TWI791687B - Polarizers and Polarizers - Google Patents

Abstract

The present invention provides a thin polarizer with excellent heat resistance. The polarizer of the present invention is composed of a polyvinyl alcohol-based resin film with an iodine content of 3.5% by weight or more, and the absolute value of the change in transmittance ΔTsa of the monomer after being placed in an environment of 105°C for 30 hours is 5.0% or less . Here, the change amount ΔTsa of the monomeric transmittance is expressed by the following formula: ΔTsa(%)=Ts ₃₀ -Ts ₀ Ts ₀ is the monomeric transmittance before heating, and Ts ₃₀ is after standing at 105°C for 30 hours single transmittance.

Description

Polarizers and Polarizers

The invention relates to a polarizer and a polarizer.

Background of the invention In a representative image display device, that is, a liquid crystal display device, due to its image formation method, polarizers (in essence, polarizers including polarizers) are arranged on both sides of the liquid crystal cell. Polarizers are typically produced by dyeing polyvinyl alcohol (PVA) resin films with dichroic substances such as iodine (eg, Patent Documents 1 and 2). In recent years, the demand for thinner image display devices has increased significantly. Therefore, there is also a demand for further thinning of the polarizer. However, the thinner the polarizer, the easier it is to change color in a high-temperature environment, and it is easy to generate cracks and warping in a high-temperature environment.

prior art literature patent documents Patent Document 1: Japanese Patent No. 5048120 Patent Document 2: Japanese Patent Application Laid-Open No. 2013-156391

Summary of the invention The problem to be solved by the invention The present invention is made to solve the above-mentioned problems, and its main purpose is to provide a thin polarizer having very excellent heat resistance.

MEANS TO SOLVE THE PROBLEM The polarizer of the present invention is composed of a polyvinyl alcohol-based resin film with an iodine content of 3.5% by weight or more, and after being left at 105°C for 30 hours, the single transmittance of the polarizer changes. The absolute value of the amount ΔTsa is 5.0% or less. Here, the change amount ΔTsa of the monomeric transmittance is expressed by the following formula: ΔTsa(%)=Ts ₃₀ -Ts ₀ Ts ₀ is the monomeric transmittance before heating, and Ts ₃₀ is after standing at 105°C for 30 hours single transmittance. In one embodiment, the polarizer contains at least one selected from sodium ions, carbonate ions, and citrate ions. According to another aspect of the present invention, a polarizer can be provided. The polarizing plate includes the above-mentioned polarizer and protective films laminated on one side or both sides of the polarizer.

Invention effect According to the present invention, it is possible to realize a long-awaited but unrealized polarizer having a thin profile and very excellent heat resistance. More specifically, according to the present invention, it is possible to realize a thin polarizer that has significantly suppressed hue change, cracks, and warpage in a high-temperature environment.

form for carrying out the invention Embodiments of the present invention will be described below, but the present invention is not limited to these embodiments.

A. Polarizer A-1. Overview of Polarizer The polarizer according to the embodiment of the present invention is made of polyvinyl alcohol (PVA) resin film, and its iodine content is more than 3.5% by weight, and after being left for 30 hours in an environment of 105°C, the change in the single transmittance The absolute value of ΔTsa is 5.0% or less.

From the viewpoint of imparting sufficient polarizing performance and optimal transmittance, the iodine content 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 less than 10 μm, the iodine content should be 3.5% by weight to 8.0% by weight; when the thickness of the polarizer is greater than 3 μm and less than 5 μm, the iodine content should be 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 to 25.0% by weight. According to the embodiment of the present invention, very excellent heat resistance can be realized in the polarizer having an extremely high iodine content as described above, which was quite difficult in the past. More specifically, in polarizers with extremely high iodine content, hue changes, cracks, and warpage in high-temperature environments can be significantly suppressed. The details of the hue change will be described later. "Iodine content" in this specification means the amount of all iodine contained in a polarizer (PVA-type resin film). More specifically, iodine exists in polarizers in the form of iodide ions (I ^- ), iodine molecules (I ₂ ), polyiodide ions (I ₃ ^- , I ₅ ^- ), and the iodine content in this specification means Contains the amount of iodine in all such forms. The iodine content can be calculated using a calibration curve method such as fluorescent X-ray analysis. In addition, polyiodide ions exist in the state of forming a PVA-iodine complex in the polarizer. By forming the complex, absorption dichroism can be exhibited in the wavelength range of visible light. Specifically, the complex of PVA and triiodide ions (PVA·I ₃ ^- ) has an absorption peak near 470nm; the complex of PVA and pentaiodide ions (PVA·I ₅ ^- ) has an absorption peak near 600nm peak. As a result, polyiodide ions can absorb light in a wide range of visible light depending on their morphology. On the other hand, iodide ion (I ^- ) has an absorption peak around 230 nm, and has no substantial relationship with the absorption of visible light. Therefore, polyiodide ions existing in a complex state with PVA are mainly related to the absorption performance of the polarizer.

