JP2012014001A - Method for manufacturing polarizer, polarizer, polarizing plate, optical film and image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a polarizer, in which a shrinkage ratio in a width direction is decreased and generation of curling can be suppressed.SOLUTION: The method for manufacturing a polarizer includes subjecting a polyvinyl alcohol film to processes of dyeing, crosslinking and stretching, followed by drying. The drying process includes a continuous or intermittent process of restriction drying, in which the film is dried while the width direction of the film is restricted without stretching. The total drying period (T) of the drying process, a period (T0) from starting the drying process until starting the restriction drying process, and a period (T1) from starting the restriction drying process to the end thereof, and a period (T2) of carrying out the restriction drying process in the period (T1), satisfy (T0/T)=0 to 0.2, (T2/T)=0.5 to 1 and (T2/T1)=0.8 to 1.

Description

  The present invention relates to a method for producing a polarizer and a polarizer obtained by the production method. The present invention also relates to a polarizing plate and an optical film using the polarizer, and further to an image display device such as a liquid crystal display device, an organic EL display device and a PDP using the polarizer, the polarizing plate and the optical film.

  Liquid crystal display devices are used in personal computers, TVs, monitors, mobile phones, PDAs and the like. Conventionally, as a polarizer used for a liquid crystal display device or the like, a dyed polyvinyl alcohol film has been used because it has both high transmittance and high degree of polarization. The polarizer is produced by subjecting a polyvinyl alcohol film to various treatments such as swelling, dyeing, cross-linking, and stretching in a bath, followed by washing treatment and drying. Moreover, the said polarizer is normally used as a polarizing plate by which protective films, such as a triacetyl cellulose, were bonded on the single side | surface or both surfaces using the adhesive agent.

  In recent years, liquid crystal display devices have been improved in performance, and liquid crystal panels have been required to improve contrast in order to obtain high visibility. That is, it is desired that black is black and white is whiter and brighter, and accordingly, further improvement in the polarization performance of the polarizer is required. Therefore, it is very important for the polarization performance to have a high transmittance while having a high degree of polarization.

  Further, the polarizer is required to be thin as the liquid crystal display device is thin, and the polarizer is required to be wide as the screen size is increased. However, since the polyvinyl alcohol film used for the polarizer has been subjected to stretching treatment, when moisture is removed by drying treatment, the film shrinks in the width direction, while in the thickness direction. The thickness tends to increase due to the shrinkage in the width direction, and the above requirement cannot be satisfied.

  For example, in the production of a polarizer, it has been proposed to improve the characteristics of the polarizer by controlling the drying process for the film subjected to each process (Patent Documents 1 and 2). Patent Document 1 describes that in the initial stage of the drying process for the film, a polarizer having good durability and optical characteristics can be obtained by rapidly drying the moisture content of the film with a hot roll or the like. ing. Patent Document 2 describes that by performing the drying process of the film while stretching between a plurality of hot rolls, shrinkage in the drying process can be controlled and a wide polarizer can be obtained.

  However, according to the method described in Patent Document 1, although a polarizer having excellent durability and optical characteristics can be obtained, shrinkage in the width direction cannot be sufficiently suppressed, and curling has occurred. Further, according to the method described in Patent Document 2, although shrinkage in the width direction in the drying process can be controlled, the film is stretched in the film running direction, so that curling in the longitudinal direction is likely to occur. Further improvement is also required for shrinkage in the width direction in the drying step.

JP 2009-163202 A JP 2009-048179 A

  An object of this invention is to provide the method of manufacturing a polarizer which can reduce the shrinkage rate in the width direction and can suppress the occurrence of curling.

  Moreover, this invention aims at providing the polarizer obtained by the said manufacturing method, the polarizing plate using the said polarizer, and an optical film. Furthermore, an object of this invention is to provide the image display apparatus using the said polarizer, a polarizing plate, and an optical film.

  As a result of intensive studies to solve the above problems, the present inventors have found that the object can be achieved by a method for producing a polarizer shown below, and have completed the present invention.

That is, the present invention
In the manufacturing method of the polarizer which gives a drying process after giving at least a dyeing process, a bridge construction process, and an extending process to a polyvinyl alcohol film,
The drying step has a constrained drying step that continuously or intermittently dries while constraining the width direction of the film, without stretching, on the film subjected to each step, and
The total drying time of the drying step (T),
The time from the start of the drying process to the start of the constrained drying process (T0),
The time from the start to the end of the constrained drying process (T1),
When the time during which the restraining drying process is performed in the time (T1) is (T2),
(T0 / T) = 0-0.2,
(T2 / T) = 0.5-1 and
(T2 / T1) = 0.8-1 is satisfied, The manufacturing method of the polarizer characterized by the above-mentioned.

  In the method for producing a polarizer, the moisture content of the film subjected to the drying step is 30 to 40% by weight, and the moisture content of the polarizer obtained by performing the drying step. Is preferably 15% by weight or less.

  According to the method for producing a polarizer, the front orientation Rpva (where Rpva = Nx−Ny, and the refractive indexes in the absorption axis direction and the transmission axis direction of the polarizer are Nx and Ny, respectively) is 0. A polarizer of 0.03 to 0.04 can be obtained.

  In the method for producing a polarizer, the constrained drying step can be performed by bringing the film into contact with a hot roll.

  Moreover, this invention relates to the polarizer obtained by the said manufacturing method.

  Moreover, this invention relates to the polarizing plate which provided the transparent protective film in the at least single side | surface of the said polarizer.

  The present invention also relates to an optical film in which at least one of the polarizer or the polarizing plate is laminated.

  The present invention also relates to an image display device using at least one of the polarizer, the polarizing plate or the optical film.

  In the method for producing a polarizer of the present invention, a film obtained by subjecting a polyvinyl alcohol film to a dyeing process, a crosslinking process, and a stretching process is constrained in the width direction without stretching when the drying process is performed. However, shrinkage and curling in the width direction of the obtained polarizer can be suppressed by applying the constrained drying step of drying under predetermined conditions with controlled time.

  In general, in the unconstrained drying in which the film is dried only by hot air or the like in a state where the film is unconstrained, free shrinkage occurs at the end of the film. That is, when moisture is removed from the film by unconstrained drying, the shrinkage rate at the edge of the film becomes larger than the shrinkage rate at the center of the film, and the difference in shrinkage between the edge and the center of the film is large. Become. As a result, the dimensional change increases in the width direction of the film, and curling occurs. The occurrence of curling reduces the yield when optical films such as polarizers (polarizing plates, etc.) are bonded to liquid crystal panels, etc., lowers the durability (such as crack resistance) in environmental tests, and yields at the time of punching. Cause a decline. Further, as described above, unconstrained drying is not preferable because shrinkage in the width direction of the film occurs, resulting in deterioration of the appearance of the obtained polarizer, and reduction in area yield.

