Method for producing polarizing plate and image display device using the same

Abstract

The object of this invention is to provide a novel polarizing plate having an adhesive layer formed from an adhesive with a sufficient production life, and capable of suppressing the decrease in transmittance when exposed to high-temperature environments. This invention provides a polarizing plate comprising: a polarizing element formed by adsorbing and orienting a dichroic pigment onto a polyvinyl alcohol-based resin layer; and a transparent protective film deposited 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 from an adhesive containing a first compound, a second compound, and a third compound, wherein the first compound is selected from at least one of the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives, the second compound is a dialdehyde, and the third compound is a dicarboxylic acid.

Description

Technical Field

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

[0002] Liquid crystal displays (LCDs) are used not only in LCD televisions but also widely in automotive applications such as personal computers, mobile phones, and navigation systems. Typically, an LCD device has a liquid crystal panel with polarizing plates bonded to both sides of liquid crystal cells using adhesive, and the display is achieved by controlling light from a backlight through the liquid crystal panel. In recent years, organic EL displays have also been widely used in automotive applications such as televisions, mobile phones, and navigation systems, similar to LCDs. In OLED displays, to suppress the reflection of external light by the metal electrode (cathode) and ensure mirror-like recognition, a circular polarizing plate (a laminate containing polarizing elements and a λ / 4 plate) is sometimes placed on the recognition side surface of the image display panel.

[0003] In polarizing plates, good adhesion between the polarizing element and the protective film can be achieved using polyvinyl alcohol (PVA) based resin adhesives. However, Patent Document 1 (Japanese Patent Application Laid-Open No. 2005-189615) points out that PVA based resin adhesives cannot achieve a sufficient pot life. The term "inability to achieve a pot life" refers to the short shelf life of the adhesive. Patent Document 2 (Japanese Patent Application Laid-Open No. 2010-276673) describes an adhesive containing a crosslinking agent and maleic acid, which achieves a sufficient pot life for production.

[0004] As mentioned above, polarizing plates are increasingly being used in vehicles as components of image display devices such as liquid crystal displays and organic EL displays. Compared to mobile applications such as televisions or mobile phones, polarizing plates used in automotive image display devices are exposed to higher temperatures, thus requiring minimal changes in characteristics at higher temperatures (high-temperature durability).

[0005] On the other hand, to prevent damage to the image display panel from impacts to the outer surface, there is an increasing trend towards configurations that include a front panel (also known as a "window layer") with a transparent resin plate or glass plate located further away from the image display panel on the recognition side. In image display devices equipped with touch panels, a configuration is widely used where the touch panel is located further away from the image display panel on the recognition side, and a front panel is located even further away from the touch panel on the recognition side.

[0006] In such a configuration, if there is an air layer between the image display panel and a transparent member such as a front panel or a touch panel, external light reflected due to light reflection at the air layer interface is generated, resulting in a tendency for the recognition of the screen to deteriorate. Therefore, the space between the polarizing plate disposed on the recognition side surface of the image display panel and the transparent member is a layer other than the air layer and generally has a tendency to increasingly adopt a configuration filled with a solid layer (hereinafter, sometimes referred to as an "interlayer filler").) (hereinafter, sometimes referred to as an "interlayer filling configuration"). The interlayer filler is preferably a material with a refractive index close to that of the polarizing plate or the transparent member. As the interlayer filler, for the purpose of suppressing the deterioration of recognition caused by reflection at the interface and fixing the members to each other, an adhesive or a UV curable adhesive can be used (for example, refer to Japanese Patent Application Laid-Open No. 11-174417 (Patent Document 3)). <00> <00>

[0007] <00> The interlayer filling configuration is increasingly being adopted in mobile applications such as mobile phones that are frequently used outdoors. Also, due to the increasing demand for recognition in recent years, in vehicle applications such as navigation devices, a study is also being conducted on an interlayer filling configuration in which a front transparent plate is disposed on the surface of the image display panel and filled with an adhesive layer or the like between the panel and the front transparent plate. <00> <00>

[0008] <00> However, it has been reported that when such a configuration is adopted, the transmittance of the polarizing plate is significantly reduced in a high-temperature environment. Japanese Patent Application Laid-Open No. 2014-102353 (Patent Document 4) has proposed a method for 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 as a countermeasure for this problem. <00> [Prior Art Documents] <00> [Patent Documents] <00> <00>

[0009] <00> <00> [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-189615 <00> [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-276673 <00> [Patent Document 3] Japanese Patent Application Laid-Open No. 11-174417 <00> [Patent Document 4] Japanese Patent Application Laid-Open No. 2014-102353 <00> Summary of the Invention <00> Problems to be Solved by the Invention <00> <00>

[0010] <00> The purpose of this invention is to provide a novel polarizing plate, an image display device using the polarizing plate, and an adhesive, wherein the novel polarizing plate has an adhesive layer formed by an adhesive having sufficient production life and can suppress the decrease in transmittance when exposed to high temperature environments. The means to solve the problem

[0011] The present invention provides a polarizing plate and an image display device as illustrated below. [1] A polarizing plate comprising: a polarizing element formed by adsorbing and orienting dichroic pigments onto a polyvinyl alcohol-based resin layer; and a transparent protective film deposited 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 from an adhesive containing the first compound, the second compound, and the third compound. The aforementioned compound 1 is selected from at least one of the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives. The aforementioned second compound is a dialdehyde. The aforementioned compound 3 is a dicarboxylic acid. [2] The polarizing plate as described in [1], wherein the aforementioned adhesive comprises a polyvinyl alcohol resin. [3] The polarizing plate as described in [2], wherein, in the aforementioned adhesive, the content of the aforementioned third compound is 0.01 parts by mass or more and 400 parts by mass or less relative to 100 parts by mass of the aforementioned polyvinyl alcohol resin. [4] The polarizing plate as described in [2] or [3], 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. [5] A polarizing plate as described in any one of [2] to [4], wherein, in the aforementioned adhesive, the content of the aforementioned second compound is 0.03 parts by mass or more and 20 parts by mass or less relative to 1 part by mass of the aforementioned first compound. [6] A polarizing plate as described in any one of [1] to [5], wherein the aforementioned dialdehyde is glyoxal. [7] A polarizing plate as described in any one of [1] to [6], wherein the thickness of the aforementioned adhesive layer is more than 0.01 μm and less than 7 μm. [8] A polarizing plate as described in any one of [1] to [7], wherein the aforementioned polarizing plate is used in an image display device. In the aforementioned image display device, the solid layer system is configured to be in contact with both sides of the aforementioned polarizing plate. [9] An image display device includes: an image display unit, a first adhesive layer laminated on the recognition side surface of the aforementioned image display unit, and a polarizing plate according to any one of [1] to [8] laminated on the recognition side surface of the aforementioned first adhesive layer.

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

[11] In the image display device according to

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

[12] In the image display device according to

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

[13] An adhesive contains a first compound, a second compound, and a third compound. The aforementioned first compound is at least one selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives. The aforementioned second compound is a dialdehyde. The aforementioned third compound is a dicarboxylic acid. Advantages of the Invention

[0012] [[ID=( According to the present invention, a polarizing plate can be provided, which has an adhesive layer formed by an adhesive having a sufficient applicable period in production and can suppress a decrease in transmittance when exposed to a high-temperature environment. Furthermore, an image display device can be provided, which can suppress a decrease in transmittance even when exposed to a high-temperature environment by using the polarizing plate of the present invention. Embodiments

[0013] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments.

[0014] [Polarizing Plate] The polarizing plate of the embodiment of the present invention has a polarizing element in which a dichroic dye is adsorbed and oriented in a layer containing a polyvinyl alcohol-based resin, and a transparent protective film. The polarizing element and the transparent protective film are bonded by an adhesive layer formed by an adhesive containing a first compound, a second compound, and a third compound.

[0015] The first compound is at least one selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives. The second compound is a dialdehyde. The third compound is a dicarboxylic acid.

[0016] Polarizing plates, known for their excellent high-temperature durability, are characterized by the ability to suppress transmittance reduction even when placed at 95°C for 1000 hours. However, even with such polarizing plates, when used in interlayer filling structures, a significant reduction in transmittance can sometimes be observed in the central area of ​​the polarizing plate when placed at 105°C. This significant reduction in transmittance at high temperatures is believed to be a problem particularly prone to occur when interlayer filling structures, where one side of the polarizing plate is bonded to the image display unit and the other side to transparent components such as a touch panel or front panel, are exposed to high temperatures.

