JP7288526B2 - POLYVINYL ALCOHOL FILM, POLARIZING FILM CONTAINING THE SAME, AND METHOD FOR MANUFACTURING THEM - Google Patents

Description

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

Polyvinyl alcohol (PVA) film is a kind of hydrophilic polymer, which has properties such as transparency, mechanical strength, water solubility, and good processability, and is especially used in packaging materials or optical films of electronic products. Widely used in polarizing films.

In the manufacturing process of preparing optical films with PVA films, functional group modification can be selectively used according to the required performance, followed by stretching. Manufacturing methods can be broadly divided into dry and wet processes. In the dry process, the PVA film is stretched under an inert gas atmosphere at constant temperature and humidity, and then dyeing and other processes are performed. In the wet process, the PVA film is dyed and then stretched in a solution. Dry-prepared PVA films often suffer from uneven surface or uneven dyeing, whereas wet-prepared PVA films have good performance (e.g. uniform color). Therefore, at present, a wet process is generally used to produce PVA films in many cases.

When producing a polarizing film, the higher the draw ratio, the higher the optical performance obtained. Therefore, when drawing, the PVA film is drawn as close to the critical point as possible to obtain a PVA film with excellent optical properties. .

A good polarizing film has properties such as uniform color, little color mottling, and no wrinkles, and can provide excellent optical properties. In order to improve the optical properties of the polarizing film, conventional techniques have been used to improve the optical properties by changing the viscosity and degree of saponification, such as by changing the structure of polyvinyl alcohol or adding functional groups (e.g., cationic groups). ing.

However, in the known production method, the distribution of residual acetoxyl groups and syndiotacticity have had a great effect on the hue of the polarizer.

The inventors discovered that red light leakage and blue light leakage in polarizing films are caused by the relative contents of I ₃ ^- and I ₅ ^- in the film. When I ₅ ⁻ is low, the absorbance at 700 nm is low and the appearance is reddish. Conversely, less I ₃ ⁻ results in lower absorption at 480 nm and a bluer appearance. Effective cross-linking between boric acid and PVA helps to form I ₅ ^-complexes and prevent I ₃ ^- efflux. Therefore, if the amount of the crosslinking reaction between boric acid and PVA is insufficient, a phenomenon may occur in which the hue of the polarizing film becomes reddish or bluish. Also, the higher the syndiotacticity, the easier it is for the I ₅ ^-compound to be formed, and the easier it is for Red leak to be reduced. Besides syndiotacticity, the relative hue is also affected by the arrangement of residual acetoxyl groups, the level of boric acid complexation, and the like. To achieve the effect of evening out the hue, it must be controlled simultaneously within a certain range.

To solve the above problems, the present invention achieves a PVA film with excellent hue by controlling the ratio of non-hydrogen-bonded carbonyl groups/hydrogen-bonded carbonyl groups in the IR absorption spectrum. Of these, the IR absorption intensity of non-hydrogen-bonded carbonyl groups is A1730 cm ^-1 , and the IR absorption intensity of hydrogen-bonded carbonyl groups is A1710 cm ^-1 .

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

In a preferred embodiment, the absorption intensity of the acetate group of the PVA film is 0.35<(A1710 cm ⁻¹ +A1730 cm ⁻¹ )/A1425 cm ⁻¹ <0.55. The absorption intensity of the acetic acid ester group was analyzed after the polyvinyl alcohol film was immersed in pure water, stirred, taken out, and dried at 105° C./1 hr.

In preferred embodiments, the PVA film has a syndiotacticity of 52% to 56%.

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

Another object of the present invention is to provide an optical film containing the above PVA film. In preferred embodiments, the optical film is a polarizing film.

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

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

Another object of the present invention is to provide a method for producing a PVA film, comprising (a) polymerizing a vinyl ester-based resin monomer to form a polyvinyl ester-based resin, followed by a saponification reaction to produce a polyvinyl A process for obtaining an alcohol resin, wherein a vinyl 2,2-bis(trifluoromethyl)propionate copolymer is added during the polymerization reaction, and the molar amount of the copolymer/vinyl (b) adding a saponified solvent having a dielectric constant of between 34 and 36, and (b) heating and dissolving the polyvinyl alcohol resin to obtain polyvinyl alcohol; (c) casting the casting solution into a casting drum; and (d) drying to form a PVA film.

