WO2023286576A1

WO2023286576A1 - Polarizing plate and image display device using said polarizing plate

Info

Publication number: WO2023286576A1
Application number: PCT/JP2022/025483
Authority: WO
Inventors: 謙一福田; 翔太佐藤
Original assignee: 住友化学株式会社
Priority date: 2021-07-13
Filing date: 2022-06-27
Publication date: 2023-01-19
Also published as: CN117597614A; JP2023012249A; KR20240023418A; TW202309566A

Abstract

The present invention aims to provide a novel polarizing plate that: has an adhesive layer formed from an adhesive that has sufficient pot life during production; and suppresses reduction in transmittance when exposed to high-temperature environments. This polarizing plate has: a polarizing element that is obtained by causing a dichroic pigment to be adsorbed and aligned on a polyvinyl alcohol resin layer; and a transparent protective film that is laminated on at least one surface of the polarizing element. The polarizing element and the transparent protective film are joined to each other by an adhesive layer that is formed from an adhesive containing a first compound, a second compound, and a third compound. The first compound is at least one type selected from the group consisting of urea, a urea derivative, thiourea, and a thiourea derivative. The second compound is a dialdehyde. The third compound is a dicarboxylic acid.

Description

Polarizing plate and image display device using the polarizing plate

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

　Liquid crystal display devices (LCDs) are widely used not only for liquid crystal televisions, but also for mobile applications such as personal computers and mobile phones, and in-vehicle applications such as car navigation systems. Generally, a liquid crystal display device has a liquid crystal panel in which polarizing plates are attached to both sides of a liquid crystal cell with an adhesive, and display is performed by controlling light from a backlight with the liquid crystal panel. In recent years, like liquid crystal display devices, organic EL display devices have also been widely used for mobile applications such as televisions and mobile phones, and in-vehicle applications such as car navigation systems. In the organic EL display device, a circular polarizing plate (a polarizing element and a λ/4 plate) is provided on the viewing side surface of the image display panel in order to prevent external light from being reflected by the metal electrode (cathode) and viewed as a mirror surface. ) may be placed.

In the polarizing plate, a polyvinyl alcohol-based resin adhesive is used for bonding the polarizing element and the protective film, since good adhesiveness can be obtained. However, Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2005-189615) points out that a polyvinyl alcohol-based resin adhesive cannot provide a sufficient pot life. Poor pot life means that the adhesive has a short shelf life. Patent Document 2 (Japanese Patent Application Laid-Open No. 2010-276673) describes that a pot life sufficient for production can be obtained by using an adhesive to which maleic acid is added together with a cross-linking agent.

As described above, polarizing plates are increasingly used in vehicles as components of image display devices such as liquid crystal display devices and organic EL display devices. Compared to mobile applications such as televisions and mobile phones, polarizing plates used in in-vehicle image display devices are often exposed to high-temperature environments. gender) is required.

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

In such a configuration, if an air layer exists between the image display panel and a transparent member such as a front panel or a touch panel, external light is reflected due to light reflection at the interface of the air layer, resulting in poor screen visibility. tend to decline. Therefore, the space between the polarizing plate and the transparent member arranged on the viewing side surface of the image display panel is a layer other than the air layer and is usually a solid layer (hereinafter sometimes referred to as an "interlayer filler". ) (hereinafter sometimes referred to as “interlayer filling configuration”). The interlayer filler is preferably a material having a refractive index close to that of the polarizing plate or transparent member. As the interlayer filler, a pressure-sensitive adhesive or a UV curable adhesive is used for the purpose of suppressing deterioration of visibility due to reflection at the interface and bonding and fixing between each member (for example, Japanese Patent Application Laid-Open No. 11-174417 (See Patent Document 3)).

The interlayer filling structure is being widely adopted for mobile applications such as mobile phones, which are often used outdoors. In addition, due to the increasing demand for visibility in recent years, in vehicle applications such as car navigation systems, 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 an adhesive layer or the like. Adoption of an interlayer filling configuration is being considered.

However, it has been reported that when adopting such a configuration, the transmittance of the polarizing plate significantly decreases in a high-temperature environment. In JP 2014-102353 A (Patent Document 4), as a solution to the problem, the water content per unit area of the polarizing plate is set to a predetermined amount or less, and the saturated water absorption amount of the transparent protective film adjacent to the polarizing element is It proposes a method of suppressing a decrease in transmittance by setting the amount to a predetermined amount or less.

JP 2005-189615 A JP 2010-276673 A JP-A-11-174417 JP 2014-102353 A

The present invention provides a novel polarizing plate having an adhesive layer formed from an adhesive having a sufficient pot life for production and suppressing a decrease in transmittance when exposed to a high-temperature environment, and the polarizing plate. An object of the present invention is to provide an image display device using the and an adhesive.

The present invention provides a polarizing plate and an image display device exemplified below.
[1] A polarizing plate having a polarizing element in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin layer, and a transparent protective film laminated on at least one 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 a first compound, a second compound, and a third compound,
The first compound is at least one selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives,
the second compound is a dialdehyde,
The polarizing plate, wherein the third compound is a dicarboxylic acid.
[2] The polarizing plate of [1], wherein the adhesive contains a polyvinyl alcohol-based resin.
[3] The polarizing plate according to [2], wherein the content of the third compound in the adhesive is 0.01 parts by mass or more and 400 parts by mass or less with respect to 100 parts by mass of the polyvinyl alcohol-based resin.
[4] Described in [2] or [3], wherein the content of the first compound in the adhesive is 0.1 parts by mass or more and 400 parts by mass or less with respect to 100 parts by mass of the polyvinyl alcohol-based resin polarizer.
[5] Any one of [2] to [4], wherein the content of the second compound in the adhesive is 0.03 parts by mass or more and 20 parts by mass or less with respect to 1 part by mass of the first compound. The polarizing plate according to item 1.
[6] The polarizing plate of any one of [1] to [5], wherein the dialdehyde is glyoxal.
[7] The polarizing plate of 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 is used in an image display device,
The polarizing plate according to any one of [1] to [7], wherein in the image display device, solid layers are provided in contact with both surfaces of the polarizing plate.
[9] An image display cell, a first adhesive layer laminated on the viewer side surface of the image display cell, and any of [1] to [8] laminated on the viewer side surface of the first adhesive layer 1. An image display device comprising the polarizing plate according to claim 1.
[10] The image display according to [9], further comprising a second adhesive layer laminated on the viewer-side surface of the polarizing plate, and a transparent member laminated on the viewer-side surface of the second adhesive layer. Device.
[11] The image display device of [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.
[13] containing a first compound, a second compound, and a third compound,
The first compound is at least one selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives,
the second compound is a dialdehyde,
The adhesive, wherein the third compound is a dicarboxylic acid.

According to the present invention, there is provided a polarizing plate which has an adhesive layer formed from an adhesive having a pot life sufficient for production and which suppresses a decrease in transmittance when exposed to a high-temperature environment. becomes possible. Furthermore, 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.

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

[Polarizer]
A polarizing plate according to an embodiment of the present invention has a polarizing element in which a dichroic dye is adsorbed and oriented in a layer containing a polyvinyl alcohol-based resin, and a transparent protective film. The polarizing element and the transparent protective film are bonded together by an adhesive layer formed from an adhesive containing the first compound, the second compound and the third compound.

The first compound is at least one selected from the group consisting of urea, urea derivatives, thiourea and thiourea derivatives. The second compound is a dialdehyde. A third compound is a dicarboxylic acid.

