TWI771278B - Polyvinyl alcohol-based film and polarizing film using the same, polarizing plate, and manufacturing method of polyvinyl alcohol-based film - Google Patents

Abstract

The present invention provides 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 the intersection angle θ (°) between the orientation axis (slow axis) and the width direction (TD direction) is 20 ° or less, and the offset Δθ(°) of the intersection angle θ is 20° or less. Therefore, it is possible to obtain a polarizing film that is excellent in extensibility at the time of polarizing film production, has high polarizing performance, and has little color unevenness. In particular, it is possible to provide a polyvinyl alcohol-based film that does not break even during the production of a thin polarizing film.

Description

Polyvinyl alcohol-based film and polarizing film using the same, polarizing plate, and manufacturing method of 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 with excellent dyeability, high polarization degree and little color unevenness, and a polarizing film using the polyvinyl alcohol-based film, The manufacturing method of a polarizing plate and a polyvinyl alcohol-type film.

Conventionally, a polyvinyl alcohol-based film has been used in many applications as a film excellent in transparency, and one of its effective applications includes a polarizing film. This polarizing film is used as a basic component of a liquid crystal display, and in recent years, its use in equipment requiring high quality and high reliability is expanding.

Among these, polarizing films with excellent optical properties are required with the increase in brightness, definition, area, and thickness of LCD TVs, multifunctional portable terminals, and the like. Specifically, the system further enhances the degree of polarization and solves color unevenness.

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 into a casting mold such as a casting drum, an endless belt, etc. to form a film, and after the film formed by the film is peeled off from the casting mold, a nip roll is used to form a film. It was conveyed in the traveling direction (MD direction), and was manufactured while being dried using a hot roll or a floating dryer. In this conveying step, the film obtained by film formation is stretched in the advancing direction (MD direction), so that the polyvinyl alcohol-based polymer is easily aligned in the MD direction, and the orientation axis (delay phase) of the obtained polyvinyl alcohol-based film is axis) is always oriented in the MD direction. If the orientation in the MD direction is too large, the in-plane retardation of the polyvinyl alcohol-based film will increase, which will eventually lead to a decrease in the polarization performance of the polarizing film. Conversely, shrinkage stress depending on Poisson's ratio and shrinkage stress due to dehydration are generated in the width direction (TD direction) of the film obtained by film formation. Therefore, if the stress in the TD direction is used , can also make polyvinyl alcohol-based polymers oriented in the TD direction to a certain extent. At this time, the orientation axis of the obtained polyvinyl alcohol-based film is oriented between the MD direction and the TD direction, and the in-plane retardation tends to decrease. In addition, the alignment axis is also called the optical axis.

On the other hand, a polarizing film is generally manufactured by making a raw material roll, ie, a polyvinyl alcohol-type film, swelled in water (including warm water), and then dyeing and stretching with a dichroic dye such as iodine. This stretching step is a step of stretching the dyed film in the traveling direction (MD direction) to align the dichroic dyes in the film to a high degree. In order to improve the polarizing performance of the polarizing film, it becomes the polyvinyl alcohol-based raw material roll. The film must have good extensibility in the MD direction. In addition, there are cases in which the order of the above-mentioned stretching step and dyeing step is reversed in the manufacture of polarizing film. That is, the raw material roll, that is, the polyvinyl alcohol-based film is swollen in water (including warm water), and then stretched and dyed with a dichroic dye such as iodine. For polarizing properties, the polyvinyl alcohol-based film must have good extensibility in the MD direction.

In addition, in recent years, the thickness of the polyvinyl alcohol-based film has also been reduced due to the reduction in thickness of the polarizing film. In the past, the thickness was about 60 μm, but the current thickness is about 45 μm, and it is expected to be 30 μm or less in the near future. This thin film has problems in productivity such as breakage due to stretching during production of the polarizing film.

As a method of improving the stretchability, for example, a method of specifying the ratio of the speed of the casting drum when the film is formed to the final film winding speed (for example, refer to Patent Document 1) has been proposed; A method of suspending and drying (for example, refer to Patent Document 2), and a method of controlling the stretching condition of a film obtained by film formation in a drying step (for example, refer to Patent Document 3). In addition, a polyvinyl alcohol-based film having reduced in-plane retardation has been proposed (for example, refer to Patent Documents 4 and 5). In addition, a polyvinyl alcohol-based film in which the inclination (alignment angle) of the optical axis is within a specific range has been proposed (for example, refer to Patent Document 6). [Prior Art Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2001-315141 [Patent Document 2] Japanese Patent Laid-Open No. 2001-315142 [Patent Document 3] Japanese Patent Laid-Open No. 2002-79531 [Patent Document 4] Japanese Patent Laid-Open No. 2006-291173 No. [Patent Document 5] Japanese Patent Application Laid-Open No. 2007-137042 [Patent Document 6] International Publication No. WO2009/028141

