TW202331310A - Polarizing element, polarizing plate, and image display device - Google Patents

Abstract

An object of the present invention is to provide a polarizing element which can satisfactorily suppress decrease in luminosity correction single transmittance even when exposed to a high-temperature environment as a member constituting an image display device having an interlayer filling structure; a polarizing plate, and an image display device. In the polarizing element, a dichroic dye is adsorbed and oriented in a polyvinyl alcohol-based resin layer. When the polarizing element is equally divided into three parts in the thickness direction to obtain three regions and the staining degree of the region with the highest staining degree is S1 and the staining degree of the region with the lowest staining degree is S2 in the three regions, the polarizing element satisfies the relationship in the following formula (1). 0 ≤ S2/S1 ≤ 0.95 (1).

Description

Polarizing element, polarizing plate and image display device

The present invention relates to a polarizing element, a polarizing plate equipped with the polarizing element, and an image display device equipped with the polarizing plate.

Liquid Crystal Display (LCD: Liquid Crystal Display) is widely used not only in LCD TVs, but also in mobile devices such as computers and mobile phones, and in-vehicle applications such as car navigation. Generally, a liquid crystal display device has a liquid crystal panel component with polarizers attached to both sides of a liquid crystal cell using an adhesive (Pressure-sensitive Adhesive), and the liquid crystal panel component controls the light from the backlight component to display. In recent years, like liquid crystal display devices, organic electroluminescent (EL: Electroluminescence) display devices have been widely used in mobile devices such as televisions and mobile phones, and in-vehicle applications such as car navigation. 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 to be viewed, a circular polarizing plate (including a polarizing element and a λ/4 plate) is arranged on the viewing side surface of the image display panel. laminated body) situation.

As described above, there are increasing opportunities for polarizing plates to be mounted on vehicles as components constituting liquid crystal display devices or organic EL display devices. Compared with TVs and mobile phones other than car use Polarizing plates for mobile devices such as mobile devices are often exposed to high-temperature environments in the case of polarizing plates used in vehicle-mounted image display devices. Therefore, it is required to have less change in characteristics at high temperatures (high temperature durability).

In the image display device, for the purpose of preventing damage to the image display panel due to impact from the outer surface, a transparent resin plate is provided on the viewing side of the polarizer of the image display panel. Or the case of a front transparent plate (sometimes called a “light-transmitting layer” etc.) such as a glass plate. In an image display device equipped with a touch panel, the touch panel is provided on the viewing side more than the polarizing plate included in the image display panel, and the front transparent plate is provided on the viewing side than the touch panel situation.

In an image display device, when there is an air layer between the image display panel and a transparent member such as a front transparent plate or a touch panel, reflection of external light occurs due to light reflection at the interface with the air layer, and there is The viewability of the screen tends to decrease. Therefore, there is a method of filling the space between the polarizing plate and the transparent member constituting the viewing side surface of the image display panel with a layer other than the air layer, usually a solid layer (hereinafter sometimes referred to as "interlayer filler") It is preferable to use a material whose refractive index is close to that of the polarizing plate and/or the transparent member to fill the space. In order to suppress deterioration of visibility due to light reflection at the interface with the air layer and to fix members together, adhesives or UV-curable adhesives are used as interlayer fillers (eg, Patent Document 1).

In mobile phones such as mobile phones that are often used outdoors, image display devices having the above-mentioned structure filled with interlayer fillers are increasingly used. Furthermore, due to the increasing requirements for visibility in recent years, in vehicle applications such as car navigation devices, it has also been considered to arrange a front transparent plate on the surface of the image display panel, and to fill the image display panel with an adhesive layer, etc. Composition with the front transparent board.

Patent Document 2 discloses that when an image display device filled with an interlayer filler is placed in an environment at a temperature of 95° C., for example, for 200 hours, a significant increase in transmittance is observed at the in-plane center of the polarizing plate. However, no significant decrease in transmittance was observed even if the polarizer was placed in an environment with a temperature of 95° C. for 1000 hours. From these results, in Patent Document 2, the significant decrease in the transmittance of the polarizing plate in an environment at a temperature of 95°C can be presumed to be due to exposure to an image display with the following configuration in an environment at a temperature of 95°C The problem specific to the device is that the image display device has a structure in which one side of the polarizer is bonded to the image display unit, and the other side is bonded to a transparent member such as a touch panel or a front transparent plate.

Patent Document 2 discloses that the water content per unit area of the polarizing plate is set below a predetermined amount, and the saturated water absorption of the transparent protective film adjacent to the polarizer is set below a predetermined amount, thereby suppressing the water content at a temperature of 95 The decrease of the transmittance of the polarizing plate under the environment of ℃.

[Prior Art Literature]

[Patent Document]

[Patent Document 1] Japanese Patent Application Laid-Open No. 11-174417

[Patent Document 2] Japanese Unexamined Patent Publication No. 2014-102353

However, it has been found that when the image display device with the above configuration is exposed to a high temperature environment of 115° C., the decrease in the transmittance of the sensitivity correction monomer of the polarizing plate cannot be sufficiently suppressed.

The object of the present invention is to provide a polarizing element, a polarizing plate equipped with a polarizing element, and an image display device equipped with a polarizing plate. When the component of the image display device formed by filling is exposed to a high temperature environment, the decrease in the transmittance of the visual sensitivity correction monomer can also be well suppressed.

The present invention provides the following polarizing elements, polarizing plates and image display devices.

[1] A polarizing element having a dichroic pigment adsorbed and aligned on a polyvinyl alcohol-based resin layer, wherein,

In the 3 regions that divide the aforementioned polarizing element into three equal parts in the thickness direction, when the dyeing degree of the region with the largest dyeing degree is set as S1, and the dyeing degree of the region with the smallest dyeing degree is set as S2, the following conditions are met. The relation of expression (1),

0≦S2/S1≦0.95 (1).

[2] The polarizing element according to [1], wherein the region with the smallest degree of dyeing among the three regions is a region located in the center in the thickness direction.

[3] The polarizing element according to [1] or [2], wherein the polarizing element contains boron, and the content of boron in the polarizing element is not less than 4.0% by mass and not more than 8.0% by mass.

[4] The polarizing element according to any one of [1] to [3], wherein the dichroic dye is iodine.

[5] A polarizing plate comprising the polarizing element described in any one of [1] to [4], and a transparent protective film.

[6] The polarizing plate as described in [5], further comprising an adhesive layer for laminating the polarizing element and the transparent protective film,

The aforementioned adhesive layer is a layer after the water-based adhesive has hardened.

[7] The polarizing plate according to [6], wherein the water-based adhesive contains methanol,

Content of the said methanol in the said water-based adhesive agent is 10 mass % or more and 70 mass % or less.

[8] The polarizing plate according to [6] or [7], wherein the water-based adhesive further contains a polyvinyl alcohol-based resin.

[9] The polarizing plate according to any one of [6] to [8], wherein the adhesive layer has a thickness of not less than 0.01 μm and not more than 7 μm.

[10] The polarizing plate according to any one of [5] to [9], wherein the polarizing plate is used in an image display device,

In the aforementioned image display device, both surfaces of the aforementioned polarizing plate may be in contact with the solid layer.

[11] An image display device comprising: an image display unit, a first adhesive layer laminated on the viewing side surface of the image display unit, and [ The polarizing plate according to any one of 5] to [10].

[12] The image display device according to [11], further comprising: a second adhesive layer laminated on the viewing side surface of the polarizing plate, and a transparent adhesive layer laminated on the viewing side surface of the second adhesive layer. member.

[13] The image display device according to [12], wherein the transparent member is a glass plate or a transparent resin plate.

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

According to the present invention, it is possible to provide a polarizing element, a polarizing plate provided with the polarizing element, and an image display device provided with the polarizing plate. The components of the finished image display device are exposed to a high-temperature environment, and the decrease in the transmittance of the sensitivity correction monomer can also be well suppressed.

1: polarizer

2: polarizer

10,10t: polarizer

11~13: area

20: polarizer

20t: sample for measurement

21: Transparent protective film

100: Thickness direction

101: Absorption axis direction (extension direction)

210,210t: transparent protective film

L: laser light

P: Measuring point

FIG. 1 is a schematic cross-sectional view schematically showing a polarizing element according to an embodiment of the present invention.

Fig. 2 is a schematic cross-sectional view schematically showing a polarizing plate according to an embodiment of the present invention.

