TW202216806A - Polyvinyl alcohol film and polarizing film in which same is used - Google Patents

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 the same

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

The polarizing plate with the functions of light penetration and shielding is the basic component of a liquid crystal display (LCD), as is the liquid crystal with the light switching function. The application field of the LCD has also expanded from small devices such as computers and watches at the early stage of development to notebook computers, LCD monitors, LCD color projectors, LCD TVs, car navigation systems, mobile phones, and indoor and outdoor use in recent years. measuring instruments and other fields.

Polarizing plates are produced by laminating protective films such as triacetate cellulose (TAC) film or cellulose acetate butyrate (CAB) film on the surface of the polarizing film. In addition, polarizing films are generally produced by subjecting a polyvinyl alcohol film (hereinafter, "polyvinyl alcohol" may be referred to as "PVA") to a dyeing treatment, followed by uniaxial stretching, and uniaxial stretching while dyeing treatment. A dyed uniaxially stretched film is produced by axial stretching, or uniaxially stretched and then dyed, and the uniaxially stretched film is immobilized with a boron compound. In addition, the immobilization treatment with the boron compound may be performed simultaneously with the uniaxial stretching or the dyeing treatment.

In products having large LCDs such as liquid crystal monitors and liquid crystal televisions, high contrast and sharp images are required. Along with this, high performance is also required for the polarizing film, and specifically, it is required to increase the degree of polarization of the polarizing film. However, in order to increase the degree of polarization of the polarizing film, the stretching ratio when the PVA film is uniaxially stretched is increased, and wrinkles are likely to be generated on the surface of the PVA film during the uniaxial stretching. As a result, it becomes easy to generate|occur|produce wrinkles on the surface also in the polarizing film obtained. When a large number of wrinkles are generated on the surface of the polarizing film, it is likely to cause image unevenness in liquid crystal monitors, liquid crystal televisions, etc., which are final products. In addition, when a large number of wrinkles are generated on the surface of the polarizing film, such a polarizing film cannot be used as a product, which also causes a decrease in the product yield (product yield) of the polarizing film.

As a method of suppressing the generation of wrinkles on the surface of the polarizing film, it has been proposed to control the relaxation time and the ratio of the components for components with a short relaxation time (components with low molecular mobility and hardness) when the PVA film is subjected to pulse NMR measurement (refer to Patent Document 1). [Prior Art Literature] [Patent Literature]

[Patent Document 1] WO 2019/189695

[The problem to be solved by the invention]

In recent years, there has been a further increase in demand for higher contrast and sharper images in LCDs, and along with this, wrinkles on the surface of the polarizing film, which have not been a problem in the past, often become a problem. In addition, in order to improve the production efficiency of the polarizing film, it is required to perform the uniaxial stretching in the stretching process when manufacturing the polarizing film at a high speed, that is, to set the maximum stretching speed of the uniaxial stretching to a high speed. However, when the maximum stretching speed is made high in the uniaxial stretching at the time of producing the polarizing film, it becomes easier to generate wrinkles on the surface of the PVA film during the uniaxial stretching. As a result, it becomes easier to generate wrinkles on the surface of the polarizing film obtained. In addition, when the maximum stretching speed is high, excessive tension may be locally applied to the PVA film during uniaxial stretching. As a result, breakage of the PVA film tends to occur during uniaxial stretching, and there is also a problem that the product yield of the so-called polarizing film decreases.

In the PVA film described in Patent Document 1, if the maximum stretching speed is set to a high speed in the uniaxial stretching during the production of the polarizing film, wrinkles are likely to be generated on the surface of the PVA film during uniaxial stretching, and polarization cannot be sufficiently suppressed. The condition of wrinkles on the surface of the film. In addition, when the maximum stretching speed is made high, the PVA film may be broken during uniaxial stretching. In addition, suppression of wrinkles on the surface of the PVA film during uniaxial stretching and suppression of cracking of the PVA film during uniaxial stretching are also important in suppressing wrinkles and cracks on the surface of optical films other than polarizing films. .

Therefore, an object of the present invention is to provide a method that makes it difficult to generate wrinkles on the surface during uniaxial stretching even when the maximum stretching speed is high in uniaxial stretching during the production of optical films such as polarizing films, and suppresses uniaxial stretching. The ruptured PVA film. [means to solve the problem]

As a result of intensive research, the inventors of the present invention found that the above problem can be achieved by adjusting the crystallinity indices of the two surfaces perpendicular to the thickness direction of the PVA film to a specific range. this invention.

That is, the present invention relates to: [1] A PVA film, which is a water-insoluble PVA film, wherein two surfaces perpendicular to the thickness direction of the PVA film are designated as a first surface and a second surface, respectively, and the crystallinity index of the first surface When set to Fd1 and Fg1, and set the crystallinity index of the second surface to be Fd2 and Fg2, the above-mentioned Fd1, Fg1, Fd2 and Fg2 satisfy the following formulae (1) to (4); Fd1≦0.8 (1) Fd1/Fg1＜1 (2) Fd2≦0.8 (3) Fd2/Fg2＜1 (4) [In the aforementioned formulas (1) to (4), Fd1 is the crystallinity index calculated using diamond fluoride when the first surface is measured by FT-IR by the ATR method, and Fg1 is the crystallinity index for the first surface The crystallinity index calculated using germanium in the FT-IR measurement by the ATR method, and Fd2 is the crystallinity index calculated using the diamond in the FT-IR measurement by the ATR method on the second surface index, Fg2 is the crystallinity index calculated using germanium when the second surface is measured by FT-IR by ATR method]; [2] The PVA film according to [1], wherein the aforementioned Fd1 and Fd2 satisfy the following formulae (5) to (6); Fd1≧0.5 (5) Fd2≧0.5 (6) [3] The PVA film according to [1] or [2], wherein the aforementioned Fd1, Fg1, Fd2 and Fg2 satisfy the following formulae (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 aforementioned Fd1, Fg1, Fd2 and Fg2 satisfy the following formulae (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 optical film production; [6] The PVA film of [5], wherein the optical film is a polarizing film. [Effect of invention]

According to the present invention, even when the maximum stretching speed is high in uniaxial stretching during the production of optical films such as polarizing films, it is possible to provide that it is difficult to generate wrinkles on the surface during uniaxial stretching, and the occurrence of uniaxial stretching can be suppressed. Cracked PVA film. According to such a PVA film, the wrinkle which arises on the surface of optical films, such as a polarizing film, can be suppressed. In addition, since cracking during uniaxial stretching is suppressed, optical films such as polarizing films can be produced with a high product yield.

[Form for carrying out the invention]

The present invention will be described in detail below.

＜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. Furthermore, the crystallinity indices Fd1, Fg1, Fd2, and Fg2 calculated by this measurement satisfy the following formulae (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 the crystallinity index calculated using diamond fluoride when the first surface 3 of the PVA film 1 is measured by FT-IR by the ATR method, and Fg1 is the crystallinity index for PVA. The crystallinity index calculated by germanium was used for the FT-IR measurement by the ATR method on the first surface 3 of the thin film 1 . In addition, Fd2 is the crystallinity index calculated using diamond fluoride when the second surface 4 of the PVA film 1 is measured by FT-IR by the ATR method, and Fg2 is the second surface 4 of the PVA film 1. The crystallinity index calculated by germanium was used in the FT-IR measurement of the ATR method. In addition, 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, as represented by the above formulae (1) and (3), Fd1 and Fd2 must be 0.8 or less. When Fd1 or Fd2 is greater than 0.8, when the maximum stretching speed is high in uniaxial stretching in the production of optical films such as polarizing films, it becomes easy to generate wrinkles on the surface of the PVA film 1 during uniaxial stretching. It becomes easy to break the PVA film 1 during uniaxial stretching. The reason for this is not clear, but it is presumed that if the crystallinity of the surface of the PVA film 1 is too high, it becomes difficult for the water in the stretching treatment liquid to penetrate into the interior of the PVA film 1 during uniaxial stretching, and the film during uniaxial stretching becomes difficult. The flexibility becomes 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, as shown in the above formulas (2) and (4), Fd1/Fg1 and Fd2/Fg2 must be less than 1. When Fd1/Fg1 or Fd2/Fg2 is 1 or more, when the maximum stretching speed is high in the uniaxial stretching in the production of optical films such as polarizing films, it becomes easy to generate on the surface of the PVA film 1 during uniaxial stretching. wrinkle. Fd1/Fg1 and Fd2/Fg2 are preferably 0.98 or less, more preferably 0.96 or less, more preferably 0.94 or less, still more preferably 0.92 or less, and particularly preferably 0.9 or less.

