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

Abstract

This polarization film comprises a polarization membrane having a transparent protective film attached to both sides thereof. The polarization membrane: is formed of a polyvinyl alcohol-based film to which iodine is adsorbed and oriented; and has an iodine concentration of 3-10 wt%. At least one of the transparent protective films has a moisture permeability of 200 g / (m2∙24 h) or less. The polarization film comprises the condition that the change amount (ΔTs) of single film transmittance represented by general formula (1): ΔTs (%) = Ts750 - Ts0. The polarization film: has excellent initial polarization performance; excels in suppressing the deterioration in single film transmittance in a high-temperature environment, such deterioration being caused by coloring of the polarization membrane; and also excels in suppressing a deterioration in polarization performance in a high-temperature / high-humidity environment (humidity resistance).

Description

[Technical Field]

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

[0002] Conventionally, dyed polyvinyl alcohol films (containing dichroic substances such as iodine or 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 polyvinyl alcohol films 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) or a front transparent member such as a touch panel on the viewing side via a pressure-sensitive adhesive layer or an adhesive layer, and is used as the various image display devices mentioned above (Patent Document 1).

[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 rearview monitors. Accordingly, the image display devices are required to have higher durability in harsher environments (for example, high-temperature environments) than has been conventionally required, and an image display device intended to ensure such durability has been proposed (Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-102353 [Patent Document 2] Japanese Patent Application Publication No. 2018-101117 Summary of the Invention [Problem to be solved by the invention]

[0006] When polarizing films or laminated polarizing films using iodine-based polarizing films are exposed to high-temperature environments, the polyvinyl alcohol that constitutes the polarizing film undergoes a dehydration reaction to become polyenated, causing coloration of the polarizing film and a decrease in its individual transmittance.

[0007] As a result of extensive research, the present inventors have found that iodine contained in iodine-based polarizing films promotes polyenation in high-temperature environments. Therefore, reducing the iodine concentration (content) in the polarizing film is effective in suppressing a decrease in the single-unit transmittance due to coloration of the polarizing film in high-temperature environments. However, when such a polarizing film is used, peeling of the polarizing film or laminated polarizing film tends to occur easily when heated, as the panels of image display devices become larger.

[0008] Furthermore, polarizing films and laminated polarizing films have the problem that, in a high-temperature and high-humidity environment, the boric acid crosslinks in the polarizing film are released and the iodine complex is broken, resulting in a decrease in polarization degree.

[0009] In view of the above circumstances, an object of the present invention is to provide a polarizing film having a polarizing film that has a good initial polarization degree, is excellent in the effect of suppressing a decrease in the single-piece transmittance due to coloration of the polarizing film in a high-temperature environment, and is also excellent in the effect of suppressing a decrease in the polarization degree in a high-temperature and high-humidity environment (humidification durability).

[0010] Another object of the present invention is to provide a laminated polarizing film, an image display panel, and an image display device using the above polarizing film. [Means for solving the problem]

[0011] That is, the present invention provides a polarizing film in which transparent protective films are bonded to both sides of a polarizing film, the polarizing film being formed by adsorbing and orienting iodine on a polyvinyl alcohol-based film, and the iodine concentration is 3% by weight or more and 10% by weight or less, and at least one of the transparent protective films has a moisture permeability of 200 g / (m 2 24h) or less, and the polarizing film has a refractive index of ΔTs(%)=Ts 750 -Ts0 (in the general formula (1), Ts0 is the single transmittance of a laminate in which a glass plate is bonded to one surface of the polarizing film via a pressure-sensitive adhesive layer, and Ts 750 represents the single-piece transmittance after the laminate is heat-treated at 105°C for 750 hours.) The polarizing film satisfies the condition that the change in single-piece transmittance (ΔTs) represented by is 0% or more and 5% or less.

[0012] The present invention also relates to a laminated polarizing film in which the polarizing film is bonded to an optical layer.

[0013] 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.

[0014] The present invention also relates to an image display device comprising a front transparent member on the polarizing film or laminated polarizing film side of the image display panel. [Effects of the Invention]

[0015] Although the details of the mechanism of action of the polarizing film of the present invention are unclear, it is presumed as follows: However, the present invention should not be construed as being limited to this mechanism of action.

[0016] The polarizing film of the present invention is a polarizing film in which transparent protective films are bonded to both sides of a polarizing film, and the polarizing film is formed by adsorbing and aligning iodine on a polyvinyl alcohol-based film, and the iodine concentration is 3% by weight or more and 10% by weight or less, and at least one of the transparent protective films has a moisture permeability of 200 g / (m 2 24h) or less, and the polarizing film has a refractive index of ΔTs(%)=Ts 750 -Ts0 (in the general formula (1), Ts0 is the single transmittance of a laminate in which a glass plate is bonded to one surface of the polarizing film via a pressure-sensitive adhesive layer, and Ts 750 represents the single-layer transmittance after the laminate is heat-treated at 105°C for 750 hours. This polarizing film satisfies the condition that the change in single-layer transmittance (ΔTs) expressed by (ΔTs) is 0% or more and 5% or less. The polarizing film of the present invention exhibits a small change in single-layer transmittance (ΔTs) after the heat treatment (in a high-temperature environment), thereby suppressing a decrease in single-layer transmittance due to coloration of the polarizing film. The reason for the small change in single-layer transmittance (ΔTs) before and after the heat treatment is presumably because the temperature at which the dehydration reaction due to polyenation occurs in the polarizing film of the present invention is higher than that of conventional polarizing films. In particular, the heat treatment is a heat durability test used as an indicator of the heat resistance of in-vehicle displays, and is more severe than conventional heat durability tests. Furthermore, by setting the iodine concentration in the polarizing film within a certain range, the polarizing film of the present invention exhibits a good initial polarization degree while controlling the temperature at which the dehydration reaction due to polyenation occurs to a higher temperature.

[0017] In addition, in the polarizing film of the present invention, at least one of the transparent protective films has a moisture permeability of 200 g / (m 2 24h or less), preventing water from entering the polarizing film and providing excellent resistance to deterioration of polarization even in high-temperature, high-humidity environments (humidity durability). DETAILED DESCRIPTION OF THE INVENTION

[0018] <Polarizing film> The polarizing film of the present invention is an iodine-based polarizing film formed by adsorbing and aligning iodine in a polyvinyl alcohol-based film, and has an iodine concentration of 3% by weight or more and 10% by weight or less. The polyvinyl alcohol (PVA)-based film can be any film that is translucent in the visible light region and disperses and adsorbs iodine. The PVA-based 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.

