WO2023022020A1

WO2023022020A1 - Polarizing plate

Info

Publication number: WO2023022020A1
Application number: PCT/JP2022/030074
Authority: WO
Inventors: 裕史太田; 慎也萩原; 範充江端; 幸弘宇田; 寿和松本
Original assignee: 住友化学株式会社
Priority date: 2021-08-17
Filing date: 2022-08-05
Publication date: 2023-02-23
Also published as: TW202314302A; CN117581126A; JP2023027631A; KR20240040733A

Abstract

The present invention addresses the problem of providing a polarizing plate that has an excellent effect of suppressing a decrease in degree of polarization even when exposed to a high-temperature environment, for example, at a temperature of 115°C. The present invention provides a polarizing plate comprising: a polarization element obtained by causing a dichroic dye to be adsorbed and aligned in a polyvinyl alcohol-based resin layer; and a transparent protection film, wherein the polarization element exhibits a half-value width of a peak derived from polyvinyl alcohol crystals, as measured by a wide-angle X-ray scattering method, of 4.80 nm-1 or higher, and contains potassium ions and metal ions other than the potassium ions, the content of the metal ions other than the potassium ions being 0.05 mass% or higher.

Description

Polarizer

The present invention relates to polarizing plates.

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

As described above, polarizing plates are increasingly used in vehicles as components of liquid crystal display devices and organic EL display devices. Polarizing plates used in in-vehicle image display devices are often exposed to high temperature environments compared to other mobile applications such as televisions and mobile phones, and their properties change less at high temperatures ( high temperature durability) is required.

As a method for producing such a polarizing element having high high-temperature durability, for example, in

Patent Documents

1 and 2, a component such as a metal salt containing zinc, copper, aluminum, or the like is added to the treatment bath to obtain the polarizing element. The inclusion of a component is disclosed to improve the durability of the polarizing element. Further,

Patent Documents

3 and 4 disclose a method of manufacturing a polarizing element in which a component such as an organic titanium compound is added to the treatment bath.

WO2016/117659 JP-A-2006-047978 JP-A-2008-46257 JP-A-6-172554

However, with conventional polarizing plates, the degree of polarization may decrease when the temperature of the high-temperature environment is increased to 115°C and the plate is exposed to this high-temperature environment for a certain period of time. SUMMARY OF THE INVENTION An object of the present invention is to provide a polarizing plate that is excellent in the effect of suppressing a decrease in the degree of polarization even when exposed to a high temperature environment of, for example, 115°C.

The present invention provides the following polarizing plate.
[1] A polarizing plate having a polarizing element in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin layer, and a transparent protective film,
In the polarizing element, the half width of a peak derived from polyvinyl alcohol crystals measured by a wide-angle X-ray scattering method is 4.80 nm ⁻¹ or more,
The polarizing element contains potassium ions and metal ions other than potassium ions,
The polarizing plate, wherein the polarizing element contains 0.05% by mass or more of metal ions other than the potassium ions.
[2] The polarized light according to [1], wherein the metal ions include at least one selected from the group consisting of cobalt, nickel, zinc, chromium, aluminum, copper, manganese, and iron ions. board.
[3] The polarizing plate according to [1] or [2], wherein the polarizing element has a boron content of 3.9% by mass or more and 8.0% by mass or less.
[4] further comprising an adhesive layer for bonding the polarizing element and the transparent protective film;
The polarizing plate according to any one of [1] to [3], wherein the adhesive layer is a coating layer of a water-based adhesive.
[5] The polarizing plate of [4], wherein the water-based adhesive has a methanol concentration of 10% by mass or more and 70% by mass or less.
[6] The polarizing plate of [4] or [5], wherein the water-based adhesive contains a polyvinyl alcohol-based resin.
[7] The polarizing plate of any one of [4] to [6], wherein the adhesive layer has a thickness of 0.01 μm or more and 7 μm or less.

According to the present invention, it is possible to provide a polarizing plate that suppresses a decrease in the degree of polarization when exposed to a high-temperature environment of, for example, 115°C, and has excellent high-temperature durability.

4 shows a graph plotting the scattering profile of the measurement sample minus the background scattering profile with respect to the wavenumber q for polarizers 1 to 3 (polarizers 1 to 3).

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

[Polarizer]
A polarizing plate according to an embodiment of the present invention has a polarizing element formed by adsorbing and aligning a dichroic dye in a layer containing a polyvinyl alcohol-based resin, and a transparent protective film. Further, in the polarizing element, the half width of a peak derived from polyvinyl alcohol crystals measured by a wide-angle X-ray scattering method is 4.80 nm ⁻¹ or more. Furthermore, the polarizing element contains potassium ions (hereinafter sometimes referred to as "first metal ions") and metal ions other than potassium ions (hereinafter sometimes referred to as "second metal ions"). and the content of the second metal ion is 0.05% by mass or more.
In the polarizing plate of the present embodiment, the half-value width of the polyvinyl alcohol crystal-derived peak measured by the wide-angle X-ray scattering method of the polarizing element, and the content of the second metal ion in the polarizing element are within the above ranges. Therefore, even when exposed to a high-temperature environment for a long time, a decrease in the degree of polarization can be suppressed.

