CN117534930A

CN117534930A - Polyvinyl alcohol film, optical film produced therefrom and process for producing the same

Info

Publication number: CN117534930A
Application number: CN202210920210.7A
Authority: CN
Inventors: 巫诚恩
Original assignee: Chang Chun Petrochemical Co Ltd
Current assignee: Chang Chun Petrochemical Co Ltd
Priority date: 2022-08-02
Filing date: 2022-08-02
Publication date: 2024-02-09

Abstract

The invention relates to a polyvinyl alcohol film, an optical film formed by the polyvinyl alcohol film and a preparation method thereof. The polyvinyl alcohol film has an ultraviolet-visible spectrum hydrophobic double bond ratio: (A) _UV280nm +A _UV320nm )/A _UV215nm Between 0.500 and 1.300. The polyvinyl alcohol film provided by the invention has the characteristics of good dyeing uniformity and difficult crease generation.

Description

Polyvinyl alcohol film, optical film produced therefrom and process for producing the same

Technical Field

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

Background

Polyvinyl alcohol (polyvinyl alcohol, PVA) film is a hydrophilic polymer having transparency, mechanical strength, water solubility, processability, etc., and thus has been widely used in packaging materials or optical films for electronic products. The polyvinyl alcohol film is an important component in the polarizing plate, and can show the polarizing characteristic after being dyed and extended, so that the light has the polarizing property to control the brightness, and is widely applied to various liquid crystal screens nowadays.

In recent years, as the screen technology advances toward thinner polarizing films, the quality requirements for the polarizing film process are increasing, and the importance of the wrinkling problem and the dyeing uniformity of the polyvinyl alcohol film is increasing during the polarizing film thinning process.

Disclosure of Invention

However, when a polyvinyl alcohol film is used to prepare a polarizing film of a large size in the prior art, uneven dyeing of the film or wrinkling of the film during dyeing and stretching still often occurs.

The inventors of the present invention have found that heat treatment can induce formation of conjugated double bonds of terminal Carbonyl groups (carboyl groups) of polyvinyl alcohol, and dehydrate the polyvinyl alcohol internally to give- (c=c) _n Bonding according to- (c=c) _n Different ultraviolet-visible spectrum (UV-VIS) characteristic peaks can be observed for different values of n, for example, the generation of characteristic peaks at 215nm can be observed when n=1; the generation of characteristic peaks at 280nm can be observed when n=2; the generation of a characteristic peak at 320nm was observed when n=3. Therefore, the absorbance of the polyvinyl alcohol film at 215nm, 280nm and 320nm can be measured by controlling the UV-VIS, so that the C=C hydrophobic double bond ratio contained in the polyvinyl alcohol film can be regulated and controlled, and the polyvinyl alcohol film which has good dyeing uniformity and is not easy to generate wrinkles can be formed.

Accordingly, it is an object of the present invention to provide a polyvinyl alcohol film having a hydrophobic double bond ratio of the ultraviolet-visible spectrum: (A) _UV280nm +A _UV320nm )/A _UV215nm Between 0.500 and 1.300.

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

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

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

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

Still another object of the present invention is to provide a method for producing the polyvinyl alcohol film, comprising: (a) a resin drying process: pumping the polymerized polyvinyl alcohol resin into a dryer, and spraying water to cool down when drying; (b) dissolution process: heating and dissolving the dried polyvinyl alcohol resin, and adjusting the concentration to form a polyvinyl alcohol casting solution; (c) a casting process: casting the polyvinyl alcohol casting solution to a casting drum, and stripping the polyvinyl alcohol casting solution from the casting drum to obtain a polyvinyl alcohol primary film; and (d) a drying process: drying the polyvinyl alcohol primary film in a plurality of hot rollers and at least two temperature-controlled ovens to obtain the polyvinyl alcohol film; wherein a starting hot roller of the plurality of hot rollers has a highest temperature of the plurality of hot rollers and a final hot roller has a lowest temperature of the plurality of hot rollers.

