JP2002030162A - Polyvinyl alcohol film and polarizing film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyvinyl alcohol film hardly curling at a high humidity or in water. SOLUTION: This polyvinyl alcohol film has a thickness of 50-100 μm and satisfies the relations represented by the expressions: Y-X<=10 and 20<=X<=60 [wherein X(%) is the degree of crystallization of one side of the film; and Y(%) is that of the other side].

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyvinyl alcohol film and a polarizing film which are less curled under high humidity or in water.

[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. The field of application of this LCD is from small devices such as calculators and watches in the early stages of development to laptop computers,
The widespread use of word processors, liquid crystal color projectors, in-vehicle navigation systems, liquid crystal televisions, and the like, and the transition from conventional black-and-white display to color display has led to a need for polarizing plates with better hue than conventional products.

[0003] A usual polarizing plate is a polyvinyl alcohol film (hereinafter abbreviated as "PVA film", and polyvinyl alcohol as a raw material thereof is referred to as a polyvinyl alcohol polymer, which is abbreviated as "PVA"). Is sometimes uniaxially stretched and dyed, and a protective film such as a cellulose triacetate (TAC) film is bonded to a polarizing film produced by dyeing.

[0004]

When the PVA film is uniaxially stretched, there are cases where moisture is adjusted in advance and then dry heat stretching or stretching in water such as an aqueous boric acid solution. In such a case, the edge of the PVA film curls and folds, which may cause meandering, wrinkles, or hinder uniform stretching. Polarized films obtained from such PVA films having curled edges often have optical spots, and are unsuitable when uniformity of optical performance is required over the entire screen such as a liquid crystal display. .

[0005] It is an object of the present invention to provide a PVA film having a small curl under high humidity or in water, and to provide a polarizing film suitably used for a liquid crystal display or the like.

[0006]

In order to solve the above problems, the PVA film of the present invention has a thickness of 50 to 100 μm.
m, and the relationship between the crystallinity (X%) of one surface of the PVA film and the crystallinity (Y%) of the other surface is Y.
-X ≦ 10 and 20 ≦ X ≦ 60 are satisfied. According to the present invention, a PVA film having a small curl under high humidity or in water can be obtained.

At this time, the relationship between the crystallinity (Z%) at the center of the thickness of the PVA film and the crystallinity (X% and Y%) on both sides of the polyvinyl alcohol film is X ≦ Y ≦ Z
Is preferably satisfied. The average crystallinity of the PVA film is preferably 40 to 70%. Furthermore, a polarizing film suitably used for a liquid crystal display or the like is obtained from the above PVA film.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
As the PVA constituting the PVA film of the present invention, those obtained by saponifying a vinyl ester polymer obtained by polymerizing a vinyl ester monomer and having a vinyl ester unit as a vinyl alcohol unit can be used. Examples of the vinyl ester monomer include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, vinyl versatate, and the like. Of these, vinyl acetate is preferably used.

When copolymerizing a vinyl ester-based monomer, a copolymerizable monomer may be added, if necessary, 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;
Methacrylates such as n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate And acrylamide,
Acrylamide derivatives such as N-methylacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide, diacetone acrylamide, acrylamidopropanesulfonic acid and its salts, acrylamidopropyldimethylamine and its salts, N-methylolacrylamide and its derivatives; methacryl Amide, N-
Methacrylamide derivatives such as methyl methacrylamide, N-ethyl methacrylamide, methacrylamidopropanesulfonic acid and salts thereof, methacrylamidopropyldimethylamine and salts thereof, N-methylol methacrylamide and derivatives thereof; N-vinylformamide, N-vinyl N-vinylamides such as acetamide and N-vinylpyrrolidone; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i
-Butyl vinyl ether, t-butyl vinyl ether,
Vinyl ethers such as dodecyl vinyl ether and stearyl vinyl ether; nitriles such as acrylonitrile and methacrylonitrile; vinyl chloride, vinylidene chloride;
Vinyl halides such as vinyl fluoride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid and its salts or esters; itaconic acid and its salts or esters; vinylsilyl compounds such as vinyltrimethoxysilane Isopropenyl acetate, N-
Examples include N-vinylamides such as vinylformamide, N-vinylacetamide, and N-vinylpyrrolidone.

