JP2002174726A - Polarizing film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizing film excellent in polarizing performance in the visible ray spectral range and excellent in durability even when the film is left under high temperature and high humidity conditions for a long time. SOLUTION: The polarizing film consists of a polyvinyl alcohol derivative having a polyvinylene structure obtained from polyvinyl alcohol having <=1.5 mol% proportion of 1,2-glycol couplings.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a polarizing film comprising a polyvinyl alcohol derivative having a polyvinylene structure.

[0002]

2. Description of the Related Art A polarizing plate having a function of transmitting and blocking light is a fundamental component of a liquid crystal display (LCD) together with a liquid crystal having a function of switching light. This LCD has been widely applied to small devices such as calculators and watches in the early days, and recently to laptop computers, word processors, liquid crystal color projectors, in-vehicle navigation systems, and liquid crystal televisions. Since the use of LCDs for a long time on a large screen and outdoor use has increased, a polarizing plate having better optical performance and durability than conventional products has been required.

In general, a polarizing plate is formed of a polyvinyl alcohol film (hereinafter, referred to as “P”).
Abbreviated as “VA film”, the polyvinyl alcohol as a raw material thereof is referred to as a polyvinyl alcohol-based polymer, and this may be abbreviated as “PVA”).
It has a configuration in which a support plate such as a cellulose triacetate (TAC) film is attached to both sides of a polarizing film produced by dyeing. Examples of the polarizing film include an iodine-based polarizing film obtained by dyeing a PVA film with iodine or the like;
A dye-based polarizing film obtained by dyeing a VA film with a dichroic dye or the like, and a polarizing film comprising a PVA derivative having a polyvinylene structure obtained by subjecting a PVA film to a dehydration reaction are known (US Pat. No. 2,173,304).
Specification).

[0004] Among these conventionally known polarizing films, an iodine-based polarizing film and a dye-based polarizing film have a problem that the polarizing performance is high but the durability is low. Further, a polarizing film made of a polyvinyl alcohol derivative having a polyvinylene structure has excellent durability but has a problem of low polarizing performance. As a solution to these problems, there has been proposed a polarizing film comprising a polyvinyl alcohol derivative having a polyvinylene structure and obtained by using a polyvinyl alcohol having a degree of polymerization of 2000 or more as a material (Japanese Patent Application Laid-Open No. Hei 10-31923).
No. 6), a great improvement effect is recognized.

However, in recent years, the development of LCD applications has been remarkable, for example, the screen has become larger and the screens have been used outdoors for mobile applications, and a polarizing plate having more excellent optical performance and durability than ever before. Is required.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a polarizing film excellent in durability and polarizing performance.

[0007]

According to the present invention, the above-mentioned object is to provide a polyvinyl alcohol having a 1,2-glycol bond amount of 1.5 mol% or less (hereinafter, this polyvinyl alcohol is distinguished from ordinary PVA). Therefore, it may be abbreviated as modified PVA.), And can be achieved by a polarizing film comprising a polyvinyl alcohol derivative having a polyvinylene structure. The polarizing film of the present invention has excellent polarization performance in the range of the visible light spectrum, and also has excellent durability when left for a long time under high temperature and high humidity.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. The modified PVA used in the present invention is 1,2.
-The glycol bond amount must be 1.5 mol% or less, more preferably 1.4 mol% or less, further preferably 1.2 mol% or less, and particularly preferably 1.0 mol% or less. . From the viewpoint of improving the heat resistance, durability and polarization performance of the polarizing film, the lower the amount of 1,2-glycol bond of the modified PVA, the more preferable. Since it itself becomes difficult, it is appropriate that the content is 0.5 mol% or more.

In the present invention, the degree of polymerization of the modified PVA is
In consideration of the strength and processing characteristics of the film made of the modified PVA, it is preferably at least 1,000, more preferably at least 1,800, particularly preferably at least 2,000. The degree of polymerization of the modified PVA is preferably 8,000 or less, more preferably 4,000 or less, and particularly preferably 3,000 or less, in view of processing characteristics such as film formation and stretching. The degree of polymerization of the modified PVA was measured according to JIS-K
6726.

