Polarizing plate and image display device using the polarizing plate

Abstract

The object of this invention is to provide a polarizing plate that prevents yellowing and exhibits excellent high-temperature durability, even when used in image display devices constructed with interlayer filling, and an image display device thereof. The polarizing plate of this invention comprises a polarizing element formed by adsorbing oriented iodine into a polyvinyl alcohol resin layer, and a transparent protective film deposited on at least one side of the aforementioned polarizing element. The amount of alcohol contained in the aforementioned polarizing plate is 4 μg / cm² to 230 μg / cm², and the moisture content of the aforementioned polarizing element is at least at an equilibrium moisture content of 20°C and 20% relative humidity, and less than or equal to an equilibrium moisture content of 50% relative humidity at 20°C.

Description

[Technical Field]

[0001] This invention relates to a polarizing plate and an image display device. [Previous Technology]

[0002] Liquid crystal displays (LCDs) are not only used in LCD televisions, but also widely used in mobile devices such as computers and mobile phones, and in automotive applications such as car navigation systems. Typically, an LCD device has a liquid crystal panel formed by bonding polarizing plates to both sides of liquid crystal cells with an adhesive, and the display is achieved by controlling the light from the backlight through the liquid crystal panel. In recent years, organic EL displays, like LCDs, have also been widely used in mobile devices such as televisions and mobile phones, and in automotive applications such as car navigation systems. In organic EL displays, to suppress the reflection of external light by the metal electrodes (cathodes) from creating a mirror-like appearance, a circular polarizing plate (a multilayer comprising polarizing elements and a λ / 4 plate) is sometimes placed on the viewing side surface of the image display panel.

[0003] As mentioned above, there is an increasing likelihood that polarizing plates will be mounted in vehicles as components of image display devices such as liquid crystal displays and organic EL displays. Polarizing plates used in automotive image display devices are mostly exposed to high-temperature environments compared to those used in mobile applications such as televisions and mobile phones, and therefore require minimal changes in characteristics at high temperatures (high-temperature durability).

[0004] On the other hand, in order to prevent damage to the image display panel from impacts from the outer surface, the configuration of providing a front panel (also called a "window layer") such as a transparent resin plate or glass plate closer to the viewing side than the image display panel is increased. Image display devices equipped with touch panels widely adopt the following configuration: a touch panel is provided closer to the viewing side than the image display panel, and a front panel is provided closer to the viewing side than the touch panel.

[0005] In such a configuration, if an air layer exists between the image display panel and a transparent component such as a front panel or touch panel, external light reflection will occur due to light reflection at the air layer interface, which tends to reduce screen visibility. Therefore, a configuration that fills the space between the polarizing plate disposed on the viewing side surface of the image display panel and the transparent component with a layer other than the air layer, usually a solid layer (hereinafter sometimes referred to as "interlayer filler"), has become common (hereinafter sometimes referred to as "interlayer filling configuration"). The interlayer filler is preferably a material with a refractive index similar to that of the polarizing plate or the transparent component. To suppress the reduction in visibility caused by reflection at the interface and to fix the components to each other, an adhesive or a UV-curing adhesive is used as the interlayer filler (see, for example, Patent Document 1).

[0006] Interlayer filling structures are widely used in mobile applications, such as mobile phones, which are mostly used outdoors. In recent years, due to the increasing demand for visibility, interlayer filling structures, in which a front transparent plate is placed on the surface of the image display panel and an adhesive layer is filled between the panel and the front transparent plate, have also begun to be studied in vehicle applications such as car navigation devices.

[0007] However, reports indicate that when this configuration is used, the polarizing plate will turn yellow (or brown) under high-temperature conditions (hereinafter sometimes referred to as yellowing), and the transmittance of the polarizing plate will decrease significantly. Patent Document 2 proposes the following method as a countermeasure to solve this problem: keep the water content per unit area of ​​the polarizing plate below a predetermined amount, and keep the saturated water absorption of the transparent protective film adjacent to the polarizing element below a predetermined amount, thereby suppressing the decrease in transmittance.

[0007] [Previous Technical Documents]

[0007] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 11-174417

[0008] [Patent Document 2] Japanese Patent Application Publication No. 2014-102353

[0009] However, even with such a polarizing plate, the effect of suppressing yellowing under high temperature conditions is still insufficient. The object of the present invention is to provide a polarizing plate that further suppresses yellowing under high temperature conditions, and an image display device using the polarizing plate.

[0010] The present invention provides a polarizing plate and an image display device, as illustrated below.

[0010] [1] A polarizing plate comprising a polarizing element formed by adsorbing and aligning iodine into a polyvinyl alcohol resin layer, and a transparent protective film deposited on at least one side of the aforementioned polarizing element, wherein the amount of alcohol contained in the aforementioned polarizing plate is 4 μg / cm2 or more and 230 μg / cm2 or less.

[0010] The moisture content of the aforementioned polarizing element is above the equilibrium moisture content at a temperature of 20°C and a relative humidity of 20% and below the equilibrium moisture content at a temperature of 20°C and a relative humidity of 50%.

[0010] [2] A polarizing plate comprising a polarizing element formed by adsorbing and aligning iodine into a polyvinyl alcohol resin layer, and a transparent protective film deposited on at least one side of the aforementioned polarizing element, wherein the amount of alcohol contained in the aforementioned polarizing plate is 4 μg / cm2 or more and 230 μg / cm2 or less.

[0010] The moisture content of the aforementioned polarizing plate is above the equilibrium moisture content at a temperature of 20°C and a relative humidity of 20% and below the equilibrium moisture content at a temperature of 20°C and a relative humidity of 50%.

[0010] [3] The polarizing plate as described in [1] or [2], wherein the aforementioned alcohol is selected from at least one of the group consisting of methanol, ethanol and n-propanol.

[0010] [4] The polarizing plate as described in any one of [1] to [3], wherein the aforementioned polarizing element and the aforementioned transparent protective film are bonded together by an adhesive layer formed by an adhesive containing the aforementioned alcohol.

[0010] [5] The polarizing plate as described in [4], wherein the aforementioned adhesive comprises a polyvinyl alcohol resin.

[0010] [6] The polarizing plate as described in [5], wherein, relative to 100 parts by mass of the aforementioned polyvinyl alcohol resin, the content of the aforementioned alcohol in the aforementioned adhesive is more than 100 parts by mass and less than 2000 parts by mass.

[0010] [7] The polarizing plate as described in any one of [4] to [6], wherein the thickness of the aforementioned adhesive layer is 0.01 to 7 μm.

[0010] [8] A polarizing plate as described in any one of [1] to [7], wherein the aforementioned polarizing plate is used in an image display device,

[0010] In the aforementioned image display device, a layer other than an air layer is provided on both sides of the aforementioned polarizing plate in such a way that it is in contact with both sides of the aforementioned polarizing plate.

[0010] [9] An image display device comprising: an image display unit; a first adhesive layer deposited on the viewing side surface of the aforementioned image display unit; and a polarizing plate as described in any one of [1] to [8], deposited on the viewing side surface of the aforementioned first adhesive layer.

[0010]

[10] The image display device as described in [9] further comprises: a second adhesive layer deposited on the viewing side surface of the aforementioned polarizing plate; and a transparent member deposited on the viewing side surface of the aforementioned second adhesive layer.

[0010]

[11] The image display device as described in

[10] , wherein the aforementioned transparent component is a glass plate or a transparent resin plate.

[0010]

[12] The image display device as described in

[10] , wherein the aforementioned transparent component is a touch panel.

[0011] According to the present invention, a polarizing plate with improved high-temperature durability can be provided, which can suppress yellowing caused by high temperature even when used in an image display device composed of interlayer filling. Furthermore, by using the polarizing plate of the present invention, an image display device that suppresses yellowing under high-temperature conditions can be provided.

Implementation Method

[0012] The following describes embodiments of the present invention, but the present invention is not limited to the following embodiments.

