KR20240037952A - Polarizer and image display device - Google Patents

Abstract

The present invention provides a polarizing plate that can suppress a decrease in transmittance under a high temperature environment. A polarizing plate has a polarizing element in which a dichroic dye is adsorbed and oriented in a polyvinyl alcohol-based resin layer, and a transparent protective film laminated on at least one side of the polarizing element. The polarizing element and the transparent protective film are bonded together by an adhesive layer formed from an adhesive containing the first compound and the second compound. The first compound is a compound having a nitroxy radical or nitroxide group. The second compound is a cyclodextrin.

Description

Polarizer and image display device

The present invention relates to polarizers and image display devices.

Liquid crystal displays (LCDs) are widely used not only in liquid crystal televisions but also in vehicle applications such as personal computers, mobile phones such as mobile phones, and car navigation systems. Usually, a liquid crystal display device has a liquid crystal panel in which a polarizing plate is bonded to both sides of a liquid crystal cell with an adhesive, and display is performed by controlling light from a backlight to the liquid crystal panel. Recently, organic EL display devices, like liquid crystal display devices, have been widely used for vehicle applications such as televisions, mobile phones such as cell phones, and car navigation systems. In an organic EL display device, a circularly polarizing plate (a laminate including a polarizing element and a λ/4 plate) is placed on the viewing side surface of the image display panel to prevent external light from being reflected from the metal electrode (cathode) and viewed as a mirror surface. There are cases where this is arranged.

As mentioned above, polarizers are a member of image display devices such as liquid crystal displays and organic EL displays, and the opportunities for their installation in cars are increasing. Polarizers used in in-vehicle image display devices are often exposed to high-temperature environments compared to mobile applications such as televisions and mobile phones, so they are required to have less change in properties at high temperatures (high-temperature durability).

Meanwhile, for the purpose of preventing damage to the image display panel due to impact from the outer surface, an entirely transparent plate such as a transparent resin plate or glass plate (sometimes called a “window layer”) is placed on the viewing side of the image display panel. The number of configurations being prepared is increasing. In image display devices equipped with a touch panel, a configuration in which the touch panel is provided on the viewer side of the image display panel and the front transparent plate is provided on the viewer side further than the touch panel is widely adopted.

In this configuration, if an air layer exists between the image display panel and a transparent member such as a front transparent plate or a touch panel, glare of external light occurs due to reflection of light at the air layer interface, and the visibility of the screen tends to decrease. Therefore, a configuration is adopted in which the space between the polarizing plate disposed on the viewing side surface of the image display panel and the transparent member is usually filled with a solid layer (hereinafter sometimes referred to as an “interlayer filler”) as a layer other than the air layer. The movement is spreading. The interlayer filler is preferably a material with a refractive index close to that of the polarizer or transparent member. As an interlayer filler, an adhesive or a UV curable adhesive is used to prevent a decrease in visibility due to reflection at the interface and to bond and fix each member (see, for example, Patent Document 1).

The structure filled with the above-described interlayer filler is increasingly being adopted for mobile applications such as mobile phones that are often used outdoors. In addition, due to the recent increase in demand for visibility, even in vehicle applications such as car navigation devices, a front transparent plate is placed on the surface of the image display panel, and the space between the panel and the front transparent plate is filled with a solid layer such as an adhesive layer. Recruitment of the composition is being considered.

However, when this configuration is adopted, it has been reported that the transmittance of the polarizing plate significantly decreases in a high temperature environment. As a solution to the problem, Patent Document 2 proposes a method of suppressing the decrease in transmittance by reducing the moisture content per unit area of the polarizing plate to a predetermined amount or less and reducing the saturated absorption amount of the transparent protective film adjacent to the polarizing element to a predetermined amount or less. I'm doing it.

Patent Document 1: Japanese Patent Publication No. Heisei 11-174417 Patent Document 2: Japanese Patent Publication No. 2014-102353

However, even with such a polarizing plate, the decrease in transmittance under a high temperature environment could not be sufficiently suppressed.

The purpose of the present invention is to provide a polarizing plate that can suppress a decrease in transmittance even when exposed to a high temperature environment, and an image display device using the polarizing plate.

The present invention provides the following polarizing plate and image display device.

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

The polarizing element and the transparent protective film are bonded together by an adhesive layer formed of an adhesive containing a first compound and a second compound,

The first compound is a compound having a nitroxy radical or nitroxide group,

A polarizing plate wherein the second compound is a cyclodextrin.

[2] The polarizing plate according to [1], wherein the first compound is an N-oxyl compound.

[3] The polarizing plate according to [1] or [2], wherein the second compound is at least one 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 contains a polyvinyl alcohol-based resin.

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

[6] The polarizing plate according to [4] or [5], wherein in the adhesive, the content of the second 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-based resin.

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

[8] The polarizer is used in an image display device,

In the image display device, the polarizing plate according to any one of [1] to [7], wherein solid layers are provided in contact with both surfaces of the polarizing plate.

[9] An image display cell, a first adhesive layer laminated on a viewing side surface of the image display cell, and a polarizing plate according to any one of [1] to [8] laminated on a viewing side surface of the first adhesive layer. An image display device having a.

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

According to the present invention, when used in an image display device with an interlayer filling configuration in which a solid layer is in contact with both surfaces of the polarizing plate, a polarizing plate in which a decrease in transmittance is suppressed even when exposed to a high temperature environment can be provided. Additionally, by using the polarizing plate according to the present invention, it is possible to provide an image display device in which a decrease in transmittance is suppressed even when exposed to a high temperature environment.

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

[Polarizer]

The polarizing plate of this embodiment has a polarizing element in which a dichroic dye is adsorbed and oriented in a polyvinyl alcohol-based resin layer, and a transparent protective film laminated on at least one surface of the polarizing element. The polarizing element and the transparent protective film are bonded together by an adhesive layer formed from an adhesive containing the first compound and the second compound. The first compound is a compound having a nitroxy radical or nitroxide group. The second compound is cyclodextrin.

As a conventional polarizing plate with excellent high-temperature durability, for example, a polarizing plate is known in which the decrease in transmittance is suppressed even when the polarizing plate alone is left in an environment at a temperature of 95° C. for 1000 hours. However, even such a polarizing plate is configured so that a solid layer is in contact with both sides of the polarizing plate, such that one side of the polarizing plate is bonded to an image display cell and the other side is bonded to a transparent member such as a touch panel or front plate. When applied to an image display device with a configuration (hereinafter sometimes referred to as an “interlayer filling configuration”), a significant decrease in transmittance may be observed in the in-plane central portion of the polarizing plate when left for 200 hours in an environment with a temperature of 95°C. It is believed that a significant decrease in the transmittance of a polarizing plate under a high-temperature environment is a problem that is particularly likely to occur when an image display device employing an interlayer filling configuration is exposed to a high-temperature environment.

