KR20240018339A - Polyvinyl alcohol film, an optical film produced thereby and manufacturing method thereof - Google Patents

Abstract

A polyvinyl alcohol film, an optical film formed therefrom, and a method for manufacturing the same are provided. The present invention relates to a polyvinyl alcohol film, an optical film formed therefrom, and a method for producing the same. The polyvinyl alcohol film has a hydrophobic double bond ratio in the ultraviolet-visible spectrum of (AUV280nm+AUV320nm)/AUV215nm, which is between 0.500 and 1.300. The polyvinyl alcohol film of the present invention can simultaneously provide good dyeing uniformity and wrinkle-resistant properties.

Description

Polyvinyl alcohol film, an optical film produced thereby and manufacturing method thereof}

The present invention relates to a polyvinyl alcohol (PVA) film and a method for producing the same, and the PVA film can be used as an optical film, especially as a polarizing film.

Polyvinyl alcohol (PVA) film is a type of hydrophilic polymer and has properties such as transparency, mechanical strength, water solubility, and good processability, so it is widely used in packaging materials and optical films for electronic products. Polyvinyl alcohol film Silver is an important component in a polarizing plate, and can exhibit polarization characteristics through dyeing and stretching. Since it can control the brightness and darkness by giving polarization to light, it is currently widely used in various liquid crystal screens.

In recent years, while screen technology is becoming thinner, quality requirements for the polarizing film manufacturing process are also gradually increasing. In the process of polarizing films becoming thinner, the degree of emphasis on wrinkle problems and dyeing uniformity of polyvinyl alcohol films is also gradually increasing. It's getting higher.

However, in the prior art, when manufacturing a large-sized polarizing film using a polyvinyl alcohol film, situations such as uneven dyeing of the film or wrinkles occurring during dyeing and stretching of the film frequently occurred.

The present inventors believe that heat treatment can induce the formation of a conjugated double bond of the terminal carbonyl group of polyvinyl alcohol, dehydrate the inside of polyvinyl alcohol to generate -(C=C) _n - bond, and -(C =C) It was discovered that different characteristic peaks of the ultraviolet-visible spectrum (UV-VIS) can be observed depending on the difference in the n value among _n -. For example, in the case of n = 1, the occurrence of a characteristic peak can be observed at 215 nm, in the case of n = 2, the occurrence of a characteristic peak can be observed at 280 nm, and in the case of n = 3, the occurrence of a characteristic peak can be observed at 320 nm. The occurrence of characteristic peaks can be observed. Therefore, if the absorbance of the polyvinyl alcohol film measured by UV-VIS is controlled at 215 nm, 280 nm, and 320 nm, the C=C hydrophobic double bond ratio contained in the polyvinyl alcohol film can be controlled to achieve good dyeing uniformity and wrinkles. It is possible to achieve the formation of a polyvinyl alcohol film that simultaneously possesses these difficult-to-occur properties.

The purpose of the present invention is to provide a polyvinyl alcohol film whose hydrophobic double bond ratio in the ultraviolet-visible spectrum is (AUV280nm+AUV320nm)/AUV215nm and is between 0.500 and 1.300.

In one or more embodiments, the polyvinyl alcohol film further has an average double bond ratio in the ultraviolet-visible spectrum of (AUV215nm*1+AUV280nm*2+AUV320nm*3)/(AUV215nm+AUV280nm+AUV320nm), which is between 1.480 and 1.820.

In one or more embodiments, the polyvinyl alcohol film further has a weight swelling of between 38.0 and 48.0.

Another object of the present invention is to provide an optical film, which is formed from the polyvinyl alcohol film described above.

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

Another object of the present invention is to provide a method for producing the above-described polyvinyl alcohol film, which includes (a) injecting the polyvinyl alcohol-based resin that has completed polymerization into a dryer, and then drying the polyvinyl alcohol-based resin. ) a resin drying step of lowering the temperature, (b) a dissolution step of raising the temperature of the dried polyvinyl alcohol-based resin to dissolve it and further adjusting the concentration to form a polyvinyl alcohol casting solution, (c) polyvinyl alcohol-based resin. A casting process comprising: injecting a vinyl alcohol casting solution into a casting drum and peeling from the casting drum to obtain a polyvinyl alcohol pre-film; (d) controlling the temperature of the polyvinyl alcohol pre-film with a plurality of heating rollers and at least two sections; A drying step of obtaining a polyvinyl alcohol film by drying in a heated oven, wherein among the plurality of heating rollers, the starting heating roller has the highest temperature among the plurality of heating rollers, and the final heating roller has the plurality of heating rollers. It has the lowest temperature among them.

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

In one or more embodiments, the degree of polymerization of the polyvinyl alcohol-based resin is between 2,300 and 3,000.

In one or more embodiments, the molecular weight of the polyvinyl alcohol-based resin is between 100,000 and 110,000 Mn.

