CN116324543A

CN116324543A - Polarizing plate and image display device using same

Info

Publication number: CN116324543A
Application number: CN202180069710.8A
Authority: CN
Inventors: 宇田幸弘; 松本寿和; 竹内智康; 斋藤邦智; 中里成志
Original assignee: Sumitomo Chemical Co Ltd
Current assignee: Sumitomo Chemical Co Ltd
Priority date: 2020-11-13
Filing date: 2021-10-25
Publication date: 2023-06-23
Also published as: KR20230098791A; JP2022078508A; WO2022102387A1; TW202229009A

Abstract

The purpose of the present invention is to provide a polarizing plate which can prevent yellowing and has excellent high-temperature durability even when used in an image display device constituted by interlayer filling, and an image display device. A polarizing plate comprising a polarizing element in which iodine is adsorbed and oriented to a polyvinyl alcohol 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 [ mu ] g/cm ² Above and 230 μg/cm ² Hereinafter, the water content of the polarizing element is equal to or higher than the equilibrium water content of 20 ℃ and 20% relative humidity, and equal to or lower than the equilibrium water content of 50% relative humidity at 20 ℃.

Description

Polarizing plate and image display device using same

Technical Field

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

Background

Liquid crystal display devices (LCDs) are widely used not only for liquid crystal televisions but also for mobile devices such as personal computers and cellular phones, and for vehicle-mounted applications such as navigation devices. In general, a liquid crystal display device includes a liquid crystal panel having polarizing plates attached to both sides of a liquid crystal cell with an adhesive, and displays by controlling light from a backlight using the liquid crystal panel. In recent years, organic EL display devices are widely used in mobile devices such as televisions and cellular phones, and in vehicle-mounted applications such as navigation devices, as well as in liquid crystal display devices. In an organic EL display device, a circularly polarizing plate (a laminate including a polarizing element and a λ/4 plate) may be disposed on the visible side surface of an image display panel in order to suppress reflection of external light at a metal electrode (cathode) and to be observed in a mirror-like manner.

As described above, the polarizing plate is increasingly mounted in vehicles as a member of an image display device such as a liquid crystal display device or an organic EL display device. Since a polarizing plate used in an image display device for a vehicle is exposed to a high temperature environment more than a mobile device such as a television and a mobile phone, a small change in characteristics at a higher temperature (high temperature durability) is required.

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

In such a configuration, when an air layer is present between the image display panel and the transparent member such as the front panel and the touch panel, reflection glare of external light due to reflection of light at an air layer interface is generated, and visibility of a screen tends to be lowered. Accordingly, there is an ongoing effort to adopt a structure in which a space between a polarizing plate disposed on the visible side surface of an image display panel and a transparent member is filled with a layer other than an air layer, and usually a solid layer (hereinafter, referred to as "interlayer filler" in some cases) (hereinafter, referred to as "interlayer filling structure" in some cases). The interlayer filler is preferably a material having a refractive index close to that of the polarizing plate or the transparent member. As the interlayer filler, an adhesive or a UV curable adhesive is used for the purpose of suppressing a decrease in visibility due to reflection at an interface and bonding and fixing the members to each other (for example, refer to patent document 1).

The interlayer filling structure is expanding in use in mobile devices such as mobile phones which are often used outdoors. In addition, in recent years, as visibility has been demanded more and more, in vehicle-mounted applications such as navigation devices, an interlayer filling structure in which a front transparent plate is disposed on the surface of an image display panel and an adhesive layer or the like is filled between the panel and the front transparent plate has been studied.

However, in the case of such a configuration, it is reported that the polarizing plate turns yellow (or brown) in a high-temperature environment (hereinafter, sometimes referred to as yellowing.) and the transmittance of the polarizing plate is significantly reduced. In patent document 2, as a solution to this problem, the following method is proposed: the water content per unit area of the polarizing plate is set to a predetermined amount or less, and the saturated water absorption of the transparent protective film adjacent to the polarizing element is set to a predetermined amount or less, thereby suppressing a decrease in transmittance.

Prior art literature

Patent literature

Patent document 1: japanese patent laid-open No. 11-174417

Patent document 2: japanese patent laid-open publication No. 2014-102353

Disclosure of Invention

Problems to be solved by the invention

However, even with such a polarizing plate, the effect of suppressing yellowing in a high-temperature environment is insufficient. The invention aims to provide a polarizing plate capable of further inhibiting yellowing under a high-temperature environment and an image display device using the polarizing plate.

Means for solving the problems

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

[1]A polarizing plate comprising a polarizing element in which iodine is adsorbed and oriented to a polyvinyl alcohol 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 [ mu ] g/cm ² Above and 230 μg/cm ² In the following the procedure is described,

the water content of the polarizing element is equal to or higher than the equilibrium water content of 20 ℃ and 20% relative humidity, and equal to or lower than the equilibrium water content of 50% relative humidity at 20 ℃.

[2]A polarizing plate comprising a polarizing element in which iodine is adsorbed and oriented to a polyvinyl alcohol 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 [ mu ] g/cm ² Above and 230 μg/cm ² In the following the procedure is described,

the water content of the polarizing plate is equal to or higher than the equilibrium water content of 20 ℃ and 20% relative humidity, and equal to or lower than the equilibrium water content of 50% relative humidity at 20 ℃.

[3] The polarizing plate according to [1] or [2], wherein the alcohol is at least one selected from the group consisting of methanol, ethanol and n-propanol.

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

[5] The polarizing plate according to [4], wherein the adhesive comprises a polyvinyl alcohol resin.

[6] The polarizing plate according to [5], wherein the content of the alcohol in the adhesive is 100 parts by mass or more and 2000 parts by mass or less based on 100 parts by mass of the polyvinyl alcohol resin.

[7] The polarizing plate according to any one of [4] to [6], wherein the adhesive layer has a thickness of 0.01 μm to 7. Mu.m.

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

in the image display device, layers other than an air layer are provided on both surfaces of the polarizing plate in contact with each other.

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

[10] The image display device according to item [9], further comprising: a 2 nd adhesive layer laminated on the visible side surface of the polarizing plate, and a transparent member laminated on the visible side surface of the 2 nd adhesive layer.

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

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

Effects of the invention

According to the present invention, a polarizing plate having improved high-temperature durability and suppressed yellowing at high temperature even when used in an image display device having an interlayer filling structure can be provided. Further, by using the polarizing plate of the present invention, an image display device in which yellowing under a high-temperature environment is suppressed can be provided.

Detailed Description

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

[ polarizing plate ]

The polarizing plate of the present embodiment includes: a polarizing element in which a dichroic dye is adsorbed and aligned to a layer containing a polyvinyl alcohol resin, and a transparent protective film. The polarizing plate contains alcohol, and the polarizing element and the transparent protective film can be bonded by an adhesive layer formed of an adhesive containing alcohol. The polarizing plate of the present embodiment has at least one of the following features (a) and (b).

(a) The water content of the polarizing element is higher than the equilibrium water content of 20% relative humidity at 20 ℃ and lower than the equilibrium water content of 50% relative humidity at 20 ℃.

(b) The water content of the polarizing plate is equal to or higher than the equilibrium water content of 20% relative humidity at 20 ℃ and equal to or lower than the equilibrium water content of 50% relative humidity at 20 ℃.