  On the other hand, the constrained drying employed in the drying process of the present invention is performed while constraining the width direction of the film, so that tension is applied in the width direction of the film during drying to remove moisture from the film. And the shrinkage at the film edge is suppressed. Therefore, the difference in shrinkage between the end portion and the central portion of the film can be controlled to be small, and the dimensional stability in the width direction of the film is increased. Moreover, although the said constrained drying exists in the state in which the tension | tensile_strength was applied to the width direction, it is not what was extended | stretched in the width direction, and the drying process of this invention is extended | stretched also in the running direction of a film. Since this is done without any shrinkage, shrinkage does not occur due to stretching in the drying process.

Further, in the present invention, it is found that the magnitude of shrinkage at the film edge in the drying process depends on the thermal conductivity coefficient (that is, the moisture content in the film). It was found that shrinkage occurred at the film edge at the initial stage. Note that the moisture content of the film is lower than that in the initial stage of the drying process. In the latter stage, moisture drying depends on the water diffusion coefficient (cm ² / sec) in the film, and It was also found that there was little effect on shrinkage in the width direction. Therefore, in the present invention, the constrained drying is performed from the initial stage of the drying process, and the constrained drying is performed for a long time so that the time from the initial stage is 1/2 or more of the time of the entire drying process. Yes. The drying conditions (drying temperature, time, etc.) are set based on the moisture content of the film subjected to the drying process and the moisture content of the obtained polarizer. However, as in the present invention, constrained drying is prolonged in the initial stage of the drying process. By applying the time, it is possible to obtain a polarizer having a wide width and good dimensional stability while maintaining the original width of the film by suppressing shrinkage at the edge of the film in the initial stage of drying.

  As described above, since the polarizer obtained by the production method of the present invention has good dimensional stability, the occurrence of curling can be suppressed. Since curling can be suppressed, an optical film such as a polarizer (polarizing plate or the like) can be satisfactorily bonded to a liquid crystal panel or the like. Further, since curling is suppressed, durability (for example, crack resistance) can be improved, and the yield at the time of punching the polarizer can be improved. Moreover, since the shrinkage | contraction of the width direction is suppressed, the external appearance of the obtained polarizer is favorable and the area yield of a polarizer is also good.

  Thus, according to the method for producing a polarizer of the present invention, since shrinkage in the width direction of the film is suppressed, the thickness of the polarizer can be reduced, and the polarizer can be made thinner. When the polarizer is thinned, products such as a polarizing plate (optical film) using the polarizer can be thinned, and it is also preferable from the viewpoint of long winding. In addition, even when the polarizer of the present invention is thinned, the durability (for example, crack resistance and the like) is good, and curling can be suppressed.

The orientation function f of the polarizer surface is represented by the following formula: f = (1-D) / (2 * D + 1) * (-2), where D is the peak absorbance at the time of incidence of parallel polarized light (absorbance in the film width direction). ) Ratio A // = a (2941 cm ⁻¹ ) / a (3300 cm ⁻¹ ) The ratio of peak absorbance (absorbance in the film stretching direction) at the time of incidence of vertically polarized light A⊥ = a (2941 cm ⁻¹ ) / a (3300 cm) ^-1 ) divided by 2 (dichroic ratio). Here, a (k) represents the peak absorbance at wave number k. A // and A⊥ can be measured by the ART method (total reflection absorption measurement method; incident angle 45 °). The higher f, the higher the orientation of the polymer and the higher the optical properties. The polarizer obtained by the production method of the present invention has a high orientation function f on the surface of the polarizer and good optical properties.

  On the other hand, the front orientation Rpva of the polarizer obtained by the production method of the present invention (where Rpva = Nx−Ny, and the refractive indexes in the absorption axis direction and the transmission axis direction of the polarizer are Nx and Ny, respectively). 0.03 to 0.04, and the value of the front orientation Rpva is equal to the front orientation Rpva of the polarizer obtained by a method other than the drying step of the present invention (when unconstrained drying is employed). Smaller than that. In the present invention, since the drying is performed in a state where tension is applied in the width direction for a long time from the initial stage of the drying process, the front orientation Rpva is small, and the front orientation Rpva is small. It can be said that this represents a small dimensional change. That is, the front orientation Rpva is considered to be a physical property value (curl, crack resistance, shrinkage in the width direction, etc.) indicating the mechanical properties of the polarizer, and the polarizer obtained by the production method of the present invention has the front orientation Rpva. It can also be specified by the value of.

It is a conceptual diagram which shows an example of the time course of the drying process in the manufacturing method of the polarizer of this invention. It is a conceptual diagram which shows an example of the time course of the drying process in the manufacturing method of the polarizer of this invention. It is a conceptual diagram which shows an example of the time course of the drying process in the manufacturing method of the polarizer of this invention. It is the schematic which shows an example which can be utilized as a drying process in the manufacturing method of the polarizer of this invention. It is the schematic which shows the drying process used by the comparative example.

  As the polyvinyl alcohol film applied to the polarizer of the present invention, a film having translucency in the visible light region and capable of dispersing and adsorbing dichroic substances such as iodine and dichroic dyes can be used without any particular limitation. . Usually, a polyvinyl alcohol film having a thickness of about 10 to 300 μm is used as a raw material. Preferably it is 20-100 micrometers. According to the production method of the present invention, the polarizer can be thinned. From the viewpoint of thinning, the polyvinyl alcohol film can be suitably used even when the thickness of the polyvinyl alcohol film is 40 to 80 μm. The width | variety of the polyvinyl alcohol-type film used as a raw fabric is about 100-5000 mm normally.

  As a polyvinyl alcohol-type film, the polyvinyl alcohol-type film conventionally used for the polarizer is used suitably, for example. Examples of the material for the polyvinyl alcohol film include polyvinyl alcohol and derivatives thereof. Derivatives of polyvinyl alcohol include polyvinyl formal, polyvinyl acetal and the like, olefins such as ethylene and propylene, unsaturated carboxylic acids such as acrylic acid, methacrylic acid and crotonic acid and alkyl esters thereof, acrylamide and the like. Can be given. The degree of polymerization of polyvinyl alcohol is preferably about 100 to 10,000, and more preferably 1,000 to 10,000. A saponification degree of about 80 to 100 mol% is generally used.

  In addition to the above, polyvinyl alcohol films include hydrophilic polymer films such as partially saponified ethylene / vinyl acetate copolymers, polyene-based oriented films such as dehydrated polyvinyl alcohol and dehydrochlorinated polyvinyl chloride. Etc.

  The polyvinyl alcohol film may contain additives such as a plasticizer and a surfactant. Examples of the plasticizer include polyols and condensates thereof, and examples thereof include glycerin, diglycerin, triglycerin, ethylene glycol, propylene glycol, and polyethylene glycol. The amount of the plasticizer used is not particularly limited, but is preferably 20% by weight or less in the polyvinyl alcohol film.

  In the present invention, the polyvinyl alcohol film is subjected to a dyeing process, a crosslinking process, and a stretching process.

