JP2017223941A - Polyvinyl alcohol film for polarization films, and method for producing the same, and polarization film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyvinyl alcohol film that has excellent swellability in the production of a polarization film, has a high degree of polarization, and can yield a polarization film with reduced color unevenness with high productivity.SOLUTION: A polyvinyl alcohol film for polarization films is characterized in that: an area swelling rate A1(%/min) in immersing a film, which has been controlled in humidity for 24 hours in an environment of 23°C 50%RH, in water at 30°C for 100 seconds is 20-30%/min.SELECTED DRAWING: None

Description

  The present invention relates to a polyvinyl alcohol film for a polarizing film, and more specifically, a polyvinyl alcohol film having excellent swellability and capable of obtaining a polarizing film having a high degree of polarization and little color unevenness. The present invention relates to a film, a production method thereof, and a polarizing film using the polyvinyl alcohol film.

  In recent years, the development of liquid crystal display devices has been remarkable, and they are widely used in smartphones, tablets, personal computers, liquid crystal televisions, projectors, in-vehicle panels, and the like. Such a liquid crystal display device uses a polarizing film. As the polarizing film, a film obtained by adsorbing and orienting a dichroic dye such as iodine on a polyvinyl alcohol film is mainly used. In recent years, with higher resolution, higher brightness, and larger screens, there is a need for a polarizing film that has a higher degree of polarization than conventional products and has no color unevenness. There is a need for a technique for producing a polarizing film well. The polarizing film is also called a polarizing film or a polarizer.

  In general, a polarizing film is obtained by unwinding a polyvinyl alcohol film as a raw material from a roll and swelling it with water (including warm water) while conveying it in the flow direction (MD direction). Manufactured through processes such as acid crosslinking. The initial swelling process has a great influence on the subsequent dyeing process and stretching process. If the polyvinyl alcohol film does not swell sufficiently, the overall production rate must be reduced. Dyeing and stretching becomes difficult. In order to improve the degree of polarization of the polarizing film, eliminate color unevenness, and improve productivity, it is necessary that the polyvinyl alcohol film has good swelling properties.

  On the other hand, a polyvinyl alcohol film generally dissolves a polyvinyl alcohol resin as a raw material in water, and discharges and flows the obtained aqueous solution (film forming stock solution) into a cast mold such as a cast drum or an endless belt. After peeling the film from the cast mold and drying it using a metal heating roll while carrying it in the flow direction (MD direction), and heat-treating it using a floating dryer as necessary Manufactured. Among these processes, the drying process greatly affects the swelling property of the polyvinyl alcohol film.

  As a technique for improving the swelling property of the polyvinyl alcohol film, for example, a polyvinyl alcohol film to which a water swelling aid is added (for example, see Patent Document 1), or a polyvinyl alcohol film having a small curl angle when immersed in water. (For example, refer patent document 2) and the manufacturing method (for example, refer patent document 3, 4, 5) of the polyvinyl alcohol-type film by specific drying conditions are proposed.

JP 2001-302867 A JP 2001-315140 A JP 2001-315142 A JP 2011-156874 A JP 2006-291173 A

  However, even with the method of the above-mentioned patent document, it was insufficient to improve the swelling property of the polyvinyl alcohol film.

  In the technique disclosed in Patent Document 1, although the degree of weight swelling can be improved, the speed and uniformity of swelling are not considered.

  In the technique disclosed in Patent Document 2, curling occurring in the swelling process during the production of the polarizing film can be prevented, but the speed and uniformity of swelling are not considered.

  In the technique disclosed in Patent Document 3, the thermal history of the polyvinyl alcohol film can be made uniform, but the swelling property is not sufficiently improved.

  In the technique disclosed in Patent Document 4, the in-plane retardation of the film can be reduced, but the swelling property is not sufficiently improved by drying at a constant temperature.

  In the disclosed technique of Patent Document 5, the film after drying (70 ° C.) or heat treatment (120 ° C.) is once cooled and then heated at 50 to 100 ° C. to reduce the in-plane retardation of the film. However, the process was complicated and the swelling property was not sufficiently improved.

  Therefore, in the present invention, under such a background, a polyvinyl alcohol film that is excellent in swellability at the time of manufacturing a polarizing film, has a high degree of polarization, and can obtain a polarizing film with little color unevenness with high productivity. It is intended to provide.

