TWI894068B - Polarizing plate, and image display device using the polarizing plate - Google Patents

Abstract

An objective of this invention is to provide a polarizing plate and a manufacturing method thereof, wherein even when the polarizing plate is used in an image display device having an interlayer filling structure, the transmittance drop under high temperature environments is small and the durability is excellent. Furthermore, another objective of the present invention is to provide an image display device with improved durability in display characteristics under high temperature environments. The present invention provides a polarizing plate comprising: a polyvinyl alcohol resin polarizing element formed by iodine adsorption and alignment; a urea-based compound-containing layer formed on at least one surface of the aforementioned polarizing element and containing at least one urea-based compound selected from urea, urea derivatives, thiourea, and thiourea derivatives; and a transparent protective film.

Description

Polarizing plate and image display device using the same

The present invention relates to a polarizing plate and a method for manufacturing the same. Furthermore, the present invention relates to an image display device formed by laminating one surface of the polarizing plate to an image display unit and the other surface to a transparent component such as a touch panel or front panel.

Liquid crystal display (LCD) devices are not only used in LCD televisions, but are also widely used in mobile devices such as computers and mobile phones, as well as in automotive applications such as car navigation systems. Typically, an LCD device consists of a liquid crystal panel component with polarizing plates attached to both sides of the liquid crystal cell using an adhesive. The LCD panel controls and displays light from a backlight component.

In recent years, organic EL display devices, like liquid crystal display devices, have also been widely used in mobile devices such as televisions and cell phones, and in vehicles such as car navigation systems.

In organic EL displays, a circularly polarizing plate (a laminate consisting of a polarizing element and a λ/4 plate, sometimes referred to as a "polarizing plate") is placed on the viewing surface of the image display panel to prevent external light from being reflected by the metal electrode (cathode) and perceived as a mirror.

As mentioned above, polarizing plates are increasingly being installed in vehicles as components of liquid crystal displays (LCDs) and organic EL displays. Polarizing plates used in automotive image display devices are often exposed to high temperatures compared to other applications such as televisions and mobile devices like cell phones. Therefore, they are required to exhibit minimal changes in their properties at higher temperatures (high-temperature durability).

On the other hand, to prevent damage to the image display panel from external impact, a configuration in which a front panel such as a transparent resin sheet or glass plate (also called a "window layer") is positioned closer to the viewing side of the image display panel than the polarizing plate is increasingly being adopted. Furthermore, in display devices equipped with a touch panel, a configuration in which the touch panel is positioned closer to the viewing side than the polarizing plate of the image display panel, and the front panel is positioned closer to the viewing side than the touch panel, is widely adopted.

In such a configuration, when an air layer exists between the image display panel and a transparent component such as a front panel or touch panel, light reflection at the air layer interface causes external light to glare, reducing screen visibility. Therefore, a configuration in which the space between the polarizer disposed on the viewing surface of the image display panel and the front transparent component is filled with a material having a refractive index similar to that of these materials (hereinafter sometimes referred to as an "interlayer filler configuration") is becoming increasingly common. Adhesives or UV-curable adhesives are used as interlayer fillers to suppress visibility degradation caused by reflection at the interface and to secure the components together (see, for example, Patent Document 1).

This interlayer filler structure is widely used in mobile devices frequently used outdoors, such as cell phones. Furthermore, due to the increasing demand for visibility in recent years, even in automotive applications such as car navigation systems, a structure in which a front panel is placed on the surface of the image display panel and an interlayer filler, such as an adhesive layer, is being considered for adoption.

However, when this structure is used, reports indicate that, based on the results 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. On the other hand, when the polarizing plate alone is used, no significant decrease in transmittance is observed at 95°C for 1000 hours. Furthermore, reports indicate that these results indicate that a significant decrease in transmittance of the polarizing plate in a high-temperature environment is a unique problem when the following image display device is exposed to high-temperature environments. The image display device employs an interlayer filler structure in which one side of the polarizing plate is bonded to the image display unit and the other side is bonded to a transparent component such as a touch panel or front panel (Patent Document 2).

Furthermore, Patent Document 2 states that the polarizing plate having a significantly reduced transmittance due to an interlayer filling structure has peaks near 1100 cm ^-1 (originating from =C-C= bonding) and near 1500 cm ^-1 (originating from -C=C- bonding) in the Raman spectrum, indicating the formation of a polyene structure (-C=C) _n- . It is speculated that the significantly reduced transmittance of the polarizing plate is caused by polyeneization of the polyvinyl alcohol constituting the polarizing element due to dehydration (Patent Document 2, paragraph [0012]).

Furthermore, the inventors conducted Raman spectroscopy on samples subjected to high-temperature durability tests using an interlayer filling structure and observed that as the transmittance decreased, the sum of the peak areas near 1100 cm ^-1 and 1500 cm ^-1 increased.

As a solution to the problem in Patent Document 2, the following method is proposed: A method for suppressing the decrease in transmittance by setting the moisture content per unit area of the polarizing plate to below a specified amount, and also setting the saturated water absorption of the transparent protective film adjacent to the polarizing element to below a specified amount.

