Polarizing plate and image display device

Abstract

This invention provides a polarizing plate capable of suppressing the decrease in transmittance under high-temperature environments. The polarizing plate comprises a polarizing element with a dichroic pigment adsorbed and aligned to 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 from an adhesive containing a first compound and a second compound. The first compound is a compound having nitrile radicals or nitric oxide groups. The second compound is a cyclodextrin.

Description

Technical Field

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

[0002] Liquid crystal displays (LCDs) are widely used not only in LCD TVs but also in personal computers, mobile devices such as cell phones, and automotive applications such as navigation systems. Typically, an LCD panel consists of liquid crystal cells with polarizing plates bonded to both sides using pressure-sensitive adhesive. The display is controlled by light from a backlight source. In recent years, organic EL (electroluminescent) displays have also been widely used, similarly in televisions, mobile devices such as cell phones, and automotive applications such as navigation systems. In organic EL displays, to prevent external light from being reflected by the metal electrodes (cathodes) and perceived as a mirror, a circular polarizing plate (a multilayer comprising polarizing elements and a λ / 4 plate) is sometimes placed on the recognition side surface of the image display panel.

[0003] As mentioned above, polarizing plates, as components of image display devices such as liquid crystal displays and organic EL displays, are increasingly likely to be installed in automobiles. Compared to mobile applications such as televisions and mobile phones, polarizing plates used in automotive image display devices are exposed to higher temperatures more frequently, thus requiring minimal changes in characteristics at higher temperatures (high-temperature durability).

[0004] On the other hand, to prevent damage to the image display panel from impacts from the outer surface, a front transparent panel (also called a "window layer") made of transparent resin or glass is often provided on the side closer to the image display panel than the image display panel itself. In image display devices equipped with touch panels, a configuration in which the touch panel is located on the side closer to the image display panel than the image display panel, and a front transparent panel is provided on the side closer to the touch panel than the touch panel itself, is widely used.

[0005] In such a configuration, when there is an air layer between the image display panel and transparent components such as a front transparent plate and a touch panel, external light reflection occurs due to the reflection of light at the air layer interface, and the visibility of the screen tends to decrease. Therefore, a configuration in which the space between the polarizing plate disposed on the recognition side surface of the image display panel and the transparent component is filled with a layer other than the air layer, usually a solid layer (hereinafter referred to as "interlayer filler"), has begun to be widely adopted. The interlayer filler is preferably a material having a refractive index close to that of the polarizing plate or the transparent component. As the interlayer filler, an adhesive or a UV-curable adhesive (see, for example, Patent Document 1) is used for the purpose of suppressing the decrease in visibility due to reflection at the interface and then fixing between the components.

[0006] The configuration in which the interlayer filler as described above is filled is widely adopted in mobile applications such as mobile phones that are frequently used outdoors. In recent years, due to the increasing requirements for visibility, even in automotive applications such as navigation devices, the adoption of a configuration in which a front transparent plate is disposed on the surface of the image display panel and the space between the panel and the front transparent plate is filled with a solid layer such as an adhesive layer is being considered.

[0007] However, in the case of adopting such a configuration, it has been reported that the transmittance of the polarizing plate is significantly reduced in a high-temperature environment. In Patent Document 2, as a solution to this problem, a method of suppressing the reduction in transmittance by setting the moisture content per unit area of the polarizing plate to a predetermined amount or less and setting the saturated water absorption of the transparent protective film adjacent to the polarizing element to a predetermined amount or less is proposed.

[0008] [Prior Art Documents]

[0009] [Patent Documents]

[0010]

[0011] [Patent Document 1] Japanese Patent Application Laid-Open No. 11-174417

[0012] [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-102353 Summary of the Invention Problems to be Solved by the Invention

[0013] However, even such a polarizing plate cannot sufficiently suppress the reduction in transmittance in a high-temperature environment.

[0014] The purpose of this invention is to provide a polarizing plate that can suppress the reduction of transmittance even when exposed to high temperature environments, and an image display device using the polarizing plate. The means to solve the problem

[0015] The present invention provides the following polarizing plate and image display device.

[0016] [1] A polarizing plate comprising a polarizing element having dichroic pigment adsorbed and aligned on a polyvinyl alcohol resin layer, and a transparent protective film laminated on at least one side of the aforementioned polarizing element;

[0017] The aforementioned polarizing element and the aforementioned transparent protective film are bonded together by an adhesive layer formed by an adhesive containing the first compound and the second compound;

[0018] The aforementioned compound 1 is a compound containing a nitroxyl radical or a nitric oxide group;

[0019] The second compound mentioned above is a cyclodextrin.

[0020] [2] The polarizing plate described in [1], wherein the first compound mentioned above is an N-oxygen compound.

[0021] [3] A polarizing plate as described in [1] or [2], wherein the second compound is selected from at least one of the group consisting of α-cyclodextrin, β-cyclodextrin and γ-cyclodextrin.

[0022] [4] The polarizing plate described in any of [1] to [3], wherein the aforementioned adhesive comprises a polyvinyl alcohol resin.

[0023] [5] As described in [4], in the aforementioned adhesive, the content of the aforementioned first compound is 0.1 parts by mass or more and 400 parts by mass or less relative to 100 parts by mass of the aforementioned polyvinyl alcohol resin.

[0024] [6] As described in [4] or [5], wherein, in the aforementioned adhesive, the content of the aforementioned second compound is more than 1 part by mass and less than 50 parts by mass relative to 100 parts by mass of the aforementioned polyvinyl alcohol resin.

[0025] [7] The polarizing plate according to any one of [1] to [6], wherein the thickness of the adhesive layer is 0.01 μm or more and 7 μm or less.

[0026] [8] The polarizing plate according to any one of [1] to [7], wherein the polarizing plate is used in an image display device;

[0027] In the image display device, it is arranged such that both sides of the polarizing plate are in contact with the solid layer.

[0028] [9] An image display device, comprising: an image display unit; a first adhesive layer laminated on the recognition side surface of the image display unit; and a polarizing plate according to any one of [1] to [8] laminated on the recognition side surface of the first adhesive layer.

[0029]

[10] The image display device according to [9], further comprising: a second adhesive layer laminated on the recognition side surface of the polarizing plate, and a transparent member laminated on the recognition side surface of the second adhesive layer.

[0030]

[11] The image display device according to

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

[0031]

[12] The image display device according to

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

[0032] According to the present invention, there can be provided a polarizing plate for use in an image display device having a layer filling structure configured such that both sides of the polarizing plate are in contact with a solid layer, which suppresses a decrease in transmittance even when exposed to a high-temperature environment. Furthermore, by using the polarizing plate of the present invention, there can be provided an image display device that suppresses a decrease in transmittance even when exposed to a high-temperature environment. Embodiments .

[0033] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments.

[0034] [Polarizing Plate]

[0035] The polarizing plate of this embodiment comprises a polarizing element with dichroic pigment adsorbed and aligned to a polyvinyl alcohol-based resin layer, and a transparent protective film deposited 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 a first compound and a second compound. The first compound is a compound having nitrile radicals or nitric oxide groups. The second compound is a cyclodextrin.