  The dyeing step is performed by adsorbing and orienting iodine or a dichroic dye on the polyvinyl alcohol film. The dyeing process can be performed together with the stretching process. Dyeing is generally performed by immersing the film in a dyeing solution. As the staining solution, an iodine solution is generally used. As the iodine aqueous solution used as the iodine solution, an aqueous solution containing iodine ions with iodine and an iodide compound which is a dissolution aid is used. Examples of the iodide compound include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. Etc. are used. As the iodide compound, potassium iodide is preferred. The iodide compound used in the present invention is the same as described above when used in other steps.

  The iodine concentration in the iodine solution is about 0.01 to 1% by weight, preferably 0.02 to 0.5% by weight. The iodide compound concentration is preferably about 0.1 to 10% by weight, more preferably 0.2 to 8% by weight. In iodine staining, the temperature of the iodine solution is usually about 20 to 50 ° C., preferably 25 to 40 ° C. The immersion time is usually about 10 to 300 seconds, preferably 20 to 240 seconds.

  The crosslinking step is usually performed using a boron compound as a crosslinking agent. The order of the crosslinking steps is not particularly limited. The crosslinking step can be performed together with the stretching step. The crosslinking step can be performed multiple times. Examples of the boron compound include boric acid and borax. The boron compound is generally used in the form of an aqueous solution or a water-organic solvent mixed solution. Usually, an aqueous boric acid solution is used. The boric acid concentration of the boric acid aqueous solution is about 2 to 15% by weight, preferably 3 to 13% by weight. In order to impart heat resistance depending on the degree of crosslinking, the boric acid concentration is preferably used. The boric acid aqueous solution or the like can contain an iodide compound such as potassium iodide. When the iodide compound is contained in the boric acid aqueous solution, the iodide compound concentration is preferably about 0.1 to 10% by weight, more preferably 0.2 to 5% by weight.

  The crosslinking step can be performed by immersing the polyvinyl alcohol film in a boric acid aqueous solution or the like. In addition, a boron compound or the like can be applied to the polyvinyl alcohol film by a coating method, a spraying method, or the like. The processing temperature in a bridge | crosslinking process is 25 degreeC or more normally, Preferably it is 30-85 degreeC, Furthermore, it is the range of 30-60 degreeC. The treatment time is usually about 5 to 800 seconds, preferably about 8 to 500 seconds.

  The stretching step is usually performed by performing uniaxial stretching. This stretching method can be applied together with the dyeing process and the crosslinking process. As the stretching method, either a wet stretching method or a dry stretching method can be employed. In the present invention, it is preferable to use a wet stretching method. As the wet stretching method, for example, it is common to perform stretching after performing a dyeing process. Moreover, it can extend | stretch with a bridge | crosslinking process. On the other hand, in the case of dry stretching, examples of the stretching means include an inter-roll stretching method, a heated roll stretching method, and a compression stretching method. In the stretching means, the unstretched film is usually heated. The stretching process can be performed in multiple stages.

  An iodide compound can be contained in the treatment liquid used in the wet stretching method. When the treatment solution contains an iodide compound, the iodide compound concentration is preferably about 0.1 to 10% by weight, more preferably 0.2 to 5% by weight. The treatment temperature in the wet stretching method is usually 25 ° C. or higher, preferably 30 to 85 ° C., more preferably 30 to 60 ° C. The immersion time is usually about 10 to 800 seconds, preferably about 30 to 500 seconds.

  In the stretching step, the total stretching ratio is set such that the total stretching ratio is in the range of 3 to 17 times the original length of the polyvinyl alcohol film. Preferably it is 4-10 times, More preferably, it is 4-8 times. That is, the total draw ratio refers to a cumulative draw ratio including stretching in those steps when stretching is involved in a swelling process described later other than the stretching process. The total draw ratio is appropriately determined in consideration of the draw ratio in the swelling process and the like. When the total draw ratio is low, the orientation is insufficient and it is difficult to obtain a polarizer having high optical properties (polarization degree). On the other hand, if the total draw ratio is too high, stretch breakage is likely to occur, and the polarizer becomes too thin, which may reduce the workability in the subsequent process.

  In the method for producing a polarizer of the present invention, at least the dyeing step, the crosslinking step, and the stretching step are performed, but a swelling step can be performed before the dyeing step. In addition to washing the surface of the polyvinyl alcohol film and the anti-blocking agent by the swelling step, there is also an effect of preventing unevenness such as uneven dyeing by swelling the polyvinyl alcohol film.

  As the treatment liquid used in the swelling process, water, distilled water, or pure water is usually used. If the main component is water, the treatment solution may contain a small amount of an iodide compound, an additive such as a surfactant, alcohol, or the like. Further, when an iodide compound is contained in the treatment liquid, the iodide compound concentration is preferably about 0.1 to 10% by weight, more preferably 0.2 to 5% by weight.

  The treatment temperature in the swelling step is usually preferably adjusted to about 20 to 45 ° C. Furthermore, it is preferable that it is 25-40 degreeC. In addition, if there is swelling unevenness, the portion becomes uneven coloring in the dyeing process, so that swelling unevenness is not generated. The immersion time is usually about 10 to 300 seconds, preferably 20 to 240 seconds.

  In the swelling step, stretching can be appropriately performed. The draw ratio is usually 6.5 times or less with respect to the original length of the polyvinyl alcohol film. Preferably, from the viewpoint of optical properties, the draw ratio is preferably 1.2 to 6.5 times, more preferably 2 to 4 times, and even more preferably 2 to 3 times. By performing stretching in the swelling process, stretching in the stretching process performed after the swelling process can be controlled to be small, and the film can be controlled so as not to be stretched and broken. On the other hand, if the stretching ratio in the swelling process is increased, the stretching ratio in the stretching process becomes too small. In particular, when the stretching process is performed after the crosslinking process, it is not preferable in terms of optical properties.

  In the method for producing a polarizer of the present invention, at least the dyeing step, the crosslinking step, and the stretching step are performed. In addition to these steps, metal ion treatment can be performed. The metal ion treatment is performed by immersing a polyvinyl alcohol film in an aqueous solution containing a metal salt. Various metal ions can be contained in the polyvinyl alcohol film by the metal ion treatment.

  As metal ions, metal ions of transition metals such as cobalt, nickel, zinc, chromium, aluminum, copper, manganese, and iron are particularly preferably used in terms of color tone adjustment and durability. Among these metal ions, zinc ions are preferable from the viewpoints of color tone adjustment and heat resistance. Examples of the zinc salt include zinc halides such as zinc chloride and zinc iodide, zinc sulfate, and zinc acetate.

  In the method for producing a polarizer of the present invention, as described above, the washing step can be performed after at least the dyeing step, the crosslinking step, and the stretching step.

  The washing step can be performed with a potassium iodide solution. The potassium iodide concentration in the potassium iodide solution is usually in the range of about 0.5 to 10% by weight, further 0.5 to 8% by weight, and further 1 to 6% by weight.

