TWI824645B - Polyvinyl alcohol film, optical film produced by the same, and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a polyvinyl alcohol (PVA) film, an optical film produced by the same, and a manufacturing method thereof. The PVA film has the UV-visible light spectrum hydrophobic double bond ratio: (A _UV280nm+A _UV320nm)/A _UV215nmbetween 0.500 and 1.300. The PVA film of the present invention has the characteristics of excellent dyeing uniformity and not east to generate wrinkles.

Description

Polyvinyl alcohol film, optical film produced therefrom and its production method

The present invention relates to a polyvinyl alcohol (PVA) film and its manufacturing method. The PVA film 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. Therefore, it has been widely used in packaging materials or optical films for electronic products. Polyvinyl alcohol film is an important component of polarizing plates. It can exhibit polarizing properties after being dyed and stretched, making light polarized and controlling light and shade. Therefore, it has been widely used in various LCD screens.

In recent years, as screen technology has moved towards thinning, the quality requirements for the polarizing film manufacturing process have gradually increased. In the process of thinning the polarizing film, more attention has been paid to the wrinkle problem of the polyvinyl alcohol film and the uniformity of dyeing. also gradually improved.

However, when polyvinyl alcohol films are used to prepare large-sized polarizing films in the prior art, uneven dyeing of the film or wrinkles in the film during dyeing and stretching often occur.

The inventor of this case found that heat treatment can induce the formation of conjugated double bonds of the terminal carbonyl group of polyvinyl alcohol, dehydrating the interior of polyvinyl alcohol to produce -(C=C) _n -bonds, and according to -(C=C ) Different n values in _n - can observe different characteristic peaks of ultraviolet-visible spectrum (UV-VIS). For example, when n=1, a characteristic peak at 215 nm can be observed; when n=2 A characteristic peak can be observed at 280 nm; when n=3, a characteristic peak can be observed at 320 nm. Therefore, the absorbance of the polyvinyl alcohol film at 215 nm, 280 nm and 320 nm can be measured by controlling UV-VIS, and then the C=C hydrophobic double bond ratio contained in the polyvinyl alcohol film can be controlled to form a A polyvinyl alcohol film with excellent dyeing uniformity and low wrinkle resistance.

Therefore, the purpose of the present invention is to provide a polyvinyl alcohol film with a hydrophobic double bond ratio in the ultraviolet-visible light spectrum: (A _UV280nm +A _UV320nm )/A _UV215nm ranging from 0.500 to 1.300.

In one or more embodiments, the polyvinyl alcohol film further has an average double bond ratio in the ultraviolet-visible light spectrum: (A _UV215nm *1 + A _UV280nm *2 + A _UV320nm *3) / (A _UV215nm + A _UV280nm + A _UV320nm ) is between 1.480 and 1.820.

In one or more embodiments, the polyvinyl alcohol film further has a weight swelling degree ranging from 38.0 to 48.0.

Another object of the present invention is to provide an optical film formed from the aforementioned polyvinyl alcohol film.

In one or more embodiments, the optical film is a polarizing film.

Another object of the present invention is to provide a method for manufacturing the aforementioned polyvinyl alcohol film, which includes: (a) resin drying process: pouring a completed polymerized polyvinyl alcohol resin into a dryer, and drying Spray water to cool down; (b) Dissolution process: The dried polyvinyl alcohol resin is heated and dissolved, and the concentration is adjusted to form a polyvinyl alcohol casting solution; (c) Casting process: The polyvinyl alcohol casting solution is cast to A casting drum, from which a polyvinyl alcohol preliminary film is obtained after peeling off; and (d) drying process: the polyvinyl alcohol preliminary film is dried in a plurality of hot rollers and at least two temperature-controlled ovens to obtain The polyvinyl alcohol film; wherein the initial heat roller among the plurality of heat rollers has the highest temperature among the plurality of heat rollers, and the final heat roller has the lowest temperature among the plurality of heat rollers.

In one or more embodiments, the alkalization degree of the polyvinyl alcohol resin is greater than 99.80 mole%.

In one or more embodiments, the degree of polymerization of the polyvinyl alcohol resin ranges from 2,300 to 3,000.

In one or more embodiments, the molecular weight of the polyvinyl alcohol resin ranges from 100,000 to 110,000 Mn.

In one or more embodiments, the speed of the casting drum is between 5.0 and 6.4 m/min.

In one or more embodiments, the temperature difference between the initial heat roller and the final heat roller in the plurality of heat rollers is between 20 and 45°C.

In one or more embodiments, the maximum temperature of the oven is between 60 and 120°C.

In one or more embodiments, the minimum temperature of the oven is between 40 and 70°C.

The effect of the present invention is that the polyvinyl alcohol film provided by the present invention can simultaneously have the characteristics of good dyeing uniformity and being less prone to wrinkles.

