Photo-aligned positive c-plate retarder

Abstract

The present invention relates to a material composition and method for producing a photo-alignable positive c-plate retarder, in which a planar alignment direction can be induced at the surface of the c-plate retarder by exposure to polarized light, so that a slave material can be aligned at the surface of the c-plate retarder with a defined azimuthal alignment direction without the need for an additional alignment layer.

Description

[Technical field]

[0001] The present invention relates to a photo-alignable positive c-plate retarder and a layer structure including a non-vertically aligned liquid crystal layer in contact with such a c-plate retarder. The present invention further relates to a method for producing a photo-alignable positive c-plate retarder, as well as materials suitable for a photo-alignable positive c-plate retarder. [Background technology]

[0002] Photoalignment has become a powerful alignment method in the manufacture of liquid crystal displays (LCDs) and optical retarder films for a variety of applications.

[0003] For optical retarder films, liquid crystal monomers are coated on top of a photo-alignment layer. After transferring the alignment information of the photo-alignment layer to the liquid crystal monomers, the monomers are polymerized and / or cross-linked to solidify the liquid crystal material. The polymerized and / or cross-linked liquid crystal monomers are also known as liquid crystal polymers (LCPs).

[0004] US Patent No. 6,717,644 discloses a stack of LCP layers with individual optical axis directions. Each of the LCP layers is oriented by an orientation layer, such as a photo-alignment layer. Thus, the total number of layers in the stack of LCP layers is at least twice the number of LCP layers. The stack of LCP layers with individual optical axis directions can be used to generate interference color filters, such as Solc filters.

[0005] WO 2018 / 019691 discloses a method for generating alignment on the surface of a material comprising a liquid crystal polymer material and a photoalignable substance. Using this method, a separate alignment layer is not required to orient the second or more LCP layers, and therefore the number of layers in a multilayer optical film can be reduced. The above patent application describes a layer structure having a polarizer comprising a planar retarder and a liquid crystal polymer, designed to act as an achromatic circular polarizer for the anti-reflection structure of an OLED display, for example. Other examples mentioned are interference color filters such as Solc or Lyot filters.

[0006] No. 5,995,184 discloses a method for reducing the inherent tilt angle of a layer of polymerizable liquid crystal on the air interface side by adding a surface-active chemical material that reduces the surface energy. The tilt angle can be reduced to 0 degrees to achieve planar liquid crystal alignment.

[0007] Planar retarders suffer from a strong dependence of retardation characteristics from the light incidence angle. Therefore, there is a strong demand for a retarder film structure that includes one or more planar retarders plus a positive c-plate retarder to optically compensate for the angle dependence of the planar retarders.

[0008] A c-plate retarder is a uniaxial retarder in which the axis of the extraordinary index (ne) is perpendicular to the plane of the retarder. If the extraordinary index is larger than the ordinary index (no) of a c-plate retarder, the c-plate retarder is called a positive c-plate retarder, as opposed to a negative c-plate retarder, in which the extraordinary index is smaller than the ordinary index.

[0009] Similar to planar retarder layers, positive c-plate retarders are also used to reduce the viewing angle dependence in LCDs with planar liquid crystal alignment, such as LCDs designed for IPS or FFS modes. Positive c-plate retarders can also be useful to reduce the angle dependence of liquid crystal layers, such as retarder layers with an optical axis tilted with respect to the substrate surface.

[0010] It is desirable to have available methods and materials that allow for the production of layer structures including positive c-plate retarders in an efficient manner, e.g. by reducing the number of layers and manufacturing steps compared to state-of-the-art methods. Summary of the Invention

[0011] It is therefore an object of the present invention to provide methods and associated materials for simplifying the manufacture of devices including positive c-plate retarders in combination with planar or tilted liquid crystal layers as retarders.

[0012] In the method according to the invention, a positive c-plate retarder layer is formed from a composition comprising a polymerizable liquid crystal and one or more photoalignable substances. The resulting retarder layer has the property that upon exposure to aligning light, the surface develops planar or tilted alignment capability for an alignable material, such as a liquid crystal material.

[0013] Since the c-plate retarder itself has no preferred azimuthal component, it is not necessary to provide an azimuthal alignment direction for the fabrication of the c-plate retarder. The substrate onto which the liquid crystalline c-plate material is applied need only support the development of homeotropic alignment of the liquid crystals in the c-plate retarder material.

[0014] In addition to interactions with the substrate, the liquid crystal-air interactions on top of the liquid crystal layer must also support homeotropic alignment, so a proper balance of surface energies in the liquid crystal c-plate material is important.

[0015] For ease of reading, the term "photo-alignable positive C-plate" uses the abbreviation PAPC.

[0016] In the context of this application, PAPC materials refer to homeotropically oriented polymerizable liquid crystals and Light alignment A PAPC layer is therefore a layer formed from a PAPC material.

[0017] Preferably, the photoalignable material has properties that allow it to develop planar or tilted alignment capability of the slave material upon exposure to aligning light.

[0018] When state-of-the-art positive c-plate retarders are made from materials that contain polymerizable liquid crystals but no photoalignable material, the c-plate retarder cannot provide a preferred azimuthal alignment direction for the liquid crystal on its surface. Furthermore, the liquid crystal molecules in the c-plate retarder are homeotropically aligned, meaning perpendicular to the substrate surface, so the surface of the c-plate retarder can provide a homeotropic alignment of the liquid crystal layer.

[0019] As mentioned above, U.S. Patent No. '184 discloses that the intrinsic tilt angle is reduced in a layer of polymerizable liquid crystal on the air interface side by adding a surface-active chemical material that reduces the surface energy. Therefore, one skilled in the art would expect that it would be almost impossible to maintain the possibility of the liquid crystal material being homeotropically oriented when a migrating substance is added to the surface.

[0020] An alignment layer for liquid crystals must provide alignment information at the surface of the layer in contact with the liquid crystal. Therefore, at least a part of the photoalignment material in the PAPC layer must migrate to the surface of the air interface of the PAPC layer. Since the photoalignment material in the PAPC material is designed for planar or tilt alignment, those skilled in the art would expect that the photoalignment material on the top surface would reduce the inherent tilt of the liquid crystal molecules at the air interface, especially when the surface energies of the liquid crystal material and the photoalignment material are different from each other, and thus homeotropic liquid crystal alignment may no longer be possible.

