TW202422132A - Polarizer capable of suppressing a decrease in transmittance and the occurrence of crossed light leakage in a high-temperature environment - Google Patents

Abstract

The object of the present invention is to provide a novel polarizer capable of suppressing a decrease in transmittance and the occurrence of crossed light leakage in a high-temperature environment. The solution is a polarizer which includes a polarizing element in which a dichroic pigment is adsorbed and oriented to a polyvinyl alcohol-based resin layer, and a transparent protective film. The polarizing element has a visual sensitivity corrected polarization degree of 99.9% or more, and an orthogonal transmittance of 1.8% or less at a wavelength of 780 nm. The polarizing element and the transparent protective film are bonded together through an adhesive layer, and the adhesive layer is formed of a water-based adhesive containing a urea-based compound.

Description

Polarizing Plate

The present invention relates to a polarizing plate.

Liquid crystal display devices (LCD) are not only used in LCD TVs, but are also widely used in mobile devices such as personal computers and mobile phones, and in-vehicle applications such as car navigation. Generally, a liquid crystal display device is a liquid crystal panel with polarizing plates attached to both sides of a liquid crystal unit with an adhesive, and uses the liquid crystal panel to control the light from the backlight for display. In recent years, organic EL display devices have also been widely used in mobile devices such as TVs and mobile phones, and in-vehicle applications such as car navigation, just like liquid crystal display devices. In an organic EL display device, external light is reflected by the metal electrode (cathode), and in order to prevent it from being seen as a mirror, a circular polarizer (a laminate of a polarizing element and a λ/4 plate) is sometimes arranged on the visual side surface of the image display panel.

As mentioned above, polarizing plates are increasingly being installed in vehicles as components of image display devices such as liquid crystal display devices and organic EL display devices. Polarizing plates used in vehicle-mounted image display devices are often exposed to high temperature environments compared to mobile devices such as TVs and mobile phones, and therefore require less change in characteristics at relatively high temperatures (high temperature durability).

On the other hand, in order to prevent the image display panel from being damaged by impact from the outside, a structure in which a front panel (also called a "window layer") such as a transparent resin plate or a glass plate is provided on the visual side of the image display panel is increasing. In image display devices having a touch panel, a structure in which the touch panel is provided on the visual side of the image display panel and the front panel is provided on the visual side of the touch panel is widely adopted.

In such a structure, if there is an air layer between the image display panel and the transparent member such as the front panel or the touch panel, light reflection at the interface of the air layer will cause the intrusion of external light, and there is a tendency to reduce the visibility of the screen. Therefore, the use of a structure (hereinafter referred to as an "interlayer filling structure") in which the space between the polarizing plate arranged on the visual side surface of the image display panel and the transparent member is filled with a layer other than the air layer, usually a solid layer (hereinafter referred to as an "interlayer filler") is expanding. The interlayer filler is preferably a material with a refractive index close to that of the polarizing plate or the transparent member. As an interlayer filler, an adhesive or a UV curing adhesive is used for the purpose of suppressing a decrease in visibility due to reflection at the interface and also for the purpose of indirectly fixing the components (see, for example, Patent Document 1).

The use of interlayer filling structures is becoming more common in mobile devices such as mobile phones that are often used outdoors. In addition, due to the increasing demand for visibility in recent years, the use of interlayer filling structures in which 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 or the like is also being examined for in-vehicle applications such as car navigation systems.

However, there are literature reports that when such a structure is adopted, the transmittance of the polarizing plate decreases significantly in a high temperature environment. Patent document 2 proposes a solution to this problem by setting the moisture content per unit area of the polarizing plate to a predetermined amount or less, and setting the saturated water absorption of the transparent protective film adjacent to the polarizing element to a predetermined amount or less to suppress the decrease in transmittance. Patent document 3 proposes a method of suppressing the decrease in transmittance by making the water-based adhesive contain a urea-based compound. [Prior art document] [Patent document]

[Patent Document 1] Japanese Patent Publication No. 11-174417 [Patent Document 2] Japanese Patent Publication No. 2014-102353 [Patent Document 3] Japanese Patent Publication No. 2020-190723

[The problem that the invention is trying to solve]

However, even if the decrease in transmittance in a high temperature environment can be suppressed, when two polarizing plates are used in an orthogonal polarization relationship, light leakage (hereinafter also referred to as "orthogonal light leakage") may occur. In particular, it is known that when the thickness of the interlayer filler is 100 μm or more, orthogonal light leakage is more likely to occur. The purpose of the present invention is to provide a novel polarizing plate that can suppress the decrease in transmittance and the occurrence of orthogonal light leakage in a high temperature environment. [Means for solving the problem]

The present invention provides the following polarizing plates. [1] A polarizing plate comprising a polarizing element formed by adsorbing and aligning a dichroic dye on a polyvinyl alcohol resin layer and a transparent protective film, wherein the polarizing element has a visual sensitivity correction polarization degree of 99.9% or more and an orthogonal transmittance at a wavelength of 780 nm of 1.8% or less. [2] A polarizing plate as in [1], wherein the polarizing element and the transparent protective film are bonded together by an adhesive layer, and the adhesive layer is formed by an aqueous adhesive containing a urea compound, wherein the urea compound is at least one selected from the group consisting of urea, a urea derivative, thiourea and a thiourea derivative. [3] A polarizing plate as in [2], wherein the urea compound is at least one selected from the group consisting of a urea derivative and a thiourea derivative. [4] A polarizing plate as described in [2] or [3], wherein the aqueous adhesive comprises a polyvinyl alcohol resin. [5] A polarizing plate as described in [4], wherein the content of the urea compound in the aqueous adhesive is 0.1 to 400 parts by mass relative to 100 parts by mass of the polyvinyl alcohol resin. [6] A polarizing plate as described in any one of [2] to [5], wherein the aqueous adhesive comprises methanol, and the concentration of the methanol is 10% to 70% by mass. [7] A polarizing plate as described in any one of [2] to [6], wherein the aqueous adhesive comprises cyclodextrins. [8] A polarizing plate as described in any one of [2] to [7], wherein the adhesive layer has a thickness of 0.01 μm to 7 μm. [9] A polarizing plate as described in any one of [1] to [8], wherein the thickness of the polarizing element is 15 μm or less. [10] A polarizing plate as described in any one of [1] to [9], wherein the moisture content of the polarizing element is greater than or equal to the equilibrium moisture content of 30% relative humidity at a temperature of 20°C and less than or equal to the equilibrium moisture content of 50% relative humidity at a temperature of 20°C. [11] A polarizing plate as described in any one of [1] to [9], wherein the moisture content of the polarizing plate is greater than or equal to the equilibrium moisture content of 30% relative humidity at a temperature of 20°C and less than or equal to the equilibrium moisture content of 50% relative humidity at a temperature of 20°C. [12] A polarizing plate as described in any one of [1] to [11], wherein an adhesive layer having a thickness of 50 μm or less is formed on one side of the polarizing plate, and an adhesive layer having a thickness of 50 μm or more is formed on the other side of the polarizing plate. [Effect of the invention]

According to the present invention, a polarizing plate having improved high temperature durability can be provided. According to the present invention, a polarizing plate can be provided, in which even when used in an image display device having an interlayer filling structure, a decrease in transmittance and occurrence of orthogonal light leakage in a high temperature environment can be suppressed.

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

[Polarizing plate] The polarizing plate associated with the embodiment of the present invention has a polarizing element and a transparent protective film that allows a dichroic pigment to be adsorbed and aligned on a layer containing a polyvinyl alcohol-based resin. The visual sensitivity corrected polarization degree of the above-mentioned polarizing element is 99.9% or more, and the orthogonal transmittance at a wavelength of 780nm is 1.8% or less. The visual sensitivity corrected polarization degree of the above-mentioned polarizing element is 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. In addition, the orthogonal transmittance at a wavelength of 780nm of the above-mentioned polarizing element is 1.8% or less, preferably 0.1% or more and 1.7% or less, preferably 0.2% or more and 1.6% or less, 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 related to the present embodiment can suppress the decrease in transmittance and the occurrence of cross light leakage even when exposed to a high temperature environment for a long time by correcting the polarization degree and the cross transmittance by visual sensitivity within the above range. It is speculated that by allowing more PVA-I ₅ complex to exist in the polarizing element, the cross light leakage that occurs in a high temperature environment accompanied by the reduction of PVA-I ₅ complex can be suppressed. In addition, the maximum absorption wavelength of PVA-I ₅ complex is around 610nm, but it is found that the cross transmittance on the longer wavelength side is easily greatly affected in terms of deterioration indicators, and it is decided to use the cross transmittance with a maximum wavelength of 780nm in the visible light region. In addition, iodine ions also have the effect of promoting polyene. It is speculated that by allowing more PVA-I ₅ complex to exist in the polarizing element, the iodine ion (I ^- ) will become less in the stage before being exposed to a high temperature environment. Allowing more PVA-I ₅ complex to exist in the polarizing element is believed to help suppress the decrease in transmittance (polyeneization) in a high temperature environment. In this specification, the visual sensitivity correction polarization degree and orthogonal transmittance of the polarizing element are values measured by the measurement method described in the embodiment.