[0036] As a traditional polarizing plate known for its excellent high-temperature durability, there are polarizing plates that, for example, suppress the decrease in transmittance even after being placed at 95°C for 1000 hours. However, even with such polarizing plates, in image display devices with a configuration where one side of the polarizing plate is bonded to an image display unit and the other side is bonded to transparent components such as a touch panel or front panel (hereinafter referred to as "interlayer filling configuration"), a significant decrease in transmittance is observed in the central part of the polarizing plate after being placed at 95°C for 200 hours. 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 using interlayer filling configurations are exposed to high temperatures.

[0037] In an image display device constructed with interlayer filling, a polarizing plate with significantly reduced transmittance is believed to have formed a polyolefin structure (-C=C)n- due to the presence of peaks near 1100 cm⁻¹ (from the -C=C bond) and near 1500 cm⁻¹ (from the -C=C bond) measured by Raman spectroscopy. The polyolefin structure is presumably produced by the polyvinyl alcohol resin constituting the polarizing element being polyolefinized due to dehydration (Patent Document 2, paragraph

[0012] ).

[0038] The polarizing plate of this embodiment, assembled in an image display device composed of interlayer filler, exhibits excellent high-temperature durability, suppressing the decrease in transmittance even when exposed to high-temperature environments such as 105°C. This effect is attributed to the adhesive layer comprising the first and second compounds in the polarizing plate, presumably due to the synergistic effect of the first and second compounds suppressing the polyolefination of the polyvinyl alcohol-based resin constituting the polarizing element. This effect is confirmed to be effective not only when the moisture content of the polarizing plate is low, but also when the moisture content of the polarizing plate is high.

[0039] The polarizing plate of this embodiment may have at least one of the features described in (a) and (b).

[0040] (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 80% relative humidity at 20°C.

[0041] (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 80% relative humidity at 20°C.

[0042] Regarding the features described in (a) or (b) above, the polarizing plate of this embodiment, even if it has the features further defined as described in (a1) or (b1) below, will still have the effect of improving high-temperature durability.

[0043] (a1) The moisture content of the polarizing element is greater than the equilibrium moisture content of 45% or 50% relative humidity at 20°C and less than the equilibrium moisture content of 80% or 70% relative humidity at 20°C.

[0044] (b1) The moisture content of the polarizing plate is greater than the equilibrium moisture content of 45% or 50% relative humidity at 20°C and less than the equilibrium moisture content of 80% or 70% relative humidity at 20°C.

[0045] The method for manufacturing the polarizing plate of this embodiment may include a step of adjusting the moisture content to give it at least one of the features in (a) and (b) above, or it may not include a step of adjusting the moisture content.

[0046] <Polarizing element>

[0047] As a polarizing element for adsorbing and aligning dichroic dyes to a polyvinyl alcohol (hereinafter referred to as "PVA")-based resin layer, conventional polarizing elements can be used. Examples of polarizing elements include: an extended film obtained by dyeing a PVA-based resin film (which serves as the PVA-based resin layer) with a dichroic dye and then uniaxially stretching it; or a laminate obtained by coating a substrate film with a coating solution containing a PVA-based resin, forming a coating layer (which serves as the PVA-based resin layer) on the substrate film, 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 it can be performed while dyeing, or dyeing can be performed after stretching.

[0048] The PVA-based resin contained in the PVA-based resin layer can be obtained by saponifying a polyvinyl acetate-based resin. Polyvinyl acetate-based resins include, in addition to polyvinyl acetate homopolymers, copolymers of vinyl acetate and other monomers that may copolymerize with it. Other monomers that may copolymerize include unsaturated carboxylic acids, olefins such as ethylene, vinyl ethers, and unsaturated sulfonic acids.

[0049] The ideal degree of saponification for PVA-based resins is 85 mol% or higher, more ideally 90 mol% or higher, and even more ideally 99 mol% or higher but less than 100 mol%. The degree of polymerization for PVA-based resins is, for example, 1000 to 10000, with an ideal value of 1500 to 5000. PVA-based resins can be modified, for example, into aldehyde-modified polyvinyl formal, polyvinyl acetal, and polyvinyl butyral.

[0050] Iodine or other dichroic pigments are used as adsorbents and oriented to polyvinyl alcohol-based resin layers. Iodine is preferred as a dichroic pigment. Examples of dichroic dyes include Red BR, Red LR, Red R, Pink LB, Rubin BL, Bordeaux GS, Sky Blue LG, Lemon Yellow, Blue BR, Blue 2R, Navy RY, Green LG, Violet LB, Violet B, Black H, Black B, Black GSP, Yellow 3G, Yellow R, Orange LR, Orange 3R, Scarlet GL, Scarlet KGL, Congo Red, Brilliant Violet BK, Supra Blue G, Supra Blue GL, Supra Orange GL, Direct Sky Blue, Direct Fast Orange S, and Fast Black.

[0051] The ideal thickness of the polarizing element is 3μm to 35μm, more ideally 4μm to 30μm, and even more ideally 5μm to 25μm. By using a polarizing element thickness of 35μm or less, the effect of polyolefination of PVA-based resin on the reduction of optical properties under high temperature conditions can be easily suppressed. By using a polarizing element thickness of 3μm or more, a polarizing plate that achieves the desired optical properties can be easily obtained.

[0052] Ideally, the polarizing element of the polarizing plate in this embodiment includes both the first compound and the second compound. Since the polarizing element and the transparent protective film are bonded together by an adhesive layer formed from an adhesive containing both the first and second compounds, it is presumed that a portion of the first compound and a portion of the second compound that migrate from the adhesive layer are included in the polarizing element. With such a polarizing element, the transmittance of the polarizing plate is not easily reduced even when exposed to high temperatures due to the adhesive layer containing both the first and second compounds. Furthermore, the polarizing plate's polarization intensity is suppressed even when exposed to high temperatures due to the adhesive layer containing both the first and second compounds. When the polarization intensity of the polarizing plate decreases, light leakage (hereinafter referred to as "crossing leakage") becomes more likely when the two polarizing plates are configured in an orthogonal polarization relationship. The polarizing plate of this embodiment easily suppresses orthogonal leakage even when exposed to high temperatures because its polarization intensity is not easily reduced. It is speculated that the polyolefination of PVA-based resin is suppressed due to the synergistic effect of the first and second compounds contained in the polarizing element, thereby suppressing the decrease in transmittance of the polarizing plate exposed to high temperature environment, and also suppressing the decrease in polarization.

[0053] As a method for including the first compound and the second compound in a polarizing element, for example: a method for moving the first compound and the second compound from the adhesive layer to the polarizing element as described above; a method for manufacturing a polarizing element containing the first compound and the second compound; or a combination of these two methods. For example, when manufacturing a polarizing element, one of the first compound and the second compound is included in the polarizing element, and both the first compound and the second compound are included in the adhesive layer constituting the polarizing plate.

[0054] As a method for manufacturing polarizing elements containing the first compound and the second compound, one method is to immerse a PVA-based resin layer in a processing solvent containing the first compound and / or the second compound, or to spray, drip, or drop the processing solvent onto the PVA-based resin layer. The method of immersing the PVA-based resin layer in a processing solvent containing both the first compound and the second compound is preferred. Specific examples of the first compound and the second compound include those contained in the adhesive described later.