[0019] 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.

[0020] 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 additives used is not particularly limited, but is preferably about 20% by weight or less of the polyvinyl alcohol film.

[0021] The polarizing film has an iodine concentration (content) of 3% by weight or more and 10% by weight or less, from the viewpoints of improving the initial polarization degree of the polarizing film and increasing the temperature at which a dehydration reaction due to polyenization occurs. The polarizing film has an iodine concentration (content) of preferably 3.5% by weight or more, and more preferably 4% by weight or more, from the viewpoints of improving the initial polarization degree of the polarizing film, and preferably 9% by weight or less, more preferably 7% by weight or less, even more preferably 6% by weight or less, and most preferably 5% by weight or less, from the viewpoint of increasing the temperature at which a dehydration reaction due to polyenization occurs.

[0022] The polarizing film preferably contains a compound having a radical scavenging function. It is believed that the compound having a radical scavenging function can capture radicals generated by heating the polyvinyl alcohol of the polarizing film, thereby enabling the temperature at which the dehydration reaction of polyenization occurs to be set to a higher temperature. Examples of the compound having a radical scavenging function include hindered phenols, hindered amines, phosphorus compounds, sulfur compounds, benzotriazoles, benzophenones, hydroxylamines, salicylic acid esters, and triazines. From the viewpoint of easily enabling the temperature at which the dehydration reaction of polyenization occurs to be set to a higher temperature, the compound having a radical scavenging function is preferably, for example, a compound having a nitroxy radical or a nitroxide group. The radical scavenging compound may be used alone or in combination of two or more types.

[0023] As the nitroxy radical or the compound having a nitroxide group, an N-oxyl compound (having a functional group of CN(-C)-O) is preferred from the viewpoint of having a radical that is relatively stable in air at room temperature. · Compounds having the formula (O · The nitroxy radical or the compound having a nitroxide group includes, for example, a compound having an organic group having the following structure: [ka] (In general formula (1), R 1 represents an oxy radical, and R 2 From R 5 are independently a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and n is 0 or 1.) In addition, in general formula (1), the left side of the dotted line represents any organic group.

[0024] Examples of the compound having the organic group include compounds represented by the following general formulas (2) to (5). [ka] (In general formula (2), R 1 ~R 5 , and n are the same as above, and R 6 represents a hydrogen atom, or an alkyl group, acyl group, or aryl group having 1 to 10 carbon atoms, and n represents 0 or 1. [ka] (In general formula (3), R 1 From R 5 , and n are the same as above, and R 7 and R 8 each independently represents a hydrogen atom, or an alkyl group, acyl group, or aryl group having 1 to 10 carbon atoms. [ka] (In general formula (4), R 1 From R 5 , and n are the same as above, and R 9 From R 11 are independently a hydrogen atom, or an alkyl group having 1 to 10 carbon atoms, an acyl group, an amino group, an alkoxy group, a hydroxy group, or an aryl group. [ka] (In general formula (5), R 1 From R 5, and n are the same as above, and R 12 represents a hydrogen atom, or an alkyl group having 1 to 10 carbon atoms, an amino group, an alkoxy group, a hydroxy group, or an aryl group.

[0025] In the general formulas (1) to (5), R 2 From R 5 From the viewpoint of availability, R is preferably an alkyl group having 1 to 6 carbon atoms, and more preferably an alkyl group having 1 to 3 carbon atoms. 6 is preferably a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and more preferably a hydrogen atom. 7 and R 8 are preferably independently a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and more preferably a hydrogen atom. 9 From R 11 is preferably a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. 12 is preferably a hydroxy group, an amino group, or an alkoxy group. In the general formulae (1) to (5), n is preferably 1 from the viewpoint of availability.

[0026] Examples of the compound having a nitroxy radical or a nitroxide group include the following compounds: [ka] (In general formula (6), R represents a hydrogen atom, or an alkyl group, acyl group, or aryl group having 1 to 10 carbon atoms.) [ka] [ka]

[0027] Furthermore, from the viewpoint of being able to efficiently capture radicals generated in the polyenation reaction, the compound having a radical scavenging function preferably has a molecular weight of 1,000 or less, more preferably 500 or less, and even more preferably 300 or less.

[0028] Furthermore, from the viewpoint of ease of migration into the moisture in the polarizing film, the compound having radical scavenging functionality is preferably a water-soluble compound that can be dissolved in 1 part by weight or more in 100 parts by weight of water at 25°C, more preferably a water-soluble compound that can be dissolved in 2 parts by weight or more in 100 parts by weight of water at 25°C, and even more preferably a water-soluble compound that can be dissolved in 5 parts by weight or more in 100 parts by weight of water at 25°C.

[0029] When the polarizing film contains the compound having a radical scavenging function, the content of the compound having a radical scavenging function in the polarizing film is preferably 0.01% by weight or more, more preferably 0.02% by weight or more, and even more preferably 0.05% by weight or more, from the viewpoint of suppressing a decrease in the single-unit transmittance due to coloration of the polarizing film in a high-temperature environment, and from the viewpoint of appearance, the content is preferably 10% by weight or less, more preferably 7% by weight or less, and even more preferably 3% by weight or less.

[0030] The polarizing film preferably contains chlorine ions (chloride ions), which are deliquescent and are thought to delay the dehydration reaction of the polyvinyl alcohol in the polarizing film caused by heating, thereby enabling the temperature at which the dehydration reaction of polyenization occurs to be set to a higher temperature.

[0031] When the polarizing film contains chlorine ions (chloride ions), the content of the chlorine ions in the polarizing film is preferably more than 2 wt %, more preferably 2.5 wt % or more, and even more preferably 3 wt % or more, from the viewpoint of suppressing a decrease in the single-piece transmittance due to coloration of the polarizing film in a high-temperature environment, and is preferably 10 wt % or less, more preferably 7 wt % or less, and even more preferably 5 wt % or less, from the viewpoint of preventing a change in hue of the polarizing film in a high-temperature environment.

[0032] <Method of manufacturing polarizing film> The polarizing film is obtained by subjecting the polyvinyl alcohol-based film to any of a swelling step, a washing step, and at least a dyeing step, a crosslinking step, and a stretching step. The iodine content in the polarizing film can be controlled by the concentration of the iodine and iodides such as potassium iodide contained in any of the treatment baths in the swelling step, the dyeing step, the crosslinking step, the stretching step, and the washing step, and by the treatment temperature and treatment time in each of the treatment baths.

