JP4664100B2 - Polyvinyl alcohol film, polarizing film, polarizing plate - Google Patents

Description

  The present invention relates to a polyvinyl alcohol film. More specifically, the present invention relates to a polyvinyl alcohol film having excellent dimensional stability and optical characteristics, and a polarizing film and a polarizing plate produced using the film.

  Conventionally, a polyvinyl alcohol film is prepared by dissolving a polyvinyl alcohol resin in a solvent such as water to prepare a stock solution, then forming a film by a solution casting method (casting method), and drying using a metal heating roll or the like. It is manufactured by heat treatment as necessary. The thus obtained polyvinyl alcohol-based film is used in many applications as a film excellent in transparency and dyeability, 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 display devices that require high definition and high reliability.

  Under such circumstances, the humidity dependency of the polarizing film is a problem. Due to the widespread use of portable applications, the usage environment of liquid crystal displays is diversifying year by year. Mobile phones, personal digital assistants, and laptop computers must maintain their display functions even in high-temperature and high-humidity environments during the rainy season and low-temperature and low-humidity environments in winter. However, a polyvinyl alcohol film used as a raw material of a polarizing film causes a dimensional change such as expansion due to moisture absorption or shrinkage due to dehumidification, and thus optical performance such as refractive index changes. In addition, due to structural changes peculiar to polymers, once the expansion or contraction occurs, it does not completely return to the original dimensions. That is, when the use under different environments is repeated, the shape and display performance at the time of manufacturing the display change. Particularly serious is the case where the dimensional recoverability differs in the film plane. Once used in a high humidity outdoor environment and then placed in a standard indoor environment (for example, 23 ° C., 50% RH), the display is deformed or display unevenness called white spots occurs.

  In addition, display degradation due to dimensional restoration is also regarded as a problem in indoor applications such as liquid crystal televisions. This is because even with a recent increase in area, even a small dimensional change affects display performance. As high definition and high reliability are required more than for portable use, there is a strong demand for improvement in dimensional restoration. Regarding the improvement of these dimensional restoration properties, for example, a polarizing film (for example, see Patent Document 1) that defines dimensional shrinkage before and after drying, a polarizing film containing an organometallic compound (for example, see Patent Document 2), a polyvalent aldehyde A crosslinked polarizing film (see, for example, Patent Document 3) has been proposed.

  However, even with these disclosed techniques, the improvement effect is not sufficient if the dimensional recoverability of the polyvinyl alcohol film that is the original fabric before stretching is inferior. The polarizing film is produced by dyeing, stretching, and boric acid crosslinking a polyvinyl alcohol film that is a raw fabric. Even if cross-linking with boric acid is performed, a phenomenon occurs that once expanded, it remains expanded, or once contracted, it contracts. As a result, warpage occurs in the liquid crystal cell to which the polarizing film is bonded. The story is further complicated when the dimensional restoration property of the polyvinyl alcohol film that is the raw fabric has anisotropy. The dimensions change not only in the stretching direction but also in the width direction or in the oblique direction. As a result, the entire liquid crystal cell undulates. If this happens, it cannot be dealt with only by improving the device structure. Accordingly, there has been a need for accurate and non-anisotropic dimensional restoration of the polyvinyl alcohol film that is the raw fabric.

JP-A-5-232316 JP-A-6-172554 JP-A-6-235815

  An object of the present invention is to provide a polyvinyl alcohol-based film, a polarizing film, and a polarizing plate that are excellent in dimensional restoration properties and excellent in optical characteristics in order to cope with an improvement in display reliability.

