JP2024062155A - Polarizer - Google Patents

Abstract

[Problem] To provide a novel polarizing plate capable of suppressing a decrease in transmittance and the occurrence of cross-stripping in a high-temperature environment. [Solution] A polarizing plate having a polarizing element formed by adsorbing and aligning a dichroic dye in a polyvinyl alcohol-based resin layer, and a transparent protective film, the polarizing element having a luminous efficiency-corrected polarization degree of 99.9% or more and a crossed transmittance of 1.8% or less at a wavelength of 780 nm. [Selected Figures] None

Description

The present invention relates to a polarizing plate.

Liquid crystal display devices (LCDs) are widely used not only in LCD televisions, but also in personal computers, mobile devices such as mobile phones, and in-vehicle applications such as car navigation systems. Typically, LCDs have a liquid crystal panel with polarizing plates attached to both sides of a liquid crystal cell with an adhesive, and display is performed by controlling the light from the backlight with the liquid crystal panel. In recent years, organic electroluminescence (EL) display devices have also been widely used in televisions, mobile devices such as mobile phones, and in-vehicle applications such as car navigation systems, in the same way as LCDs. In organic EL display devices, a circular polarizing plate (a laminate including a polarizing element and a λ/4 plate) may be placed on the viewing side surface of the image display panel to prevent external light from being reflected by the metal electrode (cathode) and being viewed as a mirror surface.

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 in-vehicle image display devices are more often exposed to high-temperature environments than those used in mobile applications such as televisions and mobile phones, and therefore are required to have small changes in properties at high temperatures (high-temperature durability).

On the other hand, in order to prevent damage to the image display panel due to impact from the outer surface, a configuration in which a front panel such as a transparent resin plate or glass plate (also called a "window layer") is provided on the viewing side of the image display panel is becoming more common. In image display devices equipped with a touch panel, a configuration in which the touch panel is provided on the viewing side of the image display panel and a front panel is provided even further on the viewing side than the touch panel is widely adopted.

In such a configuration, if there is an air layer between the image display panel and a transparent member such as a front plate or a touch panel, the light reflection at the interface of the air layer causes reflection of external light, which tends to reduce the visibility of the screen. For this reason, there is a growing trend to adopt a configuration (hereinafter sometimes referred to as an "interlayer filling configuration") in which the space between the polarizing plate and the transparent member arranged on the viewing side 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 an "interlayer filler"). The interlayer filler is preferably a material with a refractive index close to that of the polarizing plate or the transparent member. As the interlayer filler, a pressure sensitive adhesive or a UV curing adhesive is used for the purpose of preventing the decrease in visibility due to reflection at the interface and for bonding and fixing each member (see, for example, Patent Document 1).

The interlayer filling structure is being widely adopted for mobile applications such as mobile phones, which are often used outdoors. Also, due to the increasing demand for visibility in recent years, the adoption of an interlayer filling structure in which a front transparent plate is placed on the surface of an image display panel and an adhesive layer or the like is filled between the panel and the front transparent plate is being considered for in-vehicle applications such as car navigation devices.

However, it has been reported that when such a configuration is adopted, the transmittance of the polarizing plate drops significantly in a high-temperature environment. As a solution to this problem, Patent Document 2 proposes a method of suppressing the drop in transmittance by keeping the moisture content per unit area of the polarizing plate below a specified amount and by keeping the saturated water absorption amount of the transparent protective film adjacent to the polarizing element below a specified amount. Patent Document 3 proposes a method of suppressing the drop in transmittance by including a urea-based compound in the water-based adhesive.

Japanese Patent Application Laid-Open No. 11-174417 JP 2014-102353 A JP 2020-190723 A

However, even if the decrease in transmittance in a high-temperature environment can be suppressed, when two polarizing plates are arranged in a crossed Nicol relationship, a problem of light leaking out (hereinafter also referred to as "cross-through") can occur. In particular, it has been found that configurations in which the thickness of the interlayer filler is 100 μm or more are more likely to cause cross-through. The present invention aims to provide a new polarizing plate that can suppress the decrease in transmittance and the occurrence of cross-through in a high-temperature environment.

The present invention provides the following polarizing plates.
[1] A polarizing plate having a polarizing element formed by adsorbing and aligning a dichroic dye in a polyvinyl alcohol-based resin layer, and a transparent protective film,
The polarizing element is a polarizing plate having a luminosity-corrected polarization degree of 99.9% or more and a crossed transmittance at a wavelength of 780 nm of 1.8% or less.
[2] The polarizing element and the transparent protective film are attached to each other with an adhesive layer formed from an aqueous adhesive containing a urea compound,
The polarizing plate according to [1], wherein the urea-based compound is at least one selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives.
[3] The polarizing plate according to [2], wherein the urea compound is at least one selected from the group consisting of urea derivatives and thiourea derivatives.
[4] The polarizing plate according to [2] or [3], wherein the aqueous adhesive contains a polyvinyl alcohol-based resin.
[5] The polarizing plate according to [4], wherein the content of the urea compound in the aqueous adhesive is 0.1 parts by mass or more and 400 parts by mass or less with respect to 100 parts by mass of the polyvinyl alcohol resin.
[6] The aqueous adhesive contains methanol,
The polarizing plate according to any one of items [2] to [5], wherein the methanol concentration is 10% by mass or more and 70% by mass or less.
[7] The polarizing plate according to any one of [2] to [6], wherein the aqueous adhesive contains cyclodextrins.
[8] The polarizing plate according to any one of [2] to [7], wherein the adhesive layer has a thickness of 0.01 μm or more and 7 μm or less.
[9] The polarizing plate according to any one of [1] to [8], wherein the polarizing element has a thickness of 15 μm or less.
[10] The polarizing plate according to any one of [1] to [9], wherein the moisture content of the polarizing element is equal to or higher than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 30% and equal to or lower than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 50%.
[11] The polarizing plate according to any one of [1] to [9], wherein the moisture content of the polarizing plate is equal to or higher than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 30% and equal to or lower than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 50%.
[12] The polarizing plate according to any one of [1] to [11], wherein a pressure-sensitive adhesive layer having a thickness of 50 μm or less is formed on one surface of the polarizing plate, and a pressure-sensitive adhesive layer having a thickness of 50 μm or more is formed on the other surface of the polarizing plate.

According to the present invention, it is possible to provide a polarizing plate with improved high-temperature durability. According to the present invention, it is possible to provide a polarizing plate in which the decrease in transmittance and the occurrence of cross-over are suppressed in a high-temperature environment, even when used in an image display device with an interlayer filling configuration.

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

[Polarizer]
A polarizing plate according to an embodiment of the present invention includes a polarizing element in which a dichroic dye is adsorbed and aligned in a layer containing a polyvinyl alcohol-based resin, and a transparent protective film. The polarizing element has a luminosity-corrected polarization degree of 99.9% or more, and a cross transmittance of 1.8% or less at a wavelength of 780 nm. The polarizing element has a luminosity-corrected polarization degree of 99.9% or more, preferably 99.950% or more and 99.999% or less, and more preferably 99.990% or more and 99.999% or less. The polarizing element also has a cross transmittance of 1.8% or less at a wavelength of 780 nm, preferably 0.1% or more and 1.7% or less, more preferably 0.2% or more and 1.6% or less, even more preferably 0.3% or more and 1.5% or less, and most preferably 0.4% or more and 1.4% or less. The polarizing element of the polarizing plate according to this embodiment has a luminosity-corrected polarization degree and a cross transmittance within the above ranges, so that the decrease in transmittance and the occurrence of cross-drop can be suppressed even when exposed to a high-temperature environment for a long period of time. It is presumed that the cross-drop caused by the decrease in the PVA-I ₅ complex in a high-temperature environment can be suppressed by allowing a larger amount of the PVA-I ₅ complex to exist in the polarizing element. It has been found that the absorption wavelength of the PVA-I ₅ complex is maximum at around 610 nm, but the cross transmittance at longer wavelengths is more susceptible to influence as an index of deterioration, and therefore the cross transmittance at the maximum wavelength of 780 nm in the visible light region is used in particular. In addition, iodine ions have the function of promoting polyenation. It is presumed that the amount of iodine ions (I ⁻ ) is reduced at a stage before exposure to a high-temperature environment by allowing a larger amount of the PVA-I ₅ complex to exist in the polarizing element. It is considered that the presence of a larger amount of the PVA-I ₅ complex in the polarizing element contributes to suppressing the decrease in transmittance (polyenation) in a high-temperature environment. In this specification, the luminous efficiency-corrected polarization degree and cross transmittance of the polarizing element are values measured by the measurement method described in the examples.

