JP6776566B2 - Polyvinyl alcohol-based film, polarizing film, and method for producing polyvinyl alcohol-based film - Google Patents

Description

The present invention relates to a polyvinyl alcohol-based film and a polarizing film, and a method for producing a polyvinyl alcohol-based film. More specifically, the present invention relates to a polyvinyl alcohol-based film having a low haze and excellent surface smoothness, and further relating to a polyvinyl alcohol-based film capable of obtaining a polarizing film having excellent polarization degree and light transmittance. Is.

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

Under these circumstances, with the increase in size of screens of liquid crystal televisions and the like, there is a need for a wide, long and thin polarizing film having better optical characteristics than conventional products, and a polyvinyl alcohol-based film as the raw material thereof. .. When the transparency of the polyvinyl alcohol-based film is low or the surface smoothness is low, the light transmittance of the polarizing film is lowered and the polarization performance is not constant, which is an obstacle to increasing the brightness and definition of the display. Become. Further, when the polyvinyl alcohol-based film has many defects, the display defects of the polarizing film also increase as a matter of course, and it becomes 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). Further, a method for producing a polyvinyl alcohol-based film using a specific additive has been proposed (see, for example, Patent Document 2).

Japanese Unexamined Patent Publication No. 2006-308938 JP 2012-082313

However, in the disclosure technique of Patent Document 1, not only the production load becomes large because two kinds of polyvinyl alcohol-based resins must be produced, but also the molecular weights differ by 20,000 or more, so that any of the polyvinyl alcohol-based resins is produced during film formation. There is a problem that the precipitate is likely to precipitate, and such a precipitate increases the haze, surface roughness, and the number of defects of the polyvinyl alcohol-based film, and tends to be an obstacle in producing a high-quality polarizing film.

Further, the technique disclosed in Patent Document 2 reduces haze by adding a specific surfactant to a film-forming raw material (an aqueous solution of a polyvinyl alcohol-based resin), but no matter how much the film-forming raw material is optimized. , If the cast type surface is rough, a low haze film cannot be obtained.

Therefore, in the present invention, under such a background, a polyvinyl alcohol-based film having a low haze and excellent surface smoothness can be obtained, and a polarizing film having excellent polarization degree and light transmittance can be obtained. It is an object of the present invention to provide a system film and a method for producing the same.

However, as a result of intensive research in view of such circumstances, the present inventors have obtained a polarizing film having excellent degree of polarization and optical characteristics by using a polyvinyl alcohol-based film having a lower haze and excellent surface smoothness than before. We have found that it can be obtained and completed the present invention.

That is, the gist of the present invention, the thickness 5 to 60 m, more width 2m, a polyvinyl alcohol film is long 2km above state, and are haze 0.2% or less, and polyvinyl alcohol-based film surface any 1mm linear projection density than the height 1μm contained in ² of relates der Ru polyvinyl alcohol film following one.

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

The present invention is a method for producing a polyvinyl alcohol-based film obtained by discharging and salivating an aqueous solution of a polyvinyl alcohol-based resin into a cast mold to form a film, and continuously drying the film, which exists on the surface of the cast mold. Also provided is a method for producing a polyvinyl alcohol-based film using a cast type having ^two or less microcracks having a depth of 1 μm or more in 1 mm ² .

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

The present invention will be described in detail below.

Polyvinyl alcohol film of the present invention, the thickness 5 to 60 m, more width 2m, a polyvinyl alcohol film is long 2km above state, and are haze 0.2% or less, and polyvinyl alcohol-based film any 1mm linear projection density than the height 1μm contained in the ^second surface is a polyvinyl alcohol film characterized der Rukoto following one.

The haze of the polyvinyl alcohol-based film of the present invention needs to be 0.2% or less, preferably 0.1% or less, and particularly preferably 0.05% or less. If the haze exceeds the upper limit, the light transmittance of the polarizing film decreases, and the object of the present invention cannot be achieved.
The lower limit of such haze is usually 0.001%.

Examples of the method for reducing such haze include a method for reducing the surface roughness of the polyvinyl alcohol-based film and a method for adding a surfactant to the film-forming stock solution to reduce light scattering inside the polyvinyl alcohol-based film. In the present invention, a method of reducing the surface roughness of the polyvinyl alcohol-based film is preferable in that various 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 further 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 for reducing the surface roughness of the cast type, a method for blending a surfactant with the film-forming raw material, and a method for reducing the precipitate in the film-forming. In the present invention, a method of reducing the surface roughness of the cast type is preferable from the viewpoint of maintaining various properties of the polyvinyl alcohol-based film such as dyeability.

