Polarizing membrane, polarizing film, stacked polarizing film, image display panel, and image display device

Abstract

A polarizing membrane according to the present invention is formed by adsorbing and orienting iodine on a polyvinyl alcohol-based film. The polarizing membrane contains 0.05 to 0.55 wt.% of a compound having a nitroxy radical or a nitroxide group, and contains 0.05 to 0.65 wt.% of a compound having a carboxylic acid or a metal salt thereof. The polarizing membrane has high durability in high-temperature environments, high-temperature and high-humidity environments, and weather-resistant environments.

Description

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

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

[0002] Conventionally, dyed polyvinyl alcohol films (containing dichroic substances such as iodine and dichroic dyes) have been used as polarizing films for various image display devices, such as liquid crystal display devices and organic electroluminescence (EL) display devices, because they combine high transmittance and high polarization. The polarizing films are produced by subjecting a polyvinyl alcohol film to various treatments, such as swelling, dyeing, crosslinking, and stretching, in a bath, followed by washing and drying. Furthermore, the polarizing films are typically used as polarizing films (polarizing plates) with protective films, such as triacetyl cellulose, attached to one or both sides of the film using an adhesive.

[0003] The polarizing film is used as a laminated polarizing film (optical laminate) by laminating other optical layers as necessary, and 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 plate (window layer) on the viewing side or a front transparent member such as a touch panel via a pressure-sensitive adhesive layer or an adhesive layer, and is used as the various image display devices described above.

[0004] In recent years, the applications of such various image display devices have expanded, for example, to include use in mobile devices such as mobile phones and tablet terminals, as well as in-vehicle image display devices such as car navigation devices and rear monitors. Accordingly, the polarizing film and the laminated polarizing film are required to have higher durability in harsher environments (for example, high-temperature environments) than has been conventionally required, and a polarizing film intended to ensure such durability has been proposed (Patent Document 1).

[0005] A polarizing film containing a compound having a nitroxy radical or a nitroxide group is known as a polarizing film that is effective in suppressing a decrease in the single transmittance due to coloration of the polarizing film in a high-temperature environment (Patent Document 2).Furthermore, a polarizing film containing a buffer such as citric acid is known as a polarizing film that can suppress discoloration in a high-temperature environment (Patent Document 3).

[0006] JP 2012-516468 A Japanese Patent Publication No. 6695014 WO 2019 / 103003

[0007] On the other hand, polarizing films used in image display devices are required to have higher durability, i.e., durability in a high-temperature and high-humidity environment and a weather-resistant environment in addition to durability in the above-mentioned high-temperature environment. However, the polarizing films disclosed in the above-mentioned patent documents do not satisfy all of these properties.

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

[0009] Another object of the present invention is to provide a polarizing film, a laminated polarizing film, and an image display panel each having the above polarizing film.

[0010] That is, the present invention relates to a polarizing film formed by adsorbing and orienting iodine on a polyvinyl alcohol-based film, which contains 0.05% by weight or more and 0.55% by weight or less of a compound having a nitroxy radical or a nitroxide group, and 0.05% by weight or more and 0.65% by weight or less of a compound having a carboxylic acid or a metal salt thereof.

[0011] The present invention also relates to the polarizing film, wherein the carboxylic acid is preferably a carboxylic acid having two or more carboxyl groups.

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

[0013] The present invention also relates to the polarizing film, wherein the film thickness is preferably 18 μm or less.

[0014] The present invention also relates to a polarizing film in which a transparent protective film is attached to at least one surface of the polarizing film.

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

[0016] The present invention also relates to an image display panel in which the polarizing film or the laminated polarizing film is attached to an image display cell.

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

[0018] The polarizing film of the present invention is an iodine-based polarizing film formed by adsorbing and aligning iodine on a polyvinyl alcohol-based film, and contains a compound having a specific amount of a nitroxy radical or a nitroxide group, and also contains a specific amount of a compound having a carboxylic acid or a metal salt thereof, and therefore has high durability in high-temperature environments, high-temperature and high-humidity environments, and weather-resistant environments.

[0019] When the polarizing film is exposed to a high temperature environment, the dehydration reaction of PVA generates ene, which then chains together to form polyene, which absorbs visible light, causing coloration of the polarizing film. In addition, when the polarizing film is exposed to a high temperature environment, the iodine complex (PVA-I), which is responsible for red absorption (transmittance around 700 nm), ５ － Therefore, in the present invention, durability under high temperature environments is evaluated by evaluating the coloration of the polarizing film in terms of the single transmittance, and by evaluating the red color fading of the polarizing film in terms of the crossed transmittance at 700 nm.

[0020] In addition, when the polarizing film is exposed to a high temperature and humidity environment, the iodine complex (PVA-I), which is responsible for blue absorption (transmittance around 430 nm), ３ － Therefore, in the present invention, the durability under a high temperature and high humidity environment is evaluated by measuring the crossed transmittance at 430 nm for blue color fading of the polarizing film.

[0021] Furthermore, when a polarizing film is exposed to a weather-resistant environment, it undergoes photodegradation and polyenization occurs. Therefore, similarly to the above, durability in a weather-resistant environment is evaluated by the single transmittance of the polarizing film with respect to coloration.

