JPWO2019103003A1 - Polarizer manufacturing method - Google Patents

Abstract

Provided is a method capable of easily and inexpensively producing a polarizer in which discoloration is suppressed in a high temperature environment. The method for producing a polarizer of the present invention includes at least stretching and dyeing a polyvinyl alcohol-based resin film. This production method includes coating or spraying a treatment liquid on a polyvinyl alcohol-based resin film after dyeing. The pH of the treatment liquid is in the range of 3 to 8, and the treatment liquid has a buffering action in this pH range.

Description

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

A liquid crystal display device, which is a typical image display device, has polarizing plates (substantially, polarizing plates including the polarizing elements) arranged on both sides of the liquid crystal cell due to the image forming method. The polarizer is typically produced by dyeing a polyvinyl alcohol (PVA) -based resin film with a dichroic substance such as iodine (for example, Patent Documents 1 and 2). In recent years, there has been an increasing demand for thinner image display devices. Therefore, the polarizer is also required to be further thinned. However, there is a problem that the thinner the polarizer, the easier it is to discolor in a high temperature environment.

Japanese Patent No. 5048120 Japanese Unexamined Patent Publication No. 2013-156391

The present invention has been made to solve the above problems, and a main object thereof is to provide a method capable of easily and inexpensively producing a polarizer in which discoloration is suppressed in a high temperature environment.

The method for producing a polarizer of the present invention includes at least stretching and dyeing a polyvinyl alcohol-based resin film. This production method includes applying or spraying a treatment liquid on the polyvinyl alcohol-based resin film after the dyeing, the pH of the treatment liquid is in the range of 3 to 8, and the treatment liquid has the pH. It has a buffering effect in the range of.
In one embodiment, the treatment solution comprises at least one selected from 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 liquid containing a polyvinyl alcohol-based resin to a base material, and the base material and the polyvinyl alcohol-based resin film. The laminate with the resin layer is subjected to stretching and dyeing.

According to the production method of the present invention, discoloration in a high temperature environment is caused by applying or spraying a treatment liquid having a predetermined pH and buffering action on a polyvinyl alcohol-based resin film in a step after dyeing in the method for producing a polarizer. A suppressed polarizer can be obtained. Moreover, since this manufacturing method does not require any special equipment or complicated operation, the above-mentioned polarizer can be manufactured easily and inexpensively.

Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

A. Method for manufacturing a polarizer A-1. Outline of Method for Producing Polarizer The method for producing a polarizer according to the embodiment of the present invention includes at least stretching and dyeing a polyvinyl alcohol (PVA) -based resin film. Typically, the production method includes a step of preparing a PVA-based resin film, a stretching step, a swelling step, a dyeing step, a cross-linking step, a washing step, and a drying step. Each step in which the PVA-based resin film is provided can be performed in any suitable order and timing. Therefore, each step may be performed in the above order, or may be performed in a different order from the above. If necessary, one step may be performed a plurality of times. Further, a step other than the above (for example, an insolubilization step) may be performed at an arbitrary appropriate timing.

An embodiment of the present invention includes applying or spraying a treatment liquid on a PVA-based resin film after dyeing. The treatment liquid may be applied or sprayed at any appropriate timing after dyeing. Specifically, the coating or spraying of the treatment liquid may be performed before or after the crosslinking step, or may be performed before or after the cleaning step. When the stretching step is performed after the dyeing step, the application or spraying of the treatment liquid may be performed before or 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 or 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 or after the insolubilization step. Typically, the application or spraying of the treatment liquid can be performed after the cleaning step and before the drying step, or between the first drying step and the second drying step when the drying step is performed in two steps. ..

