Optical stack

Abstract

To provide an optical laminate including a liquid crystal alignment cured layer and suppressing peeling defects when peeling the alignment substrate. 【Solution means】The optical laminate according to an embodiment of the present invention has a polarizing plate including a polarizer, a retardation layer laminated on the polarizing plate via a first adhesive layer, and a substrate laminated on the retardation layer in a peelable manner; the retardation layer includes, in order from the polarizing plate side, a first liquid crystal alignment cured layer and a second liquid crystal alignment cured layer laminated on the first liquid crystal alignment cured layer via a second adhesive layer; the retardation layer as a whole has a circular polarization function or an elliptical polarization function, has a relationship of Re(450)<Re(550)<Re(650), and its Nz coefficient is 0.30 to 0.70; the substrate is an alignment substrate of the second liquid crystal alignment cured layer, and its tensile elastic modulus is 3000 N / mm 2 or more.

Description

[Technical Field]

[0001] This invention relates to an optical laminate. [Background technology]

[0002] In recent years, image display devices, such as liquid crystal displays and electroluminescent (EL) displays (e.g., organic EL displays and inorganic EL displays), have become rapidly widespread. Image display devices often utilize optical laminates containing phase difference films (e.g., anti-reflective films integrating polarizers and phase difference films). In recent years, with the increasing demand for thinner image display devices, there has also been a growing demand for thinner optical laminates. To achieve this, thinning of the phase difference layer (phase difference film), which contributes significantly to the thickness, is progressing. A typical example of a thin phase difference film is a film in which liquid crystal compounds are oriented and their orientation is fixed (hereinafter referred to as a liquid crystal film). Because liquid crystal compounds have significantly greater birefringence (Δn) than resins, the thickness required to obtain the desired in-plane phase difference for a liquid crystal film can be significantly reduced compared to a stretched resin film. A liquid crystal film is typically formed by applying a composition containing a liquid crystal compound to an orientation substrate and then solidifying or curing the coating. The formed liquid crystal film is bonded to a polarizing plate, and then the alignment substrate is peeled off. However, when using a liquid crystal film with a thin polarizing plate, peeling defects may occur when peeling off the alignment substrate. Specifically, the liquid crystal film may be peeled off together with the alignment substrate. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2014-222282 [Overview of the project] [Problems that the invention aims to solve]

[0004] The present invention has been made to solve the above-described conventional problems, and its main object is to provide an optical laminate including a liquid crystal alignment cured layer and suppressing peeling defects when peeling an alignment substrate.

Means for Solving the Problems

[0005] [1] The optical laminate according to an embodiment of the present invention has a polarizing plate including a polarizer, a retardation layer laminated on the polarizing plate via a first adhesive layer, and a substrate laminated on the retardation layer in a peelable manner; the retardation layer includes, in order from the polarizing plate side, a first liquid crystal alignment cured layer and a second liquid crystal alignment cured layer laminated on the first liquid crystal alignment cured layer via a second adhesive layer; the retardation layer has, as a whole, a circular polarization function or an elliptical polarization function, has a relationship of Re(450) < Re(550) < Re(650), and has an Nz coefficient of 0.30 to 0.70; the substrate is an alignment substrate of the second liquid crystal alignment cured layer, and its tensile elastic modulus is 3000 N / mm 2 or more. [2] In the above [1], the thickness of the substrate is 75 μm or more. [3] In the above [1] or [2], the substrate is a single film. [4] In the above [1] or [2], the substrate has a laminated structure of two or more layers. [5] In any one of the above [1] to [4], the polarizing plate includes protective layers disposed on both sides of the polarizer, and the thickness of the polarizing plate is 100 μm or less. [6] In any one of the above [1] to [5], the total thickness from the polarizing plate to the second liquid crystal alignment cured layer is 110 μm or less. [7] In any one of the above [1] to [6], the first adhesive layer is composed of an ultraviolet curable adhesive.

Effects of the Invention

[0006] According to an embodiment of the present invention, it is possible to realize an optical laminate including a liquid crystal alignment cured layer and suppressing peeling defects when peeling an alignment substrate.

Brief Description of the Drawings

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

Embodiments for Carrying Out the Invention

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

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

[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 optical laminate 100 in the illustrated example has a polarizing plate 10, a retardation layer 20 laminated on the polarizing plate 10 via a first adhesive layer 30, and a substrate 40 laminated on the retardation layer 20 in a peelable manner. 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-protection polarizing plate, a so-called single-protection polarizing plate, or may be composed of only the polarizer. The polarizing plate is preferably a double-protection polarizing plate, and the thickness of the polarizing plate is, for example, 110 μm or less, preferably 100 μm or less, and more preferably 15 μm to 100 μm. By configuring the polarizing plate with double protection and setting its thickness to a specific value or less, the effects according to the embodiments of the present invention can be remarkable.

