JPWO2013137056A1 - Ethylene-modified polyvinyl alcohol polymer film - Google Patents

Abstract

An ethylene-modified PVA polymer film containing an ethylene-modified PVA polymer having an ethylene unit content of 1 to 4 mol% and satisfying the following formulas (I) and (II), having good stretchability and productivity . Δn (MD) Ave-0.1-10-3≰Δn (TD) Ave≰Δn (MD) Ave + 0.25-10-3 (I) Δn (TD) Ave≰2.5-10-3 (II) [In the above formula, Δn (MD) Ave represents a value obtained by averaging the birefringence in the machine flow direction of the ethylene-modified PVA polymer film in the thickness direction of the film, and Δn (TD) Ave represents ethylene-modified The value which averaged the birefringence of the width direction of the PVA-type polymer film in the thickness direction of the said film is shown. ]

Description

  The present invention relates to a polyvinyl alcohol polymer film modified with ethylene (hereinafter, “polyvinyl alcohol” may be abbreviated as “PVA”) and a method for producing a polarizing film using the same. More specifically, the present invention provides a stretched film having excellent optical performance such as polarization performance without causing the film to break even when stretched at a high speed and a high magnification, and without causing interruption of the stretching work accompanying the breakage of the film. The present invention relates to an ethylene-modified PVA polymer film that can be produced with high yield and high productivity, and a method for producing a polarizing film using the same.

  A polarizing plate having a light transmission and shielding function is an important component of a liquid crystal display (LCD) together with a liquid crystal having a light switching function. The field of application of this liquid crystal display device is also used in small devices such as calculators and wristwatches in the early days of development, notebook computers, liquid crystal monitors, liquid crystal color projectors, liquid crystal televisions, in-vehicle navigation systems, mobile phones, and measurements used indoors and outdoors. It has been extended to a wide range of devices, especially for LCD monitors and LCD TVs.

  In general, a polarizing plate is obtained by uniaxially stretching a PVA polymer film and then dyeing it with iodine or a dichroic dye, and then performing a fixing treatment with a boron compound after dyeing and uniaxially stretching the PVA polymer film. A protective film such as a cellulose triacetate film or an acetic acid / butyric acid cellulose film is produced on one side or both sides of the polarizing film obtained by producing a polarizing film by the method, a method of performing fixing treatment simultaneously with dyeing in any of the above methods It is manufactured by pasting together.

In recent years, along with the expansion of applications of liquid crystal display devices, in addition to the enhancement of display quality, further cost reduction and further improvement in handling are required. From the viewpoint of cost reduction, it is possible to improve the production speed when manufacturing a polarizing film, to prevent the stretching failure (breaking) when stretching a PVA polymer film, to reduce the breaking loss and to improve the yield. It is necessary to prevent interruption of stretching work and stretching / dying work due to film breakage.
In addition, as one of the improvements in productivity when manufacturing a polarizing film, there is a demand for shortening the drying time when manufacturing a polarizing film. From this point, as a raw film for a polarizing film, In general, a PVA polymer film having a thickness of about 75 μm has been used. However, in recent years, a PVA polymer film having a thickness of less than 70 μm and a thinner film has been demanded.
However, the thinner the PVA polymer film, the more likely it is to break when stretched at a high speed and a high magnification. From this point, it is possible to stretch at a high speed and a high magnification without breaking even if it is thin. Therefore, there is a need for a PVA polymer film that can produce a polarizing film having polarization performance equal to or better than that of conventional products with good workability, high yield, low cost, and high productivity. Yes.

  Conventionally, for the purpose of improving the stretchability of a PVA polymer film, improving the uniformity during stretching, and improving the polarization performance and durability of a polarizing film obtained by stretching a PVA polymer film, In forming a film while drying using a stock solution containing a coalescence, adjustment of film forming draw (ratio of transport speed of PVA polymer film between rolls used for film formation), PVA polymer during film formation Adjustment of the moisture content of the film has been performed.

  As such a conventional technique, (1) in order to obtain a stretched film having a sufficient molecular orientation when uniaxially stretched, the film forming operation for producing a PVA polymer film is carried out to 1 or less. A method in which film forming draw is employed and film forming tension is lowered as much as possible (Patent Document 1, especially paragraphs [0008] to [0009], examples thereof); (2) High-stretching is possible When producing a PVA polymer film using a drum film forming machine for the purpose of obtaining a PVA polymer film, [winding speed of the obtained PVA polymer film] / [film forming raw material is Method of setting the speed of the drum located at the uppermost stream to be supplied] to 0.8 to 1.3 (Patent Document 2); (3) To obtain a PVA polymer film capable of being stretched at a high magnification As a PVA using a drum film forming machine In the drying step for producing the polymer film, the speed ratio (Rf / Rc) of the process speed Rc and the final winding speed Rf at the time when the volatile content of the film becomes 10% by weight or less is 0.9 to 1. 1 is known (Patent Document 3).

In addition, (4) in order to obtain a PVA-based film that can produce a wide polarizing film having uniform optical performance even in a large area, the volatile content of the PVA film is 10% or less. The tensile elongation in the MD direction is controlled by controlling the speed ratio (Rf / Rc) between the speed (Rc) and the winding speed (Rf) to 0.9 to 1.1 to reduce temperature spots in the drying process. _{(S M)} and a method (Patent Document 4) TD direction of the tensile elongation ratio of the _{(S T) (S M /} S T) to produce a PVA-based film from 0.7 to 1.3; (5) In order to obtain a PVA-based film capable of producing a wide polarizing film having uniform optical performance even in a large area, when the volatile content of the PVA film reaches 10 to 50% by weight, the drum located on the most upstream side is used. PVA film is peeled off and located on the most upstream side A method in which the speed ratio V2 / V1 of the speed V2 of the ram and the speed V2 of the drum located in the process where the volatile content of the PVA film is less than 10% by weight is set to 1.0 to 1.3 (Patent Document 5) It has been known.

Further, (6) In order to obtain a PVA polymer film comprising a specific skin layer / core layer / skin layer which can be uniformly uniaxially stretched and gives a stretched film free from fine cracks and voids when stretched, A stock solution containing a volatile polymer content of 50 to 90% by mass is heated with a first drying roll, and at the same time, hot air is blown on a PVA polymer film surface not in contact with the first drying roll under predetermined conditions to volatilize. When the fraction reaches 15 to 30% by mass, the PVA polymer film is peeled off from the first drying roll and brought into contact with the second drying roll and dried. At that time, the peripheral speed of the first drying roll ( A method of making the ratio (S ₂ / S ₁ ) between S ₁ ) and the peripheral speed (S ₂ ) of the second drying roll (S ₂ / S ₁ ) 1.000 to 1.100 (Patent Document 6) is known.

JP-A-6-136151 JP 2001-315141 A JP 2001-315146 A JP 2002-30164 A JP 2002-79531 A JP 2005-324355 A

“Polymer Science One Point 10 Photophysical Properties of Polymers”, first edition, third edition, Kyoritsu Shuppan Co., Ltd., December 15, 2007, p. 19-21

  However, in Patent Documents 1 to 6 described above, when a PVA polymer film, particularly a PVA polymer film having a thin film thickness, is uniaxially stretched at a high magnification, a measure for preventing the film from breaking. In particular, there is no disclosure of a measure for further improving the limit draw ratio of the film. Further, in the conventional techniques such as Patent Documents 1 to 6, when the stretching speed is increased, problems such as breakage of the film during the stretching process are likely to occur, and it is difficult to stretch at high speed.

The object of the present invention is to make a stretched film such as a polarizing film having optical performance equivalent to or better than that of a conventional product with good workability, high yield and low yield even when stretched at high speed and high magnification. An object of the present invention is to provide a PVA polymer film that can be manufactured with good productivity at low cost.
In particular, the object of the present invention is to have a high limit drawing ratio and a high drawing speed even if it is thinner than a PVA polymer film conventionally used in the production of a polarizing film, and to draw at a high speed and a high magnification. The film can be smoothly uniaxially stretched without causing breakage, and can be made into a thinner stretched film than before, and the drying time when manufacturing a polarizing film can be further shortened to produce more polarizing film. It is providing the PVA-type polymer film which can be manufactured with sufficient property.
Another object of the present invention is to provide a method for producing a polarizing film using the PVA polymer film.

As a result of intensive studies by the present inventors to achieve the above object, a PVA polymer film (ethylene-modified PVA polymer film) is obtained using an ethylene-modified PVA polymer containing a specific amount of ethylene units. A film was formed, and a value obtained by averaging the birefringence in the machine flow direction (length direction) of the film 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 satisfying a specific relationship and making the value obtained by averaging the birefringence in the width direction of the film in the thickness direction of the film into a specific numerical range, the film breaks even when stretched at high speed and high magnification. It has been found that a stretched film such as a polarizing film, which is less likely to occur and has excellent optical performance such as polarization performance, can be manufactured with high yield, low cost and high productivity without interrupting the stretching operation. It was.
In particular, the value obtained by averaging the birefringence in the machine flow direction of the ethylene-modified PVA polymer film in the thickness direction of the film and the value obtained by averaging the birefringence in the width direction in the thickness direction of the film have a specific relationship. The above-mentioned ethylene-modified PVA polymer film satisfying and having a value obtained by averaging the birefringence in the width direction in the thickness direction of the film in a specific range is generally used in the production of a polarizing film. Even with a thickness of about 10 to 65 μm, which is thinner than the thickness of the PVA polymer film that has been produced, it can be smoothly uniaxially stretched at a high speed and a high magnification without causing breakage. It has been found that the film can be made thinner at the time of manufacture and that the drying time can be further reduced when manufacturing the polarizing film, and further studies are made based on these findings and the present invention. Completed.

That is, the present invention
[1] An ethylene-modified PVA polymer film containing an ethylene-modified PVA polymer having an ethylene unit content of 1 to 4 mol% and satisfying the following formulas (I) and (II):
Δn (MD) _Ave −0.1 × 10 ⁻³ ≦ Δn (TD) _Ave ≦ Δn (MD) _Ave + 0.25 × 10 ⁻³ (I)
Δn (TD) _Ave ≦ 2.5 × 10 ⁻³ (II)
[In the above formula, Δn (MD) _Ave represents a value obtained by averaging the birefringence in the machine flow direction of the ethylene-modified PVA polymer film in the thickness direction of the film, and Δn (TD) _Ave represents ethylene modification. The value which averaged the birefringence of the width direction of the PVA-type polymer film in the thickness direction of the said film is shown. ]
[2] The ethylene-modified PVA polymer film of the above [1] that satisfies the following formula (III);
1.3 × 10 ⁻³ ≦ Δn (MD) _Ave ≦ 2.0 × 10 ⁻³ (III)
[3] The ethylene-modified PVA polymer film of [1] or [2] above having a thickness in the range of 10 to 65 μm;
[4] A method for producing a polarizing film, characterized by dyeing and uniaxially stretching using any one of the ethylene-modified PVA polymer films of [1] to [3] above;
[5] The production method of the above-mentioned [4], comprising a step of uniaxially stretching at a stretching rate of 300% / min or more based on the length of the ethylene-modified PVA polymer film before uniaxial stretching;
About.

