Polarizing plate and image display device

Abstract

Provided is a polarizing plate in which the decrease in transmittance in a high-temperature environment is suppressed. Provided is a polarizing plate having a polarizing element in which a dichroic dye is adsorbed to a polyvinyl alcohol-based resin layer and oriented, and a transparent protective film laminated to at least one face of the polarizing element, the polarizing element and the transparent protective film being bonded via an adhesive layer formed by an adhesive containing an ammonium ion donor, the water content of the polarizing element being equal to or higher than the equilibrium water content at a temperature of 20°C and a relative humidity of 30% and equal to or lower than the equilibrium water content at a temperature of 20°C and a relative humidity of 50%.

Description

Technical Field

[0001] This invention relates to polarizing plates and image display devices. Background Technology

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

[0003] The use of polarizing plates in automotive image display devices, such as liquid crystal displays and organic EL displays, as described above, is increasing. Compared to applications in mobile devices like televisions and mobile phones, polarizing plates used in automotive image display devices are frequently exposed to high temperatures, thus requiring less change in properties at high temperatures (high-temperature durability).

[0004] On the other hand, to prevent damage to the image display panel from impacts from external surfaces, structures with a front panel (also called a "window layer") made of transparent resin or glass on the viewable side of the image display panel are becoming increasingly common. In image display devices equipped with touch panels, a structure is widely adopted where a touch panel is placed on the viewable side of the image display panel, and a front panel is then placed on the viewable side of the touch panel.

[0005] In this structure, if an air layer exists between the image display panel and transparent components such as the front panel and touch panel, glare from reflected light at the air layer interface will occur, leading to a decrease in image visibility. Therefore, there is a growing trend towards structures that fill the space between the polarizer disposed on the visible side surface of the image display panel and the transparent component with a layer other than the air layer, typically a solid layer (hereinafter sometimes referred to as an "interlayer filler"). The interlayer filler is preferably a material with a refractive index close to that of the polarizer or the transparent component. As the interlayer filler, adhesives and UV-curable adhesives (see, for example, Patent Document 1) are used to suppress the decrease in visibility caused by reflection at the interface and to bond and fix the components together.

[0006] The use of interlayer filling structures is expanding in mobile devices such as cell phones, which are frequently used outdoors. Furthermore, due to increasing demands for visibility in recent years, research is underway into using interlayer filling structures in automotive applications such as navigation devices, where a front transparent panel is placed on the surface of the image display panel and the space between the panel and the front transparent panel is filled with an adhesive layer.

[0007] However, according to the report, the transmittance of the polarizing plate decreases significantly under high-temperature conditions when this structure is used. Patent Document 2 proposes a solution to this problem by setting the water content per unit area of ​​the polarizing plate to below a given amount and setting the saturated water absorption of the transparent protective film adjacent to the polarizing element to below a given amount, thereby suppressing the decrease in transmittance.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 11-174417

[0011] Patent Document 2: Japanese Patent Application Publication No. 2014-102353 Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] However, even with this type of polarizing plate, the effect of suppressing the decrease in transmittance under high-temperature conditions is not sufficient. The object of the present invention is to provide a polarizing plate that further suppresses the decrease in transmittance under high-temperature conditions, and an image display device using this polarizing plate.

[0014] Methods for solving problems

[0015] The present invention provides a polarizing plate and an image display device as illustrated below.

[0016] [1] A polarizing plate having a polarizing element in which dichroic pigments are adsorbed onto a polyvinyl alcohol resin layer and oriented thereon, and a transparent protective film laminated on at least one side of the polarizing element.

[0017] The aforementioned polarizing element and the aforementioned transparent protective film are bonded together by an adhesive layer formed from an adhesive containing an ammonium ion donor.

[0018] The moisture content of the aforementioned polarization element is above the equilibrium moisture content of 30% relative humidity at 20°C and below the equilibrium moisture content of 50% relative humidity at 20°C.

[0019] [2] A polarizing plate having a polarizing element in which dichroic pigments are adsorbed onto a polyvinyl alcohol resin layer and oriented thereon, and a transparent protective film laminated on at least one side of the polarizing element.

[0020] The aforementioned polarizing element and the aforementioned transparent protective film are bonded together by an adhesive layer formed from an adhesive containing an ammonium ion donor.

[0021] 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.

[0022] [3] According to the polarizing plate described in [1] or [2], wherein the adhesive comprises a polyvinyl alcohol resin.

[0023] [4] According to the polarizing plate described in [3], the content of the ammonium ion donor in the adhesive is more than 1 part by mass and less than 300 parts by mass relative to 100 parts by mass of the polyvinyl alcohol resin.

[0024] [5] According to any one of [1] to [4], the thickness of the adhesive layer is 0.01 μm or more and 7 μm or less.

[0025] [6] The polarizing plate described in any one of [1] to [5], wherein the ammonium ion donor comprises at least one selected from ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride, ammonium acetate and ammonium oxalate.

[0026] [7] The polarizing plate described in any one of [1] to [6], wherein the polarizing plate is used in an image display device.

[0027] In the above-described image display device, a solid layer is provided on both sides of the polarizing plate in contact with both sides of the polarizing plate.

[0028] [8] An image display device having an image display unit, a first adhesive layer laminated on the visible side surface of the image display unit, and a polarizing plate described in any one of [1] to [7] laminated on the visible side surface of the first adhesive layer.

[0029] [9] The image display device described in [8] further comprises a second adhesive layer laminated on the visible side surface of the polarizing plate and a transparent member laminated on the visible side surface of the second adhesive layer.

[0030]

[10] According to the image display device described in [9], the transparent component is a glass plate or a transparent resin plate.

[0031]

[11] According to the image display device described in [9], the transparent component is a touch panel.

[0032] Invention Effects

[0033] According to the present invention, a polarizing plate with improved high-temperature durability can be provided, which can suppress the decrease in transmittance caused by high temperature even when used in an image display device with an interlayer filling structure. Furthermore, by using the polarizing plate of the present invention, an image display device that suppresses the decrease in transmittance under high-temperature environments can be provided. Detailed Implementation

[0034] The embodiments of the present invention will be described below; however, the present invention is not limited to the following embodiments.

[0035] [Polarizing plate]

[0036] The polarizing plate of this embodiment has a polarizing element in which dichroic pigments are adsorbed onto a layer containing a polyvinyl alcohol resin and oriented, and a transparent protective film. The polarizing element and the transparent protective film are bonded together by an adhesive layer formed of an adhesive containing an ammonium ion donor. The polarizing plate of this embodiment has at least one of the features described in (a) and (b) below.

[0037] (a) The moisture content of the polarizing element is above the equilibrium moisture content of 30% relative humidity at 20°C and below the equilibrium moisture content of 50% relative humidity at 20°C.

