JP3478534B2 - Polyvinyl alcohol film and polarizing film - Google Patents

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 have a small curl under high humidity or in water.

[0002]

2. Description of the Related Art A polarizing plate having a light transmitting and shielding function is a basic component of a liquid crystal display (LCD) together with a liquid crystal having a light switching function. The field of application of this LCD is from small devices such as calculators and wristwatches in the early stages of development to laptop computers in recent years.
Since it has spread to a wide range of word processors, liquid crystal color projectors, in-vehicle navigation systems, liquid crystal televisions, and the like, and has changed from conventional monochrome display to color display, polarizing plates having a hue superior to that of conventional products have been demanded.

A usual polarizing plate is a polyvinyl alcohol film (hereinafter, abbreviated as "PVA film", and polyvinyl alcohol which is a raw material thereof is referred to as a polyvinyl alcohol polymer, which is abbreviated as "PVA". A polarizing film produced by uniaxially stretching and dyeing a protective film such as a cellulose triacetate (TAC) film.

[0004]

When the PVA film is uniaxially stretched, the humidity may be adjusted in advance and then the dry heat stretching may be performed, or the stretching may be performed in water such as boric acid aqueous solution. In such a case, the end portion of the PVA film may be curled and folded, which may cause meandering, wrinkles, or hinder uniform stretching. A polarizing film obtained from such a PVA film having curled edges often has optical spots, and is not suitable when uniform optical performance is required over the entire screen such as a liquid crystal display. .

An object of the present invention is to provide a PVA film having a small curl under high humidity or in water, and also to provide a polarizing film suitable for use in liquid crystal displays and the like.

[0006]

In order to solve the above problems, the PVA film of the present invention has a thickness of 50-100 μm.
m, and the relationship between the crystallinity (X%) on one surface of the PVA film and the crystallinity (Y%) on the other surface is Y
This satisfies the expressions −X ≦ 10 and 20 ≦ X ≦ 60. 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 thickness center of the PVA film and the crystallinity (X% and Y%) on both surfaces of the polyvinyl alcohol film is X≤Y≤Z.
It is preferable to satisfy the following equation. The average crystallinity of the PVA film is preferably 40 to 70%. Furthermore, a polarizing film suitable for liquid crystal displays and the like is obtained from the above PVA film.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
As the PVA constituting the PVA film of the present invention, it is possible to use one obtained by saponifying a vinyl ester-based polymer obtained by polymerizing a vinyl ester-based monomer and converting a vinyl ester unit into a vinyl alcohol unit. Examples of the vinyl ester-based 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, it is preferable to use vinyl acetate.

When the vinyl ester-based monomer is copolymerized, if necessary, the copolymerizable monomer is added within a range not impairing the effects of the invention (preferably 15 mol% or less,
More preferably, the proportion is 5 mol% or less).

Examples of the monomer copolymerizable with the vinyl ester type monomer include olefins having 3 to 30 carbon atoms such as ethylene, propylene, 1-butene and isobutene; acrylic acid and salts thereof; methyl acrylate. , Ethyl acrylate, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, acrylic acid 2
-Acrylic acid esters such as ethylhexyl and dodecyl acrylate octadecyl acrylate; methacrylic acid and its salts; methyl methacrylate, ethyl methacrylate,
Methacrylic acid esters such as n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate and octadecyl methacrylate. Kind; 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-
Methacrylic amide derivatives such as methyl methacrylamide, N-ethyl methacrylamide, methacrylamide propanesulfonic acid and its salts, methacrylamide dimethylamine and its salts, N-methylol methacrylamide and its derivatives; 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 salts thereof or esters thereof; itaconic acid and salts thereof or esters thereof; vinylsilyl compounds such as vinyltrimethoxysilane. Isopropenyl acetate, N-
N-vinylamides such as vinylformamide, N-vinylacetamide, N-vinylpyrrolidone and the like can be mentioned.

The average degree of polymerization of PVA constituting the PVA film is preferably 500 or more from the viewpoint of film strength, more preferably 1000 or more from the viewpoint of polarization performance, further preferably 2000 or more, particularly preferably 3500 or more. . Further, the upper limit of the degree of polymerization of PVA is preferably 10,000 or less from the viewpoint of film forming property of the film.