The amount of alcohol contained in the polarizing plate was 4. Mu.g/cm ² Above and 230 μg/cm ² Hereinafter, it is preferably 13. Mu.g/cm ² Above and 200 μg/cm ² Hereinafter, it is more preferably 20. Mu.g/cm ² 190. Mu.g/cm above ² Hereinafter, the concentration may be 60. Mu.g/cm ² Above, it may be 100. Mu.g/cm ² The above. By setting the amount of alcohol contained in the polarizing plate to such a range, it is possible to suppress the multiolefination without impairing the optical characteristics of the polarizing element. The detailed mechanism is not clear, but it is speculated that alcohols can inhibit the double bond-generating chains by reacting with PVA or boric acid.

As a conventional polarizing plate excellent in high temperature durability, for example, a polarizing plate capable of suppressing a decrease in transmittance even when left alone for 1000 hours in an environment of 95 ℃ is known. However, even in the case of using such a polarizing plate for interlayer filling, when the polarizing plate is left to stand in an environment at a temperature of 95 ℃ for 200 hours, the polarizing plate may be changed to yellow (or brown) at the center portion in the polarizing plate surface, and a significant decrease in transmittance may be observed at the center portion in the polarizing plate surface. When an image display device using an interlayer filling structure in which one surface of a polarizing plate is bonded to an image display unit and the other surface is bonded to a transparent member such as a touch panel or a front panel is exposed to a high-temperature environment, it is considered that a problem of significant decrease in transmittance of the polarizing plate in the high-temperature environment is particularly likely to occur.

The polarizing plate having significantly reduced transmittance due to interlayer filling composition was measured at 1100cm in Raman spectroscopy ^-1 Vicinity (from=c-c=bond) and 1500cm ^-1 Vicinity (from-c=c-bonds) have peaks, thus forming a polyene structure (-c=c) _n -. The polyene structure is presumed to be a structure due to the polyvinyl alcohol constituting the polarizing element being polyeneized by dehydration (patent documents 2, [0012 ]]Segment(s)

The polarizing plate of the present invention can further improve high temperature durability. The polarizing plate of the present invention is incorporated into an image display device comprising interlayer filling, and can suppress a decrease in transmittance even when exposed to a high-temperature environment at a temperature of 105 ℃ for a long period of time, and can suppress yellowing even when stored at a temperature of 105 ℃ for 72 hours.

< polarizing element >)

As a polarizing element in which a dichroic dye is adsorbed to a layer containing a polyvinyl alcohol (hereinafter also referred to as "PVA") resin (hereinafter also referred to as "PVA resin layer") and the dichroic dye is aligned, a known polarizing element can be used. As the polarizing element, there may be mentioned: a stretched film obtained by dyeing a PVA-based resin film with a dichroic dye and uniaxially stretching the film; a stretched layer obtained by using a laminate film having a coating layer formed by applying a coating liquid containing a PVA-based resin onto a base film, dyeing the coating layer with a dichroic dye, and uniaxially stretching the laminate film. The stretching may be performed after dyeing with a dichroic dye, stretching may be performed while dyeing, or dyeing may be performed after stretching.

The PVA-based resin can be obtained by saponifying a polyvinyl acetate-based resin. The polyvinyl acetate resin may be a copolymer of vinyl acetate and another monomer copolymerizable therewith, in addition to polyvinyl acetate which is a homopolymer of vinyl acetate. Examples of the other copolymerizable monomer include unsaturated carboxylic acids, olefins such as ethylene, vinyl ethers, and unsaturated sulfonic acids.

The saponification degree of the PVA-based resin is preferably about 85 mol% or more, more preferably about 90 mol% or more, and still more preferably about 99 mol% or more and 100 mol% or less. The polymerization degree of the PVA-based resin is, for example, 1000 to 10000, preferably 1500 to 5000. The PVA-based resin may be modified, and may be, for example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral, or the like modified with an aldehyde.

The thickness of the polarizing element is preferably 3 μm or more and 35 μm or less, more preferably 4 μm or more and 30 μm or less, and still more preferably 5 μm or more and 25 μm or less. By setting the thickness of the polarizing element to 35 μm or less, the influence of the polyene formation of the PVA-based resin on the decrease of the optical properties in a high-temperature environment can be suppressed. By setting the thickness of the polarizing element to 3 μm or more, a constitution that realizes desired optical characteristics can be easily made.

The polarizing element preferably comprises an alcohol. In this embodiment, since the polarizing element and the transparent protective film are bonded to each other by the adhesive layer formed of the adhesive containing alcohol, it is assumed that a part of the alcohol is transferred from the adhesive layer and contained in the polarizing element. The alcohol in the polarizing element may also comprise alcohol added during the manufacturing process of the polarizing element. By providing the polarizing element containing alcohol, transmittance is not easily lowered even when the polarizing plate is exposed to a high-temperature environment. The reason why this effect is presumably exerted is that: by using the alcohol contained in the polarizing element, the alcohol functioning as a protic polar solvent acts on the hydroxyl group in the PVA chain or the like through hydrogen bonding, and thus the reactivity of the dehydration reaction in the PVA chain or the like is reduced, and the polyeneization of the PVA-based resin is suppressed.

(alcohol)

Examples of the alcohol used in the present invention include lower alcohols having 1 to 4 carbon atoms. Specific examples thereof include methanol, ethanol, n-propanol, isopropanol, and t-butanol. The alcohol that the polarizing plate, polarizing element, and adhesive may contain preferably contains: at least one selected from methanol, ethanol, n-propanol, isopropanol and tert-butanol. These may be used alone or in combination of 2 or more. Methanol, ethanol, n-propanol, isopropanol are preferred. They have a low molecular weight and can be widely dispersed in a polarizing element, and are therefore advantageous for suppressing polyalkylene. The alcohol contained in the polarizing element may be the same as or different from the alcohol contained in the adhesive.

Examples of the method for incorporating alcohol into the polarizing element include: a method of immersing the PVA-based resin layer in a treatment solvent containing an alcohol, or a method of spraying, flowing down, or dripping the treatment solvent onto the PVA-based resin layer. Among them, a method of immersing the PVA-based resin layer in a treatment solvent containing alcohol is preferably used.

The step of immersing the PVA-based resin layer in the alcohol-containing treatment solvent may be performed simultaneously with or separately from the swelling, stretching, dyeing, crosslinking, cleaning, and other steps in the method for producing a polarizing element described later. The step of adding alcohol to the PVA-based resin layer is preferably performed after the PVA-based resin layer is stained with iodine, and more preferably, is performed simultaneously in the washing step. According to this method, the change in color tone is small, and the influence on the optical characteristics of the polarizing element can be reduced.

In order to contain alcohol in the polarizing element, both addition at the time of manufacturing the polarizing element and addition to the adhesive may be performed.

(feature (a))

When the polarizing element has the characteristic (a), the water content of the polarizing element is equal to or higher than the equilibrium water content of 20% relative humidity at 20 ℃ and equal to or lower than the equilibrium water content of 50% relative humidity at 20 ℃. The water content of the polarizing element is preferably not more than 45% of the equilibrium water content of the relative humidity at 20 ℃, more preferably not more than 42% of the equilibrium water content of the relative humidity at 20 ℃, and still more preferably not more than 38% of the equilibrium water content of the relative humidity at 20 ℃. If the water content of the polarizing element is lower than the equilibrium water content of 20% relative humidity at 20 ℃, the operability of the polarizing element is lowered and breakage is likely to occur. If the moisture content of the polarizing element exceeds the equilibrium moisture content of 50% relative humidity at 20 ℃, the transmittance of the polarizing element tends to decrease. It is presumed that if the water content of the polarizing element is high, the polyvinyl alcohol of the PVA-based resin tends to advance. The water content of the polarizing element is the water content of the polarizing element in the polarizing plate.