[0022] In the polarizing film of the present invention, a compound having a nitroxy radical or a nitroxide group is presumably capable of efficiently capturing radicals generated in the polyenation reaction, thereby suppressing polyenation. However, if the polarizing film contains a specific amount or more of a compound having a nitroxy radical or a nitroxide group, blue color loss is likely to occur in a high-temperature, high-humidity environment. Furthermore, a compound having a carboxylic acid or a metal salt thereof is presumably capable of suppressing the dehydration reaction in the polyenation reaction, thereby suppressing polyenation due to heating. However, it is not very effective against polyenation due to photodegradation. Furthermore, if the polarizing film contains a specific amount or more of a compound having a carboxylic acid or a metal salt thereof, red color loss is likely to occur in a crossed Nicol state upon heating.

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

[0024] The polyvinyl alcohol (PVA) film is transparent in the visible light region and can be used without any particular limitation as long as it disperses and adsorbs iodine. The PVA film typically used as a raw sheet preferably has a thickness of about 1 to 100 μm, more preferably about 1 to 50 μm, and a width of about 100 to 5,000 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 their alkyl esters, modified with acrylamide, etc. The polyvinyl alcohol preferably has an average degree of polymerization of approximately 100 to 10,000, more preferably approximately 1,000 to 10,000, and even more preferably approximately 1,500 to 4,500. The polyvinyl alcohol preferably has a saponification degree of approximately 80 to 100 mol%, more preferably approximately 95 mol% to 99.95 mol%. The average degree of polymerization and the saponification degree can be determined in accordance with JIS K 6726.

[0026] The polyvinyl alcohol film may contain additives such as plasticizers and surfactants. Examples of the plasticizer include polyols such as glycerin, diglycerin, triglycerin, ethylene glycol, propylene glycol, and polyethylene glycol, and condensates thereof. The amount of the additive used is not particularly limited, but is preferably about 20% by weight or less of the polyvinyl alcohol film.

[0027] The polarizing film preferably has an iodine content of 1% by weight or more and 15% by weight or less. From the viewpoint of suppressing color fading during a durability test, the iodine content is preferably 1.5% by weight or more, and more preferably 2% by weight or more, and from the viewpoint of preventing polyenization, the iodine content is preferably 12% by weight or less, and more preferably 10% by weight or less.

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

[0029] As the compound having the nitroxy radical or nitroxide group, an N-oxyl compound (having a functional group of C—N(—C)—O) is preferred from the viewpoint of having a radical that is relatively stable in air at room temperature. ・ A compound having the formula (O ・ represents an oxy radical), and known compounds can be used. Examples of the compound having a nitroxy radical or a nitroxide group include the compounds described in WO 2019 / 103003. The compound having a nitroxy radical or a nitroxide group may be used alone or in combination of two or more types.

[0030] Furthermore, from the viewpoint of being able to efficiently capture radicals generated in the polyenation reaction, the compound having a nitroxy radical or a nitroxide group preferably has a molecular weight of 1,000 or less, more preferably 500 or less, and even more preferably 300 or less.

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

[0032] The compound containing the carboxylic acid or its metal salt may be a known compound. From the viewpoint of efficiently suppressing the dehydration reaction in the polyenation reaction, the carboxylic acid is preferably 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, and ethylenediamine-N,N,N',N'-tetraacetic acid. 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 capable of forming a salt with the carboxylic acid and dissociating from the carboxylic acid in water. The carboxylic acid or the compound containing the metal salt may be used alone or in combination of two or more.

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

[0034] <Method for Producing Polarizing Film> The method for producing a polarizing film of the present invention includes subjecting the polyvinyl alcohol film to any of a swelling step and a washing step, and at least a dyeing step, a crosslinking step, and a stretching step, and the treatment bath in one or more of the swelling step, the washing step, the dyeing step, the crosslinking step, and the stretching step preferably contains a compound having a nitroxy radical or a nitroxide group, and / or a carboxylic acid or a compound having a metal salt thereof. The contents of the compound having a nitroxy radical or a nitroxide group and the compound having a carboxylic acid or a metal salt thereof contained in the polarizing film can be controlled by the concentrations of the compound having a nitroxy radical or a nitroxide group and the compound having a carboxylic acid or a metal salt thereof contained in any of the treatment baths in the swelling step, the dyeing step, the crosslinking step, the stretching step, and the washing step, as well as the treatment temperature and treatment time in each of the treatment baths. In particular, when a washing step is carried out after the dyeing step, crosslinking step, and stretching step, the washing step makes it easy to adjust the content of the compound having a nitroxy radical or a nitroxide group and the content of the compound having a carboxylic acid or a metal salt thereof within a desired range, from the viewpoint of allowing components of the compound having a nitroxy radical or a nitroxide group and the compound having a carboxylic acid or a metal salt thereof to be eluted from or adsorbed onto the polyvinyl alcohol-based film, while taking into consideration the treatment conditions in the dyeing step, crosslinking step, stretching step, etc.

[0035] Each treatment bath in the swelling, dyeing, crosslinking, stretching, and washing steps 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 such as acetic acid, oxalic acid, and citric acid, and their salts; and inorganic weak acids such as phosphoric acid and carbonic acid, and their salts. 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 the compound having a nitroxide group, and the compound having a carboxylic acid or a metal salt thereof contained in any of the treatment baths cannot be determined in general because they are affected by the number of treatments, treatment time, treatment temperature, etc. of each treatment. However, from the viewpoint of efficiently controlling the contents of these compounds in the polarizing film, the concentrations are usually preferably 0.01% by weight or more, more preferably 0.05% by weight or more, and even more preferably 0.1% by weight or more, and 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 is a treatment step of immersing a polyvinyl alcohol-based film in a swelling bath, which can remove dirt and blocking agents from the surface of the polyvinyl alcohol-based film and suppress uneven dyeing by swelling the polyvinyl alcohol-based film. The swelling bath typically uses a medium whose main component is water, such as distilled water or pure water. The swelling bath may contain, as appropriate, surfactants, alcohols, and the like, according to conventional methods.

