JP7655702B2 - Polarizing plate, method for producing the polarizing plate, and image display device using the polarizing plate - Google Patents

Description

The present invention relates to a polarizing plate and a manufacturing method thereof. Furthermore, the present invention relates to an image display device 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 a front panel.

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

As described above, polarizing plates are increasingly being installed in vehicles as components of liquid crystal display devices and organic EL display devices. Polarizing plates used in vehicle-mounted image display devices are more often exposed to high-temperature environments than those used in other mobile applications such as televisions and mobile phones, and are therefore required to have small changes in properties at high temperatures (high-temperature durability).
On the other hand, for the purpose of preventing damage to the image display panel due to impact from the outer surface, a configuration in which a front plate such as a transparent resin plate or a glass plate (also referred to as a "window layer" or the like) is provided on the viewing side further than the polarizing plate of the image display panel is increasingly being used. Also, in display devices equipped with a touch panel, a configuration in which the touch panel is provided on the viewing side further than the polarizing plate of the image display panel and a front plate is provided on the viewing side further 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 external light to be reflected, which tends to reduce the visibility of the screen. For this reason, there is a growing trend to adopt a configuration in which the space between the polarizing plate and the front transparent member arranged on the viewing side surface of the image display panel is filled with a material that has a refractive index close to that of these materials (hereinafter sometimes referred to as an "interlayer filling configuration"). As the interlayer filling material, 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 together (see, for example, Patent Document 1).

The above-mentioned interlayer filling structure is being widely adopted for mobile applications such as mobile phones that are often used outdoors. In addition, due to the increasing demand for visibility in recent years, the adoption of a structure in which a front plate is placed on the surface of an image display panel and an adhesive layer or the like is used to fill the gap between the panel and the front plate is being considered for in-vehicle applications such as car navigation devices.
However, when such a configuration is adopted, it has been reported that, as a result of a heat durability test (e.g., at 95°C for 200 hours), a significant decrease in transmittance is observed in the center of the polarizing plate surface, whereas, in contrast, no significant decrease in transmittance is observed in the polarizing plate alone even after 1000 hours at 95°C. Based on these results, it has also been reported that a significant decrease in the transmittance of a polarizing plate in a high-temperature environment is a problem particular to the case where an image display device employing an interlayer filling configuration in which one surface of a 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 a front panel is exposed to a high-temperature environment (Patent Document 2).

In addition, the above-mentioned Patent Document 2 states that a polarizing plate with a significantly reduced transmittance due to an interlayer filling structure has peaks in Raman spectroscopy at around 1100 cm ^-1 (derived from =C-C= bonds) and around 1500 cm ^-1 (derived from -C=C- bonds), and therefore it is believed that this has formed a polyene structure (-C=C) _n -, and that this is the result of the polyvinyl alcohol that constitutes the polarizing element being converted into a polyenone by dehydration (Patent Document 2, paragraph [0012]).
The inventors also performed Raman spectroscopy on samples that had been subjected to high-temperature durability tests with an interlayer packed configuration and observed that the sum of the peak areas near 1100 cm ⁻¹ and 1500 cm ⁻¹ increased with decreasing transmittance.

As a solution to this problem, Patent Document 2 proposes a method of suppressing the decrease in transmittance by setting the moisture content per unit area of the polarizing plate to a specified amount or less and setting the saturated water absorption amount of a transparent protective film adjacent to the polarizing element to a specified amount or less.
However, further testing by the inventors revealed that the effect of the above solutions in suppressing deterioration was not necessarily sufficient, and furthermore, it was found that in order to reduce the moisture in the polarizing plate during panel production, it becomes necessary to heat the polarizing plate or the panel to which the polarizing plate is attached, resulting in a new problem of reducing panel productivity.

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

In view of the above situation, the object of the present invention, i.e., the problem that the present invention aims to solve, is to provide a polarizing plate and a manufacturing method thereof that exhibits little decrease in transmittance in high-temperature environments and has excellent durability even when used in an image display device with an interlayer filling configuration. Another object of the present invention is to provide an image display device with improved durability and improved display characteristics in high-temperature environments.

After extensive research, the present inventors have found that in a configuration in which a transparent protective film is provided via an adhesive layer on at least one surface of a polarizing element formed by adsorbing and aligning iodine in a polyvinyl alcohol-based resin layer, by incorporating at least one type selected from urea, urea derivatives, thiourea, and thiourea derivatives (hereinafter, urea, urea derivatives, thiourea, and thiourea derivatives are also simply referred to as "urea-based compounds") in the adhesive layer, a decrease in transmittance in a high-temperature environment can be suppressed in 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.

As a result of further investigation, it was found that laminating a layer containing at least one type of urea-based compound (hereinafter also referred to as a "urea-based compound-containing layer") on at least one surface of the polarizing element has the effect of suppressing the decrease in transmittance in a high-temperature environment in an interlayer filling configuration, as in the first invention, even if the layer is not an adhesive layer.

