TW201710303A - Poly(vinyl alcohol)-based film, process for producing poly(vinyl alcohol)-based film, and polarizing film - Google Patents

Abstract

Provided is a poly(vinyl alcohol)-based film which is excellent in terms of dyeability and stretchability and which, even when produced as a continuous film having a larger width and a smaller thickness, can give a polarizing film that has a high degree of polarization and no unevenness of polarization. The poly(vinyl alcohol)-based film is characterized in that when the thickness is expressed by D (mm), the tension at the time when the film has been stretched 6 times in the running direction (MD direction) in 30 DEG C water is expressed by A (N/mm2), and the tension at the time when the film has been stretched 6 times in the running direction (MD direction) in 50 DEG C water is expressed by B (N/mm2), then the film satisfies the following relationships (1) and (2). Relationship (1) 0.6 <= D x A <=1.2 Relationship (2) 0.2 <= D x B <=0.4.

Description

Polyvinyl alcohol film, method for producing polyvinyl alcohol film, and polarizing film

The present invention relates to a polyvinyl alcohol-based film. More specifically, the present invention relates to a polyvinyl alcohol-based film which is excellent in dyeability and extensibility as a raw material roll of a polarizing film, and which is used for producing a polarizing film having excellent polarizing performance with high productivity, a method for producing the polyvinyl alcohol-based film, and a method for producing the polyvinyl alcohol-based film. A polarizing film obtained by using the polyvinyl alcohol-based film.

The polarizing film is produced by dyeing a polyvinyl alcohol-based film which is a raw material roll and dyeing it with a dye such as iodine. For example, the polyvinyl alcohol-based film is swelled with warm water, and then iodine-dyed, and the iodine molecule is stretched in order to maintain the state of the iodine molecule, and is crosslinked by a crosslinking agent such as boric acid to maintain the state after stretching. Made by drying. The various steps of water swelling, dyeing, stretching, and boric acid crosslinking sometimes replace the order, or multiple steps simultaneously. The common point is that the polyvinyl alcohol-based film is continuously wound out from the roll, and a suitable tension is applied in the flow direction using a winder or a roll, and simultaneously carried in the horizontal direction.

The polarizing film is used as a key component of a liquid crystal display device such as an action information terminal device or a television. In recent years, with the increase in brightness and high definition of liquid crystal display, a polarizing film having a high light transmittance and a high degree of polarization is desired, and a large screen or a thin film of a liquid crystal television or the like is desired. The product further broadens the growth of thin, polarizing films.

In order to meet the above expectations, it is necessary to have a polyvinyl alcohol-based film which is excellent in dyeability or elongation and which is elongated and thin. When the dyeability of the polyvinyl alcohol-based film is low, there is a tendency that a sufficient degree of polarization cannot be obtained or polarization unevenness is likely to occur. When the stretchability of the polyvinyl alcohol-based film is low, cracking occurs in the production process of the polarizing film, and it is not possible to produce a polarizing film which is widened and grown thin. At the same time, it is a matter of course that the rupture causes the continuity of the manufacturing to be interrupted, and the productivity of the polarizing film is greatly reduced. Further, if the elongation is low, the pigment may not be sufficiently aligned, and the degree of polarization may be low, or the tendency of uneven polarization may easily occur. This improvement in dyeability or extensibility becomes more difficult as the polyvinyl alcohol-based film becomes thicker and thinner. Further, even if the coating type polarizing plate is intended to be thinned, it is necessary to have the above-described steps of dyeing or stretching, and although it is present on the supporting film, it is desirable to dye or extend the polyvinyl alcohol-based film after coating. Improvement.

In order to improve the dyeability of the polyvinyl alcohol-based film, a method of controlling the bath temperature of the swelling step has been proposed (for example, refer to Patent Documents 1 and 2). Further, a polarizing plate using a polyvinyl alcohol-based film having a specific range of elongation has been proposed (for example, refer to Patent Document 3) [Prior Art Document] [Patent Literature]

Japanese Unexamined Patent Publication No. JP-A No. Hei. No. Hei. No. Hei. No. Hei. No. Hei.

[Problems to be Solved by the Invention] However, in the techniques disclosed in Patent Documents 1 and 2, although the degree of swelling can be controlled by the bath temperature, if the tension applied to the polyvinyl alcohol-based film in the bath is not appropriate, A consistent swelling state is obtained, and there is a problem that the pigment is not uniformly adsorbed in the subsequent dyeing step.

Further, the technique disclosed in the above Patent Document 3 specifies the stress (tension) when the polyvinyl alcohol-based film is stretched 4 to 6 times in water, and in actuality, the water temperature of each step is not used in the production of the polarizing film. In the same way, it is not sufficient to obtain the tension applicable to all the steps. Among them, the water temperature is mostly about 30 ° C at a lower temperature in the steps of swelling or dyeing, and is about 50 ° C at a relatively high temperature in the steps of extension or boric acid crosslinking.

