JP2002028938A - Polyvinyl alcohol polymer film, method for manufacturing the same, and polarizing film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a polyvinyl alcohol polymer film hard to generate wrinkles at the time of stretching and to also obtain a polarizing film optimum as a wide and large-sized liquid crystal display screen reduced in color irregularity. SOLUTION: The retardation difference between two points separated from each other by 1 cm in the TD direction of the polyvinyl alcohol polymer film 6 is set to 5 nm or less. Further, the length (a-b-c) of the surface drying the polyvinyl alcohol polymer film 6 is set to 3-200 m and the moisture content of the polyvinyl alcohol polymer film 6 at a time when passed along the drying surface to be peeled is set to 50 wt.% or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyvinyl alcohol-based polymer film which is useful as a raw material for producing a polarizing film having less color spots and which hardly wrinkles during stretching, a method for producing the same, and a polarizing film.

[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 application fields of this LCD range from small devices such as calculators and wristwatches in the early stages of development, to recent years, such as laptop computers, word processors, liquid crystal color projectors, navigation systems for vehicles, liquid crystal televisions, personal phones, and indoor and outdoor measuring instruments. There is a demand for a polarizing plate having a large area, which has a wider area, has less color spots than conventional products, and has a large area.

In general, a polarizing plate is formed by uniaxially stretching a polyvinyl alcohol-based polymer film (hereinafter, the polyvinyl alcohol-based polymer film may be abbreviated as “PVA film” and the polyvinyl alcohol-based polymer film may be abbreviated as “PVA film”). After being dyed or dyed and then uniaxially stretched, a polarizing film fixed with a boron compound (the dyeing and the fixing treatment may be performed simultaneously) is applied to a cellulose triacetate (T
(AC) film or cellulose acetate butyrate (CAB) film.

[0004]

By the way, even if the PVA film looks uniform in appearance, the polarizing film obtained therefrom sometimes contains color spots which are difficult to distinguish from the outside. This color spot is difficult to confirm unless it is a final product (polarizing plate) on which a protective film or the like is laminated. If color spots appear in the final product, secondary materials such as non-defective protective films are also discarded as defective products, resulting in a large cost loss. Conventionally, Japanese Patent Application Laid-Open No.
As described in Japanese Patent No. 38319, studies have been made to reduce thickness unevenness and birefringence unevenness. By reducing thickness unevenness and birefringence unevenness, color unevenness can be reduced to some extent to meet the required level at the time, but it seems to be a problem in the final product (polarizer) with improved performance in recent years. It has proven difficult to reduce high levels of color spots. Further, it has been found that even when the thickness unevenness and the birefringence unevenness are evaluated as the unevenness on the entire film surface, it is difficult to correspond to the actual color unevenness as perceived by human eyes.

Further, in order to obtain a polarizing film having a large area with an increase in the size of a liquid crystal display screen, it is necessary to secure a wide PVA film. However, the conventional wide PVA film is easily curled at the time of stretching and wrinkles are formed at both ends, and the yield in the width direction is poor. Therefore, it is difficult to obtain a large-area polarizing film. In particular, a film having a film width of 2 m or more easily wrinkles.

Therefore, an object of the present invention is to reduce color spots,
PV useful as a raw material for manufacturing a wide polarizing film that is hard to wrinkle during stretching and can cope with an increase in the size of a liquid crystal display screen
The point is that an A film can be obtained.

[0007]

In order to achieve the above object, the PVA film according to the present invention has a film TD.
The retardation difference between two points 1cm apart in the direction is 5nm
It is as follows. Here, the retardation is PVA
It is represented by the birefringence of the film times the film thickness. The birefringence is determined by the degree of molecular orientation of the film provided in the film forming step or the like. The stretching direction (MD direction) of the PVA film is the film longitudinal direction, and the direction (TD direction) orthogonal to the stretching direction is the film width direction.