In at least one embodiment, the rotational speed of the casting drum is between 5.0 and 6.4 m/min.

In one or more embodiments, among the plurality of heating rollers, the temperature difference between the starting heating roller and the final heating roller is between 20 and 45°C.

In at least one embodiment, the maximum oven speed is between 60 and 120 degrees Celsius.

In one or more embodiments, the minimum oven speed is between 40 and 70 degrees Celsius.

As an effect of the present invention, the polyvinyl alcohol film provided by the present invention can simultaneously have good dyeing uniformity and characteristics that prevent wrinkles from forming.

1 is a conceptual diagram of a preparation system for manufacturing the polyvinyl alcohol film of the present invention.

The following embodiments do not unduly limit the present invention. A person skilled in the art to which the present invention pertains can make modifications and changes to the embodiments examined in this specification without departing from the spirit or scope of the present invention, and all of them fall within the scope of the present invention.

The terms “1” and “type 1” in this specification refer to the existence of one or more (that is, at least one) object of grammar in this specification.

The purpose of the present invention is to provide a polyvinyl alcohol film whose hydrophobic double bond ratio in the ultraviolet-visible spectrum is (AUV280nm+AUV320nm)/AUV215nm and is between 0.500 and 1.300.

Polyvinyl alcohol, upon heat treatment, induces the formation of a conjugated double bond at the terminal carbonyl group of polyvinyl alcohol, and can generate -(C=C)n- bonds inside polyvinyl alcohol by dehydration. Depending on the difference in the value of n in -(C=C)n-, different UV-VIS characteristic peaks can be observed. For example, in the case of n=1, the occurrence of a characteristic peak at 215 nm can be observed. , in the case of n=2, the occurrence of a characteristic peak can be observed at 280 nm, and in the case of n=3, the occurrence of a characteristic peak can be observed at 320 nm. Therefore, the occurrence of different UV-VIS characteristic peaks indicates that adjacent double bonds of different amounts are generated in UV-VIS.

“Value of hydrophobic double bond ratio in ultraviolet-visible spectrum” described in this specification refers to the absorbance of the film under a specific spectrum after leaving the polyvinyl alcohol film in an environment of 23°C and 50% relative humidity for 24 hours. was measured, and the value of the hydrophobic double bond ratio in the ultraviolet-visible spectrum was obtained by (AUV280nm＋AUV320nm)/AUV215nm. Since the different values of the UV characteristic peaks indicate that double bonds of different amounts are occurring adjacent to each other in UV, the value of the hydrophobic double bond ratio in the ultraviolet-visible spectrum is C = C represents the ratio resulting in an apparent hydrophobic state. If the value of the hydrophobic double bond ratio in the ultraviolet-visible spectrum is excessively high, it indicates that the adjacent C=C content in the film is relatively high and the hydrophobic level of the film block is relatively high. Therefore, when the film is stretched in a stretching bath, the iodine solution does not enter the specific block of the film smoothly, and the phenomenon in which the film is dyed unevenly tends to occur. Conversely, if the value of the hydrophobic double bond ratio in the ultraviolet-visible spectrum is excessively low, it indicates that the content of adjacent C=C in the film is relatively small and the absorption rate of the film is too fast. Therefore, when the film is stretched in a dyeing bath, the phenomenon of wrinkles appearing in the swollen polyvinyl alcohol film is likely to occur. According to at least one embodiment, the value of the hydrophobic double bond ratio in the ultraviolet-visible spectrum of the polyvinyl alcohol film is between 0.500 and 1.300, 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, 1.125, 1.150, 1.175, 1.200, 1.225, 1.250, 1.275 Or it is a range between any two values of 1.300, and in this specification, the term “between” includes the values of both end points.

The “average value of the double bond ratio in the ultraviolet-visible spectrum” described in this specification refers to the absorbance of the film under a specific spectrum after leaving the polyvinyl alcohol film in an environment of 23°C and 50% relative humidity for 24 hours. By measurement, the average value of the double bond ratio of the ultraviolet-visible spectrum was obtained by (AUV215nm*1+AUV280nm*2+AUV320nm*3)/(AUV215nm+AUV280nm+AUV320nm). The average value of the double bond ratio in the ultraviolet-visible spectrum represents the average amount of C=C appearing in the polyvinyl alcohol film. If the average value of the double bond ratio in the ultraviolet-visible spectrum is too high, it indicates that the C=C content in the film is relatively high and the hydrophobicity level of the film is relatively high. Therefore, when the film is stretched in a stretching bath, the iodine solution does not smoothly submerge into specific blocks of the film, and the phenomenon in which the film is dyed unevenly tends to occur. Conversely, if the average value of the double bond ratio in the ultraviolet-visible spectrum is too low, it indicates that the C=C content in the film is relatively low and the absorption rate during swelling of the film is too fast. Therefore, when the film is stretched in a dyeing bath, the phenomenon of wrinkling is likely to occur. According to at least one embodiment, the average value of the double bond ratio in the ultraviolet-visible spectrum of the polyvinyl alcohol film is between 1.480 and 1.820, for example, 1.480, 1.500, 1.520, 1.540, 1.560, 1.580, 1.600, It is the range between any two values of 1.620, 1.640, 1.660, 1.680, 1.700, 1.720, 1.740, 1.760, 1.780, 1.800 or 1.820. In this specification, the term “between” includes the values of both end points. do.