The average degree of polymerization of the PVA constituting the PVA film is preferably at least 500 from the viewpoint of the strength of the film, more preferably at least 1,000, still more preferably at least 2,000, particularly preferably at least 3,500 from the viewpoint of the polarizing performance. . Further, the upper limit of the degree of polymerization of PVA is preferably 10,000 or less from the viewpoint of film forming properties.

The degree of polymerization (Po) of the PVA is determined according to JIS K
It is measured according to 6726. That is, after PVA is re-saponified and purified, it can be obtained from the intrinsic viscosity [η] (unit: deciliter / g) measured in water at 30 ° C. by the following formula. Po = ([η] × 10 ³ /8.29) ^{(1 / 0.62)}

The degree of saponification of the PVA constituting the PVA film is preferably 95 mol% or more, more preferably 98 mol% or more, still more preferably 99 mol% or more, and more preferably 99.9 mol%, from the viewpoint of the durability of the polarizing film. % Is particularly preferable. On the other hand, from the viewpoint of dyeability of the film, 99.99
It is preferably at most mol%. The degree of saponification indicates the ratio of units actually saponified to vinyl alcohol units among units that can be converted into vinyl alcohol units by saponification. The degree of saponification of PVA is J
The measurement was performed by the method described in IS.

When producing a PVA film, it is preferable to add a polyhydric alcohol as a plasticizer. Examples of the polyhydric alcohol include ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, and the like. One or more of these may be used. it can. Among them, ethylene glycol or glycerin is preferably used from the viewpoint of the effect of improving the stretchability.

The amount of the polyhydric alcohol to be added is PVA.
1 to 30 parts by weight, preferably 3 to 30 parts by weight, per 100 parts by weight
It is more preferably 25 parts by weight, particularly preferably 5 to 20 parts by weight. If the amount is less than 1 part by weight, the dyeing properties and the stretchability may be reduced. If the amount is more than 30 parts by weight, the film may be too flexible and the handleability may be reduced.

When producing a PVA film, it is preferable to add a surfactant. The type of the surfactant is not particularly limited, but an anionic or nonionic surfactant is preferable. As the anionic surfactant, for example, carboxylic acid type such as potassium laurate,
Sulfuric acid ester type anionic surfactants such as octyl sulfate and sulfonic acid type anionic surfactants such as dodecylbenzene sulfonate are preferred. Nonionic surfactants include, for example, alkyl ether types such as polyoxyethylene oleyl ether, alkyl phenyl ether types such as polyoxyethylene octyl phenyl ether, alkyl ester types such as polyoxyethylene laurate, and polyoxyethylene lauryl amino. Alkylamine type such as ether, alkylamide type such as polyoxyethylene lauric amide, polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether, alkanolamide type such as oleic acid diethanolamide, polyoxyalkylene allyl phenyl ether Nonionic surfactants such as allyl phenyl ether type are preferred. One or a combination of two or more of these surfactants can be used.

The amount of the surfactant added is PVA 10
0.01 to 1 part by weight is preferable for 0 part by weight, and 0.1 to 1 part by weight is preferable.
02-0.5 part by weight is more preferable, and 0.05-0.5 part by weight.
3 parts by weight are particularly preferred. If the amount is less than 0.01 part by weight, the effect of improving stretchability and dyeing property is hardly exhibited, while if it is more than 1 part by weight, it elutes on the film surface, causing blocking, and the handleability may be reduced. is there.

As a method for producing the PVA film, for example, using a PVA solution in which PVA is dissolved in a solvent, a casting film forming method, a wet film forming method (discharging into a poor solvent),
Dry-wet film forming method, gel film forming method (a method of once cooling and gelling a PVA aqueous solution, extracting and removing a solvent to obtain a PVA film), a method based on a combination thereof, and a wet PVA (including an organic solvent and the like) May be employed. Among these, the casting film forming method and the melt extrusion film forming method are preferable because a highly transparent PVA film can be obtained.