In the polarizing plate of this embodiment, the polarizing element and the transparent protective film are bonded together by an adhesive layer preferably made of an aqueous adhesive containing a urea compound. The aqueous adhesive may contain cyclodextrins. The polarizing plate according to this embodiment preferably has at least one of the following characteristics (a) and (b).
(a) The moisture content of the polarizing element is equal to or higher than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 30%, and is equal to or lower than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 50%.
(b) The moisture content of the polarizing plate is equal to or higher than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 30%, and is equal to or lower than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 50%.

Conventional polarizing plates with excellent high-temperature durability include, for example, polarizing plates in which the decrease in transmittance is suppressed even when the polarizing plate alone is left in an environment at a temperature of 95°C for 1,000 hours. However, even such polarizing plates, when used in an interlayer filling configuration, may show a significant decrease in transmittance and polarization degree in the center of the polarizing plate surface when left in an environment at a temperature of 105°C for 240 hours. The significant decrease in transmittance and polarization degree of a polarizing plate in a high-temperature environment is considered to be a problem that is particularly likely to occur when an image display device that employs 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 front panel is exposed to a high-temperature environment.

Polarizing plates with significantly reduced transmittance due to the interlayer filling structure are considered to have a polyene structure (-C=C) _n- , since Raman spectroscopy shows peaks at around 1100 cm ^-1 (derived from =C-C= bonds) and around 1500 cm ^-1 (derived from -C=C- bonds). The polyene structure is presumably formed when the polyvinyl alcohol constituting the polarizing element is polyenized by dehydration (Patent Document 2, paragraph [0012]).

The polarizing plate according to this embodiment can further improve high-temperature durability. The polarizing plate according to this embodiment is incorporated into an image display device with an interlayer filling configuration, and can suppress a decrease in transmittance and the occurrence of cross-passing even when exposed to a high-temperature environment, for example, a temperature of 105°C.

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

PVA resins are obtained by saponifying polyvinyl acetate resins. Examples of polyvinyl acetate resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, as well as copolymers of vinyl acetate and other monomers that can be copolymerized with it. Examples of other copolymerizable monomers include unsaturated carboxylic acids, olefins such as ethylene, vinyl ethers, and unsaturated sulfonic acids.

In this embodiment, it is preferable to form the PVA-based resin layer from a PVA-based resin having a boron adsorption rate of 5.70% by mass or more. That is, it is preferable that the boron adsorption rate of the PVA-based resin in the raw material stage before dyeing or stretching is 5.70% by mass or more. By using such a PVA-based resin, it is easy to obtain a polarizing element having a luminosity-corrected polarization degree of 99.9% or more and a cross transmittance of 1.8% or less at a wavelength of 780 nm. In addition, it is preferable that the boron adsorption rate of the PVA-based resin is 10% by mass or less. By using such a PVA-based resin to prepare a polarizing element, it is possible to shorten the treatment time by boric acid treatment without increasing the concentration of boric acid in the boric acid treatment tank, and it is easy to obtain a desired polarizing element and to increase the productivity of the polarizing element. If the boron adsorption rate of the PVA-based resin is 10% by mass or less, an appropriate amount of boron is incorporated into the PVA-based resin layer, and it is easy to reduce the contraction force of the polarizing element. The boron adsorption rate of PVA-based resin can be measured by the method described in the examples below.

The boron adsorption rate of a PVA-based resin is a characteristic that reflects the spacing between molecular chains and the crystal structure in the PVA-based resin. It is believed that a PVA-based resin with a boron adsorption rate of 5.70% by mass or more has wider spacing between molecular chains and fewer crystals of the PVA-based resin than a PVA-based resin with a boron adsorption rate of less than 5.70% by mass. This makes it easier for boron, the first metal ion, and the second metal ion to penetrate into the PVA-based resin layer, and it is presumed that the degree of polarization is less likely to decrease in a high-temperature environment.

The boron adsorption rate of the PVA-based resin can be adjusted, for example, by subjecting the PVA-based resin to a pretreatment such as hot water treatment, acid solution treatment, ultrasonic irradiation treatment, or radiation irradiation treatment before the production of the polarizing element. These treatments can increase the spacing between molecular chains in the PVA-based resin or destroy the crystal structure. An example of the hot water treatment is immersing the resin in pure water at 30°C to 100°C for 1 to 90 seconds and then drying. An example of the acid solution treatment is immersing the resin in an aqueous boric acid solution with a concentration of 10% by mass to 20% by mass for 1 to 90 seconds and then drying. An example of the ultrasonic treatment is irradiating the resin with ultrasonic waves at a frequency of 20 to 29 kc for 30 seconds to 10 minutes at an output of 200 W to 500 W. The ultrasonic treatment can be performed in a solvent such as water.

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

The thickness of the polarizing element is preferably 3 μm to 35 μm, more preferably 4 μm to 30 μm, even more preferably 5 μm to 25 μm, and particularly preferably 15 μm or less. By making the thickness of the polarizing element 35 μm or less, the effect of polyenation of the PVA-based resin on the deterioration of optical properties in a high-temperature environment can be suppressed. By making the thickness of the polarizing element 3 μm or more, it becomes easier to configure it to achieve the desired optical properties.

The polarizing element preferably contains a urea-based compound and cyclodextrins. In this embodiment, the polarizing element and the retardation layer consisting of a cured layer of a polymerizable liquid crystal compound are bonded together by an adhesive layer formed from an adhesive containing a urea-based compound and cyclodextrins, so it is presumed that a part of the urea-based compound and a part of the cyclodextrins are transferred from the adhesive layer and are contained in the polarizing element. The urea-based compound and cyclodextrins in the polarizing element may contain those added during the manufacturing process of the polarizing element. By providing a polarizing element containing a urea-based compound and cyclodextrins, the transmittance is less likely to decrease even when the polarizing plate is exposed to a high-temperature environment. In addition, by providing an adhesive layer containing a urea-based compound and cyclodextrins, the decrease in the polarization degree can be suppressed even when the polarizing plate is exposed to a high-temperature environment. When the polarization degree of the polarizing plate decreases, cross-passing is more likely to occur, but according to this embodiment, the polarization degree is less likely to decrease even when exposed to a high-temperature environment, so that cross-passing is also more likely to be suppressed. It is believed that this effect is achieved because the urea compounds and cyclodextrins contained in the polarizing element suppress the polyenization of the PVA-based resin.

Methods for incorporating a urea-based compound and cyclodextrins into a polarizing element include immersing a PVA-based resin layer in a treatment solvent containing a urea-based compound and/or cyclodextrins, or spraying, flowing, or dripping the treatment solvent onto the PVA-based resin layer. Among these, the method of immersing a PVA-based resin layer in a treatment solvent containing both a urea-based compound and cyclodextrins is preferably used.

The process of immersing the PVA-based resin layer in a treatment solvent containing a urea-based compound and cyclodextrins may be carried out simultaneously with the swelling, stretching, dyeing, crosslinking, washing, and other processes in the manufacturing method of a polarizing element described below, or may be provided separately from these processes. The process of incorporating a urea-based compound and cyclodextrins into the PVA-based resin layer is preferably carried out after dyeing the PVA-based resin layer with iodine, and more preferably carried out simultaneously with the crosslinking process after dyeing. This method results in small changes in hue, and can reduce the effect on the optical properties of the polarizing element.

In order to incorporate a urea-based compound and cyclodextrins into a polarizing element, they may be added both during the manufacture of the polarizing element and to the adhesive. Alternatively, one of a urea-based compound and a cyclodextrin may be incorporated during the manufacture of the polarizing element and the other or both may be incorporated into the adhesive, or both may be incorporated during the manufacture of the polarizing element and one may be incorporated into the adhesive.

The polarizing element preferably contains potassium ions (hereinafter sometimes referred to as "first metal ions"), and preferably contains metal ions other than potassium ions (hereinafter sometimes referred to as "second metal ions").