[0011] The retardation layer 20 includes, in order from the polarizing plate 10 side, a first liquid crystal alignment cured layer 21 and a second liquid crystal alignment cured layer 22 laminated on the first liquid crystal alignment cured layer 21 via a second adhesive layer 25. By using the liquid crystal alignment cured layer as the retardation layer, a desired in-plane retardation can be realized with a thickness significantly thinner than that of a stretched film of a resin film. As a result, a remarkable thinning of the optical laminate can be achieved. The retardation layer 20 as a whole (as a laminate of the first liquid crystal alignment cured layer 21 and the second liquid crystal alignment cured layer 22) has a circular polarization function or an elliptical polarization function, has a relationship of Re(450) < Re(550) < Re(650), and its Nz coefficient is 0.30 to 0.70. According to the embodiment of the present invention, in an optical laminate having such a specific retardation layer, peeling failure when peeling the substrate can be suppressed. In the present specification, the "liquid crystal alignment cured layer" refers to a layer in which a liquid crystal compound is aligned in a predetermined direction within the layer and its alignment state is fixed. The "liquid crystal alignment cured layer" is a concept including an alignment cured layer obtained by curing a liquid crystal monomer.

[0012] The substrate 40 is the orientation substrate for the second liquid crystal alignment solidification layer 22. That is, a liquid crystal composition forming the second liquid crystal alignment solidification layer is applied to the substrate 40, and the liquid crystal compounds in the composition are oriented by the orientation-regulating force of the substrate 40. The second liquid crystal alignment solidification layer 22 is formed by solidifying or curing the liquid crystal compounds in this oriented state. A laminate of the substrate 40 and the second liquid crystal alignment solidification layer 22 is then laminated onto a polarizing plate (in the illustrated example, the first liquid crystal alignment solidification layer 21 laminated onto the polarizing plate 10). Typically, the substrate 40 can be peeled off when manufacturing the final optical laminate. That is, the substrate 40 is peelably laminated onto the second liquid crystal alignment solidification layer 22. In this embodiment of the present invention, the tensile modulus of the substrate 40 is 3000 N / mm². 2 This concludes the explanation. With this configuration, peeling defects when peeling the substrate can be suppressed. Specifically, it is possible to prevent or effectively suppress the peeling of the second liquid crystal alignment solidification layer together with the substrate. The first liquid crystal alignment solidification layer 21 is also formed in the same manner as described above and laminated onto the polarizing plate, and it is preferable that the alignment substrate of the first liquid crystal alignment solidification layer 21 is the same substrate as the substrate 40.

[0013] In an optical laminate, the total thickness from the polarizing plate to the second liquid crystal alignment solidification layer (i.e., the portion that can become the final product) is, for example, 120 μm or less, preferably 110 μm or less, and more preferably 20 μm to 110 μm. In such a thin optical laminate, peeling defects are significant when peeling the substrate, but according to the embodiment of the present invention, such peeling defects can be suppressed.

[0014] The components of the optical laminate will be explained in detail below.

[0015] B. Polarizing plate B-1.Polarizer The polarizer 11 is typically composed of a polyvinyl alcohol (PVA) resin film containing a dichroic substance (e.g., iodine). Examples of PVA resins include polyvinyl alcohol, partially formalized polyvinyl alcohol, ethylene-vinyl alcohol copolymer, and partially saponified ethylene-vinyl acetate copolymer.

[0016] The PVA resin preferably includes an acetoacetyl-modified PVA resin. With such a configuration, a polarizer with the desired mechanical strength can be obtained. The amount of acetoacetyl-modified PVA resin is preferably 5% to 20% by weight, and more preferably 8% to 12% by weight, when the total PVA resin is considered to be 100% by weight. A polarizer with even better mechanical strength can be obtained when the amount is within this range.

[0017] The polarizer preferably contains iodide or sodium chloride (sometimes collectively referred to as halide). Examples of iodide include potassium iodide, sodium iodide, and lithium iodide. The halide content in the polarizer is preferably 5 to 20 parts by weight, and more preferably 10 to 15 parts by weight, per 100 parts by weight of PVA resin. In the manufacturing method described later, the halide can be incorporated into the coating solution that forms the PVA resin layer, which is a precursor of the polarizer, and finally introduced into the polarizer. By introducing a halide into the polarizer, the orientation of PVA molecules in the polarizer can be increased, making it possible to realize a polarizer with excellent optical properties (typically, a combination of high polarization degree and high single-element transmittance).

[0018] The polarizer preferably exhibits absorption dichroism at any wavelength between 380 nm and 780 nm. The 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 higher, more preferably 99.0% or higher, and even more preferably 99.9% or higher. According to embodiments of the present invention, even if the transmittance of the polarizer is within the above range, the degree of polarization can be maintained within this range.

[0019] 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 solidification layer, significant thinning of the optical laminate becomes possible. Furthermore, if the thickness of the polarizer is within the above range, curling during heating can be well suppressed, and good appearance durability during heating can be obtained.

[0020] Polarizers can be manufactured by any suitable method. For example, the resin film forming the polarizer may be a single layer of resin film or a laminate of two or more layers.

[0021] Specific examples of polarizers composed of a single layer of resin film include hydrophilic polymer films such as PVA-based films, partially formalized PVA-based films, and partially saponified ethylene-vinyl acetate copolymer films that have been dyed with dichroic substances such as iodine or dichroic dyes and stretched, as well as polyene-based oriented films such as dehydrated PVA or dehydrochlorinated polyvinyl chloride. Preferably, polarizers obtained by dyeing a PVA-based film with iodine and uniaxially stretching it are used because they have excellent optical properties.

