TW201402306A - Ethylene-modified polyvinyl alcohol polymer film - Google Patents

Abstract

The present invention provides a PVA polymer film which can produce a stretched film that is hardly broken even by stretching at high speed and high magnification, such as a polarizing film having an optical performance equal to or better than conventional products thereby film, with good workability, good productivity, in high yield and at low cost. An ethylene-modified PVA polymer film is characterized by comprising an ethylene-modified PVA polymer wherein the content of ethylene units is 1 to 4 mol%, and satisfying the following formula (I) and (II): Δ n (MD) Ave-0.1*10<SP>-3</SP> ≤ Δ n (TD) Ave ≤ Δ n (MD) Ave+0.25*10<SP>-3</SP> (I) Δ n (TD) Ave ≤ 2.5*10<SP>-3</SP> (II) [Wherein, Δ n (MD) Ave represents a value obtained by averaging the thickness direction of the film birefringence of the machine flow direction of the ethylene-modified PVA polymer film, Δ n (TD) Ave represents a value obtained by averaging the thickness direction of the film birefringence in the width direction of the ethylene-modified PVA polymer film.]

Description

Ethylene modified polyvinyl alcohol polymer film

The present invention relates to a polyvinyl alcohol polymer modified with ethylene Film (hereinafter, a case where "polyvinyl alcohol" is abbreviated as "PVA"); and a method of producing a polarizing film using the same. More specifically, the present invention relates to an ethylene-modified PVA-based polymer film which is not easily broken at a high speed and a high magnification, and which does not cause interruption of stretching operation due to film breakage, and can be produced at a high yield. An extended film excellent in optical performance such as polarizing performance, and a method for producing a polarizing film using the same are produced with good productivity.

Polarizing plate with light transmission and shielding function, and A liquid crystal or the like having a switching function of light is an important component of a liquid crystal display device (LCD). The field of application of this liquid crystal display device has been expanded to include notebook computers, liquid crystal displays, liquid crystal color projectors, liquid crystal televisions, navigation systems for vehicles, mobile phones, and indoor and outdoor use in small computers such as computers and watches. The vast range of measuring machines and the like, particularly in the field of liquid crystal displays or liquid crystal televisions, is moving toward large screens.

The manufacture of polarizing plates, in general, is by using PVA After uniaxial stretching of a polymer film, use iodine or a dichroic dye A method of performing dyeing treatment; a method of dyeing a PVA-based polymer film, performing uniaxial stretching, and then fixing it with a boron compound; and in any of the above methods, performing a fixing treatment at the same time as dyeing, etc. a polarizing film, on one or both sides of the polarizing film obtained thereby, a cellulose triacetate film or acetic acid is attached. A protective film such as a cellulose tyrosinate film.

In recent years, with the expansion of the use of liquid crystal display devices, etc. There is a need to improve the quality of the display, as well as further cost reduction or further improvement in usability. From the perspective of cost reduction, it is necessary to increase the production speed when manufacturing a polarizing film, prevent elongation breakage (breakage) when the PVA-based polymer film is extended, and reduce the breakage loss to improve the yield, and prevent the film from being broken to cause extension work or extension. . Interruption of dyeing operations, etc.

In addition, in the production of a polarizing film, one of the items for improving the productivity is to shorten the drying time when manufacturing a polarizing film. From this point of view, the raw material film for a polarizing film is generally polymerized by PVA having a thickness of about 75 μm. In recent years, there has been a demand for a PVA-based polymer film which is thinner than 70 μm and further thinned.

However, the thinner the PVA-based polymer film is, the problem that cracking easily occurs when it is stretched at a high speed and a high rate. From this point of view, a PVA-based polymer film is required, and even if it is thinned, it does not occur. The rupture can be carried out at a high speed and a high magnification, whereby a polarizing film having a polarizing performance equal to or higher than that of a conventional product can be produced with good workability, high productivity, low cost, and productivity.

In the past, in order to improve the extensibility of PVA-based polymer films Or, the uniformity of the stretching is improved, and the polarizing performance or durability of the polarizing film obtained by stretching the PVA-based polymer film is improved. When the film is dried while using a liquid solution containing a PVA-based polymer, film formation is conventionally performed. The drawing ratio (the ratio of the conveying speed of the PVA-based polymer film between the rolls used for film formation) is adjusted, and the moisture content of the PVA-based polymer film at the time of film formation is adjusted.

This prior art is known to have (1) in order to be able to get in a single A method for producing a PVA-based polymer film by using a film-drawing ratio of 1 or less and a film stretching ratio of 1 or less to form a film-forming operation for producing a PVA-based polymer film (Patent Document 1, in particular, Paragraphs [0008] to [0009], Examples, etc.); (2) The objective is to obtain a PVA-based polymer film which can be stretched at a high rate, and when a PVA-based polymer film is produced by using a drum film forming machine, The winding speed of the PVA-based polymer film] / [the speed of the drum located at the most upstream of the film-forming material] is set to 0.8 to 1.3 (Patent Document 2); (3) The purpose is to obtain a high-magnification extension. In the drying step in the case of producing a PVA-based polymer film using a drum film forming machine, the PVA-based polymer film has a step speed Rc at a time point when the ratio of the final winding speed Rf to the volatile component of the film is 10% by weight or less. The speed ratio (Rf/Rc) is set to be 0.9 to 1.1 (Patent Document 3).

In addition, it is also known that (4) a PVA-based film which can produce a polarizing film having a wide range of optical properties and a wide application range even in a large area, and which has a volatile component of the PVA film of 10% or less. The ratio of the speed (Rc) of the drying roller to the winding speed (Rf) (Rf/Rc) is controlled at 0.9 to 1.1 to reduce the temperature unevenness in the drying step, and the tensile elongation (S _M ) in the MD direction is produced and A method in which the ratio (S _M /S _T ) of the tensile elongation (S _T ) in the TD direction is a PVA-based film of 0.7 to 1.3 (Patent Document 4); (5) can be produced even in a large area. A PVA-based film having a polarizing film having a wide range of optical properties and having a wide application range, when the volatile component of the PVA film reaches 10 to 50% by weight, the PVA film is peeled off by the drum located on the most upstream side, and is located at the most upstream The speed V1 of the side drum and the speed V2 of the drum speed V2 in the step of starting the volatile component of the PVA film are set to 1.0 to 1.3 (Patent Document 5).

Further, (6) in order to obtain a PVA-based polymer film which can produce a stretched film which can uniformly perform uniaxial stretching and which has no fine cracks or voids during stretching, and which is composed of a specific skin layer/core layer/cortex layer, is known. The stock solution containing the volatile component ratio of the PVA-based polymer in an amount of 50 to 90% by mass is heated by the first drying roll, and the ratio of the hot air and the volatile component is blown to the surface of the PVA-based polymer film which is not in contact with the first drying roll under a predetermined condition. When it is 15 to 30% by mass, the PVA-based polymer film is peeled off from the first drying roll, and brought into contact with the second drying roll and dried. In this case, the number of rotations (S ₁ ) of the first drying roll and the second drying are performed. The ratio (S ₂ /S ₁ ) of the rotation speed (S ₂ ) of the rolls is set to 1.000 to 1.100 (Patent Document 6).

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. Hei 6-136151

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2001-315141

[Patent Document 3] Japanese Patent Laid-Open Publication No. 2001-315146

[Patent Document 4] Japanese Patent Laid-Open Publication No. 2002-30164

[Patent Document 5] Japanese Patent Laid-Open Publication No. 2002-79531

[Patent Document 6] Japanese Patent Laid-Open Publication No. 2005-324355

[Non-patent literature]

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

However, in the above-mentioned Patent Documents 1 to 6, there is no disclosure of a strategy for preventing the film from being broken when the PVA-based polymer film, particularly the PVA-based polymer film having a thin film thickness, is uniaxially stretched at a high magnification. In particular, a strategy to further increase the ultimate stretch ratio of the film. Further, in the prior art as in the above-described Patent Documents 1 to 6, when the stretching speed is increased, problems such as film breakage are likely to occur in the middle of the stretching step, and it is difficult to extend at a high speed.

An object of the present invention is to provide a PVA-based polymer film which is less likely to be broken even at a high speed and a high magnification, and can be produced with good workability, high productivity, low cost, and good productivity. A stretched film such as a polarizing film having optical properties equal to or higher than the product.

In particular, an object of the present invention is to provide a PVA-based polymer film which has a high ultimate stretch ratio and can correspond to a high elongation speed even if it is thinner than a PVA-based polymer film used in the conventional production of a polarizing film. It does not break when it is extended at high speed and high magnification. By uniaxially stretching, a stretched film which is thinner than the conventional one can be produced, and the drying time at the time of manufacturing a polarizing film can be further shortened, and a polarizing film can be manufactured with more favorable productivity.

Further, an object of the present invention is to provide a method for producing a polarizing film which uses the PVA-based polymer film.

In order to achieve the above object, the inventors of the present invention have found that a PVA-based polymer film (ethylene-modified PVA-based polymer film) is produced by using an ethylene-modified PVA-based polymer having a specific amount of ethylene units, and The film is made to have a value in which the birefringence in the machine direction (longitudinal direction) is averaged in the thickness direction of the film and a value obtained by averaging the birefringence in the width direction in the thickness direction of the film, while the film width is When the value of the birefringence in the direction is averaged in the thickness direction of the film, the value is set to a specific value range, and even if the film is stretched at a high speed and a high magnification, cracking of the film is less likely to occur, and the stretching operation can be performed without interruption, and the yield is high and low. A stretched film such as a polarizing film excellent in optical performance such as polarizing performance is produced with good productivity.

In particular, it has been found that a value obtained by averaging the birefringence in the machine direction of the ethylene-modified PVA-based polymer film in the thickness direction of the film and a value of averaging the birefringence in the width direction in the thickness direction of the film satisfy a specific relationship. And the ethylene-modified PVA-based polymer film having a value in which the birefringence in the width direction is averaged in the thickness direction of the film in a specific range, and the thickness of the film is higher than that of the PVA-based polymer generally used in the conventional production of the polarizing film. The thickness of the film is also thin, and it does not break even at a thickness of about 10 to 65 μm, and can be smoothly performed at a high speed and a high rate. When the polarizing film is produced, the film can be further thinned, and the drying time when the polarizing film is produced can be further shortened, and the present invention can be further reviewed based on these findings.