According to the polarizing plate of the present embodiment, it is possible to suppress a decrease in the degree of polarization even when exposed to a high temperature environment of, for example, 115°C for 500 hours or more.

<Polarization element>
A well-known polarizing element can be used as the polarizing element in which a dichroic dye is adsorbed and oriented in a layer containing a polyvinyl alcohol (PVA)-based resin (also referred to herein as a "PVA-based resin layer"). can. As such a polarizing element, a PVA-based resin film is used, and this PVA-based resin film is dyed with a dichroic dye and formed by uniaxial stretching, or a coating liquid containing a PVA-based resin is used as a base material. A laminated film obtained by coating on a film is used, the PVA-based resin layer that is the coating layer of this laminated film is dyed with a dichroic dye, and the laminated film is uniaxially stretched. .

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

In the present invention, it is preferable to form the PVA-based resin layer from a PVA-based resin having a boron adsorption rate of 5.70% by mass or more. That is, it is preferable that the PVA-based resin has a boron adsorption rate of 5.70% by mass or more in the raw material stage before being dyed or stretched. By using such a PVA-based resin, the degree of polarization is less likely to decrease even when exposed to a high temperature environment of 115° C., for example. Moreover, the boron adsorption rate of the PVA-based resin is preferably 10% by mass or less. By using such a PVA-based resin to produce a polarizing element, the boric acid concentration in the boric acid treatment tank does not have to be high, and the boric acid treatment time can be shortened. of the polarizing element can be easily obtained, and the productivity of the polarizing element can also be improved. When the boron adsorption rate of the PVA-based resin is 10% by mass or less, an appropriate amount of boron is incorporated into the PVA-based resin layer, and the shrinkage force of the polarizing element can be easily reduced. The boron adsorption rate of the PVA-based resin can be measured by the method described in Examples below.

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

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

The degree of saponification of the PVA-based resin is preferably 85 mol% or more, more preferably 90 mol% or more, still more preferably 99 mol% to 100 mol%. The degree of polymerization of the PVA-based resin is 1,000 to 10,000, preferably 1,500 to 5,000. This PVA-based resin may be modified, for example, aldehyde-modified polyvinyl formal, polyvinyl acetal, polyvinyl butyral, or the like.

The thickness of the polarizing element of the present embodiment is preferably 5-50 μm, more preferably 8-28 μm, even more preferably 12-22 μm, and most preferably 12-15 μm. When the thickness of the polarizing element is 5 μm or more, it becomes easy to achieve the desired optical characteristics.

In the polarizing element of the present invention, the half width of a peak derived from polyvinyl alcohol crystals measured by a wide-angle X-ray scattering method is 4.80 nm ⁻¹ or more, preferably 4.82 nm ⁻¹ or more, more preferably 4.87 nm ⁻¹ or more. In such a polarizing element, the crystal size of the polyvinyl alcohol is reduced due to the progress of the cross-linking reaction by boric acid, and as a result, the ratio of the amorphous portion is increased. Therefore, the content of boron and the second metal ion described later can be efficiently increased. The half width of the peak derived from polyvinyl alcohol crystals measured by wide-angle X-ray scattering can be, for example, 5.0 nm ⁻¹ or less. Since such a polarizing element has a high degree of orientation, it can have excellent optical properties. The half width of the peak derived from the polyvinyl alcohol crystal measured by the wide-angle X-ray scattering method can be measured by the method described in the examples below. The half width of the peak derived from the polyvinyl alcohol crystal measured by the wide-angle X-ray scattering method is appropriately adjusted depending on the temperature of the stretching bath, the stretching ratio, the concentration of boric acid in the cross-linking bath, the degree of saponification of the PVA-based resin used as the raw material, and the like. be able to.

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

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

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

The content of boron in the polarizing element is preferably 2.4% by mass or more and 8.0% by mass or less, and more preferably 3.9% by mass or more and 8.0% by mass or less. Satisfying such a numerical range suppresses a decrease in the degree of polarization even when exposed to a high-temperature environment.

The content of potassium ions in the polarizing element is preferably 0.28% by mass or more, more preferably 0.32% by mass or more, from the viewpoint of suppressing a decrease in the degree of polarization in a high-temperature environment. .34% by mass or more is more preferable, and from the viewpoint of suppressing hue change in a high-temperature environment, it is preferably 0.60% by mass or less, and more preferably 0.55% by mass or less. , 0.50% by mass or less. The content of potassium ions can be measured in the same manner as the content of the second metal ions, and the content of potassium ions here is the value in terms of potassium atoms.

Although the detailed mechanism is unknown, the hydroxyl group of the polyvinyl alcohol in the polarizing element is protected (stabilized) by boric acid cross-linking because the boron content is higher and the potassium ion content is lower than in conventional polarizing elements. It is presumed that the iodine ions serving as the counter ions in the polarizing element are stabilized by the content of the appropriate amount of potassium ions.

The luminosity correction single transmittance of the polarizing plate is preferably 38.8% to 44.8%, more preferably 40.4% to 43.2%, and still more preferably 40.7% to 43.0%. is. If the luminosity correction single transmittance exceeds 44.8%, the deterioration of optical characteristics such as red discoloration may increase in high temperature environments. In some cases, deterioration of optical characteristics becomes large.