[0022] The above-mentioned iodine dyeing is carried out, for example, by immersing the PVA film in an iodine aqueous solution. The stretching ratio for the above-mentioned uniaxial stretching is preferably 3 to 7 times. Stretching may be performed after the dyeing treatment, or during the dyeing process. Alternatively, dyeing may be performed after stretching. If necessary, the PVA film may be subjected to swelling, crosslinking, washing, drying, etc. For example, immersing the PVA film in water and washing it before dyeing can not only clean dirt and anti-blocking agents from the surface of the PVA film, but also swell the PVA film to prevent uneven dyeing.

[0023] Specific examples of polarizers obtained using a laminate include a laminate of a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or a polarizer obtained using a laminate of a resin substrate and a PVA-based resin layer coated on the resin substrate. A polarizer obtained using a laminate of a resin substrate and a PVA-based resin layer coated on the resin substrate can be produced, for example, by applying a PVA-based resin solution to a resin substrate, drying it to form a PVA-based resin layer on the resin substrate, and obtaining a laminate of the resin substrate and the PVA-based resin layer; or by stretching and dyeing the laminate to make the PVA-based resin layer a polarizer. In this embodiment, preferably, a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin is formed on one side of the resin substrate. Stretching typically includes immersing the laminate in an aqueous boric acid solution and stretching it. Furthermore, stretching may, if necessary, further include air-stretching the laminate at a high temperature (e.g., 95°C or higher) before stretching in the aqueous boric acid solution. In addition, in this embodiment, the laminate is preferably subjected to a drying shrinkage treatment in which it shrinks by 2% or more in the width direction by heating while being transported in the longitudinal direction. Typically, the manufacturing method of this embodiment includes applying an air-assisted stretching treatment, a dyeing treatment, a water-based stretching treatment, and a drying shrinkage treatment to the laminate in this order. By introducing auxiliary stretching, it is possible to increase the crystallinity of PVA even when PVA is coated on a thermoplastic resin, making it possible to achieve high optical properties. At the same time, by increasing the orientation of PVA in advance, it is possible to prevent problems such as a decrease in the orientation of PVA and dissolution when immersed in water in the subsequent dyeing and stretching processes, making it possible to achieve high optical properties. Furthermore, when the PVA-based resin layer is immersed in liquid, the disorder of the orientation of polyvinyl alcohol molecules and the decrease in orientation can be suppressed compared to when the PVA-based resin layer does not contain halides. As a result, the optical properties of the polarizer obtained through processing steps in which the laminate is immersed in liquid, such as dyeing and water-based stretching, can be improved. Furthermore, by shrinking the laminate in the width direction through the drying shrinkage treatment, the optical properties can be improved.The resulting 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 an appropriate protective layer may be laminated on the peeled surface obtained by removing the resin substrate from the resin substrate / polarizer laminate, or on the surface opposite to the peeled surface, depending on the purpose. Details of such polarizer manufacturing methods are described, for example, in Japanese Patent Application Publication No. 2012-73580 and Japanese Patent No. 6470455. The entire contents of these publications are incorporated herein by reference.

[0024] B-2.Protective layer The protective layers 12 and 13 are composed of any suitable resin film. Typical materials for the resin film include cellulosic resins such as triacetylcellulose (TAC), cycloolefin resins such as polynorbornene, (meth)acrylic resins, polyester resins such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), polyolefin resins such as polyethylene, and polycarbonate resins. Typical examples of (meth)acrylic resins include (meth)acrylic resins having a lactone ring structure. (Meth)acrylic resins having a lactone ring structure are described, for example, in Japanese Patent Publication No. 2000-230016, Japanese Patent Publication No. 2001-151814, Japanese Patent Publication No. 2002-120326, Japanese Patent Publication No. 2002-254544, and Japanese Patent Publication No. 2005-146084. These publications are incorporated herein by reference. From the viewpoint of ease of shaping, cellulose resins are preferred, and TAC is more preferred. From the viewpoint of obtaining polarizing plates with low moisture permeability and excellent durability, cycloolefin resins and (meth)acrylic resins are preferred.

[0025] The optical laminate is typically positioned on the viewing side of the image display device, and the protective layer 12 is typically positioned on the viewing side. Therefore, the protective layer 12 may be surface-treated as needed. Examples of surface treatments include hard coating, anti-reflective coating, anti-sticking coating, and anti-glare coating. Furthermore / or, the protective layer 12 may be treated as needed to improve visibility when viewed through polarized sunglasses (typically by providing (elliptic) polarization functionality or providing ultra-high phase difference). By applying such treatment, excellent visibility can be achieved even when the display screen is viewed through polarized lenses such as polarized sunglasses. Therefore, the optical laminate can be suitably applied to image display devices that may be used outdoors.

[0026] In one embodiment, the protective layer 13 is preferably optically isotropic. In this specification, "optically isotropic" means that the in-plane phase difference Re(550) is 0 nm to 10 nm and the phase difference Rth(550) in the thickness direction is -10 nm to +10 nm.

[0027] The thickness of 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, respectively. If protective layer 12 is surface-treated, the thickness of protective layer 12 includes the thickness of the surface treatment layer.