In one or more embodiments, the polyvinyl alcohol resin has a basicity of greater than 99.80 mole percent.

In one or more embodiments, the polyvinyl alcohol resin has a degree of polymerization of 2300 to 3000.

In one or more embodiments, the polyvinyl alcohol resin has a molecular weight of 100000 to 110000Mn.

In one or more embodiments, the casting drum is operated at a speed of between 5.0 and 6.4 meters/minute.

In one or more embodiments, the temperature difference between the initial hot roller and the final hot roller of the plurality of hot rollers is between 20 and 45 ℃.

In one or more embodiments, the oven has a maximum temperature of between 60 and 120 ℃.

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

The polyvinyl alcohol film provided by the invention has the advantages of good dyeing uniformity and difficult crease generation.

Drawings

FIG. 1 is a schematic view showing a production system for producing a polyvinyl alcohol film of the invention.

Detailed Description

The following embodiments should not be construed as unduly limiting the invention. Modifications and variations of the embodiments discussed herein may be made by those skilled in the art without departing from the spirit or scope of the invention, and remain within the scope of the invention.

The terms "a" and "an" herein mean that there is one or more than one (i.e., at least one) of the grammatical object herein.

The object of the present invention is to provide a polyvinyl alcohol film having a hydrophobic double bond ratio of ultraviolet-visible spectrum: (A) _UV280nm +A _UV320nm )/A _UV215nm Between 0.500 and 1.300.

When the polyvinyl alcohol is heat treated, carbonyl groups (Carbonyl groups) at the tail end of the polyvinyl alcohol are induced to form conjugated double bonds, so that- (C=C) is generated in the polyvinyl alcohol due to dehydration _n -bonding. According to- (c=c) _n Different values of n in, different UV-VIS characteristic peaks can be observed, for example: when n=1, the generation of characteristic peaks can be observed at 215 nm; when n=2, the generation of characteristic peaks can be observed at 280 nm; when n=3, the generation of characteristic peaks can be observed at 320nm, and thus the generation of different UV-VIS characteristic peaks represents different adjacent amounts of UV-VIS double bond generation.

As used herein, the term "UV-visible spectrum hydrophobic double bond ratio" refers to the absorbance of a polyvinyl alcohol film at 23℃and 50% relative humidity after being left for 24 hours, which is measured at a specific spectrum and is calculated according to the following UV-visible spectrum hydrophobic double bond ratio (A _UV280nm +A _UV320nm )/A _UV215nm Obtained. Since the values of the different UV characteristic peaks represent the generation of different adjacent amounts of UV double bonds, the ratio of hydrophobic double bonds in the UV-visible spectrum symbolizes the proportion of the polyvinyl alcohol film where c=c causes a pronounced hydrophobic condition. When the ratio of the hydrophobic double bonds of the ultraviolet light spectrum to the visible light spectrum is too high, the adjacent C=C content in the film is more, and the hydrophobic degree of the film block is higher, so that iodine liquid cannot smoothly enter a specific block of the film when the film is stretched in a stretching groove, and the phenomenon of uneven film dyeing is easy to occur; whereas when the ultraviolet-visible spectrum is hydrophobic double bondWhen the ratio is too low, the adjacent c=c content in the film is small, and the water absorption speed of the film is too high, so that when the film is stretched in a dyeing tank, the swelling polyvinyl alcohol film is easy to wrinkle. According to at least one embodiment, the polyvinyl alcohol film has an ultraviolet-to-visible spectrum hydrophobic double bond ratio ranging from 0.500 to 1.300, such as 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, 1.125, 1.150, 1.175, 1.200, 1.225, 1.250, 1.275, or 1.300, and the term "between" herein encompasses both end point values.

