JP2024036288A - Polarizer - Google Patents

Abstract

The present invention provides a novel polarizing plate that can suppress a decrease in transmittance in a high-temperature environment. [Solution] A polarizing plate having a polarizing element formed by adsorbing and aligning a dichroic dye to a polyvinyl alcohol resin layer, and a transparent protective film, wherein the polarizing element is measured by a wide-angle X-ray scattering method. The half width of a peak derived from polyvinyl alcohol crystals is 4.80 nm-1 or more, the polarizing element contains potassium ions and metal ions other than potassium ions, and the polarizing element contains potassium ions other than potassium ions. The content of metal ions is 0.05% by mass or more, and the polarizing element and the transparent protective film are attached by an adhesive layer formed from a water-based adhesive containing a polyvinyl alcohol resin and a cyclodextrin. Polarizing plate. [Selection diagram] None

Description

The present invention relates to a polarizing plate.

Liquid crystal display devices (LCDs) are widely used not only in liquid crystal televisions, but also in personal computers, mobile phones such as mobile phones, and in-vehicle applications such as car navigation systems. Generally, a liquid crystal display device has a liquid crystal panel member in which polarizing plates are bonded to both sides of a liquid crystal cell using an adhesive, and displays are performed by controlling light from a backlight member with the liquid crystal panel member. In recent years, organic EL display devices have also been widely used in mobile applications such as televisions, mobile phones, and in-vehicle applications such as car navigation systems, similar to liquid crystal display devices. In an organic EL display device, in order to prevent external light from being reflected by a metal electrode (cathode) and viewed as a mirror surface, a circularly polarizing plate (a polarizing element and a λ/4 plate) is installed on the viewing side surface of the image display panel. laminate) may be arranged.

As described above, polarizing plates are increasingly being installed in cars as components of liquid crystal display devices and organic EL display devices. Polarizing plates used in in-vehicle image display devices are often exposed to high temperature environments compared to other mobile applications such as televisions and mobile phones, and the characteristics change at higher temperatures are smaller ( high temperature durability) is required.

As a manufacturing method for such a polarizing element with high high temperature durability, for example, Patent Documents 1 and 2 disclose that components such as metal salts containing zinc, copper, aluminum, etc. are added to a treatment bath, and these components are added to the polarizing element. It has been disclosed that the durability of a polarizing element can be improved by including a component therein. Further, Patent Documents 3 and 4 disclose a method for manufacturing a polarizing element in which a component such as an organic titanium compound is added to a treatment bath.

On the other hand, in order to prevent damage to the image display panel due to impact from the outer surface, a front plate (also referred to as a "window layer") such as a transparent resin plate or glass plate is provided on the viewing side of the image display panel. is increasing. 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 plate is provided on the viewing side of the touch panel is widely adopted.

In such a configuration, if an air layer exists between the image display panel and a transparent member such as the front plate or touch panel, external light will be reflected due to light reflection at the air layer interface, reducing screen visibility. There is a tendency to decrease. Therefore, 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 an air layer, usually a solid layer (hereinafter sometimes referred to as "interlayer filler"). ) (hereinafter sometimes referred to as "interlayer filling structure") is becoming increasingly popular. The interlayer filler is preferably a material having 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-curable adhesive is used for the purpose of suppressing a decrease in visibility due to reflection at the interface and adhesively fixing each member (see, for example, Patent Document 5).

The interlayer filling structure is increasingly being adopted in mobile applications such as mobile phones that are often used outdoors. In addition, due to the increasing demand for visibility in recent years, in in-vehicle applications such as car navigation systems, a front transparent plate is placed on the surface of the image display panel, and the space between the panel and the front transparent plate is filled with an adhesive layer, etc. Adoption of an interlayer filling configuration is being considered.

However, it has been reported that when such a configuration is adopted, the transmittance of the polarizing plate is significantly reduced in a high-temperature environment. In Patent Document 6, as a solution to this problem, the transmittance is reduced by making the amount of water per unit area of the polarizing plate less than a predetermined amount, and making the saturated water absorption amount of the transparent protective film adjacent to the polarizing element less than a predetermined amount. We are proposing a method to suppress the decline.

International Publication No. 2016/117659 Japanese Patent Application Publication No. 2006-047978 Japanese Patent Application Publication No. 2008-46257 Japanese Unexamined Patent Publication No. 6-172554 Japanese Patent Application Publication No. 11-174417 Japanese Patent Application Publication No. 2014-102353

However, conventional polarizing plates have not had a sufficient effect of suppressing a decrease in transmittance in a high-temperature environment. An object of the present invention is to provide a novel polarizing plate that can suppress a decrease in transmittance in a high-temperature environment.

The present invention provides the following polarizing plate.
[1] A polarizing plate comprising a polarizing element formed by adsorbing and aligning a dichroic dye to a polyvinyl alcohol resin layer, and a transparent protective film,
The polarizing element has a half-value width of a peak derived from polyvinyl alcohol crystals measured by wide-angle X-ray scattering of 4.80 nm ^-1 or more,
The polarizing element includes potassium ions and metal ions other than potassium ions,
The polarizing element has a content of metal ions other than potassium ions of 0.05% by mass or more,
The polarizing element and the transparent protective film are bonded to each other by an adhesive layer formed from a water-based adhesive containing a polyvinyl alcohol resin and cyclodextrins.
[2] The polarized light according to [1], wherein the metal ion contains at least one kind from the group consisting of cobalt, nickel, zinc, chromium, aluminum, copper, manganese, and iron ions. Board.
[3] The polarizing plate according to [1] or [2], wherein the polarizing element has a boron content of 2.4% by mass or more and 8.0% by mass or less.
[4] The water-based adhesive according to [1] to [3], wherein the content of the cyclodextrin is 1 part by mass or more and 50 parts by mass or less based on 100 parts by mass of the polyvinyl alcohol resin. Polarizer.
[5] The polarizing plate according to [1] to [4], wherein the cyclodextrin is at least one selected from the group consisting of α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin.
[6] The polarizing plate according to [1] to [5], wherein the water-based adhesive has a methanol concentration of 10% by mass or more and 70% by mass or less.
[7] The polarizing plate according to [1] to [6], wherein the adhesive layer has a thickness of 0.01 μm or more and 7 μm or less.
[8] The water content of the polarizing element is at least the equilibrium water content at a temperature of 20°C and a relative humidity of 30%, and below the equilibrium water content at a temperature of 20°C and a relative humidity of 50%, according to [1] to [7]. Polarizer.
[9] The water content of the polarizing plate is at least the equilibrium water content at a temperature of 20°C and a relative humidity of 30%, and below the equilibrium water content at a temperature of 20°C and a relative humidity of 50%, according to [1] to [7]. Polarizer.

The present invention makes it possible to provide a polarizing plate with excellent high-temperature durability.

Embodiments of the present invention will be described below, but the present invention is not limited to the following embodiments.

[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 on a layer containing a polyvinyl alcohol resin, and a transparent protective film. Further, in the polarizing element, the half width of a peak derived from polyvinyl alcohol crystals measured by wide-angle X-ray scattering is 4.80 nm ^-1 or more. Further, the polarizing element contains potassium ions (hereinafter sometimes referred to as "first metal ions") and metal ions other than potassium ions (hereinafter sometimes referred to as "second metal ions"). The content of the second metal ion is 0.05% by mass or more. Further, the polarizing element and the transparent protective film are bonded together by an adhesive layer formed from a water-based adhesive containing a polyvinyl alcohol resin and cyclodextrins.
In the polarizing plate of this embodiment, the half-width of the polyvinyl alcohol crystal-derived peak measured by wide-angle X-ray scattering of the polarizing element and the content of the second metal ion in the polarizing element are within the above range. , it is possible to suppress a decrease in transmittance even when exposed to a high temperature environment for a long time. In the polarizing plate of this embodiment, the polarizing element and the transparent protective film are bonded together by the adhesive layer, thereby further suppressing a decrease in transmittance even when exposed to a high temperature environment for a long time. can do.

The polarizing plate according to this embodiment preferably has at least one of the following characteristics (a) and (b).
(a) The water content of the polarizing element is equal to or higher than the equilibrium water content at a temperature of 20° C. and a relative humidity of 30%, and below the equilibrium water content at a temperature of 20° C. and a relative humidity of 50%.
(b) The water content of the polarizing plate is equal to or higher than the equilibrium water content at a temperature of 20° C. and a relative humidity of 30%, and below the equilibrium water content at a temperature of 20° C. and a relative humidity of 50%.