In the PVA film of the present invention, as represented by the above formulae (1) and (3), Fd1 and Fd2 are 0.8 or less. Moreover, as shown in the above-mentioned formulas (2) and (4), Fd1/Fg1 and Fd2/Fg2 are less than 1. As will be described later, Fd1 and Fd2 represent the crystallinity in the deep interior of the PVA thin film 1 , while Fg1 and Fg2 represent the crystallinity in the extreme surface layer portion near the surface of the PVA thin film 1 . That is, in the PVA film of the present invention, the crystallinity of the deep interior of the PVA film 1 is below a predetermined value, and the crystallinity of the deep interior of the PVA film 1 is higher than the crystallinity of the PVA film 1 in the vicinity of the surface. The crystallinity of the extreme surface layer is high. By controlling the crystallinity of the deep inner part and the extreme surface layer part of the PVA film 1 in this way, it is difficult to uniaxially stretch even when the maximum stretching speed is high in the uniaxial stretching during the production of an optical film such as a polarizing film. Wrinkles are formed on the surface and cracking during uniaxial stretching can be suppressed. The reason for this is not clear, but it is presumed that the high crystallinity of the extreme surface layer portion of the PVA film 1 suppresses the generation of wrinkles on the surface of the PVA film 1 during uniaxial stretching, and that the deep inner portion of the PVA film 1 has a high degree of crystallinity. The low crystallinity relieves the stress generated during uniaxial elongation and suppresses cracking.

In the PVA film of the present invention, the lower limit values of Fd1 and Fd2 are not necessarily limited, but when the maximum stretching speed is high in uniaxial stretching in the production of optical films such as polarizing films, it is possible to further suppress the PVA film 1 It is preferable to satisfy the following formulae (5) and (6) from the viewpoint of cracking during uniaxial stretching. 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 of the deep inside of the PVA thin film 1 increases. As a result, the crystallinity of the central portion in the thickness direction 2 of the PVA film 1 increases, and the mechanical strength of the PVA film 1 increases. Therefore, by using such a PVA film 1 , even when the maximum stretching speed is high in uniaxial stretching in the production of optical films such as polarizing films, cracking during uniaxial stretching of the PVA film 1 is further suppressed. Fd1 and Fd2 are more preferably 0.52 or more, and more 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 in the production of optical films such as polarizing films, it is possible to further suppress the From the viewpoint of the breakage when the PVA film 1 is uniaxially stretched, it is preferable to satisfy the following formulae (7) and (8). Fd1/Fg1≧0.6 (7) Fd2/Fg2≧0.6 (8)

As shown in the above equations (7) and (8), since Fd1/Fg1 and Fd2/Fg2 are 0.6 or more, the crystallinity of the deep inner part of the PVA film 1 is higher than the crystallinity of the extreme surface layer of the PVA film 1 without becoming too small. As a result, the crystallinity of the central portion in the thickness direction 2 of the PVA film 1 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 uniaxial stretching in the production of optical films such as polarizing films, cracking during uniaxial stretching of the PVA film 1 is further suppressed. Fd1/Fg1 or Fd2/Fg2 is more preferably 0.65 or more, more 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 in the case of uniaxial stretching in the production of optical films such as polarizing films, the maximum stretching speed is high. It is preferable to satisfy the following formulae (9) and (10) in view of further suppressing the wrinkles generated on the surface of the PVA film 1 during uniaxial stretching. |Fd1-Fd2|≦0.07 (9) |Fg1-Fg2|≦0.07 (10)

As shown in the above formulas (9) and (10), since |Fd1-Fd2| and |Fg1-Fg2| are 0.07 or less, the difference in crystallinity index between the first surface 3 and the second surface 4 of the PVA film 1 The elastic modulus becomes almost the same on the two surfaces (the first surface 3 and the second surface 4 ) orthogonal to the thickness direction 2 of the PVA film 1 without being too large. Therefore, by using such a PVA film 1, it becomes difficult to generate on the surface of the PVA film 1 during uniaxial stretching even when the maximum stretching speed is high in uniaxial stretching during the production of optical films such as polarizing films. wrinkle. |Fd1-Fd2| and |Fg1-Fg2| are preferably 0.06 or less, more 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 PVA contained. The absorption peak is generally referred to as the crystallization band of the PVA film 1, and is one of the peaks originating from the stretching vibration of the carbon bond (CC) of PVA. It is known that the crystallization band is emphasized and can be observed when the phase of vibration of the polymer molecular chain of PVA in the PVA film 1 is consistent with the crystallization of the polymer molecular chain of PVA. That is, as the crystallinity of the PVA film 1 becomes higher, the peak intensity of the crystallization band becomes relatively higher. Furthermore, when the infrared absorption spectrum of the PVA thin film 1 was measured, an absorption peak was observed at 1425 cm ^-1 due to deformation vibration of the methylene group (-CH ₂ -) in the main chain of PVA. The intensity of the absorption peak is considered to be independent of the crystallinity of the PVA film 1 .

In the present invention, the absorption peak intensity of the crystallization band (1140 cm ^-1 ) and the absorption peak of the deformation vibration (1425 cm ^-1 ) of the methylene group (-CH ₂ -) of the main chain of PVA can be calculated by calculating The intensity ratio of the intensity was obtained to obtain the crystallinity index (Fg1, Fg2, Fd1 and Fd2) of the PVA film 1. Specifically, the baselines of the infrared absorption spectra at 1140 cm ^-1 and 1425 cm ^-1 were drawn, and the heights from the baseline to the peaks of 1140 cm ^-1 and 1425 cm ^-1 were regarded as the respective absorption peak intensities, and 1140 cm ^-1 The absorption peak intensity was divided by the peak intensity of 1425 cm ^-1 , and the obtained value was taken as the crystallinity index (Fg1, Fg2, Fd1 and Fd2).

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

In the present invention, the FT-IR measurement is performed by the ATR method (attenuated total reflection measurement). As shown in Fig. 3, the ATR method is to make the sample adhere to the objective lens called ATR 7, and irradiate the sample with infrared rays 8 obliquely from the inside of the ATR 7, and measure the spectrum of the reflected light, which is the reflected light. A type of IR measurement method. Compared with the normal reflection-type IR measurement method, it has the characteristic 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 that slightly penetrate the PVA film 1 side from the ATR 7 side. Therefore, by the FT-IR measurement by the ATR method, information of the surface layer of the PVA film 1 (the part that penetrates slightly in the depth direction from the surface of the PVA film 1) can be obtained. Here, when the depth of penetration of the infrared rays 8 from the side of the ATR element 7 to the side of the PVA film 1 is set as d, the value is represented by the following formula (11). As can be seen from the following formula (11), as long as ATRs 7 having different refractive indices are used, reflective infrared absorption spectra having different penetration depths can be obtained.

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

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

In the present invention, as shown in FIG. 3 , diamond with a refractive index of 2.4 or germanium with a refractive index of 4.0 is used as the base material of ATR-H7. If the refractive index of the PVA film 1 is 1.5, in the above formula (11), the incident angle of the infrared rays 8 is 45° and the wave number of the infrared rays 8 is 1140 cm ⁻¹ to calculate the infrared rays 8 that penetrate the surface layer of the PVA film 1 . The diving depth is about 2 μm in the case of using diamond as the base material of the ATR crystal 7, that is, the diving depth 5 of the infrared ray 8 in the case of using the diamond crystal. On the other hand, in the case of using germanium as the ATR element 7, that is, the penetration depth 6 of the infrared ray 8 in the case of the germanium element is about 0.5 μm. Therefore, the crystallinity index in the case of using diamond fluoride corresponds to the crystallinity up to the deep inside of the PVA film 1 . On the other hand, the crystallinity index in the case of using germanium corresponds to the crystallinity of the extreme surface layer portion near the surface of the PVA thin film 1 .

In the present invention, it is important to control Fg1 and Fg2 of the crystallinity index of the extreme surface layer portion of the PVA film 1 and Fd1 and Fd2 of the crystallinity index of the deep inner portion of the PVA film 1 within the above ranges. The crystal structure of the PVA film 1 is affected by the composition of the PVA film 1 and various factors in the manufacturing process. Therefore, in terms of the control method of the crystallinity indices (Fg1, Fg2, Fd1 and Fd2), for example: Method for the type of vinyl alcohol (degree of saponification, modified mass, blend ratio of unmodified PVA/modified PVA, etc.), method for adjusting the amount of plasticizer added, and adjusting film production conditions (surface temperature of roll support, heat treatment conditions, etc.), or a method of adjusting them in combination.

