JP7461860B2 - Polarizing plate and image display device using the same - Google Patents

Description

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

Image display devices, such as liquid crystal display devices and electroluminescence (EL) display devices (e.g., organic EL display devices, inorganic EL display devices), are rapidly becoming widespread. In image display devices, typically, a polarizing plate is attached to a display panel via an adhesive layer. In recent years, with the narrowing of the frame of image display devices and the development of so-called in-cell type image display devices in which a conductive layer for a touch panel is incorporated in the display panel, there is a demand for improving the antistatic performance of image display devices. As a result, there is a demand for an adhesive layer (low resistance adhesive layer) with excellent conductivity. However, polarizing plates including low resistance adhesive layers have a problem of insufficient durability in high temperature and high humidity environments. More specifically, polarizing plates including low resistance adhesive layers have problems such as the occurrence of granular protrusions or blisters in the protective layer, discoloration at the edges or discoloration such as red lines, and cracks in high temperature and high humidity environments, and a decrease in the single transmittance of the polarizing plate (effectively, the polarizer).

JP 2020-50879 A

The present invention has been made to solve the above-mentioned problems of the conventional art, and its main objective is to provide a polarizing plate that has excellent durability in high-temperature and high-humidity environments, despite having a low-resistance adhesive layer.

A polarizing plate according to an embodiment of the present invention has a polarizer, a protective layer provided on one side of the polarizer, a resin layer provided on the other side of the polarizer, and an adhesive layer provided on the resin layer on the side opposite the polarizer. The protective layer is made of a triacetyl cellulose film. The adhesive layer contains a conductive component and has a surface resistance value of 1.0×10 ⁸ Ω/□ to 1.0×10 ¹² Ω/□. The resin layer is a solidified or thermoset product of a coating film of a resin in an organic solvent solution, and has a thickness of 2 μm or less. A conductive component permeation suppression layer is provided between the polarizer and the protective layer.
In one embodiment, the protective layer is provided on only one side of the polarizer, and the resin layer is provided directly on the polarizer on the other side of the polarizer.
In one embodiment, the polarizing plate further has a hard coat layer on the opposite side of the protective layer to the polarizer.
In one embodiment, the resin constituting the resin layer has a glass transition temperature of 85° C. or higher and a weight average molecular weight Mw of 25,000 or higher.
In one embodiment, the conductive component permeation suppression layer is another hard coat layer. In another embodiment, the conductive component permeation suppression layer is another resin layer, which is a solidified or thermoset product of a coating film of an organic solvent solution of a resin, and which has a glass transition temperature of 85° C. or higher and a weight average molecular weight Mw of 25,000 or higher.
In one embodiment, the polarizer has a thickness of 10 μm or less.
According to another aspect of the present invention, there is provided an image display device, the image display device comprising the above polarizing plate.

According to an embodiment of the present invention, in a polarizing plate having a low-resistance adhesive layer and a protective layer composed of a triacetyl cellulose (TAC) film, a predetermined conductive component permeation suppression layer is provided between the polarizer and the protective layer, thereby realizing a polarizing plate with excellent durability in a high-temperature, high-humidity environment. More specifically, in a high-temperature, high-humidity environment, the occurrence of granular protrusions or blisters in the protective layer is suppressed, and discoloration or discoloration such as red lines at the edge of the polarizing plate and cracks are suppressed, and further, the single transmittance of the polarizing plate (effectively, the polarizer) can be maintained within an acceptable range.

1 is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention.

The following describes embodiments of the present invention, but the present invention is not limited to these embodiments.

A. Overall Configuration of Polarizing Plate FIG. 1 is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention. The polarizing plate 100 in the illustrated example has a polarizer 10, a protective layer 20 provided on one side of the polarizer 10, a resin layer 40 provided on the other side of the polarizer 10, and a pressure-sensitive adhesive layer 30 provided on the opposite side of the resin layer 40 to the polarizer 10. The resin layer 40 is a solidified or heat-cured product of a coating film of an organic solvent solution of a resin, and has a thickness of 2 μm or less. The protective layer 20 is made of a TAC film. In the polarizing plate, the protective layer 20 is preferably provided only on one side of the polarizer 10 as in the illustrated example. In this case, the resin layer 40 is provided directly on the polarizer 10 on the other side of the polarizer 10. In this specification, "provided directly on the polarizer" means that it is formed directly on the polarizer surface without an adhesive layer (typically, an adhesive layer, a pressure-sensitive adhesive layer) being interposed. If necessary, a hard coat layer 60 may be provided on the side of the protective layer 20 opposite to the polarizer 10 (i.e., the viewing side of the polarizing plate). The adhesive layer 30 is provided as the outermost layer, and the polarizing plate can be attached to an image display device (substantially, an image display panel). The adhesive layer (substantially, an adhesive composition constituting the adhesive layer) contains a conductive component, and its surface resistance value is typically 1.0×10 ⁸ Ω/□ to 1.0×10 ¹² Ω/□. For practical purposes, it is preferable that a release film is temporarily attached to the surface of the adhesive layer 30 until the polarizing plate is used. By temporarily attaching the release film, the adhesive layer is protected and the polarizing plate can be rolled.

In an embodiment of the present invention, a conductive component permeation suppression layer 50 is provided between the polarizer 10 and the protective layer 20. The conductive component permeation suppression layer 50 is a hard coat layer in one embodiment; in another embodiment, it is a resin layer that is a solidified or heat-cured product of a coating film of an organic solvent solution of a resin. The hard coat layer as the conductive component permeation suppression layer 50 and the hard coat layer 60 may have the same configuration or different configurations. Similarly, the resin layer as the conductive component permeation suppression layer 50 and the resin layer 40 may have the same configuration or different configurations. In this specification, the hard coat layer as the conductive component permeation suppression layer 50 may be referred to as "another hard coat layer" to distinguish it from the hard coat layer 60; the resin layer as the conductive component permeation suppression layer 50 may be referred to as "another resin layer" to distinguish it from the resin layer 40. By providing such a conductive component permeation suppression layer (preferably by providing the conductive component permeation suppression layer 50 and the resin layer 40 in combination), a polarizing plate with excellent durability in a high temperature and high humidity environment can be realized. More specifically, in a high-temperature, high-humidity environment, the occurrence of granular protrusions or blisters in the protective layer is suppressed, and discoloration or red lines and other discoloration at the edges of the polarizing plate, as well as cracks, are suppressed, and the single transmittance of the polarizing plate (effectively, the polarizer) can be maintained within an acceptable range.

The polarizing plate according to the embodiment of the present invention may further include a functional layer other than the resin layer and the conductive component permeation suppression layer. A typical example of such a functional layer is a retardation layer. The optical properties (e.g., refractive index properties, in-plane retardation, Nz coefficient, photoelastic coefficient), thickness, arrangement position, etc. of the retardation layer can be appropriately set according to the purpose.

The polarizing plate according to the embodiment of the present invention may be in the form of a sheet or a long sheet. In this specification, "long sheet" means a long and narrow shape whose length is sufficiently longer than its width, and includes, for example, a long and narrow shape whose length is 10 times or more, preferably 20 times or more, larger than its width. A long and narrow polarizing plate can be wound into a roll.

The total thickness of the polarizing plate is preferably 60 μm or less, more preferably 55 μm or less, even more preferably 50 μm or less, and particularly preferably 40 μm or less. The lower limit of the total thickness may be, for example, 28 μm. According to an embodiment of the present invention, in a configuration having a low-resistance adhesive layer and a protective layer only on one side of the polarizer, it is possible to obtain the same effect as a configuration having protective layers on both sides of the polarizer. As a result, one protective layer can be omitted, so that a significant thinning can be achieved. The total thickness of the polarizing plate refers to the sum of the thicknesses of the polarizer, protective layer, transmission suppression layer, resin layer, and adhesive layer or adhesive layer for laminating these (i.e., the total thickness of the polarizing plate does not include the thickness of the adhesive layer 30 and the release film that may be temporarily attached to its surface).