The volatile concentration of the PVA solution used for producing the PVA film is preferably 50 to 90% by weight, more preferably 55 to 80% by weight. If the volatile matter concentration is less than 50% by weight, the viscosity may be high, so that film formation may be difficult. On the other hand, when the volatile matter concentration is more than 90% by weight, the viscosity becomes low and the uniformity of the thickness of the film tends to be impaired.

The average thickness of the PVA film is 50-100.
It is important that the thickness is μm, and preferably 60 to 80 μm. When the crystallinity is measured using a micro X-ray diffractometer when the thickness is 50 μm or less, an error tends to increase. When the thickness is 100 μm or more, the film plane difference in crystal size becomes large, and the curl may become large in spite of the crystallinity satisfying the formulas (1) and (2) of the present invention. The thickness accuracy is preferably within ± 5 μm, more preferably within ± 3 μm, and particularly preferably within ± 2 μm with respect to the average thickness. If the thickness accuracy exceeds ± 5 μm, the optical unevenness of the manufactured polarizing film may increase.

In the PVA film of the present invention, the crystallinity of one side is defined as X% and the crystallinity of the other side is defined as Y%. Is Y), and YX is 10% or less, preferably 8% or less, particularly preferably 5% or less. 10%
Exceeding the range is not preferred because the curl increases.

At this time, the crystallinity of X is at least 20%, preferably at least 30%, more preferably at least 40%.
% Or more. The crystallinity of X is set to 60% or less,
Preferably it is 55% or less, more preferably 50% or less. If the crystallinity of X is less than 20%, the difference in crystallinity with Y becomes large, and curling is likely to occur. On the other hand, if the crystallinity of X exceeds 60%, the flexibility, stretchability and dyeability of the PVA film are reduced, which makes the PVA film unsuitable for various uses.

The crystallinity (Z%) at the center of the PVA film is determined by the crystallinity (X% and Y
%) Is preferable. If the crystallinity (Z%) at the center of the film is smaller than the crystallinity (X% and Y%) on the film surface, curling is likely to occur, and the dyeability during the production of the polarizing film may be reduced.

The average crystallinity of the PVA film is 4
It is preferably from 0 to 70%, more preferably from 45 to 65%. When the drying conditions such that the average crystallinity is less than 40% or more than 70% are given, the curl of the film may be increased.

In order to produce a polarizing film from the PVA film of the present invention, for example, the PVA film may be dyed, uniaxially stretched, fixed, dried and, if necessary, heat-treated. The order of each step is not particularly limited, and two steps such as dyeing and uniaxial stretching may be performed simultaneously. Further, each step may be repeated a plurality of times.

Dyeing can be performed before, during or after uniaxial stretching. However, PVA tends to increase the crystallinity by uniaxial stretching, and the dyeing property may be reduced. It is preferred to dye in any step or uniaxial stretching step.

Dyes used for dyeing include iodine-potassium iodide; direct black 17, 19, 154;
Direct Brown 44, 106, 195, 210,
223; Direct Red 2,23,28,31,3
7, 39, 79, 81, 240, 242, 247; Direct Blue 1, 15, 22, 78, 90, 98, 1
51, 168, 202, 236, 249, 270; Direct Violet 9, 12, 51, 98; Direct Green 1, 85; Direct Yellow 8, 12, 4
4, 86, 87; Direct Orange 26, 39, 1
Dichroic dyes such as 06 and 107 can be used alone or in a mixture of two or more. Usually, the dyeing is performed by immersing the PVA film in a solution containing the dye, but the processing conditions and the processing method are not particularly limited. For example, the PVA film is mixed with the PVA film to form a film.