  However, as a result of intensive studies in view of such circumstances, the present inventors have found that a polyvinyl alcohol film having a specific area swelling speed can solve the above-mentioned problems, and have completed the present invention.

  That is, the gist of the present invention is that the area swelling speed A1 (% / min) when a film conditioned for 24 hours in an environment of 23 ° C. and 50% RH is immersed in water at 30 ° C. for 100 seconds is 20 to 30%. It is a polyvinyl alcohol film for polarizing films characterized by being / min.

  The present invention also provides a method for producing the polyvinyl alcohol film and a polarizing film obtained using the polyvinyl alcohol film.

  Since the polyvinyl alcohol film for polarizing film of the present invention is excellent in swelling property at the time of manufacturing the polarizing film, a polarizing film having a high degree of polarization and little color unevenness can be provided with high productivity. .

The present invention is described in detail below.
The polyvinyl alcohol film for polarizing film of the present invention has an area swelling speed A1 (% / min) when a film conditioned for 24 hours in an environment of 23 ° C. and 50% RH is immersed in water at 30 ° C. for 100 seconds. It is a polyvinyl alcohol film which is 20-30% / min.

  The area swelling speed A1 needs to be 20 to 30% / min, preferably 22 to 29% / min, and more preferably 24 to 29% / min. If the area swelling speed A1 is less than 20% / min, the swellability during the production of the polarizing film is inferior, and the object of the present invention cannot be achieved. The resin elution amount increases and the object of the present invention cannot be achieved.

In addition, the area swelling speed | rate A1 in this invention is a value calculated by measuring the film area before water immersion and the film area after water immersion, and using following formula (1).
Area swelling rate (% / min) = 100 × [[(film area after water immersion) − (film area before water immersion)] / (film area before water immersion)] ÷ (100/60) Formula (1)

  The film area may be measured with a caliper or a ruler when the film is relatively large (for example, several centimeters or more). Even when the film is relatively small (for example, several millimeters or less), It is possible to measure with a microscope with high accuracy.

  In addition, the immersion condition of 30 ° C. for 100 seconds is generally a condition set because the swelling process at the time of manufacturing the polarizing film is performed at around 30 ° C. for about 100 seconds.

Moreover, humidity control conditions before the test, 23 ° C. and 50% RH for 24 hours, are general environmental conditions applied to various tests of plastic films, and the moisture content in the polyvinyl alcohol film is measured under such an environment. This is a condition for adjusting the equilibrium moisture content. Usually, the moisture content in the polyvinyl alcohol film is adjusted to about 10% by such humidity control. The film after humidity adjustment is tested under the same environment, or when the test environment is different, the film is immediately subjected to the test after humidity adjustment.
The humidity control conditions before the test are also applied to the area swelling degree described later.

  As a method for controlling the area swelling speed A1, a method for adjusting the chemical structure, molecular weight, saponification degree, etc. of a polyvinyl alcohol resin as a raw material, a method for adding an additive to an aqueous solution of a polyvinyl alcohol resin, polyvinyl alcohol Examples include a method for controlling the degree of crystallinity and orientation of the polymer in the step of forming the aqueous resin solution, a method for controlling the dry state of the film after film formation, a method for adjusting the thickness of the polyvinyl alcohol film, etc. It is done. Among these, the method of controlling the dry state of the film after film formation is preferable, and the method of controlling the dry state of the film after film formation using specific drying conditions described below is particularly preferable.

In addition, the polyvinyl alcohol film for polarizing film of the present invention has an area swelling speed A2 (% / min) when a film conditioned for 24 hours in an environment of 23 ° C. and 50% RH is immersed in water at 30 ° C. for 10 seconds. However, it is preferably 120% / min or more, particularly preferably 150% / min or more, and further preferably 180% / min or more.
If the area swelling speed A2 is too low, the swelling property at the time of producing the polarizing film tends to decrease.
In addition, the upper limit value of the area swelling speed A2 is generally about 300%, and the polyvinyl alcohol-based resin film close to the upper limit value is broken during the swelling process of manufacturing the polarizing film, and is broken during the transportation of the film. It tends to occur.

