JP2023140325A - Polarizing film, manufacturing method therefor, and polarizing plate - Google Patents

Abstract

The present invention provides a polarizing film capable of obtaining a polarizing plate having excellent long-term heat resistance and durability, a liquid crystal display device equipped with the polarizing plate, a method for manufacturing the same, and a polarizing film used in the polarizing plate. A polarizing film characterized by having a layer containing an acid scavenger on at least one surface of the polarizing film. [Selection diagram] None

Description

The present invention relates to a polarizing film, a method for manufacturing the same, and polarized light. More specifically, the present invention relates to a polarizing film (polyvinyl alcohol polarizing plate) that makes it possible to obtain a polarizing plate that has excellent long-term heat resistance and durability.

In recent years, the development of liquid crystal display devices has been remarkable, and they are widely used in smartphones, tablets, personal computers, liquid crystal televisions, projectors, car panels, etc. The above-mentioned liquid crystal display device uses a polarizing plate, and the polarizing plate is mainly a polarizing film in which iodine or dichroic dye is adsorbed and aligned on a polyvinyl alcohol film, and a protective film is laminated thereon. ing. In recent years, as the applications of liquid crystal display devices have expanded, the environment in which they are used has become wider in terms of both temperature and humidity ranges than in the past. There is a need for polarizing plates that exhibit a high degree of polarization.

Methods for improving the heat resistance and durability of polarizing plates include, for example, using a polarizing film that uses a specific azo dye (see, for example, Patent Document 1), or using a polarizing film that has iodine adsorbed and oriented, and further uses a dichroic organic dye. A method has been proposed in which a polarizing film containing a dye is used (for example, see Patent Document 2).
In addition, a polarizing plate that includes a polarizer in which iodine is adsorbed and oriented, has a retardation value Ri of iodine of 160 nm or more, and has specific optical properties (for example, see Patent Document 3), and a weight ratio of iodine and potassium. A polarizing plate in which the amount of boron element is defined as (for example, see Patent Document 4) has also been proposed as a polarizing plate with excellent heat resistance and durability.

International Publication No. 2016/186196 Japanese Patent Application Publication No. 2012-3172 Japanese Patent Application Publication No. 2016-139151 International Publication No. 2016/060087

However, in the technique disclosed in Patent Document 1, although a polarizing film having high heat resistance and durability can be obtained by using a specific dye, the degree of polarization is as low as 99.9%.
There is a problem that the contrast is insufficient.

Although a polarizing film with high polarization performance can be obtained in Patent Document 2, it is necessary to provide two or more dyeing tanks, one for dyeing with a dichroic dye and the other for dyeing with iodine, in the manufacturing process. Furthermore, in order to adjust the color tone of the polarizing film, careful density control of two or more types of dyeing tanks is required, resulting in a problem of low productivity.

Furthermore, although the technique disclosed in Patent Document 3 can suppress the deterioration of optical properties in a heat resistance test at about 85° C., there is a problem in that the heat resistance durability cannot be improved under harsher temperature conditions.
Even with the technology disclosed in Patent Document 4, the absorbance at 700 nm when left at 105°C for 30 minutes can be maintained at 2.3 or more, but the heat resistance durability cannot be improved when exposed to a high temperature environment for an even longer period of time. There is a problem.

Therefore, the present invention provides a polarizing film that can obtain a polarizing plate with excellent long-term heat resistance and durability, a liquid crystal display device equipped with the polarizing plate, and a manufacturing method thereof.
It is also an object of the present invention to provide a polarizing film for use in the above polarizing plate.

In view of these circumstances, the inventors of the present invention have conducted extensive research and have found that by providing a layer containing an acid scavenger on the surface of a polarizing film, it is possible to obtain a polarizing plate that has excellent long-term heat resistance and durability. I found out that it is possible.

That is, the first aspect of the present invention is a polarizing film characterized by having a layer containing an acid scavenger on at least one surface of the polarizing film.

The second gist is a polarizing film in which the acid scavenger is a carbodiimide compound.

