JP2013105036A - Manufacturing method of polarizer, polarizer, polarizing plate, optical film, and image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a polarizer that sufficiently suppresses generation of blue leak.SOLUTION: A manufacturing method of a polarizer includes a swelling step, a dyeing step, a cross-linking step, and a cleaning step in this order. In the cross-linking step, boric acid processing is performed in boric acid processing steps except a final boric acid processing step such that the boric acid content in a polyvinyl alcohol-based film to be subjected to the final boric acid processing step is 22 weight% or more, and a uniaxial stretching step is performed in the final boric acid processing step.

Description

  The present invention relates to a method for manufacturing a polarizer. Moreover, this invention relates to the polarizer obtained by the said manufacturing 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. For example, a polarizer is required not to generate blue leak in a low wavelength region when arranged in crossed Nicols. That is, it is required that the orthogonal transmittance when the polarizer is arranged in crossed Nicols is small and there is no light leakage.

  Many methods have been proposed so far to obtain such a polarizer. For example, as a method for producing a polarizer, a polyvinyl alcohol film is subjected to a boron compound aqueous solution treatment twice or more, and a section stretch ratio in the first boron compound treatment is 1.6 to 4.5 times. The boron atom content in the polyvinyl alcohol film in the treatment is less than 4% by weight, and the boron atom content in the polyvinyl alcohol film after the second and subsequent boron compound treatments is made 4 to 5% by weight. It has been proposed to uniaxially stretch at a total draw ratio of 5.0 to 7.0 (Patent Document 1). According to the manufacturing method described in Patent Document 1, it is described that a polarizer having excellent optical performance and extremely excellent dimensional stability at the time of heat resistance and having a higher contrast can be obtained.

  However, as described in Patent Document 1, even if the boron atom content in the polyvinyl alcohol film is controlled, a polarizer capable of sufficiently suppressing the occurrence of blue leak has not been obtained.

Japanese Patent No. 397688

  An object of this invention is to provide the manufacturing method of the polarizer which can fully suppress generation | occurrence | production of a blue leak.

  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 is a method for producing a polarizer having a polyvinyl alcohol film having a swelling process, a dyeing process, a crosslinking process and a washing process in this order, and having a stretching process,
The crosslinking step includes a boric acid treatment step with at least two boric acid treatment baths,
And in the boric acid treatment step,
The boric acid treatment is performed by the boric acid treatment step one step before the final boric acid treatment step so that the boric acid content in the polyvinyl alcohol film to be subjected to the final boric acid treatment step is 22% by weight or more. ,
And it is related with the manufacturing method of the polarizer characterized by performing a uniaxial stretching process in the last boric-acid treatment process.

  In the method for producing a polarizer, the uniaxial stretching step in the final boric acid treatment step is preferably performed so that the total stretching ratio of the polyvinyl alcohol film is 5 to 7 times.

  In the manufacturing method of the polarizer, in the step before the final boric acid treatment step, the total draw ratio of the polyvinyl alcohol film to be subjected to the final boric acid treatment step is 2.8 to 4.5 times, It is preferable to perform a uniaxial stretching process.

  In the manufacturing method of the said polarizer, it is preferable that boric acid content in the polyvinyl alcohol-type film after giving a washing | cleaning process is 15 to 30 weight%.

  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 manufacturing method of the polarizer of the present invention, at least two boric acid treatment steps are included as the crosslinking step. In the boric acid treatment step, the final boric acid treatment step has a uniaxial stretching step, but the boric acid content in the polyvinyl alcohol film used in the final boric acid treatment step is controlled to be 22% by weight or more. ing. Thus, sufficient boric acid is included in the polyvinyl alcohol film before the uniaxial stretching step in the final boric acid treatment step. As a result, the degree of boric acid crosslinking in the resulting polyvinyl alcohol film (polarizer) is increased, and the orientation of dichroic substances such as iodine and dichroic dye in the polyvinyl alcohol film (polarizer) is improved. However, it is considered that blue leak is improved in a low wavelength region when arranged in crossed Nicols. As a result, it is considered that the initial optical characteristics are also improved. Blue leak is considered to be improved by forming a highly oriented I ₃ complex, for example, when iodine staining is performed. In the present invention, polyvinyl alcohol becomes dense by forming many boric acid bridges in the boric acid treatment step (hereinafter referred to as the initial boric acid treatment step) up to one step before the final boric acid treatment step. _An environment in which _three complexes are easily formed is formed. Thus, it is considered that the I ₃ complex having high orientation could be formed by forming a large amount of the I ₃ complex in the initial boric acid treatment step and then uniaxially stretching. In addition, since it is difficult to form the I ₃ complex without a narrow space between the molecules of the polyvinyl alcohol, it is considered that there are fewer sites where the I ₃ complex can be formed when there are few boric acid bridges in the initial boric acid treatment step. .

