JP5420519B2 - Manufacturing method of polarizer, polarizer, polarizing plate, optical film, and image display device - Google Patents

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.

  Many methods have been proposed so far to obtain such a polarizer. For example, as a method for producing a polarizer, after an unoriented polyvinyl alcohol film is swollen in a swelling bath, iodine or a dichroic dye is adsorbed, and in an aqueous solution containing boric acid, crosslinking, stretching, etc. It has been proposed to perform processing (Patent Documents 1 and 2).

Japanese Patent Laid-Open No. 10-153709 JP 2004-341515 A

  However, as described in Patent Documents 1 and 2, a polarizer obtained by a production method including a treatment step in an aqueous solution containing a boron compound such as boric acid is used on the short wavelength side of the polyvinyl alcohol film. It was found that light leakage occurred and the optical characteristics could not be sufficiently satisfied. Moreover, the polarizer obtained by the said manufacturing method did not satisfy the durability under high temperature.

  The present invention is a method for producing a polarizer having a treatment step in an aqueous solution containing a boron compound, which can suppress light leakage on the short wavelength side and can satisfy durability. It aims at providing the manufacturing method of.

  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 provides a method for producing a polarizer in which a polyvinyl alcohol film is subjected to at least a dyeing step in a dyeing bath, a crosslinking step in a crosslinking bath, and a drawing step in a drawing bath.
The treatment bath according to at least one of the dyeing step, the crosslinking step and the stretching step has a mixed aqueous solution containing an iodide compound and a boron compound, and
Among the dyeing step, the crosslinking step and the stretching step, the mixed aqueous solution in the final treatment bath according to the last step in which the mixed aqueous solution is used is 0.00002 to 0.015 weight in addition to the iodide compound and the boron compound. % Of a water-soluble antioxidant, and a method for producing a polarizer.

  In the method for producing a polarizer, the mixed aqueous solution in the final treatment bath according to the last step preferably has an absorbance of 3 or less in the vicinity of a wavelength of 350 nm.

  The method for producing the polarizer can be suitably applied when the crosslinking step and the stretching step are performed after the dyeing step, the crosslinking step, and the stretching step are performed.

  The method for producing the polarizer can be suitably applied when the last step in which the mixed aqueous solution is used is a crosslinking step or a stretching step.

  In the method for producing a polarizer, the water-soluble antioxidant preferably contains at least one of ascorbic acid, erythorbic acid, chlorogenic acid, citric acid, rosmarinic acid, and salts thereof.

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

  The present invention also relates to a polarizing plate having a transparent protective film on at least one surface of the polarizer.

  The present invention also relates to an optical film comprising the polarizer or the polarizing plate.

  The present invention also relates to an image display device comprising the polarizer, a polarizing plate or an optical film.

A general polarizer can be obtained by uniaxially stretching a dyed polyvinyl alcohol film at a predetermined magnification in an aqueous solution containing a boron compound such as boric acid. Moreover, the aqueous solution containing the boron compound is often used as a mixed aqueous solution containing an iodide compound such as potassium iodide. In the production process of a polarizer, in the case of using a mixed aqueous solution containing a boron compound and iodide compounds, iodide compound is oxidized by the boron compound, I ₃ ^- ions was found to occur. In particular, when the production method of the polarizer is continuous production over a long period of time, the number of I ₃ ⁻ ions increases as the production time increases. The I ₃ ^- ions are attached to the polarizer surface, it forms a polyvinyl alcohol complexed, can not penetrate between the polyvinyl alcohol molecule chains highly oriented. Therefore, I ₃ ^- complex ions and polyvinyl alcohol causes alignment disorder of the polarizer, thereby, light leakage in the short wavelength side is caused of the polarizer, it was found to lower the optical characteristics (transmittance).

In the method for producing a polarizer of the present invention, the treatment bath according to at least one of the dyeing step, the crosslinking step, and the stretching step has a mixed aqueous solution containing an iodide compound and a boron compound. In addition, a mixed aqueous solution containing a predetermined amount of a water-soluble antioxidant is used in addition to the boron compound and the iodide compound in the final treatment bath in the final step in which the mixed aqueous solution is used. With the mixed aqueous solution containing such a water-soluble antioxidant, it is possible to suppress an increase in I ₃ ⁻ ions generated in the mixed solution in the final treatment bath, and to suppress light leakage on the short wavelength side of the polarizer, It is estimated that the deterioration of the optical characteristics could be improved. Further, in the method for producing a polarizer of the present invention, since the deterioration of the optical characteristics is prevented, the production stability is greatly improved. Moreover, according to the manufacturing method of this invention, the polarizer which satisfies durability can be obtained.

