TWI869400B - Polarizing plate, manufacturing method thereof 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, method for manufacturing polarizing plate, and image display device using the polarizing plate

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 an image display unit on one side of the polarizing plate and laminating a transparent component such as a touch panel or a front panel on the other side.

Liquid crystal display devices (LCD) are not only used in LCD TVs, but are also widely used in mobile devices such as computers and mobile phones, and in-vehicle applications such as car navigation. Usually, a liquid crystal display device has a liquid crystal panel component with polarizing plates attached to both sides of the liquid crystal unit with an adhesive, and the light from the backlight component is controlled and displayed by the liquid crystal panel component.

In addition, organic EL display devices, like liquid crystal display devices, have also been widely used in recent years in mobile devices such as televisions and mobile phones, and in-vehicle applications such as car navigation.

In an organic EL display device, in order to prevent external light from being reflected by the metal electrode (cathode) and being visually recognized as a mirror surface, a circular polarizing plate (a laminate containing a polarizing element and a λ/4 plate, sometimes referred to as a "polarizing plate") is placed on the viewing side surface of the image display panel.

As mentioned above, polarizing plates are increasingly being installed in vehicles as components of liquid crystal display devices or organic EL display devices. Polarizing plates used in vehicle-mounted image display devices are often exposed to high temperature environments compared to other uses such as TVs or mobile phones, and therefore require less characteristic changes in higher temperature environments (high temperature durability).

On the other hand, in order to prevent damage to the image display panel caused by impact from the outer surface, a transparent resin plate or glass plate or other front panel (also called "window layer" etc.) is increasingly being provided on the viewing side closer to the polarizing plate of the image display panel. In addition, in a display device having a touch panel, a touch panel is provided on the viewing side closer to the polarizing plate of the image display panel, and a front panel is provided on the viewing side closer to the touch panel. This is widely adopted.

In such a structure, when there is an air layer between the image display panel and transparent components such as the front panel or touch panel, the visibility of the screen tends to be reduced due to the reflection of external light at the interface of the air layer. Therefore, the structure of filling the space between the polarizing plate arranged on the viewing side surface of the image display panel and the front transparent component with a material with a refractive index similar to these materials (hereinafter sometimes referred to as "interlayer filling structure") is gradually being widely adopted. As for the interlayer filling material, in order to suppress the reduction of visibility caused by reflection at the interface and to fix each component, an adhesive or UV curing adhesive is used (for example, refer to patent document 1).

The above-mentioned interlayer filling structure is widely used in mobile devices such as mobile phones that are often used outdoors. In addition, due to the increasing demand for visibility in recent years, even in vehicle-mounted applications such as car navigation devices, a structure in which a front panel is arranged on the surface of the image display panel and an interlayer filling structure such as an adhesive layer is used between the panel and the front panel is being studied and adopted.

However, when this structure is adopted, there are reports that according to the results of the heat durability test (at 95°C, 200 hours, etc.), the transmittance is significantly reduced in the central part of the polarizing plate surface. On the other hand, when the polarizing plate is used alone, no significant reduction in transmittance is found at 95°C, 1000 hours. There are also reports that these results show that the significant reduction in the transmittance of the polarizing plate in a high temperature environment is a unique problem when the following image display device is exposed to a high temperature environment, wherein the image display device adopts an interlayer filling 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 a front panel (Patent Document 2).

Furthermore, the above-mentioned Patent Document 2 states that the polarizing plate whose transmittance is significantly reduced due to the interlayer filling structure has peaks near 1100 cm ^-1 (originating from =CC= bonding) and near 1500 cm ^-1 (originating from -C=C- bonding) in the Raman spectrum, indicating that a polyene structure (-C=C) _n- is formed. It is inferred that the significantly reduced transmittance of the polarizing plate is caused by the 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 a high-temperature durability test using an interlayer filling structure and observed that the sum of the peak areas near 1100 cm ^-1 and 1500 cm ^-1 increased as the transmittance decreased.

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 prescribed amount and setting the saturated water absorption of the transparent protective film adjacent to the polarizing element to below a prescribed amount.

However, according to the results of additional tests conducted by the inventors, it was found that the reduction and suppression effect of the above-mentioned solution was not sufficient. Furthermore, in order to reduce the moisture content of the polarizing plate during panel production, the polarizing plate or the panel to which the polarizing plate is attached needs to be heated, thus resulting in a new problem of reduced panel productivity.

[Prior technical literature]

[Patent Literature]

[Patent Document 1] Japanese Patent Publication No. 11-174417

[Patent Document 2] Japanese Patent Publication No. 2014-102353

In view of the above situation, the subject of the present invention, that is, the subject to be solved by the present invention, is to provide a polarizing plate and a method for manufacturing the same, which has a small reduction in transmittance in a high temperature environment and excellent durability even when used in an image display device composed of interlayer filling. Another object of the present invention is to provide an image display device with improved display characteristics and durability in a high temperature environment.

