Polarizing plates and image display devices

Abstract

To provide a polarizing plate with which it is possible to suppress a decrease in permeability under a high temperature environment.SOLUTION: The polarizer comprises a polarizing element in which a dichroic dye adsorbed and oriented to a polyvinyl alcohol resin layer, and a transparent protective film which is laminated on at least one surface of the polarizing element. The polarizing element and the transparent protective film are pasted together by an adhesive layer that is formed from an adhesive agent that contains a first and a second compound. The first compound contains a nitroxyradical or a nitroxide group. The second compound is a cyclodextrin.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to polarizing plates and image display devices. [Background technology]

[0002] Liquid crystal display (LCD) displays are widely used not only in LCD televisions but also in mobile devices such as personal computers and mobile phones, and in-vehicle applications such as car navigation systems. Typically, an LCD display has a liquid crystal panel in which polarizing plates are bonded to both sides of a liquid crystal cell with adhesive, and the display is achieved by controlling the light from the backlight with the liquid crystal panel. In recent years, organic light-emitting diode (OLED) displays have also become widely used in applications similar to LCDs, such as televisions, mobile phones, and in-vehicle applications such as car navigation systems. In OLED displays, a circular polarizing plate (a laminate containing polarizing elements and a λ / 4 plate) may be placed on the viewing surface of the image display panel to prevent ambient light from being reflected by the metal electrode (cathode) and appearing like a mirror.

[0003] As mentioned above, polarizing plates are increasingly being used in automobiles as components for image display devices such as liquid crystal displays and organic EL displays. Polarizing plates used in automotive image display devices are often exposed to high-temperature environments compared to those used in mobile applications such as televisions and mobile phones, so they require less change in properties at higher temperatures (high-temperature durability).

[0004] On the other hand, to prevent damage to the image display panel from impacts from the outer surface, there is an increasing trend to install a transparent front panel (sometimes called a "window layer") made of transparent resin or glass on the viewing side of the image display panel. In image display devices equipped with touch panels, a configuration in which the touch panel is located on the viewing side of the image display panel, and a transparent front panel is located even further on the viewing side of the touch panel, is widely adopted.

[0005] In such configurations, if an air layer exists between the image display panel and a transparent component such as a front transparent plate or touch panel, reflection of external light occurs at the air layer interface, tending to reduce the visibility of the screen. Therefore, there is a growing trend to adopt a configuration in which the space between the polarizing plate and the transparent component, which are placed on the viewing surface of the image display panel, is filled with a layer other than an air layer, which is usually a solid layer (hereinafter sometimes referred to as "interlayer filler"). The interlayer filler is preferably a material with a refractive index close to that of the polarizing plate or transparent component. As the interlayer filler, adhesives or UV-curing adhesives are used to suppress the reduction in visibility due to reflection at the interface and to bond and fix each component together (see, for example, Patent Document 1).

[0006] The above-described configuration, which uses interlayer fillers, is increasingly being adopted in mobile applications such as mobile phones, which are often used outdoors. Furthermore, due to the growing demand for visibility in recent years, the adoption of a configuration in which 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 is being considered for in-vehicle applications such as car navigation systems.

[0007] However, it has been reported that when such a configuration is adopted, the transmittance of the polarizing plate decreases significantly in high-temperature environments. Patent Document 2 proposes a method to suppress the decrease in transmittance by keeping the amount of water per unit area of ​​the polarizing plate below a predetermined amount and keeping the saturation water absorption amount of the transparent protective film adjacent to the polarizing element below a predetermined amount as a solution to this problem. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 11-174417 [Patent Document 2] Japanese Patent Publication No. 2014-102353 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] However, even with such polarizing plates, it was not possible to sufficiently suppress the decrease in transmittance in high-temperature environments.

[0010] The present invention aims to provide a polarizing plate that can suppress a decrease in transmittance even when exposed to high-temperature environments, and an image display device using the polarizing plate. [Means for solving the problem]

[0011] 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 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 a nitroxide group, The second compound is a polarizing plate, which 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 comprises a polyvinyl alcohol-based resin. [5] The polarizing plate according to [4], 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 per 100 parts by mass of the polyvinyl alcohol-based resin. [6] The polarizing plate according to [4] or [5], wherein the content of the second compound in the adhesive is 1 part by mass or more and 50 parts by mass or less per 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 polarizing plate is used in an image display device, In the image display device, a solid layer is provided in contact with both surfaces of the polarizing plate. The polarizing plate according to any one of [1] to [7]. [9] An image display device having an image display cell, a first adhesive layer laminated on the viewing-side surface of the image display cell, and a polarizing plate according to any one of [1] to [8] laminated on the viewing-side surface of the first adhesive layer.

[10] Further, an image display device according to [9], having a second adhesive layer laminated on the viewing-side surface of the polarizing plate and a transparent member laminated on the 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. [Advantages of the Invention]

[0012] According to the present invention, when used in an image display device having an interlayer filling structure configured such that solid layers are in contact with both surfaces of a polarizing plate, a polarizing plate with suppressed reduction in transmittance even when exposed to a high-temperature environment can be provided. Further, by using the polarizing plate according to the present invention, an image display device with suppressed reduction in transmittance even when exposed to a high-temperature environment can be provided. [Embodiments for Carrying Out the Invention]

[0013] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments.

[0014] [Polarizing Plate] The polarizing plate of this embodiment comprises a polarizing element formed by adsorbing and oriented a dichroic dye 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 from an adhesive containing a first compound and a second compound. The first compound is a compound having a nitroxy radical or a nitroxide group. The second compound is a cyclodextrin.

[0015] Conventional polarizing plates with excellent high-temperature durability are known, for example, polarizing plates that, when left alone in an environment at 95°C for 1000 hours, show suppressed reduction in transmittance. However, even with such polarizing plates, when applied to an image display device in which solid layers are in contact with both sides of the polarizing plate, such as when one side of the polarizing plate is bonded to an image display cell and the other side is bonded to a transparent component such as a touch panel or front panel (hereinafter sometimes referred to as an "interlayer-filled configuration"), a significant decrease in transmittance may be observed in the center of the polarizing plate's surface after being left in an environment at 95°C for 200 hours. A significant decrease in the transmittance of polarizing plates in high-temperature environments is considered to be a particularly likely problem when image display devices employing an interlayer-filled configuration are exposed to high-temperature environments.

[0016] In an image display device with a layer-filled structure, a polarizing plate with significantly reduced transmittance measured by Raman spectroscopy showed a transmittance of 1100 cm⁻¹. -1 Nearby (=CC= derived from the combination) and 1500cm -1 The presence of a peak in the vicinity (derived from the -C=C- bond) suggests the formation of 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 polyened by dehydration (Patent Document 2, paragraph

[0012] ).

