TW202314302A - Polarizing plate - Google Patents

Abstract

An object of the present invention is to provide a polarizing plate which is excellent in the effect of suppressing the decrease in the degree of polarization even when exposed in a high-temperature environment, e.g., an 115 DEG C environment. The present invention provides a polarizing plate, which contains: a polarizing element obtained by adsorbing and orienting a dichroic pigment in a polyvinyl alcohol-based resin layer, and a transparent protective film; wherein for the polarizing element, the half-width of the peak derived from polyvinyl alcohol crystal measured by wide-angle scattering X-ray techniques is 4.80 nm<SP>-1</SP> or more and, the polarizing element contains potassium ions and metal ions other than potassium ions, wherein the content of the metal ions other than potassium ions is 0.05 percent by mass or more.

Description

polarizer

The present invention relates to polarizing plates.

Liquid crystal display devices (LCD: Liquid Crystal Display) are not only used in liquid crystal televisions, but also widely used in portable devices (mobile) such as personal computers and mobile phones, and in-vehicle applications such as car navigation systems. Generally, a liquid crystal display device has a liquid crystal panel member with a polarizer attached to both sides of a liquid crystal cell by an adhesive (pressure-sensitive adhesive), and the liquid crystal panel member is used to control the light from the backlight member. show. In addition, in recent years, organic electroluminescent (EL: Electroluminescence) display devices have been widely used in portable devices such as televisions and mobile phones, and vehicle-mounted applications such as car navigation, like liquid crystal display devices. In an organic EL display device, in order to prevent external light from being reflected by the metal electrode (cathode) and appear as a mirror surface when viewed, a circular polarizing plate (laminated layer including a polarizing element and a λ/4 plate) is arranged on the viewing side surface of the image display panel. body) situation.

As mentioned above, there are increasing opportunities for polarizing plates to be mounted on vehicles as components of liquid crystal display devices or organic EL display devices. Compared with portable devices such as TVs and mobile phones other than automotive applications, polarizers used in automotive image display devices are often exposed to high-temperature environments, so characteristic changes at high temperatures are more required Small (high temperature durability).

With regard to the manufacturing method of such a polarizing element with high high-temperature durability, for example, in Patent Documents 1 to 2, it is disclosed that components such as metal salts containing zinc, copper, aluminum, etc. are added to the treatment bath, thereby making the polarizing element A method of improving the durability of a polarizing element by including these components. In addition, Patent Documents 3 to 4 disclose a method of manufacturing a polarizing element in which components such as an organic titanium compound are added to a treatment bath.

[Prior Art Literature]

[Patent Document]

[Patent Document 1] Japanese International Publication No. 2016/117659

[Patent Document 2] Japanese Unexamined Patent Publication No. 2006-047978

[Patent Document 3] Japanese Unexamined Patent Publication No. 2008-46257

[Patent Document 4] Japanese Patent Application Laid-Open No. 6-172554

However, as far as the current polarizing plates are concerned, when the temperature of the high-temperature environment is increased to 115° C. and exposed to the high-temperature environment for a certain period of time, the degree of polarization may decrease. An object of the present invention is to provide a polarizing plate having an excellent effect of suppressing a decrease in polarization degree even when exposed to a high-temperature environment at a temperature of 115° C., for example.

The present invention provides the following polarizing plates.

[1] A polarizing plate comprising: a polarizing element in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin layer; and a transparent protective film; wherein,

The half-value width of the spectral peak derived from polyvinyl alcohol crystals measured by the wide-angle X-ray scattering method of the aforementioned polarizing element is 4.80nm ^-1 or more,

The aforementioned polarizing element contains potassium ions and metal ions other than potassium ions,

The content rate of the metal ion other than the said potassium ion of the said polarizing element is 0.05 mass % or more.

[2] The polarizing plate according to [1], wherein the metal ion contains at least one member selected from the group consisting of ions of cobalt, nickel, zinc, chromium, aluminum, copper, manganese, and iron.

[3] The polarizing plate according to [1] or [2], wherein the boron content of the polarizing element is not less than 3.9% by mass and not more than 8.0% by mass.

[4] The polarizing plate according to any one of [1] to [3], which further has an adhesive layer for laminating the polarizing element and the transparent protective film,

The aforementioned adhesive layer is a coating layer of a water-based adhesive.

[5] The polarizing plate according to [4], wherein the concentration of methanol in the aqueous adhesive is 10% by mass or more and 70% by mass or less.

[6] The polarizing plate according to [4] or [5], wherein the water-based adhesive contains a polyvinyl alcohol-based resin.

[7] The polarizing plate according to any one of [4] to [6], wherein the adhesive layer has a thickness of not less than 0.01 μm and not more than 7 μm .

According to the present invention, it is possible to provide a polarizing plate having excellent high-temperature durability in which reduction in polarization degree is suppressed when exposed to a high-temperature environment at a temperature of 115° C., for example.

Fig. 1 shows the graph obtained by subtracting the scattering distribution of the background from the scattering distribution of the measurement sample against the wave number q for polarizers (polarizers 1 to 3).

Embodiments of the present invention are 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 in which a dichroic dye is adsorbed and oriented to a layer containing a polyvinyl alcohol-based resin, and a transparent protective film. In addition, the half-value width of the spectrum peak derived from polyvinyl alcohol crystals measured by the wide-angle X-ray scattering method of the above-mentioned polarizer is 4.80 nm ⁻¹ or more. Furthermore, the above-mentioned 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 ions The ratio is 0.05% by mass or more.

In the polarizing plate of this embodiment, the half-value width of the spectral peak derived from polyvinyl alcohol crystals measured by the wide-angle X-ray scattering method of the polarizing element and the content rate of the second metal ion in the polarizing element are within the above-mentioned ranges, Thereby, even if it is exposed to a high-temperature environment for a long time, the reduction of the degree of polarization can be suppressed.

According to the polarizing plate of the present embodiment, even when exposed to a high-temperature environment at a temperature of 115° C. for 500 hours or longer, the decrease in the degree of polarization can be suppressed.

<Polarizer>

As for the polarizing element in which the dichroic dye is adsorbed and oriented on a layer containing polyvinyl alcohol (PVA) resin (also referred to as "PVA resin layer" in this specification), conventional polarizing elements can be used. . Examples of such polarizing elements include: using a PVA-based resin film, dyeing the PVA-based resin film with a dichroic dye, and performing uniaxial stretching; The laminated film obtained on the material film is formed by dyeing the PVA-based resin layer of the coating layer of the laminated film with a dichroic dye, and uniaxially stretching the laminated film.

The polarizer is formed of PVA-based resin obtained by saponifying polyvinyl acetate-based resin. Examples of the polyvinyl acetate-based resin include copolymers of vinyl acetate and other monomers that can be copolymerized with vinyl acetate, in addition to polyvinyl acetate that is a homopolymer of vinyl acetate. Examples of other copolymerizable monomers include unsaturated carboxylic acids, olefins such as ethylene, vinyl ethers, and unsaturated sulfonic acids.

