KR20230067700A - Polarizer and image display device - Google Patents

Abstract

An object of the present invention is to provide a polarizing plate in which a decrease in transmittance in a high-temperature environment is suppressed. A polarizing plate having a polarizing element in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin layer, and a transparent protective film laminated on at least one surface of the polarizing element, wherein the polarizing element and the transparent protective film comprise a urea-based compound and It is bonded by an adhesive layer formed of an adhesive containing a reducing agent, the urea-based compound is at least one selected from the group consisting of urea, urea derivatives, thiourea and thiourea derivatives, and the moisture content of the polarizing element is , The equilibrium moisture content at a temperature of 20 ° C. and a relative humidity of 30% or more, and a polarizing plate having an equilibrium moisture content at a temperature of 20 ° C. and a relative humidity of 50% or less.

Description

Polarizer and image display device

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

BACKGROUND OF THE INVENTION Liquid crystal display devices (LCDs) are widely used not only for liquid crystal televisions, but also for mobile devices such as personal computers and mobile phones, and for in-vehicle applications such as car navigation systems. Usually, a liquid crystal display device has a liquid crystal panel in which polarizing plates are bonded with an adhesive to both sides of a liquid crystal cell, and display is performed by controlling light from a backlight to the liquid crystal panel. [0003] Recently, organic EL display devices, like liquid crystal display devices, have been widely used for mobile applications such as televisions and mobile phones, as well as vehicle-mounted applications such as car navigation systems. In an organic EL display device, in order to prevent external light from being reflected by a metal electrode (cathode) and being viewed as a specular surface, a circular polarizing plate (a laminate including a polarizing element and a λ/4 plate) is placed on the viewer-side surface of an image display panel. sieve) may be placed.

As described above, polarizing plates are increasingly installed in vehicles as members of image display devices such as liquid crystal display devices and organic EL display devices. Polarizing plates used in vehicle-mounted image display devices are often exposed to high temperature environments compared to mobile applications such as televisions and mobile phones, so the change in properties at higher temperatures is smaller (high temperature durability) is required.

On the other hand, for the purpose of preventing damage to the image display panel due to impact from the outer surface, etc., a configuration in which a front plate such as a transparent resin plate or glass plate (also called a "window layer") is provided on the viewer side rather than the image display panel It is increasing. BACKGROUND OF THE INVENTION [0002] In an image display device including a touch panel, a configuration in which the touch panel is provided on the viewer side rather than the image display panel and a front plate is provided on the viewer side more than the touch panel is widely adopted.

In this configuration, when an air layer exists between the image display panel and a transparent member such as a front plate or a touch panel, reflection of light at the interface between the air layer causes reflection of external light, and screen visibility tends to deteriorate. . Therefore, a structure in which the space between the transparent member and the polarizing plate disposed on the visual side surface of the image display panel is filled with a layer other than the air layer and usually a solid layer (hereinafter sometimes referred to as "interlayer filler") (hereinafter referred to as "interlayer filler"). , sometimes referred to as "interlayer filling configuration") is spreading. The interlayer filler is preferably a material having a refractive index similar to that of the polarizing plate or the transparent member. As the interlayer filler, a pressure-sensitive adhesive or a UV curable adhesive is used for the purpose of suppressing the decrease in visibility due to reflection at the interface and bonding and fixing between the respective members (see, for example, Patent Document 1).

Adoption of the interlayer charging configuration in mobile applications such as mobile phones, which are often used outdoors, is spreading. In addition, as the demand for visibility has recently increased, even in vehicle-mounted applications such as car navigation devices, interlayer filling by disposing a front transparent plate on the surface of an image display panel and filling the gap between the panel and the front transparent plate with an adhesive layer or the like Adoption of the configuration is being considered.

However, it has been reported that the transmittance of the polarizing plate significantly decreases in a high-temperature environment when such a configuration is employed. In Patent Document 2, as a solution to the problem, the amount of water per unit area of the polarizing plate is set to a predetermined amount or less, and the saturation absorption of the transparent protective film adjacent to the polarizing element is set to a predetermined amount or less, thereby suppressing the decrease in transmittance. A method is proposed. .

[Patent Document 1] Japanese Unexamined Patent Publication No. Heisei 11-174417 [Patent Document 2] Japanese Unexamined Patent Publication No. 2014-102353

However, even with such a polarizing plate, the effect of suppressing the decrease in transmittance in a high-temperature environment was not sufficient. An object of the present invention is to provide a novel polarizing plate capable of suppressing a decrease in transmittance under a high-temperature environment and an image display device using the polarizing plate.

The present invention provides a polarizing plate and an image display device exemplified below.

[1] A polarizing plate having a polarizing element in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin layer and a transparent protective film laminated on at least one side of the polarizing element,

The polarizing element and the transparent protective film are bonded by an adhesive layer formed of an adhesive containing a urea compound and a reducing agent,

The urea-based compound is at least one selected from the group consisting of urea, urea derivatives, thiourea and thiourea derivatives,

The moisture content of the polarizing element is equal to or higher than the equilibrium moisture content at a temperature of 20 ° C. and a relative humidity of 30%, and is equal to or less than the equilibrium moisture content at a temperature of 20 ° C. and a relative humidity of 50%.

[2] A polarizing plate having a polarizing element in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin layer and a transparent protective film laminated on at least one surface of the polarizing element,

The polarizing element and the transparent protective film are bonded by an adhesive layer formed of an adhesive containing a urea compound and a reducing agent,

The urea-based compound is at least one selected from the group consisting of urea, urea derivatives, thiourea and thiourea derivatives,

The moisture content of the polarizing plate is equal to or greater than the equilibrium moisture content at a temperature of 20 ° C. and a relative humidity of 30%, and less than the equilibrium moisture content at a temperature of 20 ° C. and a relative humidity of 50%.

[3] The polarizing plate according to [1] or [2], wherein the adhesive contains at least one urea-based compound selected from the group consisting of urea derivatives and thiourea derivatives.

[4] The polarizing plate according to any one of [1] to [3], wherein the adhesive contains a polyvinyl alcohol-based resin.

[5] The polarizing plate according to [4], wherein in the adhesive, the content of the urea compound is 0.1 part by mass or more and 400 parts by mass or less with respect to 100 parts by mass of the polyvinyl alcohol-based resin.

[6] The polarizing plate according to [4] or [5], wherein the content of the reducing agent in the adhesive is 1 part by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the polyvinyl alcohol-based resin.

[7] The polarizing plate according to any one of [1] to [6], wherein the adhesive layer has a thickness of 0.01 μm or more and 7 μm or less.

[8] The polarizing plate according to any one of [1] to [7], wherein the reducing agent is at least one selected from the group consisting of ascorbic acid, erythorbic acid, thiosulfuric acid, sulfurous acid, and salts thereof.

[9] The polarizing plate is used in an image display device,

The polarizing plate according to any one of [1] to [8], wherein a solid layer is formed in contact with both surfaces of the polarizing plate in the image display device.

[10] An image display cell, a first pressure sensitive adhesive layer laminated on the visual side surface of the image display cell, and the polarizing plate according to any one of [1] to [9] laminated on the visual side surface of the first pressure sensitive adhesive layer. An image display device having a

[11] The image display device according to [10], further comprising a second pressure sensitive adhesive layer laminated on the visual side surface of the polarizing plate, and a transparent member laminated on the visual side surface of the second pressure sensitive adhesive layer.