[0033] Furthermore, when producing a polarizing film containing the compound having radical scavenging function, the compound having radical scavenging function may be contained in one or more treatment baths of the swelling step, the washing step, the dyeing step, the crosslinking step, and the stretching step. The concentration of the compound having radical scavenging function contained in any of the treatment baths cannot be determined in general because it is affected by the number of treatments, treatment time, treatment temperature, etc. of each treatment. However, from the viewpoint of efficiently controlling the content of the compound having radical scavenging function in the polarizing film, the concentration is usually preferably 0.03 wt % or more, more preferably 0.05 wt % or more, and even more preferably 0.1 wt % or more, and preferably 15 wt % or less, more preferably 10 wt % or less, and even more preferably 5 wt % or less.

[0034] 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 iodine or the compound having a radical scavenging function to a desired range, from the viewpoint of allowing components such as iodine and the compound having a radical scavenging function to be eluted from or adsorbed onto the polyvinyl alcohol-based film, while taking into consideration the processing conditions in the dyeing step, crosslinking step, stretching step, etc.

[0035] Furthermore, when producing a polarizing film containing the compound having radical scavenging function, an aqueous solution containing the compound having radical scavenging function may be applied to the polarizing film to impregnate it. The application step may be performed before or after any of the swelling step, dyeing step, crosslinking step, stretching step, and washing step. In particular, it is preferable to perform the application step after the washing step, from the viewpoint of easily adjusting the content of the compound having radical scavenging function to a desired range. The application method is not particularly limited, and examples thereof include wire bar coating, gravure coating, and spraying.

[0036] Furthermore, each treatment bath in the swelling, dyeing, crosslinking, stretching, and washing processes 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 salts thereof, and inorganic weak acids such as phosphoric acid and carbonic acid, and salts thereof. 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. In particular, from the viewpoint of obtaining a polarizing film that can suppress a decrease in the single-piece transmittance due to coloration of the polarizing film in a high-temperature environment, it is preferable that one or more of the treatment baths contain a chloride.

[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 step is a treatment step in which the polyvinyl alcohol film is immersed in a dye bath (iodine solution), and iodine can be adsorbed and oriented in the polyvinyl alcohol film. The iodine solution is usually preferably an aqueous iodine solution, and contains iodine and an iodide as a solubilizing agent. Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. 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% by weight, more preferably about 0.02 to 0.5% by weight, and the concentration of iodide in the dye bath 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 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 the 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% by weight, more preferably about 1.5 to 10% by weight, and even more preferably about 2 to 5% by weight. 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 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 in which a polyvinyl alcohol-based film is stretched at least in one direction to a predetermined stretching ratio. 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 carried out only once, or may be carried out multiple times as necessary. The stretching step may be carried out at any stage in the production of a polarizing 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 the 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 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. 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 30°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 1 μm or more, more preferably 2 μm or more, from the viewpoint of improving the initial polarization degree of the polarizing film, and preferably has a thickness of 20 μm or less, more preferably 18 μm or less, and even more preferably 15 μm or less, from the viewpoint of preventing peeling due to heat. In particular, to obtain a polarizing film having a thickness of about 8 μm or less, the following method for producing a thin polarizing film can be applied, in which the polyvinyl alcohol-based film is a laminate including a polyvinyl alcohol-based resin layer formed on a thermoplastic resin substrate.

[0055] <Method for manufacturing thin polarizing film> A method for producing a thin polarizing film includes 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 form a laminate, and subjecting the laminate to an in-air auxiliary stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment, in that order. In particular, to obtain a polarizing film with excellent optical properties, a two-stage stretching method is selected, which combines an in-air auxiliary stretching treatment (dry stretching) with an underwater stretching treatment in a boric acid aqueous solution.

[0056] The laminate may be produced by any suitable method, for example, by applying a coating liquid containing the PVA resin to the surface of the thermoplastic resin substrate and drying the coating liquid. The thickness of the thermoplastic resin substrate is preferably about 20 to 300 μm, more preferably about 50 to 200 μm. The thickness of the PVA resin layer is preferably about 3 to 40 μm, more preferably about 3 to 20 μm.

[0057] The thermoplastic resin substrate preferably has a water absorption rate of about 0.2% or more, more preferably about 0.3% or more, from the viewpoint of absorbing water to significantly reduce the stretching stress and enabling high stretching ratios. On the other hand, the thermoplastic resin substrate preferably has a water absorption rate of about 3% or less, more preferably about 1% or less, from the viewpoint of preventing defects such as a significant decrease in the dimensional stability of the thermoplastic resin substrate and a deterioration in the appearance of the resulting polarizing film. The water absorption rate can be adjusted, for example, by introducing a modifying group into the constituent material of the thermoplastic resin substrate. The water absorption rate is a value determined in accordance with JIS K 7209.

[0058] The thermoplastic resin substrate preferably has a glass transition temperature (Tg) of about 120°C or less, from the viewpoint of ensuring sufficient stretchability of the laminate while suppressing crystallization of the PVA-based resin layer. Furthermore, considering the plasticization of the thermoplastic resin substrate with water and the smooth underwater stretching, the glass transition temperature (Tg) is more preferably about 100°C or less, and even more preferably about 90°C or less. On the other hand, the glass transition temperature of the thermoplastic resin substrate is preferably about 60°C or more, from the viewpoint of preventing problems such as deformation of the thermoplastic resin substrate during application and drying of the coating liquid and producing a good laminate. The glass transition temperature can be adjusted, for example, by introducing a modifying group into the constituent material of the thermoplastic resin substrate or by heating using a crystallizing material. The glass transition temperature (Tg) is a value determined in accordance with JIS K 7121.

[0059] Any suitable thermoplastic resin can be used as the constituent material of the thermoplastic resin substrate. Examples of the thermoplastic resin include ester resins such as polyethylene terephthalate resins, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene, polyamide resins, polycarbonate resins, and copolymer resins thereof. Among these, norbornene resins and amorphous polyethylene terephthalate resins are preferred. Furthermore, amorphous polyethylene terephthalate resins are preferred because the thermoplastic resin substrate has excellent stretchability and crystallization during stretching can be suppressed. Examples of amorphous polyethylene terephthalate resins include copolymers containing isophthalic acid and / or cyclohexanedicarboxylic acid as dicarboxylic acids, and copolymers containing cyclohexanedimethanol or diethylene glycol as glycols.

[0060] The thermoplastic resin substrate may be subjected to a surface treatment (e.g., corona treatment) before forming the PVA-based resin layer, or an easy-adhesion layer may be formed on the thermoplastic resin substrate. By performing such treatment, the adhesion between the thermoplastic resin substrate and the PVA-based resin layer can be improved. Furthermore, the thermoplastic resin substrate may be stretched before forming the PVA-based resin layer.