As a method for confirming whether or not the water content of the polarizing element is in a range of 20% or more in terms of equilibrium water content at 20 ℃ relative humidity and 50% or less in terms of equilibrium water content at 20 ℃ relative humidity, there are given: a method of storing the polarizing element in an environment adjusted to the temperature and the relative humidity range, and balancing the polarizing element with the environment when there is no mass change for a predetermined period of time; or a method in which the equilibrium water content of the polarizing element adjusted to the environment in the temperature and relative humidity ranges is calculated in advance and is confirmed by comparing the water content of the polarizing element with the calculated equilibrium water content.

The method for producing a polarizing element having a water content of 20% or more in terms of equilibrium water content at 20 ℃ and 50% or less in terms of equilibrium water content at 20 ℃ relative humidity is not particularly limited, but examples thereof include: a method of storing the polarizing element in an environment adjusted to the temperature and the relative humidity range for 10 minutes to 3 hours; or a method of performing a heat treatment at 30 ℃ or higher and 90 ℃ or lower.

Another preferred method for producing the polarizing element having the above water content includes: a method in which a laminate in which a protective film is laminated on at least one surface of a polarizing element, or a polarizing plate comprising a polarizing element is stored in an environment adjusted to the temperature and the relative humidity range for 10 minutes to 120 hours; or a method of performing a heat treatment at 30 ℃ or higher and 90 ℃ or lower. In the case of manufacturing an image display device using an interlayer filling structure, an image display panel obtained by laminating a polarizing plate on an image display unit may be stored in an environment adjusted to the above temperature and the above relative humidity range for 10 minutes to 3 hours or more or heated at 30 ℃ to 90 ℃ and then bonded to a front panel.

The water content of the polarizing element is preferably adjusted to the above-described numerical range in a material stage used for forming the polarizing plate, in the form of a single polarizing element or a laminate of the polarizing element and the protective film. When the water content is adjusted after the polarizing plate is formed, curling becomes excessive, and a problem is likely to occur when the polarizing plate is attached to an image display unit. The polarizing plate is formed by using the polarizing element whose water content is adjusted to the above water content at a material stage before the polarizing plate is formed, whereby the polarizing plate having the polarizing element whose water content satisfies the above numerical range can be easily formed. The water content of the polarizing element in the polarizing plate may be adjusted to the above-described numerical range in a state where the polarizing plate is bonded to the image display unit. In this case, since the polarizing plate is attached to the image display unit, curling is less likely to occur.

(feature (b))

When the polarizing plate has the characteristic (b), the water content of the polarizing plate is equal to or higher than the equilibrium water content of 20% relative humidity at 20 ℃ and equal to or lower than the equilibrium water content of 50% relative humidity at 20 ℃. The water content of the polarizing plate is preferably not more than 45% of the equilibrium water content of the relative humidity at 20 ℃, more preferably not more than 42% of the equilibrium water content of the relative humidity at 20 ℃, and still more preferably not more than 38% of the equilibrium water content of the relative humidity at 20 ℃. If the water content of the polarizing plate is lower than the equilibrium water content of 20% relative humidity at 20 ℃, the operability of the polarizing plate is lowered and breakage is likely to occur. If the water content of the polarizing plate exceeds the equilibrium water content of 50% relative humidity at 20 ℃, the transmittance of the polarizing element tends to decrease. It is presumed that if the water content of the polarizing plate is high, the polyvinyl alcohol of the PVA-based resin tends to advance.

As a method for confirming whether the water content of the polarizing plate is in a range of 20% or more in terms of equilibrium water content at 20 ℃ relative humidity and 50% or less in terms of equilibrium water content at 20 ℃ relative humidity, there are given: a method of storing the polarizing plate in an environment adjusted to the temperature and the relative humidity range, and balancing the polarizing plate with the environment when there is no mass change for a certain period of time; or a method in which the equilibrium water content of the polarizing plate in the environment adjusted to the temperature and the relative humidity ranges is calculated in advance and is confirmed by comparing the water content of the polarizing plate with the calculated equilibrium water content.

The method for producing a polarizing plate having a water content of 20% or more in terms of equilibrium water content at 20 ℃ and 50% or less in terms of equilibrium water content at 20 ℃ relative humidity is not particularly limited, but examples thereof include: a method of storing the polarizing plate in an environment adjusted to the temperature and the relative humidity range for 10 minutes to 3 hours; or a method of performing a heat treatment at 30 ℃ or higher and 90 ℃ or lower.

In the case of manufacturing an image display device using an interlayer filling structure, an image display panel obtained by laminating a polarizing plate on an image display unit may be stored in an environment adjusted to the above temperature and the above relative humidity range for 10 minutes to 3 hours or more or heated at 30 ℃ to 90 ℃ and then bonded to a front panel.

(Urea-based Compound)

The polarizing element may further comprise a urea-based compound. The polarizing element containing the urea compound can further suppress the decrease in transmittance. The urea compound may be the same as urea compound that can be contained in an adhesive to be described later. As a method for incorporating the urea compound into the polarizing element, the same method as the method for incorporating the alcohol into the polarizing element can be used. The urea compound may be contained in the polarizing element during the production of the polarizing element, or may be contained in an adhesive for laminating the polarizing element and the transparent protective film, which will be described later.

(dicarboxylic acid)

The polarizing element may further comprise a dicarboxylic acid. The polarizing element containing dicarboxylic acid can further suppress the decrease in transmittance. The dicarboxylic acid may be the same as the dicarboxylic acid that may be contained in the adhesive to be described later. As a method for incorporating the dicarboxylic acid into the polarizing element, the same method as the method for incorporating the alcohol into the polarizing element can be used. The dicarboxylic acid may be contained in the polarizing element during the production of the polarizing element, or may be contained in an adhesive for laminating the polarizing element and the transparent protective film, which will be described later.

(method for producing polarizing element)

The method for manufacturing the polarizing element is not particularly limited, and typical methods are: a method of producing a PVA-based resin film wound in advance in a roll shape by stretching, dyeing, crosslinking, or the like (hereinafter referred to as "production method 1"); a method including a step of applying a coating liquid containing a PVA-based resin onto a base film to form a PVA-based resin layer as a coating layer, and stretching the obtained laminate (hereinafter referred to as "production method 2").

The production method 1 can be produced by a step of uniaxially stretching a PVA-based resin film, a step of dyeing the PVA-based resin film with a dichroic dye such as iodine to adsorb the dichroic dye, a step of treating the PVA-based resin film adsorbed with an aqueous boric acid solution, and a step of washing with water after the treatment with the aqueous boric acid solution.

The swelling step is a treatment step of immersing the PVA-based resin film in a swelling bath. By the swelling step, not only dirt, an anti-blocking agent, or the like on the surface of the PVA-based resin film can be removed, but also uneven dyeing can be suppressed by swelling the PVA-based resin film. The swelling bath generally uses a medium containing water as a main component, such as water, distilled water, and pure water. The swelling bath may be appropriately added with a surfactant, an alcohol, or the like according to a usual method. From the viewpoint of controlling the content of potassium in the polarizing element, potassium iodide may be used in the swelling bath, and 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 still more preferably 0.5 mass% or less.

The temperature of the swelling bath is preferably 10 ℃ to 60 ℃, more preferably 15 ℃ to 45 ℃, still more preferably 18 ℃ to 30 ℃. The immersion time in the swelling bath cannot be determined in any way because the degree of swelling of the PVA-based resin film is affected by the temperature of the swelling bath, but is preferably 5 seconds to 300 seconds, more preferably 10 seconds to 200 seconds, still more preferably 20 seconds to 100 seconds. The swelling step may be performed only 1 time, or may be performed as many times as necessary.

