JPWO2016060087A1 - Polarizer and method for producing polarizer - Google Patents

Abstract

The present invention relates to a polarizer, and more particularly, a weight ratio of iodine element to potassium element (iodine element / potassium element) is 0.12 to 0.18, and contains 3 to 4.5% by weight of boron element. Thus, the present invention relates to a polarizer that exhibits a remarkably excellent degree of polarization and heat resistance.

Description

  The present invention relates to a polarizer and a method for manufacturing the same.

  Used in various image display devices such as liquid crystal display devices (LCD), electroluminescence (EL) display devices, plasma display devices (PDP), field emission display devices (FED), organic light emitting diodes (OLED, etc.) The polarizing plate generally includes a polarizer in which an iodine compound or a dichroic polarizing material is adsorbed and oriented on a polyvinyl alcohol (PVA) film, and a polarizer protective film is provided on one surface of the polarizer. The other surface of the polarizer has a multilayer structure in which a polarizer protective film, an adhesive layer bonded to a liquid crystal cell, and a release film are sequentially stacked.

  A polarizer constituting a polarizing plate is required to have high transmittance and degree of polarization in order to be applied to an image display device and provide an image having excellent color reproducibility. Also, as the application of image display devices to various fields spreads and the trend toward larger size becomes more prominent, various image display devices such as liquid crystal display devices may be used at high temperatures for a long time. As a result, the demand for improvement in durability along with improvement in polarization performance and optical performance has increased, and as a result, the conditions for the performance of the polarizing plate have become very strict. In addition, image display devices having characteristics suitable for various environments and applications are currently demanded, and optical durability including hue change under high temperature conditions is demanded.

  Korean Laid-Open Patent Publication No. 2009-70085 discloses a method for manufacturing a polarizer, but cannot provide an alternative to the above problem.

Korean Published Patent No. 2009-70085

  An object of this invention is to provide the polarizer which has the outstanding heat resistance and polarization degree.

  1. A polarizer having a weight ratio of iodine element to potassium element (iodine element / potassium element) of 0.12 to 0.18 and a boron element content of 3 to 4.5% by weight.

  2. The polarizer according to 1 above, wherein the weight ratio of iodine element to potassium element is 0.14 to 0.16.

  3. 3. The polarizer according to 1 or 2, wherein the boron element content is 3.5 to 4.0% by weight.

  4). 4. The polarizer according to any one of 1 to 3, wherein the transmittance is 43% or less.

  5. A polarizing plate comprising a protective film laminated on at least one surface of the polarizer according to any one of 1 to 4 above.

  6). An image display device comprising the polarizing plate described in 5 above.

7). In a method for producing a polarizer comprising the steps of swelling, dyeing, crosslinking, stretching, complementary color and drying a film for forming a polarizer,
The content of boric acid compound in the cross-linking liquid of the cross-linking step is 3 to 4.5% by weight, the content of potassium iodide is 11 to 13% by weight,
The method for producing a polarizer, wherein the content of boric acid compound in the complementary color solution in the complementary color step is 1.5 to 2.5% by weight and the content of potassium iodide is 4 to 8% by weight.

  8). 8. The method for producing a polarizer according to 7 above, wherein the content of the boric acid compound in the dyeing solution in the dyeing step is 0.3 to 5% by weight.

  9. In the above 7 or 8, in the polarizer, the weight ratio of iodine element to potassium element (iodine element / potassium element) is 0.12 to 0.18, and the boron element content is 3 to 4.5% by weight. A manufacturing method of a polarizer.

  10. 10. The method for producing a polarizer according to any one of 7 to 9, wherein the polarizer has a transmittance of 43% or less.

  11. 11. The method for producing a polarizer according to any one of 7 to 10, wherein the polarizer forming film is second stretched at a stretch ratio of 1.01 to 1.1 times in the complementary color step.

  The polarizer of the present invention is excellent in heat resistance. This minimizes the possibility of occurrence of red discoloration even when exposed to high temperature conditions for a long time. In particular, the polarizer of the present invention exhibits improved heat resistance when it does not have high transmittance.

