JP2006188656A - Polyvinyl alcohol film and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyvinyl alcohol film having reduced light scattering and excellent light transmittance, hardly having unevenness of diffused light transmittance in the width direction, and usable for production of a polarizing film; and to provide a method for producing the film. <P>SOLUTION: The polyvinyl alcohol film has ≤1.0% diffused light transmittance Td, and contains 100-900 ppm surfactant in the film based on the amount of a polyvinyl alcohol resin. The polyvinyl alcohol film is produced by the production method comprising (A) a step for compounding one or more kinds of additives with the polyvinyl alcohol resin, and (B) a step for forming the film by a cast method out of the polyvinyl alcohol resin compounded with the additives, wherein the content of the additive having 1.46-1.53 refractive index is regulated so as to be ≥80 wt.% based on the whole amount of the additives. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a polyvinyl alcohol film. More specifically, the present invention relates to a polyvinyl alcohol film used for the production of a polarizing film having reduced light scattering, excellent light transmittance, and having no unevenness of diffused light transmittance in the width direction, And a manufacturing method thereof.

  Conventionally, a polyvinyl alcohol film is prepared by dissolving a polyvinyl alcohol resin in a solvent such as water to prepare a stock solution, forming a film by a solution casting method (casting method), and drying using a metal heating roll or the like. It is manufactured by doing. The polyvinyl alcohol film thus obtained is used in many applications as a film having excellent transparency, and one of its useful applications 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 a device requiring high quality and high reliability.

Under such circumstances, with the increase in the size of screens for liquid crystal televisions and the like, there is a demand for a polarizing film that has fewer optical defects such as dotted defects and linear or planar defects such as color spots than conventional products. ing. As a method for producing such a polarizing film, for example, a polyvinyl alcohol film having 500 or less optical foreign matters having a size of 5 μm or more per 100 cm ² is used (see, for example, Patent Document 1), or exists on the surface of the film. It has been proposed to use a polyvinyl alcohol film having 10 or less foreign matters having a size of 20 μm or more per square meter (for example, see Patent Document 2).

  However, as in Patent Document 1 and Patent Document 2, no matter how micron-order foreign matter is removed by filtering the stock solution at the time of producing the polyvinyl alcohol film, the obtained polarizing film has optical defects. .

  This is because the cause of optical defects is not only micron-order foreign matter, and color spots are not mainly caused by foreign matter. That is, submicron order foreign matter existing in the film, an aggregate of additives generated during film formation, or a non-uniform region of the polymer structure causes optical defects. This is because the polarized light used in the liquid crystal has a visible light region, that is, a submicron-sized microregion having a submicron wavelength (generally 370 to 700 nm) and a refractive index different from that of the polyvinyl alcohol-based resin. This is to cause light reflection and interference. As a result, the transmission of polarized light is disturbed and a light scattering phenomenon occurs. Light scattering becomes an optical defect as a point defect when it occurs in a minute region, and as a line or surface defect such as a color spot when it occurs in a relatively wide range. In any case, since these optical defects lower the transmittance of polarized light in the liquid crystal display, further improvement has been desired in view of the recent increase in quality and area of the polarizing film.

JP 2001-316492 A Japanese Patent Laid-Open No. 2004-20631

  It is an object of the present invention to provide a polyvinyl alcohol film used for the production of a polarizing film having excellent light transmittance and having no unevenness of diffuse light transmittance in the width direction, and a method for producing the same. And Another object of the present invention is to provide a polarizing film having a high light transmittance, and further a polarizing plate.

  The present invention is a polyvinyl alcohol system characterized in that the diffused light transmittance Td is 1.0% or less and the amount of the surfactant contained in the film is 100 to 900 ppm with respect to the polyvinyl alcohol film. It relates to film.

In the polyvinyl alcohol film, polyvinyl alcohol satisfying the following formula (1) when the maximum value of diffused light transmittance Td measured in 10 cm increments in the width direction is A, the minimum value is B, and the average value is C: It is preferable that it is a system film.
(AB) × 100 / C ≦ 20 (1)

  In the polyvinyl alcohol-based film, it is preferable to use a polyvinyl alcohol-based resin having a weight average molecular weight of 140000 to 260000, a film thickness of preferably 30 to 70 μm, and a film width of 3.0 m. The above is preferable.

  The polyvinyl alcohol film preferably contains 80% by weight or more of an additive having a refractive index of 1.46 to 1.53, and has a refractive index of 1.46 to 1.53. It is also preferable to contain 80% by weight or more of the agent with respect to the total surfactant.

The present invention also provides:
(A) The process which mix | blends 1 or more types of additives with a polyvinyl alcohol-type resin, and the process which forms the polyvinyl alcohol-type resin with which the (B) additive was mix | blended by the casting method, and becomes all additives. On the other hand, the present invention relates to a method for producing the polyvinyl alcohol film, which contains 80% by weight or more of an additive having a refractive index of 1.46 to 1.53.

  In the said manufacturing method, it is preferable to contain 80 weight% or more of surfactant with a refractive index of 1.46 to 1.53 with respect to all the surfactants.

  Furthermore, the present invention relates to a polarizing film comprising the polyvinyl alcohol film, and further to a polarizing plate having a protective film provided on at least one surface of the polarizing film.

