KR102365676B1 - Polyvinyl alcohol-based film, manufacturing method thereof, and polarizing film using the polyvinyl alcohol-based film - Google Patents

Abstract

A polyvinyl alcohol-based film capable of obtaining a polarizing film having a high degree of polarization and having little unevenness due to excellent stretchability in manufacturing a polarizing film, particularly a polyvinyl alcohol-based film that does not break even when a thin polarizing film is produced, and the polyvinyl alcohol-based film A method for producing a film, and a polarizing film using the polyvinyl alcohol-based film are provided. The polyvinyl alcohol-based film of the present invention is a polyvinyl alcohol-based film having a length of 4 km or more, and the tensile modulus X (MPa) in the longitudinal direction (MD) in a state where the moisture content of the film is 9 wt% is 5 to 12 MPa, characterized in that do.

Description

Polyvinyl alcohol-based film, manufacturing method thereof, and polarizing film using the polyvinyl alcohol-based film

The present invention relates to a polyvinyl alcohol-based film, in particular, a polyvinyl alcohol-based film capable of obtaining a polarizing film having excellent stretchability and having a high degree of polarization and less unevenness, a method for producing the same, and a polarizing film using the polyvinyl alcohol-based film will be.

In recent years, the development of liquid crystal display devices is dazzling, and is widely used in smart phones, tablets, personal computers, liquid crystal TVs, projectors, in-vehicle panels, and the like. A polarizing film is used for such a liquid crystal display device, and as the polarizing film, a polyvinyl alcohol-based film in which iodine or a dichroic dye is adsorbed and aligned is mainly used. In recent years, as screens have been made high-definition, high-brightness, large-size, and thin, a thin polarizing film having a higher degree of polarization than conventional quality, no stains, and a wide and long width is required. In addition, the polarizing film in this invention is also called a polarizing film and a polarizer.

In general, the polarizing film unwinds a polyvinyl alcohol-based film, which is a raw material, from a roll, and swells it with water (including hot water) while conveying it in the flow direction (MD), followed by dichroism such as iodine It is prepared by dyeing with a dye and stretching. Such a stretching step is a step of stretching the dyed film in the flow direction (MD) and highly orienting the dichroic dye in the film. MD), it is necessary to have good stretchability.

Moreover, as a procedure of manufacture of a polarizing film, the case where extending|stretching and dyeing are reversed is also implemented. That is, the polyvinyl alcohol-based film as a raw material is swollen with water (including hot water), stretched, and dyed with a dichroic dye such as iodine. , it is necessary for the polyvinyl alcohol-based film to have good stretchability in the flow direction (MD). For example, when the stretching tension is too large, stretching is not possible to a predetermined stretching ratio, and the dichroic dye does not sufficiently orientate, and thus the degree of polarization does not tend to be improved. Conversely, when the stretching tension is too small, the orientation of the dichroic dye is not stable even if it is stretched to a predetermined stretching ratio, and unevenness tends to occur in the polarizing film.

On the other hand, a polyvinyl alcohol-based film as a raw material is generally produced by a continuous casting method from an aqueous solution of a polyvinyl alcohol-based resin as a raw material. Specifically, a film formed by casting an aqueous solution of a polyvinyl alcohol-based resin into a cast die such as a cast drum or an endless belt is peeled from the cast die, and then conveyed in the flow direction (MD) using a nip roll or the like while heat It is manufactured by drying using a roll, and heat-processing using a floating dryer etc. if necessary. In such a conveying process, since the formed film is stretched in the flow direction (MD), the polyvinyl alcohol-based polymer tends to be oriented in the flow direction (MD), and if this orientation is too large, the flow of the polyvinyl alcohol-based film The stretchability in the direction MD is lowered, and finally, the polarization performance of the polarizing film is lowered.

In addition, in recent years, in order to reduce the thickness of the polarizing film, polyvinyl alcohol-based films have also been made thinner. is expected to be Such a thin polyvinyl alcohol-based film had a problem of productivity, such as being fractured by stretching when manufacturing a polarizing film.

As a method of improving the stretchability of the polyvinyl alcohol-based film, for example, a method in which the ratio of the speed of the cast drum and the final film winding speed during film formation of the polyvinyl alcohol-based film is set to a specific ratio (for example, Refer to Patent Document 1), a method for floating the film after forming with a cast drum and drying it (for example, refer to Patent Document 2), a method for controlling the tensile state in the drying step of a polyvinyl alcohol-based film (for example, For example, refer to Patent Document 3) has been proposed.

In addition, a polyvinyl alcohol-based film with reduced in-plane retardation (see, for example, Patent Document 4) or a polyvinyl alcohol-based film produced by equalizing the tensile elongation in the flow direction (MD) and the width direction (TD) ( For example, refer to patent document 5), the polyvinyl alcohol-type film which reduced the Young's modulus (tensile modulus) to 20 MPa or less by electromagnetic irradiation (refer, for example, patent document 6) etc. are also proposed.

Patent Document 1 JP 2001-315141 A Patent Document 2 JP 2001-315142 A Patent Document 3 JP 2002-79531 A Patent Document 4 JP 2006-291173 A Patent Document 5 JP 2002-30164 A Patent Document 6 JP 2013-97232 A

However, even with the method of the said patent document, it is insufficient to improve the stretchability of the polyvinyl alcohol-type film at the time of manufacture of a polarizing film.

Although the disclosed technique of Patent Document 1 above specifies the degree of stretching (tensile state) in the flow direction (MD) when manufacturing a polyvinyl alcohol-based film, if drying conditions and heat treatment conditions are not considered, polyvinyl alcohol-based films The stretchability of the film is not sufficiently improved.