However, additional testing by the inventors revealed that the aforementioned solution was not sufficiently effective in reducing moisture. Furthermore, during panel production, the polarizing plate or the panel to which it is attached must be heated to reduce moisture in the polarizing plate, creating a new problem of reduced panel productivity.

[Prior Technical Literature]

[Patent Literature]

[Patent Document 1] Japanese Patent Application Laid-Open No. 11-174417

[Patent Document 2] Japanese Patent Application Laid-Open No. 2014-102353

In view of the above-mentioned situation, the subject of the present invention, and the problem to be solved by the present invention, is to provide a polarizing plate and a method for manufacturing the same. Even when used in an image display device with an interlayer filler structure, the polarizing plate exhibits minimal decrease in transmittance in high-temperature environments and exhibits excellent durability. Furthermore, another object of the present invention is to provide an image display device having improved display characteristics and durability in high-temperature environments.

The inventors of the present invention, through dedicated research, have discovered that in a configuration in which a polarizing element is formed by iodine adsorption and alignment on a polyvinyl alcohol-based resin layer, and a transparent protective film is provided on at least one side of the polarizing element via an adhesive layer, the adhesive layer contains at least one compound selected from urea, urea derivatives, thiourea, and thiourea derivatives (hereinafter referred to as "urea, urea derivatives, thiourea, and thiourea derivatives"), thereby suppressing the decrease in transmittance in high-temperature environments in an interlayer filling structure in which one side of the polarizing plate is bonded to an image display unit and the other side is bonded to a transparent member such as a touch panel or front panel.

Further research has revealed that by including at least one urea-based compound layer (hereinafter referred to as the "urea-based compound-containing layer") in at least one area of the polarizing element, even if this layer is not an adhesive layer, the interlayer filler structure can suppress the decrease in transmittance in high-temperature environments, similar to the first invention.

Furthermore, in devices employing interlayer fillers, it was discovered that the urea derivatives and thiourea derivatives of the urea-based compounds of the present invention not only exhibit excellent performance in suppressing transmittance degradation in high-temperature environments, but also exhibit excellent performance in suppressing polarization degradation (suppressing cross-light leakage) in high-temperature environments.

The inventors completed the present invention based on this newly discovered fact.

The problem to be solved by this invention can be solved by the following means.

(1) A polarizing plate having

The polarizing element is a polyvinyl alcohol resin polarizing element formed by iodine adsorption and alignment;

A urea-based compound layer is formed on at least one side of the polarizing element and contains at least one selected from urea, urea derivatives, thiourea, and thiourea derivatives; and

Transparent protective film.

(2) The polarizing plate as described in (1), wherein the urea compound-containing layer is an adhesive layer, and the transparent protective film is bonded via the adhesive layer.

(3) The polarizing plate as described in (2), wherein the adhesive layer further contains a polyvinyl alcohol resin.

(4) The polarizing plate as described in (3), wherein the total content of the urea-based compound contained in the adhesive layer is not less than 1 part by weight and not more than 400 parts by weight relative to 100 parts by weight of the polyvinyl alcohol-based resin.

(5) The polarizing plate described in any one of (1) to (4), wherein the urea compound is a urea derivative and/or a thiourea derivative.

(6) The polarizing plate as described in any one of (2) to (5), wherein the thickness of the adhesive layer is 0.01 to 7 μm.

(7) The polarizing plate as described in (1), wherein the urea compound-containing layer is a resin layer other than the adhesive layer.

(8) The polarizing plate as described in any one of (1) to (7), wherein the polarizing plate is used in an image display device having an interlayer filling structure.

(9) A method for manufacturing a polarizing plate, comprising laminating a transparent protective film on at least one side of a polarizing element, the method comprising the following steps:

The step of forming a bonding agent layer comprises forming a bonding agent layer on at least one side of a polarizing element composed of a stretched polyvinyl alcohol-based resin film on which iodine is adsorbed and aligned using a polyvinyl alcohol-based resin and a bonding agent composition, wherein the bonding agent composition contains at least one selected from urea, a urea derivative, thiourea, and a thiourea derivative; and

The laminating step is performed simultaneously with or after the step of forming the adhesive layer, and the transparent protective film is laminated through the adhesive layer.

(10) An image display device having

An image display panel having a polarizing plate as described in any one of (1) to (8) bonded to the viewing side surface of the image display unit via an adhesive layer; and

The transparent component is attached to the viewing-side polarizing plate surface of the aforementioned image display panel via an adhesive layer.

(11) The image display device as described in (10), wherein the transparent component is a glass plate or a transparent resin plate.

(12) The image display device as described in (10), wherein the transparent component is a touch panel.

The present invention provides a polarizing plate and a method for manufacturing the same. Even when used in an image display device with an interlayer filler structure, the polarizing plate exhibits minimal decrease in transmittance under high-temperature conditions and exhibits excellent high-temperature durability. Furthermore, by using the polarizing plate of the present invention, a display device can be provided in which the decrease in transmittance under high-temperature conditions is suppressed.

In one aspect of the present invention, a polarizing element formed by iodine adsorption and alignment on a polyvinyl alcohol-based resin layer is provided with a transparent protective film via an adhesive layer. The adhesive layer contains at least one selected from urea, urea derivatives, thiourea, and thiourea derivatives.

