Polarizing plate

Abstract

To provide a polarizing plate which is excellent in a suppression effect of deterioration in a polarization degree even when exposed, for example, to a high-temperature environment of 115°C.SOLUTION: A polarizing plate includes: a polarizer obtained by absorbing and orienting a dichroic dye to a polyvinyl alcohol resin layer; and a transparent protective film. The polarizer has a peak half-value width of 4.80 nm-1 or more, which is measured by a wide-angle X-ray scattering method and derived from a polyvinyl alcohol crystal, and contains a potassium ion and a metal ion other than the potassium ion. The metal ion other than the potassium ion has a content rate of 0.05 mass% or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polarizing plate. [Background technology]

[0002] Liquid crystal display devices (LCDs) are widely used not only in LCD televisions but also in personal computers, mobile devices such as mobile phones, and in-vehicle applications such as car navigation systems. Typically, LCD displays have a liquid crystal panel member in which polarizing plates are attached to both sides of a liquid crystal cell with an adhesive, and display is achieved by controlling light from a backlight member using the liquid crystal panel member. Similarly to LCD displays, organic electroluminescence (EL) display devices have also recently become widely used in televisions, mobile devices such as mobile phones, and in-vehicle applications such as car navigation systems. In organic EL display devices, a circular polarizer (a laminate including a polarizing element and a λ / 4 plate) may be placed on the viewing-side surface of the image display panel to prevent external light from being reflected by the metal electrode (cathode) and appearing as a mirror.

[0003] As mentioned above, polarizing plates are increasingly being installed in vehicles as components of liquid crystal display devices and organic EL display devices. Polarizing plates used in in-vehicle image display devices are more likely to be exposed to high-temperature environments than those used in other mobile applications such as televisions and mobile phones, and are therefore required to have minimal change in properties at higher temperatures (high-temperature durability).

[0004] As a method for manufacturing such a polarizing element with high high-temperature durability, for example, Patent Documents 1 and 2 disclose a method for improving the durability of a polarizing element by adding components such as metal salts containing zinc, copper, aluminum, etc. to a treatment bath to contain these components in the polarizing element. Also, Patent Documents 3 and 4 disclose a method for manufacturing a polarizing element by adding components such as an organic titanium compound to a treatment bath. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2016 / 117659 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-047978 [Patent Document 3] Japanese Patent Application Laid-Open No. 2008-46257 [Patent Document 4] Japanese Patent Application Publication No. 6-172554 Summary of the Invention [Problem to be solved by the invention]

[0006] However, with conventional polarizing plates, the degree of polarization may decrease when the temperature of the high-temperature environment is raised to 115°C and the plate is exposed to this high-temperature environment for a certain period of time. The present invention aims to provide a polarizing plate that is excellent in suppressing the decrease in the degree of polarization even when the plate is exposed to a high-temperature environment, for example, at a temperature of 115°C. [Means for solving the problem]

[0007] The present invention provides the following polarizing plate. [1] A polarizing plate having a polarizing element formed by adsorbing and aligning a dichroic dye in a polyvinyl alcohol-based resin layer and a transparent protective film, The polarizing element has a half-width of 4.80 nm of a peak derived from polyvinyl alcohol crystals measured by wide-angle X-ray scattering. -1 That's all, the polarizing element contains potassium ions and metal ions other than potassium ions, The polarizing element is a polarizing plate, in which the content of the metal ions other than potassium ions is 0.05% by mass or more. [2] The polarizing plate according to [1], wherein the metal ions include at least one selected from the group consisting of cobalt, nickel, zinc, chromium, aluminum, copper, manganese, and iron ions. [3] The polarizing plate according to [1] or [2], wherein the polarizing element has a boron content of 3.9% by mass or more and 8.0% by mass or less. [4] The polarizing element further includes an adhesive layer that bonds the polarizing element and the transparent protective film together, The polarizing plate according to any one of [1] to [3], wherein the adhesive layer is a coating layer of a water-based adhesive. [5] The polarizing plate according to [4], wherein the aqueous adhesive has a methanol concentration of 10% by mass or more and 70% by mass or less. [6] The polarizing plate according to [4] or [5], wherein the aqueous adhesive contains a polyvinyl alcohol-based resin. [7] The polarizing plate according to any one of [4] to [6], wherein the adhesive layer has a thickness of 0.01 μm or more and 7 μm or less. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a polarizing plate that is excellent in high-temperature durability, for example, by suppressing the decrease in polarization degree when exposed to a high-temperature environment of 115°C. [Brief explanation of the drawings]

[0009] [Figure 1] For polarizing elements 1 to 3, the scattering profile of the measurement sample minus the background scattering profile is plotted against the wave number q. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments.

[0011] [Polarizing plate] The polarizing plate according to the embodiment of the present invention includes a polarizing element having a dichroic dye adsorbed and aligned in a layer containing a polyvinyl alcohol-based resin, and a transparent protective film. The polarizing element has a half-width of 4.80 nm of a peak derived from polyvinyl alcohol crystals measured by wide-angle X-ray scattering. -1 Furthermore, the polarizing element contains potassium ions (hereinafter sometimes referred to as "first metal ions") and metal ions other than potassium ions (hereinafter sometimes referred to as "second metal ions"), and the content of the second metal ions is 0.05 mass% or more. The polarizing plate of this embodiment, and the half-width of the peak derived from polyvinyl alcohol crystals measured by wide-angle X-ray scattering of the polarizing element, and the content of the second metal ion in the polarizing element are within the above-mentioned ranges, so that the decrease in polarization degree can be suppressed even when exposed to a high-temperature environment for a long period of time.

[0012] The polarizing plate of this embodiment can suppress a decrease in the degree of polarization even when exposed to a high-temperature environment of, for example, 115° C. for 500 hours or more.

[0013] <Polarizing element> As a polarizing element formed by adsorbing and orienting a dichroic dye in a layer containing a PVA-based resin (also referred to as a "PVA-based resin layer" in this specification), a well-known polarizing element can be used. Examples of such polarizing elements include a polarizing element formed by using a PVA-based resin film, dyeing the PVA-based resin film with a dichroic dye, and uniaxially stretching the film, and a polarizing element formed by using a laminated film obtained by applying a coating liquid containing a PVA-based resin onto a substrate film, and stretching the laminated film. Examples of such a film include a film formed by dyeing a PVA-based resin layer, which is a coating layer, with a dichroic dye and uniaxially stretching the laminated film.

[0014] The polarizing element is made of a PVA resin obtained by saponifying a polyvinyl acetate resin. Examples of polyvinyl acetate resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate with other copolymerizable monomers. Examples of other copolymerizable monomers include unsaturated carboxylic acids, olefins such as ethylene, vinyl ethers, and unsaturated sulfonic acids.

[0015] In the present invention, the PVA-based resin layer is preferably formed from a PVA-based resin having a boron adsorption rate of 5.70% by mass or more. That is, the boron adsorption rate of the PVA-based resin in the raw material stage before dyeing or stretching is preferably 5.70% by mass or more. By using such a PVA-based resin, the polarization degree is less likely to decrease even when exposed to a high-temperature environment, such as a temperature of 115°C. Furthermore, the boron adsorption rate of the PVA-based resin is preferably 10% by mass or less. By using such a PVA-based resin to produce a polarizing element, the boric acid concentration in the boric acid treatment bath can be reduced and the treatment time for the boric acid treatment can be shortened, making it easier to obtain the desired polarizing element and improving the productivity of the polarizing element. When the boron adsorption rate of the PVA-based resin is 10% by mass or less, an appropriate amount of boron is incorporated into the PVA-based resin layer, which reduces the shrinkage force of the polarizing element. The boron adsorption rate of the PVA-based resin can be measured by the method described in the Examples below.