THE PROBLEM TO BE SOLVED BY THE INVENTION However, even with the method of the above-mentioned patent document, the improvement of the stretchability at the time of polarizing film production is still insufficient. The above-mentioned Patent Document 1 specifies the degree of elongation in the MD direction (stretching condition) when manufacturing a polyvinyl alcohol-based film, but if the elongation in the TD direction is not also considered, the in-plane retardation of the polyvinyl alcohol-based film cannot be reduced. Moreover, the improvement of the extensibility during the manufacture of the polarizing film is still insufficient. In general, it is difficult to extend the polyvinyl alcohol-based film that has been extended in the MD direction in the MD direction at the time of polarizing film production. That is, it is difficult to forcibly elongate the molecular chain by stretching the polyvinyl alcohol-based polymer already aligned in the MD direction in the MD direction. On the contrary, it is easier to stretch the polyvinyl alcohol-based polymer aligned in the TD direction in the MD direction. However, if the polymer orientation in the TD direction is not uniform, the polarizing film cannot be uniformly stretched in the MD direction during production. In Patent Document 1, there is an example (an example of unstretching) that is not stretched to such a degree in the MD direction during the production of a polyvinyl alcohol-based film, but only the above-mentioned shrinkage stress depending on Poisson's ratio and dehydration. The resulting shrinkage stress has a problem that the polymer alignment in the TD direction cannot be sufficiently uniformized. That is, if it does not extend to some extent in the TD direction, or if the width direction is not fixed at least, a uniform alignment state of the polymer in the TD direction cannot be obtained.

In the technique disclosed in the above-mentioned Patent Document 2, although the film after film formation can be uniformly dried, the alignment of the polymer cannot be controlled, and the improvement of the stretchability during the production of the polarizing film is still insufficient. In the technique disclosed in the above-mentioned Patent Document 3, although the film thickness of the polyvinyl alcohol-based film can be made uniform, the alignment of the polymer cannot be controlled, and the improvement of the stretchability during the production of the polarizing film is still insufficient. In the techniques disclosed in the above-mentioned Patent Documents 4 and 5, the in-plane retardation of the polyvinyl alcohol-based film can be reduced, but the in-plane retardation is not reduced in a uniform alignment state only by randomly aligning the polymers. Then, the improvement of the extensibility during the manufacture of the polarizing film is still insufficient, and there is room for improvement in this regard.

The technology disclosed in the above-mentioned Patent Document 6 is a polyvinyl alcohol-based film in which the orientation angle of the film in the width direction is 45 to 135° with respect to the longitudinal direction, but the angle range is wide and accounts for half of the whole direction, and it is difficult to say that it is a polyvinyl alcohol-based film. Controls the alignment of polymers. In the embodiment, the narrowest range of the alignment angle is 54°, and the deviation of the alignment angle is large. When there is such a large amount of shift, the stretchability is shifted in the width direction, and the resulting polarizing film tends to be uneven in color. In addition, the disclosed technology uses the peripheral speed ratio of the drying roller to control the alignment angle, and the characteristics of the film in this production method are easily fluctuated in the longitudinal direction, whether the alignment angle is within the above-mentioned range over the entire length, or whether the extensibility is constant. , are all unknown (there is no description of the film length in the examples and the measurement is only at one of the length directions). In addition, the thickness of the film in the example is 75 μm, which is difficult to meet the demand for thinning in recent years.

Therefore, under such a background, the present invention provides a polyvinyl alcohol-based film that can obtain a polarizing film having excellent extensibility during polarizing film production, high polarizing performance and less color unevenness, especially: A polyvinyl alcohol-based film that does not break even during the production of the polarizing film, further provides: a polarizing film composed of the polyvinyl alcohol-based film, a polarizing plate, and a manufacturing method of the polyvinyl alcohol-based film. [Means of Solving Problems]

The inventors of the present application have conducted intensive research in view of this matter, and found that 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, wherein the alignment axis (delay axis) and the width direction ( The intersection angle θ(°) of the TD direction) and the offset Δθ(°) of the intersection angle θ are within a specific range, which means that the polarizing film has excellent extensibility during the manufacture of polarizing films, and can produce thin polarizing films with good yield. The polarizing film obtained from the alcohol-based film has high polarizing performance and less color unevenness.

That is, the first gist 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, characterized by a difference between the orientation axis (slow axis) and the width direction (TD direction). The intersection angle θ(°) is 20° or less, and the offset Δθ(°) of the intersection angle θ is 20° or less.

In particular, when the refractive index in the width direction (TD direction) is nx and the refractive index in the direction perpendicular to it (MD direction) is ny, the birefringence ΔNxy, which is a value calculated by the following formula (A), is: The polyvinyl alcohol-based film below 0.001 is the second gist of the present invention: (A) ΔNxy=|nx-ny|.

Moreover, the polyvinyl alcohol-type film characterized by a thickness of 5-30 micrometers is made into the 3rd gist of this invention.

Moreover, this invention is characterized by using the polarizing film of the said polyvinyl alcohol-type film as a 4th gist.

Moreover, this invention is characterized by the polarizing plate provided with the polarizing film and the protective film provided on at least one side of the said polarizing film as a 5th gist.

Furthermore, 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 into a film by a continuous casting method, and after peeling from a casting mold, the film is carried out in the advancing direction (MD direction). The polyvinyl alcohol-based film was obtained by carrying, continuously drying and stretching, wherein the angle of intersection θ (°) between the orientation axis (slow phase axis) and the width direction (TD direction) of the polyvinyl alcohol-based film was 20 ° or less, and the offset Δθ(°) of the intersection angle θ is 20° or less as the sixth gist.