In an image display device with an interlayer filling configuration, the polarizer with a significantly reduced transmittance was measured by Raman spectroscopy to have a polarizer around 1100 cm ^-1 (derived from =CC= bond) and around 1500 cm ^-1 (derived from -C=C- bond). Since it has a peak at , it is thought to form a polyene structure (-C=C) _n -. It is presumed that the polyene structure is formed when the polyvinyl alcohol-based resin constituting the polarizing element is polyeneized by dehydration (Patent Document 2, paragraph [0012]).

The polarizing plate of this embodiment is included in an image display device with an interlayer filling structure and has excellent high-temperature durability, such that a decrease in transmittance can be suppressed even when exposed to a high temperature environment of, for example, a temperature of 105°C. This effect is achieved when the polarizing plate is provided with an adhesive layer containing the first compound and the second compound, and the synergistic action of the first compound and the second compound causes polyenization of the polyvinyl alcohol-based resin constituting the polarizing element. It is presumed that this is due to the fact that is suppressed. It has been confirmed that this effect is not limited to cases where the moisture content of the polarizing plate is low, and is exhibited even when the moisture content of the polarizing plate is high.

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

(a) The water content of the polarizing element is greater than or equal to the equilibrium water content at a temperature of 20°C and a relative humidity of 30%, and less than or equal to the equilibrium water content at a temperature of 20°C and a relative humidity of 80%.

(b) The water content of the polarizing plate is greater than or equal to the equilibrium water content at a temperature of 20°C and a relative humidity of 30%, and less than or equal to the equilibrium water content at a temperature of 20°C and a relative humidity of 80%.

The polarizing plate of this embodiment exhibits the effect of improving high-temperature durability even when it has more limited features such as (a1) or (b1) below with respect to the features (a) or (b) above. It will happen.

(a1) The moisture content of the polarizing element exceeds the equilibrium moisture content of 45% or 50% relative humidity at a temperature of 20°C and is below the equilibrium moisture content of 80% or 70% relative humidity at a temperature of 20°C.

(b1) The moisture content of the polarizing plate exceeds the equilibrium moisture content of 45% or 50% relative humidity at a temperature of 20°C and is below the equilibrium moisture content of 80% or 70% of relative humidity at a temperature of 20°C.

The method for manufacturing the polarizing plate of this embodiment may include a step of adjusting the moisture content so as to have at least one of the characteristics (a) and (b) above, or may not include a step of adjusting the moisture content.

<Polarizing element>

As a polarizing element in which a dichroic dye is adsorbed and oriented in a polyvinyl alcohol (hereinafter sometimes referred to as "PVA")-based resin layer, a known polarizing element can be used. As a polarizing element, a stretched film obtained by dyeing a PVA-based resin film, which becomes a PVA-based resin layer, with a dichroic dye and uniaxially stretching it, or applying a coating liquid containing PVA-based resin onto the base film. One example is one formed by obtaining a laminated film in which an application layer that becomes a PVA-based resin layer was formed, dyeing the application layer with a dichroic dye, and uniaxially stretching the laminated film. Stretching may be performed after dyeing with a dichroic dye, may be stretched while dyeing, or may be dyed after stretching.

The PVA-based resin contained in the PVA-based resin layer is obtained by saponifying polyvinyl acetate-based resin. Examples of the polyvinyl acetate-based resin include polyvinyl acetate, which is a homopolymer of vinyl acetate, as well as copolymers of vinyl acetate and other monomers copolymerizable therewith. Other copolymerizable monomers include, for example, 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 even more preferably 99 mol% or more and 100 mol% or less. The degree of polymerization 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, etc. modified with aldehydes.

Examples of the dichroic dye that is adsorbed and oriented in the PVA-based resin layer include iodine or dichroic dye. The dichroic dye is preferably iodine. As dichroic dyes, red BR, red LR, red R, pink LB, rubin BL, Bordeaux GS, sky blue LG, lemon yellow, blue BR, blue 2R, navy RY, green LG, violet LB, violet B, black H. , Black B, Black GSP, Yellow 3G, Yellow R, Orange LR, Orange 3R, Scarlet GL, Scarlet KGL, Congo-Red, Brilliant Violet BK, Supra Blue G, Supra Blue GL, Supra Orange GL, Direct Sky Blue, Direct Examples include First Orange S and First Black.

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. When the thickness of the polarizing element is 35 μm or less, it becomes easy to suppress the influence of polyenization of the PVA-based resin on the deterioration of optical properties in a high temperature environment. When the thickness of the polarizing element is 3 μm or more, it becomes easy to obtain a polarizing plate that achieves desired optical properties.

The polarizing element of the polarizing plate of this embodiment preferably contains the first compound and the second compound. In a polarizing plate, a polarizing element and a transparent protective film are bonded together by an adhesive layer formed of an adhesive containing the first compound and the second compound, so a part of the first compound and a part of the second compound migrated from the adhesive layer. It is assumed to be included in the polarizing element. By providing the polarizing plate with such a polarizing element with an adhesive layer containing the first compound and the second compound, the transmittance becomes less likely to decrease even when exposed to a high temperature environment. In addition, by providing an adhesive layer containing the first compound and the second compound, a decrease in the degree of polarization can be suppressed even when the polarizing plate is exposed to a high temperature environment. If the degree of polarization of the polarizing plate decreases, when two polarizing plates are arranged and used in a cross nicol relationship, light loss (hereinafter sometimes referred to as "cross loss") becomes likely to occur, but the polarizing plate of the present embodiment is suitable for use in a high temperature environment. Since the degree of polarization is unlikely to decrease even when exposed to sunlight, it becomes easy to suppress missing crosses. Polyenization of the PVA-based resin is suppressed due to the synergistic effect of the first compound and the second compound contained in the polarizing element, thereby suppressing a decrease in the transmittance of the polarizing plate exposed to a high temperature environment and also suppressing a decrease in the degree of polarization. It is assumed that it can be done.

Methods for incorporating the first compound and the second compound into the polarizing element include a method of transferring the first compound and the second compound from the adhesive layer to the polarizing element as described above; A method of manufacturing a polarizing element containing a first compound and a second compound; A combination of these two methods is possible. For example, when manufacturing a polarizing element, one of the first compound and the second compound may be contained in the polarizing element, and the adhesive layer constituting the polarizing plate may contain both the first compound and the second compound.