Visibility correction single transmittance can be obtained by measuring the Y value after visibility correction with a 2-degree field of view (C light source) specified in JIS Z8701-1982. The visibility correction single transmittance can be easily measured with, for example, a spectrophotometer (model number: V7100) manufactured by JASCO Corporation.

The manufacturing method of the polarizing element is not particularly limited, but a method in which a polyvinyl alcohol-based resin film wound in a roll in advance is sent out and subjected to stretching, dyeing, cross-linking, etc. (hereinafter referred to as "manufacturing method 1"). or a coating solution containing a polyvinyl alcohol-based resin on a base film to form a polyvinyl alcohol-based resin layer as a coating layer and stretching the obtained laminate (hereinafter referred to as "manufacturing method 2 ) is typical.

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

The content of boron and the content of potassium ions contained in the polarizing element are determined by the amount of boric acid, borate, boric acid, or boron contained in any of the treatment baths in the swelling process, dyeing process, cross-linking process, stretching process, and water washing process. It can be controlled by the concentration of a boron component-donating substance such as a boron compound such as sand, the concentration of a potassium component-donating substance such as potassium halide such as potassium iodide, and the treatment temperature and treatment time in each of the above treatment baths. In particular, in the cross-linking step and the stretching step, it is easy to adjust the boron content within a desired range by adjusting the processing conditions such as the concentration of the boron component-donating substance. In addition, in the water washing process, after considering the processing conditions such as the amount of the boron component-donating substance and the potassium component-donating substance used in the dyeing process, the cross-linking process, or the stretching process, components such as boron and potassium are removed from the polyvinyl. From the viewpoint of being able to be eluted from the alcohol-based resin film or adsorbed to the polyvinyl alcohol-based resin film, it is easy to adjust the content of boron and the content of potassium ions within desired ranges.

The swelling step is a treatment step in which the polyvinyl alcohol resin film is immersed in a swelling bath, which can remove stains, blocking agents, etc. on the surface of the polyvinyl alcohol resin film, and swell the polyvinyl alcohol resin film. can suppress uneven dyeing. The swelling bath usually uses a medium containing water as a main component, such as water, distilled water, or pure water. Surfactant, alcohol, etc. may be appropriately added to the swelling bath according to a conventional method. Also, from the viewpoint of controlling the potassium content of the polarizing element, potassium iodide may be used in the swelling bath. In this case, the concentration of potassium iodide in the swelling bath is 1.5% by mass or less. is preferably 1.0% by mass or less, and even more preferably 0.5% by mass or less.

The temperature of the swelling bath is preferably 10-60°C, more preferably 15-45°C, even more preferably 18-30°C. In addition, the immersion time in the swelling bath cannot be unconditionally determined because the degree of swelling of the polyvinyl alcohol resin film is affected by the temperature of the swelling bath, but it is preferably 5 to 300 seconds, and 10 to 200 seconds. It is more preferable to be 100 seconds, and more preferably 20 to 100 seconds. The swelling step may be performed only once, or may be performed multiple times as necessary.

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

The concentration of iodine in the dyeing bath is preferably 0.01-1% by mass, more preferably 0.02-0.5% by mass. The concentration of iodide in the dyeing bath is preferably 0.01 to 10% by mass, more preferably 0.05 to 5% by mass, even more preferably 0.1 to 3% by mass. .

The temperature of the dyeing bath is preferably 10-50°C, more preferably 15-45°C, even more preferably 18-30°C. In addition, the immersion time in the dyeing bath cannot be unconditionally determined because the degree of dyeing of the polyvinyl alcohol resin film is affected by the temperature of the dyeing bath, but it is preferably 10 to 300 seconds, and 20 to 240 seconds. It is more preferable to have The dyeing step may be performed only once, or may be performed multiple times as necessary.

The cross-linking step is a treatment step of immersing the polyvinyl alcohol-based resin film dyed in the dyeing step in a treatment bath (cross-linking bath) containing a boron compound, and the polyvinyl alcohol-based resin film is cross-linked by the boron compound, Iodine molecules or dye molecules can be adsorbed on the crosslinked structure. Boron compounds include, for example, boric acid, borates, and borax. The cross-linking bath is generally an aqueous solution, but may be, for example, a mixed solution of an organic solvent miscible with water and water. Moreover, the cross-linking bath preferably contains potassium iodide from the viewpoint of controlling the content of potassium in the polarizing element.

The concentration of the boron compound in the cross-linking bath is preferably 1-15% by mass, more preferably 1.5-10% by mass, and more preferably 2-5% by mass. Further, when potassium iodide is used in the cross-linking bath, the concentration of potassium iodide in the cross-linking bath is preferably 1 to 15% by mass, more preferably 1.5 to 10% by mass. It is more preferably ~5% by mass.