[0016] The boron adsorption rate of PVA-based resin is a characteristic that reflects the spacing between molecular chains and the crystalline structure of the PVA-based resin. PVA-based resins with a boron adsorption rate of 5.70% by mass or higher are thought to have wider spacing between molecular chains and fewer crystals than PVA-based resins with a boron adsorption rate of less than 5.70% by mass. This is thought to facilitate the penetration of boron, first metal ions, and second metal ions into the PVA-based resin layer, making it less likely for the polarization degree to decrease in high-temperature environments.

[0017] The boron adsorption rate of a PVA-based resin can be adjusted, for example, by subjecting the PVA-based resin to a pretreatment such as hot water treatment, acidic solution treatment, ultrasonic irradiation treatment, or radiation irradiation treatment before manufacturing a polarizing element. These treatments can increase the spacing between molecular chains in the PVA-based resin or destroy the crystalline structure. Examples of hot water treatments include immersing the resin in pure water at 30°C to 100°C for 1 to 90 seconds, followed by drying. Examples of acidic solution treatments include immersing the resin in a boric acid aqueous solution with a concentration of 10% by mass to 20% by mass for 1 to 90 seconds, followed by drying. Examples of ultrasonic treatments include irradiating the resin with ultrasonic waves at a frequency of 20 to 29 kc at an output of 200 W to 500 W for 30 seconds to 10 minutes. Ultrasonic treatments can be performed in a solvent such as water.

[0018] The saponification degree of the PVA resin is preferably about 85 mol% or more, more preferably about 90 mol% or more, and even more preferably about 99 mol% to 100 mol%. The polymerization degree of the PVA resin is 1,000 to 10,000, preferably 1,500 to 5,000. The PVA resin may be modified, and may be, for example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral, or the like, modified with aldehydes.

[0019] The thickness of the polarizing element of this embodiment is preferably 5 to 50 μm, more preferably 8 to 28 μm, even more preferably 12 to 22 μm, and most preferably 12 to 15 μm. When the thickness of the polarizing element is 5 μm or more, it becomes easy to achieve a configuration that achieves desired optical properties.

[0020] The polarizing element of the present invention has a half-width of 4.80 nm of the peak derived from polyvinyl alcohol crystals as measured by wide-angle X-ray scattering. -1 or more, preferably 4.82 nm -1 End and more preferably 4.87 nm ―1That's all. In such a polarizing element, the crystal size of the polyvinyl alcohol becomes small due to the progress of the crosslinking reaction by boric acid, and as a result, the proportion of amorphous parts becomes large. Therefore, the content of boron and the second metal ion described later can be efficiently increased. The half-width of the peak derived from the polyvinyl alcohol crystals measured by wide-angle X-ray scattering method is, for example, 5.0 nm. -1 The half-width of the peak derived from polyvinyl alcohol crystals measured by wide-angle X-ray scattering can be measured by the method described in the examples below. Polyvinyl alcohol measured by wide-angle X-ray scattering The half-value width of the peak derived from the crystals can be appropriately adjusted by the temperature of the stretching bath, the stretching ratio, the boric acid concentration in the crosslinking bath, the degree of saponification of the PVA resin used as a raw material, and the like.

[0021] The content of the second metal ions in the polarizing element is preferably 0.05% by mass or more and 10.0% by mass or less, more preferably 0.05% by mass or more and 8.0% by mass or less, and even more preferably 0.1% by mass or more and 6.0% by mass or less. If the content of the second metal ions exceeds 10.0% by mass, the polarization degree may decrease in a high-temperature and high-humidity environment. If the content of the second metal ions is less than 0.05% by mass, the effect of improving durability in a high-temperature environment may not be sufficient. The content of the second metal ions in the polarizing element may be determined by, for example, high-frequency inductively coupled plasma (ICP) emission spectroscopy. It can be calculated as the mass fraction (mass %) of the metal element relative to the mass of the optical element. The metal element is thought to exist in the polarizing element either as a metal ion or in a state in which it forms a crosslinked structure with the constituent elements of the polyvinyl alcohol resin, but the content of the second metal ion referred to here is the value as a metal atom.

[0022] The second metal ion is not limited as long as it is a metal ion other than potassium ion, and is preferably an ion of a metal other than an alkali metal, and in particular, from the viewpoints of color adjustment and durability, it is preferable to include at least one metal ion of a transition metal such as cobalt, nickel, zinc, chromium, aluminum, copper, manganese, iron, etc. Among these metal ions, zinc ion is preferred from the viewpoints of color adjustment and heat resistance.

[0023] The boron content of the polarizing element is preferably 2.4% by mass or more. The boron content is preferably 3.9% by mass or more and 8.0% by mass or less, more preferably 4.2% by mass or more and 7.0% by mass or less, and even more preferably 4.4% by mass or more and 6.0% by mass or less. If the boron content of the polarizing element exceeds 8.0% by mass, the contraction force of the polarizing element increases, which may cause problems such as peeling between the polarizing element and other components, such as the front panel, to which it is bonded when incorporated into an image display device. If the boron content is less than 2.4% by mass, the desired optical characteristics may not be achieved. The boron content of the polarizing element can be determined, for example, by inductively coupled plasma (ICP) emission spectroscopy. By analytical methods, it can be calculated as the mass fraction (mass%) of boron relative to the mass of the polarizing element. Boron is thought to exist in the polarizing element in the form of boric acid or in the form of a crosslinked structure formed between the boron and the constituent elements of the polyvinyl alcohol resin, but the boron content here is the value as boron atoms (B).

[0024] The boron content of the polarizing element is preferably 2.4% by mass to 8.0% by mass, and more preferably 3.9% by mass to 8.0% by mass. By satisfying this range, the degree of polarization is prevented from decreasing even when exposed to a high-temperature environment.

[0025] The content of potassium ions in the polarizing element is preferably 0.28% by mass or more, more preferably 0.32% by mass or more, and even more preferably 0.34% by mass or more, from the viewpoint of suppressing a decrease in the degree of polarization in a high-temperature environment. From the viewpoint of suppressing a change in hue in a high-temperature environment, the content of potassium ions is preferably 0.60% by mass or less, and even more preferably 0.60% by mass or less, from the viewpoint of suppressing a change in hue in a high-temperature environment. The potassium ion content is preferably 0.55% by mass or less, and more preferably 0.50% by mass or less. The potassium ion content can be measured in the same manner as the second metal ion content, and the potassium ion content here is the value in terms of potassium atoms.

[0026] Although the detailed mechanism is unknown, it is presumed that the hydroxyl groups of the polyvinyl alcohol in the polarizing element are protected (stabilized) by boric acid crosslinking because the polarizing element contains more boron and less potassium ions than conventional polarizing elements, and that the appropriate amount of potassium ions stabilizes the iodine ions that serve as counter ions in the polarizing element.

[0027] The luminosity-corrected single transmittance of the polarizing plate is preferably 38.8% to 44.8%, more preferably 40.4% to 43.2%, and even more preferably 40.7% to 43.0%. If the luminosity-corrected single transmittance exceeds 44.8%, the optical properties may deteriorate significantly, such as red discoloration, in high-temperature environments, whereas if the luminosity-corrected single transmittance is less than 38.8%, the optical properties may deteriorate significantly in high-temperature environments.