  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. Preferably it is 20-100 micrometers.

  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 method for producing a polarizer of the present invention, at least a dyeing process, a crosslinking process, and a stretching process are performed on the polyvinyl alcohol film. In the dyeing process, the crosslinking process, and the stretching process, treatment baths such as a dyeing bath, a crosslinking bath, and a stretching bath are used, and a treatment liquid (an aqueous solution or the like) corresponding to each process is used for each of the treatment baths.

  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 10% by weight, preferably 0.02 to 5% by weight, and more 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 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 dyeing step and 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 1 to 10% by weight, preferably 2 to 7% 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 0.5 to 8% by weight.

  The crosslinking step can be performed by immersing the polyvinyl alcohol film in a boric acid aqueous solution 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, wet stretching is used. In the wet stretching method, for example, stretching is generally performed after the dyeing step. Moreover, it can extend | stretch with a bridge | crosslinking process. 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 50 to 70 ° 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 10 times the original length of the polyvinyl alcohol film. Preferably it is 4-8 times, More preferably, it is 5-7 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.

The method for producing a polarizer of the present invention is applied in the case where a mixed aqueous solution containing an iodide compound and a boron compound is used as the treatment bath according to at least one of the dyeing step, the crosslinking step, and the stretching step. The In addition, in the final treatment bath according to the last step in which the mixed aqueous solution is used in the dyeing step, the crosslinking step, and the stretching step, 0.00002 to 0.015 wt% in addition to the iodide compound and the boron compound. A mixed aqueous solution containing a water-soluble antioxidant is used. That is, even if a mixed aqueous solution containing an iodide compound and a boron compound is used in any of the dyeing step, the crosslinking step, and the stretching step, the final treatment bath according to the last step, in which the mixed aqueous solution is used. By containing a water-soluble antioxidant therein, it is possible to suppress the generation of I ₃ ⁻ ions due to the oxidation of the mixed aqueous solution, and to suppress a decrease in optical characteristics. The temperature of the mixed aqueous solution used in the final treatment bath according to the last step, but is appropriately set according to the type of the last step, occurring oxidation of the mixed aqueous solution, I ₃ ^- ions, temperature The higher the value, the more likely it is. The method for producing a polarizer of the present invention is also suitably used when the temperature of the mixed aqueous solution used in the final treatment bath according to the last step is a high temperature of 60 ° C. or higher.

  The processing order of the dyeing process, the crosslinking process and the stretching process is not particularly limited, but can be suitably applied when the crosslinking process and the stretching process are performed after the dyeing process. The mixed aqueous solution can be applied in any of the dyeing step, the crosslinking step, and the stretching step, but the mixed aqueous solution is preferably applied in the crosslinking step or the stretching step. Therefore, it is preferable to apply so that the last process in which the mixed aqueous solution is used is a crosslinking process or a stretching process.

  In addition, the said dyeing | staining process, a bridge | crosslinking process, and an extending process can be performed by the collective process which performs a some process simultaneously. In the case where a collective process in which a plurality of processes are performed at the same time is performed, when the collective process is the last process, the mixed aqueous solution used in the collective process contains a water-soluble antioxidant. In addition, in the case where each of the dyeing process, the crosslinking process, and the stretching process is a multistage process, if the process related to the multistage process is the last process, the mixing used in the final process of the multistage process The aqueous solution contains a water-soluble antioxidant.

  As the water-soluble antioxidant used in the mixed aqueous solution of the final treatment bath according to the last step, a water-soluble antioxidant having an antioxidant function of an iodide compound by a boron compound can be used. Examples of the water-soluble antioxidant include ascorbic acid (vitamin C), erythorbic acid, chlorogenic acid, citric acid, rosmarinic acid, and salts thereof. Examples of the salt include alkali metal salts such as sodium salt and potassium salt. These water-soluble antioxidants can be used alone or in combination of two or more.