In a preferred embodiment, steps (a)-(c) in the method of manufacturing PVA film are carried out under the use of an external warming device.

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

In a preferred embodiment, the method for producing PVA film further controls the residual acetate group sequence by adjusting the pH value or adding solvents with different dielectric constants in step (a).

In a preferred embodiment, the method for producing a PVA film further comprises pulverizing and drying the polyvinyl alcohol resin obtained by the saponification reaction in the step (a). prevent skinning from occurring.

As an effect of the present invention, not only is the known PVA film manufacturing process improved, but also by controlling the ratio of non-hydrogen-bonded carbonyl groups/hydrogen-bonded carbonyl groups in the IR absorption spectrum, a PVA film with excellent hue is obtained. is achieved.

It is a conceptual diagram in which the absorption peak at C=0 in the acetate group is divided into 1710 cm ^-1 (continued with OH group) and 1730 cm ^-1 (non-hydrogen-bonded carbonyl group in block). 1 is a conceptual diagram of a syndiotactic triad, an isotactic triad, and a heterotactic triad according to an embodiment of the present invention; FIG.

The following embodiments do not unduly limit the invention. Those skilled in the art to which this invention pertains can make modifications and variations to the embodiments discussed herein without departing from the spirit or scope of the invention, any of which is within the scope of the invention. belongs to

As used herein, the terms "one" and "one" refer to the presence of one or more (ie, at least one) of the grammatical objects herein.

The present invention provides a PVA film, particularly a PVA film having a specific IR absorption intensity ratio. Also, the present invention further provides an optical film comprising the PVA film.

The above "IR absorption intensity ratio" was obtained using infrared spectroscopy, which is a technique used to detect the vibrational energy (or frequency) of molecules. Using the principle of molecular vibration produced by the action of infrared light and molecules, the vibrational modes exhibited by molecules after absorbing infrared light are recorded, and relative to the infrared light wavelength (λ) of the absorbed light. A picture obtained by recording the specific intensity is called an infrared spectrum and is used to identify specific molecules. For the IR analysis method described above, for example, referring to the JIS K 6726 standard method, a 10 cm × 10 cm PVA film is immersed in 2000 ml of pure water at 30 ° C. and stirred for 5 minutes using a magnetic stirrer. Take out. A drier is preheated to 105° C., the film after immersion is placed flat on a tray, and dried at 105° C./1 hr, then the film is taken out and subjected to IR analysis. If a negative value occurs in the IR absorption value, the data is translated appropriately and a fixed constant is added to all data to bring the lowest point of the IR spectral absorption value over the entire range to zero.

See FIG. The absorption peak at C=0 in the acetate group was divided into 1710 cm ^-1 (continued with OH group) and 1730 cm ^-1 (non-hydrogen-bonded carbonyl group in block). According to at least one example, the inventors found that the absorption peak at C=0 in the acetate group is split between 1710 cm ^-1 (connected with OH group) and 1730 cm ^-1 (within the block), and the absorption at 1730 cm ^-1 It was discovered that higher intensity (A 1730 cm ⁻¹ ) indicates more C=0 in the block and affects the hue of the polarizing film. In a preferred embodiment, the polyvinyl alcohol film of the present invention has an IR absorption intensity ratio of 0.85<A1730 cm ⁻¹ /A1710 cm ⁻¹ <0.97. Specifically, for example, a range between any two numbers of 0.85, 0.86, . . . , 0.97, but not including these numbers.

Further/or, the inventor believes that (A1710 cm ⁻¹ +A1730 cm ⁻¹ )/A1425 cm ⁻¹ represents the total remaining amount of acetic acid ester groups, and the higher this value, the lower the degree of polarization and the more red light leaks. I found a trend. In a preferred embodiment, the polyvinyl alcohol film of the present invention further has an absorption intensity of 0.35<(A1710 cm ⁻¹ +A1730 cm ⁻¹ )/A1425 cm ⁻¹ <0.55 of the acetate group, specifically, For example, a range between, but not including, any two numbers of 0.35, 0.36, ..., 0.55. The higher the absorption value at A1730 cm ⁻¹ , the more acetoxyl groups (OAc groups) in the block. By adjusting the pH value or adding solvents with different dielectric constants during the saponification process, the arrangement of the residual acetate groups can be controlled. You can control the array of