That is, the present invention relates to:

[1] An ethylene-modified PVA-based polymer film comprising an ethylene-modified PVA-based polymer having an ethylene unit content of 1 to 4 mol%, and satisfying the following formulas (I) and (II) :△n(MD) _Ave -0.1×10 ^-3 ≦△n(TD) _Ave ≦△n(MD) _Ave +0.25×10 ^-3 (I)

Δn(TD) _Ave ≦2.5×10 ^-3 (II) [In the above formula, Δn(MD) _Ave represents the birefringence in the machine direction of the ethylene-modified PVA-based polymer film along the thickness direction of the film The average value, Δn(TD) _Ave represents a value obtained by averaging the birefringence in the width direction of the ethylene-modified PVA-based polymer film along the thickness direction of the film];

[2] The ethylene-modified PVA-based polymer film according to [1] above, which satisfies the following formula (III): 1.3 × 10 ^-3 ≦ Δn (MD) _Ave ≦ 2.0 × 10 ^-3 (III);

[3] The ethylene-modified PVA-based polymer film according to [1] or [2] above, wherein the thickness is in the range of 10 to 65 μm;

[4] A method for producing a polarizing film, characterized by using the ethylene-modified PVA-based polymer film according to any one of the above [1] to [3], dyeing and uniaxial stretching;

[5] The production method according to [4] above, which comprises the step of performing uniaxial stretching at an elongation speed of 300%/min or more based on the length of the ethylene-modified PVA-based polymer film before uniaxial stretching.

In the ethylene-modified PVA-based polymer film of the present invention, even when the stretched film is produced, even if it is uniaxially stretched at a high speed and a high magnification, cracking of the film is less likely to occur, whereby the stretching operation can be performed without interruption, and the yield can be high and low. Further, a stretched film such as a polarizing film excellent in optical performance such as polarizing performance is produced with good productivity.

In particular, in the ethylene-modified PVA-based polymer film of the present invention, the thickness of the film is a thickness of about 10 to 65 μm which is thinner than the thickness of the conventional PVA-based polymer film, in order to produce a polarizing film or the like. The rupture does not occur, and the uniaxial stretching can be smoothly performed at a high speed and a high rate. Further, when the stretched film is produced, the film can be further thinned, and the drying time for manufacturing the polarizing film or the like can be further shortened, and thereby Productive improvement.

In addition, in recent years, a PVA-based polymer film having a length of more than 1000 m has been used as a raw material film for a polarizing film. However, the ethylene-modified PVA-based polymer film of the present invention has a high ultimate stretch ratio, and thus can be made higher than conventional products. Since the magnification is extended, the amount of the polarizing film obtained from the ethylene-modified PVA-based polymer film can be increased more than in the past.

In addition, by using the method for producing a polarizing film of the present invention, it is possible to produce a polarizing film excellent in polarizing performance with high productivity, low cost, and high productivity without interrupting the stretching operation.

TD‧‧‧width direction

MD‧‧‧Machining direction

Fig. 1 is a schematic view showing a method of taking a sample when Δn (MD) _Ave of the ethylene-modified PVA-based polymer film is measured.

Fig. 2 is a schematic view showing a method of taking a sample when Δn(TD) _Ave of the ethylene-modified PVA-based polymer film is measured.

[Formation of the Invention]

The invention is described in detail below.

In general, a transparent film produced by using a transparent polymer such as a PVA polymer has a polymer chain which is plastically deformed or warped due to shear stress, and is oriented in the machine direction (machining direction: length direction). The polarization directions of the radicals of the polymer are aligned in a giant view, thereby producing birefringence peculiar to the polymer (Non-Patent Document 1).

The birefringence [Δn (MD)] of the PVA-based polymer film in the machine direction can be obtained by the following formula [i], and the birefringence [Δn (TD)] in the width direction can be expressed by the following formula [ Ii] Get it.

△n(MD)=nMD-nz [i]

Δn(TD)=nTD-nz [ii] where nMD represents the refractive index of the film in the machine direction (longitudinal direction), 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. . ]

In the film produced by using a transparent polymer such as a PVA-based polymer, the polymer chain forming the film is easily aligned in the machine direction (longitudinal direction), and the above Patent Document 1 includes the above-mentioned Patent Document 1 In the PVA-based polymer film described in the above, the PVA-based polymer film generally has "birefringence in the machine direction [Δn (MD)]" > "birefringence in the width direction [△n (TD) )]] That is, the birefringence [Δn (MD)] in the machine direction tends to become larger than the birefringence [Δn (TD)] in the width direction.

In contrast, the ethylene-modified PVA polymer of the present invention The film is different from the conventional PVA-based polymer film in that it satisfies the following formulas (I) and (II).

△n(MD) _Ave -0.1×10 ^-3 ≦△n(TD) _Ave ≦△n(MD) _Ave +0.25×10 ^-3 (I)

Δn(TD) _Ave ≦2.5×10 ^-3 (II) [In the above formula, Δn(MD) _Ave represents the birefringence in the machine direction of the ethylene-modified PVA-based polymer film along the thickness direction of the film The value of averaging Δn(TD) _Ave represents a value obtained by averaging the birefringence in the width direction of the ethylene-modified PVA-based polymer film along the thickness direction of the film.

That is, as shown in the above formula (I), in the ethylene-modified PVA-based polymer film of the present invention, the mechanical direction of the ethylene-modified PVA-based polymer film (continuous production of an ethylene-modified PVA-based polymer) "Production line direction at the time of film" (hereinafter, there is a case where the birefringence in the case of "longitudinal direction (MD)"] is averaged along the thickness direction of the film, "△n(MD) _Ave " and ethylene is changed. The width direction of the PVA-based polymer film (the direction perpendicular to the longitudinal direction) (hereinafter referred to as the "width direction (TD)"], the birefringence of the polymer film is averaged along the thickness direction of the film. △n(TD) _{Ave is} equal or slightly smaller, or even if it exceeds "△n(TD) _Ave ", the amount exceeded is very small.

Further, the ethylene-modified PVA-based polymer film of the present invention has characteristics such as the above formula (I) and the above formula (II).

The ethylene-modified PVA-based polymer film of the present invention, When the thickness of the film is thinner than in the past, the film has a high ultimate stretch ratio, and the uniaxial stretching is performed at a high magnification when a stretch film such as a polarizing film is produced. The rupture of the film is also less likely to occur, and the elongation of the film is not interrupted, and the stretching operation is interrupted, and the stretched film having excellent optical properties such as polarizing performance and thin film can be produced with high productivity and productivity.

When the ethylene-modified PVA-based polymer film has a lower limit stretching ratio than the above formula (I), cracking of the film is likely to occur when uniaxially stretching at a high magnification, particularly when the thickness of the film is thin. The rupture is easy to occur.

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

△n(MD) _Ave -0.05×10 ^-3 ≦△n(TD) _Ave ≦△n(MD) _Ave +0.23×10 ^-3 (I')

△n(MD) _Ave ≦△n(TD) _Ave ≦△n(MD) _Ave +0.2×10 ^-3 (I")

△n(MD) _Ave +0.05×10 ^-3 ≦△n(TD) _Ave ≦△n(MD) _Ave +0.18×10 ^-3 (I''')

Further, when the Δn(TD) _{Ave of} the ethylene-modified PVA-based polymer film exceeds 2.5×10 ^-3 from the range of the above formula (II), the ultimate stretching ratio of the ethylene-modified PVA-based polymer film becomes low. It is difficult to extend the ethylene-modified PVA-based polymer film in the longitudinal direction (MD) at a high magnification, and it is not easy to obtain an extended film excellent in optical properties.

In order to reduce Δn(TD) _{Ave as} much as possible, in the production of the ethylene-modified PVA-based polymer film, drying shrinkage in the width direction must be allowed, and the yield of the effective width of the ethylene-modified PVA-based polymer film may be lowered. Therefore, the Δn(TD) _Ave of the ethylene-modified PVA-based polymer film of the present invention is preferably in the range of 1.5 × 10 ^-3 to 2.2 × 10 ^-3 , and is in the range of 1.6 × 10 ^-3 to 2.0 × 10 ^- The range of ³ is preferred.

The ethylene modified PVA polymer film of the invention, except In addition to the above formulas (I) and (II), it is preferred to further satisfy the following formula (III).

1.3×10 ^-3 ≦△n(MD) _Ave ≦2.0×10 ^-3 (III)

When the Δn (MD) _{Ave of the} ethylene-modified PVA-based polymer film is set to 2.0 × 10 ^-3 or less, the ultimate stretching ratio of the ethylene-modified PVA-based polymer film is further increased, and ethylene modification is easily performed. The PVA-based polymer film is stretched at a high magnification in the longitudinal direction (MD), and it is easy to obtain a stretched film excellent in optical properties. On the other hand, in order to make the Δn (MD) _{Ave of} the ethylene-modified PVA-based polymer film less than 1.3 × 10 ^-3 , it is necessary to greatly reduce the rotation speed ratio of the drying roll, so that there is a drying roll at the time of film formation. The ethylene-modified PVA-based polymer film tends to be slack.

The Δn(MD) _Ave of the ethylene-modified PVA-based polymer film of the present invention is preferably in the range of 1.4 × 10 ^-3 to 1.95 × 10 ^-3 , and is in the range of 1.5 × 10 ^-3 to 1.9 × 10 ^{-3 .} The range is better.

Further, the ethylene-modified PVA-based polymer film has a large variation in the value of Δn (MD) _Ave and/or Δn (TD) _Ave in the width direction (TD) of the film, particularly at both ends in the width direction. The portion Δn (MD) _Ave tends to be high. However, it is preferable to satisfy the formula (I) and (II) at least in the central portion of the width direction (TD) of the ethylene-modified PVA-based polymer film. - (III), which satisfies the central portion of the width direction (TD) of the ethylene-modified PVA-based polymer film, and satisfies the formula (I) and (II) in the entire region of the portion of the width direction (TD) of 80% or more. ) is better, it is suitable to satisfy the formula (I) ~ (III). The both ends of the width direction (TD) of the ethylene-modified PVA-based polymer film which do not satisfy the formulas (I) and (II) can be cut before extending the ethylene-modified PVA-based polymer film in the longitudinal direction (MD). Removed (trimmed).

"△n(MD) _Ave " of the ethylene-modified PVA-based polymer film [the value of the birefringence in the longitudinal direction (MD) of the ethylene-modified PVA-based polymer film averaged along the thickness direction of the film] and " Δn(TD) _Ave ′ [the value of the birefringence in the width direction (TD) of the ethylene-modified PVA-based polymer film in the thickness direction of the film] can be measured by the following method.

Measurement method of "1" Δn (MD) _Ave : (This is a measurement method of Δn (MD) _Ave in the center of the width direction (TD) of the ethylene-modified PVA-based polymer film.)

(i) at any position in the longitudinal direction (MD) of the ethylene-modified PVA-based polymer film, as shown in Fig. 1(a), the MD × TD is cut out from the center of the width direction (TD) of the film. A thin piece having a size of 2 mm × 10 mm, and the both sides of the thin piece were sandwiched by a PET film having a thickness of 100 μm, and further sandwiched by a wooden frame and attached to a slicing device.

(ii) Next, the fine film taken as described above is shown in Fig. 1(b) (the PET film and the wooden frame are not shown) at intervals of 10 μm in parallel with the longitudinal direction (MD) of the fine sheet. The sections for observation were prepared, and 10 observation pieces (MD × TD = 2 mm × 10 μm) shown in (c) of the first drawing were produced. Among the slices, 5 slices with smooth slice surface and no slice thickness unevenness were selected. The thickness of the slice was measured with a microscope (manufactured by KEYENCE Co., Ltd.) on a slide glass. In addition, the observation was carried out in the field of view of 10 times of the joint and 20 times of the joint (200 times in total).