As a conventional polarizing plate having excellent high-temperature durability, for example, a polarizing plate is known in which a decrease in transmittance is suppressed even when the polarizing plate alone is left in an environment at a temperature of 95° C. for 1000 hours. However, even when such a polarizing plate is used in an interlayer filling configuration, if it is left in an environment at a temperature of 105°C for 240 hours, a significant decrease in transmittance and degree of polarization may be observed in the central part of the plane of the polarizing plate. . A significant decrease in the transmittance and degree of polarization of a polarizing plate in a high-temperature environment occurs when one side of the polarizing plate is bonded to an image display cell and the other side is bonded to a transparent member such as a touch panel or front plate. This problem is thought to be particularly likely to occur when an image display device employing an interlayer filling structure is exposed to a high-temperature environment.

A polarizing plate with a significantly reduced transmittance due to the interlayer filling structure has peaks around 1100 cm ^-1 (derived from the =C-C= bond) and around 1500 cm ^-1 (derived from the -C=C- bond) in Raman spectroscopy. Therefore, it is considered that a polyene structure (-C=C) _n - is formed. It is presumed that the polyene structure is generated by polyvinyl alcohol constituting the polarizing element being polyenized by dehydration (Patent Document 6, 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 having an interlayer filling structure, and can suppress a decrease in transmittance and degree of polarization even when exposed to a high-temperature environment of, for example, 105° C.

<Polarizing element>
A well-known polarizing element can be used as a polarizing element in which a dichroic dye is adsorbed and oriented in a layer containing a PVA-based resin (herein also referred to as a "PVA-based resin layer"). Such a polarizing element may be formed by using a PVA resin film, dyeing this PVA resin film with a dichroic dye and uniaxially stretching it, or using a coating liquid containing PVA resin as a base material. Examples include those formed by using a laminated film obtained by coating on a film, dyeing the PVA resin layer that is the coating layer of this laminated film with a dichroic dye, and uniaxially stretching the laminated film. .

The polarizing element is formed from a PVA resin obtained by saponifying polyvinyl acetate resin. Examples of polyvinyl acetate-based resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith. Examples of other copolymerizable monomers include unsaturated carboxylic acids, olefins such as ethylene, vinyl ethers, and unsaturated sulfonic acids.

In the present invention, the PVA resin layer is preferably formed from a PVA resin having a boron adsorption rate of 5.70% by mass or more. That is, it is preferable that the boron adsorption rate of the PVA resin at the raw material stage before dyeing or stretching is 5.70% by mass or more. By using such a PVA-based resin, the degree of polarization is less likely to decrease even when exposed to a high-temperature environment of 115° C., for example. Moreover, it is preferable that the boron adsorption rate of the PVA-based resin is 10% by mass or less. By manufacturing a polarizing element using such a PVA resin, it is possible to avoid increasing the boric acid concentration in the boric acid treatment tank, and also to shorten the treatment time for boric acid treatment. It becomes easier to obtain a polarizing element, and the productivity of the polarizing element can also be improved. When 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, making it easy to reduce the shrinkage 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 PVA-based resin is a characteristic that reflects the spacing between molecular chains and crystal structure in PVA-based resin. PVA-based resins with a boron adsorption rate of 5.70% by mass or more have wider spacing between molecular chains, and crystals of PVA-based resins are larger than those with a boron adsorption rate of less than 5.70% by mass. It is thought that there are few. Therefore, boron, the first metal ion, and the second metal ion easily enter the PVA-based resin layer, and it is assumed that the degree of polarization is less likely to decrease in a high-temperature environment.

The boron adsorption rate of PVA-based resin can be determined by, for example, performing pre-treatments such as hot water treatment, acidic solution treatment, ultrasonic irradiation treatment, and radiation irradiation treatment on the PVA-based resin before manufacturing the polarizing element. It can be adjusted by These treatments can widen the spacing between molecular chains and destroy the crystal structure in the PVA-based resin. Examples of the hot water treatment include immersion in pure water at 30° C. to 100° C. for 1 second to 90 seconds and drying. Examples of the acidic solution treatment include immersion in a boric acid aqueous solution having a concentration of 10% by mass to 20% by mass for 1 second to 90 seconds and drying. Examples of the ultrasonic treatment include treatment in which ultrasonic waves with a frequency of 20 to 29 kc are irradiated with an output of 200 W to 500 W for 30 seconds to 10 minutes. Sonication can be performed in a solvent such as water.

The degree of saponification of the PVA resin is preferably about 85 mol% or more, more preferably about 90 mol% or more, and still more preferably about 99 mol% to 100 mol%. The degree of polymerization of the PVA resin is 1,000 to 10,000, preferably 1,500 to 5,000. This PVA-based resin may be modified, for example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral, etc. modified with aldehydes.

The thickness of the polarizing element of this embodiment is preferably 5 to 50 μm, more preferably 8 to 28 μm, even more preferably 12 to 22 μm, even more preferably 12 to 20 μm, and even more preferably 12 to 20 μm. Most preferably it is ~15 μm. When the thickness of the polarizing element is 5 μm or more, it becomes easy to achieve a configuration that achieves desired optical characteristics.

In the polarizing element according to the embodiment of the present invention, the half width of the peak derived from polyvinyl alcohol crystals measured by wide-angle X-ray scattering is 4.80 nm ^-1 or more, preferably 4.82 nm ^-1 or more. , more preferably 4.87 nm ^{−1 or} more. In such a polarizing element, the crystal size of polyvinyl alcohol becomes small due to the progress of the crosslinking reaction with boric acid, and as a result, the proportion of amorphous parts becomes large. Therefore, the content of boron and the second metal ions described below can be efficiently increased. The half width of a peak derived from polyvinyl alcohol crystals measured by wide-angle X-ray scattering can be, for example, 5.0 nm ⁻¹ or less. Since such a polarizing element has a high degree of orientation, it can have excellent optical properties. Note that the half-width of the peak derived from polyvinyl alcohol crystals measured by wide-angle X-ray scattering can be measured by the method described in Examples described later. The half-value width of the peak derived from polyvinyl alcohol crystals measured by wide-angle X-ray scattering is adjusted as appropriate by the temperature of the stretching bath, the stretching ratio, the boric acid concentration of the crosslinking bath, the degree of saponification of the PVA resin used as a raw material, etc. be able to.

The content of the second metal ion in the polarizing element is preferably 0.05% by mass or more and 10.0% by mass or less, more preferably 0.05% by mass or more and 8.0% by mass or less, and even more preferably It is 0.1% by mass or more and 6.0% by mass or less. If the content of the second metal ion exceeds 10.0% by mass, the degree of polarization may decrease in a high temperature and high humidity environment. Furthermore, 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. Note that the content rate of the second metal ion in the polarizing element is calculated as the mass fraction (mass %) of the metal element with respect to the mass of the polarizing element, for example, by high frequency inductively coupled plasma (ICP) emission spectrometry. be able to. The metal element is considered to exist in the polarizing element in the form of metal ions or in a cross-linked structure with the constituent elements of the polyvinyl alcohol resin, but the content of the second metal ion here is is the value of

The second metal ion is not limited as long as it is a metal ion other than potassium ion, and is preferably an ion of a metal other than alkali metal, especially cobalt, nickel, zinc, chromium, etc. from the viewpoint of color adjustment and durability. , transition metals such as copper, manganese, and iron; and metal ions such as aluminum. Among these metal ions, zinc ions are preferred from the viewpoint of color tone adjustment and imparting heat resistance.

The boron content of the polarizing element is preferably 2.4% by mass or more. Further, the boron content is preferably 8.0% by mass or less. When the boron content of the polarizing element is 2.4% by mass or more and 8.0% by mass or less, a decrease in the degree of polarization is easily suppressed even when exposed to a high-temperature environment. The boron content of the polarizing element is more preferably 3.9% by mass or more and 8.0% by mass or less, still more preferably 4.2% by mass or more and 7.0% by mass or less, particularly preferably 4.4% by mass or more. It is 6.0% by mass or less. If the boron content of the polarizing element exceeds 8.0% by mass, the shrinkage force of the polarizing element becomes large, and the polarizing element may peel off from other members such as the front plate to which it is attached when incorporated into an image display device. This may cause problems such as. Furthermore, if the boron content is less than 2.4% by mass, desired optical properties may not be achieved. Note that the boron content in the polarizing element can be calculated as the mass fraction (mass %) of boron relative to the mass of the polarizing element, for example, by high frequency inductively coupled plasma (ICP) emission spectrometry. Boron is thought to exist in the polarizing element in the form of boric acid or a crosslinked structure formed with the constituent elements of the polyvinyl alcohol resin, but the boron content here refers to the boron content as boron atoms (B). It is a value.