As used herein, the term "average double bond ratio of UV-visible spectrum" refers to the absorbance of a polyvinyl alcohol film at 23℃and 50% relative humidity for 24 hours, measured at a specific spectrum, and measured 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 ) Obtained. The average double bond ratio in the uv-vis spectrum symbolizes the average of the amount of c=c present in the polyvinyl alcohol film. When the average double bond ratio of the ultraviolet light spectrum to the visible light spectrum is too high, the content of C=C in the film is more, and the overall hydrophobicity degree of the film is higher, so that iodine liquid cannot smoothly enter a specific area of the film when the film is stretched in a stretching groove, and uneven dyeing of the film is easy to occur; on the contrary, when the average double bond ratio of the ultraviolet light spectrum to the visible light spectrum is too low, the content of C=C in the film is small, and the water absorption speed of the film is too high when the film swells, so that the film is easy to generate the phenomenon of wrinkling when the film is stretched in a dyeing tank. According to at least one embodiment, the polyvinyl alcohol film has an ultraviolet-to-visible spectrum average double bond ratio ranging from 1.480 to 1.820, such as 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 are herein termed"between" includes two end values.

As used herein, "weight swell" refers to the degree to which a polyvinyl alcohol film can allow water to enter the film. When the polyvinyl alcohol film is tested for its weight swell, the plasticizers and additives contained therein are precipitated and only water remains in the film. Therefore, when the weight swelling degree of the polyvinyl alcohol film is low, the film has poor water entering into the film, namely the film is hydrophobic, so that the polyvinyl alcohol film is easy to generate uneven dyeing; when the weight swelling degree of the film is higher, the film is higher in the degree of allowing water to enter the film, namely the film is more hydrophilic, so that the polyvinyl alcohol film is easier to wrinkle. The weight swelling degree is that the polyvinyl alcohol film is placed for 24 hours at 23 ℃ under the environment of 50% relative humidity, the film is put into water to swell, the film is taken out to dry the surface water, the film weight is weighed to be M1, the film is put into an oven to be dried, the film weight is weighed to be M2, and the film is obtained by (M1-M2)/M1 x 100%. According to at least one embodiment, the polyvinyl alcohol film has a weight swell in the range of 38.0 to 48.0, such as 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" herein includes both end point values.

In another aspect, the present invention also provides a method for producing the polyvinyl alcohol film, comprising: (a) a resin drying process: pumping the polymerized polyvinyl alcohol resin into a dryer, and spraying water to cool down when drying; (b) dissolution process: heating and dissolving the polyvinyl alcohol resin, and adjusting the concentration of the polyvinyl alcohol resin to form a polyvinyl alcohol casting solution; (c) a casting process: casting the polyvinyl alcohol casting solution to a casting drum, and stripping the polyvinyl alcohol casting solution from the casting drum to obtain a polyvinyl alcohol primary film; and (d) a drying process: drying the polyvinyl alcohol primary film in a plurality of hot rollers and at least two temperature-controlled ovens to obtain the polyvinyl alcohol film; the initial hot roller of the plurality of hot rollers has the highest temperature of the plurality of hot rollers, the final hot roller has the lowest temperature of the plurality of hot rollers, the hot roller temperature difference between the highest temperature and the lowest temperature is controlled within a specific range, and the highest temperature and the lowest temperature of the oven are controlled simultaneously.

The following will refer to fig. 1. FIG. 1 is not limited to the number of hot rolls and the number of oven sections, but is merely for the purpose of facilitating the clear explanation of the specification, and is not intended to represent the number of hot rolls and the number of oven sections that can be actually used. According to at least one embodiment, the resin drying process is to drive the polymerized polyvinyl alcohol resin into a dryer, and spray water to cool at a proper time during high temperature drying. According to at least one embodiment, the temperature of the dryer is preferably 80 ℃ to 130 ℃, specifically for example: 80 ℃, 90 ℃, 100 ℃, 110 ℃, 120 ℃ and 130 ℃.