In the polarizing plate of the present embodiment, the polarizing element and the transparent protective film are preferably bonded by an adhesive layer, and the adhesive layer is formed by an aqueous adhesive containing a urea compound. The aqueous adhesive may also contain cyclodextrins. The polarizing plate associated with the present embodiment preferably has at least one of the following characteristics (a) and (b). (a) The moisture content of the polarizing element is greater than the equilibrium moisture content of 30% relative humidity at a temperature of 20°C and less than the equilibrium moisture content of 50% relative humidity at a temperature of 20°C. (b) The moisture content of the polarizing plate is greater than the equilibrium moisture content of 30% relative humidity at a temperature of 20°C and less than the equilibrium moisture content of 50% relative humidity at a temperature of 20°C.

In the past, polarizing plates with excellent high-temperature durability were known, for example, polarizing plates whose transmittance reduction was suppressed even when the polarizing plates were left alone in an environment at a temperature of 95°C for 1000 hours. However, even for such polarizing plates, when an interlayer filling structure is used, a significant decrease in transmittance and polarization degree was observed in the center of the polarizing plate surface when the plates were left in an environment at a temperature of 105°C for 240 hours. The significant decrease in transmittance and polarization degree of polarizing plates in a high-temperature environment is considered to be a problem that is particularly prone to occur when an image display device using an interlayer filling structure in which one side of the polarizing plate is bonded to an image display unit and the other side is bonded to a transparent component such as a touch panel or front panel is exposed to a high-temperature environment.

Polarizing plates whose transmittance is significantly reduced by interlayer filling structures have peaks near 1100 cm ^-1 (derived from =CC= bonding) and 1500 cm ^-1 (derived from -C=C- bonding) by Raman spectroscopy, and are therefore considered to have formed a polyene structure (-C=C) _n -. The polyene structure is presumed to be a structure generated by polyeneization by dehydration of polyvinyl alcohol constituting the polarizing element (Patent Document 2, paragraph [0012]).

The polarizing plate of this embodiment can further improve the high temperature durability. The polarizing plate of this embodiment is assembled into an image display device with an interlayer filling structure, and can suppress the decrease of transmittance and the occurrence of orthogonal light leakage even when exposed to a high temperature environment such as 105°C.

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

PVA resins can be obtained by saponifying polyvinyl acetate resins. Polyvinyl acetate resins include, in addition to polyvinyl acetate which is a homopolymer of vinyl acetate, copolymers of vinyl acetate and other monomers copolymerizable therewith. Other monomers copolymerizable therewith include, for example, unsaturated carboxylic acids, olefins such as ethylene, vinyl ethers, unsaturated sulfonic acids, and the like.

In the present embodiment, it is preferred that the PVA resin layer is formed of a PVA resin having a boron adsorption rate of 5.70 mass % or more. That is, the boron adsorption rate of the PVA resin at the raw material stage before dyeing or stretching is preferably 5.70 mass % or more. By using such a PVA resin, it is easy to obtain a polarizing element having a visual sensitivity-corrected polarization degree of 99.9% or more and an orthogonal transmittance of 1.8% or less at a wavelength of 780 nm. In addition, the boron adsorption rate of the PVA resin is preferably 10 mass % or less. By using such a PVA resin to produce a polarizing element, it is not necessary to set the boric acid concentration in the boric acid treatment tank to a high concentration, and the processing time using the boric acid treatment can be shortened, making it easy to obtain the desired polarizing element and improving the productivity of the polarizing element. If the boron adsorption rate of the PVA resin is set to 10 mass % or less, the boron will be appropriately absorbed into the PVA resin layer, which can easily reduce the shrinkage force of the polarizing element. The boron adsorption rate of the PVA resin can be measured by the method described in the examples described below.

The boron adsorption rate of PVA resin is a characteristic that reflects the spacing between molecular chains or the crystal structure in PVA resin. It is believed that PVA resin with a boron adsorption rate of 5.70 mass% or more has a wider spacing between molecular chains and less crystals than PVA resin with a boron adsorption rate of less than 5.70 mass%. Therefore, it is speculated that boron, the first metal ion, and the second metal ion easily enter the PVA resin layer, and the polarization degree becomes less likely to decrease in a high temperature environment.

The boron adsorption rate of PVA resin can be adjusted by, for example, pre-treating the PVA resin with hot water, acid solution, ultrasonic irradiation, or radiation before manufacturing the polarizing element. These treatments can expand the spacing between molecular chains in the PVA resin or destroy the crystal structure. Hot water treatment includes, for example, immersing in pure water at 30°C to 100°C for 1 second to 90 seconds and drying. Acid solution treatment includes, for example, immersing in a boric acid aqueous solution with a concentration of 10% to 20% by mass for 1 second to 90 seconds and drying. Ultrasonic treatment includes, for example, treatment with an output power of 200W to 500W and an irradiation frequency of 20 to 29 kc for 30 seconds to 10 minutes. Ultrasonic treatment can be performed in a solvent such as water.

The saponification degree of the PVA resin is preferably about 85 mol% or more, preferably about 90 mol% or more, and more preferably about 99 mol% or more and 100 mol% or less. The polymerization degree of the PVA resin is, for example, 1000 or more and 10000 or less, preferably 1500 or more and 5000 or less. The PVA resin may be modified, for example, polyvinyl formal, polyvinyl acetaldehyde, 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, more preferably 5 μm to 25 μm, and particularly preferably 15 μm or less. By making the thickness of the polarizing element less than 35 μm, the effect of polyeneization of the PVA resin on the reduction of optical properties in a high temperature environment can be suppressed. By making the thickness of the polarizing element more than 3 μm, it is easy to make a structure that achieves the desired optical properties.

The polarizing element preferably contains urea compounds and cyclodextrins. In the present embodiment, the polarizing element and the phase difference layer formed by the curing layer of the polymerizable liquid crystal compound are bonded by means of an adhesive layer, and the adhesive layer is formed by an adhesive containing urea compounds and cyclodextrins. Therefore, it is inferred that a portion of the urea compounds and a portion of the cyclodextrins will be transferred from the adhesive layer and contained in the polarizing element. The urea compounds and cyclodextrins in the polarizing element may also include those added during the manufacturing process of the polarizing element. By having a polarizing element containing urea compounds and cyclodextrins, the transmittance is less likely to decrease even if the polarizing plate is exposed to a high temperature environment. In addition, by having an adhesive layer containing urea compounds and cyclodextrins, even if the polarizing plate is exposed to a high temperature environment, the decrease in polarization degree can be suppressed. If the polarization degree of the polarizing plate decreases, cross light leakage is likely to occur. According to this embodiment, the polarization degree is not easily reduced even when exposed to a high temperature environment, so it is easy to suppress cross light leakage. It is speculated that such an effect is exerted because the polyeneization of the PVA resin is suppressed by the urea compounds and cyclodextrins contained in the polarizing element.

The method of making the polarizing element contain urea compounds and cyclodextrins includes a method of immersing the PVA resin layer in a treatment solvent containing urea compounds and/or cyclodextrins, or a method of spraying, flowing or dripping the treatment solvent on the PVA resin layer. Among them, the method of immersing the PVA resin layer in a treatment solvent containing both urea compounds and cyclodextrins is suitable.

The step of immersing the PVA resin layer in a treatment solvent containing urea compounds and cyclodextrins can be performed simultaneously with the steps of swelling, stretching, dyeing, crosslinking, washing, etc. in the manufacturing method of the polarizing element described later, or can be set separately from these steps. The step of making the PVA resin layer contain urea compounds and cyclodextrins is preferably performed after the PVA resin layer is dyed with iodine, and is preferably performed simultaneously with 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 urea compounds and cyclodextrins, it can be done by adding them during the manufacture of the polarizing element and adding them to the adhesive. In addition, it is also possible to make the polarizing element contain one of the urea compounds and cyclodextrins and make the adhesive contain the other or both, or to make the polarizing element contain both and make the adhesive contain one.

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

The content of the second metal ion in the polarizing element should preferably be greater than 0.05 mass % and less than 10.0 mass %, more preferably greater than 0.05 mass % and less than 8.0 mass %, and more preferably greater than 0.1 mass % and less than 6.0 mass %. When the content of the second metal ion exceeds 10.0 mass %, the degree of polarization may decrease in a high temperature and high humidity environment. In addition, when the content of the second metal ion is less than 0.05 mass %, the effect of improving durability in a high temperature environment may be insufficient. In addition, the content of the second metal ion in the polarizing element can be calculated by, for example, high-frequency inductively coupled plasma (ICP) emission spectrometry, using the fraction (mass %) of the metal element mass relative to the mass of the polarizing element. It is believed that metal elements exist in polarizing elements in the form of metal ions or in a state where they form a cross-linked structure with constituent elements of the polyvinyl alcohol-based resin. However, the content of the second metal ion referred to here is a value calculated in terms of metal atoms.