  Since the polyvinyl alcohol film of the present invention has a low diffused light transmittance Td, it has an excellent light transmittance, and further has no unevenness in the diffused light transmittance in the width direction. As a result, a polarizing film having a high light transmittance can be produced.

  The polyvinyl alcohol film of the present invention has a diffused light transmittance Td of 1.0% or less, and the amount of the surfactant contained in the film is 100 to 900 ppm with respect to the polyvinyl alcohol resin. It is a film.

  The polyvinyl alcohol film of the present invention is obtained by forming a polyvinyl alcohol resin into a film. As the polyvinyl alcohol resin, a resin obtained by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate is usually used. However, the polyvinyl alcohol film of the present invention is not necessarily limited thereto, and a resin obtained by saponifying a copolymer of vinyl acetate and a component copolymerizable with a small amount of vinyl acetate is used. You can also. Examples of components copolymerizable with vinyl acetate include unsaturated carboxylic acids and salts, esters, amides, nitriles thereof; olefins having 2 to 30 carbon atoms such as ethylene, propylene, n-butene and isobutene; vinyl ethers Class; unsaturated sulfonates and the like can be used.

  Although the weight average molecular weight of polyvinyl alcohol-type resin is not specifically limited, Preferably it is 120000-300000, More preferably, it is 140000-200000, More preferably, it is 160000-200000. If the weight average molecular weight is less than 120,000, sufficient optical performance cannot be obtained when a polyvinyl alcohol-based resin is used as an optical film, and if it exceeds 300,000, stretching becomes difficult when the film is used as a polarizing film, and industrial production. Is difficult and undesirable. In addition, the weight average molecular weight of polyvinyl alcohol-type resin is measured by GPC-LALLS method.

  The saponification degree of the polyvinyl alcohol-based resin is preferably 97 mol% or more, more preferably 98 to 100 mol%, further preferably 99 to 100 mol%. When the saponification degree is less than 97 mol%, sufficient optical performance cannot be obtained in the case of an optical film, which is not preferable.

The polyvinyl alcohol-based film of the present invention is prepared by preparing a polyvinyl alcohol-based resin aqueous solution using a polyvinyl alcohol-based resin, casting the aqueous solution on a drum-type roll or an endless belt, preferably a drum-type roll, and forming and drying the film. It can manufacture by a method etc., and a manufacturing method is not specifically limited. For example,
(A) The step of blending one or more additives with the polyvinyl alcohol-based resin, and the step of forming a film of the polyvinyl alcohol-based resin blended with the (B) additive by a casting method can also be produced. . Here, it is preferable to contain 80% by weight or more of an additive having a refractive index of 1.46 to 1.53 with respect to all the additives to be blended.

  Hereafter, the manufacturing method which consists of said process (A) and process (B) is demonstrated.

  As a polyvinyl alcohol-type resin which forms a polyvinyl alcohol-type film, the above-mentioned resin can be used. The polyvinyl alcohol-based resin usually contains sodium acetate produced during production. Therefore, when using polyvinyl alcohol resin powder for film formation, the powder is first washed to remove sodium acetate. The washing is performed with methanol or water. However, the method of washing with methanol requires solvent recovery, and therefore, the method of washing with water is more preferable.

  Next, the water-containing polyvinyl alcohol-based resin wet cake after washing is dissolved in water to prepare a polyvinyl alcohol-based resin aqueous solution, but it is desirable that the water-containing polyvinyl alcohol-based resin wet cake after washing is dissolved in water as it is. Since a highly concentrated aqueous solution cannot be obtained, it is preferable to perform dehydration once. The dehydration method is not particularly limited, but a method using centrifugal force is common.

  The water content of the wet polyvinyl alcohol resin wet cake is preferably 50% by weight or less, more preferably 30 to 45% by washing and dehydration. When the water content exceeds 50% by weight, it is difficult to obtain a desired aqueous solution concentration, which is not preferable.

  Subsequently, the water-containing polyvinyl alcohol-based resin wet cake whose water content is adjusted is dissolved in water to prepare a polyvinyl alcohol-based resin aqueous solution. The polyvinyl alcohol resin aqueous solution has a refractive index of 1.46 to 1.53 for plasticizers, surfactants, antioxidants, ultraviolet absorbers, various fillers and the like for the purpose of improving film forming properties and thermomechanical properties. Add various additives. The additive to be blended may be one kind or two or more kinds. In particular, it is preferable from the viewpoint of film forming property to add at least one surfactant. Here, the refractive index refers to a refractive index at room temperature in the visible light wavelength, and is, for example, a refractive index at 25 ° C. in a commonly used NaD line (589 nm). Further, the refractive index in this case is the refractive index of the compound itself used as an additive, and not the refractive index diluted with a solvent or the like.

  As such an additive, an additive having a refractive index of 1.46 to 1.53 is preferably contained in an amount of 80% by weight or more, particularly preferably 90% by weight or more, more preferably all of the additives. It is to make an additive. If it is less than 80% by weight, the diffused light transmittance is undesirably increased.

  The reason why it is preferable to use an additive having a refractive index of 1.46 to 1.53 is as follows.

