CN104311853B - Polymer film of polyvinyl alcohol and its manufacturing method - Google Patents

Abstract

The present invention relates to a polyvinyl alcohol-based polymer film and a method for producing the same. The present invention is a PVA film and a method for producing a film. The PVA film is a PVA film with good stretchability and polarizing film productivity; After being discharged to the first drying roll of a film forming device equipped with a plurality of drying rolls and partially dried, the subsequent drying rolls are sequentially dried to produce; at this time, the volatile component ratio of (b) PVA film reaches 13% by mass The ratio (S _T /S ₁ ) of the peripheral speed (S _T ) of the drying roll to the peripheral speed (S ₁ ) of the first drying roll during the time is 0.990 to 1.050; (c) the peripheral speed (S _L ) to the peripheral speed (S _T ) ratio (S _L /S _T ) is 0.960-0.980; (d) the ratio (S _L /S ₁ ) is 0.970-1.010.

Description

Polyvinyl alcohol-based polymer film and method for producing the same

The application for this invention is a divisional application of the PCT patent application PCT/JP2012/056976, the application date is March 19, 2012, and the invention title is "polyvinyl alcohol-based polymer film and its manufacturing method". The application number for entering China is 201280015847.6.

technical field

The present invention relates to a polyvinyl alcohol-based polymer film, a method for producing the film, and a polarizing film made of the film. More specifically, the present invention relates to a film that has a high ultimate stretching ratio, is not easily broken even if the film is stretched at a high ratio, does not cause interruption of the stretching operation due to film breakage, and can be produced with high yield and good productivity. A polyvinyl alcohol-based polymer film for producing a stretched film having excellent optical properties such as polarizing properties, a method for producing the same, and a polarizing film made of the film.

Background technique

A polarizing plate having a function of transmitting and shielding light, a liquid crystal having a function of switching light, and the like are important components of a liquid crystal display device (LCD). The field of application of this liquid crystal display device has also expanded from small instruments such as calculators and watches at the initial stage of development to notebook computers, liquid crystal displays, liquid crystal color projectors, liquid crystal TVs, car navigation systems, mobile phones, and metering for indoor and outdoor use. In a wide range of devices such as instruments, especially in liquid crystal displays, liquid crystal televisions, etc., large screens are being developed.

Polarizers are generally manufactured as follows: after uniaxially stretching a polyvinyl alcohol-based polymer film, dyeing a polyvinyl alcohol-based polymer film with iodine or a dichroic dye and then uniaxially stretching Afterwards, a method of fixing treatment with a boron compound, a method of performing fixing treatment while dyeing in any of the above-mentioned methods, etc. are used to manufacture a polarizing film, and a cellulose triacetate film is attached to one or both sides of the polarizing film thus obtained, Protective film such as cellulose acetate-butyrate film.

In recent years, along with the expansion of applications of liquid crystal display devices, etc., further reduction in cost and further improvement in handling have been demanded in addition to enhancement in display quality. From the perspective of cost reduction, it is necessary to increase the production speed when manufacturing polarizing films, and it is necessary to prevent tensile fracture (fracture) when stretching polyvinyl alcohol-based polymer films, reduce fracture loss, improve yield, and prevent Stretching work due to film breakage, interruption of stretching-dyeing work, etc.

As a method of improving productivity in the production of polarizing films, shortening of the drying time in the production of polarizing films is required. From this point of view, the original film (original reverse film) for polarizing films has been generally used in the past with a thickness of 75 μm. There are many polyvinyl alcohol-based polymer films, but in recent years, polyvinyl alcohol-based polymer films thinner than 70 μm and further thinned are required.

However, there is a problem that the thinner the polyvinyl alcohol-based polymer film is, the easier it is to break when stretched at a high ratio. Polyvinyl alcohol-based polymer film that can be stretched at a high ratio in the case of a polarizing film with good operability, high yield, low cost, and good productivity. .

In the past, in order to improve the stretchability of polyvinyl alcohol-based polymer films, improve the uniformity of stretching, and improve the polarizing performance and durability of polarizing films obtained by stretching polyvinyl alcohol-based polymer films, etc., in When forming a film using a dope solution containing a polyvinyl alcohol-based polymer while drying, the adjustment of the film-forming draw ratio (the ratio of the conveying speed of the polyvinyl alcohol-based polymer film between the film-forming rolls) and film forming Adjustment of the moisture ratio of the polyvinyl alcohol-based polymer film during the process, etc.

As such prior art, it is known that (1) in order to obtain a stretched film sufficiently molecularly oriented at the time of uniaxial stretching, the film-forming tension is infinitely reduced by adopting a film-forming draw ratio of 1 or less. A method of film-forming operation for producing a polyvinyl alcohol-based polymer film (Patent Document 1, especially paragraphs [0008] to [0009], examples, etc.); (2) In order to obtain a film capable of stretching at a high ratio For polyvinyl alcohol-based polymer films, when a polyvinyl alcohol-based polymer film is produced by a drum film forming machine, [the winding speed of the obtained polyvinyl alcohol-based polymer film]/[is located at the most upstream of the supply of film-forming raw materials The speed of drum] is the method of 0.8～1.3 (patent document 2); In the drying process of a polymer film, the method of setting the speed ratio (Rf/Rc) between the process speed Rc and the final winding speed Rf when the volatile component ratio of the film is 10% by weight or less is 0.9 to 1.1 (Patent Document 3) Wait.

In addition, it is known (4) that in order to obtain a polyvinyl alcohol-based film capable of producing a wide polarizing film having uniform optical properties even if it is a large area, the process of reducing the volatile component located in the polyvinyl alcohol film to 10% or less is known. The speed ratio (Rf/Rc) of the speed (Rc) of the drying roll and the take-up speed (Rf) is controlled at 0.9 to 1.1 to reduce the temperature unevenness in the drying process, thereby making the tensile elongation in the MD direction (S _M ) and the ratio (S _M /S _T ) of the tensile elongation in the TD direction (S _T ) of a polyvinyl alcohol-based film of 0.7 to 1.3 (Patent Document 4); The polyvinyl alcohol-based film of the wide-width polarizing film that has a large area and uniform optical performance, when the volatile content of the polyvinyl alcohol film reaches 10 to 50% by weight, the polyvinyl alcohol film is poured from the drum located on the most upstream side. Peel off, and make the speed ratio V2/V1 of the speed V1 of the drum positioned at the most upstream side and the speed V2 of the drum positioned at the beginning of the process where the volatile component of the polyvinyl alcohol film is less than 10% by weight be 1.0 to 1.3 (patent Document 5).

It is also known (6) that in order to provide a stretched film capable of uniform uniaxial stretching, without fine cracks and voids during stretching, and a polyvinyl alcohol-based polymer film comprising a specific skin layer/core layer/skin layer, Use the first drying roll to heat the stock solution containing the volatile component ratio of 50 to 90% by mass of the polyvinyl alcohol-based polymer, and at the same time, under the specified conditions, the polyvinyl alcohol-based polymer film that is not in contact with the first drying roll Hot air is sprayed on the surface, and the polyvinyl alcohol-based polymer film is peeled off from the first drying roll when the volatile component ratio reaches 15 to 30% by mass, and it is dried in contact with the second drying roll. At this time, the first drying roll is dried. A method in which the ratio (S ₂ /S ₁ ) of the peripheral speed (S ₁ ) of the roll to the peripheral speed (S ₂ ) of the second drying roll is 1.000 to 1.100 (Patent Document 6) and the like.

However, in the above-mentioned Patent Documents 1 to 6, there is no disclosure that the polyvinyl alcohol-based polymer film, especially a thin polyvinyl alcohol-based polymer film, is uniaxially stretched at a high magnification so that the film does not break. The scheme, especially the scheme to further increase the ultimate stretching ratio of the film.

prior art literature

patent documents

Patent Document 1: Japanese Patent Laid-Open No. 6-136151

Patent Document 2: Japanese Patent Laid-Open No. 2001-315141

Patent Document 3: Japanese Patent Laid-Open No. 2001-315146

Patent Document 4: Japanese Patent Laid-Open No. 2002-30164

Patent Document 5: Japanese Patent Laid-Open No. 2002-79531

Patent Document 6: Japanese Patent Laid-Open No. 2005-324355

non-patent literature

Non-Patent Document 1: "Polymer Science One Point 10 Optical and Physical Properties of Polymers", the third printing of the first edition, Kyoritsu Publishing Co., Ltd., December 15, 2007, p.19-21.

Contents of the invention

The problem to be solved by the invention

The purpose of the present invention is to provide a high ultimate stretching ratio, which can be stretched at a high ratio without breaking, so that it can be manufactured with good operability, high yield, low cost, and good productivity. There are polyvinyl alcohol-based polymer films of stretched films such as polarizing films with optical properties equivalent to or higher than those of products.

In particular, the purpose of the present invention is to provide a polyvinyl alcohol-based polymer film that has a high ultimate draw ratio even if it is thinner than conventionally used in the manufacture of polarizing films, and can be stretched at a high ratio without breaking. A polyvinyl alcohol-based polymer film that performs uniaxial stretching smoothly, enables thinner stretched films than before, and further shortens the drying time when producing polarizing films, and can produce polarizing films with better productivity.

Another object of the present invention is to provide a method capable of smoothly and continuously producing a polyvinyl alcohol-based polymer film having the above-mentioned excellent characteristics with high productivity.

Furthermore, the object of the present invention is to provide a polarizing film made of the above-mentioned polyvinyl alcohol-based polymer film.

means to solve the problem

The inventors of the present invention have repeatedly conducted earnest studies in order to achieve the above object. As a result, it has been found that if the birefringence in the mechanical flow direction (longitudinal direction) of a polyvinyl alcohol-based polymer film is averaged in the thickness direction of the film and The value obtained by averaging the birefringence in the width direction of the film in the thickness direction of the film satisfies a specific relationship, and the value obtained by averaging the birefringence in the width direction of the polyvinyl alcohol-based polymer film in the thickness direction of the film Within a specific numerical range, the ultimate stretching ratio of the film increases, and even if it is stretched at a high ratio, it is not easy to break the film. Good productivity Manufactures stretched films such as polarizing films with excellent optical properties such as polarizing properties. It has also been found that the ultimate draw ratio of the film is further increased when the averaged value of the birefringence in the direction of mechanical flow of the polyvinyl alcohol-based polymer film in the thickness direction of the film is within a specific numerical range.