Fig. 3(a) and (b) are explanatory diagrams for explaining the steps for measuring the degree of dyeing.

FIG. 4 is an explanatory diagram for explaining a method of calculating an integrated intensity distribution from Raman Spectrum.

Hereinafter, preferred embodiments of the polarizing element, the polarizing plate, and the image display device will be described with reference to the drawings.

(polarizer)

FIG. 1 is a schematic cross-sectional view schematically showing a polarizing element of this embodiment. The polarizing element 1 is an absorption-type polarizing film that absorbs linearly polarized light having a vibration plane parallel to the absorption axis and transmits linearly polarized light having a vibration plane perpendicular to the absorption axis (parallel to the transmission axis).

The polarizing element 1 is a polarizing element in which a dichroic dye is adsorbed and aligned on a polyvinyl alcohol-based resin layer (hereinafter sometimes referred to as "PVA-based resin layer"). The polarizing element 1 can be a polarizing layer with a dichroic pigment adsorbed and aligned on a PVA-based resin layer, or it can have two or three layers laminated. The above multilayer structure of the polarizing layer. When the polarizing element 1 has a multi-layer structure, two or more polarizing layers included in the polarizing element 1 can be stacked via an adhesive layer.

As shown in Figure 1, the polarizing element 1 is divided into three regions 11 to 13 that divide the polarizing element 1 into three equal parts in the thickness direction 100, and the dyeing degree of the region with the largest dyeing degree is set as S1, and the dyed When the dyeing degree of the region with the smallest degree is S2, the relationship of the following formula (1) is satisfied.

0≦S2/S1≦0.95 (1)

As shown in FIG. 1 , the three regions 11 to 13 of the polarizer 1 are regions arranged along the thickness direction 100 of the polarizer 1 . Regions 11 and 13 among the three regions 11 to 13 are regions located on the surface side of the polarizer 1 in the thickness direction 100 , and region 12 is a region located in the center of the polarizer 1 in the thickness direction 100 .

S2/S1 in the formula (1) is preferably 0.90 or less, more preferably 0.85 or less, still more preferably 0.75 or less, and may be 0.1 or more, and may be 0.3 or more.

By satisfying the relationship of the above formula (1), the polarizing element 1 can well suppress the decrease of the transmittance Ty (hereinafter sometimes referred to as “transmittance Ty”) of the sensitivity correction unit in a high-temperature environment. This reason can be considered as follows. This can be presumed to be that the dichroic dye contained in the polarizing element 1 promotes the reaction of polyeneization of the polyvinyl alcohol-based resin (hereinafter sometimes referred to as "PVA-based resin") constituting the PVA-based resin layer through dehydration. . Since the PVA-based resin is easily dehydrated in a high-temperature environment, polyeneization of the PVA-based resin is likely to occur, and the transmittance Ty of the polarizer is likely to decrease. It is estimated that a region with a small degree of dyeing in the polarizing element 1 means that the amount of dichroic pigment present in this region is small. Therefore, by making the polarizing element 1 satisfy the relationship of the above-mentioned formula (1), by having a region with a small degree of dyeing, polyeneization of the PVA-based resin in a high-temperature environment can be well suppressed, and the polarizing element 1 can be suppressed. The decrease of the penetration rate Ty.

The so-called polyeneization of the PVA-based resin means that the PVA-based resin constituting the polarizing element 1 forms a polyene structure (-C=C) _n -, for example, it can be measured by Raman spectroscopy of the polarizing element 1 by measuring near 1100 cm ^-1 (from the =CC= bond) and the presence of peaks around 1500cm ^-1 (from the -C=C- bond) to confirm (patent document 2, paragraph [0012]).

The polarizing element 1 that satisfies the relationship of formula (1) can suppress the decrease of the sensitivity correction polarization degree Py (hereinafter sometimes referred to as "polarization degree Py") and the decrease of the hue ab even in a high temperature environment.

The region with the degree of dyeing S1 (the region with the highest degree of dyeing) can be any of the regions 11 to 13, but is preferably at least one of the regions 11 and 13 located on the surface of the polarizing element 1 in the thickness direction 100. The region with the degree of dyeing S2 (the region with the smallest degree of dyeing) may be any region among the regions 11 to 13, but is preferably the region 12 located in the center in the thickness direction 100 of the polarizing element 1 . It is presumed that the polyeneization of the PVA-based resin proceeds easily from the central portion in the thickness direction 100 of the polarizer 1 . Therefore, by making the region having the degree of dyeing S2 the region 12 located in the center in the thickness direction 100 , it is presumed that polyeneization of the PVA-based resin constituting the polarizing element 1 can be easily and effectively suppressed.

The degree of dyeing can be measured by the following steps [i] to [iv], more specifically, it can be measured by the method described in the examples below. [i] Raman spectra obtained at respective points of measurement points set at a pitch of 1 μm in the thickness direction 100 of the polarizing element 1 . [ii] Calculate the integrated intensity in the range of wavenumbers from 80 cm ^-1 to 180 cm ^-1 of the obtained Raman spectrum. [iii] Obtain the integrated intensity distribution obtained by stippling the calculated integrated intensity with respect to the position in the thickness direction 100 of the polarizing element 1 . [iv] From the obtained integral intensity distribution, obtain the integral area obtained for each of the three regions that divide the thickness direction 100 of the polarizing element 1 into three equal parts, and set these to each The degree of dyeing of the region.

The method of obtaining the polarizing element 1 satisfying the relationship of formula (1) includes: preparing two or more polarizing layers with different degrees of dyeing, and laminating these polarizing layers through the bonding layer; preparing a polarizing layer with a PVA-based resin A method of manufacturing a polarizing element 1 using a PVA-based resin layer having a multilayer structure of two or more layers having different degrees of polymerization or saponification; a polarizing layer composed of a single layer having a different degree of dyeing in the thickness direction 100 The method of element 1. A method of manufacturing a single-layer polarizing layer having a different degree of dyeing in the thickness direction 100 includes adjusting the concentration of the dichroic dye when dyeing the PVA-based resin layer with the dichroic dye in the manufacturing method of the polarizing layer described later. A method of at least one of temperature and dyeing time; in the manufacturing method of the polarizing layer described later, at least one of the boric acid concentration, temperature, and treatment time of the boric acid aqueous solution that treats the PVA-based resin layer adsorbed with the dichroic pigment is adjusted. Method 1: A polarizing layer is produced by using a laminated film with a substrate film disposed on one side of the PVA resin layer, and the processing conditions (dyeing conditions, treatment conditions by boric acid aqueous solution, etc.) relative to the laminated film are adjusted. method etc.

The polarizer 1 preferably contains boron. The content of boron in the polarizing element 1 is preferably at least 4.0% by mass, more preferably at least 4.2% by mass, more preferably at least 4.4% by mass, further preferably at most 8.0% by mass, more preferably at most 7.0% by mass or less, and more preferably not more than 6.0% by mass. The content of boron in the polarizing element 1 is the content ratio of boron when the polarizing element 1 is 100% by mass, and can be measured by the method described in the examples described later. The boron system is presumed to exist in the state of boric acid or boric acid and the components of the PVA-based resin forming a cross-linked structure in the polarizing element 1, but the content of boron here refers to the amount of boron atoms (B). The content of boron in the polarizing element 1 can be adjusted by the method of adjusting the content of boron contained in the polarizing layer described later.

By setting the content of boron in the polarizing element 1 to the above-mentioned range, it is presumed that polyeneization of the PVA-based resin is less likely to occur in a high-temperature environment. Therefore, it can be considered that even as an interlayer filling Exposing components of the image display device to a high-temperature environment can further suppress the decrease in the transmittance Ty of the polarizing element 1 well.

On the other hand, when the content of boron in the polarizing element 1 exceeds the above-mentioned range, the shrinkage force of the polarizing element 1 increases, and when it is assembled into an image display device, it is easy to cause a gap between other members such as a transparent member and a bonded one. Stripping etc. missing. When the content of boron in the polarizing element 1 is less than the above-mentioned range, it becomes difficult to obtain a polarizing element having desired optical characteristics.