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

[0039] The dyeing process is a treatment process in which a polyvinyl alcohol-based film is immersed in a dye bath (iodine solution), allowing iodine to be adsorbed and oriented in the polyvinyl alcohol-based film. The iodine solution is typically preferably an aqueous iodine solution containing iodine and an iodide as a solubilizing agent. Examples of iodides include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. Among these, potassium iodide is preferred from the viewpoint of controlling the potassium content in the polarizing film.

[0040] The concentration of iodine in the dye bath is preferably about 0.01 to 1 wt %, more preferably about 0.02 to 0.5 wt %, and the concentration of iodide in the dye bath is preferably about 0.01 to 20 wt %, more preferably about 0.05 to 10 wt %, and even more preferably about 0.1 to 5 wt %.

[0041] The temperature of the dye bath is preferably about 10 to 50°C, more preferably about 15 to 45°C, and even more preferably about 18 to 30°C. The immersion time in the dye bath cannot be determined in general because the degree of dyeing of the polyvinyl alcohol film is affected by the temperature of the dye bath, but is preferably about 10 to 300 seconds, and more preferably about 20 to 240 seconds. The dyeing step may be carried out only once, or may be carried out multiple times as necessary.

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

[0043] The concentration of the boron compound in the crosslinking bath is preferably about 1 to 15 wt %, more preferably about 1.5 to 10 wt %, and even more preferably about 2 to 5 wt %. When potassium iodide is used in the crosslinking bath, the concentration of potassium iodide in the crosslinking bath is preferably about 1 to 15 wt %, more preferably about 1.5 to 10 wt %, and even more preferably about 2 to 5 wt %.

[0044] The temperature of the crosslinking bath is preferably about 20 to 70° C., more preferably about 30 to 60° C. The immersion time in the crosslinking bath cannot be determined in general because the degree of crosslinking of the polyvinyl alcohol film is affected by the temperature of the crosslinking bath, but is preferably about 5 to 300 seconds, more preferably about 10 to 200 seconds. The crosslinking step may be carried out only once, or may be carried out multiple times as necessary.

[0045] The stretching step is a treatment step of stretching a polyvinyl alcohol-based film at a predetermined stretching ratio in at least one direction. Generally, the polyvinyl alcohol-based film is uniaxially stretched in the conveying direction (longitudinal direction). The stretching method is not particularly limited, and either a wet stretching method or a dry stretching method can be used. The stretching step may be performed only once, or may be performed 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) used in the wet stretching method can typically contain water or a solvent such as a mixture of water and a water-miscible organic solvent. The stretching bath may contain potassium iodide to control 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 wt %, more preferably about 2 to 10 wt %, and even more preferably about 3 to 6 wt %. The treatment bath (stretching bath) may also contain a boron compound to prevent film breakage during stretching. In this case, the concentration of the boron compound in the stretching bath is preferably about 1 to 15 wt %, more preferably about 1.5 to 10 wt %, and even more preferably about 2 to 5 wt %.

[0047] The temperature of the stretching bath is preferably about 25 to 80°C, more preferably about 40 to 75°C, and even more preferably about 50 to 70°C. The immersion time in the stretching bath cannot be determined in general because the degree of stretching of the polyvinyl alcohol film is affected by the temperature of the stretching bath, but is preferably about 10 to 800 seconds, and more preferably about 30 to 500 seconds. The stretching treatment in the wet stretching method may be carried out 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-to-roll stretching method, a heated roll stretching method, a compression stretching method, etc. The dry stretching method may be carried out together with the drying step.

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

[0050] The washing step is a treatment step of immersing the polyvinyl alcohol-based film in a washing bath, and can remove foreign matter remaining on the surface of the polyvinyl alcohol-based film. The washing bath typically uses a medium containing water as its main component, such as water, distilled water, or pure water. Furthermore, in order to control the potassium content in the polarizing film, the washing bath may contain potassium iodide. In this case, the concentration of potassium iodide in the washing bath is preferably about 1 to 10 wt %, more preferably about 1.5 to 4 wt %, and even more preferably about 1.8 to 3.8 wt %.

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

[0052] The method for producing 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 washed in the washing step to obtain a polarizing film, and a polarizing film having a desired moisture content can be obtained by drying. The drying can be performed by any appropriate method, for example, natural drying, air drying, or heat drying.

[0053] The drying temperature is preferably about 20 to 150° C., more preferably about 25 to 100° C. The drying time cannot be determined in general because the degree of drying of the polarizing film is affected by the drying temperature, but is preferably about 10 to 600 seconds, more preferably about 30 to 300 seconds. The drying step may be carried out only once, or may be carried out multiple times as necessary.

[0054] The polarizing film preferably has a thickness of about 1 to 50 μm, more preferably about 1 to 25 μm, and even more preferably about 5 to 18 μm, from the viewpoints of productivity and the shrinkage force of the polarizing film during a high-temperature test. In particular, to obtain a polarizing film having a thickness of 8 μm or less, the following method for producing a thin polarizing film can be applied, in which a laminate including a polyvinyl alcohol-based resin layer formed on a resin substrate such as a thermoplastic resin is used as the polyvinyl alcohol-based film.

