KR20170129095A - Polyvinyl alcohol film, method for producing same, and polarizing film - Google Patents

Abstract

A polyvinyl alcohol film having a thickness of 5 to 60 占 퐉, a width of 2 m or more, and a length of 2 km or more, and having a haze of 0.2% or less. As a result, a polyvinyl alcohol film having a low haze and excellent surface smoothness can be obtained. By using this polyvinyl alcohol film, a polarizing film excellent in polarizability and line form transmittance can be obtained.

Description

The present invention relates to a polyvinyl alcohol film, a method for producing the same, and a polarizing film,

The present invention relates to a polyvinyl alcohol-based film, a method for producing the same, and a polarizing film. More specifically, the present invention relates to a polyvinyl alcohol-based film which is low in haze and excellent in surface smoothness, and which can obtain a polarizing film excellent in polarization degree and light transmittance.

Conventionally, a polyvinyl alcohol-based film is produced by dissolving a polyvinyl alcohol-based resin in a solvent such as water, preparing a raw solution for film-forming, forming the film by a solution casting method (casting method) do. The polyvinyl alcohol film thus obtained is used for many applications as a film having excellent transparency and dyeability, and polarizing films are one useful application thereof. Such a polarizing film is used as a basic component of a liquid crystal display, and in recent years, its use as a device requiring high quality and high reliability has been expanded.

In the meantime, with the enlargement of the screen of liquid crystal TVs and the like, a polarizing film having excellent optical characteristics, a wide and wide thinner polarizing film and a polyvinyl alcohol film serving as the disc are required. When the transparency of the polyvinyl alcohol-based film is low or when the surface smoothness is low, the light transmittance of the polarizing film is lowered and the polarization performance is not constant, which results in high brightness and high definition of the display. In addition, when the polyvinyl alcohol-based film has many defects, the display defects of the polarizing film naturally increase, which makes it difficult to manufacture a high-quality display.

As a countermeasure against such a problem, for example, a polyvinyl alcohol-based film using two types of polyvinyl alcohol-based resins having different molecular weights has been proposed (see, for example, Patent Document 1). In addition, a process for producing a polyvinyl alcohol-based film using a specific additive has been proposed (for example, see Patent Document 2).

Patent Document 1 JP 2006-308938 A Patent Document 2 JP 2012-082313 A

However, in the technique disclosed in Patent Document 1, since two kinds of polyvinyl alcohol-based resins have to be produced, not only the production load is increased but also the molecular weight is different by 20,000 or more, so that any one polyvinyl alcohol-based resin tends to precipitate during film formation , And such precipitates tend to be troublesome when a high quality polarizing film is produced by increasing the haze, surface roughness, and number of defects of the polyvinyl alcohol-based film.

The technique disclosed in Patent Document 2 reduces haze by adding a specific surfactant of a film-forming raw material (an aqueous solution of a polyvinyl alcohol-based resin), but even if the surface of the casting mold becomes rough, The film can not be obtained.

Accordingly, the present invention provides a polyvinyl alcohol-based film which is a polyvinyl alcohol-based film having low haze and surface smoothness under such a background and which can obtain a polarizing film excellent in polarizability and light transmittance, a method for producing the same, and a polarizing film The purpose is to do.

Therefore, the present inventors have conducted intensive studies in view of such circumstances, and as a result, have found that a polarizing film excellent in polarization degree and optical characteristics can be obtained by using a polyvinyl alcohol-based film having a lower haze and an excellent surface smoothness Thereby completing the present invention.

That is, the gist of the present invention relates to a polyvinyl alcohol-based film having a thickness of 5 to 60 μm, a width of 2 m or more, and a length of 2 km or more, and having a haze of 0.2% or less.

The present invention also provides a polarizing film made of the above polyvinyl alcohol-based film.

The present invention also provides a method for producing a polyvinyl alcohol-based film, which is obtained by discharging and forming an aqueous solution of a polyvinyl alcohol-based resin onto a casting mold and continuously drying the same, Wherein a crack is formed in a casting frame having a size of 2 or less in 1 mm < 2 >.

Since the polyvinyl alcohol-based film of the present invention is a polyvinyl alcohol-based film having low haze and excellent surface smoothness, a polarizing film excellent in polarization degree and light transmittance can be produced by using the polyvinyl alcohol-based film.

Hereinafter, the present invention will be described in detail.

The polyvinyl alcohol-based film of the present invention is a polyvinyl alcohol-based film having a thickness of 5 to 60 탆, a width of 2 m or more, and a length of 2 km or more, and having a haze of 0.2% or less.

The haze of the polyvinyl alcohol-based film of the present invention is required to be 0.2% or less, preferably 0.1% or less, particularly preferably 0.05% or less. When the haze exceeds the upper limit, the light transmittance of the polarizing film is lowered and the object of the present invention can not be achieved. The lower limit value of such a haze is usually 0.001%.

