Polarizer and image display device

Abstract

The present invention provides a polarizing plate in which the decrease in transmittance under high-temperature environments is suppressed. The polarizing plate comprises a polarizing element in which a dichroic pigment is adsorbed and oriented on a polyvinyl alcohol-based resin layer, and a transparent protective film laminated on at least one side of the polarizing element, wherein the polarizing element and the transparent protective film are bonded by an adhesive layer formed of an adhesive containing a quaternary ammonium salt, and 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 50%.

Description

Technology Field

[0001] The present invention relates to a polarizing plate and an image display device. Background Technology

[0002] Liquid crystal displays (LCDs) are widely used not only for liquid crystal televisions but also for mobile devices such as personal computers and mobile phones, and for vehicle-mounted applications such as car navigation systems. Typically, a liquid crystal display has a liquid crystal panel in which polarizing plates are bonded to both sides of a liquid crystal cell with an adhesive, and display is achieved by controlling light from a backlight through the liquid crystal panel. Recently, organic EL displays are also widely used for mobile devices such as televisions and mobile phones, and for vehicle-mounted applications such as car navigation systems, just like liquid crystal displays. In organic EL displays, a circular polarizing plate (a laminate containing a polarizing element and a λ / 4 plate) is sometimes placed on the viewing side surface of the image display panel to suppress the external light from being reflected by the metal electrode (cathode) and appearing as a mirror.

[0003] As mentioned above, polarizers are increasingly being installed in vehicles as components of image display devices such as liquid crystal displays and organic EL displays. Since polarizers used in image display devices for vehicles are often exposed to high-temperature environments compared to those used in mobile applications such as televisions or mobile phones, they are required to have less change in characteristics at higher temperatures (high-temperature durability).

[0004] Meanwhile, configurations are increasingly adopting the installation of a front plate (also called a "window layer"), such as a transparent resin plate or glass plate, on the visible side relative to the image display panel to prevent damage to the image display panel caused by impact from the outer surface. In image display devices equipped with touch panels, a configuration is widely adopted in which the touch panel is installed on the visible side relative to the image display panel, and a front plate is provided on the visible side even further than the touch panel.

[0005] 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, reflection of external light occurs due to light reflection at the interface of the air layer, and the visibility of the screen tends to decrease. Therefore, there is a growing trend to adopt a configuration (hereinafter referred to as an "interlayer filling configuration") in which the space between the polarizing plate and the transparent member, which are positioned on the viewing side surface of the image display panel, is filled with a layer other than the air layer, which is typically a solid layer (hereinafter referred to as an "interlayer filler"). The interlayer filler is preferably a material with a refractive index similar to that of the polarizing plate or the transparent member. As the interlayer filler, an adhesive or a UV-curing adhesive is used for the purpose of suppressing the decrease in visibility caused by reflection at the interface and for bonding and fixing the members together (e.g., see Patent Document 1).

[0006] The adoption of interlayer charging configurations is spreading in mobile applications, such as mobile phones, which are frequently used outdoors. Furthermore, with the recent increase in demand for visibility, the adoption of interlayer charging configurations is also being considered for vehicle-mounted applications, such as car navigation systems. In this configuration, a transparent front plate is placed on the surface of an image display panel, and the space between the panel and the transparent front plate is filled with an adhesive layer.

[0007] However, it has been reported that when such a configuration is adopted, the transmittance of the polarizer is significantly reduced under high-temperature environments. Patent Document 2 proposes a method to suppress the reduction in transmittance as a solution to this problem by reducing the amount of moisture per unit area of ​​the polarizer to a predetermined amount or less, and also reducing the saturated absorption amount of the transparent protective film adjacent to the polarizing element to a predetermined amount or less. Prior art literature

[0008] [Patent Document 1] Japanese Patent Publication No. Heisei 11-174417 [Patent Document 2] Japanese Patent Publication No. 2014-102353 The problem to be solved

[0009] However, even with such a polarizing plate, the effect of suppressing the decrease in transmittance under high-temperature environments was not sufficient. The present invention aims to provide a polarizing plate in which the decrease in transmittance under high-temperature environments is further suppressed, and an image display device using said polarizing plate. means of solving the problem

[0010] The present invention provides a polarizing plate and an image display device as exemplified below.

[0011] [1] A polarizing plate having a polarizing element in which a dichroic pigment is adsorbed and oriented on a polyvinyl alcohol-based resin layer, and a transparent protective film laminated on at least one side of the polarizing element,

[0012] The above polarizing element and the above transparent protective film are bonded by an adhesive layer formed of an adhesive containing a quaternary ammonium salt, and

[0013] The water content of the above polarizing element is greater than or equal to the equilibrium water content at a temperature of 20°C and a relative humidity of 30%, and less than or equal to the equilibrium water content at a temperature of 20°C and a relative humidity of 50%.

[0014] [2] A polarizing plate having a polarizing element in which a dichroic pigment is adsorbed and oriented on a polyvinyl alcohol-based resin layer, and a transparent protective film laminated on at least one side of the polarizing element,

[0015] The above polarizing element and the above transparent protective film are bonded by an adhesive layer formed of an adhesive containing a quaternary ammonium salt, and

[0016] The water content of the above polarizing plate is greater than or equal to the equilibrium water content at a temperature of 20°C and a relative humidity of 30%, and less than or equal to the equilibrium water content at a temperature of 20°C and a relative humidity of 50%.

[0017] [3] The above adhesive is a polarizing plate described in [1] or [2] containing a polyvinyl alcohol-based resin.

[0018] [4] The polarizing plate described in [3] has a content of quaternary ammonium salt in the adhesive of the above amount of 1 part by mass or more and 200 parts by mass or less per 100 parts by mass of the polyvinyl alcohol-based resin.

[0019] [5] The adhesive layer is a polarizing plate described in any one of [1] to [4], having a thickness of 0.01 μm or more and 7 μm or less.

[0020] [6] The above quaternary ammonium salt is the following formula (1):

[0021]

[0022] [In the middle of the meal, R 1 ~R 4 represents an alkyl group having 1 to 10 carbon atoms, and X represents chlorine, bromine, or iodine.

[0023] A polarizing plate described in any one of [1] to [5] containing a compound represented by .

[0024] [7] The above polarizing plate is used in an image display device, and

[0025] A polarizing plate described in any one of [1] to [6], wherein a solid layer is formed in contact with both sides of the polarizing plate in the above image display device.

[0026] [8] An image display device having an image display cell, a first adhesive layer laminated on the visible side surface of the image display cell, and a polarizing plate described in any one of [1] to [7] laminated on the visible side surface of the first adhesive layer.

[0027] [9] An image display device described in [8] having a second adhesive layer laminated on the visible side surface of the polarizing plate and a transparent member laminated on the visible side surface of the second adhesive layer.

[0028]

[10] An image display device described in [9] in which the above transparent member is a glass plate or a transparent resin plate.

[0029]

[11] The image display device described in [9], in which the above transparent member is a touch panel. Effects of the invention

[0030] According to the present invention, it is possible to provide a polarizing plate with improved high-temperature durability and suppressed decrease in transmittance due to high temperature, even when used in an image display device with an interlayer filling configuration. Furthermore, by using the polarizing plate according to the present invention, it is possible to provide an image display device in which the decrease in transmittance under high-temperature environments is suppressed. Specific details for implementing the invention

[0031] Although embodiments of the present invention have been described below, the present invention is not limited to the following embodiments.

