KR20180022648A - Polyvinyl alcohol film, method for producing polyvinyl alcohol film, and polarizer film - Google Patents

Abstract

A polyvinyl alcohol film excellent in dyeability and stretchability and capable of obtaining a polarizing film having a high degree of polarization even when the film is wide and long in thickness and having no polarization unevenness can be obtained. The film has a thickness D (nm) (N / mm < 2 >) when stretched 6 times in the flow direction (MD direction) of the film in water, the tensile strength when stretched 6 times in the film flow direction B (N / mm < 2 >), the polyvinyl alcohol film satisfies the following expressions (1) and (2).
0.6? D? A? 1.2
(2) 0.2? D x B? 0.4

Description

Polyvinyl alcohol film, method for producing polyvinyl alcohol film, and polarizer film

The present invention relates to a polyvinyl alcohol-based film. More particularly, the present invention relates to a polyvinyl alcohol film for producing a polarizing film excellent in dyeability and stretchability and excellent in polarization performance as a raw material of a polarizing film, a method for producing the same, and a method for producing the same using the polyvinyl alcohol film To a polarizing film obtained.

The polarizing film is produced by dyeing and stretching a polyvinyl alcohol film as a disc using a dye such as iodine. For example, the polyvinyl alcohol film is swollen with warm water, stained with iodine, stretched to arrange iodine molecules, crosslinked with a crosslinking agent such as boric acid to maintain the stretched state, washed and dried do. Each of the processes of water swelling, dyeing, stretching, and boric acid crosslinking may be changed in sequence or a plurality of steps may be carried out at the same time. What is common is that a polyvinyl alcohol film is continuously wound from a roll and is carried out while being horizontally conveyed with a suitable tension in the flow direction by using a winding machine or a nip roll.

Such a polarizing film is used as a basic component part of a liquid crystal display device such as a portable information terminal or a television. In recent years, a polarizing film having a high degree of polarization with a high light transmittance has been demanded due to high luminance or high definition of liquid crystal displays. Further, as a result of a large screen or a thin display of a liquid crystal TV or the like, a polarizing film with a wider width and a wider thickness than conventional products is required.

In order to comply with the above-mentioned demand, a polyvinyl alcohol-based film excellent in dyeability and stretchability, and having a wide and long thin shape is required. When the dyeability of the polyvinyl alcohol-based film is low, a sufficient degree of polarization can not be obtained and polarization unevenness tends to occur easily. When the stretching property of the polyvinyl alcohol film is low, the film is broken in the manufacturing process of the polarizing film, so that a polarizing film having a wide and long thin shape can not be produced. As a matter of course, continuous production is stopped by breaking, and the productivity of the polarizing film is significantly lowered. In addition, when the stretching property is low, the dye tends not to be oriented sufficiently, so that the degree of polarization tends to decrease or polarized light tends to easily occur. Such improvement in dyeability and stretchability is more difficult as the polyvinyl alcohol-based film becomes wide and thin. In addition, in the coating type polarizing plate for so-called thinning, the above-described steps such as dyeing and drawing are essential, and although there is a support film, improvement in dyeability and stretchability of the polyvinyl alcohol-based film after application is required.

In order to improve the dyeability of a polyvinyl alcohol-based film, a method of controlling the bath temperature in the swelling process has been proposed (see, for example, Patent Documents 1 and 2). In addition, a polarizing plate using a polyvinyl alcohol-based film having a stretching property in a specific range has been proposed (see, for example, Patent Document 3).

Patent Document 1 JP 2006-065309 A Patent Document 2 JP 2014-197050 A Patent Document 3 JP 2002-236212 A

However, in the techniques described in the above Patent Documents 1 and 2, even if the swelling degree can be controlled by the bath temperature, if the tension applied to the polyvinyl alcohol film in the bathtub is not appropriate, a uniform swollen state can not be obtained, There is a problem that the dye is not adsorbed uniformly.

The technique described in the Patent Document 3 specifies the stress (tension) when the polyvinyl alcohol film is stretched 4 to 6 times in water, but in the actual production of the polarizing film, the water temperature in each step is different It was insufficient to obtain the proper tension throughout the entire process. The water temperature is often carried out at a relatively low temperature of about 30 DEG C in swelling or dyeing processes, or at a relatively high temperature of about 50 DEG C in processes such as stretching or boric acid crosslinking.

Therefore, the present invention provides a polyvinyl alcohol-based film excellent in dyeability and stretchability under such a background, which has a high degree of polarization even when the film is wide and long, and can obtain a polarizing film having no polarization unevenness do.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention As a result of intensive studies in view of such circumstances, the inventors of the present invention have found that polyvinyl alcohol films obtained by ejecting and softening an aqueous solution of polyvinyl alcohol resin into a cast mold, , The polyvinyl alcohol film produced by drawing attention to the underwater tension at 50 DEG C, particularly at a high temperature, has a high degree of polarization even when it is wide and long and thin , A polarizing film without polarization unevenness can be produced.

