TW201927876A - Method for producing polarizer - Google Patents

Abstract

Provided is a method that makes it possible to simply and inexpensively produce a polarizer in which changes in color in high-temperature environments are minimized. This polarizer production method includes at least stretching and dyeing of a polyvinyl alcohol resin film. The production method also includes applying or spraying a treatment liquid on the polyvinyl alcohol resin film after the dyeing thereof. The treatment liquid has a pH in the range of 3-8, and the treatment liquid has a buffering effect in this pH range.

Description

Manufacturing method of polarizer

The invention relates to a method for manufacturing a polarizer.

BACKGROUND OF THE INVENTION In a liquid crystal display device, which is a typical image display device, due to its image formation method, polarizers (which are essentially polarizers including polarizers) are arranged on both sides of a liquid crystal cell. The polarizer is typically manufactured by dyeing a polyvinyl alcohol (PVA) resin film with a dichroic substance such as iodine (for example, Patent Documents 1 and 2). In recent years, the demand for thinner image display devices has increased greatly. Therefore, even thinning is required for the polarizer. However, the thinner the polarizer, the more likely it is to discolor under high temperature environments.

Prior Art Literature Patent Literature Patent Literature 1: Japanese Patent No. 5048120 Patent Literature 2: Japanese Patent Laid-Open No. 2013-156391

SUMMARY OF THE INVENTION Problems to be Solved by the Invention The present invention has been made to solve the above-mentioned problems, and a main object thereof is to provide a method for producing a polarizer that has been suppressed from discoloration under a high temperature environment simply and inexpensively.

Means for Solving the Problem The method for producing a polarizer of the present invention includes stretching and dyeing a polyvinyl alcohol-based resin film at least. The manufacturing method includes coating or spraying a treatment liquid on the polyvinyl alcohol resin film after the dyeing, and the pH of the treatment liquid is in a range of 3 to 8, and the treatment liquid has a buffering effect in the pH range.
In one embodiment, the treatment liquid includes at least one selected from the group consisting of sodium bicarbonate and citric acid.
In one embodiment, the polyvinyl alcohol-based resin film is a polyvinyl alcohol-based resin layer formed by applying a coating solution containing a polyvinyl alcohol-based resin to a substrate, and the substrate and the polyvinyl alcohol The laminated system of the resin layer is used for extension and dyeing.

ADVANTAGE OF THE INVENTION According to the manufacturing method of this invention, in the post-dyeing process of the manufacturing method of a polarizer, the processing liquid which has a predetermined pH and a buffering effect is apply | coated or sprayed to a polyvinyl alcohol-type resin film, and it can be obtained. A polarizer that suppresses discoloration in high temperature environments. Moreover, this manufacturing method does not require special equipment or complicated operations, so it is possible to manufacture the polarizer as described above simply and inexpensively.

Embodiments for Implementing the Invention Embodiments of the present invention will be described below, but the present invention is not limited to these embodiments.

A. Manufacturing method of polarizer
A-1. Overview of the manufacturing method of the polarizer The manufacturing method of the polarizer according to the embodiment of the present invention includes stretching and dyeing at least a polyvinyl alcohol (PVA) -based resin film. Representatively, the manufacturing method includes a step of preparing a PVA-based resin film, an stretching step, a swelling step, a dyeing step, a crosslinking step, a washing step, and a drying step. Each step of supplying the PVA-based resin film can be performed in an arbitrary and appropriate order and timing. Therefore, the steps may be performed in the above order, or may be performed in a different order. One step can also be performed multiple times as required. In addition, steps other than the above (for example, an insolubilization step) can be performed at an arbitrary and appropriate timing.

In the embodiment of the present invention, a coating or spraying treatment solution is applied to the PVA-based resin film after dyeing. The application or spraying of the treatment liquid may be performed at any appropriate timing after dyeing. The coating or spraying of the treatment liquid may be specifically performed before the crosslinking step or may be performed after the crosslinking step; it may be performed before the washing step or may be performed after the washing step. When the stretching step is performed after the dyeing step, the application or spraying of the treatment liquid may be performed before the stretching step or may be performed after the stretching step. When the swelling step is performed after the dyeing step, the application or spraying of the treatment liquid may be performed before the swelling step or may be performed after the swelling step. When the insolubilization step is performed after the dyeing step, the application or spraying of the treatment liquid may be performed before the insolubilization step or may be performed after the insolubilization step. Representatively, the application or spraying of the treatment liquid may be performed after the washing step and before the drying step, or may be performed between the first drying step and the second drying step when the drying step is performed in two stages.