[0017] The polarizing plate of this embodiment is incorporated into an image display device with an interlayer-filled structure and has excellent high-temperature durability, suppressing a decrease in transmittance even when exposed to high-temperature environments such as 105°C. This effect is achieved by the polarizing plate comprising an adhesive layer containing the first compound and the second compound, and it is presumed that the synergistic action of the first and second compounds suppresses the polyene conversion of the polyvinyl alcohol-based resin constituting the polarizing element. It has been confirmed that this effect is not limited to cases where the water content of the polarizing plate is low, but is also achieved when the water content of the polarizing plate is high.

[0018] The polarizing plate of this embodiment may have, for example, at least one of the following features (a) and (b). (a) The moisture content of the polarizing element is equal to or greater than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30%, and equal to or less than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 80%. (b) The moisture content of the polarizing plate is equal to or greater than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30%, and equal to or less than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 80%. The polarizing plate of this embodiment has the effect of improving high-temperature durability even when it has further limited features as described in (a1) or (b1) below, in addition to the features of (a) or (b) above. (a1) The water content of the polarizing element is greater than the equilibrium water content at a temperature of 20°C and a relative humidity of 45% or 50%, and less than or equal to the equilibrium water content at a temperature of 20°C and a relative humidity of 80% or 70%. (b1) The moisture content of the polarizing plate is greater than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 45% or 50%, and less than or equal to the equilibrium moisture content at a temperature of 20°C and a relative humidity of 80% or 70%.

[0019] The method for manufacturing a polarizing plate according to this embodiment may include a step to adjust the water content so as to have at least one of the features of (a) and (b) above, or it may not include a step to adjust the water content.

[0020] <Polarizing element> As a polarizing element in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol (hereinafter sometimes referred to as "PVA")-based resin layer, known polarizing elements can be used. Examples of polarizing elements include a stretched film obtained by dyeing a PVA-based resin film, which will become the PVA-based resin layer, with a dichroic dye and uniaxially stretching it, and a laminated film obtained by applying a coating solution containing PVA-based resin to a base film to form a coating layer that will become the PVA-based resin layer on the base film, dyeing the coating layer with a dichroic dye, and then uniaxially stretching the laminated film. Stretching may be performed after dyeing with the dichroic dye, while dyeing is being performed, or after stretching is being dyed.

[0021] The PVA resin contained in the PVA resin layer is obtained by saponifying a polyvinyl acetate resin. Examples of polyvinyl acetate resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, as well as copolymers of vinyl acetate with other monomers copolymerizable thereto. Examples of other copolymerizable monomers include unsaturated carboxylic acids, olefins such as ethylene, vinyl ethers, and unsaturated sulfonic acids.

[0022] The degree of saponification of the PVA resin is preferably about 85 mol% or more, more preferably about 90 mol% or more, and even more preferably about 99 mol% or more and 100 mol% or less. The degree of polymerization of the PVA resin is, for example, 1000 or more and 10000 or less, preferably 1500 or more and 5000 or less. The PVA resin may be modified, for example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral, etc., modified with aldehydes.

[0023] Examples of dichroic dyes adsorbed and oriented on the PVA resin layer include iodine or dichroic dyes. Iodine is preferred as the dichroic dye. Examples of dichroic dyes include 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 First Orange S, First Black, etc.

[0024] The thickness of the polarizing element is preferably 3 μm to 35 μm, more preferably 4 μm to 30 μm, and even more preferably 5 μm to 25 μm. A polarizing element thickness of 35 μm or less makes it easier to suppress the effect of polyene formation of the PVA resin on the degradation of optical properties under high-temperature conditions. A polarizing element thickness of 3 μm or more makes it easier to obtain a polarizing plate that achieves the desired optical properties.

[0025] The polarizing element of the polarizing plate in this embodiment preferably contains a first compound and a second compound. Since the polarizing plate is bonded to the polarizing element and a transparent protective film by an adhesive layer formed from an adhesive containing the first compound and the second compound, it is presumed that a portion of the first compound and a portion of the second compound that migrate from the adhesive layer are contained in the polarizing element. A polarizing plate having such a polarizing element is less likely to experience a decrease in transmittance even when exposed to high-temperature environments due to the presence of an adhesive layer containing the first compound and the second compound. Furthermore, by including 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 high-temperature environments. When the degree of polarization of a polarizing plate decreases, light leakage (hereinafter sometimes referred to as "cross-cutting") is more likely to occur when two polarizing plates are used in a cross-nicol relationship, but since the polarizing plate of this embodiment is less likely to experience a decrease in the degree of polarization even when exposed to high-temperature environments, cross-cutting is also more easily suppressed. It is presumed that the synergistic effect of the first and second compounds contained in the polarizing element suppresses the polyene formation of the PVA resin, thereby suppressing the decrease in transmittance of polarizing plates exposed to high-temperature environments, and also suppressing the decrease in polarization degree.

[0026] Methods for incorporating the first and second compounds into a polarizing element include: transferring the first and second compounds from the adhesive layer to the polarizing element as described above; manufacturing a polarizing element containing the first and second compounds; and combinations of these two methods. For example, one of the first and second compounds may be incorporated into the polarizing element during its manufacture, while both the first and second compounds may be incorporated into the adhesive layer constituting the polarizing plate.

[0027] Methods for manufacturing polarizing elements containing the first and second compounds include immersing a PVA-based resin layer in a processing solvent containing the first and / or second compounds, or spraying, flowing, or dropping the processing solvent onto the PVA-based resin layer. Among these, the method of immersing a PVA-based resin layer in a processing solvent containing both the first and second compounds is preferred. Specific examples of the first and second compounds are those exemplified as being included in the adhesive described later.

[0028] The step of immersing the PVA-based resin layer in a processing solvent containing the first and second compounds may be performed simultaneously with the swelling, stretching, dyeing, crosslinking, and washing steps in the method for manufacturing the polarizing element described later, or it may be performed separately from these steps. The step of incorporating the first and second compounds into the PVA-based resin layer is preferably performed after dyeing the PVA-based resin layer with iodine, and more preferably simultaneously with the crosslinking step after dyeing. With such a method, hue change is small and the influence on the optical properties of the polarizing element can be reduced.

[0029] (1st compound) The first compound is a compound having a nitroxyl radical or a nitroxide group. From the viewpoint of having a radical that is relatively stable at room temperature and in air, examples of the first compound include N-oxyl compounds (compounds having CN(-C)-O· as a functional group (O· represents an oxyl radical and is bonded to N)), and known compounds can be used. Examples of N-oxyl compounds include compounds having an organic group with the following structure. The compounds having a nitroxyl radical or a nitroxide group may be used alone or in combination of two or more types.

[0030] [ka] [In the above formula (1), R 1 R represents an oxyradical. 2 ~R 5independently represents 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.

[0031] Examples of the compound having the above organic group include compounds represented by the following formulas (2) to (5).