[0028] C. Retardation layer As described above, the retardation layer 20 includes a first liquid crystal alignment cured layer 21 and a second liquid crystal alignment cured layer 22 in order from the polarizer side. Further, as described above, the retardation layer 20 has a circular polarization function or an elliptical polarization function as a whole (as a laminate of the first liquid crystal alignment cured layer 21 and the second liquid crystal alignment cured layer 22), has the relationship of Re(450) < Re(550) < Re(650), and its Nz coefficient is 0.30 to 0.70. Regarding the description of the retardation layer in this section, when simply referred to as the "retardation layer", it means explaining the entire retardation layer, and when simply referred to as the "liquid crystal alignment cured layer", it means explaining the first liquid crystal alignment cured layer and the second liquid crystal alignment cured layer together.

[0029] For the retardation layer 20, Re(550) is preferably 100 nm to 200 nm, more preferably 120 nm to 190 nm, still more preferably 130 nm to 180 nm, and particularly preferably 150 nm to 170 nm. If the Re(550) of the retardation layer is within such a range, the retardation layer can exhibit a good circular polarization function or elliptical polarization function in combination with a polarizer.

[0030] The Nz coefficient of the retardation layer 20 is 0.30 to 0.70 as described above. Therefore, the retardation layer 20 exhibits a refractive index characteristic of nx > nz > ny. With such a configuration, reflection in the oblique direction can be well prevented, and the wide viewing angle of the antireflection function can be achieved. The Nz coefficient is preferably 0.35 to 0.65, more preferably 0.40 to 0.60, and still more preferably 0.45 to 0.55.

[0031] The retardation layer 20 has the relationship of Re(450) < Re(550) < Re(650). That is, the retardation layer 20 preferably exhibits an inverse dispersion wavelength dependence in which the retardation value increases with the wavelength of the measurement light. With such a configuration, a good antireflection function can be realized in 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 still more preferably 0.8 to 0.9. Re(650) / Re(550) is preferably 1.0 or more and less than 1.15, more preferably 1.03 to 1.1.

[0032] Examples of the liquid crystal compound used for the liquid crystal alignment curing layer include liquid crystal polymers and liquid crystal monomers. The liquid crystal compound is preferably polymerizable (i.e., a liquid crystal monomer). When the liquid crystal compound is polymerizable, the alignment state of the liquid crystal compound can be fixed by polymerizing it after the liquid crystal compound is aligned. Here, the polymer formed by polymerization is non-liquid crystal. Therefore, in the formed liquid crystal alignment curing layer, for example, a transition from a liquid crystal phase, a glass phase, or a crystal phase due to a temperature change peculiar to the liquid crystal compound does not occur. As a result, the liquid crystal alignment curing layer becomes a retardation layer that is not affected by temperature changes and is extremely stable.

[0033] In one embodiment, the liquid crystal alignment solidification layer can be formed using a composition containing a polymerizable liquid crystal compound (a polymerizable liquid crystal compound, i.e., a liquid crystal monomer). In this specification, a polymerizable liquid crystal compound included in the composition means a compound that has a polymerizable group and is liquid crystal. A polymerizable group means a group that participates in the polymerization reaction, and is preferably a photopolymerizable group. Here, a photopolymerizable group means a group that can participate in the polymerization reaction by active radicals or acids generated from a photopolymerization initiator. As liquid crystal monomers, for example, polymerizable mesogenic compounds described in JP 2002-533742 (WO00 / 37585), EP358208 (US5211877), EP66137 (US4388453), WO93 / 22397, EP0261712, DE19504224, DE4408171, and GB2280445 can be used. Specific examples of such polymerizable mesogenic compounds include, for example, BASF's trade name LC242, Merck's trade name E7, and Wacker-Chem's trade name LC-Silicon-CC3767.

[0034] The mechanism by which the liquid crystalline properties of a liquid crystal compound are exhibited may be thermotropic or lyotropic. Furthermore, the liquid crystal phase may be composed of either a nematic or smectic liquid crystal. From the viewpoint of ease of manufacture, a thermotropic nematic liquid crystal is preferred.

[0035] The temperature range in which liquid crystal monomers exhibit liquid crystalline properties varies depending on the type. 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.

[0036] The birefringence Δn of the liquid crystal alignment solidification layer is preferably 0.06 or higher, more preferably 0.08 or higher, even more preferably 0.09 or higher, and particularly preferably 0.10 or higher. The upper limit of Δn may be, for example, 0.13 or 0.12. When Δn is within this range, the desired in-plane phase difference can be achieved with a very thin thickness. As a result, the liquid crystal alignment solidification layer and the optical laminate can be made even thinner, which can ultimately contribute to a significant reduction in the thickness of the image display device.

[0037] The liquid crystal alignment solidification layer may exhibit inverse dispersion wavelength characteristics in which the phase difference value increases with the wavelength of the measurement light, or it may exhibit positive wavelength dispersion characteristics in which the phase difference value decreases with the wavelength of the measurement light, or it may exhibit flat wavelength dispersion characteristics in which the phase difference value hardly changes with the wavelength of the measurement light.

