JPWO2016208652A1 - Polyvinyl alcohol film, method for producing polyvinyl alcohol film, and polarizing film - Google Patents

Abstract

It is a polyvinyl alcohol film excellent in dyeability and stretchability, and has a high degree of polarization even when wide, thin and thin, and can obtain a polarizing film without polarization unevenness, Thickness D (mm), A (N / mm2) tension when stretched 6 times in the film flow direction (MD direction) in water at 30 ° C., and the film flow direction (MD direction) in water at 50 ° C. A polyvinyl alcohol film characterized by satisfying the following formulas (1) and (2) when the tension when stretched 6 times is B (N / mm 2) is provided. Formula (1) 0.6 ≦ D × A ≦ 1.2 Formula (2) 0.2 ≦ D × B ≦ 0.4

Description

  The present invention relates to a polyvinyl alcohol film. More specifically, a polyvinyl alcohol film for producing a polarizing film excellent in dyeability and stretchability as a raw material of the polarizing film and excellent in polarizing performance, a production method thereof, and the polyvinyl alcohol film The present invention relates to a polarizing film obtained by use.

  The polarizing film is manufactured by dyeing and stretching a polyvinyl alcohol film as a raw material using a pigment such as iodine. For example, after a polyvinyl alcohol film is swollen with warm water, dyed with iodine, stretched to arrange iodine molecules, cross-linked with a cross-linking agent such as boric acid to maintain the stretched state, washed, And dried. The steps of water swelling, dyeing, stretching, and boric acid crosslinking may be switched in order or a plurality of steps may be performed simultaneously. What is common is that the polyvinyl alcohol film is continuously unwound from the roll, applied with appropriate tension in the flow direction using a winder or nip roll, and conveyed in the horizontal direction. .

  Such a polarizing film is used as a basic component of liquid crystal display devices such as portable information terminals and televisions. In recent years, with the increase in brightness and definition of liquid crystal displays, there has been a demand for polarizing films having high light transmittance and high degree of polarization. Furthermore, as liquid crystal televisions have become larger and thinner, conventional products have been demanded. There is a need for a polarizing film that is wider, longer, and thinner.

  In order to meet the above-described demand, a wide, long and thin polyvinyl alcohol film having excellent dyeability and stretchability is required. When the dyeability of the polyvinyl alcohol film is low, a sufficient degree of polarization cannot be obtained, and polarization unevenness tends to occur. When the stretchability of the polyvinyl alcohol-based film is low, breakage occurs in the manufacturing process of the polarizing film, so that a wide, long and thin polarizing film cannot be manufactured. As a matter of course, continuous production is interrupted by breakage, and the productivity of the polarizing film is greatly reduced. Furthermore, when the stretchability is low, the dye is not sufficiently oriented, and thus the degree of polarization tends to decrease or polarization unevenness tends to occur. Such improvement in dyeability and stretchability is more difficult as the polyvinyl alcohol film becomes wider, longer, and thinner. In addition, in the coating type polarizing plate for the purpose of so-called thinning, the above-described steps such as dyeing and stretching are indispensable and are on the support film. Improvement is desired,

  In order to improve the dyeability of the polyvinyl alcohol film, a method for controlling the bath temperature in the swelling process has been proposed (see, for example, Patent Documents 1 and 2). Moreover, a polarizing plate using a polyvinyl alcohol film having a specific range of stretchability has been proposed (see, for example, Patent Document 3).

JP 2006-065309 A JP 2014-197050 A Japanese Patent Laid-Open No. 2002-236212

  However, in the techniques disclosed in Patent Documents 1 and 2, even if the degree of swelling can be controlled by the bath temperature, a uniform swelling state cannot be obtained unless the tension applied to the polyvinyl alcohol film in the bath is appropriate. In the subsequent dyeing process, there is a problem that the dye does not adsorb uniformly.

  In addition, the technique disclosed in Patent Document 3 defines a stress (tension) when a polyvinyl alcohol film is stretched 4 to 6 times in water. In the actual production of a polarizing film, Since the water temperature of the process was different, it was insufficient to obtain a suitable tension throughout the entire process. The water temperature is often around 30 ° C., which is a relatively low temperature in processes such as swelling and dyeing, and around 50 ° C., which is a relatively high temperature, in processes such as stretching and boric acid crosslinking.

