JPWO2017033552A1 - POLYVINYL ALCOHOL RESIN FOR PRODUCING POLARIZING FILM, AND ITS MANUFACTURING METHOD, POLYVINYL ALCOHOL BASED FILM AND ITS MANUFACTURING METHOD, POLARIZING FILM, POLYVINYL ALCOHOL RESIN - Google Patents

Abstract

This invention is a polyvinyl-alcohol-type resin for polarizing film manufacture whose weight swelling degree calculated by following formula (1) is 1.4-1.65. For this reason, a polyvinyl alcohol film excellent in transparency and dyeability required for producing a polarizing film free from display defects and uneven polarization can be produced with high productivity. Degree of swelling of weight = (weight when immersed in water at 15 ° C. for 1 hour and then centrifuged at 2,000 G for 1 minute) / (weight when dried at 105 ° C. for 2 hours after centrifugation) (1) )

Description

  The present invention relates to a polyvinyl alcohol resin for producing a polarizing film. More specifically, the present invention relates to a polyvinyl alcohol resin capable of producing a polyvinyl alcohol film excellent in transparency and dyeability with high productivity, a method for producing the same, a polyvinyl alcohol film using the polyvinyl alcohol resin, and a method thereof. The present invention relates to a manufacturing method and a polarizing film using the polyvinyl alcohol film and having excellent uniformity of polarization degree.

  Conventionally, a polyvinyl alcohol film has been produced by dissolving a polyvinyl alcohol resin in water to prepare an aqueous solution (film forming stock solution), and then forming and drying the film by a solution casting method (cast method). . The polyvinyl alcohol film thus obtained is used in many applications as a film excellent in transparency and dyeability, and one of its useful applications is a polarizing film. Such a polarizing film is used as a basic component of a liquid crystal display, and in recent years, its use has been expanded to high-luminance and high-definition equipment.

  Under such circumstances, with higher resolution and larger screens of liquid crystal televisions, etc., polyvinyl alcohol films that are much more transparent and dyeable than conventional products and are less likely to cause uneven polarization in the polarizing film even when the area is large. Is needed. In order to meet such a demand, not only a process for forming a polyvinyl alcohol film but also a method for improving a polyvinyl alcohol resin as a raw material and an aqueous solution thereof have been performed.

  In general, the higher the degree of polymerization, the degree of saponification, and the higher the degree of purity of the polyvinyl alcohol-based resin, the more difficult it is to dissolve in water and the more likely it is to aggregate in water. Even if the resin is put into water at 100 ° C. or higher under pressure, undissolved substances are likely to remain, and even if a transparent aqueous solution without apparently undissolved substances is obtained, a polymer called a cluster is contained in the aqueous solution. There are aggregates. As a matter of course, the undissolved material deteriorates the transparency when formed into a film, and becomes a display defect of the polarizing film. In addition, the cluster is considered to be a cause of display defects and polarization unevenness because it causes uneven staining when manufacturing the polarizing film.

  As a countermeasure against such display defects, for example, a polyvinyl alcohol film using a polyvinyl alcohol polymer chip containing 95% by weight or more of particles having a particle size of 5 mesh pass to 100 mesh on has been proposed (for example, patents). Reference 1).

JP 2001-302817 A

  However, in the technique disclosed in Patent Document 1, particles having a small particle diameter are easily aggregated when the film-forming stock solution is adjusted. When such agglomerates are generated in a slurry state or a wet cake state, adhesion to the piping and piping blockage are likely to occur. Aggregates cause undissolved matter and clusters. Undissolved matter decreases the transparency of the polyvinyl alcohol film, and the cluster decreases the dyeability of the polyvinyl alcohol film. Furthermore, when aggregates are formed, it becomes necessary to dissolve the polyvinyl alcohol resin aqueous solution at a high temperature for a long time, and the resin and additives cause hue deterioration due to excessive heat history, resulting in an aqueous solution or film obtained. Tend to turn yellow.

