JP3917060B2 - Production method of polyvinyl alcohol film - Google Patents

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は、偏光膜の形成材料として有用であり、これ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]
BACKGROUND OF THE INVENTION
  The present invention is a method for producing a polyvinyl alcohol film having excellent uniformity of film thickness and optical performance, and good film appearance, and in particular, maintaining stable quality even when continuously produced for a long time (long run property). MadeTo the lawIt is related.
[0002]
[Prior art]
Generally, a polyvinyl alcohol film is produced by dissolving a polyvinyl alcohol resin in a solvent, defoaming to prepare a stock solution, and then forming a film by a solution casting method (casting method) using a T-type slit die. The Conventionally, as a film forming method by such a solution casting method, for example, as shown in FIG. 3, a polyvinyl alcohol-based resin aqueous solution is cast from the T-type slit die 2 'onto the surface of the drum-type roll 1 and formed into a film. The method of drying was taken. 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, a film having a uniform thickness is obtained. In recent years, it has been proposed that the slit die is inclined to cast the aqueous solution onto the roll surface (see, for example, Patent Document 1).
[0003]
[Patent Document 1]
JP 2002-144355 A
[0004]
[Problems to be solved by the invention]
However, even the above disclosed technology is not fully satisfactory in the appearance and uniformity of the film thickness, the long run property in production, and the high quality of the polarizing film.
[0005]
  The present invention has been made in view of such circumstances, and it is possible to produce a polyvinyl alcohol-based film having good long-run film-forming properties, uniform film thickness and optical performance, and excellent film appearance.LegalThe purpose is to provide.
[0006]
[Means for Solving the Problems]
  To achieve the above object, the present inventionOf Polyvinyl Alcohol FilmIs a method for producing a polyvinyl alcohol film by casting a polyvinyl alcohol resin aqueous solution from a T-type slit die to a drum-type roll to form a polyvinyl alcohol-type film, and the surface of the drum-type roll from the T-type slit die The casting angle of the polyvinyl alcohol-based resin aqueous solution is 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 25 to 50 mN / Adjust to mThe structureThe
[0007]
  And, Made abovePolyvinyl alcohol film obtained by the methodThePolarizing film obtained by using this through a stretching process, a dyeing process, and a boron compound treatment processIs excellent in optical performance without obstructions such as optical unevenness.The
[0008]
That is, the present inventors repeated a series of studies in order to solve the above-described problems and obtain a polyvinyl alcohol film having good appearance and the like. As a result, when a polyvinyl alcohol-based film is cast from a T-type slit die to a drum-type roll to form a polyvinyl alcohol-based film, the polyvinyl alcohol-based resin from the T-type slit die onto the drum-type roll surface is obtained. The casting of the aqueous solution is set so that the inclination angle is 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. As a result, the inventors have found that the object is achieved and have reached the present invention.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described in detail.
[0010]
In the method for producing a polyvinyl alcohol film of the present invention, an aqueous solution of a polyvinyl alcohol 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, and a small amount of unsaturated carboxylic acid (salt, ester, amide, nitrile, etc.) 2), 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. Moreover, what made the polyvinyl alcohol-type resin contain the silyl group may be used, and as the manufacturing method, it post-modifies using a silylating agent, or it copolymerizes with a silyl group containing olefinic unsaturated monomer, and is saponified. And the like. Examples of the silyl group-containing olefinically unsaturated monomer include vinyl silane, (meth) acrylamide, and alkyl silane.
[0012]
Although the polymerization degree in the said polyvinyl alcohol-type resin is not specifically limited, Especially the range of 1000-7000 is preferable, More preferably, it is 1200-6000, Especially preferably, it is the range of 1400-5000. That is, when the degree of polymerization is less than 1000, sufficient polarizing performance cannot be obtained when a polarizing film is formed, and when it exceeds 7000, stretching tends to be difficult and industrial production becomes difficult when forming a polarizing film. It is because it is not preferable. The degree of polymerization is measured according to JIS K 6726.
