TWI860285B - Polyvinyl alcohol film for producing polarizing film, polarizing film obtained by using the film, and polyvinyl alcohol resin aqueous solution - Google Patents

Abstract

The present invention provides a polyvinyl alcohol film for polarizing film manufacturing, which can reduce the shrinkage in the width direction during the manufacture of polarizing film, that is, can manufacture polarizing film with high width yield. The polyvinyl alcohol film for polarizing film manufacturing has a thickness of 5 to 75 μm, a width of more than 2 m, and a length of more than 2 km. The film has the following characteristics: the expansion X(%) in the width direction after immersion in water at 23.5°C for 5 minutes is 120≦X≦140, and the film width yield W(%) obtained by performing a polarizing film manufacturing test is W≧43.

Description

Polyvinyl alcohol film for producing polarizing film, polarizing film obtained by using the film, and polyvinyl alcohol resin aqueous solution

The present invention relates to a polyvinyl alcohol film which is effective as a raw material roll film when manufacturing a polarizing film. More specifically, it relates to a polyvinyl alcohol film which has a high width yield and is suitable for manufacturing a polarizing film, and a polarizing film obtained using the polyvinyl alcohol film.

In recent years, liquid crystal display devices have developed significantly and are widely used in smartphones, tablet computers, personal computers, LCD TVs, projectors, car panels, etc. Polarizing films are used in these liquid crystal display devices, and polarizing films mainly use films obtained by adsorbing and aligning iodine or dichroic dyes on polyvinyl alcohol-based films. In recent years, with the trend of high-definition, high-brightness, large-scale, and thin screens, there is a demand for a long, thin polarizing film with fewer display defects than conventional products and a wider width.

Polarizing films are produced, for example, by swelling a polyvinyl alcohol film in water (including warm water), dyeing it with iodine, stretching it in the length direction to align iodine molecules, crosslinking it with a crosslinking agent such as boric acid to maintain the stretched state, and then drying it.

Regarding polyvinyl alcohol-based films for manufacturing wide polarizing films, for example, a polyvinyl alcohol-based film has been proposed, which has a width of 3 μm or more, a phase retardation value within the film surface of 30 nm or less, and a phase retardation value shift within the film surface in the film width direction of 15 nm or less (see patent document 1). [Prior art document] [Patent document]

[Patent Document 1] Japanese Patent Application Publication No. 2007-137042

[The problem that the invention wants to solve]

However, although the technology disclosed in the above-mentioned patent document 1 can obtain a polarizing film with a width of more than 3 μm and excellent in-plane uniformity of polarization degree, in the manufacturing step of the polarizing film, before and after the extension in the length direction is implemented, the film is prone to shrinkage (neck shrinkage) in the width direction. Therefore, further improvement is required for manufacturing a polarizing film with a high shrinkage rate and a wide width, that is, for suppressing the shrinkage in the width direction during the manufacturing of the polarizing film at a high level.

Therefore, under such background, the present invention provides a polyvinyl alcohol film for manufacturing polarizing film, which can reduce the shrinkage in the width direction during the manufacturing of polarizing film, that is, it can manufacture polarizing film with high width yield, and provides a polarizing film using the polyvinyl alcohol film and a polyvinyl alcohol resin aqueous solution. [Means for solving the problem]

Afterwards, the inventors of this case conducted in-depth studies in view of the situation and found that when the swelling degree of polyvinyl alcohol-based films with a thickness of 5 to 75 μm, a width of more than 2 m, and a length of more than 2 km falls within a specific range, polarizing films can be manufactured with high width yield.

That is, the first gist of the present invention is a polyvinyl alcohol film for polarizing film manufacturing, which is a polyvinyl alcohol film with a thickness of 5 to 75 μm, a width of more than 2 m, and a length of more than 2 km. After being immersed in water at 23.5°C for 5 minutes, its swelling degree X (%) in the width direction (TD) is 120 ≦ X ≦ 140, and the film width yield W (%) obtained by performing a polarizing film manufacturing test under the following conditions is W ≧ 43. (Polarizing film manufacturing test) A test piece of 120 mm (length direction) × 50 mm (width direction) was cut out, and the distance between the clamps was set to 40 mm in an aqueous solution of 60°C, 40 g/L boric acid concentration, and 35 g/L potassium iodide concentration. The wet uniaxial stretching was performed in the length direction at a stretching speed of 0.09 m/min until the stretching ratio reached 6 times. After that, the film was dried at 80°C for 40 seconds, and the value calculated by the following formula (1) was taken as the film width yield W (%). Film width yield W (%) = (β)/(α) × 100･･･(1) However, in the formula, (α) is the width of the test piece in the center of the clamp before the test, and (β) is the width of the test piece in the center of the clamp after the test.