In particular, it was found that the value obtained by averaging the birefringence in the direction of mechanical flow of the polyvinyl alcohol-based polymer film in the thickness direction of the film and the value obtained by averaging the birefringence in the width direction in the film thickness direction In the above-mentioned polyvinyl alcohol-based polymer film that satisfies a specific relationship and has a birefringence in the width direction averaged in the thickness direction of the film within a specific range, even if the film is thicker than conventional polarizing films, The thickness of polyvinyl alcohol-based polymer films commonly used in the production of polyvinyl alcohol-based polymers is thinner, with a thickness of about 30 to 65 μm, and it also has a high ultimate draw ratio, so it can be smoothly uniaxially stretched at a high ratio without breaking. Stretching enables further thinning at the time of producing a polarizing film, and further shortens the drying time at the time of producing a polarizing film.

In addition, the inventors of the present invention have found that the above-mentioned polyvinyl alcohol-based polymer film having a high ultimate draw ratio can be smoothly and continuously produced with high productivity by discharging a film-forming stock solution containing a polyvinyl alcohol-based polymer into a After being placed on the first drying roll of the film forming device of a plurality of drying rolls, the drying rolls are sequentially dried to form a film. At this time, when the volatile component ratio of the polyvinyl alcohol-based polymer film reaches 13% by mass The ratio of the peripheral speed of the drying roll to the peripheral speed of the first drying roll is within a specific value range, and the peripheral speed of the final drying roll is dried when the volatile component ratio of the polyvinyl alcohol-based polymer film reaches 13% by mass. The ratio of the peripheral speeds of the rollers is within a specific value range, so that the ratio of the peripheral speed of the final drying roller to the peripheral speed of the first drying roller is within a specific value range.

In addition, the inventors of the present invention have found that when producing a polyvinyl alcohol-based polymer film with a high ultimate draw ratio by the above-mentioned method, it is preferable to make the volatile component ratio of the polyvinyl alcohol-based polymer film when peeled from the first drying roll be between Within a specific numerical range, it is preferable that the roll surface temperature of each drying roll is 65° C. or higher. Also, if the volatile component ratio of the film-forming stock solution containing polyvinyl alcohol-based polymer is 60 to 75% by mass, and the first drying roll If the roll surface temperature is 80-120°C, even if the peripheral speed of the first drying roll reaches a high speed of 8 m/min or more, the birefringence in the mechanical flow direction of the polyvinyl alcohol-based polymer film can be smoothly produced with good productivity. The value obtained by averaging the birefringence in the thickness direction of the film and the value obtained by averaging the birefringence in the width direction in the thickness direction of the film satisfy a specific relationship, and the birefringence in the width direction is greater than that in the thickness direction of the film. Based on these findings, the polyvinyl alcohol-based polymer film whose averaged value is within a predetermined numerical range and has a high ultimate draw ratio has been further studied, and the present invention has been completed.

That is, the present invention is:

(1) A polyvinyl alcohol-based polymer film that satisfies the following formulas (I) and (II).

Δn(MD) _Ave —0.1×10 ^-3 ≤Δn(TD) _Ave ≤Δn(MD) _Ave +0.25×10 ^-3 (I)

Δn(TD) _Ave ≤2.5×10 ^-3 (II)

[In the above formula, Δn(MD) _Ave represents the value obtained by averaging the birefringence in the direction of mechanical flow of the polyvinyl alcohol-based polymer film in the thickness direction of the film, and Δn(TD) _Ave represents the value of the polyvinyl alcohol-based polymer film. The value obtained by averaging the birefringence in the width direction of the polymer film in the thickness direction of the film].

Additionally, the invention is:

(2) The polyvinyl alcohol-based polymer film of (1) above, which satisfies the following formula (III);

1.3×10 ^-3 ≤Δn(MD) _Ave ≤2.0×10 ^-3 (III); and

(3) The polyvinyl alcohol-based polymer film of the above (1) or (2), which has a thickness in the range of 30 to 65 μm.

The invention is also:

(4) A method for producing a polyvinyl alcohol-based polymer film, characterized in that,

(a) Using a film-forming device equipped with a plurality of drying rolls whose rotation axes are parallel to each other, the film-forming stock solution containing polyvinyl alcohol-based polymers is discharged in a film form onto the first drying roll of the film-forming device and partially dried , use the subsequent drying roller to further dry to form a film; at this time,

(b) The ratio of the peripheral speed (S _T ) of the drying roll to the peripheral speed (S ₁ ) of the first drying roll (S _T /S ₁ ) when the volatile component ratio of the polyvinyl alcohol-based polymer film reaches 13% by mass ) is 0.990～1.050;

(c) The ratio of the peripheral speed (S _L ) of the final drying roll to the peripheral speed (S T ) of the drying roll when the volatile component ratio _of the polyvinyl alcohol-based polymer film is 13% by mass (S _L /S _T ) 0.960~0.980;

(d) The ratio (S _L /S _{1 ) of the peripheral speed (S L ) of the final drying roll to the peripheral speed (S 1 ) of} the first drying roll is 0.970 to 1.010.

Additionally, the invention is:

(5) The production method of (4) above, wherein the ratio of volatile components of the polyvinyl alcohol-based polymer film when peeled from the first drying roll is 17 to 30% by mass;

(6) The production method of (4) or (5) above, wherein the roll surface temperature of each drying roll is 65° C. or higher; and

(7) The production method according to any one of the above (4) to (6), wherein the volatile component ratio of the film-forming stock solution containing polyvinyl alcohol-based polymers is 60 to 75% by mass, and the roll surface of the first drying roll is The temperature is 80-120° C., and the peripheral speed (S ₁ ) of the first drying roller is 8-25 m/min.

Additionally, the invention is:

(8) A polarizing film made of the polyvinyl alcohol-based polymer film according to any one of (1) to (3) above.

The effect of the invention

The polyvinyl alcohol-based polymer film of the present invention has a high ultimate stretching ratio, so when producing a stretched film, even if it is uniaxially stretched at a high ratio, it is difficult to break the film, so it can be stretched without interrupting the stretching operation. Stretched films such as polarizing films excellent in optical properties such as polarization properties are manufactured with high yield, low cost, and good productivity.

In particular, the polyvinyl alcohol-based polymer film of the present invention has a high limit even if the thickness of the film is about 30 to 65 μm, which is thinner than that of conventionally used polyvinyl alcohol-based polymer films for the production of polarizing films. The stretching ratio can be smoothly uniaxially stretched at a high ratio without breaking, so it can realize further thinning when manufacturing a stretched film, and can further shorten the drying time when manufacturing a polarizing film, etc. And can thereby improve productivity.

In addition, in recent years, polyvinyl alcohol-based polymer films with a length of more than 1000 m have also been used as original films for polarizing films, and the polyvinyl alcohol-based polymer films of the present invention have a high ultimate stretch ratio, so they can be used more than in the past. Higher magnification stretching, so the amount of polarizing film made of polyvinyl alcohol-based polymer film is more than before.

By adopting the production method of the present invention, the polyvinyl alcohol-based polymer film of the present invention having the above-mentioned excellent characteristics can be smoothly and continuously produced with high productivity.

Description of drawings

[ Fig. 1] Fig. 1 is a schematic view showing a sampling method for measuring Δn(MD) _Ave of a polyvinyl alcohol-based polymer film.

[ Fig. 2] Fig. 2 is a schematic view showing a sampling method for measuring Δn(TD) _Ave of a polyvinyl alcohol-based polymer film.

Detailed ways

Hereinafter, the present invention will be described in detail.

Generally, in a transparent film made of transparent polymers such as polyvinyl alcohol-based polymers, the polymer chains move along the flow direction (mechanical flow direction) under the action of plastic deformation and strain caused by shear stress. : length direction) orientation, the polarization directions of the atomic groups constituting the polymer are microscopically consistent, thereby producing birefringence peculiar to polymers (Non-Patent Document 1).

The birefringence [Δn(MD)] in the mechanical flow direction of the polyvinyl alcohol-based polymer film is obtained by the following formula [i], and the birefringence [Δn(TD)] in the width direction is obtained by the following formula [ii] Get it.

Δn(MD)=nMD-nz [i]

Δn(TD)=nTD-nz [ii]

[In the formula, nMD represents the refractive index in the mechanical flow direction (longitudinal direction) of the film, nTD represents the refractive index in the width direction of the film, and nz represents the refractive index in the thickness direction of the film].

As described in Non-Patent Document 1, in a film made of a transparent polymer such as a polyvinyl alcohol-based polymer, the polymer chains forming the film are easily oriented along the mechanical flow direction (longitudinal direction), including the above-mentioned Patent Documents 1 to 10. In the polyvinyl alcohol-based polymer film described in 6, generally, "birefringence in the direction of mechanical flow [Δn(MD)]" > "birefringence in the width direction [Δn(TD) )]", that is, the birefringence [Δn(MD)] in the direction of mechanical flow tends to be larger than the birefringence [Δn(TD)] in the width direction.

In contrast, the polyvinyl alcohol-based polymer film of the present invention is different from conventional polyvinyl alcohol-based polymer films in that it satisfies the following formulas (I) and (II).

Δn(MD) _Ave —0.1×10 ^-3 ≤Δn(TD) _Ave ≤Δn(MD) _Ave +0.25×10 ^-3 (I)

Δn(TD) _Ave ≤2.5×10 ^-3 (II)

[In the above formula, Δn(MD) _Ave represents the value obtained by averaging the birefringence in the direction of mechanical flow of the polyvinyl alcohol-based polymer film in the thickness direction of the film, and Δn(TD) _Ave represents the value of the polyvinyl alcohol-based polymer film. The value obtained by averaging the birefringence in the width direction of the polymer film in the thickness direction of the film].