[0061] The coating liquid is a solution in which a PVA resin is dissolved in a solvent. Examples of the solvent include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine, with water being preferred. These can be used alone or in combination. The concentration of the PVA resin in the coating liquid is preferably about 3 to 20 parts by weight per 100 parts by weight of the solvent, from the viewpoint of forming a uniform coating film that adheres closely to the thermoplastic resin substrate.

[0062] The coating solution preferably contains a halide to improve the orientation of polyvinyl alcohol molecules during stretching. Any appropriate halide can be used as the halide, and examples thereof include iodide and sodium chloride. Examples of the iodide include potassium iodide, sodium iodide, and lithium iodide, with potassium iodide being preferred. The concentration of the halide in the coating solution is preferably about 5 to 20 parts by weight, and more preferably about 10 to 15 parts by weight, per 100 parts by weight of the PVA resin.

[0063] The coating liquid may contain additives, such as plasticizers such as ethylene glycol and glycerin, and surfactants such as nonionic surfactants.

[0064] The coating liquid may be applied by any suitable method, such as roll coating, spin coating, wire bar coating, dip coating, die coating, curtain coating, spray coating, knife coating (comma coating, etc.), etc. The drying temperature of the coating liquid is preferably about 50° C. or higher.

[0065] The in-air auxiliary stretching treatment can stretch the laminate at a high stretching ratio while suppressing crystallization of the thermoplastic resin substrate. The stretching method in the in-air auxiliary stretching treatment may be fixed-end stretching (e.g., a method of stretching using a tenter stretching machine) or free-end stretching (e.g., a method of uniaxially stretching the laminate by passing it between rolls with different peripheral speeds). However, free-end stretching is preferred from the viewpoint of obtaining high optical properties.

[0066] The stretching ratio in the auxiliary in-air stretching is preferably about 2 to 3.5. The auxiliary in-air stretching may be carried out in one stage or in multiple stages. When carried out in multiple stages, the stretching ratio is the product of the stretching ratios in each stage.

[0067] The stretching temperature in the auxiliary in-air stretching can be set to any appropriate value depending on the material forming the thermoplastic resin substrate, the stretching method, etc., and is, for example, preferably equal to or higher than the glass transition temperature (Tg) of the thermoplastic resin substrate, more preferably equal to or higher than the glass transition temperature (Tg) + 10° C., and even more preferably equal to or higher than the glass transition temperature (Tg) + 15° C. On the other hand, the upper limit of the stretching temperature is preferably about 170° C., from the viewpoint of suppressing rapid crystallization of the PVA-based resin and suppressing defects due to crystallization (for example, preventing the orientation of the PVA-based resin layer due to stretching).

[0068] If necessary, an insolubilization treatment may be carried out after the auxiliary air-stretching treatment and before the dyeing treatment or the underwater stretching treatment. The insolubilization treatment is typically carried out by immersing the PVA-based resin layer in an aqueous boric acid solution. The insolubilization treatment imparts water resistance to the PVA-based resin layer, and prevents a decrease in the orientation of PVA when immersed in water. The concentration of the aqueous boric acid solution is preferably about 1 to 5 parts by weight per 100 parts by weight of water. The liquid temperature of the insolubilization bath is preferably about 20 to 50°C.

[0069] The dyeing treatment is carried out by dyeing the PVA-based resin layer with iodine. Examples of the adsorption method include a method of immersing the PVA-based resin layer (laminate) in a dyeing solution containing iodine, a method of applying the dyeing solution to the PVA-based resin layer, and a method of spraying the dyeing solution onto the PVA-based resin layer, and the method of immersing the PVA-based resin layer (laminate) in a dyeing solution containing iodine is preferred.

[0070] The amount of iodine in the dye bath is preferably about 0.05 to 0.5 parts by weight per 100 parts by weight of water. To increase the solubility of iodine in water, the iodide is preferably added to the iodine aqueous solution. The amount of iodide is preferably about 0.1 to 10 parts by weight, more preferably about 0.3 to 5 parts by weight, per 100 parts by weight of water. The temperature of the dye bath is preferably about 20 to 50°C to suppress dissolution of the PVA-based resin. The immersion time is preferably about 5 seconds to 5 minutes, more preferably about 30 to 90 seconds, from the viewpoint of ensuring the transmittance of the PVA-based resin layer. To obtain a polarizing film with good optical properties, the ratio of the iodine content to the iodide content in the iodine aqueous solution is preferably about 1:5 to 1:20, more preferably about 1:5 to 1:10.

[0071] If necessary, a crosslinking treatment may be performed after the dyeing treatment and before the underwater stretching treatment. The crosslinking treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. The crosslinking treatment imparts water resistance to the PVA-based resin layer, thereby preventing a decrease in the orientation of the PVA when the layer is immersed in high-temperature water during the subsequent underwater stretching treatment. The boric acid concentration of the aqueous boric acid solution is preferably about 1 to 5 parts by weight per 100 parts by weight of water. Furthermore, when performing the crosslinking treatment, it is preferable to further incorporate the iodide into the crosslinking bath used in the crosslinking treatment. The incorporation of the iodide can suppress the elution of iodine adsorbed to the PVA-based resin layer. The amount of the iodide incorporated is preferably about 1 to 5 parts by weight per 100 parts by weight of water. The liquid temperature of the crosslinking bath (boric acid aqueous solution) is preferably about 20 to 50°C.

[0072] The underwater stretching treatment is carried out by immersing the laminate in a stretching bath. Underwater stretching allows stretching at a temperature lower than the glass transition temperature (typically about 80°C) of the thermoplastic resin substrate or the PVA-based resin layer, allowing the PVA-based resin layer to be stretched at a high magnification while suppressing crystallization. The underwater stretching method may be fixed-end stretching (e.g., stretching using a tenter stretching machine) or free-end stretching (e.g., uniaxial stretching by passing the laminate between rolls with different peripheral speeds). However, free-end stretching is preferred from the viewpoint of obtaining high optical properties.

[0073] The underwater stretching treatment is preferably carried out by immersing the laminate in an aqueous boric acid solution (stretching in boric acid solution). By using an aqueous boric acid solution as a stretching bath, it is possible to impart to the PVA resin layer rigidity sufficient to withstand the tension applied during stretching and water resistance sufficient to prevent dissolution in water. The boric acid concentration in the aqueous boric acid solution is preferably 1 to 10 parts by weight, more preferably 2.5 to 6 parts by weight, per 100 parts by weight of water. In addition, an iodide may be blended into the stretching bath (aqueous boric acid solution). The liquid temperature of the stretching bath is preferably about 40 to 85°C, more preferably about 60 to 75°C. The immersion time of the laminate in the stretching bath is preferably about 15 seconds to 5 minutes.