According to at least one embodiment, the dissolution process is to dissolve 1800kg of the dried polyvinyl alcohol resin, 4000kg of water and 200kg of plasticizer glycerol in the dissolution tank 110 for at least 180 minutes while stirring at a temperature of at least 140 ℃, uniformly mixing the aqueous solution of the polyvinyl alcohol resin by using a mixer, and then adding water to adjust the concentration of the aqueous solution of the polyvinyl alcohol resin to 30.0% to 50.0% to obtain a polyvinyl alcohol casting solution. According to at least one embodiment, the temperature at which the aqueous solution of the polyvinyl alcohol resin is dissolved is preferably at least 120 ℃, specifically for example: at least 120 ℃, at least 130 ℃, at least 140 ℃, at least 150 ℃, or at least 160 ℃, etc. According to at least one embodiment, the dissolution time for dissolving the polyvinyl alcohol resin is preferably at least 180 minutes, specifically, 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 at least 240 minutes, etc. According to at least one embodiment, the concentration of the aqueous solution of the polyvinyl alcohol resin 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 embodiment, the polyvinyl alcohol resin is obtained by polymerizing a vinyl ester resin monomer, and after the polyvinyl ester resin is formed, performing saponification reaction. The vinyl ester resin monomer includes vinyl esters such as vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl valerate, and vinyl caprylate, and the present invention is not limited thereto. In addition, copolymers formed by copolymerizing an olefin compound or an acrylate derivative with the vinyl ester resin monomer may be used, wherein the olefin compound contains ethylene, propylene, butylene, or the like, and the present invention is not limited thereto. The acrylate derivative includes acrylic acid, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, etc., and the present invention is not limited thereto. According to at least one embodiment, the polyvinyl alcohol resin preferably has a basicity of greater than 99.80 mole percent to obtain preferred 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 in the range of 2300 to 3000, specifically any two of the following values, for example: 2300. 2400, 2500, 2600, 2700, 2800, 2900, 3000, or the like, and the term "between" herein includes both end values. According to at least one embodiment, the molecular weight of the polyvinyl alcohol resin is between 100000 and 110000Mn, specifically in the range between any two of the following values, for example: 100000Mn, 102000Mn, 104000Mn, 106000Mn, 108000Mn, 110000Mn, or the like, and the term "between" herein includes both end point values.

The inventors found, without being limited to a particular theory, that whether the polyvinyl alcohol resin is subjected to water spray cooling during drying in the dryer, the temperature difference between the hot rollers, the highest temperature of the oven, the lowest temperature of the oven, or the speed of the casting drum affects the drying degree of the film, and further affects the dyeing of the film and the formation of wrinkles. If the polyvinyl alcohol resin is not subjected to water spraying and temperature reduction during drying by a dryer, the temperature difference between hot rollers is too small, the highest temperature of an oven is too high, the lowest temperature of the oven is too high or the casting drum speed is too slow, the film is excessively dried to generate too many adjacent C=C hydrophobic double bonds, and the film is dyed unevenly; if the temperature difference between the hot rollers is too large, the highest temperature of the oven is too low, the lowest temperature of the oven is too low or the speed of the casting drum is too fast, the film cannot be completely dried, the generation amount of the adjacent C=C hydrophobic double bonds is too small, and the film is wrinkled.

According to at least one embodiment, the above-mentioned casting process is to remove foam from the polyvinyl alcohol casting solution by a double screw extruder, then to discharge the foam from the T-shaped slit die lip 120, and to cast the foam into a rotating high temperature casting drum 130 for drying, thereby obtaining a polyvinyl alcohol primary film. When the casting process is performed, if the speed of the casting drum 130 is too slow, excessive drying of the film will cause excessive generation of adjacent c=c hydrophobic double bonds, and further cause uneven dyeing of the film; conversely, if the speed of the casting drum 130 is too high, the film will not be dried completely, resulting in too little adjacent c=c hydrophobic double bonds, and further wrinkling of the film. According to at least one embodiment, the casting drum 130 has a vehicle speed ranging between 5.0 and 6.4 meters/minute, specifically ranging between any two of the following values, for example: 5.0, 5.05, 5.1, 5.15, 5.2, 5.25, 5.3, 5.35, 5.4, 5.45, 5.5, 5.55, 5.6, 5.65, 5.7, 5.75, 5.8, 5.85, 5.9, 5.95, 6.0, 6.05, 6.1, 6.15, 6.2, 6.25, 6.3, 6.35 or 6.4 meters/min, etc., and the term "between" herein encompasses both values.

