JPWO2017195813A1 - POLYVINYL ALCOHOL FILM, PROCESS FOR PRODUCING THE SAME, AND POLARIZING FILM USING THE POLYVINYL ALCOHOL FILM - Google Patents

Abstract

  A polyvinyl alcohol film that is excellent in stretchability at the time of manufacturing a polarizing film, has a high degree of polarization, and can obtain a polarizing film with little color unevenness, particularly a polyvinyl alcohol film that does not break even when a thin polarizing film is manufactured, And a method for producing the polyvinyl alcohol film, and a polarizing film using the polyvinyl alcohol film. The polyvinyl alcohol film of the present invention is a polyvinyl alcohol film having a length of 4 km or more, and the tensile modulus X (MPa) in the length direction (MD direction) when the moisture content of the film is 9% by weight. Is 5 to 12 MPa.

Description

  The present invention relates to a polyvinyl alcohol film, in particular, a polyvinyl alcohol film having an excellent stretchability, a polarizing film having a high degree of polarization and little color unevenness, a method for producing the same, and the polyvinyl alcohol system The present invention relates to a polarizing film using a film.

  In recent years, the development of liquid crystal display devices has been remarkable, and they are widely used in smartphones, tablets, personal computers, liquid crystal televisions, projectors, in-vehicle panels, and the like. In such a liquid crystal display device, a polarizing film is used. As the polarizing film, a film obtained by adsorbing and orienting iodine or a dichroic dye on a polyvinyl alcohol film is mainly used. In recent years, as screens have become higher in definition, higher in brightness, larger in size, and thinner, there is a need for a polarizing film that is superior in polarization degree, has no color unevenness, and has a wide, long and thin thickness. In addition, the polarizing film in this invention is also called a polarizing film or a polarizer.

  In general, a polarizing film is a dichroic material such as iodine after a polyvinyl alcohol film as a raw material is unwound from a roll and swollen with water (including warm water) while being conveyed in the flow direction (MD direction). It is manufactured by dyeing with a dye and drawing. This stretching step is a step of stretching the dyed film in the flow direction (MD direction) and highly orienting the dichroic dye in the film. In order to improve the polarization degree of the polarizing film, The polyvinyl alcohol film used as a raw fabric needs to have good stretchability in the flow direction (MD direction).

  In addition, as a polarizing film manufacturing order, a case where stretching and dyeing are reversed is also carried out. That is, in this case, the polyvinyl alcohol film, which is the raw fabric, is swollen with water (including warm water), stretched, and dyed with a dichroic dye such as iodine. In order to improve the degree of polarization, the polyvinyl alcohol film needs to have good stretchability in the flow direction (MD direction). For example, when the stretching tension is too high, the film cannot be stretched to a predetermined stretching ratio, and the dichroic dye is not sufficiently oriented, so that the degree of polarization tends not to improve. On the other hand, when the stretching tension is too small, the orientation of the dichroic dye is not stable even if the stretching is performed up to a predetermined stretching ratio, and color unevenness tends to occur in the polarizing film.

  On the other hand, a polyvinyl alcohol film as a raw material is generally produced from an aqueous solution of a polyvinyl alcohol resin as a raw material by a continuous casting method. Specifically, a film formed by casting an aqueous solution of a polyvinyl alcohol resin onto a cast mold such as a cast drum or an endless belt is peeled off from the cast mold, and then the flow direction (MD direction) using a nip roll or the like. It is manufactured by drying using a heat roll while being conveyed and heat-treating using a floating dryer or the like if necessary. In such a conveyance process, since the film formed is pulled in the flow direction (MD direction), the polyvinyl alcohol polymer is easily oriented in the flow direction (MD direction). The stretchability in the flow direction (MD direction) of the system film is lowered, and finally the polarizing performance of the polarizing film is lowered.

  Furthermore, in recent years, the polyvinyl alcohol film has also been thinned to reduce the thickness of the polarizing film. Conventionally, the thickness of the polyvinyl alcohol film was about 60 μm, but now the thickness is about 45 μm. It is expected to be 30 μm in the near future. Such a thin polyvinyl alcohol-based film has a problem in productivity, such as being broken by stretching when the polarizing film is produced.

As a technique for improving the stretchability of the polyvinyl alcohol film, for example, a technique in which the ratio between the speed of the cast drum and the final film winding speed is set to a specific ratio when the polyvinyl alcohol film is formed (for example, a patent document) 1), a method of floating a film after film formation with a cast drum (for example, refer to Patent Document 2), and a method for controlling the tension in a drying process of a polyvinyl alcohol film (for example, refer to Patent Document 3). Proposed.
Moreover, the polyvinyl alcohol system film (for example, refer patent document 4) which reduced in-plane phase difference, and the polyvinyl alcohol system manufactured by making the tensile elongation of a flow direction (MD direction) and a width direction (TD direction) equivalent. A film (see, for example, Patent Document 5), a polyvinyl alcohol film (see, for example, Patent Document 6) whose Young's modulus (tensile elastic modulus) is reduced to 20 MPa or less by electromagnetic wave irradiation, and the like have also been proposed.