In Patent Document 1, the boron atom content in the polyvinyl alcohol film is controlled to be less than 4% by weight after the first boron compound treatment, and the boron atom content is expressed by the following formula: In terms of boric acid content, it is about 21.8% by weight or less. As in Patent Document 1, when the boric acid content in the polyvinyl alcohol-based film subjected to the final boric acid treatment step is less than 22% by weight, blue leak cannot be sufficiently improved.
Patent Document 1 boron compound content (wt%) = (boron atom content 4 wt% or less × 60 (molecular weight of boric acid) / 11 (boron atomic weight)) = about 21.8 wt% or less

Polyvinyl alcohol films are usually easily dissolved when immersed in high-temperature water. On the other hand, a polyvinyl alcohol-type film changes to the state which is hard to melt | dissolve by carrying out a boric acid bridge | crosslinking. Therefore, in order to subject the polyvinyl alcohol film to a uniaxial stretching process, it is preferable to crosslink the polyvinyl alcohol film to make it difficult to dissolve in high temperature water, while on the other hand immersing it in high temperature water and stretching it in a soft state. In the method for producing a polarizer of the present invention, the content of boric acid in the polyvinyl alcohol-based film subjected to the final boric acid treatment step is 22% by weight or more, and the degree of cross-linking of boric acid in the polyvinyl alcohol-based film is high. Even when the final boric acid treatment step is subjected to a uniaxial stretching step in high-temperature water, the uniaxial stretching step can be performed without dissolving the polyvinyl alcohol film, and the stretching ratio can be easily controlled. In addition, as described above, the polarizer obtained by the production method of the present invention generates a lot of boric acid crosslinks in the initial boric acid treatment step before the uniaxial stretching step in the final boric acid treatment step. Therefore, as a result of performing the uniaxial stretching step in a state where a large amount of I ₃ complex is formed, the I ₃ complex is highly oriented and highly stable, and has low temperature and high humidity durability (for example, 20 ° C., 98% RH). .) Can also be obtained.

  The polyvinyl alcohol film applied to the method for producing a polarizer of the present invention is particularly limited to those having translucency in the visible light region and dispersing and adsorbing dichroic substances such as iodine and dichroic dyes. Can be used without 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, the polyvinyl alcohol film is subjected to a swelling process, a dyeing process, a crosslinking process and a washing process in this order. Each step is performed by immersing the polyvinyl alcohol film in the treatment bath according to each step. Moreover, in the manufacturing method of the polarizer of this invention, although it has a extending process in addition to the said process or with the said process, in the manufacturing method of this invention, an extending process is employ | adopted as a bridge | crosslinking process, At least 2 boric acid It is applied in the final boric acid treatment step in the boric acid treatment step using a treatment bath.

  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 liquid may contain a small amount of an additive such as an iodide compound and a surfactant as described below, alcohol, and 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. 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.

  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 3.0 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 1.1 to 2.6 times, more preferably 1.5 to 2.2 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.

  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 has a boric acid treatment step with at least two boric acid treatment baths. In the treatment bath, boric acid 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. Hereinafter, the case where a boric acid aqueous solution is used as the treatment bath will be described.

  At least two boric acid treatment steps are provided. The boric acid treatment step will be described by dividing it into a final boric acid treatment step and a boric acid treatment step (initial boric acid treatment step) up to one step before the final boric acid treatment step.

  In the initial boric acid treatment step, the boric acid content in the polyvinyl alcohol film obtained by the initial boric acid treatment step (that is, provided for the final boric acid treatment step) is 22% by weight or more, Perform boric acid treatment. The initial boric acid treatment step can be performed by one or more steps. The boric acid content in the polyvinyl alcohol film is 22% by weight or more from the viewpoint of suppressing the occurrence of blue leak in the obtained polarizer. The boric acid content is preferably 22% by weight or more, and more preferably 24% by weight or more. On the other hand, if the boric acid content is too high, there is a possibility that the risk of stretching in the uniaxial stretching process may increase, so the boric acid content is preferably 35% by weight or less, and more preferably 30% by weight or less. It is preferable.

