Polarizing plate and image display device

Abstract

This invention provides a polarizing plate for suppressing transmittance reduction under high-temperature environments. The polarizing plate of this invention sequentially comprises a polarizing element having a dichroic pigment adsorbed and aligned on a polyvinyl alcohol resin layer, a transparent protective layer, and an adhesive layer. The aforementioned adhesive layer contains at least one urea compound selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives. The moisture content of the aforementioned polarizing element is above the equilibrium moisture content at 20°C and 30% relative humidity, and below the equilibrium moisture content at 20°C and 50% relative humidity.

Description

Technical Field

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

[0002] Liquid crystal displays (LCDs) are not only used in LCD televisions, but also widely used in portable devices such as computers and mobile phones, as well as in vehicles such as car navigation systems. Typically, an LCD device has a liquid crystal panel with polarizing plates bonded to both sides of liquid crystal cells using pressure-sensitive adhesive. The liquid crystal panel controls the light from the backlight to display the image. In recent years, similar to LCDs, organic EL displays have also been widely used in portable devices such as televisions and mobile phones, as well as in vehicles such as car navigation systems. In organic EL displays, to suppress the reflection of external light at the metal electrode (cathode) and prevent it from appearing as a mirror, a circular polarizing plate (a laminate containing polarizing elements and a λ / 4 plate) is sometimes placed on the viewing side surface of the image display panel.

[0003] As mentioned above, polarizing plates are increasingly used in automotive applications as components of image display devices such as liquid crystal displays and organic EL displays. Compared to applications in portable devices such as televisions or mobile phones, polarizing plates used in automotive image display devices are often exposed to high-temperature environments, thus requiring those with minimal changes in high-temperature characteristics (high-temperature durability).

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

[0005] In this configuration, if an air layer exists between the image display panel and transparent components such as the front panel or touch panel, external light reflection will occur due to the reflection of light at the air layer interface, which tends to reduce the visibility of the image. Therefore, the following configuration is often adopted: the space between the polarizing plate disposed on the viewing side surface of the image display panel and the transparent component is filled with a layer other than the air layer, generally a solid layer (hereinafter referred to as "interlayer filler") (hereinafter referred to as "interlayer filling configuration"). The interlayer filler is preferably a material with a refractive index close to that of the polarizing plate or the transparent component. The interlayer filler can suppress the reduction in visibility caused by interface reflection, and adhesives or UV-curing adhesives can be used for the purpose of fixing the components together (see, for example, Patent Document 1).

[0006] The interlayer filling structure is widely used for portable devices such as mobile phones that are often used outdoors. Also, in recent years, due to the increasing requirement for visibility, the interlayer filling structure has been considered for use in vehicle applications such as car navigation devices. The interlayer filling structure includes disposing a front transparent plate on the surface of an image display panel and filling the space between the panel and the front transparent plate with an adhesive layer or the like.

[0007] However, when adopting this structure, it has been pointed out that the transmittance of the polarizing plate decreases significantly in a high-temperature environment. In Patent Document 2, the following method has been proposed as a solution to this problem: making the moisture content per unit area of the polarizing plate below a specific amount and making the saturation water absorption of the transparent protective film adjacent to the polarizing element below a specific amount, thereby suppressing the decrease in transmittance. [Prior Art Documents] [Patent Documents]

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 11-174417. Patent Document 2: Japanese Patent Application Laid-Open No. 2014-102353. Summary of the Invention Problems to be Solved by the Invention

[0009] However, even for such a polarizing plate, the effect of suppressing the decrease in transmittance in a high-temperature environment is still insufficient. An object of the present invention is to provide a novel polarizing plate capable of suppressing the decrease in transmittance in a high-temperature environment and an image display device using the polarizing plate. Means for Solving the Problems

[0010] The present invention provides the following exemplary polarizing plate and image display device. [1] A polarizing plate having, in order, a polarizing element in which a dichroic dye is adsorbed and aligned on a polyvinyl alcohol-based resin layer, a transparent protective layer, and an adhesive layer, The adhesive layer contains at least one urea-based compound selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives, The moisture content of the polarizing element is not less than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30% and not more than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 50%. [2] A polarizing plate having, in order, a polarizing element in which a dichroic dye is adsorbed and aligned on a polyvinyl alcohol-based resin layer, a transparent protective layer, and an adhesive layer, The aforementioned adhesive layer contains at least one urea-based compound selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives. The moisture content of the aforementioned polarizing plate is not less than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30% and not more than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 50%. [3] The polarizing plate according to [1] or [2], wherein the moisture permeability of the aforementioned transparent protective layer at a temperature of 40°C and a relative humidity of 90% is 100 g / (m2·day) or more. [4] The polarizing plate according to any one of [1] to [3], wherein the aforementioned adhesive layer contains at least one urea-based compound selected from the group consisting of urea derivatives and thiourea derivatives. [5] The polarizing plate according to any one of [1] to [4], wherein the aforementioned adhesive layer contains a (meth)acrylic resin. In the aforementioned adhesive layer, the content of the aforementioned urea-based compound is 0.01 parts by mass or more and 100 parts by mass or less relative to 100 parts by mass of the aforementioned (meth)acrylic resin. [6] The polarizing plate according to any one of [1] to [5], wherein an adhesive layer is provided to be in contact with at least one surface of the aforementioned polarizing element, and the adhesive layer contains at least one urea-based compound selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives. [7] The polarizing plate according to [6], wherein the aforementioned adhesive layer further contains a polyvinyl alcohol-based resin. [8] The polarizing plate according to [7], wherein in the aforementioned adhesive layer, the content of the aforementioned urea-based compound is 1 part by mass or more and 400 parts by mass or less relative to 100 parts by mass of the aforementioned polyvinyl alcohol-based resin. [9] The polarizing plate according to any one of [6] to [8], wherein the aforementioned adhesive layer contains at least one urea-based compound selected from the group consisting of urea derivatives and thiourea derivatives.

[10] The polarizing plate according to any one of [1] to [9], which is used for an image display device having an interlayer filling structure.

[11] An image display device includes an image display unit, a polarizing plate according to any one of claims [1] to

[10] laminated on the viewing side of the aforementioned image display unit, and a transparent member laminated on the viewing side surface of the aforementioned polarizing plate.

[12] The image display device according to

[11] , wherein the aforementioned transparent member is a glass plate or a transparent resin plate.

[13] The image display device according to

[11] , wherein the aforementioned transparent member is a touch panel. Advantages of the Invention

[0011] According to the present invention, a polarizing plate is provided that improves high-temperature durability and, when used in an image display device constructed with interlayer filling, can suppress the decrease in transmittance caused by high temperatures. Furthermore, an image display device is provided that, when using the polarizing plate of the present invention, can suppress the decrease in transmittance under high-temperature environments. Implementation

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

[0013] [Polarizing plate] The polarizing plate of this embodiment sequentially comprises a polarizing element having a dichroic pigment adsorbed and aligned on a layer containing a polyvinyl alcohol-based resin, a transparent protective layer, and an adhesive layer. The adhesive layer contains a urea-based compound. The polarizing plate of this embodiment has at least one of the following features (a) and (b). (a) The moisture content of the polarizing element is above the equilibrium moisture content at 20°C and 30% relative humidity and below the equilibrium moisture content at 20°C and 50% relative humidity. (b) The moisture content of the polarizing plate is above the equilibrium moisture content at 20°C and 30% relative humidity and below the equilibrium moisture content at 20°C and 50% relative humidity.