When producing a stretched film, the ethylene-modified PVA polymer film of the present invention is less likely to break the film even when uniaxially stretched at a high speed and a high magnification, and thus has excellent optical performance such as polarization performance. A stretched film such as a film can be produced with high yield, low cost and high productivity without interrupting the stretching operation.
In particular, the ethylene-modified PVA polymer film of the present invention has a thickness of about 10 to 65 μm, which is thinner than the thickness of a PVA polymer film that has been conventionally used to produce a polarizing film or the like. Even so, it can be smoothly uniaxially stretched at a high speed and a high magnification without causing breakage, and accordingly, it becomes possible to further reduce the thickness of the stretched film, thereby producing a polarizing film and the like. It is possible to further shorten the drying time and improve the productivity.
In recent years, a PVA polymer film having a length of more than 1000 m has been used as a raw film for a polarizing film, but the ethylene-modified PVA polymer film of the present invention has a high limit draw ratio. Therefore, the film can be stretched at a higher magnification than the conventional one, and thereby the amount of the polarizing film obtained from the ethylene-modified PVA polymer film can be increased more than before.
Furthermore, by adopting the method for producing a polarizing film of the present invention, a polarizing film excellent in polarizing performance can be produced with high yield, low cost and high productivity without interrupting the stretching operation.

FIG. 1 is a schematic view showing a sample collection method when measuring Δn (MD) _Ave of an ethylene-modified PVA polymer film. FIG. 2 is a schematic diagram showing a sample collection method when measuring Δn (TD) _Ave of an ethylene-modified PVA polymer film.

The present invention is described in detail below.
In general, in a transparent film manufactured using a transparent polymer such as a PVA polymer, the polymer chain is oriented in the flow direction (machine flow direction: length direction) due to plastic deformation or strain due to shear stress. The polarization directions of the constituent atomic groups are macroscopically aligned, which causes birefringence specific to the polymer (Non-patent Document 1).
The birefringence [Δn (MD)] in the machine flow direction in the PVA polymer film is obtained from the following formula [i], and the birefringence [Δn (TD)] in the width direction is given by the following formula [ii]. It is requested from.
Δn (MD) = nMD−nz [i]
Δn (TD) = nTD−nz [ii]
[Where nMD is the refractive index in the machine flow direction (length direction) of the film, nTD is the refractive index in the width direction of the film, and nz is the refractive index in the thickness direction of the film. ]

  As described in Non-Patent Document 1, in a film manufactured using a transparent polymer such as a PVA polymer, the polymer chains forming the film are oriented in the machine flow direction (length direction). The PVA polymer films including the PVA polymer films described in Patent Documents 1 to 6 described above are generally “birefringence index [Δn (MD)]”> “width direction”. The birefringence [Δn (TD)] ”, that is, the birefringence [Δn (MD)] in the machine direction tends to be larger than the birefringence [Δn (TD)] in the width direction.

On the other hand, the ethylene-modified PVA polymer film of the present invention is different from the conventional PVA polymer film in that it satisfies the following formulas (I) and (II).
Δn (MD) _Ave −0.1 × 10 ⁻³ ≦ Δn (TD) _Ave ≦ Δn (MD) _Ave + 0.25 × 10 ⁻³ (I)
Δn (TD) _Ave ≦ 2.5 × 10 ⁻³ (II)
[In the above formula, Δn (MD) _Ave represents a value obtained by averaging the birefringence in the machine flow direction of the ethylene-modified PVA polymer film in the thickness direction of the film, and Δn (TD) _Ave represents ethylene modification. The value which averaged the birefringence of the width direction of the PVA-type polymer film in the thickness direction of the said film is shown. ]

That is, as seen in the above formula (I), in the ethylene-modified PVA polymer film of the present invention, the machine flow direction of the ethylene-modified PVA polymer film (when continuously forming the ethylene-modified PVA polymer film) (Δn (MD) _Ave ), which is a value obtained by averaging the birefringence of the film direction (hereinafter sometimes referred to as “length direction (MD)”) in the thickness direction of the film, is an ethylene-modified PVA-based weight. “Δn (TD)” is a value obtained by averaging the birefringence of the combined film in the width direction (a direction perpendicular to the length direction) [hereinafter sometimes referred to as “width direction (TD)”] in the thickness direction of the film. _Even if it is equal to or somewhat smaller than “ _Ave ” or exceeds “Δn (TD) _Ave ”, the amount is small.
Further, the ethylene-modified PVA polymer film of the present invention is characterized in that it satisfies the above formula (II) together with the formula (I).

By satisfying the above formulas (I) and (II), the ethylene-modified PVA polymer film of the present invention has a high limit draw ratio even when the film thickness is thinner than the conventional one. A thin film that has excellent optical performance such as polarizing performance without causing breakage of the film even when uniaxially stretched at a high magnification during the production of a stretched film such as a polarizing film, and without causing interruption of the stretching work accompanying the breakage of the film The stretched film can be manufactured with high yield and high productivity.
When deviating from the above formula (I), the limit stretching ratio of the ethylene-modified PVA polymer film becomes low, and the film tends to break when uniaxially stretched at a high ratio, particularly when the film is thin. Is likely to occur.
The ethylene-modified PVA polymer film of the present invention preferably satisfies the following formula (I ′), more preferably satisfies the following formula (I ″), and the following formula (I ′ ″) It is further preferable to satisfy
Δn (MD) _Ave −0.05 × 10 ⁻³ ≦ Δn (TD) _Ave ≦ Δn (MD) _Ave + 0.23 × 10 ⁻³ (I ′)
Δn (MD) _Ave ≦ Δn (TD) _Ave ≦ Δn (MD) _Ave + 0.2 × 10 ⁻³ (I ″)
Δn (MD) _Ave + 0.05 × 10 ⁻³ ≦ Δn (TD) _Ave ≦ Δn (MD) _Ave + 0.18 × 10 ⁻³ (I ′ ″)

Moreover, when it deviates from the range of the above-mentioned formula (II) and Δn (TD) _Ave of the ethylene-modified PVA polymer film exceeds 2.5 × 10 ⁻³ , the limit draw ratio of the ethylene-modified PVA polymer film Becomes low, it becomes difficult to stretch the ethylene-modified PVA polymer film in the length direction (MD) at a high magnification, and it becomes difficult to obtain a stretched film having excellent optical performance.
In order to make Δn (TD) _Ave too small, it is necessary to allow drying shrinkage in the width direction during production of the ethylene-modified PVA polymer film, and the effective width yield of the ethylene-modified PVA polymer film decreases. Because of the tendency, the ethylene-modified PVA polymer film of the present invention preferably has Δn (TD) _{Ave in} the range of 1.5 × 10 ^{−3 to} 2.2 × 10 ⁻³ , 1.6 It is more preferable that it is in the range of × 10 ^{−3 to} 2.0 × 10 ⁻³ .

The ethylene-modified PVA polymer film of the present invention preferably further satisfies the following formula (III) in addition to the above formulas (I) and (II).
1.3 × 10 ⁻³ ≦ Δn (MD) _Ave ≦ 2.0 × 10 ⁻³ (III)
When the Δn (MD) _{Ave of the} ethylene-modified PVA polymer film is 2.0 × 10 ⁻³ or less, the limit stretching ratio of the ethylene-modified PVA polymer film is further increased, and the ethylene-modified PVA polymer film Can be easily stretched in the length direction (MD) at a high magnification, and a stretched film excellent in optical performance can be obtained more easily. On the other hand, in order to make Δn (MD) _Ave of the ethylene-modified PVA polymer film less than 1.3 × 10 ⁻³ , it is necessary to greatly reduce the peripheral speed ratio of the drying roll. In this case, sagging tends to occur in the ethylene-modified PVA polymer film.
In the ethylene-modified PVA polymer film of the present invention, Δn (MD) _Ave is more preferably in the range of 1.4 × 10 ^{−3 to} 1.95 × 10 ⁻³ , and 1.5 × 10 ⁻³ to More preferably, it is in the range of 1.9 × 10 ⁻³ .

In the ethylene-modified PVA polymer film, the value of Δn (MD) _Ave and / or Δn (TD) _Ave often varies in the width direction (TD) of the film, particularly Δn at both ends in the width direction. (MD) _Ave tends to be high, but at least the center part in the width direction (TD) of the ethylene-modified PVA polymer film satisfies the formulas (I) and (II), and preferably satisfies the formulas (I) to (III) Formula (I) and (II) are preferably used in the entire region of 80% or more of the width direction (TD) centering on the center portion of the width direction (TD) of the ethylene-modified PVA polymer film. Preferably satisfies the formulas (I) to (III). Both ends in the width direction (TD) of the ethylene-modified PVA polymer film not satisfying the formulas (I) and (II) are cut before the ethylene-modified PVA polymer film is stretched in the length direction (MD). Can be removed.

