JP4906310B2 - Method for producing polyvinyl alcohol film - Google Patents

Description

The present invention relates to a method for producing a polyvinyl alcohol film. More specifically, the present invention is a polyvinyl alcohol film excellent in flatness, having a good appearance of a polyvinyl alcohol film roll, and excellent in long winding of the film, and further producing a polarizing film free from optical unevenness. It is related with the method of manufacturing the polyvinyl alcohol-type film for doing .

  Conventionally, a polyvinyl alcohol film is prepared by dissolving a polyvinyl alcohol resin in a solvent such as water to prepare a stock solution, forming a film by a solution casting method (casting method), and drying using a metal heating roll or the like. It is manufactured by doing. The polyvinyl alcohol film thus obtained is used in many applications as a film excellent in transparency and dyeability, and one of its useful applications is a polarizing film. Such a polarizing film is used as a basic component of a liquid crystal display, and in recent years, its use has been expanded to a device requiring high quality and high reliability.

  Under such circumstances, with an increase in the size of a screen of a liquid crystal television or the like, there is a need for a polarizing film that is much wider and flatter than conventional products and a polyvinyl alcohol film that is a raw material. If the polarizing film is not flat because of uneven thickness or waviness, the in-plane uniformity of the polarization performance is insufficient, or stress is generated in the assembled liquid crystal cell, resulting in deformation of the liquid crystal cell itself or durability. Causes a drop. As a countermeasure against such a problem, for example, it has been proposed to use a polyvinyl alcohol film having a thickness variation in the TD direction (lateral direction) of 0.5 μm / mm or less for manufacturing a polarizing film (for example, Patent Literature 1).

  However, even if only the thickness fluctuation of the polyvinyl alcohol film is reduced, the appearance of the polyvinyl alcohol film roll is not necessarily good, and the film is unwound from the film roll having a poor appearance, and the polarizing film In the case of manufacturing the film, due to the undulation of the film, the transportability of the film is inferior when it is subjected to each step such as dyeing, stretching, and boric acid treatment.

  Moreover, when a polyvinyl alcohol-type film is not flat, it is difficult not only to wind up on a roll, but a big load is applied to the film near the surface layer of a roll, and the uniformity of a film is impaired. When the uniformity is impaired, optical color unevenness occurs in the polarizing film. When the film absorbs moisture during storage and transportation, this phenomenon is further increased, and most of the film close to the surface layer must be discarded before the polarizing film is manufactured.

JP 2002-31720 A

The invention, corresponding to the wide long reduction, and an object thereof is to provide a method for producing excellent polyvinyl alcohol fill beam flatness. In particular, when wound into a roll, it shall be the purpose of the appearance of the polyvinyl alcohol film roll to provide a method of manufacturing a favorable polyvinyl alcohol film.

The present invention relates to a method for producing a polyvinyl alcohol film having a maximum surface waviness (h) of 1 cm or less when a polyvinyl alcohol film having a size of 1 m × 1 m is placed on a flat surface plate. Is.

  When the polyvinyl alcohol-based film is wound on a roll, the maximum waviness in the width direction of the outermost roll film is preferably 5 mm or less.

  Further, in the polyvinyl alcohol film, it is preferable to use a polyvinyl alcohol resin having a weight average molecular weight of 120,000 to 300,000, the film thickness is preferably 30 to 70 μm, and the film width is 2 m or more. Is preferred.

The present invention also provides:
(A) A step of forming a polyvinyl alcohol film by a casting method,
(B) heating the film-formed polyvinyl alcohol film to adjust the water content to 1 to 5% by weight;
(C) After slitting the heated polyvinyl alcohol film, winding the film in a roll with the moisture content of the film adjusted to 1 to 5% by weight, and (D) packing the wound polyvinyl alcohol film The manufacturing method of the said polyvinyl-alcohol-type film which consists of a process to do.

  The step (D) is preferably carried out in a state where the moisture content in the film is maintained at 1 to 5% by weight in an environment with a humidity of 30 to 70% RH.

In the step (C), after the heated polyvinyl alcohol film is wound around a roll once in the step (C), the film is unwound from the roll and slit, and further the moisture content in the film is 1 to 5 wt. It is preferable that it is the process of winding up to a roll in the state adjusted to%.
It is preferable that the heating from the end of the step (B) to the end of the packing in the step (D) is performed within 48 hours.

Since the polyvinyl alcohol film obtained by the production method of the present invention (hereinafter also referred to as the polyvinyl alcohol film of the present invention) is excellent in flatness, even a wide and long film can be easily wound on a roll. The appearance of the obtained film roll is also good. Moreover, since it is excellent in flatness, it is preferably used as a raw material particularly in the production of a wide and long polarizing film, and a polarizing film having no optical color unevenness can be obtained.

  The polyvinyl alcohol film of the present invention has a maximum surface waviness (h) of 1 cm or less when a polyvinyl alcohol film having a size of 1 m × 1 m is placed on a flat surface plate. It is.

  The polyvinyl alcohol film of the present invention is obtained by forming a polyvinyl alcohol resin into a film. As the polyvinyl alcohol resin, a resin obtained by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate is usually used. However, the polyvinyl alcohol film of the present invention is not necessarily limited thereto, and a resin obtained by saponifying a copolymer of vinyl acetate and a component copolymerizable with a small amount of vinyl acetate is used. You can also. Examples of the component copolymerizable with vinyl acetate include unsaturated carboxylic acids and salts, esters, amides or nitriles thereof; olefins having 2 to 30 carbon atoms such as ethylene, propylene, n-butene and isobutene; vinyl ether Class; unsaturated sulfonates and the like can be used.

