TWI893225B - Polarizing plate and image display device - Google Patents

Abstract

The present invention provides a polarizing plate capable of suppressing transmittance in high temperature environment from decreasing. A polarizing plate of the present invention has 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; wherein the polarizing element and the transparent protective film are bonded to each other viaan adhesive layer formed of an adhesive containing a urea-based compound and a dicarboxylic acid, the urea-based compound is at least one selected from the group consisting of urea, urea derivatives, thiourea and thiourea derivatives, the water content of the polarizing element is equal to or higher than the equilibrium water content at a temperature of 20℃ and a relative humidity of 30%, and equal to or lower than the equilibrium water content at a temperature of 20℃ and a relative humidity of 50%.

Description

Polarizing plate and image display device

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

Liquid crystal display (LCD) devices are widely used not only in LCD televisions but also in personal computers, mobile devices such as cell phones, and in-vehicle applications such as car navigation systems. Typically, an LCD device has a liquid crystal panel with polarizing plates attached to each side of a liquid crystal cell using an adhesive. The LCD panel controls light from a backlight to produce a display. In recent years, organic EL displays have also become widely used, similar to LCDs, in televisions, mobile devices such as cell phones, and in-vehicle applications such as car navigation systems. In organic EL displays, a circularly polarizing plate (a laminate consisting of a polarizing element and a λ/4 plate) is sometimes placed on the viewing surface of the image display panel to prevent external light from being reflected by the metal electrode (cathode) and appearing as a mirror.

As mentioned above, polarizing plates are increasingly being installed in vehicles as components of image display devices such as liquid crystal displays and organic EL displays. Polarizing plates used in automotive image display devices are more often exposed to high-temperature environments than those used in mobile devices such as televisions and cell phones, and therefore require minimal changes in their characteristics at higher temperatures (high-temperature durability).

On the other hand, to prevent damage to the image display panel from external impact, there is an increasing trend toward installing a front panel (also known as a "window layer") made of a transparent resin sheet or glass sheet on the viewing side of the image display panel. In image display devices equipped with a touch panel, a configuration in which the touch panel is installed on the viewing side of the image display panel and the front panel is also installed on the viewing side of the touch panel is widely adopted.

In this configuration, if an air layer exists between the image display panel and a transparent component such as a front panel or touch panel, light reflection from the air layer interface causes external light to enter, which tends to reduce screen visibility. Therefore, a configuration (hereinafter sometimes referred to as an "interlayer filler structure") in which a layer other than the air layer, typically a solid layer (hereinafter sometimes referred to as an "interlayer filler") is used to fill the space between the polarizer disposed on the viewing side of the image display panel and the transparent component (hereinafter sometimes referred to as an "interlayer filler structure") is being adopted. The interlayer filler is preferably made of a material with a refractive index close to that of the polarizer or transparent component. As an interlayer filler, adhesives or UV-curable adhesives are used to suppress the reduction in visibility caused by reflection at the interface and to indirectly fix the components (see, for example, Patent Document 1).

Interlayer filler structures are widely used in mobile devices, such as cell phones, which are often used outdoors. Furthermore, due to the recent increase in visibility requirements, in-vehicle applications such as car navigation systems, interlayer filler structures are being studied. These structures use an adhesive layer or other material to fill the gap between a front transparent plate and an image display panel.

However, when this structure is used, reports indicate that the transmittance of the polarizing plate decreases significantly in high-temperature environments. Patent Document 2 proposes a solution to this problem by limiting the moisture content per unit area of the polarizing plate to a specific level or less, and also limiting the saturated water absorption of the transparent protective film adjacent to the polarizing element to a specific level or less, thereby suppressing the decrease in transmittance.

[Prior Art Literature]

[Patent Literature]

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

[Patent Document 2] Japanese Patent Application Publication No. 2014-102353

However, even with this type of polarizing plate, the effect of suppressing the decrease in durability in high-temperature environments is insufficient. The present invention aims to provide a novel polarizing plate that can suppress the decrease in transmittance in high-temperature environments, and an image display device using the polarizing plate.

The present invention provides the following examples of polarizing plates and image display devices.

[1] A polarizing plate comprising a polarizing element obtained by adsorbing and aligning a dichroic pigment on a polyvinyl alcohol resin layer, and a transparent protective film laminated on at least one side of the polarizing element; wherein,

The polarizing element and the transparent protective film are bonded together via an adhesive layer, wherein the adhesive layer is formed from an adhesive containing a urea compound and a dicarboxylic acid.

The urea compound is at least one selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives.

The moisture content of the polarizing element is greater than or equal to the equilibrium moisture content of 30% at a relative humidity of 20°C and less than or equal to the equilibrium moisture content of 50% at a relative humidity of 20°C.

[2] A polarizing plate comprising a polarizing element obtained by adsorbing and aligning a dichroic pigment on a polyvinyl alcohol resin layer, and a transparent protective film laminated on at least one side of the polarizing element; wherein,

The polarizing element and the transparent protective film are bonded together via an adhesive layer, wherein the adhesive layer is formed from an adhesive containing a urea compound and a dicarboxylic acid.

The urea compound is at least one selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives.

The moisture content of the polarizing plate is greater than or equal to the equilibrium moisture content at a relative humidity of 30% at a temperature of 20°C and less than or equal to the equilibrium moisture content at a relative humidity of 50% at a temperature of 20°C.

[3] The polarizing plate as described in [1] or [2], wherein the adhesive comprises at least one urea compound selected from the group consisting of urea derivatives and thiourea derivatives.

[4] The polarizing plate as described in any one of [1] to [3], wherein the adhesive comprises a polyvinyl alcohol-based resin.

[5] The polarizing plate described in [4], wherein the content of the urea compound in the adhesive is not less than 0.1 parts by mass and not more than 400 parts by mass relative to 100 parts by mass of the polyvinyl alcohol resin.

[6] The polarizing plate according to [4] or [5], wherein the content of the dicarboxylic acid in the adhesive is not less than 1 part by mass and not more than 50 parts by mass relative to 100 parts by mass of the polyvinyl alcohol-based resin.

[7] The polarizing plate as described in any one of [1] to [6], wherein the thickness of the adhesive layer is not less than 0.01 μm and not more than 7 μm.

[8] The polarizing plate as described in any one of [1] to [7], wherein the dicarboxylic acid is at least one of maleic acid or phthalic acid.

[9] A polarizing plate as described in any one of [1] to [8], wherein the polarizing plate is used in an image display device,

In the above-mentioned image display device, the solid layer is disposed in contact with both sides of the above-mentioned polarizing plate.

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

[11] The image display device as described in [10] further comprises: 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.

[12] The image display device as described in [11], wherein the transparent component is a glass plate or a transparent resin plate.

[13] The image display device as described in [11], wherein the transparent component is a touch panel.

The present invention provides a polarizing plate with improved high-temperature durability, suppressing the decrease in transmittance caused by high temperatures even when used in image display devices with interlayer fillers. Furthermore, by using the polarizing plate of the present invention, an image display device can be provided in which the decrease in transmittance in high-temperature environments is suppressed.

