TW201730250A - Polyvinyl alcohol film, polarizing film and polarizing plate using same, and polyvinyl alcohol film production method - Google Patents

Abstract

A polyvinyl alcohol film that is 5-60 [mu]m thick, 2 m wide or wider, and 2 km long or longer. The polyvinyl alcohol film satisfies expressions (1) and (2). (1) In-plane phase difference Rxy ≤ 30 nm (2) Thickness-direction phase difference Rth ≥ 90 nm The in-plane phase difference Rxy (nm) and the thickness-direction phase difference Rth (nm) are respectively calculated from formulas (A) and (B), wherein nx is the refractive index of the polyvinyl alcohol film in the width direction (TD direction), ny is the refractive index of the polyvinyl alcohol film in the length direction (MD direction), nz is the refractive index of the polyvinyl alcohol film in the thickness direction, and d (nm) is the thickness of the polyvinyl alcohol film. (A) Rxy (nm) = |nx-ny| * d (nm) (B) Rth (nm) = {(nx+ny)/2-nz} * d (nm).

Description

Polyvinyl alcohol film, polarizing film using the polyvinyl alcohol film, polarizing plate, and polyvinyl alcohol film manufacturing method

The present invention relates to a polyvinyl alcohol-based film, and more particularly to a polyvinyl alcohol-based film which can obtain a polarizing film having excellent dyeability, a high degree of polarization and a small color unevenness, and a polarizing film using the polyvinyl alcohol-based film. A method of producing a polarizing plate and a polyvinyl alcohol film.

In the past, a polyvinyl alcohol-based film has been used as a film having excellent transparency and has been used in many applications, and one of its effective uses is a polarizing film. This polarizing film is used as a basic constituent element of a liquid crystal display, and in recent years, its use in equipment requiring high quality and high reliability is expanding.

In this case, a polarizing film having excellent optical characteristics is required as the screen of the liquid crystal television, the multi-functional portable terminal, and the like are increased in brightness, high in definition, large in area, and thinned. Specifically, the degree of polarization is improved and the color unevenness is solved.

In general, a polyvinyl alcohol-based film is produced from an aqueous solution of a polyvinyl alcohol-based resin by a continuous casting method. Specifically, an aqueous solution of a polyvinyl alcohol-based resin is cast on a casting mold such as a casting drum or an endless belt to form a film, and after the film obtained by forming the film is peeled off from the casting mold, the nip roll is used. It is conveyed in the traveling direction (MD direction), and is dried by using a hot roll or a floating dryer. In the transport step, since the film obtained by the film formation is stretched in the traveling direction (MD direction), the polyvinyl alcohol-based polymer is likely to be aligned in the MD direction, and the optical axis of the obtained polyvinyl alcohol-based film (late phase) The axis) is always oriented in the MD direction. When the orientation in the MD direction is too large, the in-plane retardation of the polyvinyl alcohol-based film increases, and eventually the polarizing performance of the polarizing film is lowered. Conversely, in the width direction (TD direction) of the film obtained by film formation, shrinkage stress depending on Poisson's ratio and shrinkage stress due to dehydration are generated, so if the stress in the TD direction is utilized Also, the polyvinyl alcohol-based polymer can be aligned to some extent in the TD direction. At this time, the optical axis of the obtained polyvinyl alcohol-based film tends to decrease between the MD direction and the TD direction, and the in-plane retardation tends to decrease.

On the other hand, in general, a polarizing film is produced by swelling a polyvinyl alcohol-based film, which is a raw material roll, in water (including warm water), followed by dyeing and stretching with a dichroic dye such as iodine. In the swelling step, the polyvinyl alcohol-based film must be swollen rapidly in the thickness direction. Further, it is necessary to uniformly swell it in the dyeing step so that the dye is smoothly immersed in the inside of the film. Further, the extending step is a step of stretching the dyed film in the traveling direction (MD direction) to highly align the dichroic dye in the film, and in order to improve the polarizing property of the polarizing film, the polyvinyl alcohol becomes a raw material roll. The mesent must have good extensibility in the MD direction. Further, in the production of the polarizing film, there are cases in which the order of the above-described stretching step and dyeing step is reversed. In other words, a case where the polyvinyl alcohol-based film, which is a raw material roll, is swollen in water (including warm water), and is stretched and dyed with a dichroic dye such as iodine, but in this case, in order to enhance the polarizing film The polarizing property, the polyvinyl alcohol film still has good swellability in the thickness direction and good elongation in the MD direction.

Further, in recent years, the polyvinyl alcohol film has been thinned due to the reduction in thickness of the polarizing film. This thin film has a problem of productivity such as breakage due to elongation at the time of manufacturing a polarizing film.

As a method of improving the swellability, for example, a method in which a polyol is added as a water swelling aid to a polyvinyl alcohol-based resin has been proposed (for example, see Patent Document 1). As a method for improving the elongation, for example, a method of specifying a ratio of a speed of a casting drum at the time of film formation to a final film winding speed (for example, see Patent Document 2), and a film after casting a film by a casting drum has been proposed. A method of drying by suspension (for example, refer to Patent Document 3), and a method of controlling the stretching state of a film obtained by film formation in a drying step (for example, see Patent Document 4). Further, a polyvinyl alcohol-based film having a reduced in-plane retardation has been proposed (see, for example, Patent Documents 5 and 6). [Prior Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Laid-Open Patent Publication No. 2001-315141 (Patent Document 3) Japanese Laid-Open Patent Publication No. 2001-315142 (Patent Document 4) JP-A-2002-79531 Japanese Laid-Open Patent Publication No. 2006-291173 [Patent Document 6] JP-A-2007-137042

[Problems to be Solved by the Invention] However, even if the method of the above patent document is provided, improvement in swelling property and elongation at the time of production of a polarizing film is not sufficient. In the technique disclosed in Patent Document 1, even if the swelling property is improved, the alignment state of the polyvinyl alcohol-based polymer is not considered, and it is difficult to improve the elongation at the time of producing the polarizing film. On the contrary, there is a tendency that the alignment state of the polymer is disturbed by the addition of the water swelling agent, and uniform stretching is not possible.

