JP2017037290A - Polyvinyl alcohol film, production method for the same, and polarizing film made of the film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyvinyl alcohol film having a small phase difference in a film width direction, achieving a broader and thinner film, and having excellent homogeneity that allows use of the film to an end portion thereof.SOLUTION: The polyvinyl alcohol film has a width of 4 m or more and a thickness of less than 50 μm; and the polyvinyl alcohol film satisfies expressions (1) Rc≤50nm and (2) 0.7≤Rc/Re≤1.0, where Rc (nm) represents an in-plane retardation in a center portion in a width direction of the film and Re (nm) represents an in-plane retardation in an end portion in the width direction of the film.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a polyvinyl alcohol film, a method for producing the same, and a polarizing film comprising the film. More specifically, the present invention relates to a polyvinyl alcohol film having a small phase difference in the film width direction, excellent in homogeneity that can be widened, thinned, and used up to the edge, and a method for producing the same, and further comprising the film. The present invention relates to a polarizing film having no optical unevenness.

  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 the increase in the size of the display screen of liquid crystal televisions and the like, a polarizing film that is wider, longer and thinner than conventional products, and excellent in homogeneity is required. The polyvinyl alcohol film to be used is also required to be wide, long, thin, and excellent in homogeneity up to the end. If the polyvinyl alcohol film is not homogeneous to the edges, the polarizing performance of the polarizing film obtained from the edges will not be uniform, and the polarizing film will easily deform, reducing the durability of displays such as liquid crystal televisions. Let
The specific demand for the polyvinyl alcohol-based film is a homogeneity that can be widened by 4 m or more and can be used without leaving the end. Furthermore, even for thin films that are thinner than 50 μm and are difficult to produce, there is a demand for homogeneity that can be used to the end.

  As a countermeasure against such a problem, for example, Patent Document 1 discloses that the in-plane retardation is 15 nm or less, and the difference between the retardation in the width direction (TD) and the central portion is 5 nm or less. Alcohol-based films have been proposed. Further, for example, Patent Document 2 proposes a polyvinyl alcohol film having an in-plane retardation value of 30 nm or less and unevenness in the retardation value in the width direction (TD) of 15 nm or less.

JP 2006-291173 A JP 2007-137042 A

  However, it is difficult for the disclosed techniques of Patent Documents 1 and 2 to cope with the recent widening and thinning. For example, the film of the example in Patent Document 1 has a substantial width of less than 4 m and a thickness of 50 μm or 75 μm because the measurement of retardation is performed 5 cm inside from both ends. . In the example of Patent Document 2, the film width is only 3 m (the retardation is measured in 1 cm increments) and the thickness is 50 μm, which is a thick film. Difficult to do.

  In addition, there is a float at the end in the width direction (TD) of the polyvinyl alcohol film, and when it is not flat, it is difficult to wind it up on a roll, and particularly when the end in the width direction is lifted, Phenomena such as winding wrinkles and edge breakage occur during conveyance in the manufacturing process of the polarizing film. Further, when the film absorbs moisture during storage and transportation, the film warp and undulation phenomenon increase, and there is a problem that the film edge must be discarded in the production of the polarizing film.

  Therefore, in the present invention, under such a background, the polyvinyl alcohol film having a small phase difference in the film width direction, wide film thickness, thinning, and excellent homogeneity that can be used up to the end, and its production method, An object of the present invention is to provide a polarizing film made of the film and free from optical unevenness.

Therefore, the present invention provides the following aspects of the invention.
[Polyvinyl alcohol film]
A polyvinyl alcohol film having a width of 4 m or more and a thickness of less than 50 μm,
Polyvinyl which satisfies the following formulas (1) and (2), where Rc (nm) is the in-plane retardation at the central portion in the width direction of the film and Re (nm) is the in-plane retardation at the end in the width direction of the film. Alcohol film.
Formula (1) Rc ≦ 50 nm
Formula (2) 0.7 ≦ Rc / Re ≦ 1.0

[Method for producing polyvinyl alcohol film]
A method for producing the polyvinyl alcohol-based film by discharging and flowing an aqueous solution of a polyvinyl alcohol-based resin into a cast mold to form a film, and continuously drying the film.
A polyvinyl alcohol system having a step in which a film whose water content is adjusted to 1 to 20% by weight is tensioned outward in the width direction so that the film width after drying is 0.92 to 1.0 times the film forming width. A method for producing a film.

[Polarizing film]
A polarizing film comprising the polyvinyl alcohol film.