As a method of adjusting the crystallinity indices Fd1 and Fd2 to be 0.8 or less, and adjusting Fd1/Fg1 and Fd2/Fg2 to be less than 1, more specifically, the degree of saponification of PVA can be 90 mol% or more, The ratio of the structural units derived from other monomers in the vinyl ester polymer of the raw material of PVA is 15 mol % or less based on the molar number of all the structural units constituting the vinyl ester polymer, and the polymerization of PVA is carried out. The degree of 200 ~ 8000 method. In this case, the addition amount of the plasticizer is preferably 1 to 40 parts by mass with respect to 100 parts by mass of PVA. In addition, at this time, the volatile content of the film-forming stock solution is preferably 50 to 90% by mass, and the surface temperature of the support body of the film-forming stock solution is preferably 65 to 110°C, and it is sprayed to the non-contact surface. The temperature of the hot air on the side is preferably below 50~150℃, and the humidity of the hot air is preferably 20~90%RH. Furthermore, at this time, the temperature of the drying furnace 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 of adjusting the crystallinity indices Fd1 and Fd2 to 0.5 or more, the saponification degree of PVA is 95 to 99.9 mol %, and the vinyl ester polymer which is the raw material of PVA is derived from other monomers. The ratio of the structural unit is 10 mol % or less based on the molar number of all the structural units constituting the vinyl ester-based polymer, and the method of making the polymerization degree of PVA 1000-4000. At this time, the addition amount of the plasticizer is preferably 5 to 20 parts by mass with respect to 100 parts by mass of PVA. In addition, at this time, the volatile content of the film-forming stock solution is preferably 60-80% by mass, and the surface temperature of the support body of the film-forming stock solution is preferably 80-110°C, and it is sprayed to the non-contact surface. The temperature of the hot air on the side is preferably below 70~110℃, and the humidity of the hot air is preferably 1~40%RH. Furthermore, at this time, the temperature of the drying furnace 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 of adjusting Fd1/Fg1 and Fd2/Fg2 to 0.6 or more, the saponification degree of PVA is 99 to 99.9 mol %, and the vinyl ester polymer of the raw material of PVA is derived from other monomers. A method in which the proportion of the structural unit of PVA is 5 mol % or less based on the molar number of all the structural units constituting the vinyl ester polymer, and the degree of polymerization of PVA is 1000-3700. At this time, the addition amount of the plasticizer is preferably 8 to 20 parts by mass with respect to 100 parts by mass of PVA. In addition, at this time, the volatile content of the film-forming stock solution is preferably 65-80% by mass, and the surface temperature of the support body of the film-forming stock solution is preferably 80-100°C, and it is sprayed to the non-contact surface. The temperature of the hot air on the side is preferably 70～100℃, and the humidity of the hot air is preferably 3～40%RH. Furthermore, at this time, the temperature of the drying furnace 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.

In the method of adjusting |Fd1-Fd2| and |Fg1-Fg2| to be 0.07 or less, it is preferable to make the volatile matter ratio of the film-forming stock solution to be 65 to 75% by mass. The surface temperature is preferably 80 to 95°C, the temperature of the hot air sprayed 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. Furthermore, at this time, the temperature of the drying furnace or the surface temperature of the drying roller is preferably 60 to 90°C, and the surface temperature of the heat treatment roller 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 vinyl ester-based monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl laurate, vinyl stearate, vinyl benzoate, and trimethyl. Vinyl Acetate, Vinyl Visaudioate, etc. Among these, vinyl acetate is more preferred as a vinyl ester monomer.

The vinyl ester-based polymer is preferably a polymer obtained by using only one or two or more vinyl ester-based monomers as a monomer, and a polymer obtained by using only one vinyl ester-based monomer as a monomer. better. In addition, the vinyl ester-based polymer may be a copolymer of one or two or more vinyl ester-based monomers and other monomers that can be copolymerized therewith.

Examples of other monomers include: ethylene; olefins having 3 to 30 carbon atoms such as propylene, 1-butene, and isobutylene; acrylic acid or its salts; methyl acrylate, ethyl acrylate, n-propyl acrylate, isobutyl acrylate Propyl, n-butyl acrylate, isobutyl acrylate, tertiary butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate and other acrylates; methacrylic acid or its salts; methacrylic acid Methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tertiary butyl methacrylate, 2- methacrylate Ethylhexyl, dodecyl methacrylate, octadecyl methacrylate and other methacrylates; acrylamide, N-methacrylamide, N-ethylacrylamide, N,N-dimethyl amide Acrylamide Derivatives; Methacrylamide, N-Methyl Methacrylamide, N-Ethyl Methacrylamide, Methacrylamide Propane Sulfonic Acid or its Salts, Methacrylamide Propyl Dimethyl methyl amine or its salt, N-methylol methacrylamide or its derivatives and other methacrylamide derivatives; N-vinylformamide, N-vinylacetamide, N-vinylpyrrole N-vinylamides such as pyridone; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, Vinyl ethers such as tertiary butyl vinyl ether, dodecyl vinyl ether and stearyl vinyl ether; vinyl cyanide such as acrylonitrile and methacrylonitrile; vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene vinyl halide such as vinyl fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid or its salt, ester or anhydride; iconic acid or its salt, ester or anhydride; ethylene such as vinyltrimethoxysilane Silicon-based compounds; isopropenyl acetate, etc. Moreover, the vinyl ester-type polymer may have the structural unit derived from 1 type or 2 or more types among these other monomers.

The proportion of the structural units derived from other monomers in the vinyl ester polymer is based on the molar number of the total structural units constituting the vinyl ester polymer, and is preferably 15 mol % or less, and 8 mol % or less. Ear % or less is better. In general, the crystallization of PVA tends to become more difficult as the ratio of the structural units derived from other monomers in the vinyl ester polymer becomes higher. Therefore, the crystallinity indices (Fg1, Fg2, Fd1, and Fd2) of the PVA film can be adjusted by appropriately copolymerizing these other monomers in the above-mentioned ratios.

The polymerization degree of PVA is preferably 200 or more, more preferably 300 or more, and even more preferably 500 or more. By making the polymerization degree of PVA more than the said lower limit, while preventing excessive crystallization of PVA, the mechanical strength of the obtained PVA film can be ensured. On the other hand, the polymerization degree 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 has a tendency that the higher the degree of polymerization of PVA, the more difficult it is to proceed. Therefore, by setting the polymerization degree of PVA to be below the above-mentioned upper limit, the crystallization of PVA can be appropriately performed, and the crystallinity indices (Fg1, Fg2, Fd1, and Fd2) of the PVA film can be adjusted. Moreover, by making the polymerization degree of PVA below the said upper limit, the viscosity of the film-forming stock solution of a PVA film does not become too high, and the productivity of a PVA film can be improved.

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 limiting viscosity (compound/g) measured in water at 30°C after re-saponification and purification of PVA.

The saponification degree of PVA is preferably 90 mol% or more, more preferably 95 mol% or more, more preferably 99 mol% or more, and particularly preferably 99.8 mol% or more. Generally, the crystallization of PVA tends to be easier to proceed with the higher the degree of saponification of PVA. Therefore, by making the saponification degree of PVA more than the above-mentioned lower limit, the crystallization of PVA can be appropriately progressed, and the crystallinity indices (Fg1, Fg2, Fd1 and Fd2) of the PVA film can be improved. That is, by using PVA with a high degree of saponification in the film-making stock solution of the PVA film, in the step of subjecting the dried PVA film to heat treatment, the extremely surface layer portion near the surface of the PVA film that is easily heated and the area between the PVA film The crystallinity of the deep inside tends to be high.

The degree of saponification of PVA refers to the total molar number of vinyl alcohol units with respect to the structural units that can be converted into vinyl alcohol units by saponification (typically vinyl ester monomer units) and vinyl alcohol units, and the molar number of vinyl alcohol units The proportion of ear count (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, degree of saponification, degree of 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 even more preferably 85% by mass or more.

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

As a plasticizer, polyhydric alcohols, such as ethylene glycol, glycerol, diglycerol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, and sorbitol, etc. are mentioned, for example. These plasticizers may be used alone or in combination of two or more. Among these, ethylene glycol or glycerin is more preferable as a plasticizer, and glycerin is more preferable from the viewpoint of difficulty in exuding to the surface of the PVA film.