In the above-mentioned Patent Document 2, the extent of stretching in the MD direction (stretching state) when the polyvinyl alcohol-based film is produced is specified. However, if the stretching in the TD direction is not considered, the in-plane retardation of the polyvinyl alcohol-based film cannot be reduced. Moreover, the improvement of the elongation at the time of manufacturing the polarizing film is still insufficient. In general, in the production of a polarizing film, it is difficult to extend the polyvinyl alcohol-based film that has been stretched in the MD direction in the MD direction. In other words, it is difficult to forcibly stretch the molecular chain by stretching the polyvinyl alcohol-based polymer that has been aligned in the MD direction in the MD direction. On the contrary, it is relatively easy to stretch the polyvinyl alcohol-based polymer which has been aligned in the TD direction in the MD direction. However, if the alignment of the polymer in the TD direction is not uniform, the polarizing film cannot be uniformly stretched in the MD direction during the production of the polarizing film. In the case of producing a polyvinyl alcohol film, Patent Document 2 has an example in which the MD direction is not extended to such an extent (unstretched example), but only the above-mentioned shrinkage stress depending on Poisson's ratio and dehydration The shrinkage stress has a problem that the alignment of the polymer in the TD direction cannot be sufficiently uniformized. That is, if the width direction is not extended to some extent in the TD direction, or the width direction is not fixed at least, the uniform alignment state of the polymer in the TD direction cannot be obtained, and the elongation at the time of improving the production of the polarizing film is insufficient. Further, there is no description about the orientation in the thickness direction, and it is not possible to control the swellability at the time of production of the polarizing film.

In the technique disclosed in the above Patent Document 3, the film after the film formation can be uniformly dried, but the alignment of the polymer cannot be controlled, and the improvement in the elongation and the swelling property at the time of producing the polarizing film is not sufficient. In the technique disclosed in Patent Document 4, the film thickness of the polyvinyl alcohol-based film can be uniformly formed, but the alignment of the polymer cannot be controlled, and the improvement in the elongation and the swelling property at the time of producing the polarizing film is not improved. enough. In the techniques disclosed in the above Patent Documents 5 and 6, although the in-plane retardation of the polyvinyl alcohol-based film can be reduced and uniformly formed, the phase difference in the thickness direction is not mentioned, and the polarizing film is manufactured. The view of extensibility and swellability has room for improvement.

Thus, the present invention provides, in such a context, a polyvinyl alcohol-based film which is excellent in swellability and elongation at the time of production of a polarizing film, and has a high polarizing property and a small color unevenness, and is particularly provided. A polyvinyl alcohol-based film that does not break during the production of a thin polarizing film, and a polarizing film comprising the polyvinyl alcohol-based film, a method of producing a polarizing plate, and a polyvinyl alcohol-based film. [Means for solving the problem]

The inventors of the present invention have intensively studied in view of the circumstances, and found that the polyvinyl alcohol-based film having a phase difference (Rxy) in the in-plane direction and a phase difference (Rth) in the thickness direction is swelled in the production of the polarizing film. It is excellent in properties and extensibility, and a polarizing film obtained by using the polyvinyl alcohol-based film has high polarizing performance and less color unevenness.

That is, the first aspect of the present invention is a polyvinyl alcohol-based film having a thickness of 5 to 60 μm, a width of 2 m or more, and a length of 2 km or more, and is characterized by satisfying the following formulas (1) and (2): (1) Internal phase difference Rxy ≦ 30 nm (2) Thickness direction phase difference Rth ≧ 90 nm Here, the in-plane phase difference Rxy (nm) and the thickness direction phase difference Rth (nm) are in the width direction of the polyvinyl alcohol film (TD) The refractive index of the direction is nx, the refractive index of the longitudinal direction (MD direction) is ny, the refractive index of the thickness direction is nz, and the thickness is d (nm), and the following formulas (A) and (B) are calculated. Values: (A) Rxy(nm)=|nx-ny|×d(nm) (B)Rth(nm)=[(nx+ny)/2-nz]×d(nm)

In particular, a polyvinyl alcohol-based film characterized by an offset ΔRxy of the in-plane retardation Rxy in the width direction (TD direction) of 5 nm or less is the second gist of the present invention.

In addition, a polyvinyl alcohol-based film characterized by a shift ΔRth of the thickness direction phase difference Rth in the width direction (TD direction) of 30 nm or less is the third gist of the present invention.

Further, when the swelling degree of the film is measured after immersing in water at 30 ° C for 15 minutes, the swelling degree X (%) in the width direction (TD direction), the swelling degree Y (%) in the longitudinal direction (MD direction), and the thickness The polyvinyl alcohol-based film having a degree of swelling Z (%) satisfying Z≧1.1X and Z≧1.1Y is the fourth gist of the present invention.

Among them, the characteristic is the offset ΔX (%) of the swelling degree X (%) in the width direction (TD direction), the offset ΔY (%) of the swelling degree Y (%) in the longitudinal direction (MD direction), and the thickness direction. The polyvinyl alcohol-based film in which the offset ΔZ (%) of the degree of swelling Z (%) is within 5% is the fifth aspect of the present invention.

Further, a polyvinyl alcohol-based film characterized by a thickness of 5 to 30 μm is the sixth gist of the present invention.

Further, the present invention relates to a polarizing film characterized in that the polyvinyl alcohol-based film is used as the seventh gist.

Moreover, the present invention provides a polarizing plate characterized by comprising the polarizing film and a protective film provided on at least one surface of the polarizing film.

Further, the present invention relates to a method for producing a polyvinyl alcohol-based film in which an aqueous solution of a polyvinyl alcohol-based resin is formed by a continuous casting method, and after being peeled off from a casting mold, it is conveyed in a traveling direction (MD direction). The polyvinyl alcohol-based film is obtained by continuously drying and stretching in the width direction (TD direction), and the polyvinyl alcohol-based film satisfies the following formulas (1) and (2) as the ninth; (1) Internal phase difference Rxy ≦ 30 nm; (2) Thickness direction phase difference Rth ≧ 90 nm; where the in-plane phase difference Rxy (nm) and the thickness direction phase difference Rth (nm) are in the width direction of the polyvinyl alcohol film The refractive index in the (TD direction) is nx, the refractive index in the traveling direction (MD direction) is ny, the refractive index in the thickness direction is nz, and the thickness is d (nm), and the following equations (A) and (B) are calculated. The obtained values are: (A) Rxy(nm)=|nx-ny|×d(nm); (B) Rth(nm)=[(nx+ny)/2-nz]×d(nm).

In particular, a method for producing a polyvinyl alcohol-based film which is characterized by extending 1.05 to 1.3 times in the width direction (TD direction) of the film is the tenth aspect of the present invention.

Further, a method for producing a polyvinyl alcohol-based film which is characterized in that the film is sequentially extended in the width direction (TD direction) of the film is the eleventh aspect of the present invention. [Effects of the Invention]

The polyvinyl alcohol-based film of the present invention can provide a polarizing film which is excellent in swellability and elongation at the time of production of a polarizing film, and which does not break even when a thin polarizing film is produced, and exhibits high polarization performance and less color unevenness. Further, the swellability and the elongation at the time of production of the polarizing film of the present invention depend on the alignment state of the polyvinyl alcohol-based polymer in the film, and in particular, the orientation state in the thickness direction, so that the index of the alignment state is controlled. That is, the phase difference is used to improve the swelling property and the elongation property.

