JP2024081558A - Polarizing plate with retardation layers and image display device - Google Patents

Abstract

To provide a highly durable polarizing plate with retardation layers.SOLUTION: A polarizing plate with retardation layers is provided, comprising a polarizing plate including a polarizer, a first retardation layer, a first adhesive layer, a second retardation layer, and a second adhesive layer arranged in the described order. The first retardation layer exhibits a refractive index characteristic satisfying a relationship expressed as nz>nx=ny, and the second retardation layer exhibits a refractive index characteristic satisfying a relationship expressed as nx>ny≥nz. The first retardation layer and the second retardation layer are resin films.SELECTED DRAWING: Figure 1

Description

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

In recent years, with the spread of thin displays, displays equipped with organic EL panels (organic EL display devices) have been proposed. Since organic EL panels have a highly reflective metal layer, they are prone to problems such as reflection of external light and reflection of the background. It is known that these problems can be prevented by providing a circular polarizing plate on the viewing side. A typical circular polarizing plate is one in which a retardation layer that functions as a λ/4 plate is laminated so that its slow axis forms an angle of about 45° with the absorption axis of the polarizer. In addition, from the viewpoint of viewing angle compensation, a retardation layer-attached polarizing plate has also been proposed in which a retardation layer exhibiting refractive index characteristics of nz>nx=ny is further laminated on the opposite side of the retardation layer from the polarizer.

JP 2019-66882 A

Conventional polarizing plates with a retardation layer may suffer from color unevenness at high temperatures, and there is room for improvement in durability. The main object of the present invention is to provide a polarizing plate with a retardation layer that has excellent durability.

[1] A polarizing plate with a retardation layer according to an embodiment of the present invention has a polarizing plate including a polarizer, a first retardation layer, a first pressure-sensitive adhesive layer, a second retardation layer, and a second pressure-sensitive adhesive layer, in this order. The first retardation layer has a refractive index characteristic that satisfies the relationship nz>nx=ny, and the second retardation layer has a refractive index characteristic that satisfies the relationship nx>ny≧nz. The first retardation layer and the second retardation layer are composed of resin films.
[2] In the above [1], the polarizing plate may include the polarizer and a protective layer arranged only on the side of the polarizer opposite to the side on which the first retardation layer is arranged.
[3] In the above [1] or [2], the second retardation layer may have an Re(550) of 120 nm to 170 nm, and the angle between the slow axis of the second retardation layer and the absorption axis of the polarizer may be 40° to 50° or 130° to 140°.
[4] In any one of the above [1] to [3], the first retardation layer may have Rth(550) of −70 nm to −165 nm.
[5] In any one of the above [1] to [4], the resin film constituting the second retardation layer may contain a polycarbonate-based resin.
[6] In any one of the above [1] to [5], the retardation layer-attached polarizing plate may be used in an organic EL display device.
[7] An image display device according to an embodiment of the present invention includes the retardation layer-attached polarizing plate according to any one of [1] to [6] above.
[8] In the above [7], the image display device may be an organic electroluminescence display device.

According to an embodiment of the present invention, a polarizing plate with a retardation layer having excellent durability is provided.

1 is a schematic cross-sectional view showing an outline of a configuration of a retardation layer-attached polarizing plate in one embodiment of the present invention. 1 is a schematic cross-sectional view showing a general configuration of an organic EL display device according to an embodiment of the present invention.

The following describes embodiments of the present invention with reference to the drawings, but the present invention is not limited to these embodiments. In order to make the description clearer, the drawings may show the width, thickness, shape, etc. of each part more diagrammatically than the embodiments, but these are merely examples and do not limit the interpretation of the present invention. In this specification, (meth)acrylic refers to acrylic and/or methacrylic. In this specification, the term "to" indicating a numerical range includes the upper and lower numerical limits.

(Definition of terms and symbols)
The definitions of terms and symbols used in this specification are as follows.
(1) Refractive index (nx, ny, nz)
"nx" is the refractive index in the direction in which the in-plane refractive index is maximum (i.e., the slow axis direction), "ny" is the refractive index in the direction perpendicular to the slow axis in the plane (i.e., the fast axis direction), and "nz" is the refractive index in the thickness direction.
(2) In-plane retardation (Re)
"Re(λ)" is the in-plane retardation measured with light having a wavelength of λ nm at 23° C. For example, "Re(550)" is the in-plane retardation measured with light having a wavelength of 550 nm at 23° C. Re(λ) is calculated by the formula: Re(λ)=(nx−ny)×d, where d (nm) is the thickness of the layer (film).
(3) Retardation in the thickness direction (Rth)
"Rth(λ)" is the retardation in the thickness direction measured with light having a wavelength of λ nm at 23° C. For example, "Rth(550)" is the retardation in the thickness direction measured with light having a wavelength of 550 nm at 23° C. Rth(λ) is calculated by the formula: Rth(λ)=(nx-nz)×d, where d (nm) is the thickness of the layer (film).
(4) Nz Coefficient The Nz coefficient is calculated by Nz=Rth/Re.
(5) Angle When referring to an angle in this specification, the angle includes both clockwise and counterclockwise angles with respect to a reference direction. Thus, for example, "45°" means 45° clockwise and 45° counterclockwise.

A. Retardation layer-attached polarizing plate The retardation layer-attached polarizing plate according to the embodiment of the present invention has a polarizing plate including a polarizer, a first retardation layer, a first adhesive layer, a second retardation layer, and a second adhesive layer in this order, the first retardation layer exhibits a refractive index characteristic of nz>nx=ny, the second retardation layer exhibits a refractive index characteristic of nx>ny≧nz, and the first retardation layer and the second retardation layer are composed of a resin film. By adopting such a configuration, a retardation layer-attached polarizing plate having excellent durability can be obtained. In addition, a retardation layer-attached polarizing plate having such a configuration can exhibit excellent anti-reflection properties.

A-1. Overall configuration of retardation layer-attached polarizing plate Fig. 1 is a schematic cross-sectional view showing the outline of the configuration of a retardation layer-attached polarizing plate according to one embodiment of the present invention. The retardation layer-attached polarizing plate 100 has a polarizing plate 10, a first retardation layer 20, a first adhesive layer 30, a second retardation layer 40, and a second adhesive layer 50, in this order. Both the first retardation layer 20 and the second retardation layer 40 are made of a resin film.

The polarizing plate 10 includes a polarizer 12 and further includes a protective layer 14 arranged on the side of the polarizer 12 opposite to the side on which the first retardation layer 20 is arranged. In the illustrated example, no protective layer is arranged between the polarizer 12 and the first retardation layer 20, and the first retardation layer 20 is arranged adjacent to the polarizer 12. Even when the protective layer is omitted in this way, the first retardation layer 20 made of a resin film can function as a protective layer for the polarizer 12, so that the durability of the retardation layer-attached polarizing plate 100 can be ensured. In addition, it can contribute to making the retardation layer-attached polarizing plate 100 thinner. The retardation layer-attached polarizing plate 100 is typically used in an image display device, and is arranged so that the polarizer 12 is closer to the viewing side than the first retardation layer 20 in the image display device. For example, the retardation layer-attached polarizing plate 100 can be attached to an image display panel included in the image display device by the second adhesive layer 50.

Although not shown, in practice, a release liner is attached to the surface of the second adhesive layer 50. The release liner can be temporarily attached until the retardation layer-attached polarizing plate is used. By using the release liner, for example, the second adhesive layer 50 is protected and the retardation layer-attached polarizing plate 100 can be formed into a roll.