[0038] (b) The moisture content of the polarizing plate is above the equilibrium moisture content of 30% relative humidity at 20°C and below the equilibrium moisture content of 50% relative humidity at 20°C.

[0039] Conventional polarizing plates known for their excellent high-temperature durability include those that, when used alone, can suppress transmittance reduction even after 1000 hours at 95°C. However, even with such polarizing plates, when used in interlayer filling structures, a significant decrease in transmittance is sometimes observed in the central portion of the polarizing plate after 200 hours at 95°C. This significant decrease in transmittance of polarizing plates at high temperatures is considered a problem that is particularly prone to occur when image display devices employing interlayer filling structures are exposed to high temperatures. These interlayer filling structures involve bonding one side of the polarizing plate to the image display unit and the other side to transparent components such as a touch panel or front panel.

[0040] The significant decrease in transmittance of a polarizing plate due to its interlayer filling structure can be attributed to the fact that, in Raman spectrometry at 1100 cm⁻¹, [the following is likely a separate, unrelated sentence fragment: "..."]. -1 Nearby (from =CC= key) and 1500cm -1 The presence of peaks near the -C=C- bond results in a polyene structure (-C=C). n- It is speculated that the polyene structure is a structure produced by polyeneification of the polyvinyl alcohol constituting the polarization element through dehydration (Patent Document 2,

[0012] paragraph).

[0041] The polarizing plate of the present invention can further improve high-temperature durability. When the polarizing plate of the present invention is installed in an image display device with an interlayer filling structure, it can suppress the decrease in transmittance even when exposed to a high-temperature environment such as 95°C for a long time. Even after being stored at 95°C for 150 hours, the decrease in transmittance can be kept to less than 5%.

[0042] <Polarization element>

[0043] As a polarizing element for orientedly adsorbing dichroic dye onto a layer containing polyvinyl alcohol (hereinafter also referred to as "PVA-based resin layer"), a known polarizing element can be used. Examples of polarizing elements include a stretched film obtained by dyeing a PVA-based resin film with a dichroic dye and then uniaxially stretching it; and a stretched layer obtained by dyeing a coating layer formed by coating a substrate film with a coating liquid containing a PVA-based resin, and then uniaxially stretching the laminated film. Stretching can be performed after dyeing with the dichroic dye, during dyeing, or after stretching.

[0044] PVA-based resins can be obtained by saponifying polyvinyl acetate-based resins. Besides polyvinyl acetate as a homopolymer of vinyl acetate, copolymers of vinyl acetate with other monomers that can be copolymerized can also be mentioned as polyvinyl acetate-based resins. Examples of other monomers that can be copolymerized include unsaturated carboxylic acids, olefins such as ethylene, vinyl ethers, and unsaturated sulfonic acids.

[0045] The degree of saponification of the 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 the PVA-based resin is, for example, 1000 or more and 10000 or less, preferably 1500 or more and 5000 or less. The PVA-based resin can be modified, for example, it can be aldehyde-modified polyvinyl formal, polyvinyl acetal, polyvinyl butyral, etc.

[0046] The thickness of the polarizing element is preferably 3 μm or more and 35 μm or less, more preferably 4 μm or more and 30 μm or less, and even more preferably 5 μm or more and 25 μm or less. 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 fabricate a structure that achieves the desired optical properties.

[0047] The polarizing element preferably includes an ammonium ion donor. In this embodiment, since the polarizing element and the transparent protective film are bonded together by an adhesive layer formed by an adhesive containing an ammonium ion donor, it is presumed that a portion of the ammonium ion donor migrates from the adhesive layer and is incorporated into the polarizing element. The ammonium ion donor in the polarizing element may include an ammonium ion donor added during the manufacturing process of the polarizing element. By having a polarizing element containing an ammonium ion donor, the transmittance is less likely to decrease even when the polarizing plate is exposed to a high-temperature environment. This is presumably because the ammonium ions contained in the polarizing element inhibit the polyolefination of the PVA-based resin.

[0048] (Ammonium ion donor)

[0049] Ammonium ion donors are compounds that can supply ammonium ions or ammonium ions. Ammonium ion donors can be used alone or in combination of two or more.

[0050] Examples of compounds that supply ammonium ions include ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride, ammonium acetate, and ammonium oxalate.

[0051] Examples of ammonium ion donors include primary ammonium ions, secondary ammonium ions, and tertiary ammonium ions. Examples of primary ammonium ion donors include decylammonium, dodecylammonium, octadecylammonium, oleylammonium, and benzylammonium. Examples of secondary ammonium ion donors include methyldodecylammonium and methyloctadecylammonium. Examples of tertiary ammonium ion donors include dimethyldodecylammonium and dimethyloctadecylammonium.

[0052] As a method for incorporating an ammonium ion donor into a polarizing element, examples include immersing a PVA-based resin layer in a processing solvent containing an ammonium ion donor, or spraying, flowing down, or dripping the processing solvent onto the PVA-based resin layer. The method of immersing the PVA-based resin layer in a processing solvent containing an ammonium ion donor is preferred.

[0053] The process of immersing the PVA-based resin layer in a treatment solvent containing an ammonium ion donor can be performed simultaneously with the swelling, stretching, dyeing, crosslinking, and cleaning processes described later in the polarization element manufacturing method, or it can be performed separately from these processes. The process of containing the ammonium ion donor in the PVA-based resin layer is preferably performed after dyeing the PVA-based resin layer with iodine, and more preferably simultaneously with the crosslinking process after dyeing. According to this method, the color tone variation is small, and the impact on the optical properties of the polarization element can be reduced.

[0054] To make the polarization element contain an ammonium ion donor, two operations can be performed: adding it during the manufacturing of the polarization element and adding it to the adhesive.

[0055] (Feature(a))

[0056] In the case of characteristic (a), the moisture content of the polarizing element is above the equilibrium moisture content of 30% 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 less than the equilibrium moisture content of 30% 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 is greater than the equilibrium moisture content of 50% relative humidity at 20°C, the transmittance of the polarizing element is prone to decrease. This is presumably because if the moisture content of the polarizing element is high, the polyolefination of the PVA-based resin is more easily promoted. The moisture content of the polarizing element refers to the moisture content of the polarizing element in the polarizing plate.

[0057] As a method to confirm whether the moisture content of a polarizing element is within the range of equilibrium moisture content above 30% relative humidity at 20°C and below 50% relative humidity at 20°C, examples include storing the polarizing element in an environment adjusted to the aforementioned temperature and relative humidity range, and considering it to have reached equilibrium with the environment if there is no change in mass over a certain period of time; or pre-calculating the equilibrium moisture content of the polarizing element in an environment adjusted to the aforementioned temperature and relative humidity range, and confirming it by comparing the moisture content of the polarizing element with the pre-calculated equilibrium moisture content.