(iii) Next, the section was inverted as shown in Fig. 1 (d) in such a manner that the sliced surface was observed, and the slice was placed face up and placed on a glass slide to cover the slide with polyoxygenated oil (refraction) The rate was 1.04), and the delay of 5 slices was measured using a two-dimensional photoelastic evaluation system "PA-micro" (manufactured by Photonic Lattice Co., Ltd.).

(iv) In a state where the delay profile of each slice is displayed on the measurement screen of "PA-micro", the line α perpendicular to the surface of the original film is drawn so as to cross the slice, and the line α is performed on the line α. The line segment was analyzed to obtain delay profile data in the thickness direction of the film. In addition, the observation was carried out in the field of view of 10 times of the joint and 20 times of the joint (200 times in total). Further, in order to suppress the error caused by the positional change of the line segment α on the slice, the average value of the delay when the line width is set to 300 pixels is employed.

(v) dividing the value of the retardation distribution in the thickness direction of the film obtained above by the thickness measured by a microscope, and determining the birefringence Δn (MD) distribution in the thickness direction of the film, and taking the thickness direction of the film The average of the birefringence Δn (MD) distribution. The average value of the birefringence Δn (MD) distribution in the thickness direction of each film obtained for the five slices was further averaged to be "Δn (MD) _Ave ".

Measurement method of "2" Δn (TD) _Ave : (This is a measurement method of Δn (TD) _Ave in the center of the width direction (TD) of the ethylene-modified PVA-based polymer film.)

(i) in the length direction (MD) of the ethylene-modified PVA-based polymer film At any position, as shown in Fig. 2(a), a small piece of MD × TD = 10 mm × 2 mm is cut out from the central portion of the width direction (TD) of the film, and the thickness of both sides of the piece is made thick. The 100 μm PET film was sandwiched, and it was further clamped in a wooden frame and mounted on a slicing device.

(ii) Next, the fine film taken as described above is shown in Fig. 2(b) (the PET film and the wooden frame are not shown) at intervals of 10 μm in parallel with the width direction (TD) of the fine sheet. The sections were sliced, and 10 observation pieces (MD × TD = 10 μm × 2 mm) as shown in Fig. 2 (c) were produced. Among the slices, five slices having a smooth slice surface and no slice thickness unevenness were selected and placed on a glass slide, and the slice thickness was measured with a microscope (manufactured by KEYENCE Co., Ltd.). In addition, the observation was carried out in the field of view of 10 times of the joint and 20 times of the joint (200 times in total).

(iii) Next, the slice was inverted as shown in Fig. 2(d) in such a manner that the sliced surface was observed, and the slice was placed face up and placed on a glass slide to cover the slide with polyoxygenated oil ( The refractive index of 1.04) was sealed, and the delay of 5 slices was measured using the two-dimensional photoelastic evaluation system "PA-micro" (manufactured by Photonic Lattice Co., Ltd.).

(iv) In a state where the delay profile of each slice is displayed on the measurement screen of "PA-micro", the line β perpendicular to the surface of the original film is drawn so as to cross the slice, and the line β is performed on the line β. The line segment was analyzed to obtain delay profile data in the thickness direction of the film. In addition, the observation was carried out in the field of view of 10 times of the joint and 20 times of the joint (200 times in total). Further, in order to suppress the error caused by the positional change of the line segment β on the slice, the average value of the delay when the line width is set to 300 pixels is employed.

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

Thickness of the ethylene-modified PVA-based polymer film of the present invention It can be set in the range of 5 to 150 μm. However, in the case of using a material for a polarizing film, it is preferably set to 10 to 65 μm. The ethylene-modified PVA-based polymer film of the present invention has a high ultimate stretch ratio and can correspond to a high elongation rate. Therefore, the thickness of the film is set to 10 to 65 μm as described above, and the thickness of the raw material used as the polarizing film is much higher than that of the prior art. When the PVA-based polymer film having a thickness of about 75 μm is still thin, the film can be prevented from being broken at a high speed and at a high rate, whereby the film can be produced with high productivity, smoothness, and productivity. The stretched film of optical characteristics such as polarizing performance, and by extending the ethylene-modified PVA-based polymer film having a thickness of 10 to 65 μm at a high magnification, the thickness of the stretched film can be made thinner than in the past, and The drying time in manufacturing the polarizing film is shortened, and the manufacturing speed of the polarizing film is improved. From the viewpoint of the above, the thickness of the ethylene-modified PVA-based polymer film is preferably 60 μm or less, more preferably 50 μm or less. In addition, when a general PVA-based polymer film is uniaxially stretched at a relatively high temperature, the film strength after dissolution or water swelling in a bath used for PVA-based polymer extension is extremely lowered and it is difficult to extend. However, as long as the ethylene-modified PVA-based polymer film of the present invention can suppress the dissolution or the extreme strength of the film in the above bath Lower, so the thickness can be made thinner. From this point of view, when the thickness of the ethylene-modified PVA-based polymer film is less than 30 μm, the effects of the present invention are more remarkable. When the thickness of the ethylene-modified PVA-based polymer film is too large, drying is not easily performed when the polarizing film is produced.

On the other hand, when the thickness of the ethylene-modified PVA-based polymer film is too small, cracking of the film is likely to occur when uniaxially stretching is performed to produce a polarizing film. From this point of view, the thickness of the ethylene-modified PVA-based polymer film is preferably 15 μm or more, more preferably 18 μm or more, and particularly preferably 20 μm or more.

Width of the ethylene-modified PVA-based polymer film of the present invention However, in recent years, liquid crystal televisions or displays are being screened. Therefore, in order to effectively use these films, the width is preferably 2 m or more, more preferably 3 m or more, and still more preferably 4 m or more. Further, in the case where the polarizing plate is produced by a real production machine, if the width of the film is too large, it may be difficult to uniformly perform uniaxial stretching. Therefore, the width of the ethylene-modified PVA polymer film is 8 m or less. good.

The ethylene-modified PVA-based polymer film of the present invention has a quality The degree of swelling is preferably 180 to 250%, preferably 185 to 240%, and more preferably 190 to 230%. When the mass-swelling degree of the ethylene-modified PVA-based polymer film is too low, stretching tends to be difficult, and it is difficult to produce a stretched film having excellent optical properties. On the other hand, if the degree of mass swelling is too high, there is an extension. The step of passivation is deteriorated, or a case of a highly durable polarizing film cannot be obtained.

The term "mass swellability" as used herein means the mass of the ethylene-modified PVA-based polymer film immersed in distilled water at 30 ° C for 30 minutes. The percentage of the value obtained by drying the mass after drying at 105 ° C for 16 hours, specifically, can be measured by the method described in the following examples.

The ethylene-modified PVA-based polymer film of the present invention contains Examples of the ethylene-modified PVA-based polymer include an ethylene-modified PVA obtained by saponifying an ethylene-modified vinyl ester polymer obtained by copolymerizing ethylene and a vinyl ester; and a main chain of the ethylene-modified PVA An ethylene-modified PVA-based polymer obtained by graft-copolymerizing an ethylene-modified PVA-based polymer produced by saponification of an ethylene-modified vinyl ester polymer obtained by copolymerizing a comonomer other than ethylene, a vinyl ester, and ethylene a polymer; an ethylene-modified PVA modified with a comonomer other than ethylene or a part of a hydroxyl group of an ethylene-modified PVA-based polymer modified with a comonomer other than ethylene, containing fumarin, butyraldehyde, and benzene An aldehyde such as formaldehyde is crosslinked, and a so-called polyvinyl acetal resin or the like.

The ethylene-modified PVA-based polymer forming the ethylene-modified PVA-based polymer film of the present invention, the ethylene-modified PVA-based polymer modified with a comonomer other than ethylene, and the ethylene-modified PVA-based polymer The amount of modification by the comonomer other than ethylene is preferably 15 mol% or less, and preferably 5 mol% or less.

The aforementioned B used in the manufacture of ethylene modified PVA polymer Examples of the enester include vinyl ester of formic acid, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl valerate, vinyl pivalate, vinyl laurate, vinyl stearate, vinyl benzoate, Tert-ethylene carbonate and the like. These vinyl esters can be used singly or in combination. Among these vinyl esters, vinyl acetate is preferred from the viewpoint of production cost.

In addition, the aforementioned comonomer (co-monomer other than ethylene) may Examples thereof include olefins (α-olefins, etc.) having 3 to 30 carbon atoms such as propylene, 1-butene, and isobutylene; acrylic acid or a salt thereof; methyl acrylate, ethyl acrylate, n-propyl acrylate, and isopropyl acrylate. Acrylates such as n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate (for example, carbon number 1 to 18 of acrylic acid) Ethyl methacrylate or its salt; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, A methacrylate such as butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate or octadecyl methacrylate (for example, carbon number of methacrylic acid 1~) 18 alkyl ester); acrylamide, N-methyl acrylamide, N-ethyl acrylamide, N,N-dimethyl acrylamide, diacetone acrylamide, acrylamide sulfonic acid or Acrylamide derivative of salt, acrylamidopropyl dimethylamine or a salt thereof, N-methylol acrylamide or a derivative thereof Biological; methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamide or its salt, methacrylamide propylamine a methacrylamide derivative such as a salt thereof, N-methylol methacrylamide or a derivative thereof; N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone, etc. N-vinyl decylamine; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, Vinyl ethers such as tributyl vinyl ether, dodecyl vinyl ether, and stearic acid vinyl ether; nitriles such as acrylonitrile and methacrylonitrile; vinyl chloride, vinylidene chloride, and vinyl fluoride , vinylidene fluoride such as vinylidene fluoride An allyl compound such as allyl acetate or allyl chloride; an unsaturated dicarboxylic acid such as maleic acid or itaconic acid, a salt thereof or a derivative thereof; a vinyl trimethoxy decane or the like; Vinyl decyl compound; isopropenyl acetate; unsaturated sulfonic acid or its derivative. Among these, α-olefin is preferred.

The ethylene-modified PVA-based polymer contained in the ethylene-modified PVA-based polymer film of the present invention has an ethylene unit content of from 1 to 4 mol%, preferably from 1.5 to 3.5 mol%. . By setting the ethylene unit content to 1 mol% or more, it is possible to cope with a high elongation rate, and even if the uniaxial stretching is performed at a high speed and a high magnification, cracking of the film is less likely to occur, whereby the stretching operation can be performed without interruption. A stretched film such as a polarizing film excellent in optical performance such as polarizing performance is produced at a low cost and with good productivity. On the other hand, by setting the ethylene unit content to 4 mol% or less, the water solubility of the ethylene-modified PVA-based polymer can be maintained at a high level, and ethylene-modified PVA-based polymerization can be produced from an aqueous film-forming stock solution. In the case of the film, the productivity is improved, and the dyeability of the obtained ethylene-modified PVA-based polymer film or the stability of the iodine complex of the polarizing element can be improved, and the obtained color tone of the polarizing film can be prevented. Blue to green.