Further, in the polyvinyl alcohol-based film of the present invention, when a virtual line having a length of 1 mm is provided at an arbitrary position on the film surface, the number of linear protrusions having a width of 1 μm or more intersecting the virtual line is 2 or less. Particularly preferably, the number is 1 or less, and more preferably 0.
If the number of such linear protrusions is too large, the color unevenness of the polarizing film tends to increase. In the present invention, a linear aspect ratio of 10 or more is used.

Examples of the method for reducing the number thereof include a method for reducing microcracks on the cast surface, a method for improving the surface smoothness of the transport roll, a method for improving the cleanliness of the manufacturing process, and the like. From the viewpoint of reducing linear protrusions, a method of reducing microcracks on the cast surface is preferable.

Further, the polyvinyl alcohol-based film of the present invention must have one or less linear protrusions having a height of 1 μm or more contained in any 1 mm ² of the film surface . Particularly preferably, the number of linear protrusions having a height of 0.5 μm or more is one or less, and more preferably, the number of linear protrusions having a height of 0.1 μm 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 color unevenness of the polarizing film tends to increase.

Examples of the method for reducing the number of linear protrusions include a method for reducing microcracks on the cast surface, a method for improving the surface smoothness of the transport roll, and a method for increasing the cleanliness of the manufacturing process. In the above, a method of reducing microcracks on the cast type surface, which will be described later, is preferable from the viewpoint of reducing linear protrusions.

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

As the polyvinyl alcohol-based resin used in the present invention, an unmodified polyvinyl alcohol-based resin, that is, a resin produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate is usually used. If necessary, a resin obtained by saponifying a copolymer of vinyl acetate and a small amount (for example, 10 mol% or less, preferably 5 mol% or less) of vinyl acetate and a copolymerizable component may be used. it can. Examples of the component copolymerizable with vinyl acetate include unsaturated carboxylic acids (including, for example, salts, esters, amides, and nitriles) and olefins having 2 to 30 carbon atoms (for example, ethylene, propylene, and n-butene). , Isobutene, etc.), vinyl ethers, unsaturated sulfonates, etc. Further, a modified polyvinyl alcohol-based resin obtained by chemically modifying the hydroxyl group after saponification can also be used.

Further, as the polyvinyl alcohol-based resin, a polyvinyl alcohol-based resin having a 1,2-diol structure in the side chain can also be used. The polyvinyl alcohol-based resin having a 1,2-diol structure in the side chain is, for example, (i) a method for saponifying a copolymer of vinyl acetate and 3,4-diacetoxy-1-butene, (ii) acetate. A method for saponifying and decarbonizing a copolymer of vinyl and vinyl ethylene carbonate, (iii) saponifying and decarbonating a copolymer of vinyl acetate and 2,2-dialkyl-4-vinyl-1,3-dioxolane. It can be obtained by a method of ketalization, (iv) a method of saponifying a copolymer of vinyl acetate and glycerin monoallyl ether, or 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 even 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, and if it is too large, it tends to be difficult to stretch the polyvinyl alcohol-based film during the production of the polarizing film. There is. The weight average molecular weight of the polyvinyl alcohol-based resin is the weight average molecular weight measured by the GPC-MALS method.

The average degree of saponification of the polyvinyl alcohol-based resin used in the present invention is usually preferably 98 mol% or more, particularly preferably 99 mol% or more, still more preferably 99.5 mol% or more, and particularly preferably 99. It is 8 mol% or more. If the average degree of saponification is too small, sufficient optical performance tends not to be obtained when a polyvinyl alcohol-based film is used as a polarizing film.
Here, the average degree of saponification in the present invention is measured according to JIS K 6726.

As the polyvinyl alcohol-based resin used in the present invention, two or more kinds having different 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 is continuously prepared by preparing a polyvinyl alcohol-based resin aqueous solution using the above-mentioned polyvinyl alcohol-based resin, discharging and casting the aqueous solution into a cast mold, forming a film by a casting method, and drying. It can be produced by the following steps, for example.
(A) A step of forming a film by a casting method.
(B) A step of heating and drying the formed film.
(C) A step of slitting the dried film and then winding it on a roll.

