WO2016027864A1

WO2016027864A1 - Method for manufacturing polarizer

Info

Publication number: WO2016027864A1
Application number: PCT/JP2015/073413
Authority: WO
Inventors: 勇介松岡; 英樹松久; 公彦矢可部; 佑介北河; 天煕趙; 容鉉權; 崔　允碩; 正寧崔
Original assignee: 住友化学株式会社
Priority date: 2014-08-22
Filing date: 2015-08-20
Publication date: 2016-02-25
Also published as: TW201613992A; KR20160023429A; CN106662696A; KR20170045265A; JPWO2016027864A1

Abstract

The present invention relates to a method for manufacturing a polarizer, and more specifically relates to a method for manufacturing the polarizer that can manufacture a polarizer with small changes in hue even when exposed to long-term high temperature conditions by including steps for swelling, coloring, cross-linking, color correction, and first drawing of a film for forming the polarizer, carrying out the swelling step, coloring step, cross-linking step, and color correction step in this order, carrying out the first drawing step before the color correction step, and carrying out second drawing with a drawing ratio of 1.010 - 1.100 for the film for forming the polarizer in the color correction step.

Description

Manufacturing method of polarizer

The present invention relates to a method for manufacturing a polarizer.

Polarized light used in various image display devices such as liquid crystal display (LCD), electroluminescence (EL) display, plasma display (PDP), field emission display (FED), organic light emitting diode (OLED), etc. The 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 sequentially formed 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.

The polarizer constituting the polarizing plate is required to have a high transmittance and polarization degree in order to be applied to an image display device and provide an image excellent in hue reproducibility. Further, as the application of flat panel display devices to various fields spreads and the tendency to increase in size becomes more prominent, various image display devices such as liquid crystal display devices may be used for a long time at high temperatures. 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 being sought. Optical durability including hue change under high temperature and high humidity conditions, high contrast through high orientation and high transmission It has been demanded.

Korean Patent Publication No. 2009-70085 discloses a method of manufacturing a polarizer, but could not present an alternative to the above problem.

Korean Open Patent No. 2009-70085

An object of the present invention is to provide a method capable of producing a polarizer having improved hue durability.

1. A step of swelling, dyeing, crosslinking, complementary color and first stretching of the film for forming a polarizer, wherein the swelling step, the dyeing step, the crosslinking step and the complementary color step are performed in this order, and the first stretching step Is performed before the complementary color step,
A method for producing a polarizer, wherein the film for forming a polarizer is second stretched at a stretch ratio of 1.010 to 1.100 times in the complementary color step.

2. 2. The method for producing a polarizer according to 1 above, wherein the staining solution in the staining step contains a boric acid compound.

3. 3. The method for producing a polarizer according to 2 above, wherein the boric acid compound is contained in an amount of 0.3 to 5% by weight of the total weight of the staining solution.

4). In 1 above, the first stretching is performed in one or more steps selected from the group consisting of swelling, dyeing and crosslinking steps.

5. In 1 above, the concentration of the boric acid compound in the complementary color liquid in the complementary color step is lower than the concentration of the boric acid compound in the crosslinking liquid.

6). 2. The method for producing a polarizer according to 1 above, wherein the ratio of the concentration of the boric acid compound in the crosslinking liquid and the concentration of the boric acid compound in the complementary color liquid is 1: 0.4 to 0.8.

7). In 1 above, the method for producing a polarizer, wherein the concentration of iodide in the complementary color solution of the complementary color step is lower than the concentration of iodide in the crosslinking solution.

8). 2. The method for producing a polarizer according to 1 above, wherein the ratio of the iodide concentration in the cross-linking solution and the iodide concentration in the complementary color solution is 1: 0.2 to 0.6.

9. A polarizer produced by the method according to any one of 1 to 8 above.

The method of the present invention can produce a polarizer with significantly improved hue durability. Thereby, even when exposed to a high temperature condition for a long time, the hue change can be minimized.

The method of the present invention can produce a polarizer having an excellent degree of polarization.

The present invention includes the steps of swelling, dyeing, cross-linking, complementary color and first stretching the polarizer-forming film, and in the complementary color step, the polarizer-forming film is secondly stretched at a stretch ratio of 1.01 to 1.1 times. The present invention relates to a method for producing a polarizer that can produce a polarizer in which a change in hue is minimized even when exposed to high temperature conditions for a long time by stretching.

The present invention will be described in detail below.

