CN117751309A

CN117751309A - Polarizing plate and image display device

Info

Publication number: CN117751309A
Application number: CN202280050005.8A
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: 2021-07-19
Filing date: 2022-06-30
Publication date: 2024-03-22
Also published as: TW202309623A; KR20240037952A; WO2023002830A1; JP2023014531A

Abstract

The invention provides a polarizing plate capable of inhibiting the reduction of transmittance in a high-temperature environment. The polarizing plate includes a polarizing element in which a dichroic dye is adsorbed and oriented on 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 of an adhesive containing the 1 st compound and the 2 nd compound. The 1 st compound is a compound having nitroxyl radical or nitroxyl radical. The 2 nd compound is cyclodextrin.

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, in order to suppress the reflection of external light by a metal electrode (cathode) and observation of the external light into a mirror surface, a circularly polarizing plate (a laminate including a polarizing element and a λ/4 plate) may be disposed on the observation side surface of an image display panel.

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

On the other hand, for the purpose of preventing breakage of an image display panel or the like due to impact from an outer surface, a front transparent plate (sometimes referred to as a "window layer") such as a transparent resin plate or a glass plate is provided on an observation 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 an observation side with respect to the image display panel, and a front transparent plate is provided on the observation side with respect to the touch panel.

In such a configuration, if an air layer is present between the image display panel and the transparent member such as the front transparent plate or the touch panel, reflection glare of external light due to reflection of light at an air layer interface is generated, and visibility of the screen tends to be lowered. Accordingly, there is an increasing trend to adopt a structure in which a space between a polarizing plate disposed on the viewing side surface of an image display panel and a transparent member is filled with a layer other than an air layer, usually with 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 respective members to each other (for example, refer to patent document 1).

The above-described constitution filled with the interlayer filler is expanding in use for mobile devices such as mobile phones which are often used outdoors. In addition, in recent years, due to an increase in visibility, in vehicle-mounted applications such as navigation devices, a structure in which a front transparent plate is disposed on a surface of an image display panel and a space between the panel and the front transparent plate is filled with a solid layer such as an adhesive layer has been studied.

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. As a solution to this problem, patent document 2 proposes a method of suppressing a decrease in transmittance by setting the amount of water 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 polarizing element to a predetermined amount or less.

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

However, even such a polarizing plate cannot sufficiently suppress the decrease in transmittance in a high-temperature environment.

The purpose of the present invention is to provide a polarizing plate capable of suppressing a decrease in transmittance even when exposed to a high-temperature environment, 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 follows.

[1] A polarizing plate comprising a polarizing element in which a dichroic dye is adsorbed and oriented on 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 of an adhesive containing a 1 st compound and a 2 nd compound,

the above-mentioned compound 1 is a compound having a nitroxyl radical or a nitroxyl radical,

the compound 2 is cyclodextrin.

[2] The polarizing plate according to [1], wherein the 1 st compound is an N-oxygen radical compound.

[3] The polarizing plate according to [1] or [2], wherein the compound 2 is at least 1 selected from the group consisting of α -cyclodextrin, β -cyclodextrin and γ -cyclodextrin.

[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 1 st 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 [4] or [5], wherein the content of the 2 nd compound in the adhesive is 1 part by mass or more and 50 parts by mass or less relative to 100 parts by mass of the polyvinyl alcohol resin.

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

[8] The polarizing plate according to any one of [1] to [7], wherein the 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.

[9] An image display device comprising an image display unit, a 1 st adhesive layer laminated on a viewing side surface of the image display unit, and the polarizing plate of any one of [1] to [8] laminated on a viewing side surface of the 1 st adhesive layer.

[10] The image display device according to [9], further comprising 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.

[11] The image display device according to [10], wherein the transparent member is a glass plate or a transparent resin plate.

[12] The image display device according to [10], 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 capable of suppressing a decrease in transmittance even when exposed to a high-temperature environment in an image display device configured by interlayer filling such that a solid layer contacts both surfaces of the polarizing plate. Further, by using the polarizing plate of the present invention, an image display device can be provided in which a decrease in transmittance can be suppressed even when exposed to a high-temperature environment.

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 and oriented on 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 of an adhesive containing the 1 st compound and the 2 nd compound. The 1 st compound is a compound having nitroxyl radical or nitroxyl radical. The 2 nd compound is cyclodextrin.

