WO2012002194A1

WO2012002194A1 - Polyvinyl alcohol film, method for producing polyvinyl alcohol film, polarizing film, and polarizing plate

Info

Publication number: WO2012002194A1
Application number: PCT/JP2011/064126
Authority: WO
Inventors: 秀一北村; 清水　俊宏
Original assignee: 日本合成化学工業株式会社
Priority date: 2010-07-02
Filing date: 2011-06-21
Publication date: 2012-01-05
Also published as: TW201206959A; CN102834235A; TWI437008B; CN102834235B; KR20130012026A; KR101257648B1; JP2012032789A; JP4870236B1

Abstract

Disclosed is a polyvinyl alcohol resin film which has excellent stretchability and is suppressed in dyeing unevenness. The polyvinyl alcohol resin film is suitable for use as an optical film such as a polarizing film. Specifically disclosed is a polyvinyl alcohol film which is obtained by forming a film-forming material that contains a polyvinyl alcohol resin (A) into a film. The polyvinyl alcohol film has a ratio of the swelling degree (X_TD) in the transverse direction (TD) to the swelling degree (X_MD) in the machine direction (MD), namely X_TD/X_MD of 1.000-1.020 when the film is immersed and swelled in water at 30˚C for 5 minutes.

Description

Polyvinyl alcohol film, method for producing polyvinyl alcohol film, polarizing film and polarizing plate

The present invention relates to a polyvinyl alcohol film, in particular, a polyvinyl alcohol film for a polarizing film, and more specifically, a polyvinyl alcohol film capable of obtaining a polarizing film having excellent stretchability and less dyeing unevenness, and such a polyvinyl alcohol film. The present invention relates to a film production method, a polarizing film, and a polarizing plate.

Conventionally, a polyvinyl alcohol film is prepared by dissolving a polyvinyl alcohol resin in a solvent such as water to prepare a stock solution, then forming a film by a solution casting method (casting method), and drying using a metal heating roll or the like. It is manufactured by doing. The polyvinyl alcohol film thus obtained is used in many applications as a film excellent in transparency, and one of its useful applications is a polarizing film. Such a polarizing film is used as a basic constituent element of a liquid crystal display, and in recent years, its use has been expanded to equipment requiring high quality and high reliability.

Under such circumstances, with the increase in brightness and definition of screens of liquid crystal televisions and the like, there is a demand for a polarizing film that is further superior in optical properties than conventional products.
In order to improve the compounding property, that is, the polarization performance, the polarizing film is obtained by dyeing and stretching the polyvinyl alcohol film, which is a raw material, with a dichroic dye such as iodine, and orienting the dichroic dye. It was necessary to increase the draw ratio.

In response to such a demand, the polarizing film obtained by improving the polyvinyl alcohol resin has, for example, a syndiotacticity of 55% or more, an ω-hydroxy-α-olefin group, an oxyalkylene group, and an amide group. A polyvinyl alcohol film for a polarizing film made of a polyvinyl alcohol polymer containing 0.01 to 1 mol% of one or more hydrophilic functional groups selected from the above has been proposed (for example, Patent Documents). 1).
In addition, with an increase in the size of screens of liquid crystal televisions or the like, there has been a demand for a polarizing film that is further superior in polarization performance, particularly in-plane uniformity of polarization performance.

In order to obtain a polarizing film with excellent in-plane uniformity of polarizing performance, the polyvinyl alcohol film that is the original film of the polarizing film must be optically homogeneous, in particular the uniformity of the in-plane retardation value. It becomes important.

As such a countermeasure, for example, the difference in the retardation value between two points that are 2 m or more in film width and 1 cm apart in the width direction is 5 nm or less, and the difference in the retardation value between two points that are 1 m apart in the width direction. Is a polyvinyl alcohol film having a thickness of 50 nm or less (for example, see Patent Document 2), a width of 3 m or more, a retardation value in the film plane of 30 nm or less, and a retardation in the film plane in the film width direction. A polyvinyl alcohol film having a value fluctuation of 15 nm or less has been proposed (for example, see Patent Document 3).

JP-A-8-201626 JP 2002-28939 A JP 2007-137042 A

However, in the disclosed technique of Patent Document 1, although the obtained polyvinyl alcohol film can obtain a polarizing film having excellent stretchability, the stretching temperature is limited to 20 to 40 ° C., and the substantial maximum stretching is achieved. The magnification was about 5.3 times, and the stretchability was still not satisfactory.

In addition, in order to cope with the further increase in the transmittance of the polarizing film accompanying the increase in brightness and definition of the liquid crystal display in recent years, the demand for in-plane uniformity of the polarizing film is increasing. Even with 2 and 3, further improvements were required.

Therefore, in the present invention, in such a background, to provide a polyvinyl alcohol film capable of obtaining a polarizing film excellent in stretchability and less dyeing unevenness and a method for producing the same, and further from such a polyvinyl alcohol film. An object of the present invention is to provide a polarizing film and a polarizing plate.

However, as a result of intensive studies by the present inventors to solve the above-mentioned problems, attention was paid to the swelling behavior of the polyvinyl alcohol-based film. As a result, the width of the film relative to the degree of swelling (X _MD ) in the machine (MD) direction (TD) ) Although the degree of swelling (X _TD ) in the direction is the same or slightly larger, by controlling the ratio (X _TD / X _MD ) smaller than that of conventional films, a polarizing film with excellent stretchability and less dyeing unevenness can be obtained. It discovered that the polyvinyl alcohol-type film which can be obtained was obtained, and completed this invention.

That is, the gist of the present invention is a polyvinyl alcohol film formed by forming a film forming material containing the polyvinyl alcohol resin (A), and the film is immersed in water at 30 ° C. for 5 minutes to swell. polyvinyl alcohol film width direction (TD) of the degree of swelling (X _TD) and machine direction (MD) of the swelling ratio _{_{(X MD) (X TD /}} X MD) is 1.000 to 1.020 when It is about.

The present invention also provides a method for producing the polyvinyl alcohol film, a polarizing film comprising the polyvinyl alcohol film, and a polarizing plate comprising a protective film provided on at least one surface of the polarizing film.

Conventionally, when producing a polyvinyl alcohol-based film, a polyvinyl alcohol-based resin aqueous solution is usually cast into a film, and dried and heat-treated using a plurality of hot rolls. At that time, a certain amount of tension must be applied in the film machine (MD) direction. At this time, shrinkage in the film width (TD) direction and further shrinkage in the film width (TD) direction due to drying with a hot roll. Arise. When the obtained polyvinyl alcohol film is swollen in water, the degree of swelling in the width (TD) direction increases, and as a result, the degree of swelling (X _TD ) in the width (TD) direction and the machine (MD) direction. the ratio of the degree of swelling _{_{(X MD) (X TD /}} X MD) increases. When a polarizing film is produced, if the degree of swelling in the width direction is large, the film does not swell uniformly, and uneven dyeing or stretching occurs. Therefore, in the present invention, as described above, in order to suppress the occurrence of uneven dyeing and stretching unevenness, the inventors have found that the predetermined swelling degree ratio is made smaller than that of the conventional film by paying attention to the swelling behavior of the polyvinyl alcohol film. It is a thing.

