Transparent multilayer system

Abstract

The present invention relates to a transparent multilayer system, comprising a transparent multilayer system comprising: a layer L1 made of a transparent material, the layer L1 having at least one surface with microstructures, the microstructures providing glare control properties for the layer L1; and a layer L2 composed of one or more transparent materials that provide anti-reflective properties to layer L2 wherein layer L2 is on top of the surface of layer L1 having these microstructures. The invention further relates to a method for producing such a multilayer system, to the use thereof as a glare control structure, and to a luminaire comprising a light emitting device and such a multilayer system.

Description

[0001] The present invention relates to: a transparent multi-layer system with improved glare control, the transparent multi-layer system comprising a layer L1 containing microstructures and a layer L2 formed on top of the layer L1; and a method of producing such a transparent multi-layer system. The present invention further relates to the use of the transparent multi-layer system for optical components and lighting devices (such as luminaires) and to luminaires comprising such a transparent multi-layer system. Background Art

[0002] Luminaires are ubiquitous in daily life in order to provide sufficient light at any time of the day. This applies to both indoor and outdoor luminaires, as luminaires are used in the home or office, but also outdoors (for example at tram stops). The classic quality characteristics of lighting are sufficient lighting levels, a harmonic distribution of brightness, prevention of reflections and mirror images, correct light color and suitable color reproduction. When light is transmitted from one medium (such as air) into a second medium (such as glass or plastic), reflection of the light rays occurs. The degree of reflection can be calculated using the Fresnel equations. Thereby, it can be determined that the reflection of yellow-green light with a wavelength of 550 nm on glass without any anti-reflection coating is approximately 4%.

[0003] When light is emitted by a luminaire, some light rays leave the luminaire at glare propagation angles, which represent large angles relative to the perpendicular of the light-emitting surface, thereby causing discomfort to the occupants in the illuminated space or even violating lighting regulations (such as in an office).

[0004] Glare control structures can be applied to suppress glare beams leaving the luminaire and to increase the total non-glare luminous flux. Such products are, for example, transparent films or rigid panels comprising microstructures on the surface, where the smooth surface is attached to the luminaire. The light rays incident on the microstructures are refracted in such a way that they are bent towards a direction perpendicular to the substrate surface of the structure at a light propagation angle. Thereby, the luminous intensity distribution curve of the luminaire is narrowed to lower angles and the glare is controlled. Glare control structures are known, for example, from CH 711561A1 and CH 711562A1, which patents disclose optical foils containing microstructures with a plurality of elevations. Such structures are widely used because they reduce glare beams and thus provide more comfortable light for people in the illuminated area. However, the inventors of the present invention have observed that the structures of the prior art are not sufficient to effectively control glare beams, as glare beams are still observed and cause discomfort or even violate lighting regulations (such as in an office). In the past, improvements have been achieved by modifying the shape of the structure, for example by changing the geometry or the angles of the corresponding microstructures.

[0005] However, although structures as described in CH 711561A1 and CH 711562A1 are applied on top of a luminaire (such as a lighting fixture), resulting in a certain degree of glare control, better control of the glare beam is still needed so that the luminaire can provide a higher non-glare luminous flux and thus a high available luminous flux, and the occupants in the illuminated space are not disturbed by the glare beam. The Unified Glare Rating (UGR) is used for the assessment of discomfort glare. When determining the UGR value, all the light in the system that contributes to the glare impression is considered. The UGR limit value is specific to the corresponding activities carried out in the illuminated room (such as technical drawing, reading, or general work in the industry). Controlling the glare beam and complying with the UGR limit value are extremely important because the glare beam causes a decrease in the attention and fatigue of the person affected by the glare.

[0006] The object of the present invention is to improve the glare control of known glare control structures and to provide a higher non-glare luminous flux. Therefore, it aims to better control the light rays leaving the prior art structures at the glare propagation angle. Thereby, glare can be reduced and the available luminous flux can be increased. In particular, the occupants in the illuminated space should not be disturbed by the glare beam. Summary of the Invention

[0007] The main object has been solved by the subject matter of the present application and by its preferred embodiments disclosed in this specification.

[0008] The first subject matter of the present invention is a transparent multi-layer system, which comprises

[0009] a) a layer L1 made of a transparent material, which layer L1 has at least one surface with microstructures that provide glare control properties for the layer L1, and

[0010] b) a layer L2 made of one or more transparent materials, which one or more transparent materials provide anti-reflection properties for the layer L2,

[0011] wherein the layer L2 is on top of the surface of the layer L1 having these microstructures.

[0012] The above-mentioned transparent multi-layer system is referred to herein as the "transparent multi-layer system according to the present invention" or the "multi-layer system according to the present invention".

[0013] The present invention further provides a method for producing a transparent multi-layer system according to the present invention as a second subject matter, which method comprises the following steps:

[0014] i. forming the layer L1, which layer includes microstructures on at least one surface, preferably on one surface, and then

[0015] ii. forming the anti-reflection layer L2 by

[0016] a. Deposit one or more coating materials on top of the microstructured surface of layer L1 to form an antireflection coating L2, or

[0017] b. Remove material from the microstructured surface portion of layer L1, thereby maintaining the shape of the microstructure and thus forming an antireflection layer L2 from the same material as layer L1.

[0018] Another subject of the present invention is a transparent multilayer system obtainable by the method according to the invention.

[0019] A fourth subject of the present invention is the use of the transparent multilayer system according to the invention as a glare control component in a lighting device, such as a luminaire. This component is intended to be located between a light source and a person exposed to the light transmitted through the component.

[0020] Yet another subject of the present invention is a luminaire comprising a light source and a transparent multilayer system according to the invention. Detailed Description

[0021] Definitions

[0022] The term "transparent" refers to the transmittance of visible light through a transparent medium, such as the materials constituting the multilayer system according to the invention.

[0023] A "transparent medium" is a medium that allows visible light to be transmitted substantially without significant scattering. This is in contrast to an opaque medium, which does not allow light to be transmitted on a medium such as opal glass, also known as translucent glass, which allows the transmission of visible light, but it is not transparent, but rather an "opal" medium. In the context of the present invention, preferably, a light transmittance of greater than 80% through each layer material of the multilayer system should be observed. The light transmittance is determined using ASTM D-1003 (Standard Test Method for Haze and Light Transmittance of Transparent Plastics).

[0024] The term "antireflection" (also commonly abbreviated as AR) refers to a type of coating or treatment applied to an optical surface, such as a lens or a screen, to reduce or eliminate light reflection at the interface between the surface and the surrounding medium. Antireflection coatings act by utilizing the interference principle of multilayer thin films with different refractive indices applied to the surface or by forming a refractive index gradient between the medium and the surface. Compared to a conventional transparent substrate, this gradient helps to reduce the sudden change in refractive index, thereby minimizing the light reflection perceived by an observer ( Figure 1B)。By reducing reflection, an anti-reflection coating enhances the clarity, contrast, and brightness of transmitted or reflected light. They are commonly used in a variety of optical applications, including glasses, camera lenses, microscopes, telescopes, solar panels, and displays. Different materials (such as magnesium fluoride or titanium dioxide) can be used to produce an anti-reflection coating, and the number and thickness of the layers can be optimized for a specific wavelength or range of light.

[0025] The term "anti-glare" (also commonly abbreviated as AG) refers to a type of optical layer or interface used to reduce or eliminate reflections or glare caused by ambient light or direct light sources, such as a screen or lens. Anti-glare coatings work by diffusing or scattering the light that strikes the surface of the external light source without reflecting it back to the viewer ( Figure 1C ). This results in a clearer and more comfortable image with less eye strain and visual fatigue. Anti-glare coatings are commonly used on computer monitors, smartphones, televisions, glasses, camera lenses, and other optical devices. The anti-glare layer can be a microstructure with many different angles of inclination to the surface, such as a randomized structure or a layer containing scattering centers, or can be made of a variety of materials (such as silica, titanium dioxide, or polyurethane), which can be applied using various methods (such as vacuum deposition, spraying, or lamination).

