Optical laminate and image display device using said optical laminate

Abstract

Provided is an optical laminate that includes solidified liquid-crystal oriented layers and is capable of suppressing specific display unevenness when applied to an image display device. An optical laminate according to an embodiment of the present invention comprises: a polarizing plate including a polarizer; and a retardation layer that is laminated on the polarizing plate with a first adhesive layer therebetween. The retardation layer includes, in order from the polarizing plate side, a first solidified liquid-crystal oriented layer and a second solidified liquid-crystal oriented layer laminated on the first solidified liquid-crystal oriented layer with a second adhesive layer therebetween. The retardation layer has a circular polarization function or an elliptical polarization function over the entirety thereof and has a relationship Re(450) < Re(550) < Re(650). The thickness of at least one of the first adhesive layer and the second adhesive layer is 300 nm or less.

Description

Optical laminate and image display device using said optical laminate

[0001] The present invention relates to an optical laminate and an image display device using the optical laminate.

[0002] In recent years, image display devices, such as liquid crystal display devices and electroluminescence (EL) display devices (e.g., organic EL display devices, inorganic EL display devices), have rapidly become widespread. Image display devices often use optical laminates containing retardation films (e.g., antireflection films integrating polarizing plates and retardation films). In recent years, as the demand for thinner image display devices has increased, the demand for thinner optical laminates has also increased. To achieve thinner optical laminates, the retardation layer (retardation film), which contributes significantly to the thickness, has been made thinner. A typical example of a thin retardation film is a film (hereinafter referred to as a liquid crystal film) in which a liquid crystal compound is oriented and the orientation state is fixed. Because liquid crystal compounds have a significantly higher birefringence (Δn) than resins, the thickness of a liquid crystal film to obtain a desired in-plane retardation can be significantly smaller than that of a stretched resin film. However, image display devices using optical laminates containing liquid crystal films may exhibit display unevenness (specifically, a phenomenon in which a thin line with a particularly noticeable pink color is visible in the absorption axis direction of the polarizer) depending on the viewing environment.

[0003] Japanese Patent Application Laid-Open No. 2014-222282

[0004] The present invention has been made to solve the above-mentioned conventional problems, and its main object is to provide an optical laminate that includes a liquid crystal alignment solidified layer and that can suppress specific display unevenness when applied to an image display device.

[0005] [1] An optical laminate according to an embodiment of the present invention comprises a polarizing plate including a polarizer and a retardation layer laminated to the polarizing plate via a first adhesive layer; the retardation layer comprises, in order from the polarizing plate side, a first liquid crystal alignment solidified layer and a second liquid crystal alignment solidified layer laminated to the first liquid crystal alignment solidified layer via a second adhesive layer; the retardation layer as a whole has a circular polarization function or an elliptically polarizing function and has a relationship of Re(450)<Re(550)<Re(650); and at least one of the first adhesive layer and the second adhesive layer has a thickness of 300 nm or less. [2] In the above [1], the thicknesses of the first adhesive layer and the second adhesive layer are each 200 nm or less. [3] In the above [1] or [2], the thickness of at least one of the first adhesive layer and the second adhesive layer is 100 nm or less. [4] In the above [3], at least one of the first adhesive layer and the second adhesive layer has a thickness of 50 nm or less. [5] In any of the above [1] to [4], the adhesive layer having a thickness of 300 nm or less is made of a water-based adhesive. [6] According to another aspect of the present invention, there is provided an image display device. The image display device includes the optical laminate of the above [1] to [5].

[0006] According to an embodiment of the present invention, it is possible to realize an optical laminate that includes a liquid crystal alignment solidified layer and that can suppress specific display unevenness when applied to an image display device.

[0007] 1 is a schematic cross-sectional view of an optical stack according to one embodiment of the present invention.

[0008] Representative embodiments of the present invention will be described below, but the present invention is not limited to these embodiments.

[0009] (Definition of Terms and Symbols) The definitions of terms and symbols used in this specification are as follows. (1) Refractive Index (nx, ny, nz) "nx" is the refractive index in the direction in which the in-plane refractive index is maximum (i.e., the slow axis direction), "ny" is the refractive index in the in-plane direction perpendicular to the slow axis (i.e., the fast axis direction), and "nz" is the refractive index in the thickness direction. (2) In-Plane Retardation (Re) "Re(λ)" is the in-plane retardation of a film measured with light having a wavelength of λ nm at 23°C. For example, "Re(550)" is the in-plane retardation of a film measured with light having a wavelength of 550 nm at 23°C. Re(λ) is calculated by the formula: Re = (nx - ny) x d, where d (nm) is the thickness of the film. (3) Thickness Direction Retardation (Rth) "Rth(λ)" is the retardation of a film measured with light having a wavelength of λ nm at 23°C. For example, "Rth(550)" is the retardation in the thickness direction of the film measured with light having a wavelength of 550 nm at 23°C. Rth(λ) is calculated by the formula: Rth = (nx - nz) x d, where d (nm) is the thickness of the film. (4) Nz coefficient The Nz coefficient is calculated by Nz = Rth / Re. (5) Angle When an angle is referred to in this specification, the angle includes angles in both clockwise and counterclockwise directions unless otherwise specified.

[0010] A. Optical Laminate FIG. 1 is a schematic cross-sectional view of an optical laminate according to one embodiment of the present invention. The illustrated optical laminate 100 includes a polarizing plate 10 and a retardation layer 20 laminated to the polarizing plate 10 via a first adhesive layer 31. The polarizing plate 10 typically includes a polarizer 11 and protective layers 12 and 13 disposed on both sides of the polarizer 11. Depending on the purpose, at least one of the protective layers 12 and 13 may be omitted. Therefore, the polarizing plate may be a so-called double-protected polarizing plate, a so-called single-protected polarizing plate, or may be composed of a polarizer alone. In one embodiment, the polarizing plate may be a single-protected polarizing plate in which the protective layer 13 is omitted.

