Polarizing film, polarizing film, laminated polarizing film, image display panel, and image display device

Abstract

To provide a polarizing film that has high durability in high-temperature environments, high-temperature and high-humidity environments, and weather-resistant environments. [Solution] A polarizing film formed by adsorbing and oriented iodine on a polyvinyl alcohol-based film, comprising 0.05% to 0.55% by weight of a compound having a nitroxy radical or a nitroxide group, and 0.05% to 0.65% by weight of a compound having a carboxylic acid or a metal salt thereof.

Description

Technical Field

[0001] The present invention relates to a polarizing film, a polarizing film, a laminated polarizing film, an image display panel, and an image display device.

Background Art

[0002] Conventionally, as a polarizing film used in various image display devices such as liquid crystal display devices and organic EL display devices, a polyvinyl alcohol-based film that has both high transmittance and high polarization degree and is dyed (contains dichroic substances such as iodine and dichroic dyes) has been used. The polarizing film is manufactured by subjecting a polyvinyl alcohol-based film to various treatments such as swelling, dyeing, crosslinking, and stretching in a bath, then performing a washing treatment, and then drying. Further, the polarizing film is usually used as a polarizing film (polarizing plate) in which a protective film such as triacetyl cellulose is adhered to one or both sides thereof using an adhesive.

[0003] The polarizing film is used as a laminated polarizing film (optical laminate) by laminating other optical layers as necessary. The polarizing film or the laminated polarizing film (optical laminate) is bonded between an image display cell such as a liquid crystal cell or an organic EL element and a front transparent member such as a front transparent plate (window layer) or a touch panel on the viewing side through an adhesive layer or an adhesive layer, and is used as the above various image display devices.

[0004] In recent years, such various image display devices are used not only in mobile devices such as mobile phones and tablet terminals but also in in-vehicle image display devices such as car navigation devices and rear monitors, and their applications are expanding. Along with this, the polarizing film and the laminated polarizing film are required to have higher durability in a more severe environment (for example, a high-temperature environment) than conventionally required, and a polarizing film aimed at ensuring such durability has been proposed (Patent Document 1).

[0005] Polarizing films containing nitroxy radicals or compounds having nitroxide groups are known to be excellent at suppressing the decrease in individual transmittance due to the coloration of the polarizing film in high-temperature environments (Patent Document 2). In addition, polarizing films containing buffers such as citric acid are known to be able to suppress discoloration in high-temperature environments (Patent Document 3). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Special Publication No. 2012-516468 [Patent Document 2] Patent No. 6695014 [Patent Document 3] International Publication No. 2019 / 103003 [Overview of the project] [Problems that the invention aims to solve]

[0007] On the other hand, polarizing films used in image display devices require even higher durability, adding durability under high-temperature, high-humidity, and weather-resistant conditions to the durability required under high-temperature environments mentioned above. The polarizing films disclosed in the aforementioned patent documents did not satisfy all of these characteristics.

[0008] In view of the above circumstances, the present invention aims to provide a polarizing film that has high durability in high-temperature environments, high-temperature and high-humidity environments, and weather-resistant environments.

[0009] Furthermore, the present invention aims to provide a polarizing film having the above-described polarizing film, a laminated polarizing film, and an image display panel. [Means for solving the problem]

[0010] In other words, the present invention relates to a polarizing film formed by adsorbing and oriented iodine on a polyvinyl alcohol-based film, the polarizing film containing 0.05% to 0.55% by weight of a compound having a nitroxy radical or a nitroxide group, and 0.05% to 0.65% by weight of a compound having a carboxylic acid or a metal salt thereof.

[0011] Furthermore, the present invention relates to the polarizing film, preferably in which the carboxylic acid has two or more carboxyl groups.

[0012] Furthermore, the present invention relates to the polarizing film, wherein the nitroxy radical or compound having a nitroxide group is preferably an N-oxyl compound.

[0013] Furthermore, the present invention relates to the polarizing film, which preferably has a film thickness of 18 μm or less.

[0014] Furthermore, the present invention relates to a polarizing film in which a transparent protective film is laminated to at least one surface of the polarizing film.

[0015] Furthermore, the present invention relates to a laminated polarizing film in which the polarizing film is bonded to an optical layer.

[0016] Furthermore, the present invention relates to an image display panel in which the polarizing film or the laminated polarizing film is bonded to an image display cell.

[0017] Furthermore, the present invention relates to an image display device comprising a front transparent member on the polarizing film side or the laminated polarizing film side of the image display panel. [Effects of the Invention]

[0018] The polarizing film of the present invention is an iodine-based polarizing film formed by the adsorption and orientation of iodine on a polyvinyl alcohol-based film, and contains a specific amount of nitroxyl radical or a compound having a nitroxide group, and a specific amount of carboxylic acid or a compound having a metal salt thereof. Therefore, it has high durability in a high-temperature environment, a high-temperature and high-humidity environment, and a weather-resistant environment.

[0019] When the polarizing film is exposed to a high-temperature environment, ene is generated by the dehydration reaction of PVA, and polyene formation occurs due to the continuous connection thereof, resulting in absorption in visible light, so the polarizing film becomes colored. In addition, when the polarizing film is exposed to a high-temperature environment, the iodine complex (PVA-I5 - complex) responsible for the absorption of red (at a transmittance of around 700 nm) deteriorates, and the color of red disappears in the crossed Nicol state. Therefore, in the present invention, the durability in a high-temperature environment is evaluated by the single transmittance for the coloring of the polarizing film, and the color loss of red in the polarizing film is evaluated by the orthogonal transmittance at 700 nm.

[0020] In addition, when the polarizing film is exposed to a high-temperature and high-humidity environment, the iodine complex (PVA-I3 - complex) responsible for the absorption of blue (at a transmittance of around 430 nm) deteriorates, and the color of blue disappears in the crossed Nicol state. Therefore, in the present invention, the durability in a high-temperature and high-humidity environment is evaluated by the orthogonal transmittance at 430 nm for the color loss of blue in the polarizing film.

[0021] Furthermore, when the polarizing film is exposed to a weather-resistant environment, polyene formation occurs due to photo-degradation. Therefore, similar to the above, the durability in a weather-resistant environment is evaluated by the single transmittance for the coloring of the polarizing film.

