JP7519861B2 - Polarizing plate and image display device - Google Patents

Description

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

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

As mentioned above, polarizing plates are increasingly being installed in vehicles as components of image display devices such as liquid crystal displays and organic EL displays. Polarizing plates used in in-vehicle image display devices are more often exposed to high-temperature environments than those used in mobile applications such as televisions and mobile phones, and therefore are required to have small changes in properties at high temperatures (high-temperature durability).

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

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

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

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

However, even with these measures, the effect of suppressing the decrease in transmittance during high-temperature durability tests was insufficient.

Japanese Patent Application Publication No. 11-174417 JP 2014-102353 A

The present invention aims to provide a novel polarizing plate that can suppress a decrease in transmittance in a high-temperature environment and has excellent water resistance, and an image display device that uses the polarizing plate.

The present invention provides a polarizing plate and an image display device as exemplified below.
[1] A polarizing plate comprising a polarizing element having a polyvinyl alcohol-based resin layer on which a dichroic dye is adsorbed and oriented, and a transparent protective film laminated on at least one surface of the polarizing element,
the polarizing element and the transparent protective film are attached to each other by an adhesive layer formed from 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 moisture content of the polarizing element is equal to or higher than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 30% and equal to or lower than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 50%.
[2] A polarizing plate comprising a polarizing element having a polyvinyl alcohol-based resin layer on which a dichroic dye is adsorbed and oriented, and a transparent protective film laminated on at least one surface of the polarizing element,
the polarizing element and the transparent protective film are attached to each other by an adhesive layer formed from 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 moisture content of the polarizing plate is equal to or higher than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 30% and equal to or lower than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 50%.
[3] The polarizing plate according to [1] or [2], wherein the adhesive contains at least one urea-based compound selected from the group consisting of urea derivatives and thiourea derivatives.
[4] The polarizing plate according to any one of [1] to [3], wherein the adhesive contains a polyvinyl alcohol-based resin.
[5] The polarizing plate according to [4], wherein the adhesive contains the urea compound in an amount of 0.1 parts by mass or more and 400 parts by mass or less with respect to 100 parts by mass of the polyvinyl alcohol-based resin.
[6] The polarizing plate according to any one of [1] to [5], wherein the adhesive has a dialdehyde content of 0.03 parts by mass or more and 20 parts by mass or less with respect to 1 part by mass of the urea compound.
[7] The polarizing plate according to any one of [1] to [6], wherein the dialdehyde is glyoxal.
[8] The polarizing plate according to any one of [1] to [7], wherein the adhesive layer has a thickness of 0.01 μm or more and 7 μm or less.
[9] The polarizing plate is used in an image display device,
The polarizing plate according to any one of items [1] to [8], wherein in the image display device, solid layers are provided on both sides of the polarizing plate in contact with each other.
[10] An image display device comprising: an image display cell; a first pressure-sensitive adhesive layer laminated on a viewing-side surface of the image display cell; and the polarizing plate according to any one of [1] to [9] laminated on the viewing-side surface of the first pressure-sensitive adhesive layer.
[11] The image display device according to [10], further comprising a second pressure-sensitive adhesive layer laminated on the viewing side surface of the polarizing plate, and a transparent member laminated on the viewing side surface of the second pressure-sensitive adhesive layer.
[12] The image display device according to [11], wherein the transparent member is a glass plate or a transparent resin plate.
[13] The image display device according to [11], wherein the transparent member is a touch panel.

According to the present invention, it is possible to provide a polarizing plate that has improved high-temperature durability and water resistance, and that suppresses the decrease in transmittance and polarization degree due to high temperatures and has excellent water resistance even when used in an image display device with an interlayer filling configuration. Furthermore, by using the polarizing plate according to the present invention, it is possible to provide an image display device that suppresses the decrease in transmittance and polarization degree in a high-temperature environment and has excellent water resistance.

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

[Polarizer]
A polarizing plate according to an embodiment of the present invention includes a polarizing element having a dichroic dye adsorbed and oriented in a layer containing a polyvinyl alcohol resin, and a transparent protective film. The polarizing element and the transparent protective film are bonded together with an adhesive layer formed from an adhesive containing a urea compound and a dialdehyde. The polarizing plate according to this embodiment has at least one of the following characteristics (a) and (b).
(a) The moisture content of the polarizing element is equal to or higher than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 30%, and is equal to or lower than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 50%.
(b) The moisture content of the polarizing plate is equal to or higher than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 30%, and is equal to or lower than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 50%.