[0013] [Polarizing plate]

[0013] The polarizing plate of this embodiment comprises a polarizing element formed by adsorbing an orientation dichroic pigment onto a layer containing a polyvinyl alcohol resin, and a transparent protective film. The polarizing plate contains alcohol, and the polarizing element and the transparent protective film can be bonded together by an adhesive layer formed by an alcohol-containing adhesive. The polarizing plate of this embodiment has at least one of the following features (a) and (b).

[0013] (a) The moisture content of the polarizing element is above the equilibrium moisture content at 20°C and 20% relative humidity, and below the equilibrium moisture content at 20°C and 50% relative humidity.

[0013] (b) The moisture content of the polarizing plate is above the equilibrium moisture content at 20°C and 20% relative humidity, and below the equilibrium moisture content at 20°C and 50% relative humidity.

[0014] The amount of alcohol contained in the polarizing plate is 4 μg / cm² to 230 μg / cm², preferably 13 μg / cm² to 200 μg / cm², more preferably 20 μg / cm² to 190 μg / cm², and may also be 60 μg / cm² or more, or 100 μg / cm² or more. By keeping the amount of alcohol contained in the polarizing plate within this range, polyene formation can be suppressed without impairing the optical characteristics of the polarizing element. Although the detailed mechanism is not yet clear, it is speculated that the formation of double bonds is suppressed by the reaction of the alcohol with PVA or boric acid.

[0015] Polarizing plates with excellent high-temperature durability are known, for example, a type of polarizing plate that can suppress the decrease in transmittance even when placed alone in an environment with a temperature of 95°C for 1000 hours. However, even such a polarizing plate, when used in an interlayer filling structure, will turn yellow (or brown) in the central part of the polarizing plate when placed in an environment with a temperature of 95°C for 200 hours, and a significant decrease in transmittance can be observed in the central part of the polarizing plate. The significant decrease in transmittance of the polarizing plate in a high-temperature environment is believed to be a problem that is particularly likely to occur when an image display device with an interlayer filling structure, in which one side of the polarizing plate is bonded to the image display unit and the other side is bonded to a transparent component such as a touch panel or front panel, is exposed to a high-temperature environment.

[0016] A polarizing plate with significantly reduced transmittance in its interlayer filling structure exhibits peaks near 1100 cm⁻¹ (originating from the =C=C bond) and near 1500 cm⁻¹ (originating from the -C=C- bond) in Raman spectroscopy measurements, suggesting the formation of a polyene structure (-C=C)n-. It is inferred that the polyene structure is generated due to the polyeneification of the polyvinyl alcohol constituting the polarizing element during dehydration (Patent Document 2, paragraph

[0012] ).

[0017] The polarizing plate of the present invention can further improve high-temperature durability. The polarizing plate of the present invention can suppress the reduction of transmittance even when assembled into an image display device with interlayer filling and exposed to a high-temperature environment such as 105°C for a long time, and can also suppress yellowing even when stored at 105°C for 72 hours.

[0018] <Polarizing element>

[0018] A conventional polarizing element can be used as a polarizing element formed by adsorbing an orientation dichroic dye onto a layer containing a polyvinyl alcohol (hereinafter also referred to as "PVA")-based resin (hereinafter also referred to as "PVA-based resin layer"). Examples of polarizing elements include: an extended film obtained by dyeing a PVA-based resin film with a dichroic dye and then uniaxially stretching it; and an extended layer obtained by dyeing a coating layer formed by coating a substrate film with a coating liquid containing a PVA-based resin onto the laminated film with a dichroic dye and then uniaxially stretching the laminated film. Stretching can be performed after dyeing with a dichroic dye, or it can be performed while dyeing, or it can be performed after stretching.

[0019] PVA-based resins are obtained by saponifying polyvinyl acetate-based resins. Polyvinyl acetate-based resins include, in addition to polyvinyl acetate as a standalone polymer, copolymers of vinyl acetate with other monomers that can copolymerize with it. Examples of other monomers that can copolymerize include, for example, unsaturated carboxylic acids, olefins such as ethylene, vinyl ethers, and unsaturated sulfonic acids.

[0020] The saponification degree of PVA-based resin is preferably about 85 mol% or more, more preferably about 90 mol% or more, and even more preferably about 99 mol% or more and 100 mol% or less. The degree of polymerization of PVA-based resin is, for example, 1000 to 10000, preferably 1500 to 5000. PVA-based resin can be modified, for example, it can also be aldehyde-modified polyvinyl formaldehyde, polyvinyl acetal, polyvinyl butyral, etc.

[0021] The thickness of the polarizing element is preferably 3 μm to 35 μm, more preferably 4 μm to 30 μm, and even more preferably 5 μm to 25 μm. By making the thickness of the polarizing element 35 μm or less, the effect of polyolefination of PVA-based resin on the reduction of optical properties under high temperature conditions can be suppressed. By making the thickness of the polarizing element 3 μm or more, it is easy to achieve the desired optical properties.

[0022] The polarizing element preferably contains an alcohol. In this embodiment, the polarizing element and the transparent protective film are bonded together by an adhesive layer formed by an alcohol-containing adhesive. Therefore, it is presumed that some of the alcohol will transfer from the adhesive layer and be contained in the polarizing element. The alcohol in the polarizing element may also be included in the polarizing element during the manufacturing process. With an alcohol-containing polarizing element, the transmittance is not easily reduced even when the polarizing plate is exposed to a high-temperature environment. It is speculated that this is because the alcohol contained in the polarizing element acts as a protic polar solvent and acts on the hydroxyl groups in the PVA chain through hydrogen bonding. This reduces the reactivity of the dehydration reaction in the PVA chain and thus inhibits the polyene formation of the PVA resin.

[0023] (Alcohol)

[0023] The alcohols used in this invention may include, for example, lower alcohols having 1 to 4 carbon atoms. Specifically, examples include: methanol, ethanol, n-propanol, isopropanol, and tributanol. The alcohols contained in the polarizing plate, polarizing element, or adhesive are preferably selected from at least one of the group consisting of methanol, ethanol, n-propanol, isopropanol, and tributanol. These may be used alone or in combination of two or more. Methanol, ethanol, n-propanol, and isopropanol are preferred. These alcohols have low molecular weights and can be widely dispersed in the polarizing element, thus helping to suppress polyene formation. The alcohols contained in the polarizing element and the alcohols contained in the adhesive may be the same or different.

[0024] Methods for making the polarizing element contain alcohol include: immersing a PVA-based resin layer in a processing solvent containing alcohol, or spraying, dripping, or dripping the processing solvent onto the PVA-based resin layer. Preferably, the method of immersing the PVA-based resin layer in a processing solvent containing alcohol is used.

[0025] The step of immersing the PVA-based resin layer in a treatment solvent containing alcohol can be performed simultaneously with the swelling, stretching, dyeing, crosslinking, and cleaning steps in the polarizing element manufacturing method described later, or it can be performed separately from these steps. The step of containing the PVA-based resin layer in alcohol is preferably performed after dyeing the PVA-based resin layer with iodine, and more preferably simultaneously with the cleaning step. According to this method, the hue change is small, thus reducing the impact on the optical characteristics of the polarizing element.

[0026] In order to make the polarizing element contain alcohol, it can be added in both the manufacturing process of the polarizing element and the adhesive.

[0027] (Feature(a))

[0027] In the case of characteristic (a), the moisture content of the polarizing element is above the equilibrium moisture content of 20% relative humidity at 20°C and below the equilibrium moisture content of 50% relative humidity at 20°C. Preferably, the moisture content of the polarizing element is below the equilibrium moisture content of 45% relative humidity at 20°C, more preferably below the equilibrium moisture content of 42% relative humidity at 20°C, and even more preferably below the equilibrium moisture content of 38% relative humidity at 20°C. If the moisture content of the polarizing element is lower than the equilibrium moisture content of 20% relative humidity at 20°C, the operability of the polarizing element decreases and it is prone to breakage. If the moisture content of the polarizing element exceeds the equilibrium moisture content of 50% relative humidity at 20°C, the transmittance of the polarizing element tends to decrease. It is inferred that if the moisture content of the polarizing element is high, the PVA resin is prone to polyolefination. The moisture content of the polarizing element is the moisture content of the polarizing element in the polarizing plate.

