JP6677081B2 - Laminate, method for producing polyvinyl alcohol-based film for producing polarizing film, method for producing polarizing film, and method for storing or transporting polyvinyl alcohol-based film for producing polarizing film - Google Patents

Description

  The present invention relates to a laminate in which a protective film is adhered to at least one surface of a polyvinyl alcohol-based film for producing a polarizing film, and more particularly to a polyvinyl alcohol-based film for producing a polarizing film which is hardly scratched or stained, has excellent appearance, and has no optical unevenness. The present invention relates to a polyvinyl alcohol-based film which is an alcohol-based film and is useful as a raw film for obtaining a thin polarizing film.

  Conventionally, a polyvinyl alcohol-based film is produced by dissolving a polyvinyl alcohol-based resin in a solvent such as water, forming a film by a solution casting method (casting method), and then drying the obtained film with a hot roll or the like. Have been. The polyvinyl alcohol-based film thus obtained is used in many applications as a film having excellent transparency and dyeability, and one of its useful applications is a polarizing film.

  The polarizing film is a film obtained by dyeing the above polyvinyl alcohol-based film with a dichroic dye such as iodine, and is used as a basic component of a liquid crystal display. In recent years, it has been used for displays requiring high quality and high reliability, especially for large-screen liquid crystal televisions and the like, and there has been a demand for in-plane uniformity of the degree of polarization and reduction of color unevenness. Further, as the thickness of the display is reduced, the thickness of the polarizing film is also required to be reduced.

  In order to meet such demands, it is necessary to improve the quality and physical properties of the polyvinyl alcohol-based film itself, and to further reduce the thickness, but the form of storage, transportation, and transportation of the film is also important. If the surface of the polyvinyl alcohol-based film is scratched or stained during storage, transportation, and transportation, unevenness in the degree of polarization and unevenness in color will occur in the obtained polarizing film. In addition, when blocking occurs between the films, it is difficult to unwind the film from the roll. Furthermore, the moisture content of the film near the outermost layer of the roll fluctuates greatly due to moisture, and the distribution of the in-plane moisture content is likely to occur. The resulting polarizing film tends to have unevenness in the degree of polarization and unevenness in color.

  In order to solve such a problem, there has been proposed a method of packaging and storing or transporting the film with a water vapor barrier resin packaging film and a packaging film made of an aluminum material (for example, see Patent Document 1). Further, there has been proposed a package in which an end of a packaging material is pushed into the inside of a core (for example, see Patent Document 2). Further, a laminate of a polyvinyl alcohol-based film and a thermoplastic film has been proposed (for example, see Patent Document 3).

JP 2005-306483 A JP 2013-227073 A WO2014 / 084154

However, even with these disclosed techniques, it has been insufficient to prevent the polyvinyl alcohol-based film from being damaged, stained, deformed, and changed in optical performance after storage, transportation, and transportation. Scratches and dirt cannot be avoided even if the entire roll is wrapped, and even if the wrapping film blocks moisture that enters from the outside, the transfer of moisture occurs due to the contact between the films, distributing the deformation and optical performance. Had occurred. Such a phenomenon is more likely to occur as the polyvinyl alcohol-based film becomes wider and longer, and becomes more conspicuous as the polyvinyl alcohol-based film becomes thinner.
Patent Document 3 is a laminate used in a polarizing film manufacturing process, and a protective film is used to prevent breakage during stretching. It is not intended to prevent deterioration such as scratches, dirt, deformation and changes in optical performance. Therefore, the properties required for the protective film are different, and the adhesive strength is preferably as low as 1 mN / 15 mm or less.

  In view of the above, the present invention provides a laminate capable of preventing deterioration such as scratching, contamination, deformation, change in optical performance, and the like that occur during storage, transportation, and transportation of a polyvinyl alcohol-based film under such a background. Further, a polyvinyl alcohol-based film for producing a polarizing film having excellent in-plane uniformity obtained from such a laminate, a polarizing film, and storage or transportation of the polyvinyl alcohol-based film for producing a polarizing film using such a laminate. It is intended to provide a method.

  However, the present inventors have conducted intensive studies in view of such circumstances, and as a result, at least one surface of a polyvinyl alcohol-based film for manufacturing a polarizing film, by forming a laminate with a specific protective film attached, storage, transport, and, Since it is possible to prevent deterioration such as scratches, contamination, deformation, and changes in optical performance that occur during transportation, a polyvinyl alcohol-based film having excellent in-plane uniformity can be obtained. It has been found that the resulting polarizing film has a high polarizing performance and has little color unevenness, and has completed the present invention.

That is, the gist of the present invention is a laminate in which a protective film is adhered to at least one surface of a polyvinyl alcohol-based film for producing a polarizing film, wherein the thickness of the polyvinyl alcohol-based film is 60 μm or less, and the polyvinyl alcohol-based film is protected. and the film are stuck by the adhesive force of 1~30mN / 20mm, the contact angle of the side of the film surface in contact with the polarizing film producing polyvinyl alcohol-based film of the protective film, characterized in der Rukoto than 80 ° It is a laminate.