The dyeing step is a treatment step of immersing the PVA-based resin film in a dyeing bath (iodine solution), and can be performed by adsorbing a dichroic dye such as iodine to the PVA-based resin film and aligning the dichroic dye. The iodine solution is generally preferably an aqueous iodine solution containing iodine and an iodide as a dissolution aid. Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. Among them, potassium iodide is suitable from the viewpoint of controlling the content of potassium in the polarizing element.

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

The temperature of the dyeing bath is preferably 10 ℃ to 50 ℃, more preferably 15 ℃ to 45 ℃, still more preferably 18 ℃ to 30 ℃. The immersion time in the dyeing bath cannot be defined as a whole because the degree of dyeing of the PVA-based resin film is affected by the temperature of the dyeing bath, but is preferably 10 seconds to 300 seconds, more preferably 20 seconds to 240 seconds. The dyeing step may be performed only 1 time, or may be performed as many times as necessary.

The crosslinking step is a treatment step of immersing the PVA-based resin film dyed in the dyeing step in a treatment bath (crosslinking bath) containing a boron compound, and crosslinking the PVA-based resin film with the boron compound, whereby iodine molecules or dye molecules can be adsorbed to the crosslinked structure. Examples of the boron compound include boric acid, borate, and borax. The crosslinking bath is generally an aqueous solution, but may be a mixed solution of an organic solvent having miscibility with water and water. From the viewpoint of controlling the content of potassium in the polarizing element, the crosslinking bath preferably contains potassium iodide.

The concentration of the boron compound 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 still 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 still more preferably 2% by mass or more and 5% by mass or less.

The temperature of the crosslinking bath is preferably 20 ℃ to 70 ℃, more preferably 30 ℃ to 60 ℃. The immersion time in the crosslinking bath cannot be defined as a whole because the degree of crosslinking of the PVA-based resin film is affected by the temperature of the crosslinking bath, but is preferably 5 seconds to 300 seconds, more preferably 10 seconds to 200 seconds. The crosslinking step may be performed only 1 time, or may be performed as many times as necessary.

The stretching step is a treatment step of stretching the PVA-based resin film at least in one direction to a predetermined magnification. Generally, the PVA-based resin film is uniaxially stretched in the conveyance direction (longitudinal direction). The stretching method is not particularly limited, and either wet stretching or dry stretching may be used. The stretching step may be performed only 1 time, or may be performed as many times as necessary. The stretching step may be performed at any stage in the production of the polarizing element.

As the treatment bath (stretching bath) in the wet stretching method, water, a mixed solution of an organic solvent having miscibility with water and water, or the like is generally used. From the viewpoint of controlling the content of potassium 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 still 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 the boron compound is contained, the concentration of the boron compound in the drawing bath is preferably 1% by mass or more and 15% by mass or less, more preferably 1.5% by mass or more and 10% by mass or less, and still more preferably 2% by mass or more and 5% by mass or less.

The temperature of the stretching bath is preferably 25 ℃ or more and 80 ℃ or less, more preferably 40 ℃ or more and 75 ℃ or less, and still more preferably 50 ℃ or more and 70 ℃ or less. The immersion time in the stretching bath cannot be defined as a whole because the extent of stretching of the PVA-based resin film is affected by the temperature of the stretching bath, but is preferably 10 seconds to 800 seconds, more preferably 30 seconds to 500 seconds. The stretching treatment in the wet stretching method may be performed together with 1 or more treatment steps selected from the swelling step, dyeing step, crosslinking step, and cleaning step.

Examples of the dry stretching method include an inter-roll stretching method, a heated roll stretching method, and a compression stretching method. The dry stretching method may be performed together with the drying step.

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

The cleaning step is a treatment step of immersing the polyvinyl alcohol resin film in a cleaning bath, and can remove foreign matters remaining on the surface of the polyvinyl alcohol resin film. The washing bath generally uses a medium containing water as a main component, such as water, distilled water, and pure water. In addition, from the viewpoint of controlling the content of potassium in the polarizing element, potassium iodide is preferably used in the cleaning bath, and 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 still more preferably 1.8% by mass or more and 3.8% by mass or less.

The temperature of the cleaning bath is preferably 5 ℃ to 50 ℃, more preferably 10 ℃ to 40 ℃, still more preferably 15 ℃ to 30 ℃. The immersion time in the washing bath cannot be determined in any way because the degree of washing of the PVA-based resin film is affected by the temperature of the washing bath, but is preferably 1 second or more and 100 seconds or less, more preferably 2 seconds or more and 50 seconds or less, and still more preferably 3 seconds or more and 20 seconds or less. The cleaning step may be performed only 1 time, or may be performed as many times as necessary.

The drying step is a step of drying the PVA-based resin film washed in the washing step to obtain a polarizing element. The drying may be carried out by any suitable method, and examples thereof include natural drying, forced air drying, and heat drying.

The manufacturing method 2 can be manufactured through the following steps: the method for producing a polarizing element comprises a step of applying a coating liquid containing a PVA-based resin onto a base film, a step of uniaxially stretching the resulting laminated film, a step of absorbing the dichroic dye by dyeing the PVA-based resin layer of the uniaxially stretched laminated film with the dichroic dye to produce a polarizing element, a step of treating the film to which the dichroic dye is absorbed with an aqueous boric acid solution, and a step of washing with water after the treatment with the aqueous boric acid solution. The base film for forming the polarizing element can also be used as a protective layer for the polarizing element. The base film may be peeled off from the polarizing element as needed.

Transparent protective film

The transparent protective film (hereinafter also simply referred to as "protective film") used in the present embodiment is attached to at least one surface of the polarizing element via an adhesive layer. The transparent protective film may be attached to one or both sides of the polarizing element, but is preferably attached to both sides.

The protective film may have other optical functions at the same time, and may be formed into a laminated structure in which a plurality of layers are laminated. From the viewpoint of optical characteristics, the film thickness of the protective film is preferably small, but if too small, the strength is reduced and the workability is poor. The film thickness is preferably 5 μm or more and 100 μm or less, more preferably 10 μm or more and 80 μm or less, and still more preferably 15 μm or more and 70 μm or less.

As the protective film, a cellulose acylate-based film, a film containing a polycarbonate-based resin, a film containing a cycloolefin-based resin such as norbornene, a (meth) acrylic polymer film, a polyester resin-based film such as polyethylene terephthalate, and the like can be used. In the case of attaching the protective film to both surfaces of the polarizing element using an aqueous adhesive such as PVA adhesive, it is preferable that at least one of the protective films is either a cellulose acylate-based film or a (meth) acrylic polymer film in terms of moisture permeability, and among these, cellulose acylate films are preferable.

For the purpose of viewing angle compensation or the like, at least one of the protective films may have a phase difference function. In this case, the protective film itself may have a retardation function, or may have a retardation layer separately, or may be a combination of both. The film having the retardation function may be directly bonded to the polarizing element via an adhesive, or may be bonded via an adhesive or an adhesive with another protective film bonded to the polarizing element interposed therebetween.

< adhesive layer >)

As the adhesive constituting the adhesive layer for bonding the protective film to the polarizing element, an adhesive containing alcohol is preferably used. The adhesive may be an aqueous adhesive, a solvent-based adhesive, an active energy ray-curable adhesive, or the like, but from the viewpoint of containing alcohol, an aqueous adhesive is preferable, and a PVA-based resin is preferably contained. By using an adhesive containing alcohol, a decrease in transmittance of the polarizing plate in a high-temperature environment can be suppressed.