[0011] The retardation layer 20 includes, in order from the polarizing plate 10 side, a first liquid crystal alignment solidified layer 21 and a second liquid crystal alignment solidified layer 22 laminated to the first liquid crystal alignment solidified layer 21 via a second adhesive layer 32. Thus, the retardation layer 20 has the first liquid crystal alignment solidified layer 21 laminated to the polarizing plate 10 via the first adhesive layer 31. By using a liquid crystal alignment solidified layer as a retardation layer, a desired in-plane retardation can be achieved with a thickness significantly thinner than that of a stretched resin film. As a result, the optical laminate can be significantly thinner. The retardation layer 20 as a whole (as a laminate of the first liquid crystal alignment solidified layer 21 and the second liquid crystal alignment solidified layer 22) has a circular polarization function or an elliptically polarization function and has a relationship of Re(450)<Re(550)<Re(650). In one embodiment, the retardation layer as a whole may have an Nz coefficient of, for example, 0.30 to 0.70. In this specification, the term "liquid crystal alignment solidified layer" refers to a layer in which liquid crystal compounds are aligned in a predetermined direction within the layer and the alignment state is fixed. The term "liquid crystal alignment solidified layer" is a concept that encompasses a hardened alignment layer obtained by hardening a liquid crystal monomer.

[0012] In an embodiment of the present invention, the thickness of at least one of the first adhesive layer 31 and the second adhesive layer 32 is 300 nm or less. That is, in an embodiment of the present invention, the thickness of the first adhesive layer 31 may be 300 nm or less, the thickness of the second adhesive layer 32 may be 300 nm or less, or each of the first adhesive layer 31 and the second adhesive layer 32 may be 300 nm or less. Furthermore, as long as the thickness of either the first adhesive layer 31 or the second adhesive layer 32 is 300 nm or less, the thickness of the other may be greater than 300 nm. The thicknesses of the first adhesive layer 31 and the second adhesive layer 32 may each independently be, for example, 250 nm or less, or, for example, 200 nm or less, or, for example, 180 nm or less, or, for example, 150 nm or less, or, for example, 100 nm or less, or, for example, 70 nm or less, or, for example, 50 nm or less. The thickness of the first adhesive layer 31 and the second adhesive layer 32 may each independently be, for example, 5 nm or more, for example, 10 nm or more, or for example, 20 nm or more. Note that the upper limit of the thickness of an adhesive layer having a thickness of more than 300 nm may be, for example, 2000 nm, for example, 1000 nm, for example, 800 nm, or for example, 500 nm.

[0013] In investigating further thinning of an optical laminate including a liquid crystal alignment solidified layer as a retardation layer, the present inventors discovered a new problem: image display devices using an optical laminate including a liquid crystal alignment solidified layer as a retardation layer may exhibit specific display unevenness depending on the viewing environment. Specifically, they found that reflection under a three-wavelength light source can result in a phenomenon (sometimes referred to as linear unevenness) in which a thin line with a particularly noticeable pink color is visible throughout the entire image in the absorption axis direction of the polarizer. Furthermore, as a result of extensive research into suppressing such linear unevenness, they found that linear unevenness can be suppressed by suppressing interference in the optical laminate. In addition, the present inventors discovered that interference in the optical laminate can be suppressed, and as a result, linear unevenness can be effectively suppressed, by setting the thickness of at least one of the adhesive layer laminating the polarizing plate and the retardation layer and the adhesive layer laminating the first liquid crystal alignment solidified layer and the second liquid crystal alignment solidified layer constituting the retardation layer to 300 nm or less, thereby completing the present invention. Furthermore, the inventors have discovered the critical significance of the thickness, that is, by setting the thickness of at least one of the layers to about 200 nm or less, linear unevenness can be significantly suppressed, and by setting the thickness of at least one of the layers to about 100 nm or less, linear unevenness can be significantly suppressed. In other words, such an effect of the embodiment of the present invention solves a newly discovered problem when considering further thinning of an optical laminate including a liquid crystal alignment solidified layer as a retardation layer, and is an unexpected and excellent effect. It goes without saying that the embodiment of the present invention can suppress display unevenness that has been recognized in the past.

[0014] Of the first adhesive layer 31 and the second adhesive layer 32, the adhesive layer having a thickness of 300 nm or less may be made of a water-based adhesive or may be made of another adhesive (for example, an active energy ray-curable adhesive). The adhesive layer having a thickness of more than 300 nm may also be made of a water-based adhesive or may be made of another adhesive (for example, an active energy ray-curable adhesive).

[0015] In the optical laminate, the total thickness from the first liquid crystal alignment solidified layer to the second liquid crystal alignment solidified layer is preferably 20 μm or less, more preferably 3 μm to 10 μm. According to an embodiment of the present invention, the problem of linear unevenness newly discovered in optical laminates including very thin liquid crystal alignment solidified layers can be solved. Note that, if the total thickness from the first liquid crystal alignment solidified layer to the second liquid crystal alignment solidified layer is within the above-described range, the total thickness from the polarizing plate to the second liquid crystal alignment solidified layer (the actual total thickness of the optical laminate, excluding the thickness of the adhesive used to attach it to the image display panel) can be, for example, 100 μm or less, or, for example, 30 μm to 80 μm.

[0016] In practice, the optical laminate has a pressure-sensitive adhesive layer (not shown) as the outermost layer on the second liquid crystal alignment solidified layer side (image display panel side), so that it can be attached to the image display panel. In this case, it is preferable that a release liner is temporarily attached to the surface of the pressure-sensitive adhesive layer until the optical laminate is used. Temporarily attaching the release liner protects the pressure-sensitive adhesive layer and enables the optical laminate to be rolled.

[0017] The components of the optical laminate will be specifically described below.

[0018] B. Polarizing Plate B-1. Polarizer The polarizer 11 is typically made of a polyvinyl alcohol (PVA)-based resin film containing a dichroic substance (e.g., iodine). Examples of PVA-based resins include polyvinyl alcohol, partially formalized polyvinyl alcohol, ethylene-vinyl alcohol copolymer, and partially saponified ethylene-vinyl acetate copolymer.

