JP7252924B2 - Organic EL display device - Google Patents

Description

The present invention relates to circular polarizers used primarily for antireflection purposes and bendable display devices using such circular polarizers.

In recent years, smart devices represented by smartphones and display devices such as digital signage and window displays are increasingly used under strong external light. Along with this, problems such as the reflection of external light and reflection of the background due to the display device itself or the touch panel portion, glass substrate, metal wiring, or other reflector used in the display device have arisen. In particular, an organic electroluminescence (EL) panel, which has been put into practical use in recent years, has a highly reflective metal layer, and therefore tends to cause problems such as external light reflection and background reflection. Therefore, it is known to prevent these problems by providing a circularly polarizing plate having a retardation film (typically a λ/4 plate) on the viewing side as an antireflection film.

By the way, in recent years, there has been an increasing demand for flexible and bendable organic EL panels. Furthermore, there is a demand for realization of bendability with a very small radius of curvature, rather than just flexibility and bendability. However, when the organic EL panel is bent with a very small radius of curvature, a large force (tensile force in part, compressive force in part) is applied to the retardation film of the circular polarizer, and the retardation at that part is change. As a result, the antireflection function of the circularly polarizing plate at the bent portion is deteriorated, and the color changes only at the bent portion, which poses a serious problem. In particular, a circularly polarizing plate including a retardation film having reverse dispersion wavelength characteristics has a remarkable problem of color change due to bending, although excellent reflection characteristics are obtained.

JP 2010-139548 A Japanese Patent Application Laid-Open No. 2003-207640 JP 2004-226842 A Patent No. 3815790

The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide a bendable display device in which excellent reflection hue is obtained and color change due to bending is suppressed. An object of the present invention is to provide a circularly polarizing plate that can be realized.

A circularly polarizing plate of the present invention is a circularly polarizing plate used in a bendable display device, and comprises a polarizer and a retardation film arranged on one side of the polarizer. The in-plane retardation of the retardation film satisfies the relationship Re(450)<Re(550)<Re(650). The circularly polarizing plate of the present invention is adjusted so that the slow axis direction of the retardation film defines an angle of 20° to 70° with respect to the bending direction of the display device, and is bent with a radius of curvature of 5 mm to 15 mm. , 25° C. and 50% humidity for 24 hours, the difference in in-plane retardation between the curved portion and the flat portion is 2 nm or less.
In one embodiment, the absolute value of the photoelastic coefficient of the retardation film is 2×10 ⁻¹² (m ² /N) or more.
In one embodiment, the circularly polarizing plate further comprises another retardation film arranged on the other side of the polarizer.
According to another aspect of the invention, a bendable display device is provided. This display device includes the circularly polarizing plate described above.
In one embodiment, the display device is an organic electroluminescent display device.

According to the present invention, in a circularly polarizing plate used in a bendable display device, a retardation film exhibiting reverse dispersion wavelength dependence (reverse dispersion wavelength characteristics) is used as a retardation film, and the retardation film is By adjusting the direction of the slow axis to a predetermined direction with respect to the bending direction of the display device, a bendable display device is realized in which excellent reflection hue is obtained and color change due to bending is suppressed. A circularly polarizing plate can be obtained.

FIG. 1(a) is a schematic cross-sectional view of a circularly polarizing plate according to one embodiment of the present invention, and FIG. 1(b) is a schematic cross-sectional view of a circularly polarizing plate according to another embodiment of the present invention. FIGS. 2(a) to 2(d) are schematic diagrams for explaining bending forms of the display device of the present invention. 1 is a schematic cross-sectional view of an organic EL display device according to one embodiment of the present invention; FIG. 1 is a schematic cross-sectional view of an organic EL element used in an organic EL display device according to one embodiment of the present invention; FIG.

Preferred embodiments of the present invention will be described below, but the present invention is not limited to these embodiments.

(Definition of terms and symbols)
Definitions of terms and symbols used herein 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., slow axis direction), and "ny" is the in-plane direction orthogonal to the slow axis (i.e., 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 of the film measured at 23° C. with light of wavelength λ nm. For example, "Re(450)" is the in-plane retardation of a film measured with light having a wavelength of 450 nm at 23°C. Re(λ) is obtained by the formula: Re=(nx−ny)×d, where d (nm) is the thickness of the film.
(3) Thickness direction retardation (Rth)
“Rth(λ)” is the retardation in the thickness direction of the film measured at 23° C. with light having a wavelength of 550 nm. For example, "Rth(450)" is the retardation in the thickness direction of the film measured at 23°C with light having a wavelength of 450 nm. Rth(λ) is determined by the formula: Rth=(nx−nz)×d, where d (nm) is the thickness of the film.
(4) Nz Coefficient The Nz coefficient is obtained by Nz=Rth/Re.

A. Overall Configuration of Circularly Polarizing Plate FIG. 1(a) is a schematic cross-sectional view of a circularly polarizing plate according to one embodiment of the present invention. A circularly polarizing plate 100 of this embodiment includes a polarizer 10 and a retardation film 20 arranged on one side of the polarizer 10 . Circularly polarizing plate 100 may include a protective film 40 (hereinafter sometimes referred to as an outer protective film) on the other side of polarizer 10, if necessary. Furthermore, another protective film (hereinafter sometimes referred to as an inner protective film: not shown) may be placed between the polarizer 10 and the retardation film 20, if necessary.

FIG. 1(b) is a schematic cross-sectional view of a circularly polarizing plate according to another embodiment of the present invention. The circularly polarizing plate 100′ of this embodiment has a polarizer 10, a retardation film 20 arranged on one side of the polarizer 10, and a retardation film 30 arranged on the other side of the polarizer 10. . The illustrated example shows a form in which the outer protective film 40 is provided. When the outer protective film 40 is provided, the retardation film 30 may be arranged further outside (viewing side) of the outer protective film 40 . The outer protective film 40 may be omitted. In this case, the retardation film 30 can function as an outer protective film. In this specification, for convenience, the retardation film 20 may be referred to as a first retardation film, and the retardation film 30 may be referred to as a second retardation film.