The “weight swelling degree” described in this specification refers to the degree obtained by immersing water in the polyvinyl alcohol film. When measuring the weight swelling degree of a polyvinyl alcohol film, the plasticizer and additives contained therein precipitate and moisture remains in the film. Therefore, when the weight swelling degree of the polyvinyl alcohol film is relatively low, the film shows a slightly poor degree of water immersion into the film. That is, the film is slightly hydrophobic, and a phenomenon in which the dyeing of the polyvinyl alcohol film becomes non-uniform is likely to occur. On the other hand, when the weight swelling degree of the film is relatively high, the film shows a relatively high degree of water immersion into the film. That is, the film is slightly hydrophilic, and it becomes easy for the polyvinyl alcohol film to wrinkle. The weight swelling degree is determined by leaving a polyvinyl alcohol film in an environment of 23°C and 50% relative humidity for 24 hours, placing the film in water to swell it, taking it out, wiping off the surface moisture, and measuring the weight of the film as M1. Then, the film was dried in an oven, the weight of the weighed film was set to M2, and it was obtained by (M1-M2)/M1*100%. According to at least one embodiment, the weight swelling degree of the polyvinyl alcohol film is between 38.0 and 48.0, 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. In this specification, the term "between" includes the values of both end points.

In another form, the present invention also provides a method for producing the above-described polyvinyl alcohol film, which includes (a) injecting the polyvinyl alcohol-based resin that has completed polymerization into a dryer, and then pouring water during drying; a resin drying step of lowering the temperature; (b) a dissolution step of raising the temperature of the polyvinyl alcohol-based resin to dissolve it, further adjusting the concentration of the polyvinyl alcohol-based resin, and forming a polyvinyl alcohol casting solution; (c) A casting process comprising: injecting a polyvinyl alcohol casting solution into a casting drum and peeling from the casting drum to obtain a polyvinyl alcohol prefilm; A drying step of obtaining a polyvinyl alcohol film by drying in a controlled oven, wherein among the plurality of heating rollers, the starting heating roller has the highest temperature among the plurality of heating rollers, and the final heating roller has the plurality of heating rollers. It has the lowest temperature among the rollers, and the difference between the highest and lowest temperature heating rollers is controlled within a certain range, and at the same time, the highest and lowest temperatures of the oven are controlled.

Below, please refer to Figure 1. Figure 1 does not limit the number of heating rollers or the number of sections of the dryer, but is merely a help to clearly illustrate the specification, and does not indicate the number of heating rollers or the number of sections of the dryer that can actually be used. According to at least one embodiment, in the above-mentioned resin drying process, the polyvinyl alcohol-based resin that has completed polymerization is injected into a dryer, and the temperature is lowered by appropriately watering during high-temperature drying. According to at least one embodiment, the temperature of the dryer is preferably 80°C to 130°C, specifically 80°C, 90°C, 100°C, 110°C, 120°C, and 130°C.

According to at least one embodiment, the above-described dissolution process involves heating 1,800 kg of dried polyvinyl alcohol-based resin, 4,000 kg of water, and 200 kg of glycerin as a plasticizer to 140°C while stirring in the dissolution tank 110. , dissolve for at least 180 minutes while maintaining the temperature at at least 140°C, further mix the polyvinyl alcohol-based resin aqueous solution uniformly using a mixer, and then add water to increase the concentration of the polyvinyl alcohol-based resin aqueous solution to 30.0% to 50.0%. This means that by adjusting to , a polyvinyl alcohol casting solution is obtained. According to at least one embodiment, the dissolution temperature in the polyvinyl alcohol-based resin aqueous solution is preferably at least 120°C, specifically, for example, at least 120°C, at least 130°C, at least 140°C, and at least 150°C. Or at least 160°C. According to at least one embodiment, the dissolution time of the polyvinyl alcohol-based resin is preferably at least 180 minutes, and specifically, for example, at least 180 minutes, at least 190 minutes, at least 200 minutes, at least 210 minutes, at least 220 minutes. minutes, at least 230 minutes, or at least 240 minutes, etc. According to at least one example, the concentration of the polyvinyl alcohol-based resin aqueous solution is preferably 30.0% to 50.0%, specifically, for example, 30.0%, 35.0%, 40.0%, 45.0%, or 50.0%. According to at least one example, the polyvinyl alcohol-based resin is obtained by polymerizing vinyl ester-based resin monomers to form a polyvinyl ester-based resin and then performing a saponification reaction. Among them, vinyl ester resin monomers include vinyl esters such as vinyl formic acid, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl pentanoate, or vinyl octanoate, but the present invention is not limited to these. Additionally, a copolymer formed by copolymerizing an olefin compound or acrylate derivative with the vinyl ester resin monomer described above can also be used. Among them, olefin compounds include ethylene, propylene, or butylene, but the present invention is not limited to these. Acrylate derivatives include acrylic acid, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, or n-butyl acrylate, but the present invention is not limited to these. According to at least one embodiment, the alkalinization degree of the polyvinyl alcohol-based resin is suitably greater than 99.80 mole%, and this allows good optical properties to be obtained, for example, greater than 99.80 mole%, 99.90 mole%. exceeds or exceeds 99.99 mole%. According to at least one embodiment, the degree of polymerization of the polyvinyl alcohol-based resin is between 2,300 and 3,000, specifically, for example, any of 2,300, 2,400, 2,500, 2,600, 2,700, 2,800, 2,900, or 3,000. It is a range between two numerical values, and in this specification, the term “between” includes the numerical values of both end points. According to at least one embodiment, the molecular weight of the polyvinyl alcohol-based resin is between 100,000 and 110,000 Mn, specifically, for example, 100,000 Mn, 102,000 Mn, 104,000 Mn, 106,000 Mn, 108,000 Mn, or 110,000 Mn. It is the range between any two numerical values, and in this specification, the term "between" includes the numerical values of both end points.