  Therefore, in the present invention, under such a background, a polyvinyl alcohol film excellent in dyeability and stretchability, and a polarizing film having a high degree of polarization and having no polarization unevenness even when widened, elongated and thinned. A polyvinyl alcohol film that can be obtained is provided.

  However, as a result of intensive studies in view of such circumstances, the present inventors have made a polyvinyl alcohol solution obtained by discharging and casting an aqueous solution of a polyvinyl alcohol resin into a cast mold and continuously drying it. The polyvinyl alcohol film produced by paying attention to the underwater tension at a higher temperature of 50 ° C. is particularly wide so that when the film is stretched in water at different temperatures, the underwater tension is in a specific range. It has been found that a polarizing film having a high degree of polarization and no polarization unevenness can be produced even when it is made thin.

That is, the gist of the present invention is that the tension when stretched 6 times in the flow direction of the film (MD direction) in water of thickness D (mm) and 30 ° C. is A (N / mm ² ) and water in 50 ° C. In which the following formulas (1) and (2) are satisfied when the tension when stretched 6 times in the film flow direction (MD direction) is B (N / mm ² ): the film.
Formula (1) 0.6 <= D * A <= 1.2
Formula (2) 0.2 <= D * B <= 0.4

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

  The polyvinyl alcohol film of the present invention is excellent in dyeability and stretchability, and has a high degree of polarization even in the case of being wide, long and thin, and can obtain a polarizing film free from uneven polarization. Can produce a polarizing film with high productivity.

The present invention is described in detail below.
The polyvinyl alcohol film of the present invention has a thickness of D (mm) and a tension of A (N / mm ² ) and 50 ° C. when stretched 6 times in the film flow direction (MD direction) in 30 ° C. water. A polyvinyl alcohol film satisfying the following formulas (1) and (2) when the tension when stretched 6 times in the film flow direction (MD direction) in water is B (N / mm ² ). Is necessary,
Formula (1) 0.6 <= D * A <= 1.2
Formula (2) 0.2 <= D * B <= 0.4
Preferably, a polyvinyl alcohol film satisfying the following formulas (1 ′) and (2 ′):
Formula (1 ′) 0.65 ≦ D × A ≦ 1.15
Formula (2 ′) 0.25 ≦ D × B ≦ 0.39
Particularly preferred is a polyvinyl alcohol film satisfying the following formulas (1 ″) and (2 ″).
Formula (1 ″) 0.7 ≦ D × A ≦ 1.1
Formula (2 ″) 0.27 ≦ D × B ≦ 0.38

Regarding the above formulas (1) to (1 ″), if the value of D × A is too low, the film is unfavorably deformed in the swelling process or the dyeing process, and if it is too high, sufficient dyeing is difficult in the dyeing process. It is not preferable.
In addition, regarding the above formulas (2) to (2 ″), if the value of D × B is too low, the degree of polarization at the time of forming the polarizing film is unfavorable, and if it is too high, breakage tends to occur during the production of the polarizing film. It is not preferable.

  Regarding the above formulas (1) to (1 ″) and the above formulas (2) to (2 ″), the value of the thickness D of the polyvinyl alcohol film is 0.04 mm or less in terms of thinning the polarizing film. Preferably, it is 0.03 mm or less from the viewpoint of further thinning the polarizing film, and more preferably 0.01 to 0.03 mm from the viewpoint of avoiding breakage of the polarizing film.

Furthermore, the polyvinyl alcohol film of the present invention preferably satisfies the following formula (3), particularly preferably satisfies the following formula (3 ′), and more preferably satisfies the following formula (3 ″).
Formula (3) 0.2 ≦ B / A ≦ 0.5
Formula (3 ′) 0.25 ≦ B / A ≦ 0.4
Formula (3 ″) 0.3 ≦ B / A ≦ 0.35

  Regarding the above formulas (3) to (3 ″), if the value of B / A is too low, the degree of polarization tends to decrease when a polarizing film is formed, and if it is too high, breakage tends to occur during the production of the polarizing film. Tend.

The polyvinyl alcohol film of the present invention preferably has a tension A of 15 to 40 N / mm ² when stretched 6 times in the film flow direction (MD direction) in water at 30 ° C., particularly preferably. Is 18 to 35 N / mm ² , more preferably 20 to 30 N / mm ² .
If the value of the tension A is too low, the film tends to be deformed in the swelling process or the dyeing process, and if it is too high, sufficient dyeing tends to be difficult in the dyeing process.