  The refractive index of the polyvinyl alcohol resin varies depending on the degree of crystallinity, but takes a value ranging from 1.49 of amorphous to 1.61 of crystal. On the other hand, the refractive index of the additive is usually in the range of 1.30 to 1.80 for organic compounds, and is generally in the range of 1.30 to 4.00 for inorganic compounds. Some additives form submicron sized aggregates during film formation. Originally, since the additive is aggregated to increase the density, the refractive index of the aggregate is slightly higher than the refractive index of the additive itself, but the order is 0.01 or less, and the refractive index of the additive itself is almost the same. Consistent with the rate. The aggregate produced in the film has a refractive index different from that of the polyvinyl alcohol resin, and thus light scattering occurs. The degree of light scattering becomes more prominent as the difference in refractive index between the two increases and as the number of aggregates increases. Further, since the additive and its aggregate are present in the amorphous part rather than the crystal part of the polyvinyl alcohol resin, the refractive index of the additive is approximately 1.50 of the amorphous part of the polyvinyl alcohol resin. If they are equal, light scattering is negligible.

  The refractive index of the additive added is 1.46 to 1.53 as described above, but is preferably 1.47 to 1.51, and more preferably 1.48 to 1.50. . When the refractive index is out of this range, light scattering increases. The optimum refractive index range of the additive is slightly lower than the refractive index 1.5 of the amorphous part of the polyvinyl alcohol-based resin because of the above-described aggregation effect (increased refractive index of the additive) and the refractive index of 1. This is because a decrease in the refractive index of the resin due to moisture absorption of 33 water is estimated.

  The total amount of additives having a refractive index of 1.46 to 1.53 is preferably 1 to 30% by weight, more preferably 5 to 20% by weight, and even more preferably 10 to 15% by weight. If it is less than 1% by weight, the stretchability at the time of producing the polarizing film is inferior, and if it exceeds 30% by weight, the thermal properties of the film are lowered, which is not preferable.

  Among the additives, the refractive index of a surfactant that easily aggregates during film formation is particularly important. As the surfactant having a refractive index of 1.46 to 1.53, a surfactant not containing a high refractive index atom such as sulfur or a low refractive index atom such as fluorine is preferable. For example, polyoxyethylene hexyl ether, polyoxyethylene heptyl ether, polyoxyethylene octyl ether, polyoxyethylene nonyl ether, polyoxyethylene decyl ether, polyoxyethylene dodecyl ether, polyoxyethylene tetradecyl ether, polyoxyethylene hexadecyl Polyoxyethylene alkyl ethers such as ether, polyoxyethylene octadecyl ether, polyoxyethylene eicosyl ether, polyoxyethylene oleyl ether, palm oil reduced alcohol ethylene oxide adduct, beef tallow reduced alcohol ethylene oxide adduct; polyoxyethylene hexyl Amine, polyoxyethylene heptylamine, polyoxyethylene octylamine, polyoxyethylene Nylamine, polyoxyethylene decylamine, polyoxyethylene dodecylamine, polyoxyethylene tetradecylamine, polyoxyethylene hexadecylamine, polyoxyethylene octadecylamine, polyoxyethylene oleylamine, polyoxyethylene eicosylamine, and other polyoxyethylene Alkylamine; polyoxyethylene caproic acid amide, polyoxyethylene caprylic acid amide, polyoxyethylene capric acid amide, polyoxyethylene lauric acid amide, polyoxyethylene myristic acid amide, polyoxyethylene palmitic acid amide, polyoxyethylene stearic acid Amide, polyoxyethylene higher fatty acid amide such as polyoxyethylene oleic acid amide, etc .; stearic acid amide, olei Acid amide, palmitic acid, myristic acid amide, lauric acid amide, and fatty acid amides such as caproic acid amides. Among these, polyoxyethylene dodecyl ether, polyoxyethylene octadecyl ether, palm oil reduced alcohol ethylene oxide adduct, polyoxyethylene dodecylamine, polyoxyethylene lauric acid amide, polyoxyethylene stearic acid amide are compatible. From the point of view, it is preferable.

  The addition amount of the surfactant is appropriately selected in consideration of the target content, but is usually determined in consideration of a decrease in the production process. Further, it is preferable that the surfactant having a refractive index of 1.46 to 1.53 is contained in an amount of 80% by weight or more, particularly preferably 90% by weight or more, and more preferably all of the interface. To make it an activator.

  Examples of the plasticizer having a refractive index of 1.46 to 1.53 include glycerin (refractive index 1.47), diisononyl phthalate (refractive index 1.48), dibutyl phthalate (refractive index 1.49), and phthalate. Diethyl acid (refractive index 1.50), dimethyl phthalate (refractive index 1.51), trimellitic acid tributyl (refractive index 1.49), trimellitic acid tri-2-ethylhexyl (refractive index 1.49), ethyl Examples thereof include phthalyl ethyl glycolate (refractive index 1.49) and epoxidized soybean oil (refractive index 1.47). Among these, glycerin is preferable from the viewpoint of compatibility. The addition amount of the plasticizer is preferably 1 to 30% by weight, more preferably 5 to 20% by weight with respect to the polyvinyl alcohol-based resin. If the addition amount is less than 1% by weight, the stretchability during the production of the polarizing film is inferior, and if it exceeds 30% by weight, the thermal properties of the film will be undesirably lowered.

  Examples of the antioxidant having a refractive index of 1.46 to 1.53 include didecylphenyl phosphite (refractive index 1.48) and diphenyldecyl phosphite (refractive index 1.52). The addition amount of the antioxidant is preferably 0 to 1000 ppm, more preferably 10 to 100 ppm with respect to the polyvinyl alcohol resin. When the added amount exceeds 1000 ppm, poor appearance due to bleeding out tends to occur.