[0014] Previous polarizing plates known for their excellent high-temperature durability include those that can suppress transmittance reduction even when placed alone at 95°C for 1000 hours. However, even with such polarizing plates, when used in interlayer filling configurations, a significant reduction in transmittance is observed in the central area of ​​the polarizing plate after 200 hours at 95°C. In interlayer filling configurations, 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. When image display devices using this interlayer filling configuration are exposed to high-temperature environments, the problem of a significant reduction in the transmittance of the polarizing plate under high-temperature conditions is particularly likely to occur.

[0015] In a polarizing plate where the transmittance is significantly reduced due to the interlayer filling structure, Raman spectrometry shows peaks near 1100 cm⁻¹ (originating from the =C=C= bond) and near 1500 cm⁻¹ (originating from the -C=C- bond), thus it is believed that a polyene structure (-C=C)n- is formed. The polyene structure is believed to be produced by the polyeneization of the polyvinyl alcohol constituting the polarizing element due to dehydration (Patent Document 2, paragraph

[0012] ).

[0016] The polarizing plate of this invention can further improve high-temperature durability. The polarizing plate of this invention is assembled into an image display device composed of interlayer filling, and can suppress the reduction of transmittance even when exposed to a high-temperature environment of 105°C.

[0017] <Polarizing element> A known polarizing element can be used in a polarizing element on which a dichroic dye is adsorbed and aligned to a layer containing polyvinyl alcohol (hereinafter 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; or an extended layer obtained by coating a substrate film with a coating solution containing a PVA-based resin to form a coating layer, using a laminated film having this coating layer, dyeing the coating layer with a dichroic dye, and then uniaxially stretching the laminated film. Stretching can be performed after dyeing with the dichroic dye, or during dyeing and stretching, or after stretching.

[0018] PVA-based resins are obtained by saponifying polyvinyl acetate-based resins. Besides polyvinyl acetate homopolymers, polyvinyl acetate-based resins can include copolymers of vinyl acetate and other monomers that can be copolymerized with it. Other monomers that can be copolymerized include, for example, unsaturated carboxylic acids, olefins such as ethylene, vinyl ethers, and unsaturated sulfonic acids.

[0019] The saponification degree of PVA-based resins is preferably 85 mol% or higher, more preferably 90 mol% or higher, and even more preferably 99 mol% or higher and 100 mol% or lower. The degree of polymerization of PVA-based resins is, for example, 1000 to 10000, preferably 1500 to 5000. PVA-based resins can be modified, for example, into aldehyde-modified polyethylene formaldehyde, polyethylene acetal, and polyethylene butyral.

[0020] The thickness of the polarizing element is preferably 3μm to 35μm, more preferably 4μm to 30μm, and even more preferably 5μm to 25μm. By making the thickness of the polarizing element 35μm 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 3μm or more, it is easy to form a structure that achieves the desired optical properties.

[0021] In this embodiment, the adhesive layer contains a urea-based compound. Furthermore, in this embodiment, the polarizing plate preferably has the adhesive layer containing the urea-based compound in contact with at least one side of the polarizing element. The polarizing element may contain a portion of the urea-based compound transferred from at least one of the adhesive layer and the bonding layer. The polarizing element can be manufactured in a manner that includes the urea-based compound before lamination.

[0022] This embodiment includes an adhesive layer containing a urea-based compound, thereby preventing a decrease in transmittance even when the polarizing plate is exposed to high temperatures. This embodiment also includes a polarizing element containing a urea-based compound, further preventing a decrease in transmittance even when the polarizing plate is exposed to high temperatures. The reason for this is still unclear, but it is speculated that the urea-based compound contained in the adhesive layer or the polarizing element inhibits the polyolefin formation of the PVA-based resin in the polarizing element, thus suppressing a decrease in transmittance.

[0023] Methods for incorporating urea compounds into polarizing elements include: immersing a PVA-based resin film or layer in a treatment solution containing a urea compound; or spraying, dripping, or dropping a treatment solution containing a urea compound onto the PVA-based resin film or layer. The method of immersing a PVA-based resin film or layer in a treatment solution containing a urea compound is preferred. Specific examples of urea compounds include those contained in the adhesive layer described later.

[0024] In the step of immersing the PVA-based resin film or PVA-based resin layer in a treatment solution containing a urea-based compound, the swelling, stretching, dyeing, crosslinking, and washing steps described later in the polarizing element manufacturing method can be performed simultaneously, or they can be performed separately from these steps. The step of containing the urea-based compound in the PVA-based resin film or PVA-based resin layer is preferably performed after iodine dyeing, and more preferably simultaneously with the crosslinking step after dyeing. This method can reduce hue changes and minimize the impact of the polarizing element on its optical properties.

[0025] To enable the polarizing element to contain urea compounds, they can be added during the manufacturing process to the adhesive layer or further added to the bonding agent layer.

[0026] (Feature(a)) When characteristic (a) is present, the moisture content of the polarizing element is above the equilibrium moisture content at 20°C and 30% relative humidity, and below the equilibrium moisture content at 20°C and 50% relative humidity. Preferably, the moisture content of the polarizing element is below the equilibrium moisture content at 20°C and 45% relative humidity, more preferably below the equilibrium moisture content at 20°C and 42% relative humidity, and even more preferably below the equilibrium moisture content at 20°C and 38% relative humidity. If the moisture content of the polarizing element is lower than the equilibrium moisture content at 20°C and 30% relative humidity, the polarizing element's properties will decrease and it will be prone to breakage. If the moisture content of the polarizing element is higher than the equilibrium moisture content at 20°C and 50% relative humidity, the transmittance of the polarizing element will easily decrease. It is speculated that if the moisture content of the polarizing element is higher, the polyolefination of the PVA-based resin will be easier to carry out. The moisture content of the polarizing element is the moisture content of the polarizing element in the polarizing plate.

[0027] Methods for confirming that the moisture content of a polarizing element is within the range of equilibrium moisture content at 20°C and 30% relative humidity but below 20°C and 50% relative humidity include: storing the element in an environment adjusted to the above temperature and relative humidity range, and considering it to be in equilibrium with the environment if there is no change in quality within a fixed time period; 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 comparing the moisture content of the polarizing element with the pre-calculated equilibrium moisture content to confirm it.

[0028] There are no particular limitations on the manufacturing method of polarizing elements with a moisture content of 20°C and 30% or higher and a moisture content of 50% or lower. Examples include storing the polarizing element in an environment adjusted to the above temperature and relative humidity range for 10 minutes to 3 hours, or heating it at 30°C to 90°C.

[0029] Other preferred methods for manufacturing polarizing elements with the aforementioned moisture content include: a laminate having a protective film on at least one single-area layer of the polarizing element; or a polarizing plate composed of the polarizing element being stored in an environment adjusted to the aforementioned temperature and relative humidity range for 10 minutes to 120 hours; or a method of heat treatment at 30°C to 90°C. When manufacturing an image display device using interlayer filling, an image display panel formed by laminating a polarizing plate onto an image display unit can be stored in an environment adjusted to the aforementioned temperature and relative humidity range for 10 minutes to 3 hours, or heated at 30°C to 90°C, and then bonded to a front panel.