  The polarizer of the present invention exhibits a significantly improved degree of polarization.

  The present invention has a weight ratio of iodine element to potassium element (iodine element / potassium element) of 0.12 to 0.18, and contains 3 to 4.5% by weight of boron element. The present invention relates to a polarizer that simultaneously exhibits heat resistance.

  The present invention will be described in detail below.

<Polarizer>
In the polarizer of the present invention, the weight ratio of iodine element to potassium element is 0.12 to 0.18, and the boron element content is 3 to 4.5% by weight.

  If the weight ratio of iodine element to potassium element is less than 0.12, the degree of polarization decreases, and if it exceeds 0.18, iodine can be decomposed to cause a reddening phenomenon if exposed to a high temperature for a long time. . From the aspect of having excellent polarization degree and heat resistance at the same time, it may be preferably 0.14 to 0.16.

If the content of boron element is less than 3% by weight, the amount of PVA-I ₃ complex having a short wavelength absorption region is small, so the degree of polarization decreases, and if it exceeds 4.5% by weight, a red phenomenon may occur. . Further, if the boron element content is 4.5% by weight or more, the thermal shock resistance is lowered, and cracks may occur during a thermal shock experiment. From the aspect of having excellent polarization degree, heat resistance and thermal shock resistance at the same time, it is preferably 3 to 4.4% by weight, more preferably 3.5 to 4.0% by weight.

  The polarizer of the present invention may have a transmittance of 43% or less. When the transmittance is 43% or less, the effect of improving the heat resistance and thermal shock resistance can be maximized.

  The polarizer of the present invention may be produced by the steps of swelling, dyeing, crosslinking and drying described later for the polarizer-forming film.

  The type of the polarizer-forming film is not particularly limited as long as it is a film that can be dyed with a dichroic substance, that is, iodine or the like. For example, a polyvinyl alcohol film, a partially saponified polyvinyl alcohol film: polyethylene Hydrophilic polymer films such as terephthalate film, ethylene-vinyl acetate copolymer film, ethylene-vinyl alcohol copolymer film, cellulose film, partially saponified films thereof; or dehydrated polyvinyl alcohol And polyene oriented films such as polyvinyl alcohol film subjected to dehydrochlorination treatment. Among these, a polyvinyl alcohol film is preferable because it not only has an excellent effect of enhancing the uniformity of the degree of polarization in the plane but also has an excellent dyeing affinity for iodine.

  In the polarizer of the present invention, the method for adjusting the weight ratio of iodine element to potassium element to have the above range is not particularly limited. For example, the concentration of potassium iodide in the cross-linking solution or complementary color solution may be changed, It can adjust by changing the residence time in the bridge | crosslinking tank or complementary color tank of a child formation film. Similarly, the polarizer is adjusted to have the boron element content by changing the concentration of the boric acid compound in the crosslinking solution or complementary color solution, or by changing the residence time of the polarizer forming film in the crosslinking vessel or complementary color vessel. You can, but you are not limited to this.

<Polarizing plate>
The present invention also provides a polarizing plate in which a protective film is laminated on at least one surface of the polarizer.

  The type of the protective film is not particularly limited as long as it is a film excellent in transparency, mechanical strength, thermal stability, moisture shielding property, isotropy, etc. Specific examples include polyethylene terephthalate, polyethylene Polyester resins such as isophthalate and polybutylene terephthalate; Cellulosic resins such as diacetyl cellulose and triacetyl cellulose; Polycarbonate resins; Polyacrylic resins such as polyethyl (meth) acrylate and polyethyl (meth) acrylate; Polystyrene and acrylonitrile Styrenic resin such as styrene copolymer; Polyolefin resin such as polyethylene, polypropylene, cyclo or polyolefin having a norbornene structure, ethylene propylene copolymer, etc .; Polyamide resin such as nylon and aromatic polyamide Imide resin, polyether sulfone resin, sulfone resin, polyether ketone resin, sulfurized polyphenylene resin, vinyl alcohol resin, vinylidene chloride resin, vinyl butyral resin, arylate resin, polyoxymethylene resin A film composed of a thermoplastic resin such as an epoxy resin may be used, and a film composed of a blend of the thermoplastic resin may be used. Moreover, you may use the film which consists of thermosetting resins, such as (meth) acrylic-type, urethane type, an epoxy type, a silicon type, or ultraviolet curable resin. Among these, a cellulose-based film having a surface soaped (saponified) by alkali or the like is particularly preferable in view of polarization characteristics or durability. Further, the protective film may have a function of the following optical layer.