As a result of the inventors' dedicated research, they found that in a structure in which a transparent protective film is provided on at least one side of a polarizing element formed by iodine adsorption and alignment on a polyvinyl alcohol-based resin layer, by making the adhesive layer contain at least one selected from urea, urea derivatives, thiourea and thiourea derivatives (hereinafter "urea, urea derivatives, thiourea and thiourea derivatives" are referred to as "urea-based compounds"), one side of the polarizing plate is bonded to an image display unit, and the other side is bonded to a transparent component such as a touch panel or a front panel, the decrease in transmittance in a high temperature environment can be suppressed.

As a result of further research, it was found that by including at least one urea compound layer (hereinafter also referred to as "urea compound-containing layer") in at least one area layer of the polarizing element, even if the layer does not belong to the adhesive layer, it is the same as the first invention, and in the interlayer filling structure, it can suppress the decrease of transmittance in a high temperature environment.

Furthermore, in the device using interlayer filling structure, it was found that the urea derivatives or thiourea derivatives in the urea-based compounds of the present invention not only have excellent performance in suppressing the reduction of transmittance in a high temperature environment, but also have excellent performance in suppressing the reduction of polarization degree (suppressing orthogonal light leakage) in a high temperature environment.

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

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

(1) A polarizing plate having

Polarizing element, which is a polyvinyl alcohol resin polarizing element formed by iodine adsorption and alignment;

The urea compound layer is formed on at least one side of the aforementioned 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) A polarizing plate as described in (3), wherein the total content of the urea 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 resin.

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

(6) A 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) A 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, which is a method for manufacturing a polarizing plate having a transparent protective film attached to at least one side of a polarizing element, and the manufacturing method comprises the following steps:

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

The laminating step is to laminate the transparent protective film through the adhesive layer at the same time as or after the step of forming the adhesive layer.

(10) An image display device having

An image display panel, wherein a polarizing plate as described in any one of (1) to (8) is 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.

According to the present invention, a polarizing plate and a method for manufacturing the same can be provided. Even when the polarizing plate is used in an image display device with an interlayer filling structure, the decrease in transmittance in a high temperature environment is small and the high temperature durability is excellent. Furthermore, by using the polarizing plate of the present invention, a display device in which the decrease in transmittance in a high temperature environment is suppressed can be provided.

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

The following is an explanation of the technical elements constituting the present invention, but the elements other than the urea-based compound-containing layer are common in other aspects (the aspect 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 adsorbing and aligning iodine on a polyvinyl alcohol (hereinafter also referred to as "PVA") resin layer, can use a known polarizing element. Such a polarizing element generally uses a PVA resin film, and is formed by dyeing the PVA resin film with iodine and uniaxially stretching it.

As mentioned above, PVA resins are generally obtained by saponifying polyvinyl acetate resins. The saponification degree is about 85 mol% or more, preferably about 90 mol% or more, and more preferably about 99 mol% to 100 mol%. As for polyvinyl acetate resins, in addition to polyvinyl acetate, which is a homopolymer of vinyl acetate, copolymers of vinyl acetate and other monomers that can be copolymerized with it can be listed, for example: ethylene-vinyl acetate copolymers, etc. As for other monomers that can be copolymerized, for example: unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, etc. can be listed. As for the polymerization degree of PVA resins, it is 1000 to 10000, preferably 1500 to 5000. This PVA resin can be modified, for example, it can be polyvinyl formaldehyde, polyvinyl acetal, polyvinyl butyral, etc. modified with aldehydes.

The manufacturing method of the polarizing element is not particularly limited, but the following method is a typical manufacturing method: a method of rolling out a polyvinyl alcohol resin film that has been rolled into a roll in advance and stretching, dyeing, crosslinking, etc., or a method of preparing a laminate of a polyvinyl alcohol resin and a resin substrate for stretching, and including a step of stretching in the laminate state. Any of these methods can be used in the present invention.

The manufacturing methods of these polarizing elements are described in paragraphs [0109] to [0128] of Japanese Patent Publication No. 2014-48497, and these methods can be used in the present invention. In addition, 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 compound containing layer]

The polarizing plate of the present invention has a urea compound layer, which is formed on at least one side of a polyvinyl alcohol 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 layer containing the urea compound does not necessarily belong to the adhesive layer. From the perspective of productivity, the adhesive layer containing the urea compound is preferred. The adhesive layer is formed by the adhesive described below.

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

[Follow-up agent]

Any appropriate adhesive can be used as the adhesive for bonding the protective film to the polarizing element. Specifically, the adhesive can be a water-based adhesive, a solvent-based adhesive, an active energy ray-curing type, etc., but a water-based adhesive is preferred.

