Spectrally selective angular shading sheet

Abstract

The present invention relates to a film for coating a glass surface that possesses shading and spectral selectivity characteristics in a single sheet or film. The present invention also relates to an insulating glazing unit whose glass surface comprises said film with shading and spectral selectivity characteristics in a single sheet or film.

Description

Spectrally selective angular shading sheet Field of invention The present invention relates to a visually transparent film for application on a glass surface having both angular and spectrally selective solar protection characteristics. The present invention also relates to an insulating glazing unit having a glass surface comprising the visually transparent film having both angular and spectrally selective solar protection characteristics. Background of the invention The angular and spectral selectivity of solar radiation and light through transparent surface elements, such as glass panels, is increasingly important in architectural and mobility applications such as automotive, trains and ships. The surface of glass can be treated physically and chemically to provide spectral selectivity by creating a partially transmissive area coating for radiation that has a wavelength within the visible wavelength range and that is absorbing or reflecting at other wavelengths, such as the UV and IR ranges. The surface of glass can also be mechanically or chemically treated to produce reflection and scattering of incident light depending on the angle of incidence. This effect can be achieved by creating reflective and absorbent parts that are angled with respect to the receiving surface so that at least some of the reflected radiation is redirected within and along the length of the glass panel. The glass panel can also be coated with films, such as daylight films, which contain optical prism elements that allow light transmission at predetermined angles of inclination, and light-reflecting films, which reflect some of the visible light striking the surface of the daylight film. In this way, the reflected light can be redirected internally to illuminate a room. In fact, the angular and spectral selectivity of the incident radiation on the glass is generally achieved by combining different devices that provide these functions separately. Applying selective angled optical elements to a glass surface to redirect portions of solar irradiance often prevents the ability to see through the glass, as the redirected light blurs the image. This is an undesirable property, as it limits the view through the glass. Therefore, there is a need for an integrated solution that combines angular and spectrally selective filtering of solar radiation in a single device, without significantly reducing the visual transparency of the glass. Therefore, an improved device that provides these functions in a single device would be advantageous, and in particular, a more efficient and reliable angular and spectrally selective shading device capable of efficiently combining these functions in a single device would be advantageous. A sheet of the prior art has been published in U.S. patent number US2019 / 339431 A1. Object of the invention An objective of the present invention is to provide an angular, spectrally selective, and visually transparent sun protection device that combines these functions in a single sheet or film suitable for application on a glass surface. It can also be considered that an objective of the present invention is to provide an alternative to the prior art. In particular, an additional objective of the present invention may be considered to be providing a film for coating or applying on a glass surface that provides angular and spectral selectivity that solves the aforementioned problems of the prior art by combining both functions in a single film. Compendium of the invention Therefore, the objective described above and several other objectives are intended to be achieved in a first aspect of the invention by providing a film for coating or applying on a glass surface, said film being defined by the features of claim 1 and comprising: at least one polymer film substrate, spectrally or spectrally selective shading means, and angular or angularly selective shading means. The film of the invention is a unique film that achieves angular and spectrally selective shading of solar radiation for application on a single pane of glass or integrated into an insulating glazing unit consisting of two or more panes of glass. The film of the invention has the appearance of a transparent film that can be mounted on the surface of a pane of glass by means of a transparent adhesive or laminated between two panes of glass, for example, using transparent lamination materials and techniques. The sheet of the invention for application on a glass surface is a sheet suitable for coating the glass surface. According to the invention, the spectrally selective shading means are or comprise one or more optically selective layers coating a first side of at least one polymer film substrate. Spectrally selective shading means may be or comprise one or more optically selective IR-reflecting or absorbing layers coating a first side of at least one polymer film substrate. In other embodiments, the spectrally selective shading means are or comprise nano- or microscopic particles suspended in the polymer film substrate or an optically transparent coating applied over said polymer film substrate. In some other embodiments, the selective angular shading means are or comprise shading elements, such as microscopic shading elements. These shading elements are visually transparent when viewed from a distance. The shading elements may also be referred to in this document as selective angular shading elements. In some embodiments, the sheet for application on a glass surface according to the first aspect of the invention further comprises joining means, which join the shading elements to a second side of the at least one polymer film substrate. The second side can be opposite to the first side. Therefore, in one aspect, the invention relates to a sheet for application on a glass surface comprising: at least one polymer film substrate; one or more optically or spectrally selective layers coating a first side of the at least one polymer film substrate; shading elements; and bonding means, which bond the shading elements to a second side of the at least one polymer film substrate. In this document, one or more optically selective layers may also be referred to as spectrally selective layers. In some embodiments, the