The third gist is a method for manufacturing a polarizing film in which a polyvinyl alcohol film is passed through a plurality of processing tanks, and after passing through the last processing tank, an acid scavenger is added to at least one surface of the polyvinyl alcohol film. This is a method of manufacturing a polarizing film by coating.

The fourth aspect is a polarizing plate having a protective film on at least one surface of the polarizing film according to claim 1 or 2.

The polarizing plate obtained using the polarizing film of the present invention does not easily undergo red discoloration even in a long-term heat resistance durability test, and has excellent heat resistance durability.

Embodiments of the present invention will be described in detail below. However, the present invention is not limited to these embodiments.

The polarizing film of the present invention is characterized by having a layer containing an acid scavenger on at least one surface of the polarizing film.

[Acid scavenger]
The acid scavenger used in the present invention is one that suppresses the polyenization of the polarizing film by the acid generated when the protective film of the polarizing plate is hydrolyzed, and prevents the polarizing film from turning red due to polyenization. It is.

Typical examples of the acid scavenger include a carbodiimide compound, a compound having an oxazoline group, and a compound having an epoxy group. Also included are compounds having an alkyl phosphoric acid, compounds having an alkyl phosphoric acid, compounds having an amino group, compounds having an oxazine, polyester resins, and the like.
Among these, carbodiimide compounds are preferred because they react quickly with acids and are highly effective in suppressing polyenization at high temperatures. Note that such a carbodiimide compound may be used alone or in combination with other acid scavengers.

Specific examples of the carbodiimide compound include diisopropylcarbodiimide, dimethylcarbodiimide, dicyclohexylcarbodiimide, dioctylcarbodiimide, diphenylcarbodiimide, t-butylisopropylcarbodiimide, di-t-butylcarbodiimide, di-β-naphthylcarbodiimide, etc., which have a low molecular weight. Both those with high molecular weight and those with high molecular weight can be used.

The molecular weight of the compound having a carbodiimide group is not particularly specified, but the weight average molecular weight is 5.
It is preferably 00 or more, and more preferably 1000 or more. On the other hand, the upper limit of the weight average molecular weight is preferably 200,000 or less, more preferably 100,000 or less. If the weight average molecular weight is too low, there will be few carbodiimide groups, and it will be less effective in suppressing polyenization at high temperatures, and the adhesive strength will tend to be weak. If it is too high, it will tend to have poor dispersibility in water, making it difficult to apply uniformly. .

In a compound having a carbodiimide group, carbodiimide group equivalent is one of the indicators representing the amount of carbodiimide group that reacts with an acid, and carbodiimide group equivalent is the molecular weight per 1 mol of carbodiimide group, and is preferably in the range of 100 to 1000. If the carbodiimide equivalent is too small, the contribution of the effect of suppressing polyenization at high temperatures tends to decrease. On the other hand, if the carbodiimide equivalent is too large, it tends to be highly hydrophobic and difficult to be miscible with water, making it difficult to handle.

Note that the acid scavenger is sometimes referred to as a hydrolysis stabilizer, acid catcher, acid scavenger, acid scavenger, acid scavenger, etc., but in the present invention, it is used regardless of these names. I can do it.

The polarizing film of the present invention can be produced, for example, by first obtaining a polyvinyl alcohol film using a polyvinyl alcohol resin as a raw material, and then using the polyvinyl alcohol film as a raw material by swelling, dyeing, boric acid crosslinking, stretching, washing, and drying. It can be manufactured through a polarizing film manufacturing process such as.
In particular, in the above polarizing film manufacturing process, the polyvinyl alcohol film is passed through a plurality of treatment tanks, and after passing through the last treatment tank, an acid scavenger is applied to at least one surface of the polyvinyl alcohol film. The production method described above is preferable in that the acid scavenger can be easily contained on the film.
Hereinafter, an example of the method for manufacturing the above polarizing film will be explained in detail in the order of steps.

