Polarizing plate, and image display device using the polarizing plate

Abstract

To provide a polarizing plate which suppresses reduction in transmittance under high temperature environment even when being used in an image display device having an interlayer filling structure.SOLUTION: The polarizing plate has a polarizing element obtained by adsorbing and orienting iodine in a polyvinyl alcohol-based resin layer, and a transparent protective film, and has an urea-based compound-containing layer containing at least one urea-based compound selected from the group consisting of urea, an urea derivative, thiourea and a thiourea-based derivative. A moisture content of the polarizing element is equal to or more than an equilibrium moisture content at a temperature of 20°C and relative humidity of 30% and equal to or less than an equilibrium moisture content at a temperature of 20°C and relative humidity of 50%.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a polarizing plate. Further, 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.

Background Art

[0002] Liquid crystal display devices (LCDs) are widely used not only in liquid crystal televisions but also in mobile devices such as personal computers and mobile phones, and in-vehicle applications such as car navigation systems. Usually, a liquid crystal display device has a liquid crystal panel member in which polarizing plates are bonded to both sides of a liquid crystal cell 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 have also been widely used in mobile applications such as televisions and mobile phones, and in-vehicle applications such as car navigation systems, similar to liquid crystal display devices. In an organic EL display device, in order to prevent external light from being reflected by a metal electrode (cathode) and being visually recognized like a mirror surface, a circular polarizing plate (a laminate including a polarizing element and a λ / 4 plate) may be disposed on the visually recognizable surface of the image display panel.

[0003] As described above, the opportunity for polarizing plates to be mounted on vehicles has been increasing as members of liquid crystal display devices and organic EL display devices. A polarizing plate used in an in-vehicle image display device is often exposed to a high-temperature environment compared to other mobile applications such as televisions and mobile phones, and it is required to have small characteristic changes at higher 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, etc., a configuration in which a front panel (also referred to as a "window layer", etc.) such as a transparent resin plate or a glass plate is provided on the more visually recognizable side than the polarizing plate of the image display panel has been increasing. In a display device provided with a touch panel, a touch panel is provided on the more visually recognizable side than the polarizing plate of the image display panel, and a configuration in which a front panel is provided on the more visually recognizable side than the touch panel is widely adopted.

[0004] In such a configuration, if there is an air layer between the image display panel and a transparent member such as a front panel or a touch panel, external light may be reflected at the air layer interface, causing external light to be reflected and reducing the visibility of the screen. Therefore, there is a growing trend to adopt a configuration in which the space between the polarizing plate disposed on the viewing side surface of the image display panel and the transparent member is filled with a layer other than the air layer (hereinafter sometimes referred to as an "interlayer filler"), preferably a material having a refractive index close to those of these materials. As the interlayer filler, an adhesive or a UV curable adhesive is used for the purpose of suppressing a decrease in visibility due to reflection at the interface and adhering and fixing the members to each other (see, for example, Patent Document 1).

[0005] The above-described interlayer filling configuration is widely adopted in mobile applications such as mobile phones that are often used outdoors. In addition, due to the increasing demand for visibility in recent years, in in-vehicle applications such as car navigation devices, an interlayer filling configuration in which a front panel is disposed on the surface of the image display panel and the space between the panel and the front panel is filled with an adhesive layer or the like is being considered. However, when such a configuration is adopted, as a result of a heat endurance test (such as 200 hours at 95°C), a significant decrease in transmittance is observed at the center of the polarizing plate in-plane. On the other hand, it has been reported that no significant decrease in transmittance is observed even after 1000 hours at 95°C for the polarizing plate alone. From these results, it has also been reported that a significant decrease in the transmittance of the polarizing plate in a high-temperature environment is a problem specific to an image display device that adopts an interlayer filling configuration in which one surface of the polarizing plate is bonded to the image display cell and the other surface is bonded to a transparent member such as a touch panel or a front panel when exposed to a high-temperature environment (Patent Document 2).

[0006] And in Patent Document 2 mentioned above, a polarizing plate with a significantly reduced transmittance in the interlayer filling configuration has peaks in the vicinity of 1100 cm -1 (derived from the =C-C= bond) and in the vicinity of 1500 cm -1 (derived from the -C=C- bond). Therefore, a polyene structure (-C=C) nIt is considered that - is formed, and it is presumed that it is formed by polyene formation of polyvinyl alcohol constituting the polarizing element due to dehydration (Patent Document 2, paragraph

[0012] ).

