TWI896775B - Polarizing plate with phase difference layer and image display device - Google Patents

Abstract

The present invention provides a polarizing plate with a phase difference layer. The polarizing plate has a simple structure, excellent visibility through polarizing sunglasses, and excellent bendability. The polarizing plate with a phase difference layer according to an embodiment of the present invention is used in a bendable image display device. A polarizing plate with a phase difference layer comprises: a polarizing plate including a polarizing element and a protective layer on at least one side of the polarizing element; and a phase difference layer disposed on the side of the polarizing plate opposite to the viewing side and having a circularly polarized light function or an elliptical polarized light function. The polarizing plate with a phase difference layer has a total thickness of 80 μm or less, an angle between a bending axis of an image display device and an absorption axis of the polarizing element is 30° to 60°, and an elastic modulus of the protective layer is 5000 MPa or less.

Description

Polarizing plate with phase difference layer and image display device

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

In recent years, image display devices, represented by liquid crystal display devices and electroluminescent (EL) display devices (e.g., organic EL display devices, inorganic EL display devices), have rapidly become popular. Polarizers and phase difference plates are typically used in image display devices. In practice, polarizers with phase difference layers, which are formed by integrating a polarizer and a phase difference plate, are widely used (e.g., Japanese Patent Document 1). However, with the recent increasing demand for thinner image display devices, the demand for thinner polarizers with phase difference layers has also become stronger. Furthermore, the use of image display devices has expanded, and with this, the requirements for image display devices have diversified. For example, with respect to smartphones, there are requirements for foldability and improved visibility through polarized sunglasses. Therefore, there is a strong demand for a polarizing plate with a phase difference layer that can realize such an image display device.

Prior Art Literature Patent Literature

Patent Document 1: Japanese Patent No. 3325560

This invention was developed to address the aforementioned problems. Its primary purpose is to provide a polarizing plate with a phase difference layer that has a simple structure, excellent visibility through polarizing sunglasses, and excellent refracting properties.

The polarizing plate with a phase difference layer of the present invention is used in a bendable image display device. The polarizing plate with a phase difference layer comprises: a polarizing plate including a polarizing element and a protective layer on at least one side of the polarizing element; and a phase difference layer disposed on the side of the polarizing plate opposite the viewing side, which has a circularly polarized or elliptical polarized light function. The total thickness of the polarizing plate with a phase difference layer is 80 μm or less, the angle between the bending axis of the image display device and the absorption axis of the polarizing element is 30° to 60°, and the elastic modulus of the protective layer is 5000 MPa or less.

In one embodiment, the total thickness of the polarizing plate with phase difference layer is less than 60 μm.

In one embodiment, the thickness of the polarizing element is less than 10 μm.

In one embodiment, the polarizing plate includes a protective layer only on the side of the polarizing element opposite to the phase difference layer.

In one embodiment, the elastic modulus of the protective layer is 4000 MPa or less.

In one embodiment, the thickness of the protective layer is 45 μm or less.

In one embodiment, the angle between the bending axis and the absorption axis of the polarizing element is 40° to 50°.

In one embodiment, the phase difference layer is an alignment-cured layer of a liquid crystal compound.

In one embodiment, the phase difference layer is a single layer, the Re(550) of the phase difference layer is 100 nm to 190 nm, the Re(450)/Re(550) of the phase difference layer is greater than 0.8 and less than 1, and the angle between the retardation axis of the phase difference layer and the absorption axis of the polarizing element is 40° to 50°. In one embodiment, the polarizing plate with the phase difference layer has another phase difference layer outside the phase difference layer, and the refractive index characteristics of the other phase difference layer show the relationship nz>nx=ny.

In one embodiment, the phase difference layer has a laminated structure of an alignment-cured layer of a first liquid crystal compound and an alignment-cured layer of a second liquid crystal compound; the alignment-cured layer of the first liquid crystal compound has a Re(550) of 200 nm to 300 nm, and the angle between its retardation axis and the absorption axis of the polarizing element is 10° to 20°; the alignment-cured layer of the second liquid crystal compound has a Re(550) of 100 nm to 190 nm, and the angle between its retardation axis and the absorption axis of the polarizing element is 70° to 80°.

According to another aspect of the present invention, an image display device is provided. The image display device comprises the aforementioned polarizing plate with a phase difference layer.

According to embodiments of the present invention, by optimizing the angle between the bending axis and the absorption axis of the polarizing element in a polarizing plate with a retardation layer when used in a bendable image display device, and optimizing the elastic modulus of the protective layer, a polarizing plate with a retardation layer can be achieved that has a simple structure, excellent visibility through polarizing sunglasses, and excellent bending properties.

10:Polarizing plate

11: Polarizing element

12,13: Protective layer

20: Phase difference layer

21: H Floor

22: Q layer

100: Polarizing plate with phase difference layer

102: Polarizing plate with phase difference layer

A: Absorption axis

F: Crankshaft

Figure 1 is a schematic perspective view showing a curved image display device employing a polarizing plate with a phase difference layer according to an embodiment of the present invention.

Figure 2 is a schematic top view of a polarizing plate with a phase difference layer according to one embodiment of the present invention.

Figure 3 is a schematic cross-sectional view of a polarizing plate with a phase difference layer according to one embodiment of the present invention.

Figure 4 is a schematic cross-sectional view of a polarizing plate with a phase difference layer according to another embodiment of the present invention.

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

(Definition of terms and symbols)

The definitions of terms and symbols in this manual are as follows.

(1) Refractive index (nx, ny, nz)

"nx" is the refractive index in the direction of maximum refractive index in the plane (i.e., the direction of the slow axis), "ny" is the refractive index in the direction perpendicular to the slow axis (i.e., the direction of the fast axis), and "nz" is the refractive index in the thickness direction.

(2) In-plane phase difference (Re)

"Re(λ)" is the in-plane retardation measured at 23°C using light of wavelength λ nm. For example, "Re(550)" is the in-plane retardation measured at 23°C using light of wavelength 550 nm. Re(λ) is calculated using the formula: Re(λ) = (nx - ny) × d, assuming the thickness of the layer (film) is d (nm).

(3) Retardation in the thickness direction (Rth)

"Rth(λ)" is the retardation in the thickness direction measured at 23°C using light of a wavelength of λ nm. For example, "Rth(550)" is the retardation in the thickness direction measured at 23°C using light of a wavelength of 550 nm. Rth(λ) is calculated using the formula: Rth(λ) = (nx - nz) × d, assuming the thickness of the layer (film) is d (nm).

(4) Nz coefficient

The Nz coefficient is calculated using the formula Nz=Rth/Re.

(5) Angle

Throughout this specification, angles are considered both clockwise and counterclockwise relative to a reference direction. Thus, for example, "45°" means ±45°; and "30° to 60°" means +30° to +60° or -30° to -60°.