According to the present invention, the retardation difference between two points 1 cm apart in the TD direction of the PVA film is 5%.
When the thickness is less than nm, color spots are small, and the reason is not clear, but wrinkles are unlikely to occur during stretching, a wide good product (polarizing film) can be obtained with a high yield, and it is possible to cope with a large liquid crystal display screen. Becomes

[0009] In the production method according to the present invention, the length of the surface on which the PVA film is dried is 3 m to 200 m, and the moisture content of the PVA film when peeling through the drying surface is 50% by weight or less. . ADVANTAGE OF THE INVENTION According to this invention, the PVA film useful as a manufacturing raw material of the objective polarizing film is obtained reliably.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows, as an example of the production of the PVA film of the present invention, a drum type film forming machine employing a melt extrusion method in which hydrated PVA (which may contain an organic solvent or the like) is melted and extruded. This film forming machine extrudes, for example, a fixed amount of molten PVA 2 from a flat die 1 onto a rotating first roll 3 for casting, and uses this circumferential surface to form PVA.
One side of the film 6 is dried. Thereafter, the other surface of the PVA film 6 is dried on the circumferential surface of the second roll 4 and finally peeled off by the peeling roll 5 to remove the PVA film 6.
And This PVA film 6 is wound around a winder through a humidity controller and an inspection machine (not shown).

[0011] In the above film forming machine, in the present invention, PV
The first roll 3 among the surfaces for drying the A film 6
Is referred to as a first dry surface 7, and the circumferential surface of the second roll 4 is referred to as a second dry surface 8. At this time, as shown in the figure,
1st roll 3, 2nd roll 4, nth roll 9, n + 1th roll
It is preferable to arrange a plurality of rolls of the roll 10 and perform drying over two or more stages. In this way, both the front and back surfaces of the PVA film 6 are uniformly dried by the first and second drying surfaces 7, 8 and the like, without causing color spots, and without wrinkling during stretching, A good PVA film 6 is obtained. In addition, retardation spots in a minute area of about 1 cm hardly become large.

The length (d-e-f) of the second drying surface 8
Is desirably set to 1.2 times or shorter than the length (ab) of the first dry surface 7. In particular, it is preferably 1 or less, more preferably 0.95 or less, and 0.9 or less.
Most preferably less than twice. The length of the second dry surface 8 (d to e
When f) is longer than 1.2 times the length (a to b to c) of the first dry surface 7, wrinkles are likely to be formed at both ends of the PVA film 6 during stretching, and the width of the obtained polarizing film is reduced. Not only the rate tends to deteriorate, but also color spots tend to occur. Also, 1c
The retardation unevenness in a minute area of about m tends to increase. Note that the length (d-e-f) of the second dry surface 8 is desirably 0.02 times or more the length (a-b-c) of the first dry surface 7.

The drying surfaces 7, 8, 11, and 12 are heated by steam, a heat medium, hot water, an electric heater, or the like.
In addition, means such as blowing hot air or cold air onto the PVA film, or suctioning air or steam around the PVA film may be used as an auxiliary. In the above embodiment, a plurality of rolls 3, 4, 9, and 10 are used, but a belt or the like may be used instead. Further, the PVA film 6 is formed by using a plurality of stages of the drying surfaces 7, 8, 11, and 12.
When drying is performed, on the subsequent stage side, not only a drying method using a roll or a belt, but also a drying method using a floating drier such as a tenter method or a free method can be adopted.

In the above-mentioned film forming machine, the length (a to b to c) of the first dry surface of the PVA film referred to in the present invention means that the molten PVA 2 is initially formed on the circumferential surface of the first roll 3. Is the length of the dry surface from the position a in contact with the position to the position c where the sheet passes through the position b and is peeled off from the first roll 3, and it is important that the length of the first dry surface is 3 m to 200 m. is there. If the length of the first dry surface is less than 3 m or more than 200 m, color spots are likely to occur on the obtained polarizing film. The length of the first drying surface is preferably 3.5 m to 150 m,
More preferably 4m to 100m, even more preferably 5m
８０80 m.

The length of the first drying surface (ab)
The moisture content of the PVA film 6 when peeled off from the first roll 3 after passing through c) is 50% by weight or less, preferably 45% by weight or less, more preferably 40% by weight or less, and 10% by weight or less. It is preferable that it is above. When the water content is more than 50% by weight, color unevenness occurs when a polarizing film is formed, and a good polarizing film cannot be obtained.
In addition, retardation spots in a minute area of about 1 cm tend to be large.

The moisture content (% by weight) of the PVA film 6 was measured using a fiber type infrared moisture meter.

In the present invention, the obtained PVA film 6
It is important that the retardation difference between two points 1 cm apart in the TD direction of the film is 5 nm or less. The retardation difference is preferably 4 nm or less, more preferably 3 nm or less. When the retardation difference exceeds 5 nm, color spots on the obtained polarizing film are easily noticeable, and a good polarizing film cannot be obtained. Even if the retardation between two points separated by more than 1 cm exceeds 5 nm, 1c
If the retardation difference between two points m apart from each other is 5 nm or less, it is difficult for a human eye to recognize the color spot as a color spot, so that it is unlikely to cause a problem.