As a method of producing a polarizing element containing the first compound and the second compound during production of the polarizing element, a method of immersing the PVA-based resin layer in a treatment solvent containing the first compound and/or the second compound, or A method of spraying, dripping, or dripping the treatment solvent onto the PVA-based resin layer is included. Among these, a method of immersing the PVA-based resin layer in a treatment solvent containing both the first compound and the second compound is preferably used. Specific examples of the first compound and the second compound include those included in the adhesive described later.

The step of immersing the PVA-based resin layer in a treatment solvent containing the first compound and the second compound may be performed simultaneously with steps such as swelling, stretching, dyeing, crosslinking, and washing in the method for manufacturing a polarizing element described later. , it may be prepared separately from these processes. The step of making the PVA-based resin layer contain the first compound and the second compound is preferably performed after dyeing the PVA-based resin layer with iodine, and is more preferably performed simultaneously with the crosslinking step after dyeing. According to this method, the color change can be small and the influence on the optical characteristics of the polarizing element can be reduced.

(First compound)

The first compound is a compound having a nitroxy radical or nitroxide group. As the first compound, an N-oxyl compound (a compound having C-N(-C)-O· as a functional group (O· represents an oxy radical and is bonded to N) from the viewpoint of having a radical that is relatively stable at room temperature and in air )), and known ones can be used. Examples of N-oxyl compounds include compounds having an organic group with the following structure. Compounds having a nitroxy radical or nitroxide group may be used individually or in combination of two or more types.

[In the above formula (1), R ¹ represents an oxyradical, R ² to ^{R 5} independently represent a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and n represents 0 or 1. ]

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

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

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

[In the above formula (3), R ¹ to ^{R 5} and n have the same meaning as above, and R ⁷ and R ⁸ are independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, or an acyl group. , or represents an aryl group.]

[In the formula (4), R ¹ to ^{R 5} and n have the same meaning as above, and R ⁹ to ^{R 11} are independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, or an acyl group. , represents an amino group, an alkoxy group, a hydroxy group, or an aryl group.]

[In the above formula (5), R ¹ to ^{R 5} and n have the same meaning as above, and R ¹² is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, an acyl group, an amino group, an alkoxy group, Represents a hydroxy group or an aryl group.]

In the above formulas (1) to (5), R ² to R ⁵ are preferably an alkyl group having 1 to 6 carbon atoms, and more preferably an alkyl group having 1 to 3 carbon atoms from the viewpoint of availability. . In the above formula (2), from the viewpoint of ease of availability, R ⁶ is preferably a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and more preferably a hydrogen atom. In the above formula (3), from the viewpoint of availability, it is preferable that R ⁷ and R ⁸ are independently a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and more preferably a hydrogen atom. In the above formula (4), from the viewpoint of ease of availability, it is preferable that R ⁹ to ^{R 11} are independently a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. In the above formula (5), from the viewpoint of availability, R ¹² is preferably a hydroxy group, an amino group, or an alkoxy group. In the above formulas (1) to (5), n is preferably 1 from the viewpoint of ease of availability.

As N-oxyl compounds, for example, N-oxyl described in JP-A-2003-64022, JP-A-11-222462, JP-A-2002-284737, International Publication No. 2016/047655, etc. Compounds may be mentioned. As the N-oxyl compound, 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl is preferably used.

Examples of the first compound include the following compounds.

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

The first compound preferably has a molecular weight of 1000 or less, more preferably 500 or less, and even more preferably 300 or less from the viewpoint of efficiently capturing radicals generated in the polyenylation reaction. The lower limit of the molecular weight is not particularly limited, but may be 80, for example.

(second compound)

The second compound is cyclodextrin. Cyclodextrin is a non-reducing cyclic oligosaccharide in which glucose is cyclically bonded through an α-1,4 bond. The greater the number of glucose constituting cyclodextrins, the larger the inner diameter of the cavity within the molecule. Cyclodextrins used as the second compound preferably contain 6 or more glucose, for example, α, β, γ, and δ-cyclodextrins with 6, 7, 8, and 9 glucose, respectively. can be mentioned. Cyclodextrins include α, β, γ, and δ-cyclodextrins, as well as branched cyclodextrins having oligosaccharides such as glucose and maltose in branched sugar chains. As cyclodextrins, the cyclodextrins or branched cyclodextrins further contain an alkyl group such as a methyl group; Cyclodextrin derivatives containing hydroxyalkyl groups such as 2-hydroxyethyl group, 2-hydroxypropyl group, 2,3-dihydroxypropyl group, and 2-hydroxybutyl group are included. Cyclodextrins can be used individually or in combination of two or more types.

(Feature (a))

When the polarizing plate has the above-described feature (a), the water content of the polarizing element is greater than or equal to the equilibrium water content at a temperature of 20°C and a relative humidity of 30%, and less than or equal to the equilibrium water content at a temperature of 20°C and a relative humidity of 80%. The water content of the polarizing element may be greater than the equilibrium water content of 45% or 50% at a temperature of 20°C and a relative humidity of 20°C, or may be below the equilibrium water content of 80% or 70% of the relative humidity at a temperature of 20°C. If the moisture content of the polarizing element is lower than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30%, the handling properties of the polarizing element deteriorate and become prone to breakage. If the water content of the polarizing element is high, such as exceeding the equilibrium water content of 45% or 50% at a temperature of 20°C and a relative humidity of 45% or 50%, it is presumed that polyenization of the PVA-based resin will easily proceed. However, the polarizing plate of the present embodiment includes the first compound and Since the adhesive layer containing the second compound is provided, polyenization of the PVA-based resin can be suppressed.

A method of confirming that the water content of the polarizing element is within the range of more than the equilibrium water content at a temperature of 20°C and 30% relative humidity and less than or equal to the equilibrium water content of 80% relative humidity at a temperature of 20°C, wherein the environment is adjusted to the range of the temperature and the relative humidity. If there is no change in mass for a certain period of time, the polarized light is stored in a storage environment and is considered to have reached equilibrium with the environment, or the equilibrium moisture content of the polarizing element in the environment adjusted to the range of the temperature and relative humidity is calculated in advance. One way to check is by comparing the water content of the device with the previously calculated equilibrium water content.

There is no particular limitation on the method of manufacturing a polarizing element whose moisture content is more than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30% and below the equilibrium moisture content at a temperature of 20°C and a relative humidity of 80%, but is, for example, adjusted to the range of the above temperature and the above relative humidity. A method of storing the polarizing element in a controlled environment for 10 minutes or more and 3 hours or less, or a method of heat treatment at a temperature of 30°C or more and 90°C or less, is included.