Polarizer 1 preferably contains potassium. From the viewpoint of suppressing the deterioration of the optical characteristics of the polarizing element 1 under high-temperature environments, the content of potassium in the polarizing element 1 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 of the polarizing element 1 in a high-temperature environment, the content of potassium in the polarizing element 1 is preferably 0.60 mass % or less, more preferably 0.55 mass % or less, still more preferably 0.50 mass % or less. The content of potassium in the polarizing element 1 is the content ratio of potassium when the polarizing element 1 is set to 100% by mass, and can be compared with potassium by, for example, high-frequency inductively coupled plasma (Inductively Coupled Plasma: ICP) emission spectroscopic analysis. Calculated based on the mass fraction (mass %) of the mass of the polarizing element. The content of potassium in the polarizing element 1 can be adjusted by the method of adjusting the content of potassium contained in the polarizing layer described later.

When the boron content and the potassium content in the polarizing element 1 are within the above-mentioned ranges, the boron content tends to be larger and the potassium content smaller than in conventional polarizing elements. Therefore, it is speculated that the hydroxyl groups of the polyvinyl alcohol in the polarizing element 1 can be protected (stabilized) by boric acid crosslinking. Furthermore, especially when the dichroic dye contained in the polarizing element 1 is iodine described later, it is presumed that iodide ions serving as counter ions can be stabilized in the polarizing element 1 by adding an appropriate amount of potassium to the polarizing element 1 . because Here, when the content of boron and the content of potassium are in the above-mentioned ranges, it is presumed that polyeneization of the PVA-based resin constituting the polarizing element 1 is more easily suppressed favorably.

The transmittance Ty of the polarizing element 1 is preferably 38.8% or more, more preferably 40.4% or more, and more preferably 40.7% or more, more preferably 44.8% or less, more preferably 43.2% or less, and more preferably It is below 43.0%. When the transmittance Ty exceeds 44.8%, the polarizing element may turn red in a high-temperature environment (this phenomenon is sometimes referred to as reddening), and the deterioration of the optical characteristics of the polarizing element 1 may increase. When the transmittance Ty is less than 38.8%, polyeneization of the PVA-based resin tends to proceed in a high-temperature environment, and the deterioration of the optical characteristics of the polarizing element 1 may be increased.

The transmittance Ty of the polarizing element 1 can be obtained by measuring the Y value after correction of the visual sensitivity with a 2-degree field of view (C light source) specified in JIS Z8701-1982. The transmittance Ty can be easily measured by, for example, a spectrophotometer (model: V7100) manufactured by JASCO Corporation, as described in Examples below.

The thickness of the polarizing element 1 is preferably at least 3 μm, more preferably at least 4 μm, more preferably at least 5 μm, further preferably at most 35 μm, more preferably at most 30 μm, and more preferably at most 25 μm. By setting the thickness of the polarizing element 1 to be 35 μm or less, it becomes easy to suppress a decrease in the optical characteristics of the polarizing element 1 due to polyeneization of the PVA-based resin in a high-temperature environment. By setting the thickness of the polarizing element 1 to be 3 μm or more, it becomes easy to obtain the polarizing element 1 having desired optical characteristics.

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

The degree of saponification of the PVA-based resin is preferably at least 85 mol%, more preferably at least 90 mol%, and more preferably at least 99 mol% and not more than 100 mol%. The degree of polymerization of the PVA-based resin is, for example, from 1,000 to 10,000, preferably from 1,500 to 5,000. PVA-based resins can be denatured, such as polyvinyl formaldehyde, polyvinyl acetal, and polyvinyl butyral, which have been denatured by aldehydes.

Examples of the dichroic dye adsorbed and aligned on the PVA-based resin layer include iodine and a dichroic dye. The dichroic dye is preferably iodine.

The polarizing layer constituting the polarizing element 1 can be, for example, using a polyvinyl alcohol-based resin film (hereinafter sometimes referred to as "PVA-based resin film") as a PVA-based resin layer, and then dyeing the PVA-based resin film with a dichroic dye. and uniaxial stretching; by coating a coating liquid containing PVA-based resin on the base film, a laminated film in which a coating layer to become a PVA-based resin layer is formed on the base film is obtained, and then Those formed by dyeing the coating layer with a dichroic dye and uniaxially stretching the laminated film, etc.

The polarizing layer may be directly used as the polarizing element 1 , or two or more polarizing layers may be bonded together using an adhesive layer to form the polarizing element 1 . When laminating two or more polarizing layers, it is preferable to laminate so that the absorption axes of the polarizing layers are parallel to each other.

(Manufacturing method of polarizing layer)

The manufacturing method of the polarizing layer constituting the polarizing element 1 is not particularly limited. A typical method of manufacturing a polarizing layer is a method in which a PVA-based resin film wound in roll form is sent out and then stretched, dyed, cross-linked, etc. (hereinafter referred to as "manufacturing method 1"); family tree A step of coating a grease coating solution on a base film to form a coating layer, and stretching the laminated film with the coating layer formed thereon (hereinafter referred to as "manufacturing method 2").

Manufacturing method 1 may include: a step of uniaxially stretching the PVA-based resin film, a step of dyeing the PVA-based resin film with a dichroic dye such as iodine to thereby adsorb the dichroic dye, and treating the adsorbed dichroic dye with a boric acid aqueous solution. The step of making the PVA-based resin film of the pigment, and the step of washing with water after the treatment with the boric acid aqueous solution.

The content of boron and potassium contained in the polarizing layer can be controlled by boric acid contained in any one of the treatment baths in the swelling step, dyeing step, crosslinking step, stretching 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 potassium component supply substances such as potassium halide such as potassium iodide, the treatment temperature and treatment time of each of the above-mentioned treatment baths. In particular, in the crosslinking step and the stretching step, the boron content can be easily adjusted to a desired range by processing conditions such as the concentration of the boron component supply substance. Furthermore, in the water washing step, boron, potassium, and other components can be removed from the PVA-based resin under treatment conditions such as the amount of the boron component supply material or the potassium component supply material used in the dyeing process, crosslinking step, or elongation step. From the viewpoint of elution into the film or adsorption to the PVA-based resin film, it is easy to adjust the content of boron and the content of potassium to a desired range.

The swelling step is a treatment step of immersing the PVA-based resin film in a swelling bath, which can remove dirt or blocking agents on the surface of the PVA-based resin film, and can suppress uneven dyeing by swelling the PVA-based resin film. Swelling baths usually use a medium with water, distilled water, pure water, etc. as the main component. In the swelling bath, surfactants, alcohols, etc. can also be added appropriately according to the usual method. Furthermore, from the viewpoint of controlling the content of potassium in the polarizing layer, potassium iodide can also be used in the swelling bath, At this time, the content of potassium iodide in the swelling bath is preferably at most 1.5% by weight, more preferably at most 1.0% by weight, and even more preferably at most 0.5% by weight.

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. Since the swelling degree of the PVA-based resin film is affected by the temperature of the swelling bath, the immersion time in the swelling bath cannot be determined uniformly, but it is preferably 5 to 300 seconds, more preferably 10 to 200 seconds, and more preferably 20 seconds. to 100 seconds. The swelling step can be performed only once or multiple times as required.

The dyeing step is a treatment step of immersing the PVA-based resin film in a dyeing bath, and can adsorb/align dichroic pigments on the PVA-based resin film. When the dichroic dye is iodine, the dyeing bath is preferably an iodine solution. The iodine solution is preferably usually an iodine aqueous solution, and contains iodine and iodide as a dissolution aid. Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. Among them, potassium iodide is more suitable from the viewpoint of controlling the potassium content in the polarizing layer.

In the dyeing bath, the concentration of the dichroic pigment is preferably from 0.01 to 1% by weight, more preferably from 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. Since the dyeing degree of the PVA-based resin film is affected by the temperature of the dyeing bath, the immersion time in the dyeing bath cannot be determined uniformly, but is preferably 10 to 300 seconds, more preferably 20 to 240 seconds. The dyeing step can be performed only once or multiple times as needed.

The cross-linking step is a treatment step in which the dyed PVA-based resin film in the dyeing step is immersed in a treatment bath (cross-linking bath) containing a boron compound, and the PVA-based resin film is made The PVA-based resin in the resin film is cross-linked, and the dichroic dye is adsorbed to 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 it may also be a mixed solution of, for example, an organic solvent having miscibility with water and water. From the viewpoint of controlling the potassium content in the polarizing layer, the crosslinking bath preferably 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. Furthermore, when potassium iodide is contained 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 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. Since the cross-linking degree of the PVA-based resin in the PVA-based resin film is affected by the temperature of the cross-linking bath, the immersion time in the cross-linking bath cannot be determined uniformly, but it is preferably 5 to 300 seconds, more preferably 10 to 300 seconds. 200 seconds. The cross-linking step can be performed only once or multiple times as needed.