[0019] The PVA-based resin preferably contains an acetoacetyl-modified PVA-based resin. With this configuration, a polarizer having desired mechanical strength can be obtained. The blending amount of the acetoacetyl-modified PVA-based resin is preferably 5 wt % to 20 wt %, and more preferably 8 wt % to 12 wt %, based on 100 wt % of the total PVA-based resin. With the blending amount in this range, a polarizer having even better mechanical strength can be obtained.

[0020] The polarizer preferably contains iodide or sodium chloride (sometimes collectively referred to as a halide). Examples of iodides include potassium iodide, sodium iodide, and lithium iodide. The content of the halide in the polarizer is preferably 5 to 20 parts by weight, more preferably 10 to 15 parts by weight, relative to 100 parts by weight of the PVA-based resin. In the manufacturing method described below, the halide is blended into a coating liquid that forms a PVA-based resin layer, which is a precursor of the polarizer, and can be finally introduced into the polarizer. Introducing a halide into the polarizer can improve the orientation of PVA molecules in the polarizer, thereby achieving a polarizer with excellent optical properties (typically, both a high degree of polarization and a high single-unit transmittance).

[0021] The polarizer preferably exhibits absorptive dichroism at any wavelength between 380 nm and 780 nm. The single transmittance of the polarizer is preferably 41.0% to 46.0%, more preferably 42.0% to 45.0%. The degree of polarization of the polarizer is preferably 97.0% or more, more preferably 99.0% or more, and even more preferably 99.9% or more. According to an embodiment of the present invention, even if the single transmittance is within the above range, the degree of polarization can be maintained within this range.

[0022] The thickness of the polarizer is, for example, 12 μm or less, preferably 10 μm or less, more preferably 1 μm to 8 μm, and even more preferably 3 μm to 7 μm. By combining such a thin polarizer with a liquid crystal alignment solidified layer, the optical laminate can be significantly thinner. Furthermore, when the polarizer thickness is within the above range, curling during heating can be effectively suppressed, and good appearance durability during heating can be achieved.

[0023] The polarizer can be produced by any appropriate method. For example, the resin film forming the polarizer may be a single-layer resin film or a laminate of two or more layers.

[0024] Specific examples of polarizers composed of a single-layer resin film include hydrophilic polymer films such as PVA films, partially formalized PVA films, and partially saponified ethylene-vinyl acetate copolymer films that have been dyed with iodine or a dichroic substance such as a dichroic dye and stretched, and polyene-based oriented films such as dehydrated PVA films and dehydrochlorinated polyvinyl chloride films. Preferably, a polarizer obtained by dyeing a PVA film with iodine and uniaxially stretching it is used because of its excellent optical properties.

[0025] The dyeing with iodine is carried out, for example, by immersing the PVA-based film in an aqueous iodine solution. The stretching ratio of the uniaxial stretching is preferably 3 to 7 times. The stretching may be carried out after the dyeing treatment or while dyeing. Alternatively, the PVA-based film may be stretched and then dyed. If necessary, the PVA-based film may be subjected to a swelling treatment, a crosslinking treatment, a washing treatment, a drying treatment, or the like. For example, by immersing the PVA-based film in water and washing it before dyeing, it is possible to wash away dirt and antiblocking agents from the surface of the PVA-based film and also to swell the PVA-based film, thereby preventing uneven dyeing and the like.

[0026] Specific examples of polarizers obtained using laminates include a laminate of a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or a laminate of a resin substrate and a PVA-based resin layer formed by coating on the resin substrate. A polarizer obtained using a laminate of a resin substrate and a PVA-based resin layer formed by coating on the resin substrate can be produced, for example, by applying a PVA-based resin solution to the resin substrate and drying the solution to form a PVA-based resin layer on the resin substrate to obtain a laminate of the resin substrate and the PVA-based resin layer, and then stretching and dyeing the laminate to form the PVA-based resin layer into a polarizer. In this embodiment, a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin is preferably formed on one side of the resin substrate. The stretching typically involves immersing the laminate in a boric acid aqueous solution and stretching it. Furthermore, the stretching may further include, if necessary, in-air stretching of the laminate at an elevated temperature (e.g., 95°C or higher) before stretching in the boric acid aqueous solution. Additionally, in this embodiment, the laminate is preferably subjected to a drying shrinkage treatment in which the laminate is heated while being transported in the longitudinal direction, thereby shrinking the laminate by 2% or more in the width direction. Typically, the manufacturing method of this embodiment includes subjecting the laminate to an auxiliary in-air stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment, in this order. By introducing auxiliary stretching, it is possible to increase the crystallinity of the PVA, even when the PVA is coated on a thermoplastic resin, thereby achieving high optical properties. Furthermore, by simultaneously increasing the orientation of the PVA in advance, problems such as a decrease in the orientation or dissolution of the PVA when immersed in water in the subsequent dyeing or stretching steps can be prevented, thereby achieving high optical properties. Furthermore, when the PVA-based resin layer is immersed in a liquid, the disordering of the orientation of polyvinyl alcohol molecules and the decrease in the orientation can be suppressed compared to when the PVA-based resin layer does not contain a halide. This can improve the optical properties of a polarizer obtained through treatment steps in which the laminate is immersed in a liquid, such as a dyeing treatment and an underwater stretching treatment. Furthermore, the optical properties can be improved by shrinking the laminate in the width direction through drying shrinkage treatment.The obtained resin substrate / polarizer laminate may be used as is (i.e., the resin substrate may be used as a protective layer for the polarizer), or any suitable protective layer may be laminated depending on the purpose on the surface obtained by peeling the resin substrate from the resin substrate / polarizer laminate or on the surface opposite to the peeled surface. Details of the method for producing such a polarizer are described in, for example, JP 2012-73580 A and Japanese Patent No. 6,470,455 A. The entire disclosures of these publications are incorporated herein by reference.

