WO2022004537A1

WO2022004537A1 - Polyvinyl alcohol film and polarizing film in which same is used

Info

Publication number: WO2022004537A1
Application number: PCT/JP2021/023877
Authority: WO
Inventors: 裕史田邊; 稔岡本; 修風藤
Original assignee: 株式会社クラレ
Priority date: 2020-06-30
Filing date: 2021-06-23
Publication date: 2022-01-06
Also published as: CN115777075A; KR20230027003A; TW202216806A; JPWO2022004537A1

Abstract

Provided is a PVA film in which breakage during uniaxial stretching is suppressed and which is not prone to surface wrinkling during uniaxial stretching, even when the maximum stretching speed is high.　A non-aqueous PVA film, wherein Fd1, Fg1, Fd2, and Fg2 satisfy expressions (1) through (4), where Fd1 and Fg1 are crystallinity indices of a first surface, and Fd2 and Fg2 are crystallinity indices of a second surface.　(1): Fd1≤0.8. (2): Fd1/Fg1<1. (3): Fd2≤0.8. (4): Fd2/Fg2<1. [In expressions (1) through (4), Fd1 and Fg1 are crystallinity indices calculated using a diamond prism and a germanium prism, respectively, in FT-IR measurement of the first surface by an ATR method, and Fd2 and Fg2 are crystallinity indices calculated using a diamond prism and a germanium prism, respectively, in the same manner with respect to the second surface.]

Description

Polyvinyl alcohol film and polarizing film using it

The present invention relates to a polyvinyl alcohol film and a polarizing film using the same.

A polarizing plate having a light transmitting and shielding function is a basic component of a liquid crystal display (LCD) together with a liquid crystal having a light switching function. The fields of application of this LCD are also used from small devices such as calculators and watches in the early days of development to notebook computers, LCD monitors, LCD color projectors, LCD TVs, in-vehicle navigation systems, mobile phones and indoors and outdoors in recent years. It is expanding to various fields such as measuring instruments.

The polarizing plate is manufactured by laminating a protective film such as a cellulose triacetate (TAC) film or a cellulose acetate / butyrate (CAB) film on the surface of a polarizing film. The polarizing film is uniaxially stretched after dyeing a polyvinyl alcohol film (hereinafter, "polyvinyl alcohol" may be referred to as "PVA"), uniaxially stretched while being dyed, or uniaxially stretched. It is generally produced by dyeing to produce a dyed uniaxially stretched film and immobilizing the uniaxially stretched film with a boron compound. The immobilization treatment with this boron compound may be performed at the same time as the uniaxial stretching or dyeing treatment.

High-contrast and clear images are required for products with large LCDs such as LCD monitors and LCD TVs. Along with this, the polarizing film is also required to have higher performance, and specifically, it is required to increase the degree of polarization of the polarizing film. However, when the draw ratio when the PVA film is uniaxially stretched is increased in order to increase the degree of polarization of the polarizing film, wrinkles are likely to occur on the surface of the PVA film in the process of uniaxial stretching. As a result, wrinkles are likely to occur on the surface of the obtained polarizing film. If many wrinkles are generated on the surface of the polarizing film, it tends to cause image unevenness in the final products such as LCD monitors and LCD televisions. Further, if many wrinkles are generated on the surface of the polarizing film, such a polarizing film cannot be used as a product, which causes a decrease in the product yield (product yield) of the polarizing film.

As a method of suppressing wrinkles generated on the surface of the polarizing film, it is possible to control the relaxation time and the component ratio for the components having a short relaxation time (a component having low molecular motility and being hard) when the PVA film is measured by pulse NMR. It has been proposed (see Patent Document 1).

WO2019 / 189695

In recent years, there has been an increasing demand for higher contrast and sharper images on LCDs, and along with this, wrinkles on the surface of polarizing films, which have not been a problem in the past, are becoming more and more problematic. Further, in order to increase the production efficiency of the polarizing film, it is required to perform uniaxial stretching at high speed in the stretching process at the time of producing the polarizing film, that is, to increase the maximum stretching speed of uniaxial stretching. However, if the maximum stretching speed is increased in the uniaxial stretching in the production of the polarizing film, wrinkles are more likely to occur on the surface of the PVA film during the uniaxial stretching. As a result, wrinkles are more likely to occur on the surface of the obtained polarizing film. Further, when the maximum stretching speed is high, excessive tension may be locally applied to the PVA film during uniaxial stretching. As a result, the PVA film is likely to break during uniaxial stretching, and there is also a problem that the product yield of the polarizing film is lowered.

In the PVA film described in Patent Document 1, if the maximum stretching speed is increased in uniaxial stretching when producing a polarizing film, wrinkles are likely to occur on the surface of the PVA film during uniaxial stretching, and the surface of the polarizing film is sufficiently wrinkled. In some cases, it could not be suppressed. Further, when the maximum stretching speed is increased, the PVA film may be broken during uniaxial stretching. It should be noted that suppressing wrinkles on the surface of the PVA film during uniaxial stretching and suppressing breakage of the PVA film during uniaxial stretching are also important for suppressing wrinkles and breakage on the surface of optical films other than the polarizing film.

Therefore, according to the present invention, even when the maximum stretching speed is high in uniaxial stretching when manufacturing an optical film such as a polarizing film, wrinkles are less likely to occur on the surface during uniaxial stretching, and breakage during uniaxial stretching is suppressed. It is an object of the present invention to provide the said PVA film.

As a result of diligent studies, the present inventors have found that the above-mentioned problems can be achieved by adjusting the crystallinity indexes of two surfaces orthogonal to the thickness direction of the PVA film within a specific range. Based on this, further studies were carried out to complete the present invention.

That is, the present invention
[1] A water-insoluble PVA film having two surfaces orthogonal to the thickness direction of the PVA film as a first surface and a second surface, respectively, and the crystallinity index of the first surface is Fd1 and When Fg1 is used and the crystallinity index of the second surface is Fd2 and Fg2, the Fd1, Fg1, Fd2 and Fg2 satisfy the following formulas (1) to (4);
Fd1 ≤ 0.8 (1)
Fd1 / Fg1 <1 (2)
Fd2 ≤ 0.8 (3)
Fd2 / Fg2 <1 (4)
[In the formulas (1) to (4), Fd1 is a crystallinity index calculated by using a diamond prism when FT-IR measurement by the ATR method is performed on the first surface, and is Fg1. Is a crystallinity index calculated by using a germanium prism when FT-IR measurement by the ATR method is performed on the first surface, and Fd2 is the crystallinity index calculated by the ATR method on the second surface. It is a crystallinity index calculated by using a diamond prism when FT-IR measurement is performed, and Fg2 uses a germanium prism when FT-IR measurement by the ATR method is performed on the second surface. It is a crystallinity index calculated by. ]
[2] The PVA film of [1], wherein the Fd1 and Fd2 satisfy the following formulas (5) to (6);
Fd1 ≧ 0.5 (5)
Fd2 ≧ 0.5 (6)
[3] The PVA film of [1] or [2], wherein the Fd1, Fg1, Fd2 and Fg2 satisfy the following formulas (7) to (8);
Fd1 / Fg1 ≧ 0.6 (7)
Fd2 / Fg2 ≧ 0.6 (8)
[4] The PVA film according to any one of [1] to [3], wherein the Fd1, Fg1, Fd2 and Fg2 satisfy the following formulas (9) to (10);
| Fd1-Fd2 | ≤0.07 (9)
| Fg1-Fg2 | ≤0.07 (10)
[5] The PVA film according to any one of [1] to [4], which is a film for producing an optical film;
[6] The PVA film of [5], wherein the optical film is a polarizing film;
Regarding.

According to the present invention, even when the maximum stretching speed is high in uniaxial stretching when manufacturing an optical film such as a polarizing film, wrinkles are less likely to occur on the surface during uniaxial stretching, and breakage occurs during uniaxial stretching. Suppressed PVA film is provided. According to such a PVA film, wrinkles generated on the surface of an optical film such as a polarizing film can be suppressed. Further, since breakage during uniaxial stretching is suppressed, an optical film such as a polarizing film can be produced with a high product yield.

It is a perspective view of the PVA film of this invention. It is a figure which looked at the side view of the PVA film of this invention. It is a figure which showed schematically the ATR method in FT-IR measurement.

Hereinafter, the present invention will be described in detail.

<PVA film>
In the present invention, as shown in FIGS. 1 and 2, two surfaces orthogonal to the thickness direction 2 of the PVA film 1 are defined as the first surface 3 and the second surface 4, respectively. Therefore, the first surface 3 and the second surface 4 of the PVA film 1 of the present invention face each other. In the present invention, FT-IR (Fourier transform infrared spectroscopy) measurement by the ATR method is performed on the first surface 3 and the second surface 4, respectively. The crystallinity indexes Fd1, Fg1, Fd2 and Fg2 calculated by this measurement satisfy the following formulas (1) to (4).
Fd1 ≤ 0.8 (1)
Fd1 / Fg1 <1 (2)
Fd2 ≤ 0.8 (3)
Fd2 / Fg2 <1 (4)

In the above formulas (1) to (4), Fd1 is a crystallinity index calculated by using a diamond prism when FT-IR measurement by the ATR method is performed on the first surface 3 of the PVA film 1. Fg1 is a crystallinity index calculated by using a germanium prism when FT-IR measurement by the ATR method is performed on the first surface 3 of the PVA film 1. Further, Fd2 is a crystallinity index calculated by using a diamond prism when FT-IR measurement by the ATR method is performed on the second surface 4 of the PVA film 1, and Fg2 is the crystallinity index of the PVA film 1. It is a crystallinity index calculated by using a germanium prism when FT-IR measurement by the ATR method is performed on the second surface 4. In the above formula (2), Fd1 / Fg1 is a value obtained by dividing Fd1 by Fg1, and in the above formula (4), Fd2 / Fg2 is a value obtained by dividing Fd2 by Fg2.