The present invention will be described in detail below. The polyvinyl alcohol-based film of the present invention has a thickness of 5 to 60 μm, a width of 2 m or more, and a length of 2 km or more, and has the following characteristics. Specifically, the aqueous solution of the polyvinyl alcohol-based resin is formed into a film by a continuous casting method, and after the film obtained by the film formation is peeled off from the casting mold, it is continuously conveyed in the traveling direction (MD direction). Drying and stretching in the width direction (TD direction) are carried out, and the physical properties of both of the following formulas (1) and (2) are satisfied. Even if only one of the physical property values is satisfied, the object of the present invention cannot be achieved. (1) In-plane phase difference Rxy ≦ 30 nm; (2) Thickness direction phase difference Rth ≧ 90 nm; where the in-plane phase difference Rxy (nm) and the thickness direction phase difference Rth (nm) are obtained by making a polyvinyl alcohol film The refractive index in the width direction (TD direction) is nx, the refractive index in the traveling direction (MD direction) is ny, the refractive index in the thickness direction is nz, and the thickness is d (nm), respectively, the following formula (A), (B) Calculated values: (A) Rxy(nm)=|nx-ny|×d(nm); (B) Rth(nm)=[(nx+ny)/2-nz]×d( Nm).

The above formulas (1) and (2) will be described. Equation (1) specifies a general in-plane phase difference, which is within the scope of the known art. The in-plane retardation Rxy (nm) of the polyvinyl alcohol-based film of the present invention is required to be 30 nm or less, preferably 20 nm or less, and particularly preferably 15 nm or less. When the in-plane retardation Rxy exceeds the upper limit value, the polarizing film is liable to cause color unevenness and is less preferable.

In the present invention, the offset ΔRxy of the in-plane retardation Rxy in the width direction (TD direction) is preferably 5 nm or less, more preferably 3 nm or less, and still more preferably 2 nm or less. When the offset ΔRxy is too large, the polarizing film tends to be uneven in color.

Then, the equation (2) specifies the phase difference in the thickness direction, and the greatest feature of the present invention is that the thickness direction phase difference Rth (nm) is a positive value and is a large value of 90 nm or more. In other words, the polyvinyl alcohol-based film of the present invention has a chemical structure in which the polymer chain mainly aligns in the surface direction and is easily swollen in the thickness direction. The thickness direction phase difference Rth (nm) must be 90 nm or more, preferably 100 nm or more, and particularly preferably 110 to 200 nm. When the thickness direction retardation Rth (nm) is smaller than the lower limit value, the swelling property in the thickness direction is lowered, which is less desirable, and if the thickness is too large, the surface orientation of the polymer chain is strong, and the surface direction of the polarizing film is produced ( The extension of the MD direction and the TD direction becomes difficult.

In the present invention, the offset ΔRth of the thickness direction phase difference Rth in the width direction (TD direction) is preferably 30 nm or less, more preferably 20 nm or less, and still more preferably 10 nm or less. When the offset ΔRth is too large, the polarizing film tends to be uneven in color.

Further, in order to satisfy the formulas (1) and (2), in addition to the method of stretching the film obtained by peeling off the casting mold in the width direction (TD direction) of the present invention, it is also possible to adjust the drying conditions of the aqueous solution. The method, the method of adjusting the chemical structure of the polyvinyl alcohol-based resin, and the like.

Here, the method for producing the polyvinyl alcohol-based film of the present invention will be described in more detail in the order of steps.

[Film material] First, the polyvinyl alcohol resin and the aqueous solution used in the present invention will be described. In the present invention, as the polyvinyl alcohol-based resin constituting the polyvinyl alcohol-based film, an unmodified polyvinyl alcohol-based resin, that is, a polyvinyl acetate obtained by polymerizing vinyl acetate, is used for saponification. The resulting resin. A resin obtained by saponifying a copolymer of vinyl acetate and a small amount (usually 10 mol% or less, preferably 5 mol% or less) copolymerizable with vinyl acetate may be used as needed. Examples of the component copolymerizable with vinyl acetate include an unsaturated carboxylic acid (including, for example, a salt, an ester, a guanamine, a nitrile, etc.); and an olefin having 2 to 30 carbon atoms (for example, ethylene, propylene, n-butene). , isobutylene, etc.); vinyl ethers; unsaturated sulfonates. Further, a modified polyvinyl alcohol-based resin obtained by chemically modifying a hydroxyl group after saponification may also be used. These may be used alone or in combination of two or more.

Further, as the polyvinyl alcohol-based resin, a polyvinyl alcohol-based resin having a 1,2-diol structure in its side chain can also be used. The polyvinyl alcohol-based resin having a 1,2-diol structure in a side chain can be obtained by, for example, (i) vinyl acetate and 3,4-diethyloxy-1-butene. a method of saponification of a copolymer; (ii) a method of saponifying and decarboxylating a copolymer of vinyl acetate and ethylene vinyl carbonate; (iii) a vinyl acetate with 2,2-dialkyl-4-ethylene A method of saponification and deketalization of a copolymer of 1,3-dioxolane; (iv) a method of saponifying a copolymer of vinyl acetate and glycerol monoallyl ether.

The weight average molecular weight of the polyvinyl alcohol-based resin is preferably from 100,000 to 300,000, preferably from 110,000 to 280,000, and more preferably from 120,000 to 260,000. When the weight average molecular weight is too small, when the polyvinyl alcohol-based resin is used as an optical film, sufficient optical performance tends to be difficult to obtain. When the polarizing film is formed by using a polyvinyl alcohol-based film, stretching may become difficult. The tendency. Further, the weight average molecular weight of the polyvinyl alcohol-based resin is measured by a GPC-MALS method.

The average saponification degree of the polyvinyl alcohol-based resin used in the present invention is usually preferably 98 mol% or more, more preferably 99 mol% or more, more preferably 99.5 mol% or more, and even more preferably 99.8 mol% or more. . When the average degree of saponification is too small, when a polyvinyl alcohol-based film is used as a polarizing film, sufficient optical performance may not be obtained. Here, the average degree of saponification in the present invention is measured in accordance with JIS K 6726.

The polyvinyl alcohol-based resin used in the present invention may be used in combination of two or more kinds of modified species, a modification amount, a weight average molecular weight, and an average degree of saponification.

In addition to the polyvinyl alcohol-based resin, the polyvinyl alcohol-based resin aqueous solution contains glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol, or trihydroxyl, if necessary. When a plasticizer such as methyl propane or a non-ionic, anionic or cationic surfactant is used, it is preferable from the viewpoint of film formability. These may be used alone or in combination of two or more.

The resin concentration of the polyvinyl alcohol-based resin aqueous solution obtained in this manner is preferably 15 to 60% by weight, particularly preferably 17 to 55% by weight, more preferably 20 to 50% by weight. When the resin concentration of the aqueous solution is too low, the drying load is increased, and the productivity tends to be lowered. When the viscosity is too high, the viscosity is too high, and the uniform dissolution tends to be difficult.