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 such a polarizing plate, when applied to an image display device having a 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, and a solid layer is in contact with both surfaces of the polarizing plate (hereinafter, sometimes referred to as an "interlayer filling structure"), a significant decrease in transmittance may be observed in the central portion in the polarizing plate surface when the polarizing plate is left in an environment at a temperature of 95 ℃ for 200 hours. A significant decrease in transmittance of the polarizing plate under a high temperature environment is considered to be a problem that particularly easily occurs when an image display device constituted by using interlayer filling is exposed to a high temperature environment.

For the polarizing plate having significantly reduced transmittance in the image display device of interlayer filling constitution, since the transmittance was measured at 1100cm in the raman spectroscopy ^-1 Vicinity (from=c-c=bond) and 1500cm ^-1 The vicinity (from-C=C-bonds) has a peak, and thus it can be considered that a polyene structure (-C=C) is formed _n -. The polyene structure is presumed to be a structure produced by the polyvinyl alcohol resin constituting the polarizing element being polyened by dehydration (patent documents 2 and [0012 ]]Segments).

The polarizing plate of the present embodiment is incorporated into an image display device constituted by interlayer filling, and has excellent high-temperature durability in which a decrease in transmittance can be suppressed even when exposed to a high-temperature environment such as 105 ℃. This effect is exerted because the polarizing plate has an adhesive layer containing the 1 st compound and the 2 nd compound, and it is presumed that the synergistic effect of the 1 st compound and the 2 nd compound suppresses the polyeneization of the polyvinyl alcohol resin constituting the polarizing element. This effect is not limited to the case where the water content of the polarizing plate is low, and it is confirmed that the effect can be exhibited even when the water content of the polarizing plate is high.

The polarizing plate of the present embodiment may have at least one of the following features (a) and (b), for example.

(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 80% 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 80% relative humidity at 20 ℃.

The polarizing plate according to the present embodiment can exhibit an effect of improving high-temperature durability even when the characteristics of (a) or (b) are further defined as (a 1) or (b 1) described below.

(a1) The water content of the polarizing element is greater than the equilibrium water content of 45% or 50% of the relative humidity at 20 ℃ and is less than the equilibrium water content of 80% or 70% of the relative humidity at 20 ℃.

(b1) The water content of the polarizing plate is greater than the equilibrium water content of 45% or 50% of the relative humidity at 20 ℃ and is less than the equilibrium water content of 80% or 70% of the relative humidity at 20 ℃.

The method for producing a polarizing plate according to the present embodiment may or may not include a step of adjusting the water content so as to have at least one of the features (a) and (b) described above.

< polarizing element >)

As a polarizing element obtained by adsorbing and aligning a dichroic dye to a polyvinyl alcohol (hereinafter, sometimes referred to as "PVA") resin layer, a known polarizing element can be used. The polarizing element may be a stretched film obtained by dyeing a PVA-based resin film serving as a PVA-based resin layer with a dichroic dye and uniaxially stretching the film; a laminated film in which a coating layer to be a PVA-based resin layer is formed on a base film is obtained by coating a coating liquid containing a PVA-based resin on the 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 contained in the PVA-based resin layer 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 85 mol% or more, more preferably 90 mol% or more, and still more preferably 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.

Examples of the dichroic dye that is adsorbed and aligned to the PVA-based resin layer include iodine and a dichroic dye. The dichroic dye is preferably iodine. Examples of the dichroic dye include Red BR (Red BR), red LR (Red LR), red R (Red R), pink LB (Pink LB), ruby Red BL (rubene BL), purplish Red GS (Bordeaux GS), sky Blue LG (Sky Blue LG), lemon Yellow, blue BR (Blue BR), blue 2R (Blue 2R), navy RY (Navy RY), green LG (Green LG), purple LB (Violet LB), purple B (Violet B), black H (Black H), black B (Black B), black GSP (Black GSP), yellow3G (Yellow 3G), yellow R (Yellow R), orange LR (Orange LR), orange 3R (Orange 3R), scarlet GL (Scarlet GL), scarlet KGL (Scarlet KGL), congo Red (con Red), brilliant Violet BK (Brilliant Violet BK), supra Blue G, supra Blue GL, supra Orange, direct Sky Blue (Direct Blue) Blue S (Direct Fast Orange S), direct Black Blue (Blue) and Direct Orange light (Blue S (Direct Fast Orange S)).

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 can be easily suppressed in a high-temperature environment. By making the thickness of the polarizing element 3 μm or more, a polarizing plate realizing desired optical characteristics is easily obtained.

