TWI907327B - Polarizing plate and image display device - Google Patents

Abstract

The present invention provides a polarizing plate capable of suppressing a decrease in transmittance in a high temperature environment and having excellent water resistance. A polarizing plate having a polarizing element in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin layer, and a transparent protective film laminated on at least one surface of the polarizing element; wherein the polarizing element and the transparent protective film are bonded to each other by an adhesive layer formed of an adhesive containing a urea-based compound and a dialdehyde, the urea compound is at least one selected from the group consisting of urea, urea derivatives, thiourea and thiourea derivatives, the water content of the polarizing element is equal to or higher than the equilibrium water content at a temperature of 20°C and a relative humidity of 30%, and equal to or lower than the equilibrium water content at a temperature of 20°C and a relative humidity of 50%.

Description

Polarizing plate and image display device

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

Liquid crystal displays (LCDs) are widely used not only in LCD televisions but also in personal computers, mobile phones, and automotive applications such as car navigation systems. Typically, LCDs have liquid crystal panels on both sides of the liquid crystal cells, with polarizing plates bonded to them using adhesive. The display is achieved by controlling the light from the backlight using these liquid crystal panels. In recent years, organic EL displays have also become widely used, similarly in televisions, mobile phones, and automotive applications like car navigation systems. In EL displays, to suppress the reflection of external light by the metal electrodes (cathodes) and prevent it from being seen like a mirror, a circular polarizing plate (a laminate containing polarizing elements and a λ/4 plate) is sometimes placed on the viewing side surface of the image display panel.

As mentioned above, polarizing plates, as components of image display devices such as liquid crystal displays and organic EL displays, are increasingly being installed in automobiles. Compared to those used in mobile applications such as televisions or mobile phones, polarizing plates used in automotive image display devices are exposed to higher temperature environments, thus requiring those with less change in characteristics at higher temperatures (high temperature durability).

On the other hand, to prevent damage to the image display panel caused by impacts from the outer surface, a front panel (also known as a "window layer") made of transparent resin or glass is added on the viewing side of the image display panel. In image display devices with touch panels, a configuration is widely adopted in which the touch panel is located on the viewing side of the image display panel, and a front panel is located on the viewing side of the touch panel.

In this configuration, if an air layer exists between the image display panel and transparent components such as the front panel or touch panel, external light will be reflected due to the reflection of light at the air layer interface, potentially reducing the visibility of the image. Therefore, the behavior of filling the space between the polarizing plate and the transparent component on the viewing side surface of the image display panel with a layer other than the air layer, usually a solid layer (hereinafter sometimes referred to as "interlayer filler") (hereinafter sometimes referred to as "interlayer filling configuration") is expanded. The interlayer filler is preferably a material with a refractive index close to that of the polarizing plate or transparent component. As an interlayer filler, adhesives or UV-curing adhesives (e.g., see Patent 1) are used to suppress the reduction in visibility caused by reflection at the interface and to indirectly fix the components.

Interlayer filling is widely used in mobile applications, such as outdoor mobile phones. In addition, due to the increasing requirements for visibility in recent years, interlayer filling is also being studied in automotive applications such as car navigation devices, where a front transparent plate is placed on the surface of the image display panel and an adhesive layer is used to fill the interlayer between the panel and the front transparent plate.

However, when this configuration is used, reports indicate a significant decrease in the transmittance of the polarizing plate under high-temperature conditions. Patent 2 proposes a solution to this problem by setting the water content per unit area of the polarizing plate to a specific amount or less, and setting the saturated water absorption of the transparent protective film adjacent to the polarizing element to a specific amount or less, thereby suppressing the decrease in transmittance.

However, even using this method, the effect of suppressing the decrease in transmittance during high-temperature durability testing is insufficient. [Prior Art Documents] [Patent Documents]

[Patent Document 1] Japanese Patent Application Publication No. Hei 11-174417 [Patent Document 2] Japanese Patent Application Publication No. 2014-102353

[Problem Solved by the Invention] The purpose of this invention is to provide a novel polarizing plate that can suppress the decrease in transmittance under high-temperature environments and has excellent water resistance, and an image display device using the polarizing plate. [Technical Means for Solving the Problem]

The present invention provides polarizing plates and image display devices exemplified below. [1] A polarizing plate having a polarizing element for adsorbing and aligning dichroic pigments to a polyvinyl alcohol-based resin layer, and a transparent protective film deposited on at least one side of the polarizing element, wherein the polarizing element and the transparent protective film are bonded together by an adhesive layer formed of an adhesive containing a urea compound and a dialdehyde, wherein the urea compound is at least one selected from the group consisting of urea, urea derivatives, thiourea and thiourea derivatives, and the moisture content of the polarizing element is above the equilibrium moisture content of 30% relative humidity at 20°C and below the equilibrium moisture content of 50% relative humidity at 20°C. [2] A polarizing plate comprising a polarizing element for adsorbing and orienting dichroic pigments to a polyvinyl alcohol-based resin layer, and a transparent protective film deposited on at least one side of the polarizing element, wherein the polarizing element and the transparent protective film are bonded together by an adhesive layer formed of an adhesive containing a urea compound and a dialdehyde, wherein the urea compound is at least one selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives, and the polarizing plate has a moisture content of at least an equilibrium moisture content of 30% relative humidity at 20°C and less than an equilibrium moisture content of 50% relative humidity at 20°C. [3] The polarizing plate as described in [1] or [2], wherein the adhesive comprises at least one urea compound selected from the group consisting of urea derivatives and thiourea derivatives. [4] The polarizing plate as described in any one of claims [1] to [3], wherein the adhesive comprises a polyvinyl alcohol resin. [5] The polarizing plate as described in [4], wherein in the adhesive, the content of the urea compound is 0.1 parts by mass to 400 parts by mass relative to 100 parts by mass of the polyvinyl alcohol resin. [6] The polarizing plate as described in any one of claims [1] to [5], wherein in the adhesive, the content of the dialdehyde is 0.03 parts by mass to 20 parts by mass relative to 1 part by mass of the urea compound. [7] The polarizing plate as described in any one of claims [1] to [6], wherein the dialdehyde is glyoxal. [8] A polarizing plate as described in any one of claims [1] to [7], wherein the thickness of the adhesive layer is 0.01 μm or more and 7 μm or less. [9] A polarizing plate as described in any one of claims [1] to [8] is used in an image display device, wherein a solid layer is provided on both sides of the polarizing plate in the image display device. [10] An image display device comprising: an image display unit; a first adhesive layer deposited on the viewing side surface of the image display unit; and a polarizing plate as described in any one of claims [1] to [9], deposited on the viewing side surface of the first adhesive layer. [11] The image display device as described in [10] further comprises: a second adhesive layer deposited on the viewing side surface of the polarizing plate; and a transparent component deposited on the viewing side surface of the second adhesive layer. [12] The image display device as described in claim 11, wherein the transparent component is a glass plate or a transparent resin plate. [13] The image display device as described in [11], wherein the transparent component is a touch panel. [Effects of the Invention]

According to the present invention, a polarizing plate is provided, which has improved high-temperature durability and water resistance. Even when used in image display devices with interlayer filling, it can suppress the decrease in transmittance and polarization caused by high temperature, and has excellent water resistance. Furthermore, by using the polarizing plate of the present invention, an image display device that suppresses the decrease in transmittance and polarization in high-temperature environments and has excellent water resistance can be provided.