[0030] The moisture content of the polarizing element is preferably adjusted so that the moisture content of the polarizing element alone or the laminate of the polarizing element and the protective film is within the aforementioned range during the material stage, which is the stage used to construct the polarizing plate. Adjusting the moisture content after constructing the polarizing plate can lead to excessive curling, which can easily cause defects when bonded to the image display unit. By adjusting the polarizing element to the aforementioned moisture content during the material stage before constructing the polarizing plate, and using this polarizing element to construct the polarizing plate, it is easy to construct a polarizing plate with polarizing elements that satisfy the aforementioned moisture content range. Alternatively, the moisture content of the polarizing elements in the polarizing plate can be adjusted to the aforementioned range while the polarizing plate is bonded to the image display unit. In this case, since the polarizing plate is bonded to the image display unit, curling is less likely to occur.

[0031] (Feature (b)) When characteristic (b) is present, the moisture content of the polarizing plate is above the equilibrium moisture content at 20°C and 30% relative humidity, and below the equilibrium moisture content at 20°C and 50% relative humidity. Preferably, the moisture content of the polarizing plate is below the equilibrium moisture content at 20°C and 45% relative humidity, more preferably below the equilibrium moisture content at 20°C and 42% relative humidity, and even more preferably below the equilibrium moisture content at 20°C and 38% relative humidity. If the moisture content of the polarizing plate is lower than the equilibrium moisture content at 20°C and 30% relative humidity, the properties of the polarizing plate will decrease, and it will be prone to cracking. If the moisture content of the polarizing plate is higher than the equilibrium moisture content at 20°C and 50% relative humidity, the transmittance of the polarizing element will easily decrease. It is speculated that if the moisture content of the polarizing plate is higher, the polyolefination of the PVA-based resin will be easier to achieve.

[0032] The method for confirming that the moisture content of the polarizing plate is above the equilibrium moisture content at 20°C and 30% relative humidity and below the equilibrium moisture content at 20°C and 50% relative humidity can be as follows: Store the plate in an environment adjusted to the above temperature and relative humidity range; if the mass does not change within a fixed time, it is considered to be in equilibrium with the environment; or pre-calculate the equilibrium moisture content of the polarizing plate in an environment adjusted to the above temperature and relative humidity range, and compare the moisture content of the polarizing plate with the pre-calculated equilibrium moisture content to confirm this.

[0033] There are no particular limitations on the manufacturing method of a polarizing plate with a moisture content of 20°C and 30% or higher and a moisture content of 50% or lower. For example, the polarizing plate can be kept in an environment adjusted to the above temperature and relative humidity range for 10 minutes to 3 hours, or it can be heated at 30°C to 90°C.

[0034] When using interlayer filling to manufacture an image display device, the image display panel formed by depositing a polarizing plate onto 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 to 30°C to 90°C before being bonded to the front panel.

[0035] (Manufacturing method of polarizing element) There is no particular limitation on the manufacturing method of polarizing elements. The most typical methods are as follows: a method of producing a PVA-based resin film pre-wound into a roller shape by feeding out and stretching, dyeing, cross-linking, etc. (hereinafter referred to as "manufacturing method 1"); or a method of forming a PVA-based resin layer by coating a coating liquid containing PVA-based resin onto a substrate film to form a coating layer, and including the step of stretching the resulting laminate (hereinafter referred to as "manufacturing method 2").

[0036] Manufacturing method 1 can be manufactured by the following steps: a step of uniaxially stretching a PVA-based resin film, a step of dyeing the PVA-based resin film with dichroic pigments such as iodine and adsorbing the dichroic pigments, a step of treating the PVA-based resin film adsorbed with dichroic pigments with a boric acid aqueous solution, and a step of washing with water after treatment with boric acid aqueous solution.

[0037] The swelling step involves immersing the PVA-based resin film in a swelling bath. This step removes dirt and anti-caking agents from the surface of the PVA-based resin film and causes it to swell, thereby inhibiting uneven dyeing. The swelling bath typically uses a water-based medium, such as water, distilled water, or pure water. Surfactants and alcohols can be added to the swelling bath as needed. From the perspective of controlling the potassium content of the polarizing element, potassium iodide can 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.

[0038] The optimal temperature for the swelling bath is 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 swelling degree of the PVA resin film is affected by the swelling bath temperature; therefore, the immersion time cannot be generalized, 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 can be performed only once or multiple times as needed.

[0039] The dyeing step involves immersing a PVA-based resin film in a dyeing bath (iodine solution), which allows for the adsorption and orientation of dichroic pigments such as iodine onto the PVA-based resin film. The iodine solution is preferably an aqueous iodine solution, containing iodine and iodides as a dissolving agent. Examples of iodides include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. From the viewpoint of controlling the potassium content in the polarizing element, potassium iodide is preferred.

[0040] The iodine concentration in the staining bath is preferably 0.01% by mass to 1% by mass, more preferably 0.02% by mass to 0.5% by mass. The iodide concentration in the staining bath is preferably 0.01% by mass to 10% by mass, more preferably 0.05% by mass to 5% by mass, and even more preferably 0.1% by mass to 3% by mass.

[0041] The preferred temperature of the dyeing bath is 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 degree of dyeing of the PVA resin film is affected by the temperature of the dyeing bath, so the immersion time in the dyeing bath cannot be generalized, but it is preferred to be 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.

[0042] The crosslinking step involves immersing the dyed PVA-based resin film in a treatment bath (crosslinking bath) containing boron compounds. The boron compounds crosslink the polyvinyl alcohol-based resin film, allowing iodine 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 it can also be a mixture of water and an organic solvent that is miscible with water. From the perspective of controlling the potassium content in the polarizing element, the crosslinking bath preferably contains potassium iodide.

[0043] In the crosslinking bath, the concentration of the boron compound 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. When potassium iodide is used in the crosslinking bath, the concentration of potassium iodide in the crosslinking 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.

[0044] The temperature of the crosslinking bath is preferably between 20°C and 70°C, and more preferably between 30°C and 60°C. The degree of crosslinking of PVA resin films is affected by the temperature of the crosslinking bath, so the immersion time in the crosslinking bath cannot be generalized, but it is preferably between 5 seconds and 300 seconds, and more preferably between 10 seconds and 200 seconds. The crosslinking step can be performed only once, or multiple times as needed.

[0045] The stretching step is a process in which a PVA-based resin film is stretched by a specific ratio in at least one direction. Generally, it involves uniaxially stretching the PVA-based resin film in the transport direction (longitudinal direction). There are no particular limitations on the stretching method; 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 of polarizing elements.

[0046] In the wet stretching method, the treatment bath (stretching bath) can typically be water, or a mixture of water and an organic solvent that is miscible with water. From the viewpoint of controlling the potassium content in the polarizing element, the stretching bath preferably contains potassium iodide. When potassium iodide is used in the stretching bath, the concentration of potassium iodide in the stretching bath is preferably 1% to 15% by mass, more preferably 2% to 10% by mass, and even more preferably 3% to 6% by mass. From the viewpoint of suppressing film rupture during stretching, the treatment bath (stretching bath) may contain boron compounds. When boron compounds are contained, the concentration of boron compounds in the stretching bath is preferably 1% to 15% by mass, more preferably 1.5% to 10% by mass, and even more preferably 2% to 5% by mass.