[0021] The PAPC layer according to the present invention exhibits homeotropic alignment of liquid crystals, although a photoalignment material is included in the PAPC composition.

[0022] In the PAPC layer according to the present invention, a preferred azimuthal alignment direction of the liquid crystal can be induced at the surface of the PAPC layer by exposure to an alignment light, which is due to the presence of a photoalignable substance at the surface of the PAPC layer. This preferred azimuthal alignment direction at the surface of the PAPC layer can be transferred to a slave material, such as a liquid crystal material, deposited on top of the PAPC layer. Surprisingly, the alignment produced by the alignment light dominates even the strong alignment force induced by the homeotropically aligned liquid crystal in the PAPC layer.

[0023] Polymerization of the liquid crystal material in the PAPC layer can be initiated, for example, by exposure to unpolarized actinic light before, simultaneously with, or after exposure to the alignment light. Preferably, the PAPC material is designed so that the wavelength sensitivity of the polymerizable liquid crystal material and the photoalignable substance is different, so that polymerization of the liquid crystal material can be initiated by light of a wavelength different from that required to produce photoalignment by the alignment light. Preferably, the PAPC material includes a photoinitiator.

[0024] On the other hand, PAPC materials can be designed such that for a certain light spectrum of the alignment light, a single exposure to the alignment light simultaneously initiates polymerization of the liquid crystal material and the generation of alignment of the photoalignable substance. By appropriately selecting the materials and exposure parameters, the liquid crystal material in the homeotropic configuration can be rapidly solidified before the alignment forces due to the photoalignment reaction induced by the alignment light become strong enough to distort the liquid crystal structure.

[0025] It is even possible to maintain the homeotropic configuration of the polymerizable liquid crystal if the PAPC layer is exposed to an orienting light prior to polymerizing the liquid crystal. In this case, the viscosity of the PAPC material must be high enough to prevent the liquid crystal molecules from tilting away from the homeotropic alignment. To this end, it is useful to maintain the temperature of the PAPC material from the time exposure to the orienting light begins until the liquid crystal has polymerized and is well below the clearing temperature of the PAPC material.

[0026] The PAPC material may contain a solvent. The solvent may be useful for preparing and storing the composition, and for proper adjustment of the viscosity for optimal printing and / or coating performance. The solvent is typically removed, for example by heating, after the PAPC material is deposited on a support. The solvent-free PAPC material should have a liquid crystal phase, and preferably the solvent-free PAPC material is in a liquid crystal phase at about room temperature. Hereinafter, the clearing temperature of the PAPC material shall mean the clearing temperature of the PAPC material from which such solvent has been removed.

[0027] In a preferred embodiment, the PAPC material contains one or more dichroic dyes that absorb light in at least one wavelength range of the visible spectrum of light. In a layer of such a PAPC material, the liquid crystal molecules are homeotropically oriented so that the layer acts as a linear polarizer with its axis of symmetry aligned perpendicular to the substrate surface.

[0028] The relative terms "top" and "bottom" used in conjunction with layers and surfaces of layers are defined with respect to the location of the support, such that the bottom of a layer faces the support, while the top side or upper surface, respectively, faces away from the support.

[0029] PAPC layers coated and processed according to the methods of the present invention have optical functionality determined by the liquid crystal material and its composition, as well as any dichroic dyes contained in the PAPC material.

[0030] Within the context of this application, the terms "polymerizable" and "polymerized" are intended to include the meanings of "crosslinkable" and "crosslinked," respectively. Similarly, "polymerization" is intended to include the meaning of "crosslinking."

[0031] In the context of this application, a "photoalignable material" is a material in which anisotropic properties can be induced upon exposure to an aligning light. Also, a "photoaligned material" refers to a photoalignable material that has been oriented by exposure to an aligning light. For the present invention, the induced anisotropy must be such that it provides an alignment capability for a slave material, in particular a liquid crystal material. The term "alignment direction" refers to a preferred direction induced in the slave material. For example, if the slave material is a liquid crystal material, the alignment direction is the direction in which the liquid crystal molecules are aligned.

[0032] In the context of the present application, the term "alignment light" is intended to mean light capable of inducing anisotropy in the photoalignable material, which is at least partially linearly or elliptically polarized and / or incident on the surface of the photoalignable material from an oblique direction. Preferably, the alignment light is linearly polarized with a polarization degree of more than 5:1. The wavelength, intensity and energy of the alignment light are selected according to the photosensitivity of the photoalignable material. Typically, the wavelength is in the UV-A, UV-B and / or UV-C range or in the visible range. Preferably, the alignment light comprises light with a wavelength of less than 450 nm. More preferably, the alignment light comprises light with a wavelength of less than 420 nm.

[0033] If the orientation light is linearly polarized, the polarization plane of the orientation light is taken to mean the plane defined by the propagation direction and the polarization direction of the orientation light. If the orientation light is elliptically polarized, the polarization plane is taken to mean the plane defined by the propagation direction of the light and the major axis of the polarization ellipse.

[0034] The terms photo-alignment, photo-alignable, and photo-aligned are used synonymously with the terms photo-orientation, photo-orientable, and photo-oriented, respectively. [Brief description of the drawings]

[0035] The invention is further illustrated by the accompanying drawings, in which it is emphasized that the various features are not necessarily drawn to scale. [Figure 1] FIG. 13 shows a PAPC layer acting as a positive c-plate retarder and providing alignment of the slave material. [Diagram 2] FIG. 13 shows a layer stack in which a layer of slave material is oriented by a PAPC layer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] According to a first aspect of the invention, a method for producing a stack of oriented LCP layers is provided.

[0037] The method of the present invention comprises the steps of: Providing a composition (PAPC material) including a homeotropically alignable polymerizable liquid crystal compound and a photoalignable substance; forming a layer of a PAPC material on a support, the liquid crystal molecules being homeotropically aligned; initiating polymerization of the polymerizable liquid crystal in the PAPC layer; exposing the PAPC layer to an alignment light to generate an alignment on a top surface of the layer for the slave material, the generated alignment direction being planar or tilted with respect to the PAPC layer surface in at least one region of the top surface; Includes.

[0038] The term "support" in the phrase "on a support" is intended to include the meaning of a substrate.

