Polyvinyl alcohol film, polarizing film comprising the same, and method for manufacturing the same

Abstract

The present invention relates to a polyvinyl alcohol film having an IR absorption intensity ratio of 0.85 < A1730cm ‑1 / A1710cm ‑1 < 0.97, a polarizing film comprising the same, and a method of manufacturing the same. The polyvinyl alcohol film of the present invention has excellent hue characteristics.

Description

TECHNICAL FIELD

[0001] The present application relates to a polyvinyl alcohol (PVA) film, which can be used as an optical film, in particular a polarizing film. BACKGROUND

[0002] Polyvinyl alcohol (PVA) film is a hydrophilic polymer, which has good transparency, mechanical strength, water solubility, and processability, and has been widely used as packaging materials or optical films for electronic products, in particular a polarizing film.

[0003] In the manufacturing process of PVA film as an optical film, functional group modification can be selectively used according to the required properties, followed by stretching. The manufacturing method can be divided into dry and wet methods. The dry method is to stretch the PVA film in an inert gas environment under fixed temperature and humidity, followed by dyeing and other processes. The wet method is to dye the PVA film, followed by stretching in a solution. Since the PVA film prepared by the dry method often has the problems of uneven surface or uneven dyeing, the PVA film prepared by the wet method has better performance (such as uniform color), so the wet method is currently used to manufacture PVA film.

[0004] When manufacturing a polarizing film, the higher the stretching ratio, the higher the optical performance that can be obtained. Therefore, the PVA film is stretched as close to the critical point near the breaking point as possible during stretching to obtain a PVA film with better optical properties.

[0005] A good polarizing film has the characteristics of uniform color, few color spots, and no wrinkles, and can provide better optical properties. In order to improve the optical properties of the polarizing film, the prior art changes the structure of polyvinyl alcohol or adds functional groups (such as cationic groups) to change the viscosity or saponification degree, thereby improving the optical properties. SUMMARY

[0006] However, the distribution of residual acetic acid groups and syndiotacticity of the conventional manufacturing method has a significant impact on the hue of the polarizing sheet.

[0007] The inventors found that the cause of red or blue light leakage of the polarizing film is the relative content of I3- and I5- in the film. If I5- is less, the 700 nm absorbance is lower, and the appearance is reddish (Red leak); on the contrary, if I3- is less, the 480 nm absorbance is low, and the appearance is bluish (Blue leak). If boric acid can effectively crosslink with PVA, it helps to form I5- complex or avoid the loss of I3-, therefore, if the crosslinking reaction amount of boric acid with PVA is insufficient, it is possible to cause the polarizing film to have the phenomenon of color phase reddish or bluish. On the other hand, if the syndiotacticity is higher, I5- complex is more likely to form, which can easily reduce Red leak. In addition to the syndiotacticity, the arrangement form of residual acetate groups, the degree of boric acid complexation, etc. also affect the relative color phase. It is necessary to control them in a certain range to achieve the effect of uniform color phase.

[0008] Therefore, in order to solve the above problems, the present application controls the ratio of non-hydrogen bonded carbonyl / hydrogen bonded carbonyl in the IR absorption spectrum to achieve a PVA film with excellent color phase, wherein the IR absorption intensity of non-hydrogen bonded carbonyl is A1730cm -1 , and the IR absorption intensity of hydrogen bonded carbonyl is A1710cm -1 .

[0009] The purpose of the present application is to provide a polyvinyl alcohol (PVA) film with an IR absorption intensity ratio of 0.85 < A1730cm -1 / A1710cm -1 <0.97, and the IR absorption intensity is analyzed after the PVA film is soaked in pure water, stirred, taken out, dried at 105°C / 1 hr.

[0010] In a preferred embodiment, the PVA film has an acetate group absorption intensity of 0.35 < (A1710cm -1 +A1730cm -1 ) / A1425cm -1 <0.55, and the acetate group absorption intensity is analyzed after the PVA film is soaked in pure water, stirred, taken out, dried at 105°C / 1 hr.

[0011] In a preferred embodiment, the PVA film has a syndiotacticity of 52% to 56%.

[0012] In a preferred embodiment, 0.12 g of the PVA film is treated with a 0.2 wt% boric acid aqueous solution, and after the aqueous solution is dissolved in water, the boron content of the aqueous solution is 16 to 19 ppm.