[0027] B-2. Protective Layer The protective layers 12 and 13 are composed of any appropriate resin film. Typical materials for the resin film include cellulose-based resins such as triacetyl cellulose (TAC), cycloolefin-based resins such as polynorbornene, (meth)acrylic resins, polyester-based resins such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), polyolefin-based resins such as polyethylene, and polycarbonate-based resins. Typical examples of (meth)acrylic resins include (meth)acrylic resins having a lactone ring structure. Examples of (meth)acrylic resins having a lactone ring structure are described in, for example, JP 2000-230016 A, JP 2001-151814 A, JP 2002-120326 A, JP 2002-254544 A, and JP 2005-146084 A. These publications are incorporated herein by reference. From the viewpoint of ease of processing into modified shapes, etc., cellulose-based resins are preferred, and TAC is more preferred. From the viewpoint of obtaining a polarizing plate with low moisture permeability and excellent durability, cycloolefin-based resins and (meth)acrylic resins are preferred.

[0028] The optical laminate is typically disposed on the viewing side of an image display device, and the protective layer 12 is typically disposed on the viewing side. Therefore, the protective layer 12 may be subjected to a surface treatment as needed. Examples of surface treatments include hard coating, anti-reflection, anti-sticking, and anti-glare treatments. Furthermore / alternatively, the protective layer 12 may be subjected to a treatment to improve visibility when viewed through polarized sunglasses (typically, by imparting an (elliptical) polarization function or an ultra-high phase difference) as needed. By performing such treatments, excellent visibility can be achieved even when the display screen is viewed through polarized lenses such as polarized sunglasses. Therefore, the optical laminate may also be suitably applied to image display devices that can be used outdoors.

[0029] In one embodiment, the protective layer 13 is preferably optically isotropic. In this specification, "optically isotropic" means that the in-plane retardation Re(550) is 0 nm to 10 nm and the retardation Rth(550) in the thickness direction is −10 nm to +10 nm.

[0030] The thickness of each of the protective layers 12 and 13 is preferably 10 μm to 80 μm, more preferably 12 μm to 40 μm, and even more preferably 15 μm to 35 μm. When the protective layer 12 is surface-treated, the thickness of the protective layer 12 includes the thickness of the surface-treated layer.

[0031] C. Retardation Layer As described above, the retardation layer 20 includes, in order from the polarizer side, a first liquid crystal alignment solidified layer 21 and a second liquid crystal alignment solidified layer 22. Furthermore, as described above, the retardation layer 20 as a whole (as a laminate of the first liquid crystal alignment solidified layer 21 and the second liquid crystal alignment solidified layer 22) has a circular polarization function or an elliptically polarization function, and has a relationship of Re(450)<Re(550)<Re(650). In the description of the retardation layer in this section, when simply referred to as a "retardation layer", it means to describe the retardation layer as a whole, and when simply referred to as a "liquid crystal alignment solidified layer", it means to describe the first liquid crystal alignment solidified layer and the second liquid crystal alignment solidified layer together.

[0032] The retardation layer 20 preferably has an Re(550) of 100 nm to 200 nm, more preferably 110 nm to 180 nm, still more preferably 120 nm to 170 nm, and particularly preferably 130 nm to 150 nm. If the Re(550) of the retardation layer is in this range, the retardation layer can exhibit a good circular polarization function or elliptically polarization function in combination with a polarizer.

[0033] The retardation layer 20 has a relationship of Re(450)<Re(550)<Re(650). That is, the retardation layer 20 preferably exhibits wavelength dependence of inverse dispersion, in which the retardation value increases according to the wavelength of the measurement light. With such a configuration, excellent anti-reflection function can be achieved over a very wide wavelength band. Re(450) / Re(550) is, for example, greater than 0.5 and less than 1.0, preferably 0.7 to 0.95, more preferably 0.75 to 0.92, and even more preferably 0.8 to 0.9. Re(650) / Re(550) is preferably 1.0 or greater but less than 1.15, more preferably 1.03 to 1.1.

[0034] In one embodiment, the retardation layer 20 may have an Nz coefficient of, for example, 0.30 to 0.70 as described above. Therefore, the retardation layer 20 exhibits a refractive index characteristic of nx>nz>ny. With this configuration, reflections in oblique directions can be effectively prevented, enabling the anti-reflection function to have a wide viewing angle. The Nz coefficient is preferably 0.35 to 0.65, more preferably 0.40 to 0.60, and even more preferably 0.45 to 0.55.

[0035] Examples of liquid crystal compounds used in the liquid crystal alignment solidified layer include liquid crystal polymers and liquid crystal monomers. The liquid crystal compound is preferably polymerizable (i.e., liquid crystal monomer). If the liquid crystal compound is polymerizable, the alignment state of the liquid crystal compound can be fixed by aligning the liquid crystal compound and then polymerizing it. Here, the polymer formed by polymerization is non-liquid crystal. Therefore, the formed liquid crystal alignment solidified layer does not undergo, for example, a transition to a liquid crystal phase, glass phase, or crystalline phase due to temperature changes, which is unique to liquid crystal compounds. As a result, the liquid crystal alignment solidified layer becomes a retardation layer that is not affected by temperature changes and has extremely excellent stability.

[0036] In one embodiment, the liquid crystal alignment solidified layer can be formed using a composition containing a polymerizable liquid crystal compound (polymerizable liquid crystal compound, i.e., liquid crystal monomer). In this specification, the polymerizable liquid crystal compound contained in the composition refers to a compound having a polymerizable group and liquid crystallinity. The polymerizable group refers to a group that participates in a polymerization reaction, preferably a photopolymerizable group. Here, the photopolymerizable group refers to a group that can participate in a polymerization reaction by an active radical or acid generated from a photopolymerization initiator. Examples of liquid crystal monomers that can be used include polymerizable mesogen compounds described in JP-A-2002-533742 (WO 00 / 37585), EP 358208 (US Pat. No. 5,211,877), EP 66137 (US Pat. No. 4,388,453), WO 93 / 22397, EP 0,261,712, DE 19504,224, DE 4,408,171, and GB 2,280,445. Specific examples of such polymerizable mesogenic compounds include LC242 (trade name) from BASF, E7 (trade name) from Merck, and LC-Silicon-CC3767 (trade name) from Wacker-Chem.