[12] The image display device according to [11], wherein the transparent member is a glass plate or a transparent resin plate.

[13] The image display device according to [11], wherein the transparent member is a touch panel.

According to the present invention, it is possible to provide a polarizing plate with improved durability at high temperatures and suppressed decrease in transmittance due to high temperatures even when used in an image display device having an interlayer filling configuration. In addition, by using the polarizing plate according to the present invention, it is possible to provide an image display device in which a decrease in transmittance under a high-temperature environment is suppressed.

Hereinafter, although embodiment of this invention was described, this invention is not limited to the following embodiment.

[Polarizer]

The polarizing plate according to the present embodiment has a polarizing element in which a dichroic dye is adsorbed and oriented in a layer containing a polyvinyl alcohol-based resin and a transparent protective film. The polarizing element and the transparent protective film are bonded together by an adhesive layer formed of an adhesive containing a urea compound and a reducing agent. The polarizing plate according to the present embodiment has at least one of the following characteristics (a) and (b).

(a) The moisture content of the polarizing element is equal to or higher than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30% and lower than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 50%.

(b) The moisture content of the polarizing plate is equal to or greater than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30%, and less than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 50%.

As a conventional polarizing plate excellent in high-temperature durability, for example, a polarizing plate in which a decrease in transmittance is suppressed even when left alone in an environment at a temperature of 95° C. for 1000 hours is known. However, even with such a polarizing plate, when used in an interlayer filling structure, a significant decrease in transmittance may be observed at the central portion of the polarizing plate in-plane when left in an environment at a temperature of 95°C for 200 hours. A significant decrease in the transmittance of the polarizing plate in a high-temperature environment is caused by an image display device employing an interlayer filling structure in which one side of the polarizing plate is bonded to an image display cell and the other side is bonded to a transparent member such as a touch panel or a front plate. It is considered to be a problem that is particularly likely to occur when exposed to a high temperature environment.

The polarizer with significantly reduced transmittance due to the interlayer filling configuration has peaks around 1100 cm ^-1 (derived from =CC= bond) and 1500 cm ^-1 (derived from -C=C- bond) in Raman spectroscopy measurement. , It is considered that the polyene structure (-C=C) _n - is formed. It is presumed that the polyene structure is formed when polyvinyl alcohol constituting the polarizing element is polyenified by dehydration (Patent Document 2, paragraph [0012]).

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

<Polarizing element>

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

PVA type resin is obtained by saponifying polyvinyl acetate type resin. Examples of the polyvinyl acetate-based resin include polyvinyl acetate which is a homopolymer of vinyl acetate, as well as copolymers of vinyl acetate and other monomers copolymerizable with this. Examples of the other copolymerizable monomer include unsaturated carboxylic acids, olefins such as ethylene, vinyl ethers, and unsaturated sulfonic acids.

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

The thickness of the polarizing element is preferably 3 μm or more and 35 μm or less, more preferably 4 μm or more and 30 μm or less, still more preferably 5 μm or more and 25 μm or less. When the thickness of the polarizing element is 35 μm or less, the influence of the polyenization of the PVA-based resin on the decrease in optical properties can be suppressed in a high-temperature environment. When the thickness of the polarizing element is 3 μm or more, it becomes easy to set it as a structure that achieves desired optical characteristics.

The polarizing element preferably contains a urea compound and a reducing agent. In this embodiment, since the polarizing element and the transparent protective film are bonded by an adhesive layer formed of an adhesive containing a urea-based compound and a reducing agent, a part of the urea-based compound and a part of the reducing agent migrated from the adhesive layer to the polarizing element. It is presumed to be included in The urea compound and reducing agent in the polarizing element may contain what was added in the manufacturing process of the polarizing element. By providing an adhesive layer containing a urea-based compound and a reducing agent, even if the polarizing plate is exposed to a high-temperature environment, the transmittance is not easily reduced. In addition, by providing an adhesive layer containing a urea-based compound and a reducing agent, even when the polarizing plate is exposed to a high-temperature environment, a decrease in polarization degree can be suppressed. When two polarizing plates are disposed and used in a cross-Nicol relationship, when the degree of polarization of the polarizing plates decreases, light leakage (hereinafter also referred to as "cross leakage") tends to occur. However, according to the present invention, even when exposed to a high-temperature environment Since the degree of polarization is not easily reduced, cross leakage is also easily suppressed. It is presumed that this is because the polyenization of the PVA-based resin is suppressed by the urea-based compound and the reducing agent contained in the polarizing element.

As a method of containing a urea-based compound and a reducing agent in the polarizing element, a method of immersing the PVA-based resin layer in a treatment solvent containing a urea-based compound and/or a reducing agent, or spraying the treatment solvent onto the PVA-based resin layer, It can be flow-down or drop-down method. Among them, a method of immersing the PVA-based resin layer in a treatment solvent containing both a urea-based compound and a reducing agent is preferably used. Specific examples of the urea compound and the reducing agent include those exemplified as being contained in an adhesive described later.

The step of immersing the PVA-based resin layer in a treatment solvent containing a urea compound and a reducing agent may be performed simultaneously with steps such as swelling, stretching, dyeing, crosslinking, and washing in a method for manufacturing a polarizing element described later. You may provide separately from a process. The step of incorporating the urea compound and the reducing agent into the PVA-based resin layer is preferably performed after dyeing the PVA-based resin layer with iodine, and more preferably performed simultaneously with the crosslinking step after dyeing. According to this method, the color change is small and the influence on the optical properties of the polarizing element can be reduced.

In order to make the polarizing element contain the urea compound and the reducing agent, both the addition at the time of producing the polarizing element and the addition to the adhesive may be performed. In addition, one of a urea compound and a reducing agent may be contained at the time of manufacturing the polarizing element, and both may be contained in the adhesive.

(urea compound)

The urea-based compound is at least one selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives. A urea compound can be used individually by 1 type or in combination of 2 or more types. Urea-based compounds include those that are water-soluble and those that are poorly water-soluble, but either urea-based compounds can be used. When a poorly water-soluble urea-based compound is used for a water-soluble adhesive, it is preferable to devise a dispersion method so that the haze or the like does not occur after forming the adhesive layer.

(urea derivative)

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

Specific examples of urea derivatives include, as monosubstituted urea, 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 As replacement elements, 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) urea, 1-acetyl-3-methyl urea, 2-imida Zolidinone (ethylene urea) and tetrahydro-2-pyrimidinone (propylene urea) are exemplified.

4 Substituents, 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.

(thiourea derivative)

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

Specific examples of thiourea derivatives include N-methylthiourea, ethylthiourea, propylthiourea, isopropylthiourea, 1-butylthiourea, cyclohexylthiourea, N-acetylthiourea, N as monosubstituted thiourea. -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.

As disubstituted thiourea, 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.

As the trisubstituted thiourea, trimethylthiourea is exemplified, and as the tetrasubstituted thiourea, tetramethylthiourea and 1,1,3,3-tetraethylthiourea are exemplified.

Among urea-based compounds, urea derivatives or thiourea derivatives are used in an image display device having an interlayer filling configuration, in that a decrease in transmittance in a high temperature environment is suppressed and a decrease in polarization degree is small (cross leakage is suppressed). is preferred, and urea derivatives are more preferred. Among urea derivatives, a monosubstituted urea or a disubstituted urea is preferable, and a monosubstituted urea is more preferable. Two-substituted elements include 1,1-substituted elements and 1,3-substituted elements, but 1,3-substituted elements are more preferred.