Chemical formula

[0032]

Chemical formula

[0033] <000​​​​​​​​​​​​​​​​​​​​​​​[In the above formula (5), R 1 ~R 5 , and n have the same meaning as above, R 12 This represents a hydrogen atom, or an alkyl group, acyl group, amino group, alkoxy group, hydroxyl group, or aryl group having 1 to 10 carbon atoms.

[0035] In the above equations (1) to (5), R 2 ~R 5 From the viewpoint of availability, R is preferably an alkyl group having 1 to 6 carbon atoms, and more preferably an alkyl group having 1 to 3 carbon atoms. In the above formula (2), from the viewpoint of availability, 6 R is preferably a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and more preferably a hydrogen atom. In formula (3) above, R is preferred from the viewpoint of availability. 7 and R 8 R is preferably 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), R is preferred from the viewpoint of availability. 9 ~R 11 Preferably, R is independently a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. In the above formula (5), R is preferred from the viewpoint of availability. 12 It is preferable that n is a hydroxyl group, an amino group, or an alkoxy group. In the above formulas (1) to (5), n is preferably 1 from the viewpoint of availability.

[0036] Examples of N-oxyl compounds include those described in Japanese Patent Publication No. 2003-64022, Japanese Patent Publication No. 11-222462, Japanese Patent Publication No. 2002-284737, and International Publication No. 2016 / 047655. 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl is preferably used as the N-oxyl compound.

[0037] Examples of the first compound include the following compounds. [ka] [In formula (6), R represents a hydrogen atom, or an alkyl group, acyl group, or aryl group having 1 to 10 carbon atoms.] [ka] [ka]

[0038] The first compound is preferably 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 polyene reaction. The lower limit of the molecular weight is not particularly limited, but it can be, for example, 80.

[0039] (Second compound) The second compound is cyclodextrins. Cyclodextrins are non-reducing cyclic oligosaccharides in which glucose molecules are cyclically linked by α-1,4 bonds. The more glucose molecules that make up a cyclodextrin, the larger the inner diameter of the cavity within the molecule. The cyclodextrins used as the second compound preferably have six or more glucose molecules, for example, α, β, γ, and δ-cyclodextrins, which have 6, 7, 8, and 9 glucose molecules, respectively. Cyclodextrins include α, β, γ, and δ-cyclodextrins, as well as branched cyclodextrins, which have glucose and oligosaccharides such as malctose in their branched sugar chains. Cyclodextrins also include cyclodextrin derivatives, which are obtained by further bonding alkyl groups such as methyl groups, hydroxyalkyl groups such as 2-hydroxyethyl groups, 2-hydroxypropyl groups, 2,3-dihydroxypropyl groups, and 2-hydroxybutyl groups to the above cyclodextrins or branched cyclodextrins. Cyclodextrins can be used individually or in combination of two or more types.

[0040] (Feature (a)) When the polarizing plate has the above-described characteristic (a), the moisture content of the polarizing element is greater than or equal to the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30%, and less than or equal to the equilibrium moisture content at a temperature of 20°C and a relative humidity of 80%. The moisture content of the polarizing element may also be greater than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 45% or 50%, and less than or equal to the equilibrium moisture content at a temperature of 20°C and a relative humidity of 80% or 70%. If the moisture content of the polarizing element falls below the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30%, the handling properties of the polarizing element will decrease, and it will become more prone to cracking. If the moisture content of the polarizing element is high, such as greater than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 45% or 50%, it is presumed that the polyene conversion of the PVA resin will proceed more easily. However, since the polarizing plate of this embodiment is equipped with an adhesive layer containing the first compound and the second compound, the polyene conversion of the PVA resin can be suppressed.

[0041] As a method for confirming that the moisture content of a polarizing element is within the range of equilibrium moisture content at a temperature of 20°C and a relative humidity of 30%, and equilibrium moisture content at a temperature of 20°C and a relative humidity of 80%, one method is to store the element in an environment adjusted to the above temperature and relative humidity range, and if there is no change in mass for a certain period of time, it is considered to have reached equilibrium with the environment. Another method is to pre-calculate the equilibrium moisture content of a polarizing element in an environment adjusted to the above temperature and relative humidity range, and confirm the moisture content of the polarizing element by comparing it with the pre-calculated equilibrium moisture content.

[0042] There are no particular limitations on the method for manufacturing a polarizing element having a moisture content that is equal to or greater than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30%, and less than or equal to the equilibrium moisture content at a temperature of 20°C and a relative humidity of 80%, but examples include storing the polarizing element in an environment adjusted to the above temperature and relative humidity range for 10 minutes to 3 hours, or heat-treating it at a temperature of 30°C to 90°C.

[0043] Another preferred method for manufacturing a polarizing element with a moisture content within the above range includes storing a laminate in which a transparent protective film is laminated on at least one side of a polarizing element, or a polarizing plate constructed using a polarizing element, in an environment adjusted to the above temperature and relative humidity range for 10 minutes to 120 hours, or heating it at 30°C to 90°C. Alternatively, when manufacturing an image display device employing a layer-filled configuration, an image display panel in which a polarizing plate is laminated on an image display cell may be stored in an environment adjusted to the above temperature and relative humidity range for 10 minutes to 3 hours, or heated at a temperature of 30°C to 90°C, before a transparent member such as a front panel is bonded to it.

[0044] (Feature (b)) When the polarizing plate has the above-described characteristic (b), the moisture content of the polarizing plate is greater than or equal to the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30%, and less than or equal to the equilibrium moisture content at a temperature of 20°C and a relative humidity of 80%. The moisture content of the polarizing plate may also be greater than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 45% or 50%, and less than or equal to the equilibrium moisture content at a temperature of 20°C and a relative humidity of 80% or 70%. If the moisture content of the polarizing plate falls below the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30%, the handling properties of the polarizing plate will decrease, and it will become more prone to cracking. If the moisture content of the polarizing plate is high, such as greater than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 45% or 50%, it is presumed that the polyene conversion of the PVA resin will proceed more easily. However, since the polarizing plate of this embodiment is equipped with an adhesive layer containing the first compound and the second compound, the polyene conversion of the PVA resin can be suppressed.

[0045] As a method for confirming that the moisture content of a polarizing plate is within the range of equilibrium moisture content at a temperature of 20°C and a relative humidity of 30%, and equilibrium moisture content at a temperature of 20°C and a relative humidity of 80%, one method is to store the polarizing plate in an environment adjusted to the above temperature and relative humidity range, and if there is no change in mass for a certain period of time, it is considered to have reached equilibrium with the environment. Another method is to pre-calculate the equilibrium moisture content of a polarizing plate in an environment adjusted to the above temperature and relative humidity range, and confirm the moisture content of the polarizing plate by comparing it with the pre-calculated equilibrium moisture content.