[0058] There are no particular limitations on the method for manufacturing a polarizing element with an equilibrium moisture content of 30% or higher at 20°C and 50% or lower at 20°C and relative humidity. However, for example, a method can be given by storing the polarizing element in an environment adjusted to the above temperature and relative humidity range for 10 minutes or more and 3 hours or less; or a method of heat treatment at 30°C or higher and 90°C or lower.

[0059] As another preferred method for manufacturing polarizing elements with the aforementioned moisture content, examples include storing a laminate in which a protective film is deposited on at least one side of the polarizing element, or a polarizing plate made using 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. In manufacturing an image display device employing an interlayer filling structure, the front panel can be bonded after storing the image display panel with the polarizing plate deposited 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.

[0060] The moisture content of the polarizing element is preferably adjusted as follows: during the material stage used to construct a polarizing plate, whether as a standalone polarizing element or as a laminate of the polarizing element and a protective film, the moisture content is within the aforementioned numerical range. If the moisture content is adjusted after the polarizing plate is constructed, excessive curling can easily occur, leading to undesirable conditions when bonded to the image display unit. By constructing the polarizing plate using a polarizing element with the aforementioned moisture content during the material stage before constructing the polarizing plate, it is easy to construct a polarizing plate having a polarizing element with a moisture content satisfying the aforementioned numerical range. Alternatively, the moisture content of the polarizing element in the polarizing plate can be adjusted to the aforementioned numerical range while the polarizing plate is bonded to the image display unit. In this case, the polarizing plate is less prone to curling since it is bonded to the image display unit.

[0061] (Feature (b))

[0062] In the case of feature (b), the moisture content of the polarizing plate is above the equilibrium moisture content of 30% 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 less than the equilibrium moisture content of 30% relative humidity at 20°C, the operability of the polarizing plate decreases, and it is prone to breakage. If the moisture content of the polarizing plate is greater than the equilibrium moisture content of 50% relative humidity at 20°C, the transmittance of the polarizing element is prone to decrease. This is presumably because if the moisture content of the polarizing plate is high, the polyolefination of the PVA-based resin is more easily promoted.

[0063] As a method to confirm whether the moisture content of the polarizing plate is within the range of equilibrium moisture content above 30% relative humidity at 20°C and below 50% relative humidity at 20°C, one can cite the method of storing the polarizing plate in an environment adjusted to the above temperature and relative humidity range, and considering it to have reached equilibrium with the environment if there is no change in mass over a certain period of time; or a method of pre-calculating the equilibrium moisture content of the polarizing plate in an environment adjusted to the above temperature and relative humidity range, and confirming it by comparing the moisture content of the polarizing plate with the pre-calculated equilibrium moisture content.

[0064] There are no particular limitations on the method for manufacturing a polarizing plate with an equilibrium moisture content of 30% or higher at 20°C and 50% or lower at 20°C and relative humidity. For example, a method can be given by storing the polarizing plate in an environment adjusted to the above temperature and relative humidity range for 10 minutes or more and 3 hours or less; or a method of heat treatment at 30°C or higher and 90°C or lower.

[0065] When manufacturing an image display device employing an interlayer filling structure, the image display panel, in which a polarizing plate is stacked on top of the 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 before being bonded to the front panel.

[0066] (Urea compounds)

[0067] The polarizing element may further contain a urea-based compound. A polarizing element containing a urea-based compound can further suppress the decrease in transmittance. The urea-based compound can be the same compound that can be contained in the adhesive described later. As a method for containing the urea-based compound in the polarizing element, the same method as the method for containing an ammonium ion donor in the polarizing element can be used. Regarding the urea-based compound, it can be included during the manufacturing process of the polarizing element, or it can be included in the adhesive used to laminate the polarizing element with the transparent protective film, as described later, thereby making the polarizing element contain a urea-based compound.

[0068] (Manufacturing method of polarization element)

[0069] There is no particular limitation on the manufacturing method of polarization elements. Typical methods include: feeding out a pre-wound PVA-based resin film in a roll shape, stretching, dyeing, cross-linking, etc. (hereinafter referred to as "manufacturing method 1"); and a method including coating a coating liquid containing PVA-based resin onto a substrate film to form a PVA-based resin layer as a coating layer and stretching the resulting laminate (hereinafter referred to as "manufacturing method 2").

[0070] Manufacturing method 1 can be carried out by a process of uniaxially stretching a PVA-based resin film, dyeing the PVA-based resin film with dichroic pigments such as iodine to adsorb dichroic pigments, treating the PVA-based resin film with adsorbed dichroic pigments with a boric acid aqueous solution, and washing with water after treatment with boric acid aqueous solution.

[0071] The swelling process involves immersing a PVA-based resin film in a swelling bath. Besides removing surface contaminants and adhesives from the PVA-based resin film, the swelling process also helps suppress uneven dyeing by causing the film to swell. The swelling bath typically uses a medium primarily composed of water, such as water, distilled water, or pure water. Surfactants, alcohols, etc., can be appropriately added to the swelling bath using conventional methods. From the viewpoint 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.

[0072] The temperature of the swelling bath is preferably 10°C or higher and 60°C or lower, more preferably 15°C or higher and 45°C or lower, and even more preferably 18°C ​​or higher and 30°C or lower. The immersion time in the swelling bath cannot be fixed because the degree of swelling of the PVA resin film is affected by the temperature of the swelling bath; it is preferably 5 seconds or higher and 300 seconds or lower, more preferably 10 seconds or higher and 200 seconds or lower, and even more preferably 20 seconds or higher and 100 seconds or lower. The swelling process can be performed only once or multiple times as needed.

[0073] The dyeing process involves immersing a PVA-based resin film in a dyeing bath (iodine solution), which allows dichroic pigments such as iodine to be adsorbed onto the PVA-based resin film and oriented. The iodine solution is typically an aqueous 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. Among these, potassium iodide is suitable from the viewpoint of controlling the potassium content in the polarization element.

[0074] The concentration of iodine in the staining bath is preferably 0.01% by mass or more and 1% by mass or less, more preferably 0.02% by mass or more and 0.5% by mass or less. The concentration of iodide in the staining bath is preferably 0.01% by mass or more and 10% by mass or less, more preferably 0.05% by mass or more and 5% by mass or less, and even more preferably 0.1% by mass or more and 3% by mass or less.

[0075] The temperature of the dyeing bath is preferably 10°C or higher and 50°C or lower, more preferably 15°C or higher and 45°C or lower, and even more preferably 18°C ​​or higher and 30°C or lower. The immersion time in the dyeing bath cannot be fixed because the degree of dyeing of the PVA-based resin film is affected by the temperature of the dyeing bath; it is preferably 10 seconds or higher and 300 seconds or lower, more preferably 20 seconds or higher and 240 seconds or lower. The dyeing process can be performed only once or multiple times as needed.

