CN115016053A

CN115016053A - Polarizing plate and image display device

Info

Publication number: CN115016053A
Application number: CN202210203813.5A
Authority: CN
Inventors: 佐藤翔太; 福田谦一
Original assignee: Sumitomo Chemical Co Ltd
Current assignee: Sumitomo Chemical Co Ltd
Priority date: 2021-03-05
Filing date: 2022-03-02
Publication date: 2022-09-06
Also published as: TW202239605A; JP2022135259A; KR20220125781A

Abstract

The invention provides a polarizing plate in which a decrease in transmittance in a high-temperature environment is suppressed. The polarizing plate of the present invention comprises a polarizing element obtained by adsorbing a dichroic dye onto a polyvinyl alcohol resin layer and orienting the dichroic dye, 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 to each other via an adhesive layer comprising a urea compound and a cyclodextrin-based adhesive, and the urea compound is at least 1 selected from urea, a urea derivative, thiourea, and a thiourea derivative.

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 Displays (LCDs) are widely used not only for liquid crystal televisions but also for mobile devices such as personal computers and mobile phones, and for vehicle-mounted applications such as navigation systems. 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 performs display by controlling light from a backlight with the liquid crystal panel. In recent years, organic EL display devices have been widely used in mobile devices such as televisions and cellular phones, and in vehicle-mounted applications such as navigation systems, as in liquid crystal display devices. In an organic EL display device, in order to suppress external light from being reflected by a metal electrode (cathode) and observed as a mirror surface, 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.

As described above, polarizing plates are increasingly mounted in vehicles as members of image display devices such as liquid crystal display devices and organic EL display devices. Polarizing plates used in image display devices for vehicles are more exposed to high-temperature environments than those used in mobile devices such as televisions and cellular phones, and therefore, are required to have less characteristic change at high temperatures (high-temperature durability).

On the other hand, for the purpose of preventing damage to the image display panel due to impact from the outer surface, a configuration 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 the visible side of the image display panel is increasing. 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 further provided on the visible side with respect to the touch panel.

In such a configuration, if an air layer is present between the image display panel and a transparent member such as a front panel or a touch panel, glare of reflection of external light due to reflection of light at an interface of the air layer is generated, and visibility of a screen tends to be reduced. Accordingly, there has been an action to adopt a structure (hereinafter, sometimes referred to as an "interlayer filling structure") in which a space between a polarizing plate and a transparent member, which is disposed on the viewing-side surface of an image display panel, is filled with a layer other than an air layer, and usually a solid layer (hereinafter, sometimes referred to as an "interlayer filler"). 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 (see, for example, patent document 1).

The interlayer filling structure is being widely used in mobile devices such as cellular phones which are often used outdoors. In addition, in recent years, as the demand for visibility has increased, in vehicle-mounted applications such as navigation devices, an interlayer filling structure has been studied in which a front transparent plate is disposed on the surface of an image display panel, and the space between the panel and the front transparent plate is filled with an adhesive layer or the like.

However, in the case of such a configuration, it has been reported that the transmittance of the polarizing plate is significantly reduced in a high-temperature environment. As a solution to this problem, patent document 2 proposes a method of suppressing a decrease in transmittance by setting the water content per unit area of the polarizing plate to a predetermined amount or less and setting the saturated water absorption amount of the transparent protective film adjacent to the polarizer to a predetermined amount or less.

Documents of the prior art

Patent literature

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

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

Disclosure of Invention

Problems to be solved by the invention

However, even such a polarizing plate has insufficient effect of suppressing the decrease in transmittance in a high-temperature environment. The present invention aims to provide a novel polarizing plate capable of suppressing a decrease in transmittance in a high-temperature environment, and an image display device using the same.

Means for solving the problems

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

[1] A polarizing plate comprising a polarizing element obtained by adsorbing a dichroic dye onto a polyvinyl alcohol resin layer and orienting the dichroic dye, and a transparent protective film laminated on at least one surface of the polarizing element,

the polarizer and the transparent protective film are bonded to each other via an adhesive layer formed of an adhesive containing a urea compound and a cyclodextrin,

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

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

[3] The polarizing plate according to any one of [1] and [2], wherein the adhesive contains a polyvinyl alcohol resin.

[4] The polarizing plate according to [3], wherein a content of the urea compound in the adhesive 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 resin.

[5] The polarizing plate according to [3] or [4], wherein a content of the cyclodextrin compound 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 resin.

[6] The polarizing plate according to any one of [1] to [5], wherein the adhesive layer has a thickness of 0.01 μm or more and 7 μm or less.

[7] The polarizing plate according to any one of [1] to [6], wherein the cyclodextrin is at least 1 selected from the group consisting of α -cyclodextrin, β -cyclodextrin and γ -cyclodextrin.

[8] The polarizing plate according to any one of [1] to [7], wherein the water content of the polarizing element is equal to or higher than an equilibrium water content at a temperature of 20 ℃ and a relative humidity of 30%, and equal to or lower than an equilibrium water content at a temperature of 20 ℃ and a relative humidity of 50%.

[9] The polarizing plate according to any one of [1] to [7], wherein the polarizing plate has a water content of not less than an equilibrium water content at a temperature of 20 ℃ and a relative humidity of 30% and not more than an equilibrium water content at a temperature of 20 ℃ and a relative humidity of 50%.

