JPH01105204A - Polarization film and its manufacture - Google Patents

Abstract

PURPOSE:To improve the heat resistance and the wet heat resistance, and the optical characteristics such as a degree of polarization and a transmittance, etc., by using a uniaxial oriented film consisting of PVA (polyvinyl alcohol) of a specific polymerization degree. CONSTITUTION:PVA having a polymerization degree of at least 2,500 is melted in a solvent so that the concentration becomes 2-35wt.%, a film is formed from an obtained PVA solution, and at the time of obtaining an oriented film by bringing an obtained film to uniaxial drawing, iodine or a dichroic pigment is contained as a polarizing element in an arbitrary process prior to drawing, a drawing process or in an arbitrary process after drawing. In such a way, the heat resistance and the wet heat resistance are improved, and also, drawing can be executed in a high level in one direction, therefore, since the orientation property of iodine and the dichroic pigment is improved, that which is excellent in such optical characteristics as a degree of polarization and a transmittance, etc., is obtained.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a polarizing film and a method for manufacturing the same.

More specifically, it uses a -axially stretched film of polyvinyl alcohol (hereinafter referred to as PVA) with a high degree of polymerization as a base material, and has significantly improved heat resistance and moist heat resistance.

Moreover, the present invention relates to a polarizing film with excellent optical properties and a method for producing the same.

(Prior Art) Uniaxially stretched PVA films on which iodine and dichroic dyes are adsorbed are conventionally known as polarizing films. In this polarizing film, the PVA film as a base film is generally made of PVA with a low polymerization degree of 2000 or less. This polarizing film can be used as a component of LCD displays such as calculators, clocks, word processors, LCD printers, LCD color televisions, gauges, and automobile instrument panels, or can be attached to glass or inserted between laminated glasses. It is widely used as an anti-glare film for sunglasses, ski goggles, etc.

However, although this polarizing film has an excellent degree of polarization, since the base material is a hydrophilic polymer, it has poor water resistance, moist heat resistance, and heat resistance. Therefore, when this polarizing film is exposed to hot, humid or high temperatures.

The degree of polarization was likely to decrease. With the development of the electronics industry, the scope of use in liquid crystal display devices has expanded, and along with this, polarizing films have improved not only optical properties such as polarization degree and transmittance, but also water resistance.

Good heat resistance, heat and humidity resistance, etc. are now required.

(Problem to be solved by the invention) Under these circumstances, as a product with improved heat resistance and moist heat resistance, a dichroic dye is kneaded into polyester, melt extruded, and then stretched. Uniaxially stretched polyester film (for example, JP-A No. 58-68008, JP-A No. 58-124621, 8-60-125804)
No. 2) has been proposed. but.

Although this film has better heat resistance and moist heat resistance than P'VA polarizing film, it has an insufficient degree of polarization and is currently less used than PVA polarizing film.

Therefore, one object of the present invention is to solve the above-mentioned problems and provide a polarizing film that has improved heat resistance and moist heat resistance, and has excellent optical properties such as polarization degree and transmittance, and a method for producing the same. That is.

(Means for Solving the Problem) As a result of intensive research under these circumstances, the present inventors have achieved the above-mentioned problem by using a uniaxially stretched film made of PVA with a high degree of polymerization as a base film. The present invention was achieved by discovering how to achieve the object.

That is, 1 the polarizing film of the present invention is a polarizing film having a uniaxially stretched film of PVA as a base material and having iodine or a dichroic dye as a polarizing element, in which PVA is at least 250%
It is heat treated to be PVA with a degree of polymerization of 0.

In addition, the method for producing a polarizing film of the present invention includes at least two
Concentration of PVA with a degree of polymerization of 5000 is 2-35% by weight
When forming a film from the resulting PVA solution and uniaxially stretching the obtained film to obtain a stretched film, any process prior to stretching, stretching process, or any post-stretching process may be performed. In the process, heat treatment is performed to incorporate iodine or dichroic dye as a polarizing element.
.

