Polarizing plate and image display device using the polarizing plate

Abstract

To provide a novel polarizing plate which comprises an adhesive layer formed of an adhesive having a sufficient pot life for manufacturing and suppresses a reduction in transmittance when exposed to a high-temperature environment.SOLUTION: A polarizing plate provided herein comprises a polarizing element obtained by adsorbing and aligning a dichroic pigment in a polyvinyl alcohol resin layer and a transparent protective film stacked on at least one surface of the polarizing element, the polarizing element and the transparent protective film being bonded via an adhesive layer formed of an adhesive containing a first compound, a second compound, and a third compound. The first compound is at least one substance selected from a group consisting of urea, urea derivatives, thiourea, and thiourea derivatives. The second compound is dialdehyde. The third compound is dicarboxylic acid.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a polarizing plate and an image display device.

Background Art

[0002] Liquid crystal display devices (LCDs) are widely used not only in liquid crystal televisions but also in mobile devices such as personal computers and mobile phones, and in-vehicle applications such as car navigation systems. Usually, a liquid crystal display device has a liquid crystal panel in which polarizing plates are bonded to both sides of a liquid crystal cell with an adhesive, and display is performed by controlling light from a backlight with the liquid crystal panel. In recent years, organic EL display devices are also widely used in mobile applications such as televisions and mobile phones, and in-vehicle applications such as car navigation systems, in the same manner as liquid crystal display devices. In an organic EL display device, in order to prevent external light from being reflected by a metal electrode (cathode) and being visually recognized like a mirror, a circular polarizing plate (a laminate including a polarizing element and a λ / 4 plate) may be disposed on the visual recognition side surface of an image display panel.

[0003] In a polarizing plate, a polyvinyl alcohol-based resin adhesive is used for bonding a polarizing element and a protective film because good adhesiveness can be obtained. However, in Patent Document 1 (Japanese Patent Application Laid-Open No. 2005-189615), it is pointed out that a sufficient pot life cannot be obtained with a polyvinyl alcohol-based resin adhesive. Not obtaining a pot life means that the usable life of the adhesive is short. In Patent Document 2 (Japanese Patent Application Laid-Open No. 2010-276673), it is described that a sufficient pot life for production can be obtained by using an adhesive to which maleic acid is added together with a crosslinking agent.

[0004] As described above, polarizing plates are increasingly being mounted in vehicles as components of image display devices such as liquid crystal display devices and organic EL display devices. A polarizing plate used in an in-vehicle image display device is often exposed to a high-temperature environment compared to mobile applications such as televisions and mobile phones, and thus is required to have smaller characteristic changes at higher temperatures (high-temperature durability).

[0005] On the other hand, to prevent damage to the image display panel from impacts from the outer surface, there is an increasing trend to install a front panel (also called a "window layer") made of transparent resin or glass on the viewing side of the image display panel. In image display devices equipped with touch panels, a configuration in which the touch panel is located on the viewing side of the image display panel, and the front panel is located even further on the viewing side of the touch panel, is widely adopted.

[0006] In such configurations, if an air layer exists between the image display panel and transparent components such as the front panel or touch panel, reflection of external light occurs at the air layer interface, tending to reduce the visibility of the screen. Therefore, there is a growing trend to adopt a configuration in which the space between the polarizing plate and the transparent component, which is placed on the viewing surface of the image display panel, is filled with a layer other than the air layer, which is usually a solid layer (hereinafter sometimes referred to as "interlayer filler") (hereinafter sometimes referred to as "interlayer-filled configuration"). The interlayer filler is preferably a material with a refractive index close to that of the polarizing plate or transparent component. As the interlayer filler, adhesives or UV-curing adhesives are used to suppress the reduction in visibility due to reflection at the interface and to bond and fix each component together (see, for example, Japanese Patent Application Publication No. 11-174417 (Patent Document 3)).

[0007] Interlayer-filled construction is gaining popularity in mobile applications such as mobile phones, which are often used outdoors. Furthermore, due to the increasing demand for visibility in recent years, interlayer-filled construction is being considered for in-vehicle applications such as car navigation systems, where a transparent front plate is placed on the surface of the image display panel, and the space between the panel and the transparent front plate is filled with an adhesive layer or the like.

[0008] However, it has been reported that when such a configuration is adopted, the transmittance of the polarizing plate decreases significantly in high-temperature environments. Japanese Patent Publication No. 2014-102353 (Patent Document 4) proposes a method to suppress the decrease in transmittance by keeping the amount of water per unit area of ​​the polarizing plate below a predetermined amount and keeping the saturation water absorption amount of the transparent protective film adjacent to the polarizing element below a predetermined amount as a solution to this problem. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2005-189615 [Patent Document 2] Japanese Patent Publication No. 2010-276673 [Patent Document 3] Japanese Patent Application Publication No. 11-174417 [Patent Document 4] Japanese Patent Publication No. 2014-102353 [Overview of the project] [Problems that the invention aims to solve]

[0010] The present invention aims to provide a novel polarizing plate having an adhesive layer formed from an adhesive with a sufficient pot life for production, and in which the decrease in transmittance when exposed to a high-temperature environment is suppressed, an image display device using the polarizing plate, and an adhesive. [Means for solving the problem]

[0011] The present invention provides a polarizing plate and an image display device as illustrated below. [1] A polarizing plate having a polarizing element in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin layer, and a transparent protective film laminated on at least one surface of the polarizing element, The polarizing element and the 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 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, and the polarizer is a polarizer. [2] The polarizing plate according to [1], wherein the adhesive contains a polyvinyl alcohol-based resin. [3] The polarizing plate according to [2], wherein the content of the third compound in the adhesive is 0.01 parts by mass or more and 400 parts by mass or less per 100 parts by mass of the polyvinyl alcohol-based resin. [4] The polarizing plate according to [2] or [3], wherein the content of the first compound in the adhesive is 0.1 parts by mass or more and 400 parts by mass or less per 100 parts by mass of the polyvinyl alcohol-based resin. [5] The polarizing plate according to any one of [2] to [4], wherein the content of the second compound in the adhesive is 0.03 parts by mass or more and 20 parts by mass or less per 1 part by mass of the first compound. [6] The polarizing plate according to any one of [1] to [5], wherein the dialdehyde is glyoxal. [7] The polarizing plate according to any one of [1] to [6], wherein the adhesive layer has a thickness of 0.01 μm or more and 7 μm or less. [8] The polarizing plate is used in an image display device, The polarizing plate according to any one of [1] to [7], wherein a solid layer is provided in contact with both sides of the polarizing plate in the image display device. [9] An image display device comprising an image display cell, a first adhesive layer laminated on the viewing-side surface of the image display cell, and a polarizing plate according to any one of [1] to [8] laminated on the viewing-side surface of the first adhesive layer.

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

[11] The image display device according to

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

[12] The image display device according to

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

[13] Containing the first compound, the second compound, and the third compound, 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, an adhesive. [Advantages of the Invention]

[0012] According to the present invention, it is possible to provide a polarizing plate having an adhesive layer formed of an adhesive having a sufficient pot life in production and suppressing a decrease in transmittance when exposed to a high-temperature environment. Furthermore, by using the polarizing plate according to the present invention, it is possible to provide an image display device in which a decrease in transmittance is suppressed even when exposed to a high-temperature environment. [Embodiments for Carrying Out the Invention]

[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 according to an embodiment of the present invention includes 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 together by an adhesive layer formed of 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] As a conventional polarizing plate excellent in high-temperature durability, for example, there is known a polarizing plate in which a decrease in transmittance is suppressed even when left in an environment at a temperature of 95°C for 1000 hours with the polarizing plate alone. However, even with such a polarizing plate, when used in an interlayer filling configuration, a significant decrease in transmittance may be observed at the center of the in-plane of the polarizing plate when left in an environment at a temperature of 105°C. A significant decrease in the transmittance of the polarizing plate in a high-temperature environment is considered to be a particularly likely problem when an image display device adopting an interlayer filling configuration in which one surface of the polarizing plate is bonded to an image display cell and the other surface is bonded to a transparent member such as a touch panel or a front panel is exposed to a high-temperature environment.