[0022] In the polarizing film of the present invention, it is presumed that a compound having a nitroxyl radical or a nitroxide group can efficiently capture radicals generated in the polyene reaction, so polyene formation can be suppressed. On the other hand, when the polarizing film contains a compound having a nitroxyl radical or a nitroxide group in a specific amount or more, color bleeding of blue is likely to occur in a high-temperature and high-humidity environment. Further, a compound having a carboxylic acid or its metal salt is presumed to be able to suppress the dehydration reaction in the polyene reaction, so polyene formation by heating can be suppressed. On the other hand, it has little effect on polyene formation due to photo-degradation. Also, when the polarizing film contains a compound having a carboxylic acid or its metal salt in a specific amount or more, color bleeding of red in a cross-Nicol state during heating is likely to occur.

Embodiments for Carrying Out the Invention

[0023] <Polarizing Film> The polarizing film of the present invention is a so-called "iodine-based polarizing film" formed by adsorbing and orienting iodine on a polyvinyl alcohol-based film.

[0024] The polyvinyl alcohol (PVA)-based film has light transmittance in the visible light region, and any film that can disperse and adsorb iodine can be used without particular limitation. Also, usually, the PVA-based film used as the raw material preferably has a thickness of about 1 to 100 μm, more preferably about 1 to 50 μm, and preferably has a width of about 100 to 5000 mm.

[0025] Examples of materials for the polyvinyl alcohol-based film include polyvinyl alcohol or its derivatives. Examples of polyvinyl alcohol derivatives include polyvinyl formal, polyvinyl acetal; olefins such as ethylene and propylene; unsaturated carboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid, and those modified with their alkyl esters, acrylamide, etc. The average degree of polymerization of the polyvinyl alcohol is preferably about 100 to 10,000, more preferably about 1,000 to 10,000, and even more preferably about 1,500 to 4,500. Furthermore, the degree of saponification of the polyvinyl alcohol is preferably about 80 to 100 mol%, and more preferably about 95 mol% to 99.95 mol. The average degree of polymerization and the degree of saponification can be determined in accordance with JIS K 6726.

[0026] The polyvinyl alcohol-based film may contain additives such as plasticizers and surfactants. Examples of plasticizers include polyols and their condensates, such as glycerin, diglycerin, triglycerin, ethylene glycol, propylene glycol, and polyethylene glycol. There are no particular restrictions on the amount of additives used, but for example, about 20% by weight or less in the polyvinyl alcohol-based film is preferred.

[0027] The polarizing film preferably contains 1% by weight or more and 15% by weight or less of iodine. The polarizing film preferably contains 1.5% by weight or more of iodine, more preferably 2% by weight or more, from the viewpoint of suppressing color fading during durability tests, and preferably 12% by weight or less, more preferably 10% by weight or less, from the viewpoint of preventing polyene formation.

[0028] The polarizing film contains 0.05% to 0.55% by weight of a nitroxy radical or a compound having a nitroxide group, and 0.05% to 0.65% by weight of a compound having a carboxylic acid or a metal salt thereof.

[0029] As for the nitroxy radical or compound having a nitroxide group, from the viewpoint of having a radical that is relatively stable at room temperature and in air, N-oxyl compounds (with CN(-C)-O as a functional group) are selected. · Compounds having (O · Examples of compounds that exhibit an oxy radical include those known as nitroxyl radicals or compounds having a nitroxide group. Examples of such compounds include those described in International Publication No. 2019 / 103003. The nitroxyl radicals or compounds having a nitroxide group may be used alone or in combination of two or more types.

[0030] Furthermore, from the viewpoint of efficiently capturing radicals generated in the polyene reaction, the nitroxy radical or compound having a nitroxide group preferably has a molecular weight of 1000 or less, more preferably 500 or less, and even more preferably 300 or less.

[0031] The content of the nitroxy radical or compound having a nitroxide group in the polarizing film is preferably 0.08% by weight or more, more preferably 0.1% by weight or more, from the viewpoint of suppressing changes in the transmittance of the individual components in high-temperature and weather-resistant environments, and preferably 0.5% by weight or less, more preferably 0.4% by weight or less, from the viewpoint of suppressing changes in the orthogonal transmittance in high-temperature and high-humidity environments.

[0032] Examples of compounds having the carboxylic acid or its metal salt include known compounds, and from the viewpoint of efficiently suppressing the dehydration reaction in the polyene reaction, it is preferable that the carboxylic acid is a carboxylic acid having two or more carboxyl groups. Examples of such compounds include oxalic acid, fumaric acid, maleic acid, malonic acid, tartaric acid, malic acid, phthalic acid, citric acid, trimellitic acid, trimesic acid, butanetetracarboxylic acid, aspartic acid, glutamic acid, iminodiacetic acid, nitrilotriacetic acid, ethylenediamine-N,N,N′,N′-tetraacetic acid, etc. Among these, phthalic acid, maleic acid, tartaric acid, citric acid, and butanetetracarboxylic acid are preferred. Furthermore, the metal in the metal salt may be any metal that can form a salt with the carboxylic acid and can dissociate from the carboxylic acid in water. The carboxylic acid or the compound having its metal salt may be used alone or in combination of two or more types.

[0033] The content of the carboxylic acid or the compound having its metal salt in the polarizing film is preferably 0.1% by weight or more, more preferably 0.2% by weight or more, from the viewpoint of suppressing changes in the transmittance of the individual compound in a high-temperature environment, and preferably 0.6% by weight or less, more preferably 0.5% by weight or less, from the viewpoint of suppressing changes in the orthogonal transmittance in a high-temperature environment.

[0034] <Method for manufacturing polarizing film> The present invention relates to a method for producing a polarizing film, which is obtained by subjecting a polyvinyl alcohol-based film to an optional swelling step and washing step, and at least a dyeing step, a crosslinking step, and a stretching step. Preferably, the treatment bath in one or more of the swelling step, washing step, dyeing step, crosslinking step, and stretching step contains a nitroxy radical or a compound having a nitroxide group, and / or a carboxylic acid or a metal salt thereof. The content of the nitroxy radical or compound having a nitroxide group and the content of the carboxylic acid or a metal salt thereof contained in the polarizing film can be controlled by the concentration of the nitroxy radical or compound having a nitroxide group and the concentration of the carboxylic acid or a metal salt thereof contained in any of the treatment baths in the swelling step, dyeing step, crosslinking step, stretching step, and washing step, as well as the treatment temperature and treatment time in each of the above treatment baths. In particular, when a washing process is performed after a dyeing process, a crosslinking process, and a stretching process, the washing process can be easily adjusted to a desired range in terms of the content of nitroxy radicals or compounds having a nitroxide group, and compounds having a carboxylic acid or a metal salt thereof, from the viewpoint of eluting or adsorbing nitroxy radicals or compounds having a nitroxide group, or compounds having a carboxylic acid or a metal salt thereof, onto the polyvinyl alcohol-based film, while taking into account the processing conditions in the dyeing process, crosslinking process, and stretching process.