[0039] The steps of polymerizing the polymerizable liquid crystal and exposing to the alignment light may be in any order. Polymerization may be initiated before or after exposure to the alignment light. In a particular embodiment of the method, polymerization and alignment are achieved in a single step of exposure to the alignment light. In either case, care must be taken that the liquid crystals maintain their homeotropic configuration while exposed to the alignment light. Preferably, this is done by a step of polymerizing the liquid crystals before exposing the PAPC layer to the alignment light.

[0040] If the PAPC layer is exposed to the orienting light before the liquid crystal is polymerized, care must be taken that the orienting light does not induce a deformation of the homeotropic liquid crystal configuration. For this purpose, it is useful to maintain the temperature of the PAPC material from the time of exposure to the orienting light until the liquid crystal is polymerized and is well below the clearing temperature of the PAPC material. From the time of exposure to the orienting light until the liquid crystal is polymerized, the temperature of the PAPC material is preferably less than 5°C or 10°C below the clearing temperature of the PAPC material. More preferably, the temperature of the PAPC material is less than 20°C, 30°C or 40°C below the clearing temperature, and most preferably, the temperature of the PAPC material is less than 50°C, 60°C or 70°C below the clearing temperature. It is even more preferred that the temperature of the PAPC material is close to room temperature. Particularly preferred is a temperature less than 50°C, more preferably less than 40°C, and most preferably less than 30°C.

[0041] In a preferred embodiment of this method, an alignment light is irradiated from an oblique direction onto the surface of the PAPC layer to generate an inclined alignment, for example to provide a pretilt angle for the liquid crystal.

[0042] When the entire area of ​​the PAPC layer is exposed to the alignment light, the result is uniaxial alignment. The alignment light can be shaped so that only a portion of the PAPC layer is exposed to the alignment light, for example by covering certain areas with a photomask or by scanning the light beam only in the desired areas. Subsequent exposure steps with different polarization planes of alignment light may be added to generate alignment patterns on the PAPC layer. Any other known method of generating alignment patterns by photoalignment, including exposure to alignment light with spatially modulated polarization planes, may be used as well. As a result, multiple alignment directions can be generated on the surface of the PAPC layer. Preferred relative alignment directions are 0°, 45°, 90°, 135° with respect to a reference direction such as the edge of the substrate. Preferred combinations of alignment directions in different areas are 0° and 45°, 0° and 90°, 45° and 135°, with the angles measured with respect to the reference direction.

[0043] The support may be rigid or flexible and may have any form or shape. It may be, for example, an object with a complex surface. In principle, it may consist of any material. Preferably, the support comprises plastic, glass or metal, or is a silicon wafer. If the support is flexible, it is preferably a plastic or metal foil. Preferably, the surface of the support is flat. Preferably, the support is transparent.

[0044] The support may be moving during deposition of the PAPC material. For example, a layer of PAPC material may be produced in a continuous roll-to-roll process by depositing the material composition onto a moving flexible foil, which is preferably plastic or metal.

[0045] The support can have additional layers, such as organic layers, dielectric layers or metal layers. The layers can have different functions, for example, an organic layer can be coated as a primer layer to enhance the compatibility of the material coated with the support. The metal layer can be used as an electrode or can have the function of a reflector, for example, when used in an electro-optical device such as a display. The support can also be an optical element or device with a specific function, such as a substrate for an LCD, which can include thin film transistors, electrodes or color filters. In another example, the support is a device that includes an OLED layer structure. The support can also be a retarder film; a polarizer, such as a polarizing film or sheet polarizer; a reflective polarizer, such as the commercially available Vikuity™ DBEF film.

[0046] The PAPC layer can be applied to the support by any suitable method, such as extrusion, casting, molding, 2D or 3D printing or coating. Suitable coating methods are, for example, spin coating, blade coating, knife coating, kiss roll coating, die coating, dipping, brushing, casting with a bar, roller coating, flow coating, wire coating, spray coating, dip coating, curtain coating, air knife coating, reverse roll coating, gravure coating, metering rod (Meyer bar) coating, slot die (extrusion) coating, roller coating, flexo coating. Suitable printing methods include silk screen printing; letterpress printing such as flexography, jet printing; intaglio printing such as direct gravure printing or offset gravure printing; lithographic printing such as offset printing, or stencil printing such as screen printing.

[0047] The layer of PAPC material need not cover the entire surface of the support, but rather may be applied in the form of a pattern, for example by printing, or may be treated after deposition to have the form of a pattern, for example by photolithographic methods.

[0048] Since the main purpose of the photo-alignable substance in the PAPC layer is to generate alignment on the top surface of the PAPC layer, it is not necessary for the photo-alignable substance to be distributed evenly along the thickness direction of the layer. Therefore, the ratio of the amount of the photo-alignable substance to the amount of other compounds preferably varies along the thickness direction of the layer, which means that there is a concentration gradient of the photo-alignable substance along the thickness direction. Preferably, the concentration of the photo-alignable substance is higher at the top surface of the PAPC layer than at the center of the layer. More preferably, the photo-alignable substance and the polymerizable liquid crystal are phase-separated. Preferably, the phase-separated photo-alignable substance is arranged as a layer above and / or below the polymerizable liquid crystal.

[0049] Since the liquid crystal molecules in a positive c-plate retarder are aligned perpendicular to the support layer, a preferred azimuthal alignment direction does not need to be provided by an alignment layer or other alignment means. It is sufficient that the interaction of the surface of the support with the PAPC material is such that the alignment is homeotropic. The support may already provide such properties without further treatment. Alternatively, a thin layer of the material may be coated on a support specifically designed to support homeotropic alignment of the liquid crystal in the PAPC layer. In either case, it may be useful to increase the temperature of the PAPC layer after deposition of the PAPC material.

[0050] In addition to any of the above variations, the method of the present invention may include the step of applying a slave material onto the oriented surface of the PAPC layer.

[0051] In the context of this application, "slave material" is intended to refer to any material that has the ability to establish anisotropy upon contact with a photo-aligned material.

[0052] The terms "anisotropic" and "anisotropy" may refer, for example, to optical absorption, birefringence, electrical conductivity, molecular alignment; orientation properties of other materials, e.g. liquid crystals, or mechanical properties such as elastic modulus. For example, if the slave material exhibits optical absorption anisotropy for visible light, it can act as a linear polarizer. The term "orientation direction" shall refer to the axis of symmetry of the anisotropic property.

[0053] The slave material may include polymerizable and / or non-polymerizable compounds.