[0017] Polarizing plates with significantly reduced transmittance due to their interlayer-filled construction showed a transmittance of 1100 cm² in Raman spectroscopy measurements. -1 Nearby (=CC= derived from the combination) and 1500cm -1 The presence of a peak in the vicinity (derived from the -C=C- bond) indicates a polyene structure (-C=C). n - is thought to be formed. The polyene structure is presumed to be produced when the polyvinyl alcohol constituting the polarizing element is dehydrated and converted into a polyene (Patent Document 4, paragraph

[0012] ).

[0018] The polarizing plate according to the present invention can further improve high-temperature durability. When incorporated into an image display device with an interlayer-filled structure, the polarizing plate according to the present invention can suppress a decrease in transmittance even when exposed to a high-temperature environment of, for example, 105°C. This effect is presumed to be due to the synergistic action of the first compound, the second compound, and the third compound present in the adhesive layer, which suppresses the polyene conversion of the polyvinyl alcohol constituting the polarizing element. This effect is not limited to cases where the water content of the polarizing plate is low, but is also achieved when the water content of the polarizing plate is high.

[0019] The polarizing plate according to the present invention preferably has at least one of the following features (a) and (b). (a) The moisture content of the polarizing element is equal to or greater than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30%, and less than or equal to the equilibrium moisture content at a temperature of 20°C and a relative humidity of 70%. (b) The moisture content of the polarizing plate is equal to or greater than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30%, and equal to or less than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 70%.

[0020] <Polarizing element> As a polarizing element in which a dichroic dye is adsorbed and oriented on a layer containing a polyvinyl alcohol (hereinafter also referred to as "PVA") resin (hereinafter also referred to as "PVA resin layer"), well-known polarizing elements can be used. Examples of polarizing elements include a stretched film obtained by dyeing a PVA resin film with a dichroic dye and uniaxially stretching it, and a stretched layer obtained by using a laminated film having a coated layer formed by applying a coating solution containing a PVA resin to a base film, dyeing the coated layer with a dichroic dye, and uniaxially stretching the laminated film. Stretching may be performed after dyeing with the dichroic dye, stretching while dyeing, or dyeing after stretching.

[0021] PVA-based resins are obtained by saponifying polyvinyl acetate-based resins. Examples of polyvinyl acetate-based resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, as well as copolymers of vinyl acetate with other monomers copolymerizable thereto. Examples of other copolymerizable monomers include unsaturated carboxylic acids, olefins such as ethylene, vinyl ethers, and unsaturated sulfonic acids.

[0022] The PVA resin layer is preferably formed from a PVA resin having a boron adsorption rate of 5.70% by mass or more. That is, the boron adsorption rate of the PVA resin at the raw material stage before dyeing or stretching is 5.70% by mass or more. By using such a PVA resin, the transmittance is less likely to decrease even when exposed to high-temperature environments such as 105°C. Furthermore, it is preferable that the boron adsorption rate of the PVA resin be 10% by mass or less. By using such a PVA resin to manufacture polarizing elements, it is possible to avoid high concentrations of boric acid in the boric acid treatment tank and shorten the treatment time for boric acid treatment, making it easier to obtain the desired polarizing element and increasing the productivity of polarizing elements. When the boron adsorption rate of the PVA resin is 10% by mass or less, an appropriate amount of boron is incorporated into the PVA resin layer, making it easier to reduce the shrinkage force of the polarizing element. As a result, when incorporated into an image display device, problems such as delamination between the polarizing plate and other components such as the front plate are less likely to occur. The boron adsorption rate of PVA resin can be measured by the method described in the examples below.

[0023] The boron adsorption rate of PVA resins is a characteristic that reflects the spacing between molecular chains and the crystal structure within the PVA resin. PVA resins with a boron adsorption rate of 5.70% by mass or higher are thought to have wider spacing between molecular chains and fewer crystals in the PVA resin compared to PVA resins with a boron adsorption rate of less than 5.70% by mass. Therefore, it is presumed that boron, primary metal ions, and secondary metal ions can more easily penetrate into the PVA resin layer, making it easier to prevent polyene formation in high-temperature environments.

[0024] The boron adsorption rate of PVA resin can be adjusted, for example, by performing pretreatments on the PVA resin before manufacturing polarizing elements, such as hot water treatment, acidic solution treatment, ultrasonic irradiation, or radiation irradiation. These treatments can widen the spacing between molecular chains or disrupt the crystal structure in the PVA resin. Examples of hot water treatment include immersion in pure water at 30°C to 100°C for 1 to 90 seconds and drying. Examples of acidic solution treatment include immersion in a boric acid aqueous solution with a concentration of 10% to 20% by mass for 1 to 90 seconds and drying. Examples of ultrasonic treatment include irradiation 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 a solvent such as water.

[0025] The degree of saponification of the PVA resin is preferably about 85 mol% or more, more preferably about 90 mol% or more, and even more preferably about 99 mol% or more and 100 mol% or less. The degree of polymerization of the PVA resin is, for example, 1000 or more and 10000 or less, preferably 1500 or more and 5000 or less. The PVA resin may be modified, for example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral, etc., modified with aldehydes.

[0026] The thickness of the polarizing element is preferably 3 μm to 35 μm, more preferably 4 μm to 30 μm, and even more preferably 5 μm to 25 μm. A polarizing element thickness of 35 μm or less suppresses the effect of polyene formation of the PVA resin on the degradation of optical properties under high-temperature environments. A polarizing element thickness of 3 μm or more facilitates the creation of a configuration that achieves desired optical properties.

[0027] The polarizing element preferably contains 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 from an adhesive containing the first compound, the second compound, and the third compound. Therefore, it is presumed that a portion of the first compound, the second compound, and the third compound that migrated from the adhesive layer are contained in the polarizing element. The first compound, the second compound, and the third compound in the polarizing element may include those added during the manufacturing process of the polarizing element. By providing an adhesive layer containing the first compound, the second compound, and the third compound, the transmittance is less likely to decrease even when the polarizing plate is exposed to a high-temperature environment. Furthermore, by providing an adhesive layer containing the first compound, the second compound, and the third compound, a decrease in the degree of polarization can be suppressed even when the polarizing plate is exposed to a high-temperature environment. When two polarizing plates are used in a crossed nicol relationship, a decrease in the degree of polarization of the polarizing plate makes it easier for light leakage (hereinafter also referred to as "cross leakage") to occur. However, according to the present invention, the degree of polarization is less likely to decrease even when exposed to a high-temperature environment, so cross leakage is also easier to suppress. It is presumed that the polyene formation of the PVA resin is suppressed due to the synergistic effect of the first, second, and third compounds contained in the polarizing element.

[0028] Methods for incorporating the first, second, and third compounds during the manufacturing of polarizing elements include immersing a PVA-based resin layer in a processing solvent containing the first and / or second and / or third compounds, or spraying, flowing, or dropping the processing solvent onto the PVA-based resin layer. Among these, the method of immersing a PVA-based resin layer in a processing solvent containing all three compounds is preferred. Specific examples of the first, second, and third compounds are those exemplified as being included in adhesives, as described later.

[0029] The step of immersing the PVA-based resin layer in a processing solvent containing the first, second, and third compounds may be performed simultaneously with the swelling, stretching, dyeing, crosslinking, and washing steps in the polarizing element manufacturing method described later, or it may be performed separately from these steps. The step of incorporating the first, second, and third compounds into the PVA-based resin layer is preferably performed after dyeing the PVA-based resin layer with iodine, and more preferably simultaneously with the crosslinking step after dyeing. With this method, hue change is small, and the impact on the optical properties of the polarizing element can be reduced.

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

[0031] (1st compound) The first compound is at least one selected from 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 water-soluble or poorly water-soluble, and either type can be used. When using a poorly water-soluble first compound in a water-soluble adhesive, it is preferable to devise a dispersion method to prevent haze formation and other issues after the adhesive layer is formed.

