JP2004160845A - Method for manufacturing polyvinyl alcohol film and polarizing film using the polyvinyl alcohol film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyvinyl alcohol film excellent in quality such as appearance or the like, and a method for in particular manufacturing the polyvinyl alcohol film for a polarizing film well over a long period of time. <P>SOLUTION: The polyvinyl alcohol film for the polarizing film is manufactured by casting an aqueous solution of a polyvinyl alcohol resin on a drum-shaped roll 1 from a T-shaped slit die 2. At this time, the casting angle of the aqueous solution of the polyvinyl alcohol resin on the surface of the drum-shaped roll 1 from the T-shaped slit die 2 is set to 25-40° in the direction opposite to the rotary direction of the drum-shaped roll 1 with respect to a perpendicular and the wet tension of the surface of the drum-shaped roll 1 is adjusted to 25-50 mN/m. <P>COPYRIGHT: (C)2004,JPO

Description

【００７８】
上記表１の結果から、実施例品のポリビニルアルコール系フィルムは、厚みムラの少なく、光学的色ムラも全く確認されなかった。さらに、ダイラインや横シマもなく、ロングラン性に優れたものであった。そして、これら実施例品を用いて得られた偏光フィルムも、光学的色ムラが全く確認されなかった。
【００７９】
これに対して、比較例品は、厚みムラが大きいものがあったり、光学的色ムラのあるポリビニルアルコール系フィルムが得られた。さらに、ダイラインや横シマも多く、ロングラン性に劣るものがあった。さらに、これら比較例品を用いて得られた偏光フィルムも、光学的色ムラが確認された。
【００８０】
【発明の効果】
以上のように、本発明は、ポリビニルアルコール系樹脂水溶液をＴ型スリットダイよりドラム型ロールに流延する際に、上記Ｔ型スリットダイからのドラム型ロール表面へのポリビニルアルコール系樹脂水溶液の流延角度を、垂線に対してドラム型ロールの回転方向と逆方向に２５〜４０°の傾斜を設け、かつ上記ロール表面の濡れ張力を２５〜５０ｍＮ／ｍに調整したポリビニルアルコール系フィルムの製法である。このため、ポリビニルアルコール系樹脂水溶液が緩やかに上記ロール表面に流延され、外観的にも良好なフィルムがロングラン性良く形成されるようになる。したがって、このようにして得られたポリビニルアルコール系フィルムを用いて作製される偏光膜は、偏光特性に優れたものとなる。
【００８１】
そして、上記Ｔ型スリットダイにおいて、Ｔ型スリットダイの長手方向に対して、両端部より１５％以内の部分が、そのスリット間隔を中央部よりも小さく設定されていると、製膜，乾燥により得られるフィルムの耳端部の膜厚が厚くなることなく、フィルム剥離性に優れた効果を奏するようになる。
【図面の簡単な説明】
【図１】本発明のポリビニルアルコール系フィルムの製法におけるＴ型スリットダイとドラム型ロールとの位置関係を模式的に示す説明図である。
【図２】本発明のポリビニルアルコール系フィルムの製法におけるＴ型スリットダイのスリット形状の一例を示す説明図である。
【図３】従来のポリビニルアルコール系フィルムの製法におけるＴ型スリットダイとドラム型ロールとの位置関係を模式的に示す説明図である。
【符号の説明】
１ ドラム型ロール
２ Ｔ型スリットダイ[0001]
TECHNICAL FIELD OF THE INVENTION
An object of the present invention is to provide a method for producing a polyvinyl alcohol-based film having excellent uniformity in film thickness and optical performance and good appearance of the film, and in particular, to maintain stable quality even when produced continuously for a long period of time (long run property). And a polarizing film excellent in optical performance without obstruction such as optical unevenness obtained by using the method.
[0002]
[Prior art]
In general, a polyvinyl alcohol-based film is produced by dissolving a polyvinyl alcohol-based resin in a solvent, defoaming to prepare a stock solution, and forming the film by a solution casting method (casting method) using a T-type slit die. You. As a film forming method by such a solution casting method, conventionally, for example, as shown in FIG. 3, a polyvinyl alcohol-based resin aqueous solution is cast from a T-shaped slit die 2 'onto the surface of a drum type roll 1 to form a film. The drying method was adopted. However, when a polyvinyl alcohol-based resin aqueous solution is vertically cast from the T-type slit die 2 'onto the surface of the drum-type roll 1 to form a film, wrinkles and the like are formed in appearance, and a film having a uniform film thickness is obtained. In some cases, it has been proposed that the aqueous solution is cast on a roll surface by tilting a slit die (for example, see Patent Document 1).