[Material for forming polyvinyl alcohol film]
First, the polyvinyl alcohol resin that is the material for forming the polyvinyl alcohol film will be explained.
As the polyvinyl alcohol resin, an unmodified polyvinyl alcohol resin, that is, a resin produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate is usually used. If necessary, a resin obtained by saponifying a copolymer of vinyl acetate and a small amount (usually 10 mol% or less, preferably 5 mol% or less) of a component copolymerizable with vinyl acetate may also be used. can. Components copolymerizable with vinyl acetate include, for example, unsaturated carboxylic acids (including salts, esters, amides, nitriles, etc.), olefins having 2 to 30 carbon atoms (such as ethylene, propylene, n-butene, etc.). , isobutene, etc.), vinyl ethers, unsaturated sulfonates, and the like. Furthermore, a modified polyvinyl alcohol resin obtained by chemically modifying the hydroxyl group after saponification can also be used.

Further, as the polyvinyl alcohol resin, a polyvinyl alcohol resin having a 1,2-diol structure in the side chain can also be used. This polyvinyl alcohol resin having a 1,2-diol structure in the side chain can be produced by, for example, (i) a method of saponifying a copolymer of vinyl acetate and 3,4-diacetoxy-1-butene, (ii) acetic acid Method for saponifying and decarboxylating copolymers of vinyl and vinyl ethylene carbonate, (iii) vinyl acetate and 2,2
- by a method of saponifying and deketalizing a copolymer with dialkyl-4-vinyl-1,3-dioxolane, (iv) a method of saponifying a copolymer of vinyl acetate and glycerin monoallyl ether, etc. can get.

The weight average molecular weight of the polyvinyl alcohol resin is preferably 100,000 to 300,000, particularly preferably 110,000 to 280,000, and even more preferably 120,000 to 260,000, from the viewpoint of manufacturing the polarizing film. be. That is, if this weight average molecular weight is too small, it tends to be difficult to obtain sufficient optical performance when making an optical film from polyvinyl alcohol-based resin, and if it is too large, it tends to be difficult to obtain sufficient optical performance when producing the above-mentioned polarizing film from polyvinyl alcohol-based film. Stretching tends to be difficult. Note that the weight average molecular weight of the polyvinyl alcohol resin is the weight average molecular weight measured by GPC-MALS method.

The average degree of saponification of the polyvinyl alcohol resin is preferably 98 mol% or more, particularly preferably 99 mol% or more, and even more preferably 99.5 mol% or more, from the viewpoint of the optical performance of the polarizing film. , particularly preferably 99.8 mol% or more. That is, if this average degree of saponification is too small, the polarizing film produced from the polyvinyl alcohol film tends not to have sufficient optical performance.
Here, the above average degree of saponification is measured according to JIS K 6726.

As the above-mentioned polyvinyl alcohol resin, two or more types having different modified species, modified amount, weight average molecular weight, average saponification degree, etc. may be used in combination.

Next, a polyvinyl alcohol resin aqueous solution is prepared using the polyvinyl alcohol resin. The polyvinyl alcohol resin aqueous solution will be explained.

The polyvinyl alcohol resin aqueous solution is obtained by dissolving the aforementioned polyvinyl alcohol resin in a solvent such as water. Examples of solvents in addition to water include dimethyl sulfoxide (DMSO); N-methylpyrrolidone; polyhydric alcohols such as glycerin, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and trimethylolpropane; ethylene diamine; Amines such as diethylenetriamine; and mixtures thereof can also be used in combination.

In addition to the polyvinyl alcohol resin, the polyvinyl alcohol resin aqueous solution may contain commonly used glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol, trimethylolpropane, etc., if necessary. A plasticizer and at least one nonionic, anionic, and cationic surfactant may be contained, and it is preferable to contain these from the viewpoint of film forming properties. One type selected from these can be used alone or two or more types can be used in combination.

