TWI771225B - Polyvinyl alcohol film, polarizing film comprising the same as well as a manufacturing method thereof - Google Patents

Abstract

The present invention relates to a polyvinyl alcohol (PVA) film, a polarizing film comprising the same as well as the manufacturing method thereof. The IR absorption intensity ratio of the PVA film is 0.85 ＜A1730 cm ^-1/ A1710 cm ^-1＜ 0.97. The PVA film of the present invention has excellent hue characteristics.

Description

Polyvinyl alcohol film, polarizing film including the same, and manufacturing method thereof

The present invention relates to a polyvinyl alcohol (PVA) film, which can be used as an optical film, especially a polarizing film.

Polyvinyl alcohol (PVA) film is a hydrophilic polymer with properties such as transparency, mechanical strength, water solubility, and good processability. It has been widely used in packaging materials or optical films for electronic products, especially polarized light. membrane.

In the manufacturing process of the PVA film being prepared into an optical film, functional groups can be selectively modified according to the desired properties and then stretched. The manufacturing method can be divided into dry type and wet type. The dry type is to stretch the PVA film in an inert gas environment under a fixed temperature and humidity, followed by dyeing and other processes; the wet type is to dye the PVA film and then put it in a solution. Stretch. Since the PVA film prepared by dry method often has the problem of uneven surface or uneven dyeing, and the PVA film produced by wet method has better properties (such as uniform color), the wet method is generally used to manufacture PVA film at present. Mostly.

When manufacturing polarizing films, the higher the stretching ratio, the higher the optical properties that can be obtained. Therefore, when stretching, the PVA film will be stretched as close to the critical point of fracture as possible to obtain better optical properties. PVA film.

A good polarizing film has the characteristics of uniform color, less 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 will change the viscosity or saponification degree by changing the structure of polyvinyl alcohol, or adding functional groups (eg, cationic groups), etc., so as to improve the optical properties.

However, the distribution and syndiotacticity of acetate groups remaining in the conventional manufacturing method have a significant impact on the hue of the polarizer.

The inventors found that the reason for the leakage of red light or blue light in the polarizing film is the relative content of I ₃ ^- and I ₅ ^- in the film. If I ₅ ^- is less, the absorption at 700 nm is lower, and the appearance is reddish (Red leak); on the contrary, if I ₃ ^- is less, the absorption at 480 nm is low, and the appearance is blue (Blue leak). If boric acid can effectively cross-link with PVA, it will help the formation of I ₅ -complex or avoid the loss of I ₃ ^{- .} Therefore, if the amount of cross-linking reaction between boric acid and PVA is insufficient, it may cause the polarizing film to have A reddish or bluish hue occurs. On the other hand, the higher the degree of alignment ^, the easier the formation of I ₅ -complexes, and the easier the reduction of Red leak. In addition to the alignment degree, the arrangement form of the remaining acetate groups and the degree of boronic acid complexation will also affect the relative hue. It must be controlled in a specific range at the same time to achieve the effect of uniform hue.

Therefore, in order to solve the above-mentioned problems, the present invention achieves a PVA film with excellent hue by controlling the ratio of the non-hydrogen-bonded carbonyl group/hydrogen-bond carbonyl group in the IR absorption spectrum, wherein the IR absorption intensity of the non-hydrogen-bonded carbonyl group is A1730 cm ^-1 , The IR absorption intensity of the hydrogen-bonded carbonyl group is A1710 cm ^-1 .

The purpose of the present invention is to provide a polyvinyl alcohol (PVA) film, which has an IR absorption intensity ratio of 0.85 < A1730 cm ^-1 /A1710 cm ^-1 < 0.97, and the IR absorption intensity is the value of the PVA film. It was immersed in pure water, stirred, taken out, dried at 105°C/1hr, and analyzed.