[0007] In Patent Document 2, as a solution to the problem, a method of suppressing a decrease in transmittance is proposed by setting the moisture content per unit area of the polarizing plate to be equal to or less than a specified amount and further setting the saturated water absorption of the transparent protective film adjacent to the polarizing element to be equal to or less than a specified amount. However, even with such means, the effect of suppressing the decrease in transmittance in the high-temperature durability test was not sufficient.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] The present invention provides the following polarizing plate, image display device, and method for manufacturing a polarizing plate. 〔1〕 A polarizing plate having a polarizing element in which iodine is adsorbed and oriented in a polyvinyl alcohol-based resin layer and a transparent protective film, having a urea-based compound-containing layer containing at least one urea-based compound selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives, wherein the water content rate of the polarizing element is equal to or higher than the equilibrium water content rate at a temperature of 20°C and a relative humidity of 30% and equal to or lower than the equilibrium water content rate at a temperature of 20°C and a relative humidity of 50%. 〔2〕 A polarizing plate having a polarizing element in which iodine is adsorbed and oriented in a polyvinyl alcohol-based resin layer and a transparent protective film, having a urea-based compound-containing layer containing at least one urea-based compound selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives, a polarizing plate, wherein the water content of the polarizing plate is equal to or higher than the equilibrium water content at a temperature of 20°C and a relative humidity of 30%, and equal to or lower than the equilibrium water content at a temperature of 20°C and a relative humidity of 50%. 〔3〕 The polarizing plate according to 〔1〕 or 〔2〕, wherein the urea-based compound-containing layer 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 urea-based compound-containing layer is in contact with the polarizing element. 〔5〕 The polarizing plate according to any one of 〔1〕 to 〔4〕, wherein the urea-based compound-containing layer is an adhesive layer. 〔6〕 The polarizing plate according to 〔5〕, wherein the urea-based compound-containing layer contains a polyvinyl alcohol-based resin. 〔7〕 The polarizing plate according to 〔6〕, wherein in the urea-based compound-containing layer, the total content of the urea-based compound is 0.1 part by mass or more and 400 parts by mass or less with respect to 100 parts by mass of the polyvinyl alcohol-based resin. 〔8〕 The polarizing plate according to any one of 〔5〕 to 〔7〕, wherein the thickness of the urea-based compound-containing layer is 0.01 to 7 μm. 〔9〕 A polarizing plate having a polarizing element formed by adsorbing and aligning iodine on a polyvinyl alcohol-based resin layer and a transparent protective film, wherein the polarizing element contains at least one urea-based compound selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives, a polarizing plate, wherein the water content of the polarizing element is equal to or higher than the equilibrium water content at a temperature of 20°C and a relative humidity of 30%, and equal to or lower than the equilibrium water content at a temperature of 20°C and a relative humidity of 50%. 〔10〕 A polarizing plate having a polarizing element formed by adsorbing and aligning iodine on a polyvinyl alcohol-based resin layer and a transparent protective film, wherein the polarizing element contains at least one urea-based compound selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives, A polarizing plate in which 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%. 〔11〕 The polarizing plate is used in an image display device, In the image display device, layers other than air layers are provided in contact with both surfaces of the polarizing plate. The polarizing plate according to any one of 〔1〕~〔10〕. 〔12〕 An image display device including an image display cell, a first adhesive layer laminated on the viewing-side surface of the image display cell, and the polarizing plate according to any one of 〔1〕~〔11〕 laminated on the viewing-side surface of the first adhesive layer. 〔13〕 The image display device according to 〔12〕, further including a second 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 adhesive layer. 〔14〕 The image display device according to 〔13〕, wherein the transparent member is a glass plate or a transparent resin plate. 〔15〕 The image display device according to 〔13〕, wherein the transparent member is a touch panel. 〔16〕 A method for manufacturing the polarizing plate according to 〔1〕 or 〔9〕, The method for manufacturing a polarizing plate includes a moisture content adjustment step of adjusting the moisture content of the polarizing element so that it 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%. 〔17〕 A method for manufacturing the polarizing plate according to 〔2〕 or 〔10〕, The method for manufacturing a polarizing plate includes a moisture content adjustment step of adjusting the moisture content of the polarizing plate so that it 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%.

Advantages of the Invention

[0010] According to the present invention, even when used in an image display device having an interlayer filling structure, it is possible to provide a polarizing plate with a small decrease in transmittance in a high-temperature environment and excellent high-temperature durability. Furthermore, by using the polarizing plate of the present invention, it is possible to provide an image display device in which a decrease in transmittance in a high-temperature environment is suppressed.

Mode for Carrying Out the Invention

[0011] ≪First Embodiment≫ The polarizing plate of the first embodiment in the present invention includes a polarizing element formed by adsorbing and aligning iodine in a polyvinyl alcohol-based resin layer, a urea-based compound layer containing at least one urea-based compound selected from urea, urea derivatives, thiourea, and thiourea derivatives, and a transparent protective film. The polarizing plate according to the present 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 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 equal to or lower than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 50%.

[0012] The polarizing plate of the present embodiment has at least one of the above characteristics (a) and (b), and further has a urea-based compound-containing layer. As a component of an image display device having an interlayer filling structure, even when exposed to a high-temperature environment for a long time, a decrease in the single transmittance can be suppressed. The polarizing plate of the present embodiment has a urea-based compound-containing layer, so that a decrease in the degree of polarization can be suppressed even when the polarizing plate is exposed to a high-temperature environment. When two polarizing plates are arranged and used in a cross-Nicol relationship, when the degree of polarization of the polarizing plate decreases, light leakage (hereinafter also referred to as "cross leakage") is likely to occur. However, according to the present invention, since the degree of polarization is less likely to decrease even when exposed to a high-temperature environment, cross leakage is also easily suppressed.

[0013] [Polarizing Element] As the polarizing element formed by adsorbing and aligning iodine in the polyvinyl alcohol (hereinafter also referred to as PVA) - based resin layer of the present invention, a well-known polarizing element can be used. Such a polarizing element is generally formed by using a PVA-based resin film, dyeing this PVA-based resin film with iodine, and uniaxially stretching it.

[0014] As described above, generally, a PVA-based resin obtained by saponifying a polyvinyl acetate-based resin is used. The degree of saponification is about 85 mol% or more, preferably about 90 mol% or more, more preferably about 99 mol% to 100 mol%. Examples of the polyvinyl acetate-based resin include polyvinyl acetate which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith, such as ethylene-vinyl acetate copolymers. Examples of other monomers copolymerizable therewith include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and the like. The degree of polymerization of the PVA-based resin is 1000 to 10000, preferably 1500 to 5000. This PVA-based resin may be modified, for example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral, etc. modified with aldehydes may also be used.

[0015] The method for manufacturing the polarizing element is not particularly limited, but a method of feeding out a polyvinyl alcohol-based resin film wound in a roll shape in advance and performing stretching, dyeing, crosslinking, etc., or a method including a step of producing a laminate of a polyvinyl alcohol-based resin and a stretching resin base material and performing stretching in the state of the laminate is typical. In the present invention, any of these methods can be used. These methods for manufacturing the polarizing element are described in paragraphs

[0109] to

[0128] of JP-A-2014-48497, and these methods can be used in the present embodiment. Further, the thickness of the polarizing element of the present embodiment is preferably 3 to 35 μm, more preferably 4 to 30 μm, and even more preferably 5 to 25 μm.

[0016] (Characteristic (a)) When having 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%. More preferably, it is equal to or lower than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 45%. Even more preferably, it is equal to or lower than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 42%. Most preferably, it is equal to or lower than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 38%. When it is lower than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30%, the handleability of the polarizing element deteriorates and it is prone to cracking. When the moisture content of the polarizing element exceeds the equilibrium moisture content at a temperature of 20°C and a relative humidity of 50%, the transmittance of the polarizing element is likely to decrease. It is presumed that this is because when the moisture content of the polarizer is high, the polyene formation of the PVA-based resin tends to proceed. The above moisture content of the polarizing element is the moisture content of the polarizing element in the polarizing plate.