Conventional polarizing plates with excellent high-temperature durability include, for example, polarizing plates in which the decrease in transmittance is suppressed even when the polarizing plate alone is left in an environment at a temperature of 95°C for 1,000 hours. However, even such polarizing plates, when used in an interlayer filling configuration, may experience a significant decrease in transmittance in the center of the polarizing plate surface when left in an environment at a temperature of 95°C for 200 hours. The significant decrease in transmittance of polarizing plates in high-temperature environments is thought to be a problem that is particularly likely to occur when an image display device that employs an interlayer filling configuration in which one surface of the polarizing plate is bonded to an image display cell and the other surface is bonded to a transparent member such as a touch panel or front panel is exposed to a high-temperature environment.

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

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

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

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

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

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

The polarizing element preferably contains a urea-based compound. 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, and it is presumed that some of the urea-based compound that migrates from the adhesive layer is contained in the polarizing element. The urea-based compound in the polarizing element may contain a compound that was added during the manufacturing process of the polarizing element. By providing an adhesive layer containing a urea-based compound, the transmittance is less likely to decrease even when the polarizing plate is exposed to a high-temperature environment. This is presumed to be because the urea-based compound contained in the polarizing element suppresses the polyenization of the PVA-based resin.

Methods for incorporating a urea-based compound into a polarizing element during the manufacturing process include immersing a PVA-based resin layer in a treatment solvent containing a urea-based compound, or spraying, pouring, or dripping the treatment solvent onto the PVA-based resin layer.

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

To incorporate a urea-based compound into a polarizing element, the compound may be added both during the manufacture of the polarizing element and to the adhesive.

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

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

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

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

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

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

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

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

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

Among urea-based compounds, urea derivatives or thiourea derivatives are preferred, and urea derivatives are more preferred, in that they suppress the decrease in transmittance in high-temperature environments when used in an image display device with an interlayer filling configuration. Among urea derivatives, mono- or di-substituted ureas are preferred, and mono-substituted ureas are more preferred. Di-substituted ureas include 1,1-substituted ureas and 1,3-substituted ureas, with 1,3-substituted ureas being more preferred.

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

To check whether the moisture content of a polarizing element is within the range of equal to or greater than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30% and equal to or less than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 50%, it can be stored in an environment adjusted to the above temperature and relative humidity ranges, and if there is no change in mass for a certain period of time, it can be considered to have reached equilibrium with the environment. Alternatively, it can be checked by previously calculating the equilibrium moisture content of the polarizing element in an environment adjusted to the above temperature and relative humidity ranges, and comparing the moisture content of the polarizing element with the previously calculated equilibrium moisture content.

Methods for producing a polarizing element having a moisture content equal to or greater than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30% and equal to or less than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 50% are not particularly limited, but examples include a method in which the polarizing element is stored in an environment adjusted to the above temperature and relative humidity range for 10 minutes to 3 hours, or a method in which the polarizing element is heat-treated at 30°C to 90°C.

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

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

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

To check whether the moisture content of a polarizing plate is within the range of equal to or greater than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30% and equal to or less than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 50%, it can be stored in an environment adjusted to the above temperature and relative humidity ranges, and if there is no change in mass for a certain period of time, it can be considered to have reached equilibrium with the environment. Alternatively, it can be checked by previously 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 previously calculated equilibrium moisture content.

There are no particular limitations on the method for producing a polarizing plate whose moisture content is equal to or greater than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30%, and equal to or less than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 50%, but examples of the method include storing the polarizing plate in an environment adjusted to the above temperature and relative humidity ranges for 10 minutes to 3 hours, or heat treating the polarizing plate at 30°C to 90°C.

When manufacturing an image display device that employs an interlayer filling configuration, the image display panel in which the polarizing plate is laminated to the image display cell may be stored in an environment adjusted to the above temperature and relative humidity range for 10 minutes to 3 hours or heated to 30°C to 90°C before laminating the front panel.

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

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

The swelling process is a process in which the PVA-based resin film is immersed in a swelling bath. The swelling process can remove dirt and blocking agents from the surface of the PVA-based resin film, and can also suppress uneven dyeing by swelling the PVA-based resin film. A medium mainly composed of water, such as water, distilled water, or pure water, is usually used for the swelling bath. The swelling bath may contain surfactants, alcohol, or the like, as appropriate, according to conventional methods. In order to control the potassium content of the polarizing element, potassium iodide may be used in the swelling bath. In this case, the concentration of potassium iodide in the swelling bath is preferably 1.5% by mass or less, more preferably 1.0% by mass or less, and even more preferably 0.5% by mass or less.