Therefore, in this context, the present invention provides a polyvinyl alcohol-based film excellent in dyeability or extensibility, which can obtain a polarizing film which has a high degree of polarization and a non-polarized unevenness when it is thinned by widening and growing. [Means for solving the problem]

Therefore, the inventors of the present invention have found that the polyvinyl alcohol-based film obtained by continuously drying the aqueous solution of the polyvinyl alcohol-based resin by discharging and casting the aqueous solution of the polyvinyl alcohol-based resin and continuously forming the film is obtained. When extending in water at different temperatures, the tension in each water is set to a specific range, and in particular, the tension in water at a higher temperature of 50 ° C is focused, and the polyvinyl alcohol-based film thus produced is thinned even if it is widened and grown. It still has a high degree of polarization and can produce a polarizing film with no polarization unevenness.

That is, the gist of the present invention is such that when the thickness is D (mm), the tension is 6 times when the flow direction (MD direction) of the film is extended in water of 30 ° C is A (N/mm ² ). When the tension in the water flow direction (MD direction) of the film at 50 ° C is 6 times and B (N/mm ² ), the following formulas (1) and (2) are satisfied; D × A ≦ 1.2; Formula (2) 0.2 ≦ D × B ≦ 0.4.

Moreover, the present invention also provides a method for producing the above polyvinyl alcohol-based film and a polarizing film obtained by using the above polyvinyl alcohol-based film. [Effects of the Invention]

The polyvinyl alcohol-based film of the present invention is excellent in dyeability and extensibility, and a polarizing film having high polarization and non-polarization unevenness even when thickness is increased and thinned, and polarized film can be produced with high productivity. membrane.

The invention will be described in detail below. The polyvinyl alcohol-based film of the present invention must have a thickness of D (mm) and a tensile force of A (N/mm ² ) when it extends 6 times in the flow direction (MD direction) of the film in water at 30 ° C. When the tension at a temperature of 50 ° C in the flow direction (MD direction) of the film is 6 times and the tension is B (N/mm ² ), the polyvinyl alcohol-based film of the following formulas (1) and (2) is satisfied. 1) 0.6≦D×A≦1.2; Formula (2) 0.2≦D×B≦0.4; It is preferably a polyvinyl alcohol-based 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 preferably a polyvinyl alcohol-based film satisfying the following formulas (1'') and (2''), formula (1'') 0.7 ≦D×A≦1.1; Equation (2'') 0.27≦D×B≦0.38.

With respect to the above formulas (1) to (1''), if the value of D×A is too low, the film may be deformed during the swelling step or the dyeing step, and it is difficult to sufficiently dye the dyeing step without being too high. ideal. Further, in the above formulas (2) to (2''), when the value of D × B is too low, the degree of polarization when the polarizing film is lowered is not preferable, and if it is too high, cracking is likely to occur during production of the polarizing film. .

In the above formulas (1) to (1'') and the above formulas (2) to (2''), the value of the thickness D of the polyvinyl alcohol-based film is preferably 0.04 mm or less from the viewpoint of reducing the thickness of the polarizing film. The viewpoint of thinner formation of the polarizing film is particularly preferably 0.03 mm or less, and further preferably from 0.01 to 0.03 mm from the viewpoint of avoiding cracking of the polarizing film.

Further, the polyvinyl alcohol-based film of the present invention preferably satisfies the following formula (3), and particularly preferably satisfies the following formula (3'), and further 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

With respect to the above formulas (3) to (3''), if the value of B/A is too low, the degree of polarization when the polarizing film is formed tends to be low, and if it is too high, the tendency of cracking tends to occur when the polarizing film is produced. .

Further, the polyvinyl alcohol-based film of the present invention preferably has a tension A of 15 to 40 N/mm ² when it extends 6 times in the flow direction (MD direction) of the film in water at 30 ° C, particularly preferably 18 to 35 N/mm. ² , further preferably 20~30N/mm ² . If the value of the tension A is too low, the film tends to be easily deformed in the swelling step or the dyeing step, and if it is too high, there is a tendency that it is difficult to sufficiently dye in the dyeing step.

Further, the value of the tension B when the polyvinyl alcohol-based film of the present invention is extended 6 times in the flow direction (MD direction) of the film in water at 50 ° C is preferably 3 to 15 N/mm ² , particularly preferably 4 to 12 N. /mm ² , further preferably 5~10N/mm ² . When the value of the tension B is too low, the degree of polarization when the polarizing film is formed tends to be low, and if it is too high, the polarizing film tends to be broken during the production of the polarizing film.

Further, the storage modulus of the polyvinyl alcohol-based film of the present invention in water at 30 ° C is E1 (Pa), and when the storage elastic modulus in water at 50 ° C is E 2 (Pa), the value of E 2 / E 1 is preferably It is 0.25~0.30, especially 0.26~0.29. If the value of E2/E1 is too low, the degree of polarization of the polarizing film obtained tends to be low, and if it is too high, cracking tends to occur during the production of the polarizing film.

