TW201928420A - Polarizer and polarizing plate - Google Patents

Abstract

Provided is a polarizer that is thin and that has exceptional heat resistance. The polarizer is made from a polyvinyl alcohol resin film and has an iodine content of 3.5 wt% or more. The absolute value of a single transmittance change amount [Delta]Tsa after the polarizer is left in an environment in which the temperature is 105 DEG C for thirty hours is 5.0% or less. The single transmittance change amount [Delta]Tsa is represented by the following formula: [Delta]Tsa (%) = Ts30 - Ts0 (wherein Ts0 is the single transmittance prior to heating and Ts30 is the single transmittance after being left for thirty hours in an environment in which the temperature is 105 DEG C).

Description

Polarizer and polarizer

The invention relates to a polarizer and a polarizing plate.

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 difficult it is to discolor in a high temperature environment and the heat resistance problem that cracks and warpage are liable to occur in a high temperature environment.

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 its main object is to provide a polarizer that is thin and has excellent heat resistance.

Means for solving the problem The polarizer of the present invention is made of a polyvinyl alcohol resin film, the iodine content is 3.5% by weight or more, and the unit transmittance of the polarizer is changed after being left for 30 hours at 105 ° C. The absolute value of the amount ΔTsa is 5.0% or less. Here, the change amount ΔTsa of the monomer transmittance is expressed by the following formula:
ΔTsa (%) = Ts ₃₀ -Ts ₀
Ts ₀ is the monomer transmittance before heating, and Ts ₃₀ is the monomer transmittance after being left for 30 hours in an environment of 105 ° C.
In one embodiment, the polarizer includes at least one selected from a sodium ion, a carbonate ion, and a citrate ion.
According to another aspect of the present invention, a polarizing plate can be provided. The polarizing plate includes the above-mentioned polarizer and a protective film laminated on one or both sides of the polarizer.

Advantageous Effects of Invention According to the present invention, it is possible to realize a thin type polarizer which has been expected for a long time but has not been realized, and has extremely excellent heat resistance. In more detail, according to the present invention, a thin polarizer that has significantly suppressed hue changes, cracks, and warpage in a high temperature environment can be realized.

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

From the viewpoint of providing 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 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. According to the embodiment of the present invention, extremely excellent heat resistance can be achieved in a polarizer having an extremely high iodine content as described above, which has been quite difficult in the past. In more detail, in a polarizer having an extremely high iodine content, hue change, cracks, and warpage in a high-temperature environment can be significantly suppressed. The details of the hue change will be described later. 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 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 if it is a thin polarizer, the desired unit transmittance as described below can be achieved, and furthermore, extremely excellent heat resistance can be achieved. On the representative, it can significantly suppress the hue change, cracks and warpage under high temperature environment.

The absolute value of the change in the transmittance ΔTsa of the monomer is preferably 3.0% or less, and 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 an extremely high iodine content as described above, and the amount of change in the transmittance of a monomer under a high-temperature environment has been significantly suppressed. Therefore, it is possible to realize a polarizer in which discoloration has been suppressed in a high-temperature environment. I speculate that the excellent effect is that, as described later, in the step after dyeing of the polarizer manufacturing method, the polyethylene The alcohol-based resin film is processed to prevent the obtained polarizer from being polyene-derived in a 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. The change in the transmittance Δtsa of the monomer is represented 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 single transmittance (Ts) of the polarizer should be 30.0% ~ 43.0%, more preferably 35.0% ~ 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 orthogonal a value of the polarizer should be 0.0 ~ 0.6; the orthogonal b value should be -0.6 ~ 0.0. The polarizer of the embodiment of the present invention can achieve the above-mentioned desired monomer transmittance and polarization degree, and very excellent heat resistance, and has a very neutral hue as described above. 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. In addition, the hue change Δab _{30 of the} polarizer after a heating test at 105 ° C. for 30 hours is preferably 5.0 or less, and more preferably 4.0 or less.

The polarizer should preferably 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 from these. Specific examples of the ion include sodium ion, carbonate ion, potassium ion, phosphate ion, citrate ion, and sodium carbonate ion. The polarizer may contain two or more of these substances and / or ions. The polarizer may preferably contain sodium ions, carbonate ions and / or citrate ions. This is because the processing (item B-1) is performed by the processing liquid in the manufacturing method (item B) described later. The polarizer contains the compound (in other words, the polarizer is manufactured by a manufacturing method including the treatment described in item B-1), and the discoloration of the polarizer under a high temperature environment can be significantly suppressed. 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 addition, by suppressing polyenelation, cracks and warpage can be suppressed. My guess on this part is as follows: once a double bond is formed in a PVA-based resin molecule due to polyenelation, the distance between monomer units near the double bond will decrease. As a result, the PVA-based resin molecules (chains) partially shrink, which may cause warpage or cracks. Therefore, by inhibiting polyenelation, the formation of the double bond can be suppressed, and as a result, warpage and cracks can be suppressed.