In a preferred embodiment, the PVA film has an acetate-based absorption strength of 0.35 < (A1710 cm ^-1 + A1730 cm ^-1 )/A1425 cm ^-1 < 0.55, and the acetate-based absorption strength is the polyvinyl alcohol The film was immersed in pure water, taken out after stirring, dried at 105°C/1hr, and analyzed.

In a preferred embodiment, the PVA film has a parallelism of 52% to 56%.

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

Another object of the present invention is to provide an optical film comprising the aforementioned PVA film. In a preferred embodiment, the optical film is a polarizing film.

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

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

Another object of the present invention is to provide a preparation method of PVA film, comprising: (a) polymerizing vinyl ester resin monomers to form polyvinyl ester resin, and then performing saponification reaction to obtain polyvinyl alcohol resin, wherein, in During the polymerization reaction, vinyl 2,2-bis(trifluoromethyl)propionate (vinyl 2,2-bis(trifluoromethyl)propionate) copolymer is added, and the copolymer molar amount/vinyl ester resin monomer molar The addition ratio of the amount is 1 to 3 mole %, adding a solvent with a saponification dielectric constant of 34 to 36; (b) heating and dissolving the polyvinyl alcohol resin to form a polyvinyl alcohol casting solution; (c) this The casting solution is cast to a casting drum; and (d) dried to form the PVA film.

In a preferred embodiment, the steps (a) to (c) in the preparation method of the PVA film are carried out by using an external heat preservation device.

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

In a preferred embodiment, the preparation method of the PVA film further adjusts the pH value in the step (a), or adds solvents with different dielectric constants to control the arrangement of the remaining acetate groups.

In a preferred embodiment, the preparation method of the PVA film is further in the step (a), the polyvinyl alcohol resin obtained by the saponification reaction is pulverized and dried, and steam is sprayed in a timely manner during the drying process to avoid excessive drying of the resin particles. crust.

The effect of the present invention is not only to improve the manufacturing process of the conventional PVA film, but also to achieve a PVA film with excellent hue by adjusting the ratio of non-hydrogen-bonded carbonyl groups/hydrogen-bonded carbonyl groups in the IR absorption spectrum.

The following embodiments should not be construed to unduly limit the invention. Modifications and variations of the embodiments discussed herein can be made by those of ordinary skill in the art to which this invention pertains without departing from the spirit or scope of the invention, and still fall within the scope of the invention.

The terms "a" and "an" herein refer to one or more than one (ie, at least one) of the grammatical objects herein.

The invention provides a PVA film, especially a PVA film with a specific IR absorption intensity ratio. In addition, the present invention also provides an optical film comprising the PVA film.

The aforementioned "IR absorption intensity ratio" is obtained by infrared spectroscopy, which is a technique used to detect the vibrational energy (or frequency) of molecules, using the principle of molecular vibrations generated by the interaction of infrared light and molecules, To record the vibrational modes of molecules after absorbing infrared light, and record the relative intensity of absorbed light versus the wavelength of infrared light (λ), which is called infrared spectroscopy, which can be used for specific molecular identification. The IR analysis method described is for example: referring to the standard method JIS k 6726, immerse a 10 cm×10 cm PVA film in 2000 ml of 30 °C pure water, stir it with a magnetic stirrer for 5 minutes, and then take it out. Preheat the oven to 105 °C, place the soaked film flat on a tray, dry at 105 °C/1hr, and then take out the film for IR analysis. If the IR absorption value has a negative value, the data is appropriately shifted, and a fixed constant is added to all the data, so that the lowest point of the full-range IR spectral absorption value is 0.

Referring to FIG. 1 , the C=0 absorption peak in the acetate group is divided into 1710 cm ⁻¹ (connected to the OH group) and 1730 cm ⁻¹ (non-hydrogen-bonded carbonyl group in the block). According to at least one embodiment, the inventors found that the C=0 absorption peak in the acetate group is divided into 1710 cm ^-1 (connected to the OH group) and 1730 cm ^-1 (in the block), if the 1730 cm ^-1 absorption intensity The higher the (A 1730 cm ^-1 ), the more C=0 in the block, which will affect the hue of the polarizer. In a preferred embodiment, the polyvinyl alcohol film of the present invention has an IR absorption intensity ratio of 0.85 < A1730 cm ^-1 /A1710 cm ^-1 < 0.97. The range between any two of the following numerical values is specified but not inclusive, for example: 0.85, 0.86, . . . , 0.97.