[0028] The luminosity-corrected single transmittance can be determined by measuring the luminosity-corrected Y value using a 2-degree visual field (C light source) as specified in JIS Z8701-1982. The luminosity-corrected single transmittance can be easily measured using, for example, a spectrophotometer (model number: V7100) manufactured by JASCO Corporation.

[0029] The method for producing a polarizing element is not particularly limited, but typical examples include a method in which a pre-wound polyvinyl alcohol-based resin film is fed out and stretched, dyed, crosslinked, etc. (hereinafter referred to as "production method 1"), and a method in which a coating liquid containing a polyvinyl alcohol-based resin is applied to a substrate film to form a polyvinyl alcohol-based resin layer as a coating layer, and the resulting laminate is stretched (hereinafter referred to as "production method 2").

[0030] Manufacturing method 1 can be achieved by carrying out the steps of uniaxially stretching a polyvinyl alcohol-based resin film, dyeing the polyvinyl alcohol-based resin film with a dichroic dye such as iodine to adsorb the dichroic dye, treating the polyvinyl alcohol-based resin film with the adsorbed dichroic dye with a boric acid aqueous solution, and washing the film with water after the treatment with the boric acid aqueous solution.

[0031] The boron and potassium ion contents in the polarizing element can be controlled by the concentrations of boron-donating substances (e.g., boron compounds such as boric acid, borate salts, and borax) and potassium-donating substances (e.g., potassium halides such as potassium iodide) contained in the treatment baths in the swelling, dyeing, crosslinking, stretching, and water-washing processes, as well as the treatment temperature and treatment time in each of the treatment baths. In particular, the crosslinking and stretching processes facilitate adjustment of the boron content within the desired range by adjusting the treatment conditions, such as the concentration of the boron-donating substance. Furthermore, the water-washing process facilitates adjustment of the boron and potassium ion contents within the desired range by taking into account the treatment conditions, such as the amount of boron-donating substance and potassium-donating substance used in the dyeing, crosslinking, or stretching processes, from the viewpoint of dissolving or adsorbing components such as boron and potassium from or onto the polyvinyl alcohol-based resin film.

[0032] The swelling step is a treatment step in which the polyvinyl alcohol-based resin film is immersed in a swelling bath, which can remove dirt and blocking agents from the surface of the polyvinyl alcohol-based resin film, and also can suppress uneven dyeing by swelling the polyvinyl alcohol-based resin film. The swelling bath usually uses a medium whose main component is water, distilled water, pure water, or the like. The swelling bath may contain surfactants, alcohol, and the like as appropriate, according to a conventional method. In addition, polarizing In order to control the potassium content of the element, potassium iodide may be used in the swelling bath. In this case, the concentration of potassium iodide in the swelling bath is preferably 1.5% by mass or less, more preferably 1.0% by mass or less, and even more preferably 0.5% by mass or less.

[0033] The temperature of the swelling bath is preferably about 10 to 60°C, more preferably about 15 to 45°C, and even more preferably about 18 to 30°C. The immersion time in the swelling bath cannot be determined in general because the degree of swelling of the polyvinyl alcohol-based resin film is affected by the temperature of the swelling bath, but is preferably about 5 to 300 seconds, more preferably about 10 to 200 seconds, and even more preferably about 20 to 100 seconds. The swelling step may be carried out only once, or may be carried out multiple times as necessary.

[0034] The dyeing process is a treatment process in which a polyvinyl alcohol-based resin film is immersed in a dye bath (iodine solution), allowing iodine or a dichroic substance such as a dichroic dye to be adsorbed and aligned in the polyvinyl alcohol-based resin film. The iodine solution is typically preferably an aqueous iodine solution containing iodine and an iodide as a solubilizing agent. Examples of iodides include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. Among these, potassium iodide is preferred from the viewpoint of controlling the potassium content in the polarizing element.

[0035] The iodine concentration in the dye bath is preferably about 0.01 to 1 mass%, more preferably about 0.02 to 0.5 mass%, and the iodide concentration in the dye bath is preferably about 0.01 to 10 mass%, more preferably about 0.05 to 5 mass%, and even more preferably about 0.1 to 3 mass%.

[0036] The temperature of the dye bath is preferably about 10 to 50°C, more preferably about 15 to 45°C, and even more preferably about 18 to 30°C. The immersion time in the dye bath cannot be determined in general because the degree of dyeing of the polyvinyl alcohol-based resin film is affected by the temperature of the dye bath, but is preferably about 10 to 300 seconds, and more preferably about 20 to 240 seconds. The dyeing step may be carried out only once, or may be carried out multiple times as necessary.

[0037] The crosslinking step is a treatment step in which the polyvinyl alcohol-based resin film dyed in the dyeing step is immersed in a treatment bath (crosslinking bath) containing a boron compound. The boron compound crosslinks the polyvinyl alcohol-based resin film, allowing iodine molecules or dye molecules to be adsorbed to the crosslinked structure. Examples of boron compounds include boric acid, borate salts, and borax. The crosslinking bath is generally an aqueous solution, but may also be, for example, a mixed solution of water and an organic solvent miscible with water. In addition, the crosslinking bath preferably contains potassium iodide in order to control the potassium content in the polarizing element.

[0038] The concentration of the boron compound in the crosslinking bath is preferably about 1 to 15 mass%, more preferably about 1.5 to 10 mass%, and even more preferably about 2 to 5 mass%. When potassium iodide is used in the crosslinking bath, the concentration of potassium iodide in the crosslinking bath is preferably about 1 to 15 mass%, more preferably about 1.5 to 10 mass%, and even more preferably about 2 to 5 mass%.

[0039] The temperature of the crosslinking bath is preferably about 20 to 70° C., more preferably about 30 to 60° C. The immersion time in the crosslinking bath cannot be determined in general because the degree of crosslinking of the polyvinyl alcohol resin film is affected by the temperature of the crosslinking bath, but is preferably 5 to 300 seconds. The crosslinking step may be carried out only once, or may be carried out multiple times as necessary.

[0040] The stretching step is a treatment step in which a polyvinyl alcohol-based resin film is stretched at least in one direction to a predetermined magnification. Generally, the polyvinyl alcohol-based resin film is uniaxially stretched in the conveying direction (longitudinal direction). The stretching method is not particularly limited, and either a wet stretching method or a dry stretching method can be used. The stretching step may be carried out only once, or may be carried out multiple times as necessary. The stretching step may be carried out at any stage in the production of a polarizing element.

[0041] The treatment bath (stretching bath) used in the wet stretching method can typically be water or a solvent such as a mixture of water and a water-miscible organic solvent. The stretching bath preferably contains potassium iodide to control the potassium ion content in the polarizing element. When potassium iodide is used in the stretching bath, the concentration of potassium iodide in the stretching bath is preferably about 1 to 15% by mass, more preferably about 2 to 10% by mass, and even more preferably about 3 to 6% by mass. Furthermore, the treatment bath (stretching bath) can contain a boron compound to prevent film breakage during stretching. In this case, the concentration of the boron compound in the stretching bath is preferably about 1 to 15% by mass, more preferably about 1.5 to 10% by mass, and even more preferably about 2 to 5% by mass.