The stretching step is a processing step of stretching the PVA-based resin film to a predetermined ratio in at least one direction. Generally, a PVA-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 may be used. The extension step can be implemented only once or multiple times as needed. The extending step can be performed in any stage of the manufacturing steps of the polarizing layer.

The treatment bath (stretching bath) in the wet stretching method can generally use a solvent such as water or a mixed solution of an organic solvent and water miscible with water. From the viewpoint of controlling the potassium content in the polarizing layer, the stretching bath preferably contains potassium iodide. When potassium iodide is used in the stretching bath, the concentration of potassium iodide in the stretching bath is preferably 1 to 15% by weight, more preferably 2 to 10% by weight, and more preferably 3 to 6% by weight. Furthermore, from the standpoint of suppressing the breakage of the film during stretching, the treatment bath (stretching Stretching bath) may contain a boron compound. At this time, the concentration of the boron compound in the stretching bath is preferably 1 to 15% by weight, more preferably 1.5 to 10% by weight, and even more preferably 2 to 5% by weight.

The temperature of the stretching bath is preferably from 25 to 80°C, more preferably from 40 to 75°C, and more preferably from 50 to 70°C. Since the stretching degree of the PVA-based resin film is affected by the temperature of the stretching bath, the immersion time in the stretching bath cannot be determined uniformly, but is preferably 10 to 800 seconds, more preferably 30 to 500 seconds. In addition, the stretching treatment in the wet stretching method may be performed together with any one or more of the swelling step, the dyeing step, the crosslinking step, and the washing step.

Examples of the dry stretching method include an inter-roll stretching method, a heating roll stretching method, a compression stretching method, and the like. In the dry stretching method, the stretching step can be performed in the drying step.

The total stretching ratio (accumulated stretching ratio) applied to the PVA-based resin film can be appropriately set depending on 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 processing step of immersing the PVA-based resin film in a cleaning bath, and can remove impurities remaining on the surface of the PVA-based resin film and the like. In the cleansing bath, a medium containing water, distilled water, pure water, etc. as the main component is usually used. Furthermore, from the viewpoint of controlling the content of potassium in the polarizing layer, the cleaning bath preferably contains potassium iodide. At this time, the concentration of potassium iodide in the cleaning bath is preferably 1 to 10% by weight, more preferably 1.5% by weight. to 4% by weight, and more preferably 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. Since the degree of cleaning of the PVA-based resin film is affected by the temperature of the cleaning bath, the immersion time in the cleaning bath cannot be determined uniformly, but it is preferably 1 to 100 seconds, more preferably 2 seconds to 50 seconds, and more preferably 3 to 20 seconds. The washing step can be performed only once or multiple times as needed.

The drying step is a step of drying the PVA-based resin film washed in the washing step to obtain a polarizing layer. Drying may be performed by any appropriate method, and examples thereof include natural drying, air drying, and heat drying.

The production method 2 may include: the step of applying the coating solution containing the above-mentioned PVA-based resin on the base film, the step of uniaxially stretching the obtained laminated film, and the step of uniaxially stretching the obtained laminated film after dyeing with a dichroic dye. The coating layer of the multilayer film, the step of absorbing the dichroic dye, the step of treating the multilayer film adsorbed with the dichroic dye with boric acid aqueous solution, and the step of washing with water after the treatment with boric acid aqueous solution. The base film used to form the polarizing layer can also be used as a transparent protective film of the polarizing plate. The substrate film can also be peeled off from the polarizing layer as needed.

(polarizer)

FIG. 2 is a schematic cross-sectional view schematically showing a polarizing plate of this embodiment. The polarizer 2 has a polarizer 1 and a transparent protective film 21 . The transparent protective film 21 can be arranged on one side or both sides of the polarizing element 1 , but as shown in FIG. 2 , it is preferably arranged on both sides. The polarizer 2 may also have an adhesive layer (not shown) for attaching the polarizer 1 and the transparent protective film 21 . The adhesive layer is usually in direct contact with the polarizer 1 and the transparent protective film 21 .

(transparent protective film)

The transparent protective film 21 may have a single-layer structure or a multi-layer structure. The transparent protective film may be a single-layer structure having an optical function itself, or a multi-layer structure having at least one layer having an optical function. From the viewpoint of optical properties, the thickness of the transparent protective film 21 is preferably thinner, but when it is too thin, the strength decreases and the processability deteriorates. The thickness of the transparent protective film 21 is, for example, more than 5 μm, preferably 10 μm Above, more preferably 15 μm or more, further, for example, 100 μm or less, preferably 80 μm or less, more preferably 70 μm or less.

The transparent protective film 21 can be used: a cellulose acylate film, a polycarbonate resin film, a film made of a cycloolefin resin such as norbornene (Norbornene), a (meth)acrylic polymer film, a polymer film made of polyparaffin Films made of polyester resins such as ethylene phthalate, etc. When there is a transparent protective film 21 on both sides of the polarizing element 1, and a water-based adhesive such as an adhesive containing PVA-based resin is used to bond the polarizing element 1 and the transparent protective film 21, from the viewpoint of moisture permeability, the polarizing plate 2 The at least one transparent protective film 21 included is preferably a cellulose acylate film or a (meth)acrylic polymer film, among which a cellulose acylate film is preferred.

For the purpose of viewing angle compensation, etc., at least one layer of the transparent protective film 21 included in the polarizing plate 2 may have a retardation function. A layer without a phase difference function and a phase difference layer (a layer with a phase difference function) are provided. When the transparent protective film 21 has a retardation layer, it may be constituted as a laminate of a layer having no retardation function and a retardation layer, and these may be bonded using an adhesive layer.

(adhesive layer)

Any appropriate adhesive may be used for the adhesive used to form the adhesive layer for laminating the polarizing element 1 and the transparent protective film 21 . As the adhesive, water-based adhesives, solvent-based adhesives, active energy ray-curable adhesives, etc. can be used, and water-based adhesives are preferred. 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 at the time of application of the adhesive agent can be set to any appropriate value. For example, it is set so that the adhesive agent layer which has a desired thickness can be obtained after hardening or heating (drying). then The thickness of the agent layer is preferably at least 0.01 μm, more preferably at most 7 μm, more preferably at most 5 μm, still more preferably at most 2 μm, and most preferably at most 1 μm.

(water-based adhesive)

As the water-based adhesive, any appropriate water-based adhesive can be used. Among them, it is preferable to use a water-based adhesive (PVA-based adhesive) containing a PVA-based resin. 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, and more preferably from 1,000 to 4,500. From the viewpoint of adhesion, the average degree of saponification is preferably from 85 mol% to 100 mol%, and more preferably from 90 mol% to 100 mol%.

The PVA-based resin contained in the water-based adhesive preferably contains an acetoacetyl group. This is because it has excellent adhesion to the PVA-based resin layer and the transparent protective film and is excellent in durability. The PVA-type resin containing an acetoacetyl group is obtained by reacting PVA-type resin and diketene (Diketene) by arbitrary methods, for example. The degree of denaturation of the acetyl acetyl group of the PVA-based resin containing acetyl acetyl group is typically 0.1 mol % or more, preferably 0.1 mol % or more and 20 mol % or less. The content of the PVA-based resin in the water-based adhesive is preferably at least 0.1% by mass, more preferably at least 0.5% by mass, and is preferably at most 15% by mass, more preferably at most 10% by mass.

The water-based adhesive may contain a crosslinking agent. As the crosslinking agent, generally 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 an acetoacetyl group, the cross-linking agent is preferably any one of glyoxal (Glyoxal), glyoxylate and methylol melamine, more preferably glyoxal and acetaldehyde. Any one of the aldehyde salts, and more preferably glyoxal.

The water-based adhesive may contain an organic solvent. In terms of miscibility with water, the organic solvent is preferably alcohols, among alcohols, more preferably at least one of methanol and ethanol, and more preferably Preferably it is methanol. Among the urea compounds that may be contained in the adhesive layer, some have low solubility in water but sufficient solubility in alcohols. In this case, one of the preferable aspects is to prepare an alcoholic solution of the urea-based compound by dissolving the urea-based compound in alcohols, and then add the alcoholic solution of the urea-based compound to an aqueous solution of the PVA-based resin to prepare a water-based adhesive.