  The structure of the polarizing plate is not particularly limited, and various optical layers satisfying necessary optical characteristics may be laminated on the polarizer. For example, a structure in which a protective film for protecting the polarizer is laminated on at least one surface of the polarizer; a hard coat layer, an antireflection layer, an anti-adhesion layer, a diffusion prevention layer on at least one surface of the polarizer or the protective film A structure in which a surface treatment layer such as an antiglare layer is laminated; a structure in which an alignment liquid crystal layer or other functional film for compensating a viewing angle is laminated on at least one surface of a polarizer or a protective film. There may be. In addition, wave plates (including λ plates) such as optical films such as polarization conversion devices, reflectors, semi-transmissive plates, half-wave plates, or quarter-wave plates used to form various image display devices A structure in which one or more of a phase difference plate, a viewing angle compensation film, and a brightness enhancement film are stacked as an optical layer. More specifically, as a polarizing plate having a structure in which a protective film is laminated on one surface of a polarizer, a reflective polarizing plate or a semi-transmissive polarizing plate in which a reflector or a semi-transmissive reflector is laminated on the laminated protective film; An elliptical or circular polarizing plate on which a phase difference plate is laminated; a wide viewing angle polarizing plate on which a viewing angle compensation layer or a viewing angle compensation film is laminated; or a polarizing plate on which a brightness enhancement film is laminated is preferable.

  Such a polarizing plate is applicable not only to a normal liquid crystal display device but also to various image display devices such as an electroluminescence display device, a plasma display device, and a field emission display device.

<Method for producing polarizer>
The method for producing a polarizer of the present invention includes the steps of swelling, dyeing, crosslinking, stretching, complementing and drying the film for forming a polarizer.

  The number of repetitions of each production step of the polarizer of the present invention, process conditions, and the like are not particularly limited as long as they do not depart from the purpose of the present invention. It may be performed simultaneously with two or more steps.

  The film for forming a polarizer is not particularly limited, and the above-mentioned film can be exemplified, and a polyvinyl alcohol film may be preferable.

  Hereinafter, a method for manufacturing a polarizer according to an embodiment of the present invention will be described in detail.

Swelling step The swelling step is performed by immersing the unstretched polarizer-forming film in a swelling tank filled with a swelling aqueous solution before dyeing it, such as dust deposited on the surface of the polarizer-forming film or an anti-blocking agent. This is a step for removing unnecessary impurities, swelling the polarizer-forming film to improve the drawing efficiency, and suppressing the unevenness of dyeing to improve the physical properties of the polarizer.

  Usually, water (pure water, deionized water) may be used alone as the swelling aqueous solution, and a small amount of glycerin may be added to improve the processability of the polymer film.

  When glycerin is included, the content is not particularly limited, and may be, for example, 5% by weight or less of the total weight of the aqueous solution for swelling.

  The temperature of the swelling tank is not particularly limited, and may be, for example, 20 to 45 ° C., preferably 20 to 40 ° C. When the temperature of a swelling tank is in said range, it is excellent in subsequent extending | stretching and dyeing | staining efficiency, and can prevent the expansion of the film by excessive swelling.

  The execution time of the swelling step (swelling bath immersion time) is not particularly limited, and may be, for example, 180 seconds or less, and preferably 90 seconds or less. When the swelling bath immersion time is within the above range, it is possible to suppress saturation due to excessive swelling, prevent breakage due to softening of the polarizer forming film, and uniform adsorption of iodine in the dyeing step The degree of polarization can be improved.