The degree of saponification of the modified PVA is preferably at least 95 mol%, more preferably at least 98 mol%, particularly preferably at least 99 mol%, in view of the polarizing performance and durability of the resulting film having a polyvinylene structure. As described above, the optimum amount is 99.5 mol% or more. Further, the higher the degree of saponification of the modified PVA, the more preferable. However, if the degree of saponification is too high, the production of the modified PVA itself becomes difficult. The degree of saponification in the present specification indicates the ratio of units actually saponified into vinyl alcohol units among units that can be converted into vinyl alcohol units by saponification. The degree of saponification of modified PVA is JIS-
It can be determined by the method described in K6726.

The polarizing film of the present invention preferably has a two-color ratio of 25 or more, more preferably 30 or more, and 3
Particularly preferred is 3 or more. As a method of improving the two-color ratio of the polarizing film, a method of dry-heating stretching a film made of PVA having a small amount of 1,2-glycol bond containing a dehydration accelerator under a low oxygen atmosphere at a high stretching ratio is used. preferable.

The maximum absorption wavelength in the visible light absorption spectrum (wavelength: 380 to 780 nm) of the polarizing film is preferably 500 nm or more, and 520 or more.
nm or more is more preferable, and 540 nm or more is particularly preferable. The upper limit of the maximum absorption wavelength is preferably 650 nm, more preferably 630 nm. Modified PVA 1,
As the amount of 2-glycol bond decreases, the maximum absorption wavelength tends to shift to a higher wavelength side. When the maximum absorption wavelength is within the above range, it is considered that the number of vinylene units of the conjugated double bond forming the polyvinylene structure is about 15 to 30.

The PVA having a 1,2-glycol bond content of 1.5 mol% or less used in the present invention is obtained by polymerizing a vinyl ester monomer at a temperature of 50 ° C. or less to obtain a vinyl ester polymer. It can be obtained by saponification.

Examples of the polymerization method of the vinyl ester monomer include a low-temperature bulk polymerization method, a low-temperature suspension polymerization method and a low-temperature emulsion polymerization method. In the low-temperature polymerization method, in a polymerization system having a large chain transfer such as a vinyl ester-based monomer, since the chain transfer is suppressed with a decrease in the polymerization temperature, the degree of polymerization usually increases, but the polymerization rate and the like are adjusted. By using a chain transfer agent in combination, it is possible to obtain PVA having a 1,2-glycol bond amount of 1.5 mol% or less and a desired degree of polymerization. The polymerization temperature is -50 from the viewpoint of easiness of polymerization and performance of the obtained polarizing film.
The range of -50C is suitable, the range of -40C to 40C is preferable, and the range of -30C to 20C is particularly preferable. Examples of the polymerization catalyst include an azo catalyst, a peroxide catalyst, and a redox catalyst. Further, from the viewpoint of the durability and polarization performance of the polarizing film, the polymerization of the vinyl ester-based monomer is preferably performed by a low-temperature emulsion polymerization method using a redox catalyst.

As the chain transfer agent that can be used for the polymerization of the vinyl ester monomer, a conventionally known chain transfer agent such as an aldehyde compound can be suitably used. Particularly, in view of the durability and the polarizing performance of the polarizing film, R '
A mercaptan represented by SH (R ′ represents a hydrocarbon group having 1 to 18 carbon atoms or a mono- or polyhydroxy hydrocarbon group, and S represents a sulfur atom) is preferably used. In the mercaptan represented by the above formula, when the number of carbon atoms of R ′ is less than 1, the reactivity of the mercaptan is too high to make handling difficult. When the number of carbon atoms exceeds 18, the obtained PVA crystal This makes it impossible to obtain the desired polarizing film having excellent durability.
Examples of mercaptans that can be used include, for example, methanethiol, ethanethiol, n-propanethiol, i
-Propanethiol, n-butanethiol, i-butanethiol, t-butanethiol, n-hexanethiol, n-octanethiol, i-octanethiol, n
-Decanethiol, n-dodecanethiol, t-dodecanethiol, n-tetradecanethiol, n-hexadecanethiol, n-octadecanethiol, 2-mercaptoethanol, 3-mercapto-1-propanol,
1-mercapto-2-propanol, 3-mercapto-
Examples thereof include 1,2-propanediol, 4-mercapto-1-butanol, and 3-mercapto-2-butanol. Among these, the odor is relatively small,
PV with good workability, relatively high reactivity, and obtained PV
From the viewpoint of not impairing the crystallinity of A, a mercaptan containing a mono- or polyhydroxyhydrocarbon group is more preferable, and 2-mercaptoethanol, 3-mercapto-1-propanol, 4-mercapto-1-butanol and the like. The mercaptan containing a monohydroxy group is particularly preferred. In the process of producing the modified PVA used in the present invention, when a mercaptan is used as a chain transfer agent at the time of polymerization of a vinyl ester-based monomer, a mercapto group is introduced into a molecular terminal of the modified PVA. From a film in which a mercapto group is introduced at the molecular terminal of the modified PVA, although the reason is not clear, a polarizing film having more excellent durability and optical performance can be obtained. You.