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 an alkali metal. In particular, from the viewpoint of adjusting the color tone or imparting durability, at least one metal ion of a transition metal such as cobalt, nickel, zinc, chromium, aluminum, copper, manganese, and iron is preferred. Among these metal ions, zinc ions are preferred from the viewpoint of adjusting the color tone or imparting heat resistance.

The boron content of the polarizing element is preferably not less than 2.4 mass %. In addition, the boron content is preferably not less than 3.9 mass % and not more than 8.0 mass %, preferably not less than 4.2 mass % and not more than 7.0 mass %, and more preferably not less than 4.4 mass % and not more than 6.0 mass %. In the case where the boron content of the polarizing element exceeds 8.0 mass %, the contraction force of the polarizing element will increase, and there may be a situation where the polarizing element is peeled off from other components such as the front panel bonded when assembled to the image display device. In addition, in the case where the boron content is less than 2.4 mass %, there may be a situation where the desired optical characteristics cannot be achieved. In addition, the boron content of the polarizing element can be calculated by, for example, high-frequency inductively coupled plasma (ICP) emission spectrometry, as the ratio of the mass of boron to the mass of the polarizing element (mass %). Boron is believed to exist in the polarizing element in the form of a cross-linked structure formed by boric acid or its constituent elements with polyvinyl alcohol resins. The boron content here is the value calculated in terms of boron atoms (B).

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

The potassium ion content in the polarizing element is preferably 0.28 mass % or more, more preferably 0.32 mass % or more, and more preferably 0.34 mass % or more from the viewpoint of suppressing the decrease in polarization degree in a high temperature environment, and is preferably 0.60 mass % or less, more preferably 0.55 mass % or less, and more preferably 0.50 mass % or less from the viewpoint of suppressing the change in hue in a high temperature environment. The potassium ion content can be measured by the same method as the second metal ion content, and the potassium ion content here refers to the value calculated in terms of potassium atoms.

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

(Urea compounds) Urea compounds are at least one selected from the group consisting of urea, urea derivatives, thiourea and thiourea derivatives. Urea compounds can be used alone or in combination of two or more. Urea compounds are of water-soluble and poorly water-soluble types, and any type of urea compound can be used. When using poorly water-soluble urea compounds in water-soluble adhesives, it is advisable to devise a method for dispersion so that the fogging does not occur after the adhesive layer is formed.

(Urea derivatives) Urea derivatives are compounds in which at least one of the four hydrogen atoms in the urea molecule is replaced by a substituent. In this case, the substituent is not particularly limited, and a substituent formed by a carbon atom, a hydrogen atom, and an oxygen atom is preferred.

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

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

Examples of the tetrasubstituted urea 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) Thiourea derivatives are compounds in which at least one of the four hydrogen atoms in the thiourea molecule is replaced by a substituent. In this case, the substituent is not particularly limited, and a substituent formed by a carbon atom, a hydrogen atom, and an oxygen atom is preferred.

Specific examples of the thiourea derivatives, monosubstituted thiourea include 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 the disubstituted thiourea include 1,1-dimethylthiourea, 1,3-dimethylthiourea, 1,1-diethylthiourea, 1,3-diethylthiourea, 1,3-dibutylthiourea, 1,3-diisopropylthiourea, 1,3-dicyclohexylthiourea, N,N-diphenylthiourea, N,N'-diphenylthiourea, 1,3-di(o-tolyl)thiourea, 1,3-di(p-tolyl)thiourea, 1-benzyl-3-phenylthiourea, 1-methyl-3-phenylthiourea, N-allyl-N'-(2-hydroxyethyl)thiourea, and ethylenethiourea.

Examples of the trisubstituted thiourea include trimethylthiourea, and examples of the tetrasubstituted thiourea include tetramethylthiourea and 1,1,3,3-tetraethylthiourea.

When used in an image display device with an interlayer filling structure, from the viewpoint that the decrease in transmittance in a high temperature environment is suppressed and the decrease in polarization degree is small (orthogonal light leakage is suppressed), among urea-based compounds, urea derivatives or thiourea derivatives are preferred, and urea derivatives are more preferred. Among urea derivatives, mono-substituted urea or di-substituted urea is preferred, and mono-substituted urea is more preferred. Di-substituted urea includes 1,1-substituted urea and 1,3-substituted urea, and 1,3-substituted urea is more preferred.

(Cyclodextrins) Cyclodextrins are non-reducing cyclic oligosaccharides in which glucose forms a ring bond with an α-1,4 bond. 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 have 6 or more glucose units in their structure, and examples thereof include α, β, γ, and δ-cyclodextrins having 6, 7, 8, and 9 glucose units in their structure, respectively. Cyclodextrins include branched cyclodextrins having oligosaccharides such as glucose and maltose on the branched sugar chains of α, β, γ, and δ-cyclodextrins. Cyclodextrins also include cyclodextrin derivatives in which an alkyl group such as a methyl group is further bonded to the above-mentioned cyclodextrin or branched cyclodextrin; hydroxyalkyl groups such as 2-hydroxyethyl, 2-hydroxypropyl, 2,3-dihydroxypropyl, 2-hydroxybutyl, etc. Cyclodextrins can be used alone or in combination of two or more.

(Feature (a)) In the case of feature (a), the moisture content of the polarizing element is greater than the equilibrium moisture content of 30% relative humidity at a temperature of 20°C and less than the equilibrium moisture content of 50% relative humidity at a temperature of 20°C. The moisture content of the polarizing element is preferably less than the equilibrium moisture content of 45% relative humidity at a temperature of 20°C, more preferably less than the equilibrium moisture content of 42% relative humidity at a temperature of 20°C, and more preferably less than the equilibrium moisture content of 38% relative humidity at a temperature of 20°C. If the moisture content of the polarizing element is lower than the equilibrium moisture content of 30% relative humidity at a temperature of 20°C, the operability of the polarizing element is reduced and it is easy to break. If the moisture content of the polarizing element is higher than the equilibrium moisture content of 50% relative humidity at a temperature of 20°C, the transmittance of the polarizing element is easy to reduce. It is speculated that if the moisture content of the polarizing element is high, the polyeneization of the PVA resin will be easy to proceed. The moisture content of the polarizing element is the moisture content of the polarizing element in the polarizing plate.

A method for confirming whether the moisture content of the polarizing element is above the equilibrium moisture content of 30% at a temperature of 20°C and a relative humidity of 20% and below the equilibrium moisture content of 50% at a temperature of 20°C can include storing the polarizing element in an environment adjusted to the above temperature and relative humidity ranges, and considering that the polarizing element is in equilibrium with the environment if there is no change in quality 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 confirming by comparing the moisture content of the polarizing element with the pre-calculated equilibrium moisture content.

The method for manufacturing a polarizing element having a moisture content higher than the equilibrium moisture content of 30% at a relative humidity of 20°C and lower than the equilibrium moisture content of 50% at a relative humidity of 20°C is not particularly limited, and examples thereof include a method of storing the polarizing element in an environment adjusted to the above temperature and relative humidity range for more than 10 minutes and less than 3 hours, or a method of heat treatment at a temperature of more than 30°C and less than 90°C.

Another suitable method for manufacturing a polarizing element with the above moisture content is to store a laminate having a protective film laminated on at least one side of the polarizing element or a polarizing plate formed using the polarizing element in an environment adjusted to the above temperature and relative humidity range for 10 minutes to 120 hours, or to heat the laminate at 30°C to 90°C. When manufacturing an image display device using an interlayer filling structure, the polarizing plate is assembled to the image display device, and the image display device with the assembled polarizing plate is stored in an environment adjusted to the above temperature and relative humidity range for 10 minutes to 3 hours, or the front panel can be attached after heating at 30°C to 90°C.

It is preferred that the moisture content of the polarizing element be adjusted to the above-mentioned numerical range at the stage of materials used to form a polarizing plate, either alone or as a laminate of a polarizing element and a protective film. In the case where the moisture content is adjusted after the polarizing plate is formed, the warp will become too large, and defects may easily occur when it is bonded to an image display unit. By forming a polarizing plate using a polarizing element whose moisture content is adjusted to the above-mentioned at the stage of materials before forming a polarizing plate, it is easy to form a polarizing plate having a polarizing element whose moisture content satisfies the above-mentioned numerical range. It is also possible to adjust the moisture content of the polarizing element in the polarizing plate to the above-mentioned numerical range when the polarizing plate is bonded to the image display unit. In this case, the polarizing plate is bonded to the image display unit, so that warp is less likely to occur.

