Device having light control structure with magnetizable particles

Abstract

To dispose, array and / or orient magnetizable particles each other in a resin using a magnetic field to form a desired structure for light control.SOLUTION: A solar device comprises: one or more photovoltaic cells disposed in an encapsulant 45; and a light control structure comprising a louver film having a series of louver structures. Each louver structure contains one or more groups of a plurality of magnetizable particles, and the plurality of magnetizable particles are dispersed in a binding matrix and aligned in at least a first orientation. The light control structure substantially transmits light incident at a first angle and substantially limits transmission of light incident at a second angle. Each louver structure is spaced apart from an adjacent louver structure, and each louver structure is substantially aligned in a plane substantially parallel to the adjacent louver structure.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This specification relates generally to devices such as, but not limited to, solar cells and solar roof panels having light control structures, such as films, that include magnetizable particles. [Background technology]

[0002] A light control film (LCF) is an optical film configured to control the transmission of light. A typical LCF includes a light-transmitting film having a plurality of parallel grooves formed in a light-absorbing material.

[0003] LCFs, as known in the art, control visible light and are used in conjunction with controlling the light available to a display. For example, an LCF can be placed close to a display surface, an image surface, or other surface to be viewed. At normal incidence (i.e., a 0-degree viewing angle), where an observer views the image through the LCF in a direction perpendicular to the film surface, the image is visible. As the viewing angle increases, the amount of light transmitted through the LCF decreases until an external viewing cutoff angle is reached, at which point substantially all (greater than about 95%) of the light is blocked by the light-absorbing material and the image is no longer visible. LCFs provide privacy to the observer by preventing other observers outside the typical range of viewing angles from viewing the image.

[0004] Originally, LCFs can be prepared by casting and ultraviolet curing a polymerizable resin onto a polycarbonate substrate. Such LCFs are commercially available from 3M Company (St. Paul, MN) under the trade name "3M™ Privacy Filters for Notebook Computers and LCD Monitors." These formation processes can be labor-intensive and expensive. Summary of the Invention

[0005] The present disclosure relates to devices that include light control structures with magnetizable particles that can be used as part of an LCF. These devices can include a variety of devices, such as solar cells and solar roof panels. The magnetizable particles can be positioned, aligned, and / or oriented relative to one another in a resin using a magnetic field to form a desired structure for light control.

[0006] Considering the processing and costs associated with conventional LCFs, the inventors recognized that LCFs could benefit, among other things, from the use of magnetizable particles that can be configured into desired structures at a lower cost. Accordingly, the inventors developed a process and apparatus for varying a magnetic field to control the orientation, position, and / or alignment of magnetizable particles relative to one another to form desired structures. The inventors discovered that a desired structure can be achieved for multiple magnetizable particles in a resin or binding matrix using an applied magnetic field that is varied, for example, by rotational modulation of the magnetizable particles or by varying the applied magnetic field at multiple angles. Once such a desired structure for multiple magnetizable particles in a resin or binding matrix is ​​achieved, the viscosity of the resin or binding matrix can be increased by partially or fully curing the resin or binding matrix. The variation in the magnetic field can be achieved by several processes, some of which are described in the following embodiments. The process can achieve a desired structure for multiple magnetizable particles.

[0007] In certain devices, including large-scale devices such as solar cells or solar roof panels, the resulting structure of the plurality of magnetizable particles can be realized as a light control film (LCF), which can be used to hide or camouflage the solar cell / solar roof panel when viewed from certain angles, while still allowing a significant amount of sunlight to pass through, enabling efficient conversion of sunlight into electrical energy.

[0008] According to one exemplary embodiment, a solar device comprises one or more photovoltaic cells disposed in an encapsulant and a light control structure including a louver film having a series of louver structures, each louver structure comprising one or more groups of a plurality of magnetizable particles dispersed in a binding matrix and aligned in at least a first orientation. The light control structure substantially transmits light incident at a first angle and substantially limits the transmission of light incident at a second angle. Each louver structure is spaced from an adjacent louver structure, and each louver structure is substantially aligned in a plane substantially parallel to the adjacent louver structures.

[0009] According to another embodiment, each louver structure is oriented at a louver angle of about 0° to about 50° from the normal to the light input surface of the light control structure.

[0010] According to another embodiment, the plurality of magnetizable particles includes multiple groups of magnetizable particles, each group of particles spaced from adjacent groups by between about 0.05 mm and about 5 mm.

[0011] According to another embodiment, a light control film comprises a series of louver structures, each louver structure comprising one or more groups of a plurality of magnetizable particles dispersed in a binding matrix and aligned in at least a first orientation. The light control film substantially transmits light incident at a first angle and substantially restricts transmission of light incident at a second angle. Each louver structure is spaced from an adjacent louver structure, and each louver structure is aligned in a plane substantially parallel to the adjacent louver structures.

[0012] According to another embodiment, light incident on the light input surface has a maximum relative brightness ratio (RBR) in the direction of the main viewing axis of 50% or more and exits the light output surface with an effective polar viewing angle (EPVA) of 150° or less.

[0013] According to another embodiment, a solar device comprises one or more photovoltaic cells disposed in an encapsulant, a twelfth light control film, and a second light control film, wherein the first light control film is oriented relative to the second light control film such that the substantially parallel louver structure for the first light control film is oblique at an angle between 10° and 90° relative to the substantially parallel louver structure for the second light control film.

[0014] According to another embodiment, the light control film comprises a plurality of magnetizable particles arranged and aligned in a binding matrix to form a louver film having alternating light transmitting and light blocking regions, the light blocking regions being aligned at a louver angle of about 0° to about 40°.

[0015] According to another embodiment, the light control film comprises a louver structure having a non-zero louver angle relative to the normal to the light incidence surface, and the EPVA is asymmetric about the incidence angle that results in the maximum relative luminance ratio.

[0016] According to another embodiment, the light control film comprises a louver structure having a non-zero louver angle relative to the normal to the light incidence surface, and the angle of incidence with the normal to the light incidence surface resulting in RBR is greater than 70° on a first side and less than 70° on a second side.

[0017] As used herein, The terms "a," "an," and "the" are used interchangeably with "at least one" and mean one or more of the elements being described.

[0018] The term "and / or" means either one or both. For example, "A and / or B" means A only, B only, or both A and B.

[0019] The terms "including," "comprising," or "having" and variations thereof are intended to encompass the items listed thereafter and equivalents thereof, as well as additional items.

[0020] Unless otherwise specified or limited, the terms "coupled," "disposed," or "deposited" and variations thereof are used broadly and include both direct and indirect coupling, disposition, deposition, etc.

[0021] The term "adjacent," as used herein, refers to the relative position of two elements, such as, for example, two layers that are in close proximity to one another, which may or may not be in contact with one another, and which may have one or more layers separating the two elements as understood by the context in which "adjacent" is used.

[0022] The term "directly adjacent" refers to the relative position of two elements, such as two layers that are adjacent to each other and in contact with each other, with no intermediate layer separating them. However, the term "directly adjacent" also encompasses situations where one or both elements (e.g., layers) have been treated with a primer or their surfaces have been modified to affect their properties, for example, by etching, embossing, etc., or by a surface treatment that may improve adhesion, such as corona or plasma treatment.

[0023] As used herein, the term "optically transparent" refers to an article (e.g., a film) that has a luminous transmittance greater than 20% and exhibits a haze value less than 40% in a given region of the electromagnetic spectrum (e.g., visible, infrared, radio, or any other range). Both luminous transmittance and total haze can be determined according to the method of ASTM-D 1003-13, Procedure A (Visibility Meter), using, for example, BYK Gardner Haze-gard Plus (catalog number 4725).

[0024] The term "film," as used herein, refers, depending on the context, to either a single layer article or a multi-layer structure in which the various layers have been treated according to the techniques described herein.

[0025] As used herein, the term "transmittance" refers to the fraction of energy transmitted across a surface in a given region of the electromagnetic spectrum (e.g., visible light, infrared, or any other range). Transmittance is measured according to the method described in ASTM 1348-15.

[0026] The term "major surface" or variations thereof is used to describe an article, such as a web, having a thickness that is small compared to its length and width. The length and width of such an article may define the "major surface" of the article, but this major surface need not be flat or planar, as is the case with the article. For example, the phrase may be used to describe an article having a first ratio (R1) of thickness (e.g., in the Z direction orthogonal to the major surface of the article at any point along the major surface) to a first surface dimension (e.g., width or length) of the major surface, and a second ratio (R2) of thickness to a second surface dimension of the major surface, where both the first ratio (R1) and the second ratio (R2) are less than 0.1. In some embodiments, the first ratio (R1) and the second ratio (R2) may be less than 0.01, in some embodiments less than 0.001, and in some embodiments less than 0.0001. The two surface dimensions do not have to be the same, and the first ratio (R1) and the second ratio (R2) do not have to be the same, so that both the first ratio (R1) and the second ratio (R2) fall within a desired range. Additionally, none of the first surface dimension, the second surface dimension, the thickness, the first ratio (R1), and the second ratio (R2) need be constant, so that both the first ratio (R1) and the second ratio (R2) fall within a desired range.

[0027] The term "light" includes one or more forms of light, alone or in combination, including, but not limited to, visible light, ultraviolet light, and infrared light, and radio frequency electromagnetic waves.

[0028] The terms "light controlling," "light control," and the like refer to an optical film configured to regulate the transmission of light through the optical film. In some embodiments, the transmission of light will be through the optical film to a substrate.

[0029] The term "relative brightness ratio" (or RBR) refers to the ratio of the brightness profile of a diffuse light source in the presence of a light control film to the brightness profile of the same light source without the light control film.

[0030] The term "angle of incidence resulting in maximum RBR," as used herein in the context of a film having mostly parallel louvers or louver structures, refers to the angle of incidence in a plane perpendicular to the length of the louvers or louver structures on the LCF such that the RBR is at its maximum value in a given region of the electromagnetic spectrum measured. For example, with respect to Figure 2B, the 30° angle is measured in a plane perpendicular to the length of the louvers and coincident with the plane of the page.

[0031] The term "effective polar viewing angle" (EPVA) refers to the range of incident angles for which the relative luminance ratio is 10% or greater. The viewing angle is the angle at which a non-zero Θ louver For a louver structure having a .gt. .times. ...