Furthermore, the second gist of the present invention is a polarizing film obtained by using the polyvinyl alcohol film for polarizing film manufacturing of the first gist. In addition, the third gist of the present invention is a polyvinyl alcohol resin aqueous solution, which is a polyvinyl alcohol resin aqueous solution containing a polyvinyl alcohol resin and a plasticizer, wherein the content of the plasticizer is 0.5 to 5 parts by weight relative to 100 parts by weight of the polyvinyl alcohol resin. [Effect of the invention]

The present invention is a polyvinyl alcohol film for manufacturing polarizing film, which is a polyvinyl alcohol film with a thickness of 5 to 75 μm, a width of more than 2 m, and a length of more than 2 km. After being immersed in water at 23.5° C. for 5 minutes, the swelling degree X (%) in the width direction is 120≦X≦140, and the film width yield W (%) obtained by performing a polarizing film manufacturing test under specific conditions is W≧43. Therefore, the polyvinyl alcohol film for manufacturing polarizing film can manufacture polarizing film with high width yield.

Furthermore, if the swelling degree Y (%) in the longitudinal direction after immersion in water at 23.5°C for 5 minutes is 110≦Y≦140, a polarizing film can be manufactured with a higher width yield.

In addition, if the area swelling rate S (%/second) is 0.2-1.6%/second when immersed in 30°C water for 30 seconds, a polarizing film can be manufactured with a higher width yield.

Moreover, when the water content is 1 to 9 wt %, the polarizing film can be manufactured with a higher width yield.

In addition, when the plasticizer content is 0.5 to 5% by weight, a polarizing film can be produced with a higher width yield.

Furthermore, the polarizing film obtained by using the polyvinyl alcohol-based film for producing the polarizing film of the present invention as described above can produce a polarizing film with high width yield.

The present invention is also a polyvinyl alcohol resin aqueous solution, which is a polyvinyl alcohol resin aqueous solution containing a polyvinyl alcohol resin and a plasticizer, wherein the content of the plasticizer is 0.5 to 5 parts by weight relative to 100 parts by weight of the polyvinyl alcohol resin. Therefore, the polyvinyl alcohol film for polarizing film production produced using the polyvinyl alcohol resin aqueous solution can produce polarizing films with high width yield.

The present invention is described in detail below. The polyvinyl alcohol film for polarizing film manufacturing of the present invention is obtained by film-forming a polyvinyl alcohol resin aqueous solution as a raw material.

As for the polyvinyl alcohol resin contained in the polyvinyl alcohol resin aqueous solution, a resin obtained by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate is generally used. However, as for the polyvinyl alcohol film of the present invention, it is not necessarily limited to this, and a modified polyvinyl alcohol resin obtained by saponifying a copolymer of vinyl acetate and a small amount of a component copolymerizable with vinyl acetate can also be used. Considering the optical performance, the weight average molecular weight of the polyvinyl alcohol resin is preferably 100,000 to 300,000, especially considering the elongation, 110,000 to 280,000 is particularly preferred, and further considering the surface hardness in water, 120,000 to 260,000 is even more preferred. Considering the optical performance, the saponification degree of the polyvinyl alcohol resin is preferably 97 to 100 mol%, preferably 98 to 100 mol%, and even more preferably 99 to 100 mol%.

The polyvinyl alcohol film used in the present invention can be manufactured by casting. As for the specific manufacturing method, for example, a plasticizer and a surfactant are added to the polyvinyl alcohol resin to prepare a polyvinyl alcohol resin aqueous solution (film-making stock solution), the aqueous solution is sprayed and poured on a casting mold such as a casting drum, a casting belt, a casting resin film, etc. to form a film, and then dried, and the two ends are cut and wound on a roll.