The present invention is a polyvinyl alcohol film having a thickness of 30 to 70 μm produced by a casting method,
After being left for 24 hours in an environment of 23 ° C. and 50% RH (dimension a), left for 24 hours in an environment of 23 ° C. and 80% RH, and again for 24 hours in an environment of 23 ° C. and 50% RH. (Dimension b) In the moisture absorption test, the dimensional change rate before and after the test in the flow direction (MD direction) and the width direction (TD direction) of the film represented by the following formula (1) is 1% or less,
100 × | b−a | / a (1)
And after being left for 24 hours in an environment of 23 ° C. and 50% RH (dimension c), left for 24 hours in an environment of 23 ° C. and 20% RH, and again for 24 hours in an environment of 23 ° C. and 50% RH. In a dehumidification test to be left (dimension d), the present invention relates to a polyvinyl alcohol film in which the dimensional change rate before and after the test in the flow direction and the width direction of the film represented by the following formula (2) is 1% or less.
100 × | d−c | / c (2)

  The difference between the dimensional change rate in the flow direction and the dimensional change rate in the width direction of the film before and after the moisture absorption test and the dehumidification test is preferably 0.5% or less, respectively.

  In the moisture absorption test and the dehumidification test, it is preferable that the time for the dimension after the test to be restored within ± 1% of the dimension before the test is within 12 hours.

  In the film flow direction, the humidity expansion coefficient at 23 ° C. and humidity 20 to 80% RH is 12 ppm /% RH or less, and the humidity expansion coefficient at 23 ° C. and humidity 20 to 50% RH is 7 ppm /% RH or less. Preferably there is.

  It is preferably made of a polyvinyl alcohol resin having a weight average molecular weight of 140,000 to 260000.

  The present invention relates to a method for producing the polyvinyl alcohol film, comprising a step of heat-treating the polyvinyl alcohol film by a floating method so that the nip tension per 1 m of the film width is 20 to 50 N.

  The present invention also relates to a polarizing film comprising the polyvinyl alcohol film.

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

  The polyvinyl alcohol film of the present invention is excellent in dimensional stability and optical properties, and can be preferably used as a raw material for a polarizing film and a polarizing plate.

The present invention is a polyvinyl alcohol film having a thickness of 30 to 70 μm produced by a casting method,
[Condition 1] After being allowed to stand for 24 hours in an environment of 23 ° C. and 50% RH (dimension a), left for 24 hours in an environment of 23 ° C. and 80% RH, and again in an environment of 23 ° C. and 50% RH. In the moisture absorption test that is allowed to stand for 24 hours (dimension b), the dimensional change rate before and after the test in the flow direction (MD direction) and the width direction (TD direction) of the film represented by the following formula (1) is 1% or less, And 100 × | b−a | / a (1)
[Condition 2] After 24 hours in an environment of 23 ° C. and 50% RH (dimension c), left in an environment of 23 ° C. and 20% RH for 24 hours, and again in an environment of 23 ° C. and 50% RH. In the dehumidification test that is allowed to stand for 24 hours (dimension d), the dimensional change rate before and after the test in the flow direction (MD direction) and the width direction (TD direction) of the film represented by the following formula (2) is 1% or less. The present invention relates to a polyvinyl alcohol film.
100 × | d−c | / c (2)

  The polyvinyl alcohol film of the present invention is produced by a casting method, and the thickness is 30 to 70 μm, preferably 35 to 65 μm, more preferably 40 to 60 μm, and particularly preferably 45 to 55 μm. When the thickness of the film is less than 30 μm, the humidity expansion coefficient tends to increase, and when it exceeds 70 μm, the dimensional restoration time becomes long.

  In the moisture absorption test of Condition 1, the dimension a is a distance measured between two points with respect to the flow direction (MD direction) and the width direction (TD direction) in the film plane, and is a reference dimension. It represents the dimensions in a standard humidity environment, and is measured using a film that is allowed to stand for 24 hours in an environment of 23 ° C. and 50% RH and is in an equilibrium state.

  Next, the film is put in a humidity environment of 23 ° C. and 80% RH for 24 hours to sufficiently absorb moisture. The film expands and the dimensions stabilize in the expanded state. The film is then returned to its original standard humidity environment of 23 ° C. and 50% RH. The film shrinks with dehumidification, and the distance between the two points approaches the original dimension a. However, due to the structural change of the polymer, it does not completely return to the original dimension a. The dimension b is a distance between two points after reaching a sufficient equilibrium state again in an environment of 23 ° C. and 50% RH for 24 hours.