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

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

In the disclosed technology of Patent Document 4, although the in-plane retardation of the film can be reduced, there is room for improvement from the viewpoint of control of the tensile modulus and improvement of the stretchability of the polyvinyl alcohol-based film during production of the polarizing film. Further, in the manufacturing method of the present disclosure, the film after drying (70°C) or heat treatment (120°C) is once cooled to 50°C or less, and heated to 50-100°C again before winding on a roll film, characterized in that However, the heating process is complicated, and there is room for improvement in terms of productivity.

In the disclosed technology of Patent Document 5, although the tensile elongation of the polyvinyl alcohol-based film can be stabilized, the tensile modulus itself is not controlled, and the stretchability of the polyvinyl alcohol-based film during manufacturing of the polarizing film is not sufficiently improved.

In the technique disclosed in Patent Document 6, although the tensile modulus can be reduced, it is 13.8 to 17.8 MPa in Examples and 27 MPa in Comparative Examples without electromagnetic wave irradiation, and further reduction of the tensile modulus is preferable.

Further, in the Examples of Patent Documents 1 to 6, only polyvinyl alcohol-based films having a thickness of 50 µm or more are described, and further improvement is desired in order to respond to the recent demand for reduction in thickness.

Therefore, under this background, the present invention is a polyvinyl alcohol-based film excellent in stretchability during the production of a polarizing film, and a polyvinyl alcohol-based film capable of obtaining a polarizing film with a high degree of polarization and less unevenness, in particular, having a thickness of 25 μm or less. Provided are a polyvinyl alcohol-based film that does not break when a thin polarizing film is produced even when it is used as a thin film, a method for producing the same, and a polarizing film using the polyvinyl alcohol-based film.

Therefore, the present inventors have conducted intensive research in consideration of such circumstances, and as a result, the length in the flow direction (MD) is greater than or equal to a specific length, and the tensile modulus of elasticity in the flow direction (length direction, MD) is controlled to a specific range. It has been found that the polyvinyl alcohol-based film has excellent stretchability in the production of a polarizing film and can be produced with a good yield of a thin polarizing film. And, it was discovered that the polarizing film obtained using such a polyvinyl alcohol-type film becomes a polarizing film with few nonuniformity while having a high polarization degree.

That is, the first aspect of the present invention is a polyvinyl alcohol-based film having a length of 4 km or more, wherein the tensile modulus X (MPa) in the longitudinal direction (MD) of the film in a state where the moisture content is 9 wt% is 5 to 12 MPa is a polyvinyl alcohol-based film.

In addition, the second aspect of the present invention includes a film forming step of forming an aqueous solution of a polyvinyl alcohol-based resin into a film by a continuous casting method, a drying step of drying the formed film, and a heat treatment step of heat-treating the dried film In one aspect, in the method for producing a polyvinyl alcohol-based film of the first aspect, the temperature for drying the film formed in the drying step is 100° C. or higher, and the heat treatment step causes the dried film to be 50° C. or less After cooling in a furnace, it is a method for producing a polyvinyl alcohol-based film, characterized in that it is a step of heating at 60 to 99°C.

And the third aspect of the present invention is a polarizing film characterized in that the polyvinyl alcohol-based film of the first aspect is used.

Since the polyvinyl alcohol-based film of the first aspect of the present invention has a tensile modulus X of 5 to 12 MPa in the longitudinal direction (MD) in a state where the moisture content is 9% by weight, it has excellent stretchability when manufacturing a polarizing film, and a thin polarizing film In the case of manufacturing, it has the effect of being able to prevent a fracture|rupture from occurring.

In particular, when the thickness D of the film is 5 to 25 μm, and the thickness D (μm) and the tensile modulus X (MPa) satisfy the following formula (1), the improvement of fracture resistance at the time of manufacturing the polarizing film is It has the effect that it can be promoted.

0.4≤X/D≤0.6...(1)

Among them, the tensile modulus Y (MPa) in the transverse direction (TD) and the tensile modulus X (MPa) in the longitudinal direction (MD) in a state where the moisture content of the film is 9 wt%, satisfying the following formula (2) In this case, it has the effect that the stretchability improvement at the time of polarizing film manufacture can be aimed at.

0.7≤Y/X≤1.3...(2)

Moreover, when the tensile strength F of the longitudinal direction MD is 100 MPa or more, it has the effect that the fracture|rupture at the time of manufacturing a thin polarizing film can be prevented.

In addition, when the refractive index in the longitudinal direction (MD) is nx, the refractive index in the width direction (TD) is ny, the refractive index in the thickness direction is nz, and the thickness is D (μm), the thickness direction calculated by the following formula (3) When the retardation Rth is 80 to 140 nm, while being able to optimize the swelling property in the thickness direction, it has the effect that the stretchability at the time of manufacture of a polarizing film can be optimized.

Rth=｛(nx+ny)/2-nz｝×1000×D...(3)

And when the width|variety of the said film is 4 m or more, it has the effect that the improvement of productivity can be aimed at.

Since the method for producing a polyvinyl alcohol-based film of the second aspect of the present invention includes a specific drying process and a heat treatment process, the polyvinyl alcohol-based film of the first aspect has excellent stretchability and fracture resistance during manufacturing of a polarizing film. has the effect of being able to manufacture

Since the polyvinyl alcohol-based film of the first aspect is used, the polarizing film of the third aspect of the present invention exhibits a high degree of polarization and has the effect that it can be made into a thing with little unevenness.

Hereinafter, the present invention will be described in detail.