The polarizing element of the polarizing plate of the present embodiment preferably includes a 1 st compound and a 2 nd compound. In the polarizing plate, since the polarizing element and the transparent protective film are bonded by an adhesive layer formed of an adhesive containing the 1 st compound and the 2 nd compound, it is presumed that a part of the 1 st compound and a part of the 2 nd compound transferred from the adhesive layer are contained in the polarizing element. By providing the polarizing plate having such a polarizing element with an adhesive layer containing the 1 st compound and the 2 nd compound, transmittance is not easily reduced even when exposed to a high-temperature environment. Further, by providing the adhesive layer containing the 1 st compound and the 2 nd compound, the decrease in the degree of polarization can be suppressed even when the polarizing plate is exposed to a high-temperature environment. If the polarization degree of the polarizing plates is reduced, light leakage (hereinafter sometimes referred to as "cross light leakage") is likely to occur when the two polarizing plates are disposed in a relationship of forming cross nicols, but the polarization degree of the polarizing plates of the present embodiment is not likely to be reduced even when the polarizing plates are exposed to a high-temperature environment, and thus cross light leakage is also likely to be suppressed. It is presumed that the use of the synergistic effect of the 1 st compound and the 2 nd compound contained in the polarizing element suppresses the polyene of the PVA-based resin, and thus the decrease in transmittance of the polarizing plate exposed to a high-temperature environment and the decrease in polarization degree can be suppressed.

As a method for incorporating the 1 st compound and the 2 nd compound into the polarizing element, there is a method for transferring the 1 st compound and the 2 nd compound from the adhesive layer to the polarizing element as described above; a method for producing a polarizing element containing a 1 st compound and a 2 nd compound; a combination of these two methods. For example, in the production of the polarizing element, one of the 1 st compound and the 2 nd compound may be contained in the polarizing element, and both the 1 st compound and the 2 nd compound may be contained in the adhesive layer constituting the polarizing plate.

Examples of the method for producing a polarizing element containing the 1 st compound and the 2 nd compound in the production of the polarizing element include a method of immersing a PVA-based resin layer in a treatment solvent containing the 1 st compound and/or the 2 nd compound, and a method of spraying, flowing down, or dripping the treatment solvent onto the PVA-based resin layer. Among them, a method of impregnating the PVA-based resin layer in a treatment solvent containing both the 1 st compound and the 2 nd compound is preferably used. Specific examples of the 1 st and 2 nd compounds include compounds exemplified as compounds to be contained in an adhesive to be described later.

The step of immersing the PVA-based resin layer in the treatment solvent containing the 1 st compound and the 2 nd compound may be performed simultaneously with or separately from the swelling, stretching, dyeing, crosslinking, washing, and the like in the method for producing a polarizing element described later. The step of containing the 1 st compound and the 2 nd 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.

(Compound 1)

The 1 st compound is a compound having nitroxyl radical or nitroxyl radical. The 1 st compound is an N-oxygen radical compound (a compound having a c—n (-C) -o·as a functional group (o·represents an oxygen radical, and is bonded to N.)) from the viewpoint of having a radical relatively stable in air at room temperature, and a known compound can be used. Examples of the N-oxygen radical compound include compounds having an organic group having the following structure. The compound having nitroxyl radical or nitroxyl radical may be used alone or in combination of 2 or more.

[ chemical 1]

[ in the above formula (1), R ¹ Represents oxygen radicals, R ² ～R ⁵ Independently represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and n represents 0 or 1.]

The left side of the dotted line in the above formula (1) represents an arbitrary organic group or a hydrogen atom.

Examples of the compound having an organic group include compounds represented by the following formulas (2) to (5).

[ chemical 2]

[ in the above formula (2), R ¹ ～R ⁵ And n represents the same meaning as above, R ⁶ Represents a hydrogen atom, or an alkyl group, an acyl group, or an aryl group having 1 to 10 carbon atoms, and n represents 0 or 1.]

[ chemical 3]

[ in the above formula (3), R ¹ ～R ⁵ And n represents the same meaning as above, R ⁷ R is R ⁸ Independently represents a hydrogen atom, or an alkyl group having 1 to 10 carbon atoms, an acyl group, or an aryl group.]

[ chemical 4]

[ in the above formula (4), R ¹ ～R ⁵ And n represents the same meaning as above, R ⁹ ～R ¹¹ Independently represents a hydrogen atom, or an alkyl group having 1 to 10 carbon atoms, an acyl group, an amino group, an alkoxy group, a hydroxyl group, or an aryl group.]

[ chemical 5]

[ in the above formula (5), R ¹ ～R ⁵ And n represents the same meaning as above, R ¹² Represents a hydrogen atom, or an alkyl group, an acyl group, an amino group, an alkoxy group, a hydroxyl group, or an aryl group having 1 to 10 carbon atoms.]

