CN116323202A

CN116323202A - Polarizing plate and image display device

Info

Publication number: CN116323202A
Application number: CN202180067370.5A
Authority: CN
Inventors: 福田谦一; 内藤亮
Original assignee: Sumitomo Chemical Co Ltd
Current assignee: Sumitomo Chemical Co Ltd
Priority date: 2020-10-05
Filing date: 2021-09-29
Publication date: 2023-06-23
Also published as: WO2022075148A1; JP2022060766A; TW202227265A; KR20230076854A

Abstract

The invention provides a polarizing plate which can inhibit the reduction of transmissivity under a high-temperature environment and has excellent water resistance. A polarizing plate comprising a polarizing element in which a dichroic dye is adsorbed to a polyvinyl alcohol resin layer and the dichroic dye is aligned, and a transparent protective film laminated on at least one surface of the polarizing element, wherein the polarizing element and the transparent protective film are bonded by an adhesive layer formed from an adhesive containing a urea compound and a dialdehyde, the urea compound is at least 1 selected from urea, urea derivatives, thiourea and thiourea derivatives, and the water content of the polarizing element is at least 30% of the equilibrium water content at a temperature of 20 ℃ and at most 50% of the equilibrium water content at a temperature of 20 ℃.

Description

Polarizing plate and image display device

Technical Field

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

Background

Liquid crystal display devices (LCDs) are widely used not only for liquid crystal televisions but also for mobile devices such as personal computers and cellular phones and for vehicle-mounted applications such as navigation devices. In general, a liquid crystal display device includes a liquid crystal panel in which polarizing plates are bonded to both sides of a liquid crystal cell with an adhesive, and displays are performed by controlling light from a backlight with the liquid crystal panel. In recent years, organic EL display devices are widely used for in-vehicle applications such as mobile devices including televisions and cellular phones, and navigator, as well as liquid crystal display devices. In an organic EL display device, a circularly polarizing plate (a laminate including a polarizing element and a λ/4 plate) may be disposed on the visible side surface of an image display panel in order to suppress reflection of external light by a metal electrode (cathode) and observation of external light into a mirror surface.

As described above, opportunities for the polarizing plate to be mounted in a vehicle as a member of an image display device such as a liquid crystal display device or an organic EL display device are increasing. Polarizing plates used in image display devices for vehicles are often exposed to high-temperature environments as compared with mobile device applications such as televisions and mobile phones, and therefore, it is required that the change in characteristics at higher temperatures (high-temperature durability) be small.

On the other hand, for the purpose of preventing breakage of an image display panel due to impact from an outer surface, there is increasing a structure in which a front panel (also referred to as a "window layer") such as a transparent resin plate or a glass plate is provided on a visible side with respect to the image display panel. In an image display device including a touch panel, a configuration is widely adopted in which the touch panel is provided on a visible side with respect to the image display panel, and a front panel is provided on a visible side with respect to the touch panel.

In such a configuration, when an air layer is present between the image display panel and the transparent member such as the front panel and the touch panel, reflection glare of external light due to reflection of light at an air layer interface is generated, and visibility of a screen tends to be lowered. Accordingly, the trend of filling the space between the polarizing plate disposed on the visible side surface of the image display panel and the transparent member with a layer other than an air layer and generally with a solid layer (hereinafter, referred to as "interlayer filler") is expanding. The interlayer filler is preferably a material having a refractive index close to that of the polarizing plate or the transparent member. As the interlayer filler, an adhesive or a UV curable adhesive is used for the purpose of suppressing a decrease in visibility due to reflection at an interface and bonding and fixing the members to each other (for example, refer to patent document 1).

The interlayer filling structure is expanding in use in mobile devices such as mobile phones which are often used outdoors. In addition, due to recent improvement in visibility, in vehicle applications such as navigation devices, an interlayer filling structure is being studied in which a front transparent plate is disposed on the surface of an image display panel and an adhesive layer or the like is filled between the panel and the front transparent plate.

However, according to the report, in the case of adopting such a constitution, the transmittance of the polarizing plate is significantly reduced in a high-temperature environment. Patent document 2 proposes a method for solving this problem, in which the amount of water per unit area of the polarizing plate is equal to or less than a predetermined amount, and the saturated water absorption amount of the transparent protective film adjacent to the polarizing element is equal to or less than a predetermined amount, so as to suppress the decrease in transmittance.

However, even with such a means, the effect of suppressing the decrease in transmittance in the high temperature endurance test is insufficient.

Prior art literature

Patent literature

Patent document 1: japanese patent laid-open No. 11-174417

Patent document 2: japanese patent laid-open publication No. 2014-102353

Disclosure of Invention

Problems to be solved by the invention

The purpose of the present invention is to provide a novel polarizing plate that can suppress a decrease in transmittance under a high-temperature environment and has excellent water resistance, and an image display device using the polarizing plate.

Means for solving the problems

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

[1] A polarizing plate comprising a polarizing element in which a dichroic dye is adsorbed to a polyvinyl alcohol resin layer and aligned, 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 dialdehyde,

the urea compound is at least 1 selected from urea, urea derivatives, thiourea and thiourea derivatives,

the water content of the polarizing element is equal to or higher than the equilibrium water content of 30% relative humidity at 20 ℃ and equal to or lower than the equilibrium water content of 50% relative humidity at 20 ℃.

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

The water content of the polarizing plate is equal to or higher than the equilibrium water content of 30% relative humidity at 20 ℃ and equal to or lower than the equilibrium water content of 50% relative humidity at 20 ℃.

[3] The polarizing plate according to [1] or [2], wherein the adhesive comprises at least one urea compound selected from urea derivatives and thiourea derivatives.

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

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

[6] The polarizing plate according to any one of [1] to [5], wherein the content of the dialdehyde in the adhesive is 0.03 parts by mass or more and 20 parts by mass or less relative to 1 part by mass of the urea compound.

[7] The polarizing plate according to any one of [1] to [6], wherein the dialdehyde is glyoxal.

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

[9] The polarizing plate according to any one of [1] to [8], wherein the polarizing plate is used for an image display device,

In the image display device, solid layers are provided on both surfaces of the polarizing plate so as to be in contact with both surfaces of the polarizing plate.

[10] An image display device comprising an image display unit, a 1 st adhesive layer laminated on a visible side surface of the image display unit, and the polarizing plate of any one of [1] to [9] laminated on a visible side surface of the 1 st adhesive layer.

[11] The image display device according to [10], further comprising a 2 nd adhesive layer laminated on a visible side surface of the polarizing plate and a transparent member laminated on a visible side surface of the 2 nd 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.

Effects of the invention

According to the present invention, it is possible to provide a polarizing plate having improved high-temperature durability and water resistance, capable of suppressing a decrease in transmittance and polarization degree due to high temperature, and having excellent water resistance even when used in an image display device constituted by interlayer filling. Further, by using the polarizing plate of the present invention, an image display device having excellent water resistance while suppressing a decrease in transmittance and polarization degree in a high-temperature environment can be provided.

Detailed Description

Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments.

[ polarizing plate ]

The polarizing plate of the present embodiment includes a polarizing element in which a dichroic dye is adsorbed to a layer including a polyvinyl alcohol resin and the dichroic dye is aligned, and a transparent protective film. The polarizing element and the transparent protective film are bonded by an adhesive layer formed of an adhesive containing a urea compound and a dialdehyde. The polarizing plate of the present embodiment has at least one of the following features (a) and (b).

(a) The water content of the polarizing element is greater than or equal to the equilibrium water content of 30% relative humidity at 20 ℃ and less than or equal to 50% relative humidity at 20 ℃.

(b) The water content of the polarizing plate is equal to or higher than the equilibrium water content of 30% relative humidity at 20 ℃ and equal to or lower than the equilibrium water content of 50% relative humidity at 20 ℃.