  Therefore, in the present invention, under such a background, a polyvinyl alcohol film that is excellent in transparency and dyeability necessary for producing a polarizing film free from display defects and polarization unevenness can be produced with high productivity. Provide resin.

  However, as a result of intensive studies in view of such circumstances, the present inventors have focused on the degree of weight swelling of the polyvinyl alcohol resin used as a raw material for the polyvinyl alcohol film, and a polyvinyl alcohol resin having a specific degree of weight swelling is obtained. Because it can suppress the generation of undissolved substances and aggregates in water, and can prevent the adhesion and blockage of these pipes, it can produce polyvinyl alcohol film with high productivity, and can also suppress the generation of clusters. The present inventors have found that a polarizing film free from display defects and uneven polarization can be produced.

That is, the gist of the present invention is a polyvinyl alcohol-based resin for producing a polarizing film, wherein the weight swelling degree calculated by the following formula (1) is 1.4 to 1.65.
Degree of swelling of weight = (weight when immersed in water at 15 ° C. for 1 hour and then centrifuged at 2,000 G for 1 minute) / (weight when dried at 105 ° C. for 2 hours after centrifugation) (1) )

Moreover, this invention is a method of manufacturing the said polyvinyl-alcohol-type resin for polarizing film manufacture, Comprising: The manufacturing method of the polyvinyl-alcohol-type resin for polarizing film manufacture including the process of drying at 120-150 degreeC for 1-4 hours, this A polyvinyl alcohol film obtained by using a polyvinyl alcohol resin for producing a polarizing film, a method for producing a polyvinyl alcohol film comprising the following steps (A) to (D), a polarizing film comprising the film, A polyvinyl alcohol resin having a weight swelling degree calculated by the above formula (1) of 1.4 to 1.65 is also provided.
(A) A step of washing the polyvinyl alcohol resin with water.
(B) A step of dewatering the polyvinyl alcohol resin after washing with water by centrifugation.
(C) The process of preparing the aqueous solution of polyvinyl alcohol-type resin in a dissolution tank.
(D) The process of forming into a film the polyvinyl alcohol-type resin aqueous solution by the casting method.

  The polyvinyl alcohol-based resin for producing a polarizing film of the present invention suppresses the generation of undissolved substances and aggregates in water, and prevents the adhesion to these pipes and the pipe clogging. Can be manufactured. Furthermore, since the generation of clusters can be suppressed, it is suitable for producing a polarizing film free from display defects and uneven polarization.

The present invention is described in detail below.
As the polyvinyl alcohol resin (for producing a polarizing film) of the present invention, an unmodified polyvinyl alcohol resin, that is, a resin produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate is used. If necessary, a resin obtained by saponifying a copolymer of vinyl acetate and a small amount (usually 10 mol% or less, preferably 5 mol% or less) of a copolymerizable component with vinyl acetate may be used. it can. Examples of components copolymerizable with vinyl acetate include unsaturated carboxylic acids (including salts, esters, amides, nitriles, etc.), and olefins having 2 to 30 carbon atoms (for example, ethylene, propylene, n-butene). , Isobutene, etc.), vinyl ethers, unsaturated sulfonates and the like. Moreover, the modified polyvinyl alcohol-type resin obtained by chemically modifying the hydroxyl group after saponification can also be used.

  Moreover, as a polyvinyl alcohol-type resin, the polyvinyl alcohol-type resin which has a 1, 2- diol structure in a side chain can also be used. Such a polyvinyl alcohol resin having a 1,2-diol structure in the side chain includes, for example, (i) a method of saponifying a copolymer of vinyl acetate and 3,4-diacetoxy-1-butene, and (ii) acetic acid. A method for saponifying and decarboxylating a copolymer of vinyl and vinyl ethylene carbonate, (iii) saponifying and decarboxylating a copolymer of vinyl acetate and 2,2-dialkyl-4-vinyl-1,3-dioxolane It is obtained by a method of ketalization, (iv) a method of saponifying a copolymer of vinyl acetate and glycerol monoallyl ether, or the like.