[0028] Methods for confirming whether the moisture content of the polarizing element is above the equilibrium moisture content at 20°C and 20% relative humidity and below the equilibrium moisture content at 20°C and 50% relative humidity may include: storing the polarizing element in an environment adjusted to the above temperature and relative humidity range, and considering the absence of mass change over a fixed period of time as reaching equilibrium with the environment; or, calculating the equilibrium moisture content of the polarizing element in an environment adjusted to the above temperature and relative humidity range in advance, and then comparing the moisture content of the polarizing element with the pre-calculated equilibrium moisture content to confirm the moisture content.

[0029] The manufacturing method of a polarizing element with a moisture content of 20°C or higher and relative humidity of 20% or lower is not particularly limited. Examples include: storing the polarizing element in an environment adjusted to the above temperature and relative humidity range for 10 minutes or more but less than 3 hours, or performing heat treatment at 30°C or more but less than 90°C.

[0030] Other preferred methods for manufacturing polarizing elements with the aforementioned moisture content include: storing a laminate with a protective film on at least one single-area layer of the polarizing element, or a polarizing plate composed of the polarizing element, in an environment adjusted to the aforementioned temperature and relative humidity range for 10 minutes to 120 hours; or performing a heat treatment at 30°C to 90°C. When manufacturing an image display device using interlayer filling, the front panel may be bonded after storing the image display panel with the polarizing plate laminated on the image display unit in an environment adjusted to the aforementioned temperature and relative humidity range for 10 minutes to 3 hours or after heating at 30°C to 90°C.

[0031] The moisture content of the polarizing element is preferably adjusted to the aforementioned value range during the material stage when the polarizing plate is constructed using either the polarizing element alone or as a laminate of the polarizing element and a protective film. Adjusting the moisture content after the polarizing plate is constructed can lead to excessive curling, potentially causing defects when bonded to the image display unit. By using a polarizing element with the aforementioned moisture content adjusted during the material stage before the polarizing plate is constructed, it is easy to construct a polarizing plate with a polarizing element whose moisture content meets the aforementioned value range. Alternatively, the moisture content of the polarizing element in the polarizing plate can be adjusted to the aforementioned value range while the polarizing plate is bonded to the image display unit. In this case, curling is less likely to occur because the polarizing plate is bonded to the image display unit.

[0032] (Feature (b))

[0032] In the case of characteristic (b), the moisture content of the polarizing plate is above the equilibrium moisture content of 20% relative humidity at 20°C and below the equilibrium moisture content of 50% relative humidity at 20°C. Preferably, the moisture content of the polarizing plate is below the equilibrium moisture content of 45% relative humidity at 20°C, more preferably below the equilibrium moisture content of 42% relative humidity at 20°C, and even more preferably below the equilibrium moisture content of 38% relative humidity at 20°C. If the moisture content of the polarizing plate is lower than the equilibrium moisture content of 20% relative humidity at 20°C, the operability of the polarizing plate decreases and it is prone to cracking. If the moisture content of the polarizing plate exceeds the equilibrium moisture content of 50% relative humidity at 20°C, the transmittance of the polarizing element tends to decrease. It is inferred that if the moisture content of the polarizing plate is high, the PVA-based resin is prone to polyolefination.

[0033] Methods for confirming whether the moisture content of the polarizing plate is above the equilibrium moisture content at 20°C and 20% relative humidity and below the equilibrium moisture content at 20°C and 50% relative humidity may include: storing the polarizing plate in an environment adjusted to the above temperature and relative humidity range, and considering the absence of mass change over a fixed period of time as reaching equilibrium with the environment; or pre-calculating the equilibrium moisture content of the polarizing plate in an environment adjusted to the above temperature and relative humidity range, and then comparing the moisture content of the polarizing plate with the pre-calculated equilibrium moisture content to confirm the moisture content.

[0034] The method for manufacturing a polarizing plate with a moisture content of 20°C or higher and relative humidity of 20% or lower is not particularly limited. Examples include: storing the polarizing plate in an environment adjusted to the above temperature and relative humidity range for 10 minutes or more but less than 3 hours, or performing heat treatment at 30°C or more but less than 90°C.

[0035] When manufacturing an image display device using interlayer filling, the image display panel with a polarizing plate laminated on the image display unit can be stored in an environment adjusted to the above-mentioned temperature and relative humidity range for 10 minutes to 3 hours or heated at 30°C to 90°C before the front panel is attached.

[0036] (Urea-based compounds)

[0036] The polarizing element may further contain a urea-based compound. A polarizing element containing a urea-based compound can further suppress the reduction in transmittance. The urea-based compound may be the same as the urea-based compound that may be contained in the adhesive described later. The method for containing a urea-based compound in the polarizing element may be the same as the method for containing an alcohol in the polarizing element. The urea-based compound may be contained during the manufacturing process of the polarizing element, or it may be contained in the adhesive used to laminate the polarizing element and the transparent protective film described later, or the polarizing element itself may contain a urea-based compound.

[0037] (Dicarboxylic acid)

[0037] The polarizing element may further contain dicarboxylic acid. A polarizing element containing dicarboxylic acid can further suppress the reduction in transmittance. The dicarboxylic acid may also be the same as that contained in the adhesive described later. The method for containing dicarboxylic acid in the polarizing element can be the same as the method for containing an alcohol in the polarizing element. This can be done by incorporating dicarboxylic acid during the manufacturing process of the polarizing element, by incorporating dicarboxylic acid into the adhesive used to laminate the polarizing element and the transparent protective film described later, or by incorporating dicarboxylic acid into the polarizing element itself.

[0038] (Manufacturing method of polarizing element)

[0038] The manufacturing method of the polarizing element is not particularly limited. Typically, it is a method of manufacturing by rolling out a PVA-based resin film pre-wound into a roll and stretching, dyeing, cross-linking, etc. (hereinafter referred to as "manufacturing method 1") or a method of coating a coating liquid containing PVA-based resin onto a substrate film to form a PVA-based resin layer as a coating layer, and then stretching the resulting laminate (hereinafter referred to as "manufacturing method 2").

[0039] In manufacturing method 1, the manufacturing process can be carried out by the following steps: a step of uniaxially stretching a PVA-based resin film, a step of dyeing the PVA-based resin film with a dichroic pigment such as iodine to adsorb the dichroic pigment, a step of treating the PVA-based resin film adsorbed with a boric acid aqueous solution, and a step of washing with water after treatment with the boric acid aqueous solution.

[0040] The swelling step is a process in which the PVA-based resin film is immersed in a swelling bath. The swelling step removes dirt and blocking agents from the surface of the PVA-based resin film, and also inhibits uneven dyeing by swelling the PVA-based resin film. The swelling bath is usually a medium with water, distilled water, or pure water as the main component. Surfactants, alcohols, etc., can be appropriately added to the swelling bath according to general methods. From the viewpoint of controlling the potassium content of the polarizing element, potassium iodide can also be used in the swelling bath. In this case, the concentration of potassium iodide in the swelling bath is preferably 1.5% by mass or less, more preferably 1.0% by mass or less, and even more preferably 0.5% by mass or less.

[0041] The temperature of the swelling bath is preferably between 10°C and 60°C, more preferably between 15°C and 45°C, and even more preferably between 18°C ​​and 30°C. The immersion time in the swelling bath varies depending on the swelling degree of the PVA resin film, but is preferably between 5 seconds and 300 seconds, more preferably between 10 seconds and 200 seconds, and even more preferably between 20 seconds and 100 seconds. The swelling step may be performed only once or multiple times as needed.