The pH of the treatment liquid is, for example, in a range of 3 to 8, preferably in a range of 5 to 8, and the treatment liquid has a buffering effect in the pH range (that is, the pH is in a range of 3 to 8). The pH of the treatment liquid is preferably 5.5 to 7.5, and more preferably 5.5 to 6.5. In another embodiment, it is more preferably 3.5 to 5.5, and more preferably 3.7 to 4.7. The treatment liquid may contain, for example, sodium bicarbonate (NaHCO ₃ ), potassium bicarbonate (KHCO ₃ ), disodium hydrogen phosphate (Na ₂ HPO ₄ ), potassium carbonate (K ₂ CO ₃ ), sodium carbonate (Na ₂ CO ₃ ), Aqueous solution of citric acid. The treatment liquid containing these compounds has a higher buffering effect in the pH region than the treatment liquid containing, for example, an acetic acid-based compound. Therefore, as a result, it has an excellent anti-tarnishing effect in a high-temperature environment. The aqueous solution may contain these compounds alone or two or more kinds. The treatment liquid is preferably an aqueous solution of sodium bicarbonate or citric acid. The concentration of the aqueous solution can be appropriately set depending on the desired pH and buffering effect. For example, the concentration of the sodium bicarbonate aqueous solution should be 0.20% to 2.0% by weight, and the concentration of the citric acid aqueous solution should be 0.10% to 3.0% by weight. Moreover, the aqueous solution may contain a pH adjuster as needed. Examples of the pH adjusting agent include sulfuric acid (lower pH) and sodium hydroxide (higher pH). Applying or spraying the treatment solution to a PVA-based resin film can significantly suppress the discoloration of the polarizer in a high-temperature environment. I speculate that this is because protons can be inhibited from being generated in the PVA-based resin by the buffering effect of the treatment solution in a predetermined pH range. As a result, multiple double bonds (polyenelation) in the PVA-based resin can be suppressed under a high temperature environment, thereby Can suppress discoloration. In consideration of manufacturing efficiency, the contact with the treatment liquid can usually be performed by immersing a PVA-based resin film in the treatment liquid. However, by including a polarizer made by immersion in a processing solution, the PVA-based resin film swells during immersion. Therefore, the state of the iodine complex in the PVA-based resin film is likely to change, and there is polarization before and after immersion It is easy for the absorption spectrum of a piece to change. On the other hand, by coating or spraying the PVA-based resin film, the problem of the absorption spectrum change of the polarizer before and after the immersion can be prevented during the immersion, so that the PVA polyenelation can be further prevented.

The treatment liquid may be applied or sprayed onto the PVA-based resin film by any appropriate method. The coating mechanism may be, for example, a reverse coater, a gravure coater (direct, reverse or indirect), a rod reverse coater, a roll coater, a die coater, a rod coater, or a rod coater. The spraying mechanism may be, for example, an arbitrary and suitable spraying device (for example, a pressurized nozzle type or a rotating disc type).

Each step is described below, but as described above, each step can be performed in an arbitrary and appropriate order without being limited by the order of description.

A-2. PVA-based resin film The PVA-based resin forming the PVA-based resin film may be, for example, polyvinyl alcohol or ethylene-vinyl alcohol copolymer. Polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. The ethylene-vinyl alcohol copolymer can be obtained by saponifying an ethylene-vinyl acetate copolymer. The degree of saponification of PVA resin is usually more than 85 mol% and less than 100 mol%, preferably 95.0 mol% to 99.95 mol%, and more preferably 99.0 mol% to 99.93 mol%. The degree of saponification is determined in accordance with JIS K 6726-1994. By using the PVA-based resin having the saponification degree, a polarizer having excellent durability can be obtained. When the saponification degree is too high, there is a risk of gelation.

