TWI735449B - Polyvinyl alcohol-based resin for polarizing film production and its manufacturing method, polyvinyl alcohol-based film and its manufacturing method, and polarizing film - Google Patents

Abstract

The present invention is a polyvinyl alcohol-based resin for the production of polarizing films, and its weight swelling degree calculated according to the following formula (1) is 1.4 to 1.65. Therefore, it is possible to produce a polyvinyl alcohol-based film with excellent transparency and dyeability required for the production of a polarizing film without display defects and uneven polarization with high productivity.

Weight swelling degree = (weight when immersed in water at 15℃ for 1 hour and centrifuged at 2,000G for 1 minute)/(weight when dried at 105℃ for 2 hours after centrifugal separation)‧‧‧(1)

Description

Polyvinyl alcohol-based resin for polarizing film production and its manufacturing method, polyvinyl alcohol-based film and its manufacturing method, and polarizing film

The present invention relates to a polyvinyl alcohol resin for polarizing film production. More specifically, the present invention relates to a polyvinyl alcohol-based resin capable of producing a polyvinyl alcohol-based film excellent in transparency and dyeability with high productivity, a method for producing the polyvinyl alcohol-based resin, and a polyvinyl alcohol-based film using the polyvinyl alcohol-based resin Its production method and the use of this polyvinyl alcohol-based film have a polarizing film excellent in the uniformity of the degree of polarization.

Conventionally, a polyvinyl alcohol-based film is prepared by dissolving a polyvinyl alcohol-based resin in water to prepare an aqueous solution (film forming stock solution), then forming a film by a solution casting method (casting method) and drying it. The polyvinyl alcohol-based film obtained in this manner is used in various applications as a film having excellent transparency and dyeability, and one of its useful applications includes a polarizing film. The polarizing film is used as the basic component of liquid crystal displays. In recent years, high-brightness and high-definition machines and their use are expanding.

Among them, with the high-definition and larger screens of LCD TVs, there is a need for polyethylene that has better transparency and dyeability than conventional products, and is less susceptible to polarization unevenness in polarizing films even if it is a large area. Alcohol-based film. In order to meet these needs, not only the film forming step of the polyvinyl alcohol-based film, but also a method of improving the polyvinyl alcohol-based resin or its aqueous solution used as a raw material.

In general, the higher the degree of polymerization, the higher the degree of saponification, and the higher the purity of the polyvinyl alcohol-based resin, the more difficult it is to dissolve in water or the easier it is to aggregate in water. Even if the resin is added to water at 100°C or higher under pressure, undissolved substances are likely to remain. Furthermore, even if a transparent aqueous solution with no undissolved substances can be obtained at first glance, there will be clusters called clusters. The polymer association exists in the aqueous solution. Of course, the undissolved matter will reduce the transparency when forming a thin film and become a display defect of the polarizing film. In addition, the clusters may cause uneven dyeing during the production of the polarizing film, which is considered to be the cause of display defects and uneven polarization.

As a countermeasure against this display defect, for example, a polyvinyl alcohol-based film has been proposed, using polyvinyl alcohol containing 95% by weight or more of 5 mesh (mesh-pass) to 100 mesh (mesh-on) particle size. It is a polymer chip (for example, refer to Patent Document 1.).

[Prior Technical Literature]

[Patent Literature]

[Patent Document 1] Japanese Patent Application Publication No. 2001-302817

However, in the technique disclosed in Patent Document 1, particles with a small particle diameter tend to aggregate during the preparation of the film-forming stock solution. In a slurry state or a wet cake state, if the aggregates are generated, it is easy to cause adhesion to the piping and clogging of the piping. In addition, agglomerates cause undissolved matters and clusters, and undissolved matters reduce the transparency of the polyvinyl alcohol-based film, and clusters reduce the dyeability of the polyvinyl alcohol-based film. Furthermore, if agglomerates are formed, it takes a long time to dissolve at a high temperature when preparing an aqueous solution of a polyvinyl alcohol-based resin. Due to excessive thermal history, the resin and additives are degraded in hue, and the resulting aqueous solution or film tends to be yellowed.

Therefore, the present invention is based on this background, and aims to provide a polyvinyl alcohol-based resin that can be produced with high productivity in order to produce a polarizing film free from display defects and uneven polarization, with excellent transparency and dyeability. The polyvinyl alcohol film.