[0026] On the other hand, as used herein, the term "glare control" refers to the ability of an optical layer or interface to reduce or eliminate the harsh, uncomfortable, and potentially dangerous effects of excessive brightness or glare from a light source (such as artificial lighting) transmitted through such a surface. That is, in contrast to "anti-glare", the observer faces a beam of light that is transmitted through the optical layer or interface rather than being diffusely reflected from the optical layer or interface. In glare control, the observer and the light source are on opposite sides of such an optical layer or interface. Glare control works by modifying the optical path of the light transmitted through the optical layer or interface such that a beam of light incident on one side of the optical layer or interface exits the other side at a lower angle (relative to the surface normal of the substrate) after passing through ( Figure 1F ).

[0027] Figures 1A to 1H Further clarifying the differences between anti-reflection (AR), anti-glare (AG), and glare control (GC) as used herein, as well as combinations of anti-reflection (AR) layers and anti-glare (AG) layers known in the literature and combinations of anti-reflection (AR) layers and glare control (GC) layers disclosed herein according to the present invention, to unexpectedly further reduce or eliminate glare caused by a beam of light transmitted through a glare control (GC) structure.

[0028] Figure 1AA schematic diagram of a light beam incident on a plane-parallel transparent substrate is given. The incident light beam is partially specularly reflected and partially transmitted. For clarity of graphical representation, the partial reflection at the second interface between the material and air is omitted. Figure 1B A schematic diagram of a light beam incident on a plane-parallel transparent substrate is given, where an antireflection layer is present on the side of the substrate facing the light source. The incident light beam is partially specularly reflected and partially transmitted. As a result, the reflection reaching the observer is strongly reduced to ideally close to zero percent.

[0029] Figure 1C A schematic diagram of a light beam incident on a plane-parallel transparent substrate is given, where an antiglare structure is present on the side of the substrate facing the light source. The incident light beam is partially reflected and partially transmitted, whereby the amount of reflection is similar to that of the transparent substrate ( Figure 1A ). Thus, the reflection is diffuse rather than specular. That is, a light beam incident on the surface from one direction is reflected in multiple directions. For this purpose, the antiglare layer can be a microstructure with many different tilt angles to the surface, such as a randomized structure or a layer containing scattering centers.

[0030] Figure 1D A schematic diagram of a light beam incident on a plane-parallel transparent substrate is given, where an antiglare structure and an antireflection layer are present on the side of the substrate facing the light source. The incident light beam is partially reflected and partially transmitted, whereby the antireflection layer strongly reduces the amount of reflection, and the antiglare layer diffuses this strongly reduced amount of reflection. Thus, the combination of the antireflection and antiglare layers results in an even stronger suppression of the glare of the reflected light rays from the same side of the substrate as the light source. Exemplary patent applications regarding "antiglare" and antireflection can be found, for example, in JP 2022015702 A1 and US2015 / 0226882 A1.

[0031] Figure 1E A schematic diagram of a light beam incident on a plane-parallel transparent substrate and transmitted through it is given. The incident light beam and the transmitted light beam have the same propagation direction. Thus, a light beam at a high angle of incidence with respect to the surface normal continues to propagate at such a high angle after leaving the substrate. In a lamp, for example, such high-angle light rays increase the glare perceived by the observer.

[0032] Figure 1FA schematic view of a light beam incident on a transparent substrate and transmitted therethrough is given, where a glare control feature is present on the surface facing away from the light source. The incident light beam and the transmitted light beam do not have the same propagation direction because the angle of the transmitted light beam is changed by the glare control structure. The transmitted light beam will propagate at an angle lower than that of the incident light beam with respect to the surface normal of the substrate. Thereby, the glare perceived by the observer is reduced. Exemplary patent applications regarding "glare control" can be found, for example, in CH711561A1 and CH 711562A1.

[0033] Figure 1G corresponds to Figure 1F the arrangement, where a partial reflection of the incident light beam at the interface between the glare control structure and air is additionally shown, and where this partially reflected light beam leaves the glare control structure at an angle higher with respect to the surface normal and thus more harmful in terms of glare after an intermediate reflection at the incident side of the substrate.

[0034] Figure 1H A schematic view of the present invention is given where a light beam is incident on a transparent substrate and transmitted through the transparent substrate, where a glare control feature and an antireflection layer (AR) are present on the surface facing away from the light source. The antireflection layer strongly reduces (ideally to zero percentage) the partial reflection at the interface between the glare control structure and air, thereby reducing the amount of glare after the intermediate internal reflection.

[0035] Transparent multilayer system.

[0036] The transparent multilayer system of the present invention comprises or consists of the following: a layer L1 made of a transparent material, which layer L1 has at least one surface with microstructures that provide glare control properties for layer L1; and an antireflection layer L2 made of one or more transparent materials, which one or more transparent materials provide antireflection properties for layer L2, where layer L2 is on top of the surface of layer L1.

[0037] Hereinafter, layer L1 is also referred to as "glare control layer L1" or simply as "glare control layer", while layer L2 is also referred to as "antireflection layer L2" or simply as "antireflection layer".

[0038] In the context of the present invention, the antireflection layer L2 improves the glare control properties of layer L1, and thus the transparent multilayer system of the present invention provides improved glare control properties.

[0039] The inventors of the present invention have found that the combination of a first layer having glare control properties and a second layer having antireflection properties results in improved glare control.

[0040] Both types of layers L1 and L2 have been found in the prior art and described in the prior art. However, a combination of the two types of layers has not been envisioned to improve glare control. Below, the two layers and their production methods are described in more detail.

[0041] Layer L1

[0042] Layer L1 provides at least one surface, preferably one surface, which has a microstructure imparting a certain degree of glare control characteristics to the layer L1, as described, for example, in CH 711561A1 or CH 711562A1.

[0043] Microstructure shape, size, and pattern of the microstructure

[0044] Like each layer, layer L1 has two surfaces, where at least one, preferably one, of these two surfaces has a microstructure. The microstructure typically forms a pattern, preferably a regular pattern, which is responsible for the glare control characteristics of the layer L1. Preferably, one surface of layer L1 has a microstructure and the other surface is a smooth surface (i.e., a flat surface without a microstructure). In the uses described below according to the invention, the smooth side is typically the side facing the light source.

[0045] The microstructure preferably has a height in the range of 5 μm to 5000 μm, more preferably 5 μm to 1000 μm, more preferably 5 μm to 500 μm or 5 to 300 μm, even more preferably 5 to 150 μm, such as 30 to 120 μm or 30 to 100 μm. The "height of the microstructure" is the height of the protrusions starting from the lowest point between the protrusions. However, the height can vary significantly while still observing the glare control characteristics. However, within the same layer L1, it is preferred that the height of each microstructure is approximately the same to achieve a uniform visual impression.

[0046] The microstructures can have various shapes. They have, for example, the shape of a cone, a pyramid, or a prism. Microstructures having a pyramid shape can have a triangular or square base, where the pyramid can also be an inverted pyramid with a triangular or square base. Other possible microstructures are prisms, Fresnel lens-like structures, microlens-like structures with a hexagonal or square grid layout, or a combination of two linear structures of a prism.

[0047] Preferably, the microstructure has a hexagonal, square, or other grid layout, most preferably a hexagonal grid layout.

[0048] Preferably, the microstructure has the shape of a cone, more preferably a cone with a hexagonal grid layout. Preferably, the cone has an apex angle of 90° to 130°, more preferably 100° to 120°, even more preferably 105° to 115°, and most preferably 110°.

[0049] Preferably, the microstructure has a base with a maximum diameter of 5 μm to 1000 μm, more preferably 50 μm to 500 μm, and most preferably 150 μm to 350 μm. Preferably, the microstructure has a base angle in the range of 10° to 60°, more preferably 20° to 55°, where the base angle is the inclination angle of these microstructures.

[0050] The material for forming layer L1

[0051] The material for forming layer L1 preferably has a refractive index n1 in the range of 1.35 to 2.00, more preferably 1.40 to 1.85, and most preferably 1.45 to 1.75, determined at a wavelength of 589 nm. As used in the present invention, the term "refractive index" describes the ratio of the speed of light in a vacuum to the speed of light in a given medium at a light wavelength of 589 nm.

[0052] Preferably, layer L1 is formed of glass or a polymer material or a blend of polymer materials or a blend of polymers and inorganic materials. The term "polymer" describes a substance composed of multiple monomeric entities that differ in degree of polymerization, molar mass, and chain length. The monomeric entities can be the same or different. A polymer material is made of or contains a polymeric substance as a main component. Thus, the term also includes a cured coating material preferably obtained from a liquid coating composition that is cured before applying layer L2.