When the water-based adhesive contains methanol, the content of methanol in the water-based adhesive is preferably at least 10% by mass, more preferably at least 15% by mass, more preferably at least 20% by mass, still more preferably 70% by mass Below, more preferably below 60 mass %. By making content of methanol 10 mass % or more, polyeneization of the PVA-type resin which comprises a polarizing element in a high-temperature environment becomes easy to be suppressed more. By making content of methanol into 70 mass % or less, deterioration of the hue of a polarizing element can be suppressed. The content of methanol in the water-based adhesive is the content ratio of methanol when the water-based adhesive is 100% by mass.

(Active energy ray hardening type adhesive)

Active energy ray-curable adhesives are adhesives that are cured by irradiating active energy rays such as ultraviolet rays. Examples include adhesives containing polymerizable compounds and photopolymerizable initiators, adhesives containing photoreactive resins, Adhesives containing adhesive resins and photoreactive crosslinking agents, etc. Examples of polymerizable compounds include photopolymerizable monomers such as photocurable epoxy monomers, photocurable acrylic monomers, and photocurable urethane monomers; and oligomers derived from these monomers. wait. Examples of photopolymerization initiators include compounds that generate active species of 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, it contains at least one selected from urea, urea derivatives, thiourea, and thiourea derivatives. The method of making the adhesive layer contain a urea compound can be listed in the above-mentioned adhesive A method in which a urea compound is contained in an agent. When the adhesive used to bond the polarizing element 1 and the transparent protective film 21 contains a urea-based compound, a part of the urea-based compound may migrate from the adhesive during the process of applying the adhesive and drying it to form an adhesive layer. To polarizer 1 and so on. That is, the polarizing element 1 may contain a urea compound. There are water-soluble and water-insoluble urea-based compounds, and any urea-based compound can be used. When using a poorly water-soluble urea-based compound in a water-based adhesive, it is preferable to carefully arrange the dispersion method of the urea-based compound in such a way that it is difficult to cause an increase in haze when forming the adhesive layer.

When the adhesive is a water-based adhesive containing a PVA-based resin and a urea-based compound, the content of the urea-based compound relative to 100% by mass of the PVA-based resin is preferably at least 0.1% by mass, more preferably at least 1% by mass, and more preferably at least 1% by mass. 3% by mass or more, and preferably at most 400% by mass, more preferably at most 200% by mass, and more preferably at most 100% by mass.

(urea derivatives)

The urea derivative is a compound in which at least one of the 4 hydrogen atoms of the urea molecule is substituted with a substituent. In this case, the substituent is not particularly limited, and is preferably a substituent containing a carbon atom and at least one of a hydrogen atom and an oxygen atom.

Specific examples of urea derivatives, 1-substituted urea include: methyl urea, ethyl urea, propionyl urea, butyl urea, isobutyl urea, N-octadecaneal urea, 2-hydroxyethyl urea, hydroxyurea, acetyl urea, allyl urea Urea, 2-propynylurea, cyclohexylurea, phenylurea, 3-hydroxyphenylurea, (4-methoxyphenyl)urea, benzylurea, benzylurea, o-tolylurea, p-tolueneurea.

Examples of 2-substituted 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.

Examples of 4-substituted urea 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 substituted with a substituent. In this case, the substituent is not particularly limited, and is preferably a substituent containing a carbon atom and at least one of a hydrogen atom and an oxygen atom.

Specific examples of thiourea derivatives, 1-substituted thiourea include: N-methylthiourea, ethylthiourea, propylthiourea, isopropylthiourea, 1-butylthiourea, cyclohexylthiourea, N-acetylthiourea Urea, N-allylthiourea, (2-methoxyethyl)thiourea, N-phenylthiourea, (4-methoxyphenyl)thiourea, N-(2-methoxyphenyl) Thiourea, N-(1-naphthyl)thiourea, (2-pyridyl)thiourea, o-toluenethiourea, p-toluenethiourea.

Examples of 2-substituted 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'-diphenylthiourea, 1,3-bis(o-tolyl ) thiourea, 1,3-di(p-tolyl)thiourea, 1-benzyl-3-phenylthiourea, 1-methyl-3-phenylthiourea, N-allyl-N'-(2 -Hydroxyethyl)thiourea.

Examples of 3-substituted urea include trimethylthiourea, and examples of 4-substituted urea include tetramethylthiourea and 1,1,3,3-tetraethylthiourea.

When the polarizing plate 2 is applied to an image display device configured by interlayer filling described later, the urea-based compound is preferably a urea derivative or a thiourea derivative from the viewpoint of suppressing the decrease in the transmittance Ty under a high-temperature environment. , more preferably a urea derivative. Among the urea derivatives, preferred are 1-substituted urea or 2-substituted urea, more preferably 1-substituted urea. The 2-substituted urea may be any of 1,1-substituted urea and 1,3-substituted urea, more preferably 1,3-substituted urea.

(Layer containing urea compound)

As mentioned above, the adhesive layer for laminating the polarizer 1 and the transparent protective film 21 may be a layer containing a urea compound. In the polarizing plate 2, from the viewpoint of improving the heat resistance of the polarizing plate 2, layers other than the above-mentioned adhesive layer may constitute a layer containing a urea compound.

In recent years, in order to respond to the thinning requirements of polarizers, a polarizer having a transparent protective film 21 on only one side of the polarizer 1 is being developed. In this polarizing plate, for the purpose of improving the physical strength, a hardened layer may be laminated on the surface of the polarizing element 1 that does not have the transparent protective film 21 . This hardened layer may be a layer containing a urea compound. The cured layer can be formed from a curable composition containing an organic solvent, or an aqueous solution of an active energy ray curable polymer composition (JP-A-2017-075986, paragraphs [0020] to [0042]). When the hardened layer is a layer containing a urea-based compound, the hardened layer can be formed by using a mixed solution containing a water-soluble urea-based compound in the above-mentioned aqueous solution.

(Manufacturing method of polarizing plate)

The manufacturing method of the polarizing plate 2 includes a lamination step of laminating the polarizing element 1 and the transparent protective film 21, and may further include a moisture content adjustment step. The lamination step may be a step of laminating the polarizer 1 and the transparent protective film 21 using an adhesive.

The moisture content adjustment step is a step of adjusting the moisture content of the polarizing element 1, for example, so that the moisture content of the polarizing element 1 becomes above the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30%, and the temperature is 20°C and the relative humidity is 80%. The step of adjusting the equilibrium moisture content in the following way. The moisture content of the polarizing element 1 may be below the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 50%, or below the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 45%.

The method of confirming that the moisture content of the polarizing element 1 is above the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30% and below the equilibrium moisture content at a temperature of 20°C and a relative humidity of 80% can be listed Example: In the environment adjusted to the above temperature and the above relative humidity range, store the polarizing element for a certain period of time, and confirm that there is no change in quality; or pre-calculate the environment adjusted to the above temperature and the above relative humidity range The equilibrium moisture content of the polarizing element below, and the method of comparing the moisture content of the polarizing element with the pre-calculated equilibrium moisture content, etc. When the polarizing element is stored for a certain period of time without any change in its quality, it can be considered that the moisture content has reached equilibrium under the storage environment.

The method of adjusting the moisture content of the polarizing element 1 to be above the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30% and below the equilibrium moisture content at a temperature of 20°C and a relative humidity of 80% is not particularly limited, and examples include: A method of storing the polarizing element in an environment adjusted to the above-mentioned temperature and the above-mentioned relative humidity range for 10 minutes to 3 hours, or a method of heat treatment at 30°C to 90°C.

In the moisture content adjustment step, the moisture content of the polarizing plate 2 may be adjusted so that it becomes more than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 30% and not more than the equilibrium moisture content at a temperature of 20°C and a relative humidity of 80%. . The moisture content of the polarizing plate 2 may be below the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 50%, or below the equilibrium moisture content at a temperature of 20° C. and a relative humidity of 45%. The method of adjusting the water content of the polarizing plate 2 may be the same method as the method of adjusting the water content of the above-mentioned polarizing element 1 .

The order of performing the moisture content adjustment step and the layering step is not limited, and the moisture content adjustment process and the layering step can also be performed at the same time.