As a conventional polarizing plate excellent in high-temperature durability, for example, a polarizing plate is known in which a 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 with such a polarizing plate, when it is used in an interlayer filling structure, if it is left in an environment at a temperature of 105° C., the transmittance may be remarkably lowered at the central portion of the plane of the polarizing plate. The significant decrease in the transmittance of the polarizing plate in a high-temperature environment is due to an interlayer filling structure in which one surface of the polarizing plate is bonded to the image display cell and the other surface is bonded to a transparent member such as a touch panel or front panel. is exposed to a high-temperature environment.

A polarizing plate with a significantly reduced transmittance due to an interlayer filling structure has peaks near 1100 cm ⁻¹ (derived from =C—C= bond) and near 1500 cm ⁻¹ (derived from −C═C− bond) in Raman spectroscopic measurement. It is considered that a polyene structure (-C=C) _n - is formed. It is presumed that the polyene structure is produced by dehydration of polyvinyl alcohol constituting the polarizing element into polyene (Patent Document 4, paragraph [0012]).

The polarizing plate according to the present invention can further improve high temperature durability. The polarizing plate according to the present invention is incorporated in an image display device having an interlayer filling structure, and can suppress a decrease in transmittance even when exposed to a high temperature environment of, for example, 105°C. Such an effect is said to be due to the synergistic action of the first compound, the second compound and the third compound present in the adhesive layer, which suppresses polyenization of the polyvinyl alcohol constituting the polarizing element. guessed. Such an effect is exhibited not only when the water content of the polarizing plate is low, but also when the water content of the polarizing plate is high.

The polarizing plate according to the present invention preferably has at least one of the following characteristics (a) and (b).
(a) The moisture content of the polarizing element is equal to or higher than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 30%, and is equal to or lower than the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 70%.
(b) The water content of the polarizing plate is equal to or higher than the equilibrium water content at a temperature of 20°C and a relative humidity of 30%, and is equal to or lower than the equilibrium water content at a temperature of 20°C and a relative humidity of 70%.

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

PVA-based resin is obtained by saponifying polyvinyl acetate-based resin. Polyvinyl acetate-based resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate with other monomers copolymerizable therewith. Other copolymerizable monomers include, for example, unsaturated carboxylic acids, olefins such as ethylene, vinyl ethers, unsaturated sulfonic acids and the like.

The PVA-based resin layer is preferably formed from a PVA-based resin having a boron adsorption rate of 5.70% by mass or more. That is, the PVA-based resin has a boron adsorption rate of 5.70% by mass or more in the raw material stage before being dyed or stretched. By using such a PVA-based resin, the transmittance is less likely to decrease even when exposed to a high temperature environment of 105° C., for example. Moreover, the boron adsorption rate of the PVA-based resin is preferably 10% by mass or less. By using such a PVA-based resin to produce a polarizing element, the boric acid concentration in the boric acid treatment tank does not have to be high, and the boric acid treatment time can be shortened. of the polarizing element can be easily obtained, and the productivity of the polarizing element can also be improved. When the boron adsorption rate of the PVA-based resin is 10% by mass or less, an appropriate amount of boron is incorporated into the PVA-based resin layer, and the shrinkage force of the polarizing element can be easily reduced. As a result, when incorporated into an image display device, problems such as separation between the polarizing plate and other members such as the front plate are less likely to occur. The boron adsorption rate of the PVA-based resin can be measured by the method described in Examples below.

The boron adsorption rate of PVA-based resin is a property that reflects the spacing between molecular chains and the crystal structure in PVA-based resin. A PVA-based resin having a boron adsorption rate of 5.70% by mass or more has a wider spacing between molecular chains than a PVA-based resin having a boron adsorption rate of less than 5.70% by mass, and the crystals of the PVA-based resin are It is thought that there are few. Therefore, it is presumed that boron, first metal ions, and second metal ions are likely to enter the PVA-based resin layer, and polyene formation is likely to be prevented in a high-temperature environment.

The boron adsorption rate of the PVA-based resin can be obtained, for example, by subjecting the PVA-based resin to pretreatment such as hot water treatment, acid solution treatment, ultrasonic irradiation treatment, and radiation irradiation treatment at the stage before manufacturing the polarizing element. can be adjusted by These treatments can widen the distance between molecular chains and destroy the crystal structure in the PVA-based resin. The hot water treatment includes, for example, immersion in pure water of 30° C. to 100° C. for 1 second to 90 seconds and drying. The acid solution treatment includes, for example, immersion in an aqueous solution of boric acid having a concentration of 10% by mass to 20% by mass for 1 second to 90 seconds, followed by drying. As the ultrasonic treatment, for example, ultrasonic waves having a frequency of 20 to 29 kc are applied at an output of 200 W to 500 W for 30 seconds to 10 minutes. Sonication can be performed in a solvent such as water.

The degree of saponification 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 degree of polymerization of the PVA-based resin is, for example, 1000 or more and 10000 or less, preferably 1500 or more and 5000 or less. The PVA-based resin may be modified, for example, aldehyde-modified polyvinyl formal, polyvinyl acetal, polyvinyl butyral, or the like.

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 is possible to suppress the influence of the polyene conversion of the PVA-based resin on the deterioration of the optical properties in a high-temperature environment. When the thickness of the polarizing element is 3 μm or more, it becomes easy to achieve the desired optical characteristics.

The polarizing element preferably contains a first compound, a second compound, and a third compound. In the present embodiment, since the polarizing element and the transparent protective film are bonded together by an adhesive layer formed from an adhesive containing the first compound, the second compound, and the third compound, the adhesive layer It is presumed that a portion of the first compound, a portion of the second compound, and a portion of the third compound migrated from the polarizer are contained in the polarizing element. The first compound, the second compound and the third compound in the polarizing element may contain those added during the manufacturing process of the polarizing element. By providing the adhesive layer containing the first compound, the second compound, and the third compound, the transmittance is less likely to decrease even when the polarizing plate is exposed to a high-temperature environment. Further, by providing the adhesive layer containing the first compound, the second compound, and the third compound, it is possible to suppress the deterioration of the degree of polarization even when the polarizing plate is exposed to a high-temperature environment. When two polarizing plates are arranged in a crossed Nicols relationship and used, if the degree of polarization of the polarizing plates decreases, light leakage (hereinafter also referred to as “cross leakage”) is likely to occur. , the degree of polarization is less likely to decrease even when exposed to a high-temperature environment, making it easier to suppress cross drop-out. It is presumed that the synergistic effect of the first compound, the second compound, and the third compound contained in the polarizing element suppresses polyenization of the PVA-based resin.

As a method for incorporating the first compound, the second compound and the third compound when manufacturing the polarizing element, a PVA-based resin layer is added to a treatment solvent containing the first compound and/or the second compound and/or the third compound. or a method of spraying, flowing or dripping the treatment solvent onto the PVA-based resin layer. Among these, a method of immersing the PVA-based resin layer in a treatment solvent containing all of the first compound, the second compound and the third compound is preferably used. Specific examples of the first compound, the second compound, and the third compound include those exemplified as those to be contained in the adhesive described later.

The step of immersing the PVA-based resin layer in the treatment solvent containing the first compound, the second compound and the third compound is performed simultaneously with the steps of swelling, stretching, dyeing, cross-linking, washing, etc. in the manufacturing method of the polarizing element described below. may be provided separately from these steps. The step of adding the first compound, the second compound and the third compound to the PVA-based resin layer is preferably performed after dyeing the PVA-based resin layer with iodine, and more preferably performed simultaneously with the cross-linking step after dyeing. According to such a method, the change in hue is small, and the influence on the optical characteristics of the polarizing element can be reduced.