The retardation layer-attached polarizing plate 100 may further have other functional layers not shown. The type, characteristics, number, combination, arrangement, etc. of the other functional layers that the retardation layer-attached polarizing plate may have may be appropriately set according to the purpose. For example, the retardation layer-attached polarizing plate may further have a conductive layer or a conductive layer-attached isotropic substrate. A retardation layer-attached polarizing plate having a conductive layer or a conductive layer-attached isotropic substrate is applied to, for example, a so-called inner touch panel type input display device in which a touch sensor is incorporated inside an image display panel. As another example, the retardation layer-attached polarizing plate may further have other retardation layers. The optical characteristics (e.g., refractive index characteristics, in-plane retardation, Nz coefficient, photoelastic coefficient), thickness, arrangement, etc. of the other retardation layers may be appropriately set according to the purpose. As a specific example, the viewing side of the polarizer may be provided with other retardation layers (typically, a layer that imparts (elliptical) polarizing function, a layer that imparts ultra-high retardation) that improve visibility when viewed through polarized sunglasses. By providing such a layer, excellent visibility can be achieved even when the display screen is viewed through polarized lenses such as polarized sunglasses, and the device can be suitably applied to image display devices that can be used outdoors.

The members constituting the retardation layer-attached polarizing plate 100 are typically laminated via any suitable adhesive layer. Specific examples of the adhesive layer include an adhesive layer and a pressure-sensitive adhesive layer. For example, as described above, the first retardation layer 20 and the second retardation layer 40 are laminated via the first pressure-sensitive adhesive layer 30. Although not shown, the protective layer 14 is attached to the polarizer 12 via an adhesive layer (preferably using an active energy ray-curable adhesive). For example, the polarizing plate 10 and the first retardation layer 20 are laminated via an adhesive layer (preferably using an active energy ray-curable adhesive) or a pressure-sensitive adhesive layer (preferably using an acrylic pressure-sensitive adhesive). The thickness of the adhesive layer is, for example, 0.1 μm or more, preferably 0.3 μm to 5 μm, and more preferably 0.5 μm to 3 μm.

The thickness of the laminated portion from the polarizing plate 10 to the second adhesive layer 50 (hereinafter sometimes referred to as the total thickness) is, for example, 150 μm or less, preferably 100 μm or less, and, for example, 30 μm or more, preferably 60 μm or more. The total thickness includes the thickness of the adhesive layer.

The retardation layer-attached polarizing plate 100 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 laminate can be wound into a roll.

A-2. Polarizing Plate The polarizing plate 10 includes a polarizer 12, and preferably further includes a protective layer 14 on the side of the polarizer 12 opposite to the side on which the first retardation layer 20 is disposed. If necessary, the polarizing plate 10 may include a protective layer on the side of the polarizer 12 on which the first retardation layer 20 is disposed.

A-2-1. Polarizer The polarizer 12 is typically a resin film containing a dichroic material (e.g., iodine). Examples of the resin film include hydrophilic polymer films such as polyvinyl alcohol (PVA)-based films, partially formalized PVA-based films, and partially saponified ethylene-vinyl acetate copolymer-based films.

The thickness of the polarizer is, for example, 18 μm or less, preferably 15 μm or less, more preferably 12 μm or less, and even more preferably 8 μm or less. The thickness of the polarizer is preferably 1 μm or more.

The polarizer preferably exhibits absorption dichroism at any wavelength between 380 nm and 780 nm. The single transmittance of the polarizer is, for example, 40.0% to 46.0%, preferably 41.0% to 45.0%, and more preferably 41.5% to 44.5%. 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.

The polarizer may be produced by any suitable method. Specifically, the polarizer may be produced from a single-layer resin film, or may be produced using a laminate including a substrate.

A typical method for producing a polarizer from the above-mentioned single-layer resin film includes subjecting the resin film to a dyeing process using a dichroic substance such as iodine or a dichroic dye, and a stretching process. As the resin film, for example, a hydrophilic polymer film such as a polyvinyl alcohol (PVA)-based film, a partially formalized PVA-based film, or an ethylene-vinyl acetate copolymer-based partially saponified film is used. The method may further include an insolubilization process, a swelling process, a crosslinking process, etc. Such a manufacturing method is well known and commonly used in the industry, so a detailed description will be omitted.

A polarizer obtained by using a laminate including the above-mentioned substrate can be produced, for example, by using a laminate of a resin substrate and a resin film or resin layer (typically, a PVA-based resin layer). Specifically, a PVA-based resin solution is applied to a resin substrate, and dried 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; and the laminate is stretched and dyed to make the PVA-based resin layer into a polarizer. In this embodiment, preferably, a PVA-based resin layer containing a halide and a PVA-based resin is formed on one side of the resin substrate. The stretching typically includes immersing the laminate in an aqueous boric acid solution and stretching it. Furthermore, the stretching may further include, as necessary, stretching the laminate in the air at a high temperature (e.g., 95°C or higher) before stretching in the aqueous boric acid solution. In addition, in this embodiment, preferably, the laminate is subjected to a drying and shrinking treatment in which the laminate is heated while being transported in the longitudinal direction to shrink the laminate by 2% or more in the width direction. Typically, the manufacturing method of the present 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 high optical properties can be achieved. In addition, by simultaneously increasing the orientation of PVA in advance, problems such as a decrease in the orientation of PVA and dissolution can be prevented when immersed in water in the subsequent dyeing and stretching steps, 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 PVA molecules can be suppressed compared to when the PVA-based resin layer does not contain a halide, and high optical properties can be achieved. Furthermore, by shrinking the laminate in the width direction by the drying shrinkage treatment, high optical properties can be achieved. A polarizing plate can be obtained by laminating a protective layer on the peeled surface obtained by peeling the resin substrate from the obtained resin substrate/polarizer laminate, or on the surface opposite to the peeled surface. Details of the manufacturing method of such a polarizer are described, for example, in JP 2012-73580 A and Japanese Patent No. 6470455. The entire disclosures of these publications are incorporated herein by reference.

A-2-2. Protective layer The protective layer 14 may be formed of any suitable resin film that can be used as a protective layer for a polarizer, for example. Specific examples of the resin that is the main component of the resin film include cellulose-based resins such as triacetyl cellulose (TAC), polyester-based resins, polyvinyl alcohol-based resins, polycarbonate-based resins, polyamide-based resins, polyimide-based resins, polyethersulfone-based resins, polysulfone-based resins, polystyrene-based resins, cycloolefin-based resins such as polynorbornene, polyolefin-based resins, (meth)acrylic resins, and acetate-based resins.

The polarizing plate with a retardation layer 100 is typically placed on the viewing side of an image display device, and the protective layer 14 is placed on the viewing side. Therefore, the protective layer 14 may be subjected to surface treatments such as hard coat (HC) treatment, anti-reflection treatment, anti-sticking treatment, and anti-glare treatment, as necessary.

The thickness of the protective layer is, for example, 5 μm to 80 μm, preferably 10 μm to 50 μm, and more preferably 15 μm to 35 μm. Note that if the above-mentioned surface treatment has been applied, the thickness of the protective layer includes the thickness of the surface treatment layer.