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

〔Polarizing plate〕

The polarizing plate of this embodiment comprises a polarizing element in which a dichroic dye is adsorbed and aligned on a layer comprising a polyvinyl alcohol-based resin, and a transparent protective film. The polarizing element and the transparent protective film are bonded together via an adhesive layer formed from an adhesive containing a urea compound and a dicarboxylic acid. The polarizing plate of this embodiment has at least one of the following characteristics (a) and (b).

(a) The moisture content of the polarizing element is greater than or equal to the equilibrium moisture content of 30% at a relative humidity of 20°C and less than or equal to the equilibrium moisture content of 50% at a relative humidity of 20°C.

(b) The moisture content of the polarizing plate is greater than the equilibrium moisture content of 30% at a relative humidity of 20°C and less than the equilibrium moisture content of 50% at a relative humidity of 20°C.

Previous polarizing plates with excellent high-temperature durability are known, for example, to suppress transmittance degradation even after exposure to a temperature of 95°C for 1000 hours. However, even these polarizing plates, when used in interlayer filler configurations, sometimes exhibit a significant decrease in transmittance and polarization within the center of the polarizing plate surface after exposure to 95°C for 200 hours. This significant decrease in transmittance and polarization in high-temperature environments is believed to be particularly problematic when image display devices employing interlayer filler configurations, where one side of the polarizing plate is bonded to an image display unit and the other side is bonded to a transparent component such as a touch panel or front panel, are exposed to high temperatures.

Polarizing plates with significantly reduced transmittance in interlayer filler structures exhibit peaks near 1100 cm ^-1 (attributed to the =C-C= bond) and 1500 cm ^-1 (attributed to the -C=C- bond) in Raman spectroscopy, suggesting the formation of a polyene structure (-C=C) _n -. This polyene structure is presumed to be generated by polyeneization of the polyvinyl alcohol (PVA) used in the polarizing element during dehydration (Patent Document 2, paragraph [0012]).

The polarizing plate of the present invention can further enhance high-temperature durability. When incorporated into an image display device with an interlayer filler structure, the polarizing plate of the present invention can suppress the decrease in transmittance and polarization even when exposed to high temperatures, such as 105°C.

<Polarizing element>

As a polarizing element that adsorbs and aligns a dichroic dye on a layer containing a polyvinyl alcohol (hereinafter also referred to as "PVA") resin (hereinafter also referred to as a "PVA resin layer"), a known polarizing element can be used. Examples of polarizing elements include a stretched film obtained by dyeing a PVA resin film with a dichroic dye and then uniaxially stretching it, or a laminated film having a coating layer formed by coating a coating liquid containing a PVA resin on a base film, and a stretched layer obtained by dyeing the coating layer with a dichroic dye and then uniaxially stretching the laminated film. Stretching can be performed after dyeing with a dichroic dye, while dyeing, or after stretching.

PVA resins are obtained by saponifying polyvinyl acetate resins. In addition to polyvinyl acetate, which is a homopolymer of vinyl acetate, polyvinyl acetate resins also include copolymers of vinyl acetate with other copolymerizable monomers. Examples of such other copolymerizable monomers include unsaturated carboxylic acids, olefins such as ethylene, vinyl ethers, and unsaturated sulfonic acids.

The saponification degree of PVA resins is preferably at least about 85 mol%, more preferably at least about 90 mol%, and even more preferably at least about 99 mol% to no more than 100 mol%. The degree of polymerization of PVA resins is, for example, from 1,000 to 10,000, preferably from 1,500 to 5,000. PVA resins may also be modified, for example, polyvinyl formaldehyde, polyvinyl acetal, or polyvinyl butyral modified with aldehydes.

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 can suppress the effects of polyeneization of the PVA resin on the degradation of optical properties in high-temperature environments. A polarizing element thickness of 3 μm or greater facilitates achieving desired optical properties.

The polarizing element preferably contains a urea compound and a dicarboxylic acid. In this embodiment, the polarizing element and the transparent protective film are bonded together via an adhesive layer. The adhesive layer is formed of an adhesive containing a urea compound and a dicarboxylic acid. Therefore, it is inferred that a portion of the urea compound and a portion of the dicarboxylic acid that migrate from the adhesive layer are contained in the polarizing element. The urea compound and the dicarboxylic acid in the polarizing element may also be included in those added during the manufacturing process of the polarizing element. By having an adhesive layer containing a urea compound and a dicarboxylic acid, the transmittance is not easily reduced even if the polarizing plate is exposed to a high temperature environment. In addition, by having an adhesive layer containing a urea compound and a dicarboxylic acid, the reduction in polarization degree can be suppressed even if the polarizing plate is exposed to a high temperature environment. When two polarizing plates are arranged in a crossed polarization relationship, light leakage (hereinafter referred to as "crossed light leakage") is likely to occur if the polarization degree of the polarizing plates decreases. However, according to the present invention, the polarization degree is not easily reduced even when exposed to high temperature environments, thus easily suppressing crossed light leakage. This is presumably because the urea compound and dicarboxylic acid contained in the polarizing element inhibit the polyeneization of the PVA resin.

Methods for incorporating urea compounds and dicarboxylic acids into polarizing elements include immersing the PVA resin layer in a treatment solvent containing the urea compound and/or dicarboxylic acid, or spraying, flowing, or dripping the treatment solvent onto the PVA resin layer. Of these, immersing the PVA resin layer in a treatment solvent containing both the urea compound and the dicarboxylic acid is preferred. Specific examples of urea compounds and dicarboxylic acids include those exemplified for inclusion in the adhesive described below.

The step of immersing the PVA resin layer in a treatment solvent containing a urea compound and a dicarboxylic acid can be performed simultaneously with the swelling, stretching, dyeing, crosslinking, and washing steps described below in the polarizing element manufacturing method, or it can be performed separately from these steps. The step of incorporating the urea compound and the dicarboxylic acid into the PVA resin layer is preferably performed after dyeing the PVA resin layer with iodine, and more preferably, simultaneously with the crosslinking step after dyeing. This method minimizes hue changes and reduces the impact on the optical properties of the polarizing element.

To incorporate the urea compound and dicarboxylic acid into the polarizing element, both the urea compound and the dicarboxylic acid can be added during polarizing element production or by adding the bonding agent. Alternatively, during polarizing element production, the bonding agent containing either the urea compound or the dicarboxylic acid can be used to incorporate both.

(Urea compounds)

The urea compound is at least one selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives. One urea compound may be used alone or in combination of two or more. Urea compounds are either water-soluble or poorly water-soluble, and any urea compound may be used. When using a poorly water-soluble urea compound in a water-soluble adhesive, it is preferable to design a dispersion method after the adhesive layer is formed so as not to increase the mist level.