Then, the obtained polyvinyl alcohol-based resin aqueous solution was subjected to defoaming treatment. Examples of the defoaming method include a method of static defoaming, and defoaming by a multiaxial extruder. As the multi-axis extruder, if it is a multi-axis extruder having a vent hole, a twin-screw extruder having a vent hole is usually used.

[Film Forming Step] After the defoaming treatment, the polyvinyl alcohol-based resin aqueous solution was introduced into the T-slot mold in a predetermined amount, and discharged and cast on a rotating casting drum, and film formation was carried out by a continuous casting method.

The continuous casting method in the present invention refers to, for example, a method in which an aqueous solution of a polyvinyl alcohol-based resin is discharged from a T-slot and cast into a casting mold such as a rotating casting drum, an endless belt, or a resin film to form a film. The film obtained by the film formation is peeled off from the casting mold, and then conveyed in the traveling direction (MD direction), and continuously dried by a hot roll. For example, the film may be heat-treated by a floating dryer.

The resin temperature of the polyvinyl alcohol-based resin aqueous solution at the outlet of the T-slot is preferably from 80 to 100 ° C, preferably from 85 to 98 ° C. When the resin temperature of the polyvinyl alcohol-based resin aqueous solution is too low, the flow tends to be poor, and if it is too high, foaming tends to occur.

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

The discharge rate of the polyvinyl alcohol-based resin aqueous solution discharged from the T-slot to the casting drum is preferably 0.2 to 5 m/min, more preferably 0.4 to 4 m/min, and even more preferably 0.6 to 3 m/min. If the discharge speed is too slow, the productivity tends to be lowered, and if it is too fast, casting tends to be difficult.

The diameter of the casting drum is preferably 2 to 5 m, preferably 2.4 to 4.5 m, and more preferably 2.8 to 4 m. If the diameter is too small, the drying zone on the casting drum tends to be short, and the speed tends to be difficult to increase. If the diameter is too large, the conveyability may be lowered.

The width of the casting 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 casting drum is too small, the productivity tends to be lowered.

The casting drum preferably has a rotation speed of 3 to 50 m/min, preferably 4 to 40 m/min, and more preferably 5 to 35 m/min. If the rotation speed is too slow, the productivity tends to be lowered, and if it is too fast, the drying tends to be insufficient.

The surface temperature of the casting drum is preferably 40 to 99 ° C, preferably 60 to 95 ° C. If the surface temperature is too low, drying tends to be poor, and if it is too high, foaming tends to occur.

[Film formed by film formation] The film obtained by film formation as described above [film before stretching in the width direction (TD direction)] preferably has a water content of 0.5 to 15% by weight, and is 1 to 13% by weight. Good, 2~12% by weight is even better. Regardless of whether the water content is too low or too high, there is a tendency for the target polymer to be aligned, that is, the tendency to exhibit a phase difference as a target tends to be difficult.

In order to adjust the water content, when the moisture content of the film before stretching in the width direction (TD direction) is too high, it is preferred to dry the film before extending in the width direction (TD direction), and conversely, in the width direction (TD) When the moisture content of the film before the stretching is too low, it is preferred to perform humidity conditioning before extending in the width direction (TD direction). It is more preferable to adjust the conditions of the drying step in such a manner that the water content is in the above range.

The drying can be carried out by a known method using a heating roll, an infrared heater or the like. In the present invention, it is preferable to use a plurality of heating rolls, and the temperature of the heating roll is preferably 40 to 150 ° C, more preferably 50 to 140 ° C. . Further, in order to adjust the water content, the humidity control zone may be provided before the extension in the width direction (TD direction).

[Transportation and Extension Step] Then, the film obtained by forming the film as described above and having the moisture content adjusted is conveyed in the traveling direction (MD direction), and is continuous and intermittent in the width direction (TD direction). Extend in at least one way.

In the present invention, it is sufficient that the film obtained by film formation is not particularly required to be stretched in the traveling direction (MD direction) and conveyed at a tensile tension to the extent that the film is not bent. As a matter of course, due to the extension in the width direction (TD direction), necking depending on the Poisson's ratio occurs in the traveling direction (MD direction), and dehydration shrinkage also occurs in the traveling direction (MD direction) during drying. Due to such shrinkage, even if the rotation speed of the conveyance roller and the heating roller is fixed, an appropriate tension can be obtained in the traveling direction (MD direction), and the control of the complicated rotation speed as in Patent Document 2 is not required. Further, from the viewpoint of manufacturability, it is preferable that the film has a dimension in the traveling direction (MD direction).

In addition, when the film obtained by film formation is conveyed in the traveling direction (MD direction), stretching in both directions of the traveling direction (MD direction) and the width direction (TD direction) disturbs the alignment of the polymer and cannot be exhibited. The phase difference in the in-plane and thickness directions of the object is less desirable. In particular, it is not preferable to extend the extent that the dimension of the traveling direction (MD direction) is stretched.

The conveying speed of the film obtained by the film formation in the traveling direction (MD direction) is preferably 5 to 30 m/min, more preferably 7 to 25 m/min, and even more preferably 8 to 20 m/min. If the conveyance speed is too slow, productivity tends to be lowered, and if it is too fast, color unevenness tends to increase.

At the same time, the method of carrying the film formed in the film in the traveling direction (MD direction) and the film in the width direction (TD direction) is not particularly limited. For example, the both ends of the film in the width direction are held by a plurality of jigs. It is ideal to carry out handling and extension at the same time. In this case, the arrangement of the jigs at the respective end portions is preferably 200 mm or less, the pitch is preferably 100 mm or less, and the pitch is 50 mm or less. When the distance between the jigs is too wide, the film after stretching may be bent, or the thickness of both ends of the obtained polyvinyl alcohol-based film in the width direction may be uneven, and the phase difference may become uneven. Further, it is preferable that the gripping position of the jig (the tip end portion of the jig) is 100 mm or less from both ends in the width direction of the film formed by the film formation. When the holding position (front end portion) of the jig is too large at the center portion in the film width direction, the end portion of the film to be discarded tends to increase and the product width tends to be narrow.

In the present invention, the stretching ratio in the width direction (TD direction) is preferably 1.05 to 1.3 times, preferably 1.05 to 1.25 times, and more preferably 1.1 to 1.2 times. Even if the stretching ratio in the width direction (TD direction) is too high or too low, the in-plane phase difference tends to increase.