[0017] As a method for confirming whether the moisture content of the polarizing element is within the range of being 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%, store it in an environment adjusted to the above temperature and relative humidity range. If there is no change in mass after a certain period of time, it can be regarded as having reached equilibrium with the environment. Alternatively, the equilibrium moisture content of the polarizing element in the environment adjusted to the above temperature and relative humidity range can be calculated in advance, and it can be confirmed by comparing the moisture content of the polarizing element with the pre-calculated equilibrium moisture content.

[0018] The method for manufacturing a polarizing element with a moisture content 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% is not particularly limited. For example, there are a method of storing the polarizing element in an environment adjusted to the above temperature and relative humidity range for 10 minutes or more and 3 hours or less, or a method of performing heat treatment at 30°C or higher and 90°C or lower.

[0019] As another preferred method for manufacturing the polarizing element having the above moisture content, a laminate in which a protective film is laminated on at least one side of the polarizing element, or a polarizing plate constituted by using the polarizing element, is stored in an environment adjusted to the above temperature and relative humidity range for 10 minutes or more and 120 hours or less, or a method of performing a heat treatment at 30°C or more and 90°C or less can be mentioned. When manufacturing an image display device employing a layer filling configuration, after storing an image display panel in which a polarizing plate is laminated on an image display cell in an environment adjusted to the above temperature and relative humidity range for 10 minutes or more and 3 hours or less or heating at 30°C or more and 90°C or less, a front panel may be bonded thereto.

[0020] It is preferable that the moisture content of the polarizing element is adjusted to be within the above numerical range at the material stage of a material that is the polarizing element alone or a laminate of the polarizing element and the protective film and is used to constitute the polarizing plate. When the moisture content is adjusted after the polarizing plate is constituted, curling may become too large and problems may easily occur when bonding to the image display cell. By constituting the polarizing plate using a polarizing element adjusted to have the above moisture content at the material stage before constituting the polarizing plate, a polarizing plate including a polarizing element whose moisture content satisfies the above numerical range can be easily constituted. Even when the moisture content of the polarizing element in the polarizing plate is adjusted to be within the above numerical range in a state where the polarizing plate is bonded to the image display cell. In this case, since the polarizing plate is bonded to the image display cell, curling is less likely to occur.

[0021] (Feature (b)) When having the feature (b), the moisture content of the polarizing plate is not less than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30%, and not more 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 not more than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 45%, more preferably not more than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 42%, and still more preferably not more than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 38%. When 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 handleability of the polarizing plate deteriorates and it is likely to crack. When the moisture content of the polarizing plate exceeds the equilibrium moisture content at a temperature of 20°C and a relative humidity of 50%, the transmittance of the polarizing element is likely to decrease. It is presumed that this is because when the moisture content of the polarizing plate is high, the polyene formation of the PVA-based resin tends to proceed.

[0022] As a method for confirming whether the moisture content of the polarizing plate is within the range not less than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30% and not more than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 50%, store it in an environment adjusted to the above temperature and relative humidity range, and if there is no change in mass for a certain period of time, it can be regarded as having reached equilibrium with the environment, or calculate in advance the equilibrium moisture content of the polarizing plate in the environment adjusted to the above temperature and relative humidity range, and confirm by comparing the moisture content of the polarizing plate with the pre-calculated equilibrium moisture content.

[0023] The method for manufacturing a polarizing plate having a moisture content not less than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30% and not more than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 50% is not particularly limited. For example, there are a method of storing the polarizing plate in an environment adjusted to the above temperature and relative humidity range for 10 minutes or more and 3 hours or less, or a method of performing heat treatment at 30°C or more and 90°C or less.

[0024] When manufacturing an image display device adopting an interlayer filling structure, after laminating the polarizing plate on the image display cell to obtain an image display panel, storing it in an environment adjusted to the above temperature and relative humidity range for 10 minutes or more and 3 hours or less or heating it at 30°C or more and 90°C or less, the front panel may be bonded.

[0025] [Urea-based compound-containing layer] The polarizing plate of the present invention has a urea-based compound-containing layer containing at least one urea-based compound selected from urea, urea derivatives, thiourea, and thiourea derivatives. The urea-based compound-containing layer is not limited as long as it is a layer containing a urea-based compound, and examples thereof include an adhesive layer and a cured layer. The urea-based compound-containing layer may or may not be in contact with the polarizing element, but it is preferably in contact with the polarizing element from the viewpoint of further suppressing a decrease in transmittance in a high-temperature environment. In the present invention, from the viewpoint of productivity, it is preferable that the adhesive layer is a urea-based compound-containing layer. The adhesive layer is formed by the following adhesives. As an adhesive layer that is a urea-based compound-containing layer, an adhesive layer for bonding a polarizing element and a protective film is exemplified. In addition, the configuration when the urea-based compound-containing layer is other than the adhesive layer will be described later.

[0026] <Adhesive layer> Any suitable adhesive can be used for the adhesive constituting the adhesive layer for bonding the protective film to the polarizing element. Specifically, as the adhesive, an aqueous adhesive, a solvent-based adhesive, an active energy ray-curable type, etc. can be used, but an aqueous adhesive is preferable. When the adhesive layer is a urea-based compound-containing layer, the adhesive contains at least one urea-based compound selected from urea, urea derivatives, thiourea, and thiourea derivatives. The thickness at the time of coating the above adhesive can be set to any appropriate value. For example, it is set so that an adhesive layer having a desired thickness can be obtained after curing or heating (drying). The thickness of the adhesive layer is preferably 0.01 μm to 7 μm, more preferably 0.01 μm to 5 μm, still more preferably 0.01 μm to 2 μm, and most preferably 0.01 μm to 1 μm.

[0027] (Aqueous adhesive) Also, as the aqueous adhesive, any suitable aqueous adhesive can be employed. Among them, an aqueous adhesive containing a PVA-based resin (PVA-based adhesive) is preferably used. From the viewpoint of adhesiveness, the average degree of polymerization of the PVA-based resin contained in the aqueous adhesive is preferably about 100 to 5500, more preferably 1000 to 4500. The average degree of saponification is preferably about 85 mol% to 100 mol% from the viewpoint of adhesiveness, and more preferably 90 mol% to 100 mol%.