  In the initial boric acid treatment step, the boric acid concentration of the boric acid aqueous solution is preferably about 2 to 8% by weight, and more preferably 3 to 5% by weight. 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 about 0.1 to 10% by weight, and more preferably 0.2 to 5% by weight. The treatment temperature in the initial boric acid treatment step is usually 25 ° C. or higher, preferably 30 to 60 ° C., more preferably 30 to 50 ° C. The treatment time is usually about 5 to 800 seconds, preferably about 8 to 500 seconds. The boric acid content can be controlled by the boric acid concentration, treatment temperature, and treatment time of the boric acid aqueous solution in the initial boric acid treatment step.

  After the initial boric acid treatment step, a final boric acid treatment step is performed. The boric acid concentration of the boric acid aqueous solution in the final boric acid treatment step is preferably about 1 to 10% by weight, and more preferably 2 to 5% by weight. 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 about 0.1 to 10% by weight, and more preferably 0.2 to 5% by weight. The treatment temperature in the final boric acid treatment step is usually 25 ° C. or higher, preferably 40 to 85 ° C., more preferably 50 to 70 ° C. The treatment time is usually about 5 to 800 seconds, preferably about 8 to 500 seconds. In addition, since an extending | stretching process is performed in the last boric-acid treatment process, it is preferable to set temperature higher than the process bath in an initial boric-acid treatment process. The boric acid content can be controlled by the boric acid concentration, treatment temperature, and treatment time of the boric acid aqueous solution in the final boric acid treatment step.

  In addition, at least two boric acid treatment steps are provided, and the final boric acid treatment step is performed together with the stretching step. The stretching process in the final boric acid treatment process is performed by performing a uniaxial stretching process. The stretching in the final boric acid treatment step is preferably performed so that the total stretching ratio is 5 to 7 times the original length of the polyvinyl alcohol film. The total draw ratio is further preferably 5.2 to 6.7 times, and more preferably 5.8 to 6.3 times. Controlling the total draw ratio in the final boric acid treatment step to be in the above range is preferable from the viewpoint of transportability and optical characteristics including stretching. In addition, the total draw ratio of the final boric acid treatment process refers to a cumulative draw ratio including drawing in those processes when the drawing process is accompanied in other processes.

  On the other hand, in the initial boric acid treatment process, the stretching process may or may not be performed. When the initial boric acid treatment step is a plurality of steps, the stretching step can be performed in at least one step. In the initial boric acid treatment step, when no stretching step is involved, the polarizer width can be secured.

  Whether or not the stretching process is performed in the initial boric acid treatment process, the total stretching ratio of the polyvinyl alcohol film (provided in the final boric acid treatment process) at the time when the initial boric acid treatment process is completed. Is preferably performed so as to be 2.8 to 4.5 times. The total draw ratio is further preferably 2.8 to 4.0 times, and more preferably 3.0 to 3.6 times. Controlling the total draw ratio of the polyvinyl alcohol film to be subjected to the final boric acid treatment step within the above range is preferable from the viewpoint of transportability including stretch breakage and optical characteristics. The total draw ratio at the time when the initial boric acid treatment step is completed refers to the cumulative draw ratio including the draw in those steps when the draw step is accompanied in other steps.

  In the method for producing a polarizer of the present invention, the washing step is performed after the swelling step, the dyeing step, and the crosslinking step (including the stretching step). Before the washing step, in addition to the above steps, a 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 are contained in the polyvinyl alcohol film by 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.

  A metal salt solution is used for the metal ion treatment. Hereinafter, zinc impregnation treatment will be described as a representative example of the case of using a zinc salt aqueous solution among metal ion treatments.

  The concentration of zinc ions in the zinc salt aqueous solution is about 0.1 to 10% by weight, preferably 0.3 to 7% by weight. The zinc salt solution is preferably an aqueous solution containing potassium ions and iodine ions with potassium iodide or the like because it is easy to impregnate zinc ions. The potassium iodide concentration in the zinc salt solution is preferably about 0.1 to 10% by weight, more preferably 0.2 to 5% by weight.