The step of extending the continuity in the width direction (TD direction) may be one stage (one time) or multiple stages (multiple times) such that the total stretching ratio becomes the range of the above stretching ratio (also referred to as successive stretching). For example, after the extension of the first stage, the simple conveyance in which the width direction (TD direction) is fixed may be performed, and the extension after the second stage may be performed. In particular, in the case of a thin film, the stress of the film can be relaxed to avoid breakage by inserting a simple transfer step of a fixed width. When the insertion step of the fixed width is inserted, the fixed width can also be set to be narrower than the width after the extension of the first stage. The film that has just been stretched easily shrinks due to stress relaxation, and shrinkage due to dehydration also occurs, so that the fixed width can be set to be narrower than the contraction width. However, if it is narrower than the shrinkage width, it is less desirable because the film is bent. This extension step is preferably carried out after the drying step of the film, but may be carried out separately at least one time before the drying step of the film and after the drying step, or may be carried out in the drying step.

As an ideal aspect of the present invention, it is possible to temporarily extend the width direction (TD direction) of the film obtained by film formation by more than 1.3 times, and then to extend the magnification in the final width direction (TD direction) to 1.05. 1.3 times the way to make its size shrink. At this time, after temporarily extending more than 1.3 times, the film may be simply conveyed at a fixed width of 1.05 to 1.3 times the stretching ratio. With this method, the stress of the film can be relaxed, especially in the case of a thin film.

In the present invention, the stretching temperature of the film obtained by film formation in the width direction (TD direction) is preferably 50 to 150 ° C, particularly preferably 60 to 140 ° C, and more preferably 70 to 130 ° C. Even if the extension temperature is too low or too high, the in-plane phase difference tends to increase. When the sequential extension is performed, the extension temperature can also be changed at each extension stage.

In the present invention, the extension time for the film obtained by film formation in the width direction (TD direction) is preferably 2 to 60 seconds, preferably 5 to 45 seconds, and 10 to 30 seconds. good. If the stretching time is too short, the film tends to be broken. On the contrary, if the stretching time is too long, the equipment load tends to increase. When the successive extension is performed, the extension time can also be changed at each extension stage.

In a preferred embodiment of the present invention, after the extension in the width direction (TD direction) is performed at a relatively low temperature, simple conveyance is performed in the fixed width direction (TD direction), and the width direction of the second stage is performed at a higher temperature. The method of extending the (TD direction). Specifically, the first stage is preferably carried out at 50 ° C or higher, more preferably 50 to 130 ° C, and the second stage is preferably carried out at 80 ° C or higher, preferably 80 to 150 ° C. According to this method, the drying can be smoothly performed to obtain a uniform polymer alignment, and the phase difference in the in-plane and thickness directions of the object can be exhibited.

In the present invention, after the film obtained by the film formation is stretched in the width direction (TD direction), the heat treatment may be performed by a floating dryer or the like. The heat treatment temperature is preferably 60 to 200 ° C, and is particularly preferably 70 to 150 ° C. When the heat treatment temperature is too low, the dimensional stability tends to be lowered. On the contrary, if the heat treatment temperature is too high, the elongation at the time of production of the polarizing film tends to be lowered. Moreover, the heat treatment time should be 1 to 60 seconds, which is particularly good for 5 to 30 seconds. When the heat treatment time is too short, the dimensional stability tends to be lowered. Conversely, if the heat treatment time is too long, the elongation at the time of production of the polarizing film tends to be lowered.

[Polyvinyl alcohol-based film] The polyvinyl alcohol-based film of the present invention is obtained in this manner, and finally wound around a roll to form a product. The thickness of the polyvinyl alcohol-based film is preferably 5 to 60 μm from the viewpoint of thinning of the polarizing film, and is particularly preferably 5 to 45 μm, more preferably 5 to 30 μm, and the viewpoint of avoiding cracking is 5 ~20μm is especially good. The thickness of the polyvinyl alcohol-based film is adjusted by the resin concentration in the polyvinyl alcohol-based resin aqueous solution, the discharge amount (discharge rate) to the casting mold, the stretching ratio, and the like.

The width of the polyvinyl alcohol-based film is preferably 2 m or more, and is preferably 3 m or more from the viewpoint of increasing the area, and is more preferably 4 to 6 m from the viewpoint of avoiding breakage.

The length of the polyvinyl alcohol-based film is preferably 2 km or more, and is preferably 3 km or more in terms of a large area, and more preferably 3 to 50 km from the viewpoint of transporting weight.

The polyvinyl alcohol-based film of the present invention is very effective as a raw material roll film of a polarizing film. Hereinafter, a method of producing a polarizing film comprising the polyvinyl alcohol-based film and a polarizing plate will be described.

[Method for Producing Polarizing Film] The polarizing film of the present invention is obtained by transferring the polyvinyl alcohol-based film from the roll and then transferring it horizontally, and performing steps such as water swelling, dyeing, boric acid crosslinking, stretching, washing, and drying. Manufacturing.

The water swelling step is usually carried out at about 30 ° C for 0.1 to 15 minutes from the viewpoint of controlling the degree of swelling of the polyvinyl alcohol film.

In the water swelling step, the swelling degree of the polyvinyl alcohol-based film of the present invention is a swelling degree X (%) in the width direction (TD direction) when the film is swollen for 15 minutes in water at 30 ° C, The degree of swelling Y (%) in the direction of travel (MD direction) and the degree of swelling Z (%) in the thickness direction satisfy Z≧1.1X and Z≧1.1Y, which is ideal for Z≧1.2X and Z≧1.2Y. Z≧1.3X and Z≧1.3Y are even better. By setting the swelling degree Z (%) in the thickness direction to be larger than the swelling degree X (%) in the width direction (TD direction) and the swelling degree Y (%) in the traveling direction (MD direction), the swelling speed can be increased and It is preferable to reduce the unevenness of the color of the polarizing film.

Further, the offset ΔX (%) of the swelling degree X (%) in the width direction (TD direction), the offset ΔY (%) of the swelling degree Y (%) in the traveling direction (MD direction), and the degree of swelling in the thickness direction The offset ΔZ (%) of Z (%) is preferably within 5%, more preferably within 4%, and even more preferably within 3%. If the offset is too large, the polarizing film tends to be uneven in color.

The dyeing step is carried out by contacting the film with a liquid containing iodine or a dichroic dye. An aqueous solution of iodine-potassium iodide is usually used, and the concentration of iodine is 0.1 to 2 g/L, and the concentration of potassium iodide is preferably 1 to 100 g/L. The dyeing time is about 30 to 500 seconds. The temperature of the treatment bath should be 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 carried out 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, and is used at a concentration of about 10 to 100 g/L. When potassium iodide is allowed to coexist in the solution, the viewpoint of stability of polarization performance is preferable. The temperature during the treatment is about 30 to 70 ° C, the treatment time is preferably about 0.1 to 20 minutes, and the extension operation can be carried out during the treatment as needed.

The extension step is to make the film 3 to 10 times in the uniaxial direction, and it is preferable to carry out the extension of 3.5 to 6 times. At this time, it is possible to perform a slight extension in the direction perpendicular to the extending direction (preventing the degree of shrinkage in the width direction or the extension thereof). The temperature at the time of extension should be 40 to 170 °C. Further, the stretching ratio may be set to be in the above range at the end, and the stretching operation may be performed not only once but also in the manufacturing step.