JP 2001-315141 A JP 2001-315142 A JP 2002-79531 A JP 2006-291173 A JP 2002-30164 A JP 2013-97232 A

  However, even the method of the above-mentioned patent document is insufficient to improve the stretchability of the polyvinyl alcohol film during the production of the polarizing film.

  The technology disclosed in Patent Document 1 specifies the degree of stretching (stretching) in the flow direction (MD direction) when producing a polyvinyl alcohol-based film, but it does not take into account drying conditions or heat treatment conditions. The stretchability of the polyvinyl alcohol film is not sufficiently improved.

  In the disclosed technique of Patent Document 2, the film after film formation can be dried uniformly, but the tensile elastic modulus cannot be controlled, and the stretchability of the polyvinyl alcohol film during the production of the polarizing film is not sufficiently improved.

  In the disclosed technique of Patent Document 3, the film thickness can be made uniform, but the tensile elastic modulus cannot be controlled, and the stretchability of the polyvinyl alcohol film during the production of the polarizing film is not sufficiently improved.

  Although the disclosed technique of Patent Document 4 can reduce the in-plane retardation of the film, there is room for improvement in terms of controlling the tensile elastic modulus and improving the stretchability of the polyvinyl alcohol film during the production of the polarizing film. Moreover, in the manufacturing method of this indication technique, the film after drying (70 degreeC) and heat processing (120 degreeC) is once cooled at 50 degrees C or less, and it heats again at 50-100 degreeC before winding up to a roll film. The heating process is complicated, and there is room for improvement in terms of productivity.

  In the disclosed technique of Patent Document 5, the tensile elongation of the polyvinyl alcohol film can be stabilized, but the tensile elastic modulus itself is not controlled, and the stretchability of the polyvinyl alcohol film during the production of the polarizing film is sufficiently improved. Not.

  In the technique disclosed in Patent Document 6, although the tensile elastic modulus can be reduced, in the examples, it is 13.8 to 17.8 MPa, and in the comparative example in which no electromagnetic wave irradiation is performed, it is 27 MPa, and further reduction of the tensile elastic modulus is desired. .

  In addition, in the Example of the said patent documents 1-6, only the polyvinyl alcohol-type film of thickness 50 micrometers or more is described, and in order to respond to the request | requirement of thickness reduction in recent years, the further improvement is requested | required. .

  Therefore, the present invention is a polyvinyl alcohol film that is excellent in stretchability at the time of manufacturing a polarizing film, and can obtain a polarizing film having a high degree of polarization and little color unevenness. A polyvinyl alcohol film that does not break when producing a thin polarizing film even when a thin film having a thickness of 25 μm or less is produced, a method for producing the same, and a polarizing film using the polyvinyl alcohol film To do.

  However, as a result of intensive studies in view of such circumstances, the present inventors have found that the length in the flow direction (MD direction) is equal to or greater than a specific length, and the tensile elasticity in the flow direction (length direction, MD direction). The present inventors have found that a polyvinyl alcohol film whose rate is controlled within a specific range is excellent in stretchability at the time of producing a polarizing film and can produce a thin polarizing film with a high yield. And it discovered that the polarizing film obtained using this polyvinyl-alcohol-type film has a high degree of polarization, and becomes a polarizing film with few color nonuniformity.

  That is, the first gist of the present invention is a polyvinyl alcohol film having a length of 4 km or more, and the tensile modulus X (in the MD direction) in the state where the moisture content of the film is 9% by weight (MD direction). (MPa) is a polyvinyl alcohol film characterized by 5-12 MPa.

  The second gist of the present invention is that a film forming process for forming an aqueous solution of a polyvinyl alcohol resin by a continuous casting method, a drying process for drying the formed film, and a heat treatment for the dried film. A method for producing the polyvinyl alcohol film according to the first aspect, wherein the temperature for drying the film formed in the drying step is 100 ° C. or higher, and the heat treatment step comprises: A method for producing a polyvinyl alcohol film, wherein the dried film is cooled to 50 ° C. or lower and then heated at 60 to 99 ° C.

  And the 3rd summary of this invention is a polarizing film characterized by using the polyvinyl-alcohol-type film of the said 1st summary.

  The polyvinyl alcohol film according to the first aspect of the present invention has a tensile modulus X in the length direction (MD direction) of 5 to 12 MPa in a state where the moisture content is 9% by weight. In the case of producing a thin polarizing film, it is possible to prevent breakage from occurring.

In particular, when the thickness D of the film is 5 to 25 μm and the thickness D (μm) and the tensile elastic modulus X (MPa) satisfy the following formula (1), There is an effect that the resistance to breakage can be improved.
0.4 ≦ X / D ≦ 0.6 (1)

Especially, the tensile elastic modulus Y (MPa) in the width direction (TD direction) in the state where the moisture content of the film is 9% by weight and the tensile elastic modulus X (MPa) in the length direction (MD direction). When the following formula (2) is satisfied, there is an effect that it is possible to improve the stretchability during the production of the polarizing film.
0.7 ≦ Y / X ≦ 1.3 (2)

  Moreover, when the tensile strength F in the length direction (MD direction) is 100 MPa or more, there is an effect that it is possible to prevent breakage when manufacturing a thin polarizing film.