(Urea derivative)

Urea derivatives are compounds in which at least one of the four hydrogen atoms in the urea molecule is replaced with a substituent. In this case, the substituent is not particularly limited, but preferably comprises a carbon atom, a hydrogen atom, and an oxygen atom.

Specific examples of urea derivatives include monosubstituted ureas such as methyl urea, ethyl urea, propyl urea, butyl urea, isobutyl urea, N-octadecyl urea, 2-hydroxyethyl urea, hydroxy urea, acetyl urea, allyl urea, 2-propynyl urea, cyclohexyl urea, phenyl urea, 3-hydroxyphenyl urea, (4-methoxyphenyl) urea, benzyl urea, benzoyl urea, o-tolyl urea, and p-tolyl urea.

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 (ethylidene urea), and tetrahydro-2-pyrimidinone (propylidene urea).

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.

(Thiocarbamide derivatives)

Thiourea derivatives are compounds in which at least one of the four hydrogen atoms in the thiourea molecule is replaced with a substituent. In this case, the substituent is not particularly limited, but preferably comprises a carbon atom, a hydrogen atom, and an oxygen atom.

Specific examples of thiourea derivatives include monosubstituted thiourea, 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, and (2-pyridyl)thiourea. Examples include o-tolylthiourea and p-tolylthiourea.

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

Examples of tri-substituted thioureas include trimethylthiourea, and examples of quadri-substituted thioureas include tetramethylthiourea and 1,1,3,3-tetraethylthiourea.

Among urea compounds, when used in image display devices with interlayer fillers, urea derivatives or thiourea derivatives are preferred, with urea derivatives being more preferred, in terms of suppressing the decrease in transmittance under high temperature conditions and reducing the decrease in polarization (suppressing cross light leakage). Among urea derivatives, mono-substituted urea or di-substituted urea are preferred, with mono-substituted urea being more preferred. Di-substituted ureas include 1,1-substituted urea and 1,3-substituted urea, with 1,3-substituted urea being more preferred.

(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, diphenylmethanedicarboxylic acid, oxalacetic acid, methylfumaric acid, and 2,6-pyridinedicarboxylic acid. Among these, citric acid, malic acid, maleic acid, or tartaric acid is preferred. These dicarboxylic acids can be used alone or in combination of two or more.

(Feature (a))

In the case of feature (a), the moisture content of the polarizing element is greater than or equal to the equilibrium moisture content at a relative humidity of 30% at a temperature of 20°C and less than or equal to the equilibrium moisture content at a relative humidity of 50% at a temperature of 20°C. The moisture content of the polarizing element is preferably less than or equal to the equilibrium moisture content at a relative humidity of 45% at a temperature of 20°C, more preferably less than or equal to the equilibrium moisture content at a relative humidity of 42% at a temperature of 20°C, and even more preferably less than or equal to the equilibrium moisture content at a relative humidity of 38% at a temperature of 20°C. If the moisture content of the polarizing element is less than the equilibrium moisture content at a relative humidity of 30% at a temperature of 20°C, the operability of the polarizing element is reduced and it is prone to cracking. If the moisture content of the polarizing element exceeds the equilibrium moisture content at a relative humidity of 50% at a temperature of 20°C, the transmittance of the polarizing element is likely to be reduced. The reason for this is presumably that a higher moisture content in the polarizing element facilitates polyene formation in the PVA resin. The moisture content of the polarizing element refers to the moisture content of the polarizing element in the polarizing plate.

Methods for confirming whether the moisture content of a polarizing element is above the equilibrium moisture content of 30% at a temperature of 20°C and below the equilibrium moisture content of 50% at a temperature of 20°C include: storing the polarizing element in an environment adjusted to the aforementioned temperature and relative humidity ranges, and assuming equilibrium with the environment if there is no change in mass over a certain period of time; or precalculating the equilibrium moisture content of the polarizing element in an environment adjusted to the aforementioned temperature and relative humidity ranges and comparing the moisture content of the polarizing element with the precalculated equilibrium moisture content for confirmation.

The method for producing a polarizing element having a moisture content of at least 30% at a relative humidity of 20°C and no more than 50% at a relative humidity of 20°C is not particularly limited. Examples include storing the polarizing element in an environment maintained within the aforementioned temperature and relative humidity range for a period of at least 10 minutes but no more than 3 hours, or performing a heat treatment at a temperature of at least 30°C but no more than 90°C.

Another preferred method for producing polarizing elements with the aforementioned moisture content includes: storing a laminate having a protective film laminated on at least one side of the polarizing element, or a polarizing plate formed using the polarizing element, in an environment maintained within the aforementioned temperature and relative humidity ranges for a period of 10 minutes to 120 hours; or performing a heat treatment at a temperature of 30°C to 90°C. When manufacturing an image display device employing interlayer filler, an image display panel having a polarizing plate laminated on an image display unit can be stored in an environment maintained within the aforementioned temperature and relative humidity ranges for a period of 10 minutes to 3 hours, or heated at a temperature of 30°C to 90°C, before being attached to a front panel.

The moisture content of the polarizing element is preferably adjusted so that the moisture content falls within the aforementioned numerical range at the stage of the material used to form the polarizing plate, either the polarizing element alone or a laminate of the polarizing element and the protective film. If the moisture content is adjusted after the polarizing plate is formed, excessive curling may occur, which may cause problems when the polarizing plate is attached to an image display unit. By using a polarizing element whose moisture content has been adjusted to the aforementioned numerical range at the stage of the material before the polarizing plate is formed, a polarizing plate having a polarizing element with a moisture content within the aforementioned numerical range can be easily constructed. When the polarizing plate is attached to an image display unit, the moisture content of the polarizing element in the polarizing plate can also be adjusted so that the moisture content falls within the aforementioned numerical range. At this point, the polarizing plate is bonded to the image display unit, making it less likely to curl.

(Feature (b))

In the case of feature (b), the moisture content of the polarizing plate is greater than or equal to the equilibrium moisture content of 30% relative humidity at 20°C and less than or equal to the equilibrium moisture content of 50% relative humidity at 20°C. The moisture content of the polarizing plate is preferably less than or equal to the equilibrium moisture content of 45% relative humidity at 20°C, more preferably less than or equal to 42% relative humidity at 20°C, and even more preferably less than or equal to 38% relative humidity at 20°C. If the moisture content of the polarizing plate is less than the equilibrium moisture content of 30% relative humidity at 20°C, the polarizing plate's operability is reduced and it is prone to cracking. If the moisture content of the polarizing plate exceeds the equilibrium moisture content of 50% relative humidity at 20°C, the transmittance of the polarizing element is likely to decrease. The reason is speculated to be that if the moisture content of the polarizing plate is higher, the polyeneization of the PVA resin will proceed more easily.

Methods for confirming whether the moisture content of a polarizing plate is above the equilibrium moisture content of 30% at a temperature of 20°C and below the equilibrium moisture content of 50% at a temperature of 20°C include: storing the plate in an environment adjusted to the aforementioned temperature and relative humidity ranges, and assuming that the plate has reached equilibrium with the environment if the quality remains unchanged for a certain period of time; or precalculating the equilibrium moisture content of the polarizing plate in an environment adjusted to the aforementioned temperature and relative humidity ranges and comparing the moisture content of the polarizing plate with the precalculated equilibrium moisture content for confirmation.