[0054] The slave material can be applied by coating and / or printing, with or without a solvent, and can be applied over the entire area of ​​the PAPC layer or only on a portion of it. Preferably, the method includes a step of heating the slave material before or after application to the PAPC layer. The method can also include a step of initiating polymerization in the slave material by thermal treatment or exposure to actinic light. Depending on the nature of the slave material, it can be useful to carry out the polymerization under an inert atmosphere, such as nitrogen, or under vacuum. The slave material can contain isotropic or anisotropic dyes and / or fluorescent dyes.

[0055] Preferably, the slave material is a self-organizing material, more preferably, the slave material is a liquid crystal material, and especially preferably, the slave material is a liquid crystal polymer (LCP) material.

[0056] Liquid crystal polymer (LCP) material as used within the context of this application shall mean a liquid crystal material comprising liquid crystal monomers and / or liquid crystal oligomers and / or liquid crystal polymers and / or crosslinked liquid crystals. When the liquid crystal material comprises liquid crystal monomers, such monomers can typically be polymerized after anisotropy is created in the LCP material, for example by contact with an alignment layer. Polymerization can be initiated by heat treatment or by exposure to actinic light, preferably UV light. The LCP material may comprise only a single type of liquid crystal compound, but may also comprise additional polymerizable and / or non-polymerizable compounds, in which case not all of the compounds need to be liquid crystal compounds. Furthermore, the LCP material may contain additives, including but not limited to photoinitiators, inhibitors, chiral additives, isotropic or anisotropic fluorescent dyes and / or non-fluorescent dyes, especially dichroic dyes.

[0057] Suitable liquid crystal monomers or prepolymers are disclosed, for example, in WO 2005 / 105932, WO 2005 / 054406, WO 2004 / 085547, WO 2003 / 027056, US 2004 / 0164272, US 6746729, US 6733690, WO 2000 / 48985, WO 2000 / 07975, WO 2000 / 04110, WO 2000 / 05189, WO 99 / 37735, US 6395351, US 5700393, US 5851424 and US 5650534. Preferred liquid crystal monomers or prepolymers have a polymerizable group that is an acrylate or diacrylate, methacrylate, dimethacrylate, allyl, vinyl or acrylamide.

[0058] According to a second aspect of the invention there is provided a PAPC material composition comprising a polymerisable liquid crystal and one or more photoalignable substances for use in the methods and devices according to the invention.

[0059] The PAPC material can contain two or more photoalignable substances.

[0060] The PAPC material may further contain photoinitiators and / or inhibitors, light stabilizers, isotropic or anisotropic fluorescent and / or non-fluorescent dyes, dichroic dyes and / or chiral additives, and other additives to improve the rheological or adhesive properties.

[0061] PAPC materials are preferred in which the weight ratio of the sum of photoalignable substances to the sum of polymerizable liquid crystal compounds is less than 0.5, more preferably less than 0.2, and most preferably less than 0.1. Depending on the thickness of the PAPC layer, the weight percentage of photoalignable substances in the PAPC material can be less than 5%, less than 1% by weight, or less than 0.1% by weight, relative to the solvent-free composition. In extreme cases, 0.01% by weight of photoalignable substances relative to the solvent-free composition is still sufficient to achieve sufficient alignment properties. Preferably, the photoalignable substances contain fluorinated and / or siloxane moieties to support phase separation, and / or are polysiloxanes. Preferably, the photoalignable substances are polymeric and contain fluorinated moieties in the side chains. Examples of photoalignable polysiloxanes are disclosed in WO 2017 / 081056. Photoalignable materials containing fluorinated moieties can be found, for example, in U.S. Pat. No. 8,173,749 (B), U.S. Pat. App. Pub. No. 2011 / 0065859 (A1), U.S. Pat. App. Pub. No. 2012 / 0316317 (A1), U.S. Pat. No. 9,097,938 (B2), U.S. Pat. App. Pub. No. 2016 / 0083655 (A1), U.S. Pat. App. Pub. No. 2016 / 0271894 (A1), and WO 2019 / 030292. These patents and patent applications are incorporated by reference with respect to fluorinated materials. The fluorinated moieties in the examples of the above patents and patent applications are mainly part of the side chains of the polymer. Thus, these side chains strongly affect phase separation. Therefore, for the purposes of the present invention, other main chain structures than the specific main chain structures of the examples in the patents listed above can be used in combination with fluorinated side chain structures. In a preferred embodiment, the PAPC material contains two different types of photoalignable substances, one of which tends to migrate to the top surface of the PAPC layer and the other of which tends to migrate to the bottom of the layer.

[0062] Preferably, the PAPC material comprises the photoalignable substance PA1 which is used in the examples below.

[0063] To support phase separation, the photoalignable material and the polymerizable liquid crystal material may be selected such that the monomer dipole moment of the photoalignable material and the monomer dipole moment of the liquid crystal molecules are different from each other. The monomer dipole moment refers to the dipole moment of the monomer or, in the case of polymers, oligomers and prepolymers, the dipole moment of the monomer units of such polymers, oligomers and prepolymers, respectively. Preferably, the monomer dipole moments differ by more than 0.5 Debye, more preferably by more than 1 Debye, and most preferably by more than 1.5 Debye.

[0064] The photoalignable substance in the PAPC material can be any kind of photosensitive material that can generate anisotropic properties that provide alignment properties for the slave material upon exposure to an orienting light, regardless of the photoreaction mechanism. Thus, suitable photoalignable substances are, for example, materials in which anisotropy is induced upon exposure to an orienting light by photodimerization reaction, photodecomposition, trans-cis isomerization or photo-Fries rearrangement. Preferred PAPC materials include photoalignable substances that can initiate a photodimerization reaction upon exposure to an orienting light.

[0065] As described above, the photo-alignable material comprises a photo-alignable portion, which when exposed to aligning light can develop a preferred direction and thus generate anisotropic properties. Such photo-alignable portion preferably has anisotropic absorption properties. Typically, such portion exhibits absorption in the wavelength range of 230 to 500 nm. Preferably, the photo-alignable portion exhibits absorption in the wavelength range of 300 to 450 nm, more preferably in the wavelength range of 310 to 380 nm.

[0066] Preferably, the photoalignable moiety has a carbon-carbon double bond, a carbon-nitrogen double bond, or a nitrogen-nitrogen double bond.