Further, the present invention provides a method for producing a polyvinyl alcohol-based film for producing a polarizing film obtained from the laminate, a method for producing a polarizing film, and a method for storing or transporting a polyvinyl alcohol-based film for producing a polarizing film using such a laminate. Is also provided.

The laminate of the present invention can prevent the deterioration such as scratching, contamination, deformation, change in optical performance, etc., occurring during storage, transportation, and transportation of a polyvinyl alcohol-based film, and a film when used in a roll form. Can be prevented from blocking.
Furthermore, since the quality of the roll film in the width direction and the longitudinal direction (from the outer periphery to the core) can be kept constant, a polyvinyl alcohol-based film having excellent in-plane uniformity can be obtained. Is a polarizing film having high polarization performance and less color unevenness.

It is a schematic diagram explaining the bonding process of a protective film.

Hereinafter, the present invention will be described specifically.
The laminate of the present invention is a laminate in which a protective film is adhered to at least one surface of a polyvinyl alcohol-based film for producing a polarizing film, and the thickness of the polyvinyl alcohol-based film is 60 μm or less, and the polyvinyl alcohol-based film is protected. and the film are stuck by the adhesive force of 1~30mN / 20mm, the contact angle of the side of the film surface in contact with the polarizing film producing polyvinyl alcohol-based film of the protective film is an der shall at least 80 °.
In the present invention, the function and effect of the present invention are obtained by using the above protective film for the purpose of preventing deterioration of the polyvinyl alcohol-based film (prevention of damage during storage and transportation).

  The polyvinyl alcohol-based film for producing a polarizing film used in the present invention is not particularly limited, and is produced by a method described later.

  The thickness of such a polyvinyl alcohol-based film needs to be 60 μm or less, and is preferably 30 μm or less from the viewpoint of thinning the polarizing film, particularly preferably 20 μm or less from the viewpoint of further thinning, and the point of avoiding breakage. And more preferably 4 to 20 μm.

  The width of such a polyvinyl alcohol-based film is preferably 2 m or more from the viewpoint of increasing the area, from the viewpoint of further increasing the area, particularly preferably 3 m or more, more preferably 4 m or more, from the viewpoint of avoiding breakage. Particularly preferably, it is 4 to 6 m.

  The length of the polyvinyl alcohol-based film is preferably 3 km or more from the viewpoint of increasing the area, particularly preferably 4 km or more from the viewpoint of further increasing the area, and more preferably 4 km or more from the viewpoint of the transport weight. ５０50 km.

  The protective film used in the present invention is preferably attached to both surfaces of a polyvinyl alcohol-based film from the viewpoint of preventing deterioration. The method of sticking is not particularly limited, and a method such as ordinary lamination or vacuum lamination can be used.

The protective film used in the present invention needs to have an adhesive strength to a polyvinyl alcohol-based film of 1 to 30 mN / 20 mm, preferably 5 to 29 mN / 20 mm, more preferably 8 to 28 mN / 20 mm, and particularly preferably 8 to 28 mN / 20 mm. Preferably it is 10 to 27 mN / 20 mm.
If the adhesive strength is less than 1 mN / 20 mm, the protective film is peeled off from the polyvinyl alcohol-based film during storage, transportation, and transportation, and rubbing is generated. Therefore, the object of the present invention cannot be achieved. Conversely, if it exceeds 30 mN / 20 mm, it is difficult to peel and remove the protective film, and the object of the present invention cannot be achieved.

Examples of a method of adjusting the adhesive force include a method of forming an adhesive layer on a base film of a protective film, a method of physically modifying the surface of a polyvinyl alcohol-based film, and the like. A method of forming an adhesive layer on a film base film is preferred.
Examples of such an adhesive layer include acrylic, rubber, silicone, urethane, polyester, and ethylene vinyl acetate.

  Further, the adhesive force preferably has a rate of change of not more than 2 times, particularly preferably not more than 1.5 times, more preferably not more than 1.2 times when subjected to a heating test at 80 ° C. for 30 minutes. . If the rate of change is too large, peeling and removal of the protective film tends to be difficult after storage, transportation, and transportation.

Furthermore, the contact angle of the film surface of the protective film on the side in contact with the polyvinyl alcohol-based film for polarizing film production needs to be 80 ° or more, particularly preferably 90 ° or more, and more preferably 95 ° or more. If the contact angle is too small, the components contained in the polyvinyl alcohol-based film tend to migrate to the protective film, and the polyvinyl alcohol-based film tends to be stained and the optical performance tends to change. Further, the upper limit of the contact angle is usually 110 °.
In addition, examples of such a migration component include water, a plasticizer, and a surfactant in a polyvinyl alcohol-based film. In particular, when moisture migrates to the protective film, the in-plane retardation tends to increase.