The following describes the technical elements that constitute this invention. However, the elements other than the urea-based compound-containing layer are common to other embodiments (the embodiment in which the urea-based compound-containing layer is a layer other than the adhesive layer).

[Polarizing element]

The polarizing element of the present invention, which is formed by aligning iodine adsorbed on a polyvinyl alcohol (hereinafter also referred to as "PVA") resin layer, can use a conventional polarizing element. Such polarizing elements are generally formed by using a PVA resin film, dyeing the PVA resin film with iodine, and then uniaxially stretching it.

As mentioned above, PVA resins are generally obtained by saponifying polyvinyl acetate resins. The degree of saponification is approximately 85 mol% or higher, preferably approximately 90 mol% or higher, and more preferably approximately 99 mol% to 100 mol%. Polyvinyl acetate resins include, in addition to polyvinyl acetate, which is a homopolymer of vinyl acetate, copolymers of vinyl acetate and other copolymerizable monomers, such as ethylene-vinyl acetate copolymers. Examples of other copolymerizable monomers include unsaturated carboxylic acids, alkenes, vinyl ethers, and unsaturated sulfonic acids. The degree of polymerization of PVA resins ranges from 1,000 to 10,000, preferably from 1,500 to 5,000. This PVA-based resin can be modified, for example, polyvinyl formaldehyde, polyvinyl acetal, polyvinyl butyral, etc. modified with aldehydes.

The method for manufacturing polarizing elements is not particularly limited, but the following methods are typical: a method of unwinding a pre-rolled polyvinyl alcohol-based resin film and then stretching, dyeing, and crosslinking it; or a method of preparing a laminate of a polyvinyl alcohol-based resin and a stretching resin substrate, which includes a step of stretching the laminate. Any of these methods can be used in the present invention.

Methods for manufacturing these polarizing elements are described in paragraphs [0109] to [0128] of Japanese Patent Application Laid-Open No. 2014-48497. These methods can be used in the present invention. Furthermore, 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-containing compound layer]

The polarizing plate of the present invention comprises a urea-containing compound layer. The urea-containing compound layer is formed on at least one surface of a polyvinyl alcohol-based resin polarizing element formed by iodine adsorption and alignment, and contains at least one selected from urea, urea derivatives, thiourea, and thiourea derivatives.

In the present invention, the urea-based compound-containing layer does not necessarily constitute the adhesive layer. However, from the perspective of productivity, the adhesive layer preferably contains a urea-based compound. The adhesive layer is formed using the adhesive described below.

In addition, the structure of the urea-based compound-containing layer other than the adhesive layer will be described later.

[Follow-up agent]

Any suitable adhesive can be used to bond the protective film to the polarizing element. Specifically, water-based adhesives, solvent-based adhesives, and active energy ray-curing adhesives can be used, but water-based adhesives are preferred.

When the adhesive layer is a urea-based compound layer, the adhesive contains at least one selected from urea, urea derivatives, thiourea, and thiourea derivatives.

The thickness of the adhesive layer during application can be set to any appropriate value. For example, it can be set so that a desired adhesive layer 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 can be used. Aqueous adhesives containing PVA resins (PVA adhesives) are particularly preferred. The average degree of polymerization of the PVA resin in the aqueous adhesive is preferably approximately 100 to 5500, more preferably 1000 to 4500, from the perspective of adhesiveness. The average degree of saponification is preferably approximately 85 mol% to 100 mol%, more preferably 90 mol% to 100 mol%.

The PVA resins used in the water-based adhesives described above are preferably those containing acetyl groups. This is because they provide excellent adhesion between the PVA resin layer and the protective film and provide excellent durability. Acetyl-containing PVA resins can be obtained by, for example, reacting a PVA resin with diketene using any method. The degree of acetyl modification in acetyl-containing PVA resins is typically 0.1 mol% or higher, and preferably between 0.1 mol% and 20 mol%.

The resin concentration of the above-mentioned water-based adhesive is preferably 0.1% to 15% by weight, more preferably 0.5% to 10% by weight.

(crosslinking agent, solvent)

The water-soluble PVA-based adhesive preferably used in the present invention may contain a crosslinking agent, in addition to the aforementioned PVA-based resin and urea-based compound, as needed. Known crosslinking agents can be used, such as water-soluble epoxy compounds, dialdehydes, and isocyanates.

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

Furthermore, the water-soluble PVA-based adhesive of the present invention may contain an organic solvent. In this case, alcohols are preferred in terms of miscibility with water, with methanol or ethanol being particularly preferred.

Furthermore, in the present invention, some urea derivatives have low solubility in water, while others have sufficient solubility in alcohol. In this case, dissolving the urea derivative in alcohol to prepare an alcoholic solution of the urea derivative is a preferred embodiment, and then adding the alcoholic solution of the urea derivative to the PVA aqueous solution to prepare the bonding agent.

(Active energy ray-curing adhesive)

Regarding the active energy ray-curing adhesive described above, any appropriate adhesive may be used as long as it is cured by irradiation with active energy rays. Examples of active energy ray-curing adhesives include ultraviolet-curing adhesives and electron beam-curing adhesives. Specific examples of the curing type of active energy ray-curing adhesives include free radical curing, cationic curing, anionic curing, and combinations thereof (e.g., a hybrid of free radical curing and cationic curing).