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

[Polarizing Plate] The polarizing plate of this embodiment comprises a polarizing element for adsorbing and aligning dichroic pigments onto a layer containing a polyvinyl alcohol-based resin, and a transparent protective film. The polarizing element and the transparent protective film are bonded together by an adhesive layer formed from an adhesive containing a urea compound and a dialdehyde. The polarizing plate of this embodiment has at least one of the following characteristics (a) and (b): (a) The moisture content of the polarizing element is above the equilibrium moisture content of 30% relative humidity at 20°C and below the equilibrium moisture content of 50% relative humidity at 20°C. (b) The moisture content of the polarizing plate is above the equilibrium moisture content of 30% relative humidity at 20°C and below the equilibrium moisture content of 50% relative humidity at 20°C.

Previous polarizing plates, known for their excellent high-temperature durability, include those that suppress transmittance reduction even when placed at 95°C for 1000 hours. However, even with such polarizing plates, when used in interlayer filling configurations, a significant reduction in transmittance can sometimes be observed in the central portion of the polarizing plate after 200 hours at 95°C. This significant reduction in transmittance under high-temperature conditions is considered a problem particularly prone to occur when interlayer filling configurations, where one side of the polarizing plate is bonded to the image display unit and the other side is bonded to transparent components such as a touch panel or front panel, are exposed to high temperatures.

It is believed that the polarizing plate with significantly reduced transmittance in the interlayer filling structure has peaks near 1100 ^cm⁻¹ (originating from the -C=C= bond) and near 1500 ^cm⁻¹ (originating from the -C=C- bond) in Raman spectrometry, thus forming a polyene structure (-C=C) _n- . It is speculated that the polyene structure is produced by the polyvinyl alcohol constituting the polarizing element through dehydration and polyene formation (Patent Document 2, paragraph [0012]).

The polarizing plate of this invention can further improve high-temperature durability and water resistance. The polarizing plate of this invention is incorporated into an image display device composed of interlayer filler, and can suppress the decrease in transmittance even when exposed to a high-temperature environment such as 105°C.

<Polarizing Element> As a polarizing element that adsorbs and aligns dichroic dyes onto a layer containing polyvinyl alcohol (hereinafter, also referred to as "PVA")-based resin (hereinafter, also referred to as "PVA-based resin layer"), a known polarizing element can be used. Examples of polarizing elements include: an extended film obtained by dyeing a PVA-based resin film with dichroic dyes and then performing uniaxial stretching; or a laminated film having a coating layer formed by coating a substrate film with a coating solution containing PVA-based resins; or an extended layer obtained by dyeing the coating layer with dichroic dyes and then performing uniaxial stretching of the laminated film. Extension can be performed after staining with dichroic pigments, or it can be performed while staining, or it can be performed after extension.

PVA-based resins are obtained by saponifying polyvinyl acetate (PVA)-based resins. Besides polyvinyl acetate homopolymers, polyvinyl acetate can be classified as a polyvinyl acetate-based resin, as can copolymers of vinyl acetate with other monomers that can copolymerize with it. Examples of other monomers that can copolymerize include: unsaturated carboxylic acids, olefins such as ethylene, vinyl ethers, and unsaturated sulfonic acids.

The saponification degree of PVA-based resins is preferably about 85 mol% or higher, more preferably about 90 mol% or higher, and even more preferably about 99 mol% or higher and 100 mol% or lower. The degree of polymerization of PVA-based resins is, for example, between 1000 and 10000, preferably between 1500 and 5000. PVA-based resins can also be modified, for example, into aldehyde-modified polyethylene formaldehyde, polyethylene acetal, and polyethylene butyral.

The thickness of the polarizing element is preferably 3μm to 35μm, more preferably 4μm to 30μm, and even more preferably 5μm to 25μm. By limiting the thickness of the polarizing element to 35μm or less, the effect of polyolefin formation in PVA resins on the reduction of optical properties under high-temperature environments can be suppressed. A thickness of 3μm or more makes it easier to achieve the desired optical properties.

The polarizing element preferably contains a urea-based compound. In this embodiment, the polarizing element and the transparent protective film are bonded together by an adhesive layer formed from an adhesive containing a urea-based compound. Therefore, it is presumed that a portion of the urea-based compound migrating from the adhesive layer is contained within the polarizing element. The urea-based compound in the polarizing element may also be added during the manufacturing process of the polarizing element. By having an adhesive layer containing a urea-based compound, the transmittance is not easily reduced even when the polarizing plate is exposed to a high-temperature environment. It is presumed that this is because the urea-based compound contained in the polarizing element inhibits the polyolefination of PVA-based resins.

Methods for incorporating urea compounds into polarizing elements during the manufacturing process include impregnating a PVA-based resin layer in a treatment solvent containing urea compounds, or spraying, dripping, or adding the treatment solvent to the PVA-based resin layer.

The step of immersing the PVA-based resin layer in a treatment solvent containing a urea-based compound can be performed simultaneously with, or separately from, the swelling, stretching, dyeing, crosslinking, and washing steps in the following method for manufacturing polarizing elements. Preferably, the step of containing the urea-based compound in the PVA-based resin layer is performed after dyeing the PVA-based resin layer with iodine, and more preferably simultaneously with the crosslinking step after dyeing. According to this method, the hue change is smaller, which reduces the impact on the optical characteristics of the polarizing element.

In order to make the polarizing element contain urea compounds, it can be added during the manufacturing of the polarizing element or by adding an adhesive.

(Urea compounds) Urea compounds are selected from at least one of the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives. A urea compound may be used alone or in combination with two or more other urea compounds. Urea compounds are available in water-soluble and water-poorly soluble forms; any type of urea compound may be used. When using water-poorly soluble urea compounds in water-soluble adhesives, it is preferable to design a dispersion method that does not cause an increase in fumes after the adhesive layer is formed.

(Urea derivatives) Urea derivatives are compounds in which at least one of the four hydrogen atoms of a urea molecule is replaced by a substituent. In this case, there are no particular limitations on the substituent, but it is preferred to have a substituent containing a carbon atom, a hydrogen atom, and an oxygen atom.

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

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

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

(Thiourea derivatives) Thiourea derivatives are compounds in which at least one of the four hydrogen atoms of a thiourea molecule is replaced by a substituent. In this case, there are no particular limitations on the substituent, but it is preferred to have a substituent containing a carbon atom, a hydrogen atom, and an oxygen atom.

Specific examples of thiourea derivatives, as monosubstituted thioureas, include: N-methylthiourea, ethylthiourea, propylthiourea, isopropylthiourea, 1-butylthiourea, cyclohexylthiourea, N-acetylatedthiourea, N-allylthiourea, (2-methoxyethyl)thiourea, N-phenylthiourea, (4-methoxyphenyl)thiourea, N-(2-methoxyphenyl)thiourea, N-(1-naphthyl)thiourea, and (2-pyridyl)thiourea. Other examples include ortho-tolylthiourea and p-tolylthiourea.

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

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

Among urea compounds, when used in image display devices with interlayer filling structures, urea derivatives or thiourea derivatives are preferred in terms of suppressing the decrease in transmittance under high-temperature environments, and urea derivatives are even more preferred. Among urea derivatives, 1-substituted urea or 2-substituted urea are preferred, and 1-substituted urea is even more preferred. 2-substituted urea includes 1,1-substituted urea and 1,3-substituted urea, but 1,3-substituted urea is more preferred.