[0037] The mechanism by which the liquid crystal compound exhibits liquid crystallinity may be thermotropic or lyotropic. The liquid crystal phase may be nematic or smectic. From the viewpoint of ease of production, the liquid crystallinity is preferably thermotropic nematic liquid crystal.

[0038] The temperature range in which the liquid crystal monomer exhibits liquid crystallinity varies depending on the type of the liquid crystal monomer. Specifically, the temperature range is preferably 40°C to 120°C, more preferably 50°C to 100°C, and most preferably 60°C to 90°C.

[0039] The birefringence Δn of the liquid crystal alignment solidified layer is preferably 0.06 or more, more preferably 0.08 or more, even more preferably 0.09 or more, and particularly preferably 0.10 or more. The upper limit of Δn may be, for example, 0.13, or may be, for example, 0.12. If Δn is within this range, the desired in-plane retardation can be achieved with a very thin thickness. As a result, it becomes possible to further thin the liquid crystal alignment solidified layer and the optical laminate, which can ultimately contribute to significantly thinner image display devices.

[0040] The liquid crystal alignment solidified layer may exhibit an inverse wavelength dispersion characteristic in which the retardation value increases according to the wavelength of the measurement light, a positive wavelength dispersion characteristic in which the retardation value decreases according to the wavelength of the measurement light, or a flat wavelength dispersion characteristic in which the retardation value changes little depending on the wavelength of the measurement light.

[0041] The first liquid crystal alignment solidified layer 21 can typically function as a λ / 2 plate, and the second liquid crystal alignment solidified layer 22 can typically function as a λ / 4 plate. Specifically, the Re(550) of the first liquid crystal alignment solidified layer is preferably 150 nm to 300 nm, more preferably 200 nm to 270 nm, and even more preferably 220 nm to 260 nm; the Re(550) of the second liquid crystal alignment solidified layer is preferably 100 nm to 200 nm, more preferably 110 nm to 160 nm, and even more preferably 120 nm to 140 nm. The thickness of the first liquid crystal alignment solidified layer can be adjusted to obtain the desired in-plane retardation of the λ / 2 plate. In one embodiment, the thickness of the first liquid crystal alignment solidified layer can be, for example, 2.0 μm to 4.0 μm. In another embodiment, the thickness of the first liquid crystal alignment solidified layer is preferably 1.7 μm or less, more preferably 1.6 μm or less, and even more preferably 1.5 μm or less. In this case, the thickness of the first liquid crystal alignment solidified layer may be, for example, 1.3 μm or more. As described above, according to an embodiment of the present invention, linear unevenness can be suppressed while the thickness of the first liquid crystal alignment solidified layer is thinner than conventional ones. The thickness of the second liquid crystal alignment solidified layer can be adjusted to obtain the desired in-plane retardation of the λ / 4 plate. Specifically, the thickness may be, for example, 0.8 μm to 2.5 μm. The angle between the slow axis of the first liquid crystal alignment solidified layer and the transmission axis of the polarizer is preferably 10° to 20°, more preferably 12° to 18°, and even more preferably 14° to 16°; and the angle between the slow axis of the second liquid crystal alignment solidified layer and the transmission axis of the polarizer is preferably 70° to 80°, more preferably 72° to 78°, and even more preferably 74° to 76°. In addition, the order of arrangement of the first liquid crystal alignment solidified layer and the second liquid crystal alignment solidified layer may be reversed, and the angle between the slow axis of the first liquid crystal alignment solidified layer and the transmission axis of the polarizer and the angle between the slow axis of the second liquid crystal alignment solidified layer and the transmission axis of the polarizer may be reversed.

[0042] The refractive index of the liquid crystal alignment solidified layer can vary depending on the composition forming the liquid crystal alignment solidified layer (substantially, the type of liquid crystal compound, the type, number, combination, and amount of additives, etc.). The refractive index of the first liquid crystal alignment solidified layer and the refractive index of the second liquid crystal alignment solidified layer may be the same or different from each other (the refractive index of the first liquid crystal alignment solidified layer may be higher, or the refractive index of the second liquid crystal alignment solidified layer may be higher). The refractive index of the first liquid crystal alignment solidified layer is preferably 1.55 to 1.75, more preferably 1.60 to 1.70. The refractive index of the second liquid crystal alignment solidified layer is preferably 1.45 to 1.65, more preferably 1.50 to 1.60. The refractive index of the first liquid crystal alignment solidified layer and the refractive index of the second liquid crystal alignment solidified layer may be reversed. The absolute value of the difference between the refractive index of the first liquid crystal alignment solidified layer and the refractive index of the second liquid crystal alignment solidified layer may be, for example, 0.00 to 0.20. The refractive index of the liquid crystal alignment solidified layer is typically determined based on the composition of the liquid crystal alignment solidified layer to obtain desired optical properties. As a result, linear unevenness may occur. However, according to an embodiment of the present invention, the thickness of at least one of the adhesive layer that laminates the polarizing plate and the retardation layer and the adhesive layer that laminates the first liquid crystal alignment solidified layer and the second liquid crystal alignment solidified layer that constitute the retardation layer is set to a predetermined value or less, thereby suppressing linear unevenness.

[0043] A side-chain thermotropic liquid crystal polymer may be introduced into the first liquid crystal alignment solidified layer and / or the second liquid crystal alignment solidified layer (essentially, the liquid crystal composition forming these). The introduction of a side-chain thermotropic liquid crystal polymer can induce homeotropic alignment (vertical alignment) of the liquid crystal monomer. As a result, the nz of the first liquid crystal alignment solidified layer and / or the second liquid crystal alignment solidified layer can be increased, and as a result, the Nz coefficient of the first liquid crystal alignment solidified layer and / or the second liquid crystal alignment solidified layer can be set within the desired range. Finally, the Nz coefficient of the retardation layer can be set within the desired range without providing a positive C plate, as described below.