The upper limit of the thickness of the polarizer is 10 μm in one embodiment, 7 μm in another embodiment, 3 μm in another embodiment, and 1 μm in another embodiment. 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 embodiment of the present invention, even with a thin polarizer, desired single transmittance as will be described later can be realized, and also very excellent heat resistance can be realized. Representatively, it can significantly suppress the hue change, cracks and warpage in high temperature environment.

The absolute value of the change in single transmittance ΔTsa is preferably 3.0% or less, more preferably 1.0% or less. The lower limit of the absolute value of ΔTsa must be 0.0% (that is, there is no change in the transmittance of the monomer before and after heating). The polarizer according to the embodiment of the present invention has a very high iodine content as mentioned above, and the variation of the single transmittance in a high temperature environment has been significantly suppressed. Therefore, a polarizer in which discoloration has been suppressed in a high-temperature environment can be realized. We speculate that the above-mentioned excellent effect is caused by treating polyethylene with a treatment solution (typically sodium bicarbonate and/or citric acid) with a predetermined pH and buffering effect in the step after dyeing of the polarizer manufacturing method as described later. The alcohol-based resin film is treated so as to prevent the obtained polarizer from being polyeneized in a high-temperature environment. It can solve the newly-discovered problem of actually making an extremely thin (for example, thickness below 7 μm) polarizer that was difficult to manufacture in the past, and it is an excellent effect beyond expectations. In addition, the change amount Δtsa of the monomer transmittance is 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 placed in an environment of 105°C Monomer transmittance after 30 hours. In addition, when the single-body transmittance is simply described as Ts in this specification, it means the single-body transmittance Ts ₀ before heating.

The single transmittance (Ts) of the polarizer is preferably 30.0%~43.0%, more preferably 35.0%~41.0%. The degree of polarization of the polarizer is preferably above 99.9%, more preferably above 99.95%, and more preferably above 99.98%. By setting the single transmittance low and the degree of polarization high, the contrast can be improved, and the black display can be displayed even blacker, so an image display device with excellent image quality can be realized. In addition, the single transmittance is a value measured by a spectrophotometer with an integrating sphere. The single transmittance is the Y value obtained by measuring the 2-degree field of view (C light source) of JIS Z8701 and correcting the optical performance. For example, a spectrophotometer with an integrating sphere (manufactured by JASCO Co., Ltd., product name : V7100) for determination.

The orthogonal a value of the polarizer should be 0.0~0.6; the orthogonal b value should be -0.6~0.0. The polarizer according to the embodiment of the present invention can realize the above-mentioned desired single transmittance and degree of polarization and very excellent heat resistance, and has a very neutral hue as described above. If it is the hue mentioned above, problems such as bluishness will not occur. In addition, the a value and the b value are respectively the a value and the b value of the Lab color system. In addition, the a value and the b value may be adjusted outside the above-mentioned ranges, respectively, depending on the purpose. In addition, the hue change Δab ₃₀ of the polarizer after a heating test at 105° C. for 30 hours is preferably less than 5.0, more preferably less than 4.0.