The following embodiments should not be considered as unduly limiting the present invention. Those skilled in the art may make modifications and changes to the embodiments discussed herein without departing from the spirit or scope of the invention, while still falling within the scope of the invention.

The terms "a" and "an" in this article represent one or more than one (ie at least one) grammatical object in this article.

The purpose of the present invention is to provide a polyvinyl alcohol film with a hydrophobic double bond ratio in the ultraviolet-visible light spectrum: (A _UV280nm +A _UV320nm )/A _UV215nm ranging from 0.500 to 1.300.

When polyvinyl alcohol is heat treated, the carbonyl group at the end of the polyvinyl alcohol will be induced to form a conjugated double bond, which can cause -(C=C) _n -bonding to occur within the polyvinyl alcohol due to dehydration. Depending on the n value in -(C=C) _n -, different UV-VIS characteristic peaks can be observed. For example: when n=1, a characteristic peak can be observed at 215 nm; when n=2 When n=3, the generation of characteristic peaks can be observed at 280 nm; when n=3, the generation of characteristic peaks can be observed at 320 nm. Therefore, the generation of different UV-VIS characteristic peaks represents different adjacent amounts of UV-VIS. Double bond generation.

The "UV-visible light spectrum hydrophobic double bond ratio" described in this article is to measure the absorbance of the polyvinyl alcohol film under a specific spectrum after placing it in an environment of 23°C and 50% relative humidity for 24 hours, and Obtained according to the following UV-visible light spectrum hydrophobic double bond ratio (A _UV280nm +A _UV320nm )/A _UV215nm . Since the values of different UV characteristic peaks represent the generation of different adjacent amounts of UV double bonds, the hydrophobic double bond ratio in the UV-visible light spectrum represents the proportion of C=C in the polyvinyl alcohol film that causes obvious hydrophobicity. When the hydrophobic double bond ratio in the UV-visible light spectrum is too high, it means that the adjacent C=C content in the film is high, and the hydrophobicity of the film block is high. Therefore, when the film is stretched in the stretching tank , the iodine solution is less able to enter specific areas of the film smoothly, resulting in uneven dyeing of the film. On the contrary, when the hydrophobic double bond ratio in the UV-visible light spectrum is too low, it means that the adjacent C=C in the film If the content is small, the film absorbs water too quickly. Therefore, when the film is stretched in the dyeing tank, the swollen polyvinyl alcohol film is prone to wrinkles. According to at least one embodiment, the hydrophobic double bond ratio of the polyvinyl alcohol film in the UV-visible light spectrum ranges from 0.500 to 1.300, such as the range between any two of the following values, for example: 0.500, 0.525, 0.550, 0.575, 0.600, 0.625, 0.650, 0.675, 0.700, 0.725, 0.750, 0.775, 0.800, 0.825, 0.850, 0.875, 0.900, 0.925, 0.950, 0.975, 1.000, 1.025, 1.050, 1.075, 1.100, 1.1 25, 1.150, 1.175, 1.200, 1.225, 1.250, 1.275 or 1.300, and the term "between" in this article includes both endpoint values.

The "UV-visible light spectrum average double bond ratio" described in this article is to measure the absorbance of the polyvinyl alcohol film under a specific spectrum after placing it in an environment of 23°C and 50% relative humidity for 24 hours, and Obtained according to the following average double bond ratio of UV-visible spectrum: (A _UV215nm *1+A _UV280nm *2+ A _UV320nm *3) / (A _UV215nm +A _UV280nm + A _UV320nm ). The average double bond ratio in the UV-visible light spectrum represents the average amount of C=C present in the polyvinyl alcohol film. Among them, when the average double bond ratio of the UV-visible light spectrum is too high, it means that the C=C content in the film is high and the overall hydrophobicity of the film is high. Therefore, when the film is stretched in the stretching tank, The iodine solution cannot smoothly enter specific areas of the film, resulting in uneven dyeing of the film. On the contrary, when the average double bond ratio of the UV-visible light spectrum is too low, it means that the C=C content in the film is low. The film absorbs water too quickly when it swells, so when the film is stretched in the dyeing tank, it is prone to wrinkles. According to at least one embodiment, the average double bond ratio of the UV-visible light spectrum of the polyvinyl alcohol film is between 1.480 and 1.820, such as the range between any two of the following values, for example: 1.480, 1.500, 1.520, 1.540, 1.560, 1.580, 1.600, 1.620, 1.640, 1.660, 1.680, 1.700, 1.720, 1.740, 1.760, 1.780, 1.800 or 1.820, and the term "between" in this article includes both endpoint values.