[0076] The crosslinking process involves immersing the dyed PVA-based resin film from the dyeing process in a treatment bath (crosslinking bath) containing a boron compound. The boron compound crosslinks 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; however, it 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.

[0077] In the crosslinking bath, the concentration of the boron compound is preferably 1% by mass or more and 15% by mass or less, more preferably 1.5% by mass or more and 10% by mass or less, and even more preferably 2% by mass or more and 5% by mass or less. 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 or less, more preferably 1.5% by mass or more and 10% by mass or less, and even more preferably 2% by mass or more and 5% by mass or less.

[0078] The temperature of the crosslinking bath is preferably 20°C or higher and 70°C or lower, more preferably 30°C or higher and 60°C or lower. The immersion time in the crosslinking bath cannot be fixed because the degree of crosslinking of the PVA resin film is affected by the temperature of the crosslinking bath; however, it is preferably 5 seconds or higher and 300 seconds or lower, more preferably 10 seconds or higher and 200 seconds or lower. The crosslinking process can be performed only once or multiple times as needed.

[0079] The stretching process is a process in which a PVA-based resin film is stretched at least in one direction at a given ratio. Generally, the PVA-based resin film is uniaxially stretched along the transport direction (length direction). There are no particular restrictions on the stretching method; either wet stretching or dry stretching can be used. The stretching process can be performed only once or multiple times as needed. The stretching process can be performed at any stage in the manufacturing of polarization elements.

[0080] The treatment bath (stretching bath) in the wet stretching process can typically be water or a solvent such as an organic solvent miscible with water and a mixture of water. From the viewpoint of controlling the potassium content in the polarization 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% by mass or more and 15% by mass or less, more preferably 2% by mass or more and 10% by mass or less, and even more preferably 3% by mass or more and 6% by mass or less. From the viewpoint of suppressing film breakage during stretching, the treatment bath (stretching bath) may contain a boron compound. When a boron compound is included, the concentration of the boron compound in the stretching bath is preferably 1% by mass or more and 15% by mass or less, more preferably 1.5% by mass or more and 10% by mass or less, and even more preferably 2% by mass or more and 5% by mass or less.

[0081] The temperature of the stretching bath is preferably 25°C or higher and 80°C or lower, more preferably 40°C or higher and 75°C or lower, and even more preferably 50°C or higher and 70°C or lower. The immersion time in the stretching bath cannot be fixed because the degree of stretching of the PVA resin film is affected by the temperature of the stretching bath; it is preferably 10 seconds or higher and 800 seconds or lower, more preferably 30 seconds or higher and 500 seconds or lower. The stretching treatment in the wet stretching method can be performed together with any one or more of the following processing steps: swelling, dyeing, crosslinking, and cleaning.

[0082] Examples of dry stretching methods include inter-roll stretching, heated roll stretching, and compression stretching. It should be noted that dry stretching can be performed concurrently with the drying process.

[0083] The total stretch ratio (cumulative stretch ratio) applied to the polyvinyl alcohol-based resin film can be appropriately set according to the purpose, preferably 2 times or more and 7 times or less, more preferably 3 times or more and 6.8 times or less, and even more preferably 3.5 times or more and 6.5 times or less.

[0084] The cleaning process 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 medium with water, distilled water, or pure water as its main component. Furthermore, from the viewpoint 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% 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.

[0085] The temperature of the cleaning bath is preferably 5°C or higher and 50°C or lower, more preferably 10°C or higher and 40°C or lower, and even more preferably 15°C or higher and 30°C or lower. The immersion time in the cleaning bath cannot be fixed because the degree of cleaning of the PVA resin film is affected by the temperature of the cleaning bath; it is preferably 1 second or higher and 100 seconds or lower, more preferably 2 seconds or higher and 50 seconds or lower, and even more preferably 3 seconds or higher and 20 seconds or lower. The cleaning process can be performed only once or multiple times as needed.

[0086] The drying process is the process of drying the PVA-based resin film cleaned in the cleaning process to obtain the polarizing element. Drying can be carried out using any appropriate method, such as natural drying, forced air drying, or heat drying.

[0087] Manufacturing method 2 can be performed by a process of coating a coating solution containing PVA-based resin onto a substrate film, uniaxially stretching the resulting laminated film, adsorbing dichroic pigments by dyeing the PVA-based resin layer of the uniaxially stretched laminated film with dichroic pigments, forming a polarizing element, treating the film with adsorbed dichroic pigments with a boric acid aqueous solution, and washing with water after the boric acid aqueous solution treatment. 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 be peeled off from the polarizing element as needed.

[0088] <Transparent Protective Film>

[0089] The transparent protective film used in this embodiment (hereinafter also simply referred to as the "protective film") is adhered to at least one side of the polarizing element via an adhesive layer. The transparent protective film is adhered to one or both sides of the polarizing element, but preferably to both sides.

[0090] The protective film can simultaneously possess other optical functions, and can also be formed in a laminated structure with multiple layers. From an optical property point of view, a thin protective film is preferred; however, if it is too thin, its strength decreases and its processability suffers. An appropriate film thickness is 5 μm or more and 100 μm or less, preferably 10 μm or more and 80 μm or less, and more preferably 15 μm or more and 70 μm or less.

[0091] The protective film can be made of cellulose acylated film, film containing polycarbonate resin, film containing cyclic olefin resin such as norbornene, (meth)acrylic polymer film, polyester resin such as polyethylene terephthalate, etc. When the protective film is bonded to both sides of the polarizing element using a water-based adhesive such as PVA adhesive, from the perspective of moisture permeability, it is preferable that at least one side of the protective film is either a cellulose acylated film or a (meth)acrylic polymer film, with a cellulose acylated film being preferred.

[0092] For purposes such as viewing angle compensation, at least one protective film may 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 a combination of both. The film with a phase difference function can be directly attached to the polarization element via an adhesive, or it may be a structure in which another protective film attached to the polarization element is sandwiched between the two films and attached via an adhesive or bonding agent.

[0093] <Adhesive layer>

[0094] An adhesive containing an ammonium ion donor is used as the adhesive layer constituting the protective film for bonding to the polarizing element. The adhesive can be a water-based adhesive, a solvent-based adhesive, or an active energy radiation-cured adhesive, but a water-based adhesive is preferred, and preferably contains a PVA-based resin. By using an adhesive containing an ammonium ion donor, the decrease in transmittance of the polarizing plate under high-temperature conditions can be suppressed.