[0017] In Raman spectroscopy, a polarizing plate with significantly reduced transmittance due to interlayer filling exhibits spikes near 1100 cm⁻¹ (originating from =C=C bonds) and 1500 cm⁻¹ (originating from -C=C- bonds), suggesting the formation of a polyene structure (-C=C)n-. It is inferred that this polyene structure is produced by the dehydration of polyvinyl alcohol constituting the polarizing element into polyene (Patent Document 4, Paragraph

[0012] ).

[0018] The polarizing plate of this invention further improves high-temperature durability. The polarizing plate of this invention is embedded in an image display device composed of interlayer fillers, and for example, even when exposed to a high-temperature environment of 105°C, it can suppress the decrease in transmittance. It is presumed that this effect is due to the synergistic effect of the first, second, and third compounds present in the adhesive layer, which suppresses the polyene content of the polyvinyl alcohol constituting the polarizing element. This effect is not limited to cases where the moisture content of the polarizing plate is low; it also works when the moisture content of the polarizing plate is high.

[0019] The polarizing plate of the present invention preferably has at least one of the features described in (a) and (b). (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 70% relative humidity at 20°C. (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 70% relative humidity at 20°C.

[0020] <Polarizing element> A polarizing element formed by adsorbing a directional dichroic dye into a layer containing polyvinyl alcohol (hereinafter, also referred to as "PVA")-based resin (hereinafter, also referred to as "PVA-based resin layer") can be any known polarizing element. Examples of polarizing elements include an extended film obtained by dyeing a PVA-based resin film with a dichroic dye and then uniaxially stretching it; or a laminated film having a coating layer formed on a substrate film by coating a coating liquid containing a PVA-based resin, and then dyeing the coating layer with a dichroic dye and uniaxially stretching the laminated film to obtain an extended layer. Stretching can be performed after dyeing with the dichroic dye, or during dyeing, or after stretching.

[0021] PVA-based resins can be obtained by saponifying polyvinyl acetate (PVA) resins. Besides polyvinyl acetate homopolymers, PVA-based resins also include copolymers of vinyl acetate and other monomers that can copolymerize with it. Other monomer systems that can be copolymerized include, for example, unsaturated carboxylic acids, olefins such as ethylene, vinyl ethers, and unsaturated sulfonic acids.

[0022] The PVA-based resin layer is preferably formed from a PVA-based resin with a boron adsorption rate of 5.70% by mass or more. That is, the boron adsorption rate of the PVA-based resin in the raw material stage before dyeing or stretching is 5.70% by mass or more. By using such a PVA-based resin, for example, even when exposed to a high-temperature environment of 105°C, the transmittance is not easily reduced. Furthermore, the boron adsorption rate of the PVA-based resin is preferably 10% by mass or less. Using such a PVA-based resin, when manufacturing polarizing elements, the boric acid concentration in the boric acid treatment bath does not become high, and the processing time for boric acid treatment can be shortened, making it easier to obtain the desired polarizing element and improving the productivity of the polarizing element. If the boron adsorption rate of the PVA-based resin is set to 10% by mass or less, boron is appropriately absorbed in the PVA-based resin layer, and the shrinkage force of the polarizing element is easily reduced. As a result, when embedded in an image display device, it is less likely to cause undesirable conditions such as peeling between the front panel and other components and the polarizing plate. The boron adsorption rate of PVA-based resins can be determined using the method described in the examples below.

[0023] The boron adsorption rate of PVA-based resins reflects the spacing between molecular chains and the characteristics of the crystalline structure within the PVA resin. It is believed that compared to PVA-based resins with a boron adsorption rate below 5.70% by mass, PVA-based resins with a boron adsorption rate above 5.70% by mass have wider spacing between molecular chains and less crystallinity. Therefore, it is inferred that boron, the first metal ion, and the second metal ion readily enter the PVA resin layer, effectively preventing polyolefin formation under high-temperature conditions.

[0024] The boron adsorption rate of PVA-based resins can be adjusted, for example, before manufacturing polarizing elements, by pretreatment such as hot water treatment, acidic solution treatment, ultrasonic irradiation treatment, or radiation irradiation treatment. These treatments can expand the spacing between the molecular chains in the PVA-based resin or disrupt its crystalline structure. Hot water treatment, for example, involves immersing the resin in pure water at 30°C to 100°C for 1 to 90 seconds and then drying it. Acidic solution treatment, for example, involves immersing the resin in an aqueous solution of boric acid with a concentration of 10% to 20% by mass for 1 to 90 seconds and then drying it. Ultrasonic treatment, for example, involves irradiating the resin with ultrasound at a frequency of 20 to 29 kC at an output of 200 W to 500 W for 30 seconds to 10 minutes. Ultrasonic treatment can be performed in solvents such as water.

[0025] The saponification degree of PVA-based resins is preferably above 85 mol%, more preferably above 90 mol%, and even more preferably above 99 mol% and below 100 mol%. The degree of polymerization of PVA-based resins is, for example, above 1000 and below 10000, preferably above 1500 and below 5000. PVA-based resins can be modified, for example, into aldehyde-modified polyethylene formaldehyde, polyethylene acetal, and polyethylene butyral.

[0026] The thickness of the polarizing element is preferably 3μm to 35μm, more preferably 4μm to 30μm, and even more preferably 5μm to 25μm. By using a polarizing element thickness of 35μm or less, the effect of polyolefin formation in PVA-based resins at high temperatures, which reduces optical properties, can be suppressed. By using a polarizing element thickness of 3μm or more, it is easier to form a structure that achieves the desired optical properties.

[0027] The polarizing element preferably includes a first compound, a second compound, and a third compound. In this embodiment, the polarizing element and the transparent protective film are bonded together by an adhesive layer formed by an adhesive comprising the first, second, and third compounds. Therefore, it is presumed that a portion of the first compound, a portion of the second compound, and a portion of the third compound migrating from the adhesive layer will be included in the polarizing element. The first, second, and third compounds in the polarizing element may also be included in those added during the manufacturing process of the polarizing element. By having an adhesive layer comprising the first, second, and third compounds, the transmittance is less likely to decrease even when the polarizing plate is exposed to a high-temperature environment. Furthermore, by having an adhesive layer comprising the first, second, and third compounds, the reduction in polarization can be suppressed even when the polarizing plate is exposed to a high-temperature environment. When two polarizing plates are configured in an orthogonal Nicol configuration, light leakage (hereinafter also referred to as "interactive light leakage") is easily generated if the polarization degree of the polarizing plates decreases. However, according to the present invention, even when exposed to a high-temperature environment, the polarization degree is not easily reduced, thus easily suppressing interactive light leakage. It is inferred that the polyolefination of PVA-based resins can be suppressed by the synergistic effect of the first, second, and third compounds contained in the polarizing element.

[0028] In manufacturing polarizing elements, methods containing the first, second, and third compounds include impregnating a PVA-based resin layer in a processing solvent containing the first and / or second and / or third compounds, or spraying, flowing in, or dripping the processing solvent into the PVA-based resin layer. Preferably, a method is used to impregnate the PVA-based resin layer in a processing solvent containing all of the first, second, and third compounds. Specific examples of the first, second, and third compounds are provided as examples of those contained in the adhesive described later.

[0029] The step of immersing the PVA-based resin layer in a treatment solvent containing compounds 1, 2, and 3 can be performed simultaneously with the swelling, stretching, dyeing, crosslinking, and cleaning steps in the polarizing element manufacturing method described later, or it can be performed separately from these steps. Preferably, the step of immersing the PVA-based resin layer containing compounds 1, 2, and 3 is performed after dyeing the PVA-based resin layer with iodine, and more preferably simultaneously with the crosslinking step after dyeing. Following this method results in minimal hue change, reducing the impact of the polarizing element on its optical properties.

[0030] To make the polarizing element contain the first compound, the second compound, and the third compound, both addition during the manufacturing of the polarizing element and addition to an adhesive can be performed. For example, an adhesive containing the first compound, the second compound, and the third compound can be used, and at least one of the first compound, the second compound, and the third compound can also be added during the manufacturing of the polarizing element.