[0038] The first liquid crystal alignment solidification layer 21 can typically function as a λ / 2 plate, and the second liquid crystal alignment solidification layer 22 can typically function as a λ / 4 plate. Specifically, the Re(550) of the first liquid crystal alignment solidification layer is preferably 200 nm to 300 nm, more preferably 230 nm to 290 nm, and even more preferably 250 nm to 280 nm; the Re(550) of the second liquid crystal alignment solidification layer is preferably 100 nm to 200 nm, more preferably 120 nm to 170 nm, and even more preferably 130 nm to 150 nm. The thickness of the first liquid crystal alignment solidification layer can be adjusted to obtain a desired in-plane phase difference for the λ / 2 plate. Specifically, its thickness may be, for example, 2.0 μm to 4.0 μm. The thickness of the second liquid crystal alignment solidification layer can be adjusted to obtain a desired in-plane phase difference for the λ / 4 plate. Specifically, its thickness may be, for example, 1.0 μm to 2.5 μm. The angle between the slow axis of the first liquid crystal alignment solidification layer and the absorption axis of the polarizer is preferably 10° to 20°, more preferably 12° to 18°, and even more preferably 14° to 16°; the angle between the slow axis of the second liquid crystal alignment solidification layer and the absorption axis of the polarizer is preferably 70° to 80°, more preferably 72° to 78°, and even more preferably 74° to 76°. The arrangement order of the first liquid crystal alignment solidification layer and the second liquid crystal alignment solidification layer may be reversed, and the angles between the slow axis of the first liquid crystal alignment solidification layer and the absorption axis of the polarizer and the angles between the slow axis of the second liquid crystal alignment solidification layer and the absorption axis of the polarizer may be reversed.

[0039] A side-chain type thermotropic liquid crystal polymer may be introduced into the first liquid crystal alignment solidification layer and / or the second liquid crystal alignment solidification layer (substantially, the liquid crystal composition forming them). Introducing a side-chain type thermotropic liquid crystal polymer can cause the liquid crystal monomers to undergo homeotropic alignment (vertical alignment). As a result, the nz of the first liquid crystal alignment solidification layer and / or the second liquid crystal alignment solidification layer can be increased, and consequently, the Nz coefficient of the first liquid crystal alignment solidification layer and / or the second liquid crystal alignment solidification layer can be set to the desired range described above. Finally, the Nz coefficient of the phase difference layer can be set to the desired range described above without providing the positive C plate described later.

[0040] Typical side-chain thermotropic liquid crystal polymers include copolymers having monomer units containing thermotropic liquid crystal fragment side chains and monomer units containing non-liquivalent fragment side chains. The presence of thermotropic liquid crystal fragments in the side chains of the polymer allows the side-chain liquid crystal polymer to be oriented when the liquid crystal composition is heated to a predetermined temperature. Furthermore, the presence of non-liquivalent fragments in the side chains of the side-chain polymer allows the non-liquivalent fragments to interact with photopolymerizable liquid crystal monomers, potentially causing homeotropic orientation of the photopolymerizable liquid crystal monomers.

[0041] 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. [ka] [ka]

[0042] In equation (I), R 1 R is a hydrogen atom or a methyl group, 2 X 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. 1 is -CO2- or -OCO-. a is an integer between 1 and 6, and b and c are independently either 1 or 2.

[0043] In equation (II), R 3 R is a hydrogen atom or a methyl group, 4 This 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). [ka]

[0044] In equation (III), R 5 is an alkyl group having 1 to 5 carbon atoms, and d is an integer from 1 to 6.

[0045] The ratio of liquid crystalline monomer units to non-liquid crystalline monomer units in a side-chain type liquid crystal monomer can be appropriately set depending on the purpose. The ratio (molar ratio) of non-liquid crystalline monomers to the total of liquid crystalline monomer units 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 orientation solidified layer exhibiting the desired refractive index characteristics (Nz coefficient) can be obtained.

[0046] The ratio of liquid crystal monomers to side-chain liquid crystal polymers in a liquid crystal composition can be appropriately set depending on the purpose. When the content of side-chain liquid crystal polymers is high, the Nz coefficient tends to be low; when the content of liquid crystal monomers is high, the Nz coefficient tends to be low. The content of liquid crystal monomers 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, relative to the content of side-chain liquid crystal polymers. With such a configuration, a liquid crystal orientation solidified layer exhibiting the desired refractive index characteristics (Nz coefficient) can be obtained.

[0047] Details of a method for forming a side-chain liquid crystal polymer and a liquid crystal alignment solidified layer having an Nz coefficient of less than 1.0 are described in Japanese Patent No. 6769921. The contents of that patent are incorporated herein by reference.

[0048] The retardation layer 20 may further include a positive C plate. The positive C plate exhibits a refractive index characteristic showing the relationship of nz > nx = ny. The retardation Rth(550) in the thickness direction of the positive C plate is preferably from -50 nm to -300 nm, more preferably from -70 nm to -250 nm, still more preferably from -90 nm to -200 nm, and particularly preferably from -100 nm to -180 nm. Here, "nx = ny" includes not only the case where nx and ny are exactly equal but also the case where nx and ny are substantially equal. That is, the in-plane retardation Re(550) of the positive C plate can be less than 10 nm.

[0049] The positive C plate can be formed, for example, using a composition containing the above side-chain type liquid crystal polymer. Specific examples of the method for forming the positive C plate include the methods described in

[0020] to

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

[0050] D. Substrate The tensile elastic modulus of the substrate 40 is 3000 N / mm or more as described above. 2 With such a configuration, peeling failure when peeling the substrate can be suppressed. Specifically, it is possible to prevent or preferably suppress the peeling of the second liquid crystal alignment curing layer together with the substrate. The tensile elastic modulus of the substrate is preferably 4000 N / mm or more, more preferably 5000 N / mm or more, still more preferably 6000 N / mm or more, and particularly preferably 6500 N / mm or more. On the other hand, the tensile elastic modulus of the substrate can be, for example, 9000 N / mm or less, or can be, for example, 8500 N / mm or less. The tensile elastic modulus can be determined in accordance with JIS K 7161. 2 above, more preferably 5000 N / mm 2 above, still more preferably 6000 N / mm 2 above, and particularly preferably 6500 N / mm 2 above. On the other hand, the tensile elastic modulus of the substrate can be, for example, 9000 N / mm 2 or less, and can also be, for example, 8500 N / mm 2 or less. The tensile elastic modulus can be determined in accordance with JIS K 7161.