Furthermore, it has been found that, among the urea-based compounds of the present invention, in a device employing an interlayer filling configuration, urea derivatives or thiourea derivatives exhibit excellent performance not only in terms of the effect of suppressing a decrease in transmittance in a high-temperature environment, but also in terms of the effect of suppressing a decrease in the degree of polarization (preventing cross loss) in a high-temperature environment.
Based on these newly discovered facts, the present inventors have completed the present invention.

The problem to be solved by the present invention can be solved by the following means.
(1) A polyvinyl alcohol-based resin polarizing element having iodine adsorbed and oriented thereon;
A polarizing plate comprising: a urea-based compound-containing layer, which contains at least one compound selected from urea, urea derivatives, thiourea and thiourea derivatives, and is formed on at least one surface of the polarizing element; and a transparent protective film.
(2) The polarizing plate according to (1), wherein the urea compound-containing layer is an adhesive layer, and the transparent protective film is attached via the adhesive layer.
(3) The polarizing plate according to (2), wherein the adhesive layer further contains a polyvinyl alcohol-based resin.
(4) The polarizing plate according to (3), wherein the total content of the urea-based compounds contained in the adhesive layer is 1 part by weight or more and 400 parts by weight or less per 100 parts by weight of the polyvinyl alcohol-based resin.

(5) The polarizing plate according to any one of (1) to (4), wherein the urea compound is a urea derivative and/or a thiourea derivative.
(6) The polarizing plate according to any one of (2) to (5), wherein the adhesive layer has a thickness of 0.01 to 7 μm.
(7) The polarizing plate according to (1), wherein the urea compound-containing layer is a resin layer other than an adhesive layer.
(8) The polarizing plate according to any one of (1) to (7), which is used in an image display device having an interlayer packing structure.

(9) A method for producing a polarizing plate having a transparent protective film attached to at least one surface of a polarizing element, comprising the steps of:
At least one surface of a polarizing element made of a stretched polyvinyl alcohol-based resin film on which iodine has been adsorbed and oriented is provided.
forming an adhesive layer using an adhesive composition containing a polyvinyl alcohol-based resin and at least one selected from urea, a urea derivative, thiourea, and a thiourea derivative;
A method for producing a polarizing plate, comprising the step of laminating a transparent protective film via the adhesive layer simultaneously with or after the step of forming the adhesive layer.

(10) An image display device comprising: an image display panel in which the polarizing plate according to any one of (1) to (9) is bonded to a viewing-side surface of an image display cell via an adhesive layer; and a transparent member bonded to a viewing-side polarizing plate surface of the image display panel via an adhesive layer.
(11) The image display device according to (10), wherein the transparent member is a glass plate or a transparent resin plate.
(12) The image display device according to (10), wherein the transparent member is a touch panel.

The present invention makes it possible to provide a polarizing plate and a manufacturing method thereof that exhibits little decrease in transmittance in high-temperature environments and has excellent high-temperature durability even when used in an image display device with an interlayer filling configuration.Furthermore, by using the polarizing plate of the present invention, it becomes possible to provide a display device in which the decrease in transmittance in high-temperature environments is suppressed.

In one embodiment of the present invention, a transparent protective film is provided via an adhesive layer on at least one surface of a polarizing element formed by adsorbing and aligning iodine in a polyvinyl alcohol-based resin layer, and the adhesive layer contains at least one selected from urea, urea derivatives, thiourea, and thiourea derivatives.

The technical elements constituting the present invention will be described below, but the elements other than the urea-based compound-containing layer are common to other embodiments (embodiments in which the urea-based compound-containing layer is a layer other than the adhesive layer).
[Polarizing element]
As the polarizing element of the present invention in which iodine is adsorbed and aligned in a polyvinyl alcohol (hereinafter also referred to as PVA)-based resin layer, a well-known polarizing element can be used. Such a polarizing element is generally formed by using a PVA-based resin film, dyeing the PVA-based resin film with iodine, and uniaxially stretching the PVA-based resin film.

As described above, the PVA resin is generally obtained by saponifying a polyvinyl acetate resin. The degree of saponification is about 85 mol% or more, preferably about 90 mol% or more, and more preferably about 99 mol% to 100 mol%. 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, such as ethylene-vinyl acetate copolymers. Examples of other monomers that can be copolymerized include unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids. The degree of polymerization of the PVA resin is 1,000 to 10,000, preferably 1,500 to 5,000. The PVA resin may be modified, such as polyvinyl formal, polyvinyl acetal, or polyvinyl butyral modified with aldehydes.