According to at least one embodiment, the drying process is to peel off the preliminary film of polyvinyl alcohol from the casting drum 130, contact and dry the upper and lower surfaces of the preliminary film of polyvinyl alcohol by a plurality of hot rollers 140, and then dry the upper and lower surfaces of the preliminary film of polyvinyl alcohol with hot air by using the oven 150, thereby obtaining the film of polyvinyl alcohol. According to at least one embodiment, the plurality of thermal rolls 140 may be 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 13.

According to at least one embodiment, when the film is dried, the temperatures of the plurality of hot rollers 140 gradually decrease from high to low, so if the temperature difference between the hot rollers 140 is too small, the film will be excessively dried to generate excessive adjacent c=c hydrophobic double bonds, and uneven dyeing of the film will be caused; on the contrary, if the temperature difference between the hot rollers 140 is too large, the film cannot be dried completely, so that the generation amount of the adjacent c=c hydrophobic double bonds is too small, and the film is wrinkled, so that the temperature difference between the highest temperature and the lowest temperature of the hot rollers 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 Wen Zhe of all heat rollers 140, and then the temperature of the successive heat rollers 140 gradually decreases until the final heat roller 140N is the lowest of all 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 ℃, specifically, any two of the following values, for example: 20 ℃, 25 ℃, 30 ℃, 35 ℃, 40 ℃, 45 ℃, etc., and the term "between" herein includes both end point values.

When drying the film, the oven 150 has multiple sections of drying areas, and the temperatures of the sections can be partially the same or completely different, wherein the section near the center of the oven 150 has the highest temperature, and the temperature of the section near the center of the oven 150 is gradually reduced to the highest temperature area 152 of the oven 150 and the section far away from the center of the oven 150 until the last section is the lowest temperature area 154 of the oven 150, and if the highest temperature of the highest temperature area 152 of the oven is too high or the temperature of the lowest temperature area 154 of the oven is too high, the film is excessively dried to generate excessive adjacent C=C hydrophobic double bonds, so that the film has uneven dyeing problem; conversely, if the highest temperature in the highest temperature zone 152 of the oven is too low or the lowest temperature in the lowest temperature zone 154 of the oven is too low, the film will not be dried completely, so that the formation of adjacent c=c hydrophobic double bonds is too low, and the film will wrinkle, so that the highest temperature and the lowest temperature in the highest temperature zone 152 and the lowest temperature zone 154 of the oven need to be controlled.

According to at least one embodiment, the oven may have a number of sections ranging from 2 to 10, such as: 2, 3, 4, 5, 6, 7, 8, 9 or 10; in a preferred embodiment 4 knots. According to at least one embodiment, the maximum temperature zone 152 of the oven has a maximum temperature ranging between 60 and 120 ℃, specifically any two of the following values, for example: 60 ℃, 70 ℃, 80 ℃, 90 ℃, 100 ℃, 110 ℃, or 120 ℃, etc., and the term "between" herein includes both end point values. According to at least one embodiment, the minimum temperature of the minimum temperature zone 154 of the oven is in the range of 40 to 70 ℃, specifically any two of the following values, for example: 40 ℃, 50 ℃, 60 ℃, or 70 ℃, etc., and the term "between" herein includes both end point values. According to at least one embodiment, the oven 150 may be, for example, but is not limited to: a floating oven.

In yet another aspect, the polyvinyl alcohol film of the invention may also be prepared as an optical film. The "optical film" as described herein refers to a polarizing film, a blue light resistant film, a filter, etc., and the present invention is not limited to these. Preferably, the polyvinyl alcohol film of the invention is used as a polarizing film.