[0047] The temperature of the stretching bath is preferably between 25°C and 80°C, more preferably between 40°C and 75°C, and even more preferably between 50°C and 70°C. The stretching degree of the PVA resin film is affected by the temperature of the stretching bath, so the immersion time in the stretching bath cannot be generalized, but it is preferably between 10 seconds and 800 seconds, and more preferably between 30 seconds and 500 seconds. The stretching treatment in the wet stretching method can be carried out together with any one or more of the following steps: swelling, dyeing, crosslinking, and washing.

[0048] Examples of dry stretching methods include inter-roll stretching, heated roll stretching, and compression stretching. Furthermore, dry stretching can be performed concurrently with the drying step.

[0049] The total elongation ratio (cumulative elongation ratio) of the polyvinyl alcohol resin film can be appropriately set according to the purpose, but it is 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.

[0050] The cleaning step involves immersing the polyvinyl alcohol (PVA) resin film in a cleaning bath to remove foreign matter remaining on the surface of the PVA resin film. The cleaning bath typically uses a water-based medium, such as water, distilled water, or pure water. Furthermore, from the perspective of controlling the potassium content in the polarizing element, potassium iodide is preferably used in the cleaning bath. In this case, the concentration of potassium iodide in the cleaning bath is preferably 1% to 10% by mass, more preferably 1.5% to 4% by mass, and even more preferably 1.8% to 3.8% by mass.

[0051] The ideal temperature for the washing bath is 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 cleanliness of the PVA resin membrane is affected by the washing bath temperature; therefore, the immersion time cannot be generalized, but it 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 washing step can be performed only once or multiple times as needed.

[0052] The drying step involves drying the PVA-based resin film, which has been washed 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.

[0053] Manufacturing method 2 can be performed through the following steps: applying a coating solution containing PVA-based resin onto a substrate film; uniaxially stretching to obtain a laminated film; dyeing the PVA-based resin layer of the uniaxially stretched laminated film with a dichroic dye to adsorb and form a polarizing element; treating the film adsorbed with the dichroic dye 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 be used as a protective layer for the polarizing element. The substrate film can be peeled off from the polarizing element as needed.

[0054] <Transparent Protective Layer> The transparent protective layer (hereinafter also referred to as "protective film") used in this embodiment is composed of a transparent protective film or a transparent resin curing layer (e.g., Japanese Patent Application Publication No. 2011-221185). The transparent protective film is adhered to at least one side of the polarizing element through an adhesive layer. The transparent protective film may be adhered to one or both sides of the polarizing element, but is preferably adhered to both sides. At least one of the adhesive layers used to adhere the transparent protective film to the surface of the polarizing element is preferably a layer containing a urea compound.

[0055] The protective layer can also possess other optical functions and can form a multilayered structure. When the protective layer is a protective film, from an optical point of view, a thinner film thickness is preferable; however, if the film thickness is too thin, the strength will decrease and the processability will deteriorate. 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.

[0056] Protective films can be made of cellulose esters, polycarbonate resins, cyclic olefin resins such as norbornene, (meth)acrylic acid polymers, polyester resins such as polyethylene terephthalate, etc.

[0057] At least one protective film can provide phase difference functionality for purposes such as viewing angle compensation. In this case, the protective layer itself can have phase difference functionality, or it can have a separate phase difference layer, or a combination of both. The film with phase difference functionality can be directly bonded to the polarizing element through an adhesive, or it can be bonded through another protective layer bonded to the polarizing element, and then through an adhesive layer or bonding agent layer.

[0058] When the protective film is composed of a transparent resin curing layer, it can be directly formed on the polarizing element without the adhesive layer. Furthermore, the transparent resin curing layer may contain a urea-based compound. The transparent resin curing layer containing a urea-based compound can be formed from a curable resin composition containing an organic solvent, for example, using an aqueous solution of an active energy line curable polymer composition as described in paragraphs

[0020] to

[0042] of Japanese Patent Application Publication No. 2017-075986. In the method of forming such a curing layer, a water-soluble urea-based compound is contained in the aforementioned aqueous solution, thereby forming the layer. The transparent resin curing layer preferably contains an adhesive. Examples of adhesives include polymer adhesives, thermosetting resin adhesives, and active energy line curable resin adhesives; any of these adhesives is preferable.

[0059] The thickness of the transparent resin curing layer is preferably 0.1μm to 20μm, more preferably 0.5μm to 15μm, and even more preferably 1μm to 10μm.

[0060] In the polarizing plate of the present invention, the transparent protective layer having an adhesive layer containing a urea compound laminated thereon preferably has a transmittance of 100 g / (m²·day) or more, more preferably 300 g / (m²·day) or more, and even more preferably 500 g / (m²·day) or more at a temperature of 40°C and a relative humidity of 90%. There is no particular upper limit; the transmittance at 40°C and a relative humidity of 90% can be 1500 g / (m²·day) or less. By forming an adhesive layer containing a urea compound in such a transparent protective layer, the transmittance of the polarizing plate does not easily decrease even when exposed to high-temperature environments. This is presumably because such a transparent protective layer facilitates the transfer of the urea compound in the adhesive layer to the polarizing element, thereby easily suppressing the polyolefination of the polarizing element. From the viewpoint of easily obtaining transmittance within the above-mentioned range, a cellulose-based membrane is suitable for use as the transparent protective layer.

[0061] <Adhesive layer> The polarizing plate preferably has an adhesive layer containing a urea-based compound, deposited on the opposite side of the polarizing element layer of the transparent protective layer, serving as an adhesive layer. The polarizing plate may further include other adhesive layers. Each adhesive layer may consist of one or more layers, but is preferably composed of one layer. The adhesive layer may be composed of an adhesive composition primarily composed of (meth)acrylic resin, rubber resin, ethyl carbamate resin, ester resin, polysiloxane resin, or polyvinyl ether resin. Preferably, the adhesive composition uses (meth)acrylic resin, which has excellent transparency, weather resistance, and heat resistance, as the base polymer. The adhesive composition may be of the active energy line curing type or the thermosetting type.

[0062] The (meth)acrylate resin (base polymer) used in the adhesive composition is suitable as a polymer or copolymer with one or more (meth)acrylate monomers such as butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. The base polymer is preferably a copolymer of polar monomers. 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, and glycidyl (meth)acrylate compounds, which possess carboxyl, hydroxyl, amide, amino, or epoxy groups.

[0063] The adhesive composition may contain only the aforementioned basic polymer, but typically further contains a crosslinking agent. Examples of crosslinking agents include, for instance, metal ions with a divalent or higher metal ion that form a carboxylic acid metal salt with a carboxyl group, polyamine compounds that form an amide bond with a carboxyl group, polyepoxide compounds or polyols that form an ester bond with a carboxyl group, and polyisocyanate compounds that form an amide bond with a carboxyl group. Polyisocyanate compounds are preferred.

[0064] Active energy line curing adhesive compositions possess the property of curing upon irradiation with active energy lines such as ultraviolet light or electron beams. They exhibit adhesiveness before irradiation and can adhere tightly to substrates such as films, curing upon irradiation with active energy lines and allowing for adjustment of adhesion. Ultraviolet curing types are preferred for active energy line curing adhesive compositions. In addition to the base polymer and crosslinking agent, active energy line curing adhesive compositions may further contain polymerizable compounds with active energy lines. Photopolymerization initiators and photosensitizers may be included as needed.