Examples of the method for reducing such haze include a method of reducing the surface roughness of the polyvinyl alcohol film and a method of reducing the light scattering inside the polyvinyl alcohol film by adding a surfactant to the film forming solution, , A technique of reducing the surface roughness of the polyvinyl alcohol film is preferable in that the characteristics of the polyvinyl alcohol-based film such as dyeability can be maintained.

The surface roughness Ra of the polyvinyl alcohol-based film of the present invention is preferably 20 nm or less, particularly preferably 15 nm or less, and more preferably 10 nm or less. If the surface roughness Ra is too large, the degree of polarization of the polarizing film tends to decrease.

Examples of the method for reducing the surface roughness include a method of reducing the surface roughness of the casting mold, a method of reducing the precipitate during film formation by adding a surfactant to the film forming raw material, and the like. In the present invention, From the viewpoint of maintaining the property of the alcohol film, it is preferable to reduce the surface roughness of the cast frame.

In the polyvinyl alcohol film of the present invention, when a virtual line having a length of 1 mm is provided at an arbitrary position on the surface of the film, the number of the projections having a width of 1 탆 or more and crossing the virtual line is preferably 2 or less, Is 1 or less, more preferably 0. When the number of such linear protrusions is too large, the unevenness of the polarizing film tends to increase. In the present invention, the aspect ratio is 10 or more.

Examples of the method of reducing the number of the casting molds include a method of reducing the microcracks on the casting mold surface, a method of improving the surface smoothness of the conveying roll, a method of increasing the cleanliness of the manufacturing process, It is preferable to reduce the micro-cracks on the casting mold surface.

In the polyvinyl alcohol film of the present invention, it is preferable that the number of linear protrusions having a height of 1 탆 or more contained in any 1 mm 2 of the surface of the film is 1 or less, particularly preferably, the number of linear protrusions having a height of 0.5 탆 or more is 1 And more preferably, the number of line-shaped projections having a height of 0.1 탆 or more is one or less. If the number of such linear protrusions is too large or the height of the linear protrusions is too high, the unevenness of the polarizing film tends to increase.

Examples of the method of reducing the number of such linear protrusions include a method of reducing micro cracks on the surface of a casting mold, a method of improving the surface smoothness of the transporting roll, and a method of increasing the cleanliness of the manufacturing process. From the effect of reducing the linear protrusions, it is preferable to reduce the micro-cracks of the casting mold surface, which will be described later.

Hereinafter, the polyvinyl alcohol film of the present invention and the polarizing film formed using the same will be described.

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 component capable of copolymerizing with a small amount (for example, 10 mol% or less, preferably 5 mol% or less) 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 monoallyl 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 saponification degree is too small, sufficient optical performance tends not to be obtained when a polarizing film is used as the polyvinyl alcohol-based 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, weight average molecular weight, average saponification degree and the like may be used in combination.

The polyvinyl alcohol-based film of the present invention can be obtained by preparing a polyvinyl alcohol-based resin aqueous solution by using the polyvinyl alcohol-based resin, discharging and flowing the aqueous solution into a casting mold, casting it by a casting method, And can be produced, for example, by the following process.

(A) A step of forming a film by casting.

(B) a step of heating and drying the formed film.

(C) a step of slitting the dried film, and then winding the film on a roll.

As the cast mold, for example, a cast drum (drum mold roll) or an endless belt may be used, but it is preferable to use cast drums from the viewpoint of widening, lengthening, and uniformity of the film thickness. Hereinafter, the case where the cast frame is a cast drum will be described as an example.

First, the step (A) will be described.

In the step (A), first, the polyvinyl alcohol-based resin is washed with a solvent such as 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 achieve the desired aqueous solution concentration. The polyvinyl alcohol-based resin wet cake is dissolved in hot water or hot water to adjust the polyvinyl alcohol-based resin aqueous solution.

The method of preparing the polyvinyl alcohol-based resin aqueous solution is not particularly limited and may be prepared, for example, by using a heated multifunctional extruder, and in a dissolving can having an upflow and downward flow generating stirring wing, An alcoholic resin wet cake is put into the can, and water vapor is blown into the can to dissolve and prepare an aqueous solution having a desired concentration.

The polyvinyl alcohol resin aqueous solution may contain, in addition to the polyvinyl alcohol-based resin, a commonly used plasticizer such as glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol, trimethylolpropane, It is preferable to include at least one surfactant of anionic, anionic, and cationic in view of film formability.

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.