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

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

The treatment bath (stretching bath) in the wet stretching method can usually use a solvent such as water or a mixed solution of an organic solvent miscible with water and water. The stretching bath preferably contains potassium iodide from the viewpoint of controlling the content of potassium ions in the polarizing element. When potassium iodide is used in the drawing bath, the concentration of potassium iodide in the drawing bath is preferably 1 to 15% by mass, more preferably 2 to 10% by mass, and 3 to 6% by mass. % is more preferred. In addition, the treatment bath (stretching bath) may contain a boron compound from the viewpoint of suppressing film breakage during stretching. In this case, the concentration of the boron compound in the stretching bath is 1 to 15% by mass. preferably 1.5 to 10% by mass, more preferably 2 to 5% by mass.

Although the temperature of the drawing bath is not limited, at least one drawing bath is preferably 25 to 80°C, more preferably 40 to 80°C, even more preferably 50 to 75°C, further preferably 65 to 80°C. 75° C. is particularly preferred, and 67° C. or higher is particularly preferred. When the temperature of the stretching bath is raised, it becomes easier to hold the second metal ions used in the metal ion treatment step described later in the PVA-based resin layer. By increasing the temperature of the stretching bath, PVA can be stretched at a temperature near the softening point of PVA in the PVA-based resin layer or at a temperature above the softening point of PVA. As a result, the crystal ratio of PVA decreases, or the crystals of PVA become smaller, the amount of second metal ions incorporated increases, and the cross-linking reaction is promoted. It becomes easy to set the half width of the peak to be 4.80 nm ⁻¹ or more. In addition, the immersion time in the stretching bath cannot be unconditionally determined because the degree of stretching of the polyvinyl alcohol resin film is affected by the temperature of the stretching bath, but it is preferably 10 to 800 seconds, and 30 to 500 seconds. It is more preferable to have The stretching step in the wet stretching method may be performed alone, or may be performed together with any one or more of the swelling step, dyeing step, cross-linking step, and washing step, or may be combined. you can go A processing step that is particularly suitable for bringing the temperature of the processing bath to 65-75° C. which is optimal for the stretching step when applied in conjunction with any one or more of the processing steps is the cross-linking step. When stretching is performed in a plurality of treatment baths, the temperature of at least one treatment bath is preferably 65 to 75°C, and the immersion time in the treatment bath at 65 to 75°C is 40 to 200 seconds. is preferred.

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

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

The washing process is a treatment process in which the polyvinyl alcohol-based resin film is immersed in a washing bath, and foreign substances remaining on the surface of the polyvinyl alcohol-based resin film can be removed. As the cleaning bath, a medium containing water as a main component, such as water, distilled water, or pure water, is usually used. Also, from the viewpoint of controlling the potassium content in the polarizing element, it is preferable to use potassium iodide in the cleaning bath. In this case, the concentration of potassium iodide in the cleaning bath is 1 to 10% by mass. , more preferably 1.5 to 4% by mass, even more preferably 1.8 to 3.8% by mass.

The temperature of the washing bath is preferably 5-50°C, more preferably 10-40°C, even more preferably 15-30°C. The immersion time in the cleaning bath cannot be unconditionally determined because the degree of cleaning of the polyvinyl alcohol resin film is affected by the temperature of the cleaning bath, but it is preferably 1 to 100 seconds, more preferably 2 to 50 seconds. It is more preferable that the period is 3 to 20 seconds. The washing step may be performed only once, or may be performed multiple times as necessary.

The manufacturing method of the polarizing element can have a metal ion treatment step in the above steps or as a separate step from the above steps. The metal ion treatment step is performed by immersing the polyvinyl alcohol-based resin film in an aqueous solution containing a metal salt of the second metal ion. The second metal ion is incorporated into the polyvinyl alcohol-based resin film by the metal ion treatment step.

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

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

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

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

After performing each of the above processes, the drying process is finally performed. The drying step is a step of drying the polyvinyl alcohol-based resin film washed in the washing step to obtain a polarizing element. Drying is performed by any appropriate method, and examples thereof include natural drying, air drying, and heat drying.

Production method 2 includes a step of applying a coating liquid containing the polyvinyl alcohol resin onto a base film, a step of uniaxially stretching the obtained laminate film, and a polyvinyl alcohol resin layer of the uniaxially stretched laminate film in two colors. by dyeing with a dichroic dye to adsorb the dichroic dye to form a polarizing element, a step of treating the film having the dichroic dye adsorbed with an aqueous boric acid solution, and washing with water after the treatment with the aqueous boric acid solution. It can be manufactured through processes. The base film used to form the polarizing element may be used as a protective layer for the polarizing element. If necessary, the base film may be peeled off from the polarizing element.

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

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

For the protective film, use a film such as a cellulose acylate film, a film made of a polycarbonate resin, a film made of a cycloolefin resin such as norbornene, a (meth)acrylic polymer film, or a polyester resin film such as polyethylene terephthalate. can be done. In the case of a structure having protective films on both sides of the polarizing element, when laminating using a water-based adhesive such as a PVA adhesive, the protective film on at least one side is a cellulose acylate film or (meth)acrylic in terms of moisture permeability. Any one of polymer films is preferable, and cellulose acylate film is particularly preferable.

At least one protective film may have a retardation for purposes such as viewing angle compensation, in which case the film itself may have a retardation, even if it has a separate retardation layer It may be a combination of both.
Although the configuration in which the film having retardation is directly attached to the polarizing element via an adhesive has been described, the film having retardation is adhered via another protective film bonded to the polarizing element. It may be laminated via an agent or an adhesive.