Both the swelling step and the stretching step may be performed. In this case, the stretching ratio may be about 1.1 to 3.5 times, preferably 1.5 to 3.0 times. When the stretch ratio is less than 1.1 times, wrinkles may occur, and when it exceeds 3.5 times, the initial optical characteristics may be deteriorated.
In the swelling step, an expander roll, a spiral roll, a crown roll, a cross guider, a bend bar or the like may be provided in the bath and / or at the entrance / exit of the bath.

Dyeing step The dyeing step is a step of immersing the polarizer-forming film in a dyeing tank filled with a dichroic substance, for example, a dyeing solution containing iodine, and adsorbing iodine to the polarizer-forming film.

  The staining liquid may further contain water, a water-soluble organic solvent, or a mixed solvent thereof and iodine. The concentration of iodine may be 0.4 to 400 mmol / L in the staining solution, preferably 0.8 to 275 mmol / L, more preferably 1 to 200 mmol / L.

  The staining solution may further contain iodide as a solubilizing agent for improving the staining efficiency.

  The type of iodide is not particularly limited. For example, potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide. And titanium iodide, and potassium iodide is preferred in that it has high solubility in water. These can be used alone or in admixture of two or more.

  The content of the iodide is not particularly limited, and may be, for example, 0.01 to 10% by weight, preferably 0.1 to 5% by weight, based on the total weight of the staining solution.

  The staining solution used in the staining step of the present invention may further contain a boric acid compound. By including the boric acid compound in the dyeing solution, the residence time of the boric acid compound can be improved before the crosslinking reaction, and the complex formation rate of the dichroic substance in the polarizer-forming film can be increased. Thereby, the hue durability of a polarizer can be improved and the degree of polarization is improved.

  The concentration of the boric acid compound in the staining solution is not particularly limited, but may be, for example, 0.3 to 5% by weight, preferably 0.5 to 3% by weight, based on the total weight of the staining solution. Good. When the concentration of the boric acid compound in the staining solution is less than 0.3% by weight, the effect of increasing the formation of iodine complex decreases, and when it exceeds 5% by weight, cutting may occur due to an increase in stress.

  The kind of the boric acid compound is not particularly limited, and examples of the boric acid compound include boric acid, sodium borate, potassium borate, and lithium borate, and boric acid may be preferable. You may use these individually or in mixture of 2 or more types.

  The temperature of the dyeing tank is not particularly limited, and may be, for example, 5 to 42 ° C., preferably 10 to 35 ° C.

  The time for immersing the polarizer forming film in the dyeing tank is not particularly limited, and may be, for example, 1 to 20 minutes, preferably 2 to 10 minutes.

  The stretching step may be performed simultaneously with the dyeing step, and the stretching ratio in this case may be 1.01 to 2.0 times, and preferably 1.1 to 1.8 times.

  Further, the cumulative stretch ratio of the polarizer up to the swelling and stretching steps is preferably 1.2 to 4.0 times. When the cumulative stretch ratio is less than 1.2 times, the film may be wrinkled, and when it exceeds 4.0 times, the initial optical properties may be deteriorated.

Cross-linking step The cross-linking step is a step of fixing the adsorbed iodine molecules by immersing the dye-forming film dyed in the cross-linking solution so that the dyeability of the physically adsorbed iodine molecules does not deteriorate due to the external environment. It is.

  The crosslinking solution used in the crosslinking step of the present invention contains a boric acid compound. When the crosslinking liquid contains a boric acid compound, it is possible to improve the crosslinking efficiency, suppress the generation of wrinkles in the film during the process, and improve the optical characteristics by forming the orientation of the dichroic substance.

  When iodine, which is a dichroic dye, is unstable in crosslinking reaction, iodine molecules may be detached by a moist heat environment, so that sufficient crosslinking reaction is required.

  The cross-linking step according to the present invention may be performed in the first cross-linking step and the second cross-linking step, and a boric acid compound may be included in the cross-linking liquid used in one or more of the cross-linking steps.