[0042] The dyeing step is a treatment step in which the PVA-based resin film is immersed in a dyeing bath (iodine solution), which allows dichroic pigments such as iodine to be adsorbed and oriented onto the PVA-based resin film. The iodine solution is usually preferably an aqueous iodine solution, containing iodine and iodides as a co-solvent. Examples of iodides include: potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, titanium iodide, etc. Among these, from the viewpoint of controlling the potassium content in the polarizing element, potassium iodide is preferable.

[0043] The iodine concentration in the staining bath is preferably 0.01% by mass or more and 1% by mass, more preferably 0.02% by mass or more and 0.5% by mass. The iodide concentration in the staining bath is preferably 0.01% by mass or more and 10% by mass, more preferably 0.05% by mass or more and 5% by mass, and even more preferably 0.1% by mass or more and 3% by mass.

[0044] The temperature of the dyeing bath is preferably between 10°C and 50°C, more preferably between 15°C and 45°C, and even more preferably between 18°C ​​and 30°C. The immersion time in the dyeing bath varies depending on the dyeing degree of the PVA resin film, but is preferably between 10 seconds and 300 seconds, more preferably between 20 seconds and 240 seconds. The dyeing step can be performed only once or multiple times as needed.

[0045] The crosslinking step involves immersing the dyed PVA-based resin film from the dyeing step in a treatment bath (crosslinking bath) containing boron compounds. The boron compounds crosslink the polyvinyl alcohol-based resin film, allowing iodine molecules or dye molecules to adsorb onto the crosslinked structure. Examples of boron compounds include boric acid, borates, and borax. The crosslinking bath is generally an aqueous solution, but can also be a mixture of an organic solvent miscible with water and water. From the viewpoint of controlling the potassium content in the polarizing element, the crosslinking bath preferably contains potassium iodide.

[0046] In the crosslinking bath, the concentration of the boron compound is preferably 1% by mass or more and 15% by mass, more preferably 1.5% by mass or more and 10% by mass, and even more preferably 2% by mass or more and 5% by mass. When potassium iodide is used in the crosslinking bath, the concentration of potassium iodide in the crosslinking bath is preferably 1% by mass or more and 15% by mass, more preferably 1.5% by mass or more and 10% by mass, and even more preferably 2% by mass or more and 5% by mass.

[0047] The temperature of the crosslinking bath is preferably between 20°C and 70°C, more preferably between 30°C and 60°C. The immersion time in the crosslinking bath varies depending on the degree of crosslinking of the PVA resin film, but is preferably between 5 seconds and 300 seconds, more preferably between 10 seconds and 200 seconds. The crosslinking step can be performed only once or multiple times as needed.

[0048] The stretching step is a process of stretching the PVA-based resin film by a predetermined ratio in at least one direction. Generally, it involves uniaxially stretching the PVA-based resin film in the transport direction (long side direction). The stretching method is not particularly limited, and either wet stretching or dry stretching can be used. The stretching step can be performed only once or multiple times as needed. The stretching step can be performed at any stage of the manufacturing process of the polarizing element.

[0049] The treatment bath (extension bath) in the wet extension method can typically be water or a mixture of water and organic solvents that are miscible with water. From the viewpoint of controlling the potassium content in the polarizing element, the extension bath preferably contains potassium iodide. When potassium iodide is used in the extension bath, the concentration of potassium iodide in the extension bath is preferably 1% by mass to 15% by mass, more preferably 2% by mass to 10% by mass, and even more preferably 3% by mass to 6% by mass. From the viewpoint of suppressing film rupture during extension, the treatment bath (extension bath) may contain a boron compound. When a boron compound is included, the concentration of the boron compound in the extension bath is preferably 1% by mass to 15% by mass, more preferably 1.5% by mass to 10% by mass, and even more preferably 2% by mass to 5% by mass.

[0050] The temperature of the stretching bath is preferably 25°C to 80°C, more preferably 40°C to 75°C, and even more preferably 50°C to 70°C. The immersion time in the stretching bath varies depending on the temperature of the stretching bath, but is preferably 10 seconds to 800 seconds, and more preferably 30 seconds to 500 seconds. The stretching treatment in the wet stretching method can also be performed together with one or more of the following steps: swelling, dyeing, crosslinking, and cleaning.

[0051] Examples of dry stretching methods include: inter-roll stretching, heated roll stretching, and compression stretching. In addition, dry stretching can also be carried out together with the drying step.

[0052] The total elongation ratio (cumulative elongation ratio) applied to the polyvinyl alcohol resin film can be appropriately set according to the target, preferably more than 2 times and less than 7 times, more preferably more than 3 times and less than 6.8 times, and even more preferably more than 3.5 times and less than 6.5 times.

[0053] The cleaning step is a process of immersing the polyvinyl alcohol-based resin film in a cleaning bath, which removes foreign matter remaining on the surface of the polyvinyl alcohol-based resin film. The cleaning bath is usually a medium with water, distilled water, or pure water as the main component. Furthermore, from the viewpoint of controlling the potassium content in the polarizing element, it is preferable to use potassium iodide in the cleaning bath. In this case, the concentration of potassium iodide in the cleaning bath is preferably 1% by mass or more and 10% by mass or less, more preferably 1.5% by mass or more and 4% by mass or less, and even more preferably 1.8% by mass or more and 3.8% by mass or less.

[0054] The temperature of the cleaning bath is preferably between 5°C and 50°C, more preferably between 10°C and 40°C, and even more preferably between 15°C and 30°C. The immersion time in the cleaning bath varies depending on the temperature, but is preferably between 1 second and 100 seconds, more preferably between 2 seconds and 50 seconds, and even more preferably between 3 seconds and 20 seconds. The cleaning process can be performed only once or multiple times as needed.

[0055] The drying step is the step of drying the PVA-based resin film that has been cleaned in the cleaning step to obtain the polarizing element. Drying can be carried out by any suitable method, such as natural drying, air drying, or heat drying.

[0056] In manufacturing method 2, the manufacturing process can be carried out by the following steps: coating a coating liquid containing a PVA-based resin onto a substrate film; uniaxially stretching the resulting laminated film; dyeing the PVA-based resin layer of the uniaxially stretched laminated film with a dichroic dye to adsorb the dichroic dye for use as a polarizing element; treating the film adsorbed with a boric acid aqueous solution; and washing with water after treatment with the boric acid aqueous solution. The substrate film used to form the polarizing element can also be used as a protective layer for the polarizing element. The substrate film can also be peeled off from the polarizing element as needed.

[0057] <Transparent Protective Film>

[0057] The transparent protective film used in this embodiment (hereinafter also referred to as "protective film") is adhered to at least one side of the polarizing element through an adhesive layer. This transparent protective film may be adhered to one or both sides of the polarizing element, but is preferably adhered to both sides.

[0058] The protective film may also have other optical functions and may form a multi-layered laminated structure. From an optical point of view, a thinner protective film is preferable, but if it is too thin, the strength will be reduced and the processability will be poor. The appropriate film thickness is 5 μm to 100 μm, preferably 10 μm to 80 μm, and even more preferably 15 μm to 70 μm.

[0059] The protective film may be a cellulose-based film, a film made of polycarbonate resin, a film made of cyclic olefin resins such as norbornene, a (meth)acrylic polymer film, a polyester resin film such as polyethylene terephthalate, or other thin films. When the protective film is bonded to both sides of the polarizing element using a water-based adhesive such as PVA adhesive, from the viewpoint of moisture permeability, it is preferable that at least one side of the protective film is either a cellulose-based film or a (meth)acrylic polymer film, with a cellulose-based film being more preferred.

[0060] For purposes such as compensating for viewing angle, at least one of the protective films may also have a phase difference function. In this case, the protective film itself may have a phase difference function, or it may have a separate phase difference layer, or it may be a combination of both. The film with the phase difference function may be directly bonded to the polarizing element through an adhesive, but it may also be a structure formed by bonding another protective film bonded to the polarizing element through an adhesive or bonding agent.