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

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

(Water-based adhesive)

In addition, as for the above-mentioned water-based adhesive, any appropriate water-based adhesive can be used. Among them, it is preferred to use a water-based adhesive containing a PVA-based resin (PVA-based adhesive). From the perspective of adhesiveness, the average degree of polymerization of the PVA-based resin contained in the water-based adhesive is preferably about 100 to 5500, and more preferably 1000 to 4500. From the perspective of adhesiveness, the average saponification degree is preferably about 85 mol% to 100 mol%, and more preferably 90 mol% to 100 mol%.

As for the PVA resin contained in the above-mentioned water-based adhesive, the one containing acetylacetyl groups is preferred because the PVA resin layer has excellent adhesion to the protective film and excellent durability. The PVA resin containing acetylacetyl groups can be obtained by, for example, reacting the PVA resin with diketene by any method. The degree of acetylacetyl group modification of the PVA resin containing acetylacetyl groups is typically 0.1 mol% or more, preferably 0.1 mol% to 20 mol%.

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

(crosslinking agent, solvent)

The water-soluble PVA-based adhesive that can be preferably used in the present invention may contain a crosslinking agent as needed in addition to the above-mentioned PVA-based resin and urea-based compound. As for the crosslinking agent, known crosslinking agents can be used. Examples include: water-soluble epoxy compounds, dialdehydes, isocyanates, etc.

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

In addition, the water-soluble PVA adhesive of the present invention may contain an organic solvent. In this case, alcohols are preferred in terms of miscibility with water, and methanol or ethanol is preferred among alcohols.

In addition, in the present invention, a part of the urea derivative has low solubility in water, whereas the solubility in alcohol is sufficient. In this case, after dissolving in alcohol to prepare an alcohol solution of the urea derivative, the alcohol solution of the urea derivative is added to the PVA aqueous solution to prepare the bonding agent, which is also one of the better embodiments.

(Active energy ray-curing adhesive)

As for the above-mentioned active energy ray curing adhesive, any appropriate adhesive can be used as long as it is an adhesive cured by irradiation with active energy rays. As for the active energy ray curing adhesive, for example, ultraviolet curing adhesive, electron beam curing adhesive, etc. can be listed. As for the specific examples of the curing type of the active energy ray curing adhesive, for example, free radical curing type, cationic curing type, anionic curing type, and combinations thereof (for example, a mixed type of free radical curing type and cationic curing type) can be listed.

As for the above-mentioned active energy ray-curable adhesive, for example, there can be cited an adhesive containing a compound (e.g., a monomer and/or an oligomer) having a free radical polymerizable group such as a (meth)acrylate group or a (meth)acrylamide group as a curing component.

Specific examples of the above-mentioned active energy ray-curable adhesive and the curing method are described in, for example, Japanese Patent Publication 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.

As for the method of making the adhesive layer contain urea compounds, it is preferred to make the above-mentioned adhesive contain urea compounds. In addition, in the process of forming the adhesive layer through the drying step, it is not a problem that part of the urea compound moves from the adhesive layer to the polarizing element, etc.

Urea compounds include water-soluble and water-insoluble ones, and both types of urea compounds can be used in the present invention. When using water-insoluble urea compounds in water-soluble adhesives, it is advisable to design a dispersion method after forming the adhesive layer so that the mist does not increase.

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, urea derivatives refer to compounds having a molecular structure in which a portion of urea is substituted by a substituent. Urea derivatives are preferably compounds in which at least one of the four hydrogen atoms of the urea molecule is substituted by a substituent.

In this case, the substituent is not particularly limited, but preferably a substituent composed of carbon atoms, hydrogen atoms and oxygen atoms.

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

2 Substituted ureas include, for example: 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), tetrahydro-2-pyrimidinone (propylene urea).

4-substituted urea can be exemplified by tetramethyl urea, 1,1,3,3-tetraethyl urea, 1,1,3,3-tetrabutyl urea, 1,3-dimethoxy-1,3-dimethyl urea, 1,3-dimethyl-2-imidazolidinone, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone.

(Thiourea or thiourea derivatives)

In the present invention, thiourea derivatives refer to compounds having a molecular structure in which a portion of thiourea is substituted by a substituent. Thiourea derivatives are preferably compounds in which at least one of the four hydrogen atoms of the thiourea molecule is substituted by a substituent.

In this case, the substituent is not particularly limited, but preferably a substituent composed of carbon atoms, hydrogen atoms and oxygen atoms.

As specific examples of thiourea derivatives, monosubstituted thiourea may include: 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, p-tolylthiourea.

2 Substituted thioureas include, for example: 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, ethylenethiourea.

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

Among the above compounds, when used in an image display device composed of interlayer filling, urea derivatives or thiourea derivatives are preferred, and urea derivatives are more preferred, from the point of less reduction in transmittance and polarization degree in a high temperature environment. Among urea derivatives, monosubstituted urea or disubstituted urea are preferred, and monosubstituted urea is more preferred. Among disubstituted ureas, there are 1,1-substituted urea and 1,3-substituted urea, and 1,3-substituted urea is more preferred.