[0055] <Method for Manufacturing a Polarizing Film (Thin Polarizing Film)> A polarizing film (thin polarizing film) can be obtained by a conventional method for manufacturing a polarizing film, for example, 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 to prepare a laminate, and then, while transporting the obtained laminate in the longitudinal direction, subjecting the laminate to optional insolubilization treatment, crosslinking treatment, and washing treatment, and at least an auxiliary in-air stretching treatment, dyeing treatment, and underwater stretching treatment. The contents of the nitroxy radical or the compound having a nitroxide group, and the carboxylic acid or the compound having a metal salt thereof contained in the thin polarizing film can be controlled by the concentrations of the nitroxy radical or the compound having a nitroxide group, and the carboxylic acid or the compound having a metal salt thereof contained 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 treatment baths.

[0056] <Polarizing Film> The polarizing film of the present invention comprises the polarizing film and a transparent protective film attached 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. Examples of materials that can be used for the transparent protective film include thermoplastic resins that are excellent in transparency, mechanical strength, thermal stability, moisture barrier properties, and isotropy. Examples of thermoplastic resins include cellulose ester resins such as triacetyl cellulose, polyester resins such as polyethylene terephthalate and polyethylene naphthalate, polyethersulfone resins, polysulfone resins, polycarbonate resins, polyamide resins such as nylon and aromatic polyamide, polyimide resins, polyolefin resins such as polyethylene, polypropylene, and ethylene-propylene copolymers, (meth)acrylic resins, cyclic polyolefin resins (norbornene resins) having a cyclo- or norbornene structure, polyarylate resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof. The transparent protective film can also include a cured layer formed from a thermosetting resin or UV-curable resin, such as a (meth)acrylic, urethane, acrylic urethane, epoxy, or silicone resin. 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. In general, from the viewpoints of strength, workability such as handleability, thinness, etc., 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 films are attached 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 be a retardation plate having a front retardation of 40 nm or more and / or a thickness retardation of 80 nm or more. The front retardation is usually controlled to be in the range of 40 to 200 nm, and the thickness retardation is usually controlled to be in the range of 80 to 300 nm. When a retardation plate is used as the transparent protective film, the retardation plate also functions as the transparent protective film, thereby enabling a thinner film to be achieved.

[0061] Examples of the retardation plate include a birefringent film obtained by uniaxially or biaxially stretching a polymer material, an oriented film of a liquid crystal polymer, and an oriented layer of a liquid crystal polymer supported by a film. The thickness of the retardation plate is not particularly limited, but is generally about 20 to 150 μm. The retardation plate may be used by being attached to a transparent protective film that does not have a retardation.

[0062] The transparent protective film may contain any appropriate additive, such as an ultraviolet absorber, an antioxidant, a lubricant, a plasticizer, a release agent, a coloring inhibitor, a flame retardant, an antistatic agent, a pigment, a colorant, etc. In particular, when the transparent protective film contains an ultraviolet absorber, the light resistance of the polarizing film can be improved.

[0063] The surface of the transparent protective film to which the polarizing film is not attached may be provided with a functional layer such as a hard coat layer, an anti-reflection layer, an anti-sticking layer, a diffusion layer, an anti-glare layer, etc. The functional layer such as the hard coat layer, the anti-reflection layer, the anti-sticking layer, the diffusion layer, or the anti-glare layer may be provided on the protective film itself, or may 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 a pressure-sensitive adhesive layer or an adhesive layer.

[0065] The pressure-sensitive adhesive that forms the pressure-sensitive adhesive layer can be any of various pressure-sensitive adhesives used in polarizing films, including, for example, rubber-based pressure-sensitive adhesives, acrylic-based pressure-sensitive adhesives, silicone-based pressure-sensitive adhesives, urethane-based pressure-sensitive adhesives, vinyl alkyl ether-based pressure-sensitive adhesives, polyvinyl alcohol-based pressure-sensitive adhesives, polyvinyl pollidone-based pressure-sensitive adhesives, polyacrylamide-based pressure-sensitive adhesives, cellulose-based pressure-sensitive adhesives, etc. Among these, acrylic-based pressure-sensitive adhesives are preferred.

[0066] Examples of methods for forming the pressure-sensitive adhesive layer include a method in which the pressure-sensitive adhesive is applied to a release-treated separator or the like, dried to form a pressure-sensitive adhesive layer, and then transferred to a polarizing film or the like, or a method in which the pressure-sensitive adhesive is applied to a polarizing film or the like, and dried to form a pressure-sensitive adhesive layer, etc. The thickness of the pressure-sensitive adhesive layer is not particularly limited and is, for example, about 1 to 100 μm, and preferably about 2 to 50 μm.

[0067] The adhesive for forming the adhesive layer can be any of various adhesives used in polarizing films, including, for example, isocyanate-based adhesives, polyvinyl alcohol-based adhesives, gelatin-based adhesives, vinyl latex-based adhesives, and water-based polyester adhesives. These adhesives are typically used as aqueous solution adhesives (water-based adhesives) and contain 0.5 to 60% by weight of solids. Among these, polyvinyl alcohol-based adhesives are preferred, and acetoacetyl group-containing polyvinyl alcohol-based adhesives are more preferred.

[0068] The aqueous adhesive may contain a crosslinking agent. The crosslinking agent is typically a compound having at least two functional groups per molecule that are reactive with the polymer or other components that make up the adhesive, such as alkylenediamines; isocyanates; epoxies; aldehydes; and amino-formaldehydes such as methylol urea and methylol melamine. 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 or other components that make up the adhesive.