Here, examples of the cast type include a cast drum (drum type roll), an endless belt, and the like, but it is preferable to use a cast drum from the viewpoint of being excellent in width, length, and uniformity of film thickness.
Hereinafter, the case where the cast type is a cast drum will be described as an example.

First, the step (A) will be described.

In the step (A), first, the above-mentioned polyvinyl alcohol-based resin is washed with a solvent such as water, dehydrated with a centrifuge or the like, and wet with a polyvinyl alcohol-based resin having a water content of 50% by weight or less. It is preferably a cake. If the water content is too high, it tends to be difficult to obtain the desired aqueous solution concentration.
The polyvinyl alcohol-based resin wet cake is dissolved in warm water or hot water to prepare a polyvinyl alcohol-based resin aqueous solution.

The method for preparing the polyvinyl alcohol-based resin aqueous solution is not particularly limited, and for example, it may be prepared using a heated multi-screw extruder, and the melting can provided with the vertical circulation flow generation type stirring blade is described above. It is also possible to add a polyvinyl alcohol-based resin wet cake and blow steam into the can to dissolve and prepare an aqueous solution having a desired concentration.

In addition to the polyvinyl alcohol-based resin, the polyvinyl alcohol-based resin aqueous solution includes commonly used plastics such as glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol, and trimethylolpropane, if necessary. It is preferable to contain an agent or a nonionic, anionic, and / or cationic surfactant from the viewpoint of film-forming property.

The resin concentration of the polyvinyl alcohol-based resin aqueous solution thus obtained is preferably 15 to 60% by weight, particularly preferably 17 to 55% by weight, and even more preferably 20 to 50% by weight. If the resin concentration is too low, the drying load becomes large and the production capacity tends to decrease. If the resin concentration is too high, the viscosity tends to be too high and uniform dissolution tends to be difficult.

Next, the obtained polyvinyl alcohol-based resin aqueous solution is defoamed. Examples of the defoaming method include static defoaming and defoaming with a multi-screw extruder. The multi-screw extruder is not particularly limited as long as it is a multi-screw extruder having a vent, but usually a twin-screw extruder having a vent is used.

After the defoaming treatment, the polyvinyl alcohol-based resin aqueous solution is introduced into the T-shaped slit die in a fixed amount, discharged and cast on a rotating cast drum, and formed by a casting method.

The temperature of the polyvinyl alcohol-based resin aqueous solution at the outlet of the T-shaped slit die is preferably 80 to 100 ° C, particularly preferably 85 to 98 ° C.
If the temperature of the polyvinyl alcohol-based resin aqueous solution is too low, the flow tends to be poor, and if it is too high, foaming tends to occur.

The viscosity of the polyvinyl alcohol-based resin aqueous solution is preferably 50 to 200 Pa · s at the time of discharge, and particularly preferably 70 to 150 Pa · s.
If the viscosity of such an aqueous solution is too low, it tends to cause poor flow, and if it is too high, it tends to be difficult to spill.

The discharge rate of the polyvinyl alcohol-based resin aqueous solution discharged from the T-type slit die to the cast drum is preferably 0.5 to 5 m / min, particularly preferably 0.6 to 4 m / min, and even more preferably 0. It is 7 to 3 m / min.
If the discharge rate is too slow, the productivity tends to decrease, and if it is too fast, the salivation tends to be difficult.

The diameter of such a cast drum is preferably 2 to 5 m, particularly preferably 2.4 to 4.5 m, and even 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 low, and if it 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, still more preferably 4 m or more, and particularly preferably 5 to 6 m.
If the width of the cast drum is too small, productivity tends to decrease.

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

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

As such a cast drum, a drum in which the surface of stainless steel (SUS) containing iron as a main component is metal-plated to prevent scratches is usually used. Examples of the metal plating include chrome plating, nickel plating, zinc plating and the like, and these are used alone or in layers of two or more layers. Among these, it is preferable that the outermost surface is a chrome-plated layer in terms of ease of smoothing of the drum surface and excellent durability.

The surface roughness Ra of the cast drum used in the present invention is preferably 20 nm or less. It is more preferably 15 nm or less, still more 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 for sealing microcracks on the surface of the cast drum and a method for polishing the surface of the cast drum. In the present invention, the microcracks on the surface of the cast drum are sealed. It is preferable to polish the periphery of the sealing portion before and / or after the sealing.