The components of the polarizing plate are explained in more detail below.

B. Polarizer The polarizer is typically composed of a resin film containing a dichroic material (typically, iodine). As the resin film, any appropriate resin film that can be used as a polarizer can be adopted. The resin film is typically a polyvinyl alcohol-based resin (hereinafter referred to as "PVA-based resin") film. The resin film may be a single-layer resin film or a laminate of two or more layers.

Specific examples of polarizers made of a single-layer resin film include a PVA-based resin film that has been dyed with iodine and stretched (typically, uniaxially stretched). The above-mentioned dyeing with iodine is performed, for example, by immersing the PVA-based film in an aqueous iodine solution. The stretching ratio of the above-mentioned uniaxial stretching is preferably 3 to 7 times. The stretching may be performed after the dyeing process or while dyeing. Alternatively, the film may be stretched and then dyed. If necessary, the PVA-based resin film may be subjected to a swelling process, a crosslinking process, a washing process, a drying process, or the like. For example, by immersing the PVA-based resin film in water and washing it before dyeing, not only can dirt and antiblocking agents on the surface of the PVA-based film be washed off, but the PVA-based resin film can also be swelled to prevent uneven dyeing, etc.

Specific examples of polarizers obtained using a laminate include a laminate of a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or a polarizer obtained using a laminate of a resin substrate and a PVA-based resin layer coated on the resin substrate. A polarizer obtained using a laminate of a resin substrate and a PVA-based resin layer coated on the resin substrate can be produced, for example, by applying a PVA-based resin solution to a resin substrate and drying the substrate to form a PVA-based resin layer on the resin substrate to obtain a laminate of the resin substrate and the PVA-based resin layer; stretching and dyeing the laminate to make the PVA-based resin layer into a polarizer. In this embodiment, a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin is preferably formed on one side of the resin substrate. The stretching typically includes immersing the laminate in an aqueous boric acid solution to stretch it. Furthermore, the stretching may further include stretching the laminate in air at a high temperature (e.g., 95°C or higher) before stretching in the aqueous boric acid solution, as necessary. In addition, in this embodiment, the laminate is preferably subjected to a drying shrinkage treatment in which the laminate is heated while being conveyed in the longitudinal direction to shrink the laminate by 2% or more in the width direction. Typically, the manufacturing method of this embodiment includes subjecting the laminate to an air-assisted stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment in this order. By introducing the auxiliary stretching, even when PVA is applied onto a thermoplastic resin, it is possible to increase the crystallinity of PVA and achieve high optical properties. In addition, by simultaneously increasing the orientation of PVA in advance, problems such as a decrease in the orientation or dissolution of PVA when immersed in water in the subsequent dyeing step or stretching step can be prevented, and high optical properties can be achieved. Furthermore, when the PVA-based resin layer is immersed in a liquid, the orientation disorder and the decrease in the orientation of polyvinyl alcohol molecules can be suppressed compared to when the PVA-based resin layer does not contain a halide. This can improve the optical properties of a polarizer obtained through a treatment step in which the laminate is immersed in a liquid, such as a dyeing treatment and an underwater stretching treatment. Furthermore, the optical properties can be improved by shrinking the laminate in the width direction by the drying shrinkage treatment. The obtained resin substrate/polarizer laminate may be used as is (i.e., the resin substrate may be used as a protective layer for the polarizer), or the resin substrate may be peeled off from the resin substrate/polarizer laminate, and any suitable protective layer may be laminated on the peeled surface depending on the purpose. Details of the method for producing such a polarizer are described in, for example, JP-A-2012-73580 and Japanese Patent No. 6,470,455. The entire disclosures of these publications are incorporated herein by reference.

The thickness of the polarizer is preferably 1 μm to 10 μm, more preferably 1 μm to 8 μm, and even more preferably 2 μm to 5 μm. If the thickness of the polarizer is in this range, it can greatly contribute to making the polarizing plate thinner.

The boric acid content of the polarizer is preferably 10% by weight or more, and more preferably 13% by weight to 25% by weight. When the boric acid content of the polarizer is in this range, the ease of curl control during lamination can be well maintained, and curl during heating can be well suppressed while improving the appearance durability during heating. The boric acid content can be calculated as the amount of boric acid contained in the polarizer per unit weight, for example, using the following formula from the neutralization method.

The iodine content of the polarizer is preferably 2% by weight or more, more preferably 2% by weight to 11% by weight, and further preferably 5% by weight to 9% by weight. When the iodine content of the polarizer is in such a range, it is possible to maintain the ease of curl control during lamination, and to improve the appearance durability during heating while suppressing curl during heating. In this specification, the "iodine content" means the amount of all iodine contained in the polarizer (PVA-based resin film). More specifically, iodine exists in the polarizer in the form of iodine ion (I ^- ), iodine molecule (I ₂ ), polyiodine ion (I ₃ ^- , I ₅ ^- ), etc., and the iodine content in this specification means the amount of iodine including all of these forms. The iodine content can be calculated, for example, by a calibration curve method of fluorescent X-ray analysis. Note that the polyiodine ion exists in the polarizer in the form of a PVA-iodine complex. The formation of such a complex can result in absorption dichroism in the wavelength range of visible light. Specifically, the complex of PVA and triiodide ion (PVA·I ₃ ⁻ ) has an absorption peak near 470 nm, and the complex of PVA and pentaiodide ion (PVA·I ₅ ⁻ ) has an absorption peak near 600 nm. As a result, polyiodine ions can absorb light in a wide range of visible light depending on their form. On the other hand, iodine ions (I ⁻ ) have an absorption peak near 230 nm and are not substantially involved in the absorption of visible light. Therefore, polyiodine ions present in a complex state with PVA can mainly contribute to the absorption performance of the polarizer.

The polarizer preferably exhibits absorption dichroism at any wavelength between 380 nm and 780 nm. The single transmittance of the polarizer is preferably 41.5% to 46.0%, more preferably 43.0% to 46.0%, and even more preferably 44.5% to 46.0%. The degree of polarization of the polarizer is preferably 97.0% or more, more preferably 99.0% or more, and even more preferably 99.9% or more.

C. Protective layer As described above, the protective layer 20 is made of a TAC film. With such a configuration, the effect of the embodiment of the present invention is remarkable. More specifically, in a polarizing plate including a low-resistance adhesive layer, when a TAC film is used for the protective layer, granular protrusions and/or blisters may occur on the protective layer due to the influence of the conductive component of the adhesive layer. According to the embodiment of the present invention, the above-mentioned appearance defects of the protective layer can be prevented by providing a predetermined conductive component permeation suppression layer between the protective layer and the polarizer.

When the polarizing plate is disposed on the viewing side of the image display device, the protective layer 20 is typically disposed on the viewing side. In this case, in addition to forming a hard coat layer, the protective layer 20 may be subjected to surface treatments such as anti-reflection treatment, anti-sticking treatment, and anti-glare treatment, as necessary.

The thickness of the protective layer is preferably 10 μm to 50 μm, and more preferably 15 μm to 35 μm. If a surface treatment has been applied, the thickness of the protective layer includes the thickness of the surface treatment layer.

D. Hard Coat Layer The hard coat layer 60 may have any suitable configuration as long as the effects of the embodiment of the present invention can be obtained. For example, the hard coat layer may contain any suitable binder resin. Examples of the binder resin include thermosetting resins and active energy ray (e.g., ultraviolet light, visible light, electron beam) curable resins. As such a curable resin, for example, a curable compound having at least one of an acrylate group and a methacrylate group that is cured by heat, light (e.g., ultraviolet light) or electron beam can be used. Specific examples include silicone resins, polyester resins, polyether resins, epoxy resins, urethane resins, alkyd resins, spiroacetal resins, polybutadiene resins, polythiolpolyene resins, oligomers or prepolymers of acrylates or methacrylates of polyfunctional compounds such as polyhydric alcohols. These may be used alone or in combination of two or more types. Commercially available products may be used as the curable resin.