Further, in view of the transportability of the polyvinyl alcohol-based film of the present invention, the storage elastic modulus E1 in the water at 30 ° C is preferably 9 to 12 MPa. Further, from the viewpoint of portability, the storage elastic modulus E2 in water at 50 ° C is preferably 2 to 4 MPa.

In the following, a method for producing a polyvinyl alcohol-based film of the present invention, that is, a method of producing a polyvinyl alcohol-based film by discharging and casting an aqueous solution of a polyvinyl alcohol-based resin into a casting mold, and continuously drying the film is carried out. Description.

In the polyvinyl alcohol-based resin used in the present invention, an unmodified polyvinyl alcohol-based resin, that is, a resin obtained by saponifying a polyvinyl acetate obtained by polymerizing vinyl acetate, is usually used. A resin obtained by saponifying a copolymer of vinyl acetate and a small amount (usually 10 mol% or less, preferably 5 mol% or less) copolymerizable with vinyl acetate may be used depending on the demand. Examples of the component copolymerizable with vinyl acetate include unsaturated carboxylic acids (for example, salts, esters, guanamines, nitriles, etc.) and olefins having 2 to 30 carbon atoms (for example, ethylene, propylene, and n-butylene). Alkene, isobutylene, etc.), vinyl ethers, unsaturated sulfonates, and the like. Further, a modified polyvinyl alcohol-based resin obtained by chemically modifying a saponified hydroxyl group can also be used.

Further, as the polyvinyl alcohol-based resin, a polyvinyl alcohol-based resin having a 1,2-diol structure in a side chain can also be used. The polyvinyl alcohol-based resin having a 1,2-diol structure in a side chain can be saponified by, for example, (i) a copolymer of vinyl acetate and 3,4-diethyloxy-1-butene. a method, (ii) a method of saponifying and decarbonating a copolymer of vinyl acetate and ethylene carbonate, and (iii) a vinyl acetate with 2,2-dialkyl-4-ethene-1,3 A method in which a copolymer of dioxolane is subjected to saponification and deketalization, and (iv) a method of saponifying a copolymer of vinyl acetate and glycerin monoallyl ether, or the like.

The weight average molecular weight of the polyvinyl alcohol-based resin is preferably from 100,000 to 300,000, particularly preferably from 110,000 to 280,000, and further preferably from 120,000 to 260,000. When the weight average molecular weight is too small, it is difficult to obtain sufficient optical properties when a polyvinyl alcohol-based resin is used as an optical film, and if it is too large, stretching of a polarizing film of a polyvinyl alcohol-based film tends to be difficult. The weight average molecular weight of the polyvinyl alcohol-based resin is a weight average molecular weight measured by a GPC-MALS method.

The average degree of saponification of the polyvinyl alcohol-based resin used in the present invention is usually preferably 98 mol% or more, more preferably 99 mol% or more, further preferably 99.5 mol% or more, and particularly preferably 99.8 mol% or more. If the average degree of saponification is too small, there is a tendency that sufficient optical properties cannot be obtained when a polyvinyl alcohol-based film is formed into a polarizing film. Here, the average degree of saponification in the present invention is measured in accordance with JIS K 6726.

The polyvinyl alcohol-based resin used in the present invention may be used in combination of two or more kinds of modified substances, modified amounts, weight average molecular weights, and average saponification degrees.

In the polyvinyl alcohol-based film of the present invention, a polyvinyl alcohol-based resin aqueous solution (film-forming stock solution) is prepared by using the polyvinyl alcohol-based resin, and the aqueous solution is discharged and cast in a casting mold, and formed into a film by a casting method to be dried. It can be manufactured continuously, for example by the following steps. Step (A) preparing a polyvinyl alcohol resin aqueous solution; Step (B) casting a polyvinyl alcohol resin aqueous solution into a casting mold and forming a film; and (C) forming a film and a plurality of metal heating rolls by film forming Contact to heat and dry; Step (D) The obtained film is heat treated using hot air.

Here, the casting mold may be, for example, a casting drum (drum type roller) or an endless belt, and it is preferable to use a casting drum in view of being excellent in widening or increasing the thickness and uniformity of film thickness. . Hereinafter, a case where the casting mold is a casting drum will be described as an example.

First, the above step (A) will be described.

In the step (A), first, the polyvinyl alcohol-based resin is washed with water, and dehydrated by a centrifugal separator or the like to obtain a polyvinyl alcohol-based resin wet cake having a water content of 50% by weight or less. If the water content is too large, there is a tendency that it is difficult to become a desired aqueous solution concentration. The polyvinyl alcohol-based resin wet cake was dissolved in warm water or hot water to prepare a polyvinyl alcohol-based resin aqueous solution.

The method for preparing the aqueous solution of the polyvinyl alcohol-based resin is not particularly limited. For example, it can be prepared by using a heated multi-axis extruder, or it can be put into a dissolution tank having a stirring flow-producing type stirring blade. A vinyl alcohol-based resin wet cake is dissolved and prepared into an aqueous solution of a desired concentration by blowing water vapor into the tank. In the present invention, the latter is preferably from the viewpoint of improving the degree of polarization, and is more preferably prepared by pressure-dissolving at 120 ° C or higher.