[0031] (Compound 1) The first compound is selected from at least one of the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives. The first compound can be used alone or in combination of two or more. The first compound can be either water-soluble or water-poorly soluble, but either type of first compound may be used. When using a water-poorly soluble first compound in a water-soluble adhesive, it is preferable to design a dispersion method after the adhesive layer is formed to prevent haze increase, etc.

[0032] (Urea derivatives) Urea derivatives are compounds in which at least one of the four hydrogen atoms of the urea molecule is substituted with a substituent. In this case, there are no particular restrictions on the substituent, but it is preferred that the substituent is composed of a carbon atom, a hydrogen atom, and an oxygen atom.

[0033] Specific examples of urea derivatives include 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.

[0034] Examples of 2-substituted urea systems include 1,1-dimethylurea, 1,3-dimethylurea, 1,1-diethylurea, 1,3-diethylurea, 1,3-bis(hydroxymethyl)urea, 1,3-tert-butylurea, 1,3-dicyclohexylurea, 1,3-diphenylurea, 1,3-bis(4-methoxyphenyl)urea, 1-acetyl-3-methylurea, 2-imidazolinone (epenylethylurea), and tetrahydro-2-pyrimidinone (epenylpropylurea).

[0035] Examples of 4-substituted urea systems 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.

[0036] (Thiocarbamide derivatives) Thiourea derivatives are compounds in which at least one of the four hydrogen atoms of the thiourea molecule is substituted with a substituent. In this case, there are no particular restrictions on the substituent, but it is preferred that the substituent is composed of a carbon atom, a hydrogen atom, and an oxygen atom.

[0037] Specific examples of thiourea derivatives include N-methylthiourea, ethylthiourea, propylthiourea, isopropylthiourea, 1-butylthiourea, cyclohexylthiourea, N-acetylatedthiourea, N-allylthiourea, (2-methoxyethyl)thiourea, N-phenylthiourea, (4-methoxyphenyl)thiourea, N-(2-methoxyphenyl)thiourea, N-(1-naphthyl)thiourea, (2-pyridyl)thiourea, o-tolylthiourea, and p-tolylthiourea.

[0038] Examples of 2-substituted thiourea systems include 1,1-dimethylthiourea, 1,3-dimethylthiourea, 1,1-diethylthiourea, 1,3-diethylthiourea, 1,3-dibutylthiourea, 1,3-diisopropylthiourea, 1,3-dicyclohexylthiourea, N,N-diphenylthiourea, N,N'-diphenylthiourea, 1,3-di(o-tolyl)thiourea, 1,3-di(p-tolyl)thiourea, 1-benzyl-3-phenylthiourea, 1-methyl-3-phenylthiourea, N-allyl-N'-(2-hydroxyethyl)thiourea, and ethylthiourea.

[0039] Examples of 3-substituted thiourea systems include trimethylthiourea, and examples of 4-substituted thiourea systems include tetramethylthiourea and 1,1,3,3-tetraethylthiourea.

[0040] In the first compound, when used in an image display device constructed with interlayer filling, from the viewpoint of suppressing the decrease in transmittance under high-temperature environments and minimizing the decrease in polarization (suppressing cross-leakage), a urea derivative or a thiourea derivative is preferred, and a urea derivative is more preferred. Among the urea derivatives, a 1-substituted urea or a 2-substituted urea is preferred, and a 1-substituted urea is more preferred. The 2-substituted urea includes 1,1-substituted ureas and 1,3-substituted ureas, but a 1,3-substituted urea is more preferred.

[0041] (Compound 2) The second compound is a dialdehyde. Examples of dialdehydes include glyoxal, malondialdehyde (propanedialdehyde), and succinaldehyde (succinaldehyde). Glyoxal, with its simple structure and high reactivity, is particularly preferred. The following description pertains to glyoxal, but since the dialdehyde is as described above, previously known compounds may be used, and the description is not limited to glyoxal.

[0042] (Compound 3) The third compound is a dicarboxylic acid. Examples of dicarboxylic acids include, for instance, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, p-phthalic acid, tartaric acid, glutamic acid, malic acid, maleic acid, fumaric acid, itconic acid, mucoconic acid, 1,4-cyclohexanedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, 2,5-pyridinedicarboxylic acid, 3,5-pyridinedicarboxylic acid, diphenylammoniadicarboxylic acid, diphenylmethanedicarboxylic acid, oxaloacetic acid, methyl fumaric acid, and 2,6-pyridinedicarboxylic acid. Citric acid, malic acid, maleic acid, or tartaric acid are preferred among these. These dicarboxylic acids can be used alone or in combination of two or more.

[0043] Polarizing elements typically contain potassium ions (also known as "first metal ions"), and more preferably, other metal ions besides potassium ions (also known as "second metal ions"). The content of second metal ions in a polarizing element is preferably 0.05% by mass to 10.0% by mass, more preferably 0.05% by mass to 8.0% by mass, and even more preferably 0.1% by mass to 6.0% by mass. When the content of second metal ions in a polarizing element exceeds 10.0% by mass, the polarization intensity may decrease under high temperature and high humidity environments. Furthermore, when the content of second metal ions is less than 0.05% by mass, the improvement in durability under high temperature environments may be insufficient. The content of second metal ions in a polarizing element can be calculated, for example, by high-frequency induction combined with plasma (ICP) luminescence spectrophotometry, as the mass fraction (mass %) of the metal element relative to the mass of the polarizing element. It is believed that the metal element exists in the polarizing element as a cross-linked structure formed by metal ions or by the constituent elements of polyvinyl alcohol resin. However, the content of the so-called second metal ion is referred to as the value of metal atoms.

[0044] The second metal ion can be any metal ion other than potassium ions, and is not limited thereto. It is preferably a metal ion other than alkali metals. Especially from the point of view of adjusting the color or imparting durability, it is preferably at least one metal ion including transition metals such as cobalt, nickel, zinc, chromium, aluminum, copper, manganese, and iron. Among these metal ions, zinc ions are preferred from the point of view of adjusting the color or imparting heat resistance.

[0045] The boron content of the polarizing element is preferably 2.4% by mass or more. Furthermore, the preferred boron content is 3.9% by mass or more and 8.0% by mass, more preferably 4.2% by mass or more and 7.0% by mass, and even more preferably 4.4% by mass or more and 6.0% by mass. When the boron content of the polarizing element exceeds 8.0% by mass, the shrinkage force of the polarizing element increases, which may lead to delamination from the front panel or other components when embedded in the image display device. Conversely, when the boron content is less than 2.4% by mass, the desired optical characteristics may not be achieved. The boron content in the polarizing element can be calculated, for example, by using high-frequency inductively coupled plasma (ICP) luminescence spectrophotometry, as the mass fraction (mass%) of boron relative to the mass of the polarizing element. It is believed that boron exists in polarizing elements as a cross-linked structure formed by boric acid or its constituent elements with polyvinyl alcohol resins, but the boron content mentioned here refers to the value of boron atoms (B).

[0046] When the boron content of the polarizing element is between 2.4% and 8.0% by mass, and it is used as a component of an image display device formed by interlayer filling, the reduction in transmittance can be further suppressed when exposed to high-temperature environments. It is speculated that this is because when the boron content of the polarizing element is between 2.4% and 8.0% by mass, polyolefin formation is less likely to occur under high-temperature environments, thus suppressing the reduction in transmittance.

[0047] From the viewpoint of suppressing the degradation of optical properties of polarizing elements under high-temperature conditions, the content of potassium ions in the polarizing element is preferably 0.28% by mass or more, more preferably 0.32% by mass or more, and even more preferably 0.34% by mass or more. Furthermore, from the viewpoint of suppressing hue changes under high-temperature conditions, it is preferably 0.60% by mass or less, more preferably 0.55% by mass or less, and even more preferably 0.50% by mass or less. The content of potassium ions can be determined using the same method as the content of the second metal ion; here, the content of potassium ions refers to the value of potassium atoms.

[0048] (Manufacturing method of polarizing element) There is no particular limitation on the manufacturing method of polarizing elements, but typically it includes the following methods: a method of pre-feeding a PVA-based resin film wound into a roll and then stretching, dyeing, cross-linking, etc. (hereinafter referred to as "Manufacturing Method 1"); or a method of coating a coating liquid containing PVA-based resin onto a substrate film to form a PVA-based resin layer belonging to the coating layer, and then stretching the resulting laminate (hereinafter referred to as "Manufacturing Method 2").