[0013]
Furthermore, it is preferable that the saponification degree of polyvinyl alcohol-type resin is 80 mol% or more, More preferably, it is 85-100 mol%, Most preferably, it is 98-100 mol%. Thus, when the degree of saponification is less than 80 mol%, it is not preferable because sufficient polarization performance is difficult to obtain in the case of a polarizing film.
[0014]
If necessary, the polyvinyl alcohol resin may include one or more commonly used plasticizers such as glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, and polyethylene glycol. You may make it contain 30 weight% or less with respect to resin, More preferably, it is 3-25 weight%, Most preferably, you may contain 5-20 weight%. If the plasticizer exceeds 30% by weight, the film strength tends to be inferior.
[0015]
Further, 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 with respect to the polyvinyl alcohol resin. If the release agent exceeds 5% by weight, the film surface tends to be poor in appearance, which is not preferable.
[0016]
In the present invention, a polyvinyl alcohol-based resin aqueous solution is prepared using the above-mentioned polyvinyl alcohol-based resin, and this aqueous solution is cast on a drum-type roll using a T-type slit die to form a polyvinyl alcohol-based resin. A film is manufactured.
[0017]
Next, a method for producing the polyvinyl alcohol film will be described.
[0018]
First, the polyvinyl alcohol-based resin is washed to remove sodium acetate contained in the powder. In washing, washing with methanol or water is required. However, since the method of washing with methanol requires solvent recovery, a washing method with water is more preferable.
[0019]
A polyvinyl alcohol-based resin aqueous solution is prepared from the water-containing polyvinyl alcohol-based resin wet cake after washing, but it may be difficult to obtain a desired high-concentration aqueous solution by dissolving the water-containing polyvinyl alcohol-based resin wet cake in water as it is. It is preferable to perform dehydration once. The dehydration method is not particularly limited, and a method using centrifugal force is common.
[0020]
A water-containing polyvinyl alcohol resin wet cake having a water content of 50% by weight or less, more preferably 30 to 45% by weight, is preferably obtained by the washing and dehydration. That is, if the water content exceeds 50% by weight, it becomes difficult to obtain a desired aqueous solution concentration, which is not preferable.
[0021]
The water-containing polyvinyl alcohol resin wet cake after dehydration is dissolved in water to prepare an aqueous solution. The above-mentioned polyvinyl alcohol resin aqueous solution is prepared by adding polyvinyl alcohol resin wet cake after dehydration to a dissolving can, additional water, plasticizer, and additives as necessary, heating and stirring to dissolve, or a multi-screw extruder Polyvinyl alcohol resin wet cake after dehydration or polyvinyl alcohol resin dried from it, and additional water, plasticizer and additives as needed, dissolved and heated and sheared .
[0022]
The concentration of the aqueous polyvinyl alcohol 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, if the concentration is less than 5% by weight, the drying load of the film becomes large and the production capacity is inferior. If it exceeds 60% by weight, the viscosity becomes too high and uniform dissolution becomes difficult, which is not preferable.
[0023]
Next, the obtained polyvinyl alcohol-based resin aqueous solution is defoamed. Examples of the defoaming treatment method include stationary defoaming and a defoaming treatment method using a multi-screw extruder. In the present invention, a defoaming treatment 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. Usually, a twin-screw extruder having a vent is used.
[0025]
The defoaming treatment by the multi-screw extruder is performed, and the polyvinyl alcohol-based resin aqueous solution discharged from the multi-screw extruder is introduced into the T-type slit die by a certain amount and cast on the surface of the drum-type roll to form a film. Dried.
[0026]
In the present invention, as shown in FIG. 1, a T-type slit die 2 for casting a polyvinyl alcohol-based resin aqueous solution on the surface of the drum-type roll 1 is placed in a direction opposite to the rotation direction of the drum-type roll 1 with respect to the vertical line It is one of the features that it is installed so as to be inclined by -40 °. Particularly preferred is an inclination angle of 25 to 35 °. When the tilt angle is out of the above range, die line scratches are likely to occur in the film, and the practicality is lowered. Thus, by casting a polyvinyl alcohol-based resin aqueous solution on the surface of the drum-type roll 1 in a state where an inclination angle is provided, the aqueous solution is gently landed, and the resulting film does not form wrinkles or die lines, A film having a uniform film thickness and excellent appearance can be obtained.