As a result of diligent research by the inventors in view of these circumstances, they focused on the weight swelling degree of the polyvinyl alcohol-based resin used as the raw material of the polyvinyl alcohol-based film, and found that the polyvinyl alcohol-based resin having a specific weight swelling degree can be suppressed in The generation of undissolved substances and aggregates in the water can prevent the attachment of pipes and pipe clogging. Therefore, the polyvinyl alcohol film can be manufactured with high productivity, and the generation of clusters can be further suppressed, so it can be manufactured without display. Disadvantages, polarizing film with uneven polarization.

That is, the gist of the present invention is a polyvinyl alcohol-based resin for producing a polarizing film, and the weight swelling degree calculated according to the following formula (1) is 1.4 to 1.65.

Weight swelling degree = (weight when immersed in water at 15℃ for 1 hour and centrifuged at 2,000G for 1 minute)/(weight when dried at 105℃ for 2 hours after centrifugal separation)‧‧‧(1)

In addition, the present invention is a method for manufacturing the above-mentioned polyvinyl alcohol-based resin for polarizing film manufacturing, and also provides: a method for manufacturing a polyvinyl alcohol-based resin for polarizing film manufacturing, including the step of drying at 120-150°C for 1 to 4 hours; A vinyl alcohol-based film is obtained by using the polyvinyl alcohol-based resin for manufacturing a polarizing film; and a method for manufacturing a polyvinyl alcohol-based film includes the following steps (A) to (D); the polarizing film is composed of the film; The vinyl alcohol-based resin has a weight swelling degree calculated by the above formula (1) of 1.4 to 1.65.

(A) Wash the polyvinyl alcohol resin with water; (B) Dehydrate the polyvinyl alcohol resin after washing with water by centrifugal separation; (C) prepare an aqueous solution of the polyvinyl alcohol resin in a dissolving tank; (D) A polyvinyl alcohol-based resin aqueous solution is formed into a film by a casting method.

The polyvinyl alcohol-based resin for polarizing film production of the present invention can suppress the generation of undissolved substances and aggregates in water, and can prevent the attachment of the pipe and the clogging of the pipe. Therefore, the polyvinyl alcohol-based resin can be manufactured with high productivity. film. Furthermore, the generation of clusters can be suppressed, so it is suitable for the production of polarizing films without display defects and uneven polarization.

The present invention will be described in detail below.

Regarding the polyvinyl alcohol resin (for the production of polarizing film) of the present invention, unmodified polyvinyl alcohol resin is usually used, that is, polyvinyl acetate obtained by polymerizing vinyl acetate is used for saponification. The resin obtained. If necessary, a resin obtained by saponifying a copolymer of vinyl acetate and a small amount (usually 10 mol% or less, 5 mol% or less) of a component copolymerizable with vinyl acetate can also be used. Components that can be copolymerized with vinyl acetate, for example, unsaturated carboxylic acids (for example, including salts, esters, amides, nitriles, etc.), olefins with 2 to 30 carbon atoms (for example, ethylene, propylene, n-butene) , Isobutylene, etc.), vinyl ethers, unsaturated sulfonates, etc. In addition, modified polyvinyl alcohol-based resins obtained by chemically modifying saponified hydroxyl groups can also be used.

In addition, as a polyvinyl alcohol-based resin, it can also be used for a polyvinyl alcohol-based resin having a 1,2-diol structure in the side chain. The polyvinyl alcohol resin having a 1,2-diol structure in the side chain, for example, can be obtained by (i) a copolymer of vinyl acetate and 3,4-diethoxy-1-butene The method of saponification, (ii) the method of saponifying and decarboxylating the copolymer of vinyl acetate and vinyl ethylene carbonate, (iii) the method of combining vinyl acetate with 2,2-dialkyl-4-vinyl-1 It can be obtained by saponifying and deketalizing the copolymer of 3-dioxolane, (iv) saponifying the copolymer of vinyl acetate and glycerol monoallyl ether, etc.

The weight average molecular weight of the polyvinyl alcohol resin is preferably 100,000 to 200,000, preferably 110,000 to 180,000, and more preferably 120,000 to 160,000.