In the polyvinyl alcohol-based resin aqueous solution, in addition to the polyvinyl alcohol-based resin, it is preferable to use a plasticizer or a surfactant which is at least one of nonionic, anionic, and cationic in consideration of film forming properties. .

The plasticizer used in the present invention may, for example, be glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol or trimethylolpropane. Among these, the viewpoint of low price is preferably glycerin.

The blending amount in the case of using glycerin is preferably 5 to 12% by weight, particularly preferably 6 to 11.5% by weight, and more preferably 7 to 11%, based on the polyvinyl alcohol-based resin. When the blending amount is too small, the tension in the water of the polyvinyl alcohol-based film tends to increase, and if it is too large, the tension in the water of the polyvinyl alcohol-based 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 solution of a polyvinyl alcohol resin.

The resin concentration of the polyvinyl alcohol-based resin aqueous solution thus obtained is preferably from 15 to 60% by weight, particularly preferably from 17 to 55% by weight, more preferably from 20 to 50% by weight. If the resin concentration is too low, the drying load will increase, and the productivity will be low. If the viscosity is too high, the viscosity tends to be too high, and there is a tendency that it is difficult to uniformly dissolve.

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

The polyvinyl alcohol-based resin aqueous solution is subjected to a defoaming treatment. Examples of the defoaming method include a method of static defoaming or defoaming by a multi-axis extruder having a vent hole. In the case of a multi-axis extruder having a vent hole, a 2-axis extruder having a vent hole is generally used.

After the defoaming treatment, the polyvinyl alcohol-based resin aqueous solution was introduced into the T-slot mold in a predetermined amount, discharged, and cast on a rotating casting drum, and formed into a film by a casting method.

The resin temperature of the T-slot die discharge port is preferably 80 to 100 ° C, and particularly preferably 85 to 99 ° C. If the temperature of the resin is too low, there is a tendency to flow poorly, and if it is too high, there is a tendency to foam.

The viscosity of the polyvinyl alcohol-based resin aqueous solution is preferably 50 to 200 Pa·s, and particularly preferably 70 to 150 Pa·s. If the viscosity of the aqueous solution is too low, the flow tends to be poor, and if it is too high, the casting tends to be difficult.

The discharge rate of the polyvinyl alcohol-based resin aqueous solution discharged from the T-slot die to the casting drum is preferably 0.2 to 5 m/min, particularly preferably 0.4 to 4 m/min, and more preferably 0.6 to 3 m/min. If the discharge speed is too slow, there is a tendency for productivity to drop, and if it is too fast, there is a tendency that casting is difficult.

The flow delay is preferably carried out by casting a drum from the viewpoints of widening or increasing, uniformity of film thickness, and the like. In the case of a casting drum, a metal plating is usually applied to the surface of stainless steel (SUS) containing iron as a main component to prevent scratches. The metal plating may, for example, be chrome plating, nickel plating, galvanization or the like, and these may be used alone or in a laminate of two or more layers. Among these, from the viewpoint of the durability of the drum surface, the outermost surface is preferably chrome-plated.

Hereinafter, a film forming method will be described by taking a case where a casting drum is used as an example. The width of the casting drum should preferably be 4 m or more, and particularly preferably 5 m or more. If the width of the casting drum is too narrow, it is difficult to obtain a tendency to widen the film.

The diameter of the casting 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, there is a tendency that the drying length is insufficient and the speed is not easily increased. If it is too large, there is a tendency to be transported.

The rotation speed of the casting 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 rotation speed is too slow, there is a tendency to be low in productivity, and if it is too fast, there is a tendency to be insufficient in drying.

The surface temperature of the casting drum is preferably 40 to 99 ° C, particularly preferably 60 to 95 ° C. If the surface temperature is too low, there is a tendency to dry poorly, and if it is too high, there is a tendency to foam.

This is done by film formation.

Next, the above step (C) will be described. The step (C) is heated and dried by bringing the film obtained by film formation into contact with a plurality of metal heating rolls.

The polyvinyl alcohol-based film obtained by casting a drum is dried by alternately contacting the surface and the back surface of the film with a plurality of metal heating rolls. The surface temperature of the metal heating roller is not particularly limited, but is usually 60 to 150 ° C, and more preferably 70 to 140 ° C. If the surface temperature is too low, there is a tendency for drying to be poor, and if it is too high, there is a tendency that excessive drying causes an appearance such as undulation.

In the present invention, from the viewpoint of controlling the water tension of the polyvinyl alcohol-based film, the temperature of the plurality of metal heating rolls is preferably 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 Among them, usually the number of metal heating rolls is 10 to 30, which is set to satisfy the above-mentioned appropriate Temperature conditions.

The film obtained by drying with a metal heating roll is subjected to heat treatment using hot air in the step (D). Next, the above step (D) will be described.