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

In addition, a polyvinyl alcohol-based film characterized in that after the film's width direction (TD direction) is stretched by more than 1.3 times, the size of the film is shrunk so that the final stretch ratio in the width direction (TD direction) becomes 1.3 times or less. The manufacturing method is the eighth gist of the present invention. [Effect of invention]

The polyvinyl alcohol-based film of the present invention can provide a polarizing film with excellent extensibility during the manufacture of polarizing films, no breakage even when manufacturing thin polarizing films, and exhibiting high polarizing performance and less color unevenness. In addition, in the present invention, since the stretchability during the production of the polarizing film depends on the alignment state of the polyvinyl alcohol-based polymer in the film, the stretchability is improved by controlling the alignment axis.

The present invention will be explained 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 is characterized in that the intersection angle θ (°) between the alignment axis (slow axis) and the width direction (TD direction) is 20 ° or less, and the offset Δθ(°) of the intersection angle θ is 20° or less.

The thickness of the polyvinyl alcohol-based film of the present invention is 5 to 60 μm, and from the viewpoint of thinning the polarizing film, it is preferably 5 to 45 μm, particularly preferably 5 to 30 μm, and particularly preferably 5 to 20 μm. 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 speed) to the casting mold, the draw ratio, and the like.

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

The length of the polyvinyl alcohol-based film of the present invention is 2 km or more, preferably 3 km or more from the viewpoint of increasing the area, and particularly preferably 3 to 50 km from the viewpoint of transport weight.

In the present invention, the intersection angle θ(°) between the alignment axis (slow axis) and the width direction (TD direction) must be 20° or less, preferably 15° or less, particularly preferably 10° or less, and 5° or less. More preferably, it is 2° or less. When this intersection angle θ(°) exceeds the upper limit value, the extensibility in the MD direction at the time of manufacture of the polarizing film is lowered, and the object of the present invention cannot be achieved. In addition, the lower limit value of the intersection angle θ(°) is usually 0°.

Further, in the present invention, the offset Δθ(°) of the intersection angle θ must be 20° or less, preferably 10° or less, particularly preferably 5° or less, and even more preferably 3° or less. If the offset Δθ(°) of the intersection angle θ is too large, the color unevenness of the polarizing film will occur, and the object of the present invention cannot be achieved. In addition, generally, the lower limit of the offset Δθ(°) of the intersection angle θ is 0°.

In the present invention, the birefringence ΔNxy is preferably 0.001 or less, particularly preferably 0.0008 or less, still more preferably 0.0006 or less, and particularly preferably 0.0005 or less. When the birefringence ΔNxy is too large, the polarizing film tends to have uneven color. In addition, ΔNxy referred to here is a numerical value calculated by |nx-ny| when the refractive index in the width direction (TD direction) is nx and the refractive index in the advancing direction (MD direction) is ny. In addition, the product (|nx-ny|*d) of the said birefringence ΔNxy and the thickness d (nm) of a film is an in-plane retardation (nm).

In the present invention, as a method of controlling the above-mentioned intersection angle θ(°), offset Δθ(°) of intersection angle θ, and birefringence ΔNxy, from the viewpoint of precise control of intersection angle θ(°), it is preferable to use The method of extending the film obtained by peeling the casting mold in the width direction (TD direction). In addition, the method of adjusting the drying conditions of an aqueous solution, the method of adjusting the chemical structure of a polyvinyl alcohol-type resin, etc. can be mentioned.

Here, the manufacturing method of the polyvinyl alcohol-type film of this invention is demonstrated in order of steps.

[Film material] First, the polyvinyl alcohol resin and its aqueous solution of the polyvinyl alcohol resin 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, polyvinyl acetate obtained by polymerization of vinyl acetate, is usually used by saponification. obtained resin. Resin obtained by saponification of a copolymer of vinyl acetate and a small amount (usually 10 mol% or less, preferably 5 mol% or less) of a component that can be copolymerized with vinyl acetate can also be used as required. Examples of components that can be copolymerized with vinyl acetate include: unsaturated carboxylic acids (including, for example, salts, esters, amides, nitriles, etc.); olefins having 2 to 30 carbon atoms (eg, ethylene, propylene, n-butene, etc.) , isobutylene, etc.); vinyl ethers; unsaturated sulfonates, etc. These can be used individually or in combination of 2 or more types. In addition, a modified polyvinyl alcohol-based resin in which the saponified hydroxyl group is chemically modified may also be used.

Moreover, as a polyvinyl alcohol-type resin, the polyvinyl alcohol-type resin which has a 1, 2- diol structure in a side chain can also be used. The polyvinyl alcohol-based resin having a 1,2-diol structure in the side chain can be obtained by the following method, for example: (i) combining vinyl acetate with 3,4-diacetoxy-1-butene The method for saponifying the copolymer of vinyl acetate; (ii) the method for saponifying and decarboxylating the copolymer of vinyl acetate and ethylene vinyl carbonate; (iii) The method for combining vinyl acetate with 2,2-dialkyl-4-vinyl - A method of saponifying and deketalizing a copolymer of 1,3-dioxolane; (iv) a method of saponifying a copolymer of vinyl acetate and glycerol monoallyl ether, and the like.

The weight average molecular weight of the polyvinyl alcohol-based resin is preferably 100,000 to 300,000, particularly preferably 110,000 to 280,000, and even more preferably 120,000 to 260,000. If the weight average molecular weight is too small, when the polyvinyl alcohol-based resin is used as an optical film, it tends to be difficult to obtain sufficient optical properties, and if it is too large, the stretching of the polyvinyl alcohol-based film during the production of the polarizing film may become difficult. tendency. In addition, the weight average molecular weight of the said polyvinyl alcohol-type resin is 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, more preferably 99.8 mol % or more . When the average saponification is too small, when a polyvinyl alcohol-based film is used as a polarizing film, there is a tendency that sufficient optical performance cannot be obtained. Here, the average degree of saponification in the present invention is measured in accordance with JIS K 6726.