Furthermore, the polyvinyl alcohol film of the present invention preferably has a value of tension B of 3 to 15 N / mm ² when stretched 6 times in the film flow direction (MD direction) in water at 50 ° C., Especially preferably, it is 4-12 N / mm < ² >, More preferably, it is 5-10 N / mm < ² >.
If the value of the tension B is too low, the degree of polarization when the polarizing film is formed tends to decrease, and if it is too high, breakage tends to occur during the production of the polarizing film.

The polyvinyl alcohol film of the present invention has an E2 / E1 value of 0 when the storage elastic modulus in water at 30 ° C. is E1 (Pa) and the storage elastic modulus in water at 50 ° C. is E2 (Pa). .25 to 0.30 is preferable, and 0.26 to 0.29 is particularly preferable.
If the value of E2 / E1 is too low, the polarization degree of the obtained polarizing film tends to decrease, and if it is too high, breakage tends to occur during the production of the polarizing film.

Furthermore, the polyvinyl alcohol film of the present invention preferably has a storage elastic modulus E1 in water of 30 ° C. of 9 to 12 MPa from the viewpoint of transportability.
Moreover, it is preferable from the point of conveyance property that the storage elastic modulus E2 in 50 degreeC water is 2-4 Mpa.

  Hereinafter, a method for producing a polyvinyl alcohol film of the present invention, that is, an aqueous solution of a polyvinyl alcohol resin is discharged and cast into a cast mold to form a film, and continuously dried to produce a polyvinyl alcohol film. A method will be described.

  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 usually 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 is difficult to stretch the polyvinyl alcohol-based film during the production of the polarizing film. Tend. 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 a polyvinyl alcohol-based resin aqueous solution (film forming stock solution) using the polyvinyl alcohol-based resin, and discharging and casting the aqueous solution into a cast mold. It can manufacture continuously by drying, for example, is manufactured by the following processes.
Step (A) A step of preparing a polyvinyl alcohol resin aqueous solution.
Step (B) A step of casting an aqueous solution of a polyvinyl alcohol resin into a cast mold to form a film.
Step (C) A step of heating and drying the formed film by bringing it into contact with a plurality of metal heating rolls.
Process (D) The process of heat-processing the obtained film using a hot air.

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 polyvinyl alcohol resin wet cake is dissolved in warm water or hot water to prepare a polyvinyl alcohol resin aqueous solution.

The method for preparing the polyvinyl alcohol-based resin aqueous solution is not particularly limited. For example, the polyvinyl alcohol-based resin aqueous solution may be prepared by using a heated multi-screw extruder. The polyvinyl alcohol-based resin wet cake thus prepared is charged and water vapor is blown into the can to prepare an aqueous solution having a desired concentration and dissolution.
In the present invention, the latter is preferable in terms of improving the degree of polarization, and it is more preferable to prepare the solution by pressure dissolution at 120 ° C. or higher.

  In addition to the polyvinyl alcohol-based resin, the polyvinyl alcohol-based resin aqueous solution may contain a plasticizer and at least one surfactant of nonionic, anionic, and cationic properties as necessary. It is preferable from the point.

  Examples of the plasticizer used in the present invention include glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol, and trimethylolpropane. Among these, glycerin is preferable because of its low cost.

The blending amount when glycerin is used is preferably 5 to 12% by weight, particularly preferably 6 to 11.5% by weight and more preferably 7 to 11% with respect to the polyvinyl alcohol resin.
If the amount is too small, the underwater tension of the polyvinyl alcohol film tends to increase, and if too large, the underwater tension of the polyvinyl alcohol film tends to be insufficient.

  The surfactant used in the present invention is preferably an anionic surfactant from the viewpoint of compatibility with an aqueous polyvinyl alcohol resin solution.

  The resin concentration of the aqueous polyvinyl alcohol resin 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 is too low, the drying load increases, so the production capacity tends to decrease. If the resin concentration is too high, the viscosity becomes too high and uniform dissolution tends to be difficult.

  Thus, a polyvinyl alcohol-based resin aqueous solution that is a film-forming stock solution is obtained. Next, the step (B) will be described.

  The 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 a T-shaped slit die by a certain amount, discharged and cast on a rotating cast drum, and formed into a film by a casting method.