(Feature (b)) In the case of feature (b), the moisture content of the polarizing plate is greater than the equilibrium moisture content of 30% relative humidity at a temperature of 20°C and less than the equilibrium moisture content of 50% relative humidity at a temperature of 20°C. The moisture content of the polarizing plate is preferably less than the equilibrium moisture content of 45% relative humidity at a temperature of 20°C, more preferably less than the equilibrium moisture content of 42% relative humidity at a temperature of 20°C, and more preferably less than the equilibrium moisture content of 38% relative humidity at a temperature of 20°C. If the moisture content of the polarizing plate is lower than the equilibrium moisture content of 30% relative humidity at a temperature of 20°C, the operability of the polarizing plate is reduced and it is easy to break. If the moisture content of the polarizing plate is higher than the equilibrium moisture content of 50% relative humidity at a temperature of 20°C, the transmittance of the polarizing element is easy to reduce. It is speculated that if the moisture content of the polarizing plate is high, the polyeneization of the PVA resin will be easy to proceed.

The method for confirming whether the moisture content of the polarizing plate is above the equilibrium moisture content of 30% at a temperature of 20°C and a relative humidity of 20% and below the equilibrium moisture content of 50% at a temperature of 20°C can be exemplified by storing the polarizing plate in an environment adjusted to the above temperature and relative humidity ranges, and considering that the polarizing plate is in equilibrium with the environment when the quality does not change for a certain period of time, or by pre-calculating 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 pre-calculated equilibrium moisture content for confirmation.

The method for manufacturing a polarizing plate having a moisture content of at least 30% relative humidity at a temperature of 20°C and at most 50% relative humidity at a temperature of 20°C is not particularly limited, and examples thereof include a method of storing the polarizing plate in an environment adjusted to the above temperature and relative humidity range for at least 10 minutes and at most 3 hours, or a method of heat treating the polarizing plate at a temperature of at least 30°C and at most 90°C.

When manufacturing an image display device using an interlayer filling structure, the polarizing plate can be assembled to the image display device, and the image display device with the polarizing plate assembled can be stored in an environment adjusted to the above temperature and relative humidity range for more than 10 minutes and less than 3 hours, or the front panel can be attached after being heated to more than 30°C and less than 90°C.

(Manufacturing method of polarizing element) The manufacturing method of polarizing element is not particularly limited. A typical method is a method of unwinding a PVA-based resin film previously wound into a roll shape, stretching, dyeing, crosslinking, etc. (hereinafter referred to as "manufacturing method 1"), or a method including the steps of applying a coating liquid containing a PVA-based resin on a base film to form a PVA-based resin layer as a coating layer, and stretching the obtained laminate (hereinafter referred to as "manufacturing method 2").

Manufacturing method 1 can be manufactured by the following steps: uniaxially stretching a PVA-based resin film, dyeing the PVA-based resin film with a dichroic dye such as iodine to make it adsorb the dichroic dye, treating the PVA-based resin film adsorbing the dichroic dye with an aqueous boric acid solution, and washing the film with water after the treatment with the aqueous boric acid solution.

The swelling step is a treatment step of immersing the PVA resin film in a swelling bath. The swelling step can remove dirt and anti-adhesion agents on the surface of the PVA resin film. In addition, uneven dyeing can be suppressed by swelling the PVA resin film. The swelling bath can generally use a medium with water as the main component, such as water, distilled water, and pure water. Surfactants, alcohols, etc. can also be appropriately added to the swelling bath according to the conventional method. From the viewpoint of controlling the potassium content of the polarizing element, potassium iodide may be used as the swelling bath. In this case, the concentration of potassium iodide in the swelling bath is preferably 1.5 mass % or less, more preferably 1.0 mass % or less, and even more preferably 0.5 mass % or less.

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

The dyeing step is a treatment step of immersing the PVA resin film in a dyeing bath (iodine solution) so that dichroic pigments such as iodine can be adsorbed and aligned on the PVA resin film. The iodine solution is usually preferably an iodine aqueous solution, which contains iodine and iodide as a dissolving aid. The iodide can be potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, titanium iodide, etc. Among them, potassium iodide is suitable from the perspective of controlling the content of potassium in the polarizing element.

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

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

The crosslinking step is a step of immersing the PVA resin film dyed in the dyeing step in a treatment bath (crosslinking bath) containing a boron compound. The boron compound causes the polyvinyl alcohol resin film to crosslink, and iodine molecules or dye molecules can be adsorbed on the crosslinked structure. Boron compounds include, for example, boric acid, borate, borax, etc. The crosslinking bath is generally an aqueous solution, but may also be a mixed solution of an organic solvent miscible with water and water. From the viewpoint of controlling the potassium content in the polarizing element, the crosslinking bath preferably contains potassium iodide.

The concentration of the boron compound in the crosslinking bath is preferably 1 mass % to 15 mass %, more preferably 1.5 mass % to 10 mass %, and more preferably 2 mass % to 5 mass %. When potassium iodide is used as the crosslinking bath, the concentration of potassium iodide in the crosslinking bath is preferably 1 mass % to 15 mass %, more preferably 1.5 mass % to 10 mass %, and more preferably 2 mass % to 5 mass %.

The temperature of the crosslinking bath is preferably 20°C to 70°C, more preferably 30°C to 60°C. The immersion time in the crosslinking bath cannot be determined in general terms because the degree of crosslinking of the PVA resin film is affected by the temperature of the crosslinking bath. It is preferably 5 seconds to 300 seconds, more preferably 10 seconds to 200 seconds. The crosslinking step can be performed only once, or multiple times as necessary.

The stretching step is a processing step of stretching the PVA resin film in at least one direction at a predetermined ratio. Generally, the PVA resin film is uniaxially stretched in the conveying direction (long side 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 can be performed only once, or can be performed multiple times as necessary. The stretching step can be performed at any stage in the manufacturing process of the polarizing element.

The treatment bath (stretching bath) in the wet stretching method can generally use a solvent such as water or an organic solvent miscible with water and a mixed solution of water. From the viewpoint of controlling the potassium content in the polarizing element, the stretching bath preferably contains potassium iodide. When potassium iodide is used in the stretching bath, the concentration of potassium iodide in the stretching bath is preferably 1 mass % to 15 mass %, preferably 2 mass % to 10 mass %, and preferably 3 mass % to 6 mass %. The treatment bath (stretching bath) may contain a boron compound from the viewpoint of suppressing film breakage during the stretching process. When a boron compound is contained, the concentration of the boron compound in the stretching bath is preferably 1 mass % to 15 mass %, more preferably 1.5 mass % to 10 mass %, and more preferably 2 mass % to 5 mass %.

The temperature of the stretching bath is preferably 25°C to 80°C, more preferably 40°C to 75°C, and even more preferably 50°C to 70°C. The immersion time in the stretching bath cannot be determined in general because the degree of stretching of the PVA resin film is affected by the temperature of the stretching bath. It is preferably 10 seconds to 800 seconds, and more preferably 30 seconds to 500 seconds. The stretching treatment in the wet stretching method can be carried out together with any one or more treatment steps of the swelling step, the dyeing step, the crosslinking step, and the washing step.

Examples of dry stretching methods include an inter-roll stretching method, a heated roll stretching method, a compression stretching method, etc. In addition, the dry stretching method can be performed together with a drying step.

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

The cleaning step is a treatment step of immersing the polyvinyl alcohol resin film in a cleaning bath, and foreign matter remaining on the surface of the polyvinyl alcohol resin film can be removed. The cleaning bath can generally use a medium with water as the main component, such as water, distilled water, and pure water. In addition, from the perspective of controlling the potassium content in the polarizing element, it is preferred to use potassium iodide in the cleaning bath. In this case, the concentration of potassium iodide in the cleaning bath is preferably 1 mass% to 10 mass%, preferably 1.5 mass% to 4 mass%, and more preferably 1.8 mass% to 3.8 mass%.

The temperature of the cleaning bath is preferably 5°C to 50°C, preferably 10°C to 40°C, and more preferably 15°C to 30°C. The immersion time in the cleaning bath cannot be determined in general because the degree of cleaning of the PVA resin film will be affected by the temperature of the cleaning bath. It is preferably 1 second to 100 seconds, preferably 2 seconds to 50 seconds, and more preferably 3 seconds to 20 seconds. The cleaning step can be performed only once or multiple times as necessary. The stretching ratio in the cleaning step is preferably 1.002 times or more, and preferably 1.003 times or more. In addition, the stretching ratio in the cleaning step is preferably 1.02 times or less, and preferably 1.01 times or less. By adjusting the stretching ratio in the cleaning step in this way, it is easy to obtain a polarizing element with a visual sensitivity correction polarization degree of 99.9% or more and an orthogonal transmittance of 1.8% or less at a wavelength of 780nm. It is speculated that this is because by adjusting the stretching ratio in the cleaning step, the orientation of the PVA crystals will be improved, and the stabilization of the iodine and PVA complex in the polarizing element will be promoted.