The thickness of the adhesive at the time of application may be set to an optional value, and for example, may be set so that an adhesive layer having a desired thickness is obtained after curing or after heating (drying). The thickness of the adhesive layer formed of the adhesive is preferably 0.01 μm or more and 7 μm or less, more preferably 0.01 μm or more and 5 μm or less, still more preferably 0.01 μm or more and 2 μm or less, and most preferably 0.01 μm or more and 1 μm or less.

The following description of the adhesive is used: the description of the preferable range is made for the case where alcohol is not contained in the polarizing element when the polarizing element is manufactured. When alcohol is contained in the polarizing element, the following values may be appropriately adjusted. As a specific example of the alcohol, the same alcohol as that contained in the polarizing element described above can be used. In the process of forming the adhesive layer through the drying step at the time of bonding the polarizing element and the protective film, a part of alcohol may move from the adhesive layer to the polarizing element or the like.

When the adhesive is an aqueous adhesive containing a PVA-based resin, the content of the alcohol in the adhesive is preferably 30 parts by mass or more and 2000 parts by mass or less, more preferably 100 parts by mass or more and 1800 parts by mass or less, still more preferably 500 parts by mass or more and 1800 parts by mass or less, and most preferably 800 parts by mass or more and 1500 parts by mass or less, relative to 100 parts by mass of the PVA-based resin. If the amount is less than 30 parts by mass, the high-temperature durability improving effect may not be sufficiently obtained. On the other hand, when the alcohol content exceeds 2000 parts by mass, the color tone may deteriorate. By setting the alcohol content in the adhesive to the above range, the drying efficiency can be improved in the drying step in which the protective film is laminated with the adhesive interposed between the polarizing elements, and the alcohol content in the polarizing plate can be easily adjusted to a desired amount.

In the configuration in which the transparent protective film is bonded to both surfaces of the polarizing element via the adhesive layer, the adhesive layer on only one surface of the adhesive layers on both surfaces of the polarizing element may be an alcohol-containing layer, but it is preferable that the adhesive layers on both surfaces be alcohol-containing layers.

In response to the demand for thickness reduction of the polarizing plate, a polarizing plate having a transparent protective film on only one surface 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 such a polarizing plate having a transparent protective film on only one surface of a polarizing element, there can be considered: first, a method is provided in which a polarizing plate having transparent protective films bonded to both surfaces thereof via an adhesive layer is produced, and then one of the transparent protective films is peeled off. In the case of using such a production method, alcohol may be contained only in one of the adhesive layers, but it is preferable that both adhesive layers contain alcohol. When an adhesive layer containing alcohol is used only on one side of the polarizing element, the adhesive layer on the side of the film that is not peeled preferably contains alcohol.

(aqueous adhesive)

As the aqueous adhesive, an optional appropriate aqueous adhesive can be used, however, an aqueous adhesive containing a PVA-based resin (PVA-based adhesive) is preferably used. The average polymerization degree of the PVA-based resin contained in the aqueous adhesive is preferably 100 to 5500, more preferably 1000 to 4500, from the viewpoint of adhesion. The average saponification degree is preferably 85 mol% or more and 100 mol% or less, more preferably 90 mol% or more and 100 mol% or less, from the viewpoint of adhesion.

The PVA-based resin contained in the aqueous adhesive is preferably an acetoacetyl group-containing resin because the PVA-based resin layer has excellent adhesion to the protective film and excellent durability. The acetoacetyl group-containing PVA-based resin can be obtained, for example, by reacting a PVA-based resin with diketene by an optional method. The degree of acetoacetyl modification of the acetoacetyl-containing PVA resin is typically 0.1 mol% or more, preferably 0.1 mol% or more and 20 mol% or less. The resin concentration of the aqueous 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.

The aqueous adhesive may contain a crosslinking agent. As the crosslinking agent, a known crosslinking agent can be used. Examples of the crosslinking agent include water-soluble epoxy compounds, dialdehydes, and isocyanates.

In the case where the PVA-based resin is an acetoacetyl group-containing PVA-based resin, the crosslinking agent is preferably any of glyoxal, glyoxylate, and methylolmelamine, more preferably any of glyoxal and glyoxylate, and particularly preferably glyoxal.

(active energy ray-curable adhesive)

The active energy ray-curable adhesive is an adhesive cured by irradiation with active energy rays such as ultraviolet rays, and examples thereof include: an adhesive containing a polymerizable compound and a photopolymerization initiator, an adhesive containing a photoreactive resin, an adhesive containing a binder resin and a photoreactive crosslinking agent, and the like. Examples of the polymerizable compound include: photo-polymerizable monomers such as photo-curable epoxy monomers, photo-curable acrylic monomers and photo-curable urethane monomers, and oligomers derived from these monomers. The photopolymerization initiator may be: a compound containing a substance that generates an active species such as a neutral radical, an anionic radical, or a cationic radical by irradiation with an active energy ray such as ultraviolet rays.

(Urea-based Compound)

The adhesive further contains at least 1 urea compound selected from urea, urea derivatives, thiourea and thiourea derivatives. By including the urea compound in the adhesive layer formed of the adhesive, the high-temperature durability can be further improved. In the process of forming the adhesive layer from the adhesive through the drying step at the time of adhesion with the protective film, a part of the urea compound may move from the adhesive layer to the polarizing element or the like. Among the urea-based compounds, there are water-soluble compounds and poorly water-soluble compounds, and any urea-based compound may be used. When a poorly water-soluble urea compound is used for the water-soluble adhesive, the dispersing method is preferably designed so that no turbidity increases or the like after the adhesive layer is formed.

When the adhesive is an aqueous adhesive containing a PVA-based resin, the amount of the urea compound to be added is preferably 0.1 part by mass or more and 400 parts by mass or less, more preferably 1 part by mass or more and 200 parts by mass or less, and still more preferably 3 parts by mass or more and 100 parts by mass or less, relative to 100 parts by mass of PVA.

(Urea derivative)

Urea derivatives are compounds in which at least 1 of the 4 hydrogen atoms of the urea molecule is substituted with a substituent. In this case, the substituent is not particularly limited, and a substituent containing a carbon atom, a hydrogen atom and an oxygen atom is preferable. Some urea derivatives have low solubility in water, but have sufficient solubility in alcohol. In this case, it is also one of preferable modes to prepare an adhesive by dissolving a urea compound in an alcohol to prepare an alcohol solution of the urea compound and then adding the alcohol solution of the urea compound to an aqueous PVA solution.

Specific examples of urea derivatives include monosubstituted ureas: methyl urea, ethyl urea, propyl urea, butyl urea, isobutyl urea, N-octadecyl urea, 2-hydroxyethyl urea, hydroxy, acetyl urea, allyl urea, 2-propynyl urea, cyclohexyl urea, phenyl urea, 3-hydroxyphenyl urea, (4-methoxyphenyl) urea, benzyl urea, benzoyl urea, o-tolyl urea, p-tolyl urea. As the di-substituted urea, there may be mentioned: 1, 1-dimethylurea, 1, 3-dimethylurea, 1-diethylurea, 1, 3-bis (hydroxymethyl) urea, 1, 3-t-butylurea, 1, 3-dicyclohexylurea, 1, 3-diphenylurea, 1, 3-bis (4-methoxyphenyl) urea, 1-acetyl-3-methylurea, 2-imidazolidinone (ethyleneurea), tetrahydro-2-pyrimidinone (propyleneurea). As the tetra-substituted urea, there may be mentioned: tetramethyl urea, 1, 3-tetraethyl urea, 1, 3-tetrabutyl urea, 1, 3-dimethoxy-1, 3-dimethylurea, 1, 3-dimethyl-2-imidazolidinone, 1, 3-dimethyl-3, 4,5, 6-tetrahydro-2 (1H) -pyrimidinone.