The polyvinyl alcohol-based film of the present invention has an effect that it is possible to obtain a polarizing film having excellent stretchability and less dyeing unevenness. Such a polyvinyl alcohol film is used for a polarizing film used for a liquid crystal display device such as polarized sunglasses or a liquid crystal television, a raw film used for a half-wave plate or a quarter-wave plate, a liquid crystal display. It is very useful as an original film of a retardation film used in an apparatus.

The present invention is described in detail below.
The polyvinyl alcohol film of the present invention is a polyvinyl alcohol film formed by forming a film forming material containing a polyvinyl alcohol resin (A), and the film is immersed in water at 30 ° C. for 5 minutes to swell. the ratio of the width (TD) direction of the degree of swelling (X _TD) and machine direction (MD) degree of swelling (X _MD) when the (hereinafter, sometimes abbreviated as "swelling ratio".) (X _TD / X _MD) is 1.000 to 1.020.

Here, the degree of swelling in the machine (MD) direction and the width (TD) direction means the elongation in the width (TD) direction and the elongation in the machine (MD) direction when immersed in water at 30 ° C. for 5 minutes. It is measured as follows.

That is, the film is cut into a 10 cm × 10 cm square so as to be parallel to the machine (MD) direction and the width (TD) direction, placed on a flat glass plate, and the dimensions in the MD direction and the TD direction are measured with calipers. To do. Next, after immersing in an ion exchange water bath adjusted to 30 ° C. for 5 minutes, the film is taken out and immediately placed on a flat glass plate, and the dimensions in the MD direction and the TD direction are each measured with calipers. The degree of swelling in the machine (MD) direction and the width (TD) direction, and further the area swelling degree can be obtained by the following equation using the measured values. The above operation is performed in an environment of 23 ° C. and 50% RH.

Swelling degree in machine (MD) direction (X _MD ) (%)
= (Dimension in MD direction after immersion / Dimension in MD direction before immersion) × 100
Swelling degree in width (TD) direction (X _TD ) (%)
= (Dimension in TD direction after immersion / Dimension in TD direction before immersion) × 100
Area swelling degree (Y) (%)
= (Swelling degree in MD direction / 100) × (swelling degree in TD direction / 100) × 100

In the present invention, the swelling ratio (X _TD / X _MD ) needs to be 1.000 to 1.020, preferably 1.000 to 1.015, particularly preferably 1.001 to 1. .015. If this value is less than the above range, the stretchability is inferior, and if it exceeds the above range, uneven dyeing occurs when a polarizing film is formed.

The range of the degree of swelling (X _MD ) (%) in the machine (MD) direction of the polyvinyl alcohol film is preferably 110 to 130%, particularly 112 to 128%, more preferably 114 to 126%. It is preferable. If the range is too small, the stretchability tends to be inferior when the polarizing film is produced, and if it is too large, the polarizing performance tends to be inferior when the polarizing film is formed.

The range of the degree of swelling (X _TD ) (%) in the width (TD) direction of the polyvinyl alcohol film is preferably 110 to 130%, particularly 112 to 128%, more preferably 114 to 126%. It is preferable. If the range is too small, the stretchability tends to be inferior when the polarizing film is produced, and if it is too large, uneven dyeing tends to occur when the polarizing film is formed.

In addition, the polyvinyl alcohol film of the present invention has an area swelling degree (Y) of 130 to 170% when the film is immersed in water at 30 ° C. for 5 minutes to swell, in terms of stretchability and polarization characteristics. Preferably, it is 135 to 165%, more preferably 140 to 160%. If the area swelling degree (Y) is too small, the film tends to be broken at the time of stretching, and if it is too large, the polarization property tends to be lowered.

The polyvinyl alcohol film of the present invention as described above is cast and formed using a film forming material containing the polyvinyl alcohol resin (A).

As the polyvinyl alcohol resin (A), an unmodified polyvinyl alcohol resin, that is, a resin produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate is usually used. If necessary, a resin obtained by saponifying a copolymer of vinyl acetate and a small amount (for example, 10 mol% or less, preferably 5 mol% or less) of vinyl acetate and a copolymerizable component may be used. it can. Examples of components copolymerizable with vinyl acetate include unsaturated carboxylic acids (including salts, esters, amides, nitriles, etc.), olefins having 2 to 30 carbon atoms (ethylene, propylene, n-butene, isobutene, etc.) , Vinyl ethers, unsaturated sulfonates and the like.

Further, as the polyvinyl alcohol resin (A), a polyvinyl alcohol resin having a 1,2-glycol bond in the side chain can also be used. Such a polyvinyl alcohol resin having a 1,2-glycol bond in the side chain includes, for example, (i) a method of saponifying a copolymer of vinyl acetate and 3,4-diacetoxy-1-butene, and (ii) acetic acid. A method of saponifying and decarboxylating a copolymer of vinyl and vinyl ethylene carbonate; and (iii) saponifying and decarboxylating a copolymer of vinyl acetate and 2,2-dialkyl-4-vinyl-1,3-dioxolane. It is obtained by a method of ketalization, (iv) a method of saponifying a copolymer of vinyl acetate and glyceryl monoallyl ether, or the like.

The average saponification degree of the polyvinyl alcohol resin (A) used in the present invention is usually preferably 90 mol% or more, particularly preferably 95 mol% or more, more preferably 98 mol% or more, and particularly preferably 99 mol%. The mol% or more, more preferably 99.5 mol% or more. When the average saponification degree is too small, there is a tendency that sufficient optical performance cannot be obtained when a polyvinyl alcohol resin is used as a polarizing film.
Here, the saponification degree in the present invention is obtained by analyzing the alkali consumption required for hydrolysis of residual vinyl acetate.

Further, the viscosity of the polyvinyl alcohol resin (A) is preferably 8 to 500 mPa · s, particularly 20 to 400 mPa · s, more preferably 40 to 400 mPa · s, as a 4 wt% aqueous solution viscosity at 20 ° C. -S is preferable. If the 4% by weight aqueous solution viscosity is too small, the stretchability at the time of producing the polarizing film tends to be insufficient, and if too large, the planar smoothness and transparency of the film tend to decrease.

As the polyvinyl alcohol resin (A) used in the present invention, in the above polyvinyl alcohol resin, two or more kinds having different modified species, average saponification degree, viscosity and the like may be used in combination.

In the present invention, a polyvinyl alcohol film is produced using a film forming material containing the polyvinyl alcohol resin (A). In film production, for example, a known compounding agent such as a plasticizer (B) or a surfactant (C) is blended and manufactured.