In the present invention, examples of the vinyl ester monomer which can be used for producing PVA having a 1,2-glycol bond content of 1.5 mol% or less include, for example, vinyl formate, vinyl acetate, vinyl propionate, valeric acid Examples thereof include vinyl, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and vinyl versatate. Among these, vinyl acetate is preferable.

When the vinyl ester monomer is copolymerized, if necessary, a copolymerizable monomer may be used within a range that does not impair the effects of the present invention (preferably 15 mol% or less,
(More preferably 5 mol% or less).

Examples of such a monomer copolymerizable with the vinyl ester monomer include olefins having 3 to 30 carbon atoms such as ethylene, propylene, 1-butene and isobutene; acrylic acid and its salts; methyl acrylate , Ethyl acrylate, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, acrylic acid 2
Acrylates such as ethylhexyl, dodecyl acrylate and octadecyl acrylate; methacrylic acid and salts thereof; methyl methacrylate, ethyl methacrylate;
Methacrylic acid such as n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadodecyl methacrylate Esters: acrylamide, N-methylacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide, diacetoneacrylamide, acrylamidepropanesulfonic acid and its salts, acrylamidopropyldimethylamine and its salts or quaternary salts, N-methylol Acrylamide derivatives such as acrylamide and its derivatives; methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidepropanesulfonic acid and salts thereof, Methacrylamide derivatives such as lylamidopropyldimethylamine and salts or quaternary salts thereof, N-methylolacrylamide and derivatives thereof; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i- Vinyl ethers such as butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether and stearyl vinyl ether; nitriles such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride and vinylidene fluoride; allyl acetate , Allyl compounds such as allyl chloride; maleic acid and its salts or esters; itaconic acid and its salts or esters; vinyltrimethoxysilane Of vinyl silyl compounds; isopropenyl acetate and the like.

In the present invention, PVA having a 1,2-glycol bond content of 1.5 mol% or less is produced by saponifying the above-mentioned polyvinyl ester-based polymer according to a known method using an alkali catalyst or an acid catalyst. can do.

The polarizing film of the present invention is produced using a film obtained by forming PVA having a 1,2-glycol bond content of 1.5 mol% or less as a material. Examples of a method for forming a film from PVA include a casting method or a die casting method in which a PVA solution is cast on a film formed of a resin, a drying drum or a drying belt. Examples of the PVA solvent in the method for forming these films include water, an organic solvent, and a mixture of water and an organic solvent. Examples of the organic solvent in this case include dimethyl sulfoxide, phenol, methanol, and ethanol. In the PVA solution, if necessary, a plasticizer,
Surfactants, dichroic dyes, inorganic salts and the like can be added. The formed PVA film may be subjected to a heat treatment as needed. The thickness of the PVA film is 5-5
00 μm is preferable, 10 to 200 μm is more preferable, and 20 to 100 μm is particularly preferable.

The polarizing film of the present invention is prepared by pre-swelling the PVA film, dehydrating to form a polyvinylene structure, uniaxial stretching (the uniaxial stretching and dehydration are often performed simultaneously), and fixing with a boron compound. It can be manufactured through steps such as treatment and drying, and the order and number of these steps are not particularly limited. The polarizing film manufactured through these steps may be further subjected to a heat treatment as needed.