  Examples of the ultraviolet absorber having a refractive index of 1.46 to 1.53 include 2,4-di-t-butylphenyl-3 ′, 5′-di-t-butyl-4′-hydroxybenzoate (refractive index). 1.53), 2- (2′-hydroxy-3 ′, 5′-di-t-butylphenyl) benzotriazole (refractive index 1.53) and the like. The addition amount of the ultraviolet absorber is preferably 0 to 1000 ppm, more preferably 10 to 100 ppm with respect to the polyvinyl alcohol resin. When the added amount exceeds 1000 ppm, poor appearance due to bleeding out tends to occur.

  Examples of the filler having a refractive index of 1.46 to 1.53 include silicon oxide (refractive index 1.50). The amount of filler added is preferably 0 to 1000 ppm, more preferably 10 to 100 ppm, relative to the polyvinyl alcohol resin. When the added amount exceeds 1000 ppm, poor appearance due to bleeding out tends to occur.

  Polyvinyl alcohol-based resin aqueous solution may be prepared by, for example, preparing a dehydrated polyvinyl alcohol-based resin wet cake, water, and additives using a melting can, heating, stirring and dissolving, multi-screw extrusion Using a machine, prepare dehydrated polyvinyl alcohol resin wet cake or polyvinyl alcohol resin dried from it, prepare water and additives by side feed, heat and dissolve while applying shear. May be. In particular, in a dissolving can equipped with a vertical circulation flow generation type stirring blade, it is preferable from the viewpoint of solubility to obtain an aqueous solution obtained by blowing water vapor into the can to dissolve the water-containing polyvinyl alcohol resin wet cake.

  When dissolving the water-containing polyvinyl alcohol-based resin wet cake in a dissolving can equipped with a vertical circulation flow generation type stirring blade, water vapor is blown, but when blowing water vapor, so that the aqueous solution has a desired concentration, Water can also be added. The amount of water vapor blown is preferably 0.5 to 5 times (by weight) with respect to the polyvinyl alcohol resin to be dissolved, and the blow time is preferably 0.5 to 3 hours. If the blowing amount is less than 0.5 times, the dissolution is insufficient, and if it exceeds 5 times, the amount of drain becomes too large and the desired concentration is not achieved. In addition, when water vapor is blown, it is preferably blown from the bottom of the can, but it may be blown from the side or the like.

  Moreover, in a melting can, it is preferable at the point which can be uniformly melt | dissolved, when water vapor | steam is blown and the resin temperature becomes 40-80 degreeC, Preferably it becomes 45-70 degreeC. If the resin temperature is less than 40 ° C., the load on the motor increases, and if the resin temperature exceeds 80 ° C., the polyvinyl alcohol resin is hardened and cannot be uniformly dissolved, which is not preferable. Furthermore, it is preferable that the inside of the can be pressurized when water vapor is blown and the resin temperature reaches 90 to 100 ° C., preferably 95 to 100 ° C., from the viewpoint of uniform dissolution. If the resin temperature is less than 90 ° C., undissolved material is formed, which is not preferable. When the resin temperature reaches 130 to 150 ° C., the blowing of water vapor is terminated, and then stirring is continued for 0.5 to 3 hours to perform dissolution. After dissolution, the concentration is adjusted so that the desired concentration is obtained.

  The concentration of the aqueous solution is adjusted by measuring the concentration using a process refractometer (manufactured by K-PATENTS) while partly extracting and circulating the solution in the can.

  The concentration of the aqueous polyvinyl alcohol resin solution thus obtained is preferably 15 to 60% by weight, more preferably 17 to 55% by weight, and still more preferably 20 to 50% by weight. If the concentration is less than 15% by weight, the drying load becomes large and the production capacity is inferior. If it exceeds 60% by weight, the viscosity becomes too high and uniform dissolution cannot be achieved.

  Next, the obtained polyvinyl alcohol-based resin aqueous solution is defoamed. Examples of the defoaming method include stationary defoaming and defoaming using a multi-screw extruder. In the production method of the present invention, defoaming is performed using a multi-screw extruder from the viewpoint of productivity. The method is preferred. The multi-screw extruder is not particularly limited as long as it is a multi-screw extruder having a vent. Usually, a twin-screw extruder having a vent is used.

In the defoaming treatment, a polyvinyl alcohol-based resin aqueous solution is supplied to a multi-screw extruder, the resin temperature of the vent is set to 105 to 180 ° C, preferably 110 to 160 ° C, and the pressure at the tip of the extruder is ² to 100 kg / cm ^2. Preferably, it is performed as 5-70 kg / cm < ² >. If the resin temperature at the vent is less than 105 ° C., defoaming is insufficient, and if it exceeds 180 ° C., resin deterioration occurs, which is not preferable. Further, if the tip pressure of the multi-screw extruder is less than 2 kg / cm ² , defoaming is insufficient, and if it exceeds 100 kg / cm ² , resin leakage or the like occurs in the piping, and stable production cannot be achieved.