[0032] The term "ferrimagnetic" refers to a material that exhibits ferrimagnetism. Ferrimagnetism is a type of permanent magnetism that occurs in solids in which the magnetic fields associated with individual atoms spontaneously align themselves—in some cases parallel or co-directional (as in ferromagnetism) and in other cases in pairs approximately anti-parallel or opposite directions (as in antiferromagnetism). The magnetic behavior of single crystals of ferrimagnetic materials can be attributed to the parallel alignment, and the dilution effect of the atoms in the anti-parallel configuration keeps the magnetic strength of these materials generally lower than that of pure ferromagnetic solids such as metallic iron. Ferrimagnetism occurs primarily in magnetic oxides known as ferrites. The spontaneous alignment that creates ferrimagnetism is completely lost above a temperature known as the Curie point, which is characteristic of each ferrimagnetic material. When the temperature of the material drops below the Curie point, the ferrimagnetism returns.

[0033] The term "magnet" can include ferromagnetic materials that respond to a magnetic field and function as a magnet. A "magnet" can be any material that exerts a magnetic field, either permanently, semi-permanently, or temporarily. The term "magnet" can be one individual magnet or an assembly of magnets that functions like a single magnet. The term "magnet" can include permanent magnets and electromagnets.

[0034] The term "ferromagnetic" refers to a material that exhibits ferromagnetic properties. Magnetism is a physical phenomenon in which certain uncharged materials strongly attract other materials. In contrast to other substances, ferromagnetic materials are easily magnetized, and in strong magnetic fields, the magnetization approaches a well-defined limit called saturation. When a magnetic field is applied and then removed, the magnetization does not return to its original value. This phenomenon is called hysteresis. When a ferromagnetic material is heated to a certain temperature called the Curie point (the Curie point is generally different for each material), it loses its properties and ceases to be magnetic, but becomes ferromagnetic again when cooled.

[0035] The terms "magnetic" and "magnetized" mean ferromagnetic or ferrimagnetic at 20°C unless otherwise specified.

[0036] The term "magnetizable" means that the article being referred to is magnetic or can be made magnetic using an applied magnetic field, and has a magnetic moment of at least 0.001 electromagnetic units (emu), in some cases at least 0.005 emu, and in still other cases 0.01 emu, and in still other cases at most 0.1 emu, although this is not a requirement.

[0037] The term "magnetic field" refers to a magnetic field that is not generated by any celestial body (e.g., the Earth or the Sun). Generally, magnetic fields used in the practice of the present disclosure have a field strength in the region where the magnetizable particles are oriented of at least about 10 Gauss (1 mT), in some cases at least about 100 Gauss (10 mT), in still other cases at least about 1000 Gauss (0.1 T), and in still other cases at least about 10,000 Gauss (1.0 T).

[0038] The term "rotation" refers to an angular displacement that is a fraction of a rotation, or a rotation, or multiple rotations.

[0039] The term "length" refers to the longest dimension of an object.

[0040] The term "width" refers to an object's longest dimension perpendicular to its length.

[0041] The term "thickness" refers to an object's longest dimension perpendicular to both its length and width.

[0042] The term "aspect ratio" refers to the length / thickness ratio of an object.

[0043] The terms "orient," "orient," "orienting," or "oriented," when referring to magnetizable particles provided by the magnetic field of the present disclosure, can refer to a non-random arrangement of at least a majority of the particles relative to a substrate (sometimes referred to herein as a backing). For example, a majority of the magnetizable particles have a major planar surface disposed at an angle of at least 70 degrees relative to the first major surface of the substrate after application of the magnetic field. These terms can also refer to the major axes and dimensions of the magnetizable particles themselves. For example, the maximum length, width, and thickness of a particle are a function of the shape of the magnetizable particle, which may or may not be uniform. The present disclosure is not limited to any particular particle shape, size, type, etc., and numerous exemplary magnetizable particles useful for the present disclosure are described in further detail below. However, for some shapes, "length," "width," and "thickness" refer to major and minor sides. Regardless of the exact shape, any magnetizable particle can have a center of gravity that can define the particle's local Cartesian axes: u (length), v (width), and w (thickness). Orientation achieved by the magnetic fields of the present disclosure can involve applying a magnetic field to change or in some way alter the spatial configuration of at least a majority of a plurality of magnetizable particles relative to the substrate and / or at the particle level. The change or alteration can be to a desired range of rotational orientation about the particle in one or more of the z-axis, y-axis, and / or x-axis, and / or to a range of rotational orientation about the particle axis.

[0044] The terms "position," "positioning," "location," or "location," when referring to magnetizable particles provided by the magnetic fields of the present disclosure, can refer to a non-random arrangement of at least a majority of the particles relative to one another. For example, a majority of the magnetizable particles may be separated by a desired distance in at least one axis after application of the magnetic field.

[0045] The terms "align," "align," "aligned," or "to align," when referring to magnetizable particles provided by the magnetic fields of the present disclosure, can refer to a non-random arrangement of at least a majority of the magnetizable particles. Specifically, "aligning" can refer to arranging a majority of the magnetizable particles such that a majority of the magnetizable particles have major surfaces that are substantially parallel to each other, substantially perpendicular to each other, and / or oriented at a desired angle relative to each other.

[0046] The term "desired structure" refers to a structure formed from a plurality of magnetizable particles, at least a majority of the particles having one or more of an orientation, position, and / or alignment relative to one another, and / or a substrate that is affected by the application of a magnetic field.

[0047] The terms "vitrification," "vitrified," "vitrifying," or "vitrifying," when referring to a resin mixture containing magnetizable particles, mean increasing the viscosity of the resin mixture so that at least a majority of the magnetizable particles can maintain their desired structure after removal from the magnetic field. Vitrification may be achieved only partially, enough to allow at least a majority of the magnetizable particles to maintain their desired structure after removal from the magnetic field. Vitrification can occur by polymerization (e.g., radiation-curable or thermosetting resin systems), solidification by removal of thermal energy (e.g., solidification of a polymer melt), or evaporation of solvent from the resin mixture. As used herein, the terms "curing," "curing 1," and "curing 2" all refer to the vitrification process.

[0048] All scientific and technical terms used herein have meanings commonly used in the art unless otherwise specified. The definitions provided herein are intended to facilitate understanding of certain terms used frequently in this application and are not intended to preclude reasonable interpretations of such terms in the context of this disclosure.

[0049] Unless otherwise indicated, all numbers in the description and claims expressing feature dimensions (feature sizes), quantities, and physical properties used in the specification and claims should be understood as being modified in all instances by the term "about." Accordingly, unless specifically indicated to the contrary, the numerical parameters set forth in the above specification and appended claims are approximations that may vary depending upon the desired properties sought to be obtained by one of ordinary skill in the art using the teachings disclosed herein. At the very least, each numerical parameter should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques; however, this is not intended to limit the application of the doctrine of equivalents to the scope of the claims. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the present disclosure are approximations, the numerical values ​​set forth in the specific examples are reported as precisely as possible. However, any numerical value inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

[0050] The term "substantially" means within 20 percent (sometimes within 15 percent, in still other cases within 10 percent, and in still other cases within 5 percent) of the referenced attribute. Thus, value A is "substantially similar" to value B if value A is within one or more of 5%, 10%, 20% of value A, plus / minus.

[0051] The features and advantages of the present disclosure will be further understood by consideration of the detailed description and appended claims.

[0052] The recitation of numerical ranges by endpoints includes all numbers subsumed within that range (e.g., a range of 1 to 5 includes, for example, 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5) and any range within that range.

[0053] This Summary is intended to provide an overview of the subject matter of this patent application. It is not intended to provide an expert or exhaustive description of the invention. The Detailed Description is included to provide further information regarding this patent application. [Brief explanation of the drawings]

[0054] [Figure 1] 1 is a schematic cross-sectional view of a device having a light control structure according to a first embodiment of the present invention; [Figure 2A] 3 is a schematic cross-sectional view of a light control structure in the form of a light control film having aligned magnetizable particles according to another embodiment of the present invention. [Figure 2B] 1 is a schematic cross-sectional view of a light control structure in the form of a light control film having aligned and tilted magnetizable particles according to another embodiment of the present invention. [Figure 3A] 1 is a schematic diagram of an exemplary solar panel installed on the roof of a residential home, according to one embodiment of the present invention. [Figure 3B] FIG. 10 is a diagram showing calculations for the viewing angle of a louver film having louver structures formed perpendicular to the light incident surface. [Figure 3C] FIG. 10 shows a calculation of the viewing angle of a louver film having louver structures formed at a non-perpendicular angle to the light incidence surface. [Figure 4A] FIG. 1 is a schematic perspective view of a magnetizable particle according to an embodiment of the present disclosure. [Figure 4B] FIG. 4B is an enlarged view of region 4B of FIG. 4A. [Figure 5] 1 is an image of a plurality of magnetizable particles arranged in a desired structure resulting from application of a magnetic field to a substrate, according to one embodiment of the present disclosure. [Figure 6] FIG. 1 is a schematic diagram of a first method for producing an optical film according to one embodiment of the present disclosure, the method applying a curing by varying a magnetic field through rotational modulation, whereby a plurality of magnetizable particles assume a desired structure under the influence of the magnetic field. [Figure 6A] 7A and 7B illustrate an example structure having a plurality of magnetizable particles resulting from the magnetic field of the method of FIG. 6, according to one embodiment of the present disclosure. [Figure 6B] FIG. 6B is a cross-sectional view of FIG. 6A. [Figure 7]FIG. 1 is a schematic diagram of an example of a magnet capable of producing the magnetic fields discussed in this disclosure. [Figure 7A] 8 is a schematic diagram illustrating the magnet of FIG. 7 having a magnetic field with rotational modulation as a result of rotation of the magnet, according to one embodiment of the present disclosure. [Figure 8A] 1A-1C illustrate an arrangement of a plurality of magnetizable particles in the cross-web, down-web, and thickness directions relative to each other, according to one embodiment of the present disclosure. [Figure 8B] 1A-1C illustrate an arrangement of a plurality of magnetizable particles in the cross-web, down-web, and thickness directions relative to each other, according to one embodiment of the present disclosure. [Figure 8C] 1A-1C illustrate an arrangement of a plurality of magnetizable particles in the cross-web, down-web, and thickness directions relative to each other, according to one embodiment of the present disclosure. [Figure 9] FIG. 1 is a cross-sectional view of an exemplary optical film having multiple layers produced by one of the methods discussed herein, some of which contain multiple magnetizable particles, according to one embodiment of the present disclosure. [Figure 10] 1 is a plot showing viscosity values ​​measured at 25° C. for sample resin mixtures. [Figure 11] 10 is an image of a cross-sectional view of a sample LCF having angled light guide structures prepared in accordance with an embodiment of the present invention. [Figure 12] 1 is a plot showing transmittance as a function of incident angle for two LCF samples prepared in accordance with embodiments of the present invention and a control LCF sample. [Figure 13] 10 shows microscope images at various thickness locations across the sample LCF. [Figure 14] 1 shows microscope images of several sample LCFs. [Figure 15] FIG. 10 shows the average louver spacing versus concentration of magnetically alignable particles in sample LCF. [Figure 16] 1 shows microscope images of several sample LCFs. [Figure 17A] 1 shows microscope images of several sample LCFs. [Figure 17B] 1 shows cross-sectional images of several sample LCFs. [Figure 18] 1 is an angular transmission plot of various sample LCFs. [Figure 19A] FIG. 10 shows a set of conoscopic angular transmission plots for various tilts of the louvered film. [Figure 19B] FIG. 10 shows a set of cross sections of conoscopic angular transmission plots for various tilts of the louver film in a plane perpendicular to the length of the louver structure. [Figure 20A] FIG. 10 shows a comparison of transmittance for simulated 15° tilted louvers (left) and fabricated films with 15° tilted particles. [Figure 20B] FIG. 10 is a cross-sectional view comparing the transmittance for a simulated 15° tilted louver (left) and a fabricated film with 15° tilted particles. [Figure 21] 1 is a plot showing a comparison of modeled transmission peak angles with Snell's Law. The present invention is amenable to various modifications and alternative forms, details of which are shown by way of example in the drawings and will be described in detail. It should be understood, however, that the invention is not intended to be limited to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the appended claims. DETAILED DESCRIPTION OF THE INVENTION