In addition/alternatively, the inventors found that (A1710 cm ^-1 +A1730 cm ^-1 )/A1425 cm ^-1 represents the total residual acetate group, and the higher the value, the lower the degree of polarization and the tendency to leak red light. In a preferred embodiment, the polyvinyl alcohol film of the present invention further has an acetate-based absorption strength of 0.35 < (A1710 cm ^-1 + A1730 cm ^-1 )/A1425 cm ^-1 < 0.55, which is any of the following values Ranges between but not inclusive of such values, eg: 0.35, 0.36, ..., 0.55. The higher the absorption value of A1730 cm ^-1 , the more acetate groups (OAc groups) in the block. This can be controlled by adjusting the pH value or adding solvents with different dielectric constants during the saponification process to control the arrangement of the remaining acetate groups. ; In addition, the alkalinization of different solvents will control the arrangement of different residual acetate groups.

The PVA film of the present invention also has a specific alignment. As used herein, "Syndiotacticity" 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 a preferred embodiment, the PVA film of the present invention has an alignment degree of 52% to 56%. Specifically, it is a range between any two of the following values, for example: 52%, 53%, . . . , 56%. According to at least one embodiment, the regulation of the alignment can be adjusted by appropriately adding a specific copolymer in the polymerization reaction, which will make the steric barrier large and become a high alignment. The aforementioned copolymers are, for example, but not limited to: vinyl 2, 2-bis(trifluoromethyl)propionate (vinyl 2,2-bis(trifluoromethyl)propionate), vinyl 5H-octafluorovalerate (vinyl 5H-octafluorovalerate), carbon trifluoride (CF ₃ ), etc.; Or adjust the polymerization temperature slightly, if the polymerization temperature is too high, it will overcome the three-dimensional barrier, reduce the alignment degree, and easily produce branches, which will affect the dyeability.

In a preferred embodiment, the PVA film of the present invention is treated with a 0.2 wt% boric acid aqueous solution, and the boron content of the aqueous solution after dissolving with water is 16 to 19 ppm, specifically a range between any two of the following values, for example: 16ppm, 16.5ppm, ..., 19ppm. In the present invention, the method for measuring the boron content comprises: cutting about 0.12 g of PVA film and putting it into a 30 ml glass sampling bottle, adding 20 g of pure water, so that the film is completely submerged under the pure water level, adding Stir the stone at 250 rpm for 1.0 hour. Then, the pure water in the bottle was poured out, and another 0.2 wt% boric acid aqueous solution was added, and the solution was allowed to stand for 1.0 hours. Then, the PVA film was taken out, rinsed with pure water, put into a 30 ml glass sampling bottle, and 20 g of pure water was added. After it was fully dissolved, the concentration of boron in the solution was analyzed by inductively coupled plasma optical emission spectrometer (ICP-OES). .

The "optical film" mentioned herein refers to a polarizing film, an anti-blue light film, an optical filter, etc., and the present invention is not limited to these. Preferably, the PVA film of the present invention is used as a polarizing film.