In the present invention, the PVA-based resin layer is preferably formed of a PVA-based resin having a boron adsorption rate of 5.70% by mass or higher. That is, the boron adsorption rate of the PVA-based resin is preferably 5.70% by mass or more in the stage where the raw material before dyeing or stretching is applied. By using this PVA-based resin, even when exposed to a high-temperature environment at a temperature of 115° C., the degree of polarization does not easily decrease. In addition, the boron adsorption rate of the PVA-based resin is preferably 10% by mass or less. By using such a PVA-based resin to make a polarizing element, the concentration of boric acid in the boric acid treatment tank will not become high, and the processing time consumed by the boric acid treatment can be shortened, and the desired polarizing element can be easily obtained. Improve the productivity of polarizing elements. 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 contraction force of the polarizing element tends to decrease. The boron adsorption rate of PVA-type resin can be measured by the method described in the Example mentioned later.

The boron adsorption rate of the PVA-based resin reflects the distance between molecular chains in the PVA-based resin or the characteristics of the crystal structure. It is believed that the distance between the molecular chains of the PVA-based resin with a boron adsorption rate of 5.70 mass % or more is wider than that of the PVA-based resin with a boron adsorption rate of less than 5.70 mass %, and the crystallization of the PVA-based resin is less. Therefore, it is presumed that boron, the first metal ion, and the second metal ion are easy to penetrate into the PVA-based resin layer, and the degree of polarization is difficult to decrease in a high-temperature environment.

The boron adsorption rate of the PVA-based resin can be adjusted, for example, by performing pre-treatments such as hot water treatment, acid solution treatment, ultrasonic irradiation treatment, and radiation irradiation treatment on the PVA-based resin before manufacturing a polarizing element. Through these treatments, the distance between the molecular chains in the PVA-based resin can be widened, or the crystal structure can be destroyed. As the hot water treatment, for example, immersion in pure water at 30° C. to 100° C. for 1 second to 90 seconds, followed by drying. The acidic solution treatment includes, for example, immersion in a boric acid aqueous solution having a concentration of 10% by mass to 20% by mass for 1 second to 90 seconds, followed by drying. Ultrasonic treatment includes, for example, the treatment of irradiating ultrasonic waves with a frequency of 20 to 29 kc for 30 seconds to 10 minutes with an output of 200 W to 500 W. Ultrasonic treatment can be carried out in solvents such as water.

The degree of saponification of the PVA-based resin is preferably above 85 mol%, preferably above 90 mol%, more preferably between 99 mol% and 100 mol%. The degree of polymerization of the PVA-based resin is 1,000 to 10,000, preferably 1,500 to 5,000. The PVA-based resin can be modified, for example, polyvinyl formaldehyde, polyvinyl acetal, polyvinyl butyral, etc. modified by aldehydes.

The thickness of the polarizing element in this embodiment is preferably 5 to 50 μm , more preferably 8 to 28 μm , more preferably 12 to 22 μm , most preferably 12 to 15 μm . By setting the thickness of the polarizing element to 5 μm or more, it is easy to achieve desired optical characteristics.

In the polarizing element of the present invention, the half-value width of the spectral peak derived from polyvinyl alcohol crystals measured by the wide-angle X-ray scattering method is 4.80nm ^-1 or more, preferably 4.82nm ^-1 or more, more preferably 4.87nm ^{- 1} or more. In such a polarizing element, the crystal size of polyvinyl alcohol is reduced due to the progress of the crosslinking reaction with boric acid, and as a result, the ratio of the amorphous part is increased. Therefore, the content of boron or the second metal ion described later can be efficiently increased. The half-value width of the peak derived from polyvinyl alcohol crystals measured by the wide-angle X-ray scattering method may be, for example, 5.0 nm ⁻¹ or less. Such a polarizing element can achieve excellent optical properties due to its high degree of orientation. In addition, the half-value width of the peak derived from polyvinyl alcohol crystals measured by the wide-angle X-ray scattering method can be measured by the method described in Examples described later. The half-value width of the peak derived from polyvinyl alcohol crystals measured by the wide-angle X-ray scattering method can be determined by the temperature of the stretching bath, the stretching ratio, the concentration of boric acid in the cross-linking bath, and the saponification of the PVA-based resin used as the raw material. degree etc. to adjust appropriately.

The content of the second metal ion in the polarizer is preferably from 0.05% by mass to 10.0% by mass, more preferably from 0.05% by mass to 8.0% by mass, still more preferably from 0.1% by mass to 6.0% by mass. When the content of the second metal ion exceeds 10.0% by mass, the degree of polarization may decrease in a high-temperature, high-humidity environment. Moreover, when the content rate of a 2nd metal ion is less than 0.05 mass %, the improvement effect of the durability in a high-temperature environment may not be enough. Also, the content of the second metal ion in the polarizing element can be determined by the mass fraction of the metal element relative to the mass of the polarizing element by, for example, high-frequency inductively coupled plasma (Inductively Coupled Plasma: ICP) emission spectroscopic analysis. (mass%) to calculate. It is believed that in the polarizing element, the metal element exists in the state of forming a cross-linked structure with metal ions, or the constituent elements of the metal element and polyvinyl alcohol-based resin. The so-called content of the second metal ion here means that Metal atomic value.

The second metal ion is not limited as long as it is a metal ion other than potassium ion, but it is preferably an ion of metal other than alkali metal, especially from the point of view of adjusting the color tone and imparting durability, preferably containing cobalt, nickel, zinc, At least one metal ion of transition metals such as chromium, aluminum, copper, manganese, and iron. Among these metal ions, zinc ions are preferred from the viewpoints of adjusting the color tone and providing heat resistance.

The content of boron in the polarizing element is preferably at least 2.4% by mass. In addition, the content of boron is preferably from 3.9% by mass to 8.0% by mass, more preferably from 4.2% by mass to 7.0% by mass, still more preferably from 4.4% by mass to 6.0% by mass. When the boron content of the polarizing element exceeds 8.0% by mass, the contraction force of the polarizing element increases, causing defects such as peeling between the front panel and other components that are attached to the image display device. situation. Moreover, when the content rate of boron is less than 2.4 mass %, desired optical characteristics may not be achieved. In addition, the content of boron in the polarizing element can be determined by the mass fraction (mass %) of boron relative to the mass of the polarizing element by, for example, high-frequency inductively coupled plasma (Inductively Coupled Plasma: ICP) emission spectrometry. figured out. It is believed that in polarizing elements, boron exists in the state of boric acid or boron and polyvinyl alcohol-based resin components forming a crosslinked structure. The so-called boron content here refers to the boron atom (B) value.

The content of boron in the polarizing element is preferably from 2.4 mass % to 8.0 mass %, more preferably from 3.9 mass % to 8.0 mass %. By satisfying such a numerical range, even when exposed to a high-temperature environment, it is possible to suppress a decrease in the degree of polarization.