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

in the image display device, a solid layer is provided in contact with both surfaces of the polarizing plate.

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

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

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

[14] The image display device according to [12], wherein the transparent member is a touch panel.

Effects of the invention

According to the present invention, a polarizing plate having improved high-temperature durability can be provided. According to the present invention, a polarizing plate in which a decrease in transmittance due to high temperature is suppressed even when the polarizing plate is used in an image display device having an interlayer filling structure can be provided. Further, by using the polarizing plate of the present invention, an image display device in which a decrease in transmittance in a high-temperature environment is suppressed can be provided.

Detailed Description

The following description will explain embodiments of the present invention, 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 layer containing a polyvinyl alcohol resin adsorbs a dichroic dye and the dichroic dye is aligned, and a transparent protective film. The polarizing element and the transparent protective film are bonded to each other via an adhesive layer formed of an adhesive containing a urea compound and a cyclodextrin compound. The polarizing plate of the present embodiment preferably has at least one of the following characteristics (a) and (b).

(a) The water content of the polarizing element is not less than the equilibrium water content at a temperature of 20 ℃ and a relative humidity of 30%, and not more than the equilibrium water content at a temperature of 20 ℃ and a relative humidity of 50%.

(b) The polarizing plate has a water content of not less than an equilibrium water content at a temperature of 20 ℃ and a relative humidity of 30% and not more than an equilibrium water content at a temperature of 20 ℃ and a relative humidity of 50%.

As a conventional polarizing plate having excellent high-temperature durability, for example, a polarizing plate alone is known which can suppress a decrease in transmittance even when left in an environment at a temperature of 95 ℃ for 1000 hours. However, even in the case of such a polarizing plate, when it is used in an interlayer filling structure, when it is left for 240 hours in an environment at a temperature of 105 ℃, a significant decrease in transmittance and polarization degree may be observed in the central portion in the polarizing plate surface. When an image display device using an interlayer filling structure in which one surface of a 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 a high-temperature environment, it is considered that the transmittance and the polarization degree of the polarizing plate in the high-temperature environment are particularly likely to be significantly reduced.

The polarizing plate having remarkably reduced transmittance due to interlayer filling structure was 1100cm in Raman spectroscopic measurement ^-1 Nearby (from ═ C-C ═ bond) and 1500cm ^-1 Nearby (from-C ═ C-bonds) has peaks, and thus the polyene structure (-C ═ C) is considered to be formed _n -. The polyene structure is presumed to be a structure resulting from polyene formation of polyvinyl alcohol forming a polarizing element by dehydration (patent documents 2 and [0012 ]]Segment).

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

< polarizing element >

As a polarizing element obtained by adsorbing a dichroic dye onto a layer containing a polyvinyl alcohol (hereinafter, also referred to as "PVA") resin (hereinafter, also referred to as "PVA-based resin layer") and orienting the dichroic dye, a known polarizing element can be used. Examples of the polarizing element include stretched films obtained by dyeing a PVA-based resin film with a dichroic dye and uniaxially stretching the PVA-based resin film; the stretched layer is obtained by using a laminated film having a coating layer formed by applying a coating liquid containing a PVA resin on a base film, dyeing the coating layer with a dichroic dye, and uniaxially stretching the laminated 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-based resin may be a copolymer of vinyl acetate and another monomer copolymerizable with vinyl acetate, 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 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, and examples thereof include polyvinyl formal, polyvinyl acetal, and 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, 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 polyene formation of the PVA-based resin on the degradation of the optical properties in a high-temperature environment can be suppressed. By making the thickness of the polarizing element 3 μm or more, a structure that realizes desired optical characteristics can be easily obtained.

The polarizing element preferably includes a urea compound and a cyclodextrin compound. In the present embodiment, since the polarizing element and the transparent protective film are bonded to each other via the adhesive layer formed of the adhesive containing the urea compound and the cyclodextrin compound, it is estimated that a part of the urea compound and a part of the cyclodextrin compound are transferred from the adhesive layer and contained in the polarizing element. The urea compound and the cyclodextrin compound in the polarizer may include urea compounds and cyclodextrin compounds added in the process of producing the polarizer. By providing a polarizing element containing a urea compound and a cyclodextrin compound, the transmittance is not easily reduced even when the polarizing plate is exposed to a high-temperature environment. Further, by providing an adhesive layer containing a urea compound and a cyclodextrin compound, the reduction in the degree of polarization can be suppressed even when the polarizing plate is exposed to a high-temperature environment. When two polarizing plates are disposed and used in a relationship of crossed nicols, light leakage (hereinafter, also referred to as "crossed light leakage") is likely to occur when the degree of polarization of the polarizing plates is reduced, but the degree of polarization is not likely to be reduced even when the polarizing plates are exposed to a high-temperature environment, and therefore the crossed light leakage is likely to be suppressed. It is presumed that the reason for this effect is that the urea compound and the cyclodextrin contained in the polarizing element inhibit the polyene formation of the PVA-based resin.

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

Among them, a method of immersing the PVA-based resin layer in a treatment solvent containing both a urea-based compound and a cyclodextrin is preferably used.

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

In order to incorporate the urea compound and the cyclodextrin compound into the polarizing element, both the addition during the production of the polarizing element and the addition to the adhesive may be performed. In addition, one of the urea compound and the cyclodextrin may be contained and the other or both of the adhesives may be contained in the production of the polarizing element, or both of the urea compound and the cyclodextrin may be contained and the one of the adhesives may be contained in the production of the polarizing element.