As a conventional polarizing plate excellent in high temperature durability, for example, a polarizing plate capable of suppressing a decrease in transmittance even when left alone for 1000 hours in an environment at a temperature of 95 ℃ is known. However, even in the case of using such a polarizing plate for interlayer filling, when the polarizing plate is left to stand in an environment at a temperature of 95 ℃ for 200 hours, a significant decrease in transmittance may be observed in the center portion in the polarizing plate surface. A significant decrease in transmittance of a polarizing plate in a high-temperature environment is considered to be a problem that occurs particularly when an image display device using an interlayer filling structure in which one surface of the polarizing plate is bonded to an image display unit and the other surface is bonded to a transparent member such as a touch panel or a front panel is exposed to the high-temperature environment.

The reason why the transmittance of the polarizing plate significantly decreases due to the interlayer filling structure is considered to be that the polarizing plate was measured at 1100cm in Raman spectroscopy ^-1 Vicinity (from=c-c=bond) and 1500cm ^-1 The vicinity (from-c=c-bonds) has a peak, thus forming a polyene structure (-c=c) _n -. The polyene structure is presumed to be a structure produced by the polyvinyl alcohol constituting the polarizing element being polyened by dehydration (patent documents 2 and [0012 ]]Segments).

The polarizing plate of the present invention can improve high temperature durability and water resistance. The polarizing plate of the present invention is incorporated into an image display device constituted by interlayer filling, and can suppress a decrease in transmittance even when exposed to a high-temperature environment such as 105 ℃.

< polarizing element >

As a polarizing element in which a dichroic dye is adsorbed to a layer containing a polyvinyl alcohol (hereinafter also referred to as "PVA") resin (hereinafter also referred to as "PVA resin layer") and the dichroic dye is aligned, a known polarizing element can be used. The polarizing element may be a stretched film obtained by dyeing a PVA-based resin film with a dichroic dye and uniaxially stretching the film; a stretched layer obtained by using a laminate film having a coating layer formed by applying a coating liquid containing a PVA-based resin onto a base film, dyeing the coating layer with a dichroic dye, and uniaxially stretching the laminate film. The stretching may be performed after dyeing with a dichroic dye, may be performed while dyeing, or may be performed after stretching.

The PVA-based resin can be obtained by saponifying a polyvinyl acetate-based resin. The polyvinyl acetate resin may be a copolymer of vinyl acetate and another monomer copolymerizable therewith, in addition to polyvinyl acetate which is a homopolymer of vinyl acetate. Examples of the other copolymerizable monomer include unsaturated carboxylic acids, olefins such as ethylene, vinyl ethers, and unsaturated sulfonic acids.

The saponification degree of the PVA-based resin is preferably about 85 mol% or more, more preferably about 90 mol% or more, and 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 to 10000, preferably 1500 to 5000. The PVA-based resin may be modified, and may be, for example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral, or the like modified with an aldehyde.

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, and still more preferably 5 μm or more and 25 μm or less. By setting the thickness of the polarizing element to 35 μm or less, the influence of the polyene formation of the PVA-based resin on the decrease of the optical properties in a high-temperature environment can be suppressed. By setting the thickness of the polarizing element to 3 μm or more, a constitution that realizes desired optical characteristics can be easily made.

The polarizing element preferably contains a urea compound. In this embodiment, since the polarizing element and the transparent protective film are bonded to each other by an adhesive layer formed of an adhesive containing a urea compound, it is assumed that a part of the urea compound that migrates from the adhesive layer is contained in the polarizing element. The urea compound in the polarizing element may include urea compound added during the production of the polarizing element. By providing the adhesive layer containing the urea compound, the transmittance is not easily lowered even when the polarizing plate is exposed to a high-temperature environment. It is presumed that the multipolymerization of the PVA-based resin is suppressed by the urea-based compound contained in the polarizing element.

Examples of the method for containing the urea compound in the polarizing element production process include a method in which the PVA-based resin layer is immersed in a treatment solvent containing the urea compound, and a method in which the treatment solvent is sprayed, flowed down, or dropped onto the PVA-based resin layer.

The step of immersing the PVA-based resin layer in the treatment solvent containing the urea-based compound may be performed simultaneously with the steps of swelling, stretching, dyeing, crosslinking, cleaning, and the like in the method for producing a polarizing element described later, or may be provided separately from these steps. The step of containing the urea compound in the PVA-based resin layer is preferably performed after the PVA-based resin layer is dyed with iodine, and more preferably simultaneously with the crosslinking step after the dyeing. According to this method, the change in color tone is small, and the influence on the optical characteristics of the polarizing element can be reduced.

In order to make the polarizing element contain the urea compound, both the addition at the time of manufacturing the polarizing element and the addition to the adhesive may be performed.

(Urea-based Compound)

The urea compound is at least 1 selected from urea, urea derivatives, thiourea and thiourea derivatives. The urea compound may be used alone or in combination of 1 or more than 2. Among the urea-based compounds, there are water-soluble compounds and poorly water-soluble compounds, and any kind of urea-based compounds can be used. When a poorly water-soluble urea compound is used for the water-soluble adhesive, the dispersing method is preferably designed so that turbidity or the like does not increase after the adhesive layer is formed.

(Urea derivative)

Urea derivatives are compounds in which at least 1 of the 4 hydrogen atoms of the urea molecule are substituted with substituents. In this case, the substituent is not particularly limited, but a substituent containing a carbon atom, a hydrogen atom and an oxygen atom is preferable.

Specific examples of urea derivatives 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.

Examples of the di-substituted urea include 1, 1-dimethylurea, 1, 3-dimethylurea, 1-diethylurea, 1, 3-bis (hydroxymethyl) urea, 1, 3-t-butylurea, 1, 3-dicyclohexylurea, 1, 3-diphenylurea, 1, 3-bis (4-methoxyphenyl) urea, 1-acetyl-3-methylurea, 2-imidazolidone (ethyleneurea), and tetrahydro-2-pyrimidinone (propyleneurea).

Examples of the tetra-substituted urea include tetramethylurea, 1, 3-tetraethylurea, 1, 3-tetrabutylurea, 1, 3-dimethoxy-1, 3-dimethylurea, 1, 3-dimethyl-2-imidazolidone, and 1, 3-dimethyl-3, 4,5, 6-tetrahydro-2 (1H) -pyrimidinone.

(thiourea derivatives)

Thiourea derivatives are compounds in which at least 1 of the 4 hydrogen atoms of the thiourea molecule is substituted with a substituent. In this case, the substituent is not particularly limited, but a substituent containing a carbon atom, a hydrogen atom and an oxygen atom is preferable.

Specific examples of the thiourea derivatives include N-methyl thiourea, ethyl thiourea, propyl thiourea, isopropyl thiourea, 1-butyl thiourea, cyclohexyl thiourea, N-acetyl thiourea, N-allyl thiourea, (2-methoxyethyl) thiourea, N-phenyl thiourea, (4-methoxyphenyl) thiourea, N- (2-methoxyphenyl) thiourea, N- (1-naphthyl) thiourea, (2-pyridyl) thiourea, o-tolyl thiourea and p-tolyl thiourea.

Examples of the di-substituted thiourea include 1, 1-dimethylthiourea, 1, 3-dimethylthiourea, 1-diethylthiourea, 1, 3-dibutylthiourea, 1, 3-diisopropylthiourea, 1, 3-dicyclohexylthiourea, N-diphenylthiourea, N '-diphenylthiourea, 1, 3-bis (o-tolyl) thiourea, 1, 3-bis (p-tolyl) thiourea, 1-benzyl-3-phenylthiourea, 1-methyl-3-phenylthiourea, N-allyl-N' - (2-hydroxyethyl) thiourea and ethylenethiourea.

The trisubstituted thiourea may be trimethyl thiourea, and the tetrasubstituted thiourea may be tetramethyl thiourea or 1, 3-tetraethyl thiourea.