The washing step can be carried out, for example, by immersing the film in an aqueous iodide solution such as water or potassium iodide to remove precipitates generated on the surface of the film. The potassium iodide concentration when using the potassium iodide aqueous solution may be about 1 to 80 g/L. The temperature during the cleaning treatment is usually 5 to 50 ° C, preferably 10 to 45 ° C. The processing time is usually 1 to 300 seconds, preferably 10 to 240 seconds. Further, the water washing and the washing with the potassium iodide aqueous solution may be carried out as appropriate.

The drying step is carried out, for example, by drying the film at 40 to 80 ° C for 1 to 10 minutes in the atmosphere.

Thus, a polarizing film can be obtained, and the polarizing film preferably has a degree of polarization of 99% or more and more preferably 99.5% or more. If the degree of polarization is too low, the contrast in the liquid crystal display tends to decrease. In addition, in general, the degree of polarization is a light transmittance (H ₁₁ ) measured at a wavelength λ in a state in which two polarizing films are stacked in such a manner that their alignment directions are the same direction, and two polarized films are used. The light transmittance (H ₁ ) measured at the wavelength λ in a state in which the films are superposed in such a manner that the alignment directions are perpendicular to each other is calculated by the following equation. Polarization = [(H ₁₁ -H ₁ )/(H ₁₁ +H ₁ )] ^1/2

Further, the polarizing film of the present invention preferably has a monomer permeability of 44% or more. When the monomer transmittance is too low, the brightness of the liquid crystal display tends to be insufficient. The monomer transmittance is a value obtained by measuring the light transmittance of the polarizing film monomer using a spectrophotometer.

Next, a method of producing the polarizing plate of the present invention using the polarizing film of the present invention will be described. The polarizing film of the present invention is suitable for producing a polarizing plate having less color unevenness and excellent polarizing performance.

The polarizing plate of the present invention is produced by adhering the adhesive to the optically isotropic resin film of the protective film on one or both sides of the polarizing film of the present invention. Examples of the protective film include cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, cycloolefin polymer, cyclic olefin copolymer, polystyrene, polyether oxime, A film or sheet of a poly(aryl) ester, poly(4-methylpentene), poly(phenylene ether) or the like.

The bonding method is carried out by a known method. For example, by uniformly applying a liquid adhesive composition to a polarizing film, a protective film, or both, the two are attached together for pressure bonding and heating. Or by irradiation with active energy rays.

In addition, a curable resin such as a urethane resin, an acrylic resin, or a urea resin may be applied to one surface or both surfaces of the polarizing film, and the cured layer may be cured to form a polarizing plate. In this manner, the hardened layer can be replaced by the protective film to achieve film formation.

The polarizing film and the polarizing plate of the polyvinyl alcohol film of the invention have excellent polarizing performance, and are suitable for use in a portable information terminal, a personal computer, a television, a projector, a signboard, a desktop computer, an electronic clock. Liquid crystal display devices such as word processor, electronic paper, game machine, video recorder, camera, photo album, thermometer, audio, automobile, and mechanical instruments, sunglasses, anti-glare glasses, stereo glasses, wearable displays, Antireflection layer, optical communication equipment, medical equipment, building materials, toys, etc. for display elements (CRT, LCD, organic EL, electronic paper, etc.). [Examples]

Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to the following examples as long as the gist of the invention is not exceeded. In addition, the "part" in the example means the weight basis.

<Measurement conditions> The properties of the polyvinyl alcohol-based film in the following examples and comparative examples were carried out as follows (in-plane phase difference, thickness direction phase difference, in-plane phase difference shift, and thickness direction phase difference). Measurement and evaluation of the characteristics of the polarizing film (polarization degree, monomer transmittance, color unevenness) of the offset film, the degree of swelling, and the degree of swelling. [In-plane phase difference Rxy (nm), thickness direction phase difference Rth (nm)] The length is cut out from the center portion and the left and right end portions (the inner side of the film edge end 10 cm) from the width direction of the obtained polyvinyl alcohol-based film. The in-plane phase difference Rxy (nm) at 590 nm and the thickness direction phase difference Rth (nm) were measured using a phase difference measuring device ("KOBRA-WR" manufactured by Oji Scientific Instruments Co., Ltd.). <Measurement conditions of Rth> Incident angle: 50° Tilting center axis: Latency axis Average refractive index: Value measured using an Abbe refractometer

[Offset of the in-plane phase difference ΔRxy (nm)] The phase difference Rxy (nm) between the central portion and the left and right end portions in the width direction obtained as described above is the phase difference between the maximum value and the minimum value. The difference offset ΔRxy(nm).

[Offset ΔRth (nm) in the thickness direction phase difference] The difference between the maximum value and the minimum value is taken as the thickness from the phase difference Rth (nm) in the thickness direction between the center portion and the left and right end portions in the width direction obtained as described above. The deviation of the directional phase difference is ΔRth (nm).

[Swelling degree (%)] One film each having a width of 100 mm × a length of 100 mm was cut out from the center portion and the left and right end portions in the width direction of the obtained polyvinyl alcohol-based film, and immersed in water at 30 ° C for 15 minutes. Swelling. The swelling degree X (%) in the width direction (TD direction) and the swelling degree Y (%) in the traveling direction (MD direction) were calculated from the dimensions before and after the immersion according to the following formula. The degree of swelling Z (%) in the thickness direction is one film each having a width of 100 mm × a length of 100 mm from the central portion and the left and right end portions in the width direction of the polyvinyl alcohol-based film, and immersed in water at 30 ° C for 15 minutes. After swelling, the film was taken out and the film was spread out on a filter paper (5A). Further, the filter paper (5A) was overlaid on the film, and a SUS plate of 150 mm × 150 mm × 4 mm (4.4 × 10 ^-2 g / mm ² ) was placed thereon for 5 seconds to remove adhering water on the surface of the film. The film was quickly placed in a weighing bottle to measure the weight and set it as "weight after impregnation". The above operation was carried out in an environment of 23 ° C and 50% RH. Then, the film was placed in a dryer at 105 ° C for 16 hours to remove moisture from the film, and then the film was taken out, quickly placed in a weighing bottle to measure the weight, and it was designated as "weight after drying". Then, the degree of swelling Z (%) in the thickness direction is calculated according to the following formula. Swelling degree X (%) = 100 × width in the TD direction after immersion (mm) / width in the TD direction before immersion (mm) Swelling degree Y (%) = 100 × width in the MD direction after immersion (mm) / Width (mm) in the MD direction before immersion, degree of swelling Z (%) = 1000000 × weight after immersion (g) / weight after drying (g) / X / Y

[Offset of swelling degree (%)] The difference between the maximum value and the minimum value among the central portion and the left and right end portions in the width direction obtained by the above measurement is determined as the swelling in the width direction (TD direction). Offset ΔX (%) of degree X (%), offset ΔY (%) of swelling degree Y (%) in the traveling direction (MD direction), and offset ΔZ (%) of swelling degree Z (%) in the thickness direction .