In the above formulae (1) to (5), R is from the viewpoint of easy availability ² ～R ⁵ The alkyl group is preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms. In the above formula (2), R is from the viewpoint of easy availability ⁶ Preferably a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, more preferably a hydrogen atom. In the above formula (3), R is from the viewpoint of availability ⁷ R is R ⁸ Preferably independently a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, more preferably a hydrogen atom. In the above formula (4), R is from the viewpoint of availability ⁹ ～R ¹¹ Preferably independently a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. In the above formula (5), R is from the viewpoint of availability ¹² Preferably hydroxy, amino, or alkoxy. In the above formulae (1) to (5), n is preferably 1 from the viewpoint of easy availability.

Examples of the N-oxyl compound include N-oxyl compounds described in JP 2003-64022, JP 11-222462, JP 2002-284737, and International publication 2016/047655. As the N-oxyl compound, 4-hydroxy-2, 6-tetramethylpiperidine 1-oxyl is preferably used.

Examples of the 1 st compound include the following compounds.

[ chemical 6]

In the formula (6), R represents a hydrogen atom, or an alkyl group having 1 to 10 carbon atoms, an acyl group, or an aryl group. ]

[ chemical 7]

[ chemical 8]

The molecular weight of the 1 st compound is preferably 1000 or less, more preferably 500 or less, and still more preferably 300 or less, from the viewpoint of being able to efficiently capture radicals generated in the polyethylenic reaction. The lower limit of the molecular weight is not particularly limited, and may be, for example, 80.

(Compound 2)

The 2 nd compound is cyclodextrin. Cyclodextrins are non-reducing cyclic oligosaccharides in which glucose is bound as a cyclic form by alpha-1, 4 linkages. The larger the number of glucose constituting cyclodextrin, the larger the inner diameter of the cavity in the molecule. The cyclodextrin used as the compound 2 is preferably 6 or more in number of glucose involved in the constitution, and examples thereof include α, β, γ, and δ -cyclodextrins in which 6, 7, 8, and 9 of glucose involved in the constitution are contained. Among the cyclodextrin compounds, α, β, γ, and δ -cyclodextrin compounds include branched cyclodextrins having oligosaccharides such as glucose and maltose in the branched sugar chain. The cyclodextrin includes a cyclodextrin wherein an alkyl group such as a methyl group is further bonded to the cyclodextrin or branched cyclodextrin; cyclodextrin derivatives such as hydroxyalkyl groups such as 2-hydroxyethyl, 2-hydroxypropyl, 2, 3-dihydroxypropyl and 2-hydroxybutyl. The cyclodextrin may be used alone or in combination of 1 or more than 2.

(feature (a))

In the case where the polarizing plate has the above-described feature (a), the water content of the polarizing element is at least the equilibrium water content of 30% relative humidity at 20 ℃ and at most the equilibrium water content of 80% relative humidity at 20 ℃. The water content of the polarizing element may be greater than the equilibrium water content of 45% or 50% of the relative humidity at 20 ℃ and less than the equilibrium water content of 80% or 70% 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 water content of the polarizing element is so high that it exceeds the equilibrium water content of 45% or 50% relative humidity at 20 ℃, it is presumed that the polyeneization of the PVA-based resin is easy to advance, but the polarizing plate of the present embodiment is provided with an adhesive layer containing the 1 st compound and the 2 nd compound, and thus the polyeneization of the PVA-based resin can be suppressed.

As a method for confirming that 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 80% 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 30% or more in terms of equilibrium water content at a temperature of 20 ℃ and 80% or less in terms of equilibrium water content at a temperature of 20 ℃ is not particularly limited, and 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 10 minutes to 3 hours; or a method of performing a heat treatment at a temperature of 30 ℃ or more and 90 ℃ or less.

Another preferable method for producing a polarizing element having a water content in the above range includes a method in which a laminate in which a transparent 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 above temperature and the above 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. Alternatively, in the case of manufacturing an image display device using an interlayer filling structure, a transparent member such as a front panel may be attached after the image display panel in which a polarizing plate is laminated in an image display unit is 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 a temperature of 30 ℃ to 90 ℃.