  In the washing step with the potassium iodide solution, the treatment temperature is usually about 15 to 60 ° C., preferably 25 to 40 ° C. The immersion time is usually about 1 to 120 seconds, preferably 3 to 90 seconds. The stage of the washing process with the potassium iodide solution is not particularly limited as long as it is before the drying process.

  Moreover, a water washing process can be given as a washing process. The water washing step is usually performed by immersing a polyvinyl alcohol film in pure water such as ion exchange water or distilled water. The water washing temperature is usually in the range of 5 to 50 ° C, preferably 10 to 45 ° C, more preferably 15 to 40 ° C. The immersion time is usually about 10 to 300 seconds, preferably about 20 to 240 seconds.

  The water washing step may be a combination of a washing step with a potassium iodide solution and a water washing step, and a solution appropriately mixed with a liquid alcohol such as methanol, ethanol, isopropyl alcohol, butanol, or propanol can also be used.

  After performing each said process, a drying process is finally given and a polarizer is manufactured. As the polarizer subjected to the drying step, one having a water content of 30 to 40% by weight is usually used. In order to adjust the moisture content to 30 to 40% by weight, it is possible to control the immersion time in the treatment bath (water bath) in each step. The moisture content of the film subjected to the drying step is usually preferably 30 to 35% by weight from the viewpoint of drying efficiency.

  In the drying step of the present invention, the polarizer having a moisture content of 30 to 40% by weight is subjected to a drying step so that the moisture content of the polarizer is usually 15% by weight or less. Since the said process is normally performed in a series of continuous processes, the said drying process can also be performed as a continuous process following the said each process. In general, the moisture content of the polarizer subjected to the drying step is preferably 8 to 15% by weight from the viewpoint of film strength and transportability. The moisture content is preferably 10 to 15% by weight.

  In addition, the moisture content of the polarizer of the present invention is a value measured as follows. That is, the polarizer was cut out to a size of 100 × 100 mm, and the initial weight of this sample was measured. Subsequently, this sample was dried at 120 ° C. for 2 hours, the dry weight was measured, and the moisture content was measured by the following formula. Moisture content (% by weight) = {(initial weight−dry weight) / initial weight} × 100. The weight is measured three times, and the average value is obtained.

  The drying step of the present invention includes a constrained drying step of drying while constraining the width direction of the polarizer without stretching the polarizer subjected to the above steps. The constrained drying step is a step that employs means for drying while constraining the width direction of the polarizer under tension in the width direction. Moreover, although the said constraint drying process is tensioned in the width direction, it dries without extending | stretching. Moreover, although the tension | tensile_strength is applied also to the flow direction (longitudinal direction) of a polarizer, it dries without extending | stretching.

  The constrained drying step is continuously or intermittently included in the entire drying step. Moreover, the said restraining drying process is performed for a long time in the initial stage of a drying process as follows. That is, the total drying time of the drying step is (T), the time from the start of the drying step to the start of the constrained drying step (T0), the time from the start of the constrained drying step to the end (T1), (T0 / T) = 0 to 0.2, (T2 / T) = 0.5 to 1, and (T2) when the time during which the constrained drying process is performed in the time (T1) , (T2 / T1) = 0.8 to 1, a constrained drying process in which time is controlled is performed. The restraint drying process in which the time is controlled will be described below with reference to FIGS. 1A to 1C showing the time course in the drying process.

  The value of (T0 / T) is the ratio of the time (TO) from the start of the drying step to the start of the constrained drying step with respect to the total drying time (T) of the drying step. Indicates that it may begin with the start of the drying process (eg, film entry into the drying oven) or may begin after entering the drying process. When the start of the constrained drying process starts with the start of the drying process, (T0 / T) = 0. This case is illustrated in FIG. 1B. On the other hand, the end point of the time (T0) is the start time of the constrained drying process, and it is considered that the shrinkage of the end portion of the film can be suppressed if the moisture content can be secured to 30% by weight or more until this start time point. It is done. The moisture content is preferably 30 to 40% by weight, more preferably 30 to 35% by weight. From this point of view, the start of the constrained drying process needs to be an initial stage of the drying process, and the time (T0) is set to a short time so that (T0 / T) is 0.2 or less. Is done. The (T0 / T) is preferably 0.15 or less, and more preferably 0.1 or less. The case of having time (T0) (in the case of 0 or more) is shown in FIGS. In addition, also in the aspect of FIG. 1B, the case where it has time (T0) (when it is 0 or more) can be set. In general, the total drying time (T) in the drying step is preferably 30 to 300 seconds, more preferably 30 to 150 seconds, and further preferably 30 to 100 seconds. The time (T0) is usually preferably 60 seconds or shorter, more preferably 30 seconds or shorter, and further preferably 12 seconds or shorter.

  The value of (T2 / T) is the ratio of the time (T2) that is subjected to the constrained drying process to the total drying time (T) of the drying process, and is in the range of (T2 / T) = 0.5-1 Time (T1) and time (T2) are set so that That is, when the value of (T2 / T) satisfies 0.5 or more, it is ensured that 1/2 or more of the total drying time (T) of the drying process is performed in the initial stage of the drying process. The value of (T2 / T) is preferably 0.7 to 0.8. In FIG. 1A, 70% of the total drying time (T) of the drying process is the time (T2) of the constrained drying process, which corresponds to (T2 / T) = 0.7. In addition, as shown in FIG. 1A, the drying means is not particularly limited in the time (T3) from the end point of the constrained drying step to the end point of the drying step (for example, the film exit into the drying oven), and is not constrained drying. Steps can be applied, and intermittent, constrained drying steps can also be provided. In FIG. 1B, the total drying time (T) of the drying process and the time (T2) of the constrained drying process coincide with each other, which corresponds to (T2 / T) = 1.

  The value of (T2 / T1) is the ratio of the time (T2) during which the constrained drying process is performed to the time (T1) from the start to the end of the constrained drying process, and (T2 / T1) = 0.8 to Time (T1) and time (T2) are set to be in the range of 1. Since the constrained drying process can be provided continuously or intermittently, the time from the start to the end of the constrained drying process (T1) does not necessarily match the time during which the constrained drying process is performed (T2). . 1A and 1B show a case where the time (T1) and the time (T2) coincide with each other and the constrained drying process is continuously performed. In this case, (T2 / T1) = 1. .

  On the other hand, the time (T1) and the time (T2) do not coincide with each other, and the constrained drying process is intermittently performed. (T2 / T1) is 0.8 or more, preferably It is set to be 0.9 or more. That is, by setting (T2 / T1) to 0.8 or more, it is possible to substantially reduce the influence of the time (T4) during which the unconstrained drying process is performed in the time (T1). FIG. 1C shows a case where time (T1) and time (T2) do not match. In FIG. 1C, 70% of the total drying time (T) of the drying process is the time (T1) from the start to the end of the constrained drying process, but the time (T1) of the constrained drying process ( This is a case where T2 ′) is provided intermittently five times. In FIG. 1C, at time (T1), the unconstrained process is sandwiched four times, and the constrained drying process is intermittently performed five times. The time (T2) of the constrained drying step in FIG. 1C is the total time of the times (T2 ′) of the five constrained drying steps. The number of intermittent drying of the constrained drying step is not particularly limited as long as it satisfies the range of (T2 / T) = 0.5 to 1 and (T2 / T1) = 0.8 to 1, but usually 10 times or less, Preferably it is 8 times or less. Similar to FIG. 1A, also in FIG. 1C, the drying means is not particularly limited in the time (T3) from the end of the constrained drying process to the end of the drying process (film exit), and an unconstrained drying process can be performed. Also, an intermittent, constrained drying process can be provided.