  As the protective film used in the present invention, polyethylene, polypropylene, polyethylene terephthalate, polyvinyl chloride, polystyrene, polymethyl methacrylate, polycarbonate and the like, among them, in terms of heat resistance and rigidity, polypropylene, polyethylene, polyethylene Terephthalate is preferred, and polypropylene is particularly preferred in terms of inexpensiveness, and more preferred is biaxially oriented polypropylene in terms of increasing the area.

The thickness of the protective film used in the present invention is preferably from 10 to 100 μm, particularly preferably from 20 to 90 μm, and further preferably from 30 to 70 μm.
If the thickness of such a protective film is too thin, the effect of preventing scratches on the polyvinyl alcohol-based film tends to decrease. If the thickness is too large, the roll diameter of the laminate as a roll increases, and transportability decreases. There is a tendency.

  The width of the protective film used in the present invention is not particularly limited as long as it is the same as the width of the polyvinyl alcohol-based film or is wider than the width of the polyvinyl alcohol-based film. It is preferable that, from the viewpoint of further enlargement of the area, particularly preferably 3 m or more, more preferably 4 m or more, the deterioration such as scratching, contamination, deformation, change in optical performance, etc. which occurs during storage, transportation, and transportation is reduced. From the viewpoint of prevention, it is particularly preferably 4 to 5 m.

  The surface of the protective film in the present invention preferably has a surface roughness (Ra) of 100 nm or less, particularly preferably 70 nm or less, more preferably 50 nm, on the side of the film in contact with the polyvinyl alcohol-based film for polarizing film production. It is as follows. If the surface roughness (Ra) of the surface in contact with the polyvinyl alcohol-based film is too large, the polyvinyl alcohol-based film tends to have surface roughness.

  Further, the surface roughness (Ra) of the opposite surface (the film surface not in contact with the polyvinyl alcohol-based film for manufacturing a polarizing film) is preferably 100 nm or more, particularly preferably 200 nm or more, more preferably 300 nm or more. Particularly preferred is a matte tone. If the surface roughness (Ra) of the opposite surface is too small, the laminated body tends to cause blocking.

Hereinafter, the polyvinyl alcohol-based film for producing a polarizing film used in the present invention will be described.
The polyvinyl alcohol-based film of the present invention is obtained by dripping an aqueous solution of a polyvinyl alcohol-based resin into a cast mold to form a film, and continuously drying the film using a hot roll.

  As the polyvinyl alcohol resin, an unmodified polyvinyl alcohol resin, that is, a resin produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate is usually used. If necessary, a resin obtained by saponifying a copolymer of vinyl acetate and a small amount (for example, 10 mol% or less, preferably 5 mol% or less) of a copolymerizable component with vinyl acetate may be used. it can. Examples of the component copolymerizable with vinyl acetate include unsaturated carboxylic acids (for example, including salts, esters, amides, nitriles, etc.) and olefins having 2 to 30 carbon atoms (for example, ethylene, propylene, n-butene). , Isobutene, etc.), vinyl ethers, unsaturated sulfonates and the like. Further, a modified polyvinyl alcohol-based resin obtained by chemically modifying a 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 a side chain can also be used. Examples of the polyvinyl alcohol-based resin having a 1,2-diol structure in the side chain include (i) a method of saponifying a copolymer of vinyl acetate and 3,4-diacetoxy-1-butene, and (ii) acetic acid. A method of saponifying and decarboxylating a copolymer of vinyl and vinylelene carbonate, and (iii) saponifying and decomposing a copolymer of vinyl acetate and 2,2-dialkyl-4-vinyl-1,3-dioxolane. It is obtained by a method of ketalization, (iv) a method of saponifying a copolymer of vinyl acetate and glycerin monoallyl ether, and the like.

  When the above-mentioned modified polyvinyl alcohol-based resin is used, the amount of modification is usually 10 mol% or less, preferably 8 mol% or less.

  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 further 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 using a polyvinyl alcohol-based resin as an optical film, and if too large, it becomes difficult to stretch when using a polyvinyl alcohol-based resin film as a polarizing film. However, industrial production is difficult and not preferable. The weight average molecular weight of the polyvinyl alcohol resin is a weight average molecular weight measured by a 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, more preferably 99.5 mol% or more, and particularly preferably 99. 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 the polarizing film.
Here, the average saponification degree 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 types having different denatured species, denaturation amount, polymerization degree, average saponification degree and the like may be used in combination.