bonding means are or comprise one or more adhesive layers between the second side of said at least one polymer film substrate and the shading elements. In some further embodiments, the one or more adhesive layers are or comprise discontinuous layers. A discontinuous layer may be a layer that covers only the surface of the shading elements in contact with the second side of the polymer film substrate. In some further embodiments, the one or more adhesive layers are or comprise continuous layers. In some preferred embodiments, the bonding means are or comprise one or more adhesive layers incorporating the shading elements. Therefore, the bonding means or bonding elements can extend over the entire surface of the second side of the polymer film substrate, extend only to the contact area between the shading elements and the polymer film substrate, or be incorporated into the shading elements. Depending on their location, the bonding means must be optically transparent, i.e., when they extend over the entire surface of one side of the polymer film substrate, or they may not be optically transparent, i.e., when they extend only to the contact area between the shading elements and the polymer film substrate. According to the invention, the selective angular shading means are or comprise a microstructured system comprising the shading elements. The shading elements may also be referred to herein as opaque elements. The selective angular shading means may consist of a spatially shaped microstructured system or a body of opaque elements that provide an essentially opaque effect, meaning that the visible portion of the solar irradiation falling on the sheet of the invention is reflected or absorbed, but not transmitted through the microstructured body. The microstructured body of opaque elements has a shape such that the openings or perforations in the microstructured body allow the transmittance of solar radiation within certain angles of inclination with respect to the normal of the sheet of the invention. This is achieved by forming opaque elements as microblades or extensions mounted essentially perpendicular to the surface of at least one polymer film substrate. The effect of the microstructured body of opaque elements is to absorb or reflect solar radiation at high angles of incidence from the normal to the at least one polymer film substrate, and to allow greater transmittance of radiation at lower angles. Above a certain angle, the cutoff angle, all the irradiation falling on the microstructured body of opaque elements is partially absorbed and reflected. In some embodiments, the sheet for application on a glass surface according to the first aspect of the invention further comprises at least one optical layer covering one or more surfaces of the shading elements. The at least one optical layer covering one or more surfaces of the shading elements can be an optically absorbent or reflective coating. In some embodiments, where the shading elements are made of naturally optically opaque materials, at least one optical layer may be absent. Accordingly, selective angular shading means may comprise a microstructured system or body comprising shading elements coated by at least one optical layer on one or more surfaces. Therefore, selective angular shading means may consist of a spatially structured body of shading elements that are either translucent or opaque, and at least one optical layer applied to the surface of these translucent or opaque elements. The at least one optical layer applied to the opaque or structural elements modifies their optical properties. The combination of the microstructured body of translucent or opaque elements and at least one optical layer coating the surface of the opaque or microstructured elements provides an essentially opaque optical effect, meaning that the visible part of the solar irradiation falling on the microstructured body is reflected or absorbed, but not transmitted through the opaque elements. The sheet of the invention integrates two fundamentally different methods for filtering and shading solar radiation: firstly, a reduction of solar irradiation by filtering certain wavelengths of the radiating spectrum and, secondly, a further reduction by filtering the irradiation from certain angles. The combination of these two filtering principles and the use of a microstructured body of opaque elements allows for a progressive and highly effective reduction of solar radiation transmitted through the film. By adjusting the specific properties of the film, the following benefits can be achieved: The sheet is transparent to view from the outside as long as the line of sight is below the cut angle through the device, and the device will appear uniformly transparent from certain distances, as long as the opaque parts of the sheet are smaller than the resolution of the eye. This differentiates the sheet from the well-known exterior blinds, slats, and screens, which are characterized by being non-transparent and visible during operation. The sheet of the invention also allows daylight transmittance from angles less than the cut angle. Since daylight originates from solar radiation scattered across the sky and reflected by the surrounding environment, it is more uniformly distributed than directly irradiated sunlight. Because the sheet exhibits increasing transmittance as the angle of incidence moves from the cut point to become parallel to the extent of the opaque elements in the microstructured body, the sheet allows for high summed daylight transmittance proportional to the daylight levels experienced on the sheet's exterior. The advantage is that the transmitted daylight level follows the normal solar cycle and helps maintain the circadian rhythm of day and night, benefiting the occupants and promoting their well-being. The color rendering of the film can be optimized without compromising shading efficiency. If color-neutral shading is attempted using only spectrally selective coatings, shading efficiency will be limited by the composition of the solar spectrum. To achieve neutral color shading, the coating's transmittance in the visible (VIS) range must be high and uniform, while the transmittance in the ultraviolet (UV) and infrared (IR) parts of the spectrum must be as low as possible. In general, it has proven difficult to obtain a total solar energy transmittance well below 0.25 to 0.30 while maintaining high color rendering, even with the use of advanced multilayer coating stacks. Solar protection coatings with a solar protection efficiency above this level will influence the composition of the visible parts of