Then, the resulting polyvinyl alcohol-based resin aqueous solution is defoamed. Examples of the defoaming method include a defoaming method using a static deformation or a multi-screw extruder. The multiaxial extruder is not particularly limited as long as it is a multiaxial extruder having a vent, but a twin-screw extruder usually having a vent is used.

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

The temperature of the polyvinyl alcohol-based resin solution at the outlet of the T-shaped slit die is preferably 80 to 100 占 폚, particularly preferably 85 to 98 占 폚. When the temperature of the aqueous solution of the polyvinyl alcohol resin is too low, flow defects tend to occur. When the temperature is too high, foaming tends to occur.

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 casting. 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 discharging rate of the polyvinyl alcohol resin aqueous solution discharged from the T-shaped slit die to the cast drum is preferably 0.5 to 5 m / min, particularly preferably 0.6 to 4 m / min, and more preferably 0.7 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.

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 width of such a cast drum is preferably 2 m or more, particularly preferably 3 m or more, more preferably 4 m or more, particularly preferably 5 to 6 m. If the cast drum width is too small, the productivity 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, the productivity tends to decrease. If the rotation speed is too fast, the 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.

As such a casting drum, a stainless steel (SUS) containing iron as a main component is usually coated with metal plating to prevent 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, it is preferable that the outermost surface is a chromium plating layer from the viewpoint of easiness of smoothing the surface of the drum and excellent durability.

The surface roughness Ra of the cast drum used in the present invention is preferably 20 nm or less. More preferably 15 nm or less, and further preferably 10 nm or less. If the surface roughness Ra is too large, the surface roughness of the polyvinyl alcohol-based film tends to increase.

Examples of the method for reducing the surface roughness include a method of sealing micro cracks on the surface of the casting drum and a method of polishing the surface of the casting drum. In the present invention, a method of sealing micro cracks on the surface of the casting drum , And it is particularly preferable to polish the periphery of the sealing portion at least either before the sealing process or after the sealing process.

The cast drum used in the present invention preferably has a microcrack having a depth of 1 mu m or more existing on the surface of the cast drum in a range of 2 or less, particularly preferably 1 or less, and more preferably, It is a cast drum. In addition, the number of microcracks having a depth of 0.1 mu m or more existing on the surface of the cast drum is preferably 10 or less, particularly preferably 7 or less, and more preferably 5 or less in 1 mm < 2 > If the number of micro cracks is too large, the surface roughness of the polyvinyl alcohol film tends to increase.

Examples of the method for reducing the number of micro cracks include a method of sealing the micro cracks on the surface of the cast drum, a method of polishing the surface of the cast drum, a method of melting the cast drum surface by etching to smooth the surface of the cast drum, , Micro cracks on the surface of the cast drum are preferably pierced, and it is particularly preferable to polish the periphery of the piercing before at least one of the piercing and the piercing. In the method of performing only the polishing alone or the etching only, microcracks are difficult to see with the naked eye. However, when the casting drum is heated and continuously operated, the size of the microcracks increases and the number of the microcracks tends to increase.

Hereinafter, a method of sealing micro cracks will be described in detail. Generally, micro-cracks exist in the plated layer, and micro-cracks exist on the surface of the cast mold preferably used in the present invention. Such micro cracks are caused by the stress of the metal plating layer and the shape and the number thereof vary depending on the thickness of the metal plating layer, the plating condition, the heat treatment, the chemical treatment, the layer structure, It is likely to occur in the case of non-uniformity.

Examples of the method for sealing micro cracks include a method of blocking micro cracks by using at least one of an organic sealing material and an inorganic sealing material, a method of repairing by light irradiation such as laser annealing, a spraying method such as arc spraying, In the present invention, from the viewpoint of durability, a method of blocking microcracks by using an inorganic sealing material and a method of repairing by light irradiation are preferable.

First, a method of blocking with an inorganic sealing material will be described. Examples of such an inorganic sealing material include inorganic polymers condensed by hydrolysis of an alkoxysilane compound, an alkoxytitanium compound, an alkoxychrom compound, and a complex compound thereof. Among them, from the viewpoint of adhesiveness with a casting mold material Is preferably an inorganic polymer in which the alkoxysilane compound of the following general formula (1) is condensed from the viewpoint of easiness of the sealing treatment at the production site.

[Formula 1]

R ¹ _n Si (OR ² ) _{4 -n}

(Wherein R ¹ is a hydrocarbon group having 1 to 10 carbon atoms, R ² is a hydrocarbon group having 1 to 3 carbon atoms, and n is an integer of 1 to 3).

Specific examples of such alkoxysilane compounds include methyltrimethoxysilane, phenyltrimethoxysilane, methyltriethoxysilane, methyltriisopropoxysilane, ethyltrimethoxysilane, butyltrimethoxysilane, dimethyldimethoxy Silane, dimethyldiethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane, phenylmethyldimethoxysilane, tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane and the like. Of these, methyltrimethoxysilane, diphenyldimethoxysilane, and mixtures thereof are preferable.