  Although the weight average molecular weight of polyvinyl alcohol-type resin is not specifically limited, Preferably it is 120000-300000, More preferably, it is 140000-200000, More preferably, it is 160000-200000. If the weight average molecular weight is less than 120,000, sufficient optical performance cannot be obtained when a polyvinyl alcohol-based resin is used as an optical film, and if it exceeds 300,000, it becomes difficult to stretch the film as a polarizing film, making industrial production difficult. It is not preferable. In addition, the weight average molecular weight of the polyvinyl alcohol-type resin in this invention is a weight average molecular weight measured by GPC-LALLS method.

  The saponification degree of the polyvinyl alcohol-based resin is not particularly limited, but is preferably 97 to 100 mol%, more preferably 98 to 100 mol%, and further preferably 99 to 100 mol%. When the saponification degree is less than 97 mol%, sufficient optical performance cannot be obtained when a polyvinyl alcohol-based resin is used as an optical film, which is not preferable.

  The polyvinyl alcohol film of the present invention needs to have a maximum surface waviness (h) of 1 cm or less when a 1 m × 1 m film is placed on a flat surface plate, preferably 7 mm or less. When the maximum height (h) exceeds 1 cm, it becomes difficult to carry the polarizing film using the film, and there is a large undulation in the manufactured polarizing film.

  In the polyvinyl alcohol film of the present invention, when a film having a length of 3000 m or more is wound on a roll, the maximum waviness in the width direction of the roll outermost layer film is preferably 5 mm or less, more preferably 3 mm. Hereinafter, it is more preferably 2 mm or less, particularly preferably 1 mm or less. The maximum wave swell here refers to the maximum wave swell according to JIS-B-0610. The low-frequency cutoff is 0.1 mm, the high-frequency cutoff is 5 cm, the measurement length is 10 cm, and the measurement speed is 1 cm / Seconds. When the maximum waviness of filtering exceeds 5 mm, when a polarizing film is produced using a film, a part of the film wound up before production is discarded, which is not preferable.

The polyvinyl alcohol film of the present invention is continuously produced by preparing a polyvinyl alcohol resin aqueous solution using a polyvinyl alcohol resin, casting the aqueous solution on a drum-type roll or an endless belt, and forming and drying the film. is, For example the other,
(A) A step of forming a polyvinyl alcohol film by a casting method,
(B) heating the film-formed polyvinyl alcohol film to adjust the water content to 1 to 5% by weight;
(C) After slitting the heated polyvinyl alcohol film, winding the film in a roll with the moisture content of the film adjusted to 1 to 5% by weight, and (D) packing the wound polyvinyl alcohol film It can manufacture by the process to do.

  Hereinafter, the manufacturing method which consists of the said process (A), a process (B), a process (C), and a process (D) is demonstrated.

  In the step (A), first, a polyvinyl alcohol resin wet cake obtained by adjusting the moisture content of the polyvinyl alcohol resin as described above is dissolved in water to prepare a polyvinyl alcohol resin aqueous solution. The method for preparing the polyvinyl alcohol-based resin aqueous solution is not particularly limited. For example, the polyvinyl alcohol resin aqueous solution may be prepared using a multi-screw extruder. In a dissolving can equipped with a vertical circulation flow generation type stirring blade, water vapor is contained in the can. Can be blown to dissolve the hydrous polyvinyl alcohol resin wet cake to prepare an aqueous solution. In addition to polyvinyl alcohol-based resins, polyvinyl alcohol-based resin aqueous solutions include generally used plasticizers such as glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, and polyethylene glycol, as well as nonions. From the viewpoint of mechanical properties and productivity, it is preferable to contain a hydrophilic, anionic or cationic surfactant.

  The concentration of the aqueous polyvinyl alcohol resin solution thus obtained is preferably 15 to 60% by weight, more preferably 17 to 55% by weight, and still more preferably 20 to 50% by weight. If the concentration is less than 15% by weight, the drying load increases, resulting in poor production capacity. If the concentration exceeds 60% by weight, the viscosity becomes too high and uniform dissolution cannot be achieved.

  Next, the obtained polyvinyl alcohol-based resin aqueous solution is defoamed. Examples of the defoaming method include stationary defoaming and defoaming with a multi-screw extruder. 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.

  After the defoaming treatment, the polyvinyl alcohol-based resin aqueous solution is introduced into a T-type slit die by a certain amount, cast onto a drum-type roll or an endless belt, particularly preferably a drum-type roll, and formed into a film by a casting method. .

  The resin temperature at the exit of the T-shaped slit die is preferably 80 to 100 ° C, more preferably 85 to 98 ° C. If the resin temperature at the exit of the T-shaped slit die is less than 80 ° C., poor flow occurs, and if it exceeds 100 ° C., foaming is not preferable.

  The casting is performed with a drum-type roll or an endless belt, but it is preferably performed with a drum-type roll from the viewpoints of widening, lengthening, and film thickness uniformity.

  The diameter of the drum type roll is preferably 2000 to 5000 mm, more preferably 2400 to 4500 mm, and particularly preferably 2800 to 4000 mm. If the diameter of the drum-type roll is less than 2000 mm, the drying length is insufficient and the speed does not come out, and if it exceeds 5000 mm, the transportability is inferior. The width of the drum type roll is preferably 1000 to 5000 mm, more preferably 2000 to 4500 mm, and particularly preferably 3000 to 4000 mm. If the width of the drum-type roll is less than 1000 mm, the productivity is inferior. The rotation speed of the drum-type roll is preferably 5 to 30 m / min, and more preferably 6 to 20 m / min. If the rotational speed is less than 5 m / min, the productivity is inferior, and if it exceeds 30 m / min, drying is insufficient, which is not preferable. Moreover, it is preferable that the surface temperature of a drum type roll is 70-99 degreeC, and it is more preferable that it is 75-97 degreeC. If the surface temperature is less than 70 ° C, drying is poor, and if it exceeds 99 ° C, foaming is not preferable.