The content of the plasticizer in the PVA film of the present invention is relative to 100 parts by mass of PVA, preferably more than 1 part by mass, more preferably more than 3 parts by mass, more preferably more than 5 parts by mass . 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 even more preferably 20 parts by mass or less, relative to 100 parts by mass of PVA. When the content of the plasticizer is in the above range, it becomes easy to adjust the crystallinity indices (Fg1, Fg2, Fd1, and Fd2) of the PVA film, and in addition, the effect of improving mechanical properties such as impact strength can be sufficiently obtained. In addition, the PVA film can be prevented from becoming too soft to lower the handleability, or the plasticizer can be prevented from oozing out to 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, if the PVA film contains an appropriate amount of plasticizer, the crystallization of PVA will proceed. It is presumed that this is because the polymer molecular chain of PVA becomes easy to move by the plasticizer, and it becomes easy to adopt a more stable crystalline or constrained amorphous structure in terms of energy. On the other hand, when the PVA film contains an excessive amount of the 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 groups of the polymer molecular chains of PVA increases, and the interaction between the polymer molecular chains of PVA becomes weak. Therefore, by adjusting the content of the plasticizer, the crystallization of PVA can be appropriately performed, and the crystallinity indices (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 including a surfactant, it is possible to improve: the handleability of the PVA film, or the peelability of the PVA film from a film-forming device during production. The surfactant is not particularly limited, and for example, anionic surfactants and nonionic surfactants can be preferably used.

Examples of anionic surfactants include carboxylic acid-type surfactants such as potassium laurate; sulfate-type surfactants such as octyl sulfate; and sulfonic acid-type surfactants such as dodecyl benzenesulfonate.

Examples of nonionic surfactants include alkyl ether-type surfactants such as polyoxyethylene lauryl ether and polyoxyethylene oleyl ether; and alkyl phenyl ether-type surfactants such as polyoxyethylene octyl phenyl ether. Active agents; alkyl ester surfactants such as polyoxyethylene laurate; alkylamine surfactants such as polyoxyethylene lauryl amino ether; alkyl amide surfactants such as polyoxyethylene laurate Polypropylene glycol ether-type surfactants such as polyoxyethylene polyoxypropylene ether; alkanolamide-type surfactants such as diethanolamide laurate and diethanolamide oleate; polyoxyalkylene allyl phenyl ether and other allyl phenyl ether surfactants.

Such surfactants may be used alone or in combination of two or more. In terms of surfactants, nonionic surfactants are preferred, and alkanolamide-type surfactants are more preferred in terms of the excellent reduction effect of surface anomalies during PVA film production. Dialkanolamides (eg, diethanolamides, etc.) of aliphatic carboxylic acids (eg, saturated or unsaturated aliphatic carboxylic acids having 8 to 30 carbon atoms) are more preferable.

The content of the surfactant in the PVA film of the present invention is relative to 100 parts by mass of PVA, preferably 0.01 part by mass or more, more preferably 0.02 part by mass or more, and even more preferably 0.05 part by mass or more . On the other hand, the content of the surfactant is relative to 100 parts by mass of PVA, preferably 10 parts by mass or less, more preferably 1 part by mass or less, more preferably 0.5 parts by mass or less, and 0.3 parts by mass or less The following is the best. When the content of the surfactant is in the above range, the peelability from the film forming apparatus of the PVA film at the time of production becomes good, and the adhesion between the PVA films (hereinafter sometimes referred to as "blocking") can be prevented. )occur. Furthermore, it is possible to prevent deterioration of the appearance of the PVA film due to exudation of the surfactant to the surface of the PVA film or aggregation of the surfactant.

(other ingredients) The PVA film of the present invention may contain, in addition to PVA, water-soluble polymers, moisture, antioxidants, ultraviolet absorbers, lubricants, cross-linking agents, colorants, fillers, antiseptics, in a range that does not hinder the effects of the present invention. agent, antifungal agent, other polymer compounds and other ingredients. 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, More preferably, it is 90 mass % or more. The ratio of the total mass of other components to the total mass of the PVA film is preferably 100 mass % or less.

(physical property) The PVA film of the present invention is water-insoluble. Since the PVA film is water-insoluble and uniaxially stretched in an aqueous solution for producing an optical film such as a polarizing film, even if the maximum stretching speed is high, the PVA film can be stretched without breaking during uniaxial stretching. Here, in the present invention, water-insolubility means that when the PVA film is immersed in water (deionized water) at 30°C in the order of <1> to <4> below, the PVA film is not completely dissolved and has Partial residue.

<1> Place the PVA film in a constant temperature and humidity chamber adjusted to 20°C and 65% RH for more than 16 hours to adjust the humidity. <2> After cutting out a rectangular sample with a length of 40mm x width of 35mm from the humidity-conditioned PVA film, cut out a rectangular window (hole) of length 35mm x width 23mm between 2 pieces of 50mm x 50mm plastic plates, Clamp and fix in such a way that the length direction of the sample is parallel to the length direction of the window and the sample is located almost in the center of the width direction of the window. <3> 300 mL of deionized water was put into a 500 mL beaker, and the water temperature was adjusted to 30° C. while stirring with an electromagnetic stirrer equipped with a 3 cm-long stirring bar at a rotational speed of 280 rpm. <4> The sample fixed to the plastic plate in the above <2> was immersed in deionized water in the beaker for 1000 seconds while taking care not to contact the stirring bar of the rotating electromagnetic stirrer.

<Manufacturing method of PVA film> The manufacturing method of the PVA film of this invention is not specifically limited, For example, the following arbitrary methods can be employ|adopted. As this method, a film-forming stock solution obtained by adding a solvent, an additive, etc. to PVA and making it homogenized can be exemplified by a casting film-forming method, a wet film-forming method (a method of discharging into a poor solvent) ), dry-wet film-making method, gel film-making method (the method of extracting and removing the solvent after the film-making stock solution is temporarily cooled and gelled), or a combination of these methods for film-making; The film-making stock solution obtained by the machine, etc. is extruded from the T-die and the like to form the film by the melt extrusion film-making method and the blow molding method. As a method for producing a PVA film, among these, a casting method and a melt extrusion method are preferred. When these methods are used, a homogeneous PVA thin film can be obtained with good productivity. Hereinafter, the case where a PVA film is produced using a cast film forming method or a melt extrusion film forming method will be described.

When the PVA film of the present invention is produced by the casting method or the melt extrusion method, first, a film-forming stock solution containing additives such as PVA, a solvent, and a required plasticizer is prepared. Next, the film-forming stock solution is cast (supplied) in a film form on a rotating support such as a metal roll and a metal belt. Thereby, a liquid coating of the membrane-forming stock solution is formed on the support. The liquid film is cured and formed into a thin film by heating and removing the solvent on the support. As a method of heating the liquid film, a method of raising the temperature of the support itself with a heating medium or the like, a method of blowing hot air to the surface opposite to the surface of the liquid film contacting the support, etc. can be exemplified. The cured long film (PVA film) is peeled from the support, dried by a drying roll, a drying oven, etc. as needed, further heat-treated as needed, and wound into a roll shape.

In the drying step (solvent removal step) of the liquid film cast on the support and the subsequent drying step of the PVA film, the PVA is crystallized during heating. The rate of crystallization at this time is affected by the moisture content in PVA, 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 plasticizer, as described above. Effects of temperature, and draw (stretching in the direction of flow). The external shrinkage is presumed to be the influence of alignment crystallization due to the stretching of the polymer molecular chain of PVA.

Usually, the drying of PVA film is carried out by the gradual volatilization of volatile components from the open film surface which is not in contact with the support and drying rolls. Therefore, in the process of drying, since the concentration distribution of volatile components such as moisture is generated in the thickness direction of the PVA film, the crystallinity index is generated in the thickness direction of the PVA film due to the temperature and shrinkage conditions that vary from time to time. distribution. The distribution of the crystallinity index can be adjusted by the volatile content of the film-forming stock solution, the temperature of the support, the contact time with the support, the temperature and amount of hot air, the temperature of the drying roller and the drying furnace, etc. Therefore, by appropriately adjusting the above factors, the crystallization of PVA can be appropriately performed, and the crystallinity indices (Fg1, Fg2, Fd1, and Fd2) of the PVA film can be adjusted.