Examples of the active energy ray-curable adhesives include those containing compounds (e.g., monomers and/or oligomers) having free radical polymerizable groups such as (meth)acrylate groups or (meth)acrylamide groups as curing components.

Specific examples of the active energy ray-curable adhesive and its curing method are described in, for example, Japanese Patent Application Laid-Open No. 2012-144690.

[Urea compounds]

The adhesive layer of the present invention contains at least one selected from urea, urea derivatives, thiourea, and thiourea derivatives.

Regarding the method of incorporating a urea compound into the adhesive layer, it is preferred to incorporate the urea compound into the above-mentioned adhesive. Furthermore, during the process of forming the adhesive layer through a drying step, etc., it is not a problem if some of the urea compound migrates from the adhesive layer to the polarizing element, etc.

Urea compounds are classified into water-soluble and poorly water-soluble types, and both can be used in the present invention. When using poorly water-soluble urea compounds in water-soluble adhesives, it is advisable to devise a dispersion method after forming the adhesive layer to prevent an increase in haze.

When the adhesive is a water-based adhesive containing a PVA resin, the amount of the urea compound added is preferably 0.1 to 400 parts by 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 the PVA resin.

(Urea or urea derivatives)

In the present invention, a urea derivative refers to a compound having a molecular structure in which a portion of urea is substituted with a substituent. Preferably, the urea derivative is a compound in which at least one of the four hydrogen atoms in the urea molecule is substituted with a substituent.

In this case, the substituents are not particularly limited, but preferably are substituents composed of carbon atoms, hydrogen atoms, and oxygen atoms.

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

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

Examples of 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, a thiourea derivative refers to a compound having a molecular structure in which a portion of the thiourea is substituted with a substituent. Preferably, the thiourea derivative is a compound in which at least one of the four hydrogen atoms in the thiourea molecule is substituted with a substituent.

In this case, the substituents are not particularly limited, but preferably are substituents composed of carbon atoms, hydrogen atoms, and oxygen atoms.

Specific examples of thiourea derivatives include monosubstituted thiourea, 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.

Examples of tri-substituted thioureas include trimethylthiourea; examples of quadri-substituted thioureas include tetramethylthiourea and 1,1,3,3-tetraethylthiourea.

Among the above compounds, when used in image display devices with interlayer fill structures, urea derivatives or thiourea derivatives are preferred, with urea derivatives being more preferred, due to minimal decrease in transmittance and polarization under high temperature conditions. Among urea derivatives, mono-substituted urea and di-substituted urea are preferred, with mono-substituted urea being more preferred. Among di-substituted ureas, 1,1-substituted urea and 1,3-substituted urea are included, with 1,3-substituted urea being more preferred.

[Transparent protective film]

The transparent protective film used in the present invention (hereinafter referred to as the "protective film") is bonded to at least one side of the polarizing element via the urea-based compound adhesive layer of the present invention. This transparent protective film is bonded to one or both sides of the polarizing element, preferably both sides.

Furthermore, in a configuration where protective films are laminated to both sides of the polarizing element via an adhesive layer, only one side of the adhesive layer on both sides of the polarizing element may be the urea-containing compound adhesive layer of the present invention. Preferably, both sides of the adhesive layer are the urea-containing compound adhesive layer of the present invention.

In recent years, to meet the demand for thinner polarizing plates, polarizing plates with a protective film on only one side of the polarizing element have been developed. In this configuration, a protective film laminated with a urea-containing adhesive layer is preferred.

As a method for producing a polarizing plate with a protective film on only one side of the polarizing element, one method is to first produce a polarizing plate with protective films laminated to both sides via an adhesive layer, and then peel off the protective film on one side. When using this production method, it is not a problem to use the adhesive layer of the present invention on only one side. However, it is more preferable to use the urea-containing compound adhesive layer of the present invention on both sides of the polarizing element.

Furthermore, when the urea-based compound adhesive layer of the present invention is used on only one side of a polarizing element, it is preferred that the adhesive layer on the film side that is not to be peeled be the urea-based compound adhesive layer of the present invention.

The protective film can also have other optical functions and can be further formed into a multilayer structure with other layers.

From the perspective of optical properties, a thinner protective film is preferred. However, if it is too thin, the strength decreases and the processability deteriorates. The appropriate film thickness is 5 to 100 μm, preferably 10 to 80 μm, and more preferably 15 to 70 μm.

The protective film may be made of acetylated cellulose resin films, polycarbonate resin films, cycloolefin resin films such as norbornene, (meth)acrylic polymer films, or polyester resin films such as polyethylene terephthalate.

When a polarizing element has protective films on both sides and is bonded using a water-based adhesive such as a PVA-based adhesive, it is preferred that the protective film on at least one side be either an acetylated cellulose film or a (meth)acrylic polymer film, with acetylated cellulose film being preferred, from the perspective of moisture permeability.

At least one of the protective films may have a retardation function for purposes such as viewing angle compensation. In this case, the film itself may have a retardation function, may have a separate retardation layer, or may be a combination of the two.