(image display device)

The polarizing plate 2 is used in various image display devices such as liquid crystal display devices and organic EL display devices. When the image display device is a structure in which both sides of the polarizing plate are in contact with a layer other than the air layer, specifically a solid layer such as an adhesive layer (hereinafter sometimes referred to as "interlayer filling structure"), at high temperature It is easy to reduce the transmittance Ty of the polarizing element under the environment. In the image display device using the polarizing plate 2 of this embodiment, even if it is an interlayer filling structure, the decrease of the transmittance Ty of the polarizing element 1 in a high-temperature environment can be suppressed. The image display device using the polarizing plate 2 can also suppress the reduction of the polarization degree Py and the hue ab of the polarizing element 1 in a high temperature environment.

As a solid layer, an adhesive layer, an adhesive layer, etc. are mentioned. When the solid layer is an adhesive layer, it is preferably an adhesive layer formed of a UV-curable adhesive.

An example of an image display device includes an image display unit, a first adhesive layer laminated on the viewing side surface of the image display unit, and a polarizing plate laminated on the viewing side surface of the first adhesive layer. The image display device may further include: a second adhesive layer laminated on the viewing side surface of the polarizing plate; and a transparent member laminated on the surface of the second adhesive layer. The image display device preferably has an interlayer filling structure in which the polarizing plate and the image display unit are bonded by the first adhesive layer, and the polarizing plate and the transparent member are bonded by the second adhesive layer.

The polarizing plate and the image display unit are not limited to the first adhesive layer, and can also be attached through the adhesive layer. The polarizing plate and the transparent member are not limited to the second adhesive layer, and may be bonded via the adhesive layer. As the adhesive layer, the adhesive layer described above may be mentioned.

(image display unit)

As the image display unit, a liquid crystal unit or an organic EL unit may be mentioned. The liquid crystal cell may be: a reflective liquid crystal cell utilizing external light, a transmissive liquid crystal cell utilizing light from a light source such as a backlight, and a transflective liquid crystal cell utilizing both external light and light from a light source any of these. When the liquid crystal unit utilizes light from a light source, the image display device (liquid crystal display device) also includes a polarizer and a light source on the side opposite to the viewing side of the image display unit (liquid crystal unit). The polarizing plate on the light source side and the liquid crystal cell are preferably bonded via an appropriate bonding layer. As the driving method of the liquid crystal cell, for example, any type such as VA mode, IPS mode, TN mode, STN mode, bend alignment (π type) is used.

The organic EL unit is suitable for use: a transparent electrode and an organic light-emitting layered metal electrode are sequentially laminated on a transparent substrate to form a luminous body (organic electroluminescence luminous body), etc. The organic light-emitting layer is a laminate of various organic thin films. For example, a laminate of a hole injection layer made of triphenylamine derivatives and a light-emitting layer made of fluorescent organic solids such as anthracene can be used. ; or a laminate of these light-emitting layers and an electron injection layer composed of perylene (Perylene) derivatives, etc.; or a laminate of a hole injection layer, a light-emitting layer, and an electron injection layer.

(Lamination of image display unit and polarizer)

It is suitable to use the first adhesive layer (adhesive sheet) for bonding the image display unit and the polarizing plate. Among them, a method of bonding a polarizing plate having an adhesive layer provided with a first adhesive layer on one side of the polarizing plate and an image display unit is preferred from the viewpoint of workability and the like. Attaching the first adhesive layer to the polarizing plate can be performed by an appropriate method. Examples of this include dissolving or dispersing 10 mass % to 40 mass % of the base polymer or its composition in a solvent composed of monomers or mixtures of appropriate solvents such as toluene or ethyl acetate to prepare adhesives. A method of directly attaching the adhesive solution to a polarizing plate by an appropriate expansion method such as pouring or coating; and forming the first adhesive layer on the separator film and transferring it (transfer printing ) in the way of polarizing plates, etc.

(1st adhesive layer, 2nd adhesive layer)

The first adhesive layer and the second adhesive layer (hereinafter both may be collectively referred to as "adhesive layer") may each independently consist of one layer or two or more layers, preferably one layer. The adhesive layer can be made of: (meth)acrylic resin, rubber resin, urethane resin, ester resin, polysilicon It is composed of adhesive composition with oxygen-based resin and polyvinyl ether-based resin as the main components. Among them, an adhesive composition using a (meth)acrylic resin having excellent transparency, weather resistance, heat resistance, etc. as a base polymer is more suitable. The adhesive composition may be an active energy ray curing type or a thermosetting type.

The (meth)acrylic resin (base polymer) used in the adhesive composition is suitable for use: butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, ( A polymer or copolymer of one or more (meth)acrylates such as 2-ethylhexyl methacrylate as a monomer. The base polymer is preferably a copolymer obtained by copolymerizing a polar monomer. 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. Examples of cross-linking agents include metal ions with a valence of more than 2, metal ions that form a metal carboxylate salt with a carboxyl group, polyamine compounds that form an amide bond with a carboxyl group, and ester bonds that form an ester bond with a carboxyl group. Polyepoxides or polyols, polyisocyanate compounds that form amide bonds with carboxyl groups. Among them, polyisocyanate compounds are preferred.

Active energy ray-curable adhesive composition has the property of being hardened by irradiation of active energy rays such as ultraviolet rays or electron rays, and has adhesiveness even before irradiation of active energy rays, and can be adhered to adherends such as films , and can be hardened by the irradiation of active energy rays and can adjust the properties of the adhesive force. The active energy ray-curable adhesive composition is preferably an ultraviolet-curable adhesive composition. In addition to the base polymer and cross-linking agent, the active energy ray-curable adhesive composition, It also contains active energy ray polymerizable compounds. A photopolymerization initiator, a photosensitizer, etc. may also be contained as needed.

The adhesive composition may contain: microparticles for imparting light scattering, beads (resin beads, glass beads, etc.), glass fibers, resins other than base polymers, adhesiveness imparting agents, fillers (metal powder or Other inorganic powders, 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. The base film is generally a thermoplastic resin film, and a typical example thereof includes a separator film subjected to mold release treatment. The separation film can be: for example, on the surface of a film made of resins such as polyethylene terephthalate, polybutylene terephthalate, polycarbonate, and polyarylate, on which an adhesive layer is formed. Release treatment such as polysiloxane treatment.

It is also possible to directly coat the adhesive composition on the release-treated surface of the separator to form an adhesive layer, and laminate the adhesive layer with the separator on the surface of the polarizing plate. It is also possible to directly coat the adhesive composition on the surface of the polarizing plate to form an adhesive layer, and laminate the separator film on the outer surface of the adhesive layer.

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

Furthermore, the adhesive composition can also be coated on the second separator to form an adhesive layer, and the adhesive sheet can be prepared by laminating the separator on the formed adhesive layer. Then, the adhesive layer with the separator film peeled off the separator film from the adhesive sheet was laminated on the polarizing plate. The second separation film is used: the adhesive force with the adhesive layer is weaker than that of the separation film and it is easy to peel off.

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

(transparent component)

Examples of the transparent member disposed on the viewing side of the image display device include a front panel (light-transmitting layer), a touch panel, and the like. The front panel uses a transparent board with appropriate mechanical strength and thickness. Examples of the transparent plate include transparent resin plates such as polyimide-based resins, acrylic resins, and polycarbonate-based resins, glass plates, and the like. Functional layers such as an anti-reflection layer may also be laminated on the viewing side of the transparent plate. Furthermore, when the transparent board is a transparent resin board, a hard coat layer for improving physical strength or a low moisture-permeable layer for reducing moisture permeability can also be laminated. Examples of the touch panel include various touch panels such as a resistive film method, an electrostatic capacitance method, an optical method, and an ultrasonic method, or a glass plate or a transparent resin plate with a touch sensor function. When using a capacitive touch panel as a transparent member, it is preferable to provide a transparent plate made of glass or a transparent resin plate on the viewing side of the touch panel.

(Adhesion of polarizing plate and transparent member)

It is suitable to use a second adhesive layer or an active energy ray-curable adhesive for bonding the polarizing plate and the transparent member. When using a 2nd adhesive layer, attachment of a 2nd adhesive layer can be performed by an appropriate method. As a specific method of attaching, for example, the method of attaching the first adhesive layer used for laminating the above-mentioned image display unit and polarizing plate may be mentioned.

When using an active energy ray-curing adhesive, it is suitable for the purpose of preventing the diffusion of the adhesive solution before hardening: Install the dam material so as to surround the peripheral part of the image display panel, and place it on the dam material The method of injecting the adhesive solution into the transparent member. After injecting the adhesive solution, alignment and defoaming can be performed as needed, and then active energy rays can be irradiated to harden the adhesive solution.