The circularly polarizing plate of the present invention is used in a bendable display device. Specific examples of bendable display devices include organic EL display devices, liquid crystal display devices using circularly polarized light (typically VA mode liquid crystal display devices), and MEMS displays. A bendable display device in which the circularly polarizing plate of the present invention is particularly preferably used is an organic EL display device. This is because bending with a very small radius of curvature is possible as will be described later, and by using the circularly polarizing plate of the present invention, a very excellent reflection hue can be obtained. At least part of the display device is bent with a radius of curvature of preferably 10 mm or less, more preferably 8 mm or less. One of the achievements of the present invention is that, in such a display device that is bent with a very small radius of curvature, the color change due to bending is suppressed while maintaining the excellent reflection hue as described above. be. More specifically, the display device is bent at any suitable portion. For example, the display device may be bent at the center like a foldable display device (for example, FIGS. 2(a) and 2(b)), from the viewpoint of maximizing design and display screen. may be bent at the ends from (e.g., FIGS. 2(c) and (d)). Furthermore, as shown in FIGS. 2(a) to 2(d), the display device may be bent along its longitudinal direction or may be bent along its lateral direction. Needless to say, specific portions of the display device may be bent (for example, part or all of the four corners obliquely) depending on the application.

The first retardation film 20 exhibits reverse dispersion wavelength characteristics. Specifically, the in-plane retardation satisfies the relationship Re(450)<Re(550)<Re(650). By satisfying such a relationship, it is possible to achieve an excellent reflection hue in the front direction of the organic EL panel. Further, the first retardation film 20 typically exhibits a refractive index characteristic of nx>ny and has a slow axis. As shown in FIGS. 2(a) to 2(d), the slow axis direction of the first retardation film 20 is adjusted to define an angle α with respect to the bending direction of the display device. The angle α is 20° to 70°, preferably 30° to 60°, more preferably 40° to 50°, particularly preferably around 45°. By adjusting the slow axis direction of the first retardation film so that the angle α falls within such a range, color change due to bending can be suppressed. The second retardation film 30 may be arranged for the purpose of preventing deterioration in visibility when viewing the display device while wearing polarized sunglasses. In this case, the second retardation film 30 may or may not exhibit reverse wavelength dispersion characteristics. It should be noted that when an angle is referred to in this specification, the angle includes angles in both clockwise and counterclockwise directions unless otherwise specified.

In one embodiment, the circular polarizer of the present invention is elongated, so the polarizer 10 and first retardation film 20 (and second retardation film 30, if present) are also It is elongated. A long circularly polarizing plate can be stored and/or transported, for example, by being wound into a roll. In this embodiment, the absorption axis of the polarizer typically corresponds to the longitudinal direction. Therefore, the angle θ between the slow axis and the longitudinal direction of the first retardation film 20 is preferably 35° ≤ θ ≤ 55°, more preferably 38° ≤ θ ≤ 52°, still more preferably 39° It satisfies the relationship ≦θ≦51°. In another embodiment, the circularly polarizing plate of the present invention is a single plate, and in this case, the absorption axis of the polarizer typically forms an angle θ with respect to the longitudinal direction, and the first retardation film The 20 slow axes are typically orthogonal or parallel to the longitudinal direction. Also in this embodiment, the preferred range of the angle θ is the same as above.

The overall thickness of the circularly polarizing plate of the present invention varies depending on its structure, but is typically about 40 μm to 300 μm. Each layer constituting the circularly polarizing plate of the present invention will be described below.

A-1. Polarizer Any appropriate polarizer can be employed as the polarizer 10 . As a specific example, a dichroic substance such as iodine or a dichroic dye is added to a hydrophilic polymer film such as a polyvinyl alcohol film, a partially formalized polyvinyl alcohol film, or a partially saponified ethylene/vinyl acetate copolymer film. polyene-based oriented films such as those subjected to dyeing treatment and stretching treatment by poly(vinyl alcohol), dehydrated polyvinyl alcohol and dehydrochlorinated polyvinyl chloride. A polarizer obtained by dyeing a polyvinyl alcohol-based film with iodine and uniaxially stretching the film is preferably used because of its excellent optical properties.

The dyeing with iodine is performed, for example, by immersing the polyvinyl alcohol film in an aqueous iodine solution. The draw ratio of the uniaxial drawing is preferably 3 to 7 times. Stretching may be performed after the dyeing treatment, or may be performed while dyeing. Moreover, you may dye after extending|stretching. If necessary, the polyvinyl alcohol film is subjected to swelling treatment, cross-linking treatment, washing treatment, drying treatment, and the like. For example, by immersing a polyvinyl alcohol film in water and washing it with water before dyeing, not only can dirt and anti-blocking agents on the surface of the polyvinyl alcohol film be washed away, but also the polyvinyl alcohol film can be swollen and dyed. Unevenness etc. can be prevented.

The thickness of the polarizer is typically about 1 μm to 80 μm.

The polarizer 10 and the first retardation film 20 are laminated such that the absorption axis of the polarizer 10 and the slow axis of the first retardation film 20 form a predetermined angle. As described above, the angle θ between the absorption axis of the polarizer 10 and the slow axis of the first retardation film 20 is preferably 35°≦θ≦55°, more preferably 38°≦θ≦52°, More preferably, the relationship of 39°≦θ≦51° is satisfied.