[0046] There are no particular limitations on the method for manufacturing a polarizing plate having a moisture content equal to or greater than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30%, and less than or equal to the equilibrium moisture content at a temperature of 20°C and a relative humidity of 80%, but examples include storing the polarizing plate in an environment adjusted to the above temperature and relative humidity range for 10 minutes to 3 hours, or heat-treating it at a temperature of 30°C to 90°C. Alternatively, when manufacturing an image display device employing an interlayer-filled structure, an image display panel in which polarizing plates are laminated on an image display cell may be stored in an environment adjusted to the above temperature and relative humidity range for 10 minutes to 3 hours, or heated at a temperature of 30°C to 90°C, before a transparent member such as a front panel is bonded to it.

[0047] (Manufacturing method for polarizing elements) The method for manufacturing polarizing elements is not particularly limited, but typical methods include a method in which a PVA-based resin film, which has been wound in a roll beforehand, is fed out and stretched, dyed, crosslinked, etc. (hereinafter referred to as "manufacturing method 1"), and a method in which a coating solution containing PVA-based resin is applied to a base film to form a coating layer, and the resulting laminate is stretched (hereinafter referred to as "manufacturing method 2").

[0048] Manufacturing method 1 may include steps of uniaxially stretching a PVA-based resin film, staining the PVA-based resin film with a dichroic dye such as iodine and adsorbing the dichroic dye, treating the PVA-based resin film on which the dichroic dye has been adsorbed with an aqueous boric acid solution, and washing with water after treatment with the aqueous boric acid solution.

[0049] The swelling process is a treatment process in which the PVA resin film is immersed in a swelling bath. The swelling process can remove dirt and blocking agents from the surface of the PVA resin film, and can also suppress uneven dyeing by swelling the PVA resin film. Typically, a water-based medium such as water, distilled water, or pure water is used as the swelling bath. The swelling bath may also have surfactants, alcohol, etc., added as appropriate according to conventional methods. 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, more preferably 1.0% by mass or less, and even more preferably 0.5% by mass or less.

[0050] The temperature of the swelling bath is preferably between 10°C and 60°C, more preferably between 15°C and 45°C, and even more preferably between 18°C ​​and 30°C. The immersion time in the swelling bath cannot be determined definitively because the degree of swelling of the PVA resin film is affected by the temperature of the swelling bath, but it is preferably between 5 seconds and 300 seconds, more preferably between 10 seconds and 200 seconds, and even more preferably between 20 seconds and 100 seconds. The swelling process may be performed only once, or multiple times as needed.

[0051] The dyeing process involves immersing a PVA-based resin film in a dyeing bath, which allows for the adsorption and orientation of a dichroic dye onto 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 aqueous iodine solution and contains iodine and an iodide as a solubilizing agent. 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. Among these, potassium iodide is preferred from the viewpoint of controlling the potassium content in the polarizing element.

[0052] The concentration of iodine in the staining bath (iodine solution) is preferably 0.01% by mass or more and 1% by mass or less, and more preferably 0.02% by mass or more and 0.5% by mass or less. The concentration of iodide in the staining 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 even more preferably 0.1% by mass or more and 3% by mass or less.

[0053] The temperature of the dyeing bath is preferably between 10°C and 50°C, more preferably between 15°C and 45°C, and even more preferably between 18°C ​​and 30°C. The immersion time in the dyeing bath cannot be determined definitively because the degree of dyeing of the PVA resin film is affected by the temperature of the dyeing bath, but it is preferably between 10 seconds and 300 seconds, and more preferably between 20 seconds and 240 seconds. The dyeing process may be performed only once, or multiple times as needed.

[0054] The crosslinking process involves immersing the PVA resin film, dyed in the dyeing process, in a treatment bath (crosslinking bath) containing a boron compound. The boron compound crosslinks the PVA resin film, allowing iodine molecules or dye molecules to be adsorbed onto the crosslinked structure. Examples of boron compounds include boric acid, borates, and borax. The crosslinking bath is generally an aqueous solution, but it may also be a mixed solution of a water-miscible organic solvent and water. From the viewpoint of controlling the potassium content in the polarizing element, the crosslinking bath preferably contains potassium iodide.

[0055] In the crosslinking bath, the concentration of the boron compound is preferably about 1% by mass or more and 15% by mass or less, more preferably about 1.5% by mass or more and 10% by mass or less, and even more preferably about 2% by mass or more and 5% by mass or less. When potassium iodide is used in the crosslinking bath, the concentration of potassium iodide in the crosslinking bath is preferably about 1% by mass or more and 15% by mass or less, more preferably about 1.5% by mass or more and 10% by mass or less, and even more preferably about 2% by mass or more and 5% by mass or less.

[0056] The temperature of the crosslinking bath is preferably between 20°C and 70°C, and more preferably between 30°C and 60°C. The immersion time in the crosslinking bath cannot be determined definitively because the degree of crosslinking of the PVA resin film is affected by the temperature of the crosslinking bath, but it is preferably between 5 seconds and 300 seconds, and more preferably between 10 seconds and 200 seconds. The crosslinking process may be performed only once, or multiple times as necessary.

[0057] The stretching process is a process in which a PVA resin film is stretched to a predetermined magnification in at least one direction. Generally, the PVA resin film is uniaxially stretched in the transport direction (longitudinal direction). The stretching method is not particularly limited, and either wet stretching or dry stretching can be used. The stretching process may be performed only once, or multiple times as needed. The stretching process may be performed at any stage in the manufacturing of the polarizing element.

[0058] In the wet stretching method, the treatment bath (stretching bath) can usually be a solvent such as water or a mixed solution of a water-miscible organic solvent and water. 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 stretching bath, the concentration of potassium iodide in the stretching bath is preferably about 1% by mass or more and 15% by mass or less, more preferably about 2% by mass or more and 10% by mass or less, and more preferably about 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 stretching bath is preferably about 1% by mass or more and 15% by mass or less, more preferably about 1.5% by mass or more and 10% by mass or less, and more preferably about 2% by mass or more and 5% by mass or less.

[0059] The temperature of the stretching bath is preferably between 25°C and 80°C, more preferably between 40°C and 75°C, and even more preferably between 50°C and 70°C. The immersion time in the stretching bath cannot be determined definitively because the degree of stretching of the PVA resin film is affected by the temperature of the stretching bath, but it is preferably between 10 seconds and 800 seconds, and more preferably between 30 seconds and 500 seconds. The stretching treatment in the wet stretching method may be performed together with one or more of the following treatment steps: swelling, dyeing, crosslinking, and washing.

[0060] Examples of dry stretching methods include the inter-roll stretching method, the heated roll stretching method, and the compression stretching method. In the case of dry stretching, the stretching process may be carried out during the drying process.

[0061] The total stretching ratio (cumulative stretching ratio) applied to the PVA resin film can be set appropriately depending on the purpose, but it is preferably between 2 and 7 times, more preferably between 3 and 6.8 times, and even more preferably between 3.5 and 6.5 times.