Although the inventor is not limited to a specific theory, the presence or absence of a fractional temperature drop when drying a polyvinyl alcohol-based resin in a dryer, the temperature difference between heating rollers, the highest temperature of the oven, the lowest temperature of the oven, or It was discovered that the speed of rotation of the casting drum affects the degree of drying of the film, and that this affects the dyeing and wrinkling of the film. If, when drying a polyvinyl alcohol-based resin with a dryer, the temperature does not drop by a fraction, the temperature difference between heating rollers is excessively small, the maximum temperature of the oven is excessively high, and the minimum temperature of the oven is excessively high, or If the rotation speed of the casting drum is too slow, the film dries excessively and the formation of adjacent C=C hydrophobic double bonds increases excessively, which causes the problem of uneven dyeing in the film. . Additionally, if the temperature difference between the heating rollers is excessively large, the maximum temperature of the oven is too low, the minimum temperature of the oven is too low, or the rotation speed of the casting drum is too fast, the film will not dry completely; The amount of adjacent C=C hydrophobic double bonds generated becomes excessively small, which causes wrinkles to form in the film.

According to at least one embodiment, the above-described casting process is performed by removing bubbles from the polyvinyl alcohol casting solution using a twin-screw extruder, discharging it from the T-shaped slit die lip 120, and extruding the polyvinyl alcohol casting solution from a high-temperature rotating casting drum ( 130) is curtain-coated and dried to obtain a polyvinyl alcohol preliminary film. When performing the casting process, if the rotation speed of the casting drum 130 is too slow, the film dries excessively, and the generation of adjacent C=C hydrophobic double bonds becomes excessive, which causes uneven dyeing in the film. It will cause problems. Conversely, if the rotation speed of the casting drum 130 is too fast, the film is not completely dried, and the amount of adjacent C=C hydrophobic double bonds generated is excessively small, which causes wrinkles to form in the film. According to at least one embodiment, the rotational speed of the casting drum 130 is between 5.0 and 6.4 m/min, specifically, for example, 5.0 m/min, 5.05 m/min, 5.1 m/min, and 5.15 m/min. m/min, 5.2m/min, 5.25m/min, 5.3m/min, 5.35m/min, 5.4m/min, 5.45m/min, 5.5m/min, 5.55m/min, 5.6m/min, 5.65 m/min, 5.7m/min, 5.75m/min, 5.8m/min, 5.85m/min, 5.9m/min, 5.95m/min, 6.0m/min, 6.05m/min, 6.1m/min, 6.15 It is the range between any two values, such as m/min, 6.2m/min, 6.25m/min, 6.3m/min, 6.35m/min, or 6.4m/min, and is referred to as "between" in this specification. The term includes numerical values of both endpoints.

According to at least one embodiment, the above-described drying process includes peeling the polyvinyl alcohol preliminary film from the casting drum 130, drying both the upper and lower sides by contacting a plurality of heating rollers 140, and then drying the polyvinyl alcohol preliminary film in an oven ( 150), the upper and lower sides of the polyvinyl alcohol preliminary film are dried with hot air to obtain a polyvinyl alcohol film. According to at least one embodiment, the plurality of heating rollers 140 may be 2 to 30, but is not limited to, for example, 2, 3, 4, 5, 6, 7, or 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 one preferred embodiment, there are 13.