The degree of polymerization (Po) of the PVA is JIS K
It is measured according to 6726. That is, PVA is re-saponified, purified, and then calculated 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 PVA constituting the PVA film is preferably 95 mol% or more, more preferably 98 mol% or more, further preferably 99 mol% or more, and more preferably 99.9 mol from the viewpoint of the durability of the polarizing film. % Or more is particularly preferable. On the other hand, from the viewpoint of film dyeability, 99.99
It is preferably not more than mol%. The degree of saponification indicates the proportion 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 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, and one or more of these may be used. it can. Among these, ethylene glycol or glycerin is preferably used because of the effect of improving the stretchability.

The amount of polyhydric alcohol added is PVA.
1 to 30 parts by weight is preferable with respect to 100 parts by weight, and 3 to
25 parts by weight is more preferable, and 5 to 20 parts by weight is particularly preferable. If it is less than 1 part by weight, the dyeability and stretchability may be lowered, and if it is more than 30 parts by weight, the film may be too soft and the handleability may be lowered.

A surfactant is preferably added when the PVA film is produced. The type of surfactant is not particularly limited, but anionic or nonionic surfactant is preferable. As the anionic surfactant, for example, a carboxylic acid type such as potassium laurate,
Sulfate type anionic surfactants such as octyl sulfate and sulfonic acid type anionic surfactants such as dodecylbenzene sulfonate are suitable. Examples of the nonionic surfactant include alkyl ether type such as polyoxyethylene oleyl ether, alkyl phenyl ether type such as polyoxyethylene octyl phenyl ether, alkyl ester type such as polyoxyethylene laurate, and polyoxyethylene lauryl amino. Alkylamine type such as ether, alkylamide type such as polyoxyethylene lauric acid amide, polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether, alkanolamide type such as oleic acid diethanolamide, polyoxyalkylene allyl phenyl ether, etc. Nonionic surfactants such as allyl phenyl ether type are preferred. These surfactants can be used alone or in combination of two or more.

The amount of surfactant added is PVA10.
0.01 to 1 part by weight is preferable with respect to 0 part by weight, and 0.
02 to 0.5 parts by weight is more preferable, and 0.05 to 0.
3 parts by weight is particularly preferred. If it is less than 0.01 part by weight, the effect of improving the stretchability and dyeing property is difficult to appear, while if it is more than 1 part by weight, it may be eluted on the film surface to cause blocking and the handleability may deteriorate. is there.

As the method for producing the PVA film, for example, a PVA solution in which PVA is dissolved in a solvent is used, and a casting film forming method, a wet film forming method (discharging into a poor solvent),
Dry-and-wet film forming method, gel film forming method (method in which PVA aqueous solution is once cooled and gelled, and then solvent is extracted and removed to obtain a PVA film), and a method by a combination thereof, or water-containing PVA (including an organic solvent, etc. It is also possible to employ a melt-extrusion film-forming method, which is carried out by melting. Among these, the casting film-forming method and the melt-extrusion film-forming method are preferable since a highly transparent PVA film can be obtained.

The PVA solution used for producing the PVA film has a volatile concentration of preferably 50 to 90% by weight, more preferably 55 to 80% by weight. If the concentration of volatile matter is less than 50% by weight, the viscosity becomes high, which may make film formation difficult. On the other hand, when the volatile content concentration is higher than 90% by weight, the viscosity tends to be low and the thickness uniformity 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 60-80 μm is preferable. If the thickness is 50 μm or less, the error tends to increase when the crystallinity is measured using a micro X-ray diffractometer. When the thickness is 100 μm or more, the film surface difference in crystal size becomes large, and the curl may become large in spite of the crystallinity satisfying the expressions (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, when the crystallinity of one surface is X% and the crystallinity of the other surface is Y% (when the crystallinity of both surfaces of the film is compared, the numerical value is larger). Is Y) and Y-X is 10% or less, preferably 8% or less, and particularly preferably 5% or less. 10%
If it exceeds, the curl becomes large, which is not preferable.

