Polarizing plate and image display device using the same

Abstract

The present application aims to provide a polarizing plate and an image display device, which can prevent yellowing and have excellent high-temperature durability even when used for an image display device configured with an interlayer filling. A polarizing plate having a polarizing element in which iodine is adsorbed to and oriented in a polyvinyl alcohol-based resin layer, and a transparent protective film laminated on at least one surface of the polarizing element, the polarizing plate containing an alcohol in an amount of 4 μg / cm 2 or more and 230 μg / cm 2 Hereinafter, the water content of the polarizing element is equal to or more than the equilibrium water content at a temperature of 20°C and a relative humidity of 20%, and is equal to or less than the equilibrium water content at a temperature of 20°C and a relative humidity of 50%.

Description

Technical Field

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

[0002] Liquid crystal displays (LCDs) are widely used not only in LCD televisions but also in personal computers, mobile devices such as mobile phones, and automotive applications such as navigation systems. Typically, an LCD has a liquid crystal panel with polarizing plates bonded to both sides of the liquid crystal cells using adhesive. Display is achieved by controlling the light from the backlight using the liquid crystal panel. In recent years, organic EL displays have also been widely used in televisions, mobile devices such as mobile phones, and automotive applications such as navigation systems, similar to LCDs. In OLED displays, to suppress the reflection of incoming light at the metal electrode (cathode) and ensure it is observed in a mirror-like manner, a circular polarizing plate (a laminate containing polarizing elements and a λ / 4 plate) is sometimes placed on the visible side surface of the image display panel.

[0003] As mentioned above, polarizing plates are increasingly being used in automobiles as components of image display devices such as liquid crystal displays and organic EL displays. Compared to their use in mobile devices such as televisions and mobile phones, polarizing plates used in automotive image display devices are exposed to higher temperatures, therefore, they require minimal changes in properties at higher temperatures (high-temperature durability).

[0004] On the other hand, for purposes such as preventing damage to the image display panel from impacts from external surfaces, there is an increasing trend of providing a front panel (also called a "window layer") such as a transparent resin plate or glass plate on the viewable side of the image display panel. In image display devices equipped with touch panels, a configuration is widely adopted in which a touch panel is provided on the viewable side of the image display panel, and further, a front panel is provided on the viewable side of the touch panel.

[0005] In this configuration, if an air layer exists between the image display panel and transparent components such as the front panel and touch panel, glare from reflected light at the air layer interface will occur, leading to a decrease in image visibility. Therefore, efforts are underway to develop a configuration where the space between the polarizer disposed on the visible side surface of the image display panel and the transparent component is filled with a layer other than the air layer, typically 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 polarizer or transparent component. As the interlayer filler, adhesives and UV-curable adhesives (see, for example, Patent Document 1) are used to suppress the decrease in visibility caused by reflection at the interface and to bond and fix the components together.

[0006] The use of interlayer filling structures is expanding in mobile devices such as smartphones, which are frequently used outdoors. Furthermore, due to increasing demands for visibility in recent years, interlayer filling structures are also being researched for automotive applications such as navigation devices. These structures involve placing a front transparent panel on the surface of the image display panel and filling the space between the panel and the front transparent panel with an adhesive layer.

[0007] However, with this configuration, there have been reports of the polarizing plate turning yellow (or brown) (hereinafter sometimes referred to as yellowing) under high-temperature conditions, and the transmittance of the polarizing plate significantly decreasing. Patent Document 2 proposes a solution to this problem by setting the water content per unit area of ​​the polarizing plate to a predetermined amount or less, and setting the saturated water absorption of the transparent protective film adjacent to the polarizing element to a predetermined amount or less, thereby suppressing the decrease in transmittance.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 11-174417

[0011] Patent Document 2: Japanese Patent Application Publication No. 2014-102353 Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] However, even with this type of polarizing plate, the effect of suppressing yellowing under high-temperature conditions is not sufficient. The object of this invention is to provide a polarizing plate that can further suppress yellowing under high-temperature conditions, and an image display device using this polarizing plate.

[0014] Methods for solving problems

[0015] The present invention provides a polarizing plate and an image display device as illustrated below.

[0016] [1] A polarizing plate comprising a polarizing element having iodine adsorbed and oriented in a polyvinyl alcohol-based resin layer, and a transparent protective film laminated on at least one surface of the polarizing element, wherein the amount of alcohol contained in the polarizing plate is 4 μg / cm³. 2 Above and 230 μg / cm 2 the following,

[0017] The moisture content of the aforementioned polarization element is above the equilibrium moisture content at a temperature of 20°C and a relative humidity of 20%, and below the equilibrium moisture content at a temperature of 20°C and a relative humidity of 50%.

[0018] [2] A polarizing plate comprising a polarizing element having iodine adsorbed and oriented in a polyvinyl alcohol-based resin layer, and a transparent protective film laminated on at least one surface of the polarizing element, wherein the amount of alcohol contained in the polarizing plate is 4 μg / cm³. 2 Above and 230 μg / cm 2 the following,

[0019] The moisture content of the aforementioned polarizing plate is above the equilibrium moisture content at a temperature of 20°C and a relative humidity of 20%, and below the equilibrium moisture content at a temperature of 20°C and a relative humidity of 50%.

[0020] [3] According to the polarizing plate described in [1] or [2], wherein the alcohol is selected from at least one of methanol, ethanol and n-propanol.

[0021] [4] The polarizing plate described in any one of [1] to [3], wherein the polarizing element and the transparent protective film are bonded together using an adhesive layer formed by an adhesive containing the alcohol.

[0022] [5] According to the polarizing plate described in [4], wherein the adhesive comprises a polyvinyl alcohol resin.

[0023] [6] According to the polarizing plate described in [5], the content of the alcohol in the adhesive is 100 parts by mass or more and 2000 parts by mass or less, relative to 100 parts by mass of the polyvinyl alcohol resin.

[0024] [7] The polarizing plate described in any one of [4] to [6], wherein the thickness of the adhesive layer is 0.01 μm to 7 μm.

[0025] [8] The polarizing plate described in any one of [1] to [7], wherein the polarizing plate is used in an image display device,

[0026] In the aforementioned image display device, a layer other than an air layer is disposed on both sides of the aforementioned polarizing plate.

[0027] [9] An image display device comprising: an image display unit, a first adhesive layer laminated on the visible side surface of the image display unit, and a polarizing plate described in any one of [1] to [8] laminated on the visible side surface of the first adhesive layer.

[0028]

[10] The image display device described in [9] further comprises: 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.

[0029]

[11] According to the image display device described in

[10] , the transparent component is a glass plate or a transparent resin plate.

[0030]

[12] According to the image display device described in

[10] , the transparent component is a touch panel.

[0031] Invention Effects

[0032] According to the present invention, a polarizing plate with improved high-temperature durability and suppressed yellowing caused by high temperatures is provided, even when used in image display devices constructed with interlayer filling. Furthermore, by using the polarizing plate of the present invention, an image display device in which yellowing is suppressed under high-temperature environments can be provided. Detailed Implementation

[0033] The embodiments of the present invention will be described below, but the present invention is not limited to the following embodiments.

[0034] [Polarizing plate]

[0035] The polarizing plate of this embodiment comprises: a polarizing element on which a dichroic pigment is adsorbed and oriented in a layer containing a polyvinyl alcohol-based resin, and a transparent protective film. The polarizing plate contains alcohol, and the polarizing element and the transparent protective film can be bonded together by an adhesive layer formed from an alcohol-containing adhesive. The polarizing plate of this embodiment has at least one of the features described in (a) and (b).