(reducing agent)

Examples of the reducing agent include ascorbic acid (vitamin C), erythorbic acid, thiosulfuric acid, sulfurous acid, chlorogenic acid, citric acid, rosmarinic acid, and salts thereof. As a salt, alkali metal salts, such as a sodium salt and a potassium salt, etc. are mentioned. Among these, ascorbic acid, erythorbic acid, thiosulfuric acid, sulfurous acid and salts thereof are preferable. These reducing agents can be used individually by 1 type or in combination of 2 or more types. Further, the reducing agent added in the manufacturing process of the polarizing element or in the adhesive is contained as the reducing agent or its oxidized form derived from the reducing agent in the polarizing plate (in the polarizing element or adhesive layer). In this invention, even if it is a case where only the oxidized form of a reducing agent is contained in a polarizing plate, it shall contain a reducing agent. For example, ascorbic acid may exist as dihydroascorbic acid, which is an oxidized form, in a polarizing plate.

(Feature (a))

In the case of having feature (a), the moisture content of the polarizing element is equal to or higher than the equilibrium moisture content at a temperature of 20°C and 30% relative humidity, and less than or equal to the equilibrium moisture content at a temperature of 20°C and 50% relative humidity. The moisture content of the polarizing element is preferably equal to or less than the equilibrium moisture content at a temperature of 20°C and 45% relative humidity, more preferably equal to or less than the equilibrium moisture content at a temperature of 20°C and 42% relative humidity, and still more preferably equal to or less than the equilibrium moisture content at a temperature of 20°C and 38% relative humidity. is less than the equilibrium moisture content of If the moisture content of the polarizing element is less than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30%, the handling properties of the polarizing element deteriorate and crack easily. When the moisture content of the polarizing element exceeds the equilibrium moisture content at a temperature of 20°C and a relative humidity of 50%, the transmittance of the polarizing element tends to decrease. When the water content of the polarizing element is high, it is estimated that polyenization of the PVA-based resin proceeds easily. The moisture content of the polarizing element is the moisture content of the polarizing element in the polarizing plate.

As a method of confirming whether the moisture content of the polarizer is within the range of more than the equilibrium moisture content at a temperature of 20 ° C and a relative humidity of 30% and less than the equilibrium moisture content at a temperature of 20 ° C and a relative humidity of 50%, When stored in the environment and there is no change in mass for a certain period of time, it is considered that equilibrium with the environment has been reached, or the equilibrium moisture content of the polarizing element in the environment adjusted to the range of the temperature and the relative humidity is calculated in advance, and the polarizing element There is a way to check by comparing the moisture content of and the equilibrium moisture content calculated in advance.

The method for producing a polarizing element having a moisture content equal to or higher than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30% and equal to or less than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 50% is not particularly limited, but is adjusted within the range of the temperature and the relative humidity, for example. a method of storing the polarizing element in a heated environment for 10 minutes or more and 3 hours or less, or a method of heat treatment at 30°C or more and 90°C or less.

As another preferable method for producing a polarizing element having the above moisture content, a laminate in which a protective film is laminated on at least one side of the polarizing element or a polarizing plate constituted using a polarizing element is prepared in an environment adjusted to the above temperature and the above relative humidity ranges. For example, a method of storing for 10 minutes or more and 120 hours or less, or a method of heat treatment at 30°C or more and 90°C or less is exemplified. In the manufacture of an image display device employing an interlayer charging configuration, an image display panel in which a polarizing plate is laminated on an image display cell is stored in an environment adjusted to the above temperature and relative humidity ranges for 10 minutes or more and 3 hours or less or 30 After heating at 90°C or more and 90°C or less, the front plate may be bonded.

The moisture content of the polarizing element is preferably adjusted so that the moisture content is within the above numerical range at the stage of the material used for constituting the polarizing plate, which is a polarizing element alone or a laminate of a polarizing element and a protective film. In the case where the water content is adjusted after forming the polarizing plate, the curl becomes excessively large, and a problem may easily occur when bonding the polarizing plate to an image display cell. By constructing a polarizing plate using a polarizing element adjusted to have the moisture content in a material step prior to constructing the polarizing plate, it is possible to easily construct a polarizing plate having a polarizing element having a moisture content satisfying the numerical range. In the state where the polarizing plate is bonded to the image display cell, the moisture content of the polarizing element in the polarizing plate may be adjusted so as to fall within the above numerical range. In this case, since the polarizing plate is bonded to the image display cell, curling is unlikely to occur.

(Feature (b))

In the case of having feature (b), the moisture content of the polarizing plate is equal to or higher than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30%, and is equal to or less than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 50%. The moisture content of the polarizing plate is preferably equal to or less than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 45%, more preferably equal to or less than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 42%, and still more preferably equal to or less than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 38%. less than the equilibrium moisture content. When the moisture content of the polarizing plate is less than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 30%, the handling properties of the polarizing plate decrease and cracking becomes easy. When the moisture content of the polarizing plate exceeds the equilibrium moisture content at a temperature of 20°C and a relative humidity of 50%, the transmittance of the polarizing element tends to decrease. When the water content of the polarizing plate is high, it is estimated that it is because polyenization of PVA-type resin advances easily.

As a method of checking whether the moisture content of the polarizer is within the range of more than the equilibrium moisture content at a temperature of 20 ° C and a relative humidity of 30% and less than the equilibrium moisture content at a temperature of 20 ° C and a relative humidity of 50%, the environment adjusted to the range of the temperature and the relative humidity Stored in, a method of considering that equilibrium has been reached with the environment if there is no change in mass for a certain period of time, or pre-calculating the equilibrium moisture content of the polarizer in the environment adjusted to the range of the temperature and the relative humidity, and the moisture content of the polarizer A method of confirming by comparing the pre-calculated equilibrium moisture content may be mentioned.

The method for producing a polarizing plate having a moisture content equal to or higher than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 30% and less than or equal to an equilibrium moisture content at a temperature of 20° C. and a relative humidity of 50% is not particularly limited, but, for example, adjusted to the range of the temperature and the relative humidity A method of storing the polarizing plate in the environment for 10 minutes or more and 3 hours or less, or a method of heat treatment at 30°C or more and 90°C or less is exemplified.

In the manufacture of an image display device employing an interlayer charging configuration, an image display panel in which a polarizing plate is laminated on an image display cell is stored in an environment adjusted to the above temperature and relative humidity ranges for 10 minutes or more and 3 hours or less or 30 After heating at 90°C or higher and lower than 90°C, the front plate may be bonded.

(Method of manufacturing polarizing element)

The manufacturing method of the polarizing element is not particularly limited, but a method of sending out a PVA-based resin film wound in a roll shape in advance and performing stretching, dyeing, crosslinking, etc. (hereinafter referred to as "manufacturing method 1") or a PVA-based resin A method including a step of applying the containing coating liquid on a base film to form a PVA-based resin layer as a coating layer and stretching the resulting laminate (hereinafter referred to as "manufacturing method 2") is typical.

Manufacturing method 1 is a step of uniaxially stretching the PVA-based resin film, a step of dyeing the PVA-based resin film with a dichroic dye such as iodine and adsorbing the dichroic dye, and a PVA-based resin film adsorbed with the dichroic dye in a boric acid solution It can be produced through a process of treating with and a process of washing with water after treatment with an aqueous solution of boric acid.