  In the zinc impregnation treatment, the temperature of the zinc salt solution is usually about 15 to 85 ° C, preferably 25 to 70 ° C. The immersion time is usually about 1 to 120 seconds, preferably 3 to 90 seconds. In the zinc impregnation treatment, the zinc content in the polyvinyl alcohol film is adjusted to the above range by adjusting the conditions such as the concentration of the zinc salt solution, the immersion temperature of the polyvinyl alcohol film in the zinc salt solution, and the immersion time. adjust. The stage of the zinc impregnation treatment is not particularly limited. Further, it may be carried out simultaneously with the dyeing step and the crosslinking step by allowing a zinc salt to coexist in the dyeing bath and the crosslinking bath.

  The washing step can be performed with water or an iodide-containing aqueous solution (treatment liquid). As the iodide in the iodide-containing aqueous solution, those described above can be used, and among them, for example, potassium iodide and sodium iodide are preferable. The remaining boric acid used in the crosslinking step can be washed away from the polyvinyl alcohol film by the washing step. When the aqueous solution is an aqueous potassium iodide solution, the concentration thereof is preferably in the range of 0.5 to 20% by weight, more preferably in the range of 1 to 15% by weight, and 1.5 to 7% by weight. Within the range is more preferable.

  Although the temperature of the said iodide containing aqueous solution is not specifically limited, Usually, the inside of the range of 15-40 degreeC is preferable, and the inside of the range which is 20-35 degreeC is more preferable. Further, the contact time with the polyvinyl alcohol film is not particularly limited, but is usually preferably in the range of 2 to 30 seconds, and more preferably in the range of 3 to 20 seconds.

  After performing each said process, a drying process is finally given and a polarizer is manufactured. As the drying step, an appropriate method such as natural drying, air drying, heat drying or the like can be used, but heat drying is usually preferably used. When performing heat drying, although heating temperature is not specifically limited, Usually, the inside of the range of 25-80 degreeC is preferable, The inside of the range of 30-70 degreeC is more preferable, The inside of the range of 30-60 degreeC is still more preferable. The drying time is preferably about 1 to 10 minutes.

  From the viewpoint of optical durability, the boric acid content in the polyvinyl alcohol film (polarizer) after the washing step (the boric acid content of the polarizer does not change even when the drying step is applied) is 15 to It is preferably 30% by weight, more preferably 18% by weight or more, and further preferably 20% by weight or more. On the other hand, if the boric acid content is excessively large, the dimensional change in a heating environment increases, which may induce panel warpage. Therefore, the boric acid content is preferably 30% by weight or less, and more preferably 27% by weight. % Or less is preferable.

  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.

  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 an adhesive layer include, for example, salicylic acid ester compounds, benzophenol compounds, benzotriazole compounds, and cyanoacrylate 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. For example, the liquid crystal cell is not particularly limited, and an arbitrary type such as a TN type, STN type, π type, VA type, IPS type, or the like can be applied.

  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.

<Boric acid content>
About the polyvinyl alcohol film (polarizer) obtained by giving the polyvinyl alcohol film taken out from the first boric acid aqueous solution after the first boric acid treatment step and the drying step (washing step), the boric acid content Was measured. The boric acid content was obtained by subjecting the polyvinyl alcohol film to be measured to heat drying at 120 ° C. for 2 hours, and then grinding to 1.0 g. To 1.0 g of the pulverized product, 500 ml of water was added and heated at 95 ° C. for 12 hours to completely dissolve the polyvinyl alcohol film in water to obtain an aqueous solution. A sample solution was prepared by adding 10 g of mannitol and 2 ml of BTB solution to this aqueous solution. To this sample solution, 0.1 mol / l sodium hydroxide was dropped until the neutralization point was reached, and the boric acid content (% by weight) in the polyvinyl alcohol film was calculated from the following formula from the amount dropped.
Boric acid molecular weight: 61.84, boron atomic weight: 10.81

Example 1
A polyvinyl alcohol film (average polymerization degree 2400, VF-PE-A # 6000 manufactured by Kuraray Co., Ltd.) having a thickness of 60 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, immersed in pure water adjusted to 30 ° C. for 60 seconds, swollen, and further uniaxially stretched at a stretch ratio of 1.6.

(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 immersed in the iodine dyeing solution adjusted to 30 ° C. for 60 seconds, while being uniaxially stretched up to a stretching ratio of 2.4 times the original length, Stained.