The uniaxial stretching performed in the length direction of the PVA film can be performed by a wet stretching method or a dry heat stretching method. The uniaxial stretching can be performed in hot water (which may be in a solution containing the dye or in a fixing bath described later) or after absorbing water. It may be performed in the air using a PVA film. At this time, the stretching ratio is preferably 4 times or more, particularly preferably 5 times or more. When the stretching ratio is smaller than 4 times, it is difficult to obtain practically sufficient polarization performance and durability performance. Stretching may be performed in one step up to a target stretching ratio, but performing multi-step stretching in two or more steps further reduces neck-in and is more effective in uniformity of optical performance. The stretching temperature is not particularly limited, but is preferably 30 to 90 ° C. when the PVA film is stretched in warm water (wet stretching), and 50 to 180 ° C. when the dry stretching is performed by dry heat. The thickness of the stretched PVA film is preferably 3 to 75 μm,
10 to 50 μm is more preferred.

The fixing treatment is performed for the purpose of strengthening the adsorption of the dye to the PVA film. Usually, boric acid and a boron compound are added to the treatment bath used for the fixing treatment. Further, an iodine compound may be added to the treatment bath as needed.

The drying treatment (heat treatment) of the PVA film is 3
It is preferably performed at 0 to 150 ° C, more preferably at 50 to 150 ° C.

The polarizing film obtained as described above is generally used as a polarizing plate by laminating an optically transparent protective film having mechanical strength on both sides or one side thereof. As the protective film, usually, a cellulose acetate film, an acrylic film, a polyester film, or the like is used.

[0032]

EXAMPLES The present invention will now be described specifically with reference to examples, but the present invention is not limited to these examples. The curls described in Examples and Comparative Examples were visually observed, and the measurement of the crystallinity of the PVA film surface and the central portion, the measurement of the crystallinity of the entire PVA film, and the calculation of the dichroic ratio were as follows. The method was performed.

(A) Measurement of Crystallinity of Surface and Center of PVA Film A micrograph of the film surface and the center was measured with a 30 μm X-ray beam by a micro X-ray diffraction method to determine the crystallinity. (B) Measurement of crystallinity of the entire PVA film The crystallinity in the direction perpendicular to the film surface was measured by a transmission method. (C) Dichroic ratio The dichroic ratio was used as an index for evaluating the polarizing performance of the obtained polarizing film. This dichroic ratio is measured with a spectrophotometer using a C light source and a 2 degree field of view in accordance with the Japan Electronics and Machinery Industries Association Standard (EIAJ) LD-201-1983.
Using the calculated transmittances TS (%) and P (%), the transmittance was obtained from the following equation. Dichroic ratio = log (TS / 100−TS / 100 × P /
100) / log (TS / 100 + TS / 100 × P /
100)

EXAMPLE 1 One of PVA having a degree of saponification of 99.9 mol% and a degree of polymerization of 2400 was prepared.
A 0% aqueous solution was cast on a stainless steel plate so as to have a thickness of 750 μm, and dried with a hot air drier at 50 ° C. for 240 minutes to obtain a film having a thickness of 75 μm. When the crystallinity of this was measured by a minute part X-ray diffraction method, the free surface side was 4
4%, 47% on the stainless steel side, and 55% at the center. The crystallinity of the entire film was 49%.
At this time, the water content of the PVA film was 6.7%.

The obtained PVA film is 10 × 10 cm
When immersed in water at 20 ° C. for 10 minutes, almost no curl was observed.

This PVA film was treated in the order of dyeing, uniaxial stretching, fixing treatment, drying and heat treatment to prepare a polarizing film. In other words, the PVA film was treated with an iodine concentration of 0.
It was immersed in a dyeing solution of 5 g / liter, potassium iodide concentration of 40 g / liter, and boric acid concentration of 40 g / liter at 30 ° C. for 1 minute to perform dyeing. Next, the film was stretched 5.5 times in a 4% aqueous solution of boric acid at 50 ° C. Furthermore, it was immersed in an aqueous solution of potassium iodide 40 g / liter and boric acid 40 g / liter at 35 ° C. for 5 minutes to perform a fixing treatment. This was washed with distilled water at 20 ° C. for 10 seconds, then dried with hot air at 40 ° C. under a constant length, and further heat-treated at 100 ° C. for 5 minutes.