The plasticizer (B) generally contributes effectively to stretchability when producing a polarizing film. For example, glycerins such as glycerin, diglycerin, triglycerin, ethylene glycol, diethylene glycol, triglycerin. Examples include alkylene glycols or polyalkylene glycols such as ethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, and polypropylene glycol, and trimethylolpropane. These plasticizers (B) can be used alone or in combination of two or more. Among them, particularly preferred are glycerin alone, glycerin and diglycerin, or a combination of glycerin and trimethylolpropane. When glycerin and diglycerin are used in combination, glycerin / diglycerin (weight ratio) is usually 20/80 to 80/20. When glycerin and trimethylolpropane are used in combination, glycerin / trimethylolpropane (weight ratio) is usually used. ) = 20/80 to 80/20.

The content of the plasticizer (B) is preferably 1 to 35 parts by weight, particularly 3 to 30 parts by weight, and more preferably 7 to 25 parts by weight with respect to 100 parts by weight of the polyvinyl alcohol resin (A). Part. When there is too little content of a plasticizer (B), there exists a tendency for a drawability to fall at the time of preparation of a polarizing film, and when too much, there exists a tendency for the temporal stability of the polyvinyl alcohol-type film obtained to fall.

In addition, the surfactant (C) generally has a function of suppressing film surface smoothness and adhesion between films when wound into a roll. For example, an anionic surfactant or a nonionic interface The activities can be used alone or in combination of two or more. In particular, the combined use of an anionic surfactant and a nonionic surfactant is preferable from the viewpoint of the transparency of the film.

Examples of such anionic surfactants include aliphatic alkyl sulfonates, alkyl sulfate esters, polyoxyethylene alkyl ether sulfates, polyoxyethylene alkyl phenyl ether sulfates, higher fatty acid alkanolamide sulfates, and the like. In addition to these anionic surfactants, sulfate esters such as sulfated oils, higher alcohol ethoxy sulfates and monoglycolates, fatty acid soaps, N-acyl amino acids and salts thereof, polyoxyethylene alkyls Carboxylate types such as ester carboxylates and acylated peptides, alkylbenzene sulfonates, alkylnaphthalene sulfonates, naphthalene sulfonic acid salt formalin polycondensates, melamine sulfonic acid salt formalin condensates, dialkyl sulfosuccinates Sulfonic acids such as ester salts, alkyl disulphates of sulfosuccinic acid, polyoxyethylene alkyl sulfosuccinic acid disalts, alkyl sulfoacetates, α-olefin sulfonates, N-acylmethyl taurates, dimethyl-5-sulfoisophthalate sodium salts Mention may also be made of anionic surfactants such as salt forms, phosphate ester salt forms such as polyoxyethylene alkyl ether phosphates, polyoxyethylene alkyl phenyl ether phosphates and alkyl phosphates.

On the other hand, as the nonionic surfactant, for example, polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, higher fatty acid mono- or dialkanolamide, higher fatty acid amide, polyoxyethylene alkylamine, polyoxyethylene higher fatty acid amide, And amine oxides. In addition to these nonionic surfactants, ethylene oxide derivatives of alkylphenol formalin condensates, polyoxyethylene polyoxypropylene block polymers, polyoxyethylene glycerin fatty acid esters, polyoxyethylene castor oil and hydrogenated castor oil, poly Ether-type surfactants such as oxyethylene sorbitan fatty acid esters and polyoxyethylene sorbitol fatty acid esters, and ester-type surfactants such as polyethylene glycol fatty acid esters, sorbitan fatty acid esters, fatty acid monoglycerides, propylene glycol fatty acid esters, and sucrose fatty acid esters , Etc.

The content of the surfactant (C) is preferably 0.01 to 1 part by weight, particularly preferably 0.02 to 0.5 part by weight based on 100 parts by weight of the polyvinyl alcohol resin (A). Part, more preferably 0.03 to 0.2 part by weight. If the content of the surfactant (C) is too small, the anti-blocking effect tends to be difficult to obtain, and if it is too large, the transparency of the film tends to decrease.

When an anionic surfactant and a nonionic surfactant are used in combination, the anionic surfactant is used in an amount of 0.01 to 1 part by weight, particularly 100 parts by weight of the polyvinyl alcohol resin (A). The amount is preferably 0.02 to 0.2 parts by weight, more preferably 0.03 to 0.1 parts by weight, and the nonionic surfactant is 0.01 to 1 part by weight, particularly 0.02 to 0.2 parts by weight. It is preferable that the amount is 0.03 to 0.1 parts by weight. If the amount of the anionic surfactant is too small, the dispersibility of the dye at the time of preparing the polarizing film tends to decrease, and the dyeing spots tend to increase.If the amount is too large, foaming occurs when the polyvinyl alcohol resin is dissolved, and bubbles are generated in the film. It tends to be mixed and cannot be used as an optical film. If the nonionic surfactant is too small, it is difficult to obtain an anti-blocking effect, and if it is too much, the transparency and flatness of the film tend to be lowered.

In the present invention, it is also useful to add an antioxidant in order to prevent yellowing of the film. Examples of the antioxidant include phenolic antioxidants, and 2,6-di- T-butyl-p-cresol, 2,2'-methylenebis (4-methyl-6-t-butylphenol), 4,4'-butylidenebis (3-methyl-6-t-butylphenol) and the like are preferable. The antioxidant is preferably used in the range of about 2 to 100 ppm relative to the polyvinyl alcohol resin (A).

Thus, in the present invention, a film-forming material is prepared using the polyvinyl alcohol-based resin (A). Preferably, the polyvinyl alcohol-based resin (A) further includes at least a plasticizer (B) and a surfactant (C). One is used to prepare a film-forming material. And this film forming material is formed into a film and a polyvinyl alcohol-type film is obtained.

<Method for producing polyvinyl alcohol film>
Hereinafter, the manufacturing method of the polyvinyl alcohol-type film of this invention is demonstrated concretely.

In the present invention, a film-forming material is prepared using at least one of a polyvinyl alcohol-based resin (A), preferably a plasticizer (B) and a surfactant (C), and an aqueous solution of the film-forming material is used as a drum-type roll. Alternatively, a polyvinyl alcohol film is produced by casting on an endless belt, preferably a drum-type roll, and forming, drying, and heat-treating.

In the production method of the present invention, the polyvinyl alcohol resin (A) powder is first washed to remove sodium acetate usually contained in the resin. In the washing, washing with methanol or water is performed, but the method of washing with methanol requires solvent recovery, so that the washing method with water is more preferable.

Next, the water-containing polyvinyl alcohol-based resin (A) wet cake after washing is dissolved to prepare a polyvinyl alcohol-based resin (A) aqueous solution. When the water-containing polyvinyl alcohol-based resin (A) wet cake is dissolved in water as it is, Since a desired high-concentration aqueous solution cannot be obtained, it is preferable to perform dehydration once. The dehydration method is not particularly limited, but a method using centrifugal force is common.

It is preferable to obtain a wet polyvinyl alcohol resin (A) wet cake having a water content of 50% by weight or less, preferably 30 to 45% by weight, by the washing and dehydration. If the water content is too high, it tends to be difficult to obtain a desired aqueous solution concentration.