[0003]
[Patent Document 1]
JP-A-2002-144355
[0004]
[Problems to be solved by the invention]
However, even in the above-mentioned disclosed technology, the film appearance and the uniformity of the film thickness, the long run property in the production aspect, and the high quality of the polarizing film are not sufficiently satisfactory.
[0005]
The present invention has been made in view of such circumstances, and a method for producing a polyvinyl alcohol-based film having good long-run film-forming properties, and uniform film thickness and optical performance, and excellent film appearance. It is an object of the present invention to provide a polarizing film having less optical unevenness obtained by using the same.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is a method for producing a polyvinyl alcohol-based film by casting a polyvinyl alcohol-based resin aqueous solution from a T-shaped slit die onto a drum-type roll to form a polyvinyl alcohol-based film, The casting angle of the aqueous solution of the polyvinyl alcohol resin from the T-shaped slit die to the surface of the drum-type roll is provided at an angle of 25 to 40 ° with respect to the perpendicular in the direction opposite to the rotation direction of the drum-type roll, and A first gist is a method for producing a polyvinyl alcohol-based film in which the wetting tension on the roll surface is adjusted to 25 to 50 mN / m.
[0007]
The second aspect of the present invention is a polarizing film that uses a polyvinyl alcohol-based film obtained by the above-described production method and passes the film through a stretching step, a dyeing step, and a boron compound treatment step.
That is, the present inventors have conducted a series of studies to solve the above problems and obtain a polyvinyl alcohol-based film having good appearance and the like. As a result, when a polyvinyl alcohol-based resin aqueous solution is cast from a T-type slit die onto a drum-type roll to form a polyvinyl alcohol-based film, the polyvinyl alcohol-based resin is transferred from the T-type slit die to the drum-type roll surface. The casting of the aqueous solution is set so that the inclination angle thereof is 25 to 40 ° in a direction opposite to the rotation direction of the drum type roll with respect to the perpendicular, and the wetting tension of the roll surface is adjusted to 25 to 50 mN / m. Then, they found that the object was achieved, and reached the present invention.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described in detail.
[0010]
In the method for producing a polyvinyl alcohol-based film of the present invention, an aqueous solution of a polyvinyl alcohol-based resin is used as a film forming material.
[0011]
The polyvinyl alcohol-based resin is usually produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate, but is not limited thereto. A small amount of unsaturated carboxylic acid (salt, ester, amide, nitrile, etc.) Olefins having 2 to 30 carbon atoms (ethylene, propylene, n-butene, isobutene, etc.), vinyl ethers, unsaturated sulfonates and the like may be contained as modifying components. Further, a polyvinyl alcohol-based resin containing a silyl group may be used, and as a method for producing the same, a post-modification using a silylating agent or copolymerization with a silyl group-containing olefinically unsaturated monomer and saponification are performed. And the like. Examples of the silyl group-containing olefinically unsaturated monomer include vinyl silane, (meth) acrylamide, and alkyl silane.
[0012]
The degree of polymerization of the polyvinyl alcohol-based resin is not particularly limited, but is preferably in the range of 1,000 to 7000, more preferably 1200 to 6000, and particularly preferably 1400 to 5000. That is, if the degree of polymerization is less than 1,000, sufficient polarizing performance cannot be obtained when a polarizing film is used, and if it exceeds 7000, stretching tends to be difficult when a polarizing film is used, and industrial production tends to be difficult. This is not preferred. In addition, the said polymerization degree is measured according to JISK6726.
[0013]
Further, the degree of saponification of the polyvinyl alcohol-based resin is preferably 80 mol% or more, more preferably 85 to 100 mol%, and particularly preferably 98 to 100 mol%. As described above, if the degree of saponification is less than 80 mol%, it is difficult to obtain sufficient polarization performance when forming a polarizing film, which is not preferable.
[0014]
The polyvinyl alcohol-based resin may include one or more commonly used plasticizers, such as glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, and polyethylene glycol, if necessary. The content may be 30% by weight or less, more preferably 3 to 25% by weight, particularly preferably 5 to 20% by weight based on the resin. If the amount of the plasticizer exceeds 30% by weight, the film strength tends to be inferior.
[0015]
The release agent may be contained in an amount of 5% by weight or less, more preferably 0.001 to 3% by weight, and particularly preferably 0.001 to 2% by weight, based on the polyvinyl alcohol resin. If the amount of the release agent exceeds 5% by weight, the appearance of the film surface tends to be poor, which is not preferable.
[0016]
In the present invention, a polyvinyl alcohol-based resin aqueous solution is prepared using the above-described polyvinyl alcohol-based resin, and the aqueous solution is cast on a drum-type roll using a T-type slit die to form a film. It is for producing films.