[0069] In addition to the above, examples of the adhesive include active energy ray-curable adhesives such as ultraviolet-curable adhesives and electron beam-curable adhesives. Examples of the active energy ray-curable adhesives include (meth)acrylate-based adhesives. Examples of the curable components in the (meth)acrylate-based adhesives include compounds having a (meth)acryloyl group and compounds having a vinyl group. Examples of the compound having a (meth)acryloyl group include alkyl (meth)acrylates such as linear alkyl (meth)acrylates, alicyclic alkyl (meth)acrylates, and polycyclic alkyl (meth)acrylates having 1 to 20 carbon atoms; hydroxyl group-containing (meth)acrylates; and epoxy group-containing (meth)acrylates such as glycidyl (meth)acrylate. The (meth)acrylate adhesive may contain a nitrogen-containing monomer such as hydroxyethyl (meth)acrylamide, N-methylol (meth)acrylamide, N-methoxymethyl (meth)acrylamide, N-ethoxymethyl (meth)acrylamide, (meth)acrylamide, or (meth)acryloylmorpholine. The (meth)acrylate adhesive may contain a polyfunctional monomer as a crosslinking component, such as tripropylene glycol diacrylate, 1,9-nonanediol diacrylate, tricyclodecane dimethanol diacrylate, cyclic trimethylolpropane formal acrylate, dioxane glycol diacrylate, or EO-modified diglycerin tetraacrylate. Furthermore, compounds containing epoxy groups or oxetanyl groups can also be used as cationic polymerization curing adhesives. The epoxy group-containing compound is not particularly limited as long as it has at least two epoxy groups in the molecule, and various commonly known curable epoxy compounds can be used.

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

[0071] The adhesive may be applied to either the transparent protective film side (or the functional layer side) or the polarizing film side, or to both. After lamination, a drying step is performed to form an adhesive layer consisting of a dried coated layer. After the drying step, ultraviolet light or electron beams may be irradiated as necessary. The thickness of the adhesive layer is not particularly limited, and is preferably about 30 to 5,000 nm, and more preferably about 100 to 1,000 nm, when a water-based adhesive or the like is used. When a UV-curable adhesive or an electron beam-curable adhesive is used, the thickness is preferably about 0.1 to 100 μm, and 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 via an intervening layer such as a surface modification treatment layer, an easy-adhesive layer, a blocking layer, or a refractive index adjustment layer.

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

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

[0075] The blocking layer has a function of preventing impurities such as oligomers and ions eluted from a transparent protective film, etc. from migrating (penetrating) into the polarizing film. The blocking layer may be any layer as long as it is transparent and can prevent impurities from eluting from a transparent protective film, etc. Examples of materials for forming the blocking layer include urethane prepolymer-based forming materials, cyanoacrylate-based forming materials, and epoxy-based forming materials.

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

[0077] <Laminated Polarizing Film> The laminated polarizing film (optical laminate) of the present invention is one in which the polarizing film is bonded to an optical layer. The optical layer is not particularly limited, and for example, one or more optical layers that are sometimes used in forming liquid crystal displays, such as a reflector, a semi-transmitting plate, a retardation plate (including a half-wave or quarter-wave plate), or a viewing angle compensation film, can be used. Examples of the laminated polarizing film include a reflective polarizing film or a semi-transmitting polarizing film obtained by laminating a reflector or semi-transmitting reflector on the polarizing film, an elliptical polarizing film or a circular polarizing film obtained by laminating a retardation plate on the polarizing film, a wide-viewing angle polarizing film obtained by laminating a viewing angle compensation film on the polarizing film, and a polarizing film obtained by laminating a brightness enhancement film on the polarizing film.

[0078] An adhesive layer may be provided on one or both surfaces 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 other components, such as a front transparent plate or a front transparent member such as a touch panel on the viewing side. A pressure-sensitive adhesive layer is suitable as the adhesive layer. The pressure-sensitive adhesive forming the pressure-sensitive adhesive layer is not particularly limited, and may be appropriately selected from those having a base polymer such as an acrylic polymer, a silicone polymer, polyester, polyurethane, polyamide, polyether, a fluorine-based polymer, or a rubber-based polymer. In particular, pressure-sensitive adhesives that have excellent optical transparency, moderate wettability, cohesion, and adhesive properties, and excellent weather resistance, heat resistance, etc., such as pressure-sensitive adhesives containing acrylic polymers, are preferably used.

[0079] The application of a pressure-sensitive adhesive layer to one or both surfaces of the polarizing film or the laminate polarizing film can be performed by any suitable method. Examples of application of a pressure-sensitive adhesive layer include preparing a pressure-sensitive adhesive solution and applying it directly to the polarizing film or the laminate polarizing film by a suitable application method such as a casting method or a coating method, or forming a pressure-sensitive adhesive layer on a separator and then transferring it onto the polarizing film or the laminate polarizing film. The thickness of the pressure-sensitive adhesive layer can be determined appropriately depending on the intended use, adhesive strength, etc., and is generally 1 to 500 μm, preferably 5 to 200 μm, and more preferably 10 to 100 μm. Thus, a polarizing film or a laminate polarizing film having a pressure-sensitive adhesive layer on at least one surface thereof is referred to as a pressure-sensitive adhesive layer-attached polarizing film or a pressure-sensitive adhesive layer-attached laminate polarizing film.

[0080] It is preferable that a separator be temporarily attached to cover the exposed surface of the pressure-sensitive adhesive layer to prevent contamination, etc., until the product is put into practical use. This prevents contamination, etc., of the pressure-sensitive adhesive layer under normal handling conditions. Examples of the separator include suitable thin sheets such as plastic films, rubber sheets, paper, cloth, nonwoven fabrics, nets, foam sheets, metal foils, and laminates thereof, which are coated with a suitable release agent, such as a silicone-based, long-chain alkyl-based, fluorine-based, or molybdenum sulfide-based release agent, as needed.