From the viewpoint of productivity, the resin concentration of the aqueous polyvinyl alcohol resin solution thus obtained is preferably 15 to 60% by weight, particularly preferably 17 to 55% by weight, and even more preferably 20 to 50% by weight. It is. In other words, if the resin concentration of this aqueous solution is too low,
Productivity tends to decrease because the drying load increases, and if it is too high, the viscosity tends to become too high and it becomes difficult to form a uniform solution.

The obtained aqueous polyvinyl alcohol resin solution is usually defoamed. Examples of the defoaming method include methods such as stationary defoaming and defoaming using a multi-screw extruder. The multi-screw extruder may be any multi-screw extruder with a vent, and usually a twin-screw extruder with a vent is used.

[Production method of polyvinyl alcohol film]
After the above defoaming treatment, the aqueous polyvinyl alcohol resin solution is introduced in fixed amounts into a T-shaped slit die, discharged and cast onto a rotating cast drum, and formed into a film by a continuous casting method. Then, by drying the formed film, a polyvinyl alcohol film is obtained. A method for producing this polyvinyl alcohol film will be explained.

The above-mentioned continuous casting method is, for example, a method for forming a film by discharging and casting an aqueous polyvinyl alcohol resin solution from a T-shaped slit die onto a rotating cast mold, an endless belt, a resin film, or the like.
The surface temperature of the cast mold such as the cast drum is preferably 40 to 99°C, particularly preferably 60 to 95°C. Drying of a film formed by a cast mold is carried out by conveying the film while bringing the front and back surfaces of the film into alternate contact with the outer periphery of a plurality of heat rolls. After drying with this hot roll, the film may be heat treated. The heat treatment is preferably carried out at a temperature of 60 to 150°C, particularly 80 to 130°C.
°C is preferred. The film that has been dried and optionally heat-treated is then cut and removed (slit) at both ends to form the polyvinyl alcohol film. The polyvinyl alcohol film is then wound around a core tube and formed into a film roll.

The thickness of the polyvinyl alcohol film is preferably 5 to 75 μm,
From the viewpoint of making the polarizing film thinner, it is particularly preferably from 10 to 60 μm, and from the viewpoint of durability, it is even more preferably from 15 to 60 μm.

Further, the width of the polyvinyl alcohol film is preferably 4 m or more,
More preferably 4.5 m or more from the viewpoint of increasing the surface area, particularly preferably 4.5 m or more from the viewpoint of avoiding breakage.
It is 6m.

Further, the length of the polyvinyl alcohol film is preferably 4 km or more, more preferably 4.5 km or more from the viewpoint of increasing the area, and particularly preferably 4.5 to 50 km from the viewpoint of transportation weight.

[Film manufacturing method]
Hereinafter, a method for producing an embodiment of the polarizing film of the present invention obtained using the above polyvinyl alcohol film will be described.

The polarizing film is manufactured by unwinding a polyvinyl alcohol film from the film roll, transporting it horizontally, and performing steps such as swelling, dyeing, boric acid crosslinking, stretching, washing, and drying. These steps will be explained.

The swelling process is performed before the dyeing process. The swelling step is usually performed by immersing the polyvinyl alcohol film in a treatment liquid in a swelling treatment tank. Due to the swelling process,
In addition to being able to clean dirt from the surface of a polyvinyl alcohol film, it also has the effect of preventing uneven dyeing by swelling the polyvinyl alcohol film. Water is usually used as the treatment liquid. If the main component of this treatment liquid is water, the iodide compound,
A small amount of additives such as surfactants, alcohol, etc. may be included. The temperature of the treatment liquid is usually about 10 to 45°C, and the immersion time in the treatment liquid is usually about 0.1 to 10 minutes.

The dyeing process is usually carried out by immersing the polyvinyl alcohol film in a liquid containing iodine or dichroic dye in a dyeing tank. The liquid is usually an aqueous solution of iodine and potassium iodide, with an iodine concentration of 0.1 to 2 g/L.
The appropriate concentration of potassium iodide is 1 to 100 g/L. Practical dyeing time is about 30 to 500 seconds. The temperature of the liquid is preferably 5 to 50°C. In addition to the water solvent, the aqueous solution may contain a small amount of an organic solvent that is compatible with water.