In the cast drum used in the present invention, the number of microcracks having a depth of 1 μm or more existing on the surface of the cast drum is preferably 2 or less in 1 mm ² , particularly preferably 1 or less, and more preferably such micro cracks. It is a cast drum that does not contain cracks.
Further, the number of microcracks having a depth of 0.1 μm or more existing on the surface of the cast drum is preferably 10 or less, particularly preferably 7 or less, and further preferably 5 or less in 1 mm ² .
If the number of such microcracks is too large, the surface roughness of the polyvinyl alcohol-based film tends to increase.

Examples of the method for reducing the number of such microcracks include a method of sealing the microcracks on the surface of the cast drum, a method of polishing the surface of the cast drum, and a method of melting and smoothing the surface of the cas drum by etching. In the present invention, a method of sealing microcracks on the surface of the cast drum is preferable, and it is particularly preferable to polish the periphery of the sealed portion before and / or after the sealing. In the method of performing only polishing or etching, the microcracks are hard to see visually, but when the cast drum is heated and continuously operated, the size of the microcracks tends to increase and the number of microcracks tends to increase.

Hereinafter, the method of sealing the microcracks will be described in detail.
In general, microcracks are present in the plating layer, and more or less microcracks are also present on the surface of the cast mold preferably used in the present invention. Such microcracks are caused by stress of the metal plating layer, and the shape and number thereof vary depending on the thickness of the metal plating layer, plating conditions, heat treatment, chemical treatment, layer composition, etc., but the thickness of the metal plating layer. It tends to occur when the plating conditions and heat treatment conditions are non-uniform.

Examples of the method for sealing the microcracks include a method of closing with an organic and / or inorganic sealing material, a method of closing by laser annealing, a thermal spraying method such as arc spraying or frame thermal spraying, and the like. From the viewpoint of properties, it is preferable to close with an inorganic sealing material.

Examples of such an inorganic sealing material include an alkoxysilane compound, an alkoxytitanium compound, an alkoxychrome compound, and an inorganic polymer obtained by condensing a composite compound thereof by hydrolysis. Among these, a cast type material is used. From the viewpoint of adhesion, an inorganic polymer in which an alkoxysilane compound is condensed is preferable, and particularly preferably, an inorganic polymer in which an alkoxysilane compound of the following general formula (1) is condensed from the viewpoint of ease of sealing treatment at a manufacturing site. ..
R ¹ _n Si (OR ² ) _4-n ... (1)
(Here, 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 carbon atoms.)

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

The method for condensing the alkoxysilane compound is not particularly limited, and the temperature is raised by adding water to the single substance or mixture of the alkylalkoxysilane compound and stirring in the presence of a catalyst such as hydrochloric acid, acetic acid, or formic acid. , Partially hydrolyze and condense.

As a sealing method using such an inorganic sealing material, the microcrack portion formed in the cast mold is polished with a grindstone as necessary, and the inorganic sealing material is applied by a known method. The inorganic sealing material can be cured at room temperature, but if necessary, heat treatment or firing treatment can be performed to complete the curing faster. If necessary, the coating may be performed under reduced pressure or pressure, and the periphery of the sealed portion may be polished after the heat treatment or the firing treatment.

Hereinafter, the above-mentioned sealing treatment will be specifically described in detail by taking the case of using a cast drum as an example, but the present invention is not limited to such a treatment method.
The specific sealing treatment is preferably performed in the following steps [I] to [IV].
[I] A step of cleaning the surface of the cast drum with a solvent.
[II] A step of applying an inorganic sealing material.
[III] A step of firing an inorganic sealing material.
[IV] A step of wiping off the residue on the surface of the cast drum with a solvent.

Examples of the solvent used in the step [I] include acetone, ethanol, water and the like. The cleaning is preferably performed a plurality of times from the viewpoint of cleaning efficiency, and it is more preferable to use a plurality of solvents. Unless such solvent cleaning is carried out, the inorganic sealing material tends not to sufficiently penetrate into the microcracks due to the resin and oil content in the microcracks. The cleaning may be carried out by pouring a solvent while rotating the cast drum, or by stopping the rotation and intensively shower cleaning the dirty portion. Generally, the cleaning temperature is 0 to 50 ° C., and the cleaning time is 1 minute to 1 hour. The solvent is preferably naturally dried, but hot air drying using a dryer or the like may be performed.
If there are many microcracks locally, the local areas may be polished before cleaning. For polishing, a commercially available grindstone or abrasive cloth can be used.