The content of potassium ions in the polarizing element is preferably 0.28% by mass or more, more preferably 0.32% by mass or more, from the viewpoint of suppressing a decrease in the degree of polarization in a high-temperature environment. It is more preferably .34% by mass or more, and from the viewpoint of suppressing hue change in a high-temperature environment, it is preferably 0.60% by mass or less, and more preferably 0.55% by mass or less. , 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 here is a value in terms of potassium atoms.

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

The polarizing element preferably contains cyclodextrins. In this embodiment, since the polarizing element and the transparent protective film are bonded together by an adhesive layer formed from a water-based adhesive containing a polyvinyl alcohol resin and cyclodextrins, some of the cyclodextrins is assumed to be migrated from the adhesive layer and included in the polarizing element. The cyclodextrins in the polarizing element may include those added during the manufacturing process of the polarizing element. By providing a polarizing element containing cyclodextrins, the transmittance is less likely to decrease even if the polarizing plate is exposed to a high temperature environment. It is presumed that this effect is produced because the cyclodextrins contained in the polarizing element suppress polyenization of the PVA resin.

Examples of methods for containing cyclodextrins in the polarizing element include a method of immersing a PVA-based resin layer in a processing solvent containing cyclodextrins, or a method of spraying, flowing, or dropping a processing solvent onto a PVA-based resin layer. It will be done. Among these, a method in which the PVA resin layer is immersed in a processing solvent containing cyclodextrins is preferably used.

The step of immersing the PVA resin layer in a processing solvent containing cyclodextrins may be performed simultaneously with the swelling, stretching, dyeing, crosslinking, washing, etc. steps in the polarizing element manufacturing method described below, or may be performed simultaneously with these steps. may be provided separately. The step of incorporating cyclodextrins into the PVA resin layer is preferably carried out after the PVA resin layer is dyed with iodine, and more preferably carried out at the same time as the crosslinking step after dyeing. According to such a method, the hue change is small, and the influence on the optical characteristics of the polarizing element can be reduced.

In order to make the polarizing element contain cyclodextrins, they may be added both at the time of manufacturing the polarizing element and to the adhesive.

(Cyclodextrins)
Cyclodextrin is a non-reducing cyclic oligosaccharide in which glucose is cyclically linked through α-1,4 bonds. The larger the number of glucose constituting the cyclodextrins, the larger the inner diameter of the intramolecular cavity. The cyclodextrins used in the present invention preferably have 6 or more glucose molecules, such as α, β, γ, and δ, which have 6, 7, 8, and 9 glucose components, respectively. - Cyclodextrins. Cyclodextrins include α, β, γ, δ-cyclodextrins, and branched cyclodextrins having oligosaccharides such as glucose and malctose in branched sugar chains. As cyclodextrins, the hydrogen atom of the above cyclodextrin or branched cyclodextrin is an alkyl group such as a methyl group; a 2-hydroxyethyl group, a 2-hydroxypropyl group, a 2,3-dihydroxypropyl group, a 2-hydroxybutyl group, etc. Cyclodextrin derivatives substituted with hydroxyalkyl groups, etc. are included. Cyclodextrins can be used alone or in combination of two or more.

The visibility correction single transmittance of the polarizing plate is preferably 38.8% to 44.8%, more preferably 40.4% to 43.2%, and even more preferably 40.7% to 43.0%. It is. If the visibility correction single transmittance exceeds 44.8%, the optical properties may deteriorate significantly, such as turning red in a high temperature environment, and if the visibility correction single transmittance is less than 38.8%, it will not work in a high temperature environment. Deterioration of optical properties may become significant.

The luminous sensitivity-corrected single transmittance can be determined by measuring the Y value after the luminous efficiency correction using the 2-degree field of view (C light source) specified in JIS Z8701-1982. Visibility correction single transmittance can be easily measured using, for example, a spectrophotometer (model number: V7100) manufactured by JASCO Corporation.

(Feature (a))
When having characteristic (a), the water content of the polarizing element is equal to or higher than the equilibrium water content at a temperature of 20° C. and a relative humidity of 30%, and below the equilibrium water content at a temperature of 20° C. and a relative humidity of 50%. The water content of the polarizing element is preferably below the equilibrium water content at a temperature of 20°C and a relative humidity of 45%, more preferably below the equilibrium water content at a temperature of 20°C and a relative humidity of 42%, even more preferably at a temperature of 20°C and a relative humidity of 45%. The humidity is below the equilibrium moisture content of 38%. When the water content of the polarizing element is lower than the equilibrium water content at a temperature of 20° C. and a relative humidity of 30%, the handling properties of the polarizing element deteriorate and the polarizing element becomes easily broken. When the water content of the polarizing element exceeds the equilibrium water content at a temperature of 20° C. and a relative humidity of 50%, the transmittance of the polarizing element tends to decrease. It is presumed that this is because when the water content of the polarizing element is high, the polyene conversion of the PVA-based resin progresses more easily. The water content of the polarizing element is the water content of the polarizing element in the polarizing plate.

As a method of checking whether the moisture content of the polarizing element is within the range of the equilibrium moisture content at a temperature of 20 degrees Celsius and relative humidity of 30% or higher and the equilibrium moisture content at a temperature of 20 degrees Celsius and a relative humidity of 50% or less, the above temperature and the above relative humidity are used. A method in which the polarizing element is stored in an environment adjusted to the above range, and if there is no change in mass for a certain period of time, it is considered to have reached equilibrium with the environment, or an environment adjusted to the above temperature and relative humidity range. An example of this method is to calculate the equilibrium water content of the polarizing element in advance, and to confirm this by comparing the water content of the polarizing element with the pre-calculated equilibrium water content.

The method for producing a polarizing element whose water content is equal to or higher than the equilibrium water content at a temperature of 20° C. and a relative humidity of 30% and below the equilibrium water content at a temperature of 20° C. and a relative humidity of 50% is not particularly limited. Examples include a method of storing the polarizing element in an environment adjusted to a relative humidity range of 10 minutes or more and 3 hours or less, or a method of heating the polarizing element at a temperature of 30° C. or more and 90° C. or less.

Another preferable method for producing a polarizing element having the above moisture content is to place a polarizing plate in which a protective film is laminated on at least one side of the polarizing element in an environment adjusted to the above temperature and relative humidity range for 10 minutes or more. Examples include a method of storing for 120 hours or less, or a method of heat treatment at 30° C. or higher and 90° C. or lower. When manufacturing an image display device that employs an interlayer filling configuration, a polarizing plate is incorporated into the image display device, and the image display device incorporating the polarizing plate is placed in an environment adjusted to the above temperature and above relative humidity ranges for 10 minutes or more. The front plate may be bonded after being stored for a period of time or after being heated at a temperature of 30° C. or higher and 90° C. or lower.

The water content of the polarizing element is adjusted so that the water content falls within the above numerical range at the stage of the material used to construct the polarizing plate, either as a polarizing element alone or as a laminate of a polarizing element and a protective film. is preferred. If the water content is adjusted after forming the polarizing plate, the curl may become too large and problems may easily occur when bonding to an image display cell. By constructing a polarizing plate using a polarizing element that has been adjusted to have the above water content at the material stage before forming the polarizing plate, it is possible to easily produce a polarizing plate that includes a polarizing element whose water content satisfies the above numerical range. It can be configured as follows. With the polarizing plate bonded to the image display cell, the water content of the polarizing element in the polarizing plate may be adjusted to fall within the above numerical range. In this case, since the polarizing plate is bonded to the image display cell, curling is less likely to occur.

(Feature (b))
When having characteristic (b), the water content of the polarizing plate is equal to or higher than the equilibrium water content at a temperature of 20° C. and a relative humidity of 30%, and below the equilibrium water content at a temperature of 20° C. and a relative humidity of 50%. The water content of the polarizing plate is preferably below the equilibrium water content at a temperature of 20°C and a relative humidity of 45%, more preferably below the equilibrium water content at a temperature of 20°C and a relative humidity of 42%, even more preferably at a temperature of 20°C and a relative humidity of 45%. The humidity is below the equilibrium moisture content of 38%. When the water content of the polarizing plate is lower than the equilibrium water content at a temperature of 20° C. and a relative humidity of 30%, the polarizing plate has poor handling properties and becomes easily broken. When the water content of the polarizing plate exceeds the equilibrium water content at a temperature of 20° C. and a relative humidity of 50%, the transmittance of the polarizing element tends to decrease. It is presumed that this is because when the water content of the polarizing plate is high, the polyene conversion of the PVA resin tends to proceed.