The average degree of polymerization of the ethylene-modified PVA-based polymer forming the ethylene-modified PVA-based polymer film of the present invention is preferably 1,000 or more, from the viewpoint of the polarizing performance and durability of the obtained polarizing film. The above is preferred, and 2000 or more is more preferable. On the other hand, from the viewpoint of easiness, elongation, and the like of producing a homogeneous ethylene-modified PVA-based polymer film, the average polymerization of the ethylene-modified PVA-based polymer The upper limit of the degree is preferably 8,000 or less, and particularly preferably 6,000 or less.

Here, the "average degree of polymerization" of the ethylene-modified PVA-based polymer in the present specification means an average degree of polymerization measured according to JIS K6726-1994, and the ethylene-modified PVA-based polymer is further saponified, and after purification, The ultimate viscosity measured in water at 30 ° C was obtained.

The ethylene-modified PVA-based polymer film of the present invention contains The degree of saponification of the ethylene-modified PVA-based polymer is preferably 95.0 mol% or more, and 98.0 mol% or more, preferably 99.0, from the viewpoints of polarizing performance and durability of the obtained polarizing film. Moore% or more is more preferable, and 99.3 mol% or more is the best. On the other hand, in order to obtain an ethylene-modified PVA-based polymer having a degree of saponification of more than 99.999 mol%, it is necessary to react with a strong saponification catalyst for a long period of time, and the production cost is likely to be high, and problems such as coloring due to side reactions are likely to occur. Therefore, the degree of saponification of the ethylene-modified PVA-based polymer is preferably 99.999 mol% or less.

Here, the "saponification degree" of the ethylene-modified PVA-based polymer in the present specification means a structural unit (typically a vinyl ester unit) and a vinyl alcohol unit which can be converted into a vinyl alcohol unit by saponification. In terms of the total number of moles, the proportion of the number of moles of the vinyl alcohol unit (% by mole). The degree of saponification of the ethylene-modified PVA-based polymer can be measured in accordance with the description in JIS K6726-1994.

The ethylene modified PVA polymer film of the invention can only The ethylene-modified PVA-based polymer is contained as the PVA-based polymer. However, in addition to the above-mentioned ethylene-modified PVA-based polymer, other PVA-based polymers other than the above may be contained. The content of the above ethylene-modified PVA-based polymer in the ethylene-modified PVA-based polymer film of the present invention is 50% by mass or more is preferable, 80% by mass or more is preferable, and 90% by mass or more is more preferable.

The method for producing the ethylene-modified PVA-based polymer film of the present invention is not particularly limited, and any method can be used as long as it can produce an ethylene-modified PVA-based polymer film satisfying the above formulas (I) and (II). A method of manufacturing the ethylene-modified PVA-based polymer film of the present invention can be smoothly and continuously manufactured with high productivity by the following manufacturing method: (a) using a rotating shaft parallel to each other In the film forming apparatus of the plurality of drying rolls, the film forming stock solution containing the ethylene-modified PVA-based polymer is discharged into a film form on the first drying roll of the film forming apparatus, partially dried, and then dried in a subsequent drying roll. In this case, (b) the rotation speed (S _T ) of the drying roll when the volatile component ratio of the ethylene-modified PVA polymer film is 13% by mass is relative to the number of rotations (S ₁ ) of the first drying roll The ratio (S _T /S ₁ ) is set to 0.990 to 1.050; (c) the drying roller when the ratio of the rotation speed (S _L ) of the final drying roll to the volatile component ratio of the ethylene-modified PVA-based polymer film is 13% by mass speed (S _T) of the ratio (S _L / S _T) is set at 0.960 ~ 0.980; (d) final drying roller Speed (S _L) ratio relative to the first drying roller speed (S ₁₎ of the (S _L / S ₁₎ is set at 0.970 ~ 1.010.

The method for producing the above ethylene-modified PVA-based polymer film will be specifically described below.

The film-forming stock solution containing the ethylene-modified PVA-based polymer can be prepared by mixing an ethylene-modified PVA-based polymer with a liquid solvent to form a solution, or melting an ethylene-modified PVA-based polymer particle or the like containing a liquid solvent or the like. The melt is prepared to prepare.

The ethylene-modified PVA-based polymer is dissolved in a liquid solvent, and the ethylene-modified PVA-based polymer particles containing a liquid solvent or the like are melted, and can be carried out using a stirring type mixing device, a melt extruder, or the like.

The liquid solvent to be used at this time may, for example, be water, dimethyl hydrazine, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylenediamine or diethylenetriamine. These liquid solvents One type may be used alone or two or more types may be used in combination. Among these, water, dimethyl hydrazine, or a mixture of the two is suitably used, and water is particularly suitable.

Promote ethylene-modified PVA-based polymers in liquid solvents It is preferable to add a plasticizer to the film forming stock solution from the viewpoint of dissolving or melting, improving the passability in the production of the film, and improving the elongation of the obtained ethylene-modified PVA-based polymer film.

The plasticizer is preferably a polyhydric alcohol, and examples thereof include ethylene glycol, glycerin, diglycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and trimethylolpropane. These plasticizers can be used. One type alone or two or more types are combined. One or two or more of glycerin, diglycerin, and ethylene glycol are preferably used among the above-mentioned ones.

The amount of plasticizer added is based on the modified PVA system relative to ethylene. It is preferably 0 to 30 parts by mass, preferably 3 to 25 parts by mass, and particularly preferably 5 to 20 parts by mass, based on 100 parts by mass of the polymer. When the amount of the plasticizer added exceeds 30 parts by mass based on 100 parts by mass of the ethylene-modified PVA-based polymer, the obtained ethylene-modified PVA-based polymer film becomes too soft and the usability is lowered. .

From the promotion of the manufacture of ethylene modified PVA polymer film by From the viewpoint of the peeling property of the drying roll peeling, the usability of the obtained ethylene-modified PVA-based polymer film, and the like, it is preferred to add a surfactant to the film forming stock solution. The type of the surfactant is not particularly limited, and an anionic surfactant or a nonionic surfactant is preferably used.

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

Further, the nonionic surfactant is preferably an alkyl ether type such as an alkyl ether type such as polyoxyethylene oleyl ether or an alkyl phenyl ether type such as polyoxyethylene octyl phenyl ether or an alkyl ester type such as polyoxyethylene laurate or the like. Alkylamine type such as oxyethylene laurylamine ether, alkylguanamine type such as polyoxyethylene laurate decylamine, polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether, oleic acid diethanolamine or the like An allyl phenyl ether type nonionic surfactant such as an alkanoguanamine type or a polyoxyalkylene allylic phenyl ether. These surfactants may be used alone or in combination of two or more.

The amount of surfactant added is relative to ethylene modified PVA It 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, based on 100 parts by mass of the polymer. When the amount is less than 0.01 parts by mass, the effect of improving the film forming property and the peeling property may not easily occur. On the other hand, if it is more than 1 part by mass, the surfactant may be eluted to the surface of the film to become sticky. The reason for the connection, the situation of reduced usability.

The ethylene-modified PVA-based polymer which does not hinder the present invention is thin The range of characteristics of the film, the film forming stock solution may also contain various additives, such as stabilizers (such as antioxidants, ultraviolet absorbers, heat stabilizers, etc.) ), a compatibilizing agent, an anti-blocking agent, a flame retardant, an antistatic agent, a lubricant, a dispersing agent, a fluidizing agent, an antibacterial agent, and the like. These additives may be used alone or in combination of two or more.

Used in the manufacture of ethylene modified PVA polymer film The ratio of the volatile component of the film forming solution is preferably 60 to 75% by mass, and preferably 65 to 70% by mass. When the ratio of the volatile component of the film-forming raw material solution is less than 60% by mass, the viscosity of the film-forming raw material solution becomes high, and it is difficult to perform filtration or defoaming, and it is also difficult to carry out the film formation itself. On the other hand, when the volatile component ratio of the film forming raw material is more than 75% by mass, the viscosity may become too low to impair the uniformity of the thickness of the ethylene-modified PVA-based polymer film.

Here, the "volatile component ratio of the film forming solution" as used herein means the ratio of the volatile component obtained by the following formula [iii].

Volatile component ratio (% by mass) of the film-forming raw material solution = {(Wa - Wb) / Wa} × 100 [iii] [wherein, Wa represents the mass (g) of the film forming stock solution, and Wb represents Wa (g). The mass (g) of the film stock solution after drying for 16 hours in an electric drier at 105 °C. ]

In the film forming apparatus including a plurality of drying rolls in which the rotation axes are parallel to each other used for the production of the ethylene-modified PVA-based polymer film, the number of drying rolls is preferably three or more, and four or more are preferable. ~30 is better.

The plurality of drying rolls are preferably formed of a metal such as nickel, chromium, copper, iron, stainless steel or the like, and particularly preferably a metal material having a specular gloss which is not easily corroded by the surface of the roll. In addition, in order to improve The durability of the drying roll is preferably a single layer or a combination of two or more layers such as a plated nickel layer, a chromium layer or a nickel/chromium alloy layer.

The roll surface temperature of each of the plurality of drying rolls is preferably 65 ° C or higher, and preferably 75 ° C or higher. Further, the roll surface temperature of each of the drying rolls may be preferably 100 ° C or more, preferably 100 to 120 ° C, of the roll surface temperature which can be used as the heat treatment roll in the final step or the step close thereto, and the other is preferably 100 to 120 ° C. The surface temperature of the roll of the drying roll is preferably 100 ° C or less.

The film forming device used in the above manufacturing method can also be adapted It is necessary to have a hot air oven type hot air drying device, a heat treatment device, a humidity control device, and the like after a plurality of drying rolls.

Ethylene modification will be carried out on the first drying roll of the film forming apparatus When the film forming raw material of the PVA-based polymer is discharged into a film form, a known film-like discharge device (film-like casting device) such as a T-slit die, a hopper plate, an I-die, or a lip coating die is used. The film forming stock solution containing the ethylene-modified PVA-based polymer was discharged onto the first drying roll to form a film (casting).

The liquid containing the ethylene-modified PVA-based polymer which is formed into a film on the first drying roll is dried on the first drying roll, and the volatile component ratio of the ethylene-modified PVA-based polymer film is preferably 17 to 30. The mass %, preferably 17 to 29% by mass, more preferably 18 to 28% by mass, is peeled off by the first drying roll.

When the volatile component ratio of the ethylene-modified PVA-based polymer film at the time of peeling from the first drying roll is less than 17% by mass, the value of Δn(MD) _Ave with respect to Δn(TD) _Ave becomes large and does not satisfy the formula. On the other hand, when the volatile component ratio of the ethylene-modified PVA-based polymer film is more than 30% by mass when peeled off from the first drying roll 1, it is difficult to peel off from the first drying roll, depending on the case. The tendency to rupture or prone to uneven markings.