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

The dyeing process is a treatment process in which the PVA-based resin film is immersed in a dye bath (iodine solution), and allows dichroic dyes such as iodine to be adsorbed and oriented in the PVA-based resin film. The iodine solution is usually preferably an aqueous iodine solution, and contains iodine and an iodide as a dissolution aid. Examples of iodides include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, titanium iodide, and the like. Among these, potassium iodide is preferred from the viewpoint of controlling the potassium content in the polarizing element.

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

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

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

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

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

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

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

The temperature of the stretching bath is preferably about 25°C to about 80°C, more preferably about 40°C to about 75°C, and even more preferably about 50°C to about 70°C. The immersion time in the stretching bath cannot be determined in general because the degree of stretching of the PVA-based resin film is affected by the temperature of the stretching bath, but is preferably about 10 seconds to about 800 seconds, and more preferably about 30 seconds to about 500 seconds. The stretching process in the wet stretching method may be performed together with one or more of the following processing steps: swelling process, dyeing process, crosslinking process, and washing process.

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

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

The cleaning process is a process in which the polyvinyl alcohol-based resin film is immersed in a cleaning bath, and foreign matter remaining on the surface of the polyvinyl alcohol-based resin film can be removed. The cleaning bath usually uses a medium whose main component is water, such as distilled water or pure water. In addition, from the viewpoint of controlling the potassium content in the polarizing element, it is preferable to use potassium iodide in the cleaning bath. In this case, the concentration of potassium iodide in the cleaning bath is preferably about 1% by mass or more and 10% by mass or less, more preferably about 1.5% by mass or more and 4% by mass or less, and even more preferably about 1.8% by mass or more and 3.8% by mass or less.

The temperature of the cleaning bath is preferably about 5°C to 50°C, more preferably about 10°C to 40°C, and even more preferably about 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-based resin film is affected by the temperature of the cleaning bath, but is preferably about 1 second to 100 seconds, more preferably about 2 seconds to 50 seconds, and even more preferably about 3 seconds to 20 seconds. The cleaning process may be carried out only once, or may be carried out multiple times as necessary.

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

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

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

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

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

At least one of the protective films may have a retardation function for the purpose of compensating for viewing angles. In that case, the protective film itself may have a retardation function, may have a separate retardation layer, or may be a combination of both. The film with a retardation function may be directly attached to the polarizing element via an adhesive, or may be attached via a pressure-sensitive adhesive or adhesive via another protective film that is attached to the polarizing element.

<Adhesive Layer>
An adhesive containing a urea-based compound and a dialdehyde is used as an adhesive constituting an adhesive layer for bonding a protective film to a polarizing element. The adhesive may be a water-based adhesive, a solvent-based adhesive, an active energy ray curing adhesive, or the like, but is preferably a water-based adhesive and preferably contains a PVA-based resin. By using an adhesive containing a urea-based compound and a dialdehyde, the decrease in transmittance of the polarizing plate in a high-temperature environment can be suppressed, and water resistance can be improved. In addition, by using an adhesive containing a urea-based compound and a dialdehyde, the decrease in the polarization degree can be suppressed even when the polarizing plate is exposed to a high-temperature environment. When two polarizing plates are used in a cross-Nicol relationship, if the polarization degree of the polarizing plate decreases, light leakage (hereinafter also referred to as "cross leakage") is likely to occur, but according to the present invention, the polarization degree is unlikely to decrease even when exposed to a high-temperature environment, so that cross leakage is also easily suppressed.

Examples of dialdehydes include glyoxal, propanedialdehyde (malondialdehyde), butanedialdehyde (succinaldehyde), etc. In particular, glyoxal, which has a simple structure and is highly reactive, is preferred. Below, glyoxal may be described, but as described above, dialdehydes that are conventionally known can be used, and are not limited to glyoxal.

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

The following description of the adhesive is a description of the preferred range for the case where the polarizing element does not contain a urea-based compound during production. If the polarizing element contains a urea-based compound, the following values can be adjusted as appropriate. As for specific examples of urea-based compounds, the examples of urea-based compounds contained in the polarizing element described above can be applied as is. During the process of forming an adhesive layer through the drying process when adhering the polarizing element and the protective film, it is acceptable if part of the urea-based compound migrates from the adhesive layer to the polarizing element, etc.

When the adhesive is a water-based adhesive containing a PVA-based resin, the content of the urea-based compound is preferably 0.1 parts by mass or more and 400 parts by mass or less, more preferably 1 part by mass or more and 200 parts by mass or less, and even more preferably 3 parts by mass or more and 100 parts by mass or less, relative to 100 parts by mass of the PVA-based resin. If it is less than 0.1 parts by mass, the effect of suppressing the polyenization of the polarizing element in a high-temperature environment may not be sufficient. On the other hand, if it exceeds 400 parts by mass, problems such as precipitation and increased haze may occur.