  The resin temperature of the T-type slit die discharge port is preferably 80 to 100 ° C, particularly preferably 85 to 99 ° C. If the resin temperature is too low, the flow tends to be poor, and if it is too high, the resin 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.
When the viscosity of the aqueous solution is too low, the flow tends to be poor, and when it is too high, casting tends to be difficult.

The discharge speed of the polyvinyl alcohol-based resin aqueous solution discharged from the T-type slit die onto the cast drum is preferably 0.2 to 5 m / min, particularly preferably 0.4 to 4 m / min, more preferably 0.8. 6-3 m / min.
If the discharge speed is too slow, the productivity tends to decrease, and if it is too fast, casting tends to be difficult.

  Casting is preferably performed with a cast drum from the viewpoints of widening, lengthening, and film thickness uniformity. As the cast drum, usually, a surface of stainless steel (SUS) whose main component is iron is subjected to metal plating to prevent damage. Examples of the metal plating include chrome plating, nickel plating, and zinc plating, and these are used alone or in a laminate of two or more layers. Among these, it is preferable that the outermost surface is chrome plating from the viewpoint of durability of the drum surface.

Hereinafter, the film forming method will be described with reference to an example in which a cast drum is used.
The width of the cast drum is preferably 4 m or more, particularly preferably 5 m or more. If the width of the cast drum is too small, it tends to be difficult to obtain a wide film.

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 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, drying tends to be insufficient.

  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, drying tends to be poor, and if it is too high, foaming tends to occur.

  Thus, film formation is performed.

  Next, the step (C) will be described. Step (C) is a step of heating and drying the formed film by bringing it into contact with a plurality of metal heating rolls.

  The polyvinyl alcohol film formed on the cast drum is dried by alternately bringing the front and back surfaces of the film into contact with a plurality of metal heating rolls. Although the surface temperature of a metal heating roll is not specifically limited, Usually, 60-150 degreeC, Furthermore, it is preferable that it is 70-140 degreeC. If the surface temperature is too low, drying tends to be poor, and if the surface temperature is too high, drying tends to be excessive, and appearance defects such as undulation tend to be caused.

In the present invention, the temperature of the plurality of metal heating rolls is preferably in the order of the following conditions (a) to (d) in terms of controlling the underwater tension of the polyvinyl alcohol film.
Condition (a) ≧ 80 ° C
Condition (b) <80 ° C
Condition (c) ≧ 100 ° C.
Condition (d) <100 ° C
In general, the number of metal heating rolls is 10 to 30, and is set so as to satisfy the above temperature condition as appropriate.

  After drying with a metal heating roll, the obtained film is heat-treated in step (D) using hot air. Next, the step (D) will be described.

The temperature of the heat treatment is preferably 110 to 140 ° C, particularly preferably 115 to 135 ° C, and more preferably 120 to 130 ° C. If the heat treatment temperature is too low, the underwater tension of the polyvinyl alcohol film tends to be insufficient, and if it is too high, the underwater tension of the polyvinyl alcohol film tends to increase.
As a method of such heat treatment, a method using a floating dryer is preferable in terms of excellent temperature control.

  The heat-treated film is slit at both ends and wound into a roll to become a roll-shaped polyvinyl alcohol film.

  The width of the polyvinyl alcohol film is preferably 4 m or more from the viewpoint of widening the polarizing film, particularly preferably 4.5 m or more from the viewpoint of further widening, and more preferably from the viewpoint of avoiding breakage. 4.5 to 6 m.

  The length of the polyvinyl alcohol film is preferably 4 km or more from the viewpoint of increasing the area of the polarizing film, particularly preferably 4.5 km or more, more preferably from the viewpoint of transport weight. To 4.5 to 50 km.

The said polyvinyl alcohol-type film is 40-80N / mm < ² > at the time of extending | stretching 4 times in the flow direction (MD direction) of a film in the air | atmosphere of 20 degreeC65% RH in the point of winding property. It is particularly preferably 43 to 75 N / mm ^{2 from} the viewpoint of stability during storage, and more preferably 46 to 70 N / mm ² from the viewpoint of easy control of the underwater tension.

  The polyvinyl alcohol film preferably has an in-plane retardation of 50 nm or less, particularly preferably 40 nm or less, and more preferably 30 nm or less, from the viewpoint of uniformity of tension in water.