[0017]
Next, a method for producing the polyvinyl alcohol-based film will be described.
[0018]
First, the polyvinyl alcohol resin is washed to remove sodium acetate contained in the powder. Washing is performed with methanol or water. However, a method of washing with methanol is more preferable because a method of washing with methanol requires solvent recovery or the like.
[0019]
A polyvinyl alcohol-based resin aqueous solution is prepared from the water-containing polyvinyl alcohol-based resin wet cake after washing.However, if the water-containing polyvinyl alcohol-based resin wet cake is directly dissolved in water, a desired high-concentration aqueous solution may not be easily obtained. It is preferable to perform dehydration once. The dehydration method is not particularly limited, and a method using centrifugal force is generally used.
[0020]
By the washing and dehydration, it is preferable to obtain a wet polyvinyl alcohol-based resin wet cake having a water content of 50% by weight or less, more preferably 30 to 45% by weight. That is, if the water content exceeds 50% by weight, it is difficult to obtain a desired aqueous solution concentration, which is not preferable.
[0021]
The aqueous polyvinyl alcohol resin wet cake after dehydration is dissolved in water to prepare an aqueous solution. The above-mentioned aqueous solution of the polyvinyl alcohol-based resin is prepared by charging a dewatered polyvinyl alcohol-based resin wet cake in a dissolving can, additional water, a plasticizer, and additives as necessary, heating, stirring, and dissolving the multi-screw extruder. Dehydrated polyvinyl alcohol-based resin wet cake or dried polyvinyl alcohol-based resin, and if necessary, additional water, plasticizer, and additives are charged and obtained by heating and dissolving while applying shear. .
[0022]
The concentration of the aqueous polyvinyl alcohol-based resin solution thus obtained is preferably 5 to 60% by weight, more preferably 17 to 55% by weight, and particularly preferably 20 to 50% by weight. That is, when the concentration is less than 5% by weight, the drying load of the film is increased and the production capacity is deteriorated. When the concentration is more than 60% by weight, the viscosity becomes too high and uniform dissolution is difficult, which is not preferable.
[0023]
Next, the obtained polyvinyl alcohol-based resin aqueous solution is subjected to a defoaming treatment. Examples of the defoaming method include a static deaeration method and a defoaming method using a multi-screw extruder. In the present invention, a defoaming method using a multi-screw extruder is preferable.
[0024]
The multi-screw extruder is not particularly limited as long as it is a multi-screw extruder having a vent, but a twin-screw extruder having a vent is usually used.
[0025]
The defoaming process is performed by the multi-screw extruder, and the polyvinyl alcohol-based resin aqueous solution discharged from the multi-screw extruder is introduced into a T-shaped slit die by a fixed amount, and is cast on a drum-type roll surface to form a film. And dried.
[0026]
In the present invention, as shown in FIG. 1, a T-type slit die 2 for casting an aqueous solution of a polyvinyl alcohol-based resin on the surface of the drum-type roll 1 is provided in a direction opposite to a rotation direction of the drum-type roll 1 with respect to a perpendicular line. It is one of the features to install so that it inclines by 40 degrees. Particularly preferably, the inclination angle is 25 to 35 °. If the inclination angle is out of the above range, die lines and scratches are likely to occur on the film, and the practicality is reduced. As described above, by casting the aqueous solution of the polyvinyl alcohol-based resin on the surface of the drum-type roll 1 in a state where the inclination angle is provided, the aqueous solution lands gently, and the resulting film does not have wrinkles and die lines. A film having a uniform thickness and excellent appearance can be obtained.
[0027]
Further, in the T-type slit die 2, a T-type slit die in which a slit interval is set smaller than a central portion in a portion within 15% of both ends with respect to a longitudinal direction of the T-type slit die 2. It is preferable to use By using such a T-shaped slit die, the film obtained at the time of film formation and drying does not have a large thickness at the edge of the film, and has an excellent effect of exfoliating the film.
[0028]
More preferably, the T-shaped slit die 2 is a T-shaped slit die in which the slit interval is 80% or less of the slit interval in the central portion within 15% of both ends. Particularly preferred is a T-shaped slit die in which the slit interval is gradually reduced from the portion within 15% of both ends toward the ends. Specifically, for example, one having a slit shape shown in FIG. 2 can be mentioned.
[0029]
When casting a film with the drum-type roll 1, for example, the rotation speed of the drum-type roll is preferably 5 to 30 m / min, and particularly preferably 6 to 20 m / min.
[0030]
The resin temperature at the outlet of the T-shaped slit die 2 is preferably 80 to 100 ° C, and more preferably 85 to 98 ° C.