According to at least one embodiment, when drying the film, the temperature of the plurality of heating rollers 140 is gradually lowered from high temperature to low temperature. If the temperature difference between the heating rollers 140 is excessively small, the film dries excessively, causing excessive formation of adjacent C=C hydrophobic double bonds, which causes the problem of uneven dyeing in the film. It becomes Conversely, if the temperature difference between the heating rollers 140 is excessively large, the film is not completely dried, and the amount of adjacent C=C hydrophobic double bonds generated is excessively small, which causes wrinkles to form in the film. Therefore, it is necessary to control the temperature difference between the highest and lowest temperatures of the heating roller within a specific range. According to at least one embodiment, among the plurality of heating rollers 140, the starting heating roller 1401 has the highest temperature among all the heating rollers 140, and the temperature of the subsequent heating rollers 140 is the final heating roller 140. The temperature of the heating roller 140 N is gradually lowered to the lowest temperature among all the heating rollers 140. According to at least one embodiment, among the plurality of heating rollers 140, the temperature difference between the starting heating roller 1401 and the final heating roller 140N is between 20 and 45 ° C., specifically, for example, 20 ° C. , 25°C, 30°C, 35°C, 40°C, or 45°C, etc., and the term “between” in this specification includes the values of both end points.

The oven 150 used to dry the film has a drying area of multiple sections, and the temperature of each section can be partially the same or all different. Among them, the section close to the center of the oven 150 has the highest temperature, the highest temperature area of the oven 150 is 152, and the temperature of the section farther from the center of the oven 150 is that of the last section, the oven 150. The lowest temperature is gradually falling to area 154. If the maximum temperature of the highest temperature area 152 of the oven is excessively high or the temperature of the lowest temperature area 154 of the oven is excessively high, the film will be excessively dry and the formation of adjacent C=C hydrophobic double bonds will be excessive. This causes the problem of uneven dyeing in the film. Conversely, if the highest temperature of the highest temperature area 152 of the oven is excessively low or the lowest temperature of the lowest temperature area 154 of the oven is excessively low, the film will not be completely dried, and the amount of adjacent C=C hydrophobic double bonds generated will be reduced. If it is too small, wrinkles will appear in the film. Therefore, it is necessary to control the highest and lowest temperatures of the highest temperature area 152 and the lowest temperature area 154 of the oven.

According to at least one embodiment, the number of sections of the oven may be 2 to 10 sections, specifically, for example, 2 sections, 3 sections, 4 sections, 5 sections, 6 sections, 7 sections, 8 sections, and 9 sections. or 10 sections, and in one preferred embodiment 4 sections. According to at least one embodiment, the highest temperature of the highest temperature area 152 of the oven is between 60 and 120°C, specifically, for example, 60°C, 70°C, 80°C, 90°C, 100°C, and 110°C. Or it is a range between any two values, such as 120°C, and in this specification, the term “between” includes the values of both end points. According to at least one embodiment, the minimum temperature of the lowest temperature area 154 of the oven is between 40 and 70°C, specifically, for example, any two of 40°C, 50°C, 60°C, or 70°C. It is a range between two numerical values, and in this specification, the term “between” includes the numerical values of both end points. According to at least one embodiment, the oven 150 may be, for example, but is not limited to a floating dryer.

As another aspect, the polyvinyl alcohol film of the present invention can also be manufactured as an optical film. The "optical film" described in this specification refers to a polarizing film, blue light cut film, filter lens, etc., but the present invention is not limited to these. Very suitably, the polyvinyl alcohol film of the present invention is made into a polarizing film.

Among preferred embodiments, a polarizing film (or polarizing plate) manufacturing method includes the following steps. A polarizing film can be obtained by swelling, dyeing, stretching, complementary coloring, drying, and adhering a polyvinyl alcohol film to a triacetylcellulose film (TAC).

When polyvinyl alcohol films are further used in the production of optical films, stretching and dyeing are performed. Taking polarizing films as an example, in the production process of polarizing films, polyvinyl alcohol is prepared with an aqueous solution of boric acid containing I3-, I5-iodide ions. Because the alcohol film is dyed, after the boric acid causes a cross-linking effect with the amorphous area of polyvinyl alcohol, the iodide ions are fixed and the elution of the iodide ions can be prevented.

(Example)

Below, the present invention will be described in more detail in conjunction with examples. However, please understand that such examples are intended to help the present invention be more easily understood and do not limit the scope of the present invention.

Production of polyvinyl alcohol film: First, a polyvinyl alcohol-based PVA resin that has completed polymerization and has a degree of polymerization of about 2400 is injected into a dryer, and when dried at high temperature, the temperature is lowered at the right time, and then dried. The polyvinyl alcohol-based resin that has gone through the process is heated and dissolved in a dissolution tank to form a polyvinyl alcohol solution, and then the polyvinyl alcohol solution is extruded through a T-slit die lip and a casting drum, and the polyvinyl alcohol solution is passed through a plurality of heating rolls. After forming the solution into a film and adjusting the moisture, the polyvinyl alcohol film-forming sample was dried in an oven to obtain a polyvinyl alcohol film.