In the PVA film of the present invention, Fd1 and Fd2 need to be 0.8 or less as shown in the above formulas (1) and (3). When Fd1 or Fd2 exceeds 0.8, wrinkles are likely to occur on the surface of the PVA film 1 during uniaxial stretching when the maximum stretching speed is high in uniaxial stretching when manufacturing an optical film such as a polarizing film. In addition, the PVA film 1 is likely to break during uniaxial stretching. The reason is not always clear, but if the crystallinity of the surface of the PVA film 1 is too high, it becomes difficult for water in the stretching treatment liquid to enter the inside of the PVA film 1 during uniaxial stretching, and the flexibility of the film during uniaxial stretching becomes difficult. It is presumed that this is due to insufficient. Fd1 and Fd2 are preferably 0.75 or less, more preferably 0.72 or less, further preferably 0.7 or less, and particularly preferably 0.68 or less.

In the PVA film of the present invention, Fd1 / Fg1 and Fd2 / Fg2 need to be less than 1 as shown in the above formulas (2) and (4). When Fd1 / Fg1 or Fd2 / Fg2 is 1 or more, wrinkles occur on the surface of the PVA film 1 during uniaxial stretching when the maximum stretching speed is high in uniaxial stretching when manufacturing an optical film such as a polarizing film. It will be easier. Fd1 / Fg1 and Fd2 / Fg2 are preferably 0.98 or less, more preferably 0.96 or less, further preferably 0.94 or less, still more preferably 0.92 or less. It is particularly preferable that it is 0.9 or less.

In the PVA film of the present invention, Fd1 and Fd2 are 0.8 or less as shown in the above formulas (1) and (3). Further, as shown in the above formulas (2) and (4), Fd1 / Fg1 and Fd2 / Fg2 are less than 1. As will be described later, Fd1 and Fd2 show the crystallinity inside the PVA film 1 relatively deeply, while Fg1 and Fg2 show the crystallinity of the polar surface layer near the surface of the PVA film 1. That is, the PVA film of the present invention has a relatively deep internal crystallinity of the PVA film 1 of a predetermined value or less, and the surface of the PVA film 1 is relative to the relatively deep internal crystallinity of the PVA film 1. The crystallinity of the nearby polar surface layer is high. By controlling the crystallinity of the relatively deep interior and the polar surface layer of the PVA film 1 in this way, even when the maximum stretching speed is high in uniaxial stretching when manufacturing an optical film such as a polarizing film, the maximum stretching speed is high. Wrinkles are less likely to occur on the surface during uniaxial stretching, and breakage during uniaxial stretching is suppressed. The reason is not always clear, but the high crystallinity of the polar surface layer of the PVA film 1 suppresses the formation of wrinkles on the surface of the PVA film 1 during uniaxial stretching, and the PVA film 1 is relatively deep. It is presumed that the low crystallinity inside alleviates the stress generated during uniaxial stretching and suppresses breakage.

In the PVA film of the present invention, the lower limit values of Fd1 and Fd2 are not necessarily limited, but the PVA film 1 is uniaxially stretched when the maximum stretching speed is high in uniaxial stretching when manufacturing an optical film such as a polarizing film. It is preferable to satisfy the following formulas (5) and (6) because the breakage at the time can be further suppressed.
Fd1 ≧ 0.5 (5)
Fd2 ≧ 0.5 (6)

As shown in the above formulas (5) and (6), when Fd1 and Fd2 are 0.5 or more, the crystallinity inside the PVA film 1 is relatively deep. As a result, the crystallinity of the central portion of the PVA film 1 in the thickness direction 2 is increased, and the mechanical strength of the PVA film 1 is improved. Therefore, by using such a PVA film 1, even when the maximum stretching speed is high in the uniaxial stretching when manufacturing an optical film such as a polarizing film, the breakage when the PVA film 1 is uniaxially stretched is broken. It is more suppressed. Fd1 and Fd2 are more preferably 0.52 or more, and further preferably 0.55 or more.

In the PVA film of the present invention, the lower limit values of Fd1 / Fg1 and Fd2 / Fg2 are not necessarily limited, but when the maximum stretching speed is high in uniaxial stretching when manufacturing an optical film such as a polarizing film, the PVA film 1 It is preferable to satisfy the following formulas (7) and (8) because it is possible to further suppress breakage when the film is uniaxially stretched.
Fd1 / Fg1 ≧ 0.6 (7)
Fd2 / Fg2 ≧ 0.6 (8)

As shown in the above formulas (7) and (8), when Fd1 / Fg1 and Fd2 / Fg2 are 0.6 or more, the crystallinity inside the PVA film 1 having a relatively deep depth is the polar surface layer portion of the PVA film 1. It is not too small compared to the crystallinity of. As a result, the crystallinity of the central portion of the PVA film 1 in the thickness direction 2 becomes relatively large, and the mechanical strength of the PVA film 1 is improved. Therefore, by using such a PVA film 1, even when the maximum stretching speed is high in the uniaxial stretching when manufacturing an optical film such as a polarizing film, the breakage when the PVA film 1 is uniaxially stretched is broken. It is more suppressed. Fd1 / Fg1 or Fd2 / Fg2 is more preferably 0.65 or more, further preferably 0.7 or more, and particularly preferably 0.75 or more.

In the PVA film of the present invention, the absolute value of the difference between Fd1 and Fd2 and the difference between Fg1 and Fg2 is not necessarily limited, but when the maximum stretching speed is high in uniaxial stretching when manufacturing an optical film such as a polarizing film. In addition, it is preferable to satisfy the following formulas (9) and (10) because wrinkles generated on the surface of the PVA film 1 during uniaxial stretching can be further suppressed.
| Fd1-Fd2 | ≤ 0.07 (9)
| Fg1-Fg2 | ≤ 0.07 (10)

As shown in the above formulas (9) and (10), when | Fd1-Fd2 | and | Fg1-Fg2 | are 0.07 or less, the first surface 3 and the second surface 4 of the PVA film 1 The difference in crystallinity index is not too large, and the elastic moduli are substantially the same on the two surfaces (first surface 3 and second surface 4) orthogonal to the thickness direction 2 of the PVA film 1. Therefore, by using such a PVA film 1, wrinkles are formed on the surface of the PVA film 1 during uniaxial stretching even when the maximum stretching speed is high in uniaxial stretching when manufacturing an optical film such as a polarizing film. It is less likely to occur. | Fd1-Fd2 | and | Fg1-Fg2 | are more preferably 0.06 or less, further preferably 0.05 or less, and particularly preferably 0.04 or less.

(FT-IR measurement)
Generally, when the infrared absorption spectrum (IR spectrum) of the PVA film 1 is measured, an absorption peak is observed at ^{1140 cm -1 due to the contained PVA.} This absorption peak is generally referred to as the crystallization band of PVA film 1, and is one of the peaks derived from the expansion and contraction vibration of the carbon bond (CC) of PVA. It is known that this crystallization band is emphasized and observed so that the phase of vibration of the polymer molecular chain of PVA is aligned by crystallization of the polymer molecular chain of PVA in PVA film 1. That is, the higher the crystallinity of the PVA film 1, the higher the peak intensity of the crystallization band. Further, when the infrared absorption spectrum of the PVA film 1 is measured, an absorption peak is observed at ^{1425 cm -1} due to the variable angle vibration of _{methylene (-CH 2-), which is the main chain of PVA.} The intensity of this absorption peak is said to be independent of the crystallinity of the PVA film 1.

In the present invention, the intensity ratio of the absorption peak intensity of this crystallization band (1140 cm ^-1 ) to the absorption peak intensity of the variable angle vibration (1425 cm ^-1 _{) of methylene (-CH 2-} ), which is the main chain of PVA. By calculating, the crystallinity index (Fg1, Fg2, Fd1 and Fd2) of the PVA film 1 can be obtained. Specifically, the baseline of the infrared absorption spectrum at ^{1140 cm -1} and 1425 cm ^-1 is drawn, and the height ^{from the baseline to the peak tops of 1140 cm -1} ^{and 1425 cm -1} is taken as the respective absorption peak intensities of 1140 cm ^-1. The value obtained by dividing the absorption peak intensity of 1425 cm ^{-1 by} the peak intensity of 1425 cm-1 was taken as the crystallinity index (Fg1, Fg2, Fd1 and Fd2).

It is well known that the values of the crystallinity index (Fg1, Fg2, Fd1 and Fd2) thus obtained are proportional to the crystallinity of the PVA film 1 (for example, NA Peppas, Macromol. Chem., 178, 595 (1977), JP-A-6-138321). Since the value of this crystallinity index varies slightly depending on the amount of moisture absorbed by the PVA film 1, in the present invention, the PVA film 1 is stored for 24 hours in an environment of a temperature of 24.0 ° C. and a relative humidity of 45.0% RH. FT-IR measurement was performed in the same environment.

In the present invention, the FT-IR measurement is performed by the ATR method (total reflection absorption measurement method). As shown in FIG. 3, in the ATR method, a sample is brought into close contact with an objective lens called an ATR prism 7, the sample is obliquely irradiated with infrared rays 8 from inside the ATR prism 7, and the spectrum of the reflected light is measured. It is a kind of reflection type IR measurement method. Compared with the usual reflection type IR measurement method, it has the feature that a sharp spectrum with less noise can be obtained. When the PVA film 1 is used as a sample in this measurement method, the infrared rays 8 are not reflected only on the surface of the PVA film 1, but also the infrared rays 8 slightly submerged from the ATR prism 7 side to the PVA film 1 side. To. Therefore, according to the FT-IR measurement by the ATR method, it is possible to obtain information on the surface layer of the PVA film 1 (a portion slightly submerged in the depth direction from the surface of the PVA film 1). Here, assuming that the depth of the infrared ray 8 that has sunk from the ATR prism 7 side to the PVA film 1 side is d, the value is expressed by the following equation (11). As is clear from the following equation (11), if ATR prisms 7 having different refractive indexes are used, it is possible to obtain a reflection type infrared absorption spectrum having different diving depths.

d = λ / 2Πn ₁ × 1 / {sin ² θ- (n ₂ / n ₁ ) ² } ^0.5 (11)

In the above equation (11), n ₁ represents the refractive index of the ATR prism 7, n ₂ represents the refractive index of the PVA film 1, λ represents the wavelength of the infrared ray 8, and θ represents the incident angle of the infrared ray 8.