The PVA film of the present invention additionally has a certain syndiotacticity. As used herein, "Syndiotacticity" refers to the stereoregularity of a molecular chain and refers to the structure in which the R groups alternate on both sides of the chain. In preferred embodiments, the PVA film of the present invention has a syndiotacticity of 52% to 56%. Specifically, for example, it is a range between any two numerical values of 52%, 53%, . . . , 56%. According to at least one embodiment, control of syndiotacticity can be adjusted by moderate addition of certain copolymers during the polymerization reaction, which increases steric hindrance and results in high syndiotacticity. You can turn it into a city. Copolymers such as vinyl 2,2-bis(trifluoromethyl)propionate, vinyl 5H-octafluorovalerate, trifluoromethane (CF ₃ ), etc. However, it is not limited to these. Alternatively, the polymerization temperature is finely adjusted, but if the polymerization temperature is too high, steric hindrance is overcome and syndiotacticity is lowered, branching is likely to occur, and dyeability is affected.

In a preferred embodiment, the PVA film of the present invention is treated with 0.2 wt% boric acid aqueous solution, and the boron content of the aqueous solution after dissolving in water is 16-19 ppm. Specifically, it is a range between any two numerical values of 16 ppm, 16.5 ppm, . . . , 19 ppm, for example. In the present invention, the method for measuring the boron content includes the following. Put a PVA film cut to about 0.12 g into a 30 ml glass sampling container, add 20 g of pure water, make the film completely below the liquid level of pure water, add a stirring ball, and stir at a speed of Set to 250 rpm and stir for 1.0 hour. Next, the pure water in the bottle was taken out, and a 0.2 wt% boric acid aqueous solution was added. Place and age. Next, the PVA film was taken out, rinsed with pure water, placed in a 30 ml glass sample collection container, added with 20 g of pure water, dissolved sufficiently, and then analyzed by an inductively coupled plasma emission spectrometer (ICP-OES). Analyze the boron concentration in the solution.

The "optical film" described in this specification refers to a polarizing film, a blue light cut film, a filter lens, etc., but the present invention is not limited to these. Preferably, the PVA film of the present invention is a polarizing film.

The polarizing film described above has a specific ratio (A/B) between the absorbance (A) at a wavelength of 480 nm and the absorbance (B) at a wavelength of 700 nm in the crossed Nicols state. As used herein, "Cross Nicol" refers to Cross Nicol transmission, which is one method used to analyze optical performance. The measurement wavelength range is set to 380 nm to 780 nm, and the transmittance when the vibration direction of the polarized light incident on the polarizing film through the Gran-Taylor polarizer is parallel to the transmission axis of the polarizing film is defined as the parallel transmittance. Crossed Nicols transmittance is defined as being perpendicular to the axis. After that, using the "polarizing film evaluation program" (manufactured by JASCO Corporation), according to the method of JIS Z 8722 (object color measurement method), using the above-mentioned parallel transmittance and crossed Nicols transmittance, C light source, Visibility correction in the visible light region of the 2-degree field of view was performed, and the single transmittance of the polarizing film and the degree of polarization were calculated, and the two values were obtained as the optical properties of the polarizing film.

Among preferred examples, the ratio (A/B) of the absorbance (A) at a wavelength of 480 nm and the absorbance (B) at a wavelength of 700 nm in the crossed Nicol state of the polarizing film of the present invention is 1.40 to 1.70. Specifically, the ratio (A/B) mentioned above is a range between any two numerical values of 1.40, 1.41, . . . , 1.70. Among more preferred examples, the ratio (A/B) of the absorbance (A) at a wavelength of 480 nm and the absorbance (B) at a wavelength of 700 nm in the crossed Nicol state of the polarizing film of the present invention is 1.51 to 1.65. The ratio (A/B) mentioned above is specifically a range between any two numerical values of 1.51, 1.52, . . . , 1.65.

In another aspect, the present invention also provides a method of making a polyvinyl alcohol film. The process includes (a) a step of polymerizing a vinyl ester resin monomer to form a polyvinyl ester resin and then performing a saponification reaction to obtain a polyvinyl alcohol resin, wherein vinyl 2,2 is added during the polymerization reaction. - bis (trifluoromethyl) propionate (vinyl 2,2-bis (trifluoromethyl) propionate) copolymer is added, and the addition amount ratio of the copolymer molar amount/vinyl ester resin monomer molar amount is 1 to 3 mole%, and the dielectric (b) heating and melting the polyvinyl alcohol resin to form a polyvinyl alcohol casting solution; and (c) applying the casting solution to a casting drum. and (d) drying to form a tar film.

