TWI468454B - Polyvinyl alcohol film - Google Patents

Description

Polyvinyl alcohol film

The present invention relates to a polyvinyl alcohol film which can be used as a raw material of a polarizing film excellent in polarizing performance.

In the early days of development, liquid crystal display devices (LCDs) were used in small computers such as electronic computers and watches. In recent years, they have been widely used in notebook computers, LCD screens, liquid crystal color projectors, LCD TVs, navigation systems for vehicles, and mobile phones. Telephone, indoor and outdoor measurement machines, etc. On the other hand, particularly in applications such as liquid crystal televisions, improvement in display quality, such as improvement in contrast, and increasing demand, there is a strong demand for an increase in polarization performance for a polarizing plate of one of LCD parts.

Conventionally, a polarizing plate generally used has a green film material (hereinafter referred to as PVA), and is subjected to uniaxial stretching, dyeing treatment using iodine or a dichroic dye, fixing treatment with a boron compound, and the like. A protective film such as a cellulose triacetate film or a cellulose acetate butyrate film is adhered to one side or both sides of the obtained polarizing film. In order to improve the polarizing performance of such a polarizing plate, various methods such as a method of improving the structure of the raw material PVA, a method of controlling the physical properties of the PVA film, and a method of designing the manufacturing conditions of the polarizing plate have been proposed, which contribute to the improvement of the contrast of the LCD.

For example, Patent Document 1 discloses a polarizing film formed of PVA having a polymerization degree of 2,500 or more, preferably 6,000 to 10,000, and is excellent in optical characteristics. The use of a high degree of polymerization of PVA is an effective means of improving the polarization performance, but it is not easy to industrially operate.

In addition, as another method of improving the polarizing performance, for example, Patent Document 2 discloses that the film-forming material is a polarizing film of a PVA-based film having a relationship between a complete dissolution temperature (X) and a balanced swelling degree (Y) in hot water. Production method.

Y>-0.0667X+6.73 ........(I)

X≧65 ........(II)

However, the degree of polymerization of the PVA used in the above invention is preferably in the range of 3,500 to 5,000, and even if this manufacturing method is directly applied to the high polymerization degree PVA, the polarizing performance of the obtained polarizing film is as described in the comparative example described later. insufficient. That is, when a polarizing film formed of a high polymerization degree PVA is produced by an industrial method, information on the structure of the PVA, the physical properties of the PVA film, and the like must be considered in an all-round manner, and the most suitable raw material conditions can be found.

Prior technical literature

Patent Document 1 JP-A-10-15204

Patent Document 2 Japanese Patent Publication No. 7-120616

SUMMARY OF THE INVENTION An object of the present invention is to provide a film formed of a high degree of polymerization PVA which can be used as a raw material for producing a polarizing film having high polarizing properties.

The present inventors have conducted research to find information on the physical properties of the PVA structure and the PVA film as much as possible. As a result, it was found that a PVA film having a degree of polymerization of 5,100 to 10,000 was formed, and the degree of swelling was 200 to 240%, and the PVA film having a retardation value of 10 to 40 nm in the central portion in the width direction satisfied the above object, and finally completed the present invention. .

At this time, the degree of saponification of the PVA is preferably 98 mol% or more.

The thickness of the PVA film is preferably from 10 to 120 μm.

The present invention also includes a method for producing the PVA film which is formed by using a film forming raw material of PVA having a degree of polymerization of 5,100 to 10,000 and water as a raw material.

The present invention further comprises a polarizing film obtained by dyeing and stretching the above PVA film.

The PVA film of the present invention can be used as a raw material of a polarizing film which is excellent in polarizing performance. The polarizing film obtained can be effectively used for manufacturing liquid crystals such as electronic computers, watches, notebook computers, liquid crystal screens, liquid crystal color projectors, liquid crystal televisions, navigation systems for vehicles, mobile phones, and indoor and outdoor measuring devices. A polarizing plate that constitutes a component of the device.

Form of implementing the invention

Hereinafter, the present invention will be described in detail.