Next, an aqueous solution of a film forming material used for forming a polyvinyl alcohol film is prepared by adding water, water-containing polyvinyl alcohol resin (A) wet cake after dehydration, plasticizer (B), and surfactant in a dissolution tank. (C) and the like are prepared, heated, stirred and dissolved. In the production method of the present invention, it is particularly preferable in terms of solubility that water-containing polyvinyl alcohol resin (A) wet cake is dissolved by blowing water vapor in a dissolution tank equipped with a vertical circulation flow generation type stirring blade. .

When the water-containing polyvinyl alcohol-based resin (A) wet cake is dissolved by blowing water vapor in a dissolution tank equipped with an up-and-down circulating flow generation type stirring blade, water vapor is blown and the resin temperature is 40 to 80 ° C., preferably 45 It is preferable to start stirring when the temperature reaches ˜70 ° C. from the viewpoint of uniform dissolution. If the resin temperature is too low, the load on the motor tends to increase. If the resin temperature is too high, the polyvinyl alcohol resin tends to be hardened and cannot be uniformly dissolved. Furthermore, it is also preferable from the viewpoint that uniform dissolution can be achieved by injecting water vapor and pressurizing the inside of the tank when the resin temperature is usually 90 to 100 ° C., preferably 95 to 100 ° C. If the resin temperature is too low, undissolved products tend to be formed. Then, when the resin temperature reaches 130 to 150 ° C., the blowing of water vapor is terminated, and stirring is continued for 0.5 to 3 hours to perform dissolution. After dissolution, the concentration is adjusted so that the desired concentration is obtained.

The concentration of the aqueous solution of the film-forming material thus obtained is usually preferably 10 to 50% by weight, more preferably 15 to 40% by weight, particularly preferably 20 to 30% by weight. If the concentration is too low, the drying load tends to increase and the production capacity tends to decrease. If the concentration is too high, the viscosity becomes too high and uniform dissolution tends to be difficult.

Next, the aqueous solution of the obtained film forming material is defoamed. Examples of the defoaming method include stationary defoaming and defoaming by a multi-screw extruder, but in the production method of the present invention, a method of defoaming using a multi-screw extruder is preferable in terms of productivity. .

After the defoaming treatment, the aqueous solution of the film forming material discharged from the multi-screw extruder is introduced into a T-type slit die by a certain amount and cast onto a drum-type roll or an endless belt to form a film, Dry and heat treated.

As the T-type slit die, a T-type slit die having an elongated rectangle is usually used. The resin temperature at the exit of the T-type slit die is usually preferably 80 to 100 ° C., more preferably 85 to 98 ° C. If the resin temperature at the exit of the T-type slit die is too low, there is a tendency to cause poor flow, and if it is too high, there is a tendency to foam.

The casting is performed with a drum-type roll or an endless belt, but it is preferably performed with a drum-type roll in terms of widening, lengthening, film thickness uniformity, and the like.
In casting a film with a drum-type roll, for example, the rotational speed of the drum is preferably 5 to 30 m / min, and particularly preferably 6 to 20 m / min. The surface temperature of the drum-type roll is preferably 70 to 99 ° C., more preferably 75 to 97 ° C. If the surface temperature of the drum-type roll is too low, drying tends to be poor. If it is too high, foaming tends to occur.

Drying of the polyvinyl alcohol film formed by the drum-type roll is performed by alternately passing the front and back surfaces of the film through a plurality of heat roll groups (Rn). The surface temperature of the heat roll group is preferably 60 to 100 ° C., more preferably 65 to 90 ° C. If the surface temperature is too low, drying tends to be poor, and if it is too high, it tends to dry too much, leading to poor appearance.
In the present invention, heat treatment is performed after drying.

The heat treatment is preferably performed at a relatively low temperature, such as 70 to 140 ° C., particularly preferably 70 to 130 ° C. If the heat treatment temperature is too low, the water resistance is insufficient or heat treatment spots increase, which tends to cause optical spots, and if it is too high, the stretchability during the production of the polarizing film tends to decrease. As the heat treatment method, for example, (1) the surface is hard chrome-plated or mirror-finished and passed through a roll having a diameter of 0.2 to 2 m (1 to 30), and (2) a floating dryer (length : 2 to 30 m).

Thus, a polyvinyl alcohol film is obtained.

In the present invention, it is preferable to include the following steps among the above production methods in that the ratio of swelling degree which is a feature of the present invention can be adjusted.

That is, a step [I] of casting an aqueous solution of a film-forming material containing the polyvinyl alcohol resin (A) onto the first hot roll, and a step of peeling from the first hot roll in a state where the film moisture content is 10 to 25% [II] includes a step [III] in which at least five or more second heat rolls having a surface temperature of 80 to 98 ° C. are alternately passed through the front and back of the film.

In step [I], the first heat roll is a drum-type roll or an endless belt, and an aqueous solution of a film forming material is cast onto the first heat roll (drum-type roll or endless belt).

In the step [II], the film is dried on the first hot roll and peeled in a state where the film moisture content is 10 to 25%, preferably 12 to 20%. If the moisture content is too low, the tension at the time of peeling tends to be high and the film tends to stretch, and if it is too high, the film tends to become uneven in the width direction at the time of peeling.

Furthermore, in the said process [III], the film peeled from the 1st hot roll is sent to an at least 5 or more 2nd hot roll group so that the surface and the back surface of a film may pass alternately. At this time, the surface temperature of at least five second heat roll groups is preferably 80 to 98 ° C., particularly 82 to 95 ° C., more preferably 85 to 95 ° C. from the viewpoint of curl prevention. Is preferred. If the surface temperature is too low, the drying efficiency tends to be poor and soot tends to enter, and if it is too high, drying unevenness tends to occur.

In the present invention, the film forming material is cast, dried and heat-treated, and the film is wound up. The draw ratio at this time is preferably 0.9 to 1.1, particularly preferably. Is from 0.95 to 1.07, more preferably from 0.98 to 1.05. If the draw ratio is too low, the film tends to sag when the film is conveyed. Tend to be higher.

Here, the draw ratio refers to a ratio determined by the film winding speed / the rotation speed of the first heat roll. The draw ratio is conventionally in the range of 0.9 to 1.1. However, in the present invention, the draw ratio is set lower than in the past from the viewpoint of suppressing swelling unevenness in the film width direction. Are preferred.

In the present invention, when an aqueous solution of a film-forming material containing the polyvinyl alcohol resin (A) is cast, a film in an area within 5% of the entire width from the end with respect to the width direction of the film. Forming the film so that the thickness (T1) is 2 to 8%, preferably 3 to 7% thicker than the film thickness (T2) at the center of the film width can also adjust the swelling ratio, which is a feature of the present invention. It is preferable in that it can be performed. If the thickness ratio is too small, the swelling ratio (X _TD / X _MD ) tends to be high, and if it is too large, the film thickness at the film end tends to be easily shaken.