When the adhesive is a water-based adhesive containing a PVA-based resin, the dialdehyde content is preferably 1 part by mass or more and 60 parts by mass or less, more preferably 1.5 parts by mass or more and 50 parts by mass or less, and even more preferably 2 parts by mass or more and 45 parts by mass or less, per 100 parts by mass of the PVA-based resin. If the content is less than 1 part by mass, the effect of improving water resistance may not be sufficient. On the other hand, if the content exceeds 60 parts by mass, the mixing stability of the adhesive decreases.

In the adhesive, the content of the dialdehyde 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, per part by mass of the urea-based compound, and is, for example, 0.03 parts by mass or more, although there is no lower limit. When the content ratio of the urea-based compound to the dialdehyde in the adhesive is within the above-mentioned range, it becomes easier to achieve both the effect of improving high-temperature durability by the urea-based compound and the effect of improving adhesion by the dialdehyde. It is understood that the effect of improving water resistance is obtained by the effect of improving adhesion by the dialdehyde. When the dialdehyde is contained in excess of 20 parts by mass per part by mass of the urea-based compound, the effect of improving high-temperature durability by the urea-based compound may not be fully exerted. The content ratio of the urea-based compound to the dialdehyde in the adhesive and the content ratio of the urea-based compound to the dialdehyde in the adhesive layer can be considered to be the same.

In a configuration in which transparent protective films are bonded to both sides of a polarizing element via adhesive layers, only one of the adhesive layers on both sides of the polarizing element may be a layer containing a urea-based compound and a dialdehyde, but it is preferable that both adhesive layers on both sides are layers containing a urea-based compound and a dialdehyde.

In order to meet the demand for thinner polarizing plates, polarizing plates having a transparent protective film on only one side of the polarizing element have been developed. A possible method for producing such a polarizing plate having a transparent protective film on only one side of the polarizing element is to first produce a polarizing plate in which transparent protective films are attached to both sides via an adhesive layer, and then peel off one of the transparent protective films. When such a production method is used, it is preferable that the adhesive layer on the film side that is not peeled off contains a urea-based compound and a dialdehyde, and both adhesive layers on both sides may be layers containing a urea-based compound and a dialdehyde.

It is also preferable for the adhesive to contain a water-soluble chelate compound. The water-soluble chelate compound can increase the degree of cross-linking between the adhesive layer and the polarizing element, and between the adhesive layer and the transparent protective film such as a cellulose-based film or an olefin-based film, thereby improving the adhesive strength and water resistance, and can also act as an additive that does not cause problems with optical durability.

Water-soluble chelating compounds have the effect of accelerating the hardening 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 they act as crosslinking catalysts.

The weight ratio of the water-soluble chelate compound contained in the adhesive layer is preferably in the range of 2 to 10 parts by weight per 100 parts by weight of the PVA-based resin. If the weight ratio of the water-soluble chelate compound is less than 2 parts by weight based on the above criteria, the adhesive layer will not exhibit sufficient water resistance when made into a polarizing plate, and if the weight ratio exceeds 10 parts by weight, the optical properties may deteriorate.

(Water-based adhesive)
As the aqueous adhesive, any suitable aqueous adhesive may be used, but preferably, an aqueous adhesive containing a PVA-based resin (PVA-based adhesive) is used. From the viewpoint of adhesiveness, the average polymerization degree of the PVA-based resin contained in the aqueous adhesive is preferably about 100 to 5500, more preferably 1000 to 4500. From the viewpoint of adhesiveness, the average saponification degree is preferably about 85 mol% to 100 mol%, more preferably 90 mol% to 100 mol%.

In the case of an aqueous adhesive containing a PVA-based resin, it is preferable that the PVA-based resin contains an acetoacetyl group, because the effect of improving the adhesive strength by the dialdehyde is more pronounced. For example, when glyoxal is used as the dialdehyde, it is presumed that the aldehyde portion of the glyoxal undergoes an addition reaction with the acetoacetyl group of the acetoacetyl-modified PVA-based resin and functions as a crosslinking agent to improve the adhesive strength. The acetoacetyl-containing PVA-based resin can be obtained, for example, by reacting a PVA-based resin with diketene by any method. The degree of acetoacetyl modification of the acetoacetyl-modified PVA-based resin is preferably 0.1 mol% or more, more preferably 0.1 mol% or more and 20 mol% or less. The concentration of the PVA-based resin in the aqueous adhesive is preferably 0.1 mass% or more and 15 mass% or less, more preferably 0.5 mass% or more and 10 mass% or less.