That is, the gist of the present invention is that the tensile strength A (N / mm 2) when stretched 6 times in the film flow direction (MD direction) in water at 30 ° C in thickness D (nm) Satisfies the following formulas (1) and (2), where B (N / mm < 2 >) is the tension when stretched at a stretch ratio of 6 in the flow direction (MD direction) of the polyvinyl alcohol film.

0.6? D? A? 1.2

(2) 0.2? D x B? 0.4

The present invention also provides a method for producing the polyvinyl alcohol film and a polarizing film obtained using the polyvinyl alcohol film.

The polyvinyl alcohol film of the present invention is excellent in dyeability and stretchability, has a high degree of polarization even when the film is made wide and long, can obtain a polarizing film free from polarization unevenness, and can produce a polarizing film with high productivity You can do it.

Hereinafter, the present invention will be described in detail.

The polyvinyl alcohol film of the present invention has a thickness D (nm) and a tensile strength A (N / mm 2) when the film is stretched 6 times in the film flow direction (MD direction) in water at 30 캜, (1) and (2), where B (N / mm < 2 >) is the tension when the film is stretched 6 times in the film flow direction (MD direction)

0.6? D? A? 1.2

(2) 0.2? D x B? 0.4

Preferably, the film is a polyvinyl alcohol-based film satisfying the following formulas (1 ') and (2'),

(1 ') 0.65? D x A? 1.15

(2 ') 0.25? D x B? 0.39

Particularly preferred are polyvinyl alcohol-based films satisfying the following formulas (1 '') and (2 '').

(1 ") 0.7 D x A < = 1.1

(2 ") 0.27? D x B? 0.38

With respect to the above formulas (1) to (1 ''), if the value of D x A is too low, the film is deformed in the swelling step and the dyeing step, which is not preferable. not.

With respect to the above formulas (2) to (2 ''), if the value of D x B is too low, the degree of polarization when the film is made into a polarizing film is undesirably decreased. It is not preferable because it is easy to do.

With respect to the formulas (1) to (1 '') and the formulas (2) to (2 ''), the value of the thickness D of the polyvinyl alcohol film is preferably 0.04 nm or less from the viewpoint of thinning of the polarizing film, Particularly preferably 0.03 nm or less from the viewpoint of further thinning of the polarizing film, and more preferably 0.01 to 0.03 nm from the viewpoint of avoiding breakage of the polarizing film.

The polyvinyl alcohol film of the present invention preferably satisfies the following formula (3), particularly preferably satisfies the following formula (3 '), and more preferably satisfies the following formula (3' ').

(3) 0.2? B / A? 0.5

(3 ') 0.25? B / A? 0.4

(3 ") 0.3? B / A? 0.35

With respect to the above formulas (3) to (3 ''), if the value of B / A is too low, the degree of polarization when the film is made into a polarizing film tends to decrease. If it is too high, It tends to be easy.

The polyvinyl alcohol film of the present invention preferably has a tension (A) of 15 to 40 N / mm 2 when stretched 6 times in the film flow direction (MD direction) in water at 30 ° C, Is 18 to 35 N / mm 2, more preferably 20 to 30 N / mm 2.

If the value of the tensile force A is too low, the film tends to be deformed in the swelling process or the dyeing process. If the value is too high, sufficient dyeing tends to be difficult in the dyeing process.

The polyvinyl alcohol film of the present invention preferably has a tensile strength (B) of 3 to 15 N / mm 2 when stretched 6 times in the film flow direction (MD direction) in water at 50 ° C, Particularly preferably 4 to 12 N / mm 2, and more preferably 5 to 10 N / mm 2.

When the value of the tension (B) is too low, the polarization degree of the polarizing film tends to decrease. When the value of the tension (B) is too high, the polarizing film tends to be broken at the time of producing the polarizing film.

In the polyvinyl alcohol film of the present invention, when the storage elastic modulus in water at 30 占 폚 is E1 (Pa) and the storage elastic modulus in water at 50 占 폚 is E2 (Pa), the value of E2 / More preferably 0.25 to 0.30, and particularly preferably 0.26 to 0.29.

If the value of E2 / E1 is too low, the degree of polarization of the obtained polarizing film tends to decrease. If the value of E2 / E1 is too high, the polarizing film tends to be broken at the time of producing the polarizing film.

The polyvinyl alcohol film of the invention preferably has a storage elastic modulus E1 of 9 to 12 MPa in water at 30 DEG C from the viewpoint of transportability. The storage elastic modulus E2 in water at 50 占 폚 is preferably 2 to 4 MPa from the viewpoint of transportability.

Hereinafter, a method for producing a polyvinyl alcohol-based film of the present invention, that is, a method for producing a polyvinyl alcohol-based film by continuously forming an aqueous solution of a polyvinyl alcohol-based resin into a cast mold by discharging, do.