[0055] According to various embodiments described herein, devices can include light control structures, such as light control films (LCFs), that can be formed using magnetizable particles dispersed in a binder matrix or resin. The magnetizable particles can be positioned, aligned, and / or oriented relative to one another in the binder matrix or matrix resin using a magnetic field to form desired structures for light control, such as louver structures. In some aspects, one or more groups of magnetizable particles can form one or more louver structures, which can be spaced, aligned, and / or angled to form desired structures for controlling the angular transmission of the film. These light control structures can be used to camouflage one or more solar cells and / or solar panels on a roof or other structure. The methods described herein can be used to form devices with assembled magnetizable particles having multiple particle lengths and heights.

[0056] While the devices and light control structures (e.g., LCFs) described herein are utilized in exemplary solar cell and solar panel applications, those skilled in the art will appreciate that such devices and / or LCFs can be utilized in numerous other applications, including privacy films, displays (for computers, automobiles, etc.), fingerprint sensors, and window films. While general LCFs are known, LCFs having specially tailored structures according to the compositions and methods described herein can be designed and manufactured in a much simpler and more cost-effective manner than known LCF manufacturing methods, such as those described in WO 2018 / 078493 and WO 2018 / 229600.

[0057] The LCFs of the present disclosure can be applied to a photovoltaic cell ("PV cell"), to one or more PV cells, and / or to an entire solar module or panel. An advantage of placing an LCF on a PV cell or module is that the LCF can hide or obscure the cell or module without significantly reducing incident solar radiation on the photovoltaic surface to observers viewing the cell or module at angles greater than one-half the external viewing cutoff angle. PV cells can be made from silicon, CIGS, perovskites, etc.

[0058] PV cells are generally relatively small in size and can be combined into physically integrated solar modules. PV modules are generally formed from a single cell or a small number of cells in one or more "strings" of PV cells, each string containing two or more PV cells, which are configured in rows and typically electrically connected in series using tinned, rectangular copper wire (also known as electrical connectors, tabbing ribbon, or bus wire). These electrical connectors are typically attached to the PV cells by a soldering process.

[0059] A functional PV cell typically comprises an actual photovoltaic cell surrounded by an encapsulant, such as an EVA- or polyolefin-based encapsulant. In a typical structure, the PV cell includes an encapsulant on both sides of the photovoltaic surface. Glass panels (or other suitable transparent polymeric materials) are bonded to the front and back surfaces of the encapsulant, respectively. The front panel is transparent to solar radiation and is typically referred to as the surface layer or surface cover. The back panel may be transparent, but is not necessarily so, and is usually referred to as the back layer or backsheet. The surface cover and backsheet may be made of the same or different materials. Typically, the surface cover is made of glass, although other transparent materials may also be used. The encapsulant is usually a transparent polymeric material bonded to the surface layer and backsheet to encapsulate the PV cell and further physically encapsulate the photovoltaic surface. This laminated structure provides mechanical support for the PV cell and also protects it from damage caused by environmental factors such as wind, snow, and ice. A typical PV module is fitted into a frame, usually made of metal, with a sealant covering the edges of the module. The frame not only protects the edges of the module but also provides additional mechanical strength to the entire assembly. However, not all modules have frames.

[0060] In some embodiments, the light control structure of the present disclosure is placed on a single photovoltaic cell or on the entire solar module. The light control structure can be placed in different locations within the solar assembly. For example, an LCF can be placed adjacent to the photovoltaic surface, embedded in the encapsulant, or adjacent to the surface layer, either next to the encapsulant or on the exterior surface of the surface layer. In certain preferred embodiments, the light control structure, such as an LCF, is placed adjacent to the surface layer, between its interior surface and the encapsulant. An adhesive or adhesive layer can be used to bond the LCF to the photovoltaic cell or to the desired substrate within the solar module. In some embodiments, the LCF of the present disclosure is placed on the exterior of the module on the surface layer. The adhesive or adhesive layer can be optically clear, tinted, or diffusive.

[0061] 1 shows a cross-sectional view of a solar cell device 10 according to one embodiment of the present invention. The device includes a cover layer 12, an LCF layer 20, one or more solar cells 40 disposed in an encapsulant 45, and a backside layer or backsheet 50. This illustration is provided to illustrate a typical solar cell / solar panel design incorporating the light control structures of the present invention. As will be understood by those skilled in the art upon reading this specification, alternative solar cell / solar panel structures can be utilized that include the light control structures (e.g., LCFs) described herein.

[0062] Cover layer 12 can be formed from a protective material such as glass, a barrier film, or an ultra-barrier film. This layer can be used to protect the internal layers of the device from external elements such as rain, dust, and sand. In the embodiment shown in FIG. 1, incident light 5 is incident on a first major surface of cover layer 12. While cover layer 12 is shown as having a smooth outer surface, it may also be smooth, textured, lensed, or coated with layers to incorporate anti-reflective and / or anti-fouling functionality.

[0063] In one embodiment of the invention, cover layer 12 is disposed on LCF 20. In this embodiment, LCF layer 20 is a separate layer from cover layer 12. In an alternative embodiment, LCF layer 20 can be combined with adhesive 42 to bond cover layer 12 to encapsulant 45. In a further alternative, a layer of optical elements 18, such as an array of integral lens structures, can be disposed between cover layer 12 and LCF 20.

[0064] The encapsulant 45, the cells 40 (eg, PV cells 40a and 40b), and the backsheet layer 50 can include the materials described above.

[0065] Specifically, LCF layer 20 can include a plurality of magnetizable particles arranged and aligned in a binding matrix or resin to form a louvered film having alternating light-transmitting regions 21 and light-blocking regions 22. LCF layer 20 includes a light input surface 23 and a light output surface 24 opposite light input surface 23. While the light input and light output surfaces are labeled for reference only, LCFs of the present disclosure may be flipped upside down. That is, in some embodiments, the light output surface in the LCFs described herein may function as the light input surface, and the light input surface may function as the light output surface, depending on the orientation of the film and the location of the light source. In some embodiments, light-blocking region 22 may extend from light input surface 23 to light output surface 24.

[0066] In another embodiment, the LCF layer 20 can be comprised of a plurality of magnetizable particles arranged and aligned in a bonding matrix to form a louver film having alternating light transmitting regions 21 and light blocking regions 22. In another aspect, the light blocking regions are angled at a louver angle of greater than 0° to about 50°.

[0067] In certain preferred embodiments, region 21 is substantially transparent to visible, ultraviolet, and infrared light. In other embodiments, the transmission characteristics of region 21 are transparent or absorptive in the visible, ultraviolet, and / or infrared spectrum, and can be tuned such that the transmission or absorptivity in each spectral range can be tuned independently of the other ranges. In some embodiments, region 22 is a spectrally selective absorbing region, where absorption is limited to a particular wavelength range of the solar spectrum. In some embodiments, region 22 is a spectrally selective reflective region, where reflection is limited to a particular wavelength range of the solar spectrum.

[0068] In certain preferred embodiments, region 22 is substantially opaque to visible light but is opaque to infrared and / or ultraviolet light, while region 21 is substantially opaque to visible, ultraviolet, and infrared light, and region 22 is substantially opaque to ultraviolet and infrared light but is substantially opaque to visible light.

[0069] As shown in FIG. 1 , regions 22 are spaced apart and aligned (non-randomly) at a non-normal angle from surface 23. These regions 22 can have depth, thickness, height, and / or length in multiple dimensions. For example, the spacing distance between regions 22 (e.g., groups of magnetizable particles / louver structures) within the same desired structure may be about 5 mm or less, or about 4 mm or less, or about 3 mm or less, or about 2 mm or less, or about 1 mm or less, or about 0.5 mm or less, or about 0.25 mm or less, or about 0.1 mm or less, or about 0.05 mm. While regions 22 are shown as non-random, the spacing may have some randomness across the extent of the article. Thus, the spacing distance between adjacent louver structures may be substantially the same, although there may be some randomness in the spacing across the extent of the article that does not significantly affect optical performance.

[0070] As described in further detail herein, these light-blocking regions can be tilted at a selected angle, thereby acting as a louver-type structure with a selected light transmission angle. The inventors have observed that by controlling the configuration and shape (geometry) of regions 22, the efficiency of the LCF can be improved in allowing a maximum amount of radiation to pass through the film toward the photovoltaic device (PV) surface, while hiding such surface from the viewer. Such control can be provided by methods described further herein.

[0071] In this manner, the light control structure can include groups of magnetizable particles (each spaced apart group of particles is referred to as a louver structure, and the light control structure comprises an array or series of louver structures), each aligned in at least a first orientation, and each group of particles spaced apart from adjacent groups, as shown in Figures 2A and 2B.

[0072] The LCF may be sized for use with conventional solar cell or solar panel structures, which may have dimensions such as 1.67 m x 1.0 m for a conventional 60-cell panel, or other conventional sizes. The louver structures may have any of the widths described herein.