The swelling step is a treatment step in which the PVA-based resin film is immersed in a swelling bath. In addition to being able to remove contamination, a blocking agent, etc. on the surface of a PVA system resin film by a swelling process, dyeing unevenness can be suppressed by swelling a PVA system resin film. A medium containing water as a main component, such as water, distilled water, and pure water, is usually used for the swelling bath. A surfactant, an alcohol, etc. may be suitably added to the swelling bath in accordance with a conventional method. From the viewpoint of controlling the potassium content of the polarizing element, potassium iodide may be used in the swelling bath. In this case, the concentration of potassium iodide in the swelling bath is preferably 1.5% by mass or less, more preferably 1.0% by mass or less, It is more preferable that it is 0.5 mass % or less.

The temperature of the swelling bath is preferably 10°C or more and 60°C or less, more preferably 15°C or more and 45°C or less, and still more preferably 18°C or more and 30°C or less. The immersion time in the swelling bath cannot be determined uniformly because the degree of swelling of the PVA-based resin film is affected by the swelling bath temperature, but is preferably 5 seconds or more and 300 seconds or less, more preferably 10 seconds or more and 200 seconds or less, , more preferably 20 seconds or more and 100 seconds or less. The swelling process may be performed only once, or may be performed a plurality of times as needed.

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

It is preferable that it is 0.01 mass % or more and 1 mass % or less, and, as for the iodine concentration in a dyeing bath, it is more preferable that it is 0.02 mass % or more and 0.5 mass % or less. The concentration of iodide in the dyeing bath is preferably 0.01 mass% or more and 10 mass% or less, more preferably 0.05 mass% or more and 5 mass% or less, and still more preferably 0.1 mass% or more and 3 mass% or less.

The temperature of the dyeing bath is preferably 10°C or more and 50°C or less, more preferably 15°C or more and 45°C or less, and still more preferably 18°C or more and 30°C or less. The immersion time in the dyeing bath cannot be determined uniformly because the degree of dyeing of the PVA-based resin film is affected by the dyeing bath temperature, but it is preferably 10 seconds or more and 300 seconds or less, and more preferably 20 seconds or more and 240 seconds or less. . The dyeing process may be performed only once, or may be performed a plurality of times as needed.

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

The concentration of the boron compound in the crosslinking bath is preferably 1% by mass or more and 15% by mass or less, more preferably 1.5% by mass or more and 10% by mass or less, and still more preferably 2% by mass or more and 5% by mass or less. When potassium iodide is used for the crosslinking bath, the concentration of potassium iodide in the crosslinking bath is preferably 1% by mass or more and 15% by mass or less, more preferably 1.5% by mass or more and 10% by mass or less, and 2% by mass or more and 5% by mass. % or less is more preferable.

The temperature of the crosslinking bath is preferably 20°C or more and 70°C or less, and more preferably 30°C or more and 60°C or less. The immersion time in the crosslinking bath cannot be determined uniformly because the degree of crosslinking of the PVA-based resin film is affected by the temperature of the crosslinking bath, but it is preferably 5 seconds or more and 300 seconds or less, and more preferably 10 seconds or more and 200 seconds or less. . The crosslinking step may be performed only once, or may be performed a plurality of times as needed.

The stretching step is a treatment step of stretching the PVA-based resin film at a predetermined magnification in at least one direction. In general, the PVA-based resin film is uniaxially stretched in the transport direction (longitudinal direction). The stretching method is not particularly limited, and either a wet stretching method or a dry stretching method can be employed. The stretching step may be performed only once, or may be performed a plurality of times as needed. The stretching step may be performed at any stage in the manufacture of the polarizing element.

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

The temperature of the stretching bath is preferably 25°C or more and 80°C or less, more preferably 40°C or more and 75°C or less, and still more preferably 50°C or more and 70°C or less. The immersion time in the stretching bath cannot be determined uniformly because the degree of stretching of the PVA-based resin film is affected by the temperature of the stretching bath, but it is preferably 10 seconds or more and 800 seconds or less, and more preferably 30 seconds or more and 500 seconds or less. . The stretching treatment in the wet stretching method may be performed together with any one or more treatment steps of a swelling step, a dyeing step, a crosslinking step, and a washing step.

Examples of the dry stretching method include an inter-roll stretching method, a heated roll stretching method, and a compression stretching method. In addition, you may perform dry stretching method together with a drying process.

The total draw ratio (cumulative draw ratio) applied to the polyvinyl alcohol-based resin film can be appropriately set depending on the purpose, but it is preferably 2 times or more and 7 times or less, more preferably 3 times or more and 6.8 times or less, and 3.5 It is more preferable that it is more than twice and 6.5 times or less.

The washing step is a treatment step in which the polyvinyl alcohol-based resin film is immersed in a washing bath, and foreign substances remaining on the surface of the polyvinyl alcohol-based resin film or the like can be removed. As the washing bath, a medium containing water as a main component, such as water, distilled water, or pure water, is usually used. Further, from the viewpoint of controlling the potassium content in the polarizing element, it is preferable to use potassium iodide in the washing bath, and in this case, the concentration of potassium iodide in the washing bath is preferably 1% by mass or more and 10% by mass or less, It is more preferable that it is 1.5 mass % or more and 4 mass % or less, and it is still more preferable that it is 1.8 mass % or more and 3.8 mass % or less.

The temperature of the washing bath is preferably 5°C or more and 50°C or less, more preferably 10°C or more and 40°C or less, and still more preferably 15°C or more and 30°C or less. The immersion time in the washing bath cannot be determined uniformly because the degree of washing of the PVA-based resin film is affected by the washing bath temperature, but it is preferably 1 second or more and 100 seconds or less, more preferably 2 seconds or more and 50 seconds or less, , more preferably 3 seconds or more and 20 seconds or less. The cleaning step may be performed only once, or may be performed a plurality of times as needed.

The drying process is a process of obtaining a polarizing element by drying the PVA-based resin film washed in the washing process. Drying is performed by any suitable method, and examples thereof include natural drying, blow drying, and heat drying.

Production method 2 is a step of applying a coating liquid containing a PVA-based resin onto a base film, a step of uniaxially stretching the obtained laminated film, and dyeing the PVA-based resin layer of the uniaxially stretched laminated film with a dichroic dye to adsorb it. It can be manufactured through a process of making a polarizing element, a process of treating a film adsorbed with a dichroic dye with an aqueous solution of boric acid, and a process of washing with water after treatment with an aqueous solution of boric acid. A base film used to form the polarizing element may be used as a protective layer for the polarizing element. You may peel and remove a base film from a polarizing element as needed.

<Transparent protective film>

The transparent protective film (hereinafter also simply referred to as "protective film") used in this embodiment is bonded to at least one surface of the polarizing element via an adhesive layer. Although this transparent protective film is bonded to one side or both sides of a polarizing element, it is preferable to be bonded to both sides.

The protective film may have different optical functions at the same time, or may be formed of a laminated structure in which a plurality of layers are laminated. The film thickness of the protective film is preferably thin from the viewpoint of optical properties, but if it is too thin, the strength is lowered and workability is poor. A suitable film thickness is 5 μm or more and 100 μm or less, preferably 10 μm or more and 80 μm or less, and more preferably 15 μm or more and 70 μm or less.