(bonded layer)

The bonding layer is an adhesive layer or an adhesive layer. Adhesive layer and adhesive layer In addition to the adhesive layer and adhesive layer (first adhesive layer, second adhesive layer) described above, there are: Adhesives formed using generally known adhesives An adhesive layer, and an adhesive layer formed using a generally known adhesive.

[Example]

Hereinafter, the present invention will be specifically described based on examples. Materials, reagents, amounts of substances, their ratios, operations, etc. shown below can be appropriately changed without departing from the gist of the present invention. Therefore, the present invention is not limited to and limited by the following examples.

[Measurement method and evaluation method]

(1) Determination of the thickness of the polarizing element

The thickness of the polarizing element was measured using a digital micrometer "MH-15M" manufactured by Nikon Corporation.

(2) Determination of the light sensitivity correction monomer transmittance, light sensitivity correction polarization degree and hue of the polarizing plate

The transmittance of the light-sensitivity correction monomer of the polarizing plate, the light-sensitivity correction polarization degree, and the hue are measured using a spectrophotometer with an integrating sphere ["V7100" manufactured by JASCO Co., Ltd., 2 degrees Field of view; C light source] to measure. The adhesive layer formed by using the transparent protective film and the adhesive for the polarizing plate described later for the production of the polarizing plate are all colorless and transparent, so the single transmittance and visual sensitivity correction are corrected for the visual sensitivity measured by the polarizing plate The degree of polarization and hue can be used as the sensitivity of the polarizing element to correct the transmittance of a single element, and the degree of polarization and hue can be modified by the sensitivity.

(3) Determination of boron content

The determination of the boron content in the polarizer is carried out by the following steps. First, 0.2 g of a polarizer was dissolved in 200 g of a 1.9 mass % mannitol (Mannitol) aqueous solution. Next, 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.

(4) Determination of dyeing degree

Fig. 3(a) and (b) are explanatory diagrams for explaining the steps for measuring the degree of dyeing. Fig. 3(a) is a diagram illustrating a method of cutting out a measurement sample 20t from a polarizing plate 20 produced in the following steps, Fig. 3(b) is a diagram illustrating Raman spectroscopic measurement of a measurement sample 20t, and The cutaway portion of the polarizing element 10t is enlarged and shown. FIG. 4 is an explanatory diagram for explaining a method of calculating an integrated intensity distribution from Raman spectroscopy.

(Preparation of samples for measurement)

Using an Ultramicrotome (trade name "LEICA RM2255" manufactured by LEICA Corporation), as shown in FIG. The polarizing plate 20 was cut to produce a measurement sample 20t having a length d (thickness of the cut piece) of about 100 nm in a direction perpendicular to the plane ( FIG. 3( a )).

(Raman spectrometry)

The apparatus and measurement conditions used for the Raman spectroscopic measurement are as described below.

‧Device: Laser Raman Spectrophotometer (NRS-5100, manufactured by JASCO Corporation)

‧Excitation wavelength: 532.23nm

‧Grating: 1800l/mm

‧Objective lens: visible 100 times

‧Measurement pitch: 1μm

In the polarizer 10t portion of the cut surface (surface formed by cutting with an Ultramicrotome) of the measurement sample 20t, measurement points at 1 μm intervals are set in the thickness direction (plane direction of the cut surface) 100 of the polarizer 10 p, and measured by Raman spectroscopy. The laser light L enters such that the plane of polarization is parallel to the absorption axis direction (extension direction) 101 of the polarizer 10t and perpendicular to the cut plane of the measurement sample 20t. A detector is provided on the side of the measurement sample 20t opposite to the incident surface of the laser light L (the rear side of the measurement sample 20t). The polarization plane of the detector is parallel to the polarization plane of the laser light L.

In any Raman spectrum measured on the polarizing element of the measurement sample produced from the polarizing plate described later, a peak corresponding to I ₃ ^- was observed around 108 cm ^-1 , and a peak corresponding to I 3 - was observed around 158 cm ^-1 I ₅ ^-peak value.

(I ₃ ^- and ^I ₅ -calculation of integral intensity distribution)

Since the main absorber in the visible light region (380nm to 780nm) is the complex formed by polyiodine (I ₃ ^- , I ₅ ^- ) and polyvinyl alcohol (polyiodine-PVA complex), so By measuring the Raman intensity of I ₃ ^- and I ₅ ^- , the effective amount of iodine that affects viewing can be compared. The specific calculation procedure is as follows.

As shown in Fig. 4, the baseline of Raman spectroscopy is approximated by a straight line by connecting the value at wavenumber 80cm ^- 1 and the value at wavenumber 130cm ^-1 in Raman spectroscopy (line ef in Fig. 4 ). Set the distance (intensity) from the approximated straight line ef as the Raman intensity, correct the slope of the baseline in the measurement of Raman spectroscopy, and then calculate the integral area of the interval from wavenumber 80cm ^-1 to 130cm ^-1 (In FIG. 4, it corresponds to the area of the oblique line surrounded by the straight line ef and the Raman spectrum from e to f), and this is assumed to be the integrated intensity of I ₃ ⁻ .

Furthermore, as shown in Figure 4, by connecting the Raman spectrum's value at a wave number of 130 cm ^-1 and the value at a wave number of 180 cm ^- 1, the baseline of the Raman spectrum is approximated by a straight line (in Figure 4 straight line fg). Set the distance (intensity) from the approximated straight line fg as the Raman intensity, correct the slope of the baseline in the measurement of Raman spectroscopy, and obtain the integral area of the interval from wavenumber 130cm ^-1 to 180cm ^-1 (In FIG. 4, it corresponds to the area of the oblique line surrounded by the straight line fg and the Raman spectrum from f to g), and this is assumed to be the integrated intensity of I ₅ ^- .

The sum of the integrated intensity of I ₃ ^- and the integrated intensity of I ₅ ^- at each measurement point p is plotted with respect to each measurement point p, thereby obtaining the integrated intensity distribution of the polarizing element 10t in the thickness direction. In this integrated intensity distribution, the integrated area is calculated for each of the three regions that divide the polarizing element 10t into three equal parts in the thickness direction, and these are set to be contained in the polarizing plate from which the measurement sample 10t is cut out. The degree of dyeing of the 3 regions of the polarizer.

(5) High temperature durability test

(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 both sides of the polarizing plate produced in the following steps to form an adhesive layer with a thickness of 25 μm. A polarizing plate with an adhesive layer formed on both sides was cut into a size of 50 mm x 100 mm, and an alkali-free glass (trade name "EAGLE XG", manufactured by Corning Corporation) was bonded to the surface of each adhesive layer. Samples for evaluation. Preparation of samples for evaluation During operation, in order to adjust the moisture content of the polarizer before laminating the non-alkali glass, store the polarizer with the adhesive layer on both sides for 72 hours at a temperature of 20°C and a relative humidity of 40%. For polarizers produced in the following steps with adhesive layers formed on both sides, no change was observed in the mass measured at each time point after 66 hours, 69 hours, and 72 hours of storage, so polarized light The equilibrium moisture content of the element, the polarizing plate, and the polarizing plate formed with the above-mentioned adhesive layer can be considered to be the same as the equilibrium moisture content at a temperature of 20°C and a relative humidity of 40%, which is the equilibrium moisture content of a 72-hour storage environment.

(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. Next, after leaving the evaluation sample for 24 hours in an environment with a temperature of 23°C and a relative humidity of 55%, the transmittance of the polarizing plate, the light sensitivity correction monomer transmittance, the light sensitivity correction polarization degree, and the hue are measured, and this is set as the initial stage. value. Then, a high-temperature durability test was carried out in which the evaluation samples were stored in a high-temperature environment at a temperature of 115°C for 144 hours, and the light-sensitivity-corrected monomer transmittance, light-sensitivity-corrected polarization degree, and hue of the polarizing plate after the high-temperature durability test were measured.

Calculate the transmittance of the polarizing plate from the sensitivity correction monomer transmittance, the sensitivity correction polarization degree and the initial value of the hue, and the measured value after the high temperature durability test. The amount of change in degree and hue. The change amount ΔTy of the light sensitivity correction monomer transmittance and the change amount ΔPy of the light sensitivity correction polarization degree are calculated by subtracting the measured value after the high temperature durability test from the initial value. In addition, the change amount Δab of hue is calculated|required by the following formula.

