Polarizer, polarizing plate, polarizing plate with optical layer, image display panel, and image display device

Abstract

To provide a polarizer capable of suppressing a hue change of the polarizer under a high temperature environment.SOLUTION: The polarizer 1 is formed of a polyvinyl alcohol-based resin film, contains lithium atoms, and has a lithium atom content of 0.005 mass% or more and 0.100 mass% or less as determined by elemental analysis. The lithium atom is ion-exchanged with a hydrogen atom of a hydroxy group of the polyvinyl alcohol, so that a dehydration reaction is suppressed, and thus polyene formation is suppressed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a polarizer, a polarizing plate, a polarizing plate with an optical layer, an image display panel, and an image display device. [Background technology]

[0002] Conventionally, polarizers formed from a film in which iodine is adsorbed onto a polyvinyl alcohol-based resin have been known (for example, Patent Document 1). Image display devices including polarizers are being used in a wide range of applications, including in-vehicle image display devices such as car navigation devices and rearview monitors. As the range of applications expands, image display devices and polarizers that form part of image display devices are being required to have higher durability in harsher environments (for example, high-temperature environments) than has been required in the past. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-71241 Summary of the Invention [Problem to be solved by the invention]

[0004] When a polarizer formed from a polyvinyl alcohol-based resin film is exposed to a high-temperature environment, polyenization of the polyvinyl alcohol proceeds, which can cause a problem of hue change in the polarizer due to polyenization. In particular, in a high-temperature environment (e.g., 105°C) such as the above-mentioned in-vehicle application, the hue change due to polyenization tends to be more pronounced. However, conventional polarizers have not always been able to sufficiently suppress hue change at such high temperatures.

[0005] The present invention has been made in view of the above-mentioned problems, and has an object to provide a polarizer capable of suppressing a hue change of the polarizer in a high-temperature environment, and a polarizing plate, a polarizing plate with an optical layer, an image display panel, and an image display device that include the polarizer. [Means for solving the problem]

[0006] The polyenation of polyvinyl alcohol (PVA) is thought to be caused by the reaction of iodine with water, which generates a strong acid, causing dehydration of the PVA. It was thought that the progression of polyenation could be suppressed by modifying the chemical structure of PVA so that dehydration is less likely to occur. Based on this idea, the inventors continued their research and completed the present invention. When polyenation occurs, the PVA-iodine complex cannot be formed, reducing light absorption by the complex, resulting in a decrease in polarization and a significant deviation of the orthogonal hue from neutral gray.

[0007] The present invention provides a polarizer formed from a polyvinyl alcohol-based resin film, which contains lithium atoms and has a lithium atom content of 0.005% by mass or more and 0.100% by mass or less as determined by elemental analysis.

[0008] In this polarizer, it is thought that the dehydration reaction is suppressed by the lithium atoms bonding to the hydroxyl groups of the PVA.

[0009] The polarizer may further contain potassium atoms, and the lithium atom content [X] determined by elemental analysis and the potassium atom content [Y] determined by elemental analysis may satisfy the following formula (1): X / Y<1 …(1)

[0010] The polarizer may have a potassium atom content of 0.01% by mass or more and 0.30% by mass or less, and in this case, a lithium atom content of 0.050% by mass or more and 0.090% by mass or less.

[0011] The polarizer may further contain boron atoms, and the content of boron atoms determined by elemental analysis may be 4.0% by mass or more and 6.0% by mass or less.

[0012] The present invention provides a polarizing plate comprising the above polarizer and a protective film laminated on at least one surface of the polarizer via an adhesive layer. This polarizing plate is provided with a protective film having a moisture permeability of 200 g / (m 2 The polarizing plate may further be a polarizing plate with an optical layer, which is formed by laminating a polarizing plate and an optical layer.

[0013] The present invention provides an image display panel comprising the above polarizing plate with an optical layer and an image display cell laminated together via a pressure-sensitive adhesive layer.

[0014] The present invention provides an image display device further comprising the image display panel described above and a transparent plate on the surface of the polarizing plate opposite to the image display cell. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a polarizer capable of suppressing a change in hue of the polarizer in a high-temperature environment, and also to provide a polarizing plate, a polarizing plate with an optical layer, an image display panel, and an image display device each including the polarizer. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 2 is a cross-sectional view of a polarizer. [Figure 2] FIG. 2 is a cross-sectional view of a polarizing plate with an optical layer. [Figure 3] FIG. 2 is a cross-sectional view of an image display panel. [Figure 4] FIG. 1 is a cross-sectional view of an image display device. DETAILED DESCRIPTION OF THE INVENTION

[0017] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and redundant explanations will be omitted.

[0018] <Polarizer> As shown in FIG. 1, a polarizer 1 of this embodiment is made of a polyvinyl alcohol-based resin and has a film shape.

[0019] The polyvinyl alcohol-based resin film may be a single film formed from a polyvinyl alcohol-based resin, or may be a laminate film in which a substrate film and a polyvinyl alcohol-based resin film are laminated. In the case of a laminate film, for example, it can be produced by applying a coating liquid containing a polyvinyl alcohol-based resin to at least one surface of a substrate film and drying it.

[0020] Examples of the substrate film include thermoplastic resin films. The thermoplastic resin film is preferably a film made of an optically transparent thermoplastic resin, and may be a transparent resin film made of a polyolefin resin such as a linear polyolefin resin (such as a polypropylene resin) or a cyclic polyolefin resin (such as a norbornene resin); a cellulose ester resin such as triacetyl cellulose or diacetyl cellulose; a polyester resin such as polyethylene terephthalate, polyethylene naphthalate, or polybutylene terephthalate; a polycarbonate resin; a (meth)acrylic resin such as a polymethyl methacrylate resin; or a mixture or copolymer thereof.