[0036] (a) The moisture content of the polarization element is above the equilibrium moisture content at 20°C and 20% relative humidity and below the equilibrium moisture content at 20°C and 50% relative humidity.

[0037] (b) The moisture content of the polarizing plate is above the equilibrium moisture content at 20°C and 20% relative humidity and below the equilibrium moisture content at 20°C and 50% relative humidity.

[0038] The amount of alcohol contained in the polarizing plate is 4 μg / cm. 2 Above and 230 μg / cm 2 The preferred value is 13 μg / cm³. 2 Above and 200 μg / cm 2 The following is more preferably 20 μg / cm 2 Above and 190 μg / cm 2 The following values ​​can also be 60 μg / cm³. 2 The above can also be 100 μg / cm 2 That's all. By setting the amount of alcohol contained in the polarizer within such a range, polyene formation can be suppressed without impairing the optical properties of the polarizing element. The detailed mechanism is not yet clear, but it is speculated that the alcohol may suppress the formation of double bonds by reacting with PVA or boric acid.

[0039] As for conventional polarizing plates with excellent high-temperature durability, for example, for standalone polarizing plates, there are known polarizing plates that can suppress the decrease in transmittance even after being placed at a temperature of 95°C for 1000 hours. However, even with such polarizing plates, when used in an interlayer filling configuration, if placed at a temperature of 95°C for 200 hours, the polarizing plate turns yellow (or brown) in the central part of the polarizing plate surface, and a significant decrease in transmittance is observed in the central part of the polarizing plate surface. When image display devices using an interlayer filling configuration are exposed to high-temperature environments, it is believed that a significant decrease in the transmittance of polarizing plates under high-temperature environments is particularly likely to occur. The interlayer filling configuration is a configuration in which one side of the polarizing plate is bonded to the image display unit, and the other side is bonded to transparent components such as a touch panel or front panel.

[0040] The polarizing plate, whose transmittance is significantly reduced due to its interlayer filling structure, showed poor performance in Raman spectrometry at 1100 cm⁻¹. -1 Nearby (from =CC= key) and 1500cm -1 The presence of peaks near the -C=C- bond suggests the formation of a polyene structure (-C=C). n - It is speculated that the polyene structure is a structure produced by the polyene formation of the polarization element due to dehydration (Patent Document 2,

[0012] paragraph).

[0041] The polarizing plate of the present invention can further improve high-temperature durability. When the polarizing plate of the present invention is incorporated into an image display device with interlayer filling, for example, even when exposed to a high temperature environment of 105°C for a long time, the decrease in transmittance can be suppressed, and even when stored at 105°C for 72 hours, yellowing can be suppressed.

[0042] <Polarization element>

[0043] Well-known polarizing elements can be used as polarizing elements in which dichroic pigments are adsorbed onto a layer containing polyvinyl alcohol (hereinafter also referred to as "PVA")-based resin (hereinafter also referred to as "PVA-based resin layer") and the dichroic pigments are oriented. Examples of polarizing elements include: a stretched film obtained by dyeing a PVA-based resin film with a dichroic pigment and then uniaxially stretching it; and a stretched layer obtained by using a laminated film having a coating layer formed by coating a substrate film with a coating liquid containing a PVA-based resin, dyeing the coating layer with a dichroic pigment, and then uniaxially stretching the laminated film. Stretching can be performed after dyeing with the dichroic pigment, or while dyeing, or after stretching.

[0044] PVA-based resins can be obtained by saponifying polyvinyl acetate-based resins. Besides polyvinyl acetate as a homopolymer of vinyl acetate, copolymers of vinyl acetate with other monomers that can be copolymerized can also be mentioned as polyvinyl acetate-based resins. Examples of other monomers that can be copolymerized include unsaturated carboxylic acids, olefins such as ethylene, vinyl ethers, and unsaturated sulfonic acids.

[0045] 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 can be modified, for example, it can be aldehyde-modified polyvinyl formal, polyvinyl acetal, polyvinyl butyral, etc.

[0046] 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 making the thickness of the polarizing element 35 μm or less, the effect of polyolefination of PVA-based resin on the reduction of optical properties under high-temperature conditions can be suppressed. By making the thickness of the polarizing element 3 μm or more, it is easy to manufacture a configuration that achieves the desired optical properties.

[0047] The polarizing element preferably contains an alcohol. In this embodiment, since the polarizing element and the transparent protective film are bonded together by an adhesive layer formed from an adhesive containing an alcohol, it is presumed that a portion of the alcohol is transferred from the adhesive layer and contained within the polarizing element. The alcohol in the polarizing element may also be an alcohol added during the manufacturing process of the polarizing element. By having a polarizing element containing an alcohol, the transmittance is less likely to decrease even when the polarizing plate is exposed to a high-temperature environment. It is presumed that this effect is achieved because the alcohol contained in the polarizing element acts as a protic polar solvent, interacting with hydroxyl groups in the PVA chain via hydrogen bonds, thereby reducing the reactivity of dehydration reactions within the PVA chain and suppressing the polyene formation of the PVA-based resin.

[0048] (alcohol)

[0049] Examples of alcohols used in this invention include lower alcohols having 1 to 4 carbon atoms. Specifically, examples include methanol, ethanol, n-propanol, isopropanol, and tert-butanol. The alcohols that may be contained in the polarizing plate, polarizing element, and adhesive preferably include at least one selected from methanol, ethanol, n-propanol, isopropanol, and tert-butanol. They can be used alone or in combination of two or more. Methanol, ethanol, n-propanol, and isopropanol are preferred. Their low molecular weight allows for wide dispersion in the polarizing element, which is advantageous for suppressing polyene formation. The alcohols contained in the polarizing element and the alcohols contained in the adhesive may be the same or different.

[0050] Examples of methods for incorporating alcohol into polarizing elements include: immersing a PVA-based resin layer in a processing solvent containing alcohol, or spraying, dripping, or sprinkling the processing solvent onto the PVA-based resin layer. The method of immersing the PVA-based resin layer in a processing solvent containing alcohol is preferred.

[0051] The process of impregnating the PVA-based resin layer in a processing solvent containing alcohol can be performed simultaneously with the swelling, stretching, dyeing, crosslinking, and cleaning processes described later in the polarization element manufacturing method, or it can be performed separately from these processes. The process of containing alcohol in the PVA-based resin layer is preferably performed after dyeing the PVA-based resin layer with iodine, and more preferably simultaneously with the cleaning process. According to this method, the color variation is small, which reduces the impact on the optical properties of the polarization element.

[0052] To make the polarizing element contain alcohol, it can be added during the manufacturing of the polarizing element and added to the adhesive.

[0053] (Feature(a))

[0054] When characteristic (a) is present, the moisture content of the polarizing element is above the equilibrium moisture content of 20% relative humidity at 20°C and below the equilibrium moisture content of 50% relative humidity at 20°C. Preferably, the moisture content of the polarizing element is below the equilibrium moisture content of 45% relative humidity at 20°C, more preferably below the equilibrium moisture content of 42% relative humidity at 20°C, and even more preferably below the equilibrium moisture content of 38% relative humidity at 20°C. If the moisture content of the polarizing element is lower than the equilibrium moisture content of 20% relative humidity at 20°C, the operability of the polarizing element decreases, and it is prone to breakage. If the moisture content of the polarizing element exceeds the equilibrium moisture content of 50% relative humidity at 20°C, the transmittance of the polarizing element is easily reduced. This is presumably because if the moisture content of the polarizing element is high, the polyolefination of the PVA-based resin is more easily promoted. The moisture content of the polarizing element refers to the moisture content of the polarizing element in the polarizing plate.