[0062] The cleaning process involves immersing the PVA resin film in a cleaning bath, which removes any foreign matter remaining on the surface of the PVA resin film. The cleaning bath typically uses a water-based medium such as water, distilled water, or pure water. 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 preferably 1% by mass or more and 10% by mass or less, more preferably 1.5% by mass or more and 4% by mass or less, and even more preferably 1.8% by mass or more and 3.8% by mass or less.

[0063] The temperature of the washing bath is preferably between 5°C and 50°C, more preferably between 10°C and 40°C, and even more preferably between 15°C and 30°C. The immersion time in the washing bath cannot be determined definitively because the degree of cleaning of the PVA resin film is affected by the temperature of the washing bath, but it is preferably between 1 second and 100 seconds, more preferably between 2 seconds and 50 seconds, and even more preferably between 3 seconds and 20 seconds. The washing process may be performed only once, or multiple times as needed.

[0064] The drying process involves drying the PVA-based resin film, which has been cleaned in the washing process, to obtain a polarizing element. Drying can be carried out by any suitable method, such as natural drying, forced-air drying, or heat drying.

[0065] Manufacturing method 2 may include the steps of applying a coating solution containing a PVA resin onto a base film, uniaxially stretching the obtained laminated film, staining the coating layer of the uniaxially stretched laminated film with a dichroic dye to adsorb the dichroic dye, treating the laminated film on which the dichroic dye has been adsorbed with an aqueous boric acid solution, and washing with water after treatment with the aqueous boric acid solution. The base film used to form the polarizing element may also be used as a transparent protective film for a polarizing plate. If necessary, the base film may be peeled off from the polarizing element.

[0066] <Transparent protective film> The transparent protective film is bonded to at least one side of the polarizing element via an adhesive layer. This transparent protective film can be bonded to one or both sides of the polarizing element, but it is preferable that it is bonded to both sides.

[0067] The transparent protective film may also have other optical functions and may have a laminated structure with multiple layers stacked on top of each other. From the viewpoint of optical properties, a thin film thickness is preferable for the transparent protective film, but if it is too thin, its strength will decrease and its processability will be poor. An appropriate film thickness is 5 μm to 100 μm, preferably 10 μm to 80 μm, and more preferably 15 μm to 70 μm.

[0068] The transparent protective film can be 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. When a transparent protective film is laminated to both sides of a polarizing element using a water-based adhesive such as PVA adhesive, it is preferable that at least one of the transparent protective films be either a cellulose acylate film or a (meth)acrylic polymer film in terms of moisture permeability, with cellulose acylate film being preferred.

[0069] At least one of the transparent protective films provided by the polarizing plate may have a phase difference function for purposes such as viewing angle compensation. In that case, the film constituting the transparent protective film itself may have a phase difference function, or the transparent protective film may have a layer that does not have a phase difference function and a phase difference layer (a layer that has a phase difference function). If the transparent protective film has a phase difference layer, it can be a laminate of a layer that does not have a phase difference function and a phase difference layer, and these may be bonded together using an adhesive or bonding agent.

[0070] <Adhesive layer> An adhesive containing the first compound and the second compound is used as the adhesive layer for bonding a transparent protective film to the polarizing element. While water-based adhesives, solvent-based adhesives, and active energy ray-curing adhesives can be used, a water-based adhesive is preferred, and it is preferable that the adhesive contains a PVA-based resin. By using an adhesive containing the first compound and the second compound to form the adhesive layer, the decrease in transmittance of the polarizing plate under high-temperature conditions can be suppressed.

[0071] The thickness of the adhesive during application can be set to any value. For example, it can be set so that an adhesive layer of a desired thickness is obtained after curing or heating (drying). The thickness of the adhesive layer is preferably 0.01 μm to 7 μm, more preferably 0.01 μm to 5 μm, even more preferably 0.01 μm to 2 μm, and most preferably 0.01 μm to 1 μm.

[0072] When manufacturing a polarizing plate using a polarizing element that does not contain the first and second compounds, the content of the first and second compounds in the adhesive used is preferably within the range described below. When manufacturing a polarizing plate using a polarizing element that contains the first and second compounds, the content of the first and second compounds in the adhesive may be appropriately changed from the range described below, depending on the first and second compounds contained in the polarizing element. Specific examples of the first and second compounds are as described above.

[0073] When the adhesive contains a PVA-based resin (for example, 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 1 part by mass or more and 200 parts by mass or less, and even more preferably 3 parts by mass or more and 100 parts by mass or less, per 100 parts by mass of the PVA-based resin. If the content is less than 0.1 parts by mass, the effect of suppressing polyene formation of the PVA-based resin under high-temperature environments may not be sufficient. On the other hand, if the content exceeds 400 parts by mass, the first compound may precipitate after the polarizing plate is manufactured.

[0074] When the adhesive contains a PVA-based resin (for example, a water-based adhesive containing a PVA-based resin), the content of the second compound is preferably 1 to 50 parts by mass, more preferably 1.5 to 40 parts by mass, and even more preferably 2 to 35 parts by mass, per 100 parts by mass of the PVA-based resin. If the content is less than 1 part by mass, the effect of suppressing polyene formation of the PVA-based resin under high-temperature environments may not be sufficient. On the other hand, if the content exceeds 50 parts by mass, the second compound may precipitate after the polarizing plate is manufactured.

[0075] In a configuration in which a transparent protective film is bonded to both sides of a polarizing element via an adhesive layer, only one of the adhesive layers on both sides of the polarizing element may contain the first compound and the second compound, but it is preferable that both adhesive layers on both sides contain the first compound and the second compound.

[0076] To meet the demand for thinner polarizing plates, polarizing plates have been developed that have a transparent protective film on only one side of the polarizing element. In this configuration as well, the transparent protective film is laminated via an adhesive layer containing the first compound and the second compound. One possible method for manufacturing such a polarizing plate having a transparent protective film on only one side of the polarizing element is to first manufacture a polarizing plate with transparent protective films laminated on both sides via adhesive layers, and then peel off one of the transparent protective films. When such a manufacturing method is used, it is acceptable for only one of the adhesive layers to contain the first compound and the second compound, but it is preferable that both adhesive layers contain the first compound and the second compound. If only one of the adhesive layers contains the first compound and the second compound, it is preferable that the adhesive layer on the film side that is not peeled off contains the first compound and the second compound.

[0077] (Water-based adhesive) Any suitable water-based adhesive can be used, but preferably a water-based adhesive containing a PVA resin (PVA adhesive) is used. From the viewpoint of adhesion, the average degree of polymerization of the PVA resin contained in the water-based adhesive is preferably 100 to 5500, and more preferably 1000 to 4500. From the viewpoint of adhesion, the average degree of saponification is preferably 85 mol% to 100 mol%, and more preferably 90 mol% to 100 mol%.