[0021] The thickness of the polarizer, i.e., the polyvinyl alcohol-based resin film, may be, for example, 30 μm or less, preferably 25 μm or less, more preferably 20 μm or less, even more preferably 15 μm or less, still more preferably 14 μm or less, particularly preferably 13 μm or less, and even more particularly preferably 12 μm or less. When the thickness of the polarizer is 30 μm or less, light leakage tends to be easily suppressed. Furthermore, reducing the thickness of the polarizer is advantageous for thinning the polarizing plate. The thickness of the polarizer is usually 2 μm or more, and may be, for example, 5 μm or more.

[0022] The polyvinyl alcohol-based resin film is preferably uniaxially stretched. A dichroic dye such as iodine may be adsorbed and oriented on the uniaxially stretched polyvinyl alcohol-based resin film.

[0023] The polarizer of this embodiment contains various atoms described below in addition to the atoms constituting the polyvinyl alcohol-based resin. Hereinafter, when describing the atoms contained in the polarizer, the term "atom" may be replaced with "element" or "ion." The content of each atom described below is expressed as mass % when the total mass of the polarizer is taken as 100. The mass % value is a value determined by elemental analysis. Specific analytical methods will be described in the Examples section.

[0024] The polarizer contains lithium atoms. The lithium atom content is 0.005% by mass or more and 0.100% by mass or less. This content may be 0.010% by mass or more and 0.090% by mass or less, 0.020% by mass or more and 0.080% by mass or less, 0.050% by mass or more and 0.080% by mass or less, or 0.060% by mass or more and 0.070% by mass or less.

[0025] The polarizer may contain potassium atoms. The content of potassium atoms may be from 0.01% to 0.30% by mass, from 0.10% to 0.25% by mass, or from 0.15% to 0.25% by mass.

[0026] It is also preferable that the lithium atom content [X] and the potassium atom content [Y] satisfy the relationship of the following formula (1). X / Y<1 …(1) In this case, the content of lithium atoms is preferably 0.050% by mass or more and 0.090% by mass or less, and more preferably 0.060% by mass or more and 0.070% by mass or less.

[0027] The numerical value on the right side of the above formula (1) may be 0.8, 0.6, 0.4, 0.1, or 0.05, and the lower limit of "X / Y" may be 0.005, 0.01, 0.03, or 0.05.

[0028] The polarizer may contain boron atoms. The content of boron atoms may be 4.0% by mass or more and 6.0% by mass or less, 4.2% by mass or more and 5.2% by mass or less, or 4.4% by mass or more and 4.8% by mass or less.

[0029] The polarizer contains iodine atoms as a dichroic dye, and the content thereof may be 2.0% by mass or more and 5.0% by mass or less, 2.4% by mass or more and 4.6% by mass or less, or 2.8% by mass or more and 3.8% by mass or less.

[0030] The polarizer may contain zinc atoms. The content of zinc atoms may be 0.005% by mass or more and 0.100% by mass or less, 0.008% by mass or more and 0.050% by mass or less, or 0.010% by mass or more and 0.030% by mass or less.

[0031] The polarizer may further contain at least one atom selected from the group consisting of halogen atoms other than iodine atoms, sulfur atoms, and nitrogen atoms. The total content of the selected atoms may be 0.1 mass % or less, 0.08 mass % or less, 0.06 mass % or less, or 0.03 mass % or less. Specific examples of the at least one atom selected from the group consisting of halogen atoms, sulfur atoms, and nitrogen atoms include Cl. - , NH3, NO3 - , SO4 2- It is contained as a molecule or ion.

[0032] The polarizer of this embodiment contains a predetermined amount of lithium atoms, and therefore, hue change of the polarizer in a high-temperature environment is suppressed. Although the reason for this is not completely clear, the inventors believe that this is because the hydrogen atoms of the hydroxyl groups in the PVA undergo ion exchange with lithium atoms, making it difficult for the dehydration reaction of the PVA to proceed.

[0033] Iodine coordinates with the hydroxyl groups of PVA to form a PVA-iodine complex, but some of this reacts with water to produce an acid. The acid produced accelerates the dehydration reaction of PVA in a high-temperature environment (for example, 105°C), leading to the formation of polyenes. As the polyene formation progresses, the polyene structure begins to absorb light in the visible light range, causing the polarizer to become colored. If lithium atoms are present, the hydroxyl groups (-OH) of PVA form an equilibrium state with lithium salts (-OLi). Because lithium salts are thermally stable, the dehydration reaction does not proceed easily, suppressing the formation of polyenes.

[0034] <Polarizer manufacturing method> The polarizer of this embodiment is manufactured through a swelling process, a dyeing process, a crosslinking process, and a drying process. The crosslinking process includes a crosslinking stage and a complementary color stage. The polarizer may be stretched during the swelling process, the dyeing process, and the crosslinking process. A manufacturing method including the swelling process, the dyeing process, the crosslinking process, and the drying process, and in which lithium atoms are introduced into the polarizer during the crosslinking process, will be described below.

[0035] (1) Swelling process The swelling treatment in this step is a treatment carried out as needed for the purposes of removing foreign matter from the polyvinyl alcohol-based resin film (raw film), removing plasticizers, imparting dyeability, plasticizing the film, etc. Specifically, it can be a treatment in which the polyvinyl alcohol-based resin film is immersed in a treatment liquid (swelling liquid) containing water. The polyvinyl alcohol-based resin film (raw film) can be appropriately immersed in the examples exemplified in the polarizer description section. The resin film may be immersed in one swelling liquid, or in two or more swelling liquids sequentially. The film may be uniaxially stretched before, during, or both before and during the swelling treatment.