  The concentration of the boric acid compound in the crosslinking liquid is 3 to 4.5% by weight, preferably 4 to 4.5% by weight. If the concentration of the boric acid compound in the cross-linking liquid is less than 3% by weight, the degree of polarization decreases, and if it exceeds 4.5% by weight, the tension increases due to excessive cross-linking and cutting may occur.

  The boric acid compound may be the same as that used in the dyeing step.

  The cross-linking liquid of the present invention may contain water used as a solvent and an organic solvent that can be mutually dissolved together with water, and in order to prevent the uniformity of the degree of polarization in the plane of the polarizer and the desorption of dyed iodine. Further, potassium iodide may be included.

  The concentration of potassium iodide in the crosslinking solution is 11 to 13% by weight, preferably 12 to 13% by weight. If the concentration of potassium iodide in the cross-linking liquid is less than 11% by weight, the degree of polarization decreases, and if it exceeds 13% by weight, the heat resistance decreases, and a red phenomenon may occur when exposed to high temperatures for a long time. .

  In addition, the crosslinking solution may further contain the above-described iodide within a range not impairing the object of the present invention.

  The temperature of the crosslinking tank is not particularly limited, but may be, for example, 20 to 70 ° C, and preferably 40 to 60 ° C.

  The time for immersing the polarizer-forming film in the crosslinking tank is not particularly limited, and may be, for example, 1 second to 15 minutes, and preferably 5 seconds to 10 minutes.

  The stretching step may be performed simultaneously with the crosslinking step, in which case the stretching ratio of the first crosslinking step may be 1.4 to 3.0 times, preferably 1.5 to 2.5 times. It is good. Further, the draw ratio of the second crosslinking step may be 1.01 to 2.0 times, and preferably 1.2 to 1.8 times.

  The cumulative stretching ratio of the first crosslinking step and the second crosslinking step may be 1.5 to 5.0 times, preferably 1.7 to 4.5 times. When the cumulative stretch ratio is less than 1.5 times, the effect of increasing the crosslinking efficiency is insignificant. When the cumulative stretch ratio exceeds 5.0 times, the film is broken by excessive stretching, and the production efficiency is lowered. obtain.

Stretching step As described above, the stretching step may be performed together with at least one of a swelling step, a dyeing step, and a crosslinking step, or may be performed in air or an inert gas while transferring the film after the step, It may be performed as an independent stretching step using a separate stretching tank filled with a stretching solution. Alternatively, an unstretched polarizer-forming film may be stretched in air or an inert gas before the swelling step, and then the film may be swollen, dyed, crosslinked, washed and dried.

  Stretching may be performed in one step or may be performed in two or more steps, but is preferably performed in two or more steps. The stretching may be performed by a method such as providing a peripheral speed difference of the nip roll. Similarly to the swelling step, an expander roll, a spiral roll, a crown roll, a cross guider, a bend bar or the like may be provided in the bath and / or at the entrance / exit of the bath.

  The total cumulative draw ratio of the present invention is preferably 4.0 to 7.0 times. In this specification, “cumulative stretch ratio” means a value obtained by multiplying the stretch ratio of each step.

Complementary color step The complementary color step is a step of adjusting the hue by immersing the film after the crosslinking step in a complementary color solution containing a boric acid compound and iodide.

  The complementary color solution used in the complementary color step of the present invention contains a boric acid compound.

  The boric acid compound may be the same as that used in the dyeing step.

  The concentration of the boric acid compound in the complementary color solution is 1.5 to 2.5% by weight, preferably 1.8 to 2.2% by weight. If the concentration of the boric acid compound in the complementary color liquid is less than 1.5% by weight, the orientation of iodine cannot be improved, and the effect of suppressing hue change and improving durability is insignificant. If the weight percentage is exceeded, the thermal shock resistance decreases.

  The complementary color solution of the present invention may contain water used as a solvent and an organic solvent that is mutually soluble with water, in order to prevent the uniformity of the degree of polarization in the plane of the polarizer and the desorption of dyed iodine. And a small amount of potassium iodide.

  The concentration of potassium iodide in the complementary color solution is 4 to 8% by weight, preferably 5 to 7% by weight. If the concentration of potassium iodide is less than 4% by weight, the degree of polarization decreases, and if it exceeds 8% by weight, the heat resistance decreases, and when it is exposed to a high temperature for a long time, a reddening phenomenon may occur.