[0078] As the PVA resin included in the water-based adhesive, a PVA resin containing an acetoacetyl group (hereinafter sometimes referred to as "acetoacetyl group-containing PVA resin") is preferred. This is because it exhibits excellent adhesion between the PVA resin layer and the transparent protective film, as well as excellent durability. The acetoacetyl group-containing PVA resin can be obtained, for example, by reacting a PVA resin with diketene in any way. The degree of acetoacetyl group modification in the acetoacetyl group-containing PVA resin is typically 0.1 mol% or more, and preferably 0.1 mol% to 20 mol%. The resin concentration of the water-based adhesive is preferably 0.1% by mass to 15% by mass, and more preferably 0.5% by mass to 10% by mass.

[0079] Water-based adhesives can also contain crosslinking agents. Known crosslinking agents can be used. Examples of crosslinking agents include water-soluble epoxy compounds, dialdehydes, and isocyanates.

[0080] When the PVA resin is an acetoacetyl group-containing PVA resin, the crosslinking agent is preferably one of glyoxal, glyoxylate, or methylolmelamine, more preferably glyoxal or glyoxylate, and particularly preferably glyoxal.

[0081] Water-based adhesives may also contain organic solvents. Alcohols are preferred as organic solvents because they are miscible with water, and methanol or ethanol are more preferred among alcohols. The methanol concentration in the water-based adhesive is preferably 10% to 70% by mass, more preferably 15% to 60% by mass, and even more preferably 20% to 60% by mass. A methanol concentration of 10% by mass or more makes it easier to suppress polyene formation of the PVA resin under high-temperature conditions. Furthermore, a methanol content of 70% by mass or less can suppress color deterioration. For example, a component that has low solubility in water but sufficient solubility in alcohol may be used as a component in the water-based adhesive. In such cases, one preferred embodiment is to dissolve the component in alcohol to prepare an alcohol solution of the component, and then add this alcohol solution to an aqueous solution of the PVA resin to prepare the adhesive.

[0082] (Active energy ray curing adhesive) Active energy ray curing adhesives are adhesives that harden when irradiated with active energy rays such as ultraviolet light. Examples include adhesives containing polymerizable compounds and photopolymerization initiators, adhesives containing photoreactive resins, and adhesives containing binder resins and photoreactive crosslinking agents. Examples of polymerizable compounds include photopolymerizable monomers such as photocurable epoxy monomers, photocurable acrylic monomers, and photocurable urethane monomers, and oligomers derived from these monomers. Examples of photopolymerization initiators include compounds containing substances that generate active species such as neutral radicals, anionic radicals, and cationic radicals when irradiated with active energy rays such as ultraviolet light.

[0083] [Manufacturing method for polarizing plates] The polarizing plate manufacturing method of this embodiment includes a lamination step of laminating a polarizing element and a transparent protective film. The polarizing plate manufacturing method may also include a moisture content adjustment step. The order in which the moisture content adjustment step and the lamination step are performed is not limited, and the moisture content adjustment step and the lamination step may be performed in parallel.

[0084] In the lamination process, the polarizing element and the transparent protective film are laminated via 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 also be a process in which a polarizing element that does not contain the first compound and the second compound is bonded to a transparent protective film using an adhesive containing the first compound and the second compound. In this case, during the process of forming the adhesive layer from the adhesive, some of the first compound and some of the second compound contained in the adhesive may move to the polarizing element, etc.

[0085] In the moisture content adjustment process, when manufacturing a polarizing plate having characteristic (a), the moisture content of the polarizing element is adjusted so that the moisture content of the polarizing element is equal to or greater than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30%, and less than or equal to the equilibrium moisture content at a temperature of 20°C and a relative humidity of 80%. 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 characteristic (b), the moisture content of the polarizing plate is adjusted so that the moisture content of the polarizing plate is equal to or greater than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30%, and less than or equal to the equilibrium moisture content at a temperature of 20°C and a relative humidity of 80%. The moisture content of the polarizing plate can be adjusted by the method described above.

[0086] [Image display device configuration] The polarizing plate of this embodiment is used in various image display devices such as liquid crystal displays and organic EL displays. In image display devices, if the polarizing plate has an interlayer-filled configuration in which layers other than the air layer, specifically solid layers such as adhesive layers, are in contact with both sides of the polarizing plate, the transmittance tends to decrease in high-temperature environments. In image display devices using the polarizing plate of this embodiment, even with an interlayer-filled configuration, the decrease in the transmittance of the polarizing plate in high-temperature environments can be suppressed.

[0087] Examples of the solid layer include an adhesive layer or a bonding agent layer. If the solid layer is a bonding agent layer, it is preferable that it is a bonding agent layer formed by a UV-curing adhesive.

[0088] An example of an image display device is one having an image display cell, a first adhesive layer laminated on the viewing-side surface of the image display cell, and a polarizing plate laminated on the viewing-side surface of the first adhesive layer. Such an image display device may further have 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 is suitably used in an image display device having an interlayer-filled configuration in which 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 bonded together by the second adhesive layer.

[0089] The polarizing plate and the image display cell may be bonded together by an adhesive layer formed using an adhesive, not limited to the first adhesive layer. The polarizing plate and the transparent member may be bonded together by an adhesive layer formed using an adhesive, not limited to the second adhesive layer. The adhesive may be any adhesive as described above, and may not contain the first compound or the second compound.

[0090] <Image display cell> Examples of image display cells include liquid crystal cells and organic EL cells. As for liquid crystal cells, any of the following types may be used: reflective liquid crystal cells that utilize ambient light, transmissive liquid crystal cells that utilize light from a light source such as a backlight, or semi-transparent and semi-reflective liquid crystal cells that utilize both external light and light from a light source. If the liquid crystal cell utilizes light from a light source, the image display device (liquid crystal display device) also has a polarizing plate on the opposite side of the image display cell (liquid crystal cell) from the viewing side, and a light source is also positioned therein. Preferably, the polarizing plate on the light source side and the liquid crystal cell are bonded together via an appropriate adhesive layer. As for the driving method of the liquid crystal cell, any type can be used, such as VA mode, IPS mode, TN mode, STN mode, or bend orientation (π type).

[0091] As an organic EL cell, a suitable example is one in which a light-emitting body (organic electroluminescent light-emitting body) is formed by sequentially stacking a transparent electrode, an organic light-emitting layer, and a metal electrode on a transparent substrate. The organic light-emitting layer is a laminate of various organic thin films, and various layer configurations can be adopted, such as a laminate of a hole injection layer made of a triphenylamine derivative and a light-emitting layer made of a fluorescent organic solid such as anthracene, a laminate of these light-emitting layers and an electron injection layer made of a perylene derivative, or a laminate of a hole injection layer, a light-emitting layer and an electron injection layer.