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

<< 1 >> Δn (MD) _Ave measurement method:
(Here, a method of measuring Δn (MD) _Ave at the center in the width direction (TD) of the ethylene-modified PVA polymer film is exemplified.)
(I) At any position in the length direction (MD) of the ethylene-modified PVA polymer film, as shown in FIG. 1 (a), MD × TD = 2 mm from the center in the width direction (TD) of the film A small piece having a size of 10 mm is cut out, and the fine piece is sandwiched on both sides by a PET film having a thickness of 100 μm, and is further sandwiched between wooden frames and attached to a microtome apparatus.
(Ii) Next, as shown in FIG. 1B (PET film and wooden frame are not shown), the strips collected in the above are spaced by 10 μm parallel to the length direction (MD) of the strips. And slice 10 pieces for observation (MD × TD = 2 mm × 10 μm) shown in FIG. From the slice pieces, five slice pieces having a smooth slice surface and no slice thickness unevenness are selected, and each slice piece is placed on a slide glass and the slice thickness is measured with a microscope (manufactured by Keyence Corporation). Observation is performed in a visual field of 10 times the eyepiece and 20 times the objective (total 200 times).
(Iii) Next, the slice piece is tilted as shown in FIG. 1D so that the slice surface can be observed and placed on the slide glass with the slice surface facing upward, and the cover glass and silicone oil (refractive index 1.04). And the retardation of five slice pieces is measured using a two-dimensional photoelasticity evaluation system “PA-micro” (manufactured by Photonic Lattice Co., Ltd.).
(Iv) With the retardation distribution of each slice piece displayed on the “PA-micro” measurement screen, a line α perpendicular to the original film surface is drawn across the slice piece, and a line is formed on the line segment α. Analysis is performed to obtain retardation distribution data in the thickness direction of the film. Observation is performed in a visual field of 10 times the eyepiece and 20 times the objective (total 200 times). Further, in order to suppress an error due to a change in the position where the line segment α passes on the slice piece, an average value of retardation is adopted with a line width of 300 pixels.
(V) The value of retardation distribution in the thickness direction of the film obtained above is divided by the thickness measured with a microscope to obtain a birefringence Δn (MD) distribution in the thickness direction of the film, and the thickness direction of the film is determined. The average value of the birefringence Δn (MD) distribution is taken. The average value of the birefringence Δn (MD) distribution in the thickness direction of each film obtained for the five slice pieces is further averaged to obtain “Δn (MD) _Ave ”.

<< 2 >> Δn (TD) _Ave Measurement Method:
(Here, a method of measuring Δn (TD) _Ave at the center in the width direction (TD) of the ethylene-modified PVA polymer film is exemplified.)
(I) At an arbitrary position in the length direction (MD) of the ethylene-modified PVA polymer film, as shown in FIG. 2 (a), MD × TD = 10 mm from the center in the width direction (TD) of the film. A strip having a size of × 2 mm is cut out, the strip is sandwiched on both sides by a 100 μm-thick PET film, and is further sandwiched between wooden frames and attached to a microtome apparatus.
(Ii) Next, as shown in FIG. 2B (PET film and wooden frame are not shown), the strips collected in the above are parallel to the width direction (TD) of the strips at intervals of 10 μm. Slicing is performed to produce 10 observation slices (MD × TD = 10 μm × 2 mm) shown in FIG. From the slice pieces, five slice pieces having a smooth slice surface and no slice thickness unevenness are selected, and each slice piece is placed on a slide glass and the slice thickness is measured with a microscope (manufactured by Keyence Corporation). Observation is performed in a visual field of 10 times the eyepiece and 20 times the objective (total 200 times).
(Iii) Next, the slice piece is tilted as shown in FIG. 2D so that the slice surface can be observed and placed on the slide glass with the slice surface facing upward, and the cover glass and silicone oil (refractive index 1.04). And the retardation of five slice pieces is measured using a two-dimensional photoelasticity evaluation system “PA-micro” (manufactured by Photonic Lattice Co., Ltd.).
(Iv) With the retardation distribution of each slice piece displayed on the “PA-micro” measurement screen, a line β perpendicular to the original film surface is drawn so as to cross the slice piece, and a line on the line segment β is drawn. Analysis is performed to obtain retardation distribution data in the thickness direction of the film. Observation is performed in a visual field of 10 times the eyepiece and 20 times the objective (total 200 times). Further, in order to suppress an error due to a change in the position where the line segment β passes on the slice piece, an average value of retardation is adopted with a line width of 300 pixels.
(V) The value of retardation distribution in the thickness direction of the film obtained above is divided by the thickness measured with a microscope to obtain the birefringence Δn (TD) distribution in the thickness direction of the film, and the thickness direction of the film is determined. The average value of the birefringence Δn (TD) distribution is taken. The average value of the birefringence Δn (TD) distribution in the thickness direction of each film obtained for five slice pieces is further averaged to obtain “Δn (TD) _Ave ”.

The thickness of the ethylene-modified PVA polymer film of the present invention can be in the range of 5 to 150 μm, but is preferably 10 to 65 μm when used as a raw material for a polarizing film. Since the ethylene-modified PVA polymer film of the present invention has a high limit drawing ratio and can cope with a high drawing speed, the thickness of the film, which has been often used as a raw material for a conventional polarizing film, is about 75 μm. When the thickness is 10 to 65 μm, which is thinner than the PVA polymer film, the film can be stretched at a high speed and a high magnification without causing breakage of the film. By stretching an ethylene-modified PVA polymer film having a thickness of 10 to 65 μm at a high magnification, the thickness of the stretched film can be increased. While it can be made thinner than before, the drying time when manufacturing a polarizing film can be shortened, It is possible to improve the production rate of the light film. From the above viewpoint, the thickness of the ethylene-modified PVA polymer film is more preferably 60 μm or less, and further preferably 50 μm or less. In addition, when uniaxial stretching is performed at a higher temperature using a general PVA polymer film, the film strength after the PVA polymer is dissolved in the bath used for stretching or the water is swollen extremely decreases. However, according to the ethylene-modified PVA polymer film of the present invention, it is possible to suppress dissolution in the bath and extreme decrease in film strength. It can be made thinner. From this viewpoint, when the thickness of the ethylene-modified PVA polymer film is less than 30 μm, the effect of the present invention is more remarkably exhibited. When the thickness of the ethylene-modified PVA polymer film is too thick, it is difficult to quickly dry the polarizing film.
On the other hand, if the thickness of the ethylene-modified PVA polymer film is too thin, the film is likely to break during uniaxial stretching for producing a polarizing film. From this viewpoint, the thickness of the ethylene-modified PVA polymer film is more preferably 15 μm or more, further preferably 18 μm or more, and particularly preferably 20 μm or more.

  The width of the ethylene-modified PVA polymer film of the present invention is not particularly limited, but in recent years, liquid crystal televisions and monitors have become larger, so that the width is 2 m or more so that they can be used effectively for them. Is preferably 3 m or more, more preferably 4 m or more. Moreover, when manufacturing a polarizing plate with a realistic production machine, since the uniform uniaxial stretching may be difficult if the width of the film is too large, the width of the ethylene-modified PVA polymer film is 8 m or less. It is preferable.

The ethylene-modified PVA polymer film of the present invention preferably has a mass swelling degree of 180 to 250%, more preferably 185 to 240%, and still more preferably 190 to 230%. If the degree of mass swelling of the ethylene-modified PVA polymer film is too low, it tends to be difficult to stretch and it becomes difficult to produce a stretched film having excellent optical performance, while if the degree of mass swelling is too high, stretching is likely to occur. Sometimes process passability deteriorates and a highly durable polarizing film may not be obtained.
The mass swelling degree referred to here is obtained by dividing the mass when an ethylene-modified PVA polymer film is immersed in distilled water at 30 ° C. for 30 minutes by the mass after drying at 105 ° C. for 16 hours after the immersion. It means the percentage of the value obtained, and can be specifically measured by the method described in the following examples.

Examples of the ethylene-modified PVA polymer contained in the ethylene-modified PVA polymer film of the present invention include, for example, an ethylene-modified vinyl ester polymer obtained by saponifying an ethylene-modified vinyl ester polymer obtained by copolymerizing ethylene and a vinyl ester. Manufactured by saponification of PVA, ethylene-modified PVA polymer obtained by graft copolymerization of comonomer to main chain of ethylene-modified PVA, ethylene-modified vinyl ester polymer obtained by copolymerization of ethylene, vinyl ester and comonomer other than ethylene A part of the hydroxyl groups of the ethylene-modified PVA polymer, ethylene-modified PVA not modified with a comonomer other than ethylene, or ethylene-modified PVA polymer modified with a comonomer other than ethylene are aldehydes such as formalin, butyraldehyde, and benzaldehyde. Kind , And the like crosslinked called polyvinyl acetal resins.
When the ethylene modified PVA polymer forming the ethylene modified PVA polymer film of the present invention is an ethylene modified PVA polymer modified with a comonomer other than ethylene, a comonomer other than ethylene in the ethylene modified PVA polymer is used. The amount of modification due to is preferably 15 mol% or less, more preferably 5 mol% or less.

  Examples of the vinyl ester used in the production of the ethylene-modified PVA polymer include, for example, vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl valerate, vinyl pivalate, vinyl laurate, vinyl stearate, benzoate. A vinyl acid, a versatic vinyl acid, etc. can be mentioned. These vinyl esters can be used alone or in combination. Of these vinyl esters, vinyl acetate is preferred from the viewpoint of production cost.

  Examples of the comonomer (comonomer other than ethylene) include olefins having 3 to 30 carbon atoms such as propylene, 1-butene and isobutene (such as α-olefin); acrylic acid or a salt thereof; methyl acrylate, Acrylic such as ethyl acrylate, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate Acid esters (for example, C1-18 alkyl esters of acrylic acid); methacrylic acid or salts thereof; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, I-butyl methacrylate, methacryl Methacrylic acid esters such as t-butyl, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate (for example, C1-C18 alkyl ester of methacrylic acid); acrylamide, N-methylacrylamide, N-ethylacrylamide, Acrylamide derivatives such as N, N-dimethylacrylamide, diacetoneacrylamide, acrylamidepropanesulfonic acid or salts thereof, acrylamidepropyldimethylamine or salts thereof, N-methylolacrylamide or derivatives thereof; methacrylamide, N-methylmethacrylamide, N- Ethyl methacrylamide, methacrylamide propane sulfonic acid or its salt, methacrylamide propyl dimethylamine or its salt, N-methylol methacrylate Methacrylamide derivatives such as luamide or derivatives thereof; N-vinylamides such as N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl Vinyl ethers such as vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether and stearyl vinyl ether; Nitriles such as acrylonitrile and methacrylonitrile; Vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride and vinylidene fluoride Allyl compounds such as allyl acetate and allyl chloride; unsaturated dicarboxylic acids such as maleic acid and itaconic acid; derivatives thereof such as salts or esters thereof; Vinyl silyl compounds such as Le trimethoxysilane; isopropenyl acetate; an unsaturated sulfonic acid or its derivatives. Of these, α-olefins are preferred.