The polyvinyl alcohol film in the present invention has a rectangular shape when placed on a flat surface plate, the direction in which the relatively long side extends is called the longitudinal direction, and the length of the relatively short side is referred to as “width”. "
In the present invention, the “film width direction” is generally a direction substantially perpendicular to the longitudinal direction of the film. Particularly in a polyvinyl alcohol film formed by discharging and flowing into a cast mold, it is a direction substantially perpendicular to the flow direction of the film at the time of film formation, typically between both edges of the film. The direction when the distance is the shortest.
“The central part in the width direction of the film” refers to a region or a point having substantially the same distance from both edges in the width direction of the film.
The “end in the width direction of the film” means a region on the center side of 1 cm from the edge in the width direction of the film.
“Outside in the width direction of the film” refers to the direction from the center to the end of the film in the width direction.
In the present invention, the width direction of the film is referred to as “TD” or “TD direction”, and the flow direction of the film is referred to as “MD” or “MD direction”.
Hereinafter, the polyvinyl alcohol film is also simply referred to as “film”.

  In the present invention, in order to obtain a large area and uniform polarizing film, it is important to reduce the in-plane retardation at both ends in the width direction of the polyvinyl alcohol film. In addition, in consideration of the fact that the film is stretched in the flow direction (MD direction) in the polarizing film manufacturing process, the in-plane retardation at both ends in the width direction should be greater than or equal to the in-plane retardation value at the center in the width direction. It is also important. That is, in the polarizing film manufacturing process, the central portion in the width direction of the film is stretched in the MD direction and only the in-plane retardation is increased, whereas the both end portions in the width direction of the film are also pulled in the TD direction. Because of the so-called neck-in phenomenon that occurs (shrinks), the in-plane phase difference tends not to increase as much as the central portion. Therefore, in the preparation stage of the polyvinyl alcohol film that is the raw material of the polarizing film, the in-plane retardation at both ends in the width direction is equal to or greater than the in-plane retardation value at the center in the width direction. The in-plane retardation can be made substantially equal at the widthwise center portion and the widthwise both ends of the film.

  Since the polyvinyl alcohol-based film of the present invention is uniform even at the end in the width direction, it is preferably used as a raw material for a wide, long and thin polarizing film to obtain a polarizing film free from optical color unevenness. it can. Furthermore, since there is no floating at both ends in the film width direction, the polarizing film can be easily manufactured, and a large-area polarizing plate can be obtained.

FIG. 1 is a diagram schematically showing the relationship between the direction of tension by a cross guider and the flow direction of a film. FIG. 2 is a diagram schematically illustrating an example of the installation position of the cross guider.

Hereinafter, although it demonstrates in detail about the structure of this invention, these show an example of a desirable embodiment, and this invention is not specified by these content.
The polyvinyl alcohol film of the present invention has a width of 4 m or more and a thickness of less than 50 μm, an in-plane retardation in the width direction (TD) center of the film is Rc (nm), and a width direction (TD) end of the film. When the in-plane retardation is Re (nm), the following expressions (1) and (2) are satisfied.
Formula (1) Rc ≦ 50 nm
Formula (2) 0.7 ≦ Rc / Re ≦ 1.0

  The in-plane retardation can be expressed by (nx−ny) × d (nm). In the formula, nx represents the maximum refractive index (slow axis direction) in the plane of the film, ny represents the refractive index in the direction (fast axis direction) perpendicular to the slow axis in the plane of the film, and d Represents the thickness of the film.

  The production method of the polyvinyl alcohol film of the present invention is not particularly limited. For example, the polyvinyl alcohol film can be obtained by discharging and flowing an aqueous solution of a polyvinyl alcohol resin into a cast mold and continuously drying the film. More specifically, the polyvinyl alcohol-based resin aqueous solution is discharged and cast onto a cast mold such as a cast drum (drum-type roll) or a cast belt, and is formed and dried by a casting method. It can be manufactured continuously. In the present invention, the method for producing the polyvinyl alcohol film is not particularly limited to the casting method. Among the cast molds, a cast drum is preferable from the viewpoints of widening, lengthening, and film thickness uniformity.

  The polyvinyl alcohol resin used in the present invention is usually an unmodified polyvinyl alcohol resin, that is, a resin produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate. If necessary, a resin obtained by saponifying a copolymer of vinyl acetate and a small amount (usually 10 mol% or less, preferably 5 mol% or less) of a copolymerizable component with vinyl acetate may be used. it can. Examples of components copolymerizable with vinyl acetate include unsaturated carboxylic acids (including salts, esters, amides, nitriles, etc.), and olefins having 2 to 30 carbon atoms (for example, ethylene, propylene, n-butene). , Isobutene, etc.), vinyl ethers, unsaturated sulfonates and the like. Moreover, the modified polyvinyl alcohol-type resin obtained by chemically modifying the hydroxyl group after saponification can also be used.