[0073] 2A and 2B show alternative cross-sectional views of LCF layers 20′ and 20″. In FIG. 2A, LCF layer 20′ comprises a plurality of magnetizable particles 25 dispersed in a binding matrix or resin 30 (described in more detail below) and arranged and aligned according to methods described herein. In this embodiment, groups of particles 25 are formed in a plane separated from one another by a spacing distance and aligned normal to surface 23 (and extending into or out of the page dimension). Optionally, LCF 20 can be formed on a removable carrier film 35 that is removed during construction of device 10. Alternatively, in FIG. 2B, LCF layer 20″ comprises several groups, each group having a plurality of magnetizable particles 25 dispersed in a binding matrix or resin 30 and separated by a spacing distance and aligned at an angle Θ relative to the normal to surface 23. louver , whereby the group of particles 25 is arranged and aligned at an angle Θ relative to the surface 23. louver The angle Θ, also referred to herein as the tilt angle or louver angle, is formed in an inclined plane. louverConsidering that 42.1° is the critical angle for glass (which has a refractive index (n)=1.5), Θ can be from about 0° to about 70°, preferably from about 0° to about 50°, more preferably from about 0° to about 40°, and even more preferably from about 0° to about 30° (depending, for example, on the transmittance of the magnetizable particles used and the refractive index of the binding matrix). In the example of Figure 2B, Θ louver is 20°. As shown in FIGS. 2A and 2B, each group of magnetizable particles 25 may have approximately the same density and / or thickness within a plane, or may have a density and / or thickness that varies within the plane, with the planes being substantially parallel to one another. Alternatively, each group of magnetizable particles 25 may have a height that varies within the plane of FIGS. 2A and 2B and / or a length that extends out of the plane of these figures. The louver structures 25 may be oriented with slightly different louver angles and may not be strictly parallel within the plane of the film or thickness direction. Some randomness in the louver structure may result in a non-uniform appearance, which may be desirable for some applications, while other applications may require a substantially uniform appearance.

[0074] In this manner, the LCFs 20, 20', 20" can be formed as louver films used to camouflage the device 10 from certain viewing areas while allowing significant sunlight transmission. For example, the louver films can be placed between an observer and the photovoltaic (e.g., Si, CIGS, perovskite, etc.) cells. The louver films can also be designed to appear a particular color to the observer, so that they can blend with roof tiles and / or have an aesthetically pleasing tile-like appearance. It is an advantage of various embodiments of the present invention that such louver films absorb or reflect only as much as is needed for a desired color appearance. Wavelengths that do not contribute to the color appearance of the module can be transmitted through the thickness of the louver film. This can be achieved by reflection from the louver film, transmission through the louver film, or a combination. The louver films can be configured to prevent light, or certain wavelengths of light, from reflecting off the solar cells, thereby hiding them from an observer (such as someone viewing a house from the street; see, e.g., FIG. 3A). The maximum transmittance can be selected to correspond to a particular roof pitch and / or latitude of the solar orbit.

[0075] With reference to Figure 2B, a ray of light shown striking the surface of the film at a 30° angle of incidence is refracted to an angle nearly parallel to the louver structure. This ray, and the parallel ray, will have the least interaction with the louver structure and therefore have the maximum angle of incidence transmittance through the film. Measurements of angular transmittance through the film can be easily measured using a standard photometric detector with a rotation stage to vary the angle of incidence. Transmittance through LCF 20, 20', and 20'' can be obtained over any wavelength band of interest. For example, for PV cells, it may be desirable to average the transmittance over the useful wavelengths of the PV cell, e.g., wavelengths from 350 nm to 1200 nm. Other applications may involve the visible wavelength band (400 nm to 700 nm) or other subbands within the electromagnetic spectrum.

[0076] The angular profile of transmission through the film can be obtained, from which the (maximum) relative luminance ratio (RBR), the angle of incidence at which maximum RBR occurs, and the effective polar viewing angle can be obtained.

[0077] FIG. 3A shows a schematic diagram of an exemplary solar device (e.g., a solar panel installed on the roof of a residential home 60) according to an embodiment of the present invention. In this illustration, the solar panel features have been removed except for the LCF 20 (shown with an exaggerated relative size). For maximum solar transmittance, the optimal louver angle (Θ) relative to the louver film surface 23 is louver optimal The louver angle (Θ) must be centered on the refracted rays from the sun's position 95° at noon on the vernal and autumnal equinoxes in the target location. louver optimal ) is the latitude (Θ latitude ) and roof pitch (Θ roof pitch ) can be selected based on the absolute value of the difference between: θ louver optimal =|θ latitude -θ roof pitch |

[0078] External viewing angle Θ view angle ext can be obtained from the louver shapes shown in Figures 3B and 3C.

[0079] FIG. 3B shows the viewing angle (Θ) for a louver film 20 having louver structures 25 (e.g., groups of magnetizable particles 25a, 25b) formed perpendicular to the light incident surface 23. view angle ext ) and calculate the inclination angle, i.e., the louver angle (Θ louver )=0°. In FIG. 3B, each louver structure 25 has a height H, a width (w l ) and separated from another louver structure by a spacing distance (d), where d = spacing distance from the edge of the louver structure to the opposite edge of the adjacent louver structure - louver width (w l ), the internal angle Θ within the light transmitting region 21 (see, for example, FIG. 1) is used to calculate the external viewing angle Θ view angle ext can be calculated according to the following formula:

number

[0080] The external viewing angle is the maximum geometric angle from the proximal edge of one louver to the distal edge of the adjacent louver. This is determined by the louver matrix refractive index (n louver ) (see, for example, area 21 in FIG. 1), louver spacing (d), louver height (H), and louver width (w l ) The interior angle is equal to the arctangent of the spacing distance (d) of regions 21 divided by the louver height. The exterior viewing angle is determined by Snell's Law and is symmetric. While FIG. 3B assumes a flat exterior surface, one skilled in the art would be able to predict the effect of an uneven, curved, or roughened exterior surface given this specification.

[0081] FIG. 3C shows the angle of the louver at a non-zero angle (Θ louver ) for a louver film 20 having louver structures 25 (e.g., groups of magnetizable particles 25a, 25b, etc.) formed with a plurality of viewing angles, (Θ view angle ext,1 ) and (Θ view angle ext,2 ), the calculation of is shown below. For such a tiled louver structure, the external viewing angle is not symmetric. The external viewing angle is determined in the same way as above:

number

[0082] As shown in Figures 3A-3C, solar cells and solar panels can be assembled with louvered films designed for specific geographic locations, roof pitches, and roof styles that maximize sunlight transmission while providing camouflage for the structure itself for aesthetic appeal.

[0083] For example, in one embodiment of the present invention, the maximum relative brightness ratio (RBR) is at least 50%, which can be achieved using an LCF structure consistent with that described herein.

[0084] In view of the description herein, and as demonstrated by the experiments below, in one embodiment, the light control film can be configured so that light incident on the light input surface exits the light output surface with a maximum relative luminance ratio (RBR) in the direction of the main viewing axis of 50% or greater and an effective polar viewing angle (EPVA) of 150° or less.

[0085] In another embodiment, the light control film can be configured so that light incident on the light input surface exits the light output surface with a maximum relative brightness ratio (RBR) in the direction of the main viewing axis of 60% or greater.

[0086] In another embodiment, the light control film can be configured so that light incident on the light input surface exits the light output surface with a maximum relative brightness ratio (RBR) in the direction of the main viewing axis of 80% or greater.

[0087] In another embodiment, the light control film is configured to provide a maximum relative brightness ratio (RBR) at an angle of incidence of 80° or less.

[0088] In another embodiment, the light control film is configured to provide a maximum relative brightness ratio (RBR) at an angle of incidence greater than 10° and less than 80°.

[0089] In another embodiment, the light control film comprises a plurality of louver structures having a non-zero louver angle relative to the light incidence plane, and the EPVA is asymmetric about the incidence angle that results in the maximum relative luminance ratio.

[0090] In another embodiment, the light control film comprises a louver structure having a non-zero louver angle relative to the normal to the light input surface, and the angle of incidence with the normal to the light input surface that results in RBR is greater than 70° on a first side and less than 70° on a second side of the normal.

[0091] Various louver film structures, such as LCF20, can be achieved according to the methods described herein. The magnetizable particles are described herein by way of example and can have various configurations. For example, the magnetizable particles can be composed of various materials, including, but not limited to, ceramics, metal alloy powders, metal alloys, magnetizable-coated glass particles, magnetizable-coated mica particles, composites, and the like. Similarly, the magnetizable particles, according to some embodiments, can be substantially entirely composed of a magnetizable material, can have magnetizable portions (e.g., iron traces) disposed therein, or can have magnetizable portions disposed as layers on one or more surfaces thereof (e.g., one or more surfaces can be coated with a magnetizable material). The magnetizable particles can be shaped according to some embodiments, such as those shown in the examples of FIGS. 4A and 4B. According to other embodiments, the magnetizable particles can include flakes, crushed grains, agglomerates, and the like. The magnetizable particles can be used in a loose form (e.g., free-flowing or in a slurry) before curing and can be incorporated into various articles, including the optical films discussed herein.

[0092] 4A and 4B, an exemplary body 100 including a plurality of magnetizable particles 125 is disclosed. The body 110 may be a molded body 110 coated with a magnetizable material 120. According to some examples, the body 110 need not be molded, but may be random. Furthermore, the body 110 can be formed of a magnetizable material and need not be coated. The magnetizable material 120 may be comprised of magnetizable particles 125 (e.g., iron) held in a binder matrix 130 (also simply referred to as a "binder"), as further shown in FIG. 4B. Although not required in many embodiments, when molded as shown in the embodiment of FIG. 4A, the body 110 may have two opposing major surfaces 160, 162 connected to each other by four minor sides 140a, 140b, 140c, and 140d. Magnetizable particles of the type shown may be movable to align with magnetic field field lines to form desired structures, as discussed below.

[0093] The magnetizable material 120 can be a monolithic magnetizable material or can include magnetizable particles in a binder matrix. Suitable binders can be, for example, glassy or organic, as described below with respect to the binder matrix 130. The binder matrix can be selected from these glassy and organic binders, for example. The body 110 can include, for example, a ferrous or non-ferrous material.

[0094] When the magnetizable material comprises a layer coated on the body 100, as shown in the embodiment of FIG. 4A, this can be achieved by any suitable method, such as dip coating, spraying, painting, physical vapor deposition, and powder coating. Individual magnetizable particles can have a magnetizable layer with different coverage and / or location. The magnetizable material can be essentially free of (i.e., containing less than 5 weight percent, and in other cases less than 1 weight percent) the material used in the molded body 110. The magnetizable layer can consist essentially of magnetizable material (e.g., greater than 99 to 100 weight percent deposited metals and their alloys) or can contain magnetizable particles held in a binder matrix. The binder matrix of the magnetizable layer, if present, can be inorganic or organic resin-based and is typically formed from a respective binder precursor.