  The ethylene unit content of the ethylene-modified PVA polymer contained in the ethylene-modified PVA polymer film of the present invention is in the range of 1 to 4 mol%, and in the range of 1.5 to 3.5 mol%. Preferably there is. When the content of the ethylene unit is 1 mol% or more, it becomes possible to cope with a high stretching speed, and even when uniaxially stretching at a high speed and a high magnification, the film is not easily broken. A stretched film such as a polarizing film having excellent optical performance can be produced with high yield, low cost and high productivity without interrupting the stretching operation. On the other hand, when the ethylene unit content is 4 mol% or less, the water-solubility of the ethylene-modified PVA polymer can be maintained at a high level, and the ethylene-modified PVA polymer film contains water as a film-forming stock solution. The productivity of the polarizing film is improved, and the color tone of the polarizing film obtained by improving the dyeability of the resulting ethylene-modified PVA polymer film and the stability of the iodine complex as a polarizing element is blue. -Prevents greenishness.

The average degree of polymerization of the ethylene-modified PVA polymer forming the ethylene-modified PVA polymer film of the present invention is preferably 1000 or more, more preferably 1500 or more, from the viewpoint of the polarization performance and durability of the obtained polarizing film. 2000 or more is more preferable. On the other hand, the upper limit of the average degree of polymerization of the ethylene-modified PVA polymer is preferably 8000 or less, particularly preferably 6000 or less, from the viewpoint of ease of production of a homogeneous ethylene-modified PVA polymer film and stretchability.
Here, the “average polymerization degree” of the ethylene-modified PVA polymer in the present specification means an average polymerization degree measured according to JIS K6726-1994, and the ethylene-modified PVA polymer is re-saponified and purified. And then obtained from the intrinsic viscosity measured in water at 30 ° C.

The saponification degree of the ethylene-modified PVA polymer contained in the ethylene-modified PVA polymer film of the present invention is preferably 95.0 mol% or more from the viewpoint of the polarizing performance and durability of the obtained polarizing film, and is 98.0. More preferably, mol% or more is more preferable, 99.0 mol% or more is further more preferable, and 99.3 mol% or more is the most preferable. On the other hand, in order to obtain an ethylene-modified PVA polymer having a degree of saponification exceeding 99.999 mol%, it is necessary to react with a strong saponification catalyst for a long time, which tends to increase the production cost, and problems such as coloring due to side reactions. The saponification degree of the ethylene-modified PVA polymer is preferably 99.999 mol% or less.
Here, the “degree of saponification” of the ethylene-modified PVA polymer in the present specification means the total number of moles of structural units (typically vinyl ester units) and vinyl alcohol units that can be converted into vinyl alcohol units by saponification. Is the ratio (mol%) occupied by the number of moles of the vinyl alcohol unit. The degree of saponification of the ethylene-modified PVA polymer can be measured according to the description of JIS K6726-1994.

  The ethylene-modified PVA polymer film of the present invention may contain only the above-mentioned ethylene-modified PVA polymer as the PVA-based polymer, but other than that together with the above-mentioned ethylene-modified PVA polymer. A PVA polymer may be included. The content of the ethylene-modified PVA polymer in the ethylene-modified PVA polymer film of the present invention is preferably 50% by mass or more, more preferably 80% by mass or more, and 90% by mass or more. More preferably.

The production method of the ethylene-modified PVA 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 polymer film satisfying the above-described formulas (I) and (II). However, the ethylene-modified PVA polymer film of the present invention is
(A) Using a film-forming apparatus provided with a plurality of drying rolls whose rotation axes are parallel to each other, a film-forming stock solution containing an ethylene-modified PVA polymer is discharged into a film on the first drying roll of the film-forming apparatus. Partially dried and then dried with a subsequent drying roll to form a film;
(B) Ratio (S _T ) of the peripheral speed (S _T ) of the drying roll when the volatile content of the ethylene-modified PVA polymer film is 13% by mass with respect to the peripheral speed (S ₁ ) of the first drying roll / S ₁ ) between 0.990 and 1.050;
(C) Ratio of the peripheral speed (S _L ) of the final drying roll to the peripheral speed (S _T ) of the drying roll when the volatile content of the ethylene-modified PVA polymer film is 13% by mass (S _L / S _T ) between 0.960 and 0.980;
(D) the peripheral speed of the first drying roll against _{(S 1),} the peripheral speed of the final drying roll ratio of _{(S L) (S L /} S 1) to 0.970 to 1.010;
By the manufacturing method which consists of this, it can manufacture smoothly and continuously with high productivity.

The manufacturing method of the above-described ethylene-modified PVA polymer film will be described more specifically below.
The film-forming stock solution containing an ethylene-modified PVA polymer is mixed with a liquid medium to form a solution, or an ethylene-modified PVA polymer pellet containing the liquid medium is melted to form a melt. Can be prepared.
Dissolution of the ethylene-modified PVA polymer in a liquid medium and melting of the ethylene-modified PVA polymer pellets including the liquid medium can be performed using a stirring mixer, a melt extruder, or the like.
Examples of the liquid medium used at that time include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylenediamine, diethylenetriamine, and the like. More than one species can be used in combination. Among these, water, dimethyl sulfoxide, or a mixture of both are preferably used, and water is more preferably used.

From the viewpoints of accelerating dissolution and melting of ethylene-modified PVA polymer in a liquid medium, improving process passability during film production, and improving stretchability of the resulting ethylene-modified PVA polymer film, It is preferable to add an agent.
As the plasticizer, polyhydric alcohol is preferably used, and examples thereof include ethylene glycol, glycerin, diglycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, and the like. 1 type can be used individually or in combination of 2 or more types. Among these, one or more of glycerin, diglycerin and ethylene glycol are preferably used because they are excellent in the effect of improving stretchability.

  The addition amount of the plasticizer is preferably 0 to 30 parts by mass, more preferably 3 to 25 parts by mass, and particularly preferably 5 to 20 parts by mass with respect to 100 parts by mass of the ethylene-modified PVA polymer. When the addition amount of the plasticizer exceeds 30 parts by mass with respect to 100 parts by mass of the ethylene-modified PVA polymer, the resulting ethylene-modified PVA polymer film may become too soft and handleability may deteriorate.

It is possible to add a surfactant to the film-forming stock solution from the viewpoint of improving the peelability from the drying roll when manufacturing the ethylene-modified PVA polymer film and the handleability of the resulting ethylene-modified PVA polymer film. preferable. The type of the surfactant is not particularly limited, but an anionic surfactant or a nonionic surfactant is preferably used.
As the anionic surfactant, for example, a carboxylic acid type such as potassium laurate, a sulfate type such as octyl sulfate, and a sulfonic acid type anionic surfactant such as dodecylbenzene sulfonate are suitable.
Examples of nonionic surfactants include alkyl ether types such as polyoxyethylene oleyl ether, alkylphenyl ether types such as polyoxyethylene octylphenyl ether, alkyl ester types such as polyoxyethylene laurate, and polyoxyethylene. Alkylamine type such as laurylamino ether, alkylamide type such as polyoxyethylene lauric acid amide, polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether, alkanolamide type such as oleic acid diethanolamide, polyoxyalkylene allylphenyl An allyl phenyl ether type nonionic surfactant such as ether is preferred. These surfactants can be used alone or in combination of two or more.

  The addition amount of the surfactant is preferably 0.01 to 1 part by weight, more preferably 0.02 to 0.5 part by weight, and 0.05 to 0.3 part per 100 parts by weight of the ethylene-modified PVA polymer. Part by mass is particularly preferred. When the amount is less than 0.01 parts by mass, the effect of improving the film-forming property and the peelability may be difficult to appear. On the other hand, when the amount is more than 1 part by mass, the surfactant elutes on the film surface and causes blocking. , The handleability may be reduced.

  The film-forming stock solution has various additives such as a stabilizer (for example, an antioxidant, a UV absorber, a heat stabilizer, etc.), a phase, and the like as long as the properties of the ethylene-modified PVA polymer film of the present invention are not impaired. A solubilizer, an antiblocking agent, a flame retardant, an antistatic agent, a lubricant, a dispersant, a fluidizing agent, an antibacterial agent, and the like may be included. These additives can be used alone or in combination of two or more.

60-75 mass% is preferable and, as for the volatile fraction of the film forming stock solution used for manufacture of an ethylene modified PVA polymer film, 65-70 mass% is more preferable. If the volatile fraction of the film-forming stock solution is less than 60% by mass, the viscosity of the film-forming stock solution becomes high, making filtration and defoaming difficult, and film-forming itself may be difficult. On the other hand, when the volatile fraction of the film-forming stock solution is larger than 75% by mass, the viscosity becomes too low and the uniformity of the thickness of the ethylene-modified PVA polymer film may be impaired.
Here, “the volatile fraction of the film-forming stock solution” as used herein refers to the volatile fraction determined by the following formula [iii].
Volatile fraction (% by mass) of the film-forming stock solution = {(Wa−Wb) / Wa} × 100 [iii]
[Wherein, Wa represents the mass (g) of the film-forming stock solution, and Wb represents the mass (g) after the Wa (g) film-forming stock solution was dried in an electrothermal dryer at 105 ° C. for 16 hours. ]

In a film forming apparatus including a plurality of drying rolls whose rotation axes are parallel to each other used for the production of an ethylene-modified PVA polymer film, the number of drying rolls is preferably 3 or more, and is preferably 4 or more. More preferably, the number is 5-30.
The plurality of drying rolls are preferably formed of a metal such as nickel, chromium, copper, iron, stainless steel, and the like, and in particular, the roll surface is hardly corroded and is formed of a metallic material having a specular gloss. It is more preferable. In order to increase the durability of the drying roll, it is more preferable to use a drying roll plated with a single layer or a combination of two or more layers such as a nickel layer, a chromium layer, and a nickel / chromium alloy layer.
The roll surface temperature of each drying roll in the plurality of drying rolls is preferably 65 ° C. or higher, and more preferably 75 ° C. or higher. The roll surface temperature of each drying roll is preferably 100 ° C. or higher, more preferably 100 to 120 ° C., for the roll surface temperature of the drying roll that can be used as a heat treatment roll in the final step or a step close thereto. The roll surface temperature of the other drying rolls is preferably 100 ° C. or lower.

  The film forming apparatus used in the above manufacturing method may have a hot air oven type hot air drying apparatus, a heat treatment apparatus, a humidity control apparatus, etc., if necessary, following a plurality of drying rolls.