  Further, in FIG. 1C, the time (T1) is represented by the time (T4) of the unconstrained process and the time (T2 ′) of each constrained drying process. The time of the constrained drying process (T2'-1 before L and T2'-2 after) is (T4) / {(T2'-1) + (T2'-2)}. Satisfying the relationship of 0.4 or less, preferably 0.3 or less can substantially reduce the influence of the unconstrained drying step in the time (T1).

  As a means that can be adopted in the constrained drying step in the drying step of the present invention, a method of drying while maintaining the width direction of the film by a tenter, a method of drying by contacting the film with a heat belt, a film on a heat roll (drum) Examples of the method include drying by contact. When a heat belt or a heat roll (drum) is used as a means for the constrained drying process, the time when the film is in contact with the heat belt or the heat roll corresponds to the constrained drying. When there is an idle running distance (distance that is not in contact with the heat belt or the hot roll), the idle running distance is not included in the restraining drying process. The means for the constrained drying step can set each time shown in FIGS. 1A to 1C.

  For example, when the constrained drying process is performed by a tenter, each time can be normally set as shown in FIG. 1A or B. The time from the start to the end of the constrained drying process (T1) and the constrained drying process The time (T2) can be matched, and furthermore, the total drying time (T) of the drying process can be matched with the time (T2) of the constrained drying process. Each time can be set as shown in FIG. 1A or B even when the constrained drying process is performed by a heat belt. Even when the constrained drying step is performed by a tenter or a heat belt, the constrained drying step can be intermittently performed as shown in FIG. 1C.

  When the constrained drying process is performed by a hot roll, each time can be normally set as shown in FIG. 1C. In the time from the start to the end of the constrained drying process (T1), the constrained drying process is performed. Can be intermittently applied every time (T2 ′), and the time (T2) of the constrained drying process can be controlled by the sum of the times (T2 ′). Usually, when the constrained drying process is performed by a hot roll, the time of the idle running distance in which the film is not in contact with the hot roll is the time (T4) of the non-restraining process. Even when the constrained drying process is performed by a hot roll, the constrained drying process is performed as shown in FIG. 1A or B by arranging the heat roll directly beside it so that there is no idle running distance of the film. Can be applied continuously.

  The drying temperature in the drying step is performed so that the moisture content of the film can be controlled within the above range. The drying temperature is usually set in the range of 40 to 100 ° C. The drying temperature is preferably 50 to 90 ° C, more preferably 60 to 80 ° C. In the case where the film is constrained and dried by bringing it into contact with a hot roll, the drying of the film is accelerated by the hot roll, and therefore the temperature of the hot roll is usually set to be equal to or higher than the temperature of the drying atmosphere.

  Hereinafter, a case where each time is set as shown in FIG. 1C when the constrained drying process is performed by a hot roll will be described with reference to FIG. In FIG. 2, heat rolls R1 to R5 are continuously provided. A guide roll G1 is provided before the upstream heat roll R1, and a guide roll G2 is provided after the downstream heat roll R6. In FIG. 1, five heat rolls are provided, but the number of heat rolls is not particularly limited. It is preferable that the number of heat rolls is usually about 1 to 40, and more preferably 4 to 30. The number of heat rolls is preferably an even number so that both surfaces of the film can be dried uniformly. Moreover, a heat roll can be provided in heating furnaces, such as oven. In FIG. 2, continuously provided heat rolls R1 to R5 are installed in the oven A, and hot air is directed toward the surface of the film F passing through each heat roll on the inner wall (upper and lower) of the oven A. A plurality of hot air vents B can be provided.

  In FIG. 2, an upstream film (polarizer) F is a film that has been subjected to the above-described steps. The time until the film F is introduced into the inlet a1 into the oven and taken out from the outlet a2 corresponds to the total drying time (T) of the drying process. The time required from the entrance a1 into the oven to the point r11 where the film F first contacts the hot roll R1 corresponds to the time (T0) from the start of the drying process to the start of the constrained drying process. In FIG. 2, the constrained drying process is performed through the heat rolls R1 to R5. The time when the film F is in contact with each of the heat rolls R1 to R5 corresponds to the time (T2 ′) during which the constrained drying process is performed in FIG. 1C. For example, at the point r12 where the film F is separated from the point r11 of the heat roll R1 and the heat roll R1, the time during which the film F is in contact with the heat roll R1 corresponds to time (T2 ′). The same applies to the other heat rolls R2 to R5. Further, the time from the point r11 where the film F first contacts the heat roll R1 to the point r52 where the film F leaves the heat roll R5 corresponds to the time from the start to the end of the constrained drying step (T1). . Further, the time required for the free running distance (L) of the film F between the point 12 of the heat roll R1 and the point 21 of the heat roll R2 corresponds to the time (T4) of the non-binding process. The time from the point r52 at which the film F is separated from the heat roll R5 to the outlet a2 is related to the time (T3). In FIG. 2, the time (T3) is represented as an unconstrained drying process.

  The temperature of the drying atmosphere in the drying furnace is 40 to 100 ° C., preferably 50 to 90 ° C., more preferably 60 to 80 ° C. The temperature of the hot rolls R1 to R5 is higher than the temperature of the drying atmosphere in the drying furnace. However, it is preferable to set the temperature so as to be about 0 to 60 ° C., further 3 to 45 ° C., further 4 to 30 ° C. In the above, the temperature of the heat rolls R1 to R5 can be all set at the same temperature.

  In FIG. 2, the temperature measurement of the heat roll (heat roll) is a value measured with a contact thermometer. Also, each time (T), (T0), (T1), (T2), (T3), (T4) in the drying step of the present invention is the contact time of the film to the hot roll (total contact time) ) And the like, it can be controlled by the hot roll diameter, the peripheral speed of the hot roll, the free running distance (L) between the hot rolls, and the like. Usually, a hot roll diameter is 200-2000 mm normally. The rotation speed of the hot roll is usually preferably in the range of 3 to 100 m / min, more preferably in the range of 6 to 100 m / min, and further preferably in the range of 10 to 100 m / min. The idle running distance (L) between the hot rolls is preferably in the range of 50 to 1000 mm, and preferably 50 to 500 mm.