The hard coat layer may contain, for example, a (meth)acrylic resin, or may contain, for example, a urethane (meth)acrylate. The hard coat layer may also contain, for example, a copolymer of an oligomer and a monomer having a functional group. Examples of monomers having a functional group include polyfunctional (meth)acrylates. The (meth)acrylate is preferably bifunctional or more, more preferably trifunctional or more. Examples of oligomers having a functional group include curable urethane (meth)acrylates. In one embodiment, the hard coat layer (substantially the composition forming the hard coat layer) contains a total of 60 parts by weight or more of curable urethane (meth)acrylate and trifunctional or more (meth)acrylate with respect to 100 parts by weight of the total binder resin. The total amount is preferably 70 parts by weight or more, more preferably 80 parts by weight or more, even more preferably 90 parts by weight or more, and particularly preferably 95 parts by weight or more. The total amount may be 100 parts by weight. That is, the binder resin may be entirely composed of a curable urethane (meth)acrylate and/or a trifunctional or higher (meth)acrylate. Examples of curable urethane (meth)acrylate include "UV-1700TL" manufactured by Mitsubishi Chemical Corporation and "UT-7314" manufactured by Mitsubishi Chemical Corporation. Examples of multifunctional (meth)acrylate include "UNIDIC 17-807" manufactured by DIC Corporation and "M-920" manufactured by Toa Gosei Co., Ltd. In this specification, "(meth)acrylic" means acrylic and/or methacrylic.

The hard coat layer may contain silicon as an element. Silicon may be a constituent element of a surface conditioner contained in the hard coat layer. Thus, the hard coat layer contains a surface conditioner (typically a leveling agent), and the surface conditioner may contain, for example, a silicon compound having a dimethylsiloxane skeleton. The silicon compound may be a dimethylsiloxane-modified methacrylic acid ester, a polydimethylsiloxane cyclic compound, or the like. A commercially available product may be used as the surface conditioner. Specific examples of commercially available products include, for example, "LE-303" manufactured by Kyoeisha Chemical Co., Ltd. and "PC4100" manufactured by DIC Corporation.

The hard coat layer (effectively, the composition forming the hard coat layer) may contain a reactive diluent having at least one of an acrylate group and a methacrylate group. Examples of reactive diluents include monofunctional (meth)acrylates and polyfunctional (meth)acrylates. Trifunctional or higher (meth)acrylates are preferred. Specific examples include butanediol glycerin ether di(meth)acrylate and (meth)acrylate of isocyanuric acid. With such a configuration, a hard coat layer having excellent hardness can be formed. The reactive diluent may be used alone or in combination of two or more types. Examples of reactive diluents are described in JP 2008-88309 A, and the description of the publication is incorporated herein by reference.

The hard coat layer may contain a thixotropy-imparting agent. Examples of the thixotropy-imparting agent include organic clay, oxidized polyolefin, and modified urea. The thixotropy-imparting agent may be, for example, a thickener. The thixotropy-imparting agent may be used alone or in combination of two or more kinds.

The hard coat layer may contain a filler. Examples of the filler include organic particles and inorganic particles. The thixotropy-imparting agent may also function as a filler. By including a filler, an uneven structure is formed on at least one surface of the resulting hard coat layer, and the desired haze value can be obtained due to the uneven structure. The haze value of the hard coat layer may be, for example, 5% or more, for example, 10% or more, for example, 15% or more, or for example, 20% or more. On the other hand, the haze value of the hard coat layer may be, for example, 50% or less, for example, 45% or less, for example, 40% or less, or for example, 35% or less. If the haze value is within such a range, the occurrence of shading and reflection from the outside are suppressed, and the deterioration of the display characteristics (for example, clarity, contrast in a dark place) of the image display device can be suppressed. The haze value may typically be measured in accordance with JIS K 7136.

The pencil hardness of the hard coat layer is preferably F or more, more preferably H or more, and even more preferably 3H or more. If the pencil hardness of the hard coat layer is in this range, a sufficient protective function can be achieved as the outermost layer on the viewing side. Furthermore, as described below, when the hard coat layer is used as a conductive component permeation suppression layer, good permeation suppression performance can be achieved.

The thickness of the hard coat layer is preferably 1 μm to 10 μm, and more preferably 2 μm to 8 μm. If the thickness of the hard coat layer is in this range, it contributes to making the polarizing plate thinner and can achieve the desired protective function and/or transmission suppression function.

E. Resin Layer As described above, the resin layer is a solidified or thermoset product of a coating film of an organic solvent solution of a resin. With such a configuration, the thickness can be made very thin (for example, 10 μm or less). The thickness of the resin layer is preferably 0.05 μm to 3 μm, more preferably 0.08 μm to 2 μm, even more preferably 0.1 μm to 1 μm, and particularly preferably 0.2 μm to 0.7 μm. Furthermore, with such a configuration, the resin layer can be formed directly on the polarizer (i.e., without an adhesive layer or a pressure-sensitive adhesive layer). According to the embodiment of the present invention, as described above, the polarizer and the resin layer are very thin, and an adhesive layer or a pressure-sensitive adhesive layer for laminating the resin layer can be omitted, so that the total thickness of the polarizing plate can be made extremely thin. Furthermore, such a resin layer has the advantage of being excellent in humidification durability because it has low moisture absorption and moisture permeability compared to a solidified product of a water-based coating film such as an aqueous solution or aqueous dispersion. As a result, a polarizing plate with excellent durability that can maintain optical properties even under high temperature and high humidity environments can be realized. In addition, such a resin layer can suppress the adverse effects of ultraviolet irradiation on a polarizing plate (polarizer) compared to, for example, a cured product of an ultraviolet-curable resin. The resin layer is preferably a solidified product of a coating film of an organic solvent solution of a resin. The solidified product shrinks less during film formation compared to a cured product, and does not contain residual monomers, etc., so deterioration of the film itself is suppressed, and adverse effects on a polarizing plate (polarizer) caused by residual monomers, etc. can be suppressed.

The glass transition temperature (Tg) of the resin constituting the resin layer is typically 85°C or higher, preferably 90°C or higher, more preferably 100°C or higher, even more preferably 110°C or higher, and particularly preferably 120°C or higher. The upper limit of Tg can be, for example, 200°C. The weight average molecular weight Mw of the resin is typically 25,000 or higher, preferably 30,000 or higher, more preferably 35,000 or higher, and even more preferably 40,000 or higher. The upper limit of Mw can be, for example, 150,000. If the Tg and Mw of the resin are in such a range, the migration of iodine in the polarizer to the image display panel can be significantly suppressed despite the very thin layer due to the synergistic effect of the resin layer being composed of a solidified or thermoset product of a coating film of an organic solvent solution of the resin. As a result, when the polarizing plate is applied to an image display device, corrosion of the metal members of the image display device can be significantly suppressed. Furthermore, with such a configuration, when the resin layer is used as a conductive component permeation suppression layer, the effect becomes significant.

As the resin constituting the resin layer, any suitable thermoplastic resin or thermosetting resin can be used. A thermoplastic resin is preferable. Examples of the thermoplastic resin include an acrylic resin and an epoxy resin. An acrylic resin and an epoxy resin may be used in combination. Representative examples of acrylic resins and epoxy resins that can be used in the resin layer are described below.