A gear pump (P1) and a gear pump (P2) are provided before and after the multi-screw extruder, and the polyvinyl alcohol-based resin aqueous solution is supplied to the multi-screw extruder by the gear pump (P1), and the gear pump (P2). The polyvinyl alcohol-based resin aqueous solution after defoaming is discharged from the multi-screw extruder. Controlling the gear pump (P1) so that the inlet pressure of the gear pump (P2) exhibits a constant value in the range of ^{2 to} 70 kg / cm ² , preferably 5 to 70 kg / cm ² , improves the film thickness accuracy. Is preferable. If the inlet pressure is less than 2 kg / cm ² , defoaming is insufficient, and if it exceeds 70 kg / cm ² , the resin comes out from the vent portion, which is not preferable. Further, even if the inlet pressure of the gear pump (P2) is in the above range, the film thickness accuracy is insufficient if it does not show a certain value, which is not preferable. Note that the constant value here allows a range within ± 2%, preferably within ± 1.5% from the specified value.

  After the defoaming treatment, the polyvinyl alcohol-based resin aqueous solution is introduced into a T-type slit die by a certain amount and cast onto a drum-type roll or an endless belt, particularly preferably a drum-type roll.

  As the T-type slit die, a T-type slit die having an elongated rectangle is usually used, but in addition, in any part within 15% from both ends with respect to the longitudinal direction of the T-type slit die, It is also possible to use a T-type slit die in which the slit interval is smaller than the central slit interval. As such a T-type slit die, a T-type slit die having a slit interval of 80% or less of the slit interval in the central portion at any portion within 15% from both end portions with respect to the longitudinal direction is preferable. In particular, a T-shaped slit die in which the slit interval is gradually decreased from the portion within 15% toward the end portion is particularly preferable. When such a T-shaped slit die is used, the film ear end portion obtained does not have a large film thickness, and therefore exhibits an effect excellent in film peelability. Moreover, it is preferable that the resin temperature of a T-type slit die exit is 80-100 degreeC, More preferably, it is 85-98 degreeC. If the resin temperature at the exit of the T-shaped slit die is less than 80 ° C., poor flow occurs.

  The casting is performed with a drum-type roll or an endless belt, but is preferably performed with a drum-type roll from the viewpoints of widening, lengthening, and film thickness uniformity.

  The rotation speed of the drum-type roll is preferably 5 to 30 m / min, and more preferably 6 to 20 m / min. If the rotational speed is less than 5 m / min, the productivity tends to be inferior, and if it exceeds 30 m / min, the moisture tends to be insufficiently dried. Moreover, it is preferable that the surface temperature of a drum type roll is 70-99 degreeC, and it is more preferable that it is 75-97 degreeC. If the surface temperature is less than 70 ° C, drying is poor, and if it exceeds 99 ° C, foaming is not preferable.

  Although it does not specifically limit about the magnitude | size of a drum type roll, 2000-4000 mm is preferable and the diameter of a roll has more preferable 2500-3800 mm. If the roll diameter is less than 2000 mm, the drying length is insufficient, the speed does not increase, and if it exceeds 4000 mm, it is difficult to manufacture the equipment, which is not preferable.

  The polyvinyl alcohol-based film can be obtained by casting a polyvinyl alcohol-based resin aqueous solution onto a drum-type roll and drying it after film formation. Drying is performed, for example, by passing the front and back surfaces of the film alternately through a plurality of drying rolls.

  The diameter of the drying roll is preferably 100 to 1000 mm, more preferably 150 to 900 mm, and particularly preferably 200 to 800 mm. If the diameter of the drying roll is less than 100 mm, an enormous number is required, and if it exceeds 1000 mm, film conveyance becomes unstable, which is not preferable. The preferable number of drying rolls is usually 2 to 30. Although the surface temperature of a drying roll is not specifically limited, It is preferable that it is 60-100 degreeC, and it is more preferable that it is 65-90 degreeC. If the surface temperature of the drying roll is less than 60 ° C., the drying is poor.

  In the method for producing a polyvinyl alcohol film of the present invention, the polyvinyl alcohol film obtained after drying can be further subjected to heat treatment, if necessary.

  In the polyvinyl alcohol film of the present invention, the degree of light scattering is evaluated by the diffused light transmittance Td based on JIS K7105. The total of the diffuse light transmittance Td and the parallel light transmittance Tp is the total light transmittance Tt.

  The diffused light transmittance Td of the polyvinyl alcohol film of the present invention is required to be 1.0% or less, preferably 0.5% or less. If it exceeds 1.0%, light scattering is large, and when used as a raw film for a polarizing film, the light transmittance of the manufactured polarizing film becomes low.

  The amount of the surfactant contained in the polyvinyl alcohol film of the present invention is 100 to 900 ppm, preferably 200 to 850 ppm, more preferably 300 to 800 ppm, particularly preferably relative to the polyvinyl alcohol resin. Is 400-700 ppm. If the content is less than 100 ppm, the ability of the surfactant will not be exhibited, and the film-forming property cannot be secured. Conversely, if the content exceeds 900 ppm, precipitation on the film surface occurs and the appearance of the film is impaired. Become.

The polyvinyl alcohol film of the present invention satisfies the following formula (1) when the maximum value of the diffused light transmittance Td measured in 10 cm increments in the width direction is A, the minimum value is B, and the average value is C. Preferably, it is 10 or less.
(AB) × 100 / C ≦ 20 (1)

  If it exceeds 20, unevenness of light scattering is large, and when it is used as an original film of a polarizing film, unevenness of light transmittance is generated, which is not preferable.