The treatment liquid has a pH in the range of, for example, 3 to 8, preferably 5 to 8, and the treatment liquid has a buffering action in the pH range (that is, the pH is in the range of 3 to 8). .. The pH of the treatment liquid is more preferably 5.5 to 7.5, and even more preferably 5.5 to 6.5. In another embodiment, it is more preferably 3.5 to 5.5, still more preferably 3.7 to 4.7. Examples of such a treatment liquid include sodium hydrogen carbonate (NaHCO ₃ ), potassium hydrogen carbonate (KHCO ₃ ), disodium hydrogen phosphate (Na ₂ HPO ₄ ), potassium carbonate (K ₂ CO ₃ ), and sodium carbonate (K ₂ CO ₃ ). It can be an aqueous solution containing Na ₂ CO ₃ ) and citric acid. The treatment liquid containing these compounds has a buffering action in a higher pH range than, for example, a treatment liquid containing an acetic acid-based compound, and as a result, can have a more excellent anti-discoloration effect in a high temperature environment. The aqueous solution may contain these compounds alone or may contain two or more of them. The treatment liquid is preferably an aqueous solution of sodium hydrogen carbonate or citric acid. The concentration of the aqueous solution can be set appropriately depending on the desired pH and buffering action. For example, the concentration of the aqueous sodium hydrogen carbonate solution can preferably be 0.20% by weight to 2.0% by weight, and the concentration of the aqueous citric acid solution can preferably be 0.10% by weight to 3.0% by weight. .. In addition, the aqueous solution may contain a pH adjuster, if necessary. Examples of the pH adjuster include sulfuric acid (lowering the pH) and sodium hydroxide (increasing the pH). By applying or spraying such a treatment liquid on the PVA-based resin film, discoloration of the polarizer in a high temperature environment can be remarkably suppressed. This can suppress the generation of protons in the PVA-based resin by the buffering action in the predetermined pH range of the treatment liquid, and as a result, the generation of a large number of double bonds in the PVA-based resin under a high temperature environment (polyene). It is presumed that it is possible to suppress the change in color and suppress the discoloration. Considering the production efficiency, such contact with the treatment liquid can usually be performed by immersing the PVA-based resin film in the treatment liquid. However, in the polarizer obtained by the manufacturing method including immersion in the treatment liquid, the PVA-based resin film swells during immersion, so that the state of the iodine complex in the PVA-based resin film is likely to change, and the polarizer before and after immersion. There is a problem that the absorption spectrum of is easily changed. On the other hand, by applying or spraying the treatment liquid on the PVA-based resin film, it is possible to prevent the problem of change in the absorption spectrum of the polarizer before and after immersion in immersion, and as a result, it is possible to further better prevent polyene formation of PVA.

The treatment liquid is applied or sprayed on the PVA-based resin film by any suitable method. Examples of the coating means include a reverse coater, a gravure coater (direct, reverse and offset), a bar reverse coater, a roll coater, a die coater, a bar coater, and a rod coater. As the spraying means, any suitable spraying device (for example, pressure nozzle type, rotary disc type) can be mentioned.

Hereinafter, each step will be described, but as described above, each step can be performed in any appropriate order, and is not limited to the description order.

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

The average degree of polymerization of the PVA-based resin can be appropriately selected depending on the intended purpose. The average degree of polymerization is usually 1000 to 10000, preferably 1200 to 4500, and more preferably 1500 to 4300. The average degree of polymerization can be determined according to 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. The laminate of the base material and the PVA-based resin layer can be obtained, for example, by a method of applying the coating liquid containing the PVA-based resin to the base material, a method of laminating a PVA-based resin film on the base material, or the like. In these cases, the laminate of the base material and the PVA-based resin layer is subjected to a stretching step, a swelling step, a dyeing step, a cross-linking step, a cleaning step, and the like.

A-3. Stretching Step In the stretching step, the PVA-based resin film is typically uniaxially stretched 3 to 7 times. The stretching direction may be the longitudinal direction of the film (MD direction) or the width direction of the film (TD direction). The stretching method may be dry stretching, wet stretching, or a combination of these. Further, the PVA-based resin film may be stretched when performing a crosslinking step, a swelling step, a dyeing step, or the like. The stretching direction can 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 is performed, for example, by immersing a PVA-based resin film in a swelling bath. As the swelling bath, water such as distilled water or pure water is usually used. The swelling bath may contain any suitable other ingredients other than water. Examples of other components include solvents such as alcohol, additives such as surfactants, and iodides. Examples of 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. And so on. Preferably, potassium iodide is 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. It is preferably carried out 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 bicolor substance, a method of applying the dyeing solution to the PVA-based resin film, and a method of spraying the dyeing solution onto the PVA-based resin film. The method of doing this can be mentioned. A method of immersing the PVA-based resin film in the dyeing solution is preferable. This is because the dichroic substance can be adsorbed well.