[0067] For example, the photoalignable moiety can be a substituted or unsubstituted azo dye, anthraquinone, coumarin, melissyanin, 2-phenylazothiazole, 2-phenylazobenzthiazole, stilbene, cyanostilbene, fluorostilbene, cinnamonitrile, chalcone, cinnamate, cyanocinnamate, stilbazolium, 1,4-bis(2-phenylethylenyl)benzene, 4,4'-bis(arylazo)stilbene, perylene, 4,8-diamino-1,5-naphthoquinone dye, aryloxycarboxylic acid derivative, aryl ester, N-arylamide, polyimide, diaryl ketone (having a ketone moiety or ketone derivative conjugated with two aromatic rings, such as substituted benzophenone, benzophenone imine, phenylhydrasmethazone, and hydracarbazone).

[0068] The preparation of the above-listed anisotropic absorbing materials is well known as shown, for example, in Hoffman et al., U.S. Pat. No. 4,565,424; Jones et al., U.S. Pat. No. 4,401,369; Cole, Jr. et al., U.S. Pat. No. 4,122,027; Etzbach et al., U.S. Pat. No. 4,667,020; and Shannon et al., U.S. Pat. No. 5,389,285.

[0069] Preferably, the photoalignable moiety comprises an arylazo, a poly(arylazo), a stilbene, a cyanostilbene, a cinnamate, or a chalcone.

[0070] The photoalignable material may in particular be a monomer, oligomer or polymer. The photoalignable moieties may be, for example, covalently bound within the backbone or side chains of a polymer or oligomer, or may be part of a monomer or other compound that is not polymerizable. The photoalignable material may furthermore be a copolymer comprising different types of photoalignable moieties, or may comprise side chains with and without photoalignable moieties.

[0071] Examples of the polymer include polyacrylate, polymethacrylate, polyimide, polyurethane, polyamic acid, polymaleimide, poly-2-chloroacrylate, poly-2-phenylacrylate, unsubstituted or C1 to C6 alkyl-substituted polyacrylamide, polymethacrylamide, poly-2-chloroacrylamide, poly-2-phenylacrylamide, polyether, polyvinyl ether, polyester, polyvinyl ester, polystyrene derivative, polysiloxane, linear or branched alkyl ester of polyacrylic acid or polymethacrylic acid, polyphenoxyalkylacrylate, polyphenoxyalkylmethacrylate, polyphenylalkylmethacrylate having an alkyl residue having 1 to 20 carbon atoms, polyacrylonitrile, polymethacrylonitrile, cycloolefin polymer, polystyrene, poly-4-methylstyrene, or a mixture thereof.

[0072] The photoalignable material may also include a photosensitizer, such as a ketocoumarin or a benzophenone.

[0073] Further preferred photoalignable monomers or oligomers or polymers are described in US Pat. No. 5,539,074, US Pat. No. 6,201,087, US Pat. No. 6,107,427, US Pat. No. 6,632,909 and US Pat. No. 7,959,990.

[0074] According to a third aspect of the invention there is provided a stack of anisotropic layers produced by using a method according to the invention, as well as associated materials.

[0075] Structure 1 in FIG. 1 shows a PAPC layer 12 on a substrate 11 used as a support. The liquid crystal in the PAPC layer is homeotropically aligned so that the PAPC layer forms a positive c-plate retarder. To support homeotropic alignment of the liquid crystal, the surface of the substrate can be modified by a surface treatment such as plasma or corona treatment. The substrate can also include a layer of a material that provides the appropriate surface energy to homeotropically align the liquid crystal in the PAPC layer. After exposure to an alignment light, which crosslinks the liquid crystal in the PAPC layer and can be performed in a single irradiation step, the surface of the PAPC layer provides alignment capability for planar or tilted alignment of a slave material such as a liquid crystal material.

[0076] In structure 2 of Figure 2, a layer 13 of a slave material, such as a cross-linkable liquid crystal material, is applied directly to the surface of the PAPC layer. was done The slave material is oriented by the surface. Preferably, the slave material comprises an LCP material. The LCP material may further comprise additives such as dichroic dyes and / or chiral additives. Thus, layer 13 may be birefringent, may act as a polarizer, may be twisted, or may be cholesteric. The LCP molecules in layer 13 may be planar or tilted.

[0077] Preferably, layer 13 is birefringent and planar Oriented It comprises liquid crystals, where planar means parallel to the surface of the layer. In this case, structure 2 in FIG. 2 combines a positive c-plate retarder with a planar retarder (a-plate). It is noted that this structure can be made with as few as two layers. Preferably, layer 13 acts as a 1 / 4 wave or 1 / 2 wave retarder. It is particularly preferred that layer 13 is an achromatic retarder.

[0078] For most applications, the out-of-plane retardation Rth of the PAPC layer is less than -10 nm, preferably less than -50 nm, more preferably less than -100 nm. Rth = ((n x +n y) / 2-n z ) × d, In the formula, n x , n y is the refractive index in the substrate plane, and n z is the refractive index perpendicular to the substrate plane, and d is the layer thickness.

[0079] For typical materials for the PAPC layer, the thickness of the PAPC layer is greater than 100 nm, preferably greater than 500 nm, and more preferably greater than 1 μm. In some applications, the thickness of the PAPC layer is greater than 2 μm, or even greater than 3 μm.

[0080] Layer structures according to the present invention may be used in combination with organic light emitting devices (OLEDs), such as, for example, brightness enhancement films for LCDs, displays or OLED lighting applications, and as part of anti-reflection structures for displays. Working Example Materials used in the examples compound Photo-alignment material PA1 [ka] Synthesised as described in WO 2019 / 030292. Liquid crystal monomer LCM1 [ka] Liquid crystal monomer LCM2 [ka] Liquid crystal monomer LCM3 [ka] Liquid crystal monomer LCM4 [ka] Liquid crystal monomer LCM5 [ka] Liquid crystal monomer LCM6 [ka] Liquid crystal monomer LCM7 [ka] Dichroic dye dDye [ka] Prepared according to WO 2015 / 177062. solution S-LCP1 33.43wt% LCM4 0.70 wt% Photoinitiator - Irgacure OXE 02 (BASF) 0.70% by weight Kayarad DPCA-20 (Nippon Kayaku) 0.07% by weight Tinuvin 123(BASF) 0.01% by weight BHT (Aldrich) 0.09wt% Tego Flow 300(Tego Chemi Essen) solvent 52.00% by weight Butyl acetate 13.00% by weight Cyclohexanone (CHN)