[0065] The adhesive composition may contain light-scattering microparticles, beads (resin beads, glass beads, etc.), glass fibers, resins other than the base polymer, adhesive agents, fillers (metal powder or other inorganic powders, etc.), antioxidants, ultraviolet absorbers, dyes, pigments, colorants, defoamers, corrosion inhibitors, photopolymerization initiators, and other additives.

[0066] An organic solvent dilution of the above-mentioned adhesive composition can be applied to the surface of a substrate film, image display unit, or polarizing plate and dried to form an adhesive layer. The substrate film is generally a thermoplastic resin film; a typical example is a release membrane that has undergone a release treatment. For example, a release membrane may be one on the surface where a release treatment, such as polysiloxane treatment, is performed on the adhesive layer of a film composed of resins such as polyethylene terephthalate, polybutylene terephthalate, polycarbonate, or polyarylate.

[0067] The method for depositing an adhesive layer containing a urea compound onto a transparent protective layer can be achieved by directly coating an adhesive composition onto the release surface of the separation membrane to form an adhesive layer, and then depositing the adhesive layer with the separation membrane onto the surface of the transparent protective layer; alternatively, the adhesive composition can be directly coated onto the surface of the transparent protective layer to form an adhesive layer, and then a separation membrane can be deposited on the outer surface of the adhesive layer. Specifically, the following methods can be used: dissolving or dispersing a base polymer or its composition in a solvent composed of a single component or mixture of suitable solvents such as toluene or ethyl acetate, preparing an adhesive solution of 10% by mass to 40% by mass, and directly applying it onto the transparent protective layer using a suitable spreading method such as casting or coating; and forming an adhesive layer on the separation membrane and transferring it to the surface of the transparent protective layer.

[0068] When an adhesive layer is applied to the surface of a transparent protective layer, it is preferable to perform surface activation treatments such as plasma treatment or corona treatment on the bonding surface of the transparent protective layer and / or the bonding surface of the adhesive layer, and more preferably to perform corona treatment.

[0069] Alternatively, an adhesive composition can be coated onto the second separation membrane to form an adhesive layer. A separation membrane can then be deposited on the adhesive layer to form an adhesive sheet. After the second separation membrane is peeled off from the adhesive sheet, the adhesive layer with the separation membrane attached is then bonded to the transparent protective layer. 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.

[0070] The thickness of the adhesive layer is not particularly limited. For example, it is preferably 1μm to 100μm, more preferably 3μm to 50μm, and can also be 20μm or more.

[0071] (Urea compounds) The urea-based compound contained in the adhesive layer is selected from at least one compound chosen from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives. The same applies to the urea-based compounds used when adding urea-based compounds to other layers such as polarizing elements and adhesive layers. One urea-based compound may be used alone or in combination of two or more. Urea-based compounds include both water-soluble and water-poorly soluble compounds, but both can be used. When using water-poorly soluble urea-based compounds in water-soluble adhesives, the dispersion method should be carefully considered after the adhesive layer is formed to prevent haze increases.

[0072] In an adhesive layer containing a urea compound, when the adhesive layer is composed of a (meth)acrylic resin, the amount of the urea compound added is preferably 0.01 parts by weight to 100 parts by weight relative to 100 parts by weight of the (meth)acrylic resin, more preferably 0.05 parts by weight to 50 parts by weight, and even more preferably 0.1 parts by weight to 10 parts by weight. By keeping the content of the urea compound at 0.01 parts by weight or more, it is easier to obtain a polyolefin suppression effect for the polarizing element. On the other hand, by keeping the content of the urea compound at 100 parts by weight or less, it is easier to prevent the urea compound from precipitating out and to prevent adverse conditions such as haze increase.

[0073] (Urea derivatives) Urea derivatives are compounds in which at least one of the four hydrogen atoms of a urea molecule is substituted with a substituent. There are no particular restrictions on the substituent, but it is preferred that the substituent is composed of a carbon atom, a hydrogen atom, and an oxygen atom.

[0074] 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.

[0075] Examples of 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-imidazolidinedione (epithelialylurea), and tetrahydro-2-pyrimidinone (epithelialylurea).

[0076] 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-imidazolidinone, and 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone.

[0077] (Thiocarbamide derivatives) Thiourea derivatives are compounds in which at least one of the four hydrogen atoms of a thiourea molecule is substituted with a substituent. There are no particular restrictions on the substituent, but it is preferred that the substituent is composed of a carbon atom, a hydrogen atom, and an oxygen atom.

[0078] Specific examples of thiourea derivatives include monosubstituted thioureas such as N-methylthiourea, ethylthiourea, propylthiourea, isopropylthiourea, 1-butylthiourea, cyclohexylthiourea, N-acetylated thiourea, N-allyl thiourea, (2-methoxyethyl)thiourea, N-phenylthiourea, (4-methoxyphenyl)thiourea, N-(2-methoxyphenyl)thiourea, N-(1-naphthyl)thiourea, (2-pyridyl)thiourea, o-tolyl thiourea, and p-tolyl thiourea.

[0079] 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 ethylthiourea.

[0080] Examples of trisubstituted thioureas include trimethylthiourea, and examples of tetrasubstituted thioureas include tetramethylthiourea and 1,1,3,3-tetraethylthiourea.

[0081] Among urea compounds, when used in image display devices constructed for interlayer filling, urea derivatives or thiourea derivatives are preferred for their ability to suppress transmittance reduction and minimize polarization reduction (suppressing cross-loss) under high-temperature conditions, and urea derivatives are even more preferred. Among urea derivatives, derivatives in which at least one of the four hydrogen atoms of the urea molecule is substituted with benzyl, phenyl, or cyclohexyl are preferred, and any one of benzylurea, cyclohexylurea, or phenylurea is even more preferred.

[0082] <Adhesive layer> The polarizing plate may have an adhesive layer for bonding two layers. For example, the polarizing element may have an adhesive layer for bonding other layers and configured to be in contact with the polarizing element. Specifically, the polarizing element may have an adhesive layer for bonding a transparent protective layer and being in contact with the polarizing element. The adhesive constituting such an adhesive layer is preferably an adhesive containing a urea-based compound. The adhesive may be a water-based adhesive, a solvent-based adhesive, or an active energy line curing adhesive, but a water-based adhesive is preferred, and it is more preferably a PVA-based resin.

[0083] The thickness of the adhesive coating can be set to any value, for example, it can be set in a way that the desired thickness of the adhesive layer can be obtained after hardening or heating (drying). The thickness of the adhesive layer formed by the adhesive is preferably 0.01μm to 7μm, more preferably 0.01μm to 5μm, even more preferably 0.01μm to 2μm, and most preferably 0.01μm to 1μm.

[0084] The adhesive layer may contain urea compounds. Having an adhesive layer containing urea compounds, and the adhesive layer in contact with the polarizing element also containing urea compounds, prevents the transmittance of the polarizing plate from easily decreasing even when exposed to high temperatures. This is presumably because such an adhesive layer facilitates the transfer of the urea compounds in the adhesive layer to the polarizing element, thus easily suppressing polyolefin formation in the polarizing element. Specific examples of urea compounds contained in the adhesive layer can be directly applied to the examples of urea compounds contained in the adhesive layer described above.