From the viewpoint of suppressing the decrease in the degree of polarization in a high-temperature environment, the content of potassium ions in the polarizing element is preferably at least 0.28% by mass, more preferably at least 0.32% by mass, and still more preferably at least 0.34% by mass. , from the viewpoint of suppressing the hue change in a high-temperature environment, it is preferably at most 0.60 mass %, more preferably at most 0.55 mass %, and more preferably at most 0.50 mass %. The content of potassium ions can be measured by the same method as the content of the second metal ion, and the content of potassium ions herein means a value in terms of potassium atoms.

Although the detailed mechanism has not been clarified, it can be speculated as follows: Compared with the conventional polarizer, since the content of boron is more and the content of potassium ion is less, the hydroxyl group of polyvinyl alcohol in the polarizer is boron It is protected (stabilized) by acid cross-linking, and iodide ions, which are counter ions in the polarizing element, are stabilized due to the appropriate content of potassium ions.

The luminescence factor corrected monomer transmittance of the polarizing plate is preferably 38.8% to 44.8%, more preferably 40.4% to 43.2%, and more preferably 40.7% to 43.0%. When the luminous factor corrected monomer transmittance exceeds 44.8%, there is an increase in the deterioration of optical properties such as redness in high temperature environments; The deterioration of the optical characteristics under the environment increases.

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

The manufacturing method of the polarizing element is not particularly limited, but a typical one is a method in which a polyvinyl alcohol-based resin film wound in a reel is sent out and stretched, dyed, cross-linked, etc. (hereinafter referred to as "manufacturing method 1") ); and a method comprising the steps of applying a coating liquid comprising a polyvinyl alcohol-based resin on a base film, forming a layer of a polyvinyl alcohol-based resin as a coating layer to obtain a laminate, and applying the The laminate is stretched (hereinafter referred to as "manufacturing method 2").

Production method 1 can be produced through the following steps: a step of uniaxially stretching a polyvinyl alcohol-based resin film; a step of dyeing a polyvinyl alcohol-based resin film with a dichroic dye such as iodine, thereby adsorbing the dichroic dye ; a step of treating the polyvinyl alcohol-based resin film on which the dichroic dye is adsorbed with an aqueous boric acid solution; and a step of washing with water after the treatment with the aqueous boric acid solution.

The boron content and potassium content contained in the polarizing element can be determined by boric acid contained in any of the treatment baths in the swelling step, dyeing step, crosslinking step, extension step, and water washing step. The concentration of boron component supply substances such as boron compounds such as borate and borax, and the concentration of halogens such as potassium iodide The concentration of potassium component supply substances such as potassium chloride, as well as the treatment temperature and treatment time of each of the above-mentioned treatment baths are controlled. In particular, in the cross-linking step and the stretching step, it is easy to adjust the boron content to a desired range according to processing conditions such as the concentration of the boron component supply substance. In addition, in consideration of processing conditions such as the amount of boron component supply material and potassium component supply material used in the dyeing step, crosslinking step, or elongation step, boron, potassium, and other components can be obtained from polyvinyl alcohol-based From the standpoint of eluting the resin film or allowing components such as boron and potassium to be adsorbed to the polyvinyl alcohol-based resin film, the water washing step makes it easy to adjust the boron content and potassium content to desired ranges.

The swelling step is a process of immersing the polyvinyl alcohol-based resin film in a swelling bath, which can remove dirt and blocking agents on the surface of the polyvinyl alcohol-based resin film. To suppress uneven dyeing. Swelling baths usually use water, distilled water, pure water and other water as the main component of the medium. In the swelling bath, a surfactant, an alcohol, etc. can be added appropriately according to a usual method. In addition, from the viewpoint of controlling the potassium content of the polarizing element, potassium iodide may also be used in the swelling bath. In this case, the concentration of potassium iodide in the swelling bath is preferably 1.5% by weight or less, more preferably 1.0% by weight. % or less, and more preferably 0.5% by weight or less.

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

The dyeing step is a treatment step of immersing the polyvinyl alcohol-based resin film in a dyeing bath (iodine solution), so that dichroic substances such as iodine or dichroic dyes can be adsorbed and oriented on the polyvinyl alcohol-based resin film. The iodine solution is preferably usually an iodine aqueous solution, and contains iodine and iodide as a cosolvent. Also, iodides can 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 them, potassium iodide is more suitable from the viewpoint of controlling the potassium content in the polarizing element.

In the dyeing bath, the concentration of iodine is preferably 0.01 to 1% by weight, more preferably 0.02 to 0.5% by weight. In the dyeing bath, the concentration of iodide is preferably 0.01 to 10% by weight, more preferably 0.05 to 5% by weight, and even more preferably 0.1 to 3% by weight.

The temperature of the dyeing bath is preferably from 10 to 50°C, more preferably from 15 to 45°C, and still more preferably from 18 to 30°C. In addition, since the degree of dyeing of the polyvinyl alcohol-based resin film is affected by the temperature of the dyeing bath, it cannot be uniformly determined by the immersion time in the dyeing bath, but it is preferably 10 to 300 seconds, more preferably 20 to 240 seconds. Second. The dyeing step may be performed only once or a plurality of 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 can be cross-linked by the boron compound. link, so that iodine molecules or dye molecules are adsorbed on the cross-linked structure. As a boron compound, boric acid, a borate, borax, etc. are mentioned, for example. The crosslinking bath is generally an aqueous solution, but may also be a mixed solution of, for example, an organic solvent miscible with water and water. In addition, from the viewpoint of controlling the content of potassium in the polarizing element, it is preferable that the crosslinking bath contains potassium iodide.

In the crosslinking bath, the concentration of the boron compound is preferably 1 to 15% by weight, more preferably 1.5 to 10% by weight, and more preferably 2 to 5% by weight. In addition, when potassium iodide is used in the crosslinking bath, the concentration of potassium iodide in the crosslinking bath is preferably 1 to 15% by weight, more preferably 1.5 to 10% by weight, and still more preferably 2 to 5% by weight.

The temperature of the crosslinking bath is preferably from 20 to 70°C, more preferably from 30 to 60°C. In addition, since the degree of crosslinking of the polyvinyl alcohol-based resin film is affected by the temperature of the crosslinking bath, it cannot be determined uniformly. It depends on the immersion time in the crosslinking bath, but it is preferably 5 to 300 seconds, more preferably 10 to 200 seconds. The crosslinking step may be performed only once or a plurality of times as necessary.

The stretching step is a processing step of stretching the polyvinyl alcohol-based resin film to a predetermined ratio in at least one direction. Generally, a polyvinyl alcohol-type resin film is uniaxially stretched in a conveyance direction (longitudinal direction). The stretching method is not particularly limited, and either wet stretching method or dry stretching method can be used. The elongation step may be performed only once or a plurality of times as necessary. The extending step can be performed at any stage in the manufacture of the polarizer.