  The polyvinyl alcohol film of the present invention is a film having high light transmittance, reduced light scattering, and no unevenness in diffused light transmittance in the width direction. Therefore, the polyvinyl alcohol film of the present invention is preferably used as a raw material for the production of a polarizing film having a high light transmittance.

  The polarizing film of the present invention is produced using the polyvinyl alcohol film of the present invention. The thickness of the polyvinyl alcohol film used for the production of the polarizing film is preferably 30 to 100 μm, more preferably 30 to 90 μm, and particularly preferably 30 to 70 μm from the viewpoint of thinning. If the film thickness is less than 30 μm, stretching is difficult and sufficient polarization performance cannot be obtained, and if it exceeds 100 μm, the film thickness accuracy is lowered, which is not preferable.

  The width of the polyvinyl alcohol film is not particularly limited, but is preferably 2.0 m or more, particularly 2.5 m or more, and more preferably 3.0 m or more in terms of productivity when manufacturing a polarizing film. Is preferred.

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

  The stretching is desirably performed in a uniaxial direction by 3 to 10 times, preferably 3.5 to 6 times. At this time, a slight stretching (stretching to prevent shrinkage in the width direction or more) may be performed in a direction perpendicular to the stretching direction. The stretching temperature is preferably selected from 40 to 170 ° C. Furthermore, the draw ratio may be finally set within the above range, and the drawing operation may be performed not only in one stage but also in any stage of the manufacturing process.

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

  The dyed film is then treated with a boron compound. As the boron compound, boric acid and borax are practical. The boron compound is used in the form of an aqueous solution or a water-organic solvent mixture at a concentration of about 0.3 to 2 mol / L, and it is practically desirable that a small amount of potassium iodide coexists in the solution. The treatment method is preferably an immersion method, but of course, an application method and a spray method can also be carried out. The temperature during the treatment is preferably about 40 to 70 ° C., and the treatment time is preferably about 3 to 20 minutes. If necessary, the stretching operation may be performed during the treatment.

  The light transmittance of the polarizing film of the present invention thus obtained is preferably 43% or more, more preferably 44% or more. If the light transmittance is less than 43%, it is impossible to achieve high brightness of the liquid crystal display. The light 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 can also be used as a polarizing plate by laminating and bonding an optically isotropic polymer film or sheet as a protective film on one or both surfaces thereof. Examples of the protective film include films or sheets of cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, polystyrene, polyethersulfone, polyarylene ester, poly-4-methylpentene, polyphenylene oxide, and the like.

  In addition, for the purpose of reducing the thickness of the polarizing film, instead of the protective film, a curable resin such as a urethane resin, an acrylic resin, or a urea resin may be applied and laminated on the surface or both surfaces thereof.

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

  The polarizing film of the present invention includes an electronic desk calculator, an electronic watch, a word processor, a personal computer, a portable information terminal, a liquid crystal display device such as an instrument for automobiles and machinery, sunglasses, eye protection glasses, stereoscopic glasses, a display element (CRT, It is preferably used for reflection-reducing layers for LCDs, medical devices, building materials, toys and the like.

  In the examples, the weight average molecular weight, the surfactant amount, the refractive index nD, the diffused light transmittance Td and the light transmittance were measured by the following methods.

(1) Weight average molecular weight It measures on condition of the following by GPC-LALLS method.

1) GPC
Apparatus: Waters type 244 gel permeation chromatograph column: Tosoh Corporation TSK-gel-GMPW _XL (inner diameter 8 mm, length 30 cm, 2 pieces)
Solvent: 0.1 M Tris buffer (pH 7.9)
Flow rate: 0.5 ml / min
Temperature: 23 ° C
Sample concentration: 0.040%
Filtration: 0.45 μm Mysori Disc W-25-5 manufactured by Tosoh Corporation
Injection volume: 0.2ml
Detection sensitivity (differential refractive index detector): 4 times

2) LALLS
Apparatus: Chromatrix KMX-6 type low angle laser light scattering photometer Temperature: 23 ° C
Wavelength: 633nm
Second virial coefficient × concentration: 0 mol / g
Refractive index density change (dn / dc): 0.159 ml / g
Filter: MILLIPORE 0.45 μm filter HAWP01300
Gain: 800mV

(2) Amount of surfactant in film From 1 g of polyvinyl alcohol film, Soxhlet extraction was carried out for 6 hours using methanol as a solvent. Measurement is performed using a high performance liquid chromatography mass spectrometer (hereinafter referred to as LC-MASS) HP1100MSD. Although detailed measurement conditions are as follows, a model and measurement conditions are not limited to this.

Column: YMC-Pack ODS-A 150 × 4.6 mm manufactured by YMC Co., Ltd. D.
Column temperature: 30 ° C
Eluent: 0.1 M aqueous ammonium acetate solution / methanol, gradient measurement (25/75 → 0/100 (15 minutes))
Flow rate: 0.7 ml / min Injection volume: 20 μL
MASS: Electron spray ionization method Negative mode

(3) Refractive index nD
It measures at 23 degreeC using the Abago refractometer by Atago Co., Ltd.

(4) Diffuse light transmittance Td
Based on JIS-K7105, measurement is performed using a turbidimeter NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd.

(5) Diffuse light transmittance unevenness When the maximum value of diffuse light transmittance Td measured in 10 cm increments in the width direction is A, the minimum value is B, and the average value is C, calculation is performed according to the following formula (2).
Diffuse light transmittance unevenness (%) = (A−B) × 100 / C (2)

(6) Light transmittance Measured at a wavelength of 550 nm using RETS-2000 manufactured by Otsuka Electronics Co., Ltd.