△ab={(a ₁ -a ₂ ) ² +(b ₁ -b ₂ ) ² } ^1/2

Here, a ₁ and b ₁ are initial values of the hue, and a ₂ and b ₂ are measured values of the hue after the high-temperature durability test.

[Production of polarizing element A]

(Preparation of PVA solution for adhesive)

Dissolve 50 g of denatured 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 Polarizing Layer 1)

After immersing a PVA-based resin film with a thickness of 20 μm in pure water at a temperature of 21.5°C for 79 seconds, immerse it in a temperature of 23 seconds at a weight ratio of potassium iodide/boric acid/water of 2/2/100 and containing 1.0 mM iodine belonging to a dichroic dye. ℃ in aqueous solution for 160 seconds. Then, it was immersed in an aqueous solution at a temperature of 60.8° C. at a weight ratio of potassium iodide/boric acid/water of 2.5/4/100 for 76 seconds. Next, it was immersed in an aqueous solution at a temperature of 45° C. at a weight ratio of potassium iodide/boric acid/water of 3/5.5/100 for 11 seconds. Then, drying was performed at a temperature of 38° C. to obtain a polarizing layer 1 having a thickness of 6.5 μm in which iodine was adsorbed and aligned to a PVA-based resin film (PVA-based resin layer). The extension is mainly carried out in the steps of iodine staining and boric acid treatment, and the total extension ratio is 5.85 times.

(Preparation of Polarizing Layer 2)

A PVA-based resin film with a thickness of 20 μm was immersed in pure water at a temperature of 21.5°C for 79 seconds, and then immersed in a temperature of 23 mM containing 1.0 mM iodine as a dichroic dye at a weight ratio of potassium iodide/boric acid/water of 2/2/100. 142 seconds in aqueous solution at ℃. Then, it was immersed in an aqueous solution at a temperature of 60.8° C. at a weight ratio of potassium iodide/boric acid/water of 2.5/4/100 for 76 seconds. Next, it was immersed in an aqueous solution at a temperature of 45° C. at a weight ratio of potassium iodide/boric acid/water of 3/5.5/100 for 11 seconds. Then proceed at a temperature of 38°C It was dried to obtain a polarizing layer 2 having a thickness of 6.5 μm in which iodine was adsorbed and aligned to the PVA-based resin film (PVA-based resin layer). The extension is mainly carried out in the steps of iodine staining and boric acid treatment, and the total extension ratio is 5.85 times.

(Production of Polarizer A)

Polarizing layer 1, polarizing layer 2, and polarizing layer 1 were sequentially laminated with PVA solution through the adhesive obtained above, and dried at a temperature of 23°C and a relative humidity of 55% to produce polarizing layer 1/polarizing layer 2/ Polarizing element A (thickness: 19.5 μm) of layer structure of polarizing layer 1 . In the polarizing element A, the absorption axes of the polarizing layer 1, the polarizing layer 2, and the polarizing layer 1 are parallel. The content of boron in the polarizing element A was 4.62% by mass.

[Production of Polarizer B]

A PVA-based resin film with a thickness of 45 μm was immersed in pure water at a temperature of 21.5°C for 79 seconds, and then immersed in a temperature of 23 mM containing iodine as a dichroic dye with a weight ratio of potassium iodide/boric acid/water of 2/2/100. 151 seconds in aqueous solution at ℃. Then, it was immersed in an aqueous solution at a temperature of 60.8° C. at a weight ratio of potassium iodide/boric acid/water of 2.5/4/100 for 76 seconds. Next, it was immersed in an aqueous solution at a temperature of 45° C. at a weight ratio of potassium iodide/boric acid/water of 3/5.5/100 for 11 seconds. Thereafter, drying was performed at a temperature of 38° C. to obtain a polarizing element B having a thickness of 18 μm in which iodine was adsorbed and aligned to a PVA-based resin film (PVA-based resin layer). The extension is mainly carried out in the steps of iodine staining and boric acid treatment, and the total extension ratio is 5.85 times. The content of boron in the polarizer B was 4.62% by mass.

[Production of Polarizing Plate 1]

(Preparation of Adhesives for Polarizing Plates)

The above-mentioned polarizer is formulated so that the content of denatured PVA-based resin containing acetyl acetyl group is 3.0% by mass, the content of methanol is 35% by mass, and the content of urea is 0.5% by mass. The PVA solution, pure water, methanol, and urea were used for the adhesive prepared in the procedure described in the item of the production of the device A to obtain the adhesive for the polarizing plate.

(production of transparent protective film)

A commercially available cellulose acylate membrane TJ40UL (manufactured by Fujifilm Co., Ltd., thickness: 40 μm) was immersed in a 1.5 mol/L NaOH aqueous solution (saponified solution) maintained at a temperature of 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 a temperature of 25°C for 30 seconds, and passed through a water bath under running water for 30 seconds to make the membrane neutral. Draining by air knife was then repeated 3 times. After draining, the film was dried in a drying zone at a temperature of 70° C. for 15 seconds to obtain a saponified cellulose acylate film, which was then formed into a transparent protective film.

(Production of Polarizing Plate 1)

A polarizing plate 1 was obtained by bonding a transparent protective film to both surfaces of the polarizing element A through the adhesive agent for polarizing plates obtained above using a roll laminating machine, and drying at a temperature of 80° C. for 3 minutes. The adhesive agent for polarizing plates between the polarizer A and the transparent protective film was prepared so that the thickness of each adhesive agent layer after drying might become 100 nm. The degree of dyeing of the polarizing element A was measured using the polarizing plate 1, and a high-temperature durability test was performed. The results are shown in Table 1. In the polarizing element A, the region with the smallest degree of dyeing is the region located in the center of the polarizing element A in the thickness direction.

[Production of polarizing plate 2]

Except that the polarizing element B is used instead of the polarizing element A, the polarizing plate 2 is fabricated in the same steps as the polarizing plate 1 . The degree of dyeing of the polarizing element B was measured using the polarizing plate 2, and a high-temperature durability test was performed. The results are shown in Table 1. In the polarizing element B, the region with the smallest degree of dyeing is the region located in the center of the polarizing element B in the thickness direction.

[Table 1]

1: polarizer

11~13: area

100: Thickness direction

Claims (14)

A polarizing element, which is adsorbed and aligned with a dichroic pigment on a polyvinyl alcohol-based resin layer, wherein, In the 3 regions that divide the aforementioned polarizing element into three equal parts in the thickness direction, when the dyeing degree of the region with the largest dyeing degree is set as S1, and the dyeing degree of the region with the smallest dyeing degree is set as S2, the following conditions are met. The relation of expression (1), 0≦S2/S1≦0.95 (1). The polarizing element according to claim 1, wherein the region with the smallest degree of dyeing among the three regions is the region located in the center in the thickness direction. The polarizing element according to claim 1 or 2, wherein the aforementioned polarizing element contains boron, The content of boron in the polarizing element is not less than 4.0% by mass and not more than 8.0% by mass. The polarizing element according to any one of claims 1 to 3, wherein the dichroic dye is iodine. A polarizing plate comprising the polarizing element described in any one of Claims 1 to 4, and a transparent protective film. The polarizing plate as described in Claim 5 further has an adhesive layer for laminating the aforementioned polarizing element and the aforementioned transparent protective film, The aforementioned adhesive layer is a layer of the water-based adhesive after hardening. The polarizing plate according to claim 6, wherein the water-based adhesive contains methanol, Content of the said methanol in the said water-based adhesive agent is 10 mass % or more and 70 mass % or less. The polarizing plate according to claim 6 or 7, wherein the water-based adhesive further contains a polyvinyl alcohol-based resin. The polarizing plate according to any one of claims 6 to 8, wherein the adhesive layer has a thickness of 0.01 μm or more and 7 μm or less. The polarizing plate according to any one of claims 5 to 9, wherein the aforementioned polarizing plate is used in an image display device, In the aforementioned image display device, both surfaces of the aforementioned polarizing plate may be in contact with the solid layer. An image display device comprising an image display unit, a first adhesive layer laminated on the viewing side surface of the image display unit, and claims 5 to 10 laminated on the viewing side surface of the first adhesive layer The polarizing plate described in any one of them. The image display device according to claim 11 further includes a second adhesive layer laminated on the viewing side surface of the polarizing plate, and a transparent member laminated on the viewing side surface of the second adhesive layer. The image display device according to claim 12, wherein the transparent member is a glass plate or a transparent resin plate. The image display device according to claim 12, wherein the transparent member is a touch panel.

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