Furthermore, although the description above focuses on a structure in which the film with a phase difference function is directly bonded to the polarizing element via an adhesive, a structure in which the film is bonded to the polarizing element via another protective film bonded to the polarizing element and then bonded via an adhesive or adhesive is also possible.

[Composition of image display device]

The polarizing plate of the present invention, comprising a polarizing element with a transparent protective film laminated to at least one side thereof via a urea-based compound adhesive layer, is used in various image display devices, such as liquid crystal displays and organic EL displays. In particular, the polarizing plate of the present invention is suitable for use in image display devices having a transparent component, such as a front panel or touch panel, disposed on the viewing side of the image display device, with the image display panel and the transparent component laminated via an adhesive layer or the like, with the interlayer filling.

(Image display unit)

Examples of image display cells include liquid crystal cells and organic EL cells. Liquid crystal cells can be either reflective or transmissive, utilizing light from a backlight or other light source, or transflective or semi-transmissive, utilizing both external and light from the light source. When the liquid crystal cell utilizes light from the light source, the image display device (liquid crystal display device) includes a polarizing plate on the side opposite the viewing side of the image display cell (liquid crystal cell) and a light source. The polarizing plate on the light source side is preferably bonded to the liquid crystal cell via an appropriate adhesive layer.

As for the driving method of the liquid crystal cell, any of the following types can be used: VA mode, IPS mode, TN mode, STN mode, or bend alignment (π type), etc.

For organic EL cells, a transparent electrode, an organic light-emitting layer, and a metal electrode are sequentially stacked on a transparent substrate to form a light-emitting element (organic electroluminescent element). The organic light-emitting layer is a laminate of various organic thin films, such as a hole-injection layer composed of a triphenylamine derivative and a light-emitting layer composed of a fluorescent organic solid such as anthracene, or a laminate of such a light-emitting layer and an electron-injection layer composed of a perylene derivative, or a laminate of a hole-injection layer, a light-emitting layer, and an electron-injection layer. Various layer configurations are possible.

(Lamination of image display unit and polarizing plate)

The image display unit and polarizing plate are bonded together using an adhesive layer (adhesive sheet). From a workability perspective, the preferred method is to bond the polarizing plate and image display unit together with an adhesive layer attached to one side of the polarizing plate. The adhesive layer can be bonded to the polarizing plate using appropriate methods. Examples of such methods include dissolving or dispersing the base polymer or the composition in a solvent consisting of a suitable solvent such as toluene or ethyl acetate, either alone or in a mixture, to prepare an adhesive solution containing approximately 10 to 40% by weight, and directly attaching the adhesive solution to the polarizing plate using a suitable spreading method such as casting or coating. Alternatively, an adhesive layer may be formed on a separator as described above and then transferred to the polarizing plate.

(Adhesive layer)

Regarding the adhesive layer, it is described in paragraphs [0103] to [0143] of Japanese Patent Application Laid-Open No. 2018-025765, and such adhesives can be used in the present invention.

(Transparent front component)

Examples of the front transparent member disposed on the viewing side of the image display unit include a front panel (window layer) or a touch panel. The front panel can be a transparent plate with appropriate mechanical strength and thickness. Examples of such a transparent plate include a transparent resin plate made of acrylic or polycarbonate resins, or a glass plate. The viewing side of the transparent plate may also be laminated with a functional layer such as an antireflection layer. Furthermore, when the transparent plate is a transparent resin plate, a hard coating layer to enhance physical strength or a low-permeability layer to reduce moisture permeability may be laminated.

Touch panels can be made of various types, including resistive film, electrostatic capacitive, optical, and ultrasonic, or glass or transparent resin sheets with touch sensor functionality. When using an electrostatic capacitive touch panel as the front transparent component, it is preferable to have a front panel made of glass or transparent resin sheet positioned closer to the viewing side than the touch panel.

(Polarizing plate and front transparent component bonded together)

The polarizing plate and the front transparent member are bonded using an adhesive or UV-curable adhesive. When using an adhesive, it can be applied using an appropriate method. Specific bonding methods include the aforementioned adhesive layer bonding method used to bond the image display unit to the polarizing plate.

When using UV-curable adhesives, to prevent the solution from spreading before curing, a suitable method is to place a weir around the edge of the image display panel, place a transparent front member on the weir, and then inject the adhesive solution. After injection, adjust the position and degas the adhesive solution as needed, then irradiate with UV light for curing.

Next, the present invention will be described regarding aspects of the polarizing element that include a urea-based compound other than an adhesive layer containing at least one urea-based compound on at least one surface of the polarizing element.

Furthermore, as previously mentioned, the technical elements constituting the present invention, such as the polarizing element, other than the urea-containing compound layer, are common to the embodiment in which the urea-containing compound layer serves as the adhesive layer.

[Urea-containing compound layer]

In this aspect of the present invention, the polarizing plate comprises a urea-based compound layer (other than the adhesive layer) formed on at least one side of a polyvinyl alcohol-based resin polarizing element formed by iodine adsorption alignment and containing at least one selected from urea, urea derivatives, thiourea, and thiourea derivatives.

The urea-based compound layer preferably comprises at least one urea-based compound and a binder. Examples of binders include polymer binders, thermosetting binders, and active energy ray-curing binders. Any of these binders can be used in the present invention.