The method for producing a polarizer of the present invention includes the steps of swelling, dyeing, crosslinking, complementary color and first stretching the polarizer-forming film. The swelling step, dyeing step, cross-linking step, and complementary color step are performed in this order, and the first stretching step is performed before the complementary color step.

In this invention, 2nd extending | stretching of the film for polarizer formation is performed by a complementary color step among the manufacturing processes of the said polarizer.

Usually, a complex is formed between the polymer constituting the polarizer forming film and the dichroic substance in the step of dyeing the polarizer forming film in the manufacturing process of the polarizer, and this is fixed in the crosslinking step. When the film for forming a polarizer is washed with water only up to the crosslinking step, the degree of orientation of the complex of the dichroic substance is low, so that the stability is inferior, the hue of the polarizer changes, or the durability is lowered There's a problem.

However, in the present invention, the complementary color step is performed after the crosslinking step, and the film for forming the polarizer is stretched in the complementary color step (second stretching), thereby increasing the degree of orientation of the complex of the dichroic substance. Thereby, the hue change of a polarizer can be suppressed and durability can be improved remarkably.

The second stretching is performed at a stretching ratio of 1.010 to 1.100. If the draw ratio is less than 1.010 times, the effect of improving the degree of orientation of the complex of the dichroic substance is negligible. If the draw ratio exceeds 1.100 times, the film may be broken by excessive stretching. Preferably, it can be performed at a draw ratio of 1.020 to 1.080.

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

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

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; a polyethylene terephthalate film, Hydrophilic polymer films such as ethylene-vinyl acetate copolymer films, ethylene-vinyl alcohol copolymer films, cellulose films, partially saponified films thereof; or dehydrated polyvinyl alcohol films, Examples include a polyene oriented film such as a 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.

<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 impurities, swelling the polarizer-forming film, improving the drawing efficiency, and preventing the uneven dyeing and improving the physical properties of the polarizer.

As the aqueous solution for swelling, water (pure water, deionized water) may be usually used alone, 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 can 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.

The swelling step and the first stretching step may be performed at the same time. In this case, the stretching ratio may be about 1.1 to 3.5 times, preferably 1.5 to 3.0 times. . If the stretching ratio is less than 1.1 times, wrinkles may occur, and if it exceeds 3.5 times, the initial optical properties 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 dyeing solution may further contain iodide as a solubilizing agent for improving the dyeing 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. You may use these individually or in mixture of 2 or more types.

The iodide content 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 dyeing 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, thereby increasing the complex formation rate of the dichroic substance in the polarizer-forming film. Thereby, the hue durability of a polarizer can be improved and the degree of polarization is improved.

The boric acid compound in the dyeing solution is included so as to have a higher concentration than the boric acid compound added to the crosslinking solution in the subsequent crosslinking step.

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 of the total weight of the staining solution, and preferably 0.5 to 3% by weight. 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. 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, and preferably 2 to 10 minutes.

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

Further, the cumulative stretching ratio of the polarizer up to the swelling and first stretching step is preferably 1.2 to 4.0 times. If the cumulative stretch ratio is less than 1.2 times, the film may wrinkle, and if it exceeds 4.0 times, the initial optical properties may be deteriorated.

<Crosslinking step>
The cross-linking step is a step of fixing the adsorbed iodine molecules by immersing the polarizer forming film dyed so that the dyeability by the physically adsorbed iodine molecules does not deteriorate due to the external environment. .

The crosslinking liquid used for the crosslinking step of the present invention contains a boric acid compound. When the cross-linking liquid contains a boric acid compound, the cross-linking efficiency can be improved, the generation of wrinkles in the film during the process can be suppressed, the orientation of the dichroic material can be formed, and the optical characteristics can be improved.

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 not particularly limited, but may be, for example, 1 to 10% by weight, preferably 2 to 6% by weight, based on the total weight of the crosslinking liquid. When the concentration of the boric acid compound in the crosslinking liquid is less than 1% by weight, the crosslinking effect may be reduced and the orientation of the film may be lowered. obtain.

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

The cross-linking liquid of the present invention may contain water used as a solvent and an organic solvent that is mutually soluble with water, and prevents the uniformity of the degree of polarization in the plane of the polarizer and the desorption of dyed iodine. Therefore, a small amount of iodide may be further contained.