As a treatment bath (stretching bath) in the wet stretching method, a solvent such as water or a mixed solution of an organic solvent miscible with water and water can generally be used. From the viewpoint of controlling the content of potassium ions in the polarizer, the stretching bath preferably contains potassium iodide. In the case of using potassium iodide in the stretching bath, the concentration of potassium iodide in the stretching bath is preferably 1 to 15% by weight, more preferably 2 to 10% by weight, and still more preferably 3 to 6% by weight. In addition, from the viewpoint of suppressing the breakage of the film being stretched, the treatment bath (stretching bath) may contain a boron compound, and in this case, the concentration of the boron compound in the stretching bath is preferably 1 to 15% by weight, more preferably It is preferably 1.5 to 10% by weight, more preferably 2 to 5% by weight.

The temperature of the stretching bath is not limited, preferably 25 to 80°C in at least one stretching bath, more preferably 40 to 80°C, more preferably 50 to 75°C, particularly preferably 65 to 75°C, most preferably Above 67°C. If the temperature of the stretching bath is increased, the second metal ions used in the metal ion treatment step described later can be easily retained in the PVA-based resin layer. By increasing the temperature of the stretching bath, the stretching process can be performed on PVA 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 crystallization rate of PVA decreases or the crystallization of PVA becomes smaller, the amount of the second metal ion incorporated increases and the crosslinking reaction is promoted, and it is easy to make the spectrum derived from polyvinyl alcohol crystals measured by wide-angle X-ray scattering method The half width of the peak was 4.80 nm ^-1 or more. In addition, since the stretching degree of the polyvinyl alcohol-based resin film is affected by the temperature of the stretching bath, it cannot be uniformly determined by the immersion time in the stretching bath, but it is preferably 10 to 800 seconds, more preferably 30 to 500 seconds. Second. The elongation step in the wet elongation 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. to implement. In the case of carrying out together with any one of the above processing steps, the processing step which is particularly suitable for setting the temperature of the processing bath to 65 to 75° C. which is most suitable for the elongation step is the crosslinking step. In the case of stretching in a plurality of treatment baths, it is preferable that the temperature of at least one treatment bath is 65 to 75°C, and furthermore, the immersion time in the treatment bath of 65°C to 75°C is preferably 40 to 200 seconds .

Examples of the dry stretching method include a roll-to-roll stretching method, a heating roll stretching method, a compression stretching method, and the like. In addition, the dry stretching method can also be implemented together with a drying step.

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

The cleaning step is a treatment step of immersing the polyvinyl alcohol-based resin film in a cleaning bath, and can remove impurities remaining on the surface of the polyvinyl alcohol-based resin film. A cleansing bath usually uses a medium mainly composed of water, distilled water, or 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. In this case, the concentration of potassium iodide in the cleaning bath is preferably 1 to 10% by weight. More preferably, it is 1.5 to 4% by weight, and more preferably, it is 1.8 to 3.8% by weight.

The temperature of the cleaning bath is preferably from 5 to 50°C, more preferably from 10 to 40°C, and still more preferably from 15 to 30°C. In addition, since the degree of cleaning of the polyvinyl alcohol-based resin film is affected by the temperature of the cleaning bath, it cannot be uniformly determined by the immersion time in the cleaning bath, but it is preferably 1 to 100 seconds, more preferably 2 to 50 seconds, more preferably 3 to 20 seconds. The washing step may be implemented only once or a plurality of times as necessary.

The method of manufacturing a polarizing element may include a metal ion treatment step in the above-mentioned steps, or in a step different from the above-mentioned steps. The metal ion treatment step is performed by immersing the polyvinyl alcohol-based resin film in an aqueous solution of a metal salt containing the second metal ion. The second metal ion is contained in the polyvinyl alcohol-based resin film by the metal ion treatment step.

The second metal ion is not limited as long as it is a metal ion other than potassium ion, and is preferably an ion of metal other than alkali metal, especially from the viewpoint of adjusting the color tone and imparting durability, preferably containing cobalt, nickel, and zinc. At least one metal ion of transition metals such as chromium, aluminum, copper, manganese, and iron. Among these metal ions, zinc ions are preferred from the viewpoints of color tone adjustment, heat resistance imparting, and the like. Examples of the zinc salt include zinc halides such as zinc chloride and zinc iodide; zinc sulfate, zinc acetate, and the like.

In the metal ion treatment step, a metal salt solution is used. Hereinafter, in the metal ion treatment step, the immersion treatment in the zinc-containing solution will be described as a representative example of the case where a zinc salt aqueous solution is used.

The concentration of zinc ions in the zinc salt solution is in the range of 0.1 to 10% by mass, preferably in the range of 0.3 to 7% by mass. In addition, the zinc salt solution is preferably an aqueous solution containing potassium ions and iodide ions by means of potassium iodide or the like because zinc ions are easily impregnated. The concentration of potassium iodide in the zinc salt solution is preferably from 0.1 to 10% by mass, more preferably from 0.2 to 5% by mass.

During the immersion treatment in the zinc-containing solution, the temperature of the zinc salt solution is usually 15 to 85°C, preferably 25 to 70°C. The dipping time is generally 1 to 120 seconds, preferably in the range of 3 to 90 seconds. During the immersion treatment in the zinc-containing solution, it is necessary to adjust the concentration of the zinc salt solution, the immersion temperature and immersion time of the polyvinyl alcohol-based resin film in the zinc-salt solution to make the polyvinyl alcohol-based resin film Adjust the zinc content rate so that it becomes the aforementioned range. There is no particular limitation as to when the immersion treatment in the zinc-containing solution is performed. The immersion treatment in the zinc-containing solution can be carried out alone, or in a dyeing bath, cross-linking bath, Coexisting the zinc salt in the stretching bath is performed simultaneously with at least one of the dyeing step, the crosslinking step, and the stretching step.

After carrying out the aforementioned steps, the last step is to carry out the drying step. 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 may be performed by any appropriate method, and examples thereof include natural drying, air drying, and heat drying.

The production method 2 can be produced through the following steps: a step of applying the coating liquid containing the above-mentioned polyvinyl alcohol-based resin on the base film; a step of uniaxially stretching the obtained laminated film; The step of dyeing the polyvinyl alcohol-based resin layer of the laminated film with a dichroic dye to absorb the dichroic dye to form a polarizing element; the step of treating the film adsorbed with the dichroic dye with boric acid aqueous solution ; and the step of washing with water after the treatment by boric acid aqueous solution. The base film used for forming the polarizer can also be used as a protective layer of the polarizer. The base film can also be peeled and removed from the polarizing element as needed.

[Transparent protective film]

The transparent protective film (hereinafter also simply referred to as "protective film") used in this embodiment is bonded to at least one side of the polarizer through an adhesive layer. The transparent protective film is pasted on one side or both sides of the polarizing element, preferably on both sides.

The protective film can have other optical functions at the same time, and can also be formed into a laminated structure with multiple layers. From the viewpoint of optical properties, the thinner the film thickness of the protective film, the better, but if it is too thin, the strength will decrease and the processability will deteriorate. A suitable film thickness is 5 to 100 μm , preferably 10 to 80 μm , more preferably 15 to 70 μm .