(7) Light transmittance unevenness When the maximum value of the light transmittance measured in steps of 10 cm in the width direction is D, the minimum value is E, and the average value is F, the light transmittance is calculated according to the following formula (3).
Light transmittance unevenness (%) = (DE) × 100 / F (3)
Measurement is performed at a wavelength of 550 nm using RETS-2000 manufactured by Otsuka Electronics Co., Ltd.

Example 1
(Manufacture of polyvinyl alcohol film)
200 kg of 18 ° C. water was placed in a 500 L tank, and while stirring, 40 kg of polyvinyl alcohol resin having a weight average molecular weight of 142000 and a saponification degree of 99.8 mol% was added, and stirring was continued for 15 minutes. Thereafter, after draining water, 200 kg of water was further added and stirred for 15 minutes. The obtained slurry was dehydrated by a super decanter (manufactured by Sakai Kogyo Co., Ltd.) to obtain a polyvinyl alcohol resin wet cake having a water content of 43% by weight.

  70 kg of the obtained polyvinyl alcohol-based resin wet cake was put into a dissolution can equipped with a Max blend type wing, and 10 g of polyoxyethylene dodecyl ether (refractive index 1.49), polyoxyethylene dodecylamine (refractive) as a surfactant. 10 g of index 1.47), 5 g of stearamide (refractive index 1.48), 4.2 kg of glycerin (refractive index 1.47) and 10 kg of water were added as a plasticizer. Water vapor was blown from the bottom of the can, and stirring (rotation speed: 5 rpm) was performed when the internal resin temperature reached 50 ° C., and the system was pressurized when the internal resin temperature reached 100 ° C. After raising the temperature to 150 ° C., the blowing of water vapor was stopped, stirring was performed for 30 minutes (rotation speed: 20 rpm), and after uniform dissolution, a polyvinyl alcohol resin aqueous solution having a concentration of 25% by weight was obtained by adjusting the concentration.

Next, the polyvinyl alcohol-based resin aqueous solution (liquid temperature 147 ° C.) was supplied from the gear pump (P1) to the twin screw extruder, defoamed, and then discharged from the gear pump (P2). The resin temperature of the vent part was 130 ° C., the tip pressure of the extruder was 30 kg / cm ² , and the inlet pressure of the gear pump (P2) was 30 kg / cm ² . The discharged polyvinyl alcohol resin aqueous solution was cast from a T-type slit die (straight manifold die) onto a drum-type roll to form a film. The conditions for casting film formation are as follows.

Drum type roll Diameter: 3200 mm, width: 4000 mm, rotation speed: 8 m / min, surface temperature: 90 ° C., resin temperature at T-type slit die outlet: 95 ° C.

  The moisture content of the obtained film was 20%. Drying was performed while alternately passing the front and back surfaces of this film through a drying roll under the following conditions.

Drying roll Diameter: 320 mm, width: 4000 mm, number: 10, rotation speed: 8 m / min, surface temperature: 70 ° C.

  The obtained polyvinyl alcohol film (width: 3200 mm, thickness: 50 μm) had a diffused light transmittance Td of 0.5%. Furthermore, the amount of the surfactant in the polyvinyl alcohol film was 550 ppm.

  Moreover, when the obtained polyvinyl alcohol-type film evaluated the diffused light transmittance nonuniformity as follows, it was 4%.

(Manufacture of polarizing film)
The obtained polyvinyl alcohol film was immersed in an aqueous solution of 0.2 g / L of iodine and 15 g / L of potassium iodide for 240 seconds at 30 ° C., and then 60 g / L of boric acid and 30 g / L of potassium iodide. While being immersed in an aqueous solution (55 ° C.) of the composition, boric acid treatment was performed for 5 minutes while simultaneously uniaxially stretching four times. Then, it dried and obtained the polarizing film. The obtained polarizing film had a light transmittance of 44.4% and a light transmittance unevenness of 0.2%.

Example 2
In addition to the surfactant of Example 1, 7 g of didecylphenyl phosphite (refractive index 1.48) as an antioxidant and 2- (2′-hydroxy-3 ′, 5′-di-) as an ultraviolet absorber. A polyvinyl alcohol film was obtained in the same manner as in Example 1 except that 7 g of t-butylphenyl) benzotriazole (refractive index 1.53) was added. The resulting film had a diffuse light transmittance of 0.7%.

  Moreover, when the obtained polyvinyl alcohol-type film was evaluated for diffused light transmittance unevenness, it was 7%. Furthermore, the amount of the surfactant in the polyvinyl alcohol film was 550 ppm.

  Further, a polarizing film was obtained in the same manner as in Example 1. The obtained polarizing film had a light transmittance of 44.2% and a light transmittance unevenness of 0.5%.

Example 3
A polyvinyl alcohol film (width: 3200 mm, thickness: 75 μm) was obtained in the same manner as in Example 1 except that an aqueous polyvinyl alcohol resin solution having a concentration of 30% by weight was used. The diffuse light transmittance of this film was 0.7%. Furthermore, the amount of the surfactant in the polyvinyl alcohol film was 570 ppm.

  Moreover, when the obtained polyvinyl alcohol-type film was evaluated for diffused light transmittance unevenness, it was 6%.

