JP6914355B2 - Polarizer and polarizing plate - Google Patents

Description

The present invention relates to a polarizer and a polarizing plate.

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 of heat resistance that the thinner the polarizer, the more easily the color changes in a high temperature environment, and the more easily cracks and warpage occur 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 polarizing element which is thin and has excellent heat resistance.

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

According to the present invention, it has been possible to realize a polarizer that is thin and has extremely excellent heat resistance, which has been desired for a long time but has not been realized. More specifically, according to the present invention, it was possible to realize a thin polarizer in which hue change, cracks and warpage in a high temperature environment are remarkably suppressed.

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

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

The iodine content 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. According to the embodiment of the present invention, in a polarizer having such an extremely high iodine content, it is possible to realize extremely excellent heat resistance, which has been difficult in the past. More specifically, in a polarizer having an extremely high iodine content, hue change, cracking and warpage in a high temperature environment can be remarkably suppressed. The details of the hue change will be described later. 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 ), polyiodine 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 dichroism 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 absorptive peak. As a result, polyiodine 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 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 be mainly involved in 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 yet another embodiment, and 1 μm in yet another embodiment. be. 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 embodiment of the present invention, it is possible to realize a desired simple substance transmittance as described later even with a polarizing element having a thin thickness, and further, it is possible to realize extremely excellent heat resistance. Typically, hue change, cracks and warpage in a high temperature environment can be remarkably suppressed.

The absolute value of the single transmittance change amount ΔTsa is preferably 3.0% or less, and more preferably 1.0% or less. The lower limit of the absolute value of ΔTsa is necessarily 0.0% (that is, there is no change in the simple substance transmittance before and after heating). As described above, the polarizer according to the embodiment of the present invention has an extremely high iodine content, and the amount of change in 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. Such an excellent effect is exhibited by polyvinyl carbonate with a treatment liquid (typically sodium hydrogen carbonate and / or citric acid) having a predetermined pH and buffering action in the post-staining step in the method for producing a polarizing element, as will be described later. It is presumed that this is achieved by treating the alcohol-based resin film to prevent polyene formation of the obtained polarizer 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. 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 simple substance transmittance (Ts) of the polarizer 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 single 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 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 according to the embodiment of the present invention has such a very neutral hue while achieving the desired elemental transmittance and degree of polarization as well as extremely excellent heat resistance. 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. _{Further, for the polarizer, the hue change Δab 30} after the heating test at 105 ° C. for 30 hours is preferably 5.0 or less, more preferably 4.0 or less.

The polarizer is preferably sodium hydrogen carbonate (NaHCO ₃ ), potassium hydrogen carbonate (KHCO ₃ ), disodium hydrogen phosphate (Na ₂ HPO ₄ ), potassium carbonate (K ₂ CO ₃ ), sodium carbonate (Na ₂ CO). ₃ ), and citric acid, and at least one of the ions derived from them may be included. Specific examples of such ions include sodium ion, carbonate ion, potassium ion, phosphate ion, citrate ion, and monosodium carbonate ion. The polarizer may contain two or more of these substances and / or ions. The polarizer may more preferably contain sodium ions, carbonate ions and / or citrate ions. This is due to the treatment with the treatment liquid (B-1 item) in the manufacturing method (B item) described later. By containing such a compound in the polarizer (in other words, by producing the polarizer by a production method including the treatment described in Item B-1), discoloration of the polarizer in a high temperature environment is significantly suppressed. can do. 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. Furthermore, by suppressing polyene formation, cracks and warpage can be suppressed. This is presumed as follows: When a double bond is formed in the PVA-based resin molecule by polyene formation, the distance between the monomer units in the vicinity of the double bond becomes small. As a result, PVA-based resin molecules (chains) may partially shrink, and such partial shrinkage may cause warpage or cracks. By suppressing polyene formation, the formation of such double bonds is suppressed, and as a result, warpage and cracks 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 an ethylene-vinyl alcohol copolymer. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. The ethylene-vinyl alcohol copolymer is obtained by saponifying the ethylene-vinyl acetate copolymer. The saponification degree 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%. be. The degree of saponification can be determined according to JIS K 6726-1994. By using a PVA-based resin having such a saponification degree, 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 base material. 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.

B. Method for manufacturing a polarizer B-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 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. When the PVA-based resin film is a PVA-based resin layer formed on a base material, a laminate of the base material and the PVA-based resin layer is subjected to the above step.