In a preferred embodiment, the method for manufacturing the polarizing film (or polarizing plate) comprises the following steps: the polyvinyl alcohol film is swelled, dyed, stretched, complemented in color, dried and laminated with a cellulose triacetate film (TAC), so that the polarizing film can be obtained.

Further, when the polyvinyl alcohol film is used for the production of an optical film, stretching and dyeing are performed, and for example, a polarizing film is used, since the polarizing film is produced by using a film containing I ₃ ^- 、I ₅ ^- Aqueous boric acid solution of iodide ions is used for dyeing the polyvinyl alcohol film, and after boric acid can generate cross-linking effect with an unshaped (amorphlus) area of the polyvinyl alcohol, iodide ions are fixed to avoid dissolution of the iodide ions.

Examples

Hereinafter, the present invention will be described in further detail with reference to the detailed description and examples. However, it should be understood that these examples are only for helping to make the present invention more easily understandable and are not intended to limit the scope of the invention.

Manufacturing a polyvinyl alcohol film: the method comprises the steps of firstly, pumping polyvinyl alcohol PVA resin which is polymerized and has the polymerization degree of about 2400 into a dryer, spraying water at right time for cooling when the polyvinyl alcohol PVA resin is dried at high temperature, then heating and melting the dried polyvinyl alcohol resin through a dissolving barrel to form polyvinyl alcohol solution, extruding the polyvinyl alcohol solution through a T-shaped slit die lip and a casting drum for molding, forming the polyvinyl alcohol solution into a film through a plurality of hot rollers, adjusting the moisture of the film, and drying a polyvinyl alcohol film forming sample through an oven to obtain a polyvinyl alcohol film.

The step of producing a polyvinyl alcohol film specifically includes: firstly, pumping the polyvinyl alcohol resin which is polymerized and has the alkalization degree of more than 99.9% and the polymerization degree of about 2400 into a dryer, controlling the temperature in the dryer to be 110 ℃, and spraying water in time in the drying process to cool the polyvinyl alcohol resin. Then 1800kg of the dried polyvinyl alcohol resin, 4000kg of water and 200kg of plasticizer glycerol are added into a dissolution barrel, the temperature is raised to 140 ℃ while stirring, the dissolution is carried out for 180 minutes at 140 ℃, and after the uniform dissolution by using a mixer, the concentration of the resin is adjusted to 30.0% by adding water, thus obtaining the film-forming stock solution. The film-making stock solution is defoamed by a double-screw extruder, then is spitted out from a T-shaped slit die lip, and is cast to a rotating high-temperature casting drum for drying film-making, and the casting drum speed is 5.4 m/min. The as-formed film was peeled from the casting drum and contacted with the upper and lower surfaces of the dried film by 13 heat rolls, wherein the 1 st heat roll was the highest Wen Zhe of all heat rolls, and the temperature of the successive heat rolls was gradually lowered, while the 1 st heat roll was 45℃different from the 13 th heat roll (the lowest of all heat rolls). And then drying the upper and lower surfaces of the film with hot air by using a drying oven with 4 sections of drying areas, wherein the temperature of the highest temperature area of the drying oven is 100 ℃ and the temperature of the lowest temperature area of the drying oven is 50 ℃, and finally obtaining the finished product of the polyvinyl alcohol film. Various examples and comparative examples herein will have one or more parameters that differ from those described above, and are presented in detail in the tables below.

Manufacturing a polarizing film: a polyvinyl alcohol film was immersed in water at 30℃to swell it and uniaxially stretched in the Machine Direction (MD) to 2.0 times the original length, then immersed in an aqueous solution at 30℃containing 0.03% by mass of iodine and 3% by mass of potassium iodide, and then stretched to 3.3 times the original length, and then immersed in an aqueous solution at 30℃containing 3% by mass of potassium iodide and 3% by mass of boric acid and further stretched to 3.6 times the original length. Then immersed in a 60 ℃ aqueous solution of 5 mass% potassium iodide and 4 mass% boric acid, and further extended to 6.0 times the original length. The polarizing film was obtained by immersing in a 3 mass% aqueous potassium iodide solution for 15 seconds and then drying at 60℃for 4 minutes.