If the weight average molecular weight is too small, there will be a tendency that sufficient optical performance cannot be obtained when the polyvinyl alcohol-based resin is formed into an optical film; if it is too large, it will become difficult to stretch the film into a polarizing film, and industrial production will tend to be difficult. . In addition, the weight average molecular weight of the polyvinyl alcohol-based resin in the present invention is the weight average molecular weight measured by the GPC-MALS method.

The average saponification degree of the polyvinyl alcohol-based resin is preferably 99.0 mol% or more, particularly preferably 99.3 mol% or more, more preferably 99.5 mol% or more, and particularly preferably 99.7 mol% or more. If the average saponification is too low, sufficient optical performance cannot be obtained when the polyvinyl alcohol-based resin is formed into an optical film, which is unfavorable. Here, the average degree of saponification in the present invention is measured in accordance with JIS K 6726.

In the present invention, the polyvinyl alcohol-based resin preferably has a weight average molecular weight of 120,000 or more and an average saponification degree of 99.5 mol% or more.

The biggest feature of the present invention is that a polyvinyl alcohol-based resin is used with a weight swelling degree of 1.4 to 1.65. In addition, the weight swelling degree in the present invention is calculated according to the following formula (1).

Weight swelling degree = (weight when immersed in water at 15℃ for 1 hour and centrifuged at 2,000G for 1 minute)/(weight when dried at 105℃ for 2 hours after centrifugal separation)‧‧‧(1)

The weight swelling degree is preferably 1.43 to 1.62, particularly preferably 1.45 to 1.60, and even more preferably 1.47 to 1.58. If the weight swelling degree exceeds the upper limit, the particles of the polyvinyl alcohol-based resin tend to agglomerate in water or in a water-containing state, and the agglomerates tend to adhere to the piping, and the object of the present invention cannot be achieved. In addition, it is difficult to dissolve in water due to aggregation, and clusters tend to remain in the aqueous solution, which cannot achieve the purpose of the present invention. Conversely, if the weight swelling degree does not reach the lower limit, it becomes difficult to dissolve in water, and the clusters tend to remain in the aqueous solution, which cannot achieve the purpose of the present invention.

As a method of controlling the weight swelling degree, a method of controlling the molecular weight or the degree of saponification, a method of drying the polyvinyl alcohol-based resin under specific conditions, a method of controlling the particle size using a sieve or the like, and the like can be cited. Among them, the method of drying the polyvinyl alcohol-based resin under specific conditions as described later is preferred. By setting the drying conditions to a specific range, a coating film (referred to as a skin layer) to avoid fusion can be appropriately formed on the surface of the particles of the polyvinyl alcohol-based resin. The weight swelling degree can be controlled by the skin layer.

Hereinafter, an example of a method of manufacturing a polyvinyl alcohol-based resin while controlling the degree of weight swelling will be described.

Generally, the synthesized polyvinyl alcohol resin can be supplied to the film formation of the polyvinyl alcohol film through subsequent steps such as solvent washing, drying, pulverization and sieving if necessary. In this subsequent step, the drying step is important to control the weight swelling degree. In the present invention, the drying step is preferably carried out at 120-150°C for 1 to 4 hours.

The above-mentioned drying temperature is preferably 121~145℃, more preferably 122~140℃, especially 123~135℃. If the drying temperature is too high, the weight swelling degree tends to decrease or the polyvinyl alcohol-based resin tends to yellow. Conversely, if it is too low, the drying will be insufficient and the weight swelling will tend to increase.

The above-mentioned drying time is preferably 1.3 to 3.7 hours, particularly preferably, 1.5 to 3.5 hours. If the drying time is too long, the weight swelling degree tends to decrease or the polyvinyl alcohol-based resin tends to yellow. On the contrary, if it is too short, the drying will be insufficient and the weight swelling will tend to increase.

The drying step may be performed by a known dry drying method such as a rotary dryer, a stirring drying tank, etc. As a preferred form of the present invention, the wet drying is performed before the dry drying step Words are conducive to the formation of a proper cortex. Regarding wet drying, generally speaking, the resin powder is blown into the heated jacket and the inside of the extruder with vent holes while water vapor is blown in. Although wet drying is impossible to completely remove water from the resin, it can reduce the water content of the resin to several%.

In this way, the polyvinyl alcohol-based resin for polarizing film production of the present invention can be obtained.