[0095] The thickness of the adhesive coating can be set to any value, for example, it can be set in such a way that an adhesive layer with a desired thickness is obtained after curing or heating (drying). The thickness of the adhesive layer including the adhesive is preferably 0.01 μm or more and 7 μm or less, more preferably 0.01 μm or more and 5 μm or less, further preferably 0.01 μm or more and 2 μm or less, and most preferably 0.01 μm or more and 1 μm or less.

[0096] The following description of the adhesive is based on a preferred scenario where the polarizing element is manufactured without containing an ammonium ion donor. If the polarizing element does contain an ammonium ion donor, the following values ​​can be adjusted appropriately. For a specific example of the ammonium ion donor, the same ammonium ion donor as described in the polarizing element above can be used. During the drying process of forming the adhesive layer when bonding the polarizing element to the protective film, a portion of the ammonium ion donor can move from the adhesive layer to the polarizing element, etc.

[0097] When the adhesive is an aqueous adhesive containing PVA-based resin, the content of ammonium ion donor in the adhesive is preferably 1 part by weight or more and 300 parts by weight or less relative to 100 parts by weight of PVA-based resin, more preferably 1.5 parts by weight or more and 250 parts by weight or less, even more preferably 2 parts by weight or more and 200 parts by weight or less, and may also be 100 parts by weight or less. If it is less than 1 part by weight, the effect of improving high-temperature durability may not be sufficiently obtained. On the other hand, if the content of ammonium ion donor is greater than 300 parts by weight, crystals may precipitate after drying.

[0098] In a structure in which a transparent protective film is bonded to both sides of a polarizing element via an adhesive layer, it is permissible for only one side of the adhesive layer on both sides of the polarizing element to be a layer containing an ammonium ion donor, but it is preferable that both sides of the adhesive layer contain an ammonium ion donor.

[0099] To meet the demand for thinner polarizing plates, a polarizing plate with a transparent protective film on only one side of the polarizing element has been developed. In this structure, the transparent protective film is also laminated via an adhesive layer containing an ammonium ion donor. As a method for manufacturing this type of polarizing plate with a transparent protective film on only one side of the polarizing element, it is possible to first manufacture a polarizing plate with transparent protective films adhered to both sides via adhesive layers, and then peel off one of the transparent protective films. In using this manufacturing method, it is possible for only one adhesive layer to contain the ammonium ion donor; however, it is preferable that both adhesive layers contain the ammonium ion donor. When the adhesive layer containing the ammonium ion donor is used only on one side of the polarizing element, it is preferable that the adhesive layer on the non-peeled film side contains the ammonium ion donor.

[0100] (Water-based adhesive)

[0101] Any suitable aqueous adhesive can be used as the aqueous adhesive, but it is preferred to use an aqueous adhesive containing PVA-based resin (PVA-based adhesive). From an adhesiveness perspective, the average degree of polymerization of the PVA-based resin contained in the aqueous adhesive is preferably 100 or more and 5500 or less, more preferably 1000 or more and 4500 or less. From an adhesiveness perspective, the average degree of saponification is preferably 85 mol% or more and 100 mol% or less, more preferably 90 mol% or more and 100 mol% or less.

[0102] As the PVA-based resin contained in the water-based adhesive, a resin containing acetyl groups is preferred because it exhibits excellent adhesion and durability to the protective film. The PVA-based resin containing acetyl groups can be obtained, for example, by reacting a PVA-based resin with a diene using any method. The degree of acetyl group modification in the PVA-based resin containing acetyl groups 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 wt% or more and 15 wt% or less, more preferably 0.5 wt% or more and 10 wt% or less.

[0103] Water-based adhesives can also contain crosslinking agents. Known crosslinking agents can be used. Examples of crosslinking agents include water-soluble epoxy compounds, dialdehydes, and isocyanates.

[0104] When the PVA resin is a PVA resin containing acetyl groups, the crosslinking agent is preferably any substance selected from glyoxal, glyoxylate, and hydroxymethyl melamine, more preferably any substance selected from glyoxal and glyoxylate, and particularly preferably glyoxal.

[0105] Aqueous adhesives may also contain organic solvents. From the perspective of miscibility with water, alcohols are preferred organic solvents, and methanol or ethanol are more preferred among alcohols. The concentration of methanol in the aqueous adhesive is preferably 10% by mass or more and 70% by mass or less, more preferably 15% by mass or more and 60% by mass or less, and even more preferably 20% by mass or more and 60% by mass or less. By keeping the methanol concentration at 10% by mass or more, it is easier to further suppress the polyolefination of PVA-based resins under high-temperature conditions. Furthermore, by keeping the methanol content at 70% by mass or less, color deterioration can be suppressed. Some urea derivatives are compounds with low solubility relative to water but sufficient solubility relative to alcohols. In this case, it is also a preferred method to prepare an alcoholic solution of the urea compound by dissolving it in an alcohol, and then adding the alcoholic solution of the urea compound to an aqueous PVA solution to prepare the adhesive.

[0106] (Active energy radiation curing adhesive)

[0107] Reactive energy radiation-cured adhesives are adhesives that are cured by irradiation with reactive energy rays such as ultraviolet light. Examples include adhesives containing polymerizable compounds and photopolymerization 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 urethane monomers, as well as oligomers derived from these monomers. Examples of photopolymerization initiators include compounds containing substances that generate reactive species such as neutral free radicals, anionic free radicals, and cationic free radicals upon irradiation with reactive energy rays such as ultraviolet light.

[0108] (Urea compounds)

[0109] The adhesive may also contain at least one urea compound selected from urea, urea derivatives, thiourea, and thiourea derivatives. By including a urea compound in the adhesive layer containing the adhesive, high-temperature durability can be further improved. During the drying process of the adhesive layer formed by the adhesive bonding to the protective film, a portion of the urea compound can migrate from the adhesive layer to polarizing elements, etc. Urea compounds include water-soluble and poorly soluble compounds; either type of urea compound can be used. When using a poorly soluble urea compound in a water-soluble adhesive, it is preferable to design the dispersion method in a way that does not cause an increase in turbidity after the adhesive layer is formed.

[0110] When the adhesive is an aqueous adhesive containing PVA-based resin, the amount of urea compound added is preferably 0.1 parts by weight or more and 400 parts by weight or less relative to 100 parts by weight of PVA, more preferably 1 part by weight or more and 200 parts by weight or less, and even more preferably 3 parts by weight or more and 100 parts by weight or less.

[0111] (Urea derivatives)

[0112] Urea derivatives are compounds in which at least one of the four hydrogen atoms of a urea molecule is substituted by a substituent. In this case, there are no particular restrictions on the substituent, but substituents containing carbon, hydrogen, and oxygen atoms are preferred.