[0049] Manufacturing method 1 can be manufactured by the following steps: a step of uniaxially stretching a PVA-based resin film; a step of dyeing the PVA-based resin film with a dichroic pigment such as iodine and adsorbing the dichroic pigment; a step of treating the PVA-based resin film adsorbed with the dichroic pigment with a boric acid aqueous solution; and a step of washing with water after treatment with the boric acid aqueous solution.

[0050] The swelling step is a process in which the PVA-based resin film is immersed in a swelling bath. Through the swelling step, in addition to removing dirt or adhesives from the surface of the PVA-based resin film, the film also swells to suppress uneven dyeing. The swelling bath is typically a medium primarily composed of water, distilled water, or pure water. Surfactants, alcohols, etc., may be added to the swelling bath as appropriate, depending on the commonly used method. 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.

[0051] The optimal temperature for the swelling bath is between 10°C and 60°C, more preferably between 15°C and 45°C, and even more preferably between 18°C ​​and 30°C. The immersion time in the swelling bath is affected by the temperature, so it cannot be fixed. However, it is preferably between 5 and 300 seconds, more preferably between 10 and 200 seconds, and even more preferably between 20 and 100 seconds. The swelling step can be performed once or multiple times as needed.

[0052] The dyeing step involves immersing a PVA-based resin film in a dyeing bath (iodine solution), which allows dichroic pigments such as iodine to be adsorbed and oriented on the PVA-based resin film. The iodine solution is usually an aqueous iodine solution, containing iodine and iodides as a dissolving agent. Examples of iodides include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. Among these, potassium iodide is suitable from the perspective of controlling the potassium content in the polarizing element.

[0053] The concentration of iodine in the staining bath is preferably 0.01% by mass to 1% by mass, more preferably 0.02% by mass to 0.5% by mass. The concentration of iodide in the staining bath is preferably 0.01% by mass to 10% by mass, more preferably 0.05% by mass to 5% by mass, and even more preferably 0.1% by mass to 3% by mass.

[0054] The optimal temperature for the dyeing bath is between 10°C and 50°C, more preferably between 15°C and 45°C, and even more preferably between 18°C ​​and 30°C. The immersion time in the dyeing bath cannot be fixed due to the influence of the temperature on the degree of dyeing of the PVA resin film; however, it is generally preferred to be between 10 seconds and 300 seconds, and even more preferably between 20 seconds and 240 seconds. The dyeing process can be performed once or multiple times as needed.

[0055] The crosslinking step involves immersing the dyed PVA-based resin film in a treatment bath (crosslinking bath) containing boron compounds. The polyvinyl alcohol-based resin film undergoes crosslinking via the boron compounds, allowing iodine or dye molecules to be adsorbed onto the crosslinked structure. Examples of boron compounds include boric acid, borates, and borax. The crosslinking bath is generally an aqueous solution, but can be a mixture of an organic solvent and water that is miscible with water. From the viewpoint of controlling the potassium content in the polarizing element, the crosslinking bath preferably contains potassium iodide.

[0056] In the crosslinking bath, the concentration of the boron compound is preferably 1% by mass to 15% by mass, more preferably 1.5% by mass to 10% by mass, and even more preferably 2% by mass to 5% by mass. When potassium iodide is used in the crosslinking bath, the concentration of potassium iodide in the crosslinking bath is preferably 1% by mass to 15% by mass, more preferably 1.5% by mass to 10% by mass, and even more preferably 2% by mass to 5% by mass.

[0057] The optimal temperature for the crosslinking bath is between 20°C and 70°C, and more preferably between 30°C and 60°C. The immersion time in the crosslinking bath cannot be fixed because the degree of crosslinking of the PVA resin film is affected by the bath temperature; it is preferably between 5 seconds and 300 seconds, and more preferably between 10 seconds and 200 seconds. The crosslinking step can be performed only once or multiple times as needed.

[0058] The stretching step is a process in which a PVA-based resin film is stretched to a predetermined ratio in at least one direction. Generally, the PVA-based resin film is uniaxially stretched along the transport direction (longitudinal direction). There are no particular limitations 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.

[0059] In the wet stretching method, the treatment bath (stretching bath) can typically be water or a mixture of water and an organic solvent that is miscible with water. From the viewpoint of controlling the potassium content in the polarizing element, the stretching bath preferably contains potassium iodide. When potassium iodide is used in the stretching bath, the concentration of potassium iodide in the stretching bath is preferably 1% to 15% by mass, more preferably 2% to 10% by mass, and even more preferably 3% to 6% by mass. From the viewpoint of suppressing film rupture during stretching, the treatment bath (stretching bath) may contain a boron compound. When a boron compound is included, the concentration of the boron compound in the stretching bath is preferably 1% to 15% by mass, more preferably 1.5% to 10% by mass, and even more preferably 2% to 5% by mass.

[0060] The optimal temperature for the stretching bath is 25 to 80°C, more preferably 40 to 80°C, even more preferably 50 to 75°C, and ideally 65 to 75°C. The immersion time in the stretching bath is affected by the temperature, so it cannot be fixed. However, it is preferably 10 to 800 seconds, and more preferably 30 to 500 seconds. In the wet stretching method, the stretching treatment can be performed together with any one or more of the following steps: swelling, dyeing, crosslinking, and washing.

[0061] Dry stretching methods include, for example, inter-roll stretching, heated roll stretching, and compression stretching. Furthermore, dry stretching can be performed together with a drying step.

[0062] The total elongation ratio (cumulative elongation ratio) applied to the polyvinyl alcohol resin film can be appropriately set according to the purpose, but it is better to be more than 2 times and less than 7 times, more preferably more than 3 times and less than 6.8 times, and even more preferably more than 3.5 times and less than 6.5 times.

[0063] The cleaning step involves immersing the polyvinyl alcohol (PVA) resin film in a cleaning bath to remove foreign matter remaining on the surface of the PVA resin film. The cleaning bath is typically a medium primarily composed of water, distilled water, or pure water. From the perspective of controlling the potassium content of the polarizing element, it is preferable to use potassium iodide in the cleaning bath. In this case, the concentration of potassium iodide in the cleaning bath is preferably 1% by mass to 10% by mass, more preferably 1.5% by mass to 4% by mass, and even more preferably 1.8% by mass to 3.8% by mass.

[0064] The ideal temperature for the cleaning bath is between 5°C and 50°C, more preferably between 10°C and 40°C, and even more preferably between 15°C and 30°C. The soaking time in the cleaning bath is affected by the temperature, so it cannot be fixed. However, it is ideally between 1 second and 100 seconds, more preferably between 2 seconds and 50 seconds, and even more preferably between 3 seconds and 20 seconds. The cleaning process can be performed once or multiple times as needed.

[0065] Furthermore, in the above steps, or as a step different from the above steps, a metal ion treatment step is preferably included. The metal ion treatment step is performed by impregnating the polyvinyl alcohol-based resin membrane in an aqueous solution containing a metal salt of a second metal ion. Through the metal ion treatment step, the polyvinyl alcohol-based resin membrane contains the second metal ion.

[0066] The second metal ion can be any metal ion other than potassium ions, and is not limited thereto. Preferably, it is a metal ion other than alkali metals, especially from the perspective of adjusting color or imparting durability. Preferably, it is a metal ion containing at least one transition metal such as cobalt, nickel, zinc, chromium, aluminum, copper, manganese, or iron. Among these metal ions, zinc ions are preferred from the perspective of adjusting color or imparting heat resistance. Examples of zinc salts include zinc chloride, zinc halides such as zinc iodide, zinc sulfate, and zinc acetate.

[0067] Metal salt solutions can be used in the metal ion treatment steps. The following describes a representative example of using an aqueous zinc salt solution for immersion treatment in a zinc-containing solution.

[0068] The concentration of zinc ions in the zinc salt aqueous solution is 0.1 to 10% by mass, preferably in the range of 0.3 to 7% by mass. Furthermore, the zinc salt solution preferably uses an aqueous solution containing potassium and iodide ions, such as potassium iodide, to easily leach zinc ions. The concentration of potassium iodide in the zinc salt solution is preferably set to 0.1 to 10% by mass, more preferably 0.2 to 5% by mass.