As the coating method of step [II], known methods such as brush coating, roller brush coating, spatula coating, tampo coating, spray coating, curtain flow coating, sink coating, and dip coating are possible. Brush coating is preferable from the viewpoint of workability. 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 close the sealing portion, and if it exceeds the upper limit value, a build-up portion is generated after sealing, which is not preferable.

Step [III] is preferably carried out at 50 to 200 ° C., more preferably 1 to 60 minutes. If the temperature and time are less than the lower limit, the condensation (curing) of the inorganic sealing material tends to be insufficient, and conversely, if the temperature and time exceed the upper limit, the condensation (curing) of the inorganic sealing material goes out of control and is inorganic. Adhesion between the system sealing material and the inner wall of the microcrack is reduced.

The step [IV] is a step of wiping off the inorganic sealing material residue on the surface of the cast drum with a solvent, and examples of the solvent include acetone, ethanol, and water. For wiping, a material such as cotton that does not damage the surface of the cast drum is preferable.
If the desired surface roughness of the film cannot be obtained after the start of production, the overlay portion and the periphery of the sealing portion of the inorganic sealing material may be polished. For polishing, a commercially available grindstone or abrasive cloth can be used.

Thus, the cast drum is repaired, but if the repair effect is not perfect, the steps [I] to [IV] described above can be repeated, or a part of the steps [I] to [IV] is repeated. You may.

Further, 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 and polished as necessary in a cycle of several months to several years. The cycle is preferably about 3 months to 2 years.

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 performed by alternately contacting the front surface and the back surface of the film with a plurality of heat rolls. The surface temperature of the heat roll is usually 40 to 150 ° C, preferably 50 to 140 ° C. If the surface temperature is too low, it tends to be poorly dried, and if it is too high, it tends to be too dry, resulting in poor appearance such as swelling.
The thermal roll is, for example, a roll having a diameter of 0.2 to 2 m whose surface is hard chrome-plated or mirror-treated, and is usually dried using 2 to 30 rolls, preferably 10 to 25 rolls. preferable.

In the present invention, it is preferable to heat-treat the film after drying with a hot roll. The heat treatment temperature is preferably 60 to 150 ° C., particularly preferably 70 to 140 ° C. If the heat treatment temperature is too low, the water resistance of the polyvinyl alcohol-based film tends to decrease or causes retardation, and if it is too high, the stretchability during the production of the polarizing film tends to decrease. Examples of such a heat treatment method include a method of contacting with a high-temperature heat roll, a method of using a floating dryer, and the like.

The film that has been dried and heat-treated if necessary becomes a product (polyvinyl alcohol-based film of the present invention) through the step (C). The step (C) is a step of slitting both ends of the film and winding the film on a roll.

The method for producing a polyvinyl alcohol-based film by preparing a polyvinyl alcohol-based resin aqueous solution, casting the aqueous solution on a rotating cast drum (drum type roll), forming a film by a casting method, and drying the film will be described. However, it is also possible to cast a polyvinyl alcohol-based resin aqueous solution on a resin film or a metal belt to form a film and dry it.

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

The polyvinyl alcohol-based film of the present invention obtained by the above production method needs to have a thickness of 5 to 60 μm, and from the viewpoint of thinning, the thickness is preferably 5 to 50 μm, particularly preferably. It is 5 to 40 μm from the viewpoint of reducing retardation, and more preferably 5 to 30 μm from the viewpoint of avoiding breakage.

The polyvinyl alcohol-based film of the present invention needs to have a width of 2 m or more, particularly preferably 3 m or more from the viewpoint of increasing the area, and further preferably 4 to 6 m from the viewpoint of avoiding breakage.

The polyvinyl alcohol-based film of the present invention needs to have a length of 2 km or more, particularly preferably 3 km or more from the viewpoint of increasing the area, and further preferably 3 to 50 km from the viewpoint of transport weight.

The polyvinyl alcohol-based film of the present invention has excellent transparency, and is preferably used as a polyvinyl alcohol-based film for optics, and more preferably as a raw material for a polarizing film.

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

The polarizing film of the present invention is produced by unwinding the polyvinyl alcohol-based film from a roll, transferring it in the horizontal direction, and performing steps such as swelling, dyeing, boric acid cross-linking, stretching, washing, and drying.