The method for producing a polarizer according to the embodiment of the present invention preferably includes treating a PVA-based resin film with a treatment liquid after dyeing. The treatment with the treatment liquid may be performed at an arbitrary appropriate timing after dyeing. Specifically, the treatment with the treatment liquid may be carried out before or after the cross-linking step, and may be carried out before or after the washing step. When the stretching step is performed after the dyeing step, the treatment with the treatment liquid may be performed before or after the stretching step. When the swelling step is performed after the dyeing step, the treatment with the treatment liquid may be performed before or after the swelling step. When the insolubilization step is performed after the dyeing step, the treatment with the treatment liquid may be performed before or after the insolubilization step. Typically, the treatment with the treatment liquid can be performed after the washing 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 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 even more preferably 5.5 to 6. It is .5. In another embodiment, it is more preferably 3.5 to 5.5, still more preferably 3.7 to 4.7. Further, the treatment liquid preferably has a buffering action in the pH range (that is, the pH is in the range of 3.0 to 8.0). Such a treatment liquid may be, for example, an aqueous solution containing sodium hydrogen carbonate, potassium hydrogen carbonate, disodium hydrogen phosphate, potassium carbonate, sodium carbonate, 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. 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 set appropriately depending on the desired pH and buffering action. For example, the concentration of the aqueous sodium hydrogen carbonate solution can be preferably 0.20% by weight to 2.0% by weight, and the concentration of the aqueous citric acid solution can be preferably 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 treating the PVA-based resin film with such a treatment liquid, discoloration of the polarizer in a high temperature environment can be remarkably suppressed. As described above, 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, a large number of double bonds in the PVA-based resin under a high temperature environment. It is presumed that the occurrence of polyene can be suppressed and discoloration can be suppressed.

Treatment with a treatment liquid typically includes contacting the treatment liquid with a PVA-based resin film. As the contact method, any suitable method can be mentioned. Specific examples include dipping the PVA-based resin film in the treatment liquid, and applying or spraying the treatment liquid on the PVA-based resin film. It is preferable to apply or spray the treatment liquid. This is because 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. As a method (means) for applying or spraying the treatment liquid to the PVA-based resin film, any appropriate method (means) can be adopted. 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.

B-2. 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.

B-3. 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.

B-4. 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 staining 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.

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. 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.

B-6. 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.

B-7. 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.

C. Polarizing Plate The polarizer according to the embodiment 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 resin such as diacetyl cellulose and triacetyl cellulose, cycloolefin resin such as norbornene resin, olefin resin such as polypropylene, and polyethylene terephthalate 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 Japanese Patent Application Laid-Open No. 161744 and Japanese Patent Application Laid-Open No. 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) 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", measurement diameter: ψ20 mm) was used. Fluorescent X-ray intensity (kcps) was measured using. 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”). The iodine content (% by weight) was determined from the obtained fluorescent X-ray intensity and thickness using the following formula.
(Iodine concentration) = 20.5 x (fluorescent X-ray intensity) / (film thickness)
The coefficient for calculating the iodine content differs depending on the measuring device, but the coefficient can be obtained by using an appropriate calibration curve.
(2) Single transmittance change amount 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, 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). The single transmittance of the polarizer before the test and after the heating test was measured using a spectrophotometer with an integrating sphere (manufactured by JASCO Corporation, product name: V7100), respectively. From the simple substance transmittance Ts ₀ before heating and the simple substance transmittance Ts ₃₀ after the heating test, the amount of change in simple substance transmittance ΔTsa was determined using the following formula.
ΔTsa (%) = Ts ₃₀ −Ts _{0
Further, ΔTsa'(%) = Ts 20 -Ts 0} when the heating time of the heating test was 20 hours was also determined.
(3) Hue change Δab
The a value and b value of the laminates obtained in Examples, Comparative Examples and Reference Examples were measured using an ultraviolet-visible spectrophotometer (V-7100 manufactured by JASCO Corporation). These were set as a ₀ value and b ₀ value. _{Further, a 20} value and b ₂₀ value after heating at 105 ° C. for 20 hours, _{and a 30} value and b ₃₀ value after heating at 105 ° C. for 30 hours were determined, respectively. From these values, the hue change amounts Δab ₂₀ and Δab ₃₀ were obtained using the following equations, 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 Polarizer The appearance of the polarizer of the laminate obtained in Examples, Comparative Examples and Reference Examples (that is, the polarizer before the heating test of (2) above) was visually observed and described as follows. Evaluated by criteria.
◯: No white turbidity was observed Δ: Slight white turbidity was observed ×: White turbidity was remarkable (5) Cracks The laminates obtained in Examples, Comparative Examples and Reference Examples were heated at 115 ° C. for 72 hours. After that, the state of cracks in the polarizer was visually observed and evaluated according to the following criteria.
◯: No cracks were observed ×: Cracks were observed (6) Warpage The surface of the laminate obtained in Example 1 and Comparative Example 1 on the polarizer side was passed through an acrylic pressure-sensitive adhesive layer having a thickness of 20 μm. Non-alkali glass having a thickness of 0.55 mm was laminated 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 was measured by measuring the height from the glass plate at each of the four corners of the test piece, and the largest value was taken as the amount of warpage. The amount of warpage of Example 1 was 0.0 mm, which was “good”, and the amount of warpage of Comparative Example 1 was 0.75 mm, which was “poor (significant warpage)”.