Examples of the dichroic substance include iodine and a dichroic dye. Iodine is preferred. When iodine is used as the dichroic substance, an aqueous iodine solution is preferably used as the dyeing solution. The iodine content of the iodine aqueous solution is preferably 0.04 parts by weight to 5.0 parts by weight with respect to 100 parts by weight of water. In order to increase the solubility of iodine in water, it is preferable to add iodide to the aqueous iodine solution. Potassium iodide is preferably used as the iodide. The content of iodide is preferably 0.3 to 15 parts by weight with respect to 100 parts by weight of water.

The liquid temperature at the time of dyeing the dyeing liquid can be set to an arbitrary 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. Preferably, it is boric acid. In the cross-linking step, the boron compound is usually used in the form of an aqueous solution.

When an aqueous boric acid solution is used, the boric acid concentration of the aqueous boric acid solution is, for example, 1% by weight to 15% by weight, preferably 1% by weight to 10% by weight. The boric acid aqueous solution may further contain an iodide such as potassium iodide and a zinc compound such as zinc sulfate and zinc chloride.

The cross-linking step can be performed by any suitable method. For example, a method of immersing a PVA-based resin film in an aqueous solution containing a boron compound, a method of applying an aqueous solution containing a boron compound to a PVA-based resin film, or a method of spraying an aqueous solution containing a boron compound onto a PVA-based resin film can be mentioned. Be done. It is preferable to immerse in an aqueous solution containing a boron 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, preferably 8 seconds to 500 seconds.

A-7. Cleaning Step The cleaning step can typically be performed after the crosslinking step. The cleaning step is typically performed by immersing a PVA-based resin film in a cleaning liquid. Pure water is a typical example of the cleaning liquid. Potassium iodide may be added to pure water.

The temperature of the cleaning liquid 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 carried out by any suitable method. Examples of the drying method include natural drying, blast drying, vacuum drying, heat drying and the like. Heat drying is preferably used. When heat-drying is performed, 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 the polarizer obtained by the production method of the present invention is 80 μm in one embodiment, 20 μm in another embodiment, and 10 μm in yet another embodiment. In yet another embodiment, it is 5 μm, in yet another embodiment it is 3 μm, and in yet 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 yet another embodiment. According to the production method of the present invention, it is possible to realize a desired simple substance transmittance as described later even with a thin polarizer, and further, the amount of change in the simple substance transmittance in a high temperature environment is remarkably suppressed. be able to.

The iodine content of the polarizer obtained by the production method of the present invention can be appropriately set according to the thickness of the polarizer from the viewpoint of imparting sufficient polarization performance and optimum transmittance. For example, if the thickness of the polarizer is more than 5 μm and less than 10 μm, the iodine content is preferably 3.5% to 8.0% by weight; the thickness of the polarizer is more than 3 μm and less than 5 μm. When the iodine content is preferably 5.0% by weight to 13.0% by weight; when the thickness of the polarizer is 3 μm or less, the iodine content is preferably 10.0% by weight. ~ 25.0% by weight. As used herein, the term "iodine content" means the amount of all iodine contained in the polarizer (PVA-based resin film). More specifically, in the polarizer, iodine exists in the form of iodine ion (I ⁻ ), iodine molecule (I ₂ ), polyiodide ion (I ₃ ⁻ , I ₅ ⁻ ), etc., as used herein. Iodine content means the amount of iodine that includes all of these forms. The iodine content can be calculated, for example, by the calibration curve method of fluorescent X-ray analysis. The polyiodine ion exists in a state in which a PVA-iodine complex is formed in the polarizer. By forming such a complex, absorption dichromatism can be exhibited in the wavelength range of visible light. Specifically, a complex of PVA and tri-iodide ion (PVA · _{I 3} ^-) has a light absorption peak around 470 nm, a complex of PVA and five iodide ion (PVA · _{I 5} ^-) is 600nm near Has an absorption peak at. As a result, polyiodine ions can absorb light in a wide range of visible light, depending on their morphology. On the other hand, iodine ion (I ⁻ ) has an absorption peak near 230 nm and is not substantially involved in the absorption of visible light. Therefore, polyiodine ions present in the form of a complex with PVA may mainly contribute to the absorption performance of the polarizer.