The aforementioned polarizing film has a ratio (A/B) of absorbance (A) at a wavelength of 480 nm and absorbance (B) at a wavelength of 700 nm in a specific crossed Nicols state. As used herein, "Cross Nicol" refers to Cross Nicol transmittance, a method used to analyze optical performance. The measurement wavelength range was set to 380 nm to 780 nm, and the transmittance when the vibration direction of the polarized light incident on the polarizing film through the Glan-Taylor polarizer was parallel to the transmission axis of the polarizing film was set as the parallel transmittance, and the same as the polarizing film. The case where the transmission axis is perpendicular is set as the crossed Nicols transmittance. Then, using the "Polarizing Film Evaluation Program" (manufactured by JASCO Corporation), in accordance with JIS Z 8722 (Method for Measuring Object Color), using the aforementioned parallel transmittance and crossed Nicol transmittance, C The optical sensitivity of the light source and the visible light region of the 2° visual field was corrected, and the individual transmittance and polarization degree of the polarizing film were calculated, and these two values were obtained as the optical properties of the polarizing film.

In a preferred embodiment, the ratio (A/B) of the absorbance (A) at a wavelength of 480 nm to the absorbance at a wavelength of 700 nm (B) of the polarizing film of the present invention in a crossed Nicols state is 1.40 to 1.70, The aforementioned ratio (A/B) is specifically a range between any two of the following values, for example: 1.40, 1.41, . . . , 1.70. In a more 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 of the polarizing film of the present invention in the crossed Nicols state is 1.51 to 1.65, The aforementioned ratio (A/B) is specifically a range between any two of the following values, for example: 1.51, 1.52, . . . , 1.65.

On the other hand, the present invention also provides a method for producing the polyvinyl alcohol film, the steps 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 (vinyl 2,2-bis(trifluoromethyl)propionate) copolymer is added during the polymerization reaction, and the copolymer is molar/vinyl ester resin The addition ratio of the molar amount of the monomer is 1 to 3 mole %, adding a solvent with a saponification dielectric constant between 34 and 36; (b) heating and dissolving the polyvinyl alcohol resin to form a polyvinyl alcohol casting solution; ( c) casting the casting solution onto a casting drum; and (d) drying to form the polyvinyl alcohol film.

In a preferred embodiment, in the manufacturing method of the PVA film of the present invention, in the (a) vinyl ester-based resin monomer polymerization step, the ratio of the added amount of copolymer molar amount/vinyl ester-based resin monomer molar amount 1 to 3 mole %. Specifically, the range between any two of the following numerical values, for example: 1, 1.2, . . . , 3 mole %, and the present invention is not limited to these. In a preferred embodiment, in the step (a), the pH value is adjusted, or solvents with different dielectric constants are added to control the arrangement of the remaining acetate groups. In another preferred embodiment, in the step (a), the polyvinyl alcohol resin obtained by the saponification reaction is pulverized and dried, and steam is sprayed in time during the drying process to avoid excessive drying of the resin particles and skin formation.

In this step (a), a solvent with a saponification permittivity between 34 and 36 is, for example, a mixed solvent of ^methanol /methyl acetate. The more methyl acetate is, the lower the saponification permittivity value is. ^-1 IR absorption intensity ratio will be higher.

The above-mentioned polyvinyl alcohol resin is obtained by polymerizing vinyl ester resin monomers to form polyvinyl ester resins, and then performing saponification reaction; wherein, the vinyl ester resin monomers include vinyl formate, vinyl acetate , vinyl propionate, vinyl butyrate, vinyl valerate, vinyl octoate and other vinyl esters, and the present invention is not limited to these, preferably vinyl acetate. In addition, olefinic compounds or acrylate derivatives, copolymers formed by copolymerization with the above vinyl ester resin monomers can also be used; the olefinic compounds such as ethylene, propylene, butene, etc., or alkenoic acid ester derivatives, For example, allyl acetate, acrylic acid, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, etc., copolymers formed by copolymerizing with the above vinyl 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 unit content of ethylene, allyl acetate and allyl alcohol is within 5 mole%, preferably 2 to 3.5 mole%.

In the polymerization, a specific copolymer can also be appropriately added to adjust the alignment, such as vinyl 2,2-bis(trifluoromethyl)propionate. Alternatively, the polymerization temperature may be slightly adjusted. When the polymerization temperature is too high, the alignment degree is reduced, and branching is also likely to occur, which affects the dyeability.