The weight average molecular weight of the polyvinyl alcohol resin is preferably 100,000 to 200,000, particularly preferably 11 to 180,000, and more preferably 120,000 to 160,000.
If the weight average molecular weight is too small, sufficient optical performance tends not to be obtained when the polyvinyl alcohol resin is used as an optical film, and if it is too large, stretching becomes difficult when the film is used as a polarizing film. Tend to be difficult. In addition, the weight average molecular weight of the polyvinyl alcohol-type resin in this invention is a weight average molecular weight measured by GPC-MALS method.

  The average saponification degree of the polyvinyl alcohol 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. It is. If the average saponification degree is too low, sufficient optical performance cannot be obtained when a polyvinyl alcohol-based resin is used as an optical film. Here, the average saponification degree in the present invention is measured according to JIS K 6726.

  In the present invention, the polyvinyl alcohol 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 greatest feature of the present invention is that a polyvinyl alcohol resin having a weight swelling degree of 1.4 to 1.65 is used. In addition, the weight swelling degree in this invention is computed by following formula (1).

  Degree of swelling of weight = (weight when immersed in water at 15 ° C. for 1 hour and then centrifuged at 2,000 G for 1 minute) / (weight when dried at 105 ° C. for 2 hours after centrifugation) (1) )

  The degree of weight swelling is preferably 1.43 to 1.62, particularly preferably 1.45 to 1.60, and more preferably 1.47 to 1.58. When the weight swelling degree exceeds the upper limit, the particles of the polyvinyl alcohol-based resin easily aggregate in water or in a state of containing moisture, and the aggregate easily adheres in the pipe, thereby achieving the object of the present invention. Can not. Moreover, it becomes difficult to dissolve in water due to agglomeration, and the clusters tend to remain in the aqueous solution, and the object of the present invention cannot be achieved. On the other hand, even if the degree of weight swelling is less than the lower limit, it becomes difficult to dissolve in water, and the clusters tend to remain in the aqueous solution, and the object of the present invention cannot be achieved.

  Examples of the technique for controlling the degree of weight swelling include a technique for controlling the molecular weight and the degree of saponification, a technique for drying the polyvinyl alcohol resin under specific conditions, and a technique for controlling the particle diameter by sieving. In these, the method of drying polyvinyl alcohol-type resin on specific conditions as mentioned later is preferable. By setting the drying conditions within a specific range, a film (called a skin layer) for avoiding fusion can be appropriately formed on the particle surface of the polyvinyl alcohol resin. With such a skin layer, the degree of weight swelling can be controlled.

Below, an example of the method of manufacturing a polyvinyl alcohol-type resin is demonstrated, controlling a weight swelling degree.
Usually, the synthesized polyvinyl alcohol resin is subjected to solvent washing, drying, and, if necessary, subsequent processes such as pulverization and sieving to be used for forming a polyvinyl alcohol film. Among these post-processes, the drying process is important for controlling the degree of weight swelling. In the present invention, the drying process is preferably performed at 120 to 150 ° C. for 1 to 4 hours.

  The drying temperature is particularly preferably 121 to 145 ° C, more preferably 122 to 140 ° C, and particularly preferably 123 to 135 ° C. If the drying temperature is too high, the degree of weight swelling tends to decrease and the polyvinyl alcohol resin tends to yellow. Conversely, if it is too low, drying tends to be insufficient and the degree of weight swelling tends to increase.

  The drying time is particularly preferably 1.3 to 3.7 hours, and further preferably 1.5 to 3.5 hours. If the drying time is too long, the degree of weight swelling tends to decrease and the polyvinyl alcohol resin tends to yellow. On the other hand, if it is too short, drying tends to be insufficient and the degree of weight swelling tends to increase.