For discharging a film-forming stock solution containing an ethylene-modified PVA-based polymer onto the first drying roll of the film-forming apparatus, for example, a T-type slit die, a hopper plate, an I-die, a lip coater die, etc. A known film-like discharge device (film-like casting device) is used to discharge (cast) a film-forming stock solution containing an ethylene-modified PVA polymer into a film on the first drying roll.
The liquid containing the ethylene-modified PVA polymer discharged in the form of a film on the first drying roll is dried on the first drying roll, and the volatile fraction of the ethylene-modified PVA polymer film is preferably 17 to 30 mass. %, More preferably 17 to 29% by mass, and even more preferably 18 to 28% by mass, when peeling from the first drying roll.
When the volatile fraction of the ethylene-modified PVA polymer film when peeled from the first drying roll is less than 17% by mass, the value of Δn (MD) _{Ave with} respect to Δn (TD) _Ave increases and the formula (I) On the other hand, when the volatile content of the ethylene-modified PVA polymer film when peeling from the first drying roll exceeds 30% by mass, peeling from the first drying roll becomes difficult. Some tend to break or become uneven.

Here, “the volatile fraction of the ethylene-modified PVA polymer film or the ethylene-modified PVA polymer film” in the present specification refers to a volatile fraction determined by the following formula [iv].
A (mass%) = {(Wc−Wd) / Wc} × 100 [iv]
[In the formula, A is the volatile fraction (% by mass) of the ethylene modified PVA polymer film or ethylene modified PVA polymer film, and Wc is taken from the ethylene modified PVA polymer film or ethylene modified PVA polymer film. The mass (g) and Wd of the sample are the mass (g) when the sample Wc (g) is placed in a vacuum dryer at a temperature of 50 ° C. and a pressure of 0.1 kPa or less and dried for 4 hours. ]

  Ethylene-modified PVA polymer film, ethylene-modified PVA polymer film or ethylene-modified PVA polymer film formed from a film-forming stock solution prepared using a polyhydric alcohol (plasticizer) such as glycerin, a surfactant and water Then, when dried under the above-mentioned conditions of “temperature of 50 ° C. and pressure of 0.1 kPa or less for 4 hours”, only water is volatilized, and most of the other components other than water are not volatilized, and the ethylene-modified PVA heavy Since it remains in the coalesced membrane or the ethylene-modified PVA polymer film, the volatile fraction of the ethylene-modified PVA polymer film or the ethylene-modified PVA polymer film depends on the ethylene-modified PVA polymer film or the ethylene-modified PVA polymer film. It can be determined by measuring the amount of water (water content) contained in the combined film.

In drying with the first drying roll, the roll surface temperature of the first drying roll is preferably 80 to 120 ° C. and 85 to 105 ° C. from the viewpoint of uniform drying property, drying speed and the like. More preferably, it is 93-99 degreeC. If the surface temperature of the first drying roll exceeds 120 ° C., the film tends to foam, whereas if it is less than 80 ° C., drying on the first drying roll becomes insufficient, which tends to cause peeling failure.
The peripheral speed (S ₁ ) of the first drying roll is preferably 8 to 25 m / min from the viewpoint of uniform drying property, drying rate, and productivity of the ethylene-modified PVA polymer film, and is preferably 11 to 23 m / min. More preferably, it is 14 to 22 m / min. When the peripheral speed (S ₁ ) of the first drying roll is less than 8 m / min, productivity is lowered and birefringence tends to increase, which is not preferable. On the other hand, if the peripheral speed (S ₁ ) of the first drying roll exceeds 25 m / min, drying on the first drying roll tends to be insufficient, such being undesirable.

Partial drying on the first drying roll of the film-forming stock solution containing the ethylene-modified PVA polymer discharged in a film form may be performed only by heat from the first drying roll, but when heated with the first drying roll, At the same time, hot air is blown onto the film surface that is not in contact with the first drying roll (hereinafter sometimes referred to as “first drying roll non-contact surface”), and heat is applied from both sides of the ethylene-modified PVA polymer film for drying. It is preferable to carry out from the viewpoints of uniform drying property, drying speed and the like.
When hot air is blown onto the first dry roll non-contact surface of the ethylene-modified PVA polymer film on the first dry roll, the wind speed is 1 to 10 m / sec with respect to the entire area of the first dry roll non-contact surface. It is preferable to blow hot air, more preferably hot air having a wind speed of 2 to 8 m / sec, and still more preferably hot air having a wind speed of 3 to 8 m / sec.
When the wind speed of the hot air sprayed on the non-contact surface of the first drying roll is too small, it becomes difficult to obtain an ethylene-modified PVA polymer film having a high limit drawing ratio as intended in the present invention and drying on the first drying roll. Condensation such as water vapor is sometimes generated, and the water droplets drop on the ethylene-modified PVA polymer film, and defects in the ethylene-modified PVA polymer film finally obtained tend to occur. On the other hand, if the wind speed of the hot air blown onto the non-contact surface of the first drying roll is too high, it becomes difficult to obtain an ethylene-modified PVA polymer film having a high limit draw ratio as intended in the present invention, and finally obtained ethylene. Thickness spots occur in the modified PVA polymer film, and troubles such as the occurrence of stained spots are likely to occur.

  The temperature of the hot air blown to the non-contact surface of the first drying roll of the ethylene-modified PVA polymer film is preferably 50 to 150 ° C. and 70 to 120 ° C. from the viewpoints of drying efficiency and drying uniformity. Is more preferable, and it is still more preferable that it is 80-95 degreeC. Moreover, it is preferable that the dew point temperature of the hot air sprayed on the non-contact surface of the first drying roll of the ethylene-modified PVA polymer film is 10 to 15 ° C. If the temperature of the hot air blown to the non-contact surface of the first drying roll of the ethylene-modified PVA polymer film is too low, the drying efficiency, uniform drying property and the like are liable to be lowered, while if too high, foaming is liable to occur.

  The method for blowing hot air to the non-contact surface of the first modified roll of the ethylene-modified PVA polymer film is not particularly limited, and hot air having a uniform wind speed and uniform temperature is applied to the first dried roll of the PVA polymer film. Any method that can spray uniformly on the contact surface, preferably the entire surface thereof, can be adopted, and among them, a nozzle method, a current plate method, or a combination thereof is preferably adopted. The first drying of the ethylene-modified PVA polymer film, even if the blowing direction of the hot air to the first drying roll non-contact surface of the ethylene-modified PVA polymer film is the direction facing the non-contact surface of the first drying roll. It may be a direction substantially along the circumferential shape of the roll non-contact surface (a direction substantially along the circumference of the roll surface of the first drying roll) or other direction.

  Moreover, when drying the ethylene-modified PVA polymer film on the first drying roll, it is preferable to exhaust the volatile matter generated from the ethylene-modified PVA polymer film by drying and the hot air after spraying. The exhaust method is not particularly limited, but it is preferable to employ an exhaust method that does not generate wind speed spots and temperature spots of hot air sprayed on the first dry roll non-contact surface of the ethylene-modified PVA polymer film.

The ethylene-modified PVA polymer film dried to a volatile content of preferably 17 to 30% by mass on the first drying roll is peeled off from the first drying roll, and this time, the first drying of the ethylene-modified PVA polymer film is performed. It is preferable that the roll non-contact surface is opposed to the second drying roll and dried by the second drying roll.
The ratio (S ₂ / S ₁ ) of the peripheral speed (S ₂ ) of the second drying roll to the peripheral speed (S ₁ ) of the first drying roll is preferably 1.005 to 1.090, and 1.010 More preferably, it is -1.080. When the ratio (S ₂ / S ₁ ) is less than 1.005, the peeling point of the ethylene-modified PVA polymer film from the first drying roll tends to be non-uniform, and the birefringence spots in the width direction become large, It may become impossible to use as an optical film original. The ratio _(S 2 / _{S 1)} is an ethylene-modified PVA polymer films of the present invention is difficult to obtain with the high limit draw ratio greater than 1.090.

  In drying with the second drying roll, the roll surface temperature of the second drying roll is preferably 65 to 100 ° C., and preferably 65 to 98 ° C. from the viewpoint of uniform drying property, drying speed and the like. More preferably, it is 75-96 degreeC.

The ethylene-modified PVA polymer film dried with the second drying roll is peeled off from the second drying roll, and the third drying roll, the fourth drying roll, It dries sequentially by several drying rolls, such as 5 drying rolls.
At that time, in the above manufacturing method, the peripheral speed of the first drying roll against (S _1), the circumferential speed of the drying roll when the volatile fraction of the ethylene-modified PVA polymer film became 13 wt% (S Drying is performed while adjusting the tension applied to the ethylene-modified PVA polymer film so that the ratio of _T ) (S _T / S ₁ ) is 0.990 to 1.050. Here, “the drying roll when the volatile content of the ethylene-modified PVA polymer film is 13% by mass” means that the volatile content of the ethylene-modified PVA polymer film is 13% by mass on the drying roll. When it becomes, it means the said drying roll, and when a volatile matter rate becomes 13 mass% between two drying rolls, it means the drying roll located behind among the said two drying rolls. By setting the ratio (S _T / S ₁ ) within the above range, troubles such as sagging and winding of the film occur in the drying process until the volatile content of the ethylene-modified PVA polymer film reaches 13% by mass. Without averaging, the value [Δn (MD) _Ave ] obtained by averaging the birefringence in the length direction (MD) in the thickness direction of the film and the birefringence in the width direction (TD) were averaged in the thickness direction of the film. The ethylene-modified PVA polymer film of the present invention in which the value [Δn (TD) _Ave ] satisfies the above formulas (I) and (II) and further the above formula (III) can be produced smoothly. .
The ratio (S _T / S ₁ ) described above when producing the ethylene-modified PVA polymer film is preferably 1.000 to 1.045.

In the above production method, an ethylene-modified PVA polymer film having a volatile content of 13% by mass is further dried with a subsequent drying roll to produce an ethylene-modified PVA polymer film. At that time, in the above production method, the peripheral speed (S _T ) of the final drying roll with respect to the peripheral speed (S _T ) of the drying roll when the volatile content of the ethylene-modified PVA polymer film is 13% by mass. Drying is performed while the ratio of _L ) (S _L / S _T ) is in the range of 0.960 to 0.980. By setting the ratio (S _L / S _T ) in the above-described range, in the drying process until the final ethylene-modified PVA polymer film is obtained, troubles such as sagging and wrapping of the film do not occur. A value [Δn (MD) _Ave ] obtained by averaging the birefringence in the thickness direction (MD) in the thickness direction of the film and a value [Δn (TD) obtained by averaging the birefringence in the width direction (TD) in the thickness direction of the film. _Ave ] can smoothly produce the ethylene-modified PVA polymer film of the present invention satisfying the above formulas (I) and (II), and further the above formula (III).
The above-described ratio (S _L / S _T ) when producing the ethylene-modified PVA polymer film is preferably 0.963 to 0.976.