[0036] The thickness of the polyvinyl alcohol resin film as the raw film is, for example, about 10 μm or more and 80 μm or less, and from the viewpoint of making the thickness of the polarizer after stretching 15 μm or less, it is preferably 40 μm or less, more preferably 30 μm or less.

[0037] The polyvinyl alcohol-based resin film as the raw film can be prepared, for example, as a roll (wound product) of a long unstretched or stretched polyvinyl alcohol-based resin film. In this case, the polarizer is also obtained as a long product.

[0038] The swelling liquid can be water (for example, pure water), or it can be an aqueous solution to which a water-soluble organic solvent such as an alcohol has been added.

[0039] The temperature of the swelling solution when the raw film is immersed is usually about 10 to 70°C, preferably about 15 to 50°C, and the immersion time of the film is usually about 10 to 600 seconds, preferably about 20 to 300 seconds.

[0040] (2) Dyeing process The dyeing treatment in this step is a treatment performed for the purpose of adsorbing and orienting iodine in the polyvinyl alcohol-based resin film. Specifically, it can be a treatment in which the polyvinyl alcohol-based resin film is immersed in a treatment liquid (dyeing liquid) containing iodine. The film may be immersed in one dyeing liquid, or may be immersed sequentially in two or more dyeing liquids. In order to enhance the dyeability of iodine, the film subjected to the dyeing step may be subjected to at least some degree of uniaxial stretching treatment. Instead of or in addition to the uniaxial stretching treatment before the dyeing treatment, uniaxial stretching treatment may be performed during the dyeing treatment.

[0041] An aqueous solution containing iodine and potassium iodide can be used as a dye solution containing iodine. Instead of potassium iodide, other iodides such as zinc iodide may be used, or potassium iodide may be used in combination with other iodides. Compounds other than iodides, such as boric acid, zinc chloride, or cobalt chloride, may also be present. Addition of boric acid is distinguished from the crosslinking treatment described below in that it contains iodine. The iodine content in the aqueous solution is typically 0.01 to 1 part by mass per 100 parts by mass of water. The content of iodides such as potassium iodide is typically 0.01 to 2 parts by mass per 100 parts by mass of water. The concentration of boric acid in the aqueous solution can be 0.01 to 5 parts by mass per 100 parts by mass of water.

[0042] The temperature of the dye solution when the film is immersed is usually 10°C or more and 45°C or less, preferably 10°C or more and 40°C or less, and more preferably 20°C or more and 35°C or less, and the immersion time of the film is usually 10 seconds or more and 600 seconds or less, and preferably 30 seconds or more and 300 seconds or less.

[0043] (3) Crosslinking process The crosslinking treatment of the polyvinyl alcohol resin film after the dyeing process with a crosslinking agent is a treatment carried out for the purpose of improving water resistance or adjusting the hue by crosslinking, and specifically, it can be a treatment of immersing the film after the dyeing process in a treatment liquid (crosslinking liquid) containing a crosslinking agent. The film may be immersed in one crosslinking liquid, or may be immersed sequentially in two or more crosslinking liquids. A uniaxial stretching treatment may be carried out during the crosslinking treatment.

[0044] (Crosslinking agent) Examples of crosslinking agents include boric acid, glyoxal, glutaraldehyde, etc., with boric acid being preferred. Two or more crosslinking agents can also be used in combination. The content of boric acid in the crosslinking solution is usually 0.1 to 15 parts by mass, preferably 2 to 6 parts by mass, per 100 parts by mass of water. By setting the boric acid concentration within this range, the polyvinyl alcohol-based resin film can be suitably crosslinked while maintaining a strength suitable for transport and without precipitation of boric acid in the treatment solution.

[0045] (iodide) When the dichroic dye is iodine, the crosslinking liquid preferably contains an iodide in addition to boric acid. The content of the iodide in the crosslinking liquid is usually 0.01 to 20 parts by mass, preferably 0.01 to 15 parts by mass, per 100 parts by mass of water. Examples of the iodide include potassium iodide and zinc iodide.

[0046] (zinc salts) The crosslinking liquid preferably further contains a zinc salt. Examples of zinc salts include zinc chloride, zinc sulfate, zinc iodide, zinc acetate, and zinc nitrate. The content of the zinc salt in the crosslinking liquid may be 0.0005 to 30 parts by mass, preferably 0.001 to 25 parts by mass, and more preferably 0.1 to 10 parts by mass per 100 parts by mass of water. When adding a zinc salt, the zinc salts listed above may be added alone or in combination of two or more. Of the zinc salts, zinc chloride and zinc sulfate are preferred.

[0047] (Other ingredients) The crosslinking liquid may contain other components in addition to the crosslinking agent, iodide, and zinc salt, such as cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, and potassium chloride.

[0048] When the polyvinyl alcohol-based resin film is immersed in a plurality of crosslinking liquids, the concentration of the zinc salt in each crosslinking liquid may be different for each crosslinking liquid.

[0049] It is expected that the water resistance of the polarizer will be improved by immersing the polyvinyl alcohol-based resin film in a crosslinking liquid containing a zinc salt.

[0050] The temperature of the crosslinking liquid when the film is immersed is usually 40°C or more and 75°C or less, preferably 50°C or more and 70°C or less, and the immersion time of the film is usually 10 seconds or more and 600 seconds or less, preferably 50 seconds or more and 200 seconds or less.

[0051] In the crosslinking step, the polyvinyl alcohol resin film may be immersed in two or more crosslinking liquids. In this case, the compositions and temperatures of the crosslinking liquids may be the same or different. When the polyvinyl alcohol resin film is immersed in two or more crosslinking liquids, it is preferable that at least one of the crosslinking liquids contains a zinc salt. It is more preferable that the zinc salt is added in the complementary color stage described below in the crosslinking step.