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

In addition, the polyvinyl alcohol-based film is formed into a polarizing film through a swelling process and a stretching process while being conveyed in the longitudinal direction (MD). Here, the polyvinyl alcohol-based film has a specific length (4 km or more), and the longitudinal direction (MD) measured in the state where the moisture content of the polyvinyl alcohol-based film is 9 wt% is a specific tensile modulus X (5 to 12 MPa), the polyvinyl alcohol-based film has excellent stretchability during manufacturing of the polarizing film and does not break even in the case of manufacturing a thin polarizing film. And the obtained polarizing film shows a high polarization degree, and becomes a thing with few nonuniformity.

First, the said tensile modulus of elasticity of the polyvinyl alcohol-type film of this invention is demonstrated.

The tensile modulus of elasticity in this invention is a value measured in the environment of 20 degreeC 65 %RH according to JISK7127:1999. In addition, the tensile modulus is also called a Young's modulus or a tensile modulus of elasticity.

The moisture content in the present invention is a value calculated from the weight before and after drying the polyvinyl alcohol-based film at an atmospheric temperature of 105° C. for 16 hours with a dryer, and the weight before drying is A, and the weight after drying is B. When it does, it computes with the following formula.

Moisture content (% by weight) = 100 × (A-B)/A

As described above, in the manufacturing process of the polarizing film, the polyvinyl alcohol-based film is stretched after swelling, but it is difficult to accurately and stably measure the tensile modulus after swelling. In the present invention, in view of the fact that the moisture content of the polyvinyl alcohol-based film generally provided for the production of the polarizing film is several %, the tensile modulus at a moisture content of 9% by weight, which is easy to control by humidity control, is taken as an index.

Although the method of the humidity control is not particularly limited, for example, a relatively dry polyvinyl alcohol-based film immediately after production is controlled for several hours to several tens of hours in an environment of 20°C and 65%RH, so that the equilibrium moisture content in the environment is close to 9 Moisture content can be stabilized by weight %. In addition, in the present invention, the "moisture content of 9% by weight" means including "the moisture content is within the range of 9.0% by weight ± 0.5% by weight", and the tensile modulus is mostly unchanged within that range. In addition, since the moisture content in the film changes to an equilibrium moisture content dependent on the environmental humidity, a test piece having a moisture content of 9 wt% is used for the measurement of the tensile modulus quickly.

In the present invention, the in-plane deviation ΔX (MPa) of the tensile modulus X in the longitudinal direction (MD) in the state where the moisture content is 9 wt%, and the tensile modulus Y (MPa) in the width direction (TD) in the state where the moisture content is 9 wt% The in-plane variation ΔY (MPa) is preferably 5 MPa or less, particularly preferably 3 MPa or less, and still more preferably 2 MPa or less.

When the in-plane deviation ?X and the in-plane deviation ?Y are too large, stretching unevenness occurs during manufacture of the polarizing film, and 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-based film of the present invention comprises a film forming step (A) of forming an aqueous solution of a polyvinyl alcohol-type resin into a film by a continuous casting method, a drying step (B) of drying the formed film, A method for producing a polyvinyl alcohol-based film having a heat treatment step (C) of heat-treating the dried film, wherein the temperature for drying the film formed in the drying step (B) is 100° C. or more, After the heat treatment step (C) cools the dried film to 50° C. or less, it is characterized in that it is heated at 60 to 99° C.

[film forming process (A)]

First, the said film forming process (A) is demonstrated in detail.

As the polyvinyl alcohol-based resin used in the present invention, an unmodified polyvinyl alcohol-based resin, that is, a resin produced by saponifying polyvinyl acetate obtained by polymerization of 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 vinyl acetate and a copolymerizable component may be used. Examples of the component copolymerizable with vinyl acetate include unsaturated carboxylic acids (including salts, esters, amides, nitriles, etc.) and olefins having 2 to 30 carbon atoms (eg, ethylene, propylene, n- butene, isobutene, etc.), vinyl ethers, and unsaturated sulfonates. Moreover, the modified polyvinyl alcohol-type resin obtained by chemically modifying the hydroxyl group after saponification can also be used.

Moreover, as polyvinyl alcohol-type resin, the polyvinyl alcohol-type resin which has 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 such a side chain is, for example, (i) a method of saponifying a copolymer of vinyl acetate and 3,4-diacetoxy-1-butene, (ii) ) A method for saponification and decarboxylation of a copolymer of vinyl acetate and vinylethylene carbonate, (iii) saponification and decarboxylation of a copolymer of vinyl acetate and 2,2-dialkyl-4-vinyl-1,3-dioxolane It can be obtained by the method of degassing, (iv) the method of saponifying the copolymer of vinyl acetate and glycerol monoaryl ether, etc.

It is preferable that the weight average molecular weights of polyvinyl alcohol-type resin are 100,000 - 300,000, Especially preferably, it is 110,000 - 280,000, More preferably, it is 120,000 - 260,000. When such a weight average molecular weight is too small, the polarization degree of a polarizing film tends to fall, and when too large, there exists a tendency for extending|stretching at the time of manufacture of a polarizing film of a polyvinyl alcohol-type film to become difficult. In addition, the weight average molecular weight of the said polyvinyl alcohol-type resin is a weight average molecular weight measured by the 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, particularly preferably 99 mol% or more, more preferably 99.5 mol% or more, particularly preferably 99.8 mol% or more. am. When such an average degree of saponification is too small, there exists a tendency for the polarization degree of a polarizing film to fall.

Here, the average degree of saponification in this invention is measured according to JISK6726.

As the polyvinyl alcohol-based resin used in the present invention, two or more kinds of polyvinyl alcohol-based resins having different modified species, modified amounts, weight average molecular weight, average degree of saponification, and the like may be used in combination.

Then, it is preferable to wash the polyvinyl alcohol-based resin using a solvent such as water and dehydrate using a centrifuge or the like to obtain a polyvinyl alcohol-based resin wet cake having a moisture content of 50 wt% or less. When the moisture content is too large, it tends to become difficult to obtain a desired aqueous solution concentration.