In addition, the area swelling speed | rate A2 in this invention measures the film area before water immersion, and the film area after water immersion, and is a value calculated using following formula (2).
Area swelling rate (% / min) = 100 × [[(film area after water immersion) − (film area before water immersion)] / (film area before water immersion)] ÷ (10/60) Formula (2)

  Hereinafter, the manufacturing method of the polyvinyl alcohol-type film of this invention is demonstrated. In general, a polyvinyl alcohol-based film is formed by continuously discharging and flowing an aqueous solution of a polyvinyl alcohol-based resin into a cast mold, peeling the obtained film from the cast mold, and then a plurality of metal heating rolls ( Hereinafter, it may be simply described as “heat roll”), and may be obtained by heat treatment if necessary, but the production method of the present invention is characterized by the drying step among these steps.

  As the polyvinyl alcohol resin used in 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-based resin is preferably 100,000 to 300,000, particularly preferably 110,000 to 280,000, and more preferably 120,000 to 260,000. If the weight average molecular weight is too small, sufficient optical performance tends to be difficult to obtain when the polyvinyl alcohol-based resin is used as an optical film, and if it is too large, it tends to be difficult to stretch the polyvinyl alcohol-based film when manufacturing a polarizing film. There is. In addition, the weight average molecular weight of the said polyvinyl alcohol-type resin is a weight average molecular weight measured by GPC-MALS method.

The average saponification degree of the polyvinyl alcohol resin used in the present invention is usually preferably 98 mol% or more, particularly preferably 99 mol% or more, further preferably 99.5 mol% or more, and particularly preferably 99.mol%. It is 8 mol% or more. If the average degree of saponification is too small, there is a tendency that sufficient optical performance cannot be obtained when a polyvinyl alcohol film is used as a polarizing film.
Here, the average saponification degree in the present invention is measured according to JIS K 6726.

  As a polyvinyl alcohol-type resin used for this invention, you may use together 2 or more types from which modified | denatured seed | species, modified | denatured amount, weight average molecular weight, average saponification degree differ.

The polyvinyl alcohol-based film of the present invention is prepared by preparing an aqueous solution of a polyvinyl alcohol-based resin using the above-mentioned polyvinyl alcohol-based resin, and continuously discharging and flowing the polyvinyl alcohol-based resin aqueous solution into a cast mold. After the film is peeled from the cast mold, it can be continuously produced by drying with a plurality of heat rolls and heat-treating as necessary. For example, it can be produced by the following steps.
(A) A step of preparing an aqueous solution of a polyvinyl alcohol resin.
(B) A step of forming a film by continuously discharging and flowing a polyvinyl alcohol-based resin aqueous solution into a cast mold.
(C) A step of peeling off the obtained film from the cast mold, heating and drying, and heat-treating as necessary.

Here, examples of the cast mold include a cast drum (drum mold roll), an endless belt, and the like. However, the cast mold is preferably performed from the viewpoint of widening, lengthening, and film thickness uniformity.
Hereinafter, a case where the cast mold is a cast drum will be described as an example.

  First, the step (A) will be described.

In the step (A), first, the polyvinyl alcohol-based resin described above is washed with water and dehydrated using a centrifuge to obtain a polyvinyl alcohol-based resin wet cake having a water content of 50% by weight or less. It is preferable. When the water content is too large, it tends to be difficult to obtain a desired aqueous solution concentration.
Such a polyvinyl alcohol resin wet cake is dissolved in warm water or hot water to prepare an aqueous solution of the polyvinyl alcohol resin.

  The method for preparing the aqueous solution of the polyvinyl alcohol-based resin is not particularly limited. For example, it may be prepared by using a heated multi-screw extruder, and in a dissolving can equipped with a vertical circulation flow generation type stirring blade, The above-mentioned polyvinyl alcohol-based resin wet cake can be introduced and water vapor can be blown into the can to prepare an aqueous solution having a desired concentration.

  In addition to polyvinyl alcohol-based resins, polyvinyl alcohol-based resin aqueous solutions include commonly used plasticizers such as glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol, trimethylolpropane, and nonions. It is preferable from the viewpoint of the film-forming property of the polyvinyl alcohol film to contain a hydrophilic, anionic and / or cationic surfactant.

  The resin concentration of the polyvinyl alcohol-based resin aqueous solution thus obtained is preferably 15 to 60% by weight, particularly preferably 17 to 55% by weight, and further preferably 20 to 50% by weight. If the resin concentration of such an aqueous solution is too low, the drying load increases and the production capacity tends to decrease. If it is too high, the viscosity becomes too high and uniform dissolution tends to be difficult.