A. Overall structure of a polarizing plate with a phase difference layer

Figure 1 is a schematic perspective view showing a bent image display device employing a polarizing plate with a phase difference layer according to an embodiment of the present invention; Figure 2 is a schematic top view of a polarizing plate with a phase difference layer according to one embodiment of the present invention; Figure 3 is a schematic cross-sectional view of a polarizing plate with a phase difference layer according to one embodiment of the present invention; and Figure 4 is a schematic cross-sectional view of a polarizing plate with a phase difference layer according to another embodiment of the present invention. The polarizing plate with a phase difference layer 100 shown in Figure 3 typically comprises, in order from the side, a polarizing plate 10 and a phase difference layer 20. In the illustrated example, the polarizing plate 10 includes a polarizing element 11 and protective layers 12 and 13 on either side of the polarizing element 11. Depending on the intended purpose, either protective layer 12 or 13 may be omitted. In one embodiment, the polarizing plate 10 includes a protective layer 12 only on the viewing side of the polarizing element 11 (the side opposite the phase difference layer 20). The components of the polarizing plate with phase difference layer are typically bonded together via any suitable bonding layer (adhesive layer or adhesive layer; not shown). For practical purposes, an adhesive layer (not shown) is provided on the side of the phase difference layer 20 opposite the polarizing plate 10 (i.e., as the outermost layer opposite the viewing side), allowing the polarizing plate with phase difference layer to be attached to an image display panel. Furthermore, it is preferred that a release film (not shown) be temporarily adhered to the surface of the adhesive layer before the polarizing plate with a phase difference layer is used. By temporarily adhering the release film, the adhesive layer is protected while the roll of the polarizing plate with a phase difference layer is formed.

As shown in Figure 1, a polarizing plate with a phase difference layer is used in a bendable image display device. As shown in Figures 1 and 2, in the polarizing plate with a phase difference layer, the angle between the bending axis F of the image display device and the absorption axis A of the polarizing element 11 is 30° to 60°, preferably 35° to 55°, more preferably 40° to 50°, further preferably 42° to 48°, and even more preferably approximately 45°. With this structure, excellent visibility when viewing through polarized sunglasses can be achieved without forming a specific layer (typically, a layer imparting (elliptical) circular polarization function, such as a λ/4 plate, or an ultra-high phase difference layer with an in-plane phase difference Re (550) exceeding 1000 nm) on the viewing side of the polarizing plate with a phase difference layer. Therefore, the polarizing plate with a phase difference layer of the embodiment of the present invention has a small number of layers, is simple and low-cost, and as a result, is thin. Furthermore, with this structure, excellent bending properties can be achieved through a synergistic effect with the optimization of the elastic modulus of the protective layer. More specifically, when the bending axis is parallel to the absorption axis of the polarizer, the polarizer with a phase difference layer (essentially a polarizer) becomes very susceptible to cracking. On the other hand, when the bending axis is orthogonal to the absorption axis of the polarizer, it is less susceptible to cracking, but visibility through polarized sunglasses is extremely poor. By optimizing the bending axis to form the aforementioned specific angle with the absorption axis of the polarizer, it is possible to achieve both excellent bending properties and excellent visibility through polarized sunglasses. Furthermore, while the bending axis F in the illustrated example is along the short side of the image display device, it can also be along the long side, or at a specific angle (diagonal) relative to the long or short side. By specifying the absorption axis direction relative to the bending axis, the aforementioned effects can be achieved even when the polarizing plate with a phase difference layer is used in image display devices with shapes other than rectangular (e.g., circular, elliptical, triangular, or irregular).

The total thickness of the polarizing plate with a retardation layer (the combined thickness of the polarizing plate, retardation layer, and the bonding layer formed by laminating the two layers in equal volume) is 80 μm or less, preferably 70 μm or less, more preferably 60 μm or less, even more preferably 50 μm or less, and particularly preferably 40 μm or less. The total thickness of the polarizing plate with a retardation layer can be, for example, 25 μm or greater. According to embodiments of the present invention, even with such a very small total thickness, excellent visibility can be achieved when viewed through polarizing sunglasses. In other words, the polarizing plate with a retardation layer can have a very small total thickness even when used for applications such as viewing through polarizing sunglasses. As a result, the second moment of area during bending is reduced, and the stress applied to each component (layer) is reduced. This not only achieves excellent visibility when viewing through sunglasses, but also achieves excellent bending properties.

In embodiments of the present invention, the elastic modulus of the protective layer 12 and/or 13 is 5000 MPa or less, preferably 4500 MPa or less, more preferably 4000 MPa or less, and even more preferably 3500 MPa or less. The lower limit of the elastic modulus of the protective layer may be, for example, 2000 MPa. Preferably, the polarizing plate with a phase difference layer (essentially a polarizing plate) comprises only the protective layer 12, and the elastic modulus of the protective layer 12 is within the above range. If the elastic modulus of the protective layer is too large, the compressive stress applied to the protective layer increases when the strain during bending is the same. As a result, the protective layer is more susceptible to cracking due to repeated bending. By optimizing the elastic modulus of the protective layer within the above range, cracking during bending can be suppressed, achieving excellent flexural properties. Furthermore, the elastic modulus can be measured in accordance with JIS Z 2284.

The phase difference layer 20 has a circular polarization function or an elliptical polarization function. The phase difference layer 20 is typically an alignment cured layer of a liquid crystal compound (liquid crystal alignment cured layer). By using a liquid crystal compound, the difference between nx and ny of the obtained phase difference layer can be significantly increased compared to non-liquid crystal materials, so the thickness of the phase difference layer that can be used to obtain the desired in-plane phase difference can be significantly reduced. Therefore, a significant thinning of the polarizing plate with a phase difference layer can be achieved. As a result, the excellent bendability (bendability) as described above can be achieved. In this specification, an "alignment cured layer" refers to a layer in which the liquid crystal compound is aligned in a specific direction within the layer, and its alignment state is fixed. Furthermore, an "alignment cured layer" refers to a concept including an alignment cured layer obtained by curing a liquid crystal monomer as described below. In the retardation layer 20, rod-shaped liquid crystal compounds are typically aligned along the retardation axis of the retardation layer (horizontally aligned). The retardation layer 20 can be a single layer as shown in Figure 3, or it can have a stacked structure of two or more layers as shown in Figure 4.