The method for producing a polarizing plate having a moisture content of at least 30% at a relative humidity of 20°C and no more than 50% at a relative humidity of 20°C is not particularly limited. Examples include storing the polarizing plate in an environment adjusted to the aforementioned temperature and relative humidity range for a period of at least 10 minutes and no more than 3 hours, or performing a heat treatment at a temperature of at least 30°C and no more than 90°C.

When manufacturing an image display device using interlayer filler, the image display panel with a polarizer laminated on the image display unit can be stored in an environment adjusted to the above temperature and relative humidity range for 10 minutes to 3 hours, or heated to 30°C to 90°C before being attached to the front panel.

(Polarizing element manufacturing method)

The method for producing a polarizing element is not particularly limited, but typically includes the following steps: a method in which a PVA-based resin film pre-wound into a roll is fed and stretched, dyed, cross-linked, etc. (hereinafter referred to as "Production Method 1"); or a method in which a coating liquid containing a PVA-based resin is applied to a substrate film to form a PVA-based resin layer as a coating layer, and the resulting laminate is stretched (hereinafter referred to as "Production Method 2").

Production method 1 can be produced by uniaxially stretching a PVA-based resin film, dyeing the PVA-based resin film with a dichroic dye such as iodine to adsorb the dichroic dye, treating the PVA-based resin film adsorbed with the dichroic dye with an aqueous boric acid solution, and then washing the film with water after the boric acid solution treatment.

The swelling step involves immersing the PVA resin film in a swelling bath. This step not only removes dirt and agglomerants from the PVA resin film's surface but also prevents uneven dyeing by allowing the film to swell. The swelling bath typically uses a water-based medium such as water, distilled water, or pure water. Surfactants, alcohols, and other additives may also be added to the swelling bath as appropriate according to conventional methods. To control the potassium content of the polarizing element, potassium iodide may also 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.

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 universally, as the degree of swelling of the PVA resin membrane is affected by the temperature of the swelling bath. However, 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 step can be performed once or multiple times as needed.

The dyeing step involves immersing the PVA resin film in a dye bath (iodine solution), allowing dichroic pigments such as iodine to adsorb and align on the PVA resin film. The iodine solution is preferably an aqueous iodine solution containing iodine and an iodide as a dissolution aid. 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 for controlling the potassium content in the polarizing element.

The iodine concentration in the dye bath is preferably 0.01% by mass to 1% by mass, more preferably 0.02% by mass to 0.5% by mass. The iodide concentration in the dye 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.

The temperature of the dye bath is preferably 10°C to 50°C, more preferably 15°C to 45°C, and even more preferably 18°C to 30°C. The immersion time in the dye bath cannot be determined universally, as the degree of dyeing of the PVA resin film is affected by the temperature of the dye bath. However, it is preferably 10 seconds to 300 seconds, more preferably 20 seconds to 240 seconds. The dyeing step can be performed once or multiple times as needed.

The crosslinking step involves immersing the PVA resin film, dyed in the dyeing step, in a treatment bath (crosslinking bath) containing a boron compound. The boron compound crosslinks the PVA resin film, allowing iodine molecules or dye molecules to adsorb onto the crosslinked structures. Examples of boron compounds include boric acid, borates, and borax. The crosslinking bath is typically an aqueous solution, but it can also be a mixed solution of a water-miscible organic solvent and water. To control the potassium content in the polarizing element, the crosslinking bath preferably contains potassium iodide.

The concentration of the boron compound 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. 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.

The temperature of the crosslinking bath is preferably between 20°C and 70°C, more preferably between 30°C and 60°C. The immersion time in the crosslinking bath cannot be determined universally, as the degree of crosslinking of the PVA resin membrane is affected by the temperature of the crosslinking bath. However, it is preferably between 5 seconds and 300 seconds, more preferably between 10 seconds and 200 seconds. The crosslinking step can be performed once or multiple times as needed.

The stretching step involves stretching the PVA resin film in at least one direction to a predetermined magnification. Generally, the PVA resin film is uniaxially stretched in the transport direction (longitudinal direction). The stretching method is not particularly limited; either wet stretching or dry stretching can be employed. The stretching step can be performed once or multiple times as needed. The stretching step can be performed at any stage during the production of polarizing elements.

The treatment bath (stretching bath) in the wet stretching method typically uses a solvent such as water or a mixed solution of an organic solvent miscible with water and water. From the perspective 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 from 1 mass% to 15 mass%, more preferably from 2 mass% to 10 mass%, and even more preferably from 3 mass% to 6 mass%. From the perspective of suppressing film breakage during stretching, the treatment bath (stretching bath) may contain a boron compound. When a boron compound is included, the concentration of the boron compound in the stretching bath is preferably 1% by mass 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.

The temperature of the stretching bath is preferably 25°C to 80°C, more preferably 40°C to 75°C, and even more preferably 50°C to 70°C. The immersion time in the stretching bath cannot be determined uniformly, as the degree of stretching of the PVA-based resin film is affected by the stretching bath temperature. However, it is preferably 10 seconds to 800 seconds, more preferably 30 seconds to 500 seconds. The stretching treatment in the wet stretching method can also be performed simultaneously with one or more of the following treatment steps: swelling, dyeing, crosslinking, and washing.

Examples of dry stretching methods include inter-roll stretching, heated roll stretching, and compression stretching. Furthermore, dry stretching can also be performed in conjunction with a drying step.

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

The cleaning step involves immersing the polyvinyl alcohol-based resin film in a cleaning bath to remove 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 perspective of controlling the potassium content in the polarizing element, it is preferred 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.

The temperature of the cleaning 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 cleaning bath cannot be determined uniformly, as the degree of cleaning of the PVA resin film is affected by the bath temperature. However, it is preferably between 1 and 100 seconds, more preferably between 2 and 50 seconds, and even more preferably between 3 and 20 seconds. The cleaning step may be performed once or multiple times as needed.

The drying step involves drying the PVA-based resin film cleaned in the washing step to obtain a polarizing element. Drying can be performed by any appropriate method, such as natural drying, air drying, and heat drying.

Manufacturing method 2 can be produced through the following steps: applying a coating liquid containing a PVA-based resin onto a substrate film; uniaxially stretching the resulting laminated film; dyeing the PVA-based resin layer of the uniaxially stretched laminated film with a dichroic dye to allow it to adsorb the dye, thereby forming a polarizing element; treating the film adsorbed with the dichroic dye with an aqueous boric acid solution; and finally, washing the film after the boric acid treatment. The substrate film used to form the polarizing element can also serve as a protective layer for the polarizing element. If necessary, the substrate film can be peeled off from the polarizing element.