The present invention will be explained in detail below.

Firstly, the polarizing film of the present invention is based on a uniaxially stretched PVA film, and the PVA of the present invention must have a degree of polymerization of at least 2500, preferably at least 4500°, and more preferably at least 4500°. It is 6000-10000. From the viewpoint of the optical properties and durability of the polarizing film, the higher the degree of polymerization of PVA, the more preferable it is, but if manufacturing costs are taken into consideration, a degree of 10,000 or less is practical. P whose degree of polymerization of PVA is less than 2500
Polarizing films made of VA films do not have sufficient optical properties, heat resistance, and moist heat resistance.

Since the PVA in the present invention has a high degree of polymerization as described above, the polarizing film of the present invention is an extremely useful film with improved heat resistance and moist heat resistance, which were fatal drawbacks of conventional PVA polarizing films. It is. Moreover, it can be highly stretched in one direction, 2 and thus has excellent optical properties such as polarization degree and transmittance, probably because the orientation of iodine and dichroic dyes is improved.

In a polarizing film, the transmittance and the degree of polarization have a contradictory relationship, and the transmittance and the degree of polarization are adjusted by the degree of dyeing by the polarizing element. The higher the concentration of polarizing elements in a polarizing film, the lower the transmittance of the film, while the degree of polarization increases, reaching a maximum value of 100%. On the contrary,
On the other hand, the lower the concentration of polarizing elements in the film, the higher the transmission.

The degree of polarization becomes lower. A polarizing film with good performance has both high transmittance and high polarization degree, and the ideal combination of transmittance and polarization values is 50% and 100%, respectively. In the polarizing film of the present invention, for example, when the transmittance is 42-45%, the degree of polarization is 100-98%, and more preferably, when the transmittance is 44-48%, the degree of polarization is 100-99%. be.

Further, it is preferable that the degree of saponification of PVA in the present invention is at least 95 mol%, particularly at least 99 mol%.

The polarizing film of the present invention can be manufactured, for example, by the following method.

First, P with a high polymerization degree of 2500 or more as described above
VA is dissolved in a solvent to a polymer concentration of 2 to 35% by weight to prepare a PVA solution. The concentration of PVA solution is 3
If it exceeds 5% by weight, the viscosity of the solution becomes high, the uniformity of the solution decreases, and the stretchability of the obtained film decreases, probably due to increased entanglement of PVA molecular chains, so it is not suitable. .

On the other hand, when the concentration of PVA solution is 2% by weight.

The concentration tends to be too low making it difficult to form a film. The polymer concentration in the PVA solution is between 4 and 18
% by weight is preferred, particularly preferably from 5 to 12%.

In the present invention, one embodiment of incorporating a polarizing element into the resulting polarizing film includes a step of preparing a solution in which iodine or a dichroic dye is dissolved in a PVA solution. The amount of polarizing element in this step depends on the type of polarizing element, but is preferably, for example, 0.2 to 3% by weight of the PVA solution. Preparation of a PVA solution in which such a polarizing element is dissolved is as follows: 6
Preferably, it is carried out at a temperature of 0 to 120°C. In this case.

When using iodine as a polarizing element, it is preferable to use a lower temperature within the above temperature range in order to prevent sublimation of iodine. As a method for preparing the above-mentioned solution, for example, a method is employed in which a polarizing element is added to a solvent for dissolving PVA, which will be described later, and PVA is dissolved under stirring.

Examples of solvents for PVA include organic solvents such as dimethyl sulfoxide (hereinafter referred to as DMSO), dimethylformamide, acetone, methyl alcohol, n-propyl alcohol, ethylene glycol, and propylene glycol, or a mixture of two or more of these. It can be used as

Further, an aqueous solution of these organic solvents and an inorganic salt such as calcium chloride or lithium chloride, or a mixed solvent of an organic solvent and water can also be used. In particular, the above organic solvents include:
DMSO is preferably used.