The "weight swelling degree" mentioned in this article refers to the degree to which a polyvinyl alcohol film can allow water to enter the film. When testing the weight swelling of a polyvinyl alcohol film, the plasticizers and additives contained in it will be precipitated, and only water will remain in the film. Therefore, when the weight swelling degree of the polyvinyl alcohol film is low, it means that the film is less able to allow water to enter the film, that is, the film is more hydrophobic, making the polyvinyl alcohol film easier to produce uneven dyeing. When the weight swelling degree of the film is high, it means that the film allows water to enter the film to a high degree, that is, the film is more hydrophilic, making the polyvinyl alcohol film more likely to wrinkle. The weight swelling degree is measured by placing the polyvinyl alcohol film in an environment of 23°C and 50% relative humidity for 24 hours, then putting the film into water to swell, then taking the film out, wiping away the surface moisture, and weighing the film weight as M1 , then put the film into an oven to dry and weigh the film weight as M2, which is obtained by (M1-M2)/M1*100%. According to at least one embodiment, the weight wetness of the polyvinyl alcohol film ranges from 38.0 to 48.0, such as a range between any two of the following values, for example: 38.0, 38.5, 39.0, 39.5, 40.0, 40.5, 41.0, 41.5, 42.0, 42.5, 43.0, 43.5, 44.0, 44.5, 45.0, 45.5, 46.0, 46.5, 47.0, 47.5 or 48.0, and the term "between" as used herein includes both endpoint values.

On the other hand, the present invention also provides a method for manufacturing the aforementioned polyvinyl alcohol film, which includes: (a) resin drying process: pouring a completed polymerized polyvinyl alcohol resin into a dryer, and drying Spray water to cool down; (b) Dissolution process: heat up a polyvinyl alcohol resin to dissolve, and adjust the concentration of the polyvinyl alcohol resin to form a polyvinyl alcohol casting solution; (c) Casting process: cast the polyvinyl alcohol The solution is cast into a casting drum, and a preliminary polyvinyl alcohol film is obtained after peeling off the casting drum; and (d) drying process: placing the preliminary polyvinyl alcohol film in a plurality of hot rollers and at least two temperature-controlled ovens After drying, the polyvinyl alcohol film is obtained; wherein, the initial heat roller among the plurality of heat rollers has the highest temperature among the plurality of heat rollers, and the final heat roller has the lowest temperature among the plurality of heat rollers. temperature, and control the temperature difference between the highest temperature and the lowest temperature of the hot roller within a specific range, and simultaneously control the highest temperature and the lowest temperature of the oven.

Please refer to Figure 1 below. Figure 1 does not limit the number of hot rollers and the number of oven sections. It is only an example to help explain the instructions clearly, and does not represent the actual number of hot rollers and oven sections that can be used. According to at least one embodiment, the resin drying process involves pouring the polymerized polyvinyl alcohol resin into a dryer, and spraying water to cool down the resin during high-temperature drying. According to at least one embodiment, the temperature of the dryer is preferably 80°C to 130°C, specific examples include: 80°C, 90°C, 100°C, 110°C, 120°C and 130°C.

According to at least one embodiment, the aforementioned dissolving process involves placing 1,800 kg of dried polyvinyl alcohol resin, 4,000 kg of water, and 200 kg of plasticizer glycerin in the dissolving barrel 110 while stirring to raise the temperature to at least 140˚C, and Dissolve at least 140˚C for at least 180 minutes, then use a mixer to mix the polyvinyl alcohol resin aqueous solution evenly, and then add water to adjust the concentration of the polyvinyl alcohol resin aqueous solution to 30.0% to 50.0% to obtain Polyvinyl alcohol casting solution. According to at least one embodiment, the temperature at which the polyvinyl alcohol resin aqueous solution is dissolved is preferably at least 120˚C, for example: at least 120˚C, at least 130˚C, at least 140˚C, at least 150˚C or at least 160˚ C etc. According to at least one embodiment, the dissolution time for dissolving the polyvinyl alcohol resin is preferably at least 180 minutes, for example: at least 180 minutes, at least 190 minutes, at least 200 minutes, at least 210 minutes, at least 220 minutes, at least 230 minutes or Wait at least 240 minutes. According to at least one embodiment, the concentration of the polyvinyl alcohol resin aqueous solution is preferably 30.0% to 50.0%, for example: 30.0%, 35.0%, 40.0%, 45.0% or 50.0%. According to at least one embodiment, the polyvinyl alcohol resin is obtained by polymerizing a vinyl ester resin monomer, and then performing a saponification reaction after forming the polyvinyl ester resin. The vinyl ester resin monomer includes vinyl esters such as vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl valerate, or vinyl octanoate, but the present invention is not limited thereto. In addition, copolymers formed by copolymerization of olefin compounds or acrylate derivatives and the aforementioned vinyl ester resin monomers can also be used, wherein the olefin compounds include ethylene, propylene, butylene, etc., but the present invention is not limited thereto. The acrylate derivative includes acrylic acid, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate or n-butyl acrylate, but the present invention is not limited thereto. According to at least one embodiment, the alkalization degree of the polyvinyl alcohol resin is preferably greater than 99.80 mole% to obtain better optical properties, such as greater than 99.80 mole%, greater than 99.90 mole% or greater than 99.99 mole%. According to at least one embodiment, the degree of polymerization of the polyvinyl alcohol resin is between 2,300 and 3,000, specifically as a range between any two of the following values, for example: 2,300, 2,400, 2,500, 2,600, 2,700, 2,800, 2,900 or 3,000, etc., and the term "between" in this article includes both endpoint values. According to at least one embodiment, the molecular weight of the polyvinyl alcohol resin is between 100,000 and 110,000 Mn, specifically as a range between any two of the following values, for example: 100,000 Mn, 102,000 Mn, 104,000 Mn, 106,000 Mn, 108,000 Mn or 110,000 Mn, etc., and the term "between" in this article includes both endpoint values.