  Such a drying step may be performed by a known dry drying technique such as a rotary dryer or a stirring drying tank, but as a preferred embodiment of the present invention, performing the wet drying before the dry drying step, It is preferable for forming an appropriate skin layer. In general, the wet drying is performed by spraying water vapor while flowing the resin powder in a heated jacket or a vented extruder. In wet drying, it is impossible to completely remove moisture from the resin, but it is possible to reduce the water content of the resin to the order of several percent.

  Thus, the polyvinyl alcohol resin for producing a polarizing film of the present invention is obtained.

Next, a method for producing a polyvinyl alcohol film will be described. A polyvinyl alcohol-type film is manufactured by the following process (A)-(D) using the polyvinyl alcohol-type resin of this invention.
(A) A step of washing the polyvinyl alcohol resin with water.
(B) A step of dewatering the polyvinyl alcohol resin after washing with water by centrifugation.
(C) The process of preparing the aqueous solution of polyvinyl alcohol-type resin in a dissolution tank.
(D) The process of forming into a film the polyvinyl alcohol-type resin aqueous solution by the casting method.

  In the step (A), the polyvinyl alcohol resin described above is washed with water in order to remove the remaining sodium acetate. The water used as the cleaning liquid may contain a small amount of auxiliary components such as alcohol and surfactant.

  In the said process (B), the polyvinyl alcohol-type resin used as the slurry state is spin-dry | dehydrated with a centrifuge, and it is set as the wet cake with a moisture content of 50 weight% or less. If the water content is too high, it tends to be difficult to prepare a desired aqueous solution concentration in the step (C). As described above, when the weight swelling degree of the polyvinyl alcohol-based resin is excessively large or excessively small, adhesion or deposition of the resin to the pipe occurs. Such a defect is most likely to occur in a wet cake state. Specifically, it occurs in SUS piping from the centrifuge outlet to the dissolution tank.

  In the above step (C), water, the obtained polyvinyl alcohol-based resin wet cake, and, if necessary, a plasticizer such as glycerin or a surfactant are charged into the dissolving tank, and dissolved by heating and stirring. Let Such dissolution is preferably carried out by blowing water vapor in a dissolution tank equipped with a vertical circulation flow generation type stirring blade in view of solubility. In such a case, it is preferable from the viewpoint that uniform stirring can be performed when steam is blown into the dissolution tank and the temperature in the tank reaches 40 to 80 ° C. If the temperature in the tank at the start of stirring is too low, the load on the motor increases, and if it is too high, the polyvinyl alcohol resin tends to be hardened and cannot be uniformly dissolved. Furthermore, when steam was blown into the tank and the temperature in the tank was normally 90 to 100 ° C., the inside of the tank was pressurized, and when the temperature in the tank reached 120 to 150 ° C., the steam was blown and 0.5% Continue stirring for ~ 3 hours to complete dissolution.

  If the dissolution temperature is too low, sufficient dissolution of the polyvinyl alcohol-based resin cannot be obtained, and the transparency of the polyvinyl alcohol-based film tends to decrease. If it is too high, the decomposition product of the polyvinyl alcohol-based resin or the surfactant is present. And the hue of the polyvinyl alcohol film tends to decrease.

  In addition, if the dissolution time is too short, sufficient dissolution of the polyvinyl alcohol-based resin cannot be obtained, and the dyeability of the polyvinyl alcohol-based film tends to decrease. If it is too long, the polyvinyl alcohol-based resin and the surfactant are decomposed. A thing arises and there exists a tendency for the hue of a polyvinyl alcohol-type film to fall.

  After the polyvinyl alcohol resin is dissolved, the concentration is adjusted so as to obtain a desired concentration. The resin concentration of the aqueous polyvinyl alcohol resin solution is preferably 15 to 60% by weight, particularly preferably 18 to 55% by weight, More preferably, it is 20 to 50% by weight. If the resin concentration is too low, the drying load of the film becomes large. Conversely, if the resin concentration is too high, the viscosity becomes too high and film formation tends to be difficult.