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.

B. Manufacturing method of polarizer
B-1. Overview of the method for manufacturing a polarizer The method for manufacturing a polarizer according to the embodiment of the present invention includes stretching and dyeing a PVA-based resin film at least. 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 addition, if the PVA-based resin layer is formed with a PVA-based resin film on the substrate, the laminated body of the substrate and the PVA-based resin layer may be supplied in the above steps.

In the method for manufacturing a polarizer according to the embodiment of the present invention, after dyeing, it is preferable to include treating the PVA-based resin film with a treatment solution. The treatment with the treatment liquid may be performed at any appropriate timing after dyeing. The treatment with 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 extension step is performed after the dyeing step, the treatment with the treatment liquid 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 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 treatment with the treatment liquid may be performed before the insolubilization step or may be performed after the insolubilization step. Representatively, 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 liquid is, for example, 3.0 to 8.0, preferably 5.0 to 8.0, more 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. In addition, the treatment solution should have a buffering effect within the pH range (that is, the pH range is 3.0 to 8.0). The treatment liquid may be, for example, an aqueous solution containing sodium bicarbonate, potassium bicarbonate, disodium hydrogen phosphate, potassium carbonate, sodium carbonate, and citric acid. The treatment liquid containing these compounds has a higher pH buffering effect than the treatment liquid containing, for example, an acetic acid-based compound, and thus has a more excellent effect of preventing discoloration in a high temperature environment as a result. 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. 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 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). Treating the PVA-based resin film with the treatment solution can significantly suppress the discoloration of the polarizer in a high-temperature environment. I speculate that the above is because the buffer solution of the treatment solution in a predetermined pH region can inhibit the generation of protons in the PVA-based resin, and as a result, the generation of multiple double bonds (polyenelation) in the PVA-based resin under high temperature environments can be suppressed. ), Thereby suppressing discoloration.

The treatment with the treatment liquid typically includes a treatment in which the treatment liquid is brought into contact with the PVA-based resin film. The contact method may be any appropriate method. As a specific example, a PVA-type resin film is immersed in a processing liquid, or a PVA-type resin film is apply | coated or sprayed. It is also preferable to apply or spray the treatment liquid. Because the problem of the change in the absorption spectrum of the polarizer before and after the immersion can be prevented during the immersion, the situation of the polyalkylene of the PVA can be further prevented. As a method (means) for coating or spraying the PVA-based resin film, any appropriate method (means) can be adopted. The coating means may include a reverse coater, a gravure coater (direct, reverse or indirect), a bar reverse coater, a roll coater, a die coater, a bar coater, and a rod coater. The spraying means may be, for example, an arbitrary and appropriate spraying device (for example, a pressurized nozzle type, a rotary 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.

B-2. 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.

B-3. 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.

B-4. 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.

B-5. 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.

B-6. 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.

B-7. 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.

C. Polarizing plate The polarizing member according to the embodiment of the present invention is used in a state where 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) Iodine content For the polarizers of the laminated body obtained in the examples, comparative examples, and reference examples, a fluorescent X-ray analyzer (manufactured by Rigaku, trade name "ZSX-PRIMUS II", measurement diameter: 20 mm) was used. The fluorescence X-ray intensity (kcps) was 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. under the 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 varies depending on the measurement device, and the coefficient can be obtained using an appropriate calibration curve.
(2) Changes in the single transmittance ΔTsa and ΔTsa´
A reflective polarizer (manufactured by 3M Corporation, trade name "DBEF") was bonded to the polarizer side of the laminated body obtained in the examples, comparative examples, and reference 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 spectrophotometer (manufactured by JASCO Corporation, product name: V7100) with an integrating sphere was used to measure the individual transmittance of the polarizer before and after the heating test. Then, from the monomer transmittance Ts ₀ before the heating and the monomer transmittance Ts ₃₀ after the heating test, the change amount ΔTsa of the monomer transmittance was obtained using the following formula.
ΔTsa (%) = Ts ₃₀ -Ts ₀
In addition, ΔTsa´ (%) = Ts ₂₀ -Ts ₀ when the heating time of the heating test is 20 hours is also obtained.
(3) Hue change Δab
The laminated bodies obtained in the examples, comparative examples, and reference examples were measured for a value and b value using an ultraviolet-visible spectrophotometer (V-7100, manufactured by JASCO Corporation). _{Consider these} values as a ₀ and b ₀ . Then, the values of a ₂₀ and b ₂₀ after heating at 105 ° C. for 20 hours, and the values of a ₃₀ and b ₃₀ after heating at 105 ° C. for 30 hours were obtained. From these values, the amounts of excellent phase change Δab ₂₀ and Δab ₃₀ were obtained from the values, respectively.
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 Observe the appearance of the polarizer of the laminated body obtained in the examples, comparative examples, and reference examples (that is, the polarizer before the heating test in (2) above) with the naked eye, and evaluate it with the following criteria .
○: No white turbidity was observed △: Some white turbidity was observed ×: White turbidity was obvious
(5) Cracks The laminated bodies obtained in the examples, comparative examples, and reference examples were heated at 115 ° C. for 72 hours, and the crack state of the polarizer was observed with the naked eye, and evaluated based on the following criteria.
○: No crack was observed ×: A crack was observed
(6) Warping The alkali-free glass having a thickness of 0.55 mm was bonded to the polarizer side surface of the laminated body obtained in Example 1 and Comparative Example 1 through an acrylic adhesive layer having a thickness of 20 μm to prepare a test sample. After heating this test sample at 115 ° C for 72 hours, the amount of warpage was measured. The amount of warpage is the height measured from the glass plate for 4 mm of the test piece, and the maximum value is taken as the amount of warpage. The amount of warpage in Example 1 was 0.0 mm, and the result was "good"; the amount of warpage in Comparative Example 1 was 0.75 mm, and the result was "poor (significant warpage)".