<Transparent protective film>

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

The protective film can also have other optical functions and can be formed into a multilayer structure consisting of multiple layers. From the perspective of optical properties, a thin protective film is preferred. However, if it is too thin, strength decreases and processability deteriorates. The appropriate film thickness is 5 μm to 100 μm, preferably 10 μm to 80 μm, and more preferably 15 μm to 70 μm.

The protective film can be made of a variety of materials, including acetylated cellulose films, films made from polycarbonate resins, films made from cycloolefin resins such as norbornene, (meth)acrylic polymer films, and films made from 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, the protective film on at least one side is preferably either an acetylated cellulose film or a (meth)acrylic polymer film, with acetylated cellulose film being preferred for its moisture permeability.

For purposes such as viewing angle compensation, at least one protective film may also have a retardation function. In this case, the protective film itself may have a retardation function, may have a separate retardation layer, or may be a combination of the two. The film with a retardation function may be directly bonded to the polarizing element via an adhesive, or may be bonded via another protective film bonded to the polarizing element via an adhesive or adhesive.

<Next layer>

An adhesive containing a urea compound and a dicarboxylic acid is used as the adhesive layer for attaching a protective film to a polarizing element. The adhesive can be a water-based adhesive, a solvent-based adhesive, or an active energy ray-curing adhesive. A water-based adhesive is preferred, and preferably contains a PVA resin. Using an adhesive containing a urea compound and a dicarboxylic acid can suppress the decrease in transmittance of the polarizing plate in high-temperature environments.

The thickness of the adhesive during application can be set to any value, for example, after curing or heating (drying) to obtain an adhesive layer of the desired thickness. 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.

The following description of adhesives describes preferred ranges for polarizing elements when the polarizing element is manufactured without urea compounds and dicarboxylic acids. If the polarizing element contains urea compounds and dicarboxylic acids, the following values can be adjusted appropriately. Specific examples of urea compounds and dicarboxylic acids can be directly applied to the urea compounds and dicarboxylic acids contained in the polarizing element described above. During the drying step during bonding between the polarizing element and the protective film to form the adhesive layer, some urea compounds and some dicarboxylic acids may migrate from the adhesive layer to the polarizing element, etc.

When the adhesive is a water-based adhesive containing a PVA resin, the content of the urea compound is preferably 0.1 to 400 parts by mass, more preferably 1 to 200 parts by mass, and even more preferably 3 to 100 parts by mass, per 100 parts by mass of the PVA resin. If the content is less than 0.1 parts by mass, the effect of suppressing polyolefination in polarizing elements under high temperature environments may be insufficient. On the other hand, if the content exceeds 400 parts by mass, urea may precipitate after polarizing plate production, increasing haze.

When the adhesive is a water-based adhesive containing a PVA resin, the dicarboxylic acid content is preferably 1 to 50 parts by mass, more preferably 1.5 to 40 parts by mass, even more preferably 2 to 35 parts by mass, and may be 20 parts by mass or less, per 100 parts by mass of the PVA resin. If the content is less than 1 part by mass, the effect of suppressing polyene formation in polarizing elements under high temperature conditions may be insufficient. On the other hand, if the content exceeds 50 parts by mass, the dicarboxylic acid may precipitate after polarizing plate production.

In a configuration where transparent protective films are laminated to both sides of a polarizing element via an adhesive layer, the adhesive layer on only one side of the polarizing element may contain a urea compound and a dicarboxylic acid. Preferably, the adhesive layers on both sides contain a urea compound and a dicarboxylic acid.

To meet the demand for thinner polarizing plates, a polarizing plate with a transparent protective film on only one side of the polarizing element has been developed. In this configuration, the transparent protective film is laminated via an adhesive layer containing a urea compound and a dicarboxylic acid. A possible method for producing a polarizing plate with a transparent protective film on only one side of the polarizing element involves first preparing a polarizing plate with the transparent protective films laminated to both sides via adhesive layers, and then peeling off one of the transparent protective films. In this production method, the adhesive layer containing the urea compound and dicarboxylic acid on only one side may be used, but preferably, both sides contain the urea compound and dicarboxylic acid. When only one side of the adhesive layer contains a urea compound and a dicarboxylic acid, it is preferred that the adhesive layer on the side of the film not to be stripped contain the urea compound and the dicarboxylic acid.

(Water-based adhesive)

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

PVA resins containing acetyl groups are preferred for inclusion in water-based adhesives because they provide excellent adhesion between the PVA resin layer and the protective film and provide excellent durability. Acetyl-containing PVA resins can be obtained, for example, by reacting a PVA resin with diketene using any method. The degree of acetyl-containing PVA resin modification is typically 0.1 mol% or higher, preferably 0.1 mol% or higher and 20 mol% or lower. The resin concentration in 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.

Water-based adhesives may also contain a crosslinking agent. Known crosslinking agents can be used as crosslinking agents. Examples of crosslinking agents include water-soluble epoxy compounds, dialdehydes, and isocyanates.

When the PVA resin is an acetyl group-containing PVA resin, the crosslinking agent is preferably any one of glyoxal, glyoxalic acid salts, and hydroxymethylmelamine, more preferably any one of glyoxal and glyoxalic acid salts, and particularly preferably glyoxal.

The aqueous adhesive may also contain an organic solvent. In terms of miscibility with water, the organic solvent is preferably an alcohol, and methanol or ethanol is more preferred among the alcohols. The methanol concentration in the aqueous adhesive is preferably 10% by mass or more and 70% by mass or less, more preferably 15% by mass or more and 60% by mass or less, and even more preferably 20% by mass or more and 60% by mass or less. By having a methanol concentration of 10% by mass or more, polyene formation of PVA-based resins in a high-temperature environment can be more easily suppressed. Furthermore, by having a methanol content of 70% by mass or less, deterioration of hue can be suppressed. Some urea derivatives have low solubility in water, but on the other hand, they have sufficient solubility in alcohol. At this point, dissolving the urea compound in alcohol to prepare an alcohol solution of the urea compound is also a preferred method. This alcohol solution is then added to the PVA aqueous solution to prepare the adhesive.

(Active energy ray-curing adhesive)

Active energy ray-curing adhesives are adhesives that cure upon exposure to active energy rays such as ultraviolet rays. Examples include adhesives containing a polymerizable compound and a photopolymerization initiator, adhesives containing a photoreactive resin, and adhesives containing an adhesive resin and a photoreactive crosslinker. Examples of polymerizable compounds include photopolymerizable monomers such as photocurable epoxy monomers, photocurable acrylic monomers, and photocurable urethane monomers, as well as oligomers derived from these monomers. Examples of the aforementioned photopolymerization initiators include compounds containing substances that generate active species such as neutral radicals, anionic radicals, and cationic radicals upon exposure to active energy rays such as ultraviolet rays.

<Urea-containing compound layer>

Urea compounds and dicarboxylic acids are not limited to being contained in the adhesive layer as described above. To improve the high-temperature durability of the polarizing plate, they can also be contained in layers other than the adhesive layer. For polarizing plates with a transparent protective film on only one side, a hardening layer can be applied to the polarizing element on the side opposite the transparent protective film to enhance physical strength.