The average degree of polymerization of the PVA-based resin can be appropriately selected according to the purpose. The average degree of polymerization is usually 1000 to 10,000, preferably 1200 to 4500, and more preferably 1500 to 4300. The average degree of polymerization can be obtained in accordance with JIS K 6726-1994.

The thickness of the PVA-based resin film is not particularly limited, and can be set according to the desired thickness of the polarizer. The thickness of the PVA-based resin film is, for example, 10 μm to 200 μm.

In one embodiment, the PVA-based resin film may be a PVA-based resin layer formed on a substrate. A laminated body of a substrate and a PVA-based resin layer can be produced by, for example, a method of applying a coating solution containing the PVA-based resin to a substrate, and a method of laminating a PVA-based resin film to a substrate. Wait. In these cases, the laminated body of the substrate and the PVA-based resin layer can be used in the stretching step, the swelling step, the dyeing step, the crosslinking step, the washing step, and the like.

A-3. Stretching step In the stretching step, the PVA-based resin film can be uniaxially stretched to 3 to 7 times. The extending direction may be the longitudinal direction (MD direction) of the film, or the width direction (TD direction) of the film. The stretching method may be dry stretching, wet stretching, or a combination of these. The PVA-based resin film may be stretched when a crosslinking step, a swelling step, a dyeing step, or the like is performed. In addition, the extension direction may correspond to the absorption axis direction of the obtained polarizer.

A-4. Swelling step The swelling step is usually performed before the dyeing step. The swelling step can be performed, for example, by immersing a PVA-based resin film in a swelling bath. The swelling bath usually uses water such as distilled water and pure water. The swelling bath may contain arbitrary and appropriate components other than water. Other components include solvents such as alcohols, additives such as surfactants, and iodides. Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. Potassium iodide should be used. The temperature of the swelling bath is, for example, 20 ° C to 45 ° C. The immersion time is, for example, 10 seconds to 300 seconds.

A-5. Dyeing step The dyeing step is a step of dyeing a PVA-based resin film with a dichroic substance. This is preferably performed by adsorbing a dichroic substance. Examples of the adsorption method include a method of immersing a PVA-based resin film in a dyeing solution containing a dichroic substance, a method of applying the dyeing solution to a PVA-based resin film, and spraying the dyeing solution onto a PVA-based resin film. Method of resin film, etc. The method of immersing a PVA-type resin film in a dyeing liquid is ideal. Because it can absorb dichroic materials well.

Examples of the dichroic material include iodine and dichroic dye. And iodine is suitable. When iodine is used as a dichroic substance, an iodine aqueous solution should be used as the dyeing solution. The iodine content of the iodine aqueous solution is preferably 0.04 to 5.0 parts by weight relative to 100 parts by weight of water. In order to improve the solubility of iodine in water, it is suitable to mix iodide with iodine solution. For iodide, potassium iodide should be used. The iodide content is preferably 0.3 to 15 parts by weight relative to 100 parts by weight of water.

The temperature of the dyeing liquid during dyeing can be set to an arbitrary and appropriate value, for example, 20 ° C to 50 ° C. When the PVA-based resin film is immersed in the dyeing solution, the immersion time is, for example, 5 seconds to 5 minutes.

A-6. Cross-linking step In the cross-linking step, a boron compound is usually used as a cross-linking agent. Examples of the boron compound include boric acid and borax. And boric acid is suitable. In the crosslinking step, the boron compound is usually used in the form of an aqueous solution.

When a boric acid aqueous solution is used, the boric acid concentration of the boric acid aqueous solution is, for example, 1% to 15% by weight, and preferably 1% to 10% by weight. Furthermore, the boric acid aqueous solution can contain iodides such as potassium iodide; zinc compounds such as zinc sulfate and zinc chloride.

The crosslinking step can be performed by any appropriate method. For example, a method of dipping a PVA-based resin film in an aqueous solution containing a boron compound, a method of applying an aqueous solution of a boron-containing compound to a PVA-based resin film, or a method of spraying an aqueous solution of a boron-containing compound onto a PVA-based resin film method. It is also preferable to immerse it in an aqueous solution of a boron-containing compound.