The boric acid crosslinking step is usually performed by immersing the polyvinyl alcohol film in a liquid containing a boron compound such as boric acid or borax in a boric acid treatment tank. The liquid is an aqueous solution or a water-organic solvent mixture, and the concentration of the boron compound in the liquid is 1.
It is about 0 to 100 g/L. It is preferable to coexist potassium iodide in the liquid from the viewpoint of stabilizing the polarization performance. The temperature of the liquid is preferably about 30 to 70°C, and the immersion time in the liquid is preferably about 0.1 to 20 minutes.

The stretching step may be performed independently or during at least part of the swelling step, dyeing step, and boric acid crosslinking step. The total stretching ratio in the uniaxial direction is preferably 3 to 10 times, preferably 3.5 to 6 times. At this time, there is no problem even if some stretching is performed in the direction perpendicular to the stretching direction (stretching to an extent that prevents shrinkage in the width direction or more).
During stretching, the temperature around the polyvinyl alcohol film to be stretched is 40 to 170°C.
°C is preferred.

The cleaning step is performed, for example, by immersing the polyvinyl alcohol film in water or an aqueous solution of iodide such as potassium iodide in a cleaning tank. The washing step can remove precipitates generated on the surface of the polyvinyl alcohol film. When using an aqueous potassium iodide solution, the potassium iodide concentration is usually about 1 to 80 g/L. The temperature of the iodide aqueous solution during washing is usually 5 to 50°C, preferably 10 to 45°C. The immersion time in the water or iodide aqueous solution is usually 1 to 300 seconds, preferably 10 seconds.
~240 seconds. Note that washing with water and washing with an aqueous potassium iodide solution may be performed in an appropriate combination.

The drying step is usually performed by drying in the air at an ambient temperature of 40 to 100°C, preferably 70 to 98°C, for 0.5 to 20 minutes after passing through the final cleaning tank in the above cleaning process. be exposed.

In the present invention, in the polarizing film manufacturing process, the polyvinyl alcohol film is passed through a plurality of processing tanks, and the acid scavenger may be applied after passing through any of the processing tanks.
The timing of such application is preferably after passing through the latter treatment tank, and it is particularly preferable to apply the acid scavenger to at least one surface of the polyvinyl alcohol film after passing through the last treatment tank. It is particularly preferred that the treatment tank is a cleaning treatment tank.
Furthermore, the last treatment tank is a cleaning treatment tank, and after passing through the last cleaning treatment tank and before the drying process, an acid scavenger layer can be easily coated on at least one surface of the polarizing film. It is preferable because it can be formed.
Moreover, it is preferable to apply an acid scavenger to both sides of the polarizing film.

When applying an acid scavenger to at least one surface of a polarizing film, it is preferable to apply the acid scavenger as an aqueous solution, and the concentration of the acid scavenger aqueous solution is usually 0.01 to 5% by weight, preferably 0.1 to 3% by weight, particularly preferably 0.3 to 1.5% by weight. If the concentration is too low, the amount of acid scavenger applied will be small and will not contribute to improving heat resistance and durability; if it is too high, the viscosity of the acid scavenger aqueous solution will be high, making it difficult to apply uniformly. .

Such a coating method may be applied according to a known general method, and examples thereof include spray coating, spin coating, die coating, knife coating, and the like. In the present invention, it is desirable that the acid scavenger layer is formed by dropping an aqueous acid scavenger solution onto the roll before the drying process, thereby maintaining productivity without requiring any additional steps from existing processes.

Here, in the present invention, the acid scavenger used has a polymer structure, so it does not volatilize during the drying process of the polarizing film, and the acid scavenger is applied in a small amount to the surface of the polarizing film cross-linked with boric acid in a short time. Therefore, penetration from the film surface into the interior is less likely to occur. Therefore, when an acid scavenger is applied to at least one surface of a polyvinyl alcohol film, a polarizing film of the present invention having a layer containing an acid scavenger on at least one surface of the polarizing film can be obtained.