In the moisture absorption test of Condition 1, the dimensional change rate is a value calculated by the following formula (1) (unit:%).
100 × | b−a | / a (1)

  That is, the dimensional difference before and after the moisture absorption test is divided by the dimension before the moisture absorption test. The range of the dimensional change rate is 1.0% or less, preferably 0.7% or less, more preferably 0.5% or less, and particularly preferably 0.3% or less. When the dimensional change rate exceeds 1%, the dimensional restoration property is insufficient.

  The condition 2 dehumidification test is the same as the condition 1 moisture absorption test.

  The dimension c measured in a standard humidity environment dehumidifies and shrinks in a dry environment of 23 ° C., 20% RH, 24 hours. When returning to the original standard humidity environment, it expands with moisture absorption and reaches an equilibrium state as a dimension d.

The dimensional change rate in the condition 2 dehumidification test is also calculated by the following formula (2) in the same manner as in the condition 1 moisture absorption test (unit:%).
100 × | d−c | / c (2)

  A preferable range of the dimensional change rate is 1% or less, preferably 0.7% or less, more preferably 0.5% or less, and particularly preferably 0.3% or less. When the dimensional change rate exceeds 1%, the dimensional restoration property is insufficient.

  In the polyvinyl alcohol film of the present invention, the difference between the dimensional change rate in the film flow direction (MD direction) and the dimensional change rate in the width direction (TD direction) before and after the moisture absorption test and the dehumidification test, respectively, It is preferably 0.5% or less, more preferably 0.3% or less, still more preferably 0.2% or less, and particularly preferably 0.1% or less. By making the dimensional change rate uniform in the two directions of the MD direction and the TD direction, the deformation of the liquid crystal cell can be simplified. If the difference between the dimensional change rates exceeds 0.5%, a complicated undulation will occur in the liquid crystal cell, which is not preferable.

  The polyvinyl alcohol-based film of the present invention preferably has a time for restoring the dimension after the test within ± 1% of the dimension before the test in the moisture absorption test and the dehumidification test within 12 hours. Preferably it is 3-11 hours, More preferably, it is 5-10 hours, Most preferably, it is 7-9 hours. When the restoration time exceeds 12 hours, it is not preferable because the time for whitening in the liquid crystal cell becomes long.

  Furthermore, in the polyvinyl alcohol film of the present invention, the humidity expansion coefficient at 23 ° C. and a humidity of 20 to 80% RH is preferably 12 ppm /% RH or less, more preferably 9 to 12 ppm in the film flow direction (MD direction). /% RH, particularly preferably 10 to 11 ppm /% RH, and a coefficient of humidity expansion at 23 ° C. and a humidity of 20 to 50% RH is preferably 7 ppm /% RH or less, more preferably 4 to 7 ppm /% RH. Preferably, it is 5 to 7 ppm /% RH. When the humidity expansion coefficient at a humidity of 20 to 80% RH exceeds 12 ppm /% RH, or when the humidity expansion coefficient at a humidity of 20 to 50% RH exceeds 7 ppm /% RH, the humidity dependency of the produced polarizing film is Large and prone to defects such as white spots.

Here, the humidity expansion coefficient at 23 ° C. and humidity 20 to 80% RH is expressed by the following equation from the dimension e at 23 ° C., 20% RH, 24 hours and the dimension f at 23 ° C., 80% RH, 24 hours. It is a value calculated based on this.
Humidity expansion coefficient (ppm /% RH) = 10 ⁶ | f−e | / 60e

Further, the humidity expansion coefficient at 23 ° C. and humidity 20 to 50% RH is based on the following formula from the dimension e at 23 ° C., 20% RH, 24 hours and the dimension g at 23 ° C., 50% RH, 24 hours. This is a calculated value.
Humidity expansion coefficient (ppm /% RH) = 10 ⁶ | ge | / 30e

  The retardation value of the polyvinyl alcohol film of the present invention is preferably 40 nm or less, more preferably 10 to 30 nm, and still more preferably 15 to 25 nm. If the retardation value exceeds 40 nm, white spots tend to occur.