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

The manufacturing method 2 can be manufactured by the following steps: applying a coating liquid containing a PVA resin on a substrate film, uniaxially stretching the obtained laminated film, dyeing the PVA resin layer of the uniaxially stretched laminated film with a dichroic dye to make it adsorbed to make a polarizing element, treating the film adsorbed with the dichroic dye with an aqueous boric acid solution, and washing the film after the treatment with the aqueous boric acid solution. The substrate film used to form the polarizing element can also be used as a protective layer of the polarizing element. The substrate film can also be peeled off from the polarizing element as needed.

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

The protective film may also have other optical functions at the same time, and may be laminated to form a laminated structure. From the perspective of optical properties, the film thickness of the protective film is preferably thinner, but the thinner the film, the lower the strength and the worse the processability. The appropriate 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 acetylated film, a film formed of a polycarbonate resin, a film formed of a cycloolefin resin such as norbornene, a (meth)acrylic polymer film, a polyester resin film such as polyethylene terephthalate, etc. In the case of a structure having protective films on both sides of the polarizing element, or in the case of bonding using a water-based adhesive such as a PVA adhesive, from the viewpoint of moisture permeability, the protective film on at least one side is preferably a cellulose acetylated film or a (meth)acrylic polymer film, and particularly preferably a cellulose acetylated film.

At least one protective film may have a phase difference function for the purpose of compensating for the viewing angle, etc. In this case, the film itself may have a phase difference function, or may have a phase difference layer separately, or may be a combination of the two. In addition, the film having a phase difference function is described as a structure in which the film is directly bonded to the polarizing element through an adhesive, but it may also be a structure in which another protective film bonded to the polarizing element is bonded through an adhesive or an adhesive.

[Adhesive layer] At least one of the adhesives constituting the adhesive layer for bonding the protective film to the polarizing element is preferably a water-based adhesive. When bonding the protective film to both sides of the polarizing element, the other adhesive may be any adhesive such as a water-based adhesive, a solvent-based adhesive, or an active energy ray-curing adhesive, but a water-based adhesive is preferred.

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

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, more preferably 1 to 200 parts by mass, and even more preferably 3 to 100 parts by mass, based on 100 parts by mass of the PVA resin.

When the adhesive is a water-based adhesive containing a PVA resin, the content of cyclodextrins is preferably 1 to 50 parts by mass, more preferably 1.5 to 40 parts by mass, and even more preferably 2 to 35 parts by mass, relative to 100 parts by mass of the PVA resin. If the content is less than 1 part by mass, the effect of suppressing polyeneization of the polarizing element in a high temperature environment may be insufficient. On the other hand, if the content exceeds 50 parts by mass, cyclodextrins may precipitate after the polarizing plate is manufactured.

When the adhesive is a water-based adhesive containing a PVA resin, it may contain dicarboxylic acids such as maleic acid and phthalic acid from the viewpoint of improving heat resistance. The content of the dicarboxylic acid is preferably 0.01 to 5 parts by mass, more preferably 0.02 to 1 part by mass, relative to 100 parts by mass of the PVA resin.

The thickness of the adhesive layer during coating can be set to any appropriate value. For example, it can be set in a manner that a desired thickness of the adhesive layer (coating layer) can be obtained after curing or heating (drying). The thickness of the adhesive layer is preferably 0.01 μm to 7 μm, more preferably 0.01 μm to 5 μm, more preferably 0.01 μm to 2 μm, and most preferably 0.01 μm to 1 μm.

(Water-based adhesive) Any appropriate water-based adhesive can be used as the water-based adhesive. In particular, a water-based adhesive containing a PVA-based resin (PVA-based adhesive) is suitable. From the viewpoint of adhesiveness, the average degree of polymerization of the PVA-based resin contained in the water-based adhesive is preferably 100 to 5500, more preferably 1000 to 4500. From the viewpoint of adhesiveness, the average degree of saponification is preferably 85 mol% to 100 mol%, more preferably 90 mol% to 100 mol%.

The PVA resin contained in the above-mentioned water-based adhesive preferably contains acetyl acetyl groups, because the PVA resin layer has excellent adhesion to the protective film and excellent durability. The acetyl acetyl group-containing PVA resin can be obtained by, for example, reacting the PVA resin with diketene in any method. The acetyl acetyl group modification degree of the acetyl acetyl group-containing PVA resin is typically 0.1 mol% or more, preferably 0.1 mol% to 20 mol%. The resin concentration of the above-mentioned water-based adhesive is preferably 0.1 mass% to 15 mass%, and more preferably 0.5 mass% to 10 mass%.

The water-based adhesive may also contain a crosslinking agent. The crosslinking agent may be a known crosslinking agent, such as a water-soluble epoxy compound, a dialdehyde, an isocyanate, etc.

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

The water-based adhesive may also contain an organic solvent. From the perspective of miscibility with water, the organic solvent is preferably an alcohol, and methanol or ethanol is more preferred among the alcohols. Some urea compounds have low solubility in water, but are sufficiently soluble in alcohol. In this case, it is also a suitable embodiment to prepare an adhesive by dissolving the urea compound in alcohol to prepare an alcohol solution of the urea compound, and then adding the alcohol solution of the urea compound to the PVA aqueous solution.

The concentration of methanol in the water-based adhesive is preferably 10 mass % to 70 mass %, more preferably 15 mass % to 60 mass %, and more preferably 20 mass % to 60 mass %. In addition, by keeping the content of methanol at 70 mass % or less, deterioration of hue can be suppressed.

(Active energy ray curing adhesive) Active energy ray curing adhesive is an adhesive that is cured by irradiation with active energy rays such as ultraviolet rays, and examples thereof include adhesives containing polymerizable compounds and photopolymerizable initiators, adhesives containing photoreactive resins, adhesives containing adhesive resins and photoreactive crosslinking agents, etc. Examples of the above-mentioned polymerizable compounds include photopolymerizable monomers such as photocurable epoxy monomers, photocurable acrylic monomers, photocurable urethane monomers, and oligomers derived from these monomers. Examples of the above-mentioned photopolymerization initiators include compounds containing substances that generate active species such as neutral free radicals, anionic free radicals, and cationic free radicals by irradiation with active energy rays such as ultraviolet rays.

<Layer containing urea compound> Urea compound is not limited to the case where it is contained in the adhesive layer as described above. From the perspective of improving the heat resistance of the polarizing plate, it can also be contained in other layers other than the adhesive layer. As described in the description of the transparent protective film, in order to meet the demand for thinner polarizing plates in recent years, a polarizing plate having a protective film only on one side of the polarizing element has been developed. In such a structure, a curing layer can be laminated on the side of the polarizing element that does not have a protective film for the purpose of improving physical strength, etc.

In the present embodiment, such a hardening layer may also contain a urea compound. Such a hardening layer is usually formed by a hardening composition containing an organic solvent, but paragraphs [0020] to [0042] of Japanese Patent Publication No. 2017-075986 describe a method of forming such a hardening layer from an aqueous solution of an active energy ray-hardening polymer composition. Urea compounds are often water-soluble, so such a composition may also contain a water-soluble urea compound.

[Polarizing plate manufacturing method] The polarizing plate manufacturing method of the present embodiment may include a moisture content adjustment step and a lamination step. In the moisture content adjustment step, when manufacturing a polarizing plate having feature (a), the moisture content of the polarizing element is adjusted so that the moisture content of the polarizing element is greater than the equilibrium moisture content of 30% relative humidity at a temperature of 20°C and less than the equilibrium moisture content of 50% relative humidity at a temperature of 20°C. The moisture content of the polarizing element may be adjusted according to the description of the moisture content of the polarizing element described above. In the moisture content adjustment step, when manufacturing a polarizing plate having feature (b), the moisture content of the polarizing plate is adjusted so that the moisture content of the polarizing plate is greater than an equilibrium moisture content of 30% relative humidity at a temperature of 20°C and less than an equilibrium moisture content of 50% relative humidity at a temperature of 20°C. 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 is laminated to the transparent protective film through the above-mentioned adhesive layer. In the lamination step, for example, a polarizing element that has not been treated with urea-based compounds and cyclodextrins is laminated to a transparent protective film through an adhesive containing urea-based compounds and cyclodextrins. The order of the moisture content adjustment step and the lamination step is not limited. In addition, the moisture content adjustment step and the lamination step can also be performed in parallel.