Next, the step (B) will be described.
The obtained polyvinyl alcohol-based resin aqueous solution is defoamed. Examples of the defoaming method include static defoaming and defoaming by a multi-screw extruder having a vent. As the multi-screw extruder having a vent, a twin-screw extruder having a vent is usually used.

  After the defoaming treatment, the polyvinyl alcohol-based resin aqueous solution is introduced into the T-shaped slit die by a certain amount, discharged and cast on a rotating cast drum, and formed into a film by a continuous casting method.

  The temperature of the polyvinyl alcohol-based resin aqueous solution at the exit of the T-shaped slit die is preferably 80 to 100 ° C, particularly preferably 85 to 98 ° C. If the temperature of the aqueous polyvinyl alcohol resin solution is too low, it tends to cause poor flow, and if it is too high, it tends to foam.

  The viscosity of the aqueous polyvinyl alcohol resin solution is preferably 50 to 200 Pa · s, particularly preferably 70 to 150 Pa · s at the time of discharge. If the viscosity of such an aqueous solution is too low, it tends to be poor in flow, and if it is too high, it tends to be difficult to flow.

  The discharge speed of the polyvinyl alcohol-based resin aqueous solution discharged from the T-type slit die onto the cast drum is preferably 0.1 to 5 m / min, particularly preferably 0.2 to 4 m / min, and more preferably 0.8. 3 to 3 m / min. If the discharge speed is too slow, the productivity tends to decrease, and if it is too fast, the fluency tends to be difficult.

  The diameter of the cast drum is preferably 2 to 5 m, particularly preferably 2.4 to 4.5 m, and further preferably 2.8 to 4 m. If the diameter is too small, the drying length is insufficient and the speed tends not to be obtained, and if it is too large, the transportability tends to decrease.

  The width of the cast drum is preferably 5 m or more, particularly preferably 5.5 m or more, and further preferably 5.5 to 7 m. If the width of the cast drum is too small, the productivity tends to decrease.

  The rotation speed of the cast drum is preferably 3 to 50 m / min, particularly preferably 4 to 40 m / min, and further preferably 5 to 35 m / min. If the rotational speed is too slow, the productivity tends to decrease, and if it is too fast, the peelability tends to decrease.

  The surface temperature of such a cast drum is preferably 40 to 99 ° C, particularly preferably 60 to 95 ° C. If the surface temperature is too low, the peelability tends to decrease, and if it is too high, foaming tends to occur.

  Thus, a film is formed, and the obtained film is peeled off from the cast drum.

  Next, the step (C) will be described. Step (C) includes a step of heating and drying the obtained film, and a step of heat treatment as necessary.

  The film peeled from the cast drum is transported in the flow direction (MD direction) and dried by bringing the front and back surfaces of the film into contact with a plurality of hot rolls alternately. The hot roll is, for example, a roll having a diameter of 0.2 to 2 m, the surface of which is hard chrome plated or mirror-finished, and usually 2 to 30, preferably 10 to 25 are used for drying.

  The drying temperature is preferably 50 to 150 ° C., particularly preferably 60 to 140 ° C., further preferably 65 to 130 ° C., particularly preferably 70 to 120 ° C. If the drying temperature is too low, drying tends to be poor, and if it is too high, appearance defects such as swell tend to be caused. The drying temperature in the present invention is the hot roll surface temperature.

  In the present invention, it is preferable to perform a heat cycle treatment during the drying step from the viewpoint of improving the swelling speed and stabilizing.

The heat cycle process in the present invention means a drying process in which temperature rise and fall, or fall and rise are included as one set of temperature changes, and the temperature difference between the rise and fall is 5 ° C. or more. .
Specifically, when the drying temperature is increased / decreased / decreased / increased or increased / decreased / increased / declined / increased / decreased with a temperature difference of 5 ° C. or more as one heat cycle process Ascending / descending / raising / falling or descending / raising / falling / raising, or ascending / descending / raising / falling / raising or descending / raising / falling / raising / falling as two heat cycle processes It is what counts.

The drying temperature (heat roll surface temperature) during the heat cycle treatment is preferably set in the range of 50 to 150 ° C, particularly preferably 60 to 140 ° C, more preferably 65 to 130 ° C, and particularly preferably 70. ~ 120 ° C.
If the drying temperature is too high, it tends to cause appearance defects such as swell, and if it is too low, it tends to cause poor drying.