The protective film can be used: cellulose acylate film, film made of polycarbonate resin, film made of cycloolefin resin such as norbornene, (meth)acrylic Films such as acid-based polymer films and polyester resin films such as polyethylene terephthalate. When a protective film is provided on both sides of the polarizing element, and a water-based adhesive such as PVA adhesive is used for lamination, it is preferable that at least one side of the protective film is made of acrylic acid from the viewpoint of moisture permeability. Any of a cellulose-based film or a (meth)acrylic polymer film, especially a cellulose acylate film.

For viewing angle compensation and other purposes, at least one protective film may have a phase difference. In this case, the film itself may have a phase difference, or it may have a phase difference layer, or a combination of both.

In addition, although the structure of the film having a phase difference is directly attached to the polarizing element through an adhesive, the structure of the film having a phase difference may also be attached to the polarizer through an adhesive or an adhesive. Other protective films for polarizing elements can be pasted together.

[adhesive layer]

Any appropriate adhesive can be used for the adhesive constituting the adhesive layer for bonding the protective film to the polarizing element. As the adhesive, water-based adhesives, solvent-based adhesives, active energy ray-curable adhesives, etc. can be used, and water-based adhesives are preferred. It is also useful that the adhesive layer preferably contains at least one urea-based compound selected from urea, urea derivatives, thiourea, and thiourea derivatives from the viewpoint of improving heat resistance.

The thickness at the time of application of the adhesive agent can be set to any appropriate value. For example, it is set so that an adhesive layer (coating layer) having a desired thickness can be obtained after curing or heating (drying). The thickness of the adhesive layer is preferably not less than 0.01 μm and not more than 7 μm , more preferably not less than 0.01 μm and not more than 5 μm , more preferably not less than 0.01 μm and not more than 2 μm , most preferably not less than 0.01 μm1 µm or less.

(water-based adhesive)

As the water-based adhesive, any appropriate water-based adhesive can be used. Among them, water-based adhesives (PVA-based adhesives) containing PVA-based resins are particularly suitable. From the viewpoint of adhesion, the average degree of polymerization of the PVA-based resin contained in the water-based adhesive is preferably from 100 to 5,500, more preferably from 1,000 to 4,500. from adhesion From this point of view, the average degree of saponification is preferably from 85 mol% to 100 mol%, more preferably from 90 mol% to 100 mol%.

The PVA-based resin contained in the above-mentioned water-based adhesive is preferably one containing an acetoacetyl group, because the PVA-based resin layer has excellent adhesion to the protective film and excellent durability. The PVA-type resin containing an acetoacetyl group can be obtained by making PVA-type resin and diketene (diketene) react by arbitrary methods, for example. The modification degree of acetyl acetyl group of the PVA-based resin containing acetyl acetyl group 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 may contain a crosslinking agent. As the crosslinking agent, known crosslinking agents can be used. Examples thereof include water-soluble epoxy compounds, dialdehydes, and isocyanates.

When the PVA-based resin is a PVA-based resin containing acetoacetyl group, the cross-linking agent is preferably any one of glyoxal (glyoxal), glyoxylate and methylol melamine, more preferably acetonitrile. Any of dialdehyde and glyoxylate, particularly preferably glyoxal.

The water-based adhesive may contain an organic solvent. In terms of miscibility with water, the organic solvent is preferably alcohols, and methanol or ethanol is particularly preferable among alcohols. Some urea compounds have low solubility in water but sufficient solubility in alcohols. In this case, "the alcohol solution of the urea compound is prepared by dissolving the urea compound in alcohol, and then the alcohol solution of the urea compound is added to the aqueous solution of the PVA resin to prepare an adhesive" is also more appropriate. One of the best looks.

The concentration of methanol in the water-based adhesive is preferably from 10% by mass to 70% by mass, more preferably from 15% by mass to 60% by mass, and more preferably from 20% by mass to 60% by mass. Moreover, deterioration of hue can be suppressed by making the content rate of methanol into 70 mass % or less.

(Active energy ray hardening adhesive)

Active energy ray-curable adhesives are adhesives that are cured by irradiating active energy rays such as ultraviolet rays, and examples thereof include adhesives containing polymerizable compounds and photopolymerizable initiators, adhesives containing photoreactive resins, Adhesives containing adhesive resins and photoreactive crosslinking agents, etc. Examples of the aforementioned 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 cationic radicals by irradiating active energy rays such as ultraviolet rays.

(urea compound)

When the adhesive layer contains a urea compound, the urea compound is at least one selected from urea, urea derivatives, thiourea, and thiourea derivatives. The method of making the adhesive layer contain a urea compound includes the method of making the above-mentioned adhesive contain a urea compound. In addition, in the process of forming an adhesive layer from an adhesive through a drying step, etc., there is no problem in that a part of the urea-based compound migrates from the adhesive layer to a polarizing element or the like. That is, the polarizing element may contain a urea compound. There are water-soluble and water-insoluble urea-based compounds, and any urea-based compound can be used in the adhesive of this embodiment. When a water-insoluble urea compound is used in a water-based adhesive, it is preferable to design a dispersion method after forming the adhesive layer so as not to increase haze.

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

(urea derivatives)

Urea derivatives are compounds in which at least one of the 4 hydrogen atoms of the urea molecule is replaced by a substituent. In this case, the substituent is not particularly limited, and is preferably a substituent composed of carbon atoms, hydrogen atoms and oxygen atoms.

As specific examples of urea derivatives, monosubstituted urea includes methyl urea, ethyl urea, propionyl urea, butyl urea, isobutyl urea, N-octadecaneal urea, 2-hydroxyethyl urea, hydroxyurea, acetyl urea , Allylurea, 2-propyneurea, cyclohexylurea, phenylurea, 3-hydroxyphenylurea, (4-methoxyphenyl)urea, benzylurea, benzylurea, o-tolylurea, p-tolueneurea.

Examples of disubstituted urea include: 1,1-dimethylurea, 1,3-dimethylurea, 1,1-diethylurea, 1,3-diethylurea, 1,3-bis(hydroxymethyl)urea, 1,3-tertiary butylurea, 1,3-dicyclohexylurea, 1,3-diphenylurea, 1,3-bis(4-methoxyphenyl)urea, 1-acetyl-3- Methylurea.

Tetrasubstituted ureas include: tetramethylurea, 1,1,3,3-tetraethylurea, 1,1,3,3-tetrabutylurea, 1,3-dimethoxy-1,3-dimethylurea .

(thiourea derivative)

Thiourea derivatives are compounds in which at least one of the four hydrogen atoms of the thiourea molecule is replaced by a substituent. In this case, the substituent is not particularly limited, and is preferably a substituent composed of carbon atoms, hydrogen atoms, and oxygen atoms.

As specific examples of thiourea derivatives, monosubstituted thiourea can include: N-methylthiourea, ethylthiourea, propylthiourea, isopropylthiourea, 1-butylthiourea, cyclohexylthiourea, N- Acetylthiourea, N-allylthiourea, (2-methoxyethyl)thiourea, N-phenylthiourea, (4-methoxyphenyl)thiourea, N-(2-methoxy Phenyl)thiourea, N-(1-naphthyl)thiourea, (2-pyridyl)thiourea, o-toluenethiourea, p-toluenethiourea.