[0027]
Further, in the T-type slit die 2, the T-type slit die is formed by setting the slit interval to be smaller than the central portion at a portion within 15% from both ends with respect to the longitudinal direction of the T-type slit die 2. Is preferably used. By using such a T-shaped slit die, an excellent film releasability can be obtained without increasing the film thickness of the end portion of the film obtained by film formation and drying.
[0028]
More preferably, the T-type slit die 2 is a T-type slit die in which the slit interval is 80% or less with respect to the slit interval in the central portion at a portion within 15% from both ends. Particularly preferred is a T-type slit die in which the slit interval gradually decreases from the portion within 15% from both ends toward the end. Specifically, for example, one having the slit shape shown in FIG.
[0029]
When the film is cast by 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]
Moreover, it is preferable that the resin temperature of the said T-type slit die 2 exit is 80-100 degreeC, More preferably, it is 85-98 degreeC.
[0031]
Although it does not specifically limit about the magnitude | size of the said drum type roll 1, For example, 2000-4000 mm is preferable and, as for the diameter of a roll, More preferably, it is 2500-3800 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 metal-plated to prevent damage. As the type of the metal plating, for example, chrome plating, nickel plating, galvanization and the like are preferably used, and can be used alone or in combination of two or more kinds of multilayers. From the viewpoint of durability, the outermost surface is preferably chrome 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 alcoholic resin solution, resulting in poor film appearance. On the other hand, if it exceeds 50 mN / m, the peelability of the film from the drum-type roll 1 is lowered, and non-uniform excessive stretching is applied to the optical performance. Adversely affect. A preferable 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 K 6768.
[0034]
The means for satisfying the surface tension of the drum-type roll 1 is not particularly limited, but a drum having a mirror-finished chromium surface is used, and the surface is an acid aqueous solution having a pH of 1 to 3 (measured at 20 ° C., the same applies hereinafter). What is necessary is just to process. Examples of the acid aqueous solution having a pH of 1 to 3 include acetic acid, sulfuric acid, hydrochloric acid, nitric acid and the like, and among them, an aqueous solution of acetic acid and nitric acid is particularly preferable. An acid aqueous solution having a pH outside the above range is not preferable because it is difficult to obtain wettability within the above range.
[0035]
Further, in the present invention, as described above, as a method of adjusting the wetting tension other than treating the surface of the drum-type roll 1 with the acid aqueous solution, the film is formed under the condition that the wetting tension of the surface falls within the above range. An anionic surfactant can be added in advance to the alcoholic resin aqueous solution, and the aqueous solution can be cast onto the drum-type roll 1 to form a film. In this case, the film thickness uniformity and film appearance characteristics In addition, it is useful in that the long-run film forming property is further improved.
[0036]
The amount of the anionic surfactant added is not particularly limited, but is 0.001 to 5 parts, particularly 0.01 to 2 parts, relative to 100 parts by weight of the polyvinyl alcohol resin (hereinafter referred to as “parts”). Furthermore, it is preferable that it is 0.01-1 part. If the addition amount is less than 0.001 part, it is difficult to adjust the wetting tension, and if it exceeds 5 parts, a blocking problem 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, alkyl benzene sulfonates, alkyl naphthalene sulfonates, Naphthalene sulfonic acid salt formalin polycondensate, melamine sulfonic acid salt formalin polycondensate, dialkyl sulfosuccinic acid ester salt, sulfosuccinic acid alkyl disalt, polyoxyethylene alkyl sulfosuccinic acid disalt, alkyl sulfoacetate, α-olefin sulfone Sulfonates such as acid salts, N-acylmethyl taurate salts, dimethyl-5-sulfoisophthalate sodium salts, sulfated oils, higher alkyl sulfates, polyoxyethylene alkyl ether sulfates, higher alcohol ethoxy Sulfate ester type salts such as sulfate, polyoxyethylene alkylphenyl ether sulfate, monoglyculate, phosphate ester salts such as polyoxyethylene alkyl ether phosphate, polyoxyethylene alkylphenyl ether phosphate, alkyl phosphate Examples include molds. In carrying out the method of the present invention, it is also possible to form a film by using both methods described above in combination.