The thickness of the urea-based compound 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-containing compound layer can be deposited directly on the polarizing element or through other layers. However, direct deposition on the polarizing element is preferred because it can more easily suppress the decrease in transmittance in high-temperature environments.

In this embodiment, the polarizing plate preferably has a transparent protective film on at least one side of the polarizing element via an adhesive layer to enhance its physical strength. The adhesive layer may or may not contain a urea-based compound, but it is more preferred to contain one.

As mentioned in the description of other types of protective films, in recent years, polarizing plates with a protective film applied only to one side of the polarizing element (hereinafter referred to as "polarizing plates with a single-sided protective film") have been developed to meet the demand for thinner polarizing plates.

In this structure, attempts have been made to form a hardened layer on the area of the protective film that does not have a polarizing element in order to improve physical strength. (For example: Japanese Patent Application Publication No. 2011-221185)

In the present invention, it is also a preferred embodiment to include a urea compound in such a hardening layer. Typically, such hardening layers are formed from a hardening composition containing an organic solvent. However, paragraphs [0020] to [0042] of Japanese Patent Application Laid-Open No. 2017-075986 describe a method for forming such a hardening layer from an aqueous solution of an active energy ray-hardening polymer composition. Since urea compounds are generally water-soluble, it is also a preferred embodiment of the present invention to include a water-soluble urea compound in such a composition to form a urea compound-containing layer.

Next, a polarizing plate of another embodiment is described, wherein a polarizing element is produced by coating a solution containing a urea-based compound on at least one side of the polarizing element and drying the solution.

This aspect is characterized by its use in interlayer filler polarizing plates, capable of suppressing the reduction of monomer transmittance even when exposed to high temperatures for extended periods. This polarizing element can be produced by coating at least one surface of a polarizing element composed of a stretched polyvinyl alcohol-based resin film with iodine adsorbed and aligned thereon with a solution containing at least one selected from urea, urea derivatives, thiourea, and thiourea derivatives, and then drying the coating.

(Urea compound solution)

The solvent for the urea-containing compound solution of the present invention is preferably water, an organic solvent, or a mixture thereof, and more preferably water or a mixture of water and alcohol. Furthermore, in the case of a mixture of water and alcohol, the alcohol is preferably methanol or ethanol.

Urea compounds mentioned above can be used as the urea compound. However, since urea compounds are less likely to precipitate on the surface of the polarizing element after drying, water-soluble urea compounds are preferred.

[Example]

The present invention is described below in detail based on the following examples. The materials, reagents, amounts and ratios of substances, and operations described in the following examples may be appropriately modified without departing from the spirit of the present invention. Therefore, the present invention is not limited to the following examples.

(Production of Polarizing Element 1)

A 40μm-thick PVA film with an average degree of polymerization of 2400 and a saponification degree of 99.9 mol% was immersed in 25°C warm water for 120 seconds to swell. The film was then immersed in a 0.6% by weight aqueous solution of iodine/potassium iodide (weight ratio = 2/3) and stretched to 2.1 times its original length while dyeing. The film was then stretched in a 60°C acid bath containing boric acid and potassium iodide, rinsed with water, and dried to produce a 15μm-thick polarizing element 1.

(Preparation of PVA solution for the next step)

Dissolve 50g of a modified PVA resin containing acetyl groups (GOHSENX Z-410, manufactured by Mitsubishi Chemical Co., Ltd.) in 950g of pure water. Heat the mixture at 90°C for 2 hours and then cool it to room temperature to obtain a PVA solution for adhesives.

(Preparation of urea compound solution)

Add 10g of urea to 90g of pure water to obtain a 10% urea aqueous solution (Solution 1). Similarly, according to Table 1, replace urea with the urea-based compounds listed in Table 1 and, if necessary, replace the solvent from pure water with methanol to prepare Solutions 2 to 9.

[Table 1]

All of the urea, methylurea, ethylurea, 1,3-dimethylurea, tetramethylurea, phenylurea, thiourea, methylthiourea, and tetrahydro-2-pyrimidinone used in the above-mentioned experiments are reagents from Tokyo Chemical Industry Co., Ltd.

(Preparation of Adhesive 1 for Polarizing Plates)

The adhesive prepared above was mixed with PVA solution, urea solution, pure water, and methanol to a PVA concentration of 3.0%, a methanol concentration of 20%, and a urea concentration of 0.3% to obtain polarizing plate adhesive 1.

(Adhesive for polarizing plates: 2 to 14 preparations)

Similarly, prepare adhesive PVA solution, the urea compound solution listed in Table 1, pure water, and methanol to a PVA concentration of 3.0%, a methanol concentration of 20%, and a urea compound concentration listed in Table 2 to obtain polarizing plate adhesives 2 to 14.

Polarizing plate adhesive 12 uses a combination of methyl urea and 1,3-dimethyl urea, which are urea-based compounds. Polarizing plate adhesive 14 does not contain any urea-based compounds.