(feature (b))

In the case where the polarizing plate has the above-described feature (b), the water content of the polarizing plate is at least the equilibrium water content of 30% relative humidity at 20 ℃ and at most the equilibrium water content of 80% relative humidity at 20 ℃. The water content of the polarizing plate may be greater than the equilibrium water content of 45% or 50% of the relative humidity at 20 ℃ and less than the equilibrium water content of 80% or 70% 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 so high that it exceeds the equilibrium water content of 45% or 50% relative humidity at 20 ℃, it is presumed that the polyeneization of the PVA-based resin is easy to advance, but the polarizing plate of the present embodiment can suppress the polyeneization of the PVA-based resin because it has an adhesive layer containing the 1 st compound and the 2 nd compound.

As a method for confirming that 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 80% relative humidity at 20 ℃, there is a method of keeping the polarizing plate in an environment adjusted to the above temperature and the above relative humidity range and considering that the polarizing plate is balanced 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 30% or more in terms of equilibrium water content at a temperature of 20 ℃ and 80% or less in terms of equilibrium water content at a temperature of 20 ℃ is not particularly limited, but examples thereof include a method of storing a polarizing plate in an environment adjusted to the above temperature and the above relative humidity range for 10 minutes to 3 hours; or a method of performing a heat treatment at a temperature of 30 ℃ or more and 90 ℃ or less. Alternatively, in the case of manufacturing an image display device using an interlayer filling structure, a transparent member such as a front panel may be attached after the image display panel in which a polarizing plate is laminated in an image display unit is 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 a temperature of 30 ℃ to 90 ℃.

(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 coating layer and stretching the obtained laminate (hereinafter referred to as "production method 2").

The production method 1 may include a step of uniaxially stretching the PVA-based resin film, a step of dyeing the PVA-based resin film with a dichroic dye such as iodine 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 defined as a whole 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, and the dichroic dye can be adsorbed and aligned on the PVA-based resin film. In the case where the dichroic dye is iodine, the dyeing bath is preferably an iodine solution. 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 (iodine solution) 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 PVA-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 in any way 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 least in one direction at a predetermined magnification. 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.

As the treatment bath (stretching bath) in the wet stretching method, water, a mixed solution of an organic solvent having miscibility with water and water, or the like is generally used. 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 washing step.

Examples of the dry stretching method include an inter-roll stretching method, a heated roll stretching method, and a compression stretching method. In the case of the dry stretching method, the stretching step may be performed in the drying step.

The total stretching ratio (cumulative stretching ratio) applied to the PVA-based resin film may 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 washing step is a treatment step of immersing the PVA-based resin film in a washing bath, and can remove foreign matters remaining on the surface of the PVA-based resin film. The washing bath generally uses a medium containing water as a main component, such as water, distilled water, and pure water. From the viewpoint of controlling the content of potassium in the polarizing element, it is preferable to use potassium iodide in the washing bath, and in this case, the concentration of potassium iodide in the washing bath is preferably 1% by mass or more and 10% by mass or less, 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 washing bath is preferably 5 ℃ to 50 ℃, more preferably 10 ℃ to 40 ℃, still more preferably 15 ℃ to 30 ℃. The immersion time in the washing bath cannot be defined as a whole because the extent of washing of the PVA-based resin film is affected by the temperature of the washing 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 washing 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 may include a step of applying a coating liquid containing a PVA-based resin onto a base film, a step of uniaxially stretching the obtained laminated film, a step of adsorbing a dichroic dye by dyeing a coating layer of the uniaxially stretched laminated film with the dichroic dye, a step of treating the laminated 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 base film used for forming the polarizing element may be used as a transparent protective film for a polarizing plate. The base film may be peeled off from the polarizing element as needed.

Transparent protective film

The transparent protective film is bonded 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 transparent protective film may have other optical functions at the same time, or may have a laminated structure in which a plurality of layers are laminated. From the viewpoint of optical characteristics, the thickness of the transparent protective film is preferably small, but if too small, 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 transparent 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 bonding the transparent 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 transparent 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 transparent protective films provided in the polarizing plate may have a phase difference function for the purpose of viewing angle compensation or the like. In this case, the film itself constituting the transparent protective film may have a retardation function, or the transparent protective film may have a layer having no retardation function and a retardation layer (layer having a retardation function). When the transparent protective film has a retardation layer, the transparent protective film may be a laminate of a layer having no retardation function and the retardation layer, and these layers may be bonded using an adhesive or an adhesive.

< adhesive layer >)

An adhesive containing the 1 st compound and the 2 nd compound is used as an adhesive constituting an adhesive layer for bonding a transparent 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 the 1 st compound and the 2 nd compound for forming the adhesive layer, 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 can be set to any value. For example, the adhesive layer having a desired thickness is obtained after curing or after heating (drying). The thickness of the adhesive layer 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.