A-2. First Retardation Film As described above, the first retardation film 20 exhibits a refractive index characteristic of nx>ny. The in-plane retardation Re(550) of the retardation film is preferably 100 nm to 180 nm, more preferably 135 nm to 155 nm.

As described above, the first retardation film exhibits so-called inverse wavelength dependence of dispersion. Specifically, the in-plane retardation satisfies the relationship Re(450)<Re(550)<Re(650). Re(450)/Re(550) is preferably 0.8 or more and less than 1.0, more preferably 0.8 to 0.95. Re(550)/Re(650) is preferably 0.8 or more and less than 1.0, more preferably 0.8 to 0.97.

The first retardation film 20 exhibits any suitable refractive index ellipsoid as long as it has a relationship of nx>ny. Preferably, the refractive index ellipsoid of the retardation film exhibits a relationship of nx>ny≧nz. The Nz coefficient of the retardation film is preferably 1 to 2, more preferably 1 to 1.5, still more preferably 1 to 1.3.

The absolute value of the photoelastic coefficient of the first retardation film 20 is preferably 2×10 ⁻¹² (m ² /N) or more, more preferably 10×10 ⁻¹² (m ² /N) to It is 100×10 ⁻¹² (m ² /N), more preferably 20×10 ⁻¹² (m ² /N) to 40×10 ⁻¹² (m ² /N). Many retardation films exhibiting reverse dispersion wavelength characteristics have a large absolute value of photoelastic coefficient, and when the display device is bent with a small radius of curvature, the color change is remarkable. To provide a circularly polarizing plate capable of suppressing color change due to bending even when a display device is bent with a small radius of curvature while maintaining the excellent effect of a retardation film exhibiting such reverse dispersion wavelength characteristics. can do. In addition, if the absolute value of the photoelastic coefficient is within the preferred range as described above, it is possible to maintain the flexibility of the display device while ensuring a sufficient retardation even with a small thickness. Change can be suppressed more.

The first retardation film 20 is made of any appropriate resin that can satisfy the optical properties described above. Resins for forming the retardation film include polycarbonate resins, polyvinyl acetal resins, cycloolefin resins, acrylic resins, cellulose ester resins, and the like. Preferred are polycarbonate resins and polyvinyl acetal resins. The resins forming the first retardation film 20 may be used alone or in combination according to desired properties.

Any appropriate polycarbonate-based resin is used as the polycarbonate-based resin. For example, a polycarbonate resin containing a structural unit derived from a dihydroxy compound is preferred. Specific examples of dihydroxy compounds include 9,9-bis(4-hydroxyphenyl)fluorene, 9,9-bis(4-hydroxy-3-methylphenyl)fluorene, 9,9-bis(4-hydroxy-3- ethylphenyl)fluorene, 9,9-bis(4-hydroxy-3-n-propylphenyl)fluorene, 9,9-bis(4-hydroxy-3-isopropylphenyl)fluorene, 9,9-bis(4-hydroxy -3-n-butylphenyl)fluorene, 9,9-bis(4-hydroxy-3-sec-butylphenyl)fluorene, 9,9-bis(4-hydroxy-3-tert-butylphenyl)fluorene, 9, 9-bis(4-hydroxy-3-cyclohexylphenyl)fluorene, 9,9-bis(4-hydroxy-3-phenylphenyl)fluorene, 9,9-bis(4-(2-hydroxyethoxy)phenyl)fluorene, 9,9-bis(4-(2-hydroxyethoxy)-3-methylphenyl)fluorene, 9,9-bis(4-(2-hydroxyethoxy)-3-isopropylphenyl)fluorene, 9,9-bis( 4-(2-hydroxyethoxy)-3-isobutylphenyl)fluorene, 9,9-bis(4-(2-hydroxyethoxy)-3-tert-butylphenyl)fluorene, 9,9-bis(4-(2 -hydroxyethoxy)-3-cyclohexylphenyl)fluorene, 9,9-bis(4-(2-hydroxyethoxy)-3-phenylphenyl)fluorene, 9,9-bis(4-(2-hydroxyethoxy)-3 ,5-dimethylphenyl)fluorene, 9,9-bis(4-(2-hydroxyethoxy)-3-tert-butyl-6-methylphenyl)fluorene, 9,9-bis(4-(3-hydroxy-2 , 2-dimethylpropoxy)phenyl)fluorene and the like. The polycarbonate resin may contain a structural unit derived from a dihydroxy compound, as well as a structural unit derived from a dihydroxy compound such as isosorbide, isomannide, isoidet, spiroglycol, dioxane glycol, and bisphenols.

Details of the polycarbonate resin as described above are described in, for example, Japanese Patent Application Laid-Open No. 2012-67300 and Japanese Patent No. 3325560. The description of the patent document is incorporated herein by reference.

The glass transition temperature of the polycarbonate resin is preferably 110° C. or higher and 250° C. or lower, more preferably 120° C. or higher and 230° C. or lower. If the glass transition temperature is excessively low, the heat resistance tends to be poor, which may cause dimensional changes after film formation, and may lower the image quality of the resulting organic EL panel. If the glass transition temperature is excessively high, the molding stability during film molding may deteriorate, and the transparency of the film may be impaired. The glass transition temperature is obtained according to JIS K 7121 (1987).

Any appropriate polyvinyl acetal resin can be used as the polyvinyl acetal resin. Typically, a polyvinyl acetal resin can be obtained by condensation reaction of at least two kinds of aldehyde compounds and/or ketone compounds and a polyvinyl alcohol-based resin. Specific examples and detailed production methods of polyvinyl acetal resins are described, for example, in JP-A-2007-161994. The description is incorporated herein by reference.

The first retardation film 20 is typically produced by stretching a resin film in at least one direction.