[0035] Furthermore, each treatment bath in the swelling step, dyeing step, crosslinking step, stretching step, and washing step may contain additives such as zinc salts, pH adjusters, pH buffers, and other salts. Examples of zinc salts include zinc halides such as zinc chloride and zinc iodide; and inorganic zinc salts such as zinc sulfate and zinc acetate. Examples of pH adjusters include strong acids such as hydrochloric acid, sulfuric acid, and nitric acid, and strong bases such as sodium hydroxide and potassium hydroxide. Examples of pH buffers include carboxylic acids and their salts such as acetic acid, oxalic acid, and citric acid, and inorganic weak acids and their salts such as phosphoric acid and carbonic acid. Examples of other salts include chlorides such as sodium chloride, potassium chloride, and barium chloride; nitrates such as sodium nitrate and potassium nitrate; sulfates such as sodium sulfate and potassium sulfate; and salts of alkali metals and alkaline earth metals.

[0036] The concentrations of the nitroxy radical, or a compound having a nitroxide group, and a compound having a carboxylic acid or a metal salt thereof, contained in any of the aforementioned treatment baths cannot be determined in general terms as they are affected by the number of treatments, treatment time, treatment temperature, etc. for each treatment. However, from the viewpoint of efficiently controlling the content of these compounds in the polarizing film, it is generally preferable that the concentration be 0.01% by weight or more, more preferably 0.05% by weight or more, even more preferably 0.1% by weight or more, and even more preferably 0.6% by weight or less, more preferably 0.4% by weight or less, and even more preferably 0.3% by weight or less.

[0037] The swelling step involves immersing a polyvinyl alcohol-based film in a swelling bath. This step removes dirt and blocking agents from the surface of the polyvinyl alcohol-based film and suppresses uneven dyeing by swelling the film. The swelling bath typically uses a water-based medium such as water, distilled water, or pure water. The swelling bath may also contain surfactants, alcohol, etc., as appropriate, according to conventional methods.

[0038] The temperature of the swelling bath is preferably around 10 to 60°C, more preferably around 15 to 45°C, and even more preferably around 18 to 30°C. The immersion time in the swelling bath cannot be determined definitively because the degree of swelling of the polyvinyl alcohol-based film is affected by the temperature of the swelling bath, but it is preferably around 5 to 300 seconds, more preferably around 10 to 200 seconds, and even more preferably around 20 to 100 seconds. The swelling process may be performed only once, or multiple times as necessary.

[0039] The dyeing process involves immersing a polyvinyl alcohol-based film in a dyeing bath (iodine solution), which allows iodine to be adsorbed and oriented onto the polyvinyl alcohol-based film. The iodine solution is preferably an aqueous iodine solution and contains 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 film.

[0040] In the staining bath, the concentration of iodine is preferably about 0.01 to 1% by weight, and more preferably about 0.02 to 0.5% by weight. In the staining bath, the concentration of iodide is preferably about 0.01 to 20% by weight, more preferably about 0.05 to 10% by weight, and even more preferably about 0.1 to 5% by weight.

[0041] The temperature of the dyeing bath is preferably around 10 to 50°C, more preferably around 15 to 45°C, and even more preferably around 18 to 30°C. The immersion time in the dyeing bath cannot be determined definitively because the degree of dyeing of the polyvinyl alcohol-based film is affected by the temperature of the dyeing bath, but it is preferably around 10 to 300 seconds, and more preferably around 20 to 240 seconds. The dyeing process may be performed only once, or multiple times as necessary.

[0042] The crosslinking step involves immersing a polyvinyl alcohol-based film in a treatment bath (crosslinking bath) containing a boron compound. The boron compound crosslinks the polyvinyl alcohol-based film, allowing iodine molecules or dye molecules to be adsorbed onto the crosslinked structure. Examples of the boron compound include boric acid, borate salts, and borax. The crosslinking bath is generally an aqueous solution, but may also be a mixed solution of a water-miscible organic solvent and water. Furthermore, the crosslinking bath may contain potassium iodide to control the potassium content in the polarizing film.

[0043] In the crosslinking bath, the concentration of the boron compound is preferably about 1 to 15% by weight, more preferably about 1.5 to 10% by weight, and even more preferably about 2 to 5% by weight. Furthermore, when potassium iodide is used in the crosslinking bath, the concentration of potassium iodide in the crosslinking bath is preferably about 1 to 15% by weight, more preferably about 1.5 to 10% by weight, and even more preferably about 2 to 5% by weight.

[0044] The temperature of the crosslinking bath is preferably around 20 to 70°C, and more preferably around 30 to 60°C. The immersion time in the crosslinking bath cannot be determined definitively because the degree of crosslinking of the polyvinyl alcohol-based film is affected by the temperature of the crosslinking bath, but it is preferably around 5 to 300 seconds, and more preferably around 10 to 200 seconds. The crosslinking process may be performed only once, or multiple times as necessary.

[0045] The stretching step is a process of stretching a polyvinyl alcohol-based film to a predetermined magnification in at least one direction. Generally, the polyvinyl alcohol-based film is uniaxially stretched in the transport direction (longitudinal direction). The stretching method is not particularly limited, and either wet stretching or dry stretching can be used. The stretching step may be performed only once, or multiple times as necessary. The stretching step may be performed at any stage in the production of a polarizing film.

[0046] The treatment bath (stretching bath) in the wet stretching method can usually be a solvent such as water or a mixed solution of a water-miscible organic solvent and water. The stretching bath may contain potassium iodide from the viewpoint of controlling the potassium content in the polarizing film. 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 weight, more preferably about 2 to 10% by weight, and more preferably about 3 to 6% by weight. In addition, the treatment bath (stretching bath) may contain the boron compound from the viewpoint of suppressing film breakage during stretching, in which case the concentration of the boron compound in the stretching bath is preferably about 1 to 15% by weight, more preferably about 1.5 to 10% by weight, and more preferably about 2 to 5% by weight.

[0047] The temperature of the stretching bath is preferably around 25 to 80°C, more preferably around 40 to 75°C, and even more preferably around 50 to 70°C. The immersion time in the stretching bath cannot be determined definitively because the degree of stretching of the polyvinyl alcohol-based film is affected by the temperature of the stretching bath, but it is preferably around 10 to 800 seconds, and more preferably around 30 to 500 seconds. The stretching treatment in the wet stretching method may be performed together with one or more of the swelling step, the dyeing step, the crosslinking step, and the washing step.

[0048] Examples of the dry stretching method include a roll stretching method, a heated roll stretching method, and a compression stretching method. The dry stretching method may be performed together with the drying process.