[0052] (Cross-linking stage and complementary stage) The crosslinking liquid may have a concentration of a crosslinking agent and an iodide, etc., and a temperature that are appropriate for the purpose of immersing the polyvinyl alcohol-based resin film. The crosslinking treatment for water resistance through crosslinking and the crosslinking treatment for hue adjustment (complementary color) may each be performed in multiple steps (e.g., in a bath containing multiple treatment solutions). These steps are called the crosslinking step and the complementary color step, respectively. The crosslinking step may include a complementary color step after the crosslinking step described above.

[0053] Generally, when both a crosslinking treatment (crosslinking stage) for water resistance by crosslinking and a crosslinking treatment for hue adjustment (complementary color) are performed, a crosslinking liquid (complementary color liquid) for performing the crosslinking treatment (complementary color stage) for hue adjustment (complementary color) is placed in the latter stage. The temperature of the complementary color liquid is, for example, 30°C or higher and 75°C or lower, preferably 40°C or higher and 65°C or lower. The immersion time for immersing the film in the complementary color liquid is usually 5 seconds or higher and 600 seconds or lower, preferably 5 seconds or higher and 60 seconds or lower.

[0054] The content of the crosslinker in the complementary color liquid is, for example, 1 part by mass to 5 parts by mass per 100 parts by mass of water, and the content of the iodide in the complementary color liquid is, for example, 1 part by mass to 30 parts by mass per 100 parts by mass of water.

[0055] (lithium atom) In the crosslinking step, the crosslinking liquid contains a compound containing a lithium atom. In particular, when the crosslinking step has a complementary color step after the crosslinking step, it is preferable that the complementary color liquid contains a compound containing a lithium atom. The compound preferably has a pH of 5 to 8. The pH here is, for example, the pH when 50 g of the compound is dissolved in 1 L of water. This is because polyenation proceeds easily when the solution is acidic (pH less than 5), while crosslinking by boric acid proceeds less easily when the solution is alkaline (pH greater than 8). Examples of the compound include lithium sulfate, lithium iodide, lithium chloride, and lithium nitrate, with lithium sulfate being preferred. The content of these compounds may be 0.05 to 10 parts by mass, 0.10 to 5 parts by mass, or 0.20 to 3 parts by mass per 100 parts by mass of water.

[0056] The complementary color solution may also contain zinc salts and other components. When the complementary color solution contains zinc chloride, the content of zinc chloride may be 0.1 to 3 parts by mass, preferably 0.2 to 0.8 parts by mass, per 100 parts by mass of water.

[0057] (Regarding extension) In the method for producing a polarizer of this embodiment, it is preferable that the polyvinyl alcohol-based resin film is uniaxially stretched (stretching step) at any one or more stages from before the swelling step to the crosslinking step. From the viewpoint of improving the dyeability of the dichroic dye, the film to be subjected to the dyeing step is preferably a film that has been subjected to at least some degree of uniaxial stretching, or it is preferable that the film be subjected to uniaxial stretching during the dyeing step instead of or in addition to the uniaxial stretching before the dyeing step.

[0058] The uniaxial stretching process may be dry stretching in air, wet stretching in liquid, or both. The uniaxial stretching process may be inter-roll stretching, in which longitudinal uniaxial stretching is performed by applying a peripheral speed difference between two nip rolls, hot roll stretching, tenter stretching, or the like, but preferably includes inter-roll stretching. The stretching ratio based on the raw film (the cumulative stretching ratio when stretching is performed in two or more stages) is approximately 3 to 8 times. In order to impart good polarization properties, the stretching ratio is preferably 4 times or more, more preferably 5 times or more.

[0059] (4)Drying process The drying step is a step for drying the polyvinyl alcohol-based resin film after the crosslinking step or the washing step, and the polyvinyl alcohol-based resin film after the crosslinking step or the washing step can be subjected to a drying treatment, thereby obtaining a polarizer.

[0060] The drying treatment is carried out using a film drying means (heating means). A suitable example of the drying means is a drying oven. The drying oven is preferably one that can control the temperature inside the oven. The drying oven is, for example, a hot air oven that can increase the temperature inside the oven by supplying hot air, etc. The drying treatment by the drying means may also be a treatment in which the polyvinyl alcohol-based resin film after the crosslinking step or the washing step is brought into close contact with one or more heating bodies having a convex curved surface, or a treatment in which the film is heated using a heater.

[0061] The heating body may be a roll (e.g., a guide roll that also functions as a heating roll) that has a heat source (e.g., a heat medium such as hot water or an infrared heater) inside and can increase the surface temperature. Examples of the heater include an infrared heater, a halogen heater, and a panel heater.

[0062] The temperature of the drying treatment (for example, the temperature inside the drying oven, the surface temperature of the heated roll, etc.) is usually 30° C. or higher and 100° C. or lower, and preferably 50° C. or higher and 90° C. or lower. The drying time is not particularly limited, but is, for example, 30 seconds or higher and 600 seconds or lower.

[0063] Through the above steps, a polarizer can be obtained in which a dichroic dye is adsorbed and oriented on a uniaxially stretched polyvinyl alcohol-based resin film.

[0064] In the manufacturing method of this embodiment, it is not necessary to provide a water washing step after the crosslinking step. If the film is washed with water, lithium atoms to be contained in the polarizer may be washed away, and the polarizer may not contain the desired amount of these atoms.

[0065] <Polarizing plate> As shown in Fig. 2, a polarizer 1 is laminated with a protective film 2 to form a polarizing plate 3, and further provided with an optical layer 4 to form a polarizing plate 10 with an optical layer. Fig. 2 shows an embodiment in which the protective film 2 is laminated on one side of the polarizer 1, but the protective film 2 may also be laminated on both sides of the polarizer 1.