The content of the second metal ion in the polarizing element is preferably 0.05% by mass to 10.0% by mass, more preferably 0.05% by mass to 8.0% by mass, and even more preferably 0.1% by mass to 6.0% by mass. If the content of the second metal ion exceeds 10.0% by mass, the polarization degree may decrease in a high-temperature and high-humidity environment. If the content of the second metal ion is less than 0.05% by mass, the effect of improving durability in a high-temperature environment may not be sufficient. The content of the second metal ion in the polarizing element can be calculated as the mass fraction (mass%) of the metal element relative to the mass of the polarizing element, for example, by inductively coupled plasma (ICP) emission spectroscopy. It is considered that the metal element exists in the polarizing element as a metal ion or in a state in which it forms a crosslinked structure with a component of the polyvinyl alcohol resin, but the content of the second metal ion here is a value as a metal atom.

The second metal ion is not limited as long as it is a metal ion other than potassium ion, but is preferably an ion of a metal other than an alkali metal, and preferably contains at least one type of metal ion of a transition metal such as cobalt, nickel, zinc, chromium, aluminum, copper, manganese, or iron, from the viewpoints of color adjustment and durability. Among these metal ions, zinc ions are preferred from the viewpoints of color adjustment and heat resistance.

The boron content of the polarizing element is preferably 2.4% by mass or more. 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 contraction force of the polarizing element increases, and problems such as peeling between the polarizing element and other members such as a front plate to which the polarizing element is bonded when the polarizing element is incorporated into an image display device may occur. If the boron content is less than 2.4% by mass, the desired optical characteristics may not be achieved. The boron content of the polarizing element can be calculated as the mass fraction (mass%) of boron relative to the mass of the polarizing element, for example, by inductively coupled plasma (ICP) emission spectroscopy. Boron is thought to be present in the polarizing element in the form of boric acid or in the form of a cross-linked structure formed between boric acid and a component of a polyvinyl alcohol-based resin, and the boron content referred to here is the value in terms of boron atoms (B).

The boron content of the polarizing element is preferably 2.4% by mass or more and 8.0% by mass or less, and more preferably 3.9% by mass or more and 8.0% by mass or less. By satisfying such a numerical range, the decrease in the polarization degree is suppressed even when exposed to a high-temperature environment.

From the viewpoint of suppressing a decrease in the degree of polarization in a high-temperature environment, 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, and from the viewpoint of suppressing a change in hue 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 manner as the second metal ion content, and the potassium ion content referred to here is the value in terms of potassium atoms.

Although the detailed mechanism is unclear, it is presumed that when the boron content is higher and the potassium ion content is lower than in conventional polarizing elements, the hydroxyl groups of the polyvinyl alcohol in the polarizing element are protected (stabilized) by boric acid crosslinking, and that the iodine ions that serve as counter ions in the polarizing element are stabilized by the appropriate potassium ion content.

(Urea compounds)
The urea-based compound is at least one selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives. The urea-based compounds can be used alone or in combination of two or more. Urea-based compounds include water-soluble and poorly water-soluble urea-based compounds, and either type of urea-based compound can be used. When a poorly water-soluble urea-based compound is used in a water-soluble adhesive, it is preferable to devise a dispersion method so that an increase in haze does not occur after the adhesive layer is formed.

(Urea Derivatives)
The 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, the substituent is not particularly limited, but is preferably a substituent consisting of a carbon atom, a hydrogen atom, and an oxygen atom.

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.

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).

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.

(Thiourea derivatives)
A thiourea derivative is a compound in which at least one of the four hydrogen atoms of a thiourea molecule is substituted with a substituent. In this case, the substituent is not particularly limited, but is preferably a substituent consisting of a carbon atom, a hydrogen atom, and an oxygen atom.

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.

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.

An example of a 3-substituted thiourea is trimethylthiourea, and an example of a 4-substituted thiourea is tetramethylthiourea or 1,1,3,3-tetraethylthiourea.

Among urea-based compounds, urea derivatives or thiourea derivatives are preferred, and urea derivatives are more preferred, in that when used in an image display device with an interlayer filling configuration, the decrease in transmittance in a high-temperature environment is suppressed and the decrease in polarization degree is small (cross loss is suppressed). Among urea derivatives, mono-substituted urea or di-substituted urea is preferred, and mono-substituted urea is more preferred. Di-substituted ureas include 1,1-substituted urea and 1,3-substituted urea, with 1,3-substituted urea being more preferred.

(Cyclodextrins)
Cyclodextrin is a non-reducing cyclic oligosaccharide in which glucose is bonded in a ring shape by α-1,4 bonds. The more glucose units that constitute cyclodextrins, the larger the inner diameter of the cavity in the molecule. The cyclodextrins used in the present invention preferably contain 6 or more glucose units, and examples of such cyclodextrins include α-, β-, γ-, and δ-cyclodextrins that contain 6, 7, 8, and 9 glucose units, respectively. Cyclodextrins include α-, β-, γ-, and δ-cyclodextrins, as well as branched cyclodextrins having oligosaccharides such as glucose and malctose on the branched sugar chain. Cyclodextrins include cyclodextrin derivatives in which alkyl groups such as methyl groups; hydroxyalkyl groups such as 2-hydroxyethyl groups, 2-hydroxypropyl groups, 2,3-dihydroxypropyl groups, and 2-hydroxybutyl groups are bonded to the above cyclodextrins or branched cyclodextrins. Cyclodextrins may be used alone or in combination of two or more types.

(Feature (a))
In the case of the characteristic (a), the moisture content of the polarizing element is equal to or higher than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 30%, and equal to or lower than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 50%. The moisture content of the polarizing element is preferably equal to or lower than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 45%, more preferably equal to or lower than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 42%, and even more preferably equal to or lower than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 38%. If the moisture content of the polarizing element is lower than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 30%, the handling property of the polarizing element is deteriorated and the polarizing element is easily broken. If the moisture content of the polarizing element is higher than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 50%, the transmittance of the polarizing element is easily deteriorated. It is presumed that if the moisture content of the polarizing element is high, the polyenation of the PVA-based resin is easily promoted. The moisture content of the polarizing element is the moisture content of the polarizing element in the polarizing plate.

Methods for checking whether the moisture content of a polarizing element is within the range of 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 50% include storing the polarizing element in an environment adjusted to the above temperature and relative humidity ranges, and assuming that the element has reached equilibrium with the environment if there is no change in mass for a certain period of time, or calculating in advance the equilibrium moisture content of the polarizing element in an environment adjusted to the above temperature and relative humidity ranges, and comparing the moisture content of the polarizing element with the previously calculated equilibrium moisture content.

Methods for producing a polarizing element having a moisture content 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 50% are not particularly limited, but examples include a method in which the polarizing element is stored in an environment adjusted to the above temperature and relative humidity range for 10 minutes to 3 hours, or a method in which the polarizing element is heat-treated at 30°C to 90°C.

Another preferred method for producing a polarizing element having the above moisture content is to store a laminate in which a protective film is laminated on at least one side of a polarizing element, or a polarizing plate constructed using a polarizing element, in an environment adjusted to the above temperature and relative humidity ranges for 10 minutes to 120 hours, or to heat treat the polarizing plate at 30°C to 90°C. When producing an image display device employing an interlayer filling configuration, a polarizing plate may be incorporated into the image display device, and the image display device in which the polarizing plate is incorporated may be stored in an environment adjusted to the above temperature and relative humidity ranges for 10 minutes to 3 hours, or may be heated at 30°C to 90°C, and then a front panel may be attached.

The moisture content of the polarizing element is preferably adjusted to be within the above numerical range at the material stage used to construct the polarizing plate, which is either the polarizing element alone or a laminate of the polarizing element and a protective film. If the moisture content is adjusted after the polarizing plate is constructed, curling may become too large, which may lead to problems when the polarizing plate is attached to an image display cell. By constructing a polarizing plate using a polarizing element that has been adjusted to have the above moisture content at the material stage before the polarizing plate is constructed, a polarizing plate having a polarizing element whose moisture content satisfies the above numerical range can be easily constructed. The moisture content of the polarizing element in the polarizing plate may be adjusted to be within the above numerical range while the polarizing plate is attached to the image display cell. In this case, the polarizing plate is less likely to curl because it is attached to the image display cell.