The temperature of the solution used for crosslinking is, for example, 25 ° C or higher, preferably 30 ° C to 85 ° C, and more preferably 40 ° C to 70 ° C. The immersion time is, for example, 5 seconds to 800 seconds, and preferably 8 seconds to 500 seconds.

A-7. Washing step The washing step is performed on behalf of the upper line after the crosslinking step. The cleaning step is performed by immersing a PVA-based resin film in a cleaning solution. A representative example of the cleaning solution is pure water. Potassium iodide can also be added to pure water.

The temperature of the cleaning solution is, for example, 5 ° C to 50 ° C. The immersion time is, for example, 1 second to 300 seconds.

A-8. Drying step The drying step can be performed by any appropriate method. Examples of the drying method include natural drying, air drying, reduced pressure drying, and heating drying. And should use heat to dry. When heating and drying, the heating temperature is, for example, 30 ° C to 100 ° C. The drying time is, for example, 20 seconds to 10 minutes.

B. Polarizer The upper limit of the thickness of a polarizer made by the manufacturing method of the present invention is 80 μm in one embodiment, 20 μm in another embodiment, 10 μm in another embodiment, and In the embodiment, it is 5 μm, in another embodiment, it is 3 μm, and in another embodiment, it is 2 μm. The lower limit of the thickness is 0.5 μm in one embodiment, 0.6 μm in another embodiment, and 0.8 μm in another embodiment. According to the manufacturing method of the present invention, even if it is a thin polarizer, the expected unit transmittance as described below can be achieved, and in addition, the change amount of unit transmittance under a high temperature environment can be significantly suppressed.

From the viewpoint of providing sufficient polarizing performance and optimal transmittance, the iodine content of the polarizer produced by the manufacturing method of the present invention can be appropriately set according to the thickness of the polarizer. For example, when the thickness of the polarizer is greater than 5 μm and 10 μm or less, the iodine content is preferably 3.5% to 8.0% by weight; when the thickness of the polarizer is greater than 3 μm and 5 μm or less, the iodine content is 5.0% to 13.0% %; When the thickness of the polarizer is 3 μm or less, the iodine content is preferably 10.0% to 25.0% by weight. The "iodine content" in this specification means the amount of all iodine contained in a polarizer (PVA-based resin film). More specifically, the iodine iodide ion (I ^-) is present in the form of a polarizer and the like, and the iodine content of the present specification is meant that molecular iodine (I _2), polyiodide ions _{^{(I 3 - -, I 5}} ) Contains the amount of iodine in all of these forms. The iodine content can be calculated by a calibration curve method such as fluorescent X-ray analysis. In addition, polyiodide ions exist in a polarizer in a state where a PVA-iodine complex is formed. By forming the complex, the absorption dichroism can be exhibited in the wavelength range of visible light. Specifically, the complexes (PVA · I ₃ ^-) PVA and tri-iodide ions having a light absorption peak around 470nm; PVA complexes with five iodide ions (PVA · I ₅ ^-) having a light absorption near 600nm peak. As a result, polyiodide ions can absorb light over a wide range of visible light depending on their morphology. On the other hand, an iodide ion (I ^-) having a light absorption peak around 230nm, absorption of visible light associated with insubstantial. Therefore, the presence of polyiodide ions in a complex with PVA is mainly related to the absorption performance of polarizers.

The single transmittance (Ts) of the polarizer made by the manufacturing method of the present invention is preferably 30.0% to 43.0%, and more preferably 35.0% to 41.0%. The polarization degree of the polarizer is preferably 99.9% or more, more preferably 99.95% or more, and more preferably 99.98% or more. By setting the individual transmittance to be low and the polarization degree to be high, the contrast can be improved, and the black display can be displayed more black, so an image display device with excellent image quality can be realized. The single transmittance is a value measured by a spectrophotometer with an integrating sphere. The single transmittance is the Y value measured by JIS Z8701's 2-degree field of view (C light source) and corrected for optical performance. : V7100).