Usually, the degree of saponification of the polyvinyl alcohol-based resin is above 90%, preferably above 99%, in order to obtain better optical properties, specifically any of the following values, such as: 90%, 91%, ..., 99%, or between any two of the preceding values. During the saponification process, the pH value can be adjusted appropriately, or solvents with different dielectric constants can be added to control the arrangement of the remaining acetate groups.

The degree of polymerization of the polyvinyl alcohol is between 800 and 10000, and preferably between 2200 and 10000, for example: 800, 900, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000 , 10000 or between any of the above two values, the degree of polymerization higher than 800 has better processing characteristics, but if the degree of polymerization is higher than 10000, it is not conducive to dissolution.

Generally speaking, if the content of polyvinyl alcohol-based resin in the used polyvinyl alcohol casting solution is insufficient, the viscosity of the casting solution will be too low, and the drying load will be too large, resulting in poor film-forming efficiency. On the other hand, when the content of the polyvinyl alcohol-based resin is too high, the polyvinyl alcohol-based resin is not easily dissolved, and clusters are likely to remain. Therefore, in the polyvinyl alcohol casting solution used in this embodiment, the content of the polyvinyl alcohol-based resin is usually between 10 and 60% by weight, preferably between 15 and 40% by weight, and more preferably between 20 to 30% by weight, specifically 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60% by weight and the like.

The best dissolving temperature of the polyvinyl alcohol casting solution is 130 to 140 °C. If the temperature is too low, clusters may remain, and if the temperature is too high, the cost will increase in addition to energy consumption. The specific temperature is, for example, 130 to 140°C, 133 to 140°C, 136 to 140°C, 139 to 140°C, 130 to 137°C, 130 to 134°C, or 130 to 131°C.

In the casting solution, in addition to the polyvinyl alcohol resin, it can also contain plasticizers to improve the processability of the film. The plasticizers that can be used include polyols, such as ethylene glycol, diethylene glycol, and triethylene glycol. , tetraethylene glycol, propylene glycol or glycerol, etc., and the present invention is not limited to these, preferably ethylene glycol and glycerol. 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: 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 of the preceding two values. If the content of the plasticizer is insufficient, the formed PVA film is likely to crystallize and affect the dyeing performance of the subsequent processing. Conversely, if the plasticizer content is too high, the mechanical properties of the PVA film will be destroyed.

The equipment used in the manufacturing method of 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. Preferably, the equipment is covered with a heat preservation device. The heat preservation device can be a metal electric heating wire, or a jacket with a liquid inside, such as oil or water, by heating the metal wire or the liquid in the jacket, the dissolving tank, filter, coating machine and The pipeline connected from the dissolving tank to the coating machine maintains a uniformly heated thermal insulation state, especially on the surface of the equipment and pipeline, so as to prevent the polyvinyl alcohol in the polyvinyl alcohol casting solution from forming a gel due to the loss of temperature on the surface of the equipment or pipeline, and Adhesion or clogging of the filter, preventing the process from continuing. On the other hand, if the heating temperature is too high, part of the solution will be dehydrated or gelled to form a scorched yellow or black gel, which is not conducive to improving the quality and uniformity of the coated film surface. In the method of the present invention, the polyvinyl alcohol is carried out in the coating and forming place under the heating and heat preservation condition of 80 to 120°C, preferably under the heating and heat preservation condition of 90 to 110°C, more preferably at 90 to 100°C. It is carried out under the heating and holding conditions of ℃, for example: 80, 85, 90, 95, 100, 105, 110, 115, 120 ℃ or between any two values mentioned above. In a preferred embodiment, the steps (a) to (c) are carried out with an external heat preservation device.