[0061] <Adhesive layer>

[0061] The adhesive constituting the adhesive layer for bonding the protective film to the polarizing element is preferably an alcohol-containing adhesive. Water-based adhesives, solvent-based adhesives, and active energy line curing adhesives can be used, but from the viewpoint of containing alcohol, a water-based adhesive is preferred, and more preferably, it contains a PVA-based resin. By using an alcohol-containing adhesive, the decrease in transmittance of the polarizing plate under high-temperature conditions can be suppressed.

[0062] The thickness of the adhesive coating can be set to any value, for example, it can be set in a way that an adhesive layer with a desired thickness can be obtained after curing or heating (drying). The thickness of the adhesive layer formed by the adhesive is preferably 0.01 μm to 7 μm, more preferably 0.01 μm to 5 μm, even more preferably 0.01 μm to 2 μm, and most preferably 0.01 μm to 1 μm.

[0063] The following description of the adhesive is a preferred approach for cases where the polarizing element is not contained in alcohol during manufacturing. If the polarizing element contains alcohol, the following values ​​can be adjusted appropriately. For specific examples of alcohol, the same alcohol contained in the polarizing element described above can be used. During the drying process of forming the adhesive layer when bonding the polarizing element to the protective film, it is acceptable for some alcohol to migrate from the adhesive layer to the polarizing element.

[0064] When the adhesive is an aqueous adhesive containing PVA-based resin, the alcohol content in the adhesive is preferably 30 parts by weight to 2000 parts by weight relative to 100 parts by weight of the PVA-based resin, more preferably 100 parts by weight to 1800 parts by weight, even more preferably 500 parts by weight to 1800 parts by weight, and most preferably 800 parts by weight to 1500 parts by weight. If it is less than 30 parts by weight, the effect of sufficiently improving high-temperature durability may not be obtained. On the other hand, if the alcohol content exceeds 2000 parts by weight, it may lead to a deterioration in color. By setting the alcohol content in the adhesive within the aforementioned range, the drying efficiency can be improved in the drying step after the protective film is deposited on the polarizing element through the adhesive, and the alcohol content in the polarizing plate can be easily adjusted to the desired amount.

[0065] In the configuration in which a transparent protective film is attached to both sides of a polarizing element with an adhesive layer between them, the adhesive layer on both sides of the polarizing element may be an alcohol-containing layer on only one side, but it is preferable that the adhesive layer on both sides is an alcohol-containing layer.

[0066] To meet the demand for thinner polarizing plates, polarizing plates with a transparent protective film on only one side of the polarizing element have been developed. This configuration also includes a transparent protective film laminated with an adhesive layer containing alcohol. Regarding the manufacturing method of this polarizing plate with a transparent protective film on only one side of the polarizing element, one has conceived of first fabricating polarizing plates with the transparent protective film bonded to both sides through an adhesive layer, and then peeling off the transparent protective film from one side. Using this manufacturing method, it is acceptable for only one side of the adhesive layer to contain alcohol, but it is preferable that both sides of the adhesive layer contain alcohol. When using an adhesive layer containing alcohol only on one side of the polarizing element, it is preferable that the adhesive layer on the unpeeled film side contains alcohol.

[0067] (Water-based adhesive)

[0067] Any suitable water-based adhesive may be used, but it is preferable to use a water-based adhesive containing PVA-based resin (PVA-based adhesive). From the viewpoint of adhesion, the average degree of polymerization of the PVA-based resin contained in the water-based adhesive is preferably 100 to 5500, and more preferably 1000 to 4500. From the viewpoint of adhesion, the average degree of saponification is preferably 85 mol% to 100 mol%, and more preferably 90 mol% to 100 mol%.

[0068] The PVA-based resin contained in the water-based adhesive preferably contains acetoacetyl, because the PVA-based resin layer has excellent adhesion and durability to the protective film. The acetoacetyl-containing PVA-based resin can be obtained, for example, by reacting the PVA-based resin with diketene by any method. The degree of acetoacetyl modification of the acetoacetyl-containing PVA-based resin is, typically, 0.1 mol% or more, preferably 0.1 mol% or more and 20 mol% or less. The resin concentration of the water-based adhesive is preferably 0.1% by mass or more and 15% by mass, and more preferably 0.5% by mass or more and 10% by mass.

[0069] Water-based adhesives may also contain crosslinking agents. Commonly known crosslinking agents may be used. Examples of crosslinking agents include water-soluble epoxides, dialdehydes, and isocyanates.

[0070] When the PVA resin is a PVA resin containing acetyl groups, the crosslinking agent is preferably any one of glyoxal, glyoxylate, and hydroxymethyl melamine, more preferably any one of glyoxal and glyoxylate, and most preferably glyoxal.

[0071] (Active Energy Line Curing Adhesive)

[0071] Active energy line curing adhesives are adhesives that cure by irradiation with active energy lines such as ultraviolet light. Examples include adhesives containing polymerizable compounds and photopolymerization initiators, adhesives containing photoreactive resins, and adhesives containing binder resins and photoreactive crosslinking agents. Examples of polymerizable compounds include photopolymerizable monomers such as photocurable epoxy monomers, photocurable acrylic monomers, and photocurable ethyl carbamate monomers, as well as oligomers derived from these monomers. Examples of photopolymerization initiators include compounds containing substances that generate active species such as neutral free radicals, anionic free radicals, and cationic free radicals when irradiated with active energy lines such as ultraviolet light.

[0072] (Urea compounds)

[0072] The adhesive may further contain at least one urea compound selected from urea, urea derivatives, thiourea, and thiourea derivatives. By including a urea compound in the adhesive layer formed by the adhesive, high-temperature durability can be further improved. During the formation of the adhesive layer through the drying step of bonding the adhesive to the protective film, it is acceptable for some of the urea compound to migrate from the adhesive layer to polarizing elements, etc. Urea compounds are available in both water-soluble and water-insoluble forms, and any type of urea compound can be used. When using a water-insoluble urea compound in a water-soluble adhesive, it is preferable to refine the dispersion method to avoid an increase in haze after the adhesive layer is formed.

[0073] When the adhesive is an aqueous adhesive containing PVA-based resin, the amount of urea compound added relative to 100 parts by weight of PVA is preferably 0.1 parts by weight to 400 parts by weight, more preferably 1 part by weight to 200 parts by weight, and even more preferably 3 parts by weight to 100 parts by weight.

[0074] (Urea derivative)

[0074] Urea derivatives are compounds in which at least one of the four hydrogen atoms of a urea molecule is replaced by a substituent. In this case, the substituent is not particularly limited, but is preferably formed by a carbon atom, a hydrogen atom, and an oxygen atom. Some urea derivatives have low solubility in water, but conversely, they have sufficient solubility in alcohols. In this case, it is also a preferred method to dissolve the urea compound in alcohol to prepare an alcoholic solution of the urea compound, and then add the alcoholic solution of the urea compound to an aqueous PVA solution to prepare an adhesive.

[0075] Specific examples of urea derivatives include: monosubstituted ureas such as methylurea, ethylurea, propylurea, butylurea, isobutylurea, N-octadecylurea, 2-hydroxyethylurea, hydroxyurea, acetylurea, allylurea, 2-propynylurea, cyclohexylurea, phenylurea, 3-hydroxyphenylurea, (4-methoxyphenyl)urea, benzylurea, benzoylurea, o-tolylurea, and p-tolylurea. Disubstituted ureas include: 1,1-dimethylurea, 1,3-dimethylurea, 1,1-diethylurea, 1,3-diethylurea, 1,3-bis(hydroxymethyl)urea, 1,3-tert-butylurea, 1,3-dicyclohexylurea, 1,3-diphenylurea, 1,3-bis(4-methoxyphenyl)urea, 1-acetyl-3-methylurea, 2-imidazolinone (vinylurea), and tetrahydro-2-pyrimidinone (acrylurea). Examples of tetrasubstituted ureas include: tetramethylurea, 1,1,3,3-tetraethylurea, 1,1,3,3-tetrabutylurea, 1,3-dimethoxy-1,3-dimethylurea, 1,3-dimethyl-2-imidazolinone, and 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone.