[0032] [Polarizing plate]

[0033] A polarizing plate according to the present embodiment has a polarizing element in which a dichroic pigment is adsorbed and oriented on a layer comprising a polyvinyl alcohol-based resin, and a transparent protective film. The polarizing element and the transparent protective film are bonded by an adhesive layer formed of an adhesive containing a quaternary ammonium salt. A polarizing plate according to the present embodiment has at least one of the following features (a) and (b).

[0034] (a) The moisture content of the polarizing element is greater than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30%, and less than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 50%.

[0035] (b) The moisture content of the polarizer is greater than or equal to the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30°F, and less than or equal to the equilibrium moisture content at a temperature of 20°C and a relative humidity of 50°F.

[0036] As a conventional polarizing plate with excellent high-temperature durability, for example, a polarizing plate is known in which the decrease in transmittance is suppressed even when the polarizing plate alone is left for 1,000 hours in an environment of 95°C. However, even with such a polarizing plate, when used in an interlayer filling configuration, a significant decrease in transmittance may be observed in the central part of the polarizing plate surface when left for 200 hours in an environment of 95°C. A significant decrease in the transmittance of a polarizing plate under a high-temperature environment is considered to be a problem that is particularly likely to occur when an image display device employing an interlayer filling configuration in which one side of the polarizing plate is bonded to an image display cell and the other side is bonded to a transparent member such as a touch panel or a front plate is exposed to a high-temperature environment.

[0037] A polarizer with significantly reduced transmittance due to an interlayer packing configuration at 1100 cm⁻¹ by Raman spectroscopic measurement -1 Nearby (derived from the=CC= bond) and 1500 cm -1 Since it has a peak in the vicinity (derived from the -C=C- bond), the polyene structure (-C=C) n It is thought that it forms a polyene structure. The polyene structure is presumed to be formed when polyvinyl alcohol constituting the polarizing element is polyenified by dehydration (Patent Document 2, paragraph

[0012] ).

[0038] The polarizing plate according to the present invention can improve high-temperature durability. The polarizing plate according to the present invention is embedded in an image display device having an interlayer filling configuration, and can suppress the decrease in transmittance even when exposed for a long time to a high-temperature environment of, for example, 105°C, and can reduce the decrease in transmittance to 5% or less even when stored at 105°C for 48 hours.

[0039] Polarizing element

[0040] As a polarizing element in which a dichroic pigment is adsorbed and oriented on a layer containing a polyvinyl alcohol (hereinafter also referred to as "PVA")-based resin (hereinafter also referred to as a "PVA-based resin layer"), a known polarizing element may be used. Examples of polarizing elements include a stretched film obtained by dyeing a PVA-based resin film with a dichroic pigment and uniaxially stretching it, or a laminated film having a coating layer formed by applying a coating solution containing a PVA-based resin onto a substrate film, wherein the coating layer is dyed with a dichroic pigment and the laminated film is uniaxially stretched. Stretching may be performed after dyeing with a dichroic pigment, while dyeing, or after stretching.

[0041] PVA-based resins are obtained by saponifying polyvinyl acetate-based resins. Examples of polyvinyl acetate-based resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, as well as copolymers of vinyl acetate and other monomers copolymerizable thereto. Examples of other copolymerizable monomers include unsaturated carboxylic acids, olefins such as ethylene, vinyl ethers, and unsaturated sulfonic acids.

[0042] The degree of saponification of the PVA-based 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-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, and may be, for example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral, etc., modified with aldehydes.

[0043] 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 even more preferably 5 μm or more and 25 μm or less. By having a thickness of 35 μm or less of the polarizing element, the effect of polyenification of the PVA-based resin on the degradation of optical properties under high-temperature environments can be suppressed. By having a thickness of 3 μm or more of the polarizing element, it becomes easier to create a configuration that achieves desired optical properties.

[0044] The polarizing element preferably comprises a quaternary ammonium salt. In the present embodiment, since the polarizing element and the transparent protective film are bonded by an adhesive layer formed from an adhesive containing a quaternary ammonium salt, it is presumed that some of the quaternary ammonium salt migrates from the adhesive layer and is contained in the polarizing element. The quaternary ammonium salt in the polarizing element may include that added during the manufacturing process of the polarizing element. By providing a polarizing element containing a quaternary ammonium salt, the transmittance does not easily decrease even when the polarizing plate is exposed to a high-temperature environment. It is presumed that this is because the polyenification of the PVA-based resin is suppressed by the quaternary ammonium ions contained in the polarizing element.

[0045] (quaternary ammonium salt)

[0046] Quaternary ammonium salts are salts of a quaternary ammonium cation and another anion.

[0047] The quaternary ammonium salt is preferably of the following formula (1):

[0048]

[0049] [In the middle of the meal, R 1 ~R 4 represents an alkyl group having 1 to 10 carbon atoms, and X represents chlorine, bromine, or iodine.

[0050] It includes compounds represented by . Quaternary ammonium salts may be used alone or in combination of two or more types.

[0051] The quaternary ammonium salt is R in Formula (1). 1 ~R 4 It is preferable that the number of carbon atoms is all 2 or more, more preferable that it is 3 or more, and even more preferable that it is 4 or more. A quaternary ammonium salt having an alkyl group with a large number of carbon atoms can further improve the high-temperature durability of the polarizer.

[0052] Specifically, as quaternary ammonium salts, examples include bases having cations such as tetramethylammonium ions, tetraethylammonium ions, tetrapropylammonium ions, tetrabutylammonium ions, triethylmethylammonium ions, and tributylmethylammonium ions, and their salts. As anions constituting the quaternary ammonium salts, examples include chloride ions, bromide ions, and iodide ions, and chloride ions are preferred.

[0053] Methods for incorporating a quaternary ammonium salt into a polarizing element include immersing a PVA-based resin layer in a treatment solvent containing a quaternary ammonium salt, or spraying, flowing, or dripping the treatment solvent onto a PVA-based resin layer. Among these, the method of immersing a PVA-based resin layer in a treatment solvent containing a quaternary ammonium salt is preferably used.

[0054] The process of immersing a PVA-based resin layer in a treatment solvent containing a quaternary ammonium salt may be performed simultaneously with processes such as swelling, stretching, dyeing, crosslinking, and washing in the method for manufacturing a polarizing element described later, or it may be performed separately from these processes. The process of incorporating a quaternary ammonium salt into the PVA-based resin layer is preferably performed after dyeing the PVA-based resin layer with iodine, and it is more preferably performed simultaneously with the crosslinking process after dyeing. According to this method, the color change is small, so the effect on the optical properties of the polarizing element can be reduced.

[0055] In order to include a quaternary ammonium salt in the polarizing element, both the addition during the manufacture of the polarizing element and the addition to the adhesive may be performed.

[0056] (Features (a))

[0057] In the case of having feature (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 50%. The moisture content of the polarizing element is preferably less than or equal to the equilibrium moisture content at a temperature of 20°C and a relative humidity of 45%, more preferably less than or equal to the equilibrium moisture content at a temperature of 20°C and a relative humidity of 42%, and even more preferably less than or equal to the equilibrium moisture content at a temperature of 20°C and a relative humidity of 38%. If the moisture content of the polarizing element is lower than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30%, the handling properties of the polarizing element are reduced, and it becomes prone to cracking. If the moisture content of the polarizing element exceeds the equilibrium moisture content at a temperature of 20°C and a relative humidity of 50%, the transmittance of the polarizing element is prone to deterioration. It is presumed that if the moisture content of the polarizing element is high, the polyenification of the PVA-based resin is more likely to proceed. The water content of the polarizing element is the water content of the polarizing element within the polarizer.