At this time, the crystallinity of X is 20% or more, preferably 30% or more, and more preferably 40.
% Or more. The crystallinity of X is 60% or less,
It is preferably 55% or less, more preferably 50% or less. If the crystallinity of X is less than 20%, the difference in crystallinity from that of Y becomes large and curling easily occurs, which is not preferable. Further, when the crystallinity of X exceeds 60%, the flexibility, stretchability and dyeability of the PVA film are deteriorated, which makes it unsuitable for various uses of the PVA film.

The crystallinity (Z%) at the center of the PVA film is the crystallinity (X% and Y) of the film surface.
%) Is preferable. When the crystallinity (Z%) of the film central portion is smaller than the crystallinity (X% and Y%) of the film surface, curling is likely to occur, and the dyeability during the production of the polarizing film may be deteriorated.

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

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 optionally heat-treated. The order of each step is not particularly limited, and two steps such as dyeing and uniaxial stretching may be performed at the same time. Also, each step may be repeated a plurality of times.

Dyeing can be performed before uniaxial stretching, during uniaxial stretching, or after uniaxial stretching. However, uniaxial stretching tends to increase the crystallinity of the PVA, which may reduce the dyeability. It is preferable to dye in any step or during the uniaxial stretching step.

The dye used for dyeing is 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 above dye, but the processing conditions and the processing method such as mixing with the PVA film to form a film are not particularly limited.

The uniaxial stretching carried out in the longitudinal direction of the PVA film can be carried out by a wet stretching method or a dry heat stretching method, which can be carried out in warm water (in a solution containing the dye or in a fixing bath described later) or after water absorption. It may be carried out in air using a PVA film. At this time, the draw ratio is preferably 4 times or more, and particularly preferably 5 times or more. When the draw ratio is less than 4 times, it is difficult to obtain practically sufficient polarization performance and durability performance. Stretching may be carried out in one stage up to the target stretching ratio, but necking is further reduced and multi-stage stretching of two or more stages is effective for 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 dry heat stretching. The thickness of the stretched PVA film is preferably 3 to 75 μm,
It is more preferably 10 to 50 μm.

A fixing treatment is carried out for the purpose of strengthening the adsorption of the dye on the PVA film. Boric acid and a boron compound are usually added to the treatment bath used for the fixing treatment. Moreover, you may add an iodine compound in a processing bath as needed.

Drying (heat treatment) of the PVA film is 3
It is preferably carried out at 0 to 150 ° C, more preferably at 50 to 150 ° C.

The polarizing film obtained as described above is usually 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, a cellulose acetate film, an acrylic film, a polyester film or the like is usually used.

[0032]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. The curls described in Examples and Comparative Examples were visually observed, and the crystallinity of the PVA film surface and the central portion was measured, the crystallinity of the entire PVA film was measured, and the dichroic ratio was calculated as follows. It was carried out by the method.

(A) Crystallinity measurement of PVA film surface and central part By the minute part X-ray diffraction method, a diffraction photograph of the film surface and central part was measured with an X-ray beam of 30 μm to determine the crystallinity. (B) Crystallinity measurement of the entire PVA film The crystallinity was measured in the direction perpendicular to the film surface by the transmission method. (C) Dichroic ratio The dichroic ratio was used as an index for evaluating the polarization performance of the obtained polarizing film. This dichroic ratio complies with the Japan Electronic Machinery Manufacturers Association Standard (EIAJ) LD-201-1983 and is measured with a C light source and a 2 degree visual field using a spectrophotometer.
The transmittance Ts (%) and P (%) obtained by the calculation were used to obtain the value from the following formula. Dichroic ratio = log (TS / 100-TS / 100 × P /
100) / log (TS / 100 + TS / 100 × P /
100)

Example 1 1 of PVA having a degree of saponification of 99.9 mol% and a degree of polymerization of 2400
A 0% aqueous solution was cast on a stainless plate to a thickness of 750 μm and dried for 240 minutes with a hot air dryer at 50 ° C. to obtain a film having a thickness of 75 μm. The crystallinity of this was measured by the minute portion X-ray diffraction method.
4%, the stainless steel surface side was 47%, and the central portion was 55%. The crystallinity of the entire film was 49%.
At this time, the moisture content of the PVA film was 6.7%.