The polarizing plate with a phase difference layer may further include other optical functional layers. The type, characteristics, number, combination, and configuration of the optical functional layers that can be provided in the polarizing plate with a phase difference layer can be appropriately set according to the purpose. For example, the polarizing plate with a phase difference layer may further include a conductive layer or an isotropic substrate with a conductive layer (neither shown). The conductive layer or the isotropic substrate with a conductive layer is typically provided on the outside of the phase difference layer 20 (on the side opposite to the polarizing plate 10). The conductive layer or the isotropic substrate with a conductive layer is typically an optional layer provided as needed and may be omitted. Furthermore, when a conductive layer or an isotropic substrate with a conductive layer is provided, a polarizing plate with a phase difference layer can be used in a so-called internal touch panel input display device, in which a touch sensor is incorporated between an image display unit (e.g., an organic EL unit) and the polarizing plate. Furthermore, for example, a polarizing plate with a phase difference layer can further include other phase difference layers. The optical properties (e.g., refractive index, in-plane phase difference, Nz coefficient, photoelastic coefficient), thickness, and placement of these other phase difference layers can be appropriately determined depending on the intended purpose.

The following describes in more detail the components of a polarizing plate with a phase difference layer.

B.Polarizing plate B-1. Polarizing Element

Any suitable polarizing element can be used as the polarizing element 11. For example, the resin film forming the polarizing element can be a single-layer resin film or a laminate of two or more layers.

Specific examples of polarizing elements composed of a single-layer resin film include hydrophilic polymer films such as polyvinyl alcohol (PVA) films, partially formalized PVA films, and partially saponified ethylene-vinyl acetate copolymer films, dyed with a dichroic substance such as iodine or a dichroic dye and then stretched; and polyene-based alignment films such as dehydrogenated PVA films or dehydrochlorinated polyvinyl chloride films. For superior optical properties, polarizing elements obtained by dyeing PVA films with iodine and then uniaxially stretching them are preferred.

Iodine dyeing can be performed, for example, by immersing the PVA film in an aqueous iodine solution. The uniaxial stretching ratio is preferably 3x to 7x. Stretching can be performed after dyeing or simultaneously with dyeing. Alternatively, dyeing can be performed after stretching. The PVA film can be subjected to swelling, crosslinking, cleaning, and drying treatments as needed. For example, immersing the PVA film in water and then washing it before dyeing not only removes stains or anti-blocking agents from the surface but also allows the film to swell, preventing uneven dyeing.

Specific examples of polarizing elements using a laminate include a laminate comprising a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or a laminate comprising a resin substrate and a PVA-based resin layer coated on the resin substrate. A polarizing element obtained by laminating 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 the resin substrate, drying the solution to form the PVA-based resin layer on the resin substrate, thereby obtaining a laminate of the resin substrate and the PVA-based resin layer; and extending and dyeing the laminate to form the PVA-based resin layer into a polarizing element. In this embodiment, it is preferred that the PVA-based resin layer comprising a halogenated compound and a PVA-based resin be formed on one side of the resin substrate. As for stretching, it typically includes immersing the laminate in an aqueous solution of boric acid for stretching. Furthermore, stretching may further include the following step as needed: before stretching in the aqueous solution of boric acid, stretching the laminate in air at a high temperature (for example, above 95°C). Moreover, in this embodiment, it is preferred to subject the laminate to the following dry shrinking treatment, that is, by transporting it in the length direction while heating it, so that it shrinks by more than 2% in the width direction. Typically, the manufacturing method of this embodiment includes sequentially performing the steps of air-assisted stretching treatment, dyeing treatment, underwater stretching treatment, and dry shrinking treatment on the laminate. By introducing assisted stretching, when coating PVA on a thermoplastic resin, the crystallinity of the PVA can be enhanced, achieving higher optical properties. Furthermore, by simultaneously enhancing the PVA's orientation, problems such as a decrease in orientation or dissolution during immersion in water during subsequent dyeing or stretching steps can be prevented, achieving even higher optical properties. Furthermore, when immersing a PVA-based resin layer in a liquid, the alignment of the polyvinyl alcohol molecules is disrupted, and a decrease in orientation is suppressed, compared to a PVA-based resin layer without halides. This improves the optical properties of polarizing elements obtained through treatments such as dyeing and underwater stretching, where the laminate is immersed in a liquid. Furthermore, shrinking the laminate in the width direction during drying and shrinking can further enhance optical properties. The resulting resin substrate/polarizing element laminate can be used directly (i.e., the resin substrate can be used as a protective layer for the polarizing element), or the resin substrate can be peeled off from the resin substrate/polarizing element laminate and any appropriate protective layer can be applied to the peeled surface for further use. Details of the manufacturing method of this polarizing element are described, for example, in Japanese Patent Application Publication No. 2012-73580 and Japanese Patent No. 6470455. All of the contents of these publications are incorporated herein by reference.

The thickness of the polarizing element is preferably 15 μm or less, more preferably 12 μm or less, even more preferably 10 μm or less, particularly preferably 3 μm to 10 μm, and even more preferably 3 μm to 8 μm. If the thickness of the polarizing element falls within this range, the desired total thickness can be achieved, resulting in excellent bending properties.

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

B-2. Protective layer

The protective layers 12 and 13 can be formed of any appropriate film that can be used as a protective layer for a polarizing element as long as they can each obtain the above-mentioned elastic modulus. Specific examples of the material that constitutes the main component of the film include cellulose resins such as triacetyl cellulose (TAC), or polyesters, polyvinyl alcohols, polycarbonates, polyamides, polyimides, polyether sulfones, polysulfones, polystyrenes, cyclic olefins (e.g., polydecenes), and polyvinyl alcohols. olefin-based), polyolefin-based, (meth)acrylic-based, acetate-based transparent resins, etc.

The polarizing plate with a phase difference layer is typically placed on the viewing side of an image display device, and the protective layer 12 is placed on this viewing side. Therefore, the protective layer 12 may also be subjected to surface treatments such as hard coating, anti-reflection treatment, anti-sticking treatment, and anti-glare treatment as needed.

The thickness of each of the protective layers 12 and 13 is preferably 60 μm or less, more preferably 45 μm or less, and even more preferably 10 μm to 40 μm. Furthermore, when surface treatment is applied, the thickness of the protective layer 12 includes the thickness of the surface treatment layer.

C. Phase difference layer

As mentioned above, the phase difference layer 20 can be a single layer or have a multilayer structure with two or more layers.

When the phase difference layer 20 is a single layer, the phase difference layer can typically function as a λ/4 plate. Specifically, the Re(550) of the phase difference layer is preferably 100nm~180nm, more preferably 110nm~170nm, and further preferably 110nm~160nm. The thickness of the phase difference layer can be adjusted in a manner that can obtain the desired in-plane phase difference of the λ/4 plate. The thickness of the phase difference layer can be, for example, 1.0μm~2.5μm. In this embodiment, the angle between the retardation axis of the phase difference layer and the absorption axis of the polarizing element is preferably 40°~50°, more preferably 42°~48°, and further preferably 44°~46°. In this embodiment, the polarizing plate with a phase difference layer may also have a phase difference layer (not shown) outside the phase difference layer 20 that exhibits a refractive index characteristic of nz>nx=ny. When the phase difference layer is a single layer, the phase difference layer preferably exhibits an inverse wavelength dispersion characteristic in which the phase difference value increases according to the wavelength of the measurement light. In this case, the Re(450)/Re(550) of the phase difference layer is preferably 0.8 or more and less than 1, and more preferably 0.8 to 0.95.