[Structure of image display device] The polarizing plate of this embodiment is used in various image display devices such as liquid crystal display devices or organic EL display devices. Regarding the image display device, in the case of an interlayer filling structure in which layers other than air layers are in contact on both sides of the polarizing plate, specifically, solid layers such as adhesive layers, the transmittance is easily reduced in a high temperature environment. In an image display device using the polarizing plate of this embodiment, even with the interlayer filling structure, the reduction in the transmittance of the polarizing plate in a high temperature environment can be suppressed. The image display device can exemplify a structure of a polarizing plate having an image display unit, a first adhesive layer laminated on the visual side surface of the image display unit, and a visual side surface of the first adhesive layer. The image display device may further include a second adhesive layer laminated on the visual side surface of the polarizing plate and a transparent member laminated on the visual side surface of the second adhesive layer. In particular, the polarizing plate of this embodiment is suitable for use in an image display device having an interlayer filling structure in which a transparent member is arranged on the visual side of the image display device, the polarizing plate and the image display unit are laminated via the first adhesive layer, and the polarizing plate and the transparent member are laminated via the second adhesive layer. In this specification, either or both of the first adhesive layer and the second adhesive layer may be referred to as "adhesive layer". In addition, in this manual, the layer structure formed by "first adhesive layer/polarizing plate/second adhesive layer", "first adhesive layer/polarizing plate", and "polarizing plate/second adhesive layer" may be referred to as "polarizing plate". In addition, the components used for bonding the polarizing plate to the image display unit and the components used for bonding the polarizing plate to the transparent component are not limited to the adhesive layer, but may also be an adhesive layer.

<Image display unit> The image display unit may be a liquid crystal unit or an organic EL unit. The liquid crystal unit may be a reflective liquid crystal unit that utilizes external light, a transmissive liquid crystal unit that utilizes light from a light source such as a backlight, or a semi-transmissive and semi-reflective liquid crystal unit that utilizes both light from the outside and light from the light source. In the case where the liquid crystal unit utilizes light from the light source, a polarizing plate is also arranged on the side opposite to the visual side of the image display unit (liquid crystal unit) in the image display device (liquid crystal display device), and a light source is further arranged. The polarizing plate on the light source side is preferably bonded to the liquid crystal unit through an appropriate adhesive layer. The driving method of the liquid crystal unit may be any type such as VA type, IPS type, TN type, STN type, or bent alignment (π type).

Organic EL units are suitable for use in which a transparent electrode, an organic light-emitting layer, and a metal electrode are sequentially laminated on a transparent substrate to form a light-emitting body (organic electroluminescent body). The organic light-emitting layer can be a composite of various organic thin films, such as a composite of a positive hole injection layer formed by a triphenylamine derivative and a light-emitting layer formed by a fluorescent organic solid such as anthracene, or a composite of these light-emitting layers and an electron injection layer formed by a perylene derivative, or a composite of a positive hole injection layer, a light-emitting layer, and an electron injection layer.

<Lamination of image display unit and polarizing plate> The bonding of the image display unit and the polarizing plate is suitable for using an adhesive layer (adhesive sheet). In particular, a method of bonding the polarizing plate and the image display unit with an adhesive layer attached to one side of the polarizing plate is suitable from the perspective of operability, etc. Attaching an adhesive layer to the polarizing plate can be performed in an appropriate manner. Examples thereof include dissolving or dispersing the base polymer or its components in a suitable solvent such as toluene or ethyl acetate alone or in a mixture to prepare an adhesive solution of 10% to 40% by mass, directly attaching it to the polarizing plate by a suitable spreading method such as casting or coating, forming an adhesive layer on a separator, and transferring it to the polarizing plate, etc.

<Adhesive layer> The adhesive layer may be formed of a single layer or two or more layers, preferably a single layer. The adhesive layer may be composed of an adhesive composition having (meth) acrylic resin, rubber resin, urethane resin, ester resin, silicone resin, or polyvinyl ether resin as a main component. In particular, an adhesive composition having (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-curing type or a heat-curing type.

The (meth)acrylic resin (base polymer) used in the adhesive composition is preferably a polymer or copolymer having one or more of (meth)acrylic acid esters such as butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, etc. as monomers. The base polymer is preferably copolymerized with a polar monomer. 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 (meth)acrylic acid compounds, 2-hydroxypropyl (meth)acrylate compounds, hydroxyethyl (meth)acrylate compounds, (meth)acrylamide compounds, N,N-dimethylaminoethyl (meth)acrylate compounds, and glycidyl (meth)acrylate compounds.

The adhesive composition may only contain the above-mentioned base polymer, and usually further contains a crosslinking agent. Examples of the crosslinking agent include metal ions having a valence of two or more and forming metal carboxylate salts between carboxyl groups, polyamine compounds forming amide bonds between carboxyl groups, polyepoxide compounds or polyols forming ester bonds between carboxyl groups, and polyisocyanate compounds forming amide bonds between carboxyl groups. Polyisocyanate compounds are particularly preferred.

The active energy ray-curing adhesive composition has the property of curing by irradiation with active energy rays such as ultraviolet rays or electron beams, and has the property of being adhesive before irradiation with active energy rays and being able to adhere to a target such as a film, and being able to adjust the adhesion by curing with active energy rays. The active energy ray-curing adhesive composition is preferably an ultraviolet-curing type. The active energy ray-curing adhesive composition further contains an active energy ray-polymerizable compound in addition to a base polymer and a crosslinking agent. It may also contain a photopolymerization initiator, a photosensitizer, etc. as necessary.

The adhesive composition may include additives such as microparticles for imparting light scattering properties, beads (resin beads, glass beads, etc.), glass fibers, resins other than base polymers, adhesive imparting agents, fillers (metal powder or other inorganic powders, etc.), antioxidants, ultraviolet absorbers, dyes, pigments, colorants, defoaming agents, anticorrosive agents, photopolymerization initiators, etc.

The adhesive layer can be formed by applying a dilute organic solvent solution of the above adhesive composition on the surface of a substrate film, an image display unit or a polarizing plate and drying it. The substrate film is generally a thermoplastic resin film, and a typical example thereof is a release film subjected to a release treatment. The release film can be, for example, a film formed of a resin such as polyethylene terephthalate, polybutylene terephthalate, polycarbonate, polyarylate, etc., on which the adhesive layer is formed and subjected to a release treatment such as a silicone treatment.

An adhesive composition is directly applied to the release treated surface of the release film to form an adhesive layer, and the adhesive layer attached to the release film can be laminated to the surface of the polarizer. An adhesive composition is directly applied to the surface of the polarizer to form an adhesive layer, and a release film can be laminated on the outside of the adhesive layer.

When the adhesive layer is provided on the surface of the polarizing plate, it is preferred 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, and it is more preferred to subject the bonding surface to corona treatment.

In addition, an adhesive composition is coated on the second release film to form an adhesive layer, and an adhesive sheet of the release film is laminated on the formed adhesive layer. After the second release film is peeled off by the adhesive sheet, the adhesive layer with the release film can be laminated to the polarizing plate. The second release film can be one whose adhesive layer has weaker adhesion than the release film and is easier to peel off.

The thickness of the adhesive layer is not particularly limited, and is preferably 1 μm to 100 μm. In the case of a first adhesive layer and a second adhesive layer, the thickness of one may be 50 μm or less, and the thickness of the other may be 50 μm or more. In the case where the thickness of the adhesive layer is 50 μm or less, it is preferably 3 μm to 50 μm or less, or it may be 20 μm to less than 50 μm. In the case where the thickness of the adhesive layer is 50 μm or more, it is preferably 50 μm to 100 μm or less, or it may be 80 μm or less.

<Transparent member> The transparent member disposed on the visual side of the image display device may be a transparent plate (window layer) or a touch panel. The transparent plate may have appropriate mechanical strength and thickness. Such a transparent plate may be a transparent resin plate such as a polyimide resin, an acrylic resin, or a polycarbonate resin, or a glass plate. A functional layer such as an anti-reflection layer may also be laminated on the visual side of the transparent plate. In addition, when the transparent plate is a transparent resin plate, a hard coating layer may be laminated to improve physical strength, or a low moisture permeability layer may be laminated to reduce moisture permeability. The touch panel can be a variety of touch panels such as resistive film, capacitive, optical, and ultrasonic, or a glass plate or transparent resin plate with a touch sensor function. When a capacitive touch panel is used in a transparent component, it is better to set a transparent plate formed of glass or a transparent resin plate on the visual side of the touch panel.

<Polarizing plate and transparent member bonding> The polarizing plate and transparent member bonding is suitable for using an adhesive or an active energy ray curing adhesive. When using an adhesive, the adhesive can be attached in an appropriate manner. Specific attachment methods include, for example, the method of attaching the adhesive layer used for bonding the image display unit and the polarizing plate.

When using an active energy ray-curing adhesive, it is suitable to use a method in which a stopper is provided to surround the peripheral portion of the image display panel in order to prevent the diffusion of the adhesive solution before curing, a transparent member is placed on the stopper, and the adhesive solution is injected. After the adhesive solution is injected, alignment and degassing are performed as necessary, and then active energy rays are irradiated to perform curing. [Example]

The present invention is described in detail below based on the following examples. The materials, reagents, substance amounts and their ratios, operations, etc. disclosed in the following examples can be appropriately changed as long as they do not deviate from the gist of the present invention. Therefore, the present invention is not limited or restricted by the following examples.