The swelling step is performed before the dyeing step. In addition to being able to clean the dirt on the surface of the polyvinyl alcohol-based film by the swelling step, there is also an effect of preventing uneven dyeing by swelling the polyvinyl alcohol-based film. In the swelling step, water is usually used as the treatment liquid. If the main component of the treatment liquid is water, it may contain a small amount of an iodide compound, an additive such as a surfactant, alcohol and the like. The temperature of the swelling bath is usually about 10 to 45 ° C., and the immersion time in the swelling bath is usually about 0.1 to 10 minutes.

The dyeing step is performed by contacting the film with a liquid containing iodine or a dichroic dye. Usually, an aqueous solution of iodine-potassium iodide is used, and an iodine concentration of 0.1 to 2 g / L and a potassium iodide concentration of 1 to 100 g / L are suitable. It is practical that the dyeing time is about 30 to 500 seconds. The temperature of the treatment bath is preferably 5 to 50 ° C. In addition to the water solvent, the aqueous solution may contain a small amount of an organic solvent compatible with water.

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

In the stretching step, it is preferable to stretch 3 to 10 times, preferably 3.5 to 6 times in the uniaxial direction. At this time, a slight stretching (stretching to the extent of preventing shrinkage in the width direction or more) may be performed in the direction perpendicular to the stretching direction. The temperature at the time of stretching is preferably 40 to 170 ° C. Further, the stretching ratio may be finally set in the above range, and the stretching operation may be performed not only in one step but also in any range of the manufacturing process.

The washing step is performed by immersing the polyvinyl alcohol-based film in, for example, an aqueous solution of iodide such as water or potassium iodide, and precipitates generated on the surface of the film can be removed. When an aqueous potassium iodide solution is used, the potassium iodide concentration may be about 1 to 80 g / L. The temperature during the cleaning treatment is usually 5 to 50 ° C, preferably 10 to 45 ° C. The processing time is usually 1 to 300 seconds, preferably 10 to 240 seconds. In addition, washing with water and washing with an aqueous solution of potassium iodide may be performed in an appropriate combination.

The drying step may be carried out in the 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, more preferably 99.8% or more. If the degree of polarization is too low, it tends to be impossible to secure the contrast in the liquid crystal display.
The degree of polarization is generally the light transmittance (H ₁₁ ) measured at wavelength λ and the two polarized light in a state where two polarizing films are superposed so that their orientation directions are the same. It is calculated according to the following formula from the light transmittance (H ₁ ) measured at the wavelength λ in a state where the films are superposed so that the orientation directions are orthogonal to each other.
[(H ₁₁ −H ₁ ) / (H ₁₁ + H ₁ )] ^1/2

Further, the simple substance transmittance of the polarizing film of the present invention is preferably 42% or more. If the single transmittance is too low, it tends to be impossible to achieve high brightness of the liquid crystal display.
The simple substance transmittance is a value obtained by measuring the light transmittance of a single polarizing film using a spectrophotometer.

Thus, the polarizing film of the present invention can be obtained, and the polarizing film of the present invention is suitable for producing a polarizing plate having less color unevenness.
Hereinafter, the method for producing the polarizing plate of the present invention will be described.

The polarizing film of the present invention is formed into a polarizing plate by laminating an optically isotropic resin film as a protective film on one or both sides thereof via an adhesive. Examples of the protective film include films such as cellulose triacetate, cellulose diacetate, polycarbonate, polymethylmethacrylate, cycloolefin polymer, cycloolefin copolymer, polystyrene, polyether sulfone, polyarylene ester, poly-4-methylpentene, and polyphenylene oxide. Or you can give a sheet.

The bonding method is a known method. For example, a liquid adhesive composition is uniformly applied to a polarizing film, a protective film, or both, and then the two are bonded and pressure-bonded to heat or activate. It is done by irradiating with energy rays.

Further, for the purpose of thinning the polarizing film, a curable resin such as a urethane resin, an acrylic resin, or a urea resin is applied to one or both sides of the protective film instead of the protective film, and the polarizing film is cured to form a polarizing plate. You can also do it.

The polarizing film and polarizing plate obtained by the present invention have excellent polarization performance without display defects and color unevenness, and are excellent in portable information terminals, personal computers, televisions, projectors, signage, electronic desk computers, electronic clocks, word processors, and electronic devices. Liquid crystal displays such as paper, game machines, videos, cameras, photo albums, thermometers, audio, automobile and mechanical instruments, sunglasses, anti-glare glasses, stereoscopic glasses, wearable displays, display elements (CRT, LCD, organic) It is preferably used for reflection reduction layers for (EL, electronic paper, etc.), optical communication equipment, medical equipment, building materials, toys, and the like.