Next, the manufacturing method of the polyvinyl alcohol-based film will be described. The polyvinyl alcohol-based film is manufactured using the polyvinyl alcohol-based resin of the present invention according to the following steps (A) to (D).

(A) Wash the polyvinyl alcohol resin with water; (B) Dehydrate the polyvinyl alcohol resin after washing with water by centrifugal separation; (C) prepare an aqueous solution of the polyvinyl alcohol resin in a dissolving tank; (D) A polyvinyl alcohol-based resin aqueous solution is formed into a film by a casting method.

In the above step (A), the polyvinyl alcohol-based resin is washed with water in order to remove the remaining sodium acetate. A small amount of auxiliary components such as alcohols and surfactants may also be contained in the water used as the cleaning solution.

In the above step (B), the polyvinyl alcohol resin in the slurry state is dehydrated by a centrifugal separator to form a wet cake with a moisture content of 50% by weight or less. If the water content is too large, it will tend to be difficult to prepare the desired aqueous solution concentration in step (C). As described above, if the weight swelling of the polyvinyl alcohol-based resin is too large or too small, adhesion and accumulation of the resin to the piping may occur. This problem is most likely to occur in the wet cake state. Specifically, it occurs in the SUS piping from the outlet of the centrifugal separator to the dissolution tank.

In the above step (C), water, the obtained wet cake of polyvinyl alcohol-based resin, plasticizers such as glycerin, surfactant, etc., are added to the dissolution tank, and they are heated and stirred to dissolve. For this dissolution, it is preferable in terms of solubility to blow water vapor into a dissolution tank equipped with an up-and-down circulation flow generating type stirring blade. In this case, if steam is blown into the dissolution tank, and the stirring is started when the temperature in the tank reaches 40 to 80°C, it is preferable in terms of uniform dissolution. If the temperature in the tank at the start of stirring is too low, the load on the motor will increase, and if it is too high, the polyvinyl alcohol resin will tend to agglomerate and be unable to dissolve uniformly. Further, blow in water vapor, and pressurize the tank when the temperature in the tank reaches 90~100°C normally. When the temperature in the tank reaches 120~150°C, the blowing of steam is finished, and the stirring is continued for 0.5~3 hours and the dissolution is finished. .

If the dissolution temperature is too low, the polyvinyl alcohol-based resin will not dissolve sufficiently, and the transparency of the polyvinyl alcohol-based film will tend to decrease. If it is too high, decomposition products of the polyvinyl alcohol-based resin and surfactant may be generated. The hue of the polyvinyl alcohol-based film tends to decrease.

In addition, if the dissolution time is too short, the polyvinyl alcohol-based resin may not dissolve sufficiently, and the dyeability of the polyvinyl alcohol-based film tends to decrease. If the dissolution time is too long, the polyvinyl alcohol-based resin and surfactant may decompose. The hue of the polyvinyl alcohol-based film tends to decrease.

After the polyvinyl alcohol resin is dissolved, the concentration is adjusted to achieve the desired concentration. The resin concentration of the polyvinyl alcohol resin aqueous solution is preferably 15-60% by weight, preferably 18-55% by weight, and 20-50% by weight. Better. If the resin concentration is too low, the drying load of the film will increase. Conversely, if the resin concentration is too high, the viscosity will become too high and film formation will tend to become difficult.

In this way, the polyvinyl alcohol-based resin aqueous solution used in the present invention can be obtained, and the obtained polyvinyl alcohol-based resin aqueous solution is preferably subjected to defoaming treatment. The defoaming method includes static defoaming and defoaming using a multi-axial extruder with vent holes. As the above-mentioned multi-screw extruder with vent holes, a biaxial extruder with vent holes is generally used.

In step (D), the polyvinyl alcohol-based resin aqueous solution is filtered, and then discharged from the T-shaped slit die and cast to a casting mold such as a casting drum and an endless belt to form a film. The obtained film is dried with a metal heating roll and a floating dryer, and the widthwise ends are cut apart and wound on a roll to become a product.

In this way, the polyvinyl alcohol-based film of the present invention can be obtained.

The thickness of the polyvinyl alcohol film of the present invention is preferably 60 μm or less, and particularly preferably 30 μm or less. If the thickness is too thick, it tends to be difficult to thin the polarizing film.