Referring to tables 1 and 2 below, experimental control factors, technical characteristics, and dyeing uniformity and wrinkle measurement results of examples 1 to 10 are shown; tables 3 and 4 show the experimental control factors, technical characteristics, and the dyeing uniformity and wrinkle measurement results of the films of comparative examples 1 to 10.

TABLE 1

Table 2 (subsequent Table 1)

TABLE 3 Table 3

Table 4 (subsequent Table 3)

In this experiment, the analysis mode used was as follows:

ultraviolet-visible spectrum hydrophobic double bond ratio analysis

The preparation method of the sample comprises the following steps: the polyvinyl alcohol film in the width direction was divided into 5 equal parts, and then cut into film samples each having an area of 5 cm in the machine direction x 5 cm in the width direction, and placed in a constant temperature and humidity cabinet at 23 ℃ and 50% relative humidity for 24 hours.

Analytical instrument analysis of film samples was performed at Perkin Elmer Lambda 365 (wavelength accuracy and wavelength repeatability meet the specifications of NIST 2034).

Test conditions: a sample of the film was subjected to constant temperature and humidity, and its absorbance at 200 to 700nm was measured at 23℃under 50% relative humidity, and the absorbance values at 215nm, 280nm and 320nm were read.

Data conversion: and (3) bringing the absorbance values read at 215nm, 280nm and 320nm of the film sample into the following ultraviolet-visible spectrum hydrophobic double bond ratio formula to obtain the hydrophobic double bond ratio of the film sample: (A) _UV280nm +A _UV320nm )/A _UV215nm Finally, the ratio of 5 hydrophobic double bonds measured in the width direction is averaged.

Ultraviolet-visible spectrum average double bond ratio analysis

Data conversion: and (3) bringing the absorbance values read at 215nm, 280nm and 320nm of the film sample into the following ultraviolet-visible spectrum average double bond ratio formula 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, averaging the ratio of the 5 average double bonds measured along the width direction.

Analysis of weight swelling degree

Test conditions: and (3) putting the polyvinyl alcohol film sample into pure water at 30 ℃ to swell for 20 minutes, taking out the film sample after swelling, wiping the surface moisture of the film sample by using facial tissue to weigh the film weight M1, and putting the film sample into an oven at 120 ℃ to dry for 120 minutes to weigh the film weight M2.

Data conversion: the film weights M1 and M2 of the film samples are taken into (M1-M2)/M1 by 100 percent to obtain the weight swelling degree of the film samples, and finally, the 5 weight swelling degrees measured along the width direction are averaged.

Analysis of film color uniformity performance

The polyvinyl alcohol film was made into a polarizer, irradiated with a lamp box having a light emittance of 14000lx, and the color uniformity of the film was observed and evaluated. The film color uniformity was evaluated as follows:

and (3) the following materials: no color unevenness;

o: weak color unevenness;

x: obvious uneven color.

Wrinkle performance analysis

The method comprises the steps of preparing a polyvinyl alcohol film into a polaroid, cutting the polaroid into samples with the width direction of 5 cm and the length direction of 20 cm, fixing the samples on an extension jig in a mode that the clamp interval is 5 cm, stretching the samples in a water bath by a polaroid process stretcher, immediately pulling the samples from the water bath after the samples extend to 2 times of the original length (namely 10 cm), and visually observing and evaluating the wrinkling situation of the film surface of the samples from a position 1 m away from the front surface of the film. Film pucker was evaluated as follows:

and (3) the following materials: no wrinkles;

o: slight wrinkles;

x: obvious wrinkles.

According to tables 1 and 2, the films of examples 1 to 10 exhibited excellent dyeing uniformity and wrinkle resistance at the same time because the ratio of hydrophobic double bonds in the ultraviolet-visible spectrum was 0.500 to 1.300; in particular, examples 2 to 4 and example 7 exhibited excellent conditions without color unevenness and without wrinkle formation at the same time. In contrast, the films of comparative examples 1 to 10 were not controlled to have excellent dyeing uniformity and wrinkle resistance at the same time because the ratio of hydrophobic double bonds in the ultraviolet-visible spectrum of the films was 0.500 to 1.300.