In order to make the polarizing element contain the first compound, the second compound, and the third compound, both the addition during the production of the polarizing element and the addition to the adhesive may be performed. For example, an adhesive containing a first compound, a second compound, and a third compound is used, and at least one of the first compound, the second compound, and the third compound is added during the production of the polarizing element. may have been

(First compound)
The first compound is at least one selected from the group consisting of urea, urea derivatives, thiourea and thiourea derivatives. A 1st compound can be used individually by 1 type or in combination of 2 or more types. The first compound may be water-soluble or poorly water-soluble, and either of the first compounds may be used. When the sparingly water-soluble first compound is used for the water-soluble adhesive, it is preferable to devise a dispersion method so as not to increase the haze after forming the adhesive layer.

(urea derivative)
A urea derivative is a compound in which at least one of the four hydrogen atoms in a urea molecule is substituted with a substituent. In this case, the substituents are not particularly limited, but substituents consisting of carbon, hydrogen and oxygen atoms are preferred.

Specific examples of urea derivatives include monosubstituted urea such as methylurea, ethylurea, propylurea, butylurea, isobutylurea, N-octadecylurea, 2-hydroxyethylurea, hydroxyurea, acetylurea, allylurea, and 2-propynyl. Urea, cyclohexyl urea, phenyl urea, 3-hydroxyphenyl urea, (4-methoxyphenyl) urea, benzyl urea, benzoyl urea, o-tolyl urea, p-tolyl urea.

Disubstituted urea, 1,1-dimethylurea, 1,3-dimethylurea, 1,1-diethylurea, 1,3-diethylurea, 1,3-bis(hydroxymethyl)urea, 1,3-tert- Butylurea, 1,3-dicyclohexylurea, 1,3-diphenylurea, 1,3-bis(4-methoxyphenyl)urea, 1-acetyl-3-methylurea, 2-imidazolidinone (ethyleneurea), tetrahydro -2-pyrimidinone (propylene urea).

Tetramethylurea, 1,1,3,3-tetraethylurea, 1,1,3,3-tetrabutylurea, 1,3-dimethoxy-1,3-dimethylurea, 1,3-dimethyl- 2-imidazolidinone, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone.

(thiourea derivative)
A thiourea derivative is a compound in which at least one of four hydrogen atoms in a thiourea molecule is substituted with a substituent. In this case, the substituents are not particularly limited, but substituents consisting of carbon, hydrogen and oxygen atoms are preferred.

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

Disubstituted thiourea, 1,1-dimethylthiourea, 1,3-dimethylthiourea, 1,1-diethylthiourea, 1,3-diethylthiourea, 1,3-dibutylthiourea, 1,3-diisopropylthiourea, 1 ,3-dicyclohexylthiourea, N,N-diphenylthiourea, N,N'-diphenylthiourea, 1,3-di(o-tolyl)thiourea, 1,3-di(p-tolyl)thiourea, 1-benzyl-3-phenylthiourea, 1-methyl-3-phenylthiourea, N-allyl-N'-(2-hydroxyethyl)thiourea, ethylenethiourea.

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

Among the first compounds, when used in an image display device having an interlayer filling structure, the decrease in transmittance in a high-temperature environment is suppressed and the decrease in the degree of polarization is small (the cross dropout is suppressed). , urea derivatives or thiourea derivatives are preferred, and urea derivatives are more preferred. Among the urea derivatives, mono-substituted urea or di-substituted urea is preferred, and mono-substituted urea is more preferred. Disubstituted urea includes 1,1-substituted urea and 1,3-substituted urea, with 1,3-substituted urea being more preferred.

(Second compound)
The second compound is a dialdehyde. Dialdehydes include, for example, glyoxal, propanedial (malondialdehyde), butanedial (succinaldehyde), and the like. Glyoxal, which has a simple structure and is highly reactive, is particularly preferred. Although glyoxal may be described below, conventionally known dialdehydes can be used as described above, and the dialdehyde is not limited to glyoxal.

(Third compound)
A third compound is a dicarboxylic acid. Examples of dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, tartaric acid, glutamic acid, malic acid, Maleic acid, fumaric acid, itaconic acid, muconic acid, 1,4-cyclohexanedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 4,4'-biphenyl dicarboxylic acids, 2,5-pyridinedicarboxylic acid, 3,5-pyridinedicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenylmethanedicarboxylic acid, oxaloacetic acid, methylfumaric acid, 2,6-pyridinedicarboxylic acid and the like. Among these, it is preferable to use citric acid, malic acid, maleic acid or tartaric acid. These dicarboxylic acids can be used singly or in combination of two or more.

The polarizing element usually contains potassium ions (also called "first metal ions"), and preferably contains metal ions other than potassium ions (also called "second metal ions"). The content of the second metal ion in the polarizing element is preferably 0.05% by mass or more and 10.0% by mass or less, more preferably 0.05% by mass or more and 8.0% by mass or less, and still more preferably It is 0.1 mass % or more and 6.0 mass % or less. If the second metal ion content of the polarizing element exceeds 10.0% by mass, the degree of polarization may decrease in a high-temperature, high-humidity environment. Moreover, when the content of the second metal ion is less than 0.05% by mass, the effect of improving the durability in a high-temperature environment may not be sufficient. The content of the second metal ions in the polarizing element is calculated as the mass fraction (% by mass) of the metal element with respect to the mass of the polarizing element by, for example, inductively coupled plasma (ICP) emission spectrometry. be able to. The metal element is considered to exist in the polarizing element in the form of a metal ion or in a state in which it forms a crosslinked structure with the constituent elements of the polyvinyl alcohol-based resin. is the value of

The second metal ions are not limited as long as they are metal ions other than potassium ions, and are preferably ions of metals other than alkali metals. , aluminum, copper, manganese, and iron. Among these metal ions, zinc ions are preferred from the viewpoint of adjusting color tone and imparting heat resistance.

The content of boron in the polarizing element is preferably 2.4% by mass or more. The boron content is preferably 3.9% by mass or more and 8.0% by mass or less, more preferably 4.2% by mass or more and 7.0% by mass or less, still more preferably 4.4% by mass or more and 6.0% by mass or more. It is 0% by mass or less. When the boron content of the polarizing element exceeds 8.0% by mass, the shrinkage force of the polarizing element increases, and the polarizing element is peeled off from other members such as a front plate that are bonded together when incorporated into an image display device. may cause problems such as If the boron content is less than 2.4% by mass, desired optical properties may not be achieved. The content of boron in the polarizing element can be calculated as a mass fraction (% by mass) of boron with respect to the mass of the polarizing element by, for example, inductively coupled plasma (ICP) emission spectrometry. Boron is considered to be present in the polarizing element in a state in which boric acid or a crosslinked structure is formed with the constituent elements of the polyvinyl alcohol-based resin. value.

When the content of boron in the polarizing element is 2.4% by mass or more and 8.0% by mass or less, the decrease in transmittance is further reduced even when exposed to a high-temperature environment as a component of an image display device having an interlayer filling structure. Suppressed. This is because when the polarizing element has a boron content of 2.4% by mass or more and 8.0% by mass or less, polyene formation is less likely to occur even in a high-temperature environment, and a decrease in transmittance is suppressed. It is assumed that

The content of potassium ions in the polarizing element is preferably 0.28% by mass or more, more preferably 0.32% by mass or more, from the viewpoint of suppressing deterioration of the optical properties of the polarizing element in a high-temperature environment. It is preferably 0.34% by mass or more, more preferably 0.34% by mass or more, and preferably 0.60% by mass or less, and 0.55% by mass or less from the viewpoint of suppressing hue change in a high-temperature environment. is more preferable, and 0.50% by mass or less is even more preferable. The content of potassium ions can be measured in the same manner as the content of the second metal ions, and the content of potassium ions here is the value in terms of potassium atoms.