(Production of polarizing element 1) A polyvinyl alcohol-based resin film with a boron adsorption rate of 5.71% by mass and a thickness of 30 μm was immersed in pure water at 21.5°C for 79 seconds (swelling treatment), and then immersed in a 23°C aqueous solution containing 1.0 mM iodine at a mass ratio of potassium iodide/boric acid/water of 2/2/100 for 151 seconds (dyeing step). Then, it was immersed in a 62.8°C aqueous solution containing a mass ratio of potassium iodide/boric acid/water of 2.5/4/100 for 76 seconds (first crosslinking step). Next, it is immersed in a 45°C aqueous solution with a mass ratio of potassium iodide/boric acid/zinc chloride/water of 3/5.5/0.6/100 for 11 seconds (second crosslinking step, metal ion treatment step). Then, it is immersed in a cleaning bath for cleaning (cleaning step) and dried at 38°C (drying step) to obtain a polarizing element with iodine adsorption and alignment on polyvinyl alcohol and a thickness of 12μm. Extension is mainly carried out in the dyeing step and the first crosslinking step, and in the final cleaning step, it is extended by 1.002 times. The total extension ratio of the polarizing element obtained in this way is 5.86 times. The obtained polarizing element has a zinc ion content of 0.07% by mass, a boron content of 4.48% by mass, and an orthogonal transmittance (Tc(780)) of 1.5% at a wavelength of 780nm.

(Production of polarizing element 2) A polyvinyl alcohol-based resin film with a boron adsorption rate of 5.71% by mass and a thickness of 30μm was immersed in pure water at 21.5℃ for 79 seconds (swelling treatment), and then immersed in a 23℃ aqueous solution containing 1.0mM iodine at a mass ratio of potassium iodide/boric acid/water of 2/2/100 for 151 seconds (dyeing step). Then, it was immersed in a 62.8℃ aqueous solution at a mass ratio of potassium iodide/boric acid/water of 2.5/4/100 for 76 seconds (first crosslinking step). Next, it was immersed in a 45℃ aqueous solution at a mass ratio of potassium iodide/boric acid/zinc chloride/water of 3/5.5/0.6/100 for 11 seconds (second crosslinking step, metal ion treatment step). Then, it was immersed in a cleaning bath for cleaning (cleaning step), and dried at 38°C (drying step), and a polarizing element with iodine adsorption and orientation on polyvinyl alcohol and a thickness of 12μm was obtained. The stretching was mainly carried out in the dyeing step and the first crosslinking step, and in the final cleaning step, it was stretched 1.005 times. The total stretching ratio of the polarizing element obtained in this way was 5.88 times. The zinc ion content of the obtained polarizing element was 0.07% by mass, the boron content was 4.48% by mass, and the orthogonal transmittance (Tc(780)) at a wavelength of 780nm was 1.0%.

(Production of polarizing element 3) A polyvinyl alcohol-based resin film with a boron adsorption rate of 5.71% by mass and a thickness of 30 μm was immersed in pure water at 21.5°C for 79 seconds (swelling treatment), and then immersed in a 23°C aqueous solution containing 1.0 mM iodine at a mass ratio of potassium iodide/boric acid/water of 2/2/100 for 151 seconds (dyeing step). Then, it was immersed in a 62.8°C aqueous solution containing a mass ratio of potassium iodide/boric acid/water of 2.5/4/100 for 76 seconds (first crosslinking step). Next, it is immersed in a 45°C aqueous solution with a mass ratio of potassium iodide/boric acid/zinc chloride/water of 3/5.5/0.6/100 for 11 seconds (second crosslinking step, metal ion treatment step). Then, it is immersed in a cleaning bath for washing (cleaning step) and dried at 38°C (drying step) to obtain a polarizing element with iodine adsorption and alignment on polyvinyl alcohol and a thickness of 12μm. Extension is mainly carried out in the dyeing step and the first crosslinking step, and in the final washing step, it is extended by 1.01 times. The total extension ratio of the polarizing element obtained in this way is 5.91 times. The obtained polarizing element has a zinc ion content of 0.07% by mass, a boron content of 4.48% by mass, and an orthogonal transmittance (Tc(780)) of 0.5% at a wavelength of 780nm.

(Production of polarizing element 4) A polyvinyl alcohol-based resin film with a boron adsorption rate of 5.71% by mass and a thickness of 30 μm was immersed in pure water at 21.5°C for 79 seconds (swelling treatment), and then immersed in a 23°C aqueous solution containing 1.0 mM iodine at a mass ratio of potassium iodide/boric acid/water of 2/2/100 for 151 seconds (dyeing step). Then, it was immersed in a 62.8°C aqueous solution containing a mass ratio of potassium iodide/boric acid/water of 2.5/4/100 for 76 seconds (first crosslinking step). Next, it was immersed in a 45°C aqueous solution with a mass ratio of potassium iodide/boric acid/zinc chloride/water of 3/5.5/0.6/100 for 11 seconds (second crosslinking step, metal ion treatment step). Then, it was immersed in a cleaning bath for washing (cleaning step) and dried at 38°C (drying step) to obtain a polarizing element with iodine adsorption oriented on polyvinyl alcohol and a thickness of 12μm. Extension was mainly carried out in the dyeing step and the first crosslinking step, and in the final washing step, it was extended by 1.00 times (no extension was performed). The total extension ratio of the polarizing element obtained in this way was 5.85 times. The obtained polarizing element has a zinc ion content of 0.07% by mass, a boron content of 4.48% by mass, and an orthogonal transmittance (Tc(780)) of 2.0% at a wavelength of 780nm.

(Production of polarizing element 5) A polyvinyl alcohol-based resin film with a boron adsorption rate of 5.71% by mass and a thickness of 30 μm was immersed in pure water at 21.5°C for 79 seconds (swelling treatment), and then immersed in a 23°C aqueous solution containing 1.0 mM iodine at a mass ratio of potassium iodide/boric acid/water of 2/2/100 for 151 seconds (dyeing step). Then, it was immersed in a 62.8°C aqueous solution containing a mass ratio of potassium iodide/boric acid/water of 2.5/4/100 for 90 seconds (first crosslinking step). Next, it is immersed in a 45°C aqueous solution with a mass ratio of potassium iodide/boric acid/zinc chloride/water of 3/5.5/0.6/100 for 11 seconds (second crosslinking step, metal ion treatment step). Then, it is immersed in a cleaning bath for washing (cleaning step) and dried at 38°C (drying step) to obtain a polarizing element with iodine adsorption and alignment on polyvinyl alcohol and a thickness of 12μm. Extension is mainly carried out in the dyeing step and the first crosslinking step, and in the final washing step, it is extended by 1.00 times. The total extension ratio of the polarizing element obtained in this way is 5.85 times. The obtained polarizing element has a zinc ion content of 0.07% by mass, a boron content of 4.48% by mass, and an orthogonal transmittance (Tc(780)) of 0.3% at a wavelength of 780nm.

(Measurement of the degree of polarization of the visual sensitivity correction of polarizing elements 1 to 5) A test piece of about 30 mm in length and about 30 mm in width was cut out from the obtained polarizing element to prepare a test sample. The single transmittance and degree of polarization of the obtained test sample were measured in the wavelength range of 380 to 780 nm. The degree of polarization (λ) is defined as 100×{(Tp(λ)-Tc(λ))/(Tp(λ)＋Tc(λ))} ^1/2 .

Tp(λ) is the parallel transmittance (%) of the polarizing element measured by the relationship between the linear polarization and the parallel polarization of the incident light wavelength λnm, and Tc(λ) is the orthogonal transmittance (%) of the polarizing element measured by the relationship between the linear polarization and the orthogonal polarization of the incident light wavelength λnm. The polarization degree (λ) obtained at each wavelength is further subjected to visual correction to obtain the visual correction polarization degree Py. Py is measured using a spectrophotometer with an integrating sphere equipped with a C light source ["V7100" manufactured by JASCO Corporation].

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

(Determination of Boron Adsorption Rate of PVA Resin Film) A PVA resin film cut into 100 mm squares was immersed in 30°C pure water for 60 seconds, and then immersed in a 60°C aqueous solution containing 5 parts of boric acid for 120 seconds. The PVA resin film removed from the boric acid aqueous solution was dried in an oven at 80°C for 11 minutes. The film was humidified 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 obtained in this way was dissolved in 200 g of a 1.9 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 the calibration curve. The boron content of the PVA-based resin film obtained in this manner is used as the boron adsorption rate of the PVA-based resin film.

(Determination of Zinc Ion Content in Polarizer) Nitric acid was added to the precisely weighed polarizer and acid decomposed using a microwave sample pretreatment device (ETHOS D) manufactured by Milestone General. The resulting solution was used as the measurement solution. The zinc ion content was determined by quantitatively measuring the zinc concentration of the solution using an ICP emission spectrometer (5110 ICP-OES) manufactured by Agilent Technologies and calculated as the mass of zinc relative to the mass of the polarizer.

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

Table 1 shows the values of the visual sensitivity correction polarization degree (Py) and the orthogonal transmittance (Tc(780)) of polarizing elements 1 to 5.