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

The preparation method of the polyvinyl alcohol-type resin aqueous solution is not specifically limited, For example, it can also prepare using a heated multi-screw extruder, In addition, in the dissolution can equipped with the up-and-down circulation flow generating type stirring blade, the above-mentioned poly A vinyl alcohol-type resin wet cake may be thrown in, and water vapor|steam may be blown into a can, and the aqueous solution of melt|dissolution and desired density|concentration can also be prepared.

In the aqueous solution of polyvinyl alcohol-based resin, in addition to polyvinyl alcohol-based resin, generally used plasticizers such as glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol, trimethylolpropane, nonionic, anionic It is preferable from the viewpoint of film forming properties of the polyvinyl alcohol-based film to contain at least one surfactant among , and cationic.

Glycerin is preferable as said plasticizer, and it is preferable that content in polyvinyl alcohol-type resin aqueous solution of this plasticizer is 1 to 20 weight%.

Polyoxyethylene alkylamine and higher fatty acid alkanolamide are preferable as said surfactant, It is preferable that content in the polyvinyl alcohol-type resin aqueous solution of the surfactant is 0.01 to 1 weight%.

Thus, it is preferable that the resin concentration of the polyvinyl alcohol-type resin aqueous solution obtained is 15 to 60 weight%, Especially preferably, it is 17 to 55 weight%, More preferably, it is 20 to 50 weight%. When the resin concentration of such an aqueous solution is too low, the drying load tends to increase, so that the production capacity tends to decrease, and when too high, the viscosity becomes too high and uniform dissolution tends to be impossible.

Next, the obtained polyvinyl alcohol-type resin aqueous solution is defoamed. As a defoaming method, methods, such as static defoaming and the defoaming by the multi-screw extruder which has a vent, are mentioned. 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-slit die in a certain amount at a time, discharged and cast on a rotating cast drum, and formed into a film by a continuous casting method.

It is preferable that the temperature of the polyvinyl alcohol-type resin aqueous solution of the T-slit die exit is 80-100 degreeC, Especially preferably, it is 85-98 degreeC. When the temperature of such polyvinyl alcohol-type resin aqueous solution is too low, there exists a tendency to become a flow defect, and when too high, there exists a tendency for foaming.

It is preferable that the viscosity of such polyvinyl alcohol-type resin aqueous solution is 50-200 Pa*s at the time of discharge, More preferably, it is 70-150 Pa*s. When the viscosity of such an aqueous solution is too low, it tends to become a flow defect, and when it is too high, there exists a tendency for casting to become difficult.

The discharge speed of the aqueous polyvinyl alcohol-based resin solution discharged from the T-slit die to the cast drum is preferably 0.1 to 3.0 m/min, particularly preferably 0.2 to 2.5 m/min, more preferably 0.3 to 2.0 m/min. is a minute When such a discharge rate is too slow, productivity tends to fall, and when it is too fast, there exists a tendency for casting to become difficult.

The diameter of such a cast drum is preferably 2 to 5 m, particularly preferably 2.4 to 4.5 m, more preferably 2.8 to 4 m. When such a diameter is too small, the drying length is insufficient and the speed tends to be difficult to come out, and when it is too large, there exists a tendency for transportability to fall.

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

It is preferable that the rotation speed of such a cast drum is 1-30 m/min, Especially preferably, it is 2-25 m/min, More preferably, it is 3-20 m/min. When such a rotation speed is too slow, there exists a tendency for productivity to fall, and when it is too fast, there exists a tendency for dehydration to become inadequate.

It is preferable that the surface temperature of such a cast drum is 40-99 degreeC, More preferably, it is 50-90 degreeC, Especially preferably, it is 55-80 degreeC. When such a surface temperature is too low, there exists a tendency for dehydration to become defective, and when too high, there exists a tendency for foaming.

In this way, the said film forming process (A) is implemented and the film formed into a film is peeled from a cast drum.

[Drying process (B)]

Next, the said drying process (B) is demonstrated in detail. This drying process (B) is a process of heating and drying the said film formed into a film.

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

The drying temperature (the temperature at which the film formed is dried) is preferably 100°C or higher, particularly preferably 100 to 120°C, still more preferably 100 to 115°C, and particularly preferably 100 to 110°C. When such a drying temperature is too low, there exists a tendency to become a drying defect, and when too high, there exists a tendency to cause appearance defects, such as a wave. In addition, the drying temperature in this invention is the surface temperature of the hot roll which is the highest among the hot rolls used.

Although drying time is not specifically limited, Usually, it is 1 to 60 second, Preferably it is 2 to 50 second, Especially preferably, it is 3 to 40 second, More preferably, it is 4 to 30 second. When the drying time is too short, there is a tendency to become defective in drying, and when it is too long, it tends to cause poor appearance such as waves.

In addition, the drying time in the present invention means the contact time between the hottest roll and the film formed, and when a plurality of such hottest hot rolls are used, the contact time with these hot rolls is the cumulative value of

As for the moisture content of the film after drying, 5 weight% or less is preferable, Especially preferably, it is 0.1 to 4 weight%, More preferably, it is 0.2 to 3 weight%, Especially preferably, it is 0.3 to 2.5 weight%. When such a moisture content is too high, there exists a tendency for the polyvinyl alcohol-type film finally obtained to become poor drying.

[Heat treatment step (C)]

Next, the heat treatment step (C) will be described in detail. This heat treatment process (C) is a process of heat-processing the said dried film. Although such a heat treatment process is generally arbitrary processes made as needed, it becomes an essential process for control of tensile elasticity modulus in this invention. 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 then again 60 to 99° C. By heating in a temperature range, the tensile modulus is set in a desired range, and the stretchability at the time of manufacturing a polarizing film is improved.