Among the urea compounds, urea derivatives or thiourea derivatives are preferable, and urea derivatives are more preferable, in terms of suppressing a decrease in transmittance in a high-temperature environment when used in an image display device constituted by interlayer filling. Among the urea derivatives, a monosubstituted urea or a disubstituted urea is preferable, and a monosubstituted urea is more preferable. Among the disubstituted ureas are 1, 1-substituted urea and 1, 3-substituted urea, however 1, 3-substituted urea is more preferred.

(feature (a))

In the case of the feature (a), the water content of the polarizing element is equal to or higher than the equilibrium water content of 30% relative humidity at 20 ℃ and equal to or lower than the equilibrium water content of 50% relative humidity at 20 ℃. The water content of the polarizing element is preferably not more than 45% of the equilibrium water content of the relative humidity at 20 ℃, more preferably not more than 42% of the equilibrium water content of the relative humidity at 20 ℃, and still more preferably not more than 38% of the equilibrium water content of the relative humidity at 20 ℃. If the water content of the polarizing element is less than the equilibrium water content of 30% relative humidity at 20 ℃, the operability of the polarizing element is lowered and breakage is likely to occur. If the moisture content of the polarizing element is greater than the equilibrium moisture content of 50% relative humidity at 20 ℃, the transmittance of the polarizing element tends to decrease. It is presumed that if the water content of the polarizing element is high, the polyvinyl alcohol of the PVA-based resin tends to advance. The water content of the polarizing element is the water content of the polarizing element in the polarizing plate.

As a method for confirming whether or not the water content of the polarizing element is within a range of not less than the equilibrium water content of 30% relative humidity at 20 ℃ and not more than the equilibrium water content of 50% relative humidity at 20 ℃, there is a method of being stored in an environment adjusted to the above temperature and above relative humidity range and being regarded as being in equilibrium with the environment when there is no change in quality for a certain period of time; or a method of preliminarily calculating the equilibrium water content of the polarizing element adjusted to the environment in the temperature and relative humidity ranges and comparing the water content of the polarizing element with the preliminarily calculated equilibrium water content to confirm the equilibrium water content.

The method for producing a polarizing element having a water content of at least 30% of the relative humidity at 20 ℃ and at most 50% of the relative humidity at 20 ℃ is not particularly limited, but examples thereof include a method of storing the polarizing element in an environment adjusted to the above temperature and the above relative humidity range for at least 10 minutes and at most 3 hours; or a method of performing a heat treatment at 30 ℃ or higher and 90 ℃ or lower.

Another preferable method for producing the polarizing element having the water content is a method in which a laminate in which a protective film is laminated on at least one surface of the polarizing element or a polarizing plate comprising the polarizing element is stored in an environment adjusted to the temperature and the relative humidity range for 10 minutes to 120 hours; or a method of performing a heat treatment at 30 ℃ or higher and 90 ℃ or lower. In the production of an image display device using an interlayer filling structure, an image display panel in which a polarizing plate is laminated in an image display unit may be stored in an environment adjusted to the above temperature and the above relative humidity range for 10 minutes to 3 hours or less or heated at 30 ℃ to 90 ℃ and then the front panel may be bonded.

The water content of the polarizing element is preferably adjusted so that the water content is within the above-described range in a material stage used for constituting the polarizing plate as a single polarizing element or as a laminate of the polarizing element and the protective film. When the water content is adjusted after the polarizing plate is formed, curling becomes excessive, and a problem is likely to occur when the polarizing plate is attached to an image display unit. By forming the polarizing plate using the polarizing element whose water content is adjusted to the above water content in the material stage before forming the polarizing plate, the polarizing plate including the polarizing element whose water content satisfies the above numerical range can be easily formed. The water content of the polarizing element in the polarizing plate may be adjusted to the above-described numerical range in a state where the polarizing plate is bonded to the image display unit. In this case, the polarizing plate is bonded to the image display unit, and therefore, curling is less likely to occur.

(feature (b))

In the case of the feature (b), the water content of the polarizing plate is equal to or higher than the equilibrium water content of 30% of the relative humidity at 20 ℃ and equal to or lower than the equilibrium water content of 50% of the relative humidity at 20 ℃. The water content of the polarizing plate is preferably not more than 45% of the equilibrium water content of the relative humidity at 20 ℃, more preferably not more than 42% of the equilibrium water content of the relative humidity at 20 ℃, and still more preferably not more than 38% of the equilibrium water content of the relative humidity at 20 ℃. If the water content of the polarizing plate is less than the equilibrium water content of 30% relative humidity at 20 ℃, the operability of the polarizing plate is lowered and breakage is liable to occur. If the water content of the polarizing plate is greater than the equilibrium water content of 50% relative humidity at 20 ℃, the transmittance of the polarizing element tends to be lowered. It is presumed that if the water content of the polarizing plate is high, the polyvinyl alcohol of the PVA-based resin tends to advance.

As a method for confirming whether or not the water content of the polarizing plate is in a range of not less than the equilibrium water content of 30% relative humidity at 20 ℃ and not more than the equilibrium water content of 50% relative humidity at 20 ℃, there is a method of being stored in an environment adjusted to the above temperature and above relative humidity range and being regarded as being in equilibrium with the environment when there is no change in quality for a certain period of time; or a method of preliminarily calculating the equilibrium water content of the polarizing plate in the environment adjusted to the temperature and the relative humidity range and comparing the water content of the polarizing plate with the preliminarily calculated equilibrium water content to confirm the equilibrium water content.

The method for producing a polarizing plate having a water content of at least 30% of the relative humidity at 20 ℃ and at most 50% of the relative humidity at 20 ℃ is not particularly limited, but examples thereof include a method of storing the polarizing plate in an environment adjusted to the above temperature and the above relative humidity range for at least 10 minutes and at most 3 hours; or a method of performing a heat treatment at 30 ℃ or higher and 90 ℃ or lower.

In the production of an image display device using an interlayer filling structure, an image display panel in which a polarizing plate is laminated in an image display unit may be stored in an environment adjusted to the above temperature and the above relative humidity range for 10 minutes to 3 hours or less or heated at 30 ℃ to 90 ℃ and then the front panel may be bonded.

(method for producing polarizing element)

The method of manufacturing the polarizing element is not particularly limited, but typical methods are: a method of producing a PVA-based resin film wound in advance in a roll shape by stretching, dyeing, crosslinking, or the like (hereinafter referred to as "production method 1"); a method including a step of applying a coating liquid containing a PVA-based resin onto a base film to form a PVA-based resin layer as a coating layer, and stretching the obtained laminate (hereinafter referred to as "production method 2").

The production method 1 can be produced by a step of uniaxially stretching a PVA-based resin film, a step of dyeing the PVA-based resin film with a dichroic dye such as iodine to adsorb the dichroic dye, a step of treating the PVA-based resin film adsorbed with an aqueous boric acid solution, and a step of washing with water after the treatment with the aqueous boric acid solution.

The swelling step is a treatment step of immersing the PVA-based resin film in a swelling bath. By the swelling step, not only dirt, blocking agent, and the like on the surface of the PVA-based resin film can be removed, but also unevenness in dyeing can be suppressed by swelling the PVA-based resin film. The swelling bath generally uses a medium containing water as a main component, such as water, distilled water, and pure water. The swelling bath may be appropriately added with a surfactant, an alcohol, or the like according to a usual method. From the viewpoint of controlling the content of potassium in the polarizing element, potassium iodide may be used in the swelling bath, and in this case, the concentration of potassium iodide in the swelling bath is preferably 1.5 mass% or less, more preferably 1.0 mass% or less, and still more preferably 0.5 mass% or less.