[0013] Another object of the present application is to provide an optical film comprising the PVA film as described above. In a preferred embodiment, the optical film is a polarizing film.

[0014] In a preferred embodiment, the ratio (A / B) of the absorbance (A) at a wavelength of 480 nm to the absorbance (B) at a wavelength of 700 nm in the crossed-Nicol state of the polarizing film is 1.40 to 1.70.

[0015] In a preferred embodiment, the ratio (A / B) of the absorbance (A) at a wavelength of 480 nm to the absorbance (B) at a wavelength of 700 nm in the crossed-Nicol state of the polarizing film is 1.51 to 1.65.

[0016] Another object of the present application is to provide a method for preparing a PVA film, comprising: (a) polymerizing a vinyl ester resin monomer to form a polyvinyl ester resin, and then performing a saponification reaction to obtain a polyvinyl alcohol resin, wherein a vinyl 2,2-bis(trifluoromethyl)propionate comonomer is added during the polymerization reaction, and the addition amount ratio of the molar amount of the comonomer to the molar amount of the vinyl ester resin monomer is 1 to 3 mole%, and a solvent having a dielectric constant of 34 to 36 is added; (b) dissolving the polyvinyl alcohol resin by heating to form a polyvinyl alcohol casting solution; (c) casting the casting solution onto a casting drum; and (d) forming the PVA film after drying.

[0017] In a preferred embodiment, steps (a) to (c) in the method for preparing the PVA film are performed using an external heat preservation device.

[0018] In a preferred embodiment, the external heat preservation device is a metal heating wire or a jacket with liquid inside.

[0019] In a preferred embodiment, the method for preparing the PVA film further adjusts the pH value or adds a solvent having a different dielectric constant in step (a) to control the arrangement of residual acetate groups.

[0020] In a preferred embodiment, the method for preparing the PVA film further pulverizes and dries the polyvinyl alcohol resin obtained by the saponification reaction in step (a), and timely sprays steam during the drying process to prevent the particles from being excessively dried and forming a crust.

[0021] The present application has the effect of not only improving the process of conventional PVA films, but also achieving PVA films with excellent color by adjusting the ratio of non-hydrogen-bonded carbonyl groups to hydrogen-bonded carbonyl groups in the IR absorption spectrum. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 11710 cm -1 and 1730 cm -1 schematic diagram of non-hydrogen bonding carbonyl groups within a block.

[0023] Figure 2 schematic diagram of a syndiotactic triad, isotactic triad, and heterotactic triad according to an embodiment of the present application. DETAILED DESCRIPTION

[0024] The following embodiments should not be considered as unduly limiting the present application. Modifications and variations of the embodiments discussed herein can be made by those skilled in the art without departing from the spirit or scope of the present application.

[0025] The terms "a" and "an" herein represent one or more than one (i.e., at least one) of the grammatical object in the context in which they appear.

[0026] The present application provides a PVA film, in particular, a PVA film having a specific IR absorbance intensity ratio. In addition, the present application also provides an optical film comprising the PVA film.

[0027] The aforementioned "IR absorbance intensity ratio" is obtained using infrared spectroscopy, which is a technique for detecting the vibrational energy (or frequency) of molecules, and records the vibrational modes exhibited by molecules after absorbing infrared light using the principle of molecular vibrations generated by the interaction of infrared light and molecules. The relative intensity of the absorbed light versus the wavelength (λ) of the infrared light is recorded as a graph, which is called an infrared spectrum, and can be used for the identification of specific molecules. The IR analysis method is, for example, the reference standard method JIS K 6726. A 10 cm x 10 cm PVA film is immersed in 2000 ml of 30°C pure water, and after stirring for 5 minutes using a magnetic stirrer, it is removed. The oven is preheated to 105°C, and the immersed film is placed flat on a tray and dried at 105°C / 1 hr. After removing the film, IR analysis is performed. If negative values are generated for the IR absorbance values, the data is appropriately translated, and a fixed constant is added to all the data so that the lowest point of the full-range IR spectrum absorbance is 0.