  The film formed in the step (A) is adjusted by heating so that the moisture content becomes 1 to 5% by weight (step (B)). Here, the heating includes heat treatment for the purpose of crystallization in addition to simple water removal (drying) of the film. The moisture content of the film is preferably 1 to 5% by weight, particularly preferably 1.5 to 4% by weight, and more preferably 2.0 to 3.0% by weight. If the moisture content of the film is less than 1% by weight, undulation tends to occur, and if it exceeds 5% by weight, drying is insufficient, which is not preferable.

  A drying method is not specifically limited, For example, it can carry out by letting the surface and back surface of a film pass alternately to several drying rolls.

  The diameter of the drying roll is preferably 100 to 1000 mm, more preferably 150 to 900 mm, and particularly preferably 200 to 800 mm. If the diameter of the drying roll is less than 100 mm, an enormous number is required, and if it exceeds 1000 mm, film conveyance becomes unstable, which is not preferable. The preferable number of drying rolls is usually 2 to 30.

  The surface temperature of the drying roll is not particularly limited, but is preferably 50 to 150 ° C, more preferably 60 to 120 ° C. If the surface temperature is less than 50 ° C., the drying is poor. If the surface temperature exceeds 150 ° C., the drying is excessive.

  The polyvinyl alcohol film whose water content is adjusted in the step (B) is slit and wound on a roll in a state where the water content in the film is adjusted to 1 to 5% by weight ((step (C)).

  The water content in the film when wound on a roll is preferably 1 to 5% by weight, more preferably 1.5 to 4% by weight, and particularly preferably 2.0 to 3.0% by weight. When the water content is less than 1% by weight, the film after winding tends to absorb water, and in particular, the roll surface layer tends to swell. When the water content exceeds 5% by weight, the film tends to dehydrate and swell. is there.

  In order to adjust the moisture content in the film to the above range, it is preferable that after the step (B), the film is transferred to an environment having a humidity of 30 to 70% RH, and slitting and winding are performed there. If the environmental humidity is too low or too high, the moisture content of the film will fluctuate greatly, which causes a new undulation in the film, which is not preferable.

  The width of the polyvinyl alcohol-based film varies depending on the application and the shipping destination. It is not realistic to change the casting process, the film forming process, and the drying process as described above for each film having a different width. Therefore, the polyvinyl alcohol film whose water content has been adjusted in the step (B) is once wound on a roll (referred to as temporary winding), stored, and then unwound from the roll again to obtain a desired width. It is preferable to be slit. The slit film is continuously wound on a roll (referred to as main winding).

  At this time, if the time from heat treatment (drying or heat treatment) to temporary winding is too short, the film is not sufficiently cooled, and stress based on thermal shrinkage occurs after temporary winding. The stress generated after the temporary winding causes the film to swell, and this swell remains even after the main winding. Therefore, the surface temperature of the outermost roll film after provisional winding is preferably 10 to 40 ° C, and more preferably 20 to 30 ° C. Although it is possible to actively cool the film with a cooling roll or the like after heating, rapid cooling is not preferable because it causes new stress, that is, swell.

  The film wound on the roll is preferably 2 m or more in width, more preferably 2.5 to 4 m. If the width is less than 2 m, the productivity during the production of the polarizing film is inferior, which is not preferable. Further, the length of the wound film is 2000 m or more, particularly 3000 m or more, and more preferably 3000 to 8000 m. If the length is less than 2000 m, the productivity at the time of producing the polarizing film is inferior, which is not preferable.

  The polyvinyl alcohol film wound on the roll in the step (C) is then quickly packed (step (D)).

  Packing is preferably performed in a state where the moisture content in the film is maintained at 1 to 5% by weight in an environment with a humidity of 30 to 70% RH. If the environmental humidity is too low or too high, the moisture content of the film will fluctuate greatly, which causes a new undulation in the film, which is not preferable.

  It is preferable to use a gas barrier film for packaging. The type of the gas barrier film is not particularly limited as long as it reduces the water vapor permeability. However, a gas barrier film coated with a hygroscopic agent may be used as necessary. For example, as a gas barrier film coated with a hygroscopic agent on the inner surface, a film obtained by depositing silicon oxide or alumina on a polyester film, a film obtained by further laminating polyethylene, polyester, aluminum foil, and a laminated film of polyethylene, etc. A composite film coated with silica gel, zeolite, magnesium oxide, calcium oxide, clay compound, porous polymer, or the like can be used.

  Further, when packing, a bag containing a hygroscopic agent may be placed inside the package in order to keep the humidity inside the package at an appropriate humidity. As the hygroscopic agent, silica gel, zeolite, magnesium oxide, calcium oxide, clay compound, porous polymer, and the like can be used. Although the moisture content of the film after heating in the step (B) is 1 to 5% by weight, the moisture content may increase by several percent before packaging, and if the moisture content increases, after packaging By removing this several percent of moisture with a hygroscopic agent, it is possible to prevent the film from absorbing moisture and increasing swell during storage and transportation.

  The time from heating in the step (B) to packing in the step (D) is within 48 hours, preferably 3 to 48 hours, more preferably 4 to 36 hours, and further preferably 5 to 24 hours. Here, the time from heating to packing is the time from the completion of the heat treatment for the desired film length until the film wound up on the roll (mainly wound) is packed. Say.