The heat treatment temperature is preferably 110 to 140 ° C, particularly preferably 115 to 135 ° C, and further preferably 120 to 130 ° C. When the heat treatment temperature is too low, the water tension of the polyvinyl alcohol-based film tends to be insufficient, and if it is too high, the water tension of the polyvinyl alcohol-based film tends to increase. As for the method of the heat treatment, the method of performing in a float dryer is preferable from the viewpoint of excellent temperature control.

The both ends of the heat-treated film were cut and wound on a roll to form a roll-shaped polyvinyl alcohol-based film.

In addition, the width of the polyvinyl alcohol-based film is preferably 4 m or more from the viewpoint of widening the polarizing film, and is particularly preferably 4.5 m or more from the viewpoint of further widening, and further preferably 4.5 to 6 m from the viewpoint of avoiding cracking.

The length of the polyvinyl alcohol-based film is preferably 4 km or more from the viewpoint of increasing the area of the polarizing film, and is particularly preferably 4.5 km or more from the viewpoint of a larger area, and further preferably 4.5 to 50 km from the viewpoint of transportation weight.

The polyvinyl alcohol-based film preferably has a tension of 40 to 80 N/mm ² when it is stretched four times in the flow direction (MD direction) of the film in the air at 20 ° C and 65% RH from the viewpoint of the winding property. The viewpoint of stability during storage is particularly preferably 43 to 75 N/mm ² , and the ease of controlling the tension in the water is further considered to be 46 to 70 N/mm ² .

The polyvinyl alcohol-based 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-based film of the present invention was obtained.

The polyvinyl alcohol-based film of the present invention is excellent in optical performance, and can be suitably used as a polyvinyl alcohol-based film for optics, and it is particularly preferable to use a raw material roll as a polarizing film.

Hereinafter, a method for producing a polarizing film obtained by using the polyvinyl alcohol-based film of the present invention will be described.

In the polarizing film of the present invention, the polyvinyl alcohol-based film is taken up from a roll and transported in a horizontal direction, and is produced by a step of swelling, dyeing, boric acid crosslinking, stretching, washing, and drying.

The swelling step is carried out before the dyeing step. By the swelling step, not only the surface of the polyvinyl alcohol-based film can be cleaned, but also the effect of preventing uneven dyeing by swelling the polyvinyl alcohol-based film. In the swelling step, water is usually used in terms of the treatment liquid. The main component of the treatment liquid may be water, and an additive such as an iodinated compound or a surfactant, or an alcohol may be added in a small amount. The temperature of the swelling bath is usually about 10 to 45 ° C, and the immersion time for the swelling bath is usually about 0.1 to 10 minutes. In addition, extension operations can be performed during processing in response to demand.

The dyeing step is carried out by contacting a liquid containing iodine or a dichroic dye with a film. Usually, an aqueous solution of iodine-potassium iodide is used, and the concentration of iodine is suitably 0.1 to 2 g/L, and the concentration of potassium iodide is suitably 1 to 100 g/L. The practical dyeing time is about 30 to 500 seconds. The temperature of the treatment bath should be 5 to 50 °C. In addition to the aqueous solvent, the aqueous solution may contain a small amount of an organic solvent compatible with water. In addition, extension operations can be performed during processing in response to demand.

The boric acid crosslinking step is carried out using a boron compound such as boric acid or borax. The boron compound is used in the form of a mixed solution of an aqueous solution or a water-organic solvent at a concentration of about 10 to 100 g/L. When potassium iodide is allowed to coexist in the liquid, it is preferable from the viewpoint of stability of polarizing performance. The temperature at the time of treatment is about 30 to 70 ° C, and the treatment time is preferably about 0.1 to 20 minutes. In addition, the stretching operation can be carried out during the treatment according to the demand.

The extension step is 3 to 10 times in the uniaxial direction, and preferably extends to 3.5 to 6 times. At this time, it is also possible to perform a slight extension in the direction perpendicular to the extending direction (to prevent the degree of contraction in the width direction, or to extend above this level). The temperature at the time of extension should be 30 to 170 °C. Further, the stretching ratio is preferably set to the above range, and the stretching operation is not limited to one stage, and can be carried out in any stage of the manufacturing step.

The washing step is performed, for example, by immersing the polyvinyl alcohol-based film in an aqueous solution of an iodide such as water or potassium iodide, and the precipitate formed on the surface of the film can be removed. When a potassium iodide aqueous solution is used, the concentration of potassium iodide may be about 1 to 80 g/L. The temperature during the cleaning treatment is usually 5 to 50 ° C, preferably 10 to 45 ° C. The processing time is usually 1 to 300 seconds, preferably 10 to 240 seconds. Among them, water washing and washing with an aqueous solution of potassium iodide can be suitably carried out.