[0028] Referring to Figure 1 1710 cm -1 and 1730 cm -1(non-hydrogen bonding carbonyl within the block). According to at least one embodiment, the inventors found that the C=0 absorption peak in the acetate group is split into 1710 cm -1 (with OH group) and 1730 cm -1 (within the block), the higher the 1730 cm -1 absorption intensity (A1730cm -1 ), the more C=0 within the block, which will have an impact on the color of the polarizer. In a preferred embodiment, the polyvinyl alcohol film of the present application has an IR absorption intensity ratio of 0.85 < A1730cm -1 / A1710cm -1 < 0.97. Specifically, a range between any two of the following values but not including the values, for example: 0.85, 0.86,..., 0.97.

[0029] In addition / alternatively, the inventors found that (A1710cm -1 + A1730cm -1 ) / A1425cm -1 represents the overall acetate group residue, the higher the value, the lower the brightness, and the tendency of red light leakage. In a preferred embodiment, the polyvinyl alcohol film of the present application further has an acetate group absorption intensity of 0.35 < (A1710cm -1 + A1730cm -1 ) / A1425cm -1 < 0.55, specifically, a range between any two of the following values but not including the values, for example: 0.35, 0.36,..., 0.55. The higher the A1730cm -1 absorption value, the more acetate groups (OAc groups) within the block, which can be controlled by adjusting the pH value during saponification or adding solvents with different dielectric constants to control the arrangement of residual acetate groups. In addition, alkalization of different solvents controls the arrangement of different residual acetate groups.

[0030] The PVA film of the present application also has a specific syndiotacticity. The "syndiotacticity" described herein refers to the stereoregularity of the molecular chain, which refers to the configuration in which R groups appear alternately on both sides of the chain. In preferred embodiments, the PVA film of the present application has a syndiotacticity of 52% to 56%. Specifically, the syndiotacticity is within a range between any two of the following values, for example: 52%, 53%,..., 56%. According to at least one embodiment, the syndiotacticity can be adjusted in the polymerization reaction by adding a specific comonomer to increase the steric hindrance and become a high-order arrangement, such as but not limited to: vinyl 2,2-bis(trifluoromethyl)propionate, vinyl 5H-octafluorovalerate, carbon trifluoride (CF3), etc.; or slightly adjusting the polymerization temperature. If the polymerization temperature is too high, the steric hindrance will be overcome, the syndiotacticity will be reduced, and branches are also likely to be generated, which will affect the dyeability.

[0031] In preferred embodiments, the PVA film of the present application is treated with 0.2 wt% boric acid aqueous solution, and after the PVA film is dissolved in water, the boron content of the aqueous solution is 16 to 19 ppm, specifically within a range between any two of the following values, for example: 16 ppm, 16.5 ppm,..., 19 ppm. In the present application, the method for measuring the boron content includes: cutting about 0.12 g of the PVA film and placing it in a 30 ml glass sampling bottle, adding 20 g of pure water so that the film is completely submerged below the water level, adding stirring stones, and stirring at a speed of 250 rpm for 1.0 hour. Then, the pure water in the bottle is poured out, and 0.2 wt% boric acid aqueous solution is added, and the PVA film is allowed to stand for 1.0 hour. Then, the boric acid aqueous solution is poured out, and the PVA film is allowed to stand in the bottle for 16.0 hours. Then, the PVA film is taken out, rinsed with pure water, placed in a 30 ml glass sampling bottle, and 20 g of pure water is added. After the PVA film is completely dissolved, the boron concentration in the solution is analyzed by inductively coupled plasma optical emission spectrometry (ICP-OES).

[0032] The "optical film" described herein refers to a polarizing film, an anti-blue light film, a filter, etc., and the present application is not limited thereto. Preferably, the PVA film of the present application is used as a polarizing film.

[0033] The aforementioned polarizing film has a ratio (A / B) of absorbance at a wavelength of 480 nm (A) to absorbance at a wavelength of 700 nm (B) in a specific cross-Nicol state. The "cross-Nicol" described herein refers to cross-Nicol transmittance, which is a method used to analyze optical properties. The wavelength range is set to 380 nm to 780 nm, the transmittance when the vibration direction of the polarized light incident to the polarizing film through a Glan-Taylor polarizer is parallel to the transmission axis of the polarizing film is set to parallel transmittance, and the case where it is perpendicular to the transmission axis of the polarizing film is set to cross-Nicol transmittance. Thereafter, using a "polarizing film evaluation program" (manufactured by Japan Spectroscopic Co., Ltd.), the parallel transmittance and the cross-Nicol transmittance are used in a manner according to JIS Z 8722 (Method for measuring object color) to perform visibility correction in the visible region of a C light source, 2° field of view, and to perform calculation of the monomer transmittance and the brightness of the polarizing film, and the two values are obtained as the optical properties of the polarizing film.