Any appropriate method can be adopted as a method for forming the resin film. For example, melt extrusion method (e.g., T die molding method), cast coating method (e.g., casting method), calendar molding method, heat press method, co-extrusion method, co-melt method, multilayer extrusion, inflation molding method, etc. be done. Preferably, the T-die molding method, the casting method and the inflation molding method are used.

The thickness of the resin film (unstretched film) can be set to any appropriate value depending on desired optical properties, stretching conditions described later, and the like. It is preferably 50 μm to 300 μm, more preferably 80 μm to 250 μm.

Any suitable drawing method and drawing conditions (eg, drawing temperature, draw ratio, drawing direction) may be employed for the above-mentioned drawing. Specifically, various stretching methods such as free-end stretching, fixed-end stretching/free-end shrinking, and fixed-end shrinking can be used singly, simultaneously, or sequentially. As for the stretching direction, it can be carried out in various directions and dimensions such as horizontal direction, vertical direction, thickness direction and diagonal direction. The stretching temperature is preferably in the range of the glass transition temperature (Tg) of the resin film ±20°C.

By appropriately selecting the stretching method and stretching conditions, a retardation film having the desired optical properties (for example, refractive index ellipsoid, in-plane retardation, Nz coefficient) can be obtained.

In one embodiment, the first retardation film 20 is produced by uniaxially stretching or fixed-end uniaxially stretching a resin film. As a specific example of uniaxial stretching, there is a method of stretching in the longitudinal direction (longitudinal direction) while running the resin film in the longitudinal direction. Another specific example of uniaxial stretching is a method of stretching in the transverse direction using a tenter. The draw ratio is preferably 10% to 500%.

In another embodiment, the retardation film is produced by continuously obliquely stretching a long resin film in the direction of an angle θ with respect to the longitudinal direction. By adopting oblique stretching, a long stretched film having an orientation angle of θ with respect to the longitudinal direction of the film can be obtained. can be simplified.

A stretching machine used for diagonal stretching includes, for example, a tenter-type stretching machine capable of applying a feeding force, a pulling force, or a taking-up force at different speeds in the horizontal and/or vertical direction. The tenter-type stretching machine includes a horizontal uniaxial stretching machine, a simultaneous biaxial stretching machine, and the like, but any suitable stretching machine can be used as long as it can continuously obliquely stretch a long resin film.

As a method of diagonal stretching, for example, JP-A-50-83482, JP-A-2-113920, JP-A-3-182701, JP-A-2000-9912, JP-A-2002-86554, A method described in JP-A-2002-22944 and the like can be mentioned.

The thickness of the first retardation film (stretched film) is preferably 20 μm to 100 μm, more preferably 30 μm to 80 μm.

As the first retardation film 20, a commercially available film may be used as it is, or a commercially available film may be subjected to secondary processing (for example, stretching treatment, surface treatment) depending on the purpose. A specific example of the commercially available film is the trade name "Pure Ace WR" manufactured by Teijin Limited.

The surface of the first retardation film 20 on the polarizer 10 side may be subjected to surface treatment. Examples of surface treatment include corona treatment, plasma treatment, flame treatment, primer coating treatment, and saponification treatment. As the corona treatment, for example, there is a method of discharging in normal pressure air using a corona treatment machine. Plasma treatment includes, for example, a method of discharging in normal pressure air using a plasma discharger. Flame treatment includes, for example, a method in which flames are brought into direct contact with the film surface. The primer coating treatment includes, for example, a method of diluting an isocyanate compound, a silane coupling agent, or the like with a solvent and thinly applying the diluted solution. The saponification treatment includes, for example, a method of immersion in an aqueous sodium hydroxide solution. Corona treatment and plasma treatment are preferred.

A-3. Second retardation film The second retardation film 30 is, as described above, the surface of the polarizer 10 opposite to the first retardation film 20 (that is, the outer (viewing side) surface of the circularly polarizing plate) placed. In one embodiment, the second retardation film 30 has a function of converting linearly polarized light emitted from the polarizer to the viewing side into elliptically polarized light or circularly polarized light. That is, in this embodiment, the second retardation film 30 can function as a so-called λ/4 plate. The second retardation film 30, the slow axis of the absorption axis of the polarizer 10 and preferably 30 ° ~ 60 °, more preferably 40 ° ~ 50 °, more preferably form an angle near 45 ° placed as follows. By arranging such a second retardation film 30 closer to the viewing side than the polarizer 10 in the above-described axial relationship, even when the display screen is viewed through polarized lenses such as polarized sunglasses, excellent Visibility can be realized. Therefore, the circularly polarizing plate of the present invention can be suitably applied to display devices that can be used outdoors. In this embodiment, as the second retardation film 30, any appropriate retardation film that can function as a λ/4 plate can be used. For example, the in-plane retardation Re(550) of the second retardation film 30 is preferably 100 nm to 180 nm, more preferably 135 nm to 155 nm. Other optical properties, mechanical properties, constituent materials, manufacturing methods, and the like can be appropriately set or selected according to the purpose. For example, the second retardation film 30 may be the film described in Section A-2 above, or may be a film using another polymer (eg, cycloolefin-based resin). It may be a coated film.

In another embodiment, the second retardation film 30 may be, for example, an ultra-high retardation film having an in-plane retardation Re(550) of 3000 nm or more. By using such a film, it is possible to prevent the deviation of the polarization state due to the wavelength from affecting the visibility. Therefore, in the same manner as described above, excellent visibility can be achieved even when the display screen is viewed through polarized lenses such as polarized sunglasses. In this embodiment, the second retardation film 30 can be, for example, a stretched film of polyethylene terephthalate (PET).