The degree of polymerization of the PVA used in the present invention is preferably from 5100 to 10,000, preferably from 5,200 to 9,500, and particularly preferably from 5,400 to 9,200, in order to achieve good polarizing properties of the polarizing film for the purpose of the present invention. When the degree of polymerization of PVA is less than 5,100, when a polarizing film is produced, it is difficult to have high polarizing performance. On the other hand, if the degree of polymerization of PVA exceeds 10,000, the productivity of PVA is lowered. The degree of polymerization of PVA in the present invention means the degree of polymerization (viscosity average degree of polymerization) measured by the method of the examples described later.

Further, the degree of saponification of PVA is preferably 98 mol% or more, more preferably 99 mol% or more, particularly preferably 99.5 mol% or more, and most preferably 99.8 mol% or more. When the degree of saponification of PVA is less than 98 mol%, in the production process of a polarizing film, PVA is easily eluted, and the eluted PVA adheres to the film, which may reduce the performance of the polarizing film.

The PVA used in the present invention can be obtained by saponifying a polyvinyl ester polymer obtained by polymerizing a vinyl ester. Vinyl esters such as vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, trimethyl vinyl acetate, vinyl versatate, vinyl laurate, vinyl stearate, vinyl benzoate, etc. One or two or more kinds are selected from them. From the viewpoints of ease of availability, ease of PVA production, cost, and the like, it is preferred to use vinyl acetate. The polymerization temperature is not particularly limited. When methanol is used as the polymerization solvent, the polymerization temperature is preferably about 60 ° C near the boiling point of methanol.

The saponification of the homopolymer of the vinyl ester is not limited insofar as it does not impair the effects of the present invention. For example, an unsaturated carboxylic acid or a derivative thereof, an unsaturated sulfonic acid or a derivative thereof, an α-olefin having 2 to 30 carbon atoms, or the like, graft-polymerized to a modified PVA of PVA at a ratio of less than 5 mol%; Saponification of modified polyvinyl esters copolymerized with esters and unsaturated carboxylic acids or derivatives thereof, unsaturated sulfonic acids or derivatives thereof, α-olefins having 2 to 30 carbon atoms, etc., copolymerized at a ratio of less than 15 mol% A polyvinyl acetal polymer which is crosslinked with a partial hydroxyl group of PVA by an aldehyde such as formalin, butyraldehyde or benzaldehyde.

The PVA film of the present invention was obtained by forming the above PVA. Film-forming method In addition to the method of melt-extruding aqueous PVA, a cast film forming method, a wet film forming method (released in a weak solvent), and a gel film forming method (such as a PVA aqueous solution temporarily cooling a gel) may be employed. After the removal, the solvent is removed, the casting film forming method (the PVA aqueous solution is allowed to flow on the substrate, and dried), a combination thereof, and the like. Among them, the melt extrusion film forming method and the casting film forming method are suitable because an excellent PVA film can be obtained. Water is preferably used as the solvent for film formation.

The volatile matter ratio of the film forming stock solution mainly formed of PVA and a solvent varies depending on the molecular weight of the film forming method or PVA, preferably 50 to 95% by mass, more preferably 60 to 95% by mass, and particularly preferably 70. ~95% by mass. If the volatile content is less than 50% by mass, the viscosity of the film forming solution is too high, and it is difficult to filter or defoam during film formation, and it is not easy to obtain a PVA film free from foreign matter or defects. If the volatile content exceeds 95% by mass, the viscosity of the film forming solution is too low, and it is difficult to obtain a PVA film having a target thickness and high thickness precision.

When the PVA film of the present invention is produced, a plasticizer can also be used. Plasticizers such as glycerin, diglycerin, ethylene glycol and the like are not limited thereto. The amount of the plasticizer to be used is also not particularly limited, and is usually in the range of 10 to 15 parts by mass based on 100 parts by mass of the PVA.

The drying method of the PVA film after film formation is, for example, drying by hot air, contact drying using a hot roll, drying by an infrared heater, or the like. One of the methods may be used alone or two or more types may be used in combination. The drying temperature is not particularly limited, and is preferably in the range of 50 to 70 °C. Moreover, the drying time at this time is about 45 to 75 minutes depending on the concentration of the film forming solution or the film forming conditions.

After the dried PVA film is conditioned and the moisture content (water content) is adjusted, only the two parallel sides of the film, preferably only the two sides in the width direction, are fixed by heat treatment in the range of 100 to 140 ° C. A stress is generated accompanying the decrease in moisture, and a stable extension of the film can be imparted. Thereby, the film can be stably provided with a low degree of retardation value to be described later. The moisture content of the film at this time is preferably from 1 to 15% by mass, more preferably from 1 to 10% by mass, even more preferably from 2 to 6% by mass. The heat treatment time is not particularly limited and varies depending on the heat treatment temperature, and is within about 5 minutes.