[0066] The protective film may be a transparent resin film made of a thermoplastic resin, for example, a polyolefin resin such as a linear polyolefin resin (such as a polypropylene resin) or a cyclic polyolefin resin (such as a norbornene resin); a cellulose ester resin such as triacetyl cellulose or diacetyl cellulose; a polyester resin such as polyethylene terephthalate, polyethylene naphthalate, or polybutylene terephthalate; a polycarbonate resin; a (meth)acrylic resin such as a polymethyl methacrylate resin; or a mixture, copolymer, or the like of these.

[0067] The thickness of the protective film 2 is preferably thin from the viewpoint of thinning the polarizing plate 3, but if it is too thin, the strength tends to decrease and the processability tends to be poor, so the thickness is preferably 5 to 150 μm, more preferably 5 to 100 μm, and even more preferably 10 to 50 μm.

[0068] The polarizing plate 3 can be obtained by attaching (laminating) the protective film 2 to the polarizer 1 via an adhesive. Examples of the adhesive include an active energy ray-curable adhesive such as an ultraviolet-curable adhesive, an aqueous solution of a polyvinyl alcohol-based resin or an aqueous solution containing a crosslinking agent, and a water-based adhesive such as a urethane-based emulsion adhesive.

[0069] The moisture permeability of the protective film 2 is 200 g / (m 2 24h) or less, 150g / (m 2 24h) or less, 100g / (m 2 24 hours or less may be acceptable.

[0070] The optical layer 4 is a film having an optical function such as a retardation film. For example, a transparent resin film made of the material of the protective film 2 may be stretched (uniaxially or biaxially stretched) or a liquid crystal layer may be formed on the film, thereby providing a retardation film with an arbitrary retardation value.

[0071] <Image display panel, image display device> As shown in FIG. 3, a polarizing plate 10 with an optical layer can be attached to an image display cell 6 using an adhesive 5 to form an image display panel 20. As shown in FIG. 4, a transparent plate (e.g., a touch panel) 7 can be further added to the image display panel 20 on the viewing side to form an image display device 30. The image display device may be any type of device, such as a liquid crystal display device or an organic EL display device, but is preferably a liquid crystal display device. A liquid crystal display device includes a liquid crystal panel having a liquid crystal cell as an image display element and a backlight. When constructing a liquid crystal display device, a polarizing plate may be used as the polarizing plate arranged on the viewing side, or may be used as the polarizing plate arranged on the backlight side, or may be used as the polarizing plate on both the viewing side and the backlight side.

[0072] The polarizing plate described above is particularly suitable for in-vehicle display devices. For example, in an in-vehicle display device, the polarizing plate is attached to an image display cell with a pressure-sensitive adhesive or adhesive, and a light-transmitting member (transparent plate) such as a glass plate or a touch panel is attached to the surface opposite to the surface attached to the image display cell with a pressure-sensitive adhesive or adhesive. The polarizing plate of an in-vehicle display device may be used for a long period of time under relatively high temperatures. In such cases, the polarizer tends to easily undergo hue changes (such as yellowing), and the polarizer according to this embodiment is highly effective in suppressing this.

[0073] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. [Example]

[0074] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0075] Example 1 (Polarizer manufacturing) A transparent, 30 μm-thick, unstretched polyvinyl alcohol film (TS3000, manufactured by Kuraray Co., Ltd.) with a saponification degree of 99.9% or higher was immersed in deionized water at 22°C for 86 seconds to swell it, and then dyed by immersing it for 160 seconds in a dye solution containing an aqueous solution of iodine / potassium iodide / water in a mass ratio of 1.00 / 2.00 / 7.00 and a dye solution containing boric acid and water in a mass ratio of 0.63 / 2.00 / 100.00, all at 23°C. The film was stretched at stretch ratios of 2.00 and 1.22 in the swelling and dyeing stages, respectively, and stretched until the dyeing stage reached a cumulative stretch ratio of 2.44.

[0076] Next, the film was immersed in a crosslinking solution prepared by heating an aqueous solution of potassium iodide / boric acid / water with a mass ratio of 2.30 / 3.70 / 100.00 to 63°C for 76 seconds (crosslinking step) to crosslink the film, while stretching it at a stretch ratio of 2.33 times.

[0077] The film was then immersed in a crosslinking solution (a 2.16 / 5.00 / 1.79 / 100.00 mass ratio aqueous solution of potassium iodide / boric acid / lithium sulfate / water) heated to 50°C for 12 seconds (complementary color step) to crosslink the film while stretching it 1.03 times, so that the total cumulative stretch ratio during the swelling, dyeing, crosslinking, and complementary color steps was 5.83 times.

[0078] After the crosslinking was completed, the polyvinyl alcohol film stretched 5.83 times was dried in an oven at 50° C. for 120 seconds to prepare the polarizer of Example 1. The polarizer had a thickness of 13.8 μm.

[0079] (Elemental analysis in polarizer) (1) Evaluation of contained metals and boron content The polarizer sample was weighed and decomposed in a microwave decomposition apparatus (Multiwave 7000; Anton Paar) to form a solution. The boron, zinc, and lithium concentrations in the test solution were measured using an inductively coupled plasma atomic emission spectrometer (ICP-AES) (Agilent 5110; Agilent Technologies), and the potassium and sodium concentrations in the test solution were measured using an atomic absorption spectrometer (Z-2010; Hitachi High-Tech Science). The content of each metal atom was calculated as a mass percentage, with the total mass of the polarizer taken as 100. (2) Evaluation of contained halogen and sulfur content The polarizer sample was weighed, decomposed and dissolved using the oxygen flask combustion method or an automatic sample combustion device (AQF-2100H; Mitsubishi Chemical Analytech) to prepare a test solution. The halogen and sulfur concentrations in the test solution were measured using an ion chromatograph (Integrion; Thermo Fisher Scientific or ICS-1000; Nippon Dionex). The content of halogen and sulfur atoms was calculated as mass % when the total mass of the polarizer was taken as 100.