Further, the above DMSO is preferably used as a mixed solvent with water. In this case, DMS055% by weight or more 100%
A mixture of less than 45% by weight water and more than 0% by weight is used, in particular a concentration of DMSO of 70-98% by weight is preferred. For example, if the mixing ratio of DMSO and water is 1, D
When a solvent consisting of 90 to 96% by weight of MS0 and 10 to 4% by weight of water is used, the affinity between PVA and the solvent is improved and P
A relatively high concentration of PVA may be due to improved solubility of VA.
Even if a solution is used, the PVA solution will not gel at room temperature or a relatively low temperature close to 15 to 35° C. within the relatively short time required to form a film. Therefore, when a mixed solvent having the above-mentioned mixing ratio is used, it has the advantage that it does not gel until it is mixed with a coagulating solution, and a homogeneous film with less uneven thickness can be formed at room temperature.

Next, in the production method of the present invention, the above-mentioned PVA
Form a film from the solution.

When forming a film, the PVA solution is once discharged into the air or an inert atmosphere such as a nitrogen gas atmosphere through a slit-shaped discharge port to form a liquid film of the PVA solution, and then introduced into the coagulation solution. to form a film. Further, the PVA solution can be formed into a liquid film in the above atmosphere using a roll coater or the like. Furthermore, a film can also be formed by directly introducing the PVA solution into the coagulation solution without passing it through the atmosphere. moreover,
A liquid film of PVA solution is formed in the atmosphere.

It is also possible to form a film by cooling this with a cooling medium such as carbon tetrachloride, decalin, paraffin, or trichloroethylene to once gel it, and then introducing it into a solvent removal solution to remove the solvent. In addition.

When a low boiling point coolant such as carbon tetrachloride or trichlorethylene is used as a cooling medium, a desolvation step is not necessarily necessary.

As such a coagulation or solvent removal liquid, one or more types of alcohols such as methanol, ethanol, propatool, isopropyl alcohol, butanol, or acetone can be used.

The liquid film of the above PVA solution varies depending on the PVA solvent mentioned above, but the temperature of the PVA solution is usually 10 to 1.
Preferably, it is carried out at 20°C. As already mentioned,
In particular, when a solvent consisting of 090-96% DMS and 10-4% water is used, a homogeneous PVA solution film with less uneven thickness can be formed at room temperature of 15-35°C or a relatively low temperature close to it. can be formed. A film is formed by introducing this liquid film through an atmosphere or directly into a coagulating liquid, or into a cooling medium followed by a desolvation liquid.

The film formed as described above, that is, the unstretched film, is stretched in one direction, usually 5 times or more, preferably 7 times or more, within a range that does not lead to breakage.

When the stretching ratio is less than 5 times, it may be difficult to obtain a polarizing film having excellent transmittance and polarization degree. The higher the stretching ratio, the better, but the upper limit is practically about 20 times. In particular, a preferable stretching ratio is about 8 to 15 times. Further, the stretching speed is 10 to 3001%/min, more preferably 50 to 200%/min, based on the original length of the film.

For stretching, both wet stretching and dry heat stretching are possible.

In wet stretching, the film is swollen by immersing the film in advance in a swelling liquid at a temperature near room temperature, for example, 15 to 35°C, or a little higher than that, in a temperature range in which the unstretched film does not dissolve. It is carried out in a liquid at a temperature of 60°C to 60°C. In this case, if the stretching temperature is too low, it will not be possible to stretch at a sufficient stretching ratio, so it is preferable that the stretching temperature is at least the lower limit of the above-mentioned swelling liquid, that is, 15° C. or higher. Note 2: When stretching in a high-temperature solution, for example, 55 to 60°C, it depends on the degree of polymerization of PVA, etc., but pre-stretching is performed at around room temperature to prevent the PVA film from dissolving, and the temperature is raised while maintaining tension. It is preferable.