Here, the polyvinyl alcohol resin aqueous solution is a polyvinyl alcohol resin aqueous solution containing a polyvinyl alcohol resin and a plasticizer, wherein the content of the plasticizer is preferably 0.5 to 5 parts by weight relative to 100 parts by weight of the polyvinyl alcohol resin. As for the plasticizer, for example: glycerol, diglycerol, triglycerol, ethylene glycol, triethylene glycol, polyethylene glycol, trihydroxymethylpropane, etc. can be listed. They can be used alone or in combination of two or more. Among them, glycerol is more ideal.

Considering the thinness of the polarizing film, the thickness of the polyvinyl alcohol film of the present invention is 5 to 75 μm. Considering the viewpoint of avoiding breakage, it is preferably 20 to 75 μm, and 20 to 60 μm is particularly preferred. In addition, the width of the polyvinyl alcohol film of the present invention is more than 2 m, preferably more than 4 m, considering the viewpoint of large area, more preferably more than 4.5 m, and more preferably 4.5 to 6 m from the viewpoint of avoiding breakage. The length of the polyvinyl alcohol film of the present invention is more than 2 km, preferably more than 4 km, considering the viewpoint of large area, more preferably more than 4.5 km, and more preferably 4.5 to 30 km from the viewpoint of transport weight.

The most significant features of the polyvinyl alcohol-based film for polarizing film manufacturing of the present invention are: the swelling degree X(%) in the width direction after being immersed in water at 23.5°C for 5 minutes is 120≦X≦140, and when the polarizing film manufacturing test is carried out, the film width yield W(%) is W≧43.

First, the expansion X(%) in the width direction of the polyvinyl alcohol film of the present invention after being immersed in water at 23.5°C for 5 minutes must be 120≦X≦140, preferably 122≦X≦138, and particularly preferably 124≦X≦136. If the expansion X(%) is larger than the upper limit, the film will produce wrinkles. If it is too small than the lower limit, the width yield of the film during the manufacture of the polarizing film will be reduced and the purpose of the present invention cannot be achieved. In addition, the above expansion X(%) can be calculated using the following formula. Expansion X(%) = (dimension in the width direction after immersion/dimension in the width direction before immersion) × 100

Then, the width yield of the above polarizing film manufacturing test is explained. As mentioned above, in the manufacturing step of the polarizing film, when the film is stretched in the length direction, it is easy to cause the film to shrink in the width direction, so it is usually advisable to suppress its shrinkage in the width direction. The polarizing film manufacturing test in the present invention is a test for evaluating the shrinkage in the width direction when stretched in the length direction. Specifically, a test piece of 120 mm (length direction) × 50 mm (width direction) is cut from the polyvinyl alcohol film of the present invention, and the distance between the clamps is set to 40 mm in an aqueous solution of 60°C, 40 g/L boric acid concentration, and 35 g/L potassium iodide concentration. The film is wet-uniaxially stretched in the length direction at a stretching speed of 0.09 m/min until the stretching ratio reaches 6 times, and then dried at 80°C for 40 seconds. In addition, the value calculated by the following formula (1) is the film width yield W (%). Film width yield W(%)=(β)/(α)×100･･･(1) However, (α) is the width of the test piece in the center between the clamps before the test, and (β) is the width of the test piece in the center between the clamps after the test.

The film width yield W (%) of the polyvinyl alcohol-based film of the present invention obtained by implementing the above-mentioned polarizing film manufacturing test must be W≧43, preferably W≧43.5, and particularly preferably W≧44. In addition, the upper limit of the width yield W is usually W≦50. If the width yield W of the film does not reach the lower limit, the yield of the polarizing film will deteriorate and the purpose of the present invention cannot be achieved.

As for the methods for controlling the above-mentioned swelling X(%) and width yield W(%), there are: a method of reducing the amount of plasticizer contained in the polyvinyl alcohol film to a smaller amount, a method of increasing the water content of the polyvinyl alcohol film to a higher amount, a method of suppressing the orientation in the width direction (TD) of the film, etc. The swelling X(%) and width yield W(%) can be controlled by using these methods alone or in combination of two or more of these methods. Among them, the method of adjusting the amount of plasticizer contained in the polyvinyl alcohol film is particularly effective.

When the plasticizer content in the polyvinyl alcohol-based film is used to control the swelling degree X(%) and the width yield W(%), the content of the plasticizer is preferably 0.5 to 5% by weight, preferably 1 to 4.5% by weight, and more preferably 2 to 4% by weight. If the content of the plasticizer is too high, the width yield of the film during the manufacture of the polarizing film tends to decrease, and if it is too low, the swelling rate tends to decrease and wrinkles tend to be easily generated.