[0053] Optical glass has a refractive index range of approximately 1.46 (fused silica glass) to 1.85 (for lanthanum heavy flint glass) at a wavelength of 589 nm.

[0054] The polymer material can be thermoplastic or thermosetting, and is preferably a thermosetting material. It can be in the form of a plastic foil, a plastic sheet, or a cured coating obtained from a curable coating composition C1.

[0055] Typical polymeric materials such as plastic foils and plastic sheets preferably consist of or include the following: polyolefins (such as polyethylene or polypropylene), polyvinyl chloride, celluloid, polystyrene, polyetheretherketone, polyamide, acrylonitrile butadiene styrene, polylactide (PL), polymethyl methacrylate (PMMA), polycarbonate, polyethylene terephthalate (PET), epoxy, polyurethane, polyurethane-acrylate, polyurea, poly(ethylene-propylene), polydiorganosiloxane, polybutadiene, polychloroprene, chlorinated polyethylene, and fluorosilicone, fluorinated polyurethane, perfluoropolyether, and / or their blends. The most preferred plastic materials are polycarbonate, PMMA, and PET, with polycarbonate being the most preferred.

[0056] Preferably, the layer L1 including microstructures is a plastic foil or sheet known, for example, from CH 711561A1 or CH 711562A1. The plastic foil according to the invention relates to a thin structure with a relatively large area. These structures typically have an area much larger than their thickness. For example, such structures can have a thickness of less than 1 mm, typically less than 0.5 mm, while the surface can have any size. Plastic sheets are considered to be thicker in size, such as 1 mm and greater, but can be made of the same material as plastic foils.

[0057] The plastic foil or plastic sheet has a refractive index n1 preferably of 1.35 to 1.65, more preferably 1.40 to 1.60, determined using a wavelength of 589 nm. Preferably, the plastic foils and sheets are made of: polycarbonate (n1 = 1.59), polyethylene (n1 = 1.50), polymethyl methacrylate (n1 = 1.49), most preferably polycarbonate.

[0058] In addition to the above typical materials (such as glass or polymeric materials), the layer L1 can also be formed by coating techniques. Thus, a cured coating obtained from a curable coating composition C1 can also be used to produce a thermosetting polymeric material.

[0059] Among the curable coating compositions C1, UV-curable coating compositions are preferred. The term "UV-curable coating composition" according to the invention should be understood to mean a coating composition that can be partially or fully cured under the action of ultraviolet radiation. Such UV-curable coating compositions preferably contain a UV-curable resin, a UV-curable reactive monomer (i.e., a UV-curable reactive diluent), a photoinitiator, a light stabilizer, and / or additional coating additives.

[0060] Preferred UV-curable resins are, for example, selected from the group consisting of: polyester (meth)acrylates; epoxy (meth)acrylates; aliphatic and / or aromatic urethane (meth)acrylates, preferably aliphatic urethane (meth)acrylates; polyether (meth)acrylates; and (meth)acrylated poly(meth)acrylates. The term “(meth)acrylic acid” or “(meth)acrylate” encompasses acrylic acid and methacrylic acid or both, and acrylate and methacrylate or both, respectively.

[0061] Suitable UV-curable reactive diluents preferably contain one or more free-radically polymerizable groups such as vinyl, allyl or (meth)acrylic groups, more preferably (meth)acrylic groups. Examples of suitable reactive diluents are mono(meth)acrylate-functional monomers, di(meth)acrylate-functional monomers and tri(meth)acrylate- and / or tetra(meth)acrylate-functional monomers. Preferred mono(meth)acrylate-functional monomers are the hydrocarbyl esters of (meth)acrylic acid, where the hydrocarbyl residue may be aliphatic or aromatic, and straight-chain, branched or cyclic, preferably a hydrocarbyl containing 1 to 20, more preferably 4 to 18 carbon atoms, where the hydrocarbyl may contain one or more ether oxygens. Preferred di(meth)acrylate-functional monomers are the alkanediol di(meth)acrylates, where the alkanediol preferably contains 2 to 16, more preferably 3 to 14 carbon atoms; the dialkylene glycol di(meth)acrylates; the trialkylene glycol di(meth)acrylates; and the neopentyl glycol-propoxy di(meth)acrylates; the tri(meth)acrylate-functional monomers of trimethylolpropane, trimethylolethane or glycerol, and the tetra(meth)acrylate-functional monomers such as pentaerythritol tetra(meth)acrylate.

[0062] The combined amount of the UV-curable resin and the UV-curable reactive diluent is preferably in the range of 80 wt.-% to 99 wt.-%, more preferably 85 wt.-% to 98 wt.-%, and most preferably 90 wt.-% to 97 wt.-% based on the total weight of the coating composition C1.

[0063] Photoinitiators are used to initiate crosslinking between any vinyl, acrylate, and methacrylate groups within the coating composition. The photoinitiators enable UV curing because they generate free radicals upon irradiation with UV light. Such photoinitiators are preferably selected from the group consisting of: α-cleavage photoinitiators such as α-hydroxy ketones (e.g., benzoin, acetophenone), α-alkoxy ketones (e.g., benzoin ethers, benzil ketals), α-amino ketones, and acylphosphine oxides. The UV photoinitiator is preferably present in the coating composition C1 in an amount of 0.5 wt.-% to 6 wt.-%, most preferably 0.75 wt.-% to 5 wt.-%, and even more preferably 1 wt.-% to 3 wt.-% based on the total weight of the coating composition C1.

[0064] The coating composition C1 may further contain a UV absorber preferably selected from the group consisting of: 2-(2'-hydroxyphenyl)benzotriazole, 2-hydroxybenzophenone, esters of substituted and unsubstituted benzoic acids, acrylates like ethyl α-cyano-β,β-diphenylacrylate, 2-(2-hydroxyphenyl)-1,3,5-triazine, and oxamides. The amount of the UV absorber is preferably in the range of 0 wt.-% to 8 wt.-%, more preferably 0.4 wt.-% to 4 wt.-%, and most preferably 0.6 wt.-% to 3 wt.-% based on the total weight of the coating composition C1.

[0065] The coating composition C1 of the present invention may also contain a light stabilizer such as a hindered amine light stabilizer (HALS), including NOR-HALS. NOR-HALS is a subclass of HALS, also known as an aminoxyl radical hindered amine light stabilizer. While HALS acts as a base and is neutralized by an acid such as hydrochloric acid, NOR-HALS is not a strong base and is not inactivated by hydrochloric acid. The amount of the light stabilizer is preferably in the range of 0 wt.-% to 8 wt.-%, more preferably 0.4 wt.-% to 4 wt.-%, and most preferably 0.6 wt.-% to 3 wt.-% based on the total weight of the coating composition C1.

[0066] The coating composition C1 may also contain typical coating additives such as adhesion promoters like (meth)acrylic acid trialkoxysilanes, (meth)acrylic acid dialkoxyalkylsilanes, glycidyl-containing trialkoxysilanes, glycidyl-containing dialkoxyalkylsilanes, and (meth)acrylic acid esterified phosphates; leveling agents; antioxidants, and defoamers, all of the above preferably but not necessarily being reactive in UV curing. The amount of the coating additive is preferably in the range of 0 to 7 wt.-%, more preferably 0 wt.-% to 5 wt.-%, and most preferably 0 to 3 wt.-% based on the total weight of the coating composition C1.

[0067] While not excluded, it is less preferred that the coating composition C1 contains organic solvents which, compared to the UV-curable reactive diluents, do not chemically react with any other compounds of the coating composition during UV curing, i.e., in the sense of the present invention, such chemically non-reactive organic solvents are single liquids or liquid blends, are volatile under the specified use conditions, and are added to the coating composition to reduce viscosity or affect other properties without causing any harmful effects. However, preferably the coating composition C1 does not contain such chemically non-reactive organic solvents.

[0068] The UV-cured layer L1 formed from the UV-curable coating composition C1 as described above can be obtained from a wide range of UV-curable components contained in the UV-curable coating composition C1, and these UV-curable components achieve a wide range of refractive indices n1.

[0069] The inventors of the present invention have surprisingly found that if a new method in which the glare control structure layer L1 is coated with an anti-reflection layer L2 is used, glare beams can be better controlled.

[0070] Layer L2

[0071] The anti-reflection coating L2 is formed on top of the layer L1, where the surface of L1 including the microstructures faces the layer L2. The layer L2 can also be formed by removing material from the surface of the layer L1, as alternatively claimed and described below. In this case, the layer L2 typically comes from the same material as the layer L1.