[0028] As the PVA-based resin contained in the aqueous adhesive, those containing an acetoacetyl group are preferred, because they have excellent adhesion between the PVA-based resin layer and the protective film and excellent durability. The acetoacetyl group-containing PVA-based resin can be obtained, for example, by reacting a PVA-based resin with diketene by any method. The degree of acetoacetyl group modification of the acetoacetyl group-containing PVA-based resin is typically 0.1 mol% or more, preferably about 0.1 mol% to 20 mol%. The resin concentration of the aqueous adhesive is preferably 0.1% by weight to 15% by weight, more preferably 0.5% by weight to 10% by weight.

[0029] (Crosslinking agent, solvent) The water-soluble PVA-based adhesive that can be preferably used in the present invention can also contain a crosslinking agent as necessary in addition to the above PVA-based resin and urea-based compound. As the crosslinking agent, known crosslinking agents can be used. For example, water-soluble epoxy compounds, dialdehydes, isocyanates, etc. can be mentioned.

[0030] When the PVA-based resin is an acetoacetyl group-containing PVA-based resin, it is preferably any one of glyoxal, glyoxylate, and methylol melamine as the crosslinking agent, preferably any one of glyoxal and glyoxylate, and particularly preferably glyoxal.

[0031] In addition, the water-soluble PVA-based adhesive of the present invention may contain an organic solvent. In that case, alcohols are preferable in terms of being miscible with water, and methanol or ethanol is more preferable among alcohols. 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 also a preferred embodiment to dissolve the urea derivative in alcohol, prepare an alcohol solution of the urea derivative, and then add the alcohol solution of the urea derivative to the PVA aqueous solution to prepare the adhesive.

[0032] (Reactive energy ray curable adhesive) As the above reactive energy ray curable adhesive, any suitable adhesive can be used as long as it can be cured by irradiation with reactive energy rays. Examples of the reactive energy ray curable adhesive include ultraviolet curable adhesives, electron beam curable adhesives, etc. Specific examples of the curing type of the reactive energy ray curable adhesive include radical curing type, cationic curing type, anionic curing type, and combinations thereof (for example, a hybrid of radical curing type and cationic curing type).

[0033] As the above reactive energy ray curable adhesive, for example, an adhesive containing a compound (for example, a monomer and / or an oligomer) having a radically polymerizable group such as a (meth)acrylate group or a (meth)acrylamide group as a curing component can be mentioned. Specific examples of the above reactive energy ray curable adhesive and its curing method are described in, for example, JP-A-2012-144690.

[0034] (Urea-based compound) When the adhesive layer is a urea-based compound-containing layer, the adhesive layer contains at least one urea-based compound selected from urea, urea derivatives, thiourea, and thiourea derivatives. As a method of incorporating a urea-based compound into the adhesive layer, it is preferable to incorporate the urea-based compound into the above-described adhesive. Incidentally, in the process of forming the adhesive layer from the adhesive through a drying process or the like, a part of the urea-based compound may move from the adhesive layer to a polarizing element or the like. Urea-based compounds include water-soluble and poorly water-soluble ones, and either type of urea-based compound can be used in the present invention. When using a poorly water-soluble urea-based compound in a water-soluble adhesive, it is preferable to devise a dispersion method so that no haze increase or the like occurs after forming the adhesive layer.

[0035] When the adhesive is an aqueous adhesive containing a PVA resin, the addition amount of the urea-based compound is preferably 0.1 to 400 parts by mass, more preferably 1 to 200 parts by mass, and even more preferably 3 to 100 parts by mass with respect to 100 parts by mass of PVA.

[0036] (Urea derivative) A urea derivative is a compound in which at least one of the four hydrogen atoms of a urea molecule is substituted with a substituent. In this case, there is no particular limitation on the substituent, but a substituent composed of a carbon atom, a hydrogen atom, and an oxygen atom is preferable.

[0037] Specific examples of urea derivatives include, as monosubstituted ureas, 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, p-tolylurea. As disubstituted ureas, 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), tetrahydro-2-pyrimidinone (propyleneurea). Examples of the tetra-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.

[0038] (Thiourea derivatives) A thiourea derivative is 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 composed of carbon atoms, hydrogen atoms, and oxygen atoms.

[0039] Specific examples of the thiourea derivatives include, as the mono-substituted thioureas, N-methylthiourea, ethylthiourea, propylthiourea, isopropylthiourea, 1-butylthiourea, cyclohexylthiourea, N-acetylthiourea, N-allylthiourea, (2-methoxyethyl)thiourea, N-phenylthiourea, (4-methoxyphenyl)thiourea, N-(2-methoxyphenyl)thiourea, N-(1-naphthyl)thiourea, (2-pyridyl)thiourea, o-tolylthiourea, and p-tolylthiourea. Examples of the di-substituted 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 ethylene thiourea. Examples of the tri-substituted thioureas include trimethylthiourea, and examples of the tetra-substituted thioureas include tetramethylthiourea and 1,1,3,3-tetraethylthiourea.

[0040] Among urea-based compounds, when used in an image display device having an intercalation structure, a urea derivative or a thiourea derivative is preferable, and a urea derivative is more preferable, in that the decrease in transmittance in a high-temperature environment is suppressed and the decrease in polarization degree is small (the point where cross leakage is suppressed). Among urea derivatives, it is preferably a mono-substituted urea or a di-substituted urea, and more preferably a mono-substituted urea. Di-substituted ureas include 1,1-substituted urea and 1,3-substituted urea, and 1,3-substituted urea is more preferable.

[0041] [Transparent protective film] The transparent protective film (hereinafter also simply referred to as "protective film") used in the present invention is bonded to at least one side of the polarizing element via an adhesive layer. This transparent protective film is bonded to one or both sides of the polarizing element, and it is more preferable that it is bonded to both sides. In one embodiment, the protective film is bonded to the polarizing element via an adhesive layer which is a urea-based compound-containing layer. Further, in a configuration in which protective films are bonded to both sides of the polarizing element via adhesive layers, among the adhesive layers on both sides of the polarizing element, only one of the adhesive layers on one side may be the urea-based compound-containing layer of the present invention, but it is more preferable that both of the adhesive layers on both sides are the urea-based compound-containing layers of the present invention.