The polarizer should contain 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 ) and At least any one of citric acid and ions derived therefrom. Specific examples of the ions include sodium ions, carbonate ions, potassium ions, phosphate ions, citrate ions, and monosodium carbonate ions. The polarizer may also contain two or more of these substances and/or ions. Preferably, the polarizer may contain sodium ions, carbonate ions and/or citrate ions. This is due to the treatment with the treatment liquid (B-1 item) in the production method (B item) described later. When the polarizer contains the compound (in other words, the polarizer is produced by the production method including the process described in B-1), discoloration of the polarizer under high temperature environment can be significantly suppressed. We speculate that this is because the generation of protons in the PVA-based resin can be suppressed by the buffering action of the treatment solution in a predetermined pH region, and as a result, the generation of multiple double bonds (polyene) in the PVA-based resin under high-temperature environments can be suppressed, thereby Can inhibit discoloration. In addition, cracking and warping can be suppressed by suppressing polyene. Regarding this part, we speculate as follows: Once a double bond is formed in the PVA-based resin molecule due to polyeneization, the distance between the monomer units near the double bond will be reduced. As a result, the PVA-based resin molecules (chains) are partially shrunk, and the shrunk may cause warpage or cracks. Therefore, by suppressing polyeneization, the formation of the double bond can be suppressed, and consequently warping and cracking can be suppressed.

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

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 1000-10000, preferably 1200-4500, more preferably 1500-4300. In addition, the average degree of polymerization can be obtained 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 also be a PVA-based resin layer formed on a substrate. The laminate of the base material and the PVA-based resin layer can be produced by, for example, a method of applying a coating solution containing the above-mentioned PVA-based resin to the base material, and a method of laminating a PVA-based resin film on the base material. wait.

B. Manufacturing method of polarizer B-1. Overview of the manufacturing method of the polarizer The method of manufacturing a polarizer according to an embodiment of the present invention includes at least stretching and dyeing a PVA-based resin film. Typically, the manufacturing method includes a step of preparing a PVA-based resin film, a 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 any appropriate order and timing. Therefore, each step can be carried out in the above order, or can be carried out in a different order. One step can also be carried out multiple times according to the requirement. In addition, steps other than the above (for example, an insolubilization step) may be performed at any appropriate timing. In addition, in the case of a PVA-based resin layer in which a PVA-based resin film is formed on a base material, a laminate of the base material and the PVA-based resin layer can be used in the above step.

In the manufacturing method of the polarizer according to the embodiment of the present invention, it is preferable to include treating the PVA-based resin film with a treating liquid after dyeing. The treatment with the treatment solution may be performed at any appropriate timing after dyeing. Specifically, the treatment with the treatment solution may be performed before or after the crosslinking step; it may be performed before or after the washing step. When the extension step is performed after the staining step, the treatment with the treatment solution may be performed before the extension step or may be performed after the extension step. When the swelling step is performed after the dyeing step, the treatment with the treatment solution may be performed before the swelling step or after the swelling step. When the insolubilization step is performed after the dyeing step, the treatment with the treatment solution may be performed before the insolubilization step or after the insolubility step. Typically, the treatment with 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 solution is, for example, 3.0-8.0, preferably 5.0-8.0, more preferably 5.5-7.5, more preferably 5.5-6.5. In another embodiment, it is more preferably 3.5-5.5, more preferably 3.7-4.7. In addition, the treatment solution preferably has a buffering effect within the pH range (ie, the pH range is 3.0-8.0). The treatment solution may be, for example, an aqueous solution containing sodium bicarbonate, potassium bicarbonate, disodium hydrogen phosphate, potassium carbonate, sodium carbonate, and citric acid. Treatment liquids containing these compounds have a buffering effect in a higher pH range than treatment liquids containing, for example, acetic acid-based compounds, and consequently have a better effect of preventing discoloration in high-temperature environments. The aqueous solution may contain these compounds alone, or may contain two or more of them. The treatment solution is preferably an aqueous solution of sodium bicarbonate or citric acid. Therefore, the polarizer according to the embodiment of the present invention may contain sodium bicarbonate and/or citric acid as described above. The concentration of the aqueous solution can be appropriately set depending on the desired pH and buffering effect. For example, the concentration of the aqueous sodium bicarbonate solution is preferably 0.20% by weight to 2.0% by weight, and the concentration of the aqueous citric acid solution is preferably 0.10% by weight to 3.0% by weight. Moreover, an aqueous solution may contain a pH adjuster as needed. Examples of pH adjusters include sulfuric acid (to lower pH), sodium hydroxide (to raise pH). Treating the PVA-based resin film with the treatment liquid can significantly inhibit the discoloration of the polarizer in a high-temperature environment. We speculate that, as mentioned above, this is because the generation of protons in the PVA-based resin can be suppressed by the buffering action of the treatment solution in the predetermined pH region, and as a result, the generation of multiple double bonds (polyenylation) in the PVA-based resin in a high-temperature environment can be suppressed. ), thereby suppressing discoloration.