The protective film is a film such as a cellulose acylate-based film, a film made of polycarbonate-based resin, a film made of cycloolefin-based resin such as norbornene, a (meth)acrylic polymer film, and a polyester resin-based film such as polyethylene terephthalate. is available. When bonding protective films on both sides of the polarizing element using a water-based adhesive such as PVA adhesive, at least one protective film is preferably either a cellulose acylate-based film or a (meth)acrylic-based polymer film from the viewpoint of moisture permeability , Among them, a cellulose acylate film is preferable.

At least one protective film may have a retardation function for the purpose of viewing angle compensation or the like. In that case, the protective film itself may have a retardation function, may have a retardation layer separately, or a combination of both may be sufficient. The film having the retardation function may be directly bonded to the polarizing element through an adhesive, but may also have a structure bonded through an adhesive or an adhesive through another protective film bonded to the polarizing element.

<Adhesive layer>

As an adhesive constituting an adhesive layer for bonding a protective film to a polarizing element, an adhesive containing a urea compound and a reducing agent is used. As the adhesive, a water-based adhesive, a solvent-based adhesive, an active energy ray curable adhesive, or the like can be used, but it is preferably a water-based adhesive, and preferably contains a PVA-based resin. By using an adhesive containing a urea compound and a reducing agent, a decrease in transmittance of the polarizing plate in a high-temperature environment can be suppressed.

The thickness at the time of application of the adhesive may be set to an arbitrary value, and may be set so that an adhesive layer having a desired thickness can be obtained after, for example, curing or heating (drying). The thickness of the adhesive layer composed of the adhesive is preferably 0.01 μm or more and 7 μm or less, more preferably 0.01 μm or more and 5 μm or less, still more preferably 0.01 μm or more and 2 μm or less, and most preferably 0.01 μm or less. It is 1 micrometer or more and 1 micrometer or less.

The following description of the adhesive is a description of a preferable range for the case where the polarizing element does not contain a urea-based compound and a reducing agent at the time of manufacturing the polarizing element. What is necessary is just to adjust the following value suitably, when the polarizing element contains a urea compound or a reducing agent. As for specific examples of the urea-based compound and the reducing agent, examples of the urea-based compound and the reducing agent contained in the polarizing element described above can be applied as they are. In the process of forming the adhesive layer through the drying step at the time of bonding the polarizing element and the protective film, a part of the urea compound and a part of the reducing agent may migrate from the adhesive layer to the polarizing element or the like.

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

When the adhesive is a water-based adhesive containing a PVA-based resin, the content of the reducing agent is preferably 1 part by mass or more and 50 parts by mass or less, more preferably 1.5 parts by mass or more and 40 parts by mass, based on 100 parts by mass of the PVA-based resin. part or less, more preferably 2 parts by mass or more and 35 parts by mass or less, and may be 20 parts by mass or less. If it is less than 1 part by mass, the effect of suppressing the polyenization of the polarizing element in a high-temperature environment may not be sufficient. On the other hand, when it exceeds 50 parts by mass, the iodine complex in the polarizing element is reduced, and the degree of polarization may decrease.

In the configuration in which the transparent protective film is bonded to both sides of the polarizing element via an adhesive layer, only one adhesive layer may be a layer containing a urea compound and a reducing agent among the adhesive layers on both sides of the polarizing element, but the adhesive layer on both sides It is preferable that all are layers containing a urea compound and a reducing agent.

In order to meet the request for thinning the polarizing plate, a polarizing plate having a transparent protective film on only one side of the polarizing element is being developed. Also in this configuration, a transparent protective film is laminated via an adhesive layer containing a urea compound and a reducing agent. As a method for producing a polarizing plate having a transparent protective film on only one side of such a polarizing element, a method in which a transparent protective film is first bonded to both surfaces through an adhesive layer to prepare a polarizing plate, and then the transparent protective film on one side is peeled off can be considered. . When such a manufacturing method is used, although only one adhesive layer may contain a urea compound and a reducing agent, it is preferable that both adhesive layers are layers containing a urea compound and a reducing agent. When only one adhesive layer contains a urea compound and a reducing agent, it is preferable that the adhesive layer on the non-peeling film side contains a urea compound and a reducing agent.

(water-based adhesive)

As the water-based adhesive, any suitable water-based adhesive may be employed, but a water-based adhesive containing a PVA-based resin (PVA-based adhesive) is preferably used. The average degree of polymerization of the PVA-based resin contained in the water-based adhesive is preferably 100 or more and 5500 or less, more preferably 1000 or more and 4500 or less, in terms of adhesiveness. The average degree of saponification is preferably 85 mol% or more and 100 mol% or less, more preferably 90 mol% or more and 100 mol% or less, from the viewpoint of adhesiveness.

As the PVA-based resin contained in the water-based adhesive, those containing an acetoacetyl group are preferable, because the adhesion between the PVA-based resin layer and the protective film is excellent and durability is excellent. The acetoacetyl group-containing PVA-based resin is obtained by, for example, reacting a PVA-based resin with diketene by an arbitrary method. The degree of acetoacetyl group modification of the acetoacetyl group-containing PVA-based resin is typically 0.1 mol% or more, and preferably 0.1 mol% or more and 20 mol% or less. The resin concentration of the water-based adhesive is preferably 0.1% by mass or more and 15% by mass or less, and more preferably 0.5% by mass or more and 10% by mass or less.

A water-based adhesive may contain a crosslinking agent. As the crosslinking agent, a known crosslinking agent can be used. Examples of the crosslinking agent include water-soluble epoxy compounds, dialdehydes, and isocyanates.

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

Water-based adhesives may contain organic solvents. Since the organic solvent has miscibility with water, alcohols are preferable, and among alcohols, methanol or ethanol is more preferable. The methanol concentration of the water-based adhesive is preferably 10 mass% or more and 70 mass% or less, more preferably 15 mass% or more and 60 mass% or less, still more preferably 20 mass% or more and 60 mass% or less. When the methanol concentration is 10% by mass or more, polyenization of the PVA-based resin in a high-temperature environment is more easily suppressed. Moreover, deterioration of hue can be suppressed because methanol content rate is 70 mass % or less. Some of the urea derivatives have low solubility in water, while some have sufficient solubility in alcohol. In that case, it is one of the preferred embodiments to prepare an adhesive by dissolving the urea compound in alcohol to prepare an alcohol solution of the urea compound, and then adding the alcohol solution of the urea compound to the PVA aqueous solution.

(active energy ray curing type adhesive)

An active energy ray-curable adhesive is an adhesive that is cured by irradiating active energy rays such as ultraviolet rays, and includes, for example, an adhesive containing a polymerizable compound and a photopolymerization initiator, an adhesive containing a photoreactive resin, a binder resin, and a photoreactive crosslinking agent. adhesives, etc. Examples of the polymerizable compound include photopolymerizable monomers such as photocurable epoxy monomers, photocurable acrylic monomers, and photocurable urethane monomers, and oligomers derived from these monomers. Examples of the photopolymerization initiator include compounds containing substances that generate active species such as neutral radicals, anion radicals, and cation radicals by irradiation with active energy rays such as ultraviolet rays.