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

This PVA film was dyed, uniaxially stretched, fixed, dried and heat-treated in this order to prepare a polarizing film. That is, the PVA film was made to have an iodine concentration of 0.
Dyeing was carried out by immersing for 1 minute 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. Then, it was stretched 5.5 times in a 4% boric acid aqueous solution at 50 ° C. Further, fixing treatment was carried out by immersing in an aqueous solution of potassium iodide 40 g / liter and boric acid 40 g / liter at 35 ° C. for 5 minutes. This was washed with distilled water at 20 ° C. for 10 seconds, dried under constant length with hot air at 40 ° C., and further heat treated at 100 ° C. for 5 minutes.

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

Example 2 3 of PVA having a degree of saponification of 99.9 mol% and a degree of polymerization 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, and dried by a hot air dryer at 110 ° C., and peeled off when the water content became 5%,
A film having a thickness of 75 μm was obtained. The crystallinity of this was measured by the X-ray diffraction method in the micro area.
%, The stainless steel surface side was 39%, and the central portion was 49%. The crystallinity of the entire film was 40%.

The PVA film obtained was treated with 10 × 10 cm
When cut into pieces and immersed in water at 20 ° C. for 10 minutes, almost no curl was observed.

The PVA film was dyed, uniaxially stretched, fixed, dried and heat-treated in this order to prepare a polarizing film. That is, the PVA film was made to have an iodine concentration of 0.
Dyeing was carried out by immersing for 1 minute 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. Next, it was stretched 5.2 times in a 4% aqueous boric acid solution at 50 ° C. Further, fixing treatment was carried out by immersing in an aqueous solution of potassium iodide 40 g / liter and boric acid 40 g / liter at 35 ° C. for 5 minutes. This was washed with distilled water at 20 ° C. for 10 seconds, dried under constant length with hot air at 40 ° C., and further heat treated at 100 ° C. for 5 minutes.

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

Comparative Example 1 1 of PVA having a degree of saponification of 99.9 mol% and a degree of polymerization of 2400
A 0% aqueous solution was cast on a stainless plate to a thickness of 750 μm and dried for 200 minutes by a hot air dryer at 50 ° C. to obtain a film having a thickness of 75 μm. The crystallinity of this was measured by the minute portion X-ray diffraction method.
8%, the stainless steel surface side was 35%, and the central portion was 48%. 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 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 the inside.

This PVA film was dyed, uniaxially stretched, fixed, dried and heat-treated in this order to prepare a polarizing film. That is, the PVA film was made to have an iodine concentration of 0.
Dyeing was carried out by immersing for 1 minute 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. Next, it was stretched 5.0 times in a 4% boric acid aqueous solution at 50 ° C. Further, fixing treatment was carried out by immersing in an aqueous solution of potassium iodide 40 g / liter and boric acid 40 g / liter at 35 ° C. for 5 minutes. This was washed with distilled water at 20 ° C. for 10 seconds, dried under constant length with hot air at 40 ° C., and further heat treated at 100 ° C. for 5 minutes.

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

Comparative Example 2 1 of PVA having a degree of saponification of 99.9 mol% and a degree of polymerization of 2,400.
A 0% aqueous solution was cast on a stainless plate to 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. When the crystallinity of this was measured by the minute portion X-ray diffraction method, it was 5 on the free surface side.
2%, 29% on the stainless steel surface side, and 45% at the central portion. The crystallinity of the entire film was 49%.
At this time, the water 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 the inner side.

This PVA film was dyed, uniaxially stretched, fixed, dried and heat-treated in this order to prepare a polarizing film. That is, the PVA film was made to have an iodine concentration of 0.
Dyeing was carried out by immersing for 1 minute 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. Then, it was stretched 4.8 times in a 4% boric acid aqueous solution at 50 ° C. Further, fixing treatment was carried out by immersing in an aqueous solution of potassium iodide 40 g / liter and boric acid 40 g / liter at 35 ° C. for 5 minutes. This was washed with distilled water at 20 ° C. for 10 seconds, dried under constant length with hot air at 40 ° C., and further heat treated at 100 ° C. for 5 minutes.