The manufacturing process of the above-described polyvinyl alcohol film is specifically, for example, first, a polyvinyl alcohol-based resin that has completed polymerization and has an alkalinization degree of >99.9% and a polymerization degree of about 2400 is injected into a dryer, and further inside the dryer. The temperature is controlled to 110°C, and the temperature of the polyvinyl alcohol-based resin is lowered by watering at the right time during the drying process. Next, add 1800 kg of dried polyvinyl alcohol resin, 4000 kg of water, and 200 kg of glycerin as a plasticizer to the dissolution tank, raise the temperature to 140°C while stirring, and dissolve for 180 minutes while maintaining the temperature at 140°C. Dissolve uniformly using a mixer. Then, water is added to adjust the resin concentration to 30.0%, and a film forming stock solution is obtained. The raw film forming solution is discharged from the lip of a T-slit die after removing bubbles with a twin-screw extruder, and then curtain-coated on a rotating high-temperature casting drum to form a dry film. At this time, the rotation speed of the casting drum is 5.4 m/min. do. After the preformed film is peeled from the casting drum, the upper and lower sides of the film are dried by contacting 13 heating rollers. Among them, the first heating roller is set to the highest temperature among all the heating rollers, and the temperature of the subsequent heating rollers is adjusted to gradually decrease. At this time, the temperature difference between the first heating roller and the thirteenth heating roller (the lowest temperature among all heating rollers) is set to 45°C. Next, using an oven equipped with four sections of drying area, both the upper and lower sides of the film are dried with hot air. Among them, the temperature of the highest temperature area of the oven is set to 100°C, and the temperature of the lowest temperature area is set to 50°C. At the end, the finished product of polyvinyl alcohol film is obtained. Each Example and Comparative Example in this specification differs from the above-described process in one or more parameters. Details are shown in the table below.

Manufacture of polarizing film: A polyvinyl alcohol film is immersed in water at 30°C to swell, and then uniaxially stretched to 2.0 times the original length in the machine direction (MD), followed by adding 0.03 mass percent of iodine and 3 mass percent of iodine. The polyvinyl alcohol film was stretched to 3.3 times its original length while being immersed in an aqueous solution at 30°C containing potassium iodide, and then immersed in an aqueous solution at 30°C containing 3% by mass of potassium iodide and 3% by mass of boric acid. , it is further stretched to 3.6 times the original length. Subsequently, it is immersed in an aqueous solution at 60°C containing 5% by mass of potassium iodide and 4% by mass of boric acid, and further stretched to 6.0 times the original length. After that, a polarizing film can be obtained by immersing it in a 3 mass percent potassium iodide aqueous solution for 15 seconds and then drying it at 60°C for 4 minutes.

Hereinafter, control of variables in the experiments of Examples 1 to 10 in Tables 1 and 2, technical characteristics, dyeing uniformity and wrinkle measurement results, and variables in the experiments of Comparative Examples 1 to 10 in Tables 3 and 4. Please refer to the controls, technical features, dyeing uniformity and wrinkle measurement results of the film.

item Presence or absence of water droplets in the PVA resin in the dryer Maximum temperature difference of heating roller (℃) Maximum temperature of oven (℃) Minimum temperature of oven (℃) Rotation speed of casting drum (m/min) -(C=C) n-hydrophobic double bond ratio -(C=C) n-double bond average number Example 1 you 45 60 50 5.4 0.692 1.612 Example 2 you 45 80 50 5.4 0.742 1.622 Example 3 you 45 100 50 5.4 0.839 1.648 Example 4 you 45 120 50 5.4 0.872 1.664 Example 5 you 30 120 50 5.4 0.977 1.714 Example 6 you 20 120 50 5.4 1.197 1.795 Example 7 you 45 100 50 5.7 0.795 1.644 Example 8 you 45 100 50 6.3 0.565 1.519 Example 9 you 30 120 70 5.0 1.298 1.816 Example 10 you 45 100 40 6.0 0.505 1.484

item Weight swelling (wt%) PVA saponification 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 2 is a continuation of Table 1)

item Presence or absence of water droplets in the PVA resin in the dryer Maximum temperature difference of heating roller (℃) Maximum temperature of oven (℃) Minimum temperature of oven (℃) Rotation speed of casting drum (m/min) -(C=C) n-hydrophobic double bond ratio -(C=C) n-double bond average number Comparative Example 1 you 55 80 50 6.3 0.442 1.435 Comparative example 2 you 55 60 50 6.0 0.490 1.474 Comparative Example 3 you 10 120 50 5.4 1.385 1.825 Comparative example 4 you 30 150 50 5.4 1.412 1.847 Comparative Example 5 you 45 50 50 5.4 0.396 1.408 Comparative Example 6 you 45 100 50 4.0 1.348 1.822 Comparative example 7 you 45 100 50 6.6 0.483 1.461 Comparative example 8 you 30 120 80 5.0 1.502 1.865 Comparative Example 9 you 45 80 30 5.4 0.485 1.471 Comparative Example 10 radish 30 120 50 5.4 1.371 1.833

item Weight swelling (wt%) PVA saponification 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 ◎

(Table 4 is a continuation of Table 3)

The analysis method used during this experiment is as follows.