In addition, the polyvinyl alcohol-based film of the present invention has a width of 4 m or more, which is preferable in terms of productivity, and a length of 4 km or more, which is more preferable in terms of productivity.

The polyvinyl alcohol film of the present invention preferably has a haze of 0.3% or less, particularly preferably 0.2% or less, and more preferably 0.1% or less. If the haze is too high, the light transmittance of the polarizing film tends to decrease. The method of reducing the haze includes the method of controlling the weight swelling degree of the polyvinyl alcohol resin, the method of adding a surfactant to the aqueous solution of the polyvinyl alcohol resin to increase the solubility, and the method of improving the surface smoothness of the casting mold. Methods etc.

The polyvinyl alcohol film of the present invention has few defects, excellent transparency and dyeability, and can be ideally used as a raw roll of a polarizing film.

Hereinafter, the polarizing film of the present invention will be described.

The polarizing film of the present invention is produced by unwinding the above-mentioned polyvinyl alcohol-based film from a roll and transporting it in the horizontal direction, and is manufactured through steps such as swelling, dyeing, boric acid crosslinking, stretching, washing, and drying.

The swelling step is implemented before the dyeing step. The swelling step not only cleans the stains on the surface of the polyvinyl alcohol-based film, but also has the effect of preventing uneven dyeing by swelling the polyvinyl alcohol-based film. In the swelling step, water is usually used as the treatment liquid. As long as the main component of the treatment liquid is water, a small amount of additives such as iodine compounds and surfactants, alcohol, etc. may also be added. The temperature of the swelling bath is usually about 10 to 45°C, and the immersion time in the swelling bath is usually about 0.1 to 10 minutes. In addition, extension operations can be performed during the treatment process if necessary.

The dyeing step is performed by contacting the film with a liquid containing iodine or a dichroic dye. Usually an aqueous solution of iodine-potassium iodide is used, and the concentration of iodine is 0.1~2g/L, and the concentration of potassium iodide is 1~100g/L. The dyeing time is about 30~500 seconds, which is more practical. The temperature of the treatment bath is preferably 5-50°C. In addition to water solvents, the aqueous solution may also contain a small amount of organic solvents compatible with water. In addition, extension operations can be performed during the treatment process if necessary.

The boric acid cross-linking step is performed using a boron compound such as boric acid or borax. The boron compound is used in the form of an aqueous solution or a water-organic solvent mixture and a concentration of about 10 to 100 g/L. If potassium iodide is coexisted in the liquid, it is preferable to stabilize the polarization performance. The temperature during the treatment is preferably about 30 to 70°C, and the treatment time is preferably about 0.1 to 20 minutes. Moreover, extension operations can also be performed during the treatment process if necessary.

The extension step should extend 3-10 times in the uniaxial direction, preferably 3.5-6 times. At this time, it does not matter even if a slight extension is performed in the direction at right angles to the extension direction (the degree of preventing shrinkage in the width direction, or the extension of more than this degree). The temperature during extension is preferably 30~170℃. Furthermore, as long as the stretching magnification is finally set within the aforementioned range, the stretching operation is not only performed in a single stage, but may be performed in a stage within an arbitrary range of the manufacturing steps.

The washing step is performed by, for example, immersing the polyvinyl alcohol-based film in water or an iodide aqueous solution such as potassium iodide to remove precipitates generated on the surface of the film. When using potassium iodide aqueous solution, the potassium iodide concentration should be about 1~80g/L. The temperature during the washing treatment is usually 5 to 50°C, preferably 10 to 45°C. The processing time is usually 1 to 300 seconds, preferably 10 to 240 seconds. In addition, washing with water and washing with a potassium iodide aqueous solution may be combined appropriately.

The drying step may be carried out in the air at 40 to 80°C for 1 to 10 minutes.

The degree of polarization of the polarizing film of the present invention is preferably 99.5% or more, more preferably 99.8% or more. If the polarization is too low, there is a tendency that the contrast of the liquid crystal display cannot be ensured.

_{In addition, the degree of polarization is generally determined by the light transmittance (H 11} ) measured at the wavelength λ in a state where two polarizing films are superimposed so that the alignment direction becomes the same direction, and when the two polarizing films are superimposed to make _{The light transmittance (H 1} ) measured at the wavelength λ in the state where the alignment directions are perpendicular to each other is calculated according to the following formula.