[0081] A solution S-LCP1 is prepared by dissolving the substance in a mixture of solvents and stirring the solution at room temperature for 30 minutes. S-LCP 2 (homeotropic alignment LCP) material 19.56wt% LCM2 4.89wt% LCM3 0.50% by weight Irgacure 369(BASF) 0.05% by weight BHT (Aldrich) solvent 60.00% by weight methyl ethyl ketone (MEK) 15.00wt% CHN

[0082] A solution of S-LCP2 is prepared by dissolving the substance in a mixture of solvents and stirring the solution at room temperature for 30 minutes. S-dLCP material 35.12wt% LCM6 4.00wt% dDye 0.80% by weight Irgacure 369(BASF) 0.08% by weight BHT (Aldrich) solvent 48.00% by weight methyl ethyl ketone (MEK) 12.00wt% CHN

[0083] Solution S-dLCP is prepared by dissolving the material in a mixture of solvents and stirring the solution at room temperature for 30 minutes. S-cLCP material 14.2wt% LCM4 9.9wt% LCM7 1wt% LumogenS 750(BASF) 0.8% by weight Irgacure 907(BASF) 0.06% by weight Irgafos 168 (BASF) 0.04% by weight BHT (Aldrich) solvent 59.2% by weight Methyl propyl ketone 7.4% by weight dioxalane 7.4wt% CHN

[0084] Solution S-cLCP is prepared by dissolving the substance in a mixture of solvents and stirring the solution at room temperature for 30 minutes. S-PAPC 1 (PAPC material) material 9.70wt% LCM1 9.70wt% LCM2 4.80wt% LCM3 0.25wt% PA1 0.50% by weight Irgacure 369(BASF) 0.05% by weight BHT (Aldrich) solvent 60.00wt% MEK 15.00wt% CHN

[0085] A solution S-PAPC1 is prepared by dissolving the substance in a mixture of solvents and stirring the solution at room temperature for 30 minutes. S-PAPC 2 (PAPC material) material 18.34wt% LCM1 6.11wt% LCM3 0.25wt% PA1 0.50% by weight Irgacure 369(BASF) 0.05% by weight BHT (Aldrich) solvent 60.00wt% MEK 15.00wt% CHN

[0086] A solution S-PAPC2 is prepared by dissolving the substance in a mixture of solvents and stirring the solution at room temperature for 30 minutes. S-PAPC3 material 19.00wt% LCM2 8.10wt% LCM5 0.30wt% PA1 0.55% by weight Irgacure 369(BASF) 0.05% by weight BHT (Aldrich) solvent 72.00wt% MEK Solution S-PAPC3 is prepared by dissolving the substance in MEK solvent and stirring the solution at room temperature for 30 minutes.

[0087] Example 1 The surface of a 100 μm cycloolefin polymer (COP, Zeonor ZF 16-100 manufactured by Zeon) plastic substrate was activated with O2 plasma: power 80% (200 W, 40 kHz), O2 flow rate 5 sccm, time 3 min.

[0088] The COP substrate was then Kbar coated (bar size 1) with solution S-PAPC1 and annealed in an oven at 50 °C for 5 min. Then, at room temperature under N2 atmosphere, 200 mJ / cm 2 The film was exposed to linearly polarized UVB light at 1000 nm. The film was then visually observed between crossed polarizers. When viewed perpendicular to the substrate, the film was found to appear dark, independent of the azimuthal angle of the substrate relative to the polarizers. However, when viewed at an oblique angle, the film became bright. It was concluded that the film produced was birefringent with its optic axis perpendicular to the substrate. Thus, the liquid crystals of the mixture were homeotropically aligned.

[0089] Then, solution S-LCP1 was directly coated onto the PAPC1 layer by bar coating (k bar 1, speed 8) and annealed in an oven at 50 °C for 2 min. Finally, 1.5 J / cm was applied under N2 atmosphere. 2 The film was crosslinked by exposure to UVA light.

[0090] The film was then again visually observed between crossed polarizers, where, when viewed perpendicular to the substrate, it was found to be uniaxially Oriented It was found that a birefringent film was produced with a well-defined alignment of the optic axis. Conoscopic observation under a polarizing microscope with a tilt compensator revealed that the optic axis was planar and parallel to the polarization direction of the UVB light irradiated on the PAPC1 layer. It was concluded that an alignment was produced on the surface of the PAPC1 layer, which oriented the LCP1 liquid crystal along the induced alignment direction.

[0091] The resulting film structure was then further evaluated with a polarimeter (AxoScan, Axometrics). Both the in-plane retardance (R0) and out-of-plane retardance (Rth) of the PAPC1 and LCP1 layers were extracted from the measurements at 550 nm, resulting in Rth=-145 nm and R0=178 nm.

[0092] The values ​​R0 and Rth are defined as follows: R0=(n x -n y )×d Rth = ((n x +n y ) / 2-n z ) × d, In the formula, n x , n y is the refractive index in the substrate plane, and n z is the refractive index perpendicular to the substrate plane, and d is the layer thickness.

[0093] Example 2 A plasma-treated COP film was used as the substrate, as in Example 1. Solution S-PAPC2 was Kbar coated (bar size 1) onto the COP substrate and annealed in an oven at 50 °C for 5 min. Then, 200 mJ / cm was applied at room temperature under N2 atmosphere. 2 The film was exposed to linearly polarized UVB light at 1000 nm. The film was then visually observed between crossed polarizers. When viewed perpendicular to the substrate, the film was found to appear dark, independent of the azimuthal angle of the substrate relative to the polarizers. However, when viewed at an oblique angle, the film became bright. It was concluded that the film produced was birefringent with its optic axis perpendicular to the substrate. Thus, the liquid crystals of the mixture were homeotropically aligned.

[0094] Solution S-LCP1 was then directly coated onto the PAPC2 layer by bar coating (k bar 1, speed 8) and annealed in an oven at 50 °C for 2 min. Finally, it was coated with 1.5 J / cm under N2 atmosphere. 2 The film was crosslinked by exposure to UVA light.

[0095] The film was then again visually observed between crossed polarizers, where, when viewed perpendicular to the substrate, it was found to be uniaxially Oriented It was found that a birefringent film was produced with a well-defined alignment of the optic axis. Conoscopic observation under a polarizing microscope with a tilt compensator showed that the optic axis was planar and parallel to the polarization direction of the UVB light irradiated on the PAPC2 layer. It was concluded that an alignment was produced on the surface of the PAPC2 layer, which oriented the LCP1 liquid crystal along the induced alignment direction.