The inventor found that, without being limited to a specific theory, whether the polyvinyl alcohol resin is sprayed with water for cooling when drying in the dryer, the temperature difference between the hot rollers, the maximum temperature of the oven, the minimum temperature of the oven or the casting drum The speed of the machine will affect the dryness of the film, which will in turn affect the dyeing and wrinkle formation of the film. If the polyvinyl alcohol resin is not cooled by spraying water when drying in the dryer, the temperature difference between the hot rollers is too small, the maximum temperature of the oven is too high, the minimum temperature of the oven is too high, or the speed of the casting drum is too slow, the film will be over-dried. Too many adjacent C=C hydrophobic double bonds are generated, which will cause uneven dyeing of the film; if the temperature difference between the hot rollers is too large, the maximum temperature of the oven is too low, the minimum temperature of the oven is too low, or the speed of the casting drum is too fast, it will cause The film cannot be completely dried, resulting in too little adjacent C=C hydrophobic double bonds, which in turn causes wrinkles in the film.

According to at least one embodiment, the aforementioned casting process involves defoaming the polyvinyl alcohol casting solution through a double screw extruder, then spitting it out from the T-shaped slit lip 120, and casting it into a rotating high-temperature casting drum 130 for drying to obtain A polyvinyl alcohol preliminary film. During the casting process, if the speed of the casting drum 130 is too slow, the film will be over-dried, resulting in the formation of too many adjacent C=C hydrophobic double bonds, which will cause uneven dyeing of the film; conversely, if the speed of the casting drum 130 When the vehicle speed is too fast, the film will not be completely dried and the amount of adjacent C=C hydrophobic double bonds will be too small, which will cause wrinkles in the film. According to at least one embodiment, the speed of the casting drum 130 is between 5.0 and 6.4 m/min, specifically a range between any two of the following values, for example: 5.0 m/min, 5.05 m/min, 5.1 m/min. min, 5.15 m/min, 5.2 m/min, 5.25 m/min, 5.3 m/min, 5.35 m/min, 5.4 m/min, 5.45 m/min, 5.5 m/min, 5.55 m/min, 5.6 m/ min, 5.65 m/min, 5.7 m/min, 5.75 m/min, 5.8 m/min, 5.85 m/min, 5.9 m/min, 5.95 m/min, 6.0 m/min, 6.05 m/min, 6.1 m/ min, 6.15 m/min, 6.2 m/min, 6.25 m/min, 6.3 m/min, 6.35 m/min or 6.4 m/min, etc., and the term "between" in this article includes the two endpoint values.

According to at least one embodiment, the aforementioned drying process involves peeling off the preliminary polyvinyl alcohol film from the casting drum 130 , contacting and drying the upper and lower sides of the polyvinyl alcohol preliminary film through a plurality of hot rollers 140 , and then using an oven 150 to dry the upper and lower sides of the preliminary polyvinyl alcohol film. After drying both sides with hot air, a polyvinyl alcohol film was obtained. According to at least one embodiment, the plurality of heat rollers 140 may be from 2 to 30, such as but not limited to: 2, 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 or 30; in a preferred embodiment, it is 13.

According to at least one embodiment, when drying the film, the temperatures of the plurality of hot rollers 140 gradually decrease from high to low. Therefore, if the temperature difference between the hot rollers 140 is too small, the film will be over-dried and result in too many adjacent C=C The formation of hydrophobic double bonds will cause uneven dyeing of the film; conversely, if the temperature difference between the hot rollers 140 is too large, the film will not be completely dry and the amount of adjacent C=C hydrophobic double bonds will be too small, thus causing the film to Wrinkles are produced, so the temperature difference between the highest temperature and the lowest temperature of the hot roller needs to be controlled within a specific range. According to at least one embodiment, among the plurality of heat rollers 140, the initial heat roller 1401 is the highest temperature among all the heat rollers 140, and the temperature of the subsequent heat rollers 140 gradually decreases until the final heat roller 140N Its temperature is the lowest among all the heat rollers 140 . According to at least one embodiment, the temperature difference between the initial heat roller 1401 and the final heat roller 140N in the plurality of heat rollers 140 is between 20 and 45°C, specifically as a range between any two of the following values. , for example: 20°C, 25°C, 30°C, 35°C, 40°C or 45°C, etc., and the term "between" in this article includes both endpoint values.