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

[0033] Specific examples of urea derivatives include monosubstituted ureas such as methylurea, ethylurea, propylurea, butylurea, isobutylurea, N-octadecylurea, 2-hydroxyethylurea, hydroxyurea, acetylurea, allylurea, 2-propynylurea, cyclohexylurea, phenylurea, 3-hydroxyphenylurea, (4-methoxyphenyl)urea, benzylurea, benzoylurea, o-tolylurea, and p-tolylurea.

[0034] Examples of disubstituted ureas include 1,1-dimethylurea, 1,3-dimethylurea, 1,1-diethylurea, 1,3-diethylurea, 1,3-bis(hydroxymethyl)urea, 1,3-tert-butylurea, 1,3-dicyclohexylurea, 1,3-diphenylurea, 1,3-bis(4-methoxyphenyl)urea, 1-acetyl-3-methylurea, 2-imidazolidinone (ethyleneurea), and tetrahydro-2-pyrimidinone (propyleneurea).

[0035] Examples of 4-substituted ureas include tetramethylurea, 1,1,3,3-tetraethylurea, 1,1,3,3-tetrabutylurea, 1,3-dimethoxy-1,3-dimethylurea, 1,3-dimethyl-2-imidazolidinone, and 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone.

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

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

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

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

[0040] Among the first compounds, urea derivatives or thiourea derivatives are preferred, and urea derivatives are more preferred, because when used in an interlayer-packed image display device, the decrease in transmittance in high-temperature environments is suppressed and the decrease in polarization degree is small (cross-cutting is suppressed). Among urea derivatives, monosubstituted urea or disubstituted urea is preferred, and monosubstituted is more preferred. Disubstituted ureas include 1,1-substituted urea and 1,3-substituted urea, but 1,3-substituted urea is more preferred.

[0041] (Second compound) The second compound is a dialdehyde. Examples of dialdehydes include glyoxal, propanedial (malondialdehyde), and butanedial (succinaldehyde). Glyoxal is particularly preferred due to its simple structure and high reactivity. While glyoxal may be described in the following, conventionally known dialdehydes can be used as described above, and the explanation is not limited to glyoxal.

[0042] (Third compound) The third compound is a dicarboxylic acid. Examples of dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, tartaric acid, glutamic acid, malic acid, maleic acid, fumaric acid, itaconic acid, muconic 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, diphenylsulfondicarboxylic acid, diphenylmethanedicarboxylic acid, oxaloacetic acid, methylfumaric acid, and 2,6-pyridinedicarboxylic acid. Among these, citric acid, malic acid, maleic acid, or tartaric acid are preferred. These dicarboxylic acids can be used individually or in combination of two or more.

[0043] Polarizing elements typically contain potassium ions (also called "first metal ions"), and preferably also contain other metal ions (also called "second metal ions"). The content of second metal ions in the polarizing element is preferably 0.05% by mass or more and 10.0% by mass or less, more preferably 0.05% by mass or more and 8.0% by mass or less, and even more preferably 0.1% by mass or more and 6.0% by mass or less. If the content of second metal ions in the polarizing element exceeds 10.0% by mass, the degree of polarization may decrease in high-temperature and high-humidity environments. Also, if the content of second metal ions is less than 0.05% by mass, the effect of improving durability in high-temperature environments may not be sufficient. The content of second metal ions in the polarizing element can be calculated, for example, as the mass fraction (mass%) of the metal element relative to the mass of the polarizing element by inductively coupled plasma (ICP) emission spectroscopy. Metal elements are thought to exist in polarizing elements either as metal ions or in a cross-linked structure with components of the polyvinyl alcohol-based resin. However, the content of secondary metal ions referred to here is the value as metal atoms.

[0044] The second metal ion is not limited to any metal ion other than potassium ions, but is preferably a metal ion other than an alkali metal, and is particularly preferably a transition metal ion such as cobalt, nickel, zinc, chromium, aluminum, copper, manganese, or iron, from the viewpoint of color adjustment and imparting durability. Among these metal ions, zinc ions are preferred from the viewpoint of color adjustment and imparting heat resistance.

[0045] The boron content of the polarizing element is preferably 2.4% by mass or more. Furthermore, the boron content is preferably 3.9% by mass or more and 8.0% by mass or less, more preferably 4.2% by mass or more and 7.0% by mass or less, and even more preferably 4.4% by mass or more and 6.0% by mass or less. If the boron content of the polarizing element exceeds 8.0% by mass, the shrinkage force of the polarizing element increases, which may cause problems such as delamination between the polarizing element and other components such as the front plate to which it is bonded when incorporated into an image display device. Also, if the boron content is less than 2.4% by mass, the desired optical properties may not be achieved. The boron content in the polarizing element can be calculated, for example, as the mass fraction (mass%) of boron relative to the mass of the polarizing element by inductively coupled plasma (ICP) emission spectroscopy. Boron is thought to exist in the polarizing element in the form of boric acid or in a cross-linked structure with components of the polyvinyl alcohol-based resin, but the boron content referred to here is the value as boron atoms (B).

[0046] When the boron content of the polarizing element is between 2.4% by mass and 8.0% by mass, the decrease in transmittance is further suppressed even when exposed to high-temperature environments as a component of an interlayer-filled image display device. This is presumed to be because, when the boron content of the polarizing element is between 2.4% by mass and 8.0% by mass, polyene formation is less likely to occur even in high-temperature environments, thus suppressing the decrease in transmittance.

[0047] The potassium ion content 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, from the viewpoint of suppressing the deterioration of the optical properties of the polarizing element in a high-temperature environment. Furthermore, from the viewpoint of suppressing hue change in a high-temperature environment, 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 potassium ion content can be measured in the same way as the content of the second metal ion, and the potassium ion content referred to here is the value as potassium atoms.

[0048] (Manufacturing method for polarizing elements) While there are no particular limitations on the manufacturing method of polarizing elements, typical methods include feeding out a pre-wound PVA resin film and performing stretching, dyeing, crosslinking, etc. (hereinafter referred to as "manufacturing method 1"), and a method that includes the step of applying a coating solution containing PVA resin onto a base film to form a PVA resin layer, which is a coating layer, and then stretching the resulting laminate (hereinafter referred to as "manufacturing method 2").

[0049] Manufacturing method 1 can be produced by following the steps of: uniaxial stretching of a PVA-based resin film; dyeing the PVA-based resin film with a dichroic dye such as iodine and adsorbing the dichroic dye; treating the PVA-based resin film on which the dichroic dye has been adsorbed with a boric acid aqueous solution; and washing with water after treatment with the boric acid aqueous solution.

[0050] The swelling process is a treatment process in which the PVA resin film is immersed in a swelling bath. The swelling process can remove dirt and blocking agents from the surface of the PVA resin film, and can also suppress uneven dyeing by swelling the PVA resin film. Typically, a water-based medium such as water, distilled water, or pure water is used as the swelling bath. The swelling bath may also have surfactants, alcohol, etc., added as appropriate according to conventional methods. From the viewpoint of controlling the potassium content of the polarizing element, potassium iodide may 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 temperature of the swelling bath is preferably between 10°C and 60°C, more preferably between 15°C and 45°C, and even more preferably between 18°C ​​and 30°C. The immersion time in the swelling bath cannot be determined definitively because the degree of swelling of the PVA resin film is affected by the temperature of the swelling bath, but it is preferably between 5 seconds and 300 seconds, more preferably between 10 seconds and 200 seconds, and even more preferably between 20 seconds and 100 seconds. The swelling process may be performed only once, or multiple times as needed.

[0052] The dyeing process involves immersing a PVA-based resin film in a dyeing bath (iodine solution), which allows for the adsorption and orientation of dichroic dyes such as iodine onto the PVA-based resin film. The iodine solution is usually preferably an aqueous iodine solution and contains iodine and iodide as a solubilizing 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 preferred from the viewpoint of controlling the potassium content in the polarizing element.