  When the time from heating to packing exceeds 48 hours, that is, as the time from temporary winding to a roll, storage, slit, main winding, and packing becomes longer, the undulation of the film increases. Causes of increased waviness include those based on stress relaxation in the film and in-plane moisture absorption unevenness. Although moderate stress relaxation and appropriate moisture absorption are necessary for film production, disturbance factors peculiar to each process produce new stresses and useless moisture absorption as the time increases. The disturbance factors peculiar to each process are, for example, the tension at the time of temporary winding and the temperature and humidity at the time of storage of the temporary winding roll. On the other hand, if the time from heating to temporary winding is too short, the film is not sufficiently cooled, and stress based on thermal shrinkage occurs after the main winding. Although it is possible to positively cool the film with a cooling roll or the like after drying, rapid cooling causes new stress, that is, swell. Considering this cooling time, the time from heating to packing is preferably 3 hours or more.

  Since the polyvinyl alcohol film of the present invention is excellent in flatness and excellent in the appearance of a film roll, it is preferably used as a raw material particularly in the production of a polarizing film.

  The thickness of the polyvinyl alcohol film used for the production of the polarizing film is preferably 30 to 100 μm, more preferably 30 to 70 μm, and particularly preferably 40 to 60 μm from the viewpoint of improving the polarizing performance. If the film thickness is less than 30 μm, stretching is difficult, and if it exceeds 100 μm, the film thickness accuracy is lowered, which is not preferable.

  The polarizing film of the present invention is produced through processes such as normal dyeing, stretching, boric acid crosslinking and heat treatment. As a method for producing a polarizing film, a polyvinyl alcohol film is stretched and dyed by dipping in an iodine or dichroic dye solution, and then treated with a boron compound. After stretching and dyeing at the same time, a boron compound treatment is performed. There are a method, a method of dyeing with iodine or a dichroic dye and stretching, and then a method of treating with a boron compound, a method of dyeing and then stretching in a solution of a boron compound, etc., which can be appropriately selected and used. As described above, the polyvinyl alcohol film (unstretched film) may be stretched and dyed and further subjected to boron compound treatment separately or simultaneously, but during at least one of the dyeing step and the boron compound treatment step. It is desirable from the viewpoint of productivity to carry out uniaxial stretching.

  The stretching is desirably performed in a uniaxial direction by 3 to 10 times, preferably 3.5 to 6 times. At this time, a slight stretching (stretching to prevent shrinkage in the width direction or more) may be performed in a direction perpendicular to the stretching direction. The stretching temperature is preferably selected from 40 to 170 ° C. Furthermore, the draw ratio may be finally set within the above range, and the drawing operation may be performed not only in one stage but also in any stage of the manufacturing process.

  The 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 2 g / L, the potassium iodide concentration is 10 to 50 g / L, and the potassium iodide / iodine weight ratio is 20 to 100. Is appropriate. The dyeing time is practically about 30 to 500 seconds. The temperature of the treatment bath is preferably 5 to 50 ° C. The aqueous solution may contain a small amount of an organic solvent compatible with water in addition to the aqueous solvent. As the contact means, any means such as dipping, coating, spraying and the like can be applied.

  The dyed film is then treated with a boron compound. As the boron compound, boric acid and borax are practical. The boron compound is used in the form of an aqueous solution or a water-organic solvent mixture at a concentration of about 0.3 to 2 mol / L, and it is practically desirable that a small amount of potassium iodide coexists in the solution. The treatment method is preferably an immersion method, but of course, an application method and a spray method can also be carried out. The temperature during the treatment is preferably about 50 to 70 ° C., and the treatment time is preferably about 3 to 20 minutes. If necessary, the stretching operation may be performed during the treatment.

  The polarization degree of the polarizing film of the present invention thus obtained is preferably 99% or more, more preferably 99.5% or more. If the degree of polarization is less than 99%, the contrast in the liquid crystal display tends not to be ensured.

The degree of polarization is the light transmittance (H ₁₁ ) measured at the wavelength λ with the two polarizing films overlapped so that the orientation directions thereof are the same direction, and the two polarizing films, It is calculated according to the following equation from the light transmittance (H ₁ ) measured at the wavelength λ in a state where the alignment directions are perpendicular to each other.
[(H ₁₁ −H ₁ ) / (H ₁₁ + H ₁ )] ^1/2

  Further, the single transmittance of the polarizing film of the present invention is preferably 43% or more. If it is less than 43%, it tends to be impossible to achieve high brightness of the liquid crystal display.

  The single transmittance is a value obtained by measuring the light transmittance of a single polarizing film using a spectrophotometer.

  The polarizing film thus obtained can be used as a polarizing plate 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, polyethersulfone, polyarylene ester, poly-4-methylpentene, polyphenylene oxide, and the like.

  In addition, for the purpose of reducing the thickness of the polarizing film, instead of the protective film, a curable resin such as a urethane resin, an acrylic resin, or a urea resin may be applied and laminated on the surface or both surfaces thereof.

  A polarizing film (including at least one surface laminated with a protective film or a curable resin) has a transparent pressure-sensitive adhesive layer formed on a surface of the polarizing film as required by a generally known method. In some cases, it may be put to practical use. Examples of the pressure-sensitive adhesive layer include acrylic acid esters such as butyl acrylate, ethyl acrylate, methyl acrylate, 2-ethylhexyl acrylate, and α-monoolefin carboxylic acids such as acrylic acid, maleic acid, itaconic acid, Copolymers with methacrylic acid, crotonic acid, etc. (including those added with vinyl monomers such as acrylonitrile, vinyl acetate, and styrene) inhibit the polarizing properties 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 or rubber may be used.