The volatile matter ratio of the film-forming stock solution (the concentration of volatile components such as solvents removed by volatilization and evaporation during film-forming, etc.) is preferably 50% by mass or more, more preferably 55% by mass or more. The volatile matter ratio of the membrane-forming stock solution is preferably 90 mass % or less, and more preferably 80 mass % or less. If the volatile content is in the above range, the viscosity of the film-forming stock solution can be adjusted to a desired range, so that the film-forming property of the liquid film cast on the support is improved, and it becomes easy to obtain a uniform film. Thickness of PVA film. In addition, when the volatile content ratio is in the above range, the crystallization of PVA will proceed moderately on the support, so that it becomes easy to adjust the crystallinity index and distribution of the obtained PVA thin film. The film-forming stock solution may also contain dichroic dyes as required. In addition, the volatile matter ratio of a membrane-forming stock solution means the value calculated|required by following formula (13).

Volatile content of the film-forming solution (mass %) = {(Wa-Wb)/Wa}×100 (13)

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

There is no particular limitation on the preparation method of the film-forming stock solution, and examples include: a method of dissolving additives such as PVA and plasticizers, surfactants, etc. in a solvent; or using a uniaxial or A method of melt-kneading PVA in a water-containing state together with additives such as plasticizers and surfactants using a biaxial extruder.

The film-forming dope system usually passes through the lip of a mold such as a T-die, and is cast in a film form onto a support such as a metal roll and a metal belt. On the support, the solvent gradually volatilizes from the surface (hereinafter sometimes referred to as the free surface) of the casted film-like stock solution that does not contact the support. It is sometimes referred to as the contact surface) volatilization, and therefore, in the thickness direction of the film, a distribution in which the solvent concentration on the free surface side is low and the solvent concentration on the contact surface side is high occurs. Therefore, the curing of PVA also proceeds from the free surface first.

In parallel with the solidification of the PVA, the crystallization of the PVA also proceeds. The crystallization of PVA is difficult to carry out because the solvent concentration is too high or too low. Although it is also related to the primary structure of the PVA molecule, it is easy when the volatile content rate of the film-making stock solution after casting is in the range of 20-60% by mass. conduct. In addition, the higher the temperature, the faster the crystallization rate of PVA becomes, but the higher the temperature, the faster the solvent volatilization rate. Therefore, in order to efficiently perform crystallization of the electrode surface layer portion near the surface of the PVA film and control the crystallinity index (Fg1 and Fg2) of the electrode surface layer portion, in addition to the temperature of the support and the contact time with the support In addition to the above, it is also important to control the temperature of the environment 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 portion near the surface of the film relative to the crystallinity in the deep inner portion of the film. Therefore, in order to obtain the PVA thin film of the present invention, it is sufficient to select conditions under which the crystallization of the extremely surface layer portion near the surface of the thin film is advanced while the crystallization of the deep inner portion of the thin film is suppressed. For example, in the initial drying stage when the volatile content rate of the polar surface layer near the surface of the film is reduced, by adopting slow drying conditions such as lowering the drying temperature, the moisture content of the polar surface layer is first increased during the crystallization process. On the other hand, in the middle to the later stage of drying in which crystallization is performed in the deep inner part of the film, conditions such as the rapid drying at a relatively high temperature make it difficult for inner crystallization to be employed, for example.

The surface temperature of the support body of the dope for casting film is preferably 65°C or higher, and more preferably 70°C or higher. The surface temperature of the support body of the casting solution is preferably 110°C or lower, more preferably 100°C or lower, and even more preferably 95°C or lower. If the surface temperature is in the above range, drying of the liquid film cast on the support and crystallization of the extreme surface layer near the surface of the film proceed at a moderate speed, whereby the crystallinity index (Fg1) of the PVA film can be adjusted. and Fg2).

While heating the liquid film on the support, it is also possible to uniformly spray hot air with a blow velocity of 1 to 10 m/sec 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. In addition, the humidity of the hot air is preferably 1% RH or more, more preferably 3% RH or more, and even more preferably 5% RH or more. The humidity of the hot air is preferably below 40%RH, more preferably below 30%RH. When the temperature and humidity of the hot air blown to the non-contact surface side are in the above-mentioned ranges, it becomes easy to adjust the crystallinity indices (Fg1, Fg2, Fd1, and Fd2) of the PVA film.

The PVA film is preferably dried on the support (solvent removal) to a volatile content ratio of 5 to 50 mass %, then peeled off from the support, and further dried as necessary. The drying method is not particularly limited, and examples thereof include a method of passing through a drying oven or a method of contacting a drying roll. When multiple drying rolls are used to dry the PVA film, it is preferred that one surface of the PVA film alternately contacts the other surface of the drying roll. Thereby, the difference (|Fd1-Fd2| and |Fg1-Fg2|) of the crystallinity index of PVA in both surfaces (two surfaces orthogonal to a thickness direction) of a PVA film can be adjusted. In this case, the number of drying rolls is preferably 3 or more, more preferably 4 or more, and still 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 particularly preferably 85°C or lower. 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 further preferably 50°C or higher. By setting the temperature of the drying furnace or the surface temperature of the drying roll within the above range, it becomes easy to adjust the crystallinity indices (Fg1, Fg2, Fd1 and Fd2) of the PVA film.

The dried PVA film can be further heat-treated as needed. By performing heat treatment, the crystallinity of the extreme surface layer near the surface of the film and the crystallinity of the deep inside of the film can be increased, and the crystallinity indices (Fg1, Fg2, Fd1 and Fd2) of the PVA film can be adjusted. In addition, properties such as mechanical strength and swelling properties of the PVA film can be adjusted.

The lower limit of the surface temperature of the heat treatment roll for 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. It becomes easy to adjust the crystallinity index (Fg1, Fg2, Fd1, and Fd2) of a PVA film by making the surface temperature of a heat treatment roll into the said range.

The PVA film produced in this way is further subjected to moisture conditioning treatment, cutting of both ends (ears) of the film, etc. as required, and then wound into a roll shape on a cylindrical core, and then packaged in a moisture-proof manner. and become a product.

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

<Manufacturing method of optical film> The PVA film of the present invention is used as a blank film when producing an optical film. As an optical film, a polarizing film, a viewing angle improvement film, a retardation film, a brightness improvement film, etc. can be illustrated, but a polarizing film is preferable. Hereinafter, as an example of the manufacturing method of an optical film, the manufacturing method of a polarizing film is mentioned, and it demonstrates concretely.

The polarizing film can usually be produced by using a PVA film as a blank film, and going through a swelling step, a dyeing step, a cross-linking step, an extension step, a fixing treatment step, and other processing steps. Specific examples of the treatment liquid used in each step include swelling treatment liquid used in swelling treatment, dyeing treatment liquid (dyeing liquid) used in dyeing treatment, crosslinking treatment liquid used in crosslinking treatment, Stretching treatment liquid for stretching treatment, immobilization treatment liquid for fixing treatment, and cleaning treatment liquid (cleaning liquid) for cleaning treatment, etc.

Each processing step that can be employed in the manufacturing method for manufacturing the polarizing film will be described in detail below. In addition, in the manufacturing method of a polarizing film, one or two or more of each of the following treatments may be omitted, the same treatment may be performed a plurality of times, or other treatments may be performed simultaneously.

(Cleaning treatment before swelling treatment) Preferably, the PVA film is washed before the swelling treatment is performed on the PVA film. The anti-blocking agent and the like adhering to the PVA film can be removed by such a cleaning treatment before the swelling treatment, and contamination of each processing solution by the anti-blocking agent and the like in the production process of the polarizing film can be prevented. The cleaning treatment is preferably performed by immersing the PVA film in the cleaning treatment liquid, but may be performed by spraying the cleaning treatment liquid on the PVA film. As the cleaning treatment liquid, for example, water can be used. 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 anti-blocking agent and the like adhering to the PVA film. Moreover, it can prevent that a part of the surface of a PVA film is melt|dissolved and a film sticks to each other and the workability|operativity falls by making temperature 40 degrees C or less. The temperature of the cleaning treatment liquid is more preferably 22°C or higher, more preferably 24°C or higher, and particularly preferably 26°C or higher. In addition, the temperature of the cleaning treatment liquid is more preferably 38°C or lower, more 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 further preferably 36°C or lower. In addition, the time of immersion in the swelling treatment liquid is, for example, preferably 0.1 minutes or more, and more preferably 0.5 minutes or more. The time of immersion in the swelling treatment liquid is, for example, preferably 5 minutes or less, and more preferably 3 minutes or less. In addition, the water used as a swelling process liquid is not limited to pure water, The aqueous solution which melt|dissolved various components, such as a boron-containing compound, may be a mixture of water and an aqueous medium. The type of the boron-containing compound is not particularly limited, but from the viewpoint of workability, boric acid or borax is preferred. When the swelling treatment liquid contains a boron-containing compound, the concentration thereof is preferably 6 mass % or less from the viewpoint of improving the stretchability of the PVA film.