When the water content in the polyvinyl alcohol film is used to control the swelling rate X(%) and the width yield W(%), the water content is preferably 1 to 9% by weight, preferably 2 to 8% by weight, and more preferably 3 to 7% by weight. If the water content is too high, the width yield of the film during the manufacture of the polarizing film tends to decrease, and if it is too low, the swelling rate tends to decrease and wrinkles tend to occur.

In addition, the expansion degree Y(%) of the polyvinyl alcohol film of the present invention in the longitudinal direction after being immersed in water at 23.5°C for 5 minutes is preferably 110≦Y≦140, 115≦Y≦135 is particularly preferred, and 120≦Y≦130 is even more preferred. If the expansion degree Y(%) is too large, the optical properties tend to be easily reduced, and if it is too low, the film tends to be easily wrinkled. The above expansion degree Y(%) can be calculated using the following formula. Expansion degree Y(%) = (length dimension after immersion/length dimension before immersion) × 100

Furthermore, when the polyvinyl alcohol film of the present invention is immersed in water at 30°C for 30 seconds to swell, the area swelling rate S (%/second) is preferably 0.2-1.6%/second, 0.4-1.4%/second is particularly preferred, and 0.6-1.2%/second is more preferred. When the area swelling rate is too fast, the film tends to easily produce wrinkles. When the area swelling rate is too slow, the polarizing film tends to be insufficiently swelled during the manufacture of the polarizing film, resulting in a deterioration in the yield of the polarizing film. In addition, the above-mentioned area swelling rate S (%/second) can be calculated using the following formula. Area swelling rate S (%/sec) = [Film area after immersion (mm ² ) - Film area before immersion (mm ² )] / [Film area before immersion (mm ² ) × 30 (sec)] × 100

Then, the polarizing film of the present invention is described.

The polarizing film of the present invention is manufactured by unrolling the polyvinyl alcohol film and transporting it horizontally, and then undergoing the steps of swelling, dyeing, boric acid crosslinking, stretching, washing, and drying.

The swelling step is performed before the dyeing step. The swelling step can be used to clean dirt on the surface of the polyvinyl alcohol film. In addition, it also has the effect of preventing uneven dyeing by swelling the polyvinyl alcohol film. In the swelling step, water is usually used as the treatment liquid. If the main component of the treatment liquid is water, a small amount of iodinated compounds, surfactants and other additives, alcohol, etc. can also be added. The temperature of the swelling bath is usually about 10 to 45°C, and the immersion time in the swelling bath is usually about 0.1 to 10 minutes. In addition, stretching operations can be performed during the treatment as needed.

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 preferably 0.1 to 2 g/L, and the concentration of potassium iodide is preferably 1 to 100 g/L. The practical dyeing time is about 30 to 500 seconds. The temperature of the treatment bath is preferably 5 to 50°C. In addition to the aqueous solvent, the aqueous solution may also contain a small amount of an organic solvent that is compatible with water. In addition, an extension operation may be carried out during the treatment as needed.

The boric acid crosslinking step is carried out using boric acid, borax and other boron compounds. The boron compound is used in the form of an aqueous solution or a water-organic solvent mixture at a concentration of about 10 to 100 g/L. It is ideal to allow potassium iodide to coexist in the solution in terms of stabilization of polarization performance. The temperature during the treatment is about 30 to 70°C, and the treatment time is about 0.1 to 20 minutes. In addition, an extension operation can be carried out during the treatment as needed.

The stretching step is to stretch the film 3 to 10 times in a uniaxial direction, preferably 3.5 to 6 times. At this time, it is also OK to stretch it slightly in a direction perpendicular to the stretching direction (to prevent shrinkage in the width direction or more). The temperature during stretching is preferably 30 to 170°C. In addition, the stretching ratio can be set to fall within the above range. The stretching operation is not limited to a single time, and can be implemented at any stage in the manufacturing step.