  Thus, the polyvinyl alcohol-based resin aqueous solution used in the present invention is obtained, but the obtained polyvinyl alcohol-based resin aqueous solution is preferably defoamed. Examples of the defoaming method include stationary defoaming and defoaming with a multi-screw extruder having a vent. As the multi-screw extruder having the vent, a twin-screw extruder having a vent is usually used.

  In the step (D), the polyvinyl alcohol-based resin aqueous solution is filtered and then discharged and fluted from a T-type slit die to a cast mold such as a cast drum or an endless belt to form a film. After the obtained film is dried with a metal heating roll or a floating dryer, both ends in the width direction are slit and wound into a roll to obtain a product.

  Thus, the polyvinyl alcohol film of the present invention is obtained.

The polyvinyl alcohol film of the present invention preferably has a thickness of 60 μm or less, particularly preferably 30 μm or less. If the thickness is too large, it is difficult to reduce the thickness of the polarizing film.
The polyvinyl alcohol film of the present invention preferably has a width of 4 m or more from the viewpoint of productivity, and more preferably 4 km or more from the viewpoint 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. As a method for reducing such haze, a method for controlling the weight swelling degree of the polyvinyl alcohol resin described above, a method for improving the solubility by adding a surfactant to the polyvinyl alcohol resin aqueous solution, a cast type surface smoothness The technique etc. which improve are mentioned.

  The polyvinyl alcohol film of the present invention has few defects, is excellent in transparency and dyeability, and is preferably used as a raw material for a polarizing film.

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

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

  The swelling process is performed before the dyeing process. In addition to washing the surface of the polyvinyl alcohol film by the swelling step, there is also an effect of preventing uneven staining by swelling the polyvinyl alcohol film. In the swelling step, water is usually used as the treatment liquid. If the main component is water, the treatment solution may contain a small amount of an iodide compound, an additive such as a surfactant, alcohol, or the like. 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. Moreover, you may perform extending | stretching operation during a process as needed.

  The dyeing step is performed by bringing the film into contact with a liquid containing iodine or a dichroic dye. Usually, an iodine-potassium iodide aqueous solution is used. The iodine concentration is suitably 0.1-2 g / L, and the potassium iodide concentration is suitably 1-100 g / L. The dyeing time is practically about 30 to 500 seconds. The temperature of the treatment bath is preferably 5 to 50 ° C. The aqueous solution may contain a small amount of an organic solvent compatible with water in addition to the aqueous solvent. Moreover, you may perform extending | stretching operation during a process as needed.

  The boric acid crosslinking 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 at a concentration of about 10 to 100 g / L, and it is preferable that potassium iodide coexists in the solution from the viewpoint of stabilizing 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. If necessary, the stretching operation may be performed during the treatment.

  In the stretching step, stretching in a uniaxial direction is preferably performed 3 to 10 times, preferably 3.5 to 6 times. At this time, a slight stretching (stretching to prevent shrinkage in the width direction or more) may be performed in a direction perpendicular to the stretching direction. The temperature during stretching is preferably 30 to 170 ° C. Furthermore, the draw ratio may be finally set within the above range, and the drawing operation may be performed not only in one stage but also in any stage of the manufacturing process.

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

  What is necessary is just to perform a drying process for 1 to 10 minutes at 40-80 degreeC in air | atmosphere.