[Transparent protective film]

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

In addition, in the structure where the protective film is laminated on 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 adhesive layer containing the urea compound of the present invention. Preferably, both sides of the adhesive layer are the adhesive layer containing the urea compound of the present invention.

In recent years, in order to meet the demand for thinner polarizing plates, polarizing plates with a protective film on only one side of the polarizing element are being developed. In this structure, it is better to laminate the protective film with the urea-containing compound adhesive layer of the present invention.

As a method for manufacturing a polarizing plate having a protective film only on one side of a polarizing element, it is conceivable to first manufacture a polarizing plate having protective films laminated on both sides via adhesive layers, and then peel off the protective film on one side. When using this manufacturing method, it is not a problem that only one side of the adhesive layer is the adhesive layer of the present invention, but it is more preferable to use the adhesive layer containing urea-based compounds of the present invention on both sides of the polarizing element.

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

The protective film can have other optical functions at the same time, and can also further form other layered structures.

At this time, the thickness of the protective film is preferably thinner from the perspective of optical properties, but if it is too thin, the strength will decrease and the processability will deteriorate. The appropriate film thickness is 5 to 100μm, preferably 10 to 80μm, and more preferably 15 to 70μm.

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

When the polarizing element has a protective film on both sides, when a water-based adhesive such as a PVA-based adhesive is used for bonding, from the perspective of moisture permeability, it is preferred that the protective film on at least one side is either an acylated cellulose film or a (meth) acrylic polymer film, among which the acylated cellulose film is preferred.

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

In addition, although the structure in which the film with phase difference function is directly attached to the polarizing element via an adhesive has been described, a structure in which the film is attached to the polarizing element via another protective film and an adhesive or adhesive is also possible.

[Composition of image display device]

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

(Image display unit)

As for the image display unit, for example, a liquid crystal unit or an organic EL unit can be cited. As for the liquid crystal unit, any of the following can be used: a reflective liquid crystal unit that uses an external light source, a transmissive liquid crystal unit that uses light from a light source such as a backlight, and a semi-transmissive and semi-reflective liquid crystal unit that uses both light from the outside and light from the light source. When the liquid crystal unit uses light from a light source, the image display device (liquid crystal display device) is configured with a polarizing plate on the side opposite to the viewing side of the image display unit (liquid crystal unit), and further configured with a light source. It is preferred that the polarizing plate on the light source side and the liquid crystal unit are bonded via an appropriate adhesive layer.

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

As for the organic EL unit, a transparent substrate in which a transparent electrode, an organic light-emitting layer, and a metal electrode are sequentially stacked to form a light-emitting body (organic electroluminescent light-emitting body) can be appropriately used. The organic light-emitting layer is a laminate of various organic thin films, for example: a laminate of a hole injection layer composed of triphenylamine derivatives and a light-emitting layer composed of fluorescent organic solids such as anthracene, or a laminate of such a light-emitting layer and an electron injection layer composed of perylene derivatives, or a laminate of a hole injection layer, a light-emitting layer, and an electron injection layer, etc., and various layer structures can be adopted.

(Attachment of image display unit and polarizing plate)

The image display unit and the polarizing plate are preferably bonded together using an adhesive layer (adhesive sheet). From the perspective of workability, it is preferred to bond the polarizing plate and the image display unit together by attaching an adhesive layer to one side of the polarizing plate. The adhesive layer can be bonded to the polarizing plate in an appropriate manner. Examples of such methods include dissolving or dispersing the base polymer or the composition in a solvent composed of a single or mixed appropriate solvent such as toluene or ethyl acetate to prepare an adhesive solution of about 10 to 40% by weight, and directly attaching the adhesive solution to the polarizing plate by a suitable spreading method such as casting or coating, or forming an adhesive layer on a separator according to the above method and transferring the adhesive layer to the polarizing plate.

(Adhesive layer)

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

(Transparent component in front)

As for the transparent components disposed in front of the visual side of the image display unit, for example, a front panel (window layer) or a touch panel can be cited. The front panel can use a transparent plate with appropriate mechanical strength and thickness. For such a transparent plate, for example, a transparent resin plate such as an acrylic resin or a polycarbonate resin, or a glass plate can be used. Functional layers such as an anti-reflection layer can also be laminated on the visual side of the transparent plate. In addition, when the transparent plate is a transparent resin plate, a hard coating layer for improving physical strength or a low moisture permeability layer for reducing moisture permeability can be laminated.

As for the touch panel, various touch panels such as the resistive film method, electrostatic capacitance method, optical method, ultrasonic method, etc., or glass plates or transparent resin plates with touch sensor functions can be used. When an electrostatic capacitance method touch panel is used as the front transparent component, it is better to have a front panel composed of glass or transparent resin plate located on the viewing side relative to the touch panel.