The method for producing the polarizing element is not particularly limited, but typically includes a method in which a polyvinyl alcohol-based resin film wound in advance into a roll is sent out and stretched, dyed, crosslinked, etc., or a method including a step of preparing a laminate of a polyvinyl alcohol-based resin and a resin substrate for stretching and stretching the laminate. Either of these methods can be used in the present invention.
Methods for producing these polarizing elements are described in paragraphs [0109] to [0128] of JP2014-48497A, and these methods can be used in the present invention. The thickness of the polarizing element of the present invention is preferably 3 to 35 μm, more preferably 4 to 30 μm, and even more preferably 5 to 25 μm.

[Urea-based compound-containing layer]
The polarizing plate of the present invention has a urea-based compound-containing layer containing at least one compound selected from urea, urea derivatives, thiourea and thiourea derivatives, formed on at least one surface of a polyvinyl alcohol-based resin polarizing element having iodine adsorbed and aligned thereon.
In the present invention, the urea compound-containing layer does not necessarily have to be an adhesive layer, but from the viewpoint of productivity, it is preferable that the adhesive layer contains a urea compound. The adhesive layer is formed from the following adhesive.
The structure of the urea compound-containing layer other than the adhesive layer will be described later.

[glue]
Any suitable adhesive can be used as the adhesive for bonding the protective film to the polarizing element. Specifically, the adhesive can be a water-based adhesive, a solvent-based adhesive, or an active energy ray curable adhesive, but a water-based adhesive is preferred.
When the adhesive layer is a layer containing a urea-based compound, the adhesive contains at least one selected from urea, urea derivatives, thiourea, and thiourea derivatives.
The thickness of the adhesive when applied can be set to any appropriate value. For example, it is set so that an adhesive layer having a desired thickness is obtained after curing or heating (drying). The thickness of the adhesive layer is preferably 0.01 μm to 7 μm, more preferably 0.01 μm to 5 μm, even more preferably 0.01 μm to 2 μm, and most preferably 0.01 μm to 1 μm.

(Water-based adhesive)
Any suitable aqueous adhesive may be used as the aqueous adhesive. Among them, an aqueous adhesive containing a PVA-based resin (PVA-based adhesive) is preferably used. The average polymerization degree of the PVA-based resin contained in the aqueous adhesive is preferably 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%, from the viewpoint of adhesiveness.

The PVA-based resin contained in the aqueous adhesive is preferably one containing an acetoacetyl group, because it has excellent adhesion between the PVA-based resin layer and the protective film and excellent durability. The acetoacetyl-containing PVA-based resin can be obtained, for example, by reacting a PVA-based resin with diketene by any method. The degree of acetoacetyl modification of the acetoacetyl-containing PVA-based resin is typically 0.1 mol% or more, and preferably about 0.1 mol% to 20 mol%.
The resin concentration of the water-based adhesive is preferably 0.1% by weight to 15% by weight, and more preferably 0.5% by weight to 10% by weight.

(Crosslinking agent, solvent)
The water-soluble PVA adhesive preferably used in the present invention may contain a crosslinking agent as required in addition to the above-mentioned PVA resin and urea compound. Known crosslinking agents can be used as the crosslinking agent. Examples of the crosslinking agent include water-soluble epoxy compounds, dialdehydes, and isocyanates.

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

The water-soluble PVA adhesive of the present invention may contain an organic solvent. In this case, the organic solvent is preferably an alcohol because of its miscibility with water, and among alcohols, methanol or ethanol is more preferable.
In the present invention, some of the urea derivatives have low solubility in water but sufficient solubility in alcohol. In such a case, it is one of the preferred embodiments to dissolve the urea derivative in alcohol to prepare an alcohol solution of the urea derivative, and then add the alcohol solution of the urea derivative to the aqueous PVA solution to prepare the adhesive.

(Active energy ray curing adhesive)
As the active energy ray curable adhesive, any suitable adhesive can be used as long as it is an adhesive that can be cured by irradiation with active energy rays. Examples of the active energy ray curable adhesive include ultraviolet ray curable adhesives and electron beam curable adhesives. Specific examples of the curing type of the active energy ray curable adhesive include radical curable type, cationic curable type, anionic curable type, and combinations thereof (for example, a hybrid of radical curable type and cationic curable type).

The active energy ray-curable adhesive may, for example, be an adhesive containing, as a curing component, a compound (for example, a monomer and/or oligomer) having a radical polymerizable group such as a (meth)acrylate group or a (meth)acrylamide group.
Specific examples of the above-mentioned active energy ray-curable adhesive and its curing method are described in, for example, JP-A-2012-144690.

[Urea compounds]
In the present invention, the adhesive layer contains at least one selected from urea, urea derivatives, thiourea and thiourea derivatives.
As a method for incorporating a urea-based compound in the adhesive layer, it is preferable to incorporate the urea-based compound in the above-mentioned adhesive. Note that, in the process of forming the adhesive layer from the adhesive through a drying process, etc., it does not matter if a part of the urea-based compound migrates from the adhesive layer to the polarizing element, etc.
Urea compounds include water-soluble and poorly water-soluble urea compounds, and both types can be used in the present invention. When a poorly water-soluble urea 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.