The simple substance transmittance (Ts) of the polarizer obtained by the production method of the present invention is preferably 30.0% to 43.0%, more preferably 35.0% to 41.0%. The degree of polarization of the polarizer is preferably 99.9% or more, more preferably 99.95% or more, and further preferably 99.98% or more. By setting the single transmittance to be low and the degree of polarization to be high, the contrast can be increased and the black display can be displayed in black, so that an image display device having excellent image quality can be realized. The simple substance transmittance is a value measured by a spectrophotometer with an integrating sphere. The single transmittance is a Y value measured by a two-degree field of view (C light source) of JIS Z8701 and corrected for luminosity factor. For example, a spectrophotometer with an integrating sphere (manufactured by JASCO Corporation, product name: V7100). Can be measured using.

The polarizer obtained by the production method of the present invention has an absolute value of elemental transmittance change ΔTsa of, for example, 7.0% or less, preferably 5.0% or less, after being left in an environment of 105 ° C. for 30 hours. It is more preferably 3.0% or less. The polarizer obtained by the production method of the present invention realizes the above-mentioned desired simple substance transmittance and degree of polarization, and the amount of change in the simple substance transmittance in a high temperature environment is remarkably suppressed. Therefore, it is possible to realize a polarizer in which discoloration is suppressed in a high temperature environment. As a result, the polarizer can be suitably used for applications that require heat resistance. Such an excellent effect can be obtained by applying or spraying a treatment liquid having a predetermined pH and a buffering action on a polyvinyl alcohol-based resin film in the step after dyeing in the method for producing a polarizer as described above. It is presumed that this will be achieved by preventing polyene formation of the offspring in a high temperature environment. This solves a new problem found by actually producing a very thin (for example, 7 μm or less) polarizer, which was difficult to produce in the past, and is unexpectedly excellent. It is an effect. Further, the simple substance transmittance change amount ΔTsa is preferably negative (that is, smaller than 0.0%). The amount of change in single transmittance ΔTsa is expressed by the following equation:
ΔTsa (%) = Ts ₃₀ −Ts ₀
Here, Ts ₀ is the simple substance transmittance before the heating test, and Ts ₃₀ is the simple substance transmittance after being left in an environment of 105 ° C. for 30 hours. Further, when the simple substance transmittance is simply described as Ts in the present specification, it means the simple substance transmittance Ts ₀ before heating.

The polarizer obtained by the production method of the present invention has a simple substance transmittance change amount ΔTsb of preferably 3.5% or less after being left in an environment of 60 ° C. and 90% RH for 500 hours, which is more preferable. Is 3.0% or less. The polarizer obtained by the production method of the present invention realizes the above-mentioned desired simple substance transmittance and degree of polarization, and the amount of change in the simple substance transmittance is remarkably suppressed even in a high humidity environment. Therefore, it is possible to realize a polarizer in which discoloration is suppressed even in a high humidity environment. Further, the simple substance transmittance change amount ΔTsb is preferably positive (that is, larger than 0.0%). The amount of change in single transmittance ΔTsb is expressed by the following equation:
ΔTsb (%) = Ts ₅₀₀ −Ts ₀
Here, Ts ₀ is the simple substance transmittance before the heating test as described above, and Ts ₅₀₀ is the simple substance transmittance after being left in an environment of 60 ° C. and 90% RH for 500 hours.