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

[0054] The temperature of the dyeing bath is preferably between 10°C and 50°C, more preferably between 15°C and 45°C, and even more preferably between 18°C ​​and 30°C. The immersion time in the dyeing bath cannot be determined definitively because the degree of dyeing of the PVA resin film is affected by the temperature of the dyeing bath, but it is preferably between 10 seconds and 300 seconds, and more preferably between 20 seconds and 240 seconds. The dyeing process may be performed only once, or multiple times as needed.

[0055] The crosslinking process involves immersing the PVA-based resin film, dyed in the dyeing process, in a treatment bath (crosslinking bath) containing a boron compound. The boron compound crosslinks the polyvinyl alcohol-based resin film, allowing iodine molecules 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 it may also be a mixed solution of a water-miscible organic solvent and 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 about 1% by mass or more and 15% by mass or less, more preferably about 1.5% by mass or more and 10% by mass or less, and even more preferably about 2% by mass or more and 5% by mass or less. When potassium iodide is used in the crosslinking bath, the concentration of potassium iodide in the crosslinking bath is preferably about 1% by mass or more and 15% by mass or less, more preferably about 1.5% by mass or more and 10% by mass or less, and even more preferably about 2% by mass or more and 5% by mass or less.

[0057] The temperature of the crosslinking bath is preferably between 20°C and 70°C, and more preferably between 30°C and 60°C. The immersion time in the crosslinking bath cannot be determined definitively because the degree of crosslinking of the PVA resin film is affected by the temperature of the crosslinking bath, but it is preferably between 5 seconds and 300 seconds, and more preferably between 10 seconds and 200 seconds. The crosslinking process may be performed only once, or multiple times as necessary.

[0058] The stretching process is a process in which a PVA-based resin film is stretched to a predetermined magnification in at least one direction. Generally, the PVA-based resin film is uniaxially stretched in the transport direction (longitudinal direction). The stretching method is not particularly limited, and either wet stretching or dry stretching can be used. The stretching process may be performed only once, or multiple times as needed. The stretching process may be performed at any stage in the manufacturing of the polarizing element.

[0059] In the wet stretching method, the treatment bath (stretching bath) can usually be a solvent such as water or a mixed solution of a water-miscible organic solvent and water. The stretching bath preferably contains potassium iodide from the viewpoint of controlling the potassium content in the polarizing element. When potassium iodide is used in the stretching bath, the concentration of potassium iodide in the stretching bath is preferably about 1% by mass or more and 15% by mass or less, more preferably about 2% by mass or more and 10% by mass or less, and more preferably about 3% by mass or more and 6% by mass or less. The treatment bath (stretching bath) may contain a boron compound from the viewpoint of suppressing film breakage during stretching. When a boron compound is included, the concentration of the boron compound in the stretching bath is preferably about 1% by mass or more and 15% by mass or less, more preferably about 1.5% by mass or more and 10% by mass or less, and more preferably about 2% by mass or more and 5% by mass or less.

[0060] The temperature of the stretching bath is preferably 25 to 80°C, more preferably 40 to 80°C, even more preferably 50 to 75°C, and particularly preferably 65 to 75°C. The immersion time in the stretching bath cannot be determined definitively because the degree of stretching of the PVA resin film is affected by the temperature of the stretching bath, but it is preferably 10 seconds to 800 seconds, and more preferably 30 seconds to 500 seconds. The stretching treatment in the wet stretching method may be performed together with one or more of the following treatment steps: swelling, dyeing, crosslinking, and washing.

[0061] Examples of dry stretching methods include the inter-roll stretching method, the heated roll stretching method, and the compression stretching method. The dry stretching method may also be performed in conjunction with the drying process.

[0062] The total stretching ratio (cumulative stretching ratio) applied to the polyvinyl alcohol-based resin film can be set appropriately depending on the purpose, but it is preferably between 2 and 7 times, more preferably between 3 and 6.8 times, and even more preferably between 3.5 and 6.5 times.

[0063] The cleaning process involves immersing the polyvinyl alcohol-based resin film in a cleaning bath, which removes any foreign matter remaining on the surface of the polyvinyl alcohol-based resin film. The cleaning bath 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 preferable to use potassium iodide in the cleaning bath. In this case, the concentration of potassium iodide in the cleaning bath is preferably 1% by mass or more and 10% by mass or less, more preferably 1.5% by mass or more and 4% by mass or less, and even more preferably 1.8% by mass or more and 3.8% by mass or less.

[0064] The temperature of the washing bath is preferably between 5°C and 50°C, more preferably between 10°C and 40°C, and even more preferably between 15°C and 30°C. The immersion time in the washing bath cannot be determined definitively because the degree of cleaning of the PVA resin film is affected by the temperature of the washing bath, but it is preferably between 1 second and 100 seconds, more preferably between 2 seconds and 50 seconds, and even more preferably between 3 seconds and 20 seconds. The washing process may be performed only once, or multiple times as needed.

[0065] Furthermore, it is preferable that the process includes a metal ion treatment step, either within or separately from the above-described steps. The metal ion treatment step is performed by immersing the polyvinyl alcohol-based resin film in an aqueous solution containing a metal salt of a second metal ion. The metal ion treatment step incorporates the second metal ion into the polyvinyl alcohol-based resin film.

[0066] The second metal ion is not limited to any metal ion other than potassium ions, but is preferably a metal ion other than an alkali metal, and is particularly preferably a transition metal ion such as cobalt, nickel, zinc, chromium, aluminum, copper, manganese, or iron, from the viewpoint of color adjustment and imparting durability. Among these metal ions, zinc ions are preferred from the viewpoint of color adjustment and imparting heat resistance. Examples of zinc salts include zinc chloride, zinc halides such as zinc iodide, zinc sulfate, and zinc acetate.

[0067] Metal ion treatment processes utilize metal salt solutions. Below, we will describe a typical example of a metal ion treatment process using a zinc salt aqueous solution: immersion in a zinc-containing solution.

[0068] The concentration of zinc ions in the zinc salt aqueous solution is approximately 0.1 to 10% by mass, preferably in the range of 0.3 to 7% by mass. Furthermore, it is preferable to use an aqueous solution containing potassium ions and iodide ions, such as potassium iodide, as this facilitates the impregnation of zinc ions. The concentration of potassium iodide in the zinc salt solution is preferably approximately 0.1 to 10% by mass, and more preferably 0.2 to 5% by mass.

[0069] When immersing the polyvinyl alcohol-based resin film in a zinc-containing solution, the temperature of the zinc salt solution is usually around 15 to 85°C, preferably 25 to 70°C. The immersion time is usually around 1 to 120 seconds, preferably 3 to 90 seconds. When immersing the polyvinyl alcohol-based resin film in a zinc-containing solution, the zinc content in the polyvinyl alcohol-based resin film is adjusted to the above range by adjusting conditions such as the concentration of the zinc salt solution, the immersion temperature of the polyvinyl alcohol-based resin film in the zinc salt solution, and the immersion time. There are no particular restrictions on when the immersion treatment in the zinc-containing solution is performed. The immersion treatment in the zinc-containing solution may be performed alone, or the zinc salt may be present in the dyeing bath, crosslinking bath, or stretching bath and performed simultaneously with at least one of the dyeing, crosslinking, or stretching processes.

[0070] The drying process involves drying the PVA-based resin film, which has been cleaned in the washing process, 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 carried out by the steps of applying a coating solution containing a PVA resin onto a base film, uniaxially stretching the obtained laminated film, staining the PVA resin layer of the uniaxially stretched laminated film with a dichroic dye to adsorb it and form a polarizing element, treating the film on which the dichroic dye has been adsorbed with an aqueous boric acid solution, and washing with water after treatment with the aqueous boric acid solution. The base film used to form the polarizing element may also be used as a protective layer for the polarizing element. If necessary, the base film may be peeled off from the polarizing element.