In the method disclosed above, the polyvinyl alcohol resin and plasticizer are dissolved in the solution to form a polyvinyl alcohol casting solution, which is filtered with a filter, and finally a gear pump and a T-shaped mold are used. The head coater is used to cast the polyvinyl alcohol casting solution to the casting drum. If the drum speed is too slow, it will be too dry, and there will be a tendency for phase difference and uneven melting point distribution; if it is too fast, the drying will be insufficient and the peelability will be reduced. If the drum temperature is raised, foaming is likely to occur. Therefore, the rotation speed of the drum is preferably 3 to 7 m/min, preferably 4 to 6 m/min, and can be a range between any two of the following values, for example: 2 m/min, 3 m/min /min….6m/min. The temperature is set between 85 and 90°C, such as 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 °C or 85 to 86 °C. If the temperature of the drum is too high, the casting solution on the drum is prone to foaming.

After being peeled off from the roller, it is further dried by a series of hot rollers, and then heat-treated to obtain a polyvinyl alcohol-based film. As the heat treatment method, (1) the polyvinyl alcohol-based film is carried out on a heated roll or (2) a floating dryer, for example. The number of hot rolls and floating dryers is not particularly limited. But preferably 115 to 130 ℃, for example, 115 to 130 ℃, 115 to 128 ℃, 115 to 126 ℃, 115 to 124 ℃, 115 to 122 ℃, 115 to 120 ℃, 115 to 118 ℃, 115 to 116 ℃ , 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 degree will deteriorate, affecting the dyeability and boric acid reactivity. If the temperature is too low, the PVA will be dissolved.

PVA film will be stretched and dyed when manufacturing optical film. Taking polarizing film as an example, since the polarizing film manufacturing process will use boric acid aqueous solution containing I ₃ ^- and I ₅ ^-iodide ions to dye PVA film, and boric acid can be combined with PVA. After the cross-linking of the amorphous regions, the iodide ions are immobilized to avoid the dissolution of the iodine ions. Example

In the following, the invention will be further described with detailed description and examples. However, it should be understood that these examples are only for helping to make the present invention easier to understand and not for limiting the scope of the present invention.

Manufacturing PVA film : firstly prepare a polyvinyl alcohol casting solution, then cast the polyvinyl alcohol casting solution to a casting drum, and form a polyvinyl alcohol-based polymer film after drying. Specifically, in the above-mentioned method for producing a polyvinyl alcohol-based polymer film, the polyvinyl alcohol casting solution mainly includes polyvinyl alcohol, a plasticizer and water, and the polyvinyl alcohol is obtained by polymerizing vinyl ester resin monomers to obtain a polymer Vinyl ester resin, and then saponification reaction.

Production of polarizing film : The polyvinyl alcohol film was immersed in water at 30° C. to swell and uniaxially stretched in the machine direction (MD) to 2.0 times the original length. % potassium iodide in a 30 ℃ aqueous solution, stretched to 3.3 times the original length, then immersed in a 30 ℃ aqueous solution of 3 mass % potassium iodide and 3 mass % boric acid, and further stretched to 3.6 times the original length. Then, it was immersed in a 60° C. aqueous solution of 5 mass % potassium iodide and 4 mass % boric acid, and further extended to 6.0 times the original. After immersing in a 3 mass % potassium iodide aqueous solution for 15 seconds and drying at 60° C. for 4 minutes, a polarizing film can be obtained.

Please refer to Table 1 below, which are the experimental control variables and the measurement results of hue uniformity of Examples 1 to 4 and Comparative Examples 1 to 3.

Table 1 project Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 control variable Resin process Polymerization temperature (℃) 67 66 65 65 67 65 67 Copolymer/Vinyl Acetate (mole %) 1 2 3 2 0 5 0 Saponification medium boundary electric constant 34 36 36 34 32 36 31 Saponification temperature (℃) 39.5 40.5 41 40 39 41.5 39.5 Saponification degree (mole %) 99.92 99.90 99.94 99.96 99.90 99.92 99.90 average coincidence 2510 2550 2560 2485 2535 2490 2500 Thin film process Melting temperature(℃) 130 130 140 140 140 140 140 Maximum heat treatment temperature (℃) (floating dryer) 130 120 118 125 140 135 135 Technical characteristics A1730 cm ^-1 / A1710 cm ^-1 0.965 0.911 0.85 0.96 0.971 0.81 0.975 (A1710 cm ^-1 +A1730 cm ^-1 )/ A1425 cm ^-1 0.55 0.47 0.35 0.38 0.56 0.33 0.54 Alignment (%) 53.11 54.39 55.61 54.11 51.08 56.69 52.1 Boron content (ppm) 16 18 19 16 14 15 15 effect UV-VIS A/B 1.51 1.58 1.62 1.65 1.95 1.33 1.85