[0031]
The size of the drum type roll 1 is not particularly limited, but for example, the roll diameter is preferably 2000 to 4000 mm, more preferably 2500 to 3800 mm.
[0032]
The material of the drum-type roll 1 is not particularly limited, but usually stainless steel is preferably used, and the roll surface is preferably plated with metal to prevent damage. As the type of the metal plating, for example, chromium plating, nickel plating, zinc plating and the like are suitably used, and can be used alone or in a combination of two or more kinds of multilayers. From the viewpoint of durability, the outermost surface is preferably chromium plating.
[0033]
Another feature of the present invention is that it is necessary to adjust the wetting tension on the surface of the drum type roll 1 to 25 to 50 mN / m during casting film formation. The cissing occurs in the aqueous alcohol-based resin solution, and the appearance of the film becomes poor. On the other hand, when it exceeds 50 mN / m, the releasability of the film from the drum-type roll 1 is reduced, and uneven and excessive stretching is applied to the optical performance. Adversely affect. The preferred range of the wetting tension on the surface of the drum type roll 1 is 30 to 45 mN / m. In the present invention, the wetting tension is measured according to JIS K6768.
[0034]
The means for satisfying the wetting tension on the surface of the drum type roll 1 is not particularly limited, but a drum having a mirror-finished chrome surface is used, and the surface is treated with an acid aqueous solution having a pH of 1 to 3 (measured at 20 ° C., the same applies hereinafter). It should be processed. Examples of the acid aqueous solution having a pH of 1 to 3 include acetic acid, sulfuric acid, hydrochloric acid, and nitric acid. Among them, an aqueous solution of acetic acid and nitric acid is particularly preferable. If the pH is outside the above range, it is difficult to obtain wettability in the above range, which is not preferable.
[0035]
In addition, in the present invention, as a method of adjusting the wetting tension other than treating the surface of the drum-type roll 1 with the acid aqueous solution as described above, a polyvinyl film is formed under the condition that the surface wetting tension is in the above range. An anionic surfactant may be added in advance to an aqueous solution of an alcoholic resin, and the aqueous solution may be cast on a drum-type roll 1 to form a film. In this case, the uniformity of the film thickness and the film appearance characteristics can be improved. In addition, it is useful in that the long-run film forming property is further improved.
[0036]
The amount of the anionic surfactant is not particularly limited, but is preferably 0.001 to 5 parts, more preferably 0.01 to 2 parts, per 100 parts by weight of the polyvinyl alcohol-based resin (hereinafter abbreviated as "part"). More preferably, it is 0.01 to 1 part. When the addition amount is less than 0.001 part, it is difficult to adjust the wetting tension, and when it exceeds 5 parts, a problem of blocking occurs in the film, which is not preferable.
[0037]
Examples of the anionic surfactant include fatty acid soaps, N-acyl amino acids and salts thereof, polyoxyethylene alkyl ester carboxylates, carboxylate types such as acylated peptides, alkylbenzene sulfonates, alkylnaphthalene sulfonates, Naphthalene sulfonic acid salt formalin polycondensate, melamine sulfonic acid salt formalin polycondensate, dialkyl sulfosuccinate ester salt, alkyl sulfosuccinate disalt, polyoxyethylene alkyl sulfosuccinate disalt, alkyl sulfoacetate, α-olefin sulfone Acid salts, N-acylmethyltaurine salts, sulfonate types such as dimethyl-5-sulfoisophthalate sodium salt, sulfated oils, higher alkyl sulfate esters, polyoxyethylene alkyl ether sulfates, higher alcohol ethoxy Sulfate ester salts such as sulfate, polyoxyethylene alkyl phenyl ether sulfate, monoglycol sulfate, etc., and phosphate ester salts such as polyoxyethylene alkyl ether phosphate, polyoxyethylene alkyl phenyl ether phosphate, alkyl phosphate, etc. And the like. In carrying out the method of the present invention, it is also possible to form a film by using both of the methods described above.
[0038]
In this way, the aqueous polyvinyl alcohol-based resin solution is cast on the drum-type roll 1 using the T-shaped slit die 2, formed into a film, and dried, and then subjected to further drying, heat treatment, and humidity control as necessary. By doing so, the intended polyvinyl alcohol-based film is obtained.
[0039]
Regarding the drying, (1) a method in which the internal temperature of the drum type roll 1 is adjusted to 80 to 100 ° C. and then drying is performed, and (2) a hard chrome plating treatment or a mirror surface is applied to the surface after passing through the drum. A method in which a treated roll (1 to 30 rolls) having a diameter of 0.2 to 2 m is adjusted to a temperature of 60 to 100 ° C so that both sides of the film pass through the roll, (3) held between a pair of rolls A method in which a dryer is provided in the middle of a belt (length: 20 to 100 m, surface: mirror-finished treatment), and the dryer passes through the dryer. Alternatively, these methods (1) to (3) may be appropriately combined.
