JP2022074422A - Polarizing plate and image display device - Google Patents

Abstract

To provide a polarizing plate that suppresses a decrease in transmittance under a high temperature environment.SOLUTION: A polarizing plate includes: a polarizing element in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin layer; and a transparent protective film laminated on at least one surface of the polarizing element. The polarizing element and the transparent protective film are bonded by an adhesive layer formed of an adhesive containing a blocked isocyanate compound. The water content of the polarizing element is equal to or higher than an equilibrium water content at a temperature of 20°C and a relative humidity of 30%, and equal to or lower than an equilibrium water content at a temperature of 20°C and a relative humidity of 50%.SELECTED DRAWING: None

Description

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

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

As described above, the polarizing plate is increasingly mounted on a vehicle as a member of an image display device such as a liquid crystal display device or an organic EL display device. Polarizers used in in-vehicle image display devices are often exposed to high-temperature environments compared to mobile applications such as televisions and mobile phones, so their characteristic changes at higher temperatures are smaller (high-temperature durability). Gender) is required.

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

In such a configuration, if an air layer exists between the image display panel and a transparent member such as a front plate or a touch panel, external light is reflected due to light reflection at the interface of the air layer, and the visibility of the screen is improved. Tends to decline. Therefore, the space between the polarizing plate and the transparent member arranged on the visible surface of the image display panel is a layer other than the air layer and is usually referred to as a solid layer (hereinafter, referred to as "interlayer filler"). The movement to adopt the structure of filling with (.) (Hereinafter, may be referred to as "interlayer filling structure") is widespread. The interlayer filler is preferably a material having a refractive index close to that of the polarizing plate or the transparent member. As the interlayer filler, an adhesive or a UV curable adhesive is used for the purpose of suppressing deterioration of visibility due to reflection at the interface and adhesively fixing between the members (see, for example, Patent Document 1).

Interlayer filling configurations are widely used in mobile applications such as mobile phones, which are often used outdoors. In addition, due to the increasing demand for visibility in recent years, even in in-vehicle applications such as car navigation devices, a front transparent plate is arranged on the surface of the image display panel, and the space between the panel and the front transparent plate is filled with an adhesive layer or the like. Adoption of an interlayer filling configuration is being considered.

However, it has been reported that when such a configuration is adopted, the transmittance of the polarizing plate is significantly reduced in a high temperature environment. In Patent Document 2, as a solution to the problem, the amount of water per unit area of the polarizing plate is set to a predetermined amount or less, and the saturated water absorption amount of the transparent protective film adjacent to the polarizing element is set to a predetermined amount or less to increase the transmittance. We are proposing a method to suppress the decline.

Japanese Unexamined Patent Publication No. 11-174417 Japanese Unexamined Patent Publication No. 2014-102353

However, even with such a polarizing plate, the effect of suppressing the decrease in transmittance in a high temperature environment is not sufficient. An object of the present invention is to provide a polarizing plate in which a decrease in transmittance is further suppressed in a high temperature environment, and an image display device using the polarizing plate.

The present invention provides a polarizing plate and an image display device exemplified below.
[1] A polarizing plate having a polarizing element in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin layer, and a transparent protective film laminated on at least one surface of the polarizing element.
The polarizing element and the transparent protective film are bonded to each other by an adhesive layer formed of an adhesive containing a blocked isocyanate compound.
A polarizing plate having a water content of the polarizing element having a temperature of 20 ° C. and a relative humidity of 30% or more and a temperature of 20 ° C. and a relative humidity of 50% or less.
[2] A polarizing plate having a polarizing element in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin layer, and a transparent protective film laminated on at least one surface of the polarizing element.
The polarizing element and the transparent protective film are bonded to each other by an adhesive layer formed of an adhesive containing a blocked isocyanate compound.
A polarizing plate having a water content of the polarizing plate having a temperature of 20 ° C. and a relative humidity of 30% or more and an equilibrium water content of a temperature of 20 ° C. and a relative humidity of 50% or less.
[3] The polarizing plate according to [1] or [2], wherein the adhesive contains a polyvinyl alcohol-based resin.
[4] The polarizing plate according to [3], wherein the content of the blocked isocyanate compound in the adhesive is 1 part by mass or more and 500 parts by mass or less with respect to 100 parts by mass of the polyvinyl alcohol-based resin.
[5] The polarizing plate according to any one of [1] to [4], wherein the adhesive layer has a thickness of 0.01 μm or more and 7 μm or less.
[6] The polarized light according to any one of [1] to [5], wherein the blocked isocyanate compound contains at least one selected from the group consisting of pyrazoles and N, N'-diarylform amidines as a blocking agent. Board.
[7] The polarizing plate is used in an image display device, and the polarizing plate is used in an image display device.
The polarizing plate according to any one of [1] to [6], wherein a solid layer is provided in contact with both surfaces of the polarizing plate in the image display device.
[8] Any of [1] to [7] laminated on the image display cell, the first pressure-sensitive adhesive layer laminated on the visible side surface of the image display cell, and the visible side surface of the first pressure-sensitive adhesive layer. An image display device having the polarizing plate described in the above.
[9] The image display according to [8], further comprising a second pressure-sensitive adhesive layer laminated on the visible side surface of the polarizing plate and a transparent member laminated on the visible side surface of the second pressure-sensitive adhesive layer. Device.
[10] The image display device according to [9], wherein the transparent member is a glass plate or a transparent resin plate.
[11] The image display device according to [9], wherein the transparent member is a touch panel.

According to the present invention, it is possible to provide a polarizing plate having improved high temperature durability and suppressed decrease in transmittance due to high temperature even when used in an image display device having an interlayer filling configuration. Further, by using the polarizing plate according to the present invention, it becomes possible to provide an image display device in which a decrease in transmittance is suppressed in a high temperature environment.

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

[Polarizer]
The polarizing plate according to the embodiment of the present invention has a polarizing element in which a dichroic dye is adsorbed and oriented on a layer containing a polyvinyl alcohol-based resin, and a transparent protective film. The polarizing element and the transparent protective film are bonded by an adhesive layer formed from an adhesive containing a blocked isocyanate compound. The polarizing plate according to the present embodiment has at least one of the following features (a) and (b).
(A) The water content of the polarizing element is equal to or higher than the equilibrium water content at a temperature of 20 ° C. and a relative humidity of 30%, and equal to or lower than the equilibrium water content at a temperature of 20 ° C. and a relative humidity of 50%.
(B) The water content of the polarizing plate is equal to or higher than the equilibrium water content at a temperature of 20 ° C. and a relative humidity of 30%, and equal to or lower than the equilibrium water content at a temperature of 20 ° C. and a relative humidity of 50%.

As a conventional polarizing plate having excellent high temperature durability, for example, a polarizing plate in which a decrease in transmittance is suppressed even when the polarizing plate alone is left in an environment of a temperature of 95 ° C. for 1000 hours is known. However, even with such a polarizing plate, when it is used in an interlayer filling configuration, when it is left in an environment of a temperature of 95 ° C. for 200 hours, a significant decrease in transmittance may be observed in the central portion of the polarizing plate surface. The significant decrease in the transmittance of the polarizing plate in a high temperature environment is due to the interlayer filling configuration in which one surface of the polarizing plate is bonded to the image display cell and the other surface is bonded to a transparent member such as a touch panel or a front plate. It is considered that this is a problem that is particularly likely to occur when the image display device that adopts the above is exposed to a high temperature environment.

The polarizing plate whose transmittance was significantly reduced due to the interlayer filling configuration peaked at around 1100 cm ^-1 (= CC = derived from the bond) and around 1500 cm ^-1 (derived from the -C = C-bond) by Raman spectroscopy. Since it has, it is considered that it forms a polyene structure (-C = C) _n- . It is presumed that the polyene structure is formed by polyeneizing polyvinyl alcohol constituting the polarizing element by dehydration (Patent Document 2, paragraph [0012]).