  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, forming a film, drying, and heat-treating as necessary. Although it manufactures by a method etc., a manufacturing method in particular is not limited. For example, it can be manufactured by a manufacturing method including a step of heat-treating a polyvinyl alcohol film by a floating method so that the tension between nips per 1 m of the film width is 20 to 50 N.

  Hereinafter, the manufacturing method of the polyvinyl alcohol-type film of this invention is demonstrated.

  The polyvinyl alcohol resin used for film formation is usually produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate, but the polyvinyl alcohol film of the present invention is not necessarily limited to this. A small amount of unsaturated carboxylic acid (including salts, esters, amides, nitriles, etc.), olefins having 2 to 30 carbon atoms (ethylene, propylene, n-butene, isobutene, etc.), vinyl ethers, unsaturated sulfonates It may contain a component copolymerizable with vinyl acetate.

  Further, as the polyvinyl alcohol resin, it is also preferable to use a polyvinyl alcohol resin having a 1,2-glycol bond in the side chain, and the polyvinyl alcohol resin having a 1,2-glycol bond in the side chain is, for example, ( A) a method of saponifying a copolymer of vinyl acetate and 3,4-diacetoxy-1-butene, (a) a method of saponifying and decarboxylating a copolymer of vinyl acetate and vinyl ethylene carbonate, A method of saponifying and deketalizing a copolymer of vinyl acetate and 2,2-dialkyl-4-vinyl-1,3-dioxolane, and (d) a copolymer of vinyl acetate and glycerol monoallyl ether. It is obtained by a saponification method or the like.

  Although the weight average molecular weight of a polyvinyl alcohol-type resin is not specifically limited, Preferably it is 120000-300000, More preferably, it is 140000-26000, More preferably, it is 160000-200000. If the weight average molecular weight is less than 120,000, the dimensional restoration property decreases due to an increase in the low molecular weight body, and if it exceeds 300,000, the dimensional restoration derived from stretching unevenness in a polarizing film produced by stretching a polyvinyl alcohol film. It is not preferable because of a decrease in the properties. This is because stress strain generally tends to occur as the molecular weight increases. At present, a polyvinyl alcohol resin for polarizing film having a weight average molecular weight of about 110000 is used, but the present invention is most effective for a high molecular weight film having a weight average molecular weight of 140,000 to 260000. . The weight average molecular weight of the polyvinyl alcohol resin is measured by gel permeation chromatography-low angle laser light scattering method (GPC-LALLS method).

  The saponification degree of the polyvinyl alcohol resin is preferably 97 to 100 mol%, more preferably 98 to 100 mol%, and still more preferably 99 to 100 mol%. When the saponification degree is less than 97 mol%, sufficient optical performance cannot be obtained when a polyvinyl alcohol-based resin is used as an optical film, which is not preferable.

  In the method for producing a polyvinyl alcohol film of the present invention, plastics generally used, such as glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol, etc., are optionally added to the polyvinyl alcohol resin. A nonionic, anionic or cationic surfactant is added.

  A polyvinyl alcohol-based resin aqueous solution is prepared using a polyvinyl alcohol-based resin and a polyvinyl alcohol-based resin composition including the plasticizer and the surfactant. The concentration of the aqueous polyvinyl alcohol resin solution is preferably 10 to 50% by weight, more preferably 15 to 40% by weight, and particularly preferably 20 to 30% by weight. If the concentration is less than 10% by weight, the drying load increases and the production capacity is inferior. If the concentration exceeds 50% by weight, the viscosity becomes too high and uniform dissolution cannot be achieved.