(thiourea derivatives)

Thiourea derivatives are compounds in which at least 1 of the 4 hydrogen atoms of the thiourea molecule is substituted with a substituent. In this case, the substituent is not particularly limited, and a substituent containing a carbon atom, a hydrogen atom and an oxygen atom is preferable.

Specific examples of the thiourea derivative include a monosubstituted thiourea: n-methyl thiourea, ethyl thiourea, propyl thiourea, isopropyl thiourea, 1-butyl thiourea, cyclohexyl thiourea, N-acetyl thiourea, N-allyl thiourea, (2-methoxyethyl) thiourea, N-phenyl thiourea, (4-methoxyphenyl) thiourea, N- (2-methoxyphenyl) thiourea, N- (1-naphthyl) thiourea, (2-pyridyl) thiourea, o-tolyl thiourea, p-tolyl thiourea. As the disubstituted thiourea, there may be mentioned: 1, 1-dimethylthiourea, 1, 3-dimethylthiourea, 1-diethylthiourea, 1, 3-dibutylthiourea, 1, 3-diisopropylthiourea, 1, 3-dicyclohexylthiourea, N-diphenylthiourea, N '-diphenylthiourea, 1, 3-bis (o-tolyl) thiourea, 1, 3-bis (p-tolyl) thiourea, 1-benzyl-3-phenylthiourea, 1-methyl-3-phenylthiourea, N-allyl-N' - (2-hydroxyethyl) thiourea, ethylene thiourea. As the trisubstituted thiourea, trimethylthiourea is exemplified. The tetrasubstituted thiourea may be tetramethylthiourea or 1, 3-tetraethylthiourea.

Among the urea compounds, urea derivatives or thiourea derivatives are preferable, and urea derivatives are more preferable, in view of further suppressing the decrease in transmittance in a high-temperature environment when used in an image display device having an interlayer filling structure. Among the urea derivatives, a monosubstituted urea or a disubstituted urea is preferable, and a monosubstituted urea is more preferable. Among the disubstituted ureas are 1, 1-substituted urea and 1, 3-substituted urea, more preferably 1, 3-substituted urea.

(dicarboxylic acid)

The adhesive may further contain a dicarboxylic acid. By using an adhesive containing a dicarboxylic acid, a decrease in transmittance of the polarizing plate in a high-temperature environment can be suppressed. Examples of the dicarboxylic acid include: oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, tartaric acid, glutamic acid, malic acid, maleic acid, fumaric acid, itaconic acid, muconic acid, 1, 4-cyclohexanedicarboxylic acid, 1, 4-naphthalenedicarboxylic acid, 2, 6-naphthalenedicarboxylic acid, 2, 7-naphthalenedicarboxylic acid, 4-diphthalic acid, 2, 5-pyridinedicarboxylic acid, 3, 5-pyridinedicarboxylic acid, diphenylsulfone dicarboxylic acid, diphenylmethane dicarboxylic acid, oxalacetic acid, methyl fumaric acid, 2, 6-pyridinedicarboxylic acid, and the like. Among them, citric acid, malic acid, maleic acid or tartaric acid is preferably used. These dicarboxylic acids may be used singly or in combination of 1 or more than 2.

[ method for producing polarizing plate ]

The method for manufacturing a polarizing plate according to the present embodiment includes a water content adjustment step and a lamination step. In the water content adjustment step, when the polarizing plate having the feature (a) is manufactured, the water content of the polarizing element is adjusted so that the water content of the polarizing element is equal to or higher than the equilibrium water content of 20% relative humidity at 20 ℃ and equal to or lower than the equilibrium water content of 50% relative humidity at 20 ℃. The water content of the polarizing element can be adjusted in accordance with the description of the water content of the polarizing element. In the water content adjustment step, when the polarizing plate having the feature (b) is manufactured, the water content of the polarizing plate is adjusted so that the water content of the polarizing plate is equal to or higher than the equilibrium water content of 20% relative humidity at 20 ℃ and equal to or lower than the equilibrium water content of 50% relative humidity at 20 ℃. The water content of the polarizing plate can be adjusted in accordance with the description of the water content of the polarizing plate. In the lamination step, the polarizing element and the transparent protective film are laminated via the adhesive layer. In the lamination step, for example, a polarizing element that has not been subjected to an alcohol-containing treatment is bonded to a transparent protective film with an adhesive containing alcohol. The order of the water content adjustment step and the lamination step is not limited, and the water content adjustment step and the lamination step may be performed in parallel.

[ constitution of image display device ]

The polarizing plate of the present embodiment can be used for various image display devices such as a liquid crystal display device and an organic EL display device. In the case of an image display device having an interlayer filling structure in which both surfaces of a polarizing plate are in contact with a layer other than an air layer, specifically, a solid layer such as an adhesive layer, transmittance tends to be reduced in a high-temperature environment. In the image display device using the polarizing plate according to the present embodiment, even in the interlayer filling structure, the decrease in transmittance of the polarizing plate in a high-temperature environment can be suppressed. As an image display device, a configuration having an image display unit, a 1 st 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 1 st adhesive layer can be exemplified. The image display device may further have a 2 nd adhesive layer laminated on the visible side surface of the polarizing plate, and a transparent member laminated on the surface of the 2 nd adhesive layer. In particular, the polarizing plate according to the present embodiment can be suitably used for an image display device having an interlayer filling structure in which a transparent member is disposed on the visible side of the image display device, the polarizing plate is bonded to the image display unit by the 1 st adhesive layer, and the polarizing plate is bonded to the transparent member by the 2 nd adhesive layer. In this specification, one or both of the 1 st adhesive layer and the 2 nd adhesive layer may be simply referred to as an "adhesive layer". The member used for bonding the polarizing plate to the image display unit and the member used for bonding the polarizing plate to the transparent member are not limited to the adhesive layer, and may be an adhesive layer.

< image display Unit >)

Examples of the image display unit include a liquid crystal unit and an organic EL unit. As the liquid crystal cell, it is possible to use: a reflective liquid crystal cell using external light, a transmissive liquid crystal cell using light from a light source such as a backlight, or a transflective liquid crystal cell using both light from the outside and light from the light source. In the case where the liquid crystal cell is a liquid crystal cell that uses light from a light source, the image display device (liquid crystal display device) is also provided with a polarizing plate on the side of the image display cell (liquid crystal cell) opposite to the viewing side, and the light source is also provided. The polarizing plate on the light source side and the liquid crystal cell are preferably bonded via an appropriate adhesive layer. As a driving method of the liquid crystal cell, for example, any type of driving method such as VA mode, IPS mode, TN mode, STN mode, and bend alignment (pi type) can be used.

As the organic EL unit, an organic EL unit or the like 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-emitting body (organic electroluminescent light-emitting body) can be suitably used. The organic light-emitting layer is a laminate of various organic thin films, and may be formed of various layers such as the following laminate: a laminate comprising a hole injection layer such as a triphenylamine derivative and a light-emitting layer comprising a fluorescent organic solid such as anthracene; a laminate of these light-emitting layers and an electron injection layer containing a perylene derivative or the like; or a laminate of a hole injection layer, a light emitting layer, and an electron injection layer.