(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 in 1 kind, or in combination in 2 or more kinds. The urea compound may be either a water-soluble compound or a poorly-soluble compound. When a sparingly soluble urea compound is used as the water-soluble adhesive, it is preferable to design the dispersion method so that the turbidity does not increase after the adhesive layer is formed.

(Urea derivative)

The urea derivative is a compound in which at least 1 of 4 hydrogen atoms of a urea molecule is substituted with a substituent. In this case, the substituent is not particularly limited, and is preferably a substituent containing a carbon atom, a hydrogen atom and an oxygen atom.

Specific examples of the urea derivative include mono-substituted urea, such as methyl urea, ethyl urea, propyl urea, butyl urea, isobutyl urea, N-octadecyl urea, 2-hydroxyethyl urea, hydroxyurea, 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-tert-butylurea, 1, 3-dicyclohexylurea, 1, 3-diphenylurea, 1, 3-bis (4-methoxyphenyl) urea, 1-acetyl-3-methylurea, 2-imidazolidinone (vinylurea), and tetrahydro-2-pyrimidinone (propyleneurea).

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

(Thiourea derivatives)

The thiourea derivative is a compound in which at least 1 of 4 hydrogen atoms of a thiourea molecule is substituted with a substituent. In this case, the substituent is not particularly limited, and is preferably a substituent containing a carbon atom, a hydrogen atom and an oxygen atom.

Specific examples of the thiourea derivative include N-methylthiourea, ethylthiourea, propylthiourea, isopropylthiourea, 1-butylthiourea, cyclohexylthiourea, N-acetylthiourea, N-allylthiourea, (2-methoxyethyl) thiourea, N-phenylthiourea, (4-methoxyphenyl) thiourea, N- (2-methoxyphenyl) thiourea, N- (1-naphthyl) thiourea, (2-pyridyl) thiourea, o-tolylthiourea and p-tolylthiourea.

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-di (o-tolyl) thiourea, 1, 3-di (p-tolyl) thiourea, 1-benzyl-3-phenylthiourea, 1-methyl-3-phenylthiourea, N-allyl-N' - (2-hydroxyethyl) thiourea and ethylenethiourea.

Examples of the tri-substituted thiourea include trimethylthiourea, and examples of the tetra-substituted thiourea include tetramethylthiourea and 1, 1, 3, 3-tetraethylthiourea.

Among the urea compounds, urea derivatives or thiourea derivatives are preferable, and urea derivatives are more preferable, from the viewpoint that the decrease in transmittance in a high-temperature environment can be suppressed and the decrease in the degree of polarization is small (the viewpoint that the orthogonal light leakage is suppressed) when used in an image display device having an interlayer filling structure. Among the urea derivatives, monosubstituted ureas or disubstituted ureas are preferred, and monosubstituted ureas are more preferred. Among the disubstituted ureas are 1, 1-substituted ureas and 1, 3-substituted ureas, more preferably 1, 3-substituted ureas.

(cyclodextrins)

Cyclodextrins are non-reducing cyclic oligosaccharides in which glucose is cyclically bonded by an alpha-1, 4 linkage. The larger the number of cyclodextrins-forming glucose, the larger the inner diameter of the intramolecular cavity. The cyclodextrin used in the present invention is preferably an α -, β -, γ -, δ -cyclodextrin in which the number of formed glucose is 6 or more, and examples thereof include 6, 7, 8, and 9 glucose. The cyclodextrin includes a branched cyclodextrin having an oligosaccharide such as glucose or maltose (Japanese patent: マルクトース) in a branched sugar chain among α -, β -, γ -, and δ -cyclodextrins. The cyclodextrin includes a cyclodextrin or a branched cyclodextrin, which further has an alkyl group such as a methyl group bonded thereto; and a cyclodextrin derivative such as a hydroxyalkyl group such as a 2-hydroxyethyl group, a 2-hydroxypropyl group, a 2, 3-dihydroxypropyl group, or a 2-hydroxybutyl group. The cyclodextrin may be used alone in 1 kind or in combination of 2 or more kinds.

(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 at a temperature of 20 ℃ and a relative humidity of 30%, and equal to or lower than the equilibrium water content at a temperature of 20 ℃ and a relative humidity of 50%. The water content of the polarizing element is preferably at most 45% at a temperature of 20 ℃ and a relative humidity, more preferably at most 42% at a temperature of 20 ℃, and still more preferably at most 38% at a temperature of 20 ℃. If the water content of the polarizer is less than the equilibrium water content at a temperature of 20 ℃ and a relative humidity of 30%, the operability of the polarizer is reduced and the polarizer is easily broken. If the water content of the polarizer is greater than the equilibrium water content at a temperature of 20 ℃ and a relative humidity of 50%, the transmittance of the polarizer is likely to decrease. It is presumed that if the water content of the polarizing element is high, the polyene formation of the PVA-based resin is easily advanced. The water content of the polarizing element is the water content of the polarizing element in the polarizing plate.