[0034] In a preferable embodiment, the polarizing film of the present application has a ratio (A / B) of absorbance at a wavelength of 480 nm (A) to absorbance at a wavelength of 700 nm (B) in a cross-Nicol state of 1.40 to 1.70, and the aforementioned ratio (A / B) is specifically in a range between any two of the following values, for example, 1.40, 1.41,..., 1.70. In a more preferable embodiment, the polarizing film of the present application has a ratio (A / B) of absorbance at a wavelength of 480 nm (A) to absorbance at a wavelength of 700 nm (B) in a cross-Nicol state of 1.51 to 1.65, and the aforementioned ratio (A / B) is specifically in a range between any two of the following values, for example, 1.51, 1.52,..., 1.65.

[0035] On the other hand, the present application also provides a method for manufacturing the polyvinyl alcohol film, which comprises the following steps: (a) polymerizing ethylene ester resin monomers to form a polyethylene ester resin, and then performing a saponification reaction to obtain a polyvinyl alcohol resin, wherein a vinyl 2, 2-bis(trifluoromethyl)propionate comonomer is added during the polymerization reaction, and the addition amount ratio of the molar amount of the comonomer to the molar amount of the ethylene ester resin monomers is 1 to 3 mole %, and a solvent having a saponification dielectric constant of 34 to 36 is added; (b) dissolving the polyvinyl alcohol resin to form a polyvinyl alcohol casting solution; (c) casting the casting solution onto a casting roller; and (d) forming the polyvinyl alcohol film after drying.

[0036] In a preferred embodiment, the method for manufacturing the PVA film of the present application, the copolymerization monomer molar amount / ethylene ester resin monomer molar amount addition ratio in the (a) ethylene ester resin monomer polymerization step is 1 to 3 mole%. The range between any two of the following values, for example: 1, 1.2,..., 3 mole%, can be used, and the present application is not limited thereto. In a preferred embodiment, the pH value is adjusted in the step (a), or a solvent with different dielectric constant is added to control the residual acetate group arrangement. In another preferred embodiment, in the step (a), the polyvinyl alcohol resin obtained by saponification is crushed and dried, and steam is sprayed in time during the drying process to avoid excessive drying of the resin particles and the formation of a crust.

[0037] The solvent with a dielectric constant of 34 to 36 in the step (a) is, for example, a mixed solvent of methanol / methyl acetate, and the more methyl acetate is added, the lower the dielectric constant value is. A1730 cm -1 / A1710 cm -1 The IR absorption intensity ratio will be higher.

[0038] The above-mentioned polyvinyl alcohol resin is obtained by saponification after polymerization of ethylene ester resin monomers to form a polyethylene ester resin. The ethylene ester resin monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl valerate, or vinyl octanoate, and the present application is not limited thereto, and vinyl acetate is preferred. In addition, a copolymer formed by copolymerization of an olefin compound or an acrylic ester derivative with the above-mentioned ethylene ester resin monomers can also be used. The olefin compound is, for example, ethylene, propylene, butylene, or the like, or an acrylic ester derivative, such as allyl acetate, acrylic acid, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, or the like, and a copolymer formed by copolymerization of the above-mentioned ethylene ester monomers can also be used. From the comprehensive consideration of manufacturing cost and film quality, ethylene, allyl acetate, and allyl alcohol are preferred. According to at least one embodiment, the content of ethylene, allyl acetate, and allyl alcohol units is within 5 mole%, and 2 to 3.5 mole% is preferred.

[0039] A specific comonomer can also be appropriately added during polymerization to adjust the syndiotacticity, such as vinyl 2,2-bis(trifluoromethyl)propionate. The polymerization temperature can also be slightly adjusted. If the polymerization temperature is too high, the syndiotacticity decreases, and branching is also likely to occur, affecting the dyeability.