[0058] As a method for determining whether the moisture content of a polarizing element is within the range of an equilibrium moisture content of 20°C and 30% relative humidity and an equilibrium moisture content of 20°C and 50% relative humidity, there may be a method of storing the polarizing element in an environment adjusted to the range of temperature and relative humidity and considering that it has reached equilibrium with the environment if there is no change in mass for a certain period of time, or a method of calculating the equilibrium moisture content of the polarizing element in the environment adjusted to the range of temperature and relative humidity in advance and confirming by comparing the moisture content of the polarizing element with the equilibrium moisture content calculated in advance.

[0059] A method for manufacturing a polarizing element having a moisture content 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 50%, is not particularly limited, but may include, for example, a method of storing the polarizing element for 10 minutes or more and 3 hours or less in an environment adjusted to the range of the above temperature and relative humidity, or a method of heat treatment at a temperature of 30°C or more and 90°C or less.

[0060] Other preferred methods for manufacturing a polarizing element with the above-mentioned moisture content include storing a laminate having a protective film laminated on at least one side of the polarizing element, or a polarizing plate constructed using the polarizing element, in an environment adjusted to the range of temperature and relative humidity for 10 minutes or more and 120 hours or less, or heat treating at 30°C or higher and 90°C or lower. When manufacturing an image display device employing an interlayer filling configuration, an image display panel in which a polarizing plate is laminated to an image display cell may be stored in an environment adjusted to the range of temperature and relative humidity for 10 minutes or more and 3 hours or heated at 30°C or higher and 90°C or lower, and then a front plate may be bonded.

[0061] It is preferable that the moisture content of the polarizing element be adjusted to the above numerical range during the material stage, whether the polarizing element alone or a laminate of the polarizing element and a protective film is used to form a polarizing plate. If the moisture content is adjusted after the polarizing plate is formed, the curl may become excessive, which may easily cause problems when bonding it to an image display cell. By forming a polarizing plate using a polarizing element that has been adjusted to the above moisture content during the material stage prior to forming the polarizing plate, a polarizing plate equipped with a polarizing element whose moisture content satisfies the above numerical range can be easily formed. It is also acceptable to adjust the moisture content of the polarizing element within the polarizing plate to the above numerical range while the polarizing plate is bonded to an image display cell. In this case, since the polarizing plate is bonded to the image display cell, curl is less likely to occur.

[0062] (Features (b))

[0063] In the case of having feature (b), the moisture content of the polarizer 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 50%. The moisture content of the polarizer is preferably less than or equal to the equilibrium moisture content at a temperature of 20°C and a relative humidity of 45%, more preferably less than or equal to the equilibrium moisture content at a temperature of 20°C and a relative humidity of 42%, and even more preferably less than or equal to the equilibrium moisture content at a temperature of 20°C and a relative humidity of 38%. If the moisture content of the polarizer falls below the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30%, the handling properties of the polarizer are reduced, making it prone to cracking. If the moisture content of the polarizer exceeds the equilibrium moisture content at a temperature of 20°C and a relative humidity of 50%, the transmittance of the polarizing element is prone to decreasing. It is presumed that if the moisture content of the polarizer is high, the polyenification of the PVA-based resin is more likely to proceed.

[0064] As a method for determining whether the moisture content of a polarizing plate is within the range of equilibrium moisture content at a temperature of 20°C and relative humidity of 30% and equilibrium moisture content at a temperature of 20°C and relative humidity of 50%, there may be a method of storing the polarizing plate in an environment adjusted to the range of temperature and relative humidity and considering that it has reached equilibrium with the environment if there is no change in mass for a certain period of time, or a method of calculating the equilibrium moisture content of the polarizing plate in advance in an environment adjusted to the range of temperature and relative humidity and confirming by comparing the moisture content of the polarizing plate with the equilibrium moisture content calculated in advance.

[0065] A method for manufacturing a polarizing plate having a moisture content 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 50%, is not particularly limited, but examples include storing the polarizing plate for 10 minutes or more and 3 hours or less in an environment adjusted to the range of the above temperature and relative humidity, or heat treating at a temperature of 30°C or more and 90°C or less.

[0066] In the production of an image display device employing an interlayer filling configuration, an image display panel in which a polarizing plate is laminated to an image display cell may be stored for 10 minutes or more and 3 hours or heated to 30°C or higher and 90°C or lower, and then a front plate may be bonded.

[0067] (Urea-based compounds)

[0068] The polarizing element may further include a urea-based compound. A polarizing element including a urea-based compound can further suppress the decrease in transmittance. As for the urea-based compound, it may be the same as the urea-based compound that can be included in the adhesive described later. As a method for including a urea-based compound in the polarizing element, the same method as the method for including a quaternary ammonium salt in the polarizing element may be used. The urea-based compound may be included during the manufacturing process of the polarizing element, or it may be included in the polarizing element by including it in the adhesive for laminating the polarizing element and the transparent protective film described later.

[0069] (Method for manufacturing a polarizing element)

[0070] The method for manufacturing a polarizing element is not particularly limited, but a typical method is to produce it by extruding a PVA-based resin film that has been wound in a roll shape and performing stretching, dyeing, crosslinking, etc. (hereinafter referred to as “Manufacturing Method 1”) or a method including a process of applying a coating solution 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”).

[0071] Manufacturing method 1 can be manufactured by following the steps of: uniaxially stretching a PVA-based resin film; dyeing the PVA-based resin film with a dichroic dye such as iodine to adsorb the dichroic dye; treating the PVA-based resin film with the adsorbed dichroic dye with an aqueous boric acid solution; and washing with water after treatment with the aqueous boric acid solution.

[0072] The swelling process is a treatment process in which a PVA-based resin film is immersed in a swelling bath. In addition to removing contaminants or blocking agents from the surface of the PVA-based resin film through the swelling process, dye stains can be suppressed by swelling the PVA-based resin film. Typically, a medium with water as the main component, such as water, distilled water, or pure water, is used in the swelling bath. Surfactants, alcohols, etc., may be appropriately added to the swelling bath according to conventional methods. Potassium iodide may be used in the swelling bath from the perspective of controlling the potassium content of the polarizing element; in this case, the concentration of potassium iodide in the swelling bath is preferably 1.5 mass% or less, more preferably 1.0 mass% or less, and even more preferably 0.5 mass% or less.

[0073] 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 determined uniformly because the degree of swelling of the PVA-based resin film is affected by the swelling bath temperature, but it is preferably 5 seconds or higher and 300 seconds or lower, more preferably 10 seconds or higher and 200 seconds or lower, and even more preferably 20 seconds or higher and 100 seconds or lower. The swelling process may be performed only once, or it may be performed multiple times as needed.

[0074] The dyeing process is a treatment process in which a PVA-based resin film is immersed in a dyeing bath (iodine solution), and dichroic pigments such as iodine can be adsorbed and oriented onto the PVA-based resin film. The iodine solution is preferably an aqueous iodine solution and contains iodine and an iodide as a dissolving 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, titanium iodide, etc. Among these, potassium iodide is suitable from the perspective of controlling the potassium content in the polarizing element.

[0075] The iodine concentration in the dyeing bath is preferably 0.01 mass% or more and 1 mass% or less, and more preferably 0.02 mass% or more and 0.5 mass% or less. The iodide concentration in the dyeing bath is preferably 0.01 mass% or more and 10 mass% or less, more preferably 0.05 mass% or more and 5 mass% or less, and even more preferably 0.1 mass% or more and 3 mass% or less.