[Adhesive layer]
Any appropriate adhesive can be used as the adhesive constituting the adhesive layer for bonding the protective film to the polarizing element. As the adhesive, a water-based adhesive, a solvent-based adhesive, an active energy ray-curable adhesive, or the like can be used, but a water-based adhesive is preferable. From the viewpoint of improving heat resistance, the adhesive layer preferably contains at least one urea-based compound selected from urea, urea derivatives, thiourea, and thiourea derivatives.

The thickness of the adhesive when applied can be set to any appropriate value. For example, settings are made so that an adhesive layer (coating layer) having a desired thickness is obtained after curing or heating (drying). The thickness of the adhesive layer 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. It is below.

(water-based adhesive)
Any appropriate water-based adhesive can be employed as the water-based adhesive. Among them, a water-based adhesive containing a PVA-based resin (PVA-based adhesive) is preferably used. The average degree of polymerization of the PVA-based resin contained in the water-based adhesive is preferably 100-5500, more preferably 1000-4500, from the viewpoint of adhesion. The average degree of saponification is preferably 85 mol % to 100 mol %, more preferably 90 mol % to 100 mol %, from the viewpoint of adhesion.

The PVA-based resin contained in the water-based adhesive preferably contains an acetoacetyl group, because the adhesion between the PVA-based resin layer and the protective film is excellent and the durability is excellent. . The acetoacetyl group-containing PVA-based resin can be obtained, for example, by reacting the PVA-based resin with diketene by any method. The acetoacetyl group modification degree of the acetoacetyl group-containing PVA resin is typically 0.1 mol % or more, preferably 0.1 mol % to 20 mol %.
The resin concentration of the water-based adhesive is preferably 0.1% by mass to 15% by mass, more preferably 0.5% by mass to 10% by mass.

The water-based adhesive can also contain a cross-linking agent. A known cross-linking agent can be used as the cross-linking agent. Examples include water-soluble epoxy compounds, dialdehydes, isocyanates, and the like.

When the PVA-based resin is an acetoacetyl group-containing PVA-based resin, the cross-linking agent is preferably glyoxal, glyoxylate, or methylolmelamine, and is preferably either glyoxal or glyoxylate. Preferably, glyoxal is particularly preferred.

The water-based adhesive can also contain organic solvents. Alcohols are preferable for the organic solvent because they are miscible with water, and among alcohols, methanol or ethanol is more preferable. Some urea-based compounds have low solubility in water, but some have sufficient solubility in alcohol. In that case, the urea-based compound is dissolved in alcohol to prepare an alcohol solution of the urea-based compound, and then the alcohol solution of the urea-based compound is added to the PVA aqueous solution to prepare the adhesive. be.

The concentration of methanol in the water-based adhesive is preferably 10% by mass or more and 70% by mass or less, more preferably 15% by mass or more and 60% by mass or less, and still more preferably 20% by mass or more and 60% by mass or less. Further, when the content of methanol is 70% by mass or less, deterioration of hue can be suppressed.

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

(Urea-based compound)
When the adhesive layer contains a urea-based compound, the urea-based compound is at least one selected from urea, urea derivatives, thiourea, and thiourea derivatives. As a method for incorporating the urea-based compound into the adhesive layer, it is preferable to incorporate the urea-based compound into the adhesive. In addition, part of the urea-based compound may be transferred from the adhesive layer to the polarizing element or the like during the process of forming the adhesive layer from the adhesive through a drying step or the like. That is, the polarizing element may contain a urea-based compound. Urea-based compounds include those that are water-soluble and those that are poorly water-soluble, and both urea-based compounds can be used in the adhesive of the present embodiment. When a poorly water-soluble urea-based compound is used in a water-based adhesive, it is preferable to devise a dispersion method after forming the adhesive layer so as not to cause an increase in haze or the like.

When the adhesive is a water-based adhesive containing a PVA-based resin, the amount of the urea-based compound added is preferably 0.1 to 400 parts by mass, preferably 1 to 200 parts by mass, with respect to 100 parts by mass of the PVA resin. more preferably 3 to 100 parts by mass.

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

Specific examples of urea derivatives include monosubstituted urea such as methylurea, ethylurea, propylurea, butylurea, isobutylurea, N-octadecylurea, 2-hydroxyethylurea, hydroxyurea, acetylurea, allylurea, and 2-propynyl. Urea, cyclohexyl urea, phenyl urea, 3-hydroxyphenyl urea, (4-methoxyphenyl) urea, benzyl urea, benzoyl urea, o-tolyl urea, p-tolyl urea.
Disubstituted urea, 1,1-dimethylurea, 1,3-dimethylurea, 1,1-diethylurea, 1,3-diethylurea, 1,3-bis(hydroxymethyl)urea, 1,3-tert- Butyl urea, 1,3-dicyclohexyl urea, 1,3-diphenyl urea, 1,3-bis(4-methoxyphenyl) urea, 1-acetyl-3-methyl urea.
Tetramethylurea, 1,1,3,3-tetraethylurea, 1,1,3,3-tetrabutylurea, and 1,3-dimethoxy-1,3-dimethylurea can be mentioned as tetrasubstituted urea.