The thickness of the PVA film 6 is preferably 5
１５０150 μm, most preferably 35-80 μm. Although the width of the PVA film 6 is not particularly limited, wrinkles tend to be formed during stretching when a film having a width of 2 m or more is stretched with a conventional film. Because it is hard to enter, especially 2m in width
It is preferred to apply to the film of.

The PVA used in the present invention is produced, for example, by saponifying a polyvinyl ester obtained by polymerizing a vinyl ester. A modified PVA obtained by graft copolymerizing the PVA with an unsaturated carboxylic acid or a derivative thereof, an unsaturated sulfonic acid or a derivative thereof, an α-olefin having 2 to 30 carbon atoms in a proportion of less than 15 mol%;
Or a vinyl ester and an unsaturated carboxylic acid or a derivative thereof, an unsaturated sulfonic acid or a derivative thereof, and having 2 to 3 carbon atoms.
0 modified α-olefin or the like at a ratio of less than 15 mol%, modified PVA produced by saponifying a modified polyvinyl ester, or unmodified or modified PVA with aldehydes such as formalin, butyraldehyde, and benzaldehyde. A so-called polyvinyl acetal resin in which a part of hydroxyl groups is crosslinked can be used.

Examples of the vinyl ester include vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate, vinyl benzoate and the like.

On the other hand, the comonomer used for the modified PVA is copolymerized mainly for the purpose of modifying the PVA, and is used within a range that does not impair the purpose of the present invention. Examples of such comonomers include olefins such as ethylene, propylene, 1-butene, and isobutene; acrylic acid and its salts; methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, and n-acrylate -Butyl, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate,
Acrylic esters such as dodecyl acrylate and octadecyl acrylate; methacrylic acid and its salts; methyl methacrylate, ethyl methacrylate, n-methacrylic acid
-Propyl, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-methacrylate
Methacrylates such as -butyl, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate; acrylamide, N-methylacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide, diacetoneacrylamide, acrylamidepropane Sulfonic acid and its salts, acrylamidopropyldimethylamine and its salts, acrylamide derivatives such as N-methylolacrylamide and its derivatives; methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidepropanesulfonic acid and its salts, Methacrylamide derivatives such as methacrylamidopropyldimethylamine and its salts, N-methylol methacrylamide and its derivatives; Cycloalkenyl formamide, N- vinyl acetamide, N- vinyl amides such as N- vinyl pyrrolidone; methyl vinyl ether, ethyl vinyl ether,
vinyl ethers such as n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether and stearyl vinyl ether; nitriles such as acrylonitrile and methacrylonitrile; vinyl chloride and vinylidene chloride , Vinyl fluoride, vinylidene fluoride, etc .; allyl compounds such as allyl acetate, allyl chloride; maleic acid and its salts or esters; itaconic acid and its salts or esters; vinylsilyl such as vinyltrimethoxysilane Compound; isopropenyl acetate and the like. Of these, α-olefins are preferred, and ethylene is particularly preferred. The amount of modification of the modified PVA is preferably less than 15 mol%.

The degree of saponification of PVA is preferably at least 90 mol%, more preferably at least 95 mol%, further preferably at least 98 mol%, particularly preferably at least 9 mol%, from the viewpoint of polarization performance and durability.
Most preferably, it is at least 9 mol%.

The degree of saponification indicates the ratio of units actually saponified to vinyl alcohol units among units that can be converted to vinyl alcohol units by saponification. In addition, the saponification degree of PVA was measured by the method described in JIS.

The degree of polymerization of PVA is preferably 500 or more, more preferably 1000 or more, still more preferably 1500 or more, and most preferably 2500 or more, from the viewpoint of polarization performance and durability. The upper limit of the PVA polymerization degree is preferably 8000 or less, more preferably 6000 or less.

The degree of polymerization of the PVA is determined according to JIS K67.
26 is measured. That is, it is determined from the intrinsic viscosity measured in water at 30 ° C. after the PVA is re-saponified and purified.