  Since the polarizing film of the present invention is manufactured using the polyvinyl alcohol-based film of the present invention having excellent flatness and excellent film roll appearance, it has no optical unevenness and excellent in-plane uniformity of polarization performance, Electronic desk calculators, electronic clocks, word processors, personal computers, personal digital assistants, liquid crystal display devices such as automobile and machinery instruments, sunglasses, eye protection glasses, stereoscopic glasses, reflection reduction layers for display elements (CRT, LCD, etc.) It is preferably used for medical equipment, building materials, toys and the like.

Weight average molecular weight: Measured by GPC-LALLS method under the following conditions.

1) GPC
Apparatus: Waters type 244 gel permeation chromatograph column: Tosoh Corporation TSK-gel-GMPW _XL (inner diameter 8 mm, length 30 cm, 2 pieces)
Solvent: 0.1 M Tris buffer (pH 7.9)
Flow rate: 0.5 ml / min
Temperature: 23 ° C
Sample concentration: 0.040%
Filtration: 0.45 μm Mysori Disc W-25-5 manufactured by Tosoh Corporation
Injection volume: 0.2ml
Detection sensitivity (differential refractive index detector): 4 times

2) LALLS
Apparatus: Chromatrix KMX-6 type low angle laser light scattering photometer Temperature: 23 ° C
Wavelength: 633nm
Second virial coefficient × concentration: 0 mol / g
Refractive index density change (dn / dc): 0.159 ml / g
Filter: MILLIPORE 0.45 μm filter HAWP01300
Gain: 800mV

Example 1
(Manufacture of polyvinyl alcohol film)
200 kg of 18 ° C. water was placed in a 500 l tank, and while stirring, 40 kg of polyvinyl alcohol resin having a weight average molecular weight of 125,000 and a saponification degree of 99.8 mol% was added, and stirring was continued for 15 minutes. Thereafter, after draining water, 200 kg of water was further added and stirred for 15 minutes. The obtained slurry was dehydrated to obtain a polyvinyl alcohol-based resin wet cake having a water content of 43% by weight.

  70 kg of the obtained polyvinyl alcohol resin wet cake was put into a dissolution can, 4.2 kg of glycerin as a plasticizer, 42 g of polyoxyethylene dodecylamine and 10 kg of water as a release agent were added, and water vapor was blown from the bottom of the can. Stirring (rotation speed: 5 rpm) was performed when the internal resin temperature reached 50 ° C, and the system was pressurized when the internal resin temperature reached 100 ° C. After raising the temperature to 150 ° C., the blowing of water vapor was stopped (the total amount of water vapor was 75 kg), and stirring was performed for 30 minutes (rotation speed: 20 rpm). After uniformly dissolving, a polyvinyl alcohol resin aqueous solution having a concentration of 29% by weight was obtained by adjusting the concentration.

  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). The discharged polyvinyl alcohol resin aqueous solution was cast from a T-type slit die (straight manifold die) onto a drum-type roll to form a film. The conditions for such casting film formation were as follows.

Drum type roll Diameter: 3200mm
Width: 4000mm
Rotational speed: 8m / min Surface temperature: 90 ° C
Resin temperature at T-type slit die outlet: 95 ° C

  After film formation, the film was dried while alternately passing through a drying roll on the front and back surfaces of the film under the following conditions.

Drying roll diameter: 320mm
Width: 4000mm
Number: 10 Rotating speed: 8m / min Surface temperature: 80 ° C

  After the dried film (moisture content: 3% by weight) is transferred to a humidity control room having a humidity of 50% RH, it is continuously wound around a roll (core tube) having an outer diameter of 165 mm and a width of 4000 mm. The film was cut when the length of the film reached 4100 m. The thickness was 60 μm. The surface temperature of the roll outermost layer film immediately after cutting was 40 ° C., and after storage for 2 hours, it was 25 ° C. Subsequently, the film was unwound from the film roll, slit to have a width of 3000 mm, and continuously wound up to a roll (core tube) having a width of 4000 mm at a length of 4000 m (water content of the wound film: 3% by weight). The time from drying to the end of the main winding was 4 hours.

  The surface of the obtained film roll with respect to the width direction of the outermost layer film with respect to the center of 10 cm and the portion with a length of 10 cm based on the position 1 m away from the center (two places on the left and right) Swelling was measured using a laser displacement meter (manufactured by Keyence Corporation, laser focus displacement meter LT). The average value of the maximum wave swells at three locations was 3 mm.

  Subsequently, the entire roll obtained was packed with a gas barrier film (Tech Barrier, manufactured by Mitsubishi Resin Co., Ltd.) (water content of the film: 3% by weight). The time from drying to the end of packing was 6 hours. At this time, the appearance of the film roll was extremely good.

  Moreover, after packing, it was once opened and a film of 1 m × 1 m was collected from the film roll surface layer part, the film roll center part, and the film roll innermost part (collection was based on the center with respect to the width direction of the film). ). The film was allowed to stand on a flat surface plate for 1 hour in a constant temperature and humidity chamber at 23 ° C. and 50% RH, and then the surface waviness of each film was measured at intervals of 1 cm using the laser displacement meter. The maximum height (h) of surface waviness with respect to the surface plate surface was 6 mm for the surface layer, 4 mm for the center, and 3 mm for the inside.