Acrylic resins typically contain repeating units derived from (meth)acrylic acid ester monomers having a linear or branched structure as the main component. In this specification, (meth)acrylic refers to acrylic and/or methacrylic. Acrylic resins may contain repeating units derived from any appropriate copolymerization monomer depending on the purpose. Examples of copolymerization monomers (copolymerization monomers) include carboxyl group-containing monomers, hydroxyl group-containing monomers, amide group-containing monomers, aromatic ring-containing (meth)acrylates, and heterocycle-containing vinyl monomers. By appropriately setting the type, number, combination, and copolymerization ratio of the monomer units, an acrylic resin having the above-mentioned specified Mw can be obtained.

（式中、Ｘはビニル基、（メタ）アクリル基、スチリル基、（メタ）アクリルアミド基、ビニルエーテル基、エポキシ基、オキセタン基、ヒドロキシル基、アミノ基、アルデヒド基、および、カルボキシル基からなる群より選択される少なくとも１種の反応性基を含む官能基を表し、Ｒ^１およびＲ^２はそれぞれ独立して、水素原子、置換基を有していてもよい脂肪族炭化水素基、置換基を有していてもよいアリール基、または、置換基を有していてもよいヘテロ環基を表し、Ｒ^１およびＲ^２は互いに連結して環を形成してもよい）。 <Boron-containing acrylic resin>
In one embodiment, the acrylic resin includes a copolymer (hereinafter, may be referred to as a boron-containing acrylic resin) obtained by polymerizing a monomer mixture containing more than 50 parts by weight of a (meth)acrylic monomer and more than 0 part by weight and less than 50 parts by weight of a monomer represented by formula (1) (hereinafter, may be referred to as a copolymerization monomer):

(In the formula, X represents a functional group containing at least one reactive group selected from the group consisting of a vinyl group, a (meth)acrylic group, a styryl group, a (meth)acrylamide group, a vinyl ether group, an epoxy group, an oxetane group, a hydroxyl group, an amino group, an aldehyde group, and a carboxyl group; R ¹ and R ² each independently represent a hydrogen atom, an optionally substituted aliphatic hydrocarbon group, an optionally substituted aryl group, or an optionally substituted heterocyclic group; and R ¹ and R ² may be linked together to form a ring).

（式中、Ｒ^６は任意の官能基を表し、jおよびｋは１以上の整数を表す）。 The boron-containing acrylic resin typically has a repeating unit represented by the following formula. By polymerizing a monomer mixture containing a copolymerization monomer represented by formula (1) and a (meth)acrylic monomer, the boron-containing acrylic resin has a boron-containing substituent (e.g., a repeating unit k in the following formula) in the side chain. This can improve adhesion to a polarizer when the resin layer is disposed adjacent to the polarizer. The boron-containing substituent may be contained continuously (i.e., in a block shape) or randomly in the boron-containing acrylic resin.

(In the formula, ^R6 represents any functional group, and j and k represent integers of 1 or more).

<(Meth)acrylic monomer>
As the (meth)acrylic monomer, any appropriate (meth)acrylic monomer can be used, for example, a (meth)acrylic acid ester monomer having a linear or branched structure, and a (meth)acrylic acid ester monomer having a cyclic structure.

Examples of (meth)acrylic acid ester monomers having a linear or branched structure include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, methyl 2-ethylhexyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate. Methyl (meth)acrylate is preferably used. Only one type of (meth)acrylic acid ester monomer may be used, or two or more types may be used in combination.

Examples of (meth)acrylic acid ester monomers having a cyclic structure include cyclohexyl (meth)acrylate, benzyl (meth)acrylate, isobornyl (meth)acrylate, 1-adamantyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, dicyclopentanyl (meth)acrylate, biphenyl (meth)acrylate, o-biphenyloxyethyl (meth)acrylate, o-biphenyloxyethoxyethyl (meth)acrylate, m-biphenyloxyethyl acrylate, p-biphenyloxyethyl (meth)acrylate, o-biphenyloxyethyl (meth)acrylate, Examples of the monomers include biphenyl group-containing monomers such as oxy-2-hydroxypropyl (meth)acrylate, p-biphenyloxy-2-hydroxypropyl (meth)acrylate, m-biphenyloxy-2-hydroxypropyl (meth)acrylate, N-(meth)acryloyloxyethyl-o-biphenyl=carbamate, N-(meth)acryloyloxyethyl-p-biphenyl=carbamate, N-(meth)acryloyloxyethyl-m-biphenyl=carbamate, and o-phenylphenol glycidyl ether acrylate, terphenyl (meth)acrylate, and o-terphenyloxyethyl (meth)acrylate. Preferably, 1-adamantyl (meth)acrylate and dicyclopentanyl (meth)acrylate are used. By using these monomers, a polymer with a high glass transition temperature can be obtained. These monomers may be used alone or in combination of two or more.

In addition, instead of the above (meth)acrylic acid ester monomer, a silsesquioxane compound having a (meth)acryloyl group may be used. By using a silsesquioxane compound, an acrylic polymer having a high glass transition temperature can be obtained. Silsesquioxane compounds are known to have various skeletal structures, such as a cage structure, a ladder structure, and a random structure. The silsesquioxane compound may have only one of these structures, or may have two or more of them. Only one type of silsesquioxane compound may be used, or two or more types may be used in combination.

As silsesquioxane compounds containing (meth)acryloyl groups, for example, the MAC grade and AC grade of the SQ series from Toagosei Co., Ltd. can be used. The MAC grade is a silsesquioxane compound containing a methacryloyl group, and specific examples include MAC-SQ TM-100, MAC-SQ SI-20, and MAC-SQ HDM. The AC grade is a silsesquioxane compound containing an acryloyl group, and specific examples include AC-SQ TA-100 and AC-SQ SI-20.

The (meth)acrylic monomer is used in an amount of more than 50 parts by weight per 100 parts by weight of the monomer mixture.

<Comonomer>
As the copolymerization monomer, a monomer represented by the above formula (1) is used. By using such a copolymerization monomer, a boron-containing substituent is introduced into the side chain of the obtained polymer. Only one type of copolymerization monomer may be used, or two or more types may be used in combination.

The aliphatic hydrocarbon group in the above formula (1) may be a linear or branched alkyl group having 1 to 20 carbon atoms, which may have a substituent, a cyclic alkyl group having 3 to 20 carbon atoms, which may have a substituent, or an alkenyl group having 2 to 20 carbon atoms. The aryl group may be a phenyl group having 6 to 20 carbon atoms, which may have a substituent, or a naphthyl group having 10 to 20 carbon atoms, which may have a substituent. The heterocyclic group may be a 5-membered or 6-membered ring group containing at least one heteroatom, which may have a substituent. R ¹ and R ² may be linked together to form a ring. R ¹ and R ² are preferably a hydrogen atom or a linear or branched alkyl group having 1 to 3 carbon atoms, and more preferably a hydrogen atom.

The reactive group contained in the functional group represented by X is at least one selected from the group consisting of a vinyl group, a (meth)acrylic group, a styryl group, a (meth)acrylamide group, a vinyl ether group, an epoxy group, an oxetane group, a hydroxyl group, an amino group, an aldehyde group, and a carboxyl group. Preferably, the reactive group is a (meth)acrylic group and/or a (meth)acrylamide group. By having these reactive groups, the adhesion to the polarizer can be further improved when the resin layer is disposed adjacent to the polarizer.

In one embodiment, the functional group represented by X is preferably a functional group represented by Z-Y-, where Z represents a functional group containing at least one reactive group selected from the group consisting of a vinyl group, a (meth)acrylic group, a styryl group, a (meth)acrylamide group, a vinyl ether group, an epoxy group, an oxetane group, a hydroxyl group, an amino group, an aldehyde group, and a carboxyl group, and Y represents a phenylene group or an alkylene group.

Specifically, the following compounds can be used as the copolymerization monomer.