When controlling the thickness ratio between the end portion and the center portion of the film, for example, when casting an aqueous solution of a film forming material from a T-type slit die to a drum-type roll or an endless belt, both end portions of the T-type slit die Examples include a method in which the clearance of a portion (corresponding to a region within 5% of the total width from the end portion with respect to the width direction of the film) is larger than the clearance of the central portion. The difference between the clearance at both ends and the clearance at the center is appropriately adjusted according to the target numerical value of the thickness ratio between the film thickness (T1) and the film thickness (T2).

In addition to the method of providing a difference between the clearance at both ends of the T-type slit die and the clearance at the center, for example, a method of sandwiching only the end of the film with a nip roll, Examples thereof include a method of drying while fixing and a method of stretching in the width direction.

Furthermore, the following method can also be used for drying the polyvinyl alcohol film in which the front and back surfaces of the film are alternately passed through a plurality of heat roll groups (Rn).

First, as for the heat roll of the said heat roll group (Rn), the roll diameter ((beta)) in any part within 20% from a both ends is larger than the roll diameter ((alpha)) of a center part with respect to a roll width direction. It preferably consists of a hot roll. By using such a heat roll group (Rn), it is possible to apply a tension in the width (TD) direction of the film, and it tends to be easy to obtain a polyvinyl alcohol film having less optical anisotropy.

And in the heat roll of this heat roll group (Rn), the relationship between the roll diameter (β) and the roll diameter (α) at the central portion in any part within 20% from the both ends of the roll is expressed by the following formula ( Satisfying 1) is preferable in terms of imparting tension in the width (TD) direction of the film. Particularly preferred is the following formula (2), and further preferred is the following formula (3). If the relationship between the roll diameter (β) and the roll diameter (α) is too small, the application of tension in the width (TD) direction of the film tends to be insufficient. Tends to occur.

0.001 ≦ (β−α) /α≦0.1 (1)
0.005 ≦ (β−α) /α≦0.07 (2)
0.010 ≦ (β−α) /α≦0.05 (3)

Furthermore, in this invention, it is a film roll that the heat roll of a heat roll group (Rn) is a heat roll formed so that it might become large gradually toward a both ends from a center part with respect to a roll width direction. This is preferable. Here, “so as to gradually increase” includes linearly increasing from the center to the end, increasing in a curve, a combination thereof, and the like.

Moreover, the angle ((theta)) which the heat roll of the said heat roll group (Rn) makes with the horizontal line in the top part of a center part, and the straight line which connects the top part of a center part, and the top part of an edge part with respect to the roll width direction. It is preferably 0.01 to 3.00 degrees from the viewpoint of imparting tension in the width (TD) direction of the film, particularly 0.02 to 2.00 degrees, more preferably 0.03 to 1.00 degrees. It is preferable that If the angle (θ) is too small, the application of tension in the width (TD) direction of the film tends to be insufficient, and if it is too large, meandering tends to occur when the film passes.

In this method, the surface temperature of the hot roll group (Rn) is usually preferably 40 to 100 ° C., particularly 60 to 100 ° C., more preferably 65 to 95 ° C. If the surface temperature is too low, drying tends to be poor, and if it is too high, drying unevenness tends to occur.

Moreover, the following method is mentioned as another method of drying a polyvinyl alcohol-type film.

First, with respect to the width direction of the discharge width (a) from the T-shaped slit die, the surface temperature of the hot roll group (Rn) in any region (S1) within 10% of the discharge width from one end ( t1) and the surface temperature (t2) of the thermal roll group (Rn) in any region (S2) within 10% of the discharge width from the other end is in the width direction of the discharge width (a). The surface temperature is preferably lower than the surface temperature (t3) of the heat roll group (Rn) in the region (S3) excluding the region (S1) and the region (S2). By adjusting the surface temperature of the heat roll group (Rn), it is possible to apply a tension in the width (TD) direction of the film, and a polyvinyl alcohol film having less optical anisotropy tends to be obtained.

In particular, the surface temperature (t1) and the surface temperature (t2) of the heat roll group (Rn) are higher than the surface temperature (t3) in terms of imparting tension in the width (TD) direction of the film and transportability of the film. The surface temperature is preferably 1 to 20 ° C. lower, more preferably 1 to 18 ° C., particularly 2 to 16 ° C. lower. If the temperature difference is too small, the tension in the film width (TD) direction tends to be insufficient, and if the temperature difference is too large, the adhesion of the film end to the hot roll becomes strong, so the machine for film conveyance. Tension in the (MD) direction increases, and as a result, the optical anisotropy of the film tends to increase.

Here, the surface temperature (t1) of the thermal roll group (Rn) in the region (S1) and the surface temperature (t2) of the thermal roll group (Rn) in the region (S2) are expressed in the width direction of the discharge width (a). In order to make the surface temperature lower than the surface temperature (t3) of the heat roll group (Rn) in the area (S3) excluding the area (S1) and the area (S2), for example, a temperature control unit inside the heat roll group Examples include a method of using a heat roll that can be divided and controlled, blowing cold air to the end of the heat roll, or installing a cooling roll at the end of the heat roll.

The region (S1) preferably occupies any region within 10% of the discharge width from one end with respect to the width direction of the discharge width (a) from the T-shaped slit die. Furthermore, it is preferable from the viewpoint of film transportability that the area is within 10%, particularly within 9%, especially within 8%. The region (S2) preferably occupies any region within 10% of the discharge width from the other end with respect to the width direction of the discharge width (a) from the T-shaped slit die. Furthermore, it is preferable from the viewpoint of film transportability that the area is within 10%, particularly within 9%, especially within 8%. When the region (S1) and the region (S2) are out of the above range, the film transportability tends to decrease. The region (S3) is a region excluding the region (S1) and the region (S2).

Furthermore, in this invention, about area | region (S3), the width | variety of the area | region (S3) which occupies a center part is larger than the film width (b) after film forming with respect to the roll width direction of a heat roll group (Rn). Is preferable in terms of in-plane uniformity of the film after film formation. In particular, the width of the region (S3) is preferably 100 to 115%, more preferably 100 to 110% with respect to the film width (b) after film formation. If the width of the region (S3) is too small, unevenness tends to occur in the surface of the film after film formation.

As described above, there are various methods for drying the polyvinyl alcohol film. And in this invention, the heat processing of a polyvinyl alcohol-type film is performed after drying. The film width (b) after film formation refers to the film width after passing through the drying process, or the film width after passing through the heat treatment process when heat treatment is performed after the drying process.

<Polyvinyl alcohol film>
The polyvinyl alcohol film of the present invention thus obtained has a predetermined swelling ratio (X _TD / X _MD ) of 1.000 to 1.020 as described above. Further, as described above, the polyvinyl alcohol film of the present invention preferably has a predetermined area swelling degree (Y) of 130 to 170%.

In addition, the polyvinyl alcohol film of the present invention preferably has a retardation value of 10 to 40 nm, particularly 10 to 30 nm, and more preferably 10 to 25 nm in that it is uniformly stretched in the width direction.