[Table 2]

(Saponification of acetylated cellulose membrane)

A commercially available acetylated cellulose membrane TD40 (Fuji Film Co., Ltd., 40 μm thick) was immersed in a 1.5 mol/L sodium hydroxide solution (saponification solution) maintained at 55°C for 2 minutes. The membrane was then rinsed with water and then immersed in a 0.05 mol/L sulfuric acid solution at 25°C for 30 seconds. The membrane was then rinsed under running water for 30 seconds to neutralize the membrane. The membrane was then drained three times using an air scraper and dried in a drying area at 70°C for 15 seconds to produce a saponified membrane.

(Production of Polarizing Plate 1)

The saponified acetylated cellulose film prepared above was applied to both sides of the polarizing element 1, with polarizing plate adhesive 1 interposed therebetween. The adhesive layer thickness after drying was adjusted to 100 nm on both sides. The layers were laminated using a roll laminator and then dried at 60°C for 10 minutes, resulting in a polarizing plate 1 with acetylated cellulose films on both sides.

(Production of polarizing plates 2 to 14)

Polarizing Plates 2 to 14 were produced by following the same procedures as for Polarizing Plate 1, except that Polarizing Plate Adhesive 1 was replaced with Polarizing Plate Adhesives 2 to 14.

(Production of Laminated Body 1)

Referring to the embodiment of Japanese Patent Application Publication No. 2018-025765, an optical laminate 1 having a 25 μm thick adhesive layer on both sides was produced by coating both sides of the polarizing plate 1 produced above with an acrylic adhesive (manufacturer: LINTEC Co., Ltd., item number: #7).

(Production of layers 2 to 14)

Optical laminates 2 to 14 are fabricated using the same process as for optical laminate 1, except that polarizer 1 is replaced with polarizers 2 to 14.

(Production of Laminated Body 15)

Optical laminate 15 is produced by performing the same operations as optical laminate 14, except that the adhesive layer is laminated only on one side.

(Evaluation of the layered structure)

The laminates produced above were evaluated with reference to the examples in Japanese Patent Application Publication Nos. 2014-102353 and 2018-025765. High-temperature durability testing was conducted at 95°C and 105°C. The high-temperature durability test was conducted at 95°C for 1000 hours. 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.

Comparing the test results in Example 1, the coloration at 105°C for 100 hours is almost identical to that at 95°C for 1000 hours.

[Evaluation of single-body permeability after high-temperature durability test (105°C)]

Optical laminates 1 to 14 produced above were each cut into 50 mm × 100 mm pieces. Evaluation samples were prepared by laminating the surfaces of the first and second adhesive layers to alkali-free glass (trade name "EAGLE XG," manufactured by Corning). Furthermore, optical laminate 15 was cut into 50 mm × 100 mm pieces. The surface of the first adhesive layer was also laminated to alkali-free glass (trade name "EAGLE XG," manufactured by Corning). These samples were prepared without heat treatment to adjust the moisture content of the glass sheets before lamination.

For these evaluation samples, the samples were autoclaved at 50°C and a pressure of 5 kgf/ ^cm² (490.3 kPa) for one hour, then placed in an environment at 23°C and a relative humidity of 55% for 24 hours. The transmittance (initial value) was then measured. The samples were then stored in a heated environment at 105°C for 100 to 200 hours, with transmittance measured every 50 hours. Evaluation was based on the time when the transmittance decreased by more than 5% from the initial value. The results are shown in Table 3.

In addition, since the evaluation sample containing optical laminate 15 has a structure with alkali-free glass laminated on only one side, the transmittance is not reduced and the evaluation result is A.

Penetration rate drops below 5% after 200 hours: A

Penetration rate drops by more than 5% between 150 and 200 hours: B

Penetration rate drops by more than 5% between 100 and 150 hours: C

If the penetration rate drops by 5% or more after 100 hours: D

[Evaluation of orthogonal light leakage 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 bonded to alkali-free glass (trade name "EAGLE XG", manufactured by Corning) to produce a sample 20 for orthogonal light leakage evaluation.

After 100 hours of high-temperature durability testing, the single-unit transmittance evaluation samples were visually evaluated for light leakage under crossed Nicols (hereinafter referred to as "crossed light leakage") of the optical multilayer and sample 20 according to the following criteria.

Those who saw no orthogonal light leakage at all: ◎

Almost no orthogonal light leakage was observed: ○

Slightly visible orthogonal light leakage: △

Those who clearly see orthogonal light leakage: ×

[Table 3]

This section explains the dosage of urea compounds in Table 3.

As mentioned above, the amount of urea-based 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 embodiment, the PVA concentration is 3.0%.

In the present invention, for any urea-based compound, the change in monomer transmittance after the high-temperature durability test decreases as the added amount increases. Conversely, the cross-light leakage after the high-temperature durability test tends to decrease as the added amount decreases.

Any of the urea-based compounds described in the examples exhibited a single-unit transmittance change of B or greater after the high-temperature durability test, and simultaneously exhibited a cross-light leakage of △ or greater, demonstrating excellent performance in both performance characteristics.

However, the dosage of the aforementioned compounds varies significantly depending on the optimal performance of each compound, namely, achieving a single-element transmittance variation of B or greater and a cross-light leakage of △ or greater. The dosage of any compound should be within the aforementioned optimal dosage range.