[(H ₁₁ -H ₁ )/(H ₁₁ +H ₁ )] ^1/2

Furthermore, the monomer transmittance of the polarizing film of the present invention is preferably 43% or more. If the transmittance of the monomer is too low, there is a tendency that the high brightness of the liquid crystal display cannot be achieved.

The monomer transmittance is a value obtained by measuring the light transmittance of the polarizing film monomer using a spectrophotometer.

In this way, the polarizing film of the present invention can be obtained, and the polarizing film of the present invention is suitable for manufacturing a polarizing plate without uneven polarization.

Hereinafter, the manufacturing method of the polarizing plate will be described.

The above-mentioned polarizing film is formed by bonding an optically isotropic resin film as a protective film on one side or both sides via an adhesive to form a polarizing plate. As the protective film, for example, cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, cyclic olefin polymer, cyclic olefin copolymer, polystyrene, polyether agglomerate, polyarylene Films or sheets of base ester, poly-4-methylpentene, polyphenylene ether, etc.

The bonding method can be performed by a known technique. For example, a liquid adhesive composition is uniformly coated on a polarizing film, a protective film, or both, and then the two are bonded and press-bonded by heating or irradiation. Active energy rays.

In order to make the film into a thin film, a curable resin such as urethane resin, acrylic resin, urea resin, etc. may be applied to one or both sides of the polarizing film instead of the protective film, and the protective film may be cured and laminated.

The polarizing film and polarizing plate obtained according to the present invention have no display defects, uneven polarization, and excellent in-plane uniformity of polarization performance, and can be ideally used in portable information terminals, personal computers, televisions, projectors, etc. Sign boards, electronic desktop computers, electronic clocks, word processors, electronic paper, game consoles, video recorders, cameras, photo albums, thermometers, audio, automotive or mechanical measuring instruments such as liquid crystal display devices, sunglasses, Anti-glare glasses, stereo glasses, wearable displays, display elements (CRT, LCD, organic EL, electronic paper, etc.) with reflection reduction layers, optical communication equipment, medical equipment, construction materials, toys, etc.

[Example]

Hereinafter, the present invention will be explained more specifically with reference to examples, but the present invention is not limited to the following examples as long as it does not exceed the gist.

In addition, "parts" and "%" in the examples mean weight basis.

About each physical property, it measures as follows.

<Measurement conditions>

(1) Weight swelling degree

1 g of polyvinyl alcohol-based resin was immersed in 10 g of water at 15°C for 1 hour to swell. Put the obtained slurry into a centrifuge tube, and use a centrifugal separator ("H-19α" manufactured by KOKUSAN Co. Ltd.) to use 2,000G Perform centrifugal separation for 1 minute and spin dry the water. After measuring the weight A (g) of the obtained cake, it was dried on an aluminum dish at 105°C for 2 hours, the weight B (g) of the obtained powder was measured, and the weight swelling degree was calculated according to the following formula.

Weight swelling degree = (weight A when immersed in water at 15°C for 1 hour and centrifuged at 2,000G for 1 minute)/(weight B when dried at 105°C for 2 hours after centrifugal separation)

(2) Haze (%)

From the obtained polyvinyl alcohol-based film, 10 test pieces of 50 mm×50 mm were cut out and measured using a haze meter NDH-2000 manufactured by Nippon Denshoku Co., Ltd., and the average value of the 10 pieces was taken as the haze.

(3) Uneven polarization

Cut out a test piece of length 30cm×width 30cm from the obtained polarizing film, and clamp it at a 45-degree angle between two polarizing plates in a cross nicol state (single transmittance 43.5%, polarization degree 99.9% ), and then use a light box with a surface illuminance of 14,000lx to observe the optical spots in the transmission mode, and evaluate them according to the following criteria.

(Evaluation criteria)

○...no stain.

×...There are stains.

(4) Display shortcomings (a)

A test piece with a length of 30 cm x a width of 13 cm was cut out from the obtained polarizing film, visually inspected under an environment of 15000 lx, and the number of displayed defects (pieces) above 100 μm was measured.

(5) Monomer transmittance (%)

A sample of 4 cm in length×4 cm in width was cut out from the obtained polarizing film, and the monomer transmittance was measured using an automatic polarizing film measuring device (manufactured by JASCO Corporation: VAP7070).