Examples of disubstituted thiourea include: 1,1-dimethylthiourea, 1,3-dimethylthiourea, 1,1-diethylthiourea, 1,3-diethylthiourea, 1,3-dibutylthiourea Urea, 1,3-diisopropylthiourea, 1,3-dicyclohexylthiourea, N,N-diphenylthiourea, N,N'-di Phenylthiourea, 1,3-bis(o-tolyl)thiourea, 1,3-bis(p-tolyl)thiourea, 1-benzyl-3-phenylthiourea, 1-methyl-3-phenylthiourea Urea, N-allyl-N'-(2-hydroxyethyl)thiourea.

Examples of tri-substituted urea include trimethylthiourea, and examples of tetra-substituted urea include tetramethylthiourea and 1,1,3,3-tetraethylthiourea.

Among urea compounds, urea derivatives or thiourea derivatives are preferred, and urea derivatives are more preferred. Among urea derivatives, monosubstituted urea or disubstituted urea is preferred, and monosubstituted urea is more preferred. The disubstituted urea system includes 1,1-substituted urea and 1,3-substituted urea, especially 1,3-substituted urea.

<Layer containing urea compound>

The urea-based compound is not limited to the case where the urea-based compound is contained in the adhesive layer as described above, and the urea-based compound may be contained in layers other than the adhesive layer from the viewpoint of improving the heat resistance of the polarizing plate. As described in the description of the transparent protective film, in response to the demand for thinner polarizing plates in recent years, a polarizing plate having a protective film on only one side of the polarizing element as another layer has been developed. In this configuration, for the purpose of improving physical strength, etc., a hardened layer may be formed on the surface of the polarizer that does not have a protective film.

In this embodiment, a urea compound may also be contained in such a hardened layer. Usually such a hardened layer is formed by a curable composition containing an organic solvent. In paragraphs [0020] to [0042] of Japanese Patent Application Laid-Open No. 2017-075986, it is described that an active energy ray-curable polymer composition A method of forming such a hardened layer from an aqueous solution of a substance. Since most urea compounds are water-soluble, such a composition can contain water-soluble urea compounds.

<Adhesive layer>

In order to bond the above-described polarizing plate to an image display device, an adhesive layer is usually laminated. The adhesive layer is used to attach the polarizer to the image display device.

The adhesive layer may be composed of one layer, or may be composed of two or more layers, but is preferably composed of one layer. The adhesive layer can be composed of an adhesive composition mainly composed of (meth)acrylic resin, rubber resin, urethane resin, ester resin, polysiloxane resin, and polyvinyl ether resin. Among them, an adhesive composition using a (meth)acrylic resin excellent in transparency, weather resistance, heat resistance, etc. as a base polymer is suitable. The adhesive composition may be an active energy ray curing type or a thermosetting type.

As far as the (meth)acrylic resin (base polymer) used in the adhesive composition is concerned, it is suitable to use: butyl (meth)acrylate, ethyl (meth)acrylate, (meth)acrylate Base) Polymers or copolymers of one or more (meth)acrylates such as isooctyl acrylate and 2-ethylhexyl (meth)acrylate as monomers. The base polymer is preferably one in which polar monomers are copolymerized. Examples of polar monomers include (meth)acrylic acid compounds, (meth)acrylic acid 2-hydroxypropyl compounds, (meth)acrylic acid hydroxyethyl ester compounds, (meth)acrylamide compounds, (meth)acrylic acid N , N-dimethylaminoethyl ester compound, glycidyl (meth)acrylate compound and other monomers having carboxyl group, hydroxyl group, amido group, amino group, epoxy group, etc.

The adhesive composition may only contain the above-mentioned base polymer, but usually further contains a cross-linking agent. The cross-linking agent can be exemplified: a metal ion having a valence of two or more, and a metal ion that forms a carboxylate metal salt with a carboxyl group; a polyamine compound that forms an amide bond with a carboxyl group; a polyepoxide or a polyol that forms an ester bond with a carboxyl group ; A polyisocyanate compound that forms an amide bond with a carboxyl group. Among them, polyisocyanate compounds are preferred.

The active energy ray-curable adhesive composition has the property of being hardened by irradiation with ultraviolet rays or active energy rays such as electron rays, and has the property of being adhesive before irradiating active energy rays and can be adhered to adherends such as films , and can be hardened by irradiating active energy rays and adjusting the properties of adhesion. The active energy ray-curable adhesive composition is preferably an ultraviolet-curable adhesive composition. live The active energy ray-curable adhesive composition further contains an active energy ray polymerizable compound in addition to a base polymer and a crosslinking agent. A photopolymerization initiator, a photosensitizer, etc. may also be contained as needed.

The adhesive composition may contain: microparticles for imparting light scattering properties, beads (resin beads, glass beads, etc.), glass fibers, resins other than base polymers, tackifiers, fillers (metal powder and other Inorganic powder, etc.), antioxidants, ultraviolet absorbers, dyes, pigments, colorants, defoamers, anti-corrosion agents, photopolymerization initiators and other additives.

The adhesive layer can be formed by applying an organic solvent dilution of the above-mentioned adhesive composition on the surface of a substrate film, an image display unit, or a polarizing plate, and drying. Generally, the base film is a thermoplastic resin film, and a typical example of the base film includes a separator film subjected to mold release treatment. The separation film may be, for example, a film made of resins such as polyethylene terephthalate, polybutylene terephthalate, polycarbonate, and polyarylate, on which an adhesive layer is formed. Silicone treatment and other mold release treatment.

For example, an adhesive composition can be directly coated on the release-treated surface of the separator to form an adhesive layer, and this adhesive layer with separator can be laminated on the surface of the polarizing plate. The adhesive composition can also be directly coated on the surface of the polarizing plate to form an adhesive layer, and a separator film can be laminated on the outside of the adhesive layer.

When the adhesive layer is arranged on the surface of the polarizing plate, it is preferable to apply surface activation treatment (such as plasma treatment, corona treatment, etc.) to the bonding surface of the polarizing plate and/or the bonding surface of the adhesive layer, It is more preferable to apply corona treatment.

In addition, it is also possible to prepare an adhesive sheet by coating the adhesive composition on the second separator to form an adhesive layer, laminate the separator on the formed adhesive layer, and peel the second separator from the adhesive sheet. 2. The adhesive layer with separator behind the separator is laminated on the polarizing plate. The 2nd separation film uses the one which is weaker than the separation film in terms of adhesion with the adhesive layer and is easy to peel off.

The thickness of the adhesive layer is not particularly limited, and is preferably, for example, not less than 1 μm and not more than 100 μm , more preferably not less than 3 μm and not more than 50 μm , and may be not less than 20 μm .

[Example]

Hereinafter, the present invention will be specifically described based on examples. Materials, reagents, amounts of substances, their ratios, operations, etc. shown in the following examples can be appropriately changed as long as they do not depart from the gist of the present invention. Therefore, the present invention is not limited and limited to the following examples.