[Polarization degree (%), monomer transmittance (%)] A test piece having a length of 4 cm × a width of 4 cm was cut out from the center portion in the width direction of the obtained polarizing film, and an automatic polarizing film measuring device (manufactured by JASCO Corporation) was used: VAP7070) measures the degree of polarization (%) and monomer penetration (%).

[Color unevenness] A test piece having a length of 30 cm × a width of 30 cm was cut out from the central portion in the width direction of the obtained polarizing film, and two polarizing plates held at an angle of 45° in the orthogonally polarized state (monomer transmittance: 43.5%) After the light transmittance was 99.9%, a color box having a surface illuminance of 14,000 lx was used, and the optical color unevenness was observed in a penetration mode, and evaluated by the following criteria. (Evaluation criteria) ○...No color unevenness △...Inconsistent color unevenness ×...Color unevenness

<Example 1> (Production of polyvinyl alcohol-based film) 1,000 kg of a polyvinyl alcohol-based resin having a weight average molecular weight of 142,000 and a saponification degree of 99.8 mol%, 2,500 kg of water, 105 kg of glycerin as a plasticizer, and an interface 0.25 kg of polyoxyethylene laurylamine as an active agent was placed in a 5,000 L dissolution tank, and the mixture was heated to 150 ° C in a stirred state to carry out pressure dissolution, and a polyvinyl alcohol-based resin having a resin concentration of 25% by weight was obtained by concentration adjustment. Aqueous solution. Then, the polyvinyl alcohol-based resin aqueous solution was supplied to a twin-screw extruder to perform defoaming, and then the temperature of the aqueous solution was set to 95 ° C, and it was discharged from the T-slot discharge port (discharge rate: 2.5 m/min) and cast in a rotation. The casting drum is used to make the film. The film obtained by the film formation was peeled off from the casting drum, and conveyed in the traveling direction (MD direction), and the surface of the film and the back surface were alternately brought into contact with a total of 10 heating rolls to perform drying. Thereby, a film (width 2 m, thickness 60 μm) having a water content of 10% by weight was obtained. Then, the left and right end portions of the film were held at a jig pitch of 45 mm, and the film was conveyed at a speed of 8 m/min in the traveling direction (MD direction), and was carried out in the width direction (TD direction) at 120 ° C using an extension machine. The film was stretched to obtain a polyvinyl alcohol film (width: 2.2 m, thickness: 55 μm, length: 2 km). The properties of the obtained polyvinyl alcohol-based film are shown in Tables 1 and 2.

(Preparation of Polarizing Film and Polarizing Plate) The obtained polyvinyl alcohol-based film was immersed in a water bath at a water temperature of 30 ° C in a state where it was taken out from a roll and conveyed in a horizontal direction, and was swollen in the traveling direction (MD). Direction) 1.7 times extension. Then, it was immersed in an aqueous solution of 30° C. consisting of 0.5 g/L of iodine and 30 g/L of potassium iodide, and was stretched 1.6 times in the traveling direction (MD direction), and then immersed in a composition of boric acid 40 g/L. In the aqueous solution (50 ° C) of potassium iodide 30 g/L, cross-linking of boric acid was carried out, and 2.1 times uniaxial stretching was performed in the traveling direction (MD direction). Finally, the mixture was washed with an aqueous solution of potassium iodide, and dried at 50 ° C for 2 minutes to obtain a polarizing film having a total stretching ratio of 5.8 times. No breakage occurred in this production, and the characteristics of the obtained polarizing film are shown in Table 3. To the both surfaces of the polarizing film obtained above, a triethyl fluorene cellulose film having a film thickness of 40 μm was bonded using an aqueous polyvinyl alcohol solution as an adhesive, and dried at 70 ° C to obtain a polarizing plate.

<Example 2> In Example 1, the film obtained by film formation was extended by 1.05 times in the width direction (TD direction) at 75 ° C, and then in the width direction (TD direction) at 120 ° C. A polyvinyl alcohol-based film (having a width of 2.2 m, a thickness of 55 μm, and a length of 2 km) was obtained in the same manner as in Example 1 except that the stretching was carried out in the same manner as in Example 1 except that the stretching was carried out in an amount of 1.05 times (the total stretching ratio was 1.1 times). The properties of the obtained polyvinyl alcohol-based film are shown in Tables 1 and 2. Further, this polyvinyl alcohol-based film was used in the same manner as in Example 1 to obtain a polarizing film and a polarizing plate. The characteristics of the obtained polarizing film are shown in Table 3.

<Example 3> In Example 1, the discharge rate at the time of film formation was set to 1.3 m/min, and the film (width: 2 m, thickness: 30 μm) having a water content of 7 wt% was subjected to 1.1 in the width direction (TD direction). A polyvinyl alcohol-based film (having a width of 2.2 m, a thickness of 27 μm, and a length of 2 km) was obtained in the same manner as in Example 1 except that the stretching was carried out. The properties of the obtained polyvinyl alcohol-based film are shown in Tables 1 and 2. Further, this polyvinyl alcohol-based film was used in the same manner as in Example 1 to obtain a polarizing film and a polarizing plate. Although the polyvinyl alcohol-based film of the raw material roll was thin, the elongation step at the time of production of the polarizing film did not break. The characteristics of the obtained polarizing film are shown in Table 3.

<Example 4> In Example 1, the discharge rate at the time of film formation was set to 0.8 m/min, and the film (width: 2 m, thickness: 20 μm) having a water content of 5% by weight was subjected to 1.2 in the width direction (TD direction). A polyvinyl alcohol-based film (having a width of 2.4 m, a thickness of 17 μm, and a length of 2 km) was obtained in the same manner as in Example 1 except that the stretching was carried out. The properties of the obtained polyvinyl alcohol-based film are shown in Tables 1 and 2. Further, this polyvinyl alcohol-based film was used in the same manner as in Example 1 to obtain a polarizing film and a polarizing plate. Although the polyvinyl alcohol-based film of the raw material roll was thin, the elongation step at the time of production of the polarizing film did not break. The characteristics of the obtained polarizing film are shown in Table 3.

<Example 5> In Example 1, the discharge rate at the time of film formation was set to 0.8 m/min, and the film (width: 2 m, thickness: 20 μm) having a water content of 5% by weight was subjected to 1.1 in the width direction (TD direction). After the extension was carried out, the conveyance was carried out at a fixed width of 2.2 m (equivalent to a 1.1-fold extension), and the extension was carried out in the width direction (TD direction) by 1.1 times (total extension magnification: 1.2 times). A polyvinyl alcohol-based film (having a width of 2.4 m, a thickness of 17 μm, and a length of 2 km) was obtained. The properties of the obtained polyvinyl alcohol-based film are shown in Tables 1 and 2. Further, this polyvinyl alcohol-based film was used in the same manner as in Example 1 to obtain a polarizing film and a polarizing plate. Although the polyvinyl alcohol-based film of the raw material roll was thin, the elongation step at the time of production of the polarizing film did not break. The characteristics of the obtained polarizing film are shown in Table 3.