The absolute value of the change in the unit transmittance ΔTsa of the polarizer made by the manufacturing method of the present invention after being left for 30 hours at 105 ° C. is, for example, 7.0% or less, preferably 5.0% or less, and more preferably 3.0% or less. . The polarizer made by the manufacturing method of the present invention can achieve the above-mentioned desired monomer transmittance and polarization degree, and at the same time, the amount of monomer transmittance change under a high temperature environment has been significantly suppressed. Therefore, it is possible to realize a polarizer which has suppressed discoloration in a high-temperature environment. As a result, the polarizer is also suitable for applications requiring heat resistance. I speculate that the excellent effect is to apply or spray a treatment solution having a predetermined pH and buffering effect on a polyvinyl alcohol-based resin film in the step after dyeing of the polarizer manufacturing method as described above, thereby preventing the obtained polarized light. The polyene is obtained under high temperature environment. It can solve the problems newly discovered by actually making extremely thin (for example, thickness less than 7 μm) polarizers that have been difficult to make in the past, and it is an excellent effect that exceeds expectations. In addition, the change amount ΔTsa of the monomer transmittance is preferably a negative value (that is, less than 0.0%). In addition, the change amount ΔTsa of the single transmittance can be expressed by the following formula:
ΔTsa (%) = Ts ₃₀ -Ts ₀
Here, Ts ₀ is the monomer transmittance before the heating test, and Ts ₃₀ is the monomer transmittance after being left for 30 hours in an environment of 105 ° C. In addition, in the present specification, when the monomer transmittance is only described as Ts, it means the monomer transmittance Ts ₀ before heating.

The absolute value of the monomer transmittance change amount ΔTsb after the polarizer made by the manufacturing method of the present invention is left for 500 hours in an environment of 60 ° C and 90% RH is preferably 3.5% or less, and more preferably 3.0% or less. The polarizer made by the manufacturing method of the present invention can achieve the above-mentioned desired monomer transmittance and polarization degree, and at the same time, the amount of monomer transmittance change has been significantly suppressed in a high humidity environment. Therefore, it is possible to realize a polarizer in which discoloration has been suppressed even in a high-humidity environment. In addition, the change amount ΔTsb of the transmittance of the monomer is preferably a positive value (that is, greater than 0.0%). In addition, the change amount ΔTsb of the single transmittance can be expressed by the following formula:
ΔTsb (%) = Ts ₅₀₀ -Ts ₀
Here, Ts ₀ is the monomer transmittance before the heating test, and Ts ₅₀₀ is the monomer transmittance after being left for 500 hours at 60 ° C and 90% RH.

The orthogonal a value of the polarizer made by the manufacturing method of the present invention is preferably 0.0 to 0.6; the orthogonal b value is preferably -0.6 to 0.0. The polarizer made by the manufacturing method of the present invention can achieve the above-mentioned desired monomer transmittance and polarization degree and durability under high temperature environment, and at the same time has a very neutral hue. With the hue, problems such as bluishness do not occur. In addition, the a value and the b value are the a value and the b value of the Lab color system, respectively. In addition, the a value and the b value may be adjusted outside the above range depending on purposes.

C. Polarizing plate The polarizing member produced by the manufacturing method of the present invention is used in a state that a protective film is laminated on one or both sides (that is, as a polarizing plate). In practical applications, the polarizing plate has an adhesive layer as the outermost layer. The adhesive layer becomes the outermost layer on the image display device side on the representative side. On the adhesive layer, the separator is temporarily adhered in a peelable state, which can protect the adhesive layer until it is actually used, and can be formed into a roll.

As the protective film, any appropriate resin film can be used. Examples of the material for forming the resin film include (meth) acrylic resins, cellulose resins such as diacetyl cellulose, triethyl cellulose, cycloolefin resins such as norbornene resin, and olefin resins such as polypropylene. , Ester resins such as polyethylene terephthalate resins, polyamide resins, polycarbonate resins, and copolymer resins thereof. The "(meth) acrylic resin" refers to an acrylic resin and / or a methacrylic resin.