As the polyvinyl alcohol-based resin used in the present invention, a resin produced by saponifying polyvinyl alcohol-based resin that is unmodified, that is, 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 (usually 10 mol% or less, preferably 5 mol% or less) of a copolymerizable component of vinyl acetate can be used. Examples of the component copolymerizable with vinyl acetate include unsaturated carboxylic acids (including salts, esters, amides, nitriles, etc.), olefins having 2 to 30 carbon atoms (e.g., ethylene, propylene, n -Butene, isobutene, etc.), vinyl ethers, and unsaturated sulfonate salts. It is also possible to use a modified polyvinyl alcohol-based resin obtained by chemically modifying a hydroxyl group after saponification.

As the polyvinyl alcohol-based resin, a polyvinyl alcohol-based resin having a 1,2-diol structure in the side chain may also be used. Such a polyvinyl alcohol-based resin having a 1,2-diol structure in the side chain can be obtained by, for example, (i) saponifying a copolymer of vinyl acetate and 3,4-diacetoxy-1-butene, (Ii) a method of saponifying and decarboxylating a copolymer of vinyl acetate and vinylethylene carbonate, (iii) saponifying and copolymerizing a copolymer of vinyl acetate and 2,2-dialkyl-4-vinyl-1,3-dioxolane, (Iv) a method of saponifying a copolymer of vinyl acetate and glycerin monoaryl ether, and the like.

The weight average molecular weight of the polyvinyl alcohol-based resin is preferably 100,000 to 300,000, particularly preferably 110,000 to 280,000, and more preferably 120,000 to 260,000. If the weight-average molecular weight is too small, it tends to be difficult to obtain sufficient optical performance when the polyvinyl alcohol-based resin is used as an optical film. If it is too large, it tends to be difficult to stretch the polyvinyl alcohol- have. The weight average molecular weight of the polyvinyl alcohol resin is a weight average molecular weight measured by the GPC-MALS method.

The average saponification degree of the polyvinyl alcohol-based resin used in the present invention is preferably 98 mol% or more, particularly preferably 99 mol% or more, more preferably 99.5 mol% or more, particularly preferably 99.8 mol% or more to be. When the average degree of saponification is too small, sufficient optical performance tends not to be obtained when the polyvinyl alcohol film is made into a polarizing film.

Here, the average degree of saponification in the present invention is measured in accordance with JIS K 6726.

As the polyvinyl alcohol-based resin to be used in the present invention, two or more kinds of modified species, modified amount, weight average molecular weight, average saponification degree and the like may be used in combination.

The polyvinyl alcohol film of the present invention is prepared by preparing an aqueous solution of polyvinyl alcohol resin (a raw film forming solution) using the polyvinyl alcohol-based resin, discharging the aqueous solution into a cast mold and pouring it, casting it by a casting method, , For example, by the following process.

Step (A) A step of preparing a polyvinyl alcohol-based resin aqueous solution.

Step (B) A step of forming a polyvinyl alcohol-based resin aqueous solution by casting into a cast mold.

Step (C) A step of heating and drying the formed film by bringing the film into contact with a plurality of metal heating rolls.

Process (D) Process of heat-treating the obtained film using hot air.

Examples of the cast mold include a cast drum (drum type roll) and an endless belt. However, it is preferable to use cast drums from the viewpoint of greatly increasing the length, length, and uniformity of the film thickness.

Hereinafter, the cast type casting drum will be described as an example.

First, the step (A) will be described.

In the step (A), it is preferable that the above-mentioned polyvinyl alcohol-based resin is washed with water and dehydrated using a centrifugal separator or the like to obtain a polyvinyl alcohol-based resin wet cake having a water content of 50% by weight or less . If the moisture content is too large, it tends to be difficult to obtain a desired aqueous solution concentration.

The polyvinyl alcohol-based resin wet cake is dissolved in hot water or hot water to prepare a polyvinyl alcohol-based resin aqueous solution.

The method of preparing the polyvinyl alcohol-based resin aqueous solution is not particularly limited, and for example, it may be prepared by using a heated multi-screw extruder, or by adding the above-mentioned polyvinyl alcohol An alcohol-based resin wet cake may be put in, and water vapor may be blown into the can to dissolve and prepare an aqueous solution of a desired concentration.

In the present invention, the latter is preferable from the viewpoint of the improvement of the degree of polarization, and it is more preferable to control the solution by pressure melting at 120 DEG C or higher.

The polyvinyl alcohol resin aqueous solution preferably contains at least one surfactant selected from plasticizers, nonionic, anionic and cationic surfactants in addition to the polyvinyl alcohol-based resin, from the viewpoint of film formability, if necessary.

Examples of the plasticizer used in the present invention include glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol, trimethylol propane and the like. Of these, glycerin is preferable from the viewpoint of low cost.

When glycerin is used, the blending amount is preferably 5 to 12% by weight, particularly preferably 6 to 11.5% by weight, and more preferably 7 to 11% by weight, based on the polyvinyl alcohol-based resin.