Further, when the refractive index in the length direction (MD direction) is nx, the refractive index in the width direction (TD direction) is ny, the refractive index in the thickness direction is nz, and the thickness is D (μm), When the retardation Rth in the thickness direction calculated in (3) is 80 to 140 nm, the swellability in the thickness direction can be optimized and the stretchability at the time of manufacturing the polarizing film is optimized. There is an effect that can be done.
Rth = {(nx + ny) / 2−nz} × 1000 × D (3)

  And when the width | variety of the said film is 4 m or more, there exists an effect that productivity can be aimed at.

  Since the method for producing a polyvinyl alcohol film according to the second aspect of the present invention includes a specific drying step and a heat treatment step, the method according to the first aspect is excellent in stretchability and rupture resistance during the production of the polarizing film. There exists an effect that a polyvinyl-alcohol-type film can be manufactured.

  The polarizing film according to the third aspect of the present invention has the effect of exhibiting a high degree of polarization and less color unevenness because the polyvinyl alcohol film according to the first aspect is used. .

The present invention is described in detail below.
The polyvinyl alcohol film of the present invention is a polyvinyl alcohol film having a length of 4 km or more, and has a tensile modulus X in the length direction (MD direction) measured in a state where the moisture content of the film is 9% by weight. 5 to 12 MPa.

  And the said polyvinyl alcohol-type film is formed in a polarizing film through a swelling process, an extending | stretching process, etc., being conveyed in the length direction (MD direction). Here, the length direction (MD direction) measured in a state where the polyvinyl alcohol film has a specific length (4 km or more) and the moisture content of the polyvinyl alcohol film is 9% by weight is specified. Therefore, the polyvinyl alcohol film is excellent in stretchability during the production of the polarizing film and does not break even when a thin polarizing film is produced. The obtained polarizing film exhibits a high degree of polarization and has little color unevenness.

First, the tensile elastic modulus of the polyvinyl alcohol film of the present invention will be described.
The tensile elastic modulus in the present invention is a value measured in an environment of 20 ° C. and 65% RH according to JIS K7127: 1999. The tensile elastic modulus is also called Young's modulus and tensile elastic modulus.

Further, the moisture content in the present invention is a value calculated from the weight before and after the polyvinyl alcohol film is dried at an atmospheric temperature of 105 ° C. for 16 hours with a dryer, and the weight before drying is A, after drying. When the weight of B is B, the following formula is used.
Moisture content (% by weight) = 100 × (A−B) / A

  As described above, the polyvinyl alcohol film is stretched after swelling in the production process of the polarizing film, but it is difficult to accurately and stably measure the tensile elastic modulus after swelling. In the present invention, in view of the moisture content of a polyvinyl alcohol film generally used for the production of a polarizing film being several percent, the tensile modulus at a moisture content of 9% by weight, which can be easily controlled by humidity control, is used as an index. .

  The method of conditioning the humidity is not particularly limited. For example, a relatively dry polyvinyl alcohol film immediately after production is conditioned in an environment of 20 ° C. and 65% RH for several hours to several tens of hours. The moisture content can be stabilized at 9% by weight, which is close to the equilibrium moisture content. In the present invention, the “water content 9% by weight” means “including a water content of 9.0% by weight ± 0.5% by weight”, and within that range, the tensile modulus of elasticity is included. Is almost unchanged. In addition, since the moisture content in the film changes to an equilibrium moisture content that depends on the environmental humidity, the specimen whose moisture content has been adjusted to 9% by weight is quickly subjected to measurement of the tensile modulus. .

In the present invention, the in-plane deflection ΔX (MPa) of the tensile elastic modulus X in the length direction (MD direction) in a state where the moisture content is 9% by weight, and the width direction ( The in-plane deflection ΔY (MPa) of the tensile elastic modulus Y (MPa) in the TD direction is preferably 5 MPa or less, particularly preferably 3 MPa or less, and further preferably 2 MPa or less.
If the in-plane deflection ΔX and the in-plane deflection ΔY are too large, stretching unevenness occurs during the production of the polarizing film, and color unevenness tends to occur in the polarizing film.

  Here, the manufacturing method of the polyvinyl alcohol-type film of this invention is demonstrated. That is, the method for producing a polyvinyl alcohol film of the present invention includes a film forming step (A) for forming an aqueous solution of a polyvinyl alcohol resin by a continuous casting method, and a drying step (B) for drying the formed film. A method for producing a polyvinyl alcohol film comprising a heat treatment step (C) for heat-treating the dried film, wherein the film-forming film is dried at a temperature of 100 ° C. or higher in the drying step (B). In the heat treatment step (C), the dried film is cooled to 50 ° C. or lower and then heated at 60 to 99 ° C.

[Film forming step (A)]
First, the film forming step (A) will be described in detail.