[0095] Magnetizable particles according to the present disclosure can be prepared, for example, by applying a magnetizable layer or its precursor to the body 110. The magnetizable layer can be provided by physical vapor deposition, as discussed below. The magnetizable layer precursor can be provided as a dispersion or slurry in a liquid vehicle. The dispersion or slurry vehicle can be made, for example, by simply mixing its components (e.g., magnetizable particles, optional binder precursor, and liquid vehicle). Exemplary liquid vehicles include water, alcohols (e.g., methanol, ethanol, propanol, butanol, ethylene glycol monomethyl ether), ethers (e.g., glyme, diglyme), and combinations thereof. The dispersion or slurry can contain additional components, such as dispersants, surfactants, release agents, colorants, defoamers, and rheology modifiers. Typically, after coating on the ceramic body, the magnetizable layer precursor is dried to remove most or all of the liquid vehicle, although this is not a requirement. If a curable binder precursor is used, this is generally followed by a curing step (eg, heating and / or exposure to actinic radiation) to provide a magnetizable layer.

[0096] The vitreous binder may be produced from a precursor composition comprising a mixture or combination of one or more raw materials that melt and / or fuse when heated to an elevated temperature to form a vitreous binder matrix. Further disclosure of suitable vitreous binders that can be used with the articles can be found in PCT Publication Nos. WO 2018 / 080703, WO 2018 / 080756, WO 2018 / 080704, WO 2018 / 080705, WO 2018 / 080765, WO 2018 / 080784, WO 2018 / 080755, and WO 2018 / 080799, each of which is incorporated herein by reference in its entirety.

[0097] In some embodiments, the magnetizable layer can be deposited using vapor deposition techniques such as physical vapor deposition (PVD), including magnetron sputtering. PVD metallization of various metals, metal oxides, and metal alloys is disclosed, for example, in U.S. Pat. Nos. 4,612,242 (Vesley) and 7,727,931 (Brey et al.). The magnetizable layer can typically be fabricated using this general method.

[0098] As mentioned above, the body of the magnetizable particles can be shaped (e.g., precisely shaped) or random (e.g., flakes, crushed, spheres, etc.). Exemplary shapes include squares, spheres, rectangles, pyramids (e.g., 3-, 4-, 5-, or 6-sided pyramids), truncated pyramids (e.g., 3-, 4-, 5-, or 6-sided truncated pyramids), cones, truncated cones, rods (e.g., cylinders, vermiforms), platelets, disks, and prisms (e.g., 3-, 4-, 5-, or 6-sided prisms).

[0099] Illustrative examples of magnetizable materials that may be suitable for use in the magnetizable particles include iron; cobalt; nickel; various alloys of nickel and iron commercially available in various grades as Permalloy; various alloys of iron, nickel, and cobalt commercially available as Fernico, Kovar, FerNiCo I, or FerNiCo II; various alloys of iron, aluminum, nickel, cobalt, and sometimes copper and / or titanium commercially available in various grades as Alnico; alloys of iron, silicon, and aluminum commercially available as Sendust alloy (typically in a weight ratio of about 85:9:6); Heusler alloys (e.g., CuMnSn); manganese bismuthide (also known as Bismanol); rare earth magnetizable materials, such as gadolinium, dysprosium, holmium, europium oxides, alloys of neodymium with iron and boron (e.g., NdFe 14 B), and alloys of samarium and cobalt (e.g., SmCo5); MnSb; MnOFe2O3; Y3Fe5O 12 Examples of suitable magnetizable materials include CrO2, MnAs, ferrites, such as ferrite, magnetite, zinc ferrite, nickel ferrite, cobalt ferrite, magnesium ferrite, barium ferrite, and strontium ferrite, yttrium iron garnet, and combinations thereof. In some embodiments, the magnetizable material comprises at least one metal selected from iron, nickel, and cobalt, an alloy of two or more such metals, or an alloy of one such metal with at least one element selected from phosphorus and manganese. In some embodiments, the magnetizable material is an alloy (e.g., an alnico alloy) containing 8-12 weight percent (wt%) aluminum, 15-26 wt% nickel, 5-24 wt% cobalt, up to 6 wt% copper, and up to 1 wt% titanium, with the balance of the material being iron.

[0100] The magnetizable particles may have a major dimension that is any size relative to the thickness of the optical film of which they are a part, and in some cases may be much smaller than the thickness of the optical film. For example, in some embodiments, the magnetizable particles may be 1 to 2000 times larger, in yet other embodiments, 100 to 2000 times larger, and in yet other embodiments, 500 to 2000 times larger, although other sizes may be used.

[0101] FIG. 5 is an image of an optical film 200 having a plurality of magnetizable particles 202 organized into a desired structure, showing a non-random arrangement of most of the magnetizable particles along magnetic field lines due to the application of a modulated magnetic field. As shown in FIG. 5, at least a majority of the plurality of magnetizable particles 202 are aligned and spaced apart into a desired structure 204 having a specific array. In FIG. 5, the plurality of magnetizable particles 202 comprises Sendust. The Sendust particles constitute substantially 20% of the optical film by weight and are applied to a substrate as a slurry. The Sendust particles are first randomly dispersed in an optically transparent resin. Types of resin systems suitable for various embodiments of the present invention include, but are not limited to, combinations of a first polymerizable component and a second polymerizable component selected from (meth)acrylate monomers, (meth)acrylate oligomers, and mixtures thereof. As used herein, "monomer" or "oligomer" refers to any substance that can be converted into a polymer. The term "(meth)acrylate" refers to both acrylate and methacrylate compounds. In some cases, the polymerizable composition can include (meth)acrylated urethane oligomers, (meth)acrylated epoxy oligomers, (meth)acrylated polyester oligomers, (meth)acrylated phenolic oligomers, (meth)acrylated acrylic oligomers, and mixtures thereof. The polymerizable resin optionally, and preferably, further includes at least one crosslinker having three or more (meth)acrylate groups. The polymerizable composition may optionally include a (e.g., monofunctional) reactive diluent. The polymerizable resin may be a radiation-curable polymer resin, such as a UV-curable resin. Radiation (e.g., UV)-curable compositions typically include at least one photoinitiator. A single photoinitiator, or a combination of photoinitiators, can be used at a concentration of about 0.1 to about 10% by weight. More preferably, the photoinitiator or combination thereof is used at a concentration of about 0.2 to about 3% by weight. Generally, the photoinitiator is at least partially soluble (e.g., at the processing temperature of the resin) and is substantially colorless after polymerization. The photoinitiator may be colored (eg, yellow) provided that the photoinitiator becomes substantially colorless after exposure to an ultraviolet light source.Types of resin systems can include, but are not limited to, polymeric resins made from high polymers, epoxides and / or siloxanes.

[0102] After the applied magnetic field organizes the Sendust particles into the desired structure, the resin can be at least partially vitrified. Due to the high aspect ratio of the Sendust flakes, and in some cases, due to the tendency of such flakes to tumble and lie flat, there may initially be little or no transmission through the slurry prior to organization by the magnetic field. Once the magnetic field is applied, the Sendust particles organize into the desired structure, with the magnetic field lines orienting the Sendust particles (including the flakes) upward and aligning them with each other. This desired structure enables the capability for light transmission normal to the optical film 200 (parallel to the z-axis) and at any angle in the xz-plane, but also limits light transmission at angles oblique to the optical film 200 (in the yz-plane). As discussed in more detail subsequently, the angle at which light is blocked and the rate at which transmission decreases as the optical film is angled from the normal to the viewing direction can be controlled by the weight content of Sendust in the optically clear resin and other techniques and features that affect the structure of the optical film.

[0103] FIG. 6 illustrates a method 300 for fabricating an optical film 302 according to one embodiment of the present disclosure. FIG. 6A illustrates a desired structure 304 of a plurality of magnetizable particles 306 resulting from the magnetic field of the method of FIG. 6. It should be noted that in FIG. 6A, and in the methods and desired structures subsequently shown and described and referenced herein, the desired structure, method, and optical film are shown at a larger scale (high level) such that individual magnetizable particles are not specifically depicted. Thus, each row (shown as a line) of the desired structure will be comprised of some of the plurality of magnetizable particles. It should be recognized that the desired structure will be comprised of a plurality of magnetizable particles, which may be separated from one another even when grouped in rows along magnetic field lines, as shown in FIG. 5. It should be further appreciated that in the disclosed methods, a majority (or more) of the plurality of magnetizable particles may exhibit a desired structure, and that the desired structure shown herein is shown in highly schematic form and does not illustrate the degree of randomness that may occur in the orientation, alignment, and / or placement of at least some (less than a majority) of the plurality of magnetizable particles. This randomness is illustrated in some areas of the optical film in FIG. 5.

[0104] The method 300 can be performed to provide a plurality of magnetizable particles 306 having a desired structure 304 in an optical film 302, as shown in FIG. 6A. FIG. 6B shows a cross-sectional view of FIG. 6A illustrating the desired structure 304 from another perspective. The plurality of magnetizable particles 306 can have a structure similar to that previously illustrated or described. According to one embodiment, and referring now to FIG. 6, the magnetizable particles can be dispersed in an optically transparent resin (in the range of the electromagnetic spectrum of interest) to form a first mixture 308. The optically transparent resin can have the same composition as the example provided with reference to FIG. 5. The first mixture 308 can be disposed on a web 310 (including a substrate 312). The plurality of magnetizable particles 306 can be anywhere from 0.01% to 90% weight percent, relative to the weight percent of the resin. The specific chemical composition and thickness of the substrate 312 can depend on the requirements of the particular optical product being constructed. That is, balancing the needs for strength, clarity, heat resistance, surface energy, and adhesion to the optical layer, among others. The thickness of the substrate 312 is typically at least about 0.025 millimeters (mm), more typically at least about 0.125 mm. Furthermore, the substrate 312 generally has a thickness of about 0.5 mm or less.

[0105] Useful substrate materials include, for example, styrene-acrylonitrile, cellulose acetate butyrate, cellulose acetate propionate, cellulose triacetate, polyethersulfone, polymethyl methacrylate, polyurethane, polyester, polycarbonate, polyvinyl chloride, polystyrene, polyethylene naphthalate, copolymers or blends based on naphthalenedicarboxylic acid, cast or oriented films of polyolefin-based materials such as polyethylene, polypropylene, and polycycloolefins, polyimide, and glass. Optionally, the substrate material may comprise a mixture or combination of these materials. In some embodiments, the substrate may be multilayered or contain dispersed components suspended or dispersed in a continuous phase.

[0106] Further examples of substrates include polyethylene terephthalate (PET) and polycarbonate. An example of a useful PET film is photograde polyethylene terephthalate available from DuPont Films (Wilmington, Del.) under the trade designation "Melinex 618."

[0107] Optionally, a second substrate (which may or may not be similar in composition and thickness to the first substrate 312) can be laminated to the optical film 302 (e.g., adhered using an optically clear adhesive) to improve transparency, protect the optical layer 304, provide desired physical properties to the optical film 302, etc.