When the adhesive is a water-based adhesive containing a PVA-based resin, the amount of the urea-based compound added is preferably 0.1 to 400 parts by weight, more preferably 1 to 200 parts by weight, and even more preferably 3 to 100 parts by weight, per 100 parts by weight of the PVA-based resin.

(Urea or urea derivatives)
In the present invention, the urea derivative means a compound having a molecular structure in which a part of urea is substituted with a substituent. The urea derivative is preferably 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 carbon atoms, hydrogen atoms and oxygen atoms.

Specific examples of the urea derivatives include mono-substituted 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 (ethylene urea), and tetrahydro-2-pyrimidinone (propylene urea).
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 or thiourea derivatives)
In the present invention, the thiourea derivative means a compound having a molecular structure in which a part of thiourea is substituted with a substituent. The thiourea derivative is preferably a compound in which at least one of the four hydrogen atoms of the thiourea molecule is substituted with a substituent.
In this case, the substituent is not particularly limited, but is preferably a substituent consisting of carbon atoms, hydrogen atoms and oxygen atoms.

Specific examples of thiourea derivatives include mono-substituted 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 the 3-substituted thiourea is trimethylthiourea, and an example of the 4-substituted thiourea is tetramethylthiourea or 1,1,3,3-tetraethylthiourea.

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

[Transparent protective film]
The transparent protective film used in the present invention (hereinafter, simply referred to as "protective film") is attached to at least one side of a polarizing element via the urea compound-containing adhesive layer of the present invention. This transparent protective film is attached to one or both sides of the polarizing element, but it is more preferable that it is attached to both sides.
In a configuration in which 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 the urea-based compound-containing adhesive layer of the present invention, but it is more preferable that both adhesive layers on both sides are the urea-based compound-containing adhesive layer of the present invention.

In recent years, in order to meet the demand for thinner polarizing plates, polarizing plates having a protective film on only one side of the polarizing element have been developed. Even in this configuration, it is preferable to laminate the protective film via the urea compound-containing adhesive layer of the present invention.
One possible method for producing a polarizing plate having a protective film on only one side of a polarizing element is to first produce a polarizing plate in which protective films are attached to both sides via an adhesive layer, and then peel off one of the protective films. When such a production method is used, it is acceptable for only one of the adhesive layers to be the adhesive layer of the present invention, but it is more preferable that the urea-based compound-containing adhesive layer of the present invention is used on both sides of the polarizing element.
When the urea compound-containing adhesive layer of the present invention is used on only one side of a polarizing element, it is preferable that the adhesive layer on the film side that is not to be peeled off is the urea compound-containing adhesive layer of the present invention.

The protective film may also have other optical functions, and may have a laminated structure in which other layers are further laminated.
In this case, the thickness of the protective film is preferably thin from the viewpoint of optical properties, but if it is too thin, the strength decreases and the processability becomes poor. The appropriate thickness is 5 to 100 μm, preferably 10 to 80 μm, and more preferably 15 to 70 μm.

The protective film may be a cellulose acylate resin film, a polycarbonate resin film, a cycloolefin resin film such as norbornene, a (meth)acrylic polymer film, or a polyester resin film such as polyethylene terephthalate.
In the case of a configuration having protective films on both sides of a polarizing element, when bonding is performed using an aqueous adhesive such as a PVA-based adhesive, it is preferable that the protective film on at least one side be either a cellulose acylate-based film or a (meth)acrylic polymer film from the standpoint 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 angle, etc. In that case, the film itself may have a retardation function, may have a separate retardation layer, or may be a combination of both.
In the above description, the film having phase difference function is directly attached to the polarizing element via an adhesive, but it may be attached via a pressure-sensitive adhesive or adhesive via another protective film attached to the polarizing element.

[Configuration of image display device]
The polarizing plate of the present invention, i.e., a polarizing plate having a transparent protective film bonded to at least one side of a polarizing element via a urea-based compound-containing adhesive layer, is used in various image display devices such as liquid crystal display devices, organic EL display devices, etc. In particular, the polarizing plate of the present invention is suitably used in an image display device having an interlayer filling configuration in which a transparent member such as a front plate or a touch panel is disposed on the viewing side of the image display device and the image display panel and the transparent member are bonded together with a pressure-sensitive adhesive layer or the like.