[0092] <Lamination of image display cell and polarizing plate> A first adhesive layer is preferably used for bonding the image display cell and the polarizing plate. In particular, a method of bonding an adhesive-layered polarizing plate, in which the first adhesive layer is attached to one side of the polarizing plate, to the image display cell is preferred from the viewpoint of workability and other factors. The first adhesive layer can be attached to the polarizing plate by any appropriate method. Examples include preparing an adhesive solution of about 10% to 40% by mass by dissolving or dispersing a base polymer or its composition in a solvent consisting of a suitable solvent such as toluene or ethyl acetate, and directly attaching it to the polarizing plate by an appropriate deployment method such as casting or coating, or forming the first adhesive layer on a separator film and transferring it to the polarizing plate.

[0093] <First adhesive layer, second adhesive layer> The first adhesive layer and the second adhesive layer (hereinafter, either one or both may be referred to as the "adhesive layer") may consist of one or more layers independently, but preferably one layer. The adhesive layer can be composed of an adhesive composition mainly composed of (meth)acrylic resin, rubber resin, urethane resin, ester resin, silicone resin, or polyvinyl ether resin. Among these, an adhesive composition using (meth)acrylic resin as the base polymer, which has excellent transparency, weather resistance, heat resistance, etc., is preferred. The adhesive composition may be of the active energy ray curing type or thermosetting type.

[0094] As the (meth)acrylic resin (base polymer) used in the adhesive composition, polymers or copolymers using one or more (meth)acrylic acid esters such as butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate as monomers are preferably used. It is preferable to copolymerize polar monomers in the base polymer. Examples of polar monomers include monomers having carboxyl groups, hydroxyl groups, amide groups, amino groups, epoxy groups, etc., such as (meth)acrylic acid compounds, 2-hydroxypropyl (meth)acrylate compounds, hydroxyethyl (meth)acrylate compounds, (meth)acrylamide compounds, N,N-dimethylaminoethyl (meth)acrylate compounds, and glycidyl (meth)acrylate compounds.

[0095] The adhesive composition may contain only the above-mentioned base polymer, but usually further contains a crosslinking agent. Examples of crosslinking agents include metal ions with a valency of 2 or higher that form a metal carboxylate salt with a carboxyl group, polyamine compounds that form an amide bond with a carboxyl group, polyepoxy compounds or polyols that form an ester bond with a carboxyl group, and polyisocyanate compounds that form an amide bond with a carboxyl group. Among these, polyisocyanate compounds are preferred.

[0096] Active energy ray curable adhesive compositions have the property of curing upon irradiation with active energy rays such as ultraviolet rays or electron beams. They possess adhesive properties even before irradiation with active energy rays, allowing them to adhere to substrates such as films, and their adhesion strength can be adjusted by curing upon irradiation with active energy rays. Active energy ray curable adhesive compositions are preferably ultraviolet curable. Active energy ray curable adhesive compositions further contain an active energy ray polymerizable compound in addition to a base polymer and a crosslinking agent. Photopolymerization initiators, photosensitizers, etc., may be included as needed.

[0097] The adhesive composition may contain additives such as fine particles for light scattering, beads (resin beads, glass beads, etc.), glass fibers, resins other than the base polymer, tackifiers, fillers (metal powders and other inorganic powders, etc.), antioxidants, UV absorbers, dyes, pigments, colorants, defoamers, corrosion inhibitors, and photopolymerization initiators.

[0098] The adhesive layer can be formed by applying a diluted organic solvent solution of the adhesive composition onto the surface of a base film, image display cell, or polarizing plate and drying it. The base film is generally a thermoplastic resin film, and a typical example of this is a release-treated separator film. The separator film may be a film made of a resin such as polyethylene terephthalate, polybutylene terephthalate, polycarbonate, or polyalate, with a release treatment such as silicone applied to the surface on which the adhesive layer is formed.

[0099] Alternatively, an adhesive composition may be directly applied to the release surface of the separator film to form an adhesive layer, and this separator film-attached adhesive layer may be laminated onto the surface of the polarizing plate. Alternatively, an adhesive composition may be directly applied to the surface of the polarizing plate to form an adhesive layer, and the separator film may be laminated onto the outer surface of the adhesive layer.

[0100] When providing an adhesive layer on the surface of a polarizing plate, it is preferable to apply a surface activation treatment such as plasma treatment or corona treatment to the bonding surface of the polarizing plate and / or the bonding surface of the adhesive layer, and it is more preferable to apply a corona treatment.

[0101] Alternatively, an adhesive sheet may be prepared by applying an adhesive composition onto a second separator film to form an adhesive layer, and then laminating a separator film onto the formed adhesive layer. The adhesive layer with the separator film attached, after peeling the second separator film from this adhesive sheet, may then be laminated onto a polarizing plate. The second separator film used is one that has weaker adhesion to the adhesive layer than the separator film and is easier to peel off.

[0102] The thickness of the adhesive layer is not particularly limited, but is preferably 1 μm to 100 μm, more preferably 3 μm to 50 μm, and may be 20 μm or more.

[0103] <Transparent material> Transparent components placed on the viewing side of an image display device include transparent plates (front plates, window layers) and touch panels. As the transparent plate, a transparent plate with appropriate mechanical strength and thickness is used. Examples of such transparent plates include transparent resin plates such as polyimide resin, acrylic resin, or polycarbonate resin, or glass plates. Functional layers, such as an anti-reflective layer, may be laminated on the viewing side of the transparent plate. Furthermore, if 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 types of touch panels such as resistive, capacitive, optical, and ultrasonic touch panels, as well as glass plates or transparent resin plates equipped with touch sensor functions, can be used. When a capacitive touch panel is used as the transparent component, it is preferable to provide a transparent plate made of glass or transparent resin further on the viewing side than the touch panel.

[0104] <Bonding of polarizing plate and transparent material> For bonding the polarizing plate and the transparent member, an adhesive or an active energy ray curing adhesive is preferably used. When an adhesive is used, the adhesive can be applied by any appropriate method. A specific application method is, for example, the method of applying the adhesive layer used in the bonding of the image display cell and the polarizing plate described above.

[0105] When using an active energy ray curing adhesive, a preferred method is to provide a dam material around the periphery of the image display panel to prevent the adhesive solution from spreading before curing, place a transparent member on the dam material, and then inject the adhesive solution. After the adhesive solution is injected, alignment and degassing are performed as needed, and then curing is performed by irradiation with active energy rays. [Examples]

[0106] The present invention will be specifically described below based on examples. The materials, reagents, amounts and proportions of substances, and procedures shown in the following examples can be modified as appropriate without departing from the spirit of the present invention. Therefore, the present invention is not limited to the following examples.