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

The polyvinyl alcohol-based resin aqueous solution contains, in addition to the polyvinyl alcohol-based resin, glycerin, diglycerol, triglycerol, ethylene glycol, triethylene glycol, polyethylene glycol, A commonly used plasticizer such as methylpropane, or at least one surfactant among nonionic, anionic, and cationic surfactants is preferable from the viewpoint of film-forming properties. These can be used individually or in combination of 2 or more types.

The resin concentration of the polyvinyl alcohol-based resin aqueous solution obtained in this way is preferably 15 to 60% by weight, particularly preferably 17 to 55% by weight, and even more preferably 20 to 50% by weight. If the resin concentration of the aqueous solution is too low, the drying load tends to decrease, and the productivity tends to decrease, and if it is too high, the viscosity becomes too high, and uniform dissolution tends to be difficult.

Then, the obtained aqueous solution of polyvinyl alcohol-based resin is subjected to defoaming treatment. As a defoaming method, the method of static defoaming, the defoaming by a multi-screw extruder, etc. are mentioned. As the multi-screw extruder, a multi-screw extruder having a vent hole may be used, and a bi-screw extruder having a vent hole is generally used.

[Film-forming step] After the defoaming treatment, the polyvinyl alcohol-based resin aqueous solution was introduced into a T-slot die in a certain amount one by one, discharged and cast on a rotating casting drum, and a film was formed by a general casting method in accordance with an ordinary method. . Among them, the continuous casting method is suitable from the viewpoint of productivity.

The continuous casting method refers to, for example, a method of forming a film by discharging an aqueous solution of a polyvinyl alcohol-based resin from a T-slot die and casting it into a casting mold such as a rotating casting drum, an endless belt, and a resin film. After the film formed by film formation is peeled from the casting mold, it is conveyed in the advancing direction (MD direction), and is continuously dried with a hot roll or the like to obtain a polyvinyl alcohol-based film, which is finally wound around a roll to obtain a product .

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

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

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

The diameter of the casting drum is preferably 2~5m, preferably 2.4~4.5m, and even more preferably 2.8~4m. When the diameter is too small, the drying section on the casting drum tends to be short, and the speed tends to be difficult to increase, and when the diameter is too large, the transportability tends to decrease.

The width of the casting drum is preferably more than 4m, more preferably more than 4.5m, more preferably more than 5m, and more preferably 5~6m. When the width of the casting drum is too small, the productivity tends to decrease.

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

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

[Film formed by film formation] The film formed by the above method [film before stretching in the width direction (TD direction)] preferably has a moisture content of 0.5 to 15 wt %, and 1 to 13 wt %. Preferably, it is 2 to 12% by weight, more preferably. Even if the water content is too low or too high, the orientation of the intended polymer, that is, the intended expression of the cross angle θ(°) tends to be difficult.

In order to adjust the moisture content, when the moisture content of the film before stretching in the width direction (TD direction) is too high, it is preferable to dry the film before stretching in the width direction (TD direction). When the moisture content of the film before stretching is too low, it is preferable to adjust the humidity before stretching in the width direction (TD direction). It is more preferable to adjust the conditions of a drying process so that a moisture content may become the said range.

The drying can be carried out by a well-known method using heating rollers, infrared heaters, etc. In the present invention, it is preferable to use a plurality of heating rollers. . Moreover, in order to adjust a moisture content, you may provide a humidity control area before extending in the width direction (TD direction).

[Conveying and Stretching Steps] Then, the film formed as described above and the film obtained by adjusting the moisture content is conveyed in the running direction (MD direction), continuously or intermittently in the width direction (TD direction) extend.

In the present invention, it is not necessary to extend the film obtained by film formation in the advancing direction (MD direction), and it is sufficient to convey the film with a tensile tension of such a degree that the film does not bend. As a matter of course, due to the extension in the width direction (TD direction), necking due to Poisson's ratio occurs in the traveling direction (MD direction), and syneresis also occurs in the traveling direction (MD direction) during drying. Due to these shrinkages, even if the rotational speed of the conveying roller and the heating roller is fixed, an appropriate tension can be obtained in the traveling direction (MD direction), and the complicated rotational speed control as described in Patent Document 1 and Patent Document 6 is not required. From the viewpoint of manufacturability, it is preferable that the dimension of the film in the advancing direction (MD direction) is fixed, and especially before and after extending in the width direction (TD direction), the dimensional change rate in the advancing direction (MD direction) is desirably 0.8 to 1.2. 0.9~1.1 is the best.

The conveying speed of the film obtained by film forming in the traveling direction (MD direction) is preferably 5~30m/min, particularly preferably 7~25m/min, and even more preferably 8~20m/min. If the conveyance speed is too slow, the productivity tends to decrease, and if it is too fast, the deviation Δθ(°) of the intersection angle θ tends to increase.