(Dyeing treatment) The dyeing treatment is preferably performed using an iodine-based dye as a dichroic dye, and the dyeing period may be any stage before the stretching treatment, during the stretching treatment, and after the stretching treatment. The dyeing treatment is preferably performed by using a solution (preferably an aqueous solution) containing iodine-potassium iodide as the dyeing treatment liquid, and immersing the PVA film in the dyeing treatment liquid. The concentration of iodine in the dyeing treatment liquid is preferably 0.005 mass % or more. The concentration of iodine in the dyeing treatment liquid is preferably 0.2% by mass or less. The potassium iodide/iodine (mass) ratio is preferably 20 or more. The potassium iodide/iodine (mass) ratio 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 treatment liquid may also contain a boron-containing compound such as boric acid as a crosslinking agent. In addition, if the PVA film used as the blank material film contains a dichroic dye in advance, the dyeing treatment can be omitted. Moreover, the PVA film used as a blank material film may contain boron-containing compounds, such as boric acid and borax, in advance.

(Crosslinking treatment) When producing a polarizing film, it is preferable to perform a crosslinking treatment after the dyeing treatment for the purpose of making the dichroic dye adsorb firmly to the PVA film. The crosslinking treatment can be performed by using a solution (preferably an aqueous solution) containing a crosslinking agent as the crosslinking treatment liquid, and immersing the PVA film in the crosslinking treatment liquid. As a crosslinking agent, one type or two or more types 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 excessively and it becomes difficult to perform sufficient extension in the subsequent extension treatment. Tendency to reduce the effect of co-processing. The concentration of the crosslinking agent in the crosslinking treatment liquid is preferably 1 mass % or more, more preferably 1.5 mass % or more, and even more preferably 2 mass % or more. The concentration of the crosslinking agent in the crosslinking treatment liquid is preferably 6 mass % or less, more preferably 5.5 mass % or less, and even more preferably 5 mass % or less.

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

If the temperature of the cross-linking treatment solution is too high, the dichroic pigments will be dissolved out and the resulting polarizing film tends to be dyed unevenly, and if it is too low, the effect of the cross-linking treatment will be reduced. . The temperature of the crosslinking treatment liquid is preferably 20°C or higher, more preferably 22°C or higher, and further preferably 25°C or higher. The temperature of the crosslinking treatment liquid is preferably 45°C or lower, more preferably 40°C or lower, and even more preferably 35°C or lower.

Different from the stretching treatment described later, the PVA film may be stretched during and between the above-described treatments. By performing such stretching (pre-stretching), the generation of wrinkles on the surface of the PVA film can be prevented. From the viewpoint of the polarizing properties of the obtained polarizing film, etc., the total stretching ratio (multiplication ratio of the stretching ratio in each treatment) before stretching is considered to be 4 times or less based on the original length of the PVA film of the blank material before stretching. More preferably, it is 3.5 times or less. From the viewpoint of the polarization performance of the obtained polarizing film, etc., the total stretching ratio before stretching is preferably 1.5 times or more based on the original length of the PVA film of the blank material before stretching. The stretching ratio in the swelling treatment is preferably 1.1 times or more, more preferably 1.2 times or more, and even more preferably 1.4 times or more. The stretching ratio in the swelling treatment is preferably 3 times or less, more preferably 2.5 times or less, and even more preferably 2.3 times or less. The stretching ratio in the dyeing treatment is preferably 2 times or less, more preferably 1.8 times or less, and even more preferably 1.5 times or less. The stretching ratio in the dyeing treatment is more preferably 1.1 times or more. The stretching ratio in the crosslinking treatment is preferably 2 times or less, more preferably 1.5 times or less, and even more preferably 1.3 times or less. The stretching ratio in the crosslinking treatment is more preferably 1.05 times or more.

(Extended Processing) The stretching treatment can be performed by either a wet stretching method or a dry stretching method. In the case of the wet stretching method, a solution (preferably an aqueous solution) containing a boron-containing compound such as boric acid can be used as a stretching treatment liquid, and it can be carried out in a stretching treatment liquid, or in a dyeing treatment liquid or a fixing treatment liquid to be described later. . In addition, in the case of the dry stretching method, it can be performed in the air using the PVA film after water absorption. Among them, the wet stretching method is more preferred, and the uniaxial stretching in an aqueous solution containing boric acid is more preferred. 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, more preferably 2.0% by mass or more, from the viewpoint of improving the stretchability of the PVA film. Preferably, it is more preferably 2.5 mass % or more. The concentration of the boron-containing compound in the stretching liquid is preferably 7 mass % or less, more preferably 6.5 mass % or less, and further preferably 6 mass % or less, from the viewpoint of improving the stretchability of the PVA film. .

In the stretching liquid, it is preferable to contain an iodine-containing compound such as potassium iodide. If the concentration of the iodine-containing compound in the stretching treatment solution is too high, the hue of the polarizing film obtained tends to be bluish, and if it is too low, the heat resistance of the polarizing film obtained is unexplained for unknown reasons. Tendency to decrease sexuality. The concentration of the iodine-containing compound in the stretching liquid is preferably 2 mass % or more, more preferably 2.5 mass % or more, and even more preferably 3 mass % or more. The concentration of the iodine-containing compound in the stretching liquid is preferably 8 mass % or less, more preferably 7.5 mass % or less, and even more preferably 7 mass % or less.

If the temperature of the stretching liquid is too high, the PVA film tends to dissolve and become soft and easily ruptured, and if it is too low, the elongation tends to decrease. The temperature of the stretching liquid is preferably 50°C or higher, more preferably 52.5°C or higher, and further preferably 55°C or higher. The temperature of the stretching liquid is preferably 70°C or lower, more preferably 67.5°C or lower, and further preferably 65°C or lower. In addition, the preferred range of the stretching temperature in the case of performing the stretching treatment by the dry stretching method is also as described above.

The stretching ratio in the stretching treatment, from the perspective of the higher one can obtain a polarizing film with more excellent polarization properties, the stretching ratio in the stretching treatment is preferably 1.2 times or more, more preferably 1.5 times or more, and 2 times or more is more preferable. In addition, from the viewpoint of the polarization performance of the obtained polarizing film, the total stretching ratio including the above-mentioned stretching ratio before stretching (multiplied by the stretching ratio in each step) is based on the raw material of the PVA film before stretching. The length is preferably 5.5 times or more, more preferably 5.7 times or more, and still more preferably 5.9 times or more. The upper limit of the stretching ratio is not particularly limited, but if it is too high, stretching cracks are likely to occur, so it is preferably 8 times or less.

There is no particular limitation on the method of the stretching treatment by uniaxial stretching, and uniaxial stretching in the longitudinal direction and lateral uniaxial stretching in the width direction can be used. The uniaxial extension in the longitudinal direction is preferable from the viewpoint of obtaining one excellent in polarization performance when producing a polarizing film. Uniaxial stretching in the longitudinal direction can be performed by using a stretching device having 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, more preferably 300%/min or more, and 400% /min or more is more preferable. Here, the maximum stretching speed refers to the fastest stretching speed among the stages when the PVA film is stretched into two or more stages using three or more rolls with different peripheral speeds. In addition, when the stretching process of the PVA film is not divided into two or more stages and is performed in one stage, the stretching speed in the stage becomes the maximum stretching speed. In addition, the extension speed refers to an increase in the length of the PVA film increased by extension with respect to the length of the PVA film before extension per unit time. For example, the extension speed of 100%/min refers to the speed at which the PVA film is deformed from the length before extension to twice the length in 1 minute. As the maximum stretching speed becomes larger, the stretching process (uniaxial stretching) of the PVA film can be performed at a higher speed, 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 large, excessive tension may be locally applied to the PVA film during the stretching process (uniaxial stretching) of the PVA film, and stretching cracks are likely to occur. From such a viewpoint, the maximum extension speed is preferably not more than 900%/min.