[0042] In recent years, in order to meet the demand for thinning of polarizing plates, polarizing plates having a protective film only on one side of a polarizing element have been developed. Also in this configuration, it is preferable to laminate the protective film via an adhesive layer which is the urea-based compound-containing layer of the present invention. As a method for producing a polarizing plate having a protective film only on one side of a polarizing element, a method of first producing a polarizing plate in which protective films are bonded to both sides via adhesive layers and then peeling off one of the protective films can be considered. When such a manufacturing method is used, only one of the adhesive layers on either side may be the urea-based compound-containing layer of the present invention, but it is more preferable that the urea-based compound-containing layer of the present invention is used on both sides of the polarizing element. In addition, when the urea compound-containing layer of the present invention is used only on one side of the polarizing element as an adhesive layer, it is preferable that the adhesive layer on the film side that does not peel off is the urea compound-containing layer of the present invention.

[0043] The protective film may simultaneously have other optical functions, and may further be formed in a laminated structure in which other layers are laminated. At this time, the film thickness of the protective film is preferably thin from the viewpoint of optical characteristics, but if it is too thin, the strength will decrease and the processability will be poor. An appropriate film thickness is 5 to 100 μm, preferably 10 to 80 μm, more preferably 15 to 70 μm.

[0044] As the protective film, a film such as a cellulose acylate resin 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 can be used. In the case of a configuration in which protective films are provided on both sides of the polarizing element, when using an aqueous adhesive such as a PVA adhesive for bonding, at least one of the protective films is preferably either a cellulose acylate film or a (meth)acrylic polymer film from the viewpoint of moisture permeability, and among them, a cellulose acylate film is preferable.

[0045] At least one of the protective films may have a retardation function for the purpose of viewing angle compensation or the like. In that case, the film itself may have a retardation function, may separately have a retardation layer, or may be a combination of both. In addition, although the film having a retardation function has been described in a configuration in which it is directly bonded to the polarizing element via an adhesive, a configuration in which it is bonded via another protective film bonded to the polarizing element via an adhesive or an adhesive is also acceptable.

[0046] [Method for manufacturing a polarizing plate] The manufacturing method of the polarizing plate according to this embodiment includes a lamination step of laminating a polarizing element and a urea-based compound-containing layer containing at least one urea-based compound selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives, and a moisture content adjustment step. In the moisture content adjustment step, when manufacturing a polarizing plate having feature (a), the moisture content of the polarizing element is adjusted so that it 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 above. In the moisture content adjustment step, when manufacturing a polarizing plate having feature (b), the moisture content of the polarizing plate is adjusted so that it 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 above. The order of the lamination step and the moisture content adjustment step is not limited, and the lamination step and the moisture content adjustment step may be performed in parallel.

[0047] [Configuration of Image Display Device] The polarizing plate of the present invention 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 having a layer filling structure in which layers other than air layers are in contact with both surfaces of the polarizing plate, the transmittance is likely to decrease in a high-temperature environment. In an image display device using the polarizing plate of the present invention, even in a layer filling structure, a decrease in the transmittance of the polarizing plate in a high-temperature environment can be suppressed. As an example of the configuration of the image display device, there 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 invention is preferably used in an image display device having a layer filling structure in which a transparent member is disposed on the viewing side of the image display device, the polarizing plate and the image display cell are bonded together by a first adhesive layer, and the polarizing plate and the transparent member are bonded together by a second adhesive layer. In this specification, either one or both of the first adhesive layer and the second adhesive layer may sometimes be simply referred to as an "adhesive layer". Note that the members used for bonding the polarizing plate and the image display cell and for bonding the polarizing plate and the transparent member are not limited to the adhesive layer and may be an adhesive layer.

[0048] <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 transflective 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, a polarizing plate is also disposed on the side opposite to the viewing side of the image display cell (liquid crystal display device), and a light source is further disposed. It is preferable that the polarizing plate on the light source side and the liquid crystal cell are bonded together via an appropriate adhesive layer. As the driving method of the liquid crystal cell, for example, any type such as a VA mode, an IPS mode, a TN mode, an STN mode, or a bend alignment (π type) can be used.

[0049] As the organic EL cell, those in which a transparent electrode, an organic light-emitting layer, and a metal electrode are sequentially laminated on a transparent substrate to form a light-emitting body (organic electroluminescence light-emitting body) are preferably used. The organic light-emitting layer is a laminate of various organic thin films. For example, 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 these light-emitting layers 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, etc. Various layer configurations can be adopted.

[0050] <Lamination of Image Display Cell and Polarizing Plate> For the lamination of the image display cell and the polarizing plate, an adhesive layer (adhesive sheet) is preferably used. Among them, the method of laminating a polarizing plate with an adhesive layer provided on one surface of the polarizing plate to the image display cell is preferable from the viewpoint of workability and the like. The attachment of the adhesive layer to the polarizing plate can be performed by an appropriate method. Examples thereof include, for example, preparing an adhesive solution of about 10 to 40% by weight in which a base polymer or its composition is dissolved or dispersed in a solvent composed of a single substance or a mixture of appropriate solvents such as toluene and ethyl acetate, and directly attaching it to the polarizing plate by an appropriate spreading method such as a casting method or a coating method, or forming an adhesive layer on a separator according to the above and transferring it to the polarizing plate.

[0051] <Adhesive Layer> The adhesive layer is described in paragraphs

[0103] to

[0143] of JP-A-2018-025765, and these adhesives can be used in the present invention.

[0052] <Transparent Member> Examples of the transparent member disposed on the viewing side of the image display device include a front panel (window layer), a touch panel, and the like. As the front panel, a front panel having appropriate mechanical strength and thickness is used. Examples of such a front panel include a transparent resin plate such as an acrylic resin or a polycarbonate resin plate, or a glass plate. A functional layer such as an antireflection layer may be laminated on the viewing side of the front panel. Further, when the front panel is a transparent resin plate, a hard coat layer may be laminated to increase physical strength, or a low moisture permeability layer may be laminated to reduce the moisture permeability. As the touch panel, various touch panels such as a resistive film type, a capacitance type, an optical type, and an ultrasonic type, or a glass plate or a transparent resin plate having a touch sensor function is used. When a capacitance type touch panel is used as the transparent member, it is preferable to provide a front panel made of glass or a transparent resin plate on the viewing side further than the touch panel.