[0072] <Transparent protective film> The transparent protective film used in this embodiment (hereinafter also simply referred to as "protective film") is bonded to at least one side of the polarizing element via an adhesive layer. This transparent protective film is bonded to one or both sides of the polarizing element, but it is preferable that it is bonded to both sides.

[0073] The protective film may also have other optical functions and may be formed in a laminated structure with multiple layers stacked on top of each other. From the viewpoint of optical properties, a thin protective film is preferable, but if it is too thin, its strength will decrease and its processability will be poor. An appropriate film thickness is 5 μm to 100 μm, preferably 10 μm to 80 μm, and more preferably 15 μm to 70 μm.

[0074] The protective film can be a cellulose acylate film, a polycarbonate resin film, a cycloolefin resin film such as norbornene, a (meth)acrylic polymer film, or a polyester resin film such as polyethylene terephthalate. When a protective film is laminated to both sides of a polarizing element using a water-based adhesive such as PVA adhesive, it is preferable that at least one of the protective films be either a cellulose acylate film or a (meth)acrylic polymer film in terms of moisture permeability, with cellulose acylate film being preferred.

[0075] At least one of the protective films may have a phase difference function for purposes such as viewing angle compensation. In this case, the protective film itself may have the phase difference function, or it may have a separate phase difference layer, or a combination of both. The film having the phase difference function may be directly bonded to the polarizing element via an adhesive, or it may be bonded via an adhesive or bonding agent through another protective film bonded to the polarizing element.

[0076] <Adhesive layer> The adhesive layer for bonding the protective film to the polarizing element is formed from the following adhesives.

[0077] (glue) The adhesive contains a first compound, a second compound, and a third compound. The adhesive is not limited to water-based adhesives, solvent-based adhesives, or active energy ray-curable adhesives, but is preferably water-based, and preferably contains a PVA-based resin. By forming an adhesive layer for bonding a polarizing element and a protective film using an adhesive containing the first compound, the second compound, and the third compound, the decrease in transmittance of the polarizing plate in high-temperature environments can be suppressed. Furthermore, by using an adhesive having the second compound and the third compound, an adhesive with a sufficient pot life for production can be obtained. The applications of the adhesive according to the present invention are not limited, and it is suitably used in optical elements, for example, in applications for bonding polarizing elements and protective films.

[0078] The thickness of the adhesive during application can be set to any value, for example, so that an adhesive layer with a desired thickness is obtained after curing or heating (drying). The thickness of the adhesive layer composed of the adhesive is preferably 0.01 μm to 7 μm, more preferably 0.01 μm to 5 μm, even more preferably 0.01 μm to 2 μm, and most preferably 0.01 μm to 1 μm.

[0079] In the case of a water-based adhesive containing a PVA resin, the content of the third compound is, for example, 0.01 parts by mass or more and 400 parts by mass or less per 100 parts by mass of the PVA resin, preferably 0.05 parts by mass or more and 50 parts by mass or less, and more preferably 0.1 parts by mass or more and 10 parts by mass or less. If the content is less than 0.01 parts by mass, the effect of improving pot life may not be sufficient, or the effect of suppressing polyene formation of the polarizing element under high temperature conditions may not be sufficient. On the other hand, if the content exceeds 400 parts by mass, the third compound may precipitate after the polarizing plate is manufactured.

[0080] When the adhesive is a water-based adhesive containing a PVA resin, the content of the first compound is preferably 0.1 parts by mass or more and 400 parts by mass or less, more preferably 1 part by mass or more and 200 parts by mass or less, and even more preferably 3 parts by mass or more and 100 parts by mass or less, per 100 parts by mass of the PVA resin. If the content is less than 0.1 parts by mass, the effect of suppressing polyene formation of the polarizing element under high-temperature environments may not be sufficient. On the other hand, if the content exceeds 400 parts by mass, the first compound may precipitate after the polarizing plate is manufactured, and the haze may increase.

[0081] In the case of a water-based adhesive containing a PVA resin, the content of the second compound is preferably 1 to 60 parts by mass, more preferably 1.5 to 50 parts by mass, and even more preferably 2 to 45 parts by mass, per 100 parts by mass of the PVA resin. If the content is less than 1 part by mass, the effect of improving water resistance may not be sufficient. On the other hand, if it exceeds 60 parts by mass, the stability of the adhesive solution may decrease.

[0082] In the adhesive, the content of the second compound, dialdehyde, 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, with no lower limit, but for example, 0.03 parts by mass or more, per 1 part by mass of the first compound, the urea-based compound. By keeping the content ratio of the urea-based compound to dialdehyde in the adhesive within the above range, it becomes easier to achieve both the effect of improving high-temperature durability by the urea-based compound and the effect of improving adhesion by dialdehyde. It is understood that the effect of improving adhesion by dialdehyde provides an improved water resistance effect. If the amount of dialdehyde exceeds 20 parts by mass per 1 part by mass of the urea-based compound, the effect of improving high-temperature durability by the urea-based compound may not be fully exhibited. The content ratio of the urea-based compound to dialdehyde in the adhesive and the content ratio of the urea-based compound to dialdehyde in the adhesive layer can be considered to be the same.

[0083] In the adhesive, the content of the third compound, dicarboxylic acid, is preferably 0.001 parts by mass or more and 100 parts by mass or less, and preferably 0.01 parts by mass or more and 80 parts by mass or less, per 1 part by mass of the second compound, dialdehyde. If the content is less than 0.001 parts by mass, the effect of improving pot life may not be sufficient. On the other hand, if it exceeds 100 parts by mass, the third compound may precipitate after the polarizing plate is manufactured.

[0084] When the above-mentioned adhesive is used to form an adhesive layer for bonding a polarizing element and a protective film, the amount of these compounds contained in the adhesive may be appropriately adjusted depending on whether or not the polarizing element to be bonded contains the first compound, the second compound, and the third compound.

[0085] In a configuration in which a transparent protective film is bonded to both sides of a polarizing element via an adhesive layer, only one of the adhesive layers on both sides of the polarizing element may contain the first compound, the second compound, and the third compound; however, it is preferable that both adhesive layers on both sides contain the first compound, the second compound, and the third compound.

[0086] To meet the demand for thinner polarizing plates, polarizing plates have been developed that have a transparent protective film on only one side of the polarizing element. In this configuration as well, the transparent protective film is laminated via an adhesive layer containing the first compound, the second compound, and the third compound. One possible method for manufacturing such a polarizing plate with a transparent protective film on only one side of the polarizing element is to first manufacture a polarizing plate with transparent protective films laminated on both sides via adhesive layers, and then peel off one of the transparent protective films. When such a manufacturing method is used, it is acceptable for only one of the adhesive layers to contain the first compound, the second compound, and the third compound, but it is preferable that both adhesive layers contain the first compound, the second compound, and the third compound. If only one of the adhesive layers contains the first compound, the second compound, and the third compound, it is preferable that the adhesive layer on the film side that is not peeled off contains the first compound, the second compound, and the third compound.

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

[0088] The PVA resin included in the water-based adhesive is preferably one containing acetoacetyl groups, because it exhibits excellent adhesion between the PVA resin layer and the protective film, as well as superior durability. The acetoacetyl group-containing PVA resin can be obtained, for example, by reacting a PVA resin with diketene by any method. The degree of acetoacetyl group modification in the acetoacetyl group-containing PVA resin is typically 0.1 mol% or more, and preferably 0.1 mol% to 20 mol%. The resin concentration of the water-based adhesive is preferably 0.1% by mass to 15% by mass, and more preferably 0.5% by mass to 10% by mass.

[0089] The second compound, a dialdehyde, can act as a crosslinking agent. Water-based adhesives may also contain crosslinking agents other than the second compound. Known crosslinking agents can be used. Examples of crosslinking agents include water-soluble epoxy compounds and isocyanates.

[0090] If the PVA resin is an acetoacetyl group-containing PVA resin, the crosslinking agent is preferably either a glyoxylate or methylolmelamine, and more preferably either a glyoxylate.