[0055] As a method to confirm whether the moisture content of a polarizing element is within the range of equilibrium moisture content at 20°C and 20% relative humidity or below the equilibrium moisture content at 20°C and 50% relative humidity, examples include: storing the polarizing element in an environment adjusted to the above temperature and relative humidity range, and considering it to have reached equilibrium with the environment if there is no change in mass over a certain period of time; or calculating the equilibrium moisture content of the polarizing element in an environment adjusted to the above temperature and relative humidity range in advance, and confirming it by comparing the moisture content of the polarizing element with the pre-calculated equilibrium moisture content.

[0056] The method for manufacturing a polarizing element with a moisture content of 20°C and 20% relative humidity or higher and a moisture content of 50% relative humidity or lower is not particularly limited, but examples include: storing the polarizing element in an environment adjusted to the above temperature and relative humidity range for 10 minutes or more and 3 hours or less; or performing heat treatment at 30°C or higher and 90°C or lower.

[0057] Other preferred methods for manufacturing polarizing elements with the aforementioned moisture content include: storing a laminate in which a protective film is deposited on at least one side of the polarizing element, or a polarizing plate made using the polarizing element, in an environment adjusted to the aforementioned temperature and relative humidity range for 10 minutes to 120 hours; or performing a heat treatment at 30°C to 90°C. When manufacturing an image display device using interlayer filling, an image display panel obtained by laminating a polarizing plate onto an image display unit can be stored in an environment adjusted to the aforementioned temperature and relative humidity range for 10 minutes to 3 hours, or heated at 30°C to 90°C, and then bonded to a front panel.

[0058] Regarding the moisture content of the polarizing element, it is preferable that the moisture content be adjusted to the aforementioned range during the material stage used to construct the polarizing plate, whether it is a single polarizing element or a laminate of a polarizing element and a protective film. If the moisture content is adjusted after the polarizing plate is constructed, excessive curling can easily occur, leading to undesirable conditions when bonded to the image display unit. By constructing the polarizing plate using a polarizing element with the aforementioned moisture content adjusted during the material stage before constructing the polarizing plate, it is easy to construct a polarizing plate having a polarizing element with a moisture content satisfying the aforementioned range. Alternatively, the moisture content of the polarizing element in the polarizing plate can be adjusted to the aforementioned range while the polarizing plate is bonded to the image display unit. In this case, since the polarizing plate is bonded to the image display unit, curling is less likely to occur.

[0059] (Feature (b))

[0060] When characteristic (b) is present, the moisture content of the polarizing plate is above the equilibrium moisture content of 20% relative humidity at 20°C and below the equilibrium moisture content of 50% relative humidity at 20°C. Preferably, the moisture content of the polarizing plate is below the equilibrium moisture content of 45% relative humidity at 20°C, more preferably below the equilibrium moisture content of 42% relative humidity at 20°C, and even more preferably below the equilibrium moisture content of 38% relative humidity at 20°C. If the moisture content of the polarizing plate is lower than the equilibrium moisture content of 20% relative humidity at 20°C, the operability of the polarizing plate decreases, and it is prone to breakage. If the moisture content of the polarizing plate exceeds the equilibrium moisture content of 50% relative humidity at 20°C, the transmittance of the polarizing element is easily reduced. This is presumably because if the moisture content of the polarizing plate is high, the polyolefination of the PVA-based resin is more easily promoted.

[0061] As a method to confirm whether the moisture content of the polarizing plate is within the range of equilibrium moisture content above 20°C and 20% relative humidity and below 50% relative humidity at 20°C, examples include: storing the polarizing plate in an environment adjusted to the above temperature and relative humidity range, and considering it to have reached equilibrium with the environment if there is no change in mass over a certain period of time; or pre-calculating the equilibrium moisture content of the polarizing plate in an environment adjusted to the above temperature and relative humidity range, and confirming it by comparing the moisture content of the polarizing plate with the pre-calculated equilibrium moisture content.

[0062] There are no particular limitations on the method for manufacturing a polarizing plate with an equilibrium moisture content of 20°C and 20% relative humidity or higher and an equilibrium moisture content of 50% relative humidity or lower. However, examples include: storing the polarizing plate in an environment adjusted to the above temperature and relative humidity range for 10 minutes or more and 3 hours or less; or performing heat treatment at 30°C or higher and 90°C or lower.

[0063] When manufacturing an image display device using interlayer filling, the image display panel obtained by laminating a polarizing plate onto the image display unit can be kept in an environment with the temperature and relative humidity adjusted to the above range for 10 minutes to 3 hours, or heated at 30°C to 90°C, and then bonded to the front panel.

[0064] (Urea compounds)

[0065] The polarizing element may further contain a urea-based compound. A polarizing element containing a urea-based compound can further suppress the decrease in transmittance. The urea-based compound may be the same as that contained in the adhesive described later. As a method for containing the urea-based compound in the polarizing element, the same method as for containing an alcohol in the polarizing element can be used. The urea-based compound may be included during the manufacturing process of the polarizing element, or it may be included in the adhesive described later for laminating the polarizing element with the transparent protective film, thereby being incorporated into the polarizing element.

[0066] (Dicarboxylic acid)

[0067] The polarizing element may also contain a dicarboxylic acid. A polarizing element containing a dicarboxylic acid can further suppress the decrease in transmittance. The dicarboxylic acid can be the same as that which may be contained in the adhesive described later. As a method for containing the dicarboxylic acid in the polarizing element, the same method as for containing an alcohol in the polarizing element can be used. The dicarboxylic acid can be included in the manufacturing process of the polarizing element, or it can be included in the adhesive described later for laminating the polarizing element with the transparent protective film, thereby being contained within the polarizing element.

[0068] (Manufacturing method of polarization element)

[0069] There is no particular limitation on the manufacturing method of polarization elements. Typical methods include: a method of producing a PVA-based resin film pre-wound into a roll and then stretching, dyeing, cross-linking, etc. (hereinafter referred to as "manufacturing method 1"); and a method including a process of coating a coating liquid containing PVA-based resin onto a substrate film to form a PVA-based resin layer as a coating layer, and stretching the resulting laminate (hereinafter referred to as "manufacturing method 2").

[0070] Manufacturing method 1 can be carried out by a process of uniaxially stretching a PVA-based resin film, dyeing the PVA-based resin film with dichroic pigments such as iodine to adsorb dichroic pigments, treating the PVA-based resin film with adsorbed dichroic pigments with a boric acid aqueous solution, and washing with water after treatment with boric acid aqueous solution.

[0071] The swelling process involves immersing a PVA-based resin film in a swelling bath. This process removes surface contaminants and anti-blocking agents from the PVA-based resin film, and also suppresses uneven dyeing by causing the film to swell. The swelling bath typically uses a water-based medium, such as water, distilled water, or pure water. Surfactants or alcohols can also be added to the swelling bath as needed. From the viewpoint of controlling the potassium content of the polarizing element, potassium iodide can 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.