  Moreover, as a polyvinyl alcohol-type resin, the polyvinyl alcohol-type resin which has a 1, 2- diol structure in a side chain can also be used. Such a polyvinyl alcohol resin having a 1,2-diol structure in the side chain includes, for example, (i) a method of saponifying a copolymer of vinyl acetate and 3,4-diacetoxy-1-butene, and (ii) acetic acid. A method for saponifying and decarboxylating a copolymer of vinyl and vinyl ethylene carbonate, (iii) saponifying and decarboxylating a copolymer of vinyl acetate and 2,2-dialkyl-4-vinyl-1,3-dioxolane It is obtained by a method of ketalization, (iv) a method of saponifying a copolymer of vinyl acetate and glycerol monoallyl ether, or the like.

The weight average molecular weight of the polyvinyl alcohol-based resin is preferably 100,000 to 300,000, particularly preferably 110,000 to 280,000, and more preferably 120,000 to 260,000.
If the weight average molecular weight is too small, sufficient optical performance tends to be difficult to obtain when the polyvinyl alcohol-based resin is used as an optical film, and if it is too large, it tends to be difficult to stretch the polyvinyl alcohol-based film when manufacturing a polarizing film. There is.
In addition, the weight average molecular weight of the said polyvinyl alcohol-type resin is a weight average molecular weight measured by GPC-MALS method.

The average saponification degree of the polyvinyl alcohol resin used in the present invention is usually preferably 98 mol% or more, particularly preferably 99 mol% or more, further preferably 99.5 mol% or more, and particularly preferably 99.mol%. It is 8 mol% or more. If the average degree of saponification is too small, there is a tendency that sufficient optical performance cannot be obtained when a polyvinyl alcohol film is used as a polarizing film.
Here, the average saponification degree in the present invention is measured according to JIS K 6726.

  As a polyvinyl alcohol-type resin used for this invention, you may use together 2 or more types from which modified | denatured seed | species, modified | denatured amount, weight average molecular weight, average saponification degree differ.

  Using this polyvinyl alcohol resin, an aqueous polyvinyl alcohol resin solution is produced. The polyvinyl alcohol resin is preferably washed with water and dehydrated with a centrifugal separator or the like to obtain a polyvinyl alcohol resin wet cake having a water content of 50% by weight or less. When the moisture content of such a wet cake is too high, it tends to be difficult to adjust to a desired aqueous solution concentration. Such polyvinyl alcohol resin wet cake is dissolved in warm water or hot 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 heated multi-screw extruder. It is also possible to prepare an aqueous solution having a desired concentration by introducing the wet polyvinyl alcohol resin wet cake and blowing water vapor into the can to dissolve it.

  In addition to polyvinyl alcohol-based resins, polyvinyl alcohol-based resin aqueous solutions include plastics commonly used such as glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol, and trimethylol propane as necessary. It is preferable from the point of film forming property to contain an agent and nonionic, anionic, and / or cationic surfactant.

The resin concentration of the aqueous polyvinyl alcohol resin solution thus obtained is preferably 10 to 60% by weight, particularly preferably 15 to 55% by weight, and further preferably 20 to 50% by weight.
If the resin concentration is too low, the drying load becomes large and the production capacity tends to be inferior. If the resin concentration is too high, the viscosity becomes too high and uniform dissolution tends to be difficult.

Using the aqueous solution of polyvinyl alcohol resin, the aqueous solution is discharged and cast onto a rotating cast drum, and the polyvinyl alcohol film of the present invention is continuously produced by, for example, casting and drying by a casting method. For example, it can be manufactured by the following steps.
(A) A step of forming a film by a casting method.
(B) The process of heating and drying the formed film.
(C) A step of slitting both ends of the dried film and then winding it on a roll.
Hereinafter, steps (A) to (C) will be sequentially described.

[Process (A)]
In the step (A), first, the polyvinyl alcohol-based resin aqueous solution is usually defoamed. Examples of the defoaming method include stationary defoaming and defoaming using a multi-screw extruder having a vent. As the multi-screw extruder having a vent, a twin-screw extruder having a vent is usually used.

  After the defoaming treatment, the polyvinyl alcohol-based resin aqueous solution is introduced into the T-shaped slit die by a certain amount, discharged and cast on a rotating cast drum, and formed into a film by a casting method.

The temperature of the polyvinyl alcohol-based resin aqueous solution at the exit of the T-shaped slit die is preferably 80 to 100 ° C, particularly preferably 85 to 98 ° C.
If the temperature of the aqueous polyvinyl alcohol resin solution is too low, there is a tendency to cause poor flow, and if it is too high, foaming tends to occur.

The viscosity of the aqueous polyvinyl alcohol resin solution is preferably 50 to 200 Pa · s, particularly preferably 70 to 150 Pa · s at the time of discharge.
When the viscosity of such an aqueous solution is too low, there is a tendency to cause poor flow, and when it is too high, it tends to be difficult to flow.