  In the method for producing a polarizer of the present invention, the polarizer produced by adjusting the concentration of the boric acid compound and potassium iodide in the crosslinking solution and the concentration of the boric acid compound and potassium iodide in the complementary color solution to the above ranges. The weight ratio of iodine element to potassium element (iodine element / potassium element) is 0.12 to 0.18, and the boron element content can be 3 to 4.5% by weight. The advantages of this are as described above.

  When the dyeing solution in the dyeing step contains a boric acid compound in the above-described concentration range, the adjustment to the above range is easier.

  In addition, the complementary color solution may further contain the above-described iodide within a range not impairing the object of the present invention.

  Further, in the present invention, the polarizer forming film may be subjected to the second stretching in the complementary color step.

  By performing the second stretching, the degree of orientation of the dichroic substance complex can be increased and the stability can be improved, whereby the polarizer produced by the method of the present invention is complex even after being exposed to a high temperature for a long time. Decomposition is minimized, and hue durability is excellent.

  The second stretching may be performed at a stretching ratio of 1.01 to 1.1 times. If the draw ratio is less than 1.01, the effect of improving the degree of orientation of the dichroic substance complex is negligible. If the draw ratio is more than 1.1 times, the film can be broken by excessive stretching.

  The temperature of the complementary color tank is 20 to 70 ° C., and the immersion time of the polarizer forming film in the complementary color tank may be 1 second to 15 minutes, preferably 5 seconds to 10 minutes.

Washing Step If necessary, the method for producing a polarizer of the present invention may further include a washing step after the complementary color is completed.

  The washing step is a step of immersing the polarizer-forming film whose complementary color has been completed in a washing tank filled with a washing solution, and removing unnecessary residues attached to the polarizer-forming film in the previous step.

  The aqueous washing solution may be water (deionized water), and iodide may be further added thereto. As the iodide, the same ones used in the dyeing step can be used, and among these, sodium iodide or potassium iodide is preferably used. The content of iodide is not particularly limited, and may be, for example, 0.1 to 10 parts by weight, preferably 3 to 8 parts by weight, based on the total weight of the aqueous washing solution.

  The temperature of the washing tank is not particularly limited, and may be, for example, 10 to 60 ° C, and preferably 15 to 40 ° C.

  The washing step can be omitted and may be performed each time a previous step such as a dyeing step, a crosslinking step, a stretching step or a complementary color step is completed. Moreover, it may be repeated one or more times, and the number of repetitions is not particularly limited.

Drying step The drying step is a step of obtaining a polarizer having excellent optical properties by drying the washed film for forming a polarizer and further improving the orientation of iodine molecules dyed by neck-in by drying.

  As drying methods, methods such as natural drying, air drying, heat drying, microwave drying, hot air drying and the like can be used. Recently, a new microwave treatment that activates and dries only the water in the film has been newly introduced. In general, hot air treatment and far-infrared treatment are mainly used.

  Although the temperature at the time of hot air drying is not particularly limited, it is preferably performed at a relatively low temperature in order to prevent deterioration of the polarizer, and may be, for example, 20 to 90 ° C., preferably 80 ° C. or less, more preferably Is preferably 60 ° C. or lower.

  The execution time of the hot air drying is not particularly limited, and may be performed, for example, for 1 to 10 minutes.

  The polarizer manufactured by the above method may have a transmittance of 43% or less. When the transmittance is 43% or less, the effect of improving the heat resistance and thermal shock resistance can be maximized.

  In the following, preferred examples are presented to aid the understanding of the present invention, but these examples are merely illustrative of the invention and are not intended to limit the scope of the appended claims. It will be apparent to those skilled in the art that various changes and modifications can be made to the embodiments within the scope of the scope and the technical idea, and such changes and modifications are also within the scope of the appended claims.