[0091] Water-based adhesives may also contain organic solvents. Alcohols are preferred as organic solvents because they are miscible with water, and methanol or ethanol are more preferred among alcohols. The methanol concentration in the water-based adhesive is preferably 10% to 70% by mass, more preferably 15% to 60% by mass, and even more preferably 20% to 60% by mass. A methanol concentration of 10% by mass or more makes it easier to suppress polyene formation of PVA resins in high-temperature environments. Furthermore, a methanol content of 70% by mass or less can suppress deterioration of color. Some urea derivatives have low solubility in water but sufficient solubility in alcohol. In such cases, it is also a preferred embodiment to dissolve the urea compound in alcohol to prepare an alcohol solution of the urea compound, and then add this alcohol solution to an aqueous PVA solution to prepare the adhesive.

[0092] (Active energy ray curing adhesive) Active energy ray curing adhesives are adhesives that harden when irradiated with active energy rays such as ultraviolet light. Examples include adhesives containing polymerizable compounds and photopolymerization initiators, adhesives containing photoreactive resins, and adhesives containing binder resins and photoreactive crosslinking agents. Examples of polymerizable compounds include photopolymerizable monomers such as photocurable epoxy monomers, photocurable acrylic monomers, and photocurable urethane monomers, and oligomers derived from these monomers. Examples of photopolymerization initiators include compounds containing substances that generate active species such as neutral radicals, anionic radicals, and cationic radicals when irradiated with active energy rays such as ultraviolet light.

[0093] <Layer containing the first compound, the second compound, and the third compound> The first, second, and third compounds are not limited to being contained in the adhesive layer as described above, and may be contained in layers other than the adhesive layer from the viewpoint of improving the high-temperature durability of the polarizing plate. In a polarizing plate having a transparent protective film on only one side, a cured layer may be laminated on the side opposite to the transparent protective film of the polarizing element from the viewpoint of improving physical strength, and such a cured layer may be a layer containing the first, second, and third compounds.

[0094] The thickness of the layer containing the first compound, the second compound, and the dicarboxylic acid 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] [Image display device configuration] The polarizing plate of this embodiment is used in various image display devices such as liquid crystal displays and organic EL displays. In image display devices, if the polarizing plate has an interlayer-filled configuration in which both sides are in contact with layers other than the air layer, specifically solid layers such as adhesive layers, the transmittance tends to decrease in high-temperature environments. In an image display device using the polarizing plate of this embodiment, even with an interlayer-filled configuration, the decrease in the transmittance of the polarizing plate in high-temperature environments can be suppressed. An example of an image display device is a configuration having an image display cell, a first adhesive layer laminated on the viewing-side surface of the image display cell, and a polarizing plate laminated on the viewing-side surface of the first adhesive layer. Such an image display device may further have a second adhesive layer laminated on the viewing-side surface of the polarizing plate and a transparent member laminated on the viewing-side surface of the second adhesive layer. In particular, the polarizing plate of this embodiment is suitably used in an image display device having an interlayer-filled configuration in which a transparent member is arranged on the viewing side of the image display device, the polarizing plate and the image display cell are bonded together by the first adhesive layer, and the polarizing plate and the transparent member are bonded together by the second adhesive layer. In this specification, either the first adhesive layer or the second adhesive layer, or both, may be simply referred to as the "adhesive layer." The component used for bonding the polarizing plate and the image display cell, and the component used for bonding the polarizing plate and the transparent component, are not limited to the adhesive layer, but may also be an adhesive layer.

[0096] <Image display cell> Examples of image display cells include liquid crystal cells and organic EL cells. As for liquid crystal cells, any of the following types may be used: reflective liquid crystal cells that utilize ambient light, transmissive liquid crystal cells that utilize light from a backlight or other light source, and semi-transparent, semi-reflective liquid crystal cells that utilize both external light and light from a light source. If the liquid crystal cell utilizes light from a light source, the image display device (liquid crystal display device) also has a polarizing plate on the opposite side of the image display cell (liquid crystal cell) from the viewing side, and a light source is also positioned therein. Preferably, the polarizing plate on the light source side and the liquid crystal cell are bonded together via an appropriate adhesive layer. As for the driving method of the liquid crystal cell, any type can be used, such as VA mode, IPS mode, TN mode, STN mode, or bend orientation (π type).

[0097] As an organic EL cell, a suitable example is one in which a light-emitting body (organic electroluminescent light-emitting body) is formed 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 laminate of various organic thin films, and various layer configurations can be adopted, such as a laminate of a hole injection layer made of a triphenylamine derivative and a light-emitting layer made of a fluorescent organic solid such as anthracene, a laminate of these light-emitting layers and an electron injection layer made of a perylene derivative, or a laminate of a hole injection layer, a light-emitting layer and an electron injection layer.

[0098] <Bonding of image display cell and polarizing plate> An adhesive layer (adhesive sheet) is preferably used to bond an image display cell and a polarizing plate. Among these, a method of bonding an adhesive-layered polarizing plate, in which an adhesive layer is attached to one side of the polarizing plate, to an image display cell is preferred from the viewpoint of workability and other factors. The adhesive layer can be attached to the polarizing plate by any appropriate method. Examples include preparing an adhesive solution of about 10% to 40% by mass by dissolving or dispersing a base polymer or its composition in a solvent consisting of a suitable solvent such as toluene or ethyl acetate, and directly attaching it to the polarizing plate by an appropriate deployment method such as casting or coating, or forming an adhesive layer on a separator and transferring it to the polarizing plate.

[0099] <Adhesive layer> The adhesive layer may consist of one or more layers, but preferably one layer. The adhesive layer can be composed of an adhesive composition mainly composed of (meth)acrylic resin, rubber resin, urethane resin, ester resin, silicone resin, or polyvinyl ether resin. Among these, an adhesive composition using (meth)acrylic resin as the base polymer, which has excellent transparency, weather resistance, and heat resistance, is preferred. The adhesive composition may be of the active energy ray curing type or thermosetting type.

[0100] As the (meth)acrylic resin (base polymer) used in the adhesive composition, polymers or copolymers using one or more (meth)acrylic acid esters such as butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate as monomers are preferably used. It is preferable to copolymerize polar monomers in the base polymer. Examples of polar monomers include monomers having carboxyl groups, hydroxyl groups, amide groups, amino groups, epoxy groups, etc., such as (meth)acrylic acid compounds, 2-hydroxypropyl (meth)acrylate compounds, hydroxyethyl (meth)acrylate compounds, (meth)acrylamide compounds, N,N-dimethylaminoethyl (meth)acrylate compounds, and glycidyl (meth)acrylate compounds.

[0101] The adhesive composition may contain only the above-mentioned base polymer, but usually further contains a crosslinking agent. Examples of crosslinking agents include metal ions with a valency of 2 or higher that form a metal carboxylate salt with a carboxyl group, polyamine compounds that form an amide bond with a carboxyl group, polyepoxy compounds or polyols that form an ester bond with a carboxyl group, and polyisocyanate compounds that form an amide bond with a carboxyl group. Among these, polyisocyanate compounds are preferred.

[0102] Active energy ray curable adhesive compositions have the property of curing upon irradiation with active energy rays such as ultraviolet rays or electron beams. They possess adhesive properties even before irradiation with active energy rays, allowing them to adhere to substrates such as films, and their adhesion strength can be adjusted by curing upon irradiation with active energy rays. Active energy ray curable adhesive compositions are preferably ultraviolet curable. Active energy ray curable adhesive compositions further contain an active energy ray polymerizable compound in addition to a base polymer and a crosslinking agent. Photopolymerization initiators, photosensitizers, etc., may be included as needed.

[0103] The adhesive composition may contain additives such as fine particles for light scattering, beads (resin beads, glass beads, etc.), glass fibers, resins other than the base polymer, tackifiers, fillers (metal powders and other inorganic powders, etc.), antioxidants, UV absorbers, dyes, pigments, colorants, defoamers, corrosion inhibitors, and photopolymerization initiators.