The discharge speed of the polyvinyl alcohol-based resin aqueous solution discharged from the T-type slit die onto the cast drum is preferably 0.2 to 5 m / min, particularly preferably 0.4 to 4 m / min, more preferably 0.8. 6-3 m / min.
If the discharge speed is too low, productivity tends to decrease, and if it is too high, fluency tends to be difficult.

The diameter of the cast drum is preferably 2 to 5 m, particularly preferably 2.4 to 4.5 m, and further preferably 2.8 to 4 m.
If the diameter is too small, the drying length is insufficient and the speed tends not to be obtained, and if it is too large, the transportability tends to decrease.

The width of the cast drum is preferably 4.5 m or more, particularly preferably 4.8 m or more, further preferably 5 m or more, and particularly preferably 5 to 7 m.
If the width of the cast drum is too small, productivity tends to decrease.

The rotation speed of the cast drum is preferably 3 to 50 m / min, particularly preferably 4 to 40 m / min, and further preferably 5 to 35 m / min.
If the rotational speed is too low, productivity tends to decrease, and if it is too high, drying tends to be insufficient.

The surface temperature of such a cast drum is preferably 40 to 99 ° C, particularly preferably 60 to 95 ° C.
If the surface temperature is too low, drying tends to be poor, and if it is too high, foaming tends to occur.

  In this invention, it is preferable that the moisture content of the film at the time of peeling from a cast drum is 10 to 30 weight%, Most preferably, it is 15 to 25 weight%.

[Process (B)]
Next, the step (B) will be described.
A process (B) is a process of heating and drying the formed film.

The film formed on the cast drum is dried by alternately bringing the front and back surfaces of the film into contact with a plurality of metal heating rolls (hereinafter referred to as “heat rolls”). The surface temperature of a hot roll is 40-150 degreeC normally, Preferably it is 50-140 degreeC. If the surface temperature is too low, drying tends to be poor, and if the surface temperature is too high, drying tends to be excessive, and appearance defects such as undulation tend to be caused.
The hot roll is, for example, a roll having a diameter of 0.2 to 2 m whose surface is hard chrome plated or mirror-finished, and drying is usually performed using 2 to 30, preferably 10 to 25 rolls. preferable.

In the present invention, a film having a moisture content adjusted to 1 to 20% by weight, preferably 5 to 10% by weight, is subjected to a relatively weak tension on the outer side in the width direction (TD direction) of the film, and then dried. The film width is preferably 0.92 to 1.0 times the film forming width from the viewpoint of controlling the in-plane retardation. Particularly preferably, the film width after drying is 0.93 to 0.97 times, more preferably 0.93 to 0.95 times the film forming width. Here, for example, when the film width is 5 m, a difference of 0.01 times corresponds to a difference of 5 cm.
The film forming width here means the width of the film immediately after being peeled off from the cast drum, and the film width after drying is the width of the polyvinyl alcohol film after being dried by a hot roll, or It is the width | variety of the polyvinyl alcohol-type film after heat-processing as needed.

  In addition, it is particularly preferable in terms of tension control to generate a tension in the film width direction (TD direction) outside by at least one device selected from a cross guider, an expander roll, a banana roll, and a mirabo roll. It is more preferable that the tension is generated by at least one device selected from expander rolls in that the tension can be accurately controlled. A cross guider is particularly preferable because the surface of the film is hardly damaged. Hereinafter, the cross guider, the expander roll, the banana roll, and the mirabo roll may be collectively referred to as a cross guider or the like.

  The cross guider in the present invention is a widening roll installed between various rolls in the film flow direction, and the two rolls that form a pair at the top and bottom are conveyed in the width direction (TD direction). It has a function of sandwiching the end from above and below (front and back of the film). As shown in FIG. 1, such roll pairs (cross guiders) are respectively installed at both ends in the width direction of the film, and the film ends are at a predetermined angle (θ1) with respect to the film flow direction (MD direction). It is possible to suppress shrinkage in the film width direction due to dehydration and neck-in. Such a cross guider can spread a running film from the center to the outside without damaging the film surface due to friction or slip. Moreover, the problem that a wrinkle, a crease | fold, shrinkage | contraction, etc. generate | occur | produce can be eliminated by pinching | interposing a film both ends from the upper and lower sides of a film.

The installation position of the cross guider and the like is not particularly limited, but is preferably before and after a plurality of heat rolls and / or before and after the heat treatment described below, and more preferably, in terms of controlling in-plane retardation. Before and after a certain heat roll, and more preferably, immediately after the final heat roll in terms of reducing the waviness width at both ends in the film width direction. FIG. 2 schematically shows an example of the installation position of a cross guider or the like.
Note that “front and back” before and after the heat roll and before and after the heat treatment refer to the upstream side and the downstream side in the flow direction (MD direction) on the basis of the heat roll or the heat treatment. Immediately after the final heat roll means a position within 1 m on each of the upstream side and the downstream side with respect to the nip roll arranged on the downstream side of the most downstream heat roll (final heat roll) among the plurality of heat rolls. .