Analysis of the value of hydrophobic double bond ratio in the ultraviolet-visible spectrum

Sample preparation method: Divide the polyvinyl alcohol film into 5 pieces in the width direction, 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 store in a constant temperature and humidity chamber at 23°C and 50% relative humidity. was left for 24 hours.

Analysis instrument: Film samples were analyzed using Perkin Elmer Lambda 365 (wavelength precision and wavelength reproducibility conform to the standards of NIST 2034).

Measurement conditions: In an environment of 23°C and 50% relative humidity, the absorbance at 200 to 700 nm of the film sample after completion of constant temperature and humidity was measured, and the absorbance values at 215 nm, 280 nm and 320 nm were read.

Data conversion: Substitute the absorbance values of the film sample read at 215nm, 280nm, and 320nm into the formula for calculating the hydrophobic double bond ratio in the ultraviolet-visible spectrum (AUV280nm＋AUV320nm)/AUV215nm, and calculate the hydrophobic double bond ratio of the film sample. After obtaining the values, the average of the values of the hydrophobic double bond ratio of the five pieces obtained by measuring along the width direction was finally obtained.

Analysis of the average value of the double bond ratio in the ultraviolet-visible spectrum

Sample preparation method: Divide the polyvinyl alcohol film into 5 pieces in the width direction, 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 store in a constant temperature and humidity chamber at 23°C and 50% relative humidity. was left for 24 hours.

Analysis instrument: Film samples were analyzed using Perkin Elmer Lambda 365 (wavelength precision and wavelength reproducibility conform to the standards of NIST 2034).

Measurement conditions: Under an environment of 23°C and 50% relative humidity, the absorbance at 200 to 700 nm of the film sample after completion of constant temperature and humidity was measured, and the absorbance values at 215 nm, 280 nm, and 320 nm were read. .

Data conversion: Substitute the absorbance values of the film sample read at 215nm, 280nm, and 320nm into the formula (AUV215nm*1+AUV280nm*2+AUV320nm*3)/(AUV215nm+AUV280nm+AUV320nm) that requires the average value of the double bond ratio of the ultraviolet-visible spectrum. After obtaining the average value of the double bond ratio of the film sample, the average value of the double bond ratio of the five pieces obtained by measuring along the width direction was finally averaged.

Analysis of weight swelling degree

Sample preparation method: Divide the polyvinyl alcohol film into 5 pieces in the width direction, 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 store in a constant temperature and humidity chamber at 23°C and 50% relative humidity. was left unattended for 24 hours.

Measurement conditions: Place the polyvinyl alcohol film sample in pure water at 30°C and allow it to swell for 20 minutes. After the swelling of the film sample is completed, take it out, wipe off the moisture on the surface of the film sample with a tissue, and then weigh the weight M1 of the film (稱). Then, the film sample was placed in a dryer at 120°C and dried for 120 minutes, and then the weight M2 of the film was measured.

Data conversion: Substitute the film weight M1 and M2 of the weighed film sample into (M1-M2)/M1*100%, obtain the weight swelling degree of the film sample, and finally measure the weight of the film sample along the width direction to obtain the 5 pieces. The average weight swelling degree was obtained.

Performance analysis on film color uniformity

A polyvinyl alcohol film was prepared as a polarizing film, irradiated using a lamp house with a luminous flux divergence = 14000 lx, and the color uniformity of the film was observed and evaluated. Evaluation of the color uniformity of the film is as follows.

◎: Color unevenness is not visible.

O: Slightly uneven color

X: Significant color unevenness

Performance analysis on wrinkles

A polyvinyl alcohol film was prepared as a polarizing film, cut into samples of 5 cm in the width direction and 20 cm in the length direction, the samples were fixed to the stretching jig with the jig spaced at 5 cm intervals, and then stretched in a water bath using a stretching machine for the polarizing film process. After stretching in water until the sample becomes twice the original length (i.e. 10 cm), it is immediately pulled out of the water bath, and at a position 1 m away from the front of the film, the surface of the sample film is visually inspected. Evaluation was made by observing the state of wrinkles. Evaluation of the wrinkles of the film is as follows.