The polarizing plate according to the present invention can improve high temperature durability. The polarizing plate according to the present invention is incorporated in an image display device having an interlayer filling configuration, and can suppress a decrease in transmittance even when exposed to a high temperature environment of, for example, a temperature of 105 ° C for a long time, and is 48 at a temperature of 105 ° C. Even after storage for a long time, the decrease in transmittance can be 5% or less.

<Polarizing element>
As a polarizing element in which a dichroic dye is adsorbed and oriented on a layer containing a polyvinyl alcohol (hereinafter, also referred to as “PVA”) resin (hereinafter, also referred to as a “PVA-based resin layer”), a well-known polarizing element is used. Can be used. As the polarizing element, a stretched film obtained by dyeing a PVA-based resin film with a dichroic dye and uniaxially stretching the film, or a coating layer formed by applying a coating liquid containing a PVA-based resin on a base film. Examples thereof include a stretched layer obtained by dyeing a coating layer with a dichroic dye using the laminated film having the film and uniaxially stretching the laminated film. Stretching may be performed after dyeing with a dichroic dye, stretching while dyeing, or stretching and then dyeing.

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

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

The thickness of the polarizing element is preferably 3 μm or more and 35 μm or less, more preferably 4 μm or more and 30 μm or less, and further preferably 5 μm or more and 25 μm or less. When the thickness of the polarizing element is 35 μm or less, it is possible to suppress the influence of polyene formation of the PVA-based resin on the deterioration of optical characteristics in a high temperature environment. When the thickness of the polarizing element is 3 μm or more, it becomes easy to configure the structure to achieve the desired optical characteristics.

The polarizing element preferably contains a blocked isocyanate compound. In the present embodiment, since the polarizing element and the transparent protective film are bonded by an adhesive layer formed of an adhesive containing a blocked isocyanate compound, a part of the blocked isocyanate compound is transferred from the adhesive layer. It is presumed that it is contained in the polarizing element. The blocked isocyanate compound in the polarizing element may include those added in the process of manufacturing the polarizing element. By providing a polarizing element containing a blocked isocyanate compound, the transmittance is less likely to decrease even when the polarizing plate is exposed to a high temperature environment. In the blocked isocyanate compound, the isocyanate compound is blocked by the blocking agent and does not cause a cross-linking reaction until heating. However, when the blocking group is removed and the isocyanate compound is activated in a high temperature environment, polyene formation of the PVA-based resin is suppressed. It is presumed to do so. The blocked isocyanate compound may be used alone or in combination of two or more.

(Blocked isocyanate compound)
The blocked isocyanate compound means a compound having a structure in which the isocyanate group of the isocyanate compound is protected (masked) with a blocking agent. The blocked isocyanate compound can be a compound in which the isocyanate group does not show reactivity at room temperature, but the blocking agent is dissociated by heating and the active isocyanate group is regenerated. As the isocyanate compound used for the blocked isocyanate compound, a compound having two or more isocyanate groups in one molecule is preferable, and for example, an aliphatic such as ethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (HDI), and dodecamethylene diisocyanate. Polyisocyanate; alicyclic polyisocyanate such as cyclopentylene diisocyanate, cyclohexylene diisocyanate, isophorone diisocyanate (IPDI), dicyclohexylmethane-4,4'-diisocyanate (hydrogenated MDI), methylcyclohexylene diisocyanate (hydrogenated TDI); 1,3- or 1,4-phenylenediocyanate, 2,4- or 2,6-tolylene diisocyanate (TDI), 2,2'-or 2,4'-or 4,4'-diphenylmethane diisocyanate (MDI) , 3-Chloro-4-methylphenyl diisocyanate, 4-chlorophenyl diisocyanate and other aromatic polyisocyanates; m- or p-xylylene diisocyanate (XDI), α, α, α', α'-tetramethylxylylene diisocyanate ( Aromatic aliphatic polyisocyanate such as TMXDI); Polymethylenepolyphenylpolyisocyanate; Trimethylolpropane / Tolylene diisocyanate trimeric adduct (manufactured by Nippon Polyurethane Industry Co., Ltd., trade name "Coronate L"), Trimethylol propane / hexamethylene Isocyanate adducts such as diisocyanate trimer adduct (manufactured by Nippon Polyurethane Industry Co., Ltd., trade name "Coronate HL"), isocyanurates of hexamethylene diisocyanate (manufactured by Japan Polyurethane Industry Co., Ltd., trade name "Coronate HX"); Examples thereof include modified products of polyisocyanate.

Examples of the blocking agent for the isocyanate compound include lactams such as ε-caprolactam, δ-valerolactam, and γ-butyrolactam; Oximes; phenols such as phenol, cresol, ethylphenol, butylphenol, nonylphenol, catechol, nitrophenol; alcohols such as methanol, ethanol, isopropyl alcohol, butanol, cyclohexanol, trimethylolpropane; butyl mercaptan, dodecyl mercaptan, etc. Mercaptans; Active oxime compounds such as dimethyl malonate, diethyl malonate, methyl acetoacetate, ethyl acetoacetate, acetylacetone; amides such as acetoanilide and acetate amide; imides such as succinic acid imide and maleate imide; 3,5 -Pyrazoles such as dimethylpyrazole; Triazoles such as 1,2,4-triazole; Sulfites such as sodium bisulfite; N, N'-diphenylform amidine, N, N'-bis (2-methylphenyl) form Amidine, N, N'-bis (3-methylphenyl) form amidine, N, N'-bis (4-methylphenyl) form amidine, N, N'-bis (3,5-dimethylphenyl) form amidine, etc. Examples thereof include N, N'-diarylformamidins and the like. These blocking agents can be used alone or in combination of two or more. Among the above blocking agents, pyrazoles and N, N'-diarylform amidines are preferable in that the crosslinking reaction proceeds at a relatively low temperature (for example, 80 ° C to 120 ° C).

As the blocked isocyanate compound, a commercially available product can be used, and BI200, BI220 and the like manufactured by Baxenden can be used. The blocked isocyanate compound can also be prepared and used by a known method. For the blocked isocyanate compound, for example, the isocyanate compound and the blocking agent are stirred in a solvent at a temperature of about 0 ° C. to 200 ° C., and separated by using known separation and purification means such as concentration, filtration, extraction, crystallization and distillation. Can be obtained by

Examples of the method of containing the blocked isocyanate compound in the polarizing element include a method of immersing the PVA-based resin layer in the treatment solvent containing the blocked isocyanate compound, and a method of spraying, flowing down or dropping the treatment solvent on the PVA-based resin layer. .. Among these, a method of immersing the PVA-based resin layer in a treatment solvent containing a blocked isocyanate compound is preferably used.

The step of immersing the PVA-based resin layer in the treatment solvent containing the blocked isocyanate compound may be performed at the same time as the steps of swelling, stretching, dyeing, cross-linking, cleaning, etc. in the method for manufacturing a polarizing element described later, or these steps. May be provided separately. The step of incorporating the blocked isocyanate compound in the PVA-based resin layer is preferably performed after dyeing the PVA-based resin layer with iodine, and more preferably performed at the same time as the cross-linking step after dyeing. According to such a method, the hue change is small and the influence on the optical characteristics of the polarizing element can be reduced.