[0049] The total stretching ratio (cumulative stretching ratio) applied to the polyvinyl alcohol-based film can be set appropriately depending on the purpose, but is preferably around 2 to 7 times, more preferably around 3 to 6.8 times, and even more preferably around 3.5 to 6.5 times.

[0050] The cleaning step involves immersing the polyvinyl alcohol-based film in a cleaning bath, which removes any foreign matter remaining on the surface of the polyvinyl alcohol-based film. The cleaning bath typically uses a water-based medium such as water, distilled water, or pure water. Furthermore, from the viewpoint of controlling the potassium content in the polarizing film, the cleaning bath may also contain potassium iodide. In this case, the concentration of potassium iodide in the cleaning bath is preferably about 1 to 10% by weight, more preferably about 1.5 to 4% by weight, and even more preferably about 1.8 to 3.8% by weight.

[0051] The temperature of the washing bath is preferably around 5 to 50°C, more preferably around 10 to 40°C, and even more preferably around 15 to 35°C. The immersion time in the washing bath cannot be determined definitively because the degree of washing of the polyvinyl alcohol-based film is affected by the temperature of the washing bath, but it is preferably around 1 to 100 seconds, more preferably around 2 to 50 seconds, and even more preferably around 3 to 20 seconds. The swelling step may be performed only once, or multiple times as necessary.

[0052] The method for manufacturing a polarizing film of the present invention may include a drying step. The drying step is a step of drying the polyvinyl alcohol-based film that has been washed in the washing step to obtain a polarizing film, and by drying, a polarizing film having a desired moisture content can be obtained. The drying can be carried out by any suitable method, such as natural drying, forced-air drying, or heat drying.

[0053] The drying temperature is preferably around 20 to 150°C, and more preferably around 25 to 100°C. The drying time cannot be determined definitively because the degree of drying of the polarizing film is affected by the drying temperature, but it is preferably around 10 to 600 seconds, and more preferably around 30 to 300 seconds. The drying process may be performed only once, or multiple times as necessary.

[0054] The polarizing film is preferably about 1 to 50 μm thick, more preferably about 1 to 25 μm thick, and even more preferably about 5 to 18 μm thick from the viewpoint of productivity and shrinkage force of the polarizing film during high-temperature testing. In particular, in order to obtain a polarizing film with a thickness of 8 μm or less, the following method for manufacturing a thin polarizing film can be applied, using a laminate containing a polyvinyl alcohol-based resin layer formed on a resin substrate such as a thermoplastic resin as the polyvinyl alcohol-based film.

[0055] <Manufacturing method for polarizing films (thin polarizing films)> A polarizing film (thin polarizing film) can be obtained by a conventional method for manufacturing polarizing films, for example, by preparing a laminate by forming a polyvinyl alcohol-based resin layer (PVA-based resin layer) containing a polyvinyl alcohol-based resin (PVA-based resin) on one side of a long thermoplastic resin substrate, and then, while transporting the obtained laminate in the longitudinal direction, subjecting the laminate to an optional insolubilization treatment, crosslinking treatment, and washing treatment, as well as at least an air-assisted stretching treatment, a dyeing treatment, and an underwater stretching treatment. The content of nitroxy radicals, compounds having a nitroxide group, and compounds having a carboxylic acid or a metal salt thereof in the thin polarizing film can be controlled by the concentration of nitroxy radicals, compounds having a nitroxide group, and compounds having a carboxylic acid or a metal salt thereof in any of the treatment baths in the insolubilization treatment, crosslinking treatment, washing treatment, dyeing treatment, and underwater stretching treatment, as well as the treatment temperature and treatment time in each of the above treatment baths.

[0056] <Polarizing film> The polarizing film of the present invention has a transparent protective film laminated to at least one surface of the polarizing film.

[0057] The transparent protective film is not particularly limited, and various transparent protective films used in polarizing films can be used. As the material constituting the transparent protective film, for example, a thermoplastic resin that is excellent in transparency, mechanical strength, thermal stability, moisture barrier properties, isotropy, etc., can be used. Examples of the thermoplastic resin include cellulose ester resins such as triacetylcellulose, polyester resins such as polyethylene terephthalate and polyethylene naphthalate, polyethersulfone resins, polysulfone resins, polycarbonate resins, polyamide resins such as nylon and aromatic polyamides, polyimide resins, polyolefin resins such as polyethylene, polypropylene, and ethylene-propylene copolymers, (meth)acrylic resins, cyclic polyolefin resins having a cyclo or norbornene structure (norbornene resins), polyarylate resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof. Furthermore, the transparent protective film can be a cured layer formed from thermosetting resins such as (meth)acrylic, urethane, acrylic urethane, epoxy, and silicone resins, or UV-curable resins. Among these, cellulose ester resins, polycarbonate resins, (meth)acrylic resins, cyclic polyolefin resins, and polyester resins are preferred.

[0058] The thickness of the transparent protective film can be determined as appropriate, but generally, from the viewpoint of strength, workability such as handling, and thinness, it is preferably about 1 to 500 μm, more preferably about 1 to 300 μm, and even more preferably about 5 to 100 μm.

[0059] When the transparent protective film is laminated to both sides of the polarizing film, the transparent protective films on both sides may be the same or different.

[0060] The transparent protective film can use a phase difference plate having a front phase difference of 40 nm or more and / or a thickness direction phase difference of 80 nm or more. The front phase difference is usually controlled in the range of 40 to 200 nm, and the thickness direction phase difference is usually controlled in the range of 80 to 300 nm. When a phase difference plate is used as the transparent protective film, the phase difference plate also functions as the transparent protective film, thus enabling a thinner design.

[0061] Examples of the phase difference plate include a birefringent film obtained by uniaxial or biaxial stretching of a polymer material, an orientation film of a liquid crystal polymer, and a liquid crystal polymer orientation layer supported by a film. The thickness of the phase difference plate is not particularly limited, but it is generally around 20 to 150 μm. The phase difference plate may also be used by laminating it to a transparent protective film that does not have a phase difference.

[0062] The transparent protective film may contain any suitable additives such as ultraviolet absorbers, antioxidants, lubricants, plasticizers, mold release agents, color inhibitors, flame retardants, antistatic agents, pigments, and colorants. In particular, if the transparent protective film contains an ultraviolet absorber, the light resistance of the polarizing film can be improved.

[0063] Functional layers such as a hard coat layer, anti-reflective layer, anti-sticking layer, diffusion layer, or anti-glare layer can be provided on the surface of the transparent protective film that does not have a polarizing film bonded to it. These functional layers can be provided on the protective film itself, or they can be provided separately from the protective film.