[0055] The step of immersing the PVA-based resin layer in a processing solvent containing the first and second compounds can be performed simultaneously with the swelling, stretching, crosslinking, and cleaning steps of the polarizing element manufacturing method described later, or it can be set separately from these steps. Ideally, the step of containing the first and second compounds in the PVA-based resin layer should be performed after staining the PVA-based resin layer with iodine, and even more ideally, it should be performed simultaneously with the crosslinking step after staining. According to this method, hue changes are small, reducing the impact on the optical properties of the polarizing element.

[0056] (Compound 1)

[0057] The first compound is a compound having a nitroxide radical or a nitrogen oxide group. From the viewpoint of having relatively stable free radicals at room temperature and in air, conventional compounds, such as N-oxygen compounds (compounds having CN(-C)-O‧ as a functional group) (O‧ represents an oxygen radical bonded to N), can be used as the first compound. Examples of N-oxygen compounds include compounds with organogroups having the following structures. Compounds having nitroxide radicals or nitrogen oxide groups can be used alone or in combination of two or more.

[0058]

[0059]

[0060] [In formula (1) above, R1 represents an oxygen free radical, R2 to R5 independently represent alkyl groups with 1 to 10 hydrogen atoms, and n represents 0 or 1.]

[0061] In the above formula (1), the left side of the dashed part represents any organic group or hydrogen atom.

[0062] Compounds having the above-mentioned organic groups include, for example, compounds represented by the following formulas (2) to (5).

[0063]

[0064]

[0065] [In formula (2) above, R1 to R5 and n have the same meaning as above, R6 represents an alkyl, acetylated or aryl group with 1 to 10 hydrogen atoms or carbon atoms, and n represents 0 or 1.]

[0066]

[0067]

[0068] [In formula (3) above, R1 to R5 and n have the same meaning as above, and R7 and R8 independently represent alkyl, acetylated or aryl groups with 1 to 10 hydrogen atoms or carbon atoms.]

[0069]

[0070]

[0071] [In formula (4) above, R1 to R5 and n have the same meaning as above, and R9 to R11 independently represent alkyl, acetyl, amino, alkoxy, hydroxyl or aryl groups with 1 to 10 hydrogen atoms or carbon atoms.]

[0072]

[0073]

[0074] [In formula (5) above, R1 to R5 and n have the same meaning as above, and R12 represents an alkyl, acetyl, amino, alkoxy, hydroxyl, or aryl group with 1 to 10 hydrogen atoms or carbon atoms.]

[0075] In formulas (1) to (5) above, from the viewpoint of ease of acquisition, R2 to R5 are preferably alkyl groups having 1 to 6 carbon atoms, and more preferably alkyl groups having 1 to 3 carbon atoms. In formula (2) above, from the viewpoint of ease of acquisition, R6 is preferably a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and more preferably a hydrogen atom. In formula (3) above, from the viewpoint of ease of acquisition, R7 and R8 are independently preferably hydrogen atoms or alkyl groups having 1 to 10 carbon atoms, and more preferably hydrogen atoms. In formula (4) above, from the viewpoint of ease of acquisition, R9 to R11 are independently preferably hydrogen atoms or alkyl groups having 1 to 10 carbon atoms. In formula (5) above, from the viewpoint of ease of acquisition, R12 is preferably a hydroxyl, amino, or alkoxy group. In formulas (1) to (5) above, from the viewpoint of ease of acquisition, n is preferably 1.

[0076] Examples of N-oxygen compounds include those disclosed in Japanese Patent Publication No. 2003-64022, Japanese Patent Publication No. 11-222462, Japanese Patent Publication No. 2002-284737, and International Patent Publication No. 2016 / 047655. Among these, 4-hydroxy-2,2,6,6-tetramethyl-1-oxypyridine is preferred.

[0077] As the first compound, it also includes, for example, the following compounds.

[0078]

[0079]

[0080] [In formula (6), R represents an alkyl, acetylated, or aryl group with 1 to 10 hydrogen atoms.]

[0081]

[0082]

[0083]

[0084]

[0085] From the viewpoint of effectively capturing free radicals that occur during the polyolefination reaction, the molecular weight of the first compound is ideally below 1000, more ideally below 500, and even more ideally below 300. There is no particular limitation on the lower limit of the molecular weight; it can be, for example, 80.

[0086] (Compound 2)

[0087] The second compound is a cyclodextrin. Cyclodextrins are non-reducing cyclic oligosaccharides composed of glucose linked by α-1,4 bonds. The more glucose molecules that make up a cyclodextrin, the larger the inner diameter of the voids within the molecule. Ideally, the cyclodextrin used as the second compound should contain six or more glucose molecules, for example, α, β, γ, and δ-cyclodextrins containing 6, 7, 8, or 9 glucose molecules. Among α, β, γ, and δ-cyclodextrins, branched cyclodextrins include those with branched sugar chains containing oligosaccharides such as glucose and maltose. Further, the cyclodextrins or branched cyclodextrins mentioned above include cyclodextrin derivatives bonded with alkyl groups such as methyl groups, hydroxyethyl groups, 2-hydroxypropyl groups, 2,3-dihydroxypropyl groups, 2-hydroxybutyl groups, etc. Cyclodextrins can be used alone or in combination of two or more.

[0088] (Feature(a))

[0089] When the polarizing plate has the aforementioned 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 80% relative humidity at 20°C. The moisture content of the polarizing element can be above the equilibrium moisture content of 45% or 50% relative humidity at 20°C and below the equilibrium moisture content of 80% or 70% relative humidity at 20°C. When the moisture content of the polarizing element is below the equilibrium moisture content of 30% relative humidity at 20°C, the polarizing element has low processability and becomes prone to breakage. When the moisture content of the polarizing element is high enough to exceed the equilibrium moisture content of 45% or 50% relative humidity at 20°C, it is presumably easy to promote the polyolefination of PVA-based resins. However, since the polarizing plate of this embodiment has an adhesive layer containing the first compound and the second compound, the polyolefination of PVA-based resins can be suppressed.

[0090] One method to confirm that the moisture content of the polarizing element is within the range of equilibrium moisture content above 30% relative humidity at 20°C and below 80% relative humidity at 20°C is as follows: For example, storing the element in an environment adjusted to the above temperature and relative humidity range, and considering that the quality does not change over a certain period of time, is considered to have reached equilibrium with the environment; or calculating the equilibrium moisture content of the polarizing element in an environment adjusted to the above temperature and relative humidity range in advance, and confirming the moisture content by comparing the moisture content of the polarizing element with the pre-calculated equilibrium moisture content.

[0091] 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 80% or lower at 20°C. For example, a method of storing the polarizing element for 10 minutes or more but less than 3 hours in an environment adjusted to the above temperature and relative humidity range, or a method of heat treatment at a temperature of 30°C or more but less than 90°C.

[0092] As another preferred method for manufacturing polarizing elements with a moisture content within the aforementioned range, for example, a method of storing a polarizing plate or a polarizing element made of a polarizing element 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 a temperature of 30°C to 90°C. Alternatively, when manufacturing an image display device using interlayer filling, a polarizing plate is deposited on the image display panel of the image display unit and stored in an environment adjusted to the aforementioned temperature and relative humidity range for 10 minutes to 3 hours, or heated at a temperature of 30°C to 90°C, and then bonded to a transparent component such as a front panel.