In the present invention, as shown in FIG. 3, diamond having a refractive index of 2.4 or germanium having a refractive index of 4.0 is used as the base material of the ATR prism 7. Since the refractive index of the PVA film 1 is 1.5, the infrared rays to the surface layer of the PVA film 1 when the incident angle of the infrared rays 8 is 45 ° and the wave number of the infrared rays 8 is 1140 cm ^{-1 in the above equation (11).} When the diving depth of 8 is calculated, the diving depth 5 of the infrared ray 8 when diamond is used as the base material of the ATR prism 7, that is, when the diamond prism is used, is about 2 μm. On the other hand, when germanium is used as the ATR prism 7, that is, in the case of the germanium prism, the depth 6 of the infrared ray 8 is about 0.5 μm. Therefore, the crystallinity index when the diamond prism is used corresponds to the crystallinity to the relatively deep inside of the PVA film 1. On the other hand, the crystallinity index when the germanium prism is used corresponds to the crystallinity of the polar surface layer portion near the surface of the PVA film 1.

In the present invention, it is important to control Fg1 and Fg2, which are the crystallinity indexes of the polar surface layer portion of the PVA film 1, and Fd1 and Fd2, which are the crystallinity indexes of the relatively deep inside of the PVA film 1, within the above ranges. Since the crystal structure of PVA film 1 is affected by various factors in the composition of PVA film 1 and the manufacturing process, as a method for controlling the crystallinity index (Fg1, Fg2, Fd1 and Fd2), for example, polyvinyl alcohol can be used. Methods for adjusting the type (destruction degree, modification amount, blend ratio of unmodified PVA / modified PVA, etc.), method for adjusting the amount of plasticizer added, film production conditions (surface temperature of roll support, heat treatment conditions, etc.) The method of adjusting, or the method of adjusting by combining these can be mentioned.

As a method of adjusting the crystallinity indexes Fd1 and Fd2 to 0.8 or less and adjusting Fd1 / Fg1 and Fd2 / Fg2 to less than 1, more specifically, the degree of saponification of PVA is set to 90 mol% or more, and the raw material of PVA is used. The ratio of structural units derived from other monomers to the vinyl ester-based polymer is 15 mol% or less based on the number of moles of all structural units constituting the vinyl ester-based polymer, and the degree of polymerization of PVA is set. The method of setting it to 200 to 8000 can be mentioned. At this time, the amount of the plasticizer added is preferably 1 to 40 parts by mass with respect to 100 parts by mass of PVA. At this time, the volatile content of the membrane-forming stock solution is preferably 50 to 90% by mass, and the surface temperature of the support for flowing the membrane-forming stock solution is preferably 65 to 110 ° C., and the non-contact surface. The temperature of the hot air blown to the side is preferably 50 to 150 ° C. or lower, and the humidity of the hot air is preferably 20 to 90% RH. Further, at this time, the temperature of the drying oven or the surface temperature of the drying roll is preferably 45 to 110 ° C, and the surface temperature of the heat treatment roll is preferably 60 to 135 ° C.

As a method for adjusting the crystallinity indexes Fd1 and Fd2 to 0.5 or more, the degree of saponification of PVA is set to 95 to 99.9 mol%, and it is derived from other monomers in the vinyl ester polymer which is the raw material of PVA. Examples thereof include a method in which the ratio of structural units is 10 mol% or less based on the number of moles of all structural units constituting the vinyl ester polymer, and the degree of polymerization of PVA is 1000 to 4000. At this time, the amount of the plasticizer added is preferably 5 to 20 parts by mass with respect to 100 parts by mass of PVA. At this time, the volatile content of the membrane-forming stock solution is preferably 60 to 80% by mass, and the surface temperature of the support for flowing the membrane-forming stock solution is preferably 80 to 110 ° C., and the non-contact surface. The temperature of the hot air blown to the side is preferably 70 to 110 ° C. or lower, and the humidity of the hot air is preferably 1 to 40% RH. Further, at this time, the temperature of the drying oven or the surface temperature of the drying roll is preferably 60 to 110 ° C, and the surface temperature of the heat treatment roll is preferably 80 to 135 ° C.

As a method for adjusting Fd1 / Fg1 and Fd2 / Fg2 to 0.6 or more, the degree of saponification of PVA is set to 99 to 99.9 mol%, and it is derived from other monomers in the vinyl ester polymer which is the raw material of PVA. There is a method in which the ratio of structural units to be polymerized is 5 mol% or less based on the number of moles of all structural units constituting the vinyl ester polymer, and the degree of polymerization of PVA is 1000 to 3700. At this time, the amount of the plasticizer added is preferably 8 to 20 parts by mass with respect to 100 parts by mass of PVA. At this time, the volatile content of the membrane-forming stock solution is preferably 65 to 80% by mass, and the surface temperature of the support for flowing the membrane-forming stock solution is preferably 80 to 100 ° C., and the non-contact surface. The temperature of the hot air blown to the side is preferably 70 to 100 ° C., and the humidity of the hot air is preferably 3 to 40% RH. Further, at this time, the temperature of the drying oven or the surface temperature of the drying roll is preferably 60 to 100 ° C., and the surface temperature of the heat treatment roll is preferably 80 to 120 ° C.

As a method for adjusting | Fd1-Fd2 | and | Fg1-Fg2 | to 0.07 or less, it is preferable to set the volatile fraction of the membrane-forming stock solution to 65 to 75% by mass, and the support for flowing the membrane-forming stock solution. The surface temperature of the hot air is preferably 80 to 95 ° C., the temperature of the hot air blown to the non-contact surface side is preferably 75 to 90 ° C., and the humidity of the hot air is preferably 5 to 40% RH. Further, at this time, the temperature of the drying oven or the surface temperature of the drying roll is preferably 60 to 90 ° C, and the surface temperature of the heat treatment roll is preferably 80 to 110 ° C.

(PVA)
In the PVA film of the present invention, as PVA, a polymer produced by saponifying a vinyl ester-based polymer obtained by polymerizing a vinyl ester-based monomer can be used. Examples of the vinyl ester-based monomer include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, vinyl versatic acid and the like. Among these, vinyl acetate is preferable as the vinyl ester-based monomer.

The vinyl ester-based polymer is preferably a polymer obtained by using only one kind or two or more kinds of vinyl ester-based monomers as a monomer, and is obtained by using only one kind of vinyl ester-based monomer as a monomer. The obtained polymer is more preferable. The vinyl ester-based polymer may be a copolymer of one or more kinds of vinyl ester-based monomers and another monomer copolymerizable therewith.

Other monomers include, for example, ethylene; olefins having 3 to 30 carbon atoms such as propylene, 1-butyl, and isobutene; acrylic acid or a salt thereof; methyl acrylate, ethyl acrylate, n-propyl acrylate, i acrylate. -Acrylic acid esters such as propyl, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate; methacrylic acid or a salt thereof; methacrylic acid Methyl, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, methacrylate Methacrylate esters such as octadecyl; acrylamide, N-methylacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide, diacetoneacrylamide, acrylamide propanesulfonic acid or its salts, acrylamidepropyldimethylamine or its salts, N-methylolacrylamide Or an acrylamide derivative such as a derivative thereof; methacrylamide, N-methylmethacrylate, N-ethylmethacrylate, methacrylamidepropanesulfonic acid or a salt thereof, methacrylamidepropyldimethylamine or a salt thereof, N-methylolmethacrylate or a derivative thereof, etc. Methacrylate derivatives; N-vinylamides such as N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone; methylvinyl ether, ethylvinyl ether, n-propylvinyl ether, i-propylvinyl ether, n-butylvinyl ether, i-butylvinyl ether Vinyl ethers such as t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether; vinyl cyanide such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride and vinylidene fluoride; allyl acetate and allyl chloride. Allyl compounds such as; maleic acid or salts thereof, esters or acid anhydrides; itaconic acid or salts thereof, esters or acid anhydrides; vinylsilyl compounds such as vinyltrimethoxysilane; isopropenyl acetate and the like. The vinyl ester-based polymer can have a structural unit derived from one or more of these other monomers.

The ratio of structural units derived from other monomers to the vinyl ester-based polymer is preferably 15 mol% or less, more preferably 8 mol% or less, based on the number of moles of all structural units constituting the vinyl ester-based polymer. preferable. In general, the crystallization of PVA tends to be more difficult to proceed as the ratio of structural units derived from other monomers in the vinyl ester-based polymer increases. Therefore, the crystallinity index (Fg1, Fg2, Fd1 and Fd2) of the PVA film can be adjusted by appropriately copolymerizing these other monomers at the above ratio.

The degree of polymerization of PVA is preferably 200 or more, more preferably 300 or more, and even more preferably 500 or more. By setting the degree of polymerization of PVA to the above lower limit or higher, it is possible to secure the mechanical strength of the obtained PVA film while preventing PVA from being excessively crystallized. On the other hand, the degree of polymerization of PVA is preferably 8,000 or less, more preferably 6,000 or less, and even more preferably 4,000 or less. Generally, the crystallization of PVA tends to be more difficult to proceed as the degree of polymerization of PVA is higher. Therefore, by setting the degree of polymerization of PVA to the above upper limit or less, the crystallization of PVA can be appropriately advanced and the crystallinity index (Fg1, Fg2, Fd1 and Fd2) of the PVA film can be adjusted. Further, by setting the degree of polymerization of PVA to the above upper limit or less, the viscosity of the film-forming stock solution of the PVA film does not become too high, and the productivity of the PVA film can be increased.

The degree of polymerization of PVA means the average degree of polymerization measured according to the description of JIS K 6726-1994. That is, the degree of polymerization (Po) is obtained by the following formula (12).