[0040] Generally, the saponification degree of the polyvinyl alcohol resin is 90% or more, preferably 99% or more, to obtain preferable optical properties, specifically any of the following values, for example: 90%, 91%,..., 99%, or between any two of the aforementioned values. The pH value can be adjusted during the saponification process, or a solvent with different dielectric constant can be added, to control the arrangement of residual acetate groups.

[0041] The polymerization degree of the polyvinyl alcohol is between 800 and 10000, preferably between 2200 and 10000, specifically for example: 800, 900, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, or between any two of the aforementioned values. A polymerization degree higher than 800 has preferable processing properties, but a polymerization degree higher than 10000 is not conducive to dissolution.

[0042] Generally, if the content of the polyvinyl alcohol resin in the polyvinyl alcohol casting solution used is insufficient, the viscosity of the casting solution is too low, and the drying load is too large, which can result in poor film forming efficiency. On the other hand, if the content of the polyvinyl alcohol resin is too high, the polyvinyl alcohol resin is not easily dissolved, and clusters are easily left behind. Therefore, in the polyvinyl alcohol casting solution used in the present embodiment, the content of the polyvinyl alcohol resin is generally between 10 and 60 wt%, preferably between 15 and 40 wt%, and more preferably between 20 and 30 wt%, specifically for example: 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60 wt%, etc.

[0043] The dissolution temperature of the polyvinyl alcohol casting solution is preferably between 130 and 140°C. If the temperature is too low, clusters are easily left behind, and if the temperature is too high, not only is energy consumed, but costs are also increased. The specific temperature is for example: between 130 and 140°C, between 133 and 140°C, between 136 and 140°C, between 139 and 140°C, between 130 and 137°C, between 130 and 134°C, or between 130 and 131°C.

[0044] In the casting solution, in addition to the polyvinyl alcohol resin, a plasticizer can also be contained to improve the processability of film formation. The plasticizer that can be used includes polyhydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, or glycerol, and the present application is not limited thereto. Preferably, ethylene glycol and glycerol are used. The amount of the plasticizer added is usually 3 to 30 parts by weight, preferably 7 to 20 parts by weight, relative to 100 parts by weight of the polyvinyl alcohol resin. For example, the amount of the plasticizer added is 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 parts by weight, or between any two of the aforementioned values. If the content of the plasticizer is insufficient, the PVA film formed is prone to crystallization, which affects the dyeing efficiency in subsequent processing. Conversely, if the content of the plasticizer is too high, the mechanical properties of the PVA film will be damaged.

[0045] The equipment used in the method for manufacturing the PVA film includes a dissolving tank, a filter, a coating machine, and a conveying pipeline connected from the dissolving tank to the coating machine. In a preferred state, the equipment is covered with a heat preservation device, which can be a metal heating wire or a jacket containing a liquid such as oil or water inside. By heating the metal wire or the liquid in the jacket, the dissolving tank, the filter, the coating machine, and the pipeline connected from the dissolving tank to the coating machine are maintained in a uniformly heated and heat-preserved state, especially the surface of the equipment and the pipeline, to prevent the polyvinyl alcohol in the polyvinyl alcohol casting solution from forming a gel due to loss of temperature on the surface of the equipment or the pipeline, thereby adhering or blocking the filter and causing the process to stop. On the other hand, if the heating temperature is too high, part of the solution will dehydrate or gel, forming a yellowish brown or black gel, which is also not conducive to improving the quality and uniformity of the surface of the film formed by coating. In the method of the present application, the polyvinyl alcohol is subjected to coating and molding under heating and heat preservation conditions of 80 to 120°C, preferably 90 to 110°C, more preferably 90 to 100°C. For example, the temperature is 80, 85, 90, 95, 100, 105, 110, 115, 120°C, or between any two of the aforementioned values. In a preferred embodiment, steps (a) to (c) are performed using an external heat preservation device.