[0113] Specific examples of urea derivatives include, for monosubstituted ureas, 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. For disubstituted ureas, examples include 1,1-dimethylurea, 1,3-dimethylurea, 1,1-diethylurea, 1,3-diethylurea, 1,3-di(hydroxymethyl)urea, 1,3-tert-butylurea, 1,3-dicyclohexylurea, 1,3-diphenylurea, 1,3-di(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.

[0114] (Thiocarbamide derivatives)

[0115] Thiourea derivatives are compounds in which at least one of the four hydrogen atoms of a thiourea molecule is substituted by a substituent. In this case, there are no particular restrictions on the substituent, but substituents containing carbon, hydrogen, and oxygen atoms are preferred.

[0116] Specific examples of thiourea derivatives, in terms of monosubstituted thioureas, include N-methylthiourea, ethylthiourea, propylthiourea, isopropylthiourea, 1-butylthiourea, cyclohexylthiourea, N-acetylthiourea, 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.

[0117] From the perspective of further suppressing the decrease in transmittance under high-temperature environments when used in image display devices with interlayer filling structures, urea derivatives or thiourea derivatives are preferred among urea compounds, and urea derivatives are more preferred. Among urea derivatives, monosubstituted urea or disubstituted urea are preferred, and monosubstituted urea is more preferred. Disubstituted urea includes 1,1-substituted urea and 1,3-substituted urea, but 1,3-substituted urea is more preferred.

[0118] <Ammonium ion donor containing layer>

[0119] The ammonium ion donor is not limited to being contained in the adhesive layer as described above; from the viewpoint of improving the high-temperature durability of the polarizing plate, it may also be contained in other layers besides the adhesive layer. In a polarizing plate with a transparent protective film on only one side, from the viewpoint of improving physical strength, a curing layer may be laminated on the side of the polarizing element opposite to the transparent protective film.

[0120] In this embodiment, the cured layer may also contain an ammonium ion donor, forming an ammonium ion donor-containing layer. Typically, this type of cured layer is formed from a curable composition containing an organic solvent. Japanese Patent Application Publication No. 2017-075986, paragraphs

[0020] to

[0042] , describes a method for forming such a cured layer from an aqueous solution of an active energy ray curable polymer composition. Regarding the ammonium ion donor, since there are many water-soluble ammonium ion donors, this composition may contain a water-soluble ammonium ion donor.

[0121] The ammonium ion donor layer preferably comprises at least one ammonium ion donor and an adhesive. Examples of adhesives include polymer adhesives, thermosetting resin adhesives, and active energy radiation-curable resin adhesives; any adhesive may be preferred.

[0122] The thickness of the ammonium ion donor containing the layer is preferably 0.1 μm or more and 20 μm or less, more preferably 0.5 μm or more and 15 μm or less, and even more preferably 1 μm or more and 10 μm or less.

[0123] [Manufacturing method of polarizing plate]

[0124] 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 a polarizing plate having feature (a), the moisture content of the polarizing element is adjusted such that it is at least equal to an equilibrium moisture content of 30% relative humidity at 20°C and less than or equal to an 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 a polarizing plate having feature (b), the moisture content of the polarizing plate is adjusted such that it is at least equal to an equilibrium moisture content of 30% relative humidity at 20°C and less than or equal to an 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 together via the aforementioned adhesive layer. In the lamination process, for example, a polarizing element that has not undergone treatment to contain an ammonium ion donor is bonded to a transparent protective film using an adhesive containing an ammonium ion donor. The order of the moisture content adjustment process and the lamination process is not limited, and the moisture content adjustment process and the lamination process can also be performed in parallel.

[0125] [Structure of an image display device]

[0126] 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 with interlayer filling structures that allow both sides of the polarizing plate to contact layers other than an air layer, specifically solid layers such as adhesive layers, the transmittance tends to decrease at high temperatures. In image display devices using the polarizing plate of this embodiment, even with an interlayer filling structure, the decrease in the transmittance of the polarizing plate at high temperatures can be suppressed. An example of an image display device is a structure comprising an image display unit, a first adhesive layer laminated to the visible side surface of the image display unit, and a polarizing plate laminated to the visible side surface of the first adhesive layer. This image display device may also include a second adhesive layer laminated to the visible side surface of the polarizing plate and a transparent member laminated to the surface of the second adhesive layer. In particular, the polarizing plate of this embodiment can be suitably used in image display devices having an interlayer filling structure in which a transparent member is disposed on the visible side of the image display device, the polarizing plate is bonded to the image display unit using the first adhesive layer, and the polarizing plate is bonded to the transparent member using the second adhesive layer. In this specification, either or both of the first adhesive layer and the second adhesive layer are sometimes referred to simply as "adhesive layer". It should be noted that the components used for bonding the polarizing plate to the image display unit and the components used for bonding the polarizing plate to the transparent component are not limited to adhesive layers and may also be adhesive layers.

[0127] <Image Display Unit>

[0128] Examples of image display units include liquid crystal cells and organic EL cells. As a liquid crystal cell, one can use a reflective liquid crystal cell that utilizes external light, a transmissive liquid crystal cell that utilizes light from a light source such as a backlight, or a semi-transmissive / semi-reflective liquid crystal cell that utilizes both external light and light from a light source. In the case where the liquid crystal cell utilizes light from a light source, the image display device (liquid crystal display device) also provides a polarizing plate on the side of the image display cell (liquid crystal cell) opposite to the viewable side, and further provides a light source. The polarizing plate on the light source side is preferably bonded to the liquid crystal cell via a suitable adhesive layer. As for the driving method of the liquid crystal cell, for example, optional types of driving methods such as VA mode, IPS mode, TN mode, STN mode, and flexural orientation (π-type) can be used.

[0129] As an organic EL unit, an organic EL unit in which a transparent electrode, an organic light-emitting layer, and a metal electrode are sequentially stacked on a transparent substrate to form a light emitter (organic electroluminescent emitter) can be appropriately used. The organic light-emitting layer is a stack of various organic thin films, such as a stack of a hole injection layer containing a triphenylamine derivative and a light-emitting layer containing a fluorescent organic solid such as anthracene, a stack of these light-emitting layers and an electron injection layer containing a perylene derivative, or a stack of a hole injection layer, a light-emitting layer, and an electron injection layer, etc.

[0130] <Attachment of image display unit to polarizing plate>

[0131] In the bonding of the image display unit and the polarizing plate, an adhesive layer (adhesive sheet) can be appropriately used. From an operational perspective, a method of bonding the image display unit to a polarizing plate with an adhesive layer attached to one side of the polarizing plate is preferred. The attachment of the adhesive layer to the polarizing plate can be performed in an appropriate manner. Examples include: preparing an adhesive solution containing 10% by mass or more and 40% by mass or less of a base polymer or a combination thereof dissolved or dispersed in a solvent containing a suitable solvent such as toluene or ethyl acetate, and directly attaching it to the polarizing plate using an appropriate spreading method such as casting or coating; or forming the adhesive layer on a spacer and transferring it to the polarizing plate.