  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 of saponifying and decarboxylating a copolymer of vinyl and vinyl ethylene carbonate; and (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, the degree of polarization of the polarizing film tends to decrease, and if it is too large, stretching of the polyvinyl alcohol film during the production of the polarizing film tends to be difficult. 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, the degree of polarization of the polarizing film tends to decrease.
Here, the average saponification degree in the present invention is measured according to JIS K 6726.

  As the polyvinyl alcohol-based resin used in the present invention, two or more types having different modified species, modified amounts, weight average molecular weights, average saponification degrees, etc. may be used in combination.

And it is preferable to wash | clean the said polyvinyl alcohol-type resin using solvents, such as water, and to spin-dry | dehydrate using a centrifuge etc. and to make a polyvinyl alcohol-type resin wet cake with a moisture content of 50 weight% or less. 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 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 addition to polyvinyl alcohol-based resins, polyvinyl alcohol-based resin aqueous solutions include generally used plasticizers such as glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol, trimethylolpropane, and nonions. It is preferable from the viewpoint of the film-forming property of the polyvinyl alcohol film to contain at least one surfactant, anionic, anionic and cationic.

A preferable plasticizer is glycerin, and the content of the plasticizer in the aqueous polyvinyl alcohol resin solution is preferably 1 to 20% by weight.
Preferable examples of the surfactant include polyoxyethylene alkylamine and higher fatty acid alkanolamide, and the content of the surfactant in the aqueous polyvinyl alcohol resin solution is preferably 0.01 to 1% by weight. .

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

  Next, the obtained polyvinyl alcohol-based resin aqueous solution is defoamed. Examples of the defoaming method include stationary defoaming and defoaming using 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 continuous casting method.

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

  The viscosity of the aqueous polyvinyl alcohol resin solution is preferably 50 to 200 Pa · s, particularly preferably 70 to 150 Pa · s at the time of discharge. 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 0.1 to 3.0 m / min, particularly preferably 0.2 to 2.5 m / min. Preferably it is 0.3-2.0 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.

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

  The width of such a cast drum is preferably 4 m or more, particularly preferably 4.5 m or more, more preferably 5 m or more, and particularly preferably 5 to 6 m. If the width of the cast drum is too small, the productivity tends to decrease.

  The rotational speed of the cast drum is preferably 1 to 30 m / min, particularly preferably 2 to 25 m / min, and further preferably 3 to 20 m / min. If the rotational speed is too slow, productivity tends to decrease, and if it is too fast, dehydration tends to be insufficient.

  The surface temperature of such a cast drum is preferably 40 to 99 ° C, more preferably 50 to 90 ° C, and particularly preferably 55 to 80 ° C. If the surface temperature is too low, dehydration tends to occur, and if it is too high, foaming tends to occur.

  Thus, the film forming step (A) is performed, and the formed film is peeled off from the cast drum.

[Drying process (B)]
Next, the drying step (B) will be described in detail. This drying step (B) is a step of heating and drying the film thus formed.

  The film peeled off from the cast drum (the film formed above) is conveyed in the flow direction (MD direction) using a nip roll or the like, and the front and back surfaces of the film are alternately brought into contact with a plurality of hot rolls. It is dried by. The hot roll is, for example, a roll having a surface of hard chrome plating or a mirror finish and having a diameter of 0.2 to 2 m, and usually 2 to 30, preferably 10 to 25 are preferably used for drying.

  The drying temperature (temperature for drying the film formed above) is preferably 100 ° C. or higher, particularly preferably 100 to 120 ° C., further preferably 100 to 115 ° C., and particularly preferably 100 to 110 ° C. If the drying temperature is too low, the drying tends to be poor, and if it is too high, appearance defects such as swell tend to be caused. In addition, the drying temperature in this invention is the surface temperature of the hottest hot roll in the hot roll used.

The drying time is not particularly limited, but is usually 1 to 60 seconds, preferably 2 to 50 seconds, particularly preferably 3 to 40 seconds, and further preferably 4 to 30 seconds. If the drying time is too short, drying tends to be poor, and if it is too long, appearance defects such as swell tend to be caused.
The drying time in the present invention means the contact time between the hottest hot roll and the film formed above, and when there are a plurality of hottest hot rolls, This is the integrated value of the contact time.

  The moisture content of the film after drying is preferably 5% by weight or less, particularly preferably 0.1 to 4% by weight, more preferably 0.2 to 3% by weight, and particularly preferably 0.3 to 2.5% by weight. %. If the moisture content is too high, the finally obtained polyvinyl alcohol film tends to be poorly dried.

[Heat treatment step (C)]
Next, the heat treatment step (C) will be described in detail. This heat treatment step (C) is a step of heat-treating the dried film. Such a heat treatment step is generally an optional step performed as necessary, but in the present invention, it is an essential step for controlling the tensile elastic modulus. That is, in this heat treatment step (C), the film dried at 100 ° C. or higher in the drying step (B) is once cooled to 50 ° C. or lower (the temperature of the dried film itself), and again 60 to 99 again. By heating at 0 ° C., the tensile elastic modulus is set to a desired range, and the stretchability at the time of producing the polarizing film is improved.