[0074] The stretching ratio in the underwater stretching is preferably about 1.5 times or more, and more preferably about 3 times or more.

[0075] The total stretching ratio of the laminate is preferably about 5 times or more, more preferably about 5.5 times or more, relative to the original length of the laminate.

[0076] The drying shrinkage treatment may be carried out by zone heating, in which the entire zone is heated, or by heating the transport rolls (using so-called heated rolls). Preferably, both methods are used. Drying using heated rolls efficiently suppresses heat curling of the laminate, allowing a polarizing film with excellent appearance to be produced. Furthermore, since the laminate can be dried while being kept flat, not only curling but also wrinkles can be suppressed. Furthermore, from the viewpoint of improving the optical properties of the resulting polarizing film by shrinking the laminate in the width direction during the drying shrinkage treatment, the shrinkage rate of the laminate in the width direction due to the drying shrinkage treatment is preferably about 1 to 10%, more preferably about 2 to 8%.

[0077] Drying conditions can be controlled by adjusting the heating temperature of the transport rolls (heating roll temperature), the number of heating rolls, the contact time with the heating rolls, etc. The temperature of the heating rolls is preferably about 60 to 120°C, more preferably about 65 to 100°C, and even more preferably 70 to 80°C. From the viewpoint of satisfactorily increasing the crystallinity of the thermoplastic resin and satisfactorily suppressing curling, the number of transport rolls is usually about 2 to 40, preferably about 4 to 30. The contact time between the laminate and the heating rolls (total contact time) is preferably about 1 to 300 seconds, more preferably 1 to 20 seconds, and even more preferably 1 to 10 seconds.

[0078] The heating rolls may be installed in a heating furnace or in a normal production line (under room temperature). Preferably, they are installed in a heating furnace equipped with a blower. By using both heating roll drying and hot air drying, it is possible to suppress abrupt temperature changes between the heating rolls, and to easily control shrinkage in the width direction. The hot air drying temperature is preferably about 30 to 100°C. The hot air drying time is preferably about 1 to 300 seconds.

[0079] After the underwater stretching treatment and before the drying shrinkage treatment, it is preferable to carry out a washing treatment, typically by immersing the PVA-based resin layer in an aqueous potassium iodide solution.

[0080] Furthermore, when producing a thin polarizing film containing the compound having radical scavenging function, the compound having radical scavenging function may be contained in one or more of the treatment baths for dyeing, underwater stretching, insolubilization, crosslinking, and washing. The concentration of the compound having radical scavenging function contained in any of the treatment baths cannot be determined in general because it is affected by the number of treatments, treatment time, treatment temperature, etc. of each treatment. However, from the viewpoint of efficiently controlling the content of the compound having radical scavenging function in the polarizing film, the concentration is usually preferably 0.03 wt % or more, more preferably 0.05 wt % or more, and even more preferably 0.1 wt % or more, and preferably 15 wt % or less, more preferably 10 wt % or less, and even more preferably 5 wt % or less.

[0081] In particular, when a washing treatment is performed, the washing treatment can easily adjust the content of iodine or the compound having a radical scavenging function to a desired range, from the viewpoint of allowing components such as iodine and the compound having a radical scavenging function to be eluted from or adsorbed onto the polyvinyl alcohol-based film, while taking into consideration the treatment conditions for the dyeing treatment, the underwater stretching treatment, etc.

[0082] Furthermore, when producing a thin polarizing film containing the compound having a radical scavenging function, an aqueous solution containing the compound having a radical scavenging function may be applied to the polarizing film to impregnate the film. The application step may be performed before or after any of the dyeing treatment, underwater stretching treatment, insolubilization treatment, crosslinking treatment, and washing treatment. In particular, it is preferable to apply the coating step after the washing treatment, from the viewpoint of easily adjusting the content of the compound having a radical scavenging function to a desired range. The application method is not particularly limited, and examples thereof include wire bar coating, gravure coating, and spraying.

[0083] Each treatment bath in the dyeing treatment, underwater stretching treatment, insolubilization treatment, crosslinking treatment, and washing treatment 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 salts thereof, and inorganic weak acids such as phosphoric acid and carbonic acid, and salts thereof. 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. In particular, from the viewpoint of obtaining a polarizing film that can suppress a decrease in the single-piece transmittance due to coloration of the polarizing film in a high-temperature environment, it is preferable that one or more of the treatment baths contain a chloride.

[0084] <Polarizing film> The polarizing film of the present invention is a polarizing film in which transparent protective films are attached to both sides of the polarizing film, and at least one of the transparent protective films has a moisture permeability of 200 g / (m 2 24h) or less, and the general formula (1): ΔTs (%) = Ts 750-Ts0 (in the general formula (1), Ts0 is the single transmittance of a laminate in which a glass plate is bonded to one surface of the polarizing film via a pressure-sensitive adhesive layer, and Ts 750 represents the single-piece transmittance after the laminate has been heat-treated at 105° C. for 750 hours. The change in the single-piece transmittance (ΔTs) represented by (ΔTs) satisfies the condition that the change in the single-piece transmittance (ΔTs) is 0% or more and 5% or less.

[0085] <Transparent protective film> The transparent protective film is attached to at least one surface of the polarizing film and has a moisture permeability of 200 g / (m 2 As long as the film has a shelf life of 24 hours or less, there are no particular limitations, and various transparent protective films used in polarizing films can be used. Examples of materials that can be used to form the transparent protective film include thermoplastic resins that are excellent in transparency, mechanical strength, thermal stability, moisture barrier properties, isotropy, and the like. 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 have a cured layer formed from a thermosetting resin or ultraviolet-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.

[0086] The thickness of the transparent protective film can be determined as appropriate, but generally, from the viewpoints of workability such as strength and handling, 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.