the transmitted light and will typically appear tinted blue, brown, or gray. An additional advantage of the sheet of the invention is that spectrally selective coatings with high color rendering can be used to achieve a moderate total solar transmittance in the range of 0.30 to 0.40. Additional shading is achieved through the angular filtering of incident solar radiation by the microstructured body comprising opaque elements, and the combined effect of the two shading mechanisms is naturally greater than that of the neutral coating alone. In this way, the sheet can achieve an effective solar transmittance in the range of 0.05 to 0.15 while maintaining excellent color rendering. The sheet provides stronger shading at steeper angles, which has the advantage that the shading will be more effective when the sun's angles are higher in summer than in winter when the sun is low in the sky. The sheet of the invention exhibits a progressive nature, providing more natural solar heating to buildings during the winter than in the summer. The advantage is that the shading effect aligns with the typical need for more shade in summer than in winter. The film provides complete shading from direct sunlight at specific angles determined by the structure and geometry of its microstructured body, which comprises opaque elements. Incident radiation at angles above the cut angle is completely blocked, while the intensity of radiation from lower angles is gradually reduced. Protection from direct sunlight is important for people who work or rest near glazed facades, as is common in office buildings, cars, trains, ships, and similar environments. Direct sun exposure causes localized heating that forms directly on the skin, which is very uncomfortable. Another effect of shielding from direct sunlight is improved protection against optical glare. Glare on computer screens and other partially reflective surfaces caused by direct sunlight through glazed or transparent areas can be very bothersome for users. The effect of glare on users is immediate, and the only way to avoid it is by effectively blocking direct sunlight by physical means. In the sheet of the invention, the microstructured body comprising opaque elements achieves this physical blocking of radiation from angles higher than the cut angle. The sheet of the invention can be prepared in such a way as to prevent visibility from the outside through the sheet. This can be done by using a partially reflective coating as a selective layer on one side of the film, or by using a reflective coating on the side of the microstructured body comprising opaque elements facing outwards. The effect of using either method is that light from the outside will be reflected from the front of the sheet and thus effectively reduce visibility to the inside through the microstructured body. The sheet of the invention can be configured to reduce the line of sight from the inside and thus limit visibility at certain angles. This effect is achieved by designing the microstructured body, which comprises opaque elements, to achieve the appropriate cutting angle. By selecting at least one optical layer or surface coating on the microstructured body comprising opaque elements, the structured body can be reflective, absorbent, or any other intermediate characteristic. The coating can also be spectrally selective. The effect of this is that solar irradiance will be reflected by the microstructured body comprising opaque elements, and, if properly oriented, this can be used to direct sunlight further into the building. Using a surface coating that absorbs the visible spectrum on the microstructured body comprising opaque elements will reduce surface reflection, making the body appear dark even when illuminated. The advantage is that visibility from the inside out through the microstructured body will be excellent, even if the body is exposed to direct sunlight. The sheet of the invention takes the form of a film and can be applied to a glass surface using a transparent pressure-sensitive adhesive or sandwiched between two glass sheets using lamination techniques and materials such as EVA, PVB, ionomer, or similar materials. Application may involve the use of equipment such as film-to-plate pressure roller lamination, heating in vacuum laminating presses, or curing in autoclaves. When the sheet of the invention is applied to glass or laminated between two glass plates, an insulating glazing unit (IGU) can be formed using this resulting glass which includes the shading device as the sun-facing outer layer. Once integrated into an IGU, the IGU, including the film, can be installed like any other conventional IGU in any automotive or architectural application using the same techniques and tools. Polymer film substrate The at least one polymer film substrate serves as the mechanical backbone of the microstructured system comprising shading elements and also provides an optical surface for the one or more optically selective layers described below. Two key parameters characterize such a polymer film substrate: 1) it must be mechanically rigid to allow manipulation of the sheet without optical distortion, and 2) it must demonstrate optically flat surfaces and high optical transparency in at least parts of the solar spectrum. The at least one polymer film substrate can be manufactured in a wide variety of base polymers, thicknesses, functionalized surfaces, and surface definitions. In some embodiments, the at least one polymer film substrate is or comprises a polyester-based film substrate, such as a polyethylene terephthalate (PET)-based film substrate. In some other embodiments, the at least one polymer film substrate is or comprises a fluorinated polymer film substrate, such as a fluorinated ethylene-propylene (FEP) or ethylenetetrafluoroethylene (ETFE) film substrate. In some additional embodiments, the at least one polymer film substrate is or comprises a polyurethane-based film substrate, or a cellulose-based film substrate, or a polyethylene or polypropylene-based film substrate. One method for manufacturing a transparent polymer film substrate is by extrusion or calendering followed by bidirectional stretching of the extruded film. The thickness of at least one polymer film substrate used in the sheet can be selected with relative freedom and depends to some extent on the specific material chosen. In a preferred embodiment, the at least one polymer film substrate has a thickness of between 10 µm and 100 µm. In another embodiment, the at least one polymer film substrate has an elastic modulus greater than 500 MPa at 23 °C and preferably greater than 1000 