[0093] (Feature (b))

[0094] When the polarizing plate has the above-described characteristic (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 80% relative humidity at 20°C. The moisture content of the polarizing plate can be above the equilibrium moisture content of 45% or 50% relative humidity at 20°C and below the equilibrium moisture content of 80% or 70% relative humidity at 20°C. When the moisture content of the polarizing plate is below the equilibrium moisture content of 30% relative humidity at 20°C, the polarizing plate has low processability and becomes prone to cracking. When the moisture content of the polarizing plate is high enough to exceed the equilibrium moisture content of 45% or 50% relative humidity at 20°C, it is presumably easy to promote the polyolefination of PVA-based resins. However, since the polarizing plate of this embodiment has an adhesive layer containing the first compound and the second compound, the polyolefination of PVA-based resins can be suppressed.

[0095] One method to confirm that the moisture content of the polarizing plate is within the range of equilibrium moisture content above 30% relative humidity at 20°C and below 80% relative humidity at 20°C is as follows: For example, storing the plate in an environment adjusted to the above temperature and relative humidity range, and considering that the quality does not change over a certain period of time, is considered to have reached equilibrium with the environment; or calculating the equilibrium moisture content of the polarizing plate in an environment adjusted to the above temperature and relative humidity range in advance, and confirming the moisture content by comparing the moisture content of the polarizing plate with the pre-calculated equilibrium moisture content.

[0096] 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 80% or lower at 20°C and relative humidity. For example, a method of storing the polarizing plate for 10 minutes to 3 hours in an environment adjusted to the above-mentioned temperature and relative humidity range, or a method of heat treatment at a temperature of 30°C to 90°C. Alternatively, when manufacturing an image display device using interlayer filling, the polarizing plate is deposited on the image display panel of the image display unit and stored for 10 minutes to 3 hours in an environment adjusted to the above-mentioned temperature and relative humidity range, or heated at a temperature of 30°C to 90°C, and then bonded to a transparent component such as a front panel.

[0097] (Manufacturing method of polarizing element)

[0098] There are no particular limitations on the manufacturing method of polarizing elements. Typical methods include: a method of manufacturing by feeding out a pre-wound PVA-based resin film and performing stretching, dyeing, cross-linking, etc. (hereinafter referred to as "manufacturing method 1"); and a method including the step of coating a coating liquid containing polyvinyl alcohol resin onto a substrate film to form a coating layer and stretching the resulting laminate (hereinafter referred to as "manufacturing method 2").

[0099] Manufacturing method 1 may include the steps of uniaxially stretching a PVA-based resin film, dyeing the PVA-based resin film with a dichroic pigment such as iodine to adsorb the dichroic pigment, treating the PVA-based resin film adsorbed with the dichroic pigment with a boric acid aqueous solution, and washing with water after treatment with the boric acid aqueous solution.

[0100] The swelling step is a process in which a PVA-based resin film is immersed in a swelling bath. Through the swelling step, not only can dirt and adhesives on the surface of the PVA-based resin film be removed, but uneven dyeing can also be suppressed by swelling the PVA-based resin film. The swelling bath typically uses a water-based medium, such as water, distilled water, or pure water. Surfactants, alcohols, etc., can be appropriately added to the swelling bath using common 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 ideally below 1.5% by mass, more ideally below 1.0% by mass, and even more ideally below 0.5% by mass.

[0101] The ideal temperature for the swelling bath is between 10°C and 60°C, more ideally between 15°C and 45°C, and even more ideally between 18°C ​​and 30°C. The immersion time in the swelling bath is affected by the temperature of the bath, as the swelling degree of the PVA resin film is influenced by the temperature of the swelling bath, and cannot be generalized. Ideally, it should be between 5 and 300 seconds, more ideally between 10 and 200 seconds, and even more ideally between 20 and 100 seconds. The swelling step can be performed only once or multiple times as needed.

[0102] The dyeing step involves immersing a PVA-based resin film in a dyeing bath, which allows the dichroic pigment to be adsorbed and oriented onto the PVA-based resin film. When the dichroic pigment is iodine, an iodine solution is ideal for the dyeing bath. The iodine solution is typically an aqueous iodine solution containing both iodine and iodides as dissolving agents. 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 polarizing element.

[0103] The ideal concentration of iodine in the dyeing bath (iodine solution) is between 0.01% and 1% by mass, and even more ideally between 0.02% and 0.5% by mass. The ideal concentration of iodide in the dyeing bath is between 0.01% and 10% by mass, even more ideally between 0.05% and 5% by mass, and even more ideally between 0.1% and 3% by mass.

[0104] The ideal temperature for the dyeing bath is between 10°C and 50°C, more ideally between 15°C and 45°C, and even more ideally between 18°C ​​and 30°C. The immersion time in the dyeing bath is not fixed due to the influence of the bath temperature on the degree of dyeing of the PVA resin film; ideally, it is between 10 seconds and 300 seconds, and even more ideally between 20 seconds and 240 seconds. The dyeing process can be performed once or multiple times as needed.

[0105] The crosslinking step involves immersing the dyed PVA-based resin film in a treatment tank (crosslinking tank) containing a boron compound. The boron compound crosslinks the PVA-based resin film, allowing iodine or dye molecules to be adsorbed into the crosslinked structure. Examples of boron compounds include boric acid, borates, and borax. The crosslinking tank is typically an aqueous solution, such as a mixture of an organic solvent miscible with water and water. From the viewpoint of controlling the potassium content in the polarizing element, a crosslinking tank containing potassium iodide is ideal.

[0106] In the crosslinking tank, the ideal concentration of boron compounds is 1% to 15% by mass, more ideally 1.5% to 10% by mass, and even more ideally 2% to 5% by mass. When potassium iodide is used in the crosslinking tank, the ideal concentration of potassium iodide is 1% to 15% by mass, more ideally 1.5% to 10% by mass, and even more ideally 2% to 5% by mass.

[0107] The ideal temperature for the crosslinking bath is between 20°C and 70°C, and even more ideally between 30°C and 60°C. The immersion time in the crosslinking bath is not fixed because the degree of crosslinking of the PVA resin film is affected by the temperature of the bath; ideally, it is between 5 and 300 seconds, and even more ideally between 10 and 200 seconds. The crosslinking step can be performed only once or multiple times as needed.

[0108] The stretching step is a process of stretching a PVA-based resin film by a predetermined ratio in at least one direction. Generally, the PVA-based resin film is uniaxially stretched in 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 step can be performed only once or multiple times as needed. The stretching step can be performed at any stage in the manufacturing of polarizing elements.

[0109] The processing tank (extension tank) for wet stretching can typically use water, or a solvent such as an organic solvent or a mixture of water and water that is miscible with water. From the viewpoint of controlling the potassium content in the polarizing element, it is ideal for the extension tank to contain potassium iodide. When potassium iodide is used in the extension tank, the concentration of potassium iodide in the extension tank is ideally 1% to 15% by mass, more ideally 2% to 10% by mass, and even more ideally 3% to 6% by mass. From the viewpoint of suppressing film rupture during stretching, boron compounds can be included in the processing tank (extension tank). When boron compounds are included, the concentration of boron compounds in the extension tank is ideally 1% to 15% by mass, more ideally 1.5% to 10% by mass, and even more ideally 2% to 5% by mass.