(Manufacturing method of polarizing element)
The manufacturing method of the polarizing element is not particularly limited, but a method in which a pre-rolled PVA-based resin film is sent out and subjected to stretching, dyeing, cross-linking, etc. (hereinafter referred to as "manufacturing method 1"), A method comprising a step of applying a coating liquid containing a PVA-based resin onto a substrate film to form a PVA-based resin layer as a coating layer, and stretching the obtained laminate (hereinafter referred to as "manufacturing method 2" ) are typical.

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

The swelling process is a treatment process in which the PVA-based resin film is immersed in a swelling bath. The swelling step can remove stains, blocking agents, and the like on the surface of the PVA-based resin film, and swelling the PVA-based resin film can suppress uneven dyeing. A medium containing water as a main component, such as water, distilled water, or pure water, is usually used for the swelling bath. Surfactants, alcohols and the like may be appropriately added to the swelling bath according to conventional methods. Potassium iodide may be used in the swelling bath from the viewpoint of controlling the potassium content of the polarizing element. In this case, the concentration of potassium iodide in the swelling bath should be 1.5% by mass or less. It is preferably 1.0% by mass or less, more preferably 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 unconditionally determined because the degree of swelling of the PVA-based resin film is affected by the temperature of the swelling bath. and more preferably 20 seconds or more and 100 seconds or less. The swelling step may be performed only once, or may be performed multiple times as necessary.

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

The concentration of iodine in the dyeing bath is preferably 0.01% by mass or more and 1% by mass or less, more preferably 0.02% by mass or more and 0.5% by mass or less. The concentration of iodide in the dyeing bath is preferably 0.01% by mass or more and 10% by mass or less, more preferably 0.05% by mass or more and 5% by mass or less, and 0.1% by mass or more and 3 % by mass or less is more preferable.

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 unconditionally determined because the degree of dyeing of the PVA-based resin film is affected by the temperature of the dyeing bath, but it is preferably 10 seconds or more and 300 seconds or less, and 20 seconds or more and 240 seconds or less. is more preferable. The dyeing step may be performed only once, or may be performed multiple times as necessary.

The cross-linking step is a treatment step in which the PVA-based resin film dyed in the dyeing step is immersed in a treatment bath (cross-linking bath) containing a boron compound. Molecules or dye molecules can adsorb to the crosslinked structures. Boron compounds include, for example, boric acid, borates, and borax. The cross-linking bath is generally an aqueous solution, but may be a mixed solution of an organic solvent miscible with water and water. The cross-linking 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 cross-linking bath is preferably 1% by mass or more and 15% by mass or less, more preferably 1.5% by mass or more and 10% by mass or less, and 2% by mass or more and 5% by mass or less. It is more preferable to have When potassium iodide is used in the cross-linking bath, the concentration of potassium iodide in the cross-linking bath is preferably 1% by mass or more and 15% by mass or less, and is preferably 1.5% by mass or more and 10% by mass or less. More preferably, it is 2% by mass or more and 5% by mass or less.

The temperature of the cross-linking bath is preferably 20°C or higher and 70°C or lower, more preferably 30°C or higher and 60°C or lower. The immersion time in the cross-linking bath cannot be unconditionally determined because the degree of cross-linking of the PVA-based resin film is affected by the temperature of the cross-linking bath, but it is preferably 5 seconds or more and 300 seconds or less, and 10 seconds or more and 200 seconds or less. is more preferable.
The cross-linking step may be performed only once, or may be performed multiple times as necessary.

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

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

The temperature of the drawing bath is preferably 25 to 80°C, more preferably 40 to 80°C, even more preferably 50 to 75°C, and particularly preferably 65 to 75°C. The immersion time in the stretching bath cannot be unconditionally determined because the degree of stretching of the PVA-based resin film is affected by the temperature of the stretching bath. is more preferable. The stretching treatment in the wet stretching method may be performed together with one or more of the swelling process, dyeing process, cross-linking process and washing process.

Examples of the dry drawing method include a roll-to-roll drawing method, a heating roll drawing method, a compression drawing method, and the like. The dry stretching method may be applied together with the drying process.

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

The washing process is a treatment process in which the polyvinyl alcohol-based resin film is immersed in a washing bath, and foreign substances remaining on the surface of the polyvinyl alcohol-based resin film can be removed. As the cleaning bath, a medium containing water as a main component, such as water, distilled water, or pure water, is usually used. Also, from the viewpoint of controlling the potassium content in the polarizing element, it is preferable to use potassium iodide in the cleaning bath. In this case, the concentration of potassium iodide in the cleaning bath is 1% by mass or more and 10% by mass. is preferably 1.5% by mass or more and 4% by mass or less, more preferably 1.8% by mass or more and 3.8% by 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 cleaning bath cannot be unconditionally determined because the degree of cleaning of the PVA-based resin film is affected by the temperature of the cleaning bath. and more preferably 3 seconds or more and 20 seconds or less. The washing step may be performed only once, or may be performed multiple times as necessary.

Furthermore, it is preferable to have a metal ion treatment step in the above steps or as a separate step from the above steps. The metal ion treatment step is performed by immersing the polyvinyl alcohol-based resin film in an aqueous solution containing a metal salt of the second metal ion. The second metal ion is incorporated into the polyvinyl alcohol-based resin film by the metal ion treatment step.

The second metal ions are not limited as long as they are metal ions other than potassium ions, and are preferably ions of metals other than alkali metals. , aluminum, copper, manganese, and iron. Among these metal ions, zinc ions are preferred from the viewpoint of adjusting color tone and imparting heat resistance. Zinc salts include zinc halides such as zinc chloride and zinc iodide, zinc sulfate, zinc acetate, and the like.

A metal salt solution is used in the metal ion treatment process. Immersion treatment in a zinc-containing solution will be described below as a typical example of using a zinc salt aqueous solution among the metal ion treatment steps.

The zinc ion concentration in the zinc salt aqueous solution is in the range of 0.1 to 10% by mass, preferably 0.3 to 7% by mass. As the zinc salt solution, it is preferable to use an aqueous solution containing potassium ions and iodine ions with potassium iodide or the like, since it is easy to impregnate with zinc ions. The concentration of potassium iodide in the zinc salt solution is preferably 0.1-10 mass %, more preferably 0.2-5 mass %.

In the immersion treatment in the zinc-containing solution, the temperature of the zinc salt solution is usually 15-85°C, preferably 25-70°C. The immersion time is usually in the range of 1 to 120 seconds, preferably 3 to 90 seconds. In the immersion treatment in the zinc-containing solution, the zinc content in the polyvinyl alcohol resin film can be adjusted by adjusting the conditions such as the concentration of the zinc salt solution, the immersion temperature of the polyvinyl alcohol resin film in the zinc salt solution, and the immersion time. Adjust so that it falls within the above range. There are no particular restrictions on when the immersion treatment in the zinc-containing solution is performed. The immersion treatment in the zinc-containing liquid may be performed alone, or a zinc salt may coexist in the dyeing bath, the cross-linking bath, and the stretching bath, and at least one step of the dyeing step, the cross-linking step, and the stretching step may be performed. You can go at the same time.

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 appropriate method, such as natural drying, air drying, and heat drying.

Production method 2 includes a step of applying a coating liquid containing a PVA-based resin onto a substrate film, a step of uniaxially stretching the obtained laminated film, and a PVA-based resin layer of the uniaxially stretched laminated film with a dichroic dye. It can be produced through a step of dyeing to adsorb a polarizing element, a step of treating a film on which a dichroic dye is adsorbed with an aqueous boric acid solution, and a step of washing with water after treatment with an aqueous boric acid solution. The base film used to form the polarizing element may be used as a protective layer for the polarizing element. If necessary, the base film may be peeled off from the polarizing element.