[0080] (Polarizer thickness measurement) The thickness of the polarizer was measured using a digital micrometer "MH-15M" manufactured by Nikon Corporation.

[0081] (Measurement of initial optical properties) The optical properties of the obtained polarizer were measured. The measurement was carried out using a spectrophotometer (V7100, manufactured by JASCO Corporation) with the polarizer surface of the polarizing film obtained above as the incident surface. The luminous efficiency-corrected single transmittance Ty (%), luminous efficiency-corrected polarization degree Py (%), orthogonal a, and orthogonal b were measured. Here, "a" and "b" represent the L * a * b * They represent orthogonal axes in color space.

[0082] (heat resistance test) After the initial optical measurements, the polarizer was stored for 500 hours under dry conditions at a temperature of 105°C. As in the initial optical property evaluation, the luminous efficiency-corrected single transmittance Ty (%), luminous efficiency-corrected polarization degree Py (%), orthogonal a, and orthogonal b were measured using a spectrophotometer.

[0083] The measurement results are shown in Tables 1 and 2.

[0084] <Example 2> (Polarizer manufacturing) A transparent, 30 μm-thick, unstretched polyvinyl alcohol film (TS3000, manufactured by Kuraray Co., Ltd.) with a saponification degree of 99.9% or higher was immersed in deionized water at 22°C for 86 seconds to swell it, and then dyed by immersing it for 160 seconds in a dye solution containing an aqueous solution of iodine / potassium iodide / water in a mass ratio of 1.00 / 2.00 / 7.00 and a dye solution containing boric acid and water in a mass ratio of 0.63 / 2.00 / 100.00, all at 23°C. The film was stretched at stretch ratios of 2.00 and 1.22 in the swelling and dyeing stages, respectively, and stretched until the dyeing stage reached a cumulative stretch ratio of 2.44.

[0085] Next, the film was immersed in a crosslinking solution prepared by heating an aqueous solution of potassium iodide / boric acid / water with a mass ratio of 2.30 / 3.70 / 100.00 to 63°C for 76 seconds (crosslinking step) to crosslink the film, while stretching it at a stretch ratio of 2.33 times.

[0086] The film was then immersed in a crosslinking solution (a 2.16 / 5.00 / 1.79 / 0.60 / 100.00 mass ratio aqueous solution of potassium iodide / boric acid / lithium sulfate / zinc chloride / water) heated to 50°C for 12 seconds (complementary color step) to crosslink the film while stretching it 1.03 times, so that the total cumulative stretch ratio during the swelling, dyeing, crosslinking, and complementary color steps was 5.83 times.

[0087] After the crosslinking was completed, the polyvinyl alcohol film stretched 5.83 times was dried in an oven at 50° C. for 150 seconds to prepare a polarizer of Example 2. The polarizer had a thickness of 13.8 μm.

[0088] (Various measurements, heat resistance tests) Various measurements and heat resistance tests were carried out in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0089] Example 3 (Polarizer manufacturing) A transparent, 30 μm-thick, unstretched polyvinyl alcohol film (TS3000, manufactured by Kuraray Co., Ltd.) with a saponification degree of 99.9% or higher was immersed in deionized water at 25°C for 72 seconds to swell it, and then dyed by immersing it for 88 seconds in a dyeing solution containing an aqueous solution of iodine / potassium iodide / water in a mass ratio of 1.00 / 2.00 / 7.00 and a dyeing solution of boric acid / water in a mass ratio of 0.80 / 2.00 / 100.00, both at 25°C. The film was stretched at stretch ratios of 2.00 and 1.13 in the swelling and dyeing stages, respectively, and stretched until the dyeing stage reached a cumulative stretch ratio of 2.26.

[0090] Next, the film was immersed in a crosslinking solution prepared by heating an aqueous solution of potassium iodide / boric acid / water in a mass ratio of 2.30 / 3.70 / 100.00 to 61°C for 85 seconds (crosslinking step) to crosslink the film, while stretching it at a stretch ratio of 2.33 times.

[0091] The film was then immersed in a crosslinking solution (a 2.10 / 5.00 / 0.59 / 100.00 mass ratio aqueous solution of potassium iodide / boric acid / lithium iodide / water) heated to 45°C for 8 seconds (complementary color step) to crosslink the film while stretching it 1.00 times, so that the total cumulative stretch ratio during the swelling, dyeing, crosslinking, and complementary color steps was 5.83 times.

[0092] After the crosslinking was completed, the polyvinyl alcohol film stretched 5.83 times was dried in an oven at 55° C. for 150 seconds to prepare a polarizer of Example 3. The polarizer had a thickness of 13.8 μm.

[0093] (Various measurements, heat resistance tests) Various measurements and heat resistance tests were carried out in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0094] Example 4 (Polarizer manufacturing) A transparent, 30 μm-thick, unstretched polyvinyl alcohol film (TS3000, manufactured by Kuraray Co., Ltd.) with a saponification degree of 99.9% or higher was immersed in deionized water at 25°C for 72 seconds to swell it, and then dyed by immersing it for 88 seconds in a dyeing solution containing an aqueous solution of iodine / potassium iodide / water in a mass ratio of 1.00 / 2.00 / 7.00 and a dyeing solution of boric acid / water in a mass ratio of 0.80 / 2.00 / 100.00, both at 25°C. The film was stretched at stretch ratios of 2.00 and 1.13 in the swelling and dyeing stages, respectively, and stretched until the dyeing stage reached a cumulative stretch ratio of 2.26.