[0072] 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. Regarding the immersion time in the swelling bath, since the degree of swelling of the PVA-based resin film is affected by the temperature of the swelling bath, it cannot be fixed indefinitely; however, 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 can be performed only once or multiple times as needed.

[0073] The dyeing process involves immersing a PVA-based resin film in a dyeing bath (iodine solution). This process allows the PVA-based resin film to adsorb dichroic pigments such as iodine and orient these pigments. The iodine solution is typically an aqueous solution containing iodine and iodides 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, and titanium iodide. Among these, potassium iodide is suitable from the viewpoint of controlling the potassium content in the polarizing element.

[0074] The concentration of iodine in the staining bath is preferably 0.01% by mass or more and 1% by mass or less, more preferably 0.02% by mass or more and 0.5% by mass or less. The concentration of iodide in the 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.

[0075] 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 fixed because the degree of dyeing of the PVA-based resin film is affected by the temperature of the dyeing bath; however, it is preferably 10 seconds or higher and 300 seconds or lower, more preferably 20 seconds or higher and 240 seconds or lower. The dyeing process can be performed only once or multiple times as needed.

[0076] The crosslinking process involves immersing a PVA-based resin film, dyed in the dyeing process, in a treatment bath (crosslinking bath) containing a boron compound. The boron compound crosslinks the polyvinyl alcohol-based resin film, allowing iodine molecules or dye molecules to adsorb onto the crosslinked structure. Examples of boron compounds include boric acid, borates, and borax. The crosslinking bath is generally an aqueous solution; however, it can also be a mixture of an organic solvent miscible with water and water. From the viewpoint of controlling the potassium content in the polarizing element, the crosslinking bath preferably contains potassium iodide.

[0077] In the crosslinking bath, the concentration of the boron compound is preferably 1% by mass or more and 15% by mass or less, more preferably 1.5% by mass or more and 10% by mass or less, and even more preferably 2% by mass or more and 5% by mass or less. When potassium iodide is used in the crosslinking bath, the concentration of potassium iodide in the crosslinking bath is preferably 1% by mass or more and 15% by mass or less, more preferably 1.5% by mass or more and 10% by mass or less, and even more preferably 2% by mass or more and 5% by mass or less.

[0078] The temperature of the crosslinking bath is preferably 20°C or higher and 70°C or lower, more preferably 30°C or higher and 60°C or lower. The immersion time in the crosslinking bath cannot be fixed because the degree of crosslinking of the PVA resin film is affected by the temperature of the crosslinking bath; however, it is preferably 5 seconds or higher and 300 seconds or lower, more preferably 10 seconds or higher and 200 seconds or lower. The crosslinking process can be performed only once or multiple times as needed.

[0079] The stretching process is a procedure in which a PVA-based resin film is stretched to a specified ratio in at least one direction. Generally, the PVA-based resin film is uniaxially stretched along the transport direction (length direction). There are no particular restrictions on the stretching method; either wet stretching or dry stretching can be used. The stretching process can be performed once or multiple times as needed. The stretching process can be performed at any stage in the manufacturing of polarization elements.

[0080] The treatment bath (stretching bath) in the wet stretching process can typically be water or a mixture of water and an organic solvent miscible with water. From the viewpoint of controlling the potassium content in the polarizing element, the stretching bath preferably contains potassium iodide. When potassium iodide is used in the stretching bath, the concentration of potassium iodide in the stretching bath is preferably 1% by mass or more and 15% by mass or less, more preferably 2% by mass or more and 10% by mass or less, and even more preferably 3% by mass or more and 6% by mass or less. From the viewpoint of suppressing film breakage during stretching, the treatment bath (stretching bath) may contain a boron compound. When a boron compound is included, the concentration of the boron compound in the stretching bath is preferably 1% by mass or more and 15% by mass or less, more preferably 1.5% by mass or more and 10% by mass or less, and even more preferably 2% by mass or more and 5% by mass or less.

[0081] 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 fixed because the degree of stretching of the PVA-based resin film is affected by the temperature of the stretching bath; however, it is preferably 10 seconds or higher and 800 seconds or lower, more preferably 30 seconds or higher and 500 seconds or lower. The stretching treatment in the wet stretching method can be performed together with any one or more of the following processing steps: swelling, dyeing, crosslinking, and cleaning.

[0082] Examples of dry stretching methods include inter-roll stretching, heated roll stretching, and compression stretching. It should be noted that dry stretching can be performed concurrently with the drying process.

[0083] The total stretch ratio (cumulative stretch ratio) applied to the polyvinyl alcohol-based resin film can be appropriately set according to the purpose, but it is preferably 2 times or more and 7 times or less, more preferably 3 times or more and 6.8 times or less, and even more preferably 3.5 times or more and 6.5 times or less.

[0084] The cleaning process involves immersing the polyvinyl alcohol (PVA) resin film in a cleaning bath to remove 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. Furthermore, from the viewpoint of controlling the potassium content in the polarizing element, potassium iodide is preferably used 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.

[0085] 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. Regarding the immersion time in the cleaning bath, since the degree of cleaning of the PVA resin film is affected by the temperature of the cleaning bath, it cannot be fixed in general; however, 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 can be performed only once or multiple times as needed.

[0086] The drying process involves drying the PVA-based resin film, which has been cleaned in the cleaning process, to obtain the polarizing element. Drying can be performed using any suitable method, such as natural drying, forced-air drying, or heat drying.

[0087] Manufacturing method 2 can be performed through the following steps: applying a coating solution containing PVA-based resin onto a substrate film; uniaxially stretching the resulting laminated film; adsorbing the dichroic pigment by dyeing the PVA-based resin layer of the uniaxially stretched laminated film with a dichroic pigment to form a polarizing element; treating the film with the adsorbed dichroic pigment with a boric acid aqueous solution; and washing with water after treatment with the boric acid aqueous solution. The substrate film used to form the polarizing element can also be used as a protective layer for the polarizing element. The substrate film can be peeled off from the polarizing element as needed.

[0088] <Transparent Protective Film>

[0089] The transparent protective film used in this embodiment (hereinafter also referred to as the "protective film") is adhered to at least one side of the polarizing element via an adhesive layer. The transparent protective film may be adhered to one or both sides of the polarizing element, but it is preferred to adhere to both sides.

[0090] The protective film can also possess other optical functions and can be fabricated into a multilayered structure. From an optical property point of view, a thin protective film is preferred; however, if it is too thin, its strength decreases and its processability suffers. An appropriate film thickness is 5 μm or more and 100 μm or less, preferably 10 μm or more and 80 μm or less, and more preferably 15 μm or more and 70 μm or less.

[0091] The protective film can be made of cellulose acylated film, polycarbonate resin-based film, cyclic olefin resin-based film containing norbornene, (meth)acrylic polymer film, polyethylene terephthalate (PET) and other polyester resin-based film. When using a water-based adhesive such as PVA adhesive to bond the protective film to both sides of the polarizing element, from a moisture permeability perspective, it is preferable that at least one side of the protective film is either a cellulose acylated film or a (meth)acrylic polymer film, with a cellulose acylated film being preferred.

[0092] For purposes such as viewing angle compensation, at least one of the protective films can have a phase difference function. In this case, the protective film itself can have a phase difference function, or it can have a separate phase difference layer, or a combination of both. The film with the phase difference function can be directly attached to the polarization element via an adhesive, or it can be a structure in which another protective film attached to the polarization element is sandwiched between the two films and attached via an adhesive or bonding agent.