When the phase difference layer 20 has a layered structure, the phase difference layer typically has a two-layer structure, as shown in FIG4 , comprising an H layer 21 and a Q layer 22, in order from the polarizer side. The H layer typically functions as a λ/2 plate, and the Q layer typically functions as a λ/4 plate. Specifically, the Re(550) of the H layer is preferably 200 nm to 300 nm, more preferably 220 nm to 290 nm, and further preferably 230 nm to 280 nm; the Re(550) of the Q layer is preferably 100 nm to 180 nm, more preferably 110 nm to 170 nm, and further preferably 110 nm to 150 nm. The thickness of the H layer can be adjusted to achieve the desired in-plane retardation of a λ/2 plate. If the H layer is a liquid crystal alignment curing layer, its thickness can be, for example, 2.0 μm to 4.0 μm. The thickness of the Q layer can be adjusted to achieve the desired in-plane retardation of a λ/4 plate. If the Q layer is a liquid crystal alignment curing layer, its thickness can be, for example, 1.0 μm to 2.5 μm. In this embodiment, the angle between the retardation axis of the H layer and the absorption axis of the polarizer is preferably 10° to 20°, more preferably 12° to 18°, and even more preferably 12° to 16°. The angle between the retardation axis of the Q layer and the absorption axis of the polarizer is preferably 70° to 80°, more preferably 72° to 78°, and even more preferably 72° to 76°. Furthermore, the order of arrangement of the H and Q layers may be reversed, and the angles between the retardation axis of the H layer and the absorption axis of the polarizer and the angles between the retardation axis of the Q layer and the absorption axis of the polarizer may also be reversed. When the retardation layer has a layered structure, each layer (e.g., the H layer and the Q layer) can exhibit inverse wavelength dispersion characteristics, where the retardation value increases with the wavelength of the measurement light; positive wavelength dispersion characteristics, where the retardation value decreases with the wavelength of the measurement light; or flat wavelength dispersion characteristics, where the retardation value remains essentially unchanged regardless of the wavelength of the measurement light.

The refractive index characteristics of the retardation layer (or each layer in the case of a layered structure) typically exhibit the relationship nx > ny = nz. Furthermore, "ny = nz" encompasses not only the case where ny and nz are completely equal, but also the case where they are substantially equal. Therefore, the relationship ny > nz or ny < nz may exist without impairing the effects of the present invention. The Nz coefficient of the retardation layer is preferably 0.9 to 1.5, more preferably 0.9 to 1.3.

As mentioned above, the phase difference layer is typically a liquid crystal alignment cured layer. Examples of liquid crystal compounds include those with a nematic phase (nematic liquid crystals). Examples of such liquid crystal compounds include liquid crystal polymers and liquid crystal monomers. The liquid crystal properties of liquid crystal compounds can be either hydrotropic or thermotropic. Liquid crystal polymers and liquid crystal monomers can be used alone or in combination.

When the liquid crystal compound is a liquid crystal monomer, it is preferably a polymerizable monomer and a crosslinking monomer. This is because polymerizing or crosslinking (i.e., curing) the liquid crystal monomer fixes its alignment. After the liquid crystal monomers are aligned, for example, by polymerizing or crosslinking the liquid crystal monomers, this alignment can be fixed. Here, polymerization forms a polymer, and crosslinking forms a three-dimensional network structure, but both are non-liquid crystal. Therefore, the resulting retardation layer does not undergo the temperature-dependent transitions to liquid crystal, glass, or crystalline phases that are characteristic of liquid crystal compounds. As a result, the retardation layer is unaffected by temperature fluctuations and exhibits exceptional stability.

The temperature range within which liquid crystal monomers exhibit liquid crystallinity varies depending on their type. Specifically, the ideal temperature range is 40°C to 120°C, more preferably 50°C to 100°C, and most preferably 60°C to 90°C.

Any suitable liquid crystal monomer can be used as the liquid crystal monomer. For example, polymerizable mesogen compounds described in Japanese Patent Publication No. 2002-533742 (WO00/37585), EP358208 (US5211877), EP66137 (US4388453), WO93/22397, EP0261712, DE19504224, DE4408171, and GB2280445 can be used. Specific examples of such polymerizable mesogen compounds include BASF's LC242, Merck's E7, and Wacker-Chem's LC-Sillicon-CC3767. Preferred liquid crystal monomers are nematic liquid crystal monomers.

D. Image display device

The polarizing plates with a phase difference layer described in Items A to C above can be applied to image display devices. Therefore, image display devices including a polarizing plate with a phase difference layer are also included in embodiments of the present invention. An image display device typically includes an image display unit and a polarizing plate with a phase difference layer attached to the image display unit via an adhesive layer. Representative examples of image display devices include liquid crystal display devices and electroluminescent (EL) display devices (e.g., organic EL display devices and inorganic EL display devices). As described above, image display devices are bendable, preferably foldable. In such image display devices, the effects of the polarizing plates with a phase difference layer according to embodiments of the present invention become significant.

[Example]

The present invention is described in detail below using examples, but the present invention is not limited to these examples. The measurement methods for various properties are described below. Furthermore, unless otherwise specified, "parts" and "%" in the examples and comparative examples are by weight.

(1)Thickness

Thicknesses below 10 μm were measured using an interferometer thickness gauge (MCPD-3000, manufactured by Otsuka Electronics Co., Ltd.). Thicknesses exceeding 10 μm were measured using a digital micrometer (KC-351C, manufactured by Amitsu Co., Ltd.).

(2) Elastic modulus

The measurement was performed in accordance with JIS Z 2284. Specifically, the method is as follows: A short strip of sample, 10 mm wide and 100 mm long, was cut from the protective layer used in the Examples and Comparative Examples. Using a high-speed continuous automatic stereogrammer (manufactured by Shimadzu Corporation), the sample was stretched in the longitudinal direction under the following conditions. The elastic modulus was determined from the resulting S-S (Stress-Strain) curve. The measurement conditions were a stretching speed of 50 mm/min, a chuck distance of 100 mm, and a measurement temperature of room temperature (25°C). The method for determining the elastic modulus from the S-S curve is as follows. Draw a tangent line at the initial rise of the S-S curve, read the strength at the point where the extension of the tangent line reaches 100% elongation, and divide it by the cross-sectional area of the sample piece (thickness × sample width (10mm)) for the measurement. The resulting value is taken as the elastic modulus.