[0042] The temperature of the stretching bath is not limited, but is preferably 25 to 80°C, more preferably 40 to 80°C, even more preferably 50 to 75°C, particularly preferably 65 to 75°C, and particularly preferably 67°C or higher, for at least one stretching bath. Increasing the temperature of the stretching bath facilitates retention of the second metal ions used in the metal ion treatment step described below in the PVA-based resin layer. Increasing the temperature of the stretching bath allows the PVA to be stretched at a temperature near the softening point of the PVA in the PVA-based resin layer or at a temperature equal to or higher than the softening point of the PVA. As a result, the crystalline fraction of the PVA decreases, or the PVA crystals become smaller, increasing the amount of second metal ion uptake and accelerating the crosslinking reaction. This reduces the half-width of the peak derived from polyvinyl alcohol crystals measured by wide-angle X-ray scattering to 4.80 nm. -1 This makes it easier to achieve a temperature of 65°C or higher. The immersion time in the stretching bath cannot be determined unconditionally because the degree of stretching of the polyvinyl alcohol-based resin film is affected by the temperature of the stretching bath, but is preferably about 10 to 800 seconds, and more preferably about 30 to 500 seconds. The stretching step in the wet stretching method may be performed alone, or may be performed together with one or more of the following treatment steps: swelling, dyeing, crosslinking, and washing, or a combination of these. When performing the stretching step together with one or more treatment steps, the crosslinking step is the treatment step that is particularly suited to maintaining the treatment bath temperature at the optimum temperature of 65°C to 75°C for the stretching step. When stretching is performed in multiple treatment baths, it is preferable that the temperature of at least one treatment bath is 65°C to 75°C, and the immersion time in the treatment bath at 65°C to 75°C is preferably 40 to 200 seconds.

[0043] Examples of the dry stretching method include a roll-to-roll stretching method, a heated roll stretching method, a compression stretching method, etc. The dry stretching method may be carried out together with a drying step.

[0044] The total stretching ratio (cumulative stretching ratio) applied to the polyvinyl alcohol-based resin film can be set appropriately depending on the purpose, but is preferably about 2 to 7 times, more preferably about 3 to 6.8 times, and even more preferably about 3.5 to 6.5 times.

[0045] The cleaning step is a treatment step in which the polyvinyl alcohol-based resin film is immersed in a cleaning bath, and foreign matter remaining on the surface of the polyvinyl alcohol-based resin film can be removed. The cleaning bath usually uses a medium whose main component is water, such as water, distilled water, or pure water. In addition, from the viewpoint of controlling the potassium content in the polarizing element, it is preferable to use potassium iodide in the cleaning bath. In this case, the concentration of potassium iodide in the cleaning bath is preferably about 1 to 10 mass %, more preferably about 1.5 to 4 mass %, and even more preferably about 1.8 to 3.8 mass %.

[0046] The temperature of the cleaning bath is preferably about 5 to 50°C, more preferably about 10 to 40°C, and even more preferably about 15 to 30°C. The immersion time in the cleaning bath cannot be determined in general because the degree of cleaning of the polyvinyl alcohol-based resin film is affected by the temperature of the cleaning bath, but is preferably about 1 to 100 seconds, more preferably about 2 to 50 seconds, and even more preferably about 3 to 20 seconds. The cleaning step may be carried out only once, or may be carried out multiple times as necessary.

[0047] The method for producing a polarizing element can include a metal ion treatment step among the steps described above or as a separate step from the steps described above. The metal ion treatment step is carried out by immersing the polyvinyl alcohol-based resin film in an aqueous solution containing a metal salt of a second metal ion. The metal ion treatment step causes the second metal ion to be incorporated into the polyvinyl alcohol-based resin film.

[0048] The second metal ion is not limited as long as it is a metal ion other than potassium ion, and is preferably an ion of a metal other than an alkali metal. In particular, from the viewpoint of color adjustment and durability, it is preferable to include at least one metal ion of a transition metal such as cobalt, nickel, zinc, chromium, aluminum, copper, manganese, or iron. Among these metal ions, zinc ion is preferred from the viewpoint of color adjustment and heat resistance. Examples of zinc salts include zinc halides such as zinc chloride and zinc iodide, zinc sulfate, and zinc acetate.

[0049] The metal ion treatment step uses a metal salt solution. Hereinafter, immersion in a zinc-containing solution will be described as a typical example of the metal ion treatment step using a zinc salt aqueous solution.

[0050] The zinc ion concentration in the zinc salt aqueous solution is about 0.1 to 10% by mass, preferably 0.3 to 7% by mass. Furthermore, it is preferable to use an aqueous solution of the zinc salt containing potassium ions and iodine ions such as potassium iodide, as this facilitates impregnation with zinc ions. The potassium iodide concentration in the zinc salt solution is about 0.1 to 10% by mass, preferably 0.2 to 5% by mass.

[0051] When immersing in a zinc-containing solution, the temperature of the zinc salt solution is usually about 15 to 85°C, preferably 25 to 70°C. The immersion time is usually about 1 to 120 seconds, preferably 3 to 90 seconds. When immersing in a zinc-containing solution, the zinc content of the polyvinyl alcohol-based resin film is adjusted to be within the above range by adjusting conditions such as the concentration of the zinc salt solution, the immersion temperature of the polyvinyl alcohol-based resin film in the zinc salt solution, and the immersion time. There are no particular restrictions on when the immersion in a zinc-containing solution is performed. The immersion in a zinc-containing solution may be performed alone, or may be performed simultaneously with at least one of the dyeing step, crosslinking step, and stretching step by adding a zinc salt to the dyeing bath, crosslinking bath, or stretching bath.

[0052] After each of the above steps, a drying step is finally performed. In the drying step, the polyvinyl alcohol-based resin film cleaned in the cleaning step is dried to obtain a polarizing element. The drying can be performed by any appropriate method, such as natural drying, air drying, or heat drying.

[0053] The production method 2 includes a step of applying a coating liquid containing the polyvinyl alcohol resin onto a substrate film, a step of uniaxially stretching the obtained laminated film, and a step of stretching the polyvinyl alcohol resin from the uniaxially stretched laminated film. The polarizing element can be manufactured by dyeing a vinyl alcohol-based resin layer with a dichroic dye to adsorb the dichroic dye, treating the film with the adsorbed dichroic dye with a boric acid aqueous solution, and washing the film with water after the treatment with the boric acid aqueous solution. The substrate film used to form the polarizing element may also be used as a protective layer for the polarizing element. If necessary, the substrate film may be peeled off and removed from the polarizing element.

[0054] [Transparent protective film] The transparent protective film used in this embodiment (hereinafter also simply referred to as "protective film") is attached to at least one surface of the polarizing element via an adhesive layer. This transparent protective film may be attached to one or both surfaces of the polarizing element, but it is more preferable that it be attached to both surfaces.

[0055] The protective film may also have other optical functions, and may be formed into a laminated structure in which multiple layers are laminated. A thin protective film is preferable from the viewpoint of optical properties, but if it is too thin, the strength decreases and the processability becomes poor. The appropriate thickness is 5 to 100 μm, preferably 10 to 80 μm, and more preferably 15 to 70 μm.

[0056] The protective film may be a cellulose acylate film, a film made of a polycarbonate resin, a film made of a cycloolefin resin such as norbornene, a (meth)acrylic polymer film, a polyester resin film such as polyethylene terephthalate, etc. In a configuration in which protective films are provided on both sides of a polarizing element, when the polarizing element is attached using a water-based adhesive such as a PVA adhesive, it is preferable that the protective film on at least one side be either a cellulose acylate film or a (meth)acrylic polymer film in terms of moisture permeability, and of these, a cellulose acylate film is preferred.