When the blending amount is too small, the underwater tension of the polyvinyl alcohol-based film tends to increase, while when it is too much, the underwater tension of the polyvinyl alcohol-based film tends to be insufficient.

As the surfactant to be used in the present invention, an anionic surfactant is preferred from the viewpoint of compatibility with a polyvinyl alcohol-based resin aqueous solution.

The resin concentration of the polyvinyl alcohol-based resin solution thus obtained is preferably 15 to 60% by weight, particularly preferably 17 to 55% by weight, and more preferably 20 to 50% by weight. If the concentration of the resin is too low, the drying load tends to increase and the production ability tends to decrease. When the resin concentration is too high, the viscosity tends to become too high, and uniform dissolution tends to be impossible.

In this way, a polyvinyl alcohol-based resin aqueous solution which is the undiluted solution can be obtained. Next, the step (B) will be described.

The polyvinyl alcohol-based resin aqueous solution is defoamed. Examples of the defoaming method include defoaming by a multi-screw extruder having a static deformation or a vent. As a multi-screw extruder having a vent, a twin-screw extruder having a vent is usually used.

After the degassing treatment, the aqueous solution of the polyvinyl alcohol-based resin is introduced into the T-shaped slit die by a predetermined amount and discharged onto the rotating casting drum, and is formed by casting.

The resin temperature of the T-shaped slit die outlet is preferably 80 to 100 占 폚, particularly preferably 85 to 99 占 폚. If the resin temperature is too low, flow defects tend to occur. If too high, the resin tends to foam.

The viscosity of such a polyvinyl alcohol-based resin aqueous solution is preferably from 50 to 200 Pa · s, more preferably from 70 to 150 Pa · s, at the time of use. When the viscosity of such an aqueous solution is too low, flow defects tend to occur. When the viscosity is too high, the flexibility tends to become difficult.

The discharge speed of the polyvinyl alcohol-based resin solution discharged from the T-shaped slit die onto the cast drum is preferably 0.2 to 5 m / min, particularly preferably 0.4 to 4 m / min, and more preferably 0.6 to 3 m / min. If the discharge speed is too low, the productivity tends to decrease. If the discharge speed is too high, the flexibility tends to become difficult.

In the case of casting, it is preferable to use cast drums from the viewpoint of considerable increase in size, lengthening, uniformity of film thickness, and the like. As the cast drum, generally, a surface of stainless steel (SUS) containing iron as a main component is subjected to metal plating for prevention of scratches. Examples of the metal plating include chromium plating, nickel plating, and zinc plating, and these are used alone or in a laminated structure of two or more layers. Among these, from the viewpoint of durability of the drum surface, it is preferable that the outermost surface is chromium-plated.

Hereinafter, a case of using a cast drum will be described.

The width of the cast drum is preferably 4 m or more, particularly preferably 5 m or more. If the width of the cast drum is too small, it tends to be difficult to obtain a large amount of film.

The diameter of such a cast drum is preferably 2 to 5 m, particularly preferably 2.4 to 4.5 m, and more preferably 2.8 to 4 m.

If the diameter is too small, the drying length tends to be insufficient, and the speed tends to be difficult to come out. When the diameter is too large, the transportability tends to decrease.

The rotation speed of the casting drum is preferably 3 to 50 m / min, particularly preferably 4 to 40 m / min, and more preferably 5 to 35 m / min. If the rotation speed is too low, productivity tends to decrease, and if it is too fast, drying tends to be insufficient.

The surface temperature of such a cast drum is preferably 40 to 99 占 폚, particularly preferably 60 to 95 占 폚. If the surface temperature is too low, drying tends to be poor, and if it is too high, it tends to foam.

Thus, the film is formed.

Next, the step (C) will be described. Step (C) is a step of heating and drying the formed film in contact with a plurality of metal heating rolls.

Drying of the polyvinyl alcohol-based film formed by the cast drum is carried out by alternately bringing the surface and the back surface of the film into contact with a plurality of metal heating rolls. The surface temperature of the metal heating roll is not particularly limited, but is preferably 60 to 150 캜, more preferably 70 to 140 캜. If the surface temperature is too low, drying tends to be defective. If it is too high, too much drying tends to result in appearance defects such as ripples.

In the present invention, it is preferable that the temperatures of the plurality of metal heating rolls are in the order of the following conditions (a) to (d) from the viewpoint of controlling the underwater tension of the polyvinyl alcohol-based film.

Condition (a) ≥80 ℃

Condition (b) < 80 DEG C

Condition (c) ≥100 ° C

Condition (d) < 100 ° C

In addition, the number of metal heating rolls is usually 10 to 30, and is suitably set to satisfy the above temperature condition.

After drying by the metal heating roll, the obtained film is heat-treated in the step (D) using hot air. Next, the step (D) will be described.