The iodide used may be the same as that used in the dyeing step, and the concentration of the iodide is not particularly limited, and is, for example, 0.05 to 15% by weight of the total weight of the crosslinking solution. Preferably 0.5 to 11% by weight. When the iodide concentration in the crosslinking tank satisfies the above range, the iodine ions adsorbed in the dyeing step are prevented from desorbing from the film or the iodine ions contained in the crosslinking liquid from penetrating the film, A change in transmittance can be suppressed.

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 first stretching step may be performed simultaneously with the crosslinking step. In this 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 to be. In addition, the stretching 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 it exceeds 5.0 times, the film is broken by excessive stretching, and the production efficiency is increased. Can be reduced.

<First stretching step>
As described above, the first stretching step may be performed simultaneously with at least one of the swelling step, the dyeing step, and the crosslinking step, or may be performed in air or an inert gas while transferring the film after the above step. Alternatively, it may be performed in an independent stretching step using a separate stretching tank filled with a stretching solution. Alternatively, an unstretched polyvinyl alcohol film may be stretched in air or an inert gas before the swelling step, and then the film may be subjected to swelling, dyeing, crosslinking, washing and drying steps.

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 of 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.

<Complementary color step>
The complementary color step is a step of adjusting the hue by immersing the film having undergone the crosslinking step in a complementary color solution containing a boric acid compound, preferably a complementary color solution containing a boric acid compound and iodide.

The present invention can improve the stability by increasing the degree of orientation of the complex of the dichroic substance by performing the second stretching of the film for forming the polarizer in the complementary color step, and thus can be produced by the method of the present invention. The polarizer is excellent in hue durability because the decomposition of the complex is minimized even after being exposed to a high temperature for a long time.

The second stretching is performed at a stretching ratio of 1.010 to 1.100. If the draw ratio is less than 1.010 times, the effect of improving the degree of orientation of the complex of the dichroic substance is negligible. If the draw ratio exceeds 1.100 times, the film may be broken by excessive stretching. The second stretching may be performed at a stretching ratio of preferably 1.020 to 1.080.

The total cumulative stretch ratio of the first and second stretches 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. .

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

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

The concentration of the boric acid compound in the complementary color solution is not particularly limited, but may be, for example, 1 to 10% by weight, preferably 2 to 6% by weight, based on the total weight of the complementary color solution. When the concentration of the boric acid compound in the complementary color liquid is less than 1% by weight, the orientation of iodine cannot be improved, and the effect of suppressing hue change and improving durability is insignificant. If it exceeds 1, the tension is generated in the film at the time of stretching due to excessive crosslinking, so that stretching is difficult and the film may be broken.

Preferably, the concentration of the boric acid compound in the complementary color solution of the present invention is lower than the concentration of the boric acid compound in the crosslinking solution.

Since the boric acid compound serves to fix the adsorbed iodine molecules in the cross-linking solution, if a large amount of the boric acid compound is contained, a large tension is generated when the polarizer-forming film is stretched. In the present invention, since the second stretching is performed in the complementary color step, it is preferable that the boric acid compound is contained in a small amount in order to reduce the tension.

The concentration ratio is not particularly limited. For example, the concentration of the boric acid compound in the crosslinking liquid and the concentration of the boric acid compound in the complementary color liquid may have a ratio of 1: 0.4 to 0.8. When the boric acid compound is contained in a small amount in the complementary color solution and the concentration ratio is less than 1: 0.4, the orientation of iodine cannot be improved, and the effect of suppressing hue change and improving durability is insignificant. If it is included in an excessive amount and exceeds 1: 0.8, a large tension is generated in the film at the time of stretching, so that stretching is difficult and the film may be broken.

The complementary color solution of the present invention may contain water used as a solvent and an organic solvent that can be mutually dissolved together with water, in order to prevent the uniformity of the degree of polarization in the polarizer plane and the desorption of dyed iodine. A small amount of iodide may be further contained.

The iodide used may be the same as that used in the dyeing step and the crosslinking step, and the concentration of the iodide is not particularly limited. For example, 0.05 to 15% by weight of the total weight of the complementary color solution It may be 0.5 to 11% by weight. When the concentration of iodide in the complementary color solution satisfies the above range, iodine ions that have not been adsorbed in the dyeing and crosslinking steps can be adsorbed to the film, and iodine ions contained in the complementary color solution can be absorbed into the film. The color and transmittance can be adjusted by increasing the penetration into the skin.

Preferably, the iodide concentration in the complementary color solution of the present invention is lower than the iodide concentration in the crosslinking solution.