[0038]
Thus, after casting the polyvinyl alcohol-based resin aqueous solution onto the drum-type roll 1 using the T-type slit die 2, forming the film and drying, further drying, heat treatment, and humidity control are performed as necessary. By doing so, the intended polyvinyl alcohol film can be 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 drying is performed, and (2) the surface is hard chrome plated or mirror-finished after passing through the drum. A method of adjusting a processed roll (1-30 rolls) having a diameter of 0.2 to 2 m to a temperature of 60 to 100 ° C. so that both surfaces of the film are in contact with the roll, (3) held between a pair of rolls For example, there is a method in which a dryer is provided in the middle of the belt (length: 20 to 100 m, surface: mirror finish) and the dryer is passed through. Alternatively, these methods (1) to (3) may be appropriately combined.
[0040]
Regarding the heat treatment, (1) a method in which the surface is hard chrome plated or mirror-finished and a roll having a diameter of 0.2 to 2 m (1 to 30 rolls) is adjusted to a temperature of 60 to 180 ° C., and (2) For example, a method using a floating dryer (length: 2 to 10 m, temperature 80 to 180 ° C.) may be used.
[0041]
For 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 represented by “Fludex” manufactured by Hirano Techseed Co., Ltd. For example, the vapor condensation method.
[0042]
As described above, when the polyvinyl alcohol-based film thus obtained is cast onto the surface of the drum-type roll 1 with the polyvinyl alcohol-based resin aqueous solution, the T-type slit die 2 is used as the drum-type roll with respect to the perpendicular. Polyvinyl alcohol film excellent in appearance and the like because it is formed to be inclined by 25 to 40 ° in the direction opposite to the rotation direction of 1 and the wetting tension of the roll 1 surface is adjusted to 25 to 50 mN / m. It becomes. And the obtained polyvinyl alcohol-type film is very useful as an optical film, especially a film for polarizing films.
[0043]
Hereinafter, a method for producing a polarizing film using the polyvinyl alcohol film thus obtained will be described.
[0044]
As a method for producing the polarizing film, the obtained polyvinyl alcohol film is stretched and dyed by dipping in a solution of iodine or dichroic dye, or stretched and dyed simultaneously, or with iodine or dichroic dye. A method of treating with a boron compound after dyeing and stretching can be mentioned. Moreover, the method of extending | stretching in the solution of a boron compound after dyeing etc. is mention | raise | lifted, and it can select suitably.
[0045]
As a film thickness of the polyvinyl alcohol-type film used for the said polarizing film, the range of 30-100 micrometers is preferable, More preferably, it is 40-90 micrometers. That is, if the film thickness is less than 30 μm, it is difficult to stretch, and if it exceeds 100 μm, problems such as a decrease in film thickness accuracy, an increase in load during drying, and an increase in the size of the stretching apparatus are undesirable. .
[0046]
The polyvinyl alcohol film (unstretched film) is subjected to stretching, dyeing, and boron compound treatment as described above. This stretching and dyeing, and further boron compound treatment are performed at the same time even if they are performed in separate steps. May be. 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 stretched 3 to 10 times in a uniaxial direction, more preferably 3.5 to 6 times. At this time, the film may be slightly stretched in the direction perpendicular to the stretching (stretching to prevent shrinkage in the width direction or more). The temperature condition during stretching is preferably set in the range of 40 to 170 ° C. Furthermore, the draw ratio may be finally set within the above range, and the drawing operation may be carried out not only in one stage but also in any stage of the production process.
[0048]
The polyvinyl alcohol film is dyed by bringing the film into contact with a liquid containing iodine or a dichroic dye. Usually, an iodine-potassium iodide aqueous solution is used, the iodine concentration is 0.1 to 20 g / liter, the potassium iodide concentration is 10 to 70 g / liter, and the mixed weight ratio of potassium iodide / iodine is: The range of potassium iodide / iodine = 10-100 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. In addition to the water solvent, a small amount of an organic solvent compatible with water may be contained. Further, as the contact means, any means such as dipping, coating, spraying and the like can be applied.