The copolymerization monomer is used in an amount of more than 0 parts by weight and less than 50 parts by weight per 100 parts by weight of the monomer mixture. The amount is preferably 0.01 parts by weight or more and less than 50 parts by weight, more preferably 0.05 parts by weight to 20 parts by weight, even more preferably 0.1 parts by weight to 10 parts by weight, and particularly preferably 0.5 parts by weight to 5 parts by weight.

<Acrylic resin containing lactone ring, etc.>
In another embodiment, the acrylic resin may have a repeating unit containing a ring structure selected from a lactone ring unit, a glutaric anhydride unit, a glutarimide unit, a maleic anhydride unit, and a maleimide (N-substituted maleimide) unit. The repeating unit containing a ring structure may contain only one type of repeating unit, or may contain two or more types. The content of the repeating unit containing a ring structure in the acrylic resin is preferably 1 mol% to 50 mol%, more preferably 10 mol% to 40 mol%, and even more preferably 20 mol% to 30 mol%. The acrylic resin contains a repeating unit derived from the above (meth)acrylic monomer as a main repeating unit.

<Epoxy resin>
As the epoxy resin, an epoxy resin having an aromatic ring is preferably used. By using an epoxy resin having an aromatic ring as the epoxy resin, when the resin layer is arranged adjacent to the polarizer, the adhesion to the polarizer can be improved. Furthermore, when the adhesive layer is arranged adjacent to the resin layer, the anchoring force of the adhesive layer can be improved. Examples of the epoxy resin having an aromatic ring include bisphenol type epoxy resins such as bisphenol A type epoxy resin, bisphenol F type epoxy resin, and bisphenol S type epoxy resin; novolac type epoxy resins such as phenol novolac epoxy resin, cresol novolac epoxy resin, and hydroxybenzaldehyde phenol novolac epoxy resin; polyfunctional epoxy resins such as glycidyl ether of tetrahydroxyphenylmethane, glycidyl ether of tetrahydroxybenzophenone, and epoxidized polyvinylphenol, naphthol type epoxy resin, naphthalene type epoxy resin, and biphenyl type epoxy resin. Preferably, bisphenol A type epoxy resin, biphenyl type epoxy resin, and bisphenol F type epoxy resin are used. Only one type of epoxy resin may be used, or two or more types may be used in combination.

The resin layer can be formed by applying an organic solvent solution of the resin as described above to form a coating film, and then solidifying or thermally curing the coating film. Any appropriate method and conditions can be used as the application method and the solidification or curing conditions.

The resin layer (essentially, the organic solvent solution of the resin) may contain any suitable additive depending on the purpose. The type, number, combination, amount of additives, etc., can be appropriately set depending on the purpose.

F. Adhesive Layer The surface resistance value of the adhesive layer 30 is typically 1.0×10 ⁸ Ω/□ to 1.0×10 ¹² Ω/□ as described above, preferably 1.0×10 ⁸ Ω/□ to 1.0×10 ¹¹ Ω/□, more preferably 1.0×10 ⁸ Ω/□ to 1.0×10 ¹⁰ Ω/□, and even more preferably 1.0×10 ⁸ Ω/□ to 1.0×10 ⁹ Ω/□. If the surface resistance value of the adhesive layer is in such a range, the desired antistatic performance can be achieved when the polarizing plate is applied to an image display device. As a result, the polarizing plate can also be suitably applied to a narrow-frame (preferably bezel-less) image display device, a so-called in-cell type image display device in which a conductive layer for a touch panel is incorporated in the display panel, and the like.

The adhesive strength of the adhesive layer to glass is preferably 1.5 N/25 mm or more and less than 5.5 N/25 mm, more preferably 2.5 N/25 mm or more and 4.5 N/25 mm or less, and even more preferably 3.0 N/25 mm or more and 4.0 N/25 mm or less. If the adhesive strength is in this range, the adhesive layer has excellent adhesion to the image display panel and excellent reworkability.

The pressure-sensitive adhesive layer has a storage modulus at 25° C. of preferably 1.0×10 ⁴ Pa to 1.0×10 ⁶ Pa, more preferably 1.0×10 ⁴ Pa to 1.0×10 ⁵ Pa. When the storage modulus of the pressure-sensitive adhesive layer is within this range, it is possible to suppress defects in the appearance of the polarizing plate in a high-temperature and high-humidity environment. The storage modulus can be obtained by dynamic viscoelasticity measurement.

The creep amount ΔCr of the adhesive layer at 70°C may be, for example, 65 μm or less, 50 μm or less, 45 μm or less, 40 μm or less, 35 μm or less, 30 μm or less, 25 μm or less, 20 μm or less, or even 15 μm or less. The lower limit of the creep amount ΔCr is, for example, 0.5 μm. If the creep amount is within such a range, it is possible to suppress the appearance defect of the polarizing plate in a high temperature and high humidity environment, as in the case of the storage elastic modulus. The creep value can be measured, for example, by the following procedure: A load of 500 gf is applied vertically downward to the adhesive layer attached to a stainless steel test plate at a bonding surface of 20 mm long x 20 mm wide, with the test plate fixed. The creep amount (displacement amount) of the adhesive layer relative to the test plate at each time point 100 seconds and 3600 seconds after the load is started to be applied is measured, and is set to Cr ₁₀₀ and Cr ₃₆₀₀ , respectively. From the measured Cr ₁₀₀ and Cr ₃₆₀₀ , the creep amount ΔCr can be calculated by the formula ΔCr=Cr ₃₆₀₀ −Cr ₁₀₀ .

The thickness of the adhesive layer is preferably 2 μm to 55 μm, more preferably 2 μm to 30 μm, even more preferably 5 μm to 25 μm, and particularly preferably 10 μm to 20 μm.

The adhesive composition that constitutes the adhesive layer typically contains a base polymer and a conductive component.

Examples of base polymers include (meth)acrylic polymers, urethane polymers, silicone polymers, and rubber polymers. (Meth)acrylic polymers are preferred. In this specification, (meth)acrylic polymers as base polymers may be referred to as (meth)acrylic base polymers.

The (meth)acrylic base polymer typically contains an alkyl (meth)acrylate as a main monomer component. Examples of the alkyl group of the alkyl (meth)acrylate include linear or branched alkyl groups having 1 to 18 carbon atoms. The average number of carbon atoms in the alkyl group is preferably 3 to 9, and more preferably 3 to 6. A preferred alkyl (meth)acrylate is butyl acrylate. The content of the alkoxy group-containing monomer in the base polymer is preferably 50 parts by weight or more, more preferably 60 parts by weight or more, even more preferably 70 parts by weight or more, and particularly preferably 80 parts by weight or more, based on 100 parts by weight of the total monomer components. The alkyl (meth)acrylate may be used alone or in combination of two or more kinds.

The (meth)acrylic base polymer typically contains a monomer component (copolymerizable monomer component) that can be copolymerized with an alkyl (meth)acrylate. Examples of the copolymerizable monomer component include a carboxyl group-containing monomer, a hydroxyl group-containing monomer, an alkoxy group-containing monomer, an amide group-containing monomer, an aromatic ring-containing (meth)acrylate, and a heterocycle-containing vinyl monomer. By appropriately adjusting the type, number, combination, amount (content), etc. of the copolymerizable monomer, a base polymer (and, as a result, a pressure-sensitive adhesive layer) having the desired properties can be obtained.

The weight average molecular weight Mw of the (meth)acrylic base polymer is preferably 1 million to 3 million, more preferably 2 million to 3 million, and even more preferably 2 million to 2.8 million. If the weight average molecular weight Mw is less than 1 million, crack suppression may be insufficient. If the weight average molecular weight Mw exceeds 3 million, an increase in viscosity and/or gelation during polymer polymerization may occur.

Typical conductive components include inorganic cationic salts and organic cationic salts.

The inorganic cation salt is specifically an inorganic cation-anion salt. A representative example of the cation constituting the cation portion of the inorganic cation salt is an alkali metal ion. Specific examples include a lithium ion, a sodium ion, and a potassium ion. The lithium ion is preferred. Therefore, the preferred inorganic cation salt is a lithium salt.