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

(Characteristic (a))
When it has the feature (a), the water content of the polarizing element is equal to or more than the equilibrium water content at a temperature of 20 ° C. and a relative humidity of 30%, and is equal to or less than the equilibrium water content at a temperature of 20 ° C. and a relative humidity of 50%. The water content of the polarizing element is preferably equal to or less than the equilibrium water content at a temperature of 20 ° C. and a relative humidity of 45%, more preferably not less than the equilibrium water content of a temperature of 20 ° C. and a relative humidity of 42%, and further preferably relative to the temperature of 20 ° C. Humidity is 38% or less and equal to or less than the equilibrium moisture content. When the water content of the polarizing element is lower than the equilibrium water content of a temperature of 20 ° C. and a relative humidity of 30%, the handleability of the polarizing element is lowered and the polarizing element is easily cracked. When the water content of the polarizing element exceeds the equilibrium water content of a temperature of 20 ° C. and a relative humidity of 50%, the transmittance of the polarizing element tends to decrease. It is presumed that when the water content of the polarizing element is high, polyene formation of the PVA-based resin is likely to proceed. The water content of the polarizing element is the water content of the polarizing element in the polarizing plate.

As a method of confirming whether the water content of the polarizing element is within the range of the equilibrium water content of temperature 20 ° C. and relative humidity of 30% or less and the equilibrium water content of temperature 20 ° C. and relative humidity of 50% or less, the above temperature and the above relative humidity. The polarizing element may be stored in an environment adjusted to the range of, and if there is no change in mass for a certain period of time, it can be considered that the balance with the environment has been reached, or adjusted to the range of the above temperature and the above relative humidity. It can be confirmed by calculating the equilibrium water content of the polarizing element in the environment in advance and comparing the water content of the polarizing element with the calculated equilibrium water content.

The method for manufacturing a polarizing element having a water content of 20 ° C. and a relative humidity of 30% or more and an equilibrium water content of a temperature of 20 ° C. and a relative humidity of 50% or less is not particularly limited. Examples thereof include a method of storing the polarizing element in an environment adjusted to a relative humidity range of 10 minutes or more and 3 hours or less, or a method of heat-treating at 30 ° C. or higher and 90 ° C. or lower.

As another preferable method for manufacturing a polarizing element having a water content, a laminate obtained by laminating a protective film on at least one surface of the polarizing element or a polarizing plate configured by using the polarizing element is provided with the temperature and the relative humidity. Examples thereof include a method of storing in an environment adjusted to the above range for 10 minutes or more and 120 hours or less, or a method of heat treatment at 30 ° C. or more and 90 ° C. or less. At the time of manufacturing the image display device adopting the interlayer filling configuration, the image display panel in which the polarizing plate is laminated on the image display cell is stored or stored in an environment adjusted to the above temperature and the above relative humidity range for 10 minutes or more and 3 hours or less. The front plate may be bonded after heating at 30 ° C. or higher and 90 ° C. or lower.

The water content of the polarizing element shall be adjusted so that the water content is within the above numerical range at the material stage of the polarizing element alone or a laminate of the polarizing element and the protective film and used to form the polarizing plate. Is preferable. If the water content is adjusted after the polarizing plate is configured, the curl becomes too large, and problems may easily occur when the polarizing plate is attached to the image display cell. By constructing a polarizing plate using a polarizing element adjusted to have the above-mentioned water content at the material stage before forming the polarizing plate, it is easy to obtain a polarizing plate having a polarizing element having a water content satisfying the above-mentioned numerical range. Can be configured in. With the polarizing plate attached to the image display cell, the water content of the polarizing element in the polarizing plate may be adjusted to be within the above numerical range. In this case, since the polarizing plate is attached to the image display cell, curling is unlikely to occur.

(Characteristic (b))
When the polarizing plate has the feature (b), the water content of the polarizing plate is equal to or higher than the equilibrium water content at a temperature of 20 ° C. and a relative humidity of 30%, and equal to or lower than the equilibrium water content at a temperature of 20 ° C. and a relative humidity of 50%. The water content of the polarizing plate is preferably equal to or less than the equilibrium water content at a temperature of 20 ° C. and a relative humidity of 45%, more preferably not less than the equilibrium water content of a temperature of 20 ° C. and a relative humidity of 42%, and further preferably relative to the temperature of 20 ° C. Humidity is 38% or less and equal to or less than the equilibrium moisture content. When the water content of the polarizing plate is lower than the equilibrium water content of a temperature of 20 ° C. and a relative humidity of 30%, the handleability of the polarizing plate is lowered and the polarizing plate is easily cracked. When the water content of the polarizing plate exceeds the equilibrium water content at a temperature of 20 ° C. and a relative humidity of 50%, the transmittance of the polarizing element tends to decrease. It is presumed that when the water content of the polarizing plate is high, polyene formation of the PVA-based resin is likely to proceed.

As a method of confirming whether the water content of the polarizing plate is within the range of the equilibrium water content of a temperature of 20 ° C. and a relative humidity of 30% or less and the equilibrium water content of a temperature of 20 ° C. and a relative humidity of 50% or less, the above temperature and the above relative humidity. The polarizing plate is stored in an environment adjusted to the range of, and if there is no change in mass for a certain period of time, it can be considered that the equilibrium with the environment has been reached, or it is adjusted to the range of the above temperature and the above relative humidity. It can be confirmed by calculating the equilibrium water content of the polarizing plate in the environment in advance and comparing the water content of the polarizing plate with the pre-calculated equilibrium water content.

The method for producing a polarizing plate having a water content of 20 ° C. and a relative humidity of 30% or more and an equilibrium water content of a temperature of 20 ° C. and a relative humidity of 50% or less is not particularly limited. Examples thereof include a method of storing the polarizing plate in an environment adjusted to a relative humidity range of 10 minutes or more and 3 hours or less, or a method of heat-treating at 30 ° C. or higher and 90 ° C. or lower.

At the time of manufacturing the image display device adopting the interlayer filling configuration, the image display panel in which the polarizing plate is laminated on the image display cell is stored or stored in an environment adjusted to the above temperature and the above relative humidity range for 10 minutes or more and 3 hours or less. The front plate may be bonded after heating at 30 ° C. or higher and 90 ° C. or lower.

(Urea compound)
The polarizing element may further contain a urea-based compound. A polarizing element containing a urea-based compound can further suppress a decrease in transmittance. The urea-based compound may be the same as the urea-based compound that can be contained in the adhesive described later. As a method for including the urea compound in the polarizing element, the same method as the method for containing the blocked isocyanate compound in the polarizing element can be used. The urea-based compound may be contained in the process of manufacturing the polarizing element, or may be contained in the adhesive for laminating the polarizing element and the transparent protective film described later, and may be contained in the polarizing element.

(Manufacturing method of polarizing element)
The manufacturing method of the polarizing element is not particularly limited, but a method of feeding out a PVA-based resin film wound in a roll shape in advance and performing stretching, dyeing, cross-linking, etc. (hereinafter referred to as “manufacturing method 1”) or A method including a step of applying a coating liquid containing a PVA-based resin on a base film to form a PVA-based resin layer as a coating layer, and stretching the obtained laminate (hereinafter referred to as "manufacturing method 2"). .) Is typical.

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

The swelling step is a treatment step of immersing the PVA-based resin film in the swelling bath. By the swelling step, stains on the surface of the PVA-based resin film, blocking agents, and the like can be removed, and by swelling the PVA-based resin film, uneven dyeing can be suppressed. For the swelling bath, a medium containing water as a main component, such as water, distilled water, and pure water, is usually used. A surfactant, alcohol or the like may be appropriately added to the swelling bath according to a conventional method. From the viewpoint of controlling the potassium content of the polarizing element, potassium iodide may be used in the swelling bath, and in this case, the concentration of potassium iodide in the swelling bath may be 1.5% by mass or less. It is more preferably 1.0% by mass or less, and even more preferably 0.5% by mass or less.