That is, as can be seen from the above formula (I), in the polyvinyl alcohol-based polymer film of the present invention (hereinafter, "polyvinyl alcohol" is sometimes referred to as "PVA"), the mechanical flow direction of the PVA-based polymer film (continuous production of PVA) The value "Δn(MD) _Ave " obtained by averaging the birefringence in the film's thickness direction) [hereinafter sometimes referred to as "longitudinal direction (MD)"] in the line direction of the polymer film) is the same as that of PVA-based polymers. "Δn(TD) _Ave "Equal or smaller, or even if it exceeds "Δn(TD) _Ave ", its amount is very small.

The PVA-based polymer film of the present invention has a feature of satisfying the above formula (II) in addition to the formula (I).

The PVA-based polymer film of the present invention satisfies the above formulas (I) and (II), so even when the thickness of the film is thinner than before, it has a high ultimate stretching ratio, so even when stretched in the manufacture of polarizing films, etc. When the film is uniaxially stretched at a high rate, it is not easy to break the film, and the stretching operation will not be interrupted due to the break of the film, and it can be produced with high yield and good productivity. Films with excellent optical properties such as polarization properties stretch film.

If the above formula (I) is not satisfied, the ultimate stretching ratio of the PVA-based polymer film is lowered, and the film tends to break when uniaxially stretched at a high ratio, especially when the thickness of the film is thin.

The PVA-based polymer film of the present invention preferably satisfies the following formula (I'), more preferably satisfies the following formula (I''), and further preferably satisfies the following formula (I''').

Δn(MD) _Ave -0.05×10 ^-3 ≤Δn(TD) _Ave ≤Δn(MD) _Ave +0.23×10 ^-3 (I')

Δn(MD) _Ave ≤Δn(TD) _Ave ≤Δn(MD) _Ave +0.2×10 ^-3 (I'')

Δn(MD) _Ave +0.05×10 ^-3 ≤Δn(TD) _Ave ≤Δn(MD) _Ave +0.18×10 ^-3 (I''')

In addition, if the Δn(TD) _Ave of the PVA-based polymer film is greater than 2.5× ^10-3 , outside the range of the above-mentioned formula (II), the ultimate draw ratio of the PVA-based polymer film will decrease, and it will be difficult to make the PVA-based polymer film A film is stretched at a high ratio in the longitudinal direction (MD), and it is difficult to obtain a stretched film having excellent optical properties.

In order to excessively reduce Δn(TD) _Ave , it is necessary to allow drying shrinkage in the width direction when producing a PVA-based polymer film, and the effective width yield of the PVA-based polymer film tends to decrease. Therefore, the PVA-based polymer of the present invention The Δn(TD) _Ave of the thin film is preferably in the range of 1.5×10 ^-3 to 2.2×10 ^-3 , more preferably in the range of 1.6×10 ^-3 to 2.0×10 ^-3 .

The PVA-based polymer film of the present invention preferably satisfies the following formula (III) in addition to the above formulas (I) and (II).

1.3×10 ^-3 ≤Δn(MD) _Ave ≤2.0×10 ^-3 (III)

When the Δn(MD) _Ave of the PVA-based polymer film is below 2.0× ^10-3 , the ultimate draw ratio of the PVA-based polymer film is further improved, and it is easy to draw the PVA-based polymer film at a high ratio in the longitudinal direction (MD). Stretching makes it easier to obtain stretched films with excellent optical properties. On the other hand, in order to make the Δn(MD) _Ave of the PVA-based polymer film less than 1.3×10 ^-3 , it is necessary to greatly reduce the peripheral speed ratio of the drying roll, so the PVA-based polymer film is likely to be caught between the drying rolls during film production. tendency to relax.

The Δn(MD) _Ave of the PVA-based polymer film of the present invention is more preferably in the range of 1.4×10 ^-3 to 1.95×10 ^-3 , still more preferably in the range of 1.5×10 ^-3 to 1.9×10 ^-3 .

In addition, in the PVA-based polymer film, the value of Δn(MD) _Ave and/or Δn(TD) _Ave often fluctuates in the width direction (TD) of the film, especially at both ends of the width direction, Δn(MD) ) _Ave is easy to rise, but as long as it satisfies formulas (I) and (II) at least in the central part of the width direction (TD) of the PVA-based polymer film, and preferably satisfies formulas (I) to (III), preferably in the following The central part of the width direction (TD) of the PVA-based polymer film is the center of the width direction (TD) 80% or more of the entire area of the part satisfies the formulas (I) and (II), preferably satisfy the formulas (I) to ( III). Both ends in the width direction (TD) of the PVA-based polymer film that does not satisfy the formulas (I) and (II) can be cut and removed (trimmed) before stretching the PVA-based polymer film in the longitudinal direction (MD). .

“Δn(MD) _Ave ” of the PVA-based polymer film [a value obtained by averaging the birefringence in the longitudinal direction (MD) of the PVA-based polymer film in the thickness direction of the film] and “Δn(TD) _Ave "[A value obtained by averaging the birefringence in the width direction (TD) of the PVA-based polymer film in the thickness direction of the film] can be measured by the following method.

《1》Determination of Δn(MD) _Ave :

(Here, the measurement method of Δn(MD) _Ave in the central part of the width direction (TD) of the PVA-based polymer film is exemplified.)

(i) At any position in the longitudinal direction (MD) of the PVA-based polymer film, cut out a size of MD×TD=2mm×10mm from the center of the film in the width direction (TD) as shown in Figure 1(a) The thin slices were clamped from both sides with PET films with a thickness of 100 μm, clamped in a wooden frame, and installed in a microtome device.

(ii) Next, cut the flakes collected as described above at intervals of 10 μm parallel to the length direction (MD) of the flakes as shown in Figure 1(b) (the PET film and wooden frame are not shown), and produce 10 A slice for observation (MD×TD=2mm×10μm) shown in Figure 1(c). Five slices with smooth cut surfaces and no unevenness in slice thickness were selected from the slices, each of which was mounted on a glass slide, and the slice thickness was measured with a microscope (manufactured by Keyence Corporation). In addition, observation was performed within the field of view of 10 times the eyepiece and 20 times the objective lens (200 times in total).

(iii) Next, in order to be able to observe the cut surface, put the section upside down as shown in Figure 1(d), place the cut surface on a glass slide, seal it with a cover glass and silicone oil (refractive index 1.04), and use a two-dimensional The photoelastic evaluation system "PA-micro" (manufactured by Photonic Lattice Co., Ltd.) measured the retardation of 5 slices.

(iv) With the retardation distribution of each slice displayed on the measurement screen of "PA-micro", draw a line α perpendicular to the original surface of the film across the slice, and perform linearization on this line segment α. For analysis, the retardation distribution data in the thickness direction of the film is obtained. In addition, observation was performed within the field of view of 10 times the eyepiece and 20 times the objective lens (200 times in total). In addition, in order to suppress the error caused by the change of the position where the line segment α passes on the slice, the line width was set to 300 pixels, and the average value of the delay was taken.

(v) Divide the value of the retardation distribution in the thickness direction of the film obtained as described above by the thickness measured with a microscope to obtain the birefringence Δn(MD) distribution in the thickness direction of the film, and take the value of the retardation distribution in the thickness direction of the film Average value of birefringence Δn(MD) distribution. The average value of the distribution of birefringence Δn(MD) in the thickness direction of the film obtained for each of the five slices was further averaged to be "Δn(MD) _Ave ".

《2》Determination of Δn(TD) _Ave :

(Here exemplified is the measurement method of Δn(TD) _Ave in the central part of the width direction (TD) of the PVA-based polymer film.)

(i) At any position in the longitudinal direction (MD) of the PVA-based polymer film, cut out a size of MD×TD=10mm×2mm from the center of the film in the width direction (TD) as shown in Figure 2(a) The thin slices were clamped from both sides with PET films with a thickness of 100 μm, clamped in a wooden frame, and installed in a microtome device.

(ii) Next, cut the flakes collected as described above at intervals of 10 μm parallel to the width direction (TD) of the flakes as shown in FIG. A section for observation (MD×TD=10μm×2mm) shown in Fig. 2(c). Five slices with smooth cut surfaces and no unevenness in slice thickness were selected from the slices, each of which was mounted on a glass slide, and the slice thickness was measured with a microscope (manufactured by Keyence Corporation). In addition, observation was performed within the field of view of 10 times the eyepiece and 20 times the objective lens (200 times in total).

(iii) Next, in order to observe the cut surface, put the slice down as shown in Figure 2(d), place the cut surface on a glass slide, seal it with a cover glass and silicone oil (refractive index 1.04), and use a two-dimensional The photoelastic evaluation system "PA-micro" (manufactured by Photonic Lattice Co., Ltd.) measured the retardation of 5 slices.

(iv) With the retardation distribution of each slice displayed on the measurement screen of "PA-micro", draw a line β perpendicular to the original surface of the film across the slice, and perform linearization on this line segment β. For analysis, the retardation distribution data in the thickness direction of the film is obtained. In addition, observation was performed within the field of view of 10 times the eyepiece and 20 times the objective lens (200 times in total). In addition, in order to suppress an error due to a change in the position where the line segment β on the slice passes, the line width was set to 300 pixels, and the average value of the delay was taken.

(v) Divide the value of the retardation distribution in the thickness direction of the film obtained as described above by the thickness measured with a microscope to obtain the birefringence Δn(TD) distribution in the thickness direction of the film, and take the value of the retardation distribution in the thickness direction of the film Average value of birefringence Δn(TD) distribution. The average value of the distribution of birefringence Δn(TD) in the thickness direction of the film obtained for each of the five slices was further averaged to be "Δn(TD) _Ave ".