[0053] <Lamination of Polarizing Plate and Transparent Member> For laminating the polarizing plate and the transparent member, an adhesive or a UV curable adhesive is preferably used. When an adhesive is used, the adhesive can be attached by an appropriate method. Specific attachment methods include, for example, the method of attaching the adhesive layer used in the lamination of the aforementioned image display cell and the polarizing plate.

[0054] When a UV curable adhesive is used, for the purpose of preventing the spread of the adhesive solution before curing, a dam material is provided so as to surround the peripheral portion on the image display panel, the transparent member is placed on the dam material, and a method of injecting the adhesive solution is preferably used. After injecting the adhesive solution, alignment and defoaming are performed as necessary, and then UV light is irradiated for curing.

[0055] Next, the urea compound-containing layer other than the adhesive layer will be described.

[0056] [Urea Compound-Containing Layer (Other than Adhesive Layer)] The urea-based compound-containing layer preferably contains at least one urea-based compound and a binder. Examples of the binder include a polymer binder, a thermosetting resin binder, and an active energy ray-curable resin binder. In the present invention, any binder can be preferably used.

[0057] The thickness of the urea-based compound-containing layer is preferably from 0.1 to 20 μm, more preferably from 0.5 to 15 μm, and still more preferably from 1 to 10 μm. The urea-based compound-containing layer may be directly laminated on the polarizing element or laminated via other layers. However, it is preferable that the urea-based compound-containing layer is directly laminated and in contact with the polarizing element in terms of easily suppressing a decrease in transmittance in a high-temperature environment. A polarizing plate having a urea-based compound-containing layer other than the adhesive layer preferably has a transparent protective film via an adhesive layer on at least one surface of the polarizing element in terms of increasing the physical strength of the polarizing plate. At this time, 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.

[0058] As described in the description of the protective film, in recent years, in order to meet the demand for thinning of polarizing plates, a polarizing plate having a protective film only on one surface of a polarizing element (hereinafter, also referred to as a "polarizing plate with a single-sided protective film") has been developed. In such a configuration, attempts have been made to laminate a cured layer on the surface of the polarizing element that does not have a protective film for the purpose of increasing the physical strength and the like. (For example, Japanese Patent Application Laid-Open No. 2011-221185)

[0059] In this embodiment, it is also one of the preferred embodiments to form a urea-based compound-containing layer by incorporating a urea-based compound into 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 JP-A No. 2017-075986 describe a method for 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 one of the preferred embodiments of this embodiment to incorporate a water-soluble urea-based compound into such a composition to form a urea-based compound-containing layer.

[0060] <<Second Embodiment>> The polarizing plate according to the second embodiment of the present invention is formed by adsorbing and aligning iodine in a polyvinyl alcohol-based resin layer, and includes a polarizing element containing at least one urea-based compound selected from urea, urea derivatives, thiourea, and thiourea derivatives, and a transparent protective film. 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 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 equal to or lower than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 50%.

[0061] The polarizing plate of this embodiment has at least one of the above characteristics (a) and (b). Further, since the polarizing element contains a urea-based compound, it is used in an image display device having an interlayer filling structure and can suppress a decrease in the single transmittance even when exposed to a high-temperature environment for a long time. The polarizing plate of this embodiment can suppress a decrease in the degree of polarization even when the polarizing plate is exposed to a high-temperature environment because the polarizing element contains a urea-based compound, and it is also easy to suppress cross leakage.

[0062] The characteristics (a) and (b) are the same as the characteristics (a) and (b) in the first embodiment.

[0063] In the method for manufacturing a polarizing element according to the present embodiment, in the method for manufacturing a polarizing element described in the first embodiment, the method includes a step of incorporating a urea-based compound into the polarizing element. As a method of incorporating a urea-based compound into the polarizing element, a polarizing element containing a urea-based compound can be obtained by manufacturing a polarizing element through steps of applying a urea-based compound-containing solution to at least one side of the polarizing element and drying it. In the manufacturing process of the polarizing element, the urea-based compound can be incorporated into the polarizing element by a method of immersing a PVA-based resin layer in a treatment solution containing a urea-based compound, or a method of spraying, flowing down, or dropping the treatment solution onto the PVA-based resin layer. Among these, the method of immersing a PVA-based resin layer in a treatment solution containing a urea-based compound is preferably used.

[0064] The step of immersing a PVA-based resin layer in a treatment solution containing a urea-based compound may be performed simultaneously with steps such as swelling, stretching, dyeing, crosslinking, and washing in the manufacturing method of the polarizing element, or may be provided separately from these steps. The step of incorporating a urea-based compound into the PVA-based resin layer is preferably performed after dyeing the PVA-based resin layer with iodine, and more preferably performed simultaneously with the crosslinking step after dyeing. According to such a method, the hue change can be small, and the influence on the optical properties of the polarizing element can be reduced.

[0065] Regarding the type and content of the urea-based compound contained in the polarizing element in the present embodiment, the description of the urea-based compound-containing layer in the first embodiment is applicable. In addition, the polarizing element according to the present embodiment can also be used as the polarizing element of the polarizing plate in the first embodiment. Regarding other configurations of the polarizing plate in the present embodiment, the configuration is the same as that of the first embodiment except that the urea-based compound-containing layer in the first embodiment is an arbitrary component.

[0066] [Urea-based compound solution] The solvent of the urea-based compound-containing solution used in this embodiment is preferably water, an organic solvent, or a mixture thereof, and more preferably water or a mixed solvent of water and alcohol. When it is a mixed solvent of water and alcohol, the alcohol is preferably either methanol or ethanol. Regarding the urea-based compound, as described in the first embodiment, the urea-based compound is preferably water-soluble in that it is difficult for the urea-based compound to precipitate on the surface of the polarizing element after drying.

[0067] [Method for manufacturing a polarizing plate] The method for manufacturing a polarizing plate according to this embodiment includes a moisture content adjustment step, which is the same as the method for manufacturing a polarizing plate in the first embodiment.