As a method for producing a PVA film using the above PVA, in addition to a film forming method by a melt extrusion method using hydrated PVA, for example, a PVA solution obtained by dissolving PVA in a solvent is used. A film forming method, a wet film forming method (discharging into a poor solvent), a 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), and a combination thereof. A method or the like can be adopted. Among these, the casting film forming method and the melt extrusion film forming method are preferable because a good polarizing film can be obtained.

Solvents for dissolving PVA used in the production of a PVA film include, for example, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol , Tetraethylene glycol, trimethylolpropane, ethylenediamine, diethylenetriamine, glycerin, water and the like, and one or more of these can be used. Among these, dimethyl sulfoxide,
Water or a mixed solvent of glycerin and water is preferably used.

The PVA solution used in producing the PVA film or the PVA ratio of the hydrated PVA is 10 to 7%.
0% by weight is preferred, 10 to 60% by weight is more preferred, 13 to 55% by weight is more preferred, and 15 to 5% by weight.
0% by weight is most preferred. If necessary, the PVA solution or the water-containing PVA may contain a plasticizer, a surfactant, a dichroic dye, and the like.

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

The amount of polyhydric alcohol added is PVA1
1 to 30 parts by weight, preferably 3 to 25 parts by weight, per 100 parts by weight
More preferred is 5 parts by weight, most preferred is 5 to 20 parts by weight. If the amount is less than 1 part by weight, the dyeing property and the stretchability may be reduced. If the amount is more than 30 parts by weight, the PVA 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, a carboxylic acid type such as potassium laurate, a sulfate type such as octyl sulfate, and a sulfonic acid type such as dodecylbenzenesulfonate are preferable. Examples of the nonionic surfactant include an alkyl ether type such as polyoxyethylene oleyl ether, an alkyl phenyl ether type such as polyoxyethylene octyl phenyl ether, an alkyl ester type 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 most preferred. When the amount is less than 0.01 part by weight, the effect of improving stretchability and dyeing property is difficult to appear, and when the amount is more than 1 part by weight, it elutes on the surface of the PVA film, causing blocking, and the handleability may be reduced. is there.

In order to produce a polarizing film from the PVA film of the present invention, for example, the PVA film may be subjected to dyeing, uniaxial stretching, fixing treatment, drying treatment and, if necessary, heat treatment. There are no particular restrictions on the order of the fixed processing operations. The uniaxial stretching may be performed twice or more.

Dyeing can be performed before, during or after uniaxial stretching. Dyes used for dyeing include iodine-potassium iodide; direct black 1
7, 19, 154; Direct Brown 44, 10
6, 195, 210, 223; Direct Red 2,
23, 28, 31, 37, 39, 79, 81, 240,
242, 247; Direct Blue 1, 15, 22,
78, 90, 98, 151, 168, 202, 236,
249, 270; Direct Violet 9, 12,
51, 98; Direct Green 1, 85; Direct Yellow 8, 12, 44, 86, 87; Direct Orange 26, 39, 106, 107 and other dichroic dyes are used in one kind or in a mixture of two or more kinds. it can.
Usually, dyeing is generally performed by immersing the PVA film in a solution containing the dye,
There are no particular restrictions on the processing conditions and processing method, such as mixing with a PVA film to form a film.

For the uniaxial stretching, a wet stretching method or a dry heat stretching method can be used, and a hot water such as an aqueous boric acid solution (which may be in a solution containing the dye or in a fixing bath described later) or a PVA film after water absorption is used. Can be done in the air. The stretching temperature is not particularly limited, but when stretching the PVA film in warm water (wet stretching), the stretching temperature is 30 to 90 ° C.
However, in the case of dry drawing, the temperature is preferably from 50 to 180 ° C. The stretching ratio of uniaxial stretching (in the case of multi-stage uniaxial stretching, the total stretching ratio) is preferably at least 4 times, particularly preferably at least 5 times, from the viewpoint of polarization performance. The upper limit of the stretching ratio is not particularly limited, but is preferably 8 times or less since uniform stretching is easily obtained. The thickness of the film after stretching is
It is preferably from 3 to 75 μm, more preferably from 5 to 50 μm.

For the purpose of strengthening the adsorption of the dye to the PVA film, a fixing treatment is often performed. Usually, boric acid and / or a boron compound is 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 of the PVA film is performed at 30 to
It is preferably performed at 150 ° C., and more preferably at 50 to 150 ° C.