[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 subjected to corona treatment, and polyvinyl alcohol (degree of polymerization 4200, degree of saponification 99.2 mol%) and acetacetyl-modified PVA (degree of polymerization 1200, degree of acetoacetyl modification 4.6) are treated on this corona-treated surface. %, Saponification degree 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 = 6.0) 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 iodine content of the obtained polarizer was 20.9% by weight, and the simple substance transmittance was 39.3% .
The obtained laminate was subjected to the evaluations (2) to (6) 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 = 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 iodine content of the obtained polarizer was 20.5% by weight, and the simple substance transmittance was 39.5%. 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 the conditions of the dyeing treatment were changed so that the single transmittance of the obtained polarizer was close to 43%. The iodine content of the obtained polarizer was 6.5% by weight, and the simple substance transmittance was 43.2%. 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 2 except that the conditions of the dyeing treatment were changed so that the single transmittance of the obtained polarizer was close to 43%. The iodine content of the obtained polarizer was 6.5% by weight, and the simple substance transmittance was 42.8%. 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 the weight of sodium hydrogen carbonate in the treatment liquid was 1.0. The iodine content of the obtained polarizer was 20.5% by weight, and the simple substance transmittance was 39.5%. 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 with the treatment liquid was not performed. The iodine content of the obtained polarizer was 21.5% by weight, and the simple substance transmittance was 39.3%. The obtained laminate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Comparative Example 2]
The polarizer was prepared in the same manner as in Example 1 except that the treatment with the treatment liquid was not performed and the conditions of the dyeing treatment were changed so that the single transmittance of the obtained polarizer was close to 43%. A laminate having was obtained. The iodine content of the obtained polarizer was 6.7% by weight, and the simple substance transmittance was 43.2%. The obtained laminate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Reference example 1]
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 single transmittance of the obtained polarizer was close to 43%. A laminate having a polarizer was obtained in the same manner as in Example 1 except for the above. The iodine content of the obtained polarizer was 3.3% by weight, and the simple substance transmittance was 43.0%. The obtained laminate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Reference example 2]
The polarizer was prepared in the same manner as in Example 1 except that the treatment with the treatment liquid was not performed and the conditions of the dyeing treatment were changed so that the single transmittance of the obtained polarizer was 45% or more. A laminate having was obtained. The iodine content of the obtained polarizer was 2.1% by weight, and the simple substance transmittance was 45.7%. 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, the polarizer of the embodiment of the present invention is excellent in all of the simple substance transmittance change, the hue change, the crack and the warp after the heating test, and has very excellent heat resistance. I understand. Furthermore, as is clear from reference to Reference Examples 1 and 2, heat resistance is a problem peculiar to a polarizer that is thin and has a very high iodine content.

The polarizer of the present invention can be widely applied to liquid crystal panels of liquid crystal televisions, liquid crystal displays, mobile phones, digital cameras, video cameras, portable game machines, car navigation systems, copiers, printers, fax machines, watches, microwave ovens, and the like. can.

Claims (3)

Consists of polyvinyl alcohol-based resin film,
Iodine content is 3.5% by weight or more,
The thickness is 0.5 μm to 1.2 μm,
The absolute value of the elemental transmittance change ΔTsa after being left in an environment of 105 ° C. for 30 hours is 5.0% or less.
Here, the amount of change in single transmittance ΔTsa is expressed by the following equation:
ΔTsa (%) = Ts ₃₀ −Ts ₀
Ts ₀ is the single transmittance before heating, and Ts ₃₀ is the single transmittance after being left in an environment of 105 ° C. for 30 hours. The polarizer according to claim 1, which comprises at least one selected from sodium ion, carbonate ion and citrate ion. A polarizing plate comprising the polarizer according to claim 1 or 2 and a protective film laminated on one side or both sides of the polarizer.