[0049]
The polyvinyl alcohol film dyed in this way 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 water-organic solvent mixed solution at a concentration of about 0.3 to 2 mol / liter, and it is practically preferable that a small amount of potassium iodide coexists in the solution. As a treatment method using the boron compound, a dipping method is preferable, but a coating method and a spraying method can also be performed. Moreover, as 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 also be used by laminating and bonding an optically isotropic polymer film or sheet as a protective film on one or both sides thereof. Examples of the protective film include films or sheets of cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, polystyrene, polyethersulfone, polyarylene ester, poly-4-methylpentene, polyphenylene oxide, and the like.
[0051]
Also, the polarizing film can be laminated by applying a curable resin such as urethane resin, acrylic resin, urea resin, etc. on one side or both sides of the polarizing film instead of the protective film. .
[0052]
Furthermore, the polarizing film (or a protective film or a curable resin laminated on at least one surface thereof) is practically used by forming a transparent pressure-sensitive adhesive layer on one surface of the polarizing film as required. In some cases, it is served. Examples of the pressure-sensitive adhesive layer include acrylic acid esters such as butyl acrylate, ethyl acrylate, methyl acrylate, 2-ethylhexyl acrylate, acrylic acid, maleic acid, itaconic acid, methacrylic acid, and crotonic acid. Copolymers with α-monoolefin carboxylic acids (including those added with vinyl monomers such as acrylonitrile, vinyl acetate, and styrene) may interfere with the polarization characteristics of the polarizing film. However, the present invention is not limited to this, and any pressure-sensitive adhesive having transparency can be used. For example, polyvinyl ether, rubber, and the like can also be used.
[0053]
The polarizing film thus obtained includes, for example, an electronic desk calculator, an electronic clock, a word processor, a personal computer, a portable information terminal, a liquid crystal display device such as an instrument for automobiles and machinery, sunglasses, anti-glare glasses, a three-dimensional Used for spectacles, a reflection reducing layer 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]
[Example 1]
200 kg of 18 ° C. water was placed in a 500 liter tank, and while stirring, 40 kg of polyvinyl alcohol resin having a polymerization degree of 1700 and a saponification degree of 99.7 mol% was added and stirring was continued for 15 minutes. Then, after draining water once, 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 polyvinyl alcohol resin wet cake was put into a dissolving can, 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, and water vapor was blown from the bottom of the can. When the temperature reaches 50 ° C, stirring (rotation speed: 5 rpm) is performed. When the internal resin temperature reaches 100 ° C, the system is pressurized and heated to 150 ° C.AndAfter stirring for 30 minutes (rotation speed: 20 rpm) and uniformly dissolving, a 45% concentration polyvinyl alcohol resin aqueous solution (including a plasticizer and a release agent as a solid content) was prepared by adjusting the concentration.
[0057]
Next, the polyvinyl alcohol-based resin aqueous solution (liquid temperature 147 ° C.) was supplied from the gear pump (P1) to the twin screw extruder, defoamed, and then discharged from the gear pump (P2). 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: 300rpm
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)
Number of revolutions: 12.3 rpm
No bubbles were observed in the aqueous polyvinyl alcohol resin solution discharged from the gear pump (P2).
[0061]
And the polyvinyl alcohol-type resin aqueous solution discharged | emitted from the said gear pump (P2) from the T-shaped slit die (a: 450mm, b: 1mm, c: 30mm, d: 0.5mm) which has the 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 polyvinyl alcohol resin aqueous solution from the T-type 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 line. The T-shaped slit die 2 was installed so as to have an inclination of 25 ° in the direction. The conditions in the casting film production are shown below.