(First boric acid treatment process: initial boric acid treatment process)
As a treatment solution for the first boric acid bath, an aqueous boric acid solution containing 5% by weight of boric acid and 3% by weight of potassium iodide was used. While transporting the treated polyvinyl alcohol film to the first boric acid bath and immersing it in the first boric acid aqueous solution adjusted to 40 ° C. for 45 seconds, the total draw ratio up to 3.3 times the original length, While uniaxially stretching, it was crosslinked with boric acid. The boric acid content of the polyvinyl alcohol film taken out from the first boric acid aqueous solution was 25.4% by weight.

(Second boric acid treatment step: final boric acid treatment step)
As the treatment solution for the second boric acid bath, an aqueous boric acid solution containing 4% by weight of boric acid and 5% by weight of potassium iodide was used. While transporting the treated polyvinyl alcohol film to a second boric acid bath and immersing in a boric acid aqueous solution adjusted to 64 ° C. for 30 seconds, uniaxially stretching up to a total stretching ratio of 6 times the original length, Cross-linked with boric acid.

(Washing process)
An aqueous solution containing 3% by weight of potassium iodide was used as a 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 27 ° 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. The boric acid content of the polarizer was 25.2% by weight.

(Creation of polarizing plate)
A triacetyl cellulose film having a thickness of 80 μm subjected to saponification treatment was laminated on both sides of the polarizer obtained above via an adhesive composed of a 5% by weight complete saponified polyvinyl alcohol aqueous solution, After adhering, it was dried at 70 ° C. for 4 minutes to produce a polarizing plate.

Examples 2-4, Comparative Examples 1-3
In Example 1, except that the concentration of boric acid aqueous solution used in the first boric acid treatment step and the second boric acid treatment step and the treatment temperature were changed as shown in Table 1, polarization was performed under the same conditions as in Example 1. A child was made. In Examples 3 and 4 and Comparative Examples 1 to 3, the stretching in the first boric acid treatment step was changed, and the total draw ratio up to the first boric acid treatment was changed as shown in Table 1. Moreover, the polarizing plate was produced like Example 1 using the obtained polarizer. Table 1 shows the boric acid contents of the polyvinyl alcohol film and the polarizer extracted from the first boric acid aqueous solution.

  The optical properties (orthogonal transmittance at a wavelength of 410 nm) of the obtained polarizer were measured by the following method. The results are shown in Table 1.

(Optical characteristics measurement method)
The optical properties 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. Note that these transmittances are Y values obtained by correcting the visibility with a J1SZ 8701 2 degree visual field (C light source). The measurement wavelength is 410 nm.

  As shown in Table 1, when the boric acid content of the polyvinyl alcohol film taken out from the first boric acid aqueous solution is 22% by weight or more, the orthogonal transmittance at a wavelength of 410 nm is small and the occurrence of blue leak is observed. It can be seen that it can be suppressed. On the other hand, as Comparative Example 3 shows, even when the boric acid content of the polyvinyl alcohol film in the obtained polarizer is 22% by weight or more, the boric acid content of the polyvinyl alcohol film taken out from the first boric acid aqueous solution It can be seen that when the amount is less than 22% by weight, the orthogonal transmittance at a wavelength of 410 nm is large, and the occurrence of blue leak can be sufficiently suppressed.

Claims (8)

A polyvinyl alcohol-based film has a swelling step, a dyeing step, a crosslinking step and a washing step in this order, and a method for producing a polarizer having a stretching step,
The crosslinking step includes a boric acid treatment step with at least two boric acid treatment baths,
And in the boric acid treatment step,
The boric acid treatment is performed by the boric acid treatment step one step before the final boric acid treatment step so that the boric acid content in the polyvinyl alcohol film to be subjected to the final boric acid treatment step is 22% by weight or more. ,
And the manufacturing method of the polarizer characterized by performing a uniaxial stretching process in the last boric-acid treatment process.   The method for producing a polarizer according to claim 1, wherein the uniaxial stretching step in the final boric acid treatment step is performed so that the total stretching ratio of the polyvinyl alcohol film is 5 to 7 times.   In the step prior to the final boric acid treatment step, the uniaxial stretching step is performed so that the total draw ratio of the polyvinyl alcohol film used in the final boric acid treatment step is 2.8 to 4.5 times. The method for producing a polarizer according to claim 1 or 2.   The method for producing a polarizing film according to any one of claims 1 to 3, wherein the boric acid content in the polyvinyl alcohol film after the washing step is 15 to 30% by weight.   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.