[0085] When the adhesive is a water-based adhesive containing PVA-based resin, the content of urea compounds relative to 100 parts by weight of PVA-based resin is preferably 1 part by weight to 400 parts by weight, more preferably 2 parts by weight to 200 parts by weight, and even more preferably 3 parts by weight to 100 parts by weight. By being 1 part by weight or more, sufficient polyolefin suppression effect on polarizing elements under high-temperature environments can be obtained. On the other hand, if it exceeds 400 parts by weight, urea compounds will precipitate, resulting in adverse conditions such as increased haze.

[0086] In the configuration of a transparent protective film bonded to both sides of a polarizing element with an adhesive layer in between, it is preferable that at least one of the adhesive layers on both sides of the polarizing element is an adhesive layer containing a urea compound, and more preferably that both adhesive layers are layers containing a urea compound.

[0087] To meet the demand for thinner polarizing plates, a polarizing plate with a transparent protective layer on only one side of the polarizing element has been developed. In this configuration, a transparent protective film can be laminated with an adhesive layer in between. As a method for manufacturing such a polarizing plate with a transparent protective film on only one side of the polarizing element, the following method is considered: firstly, a polarizing plate is manufactured by laminating a transparent protective film on both sides with an adhesive layer in between, and then the transparent protective film on one side is peeled off.

[0088] (Water-based adhesive) Any suitable water-based adhesive can be used, but it is preferred 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, more preferably 1000 to 4500. From the viewpoint of adhesion, the average degree of saponification is preferably 85 mol% to 100 mol%, more preferably 90 mol% to 100 mol%.

[0089] The PVA-based resin contained in the water-based adhesive is preferably one containing acetoacetyl, because PVA-based resin layers exhibit excellent adhesion and durability to the protective film. For example, PVA-based resin can be reacted with diacetone olefin by any method to obtain a PVA-based resin containing acetoacetyl. The degree of acetoacetyl modification in the PVA-based resin containing acetoacetyl 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, more preferably 0.5% by mass or more and 10% by mass.

[0090] Water-based adhesives may contain crosslinking agents. Known crosslinking agents may be used. Examples of crosslinking agents include water-soluble epoxy compounds, dialdehydes, and isocyanates.

[0091] When the PVA-based resin is a PVA-based resin containing acetyl groups, the crosslinking agent is preferably any one of glyoxal, glyoxylate, or hydroxymethyl melamine, more preferably any one of glyoxal or glyoxylate, and most preferably glyoxal.

[0092] Aqueous adhesives may contain organic solvents. Considering their miscibility with water, alcohols are preferred organic solvents, with methanol or ethanol being more preferred. The methanol concentration in the aqueous adhesive is preferably 10% by mass to 70% by mass, more preferably 15% by mass to 60% by mass, and even more preferably 20% by mass to 60% by mass. Maintaining a methanol concentration of 10% by mass or more makes it easier to suppress the polyolefin formation of PVA resins under high-temperature conditions. Furthermore, maintaining a methanol content of 70% by mass or less helps to suppress color deterioration. Some urea derivatives have low solubility in water but high solubility in alcohols. In this case, as a preferred approach, the urea compound can be dissolved in an alcohol to prepare an alcohol solution of the urea compound, which is then added to the PVA aqueous solution to prepare the adhesive.

[0093] (Active Energy Line Curing Adhesive) Examples of photopolymerizable adhesives include those that cure upon exposure to active energy rays such as ultraviolet light. Examples include adhesives containing polymerizable compounds and photopolymerizable initiators, adhesives containing photoreactive resins, and adhesive resins containing 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 photopolymerizable initiators include compounds containing substances that generate reactive species such as neutral free radicals, anionic free radicals, and cationic free radicals upon exposure to active energy rays such as ultraviolet light.

[0094] Examples of active energy line curing adhesives include adhesives containing compounds (e.g., monomers and / or oligomers) that are polymerizable compounds and have free radical polymerizable groups such as (meth)acrylate groups or (meth)acrylamide groups. Specific examples of active energy line curing adhesives and their curing methods are described, for example, in Japanese Patent Application Publication No. 2012-144690.

[0095] [Manufacturing Method of Polarizing Plate] The method for manufacturing a polarizing plate according to this embodiment includes a moisture content adjustment step and a lamination step. In the moisture content adjustment step, when manufacturing the polarizing plate having characteristic (a), the moisture content of the polarizing element is adjusted to a state where the equilibrium moisture content at 20°C and 30% relative humidity is higher than or equal to the equilibrium moisture content at 20°C and 50% relative humidity. 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 characteristic (b), the moisture content of the polarizing plate is adjusted to a state where the equilibrium moisture content at 20°C and 30% relative humidity is higher than or equal to the equilibrium moisture content at 20°C and 50% relative humidity. 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 layer are laminated, for example, with an adhesive layer in between, and an adhesive layer containing a urea-based compound is laminated on the surface of the transparent protective layer opposite to the polarizing element. The order of the moisture content adjustment step and the lamination step is not limited; in fact, the moisture content adjustment step and the lamination step can be performed simultaneously.

[0096] [Composition of an image display device] The polarizing plate of this embodiment is used in various image display devices such as liquid crystal display devices or organic EL display devices. The interlayer filling configuration involves the polarizing plate being in contact with layers other than an air layer on both sides; specifically, it is configured such that the polarizing plate is in contact with solid layers such as adhesive layers on both sides. When the image display device has this interlayer filling configuration, its transmittance tends to decrease at high temperatures. In the image display device using the polarizing plate of this embodiment, even with the interlayer filling configuration, the decrease in transmittance of the polarizing plate at high temperatures can be suppressed. An example image display device may have 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 may further have 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. In particular, the polarizing plate of this embodiment is suitable for use in an image display device having an interlayer filling configuration in which 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 with a first adhesive layer, and the polarizing plate and the transparent member are bonded together with a second adhesive layer. At least one of the first adhesive layer and the second adhesive layer is preferably an adhesive layer containing a urea-based compound.

[0097] <Image Display Unit> Image display units can include liquid crystal units (LCDs) or organic EL units (OLEDs). The liquid crystal unit can 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 semi-transmissive / semi-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, in the image display device (liquid crystal display device), a polarizing plate is also disposed on the opposite side of the viewing side of the image display unit (liquid crystal unit), and a light source is further disposed thereon. The polarizing plate on the light source side and the liquid crystal unit are preferably bonded together with a suitable adhesive layer in between. The driving method of the liquid crystal unit can be any type, such as VA mode, IPS mode, TN mode, STN mode, or bent alignment (π type).

[0098] Organic EL cells are suitable for use in transparent substrates where transparent electrodes, organic light-emitting layers, and metal electrodes are sequentially deposited to form a light-emitting body (organic electroluminescent body). The organic light-emitting layer is a stack of various organic thin films, such as a hole injection layer composed of triphenylamine derivatives, a light-emitting layer composed of anthracene or other fluorescent organic solids, an electron injection layer composed of such light-emitting layers and perylene derivatives, or a stack of hole injection layer, light-emitting layer, and electron injection layer, etc.

[0099] <Lamination of image display unit and polarizing plate> An adhesive layer (adhesive sheet) is suitable for bonding the image display unit to the polarizing plate. From an operability point of view, the method of bonding the polarizing plate of the present invention to the image display unit through its adhesive layer is preferred.