[0096] The resulting film structure was then further evaluated with a polarimeter (AxoScan, Axometrics). Both the in-plane retardance (R0) and out-of-plane retardance (Rth) of the PAPC2 and LCP1 layers were extracted from the measurements at 550 nm, resulting in Rth=-288 nm and R0=178 nm.

[0097] Comparative Example 1 A plasma-treated COP film was used as the substrate, as in Example 1. The COP substrate was Kbar coated (bar size 1) with solution S-LCP2 and annealed in an oven at 50 °C for 5 min. Then, 200 mJ / cm was applied at room temperature under N2 atmosphere. 2 The film was exposed to linearly polarized UVB light at 1000 nm. The film was then visually observed between crossed polarizers. When viewed perpendicular to the substrate, the film was found to appear dark, independent of the azimuthal angle of the substrate relative to the polarizers. However, when viewed at an oblique angle, the film became bright. It was concluded that the film produced was birefringent with its optic axis perpendicular to the substrate. Thus, the liquid crystals of the mixture were homeotropically aligned.

[0098] The resulting films were evaluated with a polarimeter (AxoScan, Axometrics) to determine the out-of-plane retardation (Rth) of the LCP2 layer, and a value of Rth = -306 nm was determined.

[0099] Solution S-LCP1 was then directly coated onto the LCP2 layer by bar coating (k bar 1, speed 8) and annealed in an oven at 50 °C for 2 min. Finally, 1.5 J / cm was applied under N2 atmosphere. 2 The film was crosslinked by exposure to UVA light.

[0100] The film was again visually observed between crossed polarizers. Here, the film was found to appear bright, independent of the azimuthal angle of the substrate with respect to the polarizers. However, instead of uniaxial alignment, Schlieren texture was observed, meaning that no preferred azimuthal alignment was provided by the homeotropic LCP2 layer. Thus, the liquid crystals in the LCP1 layer did not align.

[0101] Example 3: Patterned Retarder A plasma-treated COP film was used as the substrate as in Example 1. The COP substrate was Kbar coated (bar size 1) with solution S-PAPC3 and annealed in an oven at 50° C. for 5 min.

[0102] An alignment pattern was generated on the surface of the PAPC3 layer by a two-step exposure process. In the first step, the PAPC3 layer was exposed to 1000 mJ / cm2 of light in a N2 atmosphere through a photomask with opaque and transparent areas, with a polarization direction of 0° relative to the reference edge of the substrate. 2 In a second step, the PAPC3 layer was exposed to 500 mJ / cm2 of parallel linearly polarized UVB light without a photomask and with a polarization direction of 45° to the reference edge of the substrate under a N2 atmosphere. 2 The animals were exposed to 1000 Hz of parallel linearly polarized UVB light.

[0103] The film was then visually observed between crossed polarizers. When viewed perpendicular to the substrate, the film was found to appear dark, independent of the azimuthal angle of the substrate relative to the polarizers. However, when viewed at an oblique angle, the film became bright. It was concluded that the film produced was birefringent with its optic axis perpendicular to the substrate. Thus, the liquid crystals of the mixture were homeotropically aligned.

[0104] On top of the exposed PAPC3 layer, a layer was formed from LCP solution S-LCP1 by KBar coating (bar size 1). The wet film was annealed and dried in an oven at 50 °C for 60 s, followed by exposure to 1500 mJ / cm2 high pressure mercury lamp. 2 The film was crosslinked at room temperature under nitrogen by irradiation with 1000 dpi at 1000 dpi. Observation of the film through crossed polarizers showed that it acted as a patterned retarder. When the film was rotated so that the reference edge of the substrate was aligned with the polarization direction of one of the crossed polarizers, the area exposed in the first step appeared dark while the other area became light. Rotating the device by 45° reversed the appearance of the two areas, with the previously dark areas now light and the previously light areas now dark.

[0105] Example 4: Patterned polarizer A PAPC3 layer was coated onto the plasma-treated COP, annealed, dried, and exposed as in Example 3, except that 0° and 90° were selected for the polarization direction of linearly polarized UVB light (instead of 0° and 45°).

[0106] A layer was formed from solution S-dLCP on the exposed PAPC3 layer by KBar coating (bar size 3). The wet film was annealed and dried in an oven at 95 °C for 120 s, followed by exposure to 1500 mJ / cm2 high pressure mercury lamp. 2 The polymer was then crosslinked at room temperature under nitrogen by irradiation.

[0107] When the film was observed through a polarizer, it was found to act as a patterned polarizer. If the film was rotated so that the reference edge of the substrate was aligned with the absorption axis of the polarizer, the areas exposed in the first step would appear light, while the other areas would become dark. If the device was rotated 90°, the appearance of the two areas would be reversed, with the previously dark areas now light and the previously light areas now dark.

[0108] Example 5: Cholesteric Device A plasma-treated COP film was used as the substrate as in Example 1. The COP substrate was Kbar coated (bar size 1) with solution S-PAPC3 and annealed in an oven at 50° C. for 5 min.

[0109] 1000mJ / cm under N2 atmosphere at room temperature 2 The film was exposed to linearly polarized UVB light.