In the case of manufacturing a polarizing plate using a polarizing element containing no 1 st compound and no 2 nd compound, the content of the 1 st compound and the 2 nd compound contained in the adhesive is preferably in the range described below. In the case of manufacturing a polarizing plate using a polarizing element containing the 1 st compound and the 2 nd compound, the contents of the 1 st compound and the 2 nd compound contained in the adhesive may be appropriately changed from the ranges described below in correspondence with the 1 st compound and the 2 nd compound contained in the polarizing element, and the like. Specific examples of the 1 st compound and the 2 nd compound are as described above.

When the adhesive contains a PVA-based resin (for example, when the adhesive is an aqueous adhesive containing a PVA-based resin), the content of the 1 st 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 part by mass, the effect of inhibiting the polyalkylation of the PVA-based resin in a high-temperature environment may be insufficient. On the other hand, if the amount is more than 400 parts by mass, the 1 st compound may precipitate after the production of the polarizing plate.

When the adhesive contains a PVA-based resin (for example, when the adhesive is an aqueous adhesive containing a PVA-based resin), the content of the 2 nd compound 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, still more 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 inhibiting the polyalkylation of the PVA-based resin in a high-temperature environment may be insufficient. On the other hand, if the amount is more than 50 parts by mass, the compound 2 may precipitate after the production of the polarizing plate.

In the configuration in which the transparent protective film is bonded to both sides of the polarizing element via the adhesive layer, the adhesive layer on only one side of the adhesive layer on both sides of the polarizing element may be a layer containing the 1 st compound and the 2 nd compound, but it is preferable that the adhesive layers on both sides are layers containing the 1 st compound and the 2 nd compound.

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. In this structure, the transparent protective film is also laminated via an adhesive layer containing the 1 st compound and the 2 nd compound. 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 bonded to both surfaces thereof via an adhesive layer is first produced, and then one transparent protective film is peeled off. In the case of using such a manufacturing method, only any one of the adhesive layers may contain the 1 st compound and the 2 nd compound, but it is preferable that both the adhesive layers are layers containing the 1 st compound and the 2 nd compound. When only one adhesive layer contains the 1 st compound and the 2 nd compound, the adhesive layer on the film side that is not peeled preferably contains the 1 st compound and the 2 nd compound.

(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, in view of the 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.

As the PVA-based resin contained in the aqueous adhesive, an acetoacetyl-containing PVA-based resin (hereinafter, sometimes referred to as "acetoacetyl-containing PVA-based resin") is preferable. This is because the PVA-based resin layer has excellent adhesion to the transparent protective film and has excellent durability. 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-containing PVA resin is typically 0.1 mol% or more, 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.

In the case where 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 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. For example, as a component to be blended into the aqueous adhesive, a component having low solubility in water but sufficient solubility in alcohol may be used. In this case, it is also one of preferable modes to prepare an adhesive by dissolving the component in alcohol to prepare an alcohol solution of the component and then adding the alcohol solution to an aqueous solution of the PVA-based resin.

(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.

[ method for producing polarizing plate ]

The method for manufacturing a polarizing plate according to the present embodiment includes a lamination step of laminating a polarizing element and a transparent protective film. The method for producing the polarizing plate may include a water content adjustment step. The order of performing 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.

In the lamination step, the polarizing element and the transparent protective film are laminated via the adhesive layer. In the lamination step, the polarizing element and the transparent protective film are bonded using an adhesive containing the 1 st compound and the 2 nd compound. The adhesive interposed between the polarizing element and the transparent protective film is formed into an adhesive layer by, for example, a step of drying. The lamination step may be a step of bonding the polarizing element containing no 1 st compound and no 2 nd compound to the transparent protective film using an adhesive containing 1 st compound and no 2 nd compound. In this case, in the process of forming the adhesive layer from the adhesive, a part of the 1 st compound and a part of the 2 nd compound contained in the adhesive may move to the polarizing element or the like.

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 80% relative humidity at 20 ℃. The moisture content of the polarizing element can be adjusted by the method described above. 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 80% relative humidity at 20 ℃. The moisture content of the polarizing plate can be adjusted by the method described above.

[ constitution of image display device ]

The polarizing plate of the present embodiment is used in 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 a layer other than an air layer, specifically, a solid layer such as an adhesive layer is in contact with both surfaces of a polarizing plate, 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.

The solid layer may be an adhesive layer, or the like. When the solid layer is an adhesive layer, an adhesive layer formed using a UV curable adhesive is preferable.