Examples of the above-mentioned swelling liquid or stretching liquid include a dyeing liquid consisting of an aqueous solution containing water, an iodine or dichroic dye, a dyeing aid such as an inorganic salt, and a crosslinking agent such as boric acid; An aqueous solution of an inorganic salt is used. In this case, the crosslinking agent used is, for example, 0.5 to 3% by weight.

Moreover, dry heat stretching is carried out in an atmosphere of 100 to 250°C.

For example, it is carried out in air, preferably in an inert atmosphere such as nitrogen gas. If the stretching temperature is less than 100°C, it may not be possible to stretch at a sufficient stretching ratio;
If the temperature exceeds 50°C, it will be necessary to further raise the temperature in the 9th heat treatment step, and in that case there is a risk that the film will melt.

Next, the film uniaxially stretched as described above is heat treated. Such heat treatment is performed in air or in an inert gas atmosphere. Such heat treatment further improves the durability of the polarizing film, such as its dimensional stability after stretching, heat resistance, and heat-and-moisture resistance. Heat treatment temperature is 180-26
Preferably 0°C.

Particularly preferred is 200 to 240°C. The heat treatment temperature is preferably higher than the stretching temperature. Heat treatment temperature is 1
When the temperature is lower than 80°C, it may be difficult to increase the crystallinity of the film, and it may be difficult to improve the durability.

On the other hand, if the temperature exceeds 260°C, it may melt even if it is processed under tension. In addition, the heat treatment time was 0.1
~10 minutes is preferred.

It is preferable to start the above heat treatment while keeping the film under tension to the extent that it does not loosen so that the film maintains the same length as after stretching.

Conventionally known means can be applied to incorporate iodine or dichroic dye into the film. In this case, iodine and dichroic pigments are
P begins with the step of dissolving PVA in a solvent to prepare a solution.
It may be added at any stage prior to the stretching process in the VA film manufacturing process.

They can be added during stretching, or a separate step of adding them can be provided after stretching.

For example, in order to incorporate iodine, a method such as immersing the film in a mixed aqueous solution of iodine and potassium iodide is preferably adopted, and there are no particular restrictions on the treatment method. Further, for the purpose of preventing the dissipation of iodine, a crosslinking agent such as boric acid, borax, glutaraldehyde, etc. may be mixed in the above mixed aqueous solution, and after dyeing, a treatment with a solution of the crosslinking agent may be performed separately.

Dichroic pigments include yellow, orange, and blue.

Purple, red, etc. can be used without any restrictions.

Typical dichroic dyes include 1, for example, C, 1, Dir.
ect type old ack 17.19 and 154. Brow
n 44, 106, 195, 210° and 223. Re
d 2, 23.2B, 31, 37, 39.79, 81,
240, 242° and 247. Blue, 15, 22
．． 7B, 90, 98, 151, 168, 202, 236
249, and 270. Violet 9, 12, 51.
and 98. Green 1+ and 85. Yellow
8, 12, 44, 86. and E? 7. Orange 2
6+39, 106. and direct dyes such as 107, C
, 1, old Disperse ue 214. Red
60. Mention may be made of disperse dyes such as Yellow 56. Furthermore, in the present invention, two or more types of dichroic dyes may be used in combination. Furthermore, in the present invention, iodine and a dichroic dye may be used in combination for the purpose of adjusting two hues.

In the present invention, in order to make the film contain iodine and dichroic dyes, these may be mixed when preparing the PVA solution, as described above, and when a wet stretching method is adopted, During swelling or stretching, iodine or a dichroic dye may be added at the same time. In this case, in order to contain iodine, a solution containing 9% by weight of iodine to 3% by weight and 0.005 to 15% by weight of potassium iodide is preferably used, more preferably 0.03 to 4% by weight of iodine. 1% by weight
A solution containing 0.2 to 5 weight percent of potassium iodide is used.

In addition, when using a dichroic dye, its concentration is 0.00
1 to 3% by weight is preferred. After drying the film dyed and stretched in this manner, it is heat treated as described above.