The thickness of the PVA film of the present invention thus obtained is preferably from 10 to 120 μm, more preferably from 12 to 80 μm, still more preferably from 15 to 75 μm, most preferably from 20 to 60 μm. If the thickness is less than 10 μm, there is a fear that the film is liable to be broken in the stretching step described later. When the thickness exceeds 120 μm, the stress of the film during stretching is too large, and it is difficult to sufficiently extend.

The swelling degree of the PVA film of the present invention must be 200 to 240%, preferably 205 to 235%, and particularly preferably 210 to 230%. When the degree of swelling is less than 200%, the tension at the time of stretching is too large, and it is difficult to sufficiently extend. When the degree of swelling exceeds 240%, the water absorbing property is high, and in the production process of the polarizing film to be described later, the film is liable to wrinkle or curl at the edge, that is, cause cracking during stretching. In order to control the degree of swelling within a predetermined range, for example, the heat treatment temperature or time of the PVA film after film formation can be adjusted within the above range. The degree of swelling of the PVA film can be measured by the method described later in the examples.

In the PVA film of the present invention, the retardation value in the central portion in the width direction must be 10 to 40 nm, more preferably 13 to 37 nm, still more preferably 17 to 33 nm, and most preferably 20 to 30 nm. If the retardation value is less than 10 nm, the dyeing speed at the time of manufacturing the polarizing film becomes slow, so that staining tends to occur. If the retardation value exceeds 40 nm, the film breaks even at a low stretching ratio. The retardation value of the PVA film can be measured by a method described later in the examples.

In order to control the retardation value of the PVA film to a predetermined range, in addition to the above-described method of heat-treating the PVA film and then heat-treating it, for example, a method of extending the PVA film by a known method is not limited thereto. From the viewpoint of fixing the retardation value that has occurred, it is preferable to use a method of heat treatment after conditioning. At this time, it is an important step to fix only the two parallel sides of the PVA film, preferably only the two sides in the width direction, and perform heat treatment. Heating is not fixed or the four corners are fixed, so that the stress of the film is equal, and no retardation occurs, and the object cannot be achieved.

Next, a method of producing a polarizing film using the PVA film material of the present invention will be described. The manufacturing steps of the polarizing film include steps of moisture adjustment, dyeing, stretching, color adjustment, and the like. At this time, it is preferred to carry out the wet stretching of the film. Further, after the wet stretching step, the obtained stretched film may be further extended in an aqueous boric acid solution. The polarizing film can be obtained by color adjustment and drying in an aqueous solution containing boric acid and potassium iodide according to requirements.

The moisture adjustment of the PVA film is preferably carried out by immersing in pure water or distilled water. The temperature at this time is preferably 20 to 40 ° C, more preferably 25 to 35 ° C, and particularly preferably 27 to 33 ° C. If the temperature is lower than 20 ° C, the water content of the green film material is lowered, and the tension of the film after the elongation is increased, and the polarizing performance of the obtained polarizing film is lowered. If the temperature exceeds 40 ° C, the water absorption of the green film material is improved, and in the subsequent step, the film is liable to wrinkle or edge curl, which is the cause of cracking during stretching. On the other hand, the time for impregnating the green film material is in the range of about 30 to 120 seconds.

The dyeing of the PVA film is carried out, for example, in an aqueous solution of iodine-potassium iodide. In this case, the iodine concentration is preferably 0.01 to 0.1% by mass, the potassium iodide concentration is preferably 1 to 10% by mass, the iodine concentration is more preferably 0.02 to 0.08% by mass, and the potassium iodide concentration is more preferably 2 to 8% by mass. The concentration is particularly preferably 0.03 to 0.06 mass%, and the potassium iodide concentration is preferably 3 to 6 mass%. The temperature of the aqueous solution is not particularly limited, and is preferably 25 to 40 °C.