◎: No wrinkles

O: Some wrinkles are visible

X: Significant wrinkles

According to Tables 1 and 2, the films of Examples 1 to 10 have hydrophobic double bond ratio values in the ultraviolet-visible spectrum between 0.500 and 1.300, so such films simultaneously exhibit excellent dyeing uniformity and wrinkle resistance. In particular, Examples 2 to 4 and Example 7 showed extremely good conditions, with no color unevenness and no wrinkles. On the other hand, in the films of Comparative Examples 1 to 10, since the value of the hydrophobic double bond ratio in the ultraviolet-visible spectrum of the film is not controlled between 0.500 and 1.300, such films do not exhibit excellent dyeing uniformity and wrinkle resistance at the same time. I couldn't.

In summary, the polyvinyl alcohol film of the present invention has a hydrophobic double bond ratio in the ultraviolet-visible spectrum (AUV280nm + AUV320nm)/AUV215nm, which is between 0.500 and 1.300, so it has good dyeing uniformity and wrinkle-resistant properties at the same time. It can be provided.

All ranges provided in this specification are meant to include each specific range within the allocated range and a combination of secondary ranges between the allocated ranges. Additionally, unless otherwise specified, all ranges provided in this specification include the endpoints of the range. For example, the range 1 to 5 specifically includes 1, 2, 3, 4 and 5, but also includes secondary ranges such as 2 to 5, 3 to 5, 2 to 3, 2 to 4, 1 to 4, etc. do.

All publications and patent applications referred to in this specification are hereby incorporated by reference, and for all purposes, each publication or patent application is specifically and individually indicated to be incorporated by reference. In case of any inconsistency between this specification and any publications or patent applications incorporated herein by reference, this specification shall govern.

The terms “include,” “have,” and “include” used in this specification have an open and non-limiting meaning. It is natural that the terms “1” and “corresponding” are understood to include plural and singular numbers. The term “one or more” refers to “at least one” and therefore refers to a single characteristic or a mixture/combination. Characteristics may be included.

Except in the operating examples or where otherwise indicated, all numbers representing the amounts of components and/or reaction conditions can in all cases be modified using the term “about”, and can be modified by ± This means within 5%. As used herein, the terms “basically does not contain” or “substantially does not contain” mean that the specific characteristic is less than about 2%. Any element or characteristic clearly described in this specification may be negatively excluded from the scope of the patent claims.

100: Preparation system of polyvinyl alcohol film
110: dissolution tank 120: T-type slit die lip
130: casting drum 140: heating roller
1401: Start heating roller 140N: Final heating roller
150: dryer
152: Highest temperature area of dryer
154: Lowest temperature area of dryer

Claims (13)

A polyvinyl alcohol film whose hydrophobic double bond ratio in the ultraviolet-visible spectrum is (AUV280nm+AUV320nm)/AUV215nm and is between 0.500 and 1.300. According to claim 1,
Moreover, the average value of the double bond ratio of the ultraviolet-visible spectrum is (AUV215nm*1+AUV280nm*2+AUV320nm*3)/(AUV215nm+AUV280nm+AUV320nm) and is between 1.480 and 1.820, a polyvinyl alcohol film. According to claim 1,
A polyvinyl alcohol film further having a weight swelling degree of 38.0 to 48.0. An optical film formed by the polyvinyl alcohol film of any one of claims 1 to 3. According to claim 4,
Optical film, which is a polarizing film. (a) a resin drying process in which the polyvinyl alcohol-based resin that has completed polymerization is injected into a dryer and the temperature is lowered by pouring water during drying;
(b) a dissolution step of dissolving the dried polyvinyl alcohol resin by raising the temperature and adjusting the concentration to form a polyvinyl alcohol casting solution;
(c) a casting process of injecting the polyvinyl alcohol casting solution into a casting drum and peeling from the casting drum to obtain a polyvinyl alcohol preliminary film;
(d) drying the polyvinyl alcohol pre-film in a temperature-controlled oven of at least two sections with a plurality of heated rollers to obtain a polyvinyl alcohol film,
Among the plurality of heating rollers, the starting heating roller has the highest temperature among the plurality of heating rollers, and the final heating roller has the lowest temperature among the plurality of heating rollers.
A method for producing the polyvinyl alcohol film of any one of claims 1 to 3. According to claim 6,
A manufacturing method wherein the alkalization degree of the polyvinyl alcohol-based resin is greater than 99.80 mole%. According to claim 6,
A manufacturing method wherein the degree of polymerization of the polyvinyl alcohol-based resin is between 2,300 and 3,000. According to claim 6,
A manufacturing method wherein the molecular weight of the polyvinyl alcohol-based resin is between 100,000 and 110,000 Mn. According to claim 6,
A manufacturing method wherein the rotational speed of the casting drum is between 5.0 and 6.4 m/min. According to claim 6,
A manufacturing method wherein, among the plurality of heating rollers, the temperature difference between the starting heating roller and the final heating roller is between 20 and 45°C. According to claim 6,
A manufacturing method wherein the maximum temperature of the oven is between 60 and 120°C. According to claim 6,
A manufacturing method wherein the minimum temperature of the oven is between 40 and 70°C.