The temperature of the swelling bath is preferably 10 ℃ to 60 ℃, more preferably 15 ℃ to 45 ℃, still more preferably 18 ℃ to 30 ℃. The immersion time in the swelling bath cannot be determined in any way because the degree of swelling of the PVA-based resin film is affected by the temperature of the swelling bath, but is preferably 5 seconds to 300 seconds, more preferably 10 seconds to 200 seconds, still more preferably 20 seconds to 100 seconds. The swelling step may be performed only 1 time, or may be performed as many times as necessary.

The dyeing step is a treatment step of immersing the PVA-based resin film in a dyeing bath (iodine solution), and can be performed by adsorbing and aligning a dichroic dye such as iodine to the PVA-based resin film. The iodine solution is generally preferably an aqueous iodine solution containing iodine and an iodide as a dissolution aid. 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 them, potassium iodide is suitable from the viewpoint of controlling the content of potassium in the polarizing element.

The concentration of iodine in the dyeing bath is preferably 0.01 mass% or more and 1 mass% or less, more preferably 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 ℃ to 50 ℃, more preferably 15 ℃ to 45 ℃, still more preferably 18 ℃ to 30 ℃. The immersion time in the dyeing bath cannot be defined as a whole because the degree of dyeing of the PVA-based resin film is affected by the temperature of the dyeing bath, but is preferably 10 seconds to 300 seconds, more preferably 20 seconds to 240 seconds. The dyeing step may be performed only 1 time, or may be performed as many times as necessary.

The crosslinking step is a treatment step of immersing the PVA-based resin film dyed in the dyeing step in a treatment bath (crosslinking bath) containing a boron compound, and the polyvinyl alcohol-based resin film can be crosslinked with the boron compound to adsorb iodine molecules or dye molecules to the crosslinked structure. Examples of the boron compound include boric acid, borate, and borax. The crosslinking bath is generally an aqueous solution, but may be a mixed solution of an organic solvent having miscibility with water and water. From the viewpoint of controlling the content of potassium in the polarizing element, the crosslinking bath preferably contains potassium iodide.

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 in 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 still more preferably 2% by mass or more and 5% by mass or less.

The temperature of the crosslinking bath is preferably 20 ℃ to 70 ℃, more preferably 30 ℃ to 60 ℃. The immersion time in the crosslinking bath cannot be defined as a whole because the degree of crosslinking of the PVA-based resin film is affected by the temperature of the crosslinking bath, but is preferably 5 seconds to 300 seconds, more preferably 10 seconds to 200 seconds.

The crosslinking step may be performed only 1 time, or may be performed as many times as necessary.

The stretching step is a treatment step of stretching the PVA-based resin film at a predetermined magnification in at least one direction. Generally, the PVA-based resin film is uniaxially stretched in the conveyance direction (longitudinal direction). The stretching method is not particularly limited, and either wet stretching or dry stretching may be used. The stretching step may be performed only 1 time, or may be performed as many times as necessary. The stretching step may be performed at any stage in the production of the polarizing element.

The treatment bath (stretching bath) in the wet stretching method may be water, or a solvent such as an organic solvent having miscibility with water or a mixed solution of water. From the viewpoint of controlling the content of potassium in the polarizing element, the stretching bath preferably contains potassium iodide. 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 still more preferably 3% by mass or more and 6% by mass or less. From the viewpoint of suppressing film breakage during stretching, the treatment bath (stretching bath) may contain a boron compound. When the boron compound is contained, the concentration of the boron compound in the drawing 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.

The temperature of the stretching bath is preferably 25 ℃ or more and 80 ℃ or less, more preferably 40 ℃ or more and 75 ℃ or less, and still more preferably 50 ℃ or more and 70 ℃ or less. The immersion time in the stretching bath cannot be defined as a whole because the extent of stretching of the PVA-based resin film is affected by the temperature of the stretching bath, but is preferably 10 seconds to 800 seconds, more preferably 30 seconds to 500 seconds. The stretching treatment in the wet stretching method may be performed together with 1 or more treatment steps selected from the group consisting of a swelling step, a dyeing step, a crosslinking step, and a cleaning step.

Examples of the dry stretching method include an inter-roll stretching method, a heated roll stretching method, and a compression stretching method. The dry stretching method may be performed together with the drying step.

The total stretching ratio (cumulative stretching ratio) applied to the polyvinyl alcohol resin film can be set appropriately according to the purpose, and is preferably 2 times or more and 7 times or less, more preferably 3 times or more and 6.8 times or less, and still more preferably 3.5 times or more and 6.5 times or less.

The cleaning step is a treatment step of immersing the polyvinyl alcohol resin film in a cleaning bath, and can remove foreign matters remaining on the surface of the polyvinyl alcohol resin film. The washing bath generally uses a medium containing water as a main component, such as water, distilled water, and pure water. In addition, from the viewpoint of controlling the content of potassium in the polarizing element, it is preferable to use potassium iodide in the cleaning bath, and in this case, the concentration of potassium iodide in the cleaning bath is preferably 1% by mass or more and 10% by mass or less, more preferably 1.5% by mass or more and 4% by mass or less, and still more preferably 1.8% by mass or more and 3.8% by mass or less.

The temperature of the cleaning bath is preferably 5 ℃ to 50 ℃, more preferably 10 ℃ to 40 ℃, still more preferably 15 ℃ to 30 ℃. The immersion time in the cleaning bath cannot be defined as a whole because the degree of cleaning of the PVA-based resin film is affected by the temperature of the cleaning bath, but is preferably 1 second or more and 100 seconds or less, more preferably 2 seconds or more and 50 seconds or less, and still more preferably 3 seconds or more and 20 seconds or less. The cleaning step may be performed only 1 time, or may be performed as many times as necessary.

The drying step is a step of drying the PVA-based resin film washed in the washing step to obtain a polarizing element. The drying may be performed by any appropriate method, and examples thereof include natural drying, forced air drying, and heat drying.

The production method 2 can be produced by a process of applying a coating liquid containing a PVA-based resin onto a base film, a process of uniaxially stretching the obtained laminated film, a process of producing a polarizing element by dyeing a PVA-based resin layer of the uniaxially stretched laminated film with a dichroic dye to adsorb the dichroic dye, a process of treating the film adsorbed with a dichroic dye with an aqueous boric acid solution, and a process of washing with water after the treatment with an aqueous boric acid solution. The base film used for forming the polarizing element can be used as a protective layer for the polarizing element. The base film may be peeled off from the polarizing element as needed.

< transparent protective film >

The transparent protective film (hereinafter also simply referred to as "protective film") used in the present embodiment is attached to at least one surface of the polarizing element via an adhesive layer. The transparent protective film is bonded to one or both sides of the polarizing element, but is preferably bonded to both sides.

The protective film may have other optical functions at the same time, or may be formed in a laminated structure in which a plurality of layers are laminated. From the viewpoint of optical characteristics, the film thickness of the protective film is preferably thin, but if too thin, the strength is reduced and the workability is poor. The film thickness is preferably 5 μm or more and 100 μm or less, more preferably 10 μm or more and 80 μm or less, and still more preferably 15 μm or more and 70 μm or less.

As the protective film, a cellulose acylate-based film, a film containing a polycarbonate-based resin, a film containing a cycloolefin-based resin such as norbornene, a (meth) acrylic polymer film, a polyester resin-based film such as polyethylene terephthalate, and the like can be used. In the case of attaching the protective film to both surfaces of the polarizing element using an aqueous adhesive such as PVA adhesive, it is preferable that at least one of the protective films is either a cellulose acylate-based film or a (meth) acrylic polymer film in terms of moisture permeability, and among these, cellulose acylate films are preferable.

At least one of the protective films may have a phase difference function for the purpose of viewing angle compensation or the like. In this case, the protective film itself may have a retardation function, or may have a retardation layer separately, or may be a combination of both. The film having the retardation function may be directly bonded to the polarizing element via an adhesive, but may be bonded via an adhesive or an adhesive with another protective film bonded to the polarizing element interposed therebetween.