[0064] The polarizing film and the transparent protective film, or the polarizing film and the functional layer, are usually bonded together via an adhesive layer or bonding agent.

[0065] Various adhesives used in polarizing films can be applied as the adhesive forming the aforementioned adhesive layer. Examples include rubber-based adhesives, acrylic-based adhesives, silicone-based adhesives, urethane-based adhesives, vinyl alkyl ether-based adhesives, polyvinyl alcohol-based adhesives, polyvinyl polyoridone-based adhesives, polyacrylamide-based adhesives, and cellulose-based adhesives. Among these, acrylic-based adhesives are preferred.

[0066] Examples of methods for forming the adhesive layer include applying the adhesive to a peeled separator, drying it to form the adhesive layer, and then transferring it to a polarizing film, or applying the adhesive to a polarizing film and drying it to form the adhesive layer. The thickness of the adhesive layer is not particularly limited, but is preferably about 1 to 100 μm, and preferably about 2 to 50 μm.

[0067] Various adhesives used in polarizing films can be used as the adhesive for forming the adhesive layer, such as isocyanate adhesives, polyvinyl alcohol adhesives, gelatin adhesives, vinyl latex adhesives, and aqueous polyester adhesives. These adhesives are usually used as aqueous solutions (aqueous adhesives) and contain 0.5 to 60% by weight of solids. Among these, polyvinyl alcohol adhesives are preferred, and acetoacetyl group-containing polyvinyl alcohol adhesives are more preferred.

[0068] The water-based adhesive may contain a crosslinking agent. Typically, the crosslinking agent is a compound having at least two functional groups in one molecule that are reactive with the polymer and other components constituting the adhesive. Examples include alkylenediamines; isocyanates; epoxys; aldehydes; amino-formaldehydes such as methylolurea and methylolmelamine. The amount of crosslinking agent in the adhesive is typically about 10 to 60 parts by weight per 100 parts by weight of the polymer and other components constituting the adhesive.

[0069] In addition to the above, other adhesives include active energy ray curing adhesives such as ultraviolet curing adhesives and electron beam curing adhesives. Examples of active energy ray curing adhesives include (meth)acrylate adhesives. Examples of curable components in (meth)acrylate adhesives include compounds having a (meth)acryloyl group and compounds having a vinyl group. Examples of compounds having a (meth)acryloyl group include alkyl (meth)acrylates such as chain-like alkyl (meth)acrylates having 1 to 20 carbon atoms, alicyclic alkyl (meth)acrylates, and polycyclic alkyl (meth)acrylates; hydroxyl group-containing (meth)acrylates; and epoxy group-containing (meth)acrylates such as glycidyl (meth)acrylate. (Meth)acrylate adhesives may contain nitrogen-containing monomers such as hydroxyethyl (meth)acrylamide, N-methylol (meth)acrylamide, N-methoxymethyl (meth)acrylamide, N-ethoxymethyl (meth)acrylamide, (meth)acrylamide, and (meth)acryloylmorpholine. (Meth)acrylate adhesives may also contain polyfunctional monomers as crosslinking components, such as tripropylene glycol diacrylate, 1,9-nonanediol diacrylate, tricyclodecanedimethanol diacrylate, cyclic trimethylolpropaneformal acrylate, dioxane glycol diacrylate, and EO-modified diglycerin tetraacrylate. Compounds having epoxy groups or oxetanyl groups can also be used as cationic polymerization-curable adhesives. Compounds having epoxy groups are not particularly limited as long as they have at least two epoxy groups in the molecule, and various generally known curable epoxy compounds can be used.

[0070] The adhesive may contain appropriate additives as needed. Examples of such additives include coupling agents such as silane coupling agents and titanium coupling agents, adhesion promoters such as ethylene oxide, ultraviolet absorbers, degradation inhibitors, dyes, processing aids, ion trapping agents, antioxidants, tackifiers, fillers, plasticizers, leveling agents, foam inhibitors, antistatic agents, heat stabilizers, hydrolysis stabilizers, and the like.

[0071] The adhesive may be applied to either the transparent protective film side (or the functional layer side), the polarizing film side, or both. After bonding, a drying process is performed to form an adhesive layer consisting of the applied and dried layer. After the drying process, ultraviolet light or electron beams may be irradiated as necessary. The thickness of the adhesive layer is not particularly limited, but when using a water-based adhesive, it is preferably about 30 to 5000 nm, more preferably about 100 to 1000 nm, and when using an ultraviolet-curing adhesive, electron beam-curing adhesive, etc., it is preferably about 0.1 to 100 μm, more preferably about 0.5 to 10 μm.

[0072] The transparent protective film and the polarizing film, or the polarizing film and the functional layer, may be laminated with an intervening layer such as a surface modification layer, an easy-adhesion layer, a block layer, or a refractive index adjustment layer.

[0073] Examples of surface modification treatments for forming the aforementioned surface modification layer include corona treatment, plasma treatment, primer treatment, and saponification treatment.

[0074] Examples of easy-to-adhere adhesives for forming the easy-to-adhere layer include forming materials containing various resins having a polyester skeleton, polyether skeleton, polycarbonate skeleton, polyurethane skeleton, silicone-based materials, polyamide skeleton, polyimide skeleton, polyvinyl alcohol skeleton, etc. The easy-to-adhere layer is usually provided in advance on a protective film, and the easy-to-adhere layer side of the protective film and the polarizing film are laminated together with the adhesive layer or the adhesive layer.

[0075] The aforementioned block layer is a layer that functions to prevent impurities such as oligomers and ions eluted from the transparent protective film, etc., from migrating (penetrating) into the polarizing film. The block layer only needs to be transparent and capable of preventing impurities eluted from the transparent protective film, etc. Examples of materials that form the block layer include urethane prepolymer-based forming materials, cyanoacrylate-based forming materials, epoxy-based forming materials, etc.

[0076] The refractive index adjusting layer is provided to suppress the decrease in transmittance due to reflection between layers with different refractive indices, such as the transparent protective film and the polarizing film. Examples of refractive index adjusting materials for forming the refractive index adjusting layer include various resins and additives such as silica-based, acrylic-based, acrylic-styrene-based, and melamine-based resins.

[0077] <Laminated polarizing film> The laminated polarizing film (optical laminate) of the present invention is characterized in that the polarizing film is laminated to an optical layer. The optical layer is not particularly limited, but for example, one or more optical layers that are used in the formation of liquid crystal display devices such as reflectors, semitransparent plates, phase difference plates (including 1 / 2 and 1 / 4 wave plates), and viewing angle compensation films can be used. In particular, examples of the laminated polarizing film include a reflective polarizing film or a semitransparent polarizing film in which a reflector or semitransparent reflector is further laminated on the polarizing film, an elliptical polarizing film or a circular polarizing film in which a phase difference plate is further laminated on the polarizing film, a wide-viewing-angle polarizing film in which a viewing angle compensation film is further laminated on the polarizing film, or a polarizing film in which a brightness-enhancing film is further laminated on the polarizing film.