Typically, the treatment with the treatment liquid includes the treatment of bringing the treatment liquid into contact with the PVA-based resin film. Any appropriate method can be mentioned as the contact method. Specific examples include immersing a PVA-based resin film in a treatment solution, or applying or spraying a treatment solution to a PVA-based resin film. And it is advisable to apply or spray the treatment liquid. Because the problem of the absorption spectrum change of the polarizer before and after immersion can be prevented during immersion, the situation of polyeneization of PVA can be further prevented well. Any appropriate method (means) can be adopted for the method (means) of coating or spraying the treatment liquid on the PVA-based resin film. Coating means include, for example, a reverse coater, a gravure coater (direct, reverse, or indirect), a bar reverse coater, a roll coater, a die coater, a rod coater, and a rod coater. As the spraying means, any appropriate spraying device (for example, pressurized nozzle type, rotating disc type) can be mentioned.

Each step is described below, but as mentioned above, each step can be performed in any and appropriate order, and is not limited by the order of description.

B-2. Extension steps In the stretching step, the PVA-based resin film can be uniaxially stretched up to 3 to 7 times. The stretching direction may be the long side direction (MD direction) of the film, or may be the width direction (TD direction) of the film. The stretching method may be dry stretching, wet stretching, or a combination thereof. Also, the PVA-based resin film may be stretched during the crosslinking step, swelling step, dyeing step, and the like. In addition, the extending direction may correspond to the absorption axis direction of the obtained polarizer.

B-3. Swelling step The swelling step will usually be performed before the staining step. The swelling step can be performed, for example, by immersing the PVA-based resin film in a swelling bath. The swelling bath can usually use distilled water, pure water and other water. The swelling bath may contain arbitrary and appropriate other components other than water. Examples of other components include solvents such as alcohols, additives such as surfactants, iodides, and the like. 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, titanium iodide and the like. Potassium iodide is preferably used. The temperature of the swelling bath is, for example, 20°C~45°C. In addition, the immersion time is, for example, 10 seconds to 300 seconds.

B-4. Staining procedure The dyeing step is a step of dyeing the PVA-based resin film with a dichroic substance. This is preferably done by allowing it to adsorb a dichroic substance. The adsorption method can be, for example, a method of immersing the PVA resin film in a dye solution containing a dichroic substance, a method of applying the dye solution to the PVA resin film, and spraying the dye solution onto the PVA system. method of resin film, etc. Ideally, it is a method of immersing a PVA-based resin film in a dyeing solution. Because it can adsorb dichroic substances well.

Examples of the aforementioned dichroic substances include iodine and dichroic dyes. And preferably iodine. When iodine is used as the dichroic substance, 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 with respect to 100 parts by weight of water. In order to increase the solubility of iodine in water, it is advisable to mix iodide in the iodine aqueous solution. Potassium iodide is preferably used as the iodide. The iodide content is preferably 0.3 to 15 parts by weight relative to 100 parts by weight of water.

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

B-5. Cross-linking step In the crosslinking step, boron compounds are generally used as crosslinking agents. Examples of boron compounds include boric acid and borax. And preferably boric acid. 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% by weight to 15% by weight, preferably 1% by weight to 10% by weight. Furthermore, the boric acid aqueous solution may contain iodides such as potassium iodide; zinc compounds such as zinc sulfate and zinc chloride.

The crosslinking step can be performed by any and appropriate method. For example, a method of immersing a PVA-based resin film in an aqueous solution of a boron-containing 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. And it is better to immerse in the aqueous solution of boron-containing compound.