A-3. First phase difference layer The first phase difference layer 20 is a so-called positive C plate whose refractive index characteristics show the relationship of nz>nx=ny. By disposing a positive C plate between the polarizer and the second phase difference layer whose refractive index characteristics show the relationship of nx>ny≧nz, it is possible to prevent reflection in an oblique direction very well, and it is possible to further widen the viewing angle of the anti-reflection function. Here, "nx=ny" includes not only the case where nx and ny are strictly equal, but also the case where nx and ny are substantially equal. That is, the in-plane phase difference Re(550) of the first phase difference layer can be less than 10 nm.

The thickness direction retardation Rth(550) of the first retardation layer is preferably -70 nm to -165 nm, more preferably -80 nm to -155 nm, even more preferably -90 nm to -145 nm, and particularly preferably -100 nm to -135 nm.

The first phase difference layer preferably has a puncture elastic modulus of 50 g/mm or more, more preferably 52 g/mm or more, and even more preferably 55 g/mm or more. The puncture elastic modulus of the first phase difference layer is, for example, 200 g/mm or less. When the puncture elastic modulus of the first phase difference layer is within the above range, the dimensional change of the second phase difference layer (for example, expansion, contraction, etc. of the second phase difference layer composed of a stretched film of a resin film) can be suitably suppressed. In this specification, the puncture elastic modulus refers to the value obtained by dividing the force (g) just before the phase difference film breaks (or tears) when a needle (puncture tool) is pierced perpendicularly to the main surface of the phase difference film (for example, the first phase difference layer) by the strain (mm) at that time. As the needle, one with a tip diameter of 1 mmφ and 0.5R can be used. The needle piercing speed can be 0.33 cm/sec. The puncture modulus can be measured by sandwiching the retardation film between two plates with a circular hole having a diameter of 15 mm or less (for example, a diameter of 11 mm) through which a needle can pass. The puncture modulus can be measured in an environment at a temperature of 23°C. For example, the puncture modulus can be measured for five retardation films, and the average value can be used as the puncture modulus of the retardation film. Commercially available devices can be used to measure the puncture modulus. Examples of commercially available devices include a handy compression tester "KES-G5 Needle Penetration Force Measurement Specification" manufactured by Kato Tech Co., Ltd. and a small tabletop tester "EZ Test" manufactured by Shimadzu Corporation.

The first retardation layer is made of a resin film. Depending on the material used, retardation layers can be broadly divided into alignment layers of liquid crystal compounds (hereinafter, sometimes referred to as "liquid crystal alignment layers") and resin films. If the first retardation layer adjacent to the polarizing plate is a liquid crystal alignment layer, the polarizer may deteriorate (e.g., fade) due to the influence of the liquid crystal compound, polymerization initiator, etc. contained in the liquid crystal alignment layer. In contrast, if the first retardation layer is a resin film, such deterioration of the polarizer is suitably prevented. The liquid crystal alignment layer is a layer in which the liquid crystal compound is aligned in a predetermined direction within the layer and the alignment state is fixed, and an example of this is an alignment hardened layer obtained by hardening a liquid crystal monomer.

Resin materials that form the first retardation layer are typically made of resin materials with negative birefringence. Resins with negative birefringence are resins that exhibit a maximum refractive index in the direction perpendicular to the stretching direction when uniaxially stretched. Examples of resins with negative birefringence include resins in which a chemical bond or functional group with large polarization anisotropy, such as an aromatic ring or a carbonyl group, has been introduced into the side chain. Specific examples of resins with negative birefringence include acrylic resins, styrene resins, maleimide resins, modified polyolefin resins, and fumaric acid ester resins. The above resin materials can be used alone or in combination of two or more.

The acrylic resin can be obtained, for example, by addition polymerization of an acrylate monomer. Examples of acrylic resins include polymethyl methacrylate (PMMA), polybutyl methacrylate, and polycyclohexyl methacrylate.

The styrene-based resin can be obtained, for example, by addition polymerization of a styrene-based monomer. Examples of the styrene-based monomer include styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, p-chlorostyrene, p-nitrostyrene, p-aminostyrene, p-carboxystyrene, p-phenylstyrene, 2,5-dichlorostyrene, and p-t-butylstyrene.

The maleimide resin can be obtained, for example, by addition polymerization of a maleimide monomer. Examples of the maleimide monomer include N-ethylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide, N-(2-methylphenyl)maleimide, N-(2-ethylphenyl)maleimide, N-(2-propylphenyl)maleimide, N-(2-isopropylphenyl)maleimide, N-(2,6-dimethylphenyl)maleimide, N-(2,6-dipropylphenyl)maleimide, N-(2,6-diisopropylphenyl)maleimide, N-(2-methyl-6-ethylphenyl)maleimide, N-(2-chlorophenyl)maleimide, N-(2,6-dichlorophenyl)maleimide, N-(2-bromophenyl)maleimide, N-(2,6-dibromophenyl)maleimide, N-(2-biphenyl)maleimide, and N-(2-cyanophenyl)maleimide. Maleimide monomers can be obtained, for example, from Tokyo Chemical Industry Co., Ltd.

In the above addition polymerization, the birefringence properties of the resulting resin can be controlled by substituting the side chains after polymerization, or by carrying out maleimidization or grafting reactions.

The resin having negative birefringence may be copolymerized with other monomers. By copolymerizing other monomers, brittleness, moldability, and heat resistance can be improved. Examples of such other monomers include olefins such as ethylene, propylene, 1-butene, 1,3-butadiene, 2-methyl-1-butene, 2-methyl-1-pentene, and 1-hexene; acrylonitrile; (meth)acrylates such as methyl acrylate and methyl methacrylate; maleic anhydride; and vinyl esters such as vinyl acetate.

When the resin having negative birefringence is a copolymer of the styrene monomer and the other monomer, the blending ratio of the styrene monomer is preferably 50 mol% to 80 mol%. When the resin having negative birefringence is a copolymer of the maleimide monomer and the other monomer, the blending ratio of the maleimide monomer is preferably 2 mol% to 50 mol%. By blending in such a range, a resin film with excellent toughness and moldability can be obtained.

As the resin having the negative birefringence, preferably used are styrene-maleic anhydride copolymer, styrene-acrylonitrile copolymer, styrene-(meth)acrylate copolymer, styrene-maleimide copolymer, vinyl ester-maleimide copolymer, olefin-maleimide copolymer, etc. These can be used alone or in combination of two or more. These resins exhibit high negative birefringence and can have excellent heat resistance. These resins can be obtained, for example, from Nova Chemical Japan, Arakawa Chemical Industries, Ltd., etc.

As the resin having negative birefringence, a polymer having a repeating unit represented by the following general formula (I) is preferably used. Such a polymer exhibits even higher negative birefringence and can have excellent heat resistance and mechanical strength. Such a polymer can be obtained, for example, by using an N-phenyl-substituted maleimide in which a phenyl group having a substituent at least at the ortho position is introduced as the N-substituent of the maleimide monomer as the starting material.

In the above general formula (I), R ₁ to R ₅ each independently represent hydrogen, a halogen atom, a carboxylic acid, a carboxylate, a hydroxyl group, a nitro group, or a linear or branched alkyl or alkoxy group having 1 to 8 carbon atoms (provided that R ₁ and R ₅ are not simultaneously hydrogen atoms), R ₆ and R ₇ represent hydrogen or a linear or branched alkyl or alkoxy group having 1 to 8 carbon atoms, and n represents an integer of 2 or greater.