(Polarizing plate and the front transparent component are bonded together)

The polarizing plate and the front transparent component are bonded together using an adhesive or a UV curing adhesive. When using an adhesive, the adhesive can be bonded in an appropriate manner. As for the specific bonding method, for example, the bonding method of the adhesive layer used when bonding the aforementioned image display unit and the polarizing plate can be cited.

When using UV curable adhesive, in order to prevent the diffusion of the adhesive solution before curing, it is suitable to use a method in which a weir is set to surround the periphery of the image display panel, and a front transparent component is placed on the weir, and then the adhesive solution is injected. After the adhesive solution is injected, the position is adjusted as needed and degassing is performed, and then UV light is irradiated for curing.

Next, the present invention will be described in which the polarizing element has an adhesive layer containing at least one urea compound on at least one side thereof.

Furthermore, as mentioned above, 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 is an adhesive layer.

[Urea compound containing layer]

In this aspect of the present invention, the polarizing plate has 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 and orientation, and containing at least one selected from urea, urea derivatives, thiourea, and thiourea derivatives.

The urea compound-containing layer preferably has at least one urea compound and an adhesive. As for the adhesive, for example, polymer adhesives, thermosetting adhesives, active energy ray-hardening adhesives, etc., any adhesive in the present invention can be suitably used.

The thickness of the urea 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 compound layer can be directly laminated on the polarizing element or laminated through other layers. However, in terms of the ease of suppressing the reduction of transmittance in a high temperature environment, it is better to laminate directly on the polarizing element.

In this embodiment, the polarizing plate preferably has a transparent protective film on at least one side of the polarizing element through an adhesive layer in order to improve the physical strength of the polarizing plate. At this time, the adhesive layer may or may not contain urea compounds, but it is better to contain urea compounds.

As described in the description of other types of protective films, in recent years, in order to meet the requirements for thinning polarizing plates, polarizing plates with protective films only on one side of the polarizing element have been developed (hereinafter also referred to as "polarizing plates with single-sided protective films").

In such a structure, in order to improve physical strength, etc., an attempt was made to form a hardening layer on the area of the protective film without the polarizing element. (For example: Japanese Patent Publication No. 2011-221185)

In the present invention, it is also a preferred embodiment to make such a hardening layer contain urea compounds. Usually, such a hardening layer is formed by a hardening composition containing an organic solvent, but in paragraphs [0020] to [0042] of Japanese Patent Publication No. 2017-075986, a method of forming such a hardening layer from an aqueous solution of an active energy ray-hardening polymer composition is described. Since urea compounds are mostly water-soluble, it is also a preferred embodiment of the present invention to make such a composition contain water-soluble urea compounds to form a urea compound-containing layer.

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

This type of feature is that it is used in interlayer filling to form a polarizing plate, and is a polarizing element that can suppress the decrease in monomer transmittance even when exposed to a high temperature environment for a long time. This polarizing element can be manufactured by coating at least one solution selected from urea, urea derivatives, thiourea and thiourea derivatives on at least one side of a polarizing element composed of an iodine-adsorbed stretched polyvinyl alcohol-based resin film, and then drying the coating liquid.

(Urea compound solution)

The solvent of the urea compound solution of the present invention is preferably water, an organic solvent or a mixture of these, and preferably water or a mixed solvent of water and alcohol. Moreover, if it is a mixed solvent of water and alcohol, the alcohol is preferably methanol or ethanol.

Urea compounds can be applied to the aforementioned urea compounds, but since it is difficult for urea compounds to precipitate on the surface of the polarizing element after drying, water-soluble urea compounds are preferred.

[Implementation example]

The present invention is described in detail below based on the examples. The materials, reagents, substance amounts and their ratios, operations, etc. shown in the following examples can be appropriately changed within the scope of the present invention. Therefore, the present invention is not limited to those in the following examples.

(Production of polarizing element 1)

A 40μm thick PVA film with an average polymerization degree of 2400 and a saponification degree of 99.9 mol% was immersed in warm water at 25°C for 120 seconds to swell it. Then, it was immersed in an aqueous solution of iodine/potassium iodide (weight ratio = 2/3) with a concentration of 0.6 wt% to stretch it 2.1 times and dye the PVA film. Afterwards, it was stretched in an acid bath containing boric acid and potassium iodide at 60°C, and then washed with water and dried to produce a polarizing element 1 with a film thickness of 15μm.

(Preparation of PVA solution for subsequent use)

Dissolve 50g of modified PVA resin containing acetyl acetyl group (GOHSENX Z-410 manufactured by Mitsubishi Chemical Co., Ltd.) in 950g of pure water, heat at 90℃ for 2 hours and then cool to room temperature to obtain PVA solution for adhesive.