< adhesive layer >

An adhesive containing a urea compound and a dialdehyde is used as an adhesive constituting an adhesive layer for bonding a protective film to a polarizing element. The adhesive may be an aqueous adhesive, a solvent-based adhesive, an active energy ray-curable adhesive, or the like, but is preferably an aqueous adhesive, and preferably contains a PVA-based resin. By using an adhesive containing a urea compound and a dialdehyde, the decrease in transmittance of the polarizing plate in a high-temperature environment can be suppressed, and the water resistance can be improved. In addition, by using an adhesive containing a urea compound and dialdehyde, the decrease in polarization degree can be suppressed even when the polarizing plate is exposed to a high-temperature environment. When two polarizing plates are disposed so as to form a crossed nicols relationship, light leakage (hereinafter also referred to as "crossed light leakage") tends to occur when the polarization degree of the polarizing plates is reduced, but according to the present invention, the polarization degree is not easily reduced even when exposed to a high-temperature environment, and therefore crossed light leakage tends to be suppressed.

Examples of the dialdehydes include glyoxal, malondialdehyde (malondialdehyde), succinaldehyde (succinaldehyde), and the like. Glyoxal, which is structurally simple and highly reactive, is particularly preferred. Glyoxal will be described below, however, as described above, conventionally known dialdehydes may be used, and is not limited to glyoxal.

The thickness of the adhesive at the time of application may be set to any value, and may be set such that an adhesive layer having a desired thickness is obtained after curing or after heating (drying), for example. The thickness of the adhesive layer made 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 more and 1 μm or less.

The following description of the adhesive is described in terms of a preferable range in the case where the polarizing element is not made to contain a urea compound at the time of manufacturing the polarizing element. In the case of containing the urea compound in the polarizing element, the following values may be appropriately adjusted. The specific examples of the urea compound may be those contained in the polarizing element 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 may move from the adhesive layer to the polarizing element or the like.

When the adhesive is an aqueous 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 and 200 parts by mass or less, and still more preferably 3 parts by mass or more and 100 parts by mass or less, relative to 100 parts by mass of the PVA-based resin. If the amount is less than 0.1 parts by mass, the effect of suppressing the polyalkylene reaction of the polarizing element in a high-temperature environment may be insufficient. On the other hand, if the amount is more than 400 parts by mass, urea may precipitate, resulting in a problem such as an increase in turbidity.

When the adhesive is an aqueous adhesive containing a PVA-based resin, the content of dialdehyde is preferably 1 part by mass or more and 60 parts by mass or less, more preferably 1.5 parts by mass or more and 50 parts by mass or less, and still more preferably 2 parts by mass or more and 45 parts by mass or less, relative to 100 parts by mass of the PVA-based resin. If the amount is less than 1 part by mass, the effect of improving the water resistance may be insufficient. On the other hand, if the amount is more than 60 parts by mass, the liquid mixing stability of the adhesive may be lowered.

The content of the dialdehyde in the adhesive is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, still more preferably 10 parts by mass or less, relative to 1 part by mass of the urea compound, and the lower limit is not limited, but is, for example, 0.03 parts by mass or more. When the content ratio of the urea compound to the dialdehyde in the adhesive is in the above range, the effect of improving the high-temperature durability by the urea compound and the effect of improving the adhesiveness by the dialdehyde can be easily achieved. It is considered that the improvement effect of the water resistance can be obtained by utilizing the improvement effect of the adhesiveness by the dialdehyde. When the dialdehyde is contained in an amount of more than 20 parts by mass per 1 part by mass of the urea compound, the effect of improving the high-temperature durability by the urea compound may not be sufficiently exhibited. The content ratio of the urea compound to the dialdehyde in the adhesive and the content ratio of the urea compound to the dialdehyde in the adhesive layer can be regarded as the same.

In the structure in which the transparent protective film is laminated on both sides of the polarizing element via the adhesive layer, the adhesive layer on only one side of the adhesive layers on both sides of the polarizing element may be a layer containing a urea compound and a dialdehyde, but it is preferable that the adhesive layers on both sides are both layers containing a urea compound and a dialdehyde.

In response to the demand for thickness reduction of the polarizing plate, a polarizing plate having a transparent protective film on only one surface of the polarizing element has been developed. As a method for producing such a polarizing plate having a transparent protective film on only one surface of a polarizing element, a method may be considered in which a polarizing plate having transparent protective films laminated on both surfaces thereof via an adhesive layer is produced, and then one of the transparent protective films is peeled off. In the case of using such a production method, the adhesive layer on the non-peeling film side preferably contains a urea compound and a dialdehyde, or both the adhesive layers may be layers containing a urea compound and a dialdehyde.

The binder is also preferably made to contain a water-soluble chelating compound. The water-soluble chelate compound can increase the degree of crosslinking between the adhesive layer and the transparent protective film such as a polarizing element, a cellulose film, an olefin film, etc., thereby improving the adhesive strength and water resistance, and can act as an additive that does not cause any problem in optical durability.

The water-soluble chelating compound has an effect of promoting the curing of glyoxal. As the kind of the chelate compound, zinc chloride, cobalt chloride, magnesium acetate, aluminum nitrate, zinc sulfate, and the like can be added. Zinc chloride, zinc nitrate and aluminum nitrate, which are excellent in the action of the crosslinking catalyst, are particularly preferable.

The weight ratio of the water-soluble chelating compound contained in the adhesive layer is preferably in the range of 2 to 10 parts by mass relative to 100 parts by mass of the PVA-based resin. When the mass ratio of the water-soluble chelate compound is less than 2 parts by weight based on the above-mentioned reference, the adhesive layer at the time of producing the polarizing plate is difficult to sufficiently exhibit water resistance, and when the mass ratio is more than 10 parts by weight, optical characteristics may be deteriorated.

(aqueous adhesive)

Any suitable aqueous adhesive may be used as the aqueous adhesive, however, an aqueous adhesive containing a PVA-based resin (PVA-based adhesive) is preferably used. The average polymerization degree of the PVA-based resin contained in the aqueous adhesive is preferably 100 to 5500, more preferably 1000 to 4500, from the viewpoint of adhesion. The average saponification degree 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 adhesion.

In the case where the adhesive is an aqueous adhesive containing a PVA-based resin, the PVA-based resin is preferably an acetoacetyl-containing resin because the effect of improving the adhesive force by dialdehydes is more remarkable. It is assumed that, for example, when glyoxal is used as the dialdehyde, an aldehyde portion of glyoxal undergoes an addition reaction with an acetoacetyl group of the acetoacetyl-modified PVA-based resin to act as a crosslinking agent, thereby improving the adhesive strength. The acetoacetyl group-containing PVA-based resin can be obtained, for example, by reacting a PVA-based resin with diketene by any method. The degree of acetoacetyl modification of the acetoacetyl-modified PVA resin is preferably 0.1 mol% or more, more preferably 0.1 mol% or more and 20 mol% or less. The concentration of the PVA-based resin in the aqueous adhesive is preferably 0.1 mass% or more and 15 mass% or less, and more preferably 0.5 mass% or more and 10 mass% or less.

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

The aqueous adhesive may contain an organic solvent. The organic solvent is preferably an alcohol in view of having miscibility with water, and methanol or ethanol is more preferred among the alcohols. The concentration of methanol in the aqueous adhesive is preferably 10% by mass or more and 70% by mass or less, more preferably 15% by mass or more and 60% by mass or less, and still more preferably 20% by mass or more and 60% by mass or less. By setting the concentration of methanol to 10 mass% or more, the polyvinyl alcohol of the PVA-based resin in a high-temperature environment can be easily further suppressed. Further, by setting the content of methanol to 70 mass% or less, deterioration of the color tone can be suppressed. Some urea derivatives have a low solubility in water, but a sufficient solubility in alcohol. In this case, it is also one of preferable modes to prepare an adhesive by dissolving a urea compound in an alcohol to prepare an alcohol solution of the urea compound and then adding the alcohol solution of the urea compound to an aqueous PVA solution.