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

Specific examples of thiourea derivatives include monosubstituted thiourea such as N-methylthiourea, ethylthiourea, propylthiourea, isopropylthiourea, 1-butylthiourea, cyclohexylthiourea, N-acetylthiourea, N-allylthiourea, (2 -methoxyethyl)thiourea, N-phenylthiourea, (4-methoxyphenyl)thiourea, N-(2-methoxyphenyl)thiourea, N-(1-naphthyl)thiourea, (2-pyridyl)thiourea, Examples include o-tolylthiourea and p-tolylthiourea.
Disubstituted thiourea, 1,1-dimethylthiourea, 1,3-dimethylthiourea, 1,1-diethylthiourea, 1,3-diethylthiourea, 1,3-dibutylthiourea, 1,3-diisopropylthiourea, 1 ,3-dicyclohexylthiourea, N,N-diphenylthiourea, N,N'-diphenylthiourea, 1,3-di(o-tolyl)thiourea, 1,3-di(p-tolyl)thiourea, 1-benzyl-3-phenylthiourea, 1-methyl-3-phenylthiourea, N-allyl-N'-(2-hydroxyethyl)thiourea.
Tri-substituted thiourea includes trimethylthiourea, and tetra-substituted thiourea includes tetramethylthiourea and 1,1,3,3-tetraethylthiourea.

Among urea-based compounds, urea derivatives or thiourea derivatives are preferred, and urea derivatives are more preferred. Among the urea derivatives, mono-substituted urea or di-substituted urea is preferred, and mono-substituted urea is more preferred. Disubstituted urea includes 1,1-substituted urea and 1,3-substituted urea, with 1,3-substituted urea being more preferred.

<Urea compound-containing layer>
The urea-based compound is not limited to being contained in the adhesive layer as described above, and may be contained in layers other than the adhesive layer from the viewpoint of improving the heat resistance of the polarizing plate. . As another layer, as described in the explanation of the transparent protective film, in recent years, a polarizing plate having a protective film on only one side of the polarizing element has been developed in order to meet the demand for thinner polarizing plates. In such a configuration, a hardening layer may be laminated on the surface of the polarizing element having no protective film for the purpose of increasing the physical strength.

In this embodiment, such a cured layer can also contain a urea-based compound. Usually, such a cured layer is formed from a curable composition containing an organic solvent. A method of forming such a cured layer from solution is described. Since many urea-based compounds are water-soluble, such compositions may contain a water-soluble urea-based compound.

<Adhesive layer>
In order to bond the polarizing plate described above to an image display device, a pressure-sensitive adhesive layer is usually laminated. This pressure-sensitive adhesive layer is provided for bonding the polarizing plate to the image display device.

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

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

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

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

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

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

For example, the pressure-sensitive adhesive composition may be directly applied to the release-treated surface of the separate film to form a pressure-sensitive adhesive layer, and this pressure-sensitive adhesive layer with a separate film may be laminated on the surface of the polarizer. A pressure-sensitive adhesive layer may be formed by directly coating the pressure-sensitive adhesive composition on the surface of the polarizing plate, and a separate film may be laminated on the outer surface of the pressure-sensitive adhesive layer.
When the pressure-sensitive adhesive layer is provided on the surface of the polarizing plate, it is preferable to subject the bonding surface of the polarizing plate and/or the bonding surface of the pressure-sensitive adhesive layer to a surface activation treatment such as plasma treatment or corona treatment. Treatment is more preferred.
Alternatively, a pressure-sensitive adhesive composition is applied onto the second separate film to form a pressure-sensitive adhesive layer, a separate film is laminated on the formed pressure-sensitive adhesive layer to prepare a pressure-sensitive adhesive sheet, and from this pressure-sensitive adhesive sheet the second After peeling off the separate film, the pressure-sensitive adhesive layer with the separate film may be laminated on the polarizing plate. The second separate film is weaker in adhesion to the pressure-sensitive adhesive layer than the separate film and easy to peel off.

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

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

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

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

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

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

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

(6) Measurement of half width of peak derived from polyvinyl alcohol crystal of polarizing element <Measurement sample>
A sample for measurement was prepared by laminating 10 polarizing elements so that the absorption axes of the polarizing elements were aligned.

<Measurement using wide-angle X-ray scattering method>
A value calculated using the following measurement equipment and measurement requirements using the Wide-angle X-ray Scattering method.

(measuring device)
A nanoscale X-ray structure evaluation device NANO-Viewer manufactured by Rigaku Corporation was used.

(Measurement condition)
・X-ray source: Cu-kα ray ・Camera length: 71mm
・Measurement: transmission measurement ・X-ray irradiation time: 10 minutes

(calculation method)
First, the background measurement is performed without placing the measurement sample, and the circular average scattering profile is obtained for the obtained two-dimensional scattering pattern. Next, the measurement sample is measured, and the scattering profile is similarly obtained. rice field. Subsequently, for the scattering profile of the measurement sample minus the background scattering profile, the peak derived from the polyvinyl alcohol crystal near the position where the wave number q is 15 nm ⁻¹ was identified, and the half width of the peak was calculated. . FIG. 1 shows a graph obtained by subtracting the background scattering profile from the measurement sample scattering profile for polarizing elements 1 to 3, which will be described later, plotted against the wave number q. The peak at the position where the wave number q is 15 nm ⁻¹ is the peak derived from the polyvinyl alcohol crystal. The interval between two points at which the intensity of the peak is 1/2 of the maximum value is defined as the half width.

