JPH10319236A - Polarizing film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve durability and polarizing performance by using a PVA deriv. having a specified polyvinylene structure and imparting a specified dichroism ratio. SOLUTION: This polarizing film is made of a PVA deriv. having a polyvinytene structure obtd. using PVA having a polymn. degree of >=2,000 and has a dichroism ratio of >=20, preferably >=25, especially preferably >=30. By the increased polymn. degree, durability and polarizing performance are improved. The upper limit of the polymn. degree is preferably 30,000 from the viewpoint of film forming property. The polymn. degree of PVA is measured in accordance with JIS-K-6726. A method for hot-stretching a film of PVA contg. a dehydration accelerator and having a high polymn. degree in a dry state at a high stretching rate in a low oxygen atmosphere is preferably adopted as a method for increasing the dichroism ratio.

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. L
The application fields of CDs include small devices such as calculators and watches in the early days, as well as laptop computers,
There are word processors, liquid crystal color projectors, in-vehicle navigation systems, liquid crystal televisions and indoor and outdoor measuring instruments. LCDs are used in a wide range of conditions from low temperature to high temperature and low humidity to high humidity. Therefore, a polarizing plate excellent in durability such as wet heat resistance and polarization performance is demanded.

A polarizing plate is formed of polyvinyl alcohol (hereinafter, referred to as polyvinyl alcohol).
Abbreviated as PVA. ) The polarizing film obtained by using the film has a configuration in which a support plate such as cellulose triacetate is bonded to both sides. As a polarizing film, PVA
Iodine-based polarizing films whose films are dyed with iodine, etc., dye-based polarizing films obtained by dyeing PVA films with dichroic dyes, and polarizing films made of PVA derivatives having a polyvinylene structure obtained by subjecting PVA films to a dehydration reaction are known. (U.S. Pat. No. 2,173,3)
04).

[0004] Iodine-based polarizing films and dye-based polarizing films have a problem that they have high polarizing performance but low durability. 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.

[0005]

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

[0006]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present invention comprises a polyvinyl alcohol derivative having a polyvinylene structure and obtained by using a polyvinyl alcohol having a polymerization degree of 2,000 or more as a material. Was found to be 20 or more, and the present invention was completed.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. PVA used for the material of the polarizing film of the present invention
Has a polymerization degree of 2000 or more, preferably 2800 or more, more preferably 3000 or more, and particularly preferably 3500 or more. By increasing the degree of polymerization, durability and polarization performance are improved. The upper limit of the degree of polymerization is 3 from the viewpoint of film forming property.
0000 is preferred. The degree of polymerization of PVA is JIS-K-6
726.

The degree of saponification of PVA is preferably 90 mol% or more, more preferably 98 mol% or more, more preferably 99 mol% or more, from the viewpoint of polarization performance and durability.
9.5 mol% or more is particularly preferred.

The two-color ratio of the polarizing film is 20 or more, preferably 25 or more, and particularly preferably 30 or more. 2
As a method for improving the color ratio, it is preferable to dry-heat stretch a high polymerization degree PVA film containing a dehydration accelerator at a high stretching ratio in a low oxygen atmosphere.

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, more preferably 520 nm or more, and particularly preferably 540 nm or more. The upper limit of the maximum absorption wavelength is preferably 650 nm, more preferably 620 nm. As the degree of polymerization of PVA used for the material increases, 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.

As a method for producing PVA, there is a method of saponifying a polyvinyl ester polymer obtained by radical polymerization of a vinyl ester monomer such as vinyl acetate using an alkali catalyst or an acid catalyst.

Examples of the method for polymerizing vinyl ester monomers include bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. In order to obtain PVA having a degree of polymerization of 4000 or more, bulk polymerization or emulsion polymerization is preferred. Examples of the polymerization catalyst include an azo catalyst, a peroxide catalyst, and a redox catalyst.

The vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, vinyl trifluoroacetate and versatic. Vinyl acid and the like. Among these, vinyl acetate is preferred.

[0014] A copolymerizable comonomer may be copolymerized with the vinyl ester monomer. Examples of the comonomer include olefins such as ethylene, propylene, 1-butene, and isobutene; acrylic acid and salts thereof; methyl acrylate, ethyl acrylate, n-propyl acrylate;
Acrylates such as i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate; methacrylic acid and salts thereof; Methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, methacrylic acid Methacrylic esters such as octadecyl; acrylamide,
N-methylacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide, diacetone acrylamide, acrylamidopropanesulfonic acid and its salts, acrylamidopropyldimethylamine and its salts or quaternary salts, N-methylolacrylamide and its derivatives, etc. Methacrylamide, N-methyl methacrylamide, N-ethyl methacrylamide, methacrylamidopropanesulfonic acid and its salts, methacrylamidopropyldimethylamine and its salts or quaternary salts thereof, N-methylol methacrylamide and its derivatives Methacrylamide derivatives such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl Vinyl ethers such as nyl ether, i-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 compounds such as allyl acetate and allyl chloride; maleic acid and salts or esters thereof, vinylsilyl compounds such as vinyltrimethoxysilane, and isopropenyl acetate.