[0110] The ideal temperature for the stretching bath is between 25°C and 80°C, more ideally between 40°C and 75°C, and even more ideally between 50°C and 70°C. The immersion time in the stretching bath is affected by the temperature of the bath and cannot be generalized; ideally, it is between 10 seconds and 800 seconds, and even more ideally between 30 seconds and 500 seconds. The wet stretching process can be performed together with one or more of the following steps: swelling, dyeing, crosslinking, and cleaning.

[0111] Dry stretching methods include, for example, roller stretching, heated roller stretching, and compression stretching. Furthermore, in the case of dry stretching methods, the stretching step can be performed together with the drying step.

[0112] The total elongation ratio (cumulative elongation ratio) applied to PVA resin films can be appropriately set according to the purpose. Ideally, it is more than 2 times but less than 7 times; more ideally, it is more than 3 times but less than 6.8 times; and even more ideally, it is more than 3.5 times but less than 6.5 times.

[0113] The cleaning step involves immersing the PVA-based resin film in a cleaning tank to remove impurities remaining on the surface of the PVA-based resin film. The cleaning tank typically uses a water-based medium, such as water, distilled water, or pure water. Furthermore, from the viewpoint of controlling the potassium content in the polarizing element, it is ideal to use potassium iodide in the cleaning tank. In this case, the ideal concentration of potassium iodide in the cleaning tank is 1% to 10% by mass, more ideally 1.5% to 4% by mass, and even more ideally 1.8% to 3.8% by mass.

[0114] The ideal temperature for the cleaning tank is between 5°C and 50°C, more ideally between 10°C and 40°C, and even more ideally between 15°C and 30°C. The immersion time in the cleaning tank varies depending on the temperature, as the cleanliness of the PVA resin film is affected by the tank temperature. Ideally, it should be between 1 second and 100 seconds, more ideally between 2 seconds and 50 seconds, and even more ideally between 3 seconds and 20 seconds. The cleaning process can be performed once or multiple times as needed.

[0115] The drying step involves drying the PVA-based resin film that has been cleaned in the cleaning step to obtain the polarizing element. Drying can be carried out by any suitable method, such as natural drying, air drying, or heat drying.

[0116] Manufacturing method 2 may include the following steps: coating a coating solution containing a PVA-based resin onto a substrate film; uniaxially stretching the resulting laminated film; dyeing the coating layer of the uniaxially stretched laminated film with a dichroic dye to adsorb the dichroic dye; treating the laminated film with the adsorbed dichroic dye with a boric acid aqueous solution; and washing with water after treatment with the boric acid aqueous solution. A transparent protective film used as a polarizing plate may also be used as the substrate film for forming the polarizing element. The substrate film can be peeled off from the polarizing element if necessary.

[0117] <Transparent protective film>

[0118] A transparent protective film is bonded to at least one side of the polarizing element through an adhesive layer. This transparent protective film can be bonded to one or both sides of the polarizing element, but bonding to both sides is preferred.

[0119] Transparent protective films can simultaneously possess other optical functions and can also have a multilayered structure. From an optical property point of view, the ideal thickness for a transparent protective film is thin, but if it is too thin, its strength is low and its processability deteriorates. A suitable film thickness is 5 μm to 100 μm, more ideal is 10 μm to 80 μm, and even more ideal is 15 μm to 70 μm.

[0120] Transparent protective films can be made of cellulose lacquers, polycarbonate resins, cyclic olefin resins such as norbornene, methacrylic acid polymers, or polyester resins such as diethyl terephthalate. When using aqueous adhesives such as PVA adhesives to bond the transparent protective film to both sides of the polarizing element, from a moisture permeability perspective, a transparent protective film on at least one side is ideally either a cellulose lacquer or a methacrylic acid polymer film, with a cellulose lacquer being particularly preferred.

[0121] At least one of the transparent protective films in the polarizing plate may have a phase difference function for purposes such as viewing angle compensation. In this case, the film constituting the transparent protective film may have a phase difference function itself, or the transparent protective film may have a layer without a phase difference function and a phase difference layer (a layer with a phase difference function). In the case where the transparent protective film has a phase difference layer, it may be a laminate of a layer without a phase difference function and a phase difference layer, which can be bonded together using an adhesive or bonding agent.

[0122] <Adhesive layer>

[0123] The adhesive used to form the adhesive layer for bonding the transparent protective film to the polarizing element is an adhesive containing both compound 1 and compound 2. Water-based adhesives, solvent-based adhesives, and active energy line curing adhesives can be used, but water-based adhesives are preferred, especially those containing PVA-based resins. By using an adhesive containing both compound 1 and compound 2, the decrease in transmittance of the polarizing plate under high-temperature conditions can be suppressed in order to form the adhesive layer.

[0124] The thickness of the adhesive coating can be set to any value. For example, it can be set to obtain an adhesive layer with a desired thickness after curing or heating (drying). The ideal thickness of the adhesive layer is 0.01 μm to 7 μm, more ideally 0.01 μm to 5 μm, even more ideally 0.01 μm to 2 μm, and most ideally 0.01 μm to 1 μm.

[0125] When a polarizing plate is manufactured using a polarizing element that does not contain the first compound and the second compound, the content of the first compound and the second compound contained in the adhesive is preferably within the range described below. When a polarizing plate is manufactured using a polarizing element that contains the first compound and the second compound, the content of the first compound and the second compound contained in the adhesive can be appropriately changed from the range described below, depending on the first compound and the second compound contained in the polarizing element. Specific examples of the first compound and the second compound are as described above.

[0126] When the adhesive contains PVA-based resin (e.g., an aqueous adhesive containing PVA-based resin), the content of the first compound is ideally between 0.1 and 400 parts by weight, more ideally between 1 and 200 parts by weight, and even more ideally between 3 and 100 parts by weight, relative to 100 parts by weight of PVA-based resin. When the content is less than 0.1 parts by weight, the inhibition effect on the polyolefination of PVA-based resin at high temperatures may be insufficient. On the other hand, when the content exceeds 400 parts by weight, the first compound may precipitate after the polarizing plate is manufactured.

[0127] When the adhesive contains PVA-based resin (e.g., a water-based adhesive containing PVA-based resin), the content of the second compound is ideally between 1 and 50 parts by mass, more ideally between 1.5 and 40 parts by mass, and even more ideally between 2 and 35 parts by mass, relative to 100 parts by mass of PVA-based resin. If the content is less than 1 part by mass, the inhibition effect on the polyolefination of PVA-based resin at high temperatures may be insufficient. On the other hand, if the content exceeds 50 parts by mass, the second compound may precipitate after the polarizing plate is manufactured.

[0128] The polarizing element is composed of a transparent protective film bonded to both sides of the polarizing element through an adhesive layer. In the adhesive layer on both sides of the polarizing element, only one side of the adhesive layer may contain both the first compound and the second compound, but it is more ideal for both sides of the adhesive layer to contain both the first compound and the second compound.