<Example 1>

(Production of polyvinyl alcohol resin)

Using peroxyester as an initiator, vinyl acetate is polymerized in methanol to produce polyvinyl acetate. Then, saponification was performed using a 2% NaOH aqueous solution to obtain a polyvinyl alcohol-based resin composition. The obtained polyvinyl alcohol-based resin composition is washed with water and dehydrated by a centrifugal separator to obtain a polyvinyl alcohol-based resin wet cake. The obtained wet cake was put into the sheath, and after wet drying with steam, it was dried at 125°C for 2 hours using a rotary dryer. As shown in Table 1, the weight swelling degree of the obtained polyvinyl alcohol-based resin was 1.58, the weight average molecular weight was 128,000, and the average saponification degree was 99.8 mol%.

(Manufacturing of polyvinyl alcohol film)

After washing 1,000 kg of the obtained polyvinyl alcohol-based resin with 12,000 kg of water, it was dehydrated to obtain a wet cake with a moisture content of 40%. Until the wet cake was taken out from the slurry after washing with water, no adhesion of the resin to the piping was observed. Then, 1,700 kg of wet cake, 2,300 kg of water, and 120 kg of glycerin as a plasticizer were added to the pressure dissolving tank. The temperature was raised to 140°C while stirring, and the concentration was adjusted to 25% of the resin concentration to obtain a uniformly dissolved polyethylene. Alcohol-based resin aqueous solution. Then, the polyvinyl alcohol-based resin aqueous solution was supplied to a biaxial extruder with vent holes and defoamed, and the temperature of the aqueous solution was set to 95°C, and it was cast from a T-shaped slot die to a casting drum to form a film into a film. Finally, the obtained film is dried using a metal heating roller, and the two The ends were cut and wound to obtain a roll-shaped polyvinyl alcohol film (thickness 30 μm, width 5 m, length 5 km). The properties of the obtained polyvinyl alcohol-based film are shown in Table 2.

(Manufacturing of Polarizing Film)

The obtained polyvinyl alcohol-based film was immersed in a water tank with a water temperature of 25°C and stretched to 1.7 times in the flow direction while swelling. Then, it was immersed in a 28°C aqueous solution composed of 0.5 g/L of iodine and 30 g/L of potassium iodide, and extended to 1.6 times in the flow direction while dyeing; then, immersed in a composition of 40 g/L of boric acid and 30 g/L of potassium iodide. In an aqueous solution (55°C), while performing boric acid crosslinking, uniaxially stretched to 2.1 times in the flow direction. Finally, it was washed with potassium iodide aqueous solution and dried to obtain a polarizing film with a total stretching ratio of 5.7 times. The characteristics of the obtained polarizing film are shown in Table 2.

<Examples 2~4>

The drying conditions in the production process of the polyvinyl alcohol-based resin were set to the drying conditions shown in Table 1, except that the same procedure as in Example 1 was carried out to obtain a polyvinyl alcohol-based resin, a polyvinyl alcohol-based film, and a polarizing film . The respective characteristics are shown in Table 1 and Table 2.

<Comparative Example 1>

Except setting the drying conditions in the production process of the polyvinyl alcohol-based resin to the drying conditions shown in Table 1, the same procedure as in Example 1 was carried out to obtain a polyvinyl alcohol-based resin. The solubility of the obtained polyvinyl alcohol-based resin in water is reduced. Furthermore, it carried out similarly to Example 1, and obtained the polyvinyl alcohol-based film and the polarizing film. The respective characteristics are shown in Table 1 and Table 2.

<Comparative Example 2>

Except setting the drying conditions in the production process of the polyvinyl alcohol-based resin to the drying conditions shown in Table 1, the same procedure as in Example 1 was carried out to obtain a polyvinyl alcohol-based resin. The obtained polyvinyl alcohol-based resin adheres to the piping in large quantities during the production of the polyvinyl alcohol-based film, and it is difficult to stably and continuously manufacture the polyvinyl alcohol-based film. In addition, it tends to form agglomerates when dissolved in water, so it is difficult to dissolve uniformly. Furthermore, it carried out similarly to Example 1, and obtained the polyvinyl alcohol-type film and the polarizing film. The respective characteristics are shown in Table 1 and Table 2.