  As shown in FIG. 1, when the film F is allowed to pass through the oven A, an air blowing means can be provided together with the heat roll. In FIG. 1, in the oven A, air is blown by the hot air vent B toward the surface of the film F that passes through the hot rolls R1 to R5. With the hot air vent B, the drying temperature in the oven can be controlled. In this case, the temperature of the hot roll is set to be higher than the drying temperature in the oven. The wind speed of the blowing means is not particularly limited, but the wind speed is preferably 0.5 to 30 m / s, and more preferably 1 to 20 m / s. One place may be sufficient as an air blow means, and two or more places may be sufficient as it. The blowing means can also be provided when the constraining drying process is performed by a heat belt. As a drying means when the constrained drying process is performed by a tenter, hot air drying is exemplified. An example of drying means in the unconstrained drying process is hot air drying.

  As the blowing means, for example, a counter flow method can be adopted. The distance between the film and the blowing means is about 10 to 100 cm, preferably 10 to 50 cm. In addition, the said wind speed is a wind speed in a drying furnace, and can be measured with a minivan type digital anemometer.

  In the present invention, by performing the drying step, the moisture content of the obtained film is preferably controlled so as to be in the above range, but the moisture content can be further reduced thereafter. In order to further reduce the moisture content, a drying step similar to that of the present invention can be performed, and drying can be performed by ordinary drying means (hot air drying, natural drying, air drying, heat drying, etc.). In the present invention, it is preferable to control the moisture content of the obtained film to 8 to 15% by weight at the end of the constrained drying step at time (T1).

  The obtained polarizer can be made into the polarizing plate which provided the transparent protective film in the at least single side | surface according to the conventional method. As a material constituting the transparent protective film, for example, a thermoplastic resin excellent in transparency, mechanical strength, thermal stability, moisture barrier property, isotropy and the like is used. Specific examples of such thermoplastic resins include cellulose resins such as triacetyl cellulose, polyester resins, polyethersulfone resins, polysulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, (meth) acrylic resins, Examples thereof include cyclic polyolefin resins (norbornene resins), polyarylate resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof. A transparent protective film is bonded to one side of the polarizer by an adhesive layer. On the other side, as a transparent protective film, (meth) acrylic, urethane-based, acrylurethane-based, epoxy-based, silicone A thermosetting resin such as a system or an ultraviolet curable resin can be used.

  Although the thickness of a transparent protective film can be determined suitably, generally it is about 1-500 micrometers from points, such as workability | operativity, such as intensity | strength and handleability, and thin layer property. 1-300 micrometers is especially preferable, and 5-200 micrometers is more preferable. The transparent protective film is particularly suitable when the thickness is 5 to 150 μm.

  In addition, when providing a transparent protective film on both sides of a polarizer, the protective film which consists of the same polymer material may be used by the front and back, and the protective film which consists of a different polymer material etc. may be used.

  As the transparent protective film, a phase difference plate having a phase difference of 40 nm or more and / or a thickness direction retardation of 80 nm or more can be used. The front phase difference is usually controlled in the range of 40 to 200 nm, and the thickness direction phase difference is usually controlled in the range of 80 to 300 nm. When a retardation plate is used as the transparent protective film, the retardation plate functions also as a transparent protective film, so that the thickness can be reduced.

  Examples of the retardation plate include a birefringent film obtained by uniaxially or biaxially stretching a polymer material, a liquid crystal polymer alignment film, and a liquid crystal polymer alignment layer supported by a film. The thickness of the retardation plate is not particularly limited, but is generally about 20 to 150 μm.

  In addition, the film which has the said phase difference can be separately bonded to the transparent protective film which does not have a phase difference, and the said function can be provided.

  The transparent protective film may be subjected to surface modification treatment before applying the adhesive. Specific examples of the treatment include corona treatment, plasma treatment, primer treatment, and saponification treatment.

  The surface of the transparent protective film to which the polarizer is not adhered may be subjected to a treatment for hard coat treatment, antireflection treatment, sticking prevention, or diffusion or antiglare.

  An adhesive is used for the adhesion treatment between the polarizer and the transparent protective film. Examples of the adhesive include isocyanate adhesives, polyvinyl alcohol adhesives, gelatin adhesives, vinyl latexes, and water-based polyesters. The said adhesive agent is normally used as an adhesive agent which consists of aqueous solution, and contains 0.5 to 60 weight% of solid content normally. In addition to the above, examples of the adhesive between the polarizer and the transparent protective film include an ultraviolet curable adhesive and an electron beam curable adhesive. The electron beam curable polarizing plate adhesive exhibits suitable adhesion to the various transparent protective films. In particular, it exhibits good adhesion even with respect to acrylic resins for which it was difficult to satisfy the adhesion. The adhesive used in the present invention can contain a metal compound filler.

  The polarizing plate of the present invention is produced by bonding the transparent protective film and the polarizer using the adhesive. The adhesive may be applied to either the transparent protective film or the polarizer, or to both. After the bonding, a drying process is performed to form an adhesive layer composed of a coating dry layer. Bonding of a polarizer and a transparent protective film can be performed with a roll laminator or the like. The thickness of the adhesive layer is not particularly limited, but is usually about 30 to 1000 nm.

  The polarizing plate of the present invention can be used as an optical film laminated with another optical layer in practical use. The optical layer is not particularly limited. For example, for forming a liquid crystal display device such as a reflection plate, a semi-transmission plate, a retardation plate (including wavelength plates such as 1/2 and 1/4), and a viewing angle compensation film. One or more optical layers that may be used can be used. In particular, a reflective polarizing plate or a semi-transmissive polarizing plate in which a polarizing plate or a semi-transmissive reflecting plate is further laminated on the polarizing plate of the present invention, an elliptical polarizing plate or a circularly polarizing plate in which a retardation plate is further laminated on the polarizing plate. A wide viewing angle polarizing plate obtained by further laminating a viewing angle compensation film on a plate or a polarizing plate, or a polarizing plate obtained by further laminating a brightness enhancement film on the polarizing plate is preferable.

  An optical film in which the optical layer is laminated on a polarizing plate can be formed by a method of sequentially laminating separately in the manufacturing process of a liquid crystal display device or the like. There is an advantage that the manufacturing process of a liquid crystal display device or the like can be improved because of excellent stability and assembly work. For the lamination, an appropriate adhesive means such as an adhesive layer can be used. When adhering the polarizing plate and other optical films, their optical axes can be set at an appropriate arrangement angle in accordance with the target retardation characteristics.

  An adhesive layer for adhering to other members such as a liquid crystal cell may be provided on the polarizing plate described above or an optical film in which at least one polarizing plate is laminated. The pressure-sensitive adhesive forming the pressure-sensitive adhesive layer is not particularly limited. For example, an acrylic polymer, silicone-based polymer, polyester, polyurethane, polyamide, polyether, fluorine-based or rubber-based polymer is appropriately selected. Can be used. In particular, those having excellent optical transparency such as an acrylic pressure-sensitive adhesive, exhibiting appropriate wettability, cohesiveness, and adhesive pressure-sensitive adhesive properties, and being excellent in weather resistance, heat resistance and the like can be preferably used.