A-4. Protective Film Protective film 40 is formed of any suitable film that can be used as a protective layer for a polarizer. Specific examples of the material that is the main component of the film include cellulose-based resins such as triacetyl cellulose (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyethersulfone-based, and polysulfone-based resins. , polystyrene-based, polynorbornene-based, polyolefin-based, (meth)acrylic-based, and acetate-based transparent resins. Thermosetting resins such as (meth)acrylic, urethane, (meth)acrylic urethane, epoxy, and silicone, or ultraviolet curable resins may also be used. In addition, for example, a glassy polymer such as a siloxane-based polymer can also be used. Further, polymer films described in JP-A-2001-343529 (WO01/37007) can also be used. Materials for this film include, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in a side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and nitrile group in a side chain. can be used, for example, a resin composition comprising an alternating copolymer of isobutene and N-methylmaleimide and an acrylonitrile-styrene copolymer. The polymer film can be, for example, an extrudate of the resin composition.

The (meth)acrylic resin has a Tg (glass transition temperature) of preferably 115° C. or higher, more preferably 120° C. or higher, still more preferably 125° C. or higher, and particularly preferably 130° C. or higher. It is because durability can be excellent. Although the upper limit of Tg of the (meth)acrylic resin is not particularly limited, it is preferably 170° C. or less from the viewpoint of moldability and the like.

As the (meth)acrylic resin, any appropriate (meth)acrylic resin can be adopted as long as the effects of the present invention are not impaired. For example, poly(meth)acrylic acid ester such as polymethyl methacrylate, methyl methacrylate-(meth)acrylic acid copolymer, methyl methacrylate-(meth)acrylic acid ester copolymer, methyl methacrylate-acrylic acid ester - (meth)acrylic acid copolymer, methyl (meth)acrylate-styrene copolymer (MS resin, etc.), polymer having an alicyclic hydrocarbon group (e.g., methyl methacrylate-cyclohexyl methacrylate copolymer , methyl methacrylate-norbornyl (meth)acrylate copolymer, etc.). Preferable examples include C _1-6 alkyl poly(meth)acrylates such as polymethyl(meth)acrylate. Methyl methacrylate-based resins containing methyl methacrylate as a main component (50 to 100% by weight, preferably 70 to 100% by weight) are more preferred.

Specific examples of the (meth)acrylic resin include, for example, ACRYPET VH and ACRYPET VRL20A manufactured by Mitsubishi Rayon Co., Ltd., and (meth)acrylic resins having a ring structure in the molecule described in JP-A-2004-70296. Resins, and high Tg (meth)acrylic resins obtained by intramolecular cross-linking or intramolecular cyclization reaction can be mentioned.

As the (meth)acrylic resin, a (meth)acrylic resin having a lactone ring structure is particularly preferable because it has high heat resistance, high transparency, and high mechanical strength.

As the (meth)acrylic resin having the lactone ring structure, JP-A-2000-230016, JP-A-2001-151814, JP-A-2002-120326, JP-A-2002-254544, JP-A-2005 Examples thereof include (meth)acrylic resins having a lactone ring structure, such as those described in JP-A-146084.

The (meth)acrylic resin having the lactone ring structure has a mass average molecular weight (also referred to as weight average molecular weight) of preferably 1,000 to 2,000,000, more preferably 5,000 to 1,000,000, still more preferably 10,000 to 500,000, especially It is preferably 50,000 to 500,000.

The (meth)acrylic resin having a lactone ring structure has a Tg (glass transition temperature) of preferably 115°C or higher, more preferably 125°C or higher, still more preferably 130°C or higher, particularly preferably 135°C, and most preferably 135°C. is above 140°C. It is because durability can be excellent. Although the upper limit of the Tg of the (meth)acrylic resin having the lactone ring structure is not particularly limited, it is preferably 170° C. or less from the viewpoint of moldability and the like.

In this specification, "(meth)acrylic" refers to acrylic and/or methacrylic.

The thickness of the protective film 40 is preferably 10 μm to 200 μm, more preferably 10 μm to 100 μm, still more preferably 15 μm to 95 μm. The protective film 40 has an in-plane retardation Re (550) of, for example, 0 nm to 10 nm, and a thickness direction retardation Rth (550) of, for example, −80 nm to +80 nm.

The surface of the protective film 40 opposite to the polarizer may be subjected to surface treatment such as hard coat treatment, anti-reflection treatment, anti-sticking treatment, anti-glare treatment, etc., if necessary. The thickness of the protective film is typically 5 mm or less, preferably 1 mm or less, more preferably 1 μm to 500 μm, still more preferably 5 μm to 150 μm.

If an inner protective film (not shown) is provided, the inner protective film is preferably optically isotropic. As used herein, “optically isotropic” means that the in-plane retardation Re (550) is 0 nm to 10 nm and the thickness direction retardation Rth (550) is −10 nm to +10 nm. say.

The thickness of the inner protective film is preferably 20 μm to 200 μm, more preferably 30 μm to 100 μm, still more preferably 35 μm to 95 μm.

A-5. Easy-Adhesion Layer In one embodiment, an easy-adhesion layer (not shown) may be provided on the surface of the first retardation film 20 on the polarizer 10 side. When providing an easy-adhesion layer, the first retardation film 20 may or may not be subjected to the surface treatment described above. Preferably, the first retardation film 20 is surface-treated. By combining the easy-adhesion layer and the surface treatment, it is possible to promote the realization of desired adhesion between the polarizer 10 and the first retardation film 20 . The easy adhesion layer preferably contains a silane with a reactive functional group. By providing such an easy-adhesion layer, it is possible to promote the realization of desired adhesion between the polarizer 10 and the first retardation film 20 . Details of the easy-adhesion layer are described, for example, in JP-A-2006-171707.