In the cross-linking solution, iodide serves to prevent the iodine ions adsorbed in the dyeing step from desorbing from the film, but the complementary color solution also contains a large amount of iodide at a level similar to that of the cross-linking solution. When exposed to high temperature heat for a long period of time, the iodine complex can be decomposed and the durability of the polarizer can be reduced.

The concentration ratio is not particularly limited. For example, the concentration of iodide in the cross-linking solution and the concentration of iodide in the complementary color solution may have a ratio of 1: 0.2 to 0.6. If a small amount of iodide is contained in the complementary color solution and the concentration ratio is less than 1: 0.2, the hue cannot be adjusted. When exposed, the iodine complex can be decomposed to reduce durability.

The temperature of the complementary color tank is 20 to 70 ° C., and the immersion time of the polyvinyl alcohol 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 water washing step after the complementary color is completed.

The water washing step is a step of immersing the film for forming a polarizer after completion of complementary color in a water washing tank filled with a water washing solution to remove unnecessary residues attached to the film for forming a polarizer in the previous step.

The aqueous washing solution may be water (deionized water), and an 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 first stretching step or a complementary color step is completed. Further, 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 drying the washed polarizer-forming film and further improving the orientation of iodine molecules dyed by neck-in by drying to obtain a polarizer having excellent optical properties.

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.

The temperature at the time of hot air drying is not particularly limited, but 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.

Moreover, this invention provides the polarizing plate by which the protective film was laminated | stacked on at least one surface of the polarizer manufactured by said method.

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 diacetylcellulose and triacetylcellulose; Polyacrylic resins such as polycarbonate resins, polymethyl (meth) acrylate and polyethyl (meth) acrylate; Polystyrene and acrylonitrile Styrene resins such as styrene copolymers; Polyolefin resins such as polyethylene, polypropylene, cyclo- or polyolefin having a norbornene structure, and ethylene-propylene copolymers; Polyamides such as nylon and aromatic polyamides Fatty resin; imide resin; polyethersulfone resin; sulfone resin; polyetherketone resin; sulfide polyphenylene resin; vinyl alcohol resin; vinylidene chloride resin; vinyl butyral resin; 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 a (meth) acrylic type, a urethane type, an epoxy type, a silicon type, or an 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, a wave plate (including a λ plate) such as an optical film, a reflector, a semi-transmission plate, a half-wave plate, or a quarter-wave plate such as a polarization conversion device 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 including an optical layer are stacked as an optical layer may be used. 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 retardation plate is laminated, a wide viewing angle polarizing plate on which a viewing angle compensation layer or a viewing angle compensation film is laminated, a polarizing plate on which a brightness enhancement film is laminated, or the like 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.

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 modifications and variations can be made to the embodiments within the scope and spirit of the invention, and such variations and modifications fall within the scope of the appended claims. is there.

Examples and Comparative Examples (1) Example 1
A transparent unstretched polyvinyl alcohol film (PE60, KURARAY, Inc.) having a saponification degree of 99.9% or more was swelled by immersing it in water (deionized water) at 25 ° C. for 1 minute and 20 seconds. Dyeing was performed by immersing in an aqueous dyeing solution containing 25 mM / L, potassium iodide 1.25 wt% and boric acid 0.3 wt% at 30 ° C. 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 at the swelling and dyeing steps, respectively, and stretched so that the cumulative stretching ratio up to the dyeing tank was 2.56 times. Subsequently, the film was immersed in an aqueous solution for crosslinking at 56 ° C. containing 13.9% by weight of potassium iodide and 3% by weight of boric acid for 26 seconds (first crosslinking step) while being crosslinked for a stretching ratio of 1.7 times. And stretched. Thereafter, the film was immersed in an aqueous solution for crosslinking at 56 ° C. containing 13.9% by weight of potassium iodide and 3% by weight of boric acid for 20 seconds (second crosslinking step) and crosslinked at a stretch ratio of 1.34 times. Stretched. Subsequently, the film was stretched 1.01 times while immersed in a complementary color aqueous solution at 40 ° C. containing 5% by weight of potassium iodide and 2% by weight of boric acid for 10 seconds.

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

A polarizing plate was produced by laminating a triacetyl cellulose (TAC) film on both surfaces of the produced polarizer.