Resins having negative birefringence are not limited to the above, and for example, resins having negative birefringence described in JP-T-2008-544304 and JP-T-2008-544317 can be used.

The resin film forming the first retardation layer may further contain any suitable additive, if necessary. Specific examples of additives include plasticizers, heat stabilizers, light stabilizers, lubricants, antioxidants, UV absorbers, flame retardants, colorants, antistatic agents, compatibilizers, crosslinking agents, thickeners, etc. The type and content of the additives may be appropriately set depending on the purpose. The content of the additives in the resin film is, for example, about 3% to 10% by weight.

Any suitable manufacturing method can be used as a manufacturing method for the first phase difference layer composed of the resin film. In one embodiment, the resin film containing the resin material can be used as the first phase difference layer as it is after film formation (i.e., in an unstretched state). For example, when a film is formed by a solution film-forming method using a resin solution containing the resin material, stress occurs due to volume shrinkage when the resin solution is dried on the support, and the molecular chains of the polymer tend to be oriented in the in-plane direction. Therefore, when a resin material that has high birefringence expression and negative intrinsic birefringence is used, a coating film having a large thickness direction birefringence can be formed on the support due to the shrinkage action during drying, and the coating film can be used as it is as a positive C plate.

The thickness of the first retardation layer is, for example, 1 μm to 40 μm, preferably 3 μm to 35 μm, and more preferably 5 μm to 30 μm.

A-4. Second phase difference layer The second phase difference layer 40 has a refractive index characteristic of nx>ny≧nz. In one embodiment, the second phase difference layer can function as a λ/4 plate. The in-plane retardation Re(550) of the second phase difference layer is, for example, 120 nm to 170 nm, preferably 130 nm to 160 nm, and more preferably 140 nm to 150 nm. Here, "ny=nz" includes not only the case where ny and nz are completely equal, but also the case where they are substantially equal. Therefore, there may be cases where ny<nz within the range that does not impair the effects of the present invention. In this specification, a phase difference layer having a refractive index characteristic of nx>ny=nz may be referred to as a positive A plate, and a phase difference layer having a refractive index characteristic of nx>ny>nz may be referred to as a negative B plate.

The Nz coefficient of the second retardation layer is preferably 0.9 to 3, more preferably 0.9 to 2.5, even more preferably 0.9 to 1.5, and particularly preferably 0.9 to 1.3. By satisfying such a relationship, when the obtained polarizing plate with a retardation layer is used in an image display device, an extremely excellent reflection hue can be achieved.

The second retardation layer is arranged so that its slow axis forms an angle with the absorption axis of the polarizer 12 of, for example, 40° to 50° or 130° to 140°, preferably 42° to 48° or 132° to 138°, and more preferably about 45° or about 135°. By configuring in this way, a polarizing plate with a retardation layer having very good circular polarization properties (and, as a result, very good antireflection properties) can be obtained.

The second retardation layer may exhibit an inverse dispersion wavelength characteristic in which the retardation value increases with the wavelength of the measurement light, may exhibit a positive wavelength dispersion characteristic in which the retardation value decreases with the wavelength of the measurement light, or may exhibit a flat wavelength dispersion characteristic in which the retardation value hardly changes with the wavelength of the measurement light. In one embodiment, the second retardation layer exhibits an inverse dispersion wavelength characteristic. In this case, Re(450)/Re(550) of the retardation layer is, for example, 0.8 or more and less than 1, and preferably 0.8 or more and 0.95 or less. With such a configuration, very excellent anti-reflection properties can be realized.

The second retardation layer is composed of a resin film. The second retardation layer is typically a stretched resin film.

In one embodiment, the second retardation layer contains a resin having an absolute value of a photoelastic coefficient of preferably 2×10 ⁻¹¹ m ² /N or less, more preferably 2.0×10 ⁻¹³ m ² /N to 1.5× ^{10 −11} m ² /N, and even more preferably 1.0×10 ⁻¹² m ² /N to 1.2× ^{10 −11} m ² /N. If the absolute value of the photoelastic coefficient is in such a range, a change in retardation is unlikely to occur when shrinkage stress occurs during heating. As a result, the thermal unevenness of the obtained image display device can be well prevented.

Examples of resins contained in the resin film include polycarbonate-based resins, polyester carbonate-based resins, polyester-based resins, polyvinyl acetal-based resins, polyarylate-based resins, cyclic olefin-based resins, cellulose-based resins, polyvinyl alcohol-based resins, polyamide-based resins, polyimide-based resins, polyether-based resins, polystyrene-based resins, acrylic-based resins, and the like. These resins may be used alone or in combination (e.g., blended or copolymerized). When the second retardation layer exhibits reverse dispersion wavelength characteristics, a resin film containing a polycarbonate-based resin or a polyester carbonate-based resin (hereinafter sometimes simply referred to as a polycarbonate-based resin) may be suitably used.

As the polycarbonate-based resin, any suitable polycarbonate-based resin can be used as long as the effects of the present invention can be obtained. For example, the polycarbonate-based resin contains a structural unit derived from a fluorene-based dihydroxy compound, a structural unit derived from an isosorbide-based dihydroxy compound, and a structural unit derived from at least one dihydroxy compound selected from the group consisting of alicyclic diol, alicyclic dimethanol, di-, tri- or polyethylene glycol, and alkylene glycol or spiro glycol. Preferably, the polycarbonate-based resin contains a structural unit derived from a fluorene-based dihydroxy compound, a structural unit derived from an isosorbide-based dihydroxy compound, a structural unit derived from an alicyclic dimethanol and/or a structural unit derived from a di-, tri- or polyethylene glycol; more preferably, it contains a structural unit derived from a fluorene-based dihydroxy compound, a structural unit derived from an isosorbide-based dihydroxy compound, and a structural unit derived from a di-, tri- or polyethylene glycol. The polycarbonate-based resin may contain a structural unit derived from another dihydroxy compound as necessary. Details of polycarbonate-based resins that can be suitably used in the second retardation layer and methods for forming the second retardation layer are described, for example, in JP-A-2014-10291, JP-A-2014-26266, JP-A-2015-212816, JP-A-2015-212817, and JP-A-2015-212818, and the descriptions in these publications are incorporated herein by reference.

The thickness of the second retardation layer is, for example, 10 μm to 100 μm, preferably 10 μm to 70 μm, more preferably 10 μm to 60 μm, and even more preferably 20 μm to 50 μm.

A-5. First Pressure-Sensitive Adhesive Layer The first pressure-sensitive adhesive layer 30 is provided between the first retardation layer 20 and the second retardation layer 40. Typically, the first retardation layer 20 and the second retardation layer 40 are directly bonded to each other via the first pressure-sensitive adhesive layer 30.