[0051] The peeling force of the substrate 40 is preferably 1.2 N / 50 mm or less, more preferably 1.0 N / 50 mm or less, even more preferably 0.8 N / 50 mm or less, and particularly preferably 0.7 N / 50 mm or less. On the other hand, the peeling force of the substrate may be, for example, 0.1 N / 50 mm or more, or for example, 0.2 N / 50 mm or more. With such a configuration, peeling defects when peeling the substrate can be suppressed, similar to the case where the tensile modulus is set to a predetermined value or higher. Specifically, it is possible to prevent or effectively suppress the peeling of the second liquid crystal alignment solidification layer together with the substrate.

[0052] As described above, the substrate is an orientation substrate for the second liquid crystal orientation solidification layer and therefore possesses orientation restricting force. The orientation restricting force can typically be imparted by rubbing orientation, stretched substrate orientation, or photo-orientation. Preferably, it is stretched substrate orientation or photo-orientation.

[0053] The substrate can be any suitable configuration as long as the desired tensile modulus is obtained. Specifically, the substrate may be a single film or may have a laminated structure of two or more layers (it may be a laminate). The substrate is typically composed of a resin film. Therefore, the substrate may be a single film of resin film or a laminate containing a first resin film and a second resin film. A single film may be advantageous in terms of cost and versatility. A laminate can achieve both the desired orientation restricting force and the desired tensile modulus when a single film cannot achieve both by complementing these properties with multiple resin films. The laminate may be a three-layer laminate further containing a third resin film, a four-layer laminate further containing a fourth resin film, or a five-layer or more laminate. Each resin film included in the laminate is typically laminated via an adhesive layer. The laminate preferably has a configuration of a first resin film having orientation restricting force / adhesive layer / second resin film.

[0054] Typical materials that make up the resin film include cellulose resins such as TAC, cycloolefin resins such as polynorbornene, (meth)acrylic resins, polyester resins such as PET and PEN, polyolefin resins such as polyethylene and polypropylene, and polycarbonate resins. Specific substrate configurations are preferably a single film of TAC film with orientation-regulating properties, or a laminate having a configuration of TAC film with orientation-regulating properties / adhesive layer / PET film.

[0055] The thickness of the substrate may vary depending on the material and structure of the substrate. The thickness of the substrate may be, for example, 75 μm or more, 77 μm or more, 80 μm or more, 85 μm or more, or 88 μm or more. On the other hand, the thickness of the substrate may be, for example, 120 μm or less, 110 μm or less, or 100 μm or less.

[0056] E. First adhesive layer Typical adhesives that can constitute the first adhesive layer 30 include active energy ray curing adhesives. By using an active energy ray curing adhesive as the first adhesive layer, the first adhesive layer can be made thinner, and as a result, an optical laminate with excellent flexibility can be obtained. Furthermore, the refractive index of the first adhesive layer can be increased, and the refractive index difference with the adjacent first liquid crystal alignment solidification layer can be reduced. As a result, reflection at the interface between the first adhesive layer and the first liquid crystal alignment solidification layer is suppressed, and an optical laminate with excellent anti-reflective performance can be obtained. Active energy ray curing adhesives can be selected as needed, such as radical curing type, cationic curing type, and anionic curing type, and can also be used in combination as appropriate, for example, a hybrid of radical curing type and cationic curing type. Examples of radical curing adhesives include adhesives containing compounds having radical polymerizable groups such as (meth)acrylate groups and (meth)acrylamide groups (e.g., monomers and / or oligomers) as curing components. As an active energy ray curing adhesive, an active energy ray curing adhesive with desired properties (e.g., storage modulus after curing) can be obtained by adjusting the type, combination, and blending ratio of double bond-containing monomers and / or oligomers, crosslinking agents, etc. Examples of active energy rays include ultraviolet light, visible light, infrared light, and electron beams. Ultraviolet-curing adhesives are preferred because they offer excellent versatility and handling. Since active energy ray curing adhesives are well known in the industry, a detailed explanation of their composition will be omitted.

[0057] The thickness of the first adhesive layer is preferably 0.1 μm to 3.0 μm, more preferably 0.5 μm to 2.0 μm, and even more preferably 0.8 μm to 1.5 μm. Such a thickness can contribute to the thinning of the optical laminate.

[0058] F.Second adhesive layer The second adhesive layer 25 can be composed of any suitable adhesive. The thickness of the second adhesive layer is preferably 0.1 μm to 3.0 μm, more preferably 0.5 μm to 2.0 μm, and even more preferably 0.8 μm to 1.5 μm. With such a thickness, it can contribute to thinning the optical laminate, similar to the first adhesive layer. [Examples]

[0059] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. The measurement and evaluation methods in the examples are as follows.