[0110] On top of the exposed PAPC3 layer, a layer was formed from a cholesteric LCP solution, S-cLCP, by KBar coating (bar size 1). The wet film was annealed and dried in an oven at 99 °C for 60 s, followed by exposure to 1500 mJ / cm2 high pressure mercury lamp. 2 The film was crosslinked at room temperature under nitrogen by irradiation with UV light. The film was found to behave as a well-ordered cholesteric film, exhibiting a blue coloration in reflection. When the film was viewed at oblique incidence, it exhibited a red shift. The invention and different embodiments can be summarized by the following clauses. 1. Photoalignment was done Positive c-plate retarder layer A method for manufacturing an optical element (1, 2) comprising the steps of: providing a PAPC material composition comprising a homeotropically oriented polymerizable liquid crystal and a photoalignable material; forming a layer (12) of PAPC material on a support (11), in which the liquid crystal molecules are homeotropically aligned; initiating polymerization of the polymerizable liquid crystal in the PAPC layer; exposing the PAPC layer (12) to an orienting light to generate an orientation on the top surface of the layer for the slave material, the generated orientation direction being planar or tilted with respect to the PAPC layer surface in at least one region of the top surface; The method includes: 2. The method according to clause 1, wherein polymerization of the polymerizable liquid crystal is initiated before the PAPC layer (12) is exposed to the aligning light. 3. The method according to clause 1, wherein polymerization of the polymerizable liquid crystal is initiated after the PAPC layer (12) is exposed to an aligning light. 4. The method according to clause 1, wherein the polymerization and orientation of the polymerizable liquid crystal is initiated in a single step of exposing the PAPC layer (12) to an aligning light. 5. The method of any one of clauses 1 to 4, wherein the photoalignable material in the PAPC layer has a density gradient such that the concentration of photoalignable material is higher at the top surface of the PAPC layer than in the center of the layer. 6. The method of any one of clauses 1 to 5, wherein the photoalignable material comprises fluorinated and / or siloxane moieties and / or is a polysiloxane. 7. The method of any one of clauses 1 to 6, wherein in an additional step a slave material is applied on top of and in direct contact with the PAPC layer. 8. A layer structure (1, 2) comprising a PAPC layer (12), the layer structure comprises a polymerized liquid crystal monomer; the polymerized liquid crystal monomer is homeotropically oriented and provides alignment capability on the surface; The alignment capability allows the alignment of the slave material planar or at an angle to the surface of the PAPC layer, a layer structure (1, 2). 9. The layer structure of clause 8, wherein the photoalignable material in the PAPC layer (12) has a density gradient such that the concentration of photoalignable material is higher at the top surface of the PAPC layer than in the center of the layer. 10. A layer structure according to claim 8 or 9, wherein the photoalignable material comprises fluorinated and / or siloxane moieties and / or is a polysiloxane. 11. A layer structure according to any one of clauses 8 to 10, wherein the PAPC material comprises a dichroic dye. 12. A layer structure according to any one of clauses 8 to 11, having an additional anisotropic layer (13) in direct contact with the PAPC layer, said additional layer comprising a liquid crystal polymer, and the liquid crystal polymer of said additional layer being oriented according to the orientation information of the PAPC layer. 13. A layer structure according to clause 12, wherein the PAPC layer (12) acts as a positive c-plate retarder and the additional layer comprising a liquid crystal polymer acts as a planar retarder. 14. A composition comprising a homeotropically alignable polymerizable liquid crystal and a photoalignable substance, wherein the weight percentage of the photoalignable substance is less than 5%, less than 1% by weight, or even less than 0.1% by weight based on the composition without solvent, and the photoalignable substance comprises fluorinated and / or siloxane moieties and / or is a polysiloxane. 15. The composition of claim 14, wherein the photoalignable material is a polymer and contains fluorinated moieties in the side chains.

Claims

1. 1. A method for manufacturing an optical element including a photo-aligned positive c-plate retarder layer, comprising: providing a light-aligning positive C-plate (PAPC) material composition comprising a homeotropically alignable polymerizable liquid crystal and a photo-alignable material; forming a PAPC layer of the PAPC material composition on a support, the polymerizable liquid crystal being spontaneously homeotropically aligned without providing an azimuthal alignment direction; initiating polymerization of the polymerizable liquid crystal within the PAPC layer; exposing the PAPC layer to an alignment light to generate an alignment on a top surface of the PAPC layer for a slave material, the generated alignment direction being planar or tilted with respect to the PAPC layer surface in at least one region of the top surface; The method includes:

2. The method of claim 1 , wherein polymerization of the polymerizable liquid crystal is initiated before the PAPC layer is exposed to an aligning light.

3. The method of claim 1 , wherein polymerization of the polymerizable liquid crystal is initiated after the PAPC layer is exposed to an aligning light.

4. The method of claim 1 , wherein polymerization and orientation of the polymerizable liquid crystal is initiated in a single step of exposing the PAPC layer to an aligning light.

5. 5. The method of claim 1, wherein the photoalignable substance in the PAPC layer has a density gradient such that the concentration of the photoalignable substance is higher at the top surface of the PAPC layer than at the center of the PAPC layer.

6. The method according to any one of claims 1 to 5, wherein the photoalignable material comprises fluorinated and / or siloxane moieties and / or is a polysiloxane.

7. The method of any one of claims 1 to 6, wherein in an additional step a slave material is applied on top of and in direct contact with said PAPC layer.

8. A layer structure including a PAPC layer, The PAPC layer includes a homeotropically oriented liquid crystal polymer and a photoalignable material; providing orientation capability on said surface; A layer structure in which the alignment capability allows alignment of a slave material planar or at an angle to the surface of the PAPC layer.

9. 9. The layer structure of claim 8, wherein the photoalignable material in the PAPC layer has a density gradient such that the concentration of the photoalignable material is higher at the top surface of the PAPC layer than at the center of the PAPC layer.

10. 10. A layer structure according to claim 8 or 9, wherein the photoalignable material comprises fluorinated and / or siloxane moieties and / or is a polysiloxane.

11. The layer structure according to any one of claims 8 to 10, wherein the PAPC layer is obtained by a light-aligning positive C-plate (PAPC) material composition comprising a homeotropically alignable polymerizable liquid crystal, a photo-alignable substance, and one or more dichroic dyes.

12. 12. The layer structure of claim 8, further comprising an additional anisotropic layer in direct contact with the PAPC layer, the additional layer comprising a liquid crystal polymer, the liquid crystal polymer of the additional layer being oriented according to the orientation information of the PAPC layer.

13. 13. The layer structure of claim 12, wherein the PAPC layer acts as a positive c-plate retarder and the additional layer comprising a liquid crystal polymer acts as a planar retarder.

14. A composition comprising a homeotropically alignable polymerizable liquid crystal and a photoalignable material, the weight percentage of the photoalignable material being less than 5% by weight of the composition without solvent, and the photoalignable material comprising fluorinated and / or siloxane moieties and / or being a polysiloxane.

15. 15. The composition of claim 14, wherein the weight percentage of the photoalignable material is less than 1% by weight of the composition without solvent.

16. 16. The composition of claim 15, wherein the weight percentage of the photoalignable material is less than 0.1% by weight of the composition without solvent.

17. The composition of any one of claims 14 to 16, wherein the photoalignable material is a polymer and contains fluorinated moieties in the side chains.

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