The concentration of the water-soluble antioxidant in the mixed aqueous solution of the final treatment bath according to the last step is 0.00002 to 0.015% by weight. The concentration is preferably 0.0001 to 0.01% by weight, and more preferably 0.0005 to 0.01% by weight. When the concentration is less than 0.00002 wt%, the proportion of the water-soluble antioxidant in the mixed aqueous solution decreases, and the generation of I ₃ ⁻ ions cannot be sufficiently suppressed. Light leakage on the short wavelength side cannot be sufficiently suppressed, and it is not preferable from the viewpoint of durability. When the concentration exceeds 0.015% by weight, the proportion of the water-soluble antioxidant in the mixed aqueous solution increases, so that the obtained polarizer is not sufficiently dyed and the polarizer is decolored. Therefore, the optical characteristics as a polarizer cannot be satisfied.

Moreover, it is preferable that the mixed solution of the final treatment bath according to the last step has an absorbance in the vicinity of a wavelength of 350 nm of 0.1 or less. As described above, the mixed aqueous solution of the final treatment bath according to the last step contains a predetermined proportion of a water-soluble antioxidant in addition to the iodide compound and the boron compound. The ratio of the iodide compound and the boron compound depends on the ratio of the iodide compound and the boron compound described in each step depending on which of the dyeing step, the crosslinking step, and the stretching step is the last step. The mixed aqueous solution containing a boron compound and an iodide compound is designed by designing the ratio of each component of the mixed aqueous solution so that the absorbance in the vicinity of a wavelength of 350 nm is 3 or less. by oxidation of, I ₃ ^- it is possible to suppress the generation of ions. The absorbance of the mixed aqueous solution in the vicinity of a wavelength of 350 nm is preferably 3 or less, and more preferably 2 or less.

  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, when the stretching ratio in the swelling process is increased, the stretching ratio in the stretching process is decreased. In particular, when the stretching process is performed after the crosslinking process, it is not preferable in terms of optical characteristics.

  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 5 to 300 seconds, preferably about 10 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. In the drying step, a drying time and a drying temperature are appropriately set according to the moisture content required for the obtained polarizer (film). The drying temperature is usually controlled in the range of 20 to 150 ° C, preferably 40 to 100 ° C. If the drying temperature is too low, the drying time becomes longer, which is not preferable because efficient production cannot be performed. When the drying temperature is too high, the obtained polarizer is deteriorated and deteriorates in terms of optical properties and hue. The heat drying time is usually about 1 to 5 minutes.

  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 (VF-PS7500 manufactured by Kuraray Co., Ltd.) having an average degree of polymerization of 2400 and a thickness of 75 μm 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 and stretched 2.2 times while being immersed in pure water adjusted to 30 ° C. for 1 minute.

(Dyeing process)
As a treatment solution for the dyeing bath, an iodine dyeing solution having a concentration of 6% by weight of iodine: potassium iodide (weight ratio = 1: 7) was used. The polyvinyl alcohol film subjected to the swelling treatment was conveyed to a dyeing bath and immersed in the iodine dyeing solution adjusted to 30 ° C. for 30 seconds, while being stretched uniaxially to a draw ratio of 3.3 times with respect to the original length, Stained.

(Crosslinking process)
As a treatment solution for the crosslinking bath, a mixed aqueous solution (1) containing 3% by weight of boric acid and 3% by weight of potassium iodide was used. The treated polyvinyl alcohol film was transported to a crosslinking bath and uniaxially stretched to a total stretch ratio of 3.6 times the original length while being immersed in the mixed aqueous solution (1) adjusted to 30 ° C. for 28 seconds. .

(Stretching process)
As a treatment solution for the stretching bath, a mixed aqueous solution (2) containing 4% by weight of boric acid, 5% by weight of potassium iodide, and 0.0017% by weight of ascorbic acid as a water-soluble antioxidant was used. The treated polyvinyl alcohol film was conveyed to a stretching bath and uniaxially stretched up to a total stretching ratio of 6 times with respect to the original length while being immersed in a mixed aqueous solution (2) adjusted to 60 ° C. for 60 seconds. The mixed aqueous solution (2) corresponds to the mixed aqueous solution of the final treatment bath according to the last step of the present invention. The mixed aqueous solution (2) used in the above examples using a spectrophotometer (manufactured by Shimadzu Corporation of UV-3150) was measured absorption spectrum, I ₃ ^- measuring the absorbance at a wavelength of 350nm near derived from ion As a result, it was 0.

(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.

(Drying process)
Next, the treated polyvinyl alcohol film was dried in an oven at 60 ° C. for 4 minutes to obtain a polarizer.