[0072] Typically, the refractive index n2 of the layer L2 is lower than the refractive index n1 of the layer L1, and thus the material used to form the layer L2 and / or the manufacturing technique used to form the layer L2 is selected such that n1 > n2. For example, if the layer L2 is a single uniform layer, the refractive index of the material used is typically selected to satisfy n1 > n2. On the other hand, for example, porous or nanostructured surfaces can be used, which can reduce the total refractive index of such a layer L2, for example, by "trapping" air.

[0073] Generally, depending on the structure, surface, and material of the anti-reflection layer L2, the dry layer thickness d of the layer L2 L Typically is in the sub-micron range, preferably less than 700 nm, such as 10 to 700 nm, preferably 50 to 650 nm, and even more preferably in the range of 80 to 600 nm.

[0074] Therefore, the dry layer thickness d of the layer L2 L Typically is much smaller than the height of the microstructures of the layer L1. Thus, it is ensured that the microstructures of the layer L1 are transferred onto the layer L2, i.e., the valleys between the microstructures of the layer L1 are retained and not "filled" by the layer L2.

[0075] In fact, any known anti-reflection layer L2 can be formed on top of the microstructured surface of layer L1, provided that the layer is transparent and meets some requirements for making such layer L2 anti-reflective given that layer L1 meets certain conditions. Thus, the term "anti-reflection" already includes information such as the appropriate layer thickness of layer L2 or its refractive index n2 (given that the refractive index of layer L1 is n1).

[0076] Therefore, all the necessary information regarding the term "anti-reflection" is already included in the determination of anti-reflection given the characteristics of layer L2.

[0077] Furthermore, since the concept of the present invention is based on applying the anti-reflection layer L2 to layer L1 as defined above, a proof-of-concept carried out on a specific anti-reflection layer L2 can be easily transferred to another anti-reflection layer L2, which is a great advantage of the teachings disclosed herein. Different from the concept where the glare control layer itself is modified by using microstructures of different shapes with unforeseen results, the present invention can be easily applied to any kind of anti-reflection layer L2 and is thus generally applicable.

[0078] The anti-reflection layer L2 can be of various types, which can be roughly grouped under the categories of anti-reflection coating structures and anti-reflection coating surfaces, and these two categories are not necessarily mutually exclusive. A detailed description of the above anti-reflection coating structures, anti-reflection coating surfaces, and the techniques for producing such anti-reflection layers is disclosed in the review article "Anti-Reflective Coating Materials: A Holistic Review from PV Perspective" by N. Shanmugam, R. Pugazhendhi, R. Madurai Elavarasan, P. Kasiviswanathan, and N. Das, Energies 2020, 13, 2631 et seq., which is incorporated herein by reference, and the teachings thereof are briefly summarized below.

[0079] Hereinafter, different suitable anti-reflection coating structures will be described.

[0080] i. Single-layer anti-reflection coating (SLARC)

[0081] SLARC is the simplest form of an antireflection coating. In this case, Fresnel reflection losses are reduced by applying a single layer of film on the glare control layer L1, thereby creating the antireflection layer L2. To achieve the antireflection properties of SLARC, it is required that the refractive index n2 of the material forming layer L2 be lower than the refractive index n1 of layer L1. When the coating thickness is equal to one quarter of the incident light wavelength, the optimal zero reflectivity of SLARC in the multilayer coating according to the present invention is achieved. To approximate this situation, the refractive index n2 of the material of the SLARC layer L2 is selected to be approximately (n1) -0.5 , where n1 is the refractive index of the material forming layer L1.

[0082] As an example, if layer L1 is made of glass with a refractive index n1 of 1.5, the material forming the SLARC layer should optimally have a refractive index n2 of 1.22 at a quarter wavelength thickness.

[0083] Typically, it is difficult to obtain a solid material with such a low refractive index. However, for example, magnesium fluoride MgF2 with a refractive index of 1.38 is a commonly used material for producing such a coating. Considering the above equation, the optimal refractive index of the material forming layer L1 would be a high refractive index glass with a refractive index of approximately n = 1.90 at a quarter wavelength layer thickness of layer L2. In addition to MgF2, other materials such as SiO2 are commonly used to produce the SLARC layer.

[0084] Suitable organic materials for forming layer L2 are those with a low refractive index as low as n = 1.30 and typically belong to the group of fluoropolymers.

[0085] As described above, the selected layer thickness d L depends on the light source and especially the color of the light. In the case of assuming white light, a person skilled in the art can consider that such light contains all wavelengths from about 380 to about 700. Therefore, for most white light sources, it is preferred that the layer thickness d L is in the range of d L = λ / 4, where λ = 380 to 700 nm. In this case, the d L to be selected is approximately 95 nm to approximately 175 nm. Since glare caused by light with wavelengths close to UV light (wavelengths below 380 nm) should be particularly avoided, d L is preferably selected from the lower part of the range of 85 to 175 nm. Therefore, it is particularly preferred that d L is in the range of 85 to 140 nm, more preferably in the range of 90 to 120 nm and most preferably in the range of 95 to 110 nm. If MgF2 is selected as the layer material in SLARC, the above values of d L are particularly suitable.

[0086] ii. Double-layer antireflection coating (DLARC)

[0087] DLARC employs two layers (referred to herein as L 2.1 and L 2.2 ), which together form layer L2, and these layers have the same or different thicknesses. For equal film thicknesses, the condition for optimal zero reflection can be described by the following formula: (n 2.1 / n 2.2 ) = (n 空气 / n1) 0.5 , where n 空气 = the refractive index of air, n1 = the refractive index of the material of layer L1, and respectively, n 2.1 and n 2.2 = the refractive indices of layers L 2.1 and L 2.2 , and layer L 2.1 is the layer in direct contact with layer L1. Typically, when using a typical DLARC, the effective reflectance is significantly reduced and approaches zero at the target wavelength and then gradually increases, thus exhibiting a V-shaped reflectance curve within the analyzed spectral range.

[0088] iii. Multilayer antireflection coating (MLARC)

[0089] MLARC employs more than two layers to form the entire layer L2. MLARC can typically avoid the gradual increase in reflection observed for DLARC. As an example, the reflectances of MgF2 / ZnS DLARC at 500 nm and 1000 nm are 9.1% and 0.58%, respectively, while for MgF2 / Al2O3 / ZnS MLARC (three layers), the reflectances at 500 nm and 1000 nm are 5.8% and 0.88%, respectively. This shows a wider low-reflectance range in the multilayer coating.

[0090] iv. Gradient-index coating (GRINC)

[0091] A series of layers with a gradually changing refractive index at each step constitutes a gradient-index coating. Alternatively, a non-uniform film with a monotonically changing refractive index is preferred, and it also serves as a broadband antireflection coating. Different profiles of GRINC have been proposed for omnidirectional and broadband antireflection coatings, which include linear, parabolic, cubic, Gaussian, quintic, exponential, exponential sine, and Klopfenstein. The linear refractive index profile can be easily achieved on a silicon or quartz substrate. The refractive index gradient can be achieved by changing the packing density of the layers; however, this may affect the mechanical robustness and durability of the layers.

[0092] In the following, different suitable antireflection coating surfaces will be described.

[0093] v. porous layer

[0094] The porous layer, especially the nanoporous layer, can also act as an antireflection coating. For this type of layer, the size of the pores must be much smaller than the wavelength of the incident light. The refractive index of such nanoporous materials is averaged over the layer L2. The porous layer L2 can be in the form of, for example, SLARC and GRINC structures and is produced by subsequent heat treatment through a chemical etching process. In another method, a high-performance broadband antireflection coating is obtained by using a nanophase-separated polymer film and precisely varying the volume fraction, as described by Walheim, S.; Walheim, S.; Schaffer, E; Mlynek, J.; Steiner, U. in the title "Nanophase-Separated Polymer Films as High-Performance Antireflection Coatings" in Science 1999, 283, 520 - 522. Using the latter technique, a refractive index n2 in the range of 1.2 to 1.05 and a high transmittance of 99.7% over the wavelength span of visible light can be obtained.