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

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 image display cell and polarizing plate)
A pressure-sensitive adhesive layer (pressure-sensitive adhesive sheet) is preferably used for bonding the image display cell and the polarizing plate. Among them, a method of bonding a polarizing plate with a pressure-sensitive adhesive layer, in which a pressure-sensitive adhesive layer is attached to one side of the polarizing plate, to the image display cell is preferred from the viewpoint of workability and the like. The pressure-sensitive adhesive layer can be attached to the polarizing plate by a suitable method. Examples of such a method include a method in which a pressure-sensitive adhesive solution of about 10 to 40% by weight is prepared 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 the solution is directly attached to the polarizing plate by a suitable spreading method such as a casting method or a coating method, or a method in which a pressure-sensitive adhesive layer is formed on a separator in the same manner as above and then transferred to the polarizing plate.

(Adhesive Layer)
The pressure-sensitive adhesive layer is described in paragraphs [0103] to [0143] of JP2018-025765A, and these pressure-sensitive adhesives can be used in the present invention.

(Front transparent member)
Examples of the front transparent member arranged on the viewing side of the image display cell include a front plate (window layer) and a touch panel. A transparent plate having appropriate mechanical strength and thickness is used as the front plate. Examples of such transparent plates include transparent resin plates such as acrylic resins and polycarbonate resins, 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 physical strength, or a low moisture permeable layer may be laminated to reduce moisture permeability.
As the touch panel, various touch panels such as resistive, capacitive, optical, and ultrasonic touch panels, as well as glass or transparent resin plates having a touch sensor function are used. When a capacitive touch panel is used as the front transparent member, it is preferable that a front plate made of glass or transparent resin plate is provided on the viewing side further than the touch panel.

(Laminating the polarizing plate and the front transparent member)
A pressure sensitive adhesive or a UV curing adhesive is preferably used to bond the polarizing plate and the front 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 in bonding the image display cell and the polarizing plate described above can be mentioned.

When using a UV-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 the front 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 UV light to cure it.

Next, an embodiment of the present invention in which at least one surface of the polarizing element has a urea compound-containing layer other than the adhesive layer containing at least one kind of urea compound will be described.
As described above, the technical elements constituting the present invention, such as the polarizing element other than the urea-based compound-containing layer, are common to the embodiment in which the urea-based compound-containing layer is an adhesive layer.

[Urea-based compound-containing layer]
In this embodiment of the present invention, the polarizing plate has a urea-based compound-containing layer (other than the adhesive layer) that contains at least one compound selected from urea, urea derivatives, thiourea, and thiourea derivatives and is formed on at least one surface of a polyvinyl alcohol-based resin polarizing element having iodine adsorbed and oriented thereon.
The urea compound-containing layer preferably contains at least one urea compound and a binder. Examples of the binder include polymer binders, thermosetting binders, and active energy ray-curable binders, and any of these binders can be preferably used in the present invention.

The thickness of the urea compound-containing layer is preferably 0.1 to 20 μm, more preferably 0.5 to 15 μm, and even more preferably 1 to 10 μm.
The urea-based compound-containing layer may be laminated directly to the polarizing element or via another layer, but it is preferable to laminate it directly to the polarizing element, since this makes it easier to prevent a decrease in transmittance in a high-temperature environment.
In this embodiment, the polarizing plate preferably has a transparent protective film on at least one surface of the polarizing element via an adhesive layer in order to increase the physical strength of the polarizing plate. In this case, the adhesive layer may or may not contain a urea-based compound, but it is more preferable that the adhesive layer contains a urea-based compound.

As described in the explanation of the protective film in other embodiments, in recent years, in order to meet the demand for thinner polarizing plates, polarizing plates having a protective film on only one side of the polarizing element (hereinafter also referred to as "polarizing plates with one-sided protective film") have been developed.
In order to increase the physical strength of such a structure, attempts have been made to laminate a cured layer on the surface of the polarizing element that does not have a protective film (for example, JP 2011-221185 A).

In the present invention, it is also a preferred embodiment to include a urea-based compound in such a cured layer. Usually, such a cured layer is formed from a curable composition containing an organic solvent, but paragraphs [0020] to [0042] of JP2017-075986A describe a method of forming such a cured layer from an aqueous solution of an active energy ray-curable polymer composition. Since many urea-based compounds are water-soluble, it is also a preferred embodiment of the present invention to include a water-soluble urea-based compound in such a composition to form a urea-based compound-containing layer.

Next, a polarizing plate according to still another embodiment will be described, which has a polarizing element prepared by applying a solution containing a urea compound to at least one surface of the polarizing element and drying the applied solution.
This embodiment is characterized in that the polarizing element is used in a polarizing plate for interlayer filling construction and prevents a decrease in single-unit transmittance even when exposed to a high-temperature environment for a long period of time. This polarizing element can be produced by coating at least one surface of a polarizing element made of a stretched polyvinyl alcohol-based resin film on which iodine is adsorbed and oriented, with a solution containing at least one selected from urea, urea derivatives, thiourea, and thiourea derivatives, and then drying the coating liquid.