There is no particular limitation on the method of simultaneously carrying out the conveying in the running direction (MD direction) and extending in the width direction (TD direction) of the film obtained by film formation, for example, holding both ends of the film in the width direction with a plurality of clamps It is ideal to carry out handling and extension at the same time. At this time, the arrangement of the jigs at the respective ends is preferably at a pitch of 200 mm or less, particularly preferably at a pitch of 100 mm or less, and even more preferably at a pitch of 50 mm or less. When the distance between the clips is too wide, the stretched film tends to be bent, or the deviation Δθ(°) of the intersection angle θ of the obtained polyvinyl alcohol-based film tends to become large. Moreover, it is preferable that the clamping position of a jig (the front-end|tip part of a jig) is 100 mm or less from both ends of the width direction of the film obtained by film formation. If the clamping position (tip part) of the jig is located too much at the center part in the film width direction, the end part of the film to be discarded increases and the product width tends to become narrow.

In the present invention, the stretching ratio in the width direction (TD direction) is preferably 1.05 to 1.3 times, particularly preferably 1.05 to 1.25 times, and even 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 deviation Δθ(°) of the intersection angle θ tends to increase.

The continuous stretching step in the width direction (TD direction) may be one stage (one time) or multiple stages (multiple times) so that the total stretching ratio is within the range of the above stretching ratio (also called successive stretching). For example, you may implement the simple conveyance which fixes the width direction (TD direction) after carrying out the extension of the 1st stage, and then carry out the extension after the 2nd stage. Especially in the case of thin films, the stress of the film can be relaxed and breakage can be avoided by inserting a simple conveying step of constant width. When inserting the conveyance step of the fixed width, the fixed width can also be set to be narrower than the width after the extension in the first stage. The film that has just been stretched tends to shrink due to stress relaxation, and also shrinks due to dehydration. Therefore, the fixed width can be set as narrow as the shrinkage width. However, if it is narrower than the shrinkage width, the film will bend, which is not ideal. This stretching step is preferably carried out after the drying step of the film, but can be carried out at least at one point before the drying step of the film, during the drying step, and after the drying step.

As an ideal form of the present invention, after the film formed into a film is temporarily stretched by more than 1.3 times in the width direction (TD direction), the final stretching ratio in the width direction (TD direction) can be 1.05 to 1. . 3 times the way to shrink its size. In this case, after temporarily stretching over 1.3 times, the film may be simply conveyed with a fixed width of 1.05 to 1.3 times the stretching ratio. With this method, the stress of the film can be relaxed, and breakage can be avoided especially in the case of thin films.

In the present invention, it is preferable to carry out the stretching in the width direction (TD direction) of the film obtained by forming the film at 50 to 150°C. The elongation temperature is particularly preferably 60 to 140°C, and even more preferably 70 to 130°C. Even if the stretching temperature is too low or too high, the deviation Δθ(°) of the intersection angle θ tends to increase. When performing successive stretching, the stretching temperature may be changed in each stretching stage.

In the present invention, the stretching time of the film obtained by film forming in the width direction (TD direction) is preferably 2 to 60 seconds, particularly preferably 5 to 45 seconds, and further preferably 10 to 30 seconds. good. When the stretching time is too short, the film tends to be easily broken, and on the contrary, when it is too long, the equipment load tends to increase. When successive stretching is performed, the stretching time may be changed in each stretching stage.

In this invention, after extending|stretching in the width direction (TD direction) with respect to the film formed into a film, you may perform heat processing with a floating dryer etc. as needed. The temperature of the heat treatment is preferably 60 to 200°C, preferably 70 to 150°C. When the heat treatment temperature is too low, the dimensional stability tends to decrease easily, and on the contrary, when it is too high, the stretchability during the production of the polarizing film also tends to decrease. In addition, the heat treatment time is preferably 1 to 60 seconds, preferably 5 to 30 seconds. When the heat treatment time is too short, the dimensional stability tends to be lowered, and on the contrary, when the heat treatment time is too long, the stretchability at the time of producing the polarizing film tends to be lowered.

[Polyvinyl alcohol-based film] The polyvinyl alcohol-based film of the present invention can be obtained in this manner. The polyvinyl alcohol-based film of the present invention is particularly suitable for use as a raw material roll for polarizing films because of its excellent extensibility.

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

[Manufacturing method of polarizing film] The polarizing film of the present invention is produced by transferring the polyvinyl alcohol-based film described above from a roller in a horizontal direction, and going through steps such as swelling, dyeing, boric acid crosslinking, stretching, washing, and drying.

The swelling step is carried out before the dyeing step. By the swelling step, in addition to cleaning the dirt on the surface of the polyvinyl alcohol-based film, there are effects such as preventing uneven dyeing by swelling the polyvinyl-alcohol-based film. In the swelling step, water is usually used as a treatment liquid. If the main component of the treatment liquid is water, additives such as iodized compounds, surfactants, and alcohols may be added in small amounts. The temperature of the swelling bath is usually about 10 to 45° C., and the time for immersion in the swelling bath is usually about 0.1 to 10 minutes.

The dyeing step is carried out by contacting the film with a liquid containing iodine or a dichroic dye. Usually, an aqueous solution of iodine-potassium iodide is used, the concentration of iodine is 0.1~2g/L, and the concentration of potassium iodide is preferably 1~100g/L. Dyeing time of about 30 to 500 seconds is practical. The temperature of the treatment bath is preferably 5 to 50°C. In addition to the water solvent, the aqueous solution may also contain a small amount of an organic solvent that is compatible with water.