<Transparent protective film>
The transparent protective film (hereinafter also simply referred to as "protective film") used in this embodiment is attached to at least one surface of the polarizing element via an adhesive layer. The transparent protective film is laminated on one side or both sides of the polarizing element, preferably on both sides.

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

As the protective film, a film such as a cellulose acylate film, a polycarbonate resin film, a cycloolefin resin film such as norbornene, a (meth)acrylic polymer film, or a polyester resin film such as polyethylene terephthalate is used. be able to. When a water-based adhesive such as PVA is used to attach protective films to both sides of the polarizing element, the protective film on at least one side is either a cellulose acylate film or a (meth)acrylic polymer film in terms of moisture permeability. Among them, a cellulose acylate film is preferred.

At least one protective film may have a retardation function for the purpose of viewing angle compensation. In that case, the protective film itself may have a retardation function, may have a separate retardation layer, or may be a combination of both. A film having a retardation function may be directly bonded to the polarizing element via an adhesive, but may be bonded via a pressure-sensitive adhesive or adhesive via another protective film bonded to the polarizing element. configuration may be used.

<Adhesive layer>
The adhesive layer for bonding the protective film to the polarizing element is formed from the following adhesives.

(glue)
The adhesive contains a first compound, a second compound and a third compound. The adhesive is not limited and may be a water-based adhesive, a solvent-based adhesive, an active energy ray-curable adhesive, or the like, but is preferably a water-based adhesive and preferably contains a PVA-based resin. By forming an adhesive layer for bonding the polarizing element and the protective film using an adhesive containing the first compound, the second compound, and the third compound, the transmittance of the polarizing plate in a high-temperature environment can be suppressed. Also, by using an adhesive containing the second compound and the third compound, the adhesive can have a pot life sufficient for production. The application of the adhesive according to the present invention is not limited, and it is preferably used in optical elements, such as bonding a polarizing element and a protective film.

The thickness of the adhesive when applied can be set to any value, for example, it can be set so that an adhesive layer having a desired thickness is obtained after curing or after heating (drying). The thickness of the adhesive layer composed of the adhesive is preferably 0.01 μm or more and 7 μm or less, more preferably 0.01 μm or more and 5 μm or less, still more preferably 0.01 μm or more and 2 μm or less, and most preferably. is 0.01 μm or more and 1 μm or less.

When the adhesive is a water-based adhesive containing a PVA-based resin, the content of the third compound is, for example, 0.01 parts by mass or more and 400 parts by mass or less, preferably 0, with respect to 100 parts by mass of the PVA-based resin. 0.05 parts by mass or more and 50 parts by mass or less, more preferably 0.1 parts by mass or more and 10 parts by mass or less. If it is less than 0.01 parts by mass, the effect of improving the pot life may not be sufficient, or the effect of suppressing polyene conversion of the polarizing element in a high-temperature environment may not be sufficient. On the other hand, if it exceeds 400 parts by mass, the third compound may precipitate after the polarizing plate is produced.

When the adhesive is a water-based adhesive containing a PVA-based resin, the content of the first compound is preferably 0.1 parts by mass or more and 400 parts by mass or less, more preferably 100 parts by mass of the PVA-based resin. is 1 part by mass or more and 200 parts by mass or less, more preferably 3 parts by mass or more and 100 parts by mass or less. If it is less than 0.1 part by mass, the effect of suppressing polyenization of the polarizing element in a high-temperature environment may not be sufficient. On the other hand, if it exceeds 400 parts by mass, the first compound may precipitate after the polarizing plate is produced, resulting in an increase in haze.

When the adhesive is a water-based adhesive containing a PVA-based resin, the content of the second compound is preferably 1 part by mass or more and 60 parts by mass or less, more preferably 1 part by mass or more, with respect to 100 parts by mass of the PVA-based resin. .5 parts by mass or more and 50 parts by mass or less, more preferably 2 parts by mass or more and 45 parts by mass or less. If it is less than 1 part by mass, the effect of improving water resistance may not be sufficient. On the other hand, if it exceeds 60 parts by mass, the liquid preparation stability of the adhesive may deteriorate.

In the adhesive, the content of the dialdehyde, which is the second compound, is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, relative to 1 part by mass of the urea-based compound, which is the first compound, More preferably, it is 10 parts by mass or less, and although the lower limit is not limited, it is, for example, 0.03 parts by mass or more. When the content ratio of the urea-based compound and the dialdehyde in the adhesive is within the above range, it becomes easy to achieve both the effect of improving the high-temperature durability due to the urea-based compound and the effect of improving the adhesiveness due to the dialdehyde. It is understood that the water resistance improvement effect is obtained due to the adhesiveness improvement effect of the dialdehyde. If the dialdehyde content exceeds 20 parts by mass with respect to 1 part by mass of the urea-based compound, the urea-based compound may not sufficiently exhibit the effect of improving high-temperature durability. It can be considered that the content ratio of the urea-based compound and dialdehyde in the adhesive is the same as the content ratio of the urea-based compound and dialdehyde in the adhesive layer.

In the adhesive, the content of the dicarboxylic acid, which is the third compound, is preferably 0.001 parts by mass or more and 100 parts by mass or less, preferably 0.01 part by mass, relative to 1 part by mass of the dialdehyde, which is the second compound. It is more than 80 parts by mass and less than 80 parts by mass. If it is less than 0.001 part by mass, the effect of improving the pot life may not be sufficient. On the other hand, if it exceeds 100 parts by mass, the third compound may precipitate after the polarizing plate is produced.

When the above adhesive is used to form an adhesive layer for bonding the polarizing element and the protective film, the polarizing element to be bonded contains the first compound, the second compound, and the third compound. The amounts of these compounds contained in the adhesive may be appropriately adjusted depending on whether or not they are contained.

In the structure in which the transparent protective film is laminated on both sides of the polarizing element via an adhesive layer, only the adhesive layer on one side of the adhesive layers on both sides of the polarizing element contains the first compound, the second compound, and the third compound. It may be a layer containing a compound, but it is preferable that both adhesive layers are layers containing a first compound, a second compound and a third 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. Also in this configuration, the transparent protective film is laminated via the adhesive layer containing the first compound, the second compound and the third compound. As a method for producing such a polarizing plate having a transparent protective film only on one side of the polarizing element, first, a polarizing plate is produced by laminating transparent protective films on both sides via an adhesive layer, and then one transparent protective film is prepared. can be considered. When such a manufacturing method is used, only one of the adhesive layers may contain the first compound, the second compound and the third compound, but both adhesive layers may contain the first compound. It is preferably a layer containing a compound, a second compound and a third compound. When only one adhesive layer contains the first compound, the second compound and the third compound, the adhesive layer on the side of the film that is not peeled preferably contains the first compound, the second compound and the third compound. .

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

As the PVA-based resin contained in the water-based adhesive, one containing an acetoacetyl group is preferable, because it has excellent adhesion between the PVA-based resin layer and the protective film and is excellent in durability. An acetoacetyl group-containing PVA-based resin can be obtained, for example, by reacting a PVA-based resin with diketene by any method. The acetoacetyl group modification degree of the acetoacetyl group-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 water-based adhesive is preferably 0.1% by mass or more and 15% by mass or less, more preferably 0.5% by mass or more and 10% by mass or less.

The second compound, the dialdehyde, can act as a cross-linking agent. The water-based adhesive can also contain a cross-linking agent other than the second compound. A known cross-linking agent can be used as the cross-linking agent. Examples of cross-linking agents include water-soluble epoxy compounds and isocyanates.

When the PVA-based resin is an acetoacetyl group-containing PVA-based resin, the crosslinking agent is preferably either glyoxylate or methylolmelamine, more preferably glyoxylate.