The dosage amounts shown in Table 3 for each urea-based compound represent the minimum dosage required for the monomer transmittance to achieve an A rating. Furthermore, for urea and thiourea, the values for the cross light leakage are shown as the dosage is gradually reduced from the minimum dosage that achieves an A rating to the dosage where the cross light leakage changes from △ to ○ (at which point the monomer transmittance changes to B). Furthermore, for methyl urea, the values for the cross light leakage are shown as the dosage is gradually reduced from the minimum dosage that achieves an A rating to the dosage where the cross light leakage changes from ○ to ◎ (at which point the monomer transmittance changes to B).

The results shown in Table 3 reveal the following.

1. The polarizing plate of the present invention, which uses an adhesive containing a urea-based compound, can suppress the decrease in monomer transmittance even when used in image display devices with interlayer fillers or when exposed to high temperature environments for long periods of time.

2. Compared to those using urea or thiourea, those using urea derivatives or thiourea derivatives not only do not experience a decrease in monomer transmittance, but also exhibit no cross-light leakage, resulting in exceptionally high quality.

3. Using an adhesive containing two urea-based compounds to suppress the decrease in monomer permeability even when exposed to high temperature for a long time is also a preferred embodiment of the present invention.

Other examples are shown below, but these examples are not limited to the following examples.

Regarding the composition of the hardening layer-forming composition BLC-1 described in paragraphs [0075] and [0076] of Japanese Patent Application Laid-Open No. 2017-075986, methyl urea was added to achieve a solids concentration of 1% by weight, and pure water was added to achieve a total solids concentration of 26% by weight. After mixing, the mixture was irradiated with ultrasound and passed through a filter with a pore size of 5 μm to prepare a hardening composition containing a urea-based compound (UBLC-1).

With reference to the polarizing plate 1 described in paragraphs [0070] to [0080] of Japanese Patent Application Laid-Open No. 2017-075986, a polarizing plate (polarizing plate 22) having a protective film with a hardening layer on one side that does not contain a urea compound was produced.

For polarizing plate 22, the same operation was performed except that the curing forming composition (BLC-1) was replaced with the curing forming composition (UBLC-1). A polarizing plate (polarizing plate 21) with a protective film having a curing layer containing a urea compound on one side was produced.

Optical stack 14 was subjected to the same procedures, except that polarizer 14 was replaced with polarizer 21 and polarizer 22, respectively, to obtain optical stack 21 and optical stack 22. These samples were evaluated in the same manner as optical stack 14, and the results are shown in Table 4.

In addition, the evaluation of cross-sectional light leakage after high-temperature durability was conducted with the transparent protective film facing outward.

[Table 4]

The results shown in Table 4 reveal the following.

1. When the polarizing plate of the present invention, which has a urea-based compound layer disposed on at least one side of the polarizing element, is used in an image display device having an interlayer filler structure, it can suppress a decrease in the transmittance of the monomer even when exposed to a high temperature environment for a long time.

Other examples are further shown, but these examples are not limited to the following examples.

Prepare a 0.5% solution of methyl urea as the coating liquid. Apply the 0.5% methyl urea solution to one side of the polarizing element 1 produced above using a coating bar to a wet coating thickness of 10 μm. Dry at 60°C for 5 minutes to obtain polarizing element 2.

As a comparative example, pure water was applied to one side of the polarizing element produced above using a coating bar to a wet coating thickness of 10 μm, and then dried at 60°C for 5 minutes to obtain Polarizing Element 3.

For polarizing plate 14, the same operation is performed, except that polarizing element 1 is replaced with polarizing element 2 and polarizing element 3, respectively, to obtain polarizing plates 31 and 32.

Optical stack 14 was subjected to the same procedures, except that polarizer 14 was replaced with polarizer 31 and polarizer 32, respectively, to obtain optical stack 31 and optical stack 32. These samples were evaluated in the same manner as optical stack 14, and the results are shown in Table 5.

[Table 5]

The results shown in Table 5 reveal the following.

1. A solution containing a urea-based compound is coated on at least one side of a polarizing element, dried, and then produced. The polarizing plate of the present invention, having this polarizing element, when used in an image display device with an interlayer filler structure, can suppress a decrease in monomer transmittance even when exposed to high temperature for extended periods of time.

Claims (6)

A polarizing plate having: The polarizing element is a polyvinyl alcohol resin polarizing element formed by iodine adsorption and alignment; A urea-based compound layer formed on at least one side of the polarizing element and containing at least one selected from urea, a urea derivative, thiourea, and a thiourea derivative; and Transparent protective film; The urea-based compound-containing layer is a resin layer other than the adhesive layer. The polarizing plate as described in claim 1, wherein the urea-based compound is a urea derivative and/or a thiourea derivative. The polarizing plate as claimed in claim 1 or 2, wherein the polarizing plate is used in an image display device having an interlayer filler structure. An image display device comprising: An image display panel comprising a polarizing plate as described in any one of claims 1 to 3 bonded to the viewing side surface of an image display unit via an adhesive layer; and The transparent component is attached to the viewing-side polarizing plate surface of the aforementioned image display panel via an adhesive layer. The image display device as described in claim 4, wherein the transparent component is a glass plate or a transparent resin plate. The image display device as described in claim 4, wherein the transparent component is a touch panel.