Moreover, in producing an ethylene-modified PVA polymer film by the above-described method, a value obtained by averaging the birefringence in the length direction (MD) of the ethylene-modified PVA polymer film in the thickness direction of the film [ Δn (MD) _Ave ] and the value [Δn (TD) _Ave ] obtained by averaging the birefringence in the width direction (TD) in the film thickness direction are the peripheral speed (S ₁ ) of the first drying roll and the final drying roll. It fluctuates according to the ratio (S _L / S ₁ ) of the peripheral speed (S _L ). In order to smoothly produce the ethylene-modified PVA polymer film of the present invention satisfying the above formulas (I) and (II) and further the above formula (III), the peripheral speed (S ₁ ) To the ratio (S _L / S ₁ ) of the peripheral speed (S _L ) of the final drying roll to 0.970 to 1.010, and 0.972 to 1.008. Preferably, it is more preferable to set it in the range of 0.975 to 1.006. Thereby, an ethylene-modified PVA polymer film satisfying the above formulas (I) and (II) and further the above formula (III) can be smoothly produced while suppressing the generation of wrinkles and sagging. .

In the manufacturing method described above, the final drying roll or the drying roll close to the final and the final drying roll may be used as a heat treatment roll by increasing the surface temperature. When the drying roll is used as a heat treatment roll, the roll surface temperature is preferably 90 to 140 ° C, more preferably 100 to 130 ° C.
Moreover, you may provide the heat processing apparatus separately from a drying roll.

  Although there is no restriction | limiting in particular in the heating direction at the time of drying an ethylene modified PVA polymer film in the process from a 1st drying roll to a final drying roll, from being able to dry an ethylene modified PVA polymer film more uniformly. It is preferable to dry so that the front surface and the back surface of an arbitrary part of the ethylene-modified PVA polymer film are alternately in contact with the respective drying rolls from the first drying roll to the final drying roll.

The ethylene-modified PVA polymer film subjected to the above-mentioned drying treatment is subjected to heat treatment, humidity conditioning treatment, etc., if necessary, and finally wound up into a roll with a predetermined length, thereby modifying the ethylene-modified PVA of the present invention. A polymer film can be obtained.
The volatile fraction of the ethylene-modified PVA polymer film finally obtained by the above-described series of treatments is preferably in the range of 1 to 5% by mass, and more preferably in the range of 2 to 4% by mass.

  In order to produce a polarizing film from the ethylene-modified PVA polymer film of the present invention, it may be dyed and uniaxially stretched using the ethylene-modified PVA polymer film of the present invention. Using the combined film, dyeing, uniaxial stretching, fixing treatment, drying treatment, and heat treatment as necessary may be performed. The order of dyeing and uniaxial stretching is not particularly limited, and the dyeing process may be performed before the uniaxial stretching process, the dyeing process may be performed simultaneously with the uniaxial stretching process, or the dyeing process may be performed after the uniaxial stretching process. You may go. In addition, steps such as uniaxial stretching and dyeing may be repeated a plurality of times. In particular, it is preferable to divide the uniaxial stretching into two or more stages because uniform stretching is easily performed.

  Examples of dyes used for dyeing ethylene-modified PVA polymer films include iodine or dichroic organic dyes (for example, DirectBlack 17, 19, 154; Direct Brown 44, 106, 195, 210, 223; Direct Red 2, 23, 28, 31, 37, 39, 79, 81, 240, 242, 247; DirectBlue 1, 15, 22, 78, 90, 98, 151, 168, 202, 236, 249, 270; DirectViolet 9, 12, 51, 98; DirectGreen 1, 85; Direct Yellow 8, 12, 44, 86, 87; Dichroic dyes such as Direct Orange 26, 39, 106, 107) can be used. These dyes can be used alone or in combination of two or more. Dyeing can usually be carried out by immersing an ethylene-modified PVA polymer film in a solution containing the dye, but the treatment conditions and treatment method are not particularly limited.

  Uniaxial stretching for stretching the ethylene-modified PVA polymer film in the length direction (MD) may be performed by either a wet stretching method or a dry heat stretching method. From the viewpoint, the wet stretching method is preferable. Examples of the wet stretching method include a method of stretching an ethylene-modified PVA polymer film in pure water, an aqueous solution containing various components such as additives and an aqueous medium, or an aqueous dispersion in which various components are dispersed. Specific examples of the uniaxial stretching method based on the stretching method include a method of uniaxial stretching in warm water containing boric acid, a method of uniaxial stretching in a solution containing the above-described dye or a fixing treatment bath described later, and the like.

  The stretching temperature at the time of uniaxial stretching by the wet stretching method is not particularly limited. For example, a temperature within the range of 30 to 90 ° C., and further within the range of 40 to 70 ° C. can be adopted, but breakage occurs. However, it is preferable to employ a temperature within a range of 55 to 67 ° C, more preferably a temperature within a range of 57 to 65 ° C. More preferably, a temperature within the range of 64 ° C is employed. In particular, when uniaxial stretching is performed in two or more stages, it is particularly preferable to employ the above temperature at least at the stage where the draw ratio is maximized (the final stage of the uniaxial stretching process).

  The stretching speed at the time of uniaxial stretching is not particularly limited, and can be, for example, 30% / min or more, further 100% / min or more based on the length of the ethylene-modified PVA polymer film before uniaxial stretching. However, according to the ethylene-modified PVA polymer film of the present invention, even when uniaxially stretched at a high speed and a high magnification, the film is not easily broken, thereby stretching a polarizing film having excellent optical performance such as polarizing performance. Since the film can be produced with high yield, low cost, and high productivity without interrupting the stretching operation, 300% / min based on the length of the ethylene-modified PVA polymer film before uniaxial stretching. It is preferable to have a step of uniaxial stretching at the above stretching rate, more preferably to have a step of uniaxial stretching at a stretching rate of 500% / min or more, 700% It is further preferred that in minutes or more stretching rate comprises the step of uniaxially stretching. If the stretching speed is too high, problems such as breakage during stretching and non-uniform stretching tend to occur, so the stretching speed is the length of the ethylene-modified PVA polymer film before uniaxial stretching. Preferably, it does not exceed 2000% / min, more preferably does not exceed 1600% / min, further preferably does not exceed 1300% / min, and particularly preferably does not exceed 1000% / min.

The stretching ratio of the uniaxial stretching treatment (the total stretching ratio when performing uniaxial stretching in multiple stages) is preferably stretched as much as possible from the point of polarization performance until just before the film is cut, and specifically 4 times or more. Is preferably 5 times or more, more preferably 5.5 times or more. The upper limit of the stretching ratio is not particularly limited as long as the film is not broken, but is preferably 8.0 times or less in order to perform uniform stretching.
The thickness of the stretched film (polarizing film) is preferably 1 to 35 μm, particularly preferably 5 to 30 μm, but when an ethylene-modified PVA polymer film having a thickness of less than 30 μm as described above is used, The thickness of the stretched film (polarizing film) can be 15 μm or less.

  In the production of a polarizing film, a fixing treatment is often performed in order to strengthen the adsorption of the dye to the uniaxially stretched film. As the fixing treatment, a method of immersing a film in a treatment bath to which boric acid and / or a boron compound is added is generally widely adopted. In that case, you may add an iodine compound in a processing bath as needed.

  The film subjected to the uniaxial stretching treatment or the uniaxial stretching treatment and the fixing treatment is preferably subjected to a drying treatment (heat treatment). The temperature of the drying treatment (heat treatment) is preferably 30 to 150 ° C, particularly 50 to 140 ° C. If the temperature of the drying treatment (heat treatment) is too low, the dimensional stability of the obtained polarizing film tends to be lowered, while if too high, the polarizing performance is likely to deteriorate due to decomposition of the dye.

The polarizing film obtained as described above can be made into a polarizing plate by attaching a protective film that is optically transparent and has mechanical strength to both sides or one side. As the protective film in this case, a cellulose triacetate (TAC) film, an acetic acid / cellulose butyrate (CAB) film, an acrylic film, a polyester film, or the like is used. Moreover, as an adhesive for laminating a protective film, a PVA adhesive or a urethane adhesive is generally used, and among them, a PVA adhesive is preferably used.
The polarizing plate obtained as described above can be used as a component of a liquid crystal display device after being coated with an acrylic-based pressure-sensitive adhesive and then being bonded to a glass substrate. When the polarizing plate is bonded to the glass substrate, a retardation film, a viewing angle improving film, a brightness improving film, or the like may be bonded simultaneously.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following examples.
In the following Examples, Reference Examples and Comparative Examples, the volatile fraction of the film-forming stock solution, the volatile fraction (water content) of the ethylene-modified PVA polymer film or the ethylene-modified PVA polymer film, the ethylene-modified PVA polymer Each physical property of the film and the optical performance of the polarizing film were measured by the following methods.

(1) Volatile content of the film-forming stock solution:
It calculated | required by said formula [iii] according to the above-mentioned method.

(2) Volatile content (water content) of ethylene-modified PVA polymer film or ethylene-modified PVA polymer film:
It calculated | required by said formula [iv] according to the above-mentioned method.
The measurement of the volatile fraction (water content) of the ethylene-modified PVA polymer film or the ethylene-modified PVA polymer film is performed by measuring the ethylene-modified PVA polymer film or the ethylene-modified PVA polymer film taken out from the drying roll. This was performed using a sample taken from the center in the width direction (TD).

(3) Δn (MD) _{Ave of} ethylene-modified PVA polymer film:
Δn (MD) _Ave at the center in the width direction (TD) of the ethylene-modified PVA polymer film was determined by the method described above in the section “<< 1 >> Δn (MD) _Ave Measurement Method”, and this was determined as ethylene-modified PVA. It was set as Δn (MD) _Ave of the polymer film.

(4) Δn (TD) _{Ave of} ethylene-modified PVA polymer film:
Δn (TD) _Ave at the center in the width direction (TD) of the ethylene-modified PVA polymer film was determined by the method described above in the section “<< 2 >> Δn (TD) _Ave Measurement Method”, and this was determined as ethylene-modified PVA. It was set as Δn (TD) _Ave of the polymer film.