MPa at 23 °C. The tensile strength of the film can be at least 40 MPa and preferably greater than 50 MPa. A preferred polymer film substrate for the sheet includes a high-transparency PET film stabilized for UV exposure in a thickness between 10 µm and 100 µm. A polymer film substrate with a thickness outside this range can also be used, but is less ideal. Thicker polymer film substrates reduce optical transmittance and clarity through the film and increase optical haze, while thinner films are difficult to handle and mechanically less stable. An important property of transparent film is its optical transmittance in the visible range of the spectrum. A typical transparent PET film will exhibit transmittance greater than 80% at wavelengths from 330 nm to 380 nm, and over 90% transmittance from 380 nm to 740 nm. PET films stabilized for UV exposure generally absorb in the UV range, and this also slightly influences transmittance in the visible range. A typical UV-stabilized film shows a sharp increase in transmittance around 360 nm and close to 50% transmittance at 380 nm. In the 380 nm to 420 nm range, the transmittance increases further to around 90% and remains at this level up to 740 nm.For the shading device, PET films with a transmittance of 90% across most of the visible spectrum are preferred, while films showing transmittances in the range of 70 to 90% in the same part of the spectrum are also acceptable. In some embodiments, at least one polymer film substrate has an average transmittance (T%) greater than 70% at wavelengths between 380 nm and 740 nm. Average transmittance is defined as the arithmetic mean of the transmittance values ​​within the defined spectral region of interest, for example, with the Vis spectrum, i.e., between 380 nm and 740 nm. Another important property that determines optical quality is the turbidity and clarity of the polymer film substrate. Turbidity should be low and clarity as high as possible. Both parameters are determined by the optical quality of the film surfaces and by the composition and structure of the film material itself. In some embodiments, at least one polymer film substrate has a turbidity of less than 3%, and in a preferred embodiment, the turbidity is less than 1%. In some embodiments, at least one polymer film substrate has a clarity greater than 98%, and in a preferred embodiment, the clarity is greater than 99%. In some embodiments, at least one polymer film substrate is coated with an optically selective layer that reflects or absorbs infrared radiation from the sun. For example, at least one polymer film substrate can be coated with a layer of IR-absorbing or reflecting nanoparticles, such as LaB6, TiN, or Cs0, 32WO3, such as nanoparticles with the CWO® brand. Optically selective layers The spectral selectivity of one or more optically selective coatings indicates that the coating has variable transmittance and reflectance in a specific part of the spectrum. For the application on the described sheet, coatings with high optical transmittance in the visible (VIS) portion of the spectrum (wavelengths from 380 to 740 nm) and low optical transmittance in the infrared (IR) portion of the spectrum (740 to 2500 nm) are well-suited. The change in transmittance near 740 nm and the stability of the transmittance in the VIS range are important for this application. The one or more optically selective coatings for the sheet can have consistently high transmittance in the VIS range and a sharp decrease in transmittance at 740 nm. The one or more optically selective coatings can also exhibit a gradient change in the IR and VIS ranges.The one or more optically selective layers may comprise a multilayer optical stack of metallic and semiconductor material deposited in a well-controlled thickness and sequence. The thicknesses of the multilayer can be varied to adjust the exact parameters of the coating. Therefore, in some embodiments, the one or more optically selective layers are or comprise one or more metallic layers or combinations of one or more metallic layers and semiconducting layers, such as metal oxides and metal nitrides. Metallic layers can be defined as layers comprising metallic elements. In some additional embodiments, the one or more metallic layers comprise Ag, Ti, or Au. In some other embodiments, the one or more semiconductor layers comprise ZnO, Zn2, SnO4, TiOx, or TiN. Furthermore, the one or more selective optical layers, such as a multilayer optical stack, typically also contain adhesion-promoting layers, surface barriers that protect the metallic layers from oxidation, and chemical diffusion barriers that prevent contamination of the substrate materials in the optical stack. Therefore, in some embodiments, the one or more optically selective layers comprise one or more barrier layers to protect said one or more metallic layers. In some other embodiments, the one or more optically selective layers comprise one or more adhesion-promoting layers. In some additional embodiments, the one or more optically selective layers comprise one or more barrier layers for chemical diffusion. One or more optically selective layers can be prepared by sputtering or reactive sputtering in a vacuum. In reactive sputtering, the metal oxide layers are formed by sputtering the pure metal in an oxygen-containing atmosphere. Sputtering of multilayer silver coatings and similar selective coatings onto a PET film can also be used. Such selective coatings, involving single-, double-, or triple-layer silver coatings or other coatings achieving a similar effect deposited on a transparent film, are a preferred embodiment of the shading device. Transparent films incorporating such a selective coating typically exhibit a transmittance of around 75% in the 450–550 nm range and a transmittance exceeding 40% in the essential portion of the visible spectrum from 400 to 740 nm. Another way to manufacture selective optical coatings is to disperse nanoparticles in a polymer film or in a coating on a film. Such nanoparticles can be prepared using materials like TiN, LaB6, or Cs0, 32WO3. The particles can be dispersed in an acrylic (MMA) coating, which is then applied to the polymer base film. The effect of the nanoparticles is that they absorb and reflect the IR portion of the irradiation, while exhibiting only minimal absorption in the visible range. In some embodiments, the at least one polymer film substrate coated on said first side by said one or more optically selective layers has an average T% greater than 40% at wavelengths between 380 nm and 740 nm, such as between 400 nm and 740 nm. In some preferred embodiments, the