  Further, a polarizing film was obtained in the same manner as in Example 1. The obtained polarizing film had a light transmittance of 43.6% and a light transmittance unevenness of 0.5%.

Example 4
A polyvinyl alcohol film (width: 3200 mm, thickness: 50 μm) was obtained in the same manner as in Example 1 except that a polyvinyl alcohol resin having a weight average molecular weight of 175000 was used. The diffuse light transmittance of this film was 0.4%. Furthermore, the amount of the surfactant in the polyvinyl alcohol film was 530 ppm.

  The obtained polyvinyl alcohol film was evaluated for diffuse light transmittance unevenness and found to be 3%.

  Further, a polarizing film was obtained in the same manner as in Example 1. The obtained polarizing film had a light transmittance of 44.4% and a light transmittance unevenness of 0.1%.

Comparative Example 1
A polyvinyl alcohol film was obtained in the same manner as in Example 1 except that 30 g of sodium dodecylbenzenesulfonate (refractive index 1.54) was used as the surfactant. The resulting film had a diffuse light transmittance of 1.1%. Furthermore, the amount of the surfactant in the polyvinyl alcohol film was 740 ppm.

  Moreover, when the obtained polyvinyl alcohol-type film was evaluated for diffuse light transmittance unevenness, it was 13%.

  Further, a polarizing film was obtained in the same manner as in Example 1. The obtained polarizing film had a light transmittance of 42.9% and a light transmittance unevenness of 0.9%.

Comparative Example 2
A polyvinyl alcohol film was obtained in the same manner as in Example 1 except that 30 g of a silicon surfactant (refractive index: 1.45) was used as the surfactant. The film obtained had a diffused light transmittance of 1.5%. Furthermore, the amount of the surfactant in the polyvinyl alcohol film was 500 ppm.

  Moreover, when the obtained polyvinyl alcohol-type film was evaluated for diffused light transmittance unevenness, it was 21%.

  Further, a polarizing film was obtained in the same manner as in Example 1. The obtained polarizing film had a light transmittance of 41.5% and a light transmittance unevenness of 1.7%.

Comparative Example 3
Example except that 9 g of polyoxyethylene dodecyl ether (refractive index 1.49), 38 g of polyoxyethylene dodecylamine (refractive index 1.47), and 9 g of stearamide (refractive index 1.48) are used as the surfactant. In the same manner as in Example 1, a polyvinyl alcohol film (width: 3200 mm, thickness: 50 μm) was obtained. The diffuse light transmittance of this film was 1.1%. Furthermore, the amount of the surfactant in the polyvinyl alcohol film was 1200 ppm. Moreover, when the obtained polyvinyl alcohol-type film was evaluated for diffused light transmittance unevenness, it was 21%.

  Further, a polarizing film was obtained in the same manner as in Example 1. The obtained polarizing film had a light transmittance of 42.8% and a light transmittance unevenness of 1.6%.

Comparative Example 4
In Example 1, the same procedure was performed except that the surfactant was not added. However, the film could not be peeled off from the drum-type roll, and the intended film could not be obtained.

  The results of Examples 1 to 4 and Comparative Examples 1 to 4 are shown in Table 1.

Claims (12)

A polyvinyl alcohol film having a diffuse light transmittance Td of 1.0% or less and an amount of a surfactant contained in the film of 100 to 900 ppm based on the polyvinyl alcohol resin. 2. The following formula (1) is satisfied, where A is a maximum value of diffused light transmittance Td measured in steps of 10 cm in the width direction, B is a minimum value, and C is an average value. Polyvinyl alcohol film.
(AB) × 100 / C ≦ 20 (1) The polyvinyl alcohol film according to claim 1 or 2, wherein the polyvinyl alcohol resin has a weight average molecular weight of 140,000 to 260000. The polyvinyl alcohol film according to claim 1, wherein the film has a thickness of 30 to 70 μm. 5. The polyvinyl alcohol film according to claim 1, 2, 3 or 4, wherein the film width is 3.0 m or more. 6. The polyvinyl alcohol film according to claim 1, 2, 3, 4 or 5, comprising an additive having a refractive index of 1.46 to 1.53 in an amount of 80% by weight or more based on all additives. . A surfactant having a refractive index of 1.46 to 1.53 is contained in an amount of 80% by weight or more based on the total amount of the surfactants. The polyvinyl alcohol film according to the description. (A) The process which mix | blends 1 or more types of additives with polyvinyl alcohol-type resin, and the process of forming into a film by the casting method the polyvinyl alcohol-type resin with which (B) additive was mix | blended, and refractive index is 1. The production of polyvinyl alcohol-based film according to claim 1, 2, 3, 4, 5, 6 or 7, wherein the additive of .46 to 1.53 is contained in an amount of 80% by weight or more based on all additives. Method. The method for producing a polyvinyl alcohol film according to claim 8, wherein a surfactant having a refractive index of 1.46 to 1.53 is contained in an amount of 80% by weight or more based on the total surfactant. The polyvinyl alcohol film according to claim 1, wherein the polyvinyl alcohol film is used as a raw film of a polarizing film. A polarizing film comprising the polyvinyl alcohol film according to claim 1, 2, 3, 4, 5, 6 or 7. A polarizing plate comprising a protective film provided on at least one surface of the polarizing film according to claim 11.