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

Comparative Example 3 1 of PVA having a degree of saponification of 99.9 mol% and a degree of polymerization of 2400
A 0% aqueous solution was cast on a stainless plate to a thickness of 750 μm, and dried with a hot air dryer at 50 ° C. for 240 minutes,
Further heat treatment at 120 ℃ for 10 minutes, the thickness is 75μ
m film was obtained. When the crystallinity of this was measured by the minute portion X-ray diffraction method, it was 62% on the free surface side, 63% on the stainless steel surface side, and 64% on the central portion. The crystallinity of the entire film was 63%. At this time, the water 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 the inside.

This PVA film was dyed, uniaxially stretched, fixed, dried and heat-treated in this order to prepare a polarizing film. That is, the PVA film was made to have an iodine concentration of 0.
Dyeing was carried out by immersing for 1 minute 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. Next, it was stretched 5.0 times in a 4% boric acid aqueous solution at 50 ° C. Further, fixing treatment was carried out by immersing in an aqueous solution of potassium iodide 40 g / liter and boric acid 40 g / liter at 35 ° C. for 5 minutes. This was washed with distilled water at 20 ° C. for 10 seconds, dried under constant length with hot air at 40 ° C., and further heat treated at 100 ° C. for 5 minutes.

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

Comparative Example 4 1 of PVA having a degree of saponification of 99.9 mol% and a degree of polymerization of 2400
A 0% aqueous solution was cast on a stainless steel plate so as to have a thickness of 300 μm, and 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 microscopic X-ray diffraction method, but the crystallinity of the entire film was 52%. At this time, the water content of the film was 5.2%.

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

This PVA film was dyed, uniaxially stretched, fixed, dried and heat-treated in this order to prepare a polarizing film. That is, the PVA film is treated with an iodine concentration of 0.5.
g / liter, potassium iodide concentration 40 g / liter,
Dyeing was carried out by immersing for 1 minute in a dyeing solution having a boric acid concentration of 40 g / liter at 30 ° C. Next, it was stretched 5.1 times in a 4% boric acid aqueous solution at 50 ° C. Furthermore, 35 g of potassium iodide 40 g / liter and boric acid 40 g / liter
Immobilization treatment was performed by immersing it in an aqueous solution at 0 ° C. for 5 minutes. This was washed with distilled water at 20 ° C for 10 seconds, then, under constant length, 4
It was dried with hot air at 0 ° C. and further 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 1 of PVA having a degree of saponification of 99.9 mol% and a degree of polymerization of 2400
A 0% aqueous solution was cast on a stainless steel plate so as to have a thickness of 1300 μm, and 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 the minute portion X-ray diffraction method, the free surface side was 48%, the stainless steel surface side was 45%, and the central portion was 59%. The crystallinity of the entire film was 51%. At this time, the water content of the film was 4.8%.

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 free surface side was on the inside.

This PVA film was dyed, uniaxially stretched, fixed, dried and heat-treated in this order to prepare a polarizing film. That is, the PVA film is treated with an iodine concentration of 0.5.
g / liter, potassium iodide concentration 40 g / liter,
Dyeing was carried out by immersing for 1 minute in a dyeing solution having a boric acid concentration of 40 g / liter at 30 ° C. Next, it was stretched 5.3 times in a 4% boric acid aqueous solution at 50 ° C. Furthermore, 35 g of potassium iodide 40 g / liter and boric acid 40 g / liter
Immobilization treatment was performed by immersing it in an aqueous solution at 0 ° C. for 5 minutes. This was washed with distilled water at 20 ° C for 10 seconds, then, under constant length, 4
It was dried with hot air at 0 ° C. and further 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 use as a polarizing film used in a liquid crystal display or the like can be obtained.

Claims (5)

(57) [Claims] 1. A polyvinyl alcohol film having a thickness of 50 to 100 μm, and the relationship between the crystallinity (X%) of one surface of the polyvinyl alcohol film and the crystallinity (Y%) of the other surface thereof. 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 surfaces of the polyvinyl alcohol film satisfies the following expression (3). The polyvinyl alcohol film according to claim 1, wherein: X ≦ Y ≦ Z (3) 3. A polyvinyl alcohol film having an average crystallinity of 40 to 70%.
Alternatively, the polyvinyl alcohol film described in 2. 4. The polyvinyl alcohol film according to claim 1, which is used for a polarizing film. 5. A polarizing film produced using the polyvinyl alcohol film according to claim 4.