[0093] <Adhesive layer>

[0094] As the adhesive layer constituting the adhesive layer for bonding the protective film to the polarizing element, an alcohol-containing adhesive is preferred. Water-based adhesives, solvent-based adhesives, and active energy radiation-cured adhesives can be used; however, from the viewpoint of containing alcohol, a water-based adhesive is preferred, and one containing PVA-based resin is even more desirable. By using an alcohol-containing adhesive, the decrease in transmittance of the polarizing plate under high-temperature conditions can be suppressed.

[0095] The thickness of the adhesive during application can be set to an optional value, for example, in a manner that allows for the formation of an adhesive layer with a desired thickness after curing or heating (drying). The thickness of the adhesive layer formed by the adhesive is preferably 0.01 μm or more and 7 μm or less, more preferably 0.01 μm or more and 5 μm or less, further preferably 0.01 μm or more and 2 μm or less, and most preferably 0.01 μm or more and 1 μm or less.

[0096] The following description of the adhesive is based on a preferred range for the case where the polarizing element does not contain alcohol during manufacturing. If the polarizing element contains alcohol, the following values ​​can be adjusted appropriately. For a specific example of alcohol, the same alcohol as that contained in the polarizing element described above can be used. During the drying process of forming the adhesive layer when bonding the polarizing element to the protective film, a portion of the alcohol can migrate from the adhesive layer to the polarizing element, etc.

[0097] When the adhesive is an aqueous adhesive containing PVA-based resin, the alcohol content in the adhesive is preferably 30 parts by weight or more and 2000 parts by weight or less relative to 100 parts by weight of PVA-based resin, more preferably 100 parts by weight or more and 1800 parts by weight or less, further preferably 500 parts by weight or more and 1800 parts by weight or less, and most preferably 800 parts by weight or more and 1500 parts by weight or less. If it is less than 30 parts by weight, the effect of improving high-temperature durability cannot be fully obtained. On the other hand, when the alcohol content exceeds 2000 parts by weight, the color tone sometimes deteriorates. By setting the alcohol content in the adhesive to the above range, the drying efficiency can be improved in the drying process after the protective film is laminated with the adhesive between the polarizing element and the polarizing element, and the alcohol content in the polarizing plate can be easily adjusted to the desired amount.

[0098] In a configuration in which a transparent protective film is bonded to both sides of a polarizing element via an adhesive layer, the adhesive layer on both sides of the polarizing element may be an alcohol-containing layer on only one side, but it is preferable that the adhesive layer on both sides is an alcohol-containing layer.

[0099] To meet the demand for thinner polarizing plates, a polarizing plate with a transparent protective film on only one side of the polarizing element has been developed. In this configuration, the transparent protective film is also laminated via an adhesive layer containing alcohol. As a method for manufacturing this type of polarizing plate with a transparent protective film on only one side of the polarizing element, a method can be considered that involves first manufacturing a polarizing plate with transparent protective films adhered to both sides via adhesive layers, and then peeling off one side of the transparent protective film. In using this manufacturing method, alcohol can be contained in the adhesive layer on either side, but it is preferable that both adhesive layers contain alcohol. When using an adhesive layer containing alcohol only on one side of the polarizing element, it is preferable that the adhesive layer on the side of the film that is not peeled off contains alcohol.

[0100] (Water-based adhesive)

[0101] As a water-based adhesive, any suitable water-based adhesive can be used; however, it is preferred to use a water-based adhesive containing PVA-based resin (PVA-based adhesive). From an adhesiveness perspective, the average degree of polymerization of the PVA-based resin contained in the water-based adhesive is preferably 100 or more and 5500 or less, more preferably 1000 or more and 4500 or less. From an adhesiveness perspective, 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.

[0102] As the PVA-based resin contained in the water-based adhesive, a resin containing acetyl groups is preferred because it exhibits excellent adhesion and durability to the protective film. The PVA-based resin containing acetyl groups can be obtained, for example, by reacting a PVA-based resin with a diene using an optional method. The degree of acetyl group modification in the PVA-based resin containing acetyl groups is typically 0.1 mol% or more, preferably 0.1 mol% or more and 20 mol% or less. The resin concentration of the water-based adhesive is preferably 0.1% by mass or more and 15% by mass or less, more preferably 0.5% by mass or more and 10% by mass or less.

[0103] Water-based adhesives may also contain crosslinking agents. Known crosslinking agents can be used. Examples of crosslinking agents include water-soluble epoxy compounds, dialdehydes, and isocyanates.

[0104] When the PVA resin is a PVA resin containing acetyl groups, the crosslinking agent is preferably any one of glyoxal, glyoxylate, or hydroxymethyl melamine, more preferably any one of glyoxal or glyoxylate, and particularly preferably glyoxal.

[0105] (Active energy radiation curing adhesive)

[0106] Reactive energy radiation-cured adhesives are adhesives that cure upon exposure to reactive energy radiation such as ultraviolet rays. Examples include adhesives containing polymerizable compounds and photopolymerization initiators, adhesives containing photoreactive resins, and adhesive resins containing photoreactive crosslinking agents. 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 photopolymerization initiators include compounds containing substances that generate reactive species such as neutral free radicals, anionic free radicals, and cationic free radicals upon exposure to reactive energy radiation such as ultraviolet rays.

[0107] (Urea compounds)

[0108] The adhesive also contains at least one urea compound selected from urea, urea derivatives, thiourea, and thiourea derivatives. By including a urea compound in the adhesive layer formed by the adhesive, high-temperature durability can be further improved. During the drying process of the adhesive layer formed by bonding the adhesive to a protective film, a portion of the urea compound can migrate from the adhesive layer to polarizing elements, etc. Urea compounds include water-soluble and poorly water-soluble compounds; either type of urea compound can be used. When using a poorly water-soluble urea compound in a water-soluble adhesive, a dispersion method is preferably designed to prevent an increase in turbidity after the adhesive layer is formed.

[0109] When the adhesive is an aqueous adhesive containing PVA-based resin, the amount of urea compound added is preferably 0.1 parts by weight or more and 400 parts by weight or less relative to 100 parts by weight of PVA, more preferably 1 part by weight or more and 200 parts by weight or less, and even more preferably 3 parts by weight or more and 100 parts by weight or less.

[0110] (Urea derivatives)

[0111] Urea derivatives are compounds 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 limitations on the substituent, but substituents containing carbon, hydrogen, and oxygen atoms are preferred. Some urea derivatives have low solubility relative to water, but sufficient solubility relative to alcohols. In this case, dissolving the urea compound in an alcohol to prepare an alcoholic solution of the urea compound, and then adding the alcoholic solution of the urea compound to an aqueous PVA solution to prepare an adhesive, is also a preferred method.

[0112] Specific examples of urea derivatives, for monosubstituted ureas, include: methylurea, ethylurea, propylurea, butylurea, isobutylurea, N-octadecylurea, 2-hydroxyethylurea, hydroxyurea, acetylurea, allylurea, 2-propynylurea, cyclohexylurea, phenylurea, 3-hydroxyphenylurea, (4-methoxyphenyl)urea, benzylurea, benzoylurea, o-tolylurea, and p-tolylurea. For disubstituted ureas, include: 1,1-dimethylurea, 1,3-dimethylurea, 1,1-diethylurea, 1,3-diethylurea, 1,3-di(hydroxymethyl)urea, 1,3-tert-butylurea, 1,3-dicyclohexylurea, 1,3-diphenylurea, 1,3-di(4-methoxyphenyl)urea, 1-acetyl-3-methylurea, 2-imidazolinone (vinylurea), and tetrahydro-2-pyrimidinone (acrylurea). Examples of tetrasubstituted ureas include: tetramethylurea, 1,1,3,3-tetraethylurea, 1,1,3,3-tetrabutylurea, 1,3-dimethoxy-1,3-dimethylurea, 1,3-dimethyl-2-imidazolinone, and 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone.