The temperature of the swelling bath is preferably 10 ° C. or higher and 60 ° C. or lower, more preferably 15 ° C. or higher and 45 ° C. or lower, and further preferably 18 ° C. or higher and 30 ° C. or lower. The immersion time in the swelling bath cannot be unconditionally determined because the degree of swelling of the PVA-based resin film is affected by the temperature of the swelling bath, but it is preferably about 5 seconds or more and 300 seconds or less, preferably 10 seconds or more and 200 seconds. It is more preferably about 20 seconds or more, and further preferably about 100 seconds or less. The swelling step may be performed only once, or may be performed a plurality of times as needed.

The dyeing step is a treatment step of immersing the PVA-based resin film in a dyeing bath (iodine solution), and can adsorb and orient a dichroic dye such as iodine on the PVA-based resin film. The iodine solution is usually preferably an aqueous iodine solution and contains iodine and iodide as a solubilizing agent. Examples of iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, titanium iodide and the like. Can be mentioned. Among these, potassium iodide is preferable from the viewpoint of controlling the content of potassium in the polarizing element.

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

The temperature of the dyeing bath is preferably 10 ° C. or higher and 50 ° C. or lower, more preferably 15 ° C. or higher and 45 ° C. or lower, and further preferably 18 ° C. or higher and 30 ° C. or lower. The immersion time in the dyeing bath cannot be unconditionally determined because the degree of dyeing of the PVA-based resin film is affected by the temperature of the dyeing bath, but it is preferably about 10 seconds or more and 300 seconds or less, preferably 20 seconds or more and 240 seconds. It is more preferably about the following. The dyeing step may be carried out only once or may be carried out multiple times as needed.

The cross-linking step is a treatment step in which the PVA-based resin film dyed in the dyeing step is immersed in a treatment bath (cross-linking bath) containing a boron compound, and the polyvinyl alcohol-based resin film is cross-linked by the boron compound to form iodine. Mole or dye molecule can be adsorbed on the crosslinked structure. Examples of the boron compound include boric acid, borate, borax and the like. The cross-linking bath is generally an aqueous solution, but may be a mixed solution of an organic solvent and water that is miscible with water. The cross-linking bath preferably contains potassium iodide from the viewpoint of controlling the content of potassium in the polarizing element.

In the cross-linking bath, the concentration of the boron compound is preferably 1% by mass or more and 15% by mass or less, more preferably 1.5% by mass or more and 10% by mass or less, and 2% by mass or more and 5% by mass or less. It is more preferably about the following. When potassium iodide is used in the cross-linking bath, the concentration of potassium iodide in the cross-linking bath is preferably about 1% by mass or more and 15% by mass or less, and preferably about 1.5% by mass or more and about 10% by mass or less. It is more preferable, and it is more preferable that it is about 2% by mass or more and 5% by mass or less.

The temperature of the cross-linking bath is preferably about 20 ° C. or higher and 70 ° C. or lower, and more preferably about 30 ° C. or higher and 60 ° C. or lower. The immersion time in the cross-linking bath cannot be unconditionally determined because the degree of cross-linking of the PVA-based resin film is affected by the temperature of the cross-linking bath, but is preferably about 5 seconds or more and 300 seconds or less, preferably 10 seconds or more and 200 seconds. It is more preferably about the following. The cross-linking step may be carried out only once, or may be carried out a plurality of times as needed.

The stretching step is a treatment step of stretching the PVA-based resin film to a predetermined magnification in at least one direction. Generally, the PVA-based resin film is uniaxially stretched in the transport direction (longitudinal direction). The stretching method is not particularly limited, and either a wet stretching method or a dry stretching method can be adopted. The stretching step may be carried out only once, or may be carried out a plurality of times as needed. The stretching step may be performed at any stage in the manufacture of the polarizing element.

As the treatment bath (stretching bath) in the wet stretching method, a solvent such as water or an organic solvent miscible with water and a mixed solution of water can be usually used. The stretching bath preferably contains potassium iodide from the viewpoint of controlling the content of potassium in the polarizing element. When potassium iodide is used in the stretching bath, the concentration of potassium iodide in the stretching bath is preferably about 1% by mass or more and 15% by mass or less, and preferably about 2% by mass or more and about 10% by mass or less. More preferably, it is about 3% by mass or more and 6% by mass or less. The treatment bath (stretching bath) may contain a boron compound from the viewpoint of suppressing film breakage during stretching. When a boron compound is contained, the concentration of the boron compound in the stretching bath is preferably about 1% by mass or more and 15% by mass or less, and more preferably about 1.5% by mass or more and 10% by mass or less. It is more preferably about mass% or more and 5% by mass or less.

The temperature of the stretching bath is preferably 25 ° C. or higher and 80 ° C. or lower, more preferably 40 ° C. or higher and 75 ° C. or lower, and further preferably 50 ° C. or higher and 70 ° C. or lower. The immersion time in the stretching bath cannot be unconditionally determined because the degree of stretching of the PVA-based resin film is affected by the temperature of the stretching bath, but it is preferably about 10 seconds or more and 800 seconds or less, preferably 30 seconds or more and 500 seconds. It is more preferably about the following. 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. The dry stretching method may be applied together with the drying step.

The total draw ratio (cumulative draw ratio) applied to the polyvinyl alcohol-based resin film can be appropriately set according to the purpose, but is preferably about 2 times or more and 7 times or less, and is preferably about 3 times or more and 6.8 times or less. It is more preferable that the amount is 3.5 times or more and 6.5 times or less.

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

The temperature of the washing bath is preferably 5 ° C. or higher and 50 ° C. or lower, more preferably 10 ° C. or higher and 40 ° C. or lower, and further preferably 15 ° C. or higher and 30 ° C. or lower. The immersion time in the washing bath cannot be unconditionally determined because the degree of washing of the PVA-based resin film is affected by the temperature of the washing bath, but it is preferably about 1 second or more and 100 seconds or less, preferably 2 seconds or more and 50 seconds. It is more preferably about 3 seconds or more and 20 seconds or less. The cleaning step may be performed only once, or may be performed a plurality of 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 element. Drying is carried out by any suitable method, and examples thereof include natural drying, blast drying, and heat drying.

The production method 2 includes a step of applying a coating liquid containing a PVA-based resin on a base film, a step of uniaxially stretching the obtained laminated film, and a step of uniaxially stretching the PVA-based resin layer of the uniaxially stretched laminated film with a dichroic dye. It can be produced through a step of adsorbing it to form a polarizing element by dyeing, a step of treating a film on which a 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 base film used for forming the polarizing element may be used as a protective layer for the polarizing element. If necessary, the base film may be peeled off from the polarizing element.

<Transparent protective film>
The transparent protective film used in the present embodiment (hereinafter, also simply referred to as “protective film”) is bonded to at least one surface of the polarizing element via an adhesive layer. This transparent protective film is attached to one side or both sides of the polarizing element, but it is preferable that the transparent protective film is attached to both sides.

The protective film may have other optical functions at the same time, or may be formed in a laminated structure in which a plurality of layers are laminated. The film thickness of the protective film is preferably thin from the viewpoint of optical characteristics, but if it is too thin, the strength is lowered and the workability is inferior. The appropriate film thickness is 5 μm or more and 100 μm or less, preferably 10 μm or more and 80 μm or less, and more preferably 15 μm or more and 70 μm or less.

As the protective film, a film such as a cellulose acylate film, a film made of a polycarbonate resin, a film made of a cycloolefin resin such as norbornene, a (meth) acrylic polymer film, or a polyester resin film such as polyethylene terephthalate is used. be able to. When a protective film is attached to both sides of a polarizing element using a water-based adhesive such as PVA adhesive, the protective film on at least one side is either a cellulose acylate film or a (meth) acrylic polymer film in terms of moisture permeability. Of these, a cellulose acylate film is preferable.