In addition, in the polyvinyl alcohol film of the present invention, the degree of weight swelling (W) at 30 ° C. is preferably 190 to 230% from the viewpoint of dyeing property of the dye, particularly 195 to 225%, more preferably 195 It is preferably ˜220%. If the weight swelling degree (W) is too small, the stretchability at the time of producing the polarizing film tends to be lowered. If it is too large, the stretchability is improved, but the polarizing performance of the polarizing film tends to be lowered.

In order to control the weight swelling degree (W) within the above range, for example, the following method is used. The film forming material containing the polyvinyl alcohol resin (A) is cast on a drum-type roll or an endless belt, preferably a drum-type roll, and then the front and back surfaces are alternately dried by a plurality of rotary heating roll groups, so that the moisture content is After continuously forming a 5 to 30% by weight polyvinyl alcohol film, the temperature of the floating dryer or rotary heating roll is adjusted by heat treatment in the range of 70 to 140 ° C. If the moisture content in the film is too high, the crystallization rate of the polyvinyl alcohol-based resin (A) is slowed down, so that it is difficult to obtain a heat treatment effect. If the moisture content is too low, heat treatment at 140 ° C. or higher is required. Therefore, the quality of the film tends to be lowered, for example, the degree of weight swelling of the film becomes too low or the film tends to yellow.

However, without being limited to these methods, the same heat treatment conditions can be adjusted depending on the type and amount of the plasticizer. Generally, if the amount of the plasticizer added is increased, the crystallinity of the polyvinyl alcohol-based resin (A) decreases, so that the degree of weight swelling (W) tends to decrease. Moreover, even if the addition amount of a plasticizer is the same, it is possible to adjust the crystallinity degree of polyvinyl alcohol-type resin (A) with the kind of plasticizer, and it is compatible with polyvinyl alcohol-type resin (A). A good plasticizer has a high effect of lowering the crystallinity, and therefore the weight swelling degree (W) can be adjusted by reducing the amount added. On the other hand, plasticizers with poor compatibility have a low effect of reducing the crystallinity, so that the degree of weight swelling (W) can be adjusted by increasing the amount of plasticizer added.
Furthermore, even if it is the same heat processing temperature, a weight swelling degree (W) can be adjusted with the saponification degree and polymerization degree of polyvinyl alcohol-type resin (A). Furthermore, the degree of weight swelling (W) may be adjusted by drying conditions during film formation, for example, conditions for drying moisture in the film such as high temperature drying, low temperature drying, and high humidity drying. Among them, in terms of productivity, it is preferable to adjust the degree of weight swelling (W) by heat treatment after the moisture content in film formation becomes 5 to 30% by weight, and glycerin is mainly used as a plasticizer. More preferably, the weight swelling degree (W) is adjusted in the heat treatment temperature range of 70 to 140 ° C.

Here, the weight swelling degree (W) is measured as follows.
That is, the film is cut into 10 cm × 10 cm and immersed in an ion exchange water bath adjusted to 30 ° C. for 15 minutes. Next, the film is taken out and spread out on the filter paper (5A), and the filter paper (5A) is overlaid on the film, and 15 cm × 15 cm × 0.4 cm (4.4 g / cm ² ) thereon. The SUS plate is placed for 5 seconds to remove water adhering to the film surface. This film is immediately put into a weighing bottle, the weight is measured, and this is defined as the film weight A at the time of swelling. The above operation is performed in an environment of 23 ° C. and 50% RH.
Next, the film is left in a drier at 105 ° C. for 16 hours to remove moisture in the film, and then the film is taken out, immediately put into a weighing bottle, weighed, and dried. Let it be weight B. And it calculates | requires from the following Formula based on the film weight A at the time of swelling, and the film weight B after drying.
Weight swelling degree (%) = A / B × 100

In the present invention, the syndiotacticity of the polyvinyl alcohol film is preferably 40 to 60%, particularly 45 to 55%, more preferably 50 to 54%. If the syndiotacticity is too small, However, if it is too large, the stretchability tends to be lowered and the film tends to break.

In order to control the syndiotacticity within the above range, for example, a method of blending a polyvinyl alcohol resin having a high syndiotacticity with a polyvinyl alcohol resin having a low syndiotacticity, or a polymerization temperature of vinyl acetate is set. There are a method of saponifying a changed one, a method of saponifying a polymer of vinyl ester such as vinyl pivalate, vinyl trifluoroacetate, vinyl trichloroacetate and the like.

Here, syndiotacticity is measured as follows. That is, it is a value by dyad display measured by a ¹³ C-NMR method for a polyvinyl alcohol film in a solvent (D ₂ O).

Furthermore, the obtained polyvinyl alcohol film has a light transmittance of 90% or more in the entire visible light range, and is very useful as an optical polyvinyl alcohol film.
Therefore, the polyvinyl alcohol film of the present invention is preferably used as a raw film for an optical film, particularly as a raw film for a polarizing film.

<Polarizing film and polarizing plate>
Hereinafter, the manufacturing method of the polarizing film of this invention using the polyvinyl alcohol-type film of this invention is demonstrated.

The polarizing film of the present invention is produced through processes such as normal dyeing, stretching, boric acid crosslinking and heat treatment. As a method for producing a polarizing film, a polyvinyl alcohol film is stretched and dyed by dipping in an iodine or dichroic dye solution, and then treated with a boron compound. After stretching and dyeing at the same time, a boron compound treatment is performed. There are a method, a method of dyeing with iodine or a dichroic dye and stretching, and then a method of treating with a boron compound, a method of dyeing and then stretching in a solution of a boron compound, etc., which can be appropriately selected and used. As described above, the polyvinyl alcohol film (unstretched film) may be stretched and dyed, and further subjected to boron compound treatment separately or simultaneously, but during at least one of the dyeing step and the boron compound treatment step. It is desirable in terms of productivity to perform uniaxial stretching.

Stretching is desirably 2.5 to 10 times, preferably 2.8 to 7 times in a uniaxial direction. At this time, a slight stretching (stretching to prevent shrinkage in the width direction or more) may be performed in a direction perpendicular to the stretching direction. The temperature during stretching is preferably selected from 20 to 170 ° C. Furthermore, the draw ratio may be finally set within the above range, and the drawing operation may be performed not only in one stage but also in any stage of the manufacturing process.

The film is dyed by bringing the film into contact with a liquid containing iodine or a dichroic dye. Usually, an iodine-potassium iodide aqueous solution is used. The concentration of iodine is 0.1 to 2 g / L, the concentration of potassium iodide is 10 to 50 g / L, and the weight ratio of potassium iodide / iodine is 20 to 100. Is appropriate. The dyeing time is practically about 30 to 500 seconds. The temperature of the treatment bath is preferably 5 to 50 ° C. The aqueous solution may contain a small amount of an organic solvent compatible with water in addition to the aqueous solvent. As the contact means, any means such as dipping, coating, spraying and the like can be applied.