(Feature (b))
In the case of having the characteristic (b), the moisture content of the polarizing plate is equal to or higher than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 30%, and equal to or lower than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 50%. The moisture content of the polarizing plate is preferably equal to or lower than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 45%, more preferably equal to or lower than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 42%, and even more preferably equal to or lower than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 38%. If the moisture content of the polarizing plate is lower than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 30%, the handling property of the polarizing plate is deteriorated and the polarizing plate is easily cracked. If the moisture content of the polarizing plate is higher than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 50%, the transmittance of the polarizing element is easily decreased. It is presumed that the high moisture content of the polarizing plate makes it easier for the PVA-based resin to be polyenized.

Methods for checking whether the moisture content of a polarizing plate is within the range of 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 50% include storing the polarizing plate in an environment adjusted to the above temperature and relative humidity ranges, and assuming that the plate has reached equilibrium with the environment if there is no change in mass for a certain period of time, or calculating in advance the equilibrium moisture content of the polarizing plate in an environment adjusted to the above temperature and relative humidity ranges, and comparing the moisture content of the polarizing plate with the previously calculated equilibrium moisture content.

There are no particular limitations on the method for producing a polarizing plate whose moisture content 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 50%, but examples of the method include storing the polarizing plate in an environment adjusted to the above temperature and relative humidity ranges for 10 minutes to 3 hours, or heat treating the polarizing plate at 30°C to 90°C.

When manufacturing an image display device that employs an interlayer filling configuration, a polarizing plate may be incorporated into the image display device, and the image display device with the polarizing plate incorporated may be stored in an environment adjusted to the above temperature and relative humidity ranges for 10 minutes to 3 hours or heated to 30°C to 90°C, after which a front panel may be attached.

(Method of manufacturing polarizing element)
The method for producing the polarizing element is not particularly limited, but typical methods include a method in which a PVA type resin film wound in advance into a roll is sent out and stretched, dyed, crosslinked, etc. (hereinafter referred to as "production method 1"), and a method including a step of applying a coating liquid containing a PVA type resin onto a substrate film to form a PVA type resin layer as a coating layer, and stretching the obtained laminate (hereinafter referred to as "production method 2").

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

The swelling process is a process in which the PVA-based resin film is immersed in a swelling bath. The swelling process can remove dirt and blocking agents from the surface of the PVA-based resin film, and can also suppress uneven dyeing by swelling the PVA-based resin film. A medium mainly composed of water, such as water, distilled water, or pure water, is usually used for the swelling bath. The swelling bath may contain surfactants, alcohol, or the like, as appropriate, according to conventional methods. In order to control 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.

The temperature of the swelling bath is preferably 10°C or more and 60°C or less, more preferably 15°C or more and 45°C or less, and even more preferably 18°C or more and 30°C or less. The immersion time in the swelling bath cannot be determined in general because the degree of swelling of the PVA-based resin film is affected by the temperature of the swelling bath, but is preferably 5 seconds or more and 300 seconds or less, more preferably 10 seconds or more and 200 seconds or less, and even more preferably 20 seconds or more and 100 seconds or less. The swelling process may be carried out only once, or may be carried out multiple times as necessary.

The dyeing process is a treatment process in which the PVA-based resin film is immersed in a dye bath (iodine solution), and allows dichroic dyes such as iodine to be adsorbed and oriented in the PVA-based resin film. The iodine solution is usually preferably an aqueous iodine solution, and contains 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, titanium iodide, and the like. Among these, potassium iodide is preferred from the viewpoint of controlling the potassium content in the polarizing element.

The concentration of iodine 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 concentration of iodide 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 or more and 50°C or less, more preferably 15°C or more and 45°C or less, and even more preferably 18°C or more and 30°C or less. The immersion time in the dye bath cannot be determined in general because the degree of dyeing of the PVA-based resin film is affected by the temperature of the dye bath, but is preferably 10 seconds or more and 300 seconds or less, and more preferably 20 seconds or more and 240 seconds or less. The dyeing process may be carried out only once, or may be carried out multiple times as necessary.

The crosslinking process is a process in which the PVA-based resin film dyed in the dyeing process is immersed in a treatment bath (crosslinking bath) containing a boron compound. The boron compound crosslinks the polyvinyl alcohol-based resin film, and iodine molecules or dye molecules can be adsorbed to the crosslinked structure. Examples of boron compounds include boric acid, borate salts, and borax. The crosslinking bath is generally an aqueous solution, but may also be a mixed solution of water and an organic solvent that is miscible with water. The crosslinking bath preferably contains potassium iodide from the viewpoint of controlling the potassium content in the polarizing element.

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

The temperature of the crosslinking bath is preferably 20°C or higher and 70°C or lower, and more preferably 30°C or higher and 60°C or lower. The immersion time in the crosslinking bath cannot be determined in general because the degree of crosslinking of the PVA-based resin film is affected by the temperature of the crosslinking bath, but is preferably 5 seconds or higher and 300 seconds or lower, and more preferably 10 seconds or higher and 200 seconds or lower. The crosslinking process may be carried out only once, or may be carried out multiple times as necessary.

The stretching process is a process in which the PVA-based resin film is stretched to a predetermined ratio in at least one direction. In general, the PVA-based resin film is uniaxially stretched in the conveying direction (longitudinal direction). There are no particular limitations on the stretching method, and either a wet stretching method or a dry stretching method can be used. The stretching process may be carried out only once, or may be carried out multiple times as necessary. The stretching process may be carried out at any stage in the production of the polarizing element.

In the wet stretching method, the treatment bath (stretching bath) can usually use a solvent such as water or a mixed solution of water and an organic solvent miscible with 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 1% by mass or more and 15% by mass or less, more preferably 2% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 6% by mass or less. The treatment bath (stretching bath) can contain a boron compound from the viewpoint of suppressing film breakage during stretching. When a boron compound is contained, the concentration of the boron compound in the stretching bath is preferably 1% by mass or more and 15% by mass or less, more preferably 1.5% by mass or more and 10% by mass or less, and more preferably 2% by mass or more and 5% by mass or less.

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 in general because the degree of stretching of the PVA-based resin film is affected by the temperature of the stretching bath, but is preferably 10 seconds to 800 seconds, and more preferably 30 seconds to 500 seconds. The stretching process in the wet stretching method may be performed together with one or more of the following processing steps: swelling step, dyeing step, crosslinking step, and washing step.

Examples of dry stretching methods include roll-to-roll stretching, heated roll stretching, and compression stretching. The dry stretching method may be carried out together with a drying process.

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

The cleaning process is a process in which the polyvinyl alcohol-based resin film is immersed in a cleaning bath, and foreign matter remaining on the surface of the polyvinyl alcohol-based resin film can be removed. The cleaning bath usually uses a medium whose main component is water, such as distilled water or pure water. In addition, 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.

The temperature of the cleaning bath is preferably 5°C or more and 50°C or less, more preferably 10°C or more and 40°C or less, and even more preferably 15°C or more and 30°C or less. The immersion time in the cleaning bath cannot be determined in general because the degree of cleaning of the PVA-based resin film is affected by the temperature of the cleaning bath, but is preferably 1 second or more and 100 seconds or less, more preferably 2 seconds or more and 50 seconds or less, and even more preferably 3 seconds or more and 20 seconds or less. The cleaning process may be performed only once, or may be performed multiple times as necessary. The stretching ratio in the cleaning process is preferably 1.002 times or more, and more preferably 1.003 times or more. In addition, the stretching ratio in the cleaning process is preferably 1.02 times or less, and more preferably 1.01 times or less. By adjusting the stretching ratio in the cleaning process in this way, it becomes easier to obtain a polarizing element having a luminosity-corrected polarization degree of 99.9% or more and a cross transmittance of 1.8% or less at a wavelength of 780 nm. This is presumably because adjusting the stretch ratio during the washing process improves the degree of orientation of the PVA crystals, promoting the stabilization of the iodine and PVA complex in the polarizing element.

The drying process is a process in which the PVA-based resin film cleaned in the cleaning process is dried to obtain a polarizing element. The drying can be performed by any suitable method, such as natural drying, air drying, or heat drying.