The laminate of the present invention is manufactured continuously by preparing a polyvinyl alcohol-based resin aqueous solution using the above-described polyvinyl alcohol-based resin, discharging and casting the aqueous solution into a cast mold, forming a film, and drying. It is manufactured by bonding a protective film to a polyvinyl alcohol-based film. For example, it is manufactured by the following steps.
(A) Step of forming a film by a casting method (B) Step of heating and drying the formed film (C) Step of bonding a protective film to the dried polyvinyl alcohol-based film (D) After slitting both ends, winding it into a roll

Hereinafter, the step (A) will be described.
In the step (A), first, the above-mentioned polyvinyl alcohol-based resin is washed with water, and dehydrated using a centrifuge or the like to obtain a polyvinyl alcohol-based resin wet cake having a water content of 50% by weight or less. Is preferred. If the water content is too large, it tends to be difficult to obtain a desired aqueous solution concentration.
The polyvinyl alcohol resin wet cake is dissolved in warm water or hot water to prepare an aqueous solution of the polyvinyl alcohol resin.

  The method for preparing the aqueous polyvinyl alcohol-based resin solution is not particularly limited, and may be prepared, for example, using a heated multi-screw extruder. The obtained polyvinyl alcohol-based resin wet cake is charged, and steam is blown into the can to prepare an aqueous solution having a desired concentration and dissolution.

  Polyvinyl alcohol-based resin aqueous solutions include, in addition to polyvinyl alcohol-based resins, commonly used plasticizers such as glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol, and trimethylolpropane, and nonionic It is preferable to contain an anionic and / or cationic surfactant from the viewpoint of the film forming property of the polyvinyl alcohol-based film.

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

  Next, the obtained polyvinyl alcohol-based resin aqueous solution is subjected to a defoaming treatment. Examples of the defoaming method include methods such as static deaeration and defoaming with a vented multi-screw extruder. As the multi-screw extruder having a vent, a twin-screw extruder having a vent is usually used.

  After the defoaming treatment, the polyvinyl alcohol-based resin aqueous solution is introduced into a T-shaped slit die at a fixed amount, discharged and cast into a cast mold, and formed into a film by a cast method.

  Examples of the cast type include a cast drum (drum type roll) and a cast belt. In the present invention, it is preferable to use a cast drum in view of widening, lengthening, and uniformity of the film thickness.

The width of such a cast drum is preferably at least 4 m, particularly preferably at least 4.5 m, more preferably at least 5 m, particularly preferably 5 to 6 m.
If the width of the cast drum is too small, the productivity tends to decrease.

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

The drying of the film formed by the cast mold is performed by alternately bringing the front and back surfaces of the film into contact with a plurality of heat rolls. The surface temperature of the hot roll is usually 40 to 150C, preferably 50 to 140C. If the surface temperature is too low, drying tends to be poor, while if too high, the drying tends to be too dry, resulting in poor appearance such as undulation.
The heat roll is, for example, a roll having a diameter of 0.2 to 2 m, the surface of which is hard chromium-plated or mirror-finished, and is usually dried using 2 to 30 rolls, preferably 10 to 25 rolls. preferable.

  In the present invention, it is preferable to perform a heat treatment on the film after drying with the hot roll. The heat treatment temperature is preferably from 60 to 150 ° C, particularly preferably from 70 to 140 ° C. If the heat treatment temperature is too low, the water resistance of the polyvinyl alcohol-based film tends to be insufficient or the retardation tends to be blurred. If the heat treatment temperature 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 using a floating dryer, a method of once cooling to about normal temperature after drying, and then contacting a high-temperature heat roll again, or a method of irradiating near-infrared light to both surfaces of a film using an infrared lamp. Among these, a method using a floating dryer is preferable because heat treatment can be performed uniformly.

  Next, the step (C) will be described. Step (C) is a step of bonding a protective film to a polyvinyl alcohol-based film that has been dried and, if necessary, heat-treated, to produce a laminate. Hereinafter, a case of a laminate in which protective films are attached to both surfaces of a polyvinyl alcohol-based film will be described as an example.

Bonding of the protective film is performed by, for example, a method in which a protective film unwound from above and below is closely adhered to a polyvinyl alcohol-based film conveyed in a horizontal direction by upper and lower rolls as shown in FIG. Is preferred. In such a case, the upper and lower rolls may be heated.
Thus, the laminate of the present invention is manufactured. Such a laminate can be made into a roll-like laminate by the following step (D).

  The step (D) is a step of slitting the protective films at both ends of the laminate and winding the same into a roll.

  The core tube for winding the polyvinyl alcohol-based film is a cylindrical tube, and a hollow tube is preferable in terms of weight reduction. The width of the core tube is preferably longer than the above-mentioned film width.

  The material of the core tube is arbitrary such as metal, plastic or paper. Examples of the metal include carbon steel, high tensile steel, stainless steel, aluminum alloys such as aluminum and duralumin, copper, brass, and bronze. These core tubes may be laminated with soft polyvinyl chloride or low-density polyethylene, or plated with nickel, chromium, zinc, tin or the like. Examples of the plastic core tube include hard polyvinyl chloride, polypropylene, high density polyethylene, ultra high molecular weight polyethylene, polycarbonate, polyester and the like.