Other methods for producing PVA include t-
A method of hydrolyzing a polyvinyl ether-based polymer such as butyl vinyl ether, benzyl vinyl ether, and trimethylsilyl vinyl ether may be used.

In the production of the polarizing film of the present invention, a PVA film obtained by forming a PVA having a degree of polymerization of 2000 or more is used as a material. Examples of a method for forming a PVA film include a casting method and a die casting method in which a PVA solution is cast on a resin film, a drying drum or a drying belt. Examples of the PVA solvent include water, an organic solvent, or a mixture of water and an organic solvent. Examples of the organic solvent include dimethyl sulfoxide, phenol, methanol, ethanol and the like. In the PVA solution, if necessary, a plasticizer, a surfactant, a dichroic dye,
Inorganic salts and the like can be added. The PVA film may be heat-treated as needed. The thickness of the PVA film is preferably from 5 to 500 μm, and from 30 to 200 μm.
m is more preferred.

As a process for manufacturing a polarizing film, PVA is used.
Examples include a preliminary swelling treatment of the film, a dehydration treatment for forming a polyvinylene structure, a uniaxial stretching treatment (the dehydration treatment is often performed simultaneously during the uniaxial stretching), a fixing treatment with a boron compound, and a drying treatment. Further, heat treatment may be performed if necessary. There is no restriction on the order or number of each processing step.

As the dehydration treatment for forming a polyvinylene structure on the PVA film, PVA containing a dehydration accelerator is used.
Examples of the method include a method of stretching the A film and a method of heating the stretched PVA film by adding a dehydration accelerator to the stretched PVA film. P
As a method of allowing the VA film to contain a dehydration accelerator,
Examples include a method of dipping the PVA film in an aqueous solution containing a dehydration accelerator, a method of placing the PVA film in an atmosphere of a gaseous dehydration accelerator, and a method of forming a film using a PVA solution containing a dehydration accelerator. Examples of the dehydration accelerator include protic acids such as hydrochloric acid and sulfuric acid, and stannic halides such as stannic chloride and stannic bromide. The addition amount of the dehydration accelerator is preferably 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 is hardly exhibited. On the other hand, when the amount of the dehydration accelerator is more than the above range, efficient dehydration becomes difficult. Examples of the timing of adding the dehydration accelerator include before film formation, before uniaxial stretching, and before dehydration treatment. In addition, when the dehydration accelerator is added to the undiluted solution of the PVA film, care must be taken because if the drying temperature during the film formation is too high, the PVA may be thermally oxidized.

Examples of the method of uniaxial stretching include dry heat stretching, wet stretching, stretching in warm water, and stretching in air while absorbing water. The stretching temperature during dry heat stretching is 10
0 ° C. or higher is preferable, 120 ° C. or higher is more preferable, and 1
Particularly preferred is 40 ° C. or higher. The upper limit of the stretching temperature is 2
50 ° C is preferred, 230 ° C is preferred, and 220 ° C is more preferred. The stretching temperature may be changed according to the stretching state during stretching. Further, the dry heat stretching is preferably performed in a low-oxygen atmosphere such as a nitrogen atmosphere or a vacuum because coloring due to oxidation of PVA may occur. During the dry heat stretching, the PVA film turns into a colored film having polarizing properties. The stretching temperature during wet stretching is preferably 20 ° C. or higher, more preferably 40 ° C. or higher, and particularly preferably 50 ° C. or higher. The upper limit of the stretching temperature is preferably 90 ° C, more preferably 80 ° C. In addition, only by wet stretching,
Since a polyvinylene structure is not easily generated, a separate heat treatment is required. When the stretching temperature is low, it is difficult to stretch 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 performing stretching in two or more times,
Each stretching method may be changed. The stretching ratio is preferably 4 times or more, more preferably 5 times or more. As the stretching ratio increases, the maximum absorption wavelength 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 dehydration treatment (formation of the polyvinylene structure) by stretching is insufficient, the dehydration treatment is carried out by adding a dehydration accelerator and then heating the film.
The temperature of the dehydration treatment is preferably 90 to 180 ° C,
130-170 ° C is more preferred. When the thickness of the PVA film is 30 to 100 μm, the amount of dehydration from PVA is preferably 1 to 5% by weight based on the PVA film. If the amount of dehydration from PVA is small, the absorption amount 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, and it is difficult to obtain a moderately transparent polarizing film, and a cross-linking reaction between molecules occurs to reduce the number of conjugated double bonds or the film becomes brittle. Become

If the dehydration accelerator remains in the polarizing film, the polarization performance may change when the film is left at a high temperature. Therefore, the film may be used in an aqueous solution of an inorganic substance such as water, a weak alkali aqueous solution, aqueous methanol, or a saline solution. It is better to immerse to remove the dehydration accelerator.