[0040]
Regarding the heat treatment, (1) a method of passing a roll (1 to 30 rolls) having a surface of hard chrome plating or a mirror surface and having a diameter of 0.2 to 2 m adjusted to a temperature of 60 to 180 ° C., (2) A method using a floating dryer (length: 2 to 10 m, temperature: 80 to 180 ° C.) and the like can be given.
[0041]
Regarding the humidity control, (1) a method of passing through a room conditioned at a temperature of 20 to 80 ° C. and a humidity of 65 to 95% RH, and (2) an apparatus typified by “Fludex” manufactured by Hirano Techseed Co., Ltd. Steam condensation method and the like.
[0042]
As described above, when the polyvinyl alcohol-based film is cast on the surface of the drum-type roll 1, the polyvinyl alcohol-based film obtained as described above is moved through the T-type slit die 2 with respect to the perpendicular. 1 is installed at an angle of 25 to 40 ° in the direction opposite to the rotation direction, and the wet tension of the surface of the roll 1 is adjusted to 25 to 50 mN / m to form a film. It becomes. And the obtained polyvinyl alcohol-based film is very useful as an optical film, especially as a film for a polarizing film.
[0043]
Hereinafter, a method for producing a polarizing film using the polyvinyl alcohol-based film thus obtained will be described.
[0044]
As a method of manufacturing the polarizing film, the obtained polyvinyl alcohol-based film is stretched and dyed by dipping in a solution of iodine or a dichroic dye, or simultaneously with stretching and dyeing, or by iodine or a dichroic dye. After dyeing and stretching, there is a method of treating with a boron compound. In addition, a method of stretching in a solution of a boron compound after dyeing, and the like can also be mentioned, and can be appropriately selected.
[0045]
The thickness of the polyvinyl alcohol-based film used for the polarizing film is preferably in the range of 30 to 100 μm, and more preferably 40 to 90 μm. That is, if the film thickness is less than 30 μm, it is difficult to stretch the film, and if it exceeds 100 μm, problems such as a decrease in film thickness accuracy, an increase in the load at the time of drying, and an increase in the size of the stretching apparatus are not preferred. .
[0046]
The polyvinyl alcohol-based film (unstretched film) is stretched, dyed, and treated with a boron compound as described above, and the stretching, the dyeing, and the boron compound treatment are performed simultaneously even if they are performed in separate steps. You may. In the present invention, it is preferable to perform uniaxial stretching during at least one of the dyeing step and the boron compound treatment step.
[0047]
The stretching is preferably performed 3 to 10 times in the uniaxial direction, more preferably 3.5 to 6 times. At this time, slight stretching (extending to a degree that prevents shrinkage in the width direction or more) may be performed in a direction perpendicular to the stretching. The temperature condition during stretching is preferably set in the range of 40 to 170 ° C. Furthermore, the stretching ratio may be finally set in the above range, and the stretching operation may be performed not only in one stage but also in any range of the manufacturing process.
[0048]
The dyeing of the polyvinyl alcohol-based film is performed by bringing a liquid containing iodine or a dichroic dye into contact with the film. Usually, an aqueous solution of iodine-potassium iodide is used, the concentration of iodine is 0.1 to 20 g / l, the concentration of potassium iodide is 10 to 70 g / l, and the mixing weight ratio of potassium iodide / iodine is: The range of potassium iodide / iodine = 10 to 100 is preferable. The dyeing time is practically about 30 to 500 seconds, and the temperature of the dyeing bath is preferably 5 to 60 ° C. Then, a small amount of an organic solvent compatible with water may be contained in addition to the water solvent. Further, as the contact means, any means such as immersion, coating, spraying and the like can be applied.
[0049]
The polyvinyl alcohol-based film dyed in this manner is then treated with a boron compound. As the boron compound, boric acid and borax are practical. This boron compound is used as an aqueous solution or a mixed solution of water and an organic solvent at a concentration of about 0.3 to 2 mol / l, and it is practically preferable to coexist a small amount of potassium iodide in the liquid. As a treatment method using the boron compound, a dipping method is preferable, but a coating method and a spraying method can also be used. As the processing conditions, the temperature is preferably about 40 to 70 ° C., and the processing time is preferably about 2 to 20 minutes. If necessary, the stretching operation may be performed during the processing.
[0050]
The polarizing film thus obtained can be used by laminating and bonding an optically isotropic polymer film or sheet as a protective film on one or both surfaces thereof. Examples of the protective film include films or sheets of cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, polystyrene, polyether sulfone, polyarylene ester, poly-4-methylpentene, polyphenylene oxide, and the like.