[0076] 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 determined uniformly because the degree of dyeing of the PVA-based resin film is affected by the dyeing bath temperature, but it is preferably 10 seconds or higher and 300 seconds or lower, and more preferably 20 seconds or higher and 240 seconds or lower. The dyeing process may be performed only once, or it may be performed multiple times if necessary.

[0077] The crosslinking process is a treatment process in which a PVA-based resin film dyed in a dyeing process is immersed in a treatment bath (crosslinking bath) containing a boron compound, and the polyvinyl alcohol-based resin film is crosslinked by the boron compound, 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 water and an organic solvent that is miscible with water. From the perspective of controlling the potassium content in the polarizing element, it is preferable for the crosslinking bath to contain potassium iodide.

[0078] In the crosslinking bath, the concentration of the boron compound is preferably 1 mass% or more and 15 mass% or less, more preferably 1.5 mass% or more and 10 mass% or less, and even more preferably 2 mass% or more and 5 mass% or less. When potassium iodide is used in the crosslinking bath, the concentration of potassium iodide in the crosslinking bath is preferably 1 mass% or more and 15 mass% or less, more preferably 1.5 mass% or more and 10 mass% or less, and even more preferably 2 mass% or more and 5 mass% or less.

[0079] The temperature of the crosslinking bath is preferably 20°C or higher and 70°C or lower, and more preferably 30°C or higher and 60°C or lower. The immersion time in the crosslinking bath cannot be determined uniformly because the degree of crosslinking of the PVA-based resin film is affected by the temperature of the crosslinking bath, but it is preferably 5 seconds or higher and 300 seconds or lower, and more preferably 10 seconds or higher and 200 seconds or lower. The crosslinking process may be performed only once, or it may be performed multiple times if necessary.

[0080] The stretching process is a processing process that stretches a PVA-based resin film in at least one direction to a predetermined ratio. Generally, the PVA-based resin film is uniaxially stretched in the conveying direction (length direction). The stretching method is not particularly limited, and either wet stretching or dry stretching methods may be employed. The stretching process may be performed only once, or it may be performed multiple times if necessary. The stretching process may be performed at any stage in the manufacture of the polarizing element.

[0081] In the wet stretching method, the treatment bath (stretching bath) may typically use a solvent such as water or a mixed solution of an organic solvent miscible with water and water. The stretching bath preferably contains potassium iodide from the perspective 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 1 mass% or more and 15 mass% or less, more preferably 2 mass% or more and 10 mass% or less, and even more preferably 3 mass% or more and 6 mass% or less. The treatment bath (stretching bath) may contain a boron compound from the perspective of suppressing breakage of the film during stretching. When a boron compound is included, the concentration of the boron compound in the stretching bath is preferably 1 mass% or more and 15 mass% or less, more preferably 1.5 mass% or more and 10 mass% or less, and even more preferably 2 mass% or more and 5 mass% or less.

[0082] The temperature of the stretching bath is preferably 25°C or higher and 80°C or lower, more preferably 40°C or higher and 75°C or lower, and even more preferably 50°C or higher and 70°C or lower. The immersion time in the stretching bath cannot be determined uniformly because the degree of stretching of the PVA-based resin film is affected by the temperature of the stretching bath, but it is preferably 10 seconds or higher and 800 seconds or lower, and more preferably 30 seconds or higher and 500 seconds or lower. The stretching treatment in the wet stretching method may be performed together with one or more treatment processes among the swelling process, dyeing process, crosslinking process, and washing process.

[0083] Examples of dry stretching methods include roll-to-roll stretching, heated roll stretching, and compression stretching. Additionally, dry stretching may be performed together with a drying process.

[0084] The total stretching ratio (cumulative stretching ratio) applied to the polyvinyl alcohol-based resin film can be appropriately set according to the purpose, but it is preferable that it be 2 times or more and 7 times or less, more preferable that it be 3 times or more and 6.8 times or less, and even more preferable that it be 3.5 times or more and 6.5 times or less.

[0085] The cleaning process is a treatment process in which a polyvinyl alcohol-based resin film is immersed in a cleaning bath, and foreign substances remaining on the surface of the polyvinyl alcohol-based resin film can be removed. The cleaning bath typically uses a medium with water as the main component, such as water, distilled water, or pure water. In addition, from the perspective 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 mass% or more and 10 mass% or less, more preferably 1.5 mass% or more and 4 mass% or less, and even more preferably 1.8 mass% or more and 3.8 mass% or less.

[0086] The temperature of the cleaning 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 determined uniformly because the degree of cleaning of the PVA-based resin film is affected by the temperature of the cleaning bath, but it is preferably 1 second or higher and 100 seconds or lower, more preferably 2 seconds or higher and 50 seconds or lower, and even more preferably 3 seconds or higher and 20 seconds or lower. The cleaning process may be performed only once, or it may be performed multiple times as needed.

[0087] The drying process is a process of obtaining a polarizing element by drying a PVA-based resin film cleaned in the cleaning process. Drying is performed by any suitable method, such as natural drying, air drying, or heat drying.

[0088] Manufacturing method 2 can be manufactured by following the steps of: applying a coating solution containing a PVA-based resin onto a substrate film; uniaxially stretching the obtained laminated film; forming a polarizing element by adsorbing the PVA-based resin layer of the uniaxially stretched laminated film by dyeing it with a dichroic pigment; treating the film with the adsorbed dichroic pigment with an aqueous boric acid solution; and washing with water after treatment with the aqueous boric acid solution. The substrate film used to form the polarizing element may be used as a protective layer for the polarizing element. If necessary, the substrate film may be peeled off from the polarizing element.

[0089] Transparent protective film

[0090] In the present embodiment, the transparent protective film (hereinafter also simply referred to as "protective film") used is bonded to at least one side of the polarizing element through an adhesive layer. This transparent protective film is bonded to one or both sides of the polarizing element, but it is preferable that it be bonded to both sides.

[0091] The protective film may simultaneously have other optical functions and may be formed as a laminated structure in which multiple layers are stacked. From the perspective of optical properties, it is desirable for the film thickness of the protective film to be thin, but if it is excessively thin, the strength is reduced and processability is inferior. Appropriate film thickness is 5 μm or more and 100 μm or less, preferably 10 μm or more and 80 μm or less, and more preferably 15 μm or more and 70 μm or less.

[0092] The protective film may be a film such as a cellulose acylate-based film, a film containing a polycarbonate resin, a film containing a cycloolefin resin such as norbornene, a (meth)acrylic polymer film, or a polyester resin-based film such as polyethylene terephthalate. When a protective film is bonded to both sides of a polarizing element using a water-based adhesive such as PVA adhesive, in terms of moisture permeability, it is preferable that at least one of the protective films be either a cellulose acylate-based film or a (meth)acrylic polymer film, and among these, a cellulose acylate film is preferred.

[0093] At least one of the protective films may be equipped with a phase difference function for purposes such as viewing angle compensation. In this case, the protective film itself may have a phase difference function, may have a separate phase difference layer, or may be a combination of both. The film equipped with the phase difference function may be directly bonded to the polarizing element via an adhesive, or it may be bonded via an adhesive or a pressure-sensitive adhesive through another protective film bonded to the polarizing element.

[0094] <Adhesive layer>

[0095] As an adhesive forming an adhesive layer for bonding a protective film to a polarizing element, an adhesive containing a quaternary ammonium salt is used. The adhesive may be a water-based adhesive, a solvent-based adhesive, an active energy beam curing adhesive, etc., but it is preferable that it be a water-based adhesive and contain a PVA-based resin. By using an adhesive containing a quaternary ammonium salt, the decrease in transmittance of the polarizing plate under high-temperature environments can be suppressed.