[0060] (1) In-plane phase difference Re(550), thickness direction phase difference Rth(550), and Nz coefficient Re(550) and Rth(550) were measured using AXOMETRICS' "AXO-Scan". The Nz coefficient was calculated from Rth / Re.

[0061] (2) Tensile modulus Tensile tests were performed on the substrates used in the examples and comparative examples in accordance with JIS K 7161, and the tensile modulus was determined.

[0062] (3) Peeling force Measurements were taken in accordance with JIS Z 0237. Specifically, the following was done: Optical laminates obtained in the examples and comparative examples were cut to a length of 150 mm and a width of 50 mm to serve as measurement samples. Using a tensile testing machine (manufactured by Tester Industries Co., Ltd., product name "TE-702 High-Speed ​​Peel Tester"), the peel force was measured when the substrate of the measurement sample was peeled off at a peel angle of 90° and a peel speed of 15,000 mm / min.

[0063] (4) Peeling evaluation The optical laminates obtained in the examples and comparative examples were observed for any peeling defects when the substrate was peeled off from the optical laminate while it was being transported on a roll, and evaluated according to the following criteria. Good: Only the substrate material was successfully peeled off. Defect: The second liquid crystal alignment solidification layer peeled off together with the substrate.

[0064] [Example 1] 1. Fabrication of polarizing plates 1-1. Fabrication of polarizers As a thermoplastic resin substrate, an amorphous isophthalic copolymer polyethylene terephthalate film (thickness: 100 μm) in a long length with a Tg of approximately 75°C was used, and one side of the resin substrate was subjected to corona treatment. A PVA aqueous solution (coating solution) was prepared by dissolving 100 parts by weight of a PVA-based resin, which was prepared by mixing 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 "Gosephymer") in a 9:1 ratio, with 13 parts by weight of potassium iodide. A PVA aqueous solution was applied to the corona-treated surface of a resin substrate and dried at 60°C to form a 13 μm thick PVA-based resin layer, thereby creating a laminate. The resulting laminate was uniaxially stretched 2.4 times in the longitudinal direction (longitudinal direction) in an oven at 130°C (air-assisted stretching). Next, the laminate was immersed for 30 seconds in an insolubilization bath at a liquid temperature of 40°C (a boric acid aqueous solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) (insolubilization treatment). Next, the polarizers were immersed for 60 seconds in a staining bath at a liquid temperature of 30°C (an iodine aqueous solution obtained by mixing iodine and potassium iodide in a weight ratio of 1:7 with 100 parts by weight of water) while adjusting the concentration so that the final transmittance (Ts) of the polarizers obtained would be the desired value (staining treatment). Next, the material was immersed for 30 seconds in a crosslinking bath at a liquid temperature of 40°C (a boric acid aqueous solution obtained by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with 100 parts by weight of water) (crosslinking treatment). Subsequently, the laminate was immersed in a boric acid aqueous solution (boric acid concentration 4% by weight, potassium iodide concentration 5% by weight) at a liquid temperature of 70°C, and uniaxially stretched in the longitudinal direction (longitudinal direction) between rolls with different peripheral speeds to achieve a total stretch ratio of 5.5 times (underwater stretching treatment). Subsequently, the laminate was immersed in a washing bath at a liquid temperature of 20°C (an aqueous solution obtained by mixing 4 parts by weight of potassium iodide with 100 parts by weight of water) (washing treatment). Subsequently, the material was dried in an oven maintained at approximately 90°C while being brought into contact with a SUS (stainless steel) heated roll whose surface temperature was maintained at approximately 75°C (drying shrinkage treatment). In this way, a polarizer with a thickness of approximately 5 μm was formed on a resin substrate, and a polarizing plate having a resin substrate / polarizer configuration was obtained. The transmittance Ts of the polarizer alone was 43.3%.

[0065] 1-2. Fabrication of polarizing plates An HC-TAC film was bonded to the surface of the obtained polarizer (the side opposite to the resin substrate) via an ultraviolet-curing adhesive. The HC-TAC film is a triacetylcellulose (TAC) film (25 μm thick) with an HC layer (7 μm thick) formed on it, and it was bonded so that the TAC film was on the polarizer side. Next, the resin substrate was peeled off, and a TAC film (25 μm thick) was bonded to the peeled surface via an ultraviolet-curing adhesive. In this way, a polarizing plate having the structure of HC layer / TAC film (protective layer) / polarizer / TAC film (protective layer) was obtained.

[0066] 2. Fabrication of the phase difference 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 solid content of 20% by weight. To this solution, a leveling agent (DIC's "Megafac F-563"), a photopolymerization initiator (IGM Resins' "Omnirad907"), and a crosslinking agent (Shin-Nakamura Chemical Industry's "A-DCP") were added to prepare a coating liquid for forming a liquid crystal alignment solidification layer. A TAC film (thickness: 80 μm, tensile modulus: 3391 N / mm²) was used as the substrate. 2 A substrate was prepared. The above liquid crystal alignment solidification layer forming coating liquid was applied to this substrate using a spin coater, and the liquid crystal compound was aligned by heating at 100°C for 3 minutes. After cooling to room temperature, the substrate was exposed to a nitrogen atmosphere with an integrated light intensity of 600 mJ / cm². 2The orientation of the liquid crystal compound was fixed by photocuring using ultraviolet light. In this way, a laminate of substrate / first liquid crystal orientation solidified layer (thickness: 2 μm, Re(550): 270 nm) was obtained. A laminate of substrate / second liquid crystal orientation solidified layer (thickness: 1 μm, Re(550): 140 nm) was obtained in the same manner as above, except that the coating thickness was changed. [ka]