Examples

[0068] Hereinafter, the present invention will be specifically described based on examples. The materials, reagents, amounts of substances and their ratios, operations, etc. shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the present invention is not limited to and restricted by the following examples.

[0069] [Production of Polarizing Element 1] A polyvinyl alcohol film with a thickness of 40 μm made of polyvinyl alcohol having an average degree of polymerization of about 2,400 and a saponification degree of 99.9 mol% or more was uniaxially stretched about 5 times by a dry method, and then, while maintaining a strained state, it was immersed in pure water at 60°C for 1 minute, and then immersed in an aqueous solution having a weight ratio of iodine / potassium iodide / water of 0.05 / 5 / 100 at 28°C for 60 seconds. Thereafter, it was immersed in an aqueous solution having a weight ratio of potassium iodide / boric acid / water of 8.5 / 8.5 / 100 at 72°C for 300 seconds. Subsequently, it was washed with pure water at 26°C for 20 seconds and then dried at 65°C to obtain a polarizing element with a thickness of 15 μm in which iodine was adsorbed and oriented on the polyvinyl alcohol.

[0070] [Preparation of PVA Solution for Adhesive] 50 g of a modified PVA-based resin containing an acetoacetyl group (manufactured by Mitsubishi Chemical Corporation: Gosenex 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 an adhesive.

[0071] (Preparation of urea-based compound solution) 10 g of urea was added to 90 g of pure water to obtain a 10 wt% aqueous urea solution (Solution 1). Similarly, according to Table 1, urea was replaced with the urea-based compounds described in Table 1 to prepare Urea Solutions 2 to 4.

[0072]

Table 1

[0073] For urea, methylurea, ethylurea, and tetrahydro-2-pyrimidinone used above, reagents from Tokyo Chemical Industry Co., Ltd. were used.

[0074] (Preparation of Adhesive 1 for Polarizing Plate) The PVA solution for an adhesive, Urea Solution 1, pure water, and methanol prepared above were blended so that the PVA concentration was 3.0%, the methanol concentration was 20%, and the urea concentration was 0.5% to obtain Adhesive 1 for a polarizing plate.

[0075] (Preparation of Adhesive 2 for Polarizing Plate) Similarly, the PVA solution for an adhesive, Urea Solution 2 described in Table 1, pure water, and methanol were blended so that the PVA concentration was 3.0%, the methanol concentration was 20%, and the methylurea concentration was 0.7% to obtain Adhesive 2 for a polarizing plate.

[0076] (Preparation of Adhesive 3 for Polarizing Plate) Similarly, the PVA solution for an adhesive, Urea Solution 3 described in Table 1, pure water, and methanol were blended so that the PVA concentration was 3.0%, the methanol concentration was 20%, and the ethylurea concentration was 1.0% to obtain Adhesive 3 for a polarizing plate.

[0077] (Preparation of Adhesive 4 for Polarizing Plate) Similarly, an adhesive PVA solution, urea solution 4 described in Table 1, pure water, and methanol were blended so that the PVA concentration was 3.0%, the methanol concentration was 20%, and the tetrahydro-2-pyrimidinone concentration was 1.5%, to obtain an adhesive for polarizing plate 4.

[0078] (Preparation of Adhesive for Polarizing Plate 5) Similarly, an adhesive PVA solution, pure water, and methanol were blended so that the PVA concentration was 3.0% and the methanol concentration was 20%, to obtain an adhesive for polarizing plate 5.

[0079] (Saponification of Cellulose Acetate Film) A commercially available cellulose acetate film TD40 (manufactured by Fuji Film Co., Ltd.: film thickness 40 μm) was immersed in a 1.5 mol / L NaOH aqueous solution (saponification solution) maintained at 55°C for 2 minutes, then the film was washed with water. After that, it was immersed in a 0.05 mol / L sulfuric acid aqueous solution at 25°C for 30 seconds, and then further passed through a water washing bath under running water for 30 seconds to make the film in a neutral state. Then, draining with an air knife was repeated 3 times. After draining the water, it was left in a drying zone at 70°C for 15 seconds for drying, to prepare a saponified film.

[0080] (Preparation of Polarizing Plate 1) On both sides of the polarizing element 1, the saponified cellulose acetate film prepared above was adjusted via the adhesive for polarizing plate 1 so that the thickness of the dried adhesive layer was 100 nm on both sides, and after laminating using a roll laminator, it was dried at 60°C for 10 minutes to obtain a polarizing plate 1 with cellulose acetate films on both sides.

[0081] (Preparation of Polarizing Plates 2 to 5) Polarizing plates 2 to 5 were prepared in the same manner as polarizing plate 1, except that the adhesive for polarizing plate 1 was replaced with adhesives for polarizing plates 2 to 5.

[0082] (Adjustment of Water Content of Polarizing Plate (Polarizing Element)) The polarizing plates 1 to 5 obtained above were stored at a temperature of 20°C under conditions of relative humidity of 30%, 35%, 40%, 45%, 50% or 55% for 72 hours. The moisture content was measured using the Karl Fischer method at 66 hours, 69 hours and 72 hours of storage. Under any of the humidity conditions, the moisture content values did not change at 66 hours, 69 hours and 72 hours of storage. Therefore, it can be considered that the moisture content of the polarizing plates 1 to 5 is the same as the equilibrium moisture content of the 72-hour storage environment used in this experimental example. When the moisture content of the polarizing plate reaches equilibrium in a certain storage environment, it can be considered that the moisture content of the polarizing element in the polarizing plate has also reached equilibrium in that storage environment. Also, when the moisture content of the polarizing element in the polarizing plate reaches equilibrium in a certain storage environment, it can be considered that the moisture content of the polarizing plate has also reached equilibrium in that storage environment.

[0083] (Fabrication of Optical Laminate 1) Referring to the examples of JP-A-2018-025765, an acrylic adhesive (manufacturer: Lintec Corporation, product number: #7) was applied to both sides of the polarizing plate 1 fabricated above, thereby fabricating an optical laminate 1 having adhesive layers (first adhesive layer and second adhesive layer) with a thickness of 25 μm on both sides. (Fabrication of Optical Laminates 2 to 5) Optical laminates 2 to 5 were fabricated in the same manner as optical laminate 1, except that polarizing plate 1 was replaced with polarizing plates 2 to 5.