Examples and Comparative Examples Example 1
A transparent unstretched polyvinyl alcohol (PVA) film (PE60, KURARAY) having a saponification degree of 99.9% or more was swelled by being immersed in water (deionized water) at 25 ° C. for 1 minute and 20 seconds, Dyeing was carried out by immersing in an aqueous dyeing solution at 30 ° C. containing 1.25 mM / L iodine, 1.25% by weight potassium iodide and 3% by weight boric acid for 2 minutes and 30 seconds. At this time, the film was stretched at a stretching ratio of 1.56 times and 1.64 times in the swelling and dyeing steps, respectively, and stretched so that the cumulative stretching ratio after passing through the dyeing tank was 2.56 times. Subsequently, the film was immersed in a 56 ° C. aqueous solution for crosslinking containing 11% by weight of potassium iodide and 3% by weight of boric acid for 26 seconds (first cross-linking step) and cross-linked at a draw ratio of 1.7 times. did. Thereafter, the film was immersed in an aqueous solution for crosslinking at 56 ° C. containing 11% by weight of potassium iodide and 3% by weight of boric acid for 20 seconds (second crosslinking step), and stretched at a stretch ratio of 1.34 times. did. Subsequently, the film was stretched 1.01 times while immersed in an aqueous solution for complementary color at 40 ° C. containing 4% by weight of potassium iodide and 1.5% by weight of boric acid.

  At this time, the total cumulative draw ratio of the swelling, dyeing and crosslinking, and complementary color steps was set to 6 times. After the completion of crosslinking, a polyvinyl alcohol (PVA) film was dried in an oven at 70 ° C. for 4 minutes to produce a polarizer.

  A polarizing plate having a transmittance of 42.8% (deviation 0.2%) was produced by laminating a triacetyl cellulose (TAC) film on both sides of the produced polarizer.

2. Examples 2 to 9 and Comparative Examples 1 to 4
Example 1 except that the concentrations of boric acid in the dyeing solution, boric acid and potassium iodide in the crosslinking solution, and boric acid and potassium iodide in the complementary color solution were adjusted as described in Table 1 below. A polarizing plate was produced in the same manner as described above.

Experimental example Analysis of the weight ratio (K / I) of iodine and potassium in the polarizer

  A sample of 0.15 g of the polarizer sample produced in Examples and Comparative Examples was placed in a 30 mL vial (Vial) and filled with 20 g of distilled water.

  Thereafter, the vial was melted in a 90 ° C. thermostatic bath for 3 hours, and then allowed to cool for 30 minutes. The cooled sample was placed in a Liquid cup equipped with WDXRF (Axios, PANalytical), and the weight of iodine element and the weight of potassium element were measured to determine the weight ratio.

2. Content analysis of elemental boron in the polarizer 0.15 g of the polarizer sample produced in the examples and comparative examples was placed in a 30 mL vial, and ultrapure water was added to make the sample weight 25 g. The polarizer was completely dissolved in a thermostatic bath and then allowed to cool.

  The cooled sample inside the vial was transferred to a 100 mL beaker, and the sample remaining inside the vial was washed twice with a mannitol solution and placed in a 100 mL beaker. And it titrated with 0.1N NaOH and calculated | required the content of the boron element.

3. Optical properties (degree of polarization)
After the manufactured polarizer was cut into a size of 4 cm × 4 cm, the transmittance was measured using an ultraviolet-visible light spectrometer (V-7100, manufactured by JASCO). At this time, the degree of polarization is defined by Equation 1 below. For reference, it should be noted that a difference of about 0.001 in the degree of polarization greatly affects the contrast ratio. When the degree of polarization is less than 99.990, the contrast ratio is lowered and it is difficult to realize real black.

[Formula 1]
Polarization degree (P): [(T ₁ −T ₂ ) / (T ₁ + T ₂ )] ^1/2 × 100
The unit of polarization degree (P) is%.

(In the formula, T ₁ is a parallel transmittance obtained when a pair of polarizers are arranged in a state where the absorption axes are parallel, and T ₂ is a case where a pair of polarizers is arranged in a state where the absorption axes are orthogonal to each other. It is the orthogonal transmittance obtained).