(active energy ray-curable adhesive)

The active energy ray-curable adhesive is an adhesive cured by irradiation with active energy rays such as ultraviolet rays, and examples thereof include adhesives containing a polymerizable compound and a photopolymerization initiator, adhesives containing a photoreactive resin, adhesives containing a binder resin and a photoreactive crosslinking agent, and the like. 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. The photopolymerization initiator may be a compound containing an active species such as a neutral radical, an anionic radical, or a cationic radical generated by irradiation with an active energy ray such as ultraviolet rays.

< layer containing urea-based Compound >

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

In the present embodiment, the cured layer may contain a urea compound, and may be a urea compound-containing layer. Such a cured layer is generally formed from a curable composition containing an organic solvent, however, a method of forming such a cured layer from an aqueous solution of an active energy ray-curable polymer composition is described in paragraphs [0020] to [0042] of Japanese patent application laid-open No. 2017-075986. Such compositions may be made to contain water-soluble urea-based compounds.

The urea compound-containing layer preferably has at least 1 urea compound and a binder. The binder may be a polymer binder, a thermosetting resin binder, an active energy ray curable resin binder, or the like, and any binder may be preferably 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 method for manufacturing a polarizing plate according to the present embodiment includes a water content adjustment step and a lamination step. In the water content adjustment step, when the polarizing plate having the feature (a) is manufactured, the water content of the polarizing element is adjusted so that the water content of the polarizing element is equal to or higher than the equilibrium water content of 30% relative humidity at 20 ℃ and equal to or lower than the equilibrium water content of 50% relative humidity at 20 ℃. The water content of the polarizing element can be adjusted in accordance with the description of the water content of the polarizing element. In the water content adjustment step, when the polarizing plate having the feature (b) is manufactured, the water content of the polarizing plate is adjusted so that the water content of the polarizing plate is equal to or higher than the equilibrium water content of 30% relative humidity at 20 ℃ and equal to or lower than the equilibrium water content of 50% relative humidity at 20 ℃. The water content of the polarizing plate can be adjusted in accordance with the description of the water content of the polarizing plate. In the lamination step, the polarizing element and the transparent protective film are laminated via the adhesive layer. In the lamination step, for example, a polarizing element which has not been subjected to treatment containing a urea compound is bonded to a transparent protective film by an adhesive containing a urea compound and a dialdehyde. The order of the water content adjustment step and the lamination step is not limited, and the water content adjustment step and the lamination step may be performed in parallel.

[ constitution of image display device ]

The polarizing plate of the present embodiment is used for various image display devices such as a liquid crystal display device and an organic EL display device. In the case of an image display device having an interlayer filling structure in which both surfaces of a polarizing plate are in contact with a layer other than an air layer, specifically, a solid layer such as an adhesive layer, transmittance tends to be reduced in a high-temperature environment. In the image display device using the polarizing plate according to the present embodiment, even in the interlayer filling structure, the decrease in transmittance of the polarizing plate in a high-temperature environment can be suppressed. As the image display device, a configuration having an image display unit, a 1 st adhesive layer laminated on a visible side surface of the image display unit, and a polarizing plate laminated on a visible side surface of the 1 st adhesive layer can be exemplified. The image display device may further have a 2 nd adhesive layer laminated on the visible side surface of the polarizing plate and a transparent member laminated on the surface of the 2 nd adhesive layer. In particular, the polarizing plate of the present embodiment can be suitably used in an image display device having an interlayer filling structure in which a transparent member is disposed on the visible side of the image display device, the polarizing plate and the image display unit are bonded by the 1 st adhesive layer, and the polarizing plate and the transparent member are bonded by the 2 nd adhesive layer. In this specification, either one or both of the 1 st adhesive layer and the 2 nd adhesive layer may be simply referred to as an "adhesive layer". The member used for bonding the polarizing plate to the image display unit and the member used for bonding the polarizing plate to the transparent member are not limited to the adhesive layer, and may be an adhesive layer.

< image display Unit >

Examples of the image display unit include a liquid crystal unit and an organic EL unit. As the liquid crystal cell, any one of a reflective liquid crystal cell using external light, a transmissive liquid crystal cell using light from a light source such as a backlight, and a semi-transmissive and semi-reflective liquid crystal cell using both light from the outside and light from the light source can be used. In the case where the liquid crystal cell is a liquid crystal cell that uses light from a light source, the image display device (liquid crystal display device) is also provided with a polarizing plate on the side of the image display cell (liquid crystal cell) opposite to the viewing side, and the light source is also provided. The polarizing plate on the light source side and the liquid crystal cell are preferably bonded via an appropriate adhesive layer. As a driving method of the liquid crystal cell, for example, an optional type of driving method such as VA mode, IPS mode, TN mode, STN mode, and bend alignment (pi type) can be used.

As the organic EL unit, an organic EL unit or the like in which a transparent electrode, an organic light-emitting layer, and a metal electrode are sequentially stacked on a transparent substrate to form a light-emitting body (organic electroluminescent light-emitting body) can be suitably used. The organic light-emitting layer is a laminate of various organic thin films, and for example, a laminate of a hole-injecting layer containing a triphenylamine derivative or the like and a light-emitting layer containing a fluorescent organic solid such as anthracene, a laminate of these light-emitting layers and an electron-injecting layer containing a perylene derivative or the like, or a laminate of a hole-injecting layer, a light-emitting layer, and an electron-injecting layer can be used.

< adhesion of image display Unit to polarizing plate >

In the lamination of the image display unit and the polarizing plate, an adhesive layer (adhesive sheet) may be suitably used. Among them, a method of bonding a polarizing plate with an adhesive layer, which is provided with an adhesive layer on one surface of the polarizing plate, to an image display unit is preferable from the viewpoint of workability and the like. The adhesive layer may be attached to the polarizing plate in an appropriate manner. As an example thereof, there may be mentioned: a method of preparing a binder solution in which 10 mass% or more and 40 mass% or less of a base polymer or a composition thereof is dissolved or dispersed in a solvent comprising a single or a mixture of appropriate solvents such as toluene and ethyl acetate, and directly attaching the binder solution to a polarizing plate by an appropriate development method such as a casting method and a coating method; and a method of forming an adhesive layer on the spacer and transferring it to a polarizing plate.

< adhesive layer >

The adhesive layer may be formed of 1 layer or 2 layers or more, but is preferably formed of 1 layer. The adhesive layer may be composed of an adhesive composition containing a (meth) acrylic resin, a rubber resin, a urethane resin, an ester resin, a silicone resin, and a polyvinyl ether resin as a main component. Among them, an adhesive composition containing a (meth) acrylic resin as a base polymer excellent in transparency, weather resistance, heat resistance and the like is suitable. The adhesive composition may be an active energy ray-curable or thermosetting adhesive composition.

As the (meth) acrylic resin (base polymer) used in the adhesive composition, a polymer or copolymer containing 1 or 2 or more (meth) acrylic esters such as butyl (meth) acrylate, ethyl (meth) acrylate, isooctyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate as monomers can be suitably used. The polar monomer is preferably copolymerized in the base polymer. Examples of the polar monomer include monomers having a carboxyl group, a hydroxyl group, an amide group, an amino group, an epoxy group, and the like, such as a (meth) acrylic acid compound, a 2-hydroxypropyl (meth) acrylate compound, a hydroxyethyl (meth) acrylate compound, a (meth) acrylamide compound, an N, N-dimethylaminoethyl (meth) acrylate compound, and a glycidyl (meth) acrylate compound.

The adhesive composition may contain only the above base polymer, but usually also contains a crosslinking agent. Examples of the crosslinking agent include metal ions having a valence of 2 or more and forming a metal carboxylate between the metal ion and the carboxyl group; a polyamine compound forming an amide bond with a carboxyl group; polyepoxides or polyols which form ester bonds between them and the carboxyl groups; polyisocyanate compounds forming an amide bond with a carboxyl group. Among them, polyisocyanate compounds are preferable.