The method of condensing such an alkoxysilane compound is not particularly limited and water may be added to a single substance or a mixture of the alkylalkoxysilane compounds and the temperature may be raised while stirring in the presence of a catalyst such as hydrochloric acid, To cause condensation.

As the sealing method using such an inorganic sealing material, the microcracked portion formed in the casting mold is polished with a grinding stone if necessary, and the inorganic sealing material is applied by a known method. The inorganic sealing material can be cured at room temperature, but when it is heated or baked if necessary, the curing can be completed more quickly. If necessary, the coating may be performed under reduced pressure or under pressure, or the periphery of the sealing may be polished after the heat treatment or the baking treatment.

Hereinafter, with respect to the sealing process, the case of using a cast drum will be described in detail, but the present invention is not limited to such a process. The concrete sealing process is preferably carried out in the following steps [I] to [IV].

[I] Process of cleaning the cast drum surface with solvent.

[II] Process of applying an inorganic sealing material.

[III] A step of firing an inorganic sealing material.

[IV] Process of wiping residue of cast drum surface with solvent.

Examples of the solvent to be used for the step [I] include acetone, ethanol, water and the like. The cleaning is preferably carried out several times from the viewpoint of cleaning efficiency, and it is more preferable to use a plurality of solvents. If such solvent cleaning is not carried out, the inorganic sealing material tends not to sufficiently penetrate into the microcrack due to the resin or oil in the microcrack. The cleaning may be performed using a solvent while rotating the casting drum, or the contamination may be intensively showered by stopping the rotation. Usually, the cleaning temperature is 0 to 50 캜, and the cleaning time is 1 to 1 hour. Drying of the solvent is preferably natural drying, but hot air drying using a dryer or the like may also be carried out. When a micro crack is locally large, such a local portion may be polished before cleaning. The abrasive may be a commercially available abrasive or abrasive cloth.

As the method of applying the process [II], known methods such as brushing, roller brushing, spraying, spraying, spraying, curtain flow, squeezing and needle grinding can be used. Among them, Soldering is preferred. The coating amount is, for example, 1 to 100 g / m 2 in the case of an alkoxysilane compound. If it is less than the lower limit value, it is not enough to block the sealing portion, and if it exceeds the upper limit value, overlaying occurs after sealing.

The step [III] is preferably carried out at 50 to 200 ° C, more preferably for 1 to 60 minutes. Condensation (hardening) of the inorganic sealing material tends to be insufficient when the temperature or time is less than the lower limit value. On the other hand, when the temperature or time is less than the lower limit value, the condensation (curing) of the inorganic sealing material is congested and the adhesion between the inorganic sealing material and the microcrack inner wall is deteriorated .

Step [IV] is a step of wiping the residue of the sealing material on the surface of the cast drum with a solvent, and examples of the solvent include acetone, ethanol, water and the like. A material that does not damage the surface of the cast drum, such as cotton, is preferred. When the surface roughness of the intended film can not be obtained after the start of the production, it is also possible to polish the embossed portion of the sealing material or the periphery of the rod. The abrasive may be a commercially available abrasive or zippers.

The cast drums are thus repaired. However, if the repairing effect is not perfect, the above-mentioned steps [I] to [IV] can be repeated and part of the steps [I] to [IV] .

As a preferred embodiment of the present invention, it is preferable to use a cast drum in which the surface of the cast drum is periodically sealed at a period of several months to several years, and a polishing process is carried out if necessary. The period is preferably about 3 months to 2 years.

Next, a repairing method by light irradiation will be described. Such a method is difficult to completely prevent micro cracks as in the case of using an inorganic sealing material. However, since it is possible to narrow the width of micro cracks, it can be regarded as a type of sealing material. Particularly, If available. That is, repairing microcracks by light irradiation means suppressing and decreasing the number of micro cracks and the number of micro cracks formed in the metal (chromium) plating layer by light irradiation.

Generally, there are two main methods of repairing by light irradiation. (1) a method in which a surface layer of a metal plating is heated by light irradiation, and (2) a surface layer atom of a metal plating layer is vaporized by light irradiation with a high energy. In the method (1), infrared light is mainly used and is generally called infrared annealing. In the method (2), a laser having a high energy is used as a light source, and is generally called laser ablation. In the present invention, both methods and both methods can be combined.

First, (1) a method of heating the surface layer of the metal plating by light irradiation will be described. There are three heat transferring principles, direct conduction, convection and radiation. In the present invention, the surface layer of the metal plating is mainly heated by radiation.