Here, the "ethylene modified PVA polymerization" in this specification The ratio of the volatile component of the film or the ethylene-modified PVA-based polymer film refers to the ratio of the volatile component obtained by the following formula [iv].

A (% by mass) = {(Wc - Wd) / Wc} × 100 [iv] [wherein, A represents a volatile component ratio (% by mass) of the ethylene-modified PVA-based polymer film or the ethylene-modified PVA-based polymer film And Wc represents the mass (g) of the sample taken from the ethylene-modified PVA-based polymer film or the ethylene-modified PVA-based polymer film, and Wd indicates that the sample Wc (g) is placed at a temperature of 50 ° C and a pressure of 0.1 kPa or less. Mass (g) when dried in a vacuum dryer for 4 hours. ]

An ethylene-modified PVA-based polymer film or an ethylene-modified PVA system formed by using a film-forming stock solution prepared by using a polyvinyl alcohol-modified PVA-based polymer, a polyol (plasticizer) such as glycerin, a surfactant, and water. When the polymer film is dried under the conditions of "temperature of 50 ° C and pressure of 0.1 kPa or less for 4 hours", only water will volatilize, and other components other than water will hardly volatilize, and remain in the ethylene-modified PVA. In the polymer film or the ethylene-modified PVA-based polymer film, the volatile component ratio of the ethylene-modified PVA-based polymer film or the ethylene-modified PVA-based polymer film can be determined by measuring the ethylene-modified PVA-based polymer film. The moisture content (water ratio) contained in the ethylene-modified PVA-based polymer film was determined.

When drying is performed on the first drying roll, the surface temperature of the roll of the first drying roll is 80 from the viewpoint of uniform drying property, drying speed, and the like. ~120 ° C is better, 85 ~ 105 ° C is better, 93 ~ 99 ° C is better. When the surface temperature of the first drying roll exceeds 120° C., the film becomes easily foamed. On the other hand, when the temperature is less than 80° C., the drying on the first drying roll becomes insufficient, which tends to cause peeling failure.

The rotation speed (S ₁ ) of the first drying roll is preferably 8 to 25 m/min, and 11 to 23 m/min, from the viewpoints of uniform drying property, drying speed, and productivity of the ethylene-modified PVA polymer film. Preferably, 14 to 22 m/min is more preferred. When the number of revolutions (S ₁ ) of the first drying roll is less than 8 m/min, the productivity is lowered, and the birefringence tends to become large, which is not preferable. On the other hand, when the number of revolutions (S ₁ ) of the first drying roll exceeds 25 m/min, drying on the first drying roll tends to be insufficient, which is not preferable.

Ethylene-modified PVA-based polymer that is discharged into a film The film forming stock solution is partially dried on the first drying roll, and can be heated only by the first drying roll. However, from the viewpoint of uniform drying property, drying speed, etc., the first drying roll is heated, and The film surface which is not in contact with the first drying roll (hereinafter referred to as the "first drying roll non-contact surface") is blown with hot air, and it is preferable to heat and dry both surfaces of the ethylene-modified PVA-based polymer film.

When the hot air is blown to the non-contact surface of the first drying roll of the ethylene-modified PVA-based polymer film on the first drying roll, the hot air is blown at a wind speed of 1 to 10 m/sec over the entire area of the non-contact surface of the first drying roll. Preferably, the hot air is preferably blown at a wind speed of 2 to 8 m/sec, and the hot air is preferably blown at a wind speed of 3 to 8 m/sec.

If the wind speed of the hot air blown to the non-contact surface of the first drying roll is too small, it is difficult to obtain the ethylene modified PVA having a high limit elongation ratio which is the object of the present invention. It is a polymer film, and dew condensation such as water vapor occurs when drying on the first drying roll, and the water droplets are dropped into the ethylene-modified PVA-based polymer film, and the finally obtained ethylene-modified PVA-based polymer film is likely to occur. defect. On the other hand, if the wind speed of the hot air blown to the non-contact surface of the first drying roll is too large, it is difficult to obtain an ethylene-modified PVA-based polymer film having a high limit elongation ratio which is the object of the present invention, and the finally obtained ethylene-modified PVA. The polymer film is uneven in thickness, and as a result, problems such as occurrence of uneven dyeing are likely to occur.

From the viewpoints of drying efficiency, uniformity of drying, etc., The temperature of the hot air blown to the non-contact surface of the first drying roll of the ethylene-modified PVA-based polymer film is preferably 50 to 150 ° C, more preferably 70 to 120 ° C, and even more preferably 80 to 95 ° C. Further, the dew point of the hot air which is blown to the non-contact surface of the first drying roll of the ethylene-modified PVA-based polymer film is preferably 10 to 15 °C. When the temperature of the hot air blown to the non-contact surface of the first drying roll of the ethylene-modified PVA-based polymer film is too low, the drying efficiency and the uniform drying property are likely to be lowered. On the other hand, if the temperature is too high, foaming is likely to occur. .

Used for the first drying of ethylene modified PVA polymer film The method of blowing the hot air on the non-contact surface of the roller is not particularly limited, and the hot air having uniform wind speed and uniform temperature can be uniformly blown to the non-contact surface of the first drying roller of the PVA-based polymer film, which is suitable for all of them, either It can be used, and it is suitable to use a nozzle type, a rectifying plate type, or the like. The blowing direction of the hot air which is blown to the non-contact surface of the first drying roll of the ethylene-modified PVA-based polymer film may be a direction in which the first drying roll is not in contact with the first drying roll, or may be substantially along the ethylene-modified PVA system. The direction of the circumferential shape of the non-contact surface of the first drying roll of the polymer film (substantially along the roll table of the first drying roll) The direction of the circumference of the face), or a direction other than it.

In addition, it is preferable to polymerize the ethylene-modified PVA on the first drying roll. When the film is dried, the volatile component generated by the ethylene-modified PVA-based polymer film and the hot air after the blowing are discharged. The method of exhausting is not particularly limited. However, it is preferable that the hot air which is blown to the non-contact surface of the first drying roll of the ethylene-modified PVA-based polymer film does not cause wind speed unevenness and temperature unevenness.

Will be dried on the first drying roll to a suitable volatile content ratio The ethylene-modified PVA-based polymer film having a rate of 17 to 30% by mass is peeled off from the first drying roll, and this time, the first drying roll non-contact surface of the ethylene-modified PVA-based polymer film is opposed to the second drying roll, It is preferred that the second drying roll is dried.

The ratio (S ₂ /S ₁ ) of the number of rotations (S ₂ ) of the second drying rolls to the number of rotations (S ₁ ) of the first drying rolls is preferably from 1.005 to 1.090, more preferably from 1.010 to 1.080. When the ratio (S ₂ /S ₁ ) is less than 1.005, the peeling point of the ethylene-modified PVA-based polymer film peeled off by the first drying roll tends to be uneven, and the birefringence unevenness in the width direction becomes large. It is not possible to use it as a raw material for optical film. On the other hand, when the ratio (S ₂ /S ₁ ) exceeds 1.090, the ethylene-modified PVA-based polymer film of the present invention having a high ultimate stretch ratio is not easily obtained.

When the second drying roller is dried, it is uniformly dried and dried. From the viewpoint of the drying speed and the like, the surface temperature of the second drying roll is preferably 65 to 100 ° C, preferably 65 to 98 ° C, and more preferably 75 to 96 ° C.

Ethylene modified PVA after drying with a second drying roll The polymer film is peeled off by the second drying roll, and the third drying roll, the fourth drying roll, and the fifth drying roll are used in accordance with the number of drying rolls provided in the film forming apparatus. A plurality of drying rolls, etc., are sequentially dried.

In the above-mentioned production method, the number of revolutions (S _T ) of the drying rolls when the volatile component ratio of the ethylene-modified PVA-based polymer film is 13% by mass is based on the number of revolutions (S ₁ ) of the first drying rolls. The ratio (S _T /S ₁ ) is 0.990 to 1.050 to adjust the tension associated with the ethylene-modified PVA-based polymer film while drying. Here, the "drying roll when the volatile component ratio of the ethylene-modified PVA-based polymer film is 13% by mass" means that the volatile component ratio of the ethylene-modified PVA-based polymer film on the drying roll is 13% by mass. In the case where the ratio of the volatile component between the two drying rolls is 13% by mass, the drying roller means a drying roller located at the rear of the two drying rolls. By setting the ratio (S _T /S ₁ ) to the above range, in the drying step until the volatile component ratio of the ethylene-modified PVA polymer film is 13% by mass, the film does not become slack or entangled. The problem is that the birefringence in the longitudinal direction (MD) can be smoothly produced by averaging the thickness direction of the film [Δn(MD) _Ave ] and the birefringence in the width direction (TD) along the thickness direction of the film. The average value [Δn(TD) _Ave ] satisfies the above formulas (I) and (II), and further satisfies the ethylene-modified PVA-based polymer film of the present invention of the above formula (III).

The ratio (S _T /S ₁ ) in the case of producing an ethylene-modified PVA-based polymer film is preferably 1.000 to 1.045.

In the above-described production method, an ethylene-modified PVA-based polymer film having a volatile component ratio of 13% by mass is further dried by a subsequent drying roll to produce an ethylene-modified PVA-based polymer film. In the above-described production method, the ratio of the number of revolutions (S _L ) of the final drying roll to the number of revolutions (S _T ) of the drying roll when the ratio of the volatile component of the ethylene-modified PVA polymer film is 13% by mass (S _L /S _T ) is set in the range of 0.960 to 0.980 while drying. By setting the ratio (S _L /S _T ) to the above range, in the drying step until the final ethylene-modified PVA-based polymer film is obtained, problems such as slack or entanglement of the film do not occur, and the smoothness can be smoothly performed. A value obtained by averaging the birefringence in the longitudinal direction (MD) in the thickness direction of the film [Δn(MD) _Ave ] and a value in which the birefringence in the width direction (TD) is averaged along the thickness direction of the film is produced [ Δn(TD) _Ave ] satisfies the above formulas (I) and (II), and further satisfies the ethylene-modified PVA-based polymer film of the invention of the above formula (III).

The ratio (S _L /S _T ) when the ethylene-modified PVA-based polymer film is produced is preferably 0.963 to 0.976.

Further, when the ethylene-modified PVA-based polymer film is produced by the above method, the birefringence in the longitudinal direction (MD) of the ethylene-modified PVA-based polymer film is averaged along the thickness direction of the film [Δn (MD) ) _Ave ] and the value of the birefringence in the width direction (TD) averaged along the thickness direction of the film [Δn(TD) _Ave ] according to the rotation speed of the first drying roller (S ₁ ) and the rotation speed of the final drying roller ( The ratio of S _L ) (S _L /S ₁ ) varies. In order to smoothly produce the ethylene-modified PVA-based polymer film of the present invention which satisfies the above formula (III) and satisfy the above formula (I) and (II), it is necessary to adjust the number of revolutions (S _L ) of the final drying roll relative to the first The ratio of the rotation speed (S ₁ ) of the drying rolls (S _L /S ₁ ) is set in the range of 0.970 to 1.010, preferably in the range of 0.972 to 1.008, and preferably in the range of 0.975 to 1.006. Thereby, the occurrence of wrinkles or slack can be suppressed, and the ethylene-modified PVA-based polymer film which satisfies the above formula (III) and which satisfies the above formula (III) can be smoothly produced.