As another preferred method of manufacturing a polarizing element having a moisture content in the above range, a laminate in which a transparent protective film is laminated on at least one side of the polarizing element, or a polarizing plate constructed using the polarizing element, is prepared at the temperature and relative humidity. A method of storing it in an environment adjusted to the range for 10 minutes or more and 120 hours or less, or a method of heat treatment at 30°C or more and 90°C or less, is included. Alternatively, when manufacturing an image display device employing an interlayer filling configuration, an image display panel in which a polarizer is laminated to an image display cell is stored in an environment adjusted to the above temperature and relative humidity ranges for 10 minutes or more and 3 hours or less. Alternatively, after heating to a temperature of 30°C or more and 90°C or less, a transparent member such as a front plate may be bonded.

(Feature (b))

When the polarizing plate has the above-described feature (b), the water content of the polarizing plate is greater than or equal to the equilibrium water content at a temperature of 20°C and a relative humidity of 30%, and less than or equal to the equilibrium water content at a temperature of 20°C and a relative humidity of 80%. The moisture content of the polarizing plate may be greater than the equilibrium moisture content of 45% or 50% relative humidity at a temperature of 20°C, or may be below the equilibrium moisture content of 80% or 70% of the relative humidity at a temperature of 20°C. If the moisture content of the polarizing plate is lower than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30%, the handling properties of the polarizing plate deteriorate and become prone to breakage. If the water content of the polarizing plate is high, such as exceeding the equilibrium water content of 45% or 50% at a temperature of 20°C and a relative humidity of 45% or 50%, it is presumed that polyenization of the PVA-based resin will easily proceed. However, the polarizing plate of the present embodiment contains the first compound and the first compound. 2 Since the adhesive layer containing the compound is provided, polyenization of the PVA-based resin can be suppressed.

A method of confirming that the moisture content of the polarizer is within the range of more than the equilibrium moisture content at a temperature of 20°C and 30% relative humidity and below the equilibrium moisture content of 80% relative humidity at a temperature of 20°C, in an environment adjusted to the above temperature and relative humidity ranges. A method of storing it and assuming that it has reached equilibrium with the environment when there is no change in mass for a certain period of time, or calculating the equilibrium moisture content of the polarizer in an environment adjusted to the above temperature and relative humidity range in advance, and calculating the moisture content of the polarizer in advance. A method of confirmation can be given by comparing the equilibrium moisture content calculated in advance.

The method for producing a polarizing plate having a water content greater than or equal to the equilibrium water content of 30% at a temperature of 20°C and a relative humidity of 30% and less than or equal to an equilibrium water content of 80% of the temperature and relative humidity of 20°C is not particularly limited, but includes, for example, a method adjusted to the range of the temperature and the relative humidity. Examples include a method of storing the polarizing plate in the environment for 10 minutes or more and 3 hours or less, or a method of heat treatment at a temperature of 30°C or more and 90°C or less. Alternatively, when manufacturing an image display device employing an interlayer filling configuration, an image display panel in which a polarizer is laminated to an image display cell is stored in an environment adjusted to the above temperature and relative humidity ranges for 10 minutes or more and 3 hours or less. Alternatively, after heating to a temperature of 30°C or more and 90°C or less, a transparent member such as a front plate may be bonded.

(Method for manufacturing polarizing element)

The manufacturing method of the polarizing element is not particularly limited, but includes a method of producing a PVA-based resin film previously wound into a roll and performing stretching, dyeing, crosslinking, etc. (hereinafter referred to as “manufacturing method 1”); A typical method is a method (hereinafter referred to as “manufacturing method 2”) including the step of applying a coating liquid containing a PVA-based resin on a base film to form an application layer and stretching the obtained laminate.

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

The swelling process is a treatment process in which the PVA-based resin film is immersed in a swelling bath. Through the swelling process, not only can dirt and blocking agents on the surface of the PVA-based resin film be removed, but also dyeing unevenness can be suppressed by swelling the PVA-based resin film. For the swelling bath, a medium containing water as a main component, such as water, distilled water, or pure water, is usually used. Surfactant, alcohol, etc. may be appropriately added to the swelling bath 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. In this case, the concentration of potassium iodide in the swelling bath is preferably 1.5% by mass or less, and more preferably 1.0% by mass or less. And, it is more preferable that it is 0.5% by mass or less.

The temperature of the swelling bath is preferably 10°C or higher and 60°C or lower, more preferably 15°C or higher and 45°C or lower, and even more preferably 18°C or higher and 30°C or lower. The immersion time in the swelling bath cannot be uniformly 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 to 300 seconds, and more preferably 10 seconds to 200 seconds. It is preferable, and it is more preferable that it is 20 seconds or more and 100 seconds or less. The swelling process may be performed only once, or may be performed multiple times as needed.

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

The concentration of iodine in the dyeing bath (iodine solution) 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 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 even more preferably 0.1 mass% or more and 3 mass% or less.

The temperature of the dyeing bath is preferably 10°C or higher and 50°C or lower, more preferably 15°C or higher and 45°C or lower, and even more preferably 18°C or higher and 30°C or lower. The immersion time in the dyeing bath cannot be uniformly 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 to 300 seconds, and more preferably 20 seconds to 240 seconds. desirable. The dyeing process may be performed only once, or may be performed multiple times as needed.

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

The concentration of the boron compound in the crosslinking bath is preferably 1 mass% or more and 15 mass% or less, more preferably 1.5 mass% or more and 10 mass% or less, and more preferably 2 mass% or more and 5 mass% or less. When potassium iodide is used in the cross-linking bath, the concentration of potassium iodide in the cross-linking bath is preferably 1 mass% to 15 mass%, more preferably 1.5 mass% to 10 mass%, and 2 mass% to 5 mass%. It is more preferable that it is % or less.

The temperature of the crosslinking bath is preferably 20°C or higher and 70°C or lower, and more preferably 30°C or higher and 60°C or lower. The immersion time in the crosslinking bath cannot be uniformly 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 to 300 seconds, and more preferably 10 seconds to 200 seconds. desirable. The crosslinking process may be performed only once, or may be performed multiple times as needed.

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

The treatment bath (stretching bath) in the wet stretching method can usually use a solvent such as water or a mixed solution of water and an organic solvent miscible with water. The stretching bath preferably contains potassium iodide from the viewpoint of controlling the potassium content in the polarizing element. When using potassium iodide in a 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 3 mass% or more and 6 mass%. It is more preferable that it is % or less. The treatment bath (stretching bath) may contain a boron compound from the viewpoint of suppressing film breakage during stretching. When containing a boron compound, the concentration of the boron compound in the stretching 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 2 mass% or more and 5 mass% or less. It is more desirable.