[0076] (Thiocarbamide derivatives)

[0076] A thiourea derivative is a compound in which at least one of the four hydrogen atoms of the thiourea molecule is replaced by a substituent. In this case, the substituent is not particularly limited, but is preferably a substituent formed by a carbon atom, a hydrogen atom, and an oxygen atom.

[0077] Specific examples of thiourea derivatives include monosubstituted thioureas such as: N-methylthiourea, ethylthiourea, propylthiourea, isopropylthiourea, 1-butylthiourea, cyclohexylthiourea, N-acetylatedthiourea, N-allylthiourea, (2-methoxyethyl)thiourea, N-phenylthiourea, (4-methoxyphenyl)thiourea, N-(2-methoxyphenyl)thiourea, N-(1-naphthyl)thiourea, (2-pyridyl)thiourea, o-tolylthiourea, and p-tolylthiourea. Examples of disubstituted thioureas include: 1,1-dimethylthiourea, 1,3-dimethylthiourea, 1,1-diethylthiourea, 1,3-diethylthiourea, 1,3-dibutylthiourea, 1,3-diisopropylthiourea, 1,3-dicyclohexylthiourea, N,N-diphenylthiourea, N,N'-diphenylthiourea, 1,3-di(o-tolyl)thiourea, 1,3-di(p-tolyl)thiourea, 1-benzyl-3-phenylthiourea, 1-methyl-3-phenylthiourea, N-allyl-N'-(2-hydroxyethyl)thiourea, and ethylenethiourea. Examples of trisubstituted thioureas include: trimethylthiourea. Examples of tetrasubstituted thioureas include: tetramethylthiourea and 1,1,3,3-tetraethylthiourea.

[0078] Among urea compounds, from the viewpoint that they can better suppress the decrease in transmittance under high-temperature environments when used in image display devices constructed with interlayer filling, urea derivatives or thiourea derivatives are preferred, and urea derivatives are even more preferred. Among urea derivatives, monosubstituted urea or disubstituted urea are preferred, and monosubstituted urea is even more preferred. Among disubstituted urea, 1,1-substituted urea and 1,3-substituted urea are preferred, and 1,3-substituted urea is even more preferred.

[0079] (Dicarboxylic acid)

[0079] The adhesive may contain dicarboxylic acids. By using an adhesive containing dicarboxylic acids, the decrease in transmittance of the polarizing plate under high-temperature conditions can be suppressed. Examples of dicarboxylic acids include: oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, tartaric acid, glutamic acid, malic acid, maleic acid, fumaric acid, itaconic acid, mucoacic acid, 1,4-cyclohexanedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 4,4-biphenyldicarboxylic acid, 2,5-pyridinedicarboxylic acid, 3,5-pyridinedicarboxylic acid, diphenyl tannic acid, diphenylmethanedicarboxylic acid, oxaloacetic acid, methyl fumaric acid, 2,6-pyridinedicarboxylic acid, etc. Of these, citric acid, malic acid, maleic acid, or tartaric acid are preferred. These dicarboxylic acids may be used alone or in combination of two or more.

[0080] [Manufacturing Method of Polarizing Plate]

[0080] The method for manufacturing the polarizing plate of this embodiment includes a moisture content adjustment step and a lamination step. In the moisture content adjustment step, when manufacturing the polarizing plate having feature (a), the moisture content of the polarizing element is adjusted to be above the equilibrium moisture content of 20°C and 20% relative humidity, and below the equilibrium moisture content of 50% relative humidity at 20°C. The moisture content of the polarizing element can be adjusted according to the aforementioned description of the moisture content of the polarizing element. In the moisture content adjustment step, when manufacturing the polarizing plate having feature (b), the moisture content of the polarizing plate is adjusted to be above the equilibrium moisture content of 20°C and 20% relative humidity, and below the equilibrium moisture content of 50% relative humidity at 20°C. The moisture content of the polarizing plate can be adjusted according to the aforementioned description of the moisture content of the polarizing plate. In the lamination step, the polarizing element and the transparent protective film are laminated through the aforementioned adhesive layer. In the lamination step, for example, an alcohol-containing adhesive is used to bond the untreated polarizing element and the transparent protective film. The order of the moisture content adjustment step and the lamination step is not limited, and the moisture content adjustment step and the lamination step can also be performed simultaneously.

[0081] [Composition of the image display device]

[0081] The polarizing plate of this embodiment is used in various image display devices such as liquid crystal display devices and organic EL display devices. In image display devices, when the polarizing plate is constructed with interlayer filling, where both sides are in contact with a layer other than an air layer, specifically a solid layer such as an adhesive layer, the transmittance tends to decrease at high temperatures. Even with an interlayer filling structure, the image display device using the polarizing plate of this embodiment can suppress the decrease in transmittance of the polarizing plate at high temperatures. An example of an image display device is a configuration having an image display unit, a first adhesive layer deposited on the viewing side surface of the image display unit, and a polarizing plate deposited on the viewing side surface of the first adhesive layer. This image display device further includes a second adhesive layer deposited on the viewing side surface of the polarizing plate and a transparent member deposited on the surface of the second adhesive layer. The polarizing plate of this embodiment is particularly suitable for image display devices having the following interlayer filling configuration: a transparent member is disposed on the viewing side of the image display device, the polarizing plate and the image display unit are bonded together by a first adhesive layer, and the polarizing plate and the transparent member are bonded together by a second adhesive layer. In this specification, either or both of the first and second adhesive layers may sometimes be referred to as "adhesive layer". Furthermore, the member used to bond the polarizing plate to the image display unit, and the member used to bond the polarizing plate to the transparent member, are not limited to adhesive layers and may also be adhesive layers.

[0082] <Image Display Unit>

[0082] Image display units may include: liquid crystal units and organic EL units. The liquid crystal unit may be any of the following: a reflective liquid crystal unit utilizing external light, a transmissive liquid crystal unit utilizing light from a light source such as a backlight, or a transmissive / reflective liquid crystal unit utilizing both external light and light from a light source. When the liquid crystal unit utilizes light from a light source, a polarizing plate is also disposed on the side opposite to the viewing side of the image display unit (liquid crystal unit), and then a light source is disposed thereon. The polarizing plate on the light source side and the liquid crystal unit are preferably bonded together with a suitable adhesive layer. The driving method of the liquid crystal unit may be any type, such as VA mode, IPS mode, TN mode, STN mode, or bent alignment (π type).

[0083] Organic EL units are preferably formed by sequentially depositing transparent electrodes, organic light-emitting layers, and metal electrodes on a transparent substrate to create a light-emitting body (organic electroluminescent body). The organic light-emitting layer is a stack of various organic thin films, such as a stack of a hole injection layer composed of a triphenylamine derivative and a light-emitting layer composed of a fluorescent organic solid such as anthracene, a stack of such light-emitting layers and an electron injection layer composed of a perylene derivative, or a stack of a hole injection layer, a light-emitting layer, and an electron injection layer, etc.

[0084] <Lamination of image display unit and polarizing plate>

[0084] An adhesive layer (adhesive sheet) is preferably used for bonding the image display unit to the polarizing plate. From the viewpoint of workability, a method of bonding the polarizing plate with an adhesive layer attached to one side of the polarizing plate to the image display unit is preferred. The adhesive layer can be attached to the polarizing plate in a suitable manner. Examples include: preparing an adhesive solution of 10% by mass to 40% by mass, which is a solvent composed of a matrix polymer or its composition dissolved or dispersed in a suitable solvent such as toluene or ethyl acetate, and directly applying it to the polarizing plate by a suitable spreading method such as casting or coating; or forming the adhesive layer on a separator and then transferring it to the polarizing plate.