(Manufacture of polarizing film)
The obtained polyvinyl alcohol film was immersed in an aqueous solution consisting of 0.2 g / L of iodine and 15 g / L of potassium iodide for 240 seconds at 30 ° C., and then 60 g / L of boric acid and 30 g / L of potassium iodide. While being immersed in an aqueous solution (55 ° C.) of the composition, boric acid treatment was performed for 5 minutes while simultaneously uniaxially stretching four times. Then, it dried and obtained the polarizing film. The degree of polarization of the obtained polarizing film was measured using a high-speed multi-wavelength birefringence measuring apparatus (manufactured by Otsuka Electronics Co., Ltd., RETS-2000 wavelength: 550 nm). The degree of polarization was 99.9%. The single transmittance was 43.2%.

  Further, after sandwiching the obtained polarizing film between two polarizing plates in a crossed Nicols state (single transmittance 43.5%, polarization degree 99.9%) at an angle of 45 °, the surface illuminance of 14000 lux is obtained. When observed in a transmission mode using a light box, no optical color unevenness was observed.

Example 2
(Manufacture of polyvinyl alcohol film)
A film roll was obtained in the same manner as in Example 1 except that the time from drying to packing was 30 hours (storage from temporary winding to slit was 20 hours, and time from main winding to packing was 10 hours). It was. The moisture content of the film was 3% by weight after drying, 4% by weight at the time of actual winding, and 4.5% by weight at the time of packaging. The maximum wave swell of the outermost layer film of the obtained film roll was measured in the same manner as in Example 1. The average value of the maximum wave swells at the three locations was 2 mm.

  Moreover, after packaging, the film was once opened, and 1 m × 1 m films were collected from the film roll surface layer part, the film roll center part, and the film roll innermost part, and the surface waviness was measured in the same manner as in Example 1. The maximum height (h) of the surface waviness was 7 mm for the surface layer portion, 5 mm for the central portion, and 3 mm for the inside.

(Manufacture of polarizing film)
The obtained polyvinyl alcohol film was immersed in an aqueous solution consisting of 0.2 g / L of iodine and 15 g / L of potassium iodide for 240 seconds at 30 ° C., and then 60 g / L of boric acid and 30 g / L of potassium iodide. While being immersed in an aqueous solution (55 ° C.) of the composition, boric acid treatment was performed for 5 minutes while simultaneously uniaxially stretching four times. Then, it dried and obtained the polarizing film. When the degree of polarization and single transmittance of the obtained polarizing film were measured, the degree of polarization was 99.7% and the single transmittance was 43.1%.

  Further, after sandwiching the obtained polarizing film between two polarizing plates in a crossed Nicols state (single transmittance 43.5%, polarization degree 99.9%) at an angle of 45 °, the surface illuminance of 14000 lux is obtained. When observed in a transmission mode using a light box, no optical color unevenness was observed.

Example 3
(Manufacture of polyvinyl alcohol film)
200 kg of 18 ° C. water was placed in a 500 l tank, and while stirring, 40 kg of a polyvinyl alcohol resin having a weight average molecular weight of 141,000 and a saponification degree of 99.8 mol% was added, and stirring was continued for 15 minutes. Thereafter, after draining water, 200 kg of water was further added and stirred for 15 minutes. The obtained slurry was dehydrated to obtain a polyvinyl alcohol-based resin wet cake having a water content of 43% by weight.

  70 kg of the obtained polyvinyl alcohol resin wet cake was put into a dissolution can, 4.2 kg of glycerin as a plasticizer, 42 g of polyoxyethylene dodecylamine and 10 kg of water as a release agent were added, and water vapor was blown from the bottom of the can. Stirring (rotation speed: 5 rpm) was performed when the internal resin temperature reached 50 ° C, and the system was pressurized when the internal resin temperature reached 100 ° C. After raising the temperature to 150 ° C., the blowing of water vapor was stopped (the total amount of water vapor was 75 kg), and stirring was performed for 30 minutes (rotation speed: 20 rpm). After uniformly dissolving, a polyvinyl alcohol resin aqueous solution having a concentration of 27% by weight was obtained by adjusting the concentration.

  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). The discharged polyvinyl alcohol resin aqueous solution was cast from a T-type slit die (straight manifold die) onto a drum-type roll to form a film. The conditions for such casting film formation were as follows.

Drum type roll Diameter: 3200mm
Width: 4000mm
Rotational speed: 8m / min Surface temperature: 90 ° C
Resin temperature at T-type slit die outlet: 95 ° C

  After film formation, the film was dried while alternately passing through a drying roll on the front and back surfaces of the film under the following conditions.

Drying roll diameter: 320mm
Width: 4000mm
Number: 10 Rotating speed: 8m / min Surface temperature: 80 ° C

  After the dried film (moisture content: 3% by weight) is transferred to a humidity control room having a humidity of 50% RH, it is continuously wound around a roll (core tube) having an outer diameter of 165 mm and a width of 4000 mm. The film was cut when the length of the film reached 4100 m. The thickness was 50 μm. The surface temperature of the roll outermost layer film immediately after cutting was 40 ° C., and after storage for 2 hours, it was 25 ° C. Subsequently, the film was unwound from the film roll, slit to have a width of 3000 mm, and then continuously wound onto a roll (core tube) having a width of 4000 mm (water content of the wound film: 3% by weight). The time from drying to the end of the main winding was 4 hours.

  The maximum wave swell of the outermost layer film of the obtained film roll was measured in the same manner as in Example 1. The average value of the maximum wave swells at the three locations was 1 mm.

  Subsequently, the entire roll obtained was packed with a gas barrier film (Tech Barrier, manufactured by Mitsubishi Resin Co., Ltd.) (water content of the film: 3% by weight). The time from drying to the end of packing was 6 hours. At this time, the appearance of the film roll was extremely good.