The temperature of the stretching bath is preferably 25°C or higher and 80°C or lower, more preferably 40°C or higher and 75°C or lower, and even more preferably 50°C or higher and 70°C or lower. The immersion time in the stretching bath cannot be uniformly 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 to 800 seconds, and more preferably 30 seconds to 500 seconds. desirable. The stretching treatment in the wet stretching method may be performed simultaneously with any one or more of the swelling process, dyeing process, crosslinking process, and washing process.

Examples of dry stretching methods include roll-to-roll stretching methods, heated roll stretching methods, and compression stretching methods. Additionally, in the case of the dry stretching method, the stretching process may be performed in a drying process.

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

The washing process is a treatment process in which the PVA-based resin film is immersed in a washing bath, and foreign substances remaining on the surface of the PVA-based resin film, etc. can be removed. As a washing bath, a medium containing water as a main component, such as water, distilled water, or pure water, is usually used. From the viewpoint of controlling the potassium content in the polarizing element, it is preferable to use potassium iodide in the washing bath. 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, and is preferably 1.5%. It is more preferable that it is 4 mass% or less, and it is still more preferable that it is 1.8 mass% or more and 3.8 mass% or less.

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

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

Manufacturing method 2 is a process of applying a coating liquid containing a PVA-based resin onto a base film, a process of uniaxially stretching the obtained laminated film, and dyeing the coating layer of the uniaxially stretched laminated film with a dichroic dye to produce a dichroic dye. It may include a process of adsorbing, a process of treating the laminated film with the dichroic dye adsorbed with an aqueous boric acid solution, and a process of washing with water after treatment with the aqueous boric acid solution. The base film used to form a polarizing element may be used as a transparent protective film for a polarizing plate. If necessary, the base film may be peeled and removed from the polarizing element.

<Transparent protective film>

The transparent protective film is bonded to at least one side of the polarizing element through an adhesive layer. This transparent protective film is bonded to one side or both sides of the polarizing element, but is preferably bonded to both sides.

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

Transparent protective films include cellulose acylate-based films, films made of polycarbonate-based resins, films made of cycloolefin-based resins such as norbornene, (meth)acrylic polymer films, and polyester resin-based films such as polyethylene terephthalate. Film can be used. When attaching a transparent protective film to both sides of a polarizing element using a water-based adhesive such as PVA adhesive, the transparent protective film on at least one side must be either a cellulose acylate-based film or a (meth)acrylic-based polymer film in terms of moisture permeability. It is preferable, and cellulose acylate film is especially preferable.

At least one of the transparent protective films included in the polarizing plate may have a phase difference function for purposes such as viewing angle compensation. In that case, the film itself constituting the transparent protective film may have a retardation function, or the transparent protective film may have a layer that does not have a retardation function and a retardation layer (a layer with a retardation function). When the transparent protective film has a retardation layer, it can be used as a laminate of a layer that does not have a retardation function and a retardation layer, and these may be bonded together using an adhesive or adhesive.

<Adhesive layer>

As an adhesive that constitutes an adhesive layer for bonding a transparent protective film to a polarizing element, an adhesive containing the first compound and the second compound is used. The adhesive may be a water-based adhesive, a solvent-based adhesive, or an active energy ray-curable adhesive, but it is preferable that it is a water-based adhesive and that it contains a PVA-based resin. By using an adhesive containing the first compound and the second compound to form the adhesive layer, a decrease in the transmittance of the polarizing plate under a high temperature environment can be suppressed.

The thickness when applying the adhesive can be set to an arbitrary value. For example, after curing or heating (drying), it is set so that an adhesive layer with a desired thickness is obtained. 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, further preferably 0.01 μm or more and 2 μm or less, and most preferably 0.01 μm or more and 1 μm. It is as follows.

When manufacturing a polarizing plate using a polarizing element that does not contain the first compound and the second compound, the content of the first compound and the second compound contained in the adhesive is preferably within the range described below. When manufacturing a polarizing plate using a polarizing element containing a first compound and a second compound, the content of the first compound and the second compound contained in the adhesive is adjusted depending on the first compound and the second compound contained in the polarizing element, etc. , you can change it appropriately within the range described below. Specific examples of the first compound and the second compound are as described above.

When the adhesive contains a PVA-based resin (for example, in the case of a water-based adhesive containing a PVA-based resin), the content of the first compound is preferably 0.1 part by mass or more and 400 parts by mass based on 100 parts by mass of the PVA-based resin. 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. If it is less than 0.1 part by mass, the effect of suppressing polyenylation of the PVA-based resin in a high temperature environment may not be sufficient. On the other hand, when it exceeds 400 parts by mass, the first compound may precipitate after production of the polarizing plate.

When the adhesive contains a PVA-based resin (for example, in the case of a water-based adhesive containing a PVA-based resin), the content of the second compound is preferably 1 part by mass or more and 50 parts by mass based on 100 parts by mass of the PVA-based resin. or less, more preferably 1.5 parts by mass or more and 40 parts by mass or less, and even more preferably 2 parts by mass or more and 35 parts by mass or less. If it is less than 1 part by mass, the effect of suppressing polyenylation of the PVA-based resin in a high temperature environment may not be sufficient. On the other hand, when it exceeds 50 parts by mass, the second compound may precipitate after production of the polarizing plate.

In a configuration in which a transparent protective film is bonded to both sides of the polarizing element through an adhesive layer, among the adhesive layers on both sides of the polarizing element, only the adhesive layer on one side may be a layer containing the first compound and the second compound, but the adhesive on both sides It is preferred that the layers are layers that together contain the first compound and the second compound.

In order to meet the demand for thinner polarizing plates, polarizing plates having a transparent protective film on only one side of the polarizing element have been developed. In this configuration as well, a transparent protective film is laminated through an adhesive layer containing the first compound and the second compound. As a method of manufacturing a polarizing plate having a transparent protective film on only one side of such a polarizing element, a method of first manufacturing a polarizing plate in which a transparent protective film is bonded to both sides through an adhesive layer and then peeling off the transparent protective film on one side is considered. When this manufacturing method is used, only one adhesive layer may contain the first compound and the second compound, but it is preferable that the adhesive layers on both sides are layers containing the first compound and the second compound. When only one adhesive layer contains the first compound and the second compound, it is preferable that the adhesive layer on the film side that is not peeled contains the first compound and the second compound.

(Water-based adhesive)

As the water-based adhesive, any suitable water-based adhesive may be employed, but a water-based adhesive containing a PVA-based resin (PVA-based adhesive) is preferably used. The average degree of polymerization of the PVA-based resin contained in the water-based adhesive is preferably 100 or more and 5,500 or less, more preferably 1,000 or more and 4,500 or less from the viewpoint of adhesiveness. From the viewpoint of adhesiveness, the average degree of saponification is preferably 85 mol% or more and 100 mol% or less, and more preferably 90 mol% or more and 100 mol% or less.