[0096] The thickness of the adhesive when applied can be set to any value, for example, so that an adhesive layer having a desired thickness can be obtained after curing or after heating (drying). The thickness of the adhesive layer composed of 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, even more preferably 0.01 μm or more and 2 μm or less, and most preferably 0.01 μm or more and 1 μm or less.

[0097] The following description of the adhesive is provided for a preferred range in the case where the polarizing element does not contain a quaternary ammonium salt during the manufacture of the polarizing element. If the polarizing element contains a quaternary ammonium salt, the following values ​​may be appropriately adjusted. Regarding specific examples of quaternary ammonium salts, the same as the quaternary ammonium salt contained in the aforementioned polarizing element may be used. During the process of forming an adhesive layer through a drying process when bonding the polarizing element and the protective film, it is acceptable for some of the quaternary ammonium salt to migrate from the adhesive layer to the polarizing element, etc.

[0098] When the adhesive is a water-based adhesive containing a PVA-based resin, the content of the quaternary ammonium salt in the adhesive is preferably 1 part by mass or more and 200 parts by mass or less, more preferably 30 parts by mass or more and 150 parts by mass or less, and even more preferably 50 parts by mass or more and 130 parts by mass or less, with respect to 100 parts by mass of the PVA-based resin. If the content is less than 1 part by mass, the effect of improving high-temperature durability may not be sufficiently obtained. On the other hand, if the content of the quaternary ammonium salt exceeds 200 parts by mass, crystals may precipitate after drying, causing problems such as increased haze.

[0099] In a configuration in which a transparent protective film is bonded to both sides of a polarizing element through an adhesive layer, among the adhesive layers on both sides of the polarizing element, only the adhesive layer on one side may be a layer containing a quaternary ammonium salt, but it is preferable that both adhesive layers on both sides are layers containing a quaternary ammonium salt.

[0100] To meet the demand for thinning polarizers, a polarizer having a transparent protective film on only one side of the polarizing element is being developed. In this configuration, the transparent protective film is laminated through an adhesive layer containing a quaternary ammonium salt. As a method for manufacturing such a polarizer having a transparent protective film on only one side of the polarizing element, one can consider a method in which a polarizer is first manufactured by bonding transparent protective films to both sides through adhesive layers, and then peeling off one side of the transparent protective film. When this manufacturing method is used, it does not matter if only one adhesive layer contains a quaternary ammonium salt, but it is preferable that both adhesive layers contain a quaternary ammonium salt. When an adhesive layer containing a quaternary ammonium salt is used only on one side of the polarizing element, it is preferable that the adhesive layer on the film side that is not peeled off contains a quaternary ammonium salt.

[0101] (Water-based adhesive)

[0102] As for the water-based adhesive, any suitable water-based adhesive may be used, but preferably, a water-based adhesive (PVA-based adhesive) containing a PVA-based resin is used. The average degree of polymerization of the PVA-based resin included in the water-based adhesive is preferably 100 or more and 5500 or less, more preferably 1000 or more and 4500 or less, in terms of adhesion. 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, in terms of adhesion.

[0103] As for the PVA-based resin included in the water-based adhesive, it is preferable that it contains acetoacetyl groups, because the adhesion between the PVA-based resin layer and the protective film is excellent and the durability is excellent. The acetoacetyl group-containing PVA-based resin is obtained, for example, by reacting a PVA-based resin with diketene by any method. The degree of acetoacetyl group modification of the acetoacetyl group-containing PVA-based resin is typically 0.1 mol% or more, and preferably 0.1 mol% or more and 20 mol% or less. The resin concentration of the water-based adhesive is preferably 0.1 mass% or more and 15 mass% or less, and more preferably 0.5 mass% or more and 10 mass% or less.

[0104] Water-based adhesives may also contain a crosslinking agent. Known crosslinking agents may be used. Examples of crosslinking agents include water-soluble epoxy compounds, dialdehydes, isocyanates, etc.

[0105] When the PVA-based resin is an acetoacetyl group-containing PVA-based resin, it is preferable that the crosslinking agent be one of glyoxal, glyoxylate, or methylolmelamine, more preferable that it be one of glyoxal or glyoxylate, and particularly preferable that it be glyoxal.

[0106] Water-based adhesives may contain organic solvents. As for the organic solvent, alcohols are preferred because they are miscible with water, and among alcohols, methanol or ethanol is more preferable. The methanol concentration of the water-based adhesive is preferably 10 mass% or more and 70 mass% or less, more preferably 15 mass% or more and 60 mass% or less, and even more preferably 20 mass% or more and 60 mass% or less. By having a methanol concentration of 10 mass% or more, it becomes easier to suppress the polyenification of the PVA-based resin under high-temperature environments. In addition, by having a methanol content of 70 mass% or less, color deterioration can be suppressed. Some urea derivatives have low solubility in water, while having sufficient solubility in alcohol. In such cases, one preferred embodiment is to prepare an alcohol solution of the urea-based compound by dissolving the urea-based compound in alcohol, and then add the alcohol solution of the urea-based compound to an aqueous PVA solution to prepare the adhesive.

[0107] (Active energy beam curing adhesive)

[0108] Active energy beam curing adhesives are adhesives that cure by irradiating active energy beams, such as ultraviolet rays. Examples include adhesives containing a polymerizable compound and a photopolymerization initiator, adhesives containing a photoreactive resin, and adhesives containing a binder resin and a photoreactive crosslinking agent. Examples of polymerizable compounds include photopolymerizable monomers such as photocurable epoxy monomers, photocurable acrylic monomers, and photocurable urethane monomers, as well as oligomers derived from these monomers. Examples of the photopolymerization initiator include compounds containing substances that generate active species, such as neutral radicals, anionic radicals, and cationic radicals, when irradiated with active energy beams, such as ultraviolet rays.

[0109] (Urea-based compounds)

[0110] The adhesive may further contain at least one urea-based compound selected from urea, urea derivatives, thiourea, and thiourea derivatives. High-temperature durability can be further improved by the inclusion of a urea-based compound in the adhesive layer formed by the adhesive. It is acceptable for some of the urea-based compound to migrate from the adhesive layer to a polarizing element, etc., during the process of forming the adhesive layer with the adhesive through a drying process when bonding with a protective film. Urea-based compounds include water-soluble and water-insoluble types, but either type of urea-based compound may be used. When using a water-soluble urea-based compound in a water-soluble adhesive, it is desirable to devise a dispersion method to prevent haze rise, etc., after forming the adhesive layer.

[0111] When the adhesive is a water-based adhesive containing a PVA-based resin, the amount of urea-based compound added is preferably 0.1 parts by mass or more and 400 parts by mass or less per 100 parts by mass of PVA, 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.

[0112] (Utera derivative)

[0113] A urea derivative is a compound in which at least one of the four hydrogen atoms of a urea molecule is substituted with a substituent. In this case, there are no particular restrictions on the substituent, but it is preferable that the substituent include carbon atoms, hydrogen atoms, and oxygen atoms.