[0132] <Adhesive layer>

[0133] The adhesive layer can be formed in one or more layers, but preferably in one layer. The adhesive layer can be formed from an adhesive composition with (meth)acrylic resin, rubber resin, urethane resin, ester resin, silicone resin, or polyvinyl ether resin as the main component. Among these, adhesive compositions with (meth)acrylic resin as the base polymer are particularly suitable, exhibiting excellent transparency, weather resistance, and heat resistance. The adhesive composition can also be of the active energy radiation curing type or the thermosetting type.

[0134] The (meth)acrylic resin (base polymer) used in the adhesive composition can suitably be 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. It is preferable to copolymerize a polar monomer in the base polymer. Examples of polar monomers include (meth)acrylic acid 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 have carboxyl, hydroxyl, amide, amino, or epoxy groups.

[0135] The adhesive composition may contain only the aforementioned base polymer, but typically also contains a crosslinking agent. Examples of crosslinking agents include metal ions with a valence of divalent or higher that form a carboxylic acid metal salt between themselves and a carboxyl group; polyamine compounds that form an amide bond between themselves and a carboxyl group; polyepoxide compounds or polyols that form an ester bond between themselves and a carboxyl group; and polyisocyanate compounds that form an amide bond between themselves and a carboxyl group. Among these, polyisocyanate compounds are preferred.

[0136] The active energy radiation-curing adhesive composition possesses the property of curing upon irradiation by active energy radiation such as ultraviolet rays or electron beams. It also exhibits adhesiveness even before irradiation, enabling it to adhere tightly to substrates such as films, and the ability to adjust the adhesion force upon curing. The active energy radiation-curing adhesive composition is preferably ultraviolet-curing. In addition to containing a base polymer and a crosslinking agent, the active energy radiation-curing adhesive composition also contains an active energy radiation-polymerizing compound. Depending on the requirements, it may contain photopolymerization initiators, photosensitizers, etc.

[0137] The adhesive composition may contain additives such as microparticles, beads (resin beads, glass beads, etc.) for imparting light scattering properties, glass fibers, resins other than the base polymer, tackifiers, fillers (metal powders, other inorganic powders, etc.), antioxidants, ultraviolet absorbers, dyes, pigments, colorants, defoamers, corrosion inhibitors, and photopolymerization initiators.

[0138] The adhesive layer can be formed by applying an organic solvent dilution of the adhesive composition described above to the surface of a substrate film, an image display unit, or a polarizing plate and then drying it. The substrate film is typically a thermoplastic resin film; a typical example is a release film that has undergone a release treatment. For example, the release film may be a film in which the adhesive layer of a film containing resins such as polyethylene terephthalate, polybutylene terephthalate, polycarbonate, or polyarylate has undergone a silicone treatment or other release treatment.

[0139] An adhesive composition can be directly applied to the release surface of the release film to form an adhesive layer, and this adhesive layer with the release film can be laminated onto the surface of the polarizer. Alternatively, an adhesive composition can be directly applied to the surface of the polarizer to form an adhesive layer, and a release film can be laminated on the outer surface of the adhesive layer.

[0140] When the adhesive layer is applied to the surface of the 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.

[0141] Alternatively, an adhesive sheet can be prepared by coating an adhesive composition onto a second release liner to form an adhesive layer, and then stacking a release liner on the formed adhesive layer. The adhesive layer with the release liner after peeling the second release liner from the adhesive sheet is then stacked on a polarizing plate. The second release liner is a membrane with weaker adhesion to the adhesive layer and easier to peel off compared to the release liner.

[0142] The thickness of the adhesive layer is not particularly limited, but 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.

[0143] <Transparent Components>

[0144] Examples of transparent components that can be disposed on the visible side of an image display device include transparent panels (window layers) and touch panels. A transparent panel with appropriate mechanical strength and thickness is used. Examples of such transparent panels include transparent resin sheets made of polyimide-based resins, acrylic resins, polycarbonate resins, or glass sheets. Functional layers such as anti-reflective layers can also be laminated on the visible side of the transparent panel. Furthermore, when the transparent panel is a transparent resin sheet, a hard coating can be laminated to improve physical strength, and a low-permeability layer can be laminated to reduce moisture permeability. Various touch panels, such as resistive film, capacitive, optical, and ultrasonic touch panels, as well as glass sheets and transparent resin sheets with touch sensor functionality, can be used as touch panels. When using a capacitive touch panel as the transparent component, it is preferable to provide a transparent panel made of glass or a transparent resin sheet on the visible side relative to the touch panel.

[0145] <Fitting of polarizing plate with transparent component>

[0146] In bonding the polarizing plate to the transparent component, adhesives or active energy radiation-cured adhesives can be appropriately used. When using adhesives, they can be applied in a suitable manner. For example, the method of applying the adhesive layer used in the bonding of the image display unit to the polarizing plate described above can be cited as a specific application method.

[0147] When using an active energy ray-cured adhesive, to prevent the adhesive solution from spreading before curing, a suitable method can be used: a dam material is set up to surround the periphery of the image display panel; a transparent component is placed on the dam material; and the adhesive solution is injected. After the adhesive solution is injected, alignment and degassing are performed as needed, followed by curing by irradiation with active energy rays.

[0148] Example

[0149] The present invention will now be described in detail based on embodiments. The materials, reagents, quantities, proportions, and operations shown in the following embodiments may be appropriately modified without departing from the spirit of the invention.

[0150] Therefore, the present invention is not limited or restricted by the following embodiments.

[0151] (Fabrication of polarization element 1)

[0152] A 40 μm thick PVA film, formed from PVA with an average degree of polymerization of approximately 2400 and a saponification degree of 99.9 mol% or higher, was uniaxially stretched to approximately 5 times its original length using a dry method. 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 weight 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 weight ratio of 8.5 / 8.5 / 100 at 72°C for 300 seconds. After washing with pure water at 26°C for 20 seconds, it was dried at 65°C to obtain a 15 μm thick polarizing element 1 with iodine adsorbed and oriented in the PVA. The thickness of the polarizing element was measured using a digital micrometer "MH-15M" manufactured by Nikon Corporation.

[0153] (Preparation of PVA solution for adhesives)

[0154] 50g of a modified PVA resin containing acetyl groups (GOHSENX 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.

[0155] Dissolve 15g of ammonium chloride in 1000g of the above-mentioned adhesive PVA solution, and then add pure water to adjust the PVA concentration to 3.0% by mass, thus obtaining adhesive 1.