The storage modulus (25°C) of the first pressure-sensitive adhesive layer is, for example, 0.05 MPa to 1.50 MPa, preferably 0.08 MPa to 0.50 MPa. When the storage modulus of the first pressure-sensitive adhesive layer is within the above range, the effects of the present invention can be suitably obtained. The storage modulus can be measured, for example, by the following measurement method.
<Method for measuring storage modulus>
A laminate of multiple pressure-sensitive adhesive layers with a thickness of about 1.5 mm is used as a measurement sample. Dynamic viscoelasticity measurement is performed under the following conditions using an "Advanced Rheometric Expansion System (ARES)" manufactured by Rheometric Scientific as a measurement device, and the storage modulus at 25°C is read from the measurement results.
(Measurement condition)
- Deformation mode: Torsion - Frequency: 1Hz
・Crimping load: 100g
・Heating rate: 5℃/min ・Temperature range: -50℃ to 150℃
Shape: Parallel plate, 8.0 mm diameter

The first adhesive layer may be made of any suitable adhesive. Specific examples include acrylic adhesives, rubber adhesives, silicone adhesives, polyester adhesives, urethane adhesives, epoxy adhesives, and polyether adhesives. By adjusting the type, number, combination, and compounding ratio of the monomers forming the base resin of the adhesive, as well as the compounding amount of the crosslinking agent, reaction temperature, reaction time, etc., an adhesive having the desired properties according to the purpose can be prepared. The base resin of the adhesive may be used alone or in combination of two or more types. An acrylic resin is preferably used as the base resin. Specifically, the first adhesive layer is preferably made of an acrylic adhesive containing a (meth)acrylic polymer as the main component.

The (meth)acrylic polymer contains structural units derived from alkyl (meth)acrylate. The content of structural units derived from alkyl (meth)acrylate in the (meth)acrylic polymer is typically 50% by weight or more, for example 80% by weight or more, preferably 90% by weight or more, more preferably 93% by weight or more, and is, for example, 100% by weight or less, preferably 98% by weight or less.

The alkyl group of the alkyl (meth)acrylate may be linear or branched. The number of carbon atoms in the alkyl group is, for example, 1 or more and 18 or less. Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a 2-ethylhexyl group, a decyl group, an isodecyl group, and an octadecyl group. The alkyl (meth)acrylates may be used alone or in combination. The average number of carbon atoms in the alkyl group is preferably 3 to 10.

In addition to the structural units derived from alkyl (meth)acrylates, the (meth)acrylic polymer may also contain structural units derived from copolymerizable monomers polymerizable with alkyl (meth)acrylates. Examples of the copolymerizable monomers include carboxyl group-containing monomers, hydroxyl group-containing monomers, and nitrogen-containing monomers. The copolymerizable monomers can be used alone or in combination.

The carboxyl group-containing monomer is a compound that contains a carboxyl group in its structure and a polymerizable unsaturated double bond such as a (meth)acryloyl group or a vinyl group. Examples of the carboxyl group-containing monomer include (meth)acrylic acid, carboxyethyl (meth)acrylate, maleic acid, fumaric acid, and crotonic acid, and preferably (meth)acrylic acid. When the (meth)acrylic polymer contains a structural unit derived from a carboxyl group-containing monomer, the adhesive properties of the adhesive layer can be improved. When the (meth)acrylic polymer contains a structural unit derived from a carboxyl group-containing monomer, the content of the structural unit derived from the carboxyl group-containing monomer in the (meth)acrylic polymer is preferably 0.01% by weight or more and 10% by weight or less.

The hydroxyl group-containing monomer is a compound that contains a hydroxyl group in its structure and a polymerizable unsaturated double bond such as a (meth)acryloyl group or a vinyl group. Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)-methyl acrylate, preferably 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate, and more preferably 2-hydroxyethyl (meth)acrylate. When the (meth)acrylic polymer contains a structural unit derived from a hydroxyl group-containing monomer, the durability of the adhesive layer can be improved. When the (meth)acrylic polymer contains a structural unit derived from a hydroxyl group-containing monomer, the content of the structural unit derived from the hydroxyl group-containing monomer in the (meth)acrylic polymer is preferably 0.01% by weight or more and 10% by weight or less.

Examples of the nitrogen-containing monomer include nitrogen-containing vinyl monomers and cyanoacrylate monomers. Examples of the nitrogen-containing vinyl monomer include N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, (meth)acryloylmorpholine, N-vinyl carboxylic acid amides, and N-vinylcaprolactam. Examples of the cyanoacrylate monomer include acrylonitrile and methacrylonitrile. When the (meth)acrylic polymer contains a structural unit derived from a nitrogen-containing monomer, the content of the structural unit derived from the nitrogen-containing monomer in the (meth)acrylic polymer is preferably 0.01% by weight or more and 10% by weight or less.

The weight average molecular weight Mw of the (meth)acrylic polymer is, for example, 1,000,000 to 3,000,000, and preferably 1,200,000 to 2,500,000.

The content of the (meth)acrylic polymer in the adhesive is, in terms of solid content, for example, 50% by weight or more, preferably 60% by weight or more, more preferably 70% by weight or more, and even more preferably 80% by weight or more. The upper limit of the content can be, for example, 99.9% by weight or less, preferably 99.8% by weight or less.

The (meth)acrylic adhesive may also contain a crosslinking agent. Representative examples of crosslinking agents include organic crosslinking agents and polyfunctional metal chelates, and preferably organic crosslinking agents. Examples of organic crosslinking agents include isocyanate crosslinking agents, peroxide crosslinking agents, epoxy crosslinking agents, and imine crosslinking agents, and more preferably isocyanate crosslinking agents. When the adhesive contains a crosslinking agent, the content of the crosslinking agent is usually 0.01 parts by weight or more and 15 parts by weight or less, for example 0.1 parts by weight or more and 10 parts by weight or less, relative to 100 parts by weight of the (meth)acrylic polymer.

The (meth)acrylic adhesive may contain various additives, such as polymerization initiators, polymerization catalysts, crosslinking catalysts, silane coupling agents, tackifiers, plasticizers, softeners, deterioration inhibitors, fillers, colorants, UV absorbers, antioxidants, surfactants, antistatic agents, etc., as necessary, to the extent that the properties of the present invention are not impaired.

The thickness of the first adhesive layer is, for example, 5 μm or more, preferably 10 μm or more, and, for example, 100 μm or less, preferably 80 μm or less.

The first adhesive layer can be formed by coating and drying an adhesive composition containing a base resin, additives such as a crosslinking agent, and a solvent. For example, the adhesive composition can be directly coated on the first retardation layer or the second retardation layer and dried to form the first adhesive layer. Alternatively, the adhesive composition can be coated on a separately prepared substrate such as a base film and dried to form the first adhesive layer, which can then be transferred to the first retardation layer or the second retardation layer. Drying is typically performed by heating.

A-6. Second adhesive layer The second adhesive layer 50 is provided on the side of the second retardation layer 40 opposite to the side on which the first adhesive layer 30 is disposed. As described above, the retardation layer-attached polarizing plate 100 can be attached to a member constituting an image display device such as a display element via the second adhesive layer 50.

The storage modulus (25°C) of the second adhesive layer is, for example, 0.05 MPa to 1.50 MPa, and preferably 0.08 MPa to 0.50 MPa. When the storage modulus of the second adhesive layer is within the above range, the effects of the present invention can be preferably obtained.

The second adhesive layer may be made of any suitable adhesive. Specific examples include acrylic adhesives, rubber adhesives, silicone adhesives, polyester adhesives, urethane adhesives, epoxy adhesives, and polyether adhesives. By adjusting the type, number, combination, and compounding ratio of the monomers forming the base resin of the adhesive, as well as the compounding amount of the crosslinking agent, reaction temperature, reaction time, etc., an adhesive having the desired properties according to the purpose can be prepared. The base resin of the adhesive may be used alone or in combination of two or more. An acrylic resin is preferably used as the base resin. Specifically, the second adhesive layer is preferably made of an acrylic adhesive containing a (meth)acrylic polymer as a main component. The same explanation as for the adhesive constituting the first adhesive layer can be applied to the adhesive constituting the second adhesive layer.