The dyed film is then treated with a boron compound. As the boron compound, boric acid and borax are practical. The boron compound is used in the form of an aqueous solution or a water-organic solvent mixed solution at a concentration of about 0.3 to 2 mol / L, and it is practically desirable that potassium iodide coexist in the solution at 10 to 100 g / L. The treatment method is preferably an immersion method, but of course, an application method and a spray method can also be carried out. The temperature during the treatment is preferably about 20 to 60 ° C., and the treatment time is preferably about 3 to 20 minutes. If necessary, the stretching operation may be performed during the treatment.

The polarizing film of the present invention thus obtained can also be used as a polarizing plate by laminating and bonding an optically isotropic polymer film or sheet as a protective film on one or both sides thereof. Examples of the protective film used in the polarizing plate of the present invention include cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, polystyrene, polyethersulfone, polyarylene ester, poly-4-methylpentene, polyphenylene oxide, and cyclo-type. Or a film or sheet of norbornene-based polyolefin or the like can be mentioned.

Also, for the purpose of thinning the polarizing film, instead of the protective film, a curable resin such as urethane resin, acrylic resin, urea resin or the like can be applied and laminated on one side or both sides.

A polarizing film (including at least one surface laminated with a protective film or a curable resin) has a transparent pressure-sensitive adhesive layer formed on a surface of the polarizing film as required by a generally known method. In some cases, it may be put to practical use. Pressure sensitive adhesive layers include acrylic esters such as butyl acrylate, ethyl acrylate, methyl acrylate, 2-ethylhexyl acrylate, and α- such as acrylic acid, maleic acid, itaconic acid, methacrylic acid, and crotonic acid. Since the main component is a copolymer with a monoolefin carboxylic acid (including those added with vinyl monomers such as acrylonitrile, vinyl acetate, and styrene), the polarizing properties of the polarizing film are not impaired. Although it is particularly preferable, the present invention is not limited to this, and any pressure-sensitive adhesive having transparency can be used. For example, polyvinyl ether or rubber may be used.

The polarizing film of the present invention is an electronic desk calculator, electronic clock, word processor, personal computer, television, portable information terminal, liquid crystal display device such as automobiles and machinery instruments, sunglasses, eyeglasses, stereoscopic glasses, display element ( CRT, LCD, etc.) for reflection reduction layer, medical equipment, building materials, toys and the like.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited to a following example, unless the summary is exceeded.
In the examples, “parts” and “%” mean weight basis.
About each physical property, it carried out as follows.

(1) Average saponification degree (mol%) of polyvinyl alcohol resin
The analysis was carried out with the alkali consumption required for hydrolysis of the residual vinyl acetate units.

(2) 4% aqueous solution viscosity (mPa · s) of polyvinyl alcohol resin
The water temperature was adjusted to 20 ° C. and measured with a Heppler viscometer.

(3) Swelling ratio (X _TD / X _MD )
The film was cut into a 10 cm × 10 cm square so as to be parallel to the machine (MD) direction and the width (TD) direction, placed on a flat glass plate, and the dimensions in the MD direction and the TD direction were measured with calipers. Next, after immersing in an ion exchange water bath adjusted to 30 ° C. for 5 minutes, the film is taken out and immediately placed on a flat glass plate, and the dimensions in the MD direction and the TD direction are measured with calipers, Calculated by the following formula. The above operation was performed in an environment of 23 ° C. and 50% RH.
Swelling degree in the MD direction (X _MD ) (%)
= (Dimension in MD direction after immersion / Dimension in MD direction before immersion) × 100
Swelling degree in TD direction (X _TD ) (%)
= (Dimension in TD direction after immersion / Dimension in TD direction before immersion) × 100
Swelling degree ratio (X _TD / X _MD ) = swelling degree in TD direction (X _TD ) / swelling degree in MD direction (X _MD )

(4) Area swelling degree (Y) (%)
According to the method of (3) above, the degree of swelling in the MD direction (X _MD ) and the degree of swelling in the TD direction (X _TD ) were calculated and calculated from the following equations.
Area swelling degree (Y) (%)
= (Swelling degree in MD direction / 100) × (swelling degree in TD direction / 100) × 100

(5) Retardation value (nm)
Using a retardation measuring device (“KOBRA-WFD” manufactured by Oji Scientific Instruments Co., Ltd., measurement wavelength: 590 nm), the retardation value of the central portion in the width direction of the polyvinyl alcohol film was measured.

(6) Weight swelling degree (W) (%)
The film was cut into 10 cm × 10 cm and immersed in an ion exchange water bath adjusted to 30 ° C. for 15 minutes. Next, the film is taken out and spread out on the filter paper (5A), and the filter paper (5A) is overlaid on the film, and 15 cm × 15 cm × 0.4 cm (4.4 g / cm ² ) thereon. The SUS plate was placed for 5 seconds to remove water adhering to the film surface. This film was immediately put into a weighing bottle, the weight was measured, and this was defined as the film weight A at the time of swelling. The above operation was performed in an environment of 23 ° C. and 50% RH.
Next, the film is left in a drier at 105 ° C. for 16 hours to remove moisture in the film, and then the film is taken out, immediately put into a weighing bottle, weighed, and dried. Weight B. And it calculated | required from the following Formula based on the film weight A at the time of swelling, and the film weight B after drying.
Weight swelling degree (%) = A / B × 100

<Example 1>
In a 200 L tank, 4% aqueous solution viscosity of 64 mPa · s as polyvinyl alcohol resin, 42 kg of polyvinyl alcohol resin (A) having an average saponification degree of 99.8 mol%, 100 kg of water, and glycerin as plasticizer (B) 2 kg, 21 g of sodium dodecyl sulfonate as surfactant (C) and 8 g of polyoxyethylene dodecylamine were added, and the mixture was heated to 150 ° C. with pressure and heating while stirring to dissolve uniformly. A 26% aqueous solution of film forming material was obtained.

Next, an aqueous solution of film-forming material (liquid temperature 147 ° C.) was supplied to a twin screw extruder and defoamed. The defoamed aqueous solution of the film forming material was cast from a T-type slit die (straight manifold die) to a drum-type roll (heat roll: R1) to form a film. At this time, the clearance opening at both ends of the T-shaped slit die (up to 150 mm from the end) was increased by 5% with respect to the clearance opening at the center.

The conditions for the casting film formation are as follows.
Drum type roll (heat roll: R1)
Diameter: 3200 mm, width: 4.3 m, rotation speed: 8 m / min, surface temperature: 90 ° C., resin temperature at T-type slit die outlet: 90 ° C.
In addition, when the film moisture content at the time of peeling from a drum-type roll was measured, it was 17%.