Examples 2-5, Comparative Examples 1-3
In Example 1, except having changed the kind and density | concentration of the water-soluble antioxidant mix | blended with mixed aqueous solution (2) used for the process liquid of an extending | stretching process as shown in Table 1, it is the same conditions as Example 1. A polarizer was produced. In Comparative Example 1, a water-soluble antioxidant is not blended in the mixed aqueous solution (2). Further, in the same manner as in Example 1, the absorbance in the vicinity of a wavelength of 350 nm of the mixed aqueous solution (2) used in each example was measured. The results are shown in Table 1.

(Evaluation)
The optical properties of the polarizers obtained in Examples and Comparative Examples were measured by the following method. The results are shown in Table 1.

<Optical characteristics measurement method>
The optical characteristics of the polarizer were measured with a spectrophotometer with an integrating sphere (V7100 manufactured by JASCO Corporation). The transmittance for each linearly polarized light was measured with 100% of the completely polarized light obtained through the Grantera-prism polarizer.
The single transmittance is a value measured at a wavelength of 550 nm.
The contrast at a wavelength of 410 nm (Cr _{410 nm} ) was determined by the following equation: parallel transmittance at a wavelength of 410 nm (Tp _{410 nm} ) and orthogonal transmittance at a wavelength of 410 nm (Tc _{410 nm} ).
Contrast (Cr _{410 nm} ) = parallel transmittance (Tp _{410 nm} ) / orthogonal transmittance (Tc _{410 nm} )
Note that these transmittances are Y values obtained by correcting the visibility with a J1SZ 8701 2 degree visual field (C light source).

<Durability>
The durability of the polarizers obtained in Example 1 and Comparative Example 1 was evaluated by the following method.
The orthogonal hues a and b of each polarizer were measured with a spectrophotometer with an integrating sphere (V7100 manufactured by JASCO Corporation) (initial value). Next, this polarizer was left in a dry atmosphere at 80 ° C. for 2 hours to conduct a durability test. Then, the orthogonal hues a and b were measured again for the polarizer after the durability test (value after the test). The values obtained by subtracting the orthogonal hues a and b (value after the test) after the durability test from the orthogonal hues a and b (initial value) before the durability test were defined as Δa and Δb, respectively.
Δa = (initial value of orthogonal hue a) − (value after test of orthogonal hue a)
Δb = (initial value of orthogonal hue b) − (value after test of orthogonal hue b)
Further, the overall color difference Δab was obtained from Δa and Δb by the formula: Δab = Δa × Δb.
It can be determined that the greater the value of Δab, the greater the degree of discoloration during heating.
The polarizer obtained in Example 1 was Δab = 0.0007.
The polarizer obtained in Comparative Example 1 was Δab = 1.014.

Claims (9)

In the method for producing a polarizer, the polyvinyl alcohol film is subjected to at least a dyeing process in a dyeing bath, a crosslinking process in a crosslinking bath, and a stretching process in a stretching bath.
The treatment bath according to at least one of the dyeing step, the crosslinking step and the stretching step has a mixed aqueous solution containing an iodide compound and a boron compound, and
Among the dyeing step, the crosslinking step and the stretching step, the mixed aqueous solution in the final treatment bath according to the last step in which the mixed aqueous solution is used is 0.00002 to 0.015 weight in addition to the iodide compound and the boron compound. % A water-soluble antioxidant (however, except for citric acid) .   The method for producing a polarizer according to claim 1, wherein the mixed aqueous solution of the final treatment bath according to the last step has an absorbance in the vicinity of a wavelength of 350 nm of 3 or less.   The method for producing a polarizer according to claim 1, wherein the dyeing step, the crosslinking step, and the stretching step are performed after the dyeing step is performed, and then the crosslinking step and the stretching step are performed.   The method for producing a polarizer according to any one of claims 1 to 3, wherein the last step in which the mixed aqueous solution is used is a crosslinking step or a stretching step. Wherein the water-soluble antioxidant, ascorbic acid, erythorbic acid, chlorogenic acid, b Smarine acid and a polarizer according to any one of claims 1 to 4, characterized in that it comprises at least one one of these salts Manufacturing method.   The polarizer obtained by the manufacturing method in any one of Claims 1-5.   A polarizing plate comprising a transparent protective film on at least one surface of the polarizer according to claim 6.   An optical film comprising the polarizer according to claim 6 or the polarizing plate according to claim 7. An image display device comprising the polarizer according to claim 6, the polarizing plate according to claim 7, or the optical film according to claim 8.