The thickness of the second adhesive layer is, for example, 5 μm or more, preferably 10 μm or more, and, for example, 100 μm or less, preferably 80 μm or less.

A-7. Release Liner An example of the release liner is a flexible plastic film. Examples of the plastic film include a polyethylene terephthalate film, a polyethylene film, a polypropylene film, and a polyester film. The thickness of the release liner is, for example, 3 μm or more and, for example, 200 μm or less. The surface of the release liner is coated with a release agent. Specific examples of the release agent include a silicone-based release agent, a fluorine-based release agent, and a long-chain alkyl acrylate-based release agent.

B. Image display device The retardation layer-attached polarizing plate can be applied to an image display device. Therefore, an image display device according to an embodiment of the present invention includes the retardation layer-attached 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).

Figure 2 is a cross-sectional view showing a schematic configuration of an image display device (organic EL display device) according to one embodiment of the present invention. The organic EL device 200 has an organic EL panel 120 and a retardation layer-attached polarizing plate 100 arranged on the viewing side. The retardation layer-attached polarizing plate 100 is arranged so that the first retardation layer 20 is closer to the organic EL panel 120 than the polarizer 12, and is attached to the organic EL panel 120 by a second adhesive layer 50. The organic EL panel 120 includes metal members (e.g., electrodes, sensors, wiring, metal layers), but since the retardation layer-attached polarizing plate 100 has excellent anti-reflection properties, it can effectively prevent reflections caused by the metal members.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Various measurement methods are as follows. Furthermore, unless otherwise specified, "parts" and "%" in the examples and comparative examples are by weight.

1. Thickness Thicknesses of 1 μm or less were measured using a scanning electron microscope (manufactured by JEOL Ltd., product name "JSM-7100F"), and thicknesses of more than 1 μm were measured using a digital micrometer (manufactured by Anritsu Corporation, product name "KC-351C").
2. In-plane retardation Re(λ) and thickness direction retardation Rth(λ)
The in-plane retardation at each wavelength at 23° C. was measured using a Mueller matrix polarimeter (manufactured by Axometrics, product name "Axoscan").
3. Refractive Index The average refractive index was measured using an Abbe refractometer manufactured by Atago Co., Ltd., and the refractive indexes nx, ny, and nz were calculated from the above retardation value.
4. Color difference Δa ^* b ^*
The spectral reflectance was measured under the following measurement conditions using a spectrophotometer (CM-2600d, manufactured by Konica Minolta), and a ^* and b ^* in the L ^* a ^* b ^* color space were determined.
(Measurement condition)
Type of receiving optical system: SCE (specular reflection excluded)
Measurement wavelength range: 360 nm to 740 nm
Light source: D65
Measurement diameter MAV: φ8mm
The color difference (Δa ^* b ^* ) was calculated by the following formula.
Δa ^* b ^* = √(Δa ^* ^ 2 + Δb ^* ^ 2)
5. Single transmittance and degree of polarization The single transmittance Ts, parallel transmittance Tp, and crossed transmittance Tc of the polarizing plate were measured using a spectrophotometer (Otsuka Electronics Co., Ltd., "LPF-200"). These Ts, Tp, and Tc are Y values measured using a 2-degree visual field (C light source) according to JIS Z8701 and corrected for visibility. From the obtained Tp and Tc, the degree of polarization of the polarizing plate (polarizer) was calculated using the following formula.
Degree of polarization (%)={(Tp−Tc)/(Tp+Tc)} ^1/2 ×100

[Production Example 1: Preparation of Polarizing Plate A]
(Preparation of Polarizer)
As a thermoplastic resin substrate, a long amorphous isophthalic copolymerized polyethylene terephthalate film (thickness: 100 μm) having a Tg of about 75° C. was used, and 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 Mitsubishi Chemical Corporation, product name "GOHSENEX Z410") in a ratio of 9:1, and dissolving the resultant 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 2.4 times in the longitudinal direction (machine direction) in an oven at 130° C. (auxiliary in-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 have a desired 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 wt %, potassium iodide concentration: 5 wt %) at a liquid temperature of 70° C., and uniaxially stretched in the longitudinal direction (longitudinal direction) between rolls with 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, the film was dried in an oven maintained at about 90° C., while being brought into contact with a SUS heated roll whose surface temperature was maintained at about 75° C. (drying shrinkage treatment).
In this manner, a polarizer having a thickness of 5 μm was formed on the resin substrate.

(Preparation of Polarizing Plate A)
A HC-TAC film was attached as a protective layer to the surface of the obtained polarizer (the surface opposite to the resin substrate) via an ultraviolet-curing adhesive. Specifically, the ultraviolet-curing adhesive was applied to a thickness of 1.0 μm, and the two were attached using a rolling machine. Then, UV rays were irradiated from the protective layer side to cure the adhesive. The HC-TAC film was a film in which a hard coat (HC) layer (thickness 7 μm) was formed on a triacetyl cellulose (TAC) film (thickness 25 μm), and the two were attached so that the TAC film was on the polarizer side. Next, the resin substrate was peeled off and removed to obtain a polarizing plate A having a configuration of [polarizer/HC-attached TAC protective layer]. The single transmittance of the polarizing plate A was 43%, and the polarization degree was 99.9%.

[Production Example 2A: Preparation of Positive C Plate A]
In an autoclave equipped with a stirrer, a cooling tube, a nitrogen inlet tube and a thermometer, 48 parts by weight of hydroxypropyl methylcellulose (manufactured by Shin-Etsu Chemical, trade name: Metolose 60SH-50), 15601 parts by weight of distilled water, 8161 parts by weight of diisopropyl fumarate, 240 parts by weight of 3-ethyl-3-oxetanylmethyl acrylate and 45 parts by weight of t-butyl peroxypivalate as a polymerization initiator were placed, and after nitrogen bubbling for 1 hour, the mixture was stirred and held at 49°C for 24 hours to carry out radical suspension polymerization. The mixture was then cooled to room temperature, and the suspension containing the generated polymer particles was centrifuged. The obtained polymer was washed twice with distilled water and twice with methanol, and then dried under reduced pressure. The obtained fumarate ester resin was dissolved in a toluene-methyl ethyl ketone mixed solution (toluene/methyl ethyl ketone, 50% by weight/50% by weight) to prepare a 20% solution. Furthermore, 5 parts by weight of tributyl trimellitate was added as a plasticizer to 100 parts by weight of the fumarate ester resin to prepare a dope. A biaxially stretched polyester (polyethylene-terephthalate/isophthalate copolymer) film (thickness 75 μm) was used as the support film. The prepared dope was applied to the support film so that the film thickness after drying was 28 μm, and dried at 140° C. This resulted in a resin film (positive C plate A) exhibiting a refractive index characteristic of nz>nx=ny. The thickness of the positive C plate A was 28 μm, the in-plane retardation Re(550)≒0 nm, and the thickness direction retardation Rth(550) was −135 nm.