  Attachment of the adhesive layer to one or both sides of the polarizing plate or the optical film can be performed by an appropriate method. For example, a pressure sensitive adhesive solution of about 10 to 40% by weight in which a base polymer or a composition thereof is dissolved or dispersed in a solvent composed of a suitable solvent alone or a mixture such as toluene and ethyl acetate is prepared. A method in which it is directly attached on a polarizing plate or an optical film by an appropriate development method such as a casting method or a coating method, or an adhesive layer is formed on a separator according to the above, and this is applied to a polarizing plate or an optical film. The method of moving up is mentioned.

  The pressure-sensitive adhesive layer can be provided on one side or both sides of a polarizing plate or an optical film as a superimposed layer of different compositions or types. Moreover, when providing in both surfaces, it can also be set as the adhesion layers of a different composition, a kind, thickness, etc. in the front and back of a polarizing plate or an optical film. The thickness of the pressure-sensitive adhesive layer can be appropriately determined according to the purpose of use and adhesive force, and is generally 1 to 500 μm, preferably 5 to 200 μm, particularly preferably 10 to 100 μm.

  On the exposed surface of the adhesive layer, a separator is temporarily attached and covered for the purpose of preventing contamination until it is put to practical use. Thereby, it can prevent contacting an adhesion layer in the usual handling state. As the separator, except for the above thickness conditions, for example, a suitable thin leaf body such as a plastic film, rubber sheet, paper, cloth, non-woven fabric, net, foam sheet, metal foil, laminate thereof, and the like, silicone type or Appropriate conventional ones such as those coated with an appropriate release agent such as long-chain alkyl, fluorine-based, or molybdenum sulfide can be used.

  In the present invention, the polarizer, the transparent protective film, the optical film, and the like that form the polarizing plate described above, and each layer such as the adhesive layer include, for example, salicylic acid ester compounds, benzophenol compounds, benzotriazole compounds, and cyanoacrylates. It may be a compound having an ultraviolet absorbing ability by a method such as a method of treating with an ultraviolet absorber such as a compound based on nickel or a nickel complex salt compound.

  The polarizing plate or the optical film of the present invention can be preferably used for forming various devices such as a liquid crystal display device. The liquid crystal display device can be formed according to the conventional method. That is, a liquid crystal display device is generally formed by appropriately assembling components such as a liquid crystal cell, a polarizing plate or an optical film, and an illumination system as necessary, and incorporating a drive circuit. There is no limitation in particular except the point which uses the polarizing plate or optical film by invention, and it can apply according to the former. As the liquid crystal cell, any type such as a TN type, an STN type, or a π type can be used.

  An appropriate liquid crystal display device such as a liquid crystal display device in which a polarizing plate or an optical film is disposed on one side or both sides of a liquid crystal cell, or a backlight or a reflector used in an illumination system can be formed. In that case, the polarizing plate or optical film by this invention can be installed in the one side or both sides of a liquid crystal cell. When providing a polarizing plate or an optical film on both sides, they may be the same or different. Further, when forming a liquid crystal display device, for example, a single layer or a suitable part such as a diffusing plate, an antiglare layer, an antireflection film, a protective plate, a prism array, a lens array sheet, a light diffusing plate, a backlight, etc. Two or more layers can be arranged.

  The present invention will be specifically described below with reference to examples and comparative examples.

Example 1
A polyvinyl alcohol film (average polymerization degree 2400, saponification degree 99.9 mol%) having a thickness of 75 μm and a width of 400 mm was used as the raw film. The following steps were performed on the polyvinyl alcohol film in the following order.

(Swelling process)
Pure water was used as a treatment solution for the swelling bath. The polyvinyl alcohol film was conveyed to a swelling bath, immersed in pure water adjusted to 30 ° C. for 45 seconds, and uniaxially stretched twice while swelling.

(Dyeing process)
As a treatment solution for the dyeing bath, an iodine dyeing solution having a concentration of 0.3% by weight of iodine: potassium iodide (weight ratio = 0.5: 8) was used. The polyvinyl alcohol film subjected to the swelling treatment was conveyed to a dyeing bath and dyed while being uniaxially drawn up to a draw ratio of 3 times the original length while being immersed in the iodine dyeing solution adjusted to 30 ° C. for 46 seconds. .

(Crosslinking process)
As a treatment solution for the crosslinking bath, a boric acid aqueous solution containing 3% by weight of boric acid and 3% by weight of potassium iodide was used. The treated polyvinyl alcohol film was conveyed to a crosslinking bath and uniaxially stretched up to a total stretch ratio of 4 times the original length while being immersed in the boric acid aqueous solution adjusted to 30 ° C. for 19 seconds.

(Stretching process)
A boric acid aqueous solution containing 4% by weight of boric acid and 5% by weight of potassium iodide was used as a treatment solution for the stretching bath. The treated polyvinyl alcohol film was conveyed to a stretching bath and uniaxially stretched up to 6 times the total stretching ratio with respect to the original length while being immersed in a boric acid aqueous solution adjusted to 60 ° C. for 13 seconds.

(Washing process)
An aqueous solution containing 3% by weight of potassium iodide was used as the treatment solution for the washing bath. The treated polyvinyl alcohol film was conveyed to a washing bath and immersed in the aqueous solution adjusted to 30 ° C. for 10 seconds. The film obtained after the washing step had a moisture content of 32% by weight and a width of 220 mm.

(Drying process)
Next, the treated polyvinyl alcohol film was dried using an apparatus (oven) as shown in FIG. Five hot rolls (roll diameter 500 mm, peripheral speed 6 m / min) were alternately arranged up and down as shown in FIG. The idle running distance (L) between each heat roll was set to 105 mm. The temperature of R1 to R5 of each heat roll was set to 70 ° C. In the oven, air was blown at a temperature of 75 ° C. and a wind speed of 19 m / s as a blowing means. The temperature in the oven was 70 ° C.
The total drying time (T) of the drying process is 90 seconds,
The time (T0) from the start of the drying process to the start of the constrained drying process is 10 seconds,
The time (T1) from the start to the end of the constrained drying process is 59.2 seconds,
The total time (T2 ′) (T2 ′) for which the constrained drying process is performed at time (T1) is 55 seconds,
The time (T4) of the non-restraining step in the idle running distance (L) between the rolls was 1.05 seconds, and the total (4 locations) of the time (T4) of the non-restraining step was 4.2 seconds.
The moisture content before passing through the first heat roll R1 was 25% by weight.
The moisture content of the film (polarizer) obtained by the above drying was 14% by weight. The film had a thickness of 26 μm and a width of 189 mm.

Examples 2-5
In Example 1, the number and type of heat rolls, and the free running distance (L) between the heat rolls were changed as shown in Table 1, and the heat rolls were arranged so that each time became as shown in Table 1. Except for this, a polarizer was obtained in the same manner as in Example 1. Table 1 shows the moisture content, thickness, width, and the like of the obtained film (polarizer).