[0108] The first mixture 308 can be applied up-web to a magnet 314 (permanent or electromagnet). The magnet 314 can be placed in close proximity (within a few feet) to a web 310 containing the first mixture 308 of the plurality of magnetizable particles 306 and resin. To aid in understanding the placement of the web 310 relative to the magnet 314 and in understanding the desired structure 304 of FIG. 6A , a Cartesian coordinate system is provided in FIGS. 6 and 6B . According to the illustrated embodiment, the Cartesian coordinate system provided can have an axis (x-axis) oriented in the down-web / up-web direction. The (y-axis) is substantially aligned with the cross-web direction of the web 310 and with the axis of rotation AR of the magnet 314. The (z-axis) is aligned substantially perpendicular to both the x-axis and y-axis.

[0109] As shown in the example of FIG. 6, the magnet 314 is rotated relative to the web 310 about an axis of rotation AR. The rotational speed of the magnet can be 100 to 10,000 rpm or higher. The web 310 can translate relative to the magnet 314, as indicated by arrow 316. FIGS. 7 and 7A show the structure of the magnet 314 in more detail. FIG. 7 shows that the magnet 314 can include two poles, north and south, each shaped as a half cylinder and positioned on either side of the axis of rotation AR. FIG. 7A shows the magnetic field 318 generated by the magnet 314 and the rotational modulation of the magnetic field 318 resulting from the rotation of the magnet 314 about the axis of rotation AR (FIGS. 6 and 7). The optical film 302 and other details of the method 300 of FIG. 6 are not shown in FIG. 7A. The resolved magnetic field lines that would be exerted on the plurality of magnetizable particles 306 are indicated by arrow A in FIG. 7A.

[0110] Further examples of magnetic field configurations and devices for generating magnetic fields are described in U.S. Patent Application Publication No. 2008 / 0289262(A1) (Gao), and U.S. Patent Nos. 2,370,636 (Carlton), 2,857,879 (Johnson), 3,625,666 (James), 4,008,055 (Phaal), 5,181,939 (Neff), and GB Patent No. 1477767 (Edenville Engineering Works Limited), each of which is incorporated herein by reference in its entirety.

[0111] Returning now to FIG. 6 , according to an exemplary embodiment, magnets 314 are positioned to extend across the entire cross-web extension of web 310 in the y-axis direction of a provided Cartesian coordinate system. However, in some embodiments, magnets 314 may not extend the entire cross-web length as shown in FIG. 6 . FIG. 6 additionally illustrates that method 300 applies at least one cure, shown as cure 1 in FIG. 6 , to optical film 302. Cure 1 is applied in the vicinity of magnet 314 (within a few inches upweb or downweb). Cure 1 can be applied by any known technique, such as, but not limited to, application of ultraviolet light, application of an electron beam, or application or removal of thermal energy (e.g., application of heating or cooling). Cure 1 application should be applied to optical film 302 at a specific time and place where the magnetic field lines and resolved magnetic field lines are oriented in a desired configuration, such that the plurality of magnetizable particles are oriented into desired structure 304 ( FIG. 6A ) when magnetic field 318 is undergoing rotational modulation, as shown in FIG. 7A . Cure 1 can be a full cure (i.e., complete polymerization of the resin can occur), or it can be a partial cure with sufficient polymerization such that the majority of the magnetizable particles are fixed in the desired structure 304 (FIG. 6A). In the case of a full cure, a second cure (shown as cure 2) would not be necessary in the method of FIG. 6. FIG. 6 shows method 300 having a partial cure (cure 1) at the downweb location and a second cure (cure 2) to complete full polymerization.

[0112] 6 may include disposing a first mixture 308 on a substrate 310 to fabricate an optical film for controlling light. The first mixture 308 may include a plurality of magnetizable particles 306 dispersed in a first resin. The method 300 may include assembling the plurality of magnetizable particles 306 into a desired structure 304 for controlling light by rotationally modulating at least a magnetic field 318 on the plurality of magnetizable particles 306. The method 300 may further include vitrifying the first resin (e.g., by cure 1 and / or cure 2 described above) to increase its viscosity while the plurality of magnetizable particles 306 are in the desired structure 304.

[0113] FIG. 6A illustrates a desired structure 304 at a high level and in highly schematic form. As shown in FIG. 6A, the substrate 312 (FIG. 6) can be removed. However, in other embodiments, the substrate 312 can be retained. As previously mentioned, individual particles of the plurality of magnetizable particles are not shown in FIG. 6A. FIG. 6A illustrates the configuration of an optical film 302 having a desired structure 304 similar to the optical film 200 of FIG. 5. The desired structure 304 is a structure in which the plurality of magnetizable particles are arranged in spaced rows 320 extending generally downweb. The desired structure 304 is a structure that allows the optical film 302 to be substantially light-transmitting when viewed directly in the orientation shown in FIG. 6A (parallel to the x-z plane). However, the desired structure 304 also limits light transmission at oblique angles relative to the optical film 302 in the y-z plane (i.e., a plane perpendicular to the view of FIG. 6A and not in the x-z plane). It is important to note that the embodiment of Figures 6 and 6A is described with respect to applying the first mixture 308 as a single layer onto a substrate, however, the application of multiple layers using the same or different mixture compositions is also contemplated and, indeed, will be further described and exemplified in this disclosure.

[0114] 8A-8C illustrate additional possible orientations, positions, and alignments of exemplary particles of the plurality of magnetizable particles described herein. FIG. 8A illustrates a particular orientation of particles 402 and 404, with minor surfaces configured in the z and x directions of a Cartesian coordinate system (the same orientation system used in FIGS. 6-7A) and major surfaces oriented in the y direction. Such orientations are purely exemplary in nature and are used for ease of reference and explanation. In the multilayer orientation of FIG. 8A, particles 402 and 404 are stacked and spaced apart from one another. In some embodiments, particles 402 and 404 can be configured to attract or repel one another, as indicated by arrow A.

[0115] Figure 8B shows particles 406 and 408 spaced apart from one another in the crossweb direction. In some embodiments, particles 406 and 408 can be configured to be attracted to or repel one another, as indicated by arrow A. Figure 8C shows particles 410 and 412 spaced apart from one another in the downweb direction. In some embodiments, particles 410 and 412 can be configured to be attracted to or repel one another, as indicated by arrow A. Multiple configurations of particles (e.g., the configurations of Figures 8A, 8B, and / or 8C) are contemplated and, indeed, are disclosed herein.

[0116] FIG. 9 illustrates one possible configuration of another optical film 500 having multiple layers. The optical film 500 can include a substrate 502 as described above and a first layer 504. The first layer 504 can include a first mixture 506 of a first optically transparent resin 508 and a first plurality of magnetizable particles 510. The first layer 504 can be directly or indirectly bonded to the substrate 502. In FIG. 9, the relative size and spacing of the first plurality of magnetizable particles 510 are exaggerated for illustrative purposes and to facilitate the viewer's understanding. As shown in FIG. 9, the first plurality of magnetizable particles 510 has a first desired structure 511.

[0117] In Figure 9, the second layer 512 can be directly or indirectly bonded (e.g., via a second substrate) to the first layer 504. The second layer 512 can include a second mixture 514 of a second optically transparent resin 516 and a second plurality of magnetizable particles 518. In Figure 9, the relative size and spacing of the second plurality of magnetizable particles 518 are exaggerated for illustrative purposes and to aid in the viewer's understanding. As shown in Figure 9, the second plurality of magnetizable particles 518 has a second desired structure 519. The second desired structure 519 can be different from or substantially similar to the first desired structure 511.

[0118] For example, the first desired structure 511 can be a first set of louver structures including groups of magnetizable particles spaced a first spacing distance from one another, having a first tilt angle, and aligned along the X axis. The second desired structure 519 can be a second set of louver structures including groups of magnetizable particles spaced a second spacing distance from one another, having a second tilt angle, and aligned along the Y axis. In alternative embodiments, the first spacing distance and the second spacing distance can be the same or different. For example, the spacing distance between groups within the same desired structure can be about 5 mm or less, or about 4 mm or less, or about 3 mm or less, or about 2 mm or less, or about 1 mm or less, or about 0.5 mm or less, or about 0.25 mm or less, or about 0.1 mm or less, or about 0.05 mm. These spacing distances include all variations and ranges of the specified distances, for example, spacing distances between groups within the same desired structure may be from about 5 mm to about 1 mm, or from about 4 mm to about 0.25 mm, or at least about 3 mm.

[0119] In further alternative embodiments, the first and second tilt angles may be the same or different. In still further alternative embodiments, the first and second sets of louver structures may be aligned on the same or different axes.

[0120] 9, the first plurality of magnetizable particles 510 can have at least one of a shared first orientation and a first common alignment direction relative to the substrate 502, and the second plurality of particles 518 can have at least one of a shared second orientation or a second common alignment direction relative to the substrate 502. In FIG. 9, the shared first orientation or first common alignment direction is different from the shared second orientation or second common alignment direction.

[0121] Optionally, additional layers can be added to the optical film 500, including a layer having magnetizable particles with additional desired structures. The embodiment of Figure 9 shows an additional layer 520 along the side of the optical film opposite the substrate 502, which can be configured to provide a smooth surface to the optical film 500. In other cases, the additional layer 520 can provide desired texturing or other physical attributes, if desired.

[0122] Another method of forming a light control film having one or more layers for controlling light is described in US Provisional Patent Application No. 62 / 699,966, which is incorporated herein by reference in its entirety.

[0123] Experiments and Examples Since numerous modifications and variations within the scope of this disclosure will be apparent to those skilled in the art, the following embodiments and examples are intended to be illustrative only. Unless otherwise noted, all parts, percentages, and ratios reported in the following examples are by weight.

[0124] Preparation of light control films The sample comprises magnetic particles dispersed in a binding matrix comprising a mixture of (meth)acrylate resins.

[0125] Many of the example LCFs were prepared using the resin mixtures shown in Table 1 below. Photomer 6210 acrylate resin is available from IGM Resins USA, Inc. (Charlotte, NC, USA). The remaining acrylate resins listed in Table 1 are available from Photomer Americas (Chatham, VA, USA). 0.8% Darocur 4265 photoinitiator (supplied by BASF, Mobile, AL, USA) was added to each of mixtures A through G. 0.5% TPO photoinitiator (supplied by IGM Resins) was added to mixture H. Table 1 also lists viscosity values ​​measured at 25°C for some of the resin mixtures. Viscosity was measured using a Brookfield DV2T viscometer using the instructions provided with the instrument.

[0126] [Table 1]

[0127] FIG. 10 is a plot showing viscosity values ​​measured at 25° C. for the sample resin mixtures of FIG.