[0156] Dissolve 15g of ammonium sulfate in 1000g of the above-mentioned adhesive PVA solution, and then add pure water to adjust the PVA concentration to 3.0% by mass, thus obtaining adhesive 2.

[0157] Pure water was added to 1000g of the PVA solution used for the adhesive described above, thereby adjusting the PVA concentration to 3.0% by mass, resulting in adhesive 3.

[0158] (Preparation of transparent protective film)

[0159] A commercially available cellulose acylated membrane TD40 (manufactured by Fujifilm Corporation, 40 μm thick) was immersed in a 1.5 mol / L NaOH aqueous solution (saponification solution) maintained 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 then rinsed under running water for 30 seconds to neutralize the membrane. Afterward, water was removed three times using an air knife, and the membrane was dried in a drying zone at 70°C for 15 seconds to produce a saponified membrane, which serves as a transparent protective film 1.

[0160] (Making of a polarizing plate)

[0161] A transparent protective film 1 is bonded to both sides of the polarizing element 1 using a roller laminator via adhesive 1. After bonding, it is dried at 80°C for 5 minutes to obtain the polarizing plate 1. The adhesive layer is adjusted so that the thickness after drying is 100 nm on both sides.

[0162] Except for using adhesive 2 or adhesive 3 instead of adhesive 1, polarizing plate 2 and polarizing plate 3 are manufactured using the same method as the method for manufacturing polarizing plate 1.

[0163] (Adjustment of moisture content in polarizing plate (polarizing element))

[0164] The polarizing plates 1-3 obtained above were stored for 72 hours at a temperature of 20°C and relative humidity of 30%, 35%, 40%, 45%, 50%, or 55%. The moisture content was determined using the Karl Fischer method after 66, 69, and 72 hours of storage. Under any humidity conditions, the moisture content remained unchanged after 66, 69, and 72 hours of storage. Therefore, the moisture content of polarizing plates 1-3 can be considered to be the same as the equilibrium moisture content of the storage environment. When the moisture content of a polarizing plate reaches equilibrium under a certain storage environment, it can be assumed that the moisture content of the polarizing element in the polarizing plate also reaches equilibrium under that storage environment. Furthermore, when the moisture content of the polarizing element in a polarizing plate reaches equilibrium under a certain storage environment, it can be assumed that the moisture content of the polarizing plate also reaches equilibrium under that storage environment.

[0165] (Fabrication of optical laminates)

[0166] Polarizing plates 1-3 were stored at 20°C and relative humidity of 40%, 50%, or 55% for 72 hours. Optical laminates 1-6 were obtained with water content adjusted to the values ​​shown in Table 1.

[0167] An acrylic adhesive (LINTEC Corporation, model #7) was applied to both sides of optical laminates 1-6 with adjusted moisture content, and then cut into 50mm x 100mm pieces. Alkali-free glass (Corning Corporation "EAGLE XG") was then bonded to each adhesive surface to produce evaluation samples.

[0168] (Evaluation of monomer transmittance after high-temperature durability test (95℃))

[0169] The evaluation samples were subjected to a temperature of 50℃ and a pressure of 5 kgf / cm². 2 After autoclaving at (490.3 kPa) for 1 hour, the sample was placed in an environment of 23°C and 55% relative humidity for 24 hours. Subsequently, the transmittance (initial value) was measured, and the sample was stored at 95°C for 100–200 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, according to the following criteria. The results are shown in Table 1.

[0170] Samples whose transmittance decreased by less than 5% after 200 hours: A

[0171] Samples whose transmittance decreased by more than 5% over 150–200 hours: B

[0172] Samples with a transmittance decrease of more than 5% over 100–150 hours: C

[0173] Samples whose transmittance decreased by more than 5% after 100 hours: D

[0174] [Table 1]

[0175]

[0176] It is known that polarizing plates (optical laminates 1-3) with a moisture content above the equilibrium moisture content of 30% relative humidity at 20℃ and below the equilibrium moisture content of 50% relative humidity at 20℃, which have polarizing elements and transparent protective films, and in which the polarizing elements and transparent protective films are bonded together using an adhesive containing ammonium ion donors, do not easily reduce their transmittance even when exposed to a high temperature environment of 95℃ for a long time, and have excellent high temperature durability.

Claims

1. A polarizing plate comprising a polarizing element for adsorbing and oriented a dichroic pigment onto a polyvinyl alcohol-based resin layer, and a transparent protective film laminated on at least one side of the polarizing element. The polarizing element and the transparent protective film are bonded together by an adhesive layer formed by an adhesive containing an ammonium ion donor. The ammonium ion donor is selected from at least one of ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride, ammonium acetate, and ammonium oxalate. The adhesive is an aqueous adhesive comprising a polyvinyl alcohol (PVA) resin. The content of the ammonium ion donor in the adhesive is more than 2 parts by weight and less than 200 parts by weight relative to 100 parts by weight of the PVA resin. The PVA resin is a PVA resin containing acetyl groups. The moisture content of the polarizing element is above the equilibrium moisture content of 30% relative humidity at 20°C and below the equilibrium moisture content of 50% relative humidity at 20°C.

2. A polarizing plate comprising a polarizing element for adsorbing and oriented a dichroic pigment onto a polyvinyl alcohol-based resin layer, and a transparent protective film laminated on at least one side of the polarizing element. The polarizing element and the transparent protective film are bonded together by an adhesive layer formed by an adhesive containing an ammonium ion donor. The ammonium ion donor is selected from at least one of ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride, ammonium acetate, and ammonium oxalate. The adhesive is an aqueous adhesive comprising a polyvinyl alcohol (PVA) resin. The content of the ammonium ion donor in the adhesive is more than 2 parts by weight and less than 200 parts by weight relative to 100 parts by weight of the PVA resin. The PVA resin is a PVA resin containing acetyl groups. 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.

3. The polarizing plate according to claim 1 or 2, wherein, The thickness of the adhesive layer is greater than 0.01 μm and less than 7 μm.

4. The polarizing plate according to claim 1 or 2, wherein, The polarizing plate is used in an image display device. In the image display device, a solid layer is provided on both sides of the polarizing plate in contact with both sides of the polarizing plate.

5. An image display device comprising an image display unit, a first adhesive layer laminated on the visible side surface of the image display unit, and a polarizing plate laminated on the visible side surface of the first adhesive layer, as described in any one of claims 1 to 4.

6. The image display device according to claim 5, further comprising a second adhesive layer laminated on the visible side surface of the polarizing plate and a transparent member laminated on the visible side surface of the second adhesive layer.

7. The image display device according to claim 6, wherein, The transparent component is a glass plate or a transparent resin plate.

8. The image display device according to claim 6, wherein, The transparent component is a touch panel.

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