[0095] vi. biomimetic photonic nanostructures

[0096] This type of layer L2 is based on subwavelength structures (SWS). The SWS that act as an antireflection surface in a periodic arrangement were first discovered by Bernhard in the eyes of nocturnal moths in 1967. The antireflection structure of the moth eye consists of an outer surface with submicron height and an array of spaced papillae. Thus, the refractive index gradually changes between air and the substrate, thereby actively suppressing the reflection at the junction of the two media. The reflectivity of such a structure depends on the spacing between the arrays, the effective height of the nanostructure, and the wavelength. Ideally, broadband antireflection characteristics can be obtained by adjusting the space as finely as possible and by increasing the height. To replicate the papilla structure, three models with conical, paraboloidal, and Gaussian bell shapes have been proposed, and it has been reported that the paraboloidal papilla exhibits excellent antireflection performance at normal incidence. Moreover, for papillae that overlap at the substrate with a larger width, a significant reduction in reflectivity occurs and gradually decreases as the height increases. Monolayers with gradient refractive index and moth-eye patterns are known especially from Han et al. in Biosurface and Biotribology 2 (2016) 137 - 150; or Choi et al. in Polymers (2020), 12, 296.

[0097] Such nanostructures may preferably have a height of 10 nm to 500 nm, more preferably 20 nm to 400 nm, even more preferably 50 nm to 300 nm, even more preferably 100 nm to 300 nm, and most preferably 300 nm. The diameter of the nanostructures is preferably 10 nm to 500 nm, more preferably 20 nm to 300 nm, and most preferably 50 nm to 100 nm; and preferably...

[0098] vii. Textured surface

[0099] Surfaces with a textured period smaller than the target wavelength and a height that is a fraction of the wavelength are also suitable for antireflection applications. Theoretically, if the wavelength of light is much larger than the spacing between the structures, the textured surface can be treated as a layer with a gradually varying refractive index, and the optical properties can be predicted using the effective medium approximation. If the wavelength of light is shorter than the period between the textured structures, the light rays will undergo multiple reflections and be trapped within the gaps. In this case, the optical properties are defined only by the geometry and are numerically modeled using ray tracing methods.

[0100] Materials for forming layer L2

[0101] Depending on the antireflection coating structure and / or the type of surface, various different materials deposited by different techniques can be applied. Hereinafter, different suitable types of materials and their application techniques are disclosed.

[0102] Antireflection coating materials are preferably classified into the following groups of materials:

[0103] a. Silicon-based coating materials, e.g., covering silica-based and silicon-based nanomaterials;

[0104] b. Metal-based coating materials, e.g., covering metal oxides and metal fluorides;

[0105] c. Polymer-based coating materials, such as polystyrene, polymethyl methacrylate, polydimethylsiloxane, and polyethylene terephthalate; and

[0106] d. Composite coating materials.

[0107] a. Silicon-based antireflection coating materials

[0108] Silicon-based coating materials are generally and preferably in the form of silica (silicon dioxide) coating materials.

[0109] The silica monolayer can be formed, for example, as a nanoporous layer by sol-gel dip coating, as described, for example, by Mahadik, D.B.; Lakshmi, R.V.; Barshilia, H.C., “High performance single layer nano-porous antireflection coatings on glass by sol-gel process for solar energy applications”, Sol. Energy Mater. Sol. Cells 2015, 140, 61-68; or by chemical etching and thermal oxidation, as described by Cao, H.; Bai, Y.; Qiao, L., “Antireflection effect of SiO2 thin film on the pyramidal textured surface of monocrystalline silicon”, Opt. Int. J. Light Electron Opt. 2015, 126, 2643-2645.

[0110] A double-layer porous silica film having an extremely low refractive index of about 1.11 can be obtained, for example, by plasma-enhanced chemical vapor deposition techniques, as described, for example, by Nagel, H.; Metz, A.; Hezel, R., “Porous SiO2 films prepared by remote plasma-enhanced chemical vapour deposition - a novel antireflection coating technology for photovoltaic modules”, Sol. Energy Mater. Sol. Cells 2001, 65, 71-77.

[0111] The multi-layer stack of silica obtained by sol-gel evaporation-induced self-assembly technique is described by Agustin-Saenz, C.; Sanchez-Garcia, J.A.; Machado, M.; Brizuela, M.; Zubillaga, O.; Tercjak, A., "Broadband antireflective coating stack based on mesoporous silica by acid-catalyzed sol-gel method for concentrated phovoltaic application", Sol. Energy Mater. Sol. Cells 2018, 186, 154-164.

[0112] The four-layer nanoporous silica structure showing negligible reflection obtained by glancing angle deposition technique was obtained by Sobahan, K.M.A.; Park, Y.J.; Kim, J.J.; Hwangbo, C.K. and is described in "Nanostructured Porous SiO2 Films for antireflection coatings", Opt. Commun. 2011, 284, 873-876; and the five-layer structure with hollow silica nanoparticles obtained by dip coating was disclosed by Jia, G.; Ji, Z.; Wang, H.; Chen, R., "Preparation and properties of five-layer graded-refractive-index antireflection coating nanostructured by solid and hollow silica particles", Thin Solid Film 2017, 642, 174-181.

[0113] More complex but still cost-effective and readily available structures (such as, for example, nanocylinders) can be formed by sol-gel and soft-imprint lithography, as described by Van de Groep, J.; Spinelli, P.; Polman, A., “Single-Step Soft-Imprinted Large-Area Nanopatterned Antireflection Coating”, Nano Lett. 2015, 15, 4223-4228.

[0114] Silica-based moth-eye structures can also be obtained, for example, by sol-gel dip coating and electrostatic self-assembly techniques, as described by Li, D.; Han, S.; Li, A.; Wang, Y.; Shan, Y.; Huang, F., “Novel-type nanostructured SiO2 antireflection coatings and their application in Cu(In,Ga)Se2 solar cells”, Mater. Chem. Phys. 2015, 165, 97-102.

[0115] b. Metal-based antireflection coating materials

[0116] Common metal oxides in antireflection coating materials are titanium dioxide, indium tin oxide (ITO), aluminum oxide, tantalum oxide, and zinc oxide, while the most important metal fluoride is magnesium difluoride.

[0117] The fabrication of titanium dioxide thin films can be accomplished, for example, by liquid phase deposition, as described by Huang, J.-J.; Lin, C.-C.; Wuu, D.-S., “Antireflection and passivation property of titanium oxide thin film on silicon nanowire by liquid phase deposition”, Surf. Coat. Technol. 2017, 320, 252-258.

[0118] The zinc oxide thin film can be obtained by the sol-gel method, as described by Makableh, Y.F.; Vasan, R.; Sarker, J.C.; Nusir, A.I.; Seal, S.; Manasreh, M.O., "Enhancement of GaAs solar cell performance by using a ZnO sol-gel anti-reflection coating". Sol. Energy Mater. Sol. Cells 2014, 123, 178-182.

[0119] The moth-eye structure from zinc oxide is described by Shin, B.-K.; Lee, T.-I.; Xiong, J.; Hwang, C.; Noh, G.; Cho, J.-H.; Myoung, J.-M., "Bottom-up grown ZnO nanorods for an antireflective moth-eye structure on CuInGaSe2 solar cells". Sol. Energy Mater. Sol. Cells 2011, 95, 2650-2654.

[0120] The MgF2 coating can form a mesoporous nanoparticle layer, for example, by the solvothermal and dip-coating processes, as described by Pendse, S.; Chandra Sekhar Reddy, K.; Narendra, C.; Murugan, K.; Sakthivel, S., "Dual-functional broadband antireflective and hydrophobic films for solar and optical applications", Sol. Energy 2018, 163, 425-433.

[0121] c. Polymer-based antireflective coating materials

[0122] Bio-inspired nano-column and pyramid array films can be produced using polystyrene (PS) with micro-injection compression molding technology, as described, for example, by Xie, H.; Huang, H.-X.; Peng, Y.-J. "Rapid fabrication of bio-inspired nanostructure with hydrophobicity and antireflectivity on polystyrene surface replicating from cicada wings", Nanoscale 2017, 9, 11951-11958; and Peng, Y.-J.; Huang, H.-X.; Xie, H. "Rapid fabrication of antireflective pyramid structure on polystyrene film used as protective layer of solar cell", Sol. Energy Mater. Sol. Cells 2017, 171, 98-105.