As a method of confirming whether or not the water content of the polarizer is in a range of not less than the equilibrium water content at a temperature of 20 ℃ and a relative humidity of 30% and not more than the equilibrium water content at a temperature of 20 ℃ and a relative humidity of 50%, there is a method of storing the polarizer in an environment adjusted to the range of the temperature and the relative humidity, and regarding the polarizer as being in equilibrium with the environment when there is no change in mass for a certain period of time; or a method of calculating in advance the equilibrium moisture content of the polarizer in the environment adjusted to the temperature and the relative humidity range and checking the equilibrium moisture content by comparing the moisture content of the polarizer with the equilibrium moisture content calculated in advance.

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

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

The water content of the polarizer is preferably adjusted to the above numerical range in a material stage in which the polarizer is used alone or in a material stage in which the polarizer and the protective film are laminated to form a polarizing plate. When the moisture content is adjusted after the formation of the polarizing plate, the curl becomes excessively large, and a defect may easily occur when the polarizing plate is bonded to an image display unit. By forming the polarizing plate using the polarizing element whose water content is adjusted to the above-mentioned value in the material stage before forming the polarizing plate, it is possible to easily form the polarizing plate including the polarizing element whose water content satisfies the above-mentioned value range. The water content of the polarizing element in the polarizing plate may be adjusted to the above numerical range in a state where the polarizing plate is bonded to the image display unit. In this case, since the polarizing plate is bonded to the image display unit, curling is less likely to occur.

(feature (b))

In the case of 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 ℃ and a relative humidity of 30%, and equal to or lower than the equilibrium moisture content at a temperature of 20 ℃ and a relative humidity of 50%. The moisture content of the polarizing plate is preferably an equilibrium moisture content of 45% or less at a temperature of 20 ℃ and a relative humidity, more preferably an equilibrium moisture content of 42% or less at a temperature of 20 ℃, and still more preferably an equilibrium moisture content of 38% or less at a temperature of 20 ℃. If the moisture content of the polarizing plate is less than the equilibrium moisture content at a temperature of 20 ℃ and a relative humidity of 30%, the workability of the polarizing plate is lowered and the polarizing plate is easily broken. When the moisture content of the polarizing plate is greater than the equilibrium moisture content at a temperature of 20 ℃ and a relative humidity of 50%, the transmittance of the polarizing element is likely to decrease. It is presumed that if the water content of the polarizing plate is high, polyene formation of the PVA-based resin is facilitated.

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

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

In the case of manufacturing an image display device using an interlayer filling structure, the polarizing plate may be incorporated into the image display device, and the image display device incorporating the polarizing plate may be stored in an environment adjusted to the above temperature and relative humidity for 10 minutes to 3 hours or less, or heated at 30 ℃ to 90 ℃ and then bonded to the front panel.

(method for manufacturing polarizing element)

A method for producing the polarizing element is not particularly limited, and a typical method is a method in which a PVA-based resin film wound in a roll form in advance is sent out and then stretched, dyed, crosslinked, or the like is performed (hereinafter referred to as "production method 1"); a method including a step of applying a coating liquid containing a PVA-based resin to a base film to form a PVA-based resin layer as a coating layer, and stretching the resulting laminate (hereinafter referred to as "production method 2").

The production method 1 can be produced through 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 the dichroic dye with an aqueous boric acid solution, and a step of washing the PVA film 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. In the swelling step, stains, an antiblocking agent (ブロッキング) and the like on the surface of the PVA-based resin film can be removed, and uneven 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, or pure water. The swelling bath may be appropriately added with a surfactant, alcohol, or the like according to a conventional method. From the viewpoint of controlling the potassium content of 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% by mass or less, more preferably 1.0% by mass or less, and still more preferably 0.5% by mass or less.

The temperature of the swelling bath is preferably 10 ℃ to 60 ℃, more preferably 15 ℃ to 45 ℃, and still more preferably 18 ℃ to 30 ℃. The immersion time in the swelling bath is not generally determined 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 or more and 300 seconds or less, more preferably 10 seconds or more and 200 seconds or less, and still more preferably 20 seconds or more and 100 seconds or less. The swelling step may be performed only 1 time, or may be performed a plurality of times as needed.

The dyeing step is a treatment step of immersing the PVA-based resin film in a dyeing bath (iodine solution), and may be performed by adsorbing a dichroic dye such as iodine to the PVA-based resin film and aligning the dichroic dye. The iodine solution is preferably an aqueous iodine solution containing iodine and an iodide as a dissolution assistant. 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 preferable 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, and more preferably 0.02 mass% or more and 0.5 mass% or less. The concentration of the 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 ℃, and still more preferably 18 ℃ to 30 ℃. The immersion time in the dyeing bath is not generally determined 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 or more and 300 seconds or less, and more preferably 20 seconds or more and 240 seconds or less. The dyeing step may be performed only 1 time, or may be performed a plurality of times as needed.

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 is crosslinked with the boron compound, so that iodine molecules or dye molecules can be adsorbed 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 miscible 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 mass% or more and 15 mass% or less, more preferably 1.5 mass% or more and 10 mass% or less, and further preferably 2 mass% or more and 5 mass% or less. When potassium iodide is used in the crosslinking bath, the concentration of potassium iodide in the crosslinking bath is preferably 1 mass% or more and 15 mass% or less, more preferably 1.5 mass% or more and 10 mass% or less, and further preferably 2 mass% or more and 5 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 is not generally determined 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 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 1 time, or may be performed a plurality of times as needed.