Furthermore, the stretched and heat-treated film may be dyed with iodine or a dichroic dye. In this case, when iodine is used, a solution containing 0.1 to 3% by weight of iodine and 0.5 to 15% by weight of potassium iodide is preferred.

When using a dichroic dye, its concentration is preferably 0.1 to 3% by weight.

When using a dry heat stretching method and combining dry heat stretching and iodine-based dyeing, it is preferable to carry out the dyeing after heat treatment after stretching in order to prevent sublimation of iodine at high temperatures. When using a dichroic dye that does not cause loss due to heat deterioration or sublimation, the dye may be mixed in advance during the preparation of the PVA solution, dyed before stretching, or dyed. You can also do this at the end of the process. In the dry heat stretching method.

Even when iodine or dichroic dye is contained in the film, the same conventionally known means as in the wet stretching method can be applied. However, when dyeing is performed after heat treatment using the dry heat stretching method, the film has a high degree of crystallinity, making it difficult to dye, so the dyeing time is relatively long, for example, 30
minutes to 1 hour), and it is preferable to increase the concentration of iodine and dichroic dye in the dyeing solution (for example, 0.5 to 2% by weight).

The preferred process for incorporating iodine or dichroic dye into the film is the swelling or stretching process when hot stretching is used, and the swelling or stretching process when dry heat stretching is used.

This is a process after stretching. In either case, the final value is 0.5
It is preferable to carry out crosslinking treatment with a solution of a crosslinking agent such as boric acid having a repellency of 15% to 15%.

The polarizing film of the present invention can be used alone or in combination with a support or other layer. In the latter case, a film having good transparency and optical anisotropy, such as a polyarylate film, triacetate film, or (meth)acrylate film, can be used by laminating it on the polarizing film. For such lamination, 2. For example, a polyarylate film is coated with a solution of an adhesive such as an isocyanate adhesive dissolved in a solvent using a roll coater or a bar coater, and then the solvent is removed by heating and drying. The film is laminated onto the polarizing film using a laminator. An example of such a polyarylate film is a film with a thickness of about 50 to 130 μm, which is commercially available from Unitika as Enplate. A polyarylate film is optically anisotropic, has heat resistance, and does not easily allow moisture to pass through, so it is suitable as a protective film for a polarizing film.

(Example) Hereinafter, the present invention will be specifically described with reference to Examples. Note that the transmittance and polarization degree were measured by the following method.

The transmittance of light in the visible wavelength range (400 to 700 nm) was determined using a spectrometer. A polarizer is installed on the incident light side, and the transmittance of a single sheet of polarizing film is measured when the transmission axis of the polarizing film sample is aligned with the optical axis of the polarizer and when it is perpendicular to the optical axis of the polarizer, and the algebraic average value is transmitted. It was a degree. In addition,
The transmittance was determined based on JIS-Z~8701 by correcting the luminous efficiency over the visible range using the display method in the double-view XYZ system in the case of a C light source. However, when a red dichroic dye was used, the transmittance at 525 nm was determined. The degree of polarization is determined by the following formula from the transmittance (Tu) measured by stacking two polarizing films so that their stretching axes are parallel to each other and the transmittance (T) measured by stacking two polarizing films so that they are perpendicular to each other. Ta.

As mentioned above, the ideal maximum value of the transmittance and degree of polarization of the polarizing film is 50%.

The degree of polarization is 100%.

Incidentally, a polarizing film is usually used with a protective film laminated thereon, but in the following Examples and Comparative Examples, various characteristic values were measured for a polarizing film without a protective film.

Example 1. Comparative Example 1 Polymerization degree 4980. PVA with a saponification degree of 99.8%,
DMSO/water = so that the pvASW degree is 7% by weight.
A PVA film forming solution was prepared by dissolving it in a mixed solvent of 9515 (weight ratio) while heating at 80°C. This solution was maintained at 20° C. and discharged into a methanol bath through a slit-shaped discharge port to form a film with a thickness of 50 μm.