(Characteristic (a)) Under the condition of characteristic (a), the moisture content of the polarizing element is above the equilibrium moisture content of 30% relative humidity at 20°C and below the equilibrium moisture content of 50% relative humidity at 20°C. Preferably, the moisture content of the polarizing element is below the equilibrium moisture content of 45% relative humidity at 20°C, more preferably below the equilibrium moisture content of 42% relative humidity at 20°C, and even more preferably below the equilibrium moisture content of 38% relative humidity at 20°C. If the moisture content of the polarizing element is lower than the equilibrium moisture content of 30% relative humidity at 20°C, the operability of the polarizing element decreases, and it is prone to breakage. If the moisture content of the polarizing element exceeds the equilibrium moisture content of 50% relative humidity at 20°C, the transmittance of the polarizing element tends to decrease. The reason is presumably that if the moisture content of the polarizing element is higher, the polyolefination of PVA resin becomes easier. The moisture content of the polarizing element refers to the moisture content of the polarizing element in the polarizing plate.

As a method to confirm whether the moisture content of a polarizing element is within the range of equilibrium moisture content above 30% relative humidity at 20°C and below 50% relative humidity at 20°C, the following methods can be listed: storing the element in an environment adjusted to the above temperature and relative humidity range, and considering it to have reached equilibrium with the environment when its quality remains unchanged for a certain period of time; or pre-calculating the equilibrium moisture content of the polarizing element in an environment adjusted to the above temperature and relative humidity range, and confirming it by comparing the moisture content of the polarizing element with the pre-calculated equilibrium moisture content.

There are no particular limitations on the method for manufacturing a polarizing element with an equilibrium moisture content of 30% or higher at 20°C and 50% or lower at 20°C. For example, methods such as storing the polarizing element in an environment adjusted to the above temperature and relative humidity range for 10 minutes to 3 hours, or heating it at 30°C to 90°C, can be listed.

Another preferred method for manufacturing polarizing elements with the aforementioned moisture content includes: storing a laminate with a protective film on at least one side of the polarizing element, or a polarizing plate composed of polarizing elements, in an environment adjusted to the aforementioned temperature and relative humidity range for 10 minutes to 120 hours; or performing a heat treatment at 30°C to 90°C. When manufacturing an image display device using interlayer filling, the image display panel with a polarizing plate laminated in the image display unit can also be stored in an environment adjusted to the aforementioned temperature and relative humidity range for 10 minutes to 3 hours, or heated at 30°C to 90°C, and then bonded to the front panel.

Ideally, the moisture content of the polarizing element should be adjusted during the material stage of constructing the polarizing plate, either individually or in a laminate of the polarizing element and the protective film, so that the moisture content falls within the aforementioned range. Adjusting the moisture content after constructing the polarizing plate can lead to excessive curling, which can cause defects when bonded to the image display unit. By using a polarizing element with the aforementioned moisture content adjusted during the material stage before constructing the polarizing plate, it is easy to construct a polarizing plate with a moisture content that meets the aforementioned range. Even when the polarizing plate is bonded to the image display unit, the moisture content of the polarizing element within the polarizing plate can be adjusted to within the aforementioned range. At this time, the polarizing plate is not easily curled because it is attached to the image display unit.

(Characteristic (b)) Under the condition of characteristic (b), the moisture content of the polarizing plate is above the equilibrium moisture content of 30% relative humidity at 20°C and below the equilibrium moisture content of 50% relative humidity at 20°C. Preferably, the moisture content of the polarizing plate is below the equilibrium moisture content of 45% relative humidity at 20°C, more preferably below the equilibrium moisture content of 42% relative humidity at 20°C, and even more preferably below the equilibrium moisture content of 38% relative humidity at 20°C. If the moisture content of the polarizing plate is lower than the equilibrium moisture content of 30% relative humidity at 20°C, the operability of the polarizing plate decreases, and it is prone to breakage. If the moisture content of the polarizing plate exceeds the equilibrium moisture content of 50% relative humidity at 20°C, the transmittance of the polarizing element tends to decrease. The reason is speculated to be that if the moisture content of the polarizing plate is higher, the polyolefination of PVA resin becomes easier to carry out.

As a method to confirm whether the moisture content of the polarizing plate is within the range of equilibrium moisture content above 30% relative humidity at 20°C and below 50% relative humidity at 20°C, the following methods can be listed: storing the plate in an environment adjusted to the above temperature and relative humidity range, and considering it to have reached equilibrium with the environment if there is no change in quality over a certain period of time; or pre-calculating the equilibrium moisture content of the polarizing plate in an environment adjusted to the above temperature and relative humidity range, and confirming it by comparing the moisture content of the polarizing plate with the pre-calculated equilibrium moisture content.

There are no particular limitations on the method for manufacturing a polarizing plate with an equilibrium moisture content of 30% or higher at 20°C and 50% or lower at 20°C. For example, methods such as storing the polarizing plate in an environment adjusted to the above temperature and relative humidity range for 10 minutes to 3 hours, or heating it at 30°C to 90°C, can be listed.

When manufacturing an image display device that uses interlayer filling, the image display panel with a polarizing plate in the image display unit layer can be stored in an environment adjusted to the above-mentioned temperature and relative humidity range for 10 minutes to 3 hours or heated at 30°C to 90°C before being bonded to the front panel.

(Manufacturing Method of Polarizing Element) The manufacturing method of polarizing element is not particularly limited, but typically includes the following steps: a method of producing a PVA-based resin film that has been pre-wound into a roller shape by extending, dyeing, crosslinking, etc. (hereinafter referred to as "Manufacturing Method 1"); or a step of applying a coating liquid containing PVA-based resin onto a substrate film to form a PVA-based resin layer that is a coating layer, and extending the resulting laminate (hereinafter referred to as "Manufacturing Method 2").

Manufacturing method 1 can be carried out by the steps of uniaxially extending a PVA-based resin film, staining the PVA-based resin film with dichroic pigments such as iodine to adsorb dichroic pigments, treating the PVA-based resin film with adsorbed dichroic pigments with a boric acid aqueous solution, and washing with water after treatment with boric acid aqueous solution.

The swelling step involves immersing the PVA-based resin film in a swelling bath. This step removes dirt and agglomerates from the surface of the PVA-based resin film and also inhibits uneven staining by swelling the film. The swelling bath typically uses a water-based medium, such as water, distilled water, or pure water. Surfactants or alcohols can also be added to the swelling bath as needed. From the perspective of controlling the potassium content of the polarizing element, potassium iodide can also be used in the swelling bath. In this case, the concentration of potassium iodide in the swelling bath is preferably 1.5% by mass or less, more preferably 1.0% by mass or less, and even more preferably 0.5% by mass or less.

The optimal temperature for the swelling bath is between 10°C and 60°C, more preferably between 15°C and 45°C, and even more preferably between 18°C and 30°C. The immersion time in the swelling bath varies depending on the temperature, as the degree of swelling of the PVA resin film is affected by the bath temperature; therefore, a fixed time cannot be determined, but it is preferably between 5 and 300 seconds, more preferably between 10 and 200 seconds, and even more preferably between 20 and 100 seconds. The swelling process can be performed once or multiple times as needed.

The staining step involves immersing the PVA-based resin film in a staining bath (iodine solution), which allows dichroic pigments such as iodine to be adsorbed and aligned onto the PVA-based resin film. The iodine solution is typically, preferably, an aqueous iodine solution containing iodine and iodides as a dissolving agent. Examples of iodides include: potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. Of these, potassium iodide is preferred from the viewpoint of controlling the potassium content in the polarizing element.