The heating temperature of the surface layer of the metal plating is preferably 70 to 500 占 폚, particularly preferably 100 to 300 占 폚, and more preferably 150 to 200 占 폚. If the heating temperature is too low, the maintenance effect is not significant. If the heating temperature is too high, microcracks tend to expand.

The heating time is preferably 1 to 60 seconds, more preferably 2 to 30 seconds, and particularly preferably 3 to 20 seconds. If the heating time is too short, the maintenance effect is not remarkable. If the heating time is too long, the deep portion or the underlayer of the metal plating is also heated, and the casting mold tends to deteriorate.

As the light, infrared rays such as near-infrared light, heavy infrared light and far-infrared light are preferable from the viewpoint of the heating rate. Near infrared rays are more preferable from the viewpoint of heating efficiency, and particularly preferable are near infrared light with peak wavelength of 1 to 2 占 퐉. As such a light source for infrared rays, a known near infrared ray heater can be used, but a halogen heater is preferable from the viewpoint of energy efficiency.

In the present invention, an infrared laser may be used as the infrared light source in order to repair not only the front surface of the casting mold but also the local portion where micro cracks occur. As the infrared laser, a gas laser such as a He-Ne laser (1.15 占 퐉), a carbon dioxide gas laser (10.6 占 퐉, 9.6 占 퐉), an Nd: YAG laser (1.06 占 퐉, 0.94 占 퐉 1.3-1.4 占 퐉, 2.098 占 퐉) (1.3 占 퐉, 1.5 占 퐉), and the like.

When a laser is used, it is preferable that the laser beam generated from the laser light source is expanded in a plane by using a spherical lens or the like. Shaped lens using a cylindrical lens or the like, and irradiate the surface of the cast frame. The irradiation of the cast frame may be performed while moving the laser, or may be carried out while moving the cast frame. In the case where the cast frame is a cast drum, it is also possible to carry out the laser movement in the width direction while rotating the cast drum. In addition, the laser output of Class 3 (5 mW) or less is preferable from the viewpoint of the safety of the maintenance work.

Next, (2) a method of volatilizing the surface layer atoms of the metal plating layer by light irradiation at a high energy will be described.

The irradiation of the laser beam to the casting mold is preferably performed by enlarging the laser beam generated from the pulsed laser source to a plane using a spherical lens or the like. Particularly, it is preferable to form a linear beam from a cylindrical lens or the like and irradiate the surface of the cast frame in view of the irradiation area. The irradiation of the casting mold may be carried out while moving the laser, or may be carried out while moving the casting mold. In the case where the cast frame is a cast drum, it is preferable to irradiate the casting drum surface to the rotating cast drum from the viewpoint that the cast drum can be repaired without removing it from the production line. It is also possible to process the laser beam into a dashed line by means of a diffraction grating. In addition, the laser output of Class 3 (5 mW) or less is preferable from the viewpoint of the safety of the maintenance work.

The irradiation time is preferably 0.1 to 60 seconds, more preferably 0.2 to 30 seconds, and particularly preferably 0.3 to 20 seconds. If the irradiation time is too short, the maintenance effect is not remarkable. If the irradiation time is too long, the surface layer of the metal plating tends to be rough.

Such light irradiation may be conducted by direct conduction in which the entire mold frame is heated, or convection conduction using hot air. Further, after such light irradiation, the cast mold may be subjected to heat treatment because of the stress relaxation of the metal plating layer. In such a case, the heating temperature is preferably 50 to 200 ° C and the heating time is preferably 1 to 100 hours.

The above-described micro crack sealing method may be performed alone or in combination of a plurality of micro cracks. For example, in the step of baking the inorganic sealing material, the chromium plating layer may be heated by irradiating infrared rays.

Next, the step (B) will be described. The step (B) is a step of heating and drying the formed film.

Drying of the 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 heated rolls. The surface temperature of the heated roll is usually 40 to 150 占 폚, preferably 50 to 140 占 폚. If the surface temperature is too low, the drying tendency tends to become poor. If the surface temperature is too high, too much drying tends to result in appearance defects such as waves. The hot roll is, for example, a roll having a diameter of 0.2 to 2 m, which has been subjected to a hard chrome plating treatment or a mirror surface treatment, and is usually dried using 2 to 30, preferably 10 to 25 .

In the present invention, it is preferable to heat-treat the film after drying with hot roll. The heat treatment temperature is preferably 60 to 150 占 폚, particularly preferably 70 to 140 占 폚. When the heat treatment temperature is too low, the water resistance of the polyvinyl alcohol-based film tends to be lowered or cause a deviation in the retardation. When the heat treatment temperature is too high, the stretchability at the time of producing the polarizing film tends to decrease. Examples of such a heat treatment method include a method of bringing into contact with high temperature hot roll, a method of carrying out with a floating dryer, and the like.