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

In the wet stretching method, a solvent such as water or a mixed solution of an organic solvent miscible with water and water is usually used as the treatment bath (stretching bath). 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 mass% or more and 15 mass% or less, more preferably 2 mass% or more and 10 mass% or less, and further preferably 3 mass% or more and 6 mass% or less. The treatment bath (stretching bath) may contain a boron compound from the viewpoint of suppressing film breakage during stretching. When the boron compound is contained, 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 further preferably 2% by mass or more and 5% by mass or less.

The temperature of the stretching bath is preferably 25 ℃ to 80 ℃, more preferably 40 ℃ to 75 ℃, and still more preferably 50 ℃ to 70 ℃. The immersion time in the stretching bath is not generally determined because the degree of stretching of the PVA-based resin film is affected by the temperature of the stretching bath, but 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 1 or more treatment steps of the swelling step, the dyeing step, the crosslinking step, and the washing step.

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

The total stretch ratio (cumulative stretch ratio) applied to the polyvinyl alcohol resin film may be appropriately set according to the purpose, but 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 matter remaining on the surface of the polyvinyl alcohol resin film or the like. The cleaning bath generally uses a medium containing water as a main component, such as water, distilled water, or pure water. In addition, from the viewpoint of controlling the content of potassium in the polarizing element, potassium iodide is preferably used in the cleaning bath, and in this case, the concentration of potassium iodide in the cleaning bath is preferably 1 mass% or more and 10 mass% or less, more preferably 1.5 mass% or more and 4 mass% or less, and still more preferably 1.8 mass% or more and 3.8 mass% or less.

The temperature of the cleaning bath is preferably 5 ℃ to 50 ℃, more preferably 10 ℃ to 40 ℃, and still more preferably 15 ℃ to 30 ℃. The immersion time in the cleaning bath cannot be determined in a general manner since 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 further preferably 3 seconds or more and 20 seconds or less. The cleaning step may be performed only 1 time, or may be performed a plurality of times as needed.

The drying step is a step of drying the PVA-based resin film cleaned in the cleaning step to obtain the polarizing element. The drying may be carried out by any suitable method, and examples thereof include natural drying, forced air drying and heat drying.

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

< transparent protective film >

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

The protective film may have other optical functions at the same time, and may be formed into a laminated structure in which a plurality of layers are laminated. From the viewpoint of optical characteristics, the protective film is preferably thin, but if it is too thin, the strength is reduced and the processability is poor. The film thickness is preferably 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.

As the protective film, a cellulose acylate film, a film containing a polycarbonate resin, a film containing a cycloolefin resin such as norbornene, a (meth) acrylic polymer film, a polyester resin film such as polyethylene terephthalate, or the like can be used. When protective films are bonded to both surfaces of the polarizing element using a water-based adhesive such as a PVA adhesive, at least one of the protective films is preferably a cellulose acylate film or a (meth) acrylic polymer film, and among them, a cellulose acylate film is preferable in terms of moisture permeability.

At least one of the protective films may have a retardation 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 separately have a retardation layer, or may be a combination of both. The film having a retardation function may be directly bonded to the polarizer via an adhesive, or may be bonded to the polarizer via an adhesive or an adhesive with another protective film interposed therebetween.

< adhesive layer >

As the adhesive for forming the adhesive layer for attaching the protective film to the polarizing element, an adhesive containing a urea compound and a cyclodextrin is used. The adhesive may be an aqueous adhesive, a solvent 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 the adhesive containing the urea compound and the cyclodextrin, the decrease in transmittance of the polarizing plate in a high-temperature environment can be suppressed.

The thickness of the adhesive at the time of application may be set to an optional value, and for example, may be set so that an adhesive layer having a desired thickness is obtained after curing or after heating (drying). The thickness of the adhesive layer formed 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 made in terms of a preferable range in the case where the urea compound and the cyclodextrin are not contained in the polarizing element when the polarizing element is manufactured. When the polarizing element contains a urea compound or a cyclodextrin, the following values may be appropriately adjusted. As specific examples of the urea compound and the cyclodextrins, the urea compound and cyclodextrins contained in the above-described polarizing element can be directly applied. In the process of forming the adhesive layer through the drying step in the adhesion of the polarizer and the protective film, a part of the urea compound and a part of the cyclodextrin compound may move from the adhesive layer to the polarizer and 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 further 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 part by mass, the effect of suppressing the polyene formation of the polarizing element in a high-temperature environment may be insufficient. On the other hand, when the amount is more than 400 parts by mass, urea may precipitate after the polarizing plate is produced, thereby increasing the haze.

When the adhesive is an aqueous adhesive containing a PVA-based resin, the content of the cyclodextrin 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 or less, and further preferably 2 parts by mass or more and 35 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 suppressing the polyene formation of the polarizing element in a high-temperature environment may be insufficient. On the other hand, when the amount is more than 50 parts by mass, cyclodextrins may be precipitated after the polarizing plate is produced.

In the configuration in which the transparent protective films are bonded to both surfaces of the polarizing element via the adhesive layers, in the case where the polarizing element is not subjected to a treatment for containing a urea compound and cyclodextrins, only one of the adhesive layers on both surfaces of the polarizing element may be a layer containing a urea compound and cyclodextrins.