The outer diameter of the core tube is preferably at least 7.5 cm, particularly preferably at least 8.5 cm. If the outer diameter of the core tube is too large, the film may be wrinkled. It is preferable that the length of the core tube is longer than the width of the film, and it is particularly preferable that the length of the core tube projects from the end of the film roll by 10 cm or more.
By providing brackets at both ends of the projecting portion or placing both ends of the projecting portion on a gantry or the like, the film roll is floated in the air without contacting the ground or another film roll, etc. The load of the roll is prevented from being applied to the entire roll, and blocking and deterioration between films can be prevented.
The wall thickness of the core tube is preferably 1.5 to 20 mm, particularly preferably 2 to 15 mm, and more preferably 3 to 10 mm.

Thus, a roll-shaped laminate is obtained.
The obtained roll-shaped laminate can be packaged by wrapping the roll with a water vapor barrier film.

Such a water vapor barrier film is not particularly limited, but a film having a moisture permeability measured according to JIS Z 0208 of 1 g / m ² · day or less can be used. Specific examples include a single-layer film of high-density polyethylene, polypropylene, polyester, polyvinylidene chloride-coated polypropylene, glass-deposited polyester, or the like, or a laminated film of these, or a laminated film with split fabric, paper, or nonwoven fabric. Examples of the laminated film include a laminated film of glass-deposited polyester and polyethylene, a laminated film of polyvinylidene chloride-coated polypropylene and polyethylene, and the like.

  As such a water vapor barrier film, it is also preferable to use a laminate in which a moisture absorption film is laminated on the water vapor barrier film in terms of controlling the humidity in the package. As such a moisture control film, an inorganic desiccant such as calcium chloride, silica gel, or zeolite is dispersed in a moldable material such as natural celluloses, synthetic celluloses, glass cloth, and nonwoven fabric, impregnated, coated and dried to form a moisture absorbing layer. And those obtained by sandwiching these inorganic desiccants between thermoplastic resin films such as polyester films, polyethylene films, polypropylene films, and polytetrafluoroethylene films. When such a laminate is used, packaging is performed such that the moisture-absorbing film side is inside the package.

  Before packaging the roll with the water vapor barrier film, it is also possible to wind the roll with an interior film also serving as a protective film. By winding the interior film, dirt and scratches on the roll can be prevented. Such an interior film is not particularly limited, and an inexpensive polyethylene film is suitable.

  The roll may be wrapped with a water vapor barrier film and then further wrapped with a wrapping film made of an aluminum material. Examples of such a film include aluminum foil, a laminated film of an aluminum foil and a moisture-resistant plastic film (for example, a laminated film of an aluminum foil and a polyethylene film), and a laminated film of an aluminum-deposited film and a moisture-resistant plastic film (for example, an aluminum-deposited polyester film and a polyethylene film). Laminated film), a laminated film of an alumina vapor-deposited film and a moisture-resistant plastic film (for example, a laminated film of an alumina vapor-deposited polyester film and a polyethylene film), and the like. Film and polyolefin film laminated film are useful, especially stretched polypropylene film / polyethylene film / aluminum Laminated films made of configuration of the beam foil / polyethylene film, laminated film or the like made of structure of oriented polypropylene film / low density polyethylene film / aluminum foil is useful.

  The package of the laminate thus obtained can be transported to a shipping destination after storage or transportation, and can be used for manufacturing a polarizing film after unpacking and peeling of the protective film.

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

  The polarizing film of the present invention is manufactured by unwinding the above polyvinyl alcohol-based film from a roll, transporting the film in the horizontal direction, and performing steps such as swelling, dyeing, boric acid crosslinking, stretching, washing, and drying.

  The swelling step is performed before the dyeing step. By the swelling step, dirt on the surface of the polyvinyl alcohol-based film can be washed, and also, the swelling of the polyvinyl alcohol-based film has an effect of preventing uneven dyeing and the like. In the swelling step, water is usually used as a treatment liquid. When 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 ° C, and the immersion time in the swelling bath is usually about 0.1 to 10 minutes.

  The dyeing step is performed by bringing a liquid containing iodine or a dichroic dye into contact with the film. Usually, an aqueous solution of iodine-potassium iodide is used, and the concentration of iodine is suitably 0.1 to 2 g / L, and the concentration of potassium iodide is suitably 1 to 100 g / L. The dyeing time is practically about 30 to 500 seconds. The temperature of the treatment bath is preferably 5 to 50C. 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 step is performed using a boron compound such as boric acid or borax. The boron compound is used in the form of an aqueous solution or a mixed solution of water and an organic solvent at a concentration of about 10 to 100 g / L, and it is preferable to coexist potassium iodide in the liquid from the viewpoint of stabilizing polarization performance. The temperature during the treatment is preferably about 30 to 70 ° C., and the treatment time is preferably about 0.1 to 20 minutes. If necessary, a stretching operation may be performed during the treatment.