The PVA film is subjected to a dehydration treatment, whereby a polyvinylene structure is formed on the PVA. The dehydration treatment of the PVA film can be carried out by stretching the PVA film containing the dehydration accelerator, or by heating the stretched PVA film while containing the dehydration accelerator. Examples of a method for incorporating a dehydration accelerator into a PVA film include a method in which a PVA film is immersed in an aqueous solution containing a dehydration accelerator, a method in which a PVA film is exposed to an atmosphere of a gaseous dehydration accelerator.
A method of placing an A film, a method of forming a PVA solution containing a dehydration accelerator, and the like can be given. As a dehydration accelerator, hydrochloric acid, protonic acids such as sulfuric acid, and stannic chloride,
And stannic halides such as stannic bromide. The dehydration accelerator is preferably added in an amount ranging from 0.001 to 10% by weight based on PVA. When the amount of the dehydration accelerator is less than the above range, the polarization performance tends to be hardly developed. When the amount of the dehydration accelerator is more than the above range, efficient dehydration may be difficult. The time at which the dehydration accelerator is added may be, for example, during the formation of the PVA film, before the uniaxial stretching of the PVA film, or before the dehydration treatment of the PVA film. When a dehydration accelerator is added to a stock solution of a PVA film, if the drying temperature at the time of film formation is too high, PV
Care must be taken because A may be thermally oxidized.

Examples of the method of uniaxially stretching the PVA film include dry heat stretching, wet stretching, stretching in warm water, and stretching in air while absorbing the film.
Stretching temperature at the time of dry heat stretching of the PVA film is 100 ° C.
It is preferably at least 120 ° C., more preferably at least 140 ° C. Stretching temperature is 250 ° C
The temperature is preferably at most 230 ° C, more preferably at most 230 ° C, particularly preferably at most 220 ° C. The stretching temperature may be changed according to the stretching state of the film being stretched. In addition, when the PVA film is stretched by dry heat, it is preferable that the stretching be performed under a low oxygen atmosphere such as a nitrogen atmosphere or a vacuum because coloring due to oxidation of the PVA may occur.
The PVA film changes into a colored film in which a polyvinylene structure having polarization performance is formed during the dry heat stretching.
The stretching temperature during the wet stretching of the PVA film is preferably 20 ° C. or higher, more preferably 40 ° C. or higher,
A temperature of 50 ° C. or higher is particularly preferred. The stretching temperature is preferably 90 ° C. or lower, more preferably 80 ° C. If a PVA film is simply stretched by a wet method, a polyvinylene structure is hardly generated, so that a separate heat treatment is required. When the stretching temperature is low, it is difficult to stretch the film at a high magnification, and it is difficult to improve the polarization performance. On the other hand, when the stretching temperature is high, the film is likely to be cut during the stretching. In addition,
When the stretching is performed in two or more times, a combination of the same type of stretching such as dry stretching-dry stretching, wet stretching-wet stretching may be repeated, or dry stretching-wet stretching,
Different stretching combinations such as wet stretching and dry stretching may be repeated. The stretching ratio is preferably 4 times or more, more preferably 5 times or more. As the stretching ratio increases, the maximum absorption wavelength in the film shifts to the higher wavelength side, and the optical characteristics are improved. The upper limit of the stretching ratio is preferably 10 times, more preferably 9 times, from the viewpoint of uniform stretchability.

If the PVA film is not sufficiently dehydrated at the time of stretching and the formation of the polyvinylene structure is insufficient, a dehydration accelerator is added to the stretched PVA film, followed by heating to further increase the PVA film. The film is dehydrated. The heating temperature in this case is 90 to 180
C. is preferable, and a range of 130 to 170 C. is more preferable. When the thickness of the PVA film is 30 to 100 μm, the amount of dehydration from the PVA film is preferably 1 to 5% by weight based on the PVA film. P
If the amount of dehydration from the VA film is small, the amount of absorption of visible light decreases, and sufficient polarization performance is not exhibited. On the other hand, if the amount of dehydration is too large, the amount of absorption of visible light becomes excessive, making it difficult to obtain a moderately transparent polarizing film or causing a cross-linking reaction between molecules, reducing the number of conjugated double bonds. And the film becomes brittle.

If the dehydration accelerator remains in the polarizing film, the polarizing performance may be changed when the polarizing film is left at a high temperature. It is preferable to remove the dehydration accelerator by immersing in an aqueous solution of an inorganic substance such as saline.

P having a polyvinylene structure formed on PVA
The VA film is preferably immersed in a fixing bath containing 1 to 6% by weight of a boron compound (eg, boric acid).
This immersion treatment may be performed according to the required level of water resistance. It is preferable that the temperature of the fixed treatment bath is maintained in the range of 20 to 70 ° C. PV after removal from fixed treatment bath
The A film is subjected to drying, and the temperature during the drying is 30 to
Suitably, it is in the range of 80 ° C. After drying, the PVA film may be further subjected to a heat treatment at a temperature in the range of 50 to 150 ° C.