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

Further, the degree of polarization 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 no tendency to ensure a contrast in the liquid crystal display. In general, the light transmittance (H ₁₁ ) measured by the wavelength λ is superimposed on the two polarizing films so that the alignment directions thereof are in the same direction, and the two polarizing films are superposed on each other. When the alignment direction is a direction perpendicular to each other, the light transmittance (H ₁ ) measured by the wavelength λ is calculated, and the degree of polarization is calculated according to the following formula. [(H ₁₁ -H ₁ )/(H ₁₁ +H ₁ )] ^1/2

Further, the transmittance of the polarizing film of the present invention is preferably 42% or more. If the transmittance of the monomer is too low, there is a tendency that the luminance of the liquid crystal display cannot be increased. The monomer transmittance is a value obtained by measuring the light transmittance of the polarizing film monomer using a spectrophotometer.

Thus, the polarizing film of the present invention is obtained, and the polarizing film of the present invention is suitably used for producing a polarizing plate having less uneven color. Hereinafter, a method of producing a polarizing plate of the present invention will be described.

The polarizing film of the present invention is bonded to an optically isotropic resin film as a protective film on one surface or both surfaces thereof to form a polarizing plate. The protective film may, for example, be cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, cycloolefin polymer, cyclic olefin copolymer, polystyrene, polyether oxime, poly Asian. A film or sheet of an aryl ester, poly-4-methylpentene, polyphenylene ether or the like.

The bonding method can be carried out by a known method, for example, by uniformly applying a liquid adhesive composition to a polarizing film, a protective film, or both, and sticking the two together and crimping, by heating or irradiating Active energy rays are used to carry out.

In addition, the polarizing film may be coated with a curable resin such as an urethane resin, an acrylic resin or a urea resin on one or both sides instead of the protective film to form a polarizing plate. .

The polarizing film composed of the polyvinyl alcohol-based film obtained by the production method of the present invention is excellent in in-plane uniformity of polarizing performance, and is preferably used in mobile information terminal equipment, computers, televisions, projectors, billboards, and tables. Liquid crystal display devices such as electronic computers, electronic clocks, word processors, electronic papers, game consoles, video recorders, cameras, photo frames, thermometers, stereos, automobiles or mechanical instruments, sunglasses, anti-glare glasses, stereo glasses, Anti-reflection layer, optical fiber communication equipment, medical equipment, building materials, toys, etc. for wearable displays, display elements (CRT, LCD, organic EL, electronic paper, etc.). [Examples]

Hereinafter, the present invention will be more specifically described by the examples, but the present invention is not limited to the following examples within the scope of the invention. In the examples, "parts" and "%" mean the basis of weight.

<Measurement conditions> (1) Stretching tension in water (N/mm ² ) A test piece having a length (MD direction) of 50 mm × width (TD direction) of 35 mm × thickness D (mm) was cut out from the obtained polyvinyl alcohol-based film. The two ends in the longitudinal direction were sandwiched between the chucks having a width of 35 mm so that the distance between the chucks was 20 mm, and the elongation was 18 mm/min along the MD direction in the water at 30 ° C and 50 ° C by a spring balance. Time stress (N). The value obtained by dividing the stress by the cross-sectional area of the film is defined as the extension tension (N/mm ² ).

(2) Extension tension in air (N/mm ² ) The obtained polyvinyl alcohol-based film was subjected to state adjustment in air at 20 ° C and 65% RH, and the length (MD direction) was 120 mm × width (TD). In the test piece of 15 mm × thickness D (mm), the "precision universal testing machine AUTOGRAPH (AG-IS)" manufactured by Shimadzu Corporation was used to sandwich the ends of the longitudinal direction so that the distance between the chucks became 50 mm. After a chuck of 15 mm in width, the stress (N) at a speed of 1000 mm/min in the MD direction was measured in air at 65% R 65% RH. The value obtained by dividing the stress by the cross-sectional area of the film is the tensile tension (N/mm ² ) in the air.

(3) In-plane phase difference (nm) From the obtained polyvinyl alcohol-based film, a test piece having a length (MD direction) of 20 cm × width (TD direction) of 20 cm was cut out, and a two-dimensional birefringence evaluation system (Photonic Lattice, Inc.) was used. . System: "PA-110L") The in-plane phase difference (nm) was measured.

(4) Polarization degree (%), single-emission transmittance (%) A sample having a length of 4 cm × a width of 4 cm was cut out from the obtained polarizing film, and the degree of polarization was measured using an automatic polarizing film measuring apparatus (manufactured by JASCO Corporation: VAP7070). And monomer transmittance (%).