(3) Bending test

Polarizing plates with retardation layers obtained in the Examples and Comparative Examples were cut into 100 mm x 55 mm pieces to prepare test specimens. The specimens were cut so that the bending axis formed the short side of the test data. These specimens were subjected to a continuous bending test using a bending tester ("CL09 Type D01," manufactured by Yuasa System Co., Ltd.). Bending was performed at room temperature with the side protective layer visually facing inward. The radius of curvature was 3 mm. After 500,000 bends, the specimens were visually inspected for cracking and evaluated according to the following criteria.

○: No cracks were found.

×: Tortoise crack confirmed

(4) Visibility when viewing through polarized sunglasses

The polarizing plate on the viewing side of a commercially available liquid crystal display (LCD) was removed and cleaned. The polarizing plate with a retardation layer, obtained in the Examples and Comparative Examples, was laminated onto the cleaned surface. The polarizing plate with a retardation layer was laminated so that the absorption axis of the polarizing element of the LCD formed angles of 0°, 30°, 40°, 45°, 50°, 60°, and 90° with the short side of the LCD. The LCD was then displayed with a specific character, and the display was observed while wearing polarizing sunglasses. The polarizing sunglasses were aligned with the short and long sides of the LCD, respectively, and evaluated according to the following criteria.

○: When the absorption axis of the polarized sunglasses is aligned with either the short or long side, the displayed content can be recognized to an understandable degree.

×: When the absorption axis of the polarizing sunglasses is aligned with at least one of the short or long sides, the displayed image cannot be recognized.

[Example 1-1] 1. Polarizing Plate Production

As the thermoplastic resin substrate, a long, amorphous polyethylene terephthalate (PET) film (thickness: 100 μm) with a Tg of approximately 75°C was used. Corona treatment was applied to one side of the resin substrate.

To 100 parts by weight of a PVA resin prepared by mixing polyvinyl alcohol (DP 4200, DSA 99.2 mol%) and acetyl-modified PVA (GOHSEFIMER, manufactured by Nippon Gosei Kagaku Kogyo Co., Ltd.) in a ratio of 9:1, 13 parts by weight of potassium iodide was added and the mixture was dissolved in water to prepare a PVA aqueous solution (coating solution).

The PVA aqueous solution was applied to the corona-treated surface of the resin substrate and dried at 60°C to form a 13μm thick PVA resin layer to produce a laminate.

The obtained laminate was stretched uniaxially in the longitudinal direction (lengthwise) to 2.4 times in an oven at 130°C (air-assisted stretching treatment).

Next, the laminate was immersed in an insolubilization bath (a boric acid aqueous solution prepared 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 (insolubilization treatment).

Next, the polarizing element was immersed in a dye bath (an aqueous iodine solution prepared by mixing iodine and potassium iodide at a weight ratio of 1:7 per 100 parts by weight of water) at a temperature of 30°C for 60 seconds (dyeing process), while adjusting the concentration so that the resulting single-element transmittance (Ts) of the polarizing element reached a specific value.

Next, immerse 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 per 100 parts by weight of water) at a liquid temperature of 40°C for 30 seconds (crosslinking treatment).

The laminate was then immersed in a boric acid aqueous solution (boric acid concentration 4 wt%, potassium iodide concentration 5 wt%) at a temperature of 70°C and simultaneously subjected to uniaxial stretching (underwater stretching) in the longitudinal direction (lengthwise) at a stretching ratio of 5.5 times between rolls of varying circumferential speeds.

Afterwards, the laminate was immersed in a cleaning bath (an aqueous solution prepared 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).

Afterwards, the product is dried in an oven maintained at approximately 90°C while in contact with a SUS (Steel Special Use Stainless Steel) heating roller maintained at approximately 75°C (drying and shrinking treatment).

In this way, a polarizing element with a thickness of approximately 5 μm is formed on a resin substrate, resulting in a polarizing plate having a resin substrate/polarizing element structure.

A 1.0μm thick HC-TAC film was then applied to the surface of the resulting polarizing element (the side opposite the resin substrate) via a UV-curable adhesive to serve as a protective substrate (protective layer). Furthermore, the HC-TAC film, which consisted of a 7μm thick hard coat (HC) layer formed on a 25μm thick triacetyl cellulose (TAC) film, was laminated with the TAC film facing the polarizing element. This produced a polarizing plate with a protective layer/polarizing element configuration. The protective layer had an elastic modulus of 3872 MPa.

2. Fabrication of the phase difference layer

A liquid crystal composition (coating liquid) was prepared by dissolving 10 g of a polymerizable liquid crystal exhibiting a nematic liquid crystal phase ("Paliocolor LC242," manufactured by BASF, and represented by the following formula) and 3 g of a photopolymerization initiator for the polymerizable liquid crystal compound ("Irgacure 907," manufactured by BASF) in 40 g of toluene.

The surface of a polyethylene terephthalate (PET) film (38 μm thick) was rubbed with a rubbing cloth to perform an alignment treatment. The orientation of the alignment treatment was set so that when attached to a polarizing plate, the orientation was 15° relative to the absorption axis of the polarizing element when viewed from the viewing side. The liquid crystal coating liquid was applied to the alignment-treated surface using a rod coater and dried at 90°C for 2 minutes to align the liquid crystal compound. The liquid crystal layer formed in this manner was irradiated with 1 mJ/ ^cm2 of light using a metal halide lamp to harden the liquid crystal layer, thereby forming a liquid crystal alignment cured layer A on the PET film. The thickness of the liquid crystal alignment cured layer A was 2 μm, and the in-plane phase difference Re(550) was 270 nm. Furthermore, the liquid crystal alignment cured layer A has a refractive index distribution of nx>ny=nz. The liquid crystal alignment cured layer A is used as the W layer.

A liquid crystal alignment cured layer B was formed on the PET film in the same manner as above, except that the coating thickness was changed and the alignment treatment direction was adjusted to 75° relative to the absorption axis of the polarizing element when viewed from the viewing side. The liquid crystal alignment cured layer B had a thickness of 1 μm and an in-plane retardation Re(550) of 140 nm. Furthermore, the liquid crystal alignment cured layer B had a refractive index distribution of nx>ny=nz. The liquid crystal alignment cured layer B was used as the Q layer.

3. Production of polarizing plates with phase difference layers

The liquid crystal alignment cured layer A (W layer) and liquid crystal alignment cured layer B (Q layer) obtained in step 2 were sequentially transferred to the polarizer surface of the polarizing plate obtained in step 1. The transfer (lamination) was performed so that the angle between the absorption axis of the polarizing element and the retarded axis of the alignment cured layer A was 15°, and the angle between the absorption axis of the polarizing element and the retarded axis of the alignment cured layer B was 75°. Furthermore, each transfer (lamination) was performed using a UV-curable adhesive (1.0 μm thick). In this way, a polarizing plate with a retardation layer was obtained, having a structure of protective layer/adhesive/polarizing element/adhesive/W layer/adhesive/adhesive/Q layer. The obtained polarizing plate with a phase difference layer has a thickness of 43 μm. The polarizing plate with a phase difference layer is punched into a rectangle of a specific size corresponding to a bendable image display device having a bending axis along the short side. Here, the punching is performed in such a way that the absorption axis of the polarizing element is 30° relative to the bending axis. The obtained polarizing plate with a phase difference layer is subjected to the evaluations of (3) and (4) above. The results are shown in Table 1.