< adhesion of image display Unit and polarizing plate >)

In the lamination of the image display unit and the polarizing plate, an adhesive layer (adhesive sheet) may be suitably used. Among them, a method of bonding a polarizing plate with an adhesive layer, which is provided with an adhesive layer on one surface of the polarizing plate, to an image display unit is preferable from the viewpoint of operability and the like. The adhesive layer may be attached to the polarizing plate in an appropriate manner. As an example thereof, there may be mentioned: a method of preparing a binder solution in which 10 mass% or more and 40 mass% or less of a base polymer or a composition thereof is dissolved or dispersed in a solvent formed of a single or a mixture of appropriate solvents such as toluene and ethyl acetate, and directly attaching the binder solution to a polarizing plate by an appropriate development method such as a casting method and a coating method; and a manner in which an adhesive layer is formed on the separator and transferred to the polarizing plate.

< adhesive layer >)

The adhesive layer may be formed of 1 layer or 2 layers or more, and is preferably formed of 1 layer. The adhesive layer may be formed of an adhesive composition containing a (meth) acrylic resin, a rubber resin, a urethane resin, an ester resin, a silicone resin, and a polyvinyl ether resin as a main component. Among them, an adhesive composition containing a (meth) acrylic resin as a base polymer excellent in transparency, weather resistance, heat resistance and the like is suitable. The adhesive composition may be an active energy ray-curable or thermosetting adhesive composition.

As the (meth) acrylic resin (base polymer) used in the adhesive composition, it is possible to suitably use: polymers or copolymers containing 1 or more (meth) acrylic acid esters such as butyl (meth) acrylate, ethyl (meth) acrylate, isooctyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate as monomers. The polar monomer is preferably copolymerized in the base polymer. As the polar monomer, there may be mentioned: monomers having a carboxyl group, a hydroxyl group, an amide group, an amino group, an epoxy group, or the like, such as a (meth) acrylic acid compound, a 2-hydroxypropyl (meth) acrylate compound, a hydroxyethyl (meth) acrylate compound, a (meth) acrylamide compound, an N, N-dimethylaminoethyl (meth) acrylate compound, and a glycidyl (meth) acrylate compound.

The adhesive composition may contain only the above base polymer, but usually also contains a crosslinking agent. As the crosslinking agent, there can be exemplified: a metal ion having a valence of 2 or more and forming a metal carboxylate with the carboxyl group; polyamine compounds forming an amide bond with carboxyl groups; a polyepoxide or polyol that forms an ester linkage with the carboxyl group; polyisocyanate compounds forming an amide bond with a carboxyl group. Among them, polyisocyanate compounds are preferable.

The active energy ray-curable adhesive composition has a property of being cured by irradiation with active energy rays such as ultraviolet rays and electron beams, and has a property of having adhesiveness to an adherend such as a film even before irradiation with active energy rays and being cured by irradiation with active energy rays to adjust an adhesive force. The active energy ray-curable adhesive composition is preferably an ultraviolet ray-curable adhesive composition. The active energy ray-curable adhesive composition contains an active energy ray-polymerizable compound in addition to the base polymer and the crosslinking agent. If necessary, a photopolymerization initiator, a photosensitizer, and the like may be contained.

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

The adhesive layer may be formed by coating an organic solvent diluent of the above adhesive composition on the surface of a substrate film, an image display unit, or a polarizing plate and drying. The base film is usually a thermoplastic resin film, and a typical example thereof is a release film subjected to a release treatment. The separator may be, for example: a film having a release treatment such as silicone treatment on the surface of a film containing a resin such as polyethylene terephthalate, polybutylene terephthalate, polycarbonate, or polyarylate, which surface is to be formed with an adhesive layer.

The release-treated surface of the release film may be coated with the adhesive composition directly to form an adhesive layer, and the adhesive layer with the release film may be laminated on the surface of the polarizer. The pressure-sensitive adhesive layer may be formed by directly applying the pressure-sensitive adhesive composition to the surface of the polarizing plate, and the release film may be laminated on the outer surface of the pressure-sensitive adhesive layer.

When the pressure-sensitive adhesive layer is provided on the surface of the polarizing plate, the bonding surface of the polarizing plate and/or the bonding surface of the pressure-sensitive adhesive layer is preferably subjected to a surface activation treatment such as plasma treatment or corona treatment, and more preferably to corona treatment.

Alternatively, an adhesive sheet may be prepared in which the adhesive composition is applied to the 2 nd separator to form an adhesive layer, and the separator is laminated on the formed adhesive layer, and the separator-equipped adhesive layer after the 2 nd separator is peeled off from the adhesive sheet may be laminated on the polarizing plate. The 2 nd release film used was a film which was less strongly adhered to the adhesive layer than the release film and was easily peeled off.

The thickness of the pressure-sensitive adhesive layer is not particularly limited, and is preferably 1 μm or more and 100 μm or less, more preferably 3 μm or more and 50 μm or less, and may be 20 μm or more.

Transparent member

Examples of the transparent member disposed on the visible side of the image display device include a transparent plate (window layer) and a touch panel. As the transparent plate, a transparent plate having appropriate mechanical strength and thickness is used. Examples of such a transparent plate include: a transparent resin plate such as polyimide resin, acrylic resin, or polycarbonate resin, or a glass plate. A functional layer such as an antireflection layer may be laminated on the visible side of the transparent plate. In addition, in the case where the transparent plate is a transparent resin plate, a hard coat layer may be laminated for improving physical strength, and a low moisture permeability layer may be laminated for reducing moisture permeability. As the touch panel, it is possible to use: various touch panels of a resistive film type, a capacitive type, an optical type, an ultrasonic type, and the like; glass plates, transparent resin plates, etc. having touch sensor functions. In the case of using a capacitive touch panel as the transparent member, a transparent plate made of glass or a transparent resin plate is preferably further provided on the visible side with respect to the touch panel.

< adhesion of polarizing plate to transparent Member >

In the bonding of the polarizing plate and the transparent member, an adhesive or an active energy ray-curable adhesive may be suitably used. In the case of using an adhesive, the adhesive can be attached in an appropriate manner. Specific examples of the method of attaching include a method of attaching an adhesive layer used for attaching the image display unit and the polarizing plate.

In the case of using an active energy ray-curable adhesive, for the purpose of preventing the adhesive solution before curing from spreading out, the following method may be suitably used: and a method of disposing a bank material so as to surround a peripheral edge portion of the image display panel, placing a transparent member on the bank material, and injecting an adhesive solution. After the injection of the adhesive solution, the adhesive solution is cured by irradiating an active energy ray after the alignment and defoamation as necessary.

Examples

The present invention will be specifically described below based on examples. The materials, reagents, amounts of materials, proportions thereof, operations and the like shown in the following examples may be appropriately changed without departing from the gist of the present invention.

Thus, the present invention is not limited by the following examples.

(1) Measurement of the thickness of the polarizing element:

the measurement was performed using a digital micrometer "MH-15M" manufactured by Nikon corporation.

(2) Measurement of the transmittance of the visibility-correcting monomer of the polarizing plate:

a spectrophotometer with an integrating sphere (V7100, manufactured by japan spectroscopy corporation, field of view at 2 degrees; and C, measuring the light source.

(3) Determination of alcohol (methanol) in polarizing plate:

the polarizing plate was cut to 1cm square to obtain an evaluation sample. To this evaluation sample, 5mL of ultrapure water was added, and the mixture was heated at 70℃for 30 minutes, stirred, and then measured by the GC-FID method under the following conditions.