As a method of checking whether the moisture content of the polarizing plate is within the range of the equilibrium moisture content at a temperature of 20 degrees Celsius and a relative humidity of 30% and below the equilibrium moisture content at a temperature of 20 degrees Celsius and a relative humidity of 50%, the above temperature and the above relative humidity are used. A method in which a polarizing plate is stored in an environment adjusted to the above range, and if there is no change in mass for a certain period of time, it is considered to have reached equilibrium with the environment, or an environment adjusted to the above temperature and relative humidity range. An example of this method is to calculate the equilibrium water content of the polarizing plate in advance, and to confirm this by comparing the water content of the polarizing plate with the pre-calculated equilibrium water content.

The method for producing a polarizing plate whose water content is equal to or higher than the equilibrium water content at a temperature of 20° C. and a relative humidity of 30% and below the equilibrium water content at a temperature of 20° C. and a relative humidity of 50% is not particularly limited. Examples include a method of storing the polarizing plate in an environment adjusted to a relative humidity range of 10 minutes or more and 3 hours or less, or a method of heat-treating at 30° C. or more and 90° C. or less.

When manufacturing an image display device that employs an interlayer filling configuration, a polarizing plate is incorporated into the image display device, and the image display device incorporating the polarizing plate is placed in an environment adjusted to the above temperature and above relative humidity ranges for 10 minutes or more. The front plate may be bonded after being stored for a period of time or after being heated at a temperature of 30° C. or higher and 90° C. or lower.

The method for manufacturing the polarizing element is not particularly limited, but it is manufactured by sending out a polyvinyl alcohol resin film that has been rolled in advance and subjecting it to stretching, dyeing, crosslinking, etc. (hereinafter referred to as "manufacturing method 1"). A method (hereinafter referred to as "Production method 2") including a step of applying a coating solution containing a polyvinyl alcohol resin and a polyvinyl alcohol resin onto a base film to form a polyvinyl alcohol resin layer as a coating layer and stretching the obtained laminate. ) is typical.

Manufacturing method 1 includes a step of uniaxially stretching a polyvinyl alcohol resin film, a step of dyeing the polyvinyl alcohol resin film with a dichroic dye such as iodine, and a step of adsorbing the dichroic dye; It can be produced through the steps of treating the adsorbed polyvinyl alcohol resin film with an aqueous boric acid solution, and washing with water after the treatment with the aqueous boric acid solution.

The boron content and potassium ion content in the polarizing element are based on boric acid, borate, and boron contained in any of the treatment baths in the swelling process, dyeing process, crosslinking process, stretching process, and water washing process. It can be controlled by the concentration of a boron component donating substance such as a boron compound such as sand, the concentration of a potassium component donating substance such as potassium halide such as potassium iodide, and the treatment temperature and treatment time in each of the above treatment baths. In particular, in the crosslinking step and the stretching step, the boron content can be easily adjusted to a desired range by controlling the processing conditions such as the concentration of the boron component donating substance. In addition, in the water washing process, components such as boron and potassium are added to polyvinyl alcohol, taking into account processing conditions such as the amount of boron component donor and potassium component donor used in the dyeing process, crosslinking process, or stretching process. From the viewpoint of being able to be eluted from a polyvinyl alcohol based resin film or adsorbed to a polyvinyl alcohol based resin film, it is easy to adjust the boron content and potassium ion content to a desired range.

The swelling process is a treatment process in which the polyvinyl alcohol resin film is immersed in a swelling bath, which can remove dirt, blocking agents, etc. from the surface of the polyvinyl alcohol resin film, and also swell the polyvinyl alcohol resin film. can suppress uneven dyeing. For the swelling bath, a medium mainly composed of water, such as water, distilled water, or pure water, is usually used. A surfactant, alcohol, etc. may be appropriately added to the swelling bath according to a conventional method. Further, from the viewpoint of controlling the potassium content of the polarizing element, potassium iodide may be used in the swelling bath. In this case, the concentration of potassium iodide in the swelling bath is 1.5% by mass or less. It is preferably at most 1.0% by mass, more preferably at most 0.5% by mass.

The temperature of the swelling bath is preferably 10 to 60°C, more preferably 15 to 45°C, even more preferably 18 to 30°C. The immersion time in the swelling bath cannot be determined unconditionally because the degree of swelling of the polyvinyl alcohol resin film is affected by the temperature of the swelling bath, but it is preferably 5 to 300 seconds, and 10 to 200 seconds. More preferably, the time is 20 to 100 seconds. The swelling step may be performed only once, or may be performed multiple times as necessary.

The dyeing process is a process in which the polyvinyl alcohol resin film is immersed in a dye bath (iodine solution), and the polyvinyl alcohol resin film is made to adsorb and orient dichroic substances such as iodine or dichroic dyes. I can do it. The iodine solution is usually preferably an aqueous iodine solution and contains iodine and iodide as a solubilizing agent. Iodides include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. etc. 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 to 1% by mass, more preferably 0.02 to 0.5% by mass. The concentration of iodide in the dye bath is preferably 0.01 to 10% by mass, more preferably 0.05 to 5% by mass, and even more preferably 0.1 to 3% by mass. .

The temperature of the dyeing bath is preferably 10 to 50°C, more preferably 15 to 45°C, even more preferably 18 to 30°C. The immersion time in the dyeing bath cannot be determined unconditionally because the degree of dyeing of the polyvinyl alcohol resin film is affected by the temperature of the dyeing bath, but it is preferably 10 to 300 seconds, and 20 to 240 seconds. It is more preferable that there be. The dyeing step may be performed only once, or may be performed multiple times as necessary.

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

The concentration of the boron compound in the crosslinking bath is preferably 1 to 15% by weight, more preferably 1.5 to 10% by weight, and even more preferably 2 to 5% by weight. Further, when potassium iodide is used in the crosslinking bath, the concentration of potassium iodide in the crosslinking bath is preferably 1 to 15% by mass, more preferably 1.5 to 10% by mass, and 2% by mass. More preferably, it is 5% by mass.

The temperature of the crosslinking bath is preferably 20 to 70°C, more preferably 30 to 60°C. The immersion time in the crosslinking bath cannot be determined unconditionally because the degree of crosslinking of the polyvinyl alcohol resin film is affected by the temperature of the crosslinking bath, but it is preferably 5 to 300 seconds, and 10 to 200 seconds. It is more preferable that there be. The crosslinking step may be performed only once, or may be performed multiple times as necessary.

The stretching process is a process of stretching the polyvinyl alcohol resin film in at least one direction to a predetermined magnification. Generally, a polyvinyl alcohol resin film is uniaxially stretched in the transport direction (longitudinal direction). The stretching method is not particularly limited, and either a wet stretching method or a dry stretching method can be adopted. The stretching step may be performed only once, or may be performed multiple times as necessary. The stretching step may be performed at any stage in the production of the polarizing element.

As the treatment bath (stretching bath) in the wet stretching method, a solvent such as water or a mixed solution of water and an organic solvent miscible with water can be used. The stretching bath preferably contains potassium iodide from the viewpoint of controlling the content of potassium ions 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 to 15% by mass, more preferably 2 to 10% by mass, and 3 to 6% by mass. % is more preferable. Further, the treatment bath (stretching bath) may contain a boron compound from the viewpoint of suppressing film breakage during stretching, and in this case, the concentration of the boron compound in the stretching bath is 1 to 15% by mass. It is preferably 1.5 to 10% by mass, more preferably 2 to 5% by mass.

The temperature of the stretching bath is not limited, but for at least one stretching bath, it is preferably 25 to 80°C, more preferably 40 to 80°C, even more preferably 50 to 75°C, and even more preferably 65 to 80°C. The temperature is particularly preferably 75°C, and particularly preferably 67°C or higher. When the temperature of the stretching bath is increased, it becomes easier to retain the second metal ions used in the metal ion treatment step described below in the PVA resin layer. By increasing the temperature of the stretching bath, it is possible to stretch PVA at a temperature near the softening point of PVA in the PVA-based resin layer or at a temperature higher than the softening point of PVA. As a result, the crystal percentage of PVA decreases, or the PVA crystals become smaller, the amount of second metal ions taken in increases, and the crosslinking reaction is promoted, resulting in polyvinyl alcohol crystals measured by wide-angle X-ray scattering. This makes it easier to set the half-width of the peak to 4.80 nm ^-1 or more. The immersion time in the stretching bath cannot be determined unconditionally because the degree of stretching of the polyvinyl alcohol resin film is affected by the temperature of the stretching bath, but it is preferably 10 to 800 seconds, and 30 to 500 seconds. It is more preferable that there be. In addition, the stretching process in the wet stretching method may be performed alone, or may be performed together with any one or more of the swelling process, dyeing process, crosslinking process, and washing process, or a combination of these processes. You can go. A processing step that is particularly suitable for bringing the temperature of the processing bath to 65 to 75° C., which is optimal for the stretching step, is the crosslinking step when carried out in conjunction with any one or more processing steps. When stretching is performed using multiple treatment baths, the temperature of at least one treatment bath is preferably 65 to 75°C, and the immersion time in the treatment bath at 65 to 75°C is 40 to 200 seconds. is preferred.