(Preparation of PVA solution for adhesive) 50 g of modified PVA resin containing acetyl group (GOHSENX Z-410 manufactured by Mitsubishi Chemical Co., Ltd.) was dissolved in 950 g of pure water, heated at 90°C for 2 hours, and then cooled to room temperature to obtain PVA solution for adhesive.

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

(Preparation of Adhesive 1 for Polarizing Plates) The prepared adhesive PVA solution, urea aqueous solution, pure water and methanol were mixed in such a way that the PVA concentration was 3.0%, the methanol concentration was 20% and the urea concentration was 0.2%, thereby obtaining Adhesive 1 for Polarizing Plates.

(Preparation of Adhesive 2 for Polarizing Plates) The PVA solution for adhesive prepared above, pure water and methanol were mixed in such a way that the PVA concentration became 3.0% and the methanol concentration became 20%, thereby obtaining Adhesive 2 for Polarizing Plates.

(Saponification of cellulose acetate film) Immerse the commercially available cellulose acetate film TD40 (manufactured by Fuji Film Co., Ltd.: film thickness 40μm) in a 1.5mol/L NaOH aqueous solution (saponification solution) maintained at 55°C for 2 minutes. Then wash the film with water. Immerse in a 0.05mol/L sulfuric acid aqueous solution at 25°C for 30 seconds. Further, let the water bath pass under running water for 30 seconds to make the film neutral. Next, use an air knife to drain the water, repeat 3 times, and drain off the water. Stay in a drying zone at 70°C for 15 seconds to dry it, and produce a saponified film.

(Preparation of polarizing plate 1) The saponified cellulose acylate film prepared above is bonded to both sides of polarizing element 1 through polarizing plate adhesive 1 using a roller bonding machine. The thickness of the adhesive layer after drying is adjusted to 80nm on both sides. After bonding using a roller bonding machine, it is dried at 60°C for 10 minutes to obtain a polarizing plate 1 with cellulose acylate films on both sides.

(Production of polarizing plates 2 to 6) Polarizing plates 2 to 6 were produced in the same manner as polarizing plate 1, except that the polarizing element and the adhesive for the polarizing plate used the items listed in Table 2.

(Adjustment of the moisture content of polarizing plates (polarizing elements)) The polarizing plates 1 to 6 obtained above were stored at a temperature of 20°C and a relative humidity of 30%, 35%, 40%, 45%, 50% or 55% for 72 hours. The moisture content was measured using the Karl-Fischer method after 66 hours, 69 hours and 72 hours of storage. The moisture content did not change when stored for 66 hours, 69 hours and 72 hours under any humidity condition. Therefore, the moisture content of polarizing plates 1 to 6 can be regarded as the same as the equilibrium moisture content of the 72-hour storage environment used in this experimental example. When the moisture content of the polarizing plate reaches equilibrium in a certain storage environment, the moisture content of the polarizing element in the polarizing plate can also be regarded as reaching equilibrium in the 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 the storage environment.

(Production of optical laminate 1) Referring to the embodiment of Japanese Patent Publication No. 2018-025765, an acrylic adhesive (manufacturer: Lintec Co., Ltd., model number: #7) was applied to both sides of the polarizing plate 1 produced above to produce an optical laminate 1 having an adhesive layer (first adhesive layer) with a thickness of 25 μm on one side and a second adhesive layer with a thickness of 150 μm on the other side. In addition, the moisture content of the polarizing plate was the moisture content after being stored for 72 hours at a temperature of 20°C and a relative humidity of 45%.

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

(Polarizing plate 1 for inspection) An acrylic adhesive (manufacturer: Lintec Co., Ltd., model number: #7) was laminated only on one side of the polarizing plate 1 to produce the polarizing plate 1 for inspection. The polarizing plate 1 for inspection produced in this manner was cut into a size of 50 mm × 100 mm with the short side parallel to the absorption axis, and the surface of the adhesive layer was bonded to an alkali-free glass [trade name "EAGLE XG", manufactured by Corning, thickness 1.1 mm] to produce the orthogonal evaluation sample 1.

[Evaluation of single body transmittance after high temperature durability test (105°C)] The optical layer assemblies 1 to 6 prepared above were cut into a size of 50 mm × 100 mm in such a way that the long side was parallel to the absorption axis, and the first adhesive layer and the second adhesive layer were attached to alkali-free glass [trade name "EAGLE XG", manufactured by Corning] on each surface to prepare evaluation samples. The evaluation samples were subjected to autoclave treatment at a temperature of 50°C and a pressure of 5 kgf/ ^cm2 (490.3 kPa) for 1 hour, and then placed in an environment of a temperature of 23°C and a relative humidity of 55% for 24 hours. Then, the transmittance (initial value) was measured, and the transmittance was measured every 100 hours while the samples were stored in a heated environment at a temperature of 105°C. The following criteria were used to evaluate the time it takes for the transmittance to drop by 5% or more relative to the initial value. The results are shown in Table 2. The transmittance did not drop by 5% after 400 hours: A The transmittance dropped by 5% or more within 300 to 400 hours: B The transmittance dropped by 5% or more within 200 to 300 hours: C The transmittance dropped by 5% or more after 200 hours: D

[Evaluation of orthogonal light leakage after high temperature durability test] After 300 hours of evaluation of the single transmittance evaluation sample after high temperature durability, the above optical layer assembly and the orthogonal evaluation sample 1 that was not placed in a heated environment were arranged in an orthogonal polarization state and placed on a backlight. The surrounding light was shielded, and the orthogonal light leakage was visually observed and evaluated according to the following criteria. In addition, samples whose single transmittance decreased by more than 5% after 300 hours were colored due to polyeneization, and therefore were excluded from the evaluation of orthogonal light leakage. The results are shown in Table 2. No orthogonal light leakage was observed at all   ：A Almost no orthogonal light leakage was observed   ：B Slight orthogonal light leakage was observed         ：C Orthogonal light leakage was clearly observed         ：D

[Evaluation of white brightness] An evaluation sample is prepared in the same manner as described above. The evaluation sample is placed on the light-emitting surface of the white backlight module. The glass plate side bonded to the first adhesive layer faces the white backlight module. The brightness of the white backlight module is 1000 cd/ ^m3 . The brightness is measured from the glass plate side bonded to the second adhesive layer. The brightness is measured using a spectroradiometer SR-UL1 manufactured by TOPCON Co., Ltd. In addition, the measurement is performed at a 2° viewing field. The measured brightness is evaluated in three stages according to the following criteria. The results are shown in Table 2. The brightness is above 97% relative to the brightness of laminate 4: A The brightness is less than 97% relative to the brightness of laminate 4: B The brightness is less than 95% relative to the brightness of laminate 4: C

Claims (12)

A polarizing plate having a polarizing element formed by adsorbing and aligning a dichroic pigment on a polyvinyl alcohol resin layer and a transparent protective film, wherein the polarizing element has a visual sensitivity correction polarization degree of 99.9% or more and an orthogonal transmittance of 780nm wavelength is less than 1.8%. As in claim 1, the polarizing plate, wherein the polarizing element and the transparent protective film are bonded together by an adhesive layer, and the adhesive layer is formed by an aqueous adhesive containing a urea compound, The urea compound is at least one selected from the group consisting of urea, urea derivatives, thiourea and thiourea derivatives. The polarizing plate of claim 2, wherein the urea compound is at least one selected from the group consisting of urea derivatives and thiourea derivatives. The polarizing plate of claim 2 or 3, wherein the water-based adhesive comprises a polyvinyl alcohol-based resin. The polarizing plate of claim 4, wherein the content of the urea compound in the water-based adhesive is not less than 0.1 parts by mass and not more than 400 parts by mass relative to 100 parts by mass of the polyvinyl alcohol resin. For example, in the polarizing plate of claim 2 or 3, the aqueous adhesive comprises methanol, and the concentration of the methanol is not less than 10% by mass and not more than 70% by mass. The polarizing plate of claim 2 or 3, wherein the aqueous adhesive comprises cyclodextrins. As in claim 2 or 3, the polarizing plate, wherein the adhesive layer has a thickness of not less than 0.01 μm and not more than 7 μm. A polarizing plate as claimed in claim 1 or 2, wherein the thickness of the polarizing element is less than 15 μm. A polarizing plate as claimed in claim 1 or 2, wherein the moisture content of the polarizing element is greater than an equilibrium moisture content of 30% relative humidity at a temperature of 20°C and less than an equilibrium moisture content of 50% relative humidity at a temperature of 20°C. A polarizing plate as claimed in claim 1 or 2, wherein the moisture content of the polarizing plate is greater than an equilibrium moisture content of 30% at a relative humidity of 20°C and less than an equilibrium moisture content of 50% at a relative humidity of 20°C. A polarizing plate as claimed in claim 1 or 2, wherein an adhesive layer having a thickness of less than 50 μm is formed on one side of the polarizing plate, and an adhesive layer having a thickness of more than 50 μm is formed on the other side of the polarizing plate.