[Example 1-2]~[Example 1-5] and [Comparative Example 1-1]~[Comparative Example 1-2]

A polarizing plate with a retardation layer was obtained in the same manner as in Example 1-1, except that the polarizing element was punched out so that the angle between its absorption axis and bending axis was the angle shown in Table 1. The obtained polarizing plate with a retardation layer was subjected to the same evaluation as in Example 1-1. The results are shown in Table 1.

[Example 2-1]

Similar to Example 1-1, a polarizing plate having a protective layer/polarizing element structure was fabricated. Meanwhile, a retardation layer (a single retardation layer exhibiting inverse wavelength dispersion dependence and capable of functioning as a λ/4 plate) and another retardation layer (a positive C plate) were fabricated as described below.

55 parts of the compound represented by formula (II), 25 parts of the compound represented by formula (III), and 20 parts of the compound represented by formula (IV) were added to 400 parts of cyclopentanone (CPN). The mixture was then heated to 60°C and stirred to dissolve. After dissolution was confirmed, the mixture was returned to room temperature. 3 parts of Irgacure 907 (manufactured by BASF Japan Co., Ltd.), 0.2 parts of MEGAFAC F-554 (manufactured by DIC Corporation), and 0.1 parts of p-methoxyphenol (MEHQ) were added and further stirred to obtain a solution. The solution was transparent and homogeneous. The obtained solution was filtered through a 0.20 μm membrane filter to obtain a polymerizable composition. On the other hand, a spin coating method is used to apply a polyimide solution to an alignment film on a glass substrate with a thickness of 0.7 mm. After drying at 100°C for 10 minutes, the film is baked at 200°C for 60 minutes to obtain a coating. The obtained coating is rubbed to form an alignment film. The rubbing treatment is carried out using a commercially available rubbing device. The polymerizable composition obtained above is applied to a substrate (essentially an alignment film) using a spin coating method and dried at 100°C for 2 minutes. After the obtained coating is cooled to room temperature, it is irradiated with ultraviolet light at an intensity of 30 mW/ ^cm2 for 30 seconds using a high-pressure mercury lamp to obtain a liquid crystal alignment cured layer C. The thickness of the liquid crystal alignment cured layer was 3.0 μm, and the in-plane retardation Re(550) was 130 nm. Furthermore, the Re(450)/Re(550) ratio of the liquid crystal alignment cured layer was 0.851, exhibiting reverse wavelength dispersion characteristics. This liquid crystal alignment cured layer was used as a retardation layer.

[Chemistry 3]

20 parts by weight of a side-chain liquid crystal polymer represented by the following chemical formula (I) (where 65 and 35 represent the molar percentage of monomer units, and for convenience, it is expressed as a block polymer with a weight average molecular weight of 5000), 80 parts by weight of a polymerizable liquid crystal exhibiting a nematic liquid crystal phase (manufactured by BASF: Paliocolor LC242), and 5 parts by weight of a photopolymerization initiator (manufactured by Ciba Specialty Chemicals: Irgacure 907) were dissolved in 200 parts by weight of cyclopentanone to prepare a liquid crystal coating solution. The coating solution was then applied to a substrate film (reduced to 0.05 mm/s) using a rod coater. An olefin resin film (ZEONEX, manufactured by Zeon Co., Ltd., Japan) was then heat-dried at 80°C for 4 minutes to achieve liquid crystal alignment. This liquid crystal layer was then irradiated with UV light to cure, forming a liquid crystal alignment cured layer (positive C plate, 3μm thick) on the substrate, serving as another retardation layer. This layer had a Re(590) of 0nm and an Rth(590) of -100nm, exhibiting a refractive index characteristic of nz > nx = ny.

The liquid crystal alignment cured layer C was transferred to the polarizing element surface of the polarizing plate obtained above via an adhesive layer (5μm thick). Furthermore, a positive C plate was transferred to the surface of the liquid crystal alignment cured layer C. In this way, a polarizing plate with a retardation layer was obtained, consisting of a protective layer/adhesive/polarizing element/adhesive layer/retardation layer/adhesive/positive C plate. The resulting polarizing plate with a retardation layer had a thickness of 49μm. This polarizing plate with a retardation layer was punched into a rectangular shape of a specific size corresponding to a bendable image display device with a bending axis along its short side. Here, the polarizing element was punched so that its absorption axis was angled 30° relative to the bending axis. The resulting polarizing plate with a phase difference layer was subjected to the same evaluation as in Example 1-1. The results are shown in Table 1.

[Example 2-2]~[Example 2-5] and [Comparative Example 2-1]~[Comparative Example 2-2]

A polarizing plate with a retardation layer was obtained in the same manner as in Example 2-1, except that the polarizing element was punched out so that the angle between its absorption axis and bending axis was the angle shown in Table 1. The obtained polarizing plate with a retardation layer was evaluated in the same manner as in Example 1-1. The results are shown in Table 1.

[Example 3-1]

A polarizing plate with a retardation layer was obtained in the same manner as in Example 1-1, except that an acrylic resin film (20 μm thick) was used as the protective layer instead of the HC-TAC film. The elastic modulus of the protective film was 2881 MPa. The thickness of the polarizing plate with a retardation layer was 31 μm. The polarizing plate with a retardation layer was punched into a rectangular shape of specific dimensions corresponding to a bendable image display device having a bending axis along its short side. The shape was punched so that the absorption axis of the polarizer was at a 30° angle relative to the bending axis. The resulting polarizing plate with a retardation layer was subjected to the same evaluation as in Example 1-1. The results are shown in Table 1.

[Example 3-2]~[Example 3-5] and [Comparative Example 3-1]~[Comparative Example 3-2]

A polarizing plate with a retardation layer was obtained in the same manner as in Example 3-1, except that the polarizing element was punched out so that the angle between its absorption axis and bending axis was the angle shown in Table 1. The obtained polarizing plate with a retardation layer was evaluated in the same manner as in Example 1-1. The results are shown in Table 1.