[0044] A typical example of a side-chain thermotropic liquid crystal polymer is a copolymer having a monomer unit containing a thermotropic liquid crystalline fragment side chain and a monomer unit containing a non-liquid crystalline fragment side chain. When the polymer has a thermotropic liquid crystalline fragment in its side chain, the side-chain liquid crystalline polymer can be oriented when the liquid crystalline composition is heated to a predetermined temperature. Furthermore, when the side-chain polymer has a non-liquid crystalline fragment in its side chain, the non-liquid crystalline fragment can interact with the photopolymerizable liquid crystal monomer, causing the photopolymerizable liquid crystal monomer to be homeotropically oriented.

[0045] As the side chain type thermotropic liquid crystal polymer, a copolymer having a liquid crystalline monomer unit represented by general formula (I) and a non-liquid crystalline monomer unit represented by general formula (II) is preferably used.

[0046] In formula (I), R １ is a hydrogen atom or a methyl group, and R ２ is a cyano group, a fluoro group, an alkyl group having 1 to 6 carbon atoms, or an alkoxy group having 1 to 6 carbon atoms; X １ Ha-CO ２ a is an integer of 1 to 6, and b and c are each independently 1 or 2.

[0047] In formula (II), R ３ is a hydrogen atom or a methyl group, and R ４ is an alkyl group having 7 to 22 carbon atoms, a fluoroalkyl group having 1 to 22 carbon atoms, or a group represented by the following general formula (III):

[0048] In formula (III), R ５ is an alkyl group having 1 to 5 carbon atoms, and d is an integer of 1 to 6.

[0049] The ratio of the liquid crystalline monomer unit to the non-liquid crystalline monomer unit in the side chain liquid crystal monomer can be appropriately set depending on the purpose. The ratio (molar ratio) of the non-liquid crystalline monomer to the total of the liquid crystalline monomer unit and the non-liquid crystalline monomer unit is preferably 0.05 to 0.8, more preferably 0.1 to 0.6, and even more preferably 0.15 to 0.5. With such a configuration, a liquid crystal alignment solidified layer exhibiting the desired refractive index characteristics (Nz coefficient) can be obtained.

[0050] The ratio of the liquid crystal monomer to the side-chain liquid crystal polymer in the liquid crystal composition can be appropriately set depending on the purpose. When the content of the side-chain liquid crystal polymer is high, the Nz coefficient tends to be small; when the content of the liquid crystal monomer is high, the Nz coefficient tends to be small. The content of the liquid crystal monomer is preferably 1.2 to 20 times, more preferably 1.3 to 10 times, even more preferably 1.4 to 9 times, and particularly preferably 1.5 to 8 times the content of the side-chain liquid crystal polymer. With such a configuration, a liquid crystal alignment solidified layer exhibiting the desired refractive index characteristics (Nz coefficient) can be obtained.

[0051] Details of the side-chain liquid crystal polymer and the method for forming a liquid crystal alignment layer having an Nz coefficient of less than 1.0 are described in Japanese Patent No. 6769921, the disclosure of which is incorporated herein by reference.

[0052] The retardation layer 20 may further include a positive C plate. The refractive index characteristics of the positive C plate exhibit the relationship nz > nx = ny. The thickness direction retardation Rth(550) of the positive C plate is preferably -20 nm to -300 nm, more preferably -30 nm to -250 nm, even more preferably -40 nm to -200 nm, and particularly preferably -50 nm to -150 nm. Here, "nx = ny" encompasses not only the case where nx and ny are strictly equal, but also the case where nx and ny are substantially equal. In other words, the in-plane retardation Re(550) of the positive C plate can be less than 10 nm.

[0053] The positive C plate can be formed, for example, using a composition containing the above-mentioned side-chain liquid crystal polymer. Specific examples of methods for forming a positive C plate include the methods described in paragraphs

[0020] to

[0028] of JP 2002-333642 A. In this case, the thickness of the positive C plate is preferably 0.5 μm to 10 μm, more preferably 0.5 μm to 8 μm, and even more preferably 0.5 μm to 5 μm.

[0054] D. First Adhesive Layer and Second Adhesive Layer As described above, the first adhesive layer 31 and the second adhesive layer 32 having a thickness of 300 nm or less may be composed of an aqueous adhesive or another adhesive (e.g., an active energy ray-curable adhesive). The adhesive layer having a thickness greater than 300 nm may also be composed of an aqueous adhesive or another adhesive (e.g., an active energy ray-curable adhesive). The adhesive constituting the adhesive layer having a thickness greater than 300 nm may also include a pressure-sensitive adhesive for convenience. In one embodiment, both the first adhesive layer 31 and the second adhesive layer 32 may be composed of an aqueous adhesive. Because aqueous adhesives are formed by applying and drying an aqueous solution as described below, they shrink less than curable adhesives. As a result, the thickness variation of the adhesive layer is reduced, thereby suppressing interference and linear unevenness. Below, aqueous adhesives are described. Other adhesives (e.g., active energy ray-curable adhesives) may have configurations known in the industry, and therefore, detailed description thereof is omitted. In this section, unless otherwise specified, the first adhesive layer and the second adhesive layer will be collectively referred to as adhesive layers.

[0055] The aqueous adhesive typically contains a polyvinyl alcohol (PVA)-based resin. The adhesive layer can typically be formed by applying and drying an aqueous solution of the PVA-based resin. The average degree of polymerization of the PVA-based resin contained in the aqueous solution is preferably about 100 to 5000, more preferably 1000 to 4000. The average degree of saponification is preferably about 85 mol % to 100 mol %, more preferably 90 mol % to 100 mol %. When the average degree of polymerization and the average degree of saponification are within these ranges, an adhesive layer (substantially a first adhesive layer) having excellent adhesion to the polarizer can be formed.