The thickness of the PVA-based polymer film of the present invention can be within the range of 5 to 150 μm, and when used as an original film for a polarizing film, etc., it is preferably 30 to 65 μm. The PVA-based polymer film of the present invention has a high ultimate draw ratio, so even if the film thickness is 30 to 65 μm as described above, it is thinner than the PVA-based polymer film with a thickness of about 75 μm, which is often used as a raw film for polarizing films. Even in the case of the film, it can be stretched at a high ratio without breaking the film, so it is possible to produce stretched products with optical properties such as polarization performance equal to or higher than that of existing products, smoothly and with good productivity at a high yield. film, and by stretching a PVA-based polymer film with a thickness of 30 to 65 μm at a high ratio, the thickness of the stretched film can be thinner than before, and the drying time when manufacturing a polarizing film can be shortened, and the polarizing film can be improved. Membrane manufacturing speed.

If the thickness of the PVA-based polymer film is too thick, it will be difficult to dry rapidly when making a polarizing film. prone to membrane rupture.

The width of the PVA-based polymer film of the present invention is not particularly limited, but in recent years, due to the enlargement of liquid crystal televisions and display screens, in order to be effectively used therein, the width is preferably 2 m or more, more preferably 3 m or more, More preferably, it is 4 m or more. In addition, when a polarizing plate is actually produced by a production machine, uniform uniaxial stretching becomes difficult if the film width is too large, so the width of the PVA-based polymer film is preferably 8 m or less.

The mass swelling degree of the PVA-based polymer film of the present invention is preferably 180-250%, more preferably 185-240%, and still more preferably 190-230%. If the mass swelling of the PVA-based polymer film is too low, it will be difficult to stretch, and there is a tendency that it will be difficult to manufacture a stretched film with excellent optical properties. On the other hand, if the mass swelling is too high, the process passability during stretching will be difficult. It deteriorates, and a highly durable polarizing film may not be obtained.

The mass swelling degree mentioned here refers to the percentage of the value obtained by dividing the mass of the PVA-based polymer film immersed in distilled water at 30° C. for 30 minutes by the mass obtained after drying at 105° C. for 16 hours after the above-mentioned immersion. It can be determined by the method described in the following examples.

As the PVA-based polymer that forms the PVA-based polymer film of the present invention, for example, PVA obtained by saponifying polyvinyl ester obtained by polymerizing vinyl ester, graft-copolymerized comonomer on the main body of PVA, etc. Modified PVA polymers obtained on the chain, modified PVA polymers made by saponifying modified polyvinyl esters obtained by copolymerizing vinyl esters and comonomers, unmodified PVA or modified A so-called polyvinyl acetal resin obtained by cross-linking a part of the hydroxyl groups of a permanent PVA-based polymer with aldehydes such as formaldehyde, butyraldehyde, and benzaldehyde.

When the PVA-based polymer forming the PVA-based polymer film of the present invention is a modified PVA-based polymer, the modification amount of the PVA-based polymer is preferably 15 mol% or less, more preferably 5 mol% or less.

Examples of the vinyl ester used in the production of PVA-based polymers include vinyl acetate, vinyl formate, vinyl laurate, vinyl propionate, vinyl butyrate, vinyl pivalate, tertiary carbonic acid Vinyl esters, vinyl stearate, vinyl benzoate, etc. These vinyl esters may be used alone or in combination. Among these vinyl esters, vinyl acetate is preferable from the viewpoint of productivity.

In addition, as the above-mentioned copolymer, for example, olefins (α-olefins, etc.) having 2 to 30 carbon atoms such as ethylene, propylene, 1-butene, and isobutylene; acrylic acid or its salt; methyl acrylate, ethyl acrylate, Acrylates such as n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate, etc. (e.g. C1-C18 alkyl esters of acrylic acid); methacrylic acid or its salts; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, methyl n-butyl acrylate, isobutyl methacrylate, tert-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, etc. Acrylates (e.g. C1-C18 alkyl esters of methacrylic acid); acrylamide, N-methacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetone acrylamide , acrylamidopropanesulfonic acid or its salt, acrylamidopropyl dimethylamine or its salt, N-methylolacrylamide or its derivatives and other acrylamide derivatives; methacrylamide, N-methyl formaldehyde methacrylamide, N-ethylmethacrylamide, methacrylamidopropanesulfonic acid or its salts, methacrylamidopropyldimethylamine or its salts, N-methylolmethacrylamide or its salts Derivatives and other methacrylamide derivatives; N-vinyl formamide, N-vinyl acetamide, N-vinyl pyrrolidone and other N-vinyl amides; methyl vinyl ether, ethyl vinyl ether, n- Propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tert-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, etc. Base ethers; nitriles such as acrylonitrile and methacrylonitrile; vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride and other halogenated vinyl compounds; allyl compounds such as allyl acetate and chloropropene; Unsaturated dicarboxylic acids such as acid and itaconic acid, their salts or their esters and other derivatives; vinyl silyl compounds such as vinyltrimethoxysilane; isopropenyl acetate; unsaturated sulfonic acid or its derivatives, etc. Among them, α-olefins are preferred, and ethylene is particularly preferred.

From the viewpoint of the polarizing performance and durability of the resulting polarizing film, the average degree of polymerization of the PVA-based polymer forming the PVA-based polymer film of the present invention is preferably 1,000 or more, more preferably 1,500 or more, and even more preferably 2,000. above. On the other hand, the upper limit of the average degree of polymerization of the PVA-based polymer is preferably 8,000 or less, particularly preferably 6,000 or less, from the viewpoint of ease of production and stretchability of a homogeneous PVA-based polymer film.

Here, the "average degree of polymerization" of the PVA-based polymer in this specification refers to the average degree of polymerization measured in accordance with JIS K6726-1994, which is measured in water at 30°C after re-saponification and purification of the PVA-based polymer. The intrinsic viscosity is obtained.

From the viewpoint of the polarizing performance and durability of the resulting polarizing film, the degree of saponification of the PVA-based polymer forming the PVA-based polymer film of the present invention is preferably 95.0 mol% or more, more preferably 98.0 mol% or more, and furthermore Preferably it is 99.0 mol% or more, most preferably 99.3 mol% or more.

Here, the "saponification degree" of the PVA-based polymer in this specification refers to the total number of moles of structural units (typically vinyl ester units) and vinyl alcohol units that can be converted into vinyl alcohol units by saponification. Proportion (mol %) of the number of moles of vinyl alcohol units. The degree of saponification of the PVA-based polymer was measured in accordance with the description in JIS K6726-1994.

The method for making the PVA-based polymer film of the present invention is not particularly limited, as long as it is a method of meeting the PVA-based polymer film of the above formula (I) and (II), it can be manufactured by any method, and the present invention The PVA-based polymer film can be smoothly and continuously manufactured with high productivity by the manufacturing method of the present invention, and the manufacturing method comprises the steps of:

(a) Using a film-forming device equipped with a plurality of drying rollers whose rotating shafts are parallel to each other, the film-forming stock solution containing a PVA-based polymer is discharged in a film form onto the first drying roller of the film-forming device and partially dried, then Subsequent drying rolls are further dried to form a film; at this time,

(b) The ratio (S _T /S ₁ ) of the peripheral speed (S _T ) of the drying roll to the peripheral speed (S ₁ ) of the first drying roll when the volatile component ratio of the PVA-based polymer film reaches 13% by mass is: 0.990～1.050;

(c) The ratio (S _L /S _T ) of the peripheral speed (S _T ) of the drying roll when the ratio of the peripheral speed (S _L ) of the final drying roll to the volatile component of the PVA-based polymer film is 13% by mass is 0.960 ~0.980;

(d) The ratio (S _L /S _{1 ) of the peripheral speed (S L ) of the final drying roll to the peripheral speed (S 1 ) of} the first drying roll is 0.970 to 1.010.

The method for producing the above-mentioned PVA-based polymer film of the present invention will be described more specifically below.

The film-forming stock solution containing the PVA-based polymer can be prepared by mixing the PVA-based polymer with a liquid medium to form a solution, or by melting PVA-based polymer particles or the like containing a liquid medium to form a melt.

The dissolution of the PVA-based polymer in the liquid medium and the melting of the PVA-based polymer pellets containing the liquid medium or the like can be carried out using a stirring mixing device, a melt extruder, or the like.

As the liquid medium used at this time, for example, water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylenediamine, diethylenetriamine, etc., these liquid The media may be used alone or in combination of two or more. Among them, water, dimethyl sulfoxide or a mixture of both is preferably used, and water is particularly preferably used.

From the viewpoints of promoting the dissolution and melting of the PVA-based polymer in the liquid medium, improving the process passability during film production, and improving the stretchability of the obtained PVA-based polymer film, it is preferable to add an additive to the film-forming stock solution. plasticizer.

As a plasticizer, polyhydric alcohol is preferably used, such as ethylene glycol, glycerin, diglycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, etc., these plasticizers Agents can be used alone or in combination of two or more. Among them, one or more of glycerin, diglycerin, and ethylene glycol are preferably used from the viewpoint of excellent stretchability-enhancing effects.

The amount of the plasticizer added is preferably 0 to 30 parts by mass, more preferably 3 to 25 parts by mass, and particularly preferably 5 to 20 parts by mass relative to 100 parts by mass of the PVA-based polymer. When the amount of the plasticizer added is more than 30 parts by mass relative to 100 parts by mass of the PVA-based polymer, the obtained PVA-based polymer film may be too soft and handleability may decrease.

It is preferable to add a surfactant to the film-forming stock solution from the viewpoint of improving peelability from a drying roll during production of a PVA-based polymer film, handling properties of the obtained PVA-based polymer film, and the like. The type of surfactant is not particularly limited, but anionic surfactants or nonionic surfactants are preferably used.

The anionic surfactant is preferably, for example, a carboxylic acid type such as potassium laurate, a sulfate ester type such as octyl sulfate, or a sulfonic acid type such as dodecylbenzenesulfonate.

In addition, as the nonionic surfactant, for example, alkyl ether types such as polyoxyethylene oleyl ether, alkyl phenyl ether types such as polyoxyethylene octylphenyl ether, and alkyl esters such as polyoxyethylene laurate are preferable. type, alkylamine type such as polyoxyethylene lauryl amino ether, alkylamide type such as polyoxyethylene lauramide, polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether, alkanolamide type such as oleic acid diethanolamide, Allyl phenyl ether type nonionic surfactants such as polyoxyalkylene allyl phenyl ether. These surfactants may be used alone or in combination of two or more.