[0123] A polymethyl methacrylate (PMMA) coating with a nano-cone array can be produced as described by Choi, K.; Park, S.H.; Song, Y.M.; Lee, Y.T.; Hwangbo, C.K.; Yang, H.; Lee, H.S., “Nano-tailoring the Surface Structure for the Monolithic High-Performance Antireflection Polymer Film”, Adv. Mater. 2010, 22, 3713 - 3718; and simple large-scale nano-patterns can be cost-effectively produced using thermal nanoimprinting, laser lithography, and dry etching, as shown by Kim, S.; Jung, U.T.; Kim, S.-K.; Lee, J.-H.; Choi, H.S.; Kim, C.-S.; Jeong, M.Y, “Nanostructured Multifunctional Surface with Antireflective and Antimicrobial Characteristics”, ACS Appl. Mater. Interfaces 2015, 7, 326 - 331.

[0124] Other methods utilize polydimethylsiloxane (PDMS) or polyethylene terephthalate (PET) that form nano-domes, poly(methylsilsesquioxane) (PMSSQ) that provides a nano-porous film with a refractive index ranging from 1.44 down to as low as 1.18; and other materials as described in Table 5 of the aforementioned publication by N. Shanmugam et al. in Energies 2020, 13, 2631 et seq.

[0125] d. Composite coating materials

[0126] Many methods that utilize combinations of two or more of SiO2, TiO2, Al2O3, ZnO, and MgF2 are described in Table 6 of the aforementioned publication by N. Shanmugam et al. in Energies 2020, 13, 2631 et seq. and in basic science publications showing how to produce such coatings.

[0127] Additional layer L S and L A

[0128] The transparent multilayer system of the present invention can be on top of one or more additional layers, with the smooth surface of layer L1 facing the one or more additional layers. The one or more additional layers can be a support layer L S , which is suitable for supporting the transparent multilayer system of the present invention, for example, by providing a layer L S on which a coating composition C1 can be applied to form layer L1.

[0129] Preferably, layer L s is formed from a coating composition comprising a polymer selected from the group consisting of: polyolefins (such as polyethylene or polypropylene), polyvinyl chloride, celluloid, polystyrene, polyetheretherketone, polyamide, acrylonitrile butadiene styrene, polylactide, polymethyl methacrylate, polycarbonate, polyethylene terephthalate, polyetherketoneketone, polyetherketone, polyimide, polyester, chloropolymers or fluoropolymers (such as polytetrafluoroethylene, fluorinated ethylene propylene or fluorinated polyurethane), silicone, epoxy resin, polysulfide, ethylene propylene diene, fluorosilicone and / or fluoroelastomer.

[0130] Furthermore, layer L1 or layer L S of the transparent multilayer system of the present invention can be formed on an additional layer L A , which is composed of a material that enables the transparent multilayer system of the present invention to be attached to the transparent part of a lamp so that the part is equipped with an improved glare control structure. Suitable examples of the additional layer L A are, for example, layers composed of or containing an adhesive composition. Such an adhesive layer can again be covered with a backing layer L A , which will be separated before fixing the transparent multilayer system of the present invention to the transparent part of the lamp. B covering, the backing layer L B will be separated before fixing the transparent multilayer system of the present invention to the transparent part of the lamp.

[0131] Thus, the transparent multilayer system according to the present invention includes layer L1 and layer L2, where layer L2 is a single layer with a constant refractive index n2 (see Figure 2A ) or a single layer with a gradient refractive index n 2G (see Figure 2B ), or a multilayer film formed from multiple materials, where each layer has a different refractive index, and each refractive index is less than the refractive index n1 (see Figure 2C ). For simplicity, multilayer L2 is shown in Figure 2C as a two-layer structure composed of a gray layer and a black layer. However, multilayer L2 can be composed of more than two layers, as outlined above. The transparent multilayer system according to the present invention including the additional layer L S and / or L A is indicated in Figures 3A to 3C , where, for simplicity, layer L2 is as Figure 2Ais depicted as a single layer as in. The layer L1 of the transparent multi-layer system according to the present invention can be formed on top of the support layer L S (see Figure 3A ). In addition, the transparent multi-layer system according to the present invention including the support layer L S can be formed on top of another layer L A (see Figure 3B ). In addition, the transparent multi-layer system according to the present invention can be formed on top of another layer L A without a support layer L between the layer L1 and L A S (see Figure 3C ).

[0132] Method for producing a transparent multi-layer system

[0133] As described above, the present invention further provides a method for producing a transparent multi-layer system according to the present invention, the method comprising the following steps:

[0134] i. Forming a layer L1 that includes microstructures on at least one surface, preferably on one surface, and then

[0135] ii. Forming an anti-reflection layer L2 by

[0136] a. Depositing one or more coating materials on top of the surface of the layer L1 having microstructures to form an anti-reflection coating L2, or

[0137] b. Removing material from a portion of the surface of the layer L1 having microstructures, thereby maintaining the shape of the microstructures and thus forming the anti-reflection layer L2 from the same material as the layer L1.

[0138] The materials of the different mandatory layers L1 and L2 and the optional layers L s and L a have been described above for the transparent multi-layer system of the present invention, including their physical properties (such as refractive index), or their chemical composition and also their dimensions (such as layer thickness). Therefore, in this regard, reference can be made to the corresponding paragraphs above.

[0139] The term "partial removal of material" refers to ablation techniques, like etching techniques such as plasma etching, which are prone to generating sub-structures on the layer by ablating a portion of the surface of the layer L1, thereby producing the anti-reflection layer L2. "Maintaining the shape of the microstructures" means that the overall shape of the microstructures of the layer L1 remains unchanged, but the surface of such microstructures is sub-structured to obtain anti-reflection properties. Therefore, in the context of the present invention, this sub-structured surface is regarded as the anti-reflection layer L2.

[0140] Hereinafter, emphasis will be placed on how to obtain such a transparent multi-layer system.​

[0141] Step i.

[0142] In the above step i., a layer L1 including microstructures is formed on at least one of two surfaces, wherein these microstructures have a height in the range of 5 μm to 100 μm, and the layer has a refractive index n1.

[0143] The formation of such microstructures can be accomplished by several methods, such as laser ablation, hot stamping, ultraviolet casting, injection molding, compression molding, roll-to-roll process, embossing process, plasma etching process, sol-gel process, and / or 3D printing.

[0144] In the hot stamping process, pressure and heating are combined to form microstructures on a film or sheet. In this method, the film or sheet is brought into a stamping machine. The stamping machine includes a stamping head that has the desired microstructures in an inverted form. The heated stamping head is pressed against the film or sheet to imprint the desired microstructures onto the film or sheet in order to obtain the formed layer L1. The stamping temperature should be in the range of 100 °C to 250 °C. Since this method uses heat to imprint the microstructures onto the film or sheet, the materials used need to be formable under heating. Therefore, a transparent multilayer system (wherein layer L1 is formed from such materials) can be suitably used only with light sources that do not generate too much heat, such as light-emitting diodes. Otherwise, there is a risk of deformation of layer L1 or the microstructures may flatten over time.

[0145] The microstructures can also be formed using injection or compression processes, both of which also utilize heat and / or pressure. In such processes, a mold having the desired microstructures is used for the injection molding process. The molten polymer material is injected into such a mold. Then, after the cooling process, the mold is opened and the solid layer including the microstructures is ejected. For compression molding, preferably a thermoplastic material is placed into a hot mold having the desired microstructures. Subsequently, the mold is closed by a hydraulic press. Heat and pressure result in the formation of layer L1 having microstructures on at least one of the two surfaces.

[0146] Another method of using pressure to generate the desired microstructures on layer L1 is the embossing process, wherein an embossing tool having the inverted desired microstructures is used. The embossing tool is transferred to at least one of the two surfaces of layer L1 formed from the uncured composition C1 to form microstructures on at least one surface of layer L1.

[0147] The microstructures can be formed on layer L1 using a plasma etching process. For example, Ar / O2, SF6, N2, or ClF3 can be used as the plasma for etching. The microstructures are formed on the surface of a polymer film or sheet by etching the surface with plasma in a vacuum chamber. This process is called, for example and Preferably, if the microstructure is formed using a plasma etching process, layer L1 is formed of a film or sheet of polymethyl methacrylate or polycarbonate.

[0148] Roll-to-roll processing can also be used to create structures on rolls of material or flexible glass. This processing is characterized by a process of applying coatings, printing, or performing other processes that start from a roll of flexible material and are rewound after the process to produce an output roll. These processes and other processes (such as sheet pressing) can be grouped together under the general term conversion. When the rolls of material have been coated, laminated, or printed with microstructures, they can then be cut to their finished size on a slitter rewinder.