at least one polymer film substrate coated on said first side by said one or more optically selective layers has an average T% greater than 60% at wavelengths between 380 nm and 740 nm, such as between 400 nm and 740 nm. According to the invention, the one or more optically selective layers have an average T% of less than 60% at wavelengths between 740 nm and 2500 nm, i.e., in the near-infrared (NIR) region. Microstructured body comprising shading elements The microstructured body or system comprising shading or opaque elements is a key functional element of the sheet and is primarily responsible for the selective angular shading effect, the physical shading from direct illumination, and transparency. The geometry of the microstructured body comprising the opaque elements is fundamental to achieving the desired specific properties. The geometry of the opaque elements can be described and explained by two simple geometric relationships. The first parameter is the aspect ratio t / a, which is calculated from the extent t of the opaque elements and their thickness a. The second parameter is the cut angle, which is defined by the extent of the opaque elements perpendicular to the film surface, the size of the openings or perforations in the microstructured body comprising opaque elements measured parallel to the surface, and the refractive index of the material filling the space between the opaque extensions. The cut angle 1, as described in Figure 4 below, can be expressed by equation [1], where n1 and n2 denote the refractive indices of the first and second materials, l is equal to the size of the transparent opening in the second material, and t is the extent of the opaque elements perpendicular to the film surface: Shading elements can also be called elongated elements. According to the invention, the shading elements are elongated elements that have an extension ty, a thickness ay, and an aspect ratio t / a of at least 1, i.e., equal to or greater than 1 on average. In some additional realizations, the elongated elements have an aspect ratio t / a of at least 2, i.e., equal to or greater than 2 on average. In some other realizations, the elongated elements have an aspect ratio t / a of at least 4, that is, equal to or greater than 4 on average. In general, the shading efficiency of shading elements, opaque elements, or elongated elements increases with a decrease in the cut angle. For applications in temperate climate zones such as Europe, a common and suitable cut angle is close to 60°, as this corresponds to the maximum solar altitude in the region. If higher performance is required, the cut angle can be reduced to 55° or less. Similarly, the performance of the microstructured body comprising opaque elements increases with increasing aspect ratio. As the frontal area of ​​the microstructured body comprising opaque elements decreases, the opaque elements allow for greater transmittance parallel to the opaque extensions, which benefits visibility and daylight entry. The aspect ratio of a high-performance opaque element is around 4 or higher, while opaque elements with aspect ratios between 1 and 4 provide low to moderate element performance. An aspect ratio lower than 1 is not recommended. In some embodiments, the elongated elements have a predetermined extension t and are separated from each other by a predetermined value l, so that the cutting angle of the solar radiation incident on a coated glass surface is 70° or less, such as 60° or less, for example 55° or less. The size and dimensions of the microstructured body comprising the opaque elements must be shaped so that the size of each opaque element is smaller than the resolution of the human eye at a certain distance from the opaque elements. The spatial resolution angle of the human eye is approximated by the following equation [2], where λ is the wavelength of light and D is the diameter of the pupil: The maximum sensitivity is near a wavelength of 550 nm, and assuming a pupil diameter of 4 mm during the day, the spatial resolution angle is 1.68 × 10⁻⁴ rad or 9.6 × 10⁻³°. Therefore, at a viewing distance of 1 m, the resolution of the human eye is 0.167 mm, and this can serve as a guide for the maximum size and dimension for each of the thicknesses, a, in the opaque element. For most applications, a maximum thickness a of 150 µm has been found to be acceptable. In some embodiments, the elongated elements have a predetermined thickness equal to or less than 150 µm. In other preferred embodiments, the elongated elements have a predetermined thickness equal to or less than 75 µm. The spacing between the extensions, l, also plays a role in the performance of the opaque element. Because the extensions often occur in a regular, structured pattern where extensions of similar size and shape are repeated numerous times within the element, they form an optical grating, leading to diffraction of the transmitted light. Diffraction is best observed with monochromatic light sources but is also visible with broadband sunlight under certain viewing conditions. The diffraction effect is difficult to eliminate completely, but it can be suppressed by using structures with variable optical grating patterns and varying the spacing between the opaque elements. For regular structures, the absolute dimension of l is important. The smaller the distance, the stronger the diffraction.For typical applications, the spacing l should not be less than 250 µm, and good diffraction suppression is achieved with spacings greater than 300 µm. The upper limit for the spacing l is determined by the extent of the opaque element and the total thickness of the shading device. In some embodiments, the elongated elements are separated from each other by a predetermined l value equal to or greater than 250 µm. The elongated elements are coated with at least one optical layer that exhibits an average optical reflection of less than 15% in the 380 to 700 nm range. The at least one optical layer may contain at least one metallic layer and one metal oxide layer. The microstructured body containing the shading elements can be produced using multiple different techniques, including chemical milling and laser ablation of metal foils, photolithographic structuring of photosensitive polymers, or printing with UV-curable resins. Low-reflection coating on the microstructured shading element At least one optical layer or surface coating, such as a metallic coating of aluminum or silver or similar, can be used to create a low-reflection surface. These dark absorbent coatings can be achieved by creating a double-layer stack of a conductive and a