[Example 4-1]

A polarizing plate with a retardation layer was obtained in the same manner as in Example 1-1, except that an acrylic resin film (40 μm thick) was used as the protective layer instead of the HC-TAC film. The elastic modulus of the protective film was 3066 MPa. The thickness of the polarizing plate with a retardation layer was 51 μm. The polarizing plate with a retardation layer was punched into a rectangular shape of specific dimensions corresponding to a bendable image display device having a bending axis along its short side. The shape was punched so that the absorption axis of the polarizer was at a 30° angle relative to the bending axis. The resulting polarizing plate with a retardation layer was subjected to the same evaluation as in Example 1-1. The results are shown in Table 1.

[Example 4-2]~[Example 4-5] and [Comparative Example 4-1]~[Comparative Example 4-2]

A polarizing plate with a retardation layer was obtained in the same manner as in Example 4-1, except that the polarizing element was punched out so that the angle between its absorption axis and bending axis was the angle shown in Table 1. The obtained polarizing plate with a retardation layer was evaluated in the same manner as in Example 1-1. The results are shown in Table 1.

[Comparative Example 5-1]

The phase difference layer (a single phase difference layer that exhibits inverse wavelength dispersion dependence and can function as a λ/4 plate) was fabricated as follows.

The polymerization was carried out using a batch polymerization apparatus consisting of two vertical stirred reactors equipped with stirring blades and reflux condensers. 30.31 parts by mass (0.047 mol) of bis[9-(2-phenoxycarbonylethyl)fluoren-9-yl]methane (BPFM) synthesized by the method described in Japanese Patent Application Laid-Open No. 2015-25111, 39.94 parts by mass (0.273 mol) of isosorbide (ISB, manufactured by Roquette Freres), 30.20 parts by mass (0.099 mol) of spiroglycol (SPG, manufactured by Mitsubishi Gas Chemical Co., Ltd.), 69.67 parts by mass (0.325 mol) of diphenyl carbonate (DPC, manufactured by Mitsubishi Chemical Co., Ltd.), and 7.88× ^10-4 parts by mass (4.47× ^10-6 mol) of calcium acetate monohydrate as a catalyst were added. After depressurizing the reactor and replacing it with nitrogen, heating was performed using a heat medium. Stirring began when the internal temperature reached 100°C. 40 minutes after the start of the temperature increase, the internal temperature reached 220°C and was maintained at this temperature. Simultaneously, the pressure was reduced to 13.3 kPa over 90 minutes after reaching 220°C. Phenol vapor, a by-product of the polymerization reaction, was directed to a 110°C reflux condenser. A certain amount of monomer components contained in the phenol vapor was returned to the reactor. Uncondensed phenol vapor was directed to a 45°C condenser for recovery. Nitrogen was introduced into the first reactor, and after temporarily repressurizing to atmospheric pressure, the oligomerization reaction liquid in the first reactor was transferred to the second reactor. Next, the temperature and pressure in the second reactor were raised and reduced, reaching 240°C and 20 kPa over 40 minutes. Polymerization was then continued while the pressure was further reduced until the specified stirring power was reached. At the specified power, nitrogen was introduced into the reactor for re-pressurization, extruding the resulting polyester carbonate into water. The strands were then cut to obtain pellets. The ratio of the structural units derived from the various monomers in this resin was BPFM/ISB/SPG/DPC = 21.5/39.4/30.0/9.1 mass %. The resulting pellets were vacuum-dried at 100°C for at least 6 hours. A 3m long, 200mm wide, 100μm thick unstretched film strip was then produced using a film-forming apparatus equipped with a single-screw extruder (Isuzu Kakoki Co., Ltd., screw diameter 25mm, cylinder temperature setting: 250°C), a T-die (300mm width, temperature setting: 220°C), a cooling roll (temperature setting: 120-130°C), and a winder. The unstretched film strip was then stretched at its Tg (139°C) to produce a retardation film with a thickness of 37μm. The obtained retardation film exhibited the refractive index characteristics of nx>ny=nz, Re(550) was 145nm, and Re(450)/Re(550) was 0.85.

Using the retardation film obtained above as the retardation layer, the retardation film was bonded to the polarizing element via an adhesive layer (5 μm thick) instead of an adhesive layer. The positive C plate used in Example 2-1 was transferred onto the surface of the retardation layer. Similar to Example 1-1, a polarizing plate with a retardation layer was obtained, with the following structure: protective layer/adhesive/polarizing element/adhesive layer/retardation layer (retardation film)/adhesive/positive C plate. The resulting polarizing plate with a retardation layer had a thickness of 89 μm. The polarizing plate with a retardation layer was punched into a rectangular shape of a specific size corresponding to a bendable image display device having a bending axis along its short side. Here, the polarizing element was punched so that its absorption axis was at 0° relative to the bending axis. The resulting polarizing plate with a phase difference layer was subjected to the same evaluation as in Example 1-1. The results are shown in Table 1.

[Comparative Example 5-2]~[Comparative Example 5-7]

A polarizing plate with a retardation layer was obtained in the same manner as in Comparative Example 5-1, except that the polarizing element was punched so that the angle between its absorption axis and bending axis was the angle shown in Table 1. The obtained polarizing plate with a retardation layer was evaluated in the same manner as in Example 1-1. The results are shown in Table 1.

[Comparative Example 6-1]

A polarizing plate with a retardation layer was obtained in the same manner as in Example 1-1, except that an HC-COP film was used as the protective layer instead of the HC-TAC film. The elastic modulus of the protective film was 1988 MPa. The thickness of the polarizing plate with a retardation layer was 84 μm. The polarizing plate with a retardation layer was punched into a rectangular shape of specific dimensions corresponding to a bendable image display device having a bending axis along its short side. The shape was punched so that the absorption axis of the polarizing element was at a 30° angle relative to the bending axis. The resulting polarizing plate with a retardation layer was evaluated in the same manner as in Example 1-1. The results are shown in Table 1.

[Comparative Example 6-2]~[Comparative Example 6-7]

A polarizing plate with a retardation layer was obtained in the same manner as in Comparative Example 6-1, except that the polarizing element was punched so that the angle between its absorption axis and bending axis was the angle shown in Table 1. The obtained polarizing plate with a retardation layer was evaluated in the same manner as in Example 1-1. The results are shown in Table 1.

[Comparative Example 7-1]

The polarizing plate was prepared as follows.