[0100] <Transparent Components> Transparent components disposed on the viewing side of an image display device can include transparent panels (window layers) or touch panels. The transparent panel can be a transparent panel with appropriate mechanical strength and thickness. Examples of such transparent panels include transparent resin panels made of polyimide-based resin, acrylic resin, or polycarbonate resin, or glass panels. Functional layers such as anti-reflective layers can also be laminated on the viewing side of the transparent panel. Furthermore, when the transparent panel is a transparent resin panel, a hard coating to improve physical strength or a low-permeability layer to reduce moisture permeability can also be laminated. Touch panels can be various types of touch panels, such as resistive film, capacitive, optical, and ultrasonic touch panels, or glass panels or transparent resin panels with touch sensor functionality. When using a capacitive touch panel as the transparent component, it is preferable to provide a transparent panel made of glass or transparent resin on the viewing side of the touch panel.

[0101] <Bonding of polarizing plate and transparent component> The bonding system between the polarizing plate and the transparent component is suitable for using an adhesive layer or an active energy line curing adhesive layer. When using an adhesive layer, it can be the adhesive layer already present in the polarizing plate, or it can be a newly added adhesive layer. The adhesive layer can be applied in an appropriate manner. A specific application method can be exemplified by the method used for bonding the image display unit to the polarizing plate described above.

[0102] When using an active energy line curing adhesive layer, the following method is suitable for preventing the spread of the adhesive solution before curing: A weir is set up to surround the edge of the image display panel; a transparent component is placed on the weir; and the adhesive solution is injected. After the adhesive solution is injected, alignment and degassing are performed as needed, followed by irradiation with active energy lines and curing. (Example)

[0103] The present invention will be specifically illustrated below through examples. The materials, reagents, quantities, ratios, and operations shown in the following examples may be appropriately modified without departing from the spirit of the invention. Therefore, the present invention is not limited to the following examples.

[0104] <Fabrication of Polarizing Element 1> 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 mol% or higher was dry-stretched uniaxially approximately 5 times. While maintaining tension, it was then immersed in pure water at 60°C for 1 minute, followed by immersion in an aqueous solution of iodine / potassium iodide / water at a mass ratio of 0.05 / 5 / 100 at 28°C for 60 seconds. Subsequently, it was immersed in an aqueous solution of potassium iodide / boric acid / water at a mass ratio of 8.5 / 8.5 / 100 at 72°C for 300 seconds. Afterward, 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 1 with iodine adsorbed and aligned in the PVA. The thickness of the polarizing element was measured using a digital micrometer "MH-15M" manufactured by Nikon Corporation.

[0105] <Preparation of Adhesives 1 and 2> (Preparation of PVA solution for adhesive) 50g of modified PVA resin containing acetyl acetyl groups (GOSENEX Z-410 manufactured by Mitsubishi Chemical Corporation) was dissolved in 950g of pure water, heated at 90°C for 2 hours, and then cooled to room temperature to obtain a PVA solution for adhesives.

[0106] (Preparation of Adhesive 1) The adhesive is prepared by mixing PVA solution, urea, pure water, and methanol in a manner that the concentration of PVA is 3.0% by mass, the concentration of methanol is 20% by mass, and the concentration of urea is 1% by mass (which is 33 parts by mass relative to 100 parts by mass of PVA) to obtain adhesive 1 for polarizing plates.

[0107] (Preparation of Adhesive 2) The adhesive was prepared by mixing PVA solution, pure water, and methanol at a concentration of 3.0% by mass for PVA and 20% by mass for methanol to obtain adhesive 2 for polarizing plates.

[0108] Preparation of Transparent Protective Film (Transparent Protective Layer) A commercially available cellulose ester membrane TD40 (manufactured by FUJIFILM Co., Ltd., 40 μm thick) was immersed in a 1.5 mol / L NaOH aqueous solution (saponification solution) at 55°C for 2 minutes, followed by washing with water. Then, it was immersed in a 0.05 mol / L sulfuric acid aqueous solution at 25°C for 30 seconds, and further washed under running water for 30 seconds to neutralize the membrane. This was followed by repeated air-knife dehydration three times, and then drying in a 70°C drying zone for 15 seconds to produce a saponified membrane, thus obtaining a transparent protective film for polarizing plates. The permeability of this transparent protective film at 40°C and 90% relative humidity was 850 g / (m².day). The permeability was measured using the cup method specified in JIS Z 0208 at 40°C and 90% relative humidity.

[0109] <Polarizing plates 1 and 2 (Preparation before applying adhesive layer)> (Making of Polarizing Plate 1) The aforementioned transparent protective film is bonded to both sides of the polarizing element 1 using an adhesive 1 through the polarizing plate using a roller laminator. After bonding, it is dried at 60°C for 10 minutes to obtain the polarizing plate 1 before the adhesive layer is applied. The adhesive layer 1 formed by the adhesive 1 is adjusted to have a thickness of 50 nm on both sides after drying.

[0110] (Making of Polarizing Plate 2) Adhesive 1 is replaced with adhesive 2, and the polarizing plate 2 before the adhesive layer is applied is obtained in the same manner as the polarizing plate 1 before the adhesive layer is applied. The adhesive layer 2 formed by adhesive 2 is also adjusted so that the thickness on both sides is 50nm after drying.

[0111] <Preparation of Adhesive Layers 1 and 2> (Preparation of adhesive layer 1) A solution of an acrylic adhesive composition was prepared by mixing 0.1 parts by weight of isocyanate crosslinking agent, 0.2 parts by weight of silane coupling agent, and 0.34 parts by weight of phenylurea with 100 parts by weight of the solids of an acrylic polymer solution (100 parts by weight of (meth)acrylic resin). The above-mentioned acrylic adhesive composition solution was coated on one side of a polyethylene terephthalate film (separator film) treated with a polysiloxane release agent to achieve an adhesive layer thickness of 25 μm after drying, and dried at 90°C for 3 minutes to form an adhesive layer 1 on the surface of the separator film.

[0112] (Preparation of adhesive layer 2) A solution of an acrylic adhesive composition was prepared by mixing 0.1 parts by weight of isocyanate crosslinking agent and 0.2 parts by weight of silane coupling agent with 100 parts by weight of the solids of an acrylic polymer solution (100 parts by weight of (meth)acrylic resin). The above-mentioned acrylic adhesive composition solution was coated on one side of a polyethylene terephthalate film (separator film) treated with a polysiloxane release agent to achieve an adhesive layer thickness of 25 μm after drying, and dried at 90°C for 3 minutes to form an adhesive layer 2 on the surface of the separator film.

[0113] Fabrication of Optical Laminates 1 to 7 (Polarizing Plates After Adhesive Layer Application) (Fabrication of Optical Laminate 1) An adhesive layer 1 is transferred onto one side of a polarizing plate 1 to create an optical laminate 1.

[0114] (Fabrication of optical laminates 2 to 7) As shown in Table 1, optical laminates 2 to 7 are fabricated using polarizing plate 1 or polarizing plate 2, adhesive layer 1 or adhesive layer 2, and in the same manner as optical laminate 1.