When drying the film, the oven 150 used has multiple drying areas, and the temperatures of each section may be partially the same or completely different. Among them, the section close to the center of the oven 150 has the highest temperature, which is the highest temperature zone 152 of the oven 150 . The temperature of the section away from the center of the oven 150 gradually decreases until the last section is the lowest temperature zone 154 of the oven 150. If the highest temperature of the highest temperature zone 152 of the oven is too high or the temperature of the lowest temperature zone 154 of the oven is too high. , the film will be over-dried, resulting in the formation of too many adjacent C=C hydrophobic double bonds, which will cause uneven dyeing of the film; conversely, if the maximum temperature of the oven's highest temperature zone 152 is too low or the lowest temperature zone 154 of the oven is too When the minimum temperature is too low, the film will not be completely dried and the amount of adjacent C=C hydrophobic double bonds will be too small, causing wrinkles in the film. Therefore, it is necessary to control the maximum and minimum temperatures of the maximum temperature zone 152 and the minimum temperature zone 154 of the oven. temperature.

According to at least one embodiment, the number of sections of the oven may be 2 to 10 sections, for example: 2 sections, 3 sections, 4 sections, 5 sections, 6 sections, 7 sections, 8 sections, 9 sections or 10 sections; In the preferred embodiment, it is 4 sections. According to at least one embodiment, the maximum temperature of the maximum temperature zone 152 of the oven is between 60 and 120°C, specifically a range between any two of the following values, for example: 60°C, 70°C, 80°C, 90°C ℃, 100 ℃, 110 ℃ or 120 ℃, etc., and the term "between" in this article includes both endpoint values. According to at least one embodiment, the minimum temperature of the minimum temperature zone 154 of the oven is between 40 and 70°C, specifically a range between any two of the following values, for example: 40°C, 50°C, 60°C or 70°C. ℃, etc., and the term "between" in this article includes the values of both endpoints. According to at least one embodiment, the oven 150 may be, for example, but not limited to: a floating oven.

On the other hand, the polyvinyl alcohol film of the present invention can also be prepared into an optical film. The "optical film" mentioned herein refers to polarizing film, anti-blue light film, filter, etc., and the present invention is not limited to these. Preferably, the polyvinyl alcohol film of the present invention is used as a polarizing film.

In a preferred embodiment, the method of manufacturing a polarizing film (or polarizing plate) includes the following steps: swelling, dyeing, stretching, color complementing, drying and laminating the polyvinyl alcohol film with a triacetyl cellulose (TAC) film, You can get polarizing film.

When polyvinyl alcohol film is further used in the manufacture of optical films, it will be stretched and dyed. Taking polarizing film as an example, since the polarizing film production process uses a boric acid aqueous solution containing I ₃ ^- and I ₅ ^- iodide ions to dye polyethylene. Alcohol film, boric acid can cross-link with the amorphous area of polyvinyl alcohol to fix iodide ions and prevent iodide ions from dissolving. Example

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

To make a polyvinyl alcohol film : first put the polyvinyl alcohol-based PVA resin that has been polymerized and has a polymerization degree of about 2400 into a dryer, and spray water in time to cool down during high-temperature drying, and then put the dried polyvinyl alcohol-based PVA resin into a dryer. The resin is heated and melted through the dissolving barrel to form a polyvinyl alcohol solution. The polyvinyl alcohol solution is then pressed out through a T-shaped slit die lip and a casting drum. The polyvinyl alcohol solution is formed into a film and adjusted through a plurality of hot rollers. The moisture content is removed, and then the polyvinyl alcohol film-forming sample is dried in an oven to obtain a polyvinyl alcohol film.

Specifically, the aforementioned steps for producing a polyvinyl alcohol film include: first pouring the polyvinyl alcohol resin that has completed polymerization and has an alkalization degree of >99.9% and a degree of polymerization of about 2,400 into a dryer, and controls the temperature in the dryer. The temperature is 110°C, and water is sprayed in time during the drying process to cool down the polyvinyl alcohol resin. Then add 1800 kg of dried polyvinyl alcohol resin, 4000 kg of water, and 200 kg of plasticizer glycerol into the dissolution barrel, raise the temperature to 140°C while stirring, and maintain the temperature at 140°C for 180 minutes to dissolve, using a mixer After dissolving evenly, add water to adjust the resin concentration to 30.0% to obtain the film-making stock solution. After the film-making raw solution is defoamed by the double-spiral extruder, it is spit out from the T-shaped slit die lip and cast to the rotating high-temperature casting drum for drying and film formation. At this time, the casting drum speed is 5.4 m/min. After the preformed film is peeled off from the casting drum, it contacts the upper and lower sides of the drying film through 13 hot rollers. The first hot roller is the highest temperature among all the hot rollers. The temperature of the subsequent hot rollers slowly decreases. At this time, the difference between the first heat roller and the 13th heat roller (the lowest temperature among all heat rollers) is 45°C. Then use an oven with 4 sections of drying area to dry the upper and lower sides of the film with hot air. The temperature of the highest temperature area of the oven is 100°C and the temperature of the lowest temperature area is 50°C. Finally, the finished polyvinyl alcohol film is obtained. Each embodiment and comparative example in this article will have one or more parameters that are different from the aforementioned process, which will be presented in detail in the following table.