[0149] Microstructures can be formed using ultraviolet (UV) casting, where a UV-curable coating composition is subjected to a casting mold that is highly transmissive to UV light and exhibits the desired microstructure, where the UV-curable coating composition is understood to mean a coating composition that can be partially or fully cured under the action of ultraviolet radiation. Hardening occurs in the mold by ultraviolet radiation, where the ultraviolet radiation refers to radiation having a wavelength in the range of 100 nm to 380 nm, more preferably 280 nm to 380 nm, and most preferably 315 nm to 380 nm.

[0150] Particularly preferred is roll-to-roll UV nanoimprint lithography.

[0151] Step ii.

[0152] In the above sections on the structure, surface, and materials of layer L2, many coating techniques have been mentioned, which can be classified as conventional techniques and unconventional techniques.

[0153] Conventional techniques can be grouped again into "bottom-up" methods and "top-down" methods. The most important in the so-called bottom-up methods are sol-gel methods, thermal evaporation, sputtering, glancing angle deposition (GLAD), and chemical vapor deposition (CVD), which are processes according to step ii.a., while for the so-called top-down methods, wet etching and dry etching will be mentioned, which are processes according to step ii.b.

[0154] Unconventional techniques are especially lithography (such as optical lithography), focused ion beam techniques, and nanoimprint techniques; microreplication; photoalignment, and photopatterning.

[0155] All of the above-mentioned techniques are known techniques and are in principle suitable for depositing an anti-reflection coating material on top of the surface of layer L1 to form an anti-reflection layer L2. They are described above and belong to the common knowledge of those skilled in the art. For experimental details, reference is made to the review article “Anti-Reflective Coating Materials: A Holistic Review from PV Perspective [Holistic Review]” by N. Shanmugam, R. Pugazhendhi, R. Madurai Elavarasan, P. Kasiviswanathan, and N. Das, Energies [Energy] 2020, 13, 2631 et seq. (Chapter 5) and the scientific articles cross-referenced therein that provide more details on manufacturing techniques.

[0156] It is also clear to those skilled in the art that techniques that damage the integrity of layer L1 are to be excluded. For example, techniques utilizing heat can be applied, for example, to form layer L2 on glass layer L1, but may not be suitable for thermoplastic layer L1; or techniques utilizing certain non-aqueous solvents in the anti-reflection coating material to form layer L2 may be problematic if used on certain polymeric materials used for manufacturing layer L1, as these polymeric materials may swell or dissolve when such solvents are used. Such undesirable interactions are known to those skilled in the art and can be avoided by using other material combinations for L1 and L2.

[0157] A further subject matter of the present invention is a transparent multi-layer system obtainable by the method according to the present invention.

[0158] Use of the transparent multi-layer system <W

[0159] The transparent multi-layer system according to the present invention is suitable for a variety of applications, preferably as a glare reduction component of a lighting device (such as a lamp). The transparent multi-layer system according to the present invention can also be used for any other component through which light should be transmitted with a high transmittance but extremely low glare. Such further components are preferably selected from the group consisting of windows, imaging lenses, and solar cells. The transparent multi-layer system of the present invention is preferably intended to cover the light source of a lamp in the emission direction of the lamp. Thus, the multi-layer system is intended to be located between the light source and a person exposed to the light transmitted through the multi-layer system or a component comprising the multi-layer system.

[0160] Lamp comprising a transparent multi-layer system

[0161] The present invention further provides a luminaire, which comprises a light source and a transparent multi-layer system according to the present application. The transparent multi-layer system of the present invention covers the light source of the luminaire in the emission direction of the luminaire. Generally, the light source of the luminaire is separated from the multi-layer system according to the present invention by an air gap. In addition, the multi-layer system can be attached to the transparent part of the luminaire by an additional layer L A (which is an adhesive), such that such a transparent part, the additional layer L A and the multi-layer system form a stack. Such a transparent part can be, for example, a rigid substrate, such as a polymethyl methacrylate plate. Such a stack can be mounted facing the light source during or slightly after the manufacture of the luminaire, but still leaving an air gap between the light source and such a transparent part. The luminaire can be an indoor or outdoor luminaire, preferably an indoor luminaire. The indoor luminaire can be a ceiling luminaire, a wall lamp, a floor lamp, a pendant lamp or a table lamp.

[0162] Experimental section

[0163] Method

[0164] Determination of the thickness of single and multi-layer systems

[0165] The thickness of the individual layers and the multi-layer system was determined by scanning electron microscopy.

[0166] Determination of the light transmittance

[0167] The light transmittance of layers L1 and L2 and the multi-layer system of the present invention can be determined using ASTM D-1003 (Standard Test Method for Haze and Light Transmittance of Transparent Plastics).

[0168] Determination of the useful luminous flux (useΦ)

[0169] The luminous flux describes the amount of light emitted by the light source. The useful luminous flux (useΦ) describes the amount of luminous flux incident on a surface. The luminous flux is determined photometrically using a goniophotometer for measuring the light intensity distribution.

[0170] Determination of the unified glare rating (UGR)

[0171] The UGR value can be calculated by the following formula (I)

[0172]

[0173] where

[0174] L b is the background illuminance calculated as E ind π -1 in cd / m 2 units, where E ind is the vertical indirect illuminance at the observer's eye,

[0175] L is the average illuminance of each lamp in the direction of the observer's eyes, in cd / m 2 The light exits with an area unit,

[0176] Ω is the solid angle of the luminous surface of each luminaire based on the observer's eyes, in steradians (sr),

[0177] ρ is the Guth position index of each individual luminaire, depending on its spatial deviation from the subjective viewing direction.

[0178] The procedures are described in detail in CIE117:1995 or CIE190:2010 respectively. The UGR limit values for interior lighting are specified in EN12464, while the UGR limit values for exterior lighting are specified in EN 12464-2.

[0179] Determination of the refractive index

[0180] The refractive index is determined with a refractometer at a wavelength of 589 nm.

[0181] Simulation of the effect of the transparent multi-layer system of the present invention on glare beams

[0182] To study the influence of the transparent multi-layer system of the present invention on the glare beams leaving the luminaires, simulations are performed using the Fresnel equations. Simulations are carried out for three different conditions. First, the reflection of light is simulated for the prior art glare control structure known from patent CH 711562A1 as layer L1 ("GCS"). The light propagation through the glare control structure is simulated for different apex angles, as indicated in Table 1. In addition, an idealized situation is simulated, where it is assumed that the surface only transmits and does not reflect the incident light ("transmission"). Then, the light propagation of the multi-layer system according to the present invention is simulated, which includes the above-mentioned glare control structure as layer L1 and a layer L2 on top of L1, where L2 is formed of MgF2 with a dry layer thickness of 100 μm ("MgF2"). Thus, the condition "MgF2" includes the same glare control structure as in the condition "GCS". The difference between the conditions "GCS" and "MgF2" is that the glare control structure in the condition "GCS" is uncoated, while the glare control structure in the condition "MgF2" is coated with a MgF2 layer with a dry layer thickness of 100 μm.

[0183] To determine the glare level, the Unified Glare Rating (UGR) is determined using CIE117 and CIE190. The lower the UGR value, the lower the glare effect.

[0184] Table 1

[0185] Compared to the condition ("GCS") where an uncoated glare control structure is used, in the idealized condition ("transmission"), the UGR values for all apex angles are lower. The UGR values in the example "GCS" represent the glare level of using a prior art glare control structure. Compared to the uncoated glare control structure, the glare level is reduced by a transparent multi-layer system according to the present invention comprising CH 711562A1 as layer L1 and MgF2 as layer L2. For an apex angle of 110°, the lowest glare level of 16.60 (CIE 117) or 15.20 (CIE190) is observed using the transparent multi-layer system according to the present invention.

[0186] From the above data, calculate the maximum available luminous flux (in klm) / luminous surface area (in m 2 ²) (use Φ) with UGR = 19 under room dimensions 4H / 8H (and room conditions of 70% ceiling reflectance, 50% wall reflectance, 20% floor reflectance). Additionally, the gain in available luminous flux due to the transparent multi-layer system of the present invention relative to the uncoated glare control structure is calculated for both CIE117 and CIE190. Furthermore, the gain in available luminous flux in the idealized condition relative to the uncoated glare control structure is calculated. The gain values of the available luminous flux are indicated in parentheses. Simulate the values of the available luminous flux for the apex angles indicated in Table 2.