<Layer containing urea-based compound>

The urea compound and the reducing agent are not limited to the case where they are contained in the adhesive layer as described above, and may be contained in layers other than the adhesive layer from the viewpoint of improving the high-temperature durability of the polarizing plate. In a polarizing plate having a transparent protective film on only one surface, a cured layer may be laminated on the surface opposite to the transparent protective film of the polarizing element from the viewpoint of improving the physical strength.

In this embodiment, a urea-based compound and a reducing agent may be contained in such a cured layer to form a urea-based compound-containing layer. Normally, such a cured layer is formed from a curable composition containing an organic solvent, but in paragraphs [0020] to [0042] of Japanese Patent Laid-Open No. 2017-075986, such a cured layer is formed from an aqueous solution of an active energy ray-curable polymer composition. How to do it is described. A water-soluble urea compound and a reducing agent may be incorporated into this composition.

The urea-based compound-containing layer preferably has at least one urea-based compound, at least one reducing agent, and a binder. Examples of the binder include polymer binders, thermosetting resin binders, active energy ray curable resin binders, and the like, and any binder can be suitably used.

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

[Method for producing polarizing plate]

The manufacturing method of the polarizing plate of this embodiment has a moisture content adjustment process and a lamination process. In the moisture content adjustment step, when producing a polarizing plate having the feature (a), polarization is performed such that the moisture content of the polarizing element is equal to or higher than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30% and less than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 50%. Adjust the moisture content of the element. The moisture content of the polarizing element can be adjusted according to the description of the moisture content of the polarizing element described above. In the moisture content adjustment step, when producing a polarizing plate having the feature (b), the moisture content of the polarizing plate is equal to or higher than the equilibrium moisture content at a temperature of 20 ° C. and a relative humidity of 30%, and less than the equilibrium moisture content at a temperature of 20 ° C. and a relative humidity of 50%. Adjust the moisture content. The moisture content of the polarizing plate can be adjusted according to the above description of the moisture content of the polarizing plate. In the lamination process, the polarizer and the transparent protective film are laminated through the adhesive layer. In the lamination step, for example, a polarizing element and a transparent protective film that have not been treated to contain a urea-based compound and a reducing agent are bonded together with an adhesive containing a urea-based compound and a reducing agent. The order of the moisture content adjusting step and the lamination step is not limited, and the moisture content adjusting step and the lamination step may be performed in parallel.

[Configuration of image display device]

The polarizing plate of this embodiment is used for various image display devices, such as a liquid crystal display device and an organic EL display device. Regarding the image display device, in the case of an interlayer filling configuration in which both sides of the polarizing plate are configured to contact layers other than the air layer, specifically, a solid layer such as an adhesive layer, the transmittance tends to decrease in a high-temperature environment. In the image display device using the polarizing plate of the present embodiment, a decrease in transmittance of the polarizing plate in a high-temperature environment can be suppressed even in an interlayer filling configuration. As an image display device, a structure having an image display cell, a first pressure sensitive adhesive layer laminated on the visual side surface of the image display cell, and a polarizing plate laminated on the visual side surface of the first pressure sensitive adhesive layer is exemplified. Such an image display device may further have a second pressure sensitive adhesive layer laminated on the visual side surface of the polarizing plate and a transparent member laminated on the surface of the second pressure sensitive adhesive layer. In particular, in the polarizing plate of the present embodiment, a transparent member is disposed on the viewing side of the image display device, the polarizing plate and the image display cell are bonded by the first adhesive layer, and the polarizing plate and the transparent member are bonded by the second adhesive layer. It is suitably used for an image display device having a charging configuration. In this specification, either or both of the 1st adhesive layer and the 2nd adhesive layer may simply be called "adhesive layer." Moreover, as a member used for bonding a polarizing plate and an image display cell, and a member used for bonding a polarizing plate and a transparent member, it is not limited to an adhesive layer, An adhesive layer may be sufficient.

<Image display cell>

As an image display cell, a liquid crystal cell and an organic electroluminescent cell are mentioned. As the liquid crystal cell, any of a reflection type liquid crystal cell using external light, a transmissive liquid crystal cell using light from a light source such as a backlight, or a transflective liquid crystal cell using both external light and light from a light source may be used. good night. When the liquid crystal cell uses light from a light source, in the image display device (liquid crystal display device), a polarizing plate is disposed on the side opposite to the viewing side of the image display cell (liquid crystal cell), and a light source is further disposed. It is preferable that the polarizing plate and the liquid crystal cell on the light source side are bonded via an appropriate pressure-sensitive adhesive layer. As the driving method of the liquid crystal cell, any type such as VA mode, IPS mode, TN mode, STN mode, or bend orientation (π type) can be used, for example.

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

<Bonding of image display cell and polarizer>

A pressure-sensitive adhesive layer (pressure-sensitive adhesive sheet) is suitably used for bonding the image display cell and the polarizing plate. Among them, a method of bonding an image display cell to a polarizing plate with an adhesive layer in which an adhesive layer is provided on one side of the polarizing plate is preferable from the viewpoint of workability and the like. The application of the pressure-sensitive adhesive layer to the polarizing plate can be performed in an appropriate manner. As an example thereof, a pressure-sensitive adhesive solution of 10% by mass or more and 40% by mass or less is prepared by dissolving or dispersing a base polymer or its composition in a solvent consisting of a single substance or a mixture of appropriate solvents such as toluene and ethyl acetate, and then casting it. ) method or a method of directly laying on a polarizing plate by an appropriate development method such as a coating method, a method of forming an adhesive layer on a separator and attaching it to a polarizing plate, and the like.

<Adhesive layer>

The pressure-sensitive adhesive layer may consist of one layer or two or more layers, but is preferably composed of one layer. The pressure-sensitive adhesive layer may be composed of a pressure-sensitive adhesive composition containing (meth)acrylic resin, rubber-based resin, urethane-based resin, ester-based resin, silicone-based resin, or polyvinyl ether-based resin as a main component. Among them, a pressure-sensitive adhesive composition comprising a (meth)acrylic resin having excellent transparency, weather resistance, heat resistance, and the like as a base polymer is suitable. An active energy ray curing type or a heat curing type may be sufficient as an adhesive composition.

Examples of the (meth)acrylic resin (base polymer) used in the pressure-sensitive adhesive composition include (meth)acrylic acid esters such as butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. The polymer or copolymer which uses 1 type, or 2 or more types of as a monomer is used suitably. It is preferable to copolymerize a polar monomer into the base polymer. As the polar monomer, (meth)acrylic acid compound, (meth)acrylic acid 2-hydroxypropyl compound, (meth)acrylic acid hydroxyethyl compound, (meth)acrylamide compound, N,N-dimethylaminoethyl (meth)acrylate compound and monomers having a carboxyl group, a hydroxyl group, an amide group, an amino group, an epoxy group and the like, such as glycidyl (meth)acrylate compounds.

The pressure-sensitive adhesive composition may contain only the base polymer, but usually further contains a crosslinking agent. As the crosslinking agent, as a divalent or higher metal ion, a metal ion that forms a carboxylic acid metal salt between a carboxyl group, a polyamine compound that forms an amide bond between a carboxyl group, and a polyepoxy that forms an ester bond between a carboxyl group A polyisocyanate compound that forms an amide bond between a compound or polyol and a carboxyl group is exemplified. Among them, polyisocyanate compounds are preferred.