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

Examples of the heating method include a method of blowing hot air with a floating dryer and a method of contacting a hot roll. In the present invention, a method using a floating dryer is preferable from the viewpoint of stabilization of the tensile modulus.

As for heating temperature, 65-95 degreeC is preferable, Especially preferably, it is 70-90 degreeC, More preferably, it is 70-80 degreeC. When the heating temperature is too low, the tensile modulus tends to decrease, and when it is too high, the tensile modulus tends to increase. In addition, the heating temperature in this invention means the temperature of the hot air when the said heating method is the method of blowing hot air with the said floating dryer, When the said heating method is a method of making the said heat roll contact, the heat It means the surface temperature of the roll.

Although heating time is not specifically limited, When using a floating dryer, 10-120 second is preferable, Especially preferably, it is 20 to 90 second, More preferably, it is 30 to 60 second. When such a heating time is too short, there exists a tendency for the dispersion|variation in tensile elasticity modulus to increase, and when too long, there exists a tendency for productivity to fall.

As for the moisture content of the film after heating, 0.1 to 2 weight% is preferable, Especially preferably, it is 0.2 to 1.7 weight%, More preferably, it is 0.3 to 1.5 weight%. When such a moisture content is too low, the water swelling at the time of manufacturing a polarizing film tends to become difficult, and conversely, when it is too high, there exists a tendency for the polyvinyl alcohol-type film finally obtained to become poor drying.

As mentioned above, although the drying process (B) and the heat processing process (C) were demonstrated, the temperature balance of both is important in the manufacturing method of this invention, and the drying temperature in a drying process (B) is 100 degreeC or more which is the boiling point of water. It is preferable, and it is more preferable to select a relatively low temperature even within such a temperature range, and it is particularly preferable that the heating temperature in the heat treatment step (C) is less than 100° C. which is the boiling point of water.

[Polyvinyl alcohol-based film]

The polyvinyl alcohol-based film of the present invention long in the flow direction (MD) can be obtained through the drying step (B) and the heat treatment step (C). Both ends of this polyvinyl alcohol-based film are slit and wound around a core tube in a roll shape.

Thus, it is preferable that the width|variety of the polyvinyl alcohol-type film of this invention obtained is 4 m or more from a viewpoint of productivity improvement, More preferably, it is 4-6 m from a viewpoint of breakage avoidance.

In addition, the length of the polyvinyl alcohol-based film of the present invention is premised on that it is 4 km or more, and it is preferably 5 km or more from the viewpoint of corresponding to the enlargement of the polarizing film and further liquid crystal screen, and particularly preferably 5 km or more from the viewpoint of transport weight. -50 km.

The thickness D of the polyvinyl alcohol-based film is preferably 30 µm or less from the viewpoint of reducing the thickness of the polarizing film, particularly preferably, 25 µm or less from the viewpoint of further thinning, more preferably 5 to 25 µm from the viewpoint of avoidance of breakage, Especially preferably, it is 5-20 micrometers.

Such thickness D (micrometer) is adjusted by the resin density|concentration in polyvinyl alcohol-type resin aqueous solution, the amount (discharge rate) discharged to a cast type, a draw ratio, etc.

In the polyvinyl alcohol-based film of the present invention, when the thickness D of the film is 5 to 25 µm, the tensile modulus X in the flow direction (MD) measured with the thickness D (µm) and the moisture content of the film being 9 wt% It is preferable that (MPa) satisfy|fills following formula (1) from a viewpoint of the fracture-resistance improvement at the time of manufacture of a polarizing film.

0.4≤X/D≤0.6...(1)

Particularly preferably, the following formula (1') is satisfied from the viewpoint of improving the stretchability at the time of manufacturing the polarizing film.

0.45≤X/D≤0.55...(1')

The polyvinyl alcohol-based film of the present invention has a tensile modulus Y (MPa) in the width direction (TD) of a moisture content of 9% by weight, satisfying the following formula (2) from the viewpoint of improving the stretchability during the manufacture of the polarizing film It is preferable to do

0.7≤Y/X≤1.3...(2)

Particularly preferably, the following formula (2') is satisfied from the viewpoint of improving the stretchability during manufacture of the polarizing film.

0.75≤Y/X≤1.1...(2')

When such a value of Y/X is too small, there exists a tendency for the stretchability in the flow direction MD of a polarizing film manufacturing time to fall, and, conversely, when too large, there exists a tendency for stretchability not to stabilize.

The polyvinyl alcohol-based film of the present invention preferably has a tensile strength F (MPa) in the flow direction (MD) of 100 MPa or more, particularly preferably 110 MPa or more, in a state where the moisture content is 9 wt%. When such tensile strength F (MPa) is too small, there exists a tendency for a fracture|rupture to occur easily at the time of thin-shaped polarizing film manufacture. In addition, the upper limit of the tensile strength F (MPa) is 200 MPa normally.

In addition, the polyvinyl alcohol-based film of the present invention has the following formula when the refractive index in the longitudinal direction (MD) is nx, the refractive index in the width direction (TD) is ny, the refractive index in the thickness direction is nz, and the thickness is D (μm). It is preferable that the retardation Rth (nm) in the thickness direction calculated by (3) is 80-140 nm. More preferably, it is 85-130 nm, More preferably, it is 90-120 nm. When the retardation Rth (nm) in the thickness direction is too small, the swelling property in the thickness direction tends to decrease. there is.