The above-mentioned cleaning step is implemented, for example, by immersing the polyvinyl alcohol-based film in an aqueous iodide solution such as water or potassium iodide to remove precipitates generated on the surface of the film. When using an aqueous potassium iodide solution, the potassium iodide concentration is about 1 to 80 g/L. The temperature during the cleaning treatment is usually 5 to 50° C., preferably 10 to 45° C. The treatment time is usually 1 to 300 seconds, preferably 10 to 240 seconds. In addition, it can also be appropriately combined with water cleaning and cleaning with an aqueous potassium iodide solution.

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

The polarization degree of the polarizing film produced by the above series of manufacturing steps is preferably 99.5% or more, and more preferably 99.8% or more. If the polarization degree is too low, there is a tendency that the contrast in the liquid crystal display cannot be ensured. In addition, the polarization degree is generally calculated using the light transmittance ( _H11 ) measured at a wavelength λ when two polarizing films are stacked in a manner that their orientation directions are in the same direction, and the light transmittance ( _H1 ) measured at a wavelength λ when two polarizing films are stacked in a manner that their orientation directions are orthogonal to each other, and is calculated using the following formula. Polarization degree = [( _H11 - _H1 )/( _H11 + _H1 )] ^1/2

In addition, the single body transmittance of the polarizing film of the present invention is preferably 42% or more. If the single body transmittance is too low, it will tend to be impossible to achieve high brightness of the liquid crystal display. Single body transmittance is a value obtained by measuring the light transmittance of the polarizing film single body using a spectrophotometer.

In this way, the polarizing film of the present invention can be obtained, and the polarizing film of the present invention is suitable for manufacturing a polarizing plate with less polarization unevenness. The following is an explanation of the manufacturing method of the polarizing plate of the present invention.

The polarizing film of the present invention is a polarizing plate formed by bonding an optically isotropic resin film as a protective film on one or both sides thereof by means of an adhesive. As for the protective film, for example, films or sheets of cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, cycloolefin polymer, cycloolefin copolymer, polystyrene, polyether sulfone, polyarylate, poly-4-methylpentene, polyphenylene oxide, etc. can be cited.

The lamination method is implemented by a known method, for example, after uniformly applying a liquid adhesive composition on the polarizing film, the protective film, or both, the two are laminated and pressed together, and then heated and irradiated with active energy rays.

In order to make the polarizing film thinner, a curable resin such as urethane resin, acrylic resin, urea resin, etc. may be coated on one or both sides of the polarizing film and cured to replace the protective film, thereby forming a polarizing plate.

The polarizing film and polarizing plate obtained according to the present invention are preferably used in portable information terminals, personal computers, televisions, projectors, sign boards, desktop computers, electronic clocks, word processors, electronic paper, game consoles, video cameras, cameras, photo albums, thermometers, stereos, liquid crystal display devices such as automobile or mechanical instruments, sunglasses, anti-glare glasses, stereo glasses, wearable displays, anti-reflection layers for display elements (CRT, LCD, organic EL, electronic paper, etc.), optical communication equipment, medical equipment, building materials, toys, etc. [Example]

The present invention is described in more detail below with reference to the following examples, but the present invention is not limited to the following examples unless the gist thereof is exceeded. In addition, "portions" in the examples refer to weight standards. Each physical property is measured in the following manner.

<Measurement conditions> (1) Water content in film (wt%) A test piece with a width of 100 mm and a length of 100 mm was cut out from the obtained polyvinyl alcohol film, and the water content (wt%) was calculated using the following formula from the weight A (g) before drying and the weight B (g) after drying in a dryer set at an ambient temperature of 105°C for 16 hours. Water content (wt%) = (A-B)/A×100

(2) Amount of plasticizer in the film (wt%) A specimen of 100 mm in width and 100 mm in length was cut from the obtained polyvinyl alcohol film. After drying for 16 hours in a dryer set at an ambient temperature of 105°C, a 1 g specimen was further cut out. 40 mL of methanol was used as a solvent and the plasticizer was extracted using a high-speed solvent extraction device. The obtained extract was concentrated using an evaporator and then diluted to 10 mL using a quantitative bottle. 10 μL of the diluted solution was mixed with 400 μL of trimethylsilyl trifluoroacetamide (MSTFA) in the sample bottle and heated (60°C) to convert the plasticizer into trimethylsilane derivatives. The plasticizer was quantified by subjecting 1 μL of the derivatized solution to gas chromatography/mass spectrometry (GC/MS), and the amount of the plasticizer (wt%) relative to 1 g of the film was calculated from the obtained weight.