  Examples of the cooling method include natural cooling in which it is left to cool naturally, and a method of blowing cold air.

  Examples of the heating method include a method of blowing hot air with a floating dryer, a method of contacting with a hot roll, and the like. In the present invention, a method using a floating dryer in terms of stabilizing the tensile elastic modulus. preferable.

  The heating temperature is preferably 65 to 95 ° C, particularly preferably 70 to 90 ° C, and more preferably 70 to 80 ° C. If the heating temperature is too low, the tensile elastic modulus tends to decrease, and if it is too high, the tensile elastic modulus tends to increase. The heating temperature in the present invention means the temperature of the hot air when the heating method is a method of blowing hot air with the floating dryer, and when the heating method is a method of contacting the hot roll, It means the surface temperature of the hot roll.

  Although heating time is not specifically limited, When using a floating dryer, 10 to 120 second is preferable, Especially preferably, it is 20 to 90 second, More preferably, it is 30 to 60 second. If the heating time is too short, the deflection of the tensile elastic modulus tends to increase, and if it is too long, the productivity tends to decrease.

  The moisture content of the film after heating is preferably 0.1 to 2% by weight, particularly preferably 0.2 to 1.7% by weight, and more preferably 0.3 to 1.5% by weight. If the moisture content is too low, water swelling during the production of the polarizing film tends to be difficult. Conversely, if it is too high, the finally obtained polyvinyl alcohol film tends to be poorly dried.

  As described above, the drying step (B) and the heat treatment step (C) have been described. However, in the production method of the present invention, the temperature balance between the two is important, and the drying temperature in the drying step (B) is water. The boiling point is preferably 100 ° C. or higher, and it is more preferable to select a relatively low temperature in such a temperature range. Furthermore, the heating temperature in the heat treatment step (C) is 100 ° C., which is the boiling point of water. It is particularly preferred that it is less than.

[Polyvinyl alcohol film]
Through the drying step (B) and the heat treatment step (C), the polyvinyl alcohol film of the present invention that is long in the flow direction (MD direction) is obtained. This polyvinyl alcohol film is slit at both ends, and is wound around a core tube in a roll shape.

  The width of the polyvinyl alcohol film of the present invention thus obtained is preferably 4 m or more in terms of productivity improvement, and more preferably 4 to 6 m in terms of avoiding breakage.

  In addition, the length of the polyvinyl alcohol film of the present invention is premised on 4 km or more, and is preferably 5 km or more, particularly preferably in view of increasing the area of the polarizing film and thus the liquid crystal screen. In terms of transport weight, it is 5 to 50 km.

The thickness D of the polyvinyl alcohol film is preferably 30 μm or less from the viewpoint of thinning the polarizing film, particularly preferably 25 μm or less from the viewpoint of further thinning, and more preferably 5 from the viewpoint of avoiding breakage. ˜25 μm, particularly preferably 5 to 20 μm.
The thickness D (μm) is adjusted by the resin concentration in the polyvinyl alcohol-based resin aqueous solution, the discharge amount (discharge speed) to the cast mold, the draw ratio, and the like.

When the film thickness D is 5 to 25 μm, the polyvinyl alcohol film of the present invention has a thickness D (μm) and a flow direction measured in a state where the moisture content of the film is 9% by weight ( It is preferable that the tensile modulus X (MPa) in the MD direction satisfies the following formula (1) in terms of improving the fracture resistance when manufacturing the polarizing film.
0.4 ≦ X / D ≦ 0.6 (1)

Particularly preferably, the following formula (1 ′) is satisfied in terms of improving the stretchability during the production of the polarizing film.
0.45 ≦ X / D ≦ 0.55 (1 ′)

In the polyvinyl alcohol film of the present invention, the tensile modulus Y (MPa) in the width direction (TD direction) when the moisture content is 9% by weight is the following formula ( It is preferable to satisfy 2).
0.7 ≦ Y / X ≦ 1.3 (2)

Particularly preferably, the following formula (2 ′) is satisfied from the viewpoint of improving the stretchability during the production of the polarizing film.
0.75 ≦ Y / X ≦ 1.1 (2 ′)

  If the value of Y / X is too small, the stretchability in the flow direction (MD direction) during the production of the polarizing film tends to decrease, and conversely if too large, the stretchability tends not to be stabilized.

  In the polyvinyl alcohol film of the present invention, the tensile strength F (MPa) in the flow direction (MD direction) in a state where the moisture content is 9% by weight is preferably 100 MPa or more, and particularly preferably 110 MPa or more. If the tensile strength F (MPa) is too small, there is a tendency that breakage tends to occur during the production of a thin polarizing film. The upper limit of the tensile strength F (MPa) is usually 200 MPa.