[0046] In the method disclosed above, after the polyvinyl alcohol resin and plasticizer are dissolved in a solution to form a polyvinyl alcohol casting solution, the solution is filtered. Finally, a gear pump and a T-die coating machine are used to cast the polyvinyl alcohol casting solution onto a casting drum. If the drum speed is too slow, it will be over-dried, resulting in phase difference and uneven melting point distribution; if it is too fast, it will be insufficiently dried, reducing peelability. Increasing the drum temperature can easily cause blistering. Therefore, the drum rotation speed should preferably be 3 to 7 meters per minute, more preferably 4 to 6 meters per minute, and can be any range between the following values, for example: 2 meters per minute, 3 meters per minute...6 meters per minute. The temperature should be set between 85 and 90°C, for example, 85 to 90°C, 86 to 90°C, 87 to 90°C, 88 to 90°C, 89 to 90°C, 85 to 89°C, 85 to 88°C, 85 to 87°C, or 85 to 86°C. If the drum temperature is too high, the casting solution on the drum is prone to bubbling.

[0047] After being peeled off from the roller, the polyvinyl alcohol film is further dried by a series of hot rollers and then heat-treated to obtain a polyvinyl alcohol film. Examples of heat treatment methods include (1) the polyvinyl alcohol film is dried on hot rollers or (2) on a floating dryer. There is no particular limitation on the number of hot rollers or floating dryers. However, temperatures of 115 to 130°C are preferred, for example, 115 to 130°C, 115 to 128°C, 115 to 126°C, 115 to 124°C, 115 to 122°C, 115 to 120°C, 115 to 118°C, 115 to 116°C, 117 to 130°C, 119 to 130°C, 121 to 130°C, 123 to 130°C, 125 to 130°C, 127 to 130°C, or 129 to 130°C. If the temperature is too high, the swelling will deteriorate, affecting the dyeability and boric acid reactivity; if the temperature is too low, PVA will dissolve.

[0048] During the manufacturing of optical films, PVA films undergo stretching and dyeing. Taking polarizing films as an example, the polarizing film manufacturing process uses materials containing I3... - I5 - When boric acid solution containing iodide ions is used to dye PVA films, the boric acid can crosslink with the amorphous regions of PVA, thereby fixing the iodide ions and preventing them from dissolving.

[0049] Example

[0050] The invention will be further described below with detailed descriptions and embodiments. However, it should be understood that these embodiments are only for the purpose of helping to more readily understand the invention and are not intended to limit the scope of the invention.

[0051] Manufacture of PVA film: First, prepare a polyvinyl alcohol casting solution, then cast the polyvinyl alcohol casting solution to a casting roller, and after drying, form a polyvinyl alcohol-based polymer film. Specifically, in the above-mentioned polyvinyl alcohol-based polymer film manufacturing method, the polyvinyl alcohol casting solution mainly includes polyvinyl alcohol, plasticizer, and water, and the polyvinyl alcohol is obtained by polymerizing ethylene ester resin monomers to obtain a polyvinyl ester resin, and then performing a saponification reaction.

[0052] Manufacture of polarizing film: The polyvinyl alcohol film is immersed in 30°C water to swell and uniaxially stretched in the machine direction (MD) to 2.0 times the original length, then stretched to 3.3 times the original length while immersed in a 30°C aqueous solution containing 0.03 mass% iodine and 3 mass% potassium iodide, then immersed in a 30°C aqueous solution of 3 mass% potassium iodide and 3 mass% boric acid, and further stretched to 3.6 times the original length. Then, immerse in a 60°C aqueous solution of 5 mass% potassium iodide and 4 mass% boric acid, and further stretch to 6.0 times the original length. After soaking in a 3 mass% potassium iodide aqueous solution for 15 seconds, dry at 60°C for 4 minutes to obtain a polarizing film.

[0053] Table 1 below shows the experimental control factors and hue uniformity measurement results of Examples 1 to 4 and Comparative Examples 1 to 3.

[0054] Table 1

[0055]

[0056]

[0057] In this example, the IR analysis method includes: immersing a 10 cm x 10 cm PVA film in 2000 ml of 30°C pure water, stirring for 5 minutes using a magnetic stirrer, and then removing it. Preheat the oven to 105°C, place the soaked film flat on the tray, and dry at 105°C / 1 hr. After removing the film, analyze it. If negative values occur in the IR absorption values, appropriately shift the data, and add a fixed constant to all data to make the minimum point of the full-range IR spectrum absorption value 0.