In response to the demand for thinner polarizing plates, polarizing plates having a transparent protective film on only one surface of a polarizing element have been developed. In this configuration, a transparent protective film is also laminated via an adhesive layer containing a urea compound and a cyclodextrin compound. As a method for producing such a polarizing plate having a transparent protective film only on one surface of a polarizing element, there may be considered a method in which a polarizing plate having a transparent protective film bonded to both surfaces thereof via an adhesive layer is first produced, and then one of the transparent protective films is peeled off. When such a production method is used, the urea compound and the cyclodextrin may be contained only in either one of the adhesive layers, but preferably, the adhesive layers on both sides are both layers containing the urea compound and the cyclodextrin. When only one of the adhesive layers contains a urea compound and a cyclodextrin, the adhesive layer on the film side that is not peeled off preferably contains a urea compound and a cyclodextrin.

(aqueous adhesive)

As the water-based adhesive, an optional appropriate water-based adhesive can be used, but a water-based 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 or more and 5500 or less, and more preferably 1000 or more and 4500 or less, from the viewpoint of adhesiveness. The average saponification degree is preferably 85 mol% or more and 100 mol% or less, and more preferably 90 mol% or more and 100 mol% or less, from the viewpoint of adhesiveness.

The reason why the PVA-based resin contained in the aqueous adhesive preferably contains an acetoacetyl group is that the PVA-based resin layer has excellent adhesion to the protective film and excellent durability. The acetoacetyl group-containing PVA-based resin can be obtained by, for example, reacting a PVA-based resin with diketene by an optional method. The acetoacetyl group modification degree 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 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. 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 of glyoxal, glyoxylate, and methylolmelamine, more preferably any of glyoxal and glyoxylate, and particularly preferably glyoxal.

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

(active energy ray-curable adhesive)

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

< layer containing Urea-based Compound >

The urea compound and the cyclodextrin are 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 a transparent protective film on only one surface, a cured layer may be laminated on the surface of the polarizing element opposite to the transparent protective film from the viewpoint of improving physical strength.

In the present embodiment, a layer containing a urea compound may be obtained by including a urea compound and a cyclodextrin in such a cured layer. Such a cured layer is usually formed from a curable composition containing an organic solvent, and 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 jp 2017-075986 a. The composition may contain a water-soluble urea compound and a cyclodextrin.

The urea compound-containing layer preferably has at least 1 urea compound, at least 1 cyclodextrin, and a binder. Examples of the binder include a polymer binder, a thermosetting resin binder, and an active energy ray-curable resin binder, and any of these binders can be preferably used.

The thickness of the layer containing the urea compound 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 may include a water content adjusting step and a laminating step. In the moisture content adjustment step, in the case of manufacturing the polarizing plate having the characteristic (a), the moisture content of the polarizing element is adjusted so that the moisture content of the polarizing element is equal to or higher than the equilibrium moisture content at a temperature of 20 ℃ and a relative humidity of 30% and equal to or lower than the equilibrium moisture content at a temperature of 20 ℃ and a relative humidity of 50%. The water content of the polarizer can be adjusted in accordance with the description of the water content of the polarizer. In the water content adjusting step, in the case of manufacturing the polarizing plate having the characteristic (b), 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 at a temperature of 20 ℃ and a relative humidity of 30% and equal to or lower than the equilibrium water content at a temperature of 20 ℃ and a relative humidity of 50%. The water content of the polarizing plate can be adjusted in accordance with the above description of the water content of the polarizing plate. In the laminating step, the polarizing element and the transparent protective film are laminated via the adhesive layer. In the laminating step, for example, a polarizing element which has not been subjected to a treatment containing a urea compound and a cyclodextrin compound is bonded to the transparent protective film with an adhesive containing a urea compound and a cyclodextrin compound. The order of the water content adjusting step and the laminating step is not limited, and the water content adjusting step and the laminating step may be performed in parallel.

[ constitution of image display device ]

The polarizing plate of the present embodiment can be 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, the transmittance tends to be low in a high-temperature environment. In the image display device using the polarizing plate of the present embodiment, even in the interlayer filling configuration, the decrease in transmittance of the polarizing plate in a high-temperature environment can be suppressed. As an example of 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 is given. The image display device may further include a 2 nd adhesive layer laminated on the viewing-side surface of the polarizing plate, and a transparent member laminated on the viewing-side surface of the 2 nd adhesive layer. In particular, the polarizing plate of the present embodiment can be suitably used for an image display apparatus having an interlayer filling structure in which a transparent member is disposed on the viewing side of the image display apparatus, the polarizing plate and the image display unit are bonded by a 1 st adhesive layer, and the polarizing plate and the transparent member are bonded by a 2 nd adhesive layer. In the present specification, either one or both of the 1 st pressure-sensitive adhesive layer and the 2 nd pressure-sensitive adhesive layer may be simply referred to as "pressure-sensitive 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 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 transflective 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 using light from a light source, the image display device (liquid crystal display device) is provided with a polarizing plate on the side opposite to the visible side of the image display cell (liquid crystal cell) and is also provided with a light source. 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, bend alignment (pi-type) and the like can be used.

As the organic EL unit, an organic EL unit 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) or the like can be suitably used. The organic light-emitting layer is a laminate of various organic thin films, and can be formed of various layers such as a laminate of a hole-injecting layer containing 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 perylene derivative or the like, or a laminate of a hole-injecting layer, a light-emitting layer, and an electron-injecting layer.