[0057] At least one of the protective films may have a retardation function for the purpose of viewing angle compensation or the like. In this case, the film itself may have a retardation function, or may have a separate retardation layer, or may be a combination of both. Although the above description has been given of a configuration in which the film having retardation properties is directly bonded to the polarizing element via an adhesive, it may also be bonded via a pressure-sensitive adhesive or adhesive via another protective film that is bonded to the polarizing element.

[0058] [Adhesive layer] Any suitable adhesive can be used as the adhesive constituting the adhesive layer for bonding the protective film to the polarizing element. The adhesive can be a water-based adhesive, a solvent-based adhesive, an active energy ray-curable adhesive, or the like, but a water-based adhesive is preferred. From the viewpoint of improving heat resistance, it is also useful for the adhesive layer to contain at least one urea-based compound selected from urea, urea derivatives, thiourea, and thiourea derivatives.

[0059] The thickness of the adhesive when applied can be set to any appropriate value. For example, it is set so that an adhesive layer (coating layer) with the desired thickness is obtained after curing or heating (drying). The thickness of the adhesive layer is preferably 0.01 μm or more and 7 μm or less, more preferably 0.01 μm or more and 5 μm or less, even more preferably 0.01 μm or more and 2 μm or less, and most preferably 0.01 μm or more and 1 μm or less.

[0060] (water-based adhesive) Any appropriate aqueous adhesive can be used as the aqueous adhesive. Among them, an aqueous adhesive containing a PVA resin (PVA adhesive) is preferably used. The average polymerization degree of the PVA resin contained in the aqueous adhesive is preferably about 100 to 5500, more preferably 1000 to 4500, from the viewpoint of adhesiveness. The average saponification degree is preferably 85 moles / mol, from the viewpoint of adhesiveness. It is about 1 mol % to 100 mol %, and more preferably 90 mol % to 100 mol %.

[0061] The PVA resin contained in the aqueous adhesive preferably contains an acetoacetyl group, because it has excellent adhesion between the PVA resin layer and the protective film and excellent durability. The acetoacetyl group-containing PVA resin can be obtained, for example, by reacting a PVA resin with diketene using any method. The degree of acetoacetyl group modification of the acetoacetyl group-containing PVA resin is typically 0.1 mol% or more, and preferably about 0.1 mol% to 20 mol%. The resin concentration of the above-mentioned water-based adhesive is preferably 0.1% by mass to 15% by mass, and more preferably 0.5% by mass to 10% by mass.

[0062] The water-based adhesive may contain a crosslinking agent. Known crosslinking agents can be used, such as water-soluble epoxy compounds, dialdehydes, and isocyanates.

[0063] When the PVA-based resin is an acetoacetyl group-containing PVA-based resin, the crosslinking agent is preferably any one of glyoxal, glyoxylate, and methylolmelamine, more preferably any one of glyoxal and glyoxylate, and particularly preferably glyoxal.

[0064] The water-based adhesive may also contain an organic solvent. The organic solvent is preferably an alcohol because of its miscibility with water, and among alcohols, methanol or ethanol is more preferred. Some urea compounds have low solubility in water, but some have sufficient solubility in alcohol. In this case, one preferred embodiment is to dissolve the urea compound in alcohol to prepare an alcohol solution of the urea compound, and then add the alcohol solution of the urea compound to an aqueous PVA solution to prepare the adhesive.

[0065] The methanol concentration of the aqueous adhesive is preferably 10% by mass or more and 70% by mass or less, more preferably 15% by mass or more and 60% by mass or less, and even more preferably 20% by mass or more and 60% by mass or less. Furthermore, by keeping the methanol content at 70% by mass or less, deterioration of color can be suppressed.

[0066] (Active energy ray curing adhesive) The active energy ray-curable adhesive is an adhesive that cures upon irradiation with active energy rays such as ultraviolet rays, and examples thereof include adhesives containing a polymerizable compound and a photopolymerization initiator, adhesives containing a photoreactive resin, and adhesives containing a binder resin and a photoreactive crosslinking agent. Examples of the polymerizable compound include photopolymerizable monomers such as photocurable epoxy monomers, photocurable acrylic monomers, and photocurable urethane monomers, as well as oligomers derived from these monomers. Examples of the photopolymerization initiator include compounds containing substances that generate active species such as neutral radicals, anion radicals, and cation radicals upon irradiation with active energy rays such as ultraviolet rays.

[0067] (Urea-based compounds) When the adhesive layer contains a urea-based compound, the urea-based compound is at least one selected from urea, urea derivatives, thiourea, and thiourea derivatives. A preferred method for incorporating a urea-based compound into the adhesive layer is to incorporate the urea-based compound into the above-mentioned adhesive. It is acceptable for a portion of the urea-based compound to migrate from the adhesive layer to the polarizing element or the like during the process of forming the adhesive layer through a drying process or the like. In other words, the polarizing element may contain a urea-based compound. Urea-based compounds include water-soluble and poorly water-soluble compounds, and both types of urea-based compounds can be used in the adhesive of this embodiment. The poorly water-soluble urea-based compound can be incorporated into the adhesive by drying the adhesive. When used in a system adhesive, it is preferable to devise a dispersion method so as not to cause an increase in haze after forming the adhesive layer.

[0068] When the adhesive is an aqueous adhesive containing a PVA resin, the amount of the urea compound added is preferably 0.1 to 400 parts by mass, more preferably 1 to 200 parts by mass, and even more preferably 3 to 100 parts by mass, per 100 parts by mass of the PVA resin.

[0069] (urea derivative) A urea derivative is a compound in which at least one of the four hydrogen atoms of a urea molecule is substituted with a substituent. In this case, the substituent is not particularly limited, but is preferably a substituent consisting of carbon, hydrogen, and oxygen atoms.

[0070] Specific examples of the urea derivatives include mono-substituted ureas such as methylurea, ethylurea, propylurea, butylurea, isobutylurea, N-octadecylurea, 2-hydroxyethylurea, hydroxyurea, acetylurea, allylurea, 2-propynylurea, cyclohexylurea, phenylurea, 3-hydroxyphenylurea, (4-methoxyphenyl)urea, benzylurea, benzoylurea, o-tolylurea, and p-tolylurea. Examples of disubstituted ureas include 1,1-dimethylurea, 1,3-dimethylurea, 1,1-diethylurea, 1,3-diethylurea, 1,3-bis(hydroxymethyl)urea, 1,3-tert-butylurea, 1,3-dicyclohexylurea, 1,3-diphenylurea, 1,3-bis(4-methoxyphenyl)urea, and 1-acetyl-3-methylurea. Examples of 4-substituted ureas include tetramethylurea, 1,1,3,3-tetraethylurea, 1,1,3,3-tetrabutylurea, and 1,3-dimethoxy-1,3-dimethylurea.

[0071] (thiourea derivatives) A thiourea derivative is a compound in which at least one of the four hydrogen atoms of a thiourea molecule is substituted with a substituent. In this case, the substituent is not particularly limited, but is preferably a substituent consisting of carbon, hydrogen, and oxygen atoms.