The amount of the surfactant added is preferably 0.01 to 1 part by mass, more preferably 0.02 to 0.5 part by mass, and particularly preferably 0.05 to 0.3 part by mass relative to 100 parts by mass of the PVA-based polymer. If it is less than 0.01 parts by mass, it may be difficult to show the effect of improving film forming properties and peelability. On the other hand, if it is more than 1 part by mass, the surfactant may be eluted on the surface of the film, causing blocking, and the handling property is reduced. .

The film-making stock solution can contain various additives within the range that does not hinder the characteristics of the PVA-based polymer film of the present invention, such as stabilizers (such as antioxidants, ultraviolet absorbers, heat stabilizers, etc.), compatibilizers (compatibilizers, etc.) ), anti-blocking agent, flame retardant, antistatic agent, lubricant, dispersant, fluidizing agent, antibacterial agent, etc. These additives may be used alone or in combination of two or more.

The ratio of volatile components of the film-forming stock solution used in the production of the PVA-based polymer film is preferably 60 to 75% by mass, more preferably 65 to 70% by mass. If the volatile component ratio of the membrane-forming stock solution is less than 60% by mass, the viscosity of the film-forming stock solution increases, making it difficult to perform filtration and defoaming, and in addition, film formation itself may be difficult. On the other hand, if the volatile component ratio of the film-forming stock solution exceeds 75% by mass, the viscosity may be too low, and the uniformity of the thickness of the PVA-based polymer film may be impaired.

Here, the "ratio of volatile components of the film-forming stock solution" referred to in this specification refers to the ratio of volatile components obtained by the following formula [iii].

The volatile component ratio (mass%) of the film-making stock solution={(Wa-Wb)/Wa}×100 [iii]

[In the formula, Wa represents the mass (g) of the film-forming stock solution, and Wb represents the mass (g) after drying the film-forming stock solution of Wa (g) in an electric dryer at 105° C. for 16 hours. ]

In the film forming apparatus provided with a plurality of drying rolls whose rotation axes are parallel to each other used in the production of the PVA-based polymer film, the number of drying rolls is preferably 3 or more, more preferably 4 or more, and still more preferably 5 to 30.

The plurality of drying rollers are preferably made of metal such as nickel, chromium, copper, iron, and stainless steel, for example, and are particularly preferably made of a metal material whose roller surface is not easily corroded and has a specular luster. In addition, in order to improve the durability of the drying roll, it is more preferable to use a drying roll plated with a single layer or a combination of two or more layers of a nickel layer, a chromium layer, a nickel/chromium alloy layer, or the like.

The roll surface temperature of each drying roll among the plurality of drying rolls is preferably 65°C or higher, more preferably 75°C or higher. In addition, as the roll surface temperature of each drying roll, the roll surface temperature of the drying roll that can be used as a heat treatment roll in the final process or a process close thereto is preferably 100° C. or higher, more preferably 100 to 120° C. The roll surface temperature of the outer drying roll is preferably 100°C or lower.

The film forming apparatus used in the present invention may have a hot air drying apparatus of a hot air furnace type, a heat treatment apparatus, a humidity control apparatus, and the like after a plurality of drying rolls as necessary.

When the film-forming stock solution containing the PVA-based polymer is discharged in the form of a film onto the first drying roll of the film-forming device, for example, a T-shaped slot die, a hopper plate (hopper plate), an I-die, and a lip coater die are used. A known film-form discharge device (film-form casting device) such as the present invention discharges (casts) a film-forming stock solution containing a PVA-based polymer onto a first drying roll in the form of a film.

On the first drying roll, the liquid containing the PVA-based polymer discharged in film form is dried on the first drying roll, and the volatile component ratio in the PVA-based polymer film is preferably 17 to 30% by mass, more preferably 17 to 30% by mass. 29% by mass, more preferably 18 to 28% by mass, is peeled off from the first drying roll.

If the volatile component ratio of the PVA-based polymer film when peeled off from the first drying roll is less than 17% by mass, the value of Δn(MD) _Ave increases relative to Δn(TD) _Ave and does not satisfy the formula (I) Tendency, on the other hand, if the volatile component ratio of the PVA-based polymer film when peeled from the first drying roll is more than 30% by mass, it may be difficult to peel off from the first drying roll, sometimes breakage may occur, or unevenness may easily occur. tendency.

Here, "the volatile component ratio of a PVA-type polymer film or a PVA-type polymer film" in this specification means the volatile component ratio calculated|required by following formula [iv].

A(mass%)={(Wc-Wd)/Wc}×100 [iv]

[In the formula, A represents the volatile component ratio (mass %) of the PVA-based polymer film or the PVA-based polymer film, Wc represents the mass (g) of the sample collected from the PVA-based polymer film or the PVA-based polymer film, Wd It represents the mass (g) when the above-mentioned sample Wc (g) was dried in a vacuum dryer at a temperature of 50° C. and a pressure of 0.1 kPa or less for 4 hours].

In the PVA-based polymer film or PVA-based polymer film formed from a film-forming stock solution prepared with PVA-based polymers, glycerin and other polyols (plasticizers), surfactants, and water, at the above-mentioned "temperature 50°C, When drying under the conditions of pressure below 0.1kPa and 4 hours", mainly only water volatilizes, and other components other than water hardly volatilize, and remain in the PVA-based polymer film or PVA-based polymer film, so the PVA-based polymer film or The volatile component ratio of the PVA-based polymer film can be obtained by measuring the water content (water ratio) contained in the PVA-based polymer film or the PVA-based polymer film.

When drying with the first drying roll, the roll surface temperature of the first drying roll is preferably 80 to 120° C., more preferably 85 to 105° C., and even more preferably 93 to 99° C. from the viewpoint of uniform drying and drying speed. ℃. If the surface temperature of the first drying roll is higher than 120°C, the film tends to foam, while if it is lower than 80°C, the drying on the first drying roll is insufficient, causing poor peeling.

From the standpoints of uniform drying, drying speed, and productivity of PVA-based polymer films, the peripheral speed (S ₁ ) of the first drying roll is preferably 8 to 25 m/min, more preferably 11 to 23 m/min, and further Preferably it is 14 to 22 m/min. If the peripheral speed (S ₁ ) of the first drying roll is less than 8 m/min, productivity decreases and birefringence tends to increase, which is not preferable. On the other hand, when the peripheral speed (S ₁ ) of the first drying roll exceeds 25 m/min, the drying on the first drying roll tends to be insufficient, which is not preferable.

Partial drying of the film-forming stock solution containing the PVA-based polymer discharged in the form of a film on the first drying roll can be performed only by using heat from the first drying roll, but from the viewpoints of uniform drying, drying speed, etc., It is preferable to spray hot air on the film surface not in contact with the first drying roller (hereinafter sometimes referred to as "first drying roller non-contact surface") while heating with the first drying roller, and to apply heat from both sides of the PVA-based polymer film. to dry.

When the first drying roll non-contact surface of the PVA-based polymer film on the first drying roll is sprayed with hot air, it is preferred to spray hot air with a wind speed of 1 to 10 m/sec over the entire area of the first dry roll non-contact surface, more preferably spray Hot air with a wind speed of 2 to 8 m/sec, more preferably hot air with a wind speed of 3 to 8 m/sec.

If the wind speed of the hot air sprayed on the non-contact surface of the first drying roll is too small, it will be difficult to obtain a PVA-based polymer film with a high ultimate draw ratio as the object of the present invention, and water vapor will be generated during drying on the first drying roll. Such as dew condensation, the water droplets drip onto the PVA-based polymer film, and defects are likely to occur in the finally obtained PVA-based polymer film. On the other hand, if the wind speed of the hot air sprayed on the non-contact surface of the first drying roll is too high, it is difficult to obtain a PVA-based polymer film with a high ultimate draw ratio as the object of the present invention, and the PVA-based polymer film finally obtained Thickness unevenness occurs in the film, and problems such as uneven dyeing tend to occur accordingly.

From the viewpoint of drying efficiency, uniformity of drying, etc., the temperature of the hot air sprayed on the non-contact surface of the first drying roller of the PVA-based polymer film is preferably 50 to 150°C, more preferably 70 to 120°C, and even more preferably It is 80-95°C. Moreover, it is preferable that the dew point temperature of the hot air blown to the non-contact surface of the 1st drying roll of a PVA-type polymer film is 10-15 degreeC. If the temperature of the hot air sprayed on the non-contact surface of the first drying roller of the PVA-based polymer film is too low, drying efficiency, uniform drying, etc. tend to decrease, while if it is too high, foaming tends to occur.

The method for spraying hot air to the non-contact surface of the first drying roll of the PVA-based polymer film is not particularly limited, and can be used to spray the hot air at a uniform velocity to the non-contact surface of the first drying roll of the PVA-based polymer film, preferably as a whole. As for any method of hot air having a uniform temperature, it is preferable to use a nozzle method, a straightening plate method, or a combination thereof. The injection direction of the hot air on the non-contact surface of the first drying roll of the PVA-based polymer film may be the direction opposite to the non-contact surface of the first drying roll, or may be substantially along the first drying roll of the PVA-based polymer film. The direction of the circumferential shape of the non-contact surface (the direction substantially along the circumference of the roll surface of the first drying roll) or other directions may also be used.

In addition, when drying the PVA-based polymer film on the first drying roll, it is preferable to exhaust the volatile components generated from the PVA-based polymer film by drying and the sprayed hot air. The method of exhausting is not particularly limited, and it is preferable to adopt an exhausting method that does not cause uneven wind speed and uneven temperature of the hot air sprayed on the non-contact surface of the first drying roller of the PVA-based polymer film.