The film subjected to drying and heat treatment, if necessary, becomes a product (polyvinyl alcohol film of the present invention) through the above step (C). Step (C) is a step of slitting both ends of the film and winding the film on a roll.

The following explains a method of preparing a polyvinyl alcohol-based resin aqueous solution, casting this aqueous solution on a rotating cast drum (drum-type roll), casting it by a casting method, and drying it to prepare a polyvinyl alcohol-based film However, it is also possible to make the polyvinyl alcohol-based resin aqueous solution flexible on a resin film or on a metal belt, and to form and dry it.

Thus, the polyvinyl alcohol-based film of the present invention is obtained.

The polyvinyl alcohol film of the present invention obtained by the above production method needs to have a thickness of 5 to 60 占 퐉 and preferably has a thickness of 5 to 50 占 퐉 from the viewpoint of thinning, , And more preferably 5 to 30 mu m from the standpoint of avoiding breakage.

The polyvinyl alcohol film of the present invention is required to have a width of 2 m or more and particularly preferably 3 m or more from the standpoint of size reduction and more preferably 4 to 6 m from the standpoint of avoiding breakage.

The polyvinyl alcohol-based film of the present invention is required to have a length of 2 km or more, particularly preferably 3 km or more from the standpoint of size reduction, and more preferably 3 to 50 km from the viewpoint of transportation weight.

The polyvinyl alcohol film of the present invention is excellent in transparency and is suitably used as a polyvinyl alcohol 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 a horizontal direction and performing a process such as swelling, dyeing, boric acid crosslinking, stretching, washing and drying.

The swelling process is carried out before the dyeing process. In addition to being able to clean dirt on the surface of the polyvinyl alcohol-based film by the swelling process, the polyvinyl alcohol-based film is also swelled to prevent uneven dyeing. As the treatment liquid in the swelling step, water is usually used. 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 占 폚, and the immersion time for the swelling bath is usually about 0.1 to 10 minutes.

The dyeing process is carried out by bringing the film into contact with a liquid containing iodine or a dichroic dye. Normally, 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.

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 占 폚, 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, slight stretching (degree of preventing shrinkage 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 40 to 170 캜. The stretching magnification may be finally set within 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 should be 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 determined by superimposing the light transmittance (H ₁₁ ) measured at the wavelength? And the two polarizing films in a direction orthogonal to the alignment direction so that the two polarizing films are overlapped so that their alignment directions are the same Is calculated in accordance with the following equation by the light transmittance (H ₁ ) measured at the wavelength? In the combined state.

_{[(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 on which an optically isotropic resin film is attached as a protective film to one or both surfaces through an adhesive. As the protective film, for example, cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, cycloolefin polymer, cycloolefin copolymer, polystyrene, polyethersulfone, polyallylene ester, And films or sheets such as polyethylene, polypropylene, polyethylene, polypropylene, polyethylene, polypropylene, polyethylene, polypropylene,

Although the bonding method is carried out by a known method, for example, a liquid adhesive composition is uniformly applied to a polarizing film, a protective film, or both, and the two are adhered to each other, .

For the purpose of thinning the polarizing film, it is also possible to apply a curable resin such as a urethane resin, an acrylic resin, or a urea resin on one or both sides thereof instead of the protective film to cure the polarizing film.

The polarizing film and the polarizing plate obtained by the present invention are free from display defects and unevenness and have excellent polarizing performance and can be used in portable information terminals, PCs, televisions, projectors, signage, electronic tabletop calculators, electronic clocks, (CRT, LCD, organic EL, electronic paper, etc.) such as a liquid crystal display device, a sunglass, an anti-glare eyeglasses, a stereoscopic eyeglass, a wearable display, a game device, a video camera, a photo album, a thermometer, Reflection reduction layers, optical communication devices, medical instruments, building materials, toys, 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 "% " For each physical property, measurements were carried out as follows.

<Measurement Conditions>

(1) Haze (%)

Ten test pieces of 50 mm x 50 mm were taken from the roll film, and the test pieces were measured using a haze meter "NDH-2000" manufactured by Nippon Denshoku Kogyo Co., and the average value of ten sheets was defined as haze.

(2) Surface roughness Ra of the cast drum (nm)

Three points of the cast drum were measured using a laser focus microscope VK-9700 (measurement length: 0.1 mm, objective lens: 50 times) manufactured by Keyens Co. The average value was set to surface roughness.

(3) Surface roughness of film Ra (nm)

A laser focus microscope VK-9700 (measurement length: 0.1 mm, objective lens: 50 times) manufactured by Keyens Co., Ltd. was used, and 10 portions of the roll film were measured, and the average value was taken as the surface roughness.