[0078] An adhesive layer may be provided on one or both sides of the polarizing film, or the laminated polarizing film, for bonding an image display cell such as a liquid crystal cell or an organic EL element to another component such as a transparent front plate or touch panel on the viewing side. A tack layer is preferred as the adhesive layer. The tack forming the tack layer is not particularly limited, but for example, acrylic polymers, silicone polymers, polyesters, polyurethanes, polyamides, polyethers, fluorine-based polymers, rubber-based polymers, etc., can be appropriately selected and used. In particular, tacks containing acrylic polymers are preferred because they have excellent optical transparency, exhibit appropriate wettability, cohesiveness and adhesion, and have excellent weather resistance and heat resistance.

[0079] The adhesive layer can be attached to one or both sides of the polarizing film or the laminated polarizing film by any suitable method. Examples of methods for attaching the adhesive layer include preparing an adhesive solution and directly attaching it to the polarizing film or the laminated polarizing film by any suitable application method such as casting or coating, or forming an adhesive layer on a separator and transferring it to the polarizing film or the laminated polarizing film. The thickness of the adhesive layer can be appropriately determined according to the intended use and adhesive strength, and is generally 1 to 500 μm, preferably 5 to 200 μm, and more preferably 10 to 100 μm. A polarizing film or laminated polarizing film with an adhesive layer on at least one side is called a polarizing film with an adhesive layer or a laminated polarizing film with an adhesive layer.

[0080] It is preferable that a separator be temporarily attached to the exposed surface of the adhesive layer to prevent contamination until it is put into practical use. This prevents contamination of the adhesive layer under normal handling conditions. As the separator, for example, a suitable thin sheet such as a plastic film, rubber sheet, paper, cloth, nonwoven fabric, net, foam sheet, metal foil, or laminate thereof may be used, and may be coated with a suitable release agent such as silicone-based, long-chain alkyl-based, fluorine-based, or molybdenum sulfide as needed.

[0081] <Image display panel and image display device> The image display panel of the present invention has the polarizing film or the laminated polarizing film laminated onto an image display cell. Furthermore, the image display device of the present invention is provided with a front transparent member on the polarizing film or laminated polarizing film side (viewing side) of the image display panel.

[0082] Examples of the image display cell include liquid crystal cells and organic EL cells. The liquid crystal cell may be a reflective liquid crystal cell that utilizes ambient light, a transmissive liquid crystal cell that utilizes light from a backlight or other light source, or a semi-transparent, semi-reflective liquid crystal cell that utilizes both ambient light and light from a light source. If the liquid crystal cell utilizes light from a light source, the image display device (liquid crystal display device) also has a polarizing film on the side opposite to the viewing side of the image display cell (liquid crystal cell), and a light source is further positioned therein. Preferably, the polarizing film on the light source side and the liquid crystal cell are bonded together via an appropriate adhesive layer. As for the driving method of the liquid crystal cell, any type may be used, such as VA mode, IPS mode, TN mode, STN mode, or bend orientation (π type).

[0083] As the organic EL cell, for example, one in which a light-emitting body (organic electroluminescent light-emitting body) is formed by sequentially laminating a transparent electrode, an organic light-emitting layer, and a metal electrode on a transparent substrate is preferably used. The organic light-emitting layer is a laminate of various organic thin films, and various layer configurations can be adopted, such as a laminate of a hole injection layer made of a triphenylamine derivative or the like and a light-emitting layer made of a fluorescent organic solid such as anthracene, a laminate of these light-emitting layers and an electron injection layer made of a perylene derivative or the like, or a laminate of a hole injection layer, a light-emitting layer and an electron injection layer.

[0084] Examples of front transparent members positioned on the viewing side of the image display cell include a front transparent plate (window layer) and a touch panel. The front transparent plate is a transparent plate having appropriate mechanical strength and thickness. Examples of such transparent plates include transparent resin plates such as acrylic resin and polycarbonate resin, or glass plates. The touch panel is a variety of touch panels such as resistive, capacitive, optical, and ultrasonic types, or a glass plate or transparent resin plate equipped with a touch sensor function. When a capacitive touch panel is used as the front transparent member, it is preferable to provide a front transparent plate made of glass or a transparent resin plate further on the viewing side than the touch panel. [Examples]

[0085] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0086] <Example 1> <Fabrication of polarizing films> A polyvinyl alcohol film with an average degree of polymerization of 2,400, a degree of saponification of 99.9 mol%, and a thickness of 45 μm was prepared. The polyvinyl alcohol film was immersed in a 30°C swelling bath (water bath) for 30 seconds between rolls with different peripheral speed ratios to swell and stretched to 2.2 times its original size in the conveying direction (swelling process). Subsequently, it was immersed in a 30°C dyeing bath (an iodine aqueous solution obtained by mixing iodine and potassium iodide in a weight ratio of 1:7 with 100 parts by weight of water) for 30 seconds, adjusting the iodine concentration so that the polarizing film had a predetermined transmittance, and dyed while being stretched to 3.3 times its original size in the conveying direction, using the original polyvinyl alcohol film (a polyvinyl alcohol film that had not been stretched at all in the conveying direction) as a reference (dyeing process). Next, the dyed polyvinyl alcohol film was immersed for 28 seconds in a 40°C crosslinking bath (an aqueous solution with a boric acid concentration of 3.5% by weight, a potassium iodide concentration of 3.0% by weight, and a zinc sulfate concentration of 3.6% by weight) to stretch it to 3.6 times its original size in the transport direction (crosslinking process). Furthermore, the obtained polyvinyl alcohol film was immersed for 60 seconds in a 64°C stretching bath (an aqueous solution with a boric acid concentration of 4.8 wt%, a potassium iodide concentration of 5.0 wt%, and a zinc sulfate concentration of 5.0 wt) to stretch it to 6.0 times its original size in the transport direction (stretching step). Then, it was immersed for 10 seconds in a 25°C washing bath (an aqueous solution with a potassium iodide concentration of 3.0 wt%, a nitroxyl radical represented by the following general formula (1) or a compound having a nitroxide group of 0.4 wt%, and a carboxylic acid compound having a carboxylic acid represented by the following general formula (2) or a metal salt thereof of 0.5 wt) (washing step). The washed polyvinyl alcohol film was dried at 40°C for 30 seconds to produce a polarizing film. The following measurements were obtained: (A) The content of nitroxyl radicals or compounds containing nitroxide groups in the polarizing film, calculated by HPLC analysis, was 0.14% by weight; and (B) The content of carboxylic acid compounds containing carboxylic acids or their metal salts, calculated by HPLC analysis, was 0.09% by weight. Furthermore, the iodine content in the polarizing film, determined by the following measurement method, was 3.66% by weight. The thickness of the polarizing film was 17 μm. [ka] [ka]

[0087] <(A) Method for measuring the content (by weight) of nitroxy radicals or compounds containing nitroxide groups in a polarizing film> Approximately 20 mg of polarizing film was collected and quantified. It was then heated and dissolved in 1 mL of water, diluted with 4.5 mL of methanol, and the resulting extract was filtered through a membrane filter. The concentration of nitroxy radicals or compounds containing nitroxide groups in the filtrate was measured using HPLC (Thermo Fisher Scientific, Vanquish).