[0058] In this embodiment, the method for measuring the boron content comprises: cutting about 0.12 g of PVA film and placing it in a 30 ml glass sample bottle, adding 20 g of pure water, making the film completely submerged below the pure water level, adding stirring stones, the stirring speed is 250 rpm, stirring for 1.0 hour. Then pour out the pure water in the bottle, and add another 0.2 wt% boric acid solution, stand for 1.0 hour, then pour out the boric acid solution, make the PVA film close in the bottle and stand for 16.0 hours. Then take out the PVA film, rinse it with pure water, and place it in a 30 ml glass sample bottle, add 20 g of pure water, and analyze the boron concentration in the solution by ICP-OES after it is fully dissolved.

[0059] In this embodiment, the ICP-OES analysis method comprises: first, make a detection line by extrusion, take 200 ppm of ICP multi-element standard solution (purchased from Merck Company) with a micro-syringe, place it in a 100 ml volumetric flask, and then dilute it to 100 ml with deionized water to prepare the required concentration (such as: 100, 200, 500, 2000 ppb) for standby; the sample does not need pretreatment and can be directly analyzed by the machine. The selected analysis element is boron (B, 249.773 nm).

[0060] In this embodiment, the analysis method of syndiotacticity comprises: immersing a 10 cm x 10 cm test sample in 2000 ml of 30°C pure water, and taking it out after stirring for 5 min with a magnetic stirrer. The oven is preheated to 105°C, and the soaked film is placed flat on the tray for drying at 105°C / 1 hr. Then take out the film and perform NMR analysis. The solvent used is deuterated dimethyl sulfoxide (dimethyl sulfoxide-d6); the instrument is 1 H NMR. This analysis method refers to the method disclosed by T. Moritani et al. in 1972 in the Journal of Macromolecules, 5, 577, and refers to Figure 2 After obtaining the percentage (%) of triads (mm / mr / rr) by NMR, the dyads are calculated by the formula: syndiotacticity (dyads) = rr + mr / 2.

[0061] In this embodiment, the saponification degree and the average polymerization degree of the resin are referred to JIS 6726 test method.

[0062] According to Table 1, the ratio (A / B) of the absorbance (A) at a wavelength of 480 nm to the absorbance (B) at a wavelength of 700 nm in a cross-Nicol state of the polarizing film produced from the PVA film of the present application is preferably 1.40 or more from the viewpoint of color phase uniformity. On the other hand, when the ratio (A / B) is too high, there is a tendency that more red light leaks, and therefore, the ratio (A / B) is preferably 2.00 or less, more preferably 1.80 or less. The absorbance (A) and the absorbance (B) can be obtained using a spectrophotometer.

[0063] In summary, the present application is effective in not only improving the process of a conventional PVA film, but also achieving a PVA film with excellent color phase by adjusting the ratio of non-hydrogen-bonded carbonyl groups / hydrogen-bonded carbonyl groups in the IR absorption spectrum.

[0064] Herein, all ranges provided are intended to encompass each and every specific range within the given range and combinations of sub-ranges within the given range. Further, unless otherwise indicated, all ranges provided herein are inclusive of the endpoints. Thus, a range of 1-5 specifically includes 1, 2, 3, 4, and 5, as well as sub-ranges such as 2-5, 3-5, 2-3, 2-4, 1-4, etc.

[0065] All publications and patent applications cited in this specification are herein incorporated by reference in their entirety for any purpose. The citation of any publication or patent application herein should not be taken as an indication that it is considered material to the patenting of any of the applications herein. In the event of inconsistencies between the instant specification and any publication or patent application incorporated herein by reference, the instant specification shall prevail.

[0066] The terms "comprising," "having," and "including" are used herein to mean "open-ended" and "non-limiting." The terms "a" and "an" are understood to encompass the plurals as well as the singular. The term "one or more" refers to "at least one" and thus can include a single feature or a mixture / combination of features.

[0067] Except in operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients and / or reaction conditions are to be understood as being modified in all instances by the term "about," meaning ±5% of the indicated number. The terms "substantially free of" or "essentially free of" mean less than about 2% of the particular feature. All elements or features of any process or composition described herein can be positively excluded from the claims.