In one embodiment, the (meth) acrylic resin is a (meth) acrylic resin having a glutaridine imine structure. The (meth) acrylic resin having a glutariminium structure (hereinafter also referred to as a glutarimide resin) is described in, for example, Japanese Patent Laid-Open No. 2006-309033, Japanese Patent Laid-Open No. 2006-317560, Japanese Patent Application Publication No. 2006-328329, Japanese Patent Application Publication No. 2006-328334, Japanese Patent Application Publication No. 2006-337491, Japanese Patent Application Publication No. 2006-337492, Japanese Patent Application Publication No. 2006-337493, Japanese Patent Application Publication No. 2006- Japanese Patent Publication No. 337569, Japanese Patent Application Publication No. 2007-009182, Japanese Patent Application Publication No. 2009-161744, and Japanese Patent Application Publication No. 2010-284840. These references are cited in this specification.

When a polarizer is produced by using a laminate of a substrate and a PVA-based resin layer, it can be used as a protective film without peeling off the substrate.

Examples Hereinafter, the present invention will be specifically described with examples, but the present invention is not limited to these examples. The measurement method of each characteristic is as follows.

(1) Monolithic transmittance Ts ₀ and the variation of the monochromatic transmittance ΔTsa and ΔTsb
A reflective polarizer (manufactured by 3M Corporation, trade name "DBEF") was bonded to the polarizer side of the laminated body obtained in the examples and comparative examples. Next, after the thermoplastic resin substrate was peeled off, an alkali-free glass having a thickness of 1.3 mm was bonded to the peeling surface through an acrylic adhesive layer having a thickness of 20 μm to prepare a test sample. This test sample was heated at 105 ° C for 30 hours (heating test). The test sample was then heated and humidified at 60 ° C and 90% RH for 500 hours (humidity test). A spectrophotometer (manufactured by JASCO Corporation, product name: V7100) with an integrating sphere was used to measure the individual transmittance of the polarizer before the test, after the heating test, and after the humidification test. From the monomer transmittance Ts ₀ before the heating, the monomer transmittance Ts ₃₀ after the heating test, and the monomer transmittance Ts ₅₀₀ after the humidification test, the monomer transmittance change amounts ΔTsa and Tsb were calculated using the following formulas.
ΔTsa (%) = Ts ₃₀ -Ts ₀
ΔTsb (%) = Ts ₅₀₀ -Ts ₀
In addition, ΔTsa´´ (%) when the heating time of the heating test is 15 hours = Ts ₁₅ -Ts ₀ and ΔTsa´ (%) = Ts ₂₀ -Ts when the heating time of the heating test is 20 hours ₀ .
(2) Appearance of polarizer The appearance of the polarizer after the heating test and humidification test of (1) above was observed with the naked eye, and was evaluated on the basis of the following. In addition, the appearance change of the test sample of (1) under the conditions of 20 ° C and 98% RH and after heating and humidification for 50 hours and 100 hours was also observed with the naked eye, and evaluated based on the following criteria.
○: No discoloration was observed △: Slight discoloration was observed ×: Discoloration was noticeable
(3) Hue Regarding the multilayer bodies obtained in the examples and comparative examples, the orthogonal b value was measured with an ultraviolet-visible spectrophotometer (V-7100 manufactured by Japan Spectroscopy). Based on Comparative Example 1, the difference Δb was obtained.