The transmittance of the obtained polarizing film was 44.1.
%, The degree of polarization was 99.3%, and the dichroic ratio was 44.8. No optical spot was observed on the polarizing film.

Example 2 3 of PVA having a saponification degree of 99.9 mol% and a polymerization degree of 2400
A 0% aqueous solution was cast on a stainless steel drum at 100 ° C. so as to have a thickness of 250 μm, dried by a hot air dryer at 110 ° C., and peeled off when the moisture content became 5%.
A film having a thickness of 75 μm was obtained. Its crystallinity was measured by the micro X-ray diffraction method.
%, The stainless steel surface side was 39%, and the central part was 49%. The crystallinity of the entire film was 40%.

The obtained PVA film is 10 × 10 cm
And immersed in water at 20 ° C. for 10 minutes, almost no curl was observed.

This PVA film was treated in the order of dyeing, uniaxial stretching, fixing treatment, drying and heat treatment to prepare a polarizing film. In other words, the PVA film was treated with an iodine concentration of 0.
It was immersed in a dyeing solution of 5 g / liter, potassium iodide concentration of 40 g / liter, and boric acid concentration of 40 g / liter at 30 ° C. for 1 minute to perform dyeing. Next, the film was stretched 5.2 times in a 4% aqueous solution of boric acid at 50 ° C. Furthermore, it was immersed in an aqueous solution of potassium iodide 40 g / liter and boric acid 40 g / liter at 35 ° C. for 5 minutes to perform a fixing treatment. This was washed with distilled water at 20 ° C. for 10 seconds, then dried with hot air at 40 ° C. under a constant length, and further heat-treated at 100 ° C. for 5 minutes.

The transmittance of the obtained polarizing film was 42.5.
%, The degree of polarization was 99.6%, and the dichroic ratio was 38.8. No optical spot was observed on the polarizing film.

Comparative Example 1 PVA having a saponification degree of 99.9 mol% and a polymerization degree of 2400
A 0% aqueous solution was cast on a stainless steel plate so as to have a thickness of 750 μm, and was dried with a hot air dryer at 50 ° C. for 200 minutes to obtain a film having a thickness of 75 μm. When the crystallinity of this was measured by a minute part X-ray diffraction method, the free surface side was 4
8%, 35% on the stainless steel side, and 48% at the center. The crystallinity of the entire film was 49%.
At this time, the water content of the PVA film was 7.8%.

When the obtained film was cut into a size of 10 × 10 cm and immersed in water at 20 ° C. for 10 minutes, a large curl was generated so that the free surface side was inside.

This PVA film was dyed, uniaxially stretched, fixed, dried and heat-treated in this order to produce a polarizing film. In other words, the PVA film was treated with an iodine concentration of 0.
It was immersed in a dyeing solution of 5 g / liter, potassium iodide concentration of 40 g / liter, and boric acid concentration of 40 g / liter at 30 ° C. for 1 minute to perform dyeing. Next, it was stretched 5.0 times in a 4% aqueous solution of boric acid at 50 ° C. Furthermore, it was immersed in an aqueous solution of potassium iodide 40 g / liter and boric acid 40 g / liter at 35 ° C. for 5 minutes to perform a fixing treatment. This was washed with distilled water at 20 ° C. for 10 seconds, then dried with hot air at 40 ° C. under a constant length, and further heat-treated at 100 ° C. for 5 minutes.

The transmittance of the obtained polarizing film was 41.9.
%, The degree of polarization was 99.2%, and the dichroic ratio was 31.5. Optical spots were observed on the polarizing film.