(Urea compound solution)
The solvent of the urea compound-containing solution of the present invention is preferably water, an organic solvent, or a mixture thereof, more preferably water or a mixed solvent of water and alcohol. In the case of a mixed solvent of water and alcohol, the alcohol is preferably either methanol or ethanol.
As the urea compound, the above-mentioned urea compounds can be preferably used, but the urea compound is preferably water-soluble in order to prevent the urea compound from precipitating on the surface of the polarizing element after drying.

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

(Preparation of Polarizing Element 1)
A PVA film having an average degree of polymerization of 2400 and a degree of saponification of 99.9 mol% and a thickness of 40 μm was immersed in warm water at 25° C. for 120 seconds to swell. The PVA film was then immersed in an aqueous solution of iodine/potassium iodide (weight ratio=2/3) with a concentration of 0.6% by weight, and dyed while being stretched 2.1 times. The film was then stretched in an acid bath containing boric acid and potassium iodide at 60° C., washed with water, and dried to produce a polarizing element 1 having a thickness of 15 μm.

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

(Preparation of urea compound solution)
10 g of urea was added to 90 g of pure water to obtain a 10 wt % urea aqueous solution (Solution 1). Similarly, according to Table 1, solutions 2 to 9 were prepared by replacing urea with the urea-based compound shown in Table 1 and, if necessary, changing the solvent from pure water to methanol.

The urea, methylurea, ethylurea, 1,3-dimethylurea, tetramethylurea, phenylurea, thiourea, methylthiourea, and tetrahydro-2-pyrimidinone used above were all reagents from Tokyo Chemical Industry Co., Ltd.

(Preparation of Polarizing Plate Adhesive 1)
The PVA adhesive solution, urea solution, pure water, and methanol prepared above were mixed to give a PVA concentration of 3.0%, a methanol concentration of 20%, and a urea concentration of 0.3%, to obtain an adhesive 1 for polarizing plates.

(Preparation of Polarizing Plate Adhesives 2 to 14)
Similarly, a PVA solution for adhesive, a solution of a urea compound shown in Table 1, pure water, and methanol were mixed so that the PVA concentration was 3.0%, the methanol concentration was 20%, and the urea compound concentration was the concentration shown in Table 2, to obtain polarizing plate adhesives 2 to 14.
The polarizing plate adhesive 12 uses two types of urea compounds, ie, methylurea and 1,3-dimethylurea, in combination, while the polarizing plate adhesive 14 does not contain any urea compound.

(Saponification of Cellulose Acylate Film)
A commercially available cellulose acylate film TD40 (manufactured by Fujifilm Corporation: film thickness 40 μm) was immersed in a 1.5 mol/L NaOH aqueous solution (saponification solution) kept at 55° C. for 2 minutes, then the film was washed with water, and then 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 repeatedly drained three times with an air knife, and after removing the water, it was allowed to stay in a drying zone at 70° C. for 15 seconds and dried to prepare a saponified film.

(Preparation of Polarizing Plate 1)
The saponified cellulose acylate film prepared above was attached to both sides of the polarizing element 1 via polarizing plate adhesive 1, and the thickness of the adhesive layer after drying was adjusted to 100 nm on both sides. The films were then laminated using a roll laminator and dried at 60°C for 10 minutes to obtain polarizing plate 1 with cellulose acylate films on both sides.

(Preparation of Polarizing Plates 2 to 14)
Polarizing plates 2 to 14 were prepared in the same manner as polarizing plate 1, except that polarizing plate adhesive 1 was replaced with polarizing plate adhesives 2 to 14.

(Preparation of Laminate 1)
With reference to the examples of JP 2018-025765 A, an acrylic adhesive (manufacturer: Lintec Corporation, product number: #7) was applied to both sides of the polarizing plate 1 prepared above, thereby producing an optical laminate 1 having an adhesive layer with a thickness of 25 μm on both sides.
(Preparation of Laminates 2 to 14)
Optical laminates 2 to 14 were prepared in the same manner as in the optical laminate 1, except that polarizing plate 1 was replaced with polarizing plates 2 to 14.

(Preparation of Laminate 15)
Optical laminate 15 was produced in the same manner as optical laminate 14, except that a pressure-sensitive adhesive layer was laminated on only one side of optical laminate 14.

(Evaluation of the laminate)
The laminate prepared above was evaluated with reference to the examples of JP 2014-102353 A and JP 2018-025765 A. The high temperature durability test was performed at 95°C and 105°C, and the high temperature durability test was performed for 1000 hours at 95°C, but no decrease in transmittance was observed except for Comparative Example 1, which used polarizing plate adhesive 14 without the addition of a urea-based compound. Table 3 shows only the results of the high temperature durability test at 105°C.
In the test results of Comparative Example 1, the coloring at 105° C. for 100 hours was almost the same as the result at 95° C. for 1000 hours.