Among the preferred embodiments, in the method for producing a PVA film of the present invention, in the step (a) of polymerizing the vinyl ester-based resin monomer, the addition amount ratio of copolymer molar amount/vinyl ester-based resin monomer molar amount is 1 to 3 mole%. be. Specifically, for example, it is a range between any two numerical values of 1, 1.2, . . . , 3 mole %, but the present invention is not limited to these. In a preferred embodiment, in step (a), the residual acetate group sequence is controlled by adjusting the pH value or adding solvents with different dielectric constants. In another preferred embodiment, the production method further comprises pulverizing and drying the polyvinyl alcohol resin obtained by the saponification reaction in the step (a). Prevent skinning from occurring.

The saponification solvent with a dielectric constant between 34 and 36 in step (a) is, for example, a mixed solvent of methanol/methyl acetate, and the greater the amount of methyl acetate, the lower the value of the dielectric constant of the saponification solvent. , and the IR absorption intensity ratio of A1730 cm ⁻¹ /A1710 cm ⁻¹ increases.

The polyvinyl alcohol resin described above is obtained by performing a saponification reaction after forming a polyvinyl ester resin by polymerization of a vinyl ester resin monomer. Among them, vinyl ester-based resin monomers include vinyl esters such as vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl pentanoate, and vinyl octanoate, but the present invention is not limited thereto and is suitable. is vinyl acetate. A copolymer formed by copolymerizing an olefin compound or an acrylate derivative with the above vinyl ester resin monomer can also be used. Olefin compounds are ethylene, propylene, butylene, and the like. Alternatively, copolymerization of an acrylate derivative such as allyl acetate, acrylic acid, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate or n-butyl acrylate with the vinyl ester resin monomer described above. Copolymers formed by are also usable. Ethylene, allyl acetate, and allyl alcohol are preferred in consideration of production costs and film quality. According to at least one embodiment, the unit content of ethylene, allyl acetate and allyl alcohol is within 5 mole%, preferably 2-3.5 mole%.

During polymerization, syndiotacticity can be adjusted by moderate addition of certain copolymers such as vinyl 2,2-bis(trifluoromethyl)propionate. Alternatively, the polymerization temperature is fine-tuned. If the polymerization temperature is too high, the syndiotacticity is lowered and branching is likely to occur, which affects the dyeability.

Generally, the degree of saponification of the polyvinyl alcohol resin is 90% or more, preferably 99% or more to obtain good optical properties. Specifically, for example, any value among the numbers 90%, 91%, . . . , 99% or between any two numbers mentioned above. During the saponification process, the residual acetate group sequence can be controlled by adjusting the pH value or adding solvents with different dielectric constants.

The degree of polymerization of polyvinyl alcohol is between 800 and 10,000, preferably between 2,200 and 10,000. , 9000, 10000 or between any two of the above values, with a degree of polymerization above 800 having good processing properties, but a degree of polymerization above 10000 being inconvenient to dissolve.

In general, when the content of the polyvinyl alcohol-based resin in the polyvinyl alcohol casting solution used is insufficient, the viscosity of the casting solution becomes too low, the drying load becomes excessively large, and the film formation efficiency deteriorates. On the other hand, if the content of the polyvinyl alcohol-based resin is too high, the polyvinyl alcohol-based resin becomes difficult to dissolve, and clusters tend to remain. Therefore, the content of the polyvinyl alcohol resin in the polyvinyl alcohol casting solution used in this embodiment is usually 10 to 60 wt%, preferably 15 to 40 wt%, more preferably 20 to 30 wt%. Specifically, it is, for example, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60 wt%.

The melting temperature of the polyvinyl alcohol casting solution is preferably 130 to 140° C. If the temperature is too low, clusters tend to remain, and if the temperature is too high, energy is consumed and costs increase. Specifically, the temperature is, for example, 130 to 140°C, 133 to 140°C, 136 to 140°C, 139 to 140°C, 130 to 137°C, 130 to 134°C, and 130 to 131°C.