[0087] At least one of the transparent protective films (the first transparent protective film on one side of the polarizer) has a moisture permeability of 200 g / (m 2 24h) or less, and from the viewpoint of preventing the deterioration of the polarization degree of the polarizing film in a high-temperature and high-humidity environment, the moisture permeability is 180g / (m 2 24h) or less, and 150g / (m 2 24h) or less. From the viewpoint of production efficiency in the drying process after laminating the polarizing film and the transparent protective film, the other transparent protective film (the second transparent protective film on the other side of the polarizer) has a moisture permeability of 200 g / (m 2 24h) or more, and 300g / (m 2 24h) or more, and from the viewpoint of suppressing the decrease in the polarization degree of the polarizing film in a high-temperature and high-humidity environment, the moisture permeability is preferably 1200g / (m 2 24h) or less, and 1000g / (m 2 The moisture permeability can be calculated in accordance with the moisture permeability test (cup method) of JIS Z0208 by cutting a sample to a diameter of 60 mm, placing it in a moisture permeability cup containing approximately 15 g of calcium chloride, placing it in an incubator at a temperature of 40°C and a humidity of 90% RH, and measuring the increase in weight of the calcium chloride before and after leaving it for 24 hours.

[0088] 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.

[0089] 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, allowing for a thinner film.

[0090] 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.

[0091] The transparent protective film may contain any appropriate additives such as ultraviolet absorbers, antioxidants, lubricants, plasticizers, release agents, coloring inhibitors, flame retardants, antistatic agents, pigments, and colorants.

[0092] The surface of the transparent protective film on 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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, water-based polyester adhesives, etc. These adhesives are usually used as aqueous solutions and contain 0.5 to 60 wt % solids.

[0097] 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 adhesives. Examples of the curable components in the (meth)acrylate adhesives include compounds having a (meth)acryloyl group and compounds having a vinyl group. Furthermore, compounds having an epoxy group or an oxetanyl group can also be used as cationic polymerization-curable adhesives. The compound having an epoxy group 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.

[0098] 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, 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, more preferably about 0.5 to 10 μm.

[0099] 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.

[0100] Examples of the surface modification treatment for forming the surface modification layer include corona treatment, plasma treatment, primer treatment, and saponification treatment.

[0101] 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.

[0102] The blocking layer has the 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.

[0103] 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.

[0104] The polarizing film of the present invention has a structure represented by the general formula (1): ΔTs(%)=Ts 750 -Ts0 (in the general formula (1), Ts0 is the single transmittance of a laminate in which a glass plate is bonded to one surface of the polarizing film via a pressure-sensitive adhesive layer, and Ts 750 represents the single-piece transmittance after the laminate is heat-treated at 105°C for 750 hours. The change in single-piece transmittance (ΔTs) represented by (ΔTs) satisfies the condition that it is 0% or more and 5% or less. The change in single-piece transmittance (ΔTs) is preferably 0% or more and 3% or less, and more preferably 0% or more and 2% or less.

[0105] The polarizing film preferably has a polarization degree of 99.98% or more, and more preferably has a polarization degree of 99.99% or more.

[0106] <Laminated polarizing film> The laminated polarizing film (optical laminate) of the present invention has the polarizing film laminated to an optical layer. The optical layer is not particularly limited, and may be, for example, one or more optical layers that are sometimes used in the formation of liquid crystal displays, such as a reflector, a semi-transmitting plate, a retardation plate (including half-wave or quarter-wave plates), or a viewing angle compensation film. 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.

[0107] 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 adhesion, and excellent weather resistance, heat resistance, etc., such as pressure-sensitive adhesives containing acrylic polymers, are preferably used.

[0108] The application of a pressure-sensitive adhesive layer to one or both surfaces of the polarizing film or the laminated polarizing film can be carried out 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 laminated 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 laminated 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. The polarizing film or the laminated 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 laminated polarizing film.

[0109] 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.

[0110] <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.

[0111] 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 orientation (π type).

[0112] The organic EL cell preferably has a light-emitting body (organic electroluminescence light-emitting body) 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.

[0113] 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 transparent plate, 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.

[0114] The polarizing film of the present invention has a good initial polarization degree, is excellent in suppressing a decrease in the single-unit transmittance due to coloration of the polarizing film in a high-temperature environment, and further has a polarizing film that is excellent in suppressing a decrease in the polarization degree in a high-temperature, high-humidity environment.Therefore, the polarizing film of the present invention, as well as a laminated polarizing film, an image display panel, and an image display device using the polarizing film, are suitable for use in in-vehicle image display devices such as car navigation devices and backup monitors. [Example]

[0115] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Example 1 <Preparation of polarizing film> 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 30 μm was prepared. The polyvinyl alcohol film was immersed in a 20°C swelling bath (water bath) for 30 seconds between rolls with different peripheral speed ratios, where it was stretched 2.2 times in the conveying direction while swelling (swelling step). Subsequently, the film was immersed in a 30°C dye bath (iodine solution obtained by blending 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 final polarizing film had an iodine concentration of 3.8 wt%, while dyeing. The film was stretched 3.3 times in the conveying direction relative to the original polyvinyl alcohol film (polyvinyl alcohol film that was not stretched at all in the conveying direction) (dyeing step). The dyed polyvinyl alcohol film was then immersed in a 40°C crosslinking bath (aqueous solution containing 3.5 wt% boric acid, 3.0 wt% potassium iodide, and 3.6 wt% zinc sulfate) for 28 seconds and stretched in the machine direction to 3.6 times its original size (crosslinking step). The resulting polyvinyl alcohol film was then immersed in a 64°C stretching bath (aqueous solution containing 4.5 wt% boric acid, 5.0 wt% potassium iodide, and 5.0 wt% zinc sulfate) for 60 seconds and stretched in the machine direction to 6.0 times its original size (stretching step). The resulting polyvinyl alcohol film was then immersed in a 27°C washing bath (aqueous solution containing 2.3 wt% potassium iodide and 1.0 wt% of a compound represented by the following general formula (9) as a radical-scavenging compound) for 10 seconds (washing step). The washed polyvinyl alcohol film was dried at 40°C for 30 seconds to produce a polarizing film. The iodine concentration of the polarizing film was determined by the following measurement method: The obtained polarizing film had a polyenation dehydration temperature (peak temperature of maximum water intensity detected by evolved gas analysis) of 210°C, a content of the compound represented by the following general formula (9) in the polarizing film of 0.3 wt%, and a thickness of 12 μm. [ka]

[0116] [Method for measuring iodine concentration (wt%) in polarizing film] The iodine concentration (wt %) of the polarizing film was determined using a fluorescent X-ray analyzer (manufactured by Rigaku Corporation, trade name "ZSX-PRIMUS IV", measurement diameter: ψ20 mm) according to the following formula. Iodine concentration (wt%) = 14.474 × (fluorescent X-ray intensity) / (film thickness) (kcps / μm) Note that the coefficient used to calculate the concentration differs depending on the measuring device, but this coefficient can be determined using an appropriate calibration curve.