As the PVA-based resin contained in the water-based adhesive, a PVA-based resin containing an acetoacetyl group (hereinafter sometimes referred to as “acetoacetyl group-containing PVA-based resin”) is preferable. The reason for this is that the adhesion between the PVA-based resin layer and the transparent protective film is excellent and durability is excellent. PVA-based resin containing an acetoacetyl group is obtained, for example, by reacting PVA-based resin and diketene by an arbitrary method. The acetoacetyl group modification degree of the PVA-based resin containing an acetoacetyl group is typically 0.1 mol% or more, and is preferably 0.1 mol% or more and 20 mol% or less. The resin concentration of the water-based 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.

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

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

Water-based adhesives may contain organic solvents. The organic solvent is preferably alcohol because it is miscible with water, and among alcohols, methanol or ethanol is more preferable. The methanol concentration of the water-based adhesive is preferably 10 mass% or more and 70 mass% or less, more preferably 15 mass% or more and 60 mass% or less, and even more preferably 20 mass% or more and 60 mass% or less. When the concentration of methanol is 10% by mass or more, it becomes easier to suppress polyenization of the PVA-based resin in a high-temperature environment. In addition, when the methanol content is 70% by mass or less, deterioration of color can be suppressed. For example, as a component mixed in a water-based adhesive, a component may be used that has low solubility in water but sufficient solubility in alcohol. In that case, one preferred embodiment is to dissolve the above-mentioned components in alcohol to prepare an alcohol solution of the above-mentioned components, and then add the alcohol solution to an aqueous solution of PVA-based resin to prepare an adhesive.

(Active energy ray curing adhesive)

Active energy ray-curable adhesives are adhesives that are cured by irradiating active energy rays such as ultraviolet rays, and include, for example, an adhesive containing a polymerizable compound and a photopolymerization initiator, an adhesive containing a photoreactive resin, a binder resin, and a photoreactive crosslinking agent. Adhesives etc. can be mentioned. 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 a substance that generates active species such as neutral radicals, anion radicals, and cation radicals when irradiated with active energy rays such as ultraviolet rays.

[Method of manufacturing polarizer]

The manufacturing method of the polarizing plate of this embodiment has a lamination process of laminating a polarizing element and a transparent protective film. The method for manufacturing a polarizing plate may include a moisture content adjustment step. The order in which the moisture content adjustment process and the lamination process are performed is not limited, and the moisture content adjustment process and the lamination process may be performed in parallel.

In the lamination process, the polarizing element and the transparent protective film are laminated through the adhesive layer described above. In the lamination process, the polarizing element and the transparent protective film are bonded together using an adhesive containing the first compound and the second compound. The adhesive interposed between the polarizing element and the transparent protective film becomes an adhesive layer through a drying process, for example. The lamination process may be a process of bonding a polarizing element and a transparent protective film that do not contain the first compound and the second compound using an adhesive containing the first compound and the second compound. In this case, in the process of forming the adhesive layer from the adhesive, part of the first compound and part of the second compound contained in the adhesive may move to the polarizing element or the like.

In the moisture content adjustment process, when manufacturing a polarizing plate having characteristic (a), polarization is carried out so that the moisture content of the polarizing element is above the equilibrium moisture content at a temperature of 20°C and 30% relative humidity, and below the equilibrium moisture content at a temperature of 20°C and relative humidity of 80%. Adjust the moisture content of the device. The moisture content of the polarizing element can be adjusted by the method described above. In the moisture content adjustment process, when manufacturing a polarizing plate having feature (b), the moisture content of the polarizing plate is adjusted so that the moisture content of the polarizing plate is more than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30% and is below the equilibrium moisture content of 80% of the relative humidity at a temperature of 20°C. Adjust moisture content. The moisture content of the polarizing plate can be adjusted by the method described above.

[Configuration of image display device]

The polarizing plate of this embodiment is used in various image display devices, such as a liquid crystal display device and an organic EL display device. For an image display device, in the case of an interlayer filling configuration in which a layer other than an air layer, specifically a solid layer such as an adhesive layer, is in contact with both sides of the polarizing plate, the transmittance is likely to decrease in a high temperature environment. In the image display device using the polarizing plate of this embodiment, even if it is an interlayer filling configuration, a decrease in the transmittance of the polarizing plate under a high temperature environment can be suppressed.

Examples of the solid layer include an adhesive layer or an adhesive layer. When the solid layer is an adhesive layer, it is preferably an adhesive layer formed by a UV curing type adhesive.

An example of an image display device is a structure having an image display cell, a first adhesive layer laminated on the viewer-side surface of the image display cell, and a polarizing plate laminated on the viewer-side surface of the first adhesive layer. This image display device may further include a second adhesive layer laminated on the viewing side surface of the polarizing plate and a transparent member laminated on the surface of the second adhesive layer. In particular, the polarizing plate of this embodiment has a transparent member disposed on the viewing side of the image display device, the polarizing plate and the image display cell are bonded to each other by a first adhesive layer, and the polarizing plate and the transparent member are bonded to each other by a second adhesive layer. It is suitably used in an image display device having an interlayer filling configuration.

The polarizing plate and the image display cell are not limited to the first adhesive layer, and may be bonded together by an adhesive layer formed using an adhesive. The polarizing plate and the transparent member are not limited to the second adhesive layer and may be bonded together by an adhesive layer formed using an adhesive. The adhesive may be the adhesive described above, or may be one that does not contain the first compound or the second compound.

<Image display cell>

Examples of image display cells include liquid crystal cells and organic EL cells. 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, or a transflective liquid crystal cell using both light from the outside and light from the light source may be used. good night. When the liquid crystal cell uses light from a light source, the image display device (liquid crystal display device) has a polarizing plate disposed on the side opposite to the viewing side of the image display cell (liquid crystal cell), and a light source is also disposed. It is preferable that the polarizing plate on the light source side and the liquid crystal cell are bonded together through an appropriate adhesive layer. As a driving method for the liquid crystal cell, for example, any type such as VA mode, IPS mode, TN mode, STN mode, or bend orientation (π type) can be used.

As an organic EL cell, one in which a transparent electrode, an organic light-emitting layer, and a metal electrode are sequentially laminated on a transparent substrate to form a light emitting body (organic electroluminescent light emitting body) is suitably used. The organic light-emitting layer is a laminate of various organic thin films, for example, a laminate of a hole injection layer made of a triphenylamine derivative, etc., and a light-emitting layer made of a fluorescent organic solid such as anthracene, or an electronic layer made of these light-emitting layers and a perylene derivative, etc. Various layer configurations can be employed, such as a laminate of injection layers or a laminate of a hole injection layer, a light-emitting layer, and an electron injection layer.