The water-based adhesive may contain a crosslinking agent other than the dialdehyde. Any known crosslinking agent may be used. Examples of crosslinking agents include water-soluble epoxy compounds and isocyanates.

The water-based adhesive may also contain an organic solvent. The organic solvent is preferably an alcohol because it is miscible with water, and among alcohols, methanol or ethanol is more preferable. The concentration of methanol in the water-based adhesive is preferably 10% by mass or more and 70% by mass or less, more preferably 15% by mass or more and 60% by mass or less, and even more preferably 20% by mass or more and 60% by mass or less. By having a methanol concentration of 10% by mass or more, it is easier to suppress polyenation of the PVA-based resin in a high-temperature environment. In addition, by having a methanol content of 70% by mass or less, it is possible to suppress deterioration of the hue. Some urea derivatives have low solubility in water, but some have sufficient solubility in alcohol. In that case, one preferred embodiment is to dissolve a urea-based compound in alcohol to prepare an alcohol solution of the urea-based compound, and then add the alcohol solution of the urea-based compound to the PVA aqueous solution to prepare the adhesive.

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

<Urea-based compound-containing layer>
The urea-based compound is not limited to being contained in the adhesive layer as described above, and may be contained in layers other than the adhesive layer from the viewpoint of improving the high-temperature durability of the polarizing plate. In a polarizing plate having a transparent protective film only on one side, a curable layer may be laminated on the surface of the polarizing element opposite the transparent protective film from the viewpoint of improving physical strength.

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

The urea-based compound-containing layer preferably contains at least one urea-based compound and a binder. Examples of binders include polymer binders, thermosetting resin binders, and active energy ray-curable resin binders, and any of these binders can be preferably used.

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

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

[Configuration of image display device]
The polarizing plate of the present embodiment is used in various image display devices such as liquid crystal display devices and organic EL display devices. In the case of an image display device in which both sides of the polarizing plate are configured to be in contact with a layer other than an air layer, specifically a solid layer such as an adhesive layer, the transmittance is likely to decrease in a high-temperature environment. In the image display device using the polarizing plate of the present embodiment, even if the image display device has an interlayer filling configuration, the decrease in the transmittance of the polarizing plate in a high-temperature environment can be suppressed. An example of the image display device is a configuration having an image display cell, a first adhesive layer laminated on the viewing side surface of the image display cell, and a polarizing plate laminated on the viewing side surface of the first adhesive layer. Such an image display device may further have a second adhesive layer laminated on the viewing side surface of the polarizing plate and a transparent member laminated on the surface of the second adhesive layer. In particular, the polarizing plate of the present embodiment is suitably used in an image display device having an interlayer filling configuration in which a transparent member is arranged on the viewing side of the image display device, the polarizing plate and the image display cell are bonded together by the first adhesive layer, and the polarizing plate and the transparent member are bonded together by the second adhesive layer. In this specification, either one or both of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer may be simply referred to as an “adhesive layer.” Note that the member used for bonding the polarizing plate and the image display cell, and the member used for bonding the polarizing plate and the transparent member are not limited to a pressure-sensitive adhesive layer and may be an adhesive layer.

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

As an organic EL cell, a light-emitting body (organic electroluminescence light-emitting body) is preferably formed by sequentially laminating a transparent electrode, an organic light-emitting layer, and a metal electrode on a transparent substrate. The organic light-emitting layer is a laminate of various organic thin films, and various layer configurations can be adopted, such as a laminate of a hole injection layer made of a triphenylamine derivative or the like and a light-emitting layer made of a fluorescent organic solid such as anthracene, a laminate of such a light-emitting layer and an electron injection layer made of a perylene derivative or the like, or a laminate of a hole injection layer, a light-emitting layer, and an electron injection layer.

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

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

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

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

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

The adhesive composition may contain additives such as fine particles for imparting light scattering properties, beads (resin beads, glass beads, etc.), glass fibers, resins other than the base polymer, tackifiers, fillers (metal powders and other inorganic powders, etc.), antioxidants, UV absorbers, dyes, pigments, colorants, defoamers, corrosion inhibitors, and photopolymerization initiators.

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

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

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

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

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

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

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

When using an active energy ray curing adhesive, a suitable method is to provide a dam material around the periphery of the image display panel to prevent the adhesive solution from spreading before curing, place a transparent member on the dam material, and then inject the adhesive solution. After the adhesive solution is injected, it is aligned and degassed as necessary, and then irradiated with active energy rays to cause curing.