(7) High temperature endurance test (115°C)
<Preparation of sample for evaluation>
With reference to the examples of JP-A-2018-025765, an acrylic adhesive (manufactured by Lintec Corporation) is applied to one side of a polarizing plate prepared by the procedure described later to form an adhesive layer having a thickness of 25 μm. bottom. A polarizing plate having an adhesive layer formed on one side thereof was cut into a size of 40 mm×40 mm. Alkali-free glass (trade name “EAGLE XG”, manufactured by Corning Incorporated) was attached to the surface of the pressure-sensitive adhesive layer to prepare an evaluation sample (optical laminate).

<High temperature endurance test>
The evaluation sample obtained above was autoclaved for 1 hour at a temperature of 50° C. and a pressure of 5 kgf/cm ² (490.3 kPa). After the evaluation sample was allowed to stand for 24 hours in an environment with a temperature of 23° C. and a relative humidity of 55%, the luminosity-correction single transmittance, luminosity-correction degree of polarization, and hue of the polarizing plate were measured and used as initial values. Next, a high temperature durability test was performed by storing the evaluation sample in a high temperature environment at a temperature of 115 ° C. for 500 hours, and the luminosity correction single transmittance, luminosity correction polarization degree, and hue of the polarizing plate after the high temperature durability test were measured. .

From the initial values of the luminosity correction single transmittance, luminosity correction degree of polarization, and hue of the polarizing plate and the measured values after the high temperature durability test, the luminosity correction single transmittance, luminosity correction degree of polarization, and hue of the polarizing plate was calculated. The amount of change ΔTy in the luminosity-corrected single transmittance and the amount of change ΔPy in the degree of luminosity-corrected polarization were calculated as values obtained by subtracting the initial values from the measured values after the high-temperature endurance test. Further, the hue change amount Δab was obtained by the following formula.
Δab={(a1−a2) ² +(b1−b2) ² } ^1/2
Here, a1 and b1 are the initial values of the hue, and a2 and b2 are the measured values of the hue after the high temperature endurance test.

[Examples 1 and 2 and Comparative Example 1]
(Production of polarizing element 1)
After immersing a 30 μm thick polyvinyl alcohol resin film with a boron adsorption rate of 5.71% by mass in pure water at 21.5° C. for 79 seconds (swelling treatment), the mass of potassium iodide/boric acid/water It was immersed in an aqueous solution having a ratio of 2/2/100 and containing 1.0 mM iodine at 23°C for 151 seconds (dyeing step). Then, it was immersed in an aqueous solution of potassium iodide/boric acid/water at a mass ratio of 2.5/4/100 at 68.5° C. for 76 seconds (first cross-linking step). Subsequently, the mass ratio of potassium iodide/boric acid/zinc chloride/water was 3/5.5/0.6/100 and immersed in an aqueous solution at 45°C for 11 seconds (second cross-linking step, metal ion treatment step ). After that, it was washed by being immersed in a washing bath (washing step) and dried at 38° C. (drying step) to obtain a 12 μm-thick polarizing element in which iodine was adsorbed and oriented on polyvinyl alcohol. The stretching was performed mainly in the dyeing process and the first cross-linking process, and the total stretching ratio was 5.85 times. The resulting polarizing element had a zinc ion content of 0.17% by mass, a boron content of 4.62% by mass, and a polyvinyl alcohol crystal-derived peak half width of 4.90 nm ⁻¹ .

(Production of polarizing element 2)
After immersing a 30 μm thick polyvinyl alcohol resin film with a boron adsorption rate of 5.71% by mass in pure water at 21.5° C. for 79 seconds (swelling treatment), the mass of potassium iodide/boric acid/water It was immersed in an aqueous solution having a ratio of 2/2/100 and containing 1.0 mM iodine at 23°C for 151 seconds (dyeing step). Then, it was immersed in an aqueous solution of potassium iodide/boric acid/water at a mass ratio of 2.5/4/100 at 66.5° C. for 76 seconds (first cross-linking step). Subsequently, the mass ratio of potassium iodide/boric acid/zinc chloride/water was 3/5.5/0.6/100 and immersed in an aqueous solution at 45°C for 11 seconds (second cross-linking step, metal ion treatment step ). After that, it was washed by being immersed in a washing bath (washing step) and dried at 38° C. (drying step) to obtain a 12 μm-thick polarizing element in which iodine was adsorbed and oriented on polyvinyl alcohol. The stretching was performed mainly in the dyeing process and the first cross-linking process, and the total stretching ratio was 5.85 times. The resulting polarizing element had a zinc ion content of 0.17% by mass, a boron content of 4.62% by mass, and a polyvinyl alcohol crystal-derived peak half width of 4.85 nm ⁻¹ .