(4) Number of micro cracks (pieces / mm 2)

Microcracks having a depth of 1 mu m or more existing at three cast drums (each area of 1 mm2) were observed using a laser focus microscope VK-9700 (objective lens: 50 times) manufactured by Keyens Co. The average value was defined as the number of micro cracks.

(5) Number of line-shaped projections of film

Using a laser focus microscope VK-X110 (objective lens: 50 times) manufactured by Keith Co., Ltd., the number of line-shaped protrusions having a width of 1 占 퐉 or more existing at 10 positions (measurement length 1 mm) of the roll film was measured, A (number / mm). In addition, the number of line-shaped projections having a height of 1 占 퐉 or more existing at 10 positions (measurement range 1 mm 占 1 mm) of the roll film was measured, and the average value was determined as the line-shaped projection number B (number / mm2).

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

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

(7) stain

A polarizing film having a length of 30 cm and a width of 30 cm was sandwiched between two polarizing plates in a crossed Nicol state (with a single light transmittance of 43.5% and a polarization degree of 99.9%) at an angle of 45 ° and then passed through a light box with a surface illuminance of 14,000 lx Optical stains are observed and evaluated according to the following criteria.

(Evaluation standard)

○: No staining.

×: In dirt

(8) Number of display defects (pieces / ㎡)

The polarizing film having a length of 30 cm and a width of 30 cm was visually inspected under an environment of 15,000 lx and the number of defects exceeding 100 탆 was measured.

&Lt; Example 1 &gt;

(Repair of cast drums)

The surface of the chrome plated cast drum (3 m in diameter, 6 m in width) was polished with a PVA grindstone (surface roughness Rz 0.1 탆) where the surface roughness was noticeable, and then the cast drum was rotated at a low speed of 1 m / (25 占 폚) with acetone, ethanol, and distilled water in this order for 10 minutes. After drying at room temperature (25 ° C) for 10 minutes, a hydrolysis-condensation product of methyltrimethoxysilane (80% by weight) and diphenyldimethoxysilane (20% by weight) as a sealing material was used. , And the sealing material was fired at 100 DEG C for 1 hour. Finally, the residue of the sealing material on the surface of the cast drum was wiped with a cotton cloth impregnated with acetone to finish the repair. Table 1 shows the characteristics of the obtained cast drums.

(Production of polyvinyl alcohol film)

1000 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 dodecyl sulfate as a surfactant were placed in a 5000-liter dissolving can, And subjected to pressure-fusing 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 and defoamed. The temperature of the aqueous solution was adjusted to 95 占 폚, and the film was plied to the cast drum through a T-shaped slit die outlet at a discharge speed of 1.25 m / min.

Then, the obtained film was dried using hot roll, and then heat treatment was performed using a floating dryer. Finally, both ends of the film were cut with a slit, and wound up to obtain a roll-shaped polyvinyl alcohol film (thickness 30 m, width 5 m, length 4 km). Table 1 shows the properties of the obtained polyvinyl alcohol film.

(Production of polarizing film)

The resulting polyvinyl alcohol film was uniaxially stretched 1.7 times while immersed in a water bath at 25 ° C. Subsequently, it was uniaxially stretched 1.6 times while immersed in an aqueous solution at 28 ° C composed of 0.5 g / L of iodine and 30 g / L of potassium iodide. Subsequently, while being immersed in an aqueous solution of 55 캜 consisting of 40 g / L of boric acid and 30 g / L of potassium iodide, the composition was uniaxially stretched 2.1 times. Finally, the film was washed with an aqueous solution of potassium iodide and dried to obtain a polarizing film having a total draw ratio of 5.8 times. Table 2 shows the characteristics of the obtained polarizing film.

&Lt; Example 2 &gt;

A polyvinyl alcohol-based film and a polarizing film were produced in the same manner as in Example 1 except that the repair of the cast drum was performed without polishing. The characteristics of the obtained polyvinyl alcohol film are shown in Table 1, and the properties of the polarizer film are shown in Table 2.

&Lt; Example 3 &gt;

A polyvinyl alcohol film was produced in the same manner as in Example 1 except that the discharging rate of the polyvinyl alcohol resin aqueous solution was changed to 2.5 m / min and the thickness of the polyvinyl alcohol film was changed to 60 탆, And a polarizing film. The characteristics of the obtained polyvinyl alcohol film are shown in Table 1, and the properties of the polarizer film are shown in Table 2.

<Example 4>

A polyvinyl alcohol film and a polarizing film were produced in the same manner as in Example 1 except that a cast drum was used which was repaired in the following manner. The characteristics of the obtained polyvinyl alcohol film are shown in Table 1, and the properties of the polarizer film are shown in Table 2.