[Evaluation of unit transmittance after high-temperature durability test (105°C)]
The optical laminates 1 to 14 prepared above were each cut to a size of 50 mm x 100 mm, and the surfaces of the first adhesive layer and the second adhesive layer were laminated to alkali-free glass (trade name "EAGLE XG", manufactured by Corning Incorporated) to prepare evaluation samples. The optical laminate 15 was also cut to a size of 50 mm x 100 mm, and the surface of the first adhesive layer was laminated to alkali-free glass (trade name "EAGLE XG", manufactured by Corning Incorporated) to prepare evaluation samples. When preparing these samples, no heat treatment was performed to adjust the moisture content before laminating the glass plate.
This evaluation sample was autoclaved for 1 hour at a temperature of 50°C and a pressure of 5 kgf/ ^cm2 (490.3 kPa), and then left for 24 hours in an environment at a temperature of 23°C and a relative humidity of 55%. Thereafter, the transmittance was measured (initial value), and the sample was stored in a heated environment at a temperature of 105°C, 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 3.
The evaluation sample including the optical laminate 15 had a structure in which the non-alkali glass was laminated only on one side, so the transmittance did not decrease and the evaluation result was A.
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]
The optical laminate 15 was cut into a size of 30 mm x 30 mm, and the surface of the first adhesive layer was attached to non-alkali glass (product name "EAGLE XG", manufactured by Corning Incorporated) to prepare a cross-evaluation sample 20.
The single transmittance evaluation sample after high temperature durability was evaluated 100 hours later, and then the optical laminate and sample 20 were visually inspected for light leakage in a cross-Nicol state (hereinafter simply referred to as "cross leakage") and evaluated according to the following criteria.
No cross-drops are visible: ◎
Almost no cross-drops are visible: ○
Slight cross-drop defects: △
Cross-drops are clearly visible: ×

The amounts of the urea compounds added in Table 3 will be explained below.
As described above, the amount of the urea compound added to the adhesive is preferably 0.1 to 400 parts by weight, more preferably 1 to 200 parts by weight, and even more preferably 3 to 100 parts by weight, relative to 100 parts by weight of PVA.
In this example, the PVA concentration is 3.0%.
In the present invention, the greater the amount of any of the urea compounds added, the smaller the change in single unit transmittance after the high temperature durability test. Conversely, the smaller the amount of the compound added, the smaller the degree of cross loss after the high temperature durability test.
All of the urea-based compounds described in the examples exhibited excellent effects in terms of both performance, with a change in single unit transmittance of B or higher after the high-temperature durability test and a cross-drop defect rate of △ or higher.

However, regarding the amounts of the above compounds to be added, the range of amounts to be added that exhibits the preferred performance, i.e., a single transmittance change of B or more and at the same time a cross loss of △ or more, varies strictly depending on each compound, but the amount to be added of each compound is within the above-mentioned preferred amount range.
The amounts added in Table 3 indicate the minimum amount added for each urea compound at which the single-unit transmittance is rated A. Furthermore, for urea and thiourea, the amounts added are gradually reduced from the minimum amount added for which the single-unit transmittance is rated A, and the amounts added are also shown at which the cross-passage changes from △ to ○ (the change in single-unit transmittance at this time was B). Furthermore, for methylurea, the amounts added are gradually reduced from the minimum amount added for which the single-unit transmittance is rated A, and the amounts added are also shown at which the cross-passage changes from ○ to ◎ (the change in single-unit transmittance at this time was B).

The results shown in Table 3 make the following clear:
1. The polarizing plate of the present invention, which uses an adhesive containing a urea compound, can suppress a decrease in the single-unit transmittance even when used in an image display device with an interlayer filling structure and even when exposed to a high-temperature environment for a long period of time.
2. In particular, compared with the use of urea or thiourea, the use of a urea derivative or a thiourea derivative is particularly favorable since there is no decrease in the single-piece transmittance and no cross-drop occurs.
3. The adhesive containing two types of urea-based compounds can also prevent the decrease in the single-piece transmittance even when exposed to a high-temperature environment for a long period of time, and is one of the preferred embodiments of the present invention.

Next, an example of another embodiment will be described, but this embodiment is also not limited to the following example.
To the composition of the cured layer-forming composition BLC-1 described in paragraphs [0075] to [0076] of JP2017-075986A, methylurea was added so that the solid content concentration of methylurea became 1% by weight, and pure water was added so that the total solid content concentration became 26% by weight. After mixing, the mixture was irradiated with ultrasonic waves and passed through a filter having a pore size of 5 μm to prepare a urea compound-containing curable composition (UBLC-1).