Examples of the dry stretching method include an inter-roll stretching method, a heated roll stretching method, a compression stretching method, and the like. Note that the dry stretching method may be performed together with the drying step.

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

The cleaning step is a treatment step in which the polyvinyl alcohol resin film is immersed in a cleaning bath, and foreign matter remaining on the surface of the polyvinyl alcohol resin film can be removed. For the cleaning bath, a medium mainly composed of water, such as water, distilled water, or pure water, is usually used. Further, 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 1 to 10% by mass. The content is preferably from 1.5 to 4% by weight, even more preferably from 1.8 to 3.8% by weight.

The temperature of the cleaning bath is preferably 5 to 50°C, more preferably 10 to 40°C, even more preferably 15 to 30°C. In addition, the immersion time in the cleaning bath cannot be determined unconditionally because the degree of cleaning of the polyvinyl alcohol resin film is affected by the temperature of the cleaning bath, but it is preferably 1 to 100 seconds, and 2 to 50 seconds. More preferably, the time is 3 to 20 seconds. The washing step may be performed only once, or may be performed multiple times as necessary.

The method for manufacturing a polarizing element can include a metal ion treatment step in the above steps or as a step separate from the above steps. The metal ion treatment step is performed by immersing the polyvinyl alcohol resin film in an aqueous solution containing a metal salt of the second metal ion. The second metal ion is incorporated into the polyvinyl alcohol resin film through the metal ion treatment step.

A metal salt solution is used in the metal ion treatment step. Hereinafter, among the metal ion treatment steps, the immersion treatment in a zinc-containing solution will be described, taking as an example the case where a zinc salt aqueous solution is used. Examples of zinc salts include zinc halides such as zinc chloride and zinc iodide; zinc sulfate; zinc acetate, and the like.

The concentration of zinc ions in the aqueous zinc salt solution ranges from 0.1 to 10% by weight, preferably from 0.3 to 7% by weight. Further, as the zinc salt solution, it is preferable to use an aqueous solution containing potassium ions and iodine ions such as potassium iodide because it facilitates impregnation with zinc ions. The concentration of potassium iodide in the zinc salt solution is preferably 0.1 to 10% by mass, more preferably 0.2 to 5% by mass.

During the immersion treatment in the zinc-containing solution, the temperature of the zinc salt solution is usually 15 to 85°C, preferably 25 to 70°C. The immersion time is usually in the range of 1 to 120 seconds, preferably 3 to 90 seconds. During the immersion treatment in the zinc-containing solution, the zinc content in the polyvinyl alcohol-based resin film can be reduced by adjusting the conditions such as the concentration of the zinc salt solution, the immersion temperature and immersion time of the polyvinyl alcohol-based resin film in the zinc salt solution. Adjust so that it falls within the above range. There is no particular restriction on when to perform the immersion treatment in the zinc-containing solution. The immersion treatment in the zinc-containing liquid may be performed alone, or the immersion treatment may be performed in at least one of the dyeing process, crosslinking process, and stretching process by coexisting a zinc salt in the dyeing bath, crosslinking bath, and stretching bath. You can do both at the same time.

After performing each of the above steps, a drying step is finally performed. The drying step is a step of drying the polyvinyl alcohol resin film washed in the washing step to obtain a polarizing element. Drying may be performed by any appropriate method, including natural drying, blow drying, and heat drying.

Manufacturing method 2 includes a step of applying a coating liquid containing the above-mentioned polyvinyl alcohol-based resin onto a base film, a step of uniaxially stretching the obtained laminated film, and a step of uniaxially stretching the polyvinyl alcohol-based resin layer of the uniaxially stretched laminated film. A process of dyeing with a dichroic dye and adsorbing the dichroic dye to make a polarizing element, a process of treating the film with the dichroic dye adsorbed with an aqueous boric acid solution, and washing with water after treatment with an aqueous boric acid solution. It can be manufactured through a process. The base film used to form the polarizing element may be used as a protective layer of the polarizing element. If necessary, the base film may be peeled off and removed from the polarizing element.

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

The protective film may have other optical functions at the same time, and may be formed into a laminated structure in which a plurality of layers are laminated. The thickness of the protective film is preferably thin from the viewpoint of optical properties, but if it is too thin, the strength will decrease and the processability will be poor. A suitable film 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 polycarbonate resin film, a cycloolefin resin film such as norbornene, a (meth)acrylic polymer film, or a polyester resin film such as polyethylene terephthalate. I can do it. In the case of a configuration in which the polarizing element has protective films on both sides, when bonding is performed using a water-based adhesive such as PVA adhesive, the protective film on at least one side should be a cellulose acylate film or (meth)acrylic film in terms of moisture permeability. Any type of polymer film is preferred, and cellulose acylate film is particularly preferred.

At least one of the protective films may have a retardation function for the purpose of viewing angle compensation, etc. In that case, the film itself may have a retardation function, or it may have a separate retardation layer. or a combination of both.
In addition, although we have described a configuration in which the film with a retardation function is bonded directly to the polarizing element via an adhesive, it may also be attached via an adhesive or an adhesive via another protective film bonded to the polarizing element. It is also possible to have a structure in which they are bonded together.

[Adhesive layer]
At least one of the adhesives constituting the adhesive layer for pasting the protective film on the polarizing element is a water-based adhesive, and when the protective films are pasted on both sides of the polarizing element, other adhesives are used. On the one hand, any adhesive such as a water-based adhesive, a solvent-based adhesive, or an active energy ray-curable adhesive can be used, but a water-based adhesive is preferable. From the viewpoint of improving heat resistance, it is also useful for the adhesive layer to contain at least one urea compound selected from urea, urea derivatives, thiourea, and thiourea derivatives.

At least one of the water-based adhesives contains a polyvinyl alcohol resin (PVA resin) and cyclodextrins. Examples of cyclodextrins that can be added to the water-based adhesive include cyclodextrins that may be contained in a polarizing element.

When the adhesive is a water-based adhesive containing a PVA resin, the content of cyclodextrins is preferably 1 part by mass or more and 50 parts by mass or less, more preferably 1 part by mass or less, based on 100 parts by mass of the PVA resin. The content is .5 parts by mass or more and 40 parts by mass or less, more preferably 2 parts by mass or more and 35 parts by mass or less. If it 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 it exceeds 50 parts by mass, cyclodextrins may precipitate after producing a polarizing plate.

When the adhesive is a water-based adhesive containing a PVA-based resin, it may contain dicarboxylic acids such as maleic acid and phthalic acid from the viewpoint of improving heat resistance. The content of 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, based on 100 parts by mass of the PVA resin.

The thickness of the adhesive when applied may be set to any appropriate value. For example, settings are made so that an adhesive layer (coating layer) having a 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. It is as follows.

(water-based adhesive)
Any suitable water-based adhesive may be employed as the water-based adhesive. Among these, a water-based adhesive containing a PVA-based resin (PVA-based adhesive) is preferably used. The average degree of polymerization of the PVA resin contained in the water-based adhesive is preferably from 100 to 5,500, more preferably from 1,000 to 4,500 from the viewpoint of adhesiveness. The average degree of saponification is preferably 85 mol% to 100 mol%, more preferably 90 mol% to 100 mol%, from the viewpoint of adhesion.

The PVA resin contained in the above water-based adhesive is preferably one containing an acetoacetyl group, because it has excellent adhesion between the PVA resin layer and the protective film and has excellent durability. . The acetoacetyl group-containing PVA resin can be obtained, for example, by reacting a PVA resin and diketene by any method. The degree of acetoacetyl group modification of the acetoacetyl group-containing PVA resin is typically 0.1 mol% or more, 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, more preferably 0.5% by mass to 10% by mass.

The water-based adhesive can also contain a crosslinking agent. A known crosslinking agent can be used as the crosslinking agent. Examples include water-soluble epoxy compounds, dialdehydes, isocyanates, and the like.

When the PVA resin is an acetoacetyl group-containing PVA resin, the crosslinking agent is preferably glyoxal, glyoxylate, or methylolmelamine, and preferably glyoxal or glyoxylate. Preferred is glyoxal, particularly preferred.

Water-based adhesives can also contain organic solvents. Alcohols are preferable as the organic solvent because they are miscible with water, and among alcohols, methanol or ethanol is more preferable. While some urea compounds have low solubility in water, 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 PVA aqueous solution to prepare the adhesive. be.