[0085] <Adhesive layer>

[0085] The adhesive layer may consist of one or more layers, but preferably one layer. The adhesive layer may be composed of an adhesive composition with (meth)acrylic resin, rubber resin, ethyl carbamate resin, ester resin, polysiloxane resin, or polyvinyl ether resin as the main component. Preferably, the adhesive composition uses a (meth)acrylic resin as the matrix polymer, which has excellent transparency, weather resistance, and heat resistance. The adhesive composition may also be of the active energy linear curing type or the thermosetting type.

[0086] The (meth)acrylate resin (matrix polymer) used in the adhesive composition is preferably a polymer or copolymer with one or more of the following (meth)acrylates as monomers: butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, etc. Preferably, the matrix polymer is copolymerized with a polar monomer. Examples of polar monomers include: (meth)acrylate compounds, 2-hydroxypropyl (meth)acrylate compounds, hydroxyethyl (meth)acrylate compounds, (meth)acrylamide compounds, N,N-dimethylaminoethyl (meth)acrylate compounds, glycidyl (meth)acrylate compounds, etc., monomers having carboxyl, hydroxyl, acetamide, amino, epoxy, etc.

[0087] The adhesive composition may contain only the matrix polymer described above, but usually further contains a crosslinking agent. Examples of crosslinking agents include: divalent or higher metal ions that form carboxylic acid metal salts with carboxyl groups, polyamine compounds that form amide bonds with carboxyl groups, polyepoxides or polyols that form ester bonds with carboxyl groups, and polyisocyanate compounds that form amide bonds with carboxyl groups. Polyisocyanate compounds are preferred.

[0088] The active energy line curing adhesive composition has the property of curing upon irradiation with active energy lines such as ultraviolet light or electron beams. It possesses the following properties: it retains adhesiveness even before irradiation with the active energy lines and can adhere tightly to substrates such as films; it cures upon irradiation with the active energy lines, and the adhesion strength can be adjusted. The active energy line curing adhesive composition is preferably ultraviolet-curing. In addition to the matrix polymer and crosslinking agent, the active energy line curing adhesive composition contains an active energy line polymerizable compound. It may also contain photopolymerization initiators, photosensitizers, etc., depending on the requirements.

[0089] The adhesive composition may include microparticles, beads (resin beads, glass beads, etc.), glass fibers, resins other than matrix polymers, tackifiers, fillers (metal powders and other inorganic powders, etc.), antioxidants, ultraviolet absorbers, dyes, pigments, colorants, defoamers, corrosion inhibitors, photopolymerization initiators and other additives to impart light scattering properties.

[0090] An adhesive layer can be formed by applying an organic solvent dilution of the above-mentioned adhesive composition to the surface of a substrate film, an image display unit, or a polarizing plate and allowing it to dry. The substrate film is generally a thermoplastic resin film, and a typical example is a release membrane that has undergone a demolding treatment. The release membrane can be, for example, a release treatment such as polysiloxane treatment performed on the surface of a film made of resins such as polyethylene terephthalate, polybutylene terephthalate, polycarbonate, or polyarylate, to which the adhesive layer is to be formed.

[0091] Alternatively, the adhesive composition can be directly coated onto the release surface of the separation membrane to form an adhesive layer, and then this adhesive layer with the separation membrane attached can be deposited onto the surface of the polarizer. Alternatively, the adhesive composition can be directly coated onto the surface of the polarizer to form an adhesive layer, and then a separation membrane can be deposited on the outer surface of the adhesive layer.

[0092] When an adhesive layer is provided on the surface of a polarizing plate, it is preferable to perform surface activation treatments such as plasma treatment or corona treatment on the bonding surface of the polarizing plate and / or the bonding surface of the adhesive layer, and more preferably to perform corona treatment.

[0093] Alternatively, an adhesive sheet can be prepared by coating an adhesive composition onto the second separation membrane to form an adhesive layer, and then depositing the separation membrane onto the formed adhesive layer. After peeling the second separation membrane from the adhesive sheet, the adhesive layer with the separation membrane attached is then deposited onto the polarizing plate. The second separation membrane is one that has a weaker adhesion to the adhesive layer than the separation membrane and is easier to peel off.

[0094] The thickness of the adhesive layer is not particularly limited, for example, it is preferably 1 μm or more and 100 μm or less, more preferably 3 μm or more and 50 μm or less, and may also be 20 μm or more.

[0095] <Transparent Components>

[0095] Transparent components disposed on the viewing side of an image display device may include transparent panels (window layers) or touch panels. The transparent panel is a transparent panel with appropriate mechanical strength and thickness. Examples of such transparent panels include transparent resin panels made of polyimide resin, acrylic resin, or polycarbonate resin, or glass panels. It is also permissible to deposit functional layers such as anti-reflective layers on the viewing side of the transparent panel. Furthermore, if the transparent panel is a transparent resin panel, it is also permissible to deposit a hard coating to improve physical strength or a low-permeability layer to reduce moisture permeability. The touch panel may use various types of touch panels, such as resistive film, capacitive, optical, and ultrasonic touch panels, as well as glass panels or transparent resin panels with touch sensor functions. When using a capacitive touch panel as the transparent component, it is preferable to place the transparent panel, made of glass or transparent resin, closer to the viewing side than the touch panel.

[0096] <Fitting of polarizing plate and transparent component>

[0096] When bonding the polarizing plate to the transparent component, it is advisable to use an adhesive or an active energy line curing adhesive. When using an adhesive, it can be applied in an appropriate manner. Specific application methods can be exemplified by, for example, the method for applying the adhesive layer used in the aforementioned bonding of the image display unit and the polarizing plate.

[0097] When using an active energy line curing adhesive, to prevent the adhesive solution from spreading before curing, it is advisable to use a method of setting up a dam material to surround the periphery of the image display panel, placing a transparent component on the dam material, and then injecting the adhesive solution. After injecting the adhesive solution, positioning and degassing are performed as needed, followed by irradiation with active energy lines for curing.

[0097] [Example]

[0098] The present invention will be specifically described below with reference to the embodiments. The materials, reagents, quantities and proportions, operations, etc. shown in the following embodiments may be appropriately modified as long as they do not depart from the spirit of the present invention.

[0098] Therefore, the present invention is not limited to the following embodiments and is not limited thereto.

[0099] (1) Measurement of the thickness of the polarizing element:

[0099] Measurements were performed using a digital micrometer "MH-15M" manufactured by Nikon Corporation.

[0100] (2) Measurement of transmittance of polarizing plate with visual sensitivity correction:

[0100] Measurements were performed using a spectrophotometer with an integrating sphere [“V7100” manufactured by Japan Spectrophotometer Co., Ltd., 2-degree field of view; C light source].

[0101] (3) Measurement of the amount of alcohol (methanol) in the polarizing plate:

[0101] The polarizing plate was cut into 1 cm squares to obtain the evaluation sample. 5 mL of ultrapure water was added to the evaluation sample, and the mixture was heated at 70°C for 30 minutes with stirring. The sample was then measured by GC-FID under the following conditions.

[0101] (Gas Chromatography Analysis Conditions)

[0101] Series: DB-WAX 30m×0.250mm×0.25μm, ID (Agilent Technologies) or equivalent.

[0101] Carrier gas: Helium, 1.0 mL / min

[0101] Column temperature: 40℃ (hold for 5 minutes) → increase at 20℃ / minute → 240℃ (hold for 10 minutes)

[0101] Injection port temperature: 240℃, injection volume: 1μL, split ratio: 50:1

[0101] Detector temperature: 240℃, Detector: FID

[0102] (4) Measurement of yellowing index (yellowness):

[0102] Use a KONICA MINOLTA spectrophotometer CM-3700A. Measure the reflected light in SCI mode to obtain the three stimulus values ​​(X, Y, Z). Calculate the yellowing index (YI) according to the following formula based on the ASTM E 313-73 specification.