[0113] (Thiocarbamide derivatives)

[0114] Thiourea derivatives are compounds in which at least one of the four hydrogen atoms of a thiourea molecule has been substituted with a substituent. In this case, there are no particular restrictions on the substituent, but substituents containing carbon, hydrogen, and oxygen atoms are preferred.

[0115] Specific examples of thiourea derivatives, in terms of monosubstituted thioureas, include: 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. Examples of disubstituted thioureas 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. Examples of trisubstituted thioureas include trimethylthiourea. Examples of tetrasubstituted thioureas include tetramethylthiourea and 1,1,3,3-tetraethylthiourea.

[0116] From the perspective of further suppressing the decrease in transmittance under high-temperature environments when used in image display devices with interlayer filling, urea derivatives or thiourea derivatives are preferred among urea compounds, and urea derivatives are more preferred. Among urea derivatives, monosubstituted urea or disubstituted urea are preferred, and monosubstituted urea is more preferred. Disubstituted urea includes 1,1-substituted urea and 1,3-substituted urea, and 1,3-substituted urea is more preferred.

[0117] (Dicarboxylic acid)

[0118] The adhesive may also contain dicarboxylic acids. By using an adhesive containing dicarboxylic acids, the decrease in transmittance of the polarizer under high-temperature conditions can be suppressed. Examples of dicarboxylic acids include: oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, tartaric acid, glutamic acid, malic acid, maleic acid, fumaric acid, itaconic acid, kojic acid, 1,4-cyclohexanedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 4,4-biphenyldicarboxylic acid, 2,5-pyridinedicarboxylic acid, 3,5-pyridinedicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenylmethanedicarboxylic acid, oxaloacetic acid, methyl fumaric acid, 2,6-pyridinedicarboxylic acid, etc. Among these, citric acid, malic acid, maleic acid, or tartaric acid are preferred. These dicarboxylic acids can be used alone, or in combination of two or more.

[0119] [Manufacturing method of polarizing plate]

[0120] The method for manufacturing a polarizing plate according to this embodiment includes a moisture content adjustment step and a lamination step. In the moisture content adjustment step, when manufacturing a polarizing plate having feature (a), the moisture content of the polarizing element is adjusted such that it is above the equilibrium moisture content at 20°C and 20% relative humidity, and below the equilibrium moisture content at 20°C and 50% relative humidity. The moisture content of the polarizing element can be adjusted according to the aforementioned description of the moisture content of the polarizing element. In the moisture content adjustment step, when manufacturing a polarizing plate having feature (b), the moisture content of the polarizing plate is adjusted such that it is above the equilibrium moisture content at 20°C and 20% relative humidity, and below the equilibrium moisture content at 20°C and 50% relative humidity. The moisture content of the polarizing plate can be adjusted according to the aforementioned description of the moisture content of the polarizing plate. In the lamination step, the polarizing element and the transparent protective film are laminated via the aforementioned adhesive layer. In the lamination process, for example, polarizing elements that have not undergone alcohol-containing treatment are bonded to a transparent protective film using an alcohol-containing adhesive. The order of the moisture content adjustment process and the lamination process is not limited; alternatively, the moisture content adjustment process and the lamination process can be performed in parallel.

[0121] [Composition of an image display device]

[0122] The polarizing plate of this embodiment can be used in various image display devices such as liquid crystal display devices and organic EL display devices. In image display devices with an interlayer filling configuration where the polarizing plate is formed by contacting both sides of the polarizing plate with a layer other than an air layer, specifically a solid layer such as an adhesive layer, the transmittance tends to decrease at high temperatures. In the image display device using the polarizing plate of this embodiment, even with an interlayer filling configuration, the decrease in the transmittance of the polarizing plate at high temperatures can be suppressed. An example of an image display device is a configuration having an image display unit, a first adhesive layer laminated on the visible side surface of the image display unit, and a polarizing plate laminated on the visible side surface of the first adhesive layer. This image display device may also have a second adhesive layer laminated on the visible 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 can be suitably used in an image display device having an interlayer filling configuration in which a transparent member is disposed on the visible side of the image display device, the polarizing plate and the image display unit are bonded using the first adhesive layer, and the polarizing plate and the transparent member are bonded using the second adhesive layer. In this specification, either or both of the first adhesive layer and the second adhesive layer are sometimes referred to simply as "adhesive layer". It should be noted that the components used for bonding the polarizing plate to the image display unit, and the components used for bonding the polarizing plate to the transparent component, are not limited to adhesive layers, and may also be adhesive layers.

[0123] <Image Display Unit>

[0124] Examples of image display units include liquid crystal cells and organic EL cells. As a liquid crystal cell, any of the following can be used: a reflective liquid crystal cell utilizing external light, a transmissive liquid crystal cell utilizing light from a light source such as a backlight, or a semi-transmissive / semi-reflective liquid crystal cell utilizing both external light and light from a light source. In the case where the liquid crystal cell utilizes light from a light source, the image display device (liquid crystal display device) also provides a polarizing plate on the side of the image display cell (liquid crystal cell) opposite to the viewable side, and further provides a light source. The polarizing plate on the light source side is preferably bonded to the liquid crystal cell via a suitable adhesive layer. As for the driving method of the liquid crystal cell, any type of driving method can be used, such as VA mode, IPS mode, TN mode, STN mode, or π-type bending orientation.

[0125] As an organic EL unit, an organic EL unit in which a transparent electrode, an organic light-emitting layer, and a metal electrode are sequentially stacked on a transparent substrate to form a light emitter (organic electroluminescent emitter) can be appropriately used. The organic light-emitting layer is a stack of various organic thin films and can be composed of various layers, such as the following: a stack containing a hole injection layer including a triphenylamine derivative 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 including a perylene derivative; or a stack of a hole injection layer, a light-emitting layer, and an electron injection layer.

[0126] <Attachment of image display unit to polarizing plate>

[0127] In the bonding of the image display unit and the polarizing plate, an adhesive layer (adhesive sheet) can be appropriately used. From an operability perspective, a method of bonding the image display unit to a polarizing plate with an adhesive layer attached to one side of the polarizing plate is preferred. The attachment of the adhesive layer to the polarizing plate can be performed in an appropriate manner. Examples include: preparing an adhesive solution containing 10% by mass or more and 40% by mass or less of a base polymer or a combination thereof dissolved or dispersed in a solvent formed from a single substance or mixture of suitable solvents such as toluene or ethyl acetate, and directly attaching it to the polarizing plate using an appropriate spreading method such as casting or coating; or forming the adhesive layer on a separator and transferring it to the polarizing plate.

[0128] <Adhesive layer>

[0129] The adhesive layer can be formed in one or more layers, preferably in one layer. The adhesive layer can be formed from an adhesive composition with (meth)acrylic resin, rubber resin, urethane resin, ester resin, silicone resin, or polyvinyl ether resin as the main component. Among these, adhesive compositions with (meth)acrylic resin as the base polymer are particularly suitable, exhibiting excellent transparency, weather resistance, and heat resistance. The adhesive composition can also be of the active energy radiation curing type or the thermosetting type.