[0095] Next, the film was immersed in a crosslinking solution prepared by heating an aqueous solution of potassium iodide / boric acid / water in a mass ratio of 2.30 / 3.70 / 100.00 to 61°C for 85 seconds (crosslinking step) to crosslink the film, while stretching it at a stretch ratio of 2.33 times.

[0096] The film was then immersed in a crosslinking solution (a 2.10 / 5.00 / 0.19 / 100.00 mass ratio aqueous solution of potassium iodide / boric acid / lithium chloride / water) heated to 45°C for 8 seconds (complementary color step) to crosslink the film while stretching it 1.00 times, so that the total cumulative stretch ratio during the swelling, dyeing, crosslinking, and complementary color steps was 5.27 times.

[0097] After the crosslinking was completed, the polyvinyl alcohol film stretched 5.27 times was dried in an oven at 55° C. for 120 seconds to prepare a polarizer of Example 4. The polarizer had a thickness of 13.8 μm.

[0098] (Various measurements, heat resistance tests) Various measurements and heat resistance tests were carried out in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0099] <Example 5> (Polarizer manufacturing) A transparent, 30 μm-thick, unstretched polyvinyl alcohol film (TS3000, manufactured by Kuraray Co., Ltd.) with a saponification degree of 99.9% or higher was immersed in deionized water at 25°C for 72 seconds to swell it, and then dyed by immersing it for 88 seconds in a dyeing solution containing an aqueous solution of iodine / potassium iodide / water in a mass ratio of 1.00 / 2.00 / 7.00 and a dyeing solution of boric acid / water in a mass ratio of 0.80 / 2.00 / 100.00, both at 25°C. The film was stretched at stretch ratios of 2.00 and 1.13 in the swelling and dyeing stages, respectively, and stretched until the dyeing stage reached a cumulative stretch ratio of 2.26.

[0100] Next, the film was immersed in a crosslinking solution prepared by heating an aqueous solution of potassium iodide / boric acid / water in a mass ratio of 2.30 / 3.70 / 100.00 to 61°C for 85 seconds (crosslinking step) to crosslink the film, while stretching it at a stretch ratio of 2.33 times.

[0101] The film was then immersed in a crosslinking solution (a 2.10 / 5.00 / 0.73 / 100.00 mass ratio aqueous solution of potassium iodide / boric acid / lithium chloride / water) heated to 45°C for 8 seconds (complementary color step) to crosslink the film while stretching it 1.00 times, so that the total cumulative stretch ratio during the swelling, dyeing, crosslinking, and complementary color steps was 5.27 times.

[0102] After the crosslinking was completed, the polyvinyl alcohol film stretched 5.27 times was dried in an oven at 55° C. for 120 seconds to prepare a polarizer of Example 5. The polarizer had a thickness of 13.8 μm.

[0103] (Various measurements, heat resistance tests) Various measurements and heat resistance tests were carried out in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0104] <Comparative Example 1> (Polarizer manufacturing) A transparent, 75 μm-thick, unstretched polyvinyl alcohol film (PS7500, manufactured by Kuraray Co., Ltd.) with a saponification degree of 99.9% or higher was immersed in 30°C water (deionized water) for 60 seconds to swell it, and then dyed by immersing it in a dyeing solution with an iodine / potassium iodide / water mass ratio of 0.02 / 0.28 / 100.00 at 30°C for 60 seconds. During this process, the film was stretched at stretch ratios of 3.50 and 1.10 in the swelling and dyeing stages, respectively, and stretching was continued so that the cumulative stretch ratio up to the dyeing stage was 3.85.

[0105] Next, the film was immersed in a crosslinking solution prepared by heating an aqueous solution of potassium iodide / boric acid / water in a mass ratio of 3.00 / 3.00 / 100.00 to 40°C for 45 seconds (crosslinking step) to crosslink the film, while stretching it at a stretching ratio of 1.40.

[0106] Furthermore, the film was immersed in a crosslinking solution prepared by heating an aqueous solution of potassium iodide / boric acid / sodium sulfate / water in a mass ratio of 5.00 / 4.00 / 1.00 / 100.00 to 60°C for 30 seconds (complementary color stage) to crosslink the film while stretching it 1.10 times.

[0107] The fabric was then immersed in a 2.00 / 100.00 potassium iodide / water aqueous solution at 30°C for 10 seconds. The fabric was then stretched at a 1.01 stretch ratio in the washing bath (water washing step). The total cumulative stretch ratio during the swelling, dyeing, crosslinking, color correction, and water washing steps was adjusted to 5.99.

[0108] After washing with water, the polyvinyl alcohol film stretched 5.99 times was dried in an oven at 70° C. for 180 seconds to produce a polarizer of Comparative Example 1. The polarizer had a thickness of 31.6 μm.

[0109] (Various measurements, heat resistance tests) Various measurements and heat resistance tests were carried out in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0110] <Comparative Example 2> (Polarizer manufacturing) A transparent, 75 μm-thick, unstretched polyvinyl alcohol film (PS7500, manufactured by Kuraray Co., Ltd.) with a saponification degree of 99.9% or higher was immersed in 30°C water (deionized water) for 60 seconds to swell it, and then dyed by immersing it in a dyeing solution with an iodine / potassium iodide / water mass ratio of 0.02 / 0.28 / 100.00 at 30°C for 60 seconds. During this process, the film was stretched at stretch ratios of 3.50 and 1.10 in the swelling and dyeing stages, respectively, and stretching was continued so that the cumulative stretch ratio up to the dyeing stage was 3.85.