The water-based adhesive can also contain organic solvents. The organic solvent is preferably alcohols because it is miscible with water, and among alcohols, methanol or ethanol is more preferable. The concentration of methanol in the water-based 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. When the concentration of methanol is 10% by mass or more, it becomes easier to suppress polyene formation of the PVA-based resin in a high-temperature environment. Further, when the content of methanol is 70% by mass or less, deterioration of hue can be suppressed. Some urea derivatives have low solubility in water, but some have sufficient solubility in alcohol. In that case, the urea-based compound is dissolved in alcohol to prepare an alcohol solution of the urea-based compound, and then the alcohol solution of the urea-based compound is added to the PVA aqueous solution to prepare the adhesive. be.

(Active energy ray-curable adhesive)
Active energy ray-curable adhesives are adhesives that are cured by irradiation with active energy rays such as ultraviolet rays. For example, adhesives containing a polymerizable compound and a photopolymerization initiator, adhesives containing a photoreactive resin , an adhesive containing a binder resin and a photoreactive cross-linking 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. Examples of the photopolymerization initiator include compounds containing substances that generate active species such as neutral radicals, anion radicals, and cation radicals upon irradiation with active energy rays such as ultraviolet rays.

<Layer containing first compound, second compound, and third compound>
The first compound, the second compound, and the third compound are not limited to being contained in the adhesive layer as described above, and from the viewpoint of improving the high-temperature durability of the polarizing plate, may be contained in other layers. In the polarizing plate having a transparent protective film only on one side, a cured layer may be laminated on the opposite side of the polarizing element from the transparent protective film, from the viewpoint of improving physical strength. It may be a layer containing two compounds and a third compound.

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

[Configuration of image display device]
The polarizing plate of the present embodiment is used in various image display devices such as liquid crystal display devices and organic EL display devices. Regarding the image display device, when both sides of the polarizing plate are in contact with a layer other than an air layer, specifically a solid layer such as an adhesive layer, the transmittance is reduced in a high temperature environment. tends to decrease. In the image display device using the polarizing plate of this embodiment, even with the interlayer filling structure, it is possible to suppress the decrease in the transmittance of the polarizing plate in a high-temperature environment. As an image display device, a configuration 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 is exemplified. be done. Such an image display device may further have a second pressure-sensitive adhesive layer laminated on the viewer-side surface of the polarizing plate, and a transparent member laminated on the viewer-side surface of the second pressure-sensitive adhesive layer. In particular, in the polarizing plate of the present embodiment, the transparent member is arranged on the viewing side of the image display device, the polarizing plate and the image display cell are bonded together by the first adhesive layer, and the polarizing plate and the transparent member are the second adhesive layer. It is suitably used for an image display device having an interlayer filling structure bonded together by agent layers. In this specification, either one or both of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer may be simply referred to as "pressure-sensitive adhesive layer". The member used for bonding the polarizing plate and the image display cell and the member used for bonding the polarizing plate and the transparent member are not limited to the pressure-sensitive adhesive layer, and may be an adhesive layer. good too.

<Image display cell>
Examples of image display cells include liquid crystal cells and organic EL cells. Liquid crystal cells include reflective liquid crystal cells that use external light, transmissive liquid crystal cells that use light from a light source such as a backlight, and transflective liquid crystal cells that use both external light and light from a light source. Any liquid crystal cell may be used. When the liquid crystal cell uses light from a light source, the image display device (liquid crystal display device) has a polarizing plate arranged on the opposite side of the image display cell (liquid crystal cell) from the viewing side, and a light source is further arranged. be done. It is preferable that the polarizing plate on the light source side and the liquid crystal cell are bonded together via an appropriate pressure-sensitive adhesive layer. As a driving method of the liquid crystal cell, any type such as VA mode, IPS mode, TN mode, STN mode, or bend orientation (π type) can be used.

As the organic EL cell, one having a light emitter (organic electroluminescence light emitter) formed by sequentially laminating a transparent electrode, an organic light emitting layer and a metal electrode on a transparent substrate is preferably used.
The organic light-emitting layer is a laminate of various organic thin films. Various layer structures can be adopted, such as a laminate of an electron injection layer composed of a layer and a perylene derivative or the like, or a laminate of a hole injection layer, a light emitting layer and an electron injection layer.

<Bonding of image display cell and polarizing plate>
An adhesive layer (adhesive sheet) is preferably used for bonding the image display cell and the polarizing plate. Among them, a method of bonding a polarizing plate with an adhesive layer provided on one surface of the polarizing plate to the image display cell is preferable from the viewpoint of workability and the like. Attachment of the pressure-sensitive adhesive layer to the polarizing plate can be performed by an appropriate method. For example, a base polymer or its composition is dissolved or dispersed in a suitable solvent such as toluene or ethyl acetate alone or in a mixture to prepare a pressure-sensitive adhesive solution of 10% by mass or more and 40% by mass or less. , a method of directly applying it on a polarizing plate by an appropriate spreading method such as a casting method or a coating method, a method of forming an adhesive layer on a separator and transferring it to the polarizing plate, and the like.

<Adhesive layer>
The pressure-sensitive adhesive layer may consist of one layer or two or more layers, but preferably consists of one layer. The adhesive layer can be composed of an adhesive composition containing (meth)acrylic resin, rubber resin, urethane resin, ester resin, silicone resin, or polyvinyl ether resin as a main component. Among them, a pressure-sensitive adhesive composition using a (meth)acrylic resin as a base polymer, which is excellent in transparency, weather resistance, heat resistance, etc., is preferable. The adhesive composition may be active energy ray-curable or heat-curable.

The (meth)acrylic resin (base polymer) used in the adhesive composition includes butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and the like. Polymers or copolymers containing one or more of the (meth)acrylic acid esters as monomers are preferably used. Preferably, the base polymer is copolymerized with a polar monomer. Polar monomers include (meth)acrylic acid compounds, 2-hydroxypropyl (meth)acrylate compounds, hydroxyethyl (meth)acrylate compounds, (meth)acrylamide compounds, and N,N-dimethylaminoethyl (meth)acrylate compounds. , glycidyl (meth)acrylate compounds, and other monomers having a carboxyl group, a hydroxyl group, an amide group, an amino group, an epoxy group, and the like.

The adhesive composition may contain only the above base polymer, but usually further contains a cross-linking agent. As a cross-linking agent, a metal ion having a valence of 2 or more and forming a carboxylic acid metal salt with a carboxyl group, a polyamine compound forming an amide bond with a carboxyl group, and a carboxyl group Examples include polyepoxy compounds or polyols that form ester bonds with and polyisocyanate compounds that form amide bonds with carboxyl groups. Among them, polyisocyanate compounds are preferred.

The active energy ray-curable pressure-sensitive adhesive composition has the property of being cured by being irradiated with an active energy ray such as an ultraviolet ray or an electron beam. It has the property that it can be adhered to an adherend and can be cured by irradiation with active energy rays to adjust the adhesion force. The active energy ray-curable pressure-sensitive adhesive composition is preferably UV-curable. The active energy ray-curable pressure-sensitive adhesive composition further contains an active energy ray-polymerizable compound in addition to the base polymer and the cross-linking agent. If necessary, a photopolymerization initiator, a photosensitizer, etc. may be contained.

The adhesive composition contains fine particles for imparting light scattering properties, beads (resin beads, glass beads, etc.), glass fibers, resins other than base polymers, tackifiers, fillers (metal powders and other inorganic powders). etc.), antioxidants, ultraviolet absorbers, dyes, pigments, colorants, antifoaming agents, corrosion inhibitors, photopolymerization initiators, and other additives.