[0069] When immersing in a zinc-containing solution, the temperature of the zinc salt solution is typically between 15 and 85°C, preferably between 25 and 70°C. The immersion time is typically between 1 and 120 seconds, preferably between 3 and 90 seconds. During immersion in a zinc-containing solution, the zinc content in the polyvinyl alcohol (PVA) resin film is adjusted to the aforementioned range by adjusting the concentration of the zinc salt solution, the immersion temperature of the PVA film in the zinc salt solution, and the immersion time. There are no particular restrictions on when to perform the immersion treatment in the zinc-containing solution. The immersion treatment can be performed alone, or it can be performed simultaneously with at least one of the dyeing, crosslinking, or stretching steps, while the zinc salt is present in the dyeing bath, crosslinking bath, or stretching bath.

[0070] The drying step is the process of drying the PVA-based resin film, which has been cleaned in the washing step, to obtain a polarizing element. Drying can be carried out by any suitable method, such as natural drying, forced-air drying, or heat drying.

[0071] Manufacturing method 2 can be performed by the following steps: coating a coating solution containing PVA-based resin onto a substrate film; uniaxially stretching the resulting laminated film; dyeing the PVA-based resin film of the uniaxially stretched laminated film with a dichroic dye to adsorb it and form a polarizing element; treating the film adsorbed with the dichroic dye with a boric acid aqueous solution; and washing with water after treatment with the boric acid aqueous solution. The substrate film used to form the polarizing element can be used as a protective layer for the polarizing element. The substrate film can be peeled off from the polarizing element as needed.

[0072] <Transparent Protective Film> In this embodiment, the transparent protective film (hereinafter referred to as "protective film") is bonded to at least one side of the polarizing element through an adhesive layer. The transparent protective film is bonded to one or both sides of the polarizing element, but preferably to both sides.

[0073] Protective films can simultaneously possess other optical functions and can be formed into a multilayered structure. From an optical perspective, the protective film thickness is preferably thin, but if it is too thin, the strength will decrease and the processability will be poor. A suitable film thickness is 5 μm to 100 μm, preferably 10 μm to 80 μm, and even more preferably 15 μm to 70 μm.

[0074] The protective film can be made of cellulose lacquers, polycarbonate resins, cyclic olefin resins such as northocyanins, (meth)acrylic polymers, or polyester resins such as polyethylene terephthalate. When the protective film is bonded to both sides of the polarizing element using a water-based adhesive such as PVA adhesive, at least one side of the protective film is preferably either a cellulose lacquer or a (meth)acrylic polymer, with cellulose lacquers being more preferred.

[0075] For purposes such as viewing angle compensation, at least one protective film system can possess phase retardation functionality. The protective film itself can possess phase retardation functionality, or it can have a separate phase retardation layer, or a combination of both. A film system possessing phase retardation functionality can be directly bonded to a polarizing element through an adhesive, but it can also be bonded to the polarizing element through an adhesive or bonding agent, separated from another protective film bonded to the polarizing element.

[0076] <Adhesive layer> The adhesive layer used to attach the protective film to the polarizing element is formed by the following adhesives.

[0077] (Adhesive) The adhesive contains a first compound, a second compound, and a third compound. The adhesive can be a water-based adhesive, a solvent-based adhesive, an active energy line curing adhesive, etc., without limitation, but a water-based adhesive is preferred, and more preferably, it contains a PVA-based resin. By using an adhesive containing the first, second, and third compounds, an adhesive layer for bonding polarizing elements and protective films can be formed, suppressing the decrease in transmittance of the polarizing plate under high-temperature environments. Furthermore, by using an adhesive containing the second and third compounds, an adhesive with a sufficient production life can be formed. The application of the adhesive of the present invention is not limited; it is suitable for use in optical components, for example, for bonding polarizing elements and protective films.

[0078] 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 thickness of the adhesive layer is preferably 0.01 μm to 7 μm, more preferably 0.01 μm to 5 μm, even more preferably 0.01 μm to 2 μm, and most preferably 0.01 μm to 1 μm.

[0079] When the adhesive contains a water-based adhesive of PVA-based resin, the content of the third compound relative to 100 parts by weight of the PVA-based resin is, for example, 0.01 parts by weight to 400 parts by weight, preferably 0.05 parts by weight to 50 parts by weight, and more preferably 0.1 parts by weight to 10 parts by weight. If the content is less than 0.01 parts by weight, the effect of extending the pot life may be insufficient, or the effect of suppressing polyene formation in polarizing elements at high temperatures may be insufficient. On the other hand, if the content exceeds 400 parts by weight, the third compound may precipitate after the polarizing plate is manufactured.

[0080] When the adhesive contains a water-based adhesive of PVA-based resin, the content of the first compound is preferably 0.1 parts by weight to 400 parts by weight, more preferably 1 part by weight to 200 parts by weight, and even more preferably 3 parts by weight to 100 parts by weight, relative to 100 parts by weight of PVA-based resin. When the content is less than 0.1 parts by weight, the suppression effect of polyolefin formation in polarizing elements under high-temperature environments 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, resulting in increased haze.

[0081] When the adhesive contains a water-based adhesive with PVA-based resin, the content of the second compound is preferably 1 to 60 parts by weight, more preferably 1.5 to 50 parts by weight, and even more preferably 2 to 45 parts by weight, relative to 100 parts by weight of the PVA-based resin. If the content is less than 1 part by weight, the improvement in water resistance will be insufficient. On the other hand, if the content exceeds 60 parts by weight, the stability of the adhesive in solution preparation will decrease.

[0082] In the adhesive, the content of dialdehyde, belonging to the second compound, is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 10 parts by mass or less, relative to 1 part by mass of the urea-based compound belonging to the first compound. There is no lower limit, but for example, it is 0.03 parts by mass or more. By keeping the ratio of urea-based compound to dialdehyde in the adhesive within the above-mentioned range, it is easy to achieve both the improved high-temperature durability effect caused by the urea-based compound and the improved adhesion effect caused by the dialdehyde. It can be understood that the improved adhesion effect caused by the dialdehyde can lead to improved water resistance. When the content of dialdehyde exceeds 20 parts by mass relative to 1 part by mass of the urea-based compound, the improved high-temperature durability effect caused by the urea-based compound may not be fully realized. The ratio of urea-based compound to dialdehyde in the adhesive and the ratio of urea-based compound to dialdehyde in the adhesive layer can be considered the same.

[0083] In the adhesive, the content of dicarboxylic acid, which belongs to the third compound, is preferably between 0.001 and 100 parts by mass, and more preferably between 0.01 and 80 parts by mass, relative to 1 part by mass of dialdehyde, which belongs to the second compound. If it is less than 0.001 parts by mass, the effect of improving the pot life may be insufficient. On the other hand, if it exceeds 100 parts by mass, the third compound may precipitate after the polarizing plate is manufactured.

[0084] Regarding the aforementioned adhesive, when forming an adhesive layer for bonding polarizing elements and protective films, the amount of these compounds contained in the adhesive can be appropriately adjusted depending on whether the polarizing element to be bonded contains the first compound, the second compound, and the third compound, or not.

[0085] In the configuration where a transparent protective film is bonded to both sides of a polarizing element with an adhesive layer between them, it is possible that only one side of the adhesive layer contains a layer of compound 1, compound 2, and compound 3 within the adhesive layer on both sides of the polarizing element. However, it is preferable that both sides of the adhesive layer contain a layer of compound 1, compound 2, and compound 3.

[0086] To meet the requirements 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, the transparent protective film is laminated with an adhesive layer containing compounds 1, 2, and 3. The method for manufacturing this polarizing plate with a transparent protective film on only one side of the polarizing element is conceivable as initially manufacturing a polarizing plate with transparent protective films laminated on both sides with adhesive layers in between, and then peeling off the other transparent protective film. When using this manufacturing method, only one adhesive layer may contain compounds 1, 2, and 3, but it is preferable that both adhesive layers contain compounds 1, 2, and 3. When only one adhesive layer contains compounds 1, 2, and 3, it is preferable that the adhesive layer on the unpeeled film side contains compounds 1, 2, and 3.

[0087] (Water-based adhesive) The water-based adhesive can be any suitable water-based adhesive, but preferably a water-based adhesive containing PVA-based resin (PVA-based adhesive). From the perspective of adhesion, the average degree of polymerization of the PVA-based resin contained in the water-based adhesive is preferably 100 to 5500, more preferably 1000 to 4500. From the perspective of adhesion, the average degree of saponification is preferably 85 mol% to 100 mol%, more preferably 90 mol% to 100 mol%.