Degree of polymerization Po = ([η] × 10 ⁴ / 8.29) ^{(1 / 0.62)} (12)

In the above formula (12), η is the ultimate viscosity (deciliter / g) measured in water at 30 ° C. after remineralizing and purifying PVA.

The degree of saponification of PVA is preferably 90 mol% or more, more preferably 95 mol% or more, further preferably 99 mol% or more, and particularly preferably 99.8 mol% or more. .. Generally, the crystallization of PVA tends to proceed more easily as the degree of saponification of PVA increases. Therefore, by setting the saponification degree of PVA to the above lower limit or more, the crystallization of PVA can be appropriately advanced and the crystallinity index (Fg1, Fg2, Fd1 and Fd2) of the PVA film can be increased. That is, in the step of heat-treating the PVA film after the drying treatment by using PVA having a high degree of saponification as the film-forming stock solution of the PVA film, the polar surface layer portion near the surface of the PVA film and the PVA film which are susceptible to heat are used. The crystallinity inside the relatively deep interior tends to be high.

The degree of saponification of PVA is the ratio of the number of moles of vinyl alcohol units to the total number of moles of structural units (typically vinyl ester-based monomer units) that can be converted to vinyl alcohol units by saponification and vinyl alcohol units. (Mol%). The degree of saponification of PVA can be measured according to the description of JIS K 6726-1994.

The PVA film of the present invention may contain one type of PVA alone, or may contain two or more types of PVA having different degrees of polymerization, saponification, modification, and the like.

The content of PVA in the PVA film of the present invention is not necessarily limited, but is preferably 50% by mass or more, more preferably 80% by mass or more, and further preferably 85% by mass or more.

(Plasticizer)
The PVA film of the present invention preferably contains a plasticizer. By containing the plasticizer, the PVA film can be imparted with the same flexibility as other plastic films, and the PVA film can be prevented from breaking in the film forming and stretching steps of the PVA film.

Examples of the plasticizer include polyhydric alcohols such as ethylene glycol, glycerin, diglycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, and sorbitol. These plasticizers may be used alone or in combination of two or more. Among these, ethylene glycol or glycerin is preferable as the plasticizer, and glycerin is more preferable as the plasticizer because it is difficult to bleed out to the surface of the PVA film.

The content of the plasticizer in the PVA film of the present invention is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and further preferably 5 parts by mass or more with respect to 100 parts by mass of PVA. preferable. On the other hand, the content of the plasticizer is preferably 40 parts by mass or less, more preferably 30 parts by mass or less, and further preferably 20 parts by mass or less with respect to 100 parts by mass of PVA. When the content of the plasticizer is within the above range, the crystallinity index (Fg1, Fg2, Fd1 and Fd2) of the PVA film can be easily adjusted, and in addition, the effect of improving mechanical properties such as impact strength can be sufficiently obtained. be able to. In addition, it is possible to prevent the PVA film from becoming too flexible and having poor handleability, and preventing the plasticizer from bleeding out on the surface of the PVA film.

Here, the reason why the crystallinity index (Fg1, Fg2, Fd1 and Fd2) of the PVA film can be adjusted by adjusting the content of the plasticizer is as follows. Generally, when a PVA film contains an appropriate amount of a plasticizer, crystallization of PVA proceeds. It is presumed that this is because the plasticizer facilitates the movement of the polymer molecular chain of PVA and facilitates the formation of an energetically more stable crystal or constrained amorphous structure. On the other hand, if the PVA film contains an excessive amount of plasticizer, the crystallization of PVA is likely to be inhibited. It is presumed that this is because the amount of the plasticizer that interacts with the hydroxyl group of the polymer molecular chain of PVA increases and the interaction between the polymer molecular chains of PVA weakens. Therefore, by adjusting the content of the plasticizer, the crystallization of PVA can be appropriately advanced and the crystallinity index (Fg1, Fg2, Fd1 and Fd2) of the PVA film can be adjusted.

(Surfactant)
The PVA film of the present invention preferably contains a surfactant. By containing the surfactant, the handleability of the PVA film and the peelability of the PVA film from the film forming apparatus at the time of production can be improved. The surfactant is not particularly limited, and for example, an anionic surfactant and a nonionic surfactant are preferably used.

Examples of the anionic surfactant include a carboxylic acid type surfactant such as potassium laurate; a sulfate ester type surfactant such as octyl sulfate; and a sulfonic acid type surfactant such as dodecylbenzene sulfonate.

Examples of the nonionic surfactant include an alkyl ether type surfactant such as polyoxyethylene lauryl ether and polyoxyethylene oleyl ether; an alkylphenyl ether type surfactant such as polyoxyethylene octylphenyl ether; and polyoxyethylene lau. Alkyl ester type surfactant such as rate; Alkylamine type surfactant such as polyoxyethylene laurylamino ether; Alkylamide type surfactant such as polyoxyethylene lauric acid amide; Polypropylene such as polyoxyethylene polyoxypropylene ether Glycol ether type surfactants; alkanolamide type surfactants such as lauric acid diethanolamide and oleic acid diethanolamide; allylphenyl ether type surfactants such as polyoxyalkylene allylphenyl ether and the like can be mentioned.

Such a surfactant may be used alone or in combination of two or more. As the surfactant, a nonionic surfactant is preferable, an alkanolamide type surfactant is more preferable, and an aliphatic carboxylic acid (for example, carbon) is preferable because it is excellent in reducing surface abnormalities during film formation of PVA film. Dialkanolamides (eg, diethanolamides, etc.) of number 8-30 saturated or unsaturated aliphatic carboxylic acids, etc. are more preferred.

The content of the surfactant in the PVA film of the present invention is preferably 0.01 part by mass or more, more preferably 0.02 part by mass or more, and 0.05 part by mass with respect to 100 parts by mass of PVA. It is more preferable that the amount is more than one part. On the other hand, the content of the surfactant is preferably 10 parts by mass or less, more preferably 1 part by mass or less, and further preferably 0.5 parts by mass or less with respect to 100 parts by mass of PVA. , 0.3 parts by mass or less is particularly preferable. When the content of the surfactant is in the above range, the peelability of the PVA film from the film forming apparatus at the time of production becomes good, and the sticking between the PVA films (hereinafter, also referred to as “blocking”) occurs. It can be prevented from occurring. Further, it is possible to prevent the surfactant from bleeding out to the surface of the PVA film and to prevent the appearance of the PVA film from being deteriorated due to the aggregation of the surfactant.

(Other ingredients)
In addition to PVA, the PVA film of the present invention includes water-soluble polymers, moisture, antioxidants, ultraviolet absorbers, lubricants, cross-linking agents, colorants, fillers, preservatives, fungicides, other polymer compounds, etc. Ingredients may be contained within a range that does not interfere with the effects of the present invention. The ratio of the total mass of PVA, surfactant, plasticizer, and other components other than PVA to the total mass of the PVA film is preferably 60% by mass or more, more preferably 80% by mass or more. It is preferably 90% by mass or more, and more preferably 90% by mass or more. The ratio of the total mass of the other components to the total mass of the PVA film is preferably 100% by mass or less.

(Physical characteristics)
The PVA film of the present invention is water-insoluble. Since the PVA film is water-insoluble, when uniaxial stretching for producing an optical film such as a polarizing film is performed in an aqueous solution, the PVA film is broken during uniaxial stretching even if the maximum stretching speed is high. It can be stretched without causing it. Here, the term "water-insoluble" in the present invention means that the PVA film does not completely dissolve when the PVA film is immersed in water (deionized water) at 30 ° C. according to the following procedures <1> to <4>. It means that it remains undissolved even in the part.

<1> The PVA film is placed in a constant temperature and humidity chamber adjusted to 20 ° C. and 65% RH for 16 hours or more to adjust the humidity.
<2> After cutting out a rectangular sample of 40 mm in length × 35 mm in width from the humidity-controlled PVA film, two 50 mm × 50 mm plastic plates having a rectangular window (hole) of 35 mm in length × 23 mm in width opened. The sample is sandwiched and fixed so that the length direction of the sample is parallel to the length direction of the window and the sample is located substantially in the center of the width direction of the window.
<3> Put 300 mL of deionized water in a 500 mL beaker and adjust the water temperature to 30 ° C while stirring with a magnetic stirrer equipped with a 3 cm long bar at a rotation speed of 280 rpm.
<4> The sample fixed to the plastic plate in <2> above is immersed in deionized water in a beaker for 1000 seconds, being careful not to contact the bar of the rotating magnetic stirrer.

<Manufacturing method of PVA film>
The method for producing the PVA film of the present invention is not particularly limited, and for example, any method as follows can be adopted. As such a method, a cast film forming method, a wet film forming method (a method of discharging into a poor solvent), a dry-wet film forming method, etc. A gel film-forming method (a method in which a film-forming stock solution is once cooled and gelled and then the solvent is extracted and removed), a method of forming a film by a combination of these methods, or a film-forming stock solution obtained by using an extruder or the like is used as T. Examples thereof include a melt extrusion film forming method and an inflation forming method in which a film is formed by extruding from a die or the like. Among these, as a method for producing a PVA film, a casting film forming method and a melt extrusion film forming method are preferable. By using these methods, a homogeneous PVA film can be obtained with high productivity. Hereinafter, a case where the PVA film is manufactured by the casting film forming method or the melt extrusion film forming method will be described.

When the PVA film of the present invention is produced by a casting film forming method or a melt extrusion film forming method, first, a film forming stock solution containing PVA, a solvent, and if necessary, an additive such as a plasticizer is prepared. prepare. Next, this film-forming stock solution is salivated (supplied) in the form of a film onto a rotating support such as a metal roll or a metal belt. As a result, a liquid film of the film-forming stock solution is formed on the support. The liquid film is solidified and formed into a film by being heated on the support to remove the solvent. Examples of the method of heating the liquid film include a method of heating the support itself to a high temperature with a heat medium or the like, a method of blowing hot air on the opposite surface of the surface in contact with the support of the liquid film, and the like. The solidified long film (PVA film) is peeled off from the support, dried by a drying roll, a drying furnace or the like as necessary, further heat-treated as needed, and wound into a roll.