Drying was performed while the front and back surfaces of the obtained film were alternately passed through a drying roll under the following conditions.
・ First to fifth drying rolls (heat rolls: R2 to R6)
Diameter: 320 mm, width: 4.3 m, rotation speed: 8 m / min, surface temperature: 94 ° C.
・ 6th to 10th drying roll (heat roll: R7 to R11)
Diameter: 320 mm, width: 4.3 m, rotation speed: 8 m / min, surface temperature: 75 ° C.
In addition, when the film was sampled after drying and the film moisture content was measured, it was 12%.

After drying, this film is continuously heat treated at 90 ° C. with a floating dryer (length: 18.5 m) that blows warm air from both sides, width 4 m, length 4000 m, film center thickness 60 μm, film A polyvinyl alcohol film having an end thickness of 63 μm was obtained.
Table 1 shows the physical properties of the obtained polyvinyl alcohol film.

Using the polyvinyl alcohol film of the present invention obtained above, a polarizing film was obtained in the following manner, and the following evaluation was performed. The evaluation results are shown in Table 1.

The obtained polyvinyl alcohol film was stretched 1.5 times while being immersed in a water bath at a water temperature of 30 ° C. Next, it is stretched 1.3 times while being immersed for 240 seconds in a dyeing tank (30 ° C.) consisting of 0.2 g / L of iodine and 15 g / L of potassium iodide, and further 50 g / L of boric acid and 30 g of potassium iodide. / L was immersed in a boric acid treatment tank (50 ° C.) and boric acid treatment was performed for 5 minutes while simultaneously uniaxially stretching 3.08 times. Thereafter, it was dried to obtain a polarizing film having a total draw ratio of 6 times.

<< Evaluation of uneven dyeing >>
Using a polyvinyl alcohol-based aqueous solution as an adhesive on both surfaces of the polarizing film obtained above, a 80 μm thick triacetyl cellulose film was bonded and dried at 50 ° C. to obtain a polarizing plate. About this polarizing plate, the sample of 20 cm x 20 cm was cut out from the width direction, orthogonal transmittance was measured at 2 mm pitch in the width (TD) direction, the difference of the maximum value and the minimum value was calculated | required, and the dyeing | staining unevenness was evaluated.
The orthogonal transmittance was measured using a retardation measuring apparatus “RETS-1100A” manufactured by Otsuka Electronics Co., Ltd.

<< Evaluation of stretchability >>
Using the polyvinyl alcohol film obtained above, in the production of the same polarizing film as described above, the stretch ratio in the boric acid treatment layer is further increased, the film is stretched until it breaks, and the limit stretch ratio is measured. And the stretchability was evaluated.

<Examples 2 and 3, Comparative Examples 1 and 2>
In Example 1, it carried out similarly except having changed the film-forming conditions as shown in Table 1, and obtained the polyvinyl alcohol-type film, and also obtained the polarizing film similarly to Example 1. FIG.
About the obtained polyvinyl alcohol-type film and polarizing film, evaluation similar to Example 1 was performed. The evaluation results are shown in Table 1.

From the results of the above Examples and Comparative Examples, for the Example products, since the predetermined swelling degree ratio (X _TD / X _MD ) is within the predetermined range, there is no unevenness in the orthogonal transmittance in the polarizing plate, It turns out that it is a polyvinyl alcohol-type film which does not arise, and also it turns out that a limit draw ratio is also very excellent with 7 times or more. On the other hand, in the comparative product, a film satisfying both dyeing unevenness suppression and stretchability was not obtained.

In the above embodiments, specific forms in the present invention have been described. However, the above embodiments are merely examples and are not construed as limiting. Further, all modifications belonging to the equivalent scope of the claims are within the scope of the present invention.

The polyvinyl alcohol film of the present invention is a polyvinyl alcohol film formed by forming a film forming material containing a polyvinyl alcohol resin (A), and the film is immersed in water at 30 ° C. for 5 minutes to swell. width (TD) direction of the degree of swelling when the (X _TD) and machine direction (MD) of the swelling ratio (X _TD / X _MD) is polyvinyl alcohol is from 1.000 to 1.020 in (X _MD) Since it is a film, it is excellent in stretchability and has an effect that the film does not break even when stretched at a high stretch ratio to improve productivity. Furthermore, it is excellent in the effect of suppressing uneven dyeing, such as electronic desk calculators, electronic watches, word processors, personal computers, televisions, personal digital assistants, liquid crystal display devices such as automobile and machinery instruments, sunglasses, and eye protection glasses. , Stereoscopic glasses, reflection reduction layers for display elements (CRT, LCD, etc.), original films for polarizing films used for medical equipment, building materials, toys, etc. It is very useful as an anti-film and an original film of a retardation film used in a liquid crystal display device.

Claims

It is a polyvinyl alcohol film formed by forming a film forming material containing the polyvinyl alcohol resin (A), and the width (TD) direction when the film is immersed in water at 30 ° C. for 5 minutes to swell A polyvinyl alcohol film characterized in that the ratio (X TD / X MD ) of the degree of swelling (X TD ) to the degree of swelling (X MD ) in the machine (MD) direction is 1.000 to 1.020.
2. The polyvinyl alcohol film according to claim 1, wherein the area swelling degree (Y) when the film is immersed in water at 30 ° C. for 5 minutes to swell is 130 to 170%.
3. The polyvinyl alcohol film according to claim 1, wherein the retardation value is 10 to 40 nm.
The polyvinyl alcohol film according to any one of claims 1 to 3, wherein the degree of weight swelling (W) at 30 ° C is 190 to 230%.
The polyvinyl alcohol film according to any one of claims 1 to 4, wherein the polyvinyl alcohol resin (A) has an average degree of saponification of 90 mol% or more.
The polyvinyl alcohol film according to any one of claims 1 to 5, wherein the polyvinyl alcohol film is used as an original film of a polarizing film.
A step [I] of casting an aqueous solution of a film-forming material containing the polyvinyl alcohol resin (A) onto a first hot roll, and a step of peeling from the first hot roll in a state where the film moisture content is 10 to 25% [II] The method according to any one of claims 1 to 6, further comprising the step [III] of alternately passing the front and back of the film through a second heat roll group having a surface temperature of 80 to 98 ° C. at least 5 or more. A method for producing a polyvinyl alcohol film according to claim 1.
When casting an aqueous solution of a film-forming material containing the polyvinyl alcohol resin (A), the film thickness (T1) in a region within 5% of the total width from the end with respect to the width direction of the film is the film. The method for producing a polyvinyl alcohol film according to any one of claims 1 to 6, wherein the film is formed so as to be 2 to 8% thicker than the film thickness (T2) at the center of the width.
When casting an aqueous solution of a film-forming material containing the polyvinyl alcohol resin (A), the film thickness (T1) in a region within 5% of the total width from the end with respect to the width direction of the film is the film. 8. The method for producing a polyvinyl alcohol film according to claim 7, wherein the film is formed so as to be 2 to 8% thicker with respect to the film thickness (T2) at the center of the width.
A polarizing film comprising the polyvinyl alcohol film according to any one of claims 1 to 6.
A polarizing plate comprising a protective film provided on at least one side of the polarizing film according to claim 10.