Rth=｛(nx+ny)/2-nz｝×1000×D...(3)

In addition, in the said embodiment, although the method of manufacturing a polyvinyl alcohol-type film was demonstrated taking the case where a cast drum (drum-type roll) was used as a cast type, for example, a cast belt or a resin film is used as a cast type. It is also possible to manufacture it.

Since the polyvinyl alcohol-based film of the present invention has excellent stretchability, it is particularly preferably used as a master 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 a polarizing film]

The polarizing film of the present invention is manufactured by releasing the polyvinyl alcohol-based film from a roll, transporting it in a horizontal direction, swelling, dyeing, crosslinking with boric acid, stretching, washing, drying, and the like.

The swelling process is performed before the dyeing process. In addition to being able to wash the contamination on the surface of the polyvinyl alcohol-based film by the swelling step, swelling of the polyvinyl alcohol-based film also has an effect of preventing staining and the like. Usually, water is used as a process liquid in a swelling process. If the main component is water, the treatment liquid may contain a small amount of an iodide compound, an additive such as a surfactant, or alcohol. 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.

A dyeing process is performed by making a polyvinyl alcohol-type film contact the liquid containing iodine or a dichroic dye. Usually, an aqueous solution of iodine-potassium iodide is used, and the concentration of iodine is preferably 0.1 to 2 g/L, and the concentration of potassium iodide is preferably 1 to 100 g/L. About 30 to 500 seconds of dyeing time is practical. As for the temperature of a process bath, 5-50 degreeC is preferable. The aqueous solution may contain a small amount of an organic solvent compatible with water other than the aqueous solvent.

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

The stretching step is preferably 3 to 10 times, preferably 3.5 to 6 times, in the uniaxial direction [flow direction (MD)]. At this time, it does not interfere even if a little extending|stretching (stretching beyond the extent to which shrinkage|contraction in the width direction TD is prevented) may be performed also in the direction perpendicular to an extending|stretching direction. As for the temperature at the time of extending|stretching, 30-170 degreeC is preferable. In addition, the stretching ratio may be finally set within the above range, and the stretching operation may be performed not only once, but also several times in the polarizing film manufacturing process.

In this invention, as mentioned above, the extending|stretching tension|tensile_strength in such an extending process needs to be in an appropriate range. That is, when the stretching tension is too large, the polarization degree does not tend to be improved because stretching is not possible to a predetermined stretching ratio and the dichroic dye is not sufficiently oriented. Conversely, when the stretching tension is too small, even when stretching to a predetermined stretching ratio, the orientation of the dichroic dye is not stable and unevenness tends to occur in the polarizing film.

In addition, in general, since the stretching tension is set for each thickness in the polarizing film manufacturing process, it is difficult to generalize a preferable range, but in comparison with the same thickness, it is preferable to reduce the stretching tension by 10% or more, particularly preferably It is reduced by 1-3%.

The washing step is performed, for example, by immersing the polyvinyl alcohol-based film in an aqueous solution of iodide such as water or potassium iodide, and the precipitates generated on the surface of the polyvinyl alcohol-based film can be removed. When the potassium iodide aqueous solution is used, the potassium iodide concentration is about 1-80 g/L. The temperature at the time of a washing process is 5-50 degreeC normally, Preferably it is 10-45 degreeC. Processing time is 1 to 300 second normally, Preferably it is 10 to 240 second. In addition, water washing and washing|cleaning by potassium iodide aqueous solution can also be performed combining suitably.

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

In this way, the polarizing film of this 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. When the degree of polarization is too low, it exists in the tendency for the contrast in a liquid crystal display to become impossible to ensure.

In addition, the polarization degree is generally the light transmittance (H ₁₁ ) measured with respect to the wavelength λ in a state in which two polarizing films are superposed so that the orientation direction is the same, and the orientation direction of the two polarizing films is orthogonal to each other. It is computed according to the following formula from the light transmittance (H ₁ ) measured with respect to wavelength (lambda) in the state superimposed so that it may become a direction.

Polarization degree = [(H ₁₁ −H ₁ )/(H ₁₁ +H ₁ )] ^1/2

Moreover, the single transmittance|permeability of the polarizing film of this invention becomes like this. Preferably it is 42 % or more, More preferably, it is 43 % or more. When such a single transmittance|permeability is too low, there exists a tendency for the high luminance-ization of a liquid crystal display to become impossible to be achieved.

The single transmittance is a value obtained by measuring the light transmittance of the single polarizing film using a spectrophotometer.

The polarizing film of the present invention has excellent polarization degree and is very suitable for manufacturing a non-uniform polarizing plate.

Here, the manufacturing method of the polarizing plate using the polarizing film of this invention is demonstrated.

[Method for producing a polarizing plate]

The said polarizing plate is produced by bonding an optically isotropic resin film together as a protective film on the single side|surface or both surfaces of the polarizing film of this invention via an adhesive agent. As the protective film, for example, cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, cycloolefin polymer, cycloolefin copolymer, polystyrene, polyethersulfone, polyarylene ester, poly-4-methyl Films or sheets, such as pentene and polyphenylene oxide, are mentioned.

Although the bonding method is performed by a well-known method, for example, after apply|coating a liquid adhesive composition uniformly to a polarizing film, a protective film, or both, bonding and crimping|compressing both, heating or irradiating an active energy ray. is carried out as

Moreover, it is also possible to apply|coat curable resin, such as a urethane resin, an acrylic resin, and a urea resin, to one side or both surfaces of a polarizing film, and to harden|cure it to form a cured layer, and to set it as a polarizing plate. In this way, the said cured layer becomes a substitute for the said protective film, and thin film formation can be achieved.