The heat treatment temperature is preferably 110 to 140 占 폚, particularly preferably 115 to 135 占 폚, and more preferably 120 to 130 占 폚. When the heat treatment temperature is too low, the underwater tension of the polyvinyl alcohol-based film tends to be insufficient. When the heat treatment temperature is too high, the underwater tension of the polyvinyl alcohol-based film tends to increase.

As such a heat treatment method, a method of performing with a floating dryer from the viewpoint of excellent temperature control is preferable.

The heat-treated film is slit on both ends and wound on a roll to form a roll-shaped polyvinyl alcohol-based film.

The width of the polyvinyl alcohol film is preferably 4 m or more from the viewpoint of widening of the polarizing film, particularly preferably 4.5 m or more from the viewpoint of widening, and more preferably 4.5 to 6 m from the viewpoint of avoiding breakage.

The length of the polyvinyl alcohol film is preferably 4 km or more from the viewpoint of enlargement of the polarizing film, particularly preferably 4.5 km or more from the viewpoint of a larger area, and more preferably 4.5 to 50 km from the viewpoint of the transport weight.

From the viewpoint of winding property, the polyvinyl alcohol film preferably has a tensile strength of 40 to 80 N / mm < 2 > when stretched 4 times in the film flow direction (MD direction) in an atmosphere of 20 DEG C and 65% Is from 43 to 75 N / mm < 2 > from the standpoint of stability at the time of storage, and more preferably from 46 to 70 N / mm < 2 >

The polyvinyl alcohol film preferably has an in-plane phase difference of 50 nm or less, particularly preferably 40 nm or less, and more preferably 30 nm or less, from the viewpoint of uniformity of water tension.

Thus, the polyvinyl alcohol film of the present invention can be obtained.

The polyvinyl alcohol-based film of the present invention has excellent optical performance and is suitably used as a polyvinyl alcohol-based film for optical use, and is particularly preferably used as a disk for a polarizing film.

Hereinafter, a method for producing a polarizing film obtained by using the polyvinyl alcohol film of the present invention will be described.

The polarizing film of the present invention is produced by winding the polyvinyl alcohol film from a roll and transferring the film in the horizontal direction, followed by swelling, dyeing, boric acid crosslinking, stretching, washing, drying and the like.

The swelling process is carried out before the dyeing process.

In addition to being able to clean the surface of the polyvinyl alcohol film by the swelling process, the polyvinyl alcohol film is also swollen to prevent uneven dyeing. In the swelling process, water is usually used as the treatment liquid. If the main component is water, the treatment liquid may contain a small amount of an additive such as an iodide compound, a surfactant, or an alcohol. The temperature of the swelling bath is usually about 10 to 45 DEG C, and the immersion time in the swelling bath is usually about 0.1 to 10 minutes. If necessary, the stretching operation may be carried out during the treatment.

The dyeing process is carried out by bringing the film into contact with a liquid containing iodine or a dichroic dye. Usually, an aqueous solution of iodine-potassium iodide is used, the concentration of iodine is 0.1 to 2 g / L, and the concentration of potassium iodide is preferably 1 to 100 g / L. Dyeing time is practically 30 to 500 seconds. The temperature of the treatment bath is preferably 5 to 50 占 폚. The aqueous solution may contain a small amount of an organic solvent compatible with water in addition to the water solvent. If necessary, the stretching operation may be performed during the treatment.

The boric acid crosslinking process is carried out using a boron compound such as boric acid or borax. The boron compound is used at a concentration of about 10 to 100 g / L in the form of an aqueous solution or a water-organic solvent mixture, and it is preferable that potassium iodide coexists in the liquid from the viewpoint of stabilization of the polarization performance. The temperature for the treatment is preferably about 30 to 70 DEG C, and the treatment time is preferably about 0.1 to 20 minutes, and if necessary, the stretching operation may be carried out during the treatment.

The stretching process is preferably stretched by 3 to 10 times, preferably by 3.5 to 6 times in the uniaxial direction. At this time, a slight stretching (a degree of preventing the stretching in the width direction or further stretching) may also be performed in the direction perpendicular to the stretching direction. The temperature at the time of stretching is preferably 30 to 170 캜. The stretching magnification may be finally set in the above range, and the stretching operation may be performed not only at the first stage but also at any stage of the manufacturing process.

The cleaning step is carried out, for example, by immersing a polyvinyl alcohol-based film in an aqueous iodide solution such as water or potassium iodide, thereby removing precipitates generated on the surface of the film. When potassium iodide aqueous solution is used, the concentration of potassium iodide is preferably about 1 to 80 g / L. The temperature at the time of the washing treatment is usually 5 to 50 占 폚, preferably 10 to 45 占 폚. The treatment time is usually from 1 to 300 seconds, preferably from 10 to 240 seconds. The washing with water and the washing with aqueous potassium iodide solution may be carried out in appropriate combination.

The drying process may be carried out in air at 40 to 80 ° C for 1 to 10 minutes.