At least one protective film may have a phase difference function for the purpose of compensating the viewing angle or the like. In that case, the protective film itself may have a retardation function, may have a separate retardation layer, or may be a combination of both. The film having the retardation function may be directly attached to the polarizing element via an adhesive, but may be attached via an adhesive or an adhesive via another protective film attached to the polarizing element. It may have a different configuration.

<Adhesive layer>
An adhesive containing a blocked isocyanate compound is used as an adhesive constituting an adhesive layer for adhering a protective film to the polarizing element. As the adhesive, a water-based adhesive, a solvent-based adhesive, an active energy ray-curable adhesive, or the like can be used, but it is preferably a water-based adhesive and preferably contains a PVA-based resin. By using an adhesive containing a blocked isocyanate compound, it is possible to suppress a decrease in the transmittance of the polarizing plate in a high temperature environment.

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

The following description of the adhesive is a description of a preferable range in the case where the polarizing element does not contain the blocked isocyanate compound at the time of manufacturing the polarizing element. When the polarizing element contains a blocked isocyanate compound, the following values may be appropriately adjusted. As a specific example of the blocked isocyanate compound, the same blocked isocyanate compound contained in the above-mentioned polarizing element can be used. In the process of forming the adhesive layer through the drying step at the time of bonding the polarizing element and the protective film, a part of the blocked isocyanate compound may be transferred from the adhesive layer to the polarizing element or the like.

When the adhesive is a water-based adhesive containing a PVA-based resin, the content of the blocked isocyanate compound in the adhesive is preferably 1 part by mass or more and 500 parts by mass or less with respect to 100 parts by mass of the PVA-based resin. It is preferably 1.5 parts by mass or more and 400 parts by mass or less, more preferably 2 parts by mass or more and 350 parts by mass or less, and may be 10 parts by mass or more. If it is less than 1 part by mass, the effect of improving high temperature durability may not be sufficiently obtained. On the other hand, when the content of the blocked isocyanate compound exceeds 500 parts by mass, crystals may precipitate after drying, which may cause problems such as an increase in haze.

In a configuration in which a transparent protective film is bonded to both sides of a polarizing element via an adhesive layer, even if only one of the adhesive layers on both sides of the polarizing element contains a blocked isocyanate compound. However, it is preferable that the adhesive layers on both sides are both layers containing a blocked isocyanate compound.

In order to meet the demand for thinner polarizing plates, polarizing plates having a transparent protective film on only one side of the polarizing element have been developed. Also in this configuration, the transparent protective film is laminated via the adhesive layer containing the blocked isocyanate compound. As a method for producing a polarizing plate having a transparent protective film on only one side of such a polarizing element, first, a polarizing plate having a transparent protective film bonded to both sides via an adhesive layer is produced, and then one of the transparent protective films is produced. A method of peeling off is conceivable. When such a production method is used, only one of the adhesive layers may contain the blocked isocyanate compound, but the adhesive layers on both sides may both contain the blocked isocyanate compound. preferable. When the adhesive layer containing the blocked isocyanate compound is used on only one side of the polarizing element, it is preferable that the adhesive layer on the film side that does not peel off contains the blocked isocyanate compound.

(Water-based adhesive)
As the water-based adhesive, any suitable water-based adhesive can be adopted, but a water-based adhesive containing a PVA-based resin (PVA-based adhesive) is preferably used. The average degree of polymerization of the PVA-based resin contained in the water-based adhesive is preferably about 100 or more and 5500 or less, and more preferably 1000 or more and 4500 or less from the viewpoint of adhesiveness. The average saponification degree is preferably about 85 mol% or more and 100 mol% or less, and more preferably 90 mol% or more and 100 mol% or less from the viewpoint of adhesiveness.

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

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

When the PVA-based resin is an acetacetyl group-containing PVA-based resin, the cross-linking agent is preferably glyoxal, glyoxal salt, or methylol melamine, and may be glyoxal or glyoxal salt. More preferably, glyoxal is particularly preferable.

The water-based adhesive may also contain an organic solvent. The organic solvent is preferably alcohols in that it is miscible with water, and more preferably methanol or ethanol among the alcohols. The concentration of methanol in the water-based adhesive is preferably 10% by mass or more and 70% by mass or less, more preferably 15% by mass or more and 60% by mass or less, and further preferably 20% by mass or more and 60% by mass or less. When the concentration of methanol is 10% by mass or more, it becomes easier to suppress polyene formation of the PVA-based resin in a high temperature environment. Further, when the content of methanol is 70% by mass or less, deterioration of hue can be suppressed. Some urea derivatives have low solubility in water, but some have sufficient solubility in alcohol. In that case, it is also preferable to dissolve the urea compound in alcohol to prepare an alcohol solution of the urea compound, and then add the alcohol solution of the urea compound to the PVA aqueous solution to prepare an adhesive. be.

(Active energy ray-curable adhesive)
The active energy ray-curable adhesive is an adhesive that cures by irradiating with active energy rays such as ultraviolet rays, and is, for example, an adhesive containing a polymerizable compound and a photopolymerizable initiator, and an adhesive containing a photoreactive resin. , Adhesives containing a binder resin and a photoreactive cross-linking agent, and the like. Examples of the polymerizable compound include a photopolymerizable monomer such as a photocurable epoxy-based monomer, a photocurable acrylic-based monomer, and a photocurable urethane-based monomer, and an oligomer derived from these monomers. Examples of the photopolymerization initiator include compounds containing substances that generate active species such as neutral radicals, anionic radicals, and cationic radicals by irradiating them with active energy rays such as ultraviolet rays.

(Urea compound)
The adhesive may further contain at least one urea compound selected from urea, a urea derivative, thiourea and a thiourea derivative. When the adhesive layer composed of the adhesive contains a urea compound, the high temperature durability can be further improved. A part of the urea-based compound may be transferred from the adhesive layer to the polarizing element or the like in the process of forming the adhesive layer through the drying step at the time of adhering the adhesive to the protective film. Urea-based compounds include water-soluble compounds and sparingly water-soluble compounds, and either urea-based compound can be used. When a poorly water-soluble urea compound is used as a water-soluble adhesive, it is preferable to devise a dispersion method so that haze does not increase after the adhesive layer is formed.

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

(Urea derivative)
A urea derivative is a compound in which at least one of the four hydrogen atoms of a urea molecule is substituted with a substituent. In this case, the substituent is not particularly limited, but is preferably a substituent composed of a carbon atom, a hydrogen atom and an oxygen atom.

Specific examples of urea derivatives include methyl urea, ethyl urea, propyl urea, butyl urea, isobutyl urea, N-octadecyl urea, 2-hydroxyethyl urea, hydroxyurea, acetylurea, allylurea, and 2-propynyl as monosubstituted ureas. Examples thereof include urea, cyclohexyl urea, phenylurea, 3-hydroxyphenylurea, (4-methoxyphenyl) urea, benzylurea, benzoylurea, o-tolylurea and p-tolylurea. As disubstituted ureas, 1,1-dimethylurea, 1,3-dimethylurea, 1,1-diethylurea, 1,3-diethylurea, 1,3-bis (hydroxymethyl) urea, 1,3-tert- Butyl urea, 1,3-dicyclohexylurea, 1,3-diphenylurea, 1,3-bis (4-methoxyphenyl) urea, 1-acetyl-3-methylurea, 2-imidazolidinone (ethyleneurea), tetrahydro -2-Pyrimidinone (propyleneurea) can be mentioned. As 4-substituted urea, tetramethylurea, 1,1,3,3-tetraethylurea, 1,1,3,3-tetrabutylurea, 1,3-dimethoxy-1,3-dimethylurea, 1,3-dimethyl- Examples thereof include 2-imidazolidinone and 1,3-dimethyl-3,4,5,6-tetrahydro-2 (1H) -pyrimidinone.