With reference to polarizing plate 1 described in paragraphs [0070] to [0080] of JP2017-075986A, a polarizing plate (polarizing plate 22) having a cured layer and a one-sided protective film that does not contain a urea compound was produced.
A polarizing plate (polarizing plate 21) having a urea compound-containing curable layer and a one-side protective film was prepared in the same manner as in the polarizing plate 22, except that the curable forming composition (BLC-1) was replaced with the curable forming composition (UBLC-1).
Optical laminates 21 and 22 were obtained in the same manner as optical laminate 14, except that polarizing plate 14 was replaced with polarizing plate 21 and polarizing plate 22, respectively. These samples were evaluated in the same manner as optical laminate 14, and the results are shown in Table 4.
The evaluation of the loss of cloth after high temperature durability was carried out with the transparent protective film surface facing outward.

The results shown in Table 4 make the following clear:
1. The polarizing plate of the present invention, in which a urea-based compound-containing layer is provided on at least one surface of a polarizing element, can suppress a decrease in the single-unit transmittance even when used in an image display device with an interlayer filling configuration and even when exposed to a high-temperature environment for a long period of time.

Further, examples of other embodiments will be described below, but these embodiments are also not limited to the following examples.
A 0.5% solution of methylurea was prepared as a coating liquid. The 0.5% solution of methylurea was coated on one side of the polarizing element 1 prepared above using a bar coater so that the wet coating amount was 10 μm, and then dried at 60° C. for 5 minutes to obtain a polarizing element 2.
As a comparative example, pure water was applied to one surface of the polarizing element prepared above using a bar coater so that the wet coating amount was 10 μm, and then dried at 60° C. for 5 minutes to obtain polarizing element 3.

Polarizing plates 31 and 32 were obtained in the same manner as polarizing plate 14, except that polarizing element 1 was replaced with polarizing element 2 and polarizing element 3, respectively.
Optical laminates 31 and 32 were obtained in the same manner as optical laminate 14, except that polarizing plate 14 was replaced with polarizing plate 31 and polarizing plate 32, respectively. These samples were evaluated in the same manner as optical laminate 14, and the results are shown in Table 5.

The results shown in Table 5 make the following clear:
1. The polarizing plate of the present invention has a polarizing element prepared by applying a solution containing a urea compound to at least one surface of the polarizing element and drying the applied solution. Even when the polarizing plate is used in an image display device having an interlayer filling configuration, and even when the polarizing plate is exposed to a high-temperature environment for a long period of time, the decrease in the single-unit transmittance can be suppressed.

Claims (10)

A polyvinyl alcohol-based resin polarizing element having iodine adsorbed thereon and oriented thereon;
the polyvinyl alcohol-based resin polarizing element has a urea-based compound-containing layer formed on at least one surface thereof, the urea-based compound-containing layer containing at least one urea-based compound selected from urea derivatives and thiourea derivatives, and a transparent protective film;
the urea derivative is at least one urea compound selected from the group consisting of methylurea, ethylurea, phenylurea, 1,3-dimethylurea, tetrahydro-2-pyrimidinone (propyleneurea), and tetramethylurea ;
The thiourea derivative is methylthiourea.
A polarizing plate used in an image display device having an interlayer filling structure. The polarizing plate according to claim 1, characterized in that the urea-based compound-containing layer is an adhesive layer, and the transparent protective film is attached via the adhesive layer. The polarizing plate according to claim 2, characterized in that the adhesive layer further contains a polyvinyl alcohol-based resin. The polarizing plate according to claim 3, characterized in that the total content of the urea-based compounds contained in the adhesive layer is 1 part by weight or more and 400 parts by weight or less per 100 parts by weight of the polyvinyl alcohol-based resin. The polarizing plate according to any one of claims 2 to 4, characterized in that the adhesive layer has a thickness of 0.01 to 7 μm. The polarizing plate according to claim 1, characterized in that the urea-based compound-containing layer is a resin layer other than an adhesive layer. A method for producing a polarizing plate having a transparent protective film attached to at least one surface of a polarizing element, comprising the steps of:
At least one surface of a polarizing element made of a stretched polyvinyl alcohol-based resin film on which iodine has been adsorbed and oriented is provided.
forming an adhesive layer using an adhesive composition containing a polyvinyl alcohol-based resin and at least one urea-based compound selected from a urea derivative and a thiourea derivative;
The method further comprises a step of laminating a transparent protective film via the adhesive layer simultaneously with or after the step of forming the adhesive layer,
the urea derivative is at least one urea compound selected from the group consisting of methylurea, ethylurea, phenylurea, 1,3-dimethylurea, tetrahydro-2-pyrimidinone (propyleneurea), and tetramethylurea ;
The thiourea derivative is methylthiourea.
A method for producing a polarizing plate used in an image display device having an interlayer filling structure. An image display device comprising: an image display panel in which the polarizing plate according to any one of claims 1 to 6 is bonded to a viewing side surface of an image display cell via an adhesive layer; and a transparent member bonded to a viewing side polarizing plate surface of the image display panel via an adhesive layer. 9. The image display device according to claim 8 , wherein the transparent member is a glass plate or a transparent resin plate. 9. The image display device according to claim 8 , wherein the transparent member is a touch panel.