  The temperature condition for dissolving the polyvinyl alcohol-based resin composition is preferably 50 to 200 ° C, more preferably 100 to 150 ° C. If it is less than 50 degreeC, the load of a motor will become large, and when it exceeds 200 degreeC, since degradation of polyvinyl alcohol-type resin will arise, it is not preferable. The dissolution time is preferably 1 to 20 hours, more preferably 2 to 10 hours. If it is less than 1 hour, the dissolution is insufficient, and if it exceeds 20 hours, the productivity is poor.

  Next, the obtained polyvinyl alcohol-based resin aqueous solution is defoamed. Examples of the defoaming method include static defoaming and defoaming with a multi-screw extruder. In the method for producing a polyvinyl alcohol film of the present invention, a method of defoaming with a multi-screw extruder is preferable. 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.

  After the defoaming treatment by the multi-screw extruder, the polyvinyl alcohol resin aqueous solution discharged from the multi-screw extruder is introduced into a T-type slit die by a certain amount and cast onto a drum-type roll or endless belt to form a film. Is done.

  As the T-type slit die, a T-type slit die having an elongated rectangle is usually used.

  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., flow failure occurs, and if it exceeds 100 ° C., foaming is not preferable.

  The casting of the polyvinyl alcohol-based resin aqueous solution 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.

  In casting a film with a drum-type roll, for example, the rotation speed of the drum-type roll is preferably 5 to 30 m / min, and particularly preferably 6 to 20 m / min. Moreover, it is preferable that the surface temperature of a drum type roll is 70-99 degreeC, More preferably, it is 75-97 degreeC. If the surface temperature of the drum-type roll is less than 70 ° C., drying is poor, and if it exceeds 99 ° C., foaming is not preferable. The size of the drum-type roll is not particularly limited as long as a film having a width of 3 m or more is formed. For example, the diameter of the roll is preferably 3100 to 5000 mm, more preferably 3100 to 4000 mm.

  It is preferable that the moisture content of the film formed by casting with a drum-type roll is 10 to 30% by weight. Especially preferably, it is 15-25 weight%. If it exceeds 30% by weight, peeling from the roll is difficult, and the load of the drying process increases. If it is less than 10%, the retardation increases due to rapid water evaporation.

  The obtained film is dried while the front and back surfaces are alternately passed through a plurality of drying rolls.

  The total number of drying rolls used for drying is preferably 10-30, more preferably 12-25, and particularly preferably 13-20. If it is 10 or less, the drying is insufficient, and if it exceeds 30, the equipment load increases.

  The diameter of the drying roll is preferably 100 to 800 mm, more preferably 150 to 500 mm. If the diameter is less than 100 mm, the contact area with the film is insufficient and the drying efficiency is poor, and if the diameter exceeds 800 mm, the retardation tends to increase. Although the width | variety of a drying roll is not specifically limited, 3100-5000mm is preferable, More preferably, it is 3200-4200mm. The surface temperature of the drying roll is 40 to 150 ° C, preferably 50 to 120 ° C, particularly preferably 60 to 110 ° C. If the surface temperature is less than 40 ° C., the drying ability is poor, and if it exceeds 150 ° C., an appearance defect is caused, which is not preferable.

  After drying, the polyvinyl alcohol film is heat-treated for the purpose of crystallization as necessary. In the drying process and the heat treatment process of the polyvinyl alcohol film, various stresses accompanying dehydration are generated. In particular, in the heat treatment step, shrinkage stress accompanying crystallization occurs in addition to dehydration. If unnecessary tension is applied in this step, the internal stress further increases. This stress remains in the film as a permanent strain and greatly reduces the dimensional restoration. On the contrary, if there is no tension at all, a large undulation will occur in the film due to crystallization stress, making it unsuitable for use as a raw material for a polarizing film. Therefore, the heat treatment method includes a floating method in which the film between the rolls is heated with hot air from both sides and a contact heating method with a hot roll. In the manufacturing method of the present invention, the step where the tension is applied is eliminated as much as possible. Therefore, it is preferable to heat by a floating method. At this time, as described above, in a state where there is no tension at all, the film undergoes undulation due to internal stress accompanying crystallization, so it is necessary to set the tension between rolls (generally called the tension between nips) within an appropriate range. . The inter-nip tension is preferably 20 to 50 N, more preferably 21 to 45 N, and further preferably 22 to 40 N in terms of 1 m of film width. If it exceeds 50N, permanent distortion due to tension will occur, and the dimensional restoration will be reduced. Conversely, if it is less than 20N, the film will be undulated, which is not preferable.