A-6. Others Any suitable pressure-sensitive adhesive layer or adhesive layer is used for lamination of the layers constituting the circularly polarizing plate of the present invention. The adhesive layer is typically formed with an acrylic adhesive. The adhesive layer is typically formed of a polyvinyl alcohol adhesive.

Although not shown, an adhesive layer may be provided on the first retardation film 20 side of the circularly polarizing plate. Since the pressure-sensitive adhesive layer is provided in advance, it can be easily attached to another optical member (for example, an organic EL display device). In addition, it is preferable that a release film is attached to the surface of the pressure-sensitive adhesive layer until it is used.

B. Display Device A display device of the present invention includes the circularly polarizing plate. In one embodiment, the display device of the present invention is an organic EL display device. FIG. 3 is a schematic cross-sectional view of an organic EL display device according to one embodiment of the invention. The organic EL display device 300 includes an organic EL element 200 and a circularly polarizing plate 100 on the viewing side of the organic EL element 200 . The circularly polarizing plate is the circularly polarizing plate of the present invention described in item A above. The circularly polarizing plates are laminated such that the first retardation film 20 is on the organic EL device side (polarizer 10 is on the viewing side). The circular polarizer is not limited to the form shown in FIG. 3, and may be a circular polarizer 100' as shown in FIG. It may be a polarizing plate.

In the present invention, the circularly polarizing plate is such that the slow axis direction of the first retardation film 20 forms an angle α with respect to the bending direction of the organic EL display device 300 (or the organic EL element 200), as described above. adjusted to stipulate The angle α is 20° to 70°, preferably 30° to 60°, more preferably 40° to 50°, particularly preferably around 45°. By laminating the circularly polarizing plate 100 and the organic EL element 200 so that the angle α falls within this range, it is possible to obtain a bendable display device in which color change due to bending is suppressed. In one embodiment, the bending direction of the organic EL display device 300 (or the organic EL element 200) is the longitudinal direction or a direction orthogonal to the longitudinal direction (lateral direction). In such an embodiment, if the absorption axis of the polarizer 10 of the circularly polarizing plate is set orthogonally or parallel to the longitudinal direction (or the lateral direction), the first It is not necessary to align the slow axis of the retardation film 20, and the absorption axis direction of the polarizer 10 may be aligned. In this way, roll-to-roll manufacturing becomes possible.

B-1. Organic EL Element As the organic EL element 200, any suitable organic EL element can be employed as long as the effects of the present invention can be obtained. FIG. 4 is a schematic cross-sectional view illustrating one form of the organic EL element used in the present invention. The organic EL element 200 typically has a substrate 210, a first electrode 220, an organic EL layer 230, a second electrode 240, and a sealing layer 250 covering these. Organic EL element 200 may further have any appropriate layer as needed. For example, a planarization layer (not shown) may be provided on the substrate, and an insulating layer (not shown) may be provided between the first and second electrodes to prevent short circuits.

The substrate 210 can be made of any appropriate material as long as it can be bent with the predetermined radius of curvature. Substrate 210 is typically made of a flexible material. If a substrate having flexibility is used, in addition to the effects of the present invention described above, if a long circularly polarizing plate is used, the organic EL display device can be manufactured by a so-called roll-to-roll process, resulting in low cost. And mass production can be realized. Further, the substrate 210 is preferably made of a material with barrier properties. Such a substrate can protect the organic EL layer 230 from oxygen and moisture. Specific examples of materials having barrier properties and flexibility include flexible thin glass, thermoplastic resin or thermosetting resin films having barrier properties, alloys, and metals. Examples of thermoplastic resins or thermosetting resins include polyester-based resins, polyimide-based resins, epoxy-based resins, polyurethane-based resins, polystyrene-based resins, polyolefin-based resins, polyamide-based resins, polycarbonate-based resins, silicone-based resins, fluorine and acrylonitrile-butadiene-styrene copolymer resin. Examples of alloys include stainless steel, 36 alloy, and 42 alloy. Metals include, for example, copper, nickel, iron, aluminum, and titanium. The thickness of the substrate is preferably 5 μm to 500 μm, more preferably 5 μm to 300 μm, still more preferably 10 μm to 200 μm. With such a thickness, the organic EL display device can be bent with the predetermined radius of curvature, and the balance of flexibility, handleability and mechanical strength is excellent. Also, the organic EL device can be suitably used in roll-to-roll processes.

The first electrode 220 can typically function as an anode. In this case, from the viewpoint of facilitating hole injection, a material having a large work function is preferable as the material forming the first electrode. Examples of such materials include indium tin oxide (ITO), indium zinc oxide (IZO), indium tin oxide doped with silicon oxide (ITSO), indium oxide containing tungsten oxide (IWO), Transparent conductive materials such as indium zinc oxide containing tungsten oxide (IWZO), indium oxide containing titanium oxide (ITiO), indium tin oxide containing titanium oxide (ITTiO), and indium tin oxide containing molybdenum (ITMO) and metals such as gold, silver, platinum and their alloys.

The organic EL layer 230 is a laminate containing various organic thin films. In the illustrated example, the organic EL layer 230 is made of a hole-injecting organic material (for example, a triphenylamine derivative), and includes a hole-injecting layer 230a provided to improve the efficiency of hole injection from the anode and, for example, copper. A hole transport layer 230b made of phthalocyanine and a light-emitting organic substance (eg, anthracene, bis[N-(1-naphthyl)-N-phenyl]benzidine, N,N'-diphenyl-NN-bis(1- A light-emitting layer 230c made of naphthyl)-1,1′-(biphenyl)-4,4′-diamine (NPB)), an electron-transporting layer 230d made of, for example, an 8-quinolinolealuminum complex, and an electron-injecting material (for example, and an electron injection layer 230e made of a perylene derivative, lithium fluoride) and provided to improve the efficiency of electron injection from the cathode. The organic EL layer 230 is not limited to the illustrated example, and any suitable combination that can cause recombination of electrons and holes in the light emitting layer 230c to emit light can be adopted. The thickness of the organic EL layer 230 is preferably as thin as possible. This is because it is preferable to transmit the emitted light as much as possible. The organic EL layer 230 can be composed of an extremely thin laminate, eg, 5 nm to 200 nm, preferably about 10 nm.