Regarding the temperature difference (absolute value) when the temperature rises or falls during the heat cycle treatment, the maximum value of the temperature difference is preferably 10 ° C. or more, particularly preferably 15 ° C. or more, more preferably 20 ° C. or more. . Moreover, the upper limit of the maximum value of this temperature difference is 60 degrees C or less normally, Preferably it is 55 degrees C or less, Most preferably, it is 50 degrees C or less.
If the maximum value of the temperature difference is too large, it tends to cause appearance defects such as swell, and if it is too small, the effect of heat cycle treatment tends to be poor.

About the frequency | count of the heat cycle process in a drying process, Preferably it is 1 time or more, Especially preferably, it is 2 times or more, More preferably, it is 2-4 times.
When the number of heat cycle treatments is too large, appearance defects such as swell tend to be caused.

The reason why the area swellability is improved by the heat cycle treatment is presumed to be because the polyvinyl alcohol polymer is oriented in the thickness direction during the evaporation of water. That is, it is speculated that the evaporation of moisture is intermittently repeated in the thickness direction, so that the polymer chain that is easily plane-oriented in normal drying is also oriented in the thickness direction. In general, since water absorption proceeds in the form of interstices between polymer chains, such a film tends to swell in the surface direction.
In general, since heat cycle treatment is also effective for stress relaxation of a polymer molded body, the heat cycle treatment of the present invention is presumed to contribute to stabilization of dimensional changes during swelling and drying. .

  The drying time is not particularly limited, but is usually 10 to 500 seconds, preferably 20 to 300 seconds, and particularly preferably 30 to 200 seconds. If the drying time is too short, drying tends to be poor, and if it is too long, appearance defects such as swell tend to be caused. In addition, the drying time in this invention is the integration time of the contact time of a heat roll and a film.

  The moisture content of the dried film is preferably 10% by weight or less, particularly preferably 1 to 9% by weight. If the moisture content is too high, the finally obtained polyvinyl alcohol film tends to be poorly dried.

In the present invention, it is preferable to heat-treat the dried film from the viewpoint of stabilizing the swelling speed. Particularly preferred is heating from both sides of the film in that the dried state on both sides of the film can be made uniform. Examples of the heat treatment method include a method of blowing hot air on both surfaces of the film using a floating dryer, and a method of irradiating near infrared rays on both surfaces of the film using an infrared lamp.
The heat treatment temperature is preferably 60 to 150 ° C, particularly preferably 70 to 130 ° C, and further preferably 80 to 120 ° C. Although heat processing time is not specifically limited, When using a floating dryer, 10 to 100 second is preferable, Most preferably, it is 20 to 80 second. The heat treatment method in the present invention is a method that does not use a heat roll.

  The film subjected to drying and heat treatment as necessary is slit at both ends in the width direction and wound onto a roll to become a product (polyvinyl alcohol film).

  The width of the polyvinyl alcohol film thus obtained is preferably 2 m or more from the viewpoint of increasing the area of the polarizing film, and particularly preferably 2 to 6 m from the viewpoint of avoiding breakage.

  The length of the polyvinyl alcohol film is preferably 5 km or more, particularly preferably 5 to 50 km from the viewpoint of increasing the area of the polarizing film.

  The thickness of the polyvinyl alcohol film for polarizing film of the present invention is 5 to 75 μm, preferably 10 to 60 μm, particularly preferably 10 to 45 μm, and particularly preferably 10 to 40 μm. If the thickness is too thin, the film is likely to break during the production of the polarizing film. Conversely, if the thickness is too thick, it is difficult to make the polarizing film thinner. The thickness of the polyvinyl alcohol film is adjusted by the resin concentration in the polyvinyl alcohol resin aqueous solution, the discharge amount (discharge speed) to the cast mold, and the like.

  The method for producing a polyvinyl alcohol film has been described so far, taking as an example the case where a cast drum (drum-type roll) is used as the cast mold, but it is produced using an endless belt or a resin film as the cast mold. Is also possible.

Thus, the polyvinyl alcohol film of the present invention is obtained.
Since the polyvinyl alcohol film for a polarizing film of the present invention is excellent in swelling property, a polarizing film can be produced with high productivity.

  Hereinafter, the manufacturing method of the polarizing film obtained using the polyvinyl alcohol-type film of this invention is demonstrated.

  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 10 to 500 seconds.

  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.