The polarizing film or polarizing plate using the polyvinyl alcohol-based film of the present invention has excellent polarization performance, and is used in portable information terminals, PCs, televisions, projectors, signage, electronic desk calculators, electronic watches, word processors, electronic papers, game machines, video, Cameras, photo albums, thermometers, audio, liquid crystal display devices such as automobiles and machinery, sunglasses, anti-glare glasses, stereoscopic glasses, wearable displays, anti-reflection layers for display elements (CRT, LCD, organic EL, electronic paper, etc.), optical communication It is preferably used for devices, medical devices, building materials, toys, and the like.

(Example)

Hereinafter, although an Example demonstrates this invention more concretely, this invention is not limited to a following example unless the summary is exceeded.

And, in the following Examples and Comparative Examples, the characteristics of the polyvinyl alcohol-based film (moisture content, tensile modulus, tensile strength, retardation in the thickness direction, elongation tension) and the characteristics of the polarizing film (polarization degree, single transmittance, unevenness) was measured and evaluated as follows.

<Measurement conditions>

[Moisture content (wt%)]

A 100 mm x 100 mm test piece is cut from the obtained polyvinyl alcohol-based film, and the moisture content is obtained by the following formula from the initial weight A (g) and the weight B (g) after drying for 16 hours at an atmospheric temperature of 105° C. with a dryer. (% by weight) was calculated.

Moisture content (% by weight) = 100 × (A-B)/A

[Tensile modulus (MPa), tensile strength F (MPa)]

A test piece of 120 mm x 15 mm was cut from the obtained polyvinyl alcohol-based film, and the humidity was controlled so that the moisture content was 9 wt% ± 0.5 wt% in a constant temperature and humidifier at 20°C and 65%RH, and then the Shimadzu Corporation “Precision Universal Testing Machine” , autograph (AG-IS)", in accordance with JIS K 7127:1999 (tensile speed of 1000 mm/min, distance between chucks 50 mm), under an environment of 20°C and 65%RH, tensile modulus X in the flow direction (MD) (MPa) and the tensile modulus Y (MPa) of the width direction (TD) were measured. In addition, in the flow direction (MD), the tensile strength F (MPa) was measured.

[Thickness direction retardation Rth (nm)]

A test piece of 4 cm in length x 4 cm in width was cut from the central portion and both ends in the width direction (TD) of the obtained polyvinyl alcohol-based film (10 cm inside from the film end), and a retardation measuring device ("KOBRA-WR") The phase difference Rth (nm) in the thickness direction in 590 nm was measured using the Oji Keishoku Instruments company.

<Rth measurement conditions>

Incident angle: 50 °

Inclined central axis: Slow axis

Average refractive index: A value measured using an Abe refractometer

[Stretch tension (N)]

From the obtained polyvinyl alcohol-based film, a test piece of 50 mm in length [longitudinal direction (MD)] x width [width direction (TD)] 35 mm was cut out, and the distance between chucks was 20 mm in the longitudinal direction (MD). After sandwiching both ends with a chuck with a width of 35 mm, it was stretched 1.7 times (34 mm) in the longitudinal direction (MD) while immersed in hot water at 25 ° C for 60 seconds, and then in the dye solution at 28 ° C in the longitudinal direction ( MD) to 1.6 times (54.4 mm), and finally, the tension (N) at the time of extending|stretching 2.05 times (111.5 mm) in the longitudinal direction (MD) in a 55 degreeC boric acid solution was measured only with the spring. The composition of the used dyeing solution and boric acid solution is as follows.

Dyeing solution: iodine 0.9g/L, potassium iodide 30g/L

Boric acid solution: potassium iodide 30 g/L, boric acid 25 g/L

[Polarization degree (%), single transmittance (%)]

A test piece with a length of 4 cm x width of 4 cm was cut from the central portion and both ends of the obtained polarizing film in the width direction (TD) (10 cm from each end of both ends of the polarizing film), and an automatic polarizing film measuring device (Nippon Bunko) The polarization degree (%) and the single transmittance (%) were measured using the cow company make: VAP7070). Such a measurement was performed with respect to the central part and the front-end|tip part/terminal part of the flow direction (MD) of the polarizing film (set to 10 m inside from each end of the front-end|tip and terminal of a polarizing film).

〔stain〕

A test piece of 30 cm in length x 30 cm in width was cut from the central portion and both ends of the obtained polarizing film in the width direction (TD) (10 cm inside from each end of both ends of the polarizing film), and two polarizing plates in a cross nicol state. After setting at an angle of 45° between (single transmittance 43.5%, polarization degree 99.9%), optical unevenness was observed in transmission mode using a light box having a surface roughness of 14,000 lx, and evaluation was performed according to the following criteria.

(Evaluation standard)

○···No stains

×・・・Stained

Such evaluation was performed with respect to the central part and the front-end|tip part/terminal part of the flow direction (MD) of the polarizing film (set to 10 m inside from each end of the front-end|tip and terminal of a polarizing film).

<Example 1>

(Production of polyvinyl alcohol-based film)

1,000 kg of polyvinyl alcohol-based resin having a weight average molecular weight of 142,000, a degree of saponification of 99.8 mol%, 2,500 kg of water, and 120 kg of glycerin as a plasticizer, heated to 140° C. while stirring, and adjusted to a resin concentration of 25% by weight to uniformly The dissolved polyvinyl alcohol-type resin aqueous solution was obtained. Next, the polyvinyl alcohol-based resin aqueous solution is supplied to a twin screw extruder having a vent to be degassed, the aqueous solution temperature is set to 95° C., and discharged from the T-slit die outlet to the rotating cast drum (discharge rate 0.8 m/min. ) and casting to form a film. The film formed was peeled off from the cast drum, and the film was dried while contacting the front and back surfaces of the film with 20 hot rolls alternately. The drying temperature (the surface temperature of the hottest hot roll) was 120°C, and the drying time (the cumulative total of the contact time of the hottest hot roll and the film) was 12 seconds. Then, by naturally cooling the dried film, the temperature of the film itself is once cooled to 40° C., and then heated by blowing hot air at 75° C. from both sides of the film for 60 seconds using a floating dryer, and a moisture content of 1% by weight A polyvinyl alcohol-based film (thickness 20 µm, width 5 m, length 5 km) was obtained. Finally, both ends of the polyvinyl alcohol-based film were slit and wound around a core tube in a roll shape. The properties of the obtained polyvinyl alcohol-based film are shown in Table 1 below.