[0062]
[Drum type roll: Nickel-plated, further chromium-plated on a stainless steel base material, and pH 3 acetic acid aqueous solution (0.5% concentration) was applied to the mirror-finished roll surface, so that the wetting tension of the roll surface was 35 mN / m. thing〕
Diameter: 2800mm
Width: 1000mm
Rotational speed: 6m / min
Surface temperature: 90 ° C
Resin temperature at T-type slit die outlet: 95 ° C
[0063]
Then, drying [conditions: drum (diameter: 2.8 m, internal temperature: 90 ° C.), drying roll (diameter: 0.3 m, internal temperature: 70 ° C., number: 10)], heat treatment [condition: floating dryer (140 ° C., long) 6 m)], and by adjusting the humidity, a polyvinyl alcohol film (width 400 mm × thickness 75 μm) was produced.
[0064]
[Example 2]
The casting angle θ of the polyvinyl alcohol-based resin aqueous solution from the T-shaped slit die 2 to the surface of the drum-type roll 1 shown in FIG. 1 is inclined by 35 ° in the direction opposite to the rotation direction of the drum-type roll 1 with respect to the vertical line. A T-shaped slit die 2 was installed so that Otherwise in the same manner as in Example 1, a polyvinyl alcohol film (width 400 mm × thickness 75 μm) was produced. However, a polyvinyl alcohol resin having a polymerization degree of 4000 and a saponification degree of 99.7 mol% was used, and the aqueous solution concentration of this resin was 25%.
[0065]
[Example 3]
As shown in FIG. 1, the casting angle θ of the polyvinyl alcohol-based resin aqueous solution from the T-type slit die 2 to the surface of the drum-type roll 1 is inclined 30 ° in the direction opposite to the rotation direction of the drum-type roll 1 with respect to the vertical line. A T-shaped slit die 2 was installed so that Otherwise in the same manner as in Example 1, a polyvinyl alcohol film (width 400 mm × thickness 75 μm) was produced. However, the roll is not treated with an acid aqueous solution, and 0.2% sodium lauryl sulfate ester is contained in the polyvinyl alcohol resin aqueous solution, and the wetting tension on the roll surface is 36 mN / m at the time after the start of operation. Processed to be.
[0066]
[Comparative Example 1]
The T-type slit die 2 was installed so that the casting of the polyvinyl alcohol-based resin aqueous solution from the T-type slit die 2 to the surface of the drum-type roll 1 was vertical (in FIG. 1, the casting angle θ of the polyvinyl alcohol-based resin aqueous solution is 0 ° C). Otherwise in the same manner as in Example 1, a polyvinyl alcohol film (width 400 mm × thickness 75 μm) was produced.
[0067]
[Comparative Example 2]
The casting angle θ of the polyvinyl alcohol-based resin aqueous solution from the T-type slit die 2 to the surface of the drum-type roll 1 shown in FIG. 1 is inclined 20 ° in the direction opposite to the rotation direction of the drum-type roll 1 with respect to the perpendicular. A T-shaped slit die 2 was installed so that Otherwise in the same manner as in Example 1, a polyvinyl alcohol film (width 400 mm × thickness 75 μm) was produced.
[0068]
[Comparative Example 3]
The casting angle θ of the polyvinyl alcohol-based resin aqueous solution from the T-type slit die 2 to the surface of the drum-type roll 1 shown in FIG. 1 is inclined by 45 ° in the direction opposite to the rotation direction of the drum-type roll 1 with respect to the vertical line. A T-shaped slit die 2 was installed so that Otherwise in the same manner as in Example 1, a polyvinyl alcohol film (width 400 mm × thickness 75 μm) was produced.
[0069]
[Comparative Examples 4 and 5]
A polyvinyl alcohol film (width 400 mm × thickness 75 μm) was produced in the same manner as in Example 1 except that the wetting tension on the roll surface was changed to 23 mN / m (Comparative Example 4) and 57 mN / m (Comparative Example 5).
[0070]
The following evaluation was performed about the polyvinyl alcohol-type film of the Example and comparative example which were obtained in this way.
[0071]
[Measurement of thickness variation: based on JIS K 6900]
Using a film thickness tester (“K306C” manufactured by Anritsu Co., Ltd.), measure the thickness by sampling three points of film in the width direction (TD direction) at 1 m intervals in the film flow direction (MD direction), and measure per unit mm in the width direction. The maximum value of the thickness fluctuation was determined.