< bonding of image display Unit and polarizing plate >

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

< adhesive layer >

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

As the (meth) acrylic resin (base polymer) used in the adhesive composition, a polymer or copolymer containing 1 or 2 or more kinds of (meth) acrylic acid esters such as butyl (meth) acrylate, ethyl (meth) acrylate, isooctyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate as monomers can be suitably used. It is preferred to copolymerize the polar monomer 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 comprise only the above-mentioned 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 salt with a carboxyl group; a polyamine compound forming an amide bond with a carboxyl group; polyepoxy compounds or polyols which form ester bonds between them and carboxyl groups; a polyisocyanate compound which forms an amide bond with a carboxyl group. Among them, polyisocyanate compounds are preferable.

The active energy ray-curable pressure-sensitive adhesive composition has a property of being cured by irradiation with an active energy ray such as an ultraviolet ray or an electron beam, and also has a property of having adhesiveness before irradiation with an active energy ray and being capable of being brought into close contact with an adherend such as a film, and of being cured by irradiation with an active energy ray and adjusting the close contact force. The active energy ray-curable adhesive composition is preferably an ultraviolet-curable adhesive composition. The active energy ray-curable adhesive composition contains a base polymer, a crosslinking agent, and an active energy ray-polymerizable compound. If necessary, a photopolymerization initiator, a photosensitizer, and the like may be contained.

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

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

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

When the 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 adhesive layer are preferably subjected to surface activation treatment such as plasma treatment or corona treatment, and more preferably subjected to corona treatment.

Alternatively, an adhesive sheet may be prepared in which an adhesive composition is applied to the 2 nd separator to form an adhesive layer, and a separator is laminated on the adhesive layer, and the separator-attached adhesive layer obtained by peeling the 2 nd separator from the adhesive sheet may be laminated on the polarizing plate. The release film 2 used was a film that had a lower adhesion force to the pressure-sensitive adhesive layer than the release film and was easily peeled off.

The thickness of the pressure-sensitive adhesive layer is not particularly limited, and is, for example, 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 >

Examples of the transparent member disposed on the visible side of the image display device include a transparent plate (window layer), a touch panel, and the like. As the transparent plate, a transparent plate having appropriate mechanical strength and thickness is used. Examples of such transparent plates include transparent resin plates such as polyimide-based resins, acrylic resins, and polycarbonate-based resins, and glass plates. A functional layer such as an antireflection layer may be laminated on the visible side of the transparent plate. In the case where the transparent plate is a transparent resin plate, a hard coat layer may be laminated to improve physical strength, and a low moisture-permeable 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. When a capacitive touch panel is used as the transparent member, a transparent plate formed of glass or a transparent resin plate is preferably provided on the visible side of the touch panel.

< bonding of polarizing plate and transparent Member >

In the lamination of the polarizing plate and the transparent member, an adhesive or an active energy ray-curable adhesive can be suitably used. When an adhesive is used, the adhesive can be attached in an appropriate manner. As a specific attaching method, for example, the method of attaching the pressure-sensitive adhesive layer used for bonding the image display unit and the polarizing plate described above can be given.

In the case of using the active energy ray-curable adhesive, for the purpose of preventing the adhesive solution before curing from spreading, a method of providing a bank material so as to surround the peripheral edge portion on the image display panel, placing a transparent member on the bank material, and injecting the adhesive solution can be suitably used. After the adhesive solution is injected, alignment and defoaming are performed as necessary, and then curing is performed by irradiation with active energy rays.

Examples

The present invention will be specifically described below based on examples. The materials, reagents, amounts of substances, ratios thereof, operations and the like shown in the following examples can be appropriately modified without departing from the gist of the present invention. Therefore, the present invention is not limited to the following examples.

< preparation of polarizing element A >

A PVA film having a thickness of 40 μm and formed from PVA having an average polymerization degree of about 2400 and a saponification degree of 99.9 mol% or more was prepared. The PVA film was uniaxially stretched in a dry manner by about 5 times, and then immersed in pure water at 60 ℃ for 1 minute while maintaining the stretched state. Thereafter, the PVA film was immersed in an aqueous solution having an iodine/potassium iodide/water weight ratio of 0.05/5/100 at 28 ℃ for 60 seconds. Thereafter, the PVA film 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. Subsequently, the PVA film was washed with pure water at 26 ℃ for 20 seconds and then dried at 65 ℃ to obtain a polarizing element A having a thickness of 15 μm in which iodine was adsorbed to the PVA and oriented. For the measurement of the thickness of the polarizer, a digital micrometer "MH-15M" manufactured by Nikon was used.

< production of Adhesives 1 to 7 >

(preparation of PVA solution A for adhesive)

50g of a modified PVA-based resin containing an acetoacetyl group (GOHSENX Z-410, manufactured by Mitsubishi chemical corporation) was dissolved in 950g of pure water. This solution was heated at 90 ℃ for 2 hours and then cooled to normal temperature to obtain PVA solution A for adhesives.

(preparation of Adhesives 1 to 7)

Adhesives 1 to 7 were prepared by mixing PVA solution a, urea compound, cyclodextrins, and pure water so as to contain 3.0 mass% of PVA, urea compound and cyclodextrins in the amounts shown in table 1.