In this embodiment, the IR analysis method includes: soaking a 10 cm×10 cm PVA film in 2000 ml of 30°C pure water, stirring with a magnetic stirrer for 5 minutes, and then taking it out. Preheat the oven to 105°C, lay the soaked film flat on a tray, dry at 105°C/1hr, take out the film, and analyze it. If the IR absorption value has a negative value, the data is appropriately shifted, and a fixed constant is added to all the data, so that the lowest point of the full-range IR spectral absorption value is 0.

In this embodiment, the method for measuring the boron content includes: cutting a PVA film of about 0.12 g and placing it in a 30 ml glass sampling bottle, adding 20 g of pure water, so that the film is completely submerged under the pure water level, adding stirring Stone, stirring at 250 rpm for 1.0 hours. Then, the pure water in the bottle was poured out, and another 0.2 wt% boric acid aqueous solution was added, and the solution was allowed to stand for 1.0 hours. Then, the PVA film was taken out, rinsed with pure water, put into a 30 ml glass sampling bottle, and 20 g of pure water was added. After it was fully dissolved, the boron concentration in the solution was analyzed by ICP-OES.

In this embodiment, the ICP-OES analysis method includes: firstly making a calibration line by extrapolation, drawing 200 ppm of ICP multi-element standard solution (purchased from Merck) with a microdispenser and placing it in a 100 ml volumetric flask, and then adding Dilute it with deionized water to 100 ml, and prepare it to the required concentration (eg: 100, 200, 500, 2000 ppb) for later use; the sample does not need pretreatment, and can be directly analyzed on the machine. The selected analytical element for this method is boron (B, 249.773 nm).

In this embodiment, the alignment analysis method includes: immersing a 10 cm×10 cm test sample in 2000 ml of 30°C pure water, stirring with a magnetic stirrer for 5 minutes, and then taking it out. Preheat the oven to 105 °C in advance, lay the soaked film flat on a tray, and dry at 105 °C/1hr. After the film was taken out again, NMR analysis was performed. The solvent used was dimethyl sulfoxide-d ₆ ; the instrument was ¹ H NMR. The analytical method refers to the method disclosed by T. Moritani et al. in Macromolecules ( Macromolecules, 5, 577 ) in 1972. Referring to Fig. 2, the percentage (%) of triads (triads; mm/mr/rr) is obtained by NMR. ), and then calculated by the formula: Alignment (two-tuple; dyads) = rr + mr/2.

In this example, the degree of resin saponification and the average degree of coincidence are based on the test method of JIS 6726.

According to Table 1, the ratio of the absorbance (A) at a wavelength of 480 nm to the absorbance at a wavelength of 700 nm (B) in the crossed Nicols state of the polarizing film produced by the PVA film of the present invention, from the viewpoint of uniformity of hue (A/B) is preferably 1.40 or more. On the other hand, when the ratio (A/B) is too high, the leakage of red light tends to increase. Therefore, the ratio (A/B) is preferably 2.00 or less, more preferably less than 1.80. The said absorbance (A) and absorbance (B) can be calculated|required using a spectrophotometer.

To sum up, the effect of the present invention is not only to improve the manufacturing process of conventional PVA films, but also to achieve a PVA film with excellent hue by adjusting the ratio of non-hydrogen-bonded carbonyl groups/hydrogen-bonded carbonyl groups in the IR absorption spectrum.