In addition to the polyvinyl alcohol resin, the casting solution can also contain a plasticizer to enhance the workability of the film formation. Usable plasticizers include, for example, ethylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol. Polyhydric alcohols such as ethylene glycol, propylene glycol or glycerol are included, but the invention is not limited thereto, preferably ethylene glycol and glycerol. The amount of the plasticizer to be added is usually between 3 and 30 parts by weight, preferably between 7 and 20 parts by weight, with respect to 100 parts by weight of the polyvinyl alcohol resin. 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 parts by weight or between any two numbers mentioned above. If the plasticizer content is insufficient, the formed PVA film will be prone to crystals, which will affect the dyeing effect in subsequent processing. Conversely, if the plasticizer content is too high, the mechanical properties of the PVA film are compromised.

The equipment used in the PVA film manufacturing method includes a dissolution tank, a filter, a coating machine, and a transport pipe connected from the dissolution tank to the front of the coating machine. The heat retaining device can be a metal heating element (heating wire) or a jacket filled with liquid such as oil or water inside, and the metal wire or the liquid in the jacket is heated, and the dissolution tank, filter, coating machine and By uniformly heating the pipes (especially the surface of the equipment and pipes) connected from the dissolution tank to the front of the coating machine and maintaining the heat retention state, the surface temperature of the equipment or pipes is lost and the polyvinyl alcohol in the casting solution To avoid the formation of a gel in the polyvinyl alcohol, which sticks or clogs the filter, rendering the manufacturing process inoperable. Also, if the heating temperature is excessively high, part of the solution is dehydrated or gelled, forming a fox-colored or black gel, which is disadvantageous in terms of improving the quality and uniformity of the coated film surface. Become. In the method of the present invention, the polyvinyl alcohol for coating and molding is heated and kept at a temperature of 80 to 120°C, preferably at a temperature of 90 to 110°C, more preferably at a temperature of 90 to 100°C. It is carried out under heating and keeping warm conditions. Specifically, for example, 80, 85, 90, 95, 100, 105, 110, 115, 120° C. or between any two of the above values. In a preferred embodiment, steps (a)-(c) are performed under the use of an external warming device.

In the method listed above, polyvinyl alcohol resin and plasticizer are dissolved in a solvent to form a polyvinyl alcohol casting solution, followed by filtration with a filter, and finally using a gear pump and a T-type die coater. to cast the polyvinyl alcohol casting solution into the casting drum. If the speed of the drum is too slow, the film tends to be dried excessively and the distribution of retardation and melting point tends to be uneven. Also, when the temperature of the drum is raised, the foaming phenomenon is likely to occur. Therefore, the rotation speed of the drum is suitably 3-7 m/min, preferably 4-6 m/min. Specifically, it is a range between any two numerical values of 2 m/min, 3 m/min, . . . , 6 m/min, for example. The temperature is set between 85-90°C, such as 85-90°C, 86-90°C, 87-90°C, 88-90°C, 89-90°C, 85-89°C, 85-88°C, 85-90°C, 87°C or 85-86°C. If the temperature of the drum is too high, the casting solution on the drum tends to foam.

After being peeled off from the drum, the film is further dried through a series of heating rollers and then heat-treated to obtain a polyvinyl alcohol film. Examples of the heat treatment include a method in which (1) the polyvinyl alcohol film is heated on a heating roller, or (2) a floating dryer. The number of heating rollers and floating dryers is not particularly limited. However, it is preferably 115 to 130°C, for example, 115 to 130°C, 115 to 128°C, 115 to 126°C, 115 to 124°C, 115 to 122°C, 115 to 120°C, 115 to 118°C, 115°C to 116°C, 117-130°C, 119-130°C, 121-130°C, 123-130°C, 125-130°C, 127-130°C or 129-130°C. If the temperature is too high, the degree of swelling deteriorates, affecting the dyeability and the reactivity of boric acid.

When manufacturing an optical film from a PVA film, stretching and dyeing are performed. Taking the polarizing film as an example, in the manufacturing process ^of the polarizing film, PVA is treated with an aqueous solution of boric acid containing I ₃ ⁻ and I ₅ -iodide ions. As the film is dyed, the iodide ions are immobilized after the boric acid has a cross-linking action with the amorphous areas of the PVA, preventing iodide ions from eluting.

Below, the present invention will be described in more detail together with examples. However, it should be understood that these examples are intended to help make the invention more easily understood and are not intended to limit the scope of the invention.