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

The optimal temperature for the staining bath is between 10°C and 50°C, more preferably between 15°C and 45°C, and even more preferably between 18°C and 30°C. The immersion time in the staining bath varies depending on the temperature, as the degree of staining of the PVA resin film is affected by the bath temperature; therefore, a fixed time cannot be determined, but a minimum of 10 seconds to 300 seconds is preferred, and a minimum of 20 seconds to 240 seconds is even better. The staining process can be performed once or multiple times as needed.

The crosslinking step involves immersing a PVA-based resin film, which has undergone a staining step, in a treatment bath (crosslinking bath) containing boron compounds. The polyvinyl alcohol-based resin film is crosslinked by the boron compounds, allowing iodine molecules or dye molecules to adsorb onto the crosslinked structure. Examples of boron compounds include boric acid, borate, and borax. The crosslinking bath is generally an aqueous solution, but it can also be a mixture of an organic solvent miscible with water and water. From the perspective of controlling the potassium content in polarizing elements, the crosslinking bath preferably contains potassium iodide.

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

The temperature of the crosslinking bath is preferably above 20°C and below 70°C, more preferably above 30°C and below 60°C. The immersion time in the crosslinking bath varies depending on the temperature, as the degree of crosslinking of the PVA resin film is affected by the bath temperature; therefore, a fixed time cannot be determined, but it is preferably between 5 and 300 seconds, more preferably between 10 and 200 seconds. The crosslinking step can be performed only once or multiple times as needed.

The stretching step is a processing step that stretches the PVA-based resin film in at least one direction to a predetermined magnification. Generally, the PVA-based resin film is uniaxially stretched in the transport direction (length direction). There are no particular restrictions on the stretching method; either wet stretching or dry stretching can be used. The stretching step can be performed only once or multiple times as needed. The stretching step can be performed at any stage of the polarizing element manufacturing process.

In the wet stretching method, the treatment bath (stretching bath) can typically be water or a mixture of water and an organic solvent that is miscible with 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% to 15% by mass, more preferably 2% to 10% by mass, and even more preferably 3% to 6% by mass. From the viewpoint of suppressing film breakage during stretching, the treatment bath (stretching bath) may contain a boron compound. When a boron compound is included, the concentration of the boron compound in the stretching bath is preferably 1% to 15% by mass, more preferably 1.5% to 10% by mass, and even more preferably 2% to 5% by mass.

The temperature of the stretching bath is preferably between 25°C and 80°C, more preferably between 40°C and 75°C, and even more preferably between 50°C and 70°C. The soaking time in the stretching bath cannot be uniformly determined because the degree of stretching of the PVA resin film is affected by the temperature of the stretching bath, but it is preferably between 10 seconds and 800 seconds, more preferably between 30 seconds and 500 seconds. The stretching treatment in the wet stretching method can also be performed concurrently with any one or more of the following steps: swelling, staining, crosslinking, and washing.

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

The total elongation ratio (cumulative elongation ratio) of the polyvinyl alcohol resin film can be set appropriately according to the purpose, preferably 2 times or more but less than 7 times, more preferably 3 times or more but less than 6.8 times, and even more preferably 3.5 times or more but less than 6.5 times.

The cleaning step involves immersing the polyvinyl alcohol (PVA) resin film in a cleaning bath to remove foreign matter residues from the surface of the PVA resin film. The cleaning bath typically uses a water-based medium such as water, distilled water, or purified water. Furthermore, from the perspective of controlling the potassium content in the polarizing element, it is preferable to use potassium iodide in the cleaning bath. In this case, the concentration of potassium iodide in the cleaning bath is preferably 1% by mass or more and 10% by mass, more preferably 1.5% by mass or more and 4% by mass, and even more preferably 1.8% by mass or more and 3.8% by mass.

The ideal temperature for the cleansing bath is between 5°C and 50°C, more preferably between 10°C and 40°C, and even more preferably between 15°C and 30°C. The soaking time in the cleansing bath cannot be uniformly determined as the degree of cleansing of the PVA resin film is affected by the bath temperature, but it is preferably between 1 second and 100 seconds, more preferably between 2 seconds and 50 seconds, and even more preferably between 3 seconds and 20 seconds. The cleansing process can be performed once or multiple times as needed.

The drying step is the process of drying the PVA-based resin film that has been washed in the washing step to obtain the polarizing element. Drying can be carried out by any appropriate method, such as natural drying, air drying, and heat drying.

Manufacturing method 2 can be performed through the following steps: applying a coating solution containing PVA-based resin onto a substrate film; uniaxially stretching the obtained laminated film; dyeing the PVA-based resin layer of the uniaxially stretched laminated film with a dichroic dye to induce adsorption and form a polarizing element; treating the film with the adsorbed dichroic dye using a boric acid aqueous solution; and washing with water after treatment with the boric acid aqueous solution. The substrate film used to form the polarizing element can also be used as a protective layer for the polarizing element. If necessary, the substrate film can also be peeled off from the polarizing element.

<Transparent Protective Film> The transparent protective film used in this embodiment (hereinafter also referred to as "protective film") is adhered to at least one side of the polarizing element through an adhesive layer. The transparent protective film is adhered to one or both sides of the polarizing element, preferably both sides.

The protective film can simultaneously possess other optical functions and can also be formed into a multilayered structure. From an optical property perspective, a thinner protective film is preferable; however, if it is too thin, the strength decreases and the processability becomes poor. A suitable film thickness is 5 μm to 100 μm, preferably 10 μm to 80 μm, and even more preferably 15 μm to 70 μm.

The protective film can be made of: cellulose ester membranes, films containing polycarbonate resins, films containing cycloalkenyl resins such as camphene, (meth)acrylate polymer films, polyester resins such as polyethylene terephthalate, etc. When the protective film is bonded to both sides of the polarizing element using a water-based adhesive such as PVA adhesive, in terms of moisture permeability, the protective film on at least one side is preferably either a cellulose ester membrane or a (meth)acrylate polymer film, with a cellulose ester membrane being more preferred.

For purposes such as viewpoint compensation, at least one protective film may also have a phase retardation function. In this case, the protective film itself may have a phase retardation function, or it may have a separate phase retardation layer, or a combination of both. The film with a phase retardation function can be directly bonded to the polarizing element through an adhesive, or it may be a structure in which another protective film bonded to the polarizing element is bonded to it through an adhesive or bonding agent.

<Adhesive Layer> As the adhesive layer constituting the protective film for bonding to the polarizing element, an adhesive containing urea-based compounds and dialdehyde is used. The adhesive can be water-based, solvent-based, or active energy line curing adhesive, but water-based adhesives are preferred, and PVA-based resins are even more desirable. By using an adhesive containing urea-based compounds and dialdehyde, the decrease in transmittance of the polarizing plate under high-temperature environments can be suppressed, and water resistance can be improved. Furthermore, by using an adhesive containing urea-based compounds and dialdehyde, even when the polarizing plate is exposed to high-temperature environments, the decrease in polarization can be suppressed. When two polarizing plates are configured in a manner that creates a cross polarization relationship, light leakage (hereinafter also referred to as "cross polarization") is easily generated if the polarization degree of the polarizing plates decreases. However, according to the present invention, even when exposed to a high-temperature environment, the polarization degree is not easily reduced, and thus cross polarization is easily suppressed.