(Manufacture of polarizing film)

The obtained polyvinyl alcohol-based film was unwound from the roll, conveyed in the horizontal direction using a conveying roll, and stretched 1.7 times in the flow direction (MD) for 1 minute while immersing it in a water bath having a water temperature of 25° C. and swelling. Then, it is immersed in an aqueous solution at 28° C. consisting of 0.9 g/L of iodine and 30 g/L of potassium iodide and stretched 1.6 times in the flow direction (MD) for 0.5 minutes while dyeing, followed by 25 g/L of boric acid and 30 g/L of potassium iodide It uniaxially stretched 2.0 times in the flow direction (MD) while immersing in a 55 degreeC aqueous solution consisting of L and crosslinking with boric acid. Finally, it 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. Breakage did not occur during manufacture of such a polarizing film. Moreover, the characteristic of the obtained polarizing film is shown in following Table 2.

<Example 2, Comparative Example 1>

A polyvinyl alcohol-based film and a polarizing film were obtained in the same manner as in Example 1 except for manufacturing under the conditions shown in Table 1 below. The properties of the obtained polyvinyl alcohol-based film are shown in Table 1 below, and the properties of the obtained polarizing film are shown in Table 2 below.

Moreover, in the comparative example 1, although it carried out similarly to Example 1 and tried manufacture of a polarizing film, a fracture|rupture arose during extending|stretching in a boric-acid bridge|crosslinking process. The properties in Table 2 are the properties of the tip of the polarizing film that were barely obtained.

In the polyvinyl alcohol-based films of Examples 1 and 2, since the value of the tensile modulus is within the specific range of the present invention, the obtained polarizing film has a high degree of polarization and is free from unevenness, whereas the polyvinyl alcohol-based film of Comparative Example 1 has a tensile modulus of elasticity. Since it is outside the specific range of this invention, it is easy to fracture|rupture, and it turns out that the polarizing film obtained is inferior to a polarization degree, and there exists nonuniformity.

Moreover, in the same manner as in Example 1, a polyvinyl alcohol-based film having a length of 4 km and 10 km was produced. Even in the polyvinyl alcohol-based film of this length, the same results as in Examples 1 and 2 were obtained.

Although the said Example showed about the specific form in this invention, the said Example is only a mere illustration, and is not interpreted limitedly. Various modifications apparent to those skilled in the art are expected to be within the scope of the present invention.

The polarizing film or polarizing plate using the polyvinyl alcohol-based film of the present invention has excellent polarization performance, and is therefore a portable information terminal, PC, television, projector, signage, electronic desk calculator, electronic watch, word processor, electronic paper, game machine, video, camera. , photo albums, thermometers, audio, liquid crystal display devices such as instruments for automobiles and machinery, sunglasses, anti-glare glasses, stereoscopic glasses, wearable displays, anti-reflection layers for display elements (CRT, LCD, organic EL, electronic paper, etc.), optical communication devices , medical devices, building materials, toys, etc. are preferably used.

Claims (8)

It is a polyvinyl alcohol-based film having a length of 4 km or more, wherein the tensile modulus X in the longitudinal direction (MD) of the film in a state where the moisture content is 9 wt% is 5 to 12 MPa, and the thickness D of the film is 5 to 25 µm, the thickness of the film D (μm) and the tensile modulus X (MPa), polyvinyl alcohol-based film, characterized in that it satisfies the following formula (1).
0.4≤X/D≤0.6...(1) delete The method according to claim 1,
The tensile modulus Y (MPa) in the transverse direction (TD) and the tensile modulus X (MPa) in the longitudinal direction (MD) in a state where the moisture content of the film is 9 wt%, characterized in that it satisfies the following formula (2) polyvinyl alcohol-based film.
0.7≤Y/X≤1.3...(2) 4. The method of claim 1 or 3,
A polyvinyl alcohol-based film having a tensile strength F in the longitudinal direction (MD) of 100 MPa or more. 4. The method of claim 1 or 3,
When the refractive index in the longitudinal direction (MD) is nx, the refractive index in the width direction (TD) is ny, the refractive index in the thickness direction is nz, and the thickness is D (μm), the thickness direction retardation Rth calculated by the following formula (3) A, polyvinyl alcohol-based film, characterized in that 80 to 140 nm.
Rth=｛(nx+ny)/2-nz｝×1000×D...(3) 4. The method of claim 1 or 3,
A polyvinyl alcohol-based film, characterized in that the film has a width of 4 m or more. The polyvinyl alcohol-based resin according to claim 1 or 3, comprising a film forming step of forming an aqueous solution of a polyvinyl alcohol-based resin into a film by a continuous casting method, a drying step of drying the formed film, and a heat treatment step of heat treating the dried film. It is a method for producing a vinyl alcohol-based film, wherein the temperature for drying the film formed in the drying step is 100° C. or more, and the heat treatment step cools the dried film to 50° C. or less, then 60 to 99 A method for producing a polyvinyl alcohol-based film, characterized in that it is a step of heating at °C. A polarizing film characterized in that the polyvinyl alcohol-based film according to claim 1 or 3 is used.