[0129] To address 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. Even in this configuration, a transparent protective film is laminated between layers of adhesive containing a first compound and a second compound. As a method for manufacturing such a polarizing plate with a transparent protective film on only one side of the polarizing element, a method is considered whereby a polarizing plate with a transparent protective film laminated on both sides between adhesive layers is first fabricated, and then one side of the transparent protective film is peeled off. While it is possible for only one side of the adhesive layer to contain both the first and second compounds, it is more ideal for both sides of the adhesive layer to contain both compounds. In the case where only one side of the adhesive layer contains both compounds, it is more ideal for the adhesive layer on the side where the film is not peeled off to contain both compounds.

[0130] (Water-based adhesive)

[0131] Any suitable water-based adhesive can be used, but water-based adhesives containing PVA-based resins (PVA-based adhesives) are preferred. From an adhesion point of view, the average degree of polymerization of the PVA-based resin contained in the water-based adhesive is ideally between 100 and 5500, and more ideally between 1000 and 4500. The average degree of saponification from the adhesion point is ideally between 85 mol% and 100 mol%, and more ideally between 90 mol% and 100 mol%.

[0132] As a PVA-based resin included in water-based adhesives, it is preferable to have an acetyl group-containing PVA-based resin (hereinafter referred to as "acetyl-containing PVA-based resin"). This is because PVA-based resin layers have good adhesion and durability to protective films. Acetyl-containing PVA-based resins can be obtained, for example, by reacting PVA-based resins with diketene using any method. A representative example of the degree of acetyl-containing PVA-based resin modification is 0.1 mol% or more, and more preferably 0.1 mol% or more and 20 mol% or less. The resin concentration in the water-based adhesive is preferably 0.1% by mass or more and 15% by mass or less, and more preferably 0.5% by mass or more and 10% by mass or less.

[0133] Water-based adhesives may contain crosslinking agents. Commonly known crosslinking agents can be used. Examples of crosslinking agents include water-soluble epoxy compounds, dialdehydes, and isocyanates.

[0134] When the PVA resin is a PVA resin containing acetyl groups, the ideal crosslinking agent is any one of glyoxal, glyoxylate, or hydroxymethyl melamine, with glyoxal and glyoxylate being the most ideal, and glyoxal being particularly ideal.

[0135] Water-based adhesives can contain organic solvents. From the viewpoint of miscibility with water, alcohols are ideal organic solvents, with methanol or ethanol being more ideal. The ideal concentration of methanol in water-based adhesives is 10% by mass to 70% by mass, more ideally 15% by mass to 60% by mass, and even more ideally 20% by mass to 60% by mass. A methanol concentration of 10% by mass or more makes it easier to suppress the polyolefination of PVA-based resins under high-temperature conditions. Furthermore, a methanol content of 70% by mass or less helps suppress color degradation. For example, as a component formulated in a water-based adhesive, a component with low solubility in water but sufficient solubility in alcohol can be used. In this case, dissolving the component in alcohol, preparing an alcohol solution of the component, and then adding this alcohol solution to an aqueous solution of PVA-based resin to prepare the adhesive is also a preferred approach.

[0136] (Active Energy Line Curing Adhesive)

[0137] Photopolymerizable adhesives are adhesives that cure by irradiation with active energy lines such as ultraviolet light. Examples include adhesives containing polymerizable compounds and photopolymerizable initiators, adhesives containing photoreactive resins, and adhesive resins containing photoreactive crosslinking agents. 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. Photopolymerizable initiators include compounds containing substances that generate reactive species such as neutral free radicals, anionic free radicals, and cationic free radicals upon irradiation with active energy lines such as ultraviolet light.

[0138] [Manufacturing method of polarizing plate]

[0139] The method for manufacturing the polarizing plate of this embodiment includes a lamination step of stacking polarizing elements and a transparent protective film. The method for manufacturing the polarizing plate may include a moisture content adjustment step, and there is no restriction on the order of the lamination step and the moisture content adjustment step, or the lamination step and the moisture content adjustment step may be performed simultaneously.

[0140] In the lamination step, the polarizing element and the transparent protective film are laminated with the aforementioned adhesive layer in between. In the lamination step, an adhesive layer containing a first compound and a second compound is used to bond the polarizing element and the transparent protective film. The adhesive present between the polarizing element and the transparent protective film becomes an adhesive layer through a step such as drying. The lamination step can also be a step of bonding the polarizing element and the transparent protective film using an adhesive that does not contain the first and second compounds. In this case, during the formation of the adhesive layer, a portion of the first compound and a portion of the second compound contained in the adhesive can be moved to the polarizing element, etc.

[0141] In the step of adjusting the moisture content, when manufacturing a polarizing plate with characteristic (a), the moisture content of the polarizing element is adjusted to be above the equilibrium moisture content at 20°C and 30% relative humidity, and below the equilibrium moisture content at 20°C and 80% relative humidity. The moisture content of the polarizing element can be adjusted by the method described above. In the step of adjusting the moisture content, when manufacturing a polarizing plate with characteristic (b), the moisture content of the polarizing plate is adjusted to be above the equilibrium moisture content at 20°C and 30% relative humidity, and below the equilibrium moisture content at 20°C and 80% relative humidity. The moisture content of the polarizing plate can be adjusted by the method described above.

[0142] [Composition of an image display device]

[0143] The polarizing plate of this embodiment can be used in various image display devices such as liquid crystal display devices and organic EL display devices. Regarding image display devices, when the polarizing plate is configured such that its two sides are in contact with a solid layer (such as an adhesive layer) through interlayer filling, the transmittance tends to decrease at high temperatures. In image display devices using the polarizing plate of this embodiment, even with an interlayer filling configuration, the decrease in transmittance of the polarizing plate at high temperatures can be suppressed.

[0144] As a solid layer, such as an adhesive layer or bonding agent layer. When the solid layer is an adhesive layer, an adhesive layer formed by a UV-curable adhesive is more ideal.

[0145] As an image display device, for example, it comprises an image display unit, a first adhesive layer laminated on the recognition side surface of the image display unit, and a polarizing plate laminated on the recognition side surface of the first adhesive layer. Such an image display device may further include a second adhesive layer laminated on the recognition side surface of the polarizing plate and a transparent member laminated 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 structure in which a transparent member is disposed on the recognition side of the image display device, the polarizing plate and the image display unit are bonded together by the first adhesive layer, and the polarizing plate and the transparent member are bonded together by the second adhesive layer.

[0146] The polarizing plate and the image display unit are not limited to using a first adhesive layer; they can be bonded using an adhesive layer formed by an adhesive. The polarizing plate and the transparent component are not limited to using a second adhesive layer; they can be bonded using an adhesive layer formed by an adhesive. The adhesive can be one described above, and may contain both the first compound and the second compound.

[0147] <Image Display Unit>

[0148] As an image display unit, such as a liquid crystal cell (LCD) or an organic EL cell, the liquid crystal cell can be any of the following: 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, in the image display device (liquid crystal display device), a polarizing plate is also disposed on the opposite side of the image display unit (liquid crystal cell), and a light source is also disposed thereon. It is ideal for the polarizing plate on the light source side to be bonded to the liquid crystal cell with a suitable adhesive layer in between. As for the driving method of the liquid crystal cell, any mode such as VA (Vertical Alignment), IPS (In-Plane Switching), TN (Twisted Nematic), STN (Super-Twisted Nematic), or bent alignment (π-type) can be used.