Examples of dialdehydes include glyoxal, propanedialdehyde (malondialdehyde), and butanedialdehyde (butanedialdehyde). Glyoxal, with its simple structure and high reactivity, is particularly preferred. The following explanation of glyoxal may sometimes be made, but as described above, previously known dialdehydes may be used, and it is not limited to glyoxal.

The thickness of the adhesive layer can be set to any value, for example, after curing or heating (drying) to obtain an adhesive layer with the desired thickness. The thickness of the adhesive layer is preferably 0.01μm to 7μm, more preferably 0.01μm to 5μm, even more preferably 0.01μm to 2μm, and most preferably 0.01μm to 1μm.

The following description of the adhesive describes a preferred range for the case where the polarizing element does not contain urea compounds during manufacturing. When the polarizing element contains urea compounds, the following values can be adjusted appropriately. Specific examples of urea compounds can be directly applied to the examples of urea compounds contained in the polarizing element described above. During the drying step of bonding the polarizing element and the protective film to form the adhesive layer, a portion of the urea compound can also migrate from the adhesive layer to the polarizing element, etc.

When the adhesive is a water-based adhesive containing PVA-based resin, the content of the urea compound relative to 100 parts by weight of the PVA-based resin is preferably 0.1 parts by weight to 400 parts by weight, more preferably 1 part by weight to 200 parts by weight, and even more preferably 3 parts by weight to 100 parts by weight. If it is less than 0.1 parts by weight, the inhibition effect on polyolefin formation of the polarizing element under high-temperature environment may be insufficient. On the other hand, if it exceeds 400 parts by weight, urea precipitation may occur, resulting in adverse conditions such as increased fogging.

When the adhesive is a water-based adhesive containing PVA-based resin, the content of dialdehyde relative to 100 parts by weight of PVA-based resin is preferably 1 to 60 parts by weight, more preferably 1.5 to 50 parts by weight, and even more preferably 2 to 45 parts by weight. If it is less than 1 part by weight, the improvement in water resistance will be insufficient. On the other hand, if it exceeds 60 parts by weight, the stability of the adhesive in the conditioning solution will decrease.

In the adhesive, the content of dialdehyde relative to 1 part by mass of urea compound is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 10 parts by mass or less. There is no particular limitation on the lower limit; for example, it can be 0.03 parts by mass or more. By maintaining the ratio of urea compound to dialdehyde in the adhesive within the above range, it is easy to achieve both the improved high-temperature durability effect from the urea compound and the improved adhesion effect from the dialdehyde. It is understood that by utilizing the improved adhesion effect of dialdehyde, an improved water resistance effect can be obtained. When the content of dialdehyde exceeds 20 parts by mass relative to 1 part by mass of urea compound, the improved high-temperature durability effect caused by the urea compound may not be fully realized. The ratio of urea compounds to dialdehyde in the adhesive layer can be considered the same as the ratio of urea compounds to dialdehyde in the adhesive layer.

In a configuration where a transparent protective film is bonded to both sides of a polarizing element with an adhesive layer between them, the adhesive layer on both sides of the polarizing element may be a layer containing urea compounds and dialdehyde on only one side, but preferably both sides of the adhesive layer contain urea compounds and dialdehyde.

To meet the requirement for thinner polarizing plates, a polarizing plate with a transparent protective film on only one side of the polarizing element has been developed. As a manufacturing method for this type of polarizing plate with a transparent protective film on only one side of the polarizing element, a method can be considered that first a polarizing plate with a transparent protective film bonded to both sides through an adhesive layer is fabricated, and then one side of the transparent protective film is peeled off. When using this manufacturing method, it is preferable that the adhesive layer on the unpeeled film side contains urea-based compounds and dialdehyde; alternatively, both adhesive layers can contain urea-based compounds and dialdehyde.

The adhesive preferably also contains a water-soluble chelating compound. Water-soluble chelating compounds can be used to improve the crosslinking between the adhesive layer and the transparent protective film (such as polarizing elements, cellulose films, olefin films, etc.), thereby improving adhesion and water resistance, and can also serve as an additive with no problem in optical durability.

Water-soluble chelating compounds promote the curing of glyoxal. Types of chelating compounds that can be added include zinc chloride, cobalt chloride, magnesium chloride, magnesium acetate, aluminum nitrate, zinc nitrate, and zinc sulfate. Zinc chloride, zinc nitrate, and aluminum nitrate are particularly preferred as excellent cross-linking catalysts.

The weight ratio of water-soluble chelating compounds in the adhesive layer is preferably in the range of 2 to 10 parts by weight relative to 100 parts by weight of PVA-based resin. Based on the above standard, when the weight ratio of water-soluble chelating compounds is less than 2 parts by weight, it is difficult to fully demonstrate the water resistance of the adhesive layer when used as a polarizing plate, and when the weight ratio exceeds 10 parts by weight, the optical properties may sometimes decrease.

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

When the adhesive is a water-based adhesive containing PVA-based resin, it is preferable that the PVA-based resin contains acetyl groups because the adhesion-enhancing effect of dialdehyde is more significant. For example, it is speculated that when glyoxal is used as the dialdehyde, the aldehyde portion of glyoxal undergoes an addition reaction with the acetyl group of the acetyl-modified PVA-based resin, acting as a crosslinking agent to improve adhesion. Acetyl-based PVA resins can be obtained, for example, by reacting PVA-based resins with diketene using any method. The acetyl-modified PVA resin preferably has an acetyl-modified degree of 0.1 mol% or more, and more preferably 0.1 mol% or more and 20 mol% or less. The concentration of PVA resin in the aqueous adhesive preferably has an acetyl-modified degree of 0.1% by mass or more and 15% by mass, and more preferably 0.5% by mass or more and 10% by mass.

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

Aqueous adhesives may also contain organic solvents. Regarding miscibility with water, alcohols are preferred organic solvents, with methanol or ethanol being more preferred. The methanol concentration in the aqueous adhesive is preferably 10% by mass to 70% by mass, more preferably 15% by mass to 60% by mass, and even more preferably 20% by mass to 60% by mass. A methanol concentration of 10% by mass or more makes it easier to inhibit the polyolefination of PVA-based resins under high-temperature environments. Furthermore, a methanol content of 70% by mass or less can inhibit color deterioration. Some urea derivatives have low solubility in water, but on the other hand, they have sufficient solubility in alcohols. At this point, dissolving urea compounds in alcohol to prepare an alcoholic solution of urea compounds, and then adding the alcoholic solution of urea compounds to PVA aqueous solution to prepare the adhesive is also a better approach.

(Active Energy Line Curing Adhesives) Active energy line curing adhesives are adhesives that are cured by irradiation with active energy lines such as ultraviolet light. Examples include adhesives containing polymerizable compounds and photopolymerizable initiators, adhesives containing photoreactive resins, and adhesive resins containing photoreactive crosslinkers. Polymerizable compounds include photopolymerizable monomers such as photocurable epoxy monomers, photocurable acrylic monomers, and photocurable urethane monomers, as well as oligomers derived from these monomers. Photopolymerization initiators include compounds containing substances that generate reactive species such as neutral free radicals, anionic free radicals, and cation free radicals when irradiated with active energy lines such as ultraviolet light.

<Urea-based compound layer> Urea-based compounds are not limited to being contained in the adhesive layer as described above. From the viewpoint of improving the high-temperature durability of the polarizing plate, they can also be contained in other layers besides the adhesive layer. In polarizing plates with a transparent protective film on only one side, from the viewpoint of improving physical strength, a hardening layer can also be applied to the area opposite to the transparent protective film of the polarizing element.