In summary, the polyvinyl alcohol film of the invention has a hydrophobic double bond ratio of ultraviolet light to visible light spectrum: (A) _UV280nm +A _UV320nm )/A _UV215nm Between 0.500 and 1.300, the dyeing uniformity is good and wrinkles are not easy to generate.

All ranges provided herein are intended to include each specific range within the given range as well as combinations of sub-ranges between the given ranges. Moreover, unless otherwise indicated, all ranges provided herein include the endpoints of the ranges. For example, ranges 1-5 specifically include 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 herein incorporated by reference and for any and all purposes, each individual publication or patent application is specifically and individually indicated to be incorporated by reference. In the event of a discrepancy between the present disclosure and any publication or patent application incorporated by reference herein, the present disclosure controls.

The terms "comprising," "having," "including," and "containing" are used herein in an open, non-limiting sense. The terms "a" and "an" are to be construed 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 amounts of ingredients and/or reaction conditions can be modified in all instances by the term "about," meaning within + -5% of the indicated number. The term "substantially free" or "substantially free" as used herein refers to less than about 2% of a particular feature. All elements or features that are positively set forth herein are negatively excluded from the claims.

Claims

1. A polyvinyl alcohol film having an ultraviolet-visible spectrum hydrophobic double bond ratio: (A) _UV280nm +A _UV320nm )/A _UV215nm Between 0.500 and 1.300.

2. The polyvinyl alcohol film of claim 1 further having an ultraviolet-to-visible spectrum average double bond ratio: (A) _UV215nm *1+A _UV280nm *2+A _UV320nm *3)/(A _UV215nm +A _UV280nm +A _UV320nm ) Between 1.480 and 1.820.

3. The polyvinyl alcohol film of claim 1 further having a weight swell of from 38.0 to 48.0.

4. An optical film formed from the polyvinyl alcohol film according to any one of claims 1 to 3.

5. The optical film of claim 4 which is a polarizing film.

6. A method for producing the polyvinyl alcohol film according to any one of claims 1 to 3, comprising:

(a) And (3) a resin drying process: pumping the polymerized polyvinyl alcohol resin into a dryer, and spraying water to cool down when drying;

(b) The dissolution process comprises the following steps: heating and dissolving the dried polyvinyl alcohol resin, and adjusting the concentration to form a polyvinyl alcohol casting solution;

(c) Casting process: casting the polyvinyl alcohol casting solution to a casting drum, and stripping the polyvinyl alcohol casting solution from the casting drum to obtain a polyvinyl alcohol primary film; and

(d) And (3) a drying process: drying the polyvinyl alcohol primary film in a plurality of hot rollers and at least two temperature-controlled ovens to obtain the polyvinyl alcohol film;

wherein a starting hot roller of the plurality of hot rollers has a highest temperature of the plurality of hot rollers and a final hot roller has a lowest temperature of the plurality of hot rollers.

7. The method according to claim 6, wherein the polyvinyl alcohol resin has an alkalization degree of more than 99.80 mol%.

8. The method according to claim 6, wherein the polyvinyl alcohol resin has a polymerization degree of 2300 to 3000.

9. The method according to claim 6, wherein the polyvinyl alcohol resin has a molecular weight of 100000 to 110000Mn.

10. The manufacturing method according to claim 6, wherein the casting drum has a vehicle speed of 5.0 to 6.4 m/min.

11. The manufacturing method of claim 6, wherein a temperature difference between a start hot roller and a final hot roller of the plurality of hot rollers is between 20 and 45 ℃.

12. The method of manufacturing of claim 6, wherein the oven has a maximum temperature of between 60 and 120 ℃.

13. The method of manufacturing of claim 6, wherein the minimum temperature of the oven is between 40 and 70 ℃.