(fixed processing) When producing a polarizing film, it is preferable to perform a fixing treatment in order to make the adsorption of the dichroic dye to the PVA film firm. The fixation treatment can be performed by using a solution (ideally an aqueous solution) containing one or more kinds of boron-containing compounds such as boric acid and borax as the fixation treatment solution, and immersing the PVA film (ideally the PVA film after stretching treatment) in the solution. It is performed by fixing the treatment liquid. Moreover, an iodine-containing compound and a metal compound may be contained in a fixed process liquid as needed. The concentration of the boron-containing compound in the fixed treatment liquid is preferably 2 mass % or more, more preferably 3 mass % or more. The concentration of the boron-containing compound in the fixed treatment liquid is preferably 15 mass % or less, and more preferably 10 mass % or less. The temperature of the fixed treatment liquid is preferably 15°C or higher, more preferably 25°C or higher. The temperature of the fixed 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 wash the PVA film after the stretching treatment. The cleaning treatment is preferably performed by immersing the PVA film in the cleaning treatment liquid, but may be performed by spraying the cleaning treatment liquid on the PVA film. As the cleaning treatment liquid, for example, water can be used. The water is not limited to pure water, and may include, for example, an iodine-containing compound such as potassium iodide. In addition, the cleaning treatment liquid may contain a boron-containing compound, but in this case, the concentration of the boron-containing compound is preferably 2.0 mass % or less.

The temperature of the cleaning treatment liquid is preferably in the range of 5 to 40°C. The rupture of the PVA film caused by the freezing of moisture can be suppressed by setting the temperature of the cleaning solution to 5°C or higher. In addition, when the temperature of the cleaning treatment liquid is 40° C. or lower, the optical properties of the obtained polarizing film are improved. The temperature of the cleaning treatment liquid is more preferably 7°C or higher, and more preferably 10°C or higher. In addition, the temperature of the cleaning treatment liquid is more preferably 38°C or lower, and further preferably 35°C or lower.

As a specific method at the time of manufacturing a polarizing film, the method of applying a dyeing process, an extension process, and a crosslinking process and/or a fixing process to a PVA film is mentioned. A preferred example includes a method of sequentially applying swelling treatment, dyeing treatment, crosslinking treatment, stretching treatment (especially uniaxial stretching treatment), and washing treatment to the PVA film. In addition, the stretching treatment may be performed in any one of the treatment steps earlier than the above, or may be performed in two or more stages.

A polarizing film can be obtained by drying the PVA film after each process as mentioned above. The method of drying treatment is not particularly limited, and examples thereof include a contact 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 the film is floated by hot air. Dry floating method, etc.

＜Polarizer＞ The polarizing film obtained as described above is preferably used as a polarizing plate by laminating an optically transparent and mechanically strong protective film on both sides or one side thereof. As the protective film, triacetate cellulose (TAC) film, cycloolefin polymer (COP) film, cellulose acetate/butyrate (CAB) film, acrylic film, polyester film, etc. can be used. Moreover, as the adhesive used for bonding, a PVA-based adhesive, a urethane-based adhesive, and the like can be exemplified, but a PVA-based adhesive is preferred.

The polarizing plate obtained in the above-mentioned manner can be used as a component of an LCD by laminating an adhesive such as acrylic, and then bonding it to a glass substrate. It can also be laminated with retardation film, viewing angle enhancement film, brightness enhancement film, etc. at the same time. [Example]

The present invention will be specifically described below by way of examples, but the present invention is not limited at all by the following examples.

<Calculation of crystallinity index measured by FT-IR> From the PVA film obtained in the following Examples or Comparative Examples, a PVA film having a width of 30 mm and a length of 30 mm was cut out, and used as a measurement sample. The value of the crystallinity index of the PVA film varies to some extent due to the amount of moisture absorbed by the PVA film. Therefore, the measurement sample was stored for 24 hours in an environment with a temperature of 24.0°C and a relative humidity of 45.0% RH. The measurement device in the room performs the FT-IR measurement. The FT-IR measurement was performed on both surfaces of the PVA film (two surfaces perpendicular to the thickness direction of the PVA film, the first surface and the second surface) under the following conditions.

Measurement apparatus: NICOLET is 10 (manufactured by Thermo Fisher) Measurement conditions: 1-time reflection ATR method, incident angle 45° Optical resolution: 4.0 cm ^-1 Cumulative times: 32 times Measurement temperature: 24.0°C (ambient temperature) Measurement humidity: 45.0%RH (ambient relative humidity) ATR: diamond or germanium

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

<Wrinkle evaluation on the surface of polarizing film> For the polarizing films obtained in the following Examples or Comparative Examples, the surface of the polarizing films was irradiated with light obliquely with a fluorescent lamp and the reflected light was visually observed to confirm the state of wrinkles on the surfaces of the polarizing films, and Evaluation was performed using the following criteria. Evaluation benchmark: A: Wrinkle is not recognized. B: A fine wrinkle to the extent that there is no practical problem was confirmed. C: Wrinkles to such an extent as to be a problem in practical use were clearly confirmed.

<Evaluation of the frequency of extension rupture during the production of polarizing films> In the following Examples or Comparative Examples, the uniaxial stretching in the stretching treatment at the time of producing the polarizing film was continuously performed for 20 minutes. The number of times of extension ruptures occurring during the 20-minute continuous extension was measured, and the frequency of extension ruptures (times/20mim) was evaluated.

<Example 1> ＜Manufacture and evaluation of PVA film＞ 100 parts by mass of PVA (degree of saponification 99 mol%, degree of polymerization 2400), 12 parts by mass of glycerin plasticizer as a plasticizer, 0.1 part by mass of diethanolamide laurate as a surfactant, and 217.6 parts by mass of water , and melt-mixed with a melt extruder to prepare a film-forming stock solution (volatile content rate: 66% by mass). Next, the film-forming stock solution was discharged from the T-die onto a support (surface temperature of 80° C.) in a film form, and a liquid coating was formed on the support. On the support, hot air at 85° C. and 3% RH was sprayed at a speed of 5 m/sec over the entire non-contact surface of the liquid film and the support, and dried to obtain a PVA film (moisture content: 32 mass %). Next, the PVA film was peeled from the support, and one side of the PVA film and the other side of the PVA film were alternately contacted with each drying roll, and further between the first drying roll and the final drying roll (19th drying roll) immediately before the heat treatment roll After drying, peel off from the final drying roll. At this time, the surface temperature of each drying roll from a 1st drying roll to a final drying roll was made into 75 degreeC. Furthermore, the PVA film was peeled off from the final drying roll, and the heat treatment was performed so that one surface and the other surface of the PVA film alternately contacted each heat treatment roll. At this time, the heat treatment was performed using two heat treatment rolls, and the surface temperatures of the heat treatment rolls were all set to 90°C. About the obtained PVA film (thickness 30 micrometers, width 1200mm), FT-IR measurement was performed by the method mentioned above, and the crystallinity index (Fg1, Fg2, Fd1, and Fd2) was calculated. The results are shown in Table 1.

<Manufacture and evaluation of polarizing film> The obtained PVA film was cut into a width of 650 mm, and the film was sequentially subjected to swelling treatment, dyeing treatment, crosslinking treatment, stretching treatment, washing treatment, and drying treatment to continuously manufacture a polarizing film. The swelling treatment was performed by uniaxially extending 2.00 times in the longitudinal direction while being immersed in pure water (swelling treatment liquid) at 25°C. The dyeing treatment was performed by uniaxially extending 1.26 times in the longitudinal direction while being immersed in a potassium iodide/iodine dyeing solution (dyeing treatment solution) (potassium iodide/iodine (mass ratio) 23, iodine concentration 0.03 to 0.05 mass %) at a temperature of 32°C. In this dyeing treatment, the concentration of iodine in the dyeing treatment liquid is adjusted within the range of 0.03 to 0.05 mass % so that the monomer transmittance of the polarizing film obtained after uniaxial stretching in the stretching treatment becomes 43.5%± 0.2% range. The crosslinking treatment was performed by uniaxially extending 1.19 times in the longitudinal direction while being immersed in a 32° C. boric acid aqueous solution (crosslinking treatment liquid) (boric acid concentration: 2.6 mass %). The stretching treatment was performed by uniaxial stretching 2.00 times in the longitudinal direction while being immersed in a 55° C. boric acid/potassium iodide aqueous solution (stretching treatment liquid) (boric acid concentration 2.8 mass %, potassium iodide concentration 5 mass %). The maximum stretching speed of the uniaxial stretching in this stretching process is 400%/min. The cleaning treatment was performed by immersing in a potassium iodide/boric acid aqueous solution (cleaning treatment liquid) (3-6 mass % potassium iodide concentration, 1.5 mass % boric acid concentration) at 22° C. for 12 seconds without stretching. The drying process was performed by hot-air drying at 80° C. for 1.5 minutes without stretching to obtain a polarizing film. The obtained polarizing film was evaluated for the wrinkle on the surface of the polarizing film and the elongation rupture frequency at the time of producing the polarizing film by the above-mentioned method. The results are shown in Table 2.