[0128] Exemplary Light Control Films Example 1 represents an exemplary LCF with optical performance similar to that of Comparative Example 1. A 10% mixture of Permalloy (Permalloy Flake Powder; supplied by Novamet Specialty Product Corporation, Lebanon, Tenn.) was incorporated into matrix resin H (see Table 1). The mixture was coated onto a suitable substrate. Magnetic alignment and curing were performed in a manner consistent with previously described methods.

[0129] Example 2 represents an exemplary LCF with more limited optical performance than Example 1. A 20% mixture of Sendust (trade name SENDUST SP-3B; supplied by Mate Co., Ltd., Okayama Prefecture, Japan) was incorporated into Resin H (see Table 1). The mixture was coated onto a suitable substrate. Magnetic alignment and curing were performed in a manner consistent with the methods described above.

[0130] Comparative Example 1 represents an LCF made using a micro-replication manufacturing method. A cylindrical metal roll with exquisitely precise channels cut into its outer surface served as a mold. A molten resin of thermoplastic olefin copolymer (Tafmer DF9200; available from Mitsui Chemical America, Inc., Rye Brook, NY, USA) was introduced onto the mold and then pressed firmly against the metal roll to completely fill the mold. Upon cooling, the structured film was removed from the mold. The resulting structure in the polymer film was a series of evenly spaced channels, each with a nominally trapezoidal cross-section as described in WO 2018 / 229600, the entire contents of which are incorporated herein by reference. A UV-curable resinous mixture similar to that described in WO 2018 / 229600 was filled into the grooves between the transparent channels of the microstructured film prepared by the above-described method. Excess pigmented resin was wiped off from the outward-facing surfaces of the transparent channels. The pigment-filled channels were then cured using UV irradiation to obtain the LCF.

[0131] Example 3 represents exemplary LCFs of various thicknesses. A 7% mixture of SSFL (Stainless Steel Flake Fine Leafing Grade; supplied by Novamet Specialty Product Corporation, Lebanon, TN) was introduced into matrix resin B in Table 1. Two microscope slides were aligned in a wedge-shaped configuration. Four pieces of tape were used on one edge of the slide to create a wedge-shaped gap. The SSFL flakes were 95% smaller than mesh 325 (approximately 44 μm) and 0.8 μm thick.

[0132] Magnetic alignment and curing was performed in a manner consistent with previously described methods.

[0133] Examples 4, 5, 6, 7, and 8 represent exemplary LCFs with various concentrations of magnetically alignable particles. For Examples 4-8, mixtures of 2% (Example 4), 4% (Example 5), 8% (Example 6), 10% (Example 7), and 16% (Example 8) SSFL were incorporated into matrix resin B by valor coating with approximately 40 nm of copper (Cu SSFL). Samples were coated to similar thicknesses. Magnetic alignment and curing were performed consistent with previously described methods.

[0134] Example 9 represents an exemplary LCF at one matrix viscosity. 7% Cu SSFL was incorporated into matrix resin A and magnetically alignable LCF was fabricated according to the method described above.

[0135] Example 10 differs from Example 9 only in the matrix resin: 7% Cu SSFL was incorporated into matrix resin B, and magnetically alignable LCFs were fabricated according to the method described above.

[0136] Example 11 differs from Example 9 only in the matrix resin: 7% Cu SSFL was introduced into matrix resin F, and magnetically alignable LCFs were fabricated according to the method described above.

[0137] Example 12 differs from Example 9 only in the matrix resin: 7% Cu SSFL was incorporated into matrix resin G, and magnetically alignable LCFs were fabricated according to the method described above.

[0138] Examples 13-15 represent LCFs at three different thicknesses. 7% Cu SSFL was incorporated into matrix resin B, and magnetically alignable LCFs were fabricated according to the method described above. The thickness of each LCF was controlled by the number of tape strips introduced as shim material between glass microscope slides. Either two (Example 13), four (Example 14), or six (Example 15) strips of tape were introduced on each side.

[0139] Examples 16 and 17 represent LCFs with two different louver tilt angles. 5% Sendust was incorporated into matrix resin H, and magnetically alignable LCFs were fabricated according to the method described above. However, the magnetic field was tilted relative to the plane of the film (non-perpendicular to the plane of the LCF). The magnetic field tilt angle for Example 16 is smaller than that for Example 17.

[0140] Example 18 represents an LCF at a louver tilt angle. 2% Sendust was incorporated into matrix resin H, and a magnetically alignable LCF was made according to the method described above. However, the magnetic field was tilted approximately 20° relative to the plane of the film (a non-perpendicular alignment relative to the plane of the LCF).

[0141] Figure 11 shows a cross-sectional photograph of a light control film sample with angled magnetizable particles corresponding to Example 18. As mentioned above, the present researchers discovered that the linear structures are not always aligned in a perfectly upright configuration. By tilting the sample and / or the magnetic field at a specific angle, the linear features in the light-blocking region (the region of magnetizable particles) can be aligned at any angle.

[0142] Optical property evaluation of light control film Angular transmittance was measured with a spectrophotometer using a rotation stage (supplied by Oriel Instaspec Spectrograph; the stage allows the sample to be rotated out of plane for angular transmittance measurements and is illuminated with a lamp controlled by a Labsphere LPS-100 power supply). The stage was rotated from 0° to 60° in 15° increments, with measurements taken at each stage rotation. From these measurements, the average visible transmittance from 400 nm to 700 nm was calculated and plotted as a function of incident angle. Figure 12 shows plots of the visible wavelength transmittance of the LCFs of Example 1, Example 2, and Comparative Example 1. The visible wavelength transmittance is the arithmetic mean of the transmittance from 400 nm to 700 nm, and the RBR is plotted in Figure 12. Example 2 was intentionally designed to have a more limited viewing angle than Example 1 and Comparative Example 1. For the non-tilted louver structure, the RBR is greatest at an incident angle of 0 degrees when the internal ray path is parallel to the louver structure. The louver structure of Example 1 provided similar RBR to the microstructured LCF of Comparative Example 1 at all angles.

[0143] Louver spacing control (thickness) A Keyence VHX-2000 microscope with a VH Z1000UR lens was used to image the louver spacing of the LCF of Example 3 at three different locations across the microscope slide. Figure 13 shows microscope images of each thickness location across the LCF: A (61 μm), B (209 μm), and C (343 μm). The louver spacing increases as the layer thickness increases. For a given particle concentration, the louver spacing can be controlled by varying the thickness of the LCF.

[0144] Louver spacing control (concentration of magnetically alignable particles) A Keyence VHX-2000 microscope with a VH Z1000UR lens was used to image the louvers for the LCFs of Examples 4-8. Images of Examples 5, 6, and 7 are shown in Figure 14. The microscope images were processed with custom image processing software. From these images, the average louver spacing was determined by identifying individual louvers (dark areas) in each row of the image and averaging the spacing for each row across the image.

[0145] Figure 15 shows a plot of average louver spacing in micrometers versus concentration of magnetically alignable particles in an LCF. A linear regression of the experimental data is also shown. For a given resin system and thickness, the louver spacing can be controlled by the concentration of magnetically alignable particles in the LCF.

[0146] Louver orientation (viscosity of matrix resin) A Keyence VHX-2000 microscope with a VH Z1000UR lens was used to image the louvers for the LCFs of Examples 9 to 12. Figure 16 shows images of the LCFs of Examples 9 to 12. The louvers appear to be more continuous and better aligned when the matrix viscosity is lower compared to when the matrix viscosity is higher.

[0147] LCF Thickness A Keyence VHX-2000 microscope with a VH Z1000UR lens was used to image the louvers for the LCFs of Examples 13-15. FIG. 17A shows an image of the LCFs of Examples 13-15. The louvers appear to be more continuous and better aligned at smaller thicknesses compared to larger thicknesses. Using the same computer program as discussed for FIG. 15, the average length of the louver structures (i.e., the longest dimension of the louver structures extending into the page, e.g., in FIGS. 1, 2A, 2B, 3B, and 3C) is 643 μm for Example 13, 239 μm for Example 14, and 199 μm for Example 15.

[0148] Cross-sectional images of each of Examples 13-15 are shown in Figure 17B. The overall height of the louvers can be controlled by the thickness of the LCF. The film thicknesses of the two-, four-, and six-layer tape shims are 239 μm, 507 μm, and 770 μm, respectively. The louver structures generally span the entire thickness of the samples. Thus, these experiments confirm that each louver structure (by both the height and length of the louver structure) contains a plurality of individual magnetizable particles.

[0149] Sloped louvers Angular transmittance was measured using a spectrophotometer (supplied by Oriel Instaspec Spectrograph; see above) with a rotating stage. The stage was rotated from 0° to 60° in 15° increments, with measurements taken at each stage rotation. From these measurements, the average visible transmittance from 400 nm to 700 nm was calculated, and the RBR was plotted as a function of incident angle. Figure 18 shows plots of the RBR for the LCFs of Examples 16 and 17 and Comparative Example 1.

[0150] The incidence angles for maximum RBR in Examples 16-17 occur at non-zero angles due to the tilted louver structure. In Example 16, the louver structure is tilted by approximately 22°. From Snell's law, a ray of light incident on the LCF at approximately 34° travels parallel to the louver structure inside the LCF. Therefore, in Figure 18, the RBR reaches a maximum value near 30°.

[0151] In Example 17, the louver structure is tilted by about 15°. From Snell's law, a light ray incident on the LCF at about 22° will travel parallel to the louver structure inside the LCF. Therefore, in Figure 18, the RBR reaches a maximum value near 20°.

[0152] A conoscopic angular transmission plot of the model of the LCF is shown in Figure 19A.

[0153] The louver film model was created with a proprietary ray tracing program, but any commercially available ray tracing program can be used for the simulation. The louver film comprises a planar film (n=1.5, thickness=86 units) with louvers spaced 55 units apart, with each louver structure having a thickness of 7 units and a depth of 66 units. The louver length is several orders of magnitude greater than the spacing between them, and therefore appears nearly infinite. A dummy final collection surface is placed near the exit surface of the louver film. The louver film is surrounded by air.

[0154] A ray starts from a line that spans the width of the louver structure as well as a pair of louver structures. From this line, 1000 rays start in the direction of the louver film. This is a representative cross section because the louver width is much larger than the spacing. The rays are traced from the line at all angles within the hemisphere, directed at the louver film in 1° increments in both polar and azimuthal angles.

[0155] The light rays can be split into energy based on the Fresnel coefficients, the refractive index of the film, and the refractive index of air for each angle. The split rays are traced until the energy is less than 0.001% of the original ray. For each angle, the percentage of the original ray that reaches the focusing surface is shown in the plot in Figure 19A below. Polar angles are displayed as distance from the center of the plot, and azimuthal angles are configured counterclockwise from the 3 o'clock position.