The wet stretching of the PVA film material may be carried out in addition to the above steps of moisture adjustment or dyeing, but it is preferably carried out in the water for water conditioning or the aqueous solution for dyeing, because the efficiency is better, especially It is carried out in an aqueous solution for dyeing, that is, an aqueous solution of iodine-potassium iodide. The wet stretching of the PVA film material is preferably 2.0 to 2.9 times, more preferably 2.2 to 2.8 times, and particularly preferably 2.4 to 2.8 times, in terms of the stretching ratio of the film length ratio before and after stretching.

The temperature at which the PVA film is wet-stretched is preferably from 20 to 40 ° C, more preferably from 25 to 40 ° C, and particularly preferably from 25 to 35 ° C, from the viewpoint of obtaining a polarizing film having better polarizing performance. The best is 27~33 °C.

As described above, after the step of wet stretching the PVA film, the obtained stretched film may be further extended in an aqueous boric acid solution. The stretching ratio at this time is preferably 3 times or less, more preferably 1.2 to 3 times, particularly preferably 1.3 to 2.9 times, and most preferably 1.4 to 2.8 times.

The concentration of boric acid in the aqueous solution at this time is preferably 2 to 6% by mass, more preferably 2 to 5% by mass, and particularly preferably 2 to 4% by mass. If the concentration of boric acid is less than 2% by mass, the color unevenness of the obtained polarizing film increases. When the concentration of boric acid exceeds 6% by mass, the crosslinking of PVA due to boric acid is excessive, and it is difficult to stretch the film at a high magnification.

In order to make the hue of the polarizing film close to achromatic (neutral gray), it is preferred to add potassium iodide to the aqueous boric acid solution. The concentration of potassium iodide is preferably from 3 to 10% by mass, particularly preferably from 4 to 8% by mass. If the potassium iodide concentration is less than 3% by mass, the obtained polarizing film is bluish. On the other hand, if the potassium iodide concentration exceeds 10% by mass, the obtained polarizing film is reddish. The aqueous boric acid solution may also contain other components such as metal compounds such as iron and zirconium.

In the above extension, the temperature of the aqueous solution is not particularly limited, but is preferably 50 to 60 ° C, more preferably 55 to 60 ° C, and particularly preferably 57 to 60 ° C. If the extension temperature is lower than 50 ° C, the elongation cannot be sufficiently extended, and the degree of polarization of the obtained polarizing film is lowered. When the extension temperature exceeds 60 ° C, the transmittance of the obtained polarizing film is lowered.

The stretching ratio of all the steps is preferably 4.5 to 7.0 times, more preferably 4.7 to 6.5 times, and particularly preferably 5.0 to 6.0 times. If the stretching ratio is less than 4.5 times, the polarizing performance of the obtained polarizing film is lowered. If the stretching ratio exceeds 7.0 times, the film is often broken during stretching, and it is difficult to stably produce a polarizing film.

The color adjustment after stretching is preferably carried out in an aqueous solution containing boric acid and potassium iodide. At this time, a metal compound such as zinc chloride or zinc iodide may be added to the aqueous solution. In order to prevent the deterioration of the polarizing performance, the temperature of the aqueous solution is preferably lower than the stretching temperature, and specifically, it is preferably 20 to 50 ° C, particularly preferably 30 to 40 ° C. There is no particular limitation on the timing of color adjustment.

The drying of the obtained polarizing film can be carried out by a batch, a continuous connection, a continuous roll contact method or the like using various dryers. In order to prevent iodine sublimation in the polarizing film and to suppress the desorption reaction of boric acid cross-linked with PVA, the drying temperature is preferably 40 to 80 ° C, more preferably 45 to 70 ° C, and particularly preferably 50 to 60 ° C. The drying time is not particularly limited and varies depending on the apparatus or drying temperature, for example, in the range of 3 to 6 minutes.

Example

Hereinafter, the present invention will be specifically described by way of Examples and the like, but the present invention is not limited to the following examples. In the examples, the viscosity average degree of polymerization P of PVA, the degree of swelling of the PVA film, the retardation value Re of the PVA film, the transmittance Y of the polarizing film, and the degree of polarization V were evaluated by the following methods.