[0072]
Furthermore, the polyvinyl alcohol film was sandwiched between two polarizing plates in a crossed Nicol state at an angle of 45 °, and then observed in a transmission mode using a light box having a surface illuminance of 5000 lux.
[0073]
  In addition, the production of the film was continuously performed for 17 days (Examples 1 and 2, Comparative Examples 1 to 3) or 30 days (Example 3, Comparative Example).4)After continuing, the film thickness and appearance were measured and observed in the same manner.
[0074]
[Measurement of polarization unevenness]
The obtained polyvinyl alcohol film was unwound at 1.25 m / min, swelled in a washing bath (25 ° C.), and then 1.4 times in an iodine bath (22 ° C., iodine concentration 0.05 g / liter). Perform uniaxial stretching 1.6 times in an acid bath (50 ° C, iodine concentration 0.0012 g / liter, boric acid concentration 47 g / liter), and further uniaxial stretching 5 times in total at a winding speed of 6.25 m / min. A polarizing film was obtained.
[0075]
The obtained polarizing film was sandwiched between two polarizing plates in a crossed Nicol state at an angle of 45 °, and then observed in a transmission mode using a light box having a surface illuminance of 5000 lux. The target color unevenness was visually evaluated.
[0076]
These results are also shown in Table 1 below.
[0077]
[Table 1]

[0078]
From the results shown in Table 1, the polyvinyl alcohol film of the example product had little thickness unevenness and no optical color unevenness was confirmed. Furthermore, there was no die line or horizontal stripe, and it was excellent in long run performance. And the optical film nonuniformity was not confirmed at all also for the polarizing film obtained using these Example goods.
[0079]
On the other hand, some of the comparative examples had large thickness unevenness, and polyvinyl alcohol films with optical color unevenness were obtained. In addition, there were many die lines and horizontal stripes, and some were inferior in long run performance. Furthermore, optical color unevenness was also confirmed in the polarizing films obtained using these comparative examples.
[0080]
【The invention's effect】
  As described above, when the polyvinyl alcohol-based resin aqueous solution is cast from the T-type slit die to the drum-type roll, the present invention allows the polyvinyl alcohol-based resin aqueous solution to flow from the T-type slit die to the drum-type roll surface. A method for producing a polyvinyl alcohol film in which the elongation angle is set to an inclination 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. For this reason, the polyvinyl alcohol-based resin aqueous solution is gently cast on the surface of the roll, and a film having a good appearance can be formed with a long run property. Therefore, the polyvinyl alcohol film thus obtainedIs useful as a material for forming polarizing films.The polarizing film produced using the film has excellent polarization characteristics.
[0081]
In the T-shaped slit die, if the slit interval is set to be smaller than the central portion in the length direction of the T-shaped slit die within 15% of the both ends, the film is formed and dried. An effect excellent in film peelability is exhibited without increasing the film thickness of the ear end portion of the obtained 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 film of the present invention.
FIG. 2 is an explanatory view showing an example of a slit shape of a T-type slit die in the method for producing a polyvinyl alcohol film of the present invention.
FIG. 3 is an explanatory view schematically showing a positional relationship between a T-type slit die and a drum-type roll in a conventional method for producing a polyvinyl alcohol film.
[Explanation of symbols]
1 Drum type roll
2 T-shaped slit die

Claims (2)

  A method for producing a polyvinyl alcohol film in which an aqueous polyvinyl alcohol resin solution is cast from a T-shaped slit die onto a drum-type roll to form a polyvinyl alcohol-based film, wherein the T-type slit die is applied to the surface of the drum-type roll. The casting angle of the polyvinyl alcohol resin aqueous solution is 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 25 to 50 mN / m. A method for producing a polyvinyl alcohol film characterized by adjusting.   2. The die according to claim 1, wherein a portion within 15% of both ends of the T-type slit die with respect to the longitudinal direction of the T-type slit die is set with a slit interval smaller than that of the central portion. A method for producing a polyvinyl alcohol film.

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