[0104] The adhesive layer can be formed by applying a diluted organic solvent solution of the adhesive composition onto the surface of a base film, image display cell, or polarizing plate and drying it. The base film is generally a thermoplastic resin film, and a typical example of this is a release-treated separator film. The separator film may be a film made of a resin such as polyethylene terephthalate, polybutylene terephthalate, polycarbonate, or polyalate, with a release treatment such as silicone applied to the surface on which the adhesive layer is formed.

[0105] Alternatively, an adhesive composition may be directly applied to the release surface of a separator film to form an adhesive layer, and this separator film-attached adhesive layer may be laminated onto the surface of a polarizer. Or, an adhesive composition may be directly applied to the surface of a polarizer plate to form an adhesive layer, and a separator film may be laminated onto the outer surface of the adhesive layer.

[0106] When providing an adhesive layer on the surface of a polarizing plate, it is preferable to apply a surface activation treatment 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 it is more preferable to apply a corona treatment.

[0107] Alternatively, an adhesive sheet may be prepared by applying an adhesive composition onto a second separator film to form an adhesive layer, and then laminating a separator film onto the formed adhesive layer. The adhesive layer with the separator film attached, after peeling the second separator film from this adhesive sheet, may then be laminated onto a polarizing plate. The second separator film used is one that has weaker adhesion to the adhesive layer than the separator film and is easier to peel off.

[0108] The thickness of the adhesive layer is not particularly limited, but is preferably 1 μm to 100 μm, more preferably 3 μm to 50 μm, and may be 20 μm or more.

[0109] <Transparent material> Transparent components placed on the viewing side of an image display device include transparent plates (window layers) and touch panels. As the transparent plate, a transparent plate with appropriate mechanical strength and thickness is used. Examples of such transparent plates include transparent resin plates such as polyimide resin, acrylic resin, or polycarbonate resin, or glass plates. Functional layers, such as an anti-reflective layer, may be laminated on the viewing side of the transparent plate. Furthermore, if the transparent plate is a transparent resin plate, a hard coat layer may be laminated to increase physical strength, or a low-moisture permeability layer may be laminated to reduce moisture permeability. As the touch panel, various types of touch panels such as resistive, capacitive, optical, and ultrasonic touch panels, as well as glass plates or transparent resin plates equipped with touch sensor functions, can be used. When a capacitive touch panel is used as the transparent component, it is preferable to provide a transparent plate made of glass or transparent resin further on the viewing side than the touch panel.

[0110] <Bonding of polarizing plate and transparent material> For bonding the polarizing plate and the transparent member, an adhesive or an active energy ray curing adhesive is preferably used. When an adhesive is used, the adhesive can be applied by any appropriate method. A specific application method is, for example, the method of applying the adhesive layer used in the bonding of the image display cell and the polarizing plate described above.

[0111] When using an active energy ray curing adhesive, a preferred method is to provide a dam material around the periphery of the image display panel to prevent the adhesive solution from spreading before curing, place a transparent member on the dam material, and then inject the adhesive solution. After the adhesive solution is injected, alignment and degassing are performed as needed, and then curing is performed by irradiation with active energy rays. [Examples]

[0112] The present invention will be specifically described below based on examples. The materials, reagents, amounts and proportions of substances, and procedures shown in the following examples can be modified as appropriate without departing from the spirit of the present invention. Therefore, the present invention is not limited to the following examples.

[0113] (1) Measurement of the thickness of the polarizing element: The measurements were taken using a Nikon Corporation digital micrometer, model "MH-15M".

[0114] (2) Measurement of polarizing degree, luminous efficiency correction transmittance, and hue of polarizing plates: The measurements were taken using a spectrophotometer with an integrating sphere [JASCO Corporation's "V7100", 2-degree field of view; C light source].

[0115] (3) Measurement of boron content: 0.2 g of a polarizing element was dissolved in 200 g of a 1.9 mass% mannitol aqueous solution. The resulting aqueous solution was then titrated with a 1 mol / L sodium hydroxide aqueous solution, and the boron content of the polarizing element was calculated by comparing the amount of sodium hydroxide aqueous solution required for neutralization with the calibration curve.

[0116] (4) Measurement of zinc ion content: The solution obtained by adding nitric acid to a precisely weighed polarizing element and acid-decomposing it using a Milestone General microwave sample preparation device (ETHOS D) was used as the measurement solution. The zinc ion content was calculated by quantifying the zinc concentration in the measurement solution using an Agilent Technologies ICP emission spectrometer (5110 ICP-OES) and then calculating the zinc mass relative to the polarizing element mass.

[0117] (5) Measurement of the boron adsorption rate of PVA resin film: A PVA resin film cut into 100 mm squares was immersed in 30°C pure water for 60 seconds, and then immersed in a 60°C aqueous solution containing 5 parts boric acid for 120 seconds. The PVA resin film removed from the boric acid solution was dried in an 80°C oven for 11 minutes. The film was conditioned at 23°C and 55% RH for 24 hours to obtain a boron-containing PVA film. 0.2 g of the resulting boron-containing PVA resin film was dissolved in 200 g of a 1.9 mass% mannitol aqueous solution. The resulting aqueous solution was then titrated with a 1 mol / L sodium hydroxide aqueous solution, and the boron content of the PVA resin film was calculated by comparing the amount of sodium hydroxide aqueous solution required for neutralization with a calibration curve. The resulting boron content of the PVA resin film was used as the boron adsorption rate of the PVA resin film.

[0118] (Fabrication of polarizing element 1) A 30 μm thick polyvinyl alcohol-based 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), and then immersed in an aqueous solution containing 1.0 mM iodine at 23°C for 151 seconds with a mass ratio of potassium iodide / boric acid / water of 2 / 2 / 100 (dyeing process). Subsequently, it was immersed in an aqueous solution with a mass ratio of potassium iodide / boric acid / water of 2.5 / 4 / 100 at 68.5°C for 76 seconds (first crosslinking process). Subsequently, it was immersed in an aqueous solution with a mass ratio of potassium iodide / boric acid / zinc chloride / water of 3 / 5.5 / 0.6 / 100 at 45°C for 11 seconds (second crosslinking process, metal ion treatment process). Subsequently, the material was immersed in a washing bath for washing (washing step) and dried at 38°C (drying step) to obtain a 12 μm thick polarizing element in which iodine was adsorbed and oriented on polyvinyl alcohol. Stretching was mainly carried out in the dyeing step and the first crosslinking step, with a total stretching ratio of 5.85 times. The obtained polarizing element had a zinc ion content of 0.17 mass% and a boron content of 4.62 mass%.

[0119] (Preparation of PVA solution for adhesives) 50 g of a modified PVA resin containing acetoacetyl groups (Mitsubishi Chemical Corporation: Gosenex Z-410) was dissolved in 950 g of pure water, heated at 90°C for 2 hours, and then cooled to room temperature to obtain a PVA solution for adhesives.

[0120] (Preparation of polarizing film adhesives 1-3) Adhesives 1-3 were prepared by mixing PVA solution, urea, a commercially available 40% glyoxal solution, maleic acid, and pure water so that the content of PVA, urea, glyoxal, and maleic acid was as shown in Table 1. The adhesives were used three days after preparation.

[0121] [Table 1]

[0122] (Saponification of cellulose acylate film) A commercially available cellulose acylate film TJ40UL (manufactured by Fujifilm Corporation: film thickness 40 μm) was immersed in a 1.5 mol / L NaOH aqueous solution (saponification solution) maintained at 55°C for 2 minutes, and the film was washed with water. Then, the film was immersed in a 0.05 mol / L sulfuric acid aqueous solution at 25°C for 30 seconds, and then rinsed in a water bath under running water for 30 seconds to neutralize the film. The film was then drained of water using an air knife three times. After removing the water, the film was left in a drying zone at 70°C for 15 seconds to dry, and a saponified film was prepared.