The manufacturing method 2 can be produced through a process of applying a coating liquid containing a PVA-based resin onto a substrate film, a process of uniaxially stretching the obtained laminated film, a process of dyeing the PVA-based resin layer of the uniaxially stretched laminated film with a dichroic dye to adsorb it and form a polarizing element, a process of treating the film with the adsorbed dichroic dye with an aqueous boric acid solution, and a process of washing with water after the treatment with the aqueous boric acid solution. The substrate film used to form the polarizing element may be used as a protective layer for the polarizing element. If necessary, the substrate film may be peeled off and removed from the polarizing element.

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

The protective film may also have other optical functions, and may be formed into a laminated structure in which multiple layers are laminated. From the viewpoint of optical properties, it is preferable that the thickness of the protective film is thin, but if it is too thin, the strength decreases and the processability becomes poor. The appropriate thickness is 5 to 100 μm, preferably 10 to 80 μm, and more preferably 15 to 70 μm.

The protective film may be a cellulose acylate film, a film made of a polycarbonate resin, a film made of a cycloolefin resin such as norbornene, a (meth)acrylic polymer film, or a polyester resin film such as polyethylene terephthalate. In a configuration in which protective films are provided on both sides of a polarizing element, when bonding is performed using a water-based adhesive such as a PVA adhesive, it is preferable that the protective film on at least one side is either a cellulose acylate film or a (meth)acrylic polymer film in terms of moisture permeability, and of these, a cellulose acylate film is preferred.

At least one of the protective films may have a retardation function for the purpose of viewing angle compensation or the like. In this case, the film itself may have a retardation function, a separate retardation layer may be provided, or a combination of both may be used.
In the above description, the film having phase difference function is directly attached to the polarizing element via an adhesive. However, the film may be attached to the polarizing element via a pressure-sensitive adhesive or adhesive via another protective film attached to the polarizing element.

[Adhesive layer]
It is preferable that at least one of the adhesives constituting the adhesive layer for bonding the protective film to the polarizing element is an aqueous adhesive. When protective films are bonded to both sides of the polarizing element, any adhesive such as an aqueous adhesive, a solvent-based adhesive, or an active energy ray curable adhesive can be used for the other side, but an aqueous adhesive is preferable.

It is also useful for the water-based adhesive to contain a urea-based compound from the viewpoint of improving heat resistance. The water-based adhesive preferably contains a polyvinyl alcohol-based resin (PVA-based resin). The water-based adhesive preferably further contains cyclodextrins. The urea-based compound that can be added to the water-based adhesive is at least one selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives, and examples of the urea-based compound that may be contained in the polarizing element include cyclodextrins that may be contained in the polarizing element. Examples of the cyclodextrins that can be added to the water-based adhesive include cyclodextrins that may be contained in the polarizing element.

When the adhesive is a water-based adhesive containing a PVA-based resin, the amount of the urea-based compound added 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.

When the adhesive is a water-based adhesive containing a PVA-based resin, the content of cyclodextrins is preferably 1 part by mass or more and 50 parts by mass or less, more preferably 1.5 parts by mass or more and 40 parts by mass or less, and even more preferably 2 parts by mass or more and 35 parts by mass or less, per 100 parts by mass of the PVA-based resin. If the content is less than 1 part by mass, the effect of suppressing polyenization of the polarizing element in a high-temperature environment may not be sufficient. On the other hand, if the content exceeds 50 parts by mass, the cyclodextrins may precipitate after the polarizing plate is produced.

When the adhesive is a water-based adhesive containing a PVA-based resin, it may contain a dicarboxylic acid such as maleic acid or phthalic acid in order to improve heat resistance. The content of the dicarboxylic acid is preferably 0.01 parts by mass or more and 5 parts by mass or less, more preferably 0.02 parts by mass or more and 1 part by mass or less, per 100 parts by mass of the PVA-based resin.

The thickness of the adhesive when applied can be set to any appropriate value. For example, it is set so that an adhesive layer (coating layer) having the desired thickness is obtained after curing or heating (drying). The thickness of the adhesive layer is preferably 0.01 μm or more and 7 μm or less, more preferably 0.01 μm or more and 5 μm or less, even more preferably 0.01 μm or more and 2 μm or less, and most preferably 0.01 μm or more and 1 μm or less.

(Water-based adhesive)
Any suitable aqueous adhesive may be used as the aqueous adhesive. Among them, an aqueous adhesive containing a PVA-based resin (PVA-based adhesive) is preferably used. The average polymerization degree of the PVA-based resin contained in the aqueous adhesive is preferably 100 to 5500, more preferably 1000 to 4500, from the viewpoint of adhesiveness. The average saponification degree is preferably 85 mol% to 100 mol%, more preferably 90 mol% to 100 mol%, from the viewpoint of adhesiveness.

The PVA-based resin contained in the aqueous adhesive is preferably one containing an acetoacetyl group, because it has excellent adhesion between the PVA-based resin layer and the protective film and excellent durability. The acetoacetyl-containing PVA-based resin can be obtained, for example, by reacting a PVA-based resin with diketene by any method. The degree of modification of the acetoacetyl-containing PVA-based resin with an acetoacetyl group 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.

Water-based adhesives can also contain crosslinking agents. Any known crosslinking agent can be used. Examples include water-soluble epoxy compounds, dialdehydes, and isocyanates.

When the PVA-based resin is an acetoacetyl group-containing PVA-based resin, the crosslinking agent is preferably any one of glyoxal, glyoxylate, and methylolmelamine, more preferably any one of glyoxal and glyoxylate, and particularly preferably glyoxal.

The water-based adhesive may also contain an organic solvent. The organic solvent is preferably an alcohol because it is miscible with water, and among alcohols, methanol or ethanol is more preferable. Some urea compounds have low solubility in water, but some have sufficient solubility in alcohol. In that case, one preferred embodiment is to dissolve the urea compound in alcohol to prepare an alcohol solution of the urea compound, and then add the alcohol solution of the urea compound to the aqueous PVA solution to prepare the adhesive.

The methanol concentration of the water-based 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. In addition, by making the methanol content 70% by mass or less, deterioration of the hue can be suppressed.

(Active energy ray curing adhesive)
The active energy ray curable adhesive is an adhesive that is cured by irradiation with active energy rays such as ultraviolet rays, and examples thereof include an adhesive containing a polymerizable compound and a photopolymerization initiator, an adhesive containing a photoreactive resin, and an adhesive containing a binder resin and a photoreactive crosslinking agent. Examples of the polymerizable compound include photopolymerizable monomers such as photocurable epoxy monomers, photocurable acrylic monomers, and photocurable urethane monomers, and oligomers derived from these monomers. Examples of the photopolymerization initiator include a compound containing a substance that generates active species such as neutral radicals, anion radicals, and cation radicals when irradiated with active energy rays such as ultraviolet rays.

<Urea Compound-Containing Layer>
The urea compound is 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 heat resistance of the polarizing plate.As for other layers, as described in the explanation of the transparent protective film, in recent years, in order to meet the demand for thinning of the polarizing plate, a polarizing plate having a protective film only on one side of the polarizing element has been developed.In such a configuration, a cured layer may be laminated on the side of the polarizing element that does not have the protective film in order to increase the physical strength, etc.

In this embodiment, such a cured layer may contain a urea-based compound. Typically, such a cured layer is formed from a curable composition containing an organic solvent, but paragraphs [0020] to [0042] of JP2017-075986A describe a method of forming such a cured layer from an aqueous solution of an active energy ray-curable polymer composition. Since many urea-based compounds are water-soluble, such a composition may contain a water-soluble urea-based compound.

[Method of manufacturing polarizing plate]
The manufacturing method of the polarizing plate of this embodiment can have a moisture content adjusting step and a lamination step. In the moisture content adjusting step, when a polarizing plate having the characteristic (a) is manufactured, the moisture content of the polarizing element is adjusted so that the moisture content of the polarizing element is equal to or higher than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 30%, and equal to or lower than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 50%. The moisture content of the polarizing element can be adjusted according to the description of the moisture content of the polarizing element described above. In the moisture content adjusting step, when a polarizing plate having the characteristic (b) is manufactured, the moisture content of the polarizing plate is adjusted so that the moisture content of the polarizing plate is equal to or higher than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 30%, and equal to or lower than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 50%. The moisture content of the polarizing plate can be adjusted according to the description of the moisture content of the polarizing plate described above. In the lamination step, the polarizing element and the transparent protective film are laminated via the adhesive layer. In the lamination step, for example, a polarizing element that has not been treated to contain a urea compound and a cyclodextrin is bonded to a transparent protective film using an adhesive containing a urea compound and a cyclodextrin. The order of the moisture content adjustment step and the lamination step is not limited, and the moisture content adjustment step and the lamination step may be performed in parallel.