Production of PVA Film After preparing the polyvinyl alcohol casting solution, the polyvinyl alcohol casting solution is cast into a casting drum and dried to form a polyvinyl alcohol-based polymer film. Specifically, in the above-described method for producing a polyvinyl alcohol-based polymer film, the polyvinyl alcohol casting solution mainly contains polyvinyl alcohol, a plasticizer and water, and the polyvinyl alcohol is converted into polyvinyl ester by polymerization of vinyl ester-based resin monomers. It is obtained by performing a saponification reaction after obtaining the system resin.

Preparation of Polarizing Film A polyvinyl alcohol film was immersed in water at 30° C. to swell and uniaxially stretched in the machine direction (MD) to 2.0 times its original length, then 0.03 weight percent iodine. , and stretched to 3.3 times its original length while immersed in an aqueous solution containing 3% by weight of potassium iodide and 3% by weight of potassium iodide, and then 3% by weight of potassium iodide and 3% by weight of boric acid. It is further stretched to 3.6 times its original length by immersion in an aqueous solution containing 30°C. Subsequently, it is immersed in an aqueous solution containing 5% by weight of potassium iodide and 4% by weight of boric acid at 60° C., and further stretched to 6.0 times its original length. After that, it is immersed in a 3% by mass potassium iodide aqueous solution for 15 seconds and then dried at 60° C. for 4 minutes to obtain a polarizing film.

See Table 1 below, which is the test control variables and hue uniformity measurement results for Examples 1-4 and Comparative Examples 1-3.

In this example, the IR analysis method includes: A PVA film of 10 cm×10 cm is immersed in 2000 ml of pure water at 30° C., stirred for 5 minutes using a magnetic stirrer, and then taken out. A drier is preheated to 105° C., the film after immersion is placed flat on a tray and dried at 105° C./1 hr, and the film is taken out and analyzed. If a negative value occurs in the IR absorption value, the data is translated appropriately and a fixed constant is added to all data to bring the lowest point of the IR spectral absorption value over the entire range to zero.

In this example, the method for measuring the boron content includes the following. Put a PVA film cut to about 0.12 g into a 30 ml glass sampling container, add 20 g of pure water, make the film completely below the liquid level of pure water, add a stirring ball, and stir at a speed of Set to 250 rpm and stir for 1.0 hour. Next, empty the pure water in the bottle, add 0.2 wt% boric acid aqueous solution, let stand for 1.0 hour, then empty the boric acid aqueous solution and close the PVA film in the bottle. Set and age for 16.0 hours. Next, the PVA film is taken out, rinsed with pure water, placed in a 30 ml glass sampling container, 20 g of pure water is added, and dissolved sufficiently, and the boron concentration in the solution is analyzed by ICP-OES. .

In this example, the analysis method of ICP-OES includes the following. A calibration curve was prepared by the heterodyne method, 200 ppm ICP multi-element standard (purchased from Merck) was sucked with a microdispenser into a 100 ml volumetric flask and then diluted to 100 ml with deionized water to obtain the required concentration ( 100, 200, 500, 2000 ppb, etc.). Samples do not require pretreatment and are analyzed directly on the instrument. The analytical element selected for this method is boron (B, 249.773 nm).

In this example, the analysis method of syndiotacticity includes the following. A test sample of 10 cm×10 cm is immersed in 2000 ml of pure water at 30° C., stirred for 5 minutes using a magnetic stirrer, and then taken out. A dryer is preheated to 105° C., and the film after immersion is laid flat on a tray and dried at 105° C./1 hr. The film is removed and subjected to NMR analysis. The solvent used is dimethyl sulfoxide-d ₆ and the instrumentation is ¹ H NMR. The analytical method is described in T.W. The method disclosed by Moritani et al. in 1972 in "Macromolecules" (5,577) was used as a reference. Referring to FIG. 2, the percentage (%) of triads (mm/mr/rr) was obtained by NMR, and then calculated by the formula: syndiotacticity (dyads) = rr + mr/2. .

In the present examples, the saponification degree and average degree of polymerization of the resin refer to the test method of JIS 6726.