(1) Determination of viscosity average degree of polymerization P of PVA

0.28 g of PVA, 70 g of distilled water and a stir bar were placed in a 100 mL co-embossed glass Erlenmeyer flask. The above-mentioned triangular flask to be stoppered was immersed in a 95 ° C constant temperature bath, and PVA was dissolved while stirring with a stirrer to prepare a 0.4% PVA aqueous solution. The PVA aqueous solution was filtered through a Buchner funnel-shaped glass filter 3G, and cooled in a constant temperature water bath at 30 ° C to obtain a test piece for measuring the degree of polymerization. The reference test strain was placed in another 100 mL co-embossed glass Erlenmeyer flask, and 70 g of distilled water was placed and a plug was placed, and the mixture was immersed in a constant temperature water bath at 30 °C.

The evaporating dish which had been heated in a dryer at 105 ° C for 1 hour was placed in a desiccator and cooled for 30 minutes, and the mass a (g) of the evaporating dish was measured. 10 mL of the test piece for measuring the degree of polymerization was transferred to the evaporating dish by a graduated pipette, and dried in a drier at 105 ° C for 16 hours, and then cooled in a drier for 30 minutes to measure the mass b (g). The concentration c (g/L) of the test article for measuring the degree of polymerization was calculated based on the following formula.

c=1000×(b-a)/10

The test piece for measuring the degree of polymerization or distilled water was placed in an Osmometer using a 10 mL graduated pipette and allowed to stand in a constant temperature water bath at 30 ° C for 15 minutes. The number of seconds t ₁ (s) of the test product for measuring the degree of polymerization to be measured and the number of seconds t ₀ (s) of the distilled water were measured, and the viscosity average degree of polymerization P was calculated according to the following formula.

η _r =t ₁ /t ₀

[η]=2.303×Log(η _r /c)

Log(P)=1.613×Log([η]×10 ⁴ /8.29)

(2) Determination of the swelling degree of PVA film

The PVA film was cut into 5 cm × 5 cm, and immersed in 1 L of distilled water at 30 ° C for 4 hours. The PVA film was taken out from the distilled water and sandwiched between two sheets of filter paper to absorb water droplets, and the mass D was measured. It was dried in a dryer at 105 ° C for 16 hours and then cooled in a desiccator for 30 minutes to measure the mass E. The degree of swelling of the PVA film was calculated according to the following formula.

A=100×D/E(%)

(3) Determination of swelling degree of PVA film

A rectangular test piece having a width of 5 cm in the width direction and a moving direction of 10 cm was taken out from the center of the PVA film, and the retardation value Re at a measurement wavelength of 550 nm was measured using an optical material inspection device RETS-1100 manufactured by Otsuka Electronics Co., Ltd.

(4) Determination of transmittance Y of polarizing film

From the center of the width direction of the polarizing film, two square test pieces of 4 cm in the extending direction and 4 cm in the width direction were used, and a spectrophotometer U-4100 (with an integrating sphere) manufactured by Hitachi, Ltd. was used, in accordance with JIS Z 8722 (object Color measurement method), for the carbon light source, the visibility correction in the visible light region of the 2° field of view, and one polarizing film test product is measured when the light transmittance is inclined at 45° with respect to the direction of the extension axis and when tilted at −45° The light transmittance is calculated as the average value Y1 (%). The other polarizing film test article was also subjected to the same method of measuring the light transmittance at a 45° tilt and the light transmittance at a -45° tilt, and the average value Y2 (%) was obtained. According to the following formula, Y1 and Y2 are averaged as the transmittance Y (%) of the polarizing film.

Y=(Y1+Y2)/2

(5) Determination of the degree of polarization V of the polarizing film

In the same manner as (4) the transmittance of the two polarizing films taken in the above (4), the light transmittance Y y (%) when the extending directions are parallel and overlapped, and the light transmittance Y when the extending directions are vertical and overlapped are measured. ⊥ (%), the degree of polarization V (%) was determined according to the following formula.

V={(Y∥-Y⊥)/(Y∥+Y⊥)} ^1/2 ×100

(Example 1)

100 parts by mass of PVA having a degree of polymerization of 5800 and a degree of saponification of 99.8 mol%, and a 5.5% by mass of a PVA aqueous solution of 12 parts by mass of glycerin as a plasticizer were cast on a metal roll at 60 ° C and dried for 60 minutes to obtain a thickness of 40 μm. PVA film. The film was conditioned at 26 ° C, 20% RH for 16 hours, and after adjusting the water content to 3% by mass, the two ends of the film width direction were fixed to the two sides of the metal frame so that the width direction of the film did not shrink. And heat-treated at 120 ° C for 3 minutes. The degree of swelling of the PVA film after heat treatment was measured by the method of the above (2), and it was 230%. Further, the retardation value of the PVA film was measured by the method of the above (3), and it was 29 nm.