The degree of polarization of the polarizing film is preferably 99.5% or more, and more preferably 99.8% or more. When the degree of polarization is too low, the contrast in the liquid crystal display tends to be insufficient. In addition, the degree of polarization is generally determined such that the light transmittance (H ₁₁ ) measured with respect to the wavelength lambda in a state in which two polarizing films are superimposed so that their alignment directions are the same, and the two polarizing films are aligned so that their alignment directions are orthogonal to each other Is calculated from the light transmittance (H ₁ ) measured for the wavelength? In the superimposed state according to the following formula.

_{[(H 11 -H 1) / (} H 11 + H 1) ] ^{/ 2}

The single transmittance of the polarizing film of the present invention is preferably 42% or more. If such a simple mass transmittance is too low, the brightness of the liquid crystal display tends to be unable to be achieved. The mass transmittance is a value obtained by measuring the light transmittance of the single polarizing film by using a spectrophotometer.

Thus, the polarizing film of the present invention can be obtained, but the polarizing film of the present invention is very suitable for producing a polarizing plate having less unevenness.

Hereinafter, a method for producing a polarizing plate of the present invention will be described.

The polarizing film of the present invention is a polarizing plate formed by bonding an optically isotropic resin film as a protective film to one or both surfaces thereof with an adhesive. As the protective film, for example, cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, cycloolefin polymer, cycloolefin copolymer, polystyrene, polyether sulfone, polyarylene ester, And films or sheets such as polyethylene, polypropylene, polyethylene, polypropylene, polyethylene, polypropylene, polyethylene, polypropylene,

For example, a liquid adhesive composition may be uniformly applied to a polarizing film, a protective film, or both, followed by pressing and bonding the two, and then heating or irradiating an active energy ray .

For the purpose of thinning the polarizing film, a curing resin such as a urethane resin, an acrylic resin, or a urea resin may be coated on one or both sides of the protective film and cured to form a polarizing plate.

The polarizing film made of the polyvinyl alcohol film obtained by the production method of the present invention is excellent in the in-plane uniformity of the polarizing performance and can be used for a portable information terminal, a PC, a television, a projector, a signage, an electronic tabletop calculator, (CRT, LCD, organic EL, electronic paper, etc.), liquid crystal display devices such as a game machine, a video camera, a photo album, a thermometer, audio, An antireflection layer for light, an optical communication device, a medical instrument, a building material, a toy, and the like.

[Example]

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded. In the examples, " part " and "% "

<Measurement Conditions>

(1) Stretching tension in water (N / mm 2)

A test piece having a length (MD direction) of 50 nm × a width (TD direction) of 35 nm and a thickness of D (nm) was cut from the obtained polyvinyl alcohol film, and both ends in the longitudinal direction were stretched to have a width of 35 nm And then the stress (N) was measured with a spring balance when stretched at a speed of 18 nm / min in a MD direction in water at 30 캜 and 50 캜 six times. The value obtained by removing such a stress by the cross-sectional area of the film was defined as a stretching tension (N / mm &lt; 2 &gt;).

(2) Stretching tension in air (N / mm 2)

The obtained polyvinyl alcohol film was conditioned in the air at 20 占 폚 and 65% RH in the air for one day. Thereafter, test pieces having a length (MD direction) of 120 nm and a width (TD direction) of 15 nm and a thickness of D (nm) Both ends in the longitudinal direction were sandwiched by a chuck having a width of 15 nm using a "precision universal testing machine, Autograph (AG-IS)" manufactured by Sakusho Co., And the stress (N) at the time of 4-fold stretching at a speed of 1000 nm / min in the MD direction was measured. The value obtained by removing such a stress by the cross-sectional area of the film was taken as the stretching tension (N / mm &lt; 2 &gt;) in the atmosphere.

(3) In-plane phase difference (nm)

A specimen of 20 cm in length (MD direction) × 20 cm in width (TD direction) was cut out from the polyvinyl alcohol film thus obtained, and the film was cut in plane using a two-dimensional birefringence evaluation system (manufactured by Photonics Latis Co., The phase difference (nm) was measured.

(4) Polarization degree (%), unit transmittance (%)

A sample having a length of 4 cm and a width of 4 cm was cut out from the obtained polarizing film and the degree of polarization (%) and the unit transmittance (%) were measured using an automatic polarizing film measuring apparatus (VAP7070, manufactured by Nippon Bunko).

(5) Polarization stain

A test piece having a length of 30 cm and a width of 30 cm was cut from the obtained polarizing film and sandwiched between two polarizing plates in a cross-Nicol state (with a single light transmittance of 43.5% and a polarization degree of 99.9%) at an angle of 45 °. Optical luminescence was observed in a transmission mode using a light box of Lux (Ix) and evaluated according to the following criteria.