[0149] As an organic EL cell, it is suitable for use in forming a light emitter (organic electroluminescent emitter) by sequentially stacking a transparent electrode, an organic light-emitting layer, and a metal electrode on a transparent substrate. The organic light-emitting layer is a stack of various organic thin films, such as: a stack of a hole injection layer composed of a triphenylamine derivative and the like and a light-emitting layer composed of a fluorescent organic solid such as anthracene; a stack of these light-emitting layers and an electron injection layer composed of a perylene derivative and the like; or a stack of various layers such as a hole injection layer, a light-emitting layer, and an electron injection layer.

[0150] < Bonding of image display unit and polarizing plate>

[0151] The bonding of the image display unit and the polarizing plate is suitable for using a first adhesive layer. From an operational point of view, bonding the polarizing plate with the first adhesive layer attached to one side of the polarizing plate to the image display unit is more ideal. The first adhesive layer can be attached to the polarizing plate in a suitable manner. Examples include: dissolving or dispersing the matrix polymer or its components in a solvent composed of a simple substance or mixture of suitable solvents such as toluene or ethyl acetate to prepare an adhesive solution of approximately 10% to 40% by mass, and directly attaching it to the polarizing plate using a suitable spreading method such as casting or coating; or forming the first adhesive layer on a release film and transferring it to the polarizing plate.

[0152] <First adhesive layer, second adhesive layer>

[0153] The first adhesive layer and the second adhesive layer (hereinafter, either or both, referred to as "adhesive layers") may independently consist of one or more layers, with a single layer being preferred. The adhesive layer may be composed of an adhesive composition primarily composed of (meth)acrylic resins, rubber resins, ethyl carbamate resins, ester resins, polysiloxane resins, or polyvinyl ether resins. Among these, an adhesive composition using (meth)acrylic resins as the base polymer, which possess excellent transparency, weather resistance, and heat resistance, is particularly suitable. The adhesive composition may be of the active energy linear curing type or the thermosetting type.

[0154] (Meth)acrylic resins used as adhesive components are polymers or copolymers of one or more (meth)acrylate monomers, such as butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. In the matrix polymer, copolymerization with polar monomers is preferred. Polar monomers include, for example, (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 have carboxyl, hydroxyl, amide, or epoxy groups.

[0155] The adhesive composition may contain only the aforementioned matrix polymer, but usually also includes a crosslinking agent. Examples of crosslinking agents include metal ions with a valence of divalent or higher that form carboxylic acid metal salts with carboxyl groups, polyamine compounds that form amide bonds with carboxyl groups, polyepoxide compounds or polyols that form ester bonds with carboxyl groups, and polyisocyanate compounds that form amide bonds with carboxyl groups. Polyisocyanate compounds are preferred.

[0156] Active energy line curing adhesives possess the property of curing upon exposure to active energy lines such as ultraviolet light or electron beams. Before irradiation, they exhibit adhesiveness and can bond with substrates such as films. Curing occurs upon exposure to the active energy lines, and they offer adjustable adhesive strength. Ultraviolet curing is preferred for active energy line curing adhesives. In addition to matrix polymers and crosslinking agents, active energy line curing adhesives may contain polymerizable compounds. Depending on requirements, they may also contain photopolymerization initiators, photosensitizers, etc.

[0157] The adhesive composition may include microparticles, beads (resin beads, glass beads, etc.) that impart light scattering properties, glass fibers, resins other than matrix polymers, adhesive agents, fillers (metal powders, other inorganic powders, etc.), antioxidants, ultraviolet absorbers, dyes, pigments, colorants, defoamers, corrosion inhibitors, photopolymerization initiators, and other additives.

[0158] The adhesive layer can be formed by applying a diluted organic solvent solution of the adhesive composition to the surface of a substrate film, image display unit, or polarizing plate, and then drying it. The substrate film is generally a thermoplastic resin film; a typical example is a release film that has undergone a release treatment. For example, a release film is formed on the surface of a resin film such as polyethylene terephthalate, polybutylene terephthalate, polycarbonate, or polyarylate where the adhesive layer is formed, and then undergoes a release treatment such as polysiloxane treatment.

[0159] An adhesive composition can be directly coated onto the release-treated surface of the release film to form an adhesive layer, and this adhesive layer with the release film attached can be deposited onto the surface of the polarizing plate. Alternatively, an adhesive composition can be directly coated onto the surface of the polarizing plate to form an adhesive layer, and a release film can be deposited on the outer surface of the adhesive layer.

[0160] When an adhesive layer is applied to the surface of a polarizing plate, it is ideal 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, with corona treatment being even more ideal.

[0161] Furthermore, an adhesive layer is formed by coating an adhesive composition onto the second release film, and a release film is then deposited on the formed adhesive layer to prepare an adhesive sheet. The adhesive layer of the release film attached to the second release film, after being peeled off from the adhesive sheet, can be deposited onto a polarizing plate. The second release film is one that has a weaker adhesion to the adhesive layer than the release film and is easier to peel off.

[0162] There is no particular limitation on the thickness of the adhesive layer. For example, it is ideal to be between 1 μm and 100 μm, even more ideal to be between 3 μm and 50 μm, and it can be above 20 μm.

[0163] <Transparent Components>

[0164] Transparent components, such as transparent panels (front panels, window layers) and touch panels, can be used on the recognition side of an image display device. Transparent panels with suitable mechanical strength and thickness can be used. Examples of such transparent panels include transparent resin sheets made of polyimide resin, acrylic resin, or polycarbonate resin, or glass sheets. Functional layers such as anti-reflective layers can also be laminated on the recognition side of the transparent panel. Furthermore, when the transparent panel is a transparent resin sheet, a hard coating to improve physical strength or a low-permeability layer to reduce moisture permeability can be laminated. For touch panels, various types of touch panels, such as resistive film, capacitive, optical, and ultrasonic touch panels, as well as glass sheets and transparent resin sheets with touch sensing capabilities, can be used. When using a capacitive touch panel as the transparent component, it is ideal to have a transparent panel composed of glass or a transparent resin sheet positioned closer to the recognition side than the touch panel itself.

[0165] < Bonding of polarizing plate to transparent component>

[0166] When bonding the polarizing plate to the transparent component, an adhesive or an active energy line curing adhesive is suitable. When using an adhesive, it can be applied in a suitable manner. A specific method for applying the adhesive is, for example, the method used in the aforementioned bonding of the image display unit to the polarizing plate.

[0167] In cases where active energy line curing adhesives are used, to prevent the adhesive solution from spreading before curing, a method is suitable that involves setting up a dam around the perimeter of the image display panel, placing a transparent component on the dam, and then injecting the adhesive solution. After injecting the adhesive solution, alignment and degassing are performed as needed, followed by irradiation with active energy lines for curing.

[0168] [Example]

[0169] The present invention will now be described in detail with reference to the embodiments. The materials, reagents, quantities, proportions, and operations described in the following embodiments may be appropriately modified without departing from the spirit of the invention. Therefore, the present invention is not limited to the following embodiments.