The PVA-based polymer film that is preferably dried on the first drying roll until the volatile component ratio reaches 17 to 30% by mass is peeled off from the first drying roll. This time, the non-contact surface of the first drying roll of the PVA-based polymer film is preferably Opposed to the second drying roller, drying is carried out with the second drying roller,

The ratio (S ₂ /S ₁ ) of the peripheral speed (S ₂ ) of the second drying roll to the peripheral speed (S 1 ₎ of the first drying roll is preferably 1.005-1.090, more preferably 1.010-1.080. If the ratio (S ₂ /S ₁ ) is less than 1.005, the peeling point of the PVA-based polymer film from the first drying roll tends to be non-uniform, and the birefringence unevenness in the width direction increases, and sometimes it cannot be used as an optical film. Membrane original membrane. Furthermore, if the ratio (S ₂ /S ₁ ) is greater than 1.090, it is difficult to obtain the PVA-based polymer film of the present invention having a high ultimate draw ratio.

When drying with a second drying roll, the roll surface temperature of the second drying roll is preferably 65 to 100°C, more preferably 65 to 98°C, and even more preferably 75 to 96°C from the viewpoint of uniform drying, drying speed, etc. ℃.

The PVA-based polymer film dried with the second drying roll is peeled off from the second drying roll, and the third drying roll, the fourth drying roll, the fifth drying roll, ... Wait for multiple drying rollers to dry in sequence.

At this time, in the present invention, drying is performed while adjusting the tension applied to the PVA-based polymer film so that the peripheral speed (S _T ) of the drying roller when the volatile component ratio of the PVA-based polymer film reaches 13% by mass is relative to The ratio (S _T /S ₁ ) of the peripheral speed (S ₁ ) of the first drying roller is 0.990˜1.050. Here, as "the drying roll when the volatile component ratio of the PVA-based polymer film reaches 13% by mass", when the volatile component ratio of the PVA-based polymer film reaches 13% by mass on the drying roll, it refers to the drying roll, When the ratio of the volatile components reaches 13% by mass between the two drying rolls, it refers to the latter drying roll among the two drying rolls. When the ratio (S _T /S ₁ ) is within the above range, problems such as film slack and entanglement do not occur in the drying process until the volatile component ratio of the PVA-based polymer film reaches 13% by mass, and can be smoothly produced. The value obtained by averaging the birefringence in the longitudinal direction (MD) in the thickness direction of the film [Δn(MD) _Ave ] and the averaged value of the birefringence in the width direction (TD) in the thickness direction of the film [Δn(TD) _Ave ] A PVA-based polymer film of the present invention that satisfies the above formulas (I) and (II), and further satisfies the above formula (III).

The aforementioned ratio (S _T /S ₁ ) at the time of producing a PVA-based polymer film is preferably 1.000 to 1.045.

In the present invention, the PVA-based polymer film having a volatile component ratio of 13% by mass is further dried with a subsequent drying roll to obtain a PVA-based polymer film. At this time _, in _the present invention, the ratio (S _L /S _T ) in the range of 0.960 to 0.980 while drying. When the ratio (S _L /S _T ) is within the above range, problems such as film slack and entanglement do not occur in the drying process until the final PVA-based polymer film is obtained, and the longitudinal direction (MD) can be smoothly produced. The value obtained by averaging the birefringence in the thickness direction of the film [Δn(MD) _Ave ] and the value obtained by averaging the birefringence in the width direction (TD) in the thickness direction of the film [Δn(TD) _Ave ] The PVA-based polymer film of the present invention that satisfies the above formulas (I) and (II), and further satisfies the above formula (III).

The above ratio (S _L /S _T ) when producing a PVA-based polymer film is preferably 0.963 to 0.976.

In addition, when a PVA-based polymer film is produced by the above method, the birefringence in the longitudinal direction (MD) of the PVA-based polymer film is averaged in the thickness direction of the film [Δn(MD) _Ave ] and the width The value [Δn(TD) _Ave ] obtained by averaging the birefringence in the direction (TD) in the thickness direction of the film is determined by the peripheral speed (S ₁ ) of the first drying roll and the peripheral speed (S _L ) of the final drying roll The ratio (S _L /S ₁ ) changes. In order to smoothly manufacture the PVA-based polymer film of the present invention satisfying the above formulas (I) and (II), and further satisfying the above formula (III), it is necessary to make the peripheral speed (S _L ) of the final drying roll relative to that of the first drying roll. The ratio (S _L /S ₁ ) of the peripheral speed (S ₁ ) of the roller is in the range of 0.970 to 1.010, preferably in the range of 0.972 to 1.008, more preferably in the range of 0.975 to 1.006. Thereby, a PVA-based polymer film satisfying the above formulas (I) and (II) and further satisfying the above formula (III) can be smoothly produced while suppressing the occurrence of wrinkles and slack.

In the above-mentioned manufacturing method of the present invention, the final drying roll or the near-final drying roll and the final drying roll may be used as heat treatment rolls by raising the surface temperature thereof. When a drying roll is used as a heat treatment roll, the roll surface temperature is preferably 90 to 140°C, more preferably 100 to 130°C.

In addition, a heat treatment device may be provided separately from the drying roll.

The heating direction when the PVA-based polymer film is dried in the process from the first drying roll to the final drying roll is not particularly limited, because the PVA-based polymer film can be dried more uniformly, so it is preferable to use any of the PVA-based polymer films. The front and back sides of the part are dried in such a manner that they alternately come into contact with each drying roll from the first drying roll to the final drying roll.

The PVA-based polymer film subjected to the above-mentioned drying treatment may be subjected to heat treatment, humidity-conditioning treatment, etc. as necessary, and finally wound into a roll with a predetermined length to obtain the PVA-based polymer film of the present invention.

The volatile component ratio of the PVA-based polymer film finally obtained through the above series of treatments is preferably in the range of 1 to 5% by mass, more preferably in the range of 2 to 4% by mass.

When producing a polarizing film from the PVA-based polymer film of the present invention, for example, the PVA-based polymer film can be dyed, uniaxially stretched, fixed, dried, and optionally heat-treated. The order of dyeing and uniaxial stretching is not particularly limited, and dyeing may be performed before uniaxial stretching, simultaneously with uniaxial stretching, or after uniaxial stretching. deal with. In addition, processes such as uniaxial stretching and dyeing can be repeated many times.

As the dye used in the dyeing of PVA polymer film, iodine or dichroic organic dye (such as direct black (DirectBlack) 17,19,154; direct brown (DirectBrown) 44,106,195,210,223 can be used; Direct Red (DirectRed) 2, 23, 28, 31, 37, 39, 79, 81, 240, 242, 247; Direct Blue (DirectBlue) 1, 15, 22, 78, 90, 98, 151, 168, 202, 236, 249, 270; direct purple (DirectViolet) 9, 12, 51, 98; direct green (DirectGreen) 1, 85; direct yellow (DirectYellow) 8, 12, 44, 86, 87; direct orange (DirectOrange) 26, 39, 106, 107 and other dichroic dyes), etc. These dyes may be used alone or in combination of two or more. Dyeing can usually be carried out by immersing a PVA-based polymer film in a solution containing the above-mentioned dye, and the treatment conditions and treatment methods are not particularly limited.

The uniaxial stretching of the PVA-based polymer film in the longitudinal direction (MD) can be performed by either a wet stretching method or a dry heat stretching method. In the case of uniaxial stretching by a wet stretching method, it may be uniaxially stretched in warm water containing boric acid, or may be uniaxially stretched in a solution containing the above-mentioned dye or in a fixed treatment bath as described below, It is also possible to uniaxially stretch the PVA-based polymer film after water absorption in air, or to perform uniaxial stretching by other methods. The stretching temperature during the uniaxial stretching treatment is not particularly limited, and when the PVA-based polymer film is stretched in warm water (wet stretching), it is preferably 30 to 90°C, more preferably 40 to 70°C, More preferably, it is a temperature of 45 to 65°C, and in the case of dry heat stretching, a temperature of preferably 50 to 180°C is employed. In addition, as the stretching ratio of the uniaxial stretching treatment (total stretching ratio in the case of multi-step uniaxial stretching), it is preferable to stretch the film as much as possible until just before the film breaks from the viewpoint of polarization performance. , specifically, preferably 4 times or more, more preferably 5 times or more, even more preferably 5.5 times or more. The upper limit of the stretch ratio is not particularly limited as long as the film is not broken, but it is preferably 8.0 times or less in order to perform uniform stretching.

The thickness of the stretched film (polarizing film) is preferably 5 to 35 μm, particularly preferably 20 to 30 μm.

When producing a polarizing film, in order to make the adsorption|suction of the dye to the uniaxially stretched film firm, fixation processing is performed in many cases. For the fixation treatment, generally, a method of immersing the membrane in a treatment bath containing boric acid and/or a boron compound is widely used. At this time, an iodine compound may be added to the treatment bath as needed.

Next, drying treatment (heat treatment) is preferably performed on the film subjected to uniaxial stretching treatment or uniaxial stretching treatment and fixation treatment. The temperature of the drying treatment (heat treatment) is preferably 30 to 150°C, particularly preferably 50 to 140°C. If the temperature of the drying treatment (heat treatment) is too low, the dimensional stability of the resulting polarizing film tends to decrease. On the other hand, if it is too high, the polarization performance tends to decrease due to decomposition of the dye or the like.

A polarizing plate can be produced by bonding an optically transparent and mechanically strong protective film to both surfaces or one surface of the polarizing film obtained as described above. As the protective film at this time, a cellulose triacetate (TAC) film, a cellulose acetate-butyrate (CAB) film, an acrylic film, a polyester film, or the like is used. In addition, as an adhesive for laminating the protective film, PVA-based adhesives, polyurethane-based adhesives, and the like are generally used, and among them, PVA-based adhesives are preferably used.

The polarizing plate obtained as described above can be bonded to a glass substrate after being coated with an adhesive such as an acrylic system, and can be used as a member of a liquid crystal display device. When bonding a polarizing plate to a glass substrate, a retardation film, a viewing angle improvement film, a brightness improvement film, etc. can be bonded together.

Example

The present invention is specifically described below through examples, but the present invention is not limited by the following examples.

In the following examples and comparative examples, the volatile component ratio of the film-forming stock solution, the volatile component ratio (moisture ratio) of the PVA film or PVA film, the physical properties of the PVA film, and the optical properties of the polarizing film were measured by the following methods.