Next, the film was air-dried at room temperature, uniaxially stretched 7 times at 155°C, and then heat-set at 180°C for 5 minutes in a nitrogen gas atmosphere while maintaining the stretched length so as not to loosen. Next, iodine and potassium iodide aqueous solution (1
After immersing the film in a 3% by weight boric acid bath for 30 minutes, the film was immersed in a 3% by weight boric acid bath at room temperature for 15 minutes, and air-dried at room temperature to obtain a polarizing film. The obtained polarizing film is
The thickness is 11 μm, one color tone is blue-purple transparent, and the transmittance is 48
．． 3. The degree of polarization was 9969%.

In addition, the obtained polarizing film was heated at 60°C, 90% R, 11
After leaving it for 5 hours in a constant temperature and humidity chamber at 20°C, the transmittance and degree of polarization were measured. As a result, the transmittance was 52.3%.

The degree of polarization was 93.0%, and no change in shape was observed.

For comparison, a polarizing film having the same polarizing element as Example 1 (transmittance 41.
2%, degree of polarization 96.4%, thickness 13 μm, stretching ratio 4.
5 times), the transmittance and degree of polarization were similarly measured.

The transmittance was 62.7% and the degree of polarization was 72.4%.

As is clear from these results, the polarizing film of the present invention has a higher temperature of 60°C than the conventional polarizing film.

Even in an atmosphere of 90% R, H, there was little deterioration in transmittance and degree of polarization.

Example 2 A film was coated with iodine and potassium iodide aqueous solution (1% by weight15
A polarizing film was obtained in the same manner as in Example 1, except that instead of being immersed in a dye solution containing 0.05% by weight of a dichroic dye, Congo red. The obtained polarizing film is red transparent and has a wavelength of 525 nm.
The transmittance was 36.9%, and the degree of polarization was 85.1%.

Example 3 Degree of polymerization: 4980. Saponification degree 99.8% (7) PVA
DMSO/water = 9515 so that VA concentration is 7% by weight
(weight ratio) in a mixed solvent at 80℃, and
Solution A was created. This solution was applied onto a 100 μm thick polyethylene terephthalate (hereinafter referred to as PET) film at 20°C using a bar coater, immersed in a methanol bath for 10 minutes to form a film, and air-dried at room temperature to obtain a PVA film. Ta.

Next, peel the PVA film from the PET film,
This PVA film was immersed in an iodine/potassium iodide solution (0.05% by weight, 10.25% by weight) at 20°C for 5 minutes, uniaxially stretched 9 times in the same solution, and then 3% by weight of boric acid. The sample was immersed in a bath at room temperature for 15 minutes, air-dried, and then heat-treated at 65°C. The resulting polarizing film (thickness: 7 μm) had a transmittance of 44.1% and a degree of polarization of 100%.

Example 4. Comparative Example 3 Instead of immersing the film in an iodine/potassium iodide solution, methanol containing 0.5% by weight of Miketone Fast Pink RL (manufactured by Mitsui Toatsu Co., Ltd.), a dichroic disperse dye, was applied to the PVA film. A polarizing film was obtained in the same manner as in Example 3, except that the solution was used as both a coagulating solution and a staining solution. The obtained polarizing film is red transparent and has a wavelength of 525 nm.
The transmittance was 33.0%, and the degree of polarization was 98.7%.

In addition, a commercially available PVA film (polymerization degree 1700, saponification degree 99.9%) was used in the same manner as Miketon First.
Although it was dyed in methanol containing 0.5% by weight of pink RL, it was not possible to dye it.

Example 5 A PVA film forming solution prepared by the same manufacturing method as in Example 4 except that 1% by weight of iodine was added was formed into a film on a PET film using a bar coater at 20°C.

A film was obtained by immersion in a methanol bath. The obtained film was air-dried at room temperature. Next.