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

  The polyvinyl alcohol film of the present invention is excellent in optical performance, is suitably used as an optical polyvinyl alcohol film, and is particularly preferably used as a raw material for a polarizing film.

  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 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.

Further, the polarization degree of the polarizing film 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 42% 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 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

  A polarizing film comprising a polyvinyl alcohol film obtained by the production method of the present invention is excellent in in-plane uniformity of polarization performance, and is a portable information terminal, personal computer, TV, projector, signage, electronic desk calculator, electronic timepiece. , Word processors, electronic paper, game machines, videos, cameras, photo albums, thermometers, audio, liquid crystal display devices such as automobile 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, 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) Stretch tension in water (N / mm ² )
A test piece of length (MD direction) 50 mm × width (TD direction) 35 mm × thickness D (mm) was cut out from the obtained polyvinyl alcohol film, and both ends in the length direction so that the distance between chucks was 20 mm. After the part was sandwiched with a chuck having a width of 35 mm, the stress (N) when stretched 6 times in the MD direction at a speed of 18 mm / min in water at 30 ° C. and 50 ° C. was measured using only the spring. A value obtained by dividing the stress by the cross-sectional area of the film was defined as a stretching tension (N / mm ² ).

(2) Stretch tension in air (N / mm ² )
The obtained polyvinyl alcohol film was subjected to a daily condition adjustment in an atmosphere of 20 ° C. and 65% RH, and then a test piece of length (MD direction) 120 mm × width (TD direction) 15 mm × thickness D (mm) After using a “precision universal testing machine, Autograph (AG-IS)” manufactured by Shimadzu Corporation, both ends in the length direction are sandwiched by chucks with a width of 15 mm so that the distance between chucks is 50 mm. The stress (N) was measured when the film was stretched 4 times in the MD direction at a speed of 1000 mm / min in an atmosphere at 65 ° C. and RH. The value obtained by dividing the stress by the cross-sectional area of the film was taken as the stretching tension (N / mm ² ) in the atmosphere.

(3) In-plane retardation (nm)
A test piece having a length (MD direction) of 20 cm × width (TD direction) of 20 cm was cut out from the obtained polyvinyl alcohol film, and a two-dimensional birefringence evaluation system (manufactured by Photonic Lattice: “PA-110L”) was used. In-plane retardation (nm) was measured.

(4) Degree of polarization (%), 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 degree of polarization (%) and the single transmittance (%) were measured using an automatic polarizing film measuring device (manufactured by JASCO Corporation: VAP7070). .

(5) Polarization unevenness From the obtained polarizing film, a test piece having a length of 30 cm and a width of 30 cm was cut out, 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 with a surface illuminance of 14,000 lux (lx), and evaluated according to the following criteria.
(Evaluation criteria)
○ ・ ・ ・ No color unevenness △ ・ ・ ・ Slight color unevenness × ・ ・ ・ Color unevenness

<Example 1>
(Manufacture of polyvinyl alcohol film)
In a 5,000 L dissolution can, 1,000 kg of polyvinyl alcohol resin having a weight average molecular weight of 142,000 and a saponification degree of 99.8 mol%, 2,500 kg of water, 105 kg of glycerin as a plasticizer, and dodecyl sulfone as a surfactant Sodium 0.25 kg was added, heated to 150 ° C. with stirring, and dissolved under pressure to obtain a polyvinyl alcohol resin aqueous solution with a resin concentration of 25%.
Next, the polyvinyl alcohol-based resin aqueous solution is supplied to a twin-screw extruder having a vent and defoamed, and then the temperature of the aqueous solution is set to 95 ° C., and the cast drum is rotated at 20 m / min from the T-type slit die discharge port. The film was formed by discharging and casting. The obtained film was peeled off from the cast drum, and dried while bringing the front and back surfaces of the film into contact with a total of 20 metal heating rolls alternately. Such metal heating rolls are arranged in the order of 90 ° C., 70 ° C., 110 ° C., and 85 ° C. Next, after 140 ° C. hot air was blown from both sides of the film for heat treatment, the film was finally slit and wound to obtain a roll-like polyvinyl alcohol film (film thickness 0.03 mm, width 5 m, length 5 km). . The properties of the obtained polyvinyl alcohol film were as shown in Table 1.