[ TABLE 1]

< preparation of transparent protective film A >

A commercially available cellulose acylate film TD40 (manufactured by Fuji photo film Co., Ltd., film thickness 40 μm) was immersed in a 1.5mol/L NaOH aqueous solution (saponification solution) maintained at 55 ℃ for 2 minutes, and then the film was washed with water. Thereafter, the membrane was immersed in a 0.05mol/L sulfuric acid aqueous solution at 25 ℃ for 30 seconds, and then passed under running water for 30 seconds to be water-washed, thereby making the membrane neutral. The water removal by the air knife was repeated 3 times to remove water, and the film was left in a drying zone at 70 ℃ for 15 seconds to be dried, thereby obtaining a transparent protective film a subjected to saponification treatment.

< production of polarizing plates 1 to 7 >

A transparent protective film a is bonded to both surfaces of the polarizing element a via an adhesive 1. A roll laminator was used for lamination. The laminate was dried at 80 ℃ for 5 minutes to obtain polarizing plate 1. The coating thickness of the adhesive layer was adjusted so that the thickness after drying was 50nm on both sides.

In the production of the polarizing plate 1, the adhesive 1 is changed to adhesives 2 to 7, and polarizing plates 2 to 7 are obtained.

< production of optical layered bodies 1 to 7 >

An optical laminate 1 having adhesive layers with a thickness of 25 μm on both sides was produced by applying an acrylic adhesive (model #7 available from LINTECH corporation) to both sides of the polarizing plate 1 produced above.

In the production of the optical laminate 1, the polarizing plate 1 was changed to polarizing plates 2 to 7, and optical laminates 2 to 7 were obtained.

< evaluation of high temperature durability >

(preparation of sample for evaluation)

The optical layered bodies 1 to 7 were cut to a size of 50mm × 100mm so that the absorption axis was parallel to the long side. Alkali-free glass ("EAGLE XG" manufactured by Corning corporation) was bonded to the surface of each adhesive to prepare a sample for evaluation. In order to adjust the water content of the optical laminate, the optical laminate was stored at a temperature of 20 ℃ and a relative humidity of 35% for 72 hours before bonding of the glass plates. In all the samples, the weights of the polarizing element, the polarizing plate, and the optical laminate after storage for 66 hours, 69 hours, and 72 hours were measured, and since there was no change, it was considered that the water contents of the polarizing element, the polarizing plate, and the optical laminate reached an equilibrium water content of 20 ℃ and 35% relative humidity.

(evaluation of monomer transmittance after high temperature durability test (105 ℃ C.))

The samples for evaluation respectively provided with the optical laminates 1-7 are subjected to temperature of 50 ℃ and pressure of 5kgf/cm ² (490.3kPa) was subjected to autoclave treatment for 1 hour, and then the autoclave was left at a temperature of 23 ℃ and a relative humidity of 55% for 24 hours. The transmittance of the optical laminate at this time was measured as an initial value. Thereafter, the film was stored in a heated environment at a temperature of 105 ℃ and the transmittance was measured every 24 hours until 72 to 240 hours. The monomer transmittance was evaluated based on the time for which the decrease in transmittance was 5% or more with respect to the initial value according to the following criteria. The results are shown in table 2.

The decrease in transmittance at the time of 240 hours was a sample of 5% or less: a. the

The transmittance is reduced by more than 5% in 120-240 hours: b is

The transmittance is reduced by more than 5% in 72-120 hours: c

Sample in which the decrease in transmittance was 5% or more at the time of 72 hours: d

[ TABLE 2]

It is found that polarizing plates (optical laminates 1 to 4) in which a polarizing element and a transparent protective film are bonded to each other with an adhesive containing a urea compound and a cyclodextrin interposed therebetween are less likely to have a decreased transmittance even when exposed to a high-temperature environment of 105 ℃ and have excellent high-temperature durability, as compared with polarizing plates (optical laminates 5 to 7) in which a polarizing element and a transparent protective film are bonded to each other with an adhesive containing only one of a urea compound and a cyclodextrin interposed therebetween.

Claims

1. A polarizing plate comprising a polarizing element obtained by adsorbing a dichroic dye onto a polyvinyl alcohol resin layer and orienting the dichroic dye, and a transparent protective film laminated on at least one surface of the polarizing element,

the polarizer and the transparent protective film are bonded to each other via an adhesive layer formed of an adhesive containing a urea compound and a cyclodextrin compound,

2. The polarizing plate of claim 1,

the adhesive contains at least 1 urea compound selected from urea derivatives and thiourea derivatives.

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

the adhesive contains a polyvinyl alcohol resin.

4. The polarizing plate of claim 3,

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

5. The polarizing plate of claim 3 or 4,

in the adhesive, the content of the cyclodextrin compound 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 resin.

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

the adhesive layer has a thickness of 0.01 to 7 [ mu ] m.

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

the cyclodextrin is at least 1 selected from alpha-cyclodextrin, beta-cyclodextrin and gamma-cyclodextrin.

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

the water content of the polarizing element is more than or equal to equilibrium water content of 30% at a temperature of 20 ℃ and less than or equal to equilibrium water content of 50% at a temperature of 20 ℃.

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

the water content of the polarizing plate is not less than the equilibrium water content at a temperature of 20 ℃ and a relative humidity of 30%, and not more than the equilibrium water content at a temperature of 20 ℃ and a relative humidity of 50%.

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

the polarizing plate is used for an image display device,

11. 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 according to any one of claims 1 to 10 laminated on a visible-side surface of the 1 st adhesive layer.

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

13. The image display apparatus according to claim 12,

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

14. The image display apparatus according to claim 12,

the transparent member is a touch panel.