The pressure-sensitive adhesive layer can be formed by applying an organic solvent-diluted solution of the above pressure-sensitive adhesive composition onto the surface of a substrate film, an image display cell or a polarizing plate, and drying. The base film is generally a thermoplastic resin film, and a typical example thereof is a release-treated separate film. The separate film can be, for example, a film made of a resin such as polyethylene terephthalate, polybutylene terephthalate, polycarbonate, polyalate, etc., and the surface on which the pressure-sensitive adhesive layer is formed is subjected to release treatment such as silicone treatment.

A pressure-sensitive adhesive composition may be directly applied to the release-treated surface of the separate film to form a pressure-sensitive adhesive layer, and this pressure-sensitive adhesive layer with a separate film may be laminated on the surface of the polarizer. A pressure-sensitive adhesive layer may be formed by directly coating the pressure-sensitive adhesive composition on the surface of the polarizing plate, and a separate film may be laminated on the outer surface of the pressure-sensitive adhesive layer.

When the pressure-sensitive adhesive layer is provided on the surface of the polarizing plate, it is preferable to subject the bonding surface of the polarizing plate and/or the bonding surface of the pressure-sensitive adhesive layer to surface activation treatment such as plasma treatment and corona treatment. Treatment is more preferred.

Alternatively, a pressure-sensitive adhesive composition is applied onto the second separate film to form a pressure-sensitive adhesive layer, a separate film is laminated on the formed pressure-sensitive adhesive layer to prepare a pressure-sensitive adhesive sheet, and from this pressure-sensitive adhesive sheet the second After peeling off the separate film, the pressure-sensitive adhesive layer with the separate film may be laminated on the polarizing plate. The second separate film is weaker in adhesion to the pressure-sensitive adhesive layer than the separate film and easy to peel off.

Although the thickness of the pressure-sensitive adhesive layer is not particularly limited, 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>
A transparent plate (window layer), a touch panel, and the like are examples of the transparent member arranged on the viewing side of the image display device. 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 a polyimide resin, acrylic resin, or polycarbonate resin, or a glass plate. A functional layer such as an antireflection layer may be laminated on the visible side of the transparent plate. Further, when the transparent plate is a transparent resin plate, a hard coat layer for increasing physical strength and a low moisture permeable layer for decreasing moisture permeability may be laminated. As the touch panel, various types of touch panels such as resistive type, capacitive type, optical type, and ultrasonic type, and glass plates and transparent resin plates having a touch sensor function are used. When a capacitive touch panel is used as the transparent member, it is preferable to provide a transparent plate made of glass or a transparent resin plate on the viewing side of the touch panel.

<Bonding of polarizing plate and transparent member>
A pressure-sensitive adhesive or an active energy ray-curable adhesive is preferably used for bonding the polarizing plate and the transparent member. When an adhesive is used, the attachment of the adhesive can be performed by any appropriate method. A specific attachment method includes, for example, the method of attaching the pressure-sensitive adhesive layer used in bonding the image display cell and the polarizing plate described above.

When an active energy ray-curable adhesive is used, a dam material is provided so as to surround the periphery of the image display panel for the purpose of preventing spreading of the adhesive solution before curing, and a transparent member is placed on the dam material. A method of injecting an adhesive solution is preferably used. After injection of the adhesive solution, alignment and defoaming are performed as necessary, and then curing is performed by irradiating active energy rays.

EXAMPLES The present invention will be specifically described below based on examples. The materials, reagents, amounts and ratios of substances, operations, etc. shown in the following examples can be changed as appropriate without departing from the gist of the present invention.
Accordingly, the present invention is limited and not restricted to the following examples.

(1) Measurement of thickness of polarizing element:
It was measured using a digital micrometer "MH-15M" manufactured by Nikon Corporation.

(2) Measurement of luminosity correction polarization degree of polarizing plate, luminosity correction single transmittance, and hue:
Measurement was performed using a spectrophotometer with an integrating sphere ["V7100" manufactured by JASCO Corporation, 2-degree field of view; C light source].

(3) Measurement of boron content:
0.2 g of the polarizing element was dissolved in 200 g of a 1.9% by mass mannitol aqueous solution. Next, the resulting aqueous solution was titrated with a 1 mol/L sodium hydroxide aqueous solution, and the amount of sodium hydroxide aqueous solution required for neutralization was compared with the calibration curve to calculate the boron content of the polarizing element.

(4) Measurement of zinc ion content:
Nitric acid was added to the precisely weighed polarizing element, and acid decomposition was performed using a microwave sample pretreatment device (ETHOS D) manufactured by Milestone General to obtain a solution as a measurement solution. The zinc ion content was calculated by quantifying the zinc concentration of the measurement solution with an ICP emission spectrometer (5110 ICP-OES) manufactured by Agilent Technologies, and calculating the zinc mass with respect to the polarizing element mass.

(5) Measurement of boron adsorption rate of PVA-based resin film:
A PVA-based resin film cut into 100 mm squares was immersed in pure water at 30° C. for 60 seconds, and then immersed in an aqueous solution containing 5 parts of boric acid at 60° C. for 120 seconds. The PVA-based resin film taken out from the aqueous boric acid solution was dried in an oven at 80° C. for 11 minutes. A boron-containing PVA film was obtained by conditioning the humidity in an environment of 23° C. and 55% RH for 24 hours. 0.2 g of the boron-containing PVA resin film thus obtained was dissolved in 200 g of a 1.9% by mass mannitol aqueous solution. Next, the resulting aqueous solution was titrated with a 1 mol/L sodium hydroxide aqueous solution, and the boron content of the PVA-based resin film was calculated by comparing the amount of the sodium hydroxide aqueous solution required for neutralization with the calibration curve. . The boron content of the PVA-based resin film thus obtained was used as the boron adsorption rate of the PVA-based resin film.

(Production of polarizing element 1)
After immersing a 30 μm thick polyvinyl alcohol resin film with a boron adsorption rate of 5.71% by mass in pure water at 21.5° C. for 79 seconds (swelling treatment), the mass of potassium iodide/boric acid/water It was immersed in an aqueous solution having a ratio of 2/2/100 and containing 1.0 mM iodine at 23° C. for 151 seconds (dyeing step). After that, it was immersed in an aqueous solution having a mass ratio of potassium iodide/boric acid/water of 2.5/4/100 at 68.5° C. for 76 seconds (first cross-linking step). Subsequently, it was immersed in an aqueous solution of potassium iodide/boric acid/zinc chloride/water in a mass ratio of 3/5.5/0.6/100 at 45° C. for 11 seconds (second cross-linking step, metal ion treatment step). After that, it was washed by being immersed in a washing bath (washing step) and dried at 38° C. (drying step) to obtain a 12 μm-thick polarizing element in which iodine was adsorbed and oriented on polyvinyl alcohol. The stretching was performed mainly in the dyeing process and the first cross-linking process, and the total stretching ratio was 5.85 times. The resulting polarizing element had a zinc ion content of 0.17% by mass and a boron content of 4.62% by mass.

(Preparation of PVA solution for adhesive)
50 g of a modified PVA resin containing an acetoacetyl group (manufactured by Mitsubishi Chemical Corporation: Gohsenex Z-410) is dissolved in 950 g of pure water, heated at 90° C. for 2 hours, and then cooled to room temperature to obtain a PVA solution for adhesives. Obtained.

(Preparation of polarizing plate adhesives 1 to 3)
PVA solution, urea, commercially available glyoxal 40% by mass solution, maleic acid, and pure water were blended so that the contents of PVA, urea, glyoxal, and maleic acid were as shown in Table 1, and Adhesive 1 was prepared. ~3 were prepared. The adhesive was used 3 days after preparation.