[Measurement method and evaluation method]

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

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

(2) Determination of luminescence factor correction polarization degree of polarizing plate, luminescence factor correction monomer transmittance, and hue:

The transmittance of the luminescence factor-corrected monomer, the luminescence factor-corrected polarization degree, and the hue of the polarizing plate were measured using a spectrophotometer with an integrating sphere ["V7100" manufactured by JASCO Co., Ltd., 2-degree field of view; C light source] to measure To measure.

(3) Determination of the boron content of the polarizing element

The measurement of the boron content rate in the polarizing element was performed by the following procedure. First, 0.2 g of a polarizing element was dissolved in 200 g of a 1.9 mass % mannitol (mannitol) aqueous solution. Then, titrate the obtained aqueous solution with 1 mol/L sodium hydroxide aqueous solution, and calculate the boron content in the polarizing element by comparing the amount of sodium hydroxide aqueous solution required for neutralization with the calibration curve. Rate.

(4) Determination of the zinc ion content of the polarizing element

The measurement of the zinc ion content rate in the polarizing element was carried out by the following procedure. First, nitric acid was added to the precisely weighed polarizer, and the microwave sample pretreatment device manufactured by Milestone General (ETHOS D) Acid decomposition was performed, and the resulting solution was used as a measurement solution. The zinc ion content rate was calculated by quantifying the zinc concentration of the measurement liquid with an ICP emission spectrometer (5110 ICP-OES) manufactured by Agilent Technology, and calculating it as the mass of zinc relative to the mass of the polarizing element.

(5) Determination of boron adsorption rate of PVA-based resin film

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

(6) Determination of the half-value width of the spectral peak derived from polyvinyl alcohol crystals of the polarizing element

〈Sample for measurement〉

A sample in which 10 polarizing elements were laminated so as to align with the absorption axis of the polarizing element was prepared, and this was used as a sample for measurement.

<Measurement using wide-angle X-ray scattering method>

It refers to the value calculated using the Wide-angle X-ray Scattering method with the following measurement equipment and measurement conditions.

(measuring device)

A Nano-scale X-ray structure evaluation device NANO-Viewer manufactured by Rigaku Co., Ltd. was used.

(measurement conditions)

‧X-ray source: Cu-kα ray

‧Camera Length: 71mm

‧Measurement: penetration test

‧X-ray exposure time: 10 minutes

(calculation method)

First, background measurement is performed without setting a measurement sample, and a circular-averaged scattering distribution is obtained for the obtained two-dimensional scattering pattern; then, measurement of a measurement sample is performed, and a scattering distribution is obtained in the same manner. Then, for the scattering distribution of the measurement sample after subtracting the background scattering distribution, a spectral peak derived from polyvinyl alcohol crystals with a wavenumber q in the vicinity of 15 nm ^-1 was identified, and the half-value width of the spectral peak was calculated. . 1 relates to polarizing elements 1 to 3 described later, and is a graph showing the result obtained by subtracting the scattering distribution of the background from the scattering distribution of the measurement sample plotted against the wavenumber q. The peak at the position of wave number q at 15 nm ^-1 is a peak derived from polyvinyl alcohol crystals. The half-value width is defined as the interval between 2 points of the 1/2 intensity of the maximum value of the spectrum peak.

(7) High temperature durability test (115°C)

〈Preparation of samples for evaluation〉

Referring to the examples in JP-A-2018-025765, an acrylic adhesive (manufactured by Lintec Co., Ltd.) was coated on one side of the polarizing plate produced by the following procedure to form an adhesive layer with a thickness of 25 μm. The polarizing plate with the adhesive layer formed on one side was cut into a size of 40mm×40mm. Alkali-free glass Glass (trade name "EAGLE XG", manufactured by Corning Corporation) was bonded to the surface of the adhesive layer to prepare a sample for evaluation (optical laminate).

〈High temperature durability test〉

The evaluation samples obtained above were subjected to autoclave treatment at a temperature of 50°C and a pressure of 5kgf/cm ² (490.3kPa) for 1 hour. After placing the sample for evaluation in an environment with a temperature of 23°C and a relative humidity of 55% for 24 hours, the luminescence factor-corrected monomer transmittance, luminescence factor-corrected polarization degree, and hue of the polarizing plate were measured and set as initial values. Next, a high-temperature durability test was carried out in which the evaluation sample was stored in a high-temperature environment at a temperature of 115°C for 500 hours, and the luminescence factor-corrected monomer transmittance, luminescence factor-corrected polarization degree, and hue of the polarizing plate after the high-temperature durability test were measured.

From the initial values of the luminescence factor-corrected monomer transmittance, luminescence factor-corrected polarization degree and hue of the polarizing plate and the measured values after the high-temperature durability test, the luminescence factor-corrected monomer transmittance and luminescence factor-corrected polarization degree of the polarizing plate are calculated and hue changes. The change amount ΔTy of the luminescence factor-corrected monomer transmittance and the change amount ΔPy of the luminescence factor-corrected polarization degree are calculated by subtracting the initial value from the measured value after the high-temperature durability test. In addition, the change amount Δab of hue is calculated|required by the following formula.

△ab={(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 durability test.

[Example 1, 2 and Comparative Example 1]

(Fabrication of Polarizer 1)

After immersing a polyvinyl alcohol-based resin film with a thickness of 30 μm and a boron adsorption rate of 5.71% by mass in pure water at 21.5°C for 79 seconds (swelling treatment), the film was dipped in a mass ratio of potassium iodide/boric acid/water of 2/2 /100 and containing 1.0 mM iodine in an aqueous solution at 23° C. for 151 seconds (staining step). Then, it was immersed in an aqueous solution at 68.5° C. at a mass ratio of potassium iodide/boric acid/water of 2.5/4/100 for 76 seconds (first crosslinking step). Next, it was immersed for 11 seconds in a 45° C. aqueous solution having a mass ratio of potassium iodide/boric acid/zinc chloride/water of 3/5.5/0.6/100 (second crosslinking step, metal ion treatment step). Then, it was dipped in a cleaning bath for cleaning (cleaning step), and dried at 38° C. (drying step) to obtain a polarizing element having a thickness of 12 μm in which iodine was adsorbed and oriented to polyvinyl alcohol. The extension is mainly carried out in the steps of the dyeing step and the first cross-linking step, and the total extension ratio is 5.85 times. The obtained polarizer had a zinc ion content of 0.17% by mass, a boron content of 4.62% by mass, and a half-value width of a spectrum peak derived from polyvinyl alcohol crystals was 4.90 nm ^-1 .