dielectric material. Examples of such coatings include NbN-SiN, NiCr-TiOx, NiCr-SiN, Ti-TiOx, TiN-TiOx, and TiN-SiN. Alternatively, a three-layer stack of a dielectric material coated with a conductive material, which is itself coated with a dielectric material, can be used to obtain a low-reflection coating. Examples include coating stacks such as SiN-NiCr-SiN, TiN-NbN-SiN, and NbN-TiN-SiN. Countless other optical material and stack configurations are available that exhibit high visible absorption, and all of these materials can be used in the shading device. In some embodiments, the average optical reflection in the VIS range of 380 nm to 700 nm is less than 15%. In other preferred embodiments, the average optical reflection in the VIS range of 380 nm to 700 nm is less than 10%. One or more low-reflection optical layers can be deposited onto the structured element by sputtering or reactive vacuum sputtering processes. In a second aspect, the invention relates to an insulating glazing unit (IGU) having a glass surface on which the film is applied according to the first aspect of the invention. The IGU according to the second aspect of the invention comprises that the sheet according to the first aspect of the invention is a single film that achieves angular and spectrally selective shading of solar radiation on a single glass plate or integrated within the IGU consisting of two or more glass plates. In some embodiments, the IGU comprises: one or more glass plates and the sheet according to the first aspect of the invention. In some further embodiments of the IGU, the sheet is located on an external surface of one or more glass plates. In some embodiments of the IGU, the sheet is located between two of said one or more glass plates. The IGU according to the second aspect may comprise one or more glass plates and the sheet according to the first aspect of the invention applied to an external surface, i.e., a surface that will be exposed to light irradiation and the external environment during use, of one of the one or more glass plates or applied between two of the one or more glass plates of the IGU, i.e., applied to an internal surface of one of the one or more glass plates. The first, second, and other aspects and embodiments of the present invention may be combined in each case with any of the other aspects and embodiments. These and other aspects of the invention will become apparent and be clarified with reference to the embodiments described below. Brief description of the drawings The film for coating a glass surface according to the invention will now be described in more detail with reference to the accompanying figures. The figures show one way of implementing the present invention and should not be interpreted as limiting other possible embodiments that fall within the scope of the accompanying set of claims. Figure 1 is a schematic illustration of the sheet according to some embodiments of the invention having joining means that cover the entire surface of one side of the polymer film substrate. Figure 2 shows a schematic illustration of the sheet according to some embodiments of the invention having joining means that cover only the contact areas between the shading elements and the polymer film substrate. Figure 3 is a schematic illustration of the sheet according to some embodiments of the invention, which has joining means that cover the entire surface of one side of the polymer film substrate and incorporate the shading elements. Figure 4 is a schematic illustration of the sheet according to some embodiments of the invention, showing the cutting angle and related parameters. Figure 5 is a schematic illustration of actual spectrally selective coating stacks versus ideal spectrally selective coating stacks. Figure 6 is a schematic illustration of the optical reflectance of an example of a metal pile and metal oxide forming the optical layer that covers the microstructured body. Figure 7 and Figure 8 are schematic illustrations for calculating the optimal design parameters for the sheet shading elements according to some embodiments of the invention. Detailed description of a project Figure 1 shows a schematic illustration of sheet 24 according to some embodiments of the invention having joining means, such as an adhesive layer 4 covering the entire surface of one side of the polymer film substrate 1. Sheet 24, according to some embodiments of the invention, comprises a polymer film substrate 1, a transparent optically selective layer 2 coating the polymer film substrate 1, a microstructured body 3 comprising shading elements 6 having a spatially defined structure, an optical layer 5 coating at least part of the surface of the shading elements, defining the optical properties of the shading elements, and bonding means, such as an adhesive layer 4, bonding the microstructured body 3 to the polymer film substrate 1. Figure 2 shows a schematic illustration of sheet 25 according to some embodiments of the invention having joining means, such as an adhesive layer 10 covering only the contact areas between the shading elements 12 and the polymer film substrate 7. The sheet 25, according to some embodiments of the invention, comprises a polymer film substrate 7, a transparent optically selective layer 8 coating the polymer film substrate 7, a microstructured body 9 comprising shading elements 12 having a spatially defined structure, and an optical layer 11 coating at least part of the surface of the shading elements, which defines the optical properties of the shading elements. Bonding means, such as an adhesive layer 10, bonding the microstructured body 9 to the polymer film substrate 7 are located only in the contact area between the shading elements 12 and the polymer film substrate 7. Figure 3 is a schematic illustration of sheet 26 according to some embodiments of the invention having joining means, such as a polymer matrix compound 16, covering the entire surface of one side of the polymer film substrate 13 and incorporating the shading elements 18. The sheet 26, according to some embodiments of the invention, comprises a polymer film substrate 13, a transparent optically selective layer 14 coating a surface of the polymer film substrate 13, a microstructured body 15 comprising shading elements 18 having a spatially defined structure, and an optical layer 17 coating at least part of the surface of the shading elements, which defines the optical properties of the shading elements. Bonding means, such as a polymer matrix composite 16, fully incorporate the shading elements 18 and bond the microstructured body 15 to the polymer film substrate 