After the polyvinylene structure is formed in PVA, it is preferable to immerse it in a fixing treatment bath containing usually 1 to 6% by weight of a boron compound (eg, boric acid). This fixing treatment may be performed according to the required level of water resistance.
The temperature of the fixed treatment bath is preferably from 20 to 70C. The drying temperature after taking out from the fixing bath is preferably 30 to 80C. After drying the film, 50-150 ° C
Heat treatment.

The thickness of the polarizing film of the present invention is from 5 to 20.
0 μm is preferable, and 10 to 100 μm is more preferable.
In order to obtain more sufficient water resistance, the polarizing film of the present invention may be formed into a polarizing plate by bonding a transparent protective film having mechanical strength to both surfaces or one surface. As the protective film, a cellulose acetate film, an acrylic film, a polyester film or the like is usually used.

[0024]

EXAMPLES The present invention will now be described in detail with reference to examples, but the present invention is not limited to the examples. In addition,
“%” And “parts” in Examples are unless otherwise specified.
They mean "% by weight" and "parts by weight", respectively. The polyvinylene structure in the polarizing film has a visible light absorption spectrum (wavelength: 380 to 380) using an ultraviolet-visible spectrum.
It was confirmed by measuring the maximum absorption wavelength in the range of 780 nm). The transmittance, the degree of polarization and the dichroic ratio of the polarizing film are measured according to the standards of the Japan Electronics Machinery Association (EIAJ) L
In accordance with D-201-1983, C was measured using a spectrophotometer.
It was calculated by measuring with a light source and a 2 degree visual field. 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.

Example 1 PVA having a thickness of 100 μm (degree of polymerization 4000, degree of saponification 9)
9.9 mol%) film was treated with a 20 ° C sulfuric acid aqueous solution (0.0
1N) for 10 minutes. Dry at 20 ° C. for 30 minutes. The film was stretched 6.8 times uniaxially in nitrogen at 190 ° C. Next, it was immersed in a 4% boric acid aqueous solution for 10 minutes to simultaneously remove and fix the hydrochloric acid. Finally, a polarizing film having a polyvinylene structure with a thickness of 20 μm was obtained by drying with warm air at 40 ° C. Table 1 shows the evaluation results of the polarizing film.

Example 2 PVA having a thickness of 75 μm (degree of polymerization 9000, degree of saponification 9
9.9 mol%) film was treated with a 20 ° C sulfuric acid aqueous solution (0.0
1N) for 10 minutes. Dry at 20 ° C. for 30 minutes. The film was uniaxially stretched 6.5 times in nitrogen at 220 ° 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 18 μm was obtained. Table 1 shows the evaluation results of the polarizing film.

Example 3 PVA having a thickness of 75 μm (degree of polymerization: 2600, degree of saponification: 9)
9.7 mol%) film was treated with a 20 ° C. sulfuric acid aqueous solution (0.1 mol%).
) 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 PVA having a thickness of 100 μm (degree of polymerization 1700, degree of saponification 9)
9.9 mol%) film was added to a 20 ° C. aqueous sulfuric acid solution (0.5
) For 10 minutes. Dry at 20 ° C. for 30 minutes. The film was stretched 4.3 times uniaxially in air at 130 ° C. Next, it was washed with distilled water. Finally, by drying with warm air at 40 ° C., a polarizing film having a polyvinylene structure with a thickness of 51 μm was obtained. Table 1 shows the evaluation results of the polarizing film.

Comparative Example 2 PVA having a thickness of 75 μm (degree of polymerization 4000, degree of saponification 9)
9.7 mol%) The film was dyed at 30 ° C. in an aqueous dye solution (iodine 0.2 g / l, potassium iodide 20 g / l, boric acid 40
g / l) for 3 minutes. Subsequently, the film was stretched four times uniaxially in a boric acid aqueous solution (40 g / l) at 50 ° C.
It was immersed in a treatment aqueous solution at 0 ° C. (potassium iodide 20 g / l, boric acid 40 g / l, zinc chloride 10 g / l) for 4 minutes. Finally, by drying with 40 ° C. warm air, an iodine-based polarizing film (having no polyvinylene structure) having a thickness of 16 μm was obtained. Table 1 shows the evaluation results of the polarizing film.

[0030]

[Table 1]

[0031]

The polarizing film of the present invention has excellent polarization performance in the visible light spectrum range and excellent durability when left for a long time under high temperature and high humidity. The polarizing film of the present invention can be used for an in-vehicle L such as an LCD navigation system or an LCD television, which has a large temperature or humidity change.
It is effective as a polarizing plate for CD.

Claims (3)

[Claims] 1. A polyvinyl alcohol derivative having a polyvinylene structure obtained by using a polyvinyl alcohol having a degree of polymerization of 2,000 or more as a material, and having a dichroic ratio of 20.
The polarizing film as described above. 2. The polarizing film according to claim 1, wherein the maximum absorption wavelength in the visible light absorption spectrum is at least 500 nm. 3. The polarizing film according to claim 1, wherein the polyvinyl alcohol has a degree of saponification of 90 mol% or more.