In this embodiment, the curable layer can also contain a urea compound and a dicarboxylic acid, creating a layer containing a urea compound. Typically, such a curable layer is formed from a curable composition containing an organic solvent. However, paragraphs [0020] to [0042] of Japanese Patent Application Laid-Open No. 2017-075986 describe a method for forming such a curable layer from an aqueous solution of an active energy ray-curable polymer composition. Water-soluble urea compounds and dicarboxylic acids can be contained in such compositions.

The urea compound-containing layer preferably comprises at least one urea compound, at least one dicarboxylic acid, and a binder. Examples of the binder include polymer binders, thermosetting resin binders, and active energy ray-curing resin binders, and any of these binders can be preferably used.

The thickness of the urea compound-containing layer 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.

[Polarizing Plate Manufacturing Method]

The method for manufacturing a polarizing plate according to this embodiment includes a moisture content adjustment step and a lamination step. In the moisture content adjustment step, when manufacturing a polarizing plate having feature (a), the moisture content of the polarizing element is adjusted so that the moisture content of the polarizing element is greater than or equal to the equilibrium moisture content at a relative humidity of 30% at a temperature of 20°C and less than or equal to the equilibrium moisture content at a relative humidity of 50% at a temperature of 20°C. The moisture content of the polarizing element can be adjusted according to the aforementioned description of the moisture content of the polarizing element. In the moisture content adjustment step, when producing a polarizing plate having feature (b), the moisture content of the polarizing plate is adjusted so that the moisture content of the polarizing plate is at least 30% at a relative humidity of 20°C and not more than 50% at a relative humidity of 20°C. The moisture content of the polarizing plate can be adjusted according to the above-described description of the moisture content of the polarizing plate. In the lamination step, the polarizing element and the transparent protective film are laminated with the adhesive layer interposed therebetween. In the lamination step, for example, the polarizing element, which has not been treated with the urea compound and the dicarboxylic acid, is laminated to the transparent protective film using an adhesive containing a urea compound and a dicarboxylic acid. The order of the moisture content adjustment step and the layering step is not limited, and the moisture content adjustment step and the layering step can also be performed in parallel.

[Composition of image display device]

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, when both sides of the polarizing plate have interlayer fillers, where layers other than air layers, specifically, solid layers such as adhesive layers, are in contact with each other, the transmittance tends to decrease in high-temperature environments. In image display devices using the polarizing plate of this embodiment, even with the interlayer filler structure, the decrease in transmittance of the polarizing plate in high-temperature environments can be suppressed. An example of an image display device includes an image display unit, a first adhesive layer laminated on the viewing side of the image display unit, and a polarizing plate laminated on the viewing side of the first adhesive layer. The image display device may further include a second adhesive layer laminated on the viewing side of the polarizing plate, and a transparent member laminated on the surface of the second adhesive layer. In particular, the polarizing plate of this embodiment is preferably used in an image display device having an interlayer filler structure. This interlayer filler structure comprises a transparent member disposed on the viewing side of the image display device. The polarizing plate and the image display unit are bonded together via a first adhesive layer, and the polarizing plate and the transparent member are bonded together via a second adhesive layer. In this specification, either or both of the first and second adhesive layers may be referred to simply as "adhesive layers." Furthermore, the members used to bond the polarizing plate and the image display unit, and the members used to bond the polarizing plate and the transparent member, are not limited to adhesive layers and may also be adhesive layers.

<Image display unit>

Examples of image display cells include liquid crystal cells and organic electroluminescent cells. The liquid crystal cells can be reflective, utilizing external light; transmissive, utilizing light from a backlight or other light source; or transflective, utilizing both external and light from the light source. When the liquid crystal cell utilizes light from the light source, the image display device (liquid crystal display device) also includes a polarizing plate on the side of the image display cell (liquid crystal cell) opposite the viewing side, and further includes a light source. The polarizing plate on the light source side is preferably bonded to the liquid crystal cell via an appropriate adhesive layer. The liquid crystal cell drive system can employ any of the following types, including VA, IPS, TN, STN, and bend alignment (π-type).

Organic EL cells are preferably formed by sequentially stacking a transparent electrode, an organic light-emitting layer, and a metal electrode on a transparent substrate to form a light-emitting element (organic electroluminescent element). The organic light-emitting layer is a laminate of various organic films. For example, a laminate of a hole-injection layer composed of a triphenylamine derivative and a light-emitting layer composed of a fluorescent organic solid such as anthracene can be used; a laminate of these light-emitting layers and an electron-injection layer composed of a perylene derivative; or a laminate of a hole-injection layer, a light-emitting layer, and an electron-injection layer.

<Lamination of image display unit and polarizing plate>

When laminating the image display unit to the polarizing plate, an adhesive layer (adhesive sheet) is preferably used. From the perspective of workability, laminating the polarizing plate to the image display unit with an adhesive layer attached to one side of the polarizing plate is preferred. The adhesive layer can be attached to the polarizing plate using appropriate methods. Examples include: preparing an adhesive solution containing 10% to 40% by mass by dissolving or dispersing the base polymer or its components in a suitable solvent, such as toluene or ethyl acetate, either singly or in a mixture, and directly attaching the adhesive solution to the polarizing plate by a suitable spreading method such as casting or coating; and forming an adhesive layer on a separator film and transferring the adhesive layer to the polarizing plate.

<Adhesive layer>

The adhesive layer can consist of one or two or more layers, preferably one layer. The adhesive layer can be composed of an adhesive composition primarily composed of (meth)acrylic resins, rubber resins, urethane resins, ester resins, silicone resins, or polyvinyl ether resins. Among these, adhesive compositions based on (meth)acrylic resins, which exhibit excellent transparency, weather resistance, and heat resistance, are preferred. The adhesive composition can be either active energy ray-curing or thermosetting.

The (meth)acrylic resin (base polymer) used in the adhesive composition is preferably a polymer or copolymer containing one or more (meth)acrylate monomers such as butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, or 2-ethylhexyl (meth)acrylate. In the base polymer, a polar monomer is preferably copolymerized. Examples of polar monomers include (meth)acrylic acid compounds, 2-hydroxypropyl (meth)acrylate compounds, hydroxyethyl (meth)acrylate compounds, (meth)acrylamide compounds, N,N-dimethylaminoethyl (meth)acrylate compounds, and glycidyl (meth)acrylate compounds, as well as monomers having carboxyl, hydroxyl, amide, amino, or epoxy groups.

The adhesive composition may contain only the above-mentioned base polymer, but typically also contains a crosslinking agent. Examples of crosslinking agents include metal ions with a valence of two or more and forming metal carboxylates with carboxyl groups, polyamine compounds that form amide bonds with carboxyl groups, polyepoxides or polyols that form ester bonds with carboxyl groups, and polyisocyanate compounds that form amide bonds with carboxyl groups. Polyisocyanate compounds are preferred.