  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 10 to 1000 seconds. 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 40 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 thus obtained is preferably 99.8% or more, more preferably 99.9% 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.
The degree of polarization is generally determined by the light transmittance (H ₁₁ ) measured at the wavelength λ and the two polarized films in a state where two polarizing films are overlapped so that the orientation directions thereof are the same. 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 42% or more, more 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 having excellent polarization degree and no color unevenness.
Hereinafter, the manufacturing method of the polarizing plate of this invention is demonstrated.

  The polarizing film of the present invention 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 or the like is applied to one side or both sides of the protective film and cured to obtain a polarizing plate. You can also

  The polarizing film or polarizing plate comprising the polyvinyl alcohol film of the present invention has excellent polarization performance, and is a portable information terminal, personal computer, TV, projector, signage, electronic desk calculator, electronic clock, word processor, electronic paper, game machine , Video, camera, photo album, thermometer, audio, liquid crystal display devices such as automobile and machinery instruments, sunglasses, anti-glare glasses, stereoscopic glasses, wearable display, display elements (CRT, LCD, organic EL, electronic paper) Etc.) for antireflection layers, optical communication equipment, medical equipment, building materials, toys and the like.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited to a following example, unless the summary is exceeded.
In the examples, “parts” and “%” mean weight basis.

<Measurement conditions>
(1) Area swelling speed A1 (% / min), area swelling speed A2 (% / min)
The obtained polyvinyl alcohol film was conditioned for 24 hours in an environment of 23 ° C. and 50% RH, and a test of 100 mm in the length direction × 100 mm in the width direction (area 10,000 mm ² ) from the center and both ends in the width direction. Three pieces were cut out. Next, the film after humidity control was immersed in a 30 ° C. water bath for 100 seconds, the film was taken out of the water bath, and the length and width were measured in an environment of 23 ° C. and 50% RH to obtain the area after water immersion. The time from taking out the water tank to measuring is within 1 minute. From the obtained area, the area swelling speed A1 (% / min) was calculated according to the following formula, and an average value of three sheets was taken.
Formula (A1) Area swelling speed A1 (% / min) when immersed in water at 30 ° C. for 100 seconds = 100 × [[(area after water immersion) − (area before water immersion)] / (before water immersion) Area)] ÷ (100/60)
In the same manner as described above, the area swelling speed A2 (% / min) when immersed in a 30 ° C. water bath for 10 seconds was calculated according to the following formula, and the average value of the three sheets was taken.
Formula (A2) Area swelling speed A2 (% / min) when immersed in water at 30 ° C. for 10 seconds = 100 × [[(area after water immersion) − (area before water immersion)] / (before water immersion) Area)] ÷ (10/60)

(2) Polarization degree (%), single transmittance (%)
A specimen having a length of 4 cm and a width of 4 cm was cut out from the center portion and both end portions (within 10 cm from the end of the film) in the width direction of the obtained polarizing film, and an automatic polarizing film measuring device (manufactured by JASCO Corporation: The degree of polarization (%) and single transmittance (%) were measured using VAP7070). Such measurement was carried out for the central part and the tip / terminal part (within 10 m from the film end) in the flow direction (MD direction) of the polarizing film.

(3) Color unevenness From the central part and both ends (10 cm inside from the film end) in the width direction of the obtained polarizing film, a 30 cm long × 30 cm wide test piece was cut out, and two pieces of polarized light in a crossed Nicol state After sandwiching between the plates (single transmittance 43.5%, polarization degree 99.9%) at an angle of 45 °, using a light box with a surface illuminance of 14,000 lx, optical color unevenness in transmission mode Were observed and evaluated according to the following criteria.
(Evaluation criteria)
○ ・ ・ ・ There was color unevenness × ・ ・ ・ There was no color unevenness Such an evaluation was performed for the central portion of the polarizing film in the flow direction (MD direction) and the tip / end portion (within 10 m from the film end). It was.