The polarization degree of the polarizing film of the present invention is preferably 99.5% or more, more preferably 99.8% or more. If the degree of polarization is too low, there is a tendency that the contrast in the liquid crystal display cannot be secured.
Note that the degree of polarization is generally the light transmittance (H ₁₁ ) measured at the wavelength λ in the state where two polarizing films are overlapped so that their orientation directions are the same direction, and the two polarizing films. It is calculated according to the following equation from the light transmittance (H ₁ ) measured at the wavelength λ in a state where the films are superposed so that the orientation directions are orthogonal to each other.
[(H ₁₁ −H ₁ ) / (H ₁₁ + H ₁ )] ^1/2

Further, the single transmittance of the polarizing film of the present invention is preferably 43% or more. If the single transmittance is too low, it tends to be impossible to achieve high brightness of the liquid crystal display.
The single transmittance is a value obtained by measuring the light transmittance of a single polarizing film using a spectrophotometer.

Thus, although the polarizing film of the present invention is obtained, the polarizing film of the present invention is suitable for producing a polarizing plate with little polarization unevenness.
Hereinafter, the manufacturing method of this polarizing plate is demonstrated.

  The polarizing film is bonded to one surface or both surfaces of the polarizing film as a protective film by using an optically isotropic resin film via an adhesive. Examples of protective films include films of cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, cycloolefin polymer, cycloolefin copolymer, polystyrene, polyethersulfone, polyarylene ester, poly-4-methylpentene, polyphenylene oxide, and the like. Or a sheet.

  The bonding method is performed by a known method. For example, after a liquid adhesive composition is uniformly applied to a polarizing film, a protective film, or both, the two are bonded and pressure-bonded, and heated or activated. This is done by irradiating energy rays.

  In addition, for the purpose of thinning the polarizing film, instead of the protective film, a curable resin such as urethane resin, acrylic resin, urea resin, etc. is applied on one side or both sides and cured and laminated. You can also.

  The polarizing film and polarizing plate obtained by the present invention are free from display defects and uneven polarization, and have excellent in-plane polarization performance, such as portable information terminals, personal computers, televisions, projectors, signage, electronic desk calculators, electronic Watches, word processors, electronic paper, game consoles, videos, cameras, photo albums, thermometers, audio, liquid crystal display devices such as cars and machinery instruments, sunglasses, anti-glare glasses, stereoscopic glasses, wearable displays, display elements ( CRT, LCD, organic EL, electronic paper, etc.) for use in antireflection layers, optical communication equipment, medical equipment, building materials, toys and the like.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist.
In the examples, “parts” and “%” mean weight basis.
Each physical property was measured 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. The obtained slurry was put in a centrifuge tube, and centrifuged at 2,000 G for 1 minute using a centrifuge (“H-19α” manufactured by Kokusan Co., Ltd.), and the water was shaken off. 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. did.
Weight swelling degree = (weight A when immersed in water at 15 ° C. for 1 hour and then centrifuged at 2,000 G for 1 minute) / (weight B when centrifuged at 105 ° C. for 2 hours)

(2) Haze (%)
Ten test pieces of 50 mm × 50 mm were cut out from the obtained polyvinyl alcohol-based film, measured using a Nippon Denshoku haze meter NDH-2000, and the average value of the ten sheets was defined as haze.

(3) Polarization unevenness A test piece having a length of 30 cm and a width of 30 cm was cut out from the obtained polarizing film, and two polarizing plates in a crossed Nicol state (single transmittance 43.5%, polarization degree 99.9%) were obtained. After being sandwiched at an angle of 45 °, optical color unevenness was observed in a transmission mode using a light box having a surface illuminance of 14,000 lx and evaluated according to the following criteria.
(Evaluation criteria)
○: No color unevenness.
×… There is uneven color.

(4) Display defects (pieces)
A test piece having a length of 30 cm and a width of 13 cm was cut out from the obtained polarizing film, visually inspected in an environment of 15000 lx, and the number of display defects (pieces) of 100 μm or more was measured.

(5) Single transmittance (%)
A sample having a length of 4 cm and a width of 4 cm was cut out from the obtained polarizing film, and the single transmittance was measured using an automatic polarizing film measuring device (manufactured by JASCO Corporation: VAP7070).