  When a cross guider is used, an angle θ1 (°) formed by the direction of tension by the cross guider and the flow direction of the film (MD direction) is set to 5 to 35 ° so as not to disturb the flow of the conveyed film. It is preferable to set to. The angle θ1 (°) is particularly preferably 5 to 30 °, and more preferably 5 to 25 °, in terms of high-speed conveyance of the film.

The tension P (N) to the outside in the film width direction by a cross guider or the like is preferably 1 to 1000 N, particularly preferably 2 to 500 N, and further preferably 2 to 200 N. In particular, the tension P (N) to the outside in the width direction when a cross guider is used is given by the following equation when the tension by the cross guider is T (N) (see FIG. 1).
P (N) = T (N) × sin θ1

In the present invention, it is preferable to heat-treat the film after drying with a hot roll. The heat treatment temperature is preferably 60 to 150 ° C, and particularly preferably 70 to 140 ° C. When the heat treatment temperature is too low, the water resistance of the polyvinyl alcohol-based film tends to be insufficient or causes retardation unevenness, and when it is too high, the stretchability during the production of the polarizing film tends to decrease. Examples of such a heat treatment method include a method using a floating dryer, a method of once cooling to room temperature after drying, and a method of contacting a high-temperature hot roll again, and a method of irradiating both sides of a film with infrared rays using an infrared lamp. Among them, among these, a method using a floating dryer is preferable in that it can be uniformly heat-treated.
In the present invention, before and after the heat treatment, a relatively weak tension, for example, 10 to 1000 N, is applied to the outside in the film width direction (TD direction) by at least one device selected from a cross guider, an expander roll, a banana roll, and a mirabo roll. You may spend.

[Process (C)]
The polyvinyl alcohol film original fabric that has been dried in the step (B) and further subjected to heat treatment as necessary becomes a product through the step (C). A process (C) is a process of winding up to a roll, after slitting the both ends of the dried polyvinyl alcohol-type film.
As described above, when the in-plane retardation at both ends in the film width direction is significantly different from the in-plane retardation at the center in the width direction, or when there are wrinkles, bends, or shrinkage at both ends of the film, the area to be cut off by the slit Will increase.
However, according to the present invention, it is possible to reduce the in-plane phase difference between the both end portions and the center portion, and to suppress the generation of wrinkles at both end portions of the film, thereby reducing the area cut off by the slit. And has the advantage of high manufacturing efficiency.

  In the above, a method for preparing a polyvinyl alcohol film by preparing a polyvinyl alcohol resin aqueous solution, casting the aqueous solution on a rotating cast drum (drum type roll), forming a film by a casting method, and drying the film. However, it is also possible to produce a polyvinyl alcohol film by casting an aqueous polyvinyl alcohol resin solution on a resin film or a metal belt, forming a film, and drying.

[Polyvinyl alcohol film]
The polyvinyl alcohol film of the present invention thus obtained has a width of 4 m or more. It is preferably 4.5 m or more from the viewpoint of increasing the area, and more preferably 4.5 to 6 m from the viewpoint of avoiding breakage.
The thickness of the polyvinyl alcohol film is less than 50 μm, preferably 40 μm or less. The thickness is particularly preferably 5 to 30 μm from the viewpoint of thinning, and more preferably 10 to 25 μm from the viewpoint of avoiding breakage.
The length of the polyvinyl alcohol film is preferably 4 km or more from the viewpoint of increasing the area, particularly preferably 4.5 km or more, and more preferably 5 km or more from the viewpoint of transport weight.
The upper limit of the length of the film is preferably 50 km or less, particularly preferably 40 km or less, and further preferably 30 km or less from the viewpoint of avoiding breakage.

When the in-plane retardation at the center in the width direction of the film is Rc (nm) and the in-plane retardation at the end of the film in the width direction is Re (nm), the polyvinyl alcohol film of the present invention has the following formula (1 ) And (2) are satisfied.
Formula (1) Rc ≦ 50 nm
Formula (2) 0.7 (particularly 0.70) ≦ Rc / Re ≦ 1.0 (particularly 1.00)

Preferably, the following expressions (1 ′) and (2 ′) are satisfied from the viewpoint of increasing the area of the polarizing film.
Formula (1 ′) Rc ≦ 40 nm
Formula (2 ′) 0.8 (particularly 0.80) ≦ Rc / Re ≦ 1.0 (particularly 1.00)