4). Evaluation of heat resistance The spectral transmittance τ (λ) of the polarizing plates produced in Examples and Comparative Examples before and after standing at 105 ° C. for 30 minutes was measured with a spectrophotometer (V7100, JASCO Corporation) From this result, an orthogonal spectral transmission spectrum was obtained, and A700 after heat resistance represented by the following formula 2 was obtained.

[Formula 2]
A700 after heat resistance = −Log ₁₀ {(TMD _{, 700} × _{TTD, 700} ) / 10000}

(In the formula, _{TMD, 700} is a transmittance at 700 nm wavelength obtained when the manufactured polarizing plate after heat resistance is disposed in a state where the absorption axis of the polarizing plate is orthogonal to the linearly polarized light of the measuring light, T _{TD, 700} is the transmittance at a wavelength of 700 nm obtained when the manufactured polarizing plate after heat resistance is arranged in a state where the absorption axis of the polarizing plate is parallel to the linearly polarized light of the measuring light, and the unit is% Is).

  After the heat resistance evaluation, the presence or absence of red discoloration of the polarizing plate was confirmed by visual observation.

When A700 after heat resistance is 2.3 or less, a red discoloration phenomenon may be observed when the polarizing plate is visually observed. This is the content of PVA-I ₅ complex in a region that absorbs light of 600 nm or more. Means decreased.

  5. Thermal shock test evaluation (H / S)

  After the polarizer manufactured in Examples and Comparative Examples was cut to a size of 15.0 cm (MD) × 11 cm (TD), it was bonded to glass using an acrylic adhesive composition of Toyu Finechem Co., Ltd. The autoclave (50 degreeC, 20 minutes, 5 atmospheres) process was performed. Samples produced in a thermal shock oven after standing for 24 hours (repeating 200 cycles at -40 ° C for 30 minutes and 70 ° C for 30 minutes alternately until the total time is 6 hours, one cycle) And the presence or absence of cracks in the polarizer was confirmed.

  Referring to Table 2 above, the polarizing plates using the polarizers of Examples 1 to 9 showed high polarization degree and excellent heat resistance at the same time.

  However, the polarizing plates using the polarizers of Comparative Examples 1 to 4 had a decreased degree of polarization or significantly reduced heat resistance.

Claims (11)

  A polarizer having a weight ratio of iodine element to potassium element (iodine element / potassium element) of 0.12 to 0.18 and a boron element content of 3 to 4.5% by weight.   The polarizer according to claim 1, wherein a weight ratio of iodine element to potassium element is 0.14 to 0.16.   The polarizer according to claim 1 or 2, wherein the content of boron element is 3.5 to 4.0% by weight.   The polarizer as described in any one of Claims 1-3 whose transmittance | permeability is 43% or less.   A polarizing plate comprising the polarizer according to any one of claims 1 to 4 and a protective film laminated on at least one surface of the polarizer.   An image display device comprising the polarizing plate according to claim 5. In a method for producing a polarizer comprising the steps of swelling, dyeing, crosslinking, stretching, complementary color and drying a film for forming a polarizer,
The content of boric acid compound in the cross-linking liquid of the cross-linking step is 3 to 4.5% by weight, the content of potassium iodide is 11 to 13% by weight,
The method for producing a polarizer, wherein the content of boric acid compound in the complementary color solution in the complementary color step is 1.5 to 2.5% by weight and the content of potassium iodide is 4 to 8% by weight.   The method for producing a polarizer according to claim 7, wherein the content of the boric acid compound in the dyeing solution in the dyeing step is 0.3 to 5% by weight.   The weight ratio of iodine element to potassium element (iodine element / potassium element) in the polarizer is from 0.12 to 0.18, and the boron element content is from 3 to 4.5% by weight. The method for producing a polarizer according to claim 8.   The method for manufacturing a polarizer according to any one of claims 7 to 9, wherein the polarizer has a transmittance of 43% or less.   The method for producing a polarizer according to any one of claims 7 to 10, wherein the film for forming a polarizer is second stretched at a stretch ratio of 1.01 to 1.1 in the complementary color step.