The polyvinyl alcohol film of the present invention has a refractive index in the length direction (MD direction) of nx, a refractive index in the width direction (TD direction) of ny, a refractive index in the thickness direction of nz, and a thickness of D ( μm), the thickness direction retardation Rth (nm) calculated by the following formula (3) is preferably 80 to 140 nm. More preferably, it is 85-130 nm, More preferably, it is 90-120 nm.
If the retardation Rth (nm) in the thickness direction is too small, the swelling property in the thickness direction tends to be reduced. If the retardation Rth (nm) is too large, the surface orientation of the polymer chain is strong. Tends to decrease.
Rth = {(nx + ny) / 2−nz} × 1000 × D (3)

  In the above embodiment, the method for producing a polyvinyl alcohol film has been described by taking as an example the case where a cast drum (drum roll) is used as a cast mold. However, a cast belt or a resin film is used as a cast mold. It is also possible to manufacture.

  Since the polyvinyl alcohol film of the present invention is excellent in stretchability, it is particularly preferably used as a raw material for a polarizing film.

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

[Method for producing polarizing film]
The polarizing film of the present invention is produced through steps such as swelling, dyeing, boric acid crosslinking, stretching, washing, and drying by feeding the polyvinyl alcohol film out of a roll and transferring it in the horizontal direction.

  The swelling process is performed before the dyeing process. In addition to being able to clean the surface of the polyvinyl alcohol film by the swelling step, there is also an effect of preventing uneven dyeing by swelling the polyvinyl alcohol film. In the swelling step, water is usually used as the treatment liquid. As long as the main component is water, the treatment liquid may contain a small amount of an additive such as an iodide compound, a surfactant, alcohol, and 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.

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

  The boric acid crosslinking step is performed using a boron compound such as boric acid or borax. The boron compound is used in the form of an aqueous solution or a water-organic solvent mixture at a concentration of about 10 to 100 g / L, and it is preferable that potassium iodide coexists in the solution from the viewpoint of stabilizing the polarization performance. The temperature during the treatment is preferably about 30 to 70 ° C., and the treatment time is preferably about 0.1 to 20 minutes. If necessary, the stretching operation may be performed during the treatment.

  In the stretching step, stretching in the uniaxial direction [flow direction (MD direction)] is preferably 3 to 10 times, preferably 3.5 to 6 times. At this time, a slight stretching (stretching to prevent shrinkage in the width direction (TD direction) or more) may also be performed in the direction perpendicular to the stretching direction. The temperature during stretching is preferably 30 to 170 ° C. Furthermore, the stretching ratio may be finally set within the above range, and the stretching operation may be performed not only once but plural times in the polarizing film manufacturing process.

In this invention, as above-mentioned, the extending | stretching tension | tensile_strength in this extending process needs to be an appropriate range. That is, when the stretching tension is too large, the film cannot be stretched to a predetermined stretching ratio, and the dichroic dye is not sufficiently oriented, so that the degree of polarization tends not to be improved. On the other hand, when the stretching tension is too small, the orientation of the dichroic dye is not stable even if the stretching is performed up to a predetermined stretching ratio, and color unevenness tends to occur in the polarizing film.
In general, in the polarizing film manufacturing process, since the stretching tension is set for each thickness, it is difficult to generalize a preferable range. However, in the comparison with the same thickness, the stretching tension is 1 It is preferable to reduce by 10% or more, and particularly preferably to reduce by 1-30%.

  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 the deposits generated on the surface of the polyvinyl alcohol film can be removed. When using a potassium iodide aqueous solution, the potassium iodide concentration is 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.

  In the drying step, for example, the polyvinyl alcohol film is dried in the air at 40 to 80 ° C. for 1 to 10 minutes.

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

Further, the single transmittance of the polarizing film of the present invention is preferably 42% or more, more preferably 43% or more. If the single transmittance is too low, it tends to be impossible to achieve high brightness of the liquid crystal display.
The single transmittance is a value obtained by measuring the light transmittance of a single polarizing film using a spectrophotometer.

The polarizing film of the present invention is suitable for producing a polarizing plate having excellent degree of polarization and no color unevenness.
Here, the manufacturing method of the polarizing plate using the polarizing film of this invention is demonstrated.

[Production method of polarizing plate]
The polarizing plate is produced by laminating an optically isotropic resin film as a protective film on one or both sides of the polarizing film of the present invention 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 the liquid adhesive composition is uniformly applied to the polarizing film, the protective film, or both, the both are bonded and pressure-bonded. It is performed by irradiating active energy rays.

  Moreover, curable resin, such as a urethane type resin, an acrylic resin, and a urea resin, is apply | coated to the single side | surface or both surfaces of a polarizing film, it hardens | cures, a hardened layer can be formed, and it can also be set as a polarizing plate. If it does in this way, the said hardened layer becomes a substitute of the said protective film, and can attain thinning.

  Polarizing films and polarizing plates using the polyvinyl alcohol film of the present invention are excellent in polarizing performance, such as portable information terminals, personal computers, televisions, projectors, signage, electronic desk calculators, electronic watches, word processors, electronic paper, games. 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 It is preferably used for an antireflection layer for paper and the like, an optical communication device, a medical device, a building material, a toy and the like.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist.

  The properties of the polyvinyl alcohol film (water content, tensile modulus, tensile strength, thickness direction retardation, stretching tension) and polarizing film properties (polarization degree, single transmittance) in the following examples and comparative examples , Color unevenness) was measured and evaluated as follows.