[0072] Specific examples of the thiourea derivatives include mono-substituted thioureas such as N-methylthiourea, ethylthiourea, propylthiourea, isopropylthiourea, 1-butylthiourea, cyclohexylthiourea, N-acetylthiourea, N-allylthiourea, (2-methoxyethyl)thiourea, N-phenylthiourea, (4-methoxyphenyl)thiourea, N-(2-methoxyphenyl)thiourea, N-(1-naphthyl)thiourea, (2-pyridyl)thiourea, o-tolylthiourea, and p-tolylthiourea. Examples of disubstituted thioureas include 1,1-dimethylthiourea, 1,3-dimethylthiourea, 1,1-diethylthiourea, 1,3-diethylthiourea, 1,3-dibutylthiourea, 1,3-diisopropylthiourea, 1,3-dicyclohexylthiourea, N,N-diphenylthiourea, N,N'-diphenylthiourea, 1,3-di(o-tolyl)thiourea, 1,3-di(p-tolyl)thiourea, 1-benzyl-3-phenylthiourea, 1-methyl-3-phenylthiourea, and N-allyl-N'-(2-hydroxyethyl)thiourea. An example of the 3-substituted thiourea is trimethylthiourea, and an example of the 4-substituted thiourea is tetramethylthiourea or 1,1,3,3-tetraethylthiourea.

[0073] Among urea compounds, urea derivatives or thiourea derivatives are preferred, and urea derivatives are more preferred. Among urea derivatives, mono- or di-substituted ureas are preferred, and mono-substituted ureas are more preferred. Di-substituted ureas include 1,1-substituted ureas and 1,3-substituted ureas, with 1,3-substituted ureas being more preferred.

[0074] <Urea-based compound-containing layer> The urea-based compound is not limited to being contained in the adhesive layer as described above, and may be contained in a layer other than the adhesive layer from the viewpoint of improving the heat resistance of the polarizing plate. As for other layers, as described in the explanation of the transparent protective film, in recent years, in order to meet the demand for thinner polarizing plates, polarizing plates having a protective film on only one side of the polarizing element have been developed. In such a configuration, a cured layer may be laminated on the side of the polarizing element that does not have the protective film, for the purpose of increasing physical strength, etc.

[0075] In this embodiment, such a cured layer may contain a urea-based compound. Typically, such a cured layer is formed from a curable composition containing an organic solvent. However, paragraphs

[0020] to

[0042] of JP 2017-075986 A describe a method for forming such a cured layer from an aqueous solution of an active energy ray-curable polymer composition. Since many urea-based compounds are water-soluble, such a composition may contain a water-soluble urea-based compound.

[0076] <Adhesive layer> In order to attach the polarizing plate described above to an image display device, an adhesive layer is usually laminated on the polarizing plate. This adhesive layer is provided for attaching the polarizing plate to the image display device.

[0077] The pressure-sensitive adhesive layer may consist of one layer or two or more layers, but preferably consists of one layer. The pressure-sensitive adhesive layer can be composed of a pressure-sensitive adhesive composition containing a (meth)acrylic resin, a rubber resin, a urethane resin, an ester resin, a silicone resin, or a polyvinyl ether resin as a main component. Among these, a pressure-sensitive adhesive composition containing a (meth)acrylic resin as a base polymer, which is excellent in transparency, weather resistance, heat resistance, etc., is preferred. The pressure-sensitive adhesive composition may be an active energy ray-curable or thermosetting type.

[0078] The (meth)acrylic resin (base polymer) used in the pressure-sensitive adhesive composition is preferably a polymer or copolymer containing one or more (meth)acrylic acid esters as monomers, such as butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. A polar monomer is preferably copolymerized into the base polymer. Examples of polar monomers include monomers having a carboxyl group, a hydroxyl group, an amide group, an amino group, or an epoxy group, such as a (meth)acrylic acid compound, a 2-hydroxypropyl (meth)acrylate compound, a hydroxyethyl (meth)acrylate compound, a (meth)acrylamide compound, an N,N-dimethylaminoethyl (meth)acrylate compound, or a glycidyl (meth)acrylate compound.

[0079] The pressure-sensitive adhesive composition may contain only the base polymer, but usually further contains a crosslinking agent. Examples of crosslinking agents include divalent or higher metal ions that form metal carboxylates with carboxyl groups, polyamine compounds that form amide bonds with carboxyl groups, polyepoxy compounds or polyols that form ester bonds with carboxyl groups, and polyisocyanate compounds that form amide bonds with carboxyl groups. Among these, polyisocyanate compounds are preferred.

[0080] The active energy ray-curable pressure-sensitive adhesive composition has the property of being cured by irradiation with active energy rays such as ultraviolet rays or electron beams, and has adhesive properties even before irradiation with active energy rays, allowing it to adhere to an adherend such as a film, and has the property of being cured by irradiation with active energy rays, allowing the adhesive strength to be adjusted. The active energy ray-curable pressure-sensitive adhesive composition is preferably ultraviolet-curable. The active energy ray-curable pressure-sensitive adhesive composition further contains an active energy ray-polymerizable compound in addition to a base polymer and a crosslinking agent. If necessary, it may contain a photopolymerization initiator, a photosensitizer, etc.

[0081] The pressure-sensitive adhesive composition may contain additives such as fine particles for imparting light scattering properties, beads (resin beads, glass beads, etc.), glass fibers, resins other than the base polymer, tackifiers, fillers (metal powders and other inorganic powders, etc.), antioxidants, UV absorbers, dyes, pigments, colorants, defoamers, corrosion inhibitors, and photopolymerization initiators.

[0082] The pressure-sensitive adhesive layer can be formed by applying an organic solvent diluted solution of the pressure-sensitive adhesive composition to the surface of a substrate film, an image display cell, or a polarizing plate, and drying the applied solution. The substrate film is generally a thermoplastic resin film, and a typical example thereof is a release-treated separate film. The separate film can be, for example, a film made of a resin such as polyethylene terephthalate, polybutylene terephthalate, polycarbonate, or polyacrylate, which has been subjected to a release treatment such as silicone treatment on the surface on which the pressure-sensitive adhesive layer is to be formed.

[0083] For example, a pressure-sensitive adhesive composition may be directly applied to the release-treated surface of a separate film to form a pressure-sensitive adhesive layer, and this pressure-sensitive adhesive layer with a separate film may be laminated on the surface of a polarizer.A pressure-sensitive adhesive composition may be directly applied to the surface of a polarizing plate to form a pressure-sensitive adhesive layer, and a separate film may be laminated on the outer surface of the pressure-sensitive adhesive layer. When providing a pressure-sensitive adhesive layer on the surface of a polarizing plate, it is preferable to subject the bonding surface of the polarizing plate and / or the bonding surface of the pressure-sensitive adhesive layer to a surface activation treatment such as plasma treatment or corona treatment, and it is more preferable to subject the layer to corona treatment. Alternatively, a pressure-sensitive adhesive sheet may be prepared by applying a pressure-sensitive adhesive composition to a second separate film to form a pressure-sensitive adhesive layer, laminating a separate film on the formed pressure-sensitive adhesive layer, and then laminating the pressure-sensitive adhesive layer with the separate film on a polarizing plate after peeling the second separate film from the pressure-sensitive adhesive sheet. The second separate film used has weaker adhesion to the pressure-sensitive adhesive layer than the separate film and is therefore easier to peel.

[0084] The thickness of the pressure-sensitive adhesive layer is not particularly limited, but is preferably, for example, from 1 μm to 100 μm, more preferably from 3 μm to 50 μm, and may be 20 μm or more. [Example]

[0085] The present invention will be specifically described below based on examples. The materials, reagents, amounts and proportions of substances, procedures, etc. shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the present invention is not limited to or by the following examples.