The active energy ray-curable adhesive composition has a property of being cured by irradiation with active energy rays such as ultraviolet rays and electron beams, and has a property of having adhesiveness to an adherend such as a film even before irradiation with active energy rays and being cured by irradiation with active energy rays to thereby adjust an adhesive force. The active energy ray-curable adhesive composition is preferably an ultraviolet ray-curable adhesive composition. The active energy ray-curable adhesive composition contains an active energy ray-polymerizable compound in addition to the base polymer and the crosslinking agent. If necessary, a photopolymerization initiator, a photosensitizer, and the like may be contained.

The adhesive composition may contain additives such as microparticles, beads (resin beads, glass beads, etc.), glass fibers, resins other than the base polymer, tackifiers, fillers (metal powder, other inorganic powder, etc.), antioxidants, ultraviolet absorbers, dyes, pigments, colorants, defoamers, anticorrosive agents, photopolymerization initiators, etc. for imparting light scattering properties.

The adhesive layer may be formed by coating an organic solvent diluent of the above adhesive composition on the surface of a substrate film, an image display unit, or a polarizing plate and drying. The base film is usually a thermoplastic resin film, and a typical example thereof is a release film subjected to a release treatment. The release film may be, for example, a film obtained by subjecting the surface of a film containing a resin such as polyethylene terephthalate, polybutylene terephthalate, polycarbonate, or polyarylate, on which the adhesive layer is formed, to a release treatment such as silicone treatment.

The release-treated surface of the release film may be coated with the adhesive composition directly to form an adhesive layer, and the adhesive layer with the release film may be laminated on the surface of the polarizer. The pressure-sensitive adhesive layer may be formed by directly applying the pressure-sensitive adhesive composition to the surface of the polarizing plate, and the release film may be laminated on the outer surface of the pressure-sensitive adhesive layer.

When the pressure-sensitive adhesive layer is provided on the surface of the polarizing plate, the bonding surface of the polarizing plate and/or the bonding surface of the pressure-sensitive adhesive layer is preferably subjected to a surface activation treatment such as plasma treatment or corona treatment, and more preferably to corona treatment.

Alternatively, an adhesive sheet may be prepared in which the adhesive composition is applied to the 2 nd separator to form an adhesive layer, and the separator is laminated on the formed adhesive layer, and the separator-equipped adhesive layer after the 2 nd separator is peeled off from the adhesive sheet may be laminated on the polarizing plate. The 2 nd release film used was a film which was less strongly adhered to the adhesive layer than the release film and was easily peeled off.

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, for example.

< transparent Member >

Examples of the transparent member disposed on the visible side of the image display device include a transparent plate (window layer) and a touch panel. As the transparent plate, a transparent plate having appropriate mechanical strength and thickness is used. Examples of such a transparent plate include a transparent resin plate such as polyimide resin, acrylic resin, and polycarbonate resin, and a glass plate. A functional layer such as an antireflection layer may be laminated on the visible side of the transparent plate. In addition, when the transparent plate is a transparent resin plate, a hard coat layer may be laminated to improve physical strength, and a low moisture permeability layer may be laminated to reduce moisture permeability. As the touch panel, various touch panels such as a resistive film type, a capacitive type, an optical type, and an ultrasonic type, a glass plate having a touch sensor function, a transparent resin plate, and the like can be used. In the case of using a capacitive touch panel as the transparent member, a transparent plate made of glass or a transparent resin plate is preferably provided on the visible side with respect to the touch panel.

< adhesion of polarizing plate to transparent Member >

In the bonding of the polarizing plate and the transparent member, an adhesive or an active energy ray-curable adhesive may be suitably used. In the case of using an adhesive, the adhesive can be attached in an appropriate manner. Specific examples of the method of attaching include a method of attaching an adhesive layer used for attaching the image display unit and the polarizing plate.

In the case of using an active energy ray-curable adhesive, for the purpose of preventing the adhesive solution before curing from spreading, a method of providing a dam material so as to surround the peripheral edge portion on the image display panel, placing a transparent member on the dam material, and injecting the adhesive solution may be suitably used. After the injection of the adhesive solution, the adhesive solution is cured by irradiating an active energy ray after the alignment and defoamation as necessary.

Examples

The present invention will be specifically described below based on examples. The materials, reagents, amounts of materials, proportions thereof, operations and the like shown in the following examples may be appropriately changed without departing from the gist of the present invention. Thus, the present invention is not limited by the following examples.

< production of polarizing element A >

A PVA film having a thickness of 40 μm, which is formed of PVA having an average polymerization degree of about 2400 and a saponification degree of 99.9 mol% or more, was uniaxially stretched to about 5 times in a dry manner, immersed in pure water at 60℃for 1 minute while maintaining the stretched state, and then immersed in an aqueous solution having a weight ratio of iodine/potassium iodide/water of 0.05/5/100 at 28℃for 60 seconds. Thereafter, the mixture was immersed in an aqueous solution having a weight ratio of potassium iodide/boric acid/water of 8.5/8.5/100 at 72℃for 300 seconds. Then, after washing with pure water at 26℃for 20 seconds, the resultant was dried at 65℃to obtain a polarizing element A having a thickness of 15. Mu.m, in which iodine was adsorbed to PVA and oriented. 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 8 >

(preparation of PVA solution A for adhesive)

50g of an acetoacetyl group-containing modified PVA resin (GOHSENX Z-410, mitsubishi chemical Co., ltd.) was dissolved in 950g of pure water, heated at 90℃for 2 hours, and then cooled to room temperature to obtain a PVA solution for adhesives (hereinafter referred to as "PVA solution A").

(preparation of urea-based Compound solution 1)

10g of urea was added to 90g of pure water to obtain an aqueous solution (urea-based compound solution 1) having 10 mass% of urea.

(preparation of adhesives 1 to 8)

The PVA solution a, the urea compound solution 1, the commercially available glyoxal 40 mass% solution and pure water were mixed so that the PVA was 3.0 mass% and the urea compound and glyoxal were contained in the amounts shown in table 1, to prepare adhesives 1 to 8.

TABLE 1

< preparation of transparent protective film A >

A commercially available cellulose acylate film TD40 (film thickness: 40 μm, manufactured by Fuji photo Co., ltd.) was immersed in a 1.5mol/L aqueous NaOH solution (saponification solution) kept at 55℃for 2 minutes, and then the film was washed with water. Thereafter, the membrane was immersed in a sulfuric acid aqueous solution of 0.05mol/L at 25℃for 30 seconds, and then washed with water under running water for 30 seconds to thereby bring the membrane into a neutral state. After that, the water was removed by repeating the water removal with an air knife 3 times, and then the film was dried by leaving the film in a drying zone at 70 ℃ for 15 seconds, and a film subjected to saponification treatment was produced and used as a transparent protective film a.

< production of polarizing plates 1 to 8 >

Transparent protective films a were bonded to both sides of the polarizing element a via an adhesive 1 using a roll laminator. After lamination, the laminate was dried at 80℃for 5 minutes to obtain a polarizing plate 1. The thickness of the adhesive layer after drying was adjusted so that the thickness was 100nm on both sides.

In the polarizing plate 1, the adhesive 1 was changed to the adhesives 2 to 8, and the polarizing plates 2 to 8 were obtained.

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

The polarizing plates 1 to 8 obtained above were stored at a temperature of 20℃for 72 hours under a relative humidity of 30%, 35%, 40%, 45%, 50% or 55%. The water content was measured by the karl-fischer method at 66 hours, 69 hours and 72 hours of storage. The water content was unchanged at 66 hours, 69 hours and 72 hours under any humidity conditions. Therefore, the water content of the polarizing plates 1 to 8 can be regarded as the same as the equilibrium water content in the storage environment for 72 hours used in this experimental example. When the water content of the polarizing plate is balanced in a certain storage environment, it can be considered that the water content of the polarizing element in the polarizing plate is balanced in the same storage environment. In addition, when the water content of the polarizing element in the polarizing plate is balanced in a certain storage environment, it can be considered that the water content of the polarizing plate is balanced in the storage environment as well.