In this embodiment, the hardened layer may also contain a urea compound, thus forming a layer containing a urea compound. Normally, such a hardened layer is formed from a hardening composition containing an organic solvent, but paragraphs [0020] to [0042] of Japanese Patent Application Publication No. 2017-075986 describe a method for forming such a hardened layer from an aqueous solution of an active energy line hardening polymer composition. The water-soluble urea compound may be contained in these compositions.

The urea-based compound layer preferably contains at least one urea-based compound and an adhesive. Examples of adhesives include polymer adhesives, thermosetting resin adhesives, and active energy line curing resin adhesives; any of these adhesives may be preferred.

The thickness of the urea-containing compound layer is preferably 0.1 μm to 20 μm, more preferably 0.5 μm to 15 μm, and even more preferably 1 μm to 10 μm.

[Manufacturing Method of Polarizing Plate] The manufacturing method of the polarizing plate of this embodiment includes a moisture content adjustment step and a lamination step. In the moisture content adjustment step, when manufacturing the polarizing plate with feature (a), the moisture content of the polarizing element is adjusted such that it is above the equilibrium moisture content of 30% relative humidity at 20°C and below the equilibrium moisture content of 50% relative humidity at 20°C. The moisture content of the polarizing element can be adjusted according to the above-mentioned record of the moisture content of the polarizing element. In the moisture content adjustment step, when manufacturing a polarizing plate with characteristic (b), the moisture content of the polarizing plate is adjusted to a level above the equilibrium moisture content of 30% relative humidity at 20°C and below the equilibrium moisture content of 50% relative humidity at 20°C. The moisture content of the polarizing plate can be adjusted according to the above-mentioned record of the moisture content of the polarizing plate. In the lamination step, the polarizing element and the transparent protective film are laminated through the above-mentioned adhesive layer. In the lamination step, for example, the polarizing element that has not been treated with a urea compound and the transparent protective film are bonded together using an adhesive containing a urea compound and a dialdehyde. There is no limitation on the order of the moisture content adjustment steps and the lamination steps, and the moisture content adjustment steps and the lamination steps can also be performed in parallel.

[Composition of Image Display Device] The polarizing plate of this embodiment is used in various image display devices such as liquid crystal display devices or organic EL display devices. Regarding image display devices, when the polarizing plate is constructed with interlayer filling on both sides, where both sides are in contact with solid layers such as adhesive layers (other than air layers), the transmittance tends to decrease in high-temperature environments. In image display devices using the polarizing plate of this embodiment, even with an interlayer filling configuration, the decrease in transmittance of the polarizing plate in high-temperature environments can be suppressed. As an image display device, an example may be configured to have an image display unit, a first adhesive layer deposited on the viewing side surface of the image display unit, and a polarizing plate deposited on the viewing side surface of the first adhesive layer. The image display device may further have a second adhesive layer deposited on the viewing side surface of the polarizing plate, and a transparent component deposited on the surface of the second adhesive layer. In particular, the polarizing plate of this embodiment is preferably used in an image display device having an interlayer filling structure, wherein a transparent component is disposed on the viewing side of the image display device, the polarizing plate and the image display unit are bonded by a first adhesive layer, and the polarizing plate and the transparent component are bonded by a second adhesive layer. In this specification, either or both of the first adhesive layer and the second adhesive layer are sometimes simply referred to as the "adhesive layer". Furthermore, the component used for bonding the polarizing plate to the image display unit and the component used for bonding the polarizing plate to the transparent component is not limited to an adhesive layer and may also be an adhesive layer.

<Image Display Unit> Examples of image display units include liquid crystal units (LCDs) and organic EL units (OLEDs). As an LCD, it can be any of the following: a reflective LCD that utilizes external light, a transmissive LCD that utilizes light from a backlight or other light source, or a semi-transmissive/semi-reflective LCD that utilizes both external light and light from a light source. When the LCD utilizes light from a light source, the image display device (LCD device) also has a polarizing plate on the side of the LCD opposite to the viewing side, and a light source is then positioned there. The polarizing plate on the light source side and the LCD are preferably bonded together with a suitable adhesive layer. As for the driving method of the LCD, any type can be used, such as VA mode, IPS mode, TN mode, STN mode, or pi-type.

As an organic EL unit, it can be preferably used to form a light emitter (organic electroluminescent light emitter) by sequentially stacking transparent electrodes, organic light-emitting layers, and metal electrodes on a transparent substrate. The organic light-emitting layer is a stack of various organic thin films, and can be composed of, for example, a stack of a hole injection layer composed of a triphenylamine derivative and a light-emitting layer composed of a fluorescent organic solid such as anthracene, or a stack of such light-emitting layers and an electron injection layer composed of a perylene derivative, or a stack of a hole injection layer, a light-emitting layer, and an electron injection layer, etc.

<Lamination of Image Display Unit and Polarizing Plate> In bonding the image display unit and the polarizing plate, an adhesive layer (adhesive sheet) can be preferably used. From a workability perspective, a preferred method is to bond the polarizing plate, on one side of which an adhesive layer is applied, to the image display unit. The application of the adhesive layer to the polarizing plate can be performed using an appropriate method. Examples include: preparing an adhesive solution of 10% by mass to 40% by mass, which dissolves or disperses the base polymer or its components in a solvent containing a single substance or mixture of suitable solvents such as toluene or ethyl acetate, and directly attaching it to a polarizing plate by a suitable spreading method such as casting or coating; forming an adhesive layer on a release film and transferring it to a polarizing plate, etc.

<Adhesive Layer> The adhesive layer may consist of one or more layers, preferably one layer. The adhesive layer may be composed of an adhesive composition whose main components are (meth)acrylate resins, rubber resins, ethyl carbamate resins, ester resins, polysiloxane resins, or polyvinyl ether resins. Preferably, the adhesive composition is based on a (meth)acrylate resin, which has excellent transparency, weather resistance, and heat resistance. The adhesive composition may be of the active energy line curing type or the thermosetting type.

The (meth)acrylate resin (base polymer) used as an adhesive composition is preferably a polymer or copolymer that uses one or more of the following (meth)acrylates as monomers: butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. Among the base polymers, it is preferable to copolymerize polar monomers. Examples of polar monomers include: (meth)acrylate compounds, 2-hydroxypropyl (meth)acrylate compounds, hydroxyethyl (meth)acrylate compounds, (meth)acrylamide compounds, N,N-dimethylaminoethyl (meth)acrylate compounds, and glycidyl (meth)acrylate compounds, which possess carboxyl, hydroxyl, amide, amino, or epoxy groups.

The adhesive composition may also contain only the aforementioned base polymer, but usually further includes a crosslinking agent. Examples of crosslinking agents include: metal ions with a valence of divalent or higher that form a carboxylic acid metal salt with a carboxyl group; polyamine compounds that form an amide bond with a carboxyl group; polyepoxide compounds or polyols that form an ester bond with a carboxyl group; and polyisocyanate compounds that form an amide bond with a carboxyl group. Among these, polyisocyanate compounds are preferred.

Active energy line curing adhesive compositions possess the property of curing upon irradiation with active energy lines such as ultraviolet light or electron beams. They exhibit adhesiveness and adherence to substrates such as films even before irradiation, and can be cured and have their adhesion adjusted by irradiation with active energy lines. Ultraviolet-curing types are preferred for active energy line curing adhesive compositions. In addition to the base polymer and crosslinking agent, active energy line curing adhesive compositions further contain active energy line polymerizable compounds. Photopolymerization initiators and photosensitizers may also be included as needed.