The boric acid crosslinking step is performed using boron compounds such as boric acid, borax, and the like. The boron compound is used in the form of an aqueous solution or a water-organic solvent mixed solution at a concentration of about 10 to 100 g/L. If potassium iodide is coexisted in the solution, it is preferable from the viewpoint of stabilization of polarization performance. The temperature during the treatment is about 30-70°C, and the treatment time is preferably about 0.1-20 minutes, and an extension operation can also be performed during the treatment according to needs.

In the stretching step, the film is stretched 3 to 10 times in the uniaxial direction, preferably 3.5 to 6 times. At this time, even if it performs a little extension (the extent to which the shrinkage of the width direction is prevented, or the extension beyond that) in the direction perpendicular|vertical to the extension direction, it does not matter. The temperature during elongation is preferably 40 to 170°C. In addition, it is sufficient that the stretching ratio is finally within the aforementioned range, and the stretching operation may be performed not only once but also multiple times in the manufacturing process.

The cleaning step can be performed by, for example, immersing the polyvinyl alcohol-based film in an aqueous solution of iodide such as water or potassium iodide to remove precipitates generated on the surface of the film. The potassium iodide concentration in the case of 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. In addition, washing with water and washing with an aqueous potassium iodide solution may be appropriately combined and implemented.

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

In addition, the degree of polarization of the polarizing film is preferably 99.5% or more, more preferably 99.8% or more. When the polarized light is too low, there is a tendency that the contrast ratio in the liquid crystal display cannot be ensured. In addition, in general, the degree of polarization is the light transmittance (H ₁₁ ) measured at the wavelength λ in a state where two polarizing films are superimposed so that their alignment directions are the same direction, and the difference between the two polarized films The light transmittance (H ₁ ) measured at the wavelength λ when the films are superimposed in such a way that the alignment directions are perpendicular to each other is calculated according to the following formula. Polarization degree=[(H ₁₁ -H ₁ )/(H ₁₁ +H ₁ )] ^1/2

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

Hereinafter, the manufacturing method of the polarizing plate of this invention using the polarizing film of this invention is demonstrated. The polarizing film of the present invention is suitable for manufacturing a polarizing plate with less color unevenness and excellent polarizing performance.

[Manufacturing method of polarizing plate] The polarizing plate of the present invention is produced by sticking an optically isotropic resin film as a protective film on one side or both sides of the polarizing film of the present invention through an adhesive. Examples of the protective film include: cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, cycloolefin polymer, cycloolefin copolymer, polystyrene, polyether Films or sheets of polyarylate, poly(4-methylpentene), polyphenylene ether, etc.

The bonding method is implemented by a known method, for example, by uniformly coating the liquid adhesive composition on the polarizing film, the protective film, or both, and then bonding the two and performing crimping, heating, Or irradiated with active energy rays.

In addition, curable resins such as urethane resin, acrylic resin, and urea resin can be coated on one side or both sides of the polarizing film, and cured to form a cured layer to serve as a polarizing plate. In this way, the above-mentioned hardened layer can replace the above-mentioned protective film and achieve thinning.

The polarizing film and polarizing plate using the polyvinyl alcohol-based film of the present invention have excellent polarizing properties and are suitable for use in portable information terminals, personal computers, televisions, projectors, signboards, desktop computers, electronic Clocks, word processors, electronic paper, game consoles, video recorders, cameras, photo albums, thermometers, audio, automotive and mechanical instruments and other liquid crystal display devices, sunglasses, anti-glare glasses, stereo glasses, wearable displays , Display elements (CRT, LCD, organic EL, electronic paper, etc.) with reduced reflection layer, optical communication equipment, medical equipment, building materials, toys, etc. [Example]

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

Furthermore, the properties of the polyvinyl alcohol-based films (the intersection angle between the alignment axis and the width direction, the offset of the intersection angle, and the birefringence) and the properties of the polarizing films (polarization degree, Measurement and evaluation of monomer penetration rate, color unevenness). <Measurement conditions> [Intersection angle θ(°) of alignment axis (slow axis) and width direction (TD direction), offset Δθ(°) of intersection angle θ, and birefringence ΔNxy] Polyvinyl alcohol-based film obtained from A test piece with a length of 4 cm x width of 4 cm was cut out from the center and both ends (inside 10 cm from the edge of the film) in the width direction, and the alignment axis was measured using a retardation measuring device ("KOBRA-WR" made by Oji Measuring Instruments Co., Ltd.). The intersection angle θ (°) of (the retardation axis) and the width direction (TD direction), the offset Δθ (°) of the intersection angle θ, and the birefringence ΔNxy (nm) at 590 nm. This measurement was implemented with respect to the center part and front-end|tip part / terminal part (inner side of each side edge of a film 10m) of the advancing direction (MD direction) of a polyvinyl-alcohol-type film.

[Polarization degree (%), monomer transmittance (%)] A test piece of length 4 cm x width 4 cm was cut out from the center portion and both end portions (inside 10 cm from the film edge) in the width direction of the obtained polarizing film , using an automatic polarizing film measuring device (manufactured by JASCO Corporation: VAP 7070) to measure the degree of polarization (%) and monomer transmittance (%). This measurement was performed with respect to the center part and front-end|tip part/terminal part (inner side of each film edge 10m from the front-end|tip and terminal edge of a polarizing film) in the advancing direction (MD direction) of a polarizing film.