< optical layered bodies 1 to 10>

Using any one of the polarizing plates 1 to 8 shown in table 2, the optical layered bodies 1 to 10 were produced by storing the polarizing plates (polarizing elements) for 72 hours under conditions of a relative humidity of 35%, 45% or 55% at a temperature of 20 ℃ so that the water content of the polarizing plates (polarizing elements) used became the equilibrium water content of the environment shown in table 2.

< evaluation of high temperature durability >

(preparation of sample for evaluation)

The optical laminates 1 to 10 were each formed with an acrylic adhesive (model #7, manufactured by LINTEC Co., ltd.) on both sides thereof, and were cut into a size of 50mm X100 mm so that the absorption axis was parallel to the long side. An alkali-free glass (EAGLE XG, manufactured by Corning corporation) was attached to each adhesive surface, and an evaluation sample was produced.

To evaluate the cross light leakage of the evaluation sample, an optical laminate R was produced in order to produce a cross nicol prism state so as to overlap the evaluation sample. Specifically, an acrylic adhesive (model: #7, manufactured by LINTEC Co., ltd.) was formed on only one side of the polarizing plate 8, and the polarizing plate was cut into a size of 50mm×100mm so that the absorption axis was parallel to the short side. An alkali-free glass (EAGLE XG, manufactured by Corning corporation) was bonded to the adhesive surface, and thus an optical laminate R used for the orthogonal evaluation was produced.

< evaluation of monomer transmittance (105 ℃ C.) >)

Evaluation samples of the optical layered bodies 1 to 10 were subjected to a temperature of 50℃and a pressure of 5kgf/cm ² (490.3 kPa) for 1 hour, and then left to stand in an atmosphere having a temperature of 23℃and a relative humidity of 55% for 24 hours. Thereafter, the transmittance (initial value) was measured for the evaluation samples of the optical layered bodies 1 to 10, and the samples were stored in a heating environment at a temperature of 105 ℃ for every 50 hours until 100 to 200 hours. Based on the time when the decrease in transmittance was 5% or more with respect to the initial value, evaluation was performed in accordance with the following criteria. The results obtained are shown in table 2.

Samples with a decrease in transmittance of 5% or less after 200 hours: a is that

Samples with a transmittance decrease of 5% or more at 150 to 200 hours: b (B)

Samples with transmittance reduction of 5% or more at 100 to 150 hours: c (C)

Samples with a transmittance decrease of 5% or more at the time after 100 hours: d (D)

< evaluation of orthogonal light leakage after high temperature durability test >

An evaluation sample was prepared after the measurement of the monomer transmittance at 200 hours in the above-mentioned evaluation of the monomer transmittance. The optical laminate R for cross nicol prism evaluation, which is not put into a heating environment, and the evaluation sample are disposed so as to form a cross nicol prism relationship, and are placed on a backlight. The surrounding was shielded from light, and the light leakage was evaluated on a 4-scale by visual observation in accordance with the following criteria. The results obtained are shown in table 2. The evaluation samples other than the evaluation of the monomer transmittance of a were excluded from the evaluation of the cross light leakage because of the coloration due to the polyeneization.

Sample with no cross light leakage observed at all: a is that

Samples with essentially no cross light leakage were observed: b (B)

Samples with light leakage that is orthogonal were slightly observed: c (C)

Samples of orthogonal light leakage were clearly observed: d (D)

< evaluation of Water resistance (warm Water immersion test) >)

The water resistance test of this example was performed in accordance with the water resistance test described in Japanese patent application laid-open No. 2009-025728 [0060 ].

An acrylic adhesive (model #7, LINTEC Co., ltd.) was formed on one surface of the polarizing plate manufactured as described above, and the polarizing plate was cut into strips with the absorption axis (stretching direction) of the polarizing plate as a long side and a size of 50 mm. Times.20 mm, and the dimension in the long side direction was accurately measured. Here, the sample was evaluated to exhibit a unique color uniformly over the entire surface due to iodine adsorbed to the polarizing element.

One short side of the sample was held by a holder, and immersed in a water tank at 60℃for 4 hours while being 8 pieces in the longitudinal direction. Thereafter, the sample was taken out of the water tank, and the water was scraped off. The polarizer of the polarizing plate is shrunk due to immersion in warm water. The degree of shrinkage of the polarizing element was evaluated in 3 grades according to the above criteria by measuring the distance from the end of the sample (the end of the protective film) to the end of the shrunk polarizing element at the center of the short side of the sample.

A sample having a distance of 1mm or less from the end of the sample to the end of the polarizing plate: a is that

A distance from the end of the sample to the end of the polarizing plate is greater than 1mm and 3mm or less: b (B)

A sample having a distance from the end of the sample to the end of the polarizer of greater than 3 mm: c (C)

TABLE 2

It was found that the polarizing plate (optical laminate 8) containing urea in the adhesive was less likely to be reduced in transmittance and excellent in high-temperature durability even when exposed to a high-temperature environment of 105 ℃ as compared with the polarizing plates (optical laminates 9 and 10) containing no urea in the adhesive. It is found that the use of an adhesive containing urea and glyoxal can improve water resistance, and that the optical laminates 2 and 8 are less likely to suffer from cross light leakage even when exposed to high temperature environments (comparison of the optical laminates).

Claims

1. A polarizing plate, which comprises a polarizing plate,

it has the following components: a polarizing element in which a dichroic dye is adsorbed and aligned to a polyvinyl alcohol 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 by an adhesive containing a urea compound and a dialdehyde,

the water content of the polarizing element is more than the equilibrium water content of 30% relative humidity at 20 ℃ and less than the equilibrium water content of 50% relative humidity at 20 ℃.

2. A polarizing plate, which comprises a polarizing plate,

the water content of the polarizing plate is more than the equilibrium water content of 30% of the relative humidity at the temperature of 20 ℃ and less than the equilibrium water content of 50% of the relative humidity at the temperature of 20 ℃.

3. The polarizing plate according to claim 1 or 2, wherein,

the adhesive contains at least one urea compound selected from urea derivatives and thiourea derivatives.

4. The polarizing plate according to any one of claims 1 to 3, wherein,

the adhesive contains a polyvinyl alcohol resin.

5. The polarizing plate according to claim 4, wherein,

in the adhesive, the content of the urea compound is 0.1 to 400 parts by mass based on 100 parts by mass of the polyvinyl alcohol resin.

6. The polarizing plate according to any one of claims 1 to 5, wherein,

in the adhesive, the content of the dialdehyde is 0.03 parts by mass or more and 20 parts by mass or less relative to 1 part by mass of the urea compound.

7. The polarizing plate according to any one of claims 1 to 6, wherein,

the dialdehyde is glyoxal.

8. The polarizing plate according to any one of claims 1 to 7, wherein,

the thickness of the adhesive layer is 0.01 μm or more and 7 μm or less.

9. The polarizing plate according to any one of claims 1 to 8, wherein,

the polarizing plate is used for an image display device,

10. An image display device, comprising:

an image display unit,

The 1 st adhesive layer laminated on the visible side surface of the image display unit and the polarizing plate according to any one of claims 1 to 9 laminated on the visible side surface of the 1 st adhesive layer.

11. The image display device according to claim 10, further comprising a 2 nd adhesive layer laminated on a visible side surface of the polarizing plate and a transparent member laminated on a visible side surface of the 2 nd adhesive layer.

12. The image display device according to claim 11, wherein,

the transparent member is a glass plate or a transparent resin plate.

13. The image display device according to claim 11, wherein,

the transparent member is a touch panel.