13. Figure 4 is a schematic illustration of sheet 27 showing the cutting angle 1 and the parameters related to it. As mentioned above, the cut angle is defined by equation [1], where n1 and n2 denote the refractive indices of materials 19 and 20, l is equal to the size of the transparent aperture in material 20 and t is the extent of the shading elements perpendicular to the surface of the polymer film substrate, while a is the thickness of the shading elements. As shown in Figure 4, the incident light beam 21 hitting the outer surface of the sheet will be partially transmitted, i.e., light beam 22, and partially reflected, i.e., light beam 23, thus defining the cut angle 1. Figure 5 is a schematic illustration of actual spectrally selective coating stacks versus ideal spectrally selective coating stacks. The schematic illustration in Figure 5 shows transmittance curves for two selective coatings based on IR-absorbing nanoparticles dispersed in a PMMA matrix, the coating consisting of LaB6. Both examples meet the requirements described for the sheet of the invention. Coating 30 is based on LaB6 nanoparticles, while coating 29 is prepared with Cs0,32WO3 nanoparticles. Coating 30 provides higher transmittance in the visible spectrum and better color rendering than coating 29. Conversely, coating 29 exhibits the strongest shading effect in the IR spectrum. For use in the sheet of the invention, either type of coating can be used. Line 28 shows the ideal behavior with 100% transmittance in the visible spectrum and 0% transmittance in the UV and NIR regions. Selective coatings, as shown in Figure 5, can be manufactured in multiple ways. An example of an IR-absorbing coating like number 29 can be prepared using the following approach: 1. Cs0, 32WO3 nanoparticles (brand name CWO®) are commercially available in several standard formulations suitable for blending with polymers. 2. A suitable coating can be achieved by mixing 12.3 wt% of CWO particles with 54.3 wt% of methyl isobutyl ketone (MIBK) and 33.4 wt% of UV curing resin. 3. The solution containing the nanoparticles is applied to a PET film in a uniform layer 6 µm thick using a slotted matrix coating or a similar wet coating technique. 4. The coating is dried at 70 °C for 60 to 80 seconds and UV cured with a UV dose of 250 to 260 mJ / cm2 using a mercury lamp. Figure 6 includes examples of spectral reflectance curves for an optical layer 5 in Figure 1, 11 in Figure 2, or 17 in Figure 3. The low-reflection structure is prepared using a metal-metal-oxide optical stack. The base layer consists of a Ti layer with a thickness of 40 to 200 nm deposited by sputtering. The metal oxide layer consists of TiOx deposited with thicknesses of 42 nm and 45 nm. Optical reflectance curves 31 and 32 shown in Figure 6 represent 40–200 nm Ti stacks coated with 42 nm and 45 nm TiOx, respectively. Figure 7 is a schematic illustration for calculating the optimal design parameters for shading elements with a cut angle of 60°, a refractive index n2 equal to 1, and an aspect ratio equal to 4. Figure 8 is a schematic illustration for calculating the optimal design parameters for shading elements with a cut angle of 57°, a refractive index n2 equal to 1.5, and an aspect ratio equal to 4. The relationship between the design parameters (extension t 33 and 35) and the film thickness a 34 and 36 of the shading elements is illustrated in Figures 6 and 7, respectively. The graphs show that solutions using a spacer filler material with a refractive index greater than 1 result in a larger extent of the shading elements. For a given aspect ratio, this means that the previous visibility criteria of 0.150 µm will be limiting. Furthermore, the film thickness will be greater. The fabrication of a microstructured body comprising opaque elements with a high aspect ratio and a specific geometry can be achieved in several ways, including methods such as chemical milling of metallic substrates, UV lithography, and coiling of photoactive polymers.Chemical milling of metallic substrates typically limits the achievable aspect ratio to approximately 2 or 3, whereas methods involving the shaping of polymeric materials by UV structuring can achieve aspect ratios in the range of 3 to 10. A specific method for producing the structured substrate involves UV lithography of a solid film with a thickness corresponding to the desired extension t of the sheets. 1. A UV-cured film can be prepared from materials based on epoxies, acrylates, or copolymers of the two. The films are prepared using a grooved matrix coating of the dissolved polymer onto a flexible carrier film, typically a PET film. A preferred embodiment of the structured substrate includes an epoxy-acrylic copolymer film with a thickness in the range of 150 to 200 µm. 2. Structuring the coated and dried film can be achieved using UV illumination with UV radiation of a wavelength that excites the UV activators added to the UV-curing resin. Structuring occurs when parts of the polymer are shaded while other parts are illuminated. This can be done using a focused beam of UV light from a laser that creates the structure in a direct writing process, or by masking the film surface with a photomask containing a negative image of the desired structure and illuminating the masked film with a UV flood source. 3. After curing the desired structure on the film, the uncured areas are removed by dissolving them in a suitable developer solution. Developer solutions include organic solvents and aqueous systems containing alkalis such as HCO3- and CO32-. 4. The final processing stage includes cleaning and drying the developer system, followed by a post-UV treatment to ensure complete crosslinking of the UV-cured resin. Although the present invention has been described in relation to the specified embodiments, it should not be interpreted as being limited in any way to the examples presented. The scope of the present invention is set forth in the appended claims. In the context of the claims, the expressions "comprising" or "comprising" do not exclude other possible elements or steps. Furthermore, the mention of references such as "a" or "an," etc., should not be interpreted as excluding a plurality. The use of reference signs in the claims with respect to the elements indicated in the figures should also not be interpreted as limiting the scope of the invention. Moreover, the individual features mentioned in different claims may possibly be advantageously combined, and the mention of these features in different claims does not preclude the possibility that such a combination of features may be possible and advantageous.