[Color non-uniformity] A test piece of length 30cm x width 30cm was cut out from the center part and both ends (inside 10cm from the film edge) of the obtained polarizing film in the width direction, and held at an angle of 45° in a cross-polarized light After the two polarizing plates in the state (single transmittance 43.5%, polarization degree 99.9%), use a light box with a surface illuminance of 14,000lx to observe the optical color unevenness in the transmission mode, and use the following criteria for Evaluation. (Evaluation Criteria) ○...No color unevenness △...Slightly colored color unevenness ×...Colored unevenness This evaluation is for the central part and the front end/terminal part (distance from the polarizing film) in the traveling direction (MD direction) of the polarizing film The inner side of each film edge 10m of the front end and the terminal end) is implemented.

<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 and a degree of saponification 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 the active agent was placed in a 5,000L dissolving tank, and the temperature was raised to 150°C under stirring to carry out pressure dissolution, and the concentration of the polyvinyl alcohol-based resin with a resin concentration of 25% by weight was obtained by adjusting the concentration. aqueous solution. Then, after supplying this polyvinyl alcohol-based resin aqueous solution to a biaxial extruder for defoaming, the temperature of the aqueous solution was set to 95° C., the temperature of the aqueous solution was set at 95° C., and it was discharged from the discharge port of the T-slot die (discharge speed: 2.5 m/min), and cast on a rotary The casting drum for film production. The film obtained by this film formation was peeled from the casting drum (film width: 2.1 m), and the surface and the back surface of the film were alternately brought into contact with a total of 10 heating rolls while being conveyed in the advancing direction (MD direction). After drying, a film (width 2 m, thickness 60 μm) having a moisture content of 10 wt % was obtained. Then, while holding the left and right ends of the film at a clamp pitch of 45 mm, the film was conveyed in the advancing direction (MD direction) at a speed of 8 m/min, using a stretching machine at 120° C. in the width direction (TD direction) for 1.1 Double-stretched to obtain a polyvinyl alcohol-based film (width 2.2 m, thickness 55 μm, length 2 km). Table 1 shows the properties of the obtained polyvinyl alcohol-based film.

(Production of polarizing film and polarizing plate) The obtained polyvinyl alcohol-based film was extracted from a roll and conveyed in a horizontal direction, and was swelled in a water tank with a water temperature of 30° C. in the running direction (MD). direction) for a 1.7-fold extension. Then, it was immersed in an aqueous solution composed of 0.5 g/L of iodine and 30 g/L of potassium iodide at 30° C. for dyeing, and stretched 1.6 times in the running direction (MD direction), and then immersed in a boric acid with a composition of 40 g/L. 2.1-fold uniaxial extension in the traveling direction (MD direction) while carrying out boric acid crosslinking in an aqueous solution (50°C) of potassium iodide of 30 g/L. Finally, the solution was washed with an aqueous potassium iodide solution, and dried at 50° C. for 2 minutes to obtain a polarizing film with a total extension ratio of 5.8 times. No fracture occurred during this production, and the properties of the obtained polarizing film are shown in Table 2. A polyvinyl alcohol aqueous solution was used as an adhesive on both sides of the polarizing film obtained above, and a triacetyl cellulose film having a film thickness of 40 μm was bonded, and dried at 70° C. to obtain a polarizing plate.

<Example 2> In Example 1, it carried out similarly to Example 1 except having carried out 1.1 times drawing in the width direction (TD direction) of the film formed by using a drawing machine at 110°C. A polyvinyl alcohol-based film (width 2.2 m, thickness 55 μm, length 2 km) was obtained. Table 1 shows the properties of the obtained polyvinyl alcohol-based film. Moreover, using this polyvinyl alcohol-type film, it carried out similarly to Example 1, and obtained a polarizing film and a polarizing plate. The properties of the obtained polarizing film are shown in Table 2.

<Example 3> In Example 1, the discharge speed at the time of film formation was set to 0.8 m/min, and the film (width 2 m, thickness 20 μm) with a moisture content of 5 wt % was stretched at 120° C. in the width direction using a stretching machine. (TD direction), except having carried out 1.2 times stretching, it carried out similarly to Example 1, and obtained the polyvinyl alcohol-type film (width 2.4m, thickness 17 micrometers, length 2km). Table 1 shows the properties of the obtained polyvinyl alcohol-based film. Moreover, using this polyvinyl alcohol-type film, it carried out similarly to Example 1, and obtained a polarizing film and a polarizing plate. Although the polyvinyl alcohol-based film of the raw material roll was thin, it did not break in the stretching step during the production of the polarizing film. The properties of the obtained polarizing film are shown in Table 2.

<Example 4> In Example 1, the discharge speed during film formation was set to 0.8 m/min, and a film (width 2 m, thickness 20 μm) with a moisture content of 5 wt % was stretched at 120° C. in the width direction using a stretching machine. (TD direction) was stretched 1.4 times, and then shrunk to a fixed width of 2.4 m (equivalent to 1.2 times stretching) by stress relaxation, in the same manner as in Example 1, to obtain a polyvinyl alcohol-based film ( Width 2.4m, thickness 17μm, length 2km). Table 1 shows the properties of the obtained polyvinyl alcohol-based film. Moreover, using this polyvinyl alcohol-type film, it carried out similarly to Example 1, and obtained a polarizing film and a polarizing plate. Although the polyvinyl alcohol-based film of the raw material roll was thin, it did not break in the stretching step during the production of the polarizing film. The properties of the obtained polarizing film are shown in Table 2.