Next, the PVA film was cut into a flow direction of 11 cm × 10 cm in the width direction, and the flow direction was attached to a stretching jig of 4 cm between the chucks in the extending direction, and immersed in pure water at 30 ° C for 1 minute, followed by immersion in a mass of 0.03. The iodine of 3%, 3% by mass of potassium iodide (temperature: 30 ° C) was extended 2.6 times at a rate of 0.13 m/min to adsorb iodine.

Next, the stretched film was immersed in an extension liquid (temperature: 57.5 ° C) containing 4% by mass of boric acid and 6% by mass of potassium iodide, and extended 2.3 times at a rate of 0.13 m/min, and then fixed in the extending direction and dried at 50 ° C. A polarizing film was obtained in 4 minutes. According to the methods (4) and (5) above, the transmittance and the degree of polarization of the polarizing film were measured, and as a result, they were 44.0% and 99.99%, respectively, and a polarizing film having good polarizing performance was obtained.

(Example 2)

100 parts by mass of PVA containing a polymerization degree of 5800 and a degree of saponification of 99.8 mol%, and a 5.5% by mass PVA aqueous solution of 12 parts by mass of glycerin as a plasticizer were cast on a metal roll at 60 ° C and dried for 60 minutes to obtain a thickness of 40 μm. PVA film. The film was conditioned at 26 ° C, 20% RH for 16 hours, and after adjusting the water content to 3% by mass, the two ends of the film width direction were fixed to the two sides of the metal frame so that the width direction of the film did not shrink. And heat-treated at 115 ° C for 3 minutes. The degree of swelling of the PVA film after heat treatment was measured by the method of the above (2), and it was 240%. Further, the retardation value of the PVA film was measured by the method of the above (3), and it was 26 nm.

Next, in the same manner as in Example 1, while stretching the PVA film, iodine was adsorbed and further extended to obtain a polarizing film. According to the methods (4) and (5) above, the transmittance and the degree of polarization of the polarizing film were measured, and as a result, they were 44.0% and 99.96%, respectively, and a polarizing film having good polarizing performance was obtained.

(Example 3)

100 parts by mass of PVA containing a degree of polymerization of 9100 and a degree of saponification of 99.8 mol%, and a 5.5% by mass of a PVA aqueous solution of 12 parts by mass of glycerin as a plasticizer were cast on a metal roll at 60 ° C and dried for 60 minutes to obtain a thickness of 20 μm. PVA film. The film was conditioned at 26 ° C, 20% RH for 16 hours, and after adjusting the water content to 3% by mass, the two ends of the film width direction were fixed to the two sides of the metal frame so that the width direction of the film did not shrink. And heat treated at 110 ° C for 3 minutes. The degree of swelling of the PVA film after heat treatment was measured by the method of the above (2), and it was 230%. Further, the retardation value of the PVA film was measured by the method of the above (3), and it was 39 nm.

Next, in the same manner as in Example 1, except that the stretching ratio was 2.5 times, the PVA film was stretched, and iodine was adsorbed, and further extended to obtain a polarizing film. According to the methods (4) and (5) above, the transmittance and the degree of polarization of the polarizing film were measured, and as a result, they were 44.0% and 99.95%, respectively, and a polarizing film having good polarizing performance was obtained.

(Example 4)

100 parts by mass of PVA containing a degree of polymerization of 5200 and a degree of saponification of 99.8 mol%, and a 5.5% by mass of a PVA aqueous solution of 12 parts by mass of glycerin as a plasticizer were cast on a metal roll at 60 ° C and dried for 60 minutes to obtain a thickness of 40 μm. PVA film. The film was conditioned at 26 ° C, 20% RH for 16 hours, and after adjusting the water content to 3% by mass, the two ends of the film width direction were fixed to the two sides of the metal frame so that the width direction of the film did not shrink. And heat treated at 135 ° C for 3 minutes. The degree of swelling of the PVA film after heat treatment was measured by the method of the above (2), and it was 205%. Further, the retardation value of the PVA film was measured by the method of the above (3), and it was 29 nm.