[0088] The PVA-based resin contained in the aqueous adhesive preferably contains acetyl groups because PVA-based resin layers exhibit excellent adhesion and durability to the protective film. Acetyl-based PVA-based resins can be obtained, for example, by reacting PVA-based resin with diketene using any method. The degree of acetyl-based modification of 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 aqueous adhesive is preferably 0.1% by mass or more and 15% by mass, more preferably 0.5% by mass or more and 10% by mass.

[0089] Dialdehyde compounds belonging to the second group can function as crosslinking agents. Water-based adhesives may also contain crosslinking agents other than the second compound. Known crosslinking agents can be used as crosslinking agents. Examples of crosslinking agents include water-soluble epoxy compounds and isocyanates.

[0090] When the PVA-based resin is a PVA-based resin containing acetyl groups, the preferred crosslinking agent is either glyoxylate or hydroxymethyl melamine, and more preferably either glyoxylate.

[0091] Aqueous adhesives may also contain organic solvents. Regarding their miscibility with water, alcohols are preferred organic solvents, with methanol or ethanol being more preferred. The methanol concentration in aqueous adhesives is preferably 10% by mass to 70% by mass, more preferably 15% by mass to 60% by mass, and even more preferably 20% by mass to 60% by mass. A methanol concentration of 10% by mass or higher makes it easier to control the polyolefination of PVA resins at high temperatures. Furthermore, a methanol content of 70% by mass or less can suppress color deterioration. Some urea derivatives have low solubility in water but high solubility in alcohols. In this case, dissolving the urea compound in alcohol, preparing an alcohol solution of the urea compound, and then adding the alcohol solution of the urea compound to an aqueous PVA solution to prepare the adhesive is also a preferred approach.

[0092] (Active Energy Line Curing Adhesive) Active energy line curing adhesives are adhesives that cure by irradiation with active energy lines such as ultraviolet light. Examples include adhesives containing polymerizable compounds and 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 ethyl carbamate monomers, as well as oligomers derived from these monomers. Photopolymerizable initiators include compounds that generate active species such as neutral free radicals, anionic free radicals, and cationic free radicals when irradiated with active energy lines such as ultraviolet light.

[0093] <Layer containing compound 1, compound 2, and compound 3> Compound 1, Compound 2, and Compound 3 are as described above, and are not limited to being contained in the adhesive layer. From the viewpoint of improving the high-temperature durability of the polarizing plate, they can be contained in other layers besides the adhesive layer. Only in polarizing plates with a transparent protective film on one side, from the viewpoint of improving physical strength, a hardening layer can be laid on the area opposite to the transparent protective film of the polarizing element. Such a hardening layer can be a layer containing Compound 1, Compound 2, and Compound 3.

[0094] The thickness of the layer containing the first compound, the second compound and the third compound is preferably 0.1 μm to 20 μm, more preferably 0.5 μm to 15 μm, and even more preferably 1 μm to 10 μm.

[0095] [Composition of an image display device] The polarizing plate of this embodiment can be used in various image display devices such as liquid crystal display devices or organic EL display devices. In image display devices, when the two sides of the polarizing plate are configured as interlayer fillers (excluding air layers), specifically as 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 filler configuration, the decrease in transmittance of the polarizing plate at high temperatures can be suppressed. An example image display device is shown with the following configuration: an image display unit, a first adhesive layer deposited on the recognition side surface of the image display unit, and a polarizing plate deposited on the recognition side surface of the first adhesive layer. This image display device can further include a second adhesive layer deposited on the recognition side surface of the polarizing plate, and a transparent member deposited on the recognition side surface of the second adhesive layer. In particular, the polarizing plate of this embodiment is suitable for use in an image display device, which has a transparent member disposed on the recognition side of the image display device. The polarizing plate and the image display unit are bonded together by a first adhesive layer, and the polarizing plate and the transparent member are bonded together by a second adhesive layer, forming an interlayer filler. In this specification, either or both of the first and second adhesive layers may be referred to simply as "adhesive layer." Furthermore, the member used for bonding the polarizing plate to the image display unit, and the member used for bonding the polarizing plate to the transparent member, are not limited to adhesive layers but may also be bonding agent layers.

[0096] <Image Display Unit> Image display units can include liquid crystal units (LCDs) or organic EL units (OLEDs). The liquid crystal unit can be any of the following: a reflective liquid crystal unit utilizing external light, a transmissive liquid crystal unit utilizing light from a backlight or other light source, or a semi-transmissive / semi-reflective liquid crystal unit utilizing both external light and light from a light source. When the liquid crystal unit utilizes light from a light source, the image display device (liquid crystal display device) also has a polarizing plate and a light source disposed on the side opposite to the image display unit (liquid crystal unit) to the sensing side. Preferably, the polarizing plate on the light source side and the liquid crystal unit are bonded together with a suitable adhesive layer. The driving method of the liquid crystal unit can be any type, such as VA mode, IPS mode, TN mode, STN mode, or π-type bending orientation.

[0097] Organic EL units are suitable for use in forming light emitters (organic electroluminescent emitters) by sequentially stacking transparent electrodes, organic light-emitting layers, and metal electrodes on a transparent substrate. The organic light-emitting layer can be a stack of various organic thin films, such as a hole injection layer composed of triphenylamine derivatives, or a light-emitting layer composed of fluorescent organic solids such as anthracene; or a stack of such light-emitting layers and an electron injection layer composed of perylene derivatives; or a stack of hole injection layers, light-emitting layers, and electron injection layers, etc.

[0098] <Lamination of image display unit and polarizing plate> An adhesive layer (adhesive sheet) can be used in the bonding system between the image display unit and the polarizing plate. From a workability perspective, a method of bonding the polarizing plate with an adhesive layer attached to one side of the polarizing plate to the image display unit is preferred. The application of the adhesive layer to the polarizing plate can be performed in various ways. Examples include: preparing an adhesive solution of 10% to 40% by mass in a solvent composed of a single substance or mixture of suitable solvents such as toluene or ethyl acetate, in which the substrate polymer or its components are dissolved or dispersed, and then directly attaching it to the polarizing plate using a suitable spreading method such as casting or coating; or forming an adhesive layer on a separation membrane and allowing it to move and adhere to the polarizing plate.

[0099] <Adhesive layer> The adhesive layer may consist of one or more layers, but preferably one layer. The adhesive layer system may be composed of an adhesive composition with (meth)acrylic resin, rubber resin, ethyl carbamate resin, ester resin, polysiloxane resin, or polyvinyl ether resin as the main component. Among these, an adhesive composition using a (meth)acrylic resin as the base polymer, which exhibits 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.

[0100] The (meth)acrylate resins (base polymers) that can be used in adhesive compositions are suitable polymers or copolymers using 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 that the base polymer is copolymerized with polar monomers. Examples of polar monomer systems include (meth)acrylate compounds, 2-hydroxypropyl (meth)acrylate compounds, hydroxyethyl (meth)acrylate compounds, (meth)acrylamide compounds, N,N-dimethylaminoethyl (meth)acrylate compounds, and (meth)acrylate epoxy propylene oxide compounds, which contain carboxyl, hydroxyl, acetamide, amino, or epoxy groups.

[0101] The adhesive composition may consist only of the aforementioned substrate polymer, but typically also contains a crosslinking agent. Examples of crosslinking agents include divalent or higher metal ions that form carboxylic acid metal salts with carboxyl groups, polyamine compounds that form amide bonds with carboxyl groups, 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.

[0102] Active energy line curing adhesive compositions possess the property of curing upon irradiation with active energy lines such as ultraviolet light or electron beams, and exhibit the following properties: they retain adhesiveness and adhere tightly to substrates such as films even before irradiation, and the adhesion can be adjusted by curing through irradiation. Ultraviolet curing is preferred for active energy line curing adhesive compositions. In addition to the base polymer and crosslinking agent, active energy line curing adhesive compositions also contain active energy line polymerizable compounds. Photopolymerization initiators and photosensitizers may be included as needed.