As the image display device, a configuration having an image display unit, a 1 st adhesive layer laminated on the viewing side surface of the image display unit, and a polarizing plate laminated on the viewing 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 viewing 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 observation side of the image display device, the polarizing plate and the image display unit are bonded by using the 1 st adhesive layer, and the polarizing plate and the transparent member are bonded by using the 2 nd adhesive layer.

The polarizing plate and the image display unit are not limited to being bonded by the 1 st adhesive layer, and may be bonded by an adhesive layer formed by using an adhesive. The polarizing plate and the transparent member are not limited to being bonded by the 2 nd adhesive layer, and may be bonded by an adhesive layer formed by using an adhesive. The adhesive may be the adhesive described above, or may be an adhesive that does not contain the 1 st compound and the 2 nd compound.

< 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 unit (liquid crystal cell) opposite to the observation 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, any 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 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 and polarizing plate >)

In the lamination of the image display unit and the polarizing plate, the 1 st adhesive layer may be suitably used. Among them, a method of bonding the adhesive layer-equipped polarizing plate having the 1 st adhesive layer attached to one surface of the polarizing plate to the image display unit is preferable from the viewpoint of operability and the like. The adhesive layer 1 may be attached to the polarizing plate in an appropriate manner. Examples thereof include a method of preparing a binder solution in which about 10 mass% or more and about 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 suitable solvents such as toluene and ethyl acetate, and directly attaching the binder solution to a polarizing plate by a suitable development method such as a casting method and a coating method; and a mode in which the 1 st adhesive layer is formed on the release film and then transferred to the polarizing plate.

< 1 st adhesive layer, 2 nd adhesive layer >

The 1 st adhesive layer and the 2 nd adhesive layer (hereinafter, either or both may be referred to as "adhesive layer") may be independently formed of 1 layer or 2 layers or more, but are 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 comprising a (meth) acrylic resin excellent in transparency, weather resistance, heat resistance and the like as a base polymer 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 with 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 base polymer, but usually also contains a crosslinking agent. Examples of the crosslinking agent include metal ions that form a metal carboxylate between the metal ions and the carboxyl group, wherein the metal ions are metal ions having a valence of 2 or more; a polyamine compound forming an amide bond with a carboxyl group; a polyepoxide or polyol that forms an ester linkage between it and the carboxyl group; 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 after being irradiated 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 being irradiated with active energy rays and being cured by irradiation with active energy rays to 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 treatment 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 polarizing plate. 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, and is preferably 1 μm or more and 100 μm or less, more preferably 3 μm or more and 50 μm or less, and may be 20 μm or more.

Transparent member

Examples of the transparent member disposed on the observation side of the image display device include a transparent plate (front panel, 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 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 viewing 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 formed of a glass plate or a transparent resin plate is preferably provided on the observation 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 may be attached in an appropriate manner. Specific examples of the method of attaching include the 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, alignment and defoaming are performed as needed, and then active energy rays are irradiated to cure the adhesive solution.

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-based resin film having a thickness of 40 μm, which contains a PVA-based resin 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, and then kept in a stretched state, immersed in pure water at 60℃for 1 minute, and then immersed in an aqueous solution having a weight ratio of iodine/potassium iodide/water of 0.05/5/100 and a temperature of 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 and a temperature of 72℃for 300 seconds. Then, the 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. Mu.m, in which iodine was adsorbed and oriented on the PVA resin layer. For the measurement of the thickness of the polarizing element A, a digital micrometer "MH-15M" manufactured by Nikon corporation was used.

Preparation of adhesive 1-5

(preparation of PVA solution A for adhesive)

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

(preparation of adhesives 1 to 5)

The PVA solution a, the 1 st compound, the 2 nd compound, and pure water were mixed so that the concentration of the PVA-based resin was 3.0 mass% and the 1 st compound and the 2 nd compound were each in the amounts shown in table 1, to prepare adhesives 1 to 5. As the 1 st compound, 4-hydroxy-2, 6-tetramethylpiperidine 1-oxyl (hereinafter also referred to as "TEMPOL") was used.

TABLE 1

Content of PVA resin per 100 parts by mass

Preparation of transparent protective film A

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

< production of polarizing plate 1 >)

Using a roll laminator, transparent protective films a were laminated on both sides of the polarizing element a with an adhesive 1, and then dried at 80 ℃ for 5 minutes to form an adhesive layer, thereby obtaining a polarizing plate 1. The amount of the adhesive 1 used was adjusted so that the thickness of the dried adhesive layer was 50nm on both sides.

< production of polarizing plates 2 to 5 >

The polarizing plates 2 to 5 were obtained in the same manner as in the production of the polarizing plate 1 described above, except that the adhesive 1 was changed to the adhesives 2 to 5.