According to Table 1, the polarizing film produced from the PVA film of the present invention has specific characteristics of absorbance (A) at a wavelength of 480 nm and absorbance (B) at a wavelength of 700 nm in the crossed Nicols state from the viewpoint of hue uniformity. The ratio (A/B) is preferably 1.40 or more. On the other hand, if the ratio (A/B) is too high, red light leakage tends to increase, so the ratio (A/B) is preferably 2.00 or less, more preferably 1. less than .80. The above absorbance (A) and absorbance (B) can be determined with a spectrophotometer.

In summary, the effect of the present invention is not only to improve the known PVA film manufacturing process, but also to improve the hue by controlling the ratio of non-hydrogen-bonded carbonyl groups/hydrogen-bonded carbonyl groups in the IR absorption spectrum. A high PVA film is achieved.

All ranges provided herein are meant to include each particular range within the assigned range and the combination of subranges between the assigned ranges. Also, all ranges provided herein are inclusive of the range endpoints, unless stated otherwise. Thus, 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.

All publications and patent applications referred to in this specification are hereby incorporated by reference, and each and every publication or patent application is hereby incorporated by reference for any and all purposes. clearly and individually indicated. In the event of a conflict between this specification and any publication or patent application incorporated herein by reference, the specification shall control.

As used herein, the terms "include," "have," and "include" have open, non-limiting meanings. The terms "one" and "the" should be understood to include the plural and the singular. The term "one or more" refers to "at least one" and thus can include single properties or mixtures/combinations of properties.

Except in the working examples or where otherwise indicated, all numbers indicating amounts of ingredients and/or reaction conditions may be modified in all instances by the term "about" and are indicated in all instances. It means that it is within ±5% of the figure. As used herein, the terms "essentially free" or "substantially free" mean less than about 2% of the specified property. Any element or feature explicitly recited in this specification may be negatively excluded from a claim.

Claims (7)

It has an IR absorption intensity ratio of 0.85<A1730cm ^-1 /A1710cm ^-1 <0.97 and an absorption intensity of the acetate group of 0.35<(A1710cm ^-1 +A1730cm ^-1 )/A1425cm ^-1 <0.55. A polyvinyl alcohol film,
The IR absorption intensity and the absorption intensity of the acetate group were analyzed after the polyvinyl alcohol film was immersed in pure water, stirred, taken out, and dried at 105° C./1 hr.
further having a syndiotacticity of 52% to 56%;
A polyvinyl alcohol film, wherein 0.12 g of the polyvinyl alcohol film is treated with a boric acid aqueous solution of 0.2 wt %, and the boron content of the aqueous solution after dissolving in water is 16 to 19 ppm. A polarizing film comprising the polyvinyl alcohol film according to claim 1 . 3. The polarizing film according to claim 2 , wherein the ratio (A/B) of the absorbance (A) at a wavelength of 480 nm and the absorbance (B) at a wavelength of 700 nm in the crossed Nicols state is 1.40 to 1.70. 4. The polarizing film according to claim 3 , wherein the ratio (A/B) of the absorbance (A) at a wavelength of 480 nm and the absorbance (B) at a wavelength of 700 nm in the crossed Nicols state is 1.51 to 1.65. A step of polymerizing a vinyl ester-based resin monomer to form a polyvinyl ester-based resin and then performing a saponification reaction to obtain a polyvinyl alcohol resin, wherein vinyl 2,2-bis(trifluoromethyl)propionate is added during the polymerization reaction. (vinyl 2,2-bis(trifluoromethyl)propionate) copolymer is added, and the addition amount ratio of the copolymer molar amount/the vinyl ester resin monomer molar amount is 1 to 3 mole%, and the dielectric constant is between 34 and 36 step (a) of adding a saponifying solvent of
(b) heating and melting the polyvinyl alcohol resin to form a polyvinyl alcohol casting solution;
step (c) of casting the casting solution into a casting drum;
a step (d) of forming a polyvinyl alcohol film via drying;
The method for producing a polyvinyl alcohol film according to claim 1 , wherein the steps (a) to (c) are carried out under the use of an external heat retaining device, which is a metal heating wire or a jacket with a liquid inside. 6. The production method according to claim 5 , further comprising controlling the residual acetate group sequence by adjusting the pH value or adding a solvent with a different dielectric constant in the step (a). Furthermore, in the step (a), the polyvinyl alcohol resin obtained by the saponification reaction is pulverized and dried, and steam is blown in during the drying process to prevent the resin particles from excessively drying and skinning. 7. The manufacturing method according to claim 6 .

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