In the step of drying the liquid film poured on the support (solvent removal step) and then the step of drying the PVA film, PVA crystallizes while being heated. The rate of crystallization at this time includes the ratio of structural units derived from other monomers in PVA, the degree of polymerization of PVA, the degree of saponification of PVA, and the content of the plasticizer, as well as the water content and temperature in PVA. , And draw (tensile elongation in the flow direction). Regarding the draw, it is presumed to be the effect of orientation crystallization due to the tension of the polymer molecular chain of PVA.

Normally, the drying of the PVA film proceeds by volatilizing the volatile matter from the released film surface that is not in contact with the support, the drying roll, or the like. Therefore, in the step during drying, the concentration distribution of volatile components such as water is generated in the thickness direction of the PVA film, so that the crystallinity index is distributed in the thickness direction of the PVA film depending on the temperature and draw conditions at that time. The distribution of this crystallinity index can be adjusted by the volatile fraction of the membrane-forming stock solution, the support temperature, the contact time with the support, the hot air temperature and amount, the drying roll and the drying oven temperature, and the like. Therefore, by appropriately adjusting each of the above factors, the crystallization of PVA can be appropriately advanced and the crystallinity index (Fg1, Fg2, Fd1 and Fd2) of the PVA film can be adjusted.

The volatile fraction of the film-forming stock solution (concentration of volatile components such as solvents removed by volatilization or evaporation during film-forming) is preferably 50% by mass or more, more preferably 55% by mass or more. preferable. The volatile fraction of the film-forming stock solution is preferably 90% by mass or less, and more preferably 80% by mass or less. When the volatile fraction is in the above range, the viscosity of the film-forming stock solution can be adjusted to a suitable range, so that the film-forming property of the liquid film flowed on the support is improved and the film-forming property has a uniform thickness. It becomes easier to obtain a PVA film. Further, when the volatile fraction is in the above range, the crystallization of PVA proceeds appropriately on the support, so that the crystallinity index of the obtained PVA film and its distribution can be easily adjusted. The film-forming stock solution may contain a dichroic dye, if necessary. The volatile fraction of the film-forming stock solution is a value obtained by the following formula (13).

Volatile fraction (mass%) of membrane-forming stock solution = {(Wa-Wb) / Wa} x 100 (13)

In the above formula (13), Wa represents the mass (g) of the film-forming stock solution, and Wb is the mass (g) of the film-forming stock solution of Wa (g) after being dried in an electric heating dryer at 105 ° C. for 16 hours. ).

The method for preparing the film-forming stock solution is not particularly limited, and for example, a method of dissolving PVA and additives such as a plasticizer and a surfactant in a solvent in a dissolution tank or the like, or a uniaxial or biaxial extruder is used. Examples thereof include a method of melt-kneading PVA in a water-containing state together with additives such as a plasticizer and a surfactant.

The undiluted film-forming solution generally passes through the die lip of a die such as a T-die and is spilled into a film on a support such as a metal roll or a metal belt. On the support, the solvent volatilizes from the surface of the flowed film-like stock solution that is not in contact with the support (hereinafter, may be referred to as a free surface), while in contact with the support. Since it does not substantially volatilize from the existing surface (hereinafter, may be referred to as a touch surface), the distribution is such that the solvent concentration on the free surface side is low and the solvent concentration on the touch surface side is high with respect to the thickness direction of the film. Occurs. Therefore, the solidification of PVA also proceeds from the free side first.

PVA crystallization progresses in parallel with PVA solidification. Crystallization of PVA is difficult to proceed even if the solvent concentration is too high or too low, and although it depends on the primary structure of the PVA molecule, the volatile fraction of the flowed membrane-forming stock solution is in the range of 20 to 60% by mass. It is easy to progress at one time. Further, the rate of crystallization of PVA increases as the temperature increases, but the rate of volatilization of the solvent increases as the temperature increases. Therefore, in order to efficiently promote the crystallization of the polar surface layer near the surface of the PVA film and control the crystallinity index (Fg1 and Fg2) of the polar surface layer, the temperature of the support and the support are used. In addition to the contact time, it is also important to control the temperature of the atmosphere near the free surface, the vapor pressure of the solvent, and the like.

The PVA film of the present invention is a film having a high crystallinity in the extreme surface layer near the surface of the film with respect to the crystallinity inside the film, which is relatively deep inside. Therefore, in order to obtain the PVA film of the present invention, it is sufficient to select the conditions for suppressing the crystallization of the relatively deep inside of the film while proceeding with the crystallization of the polar surface layer portion near the surface of the film. For example, in the initial stage of drying when the volatile fraction of the polar surface layer near the surface of the film decreases, by adopting a condition of slow drying such as lowering the drying temperature, in the process of crystallization progressing, the polar surface layer Increase the water content. On the other hand, from the middle to late drying period when crystallization progresses in the relatively deep inside of the film, it is exemplified to adopt the condition that the internal crystallization does not proceed easily by rapidly drying at a relatively high temperature. Will be done.

The surface temperature of the support for which the membrane-forming stock solution is spilled is preferably 65 ° C. or higher, and more preferably 70 ° C. or higher. The surface temperature of the support on which the membrane-forming stock solution is spilled is preferably 110 ° C. or lower, more preferably 100 ° C. or lower, and even more preferably 95 ° C. or lower. When the surface temperature is within the above range, the crystallinity index (Fg1) of the PVA film proceeds at an appropriate rate due to the drying of the liquid film drooled on the support and the crystallization of the polar surface layer near the surface of the film. And Fg2) can be adjusted.

At the same time as heating the liquid film on the support, hot air with a wind speed of 1 to 10 m / sec may be uniformly blown over the entire area on the non-contact surface side of the liquid film. The temperature of the hot air blown to the non-contact surface side is preferably 50 ° C. or higher, more preferably 70 ° C. or higher. The temperature of the hot air blown to the non-contact surface side is preferably 150 ° C. or lower, more preferably 120 ° C. or lower. Further, the humidity of the hot air is preferably 1% RH or more, more preferably 3% RH or more, and further preferably 5% RH or more. The humidity of the hot air is preferably 40% RH or less, and more preferably 30% RH or less. When the temperature and humidity of the hot air blown to the non-contact surface side are within the above ranges, it becomes easy to adjust the crystallinity index (Fg1, Fg2, Fd1 and Fd2) of the PVA film.

The PVA film is preferably dried (solvent removed) on the support to a volatile fraction of 5 to 50% by mass, then peeled off from the support, and further dried if necessary. The method of drying is not particularly limited, and examples thereof include a method of passing through a drying oven and a method of contacting with a drying roll. When the PVA film is dried using a plurality of drying rolls, it is preferable that one surface of the PVA film and the other surface are alternately brought into contact with the drying rolls. Thereby, the difference in the crystallinity index of PVA (| Fd1-Fd2 | and | Fg1-Fg2 |) on both sides of the PVA film (two surfaces orthogonal to the thickness direction) can be adjusted. In this case, the number of dry rolls is preferably 3 or more, more preferably 4 or more, and even more preferably 5 to 30.

The upper limit of the temperature of the drying furnace or the surface temperature of the drying roll is preferably 110 ° C. or lower, more preferably 100 ° C. or lower, further preferably 90 ° C. or lower, and preferably 85 ° C. or lower. Especially preferable. On the other hand, the lower limit of the temperature of the drying furnace or the surface temperature of the drying roll is preferably 40 ° C. or higher, more preferably 45 ° C. or higher, and even more preferably 50 ° C. or higher. By keeping the temperature of the drying oven or the surface temperature of the drying roll within the above range, it becomes easy to adjust the crystallinity index (Fg1, Fg2, Fd1 and Fd2) of the PVA film.

The dried PVA film can be further heat-treated if necessary. By performing the heat treatment, the crystallinity of the polar surface layer near the surface of the film and the crystallinity of the relatively deep inside of the film can be increased, and the crystallinity index (Fg1, Fg2, Fd1 and Fd2) of the PVA film can be increased. Can be adjusted. In addition, characteristics such as mechanical strength and swellability of the PVA film can be adjusted.

The lower limit of the surface temperature of the heat treatment roll for performing the heat treatment is preferably 60 ° C. or higher. The upper limit of the surface temperature of the heat treatment roll is preferably 135 ° C. or lower, more preferably 130 ° C. or lower. By keeping the surface temperature of the heat treatment roll within the above range, it becomes easy to adjust the crystallinity index (Fg1, Fg2, Fd1 and Fd2) of the PVA film.

The PVA film thus produced is, if necessary, further subjected to humidity control treatment, cutting of both ends (ears) of the film, and then rolled up on a cylindrical core in a roll shape. , Moisture-proof packaging to make a product.

The volatile fraction of the PVA film finally obtained by a series of treatments is not necessarily limited. The volatile fraction of the PVA film is preferably 1% by mass or more, more preferably 2% by mass or more. The volatile fraction of the PVA film is preferably 5% by mass or less, and more preferably 4% by mass or less.

<Manufacturing method of optical film>
The PVA film of the present invention is used as a raw film for producing an optical film. Examples of the optical film include a polarizing film, a viewing angle improving film, a retardation film, and a brightness improving film, but a polarizing film is preferable. Hereinafter, as an example of the method for manufacturing an optical film, a method for manufacturing a polarizing film will be specifically described.

The polarizing film can usually be produced by using a PVA film as a raw film and undergoing treatment steps such as a swelling step, a dyeing step, a cross-linking step, a stretching step, and a fixing treatment step. Specific examples of the treatment liquid used in each step include a swelling treatment liquid used for swelling treatment, a dyeing treatment liquid (staining liquid) used for dyeing treatment, a cross-linking treatment liquid used for cross-linking treatment, and a stretching treatment liquid. Examples thereof include a stretching treatment liquid, a fixing treatment liquid used for the fixing treatment, and a cleaning treatment liquid (cleaning liquid) used for the cleaning treatment.