The thickness of the polarizing film of the present invention is 5 to 200.
It is preferably in the range of μm, more preferably in the range of 10 to 100 μm. In order to impart more sufficient water resistance to the polarizing film of the present invention, a transparent protective film having mechanical strength may be attached to both surfaces or one surface thereof to form a polarizing plate. Examples of the protective film used for this purpose include a cellulose acetate film, an acrylic film, and a polyester film.

[0028]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to the examples. In the examples, “%” and “parts” mean “% by weight” and “parts by weight”, respectively, unless otherwise specified. The polyvinylene structure in the polarizing film was confirmed by measuring the maximum absorption wavelength in the visible light absorption spectrum (wavelength: 380 to 780 nm) using an ultraviolet-visible spectrum. The transmittance, the degree of polarization, and the dichroic ratio of the polarizing film were measured in accordance with the standards of the Electronic Industries Association of Japan (EIAJ) LD-201-1983 using a spectrophotometer with a C light source and a 2 degree field of view. Calculated.
The polarizing film is usually used in a state in which a protective film is laminated, but in the following examples, the measurement was performed in a state of the polarizing film alone without the protective film.

The calculation of the dichroic ratio of the polarizing film described in the examples was performed by the following method. Dichroic ratio: The dichroic ratio was used as an index for evaluating the polarizing performance of the obtained polarizing film. This dichroic ratio is based on the standard of the Electronic Industries Association of Japan (EIAJ) LD-201-198.
The transmittance TS (%) and the degree of polarization P obtained by measuring and calculating with a C light source and a 2 degree field of view using a spectrophotometer according to
(%) Was determined from the following equation. Dichroic ratio = log (TS / 100−TS / 100 × P
/ 100) / log (TS / 100 + TS / 100 ×
P / 100)

Example 1 Using 2-mercaptoethanol as a chain transfer agent,
By performing the low-temperature emulsion polymerization at 0 ° C., the 1,2-glycol bond amount is 0.7 mol%, the saponification degree is 99.9 mol%,
A modified PVA having a polymerization degree of 2400 and having a hydroxyethylthio group was obtained. 100 μm thick using this modified PVA
Was immersed in a 20 ° C. aqueous hydrochloric acid solution (0.01 N) for 10 minutes, and then dried at 20 ° C. for 30 minutes. The obtained PVA film is heated at 190 ° C.
6.8 times uniaxially in a nitrogen atmosphere, and then stretched PVA film is placed in a 4% aqueous boric acid solution for 1 hour.
It was immersed for 0 minutes to remove and fix the hydrochloric acid at the same time.
Finally, the obtained film was dried with warm air at 40 ° C. to obtain a polarizing film having a polyvinylene structure with a thickness of 20 μm. The transmittance, the degree of polarization, the dichroic ratio and the maximum absorption wavelength of the obtained polarizing film were measured, and the polarizing film was further treated at 80 ° C. and 90% RH for 10 hours.
After standing for 00 hours, the transmittance, the degree of polarization and the dichroic ratio were measured. Table 1 shows the results.

Example 2 Using 4-mercapto-1-butanol as a chain transfer agent and carrying out low-temperature emulsion polymerization at -20 ° C., 1,2
-A glycol bond amount of 0.8 mol% and a saponification degree of 99.9.
A modified PVA having a molar ratio of 1900 and a hydroxybutylthio group having a degree of polymerization of 1900 was obtained. Using this modified PVA, a thickness of 7
A 5 μm PVA film was prepared and immersed in a 20 ° C. aqueous sulfuric acid solution (0.01 N) for 10 minutes.
Dry at 0 ° C. for 30 minutes. The obtained PVA film was
The film was stretched in a uniaxial direction 6.5 times in nitrogen at 20 ° C., and then the stretched PVA film was washed with distilled water. Finally, the obtained film was dried with warm air at 40 ° C. to obtain a polarizing film having a polyvinylene structure with a thickness of 18 μm. Table 1 shows the results of evaluating the optical characteristics of the polarizing film in the same manner as in Example 1.