<Comparative Example 1> In Example 1, both ends of the film formed into the film were not held by clamps, and were simply transported in the traveling direction (MD direction) at a speed of 8 m/min while being heated at 120°C. Other than that, it carried out similarly to Example 1, and obtained the polyvinyl alcohol-type film (width 2m, thickness 60 micrometers, length 2km). Table 1 shows the properties of the obtained polyvinyl alcohol-based film. Moreover, using this polyvinyl alcohol-type film, it carried out similarly to Example 1, and obtained a polarizing film and a polarizing plate. The properties of the obtained polarizing film are shown in Table 2.

<Comparative Example 2> In Example 3, both ends of the film formed by film formation were not held by clamps, and were simply transported in the traveling direction (MD direction) at a speed of 8 m/min and heated at 120°C. Other than that, it carried out similarly to Example 3, and obtained the polyvinyl alcohol-type film (width 2m, thickness 20 micrometers, length 2km). Table 1 shows the properties of the obtained polyvinyl alcohol-based film. In addition, the production of a polarizing film was attempted in the same manner as in Example 1 using this polyvinyl alcohol-based film, but fracture occurred during the stretching in the boric acid crosslinking step. Table 2 shows the properties of the leading end portion of the polarizing film obtained.

【Table 1】

【Table 2】

From the results of the above examples and comparative examples, it can be seen that the intersection angle θ(°) and the offset Δθ(°) of the intersection angle θ derived from the alignment axis (slow phase axis) and the width direction (TD direction) are both The feature of the present invention is that the polarizing films of Examples 1 to 4 of the polyvinyl alcohol-based film of 20° or less have a high degree of polarization and no color unevenness. For this, the polarizing films of Comparative Examples 1 and 2 obtained from the polyvinyl alcohol-based films of which the intersection angle θ (°) of the alignment axis (slow axis) and the width direction (TD direction) was 20° or more, the polarized light was The degree of intensity was poor and color unevenness was also observed.

It can also be known that the polyvinyl alcohol-based films of Examples 1 to 4 obtained by the manufacturing method of the present invention have an intersection angle θ (°) in the width direction (TD direction) or in the traveling direction (MD direction). It is stable and fully controls the alignment of the polymer. In addition, it can be seen that from the thin polyvinyl alcohol-based films of Examples 3 and 4, polarizing films with excellent polarization degree and no color unevenness can also be obtained.

The specific form of the present invention has been disclosed in the above-mentioned embodiments, but the above-mentioned embodiments are only illustrative and not intended to be interpreted as limiting. Various changes that are obvious to one of ordinary skill in the art are intended to be included within the scope of the present invention. [industrial applicability]

The polarizing film and polarizing plate using the polyvinyl alcohol-based film of the present invention have excellent polarizing properties and are suitable for use in portable information terminals, personal computers, televisions, projectors, signboards, desktop computers, electronic Clocks, word processors, electronic paper, game consoles, video recorders, cameras, photo albums, thermometers, audio, automotive and mechanical instruments and other liquid crystal display devices, sunglasses, anti-glare glasses, stereo glasses, wearable displays , Anti-reflection layer for display components (CRT, LCD, organic EL, electronic paper, etc.), optical communication equipment, medical equipment, building materials, toys, etc.

Claims (7)

A polyvinyl alcohol-based film having a thickness of 17-55 μm, a width of 2 m or more, and a length of 2 km or more, characterized in that the intersection angle θ (°) between the orientation axis, that is, the retardation axis, and the width direction, that is, the TD direction, is 20° or less , and the offset Δθ(°) of the intersection angle θ is 20° or less; when the refractive index in the width direction, that is, the TD direction, is nx, and the direction at right angles to the TD direction, that is, the refractive index in the MD direction, is ny, The value calculated by the following formula (A), that is, the birefringence ΔNxy is 0.001 or less: (A) ΔNxy=|nx-ny|. For example, the polyvinyl alcohol-based film of the first item of the patent application scope has a thickness of 17-30 μm. A polarizing film is characterized by using the polyvinyl alcohol-based film as claimed in item 1 or 2 of the patent application scope. A polarizing plate is characterized by comprising: a polarizing film as claimed in item 3 of the scope of the patent application; and a protective film disposed on at least one side of the polarizing film. A method for producing a polyvinyl alcohol-based film, which is a method for producing a polyvinyl alcohol-based film as claimed in item 1 or 2 of the scope of the patent application. After the tool is peeled off, it is conveyed in the traveling direction, that is, the MD direction, and is continuously dried and stretched to obtain a polyvinyl alcohol-based film, which is characterized by: the orientation axis of the polyvinyl alcohol-based film, that is, the slow axis and the width. The intersection angle θ(°) of the direction, that is, the TD direction is 20° or less, and the offset Δθ(°) of the intersection angle θ is 20° or less. For example, the manufacturing method of the polyvinyl alcohol-based film of claim 5 of the scope of the application, which is stretched by 1.05 to 1.3 times in the width direction of the film, that is, the TD direction. For the manufacturing method of the polyvinyl alcohol-based film according to claim 5 or 6 of the scope of the patent application, after the film is temporarily stretched by more than 1.3 times in the width direction, that is, the TD direction, the final stretching ratio in the width direction, that is, the TD direction becomes 1.05~1.3 times to shrink its size.