Among the above manufacturing methods, the final drying roll or The surface temperature near the final drying roll and the final drying roll is increased to be used as a heat treatment roll. In the case where the drying roll is used as a heat treatment roll, the surface temperature of the roll is preferably from 90 to 140 ° C, preferably from 100 to 130 ° C.

Further, a heat treatment device different from the drying roller may be provided.

In the process from the first drying roller to the final drying roller, The heating direction in the case where the olefin-modified PVA-based polymer film is dried is not particularly limited. However, from the viewpoint of allowing the ethylene-modified PVA-based polymer film to be more uniformly dried, any of the ethylene-modified PVA-based polymer films can be used. It is preferred that the surface of the portion and the back surface are alternately dried in such a manner as to contact the respective drying rolls of the first drying roll to the final drying roll.

Ethylene modified PVA polymer subjected to the above drying treatment The film may be subjected to heat treatment, humidity control, or the like as necessary, and finally wound into a roll shape at a predetermined length, whereby the ethylene-modified PVA-based polymer film of the present invention can be obtained.

By the above-described series of processes, the volatile component ratio of the finally obtained ethylene-modified PVA-based polymer film is preferably in the range of 1 to 5% by mass, and preferably in the range of 2 to 4% by mass.

In order to modify the PVA-based polymer film from the ethylene of the present invention The polarizing film is produced by dyeing and uniaxially stretching using the ethylene-modified PVA-based polymer film of the present invention, and for example, dyeing, uniaxial stretching, and fixing treatment using the ethylene-modified PVA-based polymer film of the present invention. Drying treatment is further carried out in accordance with the necessity of heat treatment. The order of dyeing and uniaxial stretching is not particularly limited and can be performed in a single axis The dyeing treatment may be performed before the stretching treatment, or may be performed simultaneously with the uniaxial stretching treatment, or may be performed after the uniaxial stretching treatment. In addition, the steps of uniaxial stretching, dyeing, etc. may be repeated multiple times. If the uniaxial stretching is particularly divided into two or more stages, it is easy to uniformly extend, which is suitable.

Used for dyeing ethylene modified PVA polymer film For dyes, iodine or dichroic organic dyes can be used (eg direct black 17, 19, 154; direct brown 44, 106, 195, 210, 223; direct red 2, 23, 28, 31, 37, 39, 79, 81 , 240, 242, 247; direct blue 1, 15, 22, 78, 90, 98, 151, 168, 202, 236, 249, 270; direct purple 9, 12, 51, 98; direct green 1, 85; direct Yellow 8, 12, 44, 86, 87; direct orange 26, 39, 106, 107 and other dichroic dyes). These dyes may be used alone or in combination of two or more. The dyeing can be usually carried out by immersing the ethylene-modified PVA-based polymer film in a solution containing the above dye, and the treatment conditions or treatment methods thereof are not particularly limited.

Ethylene modified PVA polymer film in the longitudinal direction The (MD) extended uniaxial stretching can be carried out by either a wet stretching method or a dry heat stretching method, but from the viewpoint of the performance and quality stability of the obtained polarizing film, it is wet. The extension method is better. The wet stretching method is a method in which an ethylene-modified PVA-based polymer film is extended in an aqueous solution containing various components such as pure water, an additive, or an aqueous solvent, or an aqueous dispersion in which various components are dispersed, and is extended by wet stretching. Specific examples of the method for performing uniaxial stretching include a method of performing uniaxial stretching in warm water containing boric acid, a solution containing the dye, or a later description. A method of performing uniaxial stretching in a fixed treatment bath or the like.

The elongation temperature at the time of uniaxial stretching by the wet stretching method It is not particularly limited, and for example, it can be used in the range of 30 to 90 ° C and further in the range of 40 to 70 ° C. However, since cracking does not occur, it is possible to smoothly perform uniaxial stretching at a relatively high speed. Preferably, the temperature in the range of 55 to 67 ° C is used, and the temperature in the range of 57 to 65 ° C is preferably used, and the temperature in the range of 59 to 64 ° C is more preferable. In particular, in the case where the uniaxial stretching is carried out in two or more stages, it is particularly preferable to use the above temperature at least in the stage where the stretching ratio is the largest (the final stage of the uniaxial stretching step).

The extension speed at the time of uniaxial stretching is not particularly limited, and examples are not particularly limited. For example, the length of the ethylene-modified PVA-based polymer film before the uniaxial stretching may be 30%/min or more, and further 100%/min or more. However, as long as the ethylene-modified PVA-based polymer film of the present invention is used, Even if the uniaxial stretching is performed at a high speed and a high magnification, the rupture of the film is less likely to occur, whereby the stretching operation can be interrupted, and the polarizing property excellent in optical performance such as polarizing performance can be produced with high productivity, low cost, and productivity. a stretched film of a film or the like, and thus it is preferable to include a step of uniaxially stretching at an elongation speed of 300%/min or more based on the length of the ethylene-modified PVA-based polymer film before uniaxial stretching, including The step of uniaxially extending at an elongation speed of 500%/min or more is preferable, and the step of performing uniaxial stretching at an elongation speed of 700%/min or more is more preferable. Further, if the stretching speed is too fast, there is a tendency that cracking or uneven stretching tends to occur during stretching. Therefore, the elongation speed is not based on the length of the ethylene-modified PVA-based polymer film before uniaxial stretching. exceed Preferably, 2000%/minute is preferred, and no more than 1600%/minute is preferred, and no more than 1300%/minute is preferred, and no more than 1000%/minute is preferred.

Stretch magnification for uniaxial extension processing (single in multiple stages) In the case of the axial extension, the total stretching ratio is preferably as far as possible from the viewpoint of the polarizing performance, and it is preferably 4 times or more, more preferably 5 times or more, and 5.5 times. The above is better. The upper limit of the stretching ratio is not particularly limited as long as the film is not broken, and is preferably 8.0 times or less in order to uniformly spread.

The thickness of the stretched film (polarizing film) is preferably from 1 to 35 μm, particularly from 5 to 30 μm. However, in the case of using an ethylene-modified PVA-based polymer film having a thickness of less than 30 μm as described above, the stretched film can be used ( The thickness of the polarizing film is set to 15 μm or less.

In order to make the dye strongly adsorbed when manufacturing a polarizing film Most of the films that are uniaxially stretched are fixed. Fixing treatment Generally, a method of immersing a film in a treatment bath to which boric acid and/or a boron compound is added can be widely used. At this time, an iodine compound may be added to the treatment bath as necessary.

Uniaxial extension processing, or uniaxial extension processing and fixing The film after the treatment is then subjected to a drying treatment (heat treatment). The drying treatment (heat treatment) has a temperature of 30 to 150 ° C, preferably 50 to 140 ° C. When the temperature of the drying treatment (heat treatment) is too low, the dimensional stability of the obtained polarizing film is likely to be lowered. On the other hand, if it is too high, the polarizing performance tends to be lowered as the dye is decomposed or the like.

An optically transparent and mechanically strong protective film can be formed on both sides or a single side of the polarizing film obtained as described above. Polarizer. In this case, the protective film can be made of cellulose triacetate (TAC) film, acetic acid. A cellulose tyrosinate (CAB) film, an acrylic film, a polyester film, or the like. Further, as the adhesive for bonding the protective film, a PVA-based adhesive or an urethane-based adhesive can be generally used, and a PVA-based adhesive is suitably used.

The polarizing plate obtained as described above can be bonded to a glass substrate after being coated with an adhesive such as acrylic, and used as a component of a liquid crystal display device. When the polarizing plate is bonded to the glass substrate, the phase difference film, the viewing angle lifting film, the brightness enhancement film, and the like may be bonded together.

[Examples]

The invention is specifically illustrated by the following examples, but the invention is not limited by the following examples.

In the following examples, reference examples, and comparative examples, the volatile component ratio of the film forming raw material solution, the volatile component ratio (moisture ratio) of the ethylene-modified PVA polymer film or the ethylene-modified PVA polymer film, and ethylene modification The physical properties of the PVA-based polymer film and the optical properties of the polarizing film were measured by the following methods.

(1) Volatile component ratio of the film forming stock solution: It is obtained by the above formula [iii] according to the above method.

(2) Volatile component ratio (water content) of the ethylene-modified PVA-based polymer film or the ethylene-modified PVA-based polymer film: It is obtained by the above formula [iv] according to the above method.

In addition, the measurement of the volatile component ratio (water content) of the ethylene-modified PVA-based polymer film or the ethylene-modified PVA-based polymer film is used. The sample taken in the center of the width direction (TD) of the ethylene-modified PVA-based polymer film or the ethylene-modified PVA-based polymer film taken out by the drying roll was carried out.

(3) Δn(MD) _{Ave of the} ethylene-modified PVA-based polymer film: an ethylene-modified PVA was obtained by the above method in the item "Measurement method of "1" Δn (MD) _Ave " △ n (MD) of the central portion based polymer film in the width direction (TD) of _Ave, which was designated as the ethylene-modified PVA polymer films △ n (MD) _Ave.

(4) Δn(TD) _{Ave of the} ethylene-modified PVA-based polymer film: The ethylene-modified PVA system was obtained by the above method by the item "Measurement method of "2" △n(TD) _Ave " △ n (TD) in the central portion of the polymer film widthwise direction (TD) of _Ave, which is defined as an ethylene-modified PVA-based polymer film △ n (TD) _Ave.

(5) Mass swellability of ethylene-modified PVA-based polymer film: The ethylene-modified PVA-based polymer film was cut into 1.5 g, immersed in 1000 g of distilled water at 30 ° C for 30 minutes, and after immersion for 30 minutes, ethylene was taken out. The PVA-based polymer film was measured for its mass (W _e ) after the surface water was absorbed by a filter paper. Next, the ethylene-modified PVA-based polymer film was dried in a dryer at 105 ° C for 16 hours, and then the mass (W _f ) thereof was measured. From the obtained masses W _e and W _f , the mass swelling degree of the ethylene-modified PVA-based polymer film was determined by the following formula [v].