[0051]
Further, for the purpose of thinning the polarizing film, a curable resin such as a urethane-based resin, an acrylic resin, or a urea-based resin may be applied on one surface or both surfaces instead of the protective film, and may be laminated. .
[0052]
Further, the above-mentioned polarizing film (or one having a protective film or a curable resin laminated on at least one surface thereof) has a transparent pressure-sensitive adhesive layer formed on one surface thereof by an ordinary method, if necessary, so that it can be used practically. It may be offered to. Examples of the pressure-sensitive adhesive layer include acrylates such as butyl acrylate, ethyl acrylate, methyl acrylate, and 2-ethylhexyl acrylate; and acrylic acid, maleic acid, itaconic acid, methacrylic acid, crotonic acid, and the like. Mainly containing a vinyl monomer such as acrylonitrile, vinyl acetate, and styrene, which inhibits the polarizing properties of the polarizing film. However, the present invention is not limited to this, and the present invention is not limited thereto, and any pressure-sensitive adhesive having transparency can be used. For example, a polyvinyl ether-based or rubber-based adhesive can be used.
[0053]
The polarizing film thus obtained is, for example, an electronic desk calculator, an electronic timepiece, a word processor, a personal computer, a personal digital assistant, a liquid crystal display device such as an instrument for automobiles and machinery, sunglasses, anti-glare glasses, It is used for glasses, reflection reduction layers for display elements (CRT, LCD, etc.), medical equipment, building materials, toys, and the like.
[0054]
Next, examples will be described together with comparative examples. “%” Is based on weight unless otherwise specified.
[0055]
Embodiment 1
200 kg of water at 18 ° C. was put into a 500-liter tank, and 40 kg of a polyvinyl alcohol-based resin having a degree of polymerization of 1700 and a degree of saponification of 99.7 mol% was added with stirring, and stirring was continued for 15 minutes. Then, after water was once drained, 200 kg of water was further added and stirred for 15 minutes. The obtained slurry was dehydrated to obtain a polyvinyl alcohol resin wet cake having a water content of 40% and a sodium content of 1500 ppm.
[0056]
Next, 70 kg of the above-mentioned polyvinyl alcohol-based resin wet cake was put into a dissolving can, and 4.2 kg of glycerin as a plasticizer, 42 g of polyoxyethylene alkylamino ether as a release agent, and 10 kg of water were added. When the temperature reached 50 ° C., the mixture was stirred (rotation speed: 5 rpm), and when the internal resin temperature reached 100 ° C., the inside of the system was pressurized. After the temperature was raised to 150 ° C., the blowing of steam was stopped. (The amount of steam blown is 75 kg in total) After stirring for 30 minutes (rotation speed: 20 rpm) to uniformly dissolve, a 45% concentration aqueous polyvinyl alcohol resin solution (including a plasticizer and a release agent is also included as a solid content by concentration adjustment). ) Was prepared.
[0057]
Next, the aqueous polyvinyl alcohol-based resin solution (liquid temperature of 147 ° C.) was supplied to a twin screw extruder from a gear pump (P1), defoamed, and then discharged from a gear pump (P2). The conditions for the gear pump (P1), twin screw extruder, and gear pump (P2) are shown below.
[0058]
[Gear pump (P1)]
Number of gears: 2 gears
Size: 50cc / rev (discharge amount per rotation)
Inlet pressure: 5 kg / cm²
[0059]
[Twin screw extruder]
Screw outer diameter: 35mm
Screw L / D: 40 (L: diameter, D: length)
Extruder tip pressure: 50 kg / cm²
Rotation speed: 300 rpm
C1 / C2 (vent) / C3 / C4 / C5 = 150/135/105/105/105
[0060]
[Gear pump (P2)]
Inlet pressure: 50 kg / cm²
Emission amount: 41 kg / hr
Number of gears: 2 gears
Size: 50cc / rev (discharge amount per rotation)
Rotation speed: 12.3 rpm
No bubbles were observed in the aqueous polyvinyl alcohol resin solution discharged from the gear pump (P2).
[0061]
Then, the aqueous polyvinyl alcohol resin solution discharged from the gear pump (P2) is passed through a T-shaped slit die (a: 450 mm, b: 1 mm, c: 30 mm, d: 0.5 mm) having a slit shape shown in FIG. The film was cast on a drum type roll. At this time, as shown in FIG. 1, the casting angle θ of the aqueous solution of the polyvinyl alcohol-based resin from the T-shaped slit die 2 to the surface of the drum-type roll 1 is opposite to the rotation direction of the drum-type roll 1 with respect to the perpendicular. The T-shaped slit die 2 was installed so as to have a 25 ° inclination in the direction. The conditions for the casting film formation are shown below.