[0114] Specific examples of urea derivatives include, as 1 substituted urea, methyl urea, ethyl urea, propyl urea, butyl urea, isobutyl urea, N-octadecyl urea, 2-hydroxyethyl urea, hydroxy urea, acetyl urea, allyl urea, 2-propynyl urea, cyclohexyl urea, phenyl urea, 3-hydroxyphenyl urea, (4-methoxyphenyl) urea, benzyl urea, benzoyl urea, o-tolyl urea, and p-tolyl urea. 2. Examples of substituted elements include 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), and tetrahydro-2-pyrimidinone (propyleneurea). 4. Examples of substituted elements include tetramethylurea, 1,1,3,3-tetraethylurea, 1,1,3,3-tetrabutylurea, 1,3-dimethoxy-1,3-dimethylurea, 1,3-dimethyl-2-imidazolidinone, and 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone.

[0115] (Thiourea derivative)

[0116] Thiourea derivatives are compounds in which at least one of the four hydrogen atoms of a thiourea molecule is substituted with a substituent. In this case, there are no particular restrictions on the substituent, but it is preferable that the substituent include a carbon atom, a hydrogen atom, and an oxygen atom.

[0117] Specific examples of thiourea derivatives include, as 1-substituted thiourea, N-methylthiourea, ethylthiourea, propylthiourea, isopropylthiourea, 1-butylthiourea, cyclohexylthiourea, N-acetylthiourea, N-allylthiourea, (2-methoxyethyl)thiourea, N-phenylthiourea, (4-methoxyphenyl)thiourea, N-(2-methoxyphenyl)thiourea, N-(1-naphthyl)thiourea, (2-pyridyl)thiourea, o-tolylthiourea, and p-tolylthiourea. 2 Examples of substituted thiourea include 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, and ethylenethiourea. 3 Examples of substituted thiourea include trimethylthiourea. 4 Examples of substituted thiourea include tetramethylthiourea and 1,1,3,3-tetraethylthiourea.

[0118] Among urea-based compounds, urea derivatives or thiourea derivatives are preferred, and urea derivatives are more preferred, in that they can further suppress the decrease in transmittance under high-temperature environments when used in an image display device with an interlayer filling configuration. Among urea derivatives, it is preferred to be a monosubstituted urea or a disubstituted urea, and a monosubstituted urea is more preferred. Among disubstituted ureas, there are 1,1-substituted ureas and 1,3-substituted ureas, but 1,3-substituted ureas are more preferred.

[0119] <Quaternary Ammonium Salt Containing Layer>

[0120] The quaternary ammonium salt is not limited to being contained in the adhesive layer as described above, but may also be contained in layers other than the adhesive layer for the purpose of improving the high-temperature durability of the polarizer. In a polarizer having a transparent protective film on only one side, a curing layer may be laminated on the side opposite to the transparent protective film of the polarizing element for the purpose of improving physical strength.

[0121] In the present embodiment, a quaternary ammonium salt may be included in this cured layer to form a quaternary ammonium salt-containing layer. Typically, such a cured layer is formed from a curable composition containing an organic solvent, but paragraphs

[0020] to

[0042] of Japanese Patent Publication No. 2017-075986 describe a method of forming such a cured layer from an aqueous solution of an active energy beam curable polymer composition. Since many quaternary ammonium salts are water-soluble, a water-soluble quaternary ammonium salt may be included in such a composition.

[0122] The quaternary ammonium salt-containing layer preferably comprises at least one type of quaternary ammonium salt and a binder. Examples of binders include polymer binders, thermosetting resin binders, active energy beam-curing resin binders, etc., but any binder can be preferably used.

[0123] The thickness of the quaternary ammonium salt-containing layer 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 even more preferably 1 μm or more and 10 μm or less.

[0124] [Method for manufacturing a polarizing plate]

[0125] The method for manufacturing a polarizing plate according to the present embodiment comprises a moisture content adjustment process and a lamination process. In the moisture content adjustment process, when manufacturing a polarizing plate having feature (a), the moisture content of the polarizing element is adjusted so that 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 50%. The moisture content of the polarizing element can be adjusted according to the description of the moisture content of the polarizing element described above. In the moisture content adjustment process, when manufacturing a polarizing plate having feature (b), the moisture content of the polarizing plate is adjusted so that the moisture content of the polarizing plate is 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 50%. The moisture content of the polarizing plate can be adjusted according to the description of the moisture content of the polarizing plate described above. In the lamination process, the polarizing element and the transparent protective film are laminated through the adhesive layer. In the lamination process, for example, a polarizing element that has not been treated to contain a quaternary ammonium salt and a transparent protective film are bonded together using an adhesive containing a quaternary ammonium salt. The order of the moisture content adjustment process and the lamination process is not limited, and the moisture content adjustment process and the lamination process may also be performed in parallel.

[0126] [Configuration of Image Display Device]

[0127] The polarizing plate of the present embodiment is used in various image display devices, such as liquid crystal display devices or organic EL display devices. In an image display device, if the polarizing plate is configured such that both sides are in contact with a layer other than an air layer, specifically a solid layer such as an adhesive layer, the transmittance is prone to decrease under high-temperature environments. In an image display device using the polarizing plate of the present embodiment, the decrease in transmittance of the polarizing plate under high-temperature environments can be suppressed even with an interlayer-filled configuration. An example of an image display device is a configuration 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 include a second adhesive layer laminated on the viewing side surface of the polarizing plate and a transparent member laminated on the surface of the second adhesive layer. In particular, the polarizing plate of the present embodiment is suitably used in an image display device having an interlayer filling configuration in which a transparent member is disposed on the viewing side of the image display device, the polarizing plate and the image display cell are bonded by a first adhesive layer, and the polarizing plate and the transparent member are bonded by a second adhesive layer. In this specification, either or both of the first adhesive layer and the second adhesive layer may simply be referred to as an "adhesive layer." Furthermore, 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 adhesive layers and may also be adhesive layers.

[0128] <Image display cell>

[0129] Examples of image display cells include liquid crystal cells or organic EL cells. As for the liquid crystal cell, any one of a reflective liquid crystal cell that uses external light, a transmissive liquid crystal cell that uses light from a light source such as a backlight, or a transflective / semi-reflective liquid crystal cell that uses both light from the outside and light from a light source 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 placed on the side opposite to the viewing side of the image display cell (liquid crystal cell) and a light source placed thereon. It is preferable that the polarizing plate on the light source side and the liquid crystal cell are bonded through a suitable adhesive layer. As for the driving method of the liquid crystal cell, any type such as VA mode, IPS mode, TN mode, STN mode, or bend orientation (π type) may be used.

[0130] As an organic EL cell, a light-emitting body (organic electroluminescent light-emitting body) formed by sequentially stacking a transparent electrode, an organic light-emitting layer, and a metal electrode on a transparent substrate is suitably used. The organic light-emitting layer is a stack of various organic thin films, and various layer configurations may be employed, such as a stack of a hole injection layer containing a triphenylamine derivative, etc., and a light-emitting layer containing a fluorescent organic solid such as anthracene, a stack of these light-emitting layers and an electron injection layer containing a perylene derivative, etc., or a stack of a hole injection layer, a light-emitting layer, and an electron injection layer.

[0131] <Synthesis of image display cell and polarizer>

[0132] An adhesive layer (adhesive sheet) is suitably used for bonding an image display cell and a polarizing plate. Among these, a method of bonding an image display cell with an adhesive-layered polarizing plate, in which an adhesive layer is attached to one side of the polarizing plate, is preferred from the perspective of workability. The attachment of the adhesive layer to the polarizing plate can be performed in an appropriate manner. Examples include preparing an adhesive solution of 10 mass% or more and 40 mass% or less by dissolving or dispersing a base polymer or its composition in a solvent containing a single or a mixture of suitable solvents such as toluene or ethyl acetate, and directly attaching it to the polarizing plate by an appropriate spreading method such as a spreading method or a coating method, or forming an adhesive layer on a separator and attaching it to the polarizing plate.