The concentration of methanol in 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, when the methanol content is 70% by mass or less, deterioration of hue can be suppressed.

(Active energy ray curable adhesive)
An active energy ray-curable adhesive is an adhesive that is cured by irradiation with active energy rays such as ultraviolet rays, and includes, for example, an adhesive containing a polymerizable compound and a photopolymerizable initiator, and an adhesive containing a photoreactive resin. , an adhesive containing a binder resin and a photoreactive crosslinking agent, and the like. 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 compounds containing substances that generate active species such as neutral radicals, anion radicals, and cation radicals when irradiated with active energy rays such as ultraviolet rays.

(Urea-based compounds)
When the adhesive layer contains a urea compound, the urea compound is at least one selected from urea, urea derivatives, thiourea, and thiourea derivatives. As a method for incorporating a urea-based compound into the adhesive layer, it is preferable to incorporate the urea-based compound into the above-mentioned adhesive. Note that during the process of forming an adhesive layer from the adhesive through a drying process, etc., a part of the urea-based compound may migrate from the adhesive layer to the polarizing element or the like. That is, the polarizing element may contain a urea-based compound. Urea compounds include water-soluble ones and poorly water-soluble ones, and either type of urea compound can be used in the adhesive of this embodiment. When a poorly water-soluble urea compound is used in a water-based adhesive, it is preferable to devise a dispersion method after forming the adhesive layer so as to prevent an increase in haze.

When the adhesive is a water-based adhesive containing a PVA resin, the amount of the urea compound added is preferably 0.1 to 400 parts by mass, and preferably 1 to 200 parts by mass, based on 100 parts by mass of the PVA resin. It is more preferable that the amount is 3 to 100 parts by mass.

(urea derivative)
A urea derivative is a compound in which at least one of the four hydrogen atoms of a urea molecule is substituted with a substituent. In this case, the substituent is not particularly limited, but a substituent consisting of a carbon atom, a hydrogen atom, and an oxygen atom is preferable. Specific examples of substituents include alkyl groups having 1 to 18 carbon atoms, aromatic hydrocarbon groups having 6 to 12 carbon atoms, allyl groups having 2 to 12 carbon atoms, alkoxy groups having 1 to 12 carbon atoms, hydroxy groups, and these. Examples include groups that combine these.

Compounds in which one hydrogen atom out of the four hydrogen atoms contained in the urea molecule is substituted with a substituent (hereinafter sometimes referred to as "single-substituted urea") include methylurea, ethylurea, propylurea, and butylurea. , monoalkyl urea such as isobutyl urea, N-octadecyl urea, cyclohexyl urea; 2-hydroxyethyl urea; hydroxy urea; acetyl urea; allyl urea; 2-propynylurea; Monoarylureas such as phenyl) urea, benzyl urea, benzoyl urea, o-tolylurea, and p-tolylurea are mentioned.
Compounds in which two of the four hydrogen atoms contained in the urea molecule are substituted with substituents (hereinafter sometimes referred to as "disubstituted urea") include 1,1-dimethylurea, 1,3- Dialkyl urea such as dimethyl urea, 1,1-diethyl urea, 1,3-diethyl urea, 1,3-bis(hydroxymethyl) urea, 1,3-tert-butyl urea, 1,3-dicyclohexyl urea; 1, Examples include diarylureas such as 3-diphenylurea and 1,3-bis(4-methoxyphenyl)urea; 1-acetyl-3-methylurea and the like. Compounds in which all four hydrogen atoms contained in the urea molecule are substituted with substituents (hereinafter sometimes referred to as "4-substituted urea") include tetramethylurea, 1,1,3,3-tetraethylurea, 1 , 1,3,3-tetrabutylurea; and 1,3-dimethoxy-1,3-dimethylurea.

(thiourea derivative)
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 a substituent consisting of a carbon atom, a hydrogen atom, and an oxygen atom is preferable. Specific examples of substituents include alkyl groups having 1 to 18 carbon atoms, aromatic hydrocarbon groups having 6 to 12 carbon atoms, allyl groups having 2 to 12 carbon atoms, alkoxy groups having 1 to 12 carbon atoms, hydroxy groups, and these. Examples include groups that combine these.

Compounds in which one of the four hydrogen atoms contained in the thiourea molecule is substituted with a substituent (hereinafter sometimes referred to as "single-substituted thiourea") include N-methylthiourea, ethylthiourea, and propylthiourea. , monoalkylthiourea such as isopropylthiourea, 1-butylthiourea, cyclohexylthiourea; N-acetylthiourea; N-allylthiourea; (2-methoxyethyl)thiourea; N-phenylthiourea, (4-methoxyphenyl)thio Examples include monoalkylthioureas such as urea, N-(2-methoxyphenyl)thiourea, N-(1-naphthyl)thiourea, (2-pyridyl)thiourea, o-tolylthiourea, and p-tolylthiourea.
Compounds in which two of the four hydrogen atoms contained in the thiourea molecule are substituted with substituents (hereinafter sometimes referred to as "disubstituted thiourea") include 1,1-dimethylthiourea, 1,3 - Dialkylthiourea such as dimethylthiourea, 1,1-diethylthiourea, 1,3-diethylthiourea, 1,3-dibutylthiourea, 1,3-diisopropylthiourea, 1,3-dicyclohexylthiourea; N,N- Diaryls such as diphenylthiourea, N,N'-diphenylthiourea, 1,3-di(o-tolyl)thiourea, 1,3-di(p-tolyl)thiourea, 1-benzyl-3-phenylthiourea, etc. Thiourea; 1-methyl-3-phenylthiourea; N-allyl-N'-(2-hydroxyethyl)thiourea and the like.
Examples of compounds in which three of the four hydrogen atoms contained in the thiourea molecule are substituted with substituents (hereinafter sometimes referred to as "trisubstituted thiourea") include trimethylthiourea and the like. Compounds in which all four hydrogen atoms contained in the thiourea molecule are substituted with substituents (hereinafter sometimes referred to as "4-substituted thiourea") include tetramethylthiourea, 1,1,3,3-tetraethyl Examples include thiourea.

Among urea compounds, urea, urea derivatives, or thiourea derivatives are preferred, and urea or urea derivatives are more preferred. Among the urea derivatives, mono-substituted urea or di-substituted urea are preferable, and mono-substituted urea is more preferable. Disubstituted ureas include 1,1-substituted ureas and 1,3-substituted ureas, with 1,3-substituted ureas being more preferred.

<Urea-based compound-containing layer>
The urea-based compound is not limited to being contained in the adhesive layer as described above, and may be contained in other layers other than the adhesive layer from the viewpoint of improving the heat resistance of the polarizing plate. . Examples of other layers include, for example, a cured layer in a configuration in which a protective film is laminated on one side of the polarizing element via an adhesive layer, and a cured layer is laminated on the other side of the polarizing element. In the configuration of a polarizing plate having a protective film on only one side of the polarizing element, a cured layer may be laminated for the purpose of increasing physical strength or the like.

In this embodiment, such a hardened layer can also contain a urea-based compound. Usually, such a cured layer is formed from a curable composition containing an organic solvent, but in paragraphs [0020] to [0042] of JP-A-2017-075986, an aqueous curable composition of an active energy ray-curable polymer composition is described. A method of forming such a hardened layer from solution is described. Since many urea compounds are water-soluble, such a composition may contain a water-soluble urea compound.

<Adhesive layer>
In order to bond the polarizing plate described above to an image display device, an adhesive layer is usually laminated. This adhesive layer is provided for bonding a polarizing plate to an image display device.

The adhesive layer may be composed of one layer or two or more layers, but is preferably composed of one layer. The adhesive layer can be composed of an adhesive composition containing a (meth)acrylic resin, a rubber resin, a urethane resin, an ester resin, a silicone resin, or a polyvinyl ether resin as a main component. Among these, pressure-sensitive adhesive compositions whose base polymer is a (meth)acrylic resin having excellent transparency, weather resistance, heat resistance, etc. are suitable. The adhesive composition may be of an active energy ray-curable type or a thermosetting type.

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

The pressure-sensitive adhesive composition may contain only the above base polymer, but usually further contains a crosslinking agent. Examples of crosslinking agents include metal ions with a valence of two or more that form carboxylic acid metal salts with carboxyl groups, polyamine compounds that form amide bonds with carboxyl groups, and metal ions that form carboxylic acid metal salts with carboxyl groups. Examples include polyepoxy compounds or polyols that form ester bonds, and polyisocyanate compounds that form amide bonds with carboxyl groups. Among these, polyisocyanate compounds are preferred.