  In the stretching step, the film is preferably stretched 3 to 10 times, preferably 3.5 to 6 times in the uniaxial direction. At this time, a slight stretching (to the extent that shrinkage in the width direction is prevented, or more) may be performed in the direction perpendicular to the stretching direction. The temperature during stretching is preferably from 30 to 170C. Further, the stretching ratio may be finally set in the above range, and the stretching operation may be performed not only in one stage but also in any range of the manufacturing process.

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

  The drying step may be performed at 40 to 80 ° C. in the atmosphere for 1 to 10 minutes.

The polarization degree of the polarizing film thus obtained is preferably at least 99.5%, particularly preferably at least 99.8%. If the degree of polarization is too low, the contrast in the liquid crystal display tends to decrease. In general, the degree of polarization is determined by measuring the light transmittance (H ₁₁ ) measured at a wavelength λ in a state where two polarizing films are superposed so that their orientation directions are the same, and In a state where the films are superposed so that the orientation directions are orthogonal to each other, it is calculated from the light transmittance (H ₁ ) measured at the wavelength λ according to the following equation.
_{[(H 11 -H 1) / (} H 11 + H 1) ] ^1/2

Further, the single transmittance of the polarizing film of the present invention is preferably 43% or more. If the single transmittance is too low, it tends to be impossible to achieve high brightness of the liquid crystal display.
The single transmittance is a value obtained by measuring the light transmittance of a single polarizing film using a spectrophotometer.

  The polarizing film of the present invention thus obtained can be formed into a polarizing plate by laminating and adhering an optically isotropic polymer film or sheet as a protective film on one or both surfaces thereof. Examples of the protective film include films of cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, cycloolefin polymer, cycloolefin copolymer, polystyrene, polyether sulfone, polyarylene ester, poly-4-methylpentene, polyphenylene oxide, and the like. Or a sheet.

  The bonding method is performed by a known method.For example, after a liquid adhesive composition is uniformly applied to a polarizing film, a protective film, or both, the two are bonded and pressed, and heated or activated. This is performed by performing energy ray irradiation.

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

  The polarizing plate obtained by the present invention is excellent in polarization performance without optical unevenness, so that a portable information terminal, a personal computer, a television, a projector, a signage, an electronic desk calculator, an electronic clock, a word processor, an electronic paper, a game machine, Liquid crystal display devices such as videos, cameras, photo albums, thermometers, audio, instruments for automobiles and machinery, sunglasses, anti-glare glasses, stereoscopic glasses, wearable displays, display elements (CRT, LCD, organic EL, electronic paper, etc.) ), Optical communication equipment, medical equipment, building materials, toys and the like.

Hereinafter, the present invention will be specifically described with reference to examples.
In the examples, “parts” and “%” are based on weight unless otherwise specified.

<Measurement conditions>
(1) Adhesive strength (mN / 20mm)
Five test pieces having a length of 200 mm and a width of 20 mm were cut out from the obtained laminate, and an autograph (AG-X manufactured by Shimadzu, load cell 50N, distance between chucks 25 mm, tensile strength was measured according to JIS K 6854-3: 1999). Using a speed of 100 mm / min), a T-peel test was performed on the polyvinyl alcohol-based film and the protective film in an environment of 23 ° C. and 50% RH, and the average value of the five sheets was regarded as the adhesive strength (mN / 20 mm).

(2) In-plane retardation of polyvinyl alcohol-based film A test piece of a polyvinyl alcohol-based film having a length of 30 cm and a width of 30 cm was cut out, and two polarizing plates in a crossed Nicols state (unit transmittance: 43.5%, degree of polarization: 99) .9%), the in-plane phase difference was observed in a transmission mode using a light box having a surface illuminance of 14,000 lx in a dark room, and evaluated according to the following criteria.
(Evaluation criteria)
・ ・ ・: No shading can be seen in the plane △: Shading can be seen in a part of the plane ×: Shading can be confirmed over the entire surface

(3) Degree of polarization of polarizing film (%), single transmittance (%)
A test piece having a length of 4 cm and a width of 4 cm from the front end / center / end in the length direction of the obtained polarizing film (the front end and the end were respectively located 10 cm from the front end and the end of the film). Are cut out, and the degree of polarization and the single transmittance are measured using an automatic polarizing film measuring device (manufactured by JASCO Corporation: VAP-7070). And

(4) Color Unevenness of Polarizing Film A test piece having a length of 30 cm and a width of 13 cm was cut out from the obtained polarizing film, and two polarizing plates in a crossed Nicols state (unit transmittance: 43.5%, degree of polarization: 99.9) %), And color unevenness was observed in a transmission mode using a light box having a surface illuminance of 14000 lx in a dark room, and evaluated according to the following criteria.
(Evaluation criteria)
○: no color unevenness Δ: slight color unevenness ×: color unevenness