(Thiourea derivative)
A thiourea derivative is a compound in which at least one of the four hydrogen atoms of a thiourea molecule is substituted with a substituent. In this case, the substituent is not particularly limited, but is preferably a substituent composed of a carbon atom, a hydrogen atom and an oxygen atom.

Specific examples of the thiourea derivative include N-methylthiourea, ethylthiourea, propylthiourea, isopropylthiourea, 1-butylthiourea, cyclohexylthiourea, N-acetylthiourea, and N-allylthiourea, as monosubstituted thioureas (2). -Methoxyethyl) thiourea, N-phenylthiourea, (4-methoxyphenyl) thiourea, N- (2-methoxyphenyl) thiourea, N- (1-naphthyl) thiourea, (2-pyridyl) thiourea, Examples thereof include o-tolylthiourea and p-tolylthiourea. As bi-substituted thiourea, 1,1-dimethylthiourea, 1,3-dimethylthiourea, 1,1-diethylthiourea, 1,3-diethylthiourea, 1,3-dibutylthiourea, 1,3-diisopropylthiourea, 1 , 3-Dicyclohexylthiourea, N, N-diphenylthiourea, N, N'-diphenylthiourea, 1,3-di (o-tolyl) thiourea, 1,3-di (p-tolyl) thiourea, Examples thereof include 1-benzyl-3-phenylthiourea, 1-methyl-3-phenylthiourea, N-allyl-N'-(2-hydroxyethyl) thiourea and ethylenethiourea. Examples of the 3-substituted thiourea include trimethylthiourea. Examples of the 4-substituted thiourea include tetramethylthiourea and 1,1,3,3-tetraethylthiourea.

Among the urea-based compounds, a urea derivative or a thiourea derivative is preferable, and a urea derivative is preferable because it can further suppress a decrease in transmittance in a high temperature environment when used in an image display device having an interlayer filling configuration. More preferred. Among the urea derivatives, mono-substituted urea or di-substituted urea is preferable, and mono-substituted urea is more preferable. The bi-substituted urea includes 1,1-substituted urea and 1,3-substituted urea, but 1,3-substituted urea is more preferable.

<Blocked isocyanate compound-containing layer>
The blocked isocyanate compound is not limited to the case where it is contained in the adhesive layer as described above, and is also contained in layers other than the adhesive layer from the viewpoint of improving the high temperature durability of the polarizing plate. May be good. In a polarizing plate having a transparent protective film on only one side, a cured layer may be laminated on the surface opposite to the transparent protective film of the polarizing element from the viewpoint of improving physical strength.

In the present embodiment, such a cured layer may contain a blocked isocyanate compound to form a blocked isocyanate compound-containing layer. Normally, such a cured layer is formed from a curable composition containing an organic solvent, but paragraphs [0020] to [0042] of JP-A-2017-075986 indicate that the active energy ray-curable polymer composition is aqueous. A method of forming such a hardened layer from a solution is described. Since many blocked isocyanate compounds are water-soluble, a water-soluble blocked isocyanate compound may be contained in such a composition.

The blocked isocyanate compound-containing layer preferably contains at least one blocked isocyanate compound and a binder. Examples of the binder include a polymer binder, a heat-curable resin binder, an active energy ray-curable resin binder, and the like, and any of these binders can be preferably used.

The thickness of the blocked isocyanate compound-containing layer is preferably 0.1 μm or more and 20 μm or less, more preferably 0.5 μm or more and 15 μm or less, and further preferably 1 μm or more and 10 μm or less.

[Manufacturing method of polarizing plate]
The method for manufacturing a polarizing plate of the present embodiment includes a water content adjusting step and a laminating step. In the water content adjusting step, when the polarizing plate having the characteristic (a) is manufactured, the water content of the polarizing element is equal to or higher than the equilibrium water content at a temperature of 20 ° C. and a relative humidity of 30%, and the equilibrium water content at a temperature of 20 ° C. and a relative humidity of 50%. Adjust the water content of the polarizing element so that it is less than or equal to the rate. The water content of the polarizing element can be adjusted according to the description of the water content of the polarizing element described above. In the water content adjusting step, when a polarizing plate having the characteristic (b) is produced, the moisture content of the polarizing plate is equal to or higher than the equilibrium water content at a temperature of 20 ° C. and a relative humidity of 30%, and the equilibrium water content at a temperature of 20 ° C. and a relative humidity of 50%. Adjust the water content of the polarizing plate so that it is less than or equal to the rate. The water content of the polarizing plate can be adjusted according to the description of the water content of the polarizing plate described above. In the laminating step, the polarizing element and the transparent protective film are laminated via the adhesive layer. In the laminating step, for example, the polarizing element that has not been treated to contain the blocked isocyanate compound and the transparent protective film are bonded together with an adhesive containing the blocked isocyanate compound. The order of the water content adjusting step and the laminating step is not limited, and the water content adjusting step and the laminating step may be performed in parallel.

[Configuration of image display device]
The polarizing plate of the present embodiment is used in various image display devices such as a liquid crystal display device and an organic EL display device. When the image display device has an interlayer filling configuration 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, the transmittance in a high temperature environment. Is easy to decrease. In the image display device using the polarizing plate of the present embodiment, it is possible to suppress a decrease in the transmittance of the polarizing plate in a high temperature environment even if the interlayer filling configuration is used. An example of the image display device is a configuration having an image display cell, a first pressure-sensitive adhesive layer laminated on the visible side surface of the image display cell, and a polarizing plate laminated on the visible side surface of the first pressure-sensitive adhesive layer. Will be done. Such an image display device may further include a second pressure-sensitive adhesive layer laminated on the visible side surface of the polarizing plate, and a transparent member laminated on the surface of the second pressure-sensitive adhesive layer. In particular, in the polarizing plate of the present embodiment, a transparent member is arranged on the visual side of the image display device, the polarizing plate and the image display cell are bonded by the first pressure-sensitive adhesive layer, and the polarizing plate and the transparent member are second-bonded. It is suitably used for an image display device having an interlayer filling structure bonded by an agent layer. In the present specification, either one or both of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer may be simply referred to as "adhesive layer". The member used for bonding the polarizing plate and the image display cell and the member used for bonding the polarizing plate and the transparent member are not limited to the pressure-sensitive adhesive layer, but are an adhesive layer. May be good.

<Image display cell>
Examples of the image display cell include a liquid crystal cell and an organic EL cell. The liquid crystal cell includes a reflective liquid crystal cell that uses external light, a transmissive liquid crystal cell that uses light from a light source such as a backlight, and a semi-transmissive semi-reflective type that uses both external light and light from a light source. Any liquid crystal cell may be used. When the liquid crystal cell uses the light from the light source, the image display device (liquid crystal display device) has a polarizing plate arranged on the side opposite to the visual recognition side of the image display cell (liquid crystal cell), and further arranges the light source. Will be done. It is preferable that the polarizing plate on the light source side and the liquid crystal cell are bonded to each other via an appropriate adhesive layer. As the driving method of the liquid crystal cell, for example, any type such as VA mode, IPS mode, TN mode, STN mode and bend orientation (π type) can be used.