(Evaluation standard)

○ · · · No staining

△ · · · There is faint smudge

× · · With dirt

&Lt; Example 1 >

(Production of polyvinyl alcohol film)

1,000 kg of a polyvinyl alcohol resin having a weight average molecular weight of 142,000, a saponification degree of 99.8 mol%, 2,500 kg of water, 105 kg of glycerin as a plasticizer and 0.25 kg of sodium dodecylsulfonate as a surfactant were placed in a 5,000 L dissolution can, Lt; 0 &gt; C and subjected to pressure melting to obtain a polyvinyl alcohol-based resin aqueous solution having a resin concentration of 25%.

Subsequently, the polyvinyl alcohol-based resin aqueous solution was fed to a twin-screw extruder having a vent and defoamed. Thereafter, the temperature of the aqueous solution was adjusted to 95 占 폚, and a cast drum rotating at 20 m / min at a T- . The obtained film was peeled off from the cast drum, and the surface and back of the film were alternately brought into contact with a total of twenty metal heating rolls while drying. These metal heating rolls are arranged in the order of 90 ° C, 70 ° C, 110 ° C and 85 ° C. Then, hot air of 140 DEG C was blown from both sides of the film and heat-treated. Finally, the film was slit and wound to obtain a roll-shaped polyvinyl alcohol film (0.03 nm after film, 5 m long, and 5 km long). The properties of the obtained polyvinyl alcohol-based film are shown in Table 1.

(Production of polarizing film)

The resulting polyvinyl alcohol film was drawn out from the roll and stretched 1.7 times in the MD direction while being transported in the horizontal direction while being immersed in a water bath having a water temperature of 30 DEG C and swelled. Subsequently, the resultant was immersed in an aqueous solution of 30 g / l of iodine and 0.5 g / l of potassium iodide and stretched 1.6 times in the MD direction while being dyed. Subsequently, an aqueous solution of boric acid of 40 g / L and potassium iodide of 30 g / 50 占 폚) and uniaxially stretched 2.1 times in the MD direction while crosslinking the boric acid. Finally, the film was washed with an aqueous solution of potassium iodide, and then dried at 50 DEG C for 2 minutes to obtain a polarizing film having a total draw ratio of 5.7 times. No breakage occurred during the production, and the characteristics of the obtained polarizing film were as shown in Table 2.

&Lt; Example 2 >

A polyvinyl alcohol-based film and a polarizing film were obtained in the same manner as in Example 1 except that the heat treatment was performed by blowing hot air at 130 캜 in Example 1. The obtained polarizing film was evaluated in the same manner as in Example 1. The evaluation results are shown in Tables 1 and 2.

&Lt; Example 3 >

In the same manner as in Example 1 except that the casting drum was rotated at a rotation speed of 10 m / min to adjust the film thickness to 0.06 nm and blowing hot air at 120 캜 to heat the polyvinyl alcohol film And a polarizing film were obtained. The obtained polarizing film was evaluated in the same manner as in Example 1. The evaluation results are shown in Tables 1 and 2.

<Example 4>

In the same manner as in Example 1 except that the rotation speed of the cast drum was changed to 10 m / min, the film thickness was set to 0.06 nm, and the heat treatment temperature was set to 110 캜, the polyvinyl alcohol film and the polarizing film Film. The obtained polarizing film was evaluated in the same manner as in Example 1. The evaluation results are shown in Tables 1 and 2.

&Lt; Comparative Example 1 &

A polyvinyl alcohol film and a polarizing film were produced in the same manner as in Example 1 except that the rotation speed of the cast drum was changed to 10 m / min, the film thickness was 0.06 nm, and the heat treatment temperature was 100 ° C in Example 1 . The obtained polarizing film was evaluated in the same manner as in Example 1. The evaluation results are shown in Tables 1 and 2.

&Lt; Comparative Example 2 &

A polyvinyl alcohol-based film was obtained in the same manner as in Example 1 except that the heat treatment temperature was set to 150 캜 in Example 1. The production of a polarizing film using the above polyvinyl alcohol film was started, but a polarizing film with a length of 1 km was produced, and a fracture occurred during the stretching of the boric acid cross-linking step, and a desired polarizing film could not be obtained.

&Lt; Comparative Example 3 &

A polyvinyl alcohol-based film and a polarizing film were obtained in the same manner as in Example 1 except that the temperature of the metal heating roll was all 80 캜 in Example 1. The obtained polarizing film was evaluated in the same manner as in Example 1. The evaluation results are shown in Tables 1 and 2.

The tensile strength when stretched 6 times in the film flow direction (MD direction) in water at 30 占 폚 is A (N / mm2) and 50 占 폚 when the polyvinyl alcohol films of Examples 1 to 4 have a thickness D (nm) (1) and (2), the values of D x A and D x B satisfy the following equations (1) and (2), respectively, when assuming that the tensile strength at the time of stretching at 6 times in the film flow direction (MD direction) , While the value of D x B in the polyvinyl alcohol film of Comparative Example 1 is outside the range of Formula (2), and the value of D x A in the polyvinyl alcohol film of Comparative Examples 2 and 3 satisfies the formula (1), and the value of D x B was out of the range of the formula (2). The polarization characteristics of the polarizing films obtained from the respective polyvinyl alcohol films were found to be superior to those of Comparative Examples 1 and 3 in Examples 1 to 4 and to the polarizing films of Comparative Example 2 due to breakage .