Active energy ray-curing adhesive compositions cure upon exposure to active energy rays, such as ultraviolet rays or electron beams. They maintain adhesiveness and close adhesion to adherends such as films even before exposure to active energy rays. Furthermore, the adhesive can be cured and its adhesion adjusted by exposure to active energy rays. Active energy ray-curing adhesive compositions are preferably ultraviolet-curing. Active energy ray-curing adhesive compositions contain, in addition to a base polymer and a crosslinking agent, an active energy ray-polymerizable compound. Optionally, they may also contain a photopolymerization initiator, a photosensitizer, and the like.

The adhesive composition may include light-scattering microparticles, beads (resin beads, glass beads, etc.), glass fibers, resins other than base polymers, adhesives, fillers (metal powder or other inorganic powders, etc.), antioxidants, UV absorbers, dyes, pigments, colorants, defoamers, corrosion inhibitors, photopolymerization initiators, and other additives.

The adhesive layer can be formed by applying a dilution of the adhesive composition in an organic solvent onto the surface of a substrate film, image display unit, or polarizing plate and drying it. The substrate film is generally a thermoplastic resin film, a typical example of which is a release-treated release film. For example, the release film can be a film made of a resin such as polyethylene terephthalate, polybutylene terephthalate, polycarbonate, or polyarylate, with the adhesive layer-forming surface subjected to a release treatment such as silicone treatment.

Alternatively, an adhesive composition can be applied directly to the release-treated surface of the release film to form an adhesive layer, and the release film-attached adhesive layer can be deposited on the surface of the polarizer. Alternatively, an adhesive composition can be applied directly to the surface of the polarizing plate to form an adhesive layer, and the release film can be deposited on the surface outside the adhesive layer.

When the adhesive layer is disposed on the surface of the polarizing plate, it is preferred to perform a surface activation treatment such as plasma treatment or corona treatment on the bonding surface of the polarizing plate and/or the bonding surface of the adhesive layer. Corona treatment is more preferred.

Alternatively, an adhesive composition may be applied to the second release film to form an adhesive layer, and a release film may be laminated on the adhesive layer to form an adhesive sheet. The second release film may be peeled off from the adhesive sheet, and the resulting release film-attached adhesive layer may be laminated on the polarizing plate. The second release film preferably has a weaker adhesion to the adhesive layer than the release film and is easily peelable.

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

<Transparent components>

Examples of transparent components placed on the viewing side of an image display device include a transparent plate (window layer) or a touch panel. The transparent plate can be one with suitable mechanical strength and thickness. Examples of such transparent plates include transparent resin plates made of polyimide, acrylic, or polycarbonate resins, or glass plates. Functional layers such as antireflection layers may also be laminated on the viewing side of the transparent plate. Furthermore, if the transparent plate is a transparent resin plate, a hard coating layer to increase physical strength or a low-permeability layer to reduce moisture permeability may also be laminated. Touch panels can be made from various materials, including resistive film, electrostatic capacitive, optical, and ultrasonic touch panels, or glass or transparent resin panels with touch sensor functionality. When using an electrostatic capacitive touch panel as a transparent component, it is preferable to place a transparent plate made of glass or transparent resin on the viewing side of the touch panel.

<Lamination of polarizing plate and transparent component>

When laminating the polarizing plate to the transparent member, it is preferred to use an adhesive or an active energy ray-curing adhesive. When using an adhesive, it can be applied using an appropriate method. Specific methods for applying the adhesive layer used in laminating the image display unit to the polarizing plate can be cited.

When using an active energy ray-curing adhesive, to prevent diffusion of the adhesive solution before curing, the following method is preferred: a barrier material is placed around the perimeter 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, alignment and degassing are performed as needed, and then active energy ray irradiation is used for curing.

[Example]

The present invention is described below in detail based on the following examples. The materials, reagents, amounts and ratios of substances, and operations shown in the following examples may be appropriately modified without departing from the spirit of the present invention. Therefore, the present invention is not limited to the following examples.

<Production of Polarizing Element A>

A 40μm-thick PVA film composed of PVA with an average degree of polymerization of approximately 2400 and a saponification degree of 99.9 mol% or greater was dry-uniaxially stretched to approximately 5 times its original length. The film, while still stretched, was immersed in pure water at 60°C for one minute. The film was then immersed in an aqueous solution of iodine/potassium iodide/water (weight ratio: 0.05/5/100) at 28°C for 60 seconds. The film was then immersed in an aqueous solution of potassium iodide/boric acid/water (weight ratio: 8.5/8.5/100) at 72°C for 300 seconds. The film was then rinsed with pure water at 26°C for 20 seconds and dried at 65°C to obtain a 15μm-thick polarizing element A with iodine adsorption alignment on the PVA. The thickness of the polarizing element was measured using a digital micrometer "MH-15M" manufactured by Nikon Corporation.

<Preparation of Adhesives 1 to 11>

(Preparation of PVA solution A for the next step)

50 g of a modified PVA resin containing acetyl groups ("GOHSENEX Z-410" manufactured by Mitsubishi Chemical Co., Ltd.) was dissolved in 950 g of pure water. The mixture was heated at 90°C for 2 hours and then cooled to room temperature to obtain a PVA solution for adhesives (hereinafter referred to as "PVA solution A").

(Preparation of adhesives 1 to 11)

Adhesives 1 to 11 were prepared by mixing PVA solution A, urea compound, dicarboxylic acid, and pure water so that the PVA content was 3.0% by mass and the urea compound and dicarboxylic acid content were as shown in Table 1.

[Table 1]

<Preparation of Transparent Protective Film A>

A commercially available acetylated cellulose membrane TD40 (Fuji Film Co., Ltd., 40 μm thick) was immersed in a 1.5 mol/L aqueous NaOH solution (saponification solution) maintained at 55°C for 2 minutes, then rinsed with water. The membrane was then immersed in a 0.05 mol/L aqueous sulfuric acid solution at 25°C for 30 seconds, then passed through a water bath under running water for 30 seconds to neutralize the membrane. This process was then repeated three times using an air knife to remove water, followed by drying in a drying zone at 70°C for 15 seconds. This produced a saponified membrane, known as Transparent Protective Film A.

<Production of Polarizing Plates 1 to 11>

Transparent protective film A was laminated to both sides of polarizing element A using a roll laminator, with adhesive 1 interposed therebetween. After lamination, the film was dried at 80°C for 5 minutes to obtain polarizing plate 1. The adhesive layer was adjusted so that the thickness on both sides after drying was 50 nm.

In polarizing plate 1, replace adhesive 1 with adhesives 2 to 11 to obtain polarizing plates 2 to 11.