<Example 2> Except that in <Production and Evaluation of PVA Film> of Example 1, the PVA used for the preparation of the film-forming stock solution was changed to PVA (degree of saponification 99 mol%, degree of polymerization 2400, ethylene modification 2.5 mol%) , and the surface temperature of the two heat treatment rolls was changed to 85° C., and it was carried out in the same manner as in Example 1 to obtain a PVA film and a polarizing film. 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> Except that in <Production and Evaluation of PVA Film> of Example 1, the surface temperature of the support was changed to 100°C, and the temperature of the hot air sprayed on the entire non-contact surface of the liquid film and the support was changed to 105°C, the surface temperature of each drying roll from the first drying roll to the final drying roll (19th drying roll) immediately before the heat treatment roll was changed to 90°C, and the surface temperature of both heat treatment rolls was changed to 80 Other than ℃, it carried out similarly to Example 1, and obtained a PVA film and a polarizing film. 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> Except that in <Manufacture and Evaluation of PVA Film> of Example 1, only one surface of the PVA film (the surface on which the liquid film on the support is in contact with the support) is brought into contact with each drying roll, and the steps from the first drying roll to the Except for drying up to the final drying roll (19th drying roll) immediately before the heat treatment roll, it was carried out in the same manner as in Example 1 to obtain a PVA film and a polarizing film. 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> Except that in <Production and Evaluation of PVA Film> of Example 1, the surface temperature of the support was changed to 115°C, and the temperature of the hot air sprayed on the entire non-contact surface of the liquid film and the support was changed to 120°C, the surface temperature of each drying roll from the first drying roll to the final drying roll (19th drying roll) immediately before the heat treatment roll was changed to 65°C, and the surface temperature of both heat treatment rolls was changed to 65°C Other than ℃, it carried out similarly to Example 1, and obtained a PVA film and a polarizing film. 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> Except that in <Production and Evaluation of PVA Film> of Example 1, the surface temperature of the support body was changed to 60°C, and the temperature of the hot air sprayed on the entire non-contact surface of the liquid film and the support body was changed to 70°C, except that the surface temperature of each drying roll from the first drying roll to the final drying roll (19th drying roll) immediately before the heat treatment roll was changed to 90°C, it was carried out in the same manner as in Example 1 to obtain PVA film and polarizing film. 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> A PVA film and a polarizing film were obtained in the same manner as in Comparative Example 1, except that in <Production and Evaluation of Polarizing Film> of Example 1, the maximum stretching speed of uniaxial stretching in the stretching process 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.

[Table 1] PVA Manufacturing conditions of PVA film Crystallinity index of PVA film degree of aggregation degree of saponification upgrade Surface temperature of support Hot air temperature Surface temperature from the first drying roll to the final drying roll Surface temperature of heat treatment roll Fd1 Fd2 Fg1 Fg2 Fd1/ Fg1 Fd2/ Fg2 |Fd1-Fd2| |Fg1-Fg2| unit [mol%] [mol%] [°C] [°C] [°C] [°C] Example 1 2400 99 none 80 85 75 90 0.60 0.60 0.74 0.73 0.81 0.82 0.00 0.01 Example 2 2400 99 Ethylene 2.5 80 85 75 85 0.57 0.58 0.71 0.72 0.80 0.81 0.01 0.01 Example 3 2400 99 none 100 105 90 80 0.58 0.58 0.64 0.62 0.91 0.94 0.00 0.02 Example 4 2400 99 none 80 85 75 90 0.60 0.52 0.74 0.63 0.81 0.83 0.08 0.11 Comparative Example 1 2400 99 none 115 120 65 65 0.55 0.53 0.52 0.51 1.06 1.04 0.02 0.01 Comparative Example 2 2400 99 none 60 70 90 90 0.81 0.82 0.9 0.91 0.90 0.90 0.01 0.01 Reference Example 1 2400 99 none 115 120 65 65 0.55 0.53 0.52 0.54 1.06 0.98 0.02 0.02

[Table 2] Manufacturing conditions of polarizing films Evaluation of polarizing films The maximum extension speed of the extension process wrinkle Extended rupture frequency unit [%/min] [times/20min] Example 1 400 A 0 Example 2 400 A 0 Example 3 400 A 1 Example 4 400 B 2 Comparative Example 1 400 C 1 Comparative Example 2 400 C 5 Reference Example 1 190 A 0

As shown in Tables 1 and 2, when polarizing films were produced using the PVA films of Examples 1 to 4, no wrinkles or fine wrinkles were observed on the surface of the obtained polarizing films, which were practically no problem. 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 during the production of the polarizing film. Therefore, it can be said that the PVA films of Examples 1 to 4 are difficult to generate wrinkles on the surface during uniaxial stretching.

As shown in Tables 1 and 2, when the PVA films of Examples 1 to 4 were used to manufacture polarizing films, when the uniaxial stretching in the stretching treatment was continuously performed for 20 minutes, the frequency of stretching rupture was 0 to 2 times/20min. Therefore, the PVA films of Examples 1 to 4 can be said to have suppressed cracking during stretching (at the time of uniaxial stretching).

Also, as shown in Reference Example 1, when the maximum stretching speed of the uniaxial stretching in the stretching process during the production of the polarizing film was relatively low (190%/min), even when the PVA film of Comparative Example 1 was used, the Wrinkles were not observed on the surface of the obtained polarizing film, and the breakage frequency at the time of stretching (at the time of uniaxial stretching) was 0 times/20 min. On the other hand, as shown in Comparative Example 1, when the maximum stretching speed was high (400%/min), when the PVA film of Comparative Example 1 was used, it was clearly confirmed on the surface of the obtained polarizing film that practically The wrinkle of the extent of the problem has a rupture frequency of 5 times/20min during elongation (during uniaxial elongation).

That is, the PVA film of Comparative Example 1 can be said to be prone to cracks during stretching (during uniaxial stretching) when the maximum stretching speed is high speed (400%/min). . On the other hand, it can be said that the PVA films of Examples 1 to 4 are difficult to generate wrinkles on the surface during uniaxial stretching even when the maximum stretching speed is high (400%/min), and the stretching (uniaxial stretching) is suppressed. time) breaker.

1: PVA film 2: Thickness direction of PVA film 3: 1st surface 4: 2nd surface 5: Infrared penetration depth (about 2μm) in the case of using a diamond crystal 6: Infrared penetration depth in the case of using germanium (about 0.5μm) 7: ATR (diamond or germanium) 8: Infrared

[Fig. 1] A perspective view of the PVA film of the present invention. [ Fig. 2 ] A view of the PVA film of the present invention viewed from the side. [ Fig. 3] Fig. 3 is a diagram schematically showing the ATR method of FT-IR measurement.

none.

Claims (6)

A polyvinyl alcohol film, which is a water-insoluble polyvinyl alcohol film, Two surfaces orthogonal to the thickness direction of the polyvinyl alcohol film were set as the first surface and the second surface, respectively, Let the crystallinity index of the first surface be Fd1 and Fg1, When the crystallinity index of the second surface is set to Fd2 and Fg2, The Fd1, Fg1, Fd2 and Fg2 satisfy the following formulae (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 the crystallinity index calculated using diamond zirconium when performing FT-IR measurement by the ATR method on the first surface, and Fg1 is the first surface The crystallinity index calculated using germanium in the FT-IR measurement by the ATR method, and Fd2 is the crystallinity index calculated using the diamond in the FT-IR measurement by the ATR method on the second surface The index, Fg2 is the crystallinity index calculated using germanium when the second surface is measured by FT-IR by the ATR method]. The polyvinyl alcohol film of claim 1, wherein the Fd1 and Fd2 satisfy the following formulas (5) to (6); Fd1≧0.5 (5) Fd2≧0.5 (6). The polyvinyl alcohol film of 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 optical film production. The polyvinyl alcohol film of claim 5, wherein the optical film is a polarizing film.

Images