[0187] Table 2

[0188]

[0189] In the idealized condition ("transmission"), the available luminous flux values are the highest for all tested apex angles. Compared to the idealized condition (which represents the available luminous flux of using a prior art glare control structure), the available luminous flux values of the glare control structure are observed to be lower. Compared to the uncoated glare control structure, the available luminous flux is increased by using a transparent multi-layer system comprising a glare control structure as layer L1 and MgF2 as layer L2. For an apex angle of 110°, the highest available luminous flux of 27.20 (CIE 117) or 40.70 (CIE190) is observed using the transparent multi-layer system according to the present invention.

[0190] Using the transparent multi-layer system according to the invention by applying MgF2 on top of the glare control structure to form layer L2, a gain in available luminous flux of about 9.6% (CIE 117) or 16.1% (CIE 190) can be achieved for a vertex angle of 110° compared to using an uncoated glare control structure. Thus, the additional coating of the glare control structure with the MgF2 layer improves the prior art glare control structures. Furthermore, the gain is close to the ideal case where a gain in available luminous flux of about 14% is achieved.

[0191] Therefore, simulations have shown that when using a glare control structure on top of a luminaire, glare beams are still observed. The occurrence of glare beams is particularly likely because a portion of the light is partially reflected and transmitted at each interface of two materials with different refractive indices. Thus, when using an uncoated glare control structure, glare beams are still observed because the light that was previously partially reflected at the cone-air interface can leave the cone structure at the glare propagation angle. Therefore, the occupants in the illuminated space are still disturbed by the glare beams. However, using a coating such as MgF2 on top of the glare control structure reduces the glare beams, as demonstrated by the data shown in Tables 1 and 2. Thus, these glare beams are suppressed by the transparent multi-layer system according to the invention. The simulation data was verified by preparing the transparent multi-layer system according to the invention.

[0192] Preparation of the transparent multi-layer system according to the invention

[0193] To verify the simulations outlined above, an uncoated glare control structure ("GCS") was compared with the transparent multi-layer system according to the invention comprising a coated glare control structure, where a MgF2 layer with a dry layer thickness of 95 mm was coated on top of the surface of the glare control structure comprising the micro-structure ("MgF2").

[0194] The glare control structure with a vertex angle of 110° was prepared according to CH 711562A1 ("GCS").

[0195] The glare control structure represents layer L1 of the transparent multi-layer system according to the invention. To prepare the transparent multi-layer system according to the invention, the glare control structure was coated with MgF2 by physical vapor deposition to form layer L2. The glare control structure (GCS) was prepared by roll-to-roll UV nanoimprint lithography on a polyethylene terephthalate substrate with a layer thickness of 250 μm.

[0196] The available luminous flux is calculated as follows: Measure the luminous intensity distribution of a luminous surface with near-Lambert emission characteristics, where there is a glare control film (with an air gap in between) on top. The measurement is carried out using a goniophotometer. As described above, calculate the UGR based on the luminous intensity distribution and thereby calculate useΦ. This is done for each sample in Table 3.

[0197] Table 3

[0198]

[0199] The results indicated in Table 3 emphasize that the transparent multilayer system according to the invention increases the available luminous flux. The gain in available luminous flux can be achieved due to the suppression of glare beams, as outlined in Table 1 above. Thus, the simulations of the three conditions "GCS", "transmission", and "MgF2" outlined in Tables 1 and 2 are confirmed by the experimental data shown in Table 3. Therefore, it is assumed that any simulation of the multilayer system will also correspond to the data obtained experimentally, and thus a good prediction of glare reduction can be given by applying layer L2.

[0200] Thus, the transparent multilayer system according to the invention improves the prior art glare control structure by suppressing glare beams, which are observed especially because light is partially reflected and transmitted at the glare control structure. Therefore, the transparent multilayer system can be applied to a luminaire (such as a lighting fixture) to provide a higher glare-free luminous flux. Moreover, the occupants in the illuminated space are not disturbed by the glare beams.

Claims

1. A transparent multilayer system, comprising a) a layer L1 made of a transparent material, the layer L1 having at least one surface with microstructures that provide antiglare control properties to the layer L1, and b) a layer L2 made of one or more transparent materials, the one or more transparent materials providing antireflection properties to the layer L2, wherein the layer L2 is on top of the surface of the layer L1 having these microstructures.

2. The transparent multi-layer system according to claim 1, characterized in that, These microstructures of the layer L1 have a height in the range of 5 μm to 5000 μm.

3. The transparent multi-layer system according to claim 1 or 2, characterized in that, The material forming the layer L1 has a refractive index n1 in the range of 1.35 to 2.00 determined at a light wavelength of 589 nm.

4. The transparent multi-layer system according to any one of claims 1 to 3, characterized in that The layer L1 is formed of glass or a polymer material or a blend of polymer materials or a blend of a polymer and an inorganic material.

5. The transparent multilayer system according to claim 4, wherein The polymer material of the layer L1 is a plastic foil or a plastic sheet or a cured coating composition C1.

6. The transparent multi-layer system according to any one of claims 1 to 5, characterized in that These microstructures of the layer L1 are designed as cones, pyramids with triangular or square bases, inverted pyramids with triangular or square bases, prisms, Fresnel lens-like structures, microlens-like structures with hexagonal or square grid layouts, a combination of two linear structures of prisms, or mixtures thereof, and / or wherein these microstructures have a hexagonal, square or other grid layout.

7. The transparent multilayer system according to any one of claims 1 to 6, characterized in that, The layer L2 is selected from the group of antireflection coating structures and / or the group of antireflection coating surfaces.

8. The transparent multilayer system according to claim 7, characterized in that, These antireflection coating structures are selected from the group consisting of single-layer antireflection coatings, double-layer antireflection coatings, multilayer antireflection coatings and gradient refractive index coatings, and these antireflection coating surfaces are selected from the group consisting of porous layers, biomimetic photonic nanostructures and textured surfaces.

9. The transparent multilayer system according to any one of claims 1 to 8, characterized in that, These materials forming the layer L2 are selected from the group consisting of: silicon-based coating materials; metal-based coating materials; polymer-based coating materials; and composite coating materials.

10. The transparent multi-layer system according to any one of claims 1 to 9, characterized in that, Layer L2 is composed of magnesium difluoride and has a dry layer thickness d in the range of 85 to 175 nm L of a single-layer antireflection coating.

11. The transparent multilayer system according to any one of claims 1 to 7, characterized in that, The layer L1 is On top of the support layer L s ; or On the top of the adhesive layer L a ; or On the top of the support layer L s The support layer L s On the top of the adhesive layer L a .

12. A method for producing a transparent multilayer system as defined in any one of claims 1 to 11, the method comprising the following steps: i. forming a layer L1 that includes microstructures on at least one surface, preferably on one surface, and subsequently ii. forming an antireflection layer L2 by a. depositing one or more coating materials on top of the surface of the layer L1 having these microstructures, thereby forming an antireflection coating L2, or b. removing material from the surface portion of the layer L1 having these microstructures, thereby maintaining the shape of these microstructures and thus forming an antireflection layer L2 from the same material as the layer L1.

13. The method for producing a transparent multi-layer system according to claim 10, characterized in that, These microstructures of the layer L1 in step i. are formed by one or more of the following: laser ablation, hot stamping, ultraviolet casting, injection molding, compression molding, roll-to-roll process, embossing process, plasma etching process, sol-gel process and / or 3D printing.

14. A method for producing a transparent multi-layer system according to claim 12 or 13, characterized in that, The layer L2 in step ii. is formed by one or more of the following techniques, which are sol-gel method, thermal evaporation, sputtering, glancing angle deposition (GLAD), chemical vapor deposition (CVD), wet etching and dry etching, lithography, focused ion beam technology, nanoimprint technology, microreplication, photoalignment and photopatterning.

15. A transparent multi-layer system, characterized in that, The transparent multi-layer system can be obtained according to one or more of the methods as defined in claims 12 to 14.

16. Use of the transparent multi-layer system according to any one of claims 1 to 11 as a glare-reducing component of a lighting device.

17. A luminaire comprising a light source and a transparent multi-layer system as defined in any one of claims 1 to 11.

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