Examples of anions constituting the anion portion of the inorganic cationic salt include Cl ^- , Br ^- , I ^- , AlCl ₄ ^- , Al ₂ Cl ₇ ^- , BF ₄ ^- , PF ₆ ^- , ClO ₄ ^- , NO ₃ ^- , CH ₃ COO ^- , CF ₃ COO ^- , CH ₃ SO ₃ ^- , CF ₃ SO ₃ ^- , (CF ₃ SO ₂ ) ₃ C ^- , AsF ₆ ^- , SbF ₆ ^- , NbF ₆ ^- , TaF ₆ ^- , (CN) ₂ N ^- , C ₄ F ₉ SO ₃ ^- , C ₃ F ₇ COO ^- , (CF ₃ SO ₂ ) (CF ₃ CO) N ^- , ^-O ₃ S(CF ₂ ) ₃ SO ₃ ⁻ and the following general formulas (1) to (4):
(1): (C _n F _2n+1 SO ₂ ) ₂ N ⁻ (n is an integer from 1 to 10);
(2): CF ₂ (C _m F _{2 m} SO ₂ ) ₂ N ⁻ (m is an integer from 1 to 10);
(3): ^-O3S ( _{CF2 ) lSO3-} (l ^is _an integer from 1 to 10);
(4): (C _p F _2p+1 SO ₂ )N ⁻ (C _q F _2q+1 SO ₂ ), (p and q are integers from 1 to 10);
[0033] Fluorine-containing anions are preferred, and fluorine-containing imide anions are more preferred.

The fluorine-containing imide anion may be, for example, an imide anion having a perfluoroalkyl group. Specific examples include the above-mentioned (CF ₃ SO ₂ )(CF ₃ CO)N ⁻ and the general formulas (1), (2) and (4).
(1): (C _n F _2n+1 SO ₂ ) ₂ N ⁻ (n is an integer from 1 to 10);
(2): CF ₂ (C _m F _{2 m} SO ₂ ) ₂ N ⁻ (m is an integer from 1 to 10);
(4): (C _p F _2p+1 SO ₂ )N ⁻ (C _q F _2q+1 SO ₂ ), (p and q are integers from 1 to 10);
Examples of the anion include those represented by the formula: Preferred are (perfluoroalkylsulfonyl)imides represented by the general formula (1), such as (CF ₃ SO ₂ ) ₂ N ^- and (C ₂ F ₅ SO ₂ ) ₂ N ^- , and more preferred are bis(trifluoromethanesulfonyl)imides represented by (CF ₃ SO ₂ ) ₂ N ^- . Thus, a preferred inorganic cation salt that can be used in the embodiment of the present invention is lithium bis(trifluoromethanesulfonyl)imide.

Specifically, the organic cation salt is an organic cation-anion salt. A typical example of the cation constituting the cation portion of the organic cation salt is an organic onium that has formed an onium ion by substitution with an organic group. Examples of the onium in the organic onium include nitrogen-containing onium, sulfur-containing onium, and phosphorus-containing onium. Nitrogen-containing onium and sulfur-containing onium are preferred. Examples of the nitrogen-containing onium include ammonium cation, piperidinium cation, pyrrolidinium cation, pyridinium cation, cation having a pyrroline skeleton, cation having a pyrrole skeleton, imidazolium cation, tetrahydropyrimidinium cation, dihydropyrimidinium cation, pyrazolium cation, and pyrazolinium cation. Examples of the sulfur-containing onium include sulfonium cation. Examples of the phosphorus-containing onium include phosphonium cation. Examples of the organic group in the organic onium include alkyl groups, alkoxyl groups, and alkenyl groups. Specific examples of preferred organic oniums include tetraalkylammonium cations (e.g., trimethylbutylammonium cation), alkylpiperidinium cations, and alkylpyrrolidinium cations. The anion constituting the anion portion of the organic cation salt is as described for the anion constituting the anion portion of the inorganic cation. Preferred organic cation salts that can be used in the embodiments of the present invention are methylpropylpyrrolidinium bis(trifluoromethanesulfonyl)imide, 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide, and trimethylbutylammonium bis(trifluoromethanesulfonyl)imide.

Inorganic cationic salts and organic cationic salts may be used in combination.

The conductive component may be a solid or a liquid (i.e., an ionic liquid).

The content of the conductive component in the adhesive composition is preferably 5 to 15 parts by weight, and more preferably 8 to 12 parts by weight, per 100 parts by weight of the base polymer. If the content of the conductive component is within this range, the desired antistatic performance can be obtained without adversely affecting other properties.

The adhesive composition typically contains a silane coupling agent and/or a crosslinking agent. Typical examples of the silane coupling agent include functional group-containing silane coupling agents. Examples of functional groups include epoxy groups, mercapto groups, amino groups, isocyanate groups, isocyanurate groups, vinyl groups, styryl groups, acetoacetyl groups, ureido groups, thiourea groups, (meth)acrylic groups, heterocyclic groups, acid anhydride groups, and combinations thereof. Functional group-containing silane coupling agents can be used alone or in combination. Examples of crosslinking agents include isocyanate-based crosslinking agents and peroxide-based crosslinking agents. Crosslinking agents can also be used alone or in combination.

The adhesive composition may contain additives. Specific examples of additives include colorants, powders such as pigments, dyes, surfactants, plasticizers, tackifiers, surface lubricants, leveling agents, softeners, antioxidants, antiaging agents, light stabilizers, UV absorbers, polymerization inhibitors, inorganic or organic fillers, metal powders, particles, and foils. A redox system may also be used by adding a reducing agent within a controllable range. The type, number, combination, and content of additives may be appropriately set according to the purpose.

G. Conductive component permeation suppression layer In the embodiment of the present invention, as described above, a conductive component permeation suppression layer is provided between the polarizer and the protective layer. By providing the conductive component permeation suppression layer, a polarizing plate having excellent durability in a high-temperature and high-humidity environment can be realized. More specifically, in a high-temperature and high-humidity environment, the occurrence of granular protrusions or blisters in the protective layer can be suppressed, and discoloration or discoloration such as red lines at the edge of the polarizing plate and cracks can be suppressed, and the single transmittance of the polarizing plate (substantially, the polarizer) can be maintained within an allowable range. Preferably, such an effect is further remarkable by providing the conductive component permeation suppression layer in combination with a resin layer.

In one embodiment, the conductive component permeation suppression layer may be a hard coat layer. The detailed configuration of the hard coat layer is as described in section D above. In another embodiment, the conductive component permeation suppression layer may be a resin layer formed as a solidified or thermoset product of a coating film of a resin in an organic solvent solution. The detailed configuration of the resin layer is as described in section E above.

The thickness of the conductive component permeation suppression layer is preferably 0.2 μm to 10 μm, more preferably 0.3 μm to 7 μm, and even more preferably 0.5 μm to 5 μm. If the thickness is too small, the conductive component permeation suppression effect and moisture permeation suppression effect will be insufficient, and it may be difficult to maintain the single transmittance of the polarizing plate within an acceptable range in a high-temperature, high-humidity environment. If the thickness is too large, cracks may occur.

H. Image display device The polarizing plate described in the above items A to G can be applied to an image display device. Therefore, the embodiment of the present invention includes an image display device using such a polarizing plate. Representative examples of the image display device include a liquid crystal display device and an electroluminescence (EL) display device (e.g., an organic EL display device, an inorganic EL display device). In one embodiment, the image display device is a narrow-frame (preferably bezel-less) image display device or an in-cell type image display device. In such an image display device, the effect of the embodiment of the present invention is remarkable.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. The methods for measuring each property are as follows. Unless otherwise specified, "parts" and "%" in the examples and comparative examples are by weight.