[0170] <Fabrication of Polarizing Element A>

[0171] A 40 μm thick PVA-based resin film, composed of PVA-based resin with an average degree of polymerization of approximately 2400 and a saponification degree of 99.9 moles or higher, was subjected to approximately 5 times uniaxial stretching in a dry process. While under tension, it was immersed in pure water at 60°C for 1 minute, followed by immersion in an aqueous solution at 28°C for 60 seconds with a weight ratio of iodine / potassium iodide / water of 0.05 / 5 / 100. Then, it was immersed in an aqueous solution at 72°C with a weight ratio of potassium iodide / boric acid / water of 8.5 / 8.5 / 100 for 30 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 A with iodine adsorbed and aligned to the PVA-based resin layer. The thickness of polarizing element A was measured using a Nikon MH-15M digital micrometer.

[0172] <Preparation of Adhesives 1 to 5>

[0173] (Preparation of PVA solution A for adhesive)

[0174] 50g of a modified PVA resin containing acetyl groups (GOHSENEX Z-410 manufactured by Mitsubishi Chemical Corporation) was dissolved in 950g of pure water. The solution was heated at 90°C for 2 hours and then cooled to room temperature to obtain PVA solution A for adhesives.

[0175] (Preparation of adhesives 1 to 5)

[0176] The concentration of the PVA-based resin was set to 3.0% by mass, and the contents of Compound 1 and Compound 2 were as shown in Table 1. PVA solution A, Compound 1, Compound 2 and pure water were prepared to form adhesives 1 to 5. As Compound 1, 4-hydroxy-2,2,6,6-tetramethyl-1-oxypiperidine (hereinafter also referred to as "TEMPOL") was used.

[0177] [Table 1]

[0178] <Preparation of Transparent Protective Film A>

[0179] A commercially available cellulose lacquer membrane (Fuji Film Co., Ltd. "TD40", 40μm thick) was immersed in a 1.5 mole / 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 mole / L sulfuric acid aqueous solution at 25°C for 30 seconds, and then rinsed in running water for 30 seconds to neutralize the membrane. After removing moisture by repeatedly dehydrating three times with an air knife, it was dried in an oven at 70°C for 15 seconds to produce a saponified cellulose lacquer membrane, which serves as transparent protective film A.

[0180] <Fabrication of Polarizing Plate 1>

[0181] Using a roller laminator and adhesive 1, a transparent protective film A is laminated onto both sides of the polarizing element A. The film is then dried at 80°C for 5 minutes to form an adhesive layer, resulting in polarizing plate 1. The amount of adhesive 1 used is adjusted so that the thickness of the dried adhesive layer is 50 nm on both sides.

[0182] <Fabrication of Polarizing Plates 2 to 5>

[0183] Except for changing adhesive 1 to adhesive 2 to 5, polarizing plates 2 to 5 are obtained in the same manner as the polarizing plate 1 described above.

[0184] (Adjustment of moisture content in polarizing plate (polarizing element))

[0185] The polarizing plates 1 to 5 obtained above were stored at 20°C and 40% relative humidity for 72 hours. The moisture content was measured using the Karl Fischer method after 66, 69, and 72 hours from the start of storage under these conditions. Since the measured moisture content values ​​did not change, the moisture content of polarizing plates 1 to 5 can be considered to be the same as the equilibrium moisture content of the 72-hour storage environment. When the moisture content of a polarizing plate reaches equilibrium under a certain storage environment, the moisture content of the polarizing element within the polarizing plate can also be considered to be in equilibrium with that storage environment. Furthermore, when the moisture content of the polarizing element within a polarizing plate reaches equilibrium under a certain storage environment, the moisture content of the polarizing plate itself can also be considered to be in equilibrium with that storage environment.

[0186] <Evaluation of High Temperature Durability>

[0187] (Preparation of the evaluation sample)

[0188] After adjusting the moisture content, an adhesive layer was formed on both sides of polarizing plates 1 to 5 using an acrylic adhesive (Lintec, product number: #7). Polarizing plates 1 to 5 were cut to 50mm x 100mm dimensions with their absorption axes parallel to their long sides. Alkali-free glass (Corning "EAGLE XG") was then bonded to the surface of each adhesive layer to create evaluation samples.

[0189] (Evaluation of changes in transmittance during high-temperature durability testing (105℃))

[0190] After autoclaving at 50°C and 5 kgf / cm² (490.3 kPa) for 1 hour, the evaluation samples were placed in an environment of 23°C and 55% relative humidity for 24 hours. The brightness of the evaluation samples at this time was measured using a spectroradiometer (Topcon Techno House SR-UL1R). The samples were placed on the illumination surface of a backlight module with a brightness of 5000 cd / cm², and the measurement was taken at a 2-degree angle and a 350 mm distance. The brightness measured under these conditions is designated as "Brightness L0". The evaluation samples were then stored at 105°C for 72 to 240 hours, with measurements taken every 24 hours in the same order. The measured brightness is designated as "Brightness L1" after the high-temperature durability test.

[0191] Using the measured luminance L0 and luminance L1, calculate the change in transmittance according to the following formula.

[0192] Change in transmittance [%] = 100 - (brightness L1 / brightness L0) × 100

[0193] Based on the storage time required under the aforementioned heating environment to obtain luminance L1 with a change in transmittance of 5% or more, the high-temperature durability was evaluated using the following evaluation criteria. The results are shown in Table 2.

[0194] (Evaluation Criteria)

[0195] The required storage time of the evaluation sample under heating environment when the change in transmittance of the evaluation sample is greater than 5% is:

[0196] Those who have worked more than 240 hours: A

[0197] For those exceeding 120 to 240 hours: B

[0198] For those exceeding 72 hours to 120 hours: C

[0199] Until 72 hours :D

[0200] [Table 2]

Claims

1. A polarizing plate comprising a polarizing element with dichroic pigment adsorbed and aligned to a polyvinyl alcohol-based resin layer, and a transparent protective film laminated on at least one side of the aforementioned polarizing element; wherein, The aforementioned polarizing element and the aforementioned transparent protective film are bonded together by an adhesive layer formed by an adhesive containing the first compound and the second compound; the aforementioned adhesive is an aqueous adhesive; the aforementioned first compound is a compound having nitric oxide radicals or nitric oxide radicals; the aforementioned second compound is at least one selected from the group consisting of α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin.

2. The polarizing plate as described in claim 1, wherein, The first compound mentioned above is an N-oxygen compound.

3. The polarizing plate as described in claim 1 or 2, wherein, The second compound mentioned above is α-cyclodextrin.

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

5. The polarizing plate as described in claim 4, wherein, In the aforementioned adhesive, the content of the aforementioned first compound is 0.1 parts by mass or more and 400 parts by mass or less, relative to 100 parts by mass of the aforementioned polyvinyl alcohol resin.

6. The polarizing plate as described in claim 4, wherein, In the aforementioned adhesive, the content of the aforementioned second compound is more than 1 part by mass and less than 50 parts by mass relative to 100 parts by mass of the aforementioned polyvinyl alcohol resin.

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

8. The polarizing plate as requested in item 1 or 2, wherein, The aforementioned polarizing plate is used in an image display device; in the aforementioned image display device, the polarizing plate is configured to be in contact with a solid layer on both sides.

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

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

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

12. The image display device as claimed in claim 10, wherein, The aforementioned transparent component is a touch panel.

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