(Repair of cast drum)

Five near-infrared lamps (UH-USF-CL1000: peak wavelength: 1.2 mu m, manufactured by Ushio DENKI KK) having a width of 1 m were used while rotating the cast drum at 1 m / min to irradiate near-infrared light over the entire width of the casting drum. The distance between the workpieces was 1 cm. The surface temperature of the cast drum immediately after the first irradiation was 100 DEG C when measured by a non-contact thermometer. The chrome plating layer on the surface of the cast drum was repaired by cooling the surface of the cast drum to room temperature (25 캜) after turning and light irradiation were continued until the surface temperature became 200 캜. Table 1 shows the characteristics of the obtained cast drums.

&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 cast drum was not repaired. The characteristics of the obtained polyvinyl alcohol film are shown in Table 1, and the properties of the polarizer film are shown in Table 2.

The polyvinyl alcohol film of Examples 1 to 4 had a haze of 0.2% or less, while the polyvinyl alcohol film of Comparative Example 1 had a high haze. It can be seen that the polarizing properties of the polarizing films obtained from the respective polyvinyl alcohol films are superior to those of the first to fourth comparative examples.

Although the embodiments of the present invention have been described with reference to specific embodiments thereof, they are merely illustrative and not restrictive. Various modifications apparent to those skilled in the art are also within the scope of the present invention.

The polarizing film and the polarizing plate obtained by the present invention are free from display defects and unevenness and excellent in polarizing performance and can be used as portable information terminals, PCs, televisions, projectors, signage, electronic tabletop calculators, electronic clocks, word processors, (CRT, LCD, organic EL, electronic paper, etc.), a liquid crystal display device such as a photo album, a thermometer, an audio, an automobile or a machine instrument, a reflection reduction layer for a sunglass, an anti- Equipment, medical equipment, building materials, toys, and the like.

Claims (19)

A polyvinyl alcohol film having a thickness of 5 to 60 탆, a width of 2 m or more, and a length of 2 km or more, and having a haze of 0.2% or less. The method according to claim 1,
Wherein the polyvinyl alcohol film has a surface roughness Ra of 20 nm or less. The method according to claim 1 or 2,
Wherein the number of linear protrusions having a width of 1 占 퐉 or more and intersecting with the imaginary line when a virtual line having a length of 1 mm is provided at an arbitrary position on the surface of the polyvinyl alcohol film is 2 or less. 4. The method according to any one of claims 1 to 3,
Wherein the number of line-shaped projections having a height of 1 탆 or more contained in any 1 mm 2 of the surface of the polyvinyl alcohol film is 1 or less. 5. The method according to any one of claims 1 to 4,
Wherein the thickness of the polyvinyl alcohol film is 5 to 30 占 퐉. 6. The method according to any one of claims 1 to 5,
A polyvinyl alcohol film characterized in that an aqueous solution of a polyvinyl alcohol-based resin is formed by discharging and forming a film on a casting mold and continuously drying the film. The method of claim 6,
Wherein the cast frame is a cast drum, and the outermost surface of the cast drum is a chromium layer formed by plating. The method according to claim 6 or 7,
Wherein the cast drum is a cast drum having a surface roughness Ra of 20 nm or less. The method according to claim 7 or 8,
Wherein a micro crack having a depth of 1 mu m or more existing on the surface of the cast drum is 2 or less in 1 mm &lt; 2 &gt;. The method according to any one of claims 7 to 9,
Wherein the cast drum is a cast drum obtained by sealing a micro crack on the surface with an inorganic sealing material. The method of claim 10,
Wherein the inorganic sealing material is an inorganic polymer condensed with an alkoxysilane compound. The method according to any one of claims 7 to 11,
Characterized in that the cast drum is a cast drum obtained by polishing the periphery of the rod before at least one of the sealing process and the sealing process. The method of claim 12,
The polyvinyl alcohol-based film is characterized in that the cast drum is a cast drum which is regularly polished and polished, if necessary, at a period of several months to several years. The method according to any one of claims 7 to 13,
Wherein the cast drum is a cast drum in which micro cracks formed on the chromium layer are repaired by light irradiation. 15. The method of claim 14,
Wherein the light is an infrared ray. 16. The method of claim 15,
Wherein the infrared ray is a near-infrared ray having a peak wavelength of 1 to 2 占 퐉. The method according to any one of claims 14 to 16,
A polyvinyl alcohol film characterized by using light irradiation and heat in combination. A polarizing film comprising the polyvinyl alcohol-based film according to any one of claims 1 to 17. A method for producing a polyvinyl alcohol-based film, which comprises obtaining an aqueous solution of a polyvinyl alcohol-based resin by discharging and forming a film by casting on a casting mold and continuously drying the microvulcanized film, Wherein a casting mold having two or less casting molds is used.