[Production Example 2B: Preparation of Positive C Plate B]
A liquid crystal coating solution was prepared by dissolving 20 parts by weight of a side-chain liquid crystal polymer represented by the following chemical formula (3) (the numbers 65 and 35 in the formula indicate the mole percent of the monomer unit, and are conveniently expressed as a block polymer: weight average molecular weight 5000), 80 parts by weight of a polymerizable liquid crystal exhibiting a nematic liquid crystal phase (manufactured by BASF: trade name Paliocolor LC242), and 5 parts by weight of a photopolymerization initiator (manufactured by Ciba Specialty Chemicals: trade name Irgacure 907) in 200 parts by weight of cyclopentanone. The coating solution was then applied to a PET substrate that had been subjected to a vertical alignment treatment using a bar coater, and the liquid crystal was aligned by heating and drying at 80°C for 4 minutes. The liquid crystal layer was irradiated with ultraviolet light to harden the liquid crystal layer, thereby forming a liquid crystal alignment solidified layer (positive C plate B) exhibiting a refractive index characteristic of nz>nx=ny on the substrate. The positive C plate B had a thickness of 4 μm and a thickness direction retardation Rth(550) of −135 nm.

[Production Example 3: Preparation of Negative B Plate A]
A batch polymerization apparatus consisting of two vertical reactors equipped with stirring blades and a reflux condenser controlled at 100° C. was charged with 29.60 parts by weight (0.046 mol) of bis[9-(2-phenoxycarbonylethyl)fluoren-9-yl]methane, 29.21 parts by weight (0.200 mol) of isosorbide (ISB), 42.28 parts by weight (0.139 mol) of spiroglycol (SPG), 63.77 parts by weight (0.298 mol) of diphenyl carbonate (DPC), and 1.19×10 ⁻² parts by weight (6.78×10 ⁻⁵ mol) of calcium acetate monohydrate as a catalyst. After the inside of the reactor was replaced with nitrogen under reduced pressure, the inside was heated with a heat medium, and stirring was started when the inside temperature reached 100° C. The internal temperature was allowed to reach 220°C 40 minutes after the start of the temperature rise, and the pressure was reduced to 13.3 kPa in 90 minutes after the temperature reached 220°C. Phenol vapor by-produced during the polymerization reaction was led to a reflux condenser at 100°C, a small amount of monomer components contained in the phenol vapor were returned to the reactor, and uncondensed phenol vapor was led to a condenser at 45°C and collected. Nitrogen was introduced into the first reactor to restore the pressure to atmospheric pressure, and the oligomerized reaction liquid in the first reactor was transferred to the second reactor. Next, the temperature rise and pressure reduction in the second reactor were started, and the internal temperature was set to 240°C and the pressure to 0.2 kPa in 50 minutes. Thereafter, polymerization was allowed to proceed until a predetermined stirring power was reached. Nitrogen was introduced into the reactor at the time the predetermined power was reached to restore the pressure, and 0.7 parts by mass of PMMA was melt-kneaded with respect to 100 parts by weight of the produced polyester carbonate resin, and then extruded into water, and the strands were cut to obtain pellets.
The obtained polyester carbonate resin (pellets) was vacuum-dried at 80 ° C. for 5 hours, and then a long resin film having a thickness of 135 μm was produced using a film-forming device equipped with a single-screw extruder (manufactured by Toshiba Machine Co., Ltd., cylinder set temperature: 250 ° C.), a T-die (width 200 mm, set temperature: 250 ° C.), a chill roll (set temperature: 120 to 130 ° C.) and a winder. The obtained long resin film was stretched about 2.8 times in the width direction at 133 ° C. while adjusting so as to obtain a predetermined retardation, thereby obtaining a stretched film (negative B plate A) having a thickness of 48 μm exhibiting a refractive index characteristic of nx>ny> nz. The Re (550) of the negative B plate A was 143 nm, the Nz coefficient was 1.1, and Re (450) / Re (550) was 0.86.

[Production Example 4: Preparation of Pressure-Sensitive Adhesive Layer A]
A monomer mixture containing 91.5 parts of butyl acrylate, 3 parts of acrylic acid, 0.5 parts of 4-hydroxybutyl acrylate and 5 parts of acryloylmorpholine was charged into a four-neck flask equipped with a stirring blade, a thermometer, a nitrogen gas inlet tube and a cooler. Furthermore, 0.1 parts of 2,2'-azobisisobutyronitrile as a polymerization initiator was charged together with 100 parts of ethyl acetate for 100 parts of this monomer mixture, and nitrogen gas was introduced while gently stirring to replace the atmosphere in the flask with nitrogen. The liquid temperature in the flask was kept at about 55°C and a polymerization reaction was carried out for 8 hours. Next, ethyl acetate was added to the obtained reaction liquid to adjust the solid concentration to 12% by weight, and a solution of an acrylic polymer having a weight average molecular weight (Mw) of 2.5 million was prepared.
An acrylic adhesive was prepared by blending 100 parts of the solid content of the obtained acrylic polymer solution with 0.3 parts of a peroxide-based crosslinking agent, benzoyl peroxide (product name: Niper BMT, manufactured by Nippon Oil & Fats Co., Ltd.), 0.2 parts of a trimethylolpropane/tolylene diisocyanate adduct (product name: Coronate L, manufactured by Tosoh Corporation), and 0.2 parts of a silane coupling agent (product name: KBM403, manufactured by Shin-Etsu Chemical Co., Ltd.).
The obtained acrylic adhesive was applied to the release surface of a 38 μm thick PET film (Mitsubishi Chemical Polyester Film Corporation, MRF38), which is a release liner with a silicone treatment applied to the release surface, and then dried to form an adhesive layer A with a thickness of 20 μm.

[Production Example 5: Preparation of UV-curable adhesive A]
An ultraviolet-curable adhesive A was prepared by blending 50 parts of unsaturated fatty acid hydroxyalkyl ester-modified ε-caprolactone (manufactured by Daicel Corporation, product name "Placcel FA-1DDM"), 10 parts of polyethylene glycol diacrylate (manufactured by Kyoeisha Chemical Co., Ltd., product name "Light Acrylate 9EG-A"), 20 parts of acryloyl morpholine, 15 parts of an acrylic polymer (manufactured by Toagosei Co., Ltd., product name "ARUFON UP-1190"), 3 parts of a photopolymerization initiator (manufactured by IGM Resins, product name "Omnirad 907"), and 2 parts of a photopolymerization initiator (manufactured by Nippon Kayaku Co., Ltd., product name "KAYACURE-DETX-S")

[Example 1]
The adhesive layer A was transferred from a release liner to one side of the positive C plate A, and the negative B plate A was laminated on top of it to obtain a laminate 1 having a configuration of [positive C plate A/adhesive layer A/negative B plate A].
The laminate 1 was attached to the polarizer side of the polarizing plate A via the ultraviolet curing adhesive A. Specifically, the ultraviolet curing adhesive A was applied to a thickness of 1.0 μm, and the laminate was attached using a roll machine. Then, UV light was irradiated from the laminate 1 side to harden the adhesive. At this time, the positive C plate A was attached to the polarizer side, and the slow axis direction of the negative B plate A was at an angle of 45° clockwise with respect to the absorption axis direction of the polarizer. Next, another adhesive layer A was attached to the laminate 1 together with the release liner. This resulted in a retardation layer-attached polarizing plate 1 having a configuration of [polarizing plate A/adhesive layer/positive C plate A/adhesive layer A/negative B plate A/adhesive layer A/release liner]. In the retardation layer-attached polarizing plate 1, the first retardation layer is the positive C plate A, and the second retardation layer is the negative B plate A.