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

<Preparation of Polarizing Element A>
A 40 μm thick PVA film made of PVA with an average degree of polymerization of about 2400 and a degree of saponification of 99.9 mol% or more was uniaxially stretched by about 5 times in a dry state, and then immersed in pure water at 60 ° C. for 1 minute while maintaining a tension state, and then immersed in an aqueous solution of iodine/potassium iodide/water with a weight ratio of 0.05/5/100 at 28 ° C. for 60 seconds. Then, immersed in an aqueous solution of potassium iodide/boric acid/water with a weight ratio of 8.5/8.5/100 at 72 ° C. for 300 seconds. Then, washed with pure water at 26 ° C. for 20 seconds, and dried at 65 ° C. to obtain a polarizing element A with a thickness of 15 μm in which iodine was adsorbed and aligned in the PVA. A digital micrometer "MH-15M" manufactured by Nikon Corporation was used to measure the thickness of the polarizing element.

<Preparation of Adhesives 1 to 8>
(Preparation of PVA solution A for adhesive)
50 g of a modified PVA-based resin containing an acetoacetyl group ("GOHSENEX Z-410" manufactured by Mitsubishi Chemical Corporation) was dissolved in 950 g of pure water, heated at 90°C for 2 hours, and then cooled to room temperature to obtain a PVA solution for adhesive (hereinafter referred to as "PVA solution A").

(Preparation of Urea Compound Solution 1)
10 g of urea was added to 90 g of pure water to obtain a 10 mass % urea aqueous solution (urea compound solution 1).

(Preparation of Adhesives 1 to 8)
PVA solution A, urea compound solution 1, a commercially available 40% by mass solution of glyoxal, and pure water were mixed so that the PVA solution A was 3.0% by mass, and the urea compound and glyoxal contents were as shown in Table 1, to prepare adhesives 1 to 8.

<Preparation of Transparent Protective Film A>
A commercially available cellulose acylate film TD40 (manufactured by Fujifilm Corporation, film thickness 40 μm) was immersed in a 1.5 mol/L NaOH aqueous solution (saponification solution) maintained at 55° C. for 2 minutes, and then washed with water. Then, the film was immersed in a 0.05 mol/L sulfuric acid aqueous solution at 25° C. for 30 seconds, and then passed through a water washing bath under running water for 30 seconds to neutralize the film. Then, the film was drained three times with an air knife to remove water, and then was allowed to stay in a drying zone at 70° C. for 15 seconds to dry, and a saponification-treated film was prepared, which was named transparent protective film A.

<Preparation of Polarizing Plates 1 to 8>
Transparent protective films A were laminated on both sides of polarizing element A via adhesive 1 using a roll laminator, and then dried at 80° C. for 5 minutes to obtain polarizing plate 1. The adhesive layer was adjusted so that the thickness after drying was 100 nm on both sides.

In polarizing plate 1, adhesive 1 was changed to adhesives 2 to 8 to obtain polarizing plates 2 to 8.

(Adjustment of Moisture Content of Polarizing Plate (Polarizing Element))
The polarizing plates 1 to 8 obtained above were stored for 72 hours at a temperature of 20° C. and at a relative humidity of 30%, 35%, 40%, 45%, 50% or 55%. The moisture content was measured using the Karl Fischer method after storage for 66, 69 and 72 hours. The moisture content did not change after storage for 66, 69 and 72 hours under any humidity condition. Therefore, the moisture content of the polarizing plates 1 to 8 can be considered to be the same as the equilibrium moisture content in the 72-hour storage environment used in this experimental example. When the moisture content of the polarizing plate reaches equilibrium in a certain storage environment, the moisture content of the polarizing element in the polarizing plate can also be considered to have reached equilibrium in that storage environment. In addition, when the moisture content of the polarizing element in the polarizing plate reaches equilibrium in a certain storage environment, the moisture content of the polarizing plate can also be considered to have reached equilibrium in that storage environment.

<Optical laminates 1 to 10>
Optical laminates 1 to 10 were prepared by using any one of polarizing plates 1 to 8 shown in Table 2 and storing the polarizing plate (polarizing element) used for 72 hours at a temperature of 20°C and a relative humidity of 35%, 45% or 55% so that the moisture content of the polarizing plate (polarizing element) used became the equilibrium moisture content of the environment shown in Table 2.

<High temperature durability evaluation>
(Preparation of evaluation samples)
For the optical laminates 1 to 10, an acrylic adhesive (manufactured by Lintec Corporation, product number: #7) was applied to both sides of each laminate, and the laminate was cut into pieces measuring 50 mm x 100 mm so that the absorption axis was parallel to the long side. An alkali-free glass ("EAGLE XG" manufactured by Corning Incorporated) was then attached to each adhesive surface to prepare evaluation samples.
In order to evaluate the cross-out of the evaluation sample, an acrylic adhesive (manufactured by Lintec Corporation, product number: #7) was applied to only one side of the polarizing plate 8 in order to create a cross-Nicol state by overlapping it with the evaluation sample, and the polarizing plate 8 was cut into a size of 50 mm x 100 mm so that the absorption axis was parallel to the short side. An alkali-free glass ("EAGLE XG" manufactured by Corning Incorporated) was then bonded to the adhesive surface to prepare an optical laminate R to be used for cross evaluation.