<Comparative Example 1> In Example 1, both ends of the film obtained by the film formation were not held by a jig, and were heated at 120 ° C while being conveyed at a speed of 8 m/min in the traveling direction (MD direction). A polyvinyl alcohol-based film (width: 2 m, thickness: 60 μm, length: 2 km) was obtained in the same manner as in Example 1. The properties of the obtained polyvinyl alcohol-based film are shown in Tables 1 and 2. Further, this polyvinyl alcohol-based film was used in the same manner as in Example 1 to obtain a polarizing film and a polarizing plate. The characteristics of the obtained polarizing film are shown in Table 3.

<Comparative Example 2> In Example 4, both ends of the film obtained by film formation were not held by a jig, and were heated at 120 ° C while being conveyed at a speed of 8 m/min in the traveling direction (MD direction). A polyvinyl alcohol-based film (having a width of 2 m, a thickness of 20 μm, and a length of 2 km) was obtained in the same manner as in Example 4. The properties of the obtained polyvinyl alcohol-based film are shown in Tables 1 and 2. Further, this polyvinyl alcohol-based film was used in the same manner as in Example 1 to obtain a polarizing film and a polarizing plate. The characteristics of the obtained polarizing film are shown in Table 3.

【Table 1】

【Table 2】

【table 3】

As a result of the above-described examples and comparative examples, it was found that the polyvinyl alcohol-based film which satisfies the range specified by the above formulas (1) and (2) from the in-plane retardation (Rxy) and the thickness direction retardation (Rth) The polarizing films of Examples 1 to 5 had a high degree of polarization and no color unevenness. On the other hand, in Comparative Examples 1 and 2 of the polyvinyl alcohol-based film having the in-plane retardation (Rxy) and the thickness direction retardation (Rth) outside the ranges specified by the above formulas (1) and (2) The polarizing film has a poor degree of polarization and uneven color is observed.

The specific embodiments of the present invention have been disclosed in the above embodiments, but the above embodiments are merely illustrative and not limiting. Various changes that are obvious to those of ordinary skill in the art are intended to be included within the scope of the present invention. [Industrial use]

The polarizing film and the polarizing plate of the polyvinyl alcohol film of the invention have excellent polarizing performance, and are suitable for use in a portable information terminal, a personal computer, a television, a projector, a signboard, a desktop computer, an electronic clock. Liquid crystal display devices such as word processor, electronic paper, game machine, video recorder, camera, photo album, thermometer, audio, automobile, and mechanical instruments, sunglasses, anti-glare glasses, stereo glasses, wearable displays, Antireflection layer, optical communication equipment, medical equipment, building materials, toys, etc. for display elements (CRT, LCD, organic EL, electronic paper, etc.).

no

no

Claims (11)

A polyvinyl alcohol-based film having a thickness of 5 to 60 μm, a width of 2 m or more, and a length of 2 km or more, and is characterized by satisfying the following formulas (1) and (2): (1) in-plane retardation Rxy ≦ 30 nm; (2) thickness The directional phase difference Rth ≧ 90 nm; where the in-plane retardation Rxy (nm) and the thickness direction phase difference Rth (nm) are such that the refractive index in the width direction of the polyvinyl alcohol-based film, that is, the TD direction is nx, and the length The direction, that is, the refractive index in the MD direction is ny, the refractive index in the thickness direction is nz, and the thickness is d (nm), and the values calculated by the following formulas (A) and (B) are respectively: (A) Rxy (nm) )=|nx-ny|×d(nm); (B) Rth(nm)=[(nx+ny)/2-nz]×d(nm). In the polyvinyl alcohol-based film of the first aspect of the invention, the offset ΔRxy of the in-plane retardation Rxy in the width direction, that is, the TD direction, is 5 nm or less. In the polyvinyl alcohol-based film of the first or second aspect of the invention, the retardation ΔRth of the thickness direction phase difference Rth in the width direction, that is, the TD direction is 30 nm or less. When the polyvinyl alcohol-based film of the first or second aspect of the patent application is immersed in water at 30 ° C for 15 minutes and the degree of swelling of the film is measured, the width direction, that is, the swelling degree X (%) in the TD direction, and the length direction are also That is, the degree of swelling Y (%) in the MD direction and the degree of swelling Z (%) in the thickness direction satisfy Z≧1.1X and Z≧1.1Y. The polyvinyl alcohol-based film of the fourth aspect of the patent application has a width ΔX (%) in the width direction, that is, a swelling degree X (%) in the TD direction, and a swelling degree Y (%) in the MD direction in the longitudinal direction. The offset ΔY (%) and the offset ΔZ (%) of the degree of swelling Z (%) in the thickness direction are both within 5%. The polyvinyl alcohol-based film of claim 1 or 2 has a thickness of 5 to 30 μm. A polarizing film characterized by using the polyvinyl alcohol-based film according to any one of claims 1 to 6. A polarizing plate comprising: a polarizing film according to claim 7; and a protective film disposed on at least one side of the polarizing film. A method for producing a polyvinyl alcohol-based film, wherein an aqueous solution of a polyvinyl alcohol-based resin is formed by a continuous casting method, and after being peeled off from a casting mold, it is continuously dried while being conveyed in the direction of travel, that is, in the MD direction. And extending in the width direction, that is, in the TD direction, to obtain a polyvinyl alcohol-based film, wherein the polyvinyl alcohol-based film satisfies the following formulas (1) and (2): (1) in-plane retardation Rxy ≦ 30 nm; 2) the thickness direction phase difference Rth ≧ 90 nm; where the in-plane phase difference Rxy (nm) and the thickness direction phase difference Rth (nm) are such that the refractive index in the width direction of the polyvinyl alcohol-based film, that is, the TD direction is Nx, the traveling direction, that is, the refractive index in the MD direction is ny, the refractive index in the thickness direction is nz, and the thickness is d (nm), and the values calculated by the following formulas (A) and (B) are respectively: (A) Rxy(nm)=|nx-ny|×d(nm); (B) Rth(nm)=[(nx+ny)/2-nz]×d(nm). The method for producing a polyvinyl alcohol-based film according to the ninth aspect of the invention is to extend 1.05 to 1.3 times in the width direction of the film, that is, in the TD direction. A method for producing a polyvinyl alcohol-based film according to claim 9 or 10, wherein the film is sequentially stretched in the width direction of the film, that is, in the TD direction.