[0102] YI=100×(1.000-0.847×Z / Y)

[0103] <Fabrication of Polarizing Elements>

[0103] A 40 μm thick PVA film, composed of PVA with an average degree of polymerization of approximately 2400 and a saponification degree of 99.9 moles or higher, was uniaxially stretched approximately 5 times using a dry method. While still under tension, it was immersed in pure water at 60°C for 1 minute, and then immersed in an aqueous solution of iodine / potassium iodide / water at a weight ratio of 0.05 / 5 / 100 at 28°C for 60 seconds. Afterward, it was immersed in an aqueous solution of potassium iodide / boric acid / water at a weight ratio of 8.5 / 8.5 / 100 at 72°C for 300 seconds. Then, it was washed with pure water at 26°C for 20 seconds and dried at 65°C to obtain a 15 μm thick polarizing element with iodine adsorbed and aligned within the PVA.

[0104] [Preparation of Adhesives 1 to 4]

[0104] (Preparation of PVA solution A for adhesive)

[0104] Dissolve 50g of modified PVA resin containing acetyl groups ("Gohsenx Z-410" manufactured by Mitsubishi Chemical Corporation) in 950g of pure water, heat at 90°C for 2 hours and then cool to room temperature to obtain a PVA solution for adhesives (hereinafter referred to as "PVA solution A").

[0105] (Preparation of adhesives 1 to 4)

[0105] Adhesives 1 to 4 are prepared by mixing the above-prepared PVA solution A, pure water, maleic acid, 40% by mass solution of glyoxal and methanol in the amounts shown in Table 1.

[0106] [Table 1]

[0107] <Preparation of Transparent Protective Film>

[0107] A commercially available cellulose ester membrane TD40N (manufactured by Fuji Film Co., Ltd., membrane thickness 40 μm) was immersed in a 1.5 mol / L NaOH aqueous solution (saponification solution) maintained at 55°C for 2 minutes, and then washed with water. Afterwards, it was immersed in a 0.05 mol / L sulfuric acid aqueous solution at 25°C for 30 seconds, and then rinsed under running water for 30 seconds to neutralize the membrane. Next, the membrane was dehydrated three times using an air knife to remove water, and then dried in a 70°C drying area for 15 seconds to produce a saponified membrane as a transparent protective film.

[0108] [Production of Polarizing Plates]

[0108] A transparent protective film is bonded to both sides of the polarizing element through adhesive 1 using a roller laminator. After bonding, the film is heated at 65°C for 12 minutes to dry the adhesive and obtain polarizing plate 1. The single-cell transmittance of polarizing plate 1 is 40.8%. The adhesive layer is adjusted so that the thickness on both sides is 50 nm after drying.

[0109] In polarizing plate 1, adhesive 1 is replaced with adhesives 2 to 4 to obtain polarizing plates 2 to 4. The monomer transmittance of polarizing plates 2 to 4 is also 40.8% respectively.

[0110] (Adjustment of moisture content in polarizing plate (polarizing element))

[0110] The polarizing plates 1 to 4 obtained above were stored for 72 hours at a temperature of 20°C and a relative humidity of 30%. The moisture content was measured using the Karl Fischer method at 66, 69, and 72 hours of storage. The moisture content values ​​did not change at the 66, 69, and 72 hour storage times. Therefore, the moisture content of polarizing plates 1 to 4 can be considered to be the same as the equilibrium moisture content of the 72-hour storage environment used in this experimental example. When the moisture content of a polarizing plate reaches equilibrium in a certain storage environment, the moisture content of the polarizing element in the polarizing plate can also be considered to have reached equilibrium in that storage environment. Furthermore, when the moisture content of the polarizing element in a polarizing plate reaches equilibrium in a certain storage environment, the moisture content of the polarizing plate can also be considered to have reached equilibrium in that storage environment.

[0111] Optical laminates 1 to 4 are manufactured in the following manner: using any one of the polarizing plates 1 to 4 shown in Table 2, the polarizing plate (polarizing element) is stored for 72 hours at a temperature of 20°C and a relative humidity of 30% so that the moisture content of the polarizing plate (polarizing element) used is equal to the equilibrium moisture content of the environment shown in Table 2.

[0112] The methanol content of the polarizing plate (optical laminate) was measured after it had been stored in a predetermined temperature and humidity environment and its moisture content had been adjusted. The measurement results are shown in Table 2.

[0113] <High Temperature Durability Evaluation>

[0113] (Preparation of the evaluation sample)

[0113] An acrylic adhesive (manufactured by Lintec Corporation, model: #7) was formed on both sides of optical laminates 1 to 4. The laminates were then cut to a size of 110mm × 60mm with the absorption axis of the polarizer parallel to its long side. Alkali-free glass (Corning Corporation "EAGLE XG", size 120mm × 70mm) was laminated onto each adhesive surface to create evaluation samples. The resulting evaluation samples were subjected to autoclaving at 50°C and 5 atm for 15 minutes, followed by exposure to 105°C for 72 hours for high-temperature durability testing.

[0113] The results of YI after 60 hours and after 72 hours are shown in Table 2.

[0114] [Table 2]

Claims

1. A polarizing plate comprising a polarizing element formed by adsorbing and aligning iodine into a polyvinyl alcohol resin layer, and a transparent protective film deposited on at least one side of the aforementioned polarizing element, wherein, The amount of alcohol contained in the aforementioned polarizing plate is between 60 μg / cm2 and 230 μg / cm2. The aforementioned polarizing element and the aforementioned transparent protective film are bonded together by an adhesive layer formed by an adhesive containing the aforementioned alcohol and dicarboxylic acid. The moisture content of the aforementioned polarizing element is above the equilibrium moisture content at a temperature of 20°C and a relative humidity of 20% and below the equilibrium moisture content at a temperature of 20°C and a relative humidity of 50%.

2. A polarizing plate comprising a polarizing element formed by adsorbing and aligning iodine into a polyvinyl alcohol resin layer, and a transparent protective film deposited on at least one side of the aforementioned polarizing element, wherein, The amount of alcohol contained in the aforementioned polarizing plate is between 60 μg / cm2 and 230 μg / cm2. The aforementioned polarizing element and the aforementioned transparent protective film are bonded together by an adhesive layer formed by an adhesive containing the aforementioned alcohol and dicarboxylic acid. The moisture content of the aforementioned polarizing plate is above the equilibrium moisture content at a temperature of 20°C and a relative humidity of 20% and below the equilibrium moisture content at a temperature of 20°C and a relative humidity of 50%.

3. The polarizing plate as described in claim 1 or 2, wherein, The aforementioned alcohol is selected from at least one of the group consisting of methanol, ethanol and n-propanol.

4. The polarizing plate as described in claim 1 or 2, wherein, The aforementioned adhesive includes polyvinyl alcohol-based resins.

5. The polarizing plate as described in claim 4, wherein, The content of the alcohol in the adhesive is more than 100 parts by weight and less than 2000 parts by weight, relative to 100 parts by weight of the aforementioned polyvinyl alcohol resin.

6. The polarizing plate as described in claim 1 or 2, wherein, The thickness of the aforementioned adhesive layer is 0.01 to 7 μm.

7. The polarizing plate as described in claim 1 or 2, wherein, The aforementioned polarizing plate is used in an image display device. In the aforementioned image display device, a layer other than an air layer is provided on both sides of the aforementioned polarizing plate in such a way that it is in contact with both sides of the aforementioned polarizing plate.

8. An image display device comprising: an image display unit; a first adhesive layer deposited on the viewing side surface of the image display unit; and a polarizing plate as described in any one of claims 1 to 7, deposited on the viewing side surface of the first adhesive layer.

9. The image display device as claimed in claim 8, further comprising: a second adhesive layer deposited on the viewing side surface of the aforementioned polarizing plate; and a transparent member deposited on the viewing side surface of the aforementioned second adhesive layer.

10. The image display device as claimed in claim 9, wherein, The aforementioned transparent component is a glass plate or a transparent resin plate.

11. The image display device as claimed in claim 9, wherein, The aforementioned transparent component is a touch panel.