Production of polarizing film : Dip the polyvinyl alcohol film in 30°C water to swell and uniaxially extend it in the machine direction (MD) to 2.0 times its original length. Then, immerse it in iodine containing 0.03 mass % and 3 mass % of potassium iodide in a 30°C aqueous solution, and then stretched the polyvinyl alcohol film to 3.3 times its original length, and then immersed in a 3% by mass of potassium iodide and 3% by mass of boric acid in a 30°C aqueous solution, and further extended to the original length. 3.6 times longer. 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 length. Subsequently, after soaking in 3 mass% potassium iodide aqueous solution for 15 seconds, drying at 60°C for 4 minutes, the polarizing film can be obtained.

Please refer to Table 1 and Table 2 below, which are the experimental control variables, technical characteristics, and dyeing uniformity and wrinkle measurement results of Examples 1 to 10; Table 3 and Table 4 are the experimental control of Comparative Examples 1 to 10. Variables, technical characteristics, and film dyeing uniformity and wrinkle measurement results.

Table 1 Project Whether the PVA resin is sprayed with water by the dryer or not? Maximum heat roller temperature difference (℃) Maximum temperature of oven (℃) Minimum temperature of oven (℃) Casting drum speed (m/min) -(C=C) _n - Hydrophobic double bond ratio -(C=C) _n - average number of double bonds Example 1 yes 45 60 50 5.4 0.692 1.612 Example 2 yes 45 80 50 5.4 0.742 1.622 Example 3 yes 45 100 50 5.4 0.839 1.648 Example 4 yes 45 120 50 5.4 0.872 1.664 Example 5 yes 30 120 50 5.4 0.977 1.714 Example 6 yes 20 120 50 5.4 1.197 1.795 Example 7 yes 45 100 50 5.7 0.795 1.644 Example 8 yes 45 100 50 6.3 0.565 1.519 Example 9 yes 30 120 70 5.0 1.298 1.816 Example 10 yes 45 100 40 6.0 0.505 1.484

Table 2 (continued from Table 1) Project Weight swelling (wt%) PVA alkalization degree (mole%) PVA polymerization degree PVA molecular weight (Mn) Dyeing uniformity Degree of wrinkles Example 1 47.2 99.90 2411 106084 ◎ O Example 2 44.9 99.92 2367 103708 ◎ ◎ Example 3 42.7 99.86 2341 103004 ◎ ◎ Example 4 41.7 99.93 2421 106504 ◎ ◎ Example 5 40.0 99.95 2463 108372 O ◎ Example 6 38.6 99.85 2318 101992 O ◎ Example 7 44.6 99.89 2309 101596 ◎ ◎ Example 8 46.4 99.90 2326 102344 ◎ O Example 9 38.2 99.92 2407 105908 O ◎ Example 10 47.5 99.88 2482 109208 ◎ O

table 3 Project Whether the PVA resin is sprayed with water by the dryer or not? Maximum heat roller temperature difference (℃) Maximum temperature of oven (℃) Minimum temperature of oven (℃) Casting drum speed (m/min) -(C=C) _n - Hydrophobic double bond ratio -(C=C) _n - average number of double bonds Comparative example 1 yes 55 80 50 6.3 0.442 1.435 Comparative example 2 yes 55 60 50 6.0 0.490 1.474 Comparative example 3 yes 10 120 50 5.4 1.385 1.825 Comparative example 4 yes 30 150 50 5.4 1.412 1.847 Comparative example 5 yes 45 50 50 5.4 0.396 1.408 Comparative example 6 yes 45 100 50 4.0 1.348 1.822 Comparative example 7 yes 45 100 50 6.6 0.483 1.461 Comparative example 8 yes 30 120 80 5.0 1.502 1.865 Comparative example 9 yes 45 80 30 5.4 0.485 1.471 Comparative example 10 no 30 120 50 5.4 1.371 1.833