[0086] [Measurement and evaluation methods] (1) Measurement of the thickness of the polarizing element: Measurements were made using a digital micrometer "MH-15M" manufactured by Nikon Corporation.

[0087] (2) Measurement of the luminosity-corrected polarization degree, luminosity-corrected single transmittance, and hue of the polarizing plate: The luminosity-corrected single transmittance, luminosity-corrected polarization degree, and hue of the polarizing plate were measured using a spectrophotometer with an integrating sphere ("V7100" manufactured by JASCO Corporation, 2-degree field of view; C light source).

[0088] (3) Measurement of boron content in polarizing elements The boron content of the polarizing element was measured as follows: First, 0.2 g of the polarizing element was dissolved in 200 g of a 1.9% by mass aqueous mannitol solution. Next, the resulting solution was titrated with a 1 mol / L aqueous sodium hydroxide solution, and the boron content of the polarizing element was calculated by comparing the amount of sodium hydroxide required for neutralization with a calibration curve.

[0089] (4) Measurement of zinc ion content in polarizing elements The zinc ion content in the polarizing element was measured by the following procedure. First, nitric acid was added to a precisely weighed polarizing element, and the polarizing element was heated in a microwave sample pretreatment device (ETHOS) manufactured by Milestone General. The solution obtained by acid decomposition in step D) was used as the measurement solution. The zinc ion content was measured by measuring the zinc concentration of the measurement solution using an ICP optical emission spectrometer (5110 ICP-OES) manufactured by Agilent Technologies. The amount was quantified and calculated as the mass of zinc relative to the mass of the polarizing element.

[0090] (5) Measurement of boron adsorption rate of PVA resin film The boron adsorption rate of PVA-based resin film was measured using the following procedure. First, a PVA-based resin film cut into a 100 mm square was immersed in pure water at 30°C for 60 seconds, and then immersed in an aqueous solution containing 5 parts of boric acid at 60°C for 120 seconds. The PVA-based resin film was removed from the boric acid aqueous solution and dried in an oven at 80°C for 11 minutes. Then, it was placed in an environment of 23°C and 55%RH. The film was then conditioned at RT for 24 hours to obtain a boron-containing PVA film. 0.2 g of the boron-containing PVA resin film thus obtained was dissolved in 200 g of a 1.9% by mass aqueous mannitol solution. The resulting aqueous solution was then titrated with a 1 mol / L aqueous sodium hydroxide solution, and the boron content of the PVA resin film was calculated by comparing the amount of sodium hydroxide required for neutralization with a calibration curve. The boron content of the PVA resin film thus obtained was used as the boron adsorption rate of the PVA resin film.

[0091] (6) Measurement of half-width of peaks derived from polyvinyl alcohol crystals in polarizing elements <Measurement sample> A sample for measurement was prepared by laminating 10 polarizing elements so that the absorption axes of the polarizing elements were aligned.

[0092] <Measurement using wide-angle X-ray scattering> This refers to a value calculated using wide-angle X-ray scattering with the following measurement equipment and measurement conditions:

[0093] (Measuring equipment) The nanoscale X-ray structure evaluation device NANO-Viewer manufactured by Rigaku Corporation was used.

[0094] (Measurement conditions) ·X-ray source: Cu-kα ray Camera length: 71mm Measurement: Transmission measurement X-ray exposure time: 10 minutes

[0095] (Calculation method) First, a background measurement was performed without placing a measurement sample, and a circularly averaged scattering profile was taken from the obtained two-dimensional scattering pattern. Next, the measurement sample was measured, and a scattering profile was obtained in the same way. Next, the scattering profile of the measurement sample was subtracted from the background scattering profile, and the result was measured at a wave number q of 15 nm. -1 The peak derived from polyvinyl alcohol crystals near the position was identified, and the half-width of the peak was calculated. Figure 1 shows a graph plotting the scattering profile of the measurement sample minus the background scattering profile for polarizing elements 1 to 3 described below against the wave number q. -1 The peak at the position is a peak derived from polyvinyl alcohol crystals. The half-width is the distance between two points where the intensity of such a peak is half of its maximum value.

[0096] (7) High temperature durability test (115℃) <Preparation of evaluation samples> An acrylic adhesive (manufactured by Lintec Corporation) was applied to one side of a polarizing plate prepared using the procedure described below with reference to the examples in JP 2018-025765 A to form a 25 μm thick adhesive layer. The polarizing plate with the adhesive layer formed on one side was cut into a size of 40 mm × 40 mm, and alkali-free glass (trade name "EAGLE XG", manufactured by Corning) was attached to the surface of the adhesive layer to prepare an evaluation sample (optical laminate).

[0097] <High temperature durability test> The evaluation sample obtained above was subjected to a temperature of 50°C and a pressure of 5 kgf / cm 2 After autoclaving for 1 hour at a pressure of 490.3 kPa, the polarizing plate was left for 24 hours in an environment at a temperature of 23°C and a relative humidity of 55%, after which the luminous efficiency-corrected single transmittance, luminous efficiency-corrected polarization degree, and hue of the polarizing plate were measured and used as the initial values. Next, a high-temperature durability test was performed in which the evaluation sample was stored in a high-temperature environment at a temperature of 115°C for 500 hours, and the luminous efficiency-corrected single transmittance, luminous efficiency-corrected polarization degree, and hue of the polarizing plate after the high-temperature durability test were measured.

[0098] The changes in the polarizing plate's luminous-corrected transmittance, luminous-corrected polarization degree, and hue were calculated from the initial values ​​and the measured values ​​after the high-temperature durability test. The changes in the luminous-corrected transmittance, luminous-corrected polarization degree, and hue were calculated by subtracting the initial values ​​from the measured values ​​after the high-temperature durability test. The changes in the hue, Δab, were calculated using the following formula: Δab={(a1-a2) 2 +(b1-b2) 2} 1 / 2 Here, a1 and b1 are the initial values ​​of the hue, and a2 and b2 are the measured values ​​of the hue after the high-temperature durability test.

[0099] [Examples 1 and 2 and Comparative Example 1] (Fabrication of Polarizing Element 1) A 30 μm-thick polyvinyl alcohol resin film with a boron adsorption rate of 5.71% by mass was immersed in pure water at 21.5°C for 79 seconds (swelling treatment), then immersed in an aqueous solution containing 1.0 mM iodine and a potassium iodide / boric acid / water ratio of 2 / 2 / 100 at 23°C for 151 seconds (dyeing step). This was followed by immersion in an aqueous solution containing 2.5 / 4 / 100 potassium iodide / boric acid / water at 68.5°C for 76 seconds (first crosslinking step). This was followed by immersion in an aqueous solution containing 3 / 5.5 / 0.6 / 100 potassium iodide / boric acid / zinc chloride / water at 45°C for 11 seconds (second crosslinking step, metal ion treatment step). The film was then immersed in a washing bath for washing (washing step) and dried at 38°C (drying step) to obtain a 12µm thick polarizing element in which iodine was adsorbed and aligned in the polyvinyl alcohol. Stretching was mainly performed in the dyeing step and the first crosslinking step, with a total stretching ratio of 5.85 times. The resulting polarizing element had a zinc ion content of 0.17% by mass, a boron content of 4.62% by mass, and a half-width of the peak derived from polyvinyl alcohol crystals of 4.90nm. -1 It was.