[0081] <Image Display Panel and Image Display Device> The image display panel of the present invention comprises an image display cell to which the polarizing film or the laminated polarizing film is attached, and the image display device of the present invention comprises 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 a liquid crystal cell and an organic EL cell. The liquid crystal cell may be, for example, a reflective liquid crystal cell that uses external light, a transmissive liquid crystal cell that uses light from a light source such as a backlight, or a semi-transmissive semi-reflective liquid crystal cell that uses both external light and light from the light source. When the liquid crystal cell uses light from a light source, the image display device (liquid crystal display device) has a polarizing film disposed on the opposite side of the image display cell (liquid crystal cell) from the viewing side, and further has a light source disposed thereon. The polarizing film on the light source side and the liquid crystal cell are preferably bonded together via an appropriate adhesive layer. The liquid crystal cell may be driven in any mode, such as VA mode, IPS mode, TN mode, STN mode, or bend alignment (π type).

[0083] The organic EL cell is preferably, for example, a cell in which a light-emitting body (organic electroluminescence light-emitting body) is formed by sequentially laminating a transparent electrode, an organic light-emitting layer, and a metal electrode on a transparent substrate. 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 such a light-emitting layer 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 the front transparent member disposed on the viewing side of the image display cell include a front transparent plate (window layer) and a touch panel. A transparent plate having appropriate mechanical strength and thickness is used as the front transparent plate. Examples of such transparent plates include transparent resin plates such as acrylic resins and polycarbonate resins, and glass plates. Examples of the touch panel include various touch panels such as resistive, capacitive, optical, and ultrasonic touch panels, as well as glass or transparent resin plates equipped with touch sensor functions. 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 on the viewing side of the touch panel.

[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 Preparation of Polarizing Film A polyvinyl alcohol film having 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 swelling bath (water bath) at 30° C. for 30 seconds between rolls with different peripheral speed ratios, and stretched 2.2 times in the conveyance direction while swelling (swelling step). Subsequently, the film was immersed in a dye bath at 30° C. (iodine aqueous solution obtained by blending iodine and potassium iodide at a weight ratio of 1:7 with 100 parts by weight of water) at 30° C. for 30 seconds while adjusting the iodine concentration so that the polarizing film had a predetermined transmittance. The film was then stretched 3.3 times in the conveyance direction relative to the original polyvinyl alcohol film (a polyvinyl alcohol film that was not stretched in the conveyance direction) while dyeing (dyeing step). Next, the dyed polyvinyl alcohol film was immersed in a crosslinking bath (aqueous solution containing boric acid at a concentration of 3.5 wt %, potassium iodide at a concentration of 3.0 wt %, and zinc sulfate at a concentration of 3.6 wt %) at 40°C for 28 seconds, and stretched to 3.6 times the original size of the polyvinyl alcohol film in the conveyance direction (crosslinking step). The resulting polyvinyl alcohol film was then immersed in a 64°C stretching bath (an aqueous solution containing 4.8 wt% boric acid, 5.0 wt% potassium iodide, and 5.0 wt% zinc sulfate) for 60 seconds to be stretched to 6.0 times the original size in the conveying direction (stretching step), followed by immersion in a 25°C washing bath (an aqueous solution containing 3.0 wt% potassium iodide, 0.4 wt% of a compound having a nitroxy radical or a nitroxide group represented by the following general formula (1), and 0.5 wt% of a carboxylic acid compound having a carboxylic acid represented by the following general formula (2) or a metal salt thereof) for 10 seconds (washing step). The washed polyvinyl alcohol film was then dried at 40°C for 30 seconds to produce a polarizing film. The following measurement methods were used to determine the content of a compound having a nitroxy radical or a nitroxide group in the polarizing film, as calculated by HPLC analysis: (A) the content of a compound having a nitroxy radical or a nitroxide group in the polarizing film was 0.14 wt %, and (B) the content of a carboxylic acid or a carboxylic acid compound having a metal salt thereof in the polarizing film, as calculated by HPLC analysis: 0.09 wt %. The iodine content in the polarizing film, as calculated by the following measurement method, was 3.66 wt %. The polarizing film had a thickness of 17 μm.

[0087] <(A) Method for Measuring the Content (% by Weight) of a Compound Having a Nitroxy Radical or a Nitroxide Group in a Polarizing Film> Approximately 20 mg of polarizing film was collected, weighed, and dissolved by heating in 1 mL of water, and then diluted with 4.5 mL of methanol. The resulting extract was filtered through a membrane filter, and the concentration of the nitroxy radical or the compound having a nitroxide group in the filtrate was measured using HPLC (manufactured by Thermo Fisher Scientific, Vanquish).

[0088] <(B) Method for Measuring the Content (% by Weight) of Carboxylic Acid or Carboxylic Acid Compound Having Metal Salt Thereof in Polarizing Film> Approximately 20 mg of polarizing film was sampled and weighed, 1 mL of DMSO was added, and the mixture was heated and extracted at 120°C for 1 hour. 3 mL of acetonitrile was added to this solution to reprecipitate the polymer component, and the supernatant was filtered through a membrane filter. The filtrate was subjected to HPLC (manufactured by Thermo Fisher Scientific, Vanquish) to measure the concentration of the carboxylic acid or the carboxylic acid compound having a metal salt thereof.