The polarizing film obtained as described above is usually used as a polarizing plate by bonding an optically transparent protective film having mechanical strength to both surfaces or one surface thereof. As the protective film, cellulose triacetate (T
AC) film, cellulose acetate / butyrate (CAB) film, acrylic film, polyester film and the like are used. Examples of the adhesive for bonding include a PVA-based adhesive and a urethane-based adhesive. Among them, a PVA-based adhesive is preferable.

[0039]

EXAMPLES The present invention will now be described specifically with reference to examples, but the present invention is not limited to these examples. The moisture content, retardation difference and dichroic ratio in the examples were evaluated by the following methods.

Moisture content: fiber type infrared moisture meter (IM-
The moisture content of the PVA film was measured using 3SCV Model-1900 (L), manufactured by Fuji Work Co., Ltd.).

Retardation difference: Automatic birefringence meter (KOB)
RA21SDH, manufactured by Oji Scientific Instruments)
The retardation at any point of the PVA film was measured. Further, the retardation at a position 1 cm apart in the width direction of the film was measured, and the difference between the two measured values was obtained.

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 standards of the Electronic Machinery Industries Association of Japan (EIAJ) LD-2.
According to 01-1983, transmittance Ts (%) obtained by measuring and calculating with a C light source and a 2 degree field of view using a spectrophotometer
And the degree of polarization P (%). Dichroic ratio = log (Ts / 100−Ts / 100 × P /
100) / log (Ts / 100 + Ts / 100 × P /
100)

Example 1 PVA10 having a saponification degree of 99.9 mol% and a polymerization degree of 1750
A solution obtained by impregnating 0 parts by weight with 10 parts by weight of glycerin and 140 parts by weight of water is melt-kneaded, and melt-extruded into a metal roll having a first dry surface of 8 m in length (corresponding to the first roll). Then, the free surface of the PVA film (the back surface of the surface in contact with the first roll) is contacted with a metal roll (corresponding to the second roll) having a length of 4 m on the second dry surface. Dried, 2.5m wide and 75μm thick
Was obtained. The maximum value of the retardation difference between two points 1 cm apart from the film was 3 nm.

The PVA film was pre-swelled, dyed, uniaxially stretched, fixed, dried and heat-treated in this order to prepare a polarizing film. That is, the PVA film is
It was immersed in water at 0 ° C. for 5 minutes for pre-swelling, and immersed in an aqueous solution of 35 ° C. having an iodine concentration of 0.4 g / l and a potassium iodide concentration of 40 g / l for 3 minutes. continue,
The film is uniaxially stretched 5.5 times in an aqueous solution of boric acid at a concentration of 4% at 40 ° C., and placed in a 30 ° C. aqueous solution having a potassium iodide concentration of 40 g / l, a boric acid concentration of 40 g / l, and a zinc chloride concentration of 10 g / l. The fixing process was performed by immersion for 5 minutes. Thereafter, the PVA film is taken out, and under a fixed length,
The resultant was dried with hot air at 40 ° C. and further heat-treated at 100 ° C. for 5 minutes.

The thickness of the obtained polarizing film was 22 μm, and it was a non-defective product without color spots. The transmittance is 43.
2%, degree of polarization is 98.8%, and dichroic ratio is 34.6.
Met.

Example 2 PVA10 having a degree of saponification of 99.9 mol% and a degree of polymerization of 4000
PVA containing 0 parts by weight and 10 parts by weight of glycerin
An aqueous solution having a concentration of 15% by weight and a first dry surface having a length of 50%
m, and peeled at a moisture content of 30% by weight. Then, the free surface of the PVA film (the back surface of the surface in contact with the belt) was brought into contact with a metal roll having a second dry surface of 4 m in length. After drying, a PVA film having a width of 3 m and a thickness of 75 μm was obtained. The maximum value of the retardation difference between two points 1 cm apart from the film was 2 nm.

The PVA film was pre-swelled, dyed, uniaxially stretched, fixed, dried and heat-treated in this order to prepare a polarizing film. That is, the PVA film was pre-swelled by immersing it in water at 30 ° C. for 5 minutes, and an iodine concentration of 0.4 g /
Liter, 35 with potassium iodide concentration of 40 g / liter
It was immersed in an aqueous solution at a temperature of 3 ° C. for 3 minutes. Subsequently, uniaxial stretching was performed 5.6 times in an aqueous solution at a temperature of 40 ° C. with a boric acid concentration of 4%.
Potassium iodide concentration 40 g / liter, boric acid concentration 40
g / l, zinc chloride concentration 10g / l at 30 ° C
Was immersed in an aqueous solution for 5 minutes to perform a fixing treatment. Thereafter, the PVA film was taken out, dried with hot air at 40 ° C. under a constant length, and further heat-treated at 100 ° C. for 5 minutes.