[0067] 3. Preparation of a positive C plate A liquid crystal coating solution was prepared by dissolving 20 parts by weight of a side-chain liquid crystal polymer with a weight-average molecular weight of 5000 (as shown in the chemical formula below, n=0.35, and shown as a block polymer for convenience), 80 parts by weight of a polymerizable liquid crystal exhibiting a nematic liquid crystal phase (BASF: trade name Paliocolor LC242), and 5 parts by weight of a photopolymerization initiator (Ciba Specialty Chemicals: trade name Irgacure 907) in 200 parts by weight of cyclopentanone. The coating solution was then applied to a vertically aligned PET substrate using a bar coater, and the liquid crystal was aligned by heating and drying at 80°C for 4 minutes. A positive C plate (3 μm thick) was formed on the substrate by irradiating this liquid crystal layer with ultraviolet light to cure the liquid crystal layer. [ka]

[0068] 4. Fabrication of optical stacks A first liquid crystal alignment solidification layer was bonded to the TAC film surface opposite the HC layer of the polarizing plate via an ultraviolet-curable adhesive (1 μm thick), and then the substrate was peeled off. Next, a positive C plate was transferred to the surface of the first liquid crystal alignment solidification layer via an ultraviolet-curable adhesive (1 μm thick). Furthermore, a second liquid crystal alignment solidification layer was bonded to the surface of the positive C plate via an ultraviolet-curable adhesive (1 μm thick) to obtain an optical laminate having the configuration of polarizing plate / phase difference layer / substrate. The Re(550) of the entire phase difference layer was 168 nm, and the Nz coefficient was 0.52. The peeling force and the presence or absence of peeling defects when peeling the substrate from the obtained optical laminate were evaluated. The results are shown in Table 1.

[0069] [Example 2] Another TAC film (thickness: 80 μm, tensile modulus: 8147 N / mm²) was used as the base material. 2 An optical laminate was fabricated in the same manner as in Example 1, except that a different material was used. The obtained optical laminate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0070] [Example 3] An optical laminate was fabricated in the same manner as in Example 1, except that a laminate of TAC film (thickness: 40 μm), adhesive layer (thickness: 10 μm), and PET film (thickness: 38 μm) was used as the base material. The base material was prepared by laminating a surface protection film (product name "RP1010M") manufactured by Nitto Denko Corporation onto the TAC film. The tensile modulus of the base material was 7143 N / mm². 2 The obtained optical laminate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0071] [Example 4] An optical laminate was fabricated in the same manner as in Example 1, except that a laminate of TAC film (thickness: 40 μm), adhesive layer (thickness: 10 μm), and PET film (thickness: 38 μm) was used as the base material. The base material was prepared by laminating a surface protection film (product name "RP109F") manufactured by Nitto Denko Corporation onto the TAC film. The tensile modulus of the base material was 6901 N / mm². 2 The obtained optical laminate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0072] [Example 5] An optical laminate was fabricated in the same manner as in Example 1, except that a laminate of TAC film (thickness: 40 μm), adhesive layer (thickness: 5 μm), and PET film (thickness: 38 μm) was used as the base material. The base material was prepared by laminating a surface protection film (product name "HP300") manufactured by Nitto Denko Corporation onto the TAC film. The tensile modulus of the base material was 4079 N / mm². 2 The obtained optical laminate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0073] [Comparative Example 1] Another TAC film (thickness: 40 μm, tensile modulus: 2021 N / mm²) is used as the base material. 2 An optical laminate was fabricated in the same manner as in Example 1, except that a different material was used. The obtained optical laminate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0074] [Comparative Example 2] An optical laminate was prepared in the same manner as in Example 1, except that a laminate of TAC film (thickness: 40 μm) / polyethylene film (thickness: 32 μm) was used as the base material. The base material was prepared by laminating a self-adhesive surface protection film (product name "Toretec") manufactured by Toray Industries, Inc. onto the TAC film. The tensile modulus of the base material was 2376 N / mm². 2 The obtained optical laminate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0075] [Table 1] [Industrial applicability]

[0076] 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). [Explanation of symbols]

[0077] 10 Polarizing plates 11 Polarizer 12 Protective layer 13 Protective layer 20 Retardation layer 21. First liquid crystal alignment solidification layer 22 Second liquid crystal alignment solidification layer 40 Base material 100 Optical laminate

Claims

1. The device comprises a polarizing plate containing a polarizer, a phase difference layer laminated to the polarizing plate via a first adhesive layer, and a substrate peelably laminated to the phase difference layer. The phase difference layer includes, in order from the polarizing plate side, a first liquid crystal alignment solidification layer and a second liquid crystal alignment solidification layer laminated to the first liquid crystal alignment solidification layer via a second adhesive layer. The phase difference layer, as a whole, has a circular polarization function or an elliptic polarization function, has the relationship Re(450) < Re(550) < Re(650), and its Nz coefficient is 0.30 to 0.

70. The substrate is an orientation substrate for the second liquid crystal orientation solidification layer, and its tensile modulus is 3000 N / mm². ２ That's all. Optical laminate.

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