(5) Polarization unevenness A test piece having a length of 30 cm × a width of 30 cm was cut out from the obtained polarizing film, and two polarizing plates were sandwiched in an orthogonally polarized state at an angle of 45° (single transmittance 43.5%, polarization degree 99.9%) After that, the optical color unevenness was observed in a transmission mode using a light box having a surface illumination of 14,000 lux (lx), and evaluation was performed by the following criteria. (Evaluation criteria) ○...No color unevenness △...A little color unevenness ×...Color unevenness

<Example 1> (Production of polyvinyl alcohol-based film) In a 5,000-liter dissolving tank, 1,000 kg of a polyvinyl alcohol-based resin having a weight average molecular weight of 142,000, a degree of saponification of 99.8 mol%, and 2,500 kg of water were added as plasticizing. 105 kg of glycerin and 0.25 kg of sodium dodecylsulfonate as a surfactant were heated to 150 ° C while stirring, and pressure-dissolved to obtain a polyvinyl alcohol-based resin aqueous solution having a resin concentration of 25%. Next, the polyvinyl alcohol-based resin aqueous solution was supplied to a 2-axis extruder having a vent hole, and after defoaming, the temperature of the aqueous solution was 95 ° C, and it was discharged from the T-slot discharge port and cast at 20 m/min. Cast the drum and make a film. The obtained film was peeled off from the casting drum, and the surface and the back surface of the film were alternately dried in contact with a total of 20 metal heating rolls. The metal heating rolls are arranged in order of temperature of 90 ° C, 70 ° C, 110 ° C, and 85 ° C. Subsequently, heat treatment was performed by blowing hot air of 140 ° C from both surfaces of the film, and finally, the film was cut and wound to obtain a roll-shaped polyvinyl alcohol-based film (film thickness: 0.03 mm, width: 5 m, length: 5 km). The properties of the obtained polyvinyl alcohol-based film are shown in Table 1.

(Production of Polarizing Film) The polyvinyl alcohol-based film which was taken up from the roll was immersed in a water bath having a water temperature of 30 ° C while being transported in the horizontal direction, and was swollen in the MD direction by 1.7 times. Next, it was immersed in an aqueous solution of 30 g of iodine (0.5 g/L, potassium iodide 30 g/L), and it was 1.6 times in the MD direction, and was immersed in a composition of 40 g/L of boric acid and 30 g/L of potassium iodide. While the boric acid was crosslinked in the aqueous solution (50 ° C), the uniaxial extension in the MD direction was 2.1 times. Finally, it was washed with an aqueous solution of potassium iodide, and then dried at 50 ° C for 2 minutes to obtain a polarizing film having a total stretching ratio of 5.7 times. No cracking occurred in this production, and the characteristics of the obtained polarizing film are shown in Table 2.

<Example 2> A polyvinyl alcohol-based film and a polarizing film were obtained in the same manner as in Example 1 except that hot air of 130 ° C was blown and heat-treated. The same evaluation as in Example 1 was carried out for the obtained polarizing film. The evaluation results are shown in Tables 1 and 2.

<Example 3> In Example 1, the same procedure as in Example 1 was carried out except that the rotational speed of the casting drum was changed to 10 m/min, the film thickness was 0.06 mm, and hot air of 120 ° C was blown to heat treatment. A vinyl alcohol film and a polarizing film. The same evaluation as in Example 1 was carried out for the obtained polarizing film. The evaluation results are shown in Tables 1 and 2.

<Example 4> In Example 1, a polyvinyl alcohol system was obtained in the same manner as in Example 1 except that the rotation speed of the casting drum was changed to 10 m/min, the film thickness was 0.06 mm, and the heat treatment temperature was 110 °C. Film and polarizing film. The same evaluation as in Example 1 was carried out for the obtained polarizing film. The evaluation results are shown in Tables 1 and 2.

<Comparative Example 1> A polyvinyl alcohol-based method was obtained in the same manner as in Example 1 except that the rotation speed of the casting drum was changed to 10 m/min, the film thickness was 0.06 mm, and the heat treatment temperature was 100 °C. Film and polarizing film. The same evaluation as in Example 1 was carried out for the obtained polarizing film. The evaluation results are shown in Tables 1 and 2.

<Comparative Example 2> A polyvinyl alcohol-based film was obtained in the same manner as in Example 1 except that the heat treatment temperature was 150 °C. Although the production of the polarizing film was started using the polyvinyl alcohol-based film, when a polarizing film having a length of 1 km was produced, cracking occurred during the extension of the boric acid crosslinking step, and the intended polarizing film could not be obtained.

<Comparative Example 3> A polyvinyl alcohol-based film and a polarizing film were obtained in the same manner as in Example 1 except that the temperature of the metal heating roll was all 80 °C. The same evaluation as in Example 1 was carried out for the obtained polarizing film. The evaluation results are shown in Tables 1 and 2.

【Table 1】

【Table 2】

The polyvinyl alcohol-based film of Examples 1 to 4 had a thickness of D (mm), and the tension of the film in water at 30 ° C was 6 times in the flow direction (MD direction), and the tension was A (N/mm ² ). When the tension of the film in water at 50 ° C is 6 times in the flow direction (MD direction), B (N/mm ² ), any of the values of D×A and D×B satisfies the formula (1). And (2), in contrast to the polyvinyl alcohol-based film of Comparative Example 1, the value of D × B is outside the range of the formula (2), and the polyvinyl alcohol-based film of Comparative Examples 2 and 3 has a value of D × A at The value outside the range of formula (1) and D x B is also outside the range of formula (2). In addition, it is understood that the polarizing characteristics of the polarizing film obtained from each of the polyvinyl alcohol-based films are superior to those of Comparative Examples 1 and 3 in Examples 1 to 4, and in Comparative Example 2, the polarizing film could not be obtained due to cracking.