(Manufacture of polarizing film)
The obtained polyvinyl alcohol film was unwound from a roll and stretched 1.7 times in the MD direction while being swelled by being immersed in a water bath at a water temperature of 30 ° C. while being conveyed in the horizontal direction. Next, the film was stretched 1.6 times in the MD direction while being immersed and dyed in an aqueous solution of 30 g / L of iodine 0.5 g / L and 30 g / L of potassium iodide, and then boric acid 40 g / L, iodine The sample was uniaxially stretched 2.1 times in the MD direction while being immersed in an aqueous solution (50 ° C.) having a composition of 30 g / L of potassium halide and cross-linking with boric acid. Finally, it was washed with an aqueous potassium iodide solution and then dried at 50 ° C. for 2 minutes to obtain a polarizing film having a total draw ratio of 5.7 times. No breakage occurred during the production, and the properties of the obtained polarizing film were as shown in Table 2.

<Example 2>
In Example 1, a polyvinyl alcohol film and a polarizing film were obtained in the same manner as in Example 1 except that heat treatment was performed by blowing hot air at 130 ° C. About the obtained polarizing film, evaluation similar to Example 1 was performed. The evaluation results are shown in Tables 1 and 2.

<Example 3>
In Example 1, the rotational speed of the cast drum was changed to 10 m / min, the film thickness was changed to 0.06 mm, and a polyvinyl alcohol film was obtained in the same manner as in Example 1 except that heat treatment was performed by blowing hot air at 120 ° C. A polarizing film was obtained. About the obtained polarizing film, evaluation similar to Example 1 was performed. The evaluation results are shown in Tables 1 and 2.

<Example 4>
In Example 1, the polyvinyl alcohol film and the polarizing film were changed in the same manner as in Example 1 except that the rotation speed of the cast drum was changed to 10 m / min to change the film thickness to 0.06 mm and the heat treatment temperature to 110 ° C. Got. About the obtained polarizing film, evaluation similar to Example 1 was performed. The evaluation results are shown in Tables 1 and 2.

<Comparative Example 1>
In Example 1, the polyvinyl alcohol film and the polarizing film were changed in the same manner as in Example 1 except that the rotation speed of the cast drum was changed to 10 m / min to change the film thickness to 0.06 mm and the heat treatment temperature to 100 ° C. Got. About the obtained polarizing film, evaluation similar to Example 1 was performed. The evaluation results are shown in Tables 1 and 2.

<Comparative example 2>
In Example 1, a polyvinyl alcohol film was obtained in the same manner as in Example 1 except that the heat treatment temperature was 150 ° C. Production of a polarizing film was started using the polyvinyl alcohol film, but when a polarizing film having a length of 1 km was produced, breakage occurred during stretching in the boric acid crosslinking step, and the intended polarizing film was not obtained. .

<Comparative Example 3>
In Example 1, a polyvinyl alcohol film and a polarizing film were obtained in the same manner as in Example 1 except that all metal heating roll temperatures were set to 80 ° C. About the obtained polarizing film, evaluation similar to Example 1 was performed. The evaluation results are shown in Tables 1 and 2.

The polyvinyl alcohol-based films of Examples 1 to 4 have a thickness D (mm) and a tension of A (N / mm ² ) when stretched 6 times in the film flow direction (MD direction) in water at 30 ° C. When the tension when stretched 6 times in the film flow direction (MD direction) in water at 50 ° C. is B (N / mm ² ), the values of D × A and D × B are both formulas (1) And the polyvinyl alcohol film of Comparative Example 1 has a D × B value outside the range of the formula (2), while the polyvinyl alcohol films of Comparative Examples 2 and 3 satisfy the conditions (2) and (2). The value of D × A was outside the range of formula (1), and the value of D × B was also outside the range of formula (2).
And it turns out that the polarization characteristic of the polarizing film obtained from each polyvinyl alcohol-type film is what Examples 1-4 are superior to Comparative Examples 1 and 3, and also in Comparative Example 2, it is a polarizing film by a fracture | rupture. Was not obtained.

  Further, for the polyvinyl alcohol films obtained in Examples 3 and 4 and Comparative Example 1, the storage elastic moduli E1 and E2 were measured according to the following method, and the value of E2 / E1 was calculated.