[0117] [Method for measuring the dehydration temperature of polyenation] The polarized film was introduced into a heating furnace-type pyrolyzer (Frontier Labs, PY-2020iD), and the generated gas was directly introduced into a TOFMS (JEOL, MS-T100GCV) for measurement by evolved gas analysis (EGA / TOFMS). The peak temperature at which the detected water had the maximum intensity was determined, and this temperature was taken as the dehydration temperature for polyenation. [Measurement conditions] Temperature rise conditions: 40℃ → +10℃ / min → 350℃ Interface: Inert fused silica tubing, 2.5m x 0.15mm id Carrier gas: He (1.0 mL / min) Inlet temperature: 300℃ Inlet: Split ratio 20:1 Interface temperature: 300℃ Mass spectrometer: TOFMS Ionization method: EI method Mass range: m / z=18

[0118] [Method for measuring the content (wt%) of compounds with radical scavenging function in polarizing film] Approximately 20 mg of polarizing film was collected, quantified, and dissolved by heating in 1 mL of water, then diluted with 4.5 mL of methanol. The resulting extract was filtered through a membrane filter, and the concentration of compounds with radical scavenging function in the filtrate was measured using HPLC (Waters ACQUITY UPLC H-class Bio).

[0119] <Preparation of polarizing film> The adhesive used was an aqueous solution containing an acetoacetyl group-containing polyvinyl alcohol resin (average polymerization degree 1,200, saponification degree 98.5 mol%, acetoacetylation degree 5 mol%) and methylol melamine in a weight ratio of 3:1. Using this adhesive, a 47 μm-thick transparent protective film (moisture permeability 380 g / (m)) made of triacetyl cellulose film (manufactured by Fujifilm, product name "TJ40UL") with HC formed thereon was applied as a second transparent protective film to one side (viewing side) of the polarizing film obtained above. 2 24h)) and on the other side (image display cell side) as a first transparent protective film, a 30 μm thick transparent protective film (manufactured by Nippon Shokubai, moisture permeability 125 g / (m 2 After laminating the polarizing film on both sides of the film using a roll laminator, the film was subsequently dried by heating in an oven (at 90°C for 10 minutes) to produce a polarizing film with transparent protective films laminated on both sides of the polarizing film.

[0120] [Method for measuring single-piece transmittance in a high-temperature environment] The polarizing film obtained above was cut into a size of 5.0 × 4.5 cm so that the absorption axis of the polarizing film was parallel to the long side. A glass plate (pseudo image display cell) was attached to the protective film surface of the polarizing film on the image display cell side via a 20 μm-thick acrylic adhesive layer, and the laminate was autoclaved at 50°C and 0.5 MPa for 15 minutes to produce a laminate. The resulting laminate was placed in a hot air oven at 105°C for 750 hours, and the single-unit transmittance (ΔTs) before and after heating was measured. The single-unit transmittance was measured using a spectrophotometer (JASCO Corporation, product name "V7100") and evaluated according to the following criteria. The measurement wavelength was 380 to 700 nm (5 nm intervals). The results are shown in Table 1. ΔTs(%)=Ts 750 -Ts0 where Ts0 is the single transmittance of the laminate before heating, and Ts 750 is the single transmittance of the laminate after heating for 750 hours.

[0121] [Evaluation of polarization degree] The degree of polarization of a polarizing film can be measured using a spectrophotometer (manufactured by JASCO Corporation, product name "V7100"). Specifically, the degree of polarization can be measured by measuring the parallel transmittance (H0) and crossed transmittance (H90) of the polarizing film and calculating it using the formula: Polarization degree (%) = {(H0 - H90) / (H0 + H90)} 1 / 2 × 100. The parallel transmittance (H0) is the transmittance value of a parallel-type laminated polarizing film made by stacking two identical polarizing films so that their absorption axes are parallel to each other. The crossed transmittance (H90) is the transmittance value of a crossed-type laminated polarizing film made by stacking two identical polarizing films so that their absorption axes are perpendicular to each other. These transmittances are Y values ​​corrected for luminosity using a 2-degree visual field (illuminant C) according to JIS Z 8701-1982. The results are shown in Table 1.

[0122] [Evaluation of humidity durability] The laminate sample was left standing in a moist heat oven at 85°C and 85% RH for 500 hours, and then the polarization degree was evaluated using the spectrophotometer (manufactured by JASCO Corporation, product name "V7100") as described above. The results are shown in Table 1. 〇: Polarization rate 90% or more ×: Polarization degree less than 90%

[0123] [Evaluation of heat peeling] The polarizing film was cut to a size of 680 x 250 mm so that the absorption axis was parallel to the long side, and a glass plate (pseudo image display cell) was fabricated by attaching a 20 μm thick acrylic adhesive layer to the protective film on the image display cell side of the polarizing film. The resulting laminate sample was left in a hot air oven at 105°C for 750 hours, and then its appearance was visually evaluated according to the following criteria. The results are shown in Table 1. ◯: There is slight peeling or bubbling at the edge, but this does not pose a problem in practical use. △: Peeling or bubbling is observed at the edge, but there is no problem in practical use unless it is for special applications (for example, a narrow-frame display in which the distance from the edge of the polarizing plate to the active area where the image is displayed is short). ×: Significant peeling at the edge, causing problems in practical use.

[0124] <Example 2> <Preparation of polarizing membranes and films> A polarizing film and a polarizing film were produced in the same manner as in Example 1, except that the iodine concentration in the dye bath was adjusted so that the iodine concentration in the final polarizing film would be 4.3 wt %. The resulting polarizing film had a peak temperature of 208°C for maximum water intensity as detected by evolved gas analysis, a content of the compound represented by general formula (9) in the polarizing film of 0.3 wt %, and a thickness of 12 μm.

[0125] Example 3 <Preparation of polarizing membranes and films> A polarizing film and a polarizing film were produced in the same manner as in Example 1, except that a 45 μm-thick polyvinyl alcohol film was used and the iodine concentration of the dye bath was adjusted so that the iodine concentration of the final polarizing film would be 3.5 wt %. The resulting polarizing film had a peak temperature of 210°C for maximum water intensity as detected by evolved gas analysis, a content of the compound represented by general formula (9) in the polarizing film of 0.2 wt %, and a thickness of 18 μm.