(3) Expansion in the width direction X (%), expansion in the length direction Y (%) A film with a width of 100 mm × a length of 100 mm was cut out from the obtained polyvinyl alcohol film, and immersed in water at 23.5°C for 5 minutes to swell. The expansion in the width direction X (%) and the expansion in the length direction Y (%) were calculated according to the following formula based on the dimensions of the film before and after immersion. Expansion X (%) = Dimension in the width direction after immersion (mm) / Dimension in the width direction before immersion (mm) × 100 Expansion Y (%) = Dimension in the length direction after immersion (mm) / Dimension in the length direction before immersion (mm) × 100

(4) Area swelling rate (%/sec) at the initial stage of immersion in water A film of 100 mm in width and 100 mm in length was cut out from the obtained polyvinyl alcohol-based film, and the film was immersed in 30°C water for 30 seconds to allow it to swell. The area swelling rate S (%/sec) at the initial stage of immersion in water was calculated according to the following formula. Area swelling rate S (%/sec) = [film area after immersion (mm ² ) - film area before immersion (mm ² )] / [film area before immersion (mm ² ) × 30 (seconds)] × 100

(5) Film width yield W (%) A test piece of 120 mm (length direction) × 50 mm (width direction) was cut from the obtained polyvinyl alcohol film. The film was placed in an aqueous solution at a temperature of 60°C, a boric acid concentration of 40 g/L, and a potassium iodide concentration of 35 g/L. The distance between the clamps was set to 40 mm. The film was wet-uniaxially stretched in the length direction at a stretching speed of 0.09 m/min until the stretching ratio reached 6 times. The film was then dried at 80°C for 40 seconds. The value calculated by the following formula (1) was taken as the film width yield W (%). Film width yield W(%)=(β)/(α)×100･･･(1) However, (α) is the width of the test piece in the center between the clamps before the test, and (β) is the width of the test piece in the center between the clamps after the test.

In addition, the above tests (1) to (5) were all carried out in an environment with a temperature of 23±1℃ and a relative humidity of 50±5%.

<Example 1> (Preparation of polyvinyl alcohol film) Add 2,000 kg of polyvinyl alcohol resin with a weight average molecular weight of 142,000 and a saponification degree of 99.8 mol%, 5,000 kg of water, and 80 kg of glycerol as a plasticizer (the total blending amount is 4 parts by weight relative to 100 parts by weight of polyvinyl alcohol resin), raise the temperature to 140°C while stirring, and adjust the concentration so that the resin concentration becomes 25% by weight. After uniform dissolution, a polyvinyl alcohol resin aqueous solution is obtained. Then, the polyvinyl alcohol resin aqueous solution is supplied to a double-shaft extruder with ventilation holes and defoamed, and then the aqueous solution temperature is adjusted to 95°C, and the film is formed by spraying from a T-type slot die nozzle (spraying speed 1.9m/min) and casting onto a rotating casting drum. The film is peeled off from the casting drum, and the front and back of the film are alternately contacted with 20 metal heating rollers to dry it, and then the moisture is adjusted. After that, the two ends in the width direction are cut to obtain a polyvinyl alcohol film (water content 2.5% by weight) with a thickness of 60μm, a width of 5m, and a length of 10km. Finally, the polyvinyl alcohol film is wound around a core tube into a roll to obtain a film roll. The properties of the obtained polyvinyl alcohol film are shown in Table 1 below.

(Manufacturing of polarizing film) A rectangular film of 120 mm (length direction) × 50 mm (width direction) was cut from the center of the film roll in the width direction, and mounted on a stretching jig (clamp distance: 40 mm) in such a way that the length direction became the stretching direction. After being immersed in a water tank at a water temperature of 27°C for 100 seconds, it was immersed in an aqueous solution of iodine 0.7 g/L and potassium iodide 25 g/L at a temperature of 27°C for 35 seconds for iodine dyeing. Then, it was immersed in an aqueous solution of boric acid concentration of 40 g/L and potassium iodide concentration of 35 g/L at a temperature of 60°C, while being crosslinked with boric acid, and wet uniaxially stretched in the length direction at a stretching speed of 0.09 m/min until the stretching ratio reached 6 times. Finally, the film was washed by immersion in a 50 g/L potassium iodide aqueous solution at 30°C for 6 seconds and dried at 80°C for 40 seconds to obtain a polarizing film with a total elongation ratio of 6 times. The properties of the obtained polarizing film are shown in Table 1 below.