(Fabrication of polarizing element 2)

After immersing a polyvinyl alcohol-based resin film with a thickness of 30 μm and a boron adsorption rate of 5.71% by mass in pure water at 21.5°C for 79 seconds (swelling treatment), the film was dipped in a mass ratio of potassium iodide/boric acid/water of 2/2 /100 and containing 1.0 mM iodine in an aqueous solution at 23° C. for 151 seconds (staining step). Then, it was immersed for 76 seconds in an aqueous solution at 66.5° C. where the mass ratio of potassium iodide/boric acid/water was 2.5/4/100 (first crosslinking step). Next, it was immersed for 11 seconds in a 45° C. aqueous solution having a mass ratio of potassium iodide/boric acid/zinc chloride/water of 3/5.5/0.6/100 (second crosslinking step, metal ion treatment step). Then, it was dipped in a cleaning bath for cleaning (cleaning step), and dried at 38° C. (drying step) to obtain a polarizing element having a thickness of 12 μm in which iodine was adsorbed and oriented to polyvinyl alcohol. The extension is mainly carried out in the steps of the dyeing step and the first cross-linking step, and the total extension ratio is 5.85 times. The obtained polarizer had a zinc ion content of 0.17% by mass, a boron content of 4.62% by mass, and a half-value width of a spectrum peak derived from polyvinyl alcohol crystals of 4.85 nm ^-1 .

(Fabrication of Polarizer 3)

After immersing a polyvinyl alcohol-based resin film with a thickness of 30 μm and a boron adsorption rate of 5.71% by mass in pure water at 21.5°C for 79 seconds (swelling treatment), the film was dipped in a mass ratio of potassium iodide/boric acid/water of 2/2 /100 and containing 1.0 mM iodine in an aqueous solution at 23° C. for 151 seconds (staining step). Then, it was immersed for 76 seconds in an aqueous solution at 60.6° C. where the mass ratio of potassium iodide/boric acid/water was 2.5/4/100 (first crosslinking step). Next, it was immersed for 11 seconds in a 45° C. aqueous solution having a mass ratio of potassium iodide/boric acid/zinc chloride/water of 3/5.5/0.6/100 (second crosslinking step, metal ion treatment step). Then, it was dipped in a cleaning bath for cleaning (cleaning step), and dried at 38° C. (drying step) to obtain a polarizing element having a thickness of 12 μm in which iodine was adsorbed and oriented to polyvinyl alcohol. The extension is mainly carried out in the steps of the dyeing step and the first cross-linking step, and the total extension ratio is 5.85 times. The obtained polarizer had a zinc ion content of 0.17% by mass, a boron content of 4.62% by mass, and a half-value width of a spectrum peak derived from polyvinyl alcohol crystals of 4.75 nm ^-1 .

(Preparation of PVA solution for adhesive)

Dissolve 50 g of modified PVA-based resin containing acetyl acetyl group (manufactured by Mitsubishi Chemical Co., Ltd.: GOHSENX Z-410) in 950 g of pure water, heat at 90°C for 2 hours, and cool to room temperature to obtain an adhesive Use PVA solution.

(Preparation of Adhesive 1 for Polarizing Plates)

The prepared PVA solution for an adhesive, pure water, and methanol were prepared so as to have a PVA concentration of 3.0%, a methanol concentration of 35%, and a urea concentration of 0.5%, to obtain an adhesive 1 for a polarizing plate.

(saponification of cellulose acylate film)

A commercially available cellulose acylate membrane TJ40UL (manufactured by Fujifilm Co., Ltd.: film thickness 40 μm ) was immersed in a 1.5 mol/L NaOH aqueous solution (saponified solution) maintained at 55° C. for 2 minutes, and the membrane was washed with water. Then, the membrane was immersed in a 0.05 mol/L sulfuric acid aqueous solution at 25°C for 30 seconds, and then passed through a water bath under running water for 30 seconds to make the membrane neutral. Then, water removal by air knife was repeated 3 times. After water removal, the film was dried in a drying zone at 70° C. for 15 seconds to produce a saponified film.

(Production of Polarizing Plate 1)

The saponified cellulose acylate film was attached to both sides of the polarizer 1 with the adhesive 1 for polarizing plates. The adhesive is adjusted so that the thickness of the adhesive layer after drying becomes 100nm on both sides. The thickness of the entire coating. Bonding is performed using a roll laminating machine. After bonding, dry at 80° C. for 3 minutes, and then connect the polarizing element 1 and the cellulose acylate film. In this way, the polarizing plate 1 in which the cellulose acylate film was bonded to both surfaces of the polarizing element 1 was obtained.

Polarizers 2 and 3 were fabricated in the same manner except that polarizer 1 of polarizer 1 was changed to polarizers 2 and 3 .

(Production of optical laminates 1 to 3)

Referring to the examples of Japanese Patent Laid-Open No. 2018-025765, an acrylic adhesive (manufacturer: Lintec Co., Ltd.) is applied to one side of the above-mentioned polarizing plates 1 to 3 to make polarizing plates. Optical laminates 1 to 3 having an adhesive layer with a thickness of 25 μm on one side of the board.

(Example 1)

In Example 1, the high temperature durability test was implemented with respect to the optical layered body 1. The change amount ΔTy of the luminescence factor correction monomer transmittance of the optical laminate 1 is 0.6%, the change amount ΔPy of the luminescence factor correction polarization degree is -0.03%, and the change amount Δab of the hue is 2.0NBS. The results are shown in Table 1.

(Example 2)

In Example 2, the high-temperature durability test was implemented on the optical layered body 2 . The change amount ΔTy of the luminescence factor correction monomer transmittance of the optical laminate 2 is 1.2%, the change amount ΔPy of the luminescence factor correction polarization degree is -0.03%, and the change amount Δab of the hue is 2.3NBS. The results are shown in Table 1.

(comparative example 1)

The change amount ΔTy of the luminescence factor correction monomer transmittance of the optical laminate 3 is 2.6%, the change amount ΔPy of the luminescence factor correction polarization degree is -0.13%, and the change amount Δab of the hue is 5.3NBS. The results are shown in Table 1.

[Table 1]

Even when the optical layered bodies 1 and 2 were exposed to a high-temperature environment at a temperature of 115° C., it was found that the effect of suppressing the decrease in the degree of polarization was superior to that of the optical layered body 3 .

Claims (7)

A polarizing plate comprising: a polarizing element in which a dichroic pigment is adsorbed and oriented on a polyvinyl alcohol-based resin layer, and a transparent protective film; The half-value width of the spectral peak derived from polyvinyl alcohol crystals measured by the wide-angle X-ray scattering method of the aforementioned polarizing element is 4.80nm ^-1 or more, The aforementioned polarizing element contains potassium ions and metal ions other than potassium ions, The content rate of the metal ion other than the said potassium ion of the said polarizing element is 0.05 mass % or more. The polarizing plate according to claim 1, wherein the metal ion contains at least one of 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 boron content of the polarizing element is not less than 2.4% by mass and not more than 8.0% by mass. The polarizing plate according to any one of claims 1 to 3, which further has an adhesive layer for bonding the polarizing element and the transparent protective film, The aforementioned adhesive layer is a coating layer of a water-based adhesive. The polarizing plate according to claim 4, wherein the concentration of methanol in the water-based adhesive is not less than 10% by mass and not more than 70% by mass. The polarizing plate according to claim 4 or 5, wherein the water-based adhesive contains a polyvinyl alcohol-based resin. The polarizing plate according to any one of claims 4 to 6, wherein the thickness of the adhesive layer is not less than 0.01 μm and not more than 7 μm .

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