(Saponification of cellulose acylate film)
A commercially available cellulose acylate film TJ40UL (manufactured by Fuji Film Co., Ltd.: film thickness 40 μm) was immersed in a 1.5 mol/L NaOH aqueous solution (saponification solution) kept at 55° C. for 2 minutes, and washed with water. Thereafter, the film was immersed in a 0.05 mol/L sulfuric acid aqueous solution at 25° C. for 30 seconds, and then passed through a washing bath under running water for 30 seconds to neutralize the film. Draining with an air knife was repeated three times. After removing the water, the film was held in a drying zone at 70° C. for 15 seconds and dried to prepare a saponified film.

(Production of polarizing plates 1 to 3)
The saponified cellulose acylate films were laminated on both sides of the polarizing element 1 via the adhesive 1 prepared above and stored for 3 days using a roll laminator, and then dried at 80° C. for 5 minutes. , a polarizing plate 1 was obtained. The adhesive layer was adjusted so that both sides had a thickness of 50 nm after drying.

In the production of polarizing plate 1, adhesive 1 was changed to adhesives 2 and 3 to obtain polarizing plates 2 and 3.

(Adjustment of water content of polarizing plate (polarizing element))
The polarizing plates 1 to 3 obtained above were stored at a temperature of 20° C. and a relative humidity of 30%, 35%, 40%, 45%, 50% or 55% for 72 hours. Moisture content was measured using the Karl Fischer method at 66, 69 and 72 hours of storage. Under any humidity conditions, the moisture content did not change after storage for 66 hours, 69 hours, and 72 hours. Therefore, it can be considered that the water content of the polarizing plates 1 to 3 is the same as the equilibrium water content of the 72-hour storage environment used in this experimental example. When the water content of the polarizing plate reaches equilibrium in a certain storage environment, it can be considered that the water content of the polarizing element in the polarizing plate also reaches equilibrium in that storage environment. Also, when the water content of the polarizing element in the polarizing plate reaches equilibrium in a certain storage environment, it can be considered that the water content of the polarizing plate also reaches equilibrium in that storage environment.

(Adjustment of moisture content of polarizing plates 1 to 3)
The polarizing plates 1 to 3 are stored for 72 hours at a temperature of 20°C and a relative humidity of 55% so that the water content of the polarizing plates 1 to 3 becomes an equilibrium water content of 55% at 20°C. It was adjusted.

<High temperature durability evaluation>
(Preparation of sample for evaluation)
For polarizing plates 1 to 3 with adjusted water content, an acrylic adhesive (manufactured by Lintec Corporation, product number: #7) is formed on both sides, and the absorption axis is 50 mm × 100 mm so that it is parallel to the long side. An evaluation sample was prepared by cutting into a size of , and laminating non-alkali glass ("EAGLE XG" manufactured by Corning Inc.) on the surface of each adhesive.

<Single Transmittance Evaluation (105° C.)>
Evaluation samples of polarizing plates 1 to 3 were subjected to autoclave treatment at a temperature of 50° C. and a pressure of 5 kgf/cm ² (490.3 kPa) for 1 hour, and then left for 24 hours in an environment of a temperature of 23° C. and a relative humidity of 55%. . After that, the evaluation samples of polarizing plates 1 to 3 were measured for transmittance (initial value), stored in a heating environment at a temperature of 105° C., and measured for transmittance every 50 hours from 100 to 200 hours. Evaluation was performed according to the following criteria based on the time at which the decrease in transmittance reached 5% or more from the initial value. Table 2 shows the results obtained.
A decrease in transmittance of 5% or less after 200 hours: A
A decrease in transmittance of 5% or more in 150 to 200 hours: B
Decrease in transmittance reached 5% or more in 100 to 150 hours: C
A decrease in transmittance of 5% or more after 100 hours: D

<Water resistance evaluation (hot water immersion test)>
The water resistance test of this example was conducted according to the water resistance test described in JP-A-2009-025728 [0060]. An acrylic adhesive (manufactured by Lintec Co., Ltd., product number: #7) is formed on one side of the polarizing plate prepared above, and a strip having a size of 50 mm × 20 mm is formed with the absorption axis (stretching direction) of the polarizing plate as the long side. It was cut into a shape and the dimension in the long side direction was measured accurately. Here, the evaluation sample exhibits a unique color uniformly over the entire surface due to iodine adsorbed on the polarizing element.
One short side of this sample was gripped with a gripper, and about 80% of the longitudinal direction was immersed in a water bath at 60° C. and held for 4 hours. The sample was then removed from the water bath and wiped dry. The polarizing element of the polarizing plate shrinks when immersed in warm water. The degree of shrinkage of the polarizing element was evaluated by measuring the distance from the edge of the sample (edge of the protective film) to the edge of the shrunk polarizing element at the center of the short side of the sample. Table 2 shows the results.
The distance from the edge of the sample to the edge of the polarizing element is 1 mm or less: A
The distance from the edge of the sample to the edge of the polarizing element is more than 1 mm and 3 mm or less: B
The distance from the edge of the sample to the edge of the polarizing element is greater than 3 mm: C

The polarizing plate containing the first compound (urea), the second compound (glyoxal), and the third compound (maleic acid) in the adhesive can be used in a high temperature environment of 105 ° C. compared to the polarizing plate without urea in the adhesive. It can be seen that the transmittance does not easily decrease even when exposed to the bottom, and the high temperature durability is excellent. Further, it can be seen that any adhesive has excellent water resistance and a sufficient pot life in terms of productivity even in the case of a polarizing plate prepared by using it after storage for 3 days.

Claims

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 from an adhesive containing a first compound, a second compound, and a third compound,
The first compound is at least one selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives,
the second compound is a dialdehyde,
The polarizing plate, wherein the third compound is a dicarboxylic acid.
The polarizing plate according to claim 1, wherein the adhesive contains a polyvinyl alcohol-based resin.
The polarizing plate according to claim 2, wherein the content of the third compound in the adhesive is 0.01 parts by mass or more and 400 parts by mass or less with respect to 100 parts by mass of the polyvinyl alcohol-based resin.
4. The polarizing plate according to claim 2, wherein the content of the first compound in the adhesive is 0.1 parts by mass or more and 400 parts by mass or less with respect to 100 parts by mass of the polyvinyl alcohol resin.
5. The adhesive according to any one of claims 2 to 4, wherein the content of the second compound is 0.03 parts by mass or more and 20 parts by mass or less with respect to 1 part by mass of the first compound. Polarizer.
The polarizing plate according to any one of claims 1 to 5, wherein the dialdehyde is glyoxal.
7. The polarizing plate according to claim 1, wherein the adhesive layer has a thickness of 0.01 μm or more and 7 μm or less.
The polarizing plate is used in an image display device,
8. The polarizing plate according to claim 1, wherein in the image display device, solid layers are provided on both sides of the polarizing plate so as to be in contact with each other.
The image display cell, the first adhesive layer laminated on the viewer side surface of the image display cell, and the first adhesive layer laminated on the viewer side surface according to any one of claims 1 to 8. and a polarizing plate.
10. The image display device according to claim 9, further comprising a second adhesive layer laminated on the viewer side surface of the polarizing plate, and a transparent member laminated on the viewer side surface of the second adhesive layer.
11. The image display device according to claim 10, wherein said transparent member is a glass plate or a transparent resin plate.
11. The image display device according to claim 10, wherein said transparent member is a touch panel.
containing a first compound, a second compound, and a third compound;
The first compound is at least one selected from the group consisting of urea, urea derivatives, thiourea, and thiourea derivatives,
the second compound is a dialdehyde,
The adhesive, wherein the third compound is a dicarboxylic acid.