The polarizer obtained by the production method of the present invention has an orthogonal a value of preferably 0.0 to 0.6; and an orthogonal b value of preferably −0.6 to 0.0. The polarizer obtained by the production method of the present invention has such a very neutral hue while achieving the above-mentioned desired elemental transmittance and degree of polarization and durability in a high temperature environment. With such a hue, problems such as blue omission do not occur. The a value and the b value are the a value and the b value of the Lab color system, respectively. The a value and the b value may be adjusted so as to be out of the above range depending on the purpose.

C. Polarizing Filter The polarizer obtained by the production method of the present invention is typically used in a state where a protective film is laminated on one side or both sides thereof (that is, as a polarizing plate). Practically, the polarizing plate has an adhesive layer as the outermost layer. The pressure-sensitive adhesive layer is typically the outermost layer on the image display device side. A separator is temporarily attached to the pressure-sensitive adhesive layer so that it can be peeled off, protecting the pressure-sensitive adhesive layer until actual use and enabling roll formation.

As the protective film, any suitable resin film is used. Examples of the resin film forming material include (meth) acrylic resin, cellulose-based resin such as diacetyl cellulose and triacetyl cellulose, cycloolefin-based resin such as norbornene-based resin, olefin-based resin such as polypropylene, and polyethylene terephthalate-based resin. Etc., ester-based resins, polyamide-based resins, polycarbonate-based resins, and copolymer resins thereof. The "(meth) acrylic resin" refers to an acrylic resin and / or a methacrylic resin.

In one embodiment, as the (meth) acrylic resin, a (meth) acrylic resin having a glutarimide structure is used. Examples of the (meth) acrylic resin having a glutarimide structure (hereinafter, also referred to as glutarimide resin) include JP-A-2006-309033, JP-A-2006-317560, JP-A-2006-328329, and JP-A. 2006-328334, 2006-337491, 2006-337492, 2006-337493, 2006-337569, 2007-009182, 2009- It is described in JP-A-161744 and JP-A-2010-284840. These statements are incorporated herein by reference.

When a polarizer is produced using a laminate of a base material and a PVA-based resin layer, the base material may be used as it is as a protective film without peeling.

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

(1) Simple substance transmittance Ts ₀ and simple substance transmittance change ΔTsa and ΔTsb
A reflective polarizer (manufactured by 3M, trade name "DBEF") was attached to the polarizer side of the laminates obtained in Examples and Comparative Examples. Next, the thermoplastic resin base material was peeled off, and non-alkali glass having a thickness of 1.3 mm was attached to the peeled surface via an acrylic pressure-sensitive 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). In addition, this test sample was heated and humidified at 60 ° C. and 90% RH for 500 hours (humidification test). The single transmittance of the polarizer after the test, the heating test, and the humidification test was measured using a spectrophotometer with an integrating sphere (manufactured by JASCO Corporation, product name: V7100). From the simple substance transmittance Ts ₀ before heating, the simple substance transmittance Ts ₃₀ after the heating test, and the simple substance transmittance Ts ₅₀₀ after the humidification test, the amounts of change in simple substance transmittance ΔTsa and Tsb were determined using the following formulas, respectively.
ΔTsa (%) = Ts ₃₀ −Ts ₀
ΔTsb (%) = Ts ₅₀₀ −Ts ₀
Further, ΔTsa ″ (%) = Ts ₁₅ −Ts ₀ when the heating time of the heating test is 15 hours, and ΔTsa ″ (%) = Ts ₂₀ −Ts when the heating time of the heating test is 20 hours. _I also asked for ₀ .
(2) Appearance of Polarizer The appearance of the polarizer after the heating test and humidification test of (1) above was visually observed and evaluated according to the following criteria. Further, the change in appearance of the test sample of (1) above after being heated and humidified at 20 ° C. and 98% RH for 50 hours and 100 hours was also visually observed and evaluated according to the following criteria.
◯: No discoloration was observed Δ: Slight discoloration was observed ×: Discoloration was remarkable (3) Hue The laminates obtained in Examples and Comparative Examples were measured with an ultraviolet-visible spectrophotometer (JASCO Corporation). The orthogonal b value was measured using V-7100). The difference Δb was determined with reference to Comparative Example 1.