<Combination of image display cell and polarizer>

A first adhesive layer is suitably used to bond an image display cell and a polarizing plate. Among them, a method of bonding a polarizing plate having an adhesive layer in which a first adhesive layer is provided on one side of the polarizing plate to an image display cell is preferable from the viewpoint of workability and the like. Laying down the first adhesive layer on the polarizing plate can be performed in an appropriate manner. As an example, prepare an adhesive solution of about 10% by mass or more and 40% by mass or less by dissolving or dispersing the base polymer or its composition in a solvent consisting of a suitable solvent such as toluene or ethyl acetate alone or in a mixture, and then softening it. Appropriate deployment methods such as a coating method or a coating method include laying directly on a polarizing plate, forming a first adhesive layer on a separate film, and attaching it to a polarizing plate.

<First adhesive layer, second adhesive layer>

The first adhesive layer and the second adhesive layer (hereinafter, either or both may be referred to as “adhesive layer”) may independently be composed of one or two or more layers, but are preferably composed of one layer. . The adhesive layer can be composed of an adhesive composition containing (meth)acrylic resin, rubber-based resin, urethane-based resin, ester-based resin, silicone-based resin, and polyvinyl ether-based resin as main components. Among them, an adhesive composition containing a (meth)acrylic resin excellent in transparency, weather resistance, heat resistance, etc. as a base polymer is suitable. The adhesive composition may be of an active energy ray curing type or a thermosetting type.

Examples of the (meth)acrylic resin (base polymer) used in the adhesive composition include (meth)acrylic acid esters such as butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. A polymer or copolymer containing one or two or more of the following as monomers is suitably used. It is preferable to copolymerize a polar monomer with the base polymer. As polar monomers, (meth)acrylic acid compounds, (meth)acrylic acid 2-hydroxypropyl compounds, (meth)acrylic acid hydroxyethyl compounds, (meth)acrylamide compounds, and N,N-dimethylaminoethyl (meth)acrylate compounds. , monomers having a carboxyl group, a hydroxyl group, an amide group, an amino group, an epoxy group, etc., such as a glycidyl (meth)acrylate compound.

The pressure-sensitive adhesive composition may contain only the base polymer, but usually further contains a crosslinking agent. The crosslinking agent is a divalent or higher metal ion, such as a metal ion that forms a carboxylic acid metal salt between carboxyl groups, a polyamine compound that forms an amide bond between carboxyl groups, and a polyepoxy that forms an ester bond between carboxyl groups. Examples include polyisocyanate compounds that form amide bonds between compounds, polyols, and carboxyl groups. Among them, polyisocyanate compounds are preferable.

The active energy ray-curable adhesive composition has the property of curing upon exposure to active energy rays such as ultraviolet rays or electron beams, and has adhesiveness even before irradiation of active energy rays and can be brought into close contact with an adherend such as a film, thereby allowing irradiation of active energy rays. It has the property of being able to adjust the adhesion by hardening. The active energy ray-curable adhesive composition is preferably of an ultraviolet ray-curable type. The active energy ray curable adhesive composition further contains an active energy ray polymerizable compound in addition to the base polymer and crosslinking agent. If necessary, a photopolymerization initiator, a photosensitizer, etc. may be contained.

The adhesive composition includes fine particles for imparting light scattering properties, beads (resin beads, glass beads, etc.), glass fibers, resins other than the base polymer, tackifiers, fillers (metal powders and other inorganic powders, etc.), antioxidants, and ultraviolet rays. It may contain additives such as absorbents, dyes, pigments, colorants, defoaming agents, corrosion inhibitors, and photopolymerization initiators.

The adhesive layer can be formed by applying an organic solvent dilution of the adhesive composition to the surface of a base film, an image display cell, or a polarizing plate and drying it. The base film is generally a thermoplastic resin film, and a typical example thereof includes a separate film to which release treatment has been performed. The separate film may be a film made of, for example, a resin such as polyethylene terephthalate, polybutylene terephthalate, polycarbonate, or polyarylate, and the surface on which the adhesive layer is formed may be subjected to a release treatment such as silicone treatment.

The pressure-sensitive adhesive composition may be applied directly to the release-treated surface of the separate film to form a pressure-sensitive adhesive layer, and the pressure-sensitive adhesive layer having this separate film may be laminated on the surface of the polarizing plate. The adhesive composition may be applied directly to the surface of the polarizing plate to form an adhesive layer, and a separate film may be laminated on the outer surface of the adhesive layer.

When providing an adhesive layer on the surface of a polarizing plate, it is preferable to perform surface activation treatment such as plasma treatment or corona treatment on the bonding surface of the polarizing plate and/or the bonding surface of the adhesive layer, and it is more preferable to perform corona treatment. do.

Additionally, a pressure-sensitive adhesive composition is applied on the second separate film to form a pressure-sensitive adhesive layer, a pressure-sensitive adhesive sheet is prepared by laminating the separate film on the formed pressure-sensitive adhesive layer, and the second separate film is peeled from the pressure-sensitive adhesive sheet. The pressure-sensitive adhesive layer may be laminated on the polarizing plate. The second separate film is used because it has weaker adhesion to the adhesive layer and is easier to peel than the separate film.

The thickness of the adhesive layer is not particularly limited, but for example, it 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 transparent members disposed on the viewing side of the image display device include transparent plates (front plates, window layers) and touch panels. 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 resin, acrylic resin, and polycarbonate resin, or glass plates. A functional layer such as an antireflection layer may be laminated on the viewing side of the transparent plate. Additionally, when the transparent plate is a transparent resin plate, a hard coat layer may be laminated to increase physical strength, or a low moisture permeability layer may be laminated to reduce moisture permeability. As the touch panel, various touch panels such as resistive type, capacitive type, optical type, and ultrasonic type, as well as glass plates and transparent resin plates with a touch sensor function, are used. When a capacitive touch panel is used as a transparent member, it is preferable that a transparent plate made of a glass plate or a transparent resin plate be provided on the viewing side of the touch panel.

<Combination of polarizer and transparent member>

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

When using an active energy ray-curable adhesive, a dam material is provided to surround the peripheral edge on the image display panel for the purpose of preventing the adhesive solution from spreading before curing, a transparent member is placed on the dam material, and the adhesive solution is injected. This is used appropriately. After injection of the adhesive solution, alignment and defoaming are performed as necessary, and then curing is performed by irradiation of active energy rays.