[0107] <Fabrication of polarizing element A> A 40 μm thick PVA resin film, made of a PVA resin with an average degree of polymerization of approximately 2400 and a degree of saponification of 99.9 mol% or more, was uniaxially stretched approximately 5 times by dry means. While maintaining tension, it was then immersed in 60°C pure water for 1 minute, followed by immersion in an aqueous solution of iodine / potassium iodide / water with a weight ratio of 0.05 / 5 / 100 at 28°C for 60 seconds. Subsequently, it was immersed in an aqueous solution of potassium iodide / boric acid / water with a weight ratio of 8.5 / 8.5 / 100 at 72°C for 300 seconds. After washing with pure water at 26°C for 20 seconds, it was dried at 65°C to obtain a 15 μm thick polarizing element A in which iodine was adsorbed and oriented on the PVA resin layer. The thickness of polarizing element A was measured using a Nikon Corporation digital micrometer "MH-15M".

[0108] <Preparation of adhesives 1-5> (Preparation of PVA solution A for adhesive) 50 g of a modified PVA resin containing acetoacetyl groups (Mitsubishi Chemical Corporation's "Gosenex Z-410") 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 adhesive.

[0109] (Preparation of adhesives 1-5) Adhesives 1 to 5 were prepared by blending PVA solution A, the first compound, the second compound, and pure water so that the concentration of the PVA resin was 3.0% by mass and the first and second compounds were in the amounts shown in Table 1. 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl (hereinafter also referred to as "TEMPOL") was used as the first compound.

[0110] [Table 1]

[0111] <Preparing transparent protective film A> A commercially available cellulose acylate film (Fujifilm Corporation's "TD40", 40 μm thick) was immersed in a 1.5 mol / L NaOH aqueous solution (saponification solution) maintained at 55°C for 2 minutes, and then the cellulose acylate film was washed with water. After that, it was immersed in a 0.05 mol / L sulfuric acid aqueous solution at 25°C for 30 seconds, and then passed through a water bath under running water for 30 seconds to neutralize the cellulose acylate film. After removing the water by repeatedly draining with an air knife three times, it was dried by staying in a drying zone at 70°C for 15 seconds to produce a saponified cellulose acylate film, which was designated as transparent protective film A.

[0112] <Fabrication of polarizing plate 1> Using a roll laminating machine, a transparent protective film A was laminated to both sides of the polarizing element A with adhesive 1, and then dried at 80°C for 5 minutes to form an adhesive layer and obtain a polarizing plate 1. The amount of adhesive 1 used was adjusted so that the thickness of the adhesive layer after drying was 50 nm on both sides.

[0113] <Preparation of polarizing plates 2-5> Polarizing plates 2 to 5 were obtained in the same manner as the preparation of polarizing plate 1 described above, except that adhesive 1 was changed to adhesives 2 to 5.

[0114] (Adjustment of the water content of polarizing plates (polarizing elements)) Polarizing plates 1-5 obtained above were stored for 72 hours under conditions of 20°C and 40% relative humidity. The moisture content was measured at 66, 69, and 72 hours after the start of storage under the above conditions using the Karl Fischer method. Since no change was observed in the moisture content values ​​obtained from the measurements, it can be assumed that the moisture content of polarizing plates 1-5 is the same as the equilibrium moisture content of the storage environment after 72 hours. When the moisture content of a polarizing plate reaches equilibrium in a certain storage environment, the moisture content of the polarizing elements in the polarizing plate can also be assumed to have reached equilibrium in that storage environment. Similarly, when the moisture content of the polarizing elements in a polarizing plate reaches equilibrium in a certain storage environment, the moisture content of the polarizing plate can also be assumed to have reached equilibrium in that storage environment.

[0115] <High-temperature durability evaluation> (Preparation of evaluation samples) After adjusting the moisture content, an adhesive layer was formed on both sides of polarizing plates 1-5 using an acrylic adhesive (Lintec Corporation, part number: #7). Polarizing plates 1-5 were cut to a size of 50mm x 100mm so that their absorption axes were parallel to their long sides, and evaluation samples were prepared by laminating alkali-free glass (Corning "EAGLE XG") to the surface of each adhesive layer.

[0116] (Evaluation of changes in transmittance due to high-temperature durability test (105°C)) The evaluation sample was subjected to a temperature of 50°C and a pressure of 5 kgf / cm². 2 After autoclaving at 490.3 kPa for 1 hour, the sample was left in an environment of 23°C and 55% relative humidity for 24 hours. The luminance of the evaluation sample at this time was measured using a spectroradiometer (SR-UL1R, manufactured by Topcon Techno House Co., Ltd.) and the luminance was 5000 cd / m². 2 The sample was placed on the illumination surface of the backlight module and measured under conditions of a measurement angle of 2 degrees and a measurement distance of 350 mm. The measured brightness was defined as "Brightness L0". Subsequently, the evaluation sample was stored in a heated environment at a temperature of 105°C, and the brightness of the evaluation sample was measured every 24 hours for a storage period of 72 to 240 hours using the same procedure as above. The measured brightness was defined as "Brightness L1" as the brightness after the high-temperature durability test.

[0117] Using the measured luminances L0 and L1, the change in transmittance was calculated according to the following formula. Change in transmittance [%] = 100 - (Luminance L1 / Luminance L0) × 100

[0118] Based on the storage time required under the above heating environment to obtain a brightness L1 when the change in transmittance was 5% or more, high-temperature durability was evaluated according to the following evaluation criteria. The results are shown in Table 2. (Evaluation Criteria) The storage time required for the evaluation sample in a heated environment until the change in transmittance of the evaluation sample exceeds 5% is: Items exceeding 240 hours: A Items exceeding 120 hours but up to 240 hours: B Items exceeding 72 hours but not exceeding 120 hours: C Up to 72 hours :D

[0119] [Table 2]

Claims

1. A polarizing plate comprising a polarizing element having a dichroic dye 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 the first compound and the second compound. The aforementioned adhesive is a water-based adhesive. The first compound is a compound having a nitroxy radical or a nitroxide group, The polarizing plate is a polarizing plate in which the second compound is at least one selected from the group consisting of α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin.

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

3. The polarizing plate according to claim 1 or 2, wherein the second compound is α-cyclodextrin.

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

5. The polarizing plate according to claim 4, 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 per 100 parts by mass of the polyvinyl alcohol-based resin.

6. The polarizing plate according to claim 4 or 5, wherein the content of the second compound in the adhesive is 1 part by mass or more and 50 parts by mass or less per 100 parts by mass of the polyvinyl alcohol-based resin.

7. 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.

8. The polarizing plate is used in an image display device. The polarizing plate according to any one of claims 1 to 7, wherein a solid layer is provided in contact with both sides of the polarizing plate in the image display device.

9. An image display device comprising: an image display cell; a first adhesive layer laminated on the viewing-side surface of the image display cell; and a polarizing plate according to any one of claims 1 to 8 laminated on the viewing-side surface of the first adhesive layer.

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

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

12. The image display device according to claim 10, wherein the transparent member is a touch panel.

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