[Example 1]
The thermoplastic resin base material is an amorphous isophthalic acid copolymerized polyethylene terephthalate (IPA copolymerized PET) film (thickness: 100 μm) having a water absorption of 0.75% and a Tg of 75 ° C. Corona treatment was applied to one side of the substrate, and the corona treated surface was coated at 25 ° C with a ratio of 9: 1 containing polyvinyl alcohol (degree of polymerization 4200, degree of saponification 99.2 mole%) and acetoacetate An aqueous solution of fluorenyl-modified PVA (degree of polymerization: 1200, acetyl-acetyl fluorenyl: 4.6%, saponification degree of 99.0 mol% or more, manufactured by Japan Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFIMER Z200") and dried, Then, a PVA-based resin layer having a thickness of 11 μm was formed to produce a laminated body.
Using a tenter stretcher, the obtained laminated body was stretched at a temperature of 140 ° C. in the direction orthogonal to the longitudinal direction of the laminated body by 4.5 times (stretching treatment).
Next, the laminated body was immersed in a dyeing bath (aqueous solution having an iodine concentration of 1.4% by weight and a potassium iodide concentration of 9.8% by weight) at a liquid temperature of 25 ° C. for 12 seconds to perform dyeing (dyeing treatment).
Next, the laminated body was immersed in a washing bath (pure water) at a liquid temperature of 25 ° C. for 6 seconds (first washing treatment).
Then, it was immersed in a crosslinking bath (aqueous solution having a boron concentration of 1% by weight and a potassium iodide concentration of 1% by weight) at a liquid temperature of 60 ° C for 16 seconds (crosslinking treatment).
Next, the laminated body was immersed in a washing bath (aqueous solution having a potassium iodide concentration of 1% by weight) at a liquid temperature of 25 ° C for 3 seconds (second washing treatment).
Then, the laminated body was dried in an oven at 60 ° C. for 21 seconds (first drying treatment).
Next, a treatment liquid (aqueous solution of 0.5% by weight of sodium bicarbonate and 50% by weight of isopropyl alcohol: pH = 3.2) was applied to the PVA-based resin layer of the laminate with a bar coater. In addition, the pH of the treatment liquid has been adjusted by mixing dilute sulfuric acid.
Finally, the laminate was dried in an oven at 50 ° C. for 60 seconds to obtain a laminate having a PVA-based resin layer (polarizer) having a thickness of 1.2 μm.
The obtained laminated body was subjected to the above evaluations (1) to (3). The results are shown in Table 1.

[Example 2]
A laminated body having a polarizer was prepared in the same manner as in Example 1 except that the treatment solution was an aqueous solution (pH = 4.8) of 0.5% by weight of sodium bicarbonate and 50% by weight of isopropyl alcohol. The obtained laminated body was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Example 3]
A laminated body having a polarizer was prepared in the same manner as in Example 1 except that the treatment solution was an aqueous solution (pH = 6.0) of 0.5% by weight of sodium bicarbonate and 50% by weight of isopropyl alcohol. The obtained laminated body was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Example 4]
A laminated body having a polarizer was prepared in the same manner as in Example 1 except that the treatment solution was an aqueous solution (pH = 7.8) of 0.5% by weight of sodium bicarbonate and 50% by weight of isopropyl alcohol. The obtained laminated body was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Example 5]
A laminated body having a polarizer was prepared in the same manner as in Example 1 except that the treatment solution was an aqueous solution (pH = 3.2) of 0.2% by weight of citric acid and 50% by weight of isopropyl alcohol. In addition, the pH of the treatment liquid has been adjusted by mixing sodium hydroxide. The obtained laminated body was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Example 6]
A laminated body having a polarizer was prepared in the same manner as in Example 1 except that the treatment solution was an aqueous solution (pH = 6.0) of 0.2% by weight of citric acid and 50% by weight of isopropyl alcohol. In addition, the pH of the treatment liquid has been adjusted by mixing sodium hydroxide. The obtained laminated body was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Example 7]
A laminated body having a polarizer was prepared in the same manner as in Example 1 except that the treatment solution was an aqueous solution (pH = 7.8) of 0.2% by weight of citric acid and 50% by weight of isopropyl alcohol. In addition, the pH of the treatment liquid has been adjusted by mixing sodium hydroxide. The obtained laminated body was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Comparative Example 1]
A laminated body having a polarizer was produced in the same manner as in Example 1 except that the treatment liquid was not applied. The obtained laminated body was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Comparative Example 2]
A laminated body having a polarizer was obtained in the same manner as in Example 1, except that the treatment liquid (that is, the laminate was immersed in the treatment liquid) was used instead of the coating treatment liquid in the second cleaning treatment. The treatment liquid was a 1.0% by weight aqueous solution of sodium bicarbonate (pH = 6.0). The obtained laminated body was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Comparative Example 3]
A laminated body having a polarizer was obtained in the same manner as in Example 1, except that the treatment liquid (that is, the laminate was immersed in the treatment liquid) was used instead of the coating treatment liquid in the second cleaning treatment. The treatment liquid was an aqueous solution (pH = 6.0) of 0.6% by weight of sodium acetate. The obtained laminated body was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Comparative Example 4]
A laminated body having a polarizer was obtained in the same manner as in Example 1, except that the treatment liquid (that is, the laminate was immersed in the treatment liquid) was used instead of the coating treatment liquid in the second cleaning treatment. The treatment liquid was a 0.4% by weight aqueous solution of citric acid (pH = 6.0). The obtained laminated body was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Comparative Example 5]
A laminated body having a polarizer was prepared in the same manner as in Example 1 except that the treatment solution was an aqueous solution (pH = 2.8) of 0.5% by weight of sodium bicarbonate and 50% by weight of isopropyl alcohol. The obtained laminated body was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Comparative Example 6]
A laminated body having a polarizer was prepared in the same manner as in Example 1 except that the treatment solution was an aqueous solution (pH = 8.2) of 0.5% by weight of sodium bicarbonate and 50% by weight of isopropyl alcohol. The obtained laminated body was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Comparative Example 7]
A laminated body having a polarizer was prepared in the same manner as in Example 1 except that the treatment solution was an aqueous solution (pH = 2.8) of 0.2% by weight of citric acid and 50% by weight of isopropyl alcohol. In addition, the pH of the treatment liquid has been adjusted by mixing sodium hydroxide. The obtained laminated body was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Comparative Example 8]
A laminated body having a polarizer was prepared in the same manner as in Example 1 except that the treatment solution was an aqueous solution (pH = 8.2) of 0.2% by weight of citric acid and 50% by weight of isopropyl alcohol. In addition, the pH of the treatment liquid has been adjusted by mixing sodium hydroxide. The obtained laminated body was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Comparative Example 9]
A laminated body having a polarizer was prepared in the same manner as in Example 1 except that the treatment solution was an aqueous solution (pH = 6.0) of 0.6% by weight of sodium acetate and 50% by weight of isopropyl alcohol. The obtained laminated body was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Comparative Example 10]
A laminated body having a polarizer was prepared in the same manner as in Example 1 except that the treatment solution was an aqueous solution (pH = 6.0) of 0.6% by weight of sodium sulfate and 50% by weight of isopropyl alcohol. The obtained laminated body was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Table 1]