Claims

1. A sheet for application on a glass surface comprising: - at least one polymer film substrate (1); - spectrally selective shading means (2), wherein said spectrally selective shading means comprise one or more optically selective layers coating a first side of said at least one polymer film substrate, wherein said one or more optically selective layers have an average transmittance of less than 60% at wavelengths between 740 nm and 2500 nm; and - selective angular shading means (3), wherein said selective angular shading means comprise shading elements and wherein said selective angular shading means comprise a microstructured system comprising said shading elements, wherein said shading elements are elongated elements having a length t and a thickness a and an aspect ratio t / a of at least 1. 2.A film for application on a glass surface according to any one of the preceding claims, further comprising bonding means that attach said shading elements to a second side of said at least one polymer film substrate, and wherein said bonding means comprise one or more adhesive layers between said second side of said at least one polymer film substrate and said shading elements.

3. A film for application on a glass surface according to claim 2, wherein said bonding means comprise one or more adhesive layers incorporating said shading elements.

4. A film for application on a glass surface according to claim 3, further comprising at least one optical layer, such as at least one low-reflection optical layer, covering one or more surfaces of said shading elements. 5.A film for application on a glass surface according to any one of the preceding claims, wherein said at least one polymer film substrate has an average transmittance greater than 70% at wavelengths between 380 nm and 740 nm.

6. A film for application on a glass surface according to any one of the preceding claims, wherein said at least one polymer film substrate comprises a polyurethane-based film substrate, or a cellulose-based film substrate, or a polyethylene or polypropylene-based film substrate.

7. A film for application on a glass surface according to any one of the preceding claims, wherein said at least one polymer film substrate is coated with a layer of nanoparticles that absorb or reflect IR. 8.A film for application on a glass surface according to claim 7, wherein said IR-absorbing or reflecting nanoparticle layer comprises LaB6.

9. A film for application on a glass surface according to any one of the preceding claims 7 to 8, wherein said IR-absorbing or reflecting nanoparticle layer comprises TiN.

10. A film for application on a glass surface according to any one of the preceding claims 7 to 9, wherein said IR-absorbing or reflecting nanoparticle layer comprises CsO, 32WO3.

11. A film for application on a glass surface according to any one of the preceding claims, wherein said one or more optically selective layers comprise one or more metallic layers and one or more barrier layers for protecting said one or more metallic layers. 12.A film for application on a glass surface according to any one of the preceding claims, wherein said at least one polymer film substrate coated on said first side by said one or more optically selective layers has an average T% greater than 40% at wavelengths between 380 nm and 740 nm.

13. A film for application on a glass surface according to any one of the preceding claims, wherein said elongated elements have an aspect ratio t / a of at least 2.

14. A film for application on a glass surface according to any one of the preceding claims, wherein said elongated elements have a predetermined length t and are separated from each other by a predetermined value l, such that the cutoff angle of the solar radiation incident on a coated glass surface is 70° or less. 15.An insulating glazing unit comprising: - one or more glass plates; and - said sheet according to any one of the preceding claims.

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