(Preparation of urea compound solution)

Add 10g of urea to 90g of pure water to obtain a 10% by weight urea aqueous solution (solution 1). Similarly, according to Table 1, replace urea with the urea-based compounds described in Table 1, and replace the solvent from pure water to methanol as needed to prepare solutions 2 to 9.

[Table 1]

Any of the urea, methyl urea, ethyl urea, 1,3-dimethyl urea, tetramethyl urea, phenyl urea, thiourea, methyl thiourea, and tetrahydro-2-pyrimidinone used in the above are reagents from Tokyo Chemical Industry Co., Ltd.

(Preparation of adhesive 1 for polarizing plate)

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

(Adhesive preparation for polarizing plates 2 to 14)

Similarly, the adhesive PVA solution, the solution of the urea compound described in Table 1, pure water, and methanol were mixed to obtain a PVA concentration of 3.0%, a methanol concentration of 20%, and a urea compound concentration described in Table 2 to obtain adhesives 2 to 14 for polarizing plates.

In addition, polarizing plate adhesive 12 uses two types of urea compounds, methyl urea and 1,3-dimethyl urea, together, while polarizing plate adhesive 14 does not contain urea compounds.

[Table 2]

(Saponification of acetylated cellulose membrane)

The commercially available acetylated cellulose membrane TD40 (Fuji Film Co., Ltd.: membrane thickness 40μm) was immersed in a 1.5mol/L NaOH aqueous solution (saponification solution) maintained at 55℃ for 2 minutes, then washed with water, and then immersed in a 0.05mol/L sulfuric acid aqueous solution at 25℃ for 30 seconds, and then washed in running water for 30 seconds to make the membrane neutral. Then, the membrane was drained three times by an air scraper, and after draining, it was retained in a drying area at 70℃ for 15 seconds for drying to produce a saponified membrane.

(Production of polarizing plate 1)

On both sides of the polarizing element 1, the saponified acetylated cellulose film prepared above is applied with adhesive 1 through the polarizing plate. The thickness of the adhesive layer after drying is adjusted to 100nm on both sides. After lamination using a roller laminating machine, it is dried at 60℃ for 10 minutes to obtain a polarizing plate 1 with acetylated cellulose films on both sides.

(Production of polarizing plates 2 to 14)

Polarizing plates 2 to 14 are made by performing the same operation as polarizing plate 1, except that polarizing plate adhesive 1 is replaced by polarizing plate adhesives 2 to 14.

(Production of laminate 1)

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

(Production of layers 2 to 14)

The same operation is performed to produce optical laminates 2 to 14, except that polarizing plate 1 is replaced by polarizing plates 2 to 14, as in optical laminate 1.

(Production of laminate 15)

Optical laminate 14 is manufactured by performing the same operation as optical laminate 14, except that the adhesive layer is laminated only on one side, thereby manufacturing optical laminate 15.

(Evaluation of multilayer bodies)

The laminates prepared above were evaluated with reference to the embodiments of Japanese Patent Publication No. 2014-102353 and Japanese Patent Publication No. 2018-025765. In addition, the high temperature durability test was conducted at 95°C and 105°C. The high temperature durability test was conducted at 95°C until 1000 hours. No decrease in transmittance was found except for Comparative Example 1 using the polarizing plate adhesive 14 without adding urea compounds. Table 3 only shows the results of the high temperature durability test at 105°C.

In the test results of Comparative Example 1, the coloring results at 105℃×100 hours are almost the same as those at 95℃×1000 hours.

[Evaluation of single body penetration after high temperature durability test (105℃)]

The optical laminates 1 to 14 prepared above were cut into a size of 50 mm × 100 mm, and the surfaces of the first adhesive layer and the second adhesive layer were bonded to alkali-free glass [trade name "EAGLE XG", manufactured by Corning] to prepare evaluation samples. In addition, the optical laminate 15 was cut into a size of 50 mm × 100 mm, and the surface of the first adhesive layer was bonded to alkali-free glass [trade name "EAGLE XG", manufactured by Corning] to prepare evaluation samples. In addition, when preparing these samples, no heat treatment for adjusting the moisture content was performed before the glass plates were bonded.

For this evaluation sample, after being treated in an autoclave at a temperature of 50°C and a pressure of 5kgf/ ^cm2 (490.3kPa) for 1 hour, it was placed in an environment at a temperature of 23°C and a relative humidity of 55% for 24 hours. Afterwards, the transmittance (initial value) was measured, and the transmittance was measured every 50 hours after being stored in a heated environment at a temperature of 105°C for 100 to 200 hours. The evaluation was based on the time when the transmittance of the initial value decreased by more than 5%, and the following criteria were used for evaluation. The results are shown in Table 3.