[0123] (Preparation of polarizing plates 1-3) Using the adhesive 1 prepared as described above and stored for 3 days, saponified cellulose acylate films were bonded to both sides of the polarizing element 1 using a roll laminating machine. The film was then dried at 80°C for 5 minutes to obtain the polarizing plate 1. The adhesive layer was adjusted so that its thickness after drying was 50 nm on both sides.

[0124] In the fabrication of polarizing plate 1, adhesive 1 was changed to adhesives 2-3 to obtain polarizing plates 2-3.

[0125] (Adjustment of the water content of polarizing plates (polarizing elements)) The polarizers 1-3 obtained above were stored for 72 hours at a temperature of 20°C under relative humidity conditions of 30%, 35%, 40%, 45%, 50%, or 55%. The moisture content was measured using the Karl Fischer method at 66, 69, and 72 hours of storage. The moisture content did not change at 66, 69, and 72 hours of storage under any humidity conditions. Therefore, the moisture content of polarizers 1-3 can be considered to be the same as the equilibrium moisture content of the 72-hour storage environment used in this experiment. When the moisture content of a polarizer reaches equilibrium in a certain storage environment, the moisture content of the polarizing elements in the polarizer can also be considered to have reached equilibrium in that storage environment. Similarly, when the moisture content of the polarizing elements in a polarizer reaches equilibrium in a certain storage environment, the moisture content of the polarizer can also be considered to have reached equilibrium in that storage environment.

[0126] (Adjusting the moisture content of polarizing plates 1-3) The moisture content of polarizing plates 1-3 was adjusted by storing them for 72 hours at a temperature of 20°C and a relative humidity of 55% so that their moisture content would reach the equilibrium moisture content of an environment with 55% humidity at 20°C.

[0127] <High-temperature durability evaluation> (Preparation of evaluation samples) For polarizing plates 1-3 with adjusted water content, an acrylic adhesive (Lintec Corporation, part number: #7) was formed on both sides. Furthermore, the plates were cut to a size of 50mm x 100mm so that the absorption axis was parallel to the long side, and alkali-free glass (Corning "EAGLE XG") was laminated to the surface of each adhesive to create evaluation samples.

[0128] <Evaluation of individual unit transmittance (105℃)> The evaluation samples of polarizing plates 1-3 were subjected to a temperature of 50°C and a pressure of 5 kgf / cm². 2After autoclaving at 490.3 kPa for 1 hour, the samples were left for 24 hours in an environment of 23°C and 55% relative humidity. Subsequently, the transmittance of evaluation samples 1-3 polarizers was measured (initial value), and they were stored in a heated environment at 105°C. The transmittance was measured every 50 hours from 100 to 200 hours. The evaluation was based on the time at which the transmittance decreased by 5% or more compared to the initial value, according to the following criteria. The results are shown in Table 2. Products with a transmittance decrease of 5% or less after 200 hours: A Products where the decrease in transmittance reached 5% or more after 150-200 hours: B Products where the decrease in transmittance reached 5% or more after 100-150 hours: C Products with a decrease in transmittance of 5% or more after 100 hours: D

[0129] <Water resistance evaluation (hot water immersion test)> The water resistance test of this embodiment was carried out in accordance with the water resistance test described in Japanese Patent Publication No. 2009-025728

[0060] . An acrylic adhesive (Lintec Corporation, product number: #7) was formed on one side of the polarizing plate prepared above, and the polarizing plate was cut into strips measuring 50 mm x 20 mm with the absorption axis (extension direction) of the polarizing plate as the longer side, and the dimensions in the direction of the longer side were accurately measured. Here, the evaluation sample exhibits a uniform characteristic color across its entire surface due to iodine adsorbed on the polarizing element. The sample was held by one short side with a gripping tool, and approximately 80% of its length was immersed in a 60°C water bath for 4 hours. After that, the sample was removed from the water bath and the moisture was wiped off. Immersion in hot water causes the polarizing element of the polarizing plate to shrink. The degree of this shrinkage of the polarizing element was evaluated on a three-point scale according to the following criteria by measuring the distance from the edge of the sample (the edge of the protective film) to the edge of the shrunk polarizing element at the center of the short side of the sample. The results are shown in Table 2. Samples where the distance from the edge of the sample to the edge of the polarizing element is 1 mm or less: A Samples where the distance from the edge of the sample to the edge of the polarizing element is greater than 1 mm but less than or equal to 3 mm: B Samples where the distance from the edge of the sample to the edge of the polarizing element is greater than 3 mm: C

[0130] [Table 2]

[0131] Polarizing plates containing the first compound (urea), the second compound (glyoxal), and the third compound (maleic acid) in the adhesive exhibit superior high-temperature durability compared to polarizing plates without urea in the adhesive, as their transmittance does not decrease significantly even when exposed to high temperatures of 105°C. Furthermore, all adhesives demonstrate excellent water resistance even when used to produce polarizing plates after being stored for three days, indicating that they are adhesives with sufficient pot life for productivity.

Claims

1. A method for manufacturing a polarizing plate, comprising a polarizing element having a dichroic dye adsorbed and oriented on a polyvinyl alcohol-based resin layer, and a transparent protective film laminated on at least one surface of the polarizing element, A step of preparing an adhesive containing a first compound, a second compound, and a third compound. The process includes bonding the polarizing element and the transparent protective film with an adhesive layer formed using the adhesive, 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, In the adhesive, the content of the second compound is 20 parts by mass or less per 1 part by mass of the first compound. The adhesive is a polyvinyl alcohol-based resin, and the method is for manufacturing a polarizing plate.

2. The method for manufacturing a polarizing plate according to claim 1, wherein the content of the third compound in the adhesive is 0.01 parts by mass or more and 400 parts by mass or less per 100 parts by mass of the polyvinyl alcohol-based resin.

3. The method for manufacturing a polarizing plate according to claim 1, wherein the content of the second compound in the adhesive is 10.0 parts by mass or more and 60 parts by mass or less per 100 parts by mass of the polyvinyl alcohol-based resin.

4. The method for manufacturing a polarizing plate according to any one of claims 1 to 3, wherein the content of the first compound in the adhesive is 0.1 parts by mass or more and 400 parts by mass or less per 100 parts by mass of the polyvinyl alcohol-based resin.

5. The method for manufacturing a polarizing plate according to any one of claims 1 to 4, wherein the content of the second compound in the adhesive is 0.03 parts by mass or more and 20 parts by mass or less per 1 part by mass of the first compound.

6. The method for manufacturing a polarizing plate according to any one of claims 1 to 5, wherein the dialdehyde is glyoxal.

7. The method for manufacturing a polarizing plate according to any one of claims 1 to 6, wherein the adhesive layer has a thickness of 0.01 μm or more and 7 μm or less.

8. A method for manufacturing an image display device including a polarizing plate, A step of obtaining a polarizing plate by a method for manufacturing a polarizing plate according to any one of claims 1 to 7, A step of providing the polarizing plate in the image display device such that solid layers are in contact with both sides thereof, A method for manufacturing an image display device.

9. The method for manufacturing an image display device according to claim 8, wherein the image display device comprises an image display cell, a first adhesive layer laminated on the viewing-side surface of the image display cell, and a polarizing plate laminated on the viewing-side surface of the first adhesive layer.

10. The method for manufacturing an image display device according to claim 9, further comprising: a second adhesive layer laminated on the viewing-side surface of the polarizing plate; and a transparent member laminated on the viewing-side surface of the second adhesive layer.

11. The method for manufacturing an image display device according to claim 10, wherein the transparent member is a glass plate or a transparent resin plate.

12. The method for manufacturing an image display device according to claim 10, wherein the transparent member is a touch panel.

13. An adhesive containing a polyvinyl alcohol resin, used for bonding a polarizing element having a dichroic dye adsorbed and oriented on a polyvinyl alcohol resin layer to a protective film, The first compound, the second compound, and the third compound are contained in the following: 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, An adhesive in which the content of the second compound is 20 parts by mass or less per 1 part by mass of the first compound.

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