  The preferable range of the heat treatment temperature is 90 to 130 ° C, more preferably 95 to 125 ° C, and still more preferably 100 to 120 ° C. If it is less than 90 ° C., crystallization becomes insufficient, and if it exceeds 130 ° C., undulation will occur in the film, which is not preferable. A preferable range of the heat treatment time is 10 to 120 seconds, more preferably 20 to 100 seconds, and further preferably 30 to 80 seconds. If it is less than 10 seconds, crystallization is insufficient, and if it exceeds 120 seconds, the productivity is poor.

  The moisture content of the film after the heat treatment is preferably 5% by weight or less. More preferably, it is 1-4 weight%, More preferably, it is 2-3 weight%. When it exceeds 5% by weight, poor appearance tends to occur during storage of the film.

  The polyvinyl alcohol film of the present invention thus obtained is excellent in dimensional restoration properties and optical characteristics, and is used as a raw film for producing a polarizing film that does not cause deformation of a liquid crystal cell.

  Hereinafter, the manufacturing method of the polarizing film of this invention using the polyvinyl alcohol-type film of this invention is demonstrated.

  As a film thickness of the polyvinyl alcohol-type film used for the polarizing film of this invention, 30-70 micrometers, Furthermore, 35-65 micrometers is preferable, More preferably, it is 40-60 micrometers. If it is less than 30 μm, stretching is difficult, and if it exceeds 70 μm, a polarizing film is produced using such a film, and when the film is bonded to a liquid crystal panel, white spots are likely to occur over time and the display quality of the panel is lowered. Inconvenience, such as doing, is likely to occur.

  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 concentration of iodine is 0.1 to 2 g / L, the concentration of potassium iodide is 10 to 50 g / L, and the weight ratio of potassium iodide / iodine 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 0.5 to 2 mol / L, and it is practically desirable for a small amount of potassium iodide to coexist 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 50 to 70 ° C., and the treatment time is preferably about 5 to 20 minutes. If necessary, the stretching operation may be performed during the treatment.

The polarization degree of the polarizing film of the present invention thus obtained is preferably 99% or more, more preferably 99.5% or more. If the degree of polarization is less than 99%, the contrast in the liquid crystal display tends not to be ensured. Note that the degree of polarization is the light transmittance (H ₁₁ ) measured at the wavelength λ in the state where the two polarizing films are superposed so that the orientation directions thereof are the same direction, and the two polarizing films It is calculated according to the following equation from the light transmittance (H ₁ ) measured at the wavelength λ in a state where the alignment directions are perpendicular to each other.
[(H ₁₁ −H ₁ ) / (H ₁₁ + H ₁ )] ^1/2

  In the present invention, the average value of 5 points when the polarization degree at the center of a 1 m × 1 m film sampled with respect to the width direction of the film as a reference and four corners 20 cm inside from each side is measured. Is the degree of polarization of the film.

  Further, the single transmittance of the polarizing film of the present invention is preferably 43% or more. If it is less than 43%, 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. In the present invention, the average of five points when the light transmittance at the center of a 1 m × 1 m size film sampled with respect to the width direction of the film as a reference and four corners 20 cm inside from each side is measured. The value is taken as the single transmittance of the film.

  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 of cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, polystyrene, polyethersulfone, polyarylene ester, poly-4-methylpentene, polyphenylene oxide, cyclo or norbornene polyolefin, and the like. Or a sheet | seat is mentioned.