Next, in the same manner as in Example 3, while the PVA film was stretched, iodine was adsorbed and further extended to obtain a polarizing film. According to the methods (4) and (5) above, the transmittance and the degree of polarization of the polarizing film were measured, and as a result, they were 44.0% and 99.95%, respectively, and a polarizing film having good polarizing performance was obtained.

(Example 5)

100 parts by mass of PVA having a polymerization degree of 5,500, a degree of saponification of 99.8 mol%, and a 5.5% by mass PVA aqueous solution of 12 parts by mass of glycerin as a plasticizer were cast on a metal roll at 60 ° C, and dried for 60 minutes to obtain a thickness of 30 μm. PVA film. The film was conditioned at 26 ° C, 20% RH for 16 hours, and after adjusting the water content to 3% by mass, the two ends of the film width direction were fixed to the two sides of the metal frame so that the width direction of the film did not shrink. And heat-treated at 130 ° C for 3 minutes. The degree of swelling of the PVA film after heat treatment was measured by the method of the above (2), and it was 215%. Further, the retardation value of the PVA film was measured by the method of the above (3), and it was 29 nm.

Next, in the same manner as in Example 1, while stretching the PVA film, iodine was adsorbed and further extended to obtain a polarizing film. According to the methods (4) and (5) above, the transmittance and the degree of polarization of the polarizing film were measured, and as a result, they were 44.0% and 99.99%, respectively, and a polarizing film having good polarizing performance was obtained.

(Comparative Example 1)

100 parts by mass of PVA containing a polymerization degree of 4800, a degree of saponification of 99.8 mol%, and a 6.5 mass% PVA aqueous solution of 12 parts by mass of glycerin as a plasticizer were cast on a metal roll at 60 ° C, and dried for 60 minutes to obtain a thickness of 40 μm. PVA film. The film was conditioned at 26 ° C, 20% RH for 16 hours, and after adjusting the water content to 3% by mass, the two ends of the film width direction were fixed to the two sides of the metal frame so that the width direction of the film did not shrink. And heat-treated at 120 ° C for 3 minutes. The degree of swelling of the PVA film after heat treatment was measured by the method of the above (2), and it was 220%. Further, the retardation value of the PVA film was measured by the method of the above (3), and it was 28 nm.

Next, in the same manner as in Example 1, except that the stretching ratio was 2.7 times, the PVA film was stretched, and iodine was adsorbed, and further extended to obtain a polarizing film. According to the methods (4) and (5) above, the transmittance and the degree of polarization of the polarizing film were measured, and the results were 44.0% and 99.92%, respectively, and the polarizing degree of the polarizing film was slightly insufficient.

(Comparative Example 2)

100 parts by mass of PVA having a degree of polymerization of 5800 and a degree of saponification of 99.8 mol%, and a 5.5% by mass of a PVA aqueous solution of 12 parts by mass of glycerin as a plasticizer were cast on a metal roll at 60 ° C and dried for 60 minutes to obtain a thickness of 40 μm. PVA film. The film was conditioned at 26 ° C, 20% RH for 16 hours, and after adjusting the water content to 3% by mass, the two ends of the film width direction were fixed to the two sides of the metal frame so that the width direction of the film did not shrink. And heat-treated at 140 ° C for 3 minutes. The degree of swelling of the PVA film after heat treatment was measured by the method of the above (2), and it was 195%. Further, the retardation value of the PVA film was measured by the method of the above (3), and it was 29 nm.

Next, in the same manner as in Example 1, while stretching the PVA film, iodine was adsorbed and further extended to obtain a polarizing film. According to the methods (4) and (5) above, the transmittance and the degree of polarization of the polarizing film were measured, and the results were 44.0% and 99.92%, respectively, and the polarizing degree of the polarizing film was slightly insufficient.

(Comparative Example 3)

100 parts by mass of PVA having a degree of polymerization of 5800 and a degree of saponification of 99.8 mol%, and a 5.5% by mass of a PVA aqueous solution of 12 parts by mass of glycerin as a plasticizer were cast on a metal roll at 60 ° C and dried for 60 minutes to obtain a thickness of 40 μm. PVA film. The film was conditioned at 26 ° C, 20% RH for 16 hours, and after adjusting the water content to 3% by mass, the two ends of the film width direction were fixed to the two sides of the metal frame so that the width direction of the film did not shrink. And heat treated at 110 ° C for 3 minutes. The degree of swelling of the PVA film after heat treatment was measured by the method of the above (2), and it was 250%. Further, the retardation value of the PVA film was measured by the method of the above (3), and it was 28 nm.