[0133] <Adhesive layer>

[0134] The adhesive layer may comprise one or two or more layers, but preferably comprises one layer. The adhesive layer may be composed of an adhesive composition having (meth)acrylic resin, rubber resin, urethane resin, ester resin, silicone resin, or polyvinyl ether resin as the main component. Among these, an adhesive composition having (meth)acrylic resin as the base polymer, which has excellent transparency, weather resistance, and heat resistance, is suitable. The adhesive composition may be an active energy beam curing type or a thermal curing type.

[0135] As a (meth)acrylic resin (base polymer) used in an adhesive composition, a polymer or copolymer having one or more monomers of (meth)acrylic acid esters such as butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate is suitably used. It is preferable to copolymerize a polar monomer into 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.

[0136] The adhesive composition may comprise only the base polymer, but typically further comprises a crosslinking agent. Examples of crosslinking agents include metal ions that form metal salts of carboxylates with carboxyl groups as divalent or higher metal ions, polyamine compounds that form amide bonds with carboxyl groups, polyepoxy compounds or polyols that form ester bonds with carboxyl groups, and polyisocyanate compounds that form amide bonds with carboxyl groups. Among these, polyisocyanate compounds are preferred.

[0137] An active energy beam-curing adhesive composition has the property of curing upon irradiation with active energy beams, such as ultraviolet rays or electron beams. It possesses adhesive properties even before irradiation with active energy beams, allowing it to adhere to substrates such as films, and it has the property of being able to adjust the adhesion strength by curing upon irradiation with active energy beams. It is preferable that the active energy beam-curing adhesive composition be of the ultraviolet curing type. In addition to a base polymer and a crosslinking agent, the active energy beam-curing adhesive composition further contains an active energy beam polymerizable compound. If necessary, it may also contain a photopolymerization initiator, a photosensitizer, etc.

[0138] The adhesive composition may include additives such as fine particles for imparting light scattering properties, beads (resin beads, glass beads, etc.), glass fibers, resins other than base polymers, tackifiers, fillers (metal powders or other inorganic powders, etc.), antioxidants, ultraviolet absorbers, dyes, pigments, colorants, defoaming agents, corrosion inhibitors, photopolymerization initiators, etc.

[0139] The adhesive layer can be formed by applying an organic solvent diluted solution of the adhesive composition onto the surface of a base film, an image display cell, or a polarizing plate and drying it. The base film is generally a thermoplastic resin film, and a typical example thereof is a separator film that has undergone a release treatment. The separator film may be one in which a release treatment, such as silicone treatment, is performed on the surface of a film containing a resin such as polyethylene terephthalate, polybutylene terephthalate, polycarbonate, or polyarylate to which the adhesive layer is formed.

[0140] An adhesive layer may be formed by directly applying an adhesive composition to the release-treated surface of a separator film, and the adhesive layer attached to the separator film may be laminated onto the surface of a polarizer. Alternatively, an adhesive layer may be formed by directly applying an adhesive composition to the surface of a polarizer plate, and a separator film may be laminated onto the outer surface of the adhesive layer.

[0141] When forming an adhesive layer on the surface of a polarizer, it is preferable to perform a surface activation treatment, such as plasma treatment or corona treatment, on the bonding surface of the polarizer and / or the bonding surface of the adhesive layer, and it is more preferable to perform corona treatment.

[0142] In addition, an adhesive composition may be applied to a second separator film to form an adhesive layer, and an adhesive sheet may be prepared by laminating a separator film onto the formed adhesive layer, and the adhesive layer attached to the separator film after peeling off the second separator film from the adhesive sheet may be laminated onto a polarizing plate. The second separator film is used to have a weaker adhesion to the adhesive layer than the separator film, making it easy to peel off.

[0143] The thickness of the adhesive layer is not particularly limited, but, for example, it is preferably 1 μm or more and 100 μm or less, more preferably 3 μm or more and 50 μm or less, and may be 20 μm or more.

[0144] Transparent Absence

[0145] Examples of transparent members positioned on the viewing side of an image display device include transparent plates (window layers) and touch panels. As the transparent plate, a transparent plate having appropriate mechanical strength and thickness is used. Examples of such transparent plates include transparent resin plates, such as polyimide resin, acrylic resin, or polycarbonate resin, or glass plates. It is acceptable for a functional layer, such as an anti-reflective layer, to be laminated on the viewing side of the transparent plate. Furthermore, if the transparent plate is a transparent resin plate, it is acceptable for a hard coat layer to be laminated to increase physical strength or a low-moisture permeability layer to reduce moisture permeability. As the touch panel, various touch panels such as resistive, capacitive, optical, or ultrasonic types, or glass plates or transparent resin plates equipped with touch sensor functions, are used. When a capacitive touch panel is used as the transparent member, it is preferable to install a transparent plate containing glass or a transparent resin plate further on the viewing side than the touch panel.

[0146] <Joining of polarizing plate and transparent component>

[0147] For bonding the polarizing plate and the transparent member, an adhesive or an active energy beam curing adhesive is suitably used. When an adhesive is used, the adhesive can be applied in an appropriate manner. As a specific application method, for example, the method of applying the adhesive layer used in bonding the image display cell and the polarizing plate described above can be cited.

[0148] When using an active energy beam curing adhesive, a method is suitably utilized in which a dam is installed to surround the periphery of an image display panel to prevent the diffusion of the adhesive solution before curing, a transparent member is placed on the dam, and the adhesive solution is injected. After the adhesive solution is injected, positioning and degassing are performed as necessary, and then active energy beams are irradiated to achieve curing.

[0149] Examples

[0150] The present invention will be described in detail below based on examples. The materials, reagents, amounts of substances and their ratios, operations, etc., shown in the following examples may be appropriately modified without departing from the spirit of the present invention. Accordingly, the present invention is not limited to the following examples.

[0151] (Fabrication of Polarizing Element 1)

[0152] A 40 μm thick PVA film containing PVA with an average degree of polymerization of approximately 2400 and a degree of saponification of 99.9 mol% or higher was uniaxially stretched approximately 5 times dry, and then immersed in pure water at 60°C for 1 minute while maintaining the tension state, followed by immersion in an aqueous solution with a weight ratio of iodine / potassium iodide / water of 0.05 / 5 / 100 at 28°C for 60 seconds. Subsequently, it was immersed in an aqueous solution with a weight ratio of potassium iodide / boric acid / water of 8.5 / 8.5 / 100 at 72°C for 300 seconds. Afterward, it was washed with pure water at 26°C for 20 seconds and dried at 65°C to obtain a 15 μm thick polarizing element 1 in which iodine is adsorbed and oriented on the PVA. A digital micrometer "MH-15M" manufactured by Kabushiki Kaisha Nikon was used to measure the thickness of the polarizing element.

[0153] (Preparation of PVA solution for adhesive)

[0154] 50 g of modified PVA resin containing acetoacetyl groups ("Gosenex Z-410" manufactured by Mitsubishi Chemical Co., Ltd.) was 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 adhesive.

[0155] Tetraethylammonium chloride, pure water, and methanol were mixed into a PVA solution for adhesive so that the PVA concentration was 3.0 mass%, the methanol concentration was 20 mass%, and the tetraethylammonium chloride concentration was 75 mass parts per 100 mass parts of PVA to obtain adhesive 1.

