contact with warm air having a temperature of 20 ° C. and a humidity of 80% RH over 10 seconds to obtain a PVA film. The obtained film had an average thickness of 42 μm, a moisture content of 4.0%, a film width of 3 m, and a retardation of 29 nm. In addition, the amount of change in the water content in the width direction of the film is 2.5%, the amount of change in the plasticizer concentration is 0.8%, and the thickness unevenness in the width direction is 3 μm. The amount was 4.9%, the amount of change in the plasticizer concentration was 1.0%, and the thickness variation was 5 μm.
The PVA film described above was processed in the same manner as in Example 1 to produce a polarizing film. The polarization 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 a 10% PVA aqueous solution (Kuraray PVA117H) adhesive to obtain a polarizing plate. When observing the color spots on the polarizing plate, there are innumerable color spots that appear visually in the flow direction over the entire surface of the polarizing plate, and color spots that appear as spots in shades, making it unsuitable as a commercial level polarizing plate. there were. When this polarizing plate was incorporated in a liquid crystal display device, the flow direction and spot-like color spots could be visually recognized, which was unsuitable as a liquid crystal display device.
[0053]
【The invention's effect】
When the optical polyvinyl alcohol film of the present invention is uniaxially stretched, the generation of wrinkles during stretching is suppressed, and the occurrence of streaks (color spots) in the flow direction of the film is reduced. The polarizing film obtained in this way can be effectively used as a part of a high-quality liquid crystal display device by taking advantage of its properties.

Claims (6)

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