(1) The proportion of volatile components in the film-making stock solution:

It can be obtained by the above formula [iii] according to the above-mentioned method.

(2) The volatile component ratio (moisture ratio) of PVA film or PVA film:

It can be obtained by the above formula [iv] according to the above-mentioned method.

In addition, the measurement of the volatile component ratio (moisture ratio) of a PVA film or a PVA film is performed using the sample collected from the center part of the width direction (TD) of the PVA film or PVA film taken out from the drying roll.

(3) Δn(MD) _Ave of PVA film:

The Δn(MD) _Ave of the central part in the width direction (TD) of the PVA film is obtained by the method described above in the item "<1>Measuring method of Δn(MD) _Ave ", and it is used as Δn of the PVA film. (MD) _Ave.

(4) Δn(TD) _Ave of PVA film:

The Δn(TD) _Ave of the central part in the width direction (TD) of the PVA film is obtained by the method described above in the item "<2>Measuring method of Δn(TD) _Ave ", and is used as Δn of the PVA film. (TD) _Ave.

(5) Mass swelling degree of PVA film:

Cut the PVA film into 1.5g, dip it in 1000g of distilled water at 30°C for 30 minutes, take out the PVA film after soaking for 30 minutes, absorb the water on the surface with filter paper, and measure its mass (W _e ). Next, after drying this PVA film with a dryer at 105° C. for 16 hours, its mass (W _f ) was measured. The mass swelling degree of the PVA film was obtained from the obtained masses We _{and Wf} by the following formula [v].

Mass swelling degree (%)=(W _e /W _f )×100 [v].

(6) Ultimate stretch ratio of PVA film:

Collect the test piece of longitudinal direction (MD) * width direction (TD) = 10cm * 5cm from the central part of the width direction (TD) of the PVA film before stretching obtained in the following examples or comparative examples, the test piece Both ends of the length direction are fixed to the stretching jig so that the size of the stretched part is the length direction (MD) x width direction (TD) = 5cm x 5cm, immersed in water at 30°C for 38 seconds, during this process with After uniaxial stretching (first step stretching) to 2.2 times the original length along the length direction (MD) at a stretching speed of 12 cm/min, iodine was contained at a concentration of 0.03% by mass, and at a concentration of 3% by mass. Potassium iodide is immersed in an iodine/potassium iodide aqueous solution at a temperature of 30°C for 90 seconds. During this process, it is uniaxially stretched along the length direction (MD) at a stretching speed of 12 cm/min (second stretching) to the original length. 3.3 times, followed by immersion in a boric acid/potassium iodide aqueous solution at a temperature of 30°C containing boric acid at a concentration of 3% by mass and potassium iodide at a concentration of 3% by mass for about 20 seconds. Speed along the longitudinal direction (MD) uniaxial stretching (third step stretching) to 3.6 times the original length, and then, while containing boric acid at a concentration of 4% by mass and potassium iodide at a concentration of about 5% by mass Immerse in boric acid/potassium iodide aqueous solution at about 60°C, while stretching uniaxially along the longitudinal direction (MD) at a tensile speed of 12 cm/min until the test piece breaks, and read the stretch ratio at breakage of the test piece ( length relative to the original length).

For the same PVA film, carry out the above-mentioned tensile test 5 times, and get the average value as the ultimate stretch ratio (times) of the PVA film.

(7) Optical properties of polarizing film:

(i) Transmittance:

From the central part of the width direction of the polarizing film obtained in the following examples or comparative examples, two samples of 1.5 cm x 1.5 cm square were collected parallel to the orientation direction of the polarizing film, and a spectrometer made by Hitachi, Ltd. was used for each sample. Photometer V-7100 (with integrating sphere) is based on JIS Z8722 (measurement method of object color) to correct the apparent brightness of C light source and the visible light region of 2-degree field of view. For a polarizing film sample, measure relative to the stretching axis The light transmittance when the direction is inclined at 45 degrees and the light transmittance when the direction is inclined at -45 degrees are obtained, and their average value (Y ₁ ) is obtained.

For another polarizing film sample, the transmittance of light at an inclination of 45° and the transmittance of light at an inclination of −45° were measured in the same manner as above, and their average value (Y ₂ ) was obtained.

_Y1 and _Y2 obtained as above were averaged, and it was made into the transmittance (Y) (%) of a polarizing film.

(ii) Degree of polarization:

For the two polarizing film samples collected in (i) above, the transmittance (Y∥) of light when the orientation directions are superimposed in parallel and the orientation directions are perpendicular The transmittance (Y⊥) of light when the method is superimposed is obtained from the following formula [vi] to obtain the degree of polarization (V) (%).

Degree of polarization (V)(%)={(Y∥-Y⊥)/(Y∥+Y⊥)} ^1/2 ×100 [vi].

(iii) Degree of polarization at 44.25% transmittance:

As described in the following examples and comparative examples, in each example or comparative example, the immersion time in the iodine/potassium iodide aqueous solution during the second step of stretching was changed to make 5 polarizing films. For each polarizing film, use The above method obtains the transmittance (Y) and the degree of polarization (V). For each embodiment or comparative example, take the transmittance (Y) as the horizontal axis and the degree of polarization (V) as the vertical axis to draw 5 points as From the figure, an approximate curve was obtained, and the value of the degree of polarization (V) when the transmittance (Y) was 44.25% was obtained from the approximate curve.

"Example 1"

(1) Manufacture of PVA film:

(i) The proportion of volatile components composed of 100 parts by mass of PVA obtained by saponification of polyvinyl acetate (saponification degree: 99.9 mol%, polymerization degree: 2400), 12 parts by mass of glycerin, 0.1 part by mass of lauric acid diethanolamide, and water The film-forming stock solution of 66% by mass was discharged from the T-die in a film form onto the first drying roller (93°C surface temperature, peripheral speed (S ₁ ) 16.7m/min), and the entire second drying roller was dried on the first drying roller. The non-contact surface of a drying roll is sprayed with hot air at 90°C at a wind speed of 5m/s, while drying until the moisture ratio reaches 18% by mass, and then peeled off from the first drying roll, and the second roll is performed at a roll surface temperature of about 85°C. After the drying roll, the surface and back of any part of the PVA film are alternately contacted with each drying roll. Finally, after heat treatment with the final drying roll (heat treatment roll) with a surface temperature of 108°C, it is wound up to obtain PVA. Thin film (thickness 60 μm, width 3 m, volatile component ratio 3% by mass). In Example 1, the drying roll at which the volatile component ratio was 13% by mass was the seventh drying roll.

_In this _Example 1, (α) the ratio (S _T /S ₁ ) is 1.000; (β) the ratio of the peripheral speed (S _L ) of the final drying roll to the peripheral speed (S _T ) of the drying roll (the seventh drying roll) when the volatile component ratio reaches 13% by mass ( S _L /S _T ) is 0.974; (γ) the ratio (S ₂ /S ₁ ) of the peripheral speed (S 2 ) of the second drying roll to the peripheral speed (S ₁ ) of the first drying roll is 1.030; ₍ δ ) _The ratio ( _{S T} /S _T+1 ) is 0.998; (ε) The ratio (S _L /S ₁ ) of the peripheral speed (S _L ) of the final drying roll to the peripheral speed (S ₁ ) of the first drying roll is 0.975. PVA film.

(ii) Δn(MD) _Ave , Δn(TD) _Ave , mass swelling degree and ultimate draw ratio of the PVA film obtained in (i) above were measured by the above method, and the results are shown in Table 1 below.

(2) Manufacture of polarizing film:

(i) Collect a test piece in the longitudinal direction (MD)×width direction (TD)=10cm×5cm from the central portion of the PVA film obtained in the above (1) in the width direction (TD), and measure the length of the test piece in the longitudinal direction. Both ends are fixed to the stretching jig so that the size of the stretched part is length direction (MD) x width direction (TD) = 5cm x 5cm, immersed in water at 30°C for 38 seconds, during this process at 12cm/min After the stretching speed is uniaxially stretched (stretched in the first step) to 2.2 times the original length along the length direction (MD), the temperature at which iodine is contained at a concentration of 0.03% by mass and potassium iodide at a concentration of 3% by mass Immerse in an iodine/potassium iodide aqueous solution at 30°C for 60 seconds, and during this process, stretch uniaxially along the length direction (MD) at a stretching speed of 12 cm/min (second step stretching) to 3.3 times the original length, Next, immerse in a boric acid/potassium iodide aqueous solution at a temperature of 30° C. containing boric acid at a concentration of 3% by mass and potassium iodide at a concentration of 3% by mass for about 20 seconds. The longitudinal direction (MD) is uniaxially stretched (third-step stretching) to 3.6 times the original length, and then, while containing boric acid at a concentration of 4% by mass and potassium iodide at a concentration of approximately 5% by mass, the temperature is about 60°C Immersed in boric acid/potassium iodide aqueous solution, while stretching along the longitudinal direction (MD) uniaxially stretching (the fourth step stretching) at a stretching speed of 12cm/min until reaching the ultimate stretching ratio of the PVA film measured as described above After the previous stretching ratio, immerse in the potassium iodide aqueous solution that contains potassium iodide with the concentration of 3 mass % for 10 seconds, carry out iodide ion impregnation treatment, then dry with 60 ℃ of drier for 4 minutes, make polarizing film (thick about 21 μm ).

Calculate the transmittance (Y) and the degree of polarization (V) of the polarizing film thus obtained by the above method, and plot this point on a graph with the transmittance (Y) as the horizontal axis and the degree of polarization (V) as the vertical axis. middle.

(ii) In (i) above, perform the same operation as in (i) above, except that the immersion time in the iodine/potassium iodide aqueous solution at a temperature of 30°C is changed from 60 seconds to 75 seconds in the second stretching step , and a polarizing film (about 21 μm in thickness) [the stretching speed in each stretching stage was 12 cm/min as in (i) above] was produced.

The transmittance (Y) and degree of polarization (V) of the polarizing film thus obtained were obtained by the method described above, and the points were plotted in the above graph (i).