[0056] The PVA-based resin preferably contains an acetoacetyl group. This is because an optical laminate having excellent adhesion to the polarizer and the protective layer and excellent durability can be obtained. The acetoacetyl-group-containing PVA-based resin can be obtained, for example, by reacting a PVA-based resin with diketene using any method. The degree of acetoacetyl group modification of the acetoacetyl-group-containing PVA-based resin is typically 0.1 mol% or more, preferably about 0.1 mol% to 40 mol%, more preferably 1 mol% to 20 mol%, and particularly preferably 2 mol% to 7 mol%. The degree of acetoacetyl group modification is a value measured by NMR.

[0057] The resin concentration in the aqueous PVA-based resin solution is preferably 0.1 wt % to 15 wt %, more preferably 0.5 wt % to 10 wt %. The viscosity of the aqueous solution is preferably 1 to 50 mPa s. The pH of the aqueous solution is preferably 2 to 6, more preferably 2.5 to 5, even more preferably 3 to 5, and particularly preferably 3.5 to 4.5. When the resin concentration and viscosity of the aqueous PVA-based resin solution are within these ranges, an adhesive layer having a desired thickness can be formed in the embodiments of the present invention.

[0058] In one embodiment, the PVA-based resin aqueous solution (and consequently the adhesive layer) may contain a metal compound colloid. The metal compound colloid is a dispersion of metal compound fine particles in a dispersion medium, which is electrostatically stabilized due to mutual repulsion of like-charged particles of the fine particles, and may have permanent stability.

[0059] The average particle size of the fine particles forming the metal compound colloid can be set to any appropriate value as long as it does not adversely affect optical properties such as transparency and polarization characteristics. It is preferably 1 nm to 100 nm, and more preferably 1 nm to 50 nm, because this allows the fine particles to be uniformly dispersed in the adhesive layer.

[0060] Any suitable compound can be used as the metal compound. Examples include metal oxides such as alumina, silica, zirconia, and titania; metal salts such as aluminum silicate, calcium carbonate, magnesium silicate, zinc carbonate, barium carbonate, and calcium phosphate; and minerals such as celite, talc, clay, and kaolin. A positively charged metal compound colloid is preferably used. Examples of the metal compound include alumina and titania, with alumina being particularly preferred.

[0061] E. Image display device The optical laminate described in the above items A to D can be applied to an image display device. Therefore, embodiments of the present invention also include image display devices using such optical laminates. Representative examples of image display devices include liquid crystal display devices and organic EL display devices. An image display device according to an embodiment of the present invention typically includes the optical laminate described in the above items A to D on the viewing side.

[0062] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Measurement and evaluation methods in the examples are as follows. Unless otherwise specified, "parts" and "%" in the examples are by weight.

[0063] (1) Thickness: Measured with an interference film thickness meter (manufactured by Otsuka Electronics Co., Ltd., "MCPD9800").

[0064] (2) Linear unevenness A normal acrylic adhesive was placed on the second liquid crystal alignment solidified layer side of the optical laminate obtained in the Examples and Comparative Examples, and the optical laminate was attached to a V3 reflector (manufactured by NEODIS) via the acrylic adhesive to prepare a test sample. The obtained test sample was visually observed under a three-wavelength fluorescent lamp and evaluated according to the following criteria: 1: No linear unevenness was observed 2: Slight linear unevenness was observed 3: Linear unevenness was observed, but to an extent that was practically acceptable 4: Linear unevenness was observed to an extent that was practically unacceptable 5: Significant linear unevenness

[0065] [Production Example 1: Preparation of aqueous adhesive] An aqueous adhesive was obtained by mixing 6.02 parts of acetoacetyl-modified PVA (degree of polymerization 1200, degree of acetoacetyl modification 4.6%, degree of saponification 99.0 mol% or more, solids concentration 4%, manufactured by Mitsubishi Chemical Corporation, trade name "Gohsenex Z-200"), 25 parts of an aqueous solution containing positively charged alumina colloid (average particle diameter 15 nm) at a solids concentration of 3.2%, and 18.98 parts of pure water.

[0066] Example 1 1. Preparation of Polarizing Plate 1-1. Preparation of Polarizer A long, amorphous, isophthalic copolymerized polyethylene terephthalate film (thickness: 100 μm) with a Tg of approximately 75°C was used as the thermoplastic resin substrate, and one side of the resin substrate was subjected to a corona treatment. A PVA-based resin (a 9:1 mixture of polyvinyl alcohol (degree of polymerization: 4200, degree of saponification: 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFIRM") was prepared by adding 13 parts by weight of potassium iodide to 100 parts by weight of the resulting PVA-based resin, and the resulting solution was dissolved in water to prepare an aqueous PVA solution (coating solution). The PVA-based resin was applied to the corona-treated surface of the resin substrate and dried at 60°C to form a 13 μm-thick PVA-based resin layer, producing a laminate. The resulting laminate was uniaxially stretched 2.4 times in the longitudinal direction (longitudinal direction) in an oven at 130°C (in-air auxiliary stretching treatment). Next, the laminate was immersed for 30 seconds in an insolubilizing bath (a boric acid aqueous solution obtained by blending 4 parts by weight of boric acid with 100 parts by weight of water) having a liquid temperature of 40°C (insolubilization treatment), then immersed for 60 seconds in a dyeing bath (an iodine aqueous solution obtained by blending iodine and potassium iodide with 100 parts by weight of water in a weight ratio of 1:7) having a liquid temperature of 30°C while adjusting the concentration so that the single transmittance (Ts) of the finally obtained polarizer would be a desired value (dyeing treatment), then immersed for 30 seconds in a crosslinking bath (a boric acid aqueous solution obtained by blending 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with 100 parts by weight of water) having a liquid temperature of 40°C (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 liquid temperature of 70°C and uniaxially stretched in the longitudinal direction (longitudinal direction) between rolls operating at different peripheral speeds to a total stretch ratio of 5.5 times (underwater stretching treatment). The laminate was then immersed in a cleaning bath (aqueous solution obtained by blending 4 parts by weight of potassium iodide with 100 parts by weight of water) at a liquid temperature of 20°C (washing treatment). The laminate was then dried in an oven maintained at approximately 90°C and contacted with a SUS heated roll maintained at a surface temperature of approximately 75°C (drying shrinkage treatment). In this way, a polarizer approximately 5 μm thick was formed on the resin substrate, resulting in a polarizing plate having a resin substrate / polarizer configuration. The polarizer's single transmittance Ts was 43.3%.