The polyvinyl alcohol-based resins of Examples 1 to 4 have a weight swelling degree within the specified range of the present invention, so there is no adhesion to the piping during the production of the polyvinyl alcohol-based film, and the obtained polyvinyl alcohol-based film has excellent transparency .

On the other hand, the polyvinyl alcohol-based resin of Comparative Example 1 whose weight swelling degree is smaller than the specific range of the present invention has lower water solubility, resulting in poor transparency of the obtained polyvinyl alcohol-based film; the weight swelling degree is lower than that of the present invention The polyvinyl alcohol-based resin of Comparative Example 2 with a large specific range adhered to the piping in large quantities during manufacture, and it was difficult to produce stably and continuously, and it was easy to form agglomerates when dissolved in water, so it was difficult to dissolve uniformly. The obtained polyvinyl alcohol-based film The transparency is poor.

Furthermore, it can be seen that Examples 1 to 4 are more excellent than Comparative Examples 1 and 2 regarding the polarization characteristics and quality of the polarizing film obtained from each polyvinyl alcohol-based film.

The above-mentioned embodiment shows the specific form of the present invention, but the above-mentioned embodiment is only an illustration, and is not a restrictive interpretation. For those with ordinary knowledge in this technical field, various modifications are still intended to be included in the scope of the present invention.

[Industrial Utilization]

The polyvinyl alcohol-based film obtained from the polyvinyl alcohol-based resin for producing the polarizing film of the present invention has excellent transparency. The polarizing film obtained from the polyvinyl alcohol-based film has no display defects, uneven polarization, and excellent quality. Ideal for use in portable information terminals, personal computers, TVs, projectors, sign boards, electronic desktop computers, electronic clocks, word processors, electronic paper, game consoles, video recorders, cameras, photo albums, thermometers , Liquid crystal display devices such as audio, automotive or mechanical measuring instruments, Sunglasses, anti-glare glasses, stereo glasses, wearable displays, display elements (CRT, LCD, organic EL, electronic paper, etc.) with reflection reduction layers, optical communication equipment, medical equipment, construction materials, toys, etc.

Claims (7)

A polyvinyl alcohol resin for polarizing film production. It is a resin obtained by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate, or copolymerizing vinyl acetate with vinyl acetate and 10 mol% or less. It is a resin obtained by saponifying the copolymer of the components and is a powdery polyvinyl alcohol resin used as a raw material for the polyvinyl alcohol film of the original roll of the polarizing film, which is calculated according to the following formula (1) The weight swelling degree is 1.4~1.65; the weight swelling degree = (the weight when immersed in water at 15°C for 1 hour and centrifuged at 2,000G for 1 minute)/(the weight when dried at 105°C for 2 hours after centrifugal separation )‧‧‧(1). For example, the polyvinyl alcohol resin for the manufacture of polarizing film in the first item of the scope of patent application, wherein the weight average molecular weight of the polyvinyl alcohol resin is 120,000 or more and the average saponification degree is 99.5 mol% or more. A method for manufacturing polyvinyl alcohol resin for polarizing film manufacturing, which is a method for manufacturing polyvinyl alcohol resin for polarizing film manufacturing such as item 1 or 2 of the scope of patent application; characterized in that it includes drying at 120~150℃1 ~4 hour steps. A polyvinyl alcohol-based film is obtained by using a polyvinyl alcohol-based resin for polarizing film manufacturing as described in item 1 or 2 of the scope of patent application. For example, the polyvinyl alcohol-based film of the fourth item in the scope of the patent application has a thickness of 30μm or less. A polarizing film is composed of a polyvinyl alcohol-based film such as item 4 or 5 in the scope of patent application. A method for manufacturing a polyvinyl alcohol film, which is a method for manufacturing a polyvinyl alcohol film such as item 4 or 5 of the scope of the patent application; it is characterized by including the following steps (A) ~ (D): (A) The alcohol-based resin is washed with water; (B) the polyvinyl alcohol-based resin after washing with water is dehydrated by centrifugal separation; (C) an aqueous solution of the polyvinyl alcohol-based resin is prepared in a dissolving tank; (D) the polyethylene The alcohol-based resin aqueous solution is formed into a film by a casting method.