[0089] <Method for Measuring Iodine Content (% by Weight) in Polarizing Film> The iodine concentration (% by weight) of a polarizing film was determined using an X-ray fluorescence analyzer (manufactured by Rigaku Corporation, trade name "ZSX-PRIMUS IV", measuring diameter: ψ20 mm) according to the following formula: Iodine concentration (wt%)=14.474×(X-ray fluorescence intensity) / (film thickness)(kc ps / μm). Note that the coefficient used to calculate the concentration differs depending on the measuring device, but the coefficient can be determined using an appropriate calibration curve.

[0090] <Preparation of Polarizing Film> An aqueous solution containing an acetoacetyl group-containing polyvinyl alcohol resin (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 as an adhesive. Using this adhesive, a 47 μm-thick triacetyl cellulose film (moisture permeability: 340 g / (m)) having a hard coat layer was attached as a transparent protective film to both sides of the polarizing film obtained above. ２The polarizing film was then heated and dried in an oven (at 60°C for 4 minutes) to produce a polarizing film in which transparent protective films were laminated on both sides of the polarizing film. The single transmittance of the polarizing film was 40.3%.

[0091] <Preparation of Polarized Film with Pressure-Sensitive Adhesive Layer> A monomer mixture containing 99 parts of butyl acrylate and 1 part of 4-hydroxybutyl acrylate was charged into a four-neck flask equipped with a stirring blade, a thermometer, a nitrogen gas inlet tube, and a condenser. Furthermore, 0.1 parts of 2,2'-azobisisobutyronitrile as a polymerization initiator and 100 parts of ethyl acetate were charged to 100 parts of the monomer mixture (solid content). Nitrogen gas was introduced with gentle stirring to replace the atmosphere with nitrogen, and the liquid temperature in the flask was maintained at around 55°C to carry out a polymerization reaction for 8 hours to prepare a solution of an acrylic polymer having a weight average molecular weight (Mw) of 1,800,000. Thereafter, 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 blended with 100 parts of the solids content of the resulting acrylic polymer solution to prepare a solution of an acrylic pressure-sensitive adhesive composition. The solution of the acrylic pressure-sensitive adhesive composition obtained above was then applied to one side of a polyethylene terephthalate film (manufactured by Mitsubishi Chemical Polyester Film Co., Ltd., trade name "MRF38", separator film) that had been treated with a silicone release agent, so that the thickness of the pressure-sensitive adhesive layer after drying would be 20 μm, and the coating was dried at 90°C for 1 minute to form a pressure-sensitive adhesive layer on the surface of the separator film. The pressure-sensitive adhesive layer formed on the separator film was then transferred to one side of the polarized film prepared above, to prepare a polarized film with a pressure-sensitive adhesive layer.

[0092] [Evaluation of Single-Phase Transmittance and Tc700nm in a High-Temperature Environment] The polarizing film with the adhesive layer obtained above was cut into a size of 40 x 40 mm, and a glass plate (pseudo-image display cell) was attached to the adhesive layer to produce a laminate. The resulting laminate was placed in a hot air oven at 110°C for 1,000 hours, and the change in single-ply transmittance (ΔTs) and the change in crossed transmittance at 700 nm (ΔTc700) before and after heating were measured. The single-ply transmittance and crossed transmittance were measured using a spectrophotometer (manufactured by Otsuka Electronics Co., Ltd., product name "LPF-200") and evaluated according to the following criteria. The transmittance was the Y value corrected for luminosity using a 2-degree visual field (light source C) according to JIS Z8701-1982. The measurement wavelength was 380 to 700 nm (5 nm intervals). The results are shown in Table 1. [Criteria for determining change in single layer transmittance] ΔTs(%) = Ts(1000h) - Ts(0h) Here, Ts(0h) is the single layer transmittance of the laminate before heating, and Ts(1000h) is the single layer transmittance of the laminate after heating for 1000 hours. ○: 5≧ΔTs(%)≧0 ×: ΔTs(%)>5 or ΔTs(%)<0 [Criteria for determining change in cross transmittance] ΔTc700(%) = Tc700(1000h) - Tc700(0h) Here, Tc700(0h) is the cross layer transmittance at 700 nm of the laminate before heating, and Tc700(1000h) is the cross layer transmittance at 700 nm of the laminate after heating for 1000 hours. ○: 10≧ΔTc700(%)≧0 ×: ΔTc700(%)>10 or ΔTc700(%)<0

[0093] [Evaluation of Tc430 in a High-Temperature, High-Humidity Environment] A laminate was prepared in the same manner as above, and the resulting laminate was left to stand in an oven at a temperature of 65°C and a humidity of 95% RH for 1000 hours. The change in cross transmittance (ΔTc430) at 430 nm before and after humidification was measured. The cross transmittance was measured using a spectrophotometer (manufactured by Otsuka Electronics Co., Ltd., product name "LPF-200") and evaluated according to the following criteria. [Criteria for Determining Change in Cross Transmittance] ΔTc430 (%) = Tc430 (1000 h) - Tc430 (0 h) Here, Tc430 (0 h) is the cross transmittance at 430 nm of the laminate before humidification, and Tc430 (1000 h) is the cross transmittance at 430 nm of the laminate after humidification for 1000 hours. ○: 2≧ΔTc430(%)≧0 ×: ΔTc430(%)>2 or ΔTc430(%)<0