[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 acetamidine Aqueous solution of acetamyl modified PVA (polymerization degree 1200, acetamyl acetamyl modification 4.6%, saponification degree above 99.0 mole%, manufactured by Japan Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFIMER Z200") and dried, and 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).
Then, a treatment liquid (aqueous solution of 0.5% by weight of sodium bicarbonate and 50% by weight of isopropyl alcohol: 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 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 polarizer had an iodine content of 20.9% by weight and a monomer transmittance of 40.3%.
The obtained laminated body was subjected to the above evaluations (2) to (6). 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 = 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 polarizer had an iodine content of 20.5% by weight and a monomer transmittance of 39.5%. 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 produced in the same manner as in Example 1 except that the conditions of the dyeing treatment were changed so that the single-element transmittance of the obtained polarizer became about 43%. The obtained polarizer had an iodine content of 6.5% by weight and a monomer transmittance of 43.2%. 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 2 except that the conditions of the dyeing treatment were changed so that the single-element transmittance of the obtained polarizer became about 43%. The obtained polarizer had an iodine content of 6.5% by weight and a monomer transmittance of 42.8%. 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 sodium bicarbonate of the treatment liquid was 1.0 weight. The obtained polarizer had an iodine content of 20.5% by weight and a monomer transmittance of 39.5%. 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 was not performed with the treatment liquid. The obtained polarizer had an iodine content of 21.5% by weight and a monomer transmittance of 39.3%. 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 produced in the same manner as in Example 1 except that the monomer transmittance of the obtained polarizer was changed to about 43% without treating with a treatment solution and changing the conditions of the dyeing treatment. The obtained polarizer had an iodine content of 6.7% by weight and a monomer transmittance of 43.2%. The obtained laminated body was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Reference Example 1]
A polarizer was prepared in the same manner as in Example 1 except that the coating thickness of the PVA aqueous solution was changed so that the thickness of the obtained polarizer was 12 μm, and the conditions of the dyeing treatment were changed so that the unit transmittance of the obtained polarizer was about 43%. Of laminated body. The obtained polarizer had an iodine content of 3.3% by weight and a monomer transmittance of 43.0%. The obtained laminated body was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Reference Example 2]
A laminated body having a polarizer was produced in the same manner as in Example 1 except that the single-crystal transmittance of the obtained polarizer was not more than 45% except that the treatment solution was not treated and the conditions of the dyeing treatment were changed. The obtained polarizer had an iodine content of 2.1% by weight and a monomer transmittance of 45.7%. 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, after the heating test, the polarizers of the examples of the present invention exhibit excellent monomer transmittance change, hue change, cracks, and warpage, and have very good heat resistance. In addition, as is clear from comparison of Reference Examples 1 and 2, heat resistance is a problem specific to polarizers that are thin and have a very large iodine content.

Industrial Applicability The polarizer of the present invention can be widely used in liquid crystal 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 polarizer is composed of a polyvinyl alcohol resin film; its iodine content is 3.5% by weight or more, and the absolute transmittance change amount ΔTsa of the monomer after leaving it at 105 ° C for 30 hours is 5.0% or less; Here, the change in the transmittance of the monomer ΔTsa is expressed by the following formula: ΔTsa (%) = Ts ₃₀ -Ts ₀ Ts ₀ is the transmittance of the monomer before heating, and Ts ₃₀ is the value after 30 hours of standing in an environment at 105 ° C. Monomer transmittance. The polarizer according to claim 1, which contains at least one selected from the group consisting of sodium ion, carbonate ion, and citrate ion. A polarizing plate includes the polarizer as claimed in claim 1 or 2 and a protective film laminated on one or both sides of the polarizer.