<Example 1>
(Manufacture of polyvinyl alcohol resin)
Using peroxyester as an initiator, vinyl acetate was polymerized in methanol to obtain polyvinyl acetate. Subsequently, the polyvinyl alcohol-type resin composition was obtained by saponifying using 2% NaOH aqueous solution. The obtained polyvinyl alcohol-based resin composition was washed with water and dehydrated with a centrifugal separator to obtain a polyvinyl alcohol-based resin wet cake. The obtained wet cake was put into a jacket, wet-dried with steam, and then 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%.

(Manufacture of polyvinyl alcohol film)
The obtained polyvinyl alcohol-based resin (1,000 kg) was washed with 12,000 kg of water and then dehydrated to obtain a wet cake having a water content of 40%. No adhesion of the resin to the piping was observed before the wet cake was removed from the slurry after water washing. Next, 1,700 kg of wet cake, 2,300 kg of water, and 120 kg of glycerin as a plasticizer are placed in a pressure dissolution can, heated to 140 ° C. while stirring, adjusted to a resin concentration of 25%, and uniformly dissolved A polyvinyl alcohol resin aqueous solution was obtained. Next, the polyvinyl alcohol-based resin aqueous solution was supplied to a twin-screw extruder having a vent and defoamed, and then the aqueous solution temperature was set to 95 ° C. and cast into a cast drum from a T-type slit die to form a film. . Finally, the obtained film is dried using a metal heating roll, both ends are cut off with a slit, and wound to form a roll-like polyvinyl alcohol film (thickness 30 μm, width 5 m, length 5 km). Obtained. Table 2 shows the characteristics of the obtained polyvinyl alcohol film.

(Manufacture of polarizing film)
The obtained polyvinyl alcohol-based film was stretched 1.7 times in the flow direction while being immersed and swollen in a water bath at a water temperature of 25 ° C. Next, the film was stretched 1.6 times in the flow direction while being immersed and dyed in an aqueous solution at 28 ° C. composed of 0.5 g / L of iodine and 30 g / L of potassium iodide. Next, the film was immersed in an aqueous solution (55 ° C.) having a composition of boric acid 40 g / L and potassium iodide 30 g / L, and uniaxially stretched 2.1 times in the flow direction while crosslinking with boric acid. Finally, it was washed with an aqueous potassium iodide solution and dried to obtain a polarizing film having a total draw ratio of 5.7 times. Table 2 shows the characteristics of the obtained polarizing film.

<Examples 2 to 4>
A polyvinyl alcohol resin, a polyvinyl alcohol film, and a polarizing film were obtained in the same manner as in Example 1 except that the drying conditions in the production process of the polyvinyl alcohol resin were the drying conditions shown in Table 1. The respective characteristics are shown in Table 1 and Table 2.

<Comparative Example 1>
A polyvinyl alcohol resin was obtained in the same manner as in Example 1 except that the drying conditions in the production process of the polyvinyl alcohol resin were the drying conditions shown in Table 1. The obtained polyvinyl alcohol-based resin had reduced water solubility. Furthermore, in the same manner as in Example 1, a polyvinyl alcohol film and a polarizing film were obtained. The respective characteristics are shown in Table 1 and Table 2.

<Comparative example 2>
A polyvinyl alcohol resin was obtained in the same manner as in Example 1 except that the drying conditions in the production process of the polyvinyl alcohol resin were the drying conditions shown in Table 1. The obtained polyvinyl alcohol-based resin has a large amount of adhesion to pipes during the production of the polyvinyl alcohol-based film, and it has been difficult to continuously produce a polyvinyl alcohol-based film stably. In addition, it is difficult to dissolve evenly because it is likely to become lumps when dissolved with water. Furthermore, in the same manner as in Example 1, a polyvinyl alcohol film and a polarizing film were obtained. The respective characteristics are shown in Table 1 and Table 2.