Further, with respect to the polyvinyl alcohol-based films obtained in Examples 3 and 4 and Comparative Example 1, the storage elastic modulus E1 and E2 were measured by the following methods, and the value of E2/E1 was calculated.

(6) Storage elastic modulus (MPa) A test piece having a length (MD direction) of 25 mm × width (TD direction) of 5 mm from the obtained polyvinyl alcohol-based film was measured using DVA-225 manufactured by ITK CO., LTD. Storage modulus of elasticity in water at 30 ° C and 50 ° C. The detailed test conditions are as follows. Frequency: 10 Hz Distance between chucks: 15 mm Load: Dynamic strain along the MD direction 0.3%, static ratio (station between static strain and dynamic strain) 6 Storage elastic modulus E1 (MPa) after being immersed in water at 30 ° C for 10 minutes E2/E1 was calculated from the storage elastic modulus E2 (MPa) after immersion in water at 50 ° C for 10 minutes. Among them, in order to calculate the film thickness of the storage elastic modulus in water, the thickness before water immersion was used.

As a result of the measurement, Example 3: E2/E1 = 0.28, Example 4: E2/E1 = 0.27, and Comparative Example 1: E2/E1 = 0.25, and when the value of E2/E1 was low, when a polarizing film was produced, The degree of polarization is low.

In the above embodiments, the specific embodiments of the present invention have been described, but the above embodiments are merely examples and are not intended to be limiting. Various changes that are obvious to those skilled in the art are intended to be included within the scope of the present invention. [Industrial use]

The polarizing film composed of the polyvinyl alcohol-based film obtained by the production method of the present invention is excellent in in-plane uniformity of polarizing performance, and is preferably used in mobile information terminal equipment, computers, televisions, projectors, billboards, and tables. Liquid crystal display devices such as electronic computers, electronic clocks, word processors, electronic papers, game consoles, video recorders, cameras, photo frames, thermometers, stereos, automobiles or mechanical instruments, sunglasses, anti-glare glasses, stereo glasses, Anti-reflection layer, optical fiber communication equipment, medical equipment, building materials, toys, etc. for wearable displays, display elements (CRT, LCD, organic EL, electronic paper, etc.).

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Claims (13)

A polyvinyl alcohol-based film characterized in that: when the thickness is D (mm), the tension is 6 (folded in the MD direction) in the water of 30 ° C, and the tension is A (N/mm ² ). When the tension in the water flowing at 50 ° C is 6 times in the flow direction (MD direction) of the film is B (N/mm ² ), the following formulas (1) and (2) are satisfied; Formula (1) 0.6≦D ×A≦1.2; Formula (2) 0.2≦D×B≦0.4. For example, the polyvinyl alcohol-based film of the first application of the patent scope satisfies the following formula (3); (3) 0.2≦B/A≦0.5. The polyvinyl alcohol-based film of claim 1 or 2, wherein the storage elastic modulus in water at 30 ° C is E1 (Pa), and the storage elastic modulus in water at 50 ° C is E 2 (Pa) When E2/E1 is 0.25~0.30. The polyvinyl alcohol-based film of the first or second aspect of the invention, wherein the polyvinyl alcohol-based film has a thickness D of 0.04 mm or less. The polyvinyl alcohol-based film of the first or second aspect of the invention, wherein the polyvinyl alcohol-based film has a width of 4 m or more and a length of 4 km or more. The polyvinyl alcohol-based film according to claim 1 or 2, wherein the tension is 40 to 80 N/mm when the film is extended 4 times in the flow direction (MD direction) of the film in the air at 20 ° C and 65% RH. ² . A polyvinyl alcohol-based film according to claim 1 or 2, wherein the in-plane retardation is 50 nm or less. A method for producing a polyvinyl alcohol-based film, which is a polyvinyl alcohol-based film according to any one of claims 1 to 7, which is characterized in that it is produced through the following steps (A) to (D): A) preparing a polyvinyl alcohol resin aqueous solution; step (B) casting an aqueous solution of the polyvinyl alcohol resin into the casting mold and forming a film; and (C) contacting the film obtained by the film forming with the plurality of metal heating rolls The film is heated and dried; in step (D), the obtained film is heat-treated using hot air. The method for producing a polyvinyl alcohol-based film according to the eighth aspect of the invention, wherein in the step (A), glycerin is blended in an amount of 5 to 12% by weight based on the polyvinyl alcohol-based resin. The method for producing a polyvinyl alcohol-based film according to claim 8 or 9, wherein the temperature of the plurality of metal heating rolls in the step (C) is 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-based film according to claim 8 or 9, wherein the heat treatment temperature in the step (D) is 110 to 140 °C. A polyvinyl alcohol-based film produced by the method for producing a polyvinyl alcohol-based film according to any one of claims 8 to 11. A polarizing film comprising a polyvinyl alcohol-based film according to any one of claims 1 to 7 and 12.