[0156] The scale on the left side of the figure shows high transmission in white. The center of each plot displays the transmission at a 0° angle of incidence. Increasing angles of incidence are plotted radially, while the azimuthal angle rotates around the plot. As the physical tilt of the louver increases, the transmission peak shifts away from the axis.

[0157] The set of cross sections of the conoscopic angular transmission plot of FIG. 19A is denoted by Θ louver = 0 degrees, and Θ louver= 10 degrees is shown in Figure 19B. The cross section is taken in a plane perpendicular to the length of the louver structure and is shown in Figure 19A from the 6 o'clock to the 12 o'clock direction. louver For Θ = 0°, the incident angle at which the maximum RBR occurs is 0°, and louver For Θ = 10°, the incident angle at which the maximum RBR occurs is 16°. These are the results of the sine of the maximum RBR angle being proportional to the refractive index of the LCF. louver This agrees with predictions from Snell's law, which can be related to the EPVA multiplied by Θ. The simulated EPVA values ​​can be calculated from the cross section in Figure 19B. louver The EPVA for Θ = 0° is symmetric around 0° and has a value of 150°. louver The EPVA for Θ = 10° is not symmetric about 0° or the incidence angle with maximum RBR due to the tilted louver structure. louver The EPVA for =10° is about 115°.

[0158] A comparison of the transmittance for a simulated 15° tilted louver (left) and a fabricated film (Example 16) with 15° tilted particles (right) is shown in Figure 20A. The measured conoscopic plot was obtained from short-circuit current measurements of a single-cell module using an NSP NS6ML-1940 solar mono cell, with data acquisition acquired with an Agilent 3497aA LXI data acquisition switch unit. The module was illuminated with a stabilized Oriel 66002 Xenon arc lamp. The module was mounted on a two-axis rotation stage capable of 90° polar and 360° azimuthal rotation, and custom software was used to control the stage and acquire the short-circuit current. Baseline measurements of the module angular response were taken at 5° polar angle increments and 15° azimuthal angle increments. For angular measurements, louver film samples can be laminated to the module. The louver film effective transmittance is obtained by dividing the sample measurement by the corresponding angular baseline measurement.

[0159] The peak transmittance for an exemplary LCF according to embodiments of the present invention is shifted by approximately the same angle (20°) as the simulated LCF (23°), as shown in FIG. 20B. The EPVA values ​​for both the fabricated and simulated LCFs are asymmetric about the incident angle at which maximum RBR occurs. The data in FIGS. 20A and 20B demonstrate that the present invention can be used to fabricate light control films with asymmetric RBR profiles (asymmetry about the incident angle at which maximum RBR occurs) and asymmetric EPVA. This is difficult, if not impossible, to achieve with known manufacturing processes for LCFs, such as those described in WO 2018 / 078493 and WO 2018 / 229600.

[0160] Differences between the model and the sample can arise from particle distribution, particle packing, absorption properties, scattering properties, irregularities in particle alignment, and / or other factors.

[0161] In another experiment, a simple ray tracing model was constructed to predict the angular transmission profile, as shown in Figure 21. In the simulation, louvered films were constructed with different inclinations relative to the film surface. The transmittance peak predictably followed Snell's law: when light is incident in air and the film's refractive index is 1.5, a louvered physical inclination of 20° results in a peak transmittance of 30.9° (sin Θ peak =n film * sinΘ louver ) As the slope of the louver film approaches the critical angle of the film's refractive index, light reflection increases rapidly, resulting in a loss of transmittance. The resulting location of the transmission peak deviates from that predicted by Snell's law.

Claims

1. one or more photovoltaic cells disposed in the encapsulant; A light control structure comprising a louver film having a series of louver structures, each louver structure comprising one or more groups of a plurality of magnetizable particles, the plurality of magnetizable particles being dispersed in a binding matrix and aligned in at least a first orientation; the light control structure substantially transmits light incident at a first angle and substantially limits transmission of light incident at a second angle; A solar device comprising: a light control structure, wherein each louver structure is spaced from an adjacent louver structure, and each louver structure is substantially aligned in a plane substantially parallel to the adjacent louver structure.

2. 10. The solar device of claim 1, wherein each louver structure is oriented at a louver angle of about 0 degrees to about 50 degrees from the normal to the light input surface of the light control structure.

3. 3. The solar device of claim 1, wherein each louver structure is oriented at a louver angle of about 0 degrees to about 40 degrees.

4. The solar device of any one of claims 1 to 3, wherein each louver structure is oriented at a louver angle of from about 0° to about 30°.

5. The solar device of any one of claims 1 to 4, wherein each louver structure is oriented at a louver angle of about 10° to about 30°.

6. The solar device according to any one of claims 1 to 5, wherein the light control structure has a maximum relative brightness ratio (RBR) that is at least 50%.

7. A solar device according to any one of claims 1 to 6, wherein the light control structure selectively absorbs a portion of the visible spectrum.

8. Solar device according to any one of claims 1 to 7, wherein at least a portion of the magnetizable particles reflect one or more selective wavelengths in the visible spectrum.

9. 9. The solar device of claim 1, wherein the plurality of magnetizable particles comprises multiple groups of magnetizable particles, each group of particles being spaced from an adjacent group by about 0.05 mm to about 5 mm.

10. 10. The solar device of claim 1, wherein the magnetizable particles comprise one or more particles selected from the group consisting of ceramics, metal alloy powders, metal alloys, magnetizable coated glass particles, magnetizable coated mica particles, composites, and combinations thereof.

11. The solar device of any one of claims 1 to 10, wherein the magnetizable particles comprise a material having a magnetizable portion disposed therein.

12. Solar device according to any one of claims 1 to 11, wherein the magnetisable particles have magnetisable portions arranged as a layer on one or more surfaces of the magnetisable particles.

13. The solar device of any one of claims 1 to 12, wherein the magnetizable particles comprise at least one of flakes, broken particles, agglomerates, and combinations thereof.

14. The solar device according to any one of claims 1 to 13, wherein the bonding matrix comprises an inorganic vitreous binder.

15. The solar device according to any one of claims 1 to 14, wherein the bonding matrix comprises a resin.

16. The solar device of any one of claims 1 to 15, wherein the encapsulant comprises one of an EVA-based encapsulant and a polyolefin-based encapsulant.

17. The solar device of any one of claims 1 to 16, wherein the device includes an encapsulant disposed on both major surfaces of the photovoltaic cell.

18. 18. The solar device of any one of claims 1 to 17, further comprising a cover layer and a backsheet layer, the encapsulated photovoltaic cell being disposed between the backsheet layer and the cover layer.

19. 20. The solar device of claim 18, wherein the cover layer comprises one of glass and an ultra-barrier film.

20. 20. The solar device of claim 18, wherein the cover layer and backsheet layer are formed from different materials.

21. The solar device of any one of claims 18 to 20, wherein the light control structure is formed as an adhesive that bonds the cover layer to the encapsulant.

22. The solar device of any one of claims 18 to 20, wherein the cover layer is disposed between the light control structure and the encapsulant.

23. The solar device according to any one of claims 1 to 22, further comprising a frame covering an edge of the solar device.

24. The solar device of any one of claims 1 to 23, wherein the solar device comprises a solar roof panel.

25. 25. The solar device of claim 24, wherein the solar device is installed on a roof having roof tiles, and the solar device has a visible color that substantially matches the roof tile color.

26. 25. The solar device of claim 24, wherein the louver angle is selected based at least in part on the pitch of the roof on which the solar device is installed.

27. a light control film having a series of louver structures, each louver structure comprising one or more groups of a plurality of magnetizable particles, the plurality of magnetizable particles being dispersed in a binding matrix and aligned in at least a first orientation; the light control film substantially transmits light incident at a first angle and substantially limits the transmission of light incident at a second angle; A light control film wherein each louver structure is spaced from an adjacent louver structure, and each louver structure is aligned in a plane substantially parallel to the adjacent louver structure.

28. 28. The light control film of claim 27, wherein light incident on the light input surface has a maximum relative luminance ratio (RBR) in the direction of the main viewing axis of 50% or more and exits the light output surface at an effective polar viewing angle (EPVA) of 150° or less.

29. 30. The light control film of claim 28, wherein light incident on said light input surface exits said light output surface with a maximum relative brightness ratio (RBR) in the direction of said main viewing axis of 60% or greater.

30. 30. The light control film of claim 29, wherein light incident on said light input surface exits said light output surface with a maximum relative brightness ratio (RBR) in the direction of said main viewing axis of 80% or greater.

31. 31. The light control film of any one of claims 27 to 30, wherein the incident angle resulting in the maximum relative luminance ratio (RBR) is 80° or less.

32. 32. The light control film of any one of claims 27 to 31, wherein the angle of incidence resulting in the maximum relative luminance ratio (RBR) is greater than 10° and less than 80°.

33. one or more photovoltaic cells disposed in the encapsulant; A solar device comprising: a first light control film according to any one of claims 28 to 32.

34. 34. The solar device of claim 33, further comprising a second light control film according to any one of claims 27 to 32, wherein the louver structure for the second light control film is oriented at an angle of 10° to 90° relative to the louver structure of the first light control film.

35. one or more photovoltaic cells disposed in the encapsulant; 33. A solar device comprising: a first light control film and a second light control film, each light control film having the structure of any one of claims 27 to 32, and the first light control film oriented relative to the second light control film such that the substantially parallel louver structure for the first light control film is oblique at an angle of between 10° and 90° relative to the substantially parallel louver structure for the second light control film.

36. 30. The light control film of claim 27, wherein light incident on the light input surface exits the light output surface with an effective polar viewing angle (EPVA) of 150 degrees or less.

37. 30. The light control film of claim 28, wherein light incident on the light input surface exits the light output surface at an effective polar viewing angle (EPVA) of 115° or less.

38. 1. A light control film comprising a plurality of magnetizable particles arranged and aligned in a binding matrix to form a louver film having alternating light transmitting and light blocking regions, the light blocking regions being aligned at a louver angle of about 0° to about 40°.

39. A light control film comprising a louver structure having a non-zero louver angle relative to the normal of the light incident surface, wherein the EPVA is asymmetric about the incident angle that results in the maximum relative brightness ratio.

40. 40. The light control film of claim 39 comprising a plurality of magnetizable particles arranged and aligned in a bonding matrix to form said louver structure.

41. A light control film comprising a louver structure having a non-zero louver angle relative to a normal to a light incident surface, wherein the incident angle with the normal to the light incident surface that results in RBR is greater than 70° on a first side and less than 70° on a second side.

Images