[0094] [Evaluation of Single Unit Transmittance in Weather-Resistant Environment] A laminate was prepared in the same manner as above, and the obtained laminate was measured using a xenon weather meter (manufactured by Suga Test Instruments Co., Ltd., product name "NX-75", irradiance: 64 W / m ２ The laminate was left to stand for 750 hours in a BPT temperature of 100°C, a temperature inside the chamber of 65°C, and a humidity inside the chamber of 30%, and the single unit transmittance (ΔTs) before and after the test was measured. The single unit transmittance was measured using a spectrophotometer (Otsuka Electronics Co., Ltd., product name "LPF-200") and evaluated according to the following criteria. The transmittance is a Y value corrected for visibility using a 2-degree visual field (C light source) according to JIS Z8701-1982. The measurement wavelength was 380 to 700 nm (every 5 nm). The results are shown in Table 1. [Criteria for determining change in single unit transmittance] ΔTs (%) = Ts (750 h) - Ts (0 h) where Ts (0 h) is the single unit transmittance of the laminate before the weather resistance test, and Ts (750 h) is the single unit transmittance of the laminate after the 750-hour weather resistance test. ○: 5≧ΔTs(%)≧0 ×: ΔTs(%)>5 or ΔTs(%)<0

[0095] Examples 2-14 Preparation of Polarizing Film and Polarizing Film A polarizing film and a polarizing film were prepared in the same manner as in Example 1, except that the concentrations of the compound having a nitroxy radical or a nitroxide group represented by general formula (1) and the carboxylic acid compound having a metal salt thereof represented by general formula (2) in the cleaning bath were changed to the values ​​shown in Table 1. The thickness of the obtained polarizing film, the single transmittance of the polarizing film, the content of the compound having a nitroxy radical or a nitroxide group in the polarizing film, and the content of the carboxylic acid or the carboxylic acid compound having a metal salt thereof in the polarizing film are shown in Table 1. In Example 14, a 47 μm-thick triacetyl cellulose film (with a moisture permeability of 342 g / (m ２ 24h) was attached to the other side of the polarizing film, and a 30 μm polymethyl methacrylate film (with a moisture permeability of 100 g / (m ２ 24h), manufactured by Toyo Kohan, product name "RZ30") was bonded to the board.

[0096] Example 15 Preparation of Polarizing Film and Polarizing Film A polarizing film and a polarizing film were prepared in the same manner as in Example 1, except that in the preparation of the polarizing film, the concentration of the compound having a nitroxy radical or a nitroxide group represented by general formula (1) in the cleaning bath was changed to the value shown in Table 1, the carboxylic acid or the carboxylic acid compound having a metal salt thereof in the cleaning bath was changed to compounds of general formulas (3) and (4), and the molar concentrations of the carboxylic acid compound having a carboxylic acid or a metal salt thereof in the cleaning bath were adjusted so that (3) was 0.05 M, (4) was 0.05 M, and the total of (3) and (4) was 0.10 M. Table 1 shows the thickness of the obtained polarizing film, the single transmittance of the polarizing film, the content of the compound having a nitroxy radical or a nitroxide group in the polarizing film, and the content of the carboxylic acid compound having a carboxylic acid or a metal salt thereof in the polarizing film.

[0097] Examples 16-19 Preparation of Polarizing Film and Polarizing Film Polarizing films and films were prepared in the same manner as in Example 1, except that in the preparation of the polarizing film, the concentration of the compound having a nitroxy radical or a nitroxide group represented by general formula (1) in the cleaning bath was changed to the value shown in Table 1, the carboxylic acid or a carboxylic acid compound having a metal salt thereof in the cleaning bath was changed to one of general formulas (5) to (8), and the molar concentration of the carboxylic acid compound having a carboxylic acid or a metal salt thereof in the cleaning bath was adjusted to 0.05 M. The thickness of the obtained polarizing film, the single transmittance of the polarizing film, the content of the compound having a nitroxy radical or a nitroxide group in the polarizing film, and the content of the carboxylic acid or a carboxylic acid compound having a metal salt thereof in the polarizing film are shown in Table 1.

[0098] Comparative Example 1-6 Preparation of Polarizing Film and Polarizing Film A polarizing film and a polarizing film were prepared in the same manner as in Example 1, except that in the preparation of the polarizing film, the concentrations of the compound having a nitroxy radical or a nitroxide group represented by general formula (1) and the carboxylic acid compound having a carboxylic acid represented by general formula (2) or a metal salt thereof in the cleaning bath were changed to the values ​​shown in Table 1. The thickness of the obtained polarizing film, the single transmittance of the polarizing film, the content of the compound having a nitroxy radical or a nitroxide group in the polarizing film, and the content of the carboxylic acid or a metal salt thereof in the polarizing film are shown in Table 1.

[0099] The polarizing films of the examples and comparative examples obtained above were used to carry out the above-mentioned evaluations. The results are shown in Table 1.

[0100]

Claims

A polarizing film formed by adsorbing and orienting iodine on a polyvinyl alcohol film, A polarizing film comprising 0.05% by weight or more and 0.55% by weight or less of a compound having a nitroxy radical or a nitroxide group, and 0.05% by weight or more and 0.65% by weight or less of a compound having a carboxylic acid or a metal salt thereof.

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

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

3. The polarizing film according to claim 1, wherein the film thickness is 18 μm or less. 　 A polarizing film comprising the polarizing film according to claim 1 or 2 and a transparent protective film attached to at least one surface of the polarizing film. 　 A laminated polarizing film, comprising the polarizing film according to claim 5 bonded to an optical layer.

6. An image display panel comprising an image display cell and the polarizing film according to claim 5 attached thereto. 　 An image display panel, comprising an image display cell and the laminated polarizing film according to claim 6 attached thereto. 　 An image display device comprising: a front transparent member on the polarizing film side of the image display panel according to claim 7.

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