As is clear from Table 1, the discoloration of the polarizer made by the manufacturing method of the embodiment of the present invention has been suppressed in a high temperature environment. In addition, compared with Comparative Example 1, the hue is also more neutral. Comparative Example 1 which had not been treated with the treatment liquid had significant discoloration and deterioration in appearance in a high-temperature environment. Comparative Examples 2 to 4 in which a PVA-based resin film was immersed in a treatment solution exhibited significant discoloration and deterioration in appearance under a high-temperature environment, and the hue was also significantly bluish. Comparative Examples 5 and 7 in which the pH of the treatment liquid was low showed significant discoloration and deterioration in appearance in a high-temperature environment. Comparative Examples 6 and 8 in which the pH of the treatment liquid was high significantly changed color in a high humidity environment. Comparative Examples 9 and 10, in which the pKa of the treatment liquid fell outside the predetermined pH range, had significant discoloration and deterioration in appearance under a high temperature environment.

INDUSTRIAL APPLICABILITY The manufacturing method of the present invention can easily and inexpensively manufacture a polarizer which has suppressed discoloration in a high temperature environment. The polarizing member produced by the manufacturing method of the present invention can be widely used in LCD televisions, liquid crystal displays, mobile phones, digital cameras, digital cameras, handheld games, car navigation, photocopiers, printers, fax machines, clocks, Microwave ovens and other LCD panels.

Claims (3)

A method for manufacturing a polarizer, comprising at least extending and dyeing a polyvinyl alcohol resin film; And the manufacturing method comprises coating or spraying the polyvinyl alcohol resin film on the treatment liquid after the dyeing; And the pH of the treatment liquid is in the range of 3 ~ 8, and the treatment liquid has a buffering effect in the pH range. The method for manufacturing a polarizer according to claim 1, wherein the treatment liquid includes at least one selected from the group consisting of sodium bicarbonate and citric acid. The method for manufacturing a polarizer according to claim 1 or 2, wherein the polyvinyl alcohol-based resin film is a polyvinyl alcohol-based resin layer formed by applying a coating solution containing a polyvinyl alcohol-based resin to a substrate, and The laminated system of the substrate and the polyvinyl alcohol-based resin layer is used for extension and dyeing.