(2) Examples 2 to 11 and Comparative Examples 1 to 4
The polarizing plate was prepared in the same manner as in Example 1 except that the concentration of boric acid in the dyeing tank, the crosslinking liquid, the concentration of potassium iodide and boric acid in the complementary color liquid, and the stretching ratio of the complementary color tank described in Table 1 were adjusted. Manufactured.

Test Example The physical properties of the polarizers produced in the above Examples and Comparative Examples were measured by the following methods, and the results are shown in Table 2 below.

1. Optical properties (degree of polarization, transmittance, A700, A480)
The manufactured polarizer was cut into a size of 4 cm × 4 cm, and 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. 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)

A700 and A480 are defined by Equations 2 and 3.

[Formula 2]
A700 = −Log ₁₀ {(TMD _{, 700} × _{TTD, 700} ) / 10000}
(In the formula, _{TMD, 700} is a transmittance at a wavelength of 700 nm obtained when the manufactured polarizing plate is disposed in a state where the absorption axis of the polarizing plate is orthogonal to the linearly polarized light of the measurement light, and T _{TD , 700} is the transmittance at a wavelength of 700 nm obtained when the manufactured polarizing plate 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 these units are in%. is there.)

[Formula 3]
A480 = −Log ₁₀ {(TMD _{, 480} × _{TTD, 480} ) / 10000}
(In the formula, _{TMD, 480} is a transmittance at a wavelength of 480 nm obtained when the manufactured polarizing plate is disposed in a state where the absorption axis of the polarizing plate is orthogonal to the linearly polarized light of the measuring light, and T _{TD , 480} is the transmittance at a wavelength of 480 nm obtained when the manufactured polarizing plate 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 these units are all in%. is there.)

When the absorbance of A700 and A480 is high, it means that the content of PVA-I5 complex (PVA and I ₅ ⁻ complex) and PVA-I3 complex (PVA and I ₃ ⁻ complex) is high and the degree of polarization is high.

2. Evaluation of heat resistance Spectral transmittance τ (λ) before and after leaving the polarizing plate produced in Examples and Comparative Examples 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 represented by the above formula 2 was obtained.

After the heat resistance evaluation, the presence or absence of red discoloration of the polarizing plate was confirmed by visual observation. In Table 1, X indicates that redness did not occur, and O indicates that redness occurred.

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 because the content of the PVA-I5 complex in the region that absorbs light of 600 nm or more is observed. It means that it decreased.

Referring to the above table, the polarizers produced by the methods of Examples 1 to 14 exhibited excellent optical characteristics, showed high absorbance even after the heat resistance test, and did not cause a red discoloration phenomenon.

However, the polarizers produced by the methods of Comparative Examples 1 to 3 were inferior in optical characteristics, and the red color phenomenon occurred in the heat resistance test. In the case of Comparative Example 4, the film broke when it was stretched in the complementary color tank.

Claims

Swelling, dyeing, crosslinking, complementary color and first stretching the polarizer-forming film,
The swelling step, the dyeing step, the crosslinking step, and the complementary color step are performed in this order,
The first stretching step is performed before the complementary color step;
A method for producing a polarizer, wherein the film for forming a polarizer is second stretched at a stretch ratio of 1.010 to 1.100 times in the complementary color step.
The method for producing a polarizer according to claim 1, wherein the staining liquid in the staining step contains a boric acid compound.
The method for producing a polarizer according to claim 2, wherein the boric acid compound is contained in an amount of 0.3 to 5% by weight of the total weight of the staining solution.
The method for producing a polarizer according to claim 1, wherein the first stretching is performed in one or more steps selected from the group consisting of swelling, dyeing, and crosslinking steps.
The method for producing a polarizer according to claim 1, wherein the concentration of the boric acid compound in the complementary color solution in the complementary color step is lower than the concentration of the boric acid compound in the crosslinking solution.
2. The method for producing a polarizer according to claim 1, wherein the ratio of the concentration of the boric acid compound in the crosslinking liquid to the concentration of the boric acid compound in the complementary color liquid is 1: 0.4 to 0.8.
The method for producing a polarizer according to claim 1, wherein the concentration of iodide in the complementary color solution in the complementary color step is lower than the concentration of iodide in the crosslinking solution.
The method for producing a polarizer according to claim 1, wherein the ratio of the iodide concentration in the cross-linking solution and the iodide concentration in the complementary color solution is 1: 0.2 to 0.6.
The polarizer manufactured by the method as described in any one of Claims 1 thru | or 8.