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 as long as the gist thereof is not exceeded.
In the example, "part" and "%" mean a weight standard.
Each physical property was measured as follows.

<Measurement conditions>
(1) Haze (%)
Ten test pieces of 50 mm × 50 mm were collected from the roll film and measured using a haze meter “NDH-2000” manufactured by Nippon Denshoku Kogyo Co., Ltd., and the average value of the 10 pieces was taken as the haze.

(2) Surface roughness Ra (nm) of the cast drum
A laser focus microscope VK-9700 (measurement length 0.1 mm, objective lens 50 times) manufactured by KEYENCE was used to measure three points on the cast drum, and the average value was taken as the surface roughness.

(3) Film surface roughness Ra (nm)
Using a laser focus microscope VK-9700 (measurement length: 0.1 mm, objective lens: 50 times) manufactured by KEYENCE Corporation, 10 points of the roll film were measured, and the average value was taken as the surface roughness.

(4) Number of microcracks (lines / mm ² )
Using a Keyence laser focus microscope VK-9700 (objective lens: 50x), microcracks with a depth of 1 μm or more existing in three cast drums (each area 1 mm ² ) were observed, and the average value was microcracks. The number was set.

(5) Number of linear projections on the film Using a laser focus microscope VK-X110 (objective lens: 50x) manufactured by Keyence, linear projections with a width of 1 μm or more existing at 10 locations (measurement length 1 mm) on the roll film. The number was measured, and the average value was defined as the number of linear protrusions A (lines / mm). Further, the number of linear protrusions having a height of 1 μm or more existing in 10 places (measurement range 1 mm × 1 mm) of the roll film was measured, and the average value was taken as the number of linear protrusions B (lines / mm ² ).

(6) Polarization degree (%), simple substance 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 single transmittance were measured using an automatic polarizing film measuring device (manufactured by JASCO Corporation: VAP7070).

(7) Color unevenness A polarizing film having a length of 30 cm and a width of 30 cm was sandwiched between two polarizing plates in a cross Nicol state (single transmittance: 43.5%, polarization degree: 99.9%) at an angle of 45 °. Later, using a light box with a surface illuminance of 14,000 lux, optical color unevenness is observed in the transmission mode and evaluated according to the following criteria.
(Evaluation criteria)
○: No color unevenness ×: Color unevenness

(8) Number of display defects (pieces / m ² )
A polarizing film having a length of 30 cm and a width of 30 cm was visually inspected in an environment of 15,000 lpx, and the number of defects of 100 μm or more was measured.

<Example 1>
(Repair of cast drum)
After polishing the part where the surface roughness of the cast drum (diameter 3 m, width 6 m) with chrome plating is conspicuous with a PVA grindstone (surface roughness Rz 0.1 μm), while rotating the cast drum at a low speed of 1 m / min, Acetone, ethanol, and distilled water were poured in this order for 10 minutes at room temperature (25 ° C.) for washing. After drying at room temperature (25 ° C.) for 10 minutes, a hydrolyzed condensate of methyltrimethoxysilane (80% by weight) and diphenyldimethoxysilane (20% by weight) was used as a sealing material, and this was brushed to 30 g / It applied in m ^2, and then calcined 1 hour Fuanazai at 100 ° C.. Finally, after cooling, the sealing material residue on the surface of the cast drum was wiped off with a cotton cloth soaked with acetone to complete the repair. The characteristics of the obtained cast drum are shown in Table 1.

(Manufacturing of polyvinyl alcohol film)
In a 5000 liter dissolution can, 1,000 kg of polyvinyl alcohol resin having a weight average molecular weight of 142,000 and a saponification degree of 99.8 mol%, 2,500 kg of water, 105 kg of glycerin as a plasticizer, and 0 sodium dodecyl sulfate as a surfactant. .25 kg was added, and the temperature was raised to 150 ° C. with stirring to dissolve under pressure to obtain a polyvinyl alcohol-based resin aqueous solution having a resin concentration of 25%.
Next, the polyvinyl alcohol-based resin aqueous solution was supplied to a twin-screw extruder to defoam, and then the aqueous solution temperature was set to 95 ° C., and the aqueous solution was flown from a T-shaped slit die discharge port to a cast drum at a discharge rate of 1.25 m / min. It was stretched to form a film.