(1) Thickness Thicknesses of 10 μm or less were measured using an interference film thickness meter (manufactured by Otsuka Electronics Co., Ltd., product name "MCPD-3000"), and thicknesses of more than 10 μm were measured using a digital micrometer (manufactured by Anritsu Co., Ltd., product name "KC-351C").

(2) Surface Resistance Value The resistance value of the surface of the adhesive layer of the polarizing plates (adhesive layer-attached polarizing plates) obtained in the Examples and Comparative Examples was measured using MCP-HT450 manufactured by Mitsubishi Chemical Analytech Co., Ltd.

(3) Appearance The polarizing plates obtained in the Examples and Comparative Examples were subjected to a reliability test (72 hours in an environment of 65°C and 90% RH), and then the presence or absence of granular protrusions or blisters on the protective layer was visually observed and evaluated according to the following criteria.
○: Neither granular protrusions nor blisters were observed. ×: At least one of granular protrusions or blisters was observed.

(4) Color loss From the polarizing plates obtained in the examples and comparative examples, test pieces (50 mm x 50 mm) were cut out with two opposing sides in the absorption axis direction and the direction perpendicular to the absorption axis direction. The test pieces were attached to a glass plate via an adhesive layer, and left in an oven at 65°C and 90% RH for 120 hours to humidify the polarizing plate (effectively, a polarizer) after humidification in a cross-Nicol state with a standard polarizing plate. The color loss state of the end of the polarizing plate (substantially, a polarizer) after humidification was examined using a microscope. Specifically, the size of the color loss from the polarizer end (amount of color loss: μm) was measured. Using an Olympus MX61L microscope, the amount of color loss at the corners was measured from an image taken at a magnification of 10 times, and evaluated according to the following criteria.
○: The amount of color loss is 300 μm or less. ×: The amount of color loss is more than 300 μm.

[Production Example 1: Preparation of Pressure-Sensitive Adhesive Layer A1]
(Preparation of Acrylic-Based Polymer)
A monomer mixture containing 80.3 parts of butyl acrylate, 16 parts of phenoxyethyl acrylate, 3 parts of N-vinyl-2-pyrrolidone (NVP), 0.3 parts of acrylic acid, and 0.4 parts of 4-hydroxybutyl acrylate was charged into a four-neck flask equipped with a stirring blade, a thermometer, a nitrogen gas inlet tube, and a cooler. Further, 0.1 parts of 2,2'-azobisisobutyronitrile as a polymerization initiator was charged together with 100 parts of ethyl acetate for 100 parts of the monomer mixture (solid content), and nitrogen gas was introduced while gently stirring to replace the atmosphere with nitrogen. The liquid temperature in the flask was kept at around 55°C, and a polymerization reaction was carried out for 8 hours to prepare a solution of an acrylic polymer having a weight average molecular weight (Mw) of 1.5 million.

(Preparation of Pressure-Sensitive Adhesive Composition)
100 parts of the solid content of the acrylic base polymer solution obtained above was mixed with 10 parts of MPP-TFSI (methylpropylpyrrolidinium bis(trifluoromethanesulfonyl)imide, an ionic liquid, as a conductive agent (antistatic agent), and further mixed with 0.1 parts of an isocyanate crosslinking agent (D160N: Takenate D-160N, trimethylolpropane hexamethylene diisocyanate, manufactured by Mitsui Chemicals, Inc.), 0.3 parts of benzoyl peroxide (BPO: Niper BMT, manufactured by Nippon Oil & Fats Co., Ltd.), and 0.1 parts of a silane coupling agent (X-41-1810, manufactured by Shin-Etsu Chemical Co., Ltd.) to prepare an acrylic adhesive composition solution. The obtained adhesive composition solution was applied to a release sheet and dried to form an adhesive layer A1 having a thickness of 15 μm. The surface resistance value of the adhesive layer A1 was 1.0 × 10 ⁹ Ω/□.

[Production Example 2: Preparation of Pressure-Sensitive Adhesive Layer A2]
Except for changing the blending amount of the conductive agent to 1 part, an acrylic adhesive composition solution was prepared in the same manner as in Production Example 1. An adhesive layer A2 having a thickness of 15 μm was formed in the same manner as in Production Example 1. The surface resistance value of the adhesive layer A2 was 1.0× ¹⁰ Ω/□.

[Example 1]
1. Preparation of Polarizer As a thermoplastic resin substrate, a long amorphous isophthalic copolymerized polyethylene terephthalate film (thickness: 100 μm) was used, which had a water absorption rate of 0.75% and a Tg of about 75° C. One side of the resin substrate was subjected to a corona treatment.
A PVA aqueous solution (coating solution) was prepared by adding 13 parts by weight of potassium iodide to 100 parts by weight of a PVA-based resin prepared by mixing polyvinyl alcohol (polymerization degree 4,200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., product name "GOHSEFFIMER Z410") in a ratio of 9:1, and dissolving the mixture in water.
The above PVA aqueous solution was applied to the corona-treated surface of a resin substrate and dried at 60° C. to form a PVA-based resin layer having a thickness of 13 μm, thereby producing a laminate.
The obtained laminate was uniaxially stretched at its free end to 2.4 times its original size in the machine direction (longitudinal direction) between rolls having different peripheral speeds in an oven at 130° C. (auxiliary air stretching treatment).
Next, the laminate was immersed in an insolubilizing bath (a boric acid aqueous solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40° C. for 30 seconds (insolubilizing treatment).
Next, the film was immersed in a dye bath (an aqueous iodine solution obtained by mixing iodine and potassium iodide in a weight ratio of 1:7 with 100 parts by weight of water) having a liquid temperature of 30° C. for 60 seconds while adjusting the concentration so that the single transmittance (Ts) of the finally obtained polarizer would be a predetermined value (dyeing treatment).
Next, the plate was immersed in a crosslinking bath (a boric acid aqueous solution obtained by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40° C. for 30 seconds (crosslinking treatment).
Thereafter, the laminate was immersed in an aqueous boric acid solution (boric acid concentration: 4.0% by weight, potassium iodide concentration: 5% by weight) at a liquid temperature of 70° C., and uniaxially stretched in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds to a total stretch ratio of 5.5 times (underwater stretching treatment).
Thereafter, the laminate was immersed in a cleaning bath (an aqueous solution obtained by mixing 4 parts by weight of potassium iodide with 100 parts by weight of water) at a liquid temperature of 20° C. (cleaning treatment).
Thereafter, while drying in an oven maintained at 90° C., the laminate was brought into contact with a SUS heated roll having a surface temperature maintained at 75° C. for about 2 seconds (drying shrinkage treatment). The shrinkage rate of the laminate in the width direction due to the drying shrinkage treatment was 5.2%.
In this manner, a polarizer having a thickness of 5 μm was formed on the resin substrate.