[0111] Next, the film was immersed in a crosslinking solution prepared by heating an aqueous solution of potassium iodide / boric acid / water in a mass ratio of 3.00 / 3.00 / 100.00 to 40°C for 45 seconds (crosslinking step) to crosslink the film, while stretching it at a stretching ratio of 1.40.

[0112] Furthermore, the film was immersed in a crosslinking solution prepared by heating an aqueous solution of potassium iodide / boric acid / sodium sulfate / water in a mass ratio of 5.00 / 4.00 / 0.50 / 100.00 to 60°C for 30 seconds (complementary color stage) to crosslink the film while stretching it 1.10 times.

[0113] The fabric was then immersed in a 2.00 / 100.00 potassium iodide / water aqueous solution at 30°C for 10 seconds. The fabric was then stretched at a 1.01 stretch ratio in the washing bath (water washing step). The total cumulative stretch ratio during the swelling, dyeing, crosslinking, color correction, and water washing steps was adjusted to 5.99.

[0114] After washing with water, the polyvinyl alcohol film stretched 5.99 times was dried in an oven at 70° C. for 180 seconds to produce a polarizer of Comparative Example 2. The polarizer had a thickness of 31.6 μm.

[0115] (Various measurements, heat resistance tests) Various measurements and heat resistance tests were carried out in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0116] <Comparative Example 3> (Polarizer manufacturing) A transparent, 75 μm-thick, unstretched polyvinyl alcohol film (PS7500, manufactured by Kuraray Co., Ltd.) with a saponification degree of 99.9% or higher was immersed in 30°C water (deionized water) for 60 seconds to swell it, and then dyed by immersing it in a dyeing solution with an iodine / potassium iodide / water mass ratio of 0.02 / 0.28 / 100.00 at 30°C for 60 seconds. During this process, the film was stretched at stretch ratios of 3.50 and 1.10 in the swelling and dyeing stages, respectively, and stretching was continued so that the cumulative stretch ratio up to the dyeing stage was 3.85.

[0117] Next, the film was immersed in a crosslinking solution prepared by heating an aqueous solution of potassium iodide / boric acid / water in a mass ratio of 3.00 / 3.00 / 100.00 to 40°C for 45 seconds (crosslinking step) to crosslink the film, while stretching it at a stretching ratio of 1.40.

[0118] Furthermore, the film was immersed in a crosslinking solution prepared by heating an aqueous solution of potassium iodide / boric acid / sodium sulfate / water in a mass ratio of 5.00 / 4.00 / 5.50 / 100.00 to 60°C for 30 seconds (complementary color stage) to crosslink the film while stretching it 1.10 times.

[0119] The fabric was then immersed in a 2.00 / 100.00 potassium iodide / water aqueous solution at 30°C for 10 seconds. The fabric was then stretched at a 1.01 stretch ratio in the washing bath (water washing step). The total cumulative stretch ratio during the swelling, dyeing, crosslinking, color correction, and water washing steps was adjusted to 5.99.

[0120] After washing with water, the polyvinyl alcohol film stretched 5.99 times was dried in an oven at 70° C. for 180 seconds to produce a polarizer of Comparative Example 3. The polarizer had a thickness of 31.6 μm.

[0121] (Various measurements, heat resistance tests) Various measurements and heat resistance tests were carried out in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0122] <Result> Table 1 shows the results of elemental analysis. Table 2 shows the measurement results after manufacturing the polarizer, the measurement results after the heat resistance test, and the difference between the two measurement results. In Comparative Examples 1 to 3, the results for luminous efficiency-corrected single transmittance Ty (%), luminous efficiency-corrected polarization degree Py (%), orthogonal a, and orthogonal b were poor, but in Examples 1 to 5, these results were good.

[0123] [Table 1]

[0124] [Table 2] [Industrial Applicability]

[0125] The present invention can be used in a polarizing plate. [Explanation of symbols]

[0126] 1...polarizer, 2...protective film, 3...polarizing plate, 4...optical layer, 5...adhesive, 6...image display cell, 7...transparent plate, 10...polarizing plate with optical layer, 20...image display panel, 30...image display device

Claims

1. A polarizer formed from a polyvinyl alcohol-based resin film, containing lithium atoms, The polarizer has a lithium atom content of 0.005% by mass or more and 0.100% by mass or less as determined by elemental analysis.

2. further comprising a potassium atom, 2. The polarizer according to claim 1, wherein the lithium atom content [X] determined by elemental analysis and the potassium atom content [Y] determined by elemental analysis satisfy the following formula (1): X / Y<1 ... (1)

3. The polarizer according to claim 2 , wherein the content of the potassium atoms is 0.01% by mass or more and 0.30% by mass or less.

4. The polarizer according to claim 3 , wherein the content of the lithium atoms is 0.050% by mass or more and 0.090% by mass or less.

5. further comprising a boron atom; 2. The polarizer according to claim 1, wherein the content of boron atoms determined by elemental analysis is 4.0% by mass or more and 6.0% by mass or less.

6. A polarizing plate comprising: the polarizer according to any one of claims 1 to 5; and a protective film laminated on at least one surface of the polarizer via an adhesive layer.

7. The moisture permeability of the protective film is 200 g / (m ２ 7. The polarizing plate according to claim 6, wherein the temperature is 24 hours or less.

8. A polarizing plate with an optical layer, which is obtained by laminating the polarizing plate according to claim 6 and an optical layer.

9. An image display panel, comprising the polarizing plate with an optical layer according to claim 8 and an image display cell laminated together via a pressure-sensitive adhesive layer.

10. An image display device comprising: the image display panel according to claim 9; and a transparent plate on a surface of the polarizing plate opposite to the image display cell.

Images