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

The polarizing plates 1 to 5 obtained above were stored at a temperature of 20℃and a relative humidity of 40% for 72 hours. The water content was measured by the karl-fischer method after 66 hours, 69 hours and 72 hours from the start of storage under the above conditions. Since no change was observed in the values of the respective water contents obtained by the measurement, the water contents of the polarizing plates 1 to 5 could be regarded as the same as the equilibrium water contents in the storage environment for 72 hours. When the water content of the polarizing plate is balanced in a certain storage environment, the water content of the polarizing element in the polarizing plate can be similarly considered to be balanced in the storage environment. In addition, when the water content of the polarizing element in the polarizing plate is balanced in a certain storage environment, the water content of the polarizing plate can be similarly considered to be balanced in the storage environment.

< evaluation of high temperature durability >

(preparation of sample for evaluation)

An acrylic pressure-sensitive adhesive (model: #7, manufactured by LINTEC Co., ltd.) was used to form pressure-sensitive adhesive layers on both sides of the polarizing plates 1 to 5 having their water contents adjusted. An evaluation sample was prepared by cutting the polarizing plates 1 to 5 to a size of 50mm×100mm so that the absorption axes thereof were parallel to the long sides, and bonding alkali-free glass (EAGLE XG, manufactured by Corning corporation) to the surfaces of the respective adhesive layers.

(evaluation of transmittance change based on high temperature durability test (105 ℃ C.))

For the sample for evaluation, the temperature was 50℃and the pressure was 5kgf/cm ² (490.3 kPa) after 1-hour autoclave treatment, the resulting mixture was left to stand at a temperature of 23℃and a relative humidity of 55% for 24 hours. The brightness was 5000cd/m using a spectroradiometer (SR-UL 1R manufactured by Kyowa Co., ltd.) under conditions of Topcon Technohouse ² The sample for evaluation was placed on the irradiation surface of the backlight module, and the brightness of the sample for evaluation at this time was measured under the conditions of a measurement angle of 2 degrees and a measurement distance of 350 mm. The brightness measured under this condition was "brightness L0". Thereafter, the sample for evaluation was stored in a heating environment at 105℃for 72 to 240 hours, and the brightness of the sample for evaluation was measured at 24-hour intervals by the same procedure as above. The measured luminance was defined as "luminance L1" which is the luminance after the high temperature endurance test.

Using the measured luminance L0 and luminance L1, the amount of change in transmittance was calculated according to the following equation.

The amount of change in transmittance [% ] =100- (luminance L1/luminance L0) ×100

Based on the storage time in the heating environment required to obtain the luminance L1 when the amount of change in transmittance is 5% or more, the high temperature durability was evaluated according to the following evaluation criteria. The results are shown in table 2.

(evaluation criterion)

For the storage time of the sample for evaluation under the heating environment required for the change amount of the transmissivity of the sample for evaluation to be more than 5%,

evaluation sample for more than 240 hours: a is that

Evaluation samples for more than 120 hours and up to 240 hours: b (B)

Evaluation samples for more than 72 hours and up to 120 hours: c (C)

Sample for evaluation up to 72 hours: d (D)

TABLE 2

Content of PVA resin per 100 parts by mass

Claims

1. A polarizing plate comprising a polarizing element in which a dichroic dye is adsorbed and oriented on 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 1 st compound and a 2 nd compound,

the 1 st compound is a compound with nitroxyl free radical or nitroxyl free radical,

the 2 nd compound is cyclodextrin.

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

the 1 st compound is an N-oxygen radical compound.

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

the 2 nd compound is at least 1 selected from alpha-cyclodextrin, beta-cyclodextrin and gamma-cyclodextrin.

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 1 st 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 claim 4 or 5, wherein,

in the adhesive, the content of the 2 nd compound is 1 to 50 parts by mass based on 100 parts by mass of the polyvinyl alcohol resin.

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

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

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

the polarizing plate is used in an image display device,

9. An image display device having an image display unit, a 1 st adhesive layer laminated on a viewing side surface of the image display unit, and the polarizing plate according to any one of claims 1 to 8 laminated on a viewing side surface of the 1 st adhesive layer.

10. The image display device according to claim 9, further comprising a 2 nd adhesive layer laminated on a viewing side surface of the polarizing plate, and a transparent member laminated on a viewing side surface of the 2 nd adhesive layer.

11. The image display device according to claim 10, wherein,

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

12. The image display device according to claim 10, wherein,

the transparent component is a touch panel.