Particularly preferably, the following expressions (1 ″) and (2 ″) are satisfied from the viewpoint of increasing the area of the polarizing plate.
Formula (1 ″) Rc ≦ 30 nm
Formula (2 ″) 0.9 (particularly 0.90) ≦ Rc / Re ≦ 1.0 (particularly 1.00)

  In the polyvinyl alcohol-based film of the present invention, when the film dried in the step (B) is placed on a flat surface plate, the waviness width at the film end is within 1 cm before the slit in the step (C). It is preferable. The waviness width is particularly preferably within 0.7 cm, more preferably within 0.5 cm. If the undulation width is too large, the end discard amount at the time of slitting tends to increase. As a method for reducing the waviness width, a method of applying a relatively weak tension in the width direction (TD direction) of the film in the drying step, a method of reducing the moisture content when peeling the film from the cast drum, Examples thereof include a technique for reducing the film peeling strength from the drum by addition and polishing of the cast drum, and a technique for reducing the discharge amount of the aqueous solution from both ends of the T-type slit die.

  In the polyvinyl alcohol-based film of the present invention, when the film is placed on a flat surface plate, the maximum value of the floating amount from the surface of the surface plate at both ends in the film width direction is preferably 1 mm or less. The maximum value of the floating amount is particularly preferably 0.8 mm or less, and more preferably 0.7 mm or less. If the maximum value of the floating amount is too large, it becomes difficult to wind up, and a phenomenon such as winding wrinkles or edge breakage occurs in the polarizing film manufacturing process, so that the manufacturing yield tends to decrease. As a method for reducing the floating amount, a method of applying a relatively weak tension in the width direction (TD direction) of the film in the drying process, a method of reducing the moisture content when peeling the film from the cast drum, Examples thereof include a technique for reducing the film peeling strength from the drum by addition and polishing of the cast drum, and a technique for reducing the discharge amount of the aqueous solution from both ends of the T-type slit die.

[Polarizing film]
The polyvinyl alcohol film of the present invention is excellent in homogeneity up to the film end, is suitably used as an optical polyvinyl alcohol film, and is particularly preferably used as a raw material for a polarizing film.

  Hereinafter, the manufacturing method of the polarizing film obtained using the polyvinyl alcohol-type film of this invention is demonstrated.

  The polarizing film of the present invention is usually produced through steps such as swelling, dyeing, boric acid crosslinking, stretching, washing and drying by unwinding the polyvinyl alcohol film from a roll and transferring it in the horizontal direction.

  The swelling process is performed before the dyeing process. In addition to washing the surface of the polyvinyl alcohol film by the swelling step, there is also an effect of preventing uneven staining by swelling the polyvinyl alcohol film. In the swelling step, water is usually used as the treatment liquid. If the main component is water, the treatment solution may contain a small amount of an iodide compound, an additive such as a surfactant, alcohol, or the like. The temperature of the swelling bath is usually about 10 to 45 ° C., and the immersion time in the swelling bath is usually about 0.1 to 10 minutes.

  The dyeing step is performed 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 suitably 0.1-2 g / L, and the potassium iodide concentration is suitably 1-100 g / L. 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.

  The boric acid crosslinking step is performed using a boron compound such as boric acid or borax. The boron compound is used in the form of an aqueous solution or a water-organic solvent mixture at a concentration of about 10 to 100 g / L, and it is preferable that potassium iodide coexists in the solution from the viewpoint of stabilizing the polarization performance. The temperature during the treatment is preferably about 30 to 70 ° C., and the treatment time is preferably about 0.1 to 20 minutes. If necessary, the stretching operation may be performed during the treatment.

  In the stretching step, stretching in a uniaxial direction is preferably performed 3 to 10 times, particularly 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 temperature during stretching is preferably 30 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 washing step is performed, for example, by immersing the polyvinyl alcohol film in an aqueous iodide solution such as water or potassium iodide, and can remove precipitates generated on the surface of the film. When using a potassium iodide aqueous solution, the potassium iodide concentration may be about 1 to 80 g / L. The temperature during the washing treatment is usually 5 to 50 ° C, preferably 10 to 45 ° C. The treatment time is usually 1 to 300 seconds, preferably 10 to 240 seconds. In addition, you may perform combining water washing | cleaning and washing | cleaning by potassium iodide aqueous solution suitably.

  What is necessary is just to perform a drying process for 1 to 10 minutes at 40-80 degreeC in air | atmosphere.

Further, the polarization degree of the polarizing film is preferably 99.5% or more, particularly preferably 99.8% or more. If the degree of polarization is too low, there is a tendency that the contrast in the liquid crystal display cannot be secured.
Note that the degree of polarization is generally the light transmittance (H ₁₁ ) measured at the wavelength λ in the state where two polarizing films are overlapped so that their orientation directions 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 films are superposed so that the orientation directions are orthogonal 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 42% or more. If the single transmittance is too low, 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.