[0088] <(B) Method for measuring the content (by weight) of carboxylic acid compounds, or metal salts thereof, in polarizing films> Approximately 20 mg of polarizing film was collected and quantified. 1 mL of DMSO was added, and the solution was heated and extracted at 120°C for 1 hour. 3 mL of acetonitrile was added to this solution to reprecipitate the polymer components. The supernatant was then filtered through a membrane filter, and the concentration of carboxylic acid compounds, or carboxylic acid compounds containing metal salts thereof, was measured using HPLC (Thermo Fisher Scientific, Vanquish) in the filtrate.

[0089] <Method for measuring the iodine content (weight %) in polarizing films> For the polarizing film, the iodine concentration (weight %) was determined using the following formula with an X-ray fluorescence analyzer (Rigaku Corporation, product name "ZSX-PRIMUS IV", measurement diameter: ψ20 mm). Iodine concentration (wt%) = 14.474 × (fluorescent X-ray intensity) / (film thickness) (kc ps / μm). Note that the coefficient used to calculate the concentration varies depending on the measuring device, but this coefficient can be determined using an appropriate calibration curve.

[0090] <Preparation of polarizing film> As an adhesive, an aqueous solution containing polyvinyl alcohol resin containing acetoacetyl groups (average degree of polymerization 1,200, degree of saponification 98.5 mol%, degree of acetoacetylation 5 mol%) and methylolmelamine in a weight ratio of 3:1 was used. Using this adhesive, a 47 μm thick triacetylcellulose film with a hard coat layer (moisture permeability 340 g / m²) was applied to both sides of the polarizing film obtained above as a transparent protective film. 2 After laminating Konica Minolta's product "KC4UYW" (24h) using a roll laminating machine, the film was subsequently heated and dried in an oven (at 60°C for 4 minutes) to produce a polarizing film with transparent protective films laminated to both sides of the polarizing film. The transmittance of the polarizing film alone was 40.3%.

[0091] <Fabrication of polarizing film with adhesive layer> A monomer mixture containing 99 parts butyl acrylate and 1 part 4-hydroxybutyl acrylate was charged into a four-necked flask equipped with a stirring blade, thermometer, nitrogen gas inlet tube, and condenser. Furthermore, 0.1 parts 2,2'-azobisisobutyronitrile was added as a polymerization initiator to 100 parts of the monomer mixture (solid content) together with 100 parts ethyl acetate. After introducing nitrogen gas and purging the mixture with nitrogen while gently stirring, the polymerization reaction was carried out for 8 hours while maintaining the liquid temperature in the flask at around 55°C to prepare a solution of an acrylic polymer with a weight-average molecular weight (Mw) of 1.8 million. Subsequently, to 100 parts of the solid content of the obtained acrylic polymer solution, 0.02 parts of an isocyanate crosslinking agent (manufactured by Tosoh Corporation, trade name "Takenate D110N", trimethylolpropane / xylylene diisocyanate adduct) and 0.2 parts of a silane coupling agent (manufactured by Shin-Etsu Chemical Co., Ltd., trade name "X-41-1056") were added to prepare an acrylic adhesive composition solution. Next, the acrylic adhesive composition solution obtained above was applied to one side of a polyethylene terephthalate film (manufactured by Mitsubishi Chemical Polyester Films, trade name "MRF38", separator film) treated with a silicone release agent, so that the thickness of the adhesive layer after drying would be 20 μm, and dried at 90°C for 1 minute to form an adhesive layer on the surface of the separator film. Next, the adhesive layer formed on the separator film was transferred to one side of the polarizing film prepared above to produce a polarizing film with an adhesive layer.

[0092] [Evaluation of single-unit transmittance and Tc700nm under high-temperature conditions] The polarizing film with adhesive layer obtained above was cut to a size of 40 × 40 mm, and a glass plate (pseudo-image display cell) was bonded to it via the adhesive layer to create a laminate. The resulting laminate was left to stand in a hot air oven at 110°C for 1000 hours, and the change in single-layer transmittance (ΔTs) and the change in orthogonal transmittance at 700 nm (ΔTc700) before and after heating were measured. The single-layer transmittance and orthogonal transmittance were measured using a spectrophotometer (Otsuka Electronics Co., Ltd., product name "LPF-200") and evaluated according to the following criteria. The transmittance is the Y value after luminous sensitivity correction using the 2-degree field of view (C light source) of JIS Z8701-1982. The measurement wavelength was 380 to 700 nm (in 5 nm increments). The results are shown in Table 1. [Criteria for determining changes in individual unit transmittance] ΔTs(%) = Ts(1000h) - Ts(0h) Here, Ts(0h) is the transmittance of the laminate before heating, and Ts(1000h) is the transmittance of the laminate after heating for 1000 hours. ○: 5≧ΔTs(%)≧0 ×: ΔTs(%)>5, or ΔTs(%)<0 [Criteria for determining changes in orthogonal transmittance] ΔTc700(%)=Tc700(1000h)-Tc700(0h) Here, Tc700(0h) is the orthogonal transmittance of the laminate at 700nm before heating, and Tc700(1000h) is the orthogonal transmittance of the laminate at 700nm after heating for 1000 hours. ○: 10≧ΔTc700(%)≧0 ×: ΔTc700(%)>10, or ΔTc700(%)<0