  For the purpose of reducing the thickness of the polarizing film of the present invention, a curable resin such as a urethane resin, an acrylic resin, or a urea resin is applied and laminated on one or both sides of the protective film instead of the protective film. You can also.

  The polarizing film of the present invention (or a laminate of a protective film or a curable resin on at least one surface thereof) is formed on a surface of one of the polarizing films as required by a generally known method. In some cases, it may be put to practical use. As the pressure-sensitive adhesive layer, acrylic acid esters such as butyl acrylate, ethyl acrylate, methyl acrylate, 2-ethylhexyl acrylate, and α- such as acrylic acid, maleic acid, itaconic acid, methacrylic acid, and crotonic acid are used. Since the main component is a copolymer with a monoolefin carboxylic acid (including those added with vinyl monomers such as acrylonitrile, vinyl acetate, and styrene), the polarizing property of the polarizing film is not particularly disturbed. Although it is preferable, the present invention is not limited to this, and any pressure-sensitive adhesive having transparency can be used. For example, a polyvinyl ether type or a rubber type may be used.

  The polarizing film of the present invention includes a mobile phone, an electronic desk calculator, an electronic watch, a word processor, a personal computer, a portable information terminal, a liquid crystal television, a liquid crystal display device such as an instrument for cars and machinery, sunglasses, eye protection glasses, and stereoscopic glasses. It is used for reflection-reducing layers for display elements (CRT, LCD, etc.), 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.

(1) Molecular weight:
Measurement is performed under the following conditions by the 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) Dimension Restorability and Humidity Expansion Coefficient A 10 × 10 mm test piece was cut out from the center with respect to the width direction (TD direction) of the film, and a thermomechanical analyzer “TMA-50” manufactured by Shimadzu Corporation. Use to measure. The load weight at this time is 0.5 g.

(3) Retardation value The obtained film is cut | disconnected to width direction (TD direction) 3000mm x flow direction (MD direction) 50mm, and a strip sample is created. Using “KOBRA-21SDH” (manufactured by Oji Scientific Instruments Co., Ltd.), the retardation value is measured over the entire width at a pitch of 100 mm from the inside 50 mm from both ends in the width direction (total 30 points), and the average value is obtained. .

(4) Polarization degree and single transmittance Measured using a high-speed multi-wavelength birefringence measuring apparatus (Otsuka Electronics Co., Ltd .: “RETS-2000”, wavelength: 550 nm).

Example 1
In a 200 l tank, 35 kg of a polyvinyl alcohol resin having a weight average molecular weight of 142,000 and a saponification degree of 99.8 mol%, 100 kg of water, 4.2 kg of glycerin as a plasticizer, and 42 g of polyoxyethylene laurylamine as a release agent are stirred. Then, the temperature was raised to 150 ° C. to obtain a uniformly dissolved polyvinyl alcohol resin aqueous solution having a resin concentration of 25%. Next, the polyvinyl alcohol-based resin aqueous solution was supplied to a twin-screw extruder and defoamed, and then cast from a T-type slit die onto a drum-type roll to form a film. The conditions for such casting film formation are as follows.
Drum type roll Diameter: 3 m, width: 3.3 m, rotation speed: 10 m / min, surface temperature: 90 ° C., resin temperature at T-type slit die outlet: 95 ° C.

The moisture content of the obtained film was 23%. Then, drying was performed while alternately passing the front and back surfaces of the film through a drying roll under the following conditions.
Drying roll Diameter: 250 mm, Width: 3.3 m, Number: 18, Rotational speed: 10 m / min, Surface temperature: 80 ° C.

The water content of the obtained film was 11%. Next, heat treatment was performed by the floating method under the following conditions.
Floating dryer Length: 6m, Conveying speed: 10m / min, Inter-nip tension: 90N (Nip tension per film width of 1m is 30N), Hot air temperature: 110 ° C, Heating time: 36 seconds

  The water content of the obtained polyvinyl alcohol film (width 3 m, thickness 50 μm) was 3%. The retardation value was 20 nm. Table 2 shows the results of evaluating the dimensional restoration property, the difference in dimensional change rate, the restoration time, and the humidity expansion coefficient.