<Example 2> In Example 1, the water content of the polyvinyl alcohol film was changed to 5.3% by weight, and the polyvinyl alcohol film and polarizing film were obtained in the same manner. The properties of the obtained polyvinyl alcohol film and polarizing film are shown in Table 1 below.

<Example 3> In Example 1, the spraying speed of the polyvinyl alcohol resin aqueous solution was set to 1.4 m/min, thereby changing the thickness of the polyvinyl alcohol film to 45 μm and the water content to 6.1% by weight. In the same manner, a polyvinyl alcohol film and a polarizing film were obtained. The properties of the obtained polarizing film are shown in Table 1 below.

<Comparative Example 1> In Example 1, the amount of plasticizer blended was changed to 240 kg of glycerol (the total blending amount was 12 parts by weight relative to 100 parts by weight of polyvinyl alcohol resin), and the water content of the polyvinyl alcohol film was changed to 2.8% by weight. The same method was followed to obtain a polyvinyl alcohol film and a polarizing film. The properties of the obtained polyvinyl alcohol film and polarizing film are shown in Table 1 below.

[Table 1]

It can be seen from the polyvinyl alcohol films of Examples 1 to 3 that polarizing films can be obtained with high width yield during polarizing film manufacturing. In contrast, the polyvinyl alcohol film of Comparative Example 1, whose expansion (X) in the width direction falls outside the specific range of the present invention, has a low width yield during polarizing film manufacturing.

The above embodiments have disclosed the specific forms of the present invention, but the above embodiments are merely illustrative and are not intended to be limiting. Various changes that are obvious to those with ordinary knowledge in the technical field are intended to be included in the scope of the present invention. [Industrial Applicability]

The polarizing film obtained from the optical polyvinyl alcohol-based film for polarizing film manufacturing of the present invention is preferably used in desktop computers, electronic clocks, word processors, personal computers, portable information terminals, LCD TVs, projectors, sign boards, game consoles, liquid crystal display devices such as automobile or mechanical instruments, sunglasses, goggles, stereoscopic glasses, reflection reducing layers for display elements (CRT, LCD, organic EL, electronic paper, etc.), medical equipment, optical communication equipment, building materials, toys, etc.

Claims (5)

A polyvinyl alcohol film for polarizing film manufacturing, which is a polyvinyl alcohol film with a thickness of 5 to 75 μm, a width of more than 2 m, and a length of more than 2 km, and is characterized by: a plasticizer content of 0.5 to 5% by weight, a swelling degree X (%) in the width direction after immersion in 23.5°C water for 5 minutes of 120 ≦ X ≦ 140, and a film width yield W (%) obtained by performing a polarizing film manufacturing test under the following conditions is W ≧ 43; (Polarizing film manufacturing test) a test piece of 120 mm (length direction) × 50 mm (width direction) is cut out and heated at a temperature of 60°C. , boric acid concentration of 40g/L, potassium iodide concentration of 35g/L, the distance between the clamps was set to 40mm, and wet uniaxial stretching was performed along the length direction at a stretching speed of 0.09m/min until the stretching ratio reached 6 times, and then dried at 80℃ for 40 seconds, and the value calculated by the following formula (1) was taken as the film width yield W(%); Film width yield W(%) = (β)/(α)×100…(1) However, in the formula, (α) is the width of the test piece in the center of the clamp before the test, and (β) is the width of the test piece in the center of the clamp after the test. For example, the polyvinyl alcohol film for polarizing film manufacturing in item 1 of the patent application, wherein the swelling degree Y (%) in the longitudinal direction after being immersed in water at 23.5°C for 5 minutes is 110≦Y≦140. For example, the polyvinyl alcohol film for polarizing film manufacturing in item 1 or 2 of the patent application scope, wherein the area swelling rate S (%/second) when it is immersed in 30°C water for 30 seconds to make it swell is 0.2~1.6%/second. For example, the polyvinyl alcohol film for manufacturing polarizing film in the patent application scope 1 or 2, wherein the water content is 1 to 9% by weight. A polarizing film, characterized in that it is obtained by using a polyvinyl alcohol-based film for manufacturing a polarizing film as described in any one of items 1 to 4 of the patent application scope.