  Further, after packing, the film was once opened, and 1 m × 1 m films were collected from the film roll surface layer part, the film roll center part, and the innermost part of the film roll (collection was based on the center with respect to the film width direction). ) When surface waviness was measured in the same manner as in Example 1, the maximum height (h) of the surface waviness was 5 mm for the surface layer, 4 mm for the central portion, and 3 mm for the inner portion.

(Manufacture of polarizing film)
The obtained polyvinyl alcohol film was immersed in an aqueous solution consisting of 0.2 g / L of iodine and 15 g / L of potassium iodide for 240 seconds at 30 ° C., and then 60 g / L of boric acid and 30 g / L of potassium iodide. While being immersed in an aqueous solution (55 ° C.) of the composition, boric acid treatment was performed for 5 minutes while simultaneously uniaxially stretching four times. Then, it dried and obtained the polarizing film. When the degree of polarization and single transmittance of the obtained polarizing film were measured, the degree of polarization was 99.9% and the single transmittance was 43.3%.

  Further, after sandwiching the obtained polarizing film between two polarizing plates in a crossed Nicols state (single transmittance 43.5%, polarization degree 99.9%) at an angle of 45 °, the surface illuminance of 14000 lux is obtained. When observed in a transmission mode using a light box, no optical color unevenness was observed.

Example 4
A film roll was obtained in the same manner as in Example 3 except that a polyvinyl alcohol resin having a weight average molecular weight of 165000 was used to form an aqueous solution having a concentration of 25% by weight. The maximum wave swell of the outermost layer film of the obtained film roll was measured in the same manner as in Example 1. The average value of the maximum wave swells at three locations was 0.5 mm.

  Moreover, after packaging, the film was once opened, and 1 m × 1 m films were collected from the film roll surface layer part, the film roll center part, and the film roll innermost part, and the surface waviness was measured in the same manner as in Example 1. The maximum height (h) of the surface waviness was 4 mm for the surface layer part, 3 mm for the central part, and 2 mm for the inside.

(Manufacture of polarizing film)
The obtained polyvinyl alcohol film was immersed in an aqueous solution consisting of 0.2 g / L of iodine and 15 g / L of potassium iodide for 240 seconds at 30 ° C., and then 60 g / L of boric acid and 30 g / L of potassium iodide. While being immersed in an aqueous solution (55 ° C.) of the composition, boric acid treatment was performed for 5 minutes while simultaneously uniaxially stretching four times. Then, it dried and obtained the polarizing film. When the polarization degree and the single transmittance of the obtained polarizing film were measured, the polarization degree was 99.9% and the single transmittance was 43.5%.

  Further, after sandwiching the obtained polarizing film between two polarizing plates in a crossed Nicols state (single transmittance 43.5%, polarization degree 99.9%) at an angle of 45 °, the surface illuminance of 14000 lux is obtained. When observed in a transmission mode using a light box, no optical color unevenness was observed.

Comparative Example 1
(Manufacture of polyvinyl alcohol film)
A film roll was obtained in the same manner as in Example 1 except that the time from drying to packing was 72 hours (storage from temporary winding to slit was 48 hours, and time from main winding to packing was 24 hours). It was. The moisture content of the film was 3% by weight after drying, 6% by weight during main winding, and 7% by weight during packaging. The maximum wave waviness of the outermost layer film of the obtained roll was measured in the same manner as in Example 1. The average value of the maximum wave swells at the three locations was 17 mm. The outer appearance of the film roll was poor with wrinkles in the width direction.

  Moreover, after packaging, the film was once opened, and 1 m × 1 m films were collected from the film roll surface layer part, the film roll center part, and the film roll innermost part, and the surface waviness was measured in the same manner as in Example 1. The maximum height (h) of the surface waviness was 20 mm for the surface layer portion, 15 mm for the central portion, and 10 mm for the inside.

(Manufacture of polarizing film)
The obtained polyvinyl alcohol film was immersed in an aqueous solution consisting of 0.2 g / L of iodine and 15 g / L of potassium iodide for 240 seconds at 30 ° C., and then 60 g / L of boric acid and 30 g / L of potassium iodide. While being immersed in an aqueous solution (55 ° C.) of the composition, boric acid treatment was performed for 5 minutes while simultaneously uniaxially stretching four times. Then, it dried and obtained the polarizing film. When the polarization degree and single transmittance of the obtained polarizing film were measured, the degree of polarization was 98.7% and the single transmittance was 43.5%.

  Further, after sandwiching the obtained polarizing film between two polarizing plates in a crossed Nicols state (single transmittance 43.5%, polarization degree 99.9%) at an angle of 45 °, the surface illuminance of 14000 lux is obtained. When observed in a transmission mode using a light box, optical color unevenness was observed.

Comparative Example 2
(Manufacture of polyvinyl alcohol film)
200 kg of 18 ° C. water was placed in a 500 l tank, and while stirring, 40 kg of polyvinyl alcohol resin having a weight average molecular weight of 125,000 and a saponification degree of 99.8 mol% was added, and stirring was continued for 15 minutes. Thereafter, after draining water, 200 kg of water was further added and stirred for 15 minutes. The obtained slurry was dehydrated to obtain a polyvinyl alcohol-based resin wet cake having a water content of 43% by weight.

  70 kg of the obtained polyvinyl alcohol resin wet cake was put into a dissolution can, 4.2 kg of glycerin as a plasticizer, 42 g of polyoxyethylene dodecylamine and 10 kg of water as a release agent were added, and water vapor was blown from the bottom of the can. Stirring (rotation speed: 5 rpm) was performed when the internal resin temperature reached 50 ° C, and the system was pressurized when the internal resin temperature reached 100 ° C. After raising the temperature to 150 ° C., the blowing of water vapor was stopped (the total amount of water vapor was 75 kg), and stirring was performed for 30 minutes (rotation speed: 20 rpm). After uniformly dissolving, a polyvinyl alcohol resin aqueous solution having a concentration of 12% by weight was obtained by adjusting the concentration.