Claims

1. A polyvinyl alcohol film, wherein, having an IR absorbance intensity ratio of 0.85 < A1730cm -1 / A1710 cm -1 <0.97, the IR absorbance intensity being analyzed after the polyvinyl alcohol film is immersed in pure water, stirred, removed, dried at 105°C / 1 hr, and analyzed; The polyvinyl alcohol film further has an acetate group absorption intensity of 0.35 < (A1710 cm -1 + A1730 cm -1 ) / A1425 cm -1 < 0.55, which is analyzed after the polyvinyl alcohol film is immersed in pure water, stirred, taken out, dried at 105°C / 1 hr, and analyzed; The polyvinyl alcohol film further has a syndiotacticity of 52% to 56%; 0.12 g of the polyvinyl alcohol film is treated with 0.2 wt% boric acid aqueous solution, and the boron content of the aqueous solution after water dissolution is 16 to 19 ppm; The polyvinyl alcohol film manufacturing method comprises: (a) polymerizing vinyl ester resin monomers to form a polyvinyl ester resin, and then performing a saponification reaction to obtain a polyvinyl alcohol resin, wherein a vinyl 2,2-bis(trifluoromethyl)propionate comonomer is added during the polymerization reaction, and the addition amount ratio of the molar amount of the comonomer to the molar amount of the vinyl ester resin monomers is 1 to 3 mole%, and a solvent with a saponification dielectric constant of 34 to 36 is added; (b) warming and dissolving the polyvinyl alcohol resin to form a polyvinyl alcohol casting solution; (c) casting the casting solution onto a casting cylinder; and (d) forming the polyvinyl alcohol film after drying; wherein steps (a) to (c) are performed using an external heating device, which is a metal heating wire or a jacket with liquid inside.

2. A polarizing film comprising the polyvinyl alcohol film according to claim 1.

3. The polarizing film of claim 2, wherein The ratio (A / B) of the absorbance (A) at a wavelength of 480 nm to the absorbance (B) at a wavelength of 700 nm in the orthogonal Nicol state is 1.40 to 1.

70.

4. The polarizing film of claim 3, wherein The ratio (A / B) of the absorbance (A) at a wavelength of 480 nm to the absorbance (B) at a wavelength of 700 nm in the orthogonal Nicol state is 1.51 to 1.

65.

5. A method for producing a polyvinyl alcohol film, wherein The manufacturing method comprises: (a) polymerizing vinyl ester resin monomers to form a polyvinyl ester resin, and then performing a saponification reaction to obtain a polyvinyl alcohol resin, wherein a vinyl 2,2-bis(trifluoromethyl)propionate comonomer is added during the polymerization reaction, and the addition amount ratio of the molar amount of the comonomer to the molar amount of the vinyl ester resin monomers is 1 to 3 mole%, and a solvent with a saponification dielectric constant of 34 to 36 is added; (b) warming and dissolving the polyvinyl alcohol resin to form a polyvinyl alcohol casting solution; (c) casting the casting solution onto a casting cylinder; and (d) forming the polyvinyl alcohol film after drying; wherein steps (a) to (c) are performed using an external heating device, which is a metal heating wire or a jacket with liquid inside. wherein said polyvinyl alcohol film has an IR absorbance intensity ratio of 0.85 < A1730cm -1 / A1710 cm -1 <0.97, said IR absorbance intensity being analyzed after soaking said polyvinyl alcohol film in pure water, stirring, removing, drying at 105°C / 1 hr, and removing. The polyvinyl alcohol film further has an acetate absorption strength of 0.35 < (A1710cm). -1 +A1730 cm -1 ) / A1425 cm -1 <0.55, the acetate group absorption strength is determined by immersing the polyvinyl alcohol film in pure water, stirring, removing it, drying it at 105℃ / 1hr, and then analyzing it; The polyvinyl alcohol film further has a syndiotacticity of 52% to 56%; 0.12 g of the polyvinyl alcohol film is treated with 0.2 wt% boric acid aqueous solution, and the boron content of the aqueous solution after water dissolution is 16 to 19 ppm.

6. The production method as defined in claim 5, wherein Further adjusting the pH value or adding a solvent with a different dielectric constant in step (a) to control the arrangement of residual acetate groups.

7. The production method as defined in claim 5, wherein Further in step (a), the polyvinyl alcohol resin obtained by saponification reaction is crushed and dried, and steam is sprayed in a timely manner during the drying process to prevent the particles from being excessively dried and forming a crust.

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