(Manufacture of polarizing films and polarizing plates)
The obtained polyvinyl alcohol film was immersed in an aqueous solution consisting 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 5 times. Then, it dried and obtained the polarizing film. The polarization degree and single transmittance of the obtained polarizing film were measured. Table 3 shows the measurement results.

  Next, using a polyvinyl alcohol-based aqueous solution as an adhesive on both surfaces of the obtained polarizing film, a 80 μm thick triacetyl cellulose film was bonded and dried at 50 ° C. to obtain a polarizing plate.

  Furthermore, after pasting the obtained polarizing plate on the glass plate through the acrylic adhesive layer so that the light absorption axis is 45 °, the polarizing plate previously pasted on the opposite surface of the glass plate On the other hand, a polarizing plate was bonded so as to be arranged in crossed Nicol, and a sample for evaluation of white spots was created. This sample was allowed to stand in an environment of 80 ° C. for 500 hours, and when light leakage, so-called white spots, was visually observed, no light leakage was observed.

Examples 2-5, Comparative Examples 1-4
A polyvinyl alcohol film was obtained in the same manner as in Example 1 except for the conditions in Table 1. Table 2 shows the results of measurement of dimensional restoration property, difference in dimensional change rate, restoration time, and humidity expansion coefficient. Further, a polarizing film and a polarizing plate were obtained in the same manner as in Example 1. The performance of the polarizing film and the polarizing plate was as shown in Table 3.

Claims (9)

A polyvinyl alcohol film having a thickness of 30 to 70 μm manufactured by a casting method,
After being left for 24 hours in an environment of 23 ° C. and 50% RH (dimension a), left for 24 hours in an environment of 23 ° C. and 80% RH, and again for 24 hours in an environment of 23 ° C. and 50% RH. (Dimension b) In the moisture absorption test, the dimensional change rate before and after the test in the flow direction and the width direction of the film represented by the following formula (1) is 1% or less,
100 × | b−a | / a (1)
And after being left for 24 hours in an environment of 23 ° C. and 50% RH (dimension c), left for 24 hours in an environment of 23 ° C. and 20% RH, and again for 24 hours in an environment of 23 ° C. and 50% RH. In a dehumidification test to be allowed to stand (dimension d), a polyvinyl alcohol film characterized in that a dimensional change rate before and after the test in the flow direction and width direction of the film represented by the following formula (2) is 1% or less.
100 × | d−c | / c (2) The polyvinyl chloride according to claim 1, wherein the difference between the dimensional change rate in the flow direction and the dimensional change rate in the width direction of the film before and after the moisture absorption test and the dehumidification test is 0.5% or less, respectively. Alcohol film. 3. The polyvinyl alcohol-based film according to claim 1 or 2, wherein in the moisture absorption test and the dehumidification test, the time for the dimension after the test to be restored within ± 1% of the dimension before the test is within 12 hours. In the film flow direction, the humidity expansion coefficient at 23 ° C. and humidity 20 to 80% RH is 12 ppm /% RH or less, and the humidity expansion coefficient at 23 ° C. and humidity 20 to 50% RH is 7 ppm /% RH or less. The polyvinyl alcohol film according to claim 1, 2 or 3. The polyvinyl alcohol film according to claim 1, 2, 3, or 4, comprising a polyvinyl alcohol resin having a weight average molecular weight of 140,000 to 260000. 6. The production of a polyvinyl alcohol film according to claim 1, further comprising a step of heat-treating the polyvinyl alcohol film by a floating method so that the tension between nips per 1 m of the film width is 20 to 50 N. Method. 6. The polyvinyl alcohol film according to claim 1, wherein the polyvinyl alcohol film is used as an original film of a polarizing film. A polarizing film comprising the polyvinyl alcohol film according to claim 1, 2, 3, 4, 5 or 7. A polarizing plate comprising a protective film provided on at least one surface of the polarizing film according to claim 8.