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

(6) Ultimate stretching ratio of the ethylene-modified PVA-based polymer film: the central portion in the width direction (TD) of the ethylene-modified PVA-based polymer film before stretching obtained in the following Examples, Reference Examples, or Comparative Examples A test piece having a length direction (MD) × a width direction (TD) = 10 cm × 5 cm was taken, and both ends of the test piece in the longitudinal direction were lengthwise (MD) × width direction (TD) = 5 cm × 5 cm, fixed to the extension jig, immersed in water at 30 ° C for 38 seconds, at this time, at a stretching speed of 12 cm / min (240% / min) uniaxial extension in the length direction (MD) (extension of the first segment) 2.2 times to the original length, and then immersed in an iodine/potassium iodide aqueous solution containing iodine at a concentration of 0.03 mass% and potassium iodide at a concentration of 3 mass% at a temperature of 30 ° C for 90 seconds, at which time, at 12 cm/min ( The extension speed of 240%/min) is uniaxially extended in the longitudinal direction (MD) (extension of the second stage) to 3.3 times the original length, and then, boric acid is contained at a concentration of 3% by mass and potassium iodide is contained at a concentration of 3% by mass. And immersed in a boric acid/potassium iodide aqueous solution at a temperature of 30 ° C for about 20 seconds, at which time, at 12 cm / min. The extension speed of (240%/min) was uniaxially extended in the longitudinal direction (MD) (extension in the third stage) to 3.6 times the original length, and then contained boric acid at a concentration of 4% by mass and a concentration of about 5% by mass. Immersed in a boric acid/potassium iodide aqueous solution containing potassium iodide and at a predetermined temperature, while uniaxially extending in the longitudinal direction (MD) at a predetermined extension speed (extension of the fourth stage) until the test piece is broken, and reading the elongation at break of the test piece (rupture) The ratio of the length of the time to the original length).

The same ethylene modified PVA-based polymer film was subjected to the above extension test 5 times, and the average value thereof was determined as an ethylene-modified PVA-based polymer film. The ultimate extension ratio (times).

(7) Optical properties of the polarizing film: (i) Transmittance: The central portion in the width direction of the polarizing film obtained in the following Examples, Reference Examples, or Comparative Examples was parallel to the alignment direction of the polarizing film, and 1.5 cm × Two samples of 1.5 cm square were used, respectively, using a spectrophotometer V-7100 (with integral sphere) manufactured by Hitachi, Ltd., according to JIS Z8722 (measurement method of object color), C light source, and visible light region of 2 degree field of view The illuminance correction of the polarizing film samples is measured for the light transmittance of the case where the polarizing film sample is inclined by 45 degrees with respect to the direction of the extension axis and the light transmittance of the case of the inclination of -45 degrees, and the average value (Y _{1 is obtained).} ).

For the other polarizing film sample, the light transmittance in the case of tilting 45 degrees and the light transmittance in the case of tilting -45 degrees were measured in the same manner as described above, and the average value (Y _{2 was obtained).} ).

The above-obtained Y ₁ and Y _{2 were} averaged to determine the transmittance (Y) (%) of the polarizing film.

(ii) Polarization degree: the light transmittance (Y ∥) in the case where the two polarizing film samples taken in the above (i) are overlapped so that the alignment directions thereof are parallel, and the alignment directions are orthogonal to each other. The light transmittance (Y ⊥) in the case was measured in the same manner as the above-described method for measuring the transmittance, and the degree of polarization (V) (%) was obtained from the following formula [vi].

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

(iii) Polarization degree at a transmittance of 44.25%: as described in the following examples, reference examples, and comparative examples, In the example, the reference example, or the comparative example, the immersion time in the iodine/potassium iodide aqueous solution at the time of the second stage extension was changed, and the transmittance (Y) was obtained by the above method for each of the five polarizing films produced. The degree of polarization (V), with the transmittance (Y) as the horizontal axis and the polarization (V) as the vertical axis, respectively, for the five points of each of the examples, the reference examples, or the comparative examples, and the approximate curves are obtained. From the approximate curve, the value of the degree of polarization (V) when the transmittance (Y) was 44.25% was obtained.

"Embodiment 1"

(1) Manufacture of ethylene-modified PVA-based polymer film: An ethylene-modified PVA-based polymer obtained by saponifying ethylene-modified polyvinyl acetate obtained by copolymerizing ethylene and vinyl acetate (ethylene unit content: 2.0 mol%, saponification degree: 99.9 mol%, polymerization) The film forming stock solution having a degree of 2400), 100 parts by mass, 12 parts by mass of glycerin, 0.1 parts by mass of lauric acid diethanolamine, and a volatile component ratio of 66% by mass of water is discharged from the T die to the first drying roll (surface temperature: 93 ° C) In the first drying roll, the hot air of 90° C. was blown to the entire non-contact surface of the first drying roll at a wind speed of 5 m/sec while drying to moisture. The rate was 18% by mass, and then peeled off by the first drying roll, and the surface of the portion of the ethylene-modified PVA-based polymer film was brought into contact with the back surface and the respective drying rolls were contacted. After the second drying roll, the surface of the roll was used. The temperature was dried at about 85 ° C, and finally, heat treatment was carried out at a final drying roll (heat treatment roll) having a surface temperature of 108 ° C, and then entangled to obtain an ethylene-modified PVA-based polymer film (thickness 60 μm, width 3 m, volatile component ratio 3 mass). %). In the first embodiment, the drying roller when the volatile component ratio is 13% by mass is the seventh drying roller.

In the first embodiment, (α) is a ratio of the number of revolutions (S _T ) of the drying roll (seventh drying roll) to the number of rotations (S ₁ ) of the first drying roll when the ratio of the volatile component is 13% by mass (S) _T / S ₁ ) is set to 1.000; (β) the ratio of the number of revolutions (S _T ) of the drying roll (seventh drying roll) when the ratio of the number of revolutions (S _L ) of the final drying roll to the volatile component is 13% by mass ( S _L /S _T ) is set to 0.974; (γ) the ratio of the rotation speed (S ₂ ) of the second drying roller to the rotation speed (S ₁ ) of the first drying roller (S ₂ /S ₁ ) is set to 1.030; δ) Ratio of the number of revolutions (S _T ) of the drying roll (seventh drying roll) when the number of revolutions (S _T+1 ) of the subsequent drying roll (the eighth drying roll) is 13% by mass with respect to the volatile component ratio ( S _T /S _T+1 ) is set to 0.998; (ε) the ratio of the rotation speed (S _L ) of the final drying roller to the rotation speed (S ₁ ) of the first drying roller (S _L /S ₁ ) is set to 0.975. An ethylene-modified PVA-based polymer film was produced.

Δn(MD) _Ave , Δn(TD) _Ave , mass swellability, and ultimate extension ratio of the obtained ethylene-modified PVA-based polymer film (the temperature of the boric acid/potassium iodide aqueous solution extended in the fourth stage was set to 63 The measurement was carried out by the above method, and the elongation was set to 48 cm/min (960%/min). The results are shown in Table 1 below.

(2) Manufacture of polarizing film: (i) a test piece in the longitudinal direction (MD) × width direction (TD) = 10 cm × 5 cm in the center portion of the width direction (TD) of the ethylene-modified PVA polymer film obtained in the above (1), Both ends of the test piece in the longitudinal direction were fixed to the extension jig so that the dimension of the extension portion was lengthwise (MD) × width direction (TD) = 5 cm × 5 cm, and immersed in water at a temperature of 30 ° C for 38 seconds. Uniaxial extension (length 1 extension) to the original length in the length direction (MD) at an extension speed of 12 cm/min (240%/min) 2.2 times, and then immersed in an iodine/potassium iodide aqueous solution containing iodine at a concentration of 0.03 mass% and containing potassium iodide at a concentration of 3 mass% and a temperature of 30 ° C for 60 seconds, at which time, at 12 cm / minute (240% / The extension speed of the minute) is uniaxially extended in the longitudinal direction (MD) (extension of the second stage) to 3.3 times the original length, and then contains boric acid at a concentration of 3% by mass and potassium iodide at a concentration of 3% by mass and the temperature is Immersion in a 30 ° C boric acid / potassium iodide aqueous solution for about 20 seconds, at this time, at a stretching speed of 12 cm / minute (240% / minute) uniaxial extension in the length direction (MD) (3rd paragraph extension) to 3.6 of the original length Then, it was immersed in a boric acid/potassium iodide aqueous solution containing boric acid at a concentration of 4% by mass and containing potassium iodide at a concentration of about 5% by mass and having a temperature of 63 ° C while being extended at a rate of 48 cm/min (960%/min). Uniaxial extension in the length direction (MD) (extension of the fourth stage) to the stretching ratio just before the ultimate extension ratio of the above-mentioned ethylene-modified PVA-based polymer film, and then containing potassium iodide at a concentration of 3% by mass Immersion in potassium iodide aqueous solution for 10 seconds for iodide ion immersion Treatment and then dried to a dryer 60 deg.] C for 4 minutes, to produce a polarizing film (thickness of about 21μm).

The transmittance (Y) and the degree of polarization (V) of the polarizing film obtained in this manner by the above method are described in the graph in which the horizontal axis is the transmittance (Y) and the vertical axis is the degree of polarization (V). That point.

(ii) in the above (i), except that the second paragraph is extended at the temperature The immersion time in the iodine/potassium iodide aqueous solution at 30 ° C was changed from 60 seconds to 75 seconds, 90 seconds, 105 seconds, or 120 seconds, and the same operation as in the above (i) was performed to produce a transmittance. Four different polarizing films (thickness of about 21 μm).

The transmittance (Y) and the degree of polarization (V) of each of the polarizing films obtained in this manner were determined by the above methods, and the points in the above (i) were traced.

(iii) plot the approximate curve of the five points described in the above figures (i) and (ii) on the graph, and obtain the degree of polarization (V) when the transmittance (Y) is 44.25% from the approximate curve. The value of the results is as shown in the following Table 1, which is 99.98.

<<Example 2》

(1) In the first embodiment, the film formation conditions when the ethylene-modified PVA polymer film is produced are changed as described in the following Table 1, and the discharge amount when the film is discharged onto the first drying roll is changed. An ethylene-modified PVA-based polymer film having a thickness of 25 μm was produced in the same manner as in (1) of Example 1.

Δn(MD) _Ave , Δn(TD) _Ave , mass swellability, and ultimate extension ratio of the ethylene-modified PVA-based polymer film obtained in this manner (the temperature of the boric acid/potassium iodide aqueous solution extended in the fourth stage) The measurement was carried out by the above method at a temperature of 64 ° C and an elongation speed of 48 cm / min (960% / min). The results are shown in Table 1 below.

(2) A test piece having a longitudinal direction (MD) × a width direction (TD) = 10 cm × 5 cm taken from a central portion in the width direction (TD) of the ethylene-modified PVA-based polymer film obtained in the above (1), Further, the temperature of the boric acid/potassium iodide aqueous solution extended in the fourth stage was changed from 63 ° C to 64 ° C, and the same operation as in the second embodiment (1) was carried out to produce five kinds of polarizing films, and the transmittance of each polarizing film was determined ( Y) and the degree of polarization (V), which are plotted in the graph in which the horizontal axis is the transmittance (Y) and the vertical axis is the director (V), and the approximate curves of the five points depicted in the graph are plotted. Graphically, obtained from the approximation curve The value of the degree of polarization (V) when the overshoot (Y) was 44.25%, and the results are shown in Table 1 below.