[0067] 1-2. Preparation of Polarizing Plate An HC-COP film was bonded to the surface of the obtained polarizer (the surface opposite to the resin substrate) via a UV-curable adhesive. The HC-COP film was a film in which an HC layer (thickness 4 μm) was formed on a cycloolefin resin (COP) film (thickness 25 μm), and the COP film was bonded so that it faced the polarizer. The COP film had an Re(550) of 135 nm. Next, the resin substrate was peeled off to obtain a polarizing plate having a configuration of HC layer / COP film (protective layer) / polarizer.

[0068] 2. Preparation of Retardation Layer A photopolymerizable liquid crystal compound exhibiting a nematic liquid crystal phase (BASF's "Paliocolor LC242," chemical formula below) was dissolved in cyclopentanone to prepare a solution with a solids concentration of 30% by weight. A surfactant (BYK-Chemie's "BYK-360") and a photopolymerization initiator (IGM Resins' "Omnirad 907") were added to this solution to prepare a liquid crystal composition solution. The amounts of surfactant and polymerization initiator added were 0.01 parts by weight and 3 parts by weight, respectively, per 100 parts by weight of the photopolymerizable liquid crystal compound. A biaxially stretched norbornene film (Zeon Corporation's "ZEONORFILM," thickness 33 μm, Re(550) = 135 nm) was prepared as a substrate. The liquid crystal composition was applied to the substrate with a bar coater so that Re(550) was 240 nm, and the substrate was heated at 100° C. for 3 minutes to align the liquid crystal. After cooling to room temperature, the substrate was irradiated with an integrated light dose of 400 mJ / cm 2 in a nitrogen atmosphere. ２ The resulting laminate was photocured by irradiating it with ultraviolet light of 1000 W at ...

[0069] 3. Preparation of Optical Laminate A first liquid crystal alignment solidified layer was bonded to the polarizer surface of a polarizing plate via the adhesive of Production Example 1 (thickness after drying: 50 nm), and then the substrate was peeled off. Next, a second liquid crystal alignment solidified layer was bonded to the surface of the first liquid crystal alignment solidified layer via the adhesive of Production Example 1 (thickness after drying: 50 nm), and the substrate was peeled off to obtain an optical laminate having a configuration of polarizing plate / first adhesive layer / first liquid crystal alignment solidified layer / second adhesive layer / second liquid crystal alignment solidified layer. In the optical laminate, the angle between the transmission axis of the polarizer of the polarizing plate and the slow axis of the first liquid crystal alignment solidified layer was 15°, and the angle between the transmission axis of the polarizer of the polarizing plate and the slow axis of the second liquid crystal alignment solidified layer was 75°. The obtained optical laminate was subjected to the evaluation of the above-mentioned "linear unevenness." The results are shown in Table 1.

[0070] Examples 2 to 17 and Comparative Examples 1 to 5 Optical laminates were obtained in the same manner as in Example 1, except that the thicknesses of the first adhesive layer and the second adhesive layer were changed as shown in Table 1. The obtained optical laminates were subjected to the same evaluations as in Example 1. The results are shown in Table 1. Note that the notation "(UV)" in Examples 9 and 10 in Table 1 means that an active energy ray (ultraviolet) curable adhesive was used instead of an aqueous adhesive.

[0071]

[0072] [Evaluation] As is clear from Table 1, linear unevenness can be suppressed according to the examples of the present invention. Furthermore, as is clear from the comparison between Example 4 and Example 7, and between Example 5 and Example 8, it is clear that the effect of the embodiment of the present invention becomes more pronounced by reducing the thickness of the second adhesive layer. In addition, as is clear from the comparison between Example 1 and Example 9, and between Example 2 and Example 10, it is clear that the effect of the embodiment of the present invention becomes more pronounced by using a water-based adhesive.

[0073] The optical laminate according to the embodiment of the present invention can be suitably used in image display devices (typically, liquid crystal display devices and organic EL display devices).

[0074] REFERENCE SIGNS LIST 10 Polarizing plate 11 Polarizer 12 Protective layer 13 Protective layer 20 Retardation layer 21 First liquid crystal alignment solidified layer 22 Second liquid crystal alignment solidified layer 31 First adhesive layer 32 Second adhesive layer 100 Optical laminate

Claims

1. An optical laminate comprising: a polarizing plate including a polarizer; and a retardation layer laminated to the polarizing plate via a first adhesive layer, the retardation layer comprising, in order from the polarizing plate side, a first liquid crystal alignment solidified layer and a second liquid crystal alignment solidified layer laminated to the first liquid crystal alignment solidified layer via a second adhesive layer, the retardation layer as a whole having a circular polarization function or an elliptical polarization function and having a relationship of Re(450)<Re(550)<Re(650), and at least one of the first adhesive layer and the second adhesive layer having a thickness of 300 nm or less.

2. The optical laminate according to claim 1, wherein the first adhesive layer and the second adhesive layer each have a thickness of 200 nm or less.

3. The optical laminate according to claim 1, wherein at least one of the first adhesive layer and the second adhesive layer has a thickness of 100 nm or less.

4. The optical laminate according to claim 3, wherein at least one of the first adhesive layer and the second adhesive layer has a thickness of 50 nm or less.

5. The optical laminate according to claim 1, wherein the adhesive layer having a thickness of 300 nm or less is composed of a water-based adhesive.

6. An image display device comprising the optical laminate according to any one of claims 1 to 5.

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