<Example 1>
(Production of laminate roll A)
1000 parts of a polyvinyl alcohol resin having a weight average molecular weight of 142,000 and a saponification degree of 99.8 mol%, 2,500 parts of water, and 105 parts of glycerin as a plasticizer were added, and the temperature was raised to 150 ° C. with stirring, and the resin concentration was reduced to 25% The adjustment was performed to obtain a uniformly dissolved polyvinyl alcohol-based resin aqueous solution. Next, the polyvinyl alcohol-based resin aqueous solution was supplied to a twin-screw extruder to remove bubbles, and then discharged and cast from a T-shaped slit die discharge port onto a cast drum to form a film. Next, the obtained film was dried with a plurality of heat rolls and heat-treated using a floating dryer to obtain a polyvinyl alcohol-based film having a thickness of 10 μm and a width of 5 m. Inspection of the in-plane retardation of the polyvinyl alcohol-based film revealed no shading in the plane.
Next, a protective film A (“Taiko FSA 010C” manufactured by Futamura Chemical Co., Ltd., contact angle: 97 °) having biaxially oriented polypropylene as a base material is attached to both sides of the polyvinyl alcohol-based film with a load of 2 kg using upper and lower rollers. Together, a laminate A was obtained. The thickness of the used protective film was 30 μm, the width was 5 m, and the adhesive strength with the polyvinyl alcohol-based film was 12 mN / 20 mm.
Next, the both ends are cut off by slits so that the laminate A has a width of 4.8 m, and finally, the laminate A is wound around an aluminum core tube having an outer diameter of 17 cmΦ to form a roll of a laminate having a length of 5 km (A). Got

(Manufacture of package A)
First, two disk-shaped polystyrene foams (18 cmφ through-hole) having a size of 60 cmφ and a thickness of 4 mm were prepared as protection pads, and the protection pads were passed through a core tube and attached to both ends of the roll. Next, a laminated film of an aluminum-evaporated polyester film (a polyethylene terephthalate film on which aluminum was vapor-deposited at 500 ° and a thickness of 12 μm) and a polyethylene film (a thickness of 25 μm) was prepared as a steam barrier film, and obtained at 23 ° C. and 50% RH. The water vapor barrier film was double-wound around the roll (A) thus obtained, and an excess portion in the width direction was wound around a core tube with a tape and sealed to obtain a package (A).

(Storage, transportation, and transportation)
The protruding part of the core tube is placed on a gantry, and the obtained package (A) is suspended in the air without grounding, stored at 25 ° C. and 50% RH for 10 days, and then transported together with the gantry to a truck. Shipped to Korea by sea. After transport, the package A was unpacked and the roll state was confirmed. There was no blocking or winding deviation. The protective films A on both sides were peeled off from the laminate around the roll, and the appearance of the polyvinyl alcohol-based film was inspected. However, no deterioration such as scratches, dirt, and deformation was observed. When the in-plane retardation of the polyvinyl alcohol-based film was measured, no difference from that immediately after the production could be confirmed.

(Production of polarizing film A)
The protective films on both sides were peeled off from the laminated body A after transportation, a test piece of a polyvinyl alcohol-based film having a width (TD direction) of 30 cm × length (MD direction) of 30 cm was cut out, and immersed in a water bath at a water temperature of 25 ° C. Stretched 0.7 times. Next, it was immersed in an aqueous solution of 0.9 g / L of iodine and 30 g / L of potassium iodide at 28 ° C., stretched 1.6 times while dyeing, and continuously 25 g / L of boric acid and potassium iodide. It was immersed in an aqueous solution (55 ° C.) having a composition of 30 g / L and uniaxially stretched 1.9 times to perform boric acid treatment. Thereafter, the resultant was washed with an aqueous solution of potassium iodide and dried to obtain a polarizing film A having a total stretching ratio of 5.2. Table 2 shows the polarization characteristics of the obtained polarizing film A.

<Example 2>
Example 1 except that “Taiko FSA 010M” (thickness 30 μm, width 5 m, adhesive strength with polyvinyl alcohol-based film 10 mN / 20 mm, contact angle 98 °, opposite matte tone) manufactured by Futamura Chemical Co., Ltd. was used as the protective film. Production of a roll, production of a package, storage, transportation, and transportation, and production of a polarizing film were performed in the same manner as in the above. The results are shown in Tables 1 and 2.

<Example 3>
Example 1 except that "Taiko FSA 100M" manufactured by Futamura Chemical Co., Ltd. (thickness 30 m, width 5 m, adhesive strength with polyvinyl alcohol-based film 27 mN / 20 mm, contact angle 94 [deg.], Opposite matte tone) was used as a protective film. Production of a roll, production of a package, storage, transportation, and transportation, and production of a polarizing film were performed in the same manner as in the above. The results are shown in Tables 1 and 2.

<Example 4>
As a protective film, “PAC3-3-30” (manufactured by San-A Kaken Co., Ltd.) (base polyethylene, thickness 30 μm, width 1.4 m, adhesive strength with polyvinyl alcohol-based film 7 mN / 20 mm, contact angle 97 °) was used. In the same manner as in Example 1 except that both ends were cut off with slits so that the laminated body had a width of 1.2 m, production of a roll, production of a package, storage, transport, transport, and production of a polarizing film were performed. Was. The results are shown in Tables 1 and 2.