<Single unit transmittance evaluation (105° C.)>
Evaluation samples of optical laminates 1 to 10 were autoclaved for 1 hour at a temperature of 50°C and a pressure of 5 kgf/cm ² (490.3 kPa), and then left for 24 hours in an environment at a temperature of 23°C and a relative humidity of 55%. Thereafter, the transmittance of the evaluation samples of optical laminates 1 to 10 was measured (initial value), and the samples were stored in a heated environment at a temperature of 105°C, and the transmittance was measured every 50 hours from 100 to 200 hours. Evaluation was performed according to the following criteria, based on the time at which the transmittance had decreased by 5% or more from the initial value. The results are shown in Table 2.
The decrease in transmittance after 200 hours is 5% or less: A
The transmittance decreased by 5% or more after 150 to 200 hours: B
The transmittance decreased by 5% or more after 100 to 150 hours: C
The decrease in transmittance after 100 hours is 5% or more: D

<Evaluation of cloth loss after high temperature durability test>
An evaluation sample was prepared after the measurement of the single transmittance after 200 hours in the evaluation of the single transmittance described above. The optical laminate R for the crossed Nicol evaluation, which was not placed in a heating environment, and the evaluation sample were arranged in a crossed Nicol relationship and placed on a backlight. The surroundings were shaded, and the cross-missing was visually evaluated in four stages according to the following criteria. The results are shown in Table 2. Evaluation samples with a single transmittance evaluation other than A were excluded from the evaluation of the cross-missing because they had coloration due to polyenation.
No cross-linking is observed: A
Almost no cross-cutting is observed: B
Cross missing is slightly seen: C
Cross-drop is clearly visible: D

<Water resistance evaluation (hot water immersion test)>
The water resistance test of this example was carried out in accordance with the water resistance test described in JP-A-2009-025728, paragraph [0060].
An acrylic adhesive (product number: #7, manufactured by Lintec Corporation) was applied to one side of the polarizing plate prepared above, and the polarizing plate was cut into a rectangular shape of 50 mm x 20 mm with the absorption axis (stretching direction) of the polarizing plate as the long side, and the dimension in the long side direction was accurately measured. Here, the evaluation sample exhibited a unique color uniformly over the entire surface due to iodine adsorbed to the polarizing element.
One short side of the sample was held with a gripper, and about 80% of the length was immersed in a water tank at 60°C and held for 4 hours. The sample was then removed from the water tank and wiped dry. The polarizer of the polarizing plate shrinks when immersed in warm water. The degree of shrinkage of the polarizing element was evaluated on a three-level scale based on the above criteria by measuring the distance from the end of the sample (the end of the protective film) to the end of the shrunk polarizing element at the center of the short side of the sample.
The distance from the edge of the sample to the edge of the polarizer is 1 mm or less: A
The distance from the end of the sample to the end of the polarizer is 3 mm or less: B
The distance from the edge of the sample to the edge of the polarizer is greater than 3 mm: C

It can be seen that the polarizing plate containing urea in the adhesive (optical laminate 8) is less likely to decrease in transmittance even when exposed to a high-temperature environment of 105°C, and has excellent high-temperature durability, compared to polarizing plates not containing urea in the adhesive (optical laminates 9 and 10). It can be seen that the use of an adhesive containing glyoxal together with urea improves water resistance, and furthermore, cross-drop is less likely to occur even when exposed to a high-temperature environment (comparison of optical laminates 2 and 8).

Claims (15)