Each processing step that can be adopted in the manufacturing method for manufacturing the polarizing film will be described in detail below. In the method for producing a polarizing film, one or two or more of the following processes may be omitted, the same process may be performed a plurality of times, or another process may be performed at the same time.

(Washing treatment before swelling treatment)
It is preferable to perform a cleaning treatment on the PVA film before performing the swelling treatment on the PVA film. By such a cleaning treatment before the swelling treatment, the blocking inhibitor or the like adhering to the PVA film can be removed, and it is possible to prevent each treatment liquid in the polarizing film manufacturing process from being contaminated by the blocking inhibitor or the like. be able to. The cleaning treatment is preferably performed by immersing the PVA film in the cleaning treatment liquid, but it can also be performed by spraying the cleaning treatment liquid on the PVA film. For example, water can be used as the cleaning treatment liquid. The temperature of the cleaning treatment liquid is preferably in the range of 20 to 40 ° C. When the temperature is 20 ° C. or higher, it becomes easy to remove the blocking inhibitor and the like adhering to the PVA film. Further, when the temperature is 40 ° C. or lower, it is possible to prevent a part of the surface of the PVA film from melting and the films from sticking to each other to deteriorate the handleability. The temperature of the cleaning treatment liquid is more preferably 22 ° C. or higher, further preferably 24 ° C. or higher, and particularly preferably 26 ° C. or higher. Further, the temperature of the cleaning treatment liquid is more preferably 38 ° C. or lower, further preferably 36 ° C. or lower, and particularly preferably 34 ° C. or lower.

(Swelling treatment)
The swelling treatment can be performed by immersing the PVA film in a swelling treatment liquid such as water. The temperature of the swelling treatment liquid is preferably 20 ° C. or higher, more preferably 22 ° C. or higher, and even more preferably 24 ° C. or higher. The temperature of the swelling treatment liquid is preferably 40 ° C. or lower, more preferably 38 ° C. or lower, and even more preferably 36 ° C. or lower. Further, the time for immersing in the swelling treatment liquid is preferably, for example, 0.1 minutes or longer, and more preferably 0.5 minutes or longer. The time for immersing in the swelling treatment liquid is, for example, preferably 5 minutes or less, and more preferably 3 minutes or less. The water used as the swelling treatment liquid is not limited to pure water, and may be an aqueous solution in which various components such as a boron-containing compound are dissolved, or may be a mixture of water and an aqueous medium. The type of the boron-containing compound is not particularly limited, but boric acid or borax is preferable from the viewpoint of handleability. When the swelling treatment liquid contains a boron-containing compound, the concentration thereof is preferably 6% by mass or less from the viewpoint of improving the stretchability of the PVA film.

(Dyeing process)
The dyeing treatment is preferably carried out using an iodine-based dye as the dichroic dye, and the dyeing time may be any stage before the stretching treatment, during the stretching treatment, or after the stretching treatment. The dyeing treatment is preferably carried out by using a solution containing iodine-potassium iodide (preferably an aqueous solution) as the dyeing treatment liquid and immersing the PVA film in the dyeing treatment liquid. The concentration of iodine in the dyeing solution is preferably 0.005% by mass or more. The concentration of iodine in the dyeing solution is preferably 0.2% by mass or less. Potassium iodide / iodine (mass) is preferably 20 or more. Potassium iodide / iodine (mass) is preferably 100 or less. The temperature of the dyeing treatment liquid is preferably 20 ° C. or higher, more preferably 25 ° C. or higher. The temperature of the dyeing treatment liquid is preferably 50 ° C. or lower, more preferably 40 ° C. or lower. The dyeing solution may contain a boron-containing compound such as boric acid as a cross-linking agent. If the PVA film used as the raw film contains a dichroic dye in advance, the dyeing process can be omitted. Further, it is also possible to preliminarily contain a boron-containing compound such as boric acid or borax in the PVA film used as the raw film.

(Crosslinking)
In the production of the polarizing film, it is preferable to carry out a cross-linking treatment after the dyeing treatment for the purpose of strengthening the adsorption of the dichroic dye on the PVA film. The cross-linking treatment can be performed by using a solution containing a cross-linking agent (preferably an aqueous solution) as the cross-linking treatment liquid and immersing the PVA film in the cross-linking treatment liquid. As the cross-linking agent, one or more kinds of boron-containing compounds such as boric acid and borax can be used. If the concentration of the cross-linking agent in the cross-linking treatment liquid is too high, the cross-linking reaction tends to proceed too much and it tends to be difficult to carry out sufficient stretching in the subsequent stretching treatment, and if it is too low, the effect of the cross-linking treatment tends to be difficult. Tends to decrease. The concentration of the cross-linking agent in the cross-linking treatment liquid is preferably 1% by mass or more, more preferably 1.5% by mass or more, and further preferably 2% by mass or more. The concentration of the cross-linking agent in the cross-linking treatment liquid is preferably 6% by mass or less, more preferably 5.5% by mass or less, and further preferably 5% by mass or less.

In order to suppress the elution of the dichroic dye from the PVA film after the dyeing treatment, the cross-linking treatment liquid may contain an iodine-containing compound such as potassium iodide. If the concentration of the iodine-containing compound in the cross-linking treatment liquid is too high, the reason is unknown, but the heat resistance of the obtained polarizing film tends to decrease. Further, if the concentration of the iodine-containing compound in the cross-linking treatment liquid is too low, the effect of suppressing the elution of the dichroic dye tends to be reduced. The concentration of the iodine-containing compound in the cross-linking treatment liquid is preferably 1% by mass or more, more preferably 1.5% by mass or more, and further preferably 2% by mass or more. The concentration of the iodine-containing compound in the cross-linking treatment liquid is preferably 6% by mass or less, more preferably 5.5% by mass or less, and further preferably 5% by mass or less.

If the temperature of the cross-linking treatment liquid is too high, the polarizing film obtained by elution of the dichroic dye tends to cause uneven dyeing, and if it is too low, the effect of the cross-linking treatment may be reduced. .. The temperature of the cross-linking treatment liquid is preferably 20 ° C. or higher, more preferably 22 ° C. or higher, and even more preferably 25 ° C. or higher. The temperature of the cross-linking treatment liquid is preferably 45 ° C. or lower, more preferably 40 ° C. or lower, and even more preferably 35 ° C. or lower.

Apart from the stretching treatment described later, the PVA film may be stretched during or between the above-mentioned treatments. By such stretching (pre-stretching), it is possible to prevent wrinkles from being generated on the surface of the PVA film. The total stretching ratio of the pre-stretching (magnification obtained by multiplying the stretching ratio in each treatment) is 4 times or less based on the original length of the PVA film of the original fabric before stretching from the viewpoint of the polarization performance of the obtained polarizing film. It is preferably 3.5 times or less, and more preferably 3.5 times or less. The total draw ratio of the pre-stretching is preferably 1.5 times or more based on the original length of the PVA film of the original fabric before stretching from the viewpoint of the polarization performance of the obtained polarizing film. The draw ratio in the swelling treatment is preferably 1.1 times or more, more preferably 1.2 times or more, and further preferably 1.4 times or more. The draw ratio in the swelling treatment is preferably 3 times or less, more preferably 2.5 times or less, and further preferably 2.3 times or less. The draw ratio in the dyeing treatment is preferably 2 times or less, more preferably 1.8 times or less, and further preferably 1.5 times or less. The draw ratio in the dyeing treatment is more preferably 1.1 times or more. The draw ratio in the crosslinking treatment is preferably 2 times or less, more preferably 1.5 times or less, and further preferably 1.3 times or less. The stretching ratio in the crosslinking treatment is more preferably 1.05 times or more.

(Stretching treatment)
The stretching treatment may be performed by either a wet stretching method or a dry stretching method. In the case of the wet stretching method, a solution containing a boron-containing compound such as boric acid (preferably an aqueous solution) can be used as the stretching treatment liquid, and the stretching treatment liquid can be used. It can also be performed in the treatment liquid. Further, in the case of the dry stretching method, it can be carried out in the air using a PVA film after water absorption. Among these, the wet stretching method is preferable, and uniaxial stretching is more preferable in an aqueous solution containing boric acid. When the stretching treatment liquid contains a boron-containing compound, the concentration of the boron-containing compound in the stretching treatment liquid is preferably 1.5% by mass or more because the stretchability of the PVA film can be improved. It is more preferably 0% by mass or more, and further preferably 2.5% by mass or more. The concentration of the boron-containing compound in the stretching treatment liquid is preferably 7% by mass or less, more preferably 6.5% by mass or less, and more preferably 6% by mass, because the stretchability of the PVA film can be improved. The following is more preferable.

It is preferable that the stretching treatment liquid contains an iodine-containing compound such as potassium iodide. If the concentration of the iodine-containing compound in the stretching solution is too high, the hue of the obtained polarizing film tends to be bluish, and if it is too low, the reason is unknown, but the heat resistance of the obtained polarizing film is high. The sex tends to decrease. The concentration of the iodine-containing compound in the stretching treatment liquid is preferably 2% by mass or more, more preferably 2.5% by mass or more, and further preferably 3% by mass or more. The concentration of the iodine-containing compound in the stretching treatment liquid is preferably 8% by mass or less, more preferably 7.5% by mass or less, and further preferably 7% by mass or less.

If the temperature of the stretching treatment liquid is too high, the PVA film tends to melt and become soft and easily break, and if it is too low, the stretchability tends to decrease. The temperature of the stretching treatment liquid is preferably 50 ° C. or higher, more preferably 52.5 ° C. or higher, and even more preferably 55 ° C. or higher. The temperature of the stretching treatment liquid is preferably 70 ° C. or lower, more preferably 67.5 ° C. or lower, and even more preferably 65 ° C. or lower. The preferred range of the stretching temperature when the stretching treatment is performed by the dry stretching method is also as described above.