The film was stretched to a stretching ratio of 6 times in a 3% by weight boric acid solution at room temperature, washed with water, and then air-dried at room temperature. The obtained polarizing film (
The transmittance of the film (thickness: 11 μm) is 46.2%, and the degree of polarization is 99.
It was 4%.

Example 6 A dry PVA film prepared by the same method as in Example 5 except that 1% by weight of Congo red was added instead of iodine was stretched to a stretching ratio of 7 times in a boric acid solution at room temperature, and after washing with water, it was stretched naturally. Dry.

The wavelength of the obtained polarizing film (thickness 11 μm) was 525 nm.
The transmittance at m was 30.1% and the degree of polarization was 99.9%.

Example 7 Degree of polymerization: 3250. A PVA film was obtained in the same manner as in Example 4, except that PVA with a saponification degree of 99.6% was used.

Next, this PVA film was immersed in an iodine/potassium iodide solution (0.03% by weight, 10.20% by weight) at 20°C for 5 minutes, uniaxially stretched 9 times in the same solution, and then 3% by weight.
The sample was immersed in a boric acid solution for 15 minutes at room temperature.

The transmittance of the obtained polarizing film (thickness: 5 μm) was 46.
0%, and the degree of polarization was 97.4%.

Example 8 Degree of polymerization 6740. PVA with saponification degree of 99.2%
DSMO/water = 9515 so that the concentration is 4% by weight
(weight ratio) in a mixed solvent under heating at 80°C, P
A VA solution was prepared. Apply this solution to P using a bar coater.
It was applied onto an ET film, immersed in a methanol bath for 10 minutes to form a film, and air-dried at room temperature to obtain a PVA film. Next, the PVA film was peeled from the PET film, and the same procedure as in Example 4 was carried out to obtain a polarizing film. The resulting polarizing film (thickness: 5 μm) had a transmittance of 46.0% and a degree of polarization of 99.2%.

(Effects of the Invention) Since the polarizing film of the present invention is made of PVA with a high degree of polymerization, the heat resistance and moist heat resistance, which were the essential drawbacks of conventional PVA polarizing films, are significantly improved, and further excellent transmittance and polarization are achieved. have a degree. Also, as mentioned above, it is made of PVA with a high degree of polymerization.

Furthermore, since organic solvents can be used, 9-disperse dyes can also be used, expanding the range of dye selections. Therefore, the usefulness as a polarizing film is significantly improved.

The polarizing film of the present invention can be used in office automation terminal displays, liquid crystal televisions, and automobile instrument panels that require strict heat resistance and heat-moisture resistance.

In addition to liquid crystal displays for measuring instruments, it can be used in a wide range of fields, including panel photo filters, sunglasses, windows of houses and buildings, and various sensors.

Furthermore, according to the manufacturing method of the present invention, commercially available PVA having a degree of polymerization of 2500 or more is used.

Compared to conventional PVA films, it can be stretched at a higher stretching ratio, and a polarizing film with excellent optical properties, heat resistance, and heat-and-moisture resistance can be produced with high productivity.

Claims (3)

[Claims] (1) In a polarizing film that uses a uniaxially stretched film of polyvinyl alcohol as a base material and uses iodine or a dichroic dye as a polarizing element, the polyvinyl alcohol contains at least 250
A polarizing film characterized by being made of polyvinyl alcohol having a degree of polymerization of 0. (2) Polyvinyl alcohol having a degree of polymerization of at least 2500 is dissolved in a solvent to a concentration of 2 to 35% by weight, a film is formed from the obtained polyvinyl alcohol solution, and the obtained film is stretched by uniaxial stretching. When obtaining a film, any steps prior to stretching, stretching step,
Alternatively, a method for producing a polarizing film, which comprises incorporating iodine or a dichroic dye as a polarizing element in any step after stretching. (3) The method for producing a polarizing film according to claim 2, wherein the stretched film is heat-treated.