Next, in the same manner as in Example 1, while stretching the PVA film, iodine was adsorbed and further extended to obtain a polarizing film. According to the methods (4) and (5) above, the transmittance and the degree of polarization of the polarizing film were measured, and the results were 44.0% and 98.77%, respectively, and the polarizing degree of the polarizing film was slightly insufficient.

(Comparative Example 4)

100 parts by mass of PVA having a degree of polymerization of 5800 and a degree of saponification of 99.8 mol%, and a 5.5% by mass of a PVA aqueous solution of 12 parts by mass of glycerin as a plasticizer were cast on a metal roll at 60 ° C and dried for 60 minutes to obtain a thickness of 40 μm. PVA film. The film was conditioned at 26 ° C and 20% RH for 16 hours, adjusted to a moisture content of 3% by mass, and fixed to all four sides of the metal frame, and heat-treated at 120 ° C for 3 minutes. The degree of swelling of the PVA film after heat treatment was measured by the method of the above (2), and it was 230%. Further, the retardation value of the PVA film was measured by the method of the above (3), and it was 5 nm.

Next, in the same manner as in Example 1, while stretching the PVA film, iodine was adsorbed and further extended to obtain a polarizing film. According to the methods (4) and (5) above, the transmittance and the degree of polarization of the polarizing film were measured, and the results were 44.0% and 99.97%, respectively. Although the polarizing performance was good, only the polarizing film was perpendicular, and a large angle was observed. Stained spots.

(Comparative Example 5)

100 parts by mass of PVA containing a polymerization degree of 5800 and a degree of saponification of 99.8 mol%, and a 5.5% by mass PVA aqueous solution of 12 parts by mass of glycerin as a plasticizer were cast on a metal roll at 60 ° C and dried for 60 minutes to obtain a thickness of 40 μm. PVA film. The film was conditioned at 26 ° C and 65% RH for 16 hours, and after adjusting the water content to 8 mass %, the two ends of the film width direction were fixed to the two sides of the metal frame so that the width direction of the film did not shrink. And heat-treated at 120 ° C for 3 minutes. The degree of swelling of the PVA film after heat treatment was measured by the method of the above (2), and it was 230%. Further, the retardation value of the PVA film was measured by the method of the above (3), and it was 70 nm.

Then, in the same manner as in Example 1, the iodine was adsorbed while the PVA film was stretched, and further, a polarizing film was obtained in the same manner as in Example 1 except that the stretching ratio was 1.8 times. According to the methods (4) and (5) above, the transmittance and the degree of polarization of the polarizing film were measured, and the results were 44.0% and 99.20%, respectively, and the polarizing degree of the polarizing film was slightly insufficient. In order to improve the degree of polarization, the target value of the stretching ratio was changed from 1.8 times to 2.3 times, and as a result, elongation fracture occurred, and a polarizing film could not be obtained.

The results of the above summary are shown in the first table.

Possibility of application in industry

The polarizing film obtained by the PVA film of the invention can be effectively used in electronic computers, watches, notebook computers, liquid crystal screens, liquid crystal color projectors, liquid crystal televisions, navigation systems for vehicles, mobile phones, indoor and outdoor use. The production of a polarizing plate that is a component of a liquid crystal display device such as a measuring device.

Claims (5)

A polyvinyl alcohol film characterized by a polyvinyl alcohol having a degree of polymerization of 5100 to 10000, a degree of swelling of 200 to 240%, and a retardation value of a central portion in the width direction of 10 to 40 nm. The polyvinyl alcohol film of claim 1, wherein the polyvinyl alcohol has a degree of saponification of 98 mol% or more. The polyvinyl alcohol film of claim 1 or 2 has a thickness of 10 to 120 μm. A method for producing a polyvinyl alcohol film according to any one of claims 1 to 3, which comprises forming a film by using a film forming stock solution of polyvinyl alcohol and water having a polymerization degree of 5,100 to 10,000 as a raw material. A polarizing film which is obtained by dyeing and stretching a polyvinyl alcohol film according to any one of claims 1 to 3.