[0093] [Evaluation of Tc430 under high temperature and high humidity conditions] A laminate was fabricated in the same manner as described above, and the resulting laminate was left standing in an oven at 65°C and 95RH for 1000 hours. The change in orthogonal transmittance at 430nm (ΔTc430) before and after immersion (humidification) was measured. Orthogonal transmittance was measured using a spectrophotometer (Otsuka Electronics Co., Ltd., product name "LPF-200") and evaluated according to the following criteria. [Criteria for determining changes in orthogonal transmittance] ΔTc430(%)=Tc430(1000h)-Tc430(0h) Here, Tc430(0h) is the orthogonal transmittance at 430nm of the laminate before humidification, and Tc430(1000h) is the orthogonal transmittance at 430nm of the laminate after 1000 hours of humidification. ○: 2≧ΔTc430(%)≧0 ×: ΔTc430(%)>2, or ΔTc430(%)<0

[0094] [Evaluation of individual light transmittance under weather-resistant conditions] A laminate was fabricated in the same manner as described above, and the resulting laminate was subjected to a xenon weather meter (manufactured by Suga Test Instruments Co., Ltd., product name "NX-75", irradiance: 64 W / m²). 2 The samples were left standing for 750 hours at a BPT temperature of 100°C, a chamber temperature of 65°C, and a chamber humidity of 30%, and the transmittance (ΔTs) of the individual samples was measured before and after immersion. The transmittance of the individual samples was measured using a spectrophotometer (Otsuka Electronics Co., Ltd., product name "LPF-200") and evaluated according to the following criteria. The transmittance is the Y value after luminous sensitivity correction using a 2-degree field of view (C light source) according to JIS Z8701-1982. The measurement wavelength was 380-700 nm (in 5 nm increments). The results are shown in Table 1. [Criteria for determining changes in individual unit transmittance] ΔTs(%) = Ts(750h) - Ts(0h) Here, Ts(0h) is the transmittance of the laminate before the weathering test, and Ts(750h) is the transmittance of the laminate after 750 hours of weathering testing. ○: 5≧ΔTs(%)≧0 ×: ΔTs(%)>5, or ΔTs(%)<0

[0095] <Example 2-14> <Fabrication of polarizing films and polarizing coatings> In the preparation of the polarizing film, the polarizing film and polarizing film were prepared using the same procedure as in Example 1, except that the concentration of the nitroxy radical represented by general formula (1) or the compound having a nitroxide group, and the concentration of the carboxylic acid or metal salt thereof represented by general formula (2) in the washing bath were changed to the values ​​shown in Table 1. The thickness of the obtained polarizing film, the transmittance of the polarizing film alone, the content of the nitroxy radical or the compound having a nitroxide group in the polarizing film, and the content of the carboxylic acid or metal salt thereof in the polarizing film are shown in Table 1. In Example 14, a 47 μm thick triacetylcellulose film with a hard coat layer (water permeability of 342 g / m²) was used as a transparent protective film on one side of the polarizing film. 2 A 24h film is laminated to the other side of the polarizing film, and a 30μm polymethyl methacrylate film (with a moisture permeability of 100g / m²) is applied. 2 (24h) Toyo Steel Plate (product name "RZ30") was bonded together.

[0096] <Example 15> <Fabrication of polarizing films and polarizing coatings> In the preparation of polarizing films, polarizing films and polarizing films were prepared using the same procedure as in Example 1, except that the concentration of nitroxy radicals represented by general formula (1) or compounds having a nitroxide group in the washing bath was changed to the values ​​shown in Table 1, the carboxylic acid compounds having carboxylic acids or their metal salts in the washing bath were changed to those of general formulas (3) and (4), and the molar concentrations of the carboxylic acid compounds having carboxylic acids or their metal salts in the washing bath were adjusted to 0.05 M for (3), 0.05 M for (4), and a total of 0.10 M for (3) and (4). The thickness of the obtained polarizing film, the transmittance of the polarizing film, the content of nitroxy radicals or compounds having a nitroxide group in the polarizing film, and the content of carboxylic acid compounds having carboxylic acids or their metal salts in the polarizing film are shown in Table 1. [ka] [ka]

[0097] <Examples 16-19> <Fabrication of polarizing films and polarizing coatings> In the preparation of polarizing films, polarizing films and polarizing films were prepared using the same procedure as in Example 1, except that the concentration of nitroxy radicals represented by general formula (1) or compounds having a nitroxide group in the washing bath was changed to the values ​​shown in Table 1, the carboxylic acid compounds having carboxylic acids or their metal salts in the washing bath were changed to those of general formulas (5) to (8), and the molar concentration of carboxylic acid compounds having carboxylic acids or their metal salts in the washing bath was adjusted to 0.05 M. The thickness of the obtained polarizing film, the transmittance of the polarizing film, the content of nitroxy radicals or compounds having a nitroxide group in the polarizing film, and the content of carboxylic acid compounds having carboxylic acids or their metal salts in the polarizing film are shown in Table 1. [ka] [ka] [ka] [ka]

[0098] <Comparative Example 1-6> <Fabrication of polarizing films and polarizing coatings> In the preparation of polarizing films, polarizing films and polarizing films were prepared using the same procedure as in Example 1, except that the concentration of the nitroxy radical represented by general formula (1) or the compound having a nitroxide group, and the concentration of the carboxylic acid or the metal salt thereof represented by general formula (2) in the washing bath were changed to the values ​​shown in Table 1. The thickness of the obtained polarizing film, the transmittance of the polarizing film alone, the content of the nitroxy radical or the compound having a nitroxide group in the polarizing film, and the content of the carboxylic acid or the metal salt thereof in the polarizing film are shown in Table 1.

[0099] The polarizing films obtained from the examples and comparative examples described above were used to perform each of the evaluations described above. The results are shown in Table 1.

[0100] [Table 1]

Claims

1. A polarizing film formed by the adsorption and orientation of iodine onto a polyvinyl alcohol-based film, A polarizing film characterized by containing 0.05% to 0.55% by weight of a nitroxyl radical or a compound having a nitroxide group, and 0.05% to 0.65% by weight of a compound having a carboxylic acid or a metal salt thereof.

2. The polarizing film according to claim 1, characterized in that the carboxylic acid is a carboxylic acid having two or more carboxyl groups.

3. The polarizing film according to claim 1 or 2, characterized in that the nitroxy radical or compound having a nitroxide group is an N-oxyl compound.

4. The polarizing film according to claim 1 or 2, characterized in that the film thickness is 18 μm or less.

5. A polarizing film characterized in that a transparent protective film is laminated to at least one surface of the polarizing film according to claim 1 or 2.

6. A laminated polarizing film characterized in that the polarizing film described in claim 5 is bonded to an optical layer.

7. An image display panel characterized in that the polarizing film described in claim 5 is bonded to an image display cell.

8. An image display panel characterized in that the laminated polarizing film described in claim 6 is bonded to an image display cell.

9. An image display device characterized by having a front transparent member on the polarizing film side of the image display panel according to claim 7.

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