[0126] Example 4 <Preparation of polarizing membranes and films> A polarizing film and a polarizing film were produced in the same manner as in Example 1, except that the iodine concentration in the dye bath was adjusted so that the iodine concentration in the final polarizing film would be 4.8 wt %, and the potassium iodide concentration in the washing bath was adjusted to 3.6 wt %, and the compound represented by general formula (8) above instead of general formula (9) above was added to 1.5 wt %. The resulting polarizing film had a peak temperature of 210°C for maximum water intensity as detected by evolved gas analysis, a content of the compound represented by general formula (8) above in the polarizing film of 0.4 wt %, and a thickness of 12 μm.

[0127] <Example 5> <Preparation of polarizing membranes and films> A polarizing film and a polarizing membrane were produced in the same manner as in Example 1, except that the iodine concentration in the dye bath was adjusted so that the iodine concentration in the final polarizing membrane was 2.5 wt %, and the potassium iodide concentration in the washing bath was adjusted to 1.8 wt %, and 1.0 wt % of a compound represented by the following general formula (10) instead of the above general formula (9), and 15 wt % of sodium chloride. The resulting polarizing membrane had a peak temperature of 209°C for maximum water intensity as detected by evolved gas analysis, a content of the compound represented by the following general formula (10) in the polarizing membrane of 0.3 wt %, a chloride ion content of 3.1 wt %, and a thickness of 12 μm. The chloride ion content was determined by the following measurement method. [ka]

[0128] [Method for measuring chloride ions (chloride ions)] 5 mg of sample was placed in a polypropylene container, 20 mL of ultrapure water was added, and the container was then capped. Next, extraction was performed at 120°C for 1 hour, and the resulting extract was filtered through a membrane filter and an organic matter removal cartridge. The chloride ion content was calculated by quantitative analysis using ion chromatography. [Measurement conditions] Apparatus (anion): Thermo Fisher Scientific ICS-3000 Separation column: Dionex IonPac AS18-fast (4 mm x 150 mm) Guard column: Dionex IonPac AG18-fast (4 mm x 30 mm) Removal system: Dionex AERS-500 (external mode) Detector: Electrical conductivity detector Eluent: KOH aqueous solution (using EGCIII eluent generator) Eluent flow rate: 1.2mL / min Sample injection volume: 250 μL

[0129] Example 6 <Preparation of polarizing membranes and films> A polarizing membrane and a polarizing film were prepared in the same manner as in Example 5, except that the compound represented by general formula (10) was not added in the preparation of the polarizing membrane. The resulting polarizing membrane had a peak temperature of 209°C for maximum water intensity as detected by evolved gas analysis, a chloride ion content of 3.2 wt %, and a thickness of 12 μm.

[0130] <Comparative Example 1> <Preparation of polarizing membranes and films> A polarizing membrane and a polarizing film were prepared in the same manner as in Example 2, except that the compound represented by general formula (9) was not added to the cleaning bath as a compound having radical scavenging properties. The resulting polarizing membrane had a peak temperature of 197°C for maximum water intensity as detected by evolved gas analysis, a content of the compound represented by general formula (9) in the polarizing membrane of 0 wt %, and a thickness of 12 μm.

[0131] <Comparative Example 2> <Preparation of polarizing membranes and films> A polarizing film and a polarizing film were produced in the same manner as in Example 1, except that the iodine concentration in the dye bath was adjusted so that the iodine concentration in the final polarizing film would be 2.5% by weight, and that the compound represented by general formula (9) above was not added to the washing bath as a compound having a radical scavenging function. The resulting polarizing film had a peak temperature of 206°C for maximum water intensity as detected by evolved gas analysis, a content of the compound represented by general formula (9) above in the polarizing film of 0% by weight, and a thickness of 12 μm.

[0132] <Comparative Example 3> <Preparation of polarizing membranes and films> The first transparent protective film has a thickness of 20 μm and a moisture permeability of 1270 g / (m 2 A polarizing film was produced in the same manner as in Example 1, except that a triacetyl cellulose film (manufactured by Konica Minolta, product name "KC2CT") was used.

[0133] <Comparative Example 4> <Preparation of polarizing membranes and films> In the production of the polarizing film, a 75 μm-thick polyvinyl alcohol film was immersed in a swelling bath (water bath) at 35°C for 30 seconds between rolls with different peripheral speed ratios, and stretched 2.2 times in the conveying direction while swelling (swelling step). The iodine concentration of the dye bath was adjusted so that the iodine concentration of the final polarizing film would be 3.1 wt %, 3 wt % sodium chloride was added to the washing bath, and the first transparent protective film was 20 μm thick and had a moisture permeability of 1270 g / m 2 A polarizing film and a polarizing membrane were prepared in the same manner as in Comparative Example 1, except that a 24-hour triacetyl cellulose film (Konica Minolta, product name "KC2CT") was used. The resulting polarizing membrane had a maximum water intensity peak temperature of 209°C as detected by evolved gas analysis, a chloride ion content of 1.1 wt %, and a thickness of 28 μm.

[0134] The polarizing films of each Example and Comparative Example obtained above were used to carry out the above-mentioned [Method for measuring single-piece transmittance under high temperature environment], [Evaluation of polarization degree], [Evaluation of humidity durability], and [Evaluation of heat peeling]. The results are shown in Table 1.

[0135] [Table 1]

Claims

1. A polarizing film in which transparent protective films are attached to both sides of a polarizing film, the polarizing film is formed by adsorbing and aligning iodine on a polyvinyl alcohol-based film, and has an iodine concentration of 3% by weight or more and 10% by weight or less; the polarizing film contains more than 2% by weight of chloride ions; At least one of the transparent protective films has a moisture permeability of 200 g / (m ２ ・24h) or less, The polarizing film satisfies the general formula (1): ΔTs(%)=Ts ７５０ -Ts ０ (In the general formula (1), Ts ０ is the single transmittance of a laminate in which a glass plate is bonded to one surface of the polarizing film via a pressure-sensitive adhesive layer, and Ts ７５０ represents the single-piece transmittance after the laminate is heat-treated at 105°C for 750 hours.) A polarizing film, characterized in that a change in single-piece transmittance (ΔTs) represented by

2. 2. The polarizing film according to claim 1, wherein the polarizing film has a thickness of 20 [mu]m or less.

3. 3. The polarizing film according to claim 1, wherein the polarization degree is 99.98% or more.

4. A laminated polarizing film characterized in that the polarizing film described in any one of claims 1 to 3 is bonded to an optical layer.

5. 10. An image display panel comprising an image display cell to which the polarizing film according to claim 1 or the laminated polarizing film according to claim 4 is attached.

6. An image display device characterized by having a front transparent member on the polarizing film or laminated polarizing film side of the image display panel described in claim 5.

7. 7. The image display device according to claim 6, which is for vehicle use.

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