As the organic EL cell, a cell in which a transparent electrode, an organic light emitting layer, and a metal electrode are sequentially laminated on a transparent substrate to form a light emitting body (organic electroluminescence light emitting body) or the like is preferably used. The organic light emitting layer is a laminated body of various organic thin films, for example, a laminated body of a hole injection layer made of a triphenylamine derivative or the like and a light emitting layer made of a fluorescent organic solid such as anthracene, or light emission thereof. Various layer configurations can be adopted, such as a laminated body of an electron-injected layer composed of a layer and a perylene derivative, or a laminated body of a hole-injected layer, a light-emitting layer, and an electron-injected layer.

<Attachment of image display cell and polarizing plate>
An adhesive layer (adhesive sheet) is preferably used for bonding the image display cell and the polarizing plate. Above all, a method of bonding a polarizing plate with an adhesive layer having an adhesive layer attached to one surface of the polarizing plate to an image display cell is preferable from the viewpoint of workability and the like. The pressure-sensitive adhesive layer may be attached to the polarizing plate by an appropriate method. As an example, a pressure-sensitive adhesive solution of about 10% by mass or more and 40% by mass or less is prepared by dissolving or dispersing the base polymer or its composition in a solvent consisting of an appropriate solvent such as toluene or ethyl acetate alone or as a mixture. Then, a method of directly attaching the adhesive layer on the polarizing plate by an appropriate developing method such as a casting method or a coating method, a method of forming an adhesive layer on the separator and transferring it to the polarizing plate, and the like can be mentioned. ..

<Adhesive layer>
The pressure-sensitive adhesive layer may be composed of one layer or two or more layers, but is preferably composed of one layer. The pressure-sensitive adhesive layer can be composed of a pressure-sensitive adhesive composition containing a (meth) acrylic resin, a rubber-based resin, a urethane-based resin, an ester-based resin, a silicone-based resin, and a polyvinyl ether-based resin as main components. Among them, a pressure-sensitive adhesive composition using a (meth) acrylic resin having excellent transparency, weather resistance, heat resistance and the like as a base polymer is preferable. The pressure-sensitive adhesive composition may be an active energy ray-curable type or a thermosetting type.

Examples of the (meth) acrylic resin (base polymer) used in the pressure-sensitive adhesive composition include butyl (meth) acrylate, ethyl (meth) acrylate, isooctyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and the like. A polymer or copolymer containing one or more of the (meth) acrylic acid esters as monomers is preferably used. It is preferable that the base polymer is copolymerized with a polar monomer. Examples of the polar monomer include (meth) acrylic acid compound, (meth) acrylic acid 2-hydroxypropyl compound, (meth) acrylic acid hydroxyethyl compound, (meth) acrylamide compound, and N, N-dimethylaminoethyl (meth) acrylate compound. , A monomer having a carboxyl group, a hydroxyl group, an amide group, an amino group, an epoxy group and the like, such as a glycidyl (meth) acrylate compound, can be mentioned.

The pressure-sensitive adhesive composition may contain only the above-mentioned base polymer, but usually further contains a cross-linking agent. The cross-linking agent is a metal ion having a valence of 2 or more, which is a metal ion that forms a carboxylic acid metal salt with a carboxyl group, a polyamine compound that forms an amide bond with the carboxyl group, and a carboxyl group. Examples thereof include polyepoxy compounds or polyols that form an ester bond in the above, and polyisocyanate compounds that form an amide bond with a carboxyl group. Of these, polyisocyanate compounds are preferable.

The active energy ray-curable pressure-sensitive adhesive composition has a property of being cured by being irradiated with active energy rays such as ultraviolet rays and electron beams, and has adhesiveness even before irradiation with active energy rays, such as a film. It has the property that it can be brought into close contact with the adherend of No. 1 and can be cured by irradiation with active energy rays to adjust the adhesion force. The active energy ray-curable pressure-sensitive adhesive composition is preferably an ultraviolet-curable type. The active energy ray-curable pressure-sensitive adhesive composition further contains an active energy ray-polymerizable compound in addition to the base polymer and the cross-linking agent. If necessary, a photopolymerization initiator, a photosensitizer, or the like may be contained.

The pressure-sensitive adhesive composition includes fine particles for imparting light scattering, beads (resin beads, glass beads, etc.), glass fibers, resins other than the base polymer, a pressure-sensitive imparting agent, and a filler (metal powder and other inorganic powders). Etc.), antioxidants, UV absorbers, dyes, pigments, colorants, defoaming agents, corrosion inhibitors, photopolymerization initiators and other additives can be included.

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

The pressure-sensitive adhesive composition may be directly applied to the release-treated surface of the separate film to form a pressure-sensitive adhesive layer, and the pressure-sensitive adhesive layer with the separate film may be laminated on the surface of the polarizing body. The pressure-sensitive adhesive composition may be directly applied to the surface of the polarizing plate to form the pressure-sensitive adhesive layer, and a separate film may be laminated on the outer surface of the pressure-sensitive adhesive layer.

When the pressure-sensitive adhesive layer is provided on the surface of the polarizing plate, it is preferable to perform surface activation treatment such as plasma treatment and corona treatment on the bonded surface of the polarizing plate and / or the bonded surface of the pressure-sensitive adhesive layer. It is more preferable to apply the treatment.

Further, the pressure-sensitive adhesive composition is applied onto the second separate film to form a pressure-sensitive adhesive layer, and a pressure-sensitive adhesive sheet in which the separate film is laminated on the formed pressure-sensitive adhesive layer is prepared, and the second pressure-sensitive adhesive sheet is used as a second. The pressure-sensitive adhesive layer with the separate film after the separate film is peeled off may be laminated on the polarizing plate. As the second separate film, a film having a weaker adhesion to the pressure-sensitive adhesive layer than the separate film and being easily peeled off is used.

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

<Transparent member>
Examples of the transparent member arranged on the visual side of the image display device include a transparent plate (window layer), a touch panel, and the like. As the transparent plate, a transparent plate having appropriate mechanical strength and thickness is used. Examples of such a transparent plate include a transparent resin plate such as a polyimide resin, an acrylic resin or a polycarbonate resin, or a glass plate. A functional layer such as an antireflection layer may be laminated on the visible side of the transparent plate. When the transparent plate is a transparent resin plate, a hard coat layer may be laminated to increase the physical strength, or a low moisture permeability layer may be laminated to reduce the moisture permeability. As the touch panel, various touch panels such as a resistance film method, a capacitance method, an optical method, an ultrasonic method, and a glass plate or a transparent resin plate having a touch sensor function are used. When a capacitive touch panel is used as the transparent member, it is preferable to provide a transparent plate made of glass or a transparent resin plate on the visual side of the touch panel.

<Lasting of polarizing plate and transparent member>
A pressure-sensitive adhesive or an active energy ray-curable adhesive is preferably used for bonding the polarizing plate and the transparent member. When a pressure-sensitive adhesive is used, the pressure-sensitive adhesive can be attached by an appropriate method. Specific examples of the attachment method include the attachment method of the pressure-sensitive adhesive layer used for bonding the image display cell and the polarizing plate described above.

When an active energy ray-curable adhesive is used, a dam material is provided so as to surround the peripheral edge on the image display panel in order to prevent the adhesive solution from spreading before curing, and a transparent member is placed on the dam material. A method of placing and injecting an adhesive solution is preferably used. After injecting the adhesive solution, alignment and defoaming are performed as necessary, and then activation energy rays are irradiated to perform curing.

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

(Manufacturing of polarizing element 1)
A 40 μm-thick PVA film made of PVA having an average degree of polymerization of about 2400 and a degree of polymerization of 99.9 mol% or more was uniaxially stretched about 5 times by a dry method, and was purely 60 ° C. while maintaining a tense state. After soaking in water for 1 minute, it was immersed in an aqueous solution having a weight ratio of iodine / potassium iodide / water of 0.05 / 5/100 at 28 ° C. for 60 seconds. Then, it was immersed in an aqueous solution having a weight ratio of potassium iodide / boric acid / water of 8.5 / 8.5 / 100 at 72 ° C. for 300 seconds. Subsequently, the mixture was washed with pure water at 26 ° C. for 20 seconds and then dried at 65 ° C. to obtain a polarizing element 1 having a thickness of 15 μm in which iodine was adsorbed and oriented on PVA. A digital micrometer "MH-15M" manufactured by Nikon Corporation was used for measuring the thickness of the polarizing element.