Second electrode 240 may typically function as a cathode. In this case, from the viewpoint of facilitating electron injection and increasing luminous efficiency, a material having a small work function is preferable as the material forming the second electrode. Specific examples of such materials include aluminum, magnesium and alloys thereof.

Encapsulation layer 250 is composed of any suitable material. The sealing layer 25 is preferably made of a material with excellent barrier properties and transparency. Typical examples of the material forming the sealing layer include epoxy resin and polyurea. In one embodiment, the sealing layer 250 may be formed by applying an epoxy resin (typically an epoxy resin adhesive) and attaching a barrier sheet thereon.

The organic EL element 200 can preferably be manufactured continuously by a roll-to-roll process. The organic EL element 200 can be manufactured, for example, according to the procedure described in Japanese Patent Application Laid-Open No. 2012-169236. The description of the publication is incorporated herein by reference. Furthermore, the organic EL element 200 and the elongated circularly polarizing plate 100 can be continuously laminated by a roll-to-roll process to continuously manufacture the organic EL display device 300 .

Details of the bendable organic EL display device are described in Japanese Patent No. 4601463 or Japanese Patent No. 4707996, for example. These descriptions are incorporated herein by reference.

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these Examples.

[Example 1]
(Production of polarizer)
After dyeing a long polyvinyl alcohol film in an aqueous solution containing iodine, it is uniaxially stretched 6 times between rolls with different speed ratios in an aqueous solution containing boric acid to obtain a long film having an absorption axis in the longitudinal direction. A polarizer with a shape was obtained. This elongated polarizer was stretched and then wound up to form a wound body.
(Protective film)
A long triacetyl cellulose film (40 μm thick, manufactured by Konica Minolta, trade name: KC4UYW) was used as the protective film. This protective film was prepared as a roll. The in-plane retardation Re(550) of this protective film was 5 nm, and the thickness direction retardation Rth(550) was 45 nm.
(retardation film)
A commercially available retardation film (manufactured by Teijin Limited, trade name “Pure Ace WR”) showing wavelength dependence of reverse dispersion was used. This retardation film has an in-plane retardation Re (550) of 147 nm, a Re (450)/Re (550) of 0.89, and a photoelastic coefficient of 65×10 ⁻¹² Pa ⁻¹ (m ² / N).

(Preparation of circularly polarizing plate)
Each of the polarizer, protective film and retardation film was cut into a size of 200 mm×300 mm. A polarizer and a protective film were bonded together via a polyvinyl alcohol-based adhesive. The polarizer/protective film laminate and the retardation film are laminated so that the polarizer and the retardation film are adjacent to each other via the acrylic pressure-sensitive adhesive layer, and the protective film/polarizer/retardation film (Second 1) was prepared. After that, the produced circularly polarizing plate was trimmed to a size of 50 mm×80 mm. The retardation film was cut out so that the slow axis and the absorption axis of the polarizer formed an angle of 45° when the film was attached. Moreover, the absorption axis of the polarizer was arranged so as to be parallel to the longitudinal direction.

(Production of organic EL display device substitutes)
A bendable organic EL display device substitute was produced as follows. First, five kinds of acrylic blocks having a size of 40 mm×120 mm×20 mm in thickness and having different curvature radii at both ends in the longitudinal direction were prepared. The radius of curvature of each acrylic block was 2 mm, 3.5 mm, 5 mm, 8 mm and 15 mm. Next, an aluminum vapor deposition film (manufactured by Toray Advanced Film Co., Ltd., product name “DMS vapor deposition X-42”, thickness 50 μm) is attached to each acrylic block with an adhesive to form a bendable organic EL display substitute. bottom.

The circularly polarizing plates obtained above were wound around an organic EL display device substitute with the longitudinal direction aligned, and the ends were fixed with tape so that the bent portions would not float. As a result, the slow axis of the retardation film (first retardation film) formed an angle of 45° with respect to the longitudinal direction and lateral direction of the organic EL display device substitute. That is, the slow axis of the retardation film (first retardation film) was made to form an angle of 45° with respect to the bending direction. Thus, a sample for evaluation was obtained. For the obtained evaluation sample, the phase difference distribution and phase difference change at the bent portion were measured in the following manner. Table 1 shows the results.

(1) Retardation Distribution and Retardation Change After holding the evaluation sample in an environment of 25° C. and 50% humidity for 24 hours, the circularly polarizing plate was removed. The phase difference between the bent portion and the flat portion of the removed circularly polarizing plate is measured with Axoscan manufactured by Axometrics, and based on the measurement results, the multi-layer analysis software attached to Axoscan is used to simulate the phase difference value. estimated by The difference between the phase difference in the curved portion of the circularly polarizing plate and the phase difference in the flat portion was defined as the phase difference change. In addition, the removed circularly polarizing plate was visually observed, and evaluated as "○" when the color change was small, and as "X" when the color change was large. Furthermore, the phase difference distribution was measured on the XY moving stage using the same method as above.
(2) Photoelastic Coefficient A sample was prepared by cutting the retardation film used in Examples and Comparative Examples into a size of 20 mm×100 mm. This sample was measured with an ellipsometer (manufactured by JASCO Corporation, M-150) with light having a wavelength of 550 nm to obtain a photoelastic coefficient.