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

B-6. Washing step The washing step represents that the upper line is performed after the crosslinking step. A representative cleaning step is performed by immersing the 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 cleaning solution temperature is, for example, 5°C to 50°C. The immersion time is, for example, 1 second to 300 seconds.

B-7. Drying step The drying step can be performed by any appropriate method. Examples of drying methods include natural drying, air drying, reduced-pressure drying, and heating drying. And should use heat drying. When heat drying is performed, the heating temperature is, for example, 30°C to 100°C. Also, the drying time is, for example, 20 seconds to 10 minutes.

C. Polarizer The polarizer of the embodiment of the present invention is typically used in a state where a protective film is laminated on one or both sides (that is, as a polarizer). In practical application, the polarizing plate has an adhesive layer as the outermost layer. Typically, the adhesive layer is the outermost layer on the image display device side. On the adhesive layer, the separator is temporarily adhered in a peelable state, which can protect the adhesive layer until actual use, and can be formed into a roll.

Any appropriate resin film can be used for the protective film. Examples of materials for forming the resin film include (meth)acrylic resins, cellulose resins such as diacetyl cellulose and triacetyl cellulose, cycloolefin resins such as norbornene resins, and olefin resins such as polypropylene. , polyester resins such as polyethylene terephthalate resins, polyamide resins, polycarbonate resins and their copolymer resins, etc. In addition, "(meth)acrylic resin" means an acrylic resin and/or a methacrylic resin.

In one embodiment, a (meth)acrylic resin having a glutarimide structure is used for the above-mentioned (meth)acrylic resin. (Meth)acrylic resins having a glutarimide structure (hereinafter also referred to as glutarimide resins) are described in the following documents, for example: Japanese Patent Laid-Open No. 2006-309033, Japanese Patent Laid-Open No. 2006-317560, JP 2006-328329, JP 2006-328334, JP 2006-337491, JP 2006-337492, JP 2006-337493, JP 2006- 337569, JP-A-2007-009182, JP-A-2009-161744, and JP-A-2010-284840. These descriptions are incorporated by reference in this specification.

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

Example Hereinafter, the present invention will be specifically described with examples, but the present invention is not limited by these examples. In addition, the measurement method of each characteristic is as follows.