Table 4 (continued from Table 3) Project Weight swelling (wt%) PVA alkalization degree (mole%) PVA polymerization degree PVA molecular weight (Mn) Dyeing uniformity Degree of wrinkles Comparative example 1 48.5 99.93 2387 105028 ◎ X Comparative example 2 48.8 99.95 2415 106260 ◎ X Comparative example 3 36.9 99.88 2455 108020 X ◎ Comparative example 4 36.5 99.87 2406 105864 X ◎ Comparative example 5 49.9 99.90 2492 109648 ◎ X Comparative example 6 37.7 99.92 2385 104940 X O Comparative example 7 48.4 99.91 2417 106348 O X Comparative example 8 36.0 99.85 2374 104456 X ◎ Comparative example 9 48.6 99.90 2310 101640 ◎ X Comparative example 10 37.5 99.92 2477 108988 X ◎

In this experiment, the analysis methods used are as follows:

UV light - Visible light spectrum analysis of hydrophobic double bond ratio

Sample preparation method: Divide the polyvinyl alcohol film in the width direction into 5 equal parts, and cut each piece into a film sample with an area of 5 cm in the machine direction x 5 cm in the width direction, and place it at 23°C and 50% relative humidity. in a constant temperature and humidity chamber for 24 hours.

Analytical instrument: Perkin Elmer Lambda 365 (wavelength accuracy and wavelength repeatability meet NIST 2034 specifications) was used for analysis of thin film samples.

Test conditions: Test the film sample with constant temperature and humidity in an environment of 23°C and 50% relative humidity from 200 to 700 nm, and read its absorbance at 215 nm, 280 nm and 320 nm. Absorption value.

Data conversion: Put the absorbance values read at 215 nm, 280 nm and 320 nm of the film sample into the following hydrophobic double bond ratio formula of UV-visible light spectrum to obtain the hydrophobic double bond ratio of the film sample: (A _UV280nm +A _UV320nm )/A _UV215nm , and finally average the five hydrophobic double bond ratios measured along the width direction.

UV light - Visible light spectrum average double bond ratio analysis

Sample preparation method: Divide the polyvinyl alcohol film in the width direction into 5 equal parts, and cut each piece into a film sample with an area of 5 cm in the machine direction x 5 cm in the width direction, and place it at 23°C and 50% relative humidity. in a constant temperature and humidity chamber for 24 hours.

Analytical instrument: Perkin Elmer Lambda 365 (wavelength accuracy and wavelength repeatability meet NIST 2034 specifications) was used for analysis of thin film samples.

Test conditions: Test the film sample with constant temperature and humidity in an environment of 23°C and 50% relative humidity from 200 to 700 nm, and read its absorbance at 215 nm, 280 nm and 320 nm. Absorption value.

Data conversion: Put the absorbance values read at 215 nm, 280 nm and 320 nm of the film sample into the following formula for the average double bond ratio of the UV-visible light spectrum to obtain the average double bond ratio of the film sample: (A _UV215nm *1+A _UV280nm *2+ A _UV320nm *3) / (A _UV215nm +A _UV280nm + A _UV320nm ), and finally average the five average double bond ratios measured along the width direction.

Gravimetric Swelling Analysis

Sample preparation method: Divide the polyvinyl alcohol film in the width direction into 5 equal parts, and cut each piece into a film sample with an area of 5 cm in the machine direction x 5 cm in the width direction, and place it at 23°C and 50% relative humidity. in a constant temperature and humidity chamber for 24 hours.

Test conditions: Put the polyvinyl alcohol film sample into pure water at 30°C and let it swell for 20 minutes. After the swelling of the film sample is completed, take it out and use tissue paper to dry the surface moisture of the film sample. Weigh the film. Weigh M1, and then put the film sample into an oven at 120°C to dry for 120 minutes and weigh the film weight M2.

Data conversion: Put the measured film weights M1 and M2 of the film sample into (M1-M2)/M1*100% to obtain the weight swelling degree of the film sample, and finally add the 5 pieces measured along the width direction. The weight swelling degree is averaged.

Film color uniformity performance analysis

The polyvinyl alcohol film was made into a polarizer and irradiated with a light box with a light output of 14000 lx. The color uniformity of the film was observed and evaluated. The film color uniformity is evaluated as follows: ◎: No color unevenness; O: slight color unevenness; X: Color unevenness is evident.

Wrinkle performance analysis

The polyvinyl alcohol film is made into a polarizer, and cut into samples with a width of 5 cm and a length of 20 cm. The sample is fixed on an extension jig with a clamp interval of 5 cm, and is then stretched using the polarizer process. The stretching machine is used to stretch the sample in a water bath. After the sample has been extended to twice the original length (i.e. 10 cm), it is immediately pulled up from the water bath and visually observed from a position 1 m away from the front of the film. Wrinkles on the membrane surface and evaluated. Film wrinkles are evaluated as follows: ◎: No wrinkles; O: slight wrinkles; X: Obvious wrinkles.