Active energy ray-curable adhesive compositions have the property of being cured by irradiation with active energy rays such as ultraviolet rays or electron beams, and have adhesive properties even before irradiation with active energy rays to form films, etc. It has the property that it can be brought into close contact with an adherend, and its adhesion can be adjusted by curing by irradiation with active energy rays. The active energy ray-curable adhesive composition is preferably an ultraviolet ray-curable adhesive composition. The active energy ray curable adhesive composition further contains an active energy ray polymerizable compound in addition to the base polymer and the crosslinking agent. If necessary, a photopolymerization initiator, a photosensitizer, etc. may be included.

The adhesive composition contains fine particles, beads (resin beads, glass beads, etc.), glass fibers, resins other than the base polymer, tackifiers, fillers (metal powders and other inorganic powders) to impart light scattering properties. etc.), antioxidants, ultraviolet absorbers, dyes, pigments, colorants, antifoaming agents, corrosion inhibitors, photopolymerization initiators, and other additives.

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

For example, an adhesive layer may be formed by directly applying an adhesive composition to the release-treated surface of a separate film, and this adhesive layer with a separate film may be laminated on the surface of a 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 an adhesive layer on the surface of a polarizing plate, it is preferable to subject the bonding surface of the polarizing plate and/or the bonding surface of the adhesive layer to surface activation treatment, such as plasma treatment or corona treatment. It is more preferable to perform a treatment.
Further, a pressure-sensitive adhesive sheet is prepared by coating a pressure-sensitive adhesive composition on a second separate film to form a pressure-sensitive adhesive layer, and a separate film is laminated on the formed pressure-sensitive adhesive layer. The adhesive layer with a separate film after peeling off the separate film may be laminated on a polarizing plate. The second separate film used has weaker adhesion to the adhesive layer than the separate film and is 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, more preferably 3 μm or more and 50 μm or less, and may be 20 μm or more.

Hereinafter, the present invention will be specifically explained based on Examples. Materials, reagents, amounts of substances, their proportions, 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 or limited to the following examples.

(1) Measurement of thickness of polarizing element:
Measurement was performed using a digital micrometer "MH-15M" manufactured by Nikon Corporation.

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

(3) Measurement of zinc ion content:
Nitric acid was added to a precisely weighed polarizing element, and the solution was acid-decomposed using a microwave sample pretreatment device (ETHOS D) manufactured by Milestone General, and the resulting solution was used as a measurement solution. The zinc ion content was calculated by quantifying the zinc concentration of the measurement solution using an ICP emission spectrometer (5110 ICP-OES) manufactured by Agilent Technologies, and calculating the zinc mass relative to the polarizing element mass.

(4) Measurement of boron adsorption rate of PVA resin film:
A PVA 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 from the boric acid aqueous solution was dried in an 80° C. oven for 11 minutes. The humidity was controlled in an environment of 23° C. and 55% RH for 24 hours to obtain a boron-containing PVA film. 0.2 g of the boron-containing PVA resin film thus obtained was dissolved in 200 g of a 1.9% by mass mannitol aqueous solution. Next, the obtained aqueous solution was titrated with a 1 mol/L sodium hydroxide aqueous solution, and the boron content of the PVA resin film was calculated by comparing the amount of sodium hydroxide aqueous solution required for neutralization with a calibration curve. . The boron content of the PVA resin film thus obtained was used as the boron adsorption rate of the PVA resin film.

(5) Measurement of half-width of peak derived from polyvinyl alcohol crystal of polarizing element <Measurement sample>
A sample for measurement was prepared by laminating 10 polarizing elements such that their absorption axes were aligned.

<Measurement using wide-angle X-ray scattering method>
This refers to the value calculated using the wide-angle X-ray scattering method using the following measurement equipment and measurement requirements.

(measuring device)
A nanoscale X-ray structure evaluation device NANO-Viewer manufactured by Rigaku Corporation was used.

(Measurement condition)
・X-ray source: Cu-kα rays ・Camera length: 71mm
・Measurement: Transmission measurement ・X-ray irradiation time: 10 minutes

(Calculation method)
First, a background measurement was performed without setting up a sample for measurement, and an annular average scattering profile was obtained for the obtained two-dimensional scattering pattern. Next, the measurement sample was measured, and a scattering profile was similarly obtained. Next, from the scattering profile of the measurement sample minus the background scattering profile, a peak derived from polyvinyl alcohol crystals near a wave number q of 15 nm ^-1 was identified, and the half-width of that peak was calculated. . The peak at a wave number q of 15 nm ⁻¹ is a peak derived from polyvinyl alcohol crystals. The interval between two points at which the intensity is 1/2 of the maximum value of such a peak is defined as the half-width.

(Preparation of polarizing element 1)
After immersing a 30 μm thick polyvinyl alcohol resin film with a boron adsorption rate of 5.71% by mass in pure water at 21.5°C for 79 seconds (swelling treatment), the mass of potassium iodide/boric acid/water was It was immersed for 151 seconds in a 23° C. aqueous solution having a ratio of 2/2/100 and containing 1.0 mM iodine (staining step). Thereafter, it was immersed for 76 seconds in an aqueous solution at 68.5° C. in which the mass ratio of potassium iodide/boric acid/water was 2.5/4/100 (first crosslinking step). Subsequently, it was immersed for 11 seconds 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 (second crosslinking step, metal ion treatment step). ). Thereafter, it was immersed in a cleaning bath for cleaning (cleaning step) and dried at 38° C. (drying step) to obtain a polarizing element with a thickness of 12 μm in which iodine was adsorbed and oriented in polyvinyl alcohol. Stretching was mainly performed in the dyeing process and the first crosslinking process, and the total stretching ratio was 5.85 times. The presence of potassium ions was confirmed in the obtained polarizing element. The resulting polarizing element had a zinc ion content of 0.17% by mass, a boron content of 4.62% by mass, and a half-value width of a peak derived from polyvinyl alcohol crystals of 4.90 nm ^-1 .

(Preparation of polarizing element 2)
After immersing a 30 μm thick polyvinyl alcohol resin film with a boron adsorption rate of 5.71% by mass in pure water at 21.5°C for 79 seconds (swelling treatment), the mass of potassium iodide/boric acid/water was It was immersed for 151 seconds in a 23° C. aqueous solution having a ratio of 2/2/100 and containing 1.0 mM iodine (staining step). Thereafter, it was immersed for 76 seconds in an aqueous solution at 60.6° C. in which the mass ratio of potassium iodide/boric acid/water was 2.5/4/100 (first crosslinking step). Subsequently, the mass ratio of potassium iodide/boric acid/zinc chloride/water was immersed in a 45°C aqueous solution of 3/5.5/0.0/100 for 11 seconds (second crosslinking step, metal ion treatment step). ). Thereafter, it was immersed in a cleaning bath for cleaning (cleaning step) and dried at 38° C. (drying step) to obtain a polarizing element with a thickness of 12 μm in which iodine was adsorbed and oriented in polyvinyl alcohol. Stretching was mainly performed in the dyeing process and the first crosslinking process, and the total stretching ratio was 5.85 times. The presence of potassium ions was confirmed in the obtained polarizing element. The resulting polarizing element had a zinc ion content of 0.00% by mass, a boron content of 4.62% by mass, and a half-value width of a peak derived from polyvinyl alcohol crystals of 4.75 nm ^-1 .

(Preparation of polarizing element 3)
After immersing a 60 μm thick polyvinyl alcohol resin film with a boron adsorption rate of 5.71% by mass in pure water at 21.5°C for 79 seconds (swelling treatment), the mass of potassium iodide/boric acid/water was It was immersed for 151 seconds in a 23° C. aqueous solution having a ratio of 2/2/100 and containing 1.0 mM iodine (staining step). Thereafter, it was immersed for 76 seconds in an aqueous solution at 60.6° C. in which the mass ratio of potassium iodide/boric acid/water was 2.5/4/100 (first crosslinking step). Subsequently, it was immersed for 11 seconds in an aqueous solution at 45°C with a mass ratio of potassium iodide/boric acid/zinc chloride/water of 3/3.5/0.0/100 (second crosslinking step, metal ion treatment step). ). Thereafter, it was immersed in a cleaning bath for cleaning (cleaning step) and dried at 38° C. (drying step) to obtain a polarizing element with a thickness of 22 μm in which iodine was adsorbed and oriented in polyvinyl alcohol. Stretching was mainly performed in the dyeing process and the first crosslinking process, and the total stretching ratio was 5.85 times. The presence of potassium ions was confirmed in the obtained polarizing element. The zinc ion content of the obtained polarizing element was 0.00% by mass, the boron content was 3.91% by mass, and the half width of the peak derived from polyvinyl alcohol crystals was 4.75 nm ^-1 .