(Adjusting the moisture content of the polarizing plate (polarizing element))

The polarizing plates 1 to 11 obtained above were stored for 72 hours at a temperature of 20°C and relative humidity of 30%, 35%, 40%, 45%, 50%, or 55%. The moisture content was measured using the Karl Fischer method after 66, 69, and 72 hours of storage. Under any humidity condition, the moisture content did not change after 66, 69, and 72 hours of storage. Therefore, the moisture content of the polarizing plates 1 to 11 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 the polarizing plate reaches equilibrium in a certain storage environment, the moisture content of the polarizing element in the polarizing plate can also be considered to have reached equilibrium in its storage environment. Furthermore, when the moisture content of the polarizing element in a polarizing plate reaches equilibrium under a certain storage environment, the moisture content of the polarizing plate can also be considered to have reached equilibrium under that storage environment.

<Optical laminates 1 to 14>

Optical laminates 1 to 14 were produced using any of the polarizing plates 1 to 11 listed in Table 2. The polarizing plates (polarizing elements) were stored at 20°C and a relative humidity of 35%, 40%, 45%, or 55% for 72 hours, with the moisture content of the polarizing plates (polarizing elements) being the equilibrium moisture content of the environment listed in Table 2.

<High-temperature durability evaluation>

(Preparation of samples for evaluation)

Optical laminates 1 through 14 were coated with an acrylic adhesive (LINTEC Co., Ltd., Model #7) on both sides and cut into 50 mm x 100 mm sections with the absorption axis parallel to the long side. Evaluation samples were prepared by laminating alkali-free glass (Corning "EAGLE XG") to each adhesive surface.

To evaluate the cross-light leakage of the aforementioned evaluation sample, an optical multilayer R was fabricated with the goal of creating a cross-polarization state by overlaying it with the evaluation sample. Specifically, an acrylic adhesive (manufactured by LINTEC Co., Ltd., model #7) was applied to only one side of the aforementioned polarizing plate 9. The plate was then cut to a size of 50 mm x 100 mm with the absorption axis parallel to the short side. Alkaline-free glass ("EAGLE XG" manufactured by Corning) was bonded to the adhesive surface to create the optical multilayer R for cross-light leakage evaluation.

<Single Body Transmittance Evaluation (105°C)>

After autoclaving for one hour at 50°C and a pressure of 5 kgf/ ^cm² (490.3 kPa), samples of optical laminates 1 through 14 were placed in an environment at 23°C and a relative humidity of 55% for 24 hours. The transmittance of samples 1 through 14 was then measured (initial value). The samples were then stored in a heated environment at 105°C and measured every 50 hours until 100 to 200 hours. Evaluation was performed based on the time it took for the transmittance to decrease by more than 5% from the initial value, using the following criteria. The results are shown in Table 2.

After 200 hours, the penetration rate decreases by less than 5%: A

Penetration rate drops by more than 5% between 150 and 200 hours: B

Transmittance drops by more than 5% between 100 and 150 hours: C

If the penetration rate decreases by 5% or more after 100 hours: D

<Evaluation of Orthogonal Light Leakage>

Evaluation samples were prepared after 200 hours of single-element transmittance measurement in the aforementioned single-element transmittance evaluation. Optical multilayer R, used for cross-polarization evaluation and not exposed to a heated environment, was placed with the evaluation sample in a crossed-polarization relationship and mounted on a backlight. With the surrounding area shielded from light, cross-light leakage was visually observed and evaluated in four stages using the following criteria. The results are shown in Table 2. Samples with a single-element transmittance rating other than A were excluded from the cross-light leakage evaluation due to coloration caused by polyeneization.

No orthogonal light leakage at all: A

Almost no orthogonal light leakage is visible: B

Those who can slightly see orthogonal light leakage: C

Clearly see the orthogonal light leak :D

[Table 2]

Polarizing plates (optical laminates 1 to 10), formed by laminating a polarizing element to a transparent protective film using an adhesive containing a urea compound and a dicarboxylic acid, exhibited excellent high-temperature durability, with little reduction in transmittance even after exposure to a high temperature of 105°C. These polarizing plates had a moisture content of at least 30% relative humidity at a temperature of 20°C and no more than 50% relative humidity at a temperature of 20°C. Optical laminates 1 to 10 also demonstrated excellent cross-light leakage evaluations, with little reduction in polarization even after exposure to a high temperature of 105°C, demonstrating excellent high-temperature durability.

Claims (13)

A polarizing plate comprises a polarizing element obtained by adsorbing and aligning a dichroic dye on a polyvinyl alcohol-based resin layer, and a transparent protective film laminated on at least one side of the polarizing element. The polarizing element and the transparent protective film are bonded together via an adhesive layer, the adhesive layer being formed from an adhesive containing a urea compound and a dicarboxylic acid, the urea compound being at least one selected from the group consisting of urea, a urea derivative, thiourea, and a thiourea derivative. The polarizing element has a moisture content that is greater than or equal to an equilibrium moisture content of 30% at a relative humidity of 20°C and less than or equal to an equilibrium moisture content of 50% at a relative humidity of 20°C. A polarizing plate comprises a polarizing element obtained by adsorbing and aligning a dichroic dye on a polyvinyl alcohol-based resin layer, and a transparent protective film laminated on at least one side of the polarizing element. The polarizing element and the transparent protective film are bonded together via an adhesive layer, the adhesive layer being formed from an adhesive containing a urea compound and a dicarboxylic acid, the urea compound being at least one selected from the group consisting of urea, a urea derivative, thiourea, and a thiourea derivative. The polarizing plate has a moisture content that is greater than or equal to an equilibrium moisture content of 30% at a relative humidity of 20°C and less than or equal to an equilibrium moisture content of 50% at a relative humidity of 20°C. The polarizing plate according to claim 1 or 2, wherein the adhesive comprises at least one urea compound selected from the group consisting of urea derivatives and thiourea derivatives. The polarizing plate according to claim 1 or 2, wherein the adhesive comprises a polyvinyl alcohol-based resin. The polarizing plate according to claim 4, wherein the content of the urea compound in the adhesive is 0.1 parts by mass to 400 parts by mass per 100 parts by mass of the polyvinyl alcohol resin. The polarizing plate according to claim 4, wherein the content of the dicarboxylic acid in the adhesive is 1 part by mass or more and 50 parts by mass or less per 100 parts by mass of the polyvinyl alcohol-based resin. The polarizing plate according to claim 1 or 2, wherein the thickness of the adhesive layer is not less than 0.01 μm and not more than 7 μm. In the polarizing plate according to claim 1 or 2, the dicarboxylic acid is at least one of maleic acid or phthalic acid. The polarizing plate as claimed in claim 1 or 2, wherein the polarizing plate is used in an image display device, and in the image display device, the solid layer is disposed in contact with both sides of the polarizing plate. An image display device comprising: an image display unit; a first adhesive layer laminated on the viewing side surface of the image display unit; and a polarizing plate as described in any one of claims 1 to 9 laminated on the viewing side surface of the first adhesive layer. The image display device as described in claim 10 further comprises: 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. The image display device as described in claim 11, wherein the transparent component is a glass plate or a transparent resin plate. The image display device as described in claim 11, wherein the transparent component is a touch panel.