The stretching ratio in the stretching treatment is preferably 1.2 times or more, more preferably 1.5 times or more, and more preferably 1.5 times or more, because a polarizing film having better polarizing performance can be obtained when the drawing ratio is high. It is more preferable that the amount is double or more. Further, the total draw ratio (magnification multiplied by the draw ratio in each step) including the draw ratio of the pre-stretch described above is the polarization performance of the obtained polarizing film based on the original length of the raw material PVA film before stretch. From this point of view, it is preferably 5.5 times or more, more preferably 5.7 times or more, and further preferably 5.9 times or more. The upper limit of the draw ratio is not particularly limited, but if it is too high, stretch breakage is likely to occur, so it is preferably 8 times or less.

There is no particular limitation on the method of performing the stretching process by uniaxial stretching, and uniaxial stretching in the long direction and lateral uniaxial stretching in the width direction can be adopted. In the case of producing a polarizing film, uniaxial stretching in the long direction is preferable from the viewpoint of obtaining an excellent polarizing film. Uniaxial stretching in the long direction can be performed by using a stretching device including a plurality of rolls parallel to each other and changing the peripheral speed between the rolls.

In the present invention, the maximum stretching speed (% / min) when the stretching treatment is performed by uniaxial stretching is not particularly limited, but is preferably 200% / min or more, and more preferably 300% / min or more. , 400% / min or more is more preferable. Here, the maximum stretching speed is the fastest stretching speed among the three or more rolls having different peripheral speeds when the PVA film is stretched in two or more stages. Say that. When the stretching treatment of the PVA film is performed in one step without dividing into two or more steps, the stretching speed at that step becomes the maximum stretching rate. Further, the stretching speed refers to an increase in the length of the PVA film increased by stretching with respect to the length of the PVA film before stretching per unit time. For example, the stretching speed of 100% / min is the speed at which the PVA film is deformed from the length before stretching to twice the length in one minute. The higher the maximum stretching speed, the higher the stretching treatment (uniaxial stretching) of the PVA film can be performed, and as a result, the productivity of the polarizing film is improved, which is preferable. On the other hand, if the maximum stretching speed becomes too high, excessive tension may be locally applied to the PVA film in the stretching treatment (uniaxial stretching) of the PVA film, and stretching fracture is likely to occur. From this point of view, it is preferable that the maximum stretching speed does not exceed 900% / min.

(Fixed processing)
In the production of the polarizing film, it is preferable to carry out a fixing treatment in order to strengthen the adsorption of the dichroic dye on the PVA film. For the fixing treatment, a solution containing one or more boron-containing compounds such as boric acid and borax (preferably an aqueous solution) is used as the fixing treatment liquid, and a PVA film (preferably after stretching treatment) is used as the fixing treatment liquid. This can be done by immersing the PVA film). Further, if necessary, the fixing treatment liquid may contain an iodine-containing compound or a metal compound. The concentration of the boron-containing compound in the fixing treatment liquid is preferably 2% by mass or more, and more preferably 3% by mass or more. The concentration of the boron-containing compound in the fixing treatment liquid is preferably 15% by mass or less, and more preferably 10% by mass or less. The temperature of the fixing treatment liquid is preferably 15 ° C. or higher, more preferably 25 ° C. or higher. The temperature of the fixing treatment liquid is preferably 60 ° C. or lower, more preferably 40 ° C. or lower.

(Washing treatment after dyeing treatment)
After the dyeing treatment, it is preferable to perform a washing treatment on the PVA film after the stretching treatment. The cleaning treatment is preferably performed by immersing the PVA film in the cleaning treatment liquid, but it can also be performed by spraying the cleaning treatment liquid on the PVA film. For example, water can be used as the cleaning treatment liquid. The water is not limited to pure water, and may contain an iodine-containing compound such as potassium iodide. The cleaning treatment liquid may contain a boron-containing compound, but in that case, the concentration of the boron-containing compound is preferably 2.0% by mass or less.

The temperature of the cleaning treatment liquid is preferably in the range of 5 to 40 ° C. When the temperature of the cleaning treatment liquid is 5 ° C. or higher, it is possible to suppress the breakage of the PVA film due to freezing of water. Further, when the temperature of the cleaning treatment liquid is 40 ° C. or lower, the optical characteristics of the obtained polarizing film are improved. The temperature of the cleaning treatment liquid is more preferably 7 ° C. or higher, further preferably 10 ° C. or higher. Further, the temperature of the cleaning treatment liquid is more preferably 38 ° C. or lower, and further preferably 35 ° C. or lower.

Specific methods for producing a polarizing film include a method of subjecting a PVA film to a dyeing treatment, a stretching treatment, a crosslinking treatment and / or a fixing treatment. As a preferable example, there is a method in which the PVA film is subjected to a swelling treatment, a dyeing treatment, a crosslinking treatment, a stretching treatment (particularly a uniaxial stretching treatment), and a washing treatment in this order. Further, the stretching treatment may be performed in any of the treatment steps prior to the above, or may be performed in multiple stages of two or more stages.

A polarizing film can be obtained by subjecting the PVA film after each of the above treatments to a drying treatment. The drying treatment method is not particularly limited, and examples thereof include a contact type method in which the film is brought into contact with a heating roll, a method in which the film is dried in a hot air dryer, and a floating type method in which the film is dried by hot air while floating. ..

<Polarizer>
The polarizing film obtained as described above is preferably used as a polarizing plate by laminating a protective film that is optically transparent and has mechanical strength on both sides or one side thereof. As the protective film, a cellulose triacetate (TAC) film, a cycloolefin polymer (COP) film, a cellulose acetate / butyrate cellulose (CAB) film, an acrylic film, a polyester film and the like are used. Further, examples of the adhesive for bonding include PVA-based adhesives and urethane-based adhesives, but PVA-based adhesives are preferable.

The polarizing plate obtained as described above can be used as a component of an LCD by laminating an adhesive such as an acrylic material and then laminating it on a glass substrate. At the same time, it may be bonded to a retardation film, a viewing angle improving film, a brightness improving film, or the like.

Hereinafter, the present invention will be specifically described with reference to Examples and the like, but the present invention is not limited to the following Examples.

<Calculation of crystallinity index by FT-IR measurement>
A PVA film having a width of 30 mm and a length of 30 mm was cut out from the PVA film obtained in the following Example or Comparative Example and used as a measurement sample. Since the value of the crystallinity index of the PVA film varies slightly depending on the amount of moisture absorbed by the PVA film, this measurement sample is stored for 24 hours in an environment with a temperature of 24.0 ° C and a relative humidity of 45.0% RH, and a room in the same environment. FT-IR measurement was performed with the measuring device installed inside. The FT-IR measurement was performed on both sides of the PVA film (two surfaces orthogonal to the thickness direction of the PVA film, the first surface and the second surface) under the following conditions.

Measuring device: NICOLET is 10 (manufactured by Thermo Fisher)
Measurement conditions: 1-time reflection ATR method Incident angle 45 °
Resolution: 4.0 cm ^-1
Number of integrations: 32 times Measurement temperature: 24.0 ° C (environmental temperature)
Measured humidity: 45.0% RH (environmental relative humidity)
ATR prism: diamond prism or germanium prism

From the infrared absorption spectrum obtained by FT-IR measurement of the PVA film, both sides of the PVA film (two surfaces orthogonal to the thickness direction of the PVA film, the first surface and the second surface) by the above method. The crystallinity index was calculated.

<Evaluation of wrinkles on the surface of polarizing film>
With respect to the polarizing film obtained in the following Example or Comparative Example, the state of wrinkles on the surface of the polarizing film was confirmed by irradiating the surface of the polarizing film with light from an angle with a fluorescent lamp and visually observing the reflected light. However, it was evaluated according to the following criteria.
Evaluation criteria:
A: No wrinkles were confirmed.
B: Slight wrinkles were confirmed to the extent that there was no problem in practical use.
C: Wrinkles that were practically problematic were clearly confirmed.

<Evaluation of stretching fracture frequency during polarizing film manufacturing>
In the following Examples or Comparative Examples, uniaxial stretching in the stretching treatment for producing a polarizing film was continuously performed for 20 minutes. The number of stretch breaks generated in this continuous stretching for 20 minutes was measured, and the stretch break frequency (times / 20 mim) was evaluated.

<Example 1>
<Manufacturing and evaluation of PVA film>
Using 100 parts by mass of PVA (sakenization degree 99 mol%, degree of polymerization 2400), 12 parts by mass of glycerin plasticizer as a plasticizer, 0.1 part by mass of lauric acid diethanolamide and 217.6 parts by mass of water as a surfactant. A film-forming stock solution (volatile content of 66% by mass) was prepared by melt-mixing with a melt extruder. Next, this film-forming stock solution was discharged from the T-die onto the support (surface temperature 80 ° C.) in the form of a film to form a liquid film on the support. A PVA film (moisture content: 32% by mass) was obtained by blowing hot air at 85 ° C. and 3% RH at a rate of 5 m / sec on the entire non-contact surface of the liquid film on the support and drying it. rice field. The PVA film is then stripped from the support and from the first drying roll to the final drying roll just before the heat treatment roll so that one side and the other side of the PVA film are in alternating contact with each drying roll. After further drying up to (19th drying roll), the film was peeled off from the final drying roll. At this time, the surface temperature of each dry roll from the first dry roll to the final dry roll was set to 75 ° C. Further, the PVA film was peeled off from the final dry roll, and heat treatment was performed so that one surface of the PVA film and the other surface were alternately in contact with each heat treatment roll. At this time, the heat treatment was performed using two heat treatment rolls, and the surface temperature of each of the heat treatment rolls was 90 ° C. The obtained PVA film (thickness 30 μm, width 1200 mm) was subjected to FT-IR measurement by the above method, and the crystallinity index (Fg1, Fg2, Fd1 and Fd2) was calculated. The results are shown in Table 1.