(Preparation of polarizing element 4)
After immersing a 60 μm thick polyvinyl alcohol resin film with a boron adsorption rate of 5.71% by mass in pure water at 21.5°C for 79 seconds (swelling treatment), the mass of potassium iodide/boric acid/water was It was immersed for 151 seconds in a 23° C. aqueous solution having a ratio of 2/2/100 and containing 1.0 mM iodine (staining step). Thereafter, it was immersed for 76 seconds in an aqueous solution at 68.5° C. in which the mass ratio of potassium iodide/boric acid/water was 2.5/4/100 (first crosslinking step). Subsequently, it was immersed for 11 seconds in an aqueous solution at 45°C with a mass ratio of potassium iodide/boric acid/zinc chloride/water of 3/3.5/0.6/100 (second crosslinking step, metal ion treatment step). ). Thereafter, it was immersed in a cleaning bath for cleaning (cleaning step) and dried at 38° C. (drying step) to obtain a polarizing element with a thickness of 22 μm in which iodine was adsorbed and oriented in polyvinyl alcohol. Stretching was mainly performed in the dyeing process and the first crosslinking process, and the total stretching ratio was 5.85 times. The presence of potassium ions was confirmed in the obtained polarizing element. The zinc ion content of the obtained polarizing element was 0.17% by mass, the boron content was 3.91% by mass, and the half width of the peak derived from polyvinyl alcohol crystals was 4.90 nm ^-1 .

(Preparation of PVA solution for adhesive)
50 g of a modified PVA resin containing an acetoacetyl group (Gosenex Z-410 manufactured by Mitsubishi Chemical Corporation) was dissolved in 950 g of pure water, heated at 90°C for 2 hours, then cooled to room temperature to form a PVA solution for adhesive. Obtained.

(Preparation of adhesives 1 to 4 for polarizing plates)
PVA solution, commercially available glyoxal 40% by mass solution, α-CD, β-CD, γ- Adhesives 1 to 4 were prepared by blending CD, maleic acid, and pure water.

(Saponification of cellulose acylate film)
A commercially available cellulose acylate film TJ40UL (manufactured by Fuji Film Co., Ltd.: film thickness 40 μm) and a commercially available cellulose acylate film: Fujitac ZRD40 (manufactured by Fuji Film Co., Ltd.: film thickness 40 μm) were prepared at 1.5 mol/min at 55°C. The film was immersed in L of NaOH aqueous solution (saponification solution) for 2 minutes, and then washed with water. Thereafter, the film was immersed in a 0.05 mol/L sulfuric acid aqueous solution at 25° C. for 30 seconds, and then passed through a washing bath under running water for 30 seconds to make the film neutral. Then, draining with an air knife was repeated three times. After removing the water, the film was dried by staying in a drying zone at 70° C. for 15 seconds to produce a saponified cellulose acylate film.

(Preparation of polarizing plates 1 to 7)
Using the adhesive 1 prepared above, a saponified cellulose acylate film TJ40UL is placed on one side of the polarizing element 1, and a saponified cellulose acylate film: FUJITAC ZRD40 is placed on the other side using a roll laminating machine. It was laminated using Thereafter, it was dried at 75° C. for 8 minutes to obtain polarizing plate 1. The adhesive layer was adjusted so that the thickness after drying was 80 nm on both sides.

In the production of polarizing plate 1, adhesives 2 to 4 were used instead of adhesive 1 to obtain polarizing plates 2 to 3 and polarizing plate 6.

In the production of polarizing plate 1, polarizing plate 4, polarizing plate 5, and polarizing plate 7 were obtained by replacing polarizing element 1 with polarizing element 2, polarizing element 3, or polarizing element 4.

(Adjustment of water content of polarizing plate (polarizing element))
The polarizing plates 1 to 7 obtained above were stored for 72 hours at a temperature of 20° C. and a relative humidity of 30%, 35%, 40%, 45%, 50% or 55%. Moisture content was measured using the Karl Fischer method at 66, 69 and 72 hours of storage. Under any humidity conditions, the moisture content did not change after storage for 66 hours, 69 hours, and 72 hours. Therefore, the moisture content of polarizing plates 1 to 3 can be considered to be the same as the equilibrium moisture content of the 72-hour storage environment used in this experimental example. When the water content of the polarizing plate reaches equilibrium in a certain storage environment, it can be considered that the water content of the polarizing element in the polarizing plate also reaches equilibrium in that storage environment. Further, when the water content of the polarizing element in the polarizing plate reaches equilibrium in a certain storage environment, it can be considered that the water content of the polarizing plate also reaches equilibrium in that storage environment.

(Adjustment of water content of polarizing plates 1 to 7)
The water content of polarizing plates 1 to 7 was stored for 72 hours at a temperature of 20°C and a relative humidity of 45% so that the moisture content of polarizing plates 1 to 7 became the equilibrium moisture content of an environment of 45% at 20°C. It was adjusted.

<High temperature durability evaluation>
(Preparation of evaluation sample)
An acrylic adhesive (manufactured by Lintec Corporation, product number: #7) was formed on both sides of polarizing plates 1 to 7 whose water content had been adjusted. Furthermore, it was cut into a size of 50 mm x 100 mm so that the absorption axis was parallel to the long side. Evaluation samples were prepared by laminating alkali-free glass ("EAGLE XG" manufactured by Corning) on the surface of each adhesive.

<Single transmittance evaluation (105°C)>
Evaluation samples of polarizing plates 1 to 7 were autoclaved at a temperature of 50°C and a pressure of 5 kgf/cm ² (490.3 kPa) for 1 hour, and then left for 24 hours in an environment of a temperature of 23°C and a relative humidity of 50%. . Thereafter, the transmittance was measured for the evaluation samples of polarizing plates 1 to 6 (initial value), stored in a heated environment at a temperature of 105° C., and the transmittance was measured every 24 hours from 192 to 240 hours. Evaluation was performed according to the following criteria based on the time when the transmittance decreased by 5% or more with respect to the initial value. The results obtained are shown in Table 2.
Those with a decrease in transmittance of less than 5% after 240 hours: A
Those whose transmittance decreased by 5% or more in 216 to 240 hours: B
Those whose transmittance decreased by 5% or more in 192 to 216 hours: C
Items with a decrease in transmittance of 5% or more after 192 hours: D

The half-value width of the peak derived from polyvinyl alcohol crystals is 4.80 nm ^-1 or more, the transparent protective film has a polarizing element containing 0.05% by mass or more of zinc ions, and is made of a water-based adhesive containing cyclodextrins. It was found that the bonded polarizing plate suppressed a decrease in transmittance and had excellent high-temperature durability.

Claims (9)

A polarizing plate comprising a polarizing element formed by adsorbing and aligning a dichroic dye to a polyvinyl alcohol resin layer, and a transparent protective film,
The polarizing element has a half-value width of a peak derived from polyvinyl alcohol crystals measured by wide-angle X-ray scattering of 4.80 nm ^-1 or more,
The polarizing element includes potassium ions and metal ions other than potassium ions,
The polarizing element has a content of metal ions other than potassium ions of 0.05% by mass or more,
The polarizing element and the transparent protective film are bonded to each other by an adhesive layer formed from a water-based adhesive containing a polyvinyl alcohol resin and cyclodextrins. The polarizing plate according to claim 1, wherein the metal ions include at least one selected from the group consisting of cobalt, nickel, zinc, chromium, aluminum, copper, manganese, and iron ions. The polarizing plate according to claim 1 or 2, wherein the polarizing element has a boron content of 2.4% by mass or more and 8.0% by mass or less. The polarizing plate according to claim 1 or 2, wherein the content of the cyclodextrin in the water-based adhesive is 1 part by mass or more and 50 parts by mass or less based on 100 parts by mass of the polyvinyl alcohol resin. 3. The polarizing plate according to claim 1, wherein the cyclodextrin is at least one selected from the group consisting of α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin. The polarizing plate according to claim 1 or 2, wherein the water-based adhesive has a methanol concentration of 10% by mass or more and 70% by mass or less. The polarizing plate according to claim 1 or 2, 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 water content of the polarizing element is greater than or equal to the equilibrium water content at a temperature of 20°C and a relative humidity of 30%, and less than or equal to an equilibrium water content at a temperature of 20°C and a relative humidity of 50%. The polarizing plate according to claim 1 or 2, wherein the water content of the polarizing plate is greater than or equal to the equilibrium water content at a temperature of 20°C and a relative humidity of 30%, and less than or equal to an equilibrium water content at a temperature of 20°C and a relative humidity of 50%.