Comparative Examples 1-3
In Example 1, as shown in FIG. 3, the drying process was performed by the same oven apparatus as in FIG. 1 (the oven temperature was 70 ° C. and the conveyance speed was 6 m / min) except that no heat roll was arranged. Except for this, a polarizer was obtained in the same manner as in Example 1. Table 1 shows each time of the drying process, moisture content, thickness, width, and the like of the obtained polarizer. However, in Comparative Example 3, in preparing the polarizer described in Example 1, the immersion time in the stretching process was changed to 17 seconds, the total draw ratio with respect to the original length was changed to 4 times, and the immersion time in the cleaning process was changed to 15 seconds. In this case, a polarizer prepared was used.

Comparative Examples 4 and 5
In Example 1, in the drying process, the peripheral speed of the first five heat rolls (R2 to R5 in FIG. 1) is set to 6 m / min, the peripheral speed of the first heat roll (R1 in FIG. 1) from the upstream side. Was set to 6.3 m / min, and a polarizer was obtained in the same manner as in Example 1 except that the film was dried while being stretched (stretching speed ratio: R2-5 / R1 = 1.05). Table 1 shows each time of the drying process, moisture content, thickness, width, and the like of the obtained polarizer. However, in Comparative Examples 4 and 5, in preparing the polarizer described in Example 1, the immersion time of the stretching process was changed to 13 seconds, and the stretching ratio with respect to the original length was changed to 5.7 times. The prepared one was used.

Comparative Examples 6-8
In Example 1, the number and type of heat rolls, and the free running distance (L) between the heat rolls were changed as shown in Table 1, and the heat rolls were arranged so that each time became as shown in Table 1. Except for this, a polarizer was obtained in the same manner as in Example 1. Table 1 shows the moisture content, thickness, width, and the like of the obtained polarizer.

  The moisture content of the film in each of the above examples was calculated by sampling the film from the measurement location, drying it at 120 ° C., and measuring the weight before and after drying. In addition, the measurement location in an Example is immediately after each conveyance roll.

  The following evaluation was performed about the polarizer obtained by the Example and the comparative example, and the polarizing plate obtained from the said polarizer. The results are shown in Table 1.

  The polarizing plate is prepared by adhering the transparent protective film on the both surfaces of the polarizer with a roll bonding machine under a temperature condition of 30 ° C. and then drying at 60 ° C. for 4 minutes. As the transparent protective film, a triacetyl cellulose film having a thickness of 80 μm was used. The adhesive comprises 30 parts by weight of methylol melamine with respect to 100 parts by weight of polyvinyl alcohol resin containing acetoacetyl groups (average polymerization degree 1200, saponification degree 98.5 mol%, acetoacetylation degree 5 mol%), An adhesive aqueous solution that was dissolved in pure water and adjusted to a solid content concentration of 3.2% was used under the temperature condition of ° C.

<Front orientation Rpva>
Measurement was performed at a wavelength of 1000 nm and 23 ° C. using a near-infrared phase difference measuring device manufactured by Oji Scientific Instruments, product name “KOBRA-31X100 / IR”.

<Film surface orientation f>
Using the product name “SPECTRUM2000” manufactured by PERKIN ELMER, the ratio of peak absorbance (absorbance in the film width direction) at the time of parallel polarized light incident by polarized ART FT-IR method A // = a (2941 cm ⁻¹ ) / a ( 3300 cm ^-1) peaks absorbance at vertically polarized incident (film stretching direction of absorbance) ratio ^{A⊥ = a (2941cm -1) /} a ( dichroic ratio divided by 3300 cm ^-1) D = (absorbance ratio a / /) / (Absorbance ratio A⊥) was measured, and the orientation function f = (1−D) / (2 * D + 1) * (− 2) was calculated. Here, a (k) represents the peak absorbance at wave number k.

<Shrinkage rate in the width direction>
From the width (X1) of the film before the drying step and the width (X2) of the film after the drying step, the shrinkage rate (%) in the width direction was determined by the following formula.
Shrinkage rate (%) = {(X1-X2) / X1} × 100

<Durability: Crack resistance>
The obtained polarizer was allowed to stand for 30 minutes under a high temperature condition of 85 ° C. and then for 30 minutes under a low temperature condition of −40 ° C., which was repeated five times. Then, the length (micrometer) of the crack which has generate | occur | produced in the polarizer was confirmed by length measurement in the state left to stand at normal temperature (23 degreeC).

<Curl>
The polarizing plate was cut out to 10 cm × 10 cm, placed on the horizontal plane so that the surface with the curl convex was on the lower side, and the distance (mm) of the longest point from the horizontal plane among the four corners was measured.

<Optical characteristics: measurement of polarization degree>
The optical properties of the polarizer were measured using a spectrophotometer with an integrating sphere (V7100 manufactured by JASCO Corporation).
Note that the degree of polarization is such that two identical polarizers are superposed so that their transmission axes are parallel (transparency: Tp) and superposed so that their transmission axes are orthogonal to each other. In this case, the transmittance (orthogonal transmittance: Tc) is determined by applying the transmittance to the following equation.
Polarization degree (%) = {(Tp−Tc) / (Tp + Tc)} ^1/2 × 100
Each transmittance is represented by a Y value obtained by correcting visibility with a two-degree field of view (C light source) of JIS Z8701, with 100% of the completely polarized light obtained through the Granteller prism polarizer. The measurement wavelength was 550 nm.

F film R1-5 Heat roll A Oven B Hot air vent

Claims (8)

In the manufacturing method of the polarizer which gives a drying process after giving at least a dyeing process, a bridge construction process, and an extending process to a polyvinyl alcohol film,
The drying step has a constrained drying step that continuously or intermittently dries while constraining the width direction of the film, without stretching, on the film subjected to each step, and
The total drying time of the drying step (T),
The time from the start of the drying process to the start of the constrained drying process (T0),
The time from the start to the end of the constrained drying process (T1),
When the time during which the restraining drying process is performed in the time (T1) is (T2),
(T0 / T) = 0-0.2,
(T2 / T) = 0.5-1 and
(T2 / T1) = 0.8-1 is satisfied, The manufacturing method of the polarizer characterized by the above-mentioned.   The moisture content of the film subjected to the drying step is 30 to 40% by weight, and the moisture content of the obtained polarizer is 15% by weight or less by performing the drying step. The method for producing a polarizer according to claim 1, wherein:   The resulting polarizer has a front orientation Rpva (where Rpva = Nx−Ny, and the refractive indices in the absorption axis direction and the transmission axis direction of the polarizer are Nx and Ny, respectively) of 0.03 to 0.04. The method for producing a polarizer according to claim 1, wherein:   The method for producing a polarizer according to claim 1, wherein the constrained drying step is performed by bringing the film into contact with a hot roll.   The polarizer obtained by the manufacturing method in any one of Claims 1-4.   A polarizing plate provided with a transparent protective film on at least one surface of the polarizer according to claim 5.   An optical film, wherein at least one of the polarizer according to claim 5 or the polarizing plate according to claim 6 is laminated. An image display device using at least one polarizer according to claim 5, a polarizing plate according to claim 6, or an optical film according to claim 7.

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