<Measurement conditions>
[Moisture content (% by weight)]
From the obtained polyvinyl alcohol film, a test piece of 100 mm × 100 mm was cut out, and from the initial weight A (g) and the weight B (g) after drying at an ambient temperature of 105 ° C. for 16 hours by a dryer, the following formula Was used to calculate the moisture content (% by weight).
Moisture content (% by weight) = 100 × (A−B) / A

[Tensile elastic modulus (MPa), tensile strength F (MPa)]
A 120 mm × 15 mm test piece was cut out from the obtained polyvinyl alcohol-based film, and the moisture content was adjusted to 9 wt% ± 0.5 wt% in a constant temperature and humidity chamber at 20 ° C. and 65% RH. Using “Precision Universal Testing Machine, Autograph (AG-IS)” manufactured by Seisakusho Co., Ltd. under an environment of 20 ° C. and 65% RH according to JIS K7127: 1999 (pulling speed 1000 mm / min, distance between chucks 50 mm). The tensile elastic modulus X (MPa) in the flow direction (MD direction) and the tensile elastic modulus Y (MPa) in the width direction (TD direction) were measured. For the flow direction (MD direction), the tensile strength F (MPa) is measured.

[Thickness direction phase difference Rth (nm)]
A test piece having a length of 4 cm and a width of 4 cm was cut out from the central portion and both end portions (within 10 cm from the end of the film) in the width direction (TD direction) of the obtained polyvinyl alcohol film, and a retardation measuring device (“KOBRA”) was obtained. -WR "(manufactured by Oji Scientific Instruments) was used to measure the thickness direction retardation Rth (nm) at 590 nm.
<Rth measurement conditions>
Incident angle: 50 °
Inclined central axis: Slow axis Average refractive index: Numerical value measured using an Abbe refractometer

[Stretching tension (N)]
A test piece having a length (MD direction) of 50 mm × width (TD direction) of 35 mm was cut out from the obtained polyvinyl alcohol film, and both end portions in the length direction (MD direction) were widened so that the distance between chucks was 20 mm. After being sandwiched by a 35 mm chuck, it was stretched 1.7 times (34 mm) in the length direction (MD direction) while being immersed in warm water at 25 ° C. for 60 seconds, and then lengthened in a staining solution at 28 ° C. Stretched 1.6 times (54.4 mm) in the direction (MD direction), and finally stretched 2.05 times (111.5 mm) in the length direction (MD direction) in a boric acid solution at 55 ° C. The tension (N) at the time was measured with a spring alone. The composition of the used dyeing solution and boric acid solution is as follows.
Staining solution: iodine 0.9 g / L, potassium iodide 30 g / L
Boric acid solution: potassium iodide 30 g / L, boric acid 25 g / L

[Degree of polarization (%), single transmittance (%)]
A test piece 4 cm long x 4 cm wide was cut out from the center and both side ends (10 cm inside from both ends of the polarizing film) in the width direction (TD direction) of the obtained polarizing film. The degree of polarization (%) and single transmittance (%) were measured using a film measuring apparatus (manufactured by JASCO Corporation: VAP7070). This measurement was performed for the central portion of the polarizing film in the flow direction (MD direction) and the tip / end portion (10 m inside from each end of the tip and end of the polarizing film).

〔Color unevenness〕
From the center and both side ends of the polarizing film (TD direction) (10 cm inside from each end of the polarizing film), a test piece 30 cm long × 30 cm wide was cut out and crossed Nicol After being sandwiched between the two polarizing plates (single transmittance 43.5%, polarization degree 99.9%) at an angle of 45 °, using a light box with a surface illumination of 14,000 lx, a transmission mode The optical color unevenness was observed and evaluated according to the following criteria.
(Evaluation criteria)
○ ・ ・ ・ No color unevenness × ・ ・ ・ There is color unevenness Such an evaluation was performed with the central part and the front end / end part of the polarizing film flowing direction (MD direction) To go).

<Example 1>
(Preparation of polyvinyl alcohol film)
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, and 120 kg of glycerin as a plasticizer are added, and the temperature is raised to 140 ° C. while stirring, and the resin concentration The concentration was adjusted to 25% by weight to obtain a uniformly dissolved polyvinyl alcohol resin aqueous solution. Next, the polyvinyl alcohol-based resin aqueous solution is supplied to a twin-screw extruder having a vent and defoamed, and then the aqueous solution temperature is set to 95 ° C. and discharged from a T-type slit die discharge port onto a rotating cast drum (discharge speed). 0.8 m / min) and cast to form a film. The film formed was peeled from the cast drum and dried while the front and back surfaces of the film were alternately brought into contact with 20 hot rolls. The drying temperature (surface temperature of the hottest hot roll) was 120 ° C., and the drying time (cumulative contact time between the hottest hot roll and the film) was 12 seconds. Next, by naturally cooling the dried film, the temperature of the film itself is once cooled to 40 ° C., and then heated by blowing 75 ° C. hot air from both sides of the film for 60 seconds using a floating dryer. A polyvinyl alcohol film (thickness 20 μm, width 5 m, length 5 km) having a moisture content of 1% by weight was obtained. Finally, both ends of the polyvinyl alcohol film were slit and wound around the core tube in a roll shape. The characteristics of the obtained polyvinyl alcohol film are shown in Table 1 below.