The thickness of the obtained polarizing film was 22 μm, and it was a non-defective product without color spots. The transmittance is 42.
9%, the degree of polarization is 99.7%, and the dichroic ratio is 43.0.
Met.

Comparative Example 1 The procedure of Example 1 was repeated, except that the moisture content of the PVA film was 53% by weight when the PVA film was peeled off after passing through the first dry surface. Obtained. The maximum value of the retardation difference between two points 1 cm apart from the film was 10 nm.

The PVA film was treated in the same manner as in Example 1. At the time of stretching, both ends were easily curled and wrinkled. The obtained polarizing film had many color spots and was not of a practical (final product) level. When physical properties were evaluated using a portion having relatively small color spots, the transmittance was 43.2%, the degree of polarization was 98.3%, and the dichroic ratio was 31.76.

Comparative Example 2 The procedure of Example 2 was repeated, except that the water content of the PVA film at the time of peeling after passing through the first drying surface was 55% by weight. Obtained. The maximum value of the retardation difference between two points 1 cm apart from the film was 7 nm.

The PVA film was treated in the same manner as in Example 2. At the time of stretching, both ends were easily curled and wrinkled. Color spots were severe, and a good polarizing film could not be obtained.

[0053]

As described above, according to the present invention, a PVA film which does not easily wrinkle during stretching can be obtained. And
Using this PVA film, it is possible to obtain a polarizing film that is optimal for wide and large liquid crystal display screens with little color spots.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a drum type film forming machine showing one embodiment when producing a polyvinyl alcohol polymer film for a polarizing film of the present invention.

[Explanation of symbols]

1. Flat die 2, molten PVA 3, first roll,
4 ... second roll, 5 ... peeling roll, 6 ... polyvinyl alcohol polymer film (PVA film), 7 ... first dry surface, 8 ... second dry surface, 9 ... nth roll, 10 ... n + 1th roll, 11: n-th dry surface, 12: n + 1-th dry surface, ab to c: length of the first dry surface, d to ef: length of the second dry surface.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B29L 7:00 B29L 7:00 C08L 29:04 C08L 29:04 Z F-term (Reference) 2H049 BA02 BA27 BB43 BC01 BC03 BC22 2H091 FA08 FB02 FC01 FC07 FC08 FC22 LA12 LA30 4F071 AA29 AF35 AG34 AH19 BB06 BC01 4F205 AA19 AG01 AH73 GA07 GB02 GC02 GN22 GN28 GN29

Claims (8)

[Claims] 1. A polyvinyl alcohol-based polymer film having a retardation difference between two points 1 cm apart in the TD direction of the film is 5 nm or less. 2. The polyvinyl alcohol polymer film according to claim 1, which is used for a polarizing film. 3. A polarizing film produced by using the polyvinyl alcohol polymer film for a polarizing film according to claim 2. 4. A method for producing a polyvinyl alcohol-based polymer film by bringing the polyvinyl alcohol-based polymer into contact with a surface on which the polyvinyl alcohol-based polymer is dried (first drying surface) and drying the film, wherein the length of the dried surface is 3 m. ~ 200m,
A method for producing a polyvinyl alcohol-based polymer film, wherein the polyvinyl alcohol-based polymer film has a water content of 50% by weight or less when peeled off through the drying surface. 5. The method according to claim 4, wherein the front and back surfaces of the polyvinyl alcohol-based polymer film are dried over two or more stages of the first drying surface and the subsequent second drying surface. A method for producing a polyvinyl alcohol-based polymer film in which the front surface is dried on the first dry surface and the back surface is dried on the second dry surface. 6. The method for producing a polyvinyl alcohol polymer film according to claim 5, wherein the length of the second dry surface is set to be 1.2 times or less than the length of the first dry surface. . 7. The method for producing a polyvinyl alcohol-based polymer film according to claim 4, which is a method for producing a polyvinyl alcohol-based polymer film for a polarizing film. 8. The polyvinyl alcohol-based polymer film according to claim 1, which is produced by the method for producing a polyvinyl alcohol-based polymer film according to any one of claims 4 to 6.