Thus, although the polarizing film of the present invention is obtained, the polarizing film of the present invention is suitable for producing a high-quality polarizing plate because it has no optical unevenness and excellent in-plane uniformity of polarization performance.
Hereinafter, a method for producing a polarizing plate from the polarizing film of the present invention will be described.

  The polarizing film of the present invention is bonded to one surface or both surfaces of the polarizing film as a protective film by using an optically isotropic resin film via an adhesive. Examples of the protective film include films of cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, cycloolefin polymer, cycloolefin copolymer, polystyrene, polyethersulfone, polyarylene ester, poly-4-methylpentene, polyphenylene oxide, and the like. Or a sheet | seat is mentioned.

  The bonding method is performed by a known method. For example, after a liquid adhesive composition is uniformly applied to a polarizing film, a protective film, or both, the two are bonded and pressure-bonded, and heating or active energy is applied. This is done by irradiating a line.

  In addition, for the purpose of thinning the polarizing film, instead of the protective film, a curable resin such as urethane resin, acrylic resin, urea resin or the like is applied to one side or both sides of the protective film and cured to obtain a polarizing plate. You can also

  Since the polarizing film of the present invention has no optical unevenness and excellent in-plane uniformity of polarization performance, a portable information terminal, personal computer, TV, projector, signage, electronic desk calculator, electronic clock, word processor, electronic paper, game Liquid crystal display devices such as cameras, videos, cameras, photo albums, thermometers, audio, automobiles and machinery instruments, sunglasses, anti-glare glasses, stereoscopic glasses, wearable displays, display elements (CRT, LCD, organic EL, electronic It is preferably used for an antireflection layer for paper, optical communication equipment, medical equipment, building materials, toys and the like.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited to a following example, unless the summary is exceeded.

The polarizing film obtained in Examples and Comparative Examples was measured for the following characteristics.
(1) In-plane retardation (nm)
The retardation value of the center part and both ends of the width direction of a polyvinyl alcohol-type film was measured using the retardation measuring apparatus ("KOBRA-WFD" Oji Scientific Instruments Co., Ltd. product, measurement wavelength: 590 nm).
(2) Waviness width (cm)
The waviness width at the end of the film after the drying process was measured.
(3) Floating amount (mm)
Take a 1m x 1m polyvinyl alcohol film, leave it on a flat surface plate for 1 hour in a constant temperature and humidity chamber at 23 ° C and 50% RH, and then use the gap gauge to maximize the amount of floating at the end. The value was measured.
(4) Degree of polarization (%) and single transmittance (%)
A strip sample of 200 mm in the stretching direction × 40 mm in the width direction was cut out from the center and both ends in the width direction of the obtained polarizing film, and 10 points were formed at a pitch of 10 mm in the stretching direction using Otsuka Electronics Co., Ltd .: RETS-1100A. The degree of polarization and single transmittance were measured and averaged.
(5) Optical unevenness A test piece having a length of 30 cm and a width of 30 cm was collected from the width direction center and both ends of the obtained polarizing film, and two polarizing plates in a crossed Nicol state (single transmittance 43.5%, The optical unevenness was visually observed in the transmission mode using a light box having a surface illuminance of 14,000 lx, and evaluated according to the following criteria.
(Evaluation criteria)
○ ・ ・ ・ No optical unevenness × ・ ・ ・ Optical unevenness

[Example 1]
(Manufacture of polyvinyl alcohol film)
1,000 kg of polyvinyl alcohol resin having a weight average molecular weight of 142,000 and a saponification degree of 99.8 mol%, 2,500 kg of water, and 100 kg of glycerin as a plasticizer are added, and the temperature is raised to 140 ° C. while stirring, and the resin concentration The concentration was adjusted to 30% by weight to obtain a uniformly dissolved polyvinyl alcohol-based resin aqueous solution.
Next, the polyvinyl alcohol-based resin aqueous solution is supplied to a twin-screw extruder having a vent and defoamed, and then the aqueous solution temperature is set to 95 ° C., and the discharge speed is 1.7 m from the T-type slit die discharge port to the cast drum. The film was cast at a rate of 1 minute. The film width after film formation was 5.5 m. The film having a moisture content of 15% by weight was peeled off from the cast drum, and drying was carried out while alternately bringing the front and back surfaces of the film into contact with a total of 10 hot rolls.
While transporting the obtained film having a moisture content of 5% by weight at a speed of 8 m / min, it was widened in the width direction using a cross guider (manufactured by Yamada Denki Kogyo Co., Ltd., ICO10U) and passed through a nip roll. The angle θ1 between the tensile direction of the cross guider and the MD direction is 20 °, and the tension in the width direction is 100N.
Next, heat treatment was performed by blowing hot air from both sides of the film. The film width after drying was 5.1 m, and the film width / film forming width after drying was 0.93. Moreover, the waviness width of the edge part after heat processing was 1 cm.
Finally, both ends of the film were slit to obtain a polyvinyl alcohol film having a width of 5 m, a thickness of 40 μm, and a length of 5 km and wound in a roll shape. The properties of the obtained polyvinyl alcohol film are shown in Table 1.