(Production of polarizing element 3)
After immersing a 30 μm thick polyvinyl alcohol resin film with a boron adsorption rate of 5.71% by mass in pure water at 21.5° C. for 79 seconds (swelling treatment), the mass of potassium iodide/boric acid/water It was immersed in an aqueous solution having a ratio of 2/2/100 and containing 1.0 mM iodine at 23° C. for 151 seconds (dyeing step). Then, it was immersed in an aqueous solution of potassium iodide/boric acid/water at a mass ratio of 2.5/4/100 at 60.6° C. for 76 seconds (first cross-linking step). Subsequently, the mass ratio of potassium iodide/boric acid/zinc chloride/water was 3/5.5/0.6/100 and immersed in an aqueous solution at 45°C for 11 seconds (second cross-linking step, metal ion treatment step ). After that, it was washed by being immersed in a washing bath (washing step) and dried at 38° C. (drying step) to obtain a 12 μm-thick polarizing element in which iodine was adsorbed and oriented on polyvinyl alcohol. The stretching was performed mainly in the dyeing process and the first cross-linking process, and the total stretching ratio was 5.85 times. The resulting polarizing element had a zinc ion content of 0.17% by mass, a boron content of 4.62% by mass, and a polyvinyl alcohol crystal-derived peak half width of 4.75 nm ⁻¹ .

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

(Preparation of Adhesive 1 for Polarizing Plate)
The prepared adhesive PVA solution, pure water, and methanol were blended so as to have a PVA concentration of 3.0%, a methanol concentration of 35%, and a urea concentration of 0.5%, thereby obtaining an adhesive 1 for polarizing plate.

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

(Preparation of polarizing plate 1)
A saponified cellulose acylate film was adhered to both surfaces of the polarizing element 1 with the adhesive 1 for polarizing plate. The thickness of the adhesive was adjusted so that the thickness of the adhesive layer after drying was 100 nm on both sides. Bonding was performed using a roll bonding machine. After lamination, the film was dried at 80° C. for 3 minutes, and the polarizing element 1 and the cellulose acylate film were adhered. Thus, a polarizing plate 1 was obtained in which the cellulose acylate films were laminated on both sides of the polarizing element 1 .

Polarizing

plates

2 and 3 were produced in the same manner, except that the polarizing element 1 of the polarizing plate 1 was changed to the

polarizing elements

2 and 3.

(Preparation of optical laminates 1 to 3)
With reference to the examples of JP-A-2018-025765, by applying an acrylic adhesive (manufacturer: Lintec Co., Ltd.) to one side of the polarizing plates 1 to 3 prepared above, the thickness Optical laminates 1 to 3 having an adhesive layer with a thickness of 25 μm were produced.

(Example 1)
A high-temperature durability test was performed on the optical layered body 1 in Example 1. FIG. The change amount ΔTy of the luminosity correction single transmittance of the optical laminate 1 is 0.6%, the change amount ΔPy of the luminosity correction polarization degree is −0.03%, and the hue change amount Δab is 2.0 NBS. Met. Table 1 shows the results.

(Example 2)
In Example 2, a high temperature endurance test was performed on the optical layered body 2 . The change amount ΔTy of the luminosity correction single transmittance of the optical laminate 2 is 1.2%, the change amount ΔPy of the luminosity correction polarization degree is −0.03%, and the hue change amount Δab is 2.3 NBS. Met. Table 1 shows the results.

(Comparative example 1)
The change amount ΔTy of the luminosity correction single transmittance of the optical laminate 3 is 2.6%, the change amount ΔPy of the luminosity correction polarization degree is −0.13%, and the hue change amount Δab is 5.3 NBS. Met. Table 1 shows the results.

It was found that the optical

layered bodies

1 and 2 are superior to the optical layered body 3 in suppressing the decrease in the degree of polarization even when exposed to a high temperature environment of 115°C.

Claims

A polarizing plate having a polarizing element obtained by adsorbing and aligning a dichroic dye on a polyvinyl alcohol-based resin layer, and a transparent protective film,
The polarizing element has a peak half width of 4.80 nm −1 or more derived from a polyvinyl alcohol crystal measured by a wide-angle X-ray scattering method,
The polarizing element contains potassium ions and metal ions other than potassium ions,
The polarizing plate, wherein the polarizing element contains 0.05% by mass or more of metal ions other than the potassium ions.
The polarizing plate of claim 1, wherein the metal ions include at least one selected from the group consisting of cobalt, nickel, zinc, chromium, aluminum, copper, manganese, and iron ions.
The polarizing plate according to claim 1 or 2, wherein the polarizing element has a boron content of 2.4% by mass or more and 8.0% by mass or less.
further comprising an adhesive layer for bonding the polarizing element and the transparent protective film;
The polarizing plate according to any one of claims 1 to 3, wherein the adhesive layer is a coating layer of a water-based adhesive.
5. The polarizing plate according to claim 4, wherein the water-based adhesive has a methanol concentration of 10% by mass or more and 70% by mass or less.
6. The polarizing plate according to claim 4, wherein said water-based adhesive contains a polyvinyl alcohol-based resin.
7. The polarizing plate according to claim 4, wherein the adhesive layer has a thickness of 0.01 μm or more and 7 μm or less.