[0156] In the same way, a PVA solution for adhesive, a quaternary ammonium salt, pure water, and methanol were mixed to the concentrations shown in Table 1 to obtain adhesives 2 to 5. The PVA concentration of all adhesives was 3.0 mass%, and the methanol concentration was 20 mass%.

[0157]

[0158] All quaternary ammonium salts used were reagents from Tokyo Kasei High School Co., Ltd. The amounts of quaternary ammonium salts in Table 1 are the amounts at which the polyenization inhibition effect of each quaternary ammonium salt is optimized.

[0159] (Preparation of transparent protective film)

[0160] A commercially available cellulose acylate film TD40 (manufactured by Fujifilm Co., Ltd., film thickness 40 μm) was immersed in a 1.5 mol / L aqueous NaOH solution (saponification solution) maintained at 55°C for 2 minutes, and then the film was washed with water. After that, the film was immersed in a 0.05 mol / L aqueous sulfuric acid solution at 25°C for 30 seconds, and then passed through a washing bath under running water for an additional 30 seconds to neutralize the film. Then, after removing moisture from the film by repeating the water removal process with an air knife three times, the film was dried by staying in a drying zone at 70°C for 15 seconds to produce a saponified film, which was then made into transparent protective film 1.

[0161] (Fabrication of polarizing plates)

[0162] Transparent protective film 1 was bonded to both sides of polarizing element 1 using a roll bonder with adhesive 1. After bonding, it was dried at 80°C for 5 minutes to obtain polarizing plate 1. The thickness of the adhesive layer after drying was adjusted to be 50 nm on both sides.

[0163] Polarizers 2 to 5 were manufactured using the same method as the manufacturing method of polarizer 1, except that adhesives 2 to 5 were used instead of adhesive 1.

[0164] (Adjustment of the water content of the polarizer (polarizing element))

[0165] Polarizers 1 to 5 were stored for 72 hours at a temperature of 20°C under conditions of relative humidity of 30%, 35%, 40%, 45%, 50%, or 55%. The moisture content was measured using the Karl Fischer method at 66, 69, and 72 hours of storage. Under any humidity condition, the values ​​of the moisture content did not change during 66, 69, and 72 hours of storage. Therefore, the moisture content of polarizers 1 to 5 can be considered to be the same as the equilibrium moisture content of the storage environment. When the moisture content of the polarizer reaches equilibrium in a certain storage environment, the moisture content of the polarizing element within the polarizer can likewise be considered to have reached equilibrium in that storage environment. Furthermore, when the moisture content of the polarizing element within the polarizer reaches equilibrium in a certain storage environment, the moisture content of the polarizer can likewise be considered to have reached equilibrium in that storage environment.

[0166] (Fabrication of optical laminates)

[0167] Polarizers 1 to 5 were stored for 72 hours at a temperature of 20°C under conditions of relative humidity of 35%, 45%, 50%, or 55%. Optical laminates 1 to 9 were obtained by adjusting the moisture content to be as shown in Table 2.

[0168] An acrylic adhesive (manufactured by Lintec Co., Ltd., part number: #7) was applied to both sides of optical laminates 1 to 9 with adjusted water content to obtain an optical laminate having an adhesive layer with a thickness of 25 μm. This optical laminate was cut to a size of 50 mm × 100 mm so that the absorption axis of the polarizing element was parallel to the long side. Evaluation samples were prepared by bonding alkali-free glass (Corning "EAGLE XG") to the surface of each adhesive.

[0169] (Evaluation of individual transmittance after high-temperature endurance test (105℃))

[0170] The evaluation samples were autoclaved for 1 hour at a temperature of 50°C and a pressure of 5 kgf / ㎠ (490.3 kPa), and then left for 24 hours in an environment with a temperature of 23°C and a relative humidity of 55%. Afterward, the transmittance was measured (initial value), stored in a heated environment at a temperature of 105°C, and the transmittance was measured at 48-hour intervals from 48 to 192 hours. Evaluation was performed based on the following criteria, using the time at which the decrease in transmittance relative to the initial value reached 5% or more. The obtained results are shown in Table 2.

[0171] Transmittance decrease of 5% or less after 192 hours: A

[0172] Transmittance reduction reaching 5% or more after 144 hours: B

[0173] Transmittance reduction reaching 5% or more after 96 hours: C

[0174] Transmittance decrease of 5% or more after 48 hours: D

[0175]

[0176] It was found that the polarizing plate (optical laminate 1 to 7), which has a polarizing element and a transparent protective film, has a water content of the polarizing element that is greater than the equilibrium water content at a temperature of 20°C and a relative humidity of 30°C, and less than the equilibrium water content at a temperature of 20°C and a relative humidity of 50°C, and the polarizing element and the transparent protective film are bonded by an adhesive containing a quaternary ammonium salt, has excellent high-temperature durability, as the transmittance does not easily decrease even when exposed for a long time to a high-temperature environment of 105°C.

Claims

Claim 1 A polarizing plate having a polarizing element in which a dichroic pigment is adsorbed and oriented on a polyvinyl alcohol-based resin layer, and a transparent protective film laminated on at least one side of the polarizing element, wherein the polarizing element and the transparent protective film are bonded by an adhesive layer formed of an adhesive containing a quaternary ammonium salt, and the content of the quaternary ammonium salt in the adhesive is 1 part by mass or more and 200 parts by mass or less per 100 parts by mass of the polyvinyl alcohol-based resin, and the moisture content of the polarizing element is at least the equilibrium moisture content at a temperature of 20°C and 30% relative humidity, and at least the equilibrium moisture content at a temperature of 20°C and 50% relative humidity. Claim 2 A polarizing plate having a polarizing element in which a dichroic pigment is adsorbed and oriented on a polyvinyl alcohol-based resin layer, and a transparent protective film laminated on at least one side of the polarizing element, wherein the polarizing element and the transparent protective film are bonded by an adhesive layer formed of an adhesive containing a quaternary ammonium salt, and the content of the quaternary ammonium salt in the adhesive is 1 part by mass or more and 200 parts by mass or less per 100 parts by mass of the polyvinyl alcohol-based resin, and the moisture content of the polarizing plate is at least the equilibrium moisture content at a temperature of 20°C and 30% relative humidity, and at least the equilibrium moisture content at a temperature of 20°C and 50% relative humidity. Claim 3 In claim 1 or 2, the adhesive comprises a polarizing plate containing a polyvinyl alcohol-based resin. Claim 4 delete Claim 5 In claim 1 or 2, the adhesive layer is a polarizing plate having a thickness of 0.01 μm or more and 7 μm or less. Claim 6 In claim 1 or 2, the quaternary ammonium salt is the following formula (1): [In the middle of the meal, R 1 ~R 4 A polarizing plate comprising a compound represented by ], where represents an alkyl group having 1 to 10 carbon atoms and X represents chlorine, bromine, or iodine. Claim 7 In claim 1 or 2, the polarizing plate is used in an image display device, and in the image display device, a polarizing plate having a solid layer formed in contact with both sides of the polarizing plate. Claim 8 An image display device having an image display cell, a first adhesive layer laminated on the visible side surface of the image display cell, and a polarizing plate described in claim 1 or 2 laminated on the visible side surface of the first adhesive layer. Claim 9 An image display device according to claim 8, further comprising a second adhesive layer laminated on the visible side surface of the polarizing plate and a transparent member laminated on the visible side surface of the second adhesive layer. Claim 10 In claim 9, an image display device wherein the transparent member is a glass plate or a transparent resin plate. Claim 11 In claim 9, the image display device wherein the transparent member is a touch panel.

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