(6) Storage elastic modulus (MPa)
From the obtained polyvinyl alcohol-based film, a test piece having a length (MD direction) of 25 mm × width (TD direction) of 5 mm was cut out and used in water at 30 ° C. and 50 ° C. using DVA-225 manufactured by IT Measurement Control Co., Ltd. The storage modulus was measured. Detailed test conditions are as follows.
Frequency: 10Hz
Distance between chucks: 15mm
Load: 0.3% dynamic strain in the MD direction, static to dynamic ratio (ratio of static strain to dynamic strain) 6
E2 / E1 was calculated from the storage elastic modulus E1 (MPa) after 10 minutes of 30 ° C. water immersion and the storage elastic modulus E2 (MPa) after 10 minutes of 50 ° C. water immersion. In addition, the thickness before water immersion was used for the film thickness for the storage elastic modulus calculation in water.

  The measurement results are Example 3: E2 / E1 = 0.28, Example 4: E2 / E1 = 0.27, Comparative Example 1: E2 / E1 = 0.25, and the value of E2 / E1 is low. In this case, it was confirmed that the degree of polarization when the polarizing film was formed decreased.

  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.

  A polarizing film comprising a polyvinyl alcohol film obtained by the production method of the present invention is excellent in in-plane uniformity of polarization performance, and is a portable information terminal, personal computer, TV, projector, signage, electronic desk calculator, electronic timepiece. , Word processors, electronic paper, game machines, videos, cameras, photo albums, thermometers, audio, liquid crystal display devices such as automobile 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.

Claims (13)

Thickness D (mm),
A (N / mm ² ) tension when stretched 6 times in the film flow direction (MD direction) in water at 30 ° C.,
The tension when stretched 6 times in the film flow direction (MD direction) in water at 50 ° C. is B (N / mm ² ).
When satisfied, the following formulas (1) and (2) are satisfied.
Formula (1) 0.6 <= D * A <= 1.2
Formula (2) 0.2 <= D * B <= 0.4 The polyvinyl alcohol film according to claim 1, wherein the following formula (3) is satisfied.
Formula (3) 0.2 ≦ B / A ≦ 0.5   When the storage elastic modulus in water at 30 ° C. is E1 (Pa) and the storage elastic modulus in water at 50 ° C. is E2 (Pa), E2 / E1 is 0.25 to 0.30. The polyvinyl alcohol film according to claim 1 or 2.   The polyvinyl alcohol film according to any one of claims 1 to 3, wherein a thickness D of the polyvinyl alcohol film is 0.04 mm or less.   The polyvinyl alcohol film according to any one of claims 1 to 4, wherein the polyvinyl alcohol film has a width of 4 m or more and a length of 4 km or more. The tension when stretched 4 times in the flow direction (MD direction) of the film in the atmosphere of 20 ° C and 65% RH is 40 to 80 N / mm ² . Polyvinyl alcohol film.   In-plane retardation is 50 nm or less, The polyvinyl alcohol-type film in any one of Claims 1-6 characterized by the above-mentioned. It is a method of manufacturing the polyvinyl alcohol-type film in any one of Claims 1-7, Comprising: It manufactures through the following process (A)-(D), The manufacturing method of the polyvinyl alcohol-type film characterized by the above-mentioned.
Step (A) A step of preparing a polyvinyl alcohol resin aqueous solution.
Step (B) A step of casting an aqueous solution of a polyvinyl alcohol resin into a cast mold to form a film.
Step (C) A step of heating and drying the formed film by bringing it into contact with a plurality of metal heating rolls.
Process (D) The process of heat-processing the obtained film using a hot air.   The process for producing a polyvinyl alcohol film according to claim 8, wherein 5 to 12% by weight of glycerin is blended with respect to the polyvinyl alcohol resin in the step (A). The method for producing a polyvinyl alcohol film according to claim 8 or 9, wherein the temperatures of the plurality of metal heating rolls in the step (C) are in the order of the following conditions (a) to (d).
Condition (a) ≧ 80 ° C
Condition (b) <80 ° C
Condition (c) ≧ 100 ° C.
Condition (d) <100 ° C   The method for producing a polyvinyl alcohol film according to any one of claims 8 to 10, wherein the heat treatment temperature in the step (D) is 110 to 140 ° C.   A polyvinyl alcohol film produced by the production method according to claim 8. A polarizing film comprising the polyvinyl alcohol film according to claim 1.