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

After 200 hours, the penetration rate drops below 5%: A

The penetration rate decreases by more than 5% between 150 and 200 hours: B

The penetration rate decreases by more than 5% between 100 and 150 hours: C

After 100 hours, the penetration rate drops by more than 5%: D

[Evaluation of orthogonal light leakage after high temperature durability test]

Cut the optical laminate 15 into a size of 30 mm × 30 mm, and adhere the surface of the first adhesive layer to alkali-free glass [trade name "EAGLE XG", manufactured by Corning] to produce a sample 20 for orthogonal light leakage evaluation.

After the single body transmittance evaluation sample after high temperature durability was evaluated for 100 hours, the light leakage of the above optical layer and sample 20 under the crossed nicols state was visually evaluated according to the following standards (hereinafter referred to as "crossed light leakage").

Those who did not see any orthogonal light leakage at all: ◎

Almost no orthogonal light leakage was seen: ○

Those who saw slight orthogonal light leakage: △

Those who can clearly see the orthogonal light leakage: ×

[Table 3]

Explain the addition amount of urea compounds in Table 3.

As mentioned above, the amount of urea compounds 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, any urea-based compound shows a smaller change in monomer transmittance after the high-temperature durability test as the amount added increases. On the contrary, the orthogonal light leakage after the high-temperature durability test tends to become smaller as the amount added decreases.

Any of the urea compounds described in the examples shows that the monomer transmittance changes to B or more after the high-temperature durability test, and at the same time shows that the orthogonal light leakage is above △, and has excellent effects in both performances.

However, regarding the amount of the above compounds, the addition amount ranges are strictly different according to the preferred performance of each compound, that is, the performance of showing a single transmittance change of B or more and showing an orthogonal light leakage of △ or more. The addition amount of any compound has an appropriate range within the aforementioned preferred addition amount range.

The addition amount described in Table 3 represents the value of the minimum addition amount for the monomer transmittance to be evaluated as A in each urea-based compound. In addition, for urea and thiourea, the addition amount is gradually reduced from the minimum addition amount for evaluation A, and the orthogonal light leakage is the value of the addition amount from △ to ○ (the monomer transmittance changes to B at this time). In addition, for methyl urea, the addition amount is gradually reduced from the minimum addition amount for evaluation A, and the orthogonal light leakage is the result of the addition amount from ○ to ◎ (the monomer transmittance changes to B at this time).

The results shown in Table 3 show the following.

1. The polarizing plate of the present invention using an adhesive containing a urea compound can suppress the decrease in the monomer transmittance even when used in an image display device composed of interlayer filling or when exposed to a high temperature environment for a long time.

2. In particular, compared to those using urea or thiourea, those using urea derivatives or thiourea derivatives not only do not reduce the monomer transmittance, but also have no orthogonal light leakage, and the quality is particularly good.

3. Using adhesives containing two urea compounds, which can also suppress the decrease of monomer penetration rate when exposed to high temperature environment for a long time, is also one of the better embodiments of the present invention.

Next, other examples are shown, but this example is not limited to the following examples.

With respect to the composition of the curable layer forming composition BLC-1 described in paragraphs [0075] to [0076] of Japanese Patent Publication No. 2017-075986, methyl urea was added so that the solid concentration of methyl urea became 1% by weight, and pure water was added so that the total solid concentration became 26% by weight. After mixing, the mixture was irradiated with ultrasound and passed through a filter with a pore size of 5μm to prepare a curable composition (UBLC-1) containing a urea-based compound.

With reference to the polarizing plate 1 described in paragraphs [0070] to [0080] of Japanese Patent Publication No. 2017-075986, a polarizing plate (polarizing plate 22) having a protective film with a hardening layer containing no urea compound on one side is manufactured.

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

For optical stack 14, the same operation is performed except that each polarizing plate 14 is replaced by polarizing plate 21 and polarizing plate 22 to obtain optical stack 21 and optical stack 22. These samples are evaluated in the same manner as optical stack 14, and the results obtained are shown in Table 4.

In addition, the evaluation of orthogonal light leakage after high temperature durability is conducted with the transparent protective film surface facing the outside.

[Table 4]

The results shown in Table 4 show the following.

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

Further examples of other aspects are shown, but such aspects are not limited to the following examples.

Prepare a 0.5% solution of methyl urea as a coating liquid. Use a coating rod to apply the 0.5% solution of methyl urea to one side of the polarizing element 1 prepared above so that the wet coating amount becomes 10μm, and dry it at 60℃ for 5 minutes to obtain the polarizing element 2.

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

For polarizing plate 14, except for replacing polarizing element 1 with polarizing element 2 and polarizing element 3, the same operation is performed to obtain polarizing plate 31 and polarizing plate 32.

For optical stack 14, the same operation is performed except that each polarizing plate 14 is replaced by polarizing plate 31 and polarizing plate 32 to obtain optical stack 31 and optical stack 32. These samples are evaluated in the same way as optical stack 14, and the results are shown in Table 5.

[Table 5]

The results shown in Table 5 show the following.