The adhesive composition may include microparticles, beads (resin beads, glass beads, etc.) for imparting light scattering properties, glass fibers, resins other than the base polymer, adhesive preservatives, fillers (metal powder or other inorganic powders, etc.), antioxidants, ultraviolet absorbers, dyes, pigments, colorants, defoamers, preservatives, photopolymerization initiators, and other additives.

The adhesive layer is formed by applying a diluted organic solvent solution of the aforementioned adhesive composition to the surface of a substrate film, image display unit, or polarizing plate and then drying it. The substrate film is generally a thermoplastic resin film, and a typical example is a release film that has undergone a release treatment. For example, a release film can be formed by applying a silicone treatment or other release treatment to the surface of a film containing resins such as polyethylene terephthalate, polybutylene terephthalate, polycarbonate, or polyarylate.

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

When the adhesive layer is applied to the surface of the polarizing plate, it is preferable to perform surface activation treatments such as plasma treatment or corona treatment on the bonding surface of the polarizing plate and/or the bonding surface of the adhesive layer, and it is even more preferable to perform corona treatment.

Alternatively, an adhesive composition can be coated onto the second separation membrane to form an adhesive layer. An adhesive sheet can be formed by layering the separation membrane onto the adhesive layer. After peeling the second separation membrane from the adhesive sheet, the adhesive layer with the separation membrane attached is deposited on the polarizing plate. The second separation membrane is one that has a weaker adhesion to the adhesive layer than the second separation membrane and is easier to peel off.

There is no particular limitation on the thickness of the adhesive layer. For example, it is preferred to be 1μm or more but less than 100μm, more preferably 3μm or more but less than 50μm, and it can also be 20μm or more.

<Transparent Components> Transparent components, configured on the viewing side of an image display device, can include transparent panels (window layers) or touch panels. As transparent panels, those with appropriate mechanical strength and thickness can be used. Examples of such transparent panels include transparent resin sheets made of polyimide, acrylic, or polycarbonate resins, or glass sheets. Functional layers such as anti-reflective layers can also be laminated on the viewing side of the transparent panel. Furthermore, when the transparent panel is a transparent resin sheet, a hard coating layer to improve physical strength or a low-permeability layer to reduce moisture permeability can also be laminated. As a touch panel, various types of touch panels can be used, such as resistive film, electrostatic capacitive, optical, and ultrasonic touch panels, or glass plates or transparent resin plates with touch sensor functions. When using an electrostatic capacitive touch panel as a transparent component, it is preferable to provide a transparent plate containing glass or transparent resin plate on the viewing side of the touch panel.

<Bonding of Polarizing Plate and Transparent Component> For bonding the polarizing plate and the transparent component, it is preferable to use an adhesive or an active energy line curing adhesive. When using an adhesive, the adhesive can be applied in an appropriate manner. Specific application methods include, for example, the application method of the adhesive layer used in the bonding of the image display unit and the polarizing plate described above.

When using active energy line curing adhesives, to prevent diffusion of the adhesive solution before curing, it is preferable to use the following method: A barrier material is provided surrounding the periphery of the image display panel; a transparent component is placed on the barrier material; and the adhesive solution is injected. After injection of the adhesive solution, alignment and degassing are performed as needed, followed by irradiation with active energy lines for curing. [Example]

The present invention will now be described in detail with reference to the embodiments. The materials, reagents, quantities and ratios of substances, operations, etc., shown in the following embodiments may be appropriately modified as long as they do not depart from the spirit of the present invention. Therefore, the present invention is not limited to the following embodiments.

<Fabrication of Polarizing Element A> A 40 μm thick PVA film composed of PVA with an average degree of polymerization of approximately 2400 and a saponification degree of 99.9 moles or higher was dry-stretched uniaxially to approximately 5 times its original thickness, further maintaining a taut state. It was then immersed in pure water at 60°C for 1 minute, followed by immersion in an aqueous solution of iodine/potassium iodide/water at 28°C for 60 seconds. Subsequently, it was immersed in an aqueous solution of potassium iodide/boric acid/water at 8.5/8.5/100 weight ratio at 72°C for 300 seconds. Finally, it was washed with pure water at 26°C for 20 seconds and dried at 65°C to obtain a 15 μm thick polarizing element A with iodine adsorbed and aligned to the PVA. The thickness of the polarizing element was measured using a digital micrometer "MH-15M" manufactured by Nikon Corporation.

<Preparation of Adhesives 1 to 8> (Preparation of PVA Solution A for Adhesive) Dissolve 50g of modified PVA resin containing acetyl acetyl groups (GOHSENEX Z-410 manufactured by Mitsubishi Chemical Co., Ltd.) in 950g of pure water, heat at 90°C for 2 hours and then cool to room temperature to obtain the PVA solution for adhesive (hereinafter referred to as "PVA Solution A").

(Preparation of urea compound solution 1) Add 10g of urea to 90g of pure water to obtain a urea 10% by mass aqueous solution (urea compound solution 1).

(Preparation of Adhesives 1 to 8) Adhesives 1 to 8 are prepared by mixing PVA solution A, urea compound solution 1, commercially available glyoxal 40% solution, and pure water in the manner shown in Table 1, with PVA at 3.0% by mass and urea compound and glyoxal at the contents shown in Table 1.

<Preparation of Transparent Protective Film A> A commercially available vinyl cellulose membrane TD40 (manufactured by Fujifilm Inc., 40μm thick) was immersed in a 1.5mol/L NaOH aqueous solution (saponification solution) maintained at 55°C for 2 minutes, followed by water washing. Then, it was immersed in a 0.05mol/L sulfuric acid aqueous solution at 25°C for 30 seconds, followed by water washing under running water for 30 seconds to neutralize the membrane. Next, the membrane was repeatedly drained three times using an air knife to remove water, and then dried in a drying zone at 70°C for 15 seconds to produce a saponified membrane, thus creating transparent protective film A.

<Fabrication of Polarizing Plates 1 to 8> Using a roller laminator, a transparent protective film A is bonded to both sides of the polarizing element A through adhesive 1. After bonding, it is dried at 80°C for 5 minutes to obtain polarizing plate 1. The adhesive layer is adjusted so that the thickness on both sides after drying is 100nm.

In polarizing plate 1, adhesive 1 is changed to adhesive 2 to 8 to obtain polarizing plate 2 to 8.

(Adjustment of Moisture Content in Polarizing Plates (Polarizing Elements)) The polarizing plates 1 to 8 obtained above were stored for 72 hours at a temperature of 20°C and relative humidity of 30%, 35%, 40%, 45%, 50%, or 55%. The moisture content was measured at 66, 69, and 72 hours using the Karl Fischer method. Under any humidity condition, the moisture content remained unchanged after 66, 69, and 72 hours of storage. Therefore, the moisture content of polarizing plates 1 to 8 can be considered to be the same as the equilibrium moisture content of the 72-hour storage environment used in this experimental example. When the moisture content of a polarizing plate reaches equilibrium under a certain storage environment, the moisture content of the polarizing element in the polarizing plate can also be considered to have reached equilibrium under its storage environment. Furthermore, when the moisture content of the polarizing element in the polarizing plate reaches equilibrium under a certain storage environment, the moisture content of the polarizing plate can also be considered to have reached equilibrium under its storage environment.