The active energy ray-curable pressure-sensitive adhesive composition has a property of being cured by being irradiated with active energy rays such as ultraviolet rays or electron beams, and has adhesiveness even before active energy ray irradiation, so that it can be adhered to an adherend such as a film, and can be applied to active energy ray irradiation. It has a property that can be hardened by adjusting the adhesion. It is preferable that the active energy ray curable adhesive composition is an ultraviolet curable type. The active energy ray-curable pressure-sensitive adhesive composition further contains an active energy ray polymerizable compound in addition to the base polymer and the crosslinking agent. You may contain a photoinitiator, a photosensitizer, etc. as needed.

The pressure-sensitive adhesive composition includes fine particles for imparting light scattering properties, beads (resin beads, glass beads, etc.), glass fibers, resins other than the base polymer, tackifiers, fillers (metal powder or other inorganic powders, etc.), antioxidants, Additives such as ultraviolet absorbers, dyes, pigments, colorants, antifoaming agents, corrosion inhibitors, and photopolymerization initiators may be included.

The pressure-sensitive adhesive layer can be formed by applying a diluted organic solvent of the pressure-sensitive adhesive composition on the surface of a substrate film, an image display cell, or a polarizing plate and drying it. It is common for a base film to be a thermoplastic resin film, and a separator film subjected to release treatment is exemplified as a typical example thereof. The separation film may be, for example, a film made of a resin such as polyethylene terephthalate, polybutylene terephthalate, polycarbonate, or polyarylate, on which a release treatment such as silicone treatment is applied to the surface on which the pressure-sensitive adhesive layer is formed.

An adhesive layer may be formed by directly applying the adhesive composition to the mold release treatment surface of the separate film, and the adhesive layer with the separate film may be laminated on the surface of the polarizer. A pressure-sensitive adhesive layer may be formed by directly applying the pressure-sensitive adhesive composition to the surface of the polarizing plate, and a separate film may be laminated on the outer surface of the pressure-sensitive adhesive layer.

When the pressure-sensitive adhesive layer is formed on the surface of the polarizing plate, it is preferable to perform a surface activation treatment such as plasma treatment or corona treatment on the bonding surface of the polarizing plate and / or the bonding surface of the pressure-sensitive adhesive layer. Corona treatment is more preferable.

Further, a pressure-sensitive adhesive composition is applied on the second separate film to form an adhesive layer, a pressure-sensitive adhesive sheet obtained by laminating the separate film on the formed pressure-sensitive adhesive layer is prepared, and the second separate film is separated from the pressure-sensitive adhesive sheet. An adhesive layer may be laminated on the polarizing plate. As for the 2nd separate film, the adhesive force with the adhesive layer is weaker than a separate film, and the thing which peels easily is used.

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

<transparent member>

A transparent plate (window layer), a touch panel, etc. are mentioned as a transparent member arrange|positioned on the viewing side of an image display apparatus. As the transparent plate, a transparent plate having appropriate mechanical strength and thickness is used. As such a transparent plate, for example, a transparent resin plate such as a polyimide-based resin, an acrylic resin, or a polycarbonate-based resin, or a glass plate, and the like are exemplified. A functional layer such as an antireflection layer may be laminated on the viewing side of the transparent plate. In addition, when the transparent board is a transparent resin board, a hard coat layer for increasing physical strength or a low moisture permeability layer for lowering the moisture permeability may be laminated. As a touch panel, various touch panels, such as a resistive film type, a capacitance type, an optical type, an ultrasonic type, etc., a glass plate with a touch sensor function, a transparent resin plate, etc. are used. When a capacitive touch panel is used as the transparent member, it is preferable that a transparent plate made of glass or a transparent resin plate is provided on the viewing side more than the touch panel.

<Bonding of polarizing plate and transparent member>

A pressure-sensitive adhesive or an active energy ray curable adhesive is suitably used for bonding between the polarizing plate and the transparent member. When an adhesive is used, the laying of the adhesive can be performed in an appropriate manner. As a specific laying method, the laying method of the adhesive layer used for bonding of the above-mentioned image display cell and polarizing plate is mentioned, for example.

In the case of using an active energy ray curable adhesive, for the purpose of preventing the diffusion of the adhesive solution before curing, a dam material is installed to surround the periphery of the image display panel, a transparent member is disposed on the dam material, and the adhesive solution is injected. are used appropriately After injection of the adhesive solution, positioning and degassing are performed as necessary, and then active energy rays are irradiated to cure the adhesive.

Example

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

<Production of Polarizing Element A>

A PVA film with a thickness of 40 μm composed of PVA having an average degree of polymerization of about 2400 and a degree of saponification of 99.9 mol% or more was uniaxially stretched about 5 times in a dry manner, and then immersed in pure water at 60 ° C. for 1 minute while maintaining a tension state, followed by iodine /potassium iodide/water was immersed in an aqueous solution having a weight ratio of 0.05/5/100 at 28°C for 60 seconds. Then, it was immersed in an aqueous solution having a weight ratio of potassium iodide/boric acid/water of 8.5/8.5/100 at 72°C for 300 seconds. Subsequently, after washing with pure water at 26°C for 20 seconds, drying was performed at 65°C to obtain a polarizing element A having a thickness of 15 µm in which iodine was adsorbed and oriented in PVA. For the measurement of the thickness of the polarizing element, a digital micrometer "MH-15M" manufactured by Nikon Corporation was used.

<Preparation of adhesives 1 to 11>

(Preparation of PVA solution A for adhesive)

50 g of a modified PVA-based resin containing an acetoacetyl group (“Gosenex Z-410” manufactured by Mitsubishi Chemical Corporation) was dissolved in 950 g of pure water, heated at 90° C. for 2 hours, cooled to room temperature, and used for adhesives. A PVA solution was obtained (hereinafter referred to as "PVA solution A").

(Preparation of adhesives 1 to 11)

Adhesives 1 to 11 were prepared by blending PVA solution A, a urea compound, a reducing agent and pure water so that PVA contained 3.0% by mass, and the urea compound and reducing agent had the contents shown in Table 1.

<Preparation of transparent protective film A>

A commercially available cellulose acylate film TD40 (manufactured by Fujifilm Co., Ltd., film thickness 40 μm) was immersed in a 1.5 mol/L NaOH aqueous solution (saponification liquid) maintained at 55° C. for 2 minutes, and then the film was washed with water. . Then, after being immersed in 0.05 mol/L sulfuric acid aqueous solution at 25° C. for 30 seconds, a water washing bath was further passed for 30 seconds under running water to neutralize the film. Then, after removing moisture by repeating water removal with an air knife 3 times, drying was carried out in a drying zone at 70°C for 15 seconds, a saponified film was prepared to obtain transparent protective film A.

<Production of Polarizing Plates 1 to 11>

A transparent protective film A was bonded to both sides of the polarizing element A through the adhesive 1 using a roll bonding machine. After bonding, it was made to dry at 80 degreeC for 5 minutes, and the polarizing plate 1 was obtained. The thickness of the adhesive layer after drying was adjusted to be 50 nm on both sides.

In the polarizing plate 1, the adhesive 1 was changed to the adhesives 2-11 to obtain the polarizing plates 2-11.