[0130] The (meth)acrylic resin (base polymer) used as a component of the adhesive can suitably be a polymer or copolymer of one or more (meth)acrylates such as butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. It is preferable to copolymerize a polar monomer in the base polymer. Examples of polar monomers include (meth)acrylate compounds, 2-hydroxypropyl (meth)acrylate compounds, hydroxyethyl (meth)acrylate compounds, (meth)acrylamide compounds, N,N-dimethylaminoethyl (meth)acrylate compounds, and glycidyl (meth)acrylate compounds, which are monomers having carboxyl, hydroxyl, amide, amino, or epoxy groups.

[0131] The adhesive composition may contain only the aforementioned base polymer, but it typically also contains a crosslinking agent. Examples of crosslinking agents include: metal ions with a valence of divalent or higher that form a carboxylic acid metal salt with a carboxyl group; polyamine compounds that form an amide bond with a carboxyl group; polyepoxide 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.

[0132] The active energy radiation-curable adhesive composition possesses the property of curing upon irradiation by active energy radiation such as ultraviolet rays or electron beams. It also exhibits adhesiveness even before irradiation, enabling it to adhere tightly to substrates such as films, and the ability to adjust the adhesion strength upon curing due to irradiation. The active energy radiation-curable adhesive composition is preferably ultraviolet-curable. In addition to containing a base polymer and a crosslinking agent, the active energy radiation-curable adhesive composition also contains an active energy radiation polymerizable compound. Depending on the requirements, it may contain photopolymerization initiators, photosensitizers, etc.

[0133] The adhesive composition may contain additives such as microparticles, beads (resin beads, glass beads, etc.) for imparting light scattering properties, glass fibers, resins other than the base polymer, tackifiers, fillers (metal powders, other inorganic powders, etc.), antioxidants, ultraviolet absorbers, dyes, pigments, colorants, defoamers, corrosion inhibitors, and photopolymerization initiators.

[0134] The adhesive layer can be formed by applying an organic solvent dilution of the adhesive composition described above to the surface of a substrate film, an image display unit, or a polarizing plate and then drying it. The substrate film is typically a thermoplastic resin film; a typical example is a release film that has undergone a release treatment. For example, the release film may be a film in which the adhesive layer-forming side of a film containing resins such as polyethylene terephthalate, polybutylene terephthalate, polycarbonate, or polyarylate has undergone a silicone treatment or other release treatment.

[0135] An adhesive composition can be directly applied to the release surface of the release film to form an adhesive layer, and this adhesive layer with the release film can be laminated onto the surface of the polarizer. Alternatively, an adhesive composition can be directly applied to the surface of the polarizer to form an adhesive layer, and a release film can be laminated on the outer surface of the adhesive layer.

[0136] When the adhesive layer is applied to the surface of the polarizing plate, it is preferable to perform surface activation treatments such as plasma treatment or corona treatment on the bonding surface of the polarizing plate and / or the bonding surface of the adhesive layer, and more preferably to perform corona treatment.

[0137] Alternatively, an adhesive sheet can be prepared by coating an adhesive composition onto a second release liner to form an adhesive layer, and then stacking a release liner on the formed adhesive layer. The adhesive layer with the release liner after peeling the second release liner from the adhesive sheet is then stacked on a polarizing plate. The second release liner is a membrane with weaker adhesion to the adhesive layer and easier to peel off compared to the release liner.

[0138] The thickness of the adhesive layer is not particularly limited, but is preferably 1 μm or more and 100 μm or less, more preferably 3 μm or more and 50 μm or less, and may also be 20 μm or more.

[0139] <Transparent Components>

[0140] Examples of transparent components that can be disposed on the visible side of an image display device include transparent panels (window layers) and touch panels. For the transparent panel, a transparent panel with appropriate mechanical strength and thickness is used. Examples of such transparent panels include transparent resin panels made of polyimide-based resins, acrylic-based resins, polycarbonate-based resins, or glass panels. Functional layers such as anti-reflective layers can also be laminated on the visible side of the transparent panel. Furthermore, when the transparent panel is a transparent resin panel, a hard coating can be laminated to improve physical strength, and a low-permeability layer can be laminated to reduce moisture permeability. For the touch panel, various touch panels using resistive film, capacitive, optical, and ultrasonic methods can be used; glass panels and transparent resin panels with touch sensor functionality can also be used. When using a capacitive touch panel as the transparent component, it is preferable to further provide a transparent panel made of glass or a transparent resin panel on the visible side relative to the touch panel.

[0141] <Fitting of polarizing plate with transparent component>

[0142] In bonding the polarizing plate to the transparent component, adhesives or active energy radiation-cured adhesives can be appropriately used. When using adhesives, they can be applied in a suitable manner. For example, the method of applying the adhesive layer used in the bonding of the image display unit to the polarizing plate described above can be cited as a specific application method.

[0143] When using an active energy ray-cured adhesive, to prevent the adhesive solution from spreading before curing, the following method can be appropriately used: a dike material is set up to surround the periphery of the image display panel; a transparent component is placed on the dike material; and the adhesive solution is then injected. After the adhesive solution is injected, alignment and degassing are performed as needed, followed by curing by irradiation with active energy rays.

[0144] Example

[0145] The present invention will now be described in detail based on embodiments. The materials, reagents, quantities, proportions, and operations shown in the following embodiments may be appropriately modified without departing from the spirit of the invention.

[0146] Therefore, the present invention is not limited or restricted by the following embodiments.

[0147] (1) Measurement of the thickness of the polarization element:

[0148] The measurements were performed using a digital micrometer "MH-15M" manufactured by Nikon Corporation.

[0149] (2) Determination of the transmittance of the polarizing plate with visibility correction:

[0150] Measurements were performed using a spectrophotometer with an integrating sphere (V7100 manufactured by Nippon Spectrophotometer Co., Ltd., 2-degree field of view; C light source).

[0151] (3) Determination of the amount of alcohol (methanol) in the polarizing plate:

[0152] The polarizing plate was cut into 1 cm square pieces to obtain the evaluation sample. 5 mL of ultrapure water was added to the evaluation sample, and the mixture was heated at 70 °C for 30 minutes. After stirring, the sample was measured using the GC-FID method under the following conditions.

[0153] (Gas Chromatography Analysis Conditions)

[0154] Column: DB-WAX 30m×0.250mm×0.25μm, ID (Agilent Technologies) or equivalent;

[0155] Carrier gas: Helium, 1.0 mL / min;

[0156] Column temperature: 40℃ (hold for 5 minutes) → increase temperature at 20℃ / minute → 240℃ (hold for 10 minutes);

[0157] Inlet temperature: 240℃, injection volume: 1μL, split ratio: 50:1;

[0158] Detector temperature: 240℃, Detector: FID.

[0159] (4) Measurement of yellow index (yellowness):

[0160] A Konica Minolta CM-3700A spectrophotometer was used. Reflected light was measured in SCI mode to determine the tristimulus values ​​(X, Y, Z). The yellow index (YI) was calculated using the following formula based on ASTM E313-73.