<Optical Laminates 1 to 10> Optical laminates 1 to 10 are manufactured using any one of the polarizing plates 1 to 8 shown in Table 2, with the moisture content of the polarizing plate (polarizing element) being the equilibrium moisture content of the environment shown in Table 2, and stored at a temperature of 20°C and relative humidity of 35%, 45%, or 55% for 72 hours.

<High Temperature Durability Evaluation> (Preparation of Evaluation Samples) For optical laminates 1 to 10, an acrylic adhesive (manufactured by LINTEC Corporation, model: #7) was formed on both sides, and the laminates were cut to a size of 50mm × 100mm with the absorption axis parallel to the long side. Evaluation samples were prepared by bonding alkaline glass ("EAGLE XG" manufactured by Corning Corporation) to the surface of each adhesive. To evaluate the cross-polarization of the above evaluation samples, an optical laminate R was prepared to create an orthogonal polarization state by overlapping with the evaluation samples. Specifically, compared to the above polarizing plate 8, an acrylic adhesive (manufactured by LINTEC Corporation, model: #7) was formed on only one side, and the laminates were cut to a size of 50mm × 100mm with the absorption axis parallel to the short side. An optical layer R for orthogonal light leakage evaluation is created by bonding an alkali-free glass ("EAGLE XG" manufactured by Corning) to an adhesive surface.

<Single-unit transmittance evaluation (105°C)> Evaluation samples of optical laminates 1 to 10 were subjected to a 1-hour autoclave treatment at 50°C and 5 kgf/cm² (490.3 kPa), followed by 24 hours of storage at 23°C and 55% relative humidity. Subsequently, the transmittance (initial value) of the evaluation samples of optical laminates 1 to 10 was measured. Transmittance was then measured every 50 hours at a heating environment of 105°C until 100 to 200 hours. Evaluation was performed based on the time it took for the transmittance to decrease by more than 5% relative to the initial value, according to the following criteria. The results are shown in Table 2. A. Transmittance reduction of less than 5% after 200 hours: B. Transmittance reduction of more than 5% after 150 to 200 hours: C. Transmittance reduction of more than 5% after 100 to 150 hours: D.

<Evaluation of Crossed Light Leakage After High-Temperature Durability Test> Evaluation samples were prepared after 200 hours of monomer transmittance measurement, as described in the monomer transmittance evaluation above. The optical laminate R used for crossed polarization evaluation, not placed in a heated environment, was configured with the evaluation sample in a crossed polarization relationship and placed on a backlight. With the surrounding light blocked, crossed light leakage was visually observed, and a four-stage evaluation was performed according to the following criteria. The results are shown in Table 2. Furthermore, evaluation samples with monomer transmittance ratings other than A were excluded from the crossed light leakage evaluation due to coloration caused by polyolefination. No crossover visible: A Almost no crossover visible: B Slight crossover visible: C Clear crossover visible: D

<Water Resistance Evaluation (Warm Water Immersion Test)> The water resistance test of this embodiment was conducted according to the water resistance test described in Japanese Patent Application Publication No. 2009-025728 [0060]. An acrylic adhesive (manufactured by LINTEC Co., Ltd., model: #7) was applied to one side of the polarizing plate prepared above. The absorption axis (extension direction) of the polarizing plate was then cut into short strips of 50mm × 20mm in size, and the dimensions in the long side direction were accurately measured. Here, the sample was evaluated because the iodine adsorbed on the polarizing element uniformly exhibited a unique color throughout the entire surface. Holding one short side of the sample with a gripper, about 80% of the sample in the length direction was immersed in a water bath at 60°C for 4 hours. Afterward, the sample was removed from the water bath and the moisture was wiped off. The polarizing element of the polarizing plate shrinks when immersed in warm water. The degree of shrinkage is evaluated in three stages based on the distance from the center of the short side of the sample (the end of the protective film) to the shrunken polarizing element. A) Distance from the sample end to the polarizing element end is less than 1 mm. B) Distance from the sample end to the polarizing element end is greater than 3 mm. C)

It can be seen that the polarizing plate containing urea in the adhesive (optical laminate 8) has better transmittance than the polarizing plate without urea in the adhesive (optical laminates 9 and 10), even when exposed to a high-temperature environment of 105°C, demonstrating superior high-temperature durability. It can also be seen that by using adhesives containing urea and glyoxal, water resistance can be improved, and consequently, even when exposed to high-temperature environments, crossed light leakage is less likely to occur (comparison of optical laminates 2 and 8).

No diagram provided.

Claims (12)

A polarizing plate comprising a polarizing element for adsorbing and aligning dichroic pigments to a polyvinyl alcohol-based resin layer, and a transparent protective film deposited on at least one side of the polarizing element, wherein the polarizing element and the transparent protective film are bonded together by an adhesive layer formed of an adhesive containing a urea compound and a dialdehyde, wherein the content of the dialdehyde in the adhesive is 0.1 parts by mass or more and 0.75 parts by mass or less relative to 1 part by mass of the urea compound, the urea compound being at least one selected from the group consisting of urea, urea derivatives, thiourea and thiourea derivatives, and the moisture content of the polarizing element being at least an equilibrium moisture content of 30% relative humidity at 20°C and less than an equilibrium moisture content of 50% relative humidity at 20°C. A polarizing plate comprising a polarizing element for adsorbing and aligning dichroic pigments to a polyvinyl alcohol-based resin layer, and a transparent protective film deposited on at least one side of the polarizing element, wherein the polarizing element and the transparent protective film are bonded together by an adhesive layer formed of an adhesive containing a urea compound and a dialdehyde, wherein the content of the dialdehyde in the adhesive is 0.1 parts by mass or more and 0.75 parts by mass or less relative to 1 part by mass of the urea compound, the urea compound being at least one selected from the group consisting of urea, urea derivatives, thiourea and thiourea derivatives, and the moisture content of the polarizing plate being an equilibrium moisture content of 30% or more at 20°C and an equilibrium moisture content of 50% or less at 20°C. The polarizing plate as described in claim 1 or 2, wherein the aforementioned adhesive comprises at least one urea compound selected from the group consisting of urea derivatives and thiourea derivatives. The polarizing plate as described in claim 1 or 2, wherein the aforementioned adhesive comprises a polyvinyl alcohol resin. The polarizing plate as described in claim 4, wherein, in the aforementioned adhesive, the content of the aforementioned urea compound is 0.1 parts by mass to 400 parts by mass relative to 100 parts by mass of the aforementioned polyvinyl alcohol resin. The polarizing plate as described in claim 1 or 2, wherein the aforementioned dialdehyde is glyoxal. The polarizing plate as described in claim 1 or 2, wherein the thickness of the aforementioned adhesive layer is 0.01 μm or more and 7 μm or less. The polarizing plate described in claim 1 or 2 is used in an image display device, wherein a solid layer is provided on both sides of the polarizing plate in the aforementioned image display device. An image display device comprising: an image display unit; a first adhesive layer deposited on the viewing side surface of the image display unit; and a polarizing plate as described in any one of claims 1 to 8, deposited on the viewing side surface of the first adhesive layer. The image display device as described in claim 9 further comprises: a second adhesive layer deposited on the viewing side surface of the aforementioned polarizing plate; and a transparent component deposited on the viewing side surface of the aforementioned second adhesive layer. The image display device as described in claim 10, wherein the aforementioned transparent component is a glass plate or a transparent resin plate. The image display device as described in claim 10, wherein the aforementioned transparent component is a touch panel.