  Since the polyvinyl alcohol-based resins of Examples 1 to 4 have a weight swelling degree within the specific range of the present invention, there is no adhesion to the piping during the production of the polyvinyl alcohol-based film, and the obtained polyvinyl alcohol-based film is transparent. It was excellent.

On the other hand, the polyvinyl alcohol-based resin of Comparative Example 1 having a degree of weight swelling smaller than the specific range of the present invention is poor in transparency of the resulting polyvinyl alcohol-based film due to a decrease in water solubility, and the weight swelling. The polyvinyl alcohol resin of Comparative Example 2 having a degree greater than the specific range of the present invention has a large amount of adhesion to the pipe during production and is difficult to be stably produced continuously. Therefore, the polyvinyl alcohol film that is difficult to dissolve uniformly is poor in transparency.
And it turns out that Examples 1-4 are superior to Comparative Examples 1 and 2 in the polarization characteristics and quality of the polarizing film obtained from each polyvinyl alcohol film.

  In the said Example, although the specific form in this invention was shown, the said Example is only a mere illustration and is not interpreted limitedly. Various modifications apparent to those skilled in the art are contemplated to be within the scope of this invention.

  The polyvinyl alcohol-based film obtained from the polyvinyl alcohol-based resin for producing the polarizing film of the present invention is excellent in transparency, and the polarizing film obtained from the polyvinyl alcohol-based film is free from display defects and uneven polarization, and is excellent in quality. , Personal digital assistants, personal computers, TVs, projectors, signage, electronic desk calculators, electronic clocks, word processors, electronic paper, game machines, videos, cameras, photo albums, thermometers, audio, automobile and machinery instruments, etc. Preferred for liquid crystal display devices, sunglasses, anti-glare glasses, stereoscopic glasses, wearable displays, antireflection reducing layers for display elements (CRT, LCD, organic EL, electronic paper, etc.), optical communication equipment, medical equipment, building materials, toys, etc. Used.

Claims (8)

A polyvinyl alcohol-based resin for producing a polarizing film, wherein the weight swelling degree calculated by the following formula (1) is 1.4 to 1.65.
Degree of swelling of weight = (weight when immersed in water at 15 ° C. for 1 hour and then centrifuged at 2,000 G for 1 minute) / (weight when dried at 105 ° C. for 2 hours after centrifugation) (1) )   The polyvinyl alcohol resin for producing a polarizing film according to claim 1, wherein the polyvinyl alcohol resin has a weight average molecular weight of 120,000 or more and an average degree of saponification of 99.5 mol% or more.   A method for producing a polyvinyl alcohol-based resin for producing a polarizing film according to claim 1, comprising a step of drying at 120 to 150 ° C. for 1 to 4 hours. Manufacturing method of resin.   A polyvinyl alcohol film obtained by using the polyvinyl alcohol resin for producing a polarizing film according to claim 1.   The polyvinyl alcohol film according to claim 4, wherein the thickness is 30 μm or less.   A polarizing film comprising the polyvinyl alcohol-based film according to claim 4 or 5. It is a method of manufacturing the polyvinyl alcohol-type film of Claim 4 or 5, Comprising: The manufacturing method of the polyvinyl alcohol-type film characterized by including the following process (A)-(D).
(A) A step of washing the polyvinyl alcohol resin with water.
(B) A step of dewatering the polyvinyl alcohol resin after washing with water by centrifugation.
(C) The process of preparing the aqueous solution of polyvinyl alcohol-type resin in a dissolution tank.
(D) The process of forming into a film the polyvinyl alcohol-type resin aqueous solution by the casting method. A polyvinyl alcohol-based resin having a weight swelling degree calculated by the following formula (1) of 1.4 to 1.65.
Weight swelling = (weight when immersed in water at 15 ° C. for 1 hour and then centrifuged at 2,000 G for 1 minute) / (weight when dried at 105 ° C. for 2 hours after centrifugation) (1) )