Example

Hereinafter, the present invention will be described in detail based on examples. Materials, reagents, amounts of substances, ratios, operations, etc. shown in the examples below can be changed appropriately as long as they do not deviate from the spirit of the present invention. Accordingly, the present invention is not limited to the following examples.

<Production of polarizing element A>

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

<Preparation of adhesives 1 to 5>

(Preparation of PVA solution A for adhesive)

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

(Preparation of adhesives 1 to 5)

Adhesives 1 to 5 were prepared by mixing PVA solution A, the first compound, the second compound, and pure water so that the concentration of the PVA-based resin was 3.0% by mass and the first compound and second compound contents were as shown in Table 1. did. As the first compound, 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl (hereinafter also referred to as “TEMPOL”) was used.

<Preparation of transparent protective film A>

A commercially available cellulose acylate film (“TD40” manufactured by Fuji Film Co., Ltd., thickness 40 μm) is immersed in a 1.5 mol/L NaOH aqueous solution (saponification solution) maintained at a temperature of 55°C for 2 minutes, and then the cellulose acylate The film was washed with water. After that, it was immersed in a 0.05 mol/L sulfuric acid aqueous solution at a temperature of 25°C for 30 seconds, and then passed through a water washing bath under running water for 30 seconds to bring the cellulose acylate film to a neutral state. Then, water was removed by repeating the removal of water with an air knife three times, and the water was dried by remaining in a drying zone at a temperature of 70°C for 15 seconds to produce a saponified cellulose acylate film, which was used as a transparent protective film A. .

<Production of Polarizer 1>

After bonding the transparent protective film A to both sides of the polarizing element A using the adhesive 1 using a roll bonding machine, it was dried at a temperature of 80°C for 5 minutes to form an adhesive layer, and polarizing plate 1 was obtained. The amount of adhesive 1 used was adjusted so that the thickness of the adhesive layer after drying was 50 nm on both sides.

<Production of polarizers 2 to 5>

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

(Adjustment of moisture content of polarizer (polarizing element))

Polarizers 1 to 5 obtained above were stored for 72 hours under conditions of a temperature of 20°C and a relative humidity of 40%. The moisture content 66 hours, 69 hours, and 72 hours after the start of storage under the above conditions was measured by the Karl Fischer method. Since no change was observed in the values of each water content obtained by measurement, the water content of polarizers 1 to 5 can be considered to be the same as the equilibrium water content in the storage environment for 72 hours. When the moisture content of the polarizing plate reaches equilibrium in a certain storage environment, the moisture content of the polarizing element in the polarizing plate can be considered to have similarly reached equilibrium in that storage environment. Additionally, when the water content of the polarizing element in the polarizing plate reaches equilibrium in a certain storage environment, the water content of the polarizing plate can be considered to have similarly reached equilibrium in that storage environment.

<High temperature durability evaluation>

(Production of samples for evaluation)

An adhesive layer was formed on both sides of polarizers 1 to 5 after adjusting the water content using an acrylic adhesive (manufactured by Lintech Co., Ltd., product number: #7). Samples for evaluation were produced by cutting the absorption axes of polarizers 1 to 5 to a size of 50 mm × 100 mm so that they were parallel to the long sides, and bonding alkali-free glass (“EAGLE did.

(Evaluation of change in transmittance by high temperature endurance test (105°C))

The evaluation sample was autoclaved at a temperature of 50°C and a pressure of 5 kgf/cm2 (490.3 kPa) for 1 hour, and then left in an environment of a temperature of 23°C and a relative humidity of 55% for 24 hours. At this time, the luminance of the evaluation sample was measured using a spectroradiometer (“SR-UL1R” manufactured by Topcon Technohouse Co., Ltd.), and the evaluation sample was placed on the irradiation surface of a backlight module with a luminance of 5000 ㏅/㎡. , the measurement angle was 2 degrees, and the measurement distance was 350 mm. The luminance measured under these conditions was referred to as “luminance L0.” Thereafter, the sample for evaluation was stored in a heating environment at a temperature of 105°C, and the luminance of the sample for evaluation was measured in the same order as above at 24-hour intervals during the storage time of 72 to 240 hours. The measured luminance was referred to as “luminance L1” as 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.

Change in transmittance [%]=100-(Brightness L1/Brightness L0)×100

Based on the storage time under the heating environment required to obtain luminance L1 when the change in transmittance was 5% or more, high-temperature durability was evaluated using the following evaluation criteria. The results are shown in Table 2.

(Evaluation standard)

The storage time of the evaluation sample in a heated environment required until the change in transmittance of the evaluation sample becomes 5% or more is,

Exceeding 240 hours: A

Over 120 hours and up to 240 hours: B

Beyond 72 hours and up to 120 hours: C

Up to 72 hours: D

Claims (12)

A polarizing plate having a polarizing element in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin layer, and a transparent protective film laminated on at least one surface of the polarizing element,
The polarizing element and the transparent protective film are bonded together by an adhesive layer formed of an adhesive containing a first compound and a second compound,
The first compound is a compound having a nitroxy radical or nitroxide group,
A polarizing plate wherein the second compound is a cyclodextrin. The polarizing plate of claim 1, wherein the first compound is an N-oxyl compound. The polarizing plate according to claim 1 or 2, wherein the second compound is at least one selected from the group consisting of α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin. The polarizing plate according to any one of claims 1 to 3, wherein the adhesive includes a polyvinyl alcohol-based resin. The polarizing plate according to claim 4, wherein in the adhesive, the content of the first compound is 0.1 part by mass or more and 400 parts by mass or less with respect to 100 parts by mass of the polyvinyl alcohol-based resin. The polarizing plate according to claim 4 or 5, wherein in the adhesive, the content of the second 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-based resin. The polarizing plate according to any one of claims 1 to 6, wherein the adhesive layer has a thickness of 0.01 μm or more and 7 μm or less. The method according to any one of claims 1 to 7, wherein the polarizing plate is used in an image display device,
In the image display device, a polarizing plate is provided on both sides of the polarizing plate in contact with a solid layer. It has an image display cell, a first adhesive layer laminated on a viewing side surface of the image display cell, and the polarizing plate according to any one of claims 1 to 8 laminated on a viewing side surface of the first adhesive layer. Image display device. The image display device according to claim 9, further comprising a second adhesive layer laminated on a viewing side surface of the polarizing plate, and a transparent member laminated on a viewing side surface of the second adhesive layer. The image display device according to claim 10, wherein the transparent member is a glass plate or a transparent resin plate. The image display device according to claim 10, wherein the transparent member is a touch panel.