(conditions for gas chromatography)

Column: DB-WAX 30m 0.250mm 0.25 μm, I.D. (Agilent Technologies) or equivalent;

carrier gas: helium, 1.0 mL/min;

column temperature: 40 ℃ (hold 5 minutes) → heating at 20 ℃/min→240 ℃ (hold 10 minutes);

injection port temperature: 240 ℃, injection amount: 1 μl, split ratio: 50:1, a step of;

detector temperature: 240 ℃, detector: and (3) FID.

(4) Determination of yellow index (yellowness):

a spectrometer CM-3700A manufactured by Konikoku Megaku was used. The reflected light was measured in SCI mode to obtain 3 stimulus values (X, Y, Z), and the Yellow Index (YI) was calculated based on the standard of ASTM E313-73 using the following formula.

YI＝100×(1.000-0.847×Z/Y)

< fabrication of polarizing element >

A PVA film of 40 μm in thickness formed of PVA having an average polymerization degree of about 2400 and a saponification degree of 99.9 mol% or more was uniaxially stretched to about 5 times in a dry manner, further immersed in pure water at 60℃for 1 minute while maintaining a stretched state, and thereafter immersed in an aqueous solution having a weight ratio of iodine/potassium iodide/water of 0.05/5/100 at 28℃for 60 seconds. Thereafter, the mixture was immersed in an aqueous solution having a weight ratio of potassium iodide/boric acid/water of 8.5/8.5/100 at 72℃for 300 seconds. Then, after washing with pure water at 26℃for 20 seconds, the resulting film was dried at 65℃to obtain a polarizing element having a thickness of 15. Mu.m, in which iodine was adsorbed to PVA and oriented.

[ preparation of adhesives 1 to 4 ]

(preparation of PVA solution A for adhesive)

50g of an acetoacetyl group-containing modified PVA resin (GOHSENX Z-410, mitsubishi chemical Co., ltd.) was dissolved in 950g of pure water, heated at 90℃for 2 hours, and then cooled to room temperature to obtain a PVA solution for adhesives (hereinafter referred to as "PVA solution A").

(preparation of adhesives 1 to 4)

The PVA solution a prepared above, pure water, maleic acid, 40 mass% glyoxal solution and methanol were mixed at the contents shown in table 1 to prepare adhesives 1 to 4.

TABLE 1

Preparation of transparent protective film

A commercially available cellulose acylate film TD40N (film thickness: 40 μm, manufactured by Fuji photo Co., ltd.) was immersed in a 1.5mol/L aqueous NaOH solution (saponification liquid) kept at 55℃for 2 minutes, and then the film was washed with water. Thereafter, the membrane was immersed in a sulfuric acid aqueous solution of 0.05mol/L at 25℃for 30 seconds, and then further washed with water under running water for 30 seconds to thereby bring the membrane into a neutral state. Then, after water was removed by repeating the water removal with an air knife 3 times, the film was left in a drying zone at 70 ℃ for 15 seconds and dried, and a film after saponification treatment was produced and used as a transparent protective film.

[ production of polarizing plate ]

Transparent protective films were bonded to both surfaces of the polarizing element via an adhesive 1 using a roll laminator. After bonding, the adhesive was dried by heat treatment at 65 ℃ for 12 minutes to obtain a polarizing plate 1. The single body transmittance of the polarizing plate 1 was 40.8%. The thickness of the adhesive layer after drying was adjusted so that it was 50nm on both sides.

The adhesive 1 was changed to the adhesives 2 to 4 in the polarizing plate 1 to obtain polarizing plates 2 to 4. The individual transmittances of the polarizing plates 2 to 4 were also 40.8%, respectively.

(adjustment of Water content of polarizing plate (polarizing element))

The polarizing plates 1 to 4 obtained above were stored at a temperature of 20℃and a relative humidity of 30% for 72 hours. The water content was measured by the karl-fischer method at 66 hours, 69 hours and 72 hours of storage. The water content was not changed at 66 hours, 69 hours and 72 hours of storage. Therefore, the water content of the polarizing plates 1 to 4 can be regarded as the same as the equilibrium water content in the storage environment for 72 hours used in this experimental example. When the water content of the polarizing plate is balanced in a certain storage environment, the water content of the polarizing element in the polarizing plate can be considered to be balanced in the storage environment as well. In addition, when the water content of the polarizing element in the polarizing plate is balanced in a certain storage environment, the water content of the polarizing plate can be considered to be balanced in the storage environment as well.

The optical layered bodies 1 to 4 were produced by using any one of the polarizing plates 1 to 4 shown in table 2 and storing the polarizing plate under a condition of a temperature of 20 ℃ and a relative humidity of 30% for 72 hours so that the water content of the polarizing plate (polarizing element) used became the equilibrium water content of the environment shown in table 2.

After this, the methanol content of the polarizing plate (optical laminate) having been stored and adjusted for water content in a predetermined temperature and humidity environment was measured. The results of the measurement are shown in Table 2.

< evaluation of high temperature durability >

(preparation of sample for evaluation)

Acrylic adhesives (model #7, manufactured by LINTEC Co., ltd.) were formed on both sides of the optical laminates 1 to 4. Then, the polarizing plate was cut into a size of 110mm×60mm so that the absorption axis was parallel to the long side. An evaluation sample was prepared by bonding alkali-free glass (EAGLE XG, size 120 mm. Times.70 mm, manufactured by Corning Co.) to each adhesive surface, and the thus obtained evaluation sample was subjected to autoclave treatment at 50℃under 5 atmospheres for 15 minutes, and then exposed to an atmosphere at 105℃for 72 hours, whereby a high-temperature durability test was performed.

The results of YI after 60 hours and after 72 hours are shown in Table 2.

TABLE 2

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Claims

1. A polarizing plate comprising a polarizing element in which iodine is adsorbed and oriented on a polyvinyl alcohol 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 was 4. Mu.g/cm ² Above and 230 μg/cm ² In the following the procedure is described,

2. A polarizing plate comprising a polarizing element in which iodine is adsorbed and oriented on a polyvinyl alcohol resin layer, and a transparent protective film laminated on at least one surface of the polarizing element,

3. The polarizing plate according to claim 1 or 2, wherein,

the alcohol is at least one selected from methanol, ethanol and n-propanol.

4. The polarizing plate according to any one of claims 1 to 3, wherein,

the polarizing element and the transparent protective film are bonded by an adhesive layer formed of an adhesive containing the alcohol.

5. The polarizing plate according to claim 4, wherein,

the adhesive contains a polyvinyl alcohol resin.

6. The polarizing plate according to claim 5, wherein,

the content of the alcohol in the adhesive is 100 to 2000 parts by mass based on 100 parts by mass of the polyvinyl alcohol resin.

7. The polarizing plate according to any one of claims 4 to 6, wherein,

The thickness of the adhesive layer is 0.01-7 mu m.

8. The polarizing plate according to any one of claims 1 to 7, wherein,

the polarizing plate is used for an image display device,

9. An image display device, comprising:

an image display unit,

A 1 st adhesive layer laminated on the visible side surface of the image display unit, and

the polarizing plate according to any one of claims 1 to 8, wherein the polarizing plate is laminated on the visible side surface of the 1 st adhesive layer.

10. The image display device according to claim 9, further comprising:

a 2 nd adhesive layer laminated on the visible side surface of the polarizing plate, and

a transparent member laminated on the visible side surface of the 2 nd adhesive layer.

11. The image display device according to claim 10, wherein,

the transparent member is a glass plate or a transparent resin plate.

12. The image display device according to claim 10, wherein,

the transparent member is a touch panel.