[Example 1]
As the thermoplastic resin base material, an amorphous isophthalic acid copolymer polyethylene terephthalate (IPA copolymer PET) film (thickness: 100 μm) having a water absorption rate of 0.75% and a Tg of 75 ° C. was used. One side of the base material is corona-treated, and polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (polymerization degree 1200, acetoacetyl-modification degree 4.6) are applied to the corona-treated surface. %, Degree of polymerization of 99.0 mol% or more, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "Gosefimer Z200") in a ratio of 9: 1 is applied and dried at 25 ° C. to a thickness of 11 μm. A PVA-based resin layer was formed to prepare a laminate.
The obtained laminate was stretched 4.5 times in the air at 140 ° C. in a direction orthogonal to the longitudinal direction of the laminate using a tenter stretching machine (stretching treatment).
Next, the laminate was immersed in a dyeing bath at a liquid temperature of 25 ° C. (an aqueous solution having an iodine concentration of 1.4% by weight and a potassium iodide concentration of 9.8% by weight) for 12 seconds for dyeing (dyeing treatment).
Next, the laminate was immersed in a washing bath (pure water) having a liquid temperature of 25 ° C. for 6 seconds (first washing treatment).
Then, it was immersed in a cross-linking bath (an 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 laminate was immersed in a washing bath (an aqueous solution having a potassium iodide concentration of 1% by weight) at a liquid temperature of 25 ° C. for 3 seconds (second washing treatment).
The laminate was then dried in an oven at 60 ° C. for 21 seconds (first drying process).
Next, a treatment liquid (an aqueous solution of 0.5% by weight of sodium hydrogen carbonate and 50% by weight of isopropyl alcohol: pH = 3.2) was applied to the PVA-based resin layer of the laminate using a bar coater. The pH of the treatment liquid was 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 laminate was subjected to the evaluations (1) to (3) above. The results are shown in Table 1.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

As is clear from Table 1, discoloration of the polarizer obtained by the production method of the examples of the present invention is suppressed in a high temperature environment. Further, the hue is also shifted in the neutral direction as compared with Comparative Example 1. In Comparative Example 1 which was not treated with the treatment liquid, discoloration and appearance deterioration in a high temperature environment were remarkable. In Comparative Examples 2 to 4 in which the PVA-based resin film was immersed in the treatment liquid, discoloration and appearance deterioration in a high temperature environment were remarkable, and further, blue loss was remarkable in the hue. In Comparative Examples 5 and 7 in which the pH of the treatment liquid is low, discoloration and appearance deterioration in a high temperature environment are remarkable. In Comparative Examples 6 and 8 in which the pH of the treatment liquid is high, discoloration in a high humidity environment is remarkable. In Comparative Examples 9 and 10 in which the pKa of the treatment liquid deviates from the predetermined pH range, discoloration and appearance deterioration in a high temperature environment are remarkable.

The production method of the present invention can easily and inexpensively produce a polarizer in which discoloration is suppressed in a high temperature environment. The polarizer obtained by the manufacturing method of the present invention is a liquid crystal panel for LCD TVs, liquid crystal displays, mobile phones, digital cameras, video cameras, portable game machines, car navigation systems, copiers, printers, fax machines, watches, microwave ovens, etc. Can be widely applied to.

Claims (3)

A method for producing a polarizer, which comprises at least stretching and dyeing a polyvinyl alcohol-based resin film.
Following the dyeing, the polyvinyl alcohol-based resin film comprises applying or spraying a treatment solution.
The pH of the treatment liquid is in the range of 3 to 8, and the treatment liquid has a buffering action in the pH range.
How to manufacture a polarizer. The production method according to claim 1, wherein the treatment liquid contains at least one selected from sodium hydrogen carbonate and citric acid. The polyvinyl alcohol-based resin film is a polyvinyl alcohol-based resin layer formed by applying a coating liquid containing a polyvinyl alcohol-based resin to a base material, and a laminate of the base material and the polyvinyl alcohol-based resin layer is formed. The production method according to claim 1 or 2, which is used for stretching and dyeing.