[Configuration of image display device]
The polarizing plate of the present embodiment is used in various image display devices such as liquid crystal display devices and organic EL display devices. In the case of an image display device in which both sides of the polarizing plate are configured to be in contact with a layer other than an air layer, specifically a solid layer such as an adhesive layer, the transmittance is likely to decrease in a high-temperature environment. In the image display device using the polarizing plate of the present embodiment, even if the image display device has an interlayer filling configuration, the decrease in the transmittance of the polarizing plate in a high-temperature environment can be suppressed. An example of the 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 the present embodiment is suitably used in an image display device having an interlayer filling 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 one or both of the first adhesive layer and the second adhesive layer may be simply referred to as "adhesive layer". In addition, in this specification, a layer structure consisting of "first adhesive layer/polarizing plate/second adhesive layer", "first adhesive layer/polarizing plate", and "polarizing plate/second adhesive layer" may also be referred to as "polarizing plate". Note that the member used to bond the polarizing plate to the image display cell and the member used to bond the polarizing plate to the transparent member are not limited to an adhesive layer and may be an adhesive layer.

<Image display cell>
Examples of the image display cell include a liquid crystal cell and an organic EL cell. As the liquid crystal cell, any of a reflective liquid crystal cell that uses external light, a transmissive liquid crystal cell that uses light from a light source such as a backlight, and a semi-transmissive semi-reflective liquid crystal cell that uses both external light and light from a light source may be used. When the liquid crystal cell uses light from a light source, the image display device (liquid crystal display device) has a polarizing plate arranged on the opposite side to the viewing side of the image display cell (liquid crystal cell), and further has a light source arranged thereon. The polarizing plate on the light source side and the liquid crystal cell are preferably bonded together via an appropriate adhesive layer. As the driving method of the liquid crystal cell, any type such as VA mode, IPS mode, TN mode, STN mode, and bend orientation (π type) can be used.

As an organic EL cell, a light-emitting body (organic electroluminescence light-emitting body) is preferably formed by sequentially laminating 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 or the like and a light-emitting layer made of a fluorescent organic solid such as anthracene, a laminate of such a light-emitting layer and an electron injection layer made of a perylene derivative or the like, or a laminate of a hole injection layer, a light-emitting layer, and an electron injection layer.

<Laminating the image display cell and the polarizing plate>
A pressure-sensitive adhesive layer (pressure-sensitive adhesive sheet) is preferably used for bonding the image display cell and the polarizing plate. Among them, a method of bonding a polarizing plate with a pressure-sensitive adhesive layer, in which a pressure-sensitive adhesive layer is attached to one side of the polarizing plate, to the image display cell is preferred from the viewpoint of workability and the like. The pressure-sensitive adhesive layer can be attached to the polarizing plate by a suitable method. Examples of such methods include a method of preparing a pressure-sensitive adhesive solution of 10% by mass or more and 40% by mass or less by dissolving or dispersing a base polymer or a composition thereof in a solvent consisting of a single or mixture of suitable solvents such as toluene and ethyl acetate, and directly attaching the solution to the polarizing plate by a suitable spreading method such as a casting method or a coating method, and a method of forming a pressure-sensitive adhesive layer on a separator and transferring the solution to the polarizing plate.

<Adhesive Layer>
The adhesive layer may be composed of one layer or two or more layers, but preferably consists of 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 them, an adhesive composition having a (meth)acrylic resin as a base polymer, which is excellent in transparency, weather resistance, heat resistance, etc., is suitable. The adhesive composition may be an active energy ray curable type or a heat curable type.

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

The adhesive composition may contain only the base polymer, but usually further contains a crosslinking agent. Examples of crosslinking agents include divalent or higher metal ions that form metal carboxylates with carboxyl groups, polyamine compounds that form amide bonds with carboxyl groups, polyepoxy compounds or polyols that form ester bonds with carboxyl groups, and polyisocyanate compounds that form amide bonds with carboxyl groups. Among these, polyisocyanate compounds are preferred.

The active energy ray curable adhesive composition has the property of being cured by irradiation with active energy rays such as ultraviolet rays or electron beams, and has adhesiveness even before irradiation with active energy rays, allowing it to be adhered to an adherend such as a film, and has the property of being cured by irradiation with active energy rays, allowing the adhesive strength to be adjusted. The active energy ray curable adhesive composition is preferably an ultraviolet ray curable type. The active energy ray curable adhesive composition further contains an active energy ray polymerizable compound in addition to a base polymer and a crosslinking agent. If necessary, a photopolymerization initiator, a photosensitizer, etc. may be contained.

The adhesive composition may contain additives such as fine particles for imparting light scattering properties, 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.

The adhesive layer can be formed by applying an organic solvent dilution of the adhesive composition onto the surface of a substrate film, an image display cell, or a polarizing plate, and drying the applied solution. The substrate film is generally a thermoplastic resin film, and a typical example of such a film is a separate film that has been subjected to a release treatment. The separate film can be, for example, a film made of a resin such as polyethylene terephthalate, polybutylene terephthalate, polycarbonate, or polyarene, and the surface on which the adhesive layer is to be formed is subjected to a release treatment such as silicone treatment.

The adhesive composition may be applied directly to the release-treated surface of the separate film to form an adhesive layer, and this adhesive layer with separate film may be laminated on the surface of the polarizer. The adhesive composition may be applied directly to the surface of the polarizing plate to form an adhesive layer, and a separate film may be laminated on the outer surface of the adhesive layer.

When providing the adhesive layer on the surface of the polarizing plate, it is preferable to subject the bonding surface of the polarizing plate and/or the bonding surface of the adhesive layer to a surface activation treatment such as plasma treatment or corona treatment, and it is more preferable to subject the surface to corona treatment.

Alternatively, an adhesive composition may be applied onto the second separate film to form an adhesive layer, an adhesive sheet may be prepared by laminating a separate film onto the formed adhesive layer, and the second separate film may be peeled off from the adhesive sheet, after which the adhesive layer with the separate film may be laminated onto a polarizing plate. The second separate film used has weaker adhesion to the adhesive layer than the separate film and is therefore easier to peel off.

The thickness of the adhesive layer is not particularly limited, but is preferably, for example, 1 μm or more and 100 μm or less. When a first adhesive layer and a second adhesive layer are provided, the thickness of one may be 50 μm or less, and the thickness of the other may be 50 μm or more. When the adhesive layer has a thickness of 50 μm or less, it is more preferable that the thickness is 3 μm or more and 50 μm or less, and it may be 20 μm or more, or it may be less than 50 μm. When the adhesive layer has a thickness of 50 μm or more, it is preferably 50 μm or more and 100 μm or less, and it may be 80 μm or less.

<Transparent materials>
Examples of the transparent member arranged on the viewing side of the image display device include a transparent plate (window layer) and a touch panel. As the transparent plate, a transparent plate having appropriate mechanical strength and thickness is used. Examples of such transparent plates include transparent resin plates such as polyimide resin, acrylic resin, and polycarbonate resin, and glass plates. A functional layer such as an anti-reflection layer may be laminated on the viewing side of the transparent plate. In addition, when the transparent plate is a transparent resin plate, a hard coat layer may be laminated to increase the physical strength, or a low moisture permeable layer may be laminated to reduce the moisture permeability. As the touch panel, various touch panels such as resistive film type, capacitive type, optical type, and ultrasonic type, and glass plate or transparent resin plate having a touch sensor function are used. When a capacitive type touch panel is used as the transparent member, it is preferable that a transparent plate made of glass or a transparent resin plate is provided on the viewing side further than the touch panel.

<Laminating a polarizing plate and a transparent member>
A pressure sensitive adhesive or an active energy ray curable adhesive is preferably used for bonding the polarizing plate and the transparent member. When a pressure sensitive adhesive is used, the pressure sensitive adhesive can be applied by an appropriate method. As a specific application method, for example, the application method of the pressure sensitive adhesive layer used for bonding the image display cell and the polarizing plate described above can be mentioned.