(1) Iodine content For the polarizers of the laminates obtained in Examples, Comparative Examples, and Reference Examples, a fluorescent X-ray analyzer (manufactured by Rigaku, trade name "ZSX-PRIMUS II", measuring diameter: ψ20mm) was used. Fluorescent X-ray intensities (kcps) were measured. On the other hand, the thickness (μm) of the polarizer was measured using a spectroscopic film thickness meter (manufactured by Otsuka Electronics Co., Ltd., trade name "MCPD-3000"). From the obtained fluorescent X-ray intensity and thickness, the iodine content (% by weight) was determined by the following formula. (Iodine concentration)=20.5×(X-ray fluorescence intensity)/(Film thickness) In addition, the coefficient when calculating the iodine content will vary depending on the measuring device, and the coefficient can be obtained using an appropriate calibration curve. (2) Individual transmittance variation ΔTsa and ΔTsa′ A reflective polarizer (manufactured by 3M, trade name "DBEF") was attached to the polarizer side of the laminates obtained in Examples, Comparative Examples, and Reference Examples. Next, after the thermoplastic resin substrate was peeled off, an alkali-free glass with a thickness of 1.3 mm was pasted on the peeled surface through an acrylic adhesive layer with a thickness of 20 μm to make a test sample. This test sample was heated at 105° C. for 30 hours (heating test). A spectrophotometer with an integrating sphere (manufactured by JASCO Co., Ltd., product name: V7100) was used to measure the single transmittance of the polarizer before the test and after the heating test. Then, the change amount ΔTsa of the single element transmittance was obtained from the single element transmittance Ts ₀ before heating and the single element transmittance Ts ₃₀ after the heating test by the following formula. ΔTsa(%)=Ts ₃₀ -Ts ₀ In addition, ΔTsa´(%)=Ts ₂₀ -Ts ₀ when the heating time of the heating test was 20 hours was also obtained. (3) Hue change Δab For the laminates obtained in Examples, Comparative Examples, and Reference Examples, a value and b value were measured with an ultraviolet-visible spectrophotometer (V-7100 manufactured by JASCO). Think of it as a ₀ value and b ₀ value. Next, calculate the a ₂₀ value and b ₂₀ value after heating at 105°C for 20 hours, and the a ₃₀ value and b ₃₀ value after heating at 105°C for 30 hours. From these equivalent values, the hue change amounts Δab ₂₀ and Δab ₃₀ were obtained by the following formulas. Δab ₂₀ ={(a ₂₀ -a ₀ ) ² +(b ₂₀ -b ₀ ) ² } ^1/2 Δab ₃₀ ={(a ₃₀ -a ₀ ) ² +(b ₃₀ -b ₀ ) ² } ^1/2 (4) Initial appearance of the polarizer The appearance of the polarizer (that is, the polarizer before the heating test in (2) above) of the laminates obtained in the examples, comparative examples, and reference examples was observed with the naked eye, and evaluated on the basis of the following . ○: No cloudiness observed Δ: Slight cloudiness observed X: Clear cloudiness (5) Cracks After heating the laminates obtained in Examples, Comparative Examples, and Reference Examples at 115°C for 72 hours, the appearance of the polarizer was observed with the naked eye. Crack condition, and evaluate it with the following benchmarks. ○: No cracks were observed ×: Cracks were observed (6) Warping The polarizer-side surface of the laminate obtained in Example 1 and Comparative Example 1 was bonded with a 0.55 mm thick acrylic adhesive layer through an acrylic adhesive layer with a thickness of 20 μm. Alkali glass, made into test specimens. After heating this test sample at 115° C. for 72 hours, the amount of warpage was measured. The amount of warpage is to measure the height from the glass plate for the 4 corners of the test piece, and take the maximum value as the amount of warpage. The amount of warping in Example 1 was 0.0 mm, and the result was "good"; the amount of warping in Comparative Example 1 was 0.75 mm, and the result was "poor (obvious warping)".

[Example 1] The thermoplastic resin substrate is an amorphous isophthalic acid copolymerized polyethylene terephthalate (IPA copolymerized PET) film (thickness: 100 μm) with a water absorption rate of 0.75% and a Tg of 75°C. Apply corona treatment to one side of the substrate, and coat polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mole%) and acetylene at a ratio of 9:1 on the corona treatment surface at 25°C Acetyl modified PVA (polymerization degree 1200, acetyl acetyl modification degree 4.6%, saponification degree 99.0 mol% or more, Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFIMER Z200") aqueous solution and dried, and A PVA-based resin layer having a thickness of 11 μm was formed to produce a laminate. The obtained laminate was stretched 4.5 times in the air in a direction perpendicular to the long side direction of the laminate at 140° C. using a tenter stretcher (stretching treatment). Next, the laminate was dipped in a dyeing bath (an 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 laminate was immersed in a cleaning bath (pure water) at a liquid temperature of 25° C. for 6 seconds (first cleaning process). Next, it was immersed in a crosslinking bath (an aqueous solution with 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 cleaning bath (aqueous solution having a potassium iodide concentration of 1% by weight) at a liquid temperature of 25° C. for 3 seconds (second cleaning treatment). Then, the laminate was dried in an oven at 60° C. for 21 seconds (the first drying process). Next, a treatment solution (an aqueous solution of 0.5% by weight of sodium bicarbonate and 50% by weight of isopropanol: pH=6.0) was applied to the PVA-based resin layer of the laminate with a bar coater. In addition, the pH of the treatment solution 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) with a thickness of 1.2 μm. The iodine content of the obtained polarizer was 20.9% by weight, and the single transmittance was 40.3%. The obtained laminate was subjected to the evaluation of (2) to (6) above. The results are listed in Table 1.

[Example 2] A laminate with a polarizer was produced 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 isopropanol was used as the treatment liquid. In addition, the pH of the treatment solution has been adjusted by mixing sodium hydroxide. The iodine content of the obtained polarizer was 20.5% by weight, and the single transmittance was 39.5%. The obtained laminate was subjected to the same evaluation as in Example 1. The results are listed in Table 1.