1. A solution containing a urea compound is coated on at least one side of a polarizing element, and the polarizing element is dried and manufactured. When the polarizing plate of the present invention having the polarizing element is used in an image display device having an interlayer filling structure, the decrease in the monomer transmittance can be suppressed even when exposed to a high temperature environment for a long time.

Claims (12)

A polarizing plate comprises a polarizing element, which is a polyvinyl alcohol resin polarizing element formed by iodine adsorption and orientation; a urea compound layer, which is formed on at least one side of the polarizing element and contains at least one urea compound selected from urea derivatives, thiourea and thiourea derivatives; and a transparent protective film, wherein the urea derivative is selected from methyl urea, ethyl urea, propyl urea, butyl urea, isobutyl urea, N-octadecyl urea, 2-hydroxyethyl urea, hydroxy urea, acetyl urea, allyl urea, 2-propynyl urea, cyclohexyl urea, phenyl urea, 3-hydroxyphenyl urea, (4-methoxyphenyl) urea, benzyl urea, benzoyl urea, o-tolyl urea, p-tolyl urea, 1,1- At least one of dimethyl urea, 1,3-dimethyl urea, 1,1-diethyl urea, 1,3-diethyl urea, 1,3-bis(hydroxymethyl)urea, 1,3-tert-butyl urea, 1,3-dicyclohexyl urea, 1,3-diphenyl urea, 1,3-bis(4-methoxyphenyl)urea, 1-acetyl-3-methyl urea, 2-imidazolidinone (ethylene urea), tetrahydro-2-pyrimidinone (propylene urea), tetramethyl urea, 1,1,3,3-tetraethyl urea, 1,1,3,3-tetrabutyl urea, 1,3-dimethoxy-1,3-dimethyl urea, 1,3-dimethyl-2-imidazolidinone, and 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone. The polarizing plate as described in claim 1, wherein the urea compound-containing layer is an adhesive layer, and the transparent protective film is bonded via the adhesive layer. The polarizing plate as described in claim 2, wherein the adhesive layer further contains a polyvinyl alcohol resin. The polarizing plate as described in claim 3, wherein the total content of the aforementioned urea-based compound contained in the aforementioned 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. A polarizing plate as described in any one of claims 1 to 4, wherein the urea compound is a urea derivative and/or a thiourea derivative. A polarizing plate as described in any one of claims 2 to 4, wherein the thickness of the adhesive layer is 0.01 to 7 μm. The polarizing plate as described in claim 1, wherein the urea compound-containing layer is a resin layer other than the adhesive layer. A polarizing plate as described in any one of claims 1 to 4, wherein the polarizing plate is used in an image display device having an interlayer filling structure. A method for manufacturing a polarizing plate is a method for manufacturing a polarizing plate having a transparent protective film attached to at least one side of a polarizing element. The method comprises the following steps: a step of forming an adhesive layer, on at least one side of a polarizing element composed of a stretched polyvinyl alcohol resin film adsorbed and aligned with iodine, using a polyvinyl alcohol resin and an adhesive composition to form an adhesive layer, wherein the adhesive composition contains a urea derivative, thiourea and a thiourea derivative. At least one urea compound in the mixture; and a laminating step, which is to laminate a transparent protective film through the adhesive layer simultaneously with or after the step of forming the adhesive layer, wherein the urea derivative is selected from methyl urea, ethyl urea, propyl urea, butyl urea, isobutyl urea, N-octadecyl urea, 2-hydroxyethyl urea, hydroxy urea, acetyl urea, allyl urea, 2-propynyl urea, cyclohexyl urea, phenyl urea, 3-Hydroxyphenyl urea, (4-methoxyphenyl) urea, benzyl urea, benzoyl urea, o-tolyl urea, p-tolyl urea, 1,1-dimethyl urea, 1,3-dimethyl urea, 1,1-diethyl urea, 1,3-diethyl urea, 1,3-bis(hydroxymethyl) urea, 1,3-tert-butyl urea, 1,3-dicyclohexyl urea, 1,3-diphenyl urea, 1,3-bis(4-methoxyphenyl) At least one of urea, 1-acetyl-3-methylurea, 2-imidazolidinone (ethylene urea), tetrahydro-2-pyrimidinone (propylene urea), tetramethyl urea, 1,1,3,3-tetraethyl urea, 1,1,3,3-tetrabutyl urea, 1,3-dimethoxy-1,3-dimethyl urea, 1,3-dimethyl-2-imidazolidinone, and 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone. An image display device, comprising: an image display panel, on which a polarizing plate as described in any one of claims 1 to 8 is bonded via an adhesive layer to the surface of the viewing side of an image display unit; and a transparent component, which is bonded to the polarizing plate surface on the viewing side of the image display panel via an adhesive layer. An image display device as described in claim 10, wherein the transparent component is a glass plate or a transparent resin plate. An image display device as described in claim 10, wherein the transparent component is a touch panel.