Example 3 Using n-butanethiol as a chain transfer agent and performing low-temperature solution polymerization at 30 ° C., the 1,2-glycol bond amount was 1.3 mol% and the saponification degree was 99.9 mol%. , Polymerization degree 1
A modified PVA having 700 butylthio groups was obtained. Using this modified PVA, a PVA film having a thickness of 75 μm was prepared and placed in a 20 ° C. aqueous sulfuric acid solution (0.1 N).
It was immersed for 0 minutes and then dried at 20 ° C. for 30 minutes. The obtained PVA film was uniaxially stretched 5.2 times in nitrogen at 160 ° C., and then the stretched PVA film was washed with distilled water. Finally, the obtained film was dried with warm air at 40 ° C. to obtain a polarizing film having a polyvinylene structure with a thickness of 24 μm. Table 1 shows the results of evaluating the optical characteristics of the polarizing film in the same manner as in Example 1.

Example 4 A 1,2-glycol bond amount of 1.3 mol%, a saponification degree of 99.9 mol%, and a polymerization degree of 1 obtained by low-temperature solution polymerization at 30 ° C.
A 75 μm thick PVA film made from 700 PVAs was immersed in a 20 ° C. aqueous sulfuric acid solution (0.1 N) for 10 minutes. Dry at 20 ° C. for 30 minutes. The film was uniaxially stretched 5.2 times in nitrogen at 160 ° C. Next, it was washed with distilled water. Finally, by drying with warm air at 40 ° C,
A polarizing film having a polyvinylene structure and having a thickness of 24 μm was obtained. Table 1 shows the evaluation results of the polarizing film.

Comparative Example 1 A PVA film having a thickness of 100 μm and obtained by forming a PVA film having a polymerization degree of 1700, a saponification degree of 99.9 mol%, and a 1,2-glycol bond amount of 1.6 mol% at 20 ° C. In sulfuric acid aqueous solution (0.5N) for 10 minutes,
For 30 minutes. The obtained PVA film was treated with 130
The film was stretched 4.3 times uniaxially in air at ℃, and then the stretched PVA film was washed with distilled water. Finally, the obtained film was dried with warm air at 40 ° C. to obtain a 51 μm-thick polarizing film having a polyvinylene structure. Table 1 shows the results of evaluating the optical characteristics of the polarizing film in the same manner as in Example 1.

Comparative Example 2 A 75 μm thick PVA film obtained by forming a PVA film having a polymerization degree of 4000, a saponification degree of 99.7 mol% and a 1,2-glycol bond amount of 1.6 mol% at 30 ° C. Dyeing aqueous solution (iodine 0.2 g / l, potassium iodide 20 g / l,
(Boric acid 40 g / l) for 3 minutes. Then, PV
A film was stretched uniaxially four times in a boric acid aqueous solution (40 g / l) at 50 ° C., and treated at 30 ° C. (potassium iodide 20 g / l, boric acid 40 g / l, zinc chloride 10 g).
g / l) for 4 minutes. Finally, the obtained film was dried with warm air at 40 ° C. to obtain a thickness of 16 μm.
(Not having a polyvinylene structure) was obtained. Table 1 shows the results of evaluating the optical characteristics of the polarizing film in the same manner as in Example 1.

[0036]

[Table 1]

[0037]

The polarizing film of the present invention has excellent polarization performance in the range of visible light spectrum, and also has excellent durability when left for a long time under high temperature and high humidity. It can be effectively used not only for manufacturing LCD navigation systems, but also for manufacturing polarizing plates for in-vehicle LCDs such as LCD televisions whose temperature and humidity change greatly.

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Claims (5)

[Claims] 1. A polarizing film comprising a polyvinyl alcohol derivative having a polyvinylene structure obtained from polyvinyl alcohol having a 1,2-glycol bond content of 1.5 mol% or less. 2. The polarizing film according to claim 1, wherein the dichroic ratio is 25 or more. 3. A polyvinyl alcohol having a 1,2-glycol bond amount of 1.5 mol% or less has an RS-group (R is a mono- or polyhydroxy hydrocarbon group at its terminal)
Represents a sulfur atom).
The polarizing film as described in the above. 4. The polarizing film according to claim 1, wherein a maximum absorption wavelength in a visible light absorption spectrum range is 500 nm or more. 5. The polyvinyl alcohol having a 1,2-glycol bond content of 1.5 mol% or less has a polymerization degree of 1,000 or more and 4000 or less, and a saponification degree of 95 mol% or more. 3. The polarizing film according to claim 1.