<Manufacturing and evaluation of polarizing film>
The obtained PVA film was slit to a width of 650 mm, and the film was continuously subjected to swelling treatment, dyeing treatment, cross-linking treatment, stretching treatment, washing treatment, and drying treatment in this order to continuously produce a polarizing film. The swelling treatment was carried out by uniaxially stretching 2.00 times in the length direction while immersing in pure water (swelling treatment liquid) at 25 ° C. The dyeing treatment is performed while being immersed in a potassium iodide / iodine staining solution (staining treatment solution) at a temperature of 32 ° C. (potassium iodide / iodine (mass ratio) 23, iodine concentration 0.03 to 0.05% by mass). It was uniaxially stretched 1.26 times in the direction. In this dyeing treatment, the iodine concentration in the dyeing treatment liquid is 0.03 to 0.05 so that the simple substance transmittance of the polarizing film obtained after uniaxial stretching in the stretching treatment is in the range of 43.5% ± 0.2%. Adjusted within the range of mass%. The cross-linking treatment was carried out by uniaxially stretching 1.19 times in the length direction while immersing in a boric acid aqueous solution (cross-linking treatment liquid) (boric acid concentration 2.6% by mass) at 32 ° C. The stretching treatment is performed 2.00 times in the length direction while being immersed in a 55 ° C. boric acid / potassium iodide aqueous solution (stretching treatment liquid) (boric acid concentration 2.8% by mass, potassium iodide concentration 5% by mass). It was uniaxially stretched. The maximum stretching speed of uniaxial stretching in this stretching treatment was 400% / min. The washing treatment is carried out by immersing in a potassium iodide / boric acid aqueous solution (washing liquid) (potassium iodide concentration 3 to 6% by mass, boric acid concentration 1.5% by mass) at 22 ° C. for 12 seconds without stretching. gone. The drying treatment was carried out by hot air drying at 80 ° C. for 1.5 minutes without stretching to obtain a polarizing film. With respect to the obtained polarizing film, wrinkles on the surface of the polarizing film and the frequency of stretch breakage during the production of the polarizing film were evaluated by the above method. The results are shown in Table 2.

<Example 2>
In <Production and Evaluation of PVA Film> of Example 1, the PVA used for preparing the film-forming stock solution is changed to PVA (sakenization degree 99 mol%, polymerization degree 2400, ethylene modification 2.5 mol%), and 2 A PVA film and a polarizing film were obtained in the same manner as in Example 1 except that the surface temperature of each of the heat-treated rolls of the book was changed to 85 ° C. The obtained PVA film and polarizing film were measured and evaluated in the same manner as in Example 1. The results are shown in Tables 1 and 2, respectively.

<Example 3>
In <Manufacturing and Evaluation of PVA Film> of Example 1, the surface temperature of the support is 100 ° C., the temperature of the hot air blown over the entire non-contact surface with the support of the liquid film is 105 ° C., and the heat treatment is performed from the first drying roll. The same as in Example 1 except that the surface temperature of each drying roll up to the final drying roll (19th drying roll) immediately before the roll was changed to 90 ° C. and the surface temperature of the two heat-treated rolls was changed to 80 ° C. A PVA film and a polarizing film were obtained. The obtained PVA film and polarizing film were measured and evaluated in the same manner as in Example 1. The results are shown in Tables 1 and 2, respectively.

<Example 4>
In <Production and Evaluation of PVA Film> of Example 1, drying from the first drying roll to the final drying roll (19th drying roll) immediately before the heat treatment roll is performed on one surface (on the support) of the PVA film. A PVA film and a polarizing film were obtained in the same manner as in Example 1 except that the drying rolls were brought into contact with each other only on the surface where the liquid film and the support were in contact with each other. The obtained PVA film and polarizing film were measured and evaluated in the same manner as in Example 1. The results are shown in Tables 1 and 2, respectively.

<Comparative Example 1>
In <Manufacturing and Evaluation of PVA Film> of Example 1, the surface temperature of the support is 115 ° C., the temperature of the hot air blown over the entire non-contact surface with the support of the liquid film is 120 ° C., and the heat treatment is performed from the first drying roll. The same as in Example 1 except that the surface temperature of each drying roll up to the final drying roll (19th drying roll) immediately before the roll was changed to 65 ° C. and the surface temperature of the two heat-treated rolls was changed to 65 ° C. A PVA film and a polarizing film were obtained. The obtained PVA film and polarizing film were measured and evaluated in the same manner as in Example 1. The results are shown in Tables 1 and 2, respectively.

<Comparative Example 2>
In <Manufacturing and Evaluation of PVA Film> of Example 1, the surface temperature of the support is 60 ° C., the temperature of the hot air blown over the entire non-contact surface of the liquid film with the support is 70 ° C., and heat treatment is performed from the first dry roll. A PVA film and a polarizing film were obtained in the same manner as in Example 1 except that the surface temperature of each dry roll up to the final dry roll (19th dry roll) immediately before the roll was changed to 90 ° C. The obtained PVA film and polarizing film were measured and evaluated in the same manner as in Example 1. The results are shown in Tables 1 and 2, respectively.

<Reference example 1>
In <Production and Evaluation of Polarizing Film> of Example 1, a PVA film and a polarizing film were obtained in the same manner as in Comparative Example 1 except that the maximum stretching speed of uniaxial stretching in the stretching treatment was changed to 190%. The obtained PVA film and polarizing film were measured and evaluated in the same manner as in Example 1. The results are shown in Tables 1 and 2, respectively.

As shown in Tables 1 and 2, when the polarizing film was produced using the PVA films of Examples 1 to 4, no wrinkles were confirmed on the surface of the obtained polarizing film, or there was no practical problem. A slight wrinkle was confirmed. Here, the wrinkles generated on the surface of the polarizing film are caused by the wrinkles on the surface of the PVA film, that is, the wrinkles on the surface of the PVA film generated during uniaxial stretching in the stretching process for producing the polarizing film. Therefore, it can be said that the PVA films of Examples 1 to 4 are less likely to have wrinkles on the surface during uniaxial stretching.

As shown in Tables 1 and 2, when the polarizing film was produced using the PVA films of Examples 1 to 4, the frequency of stretching breakage was 0 when the uniaxial stretching in the stretching treatment was continuously performed for 20 minutes. It was ~ 2 times / 20 min. Therefore, it can be said that the PVA films of Examples 1 to 4 are suppressed from breaking during stretching (at the time of uniaxial stretching).

Further, as shown in Reference Example 1, when the maximum stretching speed of uniaxial stretching in the stretching process in producing a polarizing film is relatively low (190% / min), when the PVA film of Comparative Example 1 is used. Even if there were, no wrinkles were confirmed on the surface of the obtained polarizing film, and the breaking frequency during stretching (uniaxial stretching) was 0 times / 20 min. On the other hand, as shown in Comparative Example 1, when the maximum stretching speed is high (400% / min), when the PVA film of Comparative Example 1 is used, there is a practical problem on the surface of the obtained polarizing film. The degree of wrinkles was clearly confirmed, and the breaking frequency during stretching (uniaxial stretching) was 5 times / 20 min.

That is, when the maximum stretching speed of the PVA film of Comparative Example 1 is high (400% / min), wrinkles are likely to occur on the surface during uniaxial stretching, and breakage is likely to occur during stretching (uniaxial stretching). It can be said that it is a thing. On the other hand, in the PVA films of Examples 1 to 4, even when the maximum stretching speed is high (400% / min), wrinkles are less likely to occur on the surface during uniaxial stretching, and during stretching (uniaxial stretching). It can be said that the breakage of the film is suppressed.

1 PVA film 2 PVA film thickness direction 3 First surface 4 Second surface 5 Infrared dive depth when using a diamond prism (about 2 μm)
6 Infrared dive depth when using a germanium prism (about 0.5 μm)
7 ATR prism (diamond prism or germanium prism)
8 infrared

Claims

A water-insoluble polyvinyl alcohol film
The two surfaces orthogonal to the thickness direction of the polyvinyl alcohol film are designated as the first surface and the second surface, respectively.
The crystallinity index of the first surface is Fd1 and Fg1.
When the crystallinity index of the second surface is Fd2 and Fg2,
A polyvinyl alcohol film in which Fd1, Fg1, Fd2 and Fg2 satisfy the following formulas (1) to (4).
Fd1 ≤ 0.8 (1)
Fd1 / Fg1 <1 (2)
Fd2 ≤ 0.8 (3)
Fd2 / Fg2 <1 (4)
[In the formulas (1) to (4), Fd1 is a crystallinity index calculated by using a diamond prism when FT-IR measurement by the ATR method is performed on the first surface, and is Fg1. Is a crystallinity index calculated by using a germanium prism when FT-IR measurement by the ATR method is performed on the first surface, and Fd2 is the crystallinity index calculated by the ATR method on the second surface. It is a crystallinity index calculated by using a diamond prism when FT-IR measurement is performed, and Fg2 uses a germanium prism when FT-IR measurement by the ATR method is performed on the second surface. It is a crystallinity index calculated by. ]
The polyvinyl alcohol film according to claim 1, wherein Fd1 and Fd2 satisfy the following formulas (5) to (6).
Fd1 ≧ 0.5 (5)
Fd2 ≧ 0.5 (6)
The polyvinyl alcohol film according to claim 1 or 2, wherein the Fd1, Fg1, Fd2 and Fg2 satisfy the following formulas (7) to (8).
Fd1 / Fg1 ≧ 0.6 (7)
Fd2 / Fg2 ≧ 0.6 (8)
The polyvinyl alcohol film according to any one of claims 1 to 3, wherein the Fd1, Fg1, Fd2 and Fg2 satisfy the following formulas (9) to (10).
| Fd1-Fd2 | ≤0.07 (9)
| Fg1-Fg2 | ≤0.07 (10)
The polyvinyl alcohol film according to any one of claims 1 to 4, which is a film for producing an optical film.
The polyvinyl alcohol film according to claim 5, wherein the optical film is a polarizing film.