[Example 2]
A sample for evaluation was obtained in the same manner as in Example 1, except that the following retardation film was used instead of "Pure Ace WR" as the retardation film showing the wavelength dependence of reverse dispersion. This evaluation sample was subjected to the same evaluation as in Example 1. Table 1 shows the results.
A resin is prepared according to Example 2 of Japanese Patent No. 4938151, the resin is formed into a film, uniaxially stretched at the free end at a temperature of 150 ° C. (stretch ratio: 2 times), and a retardation showing wavelength dependence of reverse dispersion. got the film. This retardation film has an in-plane retardation Re (550) of 145 nm, a Re (450)/Re (550) of 0.89, and a photoelastic coefficient of 39×10 ⁻¹² Pa ⁻¹ (m ² / N).

[Comparative Example 1]
A circularly polarizing plate having a size of 50 mm×80 mm was produced in the same manner as in Example 1. This circularly polarizing plate was wound around an organic EL display device substitute in the same manner as in Example 1, and the ends were fixed with tape so that the bent portion would not float. At that time, lamination was performed so that the slow axis of the retardation film (first retardation film) was parallel to the lateral direction of the organic EL display device substitute. That is, the slow axis of the retardation film (first retardation film) was made parallel to the bending direction. Thus, a sample for evaluation was obtained. The obtained evaluation sample was subjected to the same evaluation as in Example 1. Table 1 shows the results.

[Comparative Example 2]
An evaluation sample was obtained in the same manner as in Comparative Example 1 except that the slow axis of the retardation film (first retardation film) was perpendicular to the bending direction. The obtained evaluation sample was subjected to the same evaluation as in Example 1. Table 1 shows the results.

[Comparative Example 3]
An evaluation sample was obtained in the same manner as in Comparative Example 1 except that the circularly polarizing plate of Example 2 was used. The obtained evaluation sample was subjected to the same evaluation as in Example 1. Table 1 shows the results.

[Comparative Example 4]
An evaluation sample was obtained in the same manner as in Comparative Example 2 except that the circularly polarizing plate of Example 2 was used. The obtained evaluation sample was subjected to the same evaluation as in Example 1. Table 1 shows the results.

[Example 3]
A sample for evaluation was obtained in the same manner as in Example 1, except that the slow axis of the retardation film (first retardation film) was set at 30° with respect to the bending direction. The obtained evaluation sample was subjected to the same evaluation as in Example 1. Table 1 shows the results.

[Example 4]
A sample for evaluation was obtained in the same manner as in Example 2, except that the slow axis of the retardation film (first retardation film) was set at 30° with respect to the bending direction. The obtained evaluation sample was subjected to the same evaluation as in Example 1. Table 1 shows the results.

[Example 5]
A sample for evaluation was obtained in the same manner as in Example 1, except that the slow axis of the retardation film (first retardation film) was set at 60° with respect to the bending direction. The obtained evaluation sample was subjected to the same evaluation as in Example 1. Table 1 shows the results.

[Example 6]
A sample for evaluation was obtained in the same manner as in Example 2, except that the slow axis of the retardation film (first retardation film) was set at 60° with respect to the bending direction. The obtained evaluation sample was subjected to the same evaluation as in Example 1. Table 1 shows the results.

[Comparative Example 5]
A sample for evaluation was obtained in the same manner as in Example 1, except that the slow axis of the retardation film (first retardation film) was set at 15° with respect to the bending direction. The obtained evaluation sample was subjected to the same evaluation as in Example 1. Table 1 shows the results.

[Comparative Example 6]
A sample for evaluation was obtained in the same manner as in Example 2 except that the slow axis of the retardation film (first retardation film) was set at 15° with respect to the bending direction. The obtained evaluation sample was subjected to the same evaluation as in Example 1. Table 1 shows the results.

[Comparative Example 7]
A sample for evaluation was obtained in the same manner as in Example 1, except that the slow axis of the retardation film (first retardation film) was set at 75° with respect to the bending direction. The obtained evaluation sample was subjected to the same evaluation as in Example 1. Table 1 shows the results.

[Comparative Example 8]
A sample for evaluation was obtained in the same manner as in Example 2, except that the slow axis of the retardation film (first retardation film) was set at 75° with respect to the bending direction. The obtained evaluation sample was subjected to the same evaluation as in Example 1. Table 1 shows the results.

[evaluation]
As is clear from Table 1, according to the examples of the present invention, good results can be obtained with a smaller radius of curvature for both the color change of the bent portion and the phase difference change of the bent portion.

INDUSTRIAL APPLICABILITY The circularly polarizing plate of the present invention is suitable for bendable display devices, and particularly suitable for organic EL display devices.

10 polarizer 20 retardation film (first retardation film)
30 Second retardation film 40 Protective film 100 Circularly polarizing plate 100' Circularly polarizing plate 200 Organic EL element 300 Organic EL display device

Claims (1)

A bendable organic EL display device ,
An organic EL element and a circularly polarizing plate arranged on the viewing side of the organic EL element,
The circularly polarizing plate comprises a polarizer and a retardation film disposed on the organic EL element side of the polarizer,
The in-plane retardation of the retardation film satisfies the relationship Re(450)<Re(550)<Re(650),
The slow axis direction of the retardation film is adjusted to define an angle of 20 ° to 70 ° with respect to the bending direction of the organic EL element ,
The circularly polarizing plate is bent at all curvature radii of 2 mm, 3.5 mm, 5 mm, 8 mm and 15 mm in a state where the restraint in the bending state is released, and is placed at 25 ° C. and 50% humidity for 24 hours. The difference in in-plane retardation value between the bent portion and the flat portion after holding is 2 nm or less,
The bending direction in the bending test corresponds to the bending direction of the display device,
Organic EL display device .

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