Next, the obtained film was dried using a heat roll and then heat-treated using a floating dryer. Finally, both ends of the film were cut off with slits and wound up to obtain a roll-shaped polyvinyl alcohol-based film (thickness 30 μm, width 5 m, length 4 km). The characteristics of the obtained polyvinyl alcohol-based film are shown in Table 1.

(Manufacturing of polarizing film)
The obtained polyvinyl alcohol-based film was uniaxially stretched 1.7 times while being immersed in a water tank having a water temperature of 25 ° C. Next, it was uniaxially stretched 1.6 times while being immersed in an aqueous solution of iodine (0.5 g / L) and potassium iodide (potassium iodide) at 28 ° C. Next, it was uniaxially stretched 2.1 times while being immersed in an aqueous solution of boric acid 40 g / L and potassium iodide 30 g / L at 55 ° C. Finally, it was washed with an aqueous potassium iodide solution and dried to obtain a polarizing film having a total draw ratio of 5.8 times. The characteristics of the obtained polarizing film are shown in Table 2.

<Example 2>
A polyvinyl alcohol-based film and a polarizing film were produced in the same manner as in Example 1 except that the holes were sealed without polishing in the repair of the cast drum. Table 1 shows the characteristics of the obtained polyvinyl alcohol-based film, and Table 2 shows the characteristics of the polarizing film.

<Example 3>
The polyvinyl alcohol-based film and the polarizing film were prepared in the same manner as in Example 1 except that the discharge rate of the polyvinyl alcohol-based resin aqueous solution was changed to 2.5 m / min and the thickness of the polyvinyl alcohol-based film was set to 60 μm in Example 1. Manufactured. Table 1 shows the characteristics of the obtained polyvinyl alcohol-based film, and Table 2 shows the characteristics of the polarizing film.

<Comparative example 1>
A polyvinyl alcohol-based film and a polarizing film were produced in the same manner as in Example 1 except that the cast drum was not repaired. Table 1 shows the characteristics of the obtained polyvinyl alcohol-based film, and Table 2 shows the characteristics of the polarizing film.

The polyvinyl alcohol-based films of Examples 1 to 3 have a good haze of 0.2% or less, whereas the polyvinyl alcohol-based films of Comparative Example 1 have a high haze.
Then, it can be seen that the polarizing characteristics of the polarizing film obtained from each polyvinyl alcohol-based film are better in Examples 1 to 3 than in Comparative Example 1.

The polarizing film and polarizing plate obtained by the present invention have excellent polarization performance without display defects and color unevenness, and are excellent in portable information terminals, personal computers, televisions, projectors, signage, electronic desk computers, electronic clocks, word processors, and electronic devices. Liquid crystal displays such as paper, game machines, videos, cameras, photo albums, thermometers, audio, automobile and mechanical instruments, sunglasses, anti-glare glasses, stereoscopic glasses, wearable displays, display elements (CRT, LCD, organic) It is preferably used for reflection reduction layers for (EL, electronic paper, etc.), optical communication equipment, medical equipment, building materials, toys, and the like.

Claims (6)

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, having a haze of 0.2% or less, and being contained in any 1 mm ^{2 of the} surface of the polyvinyl alcohol-based film. A polyvinyl alcohol-based film characterized in that the number of linear protrusions having a height of 1 μm or more is one or less. The polyvinyl alcohol-based film according to claim 1, wherein the surface roughness Ra of the polyvinyl alcohol-based film is 20 nm or less. A claim that, when a virtual line having a length of 1 mm is provided at an arbitrary position on the surface of a polyvinyl alcohol-based film, the number of linear protrusions having a width of 1 μm or more intersecting the virtual line is two or less. The polyvinyl alcohol-based film according to 1 or 2. The polyvinyl alcohol-based film according to any one of claims 1 to 3, wherein the film has a thickness of 5 to 30 μm. A polarizing film comprising the polyvinyl alcohol-based film according to any one of claims 1 to 4 . This is a method for producing a polyvinyl alcohol-based film obtained by discharging and salivating an aqueous solution of a polyvinyl alcohol-based resin into a cast mold to form a film and continuously drying the film. A micro having a depth of 1 μm or more existing on the surface of the cast mold. A method for producing a polyvinyl alcohol-based film, which comprises using a cast type having ^two or less cracks in 1 mm ² .