[0103] The adhesive composition system may include microparticles, beads (resin beads, glass beads, etc.) to impart light scattering properties, glass fibers, resins other than the base polymer, tackifiers, fillers (metal powder or other inorganic powders, etc.), antioxidants, ultraviolet absorbers, dyes, pigments, colorants, defoamers, corrosion inhibitors, photopolymerization initiators, and other additives.

[0104] 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, and a typical example is a release membrane that has undergone a release treatment. For example, the release membrane may be formed by applying a polysiloxane treatment or similar release treatment to the surface of the adhesive layer formed on a film composed of resins such as polyethylene terephthalate, polybutylene terephthalate, polycarbonate, and polyaramid.

[0105] Alternatively, an adhesive composition can be directly coated onto the release treatment surface of the separation membrane to form an adhesive layer, and this adhesive layer with the separation membrane attached can be deposited on the surface of the polarizing plate. An adhesive composition can be directly coated onto the surface of the polarizing plate to form an adhesive layer, and a separation membrane can be deposited on the outer surface of the adhesive layer.

[0106] When the adhesive layer is applied to the surface of the polarizing plate, it is preferable to apply surface activation treatments such as plasma treatment or corona treatment to the bonding surface of the polarizing plate and / or the bonding surface of the adhesive layer, and more preferably to apply corona treatment.

[0107] Furthermore, an adhesive sheet is prepared, which forms an adhesive layer by coating an adhesive composition onto a second separation membrane, and a separation membrane is deposited on the formed adhesive layer. The adhesive layer with the separation membrane attached, after being peeled off from the adhesive sheet, is then deposited on a polarizing plate. The second separation membrane may be one that has a weaker adhesion to the adhesive layer than the separation membrane and is easier to peel off.

[0108] There is no particular limitation on the thickness of the adhesive layer, but it is preferable to be, for example, 1μm to 100μm, more preferably 3μm to 50μm, and can be 20μm or more.

[0109] <Transparent Components> Transparent components disposed on the recognition side of an image display device can include transparent panels (window layers) or touch panels. The transparent panel can be a transparent panel with appropriate mechanical strength and thickness. Examples of such transparent panels include transparent resin panels made of polyimide resin, acrylic resin, or polycarbonate resin, or glass panels. A functional layer, such as an anti-reflective layer, can be laminated on the recognition side of the transparent panel. Furthermore, when the transparent panel is a transparent resin panel, a hard coating layer can be laminated to improve physical strength, or a low-permeability layer can be laminated to reduce moisture permeability. The touch panel can be various types of touch panels, such as resistive film, capacitive, optical, and ultrasonic touch panels, or glass panels or transparent resin panels with touch sensor functionality. When using a capacitive touch panel as the transparent component, it is preferable to have a transparent panel made of glass or transparent resin panel located closer to the recognition side than the touch panel.

[0110] <Fitting of polarizing plate and transparent component> The bonding system between the polarizing plate and the transparent component can be suitable for using adhesives or active energy line curing adhesives. When using adhesives, the adhesive application can be carried out in an appropriate manner. Specific application methods include, for example, the application method of the adhesive layer used for bonding the aforementioned image display unit to the polarizing plate.

[0111] When using an active energy line curing adhesive, to prevent the spread of the adhesive solution before curing, it is suitable to use a method in which a barrier material is provided to surround the periphery of the image display panel, a transparent member is placed on the barrier material, and the adhesive solution is injected. After the adhesive solution is injected, it is positioned and degassed as needed, and then cured by irradiation with active energy lines. [Example]

[0112] The present invention will now be specifically described with reference to the embodiments. The materials, reagents, quantities, proportions, and operations shown in the following embodiments may be appropriately modified without departing from the spirit of the present invention. Therefore, the present invention is not limited to the following embodiments.

[0113] (1) Measurement of the thickness of the polarizing element: The measurements were taken using the Digital Micrometer "MH-15M" manufactured by NIKON Corporation.

[0114] (2) Measurement of the polarizing plate's visual sensitivity correction polarization, visual sensitivity correction monomer transmittance, and hue: Measurements were taken using a spectrophotometer with an integrating sphere (V7100 manufactured by Japan Spectrophotometer Co., Ltd., 2D field of view; C light source).

[0115] (3) Determination of boron content: Dissolve 0.2 g of the polarizing element in 200 g of a 1.9% (w / w) mannitol aqueous solution. Then, titrate the resulting aqueous solution with a 1 mole / L sodium hydroxide aqueous solution, and calculate the boron content of the polarizing element by comparing the amount of sodium hydroxide aqueous solution required for neutralization with the calibration curve.

[0116] (4) Determination of zinc ion content: Nitric acid was added to the precisely weighed polarizing element, and acid decomposition was performed using a Milestone-General microwave sample pretreatment device (ETHOS D). The resulting solution was used as the assay solution. The zinc ion content was determined by quantitatively measuring the zinc concentration in the assay solution using an AGILENT TECHNOLOGIES ICP-OES instrument (5110 ICP-OES), and the mass of the polarizing element was calculated from the zinc mass.

[0117] (5) Determination of boron adsorption rate of PVA-based resin membranes: A 100 mm² PVA-based resin membrane was immersed in pure water at 30°C for 60 seconds, followed by immersion in an aqueous solution containing 5 parts boric acid at 60°C for 120 seconds. The PVA-based resin membrane removed from the boric acid aqueous solution was dried in an oven at 80°C for 11 minutes. After conditioning at 23°C and 55% RH for 24 hours, a boron-containing PVA membrane was obtained. 0.2 g of the boron-containing PVA-based resin membrane obtained in this manner was dissolved in 200 g of a 1.9% (w / w) mannitol aqueous solution. The resulting aqueous solution was then titrated with a 1 mole / L sodium hydroxide aqueous solution. The boron content of the PVA-based resin membrane was calculated by comparing the amount of sodium hydroxide solution required for neutralization with a calibration curve. The boron content of the PVA-based resin membrane obtained in this manner was used as the boron adsorption rate of the PVA-based resin membrane.

[0118] (Fabrication of polarizing element 1) A 30 μm thick polyvinyl alcohol (PVA) resin film with a boron adsorption rate of 5.71% by mass was immersed in pure water at 21.5°C for 79 seconds (swelling treatment). Then, a potassium iodide / boric acid / water mass ratio of 2 / 2 / 100 was immersed in an aqueous solution containing 1.0 mM iodine at 23°C for 151 seconds (dyeing step). Afterward, it was immersed in an aqueous solution with a potassium iodide / boric acid / water mass ratio of 2.5 / 4 / 100 at 68.5°C for 76 seconds (first crosslinking step). Next, it was immersed in an aqueous solution with a potassium iodide / boric acid / zinc chloride / water mass ratio of 3 / 5.5 / 0.6 / 100 at 45°C for 11 seconds (second crosslinking step, metal ion treatment step). Afterward, it was immersed in a washing bath and washed (washing step), and then dried at 38°C (drying step) to obtain a 12 μm thick polarizing element with iodine adsorbed and oriented in the PVA. The extension was mainly carried out during the dyeing and first cross-linking steps, with a total extension ratio of 5.85. The resulting polarizing element contained 0.17% zinc ions and 4.62% boron by mass.

[0119] (Preparation of PVA solution for adhesive) 50g of a modified PVA resin containing acetyl groups (manufactured by Mitsubishi Chemical Corporation: GOHSENX Z-410) 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.

[0120] (Adhesive 1 to 3 are used to prepare the polarizing plate) Using the contents of PVA, urea, glyoxal, and maleic acid as shown in Table 1, prepare adhesives 1 to 3 by mixing PVA solution, urea, a commercially available 40% glyoxal solution, maleic acid, and pure water. The adhesives are used 3 days after preparation.

[0121] [Table 1]

[0122] (Saponification of cellulose acetylated membranes) A commercially available cellulose ester membrane, TJ40UL (manufactured by Fuji Film Co., Ltd.: 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 a water wash. Afterward, the membrane was immersed in a 0.05 mol / L sulfuric acid aqueous solution at 25°C for 30 seconds, and then washed under running water for 30 seconds to neutralize the membrane. Next, the membrane was dehydrated three times using an air knife. After dehydration, the membrane was held in a drying zone at 70°C for 15 seconds and dried to produce a saponified membrane.

[0123] (Fabrication of polarizing plates 1 to 3) The saponified cellulose acetate film prepared above was bonded to both sides of polarizing element 1 using a roller laminator, with adhesive 1 stored for 3 days in between. After drying at 80°C for 5 minutes, polarizing plate 1 was obtained. The adhesive layer system was adjusted so that the thickness of both sides after drying was 50 nm.