[0161] YI = 100 × (1.000 - 0.847 × Z / Y)

[0162] <Fabrication of Polarizing Elements>

[0163] A 40 μm thick PVA film, formed from PVA with an average degree of polymerization of approximately 2400 and a saponification degree of 99.9 mol% or higher, was uniaxially stretched to approximately 5 times its original length in a dry manner. While maintaining tension, it was then immersed in pure water at 60°C for 1 minute. Subsequently, it was immersed in an aqueous solution of iodine / potassium iodide / water at a weight ratio of 0.05 / 5 / 100 at 28°C for 60 seconds. Following this, it was immersed in an aqueous solution of potassium iodide / boric acid / water at a weight ratio of 8.5 / 8.5 / 100 at 72°C for 300 seconds. Finally, 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 with iodine adsorbed and oriented on the PVA.

[0164] [Preparation of Adhesives 1-4]

[0165] (Preparation of PVA solution A for adhesives)

[0166] 50g of a modified PVA resin containing acetyl groups (GOHSENX Z-410 manufactured by Mitsubishi Chemical Corporation) was dissolved in 950g of pure water. The solution was heated at 90°C for 2 hours and then cooled to room temperature to obtain a PVA solution for adhesives (hereinafter referred to as "PVA solution A").

[0167] (Preparation of adhesives 1-4)

[0168] The PVA solution A prepared above, pure water, maleic acid, 40% glyoxal solution, and methanol were combined in the amounts shown in Table 1 to prepare adhesives 1-4.

[0169] [Table 1]

[0170]

[0171] <Preparation of Transparent Protective Film>

[0172] A commercially available cellulose acylated membrane TD40N (manufactured by Fujifilm Corporation, 40 μm thick) was immersed in a 1.5 mol / L NaOH aqueous solution (saponification solution) maintained at 55°C for 2 minutes, followed by washing with water. Then, it was immersed in a 0.05 mol / L sulfuric acid aqueous solution at 25°C for 30 seconds, and further washed with running water for 30 seconds to neutralize the membrane. After repeated dehydration three times using an air knife, the membrane was dried in a drying zone at 70°C for 15 seconds to produce a saponified membrane, which was then used as a transparent protective film.

[0173] [Making a Polarizing Plate]

[0174] A transparent protective film is bonded to both sides of the polarizing element using a roller laminator via adhesive 1. After bonding, the adhesive is dried by heat treatment at 65°C for 12 minutes to obtain polarizing plate 1. The single-cell transmittance of polarizing plate 1 is 40.8%. The adhesive layer is adjusted to achieve a dried thickness of 50 nm on both sides.

[0175] In polarizing plate 1, adhesive 1 is replaced with adhesives 2-4 to obtain polarizing plates 2-4. The transmittance of each polarizing plate 2-4 is 40.8%.

[0176] (Adjustment of moisture content in polarizing plate (polarizing element))

[0177] The polarizing plates 1-4 obtained above were stored at 20°C and 30% relative humidity for 72 hours. The moisture content was measured using the Karl Fischer method after 66, 69, and 72 hours of storage. The moisture content values ​​remained unchanged after 66, 69, and 72 hours. Therefore, the moisture content of polarizing plates 1-4 can be considered the same as the equilibrium moisture content under the 72-hour storage environment used in this experimental example. When the moisture content of a polarizing plate reaches equilibrium under a certain storage environment, the moisture content of the polarizing element in the polarizing plate can also be considered to have reached equilibrium under that storage environment. Furthermore, when the moisture content of the polarizing element in a polarizing plate reaches equilibrium under a certain storage environment, the moisture content of the polarizing plate can also be considered to have reached equilibrium under that storage environment.

[0178] For optical laminates 1 to 4, any polarizing plate from the polarizing plates 1 to 4 shown in Table 2 is used, and the laminates are stored at a temperature of 20°C and a relative humidity of 30% for 72 hours to allow the moisture content of the polarizing plates (polarizing elements) to reach the equilibrium moisture content of the environment shown in Table 2, thereby enabling the fabrication process.

[0179] After this operation, the methanol content of the polarizing plate (optical laminate) was measured after being stored under specified temperature and humidity conditions and the moisture content was adjusted. The results are shown in Table 2.

[0180] <High Temperature Durability Evaluation>

[0181] (Preparation of the evaluation sample)

[0182] An acrylic adhesive (manufactured by LINTEC Corporation, model #7) is formed on both sides of optical laminates 1 to 4. The polarizer is then cut to a size of 110mm × 60mm, with the absorption axis parallel to the long side. Alkali-free glass (Corning Corporation "EAGLE XG", size 120mm × 70mm) is laminated onto each adhesive surface to create an evaluation sample. The evaluation sample thus obtained is subjected to a high-temperature durability test by autoclaving at 50°C and 5 atmospheres for 15 minutes, followed by exposure at 105°C for 72 hours.

[0183] The results of Yi after 60 hours and after 72 hours are shown in Table 2.

[0184] [Table 2]

[0185]

Claims

1. A polarizing plate comprising a polarizing element having iodine adsorbed and oriented in a polyvinyl alcohol-based resin layer, and a transparent protective film laminated on at least one surface of the polarizing element. The amount of alcohol contained in the polarizing plate is 4 μg / cm 2 The above and 230 μg / cm 2 Hereinafter, The alcohol is methanol. The polarizing element and the transparent protective film were bonded together using an adhesive layer formed from an adhesive containing the alcohol and a dicarboxylic acid. The moisture content of the polarizing element is above the equilibrium moisture content at a temperature of 20°C and a relative humidity of 20%, and below the equilibrium moisture content at a temperature of 20°C and a relative humidity of 50%.

2. A polarizing plate comprising a polarizing element having iodine adsorbed and oriented in a polyvinyl alcohol-based resin layer, and a transparent protective film laminated on at least one surface of the polarizing element. The polarizing plate contains 4 μg / cm³ of alcohol. 2 Above and 230 μg / cm 2 the following, The alcohol is methanol. The polarizing element and the transparent protective film were bonded together using an adhesive layer formed from an adhesive containing the alcohol and a dicarboxylic acid. The moisture content of the polarizing plate is above the equilibrium moisture content at a temperature of 20°C and a relative humidity of 20%, and below the equilibrium moisture content at a temperature of 20°C and a relative humidity of 50%.

3. The polarizing plate according to claim 1 or 2, wherein, The adhesive comprises a polyvinyl alcohol-based resin.

4. The polarizing plate according to claim 3, wherein, The content of alcohol in the adhesive is 100 parts by weight or more and 2000 parts by weight or less, relative to 100 parts by weight of the polyvinyl alcohol resin.

5. The polarizing plate according to any one of claims 1 to 4, wherein, The thickness of the adhesive layer is 0.01 μm to 7 μm.

6. The polarizing plate according to any one of claims 1 to 5, wherein, The polarizing plate is used in the image display device. In the image display device, a layer other than an air layer is disposed on both sides of the polarizing plate.

7. An image display device, comprising: Image display unit The first adhesive layer and the layer stacked on the visible side surface of the image display unit The polarizing plate according to any one of claims 1 to 6 is laminated on the visible side surface of the first adhesive layer.

8. The image display device according to claim 7, further comprising: The second adhesive layer and the layer laminated on the visible side surface of the polarizing plate A transparent component is laminated on the visible side surface of the second adhesive layer.

9. The image display device according to claim 8, wherein, The transparent component is a glass plate or a transparent resin plate.

10. The image display device according to claim 8, wherein, The transparent component is a touch panel.

Images