[0084] [Examples 1 to 9, Comparative Examples 1 to 6] In Examples 1 to 9 and Comparative Examples 1 to 6, using the optical laminates shown in Table 2, the optical laminates used were stored at a temperature of 20°C under conditions of relative humidity of 35%, 40%, 45%, 50% or 55% for 72 hours so that the moisture content of the optical laminates used would be the equilibrium moisture content of the environments shown in Table 2. The moisture content of the optical laminate can be considered to have reached equilibrium with the moisture content of the storage environment, and the moisture content of the polarizing plate and the polarizing element in the optical laminate can also be considered to be the same as the moisture content of the optical laminate.

[0085] (Inspection Polarizing Plate 1) An acrylic adhesive (manufacturer: Lintec Corporation, product number: #7) was laminated only on one side of the polarizing plate 1 to produce a polarizing plate 1 for inspection. The polarizing plate 1 for inspection thus produced was cut into a size of 50 mm × 100 mm so that the short side was parallel to the absorption axis, and the surface of the adhesive layer was bonded to non-alkali glass [trade name “EAGLE XG”, manufactured by Corning Incorporated] to produce a sample 1 for cross evaluation.

[0086] [Evaluation of single transmittance after high-temperature durability test (105 °C)] The optical laminates 1 to 5 produced above were each cut into a size of 50 mm × 100 mm so that the long side was parallel to the absorption axis, and evaluation samples were produced by bonding the surfaces of the first adhesive layer and the second adhesive layer to non-alkali glass [trade name “EAGLE XG”, manufactured by Corning Incorporated]. This evaluation sample was subjected to autoclave treatment at a temperature of 50 °C and a pressure of 5 kgf / cm 2 (490.3 kPa) for 1 hour, and then left to stand for 24 hours in an environment of a temperature of 23 °C and a relative humidity of 55%. Then, the transmittance was measured (initial value), stored in a heating environment at a temperature of 105 °C, and the transmittance was measured every 50 hours up to 100 to 200 hours. Evaluation was performed according to the following criteria based on the time when the transmittance decrease reached 5% or more with respect to the initial value. The results obtained are shown in Table 2. Those with a transmittance decrease of 5% or less after 200 hours: A Those with a transmittance decrease reaching 5% or more after 150 to 200 hours: B Those with a transmittance decrease reaching 5% or more after 100 to 150 hours: C Those with a transmittance decrease of 5% or more after 100 hours: D

[0087] [Evaluation of cross peeling after high-temperature durability test] After evaluating the single transmittance evaluation sample after high-temperature durability for 200 hours, the above optical laminate and the cross-evaluation sample 1 not put into the heating environment were arranged in a cross-Nicol state and placed on the backlight. The surroundings were shielded from light, and the cross leakage was visually evaluated according to the following criteria. Samples with a single transmittance reduction of 5% or more were excluded from the cross leakage evaluation because of coloring due to polyene formation. Those with no cross leakage visible at all: A Those with hardly any cross leakage visible: B Those with a slight cross leakage visible: C Those with clear cross leakage visible: D

[0088] [Table 2]

Claims

1. A polarizing plate having a polarizing element in which iodine is adsorbed and aligned in a polyvinyl alcohol-based resin layer, and a transparent protective film, a urea-based compound-containing layer containing at least one urea-based compound selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives; The polarizing element has a moisture content 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 38%.

2. A polarizing plate having a polarizing element in which iodine is adsorbed and aligned in a polyvinyl alcohol-based resin layer, and a transparent protective film, a urea-based compound-containing layer containing at least one urea-based compound selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives; The polarizing plate has a moisture content 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 38%.

3. 3. The polarizing plate according to claim 1, wherein the urea compound-containing layer contains at least one urea compound selected from the group consisting of urea derivatives and thiourea derivatives.

4. 4. The polarizing plate according to claim 1, wherein the urea compound-containing layer is in contact with the polarizing element.

5. 5. The polarizing plate according to claim 1, wherein the urea compound-containing layer is an adhesive layer.

6. The polarizing plate according to claim 5 , wherein the urea compound-containing layer contains a polyvinyl alcohol-based resin.

7. 7. The polarizing plate according to claim 6, wherein the total content of the urea compounds in the urea compound-containing layer is from 0.1 parts by mass to 400 parts by mass with respect to 100 parts by mass of the polyvinyl alcohol resin.

8. 8. The polarizing plate according to claim 5, wherein the urea compound-containing layer has a thickness of 0.01 to 7 μm.

9. A polarizing plate having a polarizing element in which iodine is adsorbed and aligned in a polyvinyl alcohol-based resin layer, and a transparent protective film, the polarizing element contains at least one urea-based compound selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives; The polarizing element has a moisture content 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 38%.

10. A polarizing plate having a polarizing element in which iodine is adsorbed and aligned in a polyvinyl alcohol-based resin layer, and a transparent protective film, the polarizing element contains at least one urea-based compound selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives; The polarizing plate has a moisture content 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 38%.

11. The polarizing plate is used in an image display device, 11. The polarizing plate according to claim 1, wherein in the image display device, a layer other than an air layer is provided on both sides of the polarizing plate in contact with the both sides.

12. An image display device comprising: an image display cell; a first adhesive layer laminated on a viewing side surface of the image display cell; and a polarizing plate according to any one of claims 1 to 11 laminated on the viewing side surface of the first adhesive layer.

13. 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.

14. The image display device according to claim 13 , wherein the transparent member is a glass plate or a transparent resin plate.

15. The image display device according to claim 13 , wherein the transparent member is a touch panel.

16. A method for producing the polarizing plate according to claim 1 or 9, comprising the steps of: A method for producing a polarizing plate, comprising a moisture content adjusting step of adjusting the moisture content of the polarizing element so that it 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 38%.

17. A method for producing the polarizing plate according to claim 2 or 10, comprising the steps of: The method for producing a polarizing plate includes a moisture content adjusting step of adjusting the moisture content of the polarizing plate to be 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 38%.

Images