[0124] In the fabrication of polarizing plate 1, adhesive 1 is replaced with adhesive 2 to 3 to obtain polarizing plate 2 to 3.

[0125] (Adjustment of moisture content in polarizing plate (polarizing element)) The polarizing plates 1 to 3 obtained above were stored at 20°C and relative humidity of 30%, 35%, 40%, 45%, 50%, or 55% for 72 hours. The moisture content was determined using the Karl Fischer method after 66, 69, and 72 hours of storage. Even under any humidity condition, the moisture content remained unchanged after 66, 69, and 72 hours of storage. Therefore, the moisture content of polarizing plates 1 to 3 can be considered to be the same as the equilibrium moisture content of the 72-hour storage environment used in this experimental example. When the moisture content of a polarizing plate reaches equilibrium in a certain storage environment, it is also the same as the moisture content of the polarizing element within the polarizing plate, and can be considered to have reached equilibrium in that storage environment. Furthermore, when the moisture content of the polarizing element within the polarizing plate reaches equilibrium in a certain storage environment, it is also the same as the moisture content of the polarizing plate, and can be considered to have reached equilibrium in that storage environment.

[0126] (Adjustment of moisture content for polarizing plates 1 to 3) The moisture content of polarizers 1 to 3 was adjusted by storing them at 20°C and 55% relative humidity for 72 hours to achieve an equilibrium moisture content of 55% in the environment.

[0127] <High Temperature Durability Assessment> (Preparation of test samples for evaluation) For polarizing plates 1 to 3 with adjusted moisture content, an acrylic adhesive (manufactured by Lintec Corporation, part number: #7) is formed on both sides. The plates are then cut into 50mm × 100mm sizes with the absorption axis parallel to the long side. Alkali-free glass (manufactured by CORNING Corporation, "EAGLE XG") is then bonded to the adhesive surface to create evaluation samples.

[0128] <Single-cell penetration rate assessment (105℃)> Evaluation samples of polarizing plates 1 to 3 were subjected to autoclave treatment at 50°C and 5 kgf / cm² (490.3 kPa) for 1 hour, followed by 24 hours of storage at 23°C and 55% relative humidity. After this, the transmittance (initial value) of the evaluation samples of polarizing plates 1 to 3 was measured, and they were stored at 105°C. Transmittance was measured every 50 hours from 100 to 200 hours. For the initial value, the time when the transmittance decreased by more than 5% was used as the benchmark, and the evaluation was performed according to the following criteria. The results are presented in Table 2. At the 200-hour mark, those with a penetration rate decrease of less than 5% are: A For those whose penetration rate decreases by more than 5% after 150 to 200 hours: B For those whose penetration rate decreases by more than 5% after 100 to 150 hours: C Those whose penetration rate decreases by more than 5% after 100 hours: D

[0129] <Water Resistance Assessment (Warm Water Immersion Test)> The water resistance test in this embodiment was conducted according to the water resistance test described in Japanese Patent Application Publication No. 2009-025728

[0060] . An acrylic adhesive (manufactured by LINTEC Co., Ltd., No.: #7) was formed on one side of the polarizing plate prepared above. Then, the plate was cut into strips of 50mm × 20mm with the absorption axis (extension direction) as the long side, and the dimensions in the long side direction were accurately measured. Here, the evaluation sample is due to the iodine adsorbed by the polarizing element, which covers the entire surface and uniformly presents a unique color. Holding the sample along one short side with a gripper, approximately 80% of its length is immersed in a water bath at 60°C for 4 hours. Afterward, the sample is removed from the water bath and the moisture is wiped off. Immersion in warm water causes the polarizing element of the polarizing plate to shrink. The degree of shrinkage of the polarizing element is measured at the center of the short side of the sample. The evaluation is performed in three stages according to the following criteria, by measuring the distance from the end of the sample (the end of the protective film) to the end of the shrunken polarizing element. The results are presented in Table 2. For samples where the distance from the end of the sample to the end of the polarizing element is less than 1 mm: A For samples where the distance from the end of the sample to the end of the polarizing element exceeds 1 mm but is less than 3 mm: B For samples where the distance from the end of the sample to the end of the polarizing element is greater than 3 mm: C

[0130] [Table 2]

[0131] Compared to polarizing plates with adhesives that do not contain urea, polarizing plates with adhesives containing compound 1 (urea), compound 2 (glyoxal), and compound 3 (maleic acid) do not show a significant decrease in transmittance even when exposed to a high temperature of 105°C, and exhibit excellent high-temperature durability. Furthermore, even for any single adhesive, polarizing plates manufactured after being stored for 3 days show excellent water resistance and possess a sufficient production lifespan.

Claims

1. A method for manufacturing a polarizing plate, comprising: a step of preparing an adhesive containing a first compound, a second compound, and a third compound; and a step of bonding a polarizing element to a transparent protective film using an adhesive layer formed by applying the aforementioned adhesive; wherein, The aforementioned polarizing plate comprises: the aforementioned polarizing element, which is formed by adsorbing and orienting dichroic pigments in a polyvinyl alcohol-based resin layer; and the aforementioned transparent protective film, which is deposited on at least one side of the aforementioned polarizing element; the aforementioned first compound is selected from at least one of the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives; the aforementioned second compound is a dialdehyde; the aforementioned third compound is a dicarboxylic acid; in the aforementioned adhesive, the content of the aforementioned second compound is 20 parts by mass or less relative to 1 part by mass of the aforementioned first compound; and the aforementioned adhesive comprises a polyvinyl alcohol-based resin.

2. The method for manufacturing a polarizing plate as described in claim 1, wherein, In the aforementioned adhesive, the content of the aforementioned third compound is 0.01 parts by mass or more and 400 parts by mass or less, relative to 100 parts by mass of the aforementioned polyvinyl alcohol resin.

3. The method for manufacturing a polarizing plate as described in claim 1, wherein, In the aforementioned adhesive, the content of the aforementioned second compound is 10.0 parts by mass or more and 60 parts by mass or less, relative to 100 parts by mass of the aforementioned polyvinyl alcohol resin.

4. A method for manufacturing a polarizing plate as described in any one of claims 1 to 3, wherein, In the aforementioned adhesive, the content of the 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.

5. A method for manufacturing a polarizing plate as described in any one of claims 1 to 3, wherein, In the aforementioned adhesive, the content of the aforementioned second compound is 0.03 parts by mass or more and 20 parts by mass or less, relative to 1 part by mass of the aforementioned first compound.

6. A method for manufacturing a polarizing plate as described in any one of claims 1 to 3, wherein, The aforementioned dialdehyde is glyoxal.

7. A method for manufacturing a polarizing plate as described in any one of claims 1 to 3, wherein, The thickness of the aforementioned adhesive layer is between 0.01 μm and 7 μm.

8. A method for manufacturing an image display device including a polarizing plate, comprising: obtaining a polarizing plate by means of the method for manufacturing a polarizing plate according to any one of claims 1 to 7; and in the aforementioned image display device, disposing a solid layer in contact with both sides of the aforementioned polarizing plate.

9. A method for manufacturing an image display device as described in claim 8, wherein, The aforementioned image display device includes: an image display unit, a first adhesive layer deposited on the recognition side surface of the aforementioned image display unit, and the aforementioned polarizing plate deposited on the recognition side surface of the aforementioned first adhesive layer.

10. A method for manufacturing an image display device as described in claim 9, wherein, The aforementioned image display device 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. A method for manufacturing an image display device as described in claim 10, wherein, The aforementioned transparent component is a glass plate or a transparent resin plate.

12. A method for manufacturing an image display device as described in claim 10, wherein, The aforementioned transparent component is a touch panel.

13. An adhesive comprising a polyvinyl alcohol-based resin, used for bonding polarizing elements and protective films; wherein, The aforementioned polarizing element is formed by adsorbing and orienting dichroic pigments in a polyvinyl alcohol-based resin layer. The aforementioned adhesive contains a first compound, a second compound, and a third compound. The first compound is selected from at least one of the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives. The second compound is a dialdehyde, and the third compound is a dicarboxylic acid. The content of the second compound is 20 parts by mass or less relative to 1 part by mass of the first compound.