(Preparation of PVA solution for adhesive)
50 g of a modified PVA resin containing an acetoacetyl group (“Gosenex Z-410” manufactured by Mitsubishi Chemical Co., Ltd.) is dissolved in 950 g of pure water, heated at 90 ° C for 2 hours, cooled to room temperature, and cooled to room temperature to provide a PVA solution for adhesives. Got

Water-based blocked isocyanate compound dispersion (“TRIXENE AQUA BI 200” manufactured by LANXESS, isocyanate is HDI trimer, blocking group is 3,5-dimethylpyrazole, and 1-methyl-2-pyrrolidone is contained as a dispersant in the PVA solution for adhesive. , Solid content 40%, NCO theoretical value 4.50%) were mixed so as to have the blending amounts shown in Table 1, and pure water was further added to prepare an adhesive 1 having a PVA concentration of 3.0% by mass.

By the same method, an adhesive 2 containing no blocked isocyanate compound and having a PVA concentration of 3.0% by mass was prepared.

(Preparation of transparent protective film)
A commercially available cellulose acylate film TD40 (manufactured by FUJIFILM Corporation, film thickness 40 μm) was immersed in a 1.5 mol / L NaOH aqueous solution (saponification solution) maintained at 55 ° C. for 2 minutes, and then the film was washed with water. Then, the film was immersed in a 0.05 mol / L sulfuric acid aqueous solution at 25 ° C. for 30 seconds and then passed through a water washing bath under running water for another 30 seconds to neutralize the film. Then, after draining water with an air knife three times to remove water from the film, the film was allowed to stay in a drying zone at 70 ° C. for 15 seconds to be dried to prepare a saponified film, which was used as a transparent protective film 1.

(Manufacturing of polarizing plate)
A transparent protective film 1 was bonded to both sides of the polarizing element 1 via an adhesive 1 using a roll bonding machine, and then dried at 80 ° C. for 5 minutes to obtain a polarizing plate 1. The adhesive layer was adjusted so that the thickness after drying was 50 nm on both sides.

The polarizing plate 2 was produced by the same method as the method for producing the polarizing plate 1, except that the adhesive 2 was used instead of the adhesive 1.

(Adjustment of water content of polarizing plate (polarizing element))
Polarizers 1 and 2 were stored at a temperature of 20 ° C. and a relative humidity of 30%, 35%, 40%, 45%, 50% or 55% for 72 hours. Moisture content was measured using the Karl Fischer method at storage 66 hours, 69 hours and 72 hours. Under any humidity condition, the water content values did not change after storage for 66 hours, 69 hours, and 72 hours. Therefore, the water content of the polarizing plates 1 and 2 can be considered to be the same as the equilibrium water content of the storage environment. When the water content of the polarizing plate reaches equilibrium in a storage environment, it can be considered that the water content of the polarizing element in the polarizing plate also reaches equilibrium in the storage environment. Further, when the water content of the polarizing element in the polarizing plate reaches equilibrium in a certain storage environment, it can be considered that the water content of the polarizing plate also reaches equilibrium in the storage environment.

(Manufacturing of optical laminate)
Polarizers 1 and 2 were stored at a temperature of 20 ° C. and a relative humidity of 35%, 45%, 50% or 55% for 72 hours. Optical laminates 1 to 7 prepared to have the water content shown in Table 2 were obtained.

Acrylic adhesive (manufactured by Lintec Corporation, product number: # 7) was applied to both sides of the optical laminates 1 to 7 having the adjusted water content to obtain an optical laminate having an adhesive layer having a thickness of 25 μm. .. This optical laminate is cut into a size of 50 mm × 100 mm so that the absorption axis of the polarizing element is parallel to the long side, and non-alkali glass (“EAGLE XG” manufactured by Corning Inc.) is applied to the surface of each adhesive. An evaluation sample was prepared by laminating.

(Evaluation of single transmittance after high temperature durability test (105 ° C))
The evaluation sample was autoclaved at a temperature of 50 ° C. and a pressure of 5 kgf / cm ² (490.3 kPa) for 1 hour, and then left to stand in an environment of a temperature of 23 ° C. and a relative humidity of 55% for 24 hours. Then, the transmittance was measured (initial value), stored in a heating environment at a temperature of 105 ° C., and the transmittance was measured every 24 hours from 48 to 120 hours. The evaluation was performed according to the following criteria based on the time when the decrease in transmittance reached 5% or more with respect to the initial value. The results obtained are shown in Table 2.
The decrease in transmittance is 5% or less after 120 hours: A
When the decrease in transmittance reached 5% or more after 96 hours: B
When the decrease in transmittance reached 5% or more after 72 hours: C
If the decrease in transmittance is 5% or more after 48 hours: D

A polarizing plate having a polarizing element and a transparent protective film, the water content of the polarizing element is equal to or higher than the equilibrium water content of a temperature of 20 ° C. and a relative humidity of 30%, and equal to or lower than the equilibrium water content of a temperature of 20 ° C. and a relative humidity of 50%. The polarizing plate (optical laminates 1 to 3) in which the polarizing element and the transparent protective film are bonded together with an adhesive containing a blocked isocyanate compound does not easily decrease in transmittance even when exposed to a high temperature environment of 105 ° C for a long time. It was found that it has excellent high temperature durability.

Claims (11)

A polarizing plate having a polarizing element in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin layer, and a transparent protective film laminated on at least one surface of the polarizing element.
The polarizing element and the transparent protective film are bonded to each other by an adhesive layer formed of an adhesive containing a blocked isocyanate compound.
A polarizing plate having a water content of the polarizing element having a temperature of 20 ° C. and a relative humidity of 30% or more and a temperature of 20 ° C. and a relative humidity of 50% or less. A polarizing plate having a polarizing element in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin layer, and a transparent protective film laminated on at least one surface of the polarizing element.
The polarizing element and the transparent protective film are bonded to each other by an adhesive layer formed of an adhesive containing a blocked isocyanate compound.
A polarizing plate having a water content of the polarizing plate having a temperature of 20 ° C. and a relative humidity of 30% or more and an equilibrium water content of a temperature of 20 ° C. and a relative humidity of 50% or less. The polarizing plate according to claim 1 or 2, wherein the adhesive contains a polyvinyl alcohol-based resin. The polarizing plate according to claim 3, wherein the content of the blocked isocyanate compound in the adhesive is 1 part by mass or more and 500 parts by mass or less with respect to 100 parts by mass of the polyvinyl alcohol-based resin. The polarizing plate according to any one of claims 1 to 4, 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 1 to 5, wherein the blocked isocyanate compound comprises at least one selected from the group consisting of pyrazoles and N, N'-diarylform amidines as a blocking agent. The polarizing plate is used in an image display device and is used.
The polarizing plate according to any one of claims 1 to 6, wherein a solid layer is provided in contact with both surfaces of the polarizing plate in the image display device. 6. An image display device having a polarizing plate of. The image display device according to claim 8, further comprising a second pressure-sensitive adhesive layer laminated on the visible side surface of the polarizing plate and a transparent member laminated on the visible side surface of the second pressure-sensitive adhesive layer. The image display device according to claim 9, wherein the transparent member is a glass plate or a transparent resin plate. The image display device according to claim 9, wherein the transparent member is a touch panel.