(Manufacture of polarizing film)
The obtained polyvinyl alcohol film was unwound from a roll and transported in the horizontal direction using a transport roll. First, it was 1.7 times in the flow direction (MD direction) in 1 minute while being immersed in a water bath at a water temperature of 25 ° C. and swollen. Stretched twice. Next, the film was stretched 1.6 times in the flow direction (MD direction) in 0.5 minutes while being immersed in a 28 ° C. aqueous solution of iodine 0.9 g / L and potassium iodide 30 g / L and dyeing. Subsequently, the film was immersed in a 55 ° C. aqueous solution composed of 25 g / L of boric acid and 30 g / L of potassium iodide, and uniaxially stretched 2.0 times in the flow direction (MD direction) while crosslinking with boric acid. Finally, it was washed with an aqueous potassium iodide solution and dried at 50 ° C. for 2 minutes to obtain a polarizing film having a total draw ratio of 5.6 times. No breakage occurred during the production of such a polarizing film. The properties of the obtained polarizing film are shown in Table 2 below.

<Example 2, Comparative Example 1>
A polyvinyl alcohol film and a polarizing film were obtained in the same manner as in Example 1 except that the production was performed under the conditions shown in Table 1 below. The properties of the obtained polyvinyl alcohol film are shown in Table 1 below, and the properties of the obtained polarizing film are shown in Table 2 below.
In Comparative Example 1, an attempt was made to produce a polarizing film in the same manner as in Example 1, but breakage occurred during stretching in the boric acid crosslinking step. The characteristics shown in Table 2 are the characteristics of the polarizing film tip obtained barely.

  The polyvinyl alcohol films of Examples 1 and 2 have a tensile modulus value within the specific range of the present invention, so that the obtained polarizing film has a high degree of polarization and no color unevenness, whereas Comparative Example 1 Since the tensile modulus of the polyvinyl alcohol film is outside the specific range of the present invention, it is easy to break, and the obtained polarizing film is inferior in the degree of polarization and has color unevenness.

  In addition, a polyvinyl alcohol film having a length of 4 km and 10 km was produced in the same manner as in Example 1. The results showing the same tendency as in Examples 1 and 2 were obtained for the polyvinyl alcohol films of these lengths.

  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.

  Polarizing films and polarizing plates using the polyvinyl alcohol film of the present invention are excellent in polarizing performance, such as portable information terminals, personal computers, televisions, projectors, signage, electronic desk calculators, electronic watches, word processors, electronic paper, games. 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 It is preferably used for an antireflection layer for paper and the like, an optical communication device, a medical device, a building material, a toy and the like.

Claims (8)

  A polyvinyl alcohol film having a length of 4 km or more, wherein the tensile modulus X in the length direction (MD direction) in a state where the moisture content of the film is 9% by weight is 5 to 12 MPa. Polyvinyl alcohol film. The thickness D of the film is 5 to 25 µm, and the thickness D (µm) and the tensile elastic modulus X (MPa) satisfy the following formula (1). Polyvinyl alcohol film.
0.4 ≦ X / D ≦ 0.6 (1) The tensile modulus Y (MPa) in the width direction (TD direction) and the tensile modulus X (MPa) in the length direction (MD direction) when the moisture content of the film is 9% by weight The polyvinyl alcohol film according to claim 1 or 2, wherein (2) is satisfied.
0.7 ≦ Y / X ≦ 1.3 (2)   The polyvinyl alcohol film according to any one of claims 1 to 3, wherein the tensile strength F in the length direction (MD direction) is 100 MPa or more. When the refractive index in the length direction (MD direction) is nx, the refractive index in the width direction (TD direction) is ny, the refractive index in the thickness direction is nz, and the thickness is D (μm), the following formula (3 The polyvinyl alcohol film according to any one of claims 1 to 4, wherein the retardation Rth in the thickness direction calculated in (1) is 80 to 140 nm.
Rth = {(nx + ny) / 2−nz} × 1000 × D (3)   The width of the said film is 4 m or more, The polyvinyl alcohol-type film as described in any one of Claims 1-5 characterized by the above-mentioned.   A film forming step of forming an aqueous solution of a polyvinyl alcohol-based resin by a continuous casting method, a drying step of drying the formed film, and a heat treatment step of heat-treating the dried film are provided. 6. The method for producing a polyvinyl alcohol film according to claim 6, wherein a temperature at which the film formed in the drying step is dried is 100 ° C. or more, and the heat treatment step is the drying step. A method for producing a polyvinyl alcohol film, which is a step of heating the film at 60 to 99 ° C after cooling to 50 ° C or lower.   A polarizing film, wherein the polyvinyl alcohol film according to any one of claims 1 to 6 is used.