(moisture content adjustment of polarizing plate (polarizing element))

The polarizing plates 1 to 11 obtained above were stored for 72 hours at a temperature of 20° C. and a relative humidity of 30%, 35%, 40%, 45%, 50% or 55%. Moisture content was measured using the Karl Fischer method at 66 hours, 69 hours, and 72 hours of storage. In any humidity conditions, the value of moisture content did not change during storage for 66 hours, 69 hours, and 72 hours. Therefore, it can be considered that the moisture content of the polarizing plates 1 to 11 is equal to the equilibrium moisture content of the 72-hour storage environment used in this experimental example. When the water content of the polarizing plate reaches equilibrium in a certain storage environment, it can be considered that the moisture content of the polarizing element in the polarizing plate has reached equilibrium in the storage environment as well. In addition, when the moisture content of the polarizing element in the polarizing plate reaches equilibrium in a certain storage environment, it can be regarded that the moisture content of the polarizing plate has reached equilibrium in the storage environment as well.

<Optical laminates 1 to 13>

In the optical laminates 1 to 13, any one of the polarizing plates 1 to 11 shown in Table 2 was used, and the moisture content of the polarizing plate (polarizing element) used was a relative humidity at a temperature of 20 ° C. It was prepared by storing for 72 hours under conditions of 35%, 45% or 55%.

<High temperature durability evaluation>

(Production of samples for evaluation)

For the optical laminates 1 to 13, an acrylic pressure-sensitive adhesive (manufactured by Lintec Co., Ltd., product number: #7) was formed on both surfaces thereof, and further, the absorption axis was made parallel to the long side to a size of 50 mm × 100 mm. It was cut. Evaluation samples were produced by bonding alkali-free glass (“EAGLE XG” manufactured by Corning Corporation) to the surface of each pressure-sensitive adhesive.

In order to evaluate the cross leakage of the evaluation sample, an optical laminate R was prepared for the purpose of overlapping with the evaluation sample to create a crossed Nicols state. Specifically, an acrylic adhesive (manufactured by Lintec Co., Ltd., product number: #7) was formed on only one side of the polarizing plate 9, and was further cut to a size of 50 mm × 100 mm so that the absorption axis was parallel to the short side. . The optical layered body R used for cross evaluation was produced by bonding alkali-free glass ("EAGLE XG" by Corning) to the adhesive surface.

(Evaluation of single transmittance (105 ° C))

Evaluation samples of the optical laminates 1 to 13 were subjected to an autoclave treatment at a temperature of 50 ° C. and a pressure of 5 kgf / cm 2 (490.3 kPa) for 1 hour, and then left for 24 hours in an environment of a temperature of 23 ° C. and a relative humidity of 55%. Thereafter, the transmittance of the evaluation samples of optical laminates 1 to 13 was measured (initial value), stored in a heated environment at a temperature of 105°C, and transmittance was measured at intervals of 50 hours from 100 to 200 hours. Based on the time at which the decrease in transmittance reached 5% or more with respect to the initial value, evaluation was performed according to the following criteria. The obtained results are shown in Table 2.

A decrease in transmittance of 5% or less after 200 hours: A

Those in which the decrease in transmittance reached 5% or more in 150 to 200 hours: B

A decrease in transmittance of 5% or more in 100 to 150 hours: C

A decrease in transmittance of 5% or more after 100 hours: D

(Evaluation of cross leakage)

An evaluation sample was prepared after measuring the single transmittance at the time of elapse of 200 hours in the evaluation of the above-described single transmittance. The optical layered body R for cross nicol evaluation and the evaluation sample, which were not put in a heating environment, were arranged so as to have a cross nicol relationship, and were placed on the backlight. By shielding the surroundings and visually confirming cross-leakage, four-level evaluation was performed based on the following criteria. The obtained results are shown in Table 2. In addition, evaluation samples whose single transmittance evaluation was other than A were excluded from evaluation of cross leakage because they were colored due to polyenization.

No cross-leakage at all : A

Almost no cross leakage :B

Slightly visible cross-leakage :C

Clearly visible cross-leakage :D

A polarizing plate having a polarizing element and a transparent protective film having a moisture content equal to or higher than the equilibrium moisture content at a temperature of 20 ° C. and a relative humidity of 30%, and less than the equilibrium moisture content at a temperature of 20 ° C. and a relative humidity of 50%, wherein the polarizing element and the transparent protective film comprise a urea compound and a reducing agent. It was found that the transmittance of the polarizing plates (optical laminates 1 to 9) bonded by the adhesive containing did not easily decrease even when exposed to a high-temperature environment of 105° C., and had excellent high-temperature durability. It was found that the optical layered bodies 1 to 9 were also excellent in evaluation of cross leakage, and the polarization degree did not easily decrease even when exposed to a high-temperature environment of 105°C.

Claims (13)

A polarizing plate having a polarizing element in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin layer and a transparent protective film laminated on at least one surface of the polarizing element,
The polarizing element and the transparent protective film are bonded by an adhesive layer formed of an adhesive containing a urea compound and a reducing agent,
The urea-based compound is at least one selected from the group consisting of urea, urea derivatives, thiourea and thiourea derivatives,
The moisture content of the polarizing element is equal to or higher than the equilibrium moisture content at a temperature of 20 ° C. and a relative humidity of 30%, and is equal to or less than the equilibrium moisture content at a temperature of 20 ° C. and a relative humidity of 50%. A polarizing plate having a polarizing element in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin layer and a transparent protective film laminated on at least one surface of the polarizing element,
The polarizing element and the transparent protective film are bonded by an adhesive layer formed of an adhesive containing a urea compound and a reducing agent,
The urea-based compound is at least one selected from the group consisting of urea, urea derivatives, thiourea and thiourea derivatives,
The moisture content of the polarizing plate is equal to or greater than the equilibrium moisture content at a temperature of 20 ° C. and a relative humidity of 30%, and less than the equilibrium moisture content at a temperature of 20 ° C. and a relative humidity of 50%. The polarizing plate according to claim 1 or 2, wherein the adhesive includes at least one urea-based compound selected from the group consisting of urea derivatives and thiourea derivatives. The polarizing plate according to any one of claims 1 to 3, wherein the adhesive comprises a polyvinyl alcohol-based resin. The polarizing plate according to claim 4, wherein in the adhesive, the content of the urea compound is 0.1 parts by mass or more and 400 parts by mass or less with respect to 100 parts by mass of the polyvinyl alcohol-based resin. The polarizing plate according to claim 4 or 5, wherein the content of the reducing agent in the adhesive is 1 part by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the polyvinyl alcohol-based resin. The polarizing plate according to any one of claims 1 to 6, wherein the adhesive layer has a thickness of 0.01 μm or more and 7 μm or less. The polarizing plate according to any one of claims 1 to 7, wherein the reducing agent is at least one selected from the group consisting of ascorbic acid, erythorbic acid, thiosulfuric acid, sulfurous acid, and salts thereof. The method according to any one of claims 1 to 8, wherein the polarizing plate is used in an image display device,
In the image display device, a polarizing plate in which a solid layer is formed in contact with both surfaces of the polarizing plate. An image display cell, a first pressure sensitive adhesive layer laminated on the visual side surface of the image display cell, and a polarizing plate according to any one of claims 1 to 9 laminated on the visual side surface of the first pressure sensitive adhesive layer. image display device. The image display device according to claim 10, further comprising a second pressure-sensitive adhesive layer laminated on the viewer-side surface of the polarizing plate, and a transparent member laminated on the viewer-side surface of the second pressure-sensitive adhesive layer. The image display device according to claim 11, wherein the transparent member is a glass plate or a transparent resin plate. The image display device according to claim 11, wherein the transparent member is a touch panel.