2. Preparation of Polarizing Plate A hard coat (HC) layer (7 μm thick) was formed on one side of a triacetyl cellulose (TAC) film (25 μm thick). Specifically, the following was done. 40 parts by weight of an ultraviolet-curable acrylate resin (manufactured by Toa Gosei Co., Ltd., product name "M-920", solid content 100%) and 60 parts by weight of an ultraviolet-curable acrylate resin (manufactured by Mitsubishi Chemical Co., Ltd., product name "UV-1700TL", solid content 80%) were prepared. 3 parts by weight of a photopolymerization initiator (manufactured by BASF, product name "OMNIRAD907") and 0.12 parts by weight of a leveling agent (manufactured by Kyoeisha Chemical Co., Ltd., product name "LE-303", solid content 40%) were mixed per 100 parts by weight of the resin solid content. The mixture was diluted with a MIBK/cyclopentanone mixed solvent (weight ratio 70/30) so that the solid content concentration was 30%, to prepare a coating liquid for forming a hard coat layer. The coating liquid for forming a hard coat layer was applied to a TAC film using a bar coater to form a coating layer. The TAC film on which the coating layer was formed was heated at 80°C for 1 minute to dry the coating layer and form a coating film. The obtained coating film was irradiated with ultraviolet light with an integrated light amount of 240 mJ/ ^cm2 from a high-pressure mercury lamp to harden the coating film, forming a HC layer with a thickness of 7 μm.
On the other surface of the TAC film, an HC layer (thickness: 7 μm) was formed in the same manner as above. This HC layer was used as a conductive component permeation suppressing layer.
A laminate of HC layer/TAC film/conductive component permeation suppression layer was attached to the surface (opposite side to the resin substrate) of the polarizer obtained in 1 above via an ultraviolet curing adhesive. Specifically, the curing adhesive was applied so that the total thickness was 1.0 μm, and the layers were attached using a rolling machine. Thereafter, the adhesive was cured by irradiating it with UV light from the protective layer side. The laminate was attached so that the conductive component permeation suppression layer was on the polarizer side.
Next, the resin substrate was peeled off, and a resin layer (thickness 0.3 μm) was formed on the peeled surface. The resin layer was formed as follows. 97.0 parts of methyl methacrylate (MMA, Fujifilm Wako Pure Chemical Industries, Ltd., trade name "methyl methacrylate monomer"), 3.0 parts of the copolymerization monomer represented by the above general formula (1e), and 0.2 parts of a polymerization initiator (Fujifilm Wako Pure Chemical Industries, Ltd., trade name "2,2'-azobis (isobutyronitrile)") were dissolved in 200 parts of toluene. Next, the polymerization reaction was carried out for 5.5 hours while heating to 70 ° C. under a nitrogen atmosphere, and a boron-containing acrylic resin solution (solid content concentration: 33%) was obtained. The obtained boron-containing acrylic polymer had a Tg of 110 ° C. and a Mw of 80,000. 20 parts of this boron-containing acrylic polymer was dissolved in 80 parts of methyl ethyl ketone to obtain a resin solution (20%). This resin solution was applied to the peeled surface of the resin substrate using a wire bar, and the applied film was dried at 60° C. for 5 minutes to form a resin layer constituted of a solidified applied film of the organic solvent solution of the resin.
Finally, the adhesive layer A1 obtained in Production Example 1 was transferred onto the surface of the resin layer. In this manner, a polarizing plate (adhesive layer-attached polarizing plate) having a structure of HC layer/protective layer (TAC film)/conductive component permeation suppressing layer/adhesive layer/polarizer/resin layer/adhesive layer was obtained. The obtained polarizing plate was subjected to the above evaluations (3) to (6). The results are shown in Table 1.

[Example 2]
A polarizing plate (adhesive layer-attached polarizing plate) was obtained in the same manner as in Example 1, except that the thickness of the conductive component permeation suppression layer (HC layer) was set to 2 μm. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Example 3]
A polarizing plate (adhesive layer-attached polarizing plate) was obtained in the same manner as in Example 1, except that the thickness of the (outermost) HC layer and the conductive component permeation suppressing layer (HC layer) on the viewing side was set to 2 μm. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Example 4]
A polarizing plate (adhesive layer-attached polarizing plate) was obtained in the same manner as in Example 1, except that the (outermost) HC layer on the viewing side was not formed and the thickness of the conductive component permeation suppression layer (HC layer) was set to 2 μm. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Example 5]
A polarizing plate (adhesive layer-attached polarizing plate) was obtained in the same manner as in Example 1, except that the (outermost) HC layer on the viewing side was not formed. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Example 6]
A polarizing plate (adhesive layer-attached polarizing plate) was obtained in the same manner as in Example 1, except that a resin layer was used instead of the HC layer as the conductive component permeation suppression layer. The resin layer was formed in the same manner as in Example 1, except that the thickness was 0.5 μm. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Comparative Example 1]
Except for not forming either the conductive component permeation suppression layer or the resin layer, a polarizing plate (adhesive layer-attached polarizing plate) was obtained in the same manner as in Example 1. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Comparative Example 2]
Except for not forming the conductive component permeation suppression layer, a polarizing plate (adhesive layer-attached polarizing plate) was obtained in the same manner as in Example 1. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Comparative Example 3]
A polarizing plate (adhesive layer-attached polarizing plate) was obtained in the same manner as in Example 1, except that the conductive component permeation suppression layer was not formed and the thickness of the resin layer was set to 5 μm. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Reference Example 1]
A polarizing plate (adhesive layer-attached polarizing plate) was obtained in the same manner as in Example 1, except that an acrylic film (thickness 40 μm) was used as the protective layer instead of the TAC film, and the conductive component permeation suppression layer was not formed. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Reference Example 2]
Except for using the pressure-sensitive adhesive layer A2 instead of the pressure-sensitive adhesive layer A1, a polarizing plate (pressure-sensitive adhesive layer-attached polarizing plate) was obtained in the same manner as in Example 1. The obtained polarizing plate was subjected to the same evaluations as in Example 1. The results are shown in Table 1.

[evaluation]
As is clear from Table 1, the polarizing plate of the embodiment of the present invention shows excellent durability in a high temperature and high humidity environment. More specifically, the polarizing plate of the embodiment of the present invention suppresses the appearance defect of the protective layer after various reliability tests, and suppresses the color loss of the polarizing plate. It was also confirmed that the polarizing plate of the embodiment of the present invention suppresses the cracking of the polarizing plate, and furthermore, the single transmittance is maintained within an allowable range. Furthermore, as is clear from the reference example, it can be seen that the durability issues of the appearance defect of the protective layer and the color loss of the polarizing plate are issues specific to a polarizing plate having a protective layer composed of a low resistance adhesive layer and a TAC film.

The polarizing plate of the present invention is suitable for use in image display devices such as liquid crystal displays, organic EL displays, and inorganic EL displays.

REFERENCE SIGNS LIST 10 Polarizer 20 Protective layer 30 Pressure-sensitive adhesive layer 40 Resin layer 50 Conductive component permeation suppressing layer 60 Hard coat layer 100 Polarizing plate

Claims (8)

a polarizer, a protective layer provided on one side of the polarizer, a resin layer provided on the other side of the polarizer, and a pressure-sensitive adhesive layer provided on a side of the resin layer opposite to the polarizer,
The protective layer is made of a triacetyl cellulose film,
the pressure-sensitive adhesive layer contains a conductive component and has a surface resistance value of 1.0×10 ⁸ Ω/□ to 1.0×10 ¹² Ω/□;
the resin layer is a solidified or thermoset product of a coating film of a resin in an organic solvent solution, and has a thickness of 2 μm or less;
a conductive component permeation suppression layer is provided between the polarizer and the protective layer;
Polarizer. The polarizing plate according to claim 1, wherein the protective layer is provided only on one side of the polarizer, and the resin layer is provided directly on the polarizer on the other side of the polarizer. The polarizing plate according to claim 1 or 2, further comprising a hard coat layer on the opposite side of the protective layer from the polarizer. The polarizing plate according to any one of claims 1 to 3, wherein the resin constituting the resin layer has a glass transition temperature of 85°C or higher and a weight average molecular weight Mw of 25,000 or higher. The polarizing plate according to any one of claims 1 to 4, wherein the conductive component permeation suppression layer is another hard coat layer. The polarizing plate according to any one of claims 1 to 4, wherein the conductive component permeation suppression layer is another resin layer, the another resin layer is a solidified or heat-cured product of a coating film of an organic solvent solution of the resin, the glass transition temperature of the resin constituting the another resin layer is 85°C or higher, and the weight average molecular weight Mw is 25,000 or higher. The polarizing plate according to any one of claims 1 to 6, wherein the polarizer has a thickness of 10 μm or less. An image display device comprising a polarizing plate according to any one of claims 1 to 7.

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