A 30μm-thick polyvinyl alcohol (PVA) resin film with an average degree of polymerization of 2,400 and a saponification degree of 99.9 mol% was prepared. The film was immersed in a 20°C swelling bath (water bath) between rolls with different peripheral speed ratios for 30 seconds to swell while simultaneously stretched to 2.4 times in the conveying direction (swelling step). The film was then immersed in a 30°C dyeing bath (an aqueous solution containing 0.03% iodine and 0.3% potassium iodide by weight) to achieve the desired monomer permeability after stretching. The film was then stretched to 3.7 times in the conveying direction relative to the original PVA film (which had not been stretched in the conveying direction) (dyeing step). The immersion time was approximately 60 seconds. The dyed PVA film was then immersed in a 40°C crosslinking bath (a 3.0 wt% boric acid, 3.0 wt% potassium iodide aqueous solution) and stretched to 4.2 times the original PVA film in the transport direction (crosslinking step). The resulting PVA film was then immersed in a 64°C stretching bath (a 4.0 wt% boric acid, 5.0 wt% potassium iodide aqueous solution) for 50 seconds, stretched to 6.0 times the original PVA film in the transport direction (stretching step), and then immersed in a 20°C cleaning bath (a 3.0 wt% potassium iodide aqueous solution) for 5 seconds (cleaning step). The washed polyvinyl alcohol film was dried at 30°C for 2 minutes to produce a polarizing element (12 μm thick). An HC-TAC film was laminated to one side of the resulting polarizing element, as in Example 1-1, and a 25 μm thick TAC film was laminated to the other side. In this manner, a polarizing plate was produced, comprising a viewing-side protective layer (HC-TAC film)/polarizing element/inner protective layer (TAC film). The elastic modulus of the viewing-side protective layer was the same as in Example 1-1: 3872 MPa.

Using the polarizing plate obtained above, a polarizing plate with a retardation layer was obtained, with the following configuration: protective layer/adhesive/polarizing element/adhesive/protective layer/adhesive layer/retardation layer (retardation film)/adhesive/positive C plate, similar to Comparative Example 5-1. The resulting polarizing plate with a retardation layer had a thickness of 116 μm. The polarizing plate with a retardation layer was punched into a rectangular shape of specific dimensions corresponding to a bendable image display device with a bending axis along its short side. Here, the punching was performed so that the absorption axis of the polarizing element was at 0° relative to the bending axis. The resulting polarizing plate with a phase difference layer was subjected to the same evaluation as in Example 1-1. The results are shown in Table 1.

[Comparative Example 7-2]~[Comparative Example 7-7]

A polarizing plate with a retardation layer was obtained in the same manner as in Comparative Example 7-1, except that the polarizing element was punched so that the angle between its absorption axis and bending axis was the angle shown in Table 1. The obtained polarizing plate with a retardation layer was evaluated in the same manner as in Example 1-1. The results are shown in Table 1.

[Comparative Example 8-1]

A brightness enhancement film (an amorphous isophthalic acid copolymer polyethylene terephthalate (IPA copolymer PET) film (30 μm thick) with a water absorption of 0.75% and a Tg of 75°C) was laminated to one side of the polarizing element produced in Comparative Example 7-1 to produce a polarizing plate having a brightness enhancement film/polarizing element configuration. Following the same sequence as in Example 1-1, a polarizing plate with a phase difference layer was obtained, having a configuration of protective layer (brightness enhancement film)/adhesive/polarizing element/adhesive/W layer/adhesive/Q layer. The elastic modulus of the protective layer was 5005 MPa. The resulting polarizing plate with a phase difference layer had a thickness of 48 μm. The polarizing plate with a retardation layer was punched into a rectangular shape of a specific size corresponding to a bendable image display device having a bending axis along its short side. Punching was performed so that the absorption axis of the polarizing element was at 0° relative to the bending axis. The resulting polarizing plate with a retardation layer was evaluated in the same manner as in Example 1-1. The results are shown in Table 1.

[Comparative Example 8-2]~[Comparative Example 8-7]

A polarizing plate with a retardation layer was obtained in the same manner as in Comparative Example 8-1, except that the polarizing element was punched so that the angle between its absorption axis and bending axis was the angle shown in Table 1. The obtained polarizing plate with a retardation layer was evaluated in the same manner as in Example 1-1. The results are shown in Table 1.

[Evaluation]

As can be clearly seen from Table 1, the embodiments of the present invention can provide a polarizing plate with a phase difference layer that exhibits excellent refracting properties and visibility when viewed through polarizing sunglasses.

[Industrial Availability]

The polarizing plate with a phase difference layer of the present invention can be suitably used in an image display device that can be bent and viewed through polarized sunglasses.

A: Absorption axis

F: Crankshaft

Claims (12)

A polarizing plate with a phase difference layer is used in a bendable image display device and comprises: a polarizing plate including a polarizing element and a protective layer on at least one side of the polarizing element; and a phase difference layer disposed on the side of the polarizing plate opposite to the viewing side and having a circularly polarized light function or an elliptical polarized light function. The polarizing plate with the phase difference layer has a total thickness of 80 μm or less, an angle between the bending axis of the image display device and the absorption axis of the polarizing element is 30° to 60°, an elastic modulus of the protective layer is 5000 MPa or less, and the absorption axis of the polarizing element is oriented in a single direction throughout the polarizing element. The polarizing plate with a phase difference layer as claimed in claim 1 has a total thickness of less than 60 μm. In the polarizing plate with a phase difference layer as claimed in claim 1 or 2, the thickness of the polarizing element is less than 10 μm. The polarizing plate with a phase difference layer as claimed in claim 1 or 2, wherein the polarizing plate includes a protective layer only on the side of the polarizing element opposite to the phase difference layer. In the polarizing plate with a phase difference layer according to claim 4, the elastic modulus of the protective layer is less than 4000 MPa. In the polarizing plate with a phase difference layer according to claim 5, the thickness of the protective layer is less than 45 μm. In the polarizing plate with a phase difference layer according to claim 1 or 2, the angle formed between the bending axis and the absorption axis of the polarizing element is 40° to 50°. The polarizing plate with a phase difference layer according to claim 1 or 2, wherein the phase difference layer is an alignment cured layer of a liquid crystal compound. A polarizing plate with a phase difference layer as claimed in claim 8, wherein the phase difference layer is a single layer, Re(550) of the phase difference layer is 100 nm to 190 nm, Re(450)/Re(550) of the phase difference layer is greater than 0.8 and less than 1, and an angle between a retardation axis of the phase difference layer and an absorption axis of the polarizing element is 40° to 50°. The polarizing plate with a phase difference layer as claimed in claim 9, wherein the polarizing plate with a phase difference layer has another phase difference layer outside the phase difference layer, and the refractive index characteristics of the other phase difference layer show the relationship of nz>nx=ny. A polarizing plate with a phase difference layer as claimed in claim 8, wherein the phase difference layer has a laminated structure of an alignment cured layer of a first liquid crystal compound and an alignment cured layer of a second liquid crystal compound, and the Re(550) of the alignment cured layer of the first liquid crystal compound is 200 nm to 300 nm, and the angle between its retardation axis and the absorption axis of the polarizing element is 10° to 20°, and the Re(550) of the alignment cured layer of the second liquid crystal compound is 100 nm to 190 nm, and the angle between its retardation axis and the absorption axis of the polarizing element is 70° to 80°. An image display device comprises a polarizing plate with a phase difference layer as claimed in any one of claims 1 to 11.