When using an active energy ray curing adhesive, a suitable 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, it is aligned and degassed as necessary, and then irradiated with active energy rays to cause curing.

The present invention will be specifically described below based on examples. The materials, reagents, amounts of substances and their ratios, operations, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the present invention is not limited to the following examples.

(Preparation of Polarizing Element 1)
A 30 μm thick polyvinyl alcohol 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 at 23° C. containing 1.0 mM iodine with a mass ratio of potassium iodide/boric acid/water of 2/2/100 for 151 seconds (dyeing process). Then, it was immersed in an aqueous solution at 62.8° C. with a mass ratio of potassium iodide/boric acid/water of 2.5/4/100 for 76 seconds (first crosslinking process). Then, it was immersed in an aqueous solution at 45° C. with a mass ratio of potassium iodide/boric acid/zinc chloride/water of 3/5.5/0.6/100 for 11 seconds (second crosslinking process, metal ion treatment process). Then, it was immersed in a cleaning bath for cleaning (cleaning process), and dried at 38° C. (drying process) to obtain a polarizing element with a thickness of 12 μm in which iodine was adsorbed and aligned in polyvinyl alcohol. The stretching was mainly performed in the dyeing step and the first crosslinking step, and the stretching was performed by 1.002 times in the final washing step. The total stretching ratio of the polarizing element thus obtained was 5.86 times. The zinc ion content of the polarizing element thus obtained was 0.07 mass%, the boron content was 4.48 mass%, and the cross transmittance (Tc(780)) at a wavelength of 780 nm was 1.5%.

(Preparation of Polarizing Element 2)
A 30 μm thick polyvinyl alcohol 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 at 23° C. containing 1.0 mM iodine with a mass ratio of potassium iodide/boric acid/water of 2/2/100 for 151 seconds (dyeing process). Then, it was immersed in an aqueous solution at 62.8° C. with a mass ratio of potassium iodide/boric acid/water of 2.5/4/100 for 76 seconds (first crosslinking process). Then, it was immersed in an aqueous solution at 45° C. with a mass ratio of potassium iodide/boric acid/zinc chloride/water of 3/5.5/0.6/100 for 11 seconds (second crosslinking process, metal ion treatment process). Then, it was immersed in a cleaning bath for cleaning (cleaning process), and dried at 38° C. (drying process) to obtain a polarizing element with a thickness of 12 μm in which iodine was adsorbed and aligned in polyvinyl alcohol. The stretching was mainly performed in the dyeing step and the first crosslinking step, and the stretching was performed by 1.005 times in the final washing step. The total stretching ratio of the polarizing element thus obtained was 5.88 times. The zinc ion content of the polarizing element thus obtained was 0.07 mass%, the boron content was 4.48 mass%, and the cross transmittance (Tc(780)) at a wavelength of 780 nm was 1.0%.

(Preparation of Polarizing Element 3)
A 30 μm thick polyvinyl alcohol 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 at 23° C. containing 1.0 mM iodine with a mass ratio of potassium iodide/boric acid/water of 2/2/100 for 151 seconds (dyeing process). Then, it was immersed in an aqueous solution at 62.8° C. with a mass ratio of potassium iodide/boric acid/water of 2.5/4/100 for 76 seconds (first crosslinking process). Then, it was immersed in an aqueous solution at 45° C. with a mass ratio of potassium iodide/boric acid/zinc chloride/water of 3/5.5/0.6/100 for 11 seconds (second crosslinking process, metal ion treatment process). Then, it was immersed in a cleaning bath for cleaning (cleaning process), and dried at 38° C. (drying process) to obtain a polarizing element with a thickness of 12 μm in which iodine was adsorbed and aligned in polyvinyl alcohol. The stretching was mainly performed in the dyeing step and the first crosslinking step, and the stretching was performed by 1.01 times in the final washing step. The total stretching ratio of the polarizing element thus obtained was 5.91 times. The zinc ion content of the polarizing element thus obtained was 0.07 mass%, the boron content was 4.48 mass%, and the cross transmittance (Tc(780)) at a wavelength of 780 nm was 0.5%.

(Preparation of Polarizing Element 4)
A 30 μm thick polyvinyl alcohol 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 at 23° C. containing 1.0 mM iodine with a mass ratio of potassium iodide/boric acid/water of 2/2/100 for 151 seconds (dyeing process). Then, it was immersed in an aqueous solution at 62.8° C. with a mass ratio of potassium iodide/boric acid/water of 2.5/4/100 for 76 seconds (first crosslinking process). Then, it was immersed in an aqueous solution at 45° C. with a mass ratio of potassium iodide/boric acid/zinc chloride/water of 3/5.5/0.6/100 for 11 seconds (second crosslinking process, metal ion treatment process). Then, it was immersed in a cleaning bath for cleaning (cleaning process), and dried at 38° C. (drying process) to obtain a polarizing element with a thickness of 12 μm in which iodine was adsorbed and aligned in the polyvinyl alcohol. The stretching was mainly performed in the dyeing step and the first crosslinking step, and the stretching was performed by 1.00 times (no stretching) in the final washing step. The total stretching ratio of the polarizing element thus obtained was 5.85 times. The zinc ion content of the polarizing element thus obtained was 0.07 mass%, the boron content was 4.48 mass%, and the cross transmittance (Tc(780)) at a wavelength of 780 nm was 2.0%.

(Preparation of Polarizing Element 5)
A 30 μm thick polyvinyl alcohol 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 at 23° C. containing 1.0 mM iodine with a mass ratio of potassium iodide/boric acid/water of 2/2/100 for 151 seconds (dyeing process). Then, it was immersed in an aqueous solution at 62.8° C. with a mass ratio of potassium iodide/boric acid/water of 2.5/4/100 for 90 seconds (first crosslinking process). Then, it was immersed in an aqueous solution at 45° C. with a mass ratio of potassium iodide/boric acid/zinc chloride/water of 3/5.5/0.6/100 for 11 seconds (second crosslinking process, metal ion treatment process). Then, it was immersed in a cleaning bath for cleaning (cleaning process), and dried at 38° C. (drying process) to obtain a polarizing element with a thickness of 12 μm in which iodine was adsorbed and aligned in polyvinyl alcohol. The stretching was mainly performed in the dyeing step and the first crosslinking step, and the stretching was performed by 1.00 times in the final washing step. The total stretching ratio of the polarizing element thus obtained was 5.85 times. The zinc ion content of the polarizing element thus obtained was 0.07 mass%, the boron content was 4.48 mass%, and the cross transmittance (Tc(780)) at a wavelength of 780 nm was 0.3%.

(Measurement of Visibility-Corrected Polarization Degrees of Polarizing Elements 1 to 5)
A test piece measuring approximately 30 mm in length and approximately 30 mm in width was cut out from the obtained polarizing element to prepare a measurement sample. The single transmittance and the degree of polarization of the obtained measurement sample in the wavelength range of 380 to 780 nm were measured.
Degree of polarization (λ) = 100 × {(Tp(λ) - Tc(λ)) / (Tp(λ) + Tc(λ))} ^1/2
is defined as:

Tp(λ) is the parallel transmittance (%) of the polarizing element measured in a parallel Nicol relationship with the incident linearly polarized light of wavelength λ nm, and Tc(λ) is the orthogonal transmittance (%) of the polarizing element measured in a crossed Nicol relationship with the incident linearly polarized light of wavelength λ nm. Furthermore, the luminosity correction was performed on the polarization degree (λ) calculated for each wavelength to determine the luminosity-corrected polarization degree Py. Py was measured using a spectrophotometer with an integrating sphere equipped with a C light source [V7100 manufactured by JASCO Corporation].

(Measurement of cross transmittance at wavelength 780 nm for polarizing elements 1 to 5)
The cross transmittance at a wavelength of 780 nm measured above, that is, Tc(780), was used.

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

(Measurement of zinc ion content in polarizing element)
Nitric acid was added to the precisely weighed polarizing element, and the solution obtained by acid decomposition using a Milestone General microwave sample pretreatment 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 optical emission spectrometer (5110 ICP-OES) and calculating the zinc mass relative to the polarizing element mass.

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

Table 1 shows the luminosity-corrected polarization degree (Py) and cross transmittance (Tc(780)) values of polarizing elements 1 to 5.