[0115] <Adjustment of water content in optical laminates (polarizing elements)> The optical laminates 1 to 7 obtained above were stored at 20°C and relative humidity of 30%, 35%, 40%, 45%, 50%, or 55% for 72 hours. The moisture content was measured using the Karl Fischer method after 66, 69, and 72 hours of storage. Under any humidity conditions, the moisture content values ​​remained unchanged after 66, 69, and 72 hours of storage. Therefore, the moisture content of optical laminates 1 to 7 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 an optical laminate (polarizing plate) reaches equilibrium with a storage environment, the moisture content of the polarizing element in the optical laminate (polarizing plate) can also be considered to be in equilibrium with that storage environment. Furthermore, when the moisture content of the polarizing element in an optical laminate (polarizing plate) reaches equilibrium with a storage environment, the moisture content of the optical laminate (polarizing plate) can also be considered to be in equilibrium with that storage environment.

[0116] The optical laminates 1 to 7 were manufactured by storing them at a temperature of 20°C and relative humidity of 35%, 45%, 50%, or 55% for 72 hours, with the moisture content of the optical laminates 1 to 7 being equal to the equilibrium moisture content of the environment shown in Table 1.

[0117] <High Temperature Durability Evaluation> (Preparation of the evaluation sample) Using optical laminates 1 to 7, an acrylic adhesive layer (manufactured by LINTEC Corporation, product number: #7) is formed on the opposite side of the side where the adhesive layer is formed. The laminate is then cut to a size of 50mm × 100mm with the absorption axis parallel to the long side. Alkali-free glass (manufactured by Corning Incorporated "EAGLE XG") is then laminated onto both adhesive surfaces to create an evaluation sample.

[0118] (Single-cell penetration evaluation (105℃)) Evaluation samples of optical laminates 1 to 7 were subjected to autoclave treatment at 50°C and 5 kgf / cm² (490.3 kPa) for 1 hour, followed by placement in an environment at 23°C and 55% relative humidity for 24 hours. The transmittance (initial value) of the evaluation samples of optical laminates 1 to 7 was then measured, and the samples were stored at 105°C for 200 to 500 hours, with transmittance measured every 50 hours. Evaluation was based on the time it took for the transmittance to decrease by more than 5% relative to the initial value. The results are shown in Table 1. A. Penetration rate decreases to below 5% after 400 hours: Those whose penetration rate decreases by more than 5% within 300 to 400 hours: B Those whose penetration rate decreases by more than 5% within 200 to 300 hours: C Those whose penetration rate decreases to 5% or more after 200 hours: D

[0119] [Table 1]

[0120] The polarizing plate (optical laminates 1 to 4) has a polarizing element with a water content of more than the equilibrium water content of 20°C and 30% relative humidity and less than the equilibrium water content of 20°C and 50% relative humidity, and a transparent protective film. Furthermore, it has an adhesive layer containing a urea compound. It can be seen that the transmittance of the polarizing plate (optical laminates 1 to 4) is not easily reduced even when exposed to a high temperature environment of 105°C.

Claims

1. A polarizing plate, comprising, sequentially, a polarizing element having a dichroic pigment adsorbed and aligned on a polyvinyl alcohol-based resin layer, a transparent protective layer, and an adhesive layer, wherein the adhesive layer contains at least one urea compound selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives, wherein the urea derivative is 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, p-tolylurea, 1,1-dimethylurea, 1,3-dimethylurea, 1,1-diethylurea, 1,3-diethylurea, 1,3-bis(hydroxymethyl)urea, 1,3-tert-butylurea, etc. The polarizing element contains 1,3-dicyclohexylurea, 1,3-diphenylurea, 1,3-bis(4-methoxyphenyl)urea, 1-acetyl-3-methylurea, 2-imidazolidineone (epidoxuridine), tetrahydro-2-pyrimidinone (epidoxuridine), tetramethylurea, 1,1,3,3-tetraethylurea, 1,1,3,3-tetrabutylurea, 1,3-dimethoxy-1,3-dimethylurea, 1,3-dimethyl-2-imidazolidineone, or 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone. The moisture content of the aforementioned polarizing element is above the equilibrium moisture content at 20°C and 30% relative humidity and below the equilibrium moisture content at 20°C and 50% relative humidity.

2. A polarizing plate, comprising, in sequence, a polarizing element having a dichroic pigment adsorbed and aligned to a polyvinyl alcohol-based resin layer, a transparent protective layer, and an adhesive layer, wherein the adhesive layer contains at least one urea compound selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives, wherein the urea derivative is 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, p-tolylurea, 1,1-dimethylurea, 1,3-dimethylurea, 1,1-diethylurea, 1,3-diethylurea, 1,3-bis(hydroxymethyl)urea, 1,3-tert-butylurea, etc. The polarizing plate contains 1,3-dicyclohexylurea, 1,3-diphenylurea, 1,3-bis(4-methoxyphenyl)urea, 1-acetyl-3-methylurea, 2-imidazolidineone (epidoxuridine), tetrahydro-2-pyrimidinone (epidoxuridine), tetramethylurea, 1,1,3,3-tetraethylurea, 1,1,3,3-tetrabutylurea, 1,3-dimethoxy-1,3-dimethylurea, 1,3-dimethyl-2-imidazolidineone, or 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone. The moisture content of the aforementioned polarizing plate is above the equilibrium moisture content at 20°C and 30% relative humidity and below the equilibrium moisture content at 20°C and 50% relative humidity.

3. The polarizing plate as described in claim 1 or 2, wherein the aforementioned transparent protective layer has a moisture permeability of 100 g / (m2·day) or more at a temperature of 40°C and a relative humidity of 90%.

4. The polarizing plate as claimed in claim 1 or 2, wherein the aforementioned adhesive layer contains at least one urea compound selected from the group consisting of urea derivatives and thiourea derivatives.

5. The polarizing plate as claimed in claim 1 or 2, wherein the aforementioned adhesive layer contains a (meth)acrylic resin, and the content of the aforementioned urea compound in the aforementioned adhesive layer is more than 0.01 parts by weight and less than 100 parts by weight relative to 100 parts by weight of the aforementioned (meth)acrylic resin.

6. The polarizing plate as claimed in claim 1 or 2, wherein the adhesive layer is configured to be in contact with at least one side of the aforementioned polarizing element, the aforementioned adhesive layer containing at least one urea compound selected from the group consisting of urea, urea derivatives, thiourea and thiourea derivatives.

7. The polarizing plate as claimed in claim 6, wherein the aforementioned adhesive layer system further comprises a polyvinyl alcohol-based resin.

8. The polarizing plate as claimed in claim 7, wherein in the aforementioned adhesive layer, the content of the aforementioned urea compound is more than 1 part by mass and less than 400 parts by mass relative to 100 parts by mass of the aforementioned polyvinyl alcohol resin.

9. The polarizing plate as claimed in claim 6, wherein the aforementioned adhesive layer contains at least one urea compound selected from the group consisting of urea derivatives and thiourea derivatives.

10. The polarizing plate as described in claim 1 or 2 is used in an image display device having an interlayer filling configuration.

11. An image display device comprising an image display unit, a polarizing plate as described in any one of claims 1 to 10 laminated on the viewing side of the image display unit, and a transparent member laminated on the viewing side surface of the polarizing plate.

12. The image display device as claimed in claim 11, wherein the aforementioned transparent member is a glass plate or a transparent resin plate.

13. The image display device as claimed in claim 11, wherein the aforementioned transparent member is a touch panel.