With respect to the polyvinyl alcohol film obtained in Examples 3 and 4 and Comparative Example 1, the storage elastic moduli E1 and E2 were measured according to the following method to calculate the value of E2 / E1.

(6) Storage modulus (MPa)

A test piece having a length (MD direction) of 25 nm × a width (TD direction) of 5 nm was cut out from the obtained polyvinyl alcohol film and stored in water at 50 ° C at 30 ° C using DVA-225 manufactured by Haitian Instrumentation Control Co. The elastic modulus was measured. The detailed test conditions are as follows.

Frequency: 10Hz

Chuck distance: 15nm

Load: Dynamic twist in MD direction 0.3%, static ratio (ratio of static twist to dynamic twist) 6

E2 / E1 was calculated from the storage elastic modulus E1 (MPa) after 10 minutes of immersion in water at 30 占 폚 and the storage elastic modulus E2 (MPa) after 10 minutes of immersion in water at 50 占 폚. The film thickness for calculating the storage modulus in water was the thickness before water immersion.

The results of the measurement are as follows. E2 / E1 = 0.28 Example 3: E2 / E1 = 0.27 Comparative Example 1 E2 / E1 = 0.25 When the value of E2 / E1 is low, It was confirmed that the degree of polarization of the film was lowered.

Although the embodiment has been described in the concrete form of the present invention, the embodiment is merely an example and is not to be construed as limiting. Various modifications that are obvious to those skilled in the art are intended to be within the scope of the present invention.

The polarizing film made of the polyvinyl alcohol film obtained by the production method of the present invention is excellent in the in-plane uniformity of the polarizing performance and can be used for a portable information terminal, a PC, a television, a projector, a signage, an electronic tabletop calculator, (CRT, LCD, organic EL, electronic paper, etc.), liquid crystal display devices such as a game machine, a video camera, a photo album, a thermometer, audio, An antireflection layer for light, an optical communication device, a medical instrument, a building material, a toy, and the like.

Claims (13)

Thickness D (nm),
A (N / mm &lt; 2 &gt;) is the tensile strength when the film is stretched 6 times in the film flow direction (MD direction)
(N / mm &lt; 2 &gt;) when the film is stretched 6 times in the film flow direction (MD direction) in water at 50 DEG C,
A polyvinyl alcohol-based film characterized by satisfying the following formulas (1) and (2).
0.6? D? A? 1.2
(2) 0.2? D x B? 0.4 The method according to claim 1,
Wherein the polyvinyl alcohol film satisfies the following formula (3).
(3) 0.2? B / A? 0.5 The method according to claim 1 or 2,
Wherein E2 / E1 is 0.25 to 0.30 when E1 (Pa) is the storage elastic modulus in water at 30 DEG C and E2 (Pa) is the storage elastic modulus in water at 50 DEG C, film. 4. The method according to any one of claims 1 to 3,
Wherein the polyvinyl alcohol film has a thickness (D) of 0.04 nm or less. 5. The method according to any one of claims 1 to 4,
Wherein the polyvinyl alcohol film has a width of 4 m or more and a length of 4 km or more. 6. The method according to any one of claims 1 to 5,
Wherein the polyvinyl alcohol film has a tensile strength of 40 to 80 N / mm &lt; 2 &gt; when stretched 4 times in the flow direction (MD direction) of the film in an atmosphere of 20 DEG C and 65% RH. 7. The method according to any one of claims 1 to 6,
Wherein the in-plane phase difference is 50 nm or less. A process for producing the polyvinyl alcohol film according to any one of claims 1 to 7, which comprises producing the polyvinyl alcohol film through the following steps (A) to (D).
Step (A) A step of preparing a polyvinyl alcohol-based resin aqueous solution.
Step (B) A step of forming a polyvinyl alcohol-based resin aqueous solution by casting into a cast mold.
Step (C) A step of heating and drying the formed film by bringing the film into contact with a plurality of metal heating rolls.
Process (D) Process of heat-treating the obtained film using hot air. The method of claim 8,
A process for producing a polyvinyl alcohol-based film, which comprises blending 5 to 12% by weight of glycerin with respect to the polyvinyl alcohol-based resin in the step (A). The method according to claim 8 or 9,
Wherein the temperature of the plurality of metal heating rolls in the step (C) is in the order of the following conditions (a) to (d).
Condition (a) ≥80 ℃
Condition (b) &lt; 80 DEG C
Condition (c) ≥100 ° C
Condition (d) &lt; 100 ° C The method according to any one of claims 8 to 10,
Wherein the heat treatment temperature in the step (D) is 110 to 140 占 폚. A polyvinyl alcohol-based film produced by the production method according to any one of claims 8 to 11. A polarizing film comprising the polyvinyl alcohol film according to any one of claims 1 to 7 and 12.