(5) Mass swelling degree of ethylene-modified PVA polymer film:
Cut the ethylene-modified PVA polymer film to 1.5 g, immerse in 1000 g of distilled water at 30 ° C. for 30 minutes, take out the ethylene-modified PVA polymer film after immersion for 30 minutes, and remove the surface water with filter paper. After sucking up, the mass (W _e ) was measured. Subsequently, the ethylene-modified PVA polymer film was dried with a dryer at 105 ° C. for 16 hours, and then its mass (W _f ) was measured. From the obtained mass W _e and W _f, the following formula [v], was determined by mass degree of swelling of the ethylene-modified PVA polymer films.
Mass swelling degree (%) = (W _e / W _f ) × 100 [v]

(6) Limiting draw ratio of ethylene-modified PVA polymer film:
From the center of the width direction (TD) of the ethylene-modified PVA polymer film before stretching obtained in the following Examples, Reference Examples or Comparative Examples, the length direction (MD) × width direction (TD) = 10 cm × 5 cm The test piece was collected, and both ends in the length direction of the test piece were fixed to a drawing jig so that the size of the drawn portion was length direction (MD) × width direction (TD) = 5 cm × 5 cm, While immersed in water at 30 ° C for 38 seconds, uniaxial stretching (MD) in the length direction (MD) to 2.2 times the original length at a stretching speed of 12 cm / min (240% / min) And 12 cm / min (240%) while being immersed in an iodine / potassium iodide aqueous solution at a temperature of 30 ° C. containing 0.03% by mass of iodine and 3% by mass of potassium iodide for 90 seconds. / Min) in the length direction (MD) up to 3.3 times the original length It is axially stretched (second-stage stretching) and then immersed in a boric acid / potassium iodide aqueous solution at a temperature of 30 ° C. containing 3% by weight of boric acid and 3% by weight of potassium iodide for about 20 seconds. In between, uniaxial stretching (third stage stretching) in the length direction (MD) up to 3.6 times the original length at a stretching speed of 12 cm / min (240% / min), followed by 4% by mass of boric acid And uniaxially stretching in the length direction (MD) until the specimen breaks at a predetermined stretching rate while being immersed in a boric acid / potassium iodide aqueous solution at a predetermined temperature containing potassium iodide at a concentration of about 5% by mass. (Fourth stage stretching) was performed, and the stretching ratio (ratio of the length at break to the original length) when the test piece broke was read.
The same ethylene-modified PVA polymer film was subjected to the stretching test described above five times, and the average value was taken as the limit stretching ratio (times) of the ethylene-modified PVA polymer film.

(7) Optical performance of polarizing film:
(I) Transmittance:
From the central part in the width direction of the polarizing film obtained in the following examples, reference examples or comparative examples, two 1.5 cm × 1.5 cm square samples were taken in parallel to the orientation direction of the polarizing film, respectively. Using Hitachi spectrophotometer V-7100 (with an integrating sphere), in accordance with JIS Z8722 (object color measurement method), C light source, visibility correction of visible light region of 2 degrees visual field, For one polarizing film sample, the light transmittance when tilted by 45 degrees with respect to the stretching axis direction and the light transmittance when tilted by −45 degrees are measured, and the average value (Y ₁ ) is calculated. Asked.
For the other polarizing film sample, the light transmittance when tilted by 45 degrees and the light transmittance when tilted by -45 degrees were measured in the same manner as described above, and the average value (Y ₂ ) thereof was measured. Asked.
Y ₁ and Y ₂ obtained above were averaged to obtain the transmittance (Y) (%) of the polarizing film.
(Ii) Polarization degree:
Light transmittance (Y‖) when the two polarizing film samples collected in (i) above are stacked so that the alignment directions are parallel, and light when the alignment directions are orthogonal to each other Was measured by the same method as the above transmittance measurement method, and the degree of polarization (V) (%) was determined from the following formula [vi].
Degree of 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, each Example, Reference Example or Comparative Example was produced by changing the immersion time in the iodine / potassium iodide aqueous solution at the time of the second stage stretching. For each of the five polarizing films, the transmittance (Y) and the degree of polarization (V) were determined by the method described above, and for each example, reference example or comparative example, the transmittance (Y) was plotted on the horizontal axis and the degree of polarization ( An approximate curve was obtained by plotting five points on a graph with V) as the vertical axis, and the value of the degree of polarization (V) when the transmittance (Y) was 44.25% was obtained from the approximate curve.

Example 1
(1) Production of ethylene-modified PVA polymer film:
Ethylene-modified PVA polymer obtained by saponifying ethylene-modified polyvinyl acetate obtained by copolymerizing ethylene and vinyl acetate (content of ethylene unit 2.0 mol%, saponification degree 99.9 mol) %, Polymerization degree 2400) 100 parts by mass, glycerin 12 parts by mass, lauric acid diethanolamide 0.1 part by mass, and a volatile fraction 66 mass% film-forming stock solution from the T die to the first drying roll (surface temperature 93 At a peripheral speed (S ₁ ) of 16.7 m / min), and hot air of 90 ° C. is applied to the entire surface of the first drying roll non-contact on the first drying roll at a wind speed of 5 m / sec. It is dried until spraying until the moisture content reaches 18% by mass, then peeled off from the first drying roll, and the front and back surfaces of any part of the ethylene-modified PVA polymer film are in contact with each drying roll alternately. As described above, the drying after the second drying roll is performed at a roll surface temperature of about 85 ° C., and finally a heat treatment is performed with a final drying roll (heat treatment roll) having a surface temperature of 108 ° C. A film (thickness 60 μm, width 3 m, volatile content 3 mass%) was obtained. In Example 1, the drying roll when the volatile content rate was 13% by mass was the seventh drying roll.
In Example 1, (α) the peripheral speed (S _T ) of the drying roll (seventh drying roll) when the volatile content rate became 13% by mass with respect to the peripheral speed (S ₁ ) of the first drying roll. The ratio (S _T / S ₁ ) is 1.000; (β) of the final drying roll with respect to the peripheral speed (S _T ) of the drying roll (seventh drying roll) when the volatile content rate is 13% by mass The ratio (S _L / S _T ) of the peripheral speed (S _L ) is 0.974; (γ) the ratio of the peripheral speed (S ₂ ) of the second drying roll to the peripheral speed (S ₁ ) of the first drying roll (S ₂ / S ₁ ) is set to 1.030; (δ) the following drying roll (S _T ) with respect to the peripheral speed (S _T ) of the drying roll (seventh drying roll) when the volatile content rate becomes 13% by mass ( eighth ratio of the peripheral speed of the drying roll) _{(S T + 1)} a _{(S T / S T + 1} ) and 0.998; (epsilon) the peripheral speed of the first drying roll ( For _1), the peripheral speed of the final drying roll (ratio of _{S L) (S L / S} 1) as 0.975, and produce ethylene-modified PVA polymer films.
Δn (MD) _Ave , Δn (TD) _Ave , mass swelling degree and limit draw ratio of the obtained ethylene-modified PVA polymer film (the temperature of the boric acid / potassium iodide aqueous solution in the fourth stage drawing was stretched at 63 ° C. The speed was set to 48 cm / min (960% / min) by the method described above, and the results were as shown in Table 1 below.

(2) Production of polarizing film:
(I) A test piece of length direction (MD) × width direction (TD) = 10 cm × 5 cm was collected from the center in the width direction (TD) of the ethylene-modified PVA polymer film obtained in the above (1). The both ends of the test piece in the length direction are fixed to a stretching jig so that the size of the stretched portion is length direction (MD) × width direction (TD) = 5 cm × 5 cm, and is placed in water at a temperature of 30 ° C. While immersed for 38 seconds, the film was uniaxially stretched (MD) in the length direction (MD) to 2.2 times the original length at a stretching speed of 12 cm / min (240% / min), and then iodine. Of 12 cm / min (240% / min) while immersed in an iodine / potassium iodide aqueous solution at a temperature of 30 ° C. containing 0.03 wt% of potassium and 3 wt% of potassium iodide for 60 seconds Uniaxial stretching in the length direction (MD) up to 3.3 times the original length at speed (second stage stretching) Then, while being immersed in a boric acid / potassium iodide aqueous solution at a temperature of 30 ° C. containing 3% by weight boric acid and 3% by weight potassium iodide for about 20 seconds, 12 cm / min (240% Uniaxial stretching (third-stage stretching) in the length direction (MD) up to 3.6 times the original length at a stretching speed of 3 min / min), followed by 4 mass% boric acid and about 5 mass potassium iodide. % Stretching of the ethylene-modified PVA polymer film measured above at a stretching speed of 48 cm / min (960% / min) while immersed in a boric acid / potassium iodide aqueous solution at a temperature of 63 ° C. containing at a concentration of 60%. After uniaxial stretching (fourth-stage stretching) in the length direction (MD) up to the stretching ratio immediately before the magnification, it was immersed in an aqueous potassium iodide solution containing 3% by mass of potassium iodide for 10 seconds to form iodine ions. Impregnation treatment is performed, and then 60 And dried in a drier 4 minutes to produce a polarizing film (thickness of about 21 [mu] m).
The transmittance (Y) and the degree of polarization (V) of the polarizing film thus obtained are obtained by the above-described method, and the points are shown in the graph in which the horizontal axis represents the transmittance (Y) and the vertical axis represents the degree of polarization (V). Plotted.

(Ii) In the above (i), the immersion time in the iodine / potassium iodide aqueous solution at the temperature of 30 ° C. at the second stage stretching was changed from 60 seconds to 75 seconds, 90 seconds, 105 seconds or 120 seconds. Except for the above, the same operation as in the above (i) was performed to produce four types of polarizing films (thickness: about 21 μm) having different transmittances.
The transmittance (Y) and the degree of polarization (V) of each polarizing film thus obtained were determined by the method described above, and each point was plotted in the graph of (i) above.
(Iii) The approximate curve of the five points plotted on the graphs in (i) and (ii) above is drawn on the graph, and the degree of polarization when the transmittance (Y) is 44.25% from the approximate curve. When the value of (V) was determined, it was 99.98 as shown in Table 1 below.

Example 2
(1) In Example 1, the film-forming conditions for producing the ethylene-modified PVA polymer film were changed as described in Table 1 below, and the discharge was carried out in the form of a film on the first drying roll By changing the amount, an ethylene-modified PVA 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 swelling degree and limit draw ratio of the ethylene-modified PVA polymer film obtained in this way (the temperature of the boric acid / potassium iodide aqueous solution in the fourth-stage drawing is 64 ° C. When the stretching speed was 48 cm / min (960% / min) was measured by the method described above, it was as shown in Table 1 below.
(2) A test piece of length direction (MD) × width direction (TD) = 10 cm × 5 cm taken from the center in the width direction (TD) of the ethylene-modified PVA polymer film obtained in (1) above. Using and changing the temperature of the 4-stage stretched boric acid / potassium iodide aqueous solution from 63 ° C. to 64 ° C., the same operation as (2) of Example 1 was performed to produce 5 types of polarizing films, The transmittance (Y) and the degree of polarization (V) of each polarizing film were determined, and the points were plotted on a graph with the horizontal axis representing the transmittance (Y) and the vertical axis representing the degree of polarization (V). The approximate curve of five points is drawn on the graph, and the value of the degree of polarization (V) when the transmittance (Y) is 44.25% is obtained from the approximate curve. It was as follows.