Comparative Example 2 One of PVA having a saponification degree of 99.9 mol% and a polymerization degree of 2400 was prepared.
A 0% aqueous solution was cast on a stainless steel plate so as to have a thickness of 750 μm, and dried with a hot-air dryer at 50 ° C. for 130 minutes to obtain a film having a thickness of 75 μm. The crystallinity of the sample was measured by a microscopic X-ray diffraction method.
2%, 29% on the stainless steel side, and 45% at the center. The crystallinity of the entire film was 49%.
At this time, the moisture content of the film was 9.1%.

When the obtained film was cut into a size of 10 × 10 cm and immersed in water at 20 ° C. for 10 minutes, a large curl was generated so that the free surface side was inside.

This PVA film was treated in the order of dyeing, uniaxial stretching, fixing treatment, drying and heat treatment to prepare a polarizing film. In other words, the PVA film was treated with an iodine concentration of 0.
It was immersed in a dyeing solution of 5 g / liter, potassium iodide concentration of 40 g / liter, and boric acid concentration of 40 g / liter at 30 ° C. for 1 minute to perform dyeing. Next, the film was stretched 4.8 times in a 4% aqueous solution of boric acid at 50 ° C. Furthermore, it was immersed in an aqueous solution of potassium iodide 40 g / liter and boric acid 40 g / liter at 35 ° C. for 5 minutes to perform a fixing treatment. This was washed with distilled water at 20 ° C. for 10 seconds, then dried with hot air at 40 ° C. under a constant length, and further heat-treated at 100 ° C. for 5 minutes.

The transmittance of the obtained polarizing film was 41.0.
%, The degree of polarization was 99.4%, and the dichroic ratio was 29.8. Optical spots were observed on the polarizing film.

Comparative Example 3 One of PVA having a saponification degree of 99.9 mol% and a polymerization degree of 2400 was prepared.
A 0% aqueous solution was cast on a stainless steel plate so as to have a thickness of 750 μm, and dried with a hot air dryer at 50 ° C. for 240 minutes.
Further heat treatment at 120 ° C. for 10 minutes, thickness
m was obtained. Its crystallinity was measured by a micropart X-ray diffraction method. As a result, the free surface side was 62%, the stainless steel surface side was 63%, and the central portion was 64%. The crystallinity of the entire film was 63%. At this time, the moisture content of the film was 2.8%.

When the obtained film was cut into 10 × 10 cm and immersed in water at 20 ° C. for 10 minutes, a large curl was generated so that the stainless steel surface side was inside.

This PVA film was treated in the order of dyeing, uniaxial stretching, fixing treatment, drying and heat treatment to prepare a polarizing film. In other words, the PVA film was treated with an iodine concentration of 0.
It was immersed in a dyeing solution of 5 g / liter, potassium iodide concentration of 40 g / liter, and boric acid concentration of 40 g / liter at 30 ° C. for 1 minute to perform dyeing. Next, it was stretched 5.0 times in a 4% aqueous solution of boric acid at 50 ° C. Furthermore, it was immersed in an aqueous solution of potassium iodide 40 g / liter and boric acid 40 g / liter at 35 ° C. for 5 minutes to perform a fixing treatment. This was washed with distilled water at 20 ° C. for 10 seconds, then dried with hot air at 40 ° C. under a constant length, and further heat-treated at 100 ° C. for 5 minutes.

The transmittance of the obtained polarizing film was 41.9.
%, The degree of polarization was 99.2%, and the dichroic ratio was 31.5. Optical spots were observed on the polarizing film.

Comparative Example 4 One of PVA having a saponification degree of 99.9 mol% and a polymerization degree of 2400 was prepared.
A 0% aqueous solution was cast on a stainless steel plate so as to have a thickness of 300 μm, and was dried with a hot air dryer at 50 ° C. for 240 minutes to obtain a film having a thickness of 30 μm. Since the thickness of this film was thin, the crystallinity could not be measured by the minute part X-ray diffraction method, but the crystallinity of the whole film was 52%. At this time, the water content of the film was 5.2%.

When the obtained film was cut into a size of 10 × 10 cm and immersed in water at 20 ° C. for 10 minutes, a large curl was generated so that the free surface side was inside.