[0062]
[Drum type roll: A stainless steel base material is subjected to nickel plating and further chromium plating, and an aqueous acetic acid solution (0.5% concentration) of pH 3 is applied to the mirror-finished roll surface, and the wetting tension of the roll surface is 35 mN / m. thing〕
Diameter: 2800mm
Width: 1000mm
Rotation speed: 6m / min
Surface temperature: 90 ° C
Resin temperature at T-type slit die outlet: 95 ° C
[0063]
Thereafter, drying (conditions: drum (diameter 2.8 m, internal temperature 90 ° C.), drying roll (diameter 0.3 m, internal temperature 70 ° C., 10 pieces)), heat treatment [conditions: floating type dryer (140 ° C., long) Thickness 6 m)], and a humidity control was performed to prepare a polyvinyl alcohol-based film (width 400 mm × thickness 75 μm).
[0064]
Embodiment 2
The casting angle θ of the aqueous solution of the polyvinyl alcohol-based resin from the T-shaped slit die 2 to the surface of the drum-type roll 1 shown in FIG. The T-shaped slit die 2 was installed so that Otherwise in the same manner as in Example 1, a polyvinyl alcohol-based film (width 400 mm × thickness 75 μm) was produced. However, a polyvinyl alcohol resin having a degree of polymerization of 4,000 and a degree of saponification of 99.7 mol% was used, and the aqueous solution concentration of this resin was 25%.
[0065]
Embodiment 3
The casting angle θ of the aqueous solution of the polyvinyl alcohol-based resin from the T-shaped slit die 2 to the surface of the drum-type roll 1 shown in FIG. 1 is inclined by 30 ° with respect to the perpendicular in the direction opposite to the rotation direction of the drum-type roll 1. The T-shaped slit die 2 was installed so that Otherwise in the same manner as in Example 1, a polyvinyl alcohol-based film (width 400 mm × thickness 75 μm) was produced. However, the roll was not treated with an aqueous acid solution, but contained 0.2% of sodium lauryl sulfate in a polyvinyl alcohol-based resin aqueous solution, and the wet tension of the roll surface was 36 mN / m at the time after the start of operation. It was processed to become.
[0066]
[Comparative Example 1]
The T-shaped slit die 2 was installed so that the casting of the aqueous solution of the polyvinyl alcohol-based resin from the T-shaped slit die 2 to the surface of the drum-type roll 1 was vertical (in FIG. 1, the casting angle θ of the aqueous solution of the polyvinyl alcohol-based resin was 0 ° C). Otherwise in the same manner as in Example 1, a polyvinyl alcohol-based film (width 400 mm × thickness 75 μm) was produced.
[0067]
[Comparative Example 2]
As shown in FIG. 1, the casting angle θ of the aqueous solution of the polyvinyl alcohol-based resin from the T-shaped slit die 2 to the surface of the drum-type roll 1 is inclined by 20 ° with respect to the perpendicular to the direction of rotation of the drum-type roll 1. The T-shaped slit die 2 was installed so that Otherwise in the same manner as in Example 1, a polyvinyl alcohol-based film (width 400 mm × thickness 75 μm) was produced.
[0068]
[Comparative Example 3]
As shown in FIG. 1, the casting angle θ of the aqueous solution of the polyvinyl alcohol-based resin from the T-shaped slit die 2 to the surface of the drum-type roll 1 is inclined by 45 ° with respect to the perpendicular in the direction opposite to the rotation direction of the drum-type roll 1. The T-shaped slit die 2 was installed so that Otherwise in the same manner as in Example 1, a polyvinyl alcohol-based film (width 400 mm × thickness 75 μm) was produced.
[0069]
[Comparative Examples 4 and 5]
A polyvinyl alcohol-based film (width 400 mm × thickness 75 μm) was produced in the same manner as in Example 1 except that the wetting tension of the roll surface was changed to 23 mN / m (Comparative Example 4) and 57 mN / m (Comparative Example 5).
[0070]
The following evaluations were performed on the thus obtained polyvinyl alcohol-based films of Examples and Comparative Examples.
[0071]
[Measurement of thickness variation: based on JIS K 6900]
Using a film thick nest tester (“K306C” manufactured by Anritsu Corporation), three points of the film are sampled in the width direction (TD direction) at 1 m intervals in the film flow direction (MD direction), and the thickness is measured. The maximum value of the thickness variation was determined.
[0072]
Furthermore, after sandwiching a polyvinyl alcohol-based film at an angle of 45 ° between two polarizing plates in a crossed Nicols state, observation was performed in a transmission mode using a light box having a surface illuminance of 5000 lux.