(iii) In (i) above, the same operation as in (i) above was performed except that the immersion time in the iodine/potassium iodide aqueous solution at a temperature of 30°C was changed from 60 seconds to 90 seconds in the second stretching step , and a polarizing film (about 21 μm in thickness) [the stretching speed in each stretching stage was 12 cm/min as in (i) above] was produced.

The transmittance (Y) and degree of polarization (V) of the polarizing film thus obtained were obtained by the method described above, and the points were plotted in the above graph (i).

(iv) In the above (i), the same operation as in the above (i) was performed except that the immersion time in the iodine/potassium iodide aqueous solution at a temperature of 30°C was changed from 60 seconds to 105 seconds in the second stretching step , and a polarizing film (about 21 μm in thickness) [the stretching speed in each stretching stage was 12 cm/min as in (i) above] was prepared.

The transmittance (Y) and degree of polarization (V) of the polarizing film thus obtained were obtained by the method described above, and the points were plotted in the above graph (i).

(v) In (i) above, the same operation as in (i) above was performed except that the immersion time in the iodine/potassium iodide aqueous solution at a temperature of 30°C was changed from 60 seconds to 120 seconds in the second stretching step , and a polarizing film (about 21 μm in thickness) [the stretching speed in each stretching stage was 12 cm/min as in (i) above] was prepared.

The transmittance (Y) and degree of polarization (V) of the polarizing film thus obtained were obtained by the method described above, and the points were plotted in the above graph (i).

(vi) Draw an approximate curve of the five points drawn in the figure in (i) to (v) above on the figure, and obtain the degree of polarization (V) when the transmittance (Y) is 44.25% from the approximate curve value, the result is 99.98 as shown in Table 1 below.

"Example 2-5"

(1) In Example 1, a PVA film was produced in the same manner as in Example 1 (1) by changing the film-forming conditions when producing the PVA film as described in Table 1 below. However, in Example 2, 100 parts by mass of PVA obtained by saponification of polyvinyl acetate (saponification degree 99.9 mol%, polymerization degree 2400), 12 parts by mass of glycerin, diethyl laurate A film-forming stock solution having a volatile component ratio of 73% by mass consisting of 0.1 parts by mass of amide and water.

The Δn(MD) _Ave , Δn(TD) _Ave , mass swelling degree and ultimate draw ratio of each PVA film thus obtained were measured by the above method, and the results are shown in Table 1 below.

(2) Using a test piece in the longitudinal direction (MD)×width direction (TD)=10cm×5cm collected from the central portion of each PVA film obtained in the above (1) in the width direction (TD), carry out the same procedure as in Example 1. (2) The same operation, manufacture 5 kinds of polarizing films respectively for each embodiment, find out the transmittance (Y) and the degree of polarization (V) of each polarizing film, and this point is plotted on the horizontal plane with the transmittance (Y) Axis, in the figure with the degree of polarization (V) as the vertical axis, draw an approximate curve drawn at the five points in the figure on the figure, and obtain the degree of polarization when the transmittance (Y) is 44.25% from the approximate curve (V), the results are shown in Table 1 below.

"Comparative Examples 1-5"

(1) In Example 1, a PVA film was produced in the same manner as in (1) of Example 1 by changing the film forming conditions when producing the PVA film as described in Table 2 below.

The Δn(MD) _Ave , Δn(TD) _Ave , mass swelling degree and ultimate draw ratio of each PVA film thus obtained were measured by the above method, and the results are shown in Table 2 below.

(2) Using a test piece in the longitudinal direction (MD)×width direction (TD)=10cm×5cm collected from the central portion of each PVA film obtained in the above (1) in the width direction (TD), carry out the same procedure as in Example 1. (2) The same operation, manufacture 5 kinds of polarizing films respectively for each comparative example, obtain the transmittance (Y) and polarization degree (V) of each polarizing film, and draw this point on the horizontal plane with the transmittance (Y) as Axis, in the figure with the degree of polarization (V) as the vertical axis, draw an approximate curve drawn at the five points in the figure on the figure, and obtain the degree of polarization when the transmittance (Y) is 44.25% from the approximate curve (V), the results are shown in Table 2 below.

[Table 1]

[Table 2]

As can be seen from the above Tables 1 and 2, the Δn(MD) _Ave [value obtained by averaging the birefringence in the longitudinal direction (MD) of the PVA film in the thickness direction of the film] and Δn(TD) _Ave [a value obtained by averaging the birefringence in the width direction (TD) of the PVA film in the thickness direction of the film] satisfies the formulas (I) and (II), so it has a high limit of 6.72 to 6.94 Moreover, the polarizing films obtained from the PVA films of Examples 1 to 5 had excellent polarizing properties equal to or higher than conventional polarizing films.

In contrast, the PVA films of Comparative Examples 1 to 4 do not satisfy the formula (I), and the PVA films of Comparative Examples 4 and 5 do not satisfy the formula (II). Therefore, compared with the PVA films of Examples 1 to 5, the limit pull The elongation ratio is low.

When producing a polarizing film from a PVA-based polymer film, it is usually uniaxially stretched at a stretching ratio slightly lower than the ultimate stretching ratio in order to avoid film breakage during stretching, but because the PVA films of Examples 1 to 5 The ultimate stretching ratios are all as high as 6.72 or more, so when manufacturing polarizing films under the conditions of this embodiment, the PVA films of Examples 1 to 5 can be uniaxially stretched at a high stretching ratio of more than 6 times, even at 6.5 Even if the uniaxial stretching is carried out at a high draw ratio of 2 times or more, the film can be stretched smoothly without breaking the film.

In contrast, among the PVA films of Comparative Examples 1 to 5, since the ultimate stretch ratio of the PVA film of Comparative Example 4 was less than 6, when a polarizing film was produced under the conditions of this Comparative Example, it was not possible to stretch the film at a stretching ratio of 6 times or more. Ratio of uniaxial stretching, the film is easy to break during stretching, in addition, when the PVA films of Comparative Examples 1 to 3 and 5 are uniaxially stretched at a stretching ratio of 6 times or more, the fracture of the film is difficult. People are worried.

In addition, among the original films for polarizing films, there are also original films with a length of more than 1000m in one roll. The length of the stretched film obtained by stretching is increased by 100 m (1000 m×0.1 times=100 m), and more polarizing films can be obtained from the original film of the same length.

Regarding this point, it can be seen from Examples 1 to 5 that the PVA films of Examples 1 to 5 have an ultimate draw ratio as high as 0.10 to 0.98 points (times) compared with the PVA films of Comparative Examples 1 to 5. For example, if PVA The length of film is 1000m, then under the situation of making polarizing film with PVA film it under the condition of above-mentioned embodiment, the length of polarizing film will be long 100～980m compared with the situation of using the PVA film of Comparative Examples 1～5, can Get more polarizing film.

Industrial applicability

The PVA-based polymer film of the present invention has a high limit stretching ratio even when the film thickness is relatively thin, about 30 to 65 μm, and it is not easy to uniaxially stretch at a high ratio when producing a polarizing film or the like. Since the breakage of the film occurs, stretched films such as polarizing films with excellent optical properties such as polarization properties can be manufactured with a high yield without interrupting the stretching operation, and with a shorter drying time than before, and with good productivity. Therefore, it is extremely useful as an original film for producing stretched films such as polarizing films, and the production method of the present invention is useful as a method for smoothly and continuously producing the PVA-based polymer film of the present invention with high productivity.

Claims (5)

1. polymer film of polyvinyl alcohol, which is characterized in that meet lower formula (I) and (II)；

Δn(MD)_Ave—0.1×10^-3≤Δn(TD)_Ave≤Δn(MD)_Ave+0.25×10^-3 (I)

Δn(TD)_Ave≤2.5×10^-3 (II)

In above formula, Δ n (MD)_AveRepresent the birefringence in the mechanical flow direction of polymer film of polyvinyl alcohol in the film Value, Δ n (TD) obtained by being equalized on thickness direction_AveRepresent the birefringence of the width of polymer film of polyvinyl alcohol Rate is worth obtained by being equalized on the thickness direction of the film,

The polymer film of polyvinyl alcohol meets lower formula (III)；

1.3×10^-3≤Δn(MD)_Ave≤2.0×10^-3(III),

The polymer film of polyvinyl alcohol, thickness in the range of 30~65 μm,

The polymer film of polyvinyl alcohol is prepared by following manufacturing methods, and the manufacturing method is characterized in that,

(a) using the film forming apparatus for possessing the more dryer rolls that shaft is mutually parallel, by the system containing vinol series polymer Film stoste with it is membranaceous spue on the first dryer roll of the film forming apparatus and carry out it is partially dried after, with subsequent dryer roll into one Step is dried to be film-made；At this point,

(b) peripheral speed (S of the dryer roll when volatile ingredient ratio of Polyvinyl alcohol film reaches 13 mass %_T) phase For the peripheral speed (S of the first dryer roll₁) ratio (S_T/S₁) it is 0.990~1.050；

(c) peripheral speed (S of final dryer roll_L) compared with the volatile ingredient ratio of Polyvinyl alcohol film reach 13 matter Peripheral speed (the S of dryer roll during amount %_T) ratio (S_L/S_T) it is 0.960~0.980；

(d) peripheral speed (S of final dryer roll_L) compared with the peripheral speed (S of the first dryer roll₁) ratio (S_L/S₁) be 0.970~1.010.

2. polymer film of polyvinyl alcohol according to claim 1, wherein, polyethylene when being removed from the first dryer roll The volatile ingredient ratio of alcohol based polymer film is 17~30 mass %.

3. polymer film of polyvinyl alcohol according to claim 1, wherein, the roll surface temperature of each dryer roll is 65 DEG C More than.

4. polymer film of polyvinyl alcohol according to claim 1, wherein, the film containing vinol series polymer The volatile ingredient ratio of stoste is 60~75 mass %, and the roll surface temperature of the first dryer roll is 80~120 DEG C, the first dryer roll Peripheral speed (S₁) it is 8~25m/ minutes.

5. polarizing coating is made of polymer film of polyvinyl alcohol described in claim 1.