A polarizing plate comprising a polarizing element having a polyvinyl alcohol-based resin layer on which a dichroic dye is adsorbed and oriented, and a transparent protective film laminated on at least one surface of the polarizing element,
the polarizing element and the transparent protective film are attached to each other by an adhesive layer formed from an adhesive containing a urea-based compound and a dialdehyde;
The urea compound is at least one selected from the group consisting of urea derivatives, thiourea, and thiourea derivatives,
The urea derivatives 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, p-tolyl urea, 1,1-dimethyl urea, 1,3-dimethyl urea, 1,1-diethyl urea, 1,3-diethyl urea, 1,3-bis(hydroxymethyl) urea, 1,3-t tert-butyl urea, 1,3-dicyclohexyl urea, 1,3-diphenyl urea, 1,3-bis(4-methoxyphenyl) urea, 1-acetyl-3-methyl urea, 2-imidazolidinone (ethylene urea), tetrahydro-2-pyrimidinone (propylene urea), tetramethyl urea, 1,1,3,3-tetraethyl urea, 1,1,3,3-tetrabutyl urea, 1,3-dimethoxy-1,3-dimethyl urea, 1,3-dimethyl-2-imidazolidinone, or 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone;
The moisture content of the polarizing element is equal to or higher than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 30% and equal to or lower than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 50%. A polarizing plate comprising a polarizing element having a polyvinyl alcohol-based resin layer on which a dichroic dye is adsorbed and oriented, and a transparent protective film laminated on at least one surface of the polarizing element,
the polarizing element and the transparent protective film are attached to each other by an adhesive layer formed from an adhesive containing a urea-based compound and a dialdehyde;
The urea compound is at least one selected from the group consisting of urea derivatives, thiourea, and thiourea derivatives,
The urea derivatives 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, p-tolyl urea, 1,1-dimethyl urea, 1,3-dimethyl urea, 1,1-diethyl urea, 1,3-diethyl urea, 1,3-bis(hydroxymethyl) urea, 1,3-t tert-butyl urea, 1,3-dicyclohexyl urea, 1,3-diphenyl urea, 1,3-bis(4-methoxyphenyl) urea, 1-acetyl-3-methyl urea, 2-imidazolidinone (ethylene urea), tetrahydro-2-pyrimidinone (propylene urea), tetramethyl urea, 1,1,3,3-tetraethyl urea, 1,1,3,3-tetrabutyl urea, 1,3-dimethoxy-1,3-dimethyl urea, 1,3-dimethyl-2-imidazolidinone, or 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone;
The moisture content of the polarizing plate is equal to or higher than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 30% and equal to or lower than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 50%. A polarizing plate comprising a polarizing element having a polyvinyl alcohol-based resin layer on which a dichroic dye is adsorbed and oriented, and a transparent protective film laminated on at least one surface of the polarizing element,
the polarizing element and the transparent protective film are attached to each other by an adhesive layer formed from an adhesive containing a urea-based compound and a dialdehyde;
In the adhesive, the content of the dialdehyde 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-based compound is at least one selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives,
The moisture content of the polarizing element is equal to or higher than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 30% and equal to or lower than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 50%. A polarizing plate comprising a polarizing element having a polyvinyl alcohol-based resin layer on which a dichroic dye is adsorbed and oriented, and a transparent protective film laminated on at least one surface of the polarizing element,
the polarizing element and the transparent protective film are attached to each other by an adhesive layer formed from an adhesive containing a urea-based compound and a dialdehyde;
In the adhesive, the content of the dialdehyde 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-based compound is at least one selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives,
The moisture content of the polarizing plate is equal to or higher than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 30% and equal to or lower than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 50%. 5. The polarizing plate according to claim 1 , wherein the adhesive contains at least one urea compound selected from the group consisting of urea derivatives and thiourea derivatives. The polarizing plate according to claim 1 , wherein the adhesive contains a polyvinyl alcohol-based resin. The polarizing plate according to claim 6 , wherein the adhesive contains the urea compound in an amount of 0.1 parts by mass to 400 parts by mass with respect to 100 parts by mass of the polyvinyl alcohol resin. 3. The polarizing plate according to claim 1 , wherein the adhesive contains the dialdehyde in an amount of 0.03 parts by mass or more and 20 parts by mass or less with respect to 1 part by mass of the urea compound. The polarizing plate according to any one of claims 1 to 8 , wherein the dialdehyde is glyoxal. The polarizing plate according to any one of claims 1 to 9 , wherein the adhesive layer has a thickness of 0.01 µm or more and 7 µm or less. The polarizing plate is used in an image display device,
11. The polarizing plate according to claim 1, wherein in the image display device, solid layers are provided on both sides of the polarizing plate in contact with each other. An image display device comprising: an image display cell; a first pressure-sensitive adhesive layer laminated on a viewing side surface of the image display cell; and the polarizing plate according to any one of claims 1 to 11 laminated on the viewing side surface of the first pressure-sensitive adhesive layer. The image display device according to claim 12 , further comprising: a second adhesive layer laminated on the viewer-side surface of the polarizing plate; and a transparent member laminated on the viewer-side surface of the second adhesive layer. The image display device according to claim 13 , wherein the transparent member is a glass plate or a transparent resin plate. The image display device according to claim 13 , wherein the transparent member is a touch panel.