[0073]
In addition, after continuously producing the above film for 17 days (Examples 1 and 2, Comparative Examples 1 to 3) or 30 days (Example 3, Comparative Examples 4 to 5), the film thickness and The appearance was measured and observed.
[0074]
[Measurement of polarization unevenness]
The obtained polyvinyl alcohol-based film is unwound at 1.25 m / min, swollen in a water washing tank (25 ° C.), and then 1.4 times in an iodine tank (22 ° C., iodine concentration 0.05 g / liter). Perform 1.6 times uniaxial stretching in an acid bath (50 ° C, iodine concentration 0.0012 g / liter, boric acid concentration 47 g / liter), and further perform total 5 times uniaxial stretching at a winding speed of 6.25 m / min. Thus, a polarizing film was obtained.
[0075]
After the obtained polarizing film is sandwiched between two polarizing plates in a crossed Nicols state at an angle of 45 °, the surface illuminance is observed in a transmission mode using a light box having a lux of 5000 lux, and the optics caused by the polyvinyl alcohol-based film is observed. The target color unevenness was visually evaluated.
[0076]
The results are shown in Table 1 below.
[0077]
[Table 1]

[0078]
From the results in Table 1 above, the polyvinyl alcohol-based film of the example had little thickness unevenness and no optical color unevenness was confirmed at all. Furthermore, there was no die line and no horizontal stripe, and it was excellent in long run property. The polarizing films obtained by using these examples also showed no optical color unevenness.
[0079]
On the other hand, some of the comparative example products had a large thickness unevenness and a polyvinyl alcohol-based film having optical color unevenness. Furthermore, there were many die lines and horizontal stripes, and some of them were inferior in long-run property. Furthermore, optical color unevenness was also observed in the polarizing films obtained using these comparative examples.
[0080]
【The invention's effect】
As described above, in the present invention, when the aqueous solution of the polyvinyl alcohol-based resin is cast from the T-shaped slit die to the drum-type roll, the flow of the aqueous solution of the polyvinyl alcohol-based resin from the T-shaped slit die to the surface of the drum-type roll is controlled. A method for producing a polyvinyl alcohol-based film in which the extension angle is provided at an angle of 25 to 40 ° in the direction opposite to the rotation direction of the drum type roll with respect to the perpendicular and the wetting tension of the roll surface is adjusted to 25 to 50 mN / m. is there. Therefore, the aqueous solution of the polyvinyl alcohol-based resin is gently cast on the surface of the roll, and a film having good external appearance is formed with a long running property. Therefore, a polarizing film produced using the polyvinyl alcohol-based film thus obtained has excellent polarization characteristics.
[0081]
In the above-mentioned T-shaped slit die, if the slit interval is set to be smaller than the central portion by 15% or less from both ends in the longitudinal direction of the T-shaped slit die, the film is formed and dried. The resulting film has an excellent effect of exfoliating the film without increasing the thickness of the edge portion of the film.
[Brief description of the drawings]
FIG. 1 is an explanatory view schematically showing a positional relationship between a T-type slit die and a drum-type roll in a method for producing a polyvinyl alcohol-based film of the present invention.
FIG. 2 is an explanatory view showing an example of a slit shape of a T-shaped slit die in the method for producing a polyvinyl alcohol-based film of the present invention.
FIG. 3 is an explanatory view schematically showing a positional relationship between a T-shaped slit die and a drum-type roll in a conventional method for producing a polyvinyl alcohol-based film.
[Explanation of symbols]
1 Drum type roll
2 T-type slit die

Claims (3)

A method for producing a polyvinyl alcohol-based film in which a polyvinyl alcohol-based resin aqueous solution is cast from a T-shaped slit die onto a drum-type roll to form a polyvinyl alcohol-based film. The casting angle of the aqueous solution of the polyvinyl alcohol-based resin is provided with an inclination of 25 to 40 ° in a direction opposite to the rotation direction of the drum-type roll with respect to the perpendicular, and the wetting tension of the roll surface is adjusted to 25 to 50 mN / m. A method for producing a polyvinyl alcohol-based film, which comprises adjusting. 2. The die according to claim 1, wherein, as the T-shaped slit die, a portion in which 15% or less of both ends of the T-shaped slit die has a slit interval set smaller than a central portion with respect to a longitudinal direction of the T-shaped slit die. A method for producing a polyvinyl alcohol-based film. A polarizing film obtained by using the polyvinyl alcohol-based film obtained by the method for producing a polyvinyl alcohol-based film according to claim 1 or 2, and passing the film through a stretching step, a dyeing step, and a boron compound treatment step.

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