The degree of polarization of the polarizing film is preferably 99.90% or more, particularly preferably 99.9%.
It is 2% or more. If this degree of polarization is too low, there is a tendency that contrast in a liquid crystal display device such as a liquid crystal display cannot be ensured.

Furthermore, the single transmittance of the polarizing film is preferably 42% or more. If this single transmittance is too low, there is a tendency that high brightness of a liquid crystal display device such as a liquid crystal display cannot be achieved.
Single transmittance is a value obtained by measuring the light transmittance of a single polarizing film using a spectrophotometer.

[Manufacturing method of polarizing plate]
Then, by laminating an optically isotropic protective film to one or both sides of the obtained polarizing film via an adhesive, a polarizing plate having a protective film on at least one side can be obtained.

Examples of the protective film include a film made of acetylcellulose resin such as triacetylcellulose and diacetylcellulose, a film made of polyester resin such as polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate, a polycarbonate resin film, Cycloolefin resin film,
Examples include acrylic resin films and films made of chain olefin resins such as polypropylene resins.

The above-mentioned polarizing film and protective film are laminated by a known method, for example,
This is carried out by uniformly applying a liquid adhesive composition to a polarizing film, a protective film, or both, and then bonding and pressing the two together, followed by heating or irradiation with active energy rays.

The degree of polarization of the polarizing plate is preferably 99.9% or more, particularly preferably 99.92% or more. If this degree of polarization is too low, there is a tendency that contrast in a liquid crystal display device such as a liquid crystal display cannot be ensured.
The degree of polarization is generally determined by the light transmittance (H ₁₁ ) measured at wavelength λ with two polarizing plates stacked so that their orientation directions are the same, and the polarization of the two plates. It is calculated according to the following formula from the light transmittance (H ₁ ) measured at wavelength λ with the plates stacked so that their orientation directions are orthogonal to each other.
Degree of polarization = [(H ₁₁ - H ₁ )/(H ₁₁ + H ₁ )] ^1/2

Furthermore, the single transmittance of the polarizing plate is preferably 42% or more. If this single transmittance is too low, there is a tendency that high brightness of a liquid crystal display device such as a liquid crystal display cannot be achieved.
Single transmittance is a value obtained by measuring the light transmittance of a single polarizing plate using a spectrophotometer.

The above-mentioned polarizing film and a polarizing plate made using the same have excellent heat resistance and durability and polarization performance, and can be used in mobile information terminals, personal computers, televisions, projectors, signage, electronic desk calculators, electronic watches, word processors, electronic paper, game consoles, etc. video, camera, photo album, thermometer,
Audio, liquid crystal display devices for automobiles and mechanical instruments, sunglasses, anti-glare glasses, stereoscopic glasses, wearable displays, antireflection layers for display elements (CRT, LCD, organic EL, electronic paper, etc.), optical communication equipment, Preferably used for medical equipment, building materials, toys, etc.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples unless it exceeds the gist thereof.
Each physical property was measured as follows.

<Measurement conditions>
(1) Heat resistance and durability test First, adhesive sheets were pasted on both sides of the obtained polarizing plate, cut into 3.8 cm squares, and then pasted with a 4.0 cm x 8.0 cm glass plate (1 mm thick). Lamination was performed in the order of plate/adhesive sheet/polarizing plate/adhesive sheet/glass plate. This laminate was bonded to the laminate using a cylindrical pressure degassing device for liquid crystals at 50° C. under a pressure of 0.5 MPa for 20 minutes to obtain a heat resistance and durability test sample.
The produced heat resistance durability test sample was placed in a dryer at 105°C, and after 550 hours and 1
The appearance of the sample after 0.5 hours was evaluated according to the following criteria.
(Evaluation criteria)
〇: No red change was observed on the polarizing plate. △: A part of the polarizing plate turned slightly red. ×: The entire polarizing plate turned deep red.