"Examples 3~5"

(1) In the first embodiment, the film formation conditions when the ethylene-modified PVA-based polymer film was produced were changed as described in the following Table 1, and a thickness of 60 μm was produced in the same manner as in the first embodiment (1). Ethylene modified PVA based polymer film.

Δn(MD) _Ave , Δn(TD) _Ave , mass swellability, and ultimate extension ratio of each of the ethylene-modified PVA-based polymer films obtained in this manner (the boric acid/potassium iodide aqueous solution extended in the fourth stage) The temperature was set to 63 ° C and the stretching speed was set to 48 cm / min (960% / min). The measurement was carried out by the above method, and the results are shown in Table 1 below.

(2) A test piece in the longitudinal direction (MD) × width direction (TD) = 10 cm × 5 cm taken from the center portion of the width direction (TD) of each of the ethylene-modified PVA-based polymer films obtained in the above (1) The same operation as in (2) of the first embodiment was carried out, and five kinds of polarizing films were produced in each of the examples, and the transmittance (Y) and the degree of polarization (V) of each of the polarizing films were determined, and the transverse axis was transmitted. The point is plotted in the graph of the rate (Y) and the polarization (V) on the vertical axis, and the approximate curve of the five points traced in the graph is plotted on the graph, and the transmittance (Y) is obtained from the approximate curve. The value of the degree of polarization (V) at 44.25% was as shown in Table 1 below.

Reference Example 1

(1) In Example 1, the ethylene-modified PVA-based polymer was changed to an unmodified PVA which was not subjected to ethylene modification (an article obtained by saponifying polyvinyl acetate). The degree of saponification was 99.9 mol. %, degree of polymerization 2400), A PVA film having a thickness of 60 μm was produced in the same manner as in (1) of Example 1.

Δn(MD) _Ave , Δn(TD) _Ave , mass swellability, and ultimate extension ratio of the PVA film obtained in this manner (the temperature of the boric acid/potassium iodide aqueous solution extended in the fourth stage was set to 60 ° C, and the elongation was extended. The speed was determined to be 48 cm/min (960%/min) by the above method (the PVA film was measured as an ethylene-modified PVA-based polymer film), and the results are shown in Table 1 below.

(2) A test piece having a longitudinal direction (MD) × a width direction (TD) = 10 cm × 5 cm taken from a central portion in the width direction (TD) of the PVA film obtained in the above (1), and extending the fourth segment The temperature of the boric acid/potassium iodide aqueous solution was changed from 63 ° C to 60 ° C, and the same operation as in (2) of Example 1 was carried out to produce five kinds of polarizing films, and the transmittance (Y) and the degree of polarization of each polarizing film were determined ( V), the point is drawn in the graph in which the horizontal axis is the transmittance (Y) and the vertical axis is the degree of polarization (V), and the approximate curve of the five points traced in the graph is plotted on the graph. The curve was used to obtain the value of the degree of polarization (V) when the transmittance (Y) was 44.25%. The results are shown in Table 1 below.

Reference Example 2

(1) With respect to the PVA film obtained in (1) of Reference Example 1, the temperature of the boric acid/potassium iodide aqueous solution extended in the fourth stage was set to 63 ° C, and the stretching speed was set to 48 cm/min (960%/min) by The ultimate stretching ratio was measured by the above method (the PVA film was regarded as an ethylene-modified PVA-based polymer film), and the results are shown in Table 1 below.

(2) Further, the longitudinal direction (MD) × width direction taken in the central portion of the width direction (TD) of the PVA film obtained in (1) of Reference Example 1 was used. (TD) = 10 cm × 5 cm test piece, the same operation as in (2) of Example 1 was carried out, and five kinds of polarizing films were produced, and the transmittance (Y) and the degree of polarization (V) of each polarizing film were determined. The point is drawn in the graph in which the horizontal axis is the transmittance (Y) and the vertical axis is the degree of polarization (V), and the approximate curve of the five points traced in the graph is plotted on the graph, and the approximate curve is obtained. The value of the degree of polarization (V) when the transmittance (Y) was 44.25%, and the results are shown in Table 1 below.

Comparative Example 1~7

(1) In the first embodiment, the type of the ethylene-modified PVA-based polymer to be used and the film-forming conditions in the production of the ethylene-modified PVA-based polymer film are changed as described in the following Table 2, and examples In the same manner as (1), an ethylene-modified PVA-based polymer film having a thickness of 60 μm was produced.

Δn(MD) _Ave , Δn(TD) _Ave , mass swellability, and ultimate extension ratio of each of the ethylene-modified PVA-based polymer films obtained in this manner (the boric acid/potassium iodide aqueous solution extended in the fourth stage) The temperature was set to 63 ° C and the elongation rate was set to 48 cm / min (960% / min). The measurement was carried out by the above method, and the results are shown in Table 2 below.

(2) A test piece in the longitudinal direction (MD) × width direction (TD) = 10 cm × 5 cm taken from the center portion of the width direction (TD) of each of the ethylene-modified PVA-based polymer films obtained in the above (1) The same operation as in (2) of Example 1 was carried out, and five kinds of polarizing films were produced in each comparative example, and the transmittance (Y) and the degree of polarization (V) of each polarizing film were determined, and the transverse axis was transmitted. The point is plotted in the graph of the rate (Y) and the polarization (V) on the vertical axis, and the approximate curve of the five points traced in the graph is plotted on the graph, and the transmittance (Y) is obtained from the approximate curve. The value of the degree of polarization (V) at 44.25% was as shown in Table 2 below.

As shown in Tables 1 and 2 above, the ethylene-modified PVA-based polymer films of Examples 1 to 5 contain Δn(MD) _Ave by containing an ethylene-modified PVA-based polymer having a specific amount of ethylene units. The value of the birefringence in the longitudinal direction (MD) of the ethylene-modified PVA-based polymer film averaged along the thickness direction of the film] and Δn(TD) _Ave [the width direction of the ethylene-modified PVA-based polymer film ( The value of the birefringence of TD) averaged along the thickness direction of the film] satisfies the formulas (I) and (II), and even if it is extended at a high speed, it has a high limit stretch ratio of 6.76 to 6.92, and is implemented by The polarizing film obtained from the ethylene-modified PVA-based polymer film of Examples 1 to 5 has excellent polarizing performance equivalent to or higher than that of the conventional polarizing film.

In particular, in the second embodiment, the ethylene-modified PVA-based polymer film has a thickness of 25 μm, and similarly to the other examples, even at a high speed, a high limit stretch ratio and excellent polarized light are achieved. performance.

In contrast, the ethylene modified PVA of Comparative Examples 1 to 3 The polymer film did not satisfy the formula (I), the ethylene modified PVA polymer films of Comparative Examples 4 and 5 did not satisfy the formula (II), and the ethylene modified PVA polymer films of Comparative Examples 6 and 7 did not have Since the ethylene-modified PVA-based polymer of the specific amount of the ethylene unit is lower than the ethylene-modified PVA-based polymer film of Examples 1 to 5, the ultimate stretching ratio is low in any case, and the obtained in Comparative Example 7 is obtained. The polarizing film was blue in comparison with the polarizing films of Examples 1 to 5.

Further, since the PVA films of Reference Examples 1 and 2 do not contain an ethylene-modified PVA-based polymer having a specific amount of ethylene units, the limit stretching ratio is lowered at a high speed, and the polarized film obtained is polarized. Performance is also reduced.

When a polarizing film is produced from a PVA-based polymer film, In order to avoid cracking of the film during stretching, uniaxial stretching is performed at a stretching ratio slightly lower than the ultimate stretching ratio, and the limit extension ratio of the ethylene-modified PVA-based polymer film of Examples 1 to 5 is as high as either. 6.76 or more, the ethylene-modified PVA-based polymer film of Examples 1 to 5 can be uniaxially stretched at a high stretching ratio of 6 times or more even when the polarizing film is produced under the conditions of the examples, even if it is 6.5. The uniaxial stretching is performed at a high stretching ratio of more than twice, and the film does not rupture and can be smoothly extended.

On the other hand, in the ethylene-modified PVA-based polymer film of Comparative Examples 1 to 7, when the polarizing film was produced under the conditions of the comparative example, when the film was uniaxially stretched at a stretching ratio of 6 times or more, the film was broken. concern.

In addition, in the raw material film for a polarizing film, there is also 1 In the case where the length of the roll is 1000 m or more, for example, in the case of a PVA-based polymer film having a total length of 1000 m, the limit stretch ratio is increased by 0.1 point (0.1 times), and the length of the stretched film obtained by uniaxial stretching is increased by 100 m (1000 m). ×0.1 times=100 m), a large number of polarizing films can be obtained from the raw material film of the same length.

From the results of Examples 1 to 5, the ethylene-modified PVA-based polymer films of Examples 1 to 5 had higher limit extension ratios than the ethylene-modified PVA-based polymer films of Comparative Examples 1 to 7, It is 0.13 to 0.90 point (times). Therefore, for example, when the length of the ethylene-modified PVA-based polymer film is 1000 m, the polarizing film is produced under the conditions of the above examples using this article, and Comparative Examples 1 to 7 are used. The situation of the PVA film In comparison, the length of the polarizing film becomes longer, and it becomes 130 to 900 m, and a large polarizing film can be obtained.

Claims (5)

An ethylene-modified polyvinyl alcohol-based polymer film characterized by comprising an ethylene-modified polyvinyl alcohol-based polymer having an ethylene unit content of 1 to 4 mol%, and satisfying the following formulas (I) and (II) ): △n(MD) _Ave -0.1×10 ^-3 ≦△n(TD) _Ave ≦△n(MD) _Ave +0.25×10 ^-3 (I) △n(TD) _Ave ≦2.5×10 ^-3 ( II) [In the above formula, Δn(MD) _Ave represents a value obtained by averaging the birefringence in the machine direction of the ethylene-modified polyvinyl alcohol-based polymer film along the thickness direction of the film, Δn(TD) _Ave The value obtained by averaging the birefringence in the width direction of the ethylene-modified polyvinyl alcohol-based polymer film along the thickness direction of the film]. An ethylene-modified polyvinyl alcohol-based polymer film according to claim 1 which satisfies the following formula (III): 1.3 × 10 ^-3 ≦ Δn (MD) _Ave ≦ 2.0 × 10 ^-3 (III) . The ethylene-modified polyvinyl alcohol-based polymer film of claim 1 or 2 has a thickness in the range of 10 to 65 μm. A method for producing a polarizing film, which comprises dyeing and uniaxially stretching using an ethylene-modified polyvinyl alcohol-based polymer film according to any one of claims 1 to 3. The production method of claim 4, which comprises the step of uniaxially stretching at an elongation speed of 300%/min or more based on the length of the ethylene-modified polyvinyl alcohol polymer film before uniaxial stretching.