<< Examples 3 to 5 >>
(1) In Example 1, the film forming conditions for producing an ethylene-modified PVA polymer film were changed as described in Table 1 below, and the thickness was 60 μm in the same manner as in (1) of Example 1. An ethylene-modified PVA polymer film was produced.
Δn (MD) _Ave , Δn (TD) _Ave , mass swelling degree and limit draw ratio of each ethylene-modified PVA polymer film thus obtained (the temperature of the boric acid / potassium iodide aqueous solution in the fourth stage drawing was set to 63 The results were as shown in Table 1 below when measured by the method described above at a temperature of 48 ° C./min (960% / min).
(2) A test piece of length direction (MD) × width direction (TD) = 10 cm × 5 cm taken from the center in the width direction (TD) of each ethylene-modified PVA polymer film obtained in the above (1) The same operation as (2) of Example 1 was performed, and five types of polarizing films were produced for each Example, and the transmittance (Y) and the degree of polarization (V) of each polarizing film were obtained. The point is plotted on a graph with the horizontal axis representing the transmittance (Y) and the vertical axis representing the degree of polarization (V), and an approximated curve of five points plotted on the graph is drawn on the graph. When the value of polarization degree (V) when the transmittance (Y) was 44.25% was determined, it was as shown in Table 1 below.

<< Reference Example 1 >>
(1) In Example 1, unmodified PVA in which the ethylene-modified PVA polymer was not ethylene-modified (obtained by saponifying polyvinyl acetate. Saponification degree 99.9 mol%, polymerization degree 2400) Instead, a PVA film having a thickness of 60 μm was produced in the same manner as in Example 1 (1).
The PVA film thus obtained has Δn (MD) _Ave , Δn (TD) _Ave , mass swelling degree and limit draw ratio (the temperature of the boric acid / potassium iodide aqueous solution in the fourth stage drawing is 60 ° C., and the drawing speed is 48 cm. / Min (960% / min) was measured by the above-described method (measured by regarding the PVA film as an ethylene-modified PVA polymer film), and the results were as shown in Table 1 below.
(2) While using the test piece of length direction (MD) x width direction (TD) = 10cmx5cm extract | collected from the center part of the width direction (TD) of the PVA film obtained by said (1), it is the 4th step | paragraph By changing the temperature of the stretched boric acid / potassium iodide aqueous solution from 63 ° C. to 60 ° C., the same operation as (2) of Example 1 was carried out to produce five types of polarizing films. Obtain the transmittance (Y) and the degree of polarization (V), plot the point on a graph with the transmittance on the horizontal axis (Y) and the degree of polarization (V) on the vertical axis, and approximate the five points plotted on the graph When the curve was drawn on the graph and the degree of polarization (V) when the transmittance (Y) was 44.25% was determined from the approximate curve, it was as shown in Table 1 below.

<< Reference Example 2 >>
(1) Regarding the PVA film obtained in (1) of Reference Example 1, the temperature of the boric acid / potassium iodide aqueous solution in the fourth stage stretching was 63 ° C., and the stretching speed was 48 cm / min (960% / min), When the limit draw ratio was measured by the above-described method (measured by regarding the PVA film as an ethylene-modified PVA polymer film), it was as shown in Table 1 below.
(2) In addition, a test piece of length direction (MD) × width direction (TD) = 10 cm × 5 cm collected from the central portion in the width direction (TD) of the PVA film obtained in (1) of Reference Example 1 The same operation as (2) of Example 1 was performed to produce five types of polarizing films, the transmittance (Y) and the degree of polarization (V) of each polarizing film were determined, and the horizontal axis represents the transmittance. The point is plotted on a graph with (Y) and the vertical axis representing the degree of polarization (V), an approximate curve of five points plotted on the graph is drawn on the graph, and the transmittance (Y) is calculated from the approximate curve. When the value of the degree of polarization (V) was 44.25%, it was as shown in Table 1 below.

<< Comparative Examples 1-7 >>
(1) In Example 1, the type of ethylene-modified PVA polymer used and the film forming conditions for producing the ethylene-modified PVA polymer film were changed as shown in Table 2 below. In the same manner as in (1) of 1, an ethylene-modified PVA polymer film having a thickness of 60 μm was produced.
Δn (MD) _Ave , Δn (TD) _Ave , mass swelling degree and limit draw ratio of each ethylene-modified PVA polymer film thus obtained (the temperature of the boric acid / potassium iodide aqueous solution in the fourth stage drawing was set to 63 The temperature was measured by the method described above at a temperature of 48 ° C./min (960% / min), and the results were as shown in Table 2 below.
(2) A test piece of length direction (MD) × width direction (TD) = 10 cm × 5 cm taken from the center in the width direction (TD) of each ethylene-modified PVA polymer film obtained in the above (1) The same operation as (2) of Example 1 was performed, and five types of polarizing films were produced for each comparative example, and the transmittance (Y) and the degree of polarization (V) of each polarizing film were obtained. The point is plotted on a graph with the horizontal axis representing the transmittance (Y) and the vertical axis representing the degree of polarization (V), and an approximated curve of five points plotted on the graph is drawn on the graph. When the value of polarization degree (V) when the transmittance (Y) was 44.25% was determined, it was as shown in Table 2 below.

As seen in Table 1 and Table 2 above, the ethylene-modified PVA polymer films of Examples 1 to 5 contain an ethylene-modified PVA polymer containing a specific amount of ethylene units, and Δn (MD) _Ave [ Value obtained by averaging the birefringence in the length direction (MD) of the ethylene-modified PVA polymer film in the thickness direction of the film] and Δn (TD) _Ave [in the width direction (TD) of the ethylene-modified PVA polymer film] A value obtained by averaging the birefringence in the thickness direction of the film] satisfies the formulas (I) and (II), so that even when the film is stretched at a high speed, a high limit stretching of 6.76 to 6.92. The polarizing film obtained from the ethylene-modified PVA polymer films of Examples 1 to 5 has excellent polarizing performance equivalent to or higher than that of conventional polarizing films.
In particular, in Example 2, even though the thickness of the ethylene-modified PVA polymer film is 25 μm, which is thinner, even in the case of stretching at a high speed as in the other examples, a high limit stretch ratio and excellent Polarization performance has been achieved.

On the other hand, the ethylene-modified PVA polymer films of Comparative Examples 1 to 3 do not satisfy the formula (I), and the ethylene-modified PVA polymer films of Comparative Examples 4 and 5 do not satisfy the formula (II). Since the ethylene-modified PVA polymer films of Comparative Examples 6 and 7 do not contain an ethylene-modified PVA polymer containing a specific amount of ethylene units, the ethylene-modified PVA polymer films of Examples 1 to 5 As compared with the polarizing film, the limiting stretch ratio is low, and the polarizing film obtained in Comparative Example 7 is more bluish than the polarizing films of Examples 1 to 5.
Moreover, since the PVA films of Reference Examples 1 and 2 do not contain an ethylene-modified PVA polymer containing a specific amount of ethylene units, the limiting draw ratio when stretched at high speed is reduced, and the obtained polarizing film The polarization performance is also degraded.

When producing a polarizing film from a PVA polymer film, uniaxial stretching is usually performed at a stretching ratio somewhat lower than the limit stretching ratio in order to avoid breakage of the film during stretching. The ethylene-modified PVA polymer films of Examples 1 to 5 are manufactured as polarizing films under the conditions of the examples, because the limiting stretch ratio of the ethylene-modified PVA polymer films of 5 is as high as 6.76 or more. In this case, uniaxial stretching can be performed at a high stretching ratio of 6 times or more, and even if uniaxial stretching is performed at a high stretching ratio of 6.5 times or more, the film can be smoothly stretched without causing breakage. .
On the other hand, the ethylene-modified PVA polymer films of Comparative Examples 1 to 7 are ruptured to uniaxially stretch at a stretching ratio of 6 times or more when producing a polarizing film under the conditions of the comparative example. I ’m worried.

In addition, in a raw film for a polarizing film, there is a roll having a length of 1000 m or more. For example, in a PVA polymer film having a total length of 1000 m, the limit draw ratio is 0.1 point (0.1 Increase) means that the length of the stretched film obtained by uniaxial stretching is increased by 100 m (1000 m × 0.1 times = 100 m), so that more polarized light from the same length of the original film. A film is obtained.
When this is seen about Examples 1-5, compared with the ethylene modified PVA polymer film of Comparative Examples 1-7, the limiting draw ratio of the ethylene modified PVA polymer film of Examples 1-5 is 0. Since the length of the ethylene-modified PVA polymer film is 1000 m, for example, when a polarizing film is produced using the same under the conditions of the above examples, the .13 to 0.90 point (times) is also high. The length of the polarizing film is 130 to 900 m longer than when the PVA films of Comparative Examples 1 to 7 are used, and more polarizing films can be obtained.

Claims (5)

An ethylene-modified polyvinyl alcohol polymer film comprising an ethylene-modified polyvinyl alcohol polymer having an ethylene unit content of 1 to 4 mol% and satisfying the following formulas (I) and (II):
Δn (MD) _Ave −0.1 × 10 ⁻³ ≦ Δn (TD) _Ave ≦ Δn (MD) _Ave + 0.25 × 10 ⁻³ (I)
Δn (TD) _Ave ≦ 2.5 × 10 ⁻³ (II)
[In the above formula, Δn (MD) _Ave represents a value obtained by averaging the birefringence in the machine flow direction of the ethylene-modified polyvinyl alcohol polymer film in the thickness direction of the film, and Δn (TD) _Ave represents ethylene. The value which averaged the birefringence of the width direction of the modified polyvinyl alcohol-type polymer film in the thickness direction of the said film is shown. ] The ethylene-modified polyvinyl alcohol 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 polymer film according to claim 1 or 2, wherein the thickness is in the range of 10 to 65 µm.   The manufacturing method of the polarizing film characterized by dyeing and uniaxially stretching using the ethylene modified polyvinyl alcohol-type polymer film of any one of Claims 1-3.   The manufacturing method of Claim 4 which has the process of carrying out uniaxial stretching with the extending | stretching speed of 300% / min or more based on the length of the ethylene modified polyvinyl alcohol-type polymer film before uniaxial stretching.

Images