[Comparative Example 1]
The negative B plate A was bonded to one side of the positive C plate B via an ultraviolet-curing adhesive A (thickness after curing: 1 μm) in the same manner as described above, to obtain a laminate 2 having a configuration of [positive C plate B/adhesive layer/negative B plate A].
The laminate 2 was attached to the polarizer side of the polarizing plate A via the adhesive layer A. At this time, the attachment was performed so that the negative B plate A was on the polarizer side and the slow axis direction of the negative B plate A was at an angle of 45° clockwise with respect to the absorption axis direction of the polarizer. Next, the adhesive layer A was further attached together with the release liner onto the laminate 2. As a result, a retardation layer-attached polarizing plate C1 having a configuration of [polarizing plate A/adhesive layer A/negative B plate A/adhesive layer/positive C plate B/adhesive layer A/release liner] was obtained.

[Comparative Example 2]
The negative B plate A was bonded to one side of the positive C plate A via an ultraviolet-curing adhesive A (thickness after curing: 1 μm) in the same manner as described above, to obtain a laminate 3 having a configuration of [positive C plate A/adhesive layer/negative B plate A].
The laminate 3 was attached to the polarizer side of the polarizing plate A via the adhesive layer A. At this time, the attachment was performed so that the negative B plate A was on the polarizer side and the slow axis direction of the negative B plate A was at an angle of 45° clockwise with respect to the absorption axis direction of the polarizer. Next, the adhesive layer A was further attached together with the release liner onto the laminate 3. As a result, a retardation layer-attached polarizing plate C2 having a configuration of [polarizing plate A/adhesive layer A/negative B plate A/adhesive layer/positive C plate A/adhesive layer A/release liner] was obtained.

[Comparative Example 3]
The laminate 3 similar to that of Comparative Example 2 was attached to the polarizer side of the polarizing plate A via the adhesive layer A. At this time, the attachment was performed so that the positive C plate A was on the polarizer side and the slow axis direction of the negative B plate A was at an angle of 45° clockwise with respect to the absorption axis direction of the polarizer. Next, the adhesive layer A was further attached together with the release liner onto the laminate 3. As a result, a retardation layer-attached polarizing plate C3 having a configuration of [polarizing plate A/adhesive layer A/positive C plate A/adhesive layer/negative B plate A/adhesive layer A/release liner] was obtained.

[Comparative Example 4]
The adhesive layer A was transferred from a release liner to one side of the positive C plate B, and the negative B plate A was laminated on top of it to obtain a laminate 4 having a configuration of [positive C plate B/adhesive layer A/negative B plate A].
The laminate 4 was attached to the polarizer side of the polarizing plate A via an ultraviolet-curable adhesive A (thickness after curing: 1 μm) in the same manner as above. At this time, the positive C plate B was attached to the polarizer side, and the slow axis direction of the negative B plate A was at an angle of 45° clockwise with respect to the absorption axis direction of the polarizer. Next, another adhesive layer A was attached to the laminate 4 together with the release liner. As a result, a retardation layer-attached polarizing plate C4 having a configuration of [polarizing plate A/adhesive layer/positive C plate B/adhesive layer A/negative B plate A/adhesive layer A/release liner] was obtained.

<Durability evaluation>
The retardation layer-attached polarizing plates obtained in the above Examples and Comparative Examples were cut into a size of 150 mm x 70 mm so that the slow axis direction of the negative B plate A was the longitudinal direction, and the release liner was peeled off to expose the adhesive layer A, which was then attached to a glass plate via the adhesive layer A. The plate was then placed in an oven at 85°C and removed after 240 hours. The glass plate side was attached to a reflector (manufactured by Toray Film Processing Co., Ltd., product name "Cerapeel DMS-X42", total light reflectance: 86%) via an acrylic adhesive to prepare a measurement sample. For the measurement sample, a ^* and b ^* were measured at the center and end of the center line extending in the longitudinal direction, and the color difference (Δa ^* b ^* ) between them was calculated. The results are shown in Table 1 together with the configuration of each retardation layer-attached polarizing plate.

As shown in Table 1, the retardation layer-attached polarizing plate of the embodiment, which has a polarizing plate, a first retardation layer having a refractive index characteristic of nz>nx=ny and made of a resin film, a first adhesive layer, a second retardation layer having a refractive index characteristic of nx>ny≧nz and made of a resin film, and a second adhesive layer, in that order, has a smaller color difference than the retardation layer-attached polarizing plates of Comparative Examples 1 to 3. In addition, the polarizer of the retardation layer-attached polarizing plate of Comparative Example 4 faded due to heat treatment. This shows that the retardation layer-attached polarizing plate of the embodiment has excellent durability and suppresses the occurrence of color unevenness at high temperatures.

The reason why the above effect is achieved is presumed to be as follows, although it does not limit the present invention in any way. When a polarizing plate with a retardation layer is placed at high temperatures, dimensional changes occur in both the polarizer and the retardation layer due to heating. In a λ/4 plate made of a resin film, in addition to stress due to its own dimensional change, stress due to dimensional change of the polarizer also accumulates, causing retardation unevenness, and as a result, color unevenness (color difference) is observed. In contrast, according to the configuration according to the embodiment of the present invention, the first retardation layer made of a resin film suppresses dimensional change of the polarizer, and the first adhesive layer and the second adhesive layer arranged on both sides of the second retardation layer suppress the accumulation of stress in the second retardation layer, and as a result, it is presumed that the occurrence of color unevenness (color difference) is suppressed.

The polarizing plate with a retardation layer according to the embodiment of the present invention can be used, for example, in an image display device. Representative examples of the image display device include a liquid crystal display device, an organic EL display device, and an inorganic EL display device.

REFERENCE SIGNS LIST 10 Polarizing plate 12 Polarizer 14 Protective layer 20 First retardation layer 30 First pressure-sensitive adhesive layer 40 Second retardation layer 50 Second pressure-sensitive adhesive layer 100 Retardation layer-attached polarizing plate 200 Image display device

Claims (8)

A polarizing plate including a polarizer, a first retardation layer, a first pressure-sensitive adhesive layer, a second retardation layer, and a second pressure-sensitive adhesive layer, in this order;
The first retardation layer has a refractive index characteristic that exhibits a relationship of nz>nx=ny,
The second retardation layer has a refractive index characteristic that satisfies the relationship of nx>ny≧nz,
The first retardation layer and the second retardation layer are made of a resin film.
Polarizing plate with retardation layer. The polarizing plate with a retardation layer according to claim 1, wherein the polarizing plate includes the polarizer and a protective layer arranged only on the side of the polarizer opposite to the side on which the first retardation layer is arranged. The second retardation layer has an Re(550) of 120 nm to 170 nm,
2. The polarizing plate with a retardation layer according to claim 1, wherein an angle between a slow axis of the second retardation layer and an absorption axis of the polarizer is from 40° to 50° or from 130° to 140°. The polarizing plate with a retardation layer according to claim 1, wherein the first retardation layer has an Rth(550) of -70 nm to -165 nm. The polarizing plate with a retardation layer according to claim 1, wherein the resin film constituting the second retardation layer contains a polycarbonate-based resin. The polarizing plate with a retardation layer according to claim 1, which is used in an organic EL display device. An image display device comprising a polarizing plate with a retardation layer according to any one of claims 1 to 6. The image display device according to claim 7, which is an organic electroluminescence display device.

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