According to Table 1 and Table 2, the films of Examples 1 to 10 have hydrophobic double bond ratios in the UV-visible light spectrum ranging from 0.500 to 1.300, so these films can exhibit excellent dyeing uniformity and wrinkle resistance at the same time; especially Examples 2 to 4 and Example 7 also showed excellent conditions with no color unevenness and no wrinkles. In comparison, the films of Comparative Examples 1 to 10 did not control the hydrophobic double bond ratio of the film in the UV-visible light spectrum to be between 0.500 and 1.300, making it impossible for the films to have excellent dyeing uniformity and wrinkle resistance at the same time. ability.

To sum up, the polyvinyl alcohol film of the present invention has a hydrophobic double bond ratio in the ultraviolet-visible light spectrum: (A _UV280nm +A _UV320nm )/A _UV215nm ranging from 0.500 to 1.300, so it can have both good dyeing uniformity and Resistant to wrinkles.

All ranges provided herein are intended to include each specific range within the given range and every combination of subranges between the given ranges. Furthermore, unless otherwise indicated, all ranges provided herein include the endpoints of the ranges. For example, 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 hereby incorporated 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 any inconsistency between this document and any publication or patent application incorporated by reference, this document shall control.

The terms "includes," "has," and "includes" are used herein in an open, non-limiting sense. The terms "a" and "the" shall be understood to cover 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 operating examples or where otherwise indicated, all numbers expressing quantities of ingredients and/or reaction conditions may in all cases be modified by the term "about" meaning within ±5% of the indicated number. . As used herein, the terms "substantially free" or "substantially free" mean less than about 2% of a specified characteristic. All elements or features affirmatively set forth herein are negligibly excluded from the scope of the claim.

100: Polyvinyl alcohol film preparation system 110:Dissolution barrel 120: T-type slit die lip 130: Casting drum 140:Hot roller 1401: Starting hot roller 140N: Final hot roller 150:Oven 152: The highest temperature zone of the oven 154: The lowest temperature zone of the oven

Figure 1 shows a schematic diagram of the preparation system for manufacturing the polyvinyl alcohol film of the present invention.

without.

100: Polyvinyl alcohol film preparation system

110:Dissolution barrel

120: T-type slit die lip

130: Casting drum

140:Hot roller

1401: Starting hot roller

140N: Final hot roller

150:Oven

152: The highest temperature zone of the oven

154: The lowest temperature zone of the oven

Claims (13)

A polyvinyl alcohol film having a hydrophobic double bond ratio in the ultraviolet-visible light spectrum: (A _UV280nm +A _UV320nm )/A _UV215nm ranging from 0.500 to 1.300; wherein, the spectral absorbance of the polyvinyl alcohol film is at 23°C and Measured after being placed in an environment with 50% relative humidity for 24 hours. Such as the polyvinyl alcohol film of claim 1, which further has an average double bond ratio of ultraviolet light-visible light spectrum: (A _UV215nm *1+A _UV280nm *2+A _UV320nm *3)/(A _UV215nm +A _UV280nm +A _UV320nm ) Between 1.480 and 1.820. The polyvinyl alcohol film of claim 1 further has a weight swelling degree between 38.0 and 48.0 An optical film formed of the polyvinyl alcohol film according to any one of claims 1 to 3. Such as the optical film of claim 4, which is a polarizing film. A method for manufacturing a polyvinyl alcohol film according to any one of claims 1 to 3, including: (a) resin drying process: pouring a completed polymerized polyvinyl alcohol resin into a dryer, and drying Spray water to cool down when drying; (b) dissolution process: heat the dried polyvinyl alcohol resin to dissolve, and adjust the concentration to form a polyvinyl alcohol casting solution; (c) casting process: cast the polyvinyl alcohol casting solution to a casting drum, and then peeled off from the casting drum to obtain a preliminary polyvinyl alcohol film; and (d) drying process: dry the preliminary polyvinyl alcohol film in a plurality of hot rollers and at least two temperature-controlled ovens. The polyvinyl alcohol film is obtained; wherein the initial heat roller among the plurality of heat rollers has the highest temperature among the plurality of heat rollers, and the final heat roller has the lowest temperature among the plurality of heat rollers. The manufacturing method of claim 6, wherein the alkalization degree of the polyvinyl alcohol resin is greater than 99.80 mole%. The manufacturing method of claim 6, wherein the degree of polymerization of the polyvinyl alcohol resin is between 2,300 and 3,000. The manufacturing method of claim 6, wherein the molecular weight of the polyvinyl alcohol resin is between 100,000 and 110,000Mn. For example, claim 6 for the manufacturing method, wherein the speed of the casting drum is between 5.0 and 6.4m/min. The manufacturing method of claim 6, wherein the temperature difference between the initial heat roller and the final heat roller among the plurality of heat rollers is between 20 and 45°C. For example, the manufacturing method of claim 6, wherein the maximum temperature of the oven is between 60 and 120°C. For example, the manufacturing method of claim 6, wherein the minimum temperature of the oven is between 40 and 70°C.