(Manufacture of polarizing film)
The obtained polyvinyl alcohol film was unwound from a roll, transported in the horizontal direction using a transport roll, and stretched 1.7 times in the flow direction while being immersed and swollen in a water bath having a water temperature of 25 ° C. Next, the film was stretched 1.6 times in the flow direction while being immersed and dyed in a 28 ° C. aqueous solution composed of 0.5 g / L of iodine and 30 g / L of potassium iodide. Next, the film was immersed in an aqueous solution (55 ° C.) having a composition of boric acid 40 g / L and potassium iodide 30 g / L, and uniaxially stretched 2.1 times in the flow direction while crosslinking with boric acid. Thereafter, the film was washed with an aqueous potassium iodide solution and dried at 50 ° C. for 2 minutes to obtain a polarizing film having a total draw ratio of 5.7 times. Table 2 shows the polarization characteristics of the obtained polarizing film.

[Example 2]
In Example 1, a polarizing film was produced in the same manner as in Example 1 using a polyvinyl alcohol film having a discharge speed of 0.8 m / min and a thickness changed to 20 μm, and various characteristics were measured. The results are summarized in Tables 1 and 2.

[Comparative Example 1]
A polarizing film was produced in the same manner as in Example 1 except that no widening in the width direction in the drying process was performed, and various characteristics were measured. The results are summarized in Tables 1 and 2.

  As shown in Tables 1 and 2, the polyvinyl alcohol films of Examples 1 and 2 whose Rc / Re values are within the range defined by the present invention have Rc / Re values outside the range defined by the present invention. Compared with the polyvinyl alcohol-based film of Comparative Example 1, the maximum values of the waviness width and the floating amount are low, which indicates that the polyvinyl alcohol-based film has excellent homogeneity that can be used up to the end in the width direction. Moreover, the polarizing film obtained from the polyvinyl alcohol film of Examples 1 and 2 has a uniform degree of polarization and single transmittance, compared with the polarizing film obtained from the polyvinyl alcohol film of Comparative Example 1. In addition, it can be seen that there is no optical unevenness in the central portion and both end portions in the width direction, and that the polarization characteristics are excellent.

  Polarizing films produced from the polyvinyl alcohol film targeted by the present invention are portable information terminals, personal computers, televisions, projectors, signage, electronic desk calculators, electronic watches, word processors, electronic paper, game machines, videos, cameras, Anti-reflection for photo albums, thermometers, audio, liquid crystal display devices such as cars and machinery instruments, sunglasses, anti-glare glasses, stereoscopic glasses, wearable displays, display elements (CRT, LCD, organic EL, electronic paper, etc.) It is preferably used for layers, optical communication equipment, medical equipment, building materials, toys and the like.

PVA film: Polyvinyl alcohol film

Claims (7)

A polyvinyl alcohol film having a width of 4 m or more and a thickness of less than 50 μm,
Polyvinyl which satisfies the following formulas (1) and (2), where Rc (nm) is the in-plane retardation at the central portion in the width direction of the film and Re (nm) is the in-plane retardation at the end in the width direction of the film. Alcohol film.
Formula (1) Rc ≦ 50 nm
Formula (2) 0.7 ≦ Rc / Re ≦ 1.0   2. The polyvinyl alcohol film according to claim 1, wherein when the film is placed on a flat surface plate, the maximum value of the floating amount from the surface of the surface plate at both ends in the film width direction is 1 mm or less. A method for producing a polyvinyl alcohol film according to claim 1, wherein an aqueous solution of a polyvinyl alcohol resin is discharged and poured into a cast mold to form a film, and is continuously dried.
A polyvinyl alcohol system having a step in which a film whose water content is adjusted to 1 to 20% by weight is tensioned outward in the width direction so that the film width after drying is 0.92 to 1.0 times the film forming width. A method for producing a film.   The manufacturing method of the polyvinyl alcohol-type film of Claim 3 which generate | occur | produces the tension | tensile_strength to a film width direction with the at least 1 sort (s) apparatus chosen from a cross guider and an expander roll.   The manufacturing method of the polyvinyl-alcohol-type film of Claim 4 whose angle which the direction of the tension | tensile_strength by a cross guider and the flow direction of a film make is 5-35 degrees.   The manufacturing method of the polyvinyl alcohol-type film of Claim 5 whose tension | tensile_strength by the cross guider to the film width direction outer side is 10-1000N.   A polarizing film comprising the polyvinyl alcohol-based film according to claim 1.

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