The PVA film was dyed, uniaxially stretched, fixed, dried and heat-treated in this order to produce a polarizing film. That is, when the PVA film is used with an iodine concentration of 0.5
g / liter, potassium iodide concentration 40 g / liter,
It was immersed in a dyeing solution at 30 ° C. with a boric acid concentration of 40 g / liter for 1 minute to perform dyeing. Next, the film was stretched 5.1 times in a 4% aqueous solution of boric acid at 50 ° C. Further, 35 g of potassium iodide 40 g / l and boric acid 40 g / l.
It was immersed in an aqueous solution of 5 ° C. for 5 minutes to perform a fixing treatment. After washing this with distilled water at 20 ° C. for 10 seconds,
The resultant was dried with hot air at 0 ° C. and heat-treated at 100 ° C. for 5 minutes.

The transmittance of the obtained polarizing film was 46.2.
%, The degree of polarization was 95.3%, and the dichroic ratio was 37.2. Optical spots were observed on the polarizing film.

Comparative Example 5 One of PVA having a saponification degree of 99.9 mol% and a polymerization degree of 2400 was prepared.
A 0% aqueous solution was cast on a stainless steel plate so as to have a thickness of 1300 μm, and was dried by a hot air dryer at 80 ° C. for 350 minutes to obtain a film having a thickness of 130 μm. When the crystallinity of this was measured by a micropart X-ray diffraction method, it was 48% on the free surface side, 45% on the stainless steel surface side, and 59% on the central part. The crystallinity of the entire film was 51%. At this time, the moisture content of the film was 4.8%.

When the obtained film was cut into a size of 10 × 10 cm and immersed in water at 20 ° C. for 10 minutes, a large curl was generated so that the free surface side was inside.

The PVA film was dyed, uniaxially stretched, fixed, dried and heat-treated in this order to produce a polarizing film. That is, when the PVA film is used with an iodine concentration of 0.5
g / liter, potassium iodide concentration 40 g / liter,
It was immersed in a dyeing solution at a temperature of 30 ° C. with a boric acid concentration of 40 g / liter for 1 minute to perform dyeing. Next, the film was stretched 5.3 times in a 4% aqueous solution of boric acid at 50 ° C. Further, 35 g of potassium iodide 40 g / l and boric acid 40 g / l.
It was immersed in an aqueous solution of 5 ° C. for 5 minutes to perform a fixing treatment. After washing this with distilled water at 20 ° C. for 10 seconds,
The resultant was dried with hot air at 0 ° C. and heat-treated at 100 ° C. for 5 minutes.

The transmittance of the obtained polarizing film was 44.3.
%, The degree of polarization was 98.0%, and the dichroic ratio was 36.1. Optical spots were observed on the polarizing film.

[0062]

As described above, according to the present invention, a PVA film having a small curl under high humidity or in water can be obtained.
In particular, a PVA film suitable for a polarizing film used for a liquid crystal display or the like can be obtained.

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Claims (5)

[Claims] 1. A polyvinyl alcohol film having a thickness of 50 to 100 μm, wherein the relationship between the crystallinity (X%) of one surface of the polyvinyl alcohol film and the crystallinity (Y%) of the other surface is: And a polyvinyl alcohol film satisfying the following formulas (1) and (2). Y−X ≦ 10 {(1) 20 ≦ X ≦ 60} (2) 2. The relationship between the crystallinity (Z%) at the center of the thickness of the polyvinyl alcohol film and the crystallinity (X% and Y%) on both sides of the polyvinyl alcohol film satisfies the following equation (3). The polyvinyl alcohol film according to claim 1, wherein: X ≦ Y ≦ Z ‥‥ (3) 3. The polyvinyl alcohol film has an average crystallinity of 40 to 70%.
Or the polyvinyl alcohol film according to 2. 4. The polyvinyl alcohol film according to claim 1, which is for a polarizing film. 5. A polarizing film produced by using the polyvinyl alcohol film according to claim 4.