(Preparation of acid scavenger aqueous solution)
・Coating agent (A)
A carbodiimide-containing substance (manufactured by Nisshinbo Chemical Co., Ltd.) was added to 198.5 g of water as an acid scavenger.
V-04" active ingredient 40%) was dissolved to obtain a 0.3% by weight aqueous solution of carbodiimide.
・Coating agent (B)
A substance containing carbodiimide (manufactured by Nisshinbo Chemical Co., Ltd.) was added to 192.5 g of water as an acid scavenger.
V-04" active ingredient 40%) was dissolved to obtain a 1.5% by weight aqueous solution of carbodiimide.

<Example 1>
(Preparation of polarizing film and polarizing plate)
A polyvinyl alcohol film with a film thickness of 30 μm is unrolled from a roll, and while being conveyed horizontally, it is immersed in a water tank with a water temperature of 22°C to swell while being swollen by 1.2 μm in the machine direction (MD direction).
Stretched twice. Next, it was immersed in an aqueous solution at 28°C containing 1.2 g/L of iodine and 25 g/L of potassium iodide, and stretched to 2.2 times in the machine direction (MD direction) while dyeing, and then 30 g/L of boric acid/ L, potassium iodide was immersed in an aqueous solution (57° C.) having a composition of 30 g/L, and uniaxially stretched 5.7 times in the machine direction (MD direction) while crosslinking with boric acid. Finally, the polyvinyl alcohol film was washed with an aqueous potassium iodide solution, and the coating agent (A) was applied to both sides of the polyvinyl alcohol film transported from the last washing tank. Thereafter, it was dried at 80° C. for 40 seconds to obtain a polarizing film with a total stretching ratio of 5.9 times.
Using polyvinyl alcohol aqueous solution as an adhesive on both sides of the obtained polarizing film,
A triacetylcellulose film with a thickness of 40 μm was laminated and dried at 80° C. to obtain a polarizing plate with a single transmittance of 42.7% and a degree of polarization of 99.99%.
A heat resistance and durability test was conducted using the obtained polarizing plate. The results are shown in Table 1 below.

<Example 2>
A polarizing film and a polarizing plate were obtained in the same manner as in Example 1 except that coating agent (A) in Example 1 was changed to coating agent (B). A heat resistance and durability test was conducted using the obtained polarizing plate. The results are shown in Table 1 below.

<Comparative example 1>
A polarizing film and a polarizing plate were obtained in the same manner as in Example 1 except that the coating agent (A) was not applied in Example 1. A heat resistance and durability test was conducted using the obtained polarizing plate. The results are shown in Table 1 below.

Since the polarizing plates obtained in Examples 1 and 2 were obtained using a polarizing film having a layer containing an acid scavenger on at least one surface of the polarizing film, the comparative examples did not have the layer. It can be seen that this polarizing plate has excellent long-term heat resistance and durability compared to polarizing plate No. 1.

In the above embodiments, specific embodiments of the present invention have been shown, but the above embodiments are merely illustrative and should not be construed as limiting. Various modifications apparent to those skilled in the art are intended to be within the scope of the invention.

The polarizing plate obtained using the polarizing film of the present invention has excellent long-term heat resistance and durability, and is used in various liquid crystal display devices, automotive applications that require high durability and polarization performance, and industrial instruments required in various environments. It is preferably used for display purposes, etc.

Claims (4)

A polarizing film comprising a layer containing an acid scavenger on at least one surface of the polarizing film. The polarizing film according to claim 1, wherein the acid scavenger is a carbodiimide compound. 3. The method for producing a polarizing film according to claim 1, wherein the polyvinyl alcohol film is passed through a plurality of processing tanks, and after passing through the last processing tank, acid trapping is performed on at least one surface of the polyvinyl alcohol film. 1. A method for producing a polarizing film, which comprises applying an agent. A polarizing plate comprising a protective film on at least one surface of the polarizing film according to claim 1 or 2.