(Preparation of PVA solution for adhesive)
50 g of a modified PVA resin containing an acetoacetyl group (Mitsubishi Chemical Corporation: Gohsenex 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 adhesive.

(Preparation of urea aqueous solution)
10 g of urea (a reagent from Tokyo Chemical Industry Co., Ltd.) was added to 90 g of pure water to obtain a 10 wt % urea aqueous solution.

(Preparation of Polarizing Plate Adhesive 1)
The PVA solution for adhesive, the urea aqueous solution, pure water and methanol prepared above were mixed so that the PVA concentration was 3.0%, the methanol concentration was 20% and the urea concentration was 0.2%, to obtain an adhesive 1 for polarizing plates.

(Preparation of Polarizing Plate Adhesive 2)
The PVA solution for adhesive prepared above, pure water and methanol were mixed so that the PVA concentration was 3.0% and the methanol concentration was 20%, to obtain an adhesive 2 for polarizing plates.

(Saponification of Cellulose Acylate Film)
A commercially available cellulose acylate film TD40 (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. The film was then washed with water. The film was then immersed in a 0.05 mol/L sulfuric acid aqueous solution at 25° C. for 30 seconds. The film was then passed through a water washing bath under running water for 30 seconds to neutralize the film. The film was then drained three times with an air knife to remove the water. The film was then allowed to remain in a drying zone at 70° C. for 15 seconds to dry, and a saponification-treated film was produced.

(Preparation of Polarizing Plate 1)
The saponified cellulose acylate film prepared above was laminated on both sides of the polarizing element 1 using a roll laminator via the polarizing plate adhesive 1. The thickness of the adhesive layer on both sides was adjusted to 80 nm after drying. After lamination using the roll laminator, the film was dried at 60° C. for 10 minutes to obtain a polarizing plate 1 having cellulose acylate films on both sides.

(Preparation of Polarizing Plates 2 to 6)
Polarizing plates 2 to 6 were prepared in the same manner as polarizing plate 1, except that the polarizing elements and polarizing plate adhesives shown in Table 2 were used.

(Adjustment of Moisture Content of Polarizing Plate (Polarizing Element))
The polarizing plates 1 to 6 obtained above were stored for 72 hours at a temperature of 20° C. and at a relative humidity of 30%, 35%, 40%, 45%, 50% or 55%. The moisture content was measured using the Karl Fischer method after storage for 66, 69 and 72 hours. The moisture content did not change after storage for 66, 69 and 72 hours under any humidity condition. Therefore, the moisture content of the polarizing plates 1 to 6 can be considered to be the same as the equilibrium moisture content in 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 that storage environment. In addition, when the moisture content of the polarizing element in the polarizing plate reaches equilibrium in a certain storage environment, the moisture content of the polarizing plate can also be considered to have reached equilibrium in that storage environment.

(Preparation of Optical Laminate 1)
With reference to the examples of JP2018-025765A, an acrylic adhesive (manufacturer: Lintec Corporation, product number: #7) was applied to both sides of the polarizing plate 1 prepared above to produce an optical laminate 1 having a 25 μm thick adhesive layer (first adhesive layer) on one side and a 150 μm thick second adhesive layer on the other side. The moisture content of the polarizing plate used was that which had been stored for 72 hours under conditions of a temperature of 20° C. and a relative humidity of 45%.

(Preparation of Optical Laminates 2 to 6)
Optical laminates 2 to 6 were produced in the same manner as for optical laminate 1, except that the polarizing plates shown in Table 2 were used.

(Inspection polarizing plate 1)
An acrylic adhesive (manufacturer: Lintec Corporation, product number: #7) was laminated only on one surface of the polarizing plate 1 to prepare a polarizing plate for inspection 1. The polarizing plate for inspection 1 thus prepared was cut into a size of 50 mm x 100 mm so that the short side was parallel to the absorption axis, and the surface of the adhesive layer was attached to alkali-free glass (product name "EAGLE XG", manufactured by Corning Incorporated, thickness 1.1 mm) to prepare a cross evaluation sample 1.

[Evaluation of unit transmittance after high-temperature durability test (105°C)]
Each of the optical laminates 1 to 6 prepared above was cut into a size of 50 mm x 100 mm so that the long side was parallel to the absorption axis, and the surfaces of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer were bonded to alkali-free glass (product name "EAGLE XG", manufactured by Corning Incorporated) to prepare evaluation samples.
The evaluation sample was autoclaved for 1 hour at a temperature of 50°C and a pressure of 5 kgf/ ^cm2 (490.3 kPa), and then left for 24 hours in an environment at a temperature of 23°C and a relative humidity of 55%. Thereafter, the transmittance was measured (initial value), and the sample was stored in a heated environment at a temperature of 105°C, with the transmittance measured every 100 hours. Evaluation was performed according to the following criteria, based on the time at which the transmittance had decreased by 5% or more from the initial value. The results are shown in Table 2.
The decrease in transmittance after 400 hours is less than 5%: A
The transmittance decreased by 5% or more in 300 to 400 hours: B
The transmittance decreased by 5% or more in 200 to 300 hours: C
The transmittance decreases by 5% or more after 200 hours: D

[Evaluation of cloth loss after high temperature durability test]
After the evaluation of the single transmittance evaluation sample after high temperature durability for 300 hours, the optical laminate and the cross evaluation sample 1 that was not placed in a heating environment were arranged in a cross Nicol state and placed on a backlight. The surroundings were shaded, and cross-drop was visually evaluated according to the following criteria. In addition, samples whose single transmittance had decreased by 5% or more after 300 hours were excluded from the evaluation of cross-drop because they had coloration due to polyenation. The results are shown in Table 2.
No cross-linking is observed: A
Almost no cross-cutting is observed: B
A small amount of cross-cutting is visible: C
Cross-drop is clearly visible: D

[Evaluation of White Luminance]
An evaluation sample was prepared in the same manner as above. The evaluation sample was placed on the light-emitting surface of the white backlight module. The glass plate side attached to the first adhesive layer faced the white backlight module. The brightness of the white backlight module was 1000 cd/ ^m3 . The brightness was measured from the glass plate side attached to the second adhesive layer. The brightness was measured using a spectroradiometer SR-UL1 manufactured by Topcon Corporation. The measurement was performed in a 2° visual field. The measured brightness was evaluated in three stages according to the following criteria. The results are shown in Table 2.
The luminance is 97% or more relative to the luminance of the laminate 4: A
The luminance is lower than 97% of the luminance of the laminate 4: B
The luminance is lower than 95% of the luminance of the laminate 4: C

Claims (12)

A polarizing plate having a polarizing element formed by adsorbing and aligning a dichroic dye in a polyvinyl alcohol-based resin layer and a transparent protective film,
The polarizing element is a polarizing plate having a luminosity-corrected polarization degree of 99.9% or more and a crossed transmittance at a wavelength of 780 nm of 1.8% or less. the polarizing element and the transparent protective film are attached to each other with an adhesive layer formed from a water-based adhesive containing a urea compound,
The polarizing plate according to claim 1 , wherein the urea-based compound is at least one selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives. The polarizing plate according to claim 2, wherein the urea-based compound is at least one selected from the group consisting of urea derivatives and thiourea derivatives. The polarizing plate according to claim 2 or 3, wherein the water-based adhesive contains a polyvinyl alcohol-based resin. The polarizing plate according to claim 4, wherein the content of the urea-based compound in the aqueous 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. The water-based adhesive contains methanol,
The polarizing plate according to claim 2 , wherein the concentration of the methanol is from 10% by mass to 70% by mass. The polarizing plate according to claim 2 or 3, wherein the water-based adhesive contains cyclodextrins. The polarizing plate according to claim 2 or 3, wherein the adhesive layer has a thickness of 0.01 μm or more and 7 μm or less. The polarizing plate according to claim 1 or 2, wherein the thickness of the polarizing element is 15 μm or less. The polarizing plate according to claim 1 or 2, wherein 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 equal to or less than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 50%. The polarizing plate according to claim 1 or 2, wherein 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 50%. The polarizing plate according to claim 1 or 2, in which an adhesive layer having a thickness of 50 μm or less is formed on one surface of the polarizing plate, and an adhesive layer having a thickness of 50 μm or more is formed on the other surface of the polarizing plate.