[0100] (Fabrication of Polarizing Element 2) A 30 μm thick polyvinyl alcohol resin film with a boron adsorption rate of 5.71% by mass was immersed in pure water at 21.5°C for 79 seconds (swelling treatment), then immersed in an aqueous solution containing 1.0 mM iodine and a potassium iodide / boric acid / water mass ratio of 2 / 2 / 100 at 23°C for 151 seconds (dyeing step). This was followed by immersion in an aqueous solution containing 2.5 / 4 / 100 potassium iodide / boric acid / water mass ratios at 66.5°C for 76 seconds (first crosslinking step). This was followed by immersion in an aqueous solution containing 3 / 5.5 / 0.6 / 100 potassium iodide / boric acid / zinc chloride / water mass ratios at 45°C for 11 seconds (second crosslinking step, metal ion treatment step). Thereafter, the film was immersed in a washing bath for washing (washing step) and dried at 38°C (drying step) to obtain a polarizing element having a thickness of 12 μm, in which iodine was adsorbed and aligned in the polyvinyl alcohol. The total stretching ratio was 5.85 times. The obtained polarizing element had a zinc ion content of 0.17% by mass, a boron content of 4.62% by mass, and a half-value width of the peak derived from polyvinyl alcohol crystals of 4.85 nm.-1 It was.

[0101] (Fabrication of Polarizing Element 3) A 30 μm-thick polyvinyl alcohol resin film with a boron adsorption rate of 5.71% by mass was immersed in pure water at 21.5°C for 79 seconds (swelling treatment), then immersed in an aqueous solution containing 1.0 mM iodine and a potassium iodide / boric acid / water ratio of 2 / 2 / 100 at 23°C for 151 seconds (dyeing step). This was followed by immersion in an aqueous solution containing 2.5 / 4 / 100 potassium iodide / boric acid / water at 60.6°C for 76 seconds (first crosslinking step). This was followed by immersion in an aqueous solution containing 3 / 5.5 / 0.6 / 100 potassium iodide / boric acid / zinc chloride / water at 45°C for 11 seconds (second crosslinking step, metal ion treatment step). The film was then immersed in a washing bath for washing (washing step) and dried at 38°C (drying step) to obtain a 12µm thick polarizing element in which iodine was adsorbed and aligned in the polyvinyl alcohol. Stretching was mainly performed in the dyeing step and the first crosslinking step, with a total stretching ratio of 5.85 times. The resulting polarizing element had a zinc ion content of 0.17% by mass, a boron content of 4.62% by mass, and a half-width of the peak derived from polyvinyl alcohol crystals of 4.75nm. -1 It was.

[0102] (Preparation of PVA solution for adhesive) 50 g of modified PVA resin containing acetoacetyl groups (Mitsubishi Chemical Corporation: Gohsenex Z-410) was dissolved in 950 g of pure water, heated at 90°C for 2 hours, and then cooled to room temperature to obtain a PVA solution for adhesive.

[0103] (Preparation of polarizing plate adhesive 1) The prepared PVA solution for adhesive, pure water, and methanol were mixed to give a PVA concentration of 3.0%, a methanol concentration of 35%, and a urea concentration of 0.5%, to obtain an adhesive 1 for polarizing plates.

[0104] (Saponification of Cellulose Acylate Film) A commercially available cellulose acylate film TJ40UL (manufactured by Fujifilm Corporation: film thickness 40 μm) was immersed in a 1.5 mol / L NaOH aqueous solution (saponification solution) maintained at 55°C for 2 minutes, and then washed with water. The film was then immersed in a 0.05 mol / L sulfuric acid aqueous solution at 25°C for 30 seconds, and then passed through a water washing bath under running water for 30 seconds to neutralize the film. The water was then drained three times using an air knife. After the water was removed, the film was allowed to remain in a drying zone at 70°C for 15 seconds and dried to produce a saponified film.

[0105] (Preparation of Polarizing Plate 1) Saponified cellulose acylate films were bonded to both sides of the polarizing element 1 using polarizing plate adhesive 1. The thickness of the adhesive was adjusted so that the adhesive layer would have a thickness of 100 nm on both sides after drying. The bonding was performed using a roll laminator. After bonding, the film was dried at 80°C for 3 minutes to bond the polarizing element 1 and the cellulose acylate film together. In this way, a polarizing plate 1 with cellulose acylate films on both sides was obtained.

[0106] Polarizing plates 2 and 3 were prepared in the same manner as polarizing plate 1, except that polarizing element 1 was replaced with polarizing elements 2 and 3.

[0107] (Preparation of Optical Laminates 1 to 3) With reference to the examples in JP 2018-025765 A, an acrylic adhesive (manufacturer: Lintec Corporation) was applied to one side of the polarizing plates 1 to 3 prepared above, thereby producing optical laminates 1 to 3 having an adhesive layer with a thickness of 25 μm on one side of the polarizing plate.

[0108] Example 1 In Example 1, a high-temperature durability test was conducted on the optical laminate 1. The change in luminous efficacy-corrected single transmittance ΔTy of the optical laminate 1 was 0.6%, the change in luminous efficacy-corrected polarization degree ΔPy was −0.03%, and the change in hue Δab was 2.0 NBS. The results are shown in Table 1.

[0109] Example 2 In Example 2, a high-temperature durability test was conducted on the optical laminate 2. The change in luminous efficacy-corrected single transmittance ΔTy of the optical laminate 2 was 1.2%, the change in luminous efficacy-corrected polarization degree ΔPy was −0.03%, and the change in hue Δab was 2.3 NBS. The results are shown in Table 1.

[0110] (Comparative Example 1) The change in luminous efficacy-corrected single transmittance ΔTy of the optical laminate 3 was 2.6%, the change in luminous efficacy-corrected polarization degree ΔPy was −0.13%, and the change in hue Δab was 5.3 NBS. Table 1 shows the results.

[0111] [Table 1]

[0112] It was found that the optical laminates 1 and 2 were superior to the optical laminate 3 in the effect of suppressing the decrease in the degree of polarization even when exposed to a high-temperature environment at a temperature of 115°C.

Claims

1. A polarizing plate having a polarizing element formed by adsorbing and aligning a dichroic dye in a polyvinyl alcohol-based resin layer, and a transparent protective film, The polarizing element has a half-width of 4.80 nm of a peak derived from polyvinyl alcohol crystals measured by wide-angle X-ray scattering. －１ That's all, the polarizing element contains potassium ions and metal ions other than potassium ions, The polarizing element has a content of the metal ions other than potassium ions of 0.05% by mass or more.

2. 2. The polarizing plate according to claim 1, wherein the metal ions include at least one selected from the group consisting of ions of cobalt, nickel, zinc, chromium, aluminum, copper, manganese, and iron.

3. 3. The polarizing plate according to claim 1, wherein the polarizing element has a boron content of 2.4% by mass or more and 8.0% by mass or less.

4. The polarizing element further has an adhesive layer that bonds the polarizing element and the transparent protective film together, 4. The polarizing plate according to claim 1, wherein the adhesive layer is a coating layer of a water-based adhesive.

5. The polarizing plate according to claim 4 , wherein the aqueous adhesive has a methanol concentration of 10% by mass or more and 70% by mass or less.

6. The polarizing plate according to claim 4 , wherein the water-based adhesive contains a polyvinyl alcohol-based resin.

7. 7. The polarizing plate according to claim 4, wherein the adhesive layer has a thickness of 0.01 μm or more and 7 μm or less.

Images