<Example 5>
As a protective film, a laminated body using “Tretec 7332” manufactured by Toray Film Processing Co., Ltd. (base polyethylene, thickness 30 μm, width 1.4 m, adhesive strength to polyvinyl alcohol-based film 14 mN / 15 mm, contact angle 95 °) In the same manner as in Example 1 except that both ends were cut off with slits so that the width became 1.2 m, production of a roll, production of a package, storage, transport, and transport, and production of a polarizing film were performed. The results are shown in Tables 1 and 2.

<Example 6>
As a protective film, a laminated body using Toray Film Processing Co., Ltd. “Tretec 7571” (base polyethylene, thickness 50 μm, width 1.4 m, adhesion to polyvinyl alcohol-based film 22 mN / 15 mm, contact angle 98 °) In the same manner as in Example 1 except that both ends were cut off with slits so that the width became 1.2 m, production of a roll, production of a package, storage, transport, and transport, and production of a polarizing film were performed. The results are shown in Tables 1 and 2.

<Comparative Example 1>
Example 1 except that "Taiko FSA 300M" manufactured by Futamura Chemical Co., Ltd. (thickness: 30 μm, width: 5 m, adhesive strength to polyvinyl alcohol-based film: 40 mN / 15 mm, contact angle: 95 °, opposite matte tone) was used as a protective film. Production of rolls, production, storage, transportation, and transportation of a package were performed in the same manner as described above. After transport, the protective film could not be peeled from the polyvinyl alcohol-based film, and no polarizing film could be produced. The results are shown in Tables 1 and 2.

<Comparative Example 2>
Roll production, package production, storage, transport, and transport were performed in the same manner as in Example 1 except that the protective film was not used. After transport, when the protective film was peeled off from the polyvinyl alcohol-based film, fine scratches, dirt, partial deformation (undulation) were observed, and in-plane retardation was also observed. Furthermore, when a polarizing film was produced, the degree of polarization was low and color unevenness was observed. The results are shown in Tables 1 and 2.

  As is clear from the comparison between Examples 1 to 6 and Comparative Examples 1 and 2, since the polyvinyl alcohol-based film transported by the laminate of the present invention is protected on both sides by the protective films, the polyvinyl alcohol-based film is damaged even after transport. No dirt or deformation, and no change in in-plane retardation. In addition, the polarizing film manufactured from the laminate of the present invention has a high degree of polarization and light transmittance, and color unevenness occurs because the deformation and deterioration of the optical characteristics of the polyvinyl alcohol-based film used in the manufacturing are suppressed. Hateful.

  The polarizing film obtained by the present invention is excellent in polarization performance without optical unevenness, so that a portable information terminal, a personal computer, a television, a projector, a signage, an electronic desk calculator, an electronic clock, a word processor, an electronic paper, a game machine, Liquid crystal display devices such as videos, cameras, photo albums, thermometers, audio, instruments for automobiles and machinery, sunglasses, anti-glare glasses, stereoscopic glasses, wearable displays, display elements (CRT, LCD, organic EL, electronic paper, etc.) ), Optical communication equipment, medical equipment, building materials, toys and the like.

Claims (9)

A laminate having a protective film attached to at least one surface of a polyvinyl alcohol-based film for polarizing film production,
The thickness of the polyvinyl alcohol-based film is 60 μm or less,
A polyvinyl alcohol-based film and a protective film are attached with an adhesive force of 1 to 30 mN / 20 mm ,
Polarizing film contact angle on the side of the film surface in contact with the manufacturing polyvinyl alcohol-based film is a laminate, characterized in der Rukoto than 80 ° of the protective film.   The laminate according to claim 1, wherein the protective film is attached to both surfaces of the polyvinyl alcohol-based film for manufacturing a polarizing film.   3. The laminate according to claim 1, wherein the thickness of the polyvinyl alcohol-based film for producing a polarizing film is 4 to 20 [mu] m. The laminate according to any one of claims 1 to 3 , wherein the protective film is a biaxially stretched polypropylene film. The thickness of the protective film, according to claim 1-4 laminate according any, which is a 30 to 70 .mu.m. The width | variety of a protective film is 2 m or more, The laminated body as described in any one of Claims 1-5 characterized by the above-mentioned. A method for producing a polyvinyl alcohol-based film for producing a polarizing film, which is obtained by peeling a protective film from the laminate according to any one of claims 1 to 6 . A method for producing a polarizing film , which is obtained by using a polyvinyl alcohol-based film for producing a polarizing film obtained by peeling a protective film from the laminate according to any one of claims 1 to 6 . A method for storing or transporting a polyvinyl alcohol-based film for producing a polarizing film, comprising storing or transporting the laminate according to any one of claims 1 to 6 in a roll state.