[Example 3] A laminate with a polarizer was produced in the same manner as in Example 1 except that the conditions of the dyeing treatment were changed so that the single transmittance of the obtained polarizer was about 43%. The iodine content of the obtained polarizer was 6.5% by weight, and the single transmittance was 43.2%. The obtained laminate was subjected to the same evaluation as in Example 1. The results are listed in Table 1.

[Example 4] A laminate with a polarizer was produced in the same manner as in Example 2, except that the conditions of the dyeing treatment were changed so that the single transmittance of the obtained polarizer was about 43%. The iodine content of the obtained polarizer was 6.5% by weight, and the single transmittance was 42.8%. The obtained laminate was subjected to the same evaluation as in Example 1. The results are listed in Table 1.

[Example 5] A laminate with a polarizer was produced in the same manner as in Example 1 except that the sodium bicarbonate in the treatment solution was 1.0 by weight. The iodine content of the obtained polarizer was 20.5% by weight, and the single transmittance was 39.5%. The obtained laminate was subjected to the same evaluation as in Example 1. The results are listed in Table 1.

[Comparative example 1] A laminate having a polarizer was produced in the same manner as in Example 1 except that the treatment liquid was not used. The iodine content of the obtained polarizer was 21.5% by weight, and the single transmittance was 39.3%. The obtained laminate was subjected to the same evaluation as in Example 1. The results are listed in Table 1.

[Comparative example 2] A laminate with a polarizer was produced in the same manner as in Example 1, except that the treatment solution was not used, and the conditions of the dyeing treatment were changed so that the single transmittance of the obtained polarizer was about 43%. The iodine content of the obtained polarizer was 6.7% by weight, and the single transmittance was 43.2%. The obtained laminate was subjected to the same evaluation as in Example 1. The results are listed in Table 1.

[Reference example 1] Except changing the coating thickness of the PVA aqueous solution so that the thickness of the obtained polarizer becomes 12 μm, and changing the conditions of the dyeing treatment so that the monomer transmittance of the obtained polarizer becomes about 43%, a polarizer with polarizer is prepared in the same manner as in Example 1. The laminate. The iodine content of the obtained polarizer was 3.3% by weight, and the single transmittance was 43.0%. The obtained laminate was subjected to the same evaluation as in Example 1. The results are listed in Table 1.

[Reference example 2] A laminate with a polarizer was produced in the same manner as in Example 1, except that the treatment solution was not used, and the conditions of the dyeing treatment were changed so that the single transmittance of the obtained polarizer became 45% or more. The iodine content of the obtained polarizer was 2.1% by weight, and the single transmittance was 45.7%. The obtained laminate was subjected to the same evaluation as in Example 1. The results are listed in Table 1.

[Table 1]

As can be seen from Table 1, the polarizers of the embodiments of the present invention have excellent single transmittance change, hue change, cracks and warpage after the heating test, and have very good heat resistance. In addition, as is clear from the comparison of Reference Examples 1 and 2, heat resistance is a problem specific to polarizers that are thin and have a very high iodine content.

Industrial availability The polarizer of the present invention can be widely used on LCD panels of LCD TVs, LCD monitors, mobile phones, digital cameras, digital video cameras, handheld game consoles, car navigation, photocopiers, printers, fax machines, clocks, microwave ovens, etc. .

(none)

Claims (3)

A polarizer, which is composed of polyvinyl alcohol-based resin film; its iodine content is more than 3.5% by weight, its thickness is 0.5μm~1.2μm, and the amount of change in single transmittance after being placed in an environment of 105°C for 30 hours The absolute value of △Tsa is less than 5.0%; here, the change of monomer transmittance △Tsa is expressed by the following formula: △Tsa(%)=Ts ₃₀ -Ts ₀ Ts ₀ is the monomer transmittance before heating, Ts ₃₀ It is the transmittance of the monomer after being placed in an environment of 105°C for 30 hours. The polarizer according to claim 1, which contains at least one member selected from sodium ions, carbonate ions, and citrate ions. A polarizing plate comprising the polarizer according to claim 1 or 2 and a protective film laminated on one or both sides of the polarizer.