  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). The discharged polyvinyl alcohol resin aqueous solution was cast from a T-type slit die (straight manifold die) onto a drum-type roll to form a film. The conditions for such casting film formation were as follows.

Drum type roll Diameter: 3200mm
Width: 4000mm
Rotational speed: 6m / min Surface temperature: 80 ° C
Resin temperature at T-type slit die outlet: 70 ° C

  After film formation, the film was dried while alternately passing through a drying roll on the front and back surfaces of the film under the following conditions.

Drying roll diameter: 320mm
Width: 4000mm
Number: 10 Rotating speed: 6m / min Surface temperature: 80 ° C

  After the dried film (moisture content: 12% by weight) is transferred to a humidity control room with a humidity of 50% RH, it is continuously temporarily wound around a roll (core tube) having an outer diameter of 165 mm and a width of 4000 mm. The film was cut when the length of the film reached 4100 m. The thickness was 50 μm. The surface temperature of the roll outermost layer film immediately after cutting was 40 ° C., and after storage for 2 hours, it was 25 ° C. Subsequently, the film was unwound from the film roll, slit to have a width of 3000 mm, and continuously wound up to a roll (core tube) having a width of 4000 mm at a length of 4000 m (water content of the wound film: 11% by weight). The time from drying to the end of the main winding was 4 hours.

  The maximum wave swell of the outermost layer film of the obtained film roll was measured in the same manner as in Example 1. The average value of the maximum waviness of the three filtered waves was 15 mm.

  Subsequently, the entire roll obtained was packed with a gas barrier film (manufactured by Mitsubishi Resin Co., Ltd., Tech Barrier) (water content of the film: 10% by weight). The time from drying to the end of packing was 6 hours. At this time, the appearance of the film roll was extremely good.

  Further, after packing, the film was once opened, and 1 m × 1 m films were collected from the film roll surface layer part, the film roll center part, and the innermost part of the film roll (collection was based on the center with respect to the film width direction). ) When surface waviness was measured in the same manner as in Example 1, the maximum height (h) of the surface waviness was 18 mm for the surface layer, 15 mm for the central portion, and 10 mm for the inside.

(Manufacture of polarizing film)
The obtained polyvinyl alcohol film was immersed in an aqueous solution consisting of 0.2 g / L of iodine and 15 g / L of potassium iodide for 240 seconds at 30 ° C., and then 60 g / L of boric acid and 30 g / L of potassium iodide. While being immersed in an aqueous solution (55 ° C.) of the composition, boric acid treatment was performed for 5 minutes while simultaneously uniaxially stretching four times. Then, it dried and obtained the polarizing film. When the degree of polarization and single transmittance of the obtained polarizing film were measured, the degree of polarization was 98.2%, and the single transmittance was 43.4%.

  Further, after sandwiching the obtained polarizing film between two polarizing plates in a crossed Nicols state (single transmittance 43.5%, polarization degree 99.9%) at an angle of 45 °, the surface illuminance of 14000 lux is obtained. When observed in a transmission mode using a light box, optical color unevenness was observed.

  The results of Examples and Comparative Examples are shown in Table 1.

Claims (7)

When a polyvinyl alcohol film having a size of 1 m × 1 m is set on a flat surface plate, the maximum height of the surface waviness (h) is 1 cm or less to produce a polyvinyl alcohol film.
(A) A step of forming a polyvinyl alcohol film by a casting method,
(B) heating the film-formed polyvinyl alcohol film to adjust the water content to 1 to 5% by weight;
(C) after slitting the heated polyvinyl alcohol film, winding the film in a roll with the moisture content in the film adjusted to 1 to 5% by weight, and
(D) The process of packing the wound polyvinyl alcohol film
And moreover,
In the step (C), the heated polyvinyl alcohol film is once wound on a roll, then unwound from the roll and slit, and further the roll is adjusted in a moisture content of 1 to 5% by weight. A method for producing a polyvinyl alcohol-based film, which is a step of winding the film on a film . In the step (C), the polyvinyl alcohol film wound around the roll with the moisture content adjusted to 1 to 5% by weight is a roll-shaped polyvinyl alcohol film wound up with a length of 3000 m or more. The method for producing a polyvinyl alcohol film according to claim 1, wherein the maximum waviness in the width direction of the roll outermost layer film is 5 mm or less. The method for producing a polyvinyl alcohol film according to claim 1 or 2, wherein the polyvinyl alcohol film uses a polyvinyl alcohol resin having a weight average molecular weight of 120,000 to 300,000. The film thickness of a polyvinyl alcohol-type film is 30-70 micrometers, The manufacturing method of the polyvinyl alcohol-type film in any one of Claims 1-3 characterized by the above-mentioned. The method for producing a polyvinyl alcohol film according to any one of claims 1 to 4 , wherein a film width of the polyvinyl alcohol film slit in the step (C) is 2 m or more. The polyvinyl alcohol according to any one of claims 1 to 5 , wherein the step (D) is performed in a state where the moisture content in the film is maintained at 1 to 5% by weight in an environment of a humidity of 30 to 70% RH. -Based film manufacturing method. The method for producing a polyvinyl alcohol film according to any one of claims 1 to 6 , wherein the heating from the step (B) to the packing in the step (D) is performed within 48 hours.