<Example 1>
(Preparation of polyvinyl alcohol film)
A polyvinyl alcohol resin having a weight average molecular weight of 142,000, a saponification degree of 99.8 mol%, 1,000 kg of water, 2500 kg of water, and 110 kg of glycerin as a plasticizer are added, and the temperature is raised to 140 ° C. with stirring, and the resin concentration is 25%. The concentration was adjusted to obtain a polyvinyl alcohol resin aqueous solution that was uniformly dissolved. Next, the polyvinyl alcohol-based resin aqueous solution is supplied to a twin-screw extruder having a vent and defoamed, and then the aqueous solution temperature is set to 95 ° C. and discharged from a T-type slit die discharge port onto a rotating cast drum (discharge speed). 2.5 m / min) and cast to form a film. When the film is peeled off from the cast drum and the front and back surfaces of the film are alternately brought into contact with a total of 20 hot rolls, the moisture content of the film is 60 seconds in the drying time (integrated time of the contact time between the hot rolls and the film). Drying was performed until 9% by weight. In the drying process where the drying temperature (surface temperature of the hot roll) is 70 to 120 ° C., the heat cycle treatment was performed twice (the maximum temperature of the hot roll was 95 ° C., and the maximum temperature difference during the heat cycle treatment was 25 ° C.). . After drying, hot air was blown from both sides of the film using a floating dryer, and heat treatment was performed until the moisture content of the film reached 2% by weight. Finally, both ends were slit and wound on a roll to obtain a polyvinyl alcohol film having a thickness of 60 μm, a width of 5 m, and a length of 5 km. The properties of the obtained polyvinyl alcohol film are shown in Table 1.

(Manufacture of polarizing film)
The obtained polyvinyl alcohol film was unwound from a roll, transported in the horizontal direction using a transport roll, and first stretched 1.7 times while being immersed in a water bath with a water temperature of 30 ° C. (100 seconds). Next, it is stretched 1.6 times while dyeing by dipping in an aqueous solution of 30 g / L of iodine 0.5 g / L and potassium iodide 30 g / L, then boric acid 40 g / L, potassium iodide 30 g / L. The film was immersed in an aqueous solution (50 ° C.) having a composition of L and uniaxially stretched 2.1 times while crosslinking with boric acid. Finally, it was washed with an aqueous potassium iodide solution and dried at 50 ° C. for 2 minutes to obtain a polarizing film having a total draw ratio of 5.7 times. Table 2 shows the characteristics of the obtained polarizing film. No breakage occurred during the production, and the properties of the obtained polarizing film were as shown in Table 2.

<Examples 2-8, Comparative Examples 1-4>
A polyvinyl alcohol film and a polarizing film were obtained in the same manner as in Example 1 except that the production was performed under the conditions shown in Table 1. Table 1 shows the characteristics of the obtained polyvinyl alcohol film, and Table 2 shows the characteristics of the obtained polarizing film.
In Comparative Examples 1 and 2, it was confirmed that the film edge was broken in the swelling step, and that swelling was excessive when the swelling time was 100 seconds.
In comparisons 3 and 4, it was confirmed that the stretching tension was not stable in the swelling process, and the swelling was insufficient when the swelling time was 100 seconds.

  Since the polyvinyl alcohol film of Examples 1 to 8 has a swelling rate within the specific range of the present application, the obtained polarizing film has a high degree of polarization and no color unevenness, whereas the polyvinyl alcohol films of Comparative Examples 1 to 4 It can be seen that the alcohol film has a swelling speed outside the specific range of the present application, and as a result, the obtained polarizing film is inferior in the degree of polarization and has color unevenness.

Claims (7)

  The area swelling speed A1 (% / min) when a film conditioned for 24 hours in an environment of 23 ° C. and 50% RH is immersed in water at 30 ° C. for 100 seconds is 20 to 30% / min. A polyvinyl alcohol film for polarizing film.   The area swelling speed A2 (% / min) when a film conditioned for 24 hours in an environment of 23 ° C. and 50% RH is immersed in water at 30 ° C. for 10 seconds is 120% / min or more. The polyvinyl alcohol film for polarizing films according to claim 1.   The polyvinyl alcohol film for a polarizing film according to claim 1 or 2, wherein the film has a thickness of 10 to 40 µm, a width of 2 m or more, and a length of 5 km or more.   A process for producing a polyvinyl alcohol-based film in which an aqueous solution of a polyvinyl alcohol-based resin is continuously discharged and fluted into a cast mold to form a film, and dried with a plurality of metal heating rolls, the process being dried at 70 to 120 ° C. The method for producing a polyvinyl alcohol film for a polarizing film according to any one of claims 1 to 3, wherein a heat cycle treatment is performed during the drying step.   The method for producing a polyvinyl alcohol film for a polarizing film according to claim 4, wherein the heat cycle treatment is performed twice or more.   A polyvinyl alcohol film for a polarizing film, which is produced by the production method according to claim 4.   A polarizing film comprising the polyvinyl alcohol-based film according to claim 1.