All ranges provided herein are intended to include each specific range within the given range and combinations of subranges between the given ranges. Furthermore, all ranges provided herein are inclusive of the endpoints of the stated range unless otherwise indicated. Thus, the range 1-5 specifically includes 1, 2, 3, 4, and 5, as well as subranges such as 2-5, 3-5, 2-3, 2-4, 1-4, and the like.

All publications and patent applications cited in this specification are incorporated herein by reference, and each individual publication or patent application is expressly and individually indicated to be incorporated by reference for any and all purposes. In the event of inconsistency between this document and any publication or patent application incorporated herein by reference, this document controls.

The terms "including", "having" and "comprising" as used herein have an open, non-limiting meaning. The terms "a" and "the" should be understood to encompass both the plural and the singular. The term "one or more" means "at least one" and thus may include a single feature or a mixture/combination of features.

Except in the working examples or where otherwise indicated, all numbers indicating amounts of ingredients and/or reaction conditions may in all cases be modified using the term "about", meaning within ±5% of the indicated number . As used herein, the terms "substantially free" or "substantially free" refer to less than about 2% of a particular characteristic. All elements or features expressly stated herein may be negatively excluded from the scope of the claim.

none.

Figure 1 is a schematic diagram showing that the C=0 absorption peak in the acetate group is divided into 1710 cm ^-1 (connected to OH group) and 1730 cm ^-1 (non-hydrogen-bonded carbonyl group in the block).

2 is a schematic diagram of a syndiotactic triad, an Isotactic triad, and a heterotactic triad according to an embodiment of the present invention.

none.

Claims (9)

A polyvinyl alcohol film, which has: IR absorption intensity ratio of 0.85<A1730cm ^-1 /A1710cm ^-1 <0.97, and acetate-based absorption intensity of 0.35<(A1710cm ^-1 +A1730cm ^-1 )/A1425cm ^-1 <0.55 ; The IR absorption strength and the acetate-based absorption strength are immersed in the polyvinyl alcohol film in pure water, taken out after stirring, dried at 105°C/1hr, and analyzed. The polyvinyl alcohol film of claim 1, further having an alignment degree of 52% to 56%. The polyvinyl alcohol film of claim 2, wherein 0.12 g of the polyvinyl alcohol film is treated with a 0.2 wt % boric acid aqueous solution, and the boron content of the aqueous solution after dissolving with water is 16-19 ppm. A polarizing film comprising the polyvinyl alcohol film according to any one of claims 1 to 3. The polarizing film of claim 4, 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 crossed Nicols state is 1.40 to 1.70. The polarizing film of claim 5, wherein the ratio (A/B) of the absorbance (A) at a wavelength of 480 nm to the absorbance at a wavelength of 700 nm (B) in the crossed Nicols state is 1.51 to 1.65. A method for producing a polyvinyl alcohol film as claimed in any one of claims 1 to 3, 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 (vinyl 2,2-bis(trifluoromethyl)propionate) copolymer is added during the polymerization reaction, and the copolymer molar weight/ethylene The molar ratio of the ester resin monomer is 1 to 3, and a solvent with a saponification dielectric constant of 34 to 36 is added; (b) the polyvinyl alcohol resin is heated and dissolved to form a polyvinyl alcohol casting solution; (c) casting the casting solution into a casting drum; and (d) forming the polyvinyl alcohol film after drying; wherein the steps (a) to (c) utilize an external heat preservation device for a metal heating wire or a liquid inside Under the jacket. The manufacturing method of claim 7, wherein in the step (a), the pH value is further adjusted, or solvents with different dielectric constants are added to control the arrangement of the remaining acetate groups. The manufacturing method of claim 7, wherein further in the step (a), the polyvinyl alcohol resin obtained by the saponification reaction is pulverized and dried, and steam is injected in a timely manner during the drying process to avoid excessive drying of the resin particles and skin formation.

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